Synced java.util.concurrent library up to 2013.07.01.

Compared to the reference code base I re-added
AbstracMap as a base class for ConcurrentHashMap.

Change-Id: I0751638784e962425418ea8640721c00d7200873

7 files changed, 3760 insertions, 2041 deletions

diff --git a/libdvm/src/main/java/java/lang/Class.java b/libdvm/src/main/java/java/lang/Class.java
index 2f26688..c8064cb 100644
--- a/libdvm/src/main/java/java/lang/Class.java
+++ b/libdvm/src/main/java/java/lang/Class.java
@@ -54,13 +54,14 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 import libcore.util.CollectionUtils;
 import libcore.util.EmptyArray;
 import org.apache.harmony.kernel.vm.StringUtils;
 import libcore.reflect.AnnotationAccess;
 import libcore.reflect.GenericSignatureParser;
 import libcore.reflect.Types;
-
+import libcore.util.BasicLruCache;
 /**
  * The in-memory representation of a Java class. This representation serves as
  * the starting point for querying class-related information, a process usually
@@ -779,9 +780,17 @@ public final class Class<T> implements Serializable, AnnotatedElement, GenericDe
      * void} then an empty array is returned.
      */
     public Type[] getGenericInterfaces() {
-        GenericSignatureParser parser = new GenericSignatureParser(getClassLoader());
-        parser.parseForClass(this, getSignatureAttribute());
-        return Types.getClonedTypeArray(parser.interfaceTypes);
+        Type[] result;
+        synchronized (Caches.genericInterfaces) {
+            result = Caches.genericInterfaces.get(this);
+            if (result == null) {
+                GenericSignatureParser parser = new GenericSignatureParser(getClassLoader());
+                parser.parseForClass(this, getSignatureAttribute());
+                result = Types.getClonedTypeArray(parser.interfaceTypes);
+                Caches.genericInterfaces.put(this, result);
+            }
+       }
+       return result;
     }
 
     /**
@@ -1262,4 +1271,9 @@ public final class Class<T> implements Serializable, AnnotatedElement, GenericDe
         return AnnotationAccess.typeIndexToAnnotationDirectoryOffset(getDex(), getTypeIndex());
     }
 
+    private static class Caches {
+        private static final BasicLruCache<Class, Type[]> genericInterfaces
+            = new BasicLruCache<Class, Type[]>(50);
+    }
+
 }
diff --git a/luni/src/main/java/java/util/concurrent/ConcurrentHashMap.java b/luni/src/main/java/java/util/concurrent/ConcurrentHashMap.java
index c85a5cc..515cc38 100644
--- a/luni/src/main/java/java/util/concurrent/ConcurrentHashMap.java
+++ b/luni/src/main/java/java/util/concurrent/ConcurrentHashMap.java
@@ -5,865 +5,729 @@
  */
 
 package java.util.concurrent;
-import java.util.concurrent.locks.*;
-import java.util.*;
+
+import java.io.ObjectStreamField;
 import java.io.Serializable;
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Comparator;
+import java.util.ConcurrentModificationException;
+import java.util.Enumeration;
+import java.util.HashMap;
+import java.util.Hashtable;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Set;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.ForkJoinPool;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.LockSupport;
+import java.util.concurrent.locks.ReentrantLock;
 
 // BEGIN android-note
 // removed link to collections framework docs
+// removed links to hidden api
 // END android-note
 
 /**
  * A hash table supporting full concurrency of retrievals and
- * adjustable expected concurrency for updates. This class obeys the
+ * high expected concurrency for updates. This class obeys the
  * same functional specification as {@link java.util.Hashtable}, and
  * includes versions of methods corresponding to each method of
- * <tt>Hashtable</tt>. However, even though all operations are
+ * {@code Hashtable}. However, even though all operations are
  * thread-safe, retrieval operations do <em>not</em> entail locking,
  * and there is <em>not</em> any support for locking the entire table
  * in a way that prevents all access.  This class is fully
- * interoperable with <tt>Hashtable</tt> in programs that rely on its
+ * interoperable with {@code Hashtable} in programs that rely on its
  * thread safety but not on its synchronization details.
  *
- * <p> Retrieval operations (including <tt>get</tt>) generally do not
- * block, so may overlap with update operations (including
- * <tt>put</tt> and <tt>remove</tt>). Retrievals reflect the results
- * of the most recently <em>completed</em> update operations holding
- * upon their onset.  For aggregate operations such as <tt>putAll</tt>
- * and <tt>clear</tt>, concurrent retrievals may reflect insertion or
- * removal of only some entries.  Similarly, Iterators and
- * Enumerations return elements reflecting the state of the hash table
- * at some point at or since the creation of the iterator/enumeration.
- * They do <em>not</em> throw {@link ConcurrentModificationException}.
- * However, iterators are designed to be used by only one thread at a time.
+ * <p>Retrieval operations (including {@code get}) generally do not
+ * block, so may overlap with update operations (including {@code put}
+ * and {@code remove}). Retrievals reflect the results of the most
+ * recently <em>completed</em> update operations holding upon their
+ * onset. (More formally, an update operation for a given key bears a
+ * <em>happens-before</em> relation with any (non-null) retrieval for
+ * that key reporting the updated value.)  For aggregate operations
+ * such as {@code putAll} and {@code clear}, concurrent retrievals may
+ * reflect insertion or removal of only some entries.  Similarly,
+ * Iterators and Enumerations return elements reflecting the state of
+ * the hash table at some point at or since the creation of the
+ * iterator/enumeration.  They do <em>not</em> throw {@link
+ * ConcurrentModificationException}.  However, iterators are designed
+ * to be used by only one thread at a time.  Bear in mind that the
+ * results of aggregate status methods including {@code size}, {@code
+ * isEmpty}, and {@code containsValue} are typically useful only when
+ * a map is not undergoing concurrent updates in other threads.
+ * Otherwise the results of these methods reflect transient states
+ * that may be adequate for monitoring or estimation purposes, but not
+ * for program control.
  *
- * <p> The allowed concurrency among update operations is guided by
- * the optional <tt>concurrencyLevel</tt> constructor argument
- * (default <tt>16</tt>), which is used as a hint for internal sizing.  The
- * table is internally partitioned to try to permit the indicated
- * number of concurrent updates without contention. Because placement
- * in hash tables is essentially random, the actual concurrency will
- * vary.  Ideally, you should choose a value to accommodate as many
- * threads as will ever concurrently modify the table. Using a
- * significantly higher value than you need can waste space and time,
- * and a significantly lower value can lead to thread contention. But
- * overestimates and underestimates within an order of magnitude do
- * not usually have much noticeable impact. A value of one is
- * appropriate when it is known that only one thread will modify and
- * all others will only read. Also, resizing this or any other kind of
- * hash table is a relatively slow operation, so, when possible, it is
- * a good idea to provide estimates of expected table sizes in
- * constructors.
+ * <p>The table is dynamically expanded when there are too many
+ * collisions (i.e., keys that have distinct hash codes but fall into
+ * the same slot modulo the table size), with the expected average
+ * effect of maintaining roughly two bins per mapping (corresponding
+ * to a 0.75 load factor threshold for resizing). There may be much
+ * variance around this average as mappings are added and removed, but
+ * overall, this maintains a commonly accepted time/space tradeoff for
+ * hash tables.  However, resizing this or any other kind of hash
+ * table may be a relatively slow operation. When possible, it is a
+ * good idea to provide a size estimate as an optional {@code
+ * initialCapacity} constructor argument. An additional optional
+ * {@code loadFactor} constructor argument provides a further means of
+ * customizing initial table capacity by specifying the table density
+ * to be used in calculating the amount of space to allocate for the
+ * given number of elements.  Also, for compatibility with previous
+ * versions of this class, constructors may optionally specify an
+ * expected {@code concurrencyLevel} as an additional hint for
+ * internal sizing.  Note that using many keys with exactly the same
+ * {@code hashCode()} is a sure way to slow down performance of any
+ * hash table. To ameliorate impact, when keys are {@link Comparable},
+ * this class may use comparison order among keys to help break ties.
  *
  * <p>This class and its views and iterators implement all of the
  * <em>optional</em> methods of the {@link Map} and {@link Iterator}
  * interfaces.
  *
- * <p> Like {@link Hashtable} but unlike {@link HashMap}, this class
- * does <em>not</em> allow <tt>null</tt> to be used as a key or value.
+ * <p>Like {@link Hashtable} but unlike {@link HashMap}, this class
+ * does <em>not</em> allow {@code null} to be used as a key or value.
  *
  * @since 1.5
  * @author Doug Lea
  * @param <K> the type of keys maintained by this map
  * @param <V> the type of mapped values
  */
-public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>
-        implements ConcurrentMap<K, V>, Serializable {
+public class ConcurrentHashMap<K,V> extends java.util.AbstractMap<K,V>
+        implements ConcurrentMap<K,V>, Serializable {
     private static final long serialVersionUID = 7249069246763182397L;
 
     /*
-     * The basic strategy is to subdivide the table among Segments,
-     * each of which itself is a concurrently readable hash table.  To
-     * reduce footprint, all but one segments are constructed only
-     * when first needed (see ensureSegment). To maintain visibility
-     * in the presence of lazy construction, accesses to segments as
-     * well as elements of segment's table must use volatile access,
-     * which is done via Unsafe within methods segmentAt etc
-     * below. These provide the functionality of AtomicReferenceArrays
-     * but reduce the levels of indirection. Additionally,
-     * volatile-writes of table elements and entry "next" fields
-     * within locked operations use the cheaper "lazySet" forms of
-     * writes (via putOrderedObject) because these writes are always
-     * followed by lock releases that maintain sequential consistency
-     * of table updates.
-     *
-     * Historical note: The previous version of this class relied
-     * heavily on "final" fields, which avoided some volatile reads at
-     * the expense of a large initial footprint.  Some remnants of
-     * that design (including forced construction of segment 0) exist
-     * to ensure serialization compatibility.
+     * Overview:
+     *
+     * The primary design goal of this hash table is to maintain
+     * concurrent readability (typically method get(), but also
+     * iterators and related methods) while minimizing update
+     * contention. Secondary goals are to keep space consumption about
+     * the same or better than java.util.HashMap, and to support high
+     * initial insertion rates on an empty table by many threads.
+     *
+     * This map usually acts as a binned (bucketed) hash table.  Each
+     * key-value mapping is held in a Node.  Most nodes are instances
+     * of the basic Node class with hash, key, value, and next
+     * fields. However, various subclasses exist: TreeNodes are
+     * arranged in balanced trees, not lists.  TreeBins hold the roots
+     * of sets of TreeNodes. ForwardingNodes are placed at the heads
+     * of bins during resizing. ReservationNodes are used as
+     * placeholders while establishing values in computeIfAbsent and
+     * related methods.  The types TreeBin, ForwardingNode, and
+     * ReservationNode do not hold normal user keys, values, or
+     * hashes, and are readily distinguishable during search etc
+     * because they have negative hash fields and null key and value
+     * fields. (These special nodes are either uncommon or transient,
+     * so the impact of carrying around some unused fields is
+     * insignificant.)
+     *
+     * The table is lazily initialized to a power-of-two size upon the
+     * first insertion.  Each bin in the table normally contains a
+     * list of Nodes (most often, the list has only zero or one Node).
+     * Table accesses require volatile/atomic reads, writes, and
+     * CASes.  Because there is no other way to arrange this without
+     * adding further indirections, we use intrinsics
+     * (sun.misc.Unsafe) operations.
+     *
+     * We use the top (sign) bit of Node hash fields for control
+     * purposes -- it is available anyway because of addressing
+     * constraints.  Nodes with negative hash fields are specially
+     * handled or ignored in map methods.
+     *
+     * Insertion (via put or its variants) of the first node in an
+     * empty bin is performed by just CASing it to the bin.  This is
+     * by far the most common case for put operations under most
+     * key/hash distributions.  Other update operations (insert,
+     * delete, and replace) require locks.  We do not want to waste
+     * the space required to associate a distinct lock object with
+     * each bin, so instead use the first node of a bin list itself as
+     * a lock. Locking support for these locks relies on builtin
+     * "synchronized" monitors.
+     *
+     * Using the first node of a list as a lock does not by itself
+     * suffice though: When a node is locked, any update must first
+     * validate that it is still the first node after locking it, and
+     * retry if not. Because new nodes are always appended to lists,
+     * once a node is first in a bin, it remains first until deleted
+     * or the bin becomes invalidated (upon resizing).
+     *
+     * The main disadvantage of per-bin locks is that other update
+     * operations on other nodes in a bin list protected by the same
+     * lock can stall, for example when user equals() or mapping
+     * functions take a long time.  However, statistically, under
+     * random hash codes, this is not a common problem.  Ideally, the
+     * frequency of nodes in bins follows a Poisson distribution
+     * (http://en.wikipedia.org/wiki/Poisson_distribution) with a
+     * parameter of about 0.5 on average, given the resizing threshold
+     * of 0.75, although with a large variance because of resizing
+     * granularity. Ignoring variance, the expected occurrences of
+     * list size k are (exp(-0.5) * pow(0.5, k) / factorial(k)). The
+     * first values are:
+     *
+     * 0:    0.60653066
+     * 1:    0.30326533
+     * 2:    0.07581633
+     * 3:    0.01263606
+     * 4:    0.00157952
+     * 5:    0.00015795
+     * 6:    0.00001316
+     * 7:    0.00000094
+     * 8:    0.00000006
+     * more: less than 1 in ten million
+     *
+     * Lock contention probability for two threads accessing distinct
+     * elements is roughly 1 / (8 * #elements) under random hashes.
+     *
+     * Actual hash code distributions encountered in practice
+     * sometimes deviate significantly from uniform randomness.  This
+     * includes the case when N > (1<<30), so some keys MUST collide.
+     * Similarly for dumb or hostile usages in which multiple keys are
+     * designed to have identical hash codes or ones that differs only
+     * in masked-out high bits. So we use a secondary strategy that
+     * applies when the number of nodes in a bin exceeds a
+     * threshold. These TreeBins use a balanced tree to hold nodes (a
+     * specialized form of red-black trees), bounding search time to
+     * O(log N).  Each search step in a TreeBin is at least twice as
+     * slow as in a regular list, but given that N cannot exceed
+     * (1<<64) (before running out of addresses) this bounds search
+     * steps, lock hold times, etc, to reasonable constants (roughly
+     * 100 nodes inspected per operation worst case) so long as keys
+     * are Comparable (which is very common -- String, Long, etc).
+     * TreeBin nodes (TreeNodes) also maintain the same "next"
+     * traversal pointers as regular nodes, so can be traversed in
+     * iterators in the same way.
+     *
+     * The table is resized when occupancy exceeds a percentage
+     * threshold (nominally, 0.75, but see below).  Any thread
+     * noticing an overfull bin may assist in resizing after the
+     * initiating thread allocates and sets up the replacement
+     * array. However, rather than stalling, these other threads may
+     * proceed with insertions etc.  The use of TreeBins shields us
+     * from the worst case effects of overfilling while resizes are in
+     * progress.  Resizing proceeds by transferring bins, one by one,
+     * from the table to the next table. To enable concurrency, the
+     * next table must be (incrementally) prefilled with place-holders
+     * serving as reverse forwarders to the old table.  Because we are
+     * using power-of-two expansion, the elements from each bin must
+     * either stay at same index, or move with a power of two
+     * offset. We eliminate unnecessary node creation by catching
+     * cases where old nodes can be reused because their next fields
+     * won't change.  On average, only about one-sixth of them need
+     * cloning when a table doubles. The nodes they replace will be
+     * garbage collectable as soon as they are no longer referenced by
+     * any reader thread that may be in the midst of concurrently
+     * traversing table.  Upon transfer, the old table bin contains
+     * only a special forwarding node (with hash field "MOVED") that
+     * contains the next table as its key. On encountering a
+     * forwarding node, access and update operations restart, using
+     * the new table.
+     *
+     * Each bin transfer requires its bin lock, which can stall
+     * waiting for locks while resizing. However, because other
+     * threads can join in and help resize rather than contend for
+     * locks, average aggregate waits become shorter as resizing
+     * progresses.  The transfer operation must also ensure that all
+     * accessible bins in both the old and new table are usable by any
+     * traversal.  This is arranged by proceeding from the last bin
+     * (table.length - 1) up towards the first.  Upon seeing a
+     * forwarding node, traversals (see class Traverser) arrange to
+     * move to the new table without revisiting nodes.  However, to
+     * ensure that no intervening nodes are skipped, bin splitting can
+     * only begin after the associated reverse-forwarders are in
+     * place.
+     *
+     * The traversal scheme also applies to partial traversals of
+     * ranges of bins (via an alternate Traverser constructor)
+     * to support partitioned aggregate operations.  Also, read-only
+     * operations give up if ever forwarded to a null table, which
+     * provides support for shutdown-style clearing, which is also not
+     * currently implemented.
+     *
+     * Lazy table initialization minimizes footprint until first use,
+     * and also avoids resizings when the first operation is from a
+     * putAll, constructor with map argument, or deserialization.
+     * These cases attempt to override the initial capacity settings,
+     * but harmlessly fail to take effect in cases of races.
+     *
+     * The element count is maintained using a specialization of
+     * LongAdder. We need to incorporate a specialization rather than
+     * just use a LongAdder in order to access implicit
+     * contention-sensing that leads to creation of multiple
+     * CounterCells.  The counter mechanics avoid contention on
+     * updates but can encounter cache thrashing if read too
+     * frequently during concurrent access. To avoid reading so often,
+     * resizing under contention is attempted only upon adding to a
+     * bin already holding two or more nodes. Under uniform hash
+     * distributions, the probability of this occurring at threshold
+     * is around 13%, meaning that only about 1 in 8 puts check
+     * threshold (and after resizing, many fewer do so).
+     *
+     * TreeBins use a special form of comparison for search and
+     * related operations (which is the main reason we cannot use
+     * existing collections such as TreeMaps). TreeBins contain
+     * Comparable elements, but may contain others, as well as
+     * elements that are Comparable but not necessarily Comparable
+     * for the same T, so we cannot invoke compareTo among them. To
+     * handle this, the tree is ordered primarily by hash value, then
+     * by Comparable.compareTo order if applicable.  On lookup at a
+     * node, if elements are not comparable or compare as 0 then both
+     * left and right children may need to be searched in the case of
+     * tied hash values. (This corresponds to the full list search
+     * that would be necessary if all elements were non-Comparable and
+     * had tied hashes.)  The red-black balancing code is updated from
+     * pre-jdk-collections
+     * (http://gee.cs.oswego.edu/dl/classes/collections/RBCell.java)
+     * based in turn on Cormen, Leiserson, and Rivest "Introduction to
+     * Algorithms" (CLR).
+     *
+     * TreeBins also require an additional locking mechanism.  While
+     * list traversal is always possible by readers even during
+     * updates, tree traversal is not, mainly because of tree-rotations
+     * that may change the root node and/or its linkages.  TreeBins
+     * include a simple read-write lock mechanism parasitic on the
+     * main bin-synchronization strategy: Structural adjustments
+     * associated with an insertion or removal are already bin-locked
+     * (and so cannot conflict with other writers) but must wait for
+     * ongoing readers to finish. Since there can be only one such
+     * waiter, we use a simple scheme using a single "waiter" field to
+     * block writers.  However, readers need never block.  If the root
+     * lock is held, they proceed along the slow traversal path (via
+     * next-pointers) until the lock becomes available or the list is
+     * exhausted, whichever comes first. These cases are not fast, but
+     * maximize aggregate expected throughput.
+     *
+     * Maintaining API and serialization compatibility with previous
+     * versions of this class introduces several oddities. Mainly: We
+     * leave untouched but unused constructor arguments refering to
+     * concurrencyLevel. We accept a loadFactor constructor argument,
+     * but apply it only to initial table capacity (which is the only
+     * time that we can guarantee to honor it.) We also declare an
+     * unused "Segment" class that is instantiated in minimal form
+     * only when serializing.
+     *
+     * This file is organized to make things a little easier to follow
+     * while reading than they might otherwise: First the main static
+     * declarations and utilities, then fields, then main public
+     * methods (with a few factorings of multiple public methods into
+     * internal ones), then sizing methods, trees, traversers, and
+     * bulk operations.
      */
 
     /* ---------------- Constants -------------- */
 
     /**
-     * The default initial capacity for this table,
-     * used when not otherwise specified in a constructor.
+     * The largest possible table capacity.  This value must be
+     * exactly 1<<30 to stay within Java array allocation and indexing
+     * bounds for power of two table sizes, and is further required
+     * because the top two bits of 32bit hash fields are used for
+     * control purposes.
      */
-    static final int DEFAULT_INITIAL_CAPACITY = 16;
+    private static final int MAXIMUM_CAPACITY = 1 << 30;
 
     /**
-     * The default load factor for this table, used when not
-     * otherwise specified in a constructor.
+     * The default initial table capacity.  Must be a power of 2
+     * (i.e., at least 1) and at most MAXIMUM_CAPACITY.
      */
-    static final float DEFAULT_LOAD_FACTOR = 0.75f;
+    private static final int DEFAULT_CAPACITY = 16;
 
     /**
-     * The default concurrency level for this table, used when not
-     * otherwise specified in a constructor.
+     * The largest possible (non-power of two) array size.
+     * Needed by toArray and related methods.
      */
-    static final int DEFAULT_CONCURRENCY_LEVEL = 16;
+    static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
 
     /**
-     * The maximum capacity, used if a higher value is implicitly
-     * specified by either of the constructors with arguments.  MUST
-     * be a power of two <= 1<<30 to ensure that entries are indexable
-     * using ints.
+     * The default concurrency level for this table. Unused but
+     * defined for compatibility with previous versions of this class.
      */
-    static final int MAXIMUM_CAPACITY = 1 << 30;
+    private static final int DEFAULT_CONCURRENCY_LEVEL = 16;
 
     /**
-     * The minimum capacity for per-segment tables.  Must be a power
-     * of two, at least two to avoid immediate resizing on next use
-     * after lazy construction.
+     * The load factor for this table. Overrides of this value in
+     * constructors affect only the initial table capacity.  The
+     * actual floating point value isn't normally used -- it is
+     * simpler to use expressions such as {@code n - (n >>> 2)} for
+     * the associated resizing threshold.
      */
-    static final int MIN_SEGMENT_TABLE_CAPACITY = 2;
+    private static final float LOAD_FACTOR = 0.75f;
 
     /**
-     * The maximum number of segments to allow; used to bound
-     * constructor arguments. Must be power of two less than 1 << 24.
+     * The bin count threshold for using a tree rather than list for a
+     * bin.  Bins are converted to trees when adding an element to a
+     * bin with at least this many nodes. The value must be greater
+     * than 2, and should be at least 8 to mesh with assumptions in
+     * tree removal about conversion back to plain bins upon
+     * shrinkage.
      */
-    static final int MAX_SEGMENTS = 1 << 16; // slightly conservative
+    static final int TREEIFY_THRESHOLD = 8;
 
     /**
-     * Number of unsynchronized retries in size and containsValue
-     * methods before resorting to locking. This is used to avoid
-     * unbounded retries if tables undergo continuous modification
-     * which would make it impossible to obtain an accurate result.
+     * The bin count threshold for untreeifying a (split) bin during a
+     * resize operation. Should be less than TREEIFY_THRESHOLD, and at
+     * most 6 to mesh with shrinkage detection under removal.
      */
-    static final int RETRIES_BEFORE_LOCK = 2;
-
-    /* ---------------- Fields -------------- */
+    static final int UNTREEIFY_THRESHOLD = 6;
 
     /**
-     * Mask value for indexing into segments. The upper bits of a
-     * key's hash code are used to choose the segment.
+     * The smallest table capacity for which bins may be treeified.
+     * (Otherwise the table is resized if too many nodes in a bin.)
+     * The value should be at least 4 * TREEIFY_THRESHOLD to avoid
+     * conflicts between resizing and treeification thresholds.
      */
-    final int segmentMask;
+    static final int MIN_TREEIFY_CAPACITY = 64;
 
     /**
-     * Shift value for indexing within segments.
+     * Minimum number of rebinnings per transfer step. Ranges are
+     * subdivided to allow multiple resizer threads.  This value
+     * serves as a lower bound to avoid resizers encountering
+     * excessive memory contention.  The value should be at least
+     * DEFAULT_CAPACITY.
      */
-    final int segmentShift;
+    private static final int MIN_TRANSFER_STRIDE = 16;
 
-    /**
-     * The segments, each of which is a specialized hash table.
+    /*
+     * Encodings for Node hash fields. See above for explanation.
      */
-    final Segment<K,V>[] segments;
+    static final int MOVED     = 0x8fffffff; // (-1) hash for forwarding nodes
+    static final int TREEBIN   = 0x80000000; // hash for roots of trees
+    static final int RESERVED  = 0x80000001; // hash for transient reservations
+    static final int HASH_BITS = 0x7fffffff; // usable bits of normal node hash
+
+    /** Number of CPUS, to place bounds on some sizings */
+    static final int NCPU = Runtime.getRuntime().availableProcessors();
 
-    transient Set<K> keySet;
-    transient Set<Map.Entry<K,V>> entrySet;
-    transient Collection<V> values;
+    /** For serialization compatibility. */
+    private static final ObjectStreamField[] serialPersistentFields = {
+        new ObjectStreamField("segments", Segment[].class),
+        new ObjectStreamField("segmentMask", Integer.TYPE),
+        new ObjectStreamField("segmentShift", Integer.TYPE)
+    };
+
+    /* ---------------- Nodes -------------- */
 
     /**
-     * ConcurrentHashMap list entry. Note that this is never exported
-     * out as a user-visible Map.Entry.
+     * Key-value entry.  This class is never exported out as a
+     * user-mutable Map.Entry (i.e., one supporting setValue; see
+     * MapEntry below), but can be used for read-only traversals used
+     * in bulk tasks.  Subclasses of Node with a negative hash field
+     * are special, and contain null keys and values (but are never
+     * exported).  Otherwise, keys and vals are never null.
      */
-    static final class HashEntry<K,V> {
+    static class Node<K,V> implements Map.Entry<K,V> {
         final int hash;
         final K key;
-        volatile V value;
-        volatile HashEntry<K,V> next;
+        volatile V val;
+        Node<K,V> next;
 
-        HashEntry(int hash, K key, V value, HashEntry<K,V> next) {
+        Node(int hash, K key, V val, Node<K,V> next) {
             this.hash = hash;
             this.key = key;
-            this.value = value;
+            this.val = val;
             this.next = next;
         }
 
-        /**
-         * Sets next field with volatile write semantics.  (See above
-         * about use of putOrderedObject.)
-         */
-        final void setNext(HashEntry<K,V> n) {
-            UNSAFE.putOrderedObject(this, nextOffset, n);
+        public final K getKey()       { return key; }
+        public final V getValue()     { return val; }
+        public final int hashCode()   { return key.hashCode() ^ val.hashCode(); }
+        public final String toString(){ return key + "=" + val; }
+        public final V setValue(V value) {
+            throw new UnsupportedOperationException();
         }
 
-        // Unsafe mechanics
-        static final sun.misc.Unsafe UNSAFE;
-        static final long nextOffset;
-        static {
-            try {
-                UNSAFE = sun.misc.Unsafe.getUnsafe();
-                Class<?> k = HashEntry.class;
-                nextOffset = UNSAFE.objectFieldOffset
-                    (k.getDeclaredField("next"));
-            } catch (Exception e) {
-                throw new Error(e);
+        public final boolean equals(Object o) {
+            Object k, v, u; Map.Entry<?,?> e;
+            return ((o instanceof Map.Entry) &&
+                    (k = (e = (Map.Entry<?,?>)o).getKey()) != null &&
+                    (v = e.getValue()) != null &&
+                    (k == key || k.equals(key)) &&
+                    (v == (u = val) || v.equals(u)));
+        }
+
+        /**
+         * Virtualized support for map.get(); overridden in subclasses.
+         */
+        Node<K,V> find(int h, Object k) {
+            Node<K,V> e = this;
+            if (k != null) {
+                do {
+                    K ek;
+                    if (e.hash == h &&
+                        ((ek = e.key) == k || (ek != null && k.equals(ek))))
+                        return e;
+                } while ((e = e.next) != null);
             }
+            return null;
         }
     }
 
+    /* ---------------- Static utilities -------------- */
+
     /**
-     * Gets the ith element of given table (if nonnull) with volatile
-     * read semantics. Note: This is manually integrated into a few
-     * performance-sensitive methods to reduce call overhead.
+     * Spreads (XORs) higher bits of hash to lower and also forces top
+     * bit to 0. Because the table uses power-of-two masking, sets of
+     * hashes that vary only in bits above the current mask will
+     * always collide. (Among known examples are sets of Float keys
+     * holding consecutive whole numbers in small tables.)  So we
+     * apply a transform that spreads the impact of higher bits
+     * downward. There is a tradeoff between speed, utility, and
+     * quality of bit-spreading. Because many common sets of hashes
+     * are already reasonably distributed (so don't benefit from
+     * spreading), and because we use trees to handle large sets of
+     * collisions in bins, we just XOR some shifted bits in the
+     * cheapest possible way to reduce systematic lossage, as well as
+     * to incorporate impact of the highest bits that would otherwise
+     * never be used in index calculations because of table bounds.
      */
-    @SuppressWarnings("unchecked")
-    static final <K,V> HashEntry<K,V> entryAt(HashEntry<K,V>[] tab, int i) {
-        return (tab == null) ? null :
-            (HashEntry<K,V>) UNSAFE.getObjectVolatile
-            (tab, ((long)i << TSHIFT) + TBASE);
+    static final int spread(int h) {
+        return (h ^ (h >>> 16)) & HASH_BITS;
     }
 
     /**
-     * Sets the ith element of given table, with volatile write
-     * semantics. (See above about use of putOrderedObject.)
+     * Returns a power of two table size for the given desired capacity.
+     * See Hackers Delight, sec 3.2
      */
-    static final <K,V> void setEntryAt(HashEntry<K,V>[] tab, int i,
-                                       HashEntry<K,V> e) {
-        UNSAFE.putOrderedObject(tab, ((long)i << TSHIFT) + TBASE, e);
+    private static final int tableSizeFor(int c) {
+        int n = c - 1;
+        n |= n >>> 1;
+        n |= n >>> 2;
+        n |= n >>> 4;
+        n |= n >>> 8;
+        n |= n >>> 16;
+        return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
     }
 
+
     /**
-     * Applies a supplemental hash function to a given hashCode, which
-     * defends against poor quality hash functions.  This is critical
-     * because ConcurrentHashMap uses power-of-two length hash tables,
-     * that otherwise encounter collisions for hashCodes that do not
-     * differ in lower or upper bits.
+     * Returns x's Class if it is of the form "class C implements
+     * Comparable<C>", else null.
      */
-    private static int hash(int h) {
-        // Spread bits to regularize both segment and index locations,
-        // using variant of single-word Wang/Jenkins hash.
-        h += (h <<  15) ^ 0xffffcd7d;
-        h ^= (h >>> 10);
-        h += (h <<   3);
-        h ^= (h >>>  6);
-        h += (h <<   2) + (h << 14);
-        return h ^ (h >>> 16);
+    static Class<?> comparableClassFor(Object x) {
+        if (x instanceof Comparable) {
+            Class<?> c; Type[] ts, as; Type t; ParameterizedType p;
+            if ((c = x.getClass()) == String.class) // bypass checks
+                return c;
+            if ((ts = c.getGenericInterfaces()) != null) {
+                for (int i = 0; i < ts.length; ++i) {
+                    if (((t = ts[i]) instanceof ParameterizedType) &&
+                        ((p = (ParameterizedType)t).getRawType() ==
+                         Comparable.class) &&
+                        (as = p.getActualTypeArguments()) != null &&
+                        as.length == 1 && as[0] == c) // type arg is c
+                        return c;
+                }
+            }
+        }
+        return null;
     }
 
     /**
-     * Segments are specialized versions of hash tables.  This
-     * subclasses from ReentrantLock opportunistically, just to
-     * simplify some locking and avoid separate construction.
+     * Returns k.compareTo(x) if x matches kc (k's screened comparable
+     * class), else 0.
      */
-    static final class Segment<K,V> extends ReentrantLock implements Serializable {
-        /*
-         * Segments maintain a table of entry lists that are always
-         * kept in a consistent state, so can be read (via volatile
-         * reads of segments and tables) without locking.  This
-         * requires replicating nodes when necessary during table
-         * resizing, so the old lists can be traversed by readers
-         * still using old version of table.
-         *
-         * This class defines only mutative methods requiring locking.
-         * Except as noted, the methods of this class perform the
-         * per-segment versions of ConcurrentHashMap methods.  (Other
-         * methods are integrated directly into ConcurrentHashMap
-         * methods.) These mutative methods use a form of controlled
-         * spinning on contention via methods scanAndLock and
-         * scanAndLockForPut. These intersperse tryLocks with
-         * traversals to locate nodes.  The main benefit is to absorb
-         * cache misses (which are very common for hash tables) while
-         * obtaining locks so that traversal is faster once
-         * acquired. We do not actually use the found nodes since they
-         * must be re-acquired under lock anyway to ensure sequential
-         * consistency of updates (and in any case may be undetectably
-         * stale), but they will normally be much faster to re-locate.
-         * Also, scanAndLockForPut speculatively creates a fresh node
-         * to use in put if no node is found.
-         */
+    @SuppressWarnings({"rawtypes","unchecked"}) // for cast to Comparable
+    static int compareComparables(Class<?> kc, Object k, Object x) {
+        return (x == null || x.getClass() != kc ? 0 :
+                ((Comparable)k).compareTo(x));
+    }
 
-        private static final long serialVersionUID = 2249069246763182397L;
+    /* ---------------- Table element access -------------- */
 
-        /**
-         * The maximum number of times to tryLock in a prescan before
-         * possibly blocking on acquire in preparation for a locked
-         * segment operation. On multiprocessors, using a bounded
-         * number of retries maintains cache acquired while locating
-         * nodes.
-         */
-        static final int MAX_SCAN_RETRIES =
-            Runtime.getRuntime().availableProcessors() > 1 ? 64 : 1;
+    /*
+     * Volatile access methods are used for table elements as well as
+     * elements of in-progress next table while resizing.  All uses of
+     * the tab arguments must be null checked by callers.  All callers
+     * also paranoically precheck that tab's length is not zero (or an
+     * equivalent check), thus ensuring that any index argument taking
+     * the form of a hash value anded with (length - 1) is a valid
+     * index.  Note that, to be correct wrt arbitrary concurrency
+     * errors by users, these checks must operate on local variables,
+     * which accounts for some odd-looking inline assignments below.
+     * Note that calls to setTabAt always occur within locked regions,
+     * and so do not need full volatile semantics, but still require
+     * ordering to maintain concurrent readability.
+     */
 
-        /**
-         * The per-segment table. Elements are accessed via
-         * entryAt/setEntryAt providing volatile semantics.
-         */
-        transient volatile HashEntry<K,V>[] table;
+    @SuppressWarnings("unchecked")
+    static final <K,V> Node<K,V> tabAt(Node<K,V>[] tab, int i) {
+        return (Node<K,V>)U.getObjectVolatile(tab, ((long)i << ASHIFT) + ABASE);
+    }
 
-        /**
-         * The number of elements. Accessed only either within locks
-         * or among other volatile reads that maintain visibility.
-         */
-        transient int count;
+    static final <K,V> boolean casTabAt(Node<K,V>[] tab, int i,
+                                        Node<K,V> c, Node<K,V> v) {
+        return U.compareAndSwapObject(tab, ((long)i << ASHIFT) + ABASE, c, v);
+    }
 
-        /**
-         * The total number of mutative operations in this segment.
-         * Even though this may overflows 32 bits, it provides
-         * sufficient accuracy for stability checks in CHM isEmpty()
-         * and size() methods.  Accessed only either within locks or
-         * among other volatile reads that maintain visibility.
-         */
-        transient int modCount;
+    static final <K,V> void setTabAt(Node<K,V>[] tab, int i, Node<K,V> v) {
+        U.putOrderedObject(tab, ((long)i << ASHIFT) + ABASE, v);
+    }
 
-        /**
-         * The table is rehashed when its size exceeds this threshold.
-         * (The value of this field is always <tt>(int)(capacity *
-         * loadFactor)</tt>.)
-         */
-        transient int threshold;
+    /* ---------------- Fields -------------- */
 
-        /**
-         * The load factor for the hash table.  Even though this value
-         * is same for all segments, it is replicated to avoid needing
-         * links to outer object.
-         * @serial
-         */
-        final float loadFactor;
+    /**
+     * The array of bins. Lazily initialized upon first insertion.
+     * Size is always a power of two. Accessed directly by iterators.
+     */
+    transient volatile Node<K,V>[] table;
 
-        Segment(float lf, int threshold, HashEntry<K,V>[] tab) {
-            this.loadFactor = lf;
-            this.threshold = threshold;
-            this.table = tab;
-        }
+    /**
+     * The next table to use; non-null only while resizing.
+     */
+    private transient volatile Node<K,V>[] nextTable;
 
-        final V put(K key, int hash, V value, boolean onlyIfAbsent) {
-            HashEntry<K,V> node = tryLock() ? null :
-                scanAndLockForPut(key, hash, value);
-            V oldValue;
-            try {
-                HashEntry<K,V>[] tab = table;
-                int index = (tab.length - 1) & hash;
-                HashEntry<K,V> first = entryAt(tab, index);
-                for (HashEntry<K,V> e = first;;) {
-                    if (e != null) {
-                        K k;
-                        if ((k = e.key) == key ||
-                            (e.hash == hash && key.equals(k))) {
-                            oldValue = e.value;
-                            if (!onlyIfAbsent) {
-                                e.value = value;
-                                ++modCount;
-                            }
-                            break;
-                        }
-                        e = e.next;
-                    }
-                    else {
-                        if (node != null)
-                            node.setNext(first);
-                        else
-                            node = new HashEntry<K,V>(hash, key, value, first);
-                        int c = count + 1;
-                        if (c > threshold && tab.length < MAXIMUM_CAPACITY)
-                            rehash(node);
-                        else
-                            setEntryAt(tab, index, node);
-                        ++modCount;
-                        count = c;
-                        oldValue = null;
-                        break;
-                    }
-                }
-            } finally {
-                unlock();
-            }
-            return oldValue;
-        }
+    /**
+     * Base counter value, used mainly when there is no contention,
+     * but also as a fallback during table initialization
+     * races. Updated via CAS.
+     */
+    private transient volatile long baseCount;
 
-        /**
-         * Doubles size of table and repacks entries, also adding the
-         * given node to new table
-         */
-        @SuppressWarnings("unchecked")
-        private void rehash(HashEntry<K,V> node) {
-            /*
-             * Reclassify nodes in each list to new table.  Because we
-             * are using power-of-two expansion, the elements from
-             * each bin must either stay at same index, or move with a
-             * power of two offset. We eliminate unnecessary node
-             * creation by catching cases where old nodes can be
-             * reused because their next fields won't change.
-             * Statistically, at the default threshold, only about
-             * one-sixth of them need cloning when a table
-             * doubles. The nodes they replace will be garbage
-             * collectable as soon as they are no longer referenced by
-             * any reader thread that may be in the midst of
-             * concurrently traversing table. Entry accesses use plain
-             * array indexing because they are followed by volatile
-             * table write.
-             */
-            HashEntry<K,V>[] oldTable = table;
-            int oldCapacity = oldTable.length;
-            int newCapacity = oldCapacity << 1;
-            threshold = (int)(newCapacity * loadFactor);
-            HashEntry<K,V>[] newTable =
-                (HashEntry<K,V>[]) new HashEntry<?,?>[newCapacity];
-            int sizeMask = newCapacity - 1;
-            for (int i = 0; i < oldCapacity ; i++) {
-                HashEntry<K,V> e = oldTable[i];
-                if (e != null) {
-                    HashEntry<K,V> next = e.next;
-                    int idx = e.hash & sizeMask;
-                    if (next == null)   //  Single node on list
-                        newTable[idx] = e;
-                    else { // Reuse consecutive sequence at same slot
-                        HashEntry<K,V> lastRun = e;
-                        int lastIdx = idx;
-                        for (HashEntry<K,V> last = next;
-                             last != null;
-                             last = last.next) {
-                            int k = last.hash & sizeMask;
-                            if (k != lastIdx) {
-                                lastIdx = k;
-                                lastRun = last;
-                            }
-                        }
-                        newTable[lastIdx] = lastRun;
-                        // Clone remaining nodes
-                        for (HashEntry<K,V> p = e; p != lastRun; p = p.next) {
-                            V v = p.value;
-                            int h = p.hash;
-                            int k = h & sizeMask;
-                            HashEntry<K,V> n = newTable[k];
-                            newTable[k] = new HashEntry<K,V>(h, p.key, v, n);
-                        }
-                    }
-                }
-            }
-            int nodeIndex = node.hash & sizeMask; // add the new node
-            node.setNext(newTable[nodeIndex]);
-            newTable[nodeIndex] = node;
-            table = newTable;
-        }
+    /**
+     * Table initialization and resizing control.  When negative, the
+     * table is being initialized or resized: -1 for initialization,
+     * else -(1 + the number of active resizing threads).  Otherwise,
+     * when table is null, holds the initial table size to use upon
+     * creation, or 0 for default. After initialization, holds the
+     * next element count value upon which to resize the table.
+     */
+    private transient volatile int sizeCtl;
 
-        /**
-         * Scans for a node containing given key while trying to
-         * acquire lock, creating and returning one if not found. Upon
-         * return, guarantees that lock is held. Unlike in most
-         * methods, calls to method equals are not screened: Since
-         * traversal speed doesn't matter, we might as well help warm
-         * up the associated code and accesses as well.
-         *
-         * @return a new node if key not found, else null
-         */
-        private HashEntry<K,V> scanAndLockForPut(K key, int hash, V value) {
-            HashEntry<K,V> first = entryForHash(this, hash);
-            HashEntry<K,V> e = first;
-            HashEntry<K,V> node = null;
-            int retries = -1; // negative while locating node
-            while (!tryLock()) {
-                HashEntry<K,V> f; // to recheck first below
-                if (retries < 0) {
-                    if (e == null) {
-                        if (node == null) // speculatively create node
-                            node = new HashEntry<K,V>(hash, key, value, null);
-                        retries = 0;
-                    }
-                    else if (key.equals(e.key))
-                        retries = 0;
-                    else
-                        e = e.next;
-                }
-                else if (++retries > MAX_SCAN_RETRIES) {
-                    lock();
-                    break;
-                }
-                else if ((retries & 1) == 0 &&
-                         (f = entryForHash(this, hash)) != first) {
-                    e = first = f; // re-traverse if entry changed
-                    retries = -1;
-                }
-            }
-            return node;
-        }
+    /**
+     * The next table index (plus one) to split while resizing.
+     */
+    private transient volatile int transferIndex;
 
-        /**
-         * Scans for a node containing the given key while trying to
-         * acquire lock for a remove or replace operation. Upon
-         * return, guarantees that lock is held.  Note that we must
-         * lock even if the key is not found, to ensure sequential
-         * consistency of updates.
-         */
-        private void scanAndLock(Object key, int hash) {
-            // similar to but simpler than scanAndLockForPut
-            HashEntry<K,V> first = entryForHash(this, hash);
-            HashEntry<K,V> e = first;
-            int retries = -1;
-            while (!tryLock()) {
-                HashEntry<K,V> f;
-                if (retries < 0) {
-                    if (e == null || key.equals(e.key))
-                        retries = 0;
-                    else
-                        e = e.next;
-                }
-                else if (++retries > MAX_SCAN_RETRIES) {
-                    lock();
-                    break;
-                }
-                else if ((retries & 1) == 0 &&
-                         (f = entryForHash(this, hash)) != first) {
-                    e = first = f;
-                    retries = -1;
-                }
-            }
-        }
+    /**
+     * The least available table index to split while resizing.
+     */
+    private transient volatile int transferOrigin;
 
-        /**
-         * Remove; match on key only if value null, else match both.
-         */
-        final V remove(Object key, int hash, Object value) {
-            if (!tryLock())
-                scanAndLock(key, hash);
-            V oldValue = null;
-            try {
-                HashEntry<K,V>[] tab = table;
-                int index = (tab.length - 1) & hash;
-                HashEntry<K,V> e = entryAt(tab, index);
-                HashEntry<K,V> pred = null;
-                while (e != null) {
-                    K k;
-                    HashEntry<K,V> next = e.next;
-                    if ((k = e.key) == key ||
-                        (e.hash == hash && key.equals(k))) {
-                        V v = e.value;
-                        if (value == null || value == v || value.equals(v)) {
-                            if (pred == null)
-                                setEntryAt(tab, index, next);
-                            else
-                                pred.setNext(next);
-                            ++modCount;
-                            --count;
-                            oldValue = v;
-                        }
-                        break;
-                    }
-                    pred = e;
-                    e = next;
-                }
-            } finally {
-                unlock();
-            }
-            return oldValue;
-        }
+    /**
+     * Spinlock (locked via CAS) used when resizing and/or creating CounterCells.
+     */
+    private transient volatile int cellsBusy;
 
-        final boolean replace(K key, int hash, V oldValue, V newValue) {
-            if (!tryLock())
-                scanAndLock(key, hash);
-            boolean replaced = false;
-            try {
-                HashEntry<K,V> e;
-                for (e = entryForHash(this, hash); e != null; e = e.next) {
-                    K k;
-                    if ((k = e.key) == key ||
-                        (e.hash == hash && key.equals(k))) {
-                        if (oldValue.equals(e.value)) {
-                            e.value = newValue;
-                            ++modCount;
-                            replaced = true;
-                        }
-                        break;
-                    }
-                }
-            } finally {
-                unlock();
-            }
-            return replaced;
-        }
+    /**
+     * Table of counter cells. When non-null, size is a power of 2.
+     */
+    private transient volatile CounterCell[] counterCells;
 
-        final V replace(K key, int hash, V value) {
-            if (!tryLock())
-                scanAndLock(key, hash);
-            V oldValue = null;
-            try {
-                HashEntry<K,V> e;
-                for (e = entryForHash(this, hash); e != null; e = e.next) {
-                    K k;
-                    if ((k = e.key) == key ||
-                        (e.hash == hash && key.equals(k))) {
-                        oldValue = e.value;
-                        e.value = value;
-                        ++modCount;
-                        break;
-                    }
-                }
-            } finally {
-                unlock();
-            }
-            return oldValue;
-        }
+    // views
+    private transient KeySetView<K,V> keySet;
+    private transient ValuesView<K,V> values;
+    private transient EntrySetView<K,V> entrySet;
 
-        final void clear() {
-            lock();
-            try {
-                HashEntry<K,V>[] tab = table;
-                for (int i = 0; i < tab.length ; i++)
-                    setEntryAt(tab, i, null);
-                ++modCount;
-                count = 0;
-            } finally {
-                unlock();
-            }
-        }
-    }
 
-    // Accessing segments
+    /* ---------------- Public operations -------------- */
 
     /**
-     * Gets the jth element of given segment array (if nonnull) with
-     * volatile element access semantics via Unsafe. (The null check
-     * can trigger harmlessly only during deserialization.) Note:
-     * because each element of segments array is set only once (using
-     * fully ordered writes), some performance-sensitive methods rely
-     * on this method only as a recheck upon null reads.
+     * Creates a new, empty map with the default initial table size (16).
      */
-    @SuppressWarnings("unchecked")
-    static final <K,V> Segment<K,V> segmentAt(Segment<K,V>[] ss, int j) {
-        long u = (j << SSHIFT) + SBASE;
-        return ss == null ? null :
-            (Segment<K,V>) UNSAFE.getObjectVolatile(ss, u);
+    public ConcurrentHashMap() {
     }
 
     /**
-     * Returns the segment for the given index, creating it and
-     * recording in segment table (via CAS) if not already present.
+     * Creates a new, empty map with an initial table size
+     * accommodating the specified number of elements without the need
+     * to dynamically resize.
      *
-     * @param k the index
-     * @return the segment
-     */
-    @SuppressWarnings("unchecked")
-    private Segment<K,V> ensureSegment(int k) {
-        final Segment<K,V>[] ss = this.segments;
-        long u = (k << SSHIFT) + SBASE; // raw offset
-        Segment<K,V> seg;
-        if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u)) == null) {
-            Segment<K,V> proto = ss[0]; // use segment 0 as prototype
-            int cap = proto.table.length;
-            float lf = proto.loadFactor;
-            int threshold = (int)(cap * lf);
-            HashEntry<K,V>[] tab = (HashEntry<K,V>[])new HashEntry<?,?>[cap];
-            if ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u))
-                == null) { // recheck
-                Segment<K,V> s = new Segment<K,V>(lf, threshold, tab);
-                while ((seg = (Segment<K,V>)UNSAFE.getObjectVolatile(ss, u))
-                       == null) {
-                    if (UNSAFE.compareAndSwapObject(ss, u, null, seg = s))
-                        break;
-                }
-            }
-        }
-        return seg;
-    }
-
-    // Hash-based segment and entry accesses
-
-    /**
-     * Gets the segment for the given hash code.
+     * @param initialCapacity The implementation performs internal
+     * sizing to accommodate this many elements.
+     * @throws IllegalArgumentException if the initial capacity of
+     * elements is negative
      */
-    @SuppressWarnings("unchecked")
-    private Segment<K,V> segmentForHash(int h) {
-        long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE;
-        return (Segment<K,V>) UNSAFE.getObjectVolatile(segments, u);
+    public ConcurrentHashMap(int initialCapacity) {
+        if (initialCapacity < 0)
+            throw new IllegalArgumentException();
+        int cap = ((initialCapacity >= (MAXIMUM_CAPACITY >>> 1)) ?
+                   MAXIMUM_CAPACITY :
+                   tableSizeFor(initialCapacity + (initialCapacity >>> 1) + 1));
+        this.sizeCtl = cap;
     }
 
     /**
-     * Gets the table entry for the given segment and hash code.
+     * Creates a new map with the same mappings as the given map.
+     *
+     * @param m the map
      */
-    @SuppressWarnings("unchecked")
-    static final <K,V> HashEntry<K,V> entryForHash(Segment<K,V> seg, int h) {
-        HashEntry<K,V>[] tab;
-        return (seg == null || (tab = seg.table) == null) ? null :
-            (HashEntry<K,V>) UNSAFE.getObjectVolatile
-            (tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE);
+    public ConcurrentHashMap(Map<? extends K, ? extends V> m) {
+        this.sizeCtl = DEFAULT_CAPACITY;
+        putAll(m);
     }
 
-    /* ---------------- Public operations -------------- */
-
     /**
-     * Creates a new, empty map with the specified initial
-     * capacity, load factor and concurrency level.
+     * Creates a new, empty map with an initial table size based on
+     * the given number of elements ({@code initialCapacity}) and
+     * initial table density ({@code loadFactor}).
      *
      * @param initialCapacity the initial capacity. The implementation
-     * performs internal sizing to accommodate this many elements.
-     * @param loadFactor  the load factor threshold, used to control resizing.
-     * Resizing may be performed when the average number of elements per
-     * bin exceeds this threshold.
-     * @param concurrencyLevel the estimated number of concurrently
-     * updating threads. The implementation performs internal sizing
-     * to try to accommodate this many threads.
-     * @throws IllegalArgumentException if the initial capacity is
-     * negative or the load factor or concurrencyLevel are
-     * nonpositive.
-     */
-    @SuppressWarnings("unchecked")
-    public ConcurrentHashMap(int initialCapacity,
-                             float loadFactor, int concurrencyLevel) {
-        if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0)
-            throw new IllegalArgumentException();
-        if (concurrencyLevel > MAX_SEGMENTS)
-            concurrencyLevel = MAX_SEGMENTS;
-        // Find power-of-two sizes best matching arguments
-        int sshift = 0;
-        int ssize = 1;
-        while (ssize < concurrencyLevel) {
-            ++sshift;
-            ssize <<= 1;
-        }
-        this.segmentShift = 32 - sshift;
-        this.segmentMask = ssize - 1;
-        if (initialCapacity > MAXIMUM_CAPACITY)
-            initialCapacity = MAXIMUM_CAPACITY;
-        int c = initialCapacity / ssize;
-        if (c * ssize < initialCapacity)
-            ++c;
-        int cap = MIN_SEGMENT_TABLE_CAPACITY;
-        while (cap < c)
-            cap <<= 1;
-        // create segments and segments[0]
-        Segment<K,V> s0 =
-            new Segment<K,V>(loadFactor, (int)(cap * loadFactor),
-                             (HashEntry<K,V>[])new HashEntry<?,?>[cap]);
-        Segment<K,V>[] ss = (Segment<K,V>[])new Segment<?,?>[ssize];
-        UNSAFE.putOrderedObject(ss, SBASE, s0); // ordered write of segments[0]
-        this.segments = ss;
-    }
-
-    /**
-     * Creates a new, empty map with the specified initial capacity
-     * and load factor and with the default concurrencyLevel (16).
-     *
-     * @param initialCapacity The implementation performs internal
-     * sizing to accommodate this many elements.
-     * @param loadFactor  the load factor threshold, used to control resizing.
-     * Resizing may be performed when the average number of elements per
-     * bin exceeds this threshold.
+     * performs internal sizing to accommodate this many elements,
+     * given the specified load factor.
+     * @param loadFactor the load factor (table density) for
+     * establishing the initial table size
      * @throws IllegalArgumentException if the initial capacity of
      * elements is negative or the load factor is nonpositive
      *
      * @since 1.6
      */
     public ConcurrentHashMap(int initialCapacity, float loadFactor) {
-        this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);
+        this(initialCapacity, loadFactor, 1);
     }
 
     /**
-     * Creates a new, empty map with the specified initial capacity,
-     * and with default load factor (0.75) and concurrencyLevel (16).
+     * Creates a new, empty map with an initial table size based on
+     * the given number of elements ({@code initialCapacity}), table
+     * density ({@code loadFactor}), and number of concurrently
+     * updating threads ({@code concurrencyLevel}).
      *
      * @param initialCapacity the initial capacity. The implementation
-     * performs internal sizing to accommodate this many elements.
-     * @throws IllegalArgumentException if the initial capacity of
-     * elements is negative.
+     * performs internal sizing to accommodate this many elements,
+     * given the specified load factor.
+     * @param loadFactor the load factor (table density) for
+     * establishing the initial table size
+     * @param concurrencyLevel the estimated number of concurrently
+     * updating threads. The implementation may use this value as
+     * a sizing hint.
+     * @throws IllegalArgumentException if the initial capacity is
+     * negative or the load factor or concurrencyLevel are
+     * nonpositive
      */
-    public ConcurrentHashMap(int initialCapacity) {
-        this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
+    public ConcurrentHashMap(int initialCapacity,
+                             float loadFactor, int concurrencyLevel) {
+        if (!(loadFactor > 0.0f) || initialCapacity < 0 || concurrencyLevel <= 0)
+            throw new IllegalArgumentException();
+        if (initialCapacity < concurrencyLevel)   // Use at least as many bins
+            initialCapacity = concurrencyLevel;   // as estimated threads
+        long size = (long)(1.0 + (long)initialCapacity / loadFactor);
+        int cap = (size >= (long)MAXIMUM_CAPACITY) ?
+            MAXIMUM_CAPACITY : tableSizeFor((int)size);
+        this.sizeCtl = cap;
     }
 
-    /**
-     * Creates a new, empty map with a default initial capacity (16),
-     * load factor (0.75) and concurrencyLevel (16).
-     */
-    public ConcurrentHashMap() {
-        this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
-    }
+    // Original (since JDK1.2) Map methods
 
     /**
-     * Creates a new map with the same mappings as the given map.
-     * The map is created with a capacity of 1.5 times the number
-     * of mappings in the given map or 16 (whichever is greater),
-     * and a default load factor (0.75) and concurrencyLevel (16).
-     *
-     * @param m the map
+     * {@inheritDoc}
      */
-    public ConcurrentHashMap(Map<? extends K, ? extends V> m) {
-        this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1,
-                      DEFAULT_INITIAL_CAPACITY),
-             DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
-        putAll(m);
+    public int size() {
+        long n = sumCount();
+        return ((n < 0L) ? 0 :
+                (n > (long)Integer.MAX_VALUE) ? Integer.MAX_VALUE :
+                (int)n);
     }
 
     /**
-     * Returns <tt>true</tt> if this map contains no key-value mappings.
-     *
-     * @return <tt>true</tt> if this map contains no key-value mappings
+     * {@inheritDoc}
      */
     public boolean isEmpty() {
-        /*
-         * Sum per-segment modCounts to avoid mis-reporting when
-         * elements are concurrently added and removed in one segment
-         * while checking another, in which case the table was never
-         * actually empty at any point. (The sum ensures accuracy up
-         * through at least 1<<31 per-segment modifications before
-         * recheck.)  Methods size() and containsValue() use similar
-         * constructions for stability checks.
-         */
-        long sum = 0L;
-        final Segment<K,V>[] segments = this.segments;
-        for (int j = 0; j < segments.length; ++j) {
-            Segment<K,V> seg = segmentAt(segments, j);
-            if (seg != null) {
-                if (seg.count != 0)
-                    return false;
-                sum += seg.modCount;
-            }
-        }
-        if (sum != 0L) { // recheck unless no modifications
-            for (int j = 0; j < segments.length; ++j) {
-                Segment<K,V> seg = segmentAt(segments, j);
-                if (seg != null) {
-                    if (seg.count != 0)
-                        return false;
-                    sum -= seg.modCount;
-                }
-            }
-            if (sum != 0L)
-                return false;
-        }
-        return true;
-    }
-
-    /**
-     * Returns the number of key-value mappings in this map.  If the
-     * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
-     * <tt>Integer.MAX_VALUE</tt>.
-     *
-     * @return the number of key-value mappings in this map
-     */
-    public int size() {
-        // Try a few times to get accurate count. On failure due to
-        // continuous async changes in table, resort to locking.
-        final Segment<K,V>[] segments = this.segments;
-        final int segmentCount = segments.length;
-
-        long previousSum = 0L;
-        for (int retries = -1; retries < RETRIES_BEFORE_LOCK; retries++) {
-            long sum = 0L;    // sum of modCounts
-            long size = 0L;
-            for (int i = 0; i < segmentCount; i++) {
-                Segment<K,V> segment = segmentAt(segments, i);
-                if (segment != null) {
-                    sum += segment.modCount;
-                    size += segment.count;
-                }
-            }
-            if (sum == previousSum)
-                return ((size >>> 31) == 0) ? (int) size : Integer.MAX_VALUE;
-            previousSum = sum;
-        }
-
-        long size = 0L;
-        for (int i = 0; i < segmentCount; i++) {
-            Segment<K,V> segment = ensureSegment(i);
-            segment.lock();
-            size += segment.count;
-        }
-        for (int i = 0; i < segmentCount; i++)
-            segments[i].unlock();
-        return ((size >>> 31) == 0) ? (int) size : Integer.MAX_VALUE;
+        return sumCount() <= 0L; // ignore transient negative values
     }
 
     /**
@@ -878,18 +742,20 @@ public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>
      * @throws NullPointerException if the specified key is null
      */
     public V get(Object key) {
-        Segment<K,V> s; // manually integrate access methods to reduce overhead
-        HashEntry<K,V>[] tab;
-        int h = hash(key.hashCode());
-        long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE;
-        if ((s = (Segment<K,V>)UNSAFE.getObjectVolatile(segments, u)) != null &&
-            (tab = s.table) != null) {
-            for (HashEntry<K,V> e = (HashEntry<K,V>) UNSAFE.getObjectVolatile
-                     (tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE);
-                 e != null; e = e.next) {
-                K k;
-                if ((k = e.key) == key || (e.hash == h && key.equals(k)))
-                    return e.value;
+        Node<K,V>[] tab; Node<K,V> e, p; int n, eh; K ek;
+        int h = spread(key.hashCode());
+        if ((tab = table) != null && (n = tab.length) > 0 &&
+            (e = tabAt(tab, (n - 1) & h)) != null) {
+            if ((eh = e.hash) == h) {
+                if ((ek = e.key) == key || (ek != null && key.equals(ek)))
+                    return e.val;
+            }
+            else if (eh < 0)
+                return (p = e.find(h, key)) != null ? p.val : null;
+            while ((e = e.next) != null) {
+                if (e.hash == h &&
+                    ((ek = e.key) == key || (ek != null && key.equals(ek))))
+                    return e.val;
             }
         }
         return null;
@@ -898,149 +764,121 @@ public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>
     /**
      * Tests if the specified object is a key in this table.
      *
-     * @param  key   possible key
-     * @return <tt>true</tt> if and only if the specified object
+     * @param  key possible key
+     * @return {@code true} if and only if the specified object
      *         is a key in this table, as determined by the
-     *         <tt>equals</tt> method; <tt>false</tt> otherwise.
+     *         {@code equals} method; {@code false} otherwise
      * @throws NullPointerException if the specified key is null
      */
-    @SuppressWarnings("unchecked")
     public boolean containsKey(Object key) {
-        Segment<K,V> s; // same as get() except no need for volatile value read
-        HashEntry<K,V>[] tab;
-        int h = hash(key.hashCode());
-        long u = (((h >>> segmentShift) & segmentMask) << SSHIFT) + SBASE;
-        if ((s = (Segment<K,V>)UNSAFE.getObjectVolatile(segments, u)) != null &&
-            (tab = s.table) != null) {
-            for (HashEntry<K,V> e = (HashEntry<K,V>) UNSAFE.getObjectVolatile
-                     (tab, ((long)(((tab.length - 1) & h)) << TSHIFT) + TBASE);
-                 e != null; e = e.next) {
-                K k;
-                if ((k = e.key) == key || (e.hash == h && key.equals(k)))
-                    return true;
-            }
-        }
-        return false;
+        return get(key) != null;
     }
 
     /**
-     * Returns <tt>true</tt> if this map maps one or more keys to the
-     * specified value. Note: This method requires a full internal
-     * traversal of the hash table, and so is much slower than
-     * method <tt>containsKey</tt>.
+     * Returns {@code true} if this map maps one or more keys to the
+     * specified value. Note: This method may require a full traversal
+     * of the map, and is much slower than method {@code containsKey}.
      *
      * @param value value whose presence in this map is to be tested
-     * @return <tt>true</tt> if this map maps one or more keys to the
+     * @return {@code true} if this map maps one or more keys to the
      *         specified value
      * @throws NullPointerException if the specified value is null
      */
     public boolean containsValue(Object value) {
-        // Same idea as size()
         if (value == null)
             throw new NullPointerException();
-        final Segment<K,V>[] segments = this.segments;
-        long previousSum = 0L;
-        int lockCount = 0;
-        try {
-            for (int retries = -1; ; retries++) {
-                long sum = 0L;    // sum of modCounts
-                for (int j = 0; j < segments.length; j++) {
-                    Segment<K,V> segment;
-                    if (retries == RETRIES_BEFORE_LOCK) {
-                        segment = ensureSegment(j);
-                        segment.lock();
-                        lockCount++;
-                    } else {
-                        segment = segmentAt(segments, j);
-                        if (segment == null)
-                            continue;
-                    }
-                    HashEntry<K,V>[] tab = segment.table;
-                    if (tab != null) {
-                        for (int i = 0 ; i < tab.length; i++) {
-                            HashEntry<K,V> e;
-                            for (e = entryAt(tab, i); e != null; e = e.next) {
-                                V v = e.value;
-                                if (v != null && value.equals(v))
-                                    return true;
-                            }
-                        }
-                        sum += segment.modCount;
-                    }
-                }
-                if ((retries >= 0 && sum == previousSum) || lockCount > 0)
-                    return false;
-                previousSum = sum;
+        Node<K,V>[] t;
+        if ((t = table) != null) {
+            Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
+            for (Node<K,V> p; (p = it.advance()) != null; ) {
+                V v;
+                if ((v = p.val) == value || (v != null && value.equals(v)))
+                    return true;
             }
-        } finally {
-            for (int j = 0; j < lockCount; j++)
-                segments[j].unlock();
         }
-    }
-
-    /**
-     * Legacy method testing if some key maps into the specified value
-     * in this table.  This method is identical in functionality to
-     * {@link #containsValue}, and exists solely to ensure
-     * full compatibility with class {@link java.util.Hashtable},
-     * which supported this method prior to introduction of the
-     * Java Collections framework.
-     *
-     * @param  value a value to search for
-     * @return <tt>true</tt> if and only if some key maps to the
-     *         <tt>value</tt> argument in this table as
-     *         determined by the <tt>equals</tt> method;
-     *         <tt>false</tt> otherwise
-     * @throws NullPointerException if the specified value is null
-     */
-    public boolean contains(Object value) {
-        return containsValue(value);
+        return false;
     }
 
     /**
      * Maps the specified key to the specified value in this table.
      * Neither the key nor the value can be null.
      *
-     * <p> The value can be retrieved by calling the <tt>get</tt> method
+     * <p>The value can be retrieved by calling the {@code get} method
      * with a key that is equal to the original key.
      *
      * @param key key with which the specified value is to be associated
      * @param value value to be associated with the specified key
-     * @return the previous value associated with <tt>key</tt>, or
-     *         <tt>null</tt> if there was no mapping for <tt>key</tt>
+     * @return the previous value associated with {@code key}, or
+     *         {@code null} if there was no mapping for {@code key}
      * @throws NullPointerException if the specified key or value is null
      */
-    @SuppressWarnings("unchecked")
     public V put(K key, V value) {
-        Segment<K,V> s;
-        if (value == null)
-            throw new NullPointerException();
-        int hash = hash(key.hashCode());
-        int j = (hash >>> segmentShift) & segmentMask;
-        if ((s = (Segment<K,V>)UNSAFE.getObject          // nonvolatile; recheck
-             (segments, (j << SSHIFT) + SBASE)) == null) //  in ensureSegment
-            s = ensureSegment(j);
-        return s.put(key, hash, value, false);
+        return putVal(key, value, false);
     }
 
-    /**
-     * {@inheritDoc}
-     *
-     * @return the previous value associated with the specified key,
-     *         or <tt>null</tt> if there was no mapping for the key
-     * @throws NullPointerException if the specified key or value is null
-     */
-    @SuppressWarnings("unchecked")
-    public V putIfAbsent(K key, V value) {
-        Segment<K,V> s;
-        if (value == null)
-            throw new NullPointerException();
-        int hash = hash(key.hashCode());
-        int j = (hash >>> segmentShift) & segmentMask;
-        if ((s = (Segment<K,V>)UNSAFE.getObject
-             (segments, (j << SSHIFT) + SBASE)) == null)
-            s = ensureSegment(j);
-        return s.put(key, hash, value, true);
+    /** Implementation for put and putIfAbsent */
+    final V putVal(K key, V value, boolean onlyIfAbsent) {
+        if (key == null || value == null) throw new NullPointerException();
+        int hash = spread(key.hashCode());
+        int binCount = 0;
+        for (Node<K,V>[] tab = table;;) {
+            Node<K,V> f; int n, i, fh;
+            if (tab == null || (n = tab.length) == 0)
+                tab = initTable();
+            else if ((f = tabAt(tab, i = (n - 1) & hash)) == null) {
+                if (casTabAt(tab, i, null,
+                             new Node<K,V>(hash, key, value, null)))
+                    break;                   // no lock when adding to empty bin
+            }
+            else if ((fh = f.hash) == MOVED)
+                tab = helpTransfer(tab, f);
+            else {
+                V oldVal = null;
+                synchronized (f) {
+                    if (tabAt(tab, i) == f) {
+                        if (fh >= 0) {
+                            binCount = 1;
+                            for (Node<K,V> e = f;; ++binCount) {
+                                K ek;
+                                if (e.hash == hash &&
+                                    ((ek = e.key) == key ||
+                                     (ek != null && key.equals(ek)))) {
+                                    oldVal = e.val;
+                                    if (!onlyIfAbsent)
+                                        e.val = value;
+                                    break;
+                                }
+                                Node<K,V> pred = e;
+                                if ((e = e.next) == null) {
+                                    pred.next = new Node<K,V>(hash, key,
+                                                              value, null);
+                                    break;
+                                }
+                            }
+                        }
+                        else if (f instanceof TreeBin) {
+                            Node<K,V> p;
+                            binCount = 2;
+                            if ((p = ((TreeBin<K,V>)f).putTreeVal(hash, key,
+                                                           value)) != null) {
+                                oldVal = p.val;
+                                if (!onlyIfAbsent)
+                                    p.val = value;
+                            }
+                        }
+                    }
+                }
+                if (binCount != 0) {
+                    if (binCount >= TREEIFY_THRESHOLD)
+                        treeifyBin(tab, i);
+                    if (oldVal != null)
+                        return oldVal;
+                    break;
+                }
+            }
+        }
+        addCount(1L, binCount);
+        return null;
     }
 
     /**
@@ -1051,8 +889,9 @@ public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>
      * @param m mappings to be stored in this map
      */
     public void putAll(Map<? extends K, ? extends V> m) {
+        tryPresize(m.size());
         for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
-            put(e.getKey(), e.getValue());
+            putVal(e.getKey(), e.getValue(), false);
     }
 
     /**
@@ -1060,87 +899,147 @@ public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>
      * This method does nothing if the key is not in the map.
      *
      * @param  key the key that needs to be removed
-     * @return the previous value associated with <tt>key</tt>, or
-     *         <tt>null</tt> if there was no mapping for <tt>key</tt>
+     * @return the previous value associated with {@code key}, or
+     *         {@code null} if there was no mapping for {@code key}
      * @throws NullPointerException if the specified key is null
      */
     public V remove(Object key) {
-        int hash = hash(key.hashCode());
-        Segment<K,V> s = segmentForHash(hash);
-        return s == null ? null : s.remove(key, hash, null);
-    }
-
-    /**
-     * {@inheritDoc}
-     *
-     * @throws NullPointerException if the specified key is null
-     */
-    public boolean remove(Object key, Object value) {
-        int hash = hash(key.hashCode());
-        Segment<K,V> s;
-        return value != null && (s = segmentForHash(hash)) != null &&
-            s.remove(key, hash, value) != null;
-    }
-
-    /**
-     * {@inheritDoc}
-     *
-     * @throws NullPointerException if any of the arguments are null
-     */
-    public boolean replace(K key, V oldValue, V newValue) {
-        int hash = hash(key.hashCode());
-        if (oldValue == null || newValue == null)
-            throw new NullPointerException();
-        Segment<K,V> s = segmentForHash(hash);
-        return s != null && s.replace(key, hash, oldValue, newValue);
+        return replaceNode(key, null, null);
     }
 
     /**
-     * {@inheritDoc}
-     *
-     * @return the previous value associated with the specified key,
-     *         or <tt>null</tt> if there was no mapping for the key
-     * @throws NullPointerException if the specified key or value is null
+     * Implementation for the four public remove/replace methods:
+     * Replaces node value with v, conditional upon match of cv if
+     * non-null.  If resulting value is null, delete.
      */
-    public V replace(K key, V value) {
-        int hash = hash(key.hashCode());
-        if (value == null)
-            throw new NullPointerException();
-        Segment<K,V> s = segmentForHash(hash);
-        return s == null ? null : s.replace(key, hash, value);
+    final V replaceNode(Object key, V value, Object cv) {
+        int hash = spread(key.hashCode());
+        for (Node<K,V>[] tab = table;;) {
+            Node<K,V> f; int n, i, fh;
+            if (tab == null || (n = tab.length) == 0 ||
+                (f = tabAt(tab, i = (n - 1) & hash)) == null)
+                break;
+            else if ((fh = f.hash) == MOVED)
+                tab = helpTransfer(tab, f);
+            else {
+                V oldVal = null;
+                boolean validated = false;
+                synchronized (f) {
+                    if (tabAt(tab, i) == f) {
+                        if (fh >= 0) {
+                            validated = true;
+                            for (Node<K,V> e = f, pred = null;;) {
+                                K ek;
+                                if (e.hash == hash &&
+                                    ((ek = e.key) == key ||
+                                     (ek != null && key.equals(ek)))) {
+                                    V ev = e.val;
+                                    if (cv == null || cv == ev ||
+                                        (ev != null && cv.equals(ev))) {
+                                        oldVal = ev;
+                                        if (value != null)
+                                            e.val = value;
+                                        else if (pred != null)
+                                            pred.next = e.next;
+                                        else
+                                            setTabAt(tab, i, e.next);
+                                    }
+                                    break;
+                                }
+                                pred = e;
+                                if ((e = e.next) == null)
+                                    break;
+                            }
+                        }
+                        else if (f instanceof TreeBin) {
+                            validated = true;
+                            TreeBin<K,V> t = (TreeBin<K,V>)f;
+                            TreeNode<K,V> r, p;
+                            if ((r = t.root) != null &&
+                                (p = r.findTreeNode(hash, key, null)) != null) {
+                                V pv = p.val;
+                                if (cv == null || cv == pv ||
+                                    (pv != null && cv.equals(pv))) {
+                                    oldVal = pv;
+                                    if (value != null)
+                                        p.val = value;
+                                    else if (t.removeTreeNode(p))
+                                        setTabAt(tab, i, untreeify(t.first));
+                                }
+                            }
+                        }
+                    }
+                }
+                if (validated) {
+                    if (oldVal != null) {
+                        if (value == null)
+                            addCount(-1L, -1);
+                        return oldVal;
+                    }
+                    break;
+                }
+            }
+        }
+        return null;
     }
 
     /**
      * Removes all of the mappings from this map.
      */
     public void clear() {
-        final Segment<K,V>[] segments = this.segments;
-        for (int j = 0; j < segments.length; ++j) {
-            Segment<K,V> s = segmentAt(segments, j);
-            if (s != null)
-                s.clear();
+        long delta = 0L; // negative number of deletions
+        int i = 0;
+        Node<K,V>[] tab = table;
+        while (tab != null && i < tab.length) {
+            int fh;
+            Node<K,V> f = tabAt(tab, i);
+            if (f == null)
+                ++i;
+            else if ((fh = f.hash) == MOVED) {
+                tab = helpTransfer(tab, f);
+                i = 0; // restart
+            }
+            else {
+                synchronized (f) {
+                    if (tabAt(tab, i) == f) {
+                        Node<K,V> p = (fh >= 0 ? f :
+                                       (f instanceof TreeBin) ?
+                                       ((TreeBin<K,V>)f).first : null);
+                        while (p != null) {
+                            --delta;
+                            p = p.next;
+                        }
+                        setTabAt(tab, i++, null);
+                    }
+                }
+            }
         }
+        if (delta != 0L)
+            addCount(delta, -1);
     }
 
     /**
      * Returns a {@link Set} view of the keys contained in this map.
      * The set is backed by the map, so changes to the map are
-     * reflected in the set, and vice-versa.  The set supports element
+     * reflected in the set, and vice-versa. The set supports element
      * removal, which removes the corresponding mapping from this map,
-     * via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
-     * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
-     * operations.  It does not support the <tt>add</tt> or
-     * <tt>addAll</tt> operations.
+     * via the {@code Iterator.remove}, {@code Set.remove},
+     * {@code removeAll}, {@code retainAll}, and {@code clear}
+     * operations.  It does not support the {@code add} or
+     * {@code addAll} operations.
      *
-     * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
+     * <p>The view's {@code iterator} is a "weakly consistent" iterator
      * that will never throw {@link ConcurrentModificationException},
      * and guarantees to traverse elements as they existed upon
      * construction of the iterator, and may (but is not guaranteed to)
      * reflect any modifications subsequent to construction.
+     *
+     * @return the set view
+     *
      */
     public Set<K> keySet() {
-        Set<K> ks = keySet;
-        return (ks != null) ? ks : (keySet = new KeySet());
+        KeySetView<K,V> ks;
+        return (ks = keySet) != null ? ks : (keySet = new KeySetView<K,V>(this, null));
     }
 
     /**
@@ -1148,20 +1047,22 @@ public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>
      * The collection is backed by the map, so changes to the map are
      * reflected in the collection, and vice-versa.  The collection
      * supports element removal, which removes the corresponding
-     * mapping from this map, via the <tt>Iterator.remove</tt>,
-     * <tt>Collection.remove</tt>, <tt>removeAll</tt>,
-     * <tt>retainAll</tt>, and <tt>clear</tt> operations.  It does not
-     * support the <tt>add</tt> or <tt>addAll</tt> operations.
+     * mapping from this map, via the {@code Iterator.remove},
+     * {@code Collection.remove}, {@code removeAll},
+     * {@code retainAll}, and {@code clear} operations.  It does not
+     * support the {@code add} or {@code addAll} operations.
      *
-     * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
+     * <p>The view's {@code iterator} is a "weakly consistent" iterator
      * that will never throw {@link ConcurrentModificationException},
      * and guarantees to traverse elements as they existed upon
      * construction of the iterator, and may (but is not guaranteed to)
      * reflect any modifications subsequent to construction.
+     *
+     * @return the collection view
      */
     public Collection<V> values() {
-        Collection<V> vs = values;
-        return (vs != null) ? vs : (values = new Values());
+        ValuesView<K,V> vs;
+        return (vs = values) != null ? vs : (values = new ValuesView<K,V>(this));
     }
 
     /**
@@ -1169,20 +1070,329 @@ public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>
      * The set is backed by the map, so changes to the map are
      * reflected in the set, and vice-versa.  The set supports element
      * removal, which removes the corresponding mapping from the map,
-     * via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>,
-     * <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt>
-     * operations.  It does not support the <tt>add</tt> or
-     * <tt>addAll</tt> operations.
+     * via the {@code Iterator.remove}, {@code Set.remove},
+     * {@code removeAll}, {@code retainAll}, and {@code clear}
+     * operations.
      *
-     * <p>The view's <tt>iterator</tt> is a "weakly consistent" iterator
+     * <p>The view's {@code iterator} is a "weakly consistent" iterator
      * that will never throw {@link ConcurrentModificationException},
      * and guarantees to traverse elements as they existed upon
      * construction of the iterator, and may (but is not guaranteed to)
      * reflect any modifications subsequent to construction.
+     *
+     * @return the set view
      */
     public Set<Map.Entry<K,V>> entrySet() {
-        Set<Map.Entry<K,V>> es = entrySet;
-        return (es != null) ? es : (entrySet = new EntrySet());
+        EntrySetView<K,V> es;
+        return (es = entrySet) != null ? es : (entrySet = new EntrySetView<K,V>(this));
+    }
+
+    /**
+     * Returns the hash code value for this {@link Map}, i.e.,
+     * the sum of, for each key-value pair in the map,
+     * {@code key.hashCode() ^ value.hashCode()}.
+     *
+     * @return the hash code value for this map
+     */
+    public int hashCode() {
+        int h = 0;
+        Node<K,V>[] t;
+        if ((t = table) != null) {
+            Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
+            for (Node<K,V> p; (p = it.advance()) != null; )
+                h += p.key.hashCode() ^ p.val.hashCode();
+        }
+        return h;
+    }
+
+    /**
+     * Returns a string representation of this map.  The string
+     * representation consists of a list of key-value mappings (in no
+     * particular order) enclosed in braces ("{@code {}}").  Adjacent
+     * mappings are separated by the characters {@code ", "} (comma
+     * and space).  Each key-value mapping is rendered as the key
+     * followed by an equals sign ("{@code =}") followed by the
+     * associated value.
+     *
+     * @return a string representation of this map
+     */
+    public String toString() {
+        Node<K,V>[] t;
+        int f = (t = table) == null ? 0 : t.length;
+        Traverser<K,V> it = new Traverser<K,V>(t, f, 0, f);
+        StringBuilder sb = new StringBuilder();
+        sb.append('{');
+        Node<K,V> p;
+        if ((p = it.advance()) != null) {
+            for (;;) {
+                K k = p.key;
+                V v = p.val;
+                sb.append(k == this ? "(this Map)" : k);
+                sb.append('=');
+                sb.append(v == this ? "(this Map)" : v);
+                if ((p = it.advance()) == null)
+                    break;
+                sb.append(',').append(' ');
+            }
+        }
+        return sb.append('}').toString();
+    }
+
+    /**
+     * Compares the specified object with this map for equality.
+     * Returns {@code true} if the given object is a map with the same
+     * mappings as this map.  This operation may return misleading
+     * results if either map is concurrently modified during execution
+     * of this method.
+     *
+     * @param o object to be compared for equality with this map
+     * @return {@code true} if the specified object is equal to this map
+     */
+    public boolean equals(Object o) {
+        if (o != this) {
+            if (!(o instanceof Map))
+                return false;
+            Map<?,?> m = (Map<?,?>) o;
+            Node<K,V>[] t;
+            int f = (t = table) == null ? 0 : t.length;
+            Traverser<K,V> it = new Traverser<K,V>(t, f, 0, f);
+            for (Node<K,V> p; (p = it.advance()) != null; ) {
+                V val = p.val;
+                Object v = m.get(p.key);
+                if (v == null || (v != val && !v.equals(val)))
+                    return false;
+            }
+            for (Map.Entry<?,?> e : m.entrySet()) {
+                Object mk, mv, v;
+                if ((mk = e.getKey()) == null ||
+                    (mv = e.getValue()) == null ||
+                    (v = get(mk)) == null ||
+                    (mv != v && !mv.equals(v)))
+                    return false;
+            }
+        }
+        return true;
+    }
+
+    /**
+     * Stripped-down version of helper class used in previous version,
+     * declared for the sake of serialization compatibility
+     */
+    static class Segment<K,V> extends ReentrantLock implements Serializable {
+        private static final long serialVersionUID = 2249069246763182397L;
+        final float loadFactor;
+        Segment(float lf) { this.loadFactor = lf; }
+    }
+
+    /**
+     * Saves the state of the {@code ConcurrentHashMap} instance to a
+     * stream (i.e., serializes it).
+     * @param s the stream
+     * @serialData
+     * the key (Object) and value (Object)
+     * for each key-value mapping, followed by a null pair.
+     * The key-value mappings are emitted in no particular order.
+     */
+    private void writeObject(java.io.ObjectOutputStream s)
+        throws java.io.IOException {
+        // For serialization compatibility
+        // Emulate segment calculation from previous version of this class
+        int sshift = 0;
+        int ssize = 1;
+        while (ssize < DEFAULT_CONCURRENCY_LEVEL) {
+            ++sshift;
+            ssize <<= 1;
+        }
+        int segmentShift = 32 - sshift;
+        int segmentMask = ssize - 1;
+        @SuppressWarnings("unchecked") Segment<K,V>[] segments = (Segment<K,V>[])
+            new Segment<?,?>[DEFAULT_CONCURRENCY_LEVEL];
+        for (int i = 0; i < segments.length; ++i)
+            segments[i] = new Segment<K,V>(LOAD_FACTOR);
+        s.putFields().put("segments", segments);
+        s.putFields().put("segmentShift", segmentShift);
+        s.putFields().put("segmentMask", segmentMask);
+        s.writeFields();
+
+        Node<K,V>[] t;
+        if ((t = table) != null) {
+            Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
+            for (Node<K,V> p; (p = it.advance()) != null; ) {
+                s.writeObject(p.key);
+                s.writeObject(p.val);
+            }
+        }
+        s.writeObject(null);
+        s.writeObject(null);
+        segments = null; // throw away
+    }
+
+    /**
+     * Reconstitutes the instance from a stream (that is, deserializes it).
+     * @param s the stream
+     */
+    private void readObject(java.io.ObjectInputStream s)
+        throws java.io.IOException, ClassNotFoundException {
+        /*
+         * To improve performance in typical cases, we create nodes
+         * while reading, then place in table once size is known.
+         * However, we must also validate uniqueness and deal with
+         * overpopulated bins while doing so, which requires
+         * specialized versions of putVal mechanics.
+         */
+        sizeCtl = -1; // force exclusion for table construction
+        s.defaultReadObject();
+        long size = 0L;
+        Node<K,V> p = null;
+        for (;;) {
+            @SuppressWarnings("unchecked") K k = (K) s.readObject();
+            @SuppressWarnings("unchecked") V v = (V) s.readObject();
+            if (k != null && v != null) {
+                p = new Node<K,V>(spread(k.hashCode()), k, v, p);
+                ++size;
+            }
+            else
+                break;
+        }
+        if (size == 0L)
+            sizeCtl = 0;
+        else {
+            int n;
+            if (size >= (long)(MAXIMUM_CAPACITY >>> 1))
+                n = MAXIMUM_CAPACITY;
+            else {
+                int sz = (int)size;
+                n = tableSizeFor(sz + (sz >>> 1) + 1);
+            }
+            @SuppressWarnings({"rawtypes","unchecked"})
+                Node<K,V>[] tab = (Node<K,V>[])new Node[n];
+            int mask = n - 1;
+            long added = 0L;
+            while (p != null) {
+                boolean insertAtFront;
+                Node<K,V> next = p.next, first;
+                int h = p.hash, j = h & mask;
+                if ((first = tabAt(tab, j)) == null)
+                    insertAtFront = true;
+                else {
+                    K k = p.key;
+                    if (first.hash < 0) {
+                        TreeBin<K,V> t = (TreeBin<K,V>)first;
+                        if (t.putTreeVal(h, k, p.val) == null)
+                            ++added;
+                        insertAtFront = false;
+                    }
+                    else {
+                        int binCount = 0;
+                        insertAtFront = true;
+                        Node<K,V> q; K qk;
+                        for (q = first; q != null; q = q.next) {
+                            if (q.hash == h &&
+                                ((qk = q.key) == k ||
+                                 (qk != null && k.equals(qk)))) {
+                                insertAtFront = false;
+                                break;
+                            }
+                            ++binCount;
+                        }
+                        if (insertAtFront && binCount >= TREEIFY_THRESHOLD) {
+                            insertAtFront = false;
+                            ++added;
+                            p.next = first;
+                            TreeNode<K,V> hd = null, tl = null;
+                            for (q = p; q != null; q = q.next) {
+                                TreeNode<K,V> t = new TreeNode<K,V>
+                                    (q.hash, q.key, q.val, null, null);
+                                if ((t.prev = tl) == null)
+                                    hd = t;
+                                else
+                                    tl.next = t;
+                                tl = t;
+                            }
+                            setTabAt(tab, j, new TreeBin<K,V>(hd));
+                        }
+                    }
+                }
+                if (insertAtFront) {
+                    ++added;
+                    p.next = first;
+                    setTabAt(tab, j, p);
+                }
+                p = next;
+            }
+            table = tab;
+            sizeCtl = n - (n >>> 2);
+            baseCount = added;
+        }
+    }
+
+    // ConcurrentMap methods
+
+    /**
+     * {@inheritDoc}
+     *
+     * @return the previous value associated with the specified key,
+     *         or {@code null} if there was no mapping for the key
+     * @throws NullPointerException if the specified key or value is null
+     */
+    public V putIfAbsent(K key, V value) {
+        return putVal(key, value, true);
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @throws NullPointerException if the specified key is null
+     */
+    public boolean remove(Object key, Object value) {
+        if (key == null)
+            throw new NullPointerException();
+        return value != null && replaceNode(key, null, value) != null;
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @throws NullPointerException if any of the arguments are null
+     */
+    public boolean replace(K key, V oldValue, V newValue) {
+        if (key == null || oldValue == null || newValue == null)
+            throw new NullPointerException();
+        return replaceNode(key, newValue, oldValue) != null;
+    }
+
+    /**
+     * {@inheritDoc}
+     *
+     * @return the previous value associated with the specified key,
+     *         or {@code null} if there was no mapping for the key
+     * @throws NullPointerException if the specified key or value is null
+     */
+    public V replace(K key, V value) {
+        if (key == null || value == null)
+            throw new NullPointerException();
+        return replaceNode(key, value, null);
+    }
+    // Hashtable legacy methods
+
+    /**
+     * Legacy method testing if some key maps into the specified value
+     * in this table.  This method is identical in functionality to
+     * {@link #containsValue(Object)}, and exists solely to ensure
+     * full compatibility with class {@link java.util.Hashtable}.
+     *
+     * @param  value a value to search for
+     * @return {@code true} if and only if some key maps to the
+     *         {@code value} argument in this table as
+     *         determined by the {@code equals} method;
+     *         {@code false} otherwise
+     * @throws NullPointerException if the specified value is null
+     */
+    public boolean contains(Object value) {
+        // BEGIN android-note
+        // removed deprecation
+        // END android-note
+        return containsValue(value);
     }
 
     /**
@@ -1192,7 +1402,9 @@ public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>
      * @see #keySet()
      */
     public Enumeration<K> keys() {
-        return new KeyIterator();
+        Node<K,V>[] t;
+        int f = (t = table) == null ? 0 : t.length;
+        return new KeyIterator<K,V>(t, f, 0, f, this);
     }
 
     /**
@@ -1202,281 +1414,1787 @@ public class ConcurrentHashMap<K, V> extends AbstractMap<K, V>
      * @see #values()
      */
     public Enumeration<V> elements() {
-        return new ValueIterator();
+        Node<K,V>[] t;
+        int f = (t = table) == null ? 0 : t.length;
+        return new ValueIterator<K,V>(t, f, 0, f, this);
     }
 
-    /* ---------------- Iterator Support -------------- */
+    // ConcurrentHashMap-only methods
 
-    abstract class HashIterator {
-        int nextSegmentIndex;
-        int nextTableIndex;
-        HashEntry<K,V>[] currentTable;
-        HashEntry<K, V> nextEntry;
-        HashEntry<K, V> lastReturned;
+    /**
+     * Returns the number of mappings. This method should be used
+     * instead of {@link #size} because a ConcurrentHashMap may
+     * contain more mappings than can be represented as an int. The
+     * value returned is an estimate; the actual count may differ if
+     * there are concurrent insertions or removals.
+     *
+     * @return the number of mappings
+     * @since 1.8
+     *
+     * @hide
+     */
+    public long mappingCount() {
+        long n = sumCount();
+        return (n < 0L) ? 0L : n; // ignore transient negative values
+    }
 
-        HashIterator() {
-            nextSegmentIndex = segments.length - 1;
-            nextTableIndex = -1;
-            advance();
+    /**
+     * Creates a new {@link Set} backed by a ConcurrentHashMap
+     * from the given type to {@code Boolean.TRUE}.
+     *
+     * @return the new set
+     * @since 1.8
+     *
+     * @hide
+     */
+    public static <K> KeySetView<K,Boolean> newKeySet() {
+        return new KeySetView<K,Boolean>
+            (new ConcurrentHashMap<K,Boolean>(), Boolean.TRUE);
+    }
+
+    /**
+     * Creates a new {@link Set} backed by a ConcurrentHashMap
+     * from the given type to {@code Boolean.TRUE}.
+     *
+     * @param initialCapacity The implementation performs internal
+     * sizing to accommodate this many elements.
+     * @throws IllegalArgumentException if the initial capacity of
+     * elements is negative
+     * @return the new set
+     * @since 1.8
+     *
+     * @hide
+     */
+    public static <K> KeySetView<K,Boolean> newKeySet(int initialCapacity) {
+        return new KeySetView<K,Boolean>
+            (new ConcurrentHashMap<K,Boolean>(initialCapacity), Boolean.TRUE);
+    }
+
+    /**
+     * Returns a {@link Set} view of the keys in this map, using the
+     * given common mapped value for any additions (i.e., {@link
+     * Collection#add} and {@link Collection#addAll(Collection)}).
+     * This is of course only appropriate if it is acceptable to use
+     * the same value for all additions from this view.
+     *
+     * @param mappedValue the mapped value to use for any additions
+     * @return the set view
+     * @throws NullPointerException if the mappedValue is null
+     *
+     * @hide
+     */
+    public Set<K> keySet(V mappedValue) {
+        if (mappedValue == null)
+            throw new NullPointerException();
+        return new KeySetView<K,V>(this, mappedValue);
+    }
+
+    /* ---------------- Special Nodes -------------- */
+
+    /**
+     * A node inserted at head of bins during transfer operations.
+     */
+    static final class ForwardingNode<K,V> extends Node<K,V> {
+        final Node<K,V>[] nextTable;
+        ForwardingNode(Node<K,V>[] tab) {
+            super(MOVED, null, null, null);
+            this.nextTable = tab;
+        }
+
+        Node<K,V> find(int h, Object k) {
+            Node<K,V> e; int n;
+            Node<K,V>[] tab = nextTable;
+            if (k != null && tab != null && (n = tab.length) > 0 &&
+                (e = tabAt(tab, (n - 1) & h)) != null) {
+                do {
+                    int eh; K ek;
+                    if ((eh = e.hash) == h &&
+                        ((ek = e.key) == k || (ek != null && k.equals(ek))))
+                        return e;
+                    if (eh < 0)
+                        return e.find(h, k);
+                } while ((e = e.next) != null);
+            }
+            return null;
+        }
+    }
+
+    /**
+     * A place-holder node used in computeIfAbsent and compute
+     */
+    static final class ReservationNode<K,V> extends Node<K,V> {
+        ReservationNode() {
+            super(RESERVED, null, null, null);
+        }
+
+        Node<K,V> find(int h, Object k) {
+            return null;
+        }
+    }
+
+    /* ---------------- Table Initialization and Resizing -------------- */
+
+    /**
+     * Initializes table, using the size recorded in sizeCtl.
+     */
+    private final Node<K,V>[] initTable() {
+        Node<K,V>[] tab; int sc;
+        while ((tab = table) == null || tab.length == 0) {
+            if ((sc = sizeCtl) < 0)
+                Thread.yield(); // lost initialization race; just spin
+            else if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
+                try {
+                    if ((tab = table) == null || tab.length == 0) {
+                        int n = (sc > 0) ? sc : DEFAULT_CAPACITY;
+                        @SuppressWarnings({"rawtypes","unchecked"})
+                            Node<K,V>[] nt = (Node<K,V>[])new Node[n];
+                        table = tab = nt;
+                        sc = n - (n >>> 2);
+                    }
+                } finally {
+                    sizeCtl = sc;
+                }
+                break;
+            }
+        }
+        return tab;
+    }
+
+    /**
+     * Adds to count, and if table is too small and not already
+     * resizing, initiates transfer. If already resizing, helps
+     * perform transfer if work is available.  Rechecks occupancy
+     * after a transfer to see if another resize is already needed
+     * because resizings are lagging additions.
+     *
+     * @param x the count to add
+     * @param check if <0, don't check resize, if <= 1 only check if uncontended
+     */
+    private final void addCount(long x, int check) {
+        CounterCell[] as; long b, s;
+        if ((as = counterCells) != null ||
+            !U.compareAndSwapLong(this, BASECOUNT, b = baseCount, s = b + x)) {
+            CounterHashCode hc; CounterCell a; long v; int m;
+            boolean uncontended = true;
+            if ((hc = threadCounterHashCode.get()) == null ||
+                as == null || (m = as.length - 1) < 0 ||
+                (a = as[m & hc.code]) == null ||
+                !(uncontended =
+                  U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))) {
+                fullAddCount(x, hc, uncontended);
+                return;
+            }
+            if (check <= 1)
+                return;
+            s = sumCount();
+        }
+        if (check >= 0) {
+            Node<K,V>[] tab, nt; int sc;
+            while (s >= (long)(sc = sizeCtl) && (tab = table) != null &&
+                   tab.length < MAXIMUM_CAPACITY) {
+                if (sc < 0) {
+                    if (sc == -1 || transferIndex <= transferOrigin ||
+                        (nt = nextTable) == null)
+                        break;
+                    if (U.compareAndSwapInt(this, SIZECTL, sc, sc - 1))
+                        transfer(tab, nt);
+                }
+                else if (U.compareAndSwapInt(this, SIZECTL, sc, -2))
+                    transfer(tab, null);
+                s = sumCount();
+            }
+        }
+    }
+
+    /**
+     * Helps transfer if a resize is in progress.
+     */
+    final Node<K,V>[] helpTransfer(Node<K,V>[] tab, Node<K,V> f) {
+        Node<K,V>[] nextTab; int sc;
+        if ((f instanceof ForwardingNode) &&
+            (nextTab = ((ForwardingNode<K,V>)f).nextTable) != null) {
+            if (nextTab == nextTable && tab == table &&
+                transferIndex > transferOrigin && (sc = sizeCtl) < -1 &&
+                U.compareAndSwapInt(this, SIZECTL, sc, sc - 1))
+                transfer(tab, nextTab);
+            return nextTab;
+        }
+        return table;
+    }
+
+    /**
+     * Tries to presize table to accommodate the given number of elements.
+     *
+     * @param size number of elements (doesn't need to be perfectly accurate)
+     */
+    private final void tryPresize(int size) {
+        int c = (size >= (MAXIMUM_CAPACITY >>> 1)) ? MAXIMUM_CAPACITY :
+            tableSizeFor(size + (size >>> 1) + 1);
+        int sc;
+        while ((sc = sizeCtl) >= 0) {
+            Node<K,V>[] tab = table; int n;
+            if (tab == null || (n = tab.length) == 0) {
+                n = (sc > c) ? sc : c;
+                if (U.compareAndSwapInt(this, SIZECTL, sc, -1)) {
+                    try {
+                        if (table == tab) {
+                            @SuppressWarnings({"rawtypes","unchecked"})
+                                Node<K,V>[] nt = (Node<K,V>[])new Node[n];
+                            table = nt;
+                            sc = n - (n >>> 2);
+                        }
+                    } finally {
+                        sizeCtl = sc;
+                    }
+                }
+            }
+            else if (c <= sc || n >= MAXIMUM_CAPACITY)
+                break;
+            else if (tab == table &&
+                     U.compareAndSwapInt(this, SIZECTL, sc, -2))
+                transfer(tab, null);
+        }
+    }
+
+    /**
+     * Moves and/or copies the nodes in each bin to new table. See
+     * above for explanation.
+     */
+    private final void transfer(Node<K,V>[] tab, Node<K,V>[] nextTab) {
+        int n = tab.length, stride;
+        if ((stride = (NCPU > 1) ? (n >>> 3) / NCPU : n) < MIN_TRANSFER_STRIDE)
+            stride = MIN_TRANSFER_STRIDE; // subdivide range
+        if (nextTab == null) {            // initiating
+            try {
+                @SuppressWarnings({"rawtypes","unchecked"})
+                    Node<K,V>[] nt = (Node<K,V>[])new Node[n << 1];
+                nextTab = nt;
+            } catch (Throwable ex) {      // try to cope with OOME
+                sizeCtl = Integer.MAX_VALUE;
+                return;
+            }
+            nextTable = nextTab;
+            transferOrigin = n;
+            transferIndex = n;
+            ForwardingNode<K,V> rev = new ForwardingNode<K,V>(tab);
+            for (int k = n; k > 0;) {    // progressively reveal ready slots
+                int nextk = (k > stride) ? k - stride : 0;
+                for (int m = nextk; m < k; ++m)
+                    nextTab[m] = rev;
+                for (int m = n + nextk; m < n + k; ++m)
+                    nextTab[m] = rev;
+                U.putOrderedInt(this, TRANSFERORIGIN, k = nextk);
+            }
+        }
+        int nextn = nextTab.length;
+        ForwardingNode<K,V> fwd = new ForwardingNode<K,V>(nextTab);
+        boolean advance = true;
+        for (int i = 0, bound = 0;;) {
+            int nextIndex, nextBound, fh; Node<K,V> f;
+            while (advance) {
+                if (--i >= bound)
+                    advance = false;
+                else if ((nextIndex = transferIndex) <= transferOrigin) {
+                    i = -1;
+                    advance = false;
+                }
+                else if (U.compareAndSwapInt
+                         (this, TRANSFERINDEX, nextIndex,
+                          nextBound = (nextIndex > stride ?
+                                       nextIndex - stride : 0))) {
+                    bound = nextBound;
+                    i = nextIndex - 1;
+                    advance = false;
+                }
+            }
+            if (i < 0 || i >= n || i + n >= nextn) {
+                for (int sc;;) {
+                    if (U.compareAndSwapInt(this, SIZECTL, sc = sizeCtl, ++sc)) {
+                        if (sc == -1) {
+                            nextTable = null;
+                            table = nextTab;
+                            sizeCtl = (n << 1) - (n >>> 1);
+                        }
+                        return;
+                    }
+                }
+            }
+            else if ((f = tabAt(tab, i)) == null) {
+                if (casTabAt(tab, i, null, fwd)) {
+                    setTabAt(nextTab, i, null);
+                    setTabAt(nextTab, i + n, null);
+                    advance = true;
+                }
+            }
+            else if ((fh = f.hash) == MOVED)
+                advance = true; // already processed
+            else {
+                synchronized (f) {
+                    if (tabAt(tab, i) == f) {
+                        Node<K,V> ln, hn;
+                        if (fh >= 0) {
+                            int runBit = fh & n;
+                            Node<K,V> lastRun = f;
+                            for (Node<K,V> p = f.next; p != null; p = p.next) {
+                                int b = p.hash & n;
+                                if (b != runBit) {
+                                    runBit = b;
+                                    lastRun = p;
+                                }
+                            }
+                            if (runBit == 0) {
+                                ln = lastRun;
+                                hn = null;
+                            }
+                            else {
+                                hn = lastRun;
+                                ln = null;
+                            }
+                            for (Node<K,V> p = f; p != lastRun; p = p.next) {
+                                int ph = p.hash; K pk = p.key; V pv = p.val;
+                                if ((ph & n) == 0)
+                                    ln = new Node<K,V>(ph, pk, pv, ln);
+                                else
+                                    hn = new Node<K,V>(ph, pk, pv, hn);
+                            }
+                        }
+                        else if (f instanceof TreeBin) {
+                            TreeBin<K,V> t = (TreeBin<K,V>)f;
+                            TreeNode<K,V> lo = null, loTail = null;
+                            TreeNode<K,V> hi = null, hiTail = null;
+                            int lc = 0, hc = 0;
+                            for (Node<K,V> e = t.first; e != null; e = e.next) {
+                                int h = e.hash;
+                                TreeNode<K,V> p = new TreeNode<K,V>
+                                    (h, e.key, e.val, null, null);
+                                if ((h & n) == 0) {
+                                    if ((p.prev = loTail) == null)
+                                        lo = p;
+                                    else
+                                        loTail.next = p;
+                                    loTail = p;
+                                    ++lc;
+                                }
+                                else {
+                                    if ((p.prev = hiTail) == null)
+                                        hi = p;
+                                    else
+                                        hiTail.next = p;
+                                    hiTail = p;
+                                    ++hc;
+                                }
+                            }
+                            ln = (lc <= UNTREEIFY_THRESHOLD) ? untreeify(lo) :
+                                (hc != 0) ? new TreeBin<K,V>(lo) : t;
+                            hn = (hc <= UNTREEIFY_THRESHOLD) ? untreeify(hi) :
+                                (lc != 0) ? new TreeBin<K,V>(hi) : t;
+                        }
+                        else
+                            ln = hn = null;
+                        setTabAt(nextTab, i, ln);
+                        setTabAt(nextTab, i + n, hn);
+                        setTabAt(tab, i, fwd);
+                        advance = true;
+                    }
+                }
+            }
+        }
+    }
+
+    /* ---------------- Conversion from/to TreeBins -------------- */
+
+    /**
+     * Replaces all linked nodes in bin at given index unless table is
+     * too small, in which case resizes instead.
+     */
+    private final void treeifyBin(Node<K,V>[] tab, int index) {
+        Node<K,V> b; int n, sc;
+        if (tab != null) {
+            if ((n = tab.length) < MIN_TREEIFY_CAPACITY) {
+                if (tab == table && (sc = sizeCtl) >= 0 &&
+                    U.compareAndSwapInt(this, SIZECTL, sc, -2))
+                    transfer(tab, null);
+            }
+            else if ((b = tabAt(tab, index)) != null) {
+                synchronized (b) {
+                    if (tabAt(tab, index) == b) {
+                        TreeNode<K,V> hd = null, tl = null;
+                        for (Node<K,V> e = b; e != null; e = e.next) {
+                            TreeNode<K,V> p =
+                                new TreeNode<K,V>(e.hash, e.key, e.val,
+                                                  null, null);
+                            if ((p.prev = tl) == null)
+                                hd = p;
+                            else
+                                tl.next = p;
+                            tl = p;
+                        }
+                        setTabAt(tab, index, new TreeBin<K,V>(hd));
+                    }
+                }
+            }
+        }
+    }
+
+    /**
+     * Returns a list on non-TreeNodes replacing those in given list.
+     */
+    static <K,V> Node<K,V> untreeify(Node<K,V> b) {
+        Node<K,V> hd = null, tl = null;
+        for (Node<K,V> q = b; q != null; q = q.next) {
+            Node<K,V> p = new Node<K,V>(q.hash, q.key, q.val, null);
+            if (tl == null)
+                hd = p;
+            else
+                tl.next = p;
+            tl = p;
+        }
+        return hd;
+    }
+
+    /* ---------------- TreeNodes -------------- */
+
+    /**
+     * Nodes for use in TreeBins
+     */
+    static final class TreeNode<K,V> extends Node<K,V> {
+        TreeNode<K,V> parent;  // red-black tree links
+        TreeNode<K,V> left;
+        TreeNode<K,V> right;
+        TreeNode<K,V> prev;    // needed to unlink next upon deletion
+        boolean red;
+
+        TreeNode(int hash, K key, V val, Node<K,V> next,
+                 TreeNode<K,V> parent) {
+            super(hash, key, val, next);
+            this.parent = parent;
+        }
+
+        Node<K,V> find(int h, Object k) {
+            return findTreeNode(h, k, null);
         }
 
         /**
-         * Sets nextEntry to first node of next non-empty table
-         * (in backwards order, to simplify checks).
+         * Returns the TreeNode (or null if not found) for the given key
+         * starting at given root.
          */
-        final void advance() {
-            for (;;) {
-                if (nextTableIndex >= 0) {
-                    if ((nextEntry = entryAt(currentTable,
-                                             nextTableIndex--)) != null)
+        final TreeNode<K,V> findTreeNode(int h, Object k, Class<?> kc) {
+            if (k != null) {
+                TreeNode<K,V> p = this;
+                do  {
+                    int ph, dir; K pk; TreeNode<K,V> q;
+                    TreeNode<K,V> pl = p.left, pr = p.right;
+                    if ((ph = p.hash) > h)
+                        p = pl;
+                    else if (ph < h)
+                        p = pr;
+                    else if ((pk = p.key) == k || (pk != null && k.equals(pk)))
+                        return p;
+                    else if (pl == null && pr == null)
                         break;
+                    else if ((kc != null ||
+                              (kc = comparableClassFor(k)) != null) &&
+                             (dir = compareComparables(kc, k, pk)) != 0)
+                        p = (dir < 0) ? pl : pr;
+                    else if (pl == null)
+                        p = pr;
+                    else if (pr == null ||
+                             (q = pr.findTreeNode(h, k, kc)) == null)
+                        p = pl;
+                    else
+                        return q;
+                } while (p != null);
+            }
+            return null;
+        }
+    }
+
+    /* ---------------- TreeBins -------------- */
+
+    /**
+     * TreeNodes used at the heads of bins. TreeBins do not hold user
+     * keys or values, but instead point to list of TreeNodes and
+     * their root. They also maintain a parasitic read-write lock
+     * forcing writers (who hold bin lock) to wait for readers (who do
+     * not) to complete before tree restructuring operations.
+     */
+    static final class TreeBin<K,V> extends Node<K,V> {
+        TreeNode<K,V> root;
+        volatile TreeNode<K,V> first;
+        volatile Thread waiter;
+        volatile int lockState;
+        // values for lockState
+        static final int WRITER = 1; // set while holding write lock
+        static final int WAITER = 2; // set when waiting for write lock
+        static final int READER = 4; // increment value for setting read lock
+
+        /**
+         * Creates bin with initial set of nodes headed by b.
+         */
+        TreeBin(TreeNode<K,V> b) {
+            super(TREEBIN, null, null, null);
+            this.first = b;
+            TreeNode<K,V> r = null;
+            for (TreeNode<K,V> x = b, next; x != null; x = next) {
+                next = (TreeNode<K,V>)x.next;
+                x.left = x.right = null;
+                if (r == null) {
+                    x.parent = null;
+                    x.red = false;
+                    r = x;
                 }
-                else if (nextSegmentIndex >= 0) {
-                    Segment<K,V> seg = segmentAt(segments, nextSegmentIndex--);
-                    if (seg != null && (currentTable = seg.table) != null)
-                        nextTableIndex = currentTable.length - 1;
+                else {
+                    Object key = x.key;
+                    int hash = x.hash;
+                    Class<?> kc = null;
+                    for (TreeNode<K,V> p = r;;) {
+                        int dir, ph;
+                        if ((ph = p.hash) > hash)
+                            dir = -1;
+                        else if (ph < hash)
+                            dir = 1;
+                        else if ((kc != null ||
+                                  (kc = comparableClassFor(key)) != null))
+                            dir = compareComparables(kc, key, p.key);
+                        else
+                            dir = 0;
+                        TreeNode<K,V> xp = p;
+                        if ((p = (dir <= 0) ? p.left : p.right) == null) {
+                            x.parent = xp;
+                            if (dir <= 0)
+                                xp.left = x;
+                            else
+                                xp.right = x;
+                            r = balanceInsertion(r, x);
+                            break;
+                        }
+                    }
                 }
-                else
+            }
+            this.root = r;
+        }
+
+        /**
+         * Acquires write lock for tree restructuring.
+         */
+        private final void lockRoot() {
+            if (!U.compareAndSwapInt(this, LOCKSTATE, 0, WRITER))
+                contendedLock(); // offload to separate method
+        }
+
+        /**
+         * Releases write lock for tree restructuring.
+         */
+        private final void unlockRoot() {
+            lockState = 0;
+        }
+
+        /**
+         * Possibly blocks awaiting root lock.
+         */
+        private final void contendedLock() {
+            boolean waiting = false;
+            for (int s;;) {
+                if (((s = lockState) & WRITER) == 0) {
+                    if (U.compareAndSwapInt(this, LOCKSTATE, s, WRITER)) {
+                        if (waiting)
+                            waiter = null;
+                        return;
+                    }
+                }
+                else if ((s | WAITER) == 0) {
+                    if (U.compareAndSwapInt(this, LOCKSTATE, s, s | WAITER)) {
+                        waiting = true;
+                        waiter = Thread.currentThread();
+                    }
+                }
+                else if (waiting)
+                    LockSupport.park(this);
+            }
+        }
+
+        /**
+         * Returns matching node or null if none. Tries to search
+         * using tree comparisons from root, but continues linear
+         * search when lock not available.
+         */
+        final Node<K,V> find(int h, Object k) {
+            if (k != null) {
+                for (Node<K,V> e = first; e != null; e = e.next) {
+                    int s; K ek;
+                    if (((s = lockState) & (WAITER|WRITER)) != 0) {
+                        if (e.hash == h &&
+                            ((ek = e.key) == k || (ek != null && k.equals(ek))))
+                            return e;
+                    }
+                    else if (U.compareAndSwapInt(this, LOCKSTATE, s,
+                                                 s + READER)) {
+                        TreeNode<K,V> r, p;
+                        try {
+                            p = ((r = root) == null ? null :
+                                 r.findTreeNode(h, k, null));
+                        } finally {
+
+                            Thread w;
+                            int ls;
+                            do {} while (!U.compareAndSwapInt
+                                         (this, LOCKSTATE,
+                                          ls = lockState, ls - READER));
+                            if (ls == (READER|WAITER) && (w = waiter) != null)
+                                LockSupport.unpark(w);
+                        }
+                        return p;
+                    }
+                }
+            }
+            return null;
+        }
+
+        /**
+         * Finds or adds a node.
+         * @return null if added
+         */
+        final TreeNode<K,V> putTreeVal(int h, K k, V v) {
+            Class<?> kc = null;
+            for (TreeNode<K,V> p = root;;) {
+                int dir, ph; K pk; TreeNode<K,V> q, pr;
+                if (p == null) {
+                    first = root = new TreeNode<K,V>(h, k, v, null, null);
+                    break;
+                }
+                else if ((ph = p.hash) > h)
+                    dir = -1;
+                else if (ph < h)
+                    dir = 1;
+                else if ((pk = p.key) == k || (pk != null && k.equals(pk)))
+                    return p;
+                else if ((kc == null &&
+                          (kc = comparableClassFor(k)) == null) ||
+                         (dir = compareComparables(kc, k, pk)) == 0) {
+                    if (p.left == null)
+                        dir = 1;
+                    else if ((pr = p.right) == null ||
+                             (q = pr.findTreeNode(h, k, kc)) == null)
+                        dir = -1;
+                    else
+                        return q;
+                }
+                TreeNode<K,V> xp = p;
+                if ((p = (dir < 0) ? p.left : p.right) == null) {
+                    TreeNode<K,V> x, f = first;
+                    first = x = new TreeNode<K,V>(h, k, v, f, xp);
+                    if (f != null)
+                        f.prev = x;
+                    if (dir < 0)
+                        xp.left = x;
+                    else
+                        xp.right = x;
+                    if (!xp.red)
+                        x.red = true;
+                    else {
+                        lockRoot();
+                        try {
+                            root = balanceInsertion(root, x);
+                        } finally {
+                            unlockRoot();
+                        }
+                    }
                     break;
+                }
             }
+            assert checkInvariants(root);
+            return null;
         }
 
-        final HashEntry<K,V> nextEntry() {
-            HashEntry<K,V> e = nextEntry;
-            if (e == null)
-                throw new NoSuchElementException();
-            lastReturned = e; // cannot assign until after null check
-            if ((nextEntry = e.next) == null)
-                advance();
-            return e;
+        /**
+         * Removes the given node, that must be present before this
+         * call.  This is messier than typical red-black deletion code
+         * because we cannot swap the contents of an interior node
+         * with a leaf successor that is pinned by "next" pointers
+         * that are accessible independently of lock. So instead we
+         * swap the tree linkages.
+         *
+         * @return true if now too small, so should be untreeified
+         */
+        final boolean removeTreeNode(TreeNode<K,V> p) {
+            TreeNode<K,V> next = (TreeNode<K,V>)p.next;
+            TreeNode<K,V> pred = p.prev;  // unlink traversal pointers
+            TreeNode<K,V> r, rl;
+            if (pred == null)
+                first = next;
+            else
+                pred.next = next;
+            if (next != null)
+                next.prev = pred;
+            if (first == null) {
+                root = null;
+                return true;
+            }
+            if ((r = root) == null || r.right == null || // too small
+                (rl = r.left) == null || rl.left == null)
+                return true;
+            lockRoot();
+            try {
+                TreeNode<K,V> replacement;
+                TreeNode<K,V> pl = p.left;
+                TreeNode<K,V> pr = p.right;
+                if (pl != null && pr != null) {
+                    TreeNode<K,V> s = pr, sl;
+                    while ((sl = s.left) != null) // find successor
+                        s = sl;
+                    boolean c = s.red; s.red = p.red; p.red = c; // swap colors
+                    TreeNode<K,V> sr = s.right;
+                    TreeNode<K,V> pp = p.parent;
+                    if (s == pr) { // p was s's direct parent
+                        p.parent = s;
+                        s.right = p;
+                    }
+                    else {
+                        TreeNode<K,V> sp = s.parent;
+                        if ((p.parent = sp) != null) {
+                            if (s == sp.left)
+                                sp.left = p;
+                            else
+                                sp.right = p;
+                        }
+                        if ((s.right = pr) != null)
+                            pr.parent = s;
+                    }
+                    p.left = null;
+                    if ((p.right = sr) != null)
+                        sr.parent = p;
+                    if ((s.left = pl) != null)
+                        pl.parent = s;
+                    if ((s.parent = pp) == null)
+                        r = s;
+                    else if (p == pp.left)
+                        pp.left = s;
+                    else
+                        pp.right = s;
+                    if (sr != null)
+                        replacement = sr;
+                    else
+                        replacement = p;
+                }
+                else if (pl != null)
+                    replacement = pl;
+                else if (pr != null)
+                    replacement = pr;
+                else
+                    replacement = p;
+                if (replacement != p) {
+                    TreeNode<K,V> pp = replacement.parent = p.parent;
+                    if (pp == null)
+                        r = replacement;
+                    else if (p == pp.left)
+                        pp.left = replacement;
+                    else
+                        pp.right = replacement;
+                    p.left = p.right = p.parent = null;
+                }
+
+                root = (p.red) ? r : balanceDeletion(r, replacement);
+
+                if (p == replacement) {  // detach pointers
+                    TreeNode<K,V> pp;
+                    if ((pp = p.parent) != null) {
+                        if (p == pp.left)
+                            pp.left = null;
+                        else if (p == pp.right)
+                            pp.right = null;
+                        p.parent = null;
+                    }
+                }
+            } finally {
+                unlockRoot();
+            }
+            assert checkInvariants(root);
+            return false;
+        }
+
+        /* ------------------------------------------------------------ */
+        // Red-black tree methods, all adapted from CLR
+
+        static <K,V> TreeNode<K,V> rotateLeft(TreeNode<K,V> root,
+                                              TreeNode<K,V> p) {
+            TreeNode<K,V> r, pp, rl;
+            if (p != null && (r = p.right) != null) {
+                if ((rl = p.right = r.left) != null)
+                    rl.parent = p;
+                if ((pp = r.parent = p.parent) == null)
+                    (root = r).red = false;
+                else if (pp.left == p)
+                    pp.left = r;
+                else
+                    pp.right = r;
+                r.left = p;
+                p.parent = r;
+            }
+            return root;
+        }
+
+        static <K,V> TreeNode<K,V> rotateRight(TreeNode<K,V> root,
+                                               TreeNode<K,V> p) {
+            TreeNode<K,V> l, pp, lr;
+            if (p != null && (l = p.left) != null) {
+                if ((lr = p.left = l.right) != null)
+                    lr.parent = p;
+                if ((pp = l.parent = p.parent) == null)
+                    (root = l).red = false;
+                else if (pp.right == p)
+                    pp.right = l;
+                else
+                    pp.left = l;
+                l.right = p;
+                p.parent = l;
+            }
+            return root;
         }
 
-        public final boolean hasNext() { return nextEntry != null; }
-        public final boolean hasMoreElements() { return nextEntry != null; }
+        static <K,V> TreeNode<K,V> balanceInsertion(TreeNode<K,V> root,
+                                                    TreeNode<K,V> x) {
+            x.red = true;
+            for (TreeNode<K,V> xp, xpp, xppl, xppr;;) {
+                if ((xp = x.parent) == null) {
+                    x.red = false;
+                    return x;
+                }
+                else if (!xp.red || (xpp = xp.parent) == null)
+                    return root;
+                if (xp == (xppl = xpp.left)) {
+                    if ((xppr = xpp.right) != null && xppr.red) {
+                        xppr.red = false;
+                        xp.red = false;
+                        xpp.red = true;
+                        x = xpp;
+                    }
+                    else {
+                        if (x == xp.right) {
+                            root = rotateLeft(root, x = xp);
+                            xpp = (xp = x.parent) == null ? null : xp.parent;
+                        }
+                        if (xp != null) {
+                            xp.red = false;
+                            if (xpp != null) {
+                                xpp.red = true;
+                                root = rotateRight(root, xpp);
+                            }
+                        }
+                    }
+                }
+                else {
+                    if (xppl != null && xppl.red) {
+                        xppl.red = false;
+                        xp.red = false;
+                        xpp.red = true;
+                        x = xpp;
+                    }
+                    else {
+                        if (x == xp.left) {
+                            root = rotateRight(root, x = xp);
+                            xpp = (xp = x.parent) == null ? null : xp.parent;
+                        }
+                        if (xp != null) {
+                            xp.red = false;
+                            if (xpp != null) {
+                                xpp.red = true;
+                                root = rotateLeft(root, xpp);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+        static <K,V> TreeNode<K,V> balanceDeletion(TreeNode<K,V> root,
+                                                   TreeNode<K,V> x) {
+            for (TreeNode<K,V> xp, xpl, xpr;;)  {
+                if (x == null || x == root)
+                    return root;
+                else if ((xp = x.parent) == null) {
+                    x.red = false;
+                    return x;
+                }
+                else if (x.red) {
+                    x.red = false;
+                    return root;
+                }
+                else if ((xpl = xp.left) == x) {
+                    if ((xpr = xp.right) != null && xpr.red) {
+                        xpr.red = false;
+                        xp.red = true;
+                        root = rotateLeft(root, xp);
+                        xpr = (xp = x.parent) == null ? null : xp.right;
+                    }
+                    if (xpr == null)
+                        x = xp;
+                    else {
+                        TreeNode<K,V> sl = xpr.left, sr = xpr.right;
+                        if ((sr == null || !sr.red) &&
+                            (sl == null || !sl.red)) {
+                            xpr.red = true;
+                            x = xp;
+                        }
+                        else {
+                            if (sr == null || !sr.red) {
+                                if (sl != null)
+                                    sl.red = false;
+                                xpr.red = true;
+                                root = rotateRight(root, xpr);
+                                xpr = (xp = x.parent) == null ?
+                                    null : xp.right;
+                            }
+                            if (xpr != null) {
+                                xpr.red = (xp == null) ? false : xp.red;
+                                if ((sr = xpr.right) != null)
+                                    sr.red = false;
+                            }
+                            if (xp != null) {
+                                xp.red = false;
+                                root = rotateLeft(root, xp);
+                            }
+                            x = root;
+                        }
+                    }
+                }
+                else { // symmetric
+                    if (xpl != null && xpl.red) {
+                        xpl.red = false;
+                        xp.red = true;
+                        root = rotateRight(root, xp);
+                        xpl = (xp = x.parent) == null ? null : xp.left;
+                    }
+                    if (xpl == null)
+                        x = xp;
+                    else {
+                        TreeNode<K,V> sl = xpl.left, sr = xpl.right;
+                        if ((sl == null || !sl.red) &&
+                            (sr == null || !sr.red)) {
+                            xpl.red = true;
+                            x = xp;
+                        }
+                        else {
+                            if (sl == null || !sl.red) {
+                                if (sr != null)
+                                    sr.red = false;
+                                xpl.red = true;
+                                root = rotateLeft(root, xpl);
+                                xpl = (xp = x.parent) == null ?
+                                    null : xp.left;
+                            }
+                            if (xpl != null) {
+                                xpl.red = (xp == null) ? false : xp.red;
+                                if ((sl = xpl.left) != null)
+                                    sl.red = false;
+                            }
+                            if (xp != null) {
+                                xp.red = false;
+                                root = rotateRight(root, xp);
+                            }
+                            x = root;
+                        }
+                    }
+                }
+            }
+        }
+
+        /**
+         * Recursive invariant check
+         */
+        static <K,V> boolean checkInvariants(TreeNode<K,V> t) {
+            TreeNode<K,V> tp = t.parent, tl = t.left, tr = t.right,
+                tb = t.prev, tn = (TreeNode<K,V>)t.next;
+            if (tb != null && tb.next != t)
+                return false;
+            if (tn != null && tn.prev != t)
+                return false;
+            if (tp != null && t != tp.left && t != tp.right)
+                return false;
+            if (tl != null && (tl.parent != t || tl.hash > t.hash))
+                return false;
+            if (tr != null && (tr.parent != t || tr.hash < t.hash))
+                return false;
+            if (t.red && tl != null && tl.red && tr != null && tr.red)
+                return false;
+            if (tl != null && !checkInvariants(tl))
+                return false;
+            if (tr != null && !checkInvariants(tr))
+                return false;
+            return true;
+        }
+
+        private static final sun.misc.Unsafe U;
+        private static final long LOCKSTATE;
+        static {
+            try {
+                U = sun.misc.Unsafe.getUnsafe();
+                Class<?> k = TreeBin.class;
+                LOCKSTATE = U.objectFieldOffset
+                    (k.getDeclaredField("lockState"));
+            } catch (Exception e) {
+                throw new Error(e);
+            }
+        }
+    }
+
+    /* ----------------Table Traversal -------------- */
+
+    /**
+     * Encapsulates traversal for methods such as containsValue; also
+     * serves as a base class for other iterators.
+     *
+     * Method advance visits once each still-valid node that was
+     * reachable upon iterator construction. It might miss some that
+     * were added to a bin after the bin was visited, which is OK wrt
+     * consistency guarantees. Maintaining this property in the face
+     * of possible ongoing resizes requires a fair amount of
+     * bookkeeping state that is difficult to optimize away amidst
+     * volatile accesses.  Even so, traversal maintains reasonable
+     * throughput.
+     *
+     * Normally, iteration proceeds bin-by-bin traversing lists.
+     * However, if the table has been resized, then all future steps
+     * must traverse both the bin at the current index as well as at
+     * (index + baseSize); and so on for further resizings. To
+     * paranoically cope with potential sharing by users of iterators
+     * across threads, iteration terminates if a bounds checks fails
+     * for a table read.
+     */
+    static class Traverser<K,V> {
+        Node<K,V>[] tab;        // current table; updated if resized
+        Node<K,V> next;         // the next entry to use
+        int index;              // index of bin to use next
+        int baseIndex;          // current index of initial table
+        int baseLimit;          // index bound for initial table
+        final int baseSize;     // initial table size
+
+        Traverser(Node<K,V>[] tab, int size, int index, int limit) {
+            this.tab = tab;
+            this.baseSize = size;
+            this.baseIndex = this.index = index;
+            this.baseLimit = limit;
+            this.next = null;
+        }
+
+        /**
+         * Advances if possible, returning next valid node, or null if none.
+         */
+        final Node<K,V> advance() {
+            Node<K,V> e;
+            if ((e = next) != null)
+                e = e.next;
+            for (;;) {
+                Node<K,V>[] t; int i, n; K ek;  // must use locals in checks
+                if (e != null)
+                    return next = e;
+                if (baseIndex >= baseLimit || (t = tab) == null ||
+                    (n = t.length) <= (i = index) || i < 0)
+                    return next = null;
+                if ((e = tabAt(t, index)) != null && e.hash < 0) {
+                    if (e instanceof ForwardingNode) {
+                        tab = ((ForwardingNode<K,V>)e).nextTable;
+                        e = null;
+                        continue;
+                    }
+                    else if (e instanceof TreeBin)
+                        e = ((TreeBin<K,V>)e).first;
+                    else
+                        e = null;
+                }
+                if ((index += baseSize) >= n)
+                    index = ++baseIndex;    // visit upper slots if present
+            }
+        }
+    }
+
+    /**
+     * Base of key, value, and entry Iterators. Adds fields to
+     * Traverser to support iterator.remove.
+     */
+    static class BaseIterator<K,V> extends Traverser<K,V> {
+        final ConcurrentHashMap<K,V> map;
+        Node<K,V> lastReturned;
+        BaseIterator(Node<K,V>[] tab, int size, int index, int limit,
+                    ConcurrentHashMap<K,V> map) {
+            super(tab, size, index, limit);
+            this.map = map;
+            advance();
+        }
+
+        public final boolean hasNext() { return next != null; }
+        public final boolean hasMoreElements() { return next != null; }
 
         public final void remove() {
-            if (lastReturned == null)
+            Node<K,V> p;
+            if ((p = lastReturned) == null)
                 throw new IllegalStateException();
-            ConcurrentHashMap.this.remove(lastReturned.key);
             lastReturned = null;
+            map.replaceNode(p.key, null, null);
+        }
+    }
+
+    static final class KeyIterator<K,V> extends BaseIterator<K,V>
+        implements Iterator<K>, Enumeration<K> {
+        KeyIterator(Node<K,V>[] tab, int index, int size, int limit,
+                    ConcurrentHashMap<K,V> map) {
+            super(tab, index, size, limit, map);
+        }
+
+        public final K next() {
+            Node<K,V> p;
+            if ((p = next) == null)
+                throw new NoSuchElementException();
+            K k = p.key;
+            lastReturned = p;
+            advance();
+            return k;
         }
+
+        public final K nextElement() { return next(); }
     }
 
-    final class KeyIterator
-        extends HashIterator
-        implements Iterator<K>, Enumeration<K>
-    {
-        public final K next()        { return super.nextEntry().key; }
-        public final K nextElement() { return super.nextEntry().key; }
+    static final class ValueIterator<K,V> extends BaseIterator<K,V>
+        implements Iterator<V>, Enumeration<V> {
+        ValueIterator(Node<K,V>[] tab, int index, int size, int limit,
+                      ConcurrentHashMap<K,V> map) {
+            super(tab, index, size, limit, map);
+        }
+
+        public final V next() {
+            Node<K,V> p;
+            if ((p = next) == null)
+                throw new NoSuchElementException();
+            V v = p.val;
+            lastReturned = p;
+            advance();
+            return v;
+        }
+
+        public final V nextElement() { return next(); }
     }
 
-    final class ValueIterator
-        extends HashIterator
-        implements Iterator<V>, Enumeration<V>
-    {
-        public final V next()        { return super.nextEntry().value; }
-        public final V nextElement() { return super.nextEntry().value; }
+    static final class EntryIterator<K,V> extends BaseIterator<K,V>
+        implements Iterator<Map.Entry<K,V>> {
+        EntryIterator(Node<K,V>[] tab, int index, int size, int limit,
+                      ConcurrentHashMap<K,V> map) {
+            super(tab, index, size, limit, map);
+        }
+
+        public final Map.Entry<K,V> next() {
+            Node<K,V> p;
+            if ((p = next) == null)
+                throw new NoSuchElementException();
+            K k = p.key;
+            V v = p.val;
+            lastReturned = p;
+            advance();
+            return new MapEntry<K,V>(k, v, map);
+        }
     }
 
     /**
-     * Custom Entry class used by EntryIterator.next(), that relays
-     * setValue changes to the underlying map.
+     * Exported Entry for EntryIterator
      */
-    final class WriteThroughEntry
-        extends AbstractMap.SimpleEntry<K,V>
-    {
-        WriteThroughEntry(K k, V v) {
-            super(k,v);
+    static final class MapEntry<K,V> implements Map.Entry<K,V> {
+        final K key; // non-null
+        V val;       // non-null
+        final ConcurrentHashMap<K,V> map;
+        MapEntry(K key, V val, ConcurrentHashMap<K,V> map) {
+            this.key = key;
+            this.val = val;
+            this.map = map;
+        }
+        public K getKey()        { return key; }
+        public V getValue()      { return val; }
+        public int hashCode()    { return key.hashCode() ^ val.hashCode(); }
+        public String toString() { return key + "=" + val; }
+
+        public boolean equals(Object o) {
+            Object k, v; Map.Entry<?,?> e;
+            return ((o instanceof Map.Entry) &&
+                    (k = (e = (Map.Entry<?,?>)o).getKey()) != null &&
+                    (v = e.getValue()) != null &&
+                    (k == key || k.equals(key)) &&
+                    (v == val || v.equals(val)));
         }
 
         /**
          * Sets our entry's value and writes through to the map. The
-         * value to return is somewhat arbitrary here. Since a
-         * WriteThroughEntry does not necessarily track asynchronous
-         * changes, the most recent "previous" value could be
-         * different from what we return (or could even have been
-         * removed in which case the put will re-establish). We do not
-         * and cannot guarantee more.
+         * value to return is somewhat arbitrary here. Since we do not
+         * necessarily track asynchronous changes, the most recent
+         * "previous" value could be different from what we return (or
+         * could even have been removed, in which case the put will
+         * re-establish). We do not and cannot guarantee more.
          */
         public V setValue(V value) {
             if (value == null) throw new NullPointerException();
-            V v = super.setValue(value);
-            ConcurrentHashMap.this.put(getKey(), value);
+            V v = val;
+            val = value;
+            map.put(key, value);
             return v;
         }
     }
 
-    final class EntryIterator
-        extends HashIterator
-        implements Iterator<Entry<K,V>>
-    {
-        public Map.Entry<K,V> next() {
-            HashEntry<K,V> e = super.nextEntry();
-            return new WriteThroughEntry(e.key, e.value);
+    /* ----------------Views -------------- */
+
+    /**
+     * Base class for views.
+     *
+     */
+    abstract static class CollectionView<K,V,E>
+        implements Collection<E>, java.io.Serializable {
+        private static final long serialVersionUID = 7249069246763182397L;
+        final ConcurrentHashMap<K,V> map;
+        CollectionView(ConcurrentHashMap<K,V> map)  { this.map = map; }
+
+        /**
+         * Returns the map backing this view.
+         *
+         * @return the map backing this view
+         */
+        public ConcurrentHashMap<K,V> getMap() { return map; }
+
+        /**
+         * Removes all of the elements from this view, by removing all
+         * the mappings from the map backing this view.
+         */
+        public final void clear()      { map.clear(); }
+        public final int size()        { return map.size(); }
+        public final boolean isEmpty() { return map.isEmpty(); }
+
+        // implementations below rely on concrete classes supplying these
+        // abstract methods
+        /**
+         * Returns a "weakly consistent" iterator that will never
+         * throw {@link ConcurrentModificationException}, and
+         * guarantees to traverse elements as they existed upon
+         * construction of the iterator, and may (but is not
+         * guaranteed to) reflect any modifications subsequent to
+         * construction.
+         */
+        public abstract Iterator<E> iterator();
+        public abstract boolean contains(Object o);
+        public abstract boolean remove(Object o);
+
+        private static final String oomeMsg = "Required array size too large";
+
+        public final Object[] toArray() {
+            long sz = map.mappingCount();
+            if (sz > MAX_ARRAY_SIZE)
+                throw new OutOfMemoryError(oomeMsg);
+            int n = (int)sz;
+            Object[] r = new Object[n];
+            int i = 0;
+            for (E e : this) {
+                if (i == n) {
+                    if (n >= MAX_ARRAY_SIZE)
+                        throw new OutOfMemoryError(oomeMsg);
+                    if (n >= MAX_ARRAY_SIZE - (MAX_ARRAY_SIZE >>> 1) - 1)
+                        n = MAX_ARRAY_SIZE;
+                    else
+                        n += (n >>> 1) + 1;
+                    r = Arrays.copyOf(r, n);
+                }
+                r[i++] = e;
+            }
+            return (i == n) ? r : Arrays.copyOf(r, i);
+        }
+
+        @SuppressWarnings("unchecked")
+        public final <T> T[] toArray(T[] a) {
+            long sz = map.mappingCount();
+            if (sz > MAX_ARRAY_SIZE)
+                throw new OutOfMemoryError(oomeMsg);
+            int m = (int)sz;
+            T[] r = (a.length >= m) ? a :
+                (T[])java.lang.reflect.Array
+                .newInstance(a.getClass().getComponentType(), m);
+            int n = r.length;
+            int i = 0;
+            for (E e : this) {
+                if (i == n) {
+                    if (n >= MAX_ARRAY_SIZE)
+                        throw new OutOfMemoryError(oomeMsg);
+                    if (n >= MAX_ARRAY_SIZE - (MAX_ARRAY_SIZE >>> 1) - 1)
+                        n = MAX_ARRAY_SIZE;
+                    else
+                        n += (n >>> 1) + 1;
+                    r = Arrays.copyOf(r, n);
+                }
+                r[i++] = (T)e;
+            }
+            if (a == r && i < n) {
+                r[i] = null; // null-terminate
+                return r;
+            }
+            return (i == n) ? r : Arrays.copyOf(r, i);
+        }
+
+        /**
+         * Returns a string representation of this collection.
+         * The string representation consists of the string representations
+         * of the collection's elements in the order they are returned by
+         * its iterator, enclosed in square brackets ({@code "[]"}).
+         * Adjacent elements are separated by the characters {@code ", "}
+         * (comma and space).  Elements are converted to strings as by
+         * {@link String#valueOf(Object)}.
+         *
+         * @return a string representation of this collection
+         */
+        public final String toString() {
+            StringBuilder sb = new StringBuilder();
+            sb.append('[');
+            Iterator<E> it = iterator();
+            if (it.hasNext()) {
+                for (;;) {
+                    Object e = it.next();
+                    sb.append(e == this ? "(this Collection)" : e);
+                    if (!it.hasNext())
+                        break;
+                    sb.append(',').append(' ');
+                }
+            }
+            return sb.append(']').toString();
         }
+
+        public final boolean containsAll(Collection<?> c) {
+            if (c != this) {
+                for (Object e : c) {
+                    if (e == null || !contains(e))
+                        return false;
+                }
+            }
+            return true;
+        }
+
+        public final boolean removeAll(Collection<?> c) {
+            boolean modified = false;
+            for (Iterator<E> it = iterator(); it.hasNext();) {
+                if (c.contains(it.next())) {
+                    it.remove();
+                    modified = true;
+                }
+            }
+            return modified;
+        }
+
+        public final boolean retainAll(Collection<?> c) {
+            boolean modified = false;
+            for (Iterator<E> it = iterator(); it.hasNext();) {
+                if (!c.contains(it.next())) {
+                    it.remove();
+                    modified = true;
+                }
+            }
+            return modified;
+        }
+
     }
 
-    final class KeySet extends AbstractSet<K> {
-        public Iterator<K> iterator() {
-            return new KeyIterator();
+    /**
+     * A view of a ConcurrentHashMap as a {@link Set} of keys, in
+     * which additions may optionally be enabled by mapping to a
+     * common value.  This class cannot be directly instantiated.
+     * See {@link #keySet() keySet()},
+     * {@link #keySet(Object) keySet(V)},
+     * {@link #newKeySet() newKeySet()},
+     * {@link #newKeySet(int) newKeySet(int)}.
+     *
+     * @since 1.8
+     *
+     * @hide
+     */
+    public static class KeySetView<K,V> extends CollectionView<K,V,K>
+        implements Set<K>, java.io.Serializable {
+        private static final long serialVersionUID = 7249069246763182397L;
+        private final V value;
+        KeySetView(ConcurrentHashMap<K,V> map, V value) {  // non-public
+            super(map);
+            this.value = value;
         }
-        public int size() {
-            return ConcurrentHashMap.this.size();
+
+        /**
+         * Returns the default mapped value for additions,
+         * or {@code null} if additions are not supported.
+         *
+         * @return the default mapped value for additions, or {@code null}
+         * if not supported
+         */
+        public V getMappedValue() { return value; }
+
+        /**
+         * {@inheritDoc}
+         * @throws NullPointerException if the specified key is null
+         */
+        public boolean contains(Object o) { return map.containsKey(o); }
+
+        /**
+         * Removes the key from this map view, by removing the key (and its
+         * corresponding value) from the backing map.  This method does
+         * nothing if the key is not in the map.
+         *
+         * @param  o the key to be removed from the backing map
+         * @return {@code true} if the backing map contained the specified key
+         * @throws NullPointerException if the specified key is null
+         */
+        public boolean remove(Object o) { return map.remove(o) != null; }
+
+        /**
+         * @return an iterator over the keys of the backing map
+         */
+        public Iterator<K> iterator() {
+            Node<K,V>[] t;
+            ConcurrentHashMap<K,V> m = map;
+            int f = (t = m.table) == null ? 0 : t.length;
+            return new KeyIterator<K,V>(t, f, 0, f, m);
         }
-        public boolean isEmpty() {
-            return ConcurrentHashMap.this.isEmpty();
+
+        /**
+         * Adds the specified key to this set view by mapping the key to
+         * the default mapped value in the backing map, if defined.
+         *
+         * @param e key to be added
+         * @return {@code true} if this set changed as a result of the call
+         * @throws NullPointerException if the specified key is null
+         * @throws UnsupportedOperationException if no default mapped value
+         * for additions was provided
+         */
+        public boolean add(K e) {
+            V v;
+            if ((v = value) == null)
+                throw new UnsupportedOperationException();
+            return map.putVal(e, v, true) == null;
         }
-        public boolean contains(Object o) {
-            return ConcurrentHashMap.this.containsKey(o);
+
+        /**
+         * Adds all of the elements in the specified collection to this set,
+         * as if by calling {@link #add} on each one.
+         *
+         * @param c the elements to be inserted into this set
+         * @return {@code true} if this set changed as a result of the call
+         * @throws NullPointerException if the collection or any of its
+         * elements are {@code null}
+         * @throws UnsupportedOperationException if no default mapped value
+         * for additions was provided
+         */
+        public boolean addAll(Collection<? extends K> c) {
+            boolean added = false;
+            V v;
+            if ((v = value) == null)
+                throw new UnsupportedOperationException();
+            for (K e : c) {
+                if (map.putVal(e, v, true) == null)
+                    added = true;
+            }
+            return added;
         }
-        public boolean remove(Object o) {
-            return ConcurrentHashMap.this.remove(o) != null;
+
+        public int hashCode() {
+            int h = 0;
+            for (K e : this)
+                h += e.hashCode();
+            return h;
         }
-        public void clear() {
-            ConcurrentHashMap.this.clear();
+
+        public boolean equals(Object o) {
+            Set<?> c;
+            return ((o instanceof Set) &&
+                    ((c = (Set<?>)o) == this ||
+                     (containsAll(c) && c.containsAll(this))));
         }
+
     }
 
-    final class Values extends AbstractCollection<V> {
-        public Iterator<V> iterator() {
-            return new ValueIterator();
+    /**
+     * A view of a ConcurrentHashMap as a {@link Collection} of
+     * values, in which additions are disabled. This class cannot be
+     * directly instantiated. See {@link #values()}.
+     */
+    static final class ValuesView<K,V> extends CollectionView<K,V,V>
+        implements Collection<V>, java.io.Serializable {
+        private static final long serialVersionUID = 2249069246763182397L;
+        ValuesView(ConcurrentHashMap<K,V> map) { super(map); }
+        public final boolean contains(Object o) {
+            return map.containsValue(o);
         }
-        public int size() {
-            return ConcurrentHashMap.this.size();
+
+        public final boolean remove(Object o) {
+            if (o != null) {
+                for (Iterator<V> it = iterator(); it.hasNext();) {
+                    if (o.equals(it.next())) {
+                        it.remove();
+                        return true;
+                    }
+                }
+            }
+            return false;
         }
-        public boolean isEmpty() {
-            return ConcurrentHashMap.this.isEmpty();
+
+        public final Iterator<V> iterator() {
+            ConcurrentHashMap<K,V> m = map;
+            Node<K,V>[] t;
+            int f = (t = m.table) == null ? 0 : t.length;
+            return new ValueIterator<K,V>(t, f, 0, f, m);
         }
-        public boolean contains(Object o) {
-            return ConcurrentHashMap.this.containsValue(o);
+
+        public final boolean add(V e) {
+            throw new UnsupportedOperationException();
         }
-        public void clear() {
-            ConcurrentHashMap.this.clear();
+        public final boolean addAll(Collection<? extends V> c) {
+            throw new UnsupportedOperationException();
         }
+
     }
 
-    final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
-        public Iterator<Map.Entry<K,V>> iterator() {
-            return new EntryIterator();
-        }
+    /**
+     * A view of a ConcurrentHashMap as a {@link Set} of (key, value)
+     * entries.  This class cannot be directly instantiated. See
+     * {@link #entrySet()}.
+     */
+    static final class EntrySetView<K,V> extends CollectionView<K,V,Map.Entry<K,V>>
+        implements Set<Map.Entry<K,V>>, java.io.Serializable {
+        private static final long serialVersionUID = 2249069246763182397L;
+        EntrySetView(ConcurrentHashMap<K,V> map) { super(map); }
+
         public boolean contains(Object o) {
-            if (!(o instanceof Map.Entry))
-                return false;
-            Map.Entry<?,?> e = (Map.Entry<?,?>)o;
-            V v = ConcurrentHashMap.this.get(e.getKey());
-            return v != null && v.equals(e.getValue());
+            Object k, v, r; Map.Entry<?,?> e;
+            return ((o instanceof Map.Entry) &&
+                    (k = (e = (Map.Entry<?,?>)o).getKey()) != null &&
+                    (r = map.get(k)) != null &&
+                    (v = e.getValue()) != null &&
+                    (v == r || v.equals(r)));
         }
+
         public boolean remove(Object o) {
-            if (!(o instanceof Map.Entry))
-                return false;
-            Map.Entry<?,?> e = (Map.Entry<?,?>)o;
-            return ConcurrentHashMap.this.remove(e.getKey(), e.getValue());
+            Object k, v; Map.Entry<?,?> e;
+            return ((o instanceof Map.Entry) &&
+                    (k = (e = (Map.Entry<?,?>)o).getKey()) != null &&
+                    (v = e.getValue()) != null &&
+                    map.remove(k, v));
         }
-        public int size() {
-            return ConcurrentHashMap.this.size();
+
+        /**
+         * @return an iterator over the entries of the backing map
+         */
+        public Iterator<Map.Entry<K,V>> iterator() {
+            ConcurrentHashMap<K,V> m = map;
+            Node<K,V>[] t;
+            int f = (t = m.table) == null ? 0 : t.length;
+            return new EntryIterator<K,V>(t, f, 0, f, m);
         }
-        public boolean isEmpty() {
-            return ConcurrentHashMap.this.isEmpty();
+
+        public boolean add(Entry<K,V> e) {
+            return map.putVal(e.getKey(), e.getValue(), false) == null;
         }
-        public void clear() {
-            ConcurrentHashMap.this.clear();
+
+        public boolean addAll(Collection<? extends Entry<K,V>> c) {
+            boolean added = false;
+            for (Entry<K,V> e : c) {
+                if (add(e))
+                    added = true;
+            }
+            return added;
         }
+
+        public final int hashCode() {
+            int h = 0;
+            Node<K,V>[] t;
+            if ((t = map.table) != null) {
+                Traverser<K,V> it = new Traverser<K,V>(t, t.length, 0, t.length);
+                for (Node<K,V> p; (p = it.advance()) != null; ) {
+                    h += p.hashCode();
+                }
+            }
+            return h;
+        }
+
+        public final boolean equals(Object o) {
+            Set<?> c;
+            return ((o instanceof Set) &&
+                    ((c = (Set<?>)o) == this ||
+                     (containsAll(c) && c.containsAll(this))));
+        }
+
     }
 
-    /* ---------------- Serialization Support -------------- */
+
+    /* ---------------- Counters -------------- */
+
+    // Adapted from LongAdder and Striped64.
+    // See their internal docs for explanation.
+
+    // A padded cell for distributing counts
+    static final class CounterCell {
+        volatile long p0, p1, p2, p3, p4, p5, p6;
+        volatile long value;
+        volatile long q0, q1, q2, q3, q4, q5, q6;
+        CounterCell(long x) { value = x; }
+    }
 
     /**
-     * Saves the state of the <tt>ConcurrentHashMap</tt> instance to a
-     * stream (i.e., serializes it).
-     * @param s the stream
-     * @serialData
-     * the key (Object) and value (Object)
-     * for each key-value mapping, followed by a null pair.
-     * The key-value mappings are emitted in no particular order.
+     * Holder for the thread-local hash code determining which
+     * CounterCell to use. The code is initialized via the
+     * counterHashCodeGenerator, but may be moved upon collisions.
      */
-    private void writeObject(java.io.ObjectOutputStream s)
-            throws java.io.IOException {
-        // force all segments for serialization compatibility
-        for (int k = 0; k < segments.length; ++k)
-            ensureSegment(k);
-        s.defaultWriteObject();
-
-        final Segment<K,V>[] segments = this.segments;
-        for (int k = 0; k < segments.length; ++k) {
-            Segment<K,V> seg = segmentAt(segments, k);
-            seg.lock();
-            try {
-                HashEntry<K,V>[] tab = seg.table;
-                for (int i = 0; i < tab.length; ++i) {
-                    HashEntry<K,V> e;
-                    for (e = entryAt(tab, i); e != null; e = e.next) {
-                        s.writeObject(e.key);
-                        s.writeObject(e.value);
-                    }
-                }
-            } finally {
-                seg.unlock();
-            }
-        }
-        s.writeObject(null);
-        s.writeObject(null);
+    static final class CounterHashCode {
+        int code;
     }
 
     /**
-     * Reconstitutes the <tt>ConcurrentHashMap</tt> instance from a
-     * stream (i.e., deserializes it).
-     * @param s the stream
+     * Generates initial value for per-thread CounterHashCodes.
      */
-    @SuppressWarnings("unchecked")
-    private void readObject(java.io.ObjectInputStream s)
-            throws java.io.IOException, ClassNotFoundException {
-        s.defaultReadObject();
+    static final AtomicInteger counterHashCodeGenerator = new AtomicInteger();
 
-        // Re-initialize segments to be minimally sized, and let grow.
-        int cap = MIN_SEGMENT_TABLE_CAPACITY;
-        final Segment<K,V>[] segments = this.segments;
-        for (int k = 0; k < segments.length; ++k) {
-            Segment<K,V> seg = segments[k];
-            if (seg != null) {
-                seg.threshold = (int)(cap * seg.loadFactor);
-                seg.table = (HashEntry<K,V>[]) new HashEntry<?,?>[cap];
+    /**
+     * Increment for counterHashCodeGenerator. See class ThreadLocal
+     * for explanation.
+     */
+    static final int SEED_INCREMENT = 0x61c88647;
+
+    /**
+     * Per-thread counter hash codes. Shared across all instances.
+     */
+    static final ThreadLocal<CounterHashCode> threadCounterHashCode =
+        new ThreadLocal<CounterHashCode>();
+
+    final long sumCount() {
+        CounterCell[] as = counterCells; CounterCell a;
+        long sum = baseCount;
+        if (as != null) {
+            for (int i = 0; i < as.length; ++i) {
+                if ((a = as[i]) != null)
+                    sum += a.value;
             }
         }
+        return sum;
+    }
 
-        // Read the keys and values, and put the mappings in the table
+    // See LongAdder version for explanation
+    private final void fullAddCount(long x, CounterHashCode hc,
+                                    boolean wasUncontended) {
+        int h;
+        if (hc == null) {
+            hc = new CounterHashCode();
+            int s = counterHashCodeGenerator.addAndGet(SEED_INCREMENT);
+            h = hc.code = (s == 0) ? 1 : s; // Avoid zero
+            threadCounterHashCode.set(hc);
+        }
+        else
+            h = hc.code;
+        boolean collide = false;                // True if last slot nonempty
         for (;;) {
-            K key = (K) s.readObject();
-            V value = (V) s.readObject();
-            if (key == null)
-                break;
-            put(key, value);
+            CounterCell[] as; CounterCell a; int n; long v;
+            if ((as = counterCells) != null && (n = as.length) > 0) {
+                if ((a = as[(n - 1) & h]) == null) {
+                    if (cellsBusy == 0) {            // Try to attach new Cell
+                        CounterCell r = new CounterCell(x); // Optimistic create
+                        if (cellsBusy == 0 &&
+                            U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
+                            boolean created = false;
+                            try {               // Recheck under lock
+                                CounterCell[] rs; int m, j;
+                                if ((rs = counterCells) != null &&
+                                    (m = rs.length) > 0 &&
+                                    rs[j = (m - 1) & h] == null) {
+                                    rs[j] = r;
+                                    created = true;
+                                }
+                            } finally {
+                                cellsBusy = 0;
+                            }
+                            if (created)
+                                break;
+                            continue;           // Slot is now non-empty
+                        }
+                    }
+                    collide = false;
+                }
+                else if (!wasUncontended)       // CAS already known to fail
+                    wasUncontended = true;      // Continue after rehash
+                else if (U.compareAndSwapLong(a, CELLVALUE, v = a.value, v + x))
+                    break;
+                else if (counterCells != as || n >= NCPU)
+                    collide = false;            // At max size or stale
+                else if (!collide)
+                    collide = true;
+                else if (cellsBusy == 0 &&
+                         U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
+                    try {
+                        if (counterCells == as) {// Expand table unless stale
+                            CounterCell[] rs = new CounterCell[n << 1];
+                            for (int i = 0; i < n; ++i)
+                                rs[i] = as[i];
+                            counterCells = rs;
+                        }
+                    } finally {
+                        cellsBusy = 0;
+                    }
+                    collide = false;
+                    continue;                   // Retry with expanded table
+                }
+                h ^= h << 13;                   // Rehash
+                h ^= h >>> 17;
+                h ^= h << 5;
+            }
+            else if (cellsBusy == 0 && counterCells == as &&
+                     U.compareAndSwapInt(this, CELLSBUSY, 0, 1)) {
+                boolean init = false;
+                try {                           // Initialize table
+                    if (counterCells == as) {
+                        CounterCell[] rs = new CounterCell[2];
+                        rs[h & 1] = new CounterCell(x);
+                        counterCells = rs;
+                        init = true;
+                    }
+                } finally {
+                    cellsBusy = 0;
+                }
+                if (init)
+                    break;
+            }
+            else if (U.compareAndSwapLong(this, BASECOUNT, v = baseCount, v + x))
+                break;                          // Fall back on using base
         }
+        hc.code = h;                            // Record index for next time
     }
 
     // Unsafe mechanics
-    private static final sun.misc.Unsafe UNSAFE;
-    private static final long SBASE;
-    private static final int SSHIFT;
-    private static final long TBASE;
-    private static final int TSHIFT;
+    private static final sun.misc.Unsafe U;
+    private static final long SIZECTL;
+    private static final long TRANSFERINDEX;
+    private static final long TRANSFERORIGIN;
+    private static final long BASECOUNT;
+    private static final long CELLSBUSY;
+    private static final long CELLVALUE;
+    private static final long ABASE;
+    private static final int ASHIFT;
 
     static {
-        int ss, ts;
         try {
-            UNSAFE = sun.misc.Unsafe.getUnsafe();
-            Class<?> tc = HashEntry[].class;
-            Class<?> sc = Segment[].class;
-            TBASE = UNSAFE.arrayBaseOffset(tc);
-            SBASE = UNSAFE.arrayBaseOffset(sc);
-            ts = UNSAFE.arrayIndexScale(tc);
-            ss = UNSAFE.arrayIndexScale(sc);
+            U = sun.misc.Unsafe.getUnsafe();
+            Class<?> k = ConcurrentHashMap.class;
+            SIZECTL = U.objectFieldOffset
+                (k.getDeclaredField("sizeCtl"));
+            TRANSFERINDEX = U.objectFieldOffset
+                (k.getDeclaredField("transferIndex"));
+            TRANSFERORIGIN = U.objectFieldOffset
+                (k.getDeclaredField("transferOrigin"));
+            BASECOUNT = U.objectFieldOffset
+                (k.getDeclaredField("baseCount"));
+            CELLSBUSY = U.objectFieldOffset
+                (k.getDeclaredField("cellsBusy"));
+            Class<?> ck = CounterCell.class;
+            CELLVALUE = U.objectFieldOffset
+                (ck.getDeclaredField("value"));
+            Class<?> ak = Node[].class;
+            ABASE = U.arrayBaseOffset(ak);
+            int scale = U.arrayIndexScale(ak);
+            if ((scale & (scale - 1)) != 0)
+                throw new Error("data type scale not a power of two");
+            ASHIFT = 31 - Integer.numberOfLeadingZeros(scale);
         } catch (Exception e) {
             throw new Error(e);
         }
-        if ((ss & (ss-1)) != 0 || (ts & (ts-1)) != 0)
-            throw new Error("data type scale not a power of two");
-        SSHIFT = 31 - Integer.numberOfLeadingZeros(ss);
-        TSHIFT = 31 - Integer.numberOfLeadingZeros(ts);
     }
 
 }
diff --git a/luni/src/main/java/java/util/concurrent/ConcurrentLinkedQueue.java b/luni/src/main/java/java/util/concurrent/ConcurrentLinkedQueue.java
index 873f825..b39a533 100644
--- a/luni/src/main/java/java/util/concurrent/ConcurrentLinkedQueue.java
+++ b/luni/src/main/java/java/util/concurrent/ConcurrentLinkedQueue.java
@@ -31,7 +31,7 @@ import java.util.Queue;
  * Like most other concurrent collection implementations, this class
  * does not permit the use of {@code null} elements.
  *
- * <p>This implementation employs an efficient &quot;wait-free&quot;
+ * <p>This implementation employs an efficient <em>non-blocking</em>
  * algorithm based on one described in <a
  * href="http://www.cs.rochester.edu/u/michael/PODC96.html"> Simple,
  * Fast, and Practical Non-Blocking and Blocking Concurrent Queue
diff --git a/luni/src/main/java/java/util/concurrent/CountedCompleter.java b/luni/src/main/java/java/util/concurrent/CountedCompleter.java
index ffe7582..d5f794e 100644
--- a/luni/src/main/java/java/util/concurrent/CountedCompleter.java
+++ b/luni/src/main/java/java/util/concurrent/CountedCompleter.java
@@ -8,14 +8,15 @@ package java.util.concurrent;
 
 /**
  * A {@link ForkJoinTask} with a completion action performed when
- * triggered and there are no remaining pending
- * actions. CountedCompleters are in general more robust in the
+ * triggered and there are no remaining pending actions.
+ * CountedCompleters are in general more robust in the
  * presence of subtask stalls and blockage than are other forms of
  * ForkJoinTasks, but are less intuitive to program.  Uses of
  * CountedCompleter are similar to those of other completion based
  * components (such as {@link java.nio.channels.CompletionHandler})
  * except that multiple <em>pending</em> completions may be necessary
- * to trigger the completion action {@link #onCompletion}, not just one.
+ * to trigger the completion action {@link #onCompletion(CountedCompleter)},
+ * not just one.
  * Unless initialized otherwise, the {@linkplain #getPendingCount pending
  * count} starts at zero, but may be (atomically) changed using
  * methods {@link #setPendingCount}, {@link #addToPendingCount}, and
@@ -40,9 +41,10 @@ package java.util.concurrent;
  * <p>A concrete CountedCompleter class must define method {@link
  * #compute}, that should in most cases (as illustrated below), invoke
  * {@code tryComplete()} once before returning. The class may also
- * optionally override method {@link #onCompletion} to perform an
- * action upon normal completion, and method {@link
- * #onExceptionalCompletion} to perform an action upon any exception.
+ * optionally override method {@link #onCompletion(CountedCompleter)}
+ * to perform an action upon normal completion, and method
+ * {@link #onExceptionalCompletion(Throwable, CountedCompleter)} to
+ * perform an action upon any exception.
  *
  * <p>CountedCompleters most often do not bear results, in which case
  * they are normally declared as {@code CountedCompleter<Void>}, and
@@ -63,13 +65,14 @@ package java.util.concurrent;
  * only as an internal helper for other computations, so its own task
  * status (as reported in methods such as {@link ForkJoinTask#isDone})
  * is arbitrary; this status changes only upon explicit invocations of
- * {@link #complete}, {@link ForkJoinTask#cancel}, {@link
- * ForkJoinTask#completeExceptionally} or upon exceptional completion
- * of method {@code compute}. Upon any exceptional completion, the
- * exception may be relayed to a task's completer (and its completer,
- * and so on), if one exists and it has not otherwise already
- * completed. Similarly, cancelling an internal CountedCompleter has
- * only a local effect on that completer, so is not often useful.
+ * {@link #complete}, {@link ForkJoinTask#cancel},
+ * {@link ForkJoinTask#completeExceptionally(Throwable)} or upon
+ * exceptional completion of method {@code compute}. Upon any
+ * exceptional completion, the exception may be relayed to a task's
+ * completer (and its completer, and so on), if one exists and it has
+ * not otherwise already completed. Similarly, cancelling an internal
+ * CountedCompleter has only a local effect on that completer, so is
+ * not often useful.
  *
  * <p><b>Sample Usages.</b>
  *
@@ -96,8 +99,8 @@ package java.util.concurrent;
  * improve load balancing. In the recursive case, the second of each
  * pair of subtasks to finish triggers completion of its parent
  * (because no result combination is performed, the default no-op
- * implementation of method {@code onCompletion} is not overridden). A
- * static utility method sets up the base task and invokes it
+ * implementation of method {@code onCompletion} is not overridden).
+ * A static utility method sets up the base task and invokes it
  * (here, implicitly using the {@link ForkJoinPool#commonPool()}).
  *
  * <pre> {@code
@@ -152,12 +155,11 @@ package java.util.concurrent;
  *   }
  * }</pre>
  *
- * As a further improvement, notice that the left task need not even
- * exist.  Instead of creating a new one, we can iterate using the
- * original task, and add a pending count for each fork. Additionally,
- * because no task in this tree implements an {@link #onCompletion}
- * method, {@code tryComplete()} can be replaced with {@link
- * #propagateCompletion}.
+ * As a further improvement, notice that the left task need not even exist.
+ * Instead of creating a new one, we can iterate using the original task,
+ * and add a pending count for each fork.  Additionally, because no task
+ * in this tree implements an {@link #onCompletion(CountedCompleter)} method,
+ * {@code tryComplete()} can be replaced with {@link #propagateCompletion}.
  *
  * <pre> {@code
  * class ForEach<E> ...
@@ -235,7 +237,7 @@ package java.util.concurrent;
  *
  * <p><b>Recording subtasks.</b> CountedCompleter tasks that combine
  * results of multiple subtasks usually need to access these results
- * in method {@link #onCompletion}. As illustrated in the following
+ * in method {@link #onCompletion(CountedCompleter)}. As illustrated in the following
  * class (that performs a simplified form of map-reduce where mappings
  * and reductions are all of type {@code E}), one way to do this in
  * divide and conquer designs is to have each subtask record its
@@ -357,7 +359,7 @@ package java.util.concurrent;
  *
  * <p><b>Triggers.</b> Some CountedCompleters are themselves never
  * forked, but instead serve as bits of plumbing in other designs;
- * including those in which the completion of one of more async tasks
+ * including those in which the completion of one or more async tasks
  * triggers another async task. For example:
  *
  * <pre> {@code
@@ -438,20 +440,21 @@ public abstract class CountedCompleter<T> extends ForkJoinTask<T> {
     }
 
     /**
-     * Performs an action when method {@link #completeExceptionally}
-     * is invoked or method {@link #compute} throws an exception, and
-     * this task has not otherwise already completed normally. On
-     * entry to this method, this task {@link
-     * ForkJoinTask#isCompletedAbnormally}.  The return value of this
-     * method controls further propagation: If {@code true} and this
-     * task has a completer, then this completer is also completed
-     * exceptionally.  The default implementation of this method does
-     * nothing except return {@code true}.
+     * Performs an action when method {@link
+     * #completeExceptionally(Throwable)} is invoked or method {@link
+     * #compute} throws an exception, and this task has not already
+     * otherwise completed normally. On entry to this method, this task
+     * {@link ForkJoinTask#isCompletedAbnormally}.  The return value
+     * of this method controls further propagation: If {@code true}
+     * and this task has a completer that has not completed, then that
+     * completer is also completed exceptionally, with the same
+     * exception as this completer.  The default implementation of
+     * this method does nothing except return {@code true}.
      *
      * @param ex the exception
      * @param caller the task invoking this method (which may
      * be this task itself)
-     * @return true if this exception should be propagated to this
+     * @return {@code true} if this exception should be propagated to this
      * task's completer, if one exists
      */
     public boolean onExceptionalCompletion(Throwable ex, CountedCompleter<?> caller) {
@@ -492,7 +495,7 @@ public abstract class CountedCompleter<T> extends ForkJoinTask<T> {
      * @param delta the value to add
      */
     public final void addToPendingCount(int delta) {
-        int c; // note: can replace with intrinsic in jdk8
+        int c;
         do {} while (!U.compareAndSwapInt(this, PENDING, c = pending, c+delta));
     }
 
@@ -502,7 +505,7 @@ public abstract class CountedCompleter<T> extends ForkJoinTask<T> {
      *
      * @param expected the expected value
      * @param count the new value
-     * @return true if successful
+     * @return {@code true} if successful
      */
     public final boolean compareAndSetPendingCount(int expected, int count) {
         return U.compareAndSwapInt(this, PENDING, expected, count);
@@ -536,9 +539,9 @@ public abstract class CountedCompleter<T> extends ForkJoinTask<T> {
 
     /**
      * If the pending count is nonzero, decrements the count;
-     * otherwise invokes {@link #onCompletion} and then similarly
-     * tries to complete this task's completer, if one exists,
-     * else marks this task as complete.
+     * otherwise invokes {@link #onCompletion(CountedCompleter)}
+     * and then similarly tries to complete this task's completer,
+     * if one exists, else marks this task as complete.
      */
     public final void tryComplete() {
         CountedCompleter<?> a = this, s = a;
@@ -557,12 +560,12 @@ public abstract class CountedCompleter<T> extends ForkJoinTask<T> {
 
     /**
      * Equivalent to {@link #tryComplete} but does not invoke {@link
-     * #onCompletion} along the completion path: If the pending count
-     * is nonzero, decrements the count; otherwise, similarly tries to
-     * complete this task's completer, if one exists, else marks this
-     * task as complete. This method may be useful in cases where
-     * {@code onCompletion} should not, or need not, be invoked for
-     * each completer in a computation.
+     * #onCompletion(CountedCompleter)} along the completion path:
+     * If the pending count is nonzero, decrements the count;
+     * otherwise, similarly tries to complete this task's completer, if
+     * one exists, else marks this task as complete. This method may be
+     * useful in cases where {@code onCompletion} should not, or need
+     * not, be invoked for each completer in a computation.
      */
     public final void propagateCompletion() {
         CountedCompleter<?> a = this, s = a;
@@ -579,13 +582,15 @@ public abstract class CountedCompleter<T> extends ForkJoinTask<T> {
     }
 
     /**
-     * Regardless of pending count, invokes {@link #onCompletion},
-     * marks this task as complete and further triggers {@link
-     * #tryComplete} on this task's completer, if one exists.  The
-     * given rawResult is used as an argument to {@link #setRawResult}
-     * before invoking {@link #onCompletion} or marking this task as
-     * complete; its value is meaningful only for classes overriding
-     * {@code setRawResult}.
+     * Regardless of pending count, invokes
+     * {@link #onCompletion(CountedCompleter)}, marks this task as
+     * complete and further triggers {@link #tryComplete} on this
+     * task's completer, if one exists.  The given rawResult is
+     * used as an argument to {@link #setRawResult} before invoking
+     * {@link #onCompletion(CountedCompleter)} or marking this task
+     * as complete; its value is meaningful only for classes
+     * overriding {@code setRawResult}.  This method does not modify
+     * the pending count.
      *
      * <p>This method may be useful when forcing completion as soon as
      * any one (versus all) of several subtask results are obtained.
@@ -604,7 +609,6 @@ public abstract class CountedCompleter<T> extends ForkJoinTask<T> {
             p.tryComplete();
     }
 
-
     /**
      * If this task's pending count is zero, returns this task;
      * otherwise decrements its pending count and returns {@code
@@ -668,8 +672,9 @@ public abstract class CountedCompleter<T> extends ForkJoinTask<T> {
     void internalPropagateException(Throwable ex) {
         CountedCompleter<?> a = this, s = a;
         while (a.onExceptionalCompletion(ex, s) &&
-               (a = (s = a).completer) != null && a.status >= 0)
-            a.recordExceptionalCompletion(ex);
+               (a = (s = a).completer) != null && a.status >= 0 &&
+               a.recordExceptionalCompletion(ex) == EXCEPTIONAL)
+            ;
     }
 
     /**
diff --git a/luni/src/main/java/java/util/concurrent/ForkJoinPool.java b/luni/src/main/java/java/util/concurrent/ForkJoinPool.java
index 87ffff3..5ac01c8 100644
--- a/luni/src/main/java/java/util/concurrent/ForkJoinPool.java
+++ b/luni/src/main/java/java/util/concurrent/ForkJoinPool.java
@@ -6,6 +6,7 @@
 
 package java.util.concurrent;
 
+import java.lang.Thread.UncaughtExceptionHandler;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -17,6 +18,7 @@ import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Future;
 import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.RunnableFuture;
+import java.util.concurrent.ThreadLocalRandom;
 import java.util.concurrent.TimeUnit;
 
 /**
@@ -49,9 +51,9 @@ import java.util.concurrent.TimeUnit;
  * level; by default, equal to the number of available processors. The
  * pool attempts to maintain enough active (or available) threads by
  * dynamically adding, suspending, or resuming internal worker
- * threads, even if some tasks are stalled waiting to join
- * others. However, no such adjustments are guaranteed in the face of
- * blocked I/O or other unmanaged synchronization. The nested {@link
+ * threads, even if some tasks are stalled waiting to join others.
+ * However, no such adjustments are guaranteed in the face of blocked
+ * I/O or other unmanaged synchronization. The nested {@link
  * ManagedBlocker} interface enables extension of the kinds of
  * synchronization accommodated.
  *
@@ -75,38 +77,45 @@ import java.util.concurrent.TimeUnit;
  * there is little difference among choice of methods.
  *
  * <table BORDER CELLPADDING=3 CELLSPACING=1>
+ * <caption>Summary of task execution methods</caption>
  *  <tr>
  *    <td></td>
  *    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
  *    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
  *  </tr>
  *  <tr>
- *    <td> <b>Arrange async execution</td>
+ *    <td> <b>Arrange async execution</b></td>
  *    <td> {@link #execute(ForkJoinTask)}</td>
  *    <td> {@link ForkJoinTask#fork}</td>
  *  </tr>
  *  <tr>
- *    <td> <b>Await and obtain result</td>
+ *    <td> <b>Await and obtain result</b></td>
  *    <td> {@link #invoke(ForkJoinTask)}</td>
  *    <td> {@link ForkJoinTask#invoke}</td>
  *  </tr>
  *  <tr>
- *    <td> <b>Arrange exec and obtain Future</td>
+ *    <td> <b>Arrange exec and obtain Future</b></td>
  *    <td> {@link #submit(ForkJoinTask)}</td>
  *    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
  *  </tr>
  * </table>
  *
  * <p>The common pool is by default constructed with default
- * parameters, but these may be controlled by setting three {@link
- * System#getProperty system properties} with prefix {@code
- * java.util.concurrent.ForkJoinPool.common}: {@code parallelism} --
- * an integer greater than zero, {@code threadFactory} -- the class
- * name of a {@link ForkJoinWorkerThreadFactory}, and {@code
- * exceptionHandler} -- the class name of a {@link
- * java.lang.Thread.UncaughtExceptionHandler
- * Thread.UncaughtExceptionHandler}. Upon any error in establishing
- * these settings, default parameters are used.
+ * parameters, but these may be controlled by setting three
+ * {@linkplain System#getProperty system properties}:
+ * <ul>
+ * <li>{@code java.util.concurrent.ForkJoinPool.common.parallelism}
+ * - the parallelism level, a non-negative integer
+ * <li>{@code java.util.concurrent.ForkJoinPool.common.threadFactory}
+ * - the class name of a {@link ForkJoinWorkerThreadFactory}
+ * <li>{@code java.util.concurrent.ForkJoinPool.common.exceptionHandler}
+ * - the class name of a {@link UncaughtExceptionHandler}
+ * </ul>
+ * The system class loader is used to load these classes.
+ * Upon any error in establishing these settings, default parameters
+ * are used. It is possible to disable or limit the use of threads in
+ * the common pool by setting the parallelism property to zero, and/or
+ * using a factory that may return {@code null}.
  *
  * <p><b>Implementation notes</b>: This implementation restricts the
  * maximum number of running threads to 32767. Attempts to create
@@ -153,32 +162,35 @@ public class ForkJoinPool extends AbstractExecutorService {
      * (http://research.sun.com/scalable/pubs/index.html) and
      * "Idempotent work stealing" by Michael, Saraswat, and Vechev,
      * PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186).
-     * The main differences ultimately stem from GC requirements that
-     * we null out taken slots as soon as we can, to maintain as small
-     * a footprint as possible even in programs generating huge
-     * numbers of tasks. To accomplish this, we shift the CAS
-     * arbitrating pop vs poll (steal) from being on the indices
-     * ("base" and "top") to the slots themselves.  So, both a
-     * successful pop and poll mainly entail a CAS of a slot from
-     * non-null to null.  Because we rely on CASes of references, we
-     * do not need tag bits on base or top.  They are simple ints as
-     * used in any circular array-based queue (see for example
-     * ArrayDeque).  Updates to the indices must still be ordered in a
-     * way that guarantees that top == base means the queue is empty,
-     * but otherwise may err on the side of possibly making the queue
-     * appear nonempty when a push, pop, or poll have not fully
-     * committed. Note that this means that the poll operation,
-     * considered individually, is not wait-free. One thief cannot
-     * successfully continue until another in-progress one (or, if
-     * previously empty, a push) completes.  However, in the
-     * aggregate, we ensure at least probabilistic non-blockingness.
-     * If an attempted steal fails, a thief always chooses a different
-     * random victim target to try next. So, in order for one thief to
-     * progress, it suffices for any in-progress poll or new push on
-     * any empty queue to complete. (This is why we normally use
-     * method pollAt and its variants that try once at the apparent
-     * base index, else consider alternative actions, rather than
-     * method poll.)
+     * See also "Correct and Efficient Work-Stealing for Weak Memory
+     * Models" by Le, Pop, Cohen, and Nardelli, PPoPP 2013
+     * (http://www.di.ens.fr/~zappa/readings/ppopp13.pdf) for an
+     * analysis of memory ordering (atomic, volatile etc) issues.  The
+     * main differences ultimately stem from GC requirements that we
+     * null out taken slots as soon as we can, to maintain as small a
+     * footprint as possible even in programs generating huge numbers
+     * of tasks. To accomplish this, we shift the CAS arbitrating pop
+     * vs poll (steal) from being on the indices ("base" and "top") to
+     * the slots themselves.  So, both a successful pop and poll
+     * mainly entail a CAS of a slot from non-null to null.  Because
+     * we rely on CASes of references, we do not need tag bits on base
+     * or top.  They are simple ints as used in any circular
+     * array-based queue (see for example ArrayDeque).  Updates to the
+     * indices must still be ordered in a way that guarantees that top
+     * == base means the queue is empty, but otherwise may err on the
+     * side of possibly making the queue appear nonempty when a push,
+     * pop, or poll have not fully committed. Note that this means
+     * that the poll operation, considered individually, is not
+     * wait-free. One thief cannot successfully continue until another
+     * in-progress one (or, if previously empty, a push) completes.
+     * However, in the aggregate, we ensure at least probabilistic
+     * non-blockingness.  If an attempted steal fails, a thief always
+     * chooses a different random victim target to try next. So, in
+     * order for one thief to progress, it suffices for any
+     * in-progress poll or new push on any empty queue to
+     * complete. (This is why we normally use method pollAt and its
+     * variants that try once at the apparent base index, else
+     * consider alternative actions, rather than method poll.)
      *
      * This approach also enables support of a user mode in which local
      * task processing is in FIFO, not LIFO order, simply by using
@@ -197,18 +209,18 @@ public class ForkJoinPool extends AbstractExecutorService {
      * for work-stealing (this would contaminate lifo/fifo
      * processing). Instead, we randomly associate submission queues
      * with submitting threads, using a form of hashing.  The
-     * ThreadLocal Submitter class contains a value initially used as
-     * a hash code for choosing existing queues, but may be randomly
-     * repositioned upon contention with other submitters.  In
-     * essence, submitters act like workers except that they are
-     * restricted to executing local tasks that they submitted (or in
-     * the case of CountedCompleters, others with the same root task).
-     * However, because most shared/external queue operations are more
-     * expensive than internal, and because, at steady state, external
-     * submitters will compete for CPU with workers, ForkJoinTask.join
-     * and related methods disable them from repeatedly helping to
-     * process tasks if all workers are active.  Insertion of tasks in
-     * shared mode requires a lock (mainly to protect in the case of
+     * Submitter probe value serves as a hash code for
+     * choosing existing queues, and may be randomly repositioned upon
+     * contention with other submitters.  In essence, submitters act
+     * like workers except that they are restricted to executing local
+     * tasks that they submitted (or in the case of CountedCompleters,
+     * others with the same root task).  However, because most
+     * shared/external queue operations are more expensive than
+     * internal, and because, at steady state, external submitters
+     * will compete for CPU with workers, ForkJoinTask.join and
+     * related methods disable them from repeatedly helping to process
+     * tasks if all workers are active.  Insertion of tasks in shared
+     * mode requires a lock (mainly to protect in the case of
      * resizing) but we use only a simple spinlock (using bits in
      * field qlock), because submitters encountering a busy queue move
      * on to try or create other queues -- they block only when
@@ -298,37 +310,35 @@ public class ForkJoinPool extends AbstractExecutorService {
      * has not yet entered the wait queue. We solve this by requiring
      * a full sweep of all workers (via repeated calls to method
      * scan()) both before and after a newly waiting worker is added
-     * to the wait queue. During a rescan, the worker might release
-     * some other queued worker rather than itself, which has the same
-     * net effect. Because enqueued workers may actually be rescanning
-     * rather than waiting, we set and clear the "parker" field of
-     * WorkQueues to reduce unnecessary calls to unpark.  (This
-     * requires a secondary recheck to avoid missed signals.)  Note
-     * the unusual conventions about Thread.interrupts surrounding
-     * parking and other blocking: Because interrupts are used solely
-     * to alert threads to check termination, which is checked anyway
-     * upon blocking, we clear status (using Thread.interrupted)
-     * before any call to park, so that park does not immediately
-     * return due to status being set via some other unrelated call to
-     * interrupt in user code.
+     * to the wait queue.  Because enqueued workers may actually be
+     * rescanning rather than waiting, we set and clear the "parker"
+     * field of WorkQueues to reduce unnecessary calls to unpark.
+     * (This requires a secondary recheck to avoid missed signals.)
+     * Note the unusual conventions about Thread.interrupts
+     * surrounding parking and other blocking: Because interrupts are
+     * used solely to alert threads to check termination, which is
+     * checked anyway upon blocking, we clear status (using
+     * Thread.interrupted) before any call to park, so that park does
+     * not immediately return due to status being set via some other
+     * unrelated call to interrupt in user code.
      *
      * Signalling.  We create or wake up workers only when there
      * appears to be at least one task they might be able to find and
-     * execute. However, many other threads may notice the same task
-     * and each signal to wake up a thread that might take it. So in
-     * general, pools will be over-signalled.  When a submission is
-     * added or another worker adds a task to a queue that has fewer
-     * than two tasks, they signal waiting workers (or trigger
-     * creation of new ones if fewer than the given parallelism level
-     * -- signalWork), and may leave a hint to the unparked worker to
-     * help signal others upon wakeup).  These primary signals are
-     * buttressed by others (see method helpSignal) whenever other
-     * threads scan for work or do not have a task to process.  On
-     * most platforms, signalling (unpark) overhead time is noticeably
+     * execute.  When a submission is added or another worker adds a
+     * task to a queue that has fewer than two tasks, they signal
+     * waiting workers (or trigger creation of new ones if fewer than
+     * the given parallelism level -- signalWork).  These primary
+     * signals are buttressed by others whenever other threads remove
+     * a task from a queue and notice that there are other tasks there
+     * as well.  So in general, pools will be over-signalled. On most
+     * platforms, signalling (unpark) overhead time is noticeably
      * long, and the time between signalling a thread and it actually
      * making progress can be very noticeably long, so it is worth
      * offloading these delays from critical paths as much as
-     * possible.
+     * possible. Additionally, workers spin-down gradually, by staying
+     * alive so long as they see the ctl state changing.  Similar
+     * stability-sensing techniques are also used before blocking in
+     * awaitJoin and helpComplete.
      *
      * Trimming workers. To release resources after periods of lack of
      * use, a worker starting to wait when the pool is quiescent will
@@ -441,7 +451,7 @@ public class ForkJoinPool extends AbstractExecutorService {
      * Common Pool
      * ===========
      *
-     * The static commonPool always exists after static
+     * The static common pool always exists after static
      * initialization.  Since it (or any other created pool) need
      * never be used, we minimize initial construction overhead and
      * footprint to the setup of about a dozen fields, with no nested
@@ -449,8 +459,11 @@ public class ForkJoinPool extends AbstractExecutorService {
      * fullExternalPush during the first submission to the pool.
      *
      * When external threads submit to the common pool, they can
-     * perform some subtask processing (see externalHelpJoin and
-     * related methods).  We do not need to record whether these
+     * perform subtask processing (see externalHelpJoin and related
+     * methods).  This caller-helps policy makes it sensible to set
+     * common pool parallelism level to one (or more) less than the
+     * total number of available cores, or even zero for pure
+     * caller-runs.  We do not need to record whether external
      * submissions are to the common pool -- if not, externalHelpJoin
      * returns quickly (at the most helping to signal some common pool
      * workers). These submitters would otherwise be blocked waiting
@@ -520,6 +533,7 @@ public class ForkJoinPool extends AbstractExecutorService {
          *
          * @param pool the pool this thread works in
          * @throws NullPointerException if the pool is null
+         * @return the new worker thread
          */
         public ForkJoinWorkerThread newThread(ForkJoinPool pool);
     }
@@ -536,26 +550,6 @@ public class ForkJoinPool extends AbstractExecutorService {
     }
 
     /**
-     * Per-thread records for threads that submit to pools. Currently
-     * holds only pseudo-random seed / index that is used to choose
-     * submission queues in method externalPush. In the future, this may
-     * also incorporate a means to implement different task rejection
-     * and resubmission policies.
-     *
-     * Seeds for submitters and workers/workQueues work in basically
-     * the same way but are initialized and updated using slightly
-     * different mechanics. Both are initialized using the same
-     * approach as in class ThreadLocal, where successive values are
-     * unlikely to collide with previous values. Seeds are then
-     * randomly modified upon collisions using xorshifts, which
-     * requires a non-zero seed.
-     */
-    static final class Submitter {
-        int seed;
-        Submitter(int s) { seed = s; }
-    }
-
-    /**
      * Class for artificial tasks that are used to replace the target
      * of local joins if they are removed from an interior queue slot
      * in WorkQueue.tryRemoveAndExec. We don't need the proxy to
@@ -614,17 +608,8 @@ public class ForkJoinPool extends AbstractExecutorService {
      * do not want multiple WorkQueue instances or multiple queue
      * arrays sharing cache lines. (It would be best for queue objects
      * and their arrays to share, but there is nothing available to
-     * help arrange that).  Unfortunately, because they are recorded
-     * in a common array, WorkQueue instances are often moved to be
-     * adjacent by garbage collectors. To reduce impact, we use field
-     * padding that works OK on common platforms; this effectively
-     * trades off slightly slower average field access for the sake of
-     * avoiding really bad worst-case access. (Until better JVM
-     * support is in place, this padding is dependent on transient
-     * properties of JVM field layout rules.) We also take care in
-     * allocating, sizing and resizing the array. Non-shared queue
-     * arrays are initialized by workers before use. Others are
-     * allocated on first use.
+     * help arrange that). The @Contended annotation alerts JVMs to
+     * try to keep instances apart.
      */
     static final class WorkQueue {
         /**
@@ -650,13 +635,12 @@ public class ForkJoinPool extends AbstractExecutorService {
         // Heuristic padding to ameliorate unfortunate memory placements
         volatile long pad00, pad01, pad02, pad03, pad04, pad05, pad06;
 
-        int seed;                  // for random scanning; initialize nonzero
         volatile int eventCount;   // encoded inactivation count; < 0 if inactive
         int nextWait;              // encoded record of next event waiter
-        int hint;                  // steal or signal hint (index)
-        int poolIndex;             // index of this queue in pool (or 0)
-        final int mode;            // 0: lifo, > 0: fifo, < 0: shared
         int nsteals;               // number of steals
+        int hint;                  // steal index hint
+        short poolIndex;           // index of this queue in pool
+        final short mode;          // 0: lifo, > 0: fifo, < 0: shared
         volatile int qlock;        // 1: locked, -1: terminate; else 0
         volatile int base;         // index of next slot for poll
         int top;                   // index of next slot for push
@@ -674,8 +658,8 @@ public class ForkJoinPool extends AbstractExecutorService {
                   int seed) {
             this.pool = pool;
             this.owner = owner;
-            this.mode = mode;
-            this.seed = seed;
+            this.mode = (short)mode;
+            this.hint = seed; // store initial seed for runWorker
             // Place indices in the center of array (that is not yet allocated)
             base = top = INITIAL_QUEUE_CAPACITY >>> 1;
         }
@@ -688,7 +672,7 @@ public class ForkJoinPool extends AbstractExecutorService {
             return (n >= 0) ? 0 : -n; // ignore transient negative
         }
 
-       /**
+        /**
          * Provides a more accurate estimate of whether this queue has
          * any tasks than does queueSize, by checking whether a
          * near-empty queue has at least one unclaimed task.
@@ -713,20 +697,18 @@ public class ForkJoinPool extends AbstractExecutorService {
          */
         final void push(ForkJoinTask<?> task) {
             ForkJoinTask<?>[] a; ForkJoinPool p;
-            int s = top, m, n;
+            int s = top, n;
             if ((a = array) != null) {    // ignore if queue removed
-                int j = (((m = a.length - 1) & s) << ASHIFT) + ABASE;
-                U.putOrderedObject(a, j, task);
-                if ((n = (top = s + 1) - base) <= 2) {
-                    if ((p = pool) != null)
-                        p.signalWork(this);
-                }
+                int m = a.length - 1;
+                U.putOrderedObject(a, ((m & s) << ASHIFT) + ABASE, task);
+                if ((n = (top = s + 1) - base) <= 2)
+                    (p = pool).signalWork(p.workQueues, this);
                 else if (n >= m)
                     growArray();
             }
         }
 
-       /**
+        /**
          * Initializes or doubles the capacity of array. Call either
          * by owner or with lock held -- it is OK for base, but not
          * top, to move while resizings are in progress.
@@ -784,9 +766,8 @@ public class ForkJoinPool extends AbstractExecutorService {
             if ((a = array) != null) {
                 int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
                 if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null &&
-                    base == b &&
-                    U.compareAndSwapObject(a, j, t, null)) {
-                    base = b + 1;
+                    base == b && U.compareAndSwapObject(a, j, t, null)) {
+                    U.putOrderedInt(this, QBASE, b + 1);
                     return t;
                 }
             }
@@ -802,9 +783,8 @@ public class ForkJoinPool extends AbstractExecutorService {
                 int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
                 t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
                 if (t != null) {
-                    if (base == b &&
-                        U.compareAndSwapObject(a, j, t, null)) {
-                        base = b + 1;
+                    if (U.compareAndSwapObject(a, j, t, null)) {
+                        U.putOrderedInt(this, QBASE, b + 1);
                         return t;
                     }
                 }
@@ -861,46 +841,43 @@ public class ForkJoinPool extends AbstractExecutorService {
                 ForkJoinTask.cancelIgnoringExceptions(t);
         }
 
-        /**
-         * Computes next value for random probes.  Scans don't require
-         * a very high quality generator, but also not a crummy one.
-         * Marsaglia xor-shift is cheap and works well enough.  Note:
-         * This is manually inlined in its usages in ForkJoinPool to
-         * avoid writes inside busy scan loops.
-         */
-        final int nextSeed() {
-            int r = seed;
-            r ^= r << 13;
-            r ^= r >>> 17;
-            return seed = r ^= r << 5;
-        }
-
         // Specialized execution methods
 
         /**
-         * Pops and runs tasks until empty.
+         * Polls and runs tasks until empty.
          */
-        private void popAndExecAll() {
-            // A bit faster than repeated pop calls
-            ForkJoinTask<?>[] a; int m, s; long j; ForkJoinTask<?> t;
-            while ((a = array) != null && (m = a.length - 1) >= 0 &&
-                   (s = top - 1) - base >= 0 &&
-                   (t = ((ForkJoinTask<?>)
-                         U.getObject(a, j = ((m & s) << ASHIFT) + ABASE)))
-                   != null) {
-                if (U.compareAndSwapObject(a, j, t, null)) {
-                    top = s;
-                    t.doExec();
-                }
-            }
+        final void pollAndExecAll() {
+            for (ForkJoinTask<?> t; (t = poll()) != null;)
+                t.doExec();
         }
 
         /**
-         * Polls and runs tasks until empty.
+         * Executes a top-level task and any local tasks remaining
+         * after execution.
          */
-        private void pollAndExecAll() {
-            for (ForkJoinTask<?> t; (t = poll()) != null;)
-                t.doExec();
+        final void runTask(ForkJoinTask<?> task) {
+            if ((currentSteal = task) != null) {
+                task.doExec();
+                ForkJoinTask<?>[] a = array;
+                int md = mode;
+                ++nsteals;
+                currentSteal = null;
+                if (md != 0)
+                    pollAndExecAll();
+                else if (a != null) {
+                    int s, m = a.length - 1;
+                    while ((s = top - 1) - base >= 0) {
+                        long i = ((m & s) << ASHIFT) + ABASE;
+                        ForkJoinTask<?> t = (ForkJoinTask<?>)U.getObject(a, i);
+                        if (t == null)
+                            break;
+                        if (U.compareAndSwapObject(a, i, t, null)) {
+                            top = s;
+                            t.doExec();
+                        }
+                    }
+                }
+            }
         }
 
         /**
@@ -911,13 +888,15 @@ public class ForkJoinPool extends AbstractExecutorService {
          * @return false if no progress can be made, else true
          */
         final boolean tryRemoveAndExec(ForkJoinTask<?> task) {
-            boolean stat = true, removed = false, empty = true;
+            boolean stat;
             ForkJoinTask<?>[] a; int m, s, b, n;
-            if ((a = array) != null && (m = a.length - 1) >= 0 &&
+            if (task != null && (a = array) != null && (m = a.length - 1) >= 0 &&
                 (n = (s = top) - (b = base)) > 0) {
+                boolean removed = false, empty = true;
+                stat = true;
                 for (ForkJoinTask<?> t;;) {           // traverse from s to b
-                    int j = ((--s & m) << ASHIFT) + ABASE;
-                    t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
+                    long j = ((--s & m) << ASHIFT) + ABASE;
+                    t = (ForkJoinTask<?>)U.getObject(a, j);
                     if (t == null)                    // inconsistent length
                         break;
                     else if (t == task) {
@@ -945,68 +924,95 @@ public class ForkJoinPool extends AbstractExecutorService {
                         break;
                     }
                 }
+                if (removed)
+                    task.doExec();
             }
-            if (removed)
-                task.doExec();
+            else
+                stat = false;
             return stat;
         }
 
         /**
-         * Polls for and executes the given task or any other task in
-         * its CountedCompleter computation.
+         * Tries to poll for and execute the given task or any other
+         * task in its CountedCompleter computation.
          */
-        final boolean pollAndExecCC(ForkJoinTask<?> root) {
-            ForkJoinTask<?>[] a; int b; Object o;
-            outer: while ((b = base) - top < 0 && (a = array) != null) {
+        final boolean pollAndExecCC(CountedCompleter<?> root) {
+            ForkJoinTask<?>[] a; int b; Object o; CountedCompleter<?> t, r;
+            if ((b = base) - top < 0 && (a = array) != null) {
                 long j = (((a.length - 1) & b) << ASHIFT) + ABASE;
-                if ((o = U.getObject(a, j)) == null ||
-                    !(o instanceof CountedCompleter))
-                    break;
-                for (CountedCompleter<?> t = (CountedCompleter<?>)o, r = t;;) {
-                    if (r == root) {
-                        if (base == b &&
-                            U.compareAndSwapObject(a, j, t, null)) {
-                            base = b + 1;
-                            t.doExec();
+                if ((o = U.getObjectVolatile(a, j)) == null)
+                    return true; // retry
+                if (o instanceof CountedCompleter) {
+                    for (t = (CountedCompleter<?>)o, r = t;;) {
+                        if (r == root) {
+                            if (base == b &&
+                                U.compareAndSwapObject(a, j, t, null)) {
+                                U.putOrderedInt(this, QBASE, b + 1);
+                                t.doExec();
+                            }
                             return true;
                         }
-                        else
-                            break; // restart
+                        else if ((r = r.completer) == null)
+                            break; // not part of root computation
                     }
-                    if ((r = r.completer) == null)
-                        break outer; // not part of root computation
                 }
             }
             return false;
         }
 
         /**
-         * Executes a top-level task and any local tasks remaining
-         * after execution.
+         * Tries to pop and execute the given task or any other task
+         * in its CountedCompleter computation.
          */
-        final void runTask(ForkJoinTask<?> t) {
-            if (t != null) {
-                (currentSteal = t).doExec();
-                currentSteal = null;
-                ++nsteals;
-                if (base - top < 0) {       // process remaining local tasks
-                    if (mode == 0)
-                        popAndExecAll();
-                    else
-                        pollAndExecAll();
+        final boolean externalPopAndExecCC(CountedCompleter<?> root) {
+            ForkJoinTask<?>[] a; int s; Object o; CountedCompleter<?> t, r;
+            if (base - (s = top) < 0 && (a = array) != null) {
+                long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
+                if ((o = U.getObject(a, j)) instanceof CountedCompleter) {
+                    for (t = (CountedCompleter<?>)o, r = t;;) {
+                        if (r == root) {
+                            if (U.compareAndSwapInt(this, QLOCK, 0, 1)) {
+                                if (top == s && array == a &&
+                                    U.compareAndSwapObject(a, j, t, null)) {
+                                    top = s - 1;
+                                    qlock = 0;
+                                    t.doExec();
+                                }
+                                else
+                                    qlock = 0;
+                            }
+                            return true;
+                        }
+                        else if ((r = r.completer) == null)
+                            break;
+                    }
                 }
             }
+            return false;
         }
 
         /**
-         * Executes a non-top-level (stolen) task.
+         * Internal version
          */
-        final void runSubtask(ForkJoinTask<?> t) {
-            if (t != null) {
-                ForkJoinTask<?> ps = currentSteal;
-                (currentSteal = t).doExec();
-                currentSteal = ps;
+        final boolean internalPopAndExecCC(CountedCompleter<?> root) {
+            ForkJoinTask<?>[] a; int s; Object o; CountedCompleter<?> t, r;
+            if (base - (s = top) < 0 && (a = array) != null) {
+                long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
+                if ((o = U.getObject(a, j)) instanceof CountedCompleter) {
+                    for (t = (CountedCompleter<?>)o, r = t;;) {
+                        if (r == root) {
+                            if (U.compareAndSwapObject(a, j, t, null)) {
+                                top = s - 1;
+                                t.doExec();
+                            }
+                            return true;
+                        }
+                        else if ((r = r.completer) == null)
+                            break;
+                    }
+                }
             }
+            return false;
         }
 
         /**
@@ -1023,6 +1029,7 @@ public class ForkJoinPool extends AbstractExecutorService {
 
         // Unsafe mechanics
         private static final sun.misc.Unsafe U;
+        private static final long QBASE;
         private static final long QLOCK;
         private static final int ABASE;
         private static final int ASHIFT;
@@ -1031,6 +1038,8 @@ public class ForkJoinPool extends AbstractExecutorService {
                 U = sun.misc.Unsafe.getUnsafe();
                 Class<?> k = WorkQueue.class;
                 Class<?> ak = ForkJoinTask[].class;
+                QBASE = U.objectFieldOffset
+                    (k.getDeclaredField("base"));
                 QLOCK = U.objectFieldOffset
                     (k.getDeclaredField("qlock"));
                 ABASE = U.arrayBaseOffset(ak);
@@ -1047,13 +1056,6 @@ public class ForkJoinPool extends AbstractExecutorService {
     // static fields (initialized in static initializer below)
 
     /**
-     * Creates a new ForkJoinWorkerThread. This factory is used unless
-     * overridden in ForkJoinPool constructors.
-     */
-    public static final ForkJoinWorkerThreadFactory
-        defaultForkJoinWorkerThreadFactory;
-
-    /**
      * Per-thread submission bookkeeping. Shared across all pools
      * to reduce ThreadLocal pollution and because random motion
      * to avoid contention in one pool is likely to hold for others.
@@ -1063,6 +1065,13 @@ public class ForkJoinPool extends AbstractExecutorService {
     static final ThreadLocal<Submitter> submitters;
 
     /**
+     * Creates a new ForkJoinWorkerThread. This factory is used unless
+     * overridden in ForkJoinPool constructors.
+     */
+    public static final ForkJoinWorkerThreadFactory
+        defaultForkJoinWorkerThreadFactory;
+
+    /**
      * Permission required for callers of methods that may start or
      * kill threads.
      */
@@ -1074,12 +1083,15 @@ public class ForkJoinPool extends AbstractExecutorService {
      * to paranoically avoid potential initialization circularities
      * as well as to simplify generated code.
      */
-    static final ForkJoinPool commonPool;
+    static final ForkJoinPool common;
 
     /**
-     * Common pool parallelism. Must equal commonPool.parallelism.
+     * Common pool parallelism. To allow simpler use and management
+     * when common pool threads are disabled, we allow the underlying
+     * common.parallelism field to be zero, but in that case still report
+     * parallelism as 1 to reflect resulting caller-runs mechanics.
      */
-    static final int commonPoolParallelism;
+    static final int commonParallelism;
 
     /**
      * Sequence number for creating workerNamePrefix.
@@ -1114,7 +1126,7 @@ public class ForkJoinPool extends AbstractExecutorService {
     /**
      * Tolerance for idle timeouts, to cope with timer undershoots
      */
-    private static final long TIMEOUT_SLOP = 2000000L; // 20ms
+    private static final long TIMEOUT_SLOP = 2000000L;
 
     /**
      * The maximum stolen->joining link depth allowed in method
@@ -1216,30 +1228,19 @@ public class ForkJoinPool extends AbstractExecutorService {
     static final int FIFO_QUEUE          =  1;
     static final int SHARED_QUEUE        = -1;
 
-    // bounds for #steps in scan loop -- must be power 2 minus 1
-    private static final int MIN_SCAN    = 0x1ff;   // cover estimation slop
-    private static final int MAX_SCAN    = 0x1ffff; // 4 * max workers
-
-    // Instance fields
-
-    /*
-     * Field layout of this class tends to matter more than one would
-     * like. Runtime layout order is only loosely related to
-     * declaration order and may differ across JVMs, but the following
-     * empirically works OK on current JVMs.
-     */
-
     // Heuristic padding to ameliorate unfortunate memory placements
     volatile long pad00, pad01, pad02, pad03, pad04, pad05, pad06;
 
+    // Instance fields
     volatile long stealCount;                  // collects worker counts
     volatile long ctl;                         // main pool control
     volatile int plock;                        // shutdown status and seqLock
     volatile int indexSeed;                    // worker/submitter index seed
-    final int config;                          // mode and parallelism level
+    final short parallelism;                   // parallelism level
+    final short mode;                          // LIFO/FIFO
     WorkQueue[] workQueues;                    // main registry
     final ForkJoinWorkerThreadFactory factory;
-    final Thread.UncaughtExceptionHandler ueh; // per-worker UEH
+    final UncaughtExceptionHandler ueh;        // per-worker UEH
     final String workerNamePrefix;             // to create worker name string
 
     volatile Object pad10, pad11, pad12, pad13, pad14, pad15, pad16, pad17;
@@ -1254,24 +1255,13 @@ public class ForkJoinPool extends AbstractExecutorService {
      * a more conservative alternative to a pure spinlock.
      */
     private int acquirePlock() {
-        int spins = PL_SPINS, r = 0, ps, nps;
+        int spins = PL_SPINS, ps, nps;
         for (;;) {
             if (((ps = plock) & PL_LOCK) == 0 &&
                 U.compareAndSwapInt(this, PLOCK, ps, nps = ps + PL_LOCK))
                 return nps;
-            else if (r == 0) { // randomize spins if possible
-                Thread t = Thread.currentThread(); WorkQueue w; Submitter z;
-                if ((t instanceof ForkJoinWorkerThread) &&
-                    (w = ((ForkJoinWorkerThread)t).workQueue) != null)
-                    r = w.seed;
-                else if ((z = submitters.get()) != null)
-                    r = z.seed;
-                else
-                    r = 1;
-            }
             else if (spins >= 0) {
-                r ^= r << 1; r ^= r >>> 3; r ^= r << 10; // xorshift
-                if (r >= 0)
+                if (ThreadLocalRandom.current().nextInt() >= 0)
                     --spins;
             }
             else if (U.compareAndSwapInt(this, PLOCK, ps, ps | PL_SIGNAL)) {
@@ -1303,48 +1293,15 @@ public class ForkJoinPool extends AbstractExecutorService {
     }
 
     /**
-     * Performs secondary initialization, called when plock is zero.
-     * Creates workQueue array and sets plock to a valid value.  The
-     * lock body must be exception-free (so no try/finally) so we
-     * optimistically allocate new array outside the lock and throw
-     * away if (very rarely) not needed. (A similar tactic is used in
-     * fullExternalPush.)  Because the plock seq value can eventually
-     * wrap around zero, this method harmlessly fails to reinitialize
-     * if workQueues exists, while still advancing plock.
-     *
-     * Additionally tries to create the first worker.
-     */
-    private void initWorkers() {
-        WorkQueue[] ws, nws; int ps;
-        int p = config & SMASK;        // find power of two table size
-        int n = (p > 1) ? p - 1 : 1;   // ensure at least 2 slots
-        n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16;
-        n = (n + 1) << 1;
-        if ((ws = workQueues) == null || ws.length == 0)
-            nws = new WorkQueue[n];
-        else
-            nws = null;
-        if (((ps = plock) & PL_LOCK) != 0 ||
-            !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
-            ps = acquirePlock();
-        if (((ws = workQueues) == null || ws.length == 0) && nws != null)
-            workQueues = nws;
-        int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
-        if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
-            releasePlock(nps);
-        tryAddWorker();
-    }
-
-    /**
      * Tries to create and start one worker if fewer than target
      * parallelism level exist. Adjusts counts etc on failure.
      */
     private void tryAddWorker() {
-        long c; int u;
+        long c; int u, e;
         while ((u = (int)((c = ctl) >>> 32)) < 0 &&
-               (u & SHORT_SIGN) != 0 && (int)c == 0) {
-            long nc = (long)(((u + UTC_UNIT) & UTC_MASK) |
-                             ((u + UAC_UNIT) & UAC_MASK)) << 32;
+               (u & SHORT_SIGN) != 0 && (e = (int)c) >= 0) {
+            long nc = ((long)(((u + UTC_UNIT) & UTC_MASK) |
+                              ((u + UAC_UNIT) & UAC_MASK)) << 32) | (long)e;
             if (U.compareAndSwapLong(this, CTL, c, nc)) {
                 ForkJoinWorkerThreadFactory fac;
                 Throwable ex = null;
@@ -1355,8 +1312,8 @@ public class ForkJoinPool extends AbstractExecutorService {
                         wt.start();
                         break;
                     }
-                } catch (Throwable e) {
-                    ex = e;
+                } catch (Throwable rex) {
+                    ex = rex;
                 }
                 deregisterWorker(wt, ex);
                 break;
@@ -1377,14 +1334,14 @@ public class ForkJoinPool extends AbstractExecutorService {
      * @return the worker's queue
      */
     final WorkQueue registerWorker(ForkJoinWorkerThread wt) {
-        Thread.UncaughtExceptionHandler handler; WorkQueue[] ws; int s, ps;
+        UncaughtExceptionHandler handler; WorkQueue[] ws; int s, ps;
         wt.setDaemon(true);
         if ((handler = ueh) != null)
             wt.setUncaughtExceptionHandler(handler);
         do {} while (!U.compareAndSwapInt(this, INDEXSEED, s = indexSeed,
                                           s += SEED_INCREMENT) ||
                      s == 0); // skip 0
-        WorkQueue w = new WorkQueue(this, wt, config >>> 16, s);
+        WorkQueue w = new WorkQueue(this, wt, mode, s);
         if (((ps = plock) & PL_LOCK) != 0 ||
             !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
             ps = acquirePlock();
@@ -1404,14 +1361,15 @@ public class ForkJoinPool extends AbstractExecutorService {
                         }
                     }
                 }
-                w.eventCount = w.poolIndex = r; // volatile write orders
+                w.poolIndex = (short)r;
+                w.eventCount = r; // volatile write orders
                 ws[r] = w;
             }
         } finally {
             if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
                 releasePlock(nps);
         }
-        wt.setName(workerNamePrefix.concat(Integer.toString(w.poolIndex)));
+        wt.setName(workerNamePrefix.concat(Integer.toString(w.poolIndex >>> 1)));
         return w;
     }
 
@@ -1421,17 +1379,17 @@ public class ForkJoinPool extends AbstractExecutorService {
      * array, and adjusts counts. If pool is shutting down, tries to
      * complete termination.
      *
-     * @param wt the worker thread or null if construction failed
+     * @param wt the worker thread, or null if construction failed
      * @param ex the exception causing failure, or null if none
      */
     final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
         WorkQueue w = null;
         if (wt != null && (w = wt.workQueue) != null) {
-            int ps;
+            int ps; long sc;
             w.qlock = -1;                // ensure set
-            long ns = w.nsteals, sc;     // collect steal count
             do {} while (!U.compareAndSwapLong(this, STEALCOUNT,
-                                               sc = stealCount, sc + ns));
+                                               sc = stealCount,
+                                               sc + w.nsteals));
             if (((ps = plock) & PL_LOCK) != 0 ||
                 !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
                 ps = acquirePlock();
@@ -1460,7 +1418,7 @@ public class ForkJoinPool extends AbstractExecutorService {
                 if (e > 0) {             // activate or create replacement
                     if ((ws = workQueues) == null ||
                         (i = e & SMASK) >= ws.length ||
-                        (v = ws[i]) != null)
+                        (v = ws[i]) == null)
                         break;
                     long nc = (((long)(v.nextWait & E_MASK)) |
                                ((long)(u + UAC_UNIT) << 32));
@@ -1489,6 +1447,26 @@ public class ForkJoinPool extends AbstractExecutorService {
     // Submissions
 
     /**
+     * Per-thread records for threads that submit to pools. Currently
+     * holds only pseudo-random seed / index that is used to choose
+     * submission queues in method externalPush. In the future, this may
+     * also incorporate a means to implement different task rejection
+     * and resubmission policies.
+     *
+     * Seeds for submitters and workers/workQueues work in basically
+     * the same way but are initialized and updated using slightly
+     * different mechanics. Both are initialized using the same
+     * approach as in class ThreadLocal, where successive values are
+     * unlikely to collide with previous values. Seeds are then
+     * randomly modified upon collisions using xorshifts, which
+     * requires a non-zero seed.
+     */
+    static final class Submitter {
+        int seed;
+        Submitter(int s) { seed = s; }
+    }
+
+    /**
      * Unless shutting down, adds the given task to a submission queue
      * at submitter's current queue index (modulo submission
      * range). Only the most common path is directly handled in this
@@ -1497,19 +1475,21 @@ public class ForkJoinPool extends AbstractExecutorService {
      * @param task the task. Caller must ensure non-null.
      */
     final void externalPush(ForkJoinTask<?> task) {
-        WorkQueue[] ws; WorkQueue q; Submitter z; int m; ForkJoinTask<?>[] a;
-        if ((z = submitters.get()) != null && plock > 0 &&
-            (ws = workQueues) != null && (m = (ws.length - 1)) >= 0 &&
-            (q = ws[m & z.seed & SQMASK]) != null &&
+        Submitter z = submitters.get();
+        WorkQueue q; int r, m, s, n, am; ForkJoinTask<?>[] a;
+        int ps = plock;
+        WorkQueue[] ws = workQueues;
+        if (z != null && ps > 0 && ws != null && (m = (ws.length - 1)) >= 0 &&
+            (q = ws[m & (r = z.seed) & SQMASK]) != null && r != 0 &&
             U.compareAndSwapInt(q, QLOCK, 0, 1)) { // lock
-            int b = q.base, s = q.top, n, an;
-            if ((a = q.array) != null && (an = a.length) > (n = s + 1 - b)) {
-                int j = (((an - 1) & s) << ASHIFT) + ABASE;
+            if ((a = q.array) != null &&
+                (am = a.length - 1) > (n = (s = q.top) - q.base)) {
+                int j = ((am & s) << ASHIFT) + ABASE;
                 U.putOrderedObject(a, j, task);
                 q.top = s + 1;                     // push on to deque
                 q.qlock = 0;
-                if (n <= 2)
-                    signalWork(q);
+                if (n <= 1)
+                    signalWork(ws, q);
                 return;
             }
             q.qlock = 0;
@@ -1520,13 +1500,19 @@ public class ForkJoinPool extends AbstractExecutorService {
     /**
      * Full version of externalPush. This method is called, among
      * other times, upon the first submission of the first task to the
-     * pool, so must perform secondary initialization (via
-     * initWorkers). It also detects first submission by an external
-     * thread by looking up its ThreadLocal, and creates a new shared
-     * queue if the one at index if empty or contended. The plock lock
-     * body must be exception-free (so no try/finally) so we
-     * optimistically allocate new queues outside the lock and throw
-     * them away if (very rarely) not needed.
+     * pool, so must perform secondary initialization.  It also
+     * detects first submission by an external thread by looking up
+     * its ThreadLocal, and creates a new shared queue if the one at
+     * index if empty or contended. The plock lock body must be
+     * exception-free (so no try/finally) so we optimistically
+     * allocate new queues outside the lock and throw them away if
+     * (very rarely) not needed.
+     *
+     * Secondary initialization occurs when plock is zero, to create
+     * workQueue array and set plock to a valid value.  This lock body
+     * must also be exception-free. Because the plock seq value can
+     * eventually wrap around zero, this method harmlessly fails to
+     * reinitialize if workQueues exists, while still advancing plock.
      */
     private void fullExternalPush(ForkJoinTask<?> task) {
         int r = 0; // random index seed
@@ -1537,17 +1523,31 @@ public class ForkJoinPool extends AbstractExecutorService {
                                         r += SEED_INCREMENT) && r != 0)
                     submitters.set(z = new Submitter(r));
             }
-            else if (r == 0) {               // move to a different index
+            else if (r == 0) {                  // move to a different index
                 r = z.seed;
-                r ^= r << 13;                // same xorshift as WorkQueues
+                r ^= r << 13;                   // same xorshift as WorkQueues
                 r ^= r >>> 17;
-                z.seed = r ^ (r << 5);
+                z.seed = r ^= (r << 5);
             }
-            else if ((ps = plock) < 0)
+            if ((ps = plock) < 0)
                 throw new RejectedExecutionException();
             else if (ps == 0 || (ws = workQueues) == null ||
-                     (m = ws.length - 1) < 0)
-                initWorkers();
+                     (m = ws.length - 1) < 0) { // initialize workQueues
+                int p = parallelism;            // find power of two table size
+                int n = (p > 1) ? p - 1 : 1;    // ensure at least 2 slots
+                n |= n >>> 1; n |= n >>> 2;  n |= n >>> 4;
+                n |= n >>> 8; n |= n >>> 16; n = (n + 1) << 1;
+                WorkQueue[] nws = ((ws = workQueues) == null || ws.length == 0 ?
+                                   new WorkQueue[n] : null);
+                if (((ps = plock) & PL_LOCK) != 0 ||
+                    !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+                    ps = acquirePlock();
+                if (((ws = workQueues) == null || ws.length == 0) && nws != null)
+                    workQueues = nws;
+                int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
+                if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+                    releasePlock(nps);
+            }
             else if ((q = ws[k = r & m & SQMASK]) != null) {
                 if (q.qlock == 0 && U.compareAndSwapInt(q, QLOCK, 0, 1)) {
                     ForkJoinTask<?>[] a = q.array;
@@ -1565,7 +1565,7 @@ public class ForkJoinPool extends AbstractExecutorService {
                         q.qlock = 0;  // unlock
                     }
                     if (submitted) {
-                        signalWork(q);
+                        signalWork(ws, q);
                         return;
                     }
                 }
@@ -1573,6 +1573,7 @@ public class ForkJoinPool extends AbstractExecutorService {
             }
             else if (((ps = plock) & PL_LOCK) == 0) { // create new queue
                 q = new WorkQueue(this, null, SHARED_QUEUE, r);
+                q.poolIndex = (short)k;
                 if (((ps = plock) & PL_LOCK) != 0 ||
                     !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
                     ps = acquirePlock();
@@ -1583,7 +1584,7 @@ public class ForkJoinPool extends AbstractExecutorService {
                     releasePlock(nps);
             }
             else
-                r = 0; // try elsewhere while lock held
+                r = 0;
         }
     }
 
@@ -1594,41 +1595,42 @@ public class ForkJoinPool extends AbstractExecutorService {
      */
     final void incrementActiveCount() {
         long c;
-        do {} while (!U.compareAndSwapLong(this, CTL, c = ctl, c + AC_UNIT));
+        do {} while (!U.compareAndSwapLong
+                     (this, CTL, c = ctl, ((c & ~AC_MASK) |
+                                           ((c & AC_MASK) + AC_UNIT))));
     }
 
     /**
      * Tries to create or activate a worker if too few are active.
      *
-     * @param q the (non-null) queue holding tasks to be signalled
+     * @param ws the worker array to use to find signallees
+     * @param q if non-null, the queue holding tasks to be processed
      */
-    final void signalWork(WorkQueue q) {
-        int hint = q.poolIndex;
-        long c; int e, u, i, n; WorkQueue[] ws; WorkQueue w; Thread p;
-        while ((u = (int)((c = ctl) >>> 32)) < 0) {
-            if ((e = (int)c) > 0) {
-                if ((ws = workQueues) != null && ws.length > (i = e & SMASK) &&
-                    (w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) {
-                    long nc = (((long)(w.nextWait & E_MASK)) |
-                               ((long)(u + UAC_UNIT) << 32));
-                    if (U.compareAndSwapLong(this, CTL, c, nc)) {
-                        w.hint = hint;
-                        w.eventCount = (e + E_SEQ) & E_MASK;
-                        if ((p = w.parker) != null)
-                            U.unpark(p);
-                        break;
-                    }
-                    if (q.top - q.base <= 0)
-                        break;
-                }
-                else
-                    break;
-            }
-            else {
+    final void signalWork(WorkQueue[] ws, WorkQueue q) {
+        for (;;) {
+            long c; int e, u, i; WorkQueue w; Thread p;
+            if ((u = (int)((c = ctl) >>> 32)) >= 0)
+                break;
+            if ((e = (int)c) <= 0) {
                 if ((short)u < 0)
                     tryAddWorker();
                 break;
             }
+            if (ws == null || ws.length <= (i = e & SMASK) ||
+                (w = ws[i]) == null)
+                break;
+            long nc = (((long)(w.nextWait & E_MASK)) |
+                       ((long)(u + UAC_UNIT)) << 32);
+            int ne = (e + E_SEQ) & E_MASK;
+            if (w.eventCount == (e | INT_SIGN) &&
+                U.compareAndSwapLong(this, CTL, c, nc)) {
+                w.eventCount = ne;
+                if ((p = w.parker) != null)
+                    U.unpark(p);
+                break;
+            }
+            if (q != null && q.base >= q.top)
+                break;
         }
     }
 
@@ -1639,214 +1641,154 @@ public class ForkJoinPool extends AbstractExecutorService {
      */
     final void runWorker(WorkQueue w) {
         w.growArray(); // allocate queue
-        do { w.runTask(scan(w)); } while (w.qlock >= 0);
+        for (int r = w.hint; scan(w, r) == 0; ) {
+            r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // xorshift
+        }
     }
 
     /**
-     * Scans for and, if found, returns one task, else possibly
+     * Scans for and, if found, runs one task, else possibly
      * inactivates the worker. This method operates on single reads of
      * volatile state and is designed to be re-invoked continuously,
      * in part because it returns upon detecting inconsistencies,
      * contention, or state changes that indicate possible success on
      * re-invocation.
      *
-     * The scan searches for tasks across queues (starting at a random
-     * index, and relying on registerWorker to irregularly scatter
-     * them within array to avoid bias), checking each at least twice.
-     * The scan terminates upon either finding a non-empty queue, or
-     * completing the sweep. If the worker is not inactivated, it
-     * takes and returns a task from this queue. Otherwise, if not
-     * activated, it signals workers (that may include itself) and
-     * returns so caller can retry. Also returns for true if the
-     * worker array may have changed during an empty scan.  On failure
-     * to find a task, we take one of the following actions, after
-     * which the caller will retry calling this method unless
-     * terminated.
-     *
-     * * If pool is terminating, terminate the worker.
-     *
-     * * If not already enqueued, try to inactivate and enqueue the
-     * worker on wait queue. Or, if inactivating has caused the pool
-     * to be quiescent, relay to idleAwaitWork to possibly shrink
-     * pool.
-     *
-     * * If already enqueued and none of the above apply, possibly
-     * park awaiting signal, else lingering to help scan and signal.
-     *
-     * * If a non-empty queue discovered or left as a hint,
-     * help wake up other workers before return.
+     * The scan searches for tasks across queues starting at a random
+     * index, checking each at least twice.  The scan terminates upon
+     * either finding a non-empty queue, or completing the sweep. If
+     * the worker is not inactivated, it takes and runs a task from
+     * this queue. Otherwise, if not activated, it tries to activate
+     * itself or some other worker by signalling. On failure to find a
+     * task, returns (for retry) if pool state may have changed during
+     * an empty scan, or tries to inactivate if active, else possibly
+     * blocks or terminates via method awaitWork.
      *
      * @param w the worker (via its WorkQueue)
-     * @return a task or null if none found
+     * @param r a random seed
+     * @return worker qlock status if would have waited, else 0
      */
-    private final ForkJoinTask<?> scan(WorkQueue w) {
+    private final int scan(WorkQueue w, int r) {
         WorkQueue[] ws; int m;
-        int ps = plock;                          // read plock before ws
-        if (w != null && (ws = workQueues) != null && (m = ws.length - 1) >= 0) {
-            int ec = w.eventCount;               // ec is negative if inactive
-            int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
-            w.hint = -1;                         // update seed and clear hint
-            int j = ((m + m + 1) | MIN_SCAN) & MAX_SCAN;
-            do {
-                WorkQueue q; ForkJoinTask<?>[] a; int b;
-                if ((q = ws[(r + j) & m]) != null && (b = q.base) - q.top < 0 &&
-                    (a = q.array) != null) {     // probably nonempty
-                    int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
-                    ForkJoinTask<?> t = (ForkJoinTask<?>)
-                        U.getObjectVolatile(a, i);
-                    if (q.base == b && ec >= 0 && t != null &&
-                        U.compareAndSwapObject(a, i, t, null)) {
-                        if ((q.base = b + 1) - q.top < 0)
-                            signalWork(q);
-                        return t;                // taken
-                    }
-                    else if ((ec < 0 || j < m) && (int)(ctl >> AC_SHIFT) <= 0) {
-                        w.hint = (r + j) & m;    // help signal below
-                        break;                   // cannot take
+        long c = ctl;                            // for consistency check
+        if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 && w != null) {
+            for (int j = m + m + 1, ec = w.eventCount;;) {
+                WorkQueue q; int b, e; ForkJoinTask<?>[] a; ForkJoinTask<?> t;
+                if ((q = ws[(r - j) & m]) != null &&
+                    (b = q.base) - q.top < 0 && (a = q.array) != null) {
+                    long i = (((a.length - 1) & b) << ASHIFT) + ABASE;
+                    if ((t = ((ForkJoinTask<?>)
+                              U.getObjectVolatile(a, i))) != null) {
+                        if (ec < 0)
+                            helpRelease(c, ws, w, q, b);
+                        else if (q.base == b &&
+                                 U.compareAndSwapObject(a, i, t, null)) {
+                            U.putOrderedInt(q, QBASE, b + 1);
+                            if ((b + 1) - q.top < 0)
+                                signalWork(ws, q);
+                            w.runTask(t);
+                        }
                     }
+                    break;
                 }
-            } while (--j >= 0);
-
-            int h, e, ns; long c, sc; WorkQueue q;
-            if ((ns = w.nsteals) != 0) {
-                if (U.compareAndSwapLong(this, STEALCOUNT,
-                                         sc = stealCount, sc + ns))
-                    w.nsteals = 0;               // collect steals and rescan
-            }
-            else if (plock != ps)                // consistency check
-                ;                                // skip
-            else if ((e = (int)(c = ctl)) < 0)
-                w.qlock = -1;                    // pool is terminating
-            else {
-                if ((h = w.hint) < 0) {
-                    if (ec >= 0) {               // try to enqueue/inactivate
-                        long nc = (((long)ec |
-                                    ((c - AC_UNIT) & (AC_MASK|TC_MASK))));
-                        w.nextWait = e;          // link and mark inactive
+                else if (--j < 0) {
+                    if ((ec | (e = (int)c)) < 0) // inactive or terminating
+                        return awaitWork(w, c, ec);
+                    else if (ctl == c) {         // try to inactivate and enqueue
+                        long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
+                        w.nextWait = e;
                         w.eventCount = ec | INT_SIGN;
-                        if (ctl != c || !U.compareAndSwapLong(this, CTL, c, nc))
-                            w.eventCount = ec;   // unmark on CAS failure
-                        else if ((int)(c >> AC_SHIFT) == 1 - (config & SMASK))
-                            idleAwaitWork(w, nc, c);
-                    }
-                    else if (w.eventCount < 0 && !tryTerminate(false, false) &&
-                             ctl == c) {         // block
-                        Thread wt = Thread.currentThread();
-                        Thread.interrupted();    // clear status
-                        U.putObject(wt, PARKBLOCKER, this);
-                        w.parker = wt;           // emulate LockSupport.park
-                        if (w.eventCount < 0)    // recheck
-                            U.park(false, 0L);
-                        w.parker = null;
-                        U.putObject(wt, PARKBLOCKER, null);
-                    }
-                }
-                if ((h >= 0 || (h = w.hint) >= 0) &&
-                    (ws = workQueues) != null && h < ws.length &&
-                    (q = ws[h]) != null) {      // signal others before retry
-                    WorkQueue v; Thread p; int u, i, s;
-                    for (int n = (config & SMASK) >>> 1;;) {
-                        int idleCount = (w.eventCount < 0) ? 0 : -1;
-                        if (((s = idleCount - q.base + q.top) <= n &&
-                             (n = s) <= 0) ||
-                            (u = (int)((c = ctl) >>> 32)) >= 0 ||
-                            (e = (int)c) <= 0 || m < (i = e & SMASK) ||
-                            (v = ws[i]) == null)
-                            break;
-                        long nc = (((long)(v.nextWait & E_MASK)) |
-                                   ((long)(u + UAC_UNIT) << 32));
-                        if (v.eventCount != (e | INT_SIGN) ||
-                            !U.compareAndSwapLong(this, CTL, c, nc))
-                            break;
-                        v.hint = h;
-                        v.eventCount = (e + E_SEQ) & E_MASK;
-                        if ((p = v.parker) != null)
-                            U.unpark(p);
-                        if (--n <= 0)
-                            break;
+                        if (!U.compareAndSwapLong(this, CTL, c, nc))
+                            w.eventCount = ec;   // back out
                     }
+                    break;
                 }
             }
         }
-        return null;
+        return 0;
     }
 
     /**
-     * If inactivating worker w has caused the pool to become
-     * quiescent, checks for pool termination, and, so long as this is
-     * not the only worker, waits for event for up to a given
-     * duration.  On timeout, if ctl has not changed, terminates the
-     * worker, which will in turn wake up another worker to possibly
-     * repeat this process.
+     * A continuation of scan(), possibly blocking or terminating
+     * worker w. Returns without blocking if pool state has apparently
+     * changed since last invocation.  Also, if inactivating w has
+     * caused the pool to become quiescent, checks for pool
+     * termination, and, so long as this is not the only worker, waits
+     * for event for up to a given duration.  On timeout, if ctl has
+     * not changed, terminates the worker, which will in turn wake up
+     * another worker to possibly repeat this process.
      *
      * @param w the calling worker
-     * @param currentCtl the ctl value triggering possible quiescence
-     * @param prevCtl the ctl value to restore if thread is terminated
-     */
-    private void idleAwaitWork(WorkQueue w, long currentCtl, long prevCtl) {
-        if (w != null && w.eventCount < 0 &&
-            !tryTerminate(false, false) && (int)prevCtl != 0) {
-            int dc = -(short)(currentCtl >>> TC_SHIFT);
-            long parkTime = dc < 0 ? FAST_IDLE_TIMEOUT: (dc + 1) * IDLE_TIMEOUT;
-            long deadline = System.nanoTime() + parkTime - TIMEOUT_SLOP;
-            Thread wt = Thread.currentThread();
-            while (ctl == currentCtl) {
-                Thread.interrupted();  // timed variant of version in scan()
-                U.putObject(wt, PARKBLOCKER, this);
-                w.parker = wt;
-                if (ctl == currentCtl)
-                    U.park(false, parkTime);
-                w.parker = null;
-                U.putObject(wt, PARKBLOCKER, null);
-                if (ctl != currentCtl)
-                    break;
-                if (deadline - System.nanoTime() <= 0L &&
-                    U.compareAndSwapLong(this, CTL, currentCtl, prevCtl)) {
-                    w.eventCount = (w.eventCount + E_SEQ) | E_MASK;
-                    w.qlock = -1;   // shrink
-                    break;
+     * @param c the ctl value on entry to scan
+     * @param ec the worker's eventCount on entry to scan
+     */
+    private final int awaitWork(WorkQueue w, long c, int ec) {
+        int stat, ns; long parkTime, deadline;
+        if ((stat = w.qlock) >= 0 && w.eventCount == ec && ctl == c &&
+            !Thread.interrupted()) {
+            int e = (int)c;
+            int u = (int)(c >>> 32);
+            int d = (u >> UAC_SHIFT) + parallelism; // active count
+
+            if (e < 0 || (d <= 0 && tryTerminate(false, false)))
+                stat = w.qlock = -1;          // pool is terminating
+            else if ((ns = w.nsteals) != 0) { // collect steals and retry
+                long sc;
+                w.nsteals = 0;
+                do {} while (!U.compareAndSwapLong(this, STEALCOUNT,
+                                                   sc = stealCount, sc + ns));
+            }
+            else {
+                long pc = ((d > 0 || ec != (e | INT_SIGN)) ? 0L :
+                           ((long)(w.nextWait & E_MASK)) | // ctl to restore
+                           ((long)(u + UAC_UNIT)) << 32);
+                if (pc != 0L) {               // timed wait if last waiter
+                    int dc = -(short)(c >>> TC_SHIFT);
+                    parkTime = (dc < 0 ? FAST_IDLE_TIMEOUT:
+                                (dc + 1) * IDLE_TIMEOUT);
+                    deadline = System.nanoTime() + parkTime - TIMEOUT_SLOP;
+                }
+                else
+                    parkTime = deadline = 0L;
+                if (w.eventCount == ec && ctl == c) {
+                    Thread wt = Thread.currentThread();
+                    U.putObject(wt, PARKBLOCKER, this);
+                    w.parker = wt;            // emulate LockSupport.park
+                    if (w.eventCount == ec && ctl == c)
+                        U.park(false, parkTime);  // must recheck before park
+                    w.parker = null;
+                    U.putObject(wt, PARKBLOCKER, null);
+                    if (parkTime != 0L && ctl == c &&
+                        deadline - System.nanoTime() <= 0L &&
+                        U.compareAndSwapLong(this, CTL, c, pc))
+                        stat = w.qlock = -1;  // shrink pool
                 }
             }
         }
+        return stat;
     }
 
     /**
-     * Scans through queues looking for work while joining a task; if
-     * any present, signals. May return early if more signalling is
-     * detectably unneeded.
-     *
-     * @param task return early if done
-     * @param origin an index to start scan
-     */
-    private void helpSignal(ForkJoinTask<?> task, int origin) {
-        WorkQueue[] ws; WorkQueue w; Thread p; long c; int m, u, e, i, s;
-        if (task != null && task.status >= 0 &&
-            (u = (int)(ctl >>> 32)) < 0 && (u >> UAC_SHIFT) < 0 &&
-            (ws = workQueues) != null && (m = ws.length - 1) >= 0) {
-            outer: for (int k = origin, j = m; j >= 0; --j) {
-                WorkQueue q = ws[k++ & m];
-                for (int n = m;;) { // limit to at most m signals
-                    if (task.status < 0)
-                        break outer;
-                    if (q == null ||
-                        ((s = -q.base + q.top) <= n && (n = s) <= 0))
-                        break;
-                    if ((u = (int)((c = ctl) >>> 32)) >= 0 ||
-                        (e = (int)c) <= 0 || m < (i = e & SMASK) ||
-                        (w = ws[i]) == null)
-                        break outer;
-                    long nc = (((long)(w.nextWait & E_MASK)) |
-                               ((long)(u + UAC_UNIT) << 32));
-                    if (w.eventCount != (e | INT_SIGN))
-                        break outer;
-                    if (U.compareAndSwapLong(this, CTL, c, nc)) {
-                        w.eventCount = (e + E_SEQ) & E_MASK;
-                        if ((p = w.parker) != null)
-                            U.unpark(p);
-                        if (--n <= 0)
-                            break;
-                    }
-                }
+     * Possibly releases (signals) a worker. Called only from scan()
+     * when a worker with apparently inactive status finds a non-empty
+     * queue. This requires revalidating all of the associated state
+     * from caller.
+     */
+    private final void helpRelease(long c, WorkQueue[] ws, WorkQueue w,
+                                   WorkQueue q, int b) {
+        WorkQueue v; int e, i; Thread p;
+        if (w != null && w.eventCount < 0 && (e = (int)c) > 0 &&
+            ws != null && ws.length > (i = e & SMASK) &&
+            (v = ws[i]) != null && ctl == c) {
+            long nc = (((long)(v.nextWait & E_MASK)) |
+                       ((long)((int)(c >>> 32) + UAC_UNIT)) << 32);
+            int ne = (e + E_SEQ) & E_MASK;
+            if (q != null && q.base == b && w.eventCount < 0 &&
+                v.eventCount == (e | INT_SIGN) &&
+                U.compareAndSwapLong(this, CTL, c, nc)) {
+                v.eventCount = ne;
+                if ((p = v.parker) != null)
+                    U.unpark(p);
             }
         }
     }
@@ -1871,7 +1813,8 @@ public class ForkJoinPool extends AbstractExecutorService {
      */
     private int tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
         int stat = 0, steps = 0;                    // bound to avoid cycles
-        if (joiner != null && task != null) {       // hoist null checks
+        if (task != null && joiner != null &&
+            joiner.base - joiner.top >= 0) {        // hoist checks
             restart: for (;;) {
                 ForkJoinTask<?> subtask = task;     // current target
                 for (WorkQueue j = joiner, v;;) {   // v is stealer of subtask
@@ -1898,7 +1841,7 @@ public class ForkJoinPool extends AbstractExecutorService {
                         }
                     }
                     for (;;) { // help stealer or descend to its stealer
-                        ForkJoinTask[] a;  int b;
+                        ForkJoinTask[] a; int b;
                         if (subtask.status < 0)     // surround probes with
                             continue restart;       //   consistency checks
                         if ((b = v.base) - v.top < 0 && (a = v.array) != null) {
@@ -1909,13 +1852,23 @@ public class ForkJoinPool extends AbstractExecutorService {
                                 v.currentSteal != subtask)
                                 continue restart;   // stale
                             stat = 1;               // apparent progress
-                            if (t != null && v.base == b &&
-                                U.compareAndSwapObject(a, i, t, null)) {
-                                v.base = b + 1;     // help stealer
-                                joiner.runSubtask(t);
+                            if (v.base == b) {
+                                if (t == null)
+                                    break restart;
+                                if (U.compareAndSwapObject(a, i, t, null)) {
+                                    U.putOrderedInt(v, QBASE, b + 1);
+                                    ForkJoinTask<?> ps = joiner.currentSteal;
+                                    int jt = joiner.top;
+                                    do {
+                                        joiner.currentSteal = t;
+                                        t.doExec(); // clear local tasks too
+                                    } while (task.status >= 0 &&
+                                             joiner.top != jt &&
+                                             (t = joiner.pop()) != null);
+                                    joiner.currentSteal = ps;
+                                    break restart;
+                                }
                             }
-                            else if (v.base == b && ++steps == MAX_HELP)
-                                break restart;      // v apparently stalled
                         }
                         else {                      // empty -- try to descend
                             ForkJoinTask<?> next = v.currentJoin;
@@ -1942,27 +1895,33 @@ public class ForkJoinPool extends AbstractExecutorService {
      * and run tasks within the target's computation.
      *
      * @param task the task to join
-     * @param mode if shared, exit upon completing any task
-     * if all workers are active
-     */
-    private int helpComplete(ForkJoinTask<?> task, int mode) {
-        WorkQueue[] ws; WorkQueue q; int m, n, s, u;
-        if (task != null && (ws = workQueues) != null &&
-            (m = ws.length - 1) >= 0) {
-            for (int j = 1, origin = j;;) {
+     */
+    private int helpComplete(WorkQueue joiner, CountedCompleter<?> task) {
+        WorkQueue[] ws; int m;
+        int s = 0;
+        if ((ws = workQueues) != null && (m = ws.length - 1) >= 0 &&
+            joiner != null && task != null) {
+            int j = joiner.poolIndex;
+            int scans = m + m + 1;
+            long c = 0L;              // for stability check
+            for (int k = scans; ; j += 2) {
+                WorkQueue q;
                 if ((s = task.status) < 0)
-                    return s;
-                if ((q = ws[j & m]) != null && q.pollAndExecCC(task)) {
-                    origin = j;
-                    if (mode == SHARED_QUEUE &&
-                        ((u = (int)(ctl >>> 32)) >= 0 || (u >> UAC_SHIFT) >= 0))
+                    break;
+                else if (joiner.internalPopAndExecCC(task))
+                    k = scans;
+                else if ((s = task.status) < 0)
+                    break;
+                else if ((q = ws[j & m]) != null && q.pollAndExecCC(task))
+                    k = scans;
+                else if (--k < 0) {
+                    if (c == (c = ctl))
                         break;
+                    k = scans;
                 }
-                else if ((j = (j + 2) & m) == origin)
-                    break;
             }
         }
-        return 0;
+        return s;
     }
 
     /**
@@ -1971,17 +1930,22 @@ public class ForkJoinPool extends AbstractExecutorService {
      * for blocking. Fails on contention or termination. Otherwise,
      * adds a new thread if no idle workers are available and pool
      * may become starved.
+     *
+     * @param c the assumed ctl value
      */
-    final boolean tryCompensate() {
-        int pc = config & SMASK, e, i, tc; long c;
-        WorkQueue[] ws; WorkQueue w; Thread p;
-        if ((ws = workQueues) != null && (e = (int)(c = ctl)) >= 0) {
-            if (e != 0 && (i = e & SMASK) < ws.length &&
-                (w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) {
+    final boolean tryCompensate(long c) {
+        WorkQueue[] ws = workQueues;
+        int pc = parallelism, e = (int)c, m, tc;
+        if (ws != null && (m = ws.length - 1) >= 0 && e >= 0 && ctl == c) {
+            WorkQueue w = ws[e & m];
+            if (e != 0 && w != null) {
+                Thread p;
                 long nc = ((long)(w.nextWait & E_MASK) |
                            (c & (AC_MASK|TC_MASK)));
-                if (U.compareAndSwapLong(this, CTL, c, nc)) {
-                    w.eventCount = (e + E_SEQ) & E_MASK;
+                int ne = (e + E_SEQ) & E_MASK;
+                if (w.eventCount == (e | INT_SIGN) &&
+                    U.compareAndSwapLong(this, CTL, c, nc)) {
+                    w.eventCount = ne;
                     if ((p = w.parker) != null)
                         U.unpark(p);
                     return true;   // replace with idle worker
@@ -2024,23 +1988,20 @@ public class ForkJoinPool extends AbstractExecutorService {
      */
     final int awaitJoin(WorkQueue joiner, ForkJoinTask<?> task) {
         int s = 0;
-        if (joiner != null && task != null && (s = task.status) >= 0) {
+        if (task != null && (s = task.status) >= 0 && joiner != null) {
             ForkJoinTask<?> prevJoin = joiner.currentJoin;
             joiner.currentJoin = task;
-            do {} while ((s = task.status) >= 0 && !joiner.isEmpty() &&
-                         joiner.tryRemoveAndExec(task)); // process local tasks
-            if (s >= 0 && (s = task.status) >= 0) {
-                helpSignal(task, joiner.poolIndex);
-                if ((s = task.status) >= 0 &&
-                    (task instanceof CountedCompleter))
-                    s = helpComplete(task, LIFO_QUEUE);
-            }
+            do {} while (joiner.tryRemoveAndExec(task) && // process local tasks
+                         (s = task.status) >= 0);
+            if (s >= 0 && (task instanceof CountedCompleter))
+                s = helpComplete(joiner, (CountedCompleter<?>)task);
+            long cc = 0;        // for stability checks
             while (s >= 0 && (s = task.status) >= 0) {
-                if ((!joiner.isEmpty() ||           // try helping
-                     (s = tryHelpStealer(joiner, task)) == 0) &&
+                if ((s = tryHelpStealer(joiner, task)) == 0 &&
                     (s = task.status) >= 0) {
-                    helpSignal(task, joiner.poolIndex);
-                    if ((s = task.status) >= 0 && tryCompensate()) {
+                    if (!tryCompensate(cc))
+                        cc = ctl;
+                    else {
                         if (task.trySetSignal() && (s = task.status) >= 0) {
                             synchronized (task) {
                                 if (task.status >= 0) {
@@ -2053,9 +2014,11 @@ public class ForkJoinPool extends AbstractExecutorService {
                                     task.notifyAll();
                             }
                         }
-                        long c;                          // re-activate
+                        long c; // reactivate
                         do {} while (!U.compareAndSwapLong
-                                     (this, CTL, c = ctl, c + AC_UNIT));
+                                     (this, CTL, c = ctl,
+                                      ((c & ~AC_MASK) |
+                                       ((c & AC_MASK) + AC_UNIT))));
                     }
                 }
             }
@@ -2077,15 +2040,11 @@ public class ForkJoinPool extends AbstractExecutorService {
         if (joiner != null && task != null && (s = task.status) >= 0) {
             ForkJoinTask<?> prevJoin = joiner.currentJoin;
             joiner.currentJoin = task;
-            do {} while ((s = task.status) >= 0 && !joiner.isEmpty() &&
-                         joiner.tryRemoveAndExec(task));
-            if (s >= 0 && (s = task.status) >= 0) {
-                helpSignal(task, joiner.poolIndex);
-                if ((s = task.status) >= 0 &&
-                    (task instanceof CountedCompleter))
-                    s = helpComplete(task, LIFO_QUEUE);
-            }
-            if (s >= 0 && joiner.isEmpty()) {
+            do {} while (joiner.tryRemoveAndExec(task) && // process local tasks
+                         (s = task.status) >= 0);
+            if (s >= 0) {
+                if (task instanceof CountedCompleter)
+                    helpComplete(joiner, (CountedCompleter<?>)task);
                 do {} while (task.status >= 0 &&
                              tryHelpStealer(joiner, task) > 0);
             }
@@ -2095,29 +2054,22 @@ public class ForkJoinPool extends AbstractExecutorService {
 
     /**
      * Returns a (probably) non-empty steal queue, if one is found
-     * during a random, then cyclic scan, else null.  This method must
-     * be retried by caller if, by the time it tries to use the queue,
-     * it is empty.
-     * @param r a (random) seed for scanning
-     */
-    private WorkQueue findNonEmptyStealQueue(int r) {
-        for (WorkQueue[] ws;;) {
-            int ps = plock, m, n;
-            if ((ws = workQueues) == null || (m = ws.length - 1) < 1)
-                return null;
-            for (int j = (m + 1) << 2; ;) {
-                WorkQueue q = ws[(((r + j) << 1) | 1) & m];
-                if (q != null && (n = q.base - q.top) < 0) {
-                    if (n < -1)
-                        signalWork(q);
-                    return q;
-                }
-                else if (--j < 0) {
-                    if (plock == ps)
-                        return null;
-                    break;
+     * during a scan, else null.  This method must be retried by
+     * caller if, by the time it tries to use the queue, it is empty.
+     */
+    private WorkQueue findNonEmptyStealQueue() {
+        int r = ThreadLocalRandom.current().nextInt();
+        for (;;) {
+            int ps = plock, m; WorkQueue[] ws; WorkQueue q;
+            if ((ws = workQueues) != null && (m = ws.length - 1) >= 0) {
+                for (int j = (m + 1) << 2; j >= 0; --j) {
+                    if ((q = ws[(((r - j) << 1) | 1) & m]) != null &&
+                        q.base - q.top < 0)
+                        return q;
                 }
             }
+            if (plock == ps)
+                return null;
         }
     }
 
@@ -2128,38 +2080,36 @@ public class ForkJoinPool extends AbstractExecutorService {
      * find tasks either.
      */
     final void helpQuiescePool(WorkQueue w) {
+        ForkJoinTask<?> ps = w.currentSteal;
         for (boolean active = true;;) {
-            ForkJoinTask<?> localTask; // exhaust local queue
-            while ((localTask = w.nextLocalTask()) != null)
-                localTask.doExec();
-            // Similar to loop in scan(), but ignoring submissions
-            WorkQueue q = findNonEmptyStealQueue(w.nextSeed());
-            if (q != null) {
-                ForkJoinTask<?> t; int b;
+            long c; WorkQueue q; ForkJoinTask<?> t; int b;
+            while ((t = w.nextLocalTask()) != null)
+                t.doExec();
+            if ((q = findNonEmptyStealQueue()) != null) {
                 if (!active) {      // re-establish active count
-                    long c;
                     active = true;
                     do {} while (!U.compareAndSwapLong
-                                 (this, CTL, c = ctl, c + AC_UNIT));
+                                 (this, CTL, c = ctl,
+                                  ((c & ~AC_MASK) |
+                                   ((c & AC_MASK) + AC_UNIT))));
+                }
+                if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null) {
+                    (w.currentSteal = t).doExec();
+                    w.currentSteal = ps;
                 }
-                if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
-                    w.runSubtask(t);
             }
-            else {
-                long c;
-                if (active) {       // decrement active count without queuing
+            else if (active) {       // decrement active count without queuing
+                long nc = ((c = ctl) & ~AC_MASK) | ((c & AC_MASK) - AC_UNIT);
+                if ((int)(nc >> AC_SHIFT) + parallelism == 0)
+                    break;          // bypass decrement-then-increment
+                if (U.compareAndSwapLong(this, CTL, c, nc))
                     active = false;
-                    do {} while (!U.compareAndSwapLong
-                                 (this, CTL, c = ctl, c -= AC_UNIT));
-                }
-                else
-                    c = ctl;        // re-increment on exit
-                if ((int)(c >> AC_SHIFT) + (config & SMASK) == 0) {
-                    do {} while (!U.compareAndSwapLong
-                                 (this, CTL, c = ctl, c + AC_UNIT));
-                    break;
-                }
             }
+            else if ((int)((c = ctl) >> AC_SHIFT) + parallelism <= 0 &&
+                     U.compareAndSwapLong
+                     (this, CTL, c, ((c & ~AC_MASK) |
+                                     ((c & AC_MASK) + AC_UNIT))))
+                break;
         }
     }
 
@@ -2173,7 +2123,7 @@ public class ForkJoinPool extends AbstractExecutorService {
             WorkQueue q; int b;
             if ((t = w.nextLocalTask()) != null)
                 return t;
-            if ((q = findNonEmptyStealQueue(w.nextSeed())) == null)
+            if ((q = findNonEmptyStealQueue()) == null)
                 return null;
             if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
                 return t;
@@ -2229,7 +2179,7 @@ public class ForkJoinPool extends AbstractExecutorService {
     static int getSurplusQueuedTaskCount() {
         Thread t; ForkJoinWorkerThread wt; ForkJoinPool pool; WorkQueue q;
         if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) {
-            int p = (pool = (wt = (ForkJoinWorkerThread)t).pool).config & SMASK;
+            int p = (pool = (wt = (ForkJoinWorkerThread)t).pool).parallelism;
             int n = (q = wt.workQueue).top - q.base;
             int a = (int)(pool.ctl >> AC_SHIFT) + p;
             return n - (a > (p >>>= 1) ? 0 :
@@ -2258,45 +2208,47 @@ public class ForkJoinPool extends AbstractExecutorService {
      * @return true if now terminating or terminated
      */
     private boolean tryTerminate(boolean now, boolean enable) {
-        if (this == commonPool)                     // cannot shut down
+        int ps;
+        if (this == common)                        // cannot shut down
             return false;
+        if ((ps = plock) >= 0) {                   // enable by setting plock
+            if (!enable)
+                return false;
+            if ((ps & PL_LOCK) != 0 ||
+                !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
+                ps = acquirePlock();
+            int nps = ((ps + PL_LOCK) & ~SHUTDOWN) | SHUTDOWN;
+            if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
+                releasePlock(nps);
+        }
         for (long c;;) {
-            if (((c = ctl) & STOP_BIT) != 0) {      // already terminating
-                if ((short)(c >>> TC_SHIFT) == -(config & SMASK)) {
+            if (((c = ctl) & STOP_BIT) != 0) {     // already terminating
+                if ((short)(c >>> TC_SHIFT) + parallelism <= 0) {
                     synchronized (this) {
-                        notifyAll();                // signal when 0 workers
+                        notifyAll();               // signal when 0 workers
                     }
                 }
                 return true;
             }
-            if (plock >= 0) {                       // not yet enabled
-                int ps;
-                if (!enable)
-                    return false;
-                if (((ps = plock) & PL_LOCK) != 0 ||
-                    !U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
-                    ps = acquirePlock();
-                if (!U.compareAndSwapInt(this, PLOCK, ps, SHUTDOWN))
-                    releasePlock(SHUTDOWN);
-            }
-            if (!now) {                             // check if idle & no tasks
-                if ((int)(c >> AC_SHIFT) != -(config & SMASK) ||
-                    hasQueuedSubmissions())
+            if (!now) {                            // check if idle & no tasks
+                WorkQueue[] ws; WorkQueue w;
+                if ((int)(c >> AC_SHIFT) + parallelism > 0)
                     return false;
-                // Check for unqueued inactive workers. One pass suffices.
-                WorkQueue[] ws = workQueues; WorkQueue w;
-                if (ws != null) {
-                    for (int i = 1; i < ws.length; i += 2) {
-                        if ((w = ws[i]) != null && w.eventCount >= 0)
+                if ((ws = workQueues) != null) {
+                    for (int i = 0; i < ws.length; ++i) {
+                        if ((w = ws[i]) != null &&
+                            (!w.isEmpty() ||
+                             ((i & 1) != 0 && w.eventCount >= 0))) {
+                            signalWork(ws, w);
                             return false;
+                        }
                     }
                 }
             }
             if (U.compareAndSwapLong(this, CTL, c, c | STOP_BIT)) {
                 for (int pass = 0; pass < 3; ++pass) {
-                    WorkQueue[] ws = workQueues;
-                    if (ws != null) {
-                        WorkQueue w; Thread wt;
+                    WorkQueue[] ws; WorkQueue w; Thread wt;
+                    if ((ws = workQueues) != null) {
                         int n = ws.length;
                         for (int i = 0; i < n; ++i) {
                             if ((w = ws[i]) != null) {
@@ -2307,7 +2259,7 @@ public class ForkJoinPool extends AbstractExecutorService {
                                         if (!wt.isInterrupted()) {
                                             try {
                                                 wt.interrupt();
-                                            } catch (SecurityException ignore) {
+                                            } catch (Throwable ignore) {
                                             }
                                         }
                                         U.unpark(wt);
@@ -2318,7 +2270,7 @@ public class ForkJoinPool extends AbstractExecutorService {
                         // Wake up workers parked on event queue
                         int i, e; long cc; Thread p;
                         while ((e = (int)(cc = ctl) & E_MASK) != 0 &&
-                               (i = e & SMASK) < n &&
+                               (i = e & SMASK) < n && i >= 0 &&
                                (w = ws[i]) != null) {
                             long nc = ((long)(w.nextWait & E_MASK) |
                                        ((cc + AC_UNIT) & AC_MASK) |
@@ -2344,9 +2296,9 @@ public class ForkJoinPool extends AbstractExecutorService {
      * least one task.
      */
     static WorkQueue commonSubmitterQueue() {
-        ForkJoinPool p; WorkQueue[] ws; int m; Submitter z;
+        Submitter z; ForkJoinPool p; WorkQueue[] ws; int m, r;
         return ((z = submitters.get()) != null &&
-                (p = commonPool) != null &&
+                (p = common) != null &&
                 (ws = p.workQueues) != null &&
                 (m = ws.length - 1) >= 0) ?
             ws[m & z.seed & SQMASK] : null;
@@ -2355,127 +2307,57 @@ public class ForkJoinPool extends AbstractExecutorService {
     /**
      * Tries to pop the given task from submitter's queue in common pool.
      */
-    static boolean tryExternalUnpush(ForkJoinTask<?> t) {
-        ForkJoinPool p; WorkQueue[] ws; WorkQueue q; Submitter z;
-        ForkJoinTask<?>[] a;  int m, s;
-        if (t != null &&
-            (z = submitters.get()) != null &&
-            (p = commonPool) != null &&
-            (ws = p.workQueues) != null &&
-            (m = ws.length - 1) >= 0 &&
-            (q = ws[m & z.seed & SQMASK]) != null &&
-            (s = q.top) != q.base &&
-            (a = q.array) != null) {
+    final boolean tryExternalUnpush(ForkJoinTask<?> task) {
+        WorkQueue joiner; ForkJoinTask<?>[] a; int m, s;
+        Submitter z = submitters.get();
+        WorkQueue[] ws = workQueues;
+        boolean popped = false;
+        if (z != null && ws != null && (m = ws.length - 1) >= 0 &&
+            (joiner = ws[z.seed & m & SQMASK]) != null &&
+            joiner.base != (s = joiner.top) &&
+            (a = joiner.array) != null) {
             long j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE;
-            if (U.getObject(a, j) == t &&
-                U.compareAndSwapInt(q, QLOCK, 0, 1)) {
-                if (q.array == a && q.top == s && // recheck
-                    U.compareAndSwapObject(a, j, t, null)) {
-                    q.top = s - 1;
-                    q.qlock = 0;
-                    return true;
+            if (U.getObject(a, j) == task &&
+                U.compareAndSwapInt(joiner, QLOCK, 0, 1)) {
+                if (joiner.top == s && joiner.array == a &&
+                    U.compareAndSwapObject(a, j, task, null)) {
+                    joiner.top = s - 1;
+                    popped = true;
                 }
-                q.qlock = 0;
+                joiner.qlock = 0;
             }
         }
-        return false;
+        return popped;
     }
 
-    /**
-     * Tries to pop and run local tasks within the same computation
-     * as the given root. On failure, tries to help complete from
-     * other queues via helpComplete.
-     */
-    private void externalHelpComplete(WorkQueue q, ForkJoinTask<?> root) {
-        ForkJoinTask<?>[] a; int m;
-        if (q != null && (a = q.array) != null && (m = (a.length - 1)) >= 0 &&
-            root != null && root.status >= 0) {
-            for (;;) {
-                int s, u; Object o; CountedCompleter<?> task = null;
-                if ((s = q.top) - q.base > 0) {
-                    long j = ((m & (s - 1)) << ASHIFT) + ABASE;
-                    if ((o = U.getObject(a, j)) != null &&
-                        (o instanceof CountedCompleter)) {
-                        CountedCompleter<?> t = (CountedCompleter<?>)o, r = t;
-                        do {
-                            if (r == root) {
-                                if (U.compareAndSwapInt(q, QLOCK, 0, 1)) {
-                                    if (q.array == a && q.top == s &&
-                                        U.compareAndSwapObject(a, j, t, null)) {
-                                        q.top = s - 1;
-                                        task = t;
-                                    }
-                                    q.qlock = 0;
-                                }
-                                break;
-                            }
-                        } while ((r = r.completer) != null);
-                    }
-                }
-                if (task != null)
-                    task.doExec();
-                if (root.status < 0 ||
-                    (u = (int)(ctl >>> 32)) >= 0 || (u >> UAC_SHIFT) >= 0)
+    final int externalHelpComplete(CountedCompleter<?> task) {
+        WorkQueue joiner; int m, j;
+        Submitter z = submitters.get();
+        WorkQueue[] ws = workQueues;
+        int s = 0;
+        if (z != null && ws != null && (m = ws.length - 1) >= 0 &&
+            (joiner = ws[(j = z.seed) & m & SQMASK]) != null && task != null) {
+            int scans = m + m + 1;
+            long c = 0L;             // for stability check
+            j |= 1;                  // poll odd queues
+            for (int k = scans; ; j += 2) {
+                WorkQueue q;
+                if ((s = task.status) < 0)
                     break;
-                if (task == null) {
-                    helpSignal(root, q.poolIndex);
-                    if (root.status >= 0)
-                        helpComplete(root, SHARED_QUEUE);
+                else if (joiner.externalPopAndExecCC(task))
+                    k = scans;
+                else if ((s = task.status) < 0)
                     break;
+                else if ((q = ws[j & m]) != null && q.pollAndExecCC(task))
+                    k = scans;
+                else if (--k < 0) {
+                    if (c == (c = ctl))
+                        break;
+                    k = scans;
                 }
             }
         }
-    }
-
-    /**
-     * Tries to help execute or signal availability of the given task
-     * from submitter's queue in common pool.
-     */
-    static void externalHelpJoin(ForkJoinTask<?> t) {
-        // Some hard-to-avoid overlap with tryExternalUnpush
-        ForkJoinPool p; WorkQueue[] ws; WorkQueue q, w; Submitter z;
-        ForkJoinTask<?>[] a;  int m, s, n;
-        if (t != null &&
-            (z = submitters.get()) != null &&
-            (p = commonPool) != null &&
-            (ws = p.workQueues) != null &&
-            (m = ws.length - 1) >= 0 &&
-            (q = ws[m & z.seed & SQMASK]) != null &&
-            (a = q.array) != null) {
-            int am = a.length - 1;
-            if ((s = q.top) != q.base) {
-                long j = ((am & (s - 1)) << ASHIFT) + ABASE;
-                if (U.getObject(a, j) == t &&
-                    U.compareAndSwapInt(q, QLOCK, 0, 1)) {
-                    if (q.array == a && q.top == s &&
-                        U.compareAndSwapObject(a, j, t, null)) {
-                        q.top = s - 1;
-                        q.qlock = 0;
-                        t.doExec();
-                    }
-                    else
-                        q.qlock = 0;
-                }
-            }
-            if (t.status >= 0) {
-                if (t instanceof CountedCompleter)
-                    p.externalHelpComplete(q, t);
-                else
-                    p.helpSignal(t, q.poolIndex);
-            }
-        }
-    }
-
-    /**
-     * Restricted version of helpQuiescePool for external callers
-     */
-    static void externalHelpQuiescePool() {
-        ForkJoinPool p; ForkJoinTask<?> t; WorkQueue q; int b;
-        if ((p = commonPool) != null &&
-            (q = p.findNonEmptyStealQueue(1)) != null &&
-            (b = q.base) - q.top < 0 &&
-            (t = q.pollAt(b)) != null)
-            t.doExec();
+        return s;
     }
 
     // Exported methods
@@ -2529,49 +2411,65 @@ public class ForkJoinPool extends AbstractExecutorService {
      */
     public ForkJoinPool(int parallelism,
                         ForkJoinWorkerThreadFactory factory,
-                        Thread.UncaughtExceptionHandler handler,
+                        UncaughtExceptionHandler handler,
                         boolean asyncMode) {
+        this(checkParallelism(parallelism),
+             checkFactory(factory),
+             handler,
+             (asyncMode ? FIFO_QUEUE : LIFO_QUEUE),
+             "ForkJoinPool-" + nextPoolId() + "-worker-");
         checkPermission();
-        if (factory == null)
-            throw new NullPointerException();
+    }
+
+    private static int checkParallelism(int parallelism) {
         if (parallelism <= 0 || parallelism > MAX_CAP)
             throw new IllegalArgumentException();
-        this.factory = factory;
-        this.ueh = handler;
-        this.config = parallelism | (asyncMode ? (FIFO_QUEUE << 16) : 0);
-        long np = (long)(-parallelism); // offset ctl counts
-        this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
-        int pn = nextPoolId();
-        StringBuilder sb = new StringBuilder("ForkJoinPool-");
-        sb.append(Integer.toString(pn));
-        sb.append("-worker-");
-        this.workerNamePrefix = sb.toString();
+        return parallelism;
+    }
+
+    private static ForkJoinWorkerThreadFactory checkFactory
+        (ForkJoinWorkerThreadFactory factory) {
+        if (factory == null)
+            throw new NullPointerException();
+        return factory;
     }
 
     /**
-     * Constructor for common pool, suitable only for static initialization.
-     * Basically the same as above, but uses smallest possible initial footprint.
+     * Creates a {@code ForkJoinPool} with the given parameters, without
+     * any security checks or parameter validation.  Invoked directly by
+     * makeCommonPool.
      */
-    ForkJoinPool(int parallelism, long ctl,
-                 ForkJoinWorkerThreadFactory factory,
-                 Thread.UncaughtExceptionHandler handler) {
-        this.config = parallelism;
-        this.ctl = ctl;
+    private ForkJoinPool(int parallelism,
+                         ForkJoinWorkerThreadFactory factory,
+                         UncaughtExceptionHandler handler,
+                         int mode,
+                         String workerNamePrefix) {
+        this.workerNamePrefix = workerNamePrefix;
         this.factory = factory;
         this.ueh = handler;
-        this.workerNamePrefix = "ForkJoinPool.commonPool-worker-";
+        this.mode = (short)mode;
+        this.parallelism = (short)parallelism;
+        long np = (long)(-parallelism); // offset ctl counts
+        this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
     }
 
     /**
-     * Returns the common pool instance.
+     * Returns the common pool instance. This pool is statically
+     * constructed; its run state is unaffected by attempts to {@link
+     * #shutdown} or {@link #shutdownNow}. However this pool and any
+     * ongoing processing are automatically terminated upon program
+     * {@link System#exit}.  Any program that relies on asynchronous
+     * task processing to complete before program termination should
+     * invoke {@code commonPool().}{@link #awaitQuiescence awaitQuiescence},
+     * before exit.
      *
      * @return the common pool instance
      * @since 1.8
      * @hide
      */
     public static ForkJoinPool commonPool() {
-        // assert commonPool != null : "static init error";
-        return commonPool;
+        // assert common != null : "static init error";
+        return common;
     }
 
     // Execution methods
@@ -2627,7 +2525,7 @@ public class ForkJoinPool extends AbstractExecutorService {
         if (task instanceof ForkJoinTask<?>) // avoid re-wrap
             job = (ForkJoinTask<?>) task;
         else
-            job = new ForkJoinTask.AdaptedRunnableAction(task);
+            job = new ForkJoinTask.RunnableExecuteAction(task);
         externalPush(job);
     }
 
@@ -2729,7 +2627,7 @@ public class ForkJoinPool extends AbstractExecutorService {
      *
      * @return the handler, or {@code null} if none
      */
-    public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
+    public UncaughtExceptionHandler getUncaughtExceptionHandler() {
         return ueh;
     }
 
@@ -2739,7 +2637,8 @@ public class ForkJoinPool extends AbstractExecutorService {
      * @return the targeted parallelism level of this pool
      */
     public int getParallelism() {
-        return config & SMASK;
+        int par;
+        return ((par = parallelism) > 0) ? par : 1;
     }
 
     /**
@@ -2750,7 +2649,7 @@ public class ForkJoinPool extends AbstractExecutorService {
      * @hide
      */
     public static int getCommonPoolParallelism() {
-        return commonPoolParallelism;
+        return commonParallelism;
     }
 
     /**
@@ -2762,7 +2661,7 @@ public class ForkJoinPool extends AbstractExecutorService {
      * @return the number of worker threads
      */
     public int getPoolSize() {
-        return (config & SMASK) + (short)(ctl >>> TC_SHIFT);
+        return parallelism + (short)(ctl >>> TC_SHIFT);
     }
 
     /**
@@ -2772,7 +2671,7 @@ public class ForkJoinPool extends AbstractExecutorService {
      * @return {@code true} if this pool uses async mode
      */
     public boolean getAsyncMode() {
-        return (config >>> 16) == FIFO_QUEUE;
+        return mode == FIFO_QUEUE;
     }
 
     /**
@@ -2803,7 +2702,7 @@ public class ForkJoinPool extends AbstractExecutorService {
      * @return the number of active threads
      */
     public int getActiveThreadCount() {
-        int r = (config & SMASK) + (int)(ctl >> AC_SHIFT);
+        int r = parallelism + (int)(ctl >> AC_SHIFT);
         return (r <= 0) ? 0 : r; // suppress momentarily negative values
     }
 
@@ -2819,7 +2718,7 @@ public class ForkJoinPool extends AbstractExecutorService {
      * @return {@code true} if all threads are currently idle
      */
     public boolean isQuiescent() {
-        return (int)(ctl >> AC_SHIFT) + (config & SMASK) == 0;
+        return parallelism + (int)(ctl >> AC_SHIFT) <= 0;
     }
 
     /**
@@ -2982,7 +2881,7 @@ public class ForkJoinPool extends AbstractExecutorService {
                 }
             }
         }
-        int pc = (config & SMASK);
+        int pc = parallelism;
         int tc = pc + (short)(c >>> TC_SHIFT);
         int ac = pc + (int)(c >> AC_SHIFT);
         if (ac < 0) // ignore transient negative
@@ -3012,11 +2911,6 @@ public class ForkJoinPool extends AbstractExecutorService {
      * already shut down.  Tasks that are in the process of being
      * submitted concurrently during the course of this method may or
      * may not be rejected.
-     *
-     * @throws SecurityException if a security manager exists and
-     *         the caller is not permitted to modify threads
-     *         because it does not hold {@link
-     *         java.lang.RuntimePermission}{@code ("modifyThread")}
      */
     public void shutdown() {
         checkPermission();
@@ -3051,7 +2945,7 @@ public class ForkJoinPool extends AbstractExecutorService {
     public boolean isTerminated() {
         long c = ctl;
         return ((c & STOP_BIT) != 0L &&
-                (short)(c >>> TC_SHIFT) == -(config & SMASK));
+                (short)(c >>> TC_SHIFT) + parallelism <= 0);
     }
 
     /**
@@ -3070,7 +2964,7 @@ public class ForkJoinPool extends AbstractExecutorService {
     public boolean isTerminating() {
         long c = ctl;
         return ((c & STOP_BIT) != 0L &&
-                (short)(c >>> TC_SHIFT) != -(config & SMASK));
+                (short)(c >>> TC_SHIFT) + parallelism > 0);
     }
 
     /**
@@ -3085,9 +2979,10 @@ public class ForkJoinPool extends AbstractExecutorService {
     /**
      * Blocks until all tasks have completed execution after a
      * shutdown request, or the timeout occurs, or the current thread
-     * is interrupted, whichever happens first. Note that the {@link
-     * #commonPool()} never terminates until program shutdown so
-     * this method will always time out.
+     * is interrupted, whichever happens first. Because the {@link
+     * #commonPool()} never terminates until program shutdown, when
+     * applied to the common pool, this method is equivalent to {@link
+     * #awaitQuiescence(long, TimeUnit)} but always returns {@code false}.
      *
      * @param timeout the maximum time to wait
      * @param unit the time unit of the timeout argument
@@ -3097,6 +2992,12 @@ public class ForkJoinPool extends AbstractExecutorService {
      */
     public boolean awaitTermination(long timeout, TimeUnit unit)
         throws InterruptedException {
+        if (Thread.interrupted())
+            throw new InterruptedException();
+        if (this == common) {
+            awaitQuiescence(timeout, unit);
+            return false;
+        }
         long nanos = unit.toNanos(timeout);
         if (isTerminated())
             return true;
@@ -3117,6 +3018,59 @@ public class ForkJoinPool extends AbstractExecutorService {
     }
 
     /**
+     * If called by a ForkJoinTask operating in this pool, equivalent
+     * in effect to {@link ForkJoinTask#helpQuiesce}. Otherwise,
+     * waits and/or attempts to assist performing tasks until this
+     * pool {@link #isQuiescent} or the indicated timeout elapses.
+     *
+     * @param timeout the maximum time to wait
+     * @param unit the time unit of the timeout argument
+     * @return {@code true} if quiescent; {@code false} if the
+     * timeout elapsed.
+     */
+    public boolean awaitQuiescence(long timeout, TimeUnit unit) {
+        long nanos = unit.toNanos(timeout);
+        ForkJoinWorkerThread wt;
+        Thread thread = Thread.currentThread();
+        if ((thread instanceof ForkJoinWorkerThread) &&
+            (wt = (ForkJoinWorkerThread)thread).pool == this) {
+            helpQuiescePool(wt.workQueue);
+            return true;
+        }
+        long startTime = System.nanoTime();
+        WorkQueue[] ws;
+        int r = 0, m;
+        boolean found = true;
+        while (!isQuiescent() && (ws = workQueues) != null &&
+               (m = ws.length - 1) >= 0) {
+            if (!found) {
+                if ((System.nanoTime() - startTime) > nanos)
+                    return false;
+                Thread.yield(); // cannot block
+            }
+            found = false;
+            for (int j = (m + 1) << 2; j >= 0; --j) {
+                ForkJoinTask<?> t; WorkQueue q; int b;
+                if ((q = ws[r++ & m]) != null && (b = q.base) - q.top < 0) {
+                    found = true;
+                    if ((t = q.pollAt(b)) != null)
+                        t.doExec();
+                    break;
+                }
+            }
+        }
+        return true;
+    }
+
+    /**
+     * Waits and/or attempts to assist performing tasks indefinitely
+     * until the {@link #commonPool()} {@link #isQuiescent}.
+     */
+    static void quiesceCommonPool() {
+        common.awaitQuiescence(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
+    }
+
+    /**
      * Interface for extending managed parallelism for tasks running
      * in {@link ForkJoinPool}s.
      *
@@ -3125,9 +3079,9 @@ public class ForkJoinPool extends AbstractExecutorService {
      * not necessary. Method {@code block} blocks the current thread
      * if necessary (perhaps internally invoking {@code isReleasable}
      * before actually blocking). These actions are performed by any
-     * thread invoking {@link ForkJoinPool#managedBlock}.  The
-     * unusual methods in this API accommodate synchronizers that may,
-     * but don't usually, block for long periods. Similarly, they
+     * thread invoking {@link ForkJoinPool#managedBlock(ManagedBlocker)}.
+     * The unusual methods in this API accommodate synchronizers that
+     * may, but don't usually, block for long periods. Similarly, they
      * allow more efficient internal handling of cases in which
      * additional workers may be, but usually are not, needed to
      * ensure sufficient parallelism.  Toward this end,
@@ -3185,6 +3139,7 @@ public class ForkJoinPool extends AbstractExecutorService {
 
         /**
          * Returns {@code true} if blocking is unnecessary.
+         * @return {@code true} if blocking is unnecessary
          */
         boolean isReleasable();
     }
@@ -3214,21 +3169,8 @@ public class ForkJoinPool extends AbstractExecutorService {
         Thread t = Thread.currentThread();
         if (t instanceof ForkJoinWorkerThread) {
             ForkJoinPool p = ((ForkJoinWorkerThread)t).pool;
-            while (!blocker.isReleasable()) { // variant of helpSignal
-                WorkQueue[] ws; WorkQueue q; int m, u;
-                if ((ws = p.workQueues) != null && (m = ws.length - 1) >= 0) {
-                    for (int i = 0; i <= m; ++i) {
-                        if (blocker.isReleasable())
-                            return;
-                        if ((q = ws[i]) != null && q.base - q.top < 0) {
-                            p.signalWork(q);
-                            if ((u = (int)(p.ctl >>> 32)) >= 0 ||
-                                (u >> UAC_SHIFT) >= 0)
-                                break;
-                        }
-                    }
-                }
-                if (p.tryCompensate()) {
+            while (!blocker.isReleasable()) {
+                if (p.tryCompensate(p.ctl)) {
                     try {
                         do {} while (!blocker.isReleasable() &&
                                      !blocker.block());
@@ -3266,6 +3208,7 @@ public class ForkJoinPool extends AbstractExecutorService {
     private static final long STEALCOUNT;
     private static final long PLOCK;
     private static final long INDEXSEED;
+    private static final long QBASE;
     private static final long QLOCK;
 
     static {
@@ -3285,6 +3228,8 @@ public class ForkJoinPool extends AbstractExecutorService {
             PARKBLOCKER = U.objectFieldOffset
                 (tk.getDeclaredField("parkBlocker"));
             Class<?> wk = WorkQueue.class;
+            QBASE = U.objectFieldOffset
+                (wk.getDeclaredField("base"));
             QLOCK = U.objectFieldOffset
                 (wk.getDeclaredField("qlock"));
             Class<?> ak = ForkJoinTask[].class;
@@ -3298,45 +3243,51 @@ public class ForkJoinPool extends AbstractExecutorService {
         }
 
         submitters = new ThreadLocal<Submitter>();
-        ForkJoinWorkerThreadFactory fac = defaultForkJoinWorkerThreadFactory =
+        defaultForkJoinWorkerThreadFactory =
             new DefaultForkJoinWorkerThreadFactory();
         modifyThreadPermission = new RuntimePermission("modifyThread");
 
-        /*
-         * Establish common pool parameters.  For extra caution,
-         * computations to set up common pool state are here; the
-         * constructor just assigns these values to fields.
-         */
+        common = java.security.AccessController.doPrivileged
+            (new java.security.PrivilegedAction<ForkJoinPool>() {
+                public ForkJoinPool run() { return makeCommonPool(); }});
+        int par = common.parallelism; // report 1 even if threads disabled
+        commonParallelism = par > 0 ? par : 1;
+    }
 
-        int par = 0;
-        Thread.UncaughtExceptionHandler handler = null;
-        try {  // TBD: limit or report ignored exceptions?
+    /**
+     * Creates and returns the common pool, respecting user settings
+     * specified via system properties.
+     */
+    private static ForkJoinPool makeCommonPool() {
+        int parallelism = -1;
+        ForkJoinWorkerThreadFactory factory
+            = defaultForkJoinWorkerThreadFactory;
+        UncaughtExceptionHandler handler = null;
+        try {  // ignore exceptions in accessing/parsing properties
             String pp = System.getProperty
                 ("java.util.concurrent.ForkJoinPool.common.parallelism");
-            String hp = System.getProperty
-                ("java.util.concurrent.ForkJoinPool.common.exceptionHandler");
             String fp = System.getProperty
                 ("java.util.concurrent.ForkJoinPool.common.threadFactory");
+            String hp = System.getProperty
+                ("java.util.concurrent.ForkJoinPool.common.exceptionHandler");
+            if (pp != null)
+                parallelism = Integer.parseInt(pp);
             if (fp != null)
-                fac = ((ForkJoinWorkerThreadFactory)ClassLoader.
-                       getSystemClassLoader().loadClass(fp).newInstance());
+                factory = ((ForkJoinWorkerThreadFactory)ClassLoader.
+                           getSystemClassLoader().loadClass(fp).newInstance());
             if (hp != null)
-                handler = ((Thread.UncaughtExceptionHandler)ClassLoader.
+                handler = ((UncaughtExceptionHandler)ClassLoader.
                            getSystemClassLoader().loadClass(hp).newInstance());
-            if (pp != null)
-                par = Integer.parseInt(pp);
         } catch (Exception ignore) {
         }
 
-        if (par <= 0)
-            par = Runtime.getRuntime().availableProcessors();
-        if (par > MAX_CAP)
-            par = MAX_CAP;
-        commonPoolParallelism = par;
-        long np = (long)(-par); // precompute initial ctl value
-        long ct = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
-
-        commonPool = new ForkJoinPool(par, ct, fac, handler);
+        if (parallelism < 0 && // default 1 less than #cores
+            (parallelism = Runtime.getRuntime().availableProcessors() - 1) < 0)
+            parallelism = 0;
+        if (parallelism > MAX_CAP)
+            parallelism = MAX_CAP;
+        return new ForkJoinPool(parallelism, factory, handler, LIFO_QUEUE,
+                                "ForkJoinPool.commonPool-worker-");
     }
 
 }
diff --git a/luni/src/main/java/java/util/concurrent/ForkJoinTask.java b/luni/src/main/java/java/util/concurrent/ForkJoinTask.java
index 818788e..6d25775 100644
--- a/luni/src/main/java/java/util/concurrent/ForkJoinTask.java
+++ b/luni/src/main/java/java/util/concurrent/ForkJoinTask.java
@@ -136,7 +136,7 @@ import java.lang.reflect.Constructor;
  * supports other methods and techniques (for example the use of
  * {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
  * may be of use in constructing custom subclasses for problems that
- * are not statically structured as DAGs. To support such usages a
+ * are not statically structured as DAGs. To support such usages, a
  * ForkJoinTask may be atomically <em>tagged</em> with a {@code short}
  * value using {@link #setForkJoinTaskTag} or {@link
  * #compareAndSetForkJoinTaskTag} and checked using {@link
@@ -286,25 +286,35 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
      */
     private int externalAwaitDone() {
         int s;
-        ForkJoinPool.externalHelpJoin(this);
-        boolean interrupted = false;
-        while ((s = status) >= 0) {
-            if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
-                synchronized (this) {
-                    if (status >= 0) {
-                        try {
-                            wait();
-                        } catch (InterruptedException ie) {
-                            interrupted = true;
+        ForkJoinPool cp = ForkJoinPool.common;
+        if ((s = status) >= 0) {
+            if (cp != null) {
+                if (this instanceof CountedCompleter)
+                    s = cp.externalHelpComplete((CountedCompleter<?>)this);
+                else if (cp.tryExternalUnpush(this))
+                    s = doExec();
+            }
+            if (s >= 0 && (s = status) >= 0) {
+                boolean interrupted = false;
+                do {
+                    if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
+                        synchronized (this) {
+                            if (status >= 0) {
+                                try {
+                                    wait();
+                                } catch (InterruptedException ie) {
+                                    interrupted = true;
+                                }
+                            }
+                            else
+                                notifyAll();
                         }
                     }
-                    else
-                        notifyAll();
-                }
+                } while ((s = status) >= 0);
+                if (interrupted)
+                    Thread.currentThread().interrupt();
             }
         }
-        if (interrupted)
-            Thread.currentThread().interrupt();
         return s;
     }
 
@@ -313,9 +323,15 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
      */
     private int externalInterruptibleAwaitDone() throws InterruptedException {
         int s;
+        ForkJoinPool cp = ForkJoinPool.common;
         if (Thread.interrupted())
             throw new InterruptedException();
-        ForkJoinPool.externalHelpJoin(this);
+        if ((s = status) >= 0 && cp != null) {
+            if (this instanceof CountedCompleter)
+                cp.externalHelpComplete((CountedCompleter<?>)this);
+            else if (cp.tryExternalUnpush(this))
+                doExec();
+        }
         while ((s = status) >= 0) {
             if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
                 synchronized (this) {
@@ -329,7 +345,6 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
         return s;
     }
 
-
     /**
      * Implementation for join, get, quietlyJoin. Directly handles
      * only cases of already-completed, external wait, and
@@ -601,14 +616,9 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
     /**
      * A version of "sneaky throw" to relay exceptions
      */
-    static void rethrow(final Throwable ex) {
-        if (ex != null) {
-            if (ex instanceof Error)
-                throw (Error)ex;
-            if (ex instanceof RuntimeException)
-                throw (RuntimeException)ex;
-            throw uncheckedThrowable(ex, RuntimeException.class);
-        }
+    static void rethrow(Throwable ex) {
+        if (ex != null)
+            ForkJoinTask.<RuntimeException>uncheckedThrow(ex);
     }
 
     /**
@@ -617,8 +627,8 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
      * unchecked exceptions
      */
     @SuppressWarnings("unchecked") static <T extends Throwable>
-        T uncheckedThrowable(final Throwable t, final Class<T> c) {
-        return (T)t; // rely on vacuous cast
+        void uncheckedThrow(Throwable t) throws T {
+        throw (T)t; // rely on vacuous cast
     }
 
     /**
@@ -653,7 +663,7 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
         if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
             ((ForkJoinWorkerThread)t).workQueue.push(this);
         else
-            ForkJoinPool.commonPool.externalPush(this);
+            ForkJoinPool.common.externalPush(this);
         return this;
     }
 
@@ -774,8 +784,6 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
      * @param tasks the collection of tasks
      * @return the tasks argument, to simplify usage
      * @throws NullPointerException if tasks or any element are null
-
-     * @hide
      */
     public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
         if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
@@ -831,7 +839,7 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
      * <p>This method is designed to be invoked by <em>other</em>
      * tasks. To terminate the current task, you can just return or
      * throw an unchecked exception from its computation method, or
-     * invoke {@link #completeExceptionally}.
+     * invoke {@link #completeExceptionally(Throwable)}.
      *
      * @param mayInterruptIfRunning this value has no effect in the
      * default implementation because interrupts are not used to
@@ -984,6 +992,7 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
         // Messy in part because we measure in nanosecs, but wait in millisecs
         int s; long ms;
         long ns = unit.toNanos(timeout);
+        ForkJoinPool cp;
         if ((s = status) >= 0 && ns > 0L) {
             long deadline = System.nanoTime() + ns;
             ForkJoinPool p = null;
@@ -995,8 +1004,12 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
                 w = wt.workQueue;
                 p.helpJoinOnce(w, this); // no retries on failure
             }
-            else
-                ForkJoinPool.externalHelpJoin(this);
+            else if ((cp = ForkJoinPool.common) != null) {
+                if (this instanceof CountedCompleter)
+                    cp.externalHelpComplete((CountedCompleter<?>)this);
+                else if (cp.tryExternalUnpush(this))
+                    doExec();
+            }
             boolean canBlock = false;
             boolean interrupted = false;
             try {
@@ -1004,7 +1017,7 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
                     if (w != null && w.qlock < 0)
                         cancelIgnoringExceptions(this);
                     else if (!canBlock) {
-                        if (p == null || p.tryCompensate())
+                        if (p == null || p.tryCompensate(p.ctl))
                             canBlock = true;
                     }
                     else {
@@ -1080,7 +1093,7 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
             wt.pool.helpQuiescePool(wt.workQueue);
         }
         else
-            ForkJoinPool.externalHelpQuiescePool();
+            ForkJoinPool.quiesceCommonPool();
     }
 
     /**
@@ -1145,7 +1158,7 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
         Thread t;
         return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
                 ((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
-                ForkJoinPool.tryExternalUnpush(this));
+                ForkJoinPool.common.tryExternalUnpush(this));
     }
 
     /**
@@ -1316,7 +1329,7 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
      *
      * @param e the expected tag value
      * @param tag the new tag value
-     * @return true if successful; i.e., the current value was
+     * @return {@code true} if successful; i.e., the current value was
      * equal to e and is now tag.
      * @since 1.8
      * @hide
@@ -1370,6 +1383,24 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
     }
 
     /**
+     * Adaptor for Runnables in which failure forces worker exception
+     */
+    static final class RunnableExecuteAction extends ForkJoinTask<Void> {
+        final Runnable runnable;
+        RunnableExecuteAction(Runnable runnable) {
+            if (runnable == null) throw new NullPointerException();
+            this.runnable = runnable;
+        }
+        public final Void getRawResult() { return null; }
+        public final void setRawResult(Void v) { }
+        public final boolean exec() { runnable.run(); return true; }
+        void internalPropagateException(Throwable ex) {
+            rethrow(ex); // rethrow outside exec() catches.
+        }
+        private static final long serialVersionUID = 5232453952276885070L;
+    }
+
+    /**
      * Adaptor for Callables
      */
     static final class AdaptedCallable<T> extends ForkJoinTask<T>
@@ -1480,5 +1511,4 @@ public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
             throw new Error(e);
         }
     }
-
 }
diff --git a/luni/src/main/java/java/util/concurrent/ForkJoinWorkerThread.java b/luni/src/main/java/java/util/concurrent/ForkJoinWorkerThread.java
index f31763c..5f2799b 100644
--- a/luni/src/main/java/java/util/concurrent/ForkJoinWorkerThread.java
+++ b/luni/src/main/java/java/util/concurrent/ForkJoinWorkerThread.java
@@ -14,8 +14,8 @@ package java.util.concurrent;
  * scheduling or execution.  However, you can override initialization
  * and termination methods surrounding the main task processing loop.
  * If you do create such a subclass, you will also need to supply a
- * custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to use it
- * in a {@code ForkJoinPool}.
+ * custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to
+ * {@linkplain ForkJoinPool#ForkJoinPool use it} in a {@code ForkJoinPool}.
  *
  * @since 1.7
  * @hide
@@ -61,16 +61,17 @@ public class ForkJoinWorkerThread extends Thread {
     }
 
     /**
-     * Returns the index number of this thread in its pool.  The
-     * returned value ranges from zero to the maximum number of
-     * threads (minus one) that have ever been created in the pool.
-     * This method may be useful for applications that track status or
-     * collect results per-worker rather than per-task.
+     * Returns the unique index number of this thread in its pool.
+     * The returned value ranges from zero to the maximum number of
+     * threads (minus one) that may exist in the pool, and does not
+     * change during the lifetime of the thread.  This method may be
+     * useful for applications that track status or collect results
+     * per-worker-thread rather than per-task.
      *
      * @return the index number
      */
     public int getPoolIndex() {
-        return workQueue.poolIndex;
+        return workQueue.poolIndex >>> 1; // ignore odd/even tag bit
     }
 
     /**