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-rw-r--r--luni/src/main/java/java/util/concurrent/ArrayBlockingQueue.java849
1 files changed, 709 insertions, 140 deletions
diff --git a/luni/src/main/java/java/util/concurrent/ArrayBlockingQueue.java b/luni/src/main/java/java/util/concurrent/ArrayBlockingQueue.java
index a622832..e30ab67 100644
--- a/luni/src/main/java/java/util/concurrent/ArrayBlockingQueue.java
+++ b/luni/src/main/java/java/util/concurrent/ArrayBlockingQueue.java
@@ -1,12 +1,17 @@
/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
- * http://creativecommons.org/licenses/publicdomain
+ * http://creativecommons.org/publicdomain/zero/1.0/
*/
package java.util.concurrent;
-import java.util.concurrent.locks.*;
-import java.util.*;
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.ReentrantLock;
+import java.util.AbstractQueue;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import java.lang.ref.WeakReference;
// BEGIN android-note
// removed link to collections framework docs
@@ -73,11 +78,20 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
/** Main lock guarding all access */
final ReentrantLock lock;
+
/** Condition for waiting takes */
private final Condition notEmpty;
+
/** Condition for waiting puts */
private final Condition notFull;
+ /**
+ * Shared state for currently active iterators, or null if there
+ * are known not to be any. Allows queue operations to update
+ * iterator state.
+ */
+ transient Itrs itrs = null;
+
// Internal helper methods
/**
@@ -94,16 +108,12 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
return ((i == 0) ? items.length : i) - 1;
}
- @SuppressWarnings("unchecked")
- static <E> E cast(Object item) {
- return (E) item;
- }
-
/**
* Returns item at index i.
*/
final E itemAt(int i) {
- return this.<E>cast(items[i]);
+ @SuppressWarnings("unchecked") E x = (E) items[i];
+ return x;
}
/**
@@ -120,10 +130,12 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
* Inserts element at current put position, advances, and signals.
* Call only when holding lock.
*/
- private void insert(E x) {
+ private void enqueue(E x) {
+ // assert lock.getHoldCount() == 1;
+ // assert items[putIndex] == null;
items[putIndex] = x;
putIndex = inc(putIndex);
- ++count;
+ count++;
notEmpty.signal();
}
@@ -131,42 +143,57 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
* Extracts element at current take position, advances, and signals.
* Call only when holding lock.
*/
- private E extract() {
+ private E dequeue() {
+ // assert lock.getHoldCount() == 1;
+ // assert items[takeIndex] != null;
final Object[] items = this.items;
- E x = this.<E>cast(items[takeIndex]);
+ @SuppressWarnings("unchecked") E x = (E) items[takeIndex];
items[takeIndex] = null;
takeIndex = inc(takeIndex);
- --count;
+ count--;
+ if (itrs != null)
+ itrs.elementDequeued();
notFull.signal();
return x;
}
/**
- * Deletes item at position i.
- * Utility for remove and iterator.remove.
+ * Deletes item at array index removeIndex.
+ * Utility for remove(Object) and iterator.remove.
* Call only when holding lock.
*/
- void removeAt(int i) {
+ void removeAt(final int removeIndex) {
+ // assert lock.getHoldCount() == 1;
+ // assert items[removeIndex] != null;
+ // assert removeIndex >= 0 && removeIndex < items.length;
final Object[] items = this.items;
- // if removing front item, just advance
- if (i == takeIndex) {
+ if (removeIndex == takeIndex) {
+ // removing front item; just advance
items[takeIndex] = null;
takeIndex = inc(takeIndex);
+ count--;
+ if (itrs != null)
+ itrs.elementDequeued();
} else {
+ // an "interior" remove
+
// slide over all others up through putIndex.
- for (;;) {
- int nexti = inc(i);
- if (nexti != putIndex) {
- items[i] = items[nexti];
- i = nexti;
+ final int putIndex = this.putIndex;
+ for (int i = removeIndex;;) {
+ int next = inc(i);
+ if (next != putIndex) {
+ items[i] = items[next];
+ i = next;
} else {
items[i] = null;
- putIndex = i;
+ this.putIndex = i;
break;
}
}
+ count--;
+ if (itrs != null)
+ itrs.removedAt(removeIndex);
}
- --count;
notFull.signal();
}
@@ -271,7 +298,7 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
if (count == items.length)
return false;
else {
- insert(e);
+ enqueue(e);
return true;
}
} finally {
@@ -293,7 +320,7 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
try {
while (count == items.length)
notFull.await();
- insert(e);
+ enqueue(e);
} finally {
lock.unlock();
}
@@ -320,7 +347,7 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
return false;
nanos = notFull.awaitNanos(nanos);
}
- insert(e);
+ enqueue(e);
return true;
} finally {
lock.unlock();
@@ -331,7 +358,7 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
final ReentrantLock lock = this.lock;
lock.lock();
try {
- return (count == 0) ? null : extract();
+ return (count == 0) ? null : dequeue();
} finally {
lock.unlock();
}
@@ -343,7 +370,7 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
try {
while (count == 0)
notEmpty.await();
- return extract();
+ return dequeue();
} finally {
lock.unlock();
}
@@ -359,7 +386,7 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
return null;
nanos = notEmpty.awaitNanos(nanos);
}
- return extract();
+ return dequeue();
} finally {
lock.unlock();
}
@@ -438,11 +465,15 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
final ReentrantLock lock = this.lock;
lock.lock();
try {
- for (int i = takeIndex, k = count; k > 0; i = inc(i), k--) {
- if (o.equals(items[i])) {
- removeAt(i);
- return true;
- }
+ if (count > 0) {
+ final int putIndex = this.putIndex;
+ int i = takeIndex;
+ do {
+ if (o.equals(items[i])) {
+ removeAt(i);
+ return true;
+ }
+ } while ((i = inc(i)) != putIndex);
}
return false;
} finally {
@@ -464,9 +495,14 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
final ReentrantLock lock = this.lock;
lock.lock();
try {
- for (int i = takeIndex, k = count; k > 0; i = inc(i), k--)
- if (o.equals(items[i]))
- return true;
+ if (count > 0) {
+ final int putIndex = this.putIndex;
+ int i = takeIndex;
+ do {
+ if (o.equals(items[i]))
+ return true;
+ } while ((i = inc(i)) != putIndex);
+ }
return false;
} finally {
lock.unlock();
@@ -522,8 +558,7 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
* The following code can be used to dump the queue into a newly
* allocated array of {@code String}:
*
- * <pre>
- * String[] y = x.toArray(new String[0]);</pre>
+ * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
*
* Note that {@code toArray(new Object[0])} is identical in function to
* {@code toArray()}.
@@ -589,12 +624,20 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
final ReentrantLock lock = this.lock;
lock.lock();
try {
- for (int i = takeIndex, k = count; k > 0; i = inc(i), k--)
- items[i] = null;
- count = 0;
- putIndex = 0;
- takeIndex = 0;
- notFull.signalAll();
+ int k = count;
+ if (k > 0) {
+ final int putIndex = this.putIndex;
+ int i = takeIndex;
+ do {
+ items[i] = null;
+ } while ((i = inc(i)) != putIndex);
+ takeIndex = putIndex;
+ count = 0;
+ if (itrs != null)
+ itrs.queueIsEmpty();
+ for (; k > 0 && lock.hasWaiters(notFull); k--)
+ notFull.signal();
+ }
} finally {
lock.unlock();
}
@@ -607,32 +650,7 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
* @throws IllegalArgumentException {@inheritDoc}
*/
public int drainTo(Collection<? super E> c) {
- checkNotNull(c);
- if (c == this)
- throw new IllegalArgumentException();
- final Object[] items = this.items;
- final ReentrantLock lock = this.lock;
- lock.lock();
- try {
- int i = takeIndex;
- int n = 0;
- int max = count;
- while (n < max) {
- c.add(this.<E>cast(items[i]));
- items[i] = null;
- i = inc(i);
- ++n;
- }
- if (n > 0) {
- count = 0;
- putIndex = 0;
- takeIndex = 0;
- notFull.signalAll();
- }
- return n;
- } finally {
- lock.unlock();
- }
+ return drainTo(c, Integer.MAX_VALUE);
}
/**
@@ -651,21 +669,33 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
final ReentrantLock lock = this.lock;
lock.lock();
try {
- int i = takeIndex;
- int n = 0;
- int max = (maxElements < count) ? maxElements : count;
- while (n < max) {
- c.add(this.<E>cast(items[i]));
- items[i] = null;
- i = inc(i);
- ++n;
- }
- if (n > 0) {
- count -= n;
- takeIndex = i;
- notFull.signalAll();
+ int n = Math.min(maxElements, count);
+ int take = takeIndex;
+ int i = 0;
+ try {
+ while (i < n) {
+ @SuppressWarnings("unchecked") E x = (E) items[take];
+ c.add(x);
+ items[take] = null;
+ take = inc(take);
+ i++;
+ }
+ return n;
+ } finally {
+ // Restore invariants even if c.add() threw
+ if (i > 0) {
+ count -= i;
+ takeIndex = take;
+ if (itrs != null) {
+ if (count == 0)
+ itrs.queueIsEmpty();
+ else if (i > take)
+ itrs.takeIndexWrapped();
+ }
+ for (; i > 0 && lock.hasWaiters(notFull); i--)
+ notFull.signal();
+ }
}
- return n;
} finally {
lock.unlock();
}
@@ -675,12 +705,12 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
* Returns an iterator over the elements in this queue in proper sequence.
* The elements will be returned in order from first (head) to last (tail).
*
- * <p>The returned {@code Iterator} is a "weakly consistent" iterator that
+ * <p>The returned iterator is a "weakly consistent" iterator that
* will never throw {@link java.util.ConcurrentModificationException
- * 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.
+ * 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 an iterator over the elements in this queue in proper sequence
*/
@@ -689,88 +719,627 @@ public class ArrayBlockingQueue<E> extends AbstractQueue<E>
}
/**
- * Iterator for ArrayBlockingQueue. To maintain weak consistency
- * with respect to puts and takes, we (1) read ahead one slot, so
- * as to not report hasNext true but then not have an element to
- * return -- however we later recheck this slot to use the most
- * current value; (2) ensure that each array slot is traversed at
- * most once (by tracking "remaining" elements); (3) skip over
- * null slots, which can occur if takes race ahead of iterators.
- * However, for circular array-based queues, we cannot rely on any
- * well established definition of what it means to be weakly
- * consistent with respect to interior removes since these may
- * require slot overwrites in the process of sliding elements to
- * cover gaps. So we settle for resiliency, operating on
- * established apparent nexts, which may miss some elements that
- * have moved between calls to next.
+ * Shared data between iterators and their queue, allowing queue
+ * modifications to update iterators when elements are removed.
+ *
+ * This adds a lot of complexity for the sake of correctly
+ * handling some uncommon operations, but the combination of
+ * circular-arrays and supporting interior removes (i.e., those
+ * not at head) would cause iterators to sometimes lose their
+ * places and/or (re)report elements they shouldn't. To avoid
+ * this, when a queue has one or more iterators, it keeps iterator
+ * state consistent by:
+ *
+ * (1) keeping track of the number of "cycles", that is, the
+ * number of times takeIndex has wrapped around to 0.
+ * (2) notifying all iterators via the callback removedAt whenever
+ * an interior element is removed (and thus other elements may
+ * be shifted).
+ *
+ * These suffice to eliminate iterator inconsistencies, but
+ * unfortunately add the secondary responsibility of maintaining
+ * the list of iterators. We track all active iterators in a
+ * simple linked list (accessed only when the queue's lock is
+ * held) of weak references to Itr. The list is cleaned up using
+ * 3 different mechanisms:
+ *
+ * (1) Whenever a new iterator is created, do some O(1) checking for
+ * stale list elements.
+ *
+ * (2) Whenever takeIndex wraps around to 0, check for iterators
+ * that have been unused for more than one wrap-around cycle.
+ *
+ * (3) Whenever the queue becomes empty, all iterators are notified
+ * and this entire data structure is discarded.
+ *
+ * So in addition to the removedAt callback that is necessary for
+ * correctness, iterators have the shutdown and takeIndexWrapped
+ * callbacks that help remove stale iterators from the list.
+ *
+ * Whenever a list element is examined, it is expunged if either
+ * the GC has determined that the iterator is discarded, or if the
+ * iterator reports that it is "detached" (does not need any
+ * further state updates). Overhead is maximal when takeIndex
+ * never advances, iterators are discarded before they are
+ * exhausted, and all removals are interior removes, in which case
+ * all stale iterators are discovered by the GC. But even in this
+ * case we don't increase the amortized complexity.
+ *
+ * Care must be taken to keep list sweeping methods from
+ * reentrantly invoking another such method, causing subtle
+ * corruption bugs.
+ */
+ class Itrs {
+
+ /**
+ * Node in a linked list of weak iterator references.
+ */
+ private class Node extends WeakReference<Itr> {
+ Node next;
+
+ Node(Itr iterator, Node next) {
+ super(iterator);
+ this.next = next;
+ }
+ }
+
+ /** Incremented whenever takeIndex wraps around to 0 */
+ int cycles = 0;
+
+ /** Linked list of weak iterator references */
+ private Node head;
+
+ /** Used to expunge stale iterators */
+ private Node sweeper = null;
+
+ private static final int SHORT_SWEEP_PROBES = 4;
+ private static final int LONG_SWEEP_PROBES = 16;
+
+ Itrs(Itr initial) {
+ register(initial);
+ }
+
+ /**
+ * Sweeps itrs, looking for and expunging stale iterators.
+ * If at least one was found, tries harder to find more.
+ * Called only from iterating thread.
+ *
+ * @param tryHarder whether to start in try-harder mode, because
+ * there is known to be at least one iterator to collect
+ */
+ void doSomeSweeping(boolean tryHarder) {
+ // assert lock.getHoldCount() == 1;
+ // assert head != null;
+ int probes = tryHarder ? LONG_SWEEP_PROBES : SHORT_SWEEP_PROBES;
+ Node o, p;
+ final Node sweeper = this.sweeper;
+ boolean passedGo; // to limit search to one full sweep
+
+ if (sweeper == null) {
+ o = null;
+ p = head;
+ passedGo = true;
+ } else {
+ o = sweeper;
+ p = o.next;
+ passedGo = false;
+ }
+
+ for (; probes > 0; probes--) {
+ if (p == null) {
+ if (passedGo)
+ break;
+ o = null;
+ p = head;
+ passedGo = true;
+ }
+ final Itr it = p.get();
+ final Node next = p.next;
+ if (it == null || it.isDetached()) {
+ // found a discarded/exhausted iterator
+ probes = LONG_SWEEP_PROBES; // "try harder"
+ // unlink p
+ p.clear();
+ p.next = null;
+ if (o == null) {
+ head = next;
+ if (next == null) {
+ // We've run out of iterators to track; retire
+ itrs = null;
+ return;
+ }
+ }
+ else
+ o.next = next;
+ } else {
+ o = p;
+ }
+ p = next;
+ }
+
+ this.sweeper = (p == null) ? null : o;
+ }
+
+ /**
+ * Adds a new iterator to the linked list of tracked iterators.
+ */
+ void register(Itr itr) {
+ // assert lock.getHoldCount() == 1;
+ head = new Node(itr, head);
+ }
+
+ /**
+ * Called whenever takeIndex wraps around to 0.
+ *
+ * Notifies all iterators, and expunges any that are now stale.
+ */
+ void takeIndexWrapped() {
+ // assert lock.getHoldCount() == 1;
+ cycles++;
+ for (Node o = null, p = head; p != null;) {
+ final Itr it = p.get();
+ final Node next = p.next;
+ if (it == null || it.takeIndexWrapped()) {
+ // unlink p
+ // assert it == null || it.isDetached();
+ p.clear();
+ p.next = null;
+ if (o == null)
+ head = next;
+ else
+ o.next = next;
+ } else {
+ o = p;
+ }
+ p = next;
+ }
+ if (head == null) // no more iterators to track
+ itrs = null;
+ }
+
+ /**
+ * Called whenever an interior remove (not at takeIndex) occured.
+ *
+ * Notifies all iterators, and expunges any that are now stale.
+ */
+ void removedAt(int removedIndex) {
+ for (Node o = null, p = head; p != null;) {
+ final Itr it = p.get();
+ final Node next = p.next;
+ if (it == null || it.removedAt(removedIndex)) {
+ // unlink p
+ // assert it == null || it.isDetached();
+ p.clear();
+ p.next = null;
+ if (o == null)
+ head = next;
+ else
+ o.next = next;
+ } else {
+ o = p;
+ }
+ p = next;
+ }
+ if (head == null) // no more iterators to track
+ itrs = null;
+ }
+
+ /**
+ * Called whenever the queue becomes empty.
+ *
+ * Notifies all active iterators that the queue is empty,
+ * clears all weak refs, and unlinks the itrs datastructure.
+ */
+ void queueIsEmpty() {
+ // assert lock.getHoldCount() == 1;
+ for (Node p = head; p != null; p = p.next) {
+ Itr it = p.get();
+ if (it != null) {
+ p.clear();
+ it.shutdown();
+ }
+ }
+ head = null;
+ itrs = null;
+ }
+
+ /**
+ * Called whenever an element has been dequeued (at takeIndex).
+ */
+ void elementDequeued() {
+ // assert lock.getHoldCount() == 1;
+ if (count == 0)
+ queueIsEmpty();
+ else if (takeIndex == 0)
+ takeIndexWrapped();
+ }
+ }
+
+ /**
+ * Iterator for ArrayBlockingQueue.
+ *
+ * To maintain weak consistency with respect to puts and takes, we
+ * read ahead one slot, so as to not report hasNext true but then
+ * not have an element to return.
+ *
+ * We switch into "detached" mode (allowing prompt unlinking from
+ * itrs without help from the GC) when all indices are negative, or
+ * when hasNext returns false for the first time. This allows the
+ * iterator to track concurrent updates completely accurately,
+ * except for the corner case of the user calling Iterator.remove()
+ * after hasNext() returned false. Even in this case, we ensure
+ * that we don't remove the wrong element by keeping track of the
+ * expected element to remove, in lastItem. Yes, we may fail to
+ * remove lastItem from the queue if it moved due to an interleaved
+ * interior remove while in detached mode.
*/
private class Itr implements Iterator<E> {
- private int remaining; // Number of elements yet to be returned
- private int nextIndex; // Index of element to be returned by next
- private E nextItem; // Element to be returned by next call to next
- private E lastItem; // Element returned by last call to next
- private int lastRet; // Index of last element returned, or -1 if none
+ /** Index to look for new nextItem; NONE at end */
+ private int cursor;
+
+ /** Element to be returned by next call to next(); null if none */
+ private E nextItem;
+
+ /** Index of nextItem; NONE if none, REMOVED if removed elsewhere */
+ private int nextIndex;
+
+ /** Last element returned; null if none or not detached. */
+ private E lastItem;
+
+ /** Index of lastItem, NONE if none, REMOVED if removed elsewhere */
+ private int lastRet;
+
+ /** Previous value of takeIndex, or DETACHED when detached */
+ private int prevTakeIndex;
+
+ /** Previous value of iters.cycles */
+ private int prevCycles;
+
+ /** Special index value indicating "not available" or "undefined" */
+ private static final int NONE = -1;
+
+ /**
+ * Special index value indicating "removed elsewhere", that is,
+ * removed by some operation other than a call to this.remove().
+ */
+ private static final int REMOVED = -2;
+
+ /** Special value for prevTakeIndex indicating "detached mode" */
+ private static final int DETACHED = -3;
Itr() {
+ // assert lock.getHoldCount() == 0;
+ lastRet = NONE;
final ReentrantLock lock = ArrayBlockingQueue.this.lock;
lock.lock();
try {
- lastRet = -1;
- if ((remaining = count) > 0)
+ if (count == 0) {
+ // assert itrs == null;
+ cursor = NONE;
+ nextIndex = NONE;
+ prevTakeIndex = DETACHED;
+ } else {
+ final int takeIndex = ArrayBlockingQueue.this.takeIndex;
+ prevTakeIndex = takeIndex;
nextItem = itemAt(nextIndex = takeIndex);
+ cursor = incCursor(takeIndex);
+ if (itrs == null) {
+ itrs = new Itrs(this);
+ } else {
+ itrs.register(this); // in this order
+ itrs.doSomeSweeping(false);
+ }
+ prevCycles = itrs.cycles;
+ // assert takeIndex >= 0;
+ // assert prevTakeIndex == takeIndex;
+ // assert nextIndex >= 0;
+ // assert nextItem != null;
+ }
} finally {
lock.unlock();
}
}
+ boolean isDetached() {
+ // assert lock.getHoldCount() == 1;
+ return prevTakeIndex < 0;
+ }
+
+ private int incCursor(int index) {
+ // assert lock.getHoldCount() == 1;
+ index = inc(index);
+ if (index == putIndex)
+ index = NONE;
+ return index;
+ }
+
+ /**
+ * Returns true if index is invalidated by the given number of
+ * dequeues, starting from prevTakeIndex.
+ */
+ private boolean invalidated(int index, int prevTakeIndex,
+ long dequeues, int length) {
+ if (index < 0)
+ return false;
+ int distance = index - prevTakeIndex;
+ if (distance < 0)
+ distance += length;
+ return dequeues > distance;
+ }
+
+ /**
+ * Adjusts indices to incorporate all dequeues since the last
+ * operation on this iterator. Call only from iterating thread.
+ */
+ private void incorporateDequeues() {
+ // assert lock.getHoldCount() == 1;
+ // assert itrs != null;
+ // assert !isDetached();
+ // assert count > 0;
+
+ final int cycles = itrs.cycles;
+ final int takeIndex = ArrayBlockingQueue.this.takeIndex;
+ final int prevCycles = this.prevCycles;
+ final int prevTakeIndex = this.prevTakeIndex;
+
+ if (cycles != prevCycles || takeIndex != prevTakeIndex) {
+ final int len = items.length;
+ // how far takeIndex has advanced since the previous
+ // operation of this iterator
+ long dequeues = (cycles - prevCycles) * len
+ + (takeIndex - prevTakeIndex);
+
+ // Check indices for invalidation
+ if (invalidated(lastRet, prevTakeIndex, dequeues, len))
+ lastRet = REMOVED;
+ if (invalidated(nextIndex, prevTakeIndex, dequeues, len))
+ nextIndex = REMOVED;
+ if (invalidated(cursor, prevTakeIndex, dequeues, len))
+ cursor = takeIndex;
+
+ if (cursor < 0 && nextIndex < 0 && lastRet < 0)
+ detach();
+ else {
+ this.prevCycles = cycles;
+ this.prevTakeIndex = takeIndex;
+ }
+ }
+ }
+
+ /**
+ * Called when itrs should stop tracking this iterator, either
+ * because there are no more indices to update (cursor < 0 &&
+ * nextIndex < 0 && lastRet < 0) or as a special exception, when
+ * lastRet >= 0, because hasNext() is about to return false for the
+ * first time. Call only from iterating thread.
+ */
+ private void detach() {
+ // Switch to detached mode
+ // assert lock.getHoldCount() == 1;
+ // assert cursor == NONE;
+ // assert nextIndex < 0;
+ // assert lastRet < 0 || nextItem == null;
+ // assert lastRet < 0 ^ lastItem != null;
+ if (prevTakeIndex >= 0) {
+ // assert itrs != null;
+ prevTakeIndex = DETACHED;
+ // try to unlink from itrs (but not too hard)
+ itrs.doSomeSweeping(true);
+ }
+ }
+
+ /**
+ * For performance reasons, we would like not to acquire a lock in
+ * hasNext in the common case. To allow for this, we only access
+ * fields (i.e. nextItem) that are not modified by update operations
+ * triggered by queue modifications.
+ */
public boolean hasNext() {
- return remaining > 0;
+ // assert lock.getHoldCount() == 0;
+ if (nextItem != null)
+ return true;
+ noNext();
+ return false;
+ }
+
+ private void noNext() {
+ final ReentrantLock lock = ArrayBlockingQueue.this.lock;
+ lock.lock();
+ try {
+ // assert cursor == NONE;
+ // assert nextIndex == NONE;
+ if (!isDetached()) {
+ // assert lastRet >= 0;
+ incorporateDequeues(); // might update lastRet
+ if (lastRet >= 0) {
+ lastItem = itemAt(lastRet);
+ // assert lastItem != null;
+ detach();
+ }
+ }
+ // assert isDetached();
+ // assert lastRet < 0 ^ lastItem != null;
+ } finally {
+ lock.unlock();
+ }
}
public E next() {
+ // assert lock.getHoldCount() == 0;
+ final E x = nextItem;
+ if (x == null)
+ throw new NoSuchElementException();
final ReentrantLock lock = ArrayBlockingQueue.this.lock;
lock.lock();
try {
- if (remaining <= 0)
- throw new NoSuchElementException();
+ if (!isDetached())
+ incorporateDequeues();
+ // assert nextIndex != NONE;
+ // assert lastItem == null;
lastRet = nextIndex;
- E x = itemAt(nextIndex); // check for fresher value
- if (x == null) {
- x = nextItem; // we are forced to report old value
- lastItem = null; // but ensure remove fails
+ final int cursor = this.cursor;
+ if (cursor >= 0) {
+ nextItem = itemAt(nextIndex = cursor);
+ // assert nextItem != null;
+ this.cursor = incCursor(cursor);
+ } else {
+ nextIndex = NONE;
+ nextItem = null;
}
- else
- lastItem = x;
- while (--remaining > 0 && // skip over nulls
- (nextItem = itemAt(nextIndex = inc(nextIndex))) == null)
- ;
- return x;
} finally {
lock.unlock();
}
+ return x;
}
public void remove() {
+ // assert lock.getHoldCount() == 0;
final ReentrantLock lock = ArrayBlockingQueue.this.lock;
lock.lock();
try {
- int i = lastRet;
- if (i == -1)
+ if (!isDetached())
+ incorporateDequeues(); // might update lastRet or detach
+ final int lastRet = this.lastRet;
+ this.lastRet = NONE;
+ if (lastRet >= 0) {
+ if (!isDetached())
+ removeAt(lastRet);
+ else {
+ final E lastItem = this.lastItem;
+ // assert lastItem != null;
+ this.lastItem = null;
+ if (itemAt(lastRet) == lastItem)
+ removeAt(lastRet);
+ }
+ } else if (lastRet == NONE)
throw new IllegalStateException();
- lastRet = -1;
- E x = lastItem;
- lastItem = null;
- // only remove if item still at index
- if (x != null && x == items[i]) {
- boolean removingHead = (i == takeIndex);
- removeAt(i);
- if (!removingHead)
- nextIndex = dec(nextIndex);
- }
+ // else lastRet == REMOVED and the last returned element was
+ // previously asynchronously removed via an operation other
+ // than this.remove(), so nothing to do.
+
+ if (cursor < 0 && nextIndex < 0)
+ detach();
} finally {
lock.unlock();
+ // assert lastRet == NONE;
+ // assert lastItem == null;
}
}
- }
+ /**
+ * Called to notify the iterator that the queue is empty, or that it
+ * has fallen hopelessly behind, so that it should abandon any
+ * further iteration, except possibly to return one more element
+ * from next(), as promised by returning true from hasNext().
+ */
+ void shutdown() {
+ // assert lock.getHoldCount() == 1;
+ cursor = NONE;
+ if (nextIndex >= 0)
+ nextIndex = REMOVED;
+ if (lastRet >= 0) {
+ lastRet = REMOVED;
+ lastItem = null;
+ }
+ prevTakeIndex = DETACHED;
+ // Don't set nextItem to null because we must continue to be
+ // able to return it on next().
+ //
+ // Caller will unlink from itrs when convenient.
+ }
+
+ private int distance(int index, int prevTakeIndex, int length) {
+ int distance = index - prevTakeIndex;
+ if (distance < 0)
+ distance += length;
+ return distance;
+ }
+
+ /**
+ * Called whenever an interior remove (not at takeIndex) occured.
+ *
+ * @return true if this iterator should be unlinked from itrs
+ */
+ boolean removedAt(int removedIndex) {
+ // assert lock.getHoldCount() == 1;
+ if (isDetached())
+ return true;
+
+ final int cycles = itrs.cycles;
+ final int takeIndex = ArrayBlockingQueue.this.takeIndex;
+ final int prevCycles = this.prevCycles;
+ final int prevTakeIndex = this.prevTakeIndex;
+ final int len = items.length;
+ int cycleDiff = cycles - prevCycles;
+ if (removedIndex < takeIndex)
+ cycleDiff++;
+ final int removedDistance =
+ (cycleDiff * len) + (removedIndex - prevTakeIndex);
+ // assert removedDistance >= 0;
+ int cursor = this.cursor;
+ if (cursor >= 0) {
+ int x = distance(cursor, prevTakeIndex, len);
+ if (x == removedDistance) {
+ if (cursor == putIndex)
+ this.cursor = cursor = NONE;
+ }
+ else if (x > removedDistance) {
+ // assert cursor != prevTakeIndex;
+ this.cursor = cursor = dec(cursor);
+ }
+ }
+ int lastRet = this.lastRet;
+ if (lastRet >= 0) {
+ int x = distance(lastRet, prevTakeIndex, len);
+ if (x == removedDistance)
+ this.lastRet = lastRet = REMOVED;
+ else if (x > removedDistance)
+ this.lastRet = lastRet = dec(lastRet);
+ }
+ int nextIndex = this.nextIndex;
+ if (nextIndex >= 0) {
+ int x = distance(nextIndex, prevTakeIndex, len);
+ if (x == removedDistance)
+ this.nextIndex = nextIndex = REMOVED;
+ else if (x > removedDistance)
+ this.nextIndex = nextIndex = dec(nextIndex);
+ }
+ else if (cursor < 0 && nextIndex < 0 && lastRet < 0) {
+ this.prevTakeIndex = DETACHED;
+ return true;
+ }
+ return false;
+ }
+
+ /**
+ * Called whenever takeIndex wraps around to zero.
+ *
+ * @return true if this iterator should be unlinked from itrs
+ */
+ boolean takeIndexWrapped() {
+ // assert lock.getHoldCount() == 1;
+ if (isDetached())
+ return true;
+ if (itrs.cycles - prevCycles > 1) {
+ // All the elements that existed at the time of the last
+ // operation are gone, so abandon further iteration.
+ shutdown();
+ return true;
+ }
+ return false;
+ }
+
+// /** Uncomment for debugging. */
+// public String toString() {
+// return ("cursor=" + cursor + " " +
+// "nextIndex=" + nextIndex + " " +
+// "lastRet=" + lastRet + " " +
+// "nextItem=" + nextItem + " " +
+// "lastItem=" + lastItem + " " +
+// "prevCycles=" + prevCycles + " " +
+// "prevTakeIndex=" + prevTakeIndex + " " +
+// "size()=" + size() + " " +
+// "remainingCapacity()=" + remainingCapacity());
+// }
+ }
}
generated by cgit v1.1 at 2024-05-29 00:12:50 +0000