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Diffstat (limited to 'luni/src/main/java/java/util/concurrent/ForkJoinPool.java')
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diff --git a/luni/src/main/java/java/util/concurrent/ForkJoinPool.java b/luni/src/main/java/java/util/concurrent/ForkJoinPool.java new file mode 100644 index 0000000..ee15ac8 --- /dev/null +++ b/luni/src/main/java/java/util/concurrent/ForkJoinPool.java @@ -0,0 +1,2127 @@ +/* + * 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/publicdomain/zero/1.0/ + */ + +package java.util.concurrent; + +import java.util.ArrayList; +import java.util.Arrays; +import java.util.Collection; +import java.util.Collections; +import java.util.List; +import java.util.Random; +import java.util.concurrent.AbstractExecutorService; +import java.util.concurrent.Callable; +import java.util.concurrent.ExecutorService; +import java.util.concurrent.Future; +import java.util.concurrent.RejectedExecutionException; +import java.util.concurrent.RunnableFuture; +import java.util.concurrent.TimeUnit; +import java.util.concurrent.atomic.AtomicInteger; +import java.util.concurrent.locks.LockSupport; +import java.util.concurrent.locks.ReentrantLock; +import java.util.concurrent.locks.Condition; +import libcore.util.SneakyThrow; + +// BEGIN android-note +// removed security manager docs +// END android-note + +/** + * An {@link ExecutorService} for running {@link ForkJoinTask}s. + * A {@code ForkJoinPool} provides the entry point for submissions + * from non-{@code ForkJoinTask} clients, as well as management and + * monitoring operations. + * + * <p>A {@code ForkJoinPool} differs from other kinds of {@link + * ExecutorService} mainly by virtue of employing + * <em>work-stealing</em>: all threads in the pool attempt to find and + * execute subtasks created by other active tasks (eventually blocking + * waiting for work if none exist). This enables efficient processing + * when most tasks spawn other subtasks (as do most {@code + * ForkJoinTask}s). When setting <em>asyncMode</em> to true in + * constructors, {@code ForkJoinPool}s may also be appropriate for use + * with event-style tasks that are never joined. + * + * <p>A {@code ForkJoinPool} is constructed with a given target + * parallelism 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 IO or other unmanaged synchronization. The nested + * {@link ManagedBlocker} interface enables extension of the kinds of + * synchronization accommodated. + * + * <p>In addition to execution and lifecycle control methods, this + * class provides status check methods (for example + * {@link #getStealCount}) that are intended to aid in developing, + * tuning, and monitoring fork/join applications. Also, method + * {@link #toString} returns indications of pool state in a + * convenient form for informal monitoring. + * + * <p> As is the case with other ExecutorServices, there are three + * main task execution methods summarized in the following + * table. These are designed to be used by clients not already engaged + * in fork/join computations in the current pool. The main forms of + * these methods accept instances of {@code ForkJoinTask}, but + * overloaded forms also allow mixed execution of plain {@code + * Runnable}- or {@code Callable}- based activities as well. However, + * tasks that are already executing in a pool should normally + * <em>NOT</em> use these pool execution methods, but instead use the + * within-computation forms listed in the table. + * + * <table BORDER CELLPADDING=3 CELLSPACING=1> + * <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> {@link #execute(ForkJoinTask)}</td> + * <td> {@link ForkJoinTask#fork}</td> + * </tr> + * <tr> + * <td> <b>Await and obtain result</td> + * <td> {@link #invoke(ForkJoinTask)}</td> + * <td> {@link ForkJoinTask#invoke}</td> + * </tr> + * <tr> + * <td> <b>Arrange exec and obtain Future</td> + * <td> {@link #submit(ForkJoinTask)}</td> + * <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td> + * </tr> + * </table> + * + * <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is + * used for all parallel task execution in a program or subsystem. + * Otherwise, use would not usually outweigh the construction and + * bookkeeping overhead of creating a large set of threads. For + * example, a common pool could be used for the {@code SortTasks} + * illustrated in {@link RecursiveAction}. Because {@code + * ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon + * daemon} mode, there is typically no need to explicitly {@link + * #shutdown} such a pool upon program exit. + * + * <pre> {@code + * static final ForkJoinPool mainPool = new ForkJoinPool(); + * ... + * public void sort(long[] array) { + * mainPool.invoke(new SortTask(array, 0, array.length)); + * }}</pre> + * + * <p><b>Implementation notes</b>: This implementation restricts the + * maximum number of running threads to 32767. Attempts to create + * pools with greater than the maximum number result in + * {@code IllegalArgumentException}. + * + * <p>This implementation rejects submitted tasks (that is, by throwing + * {@link RejectedExecutionException}) only when the pool is shut down + * or internal resources have been exhausted. + * + * @since 1.7 + * @hide + * @author Doug Lea + */ +public class ForkJoinPool extends AbstractExecutorService { + + /* + * Implementation Overview + * + * This class provides the central bookkeeping and control for a + * set of worker threads: Submissions from non-FJ threads enter + * into a submission queue. Workers take these tasks and typically + * split them into subtasks that may be stolen by other workers. + * Preference rules give first priority to processing tasks from + * their own queues (LIFO or FIFO, depending on mode), then to + * randomized FIFO steals of tasks in other worker queues, and + * lastly to new submissions. + * + * The main throughput advantages of work-stealing stem from + * decentralized control -- workers mostly take tasks from + * themselves or each other. We cannot negate this in the + * implementation of other management responsibilities. The main + * tactic for avoiding bottlenecks is packing nearly all + * essentially atomic control state into a single 64bit volatile + * variable ("ctl"). This variable is read on the order of 10-100 + * times as often as it is modified (always via CAS). (There is + * some additional control state, for example variable "shutdown" + * for which we can cope with uncoordinated updates.) This + * streamlines synchronization and control at the expense of messy + * constructions needed to repack status bits upon updates. + * Updates tend not to contend with each other except during + * bursts while submitted tasks begin or end. In some cases when + * they do contend, threads can instead do something else + * (usually, scan for tasks) until contention subsides. + * + * To enable packing, we restrict maximum parallelism to (1<<15)-1 + * (which is far in excess of normal operating range) to allow + * ids, counts, and their negations (used for thresholding) to fit + * into 16bit fields. + * + * Recording Workers. Workers are recorded in the "workers" array + * that is created upon pool construction and expanded if (rarely) + * necessary. This is an array as opposed to some other data + * structure to support index-based random steals by workers. + * Updates to the array recording new workers and unrecording + * terminated ones are protected from each other by a seqLock + * (scanGuard) but the array is otherwise concurrently readable, + * and accessed directly by workers. To simplify index-based + * operations, the array size is always a power of two, and all + * readers must tolerate null slots. To avoid flailing during + * start-up, the array is presized to hold twice #parallelism + * workers (which is unlikely to need further resizing during + * execution). But to avoid dealing with so many null slots, + * variable scanGuard includes a mask for the nearest power of two + * that contains all current workers. All worker thread creation + * is on-demand, triggered by task submissions, replacement of + * terminated workers, and/or compensation for blocked + * workers. However, all other support code is set up to work with + * other policies. To ensure that we do not hold on to worker + * references that would prevent GC, ALL accesses to workers are + * via indices into the workers array (which is one source of some + * of the messy code constructions here). In essence, the workers + * array serves as a weak reference mechanism. Thus for example + * the wait queue field of ctl stores worker indices, not worker + * references. Access to the workers in associated methods (for + * example signalWork) must both index-check and null-check the + * IDs. All such accesses ignore bad IDs by returning out early + * from what they are doing, since this can only be associated + * with termination, in which case it is OK to give up. + * + * All uses of the workers array, as well as queue arrays, check + * that the array is non-null (even if previously non-null). This + * allows nulling during termination, which is currently not + * necessary, but remains an option for resource-revocation-based + * shutdown schemes. + * + * Wait Queuing. Unlike HPC work-stealing frameworks, we cannot + * let workers spin indefinitely scanning for tasks when none can + * be found immediately, and we cannot start/resume workers unless + * there appear to be tasks available. On the other hand, we must + * quickly prod them into action when new tasks are submitted or + * generated. We park/unpark workers after placing in an event + * wait queue when they cannot find work. This "queue" is actually + * a simple Treiber stack, headed by the "id" field of ctl, plus a + * 15bit counter value to both wake up waiters (by advancing their + * count) and avoid ABA effects. Successors are held in worker + * field "nextWait". Queuing deals with several intrinsic races, + * mainly that a task-producing thread can miss seeing (and + * signalling) another thread that gave up looking for work but + * has not yet entered the wait queue. We solve this by requiring + * a full sweep of all workers both before (in scan()) and after + * (in tryAwaitWork()) 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 "parked" field of + * ForkJoinWorkerThread to reduce unnecessary calls to unpark. + * (Use of the parked field requires a secondary recheck to avoid + * missed signals.) + * + * 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. When a submission is added or another worker adds a + * task to a queue that previously had two or fewer tasks, they + * signal waiting workers (or trigger creation of new ones if + * fewer than the given parallelism level -- see signalWork). + * These primary signals are buttressed by signals during rescans + * as well as those performed when a worker steals a task and + * notices that there are more tasks too; together these cover the + * signals needed in cases when more than two tasks are pushed + * but untaken. + * + * Trimming workers. To release resources after periods of lack of + * use, a worker starting to wait when the pool is quiescent will + * time out and terminate if the pool has remained quiescent for + * SHRINK_RATE nanosecs. This will slowly propagate, eventually + * terminating all workers after long periods of non-use. + * + * Submissions. External submissions are maintained in an + * array-based queue that is structured identically to + * ForkJoinWorkerThread queues except for the use of + * submissionLock in method addSubmission. Unlike the case for + * worker queues, multiple external threads can add new + * submissions, so adding requires a lock. + * + * Compensation. Beyond work-stealing support and lifecycle + * control, the main responsibility of this framework is to take + * actions when one worker is waiting to join a task stolen (or + * always held by) another. Because we are multiplexing many + * tasks on to a pool of workers, we can't just let them block (as + * in Thread.join). We also cannot just reassign the joiner's + * run-time stack with another and replace it later, which would + * be a form of "continuation", that even if possible is not + * necessarily a good idea since we sometimes need both an + * unblocked task and its continuation to progress. Instead we + * combine two tactics: + * + * Helping: Arranging for the joiner to execute some task that it + * would be running if the steal had not occurred. Method + * ForkJoinWorkerThread.joinTask tracks joining->stealing + * links to try to find such a task. + * + * Compensating: Unless there are already enough live threads, + * method tryPreBlock() may create or re-activate a spare + * thread to compensate for blocked joiners until they + * unblock. + * + * The ManagedBlocker extension API can't use helping so relies + * only on compensation in method awaitBlocker. + * + * It is impossible to keep exactly the target parallelism number + * of threads running at any given time. Determining the + * existence of conservatively safe helping targets, the + * availability of already-created spares, and the apparent need + * to create new spares are all racy and require heuristic + * guidance, so we rely on multiple retries of each. Currently, + * in keeping with on-demand signalling policy, we compensate only + * if blocking would leave less than one active (non-waiting, + * non-blocked) worker. Additionally, to avoid some false alarms + * due to GC, lagging counters, system activity, etc, compensated + * blocking for joins is only attempted after rechecks stabilize + * (retries are interspersed with Thread.yield, for good + * citizenship). The variable blockedCount, incremented before + * blocking and decremented after, is sometimes needed to + * distinguish cases of waiting for work vs blocking on joins or + * other managed sync. Both cases are equivalent for most pool + * control, so we can update non-atomically. (Additionally, + * contention on blockedCount alleviates some contention on ctl). + * + * Shutdown and Termination. A call to shutdownNow atomically sets + * the ctl stop bit and then (non-atomically) sets each workers + * "terminate" status, cancels all unprocessed tasks, and wakes up + * all waiting workers. Detecting whether termination should + * commence after a non-abrupt shutdown() call requires more work + * and bookkeeping. We need consensus about quiescence (i.e., that + * there is no more work) which is reflected in active counts so + * long as there are no current blockers, as well as possible + * re-evaluations during independent changes in blocking or + * quiescing workers. + * + * Style notes: There is a lot of representation-level coupling + * among classes ForkJoinPool, ForkJoinWorkerThread, and + * ForkJoinTask. Most fields of ForkJoinWorkerThread maintain + * data structures managed by ForkJoinPool, so are directly + * accessed. Conversely we allow access to "workers" array by + * workers, and direct access to ForkJoinTask.status by both + * ForkJoinPool and ForkJoinWorkerThread. There is little point + * trying to reduce this, since any associated future changes in + * representations will need to be accompanied by algorithmic + * changes anyway. All together, these low-level implementation + * choices produce as much as a factor of 4 performance + * improvement compared to naive implementations, and enable the + * processing of billions of tasks per second, at the expense of + * some ugliness. + * + * Methods signalWork() and scan() are the main bottlenecks so are + * especially heavily micro-optimized/mangled. There are lots of + * inline assignments (of form "while ((local = field) != 0)") + * which are usually the simplest way to ensure the required read + * orderings (which are sometimes critical). This leads to a + * "C"-like style of listing declarations of these locals at the + * heads of methods or blocks. There are several occurrences of + * the unusual "do {} while (!cas...)" which is the simplest way + * to force an update of a CAS'ed variable. There are also other + * coding oddities that help some methods perform reasonably even + * when interpreted (not compiled). + * + * The order of declarations in this file is: (1) declarations of + * statics (2) fields (along with constants used when unpacking + * some of them), listed in an order that tends to reduce + * contention among them a bit under most JVMs. (3) internal + * control methods (4) callbacks and other support for + * ForkJoinTask and ForkJoinWorkerThread classes, (5) exported + * methods (plus a few little helpers). (6) static block + * initializing all statics in a minimally dependent order. + */ + + /** + * Factory for creating new {@link ForkJoinWorkerThread}s. + * A {@code ForkJoinWorkerThreadFactory} must be defined and used + * for {@code ForkJoinWorkerThread} subclasses that extend base + * functionality or initialize threads with different contexts. + */ + public static interface ForkJoinWorkerThreadFactory { + /** + * Returns a new worker thread operating in the given pool. + * + * @param pool the pool this thread works in + * @throws NullPointerException if the pool is null + */ + public ForkJoinWorkerThread newThread(ForkJoinPool pool); + } + + /** + * Default ForkJoinWorkerThreadFactory implementation; creates a + * new ForkJoinWorkerThread. + */ + static class DefaultForkJoinWorkerThreadFactory + implements ForkJoinWorkerThreadFactory { + public ForkJoinWorkerThread newThread(ForkJoinPool pool) { + return new ForkJoinWorkerThread(pool); + } + } + + /** + * 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. + */ + private static final RuntimePermission modifyThreadPermission; + + /** + * If there is a security manager, makes sure caller has + * permission to modify threads. + */ + private static void checkPermission() { + SecurityManager security = System.getSecurityManager(); + if (security != null) + security.checkPermission(modifyThreadPermission); + } + + /** + * Generator for assigning sequence numbers as pool names. + */ + private static final AtomicInteger poolNumberGenerator; + + /** + * Generator for initial random seeds for worker victim + * selection. This is used only to create initial seeds. Random + * steals use a cheaper xorshift generator per steal attempt. We + * don't expect much contention on seedGenerator, so just use a + * plain Random. + */ + static final Random workerSeedGenerator; + + /** + * Array holding all worker threads in the pool. Initialized upon + * construction. Array size must be a power of two. Updates and + * replacements are protected by scanGuard, but the array is + * always kept in a consistent enough state to be randomly + * accessed without locking by workers performing work-stealing, + * as well as other traversal-based methods in this class, so long + * as reads memory-acquire by first reading ctl. All readers must + * tolerate that some array slots may be null. + */ + ForkJoinWorkerThread[] workers; + + /** + * Initial size for submission queue array. Must be a power of + * two. In many applications, these always stay small so we use a + * small initial cap. + */ + private static final int INITIAL_QUEUE_CAPACITY = 8; + + /** + * Maximum size for submission queue array. Must be a power of two + * less than or equal to 1 << (31 - width of array entry) to + * ensure lack of index wraparound, but is capped at a lower + * value to help users trap runaway computations. + */ + private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 24; // 16M + + /** + * Array serving as submission queue. Initialized upon construction. + */ + private ForkJoinTask<?>[] submissionQueue; + + /** + * Lock protecting submissions array for addSubmission + */ + private final ReentrantLock submissionLock; + + /** + * Condition for awaitTermination, using submissionLock for + * convenience. + */ + private final Condition termination; + + /** + * Creation factory for worker threads. + */ + private final ForkJoinWorkerThreadFactory factory; + + /** + * The uncaught exception handler used when any worker abruptly + * terminates. + */ + final Thread.UncaughtExceptionHandler ueh; + + /** + * Prefix for assigning names to worker threads + */ + private final String workerNamePrefix; + + /** + * Sum of per-thread steal counts, updated only when threads are + * idle or terminating. + */ + private volatile long stealCount; + + /** + * Main pool control -- a long packed with: + * AC: Number of active running workers minus target parallelism (16 bits) + * TC: Number of total workers minus target parallelism (16 bits) + * ST: true if pool is terminating (1 bit) + * EC: the wait count of top waiting thread (15 bits) + * ID: ~poolIndex of top of Treiber stack of waiting threads (16 bits) + * + * When convenient, we can extract the upper 32 bits of counts and + * the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e = + * (int)ctl. The ec field is never accessed alone, but always + * together with id and st. The offsets of counts by the target + * parallelism and the positionings of fields makes it possible to + * perform the most common checks via sign tests of fields: When + * ac is negative, there are not enough active workers, when tc is + * negative, there are not enough total workers, when id is + * negative, there is at least one waiting worker, and when e is + * negative, the pool is terminating. To deal with these possibly + * negative fields, we use casts in and out of "short" and/or + * signed shifts to maintain signedness. + */ + volatile long ctl; + + // bit positions/shifts for fields + private static final int AC_SHIFT = 48; + private static final int TC_SHIFT = 32; + private static final int ST_SHIFT = 31; + private static final int EC_SHIFT = 16; + + // bounds + private static final int MAX_ID = 0x7fff; // max poolIndex + private static final int SMASK = 0xffff; // mask short bits + private static final int SHORT_SIGN = 1 << 15; + private static final int INT_SIGN = 1 << 31; + + // masks + private static final long STOP_BIT = 0x0001L << ST_SHIFT; + private static final long AC_MASK = ((long)SMASK) << AC_SHIFT; + private static final long TC_MASK = ((long)SMASK) << TC_SHIFT; + + // units for incrementing and decrementing + private static final long TC_UNIT = 1L << TC_SHIFT; + private static final long AC_UNIT = 1L << AC_SHIFT; + + // masks and units for dealing with u = (int)(ctl >>> 32) + private static final int UAC_SHIFT = AC_SHIFT - 32; + private static final int UTC_SHIFT = TC_SHIFT - 32; + private static final int UAC_MASK = SMASK << UAC_SHIFT; + private static final int UTC_MASK = SMASK << UTC_SHIFT; + private static final int UAC_UNIT = 1 << UAC_SHIFT; + private static final int UTC_UNIT = 1 << UTC_SHIFT; + + // masks and units for dealing with e = (int)ctl + private static final int E_MASK = 0x7fffffff; // no STOP_BIT + private static final int EC_UNIT = 1 << EC_SHIFT; + + /** + * The target parallelism level. + */ + final int parallelism; + + /** + * Index (mod submission queue length) of next element to take + * from submission queue. Usage is identical to that for + * per-worker queues -- see ForkJoinWorkerThread internal + * documentation. + */ + volatile int queueBase; + + /** + * Index (mod submission queue length) of next element to add + * in submission queue. Usage is identical to that for + * per-worker queues -- see ForkJoinWorkerThread internal + * documentation. + */ + int queueTop; + + /** + * True when shutdown() has been called. + */ + volatile boolean shutdown; + + /** + * True if use local fifo, not default lifo, for local polling. + * Read by, and replicated by ForkJoinWorkerThreads. + */ + final boolean locallyFifo; + + /** + * The number of threads in ForkJoinWorkerThreads.helpQuiescePool. + * When non-zero, suppresses automatic shutdown when active + * counts become zero. + */ + volatile int quiescerCount; + + /** + * The number of threads blocked in join. + */ + volatile int blockedCount; + + /** + * Counter for worker Thread names (unrelated to their poolIndex) + */ + private volatile int nextWorkerNumber; + + /** + * The index for the next created worker. Accessed under scanGuard. + */ + private int nextWorkerIndex; + + /** + * SeqLock and index masking for updates to workers array. Locked + * when SG_UNIT is set. Unlocking clears bit by adding + * SG_UNIT. Staleness of read-only operations can be checked by + * comparing scanGuard to value before the reads. The low 16 bits + * (i.e, anding with SMASK) hold (the smallest power of two + * covering all worker indices, minus one, and is used to avoid + * dealing with large numbers of null slots when the workers array + * is overallocated. + */ + volatile int scanGuard; + + private static final int SG_UNIT = 1 << 16; + + /** + * The wakeup interval (in nanoseconds) for a worker waiting for a + * task when the pool is quiescent to instead try to shrink the + * number of workers. The exact value does not matter too + * much. It must be short enough to release resources during + * sustained periods of idleness, but not so short that threads + * are continually re-created. + */ + private static final long SHRINK_RATE = + 4L * 1000L * 1000L * 1000L; // 4 seconds + + /** + * Top-level loop for worker threads: On each step: if the + * previous step swept through all queues and found no tasks, or + * there are excess threads, then possibly blocks. Otherwise, + * scans for and, if found, executes a task. Returns when pool + * and/or worker terminate. + * + * @param w the worker + */ + final void work(ForkJoinWorkerThread w) { + boolean swept = false; // true on empty scans + long c; + while (!w.terminate && (int)(c = ctl) >= 0) { + int a; // active count + if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0) + swept = scan(w, a); + else if (tryAwaitWork(w, c)) + swept = false; + } + } + + // Signalling + + /** + * Wakes up or creates a worker. + */ + final void signalWork() { + /* + * The while condition is true if: (there is are too few total + * workers OR there is at least one waiter) AND (there are too + * few active workers OR the pool is terminating). The value + * of e distinguishes the remaining cases: zero (no waiters) + * for create, negative if terminating (in which case do + * nothing), else release a waiter. The secondary checks for + * release (non-null array etc) can fail if the pool begins + * terminating after the test, and don't impose any added cost + * because JVMs must perform null and bounds checks anyway. + */ + long c; int e, u; + while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) & + (INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN) && e >= 0) { + if (e > 0) { // release a waiting worker + int i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws; + if ((ws = workers) == null || + (i = ~e & SMASK) >= ws.length || + (w = ws[i]) == null) + break; + long nc = (((long)(w.nextWait & E_MASK)) | + ((long)(u + UAC_UNIT) << 32)); + if (w.eventCount == e && + UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) { + w.eventCount = (e + EC_UNIT) & E_MASK; + if (w.parked) + UNSAFE.unpark(w); + break; + } + } + else if (UNSAFE.compareAndSwapLong + (this, ctlOffset, c, + (long)(((u + UTC_UNIT) & UTC_MASK) | + ((u + UAC_UNIT) & UAC_MASK)) << 32)) { + addWorker(); + break; + } + } + } + + /** + * Variant of signalWork to help release waiters on rescans. + * Tries once to release a waiter if active count < 0. + * + * @return false if failed due to contention, else true + */ + private boolean tryReleaseWaiter() { + long c; int e, i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws; + if ((e = (int)(c = ctl)) > 0 && + (int)(c >> AC_SHIFT) < 0 && + (ws = workers) != null && + (i = ~e & SMASK) < ws.length && + (w = ws[i]) != null) { + long nc = ((long)(w.nextWait & E_MASK) | + ((c + AC_UNIT) & (AC_MASK|TC_MASK))); + if (w.eventCount != e || + !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) + return false; + w.eventCount = (e + EC_UNIT) & E_MASK; + if (w.parked) + UNSAFE.unpark(w); + } + return true; + } + + // Scanning for tasks + + /** + * Scans for and, if found, executes one task. Scans start at a + * random index of workers array, and randomly select the first + * (2*#workers)-1 probes, and then, if all empty, resort to 2 + * circular sweeps, which is necessary to check quiescence. and + * taking a submission only if no stealable tasks were found. The + * steal code inside the loop is a specialized form of + * ForkJoinWorkerThread.deqTask, followed bookkeeping to support + * helpJoinTask and signal propagation. The code for submission + * queues is almost identical. On each steal, the worker completes + * not only the task, but also all local tasks that this task may + * have generated. On detecting staleness or contention when + * trying to take a task, this method returns without finishing + * sweep, which allows global state rechecks before retry. + * + * @param w the worker + * @param a the number of active workers + * @return true if swept all queues without finding a task + */ + private boolean scan(ForkJoinWorkerThread w, int a) { + int g = scanGuard; // mask 0 avoids useless scans if only one active + int m = (parallelism == 1 - a && blockedCount == 0) ? 0 : g & SMASK; + ForkJoinWorkerThread[] ws = workers; + if (ws == null || ws.length <= m) // staleness check + return false; + for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) { + ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i; + ForkJoinWorkerThread v = ws[k & m]; + if (v != null && (b = v.queueBase) != v.queueTop && + (q = v.queue) != null && (i = (q.length - 1) & b) >= 0) { + long u = (i << ASHIFT) + ABASE; + if ((t = q[i]) != null && v.queueBase == b && + UNSAFE.compareAndSwapObject(q, u, t, null)) { + int d = (v.queueBase = b + 1) - v.queueTop; + v.stealHint = w.poolIndex; + if (d != 0) + signalWork(); // propagate if nonempty + w.execTask(t); + } + r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5); + return false; // store next seed + } + else if (j < 0) { // xorshift + r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5; + } + else + ++k; + } + if (scanGuard != g) // staleness check + return false; + else { // try to take submission + ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i; + if ((b = queueBase) != queueTop && + (q = submissionQueue) != null && + (i = (q.length - 1) & b) >= 0) { + long u = (i << ASHIFT) + ABASE; + if ((t = q[i]) != null && queueBase == b && + UNSAFE.compareAndSwapObject(q, u, t, null)) { + queueBase = b + 1; + w.execTask(t); + } + return false; + } + return true; // all queues empty + } + } + + /** + * Tries to enqueue worker w in wait queue and await change in + * worker's eventCount. If the pool is quiescent and there is + * more than one worker, possibly terminates worker upon exit. + * Otherwise, before blocking, rescans queues to avoid missed + * signals. Upon finding work, releases at least one worker + * (which may be the current worker). Rescans restart upon + * detected staleness or failure to release due to + * contention. Note the unusual conventions about Thread.interrupt + * here and elsewhere: Because interrupts are used solely to alert + * threads to check termination, which is checked here anyway, 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. + * + * @param w the calling worker + * @param c the ctl value on entry + * @return true if waited or another thread was released upon enq + */ + private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) { + int v = w.eventCount; + w.nextWait = (int)c; // w's successor record + long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK)); + if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) { + long d = ctl; // return true if lost to a deq, to force scan + return (int)d != (int)c && (d & AC_MASK) >= (c & AC_MASK); + } + for (int sc = w.stealCount; sc != 0;) { // accumulate stealCount + long s = stealCount; + if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s + sc)) + sc = w.stealCount = 0; + else if (w.eventCount != v) + return true; // update next time + } + if ((!shutdown || !tryTerminate(false)) && + (int)c != 0 && parallelism + (int)(nc >> AC_SHIFT) == 0 && + blockedCount == 0 && quiescerCount == 0) + idleAwaitWork(w, nc, c, v); // quiescent + for (boolean rescanned = false;;) { + if (w.eventCount != v) + return true; + if (!rescanned) { + int g = scanGuard, m = g & SMASK; + ForkJoinWorkerThread[] ws = workers; + if (ws != null && m < ws.length) { + rescanned = true; + for (int i = 0; i <= m; ++i) { + ForkJoinWorkerThread u = ws[i]; + if (u != null) { + if (u.queueBase != u.queueTop && + !tryReleaseWaiter()) + rescanned = false; // contended + if (w.eventCount != v) + return true; + } + } + } + if (scanGuard != g || // stale + (queueBase != queueTop && !tryReleaseWaiter())) + rescanned = false; + if (!rescanned) + Thread.yield(); // reduce contention + else + Thread.interrupted(); // clear before park + } + else { + w.parked = true; // must recheck + if (w.eventCount != v) { + w.parked = false; + return true; + } + LockSupport.park(this); + rescanned = w.parked = false; + } + } + } + + /** + * If inactivating worker w has caused pool to become + * quiescent, check for pool termination, and wait for event + * for up to SHRINK_RATE nanosecs (rescans are unnecessary in + * this case because quiescence reflects consensus about lack + * of work). On timeout, if ctl has not changed, terminate the + * worker. Upon its termination (see deregisterWorker), it may + * wake up another worker to possibly repeat this process. + * + * @param w the calling worker + * @param currentCtl the ctl value after enqueuing w + * @param prevCtl the ctl value if w terminated + * @param v the eventCount w awaits change + */ + private void idleAwaitWork(ForkJoinWorkerThread w, long currentCtl, + long prevCtl, int v) { + if (w.eventCount == v) { + if (shutdown) + tryTerminate(false); + ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs + while (ctl == currentCtl) { + long startTime = System.nanoTime(); + w.parked = true; + if (w.eventCount == v) // must recheck + LockSupport.parkNanos(this, SHRINK_RATE); + w.parked = false; + if (w.eventCount != v) + break; + else if (System.nanoTime() - startTime < + SHRINK_RATE - (SHRINK_RATE / 10)) // timing slop + Thread.interrupted(); // spurious wakeup + else if (UNSAFE.compareAndSwapLong(this, ctlOffset, + currentCtl, prevCtl)) { + w.terminate = true; // restore previous + w.eventCount = ((int)currentCtl + EC_UNIT) & E_MASK; + break; + } + } + } + } + + // Submissions + + /** + * Enqueues the given task in the submissionQueue. Same idea as + * ForkJoinWorkerThread.pushTask except for use of submissionLock. + * + * @param t the task + */ + private void addSubmission(ForkJoinTask<?> t) { + final ReentrantLock lock = this.submissionLock; + lock.lock(); + try { + ForkJoinTask<?>[] q; int s, m; + if ((q = submissionQueue) != null) { // ignore if queue removed + long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE; + UNSAFE.putOrderedObject(q, u, t); + queueTop = s + 1; + if (s - queueBase == m) + growSubmissionQueue(); + } + } finally { + lock.unlock(); + } + signalWork(); + } + + // (pollSubmission is defined below with exported methods) + + /** + * Creates or doubles submissionQueue array. + * Basically identical to ForkJoinWorkerThread version. + */ + private void growSubmissionQueue() { + ForkJoinTask<?>[] oldQ = submissionQueue; + int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY; + if (size > MAXIMUM_QUEUE_CAPACITY) + throw new RejectedExecutionException("Queue capacity exceeded"); + if (size < INITIAL_QUEUE_CAPACITY) + size = INITIAL_QUEUE_CAPACITY; + ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size]; + int mask = size - 1; + int top = queueTop; + int oldMask; + if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) { + for (int b = queueBase; b != top; ++b) { + long u = ((b & oldMask) << ASHIFT) + ABASE; + Object x = UNSAFE.getObjectVolatile(oldQ, u); + if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null)) + UNSAFE.putObjectVolatile + (q, ((b & mask) << ASHIFT) + ABASE, x); + } + } + } + + // Blocking support + + /** + * Tries to increment blockedCount, decrement active count + * (sometimes implicitly) and possibly release or create a + * compensating worker in preparation for blocking. Fails + * on contention or termination. + * + * @return true if the caller can block, else should recheck and retry + */ + private boolean tryPreBlock() { + int b = blockedCount; + if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) { + int pc = parallelism; + do { + ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w; + int e, ac, tc, i; + long c = ctl; + int u = (int)(c >>> 32); + if ((e = (int)c) < 0) { + // skip -- terminating + } + else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 && + (ws = workers) != null && + (i = ~e & SMASK) < ws.length && + (w = ws[i]) != null) { + long nc = ((long)(w.nextWait & E_MASK) | + (c & (AC_MASK|TC_MASK))); + if (w.eventCount == e && + UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) { + w.eventCount = (e + EC_UNIT) & E_MASK; + if (w.parked) + UNSAFE.unpark(w); + return true; // release an idle worker + } + } + else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) { + long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK); + if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) + return true; // no compensation needed + } + else if (tc + pc < MAX_ID) { + long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK); + if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) { + addWorker(); + return true; // create a replacement + } + } + // try to back out on any failure and let caller retry + } while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset, + b = blockedCount, b - 1)); + } + return false; + } + + /** + * Decrements blockedCount and increments active count. + */ + private void postBlock() { + long c; + do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, // no mask + c = ctl, c + AC_UNIT)); + int b; + do {} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset, + b = blockedCount, b - 1)); + } + + /** + * Possibly blocks waiting for the given task to complete, or + * cancels the task if terminating. Fails to wait if contended. + * + * @param joinMe the task + */ + final void tryAwaitJoin(ForkJoinTask<?> joinMe) { + Thread.interrupted(); // clear interrupts before checking termination + if (joinMe.status >= 0) { + if (tryPreBlock()) { + joinMe.tryAwaitDone(0L); + postBlock(); + } + else if ((ctl & STOP_BIT) != 0L) + joinMe.cancelIgnoringExceptions(); + } + } + + /** + * Possibly blocks the given worker waiting for joinMe to + * complete or timeout. + * + * @param joinMe the task + * @param nanos the wait time for underlying Object.wait + */ + final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) { + while (joinMe.status >= 0) { + Thread.interrupted(); + if ((ctl & STOP_BIT) != 0L) { + joinMe.cancelIgnoringExceptions(); + break; + } + if (tryPreBlock()) { + long last = System.nanoTime(); + while (joinMe.status >= 0) { + long millis = TimeUnit.NANOSECONDS.toMillis(nanos); + if (millis <= 0) + break; + joinMe.tryAwaitDone(millis); + if (joinMe.status < 0) + break; + if ((ctl & STOP_BIT) != 0L) { + joinMe.cancelIgnoringExceptions(); + break; + } + long now = System.nanoTime(); + nanos -= now - last; + last = now; + } + postBlock(); + break; + } + } + } + + /** + * If necessary, compensates for blocker, and blocks. + */ + private void awaitBlocker(ManagedBlocker blocker) + throws InterruptedException { + while (!blocker.isReleasable()) { + if (tryPreBlock()) { + try { + do {} while (!blocker.isReleasable() && !blocker.block()); + } finally { + postBlock(); + } + break; + } + } + } + + // Creating, registering and deregistring workers + + /** + * Tries to create and start a worker; minimally rolls back counts + * on failure. + */ + private void addWorker() { + Throwable ex = null; + ForkJoinWorkerThread t = null; + try { + t = factory.newThread(this); + } catch (Throwable e) { + ex = e; + } + if (t == null) { // null or exceptional factory return + long c; // adjust counts + do {} while (!UNSAFE.compareAndSwapLong + (this, ctlOffset, c = ctl, + (((c - AC_UNIT) & AC_MASK) | + ((c - TC_UNIT) & TC_MASK) | + (c & ~(AC_MASK|TC_MASK))))); + // Propagate exception if originating from an external caller + if (!tryTerminate(false) && ex != null && + !(Thread.currentThread() instanceof ForkJoinWorkerThread)) + SneakyThrow.sneakyThrow(ex); // android-changed + } + else + t.start(); + } + + /** + * Callback from ForkJoinWorkerThread constructor to assign a + * public name + */ + final String nextWorkerName() { + for (int n;;) { + if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset, + n = nextWorkerNumber, ++n)) + return workerNamePrefix + n; + } + } + + /** + * Callback from ForkJoinWorkerThread constructor to + * determine its poolIndex and record in workers array. + * + * @param w the worker + * @return the worker's pool index + */ + final int registerWorker(ForkJoinWorkerThread w) { + /* + * In the typical case, a new worker acquires the lock, uses + * next available index and returns quickly. Since we should + * not block callers (ultimately from signalWork or + * tryPreBlock) waiting for the lock needed to do this, we + * instead help release other workers while waiting for the + * lock. + */ + for (int g;;) { + ForkJoinWorkerThread[] ws; + if (((g = scanGuard) & SG_UNIT) == 0 && + UNSAFE.compareAndSwapInt(this, scanGuardOffset, + g, g | SG_UNIT)) { + int k = nextWorkerIndex; + try { + if ((ws = workers) != null) { // ignore on shutdown + int n = ws.length; + if (k < 0 || k >= n || ws[k] != null) { + for (k = 0; k < n && ws[k] != null; ++k) + ; + if (k == n) + ws = workers = Arrays.copyOf(ws, n << 1); + } + ws[k] = w; + nextWorkerIndex = k + 1; + int m = g & SMASK; + g = (k > m) ? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1); + } + } finally { + scanGuard = g; + } + return k; + } + else if ((ws = workers) != null) { // help release others + for (ForkJoinWorkerThread u : ws) { + if (u != null && u.queueBase != u.queueTop) { + if (tryReleaseWaiter()) + break; + } + } + } + } + } + + /** + * Final callback from terminating worker. Removes record of + * worker from array, and adjusts counts. If pool is shutting + * down, tries to complete termination. + * + * @param w the worker + */ + final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) { + int idx = w.poolIndex; + int sc = w.stealCount; + int steps = 0; + // Remove from array, adjust worker counts and collect steal count. + // We can intermix failed removes or adjusts with steal updates + do { + long s, c; + int g; + if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 && + UNSAFE.compareAndSwapInt(this, scanGuardOffset, + g, g |= SG_UNIT)) { + ForkJoinWorkerThread[] ws = workers; + if (ws != null && idx >= 0 && + idx < ws.length && ws[idx] == w) + ws[idx] = null; // verify + nextWorkerIndex = idx; + scanGuard = g + SG_UNIT; + steps = 1; + } + if (steps == 1 && + UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl, + (((c - AC_UNIT) & AC_MASK) | + ((c - TC_UNIT) & TC_MASK) | + (c & ~(AC_MASK|TC_MASK))))) + steps = 2; + if (sc != 0 && + UNSAFE.compareAndSwapLong(this, stealCountOffset, + s = stealCount, s + sc)) + sc = 0; + } while (steps != 2 || sc != 0); + if (!tryTerminate(false)) { + if (ex != null) // possibly replace if died abnormally + signalWork(); + else + tryReleaseWaiter(); + } + } + + // Shutdown and termination + + /** + * Possibly initiates and/or completes termination. + * + * @param now if true, unconditionally terminate, else only + * if shutdown and empty queue and no active workers + * @return true if now terminating or terminated + */ + private boolean tryTerminate(boolean now) { + long c; + while (((c = ctl) & STOP_BIT) == 0) { + if (!now) { + if ((int)(c >> AC_SHIFT) != -parallelism) + return false; + if (!shutdown || blockedCount != 0 || quiescerCount != 0 || + queueBase != queueTop) { + if (ctl == c) // staleness check + return false; + continue; + } + } + if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT)) + startTerminating(); + } + if ((short)(c >>> TC_SHIFT) == -parallelism) { // signal when 0 workers + final ReentrantLock lock = this.submissionLock; + lock.lock(); + try { + termination.signalAll(); + } finally { + lock.unlock(); + } + } + return true; + } + + /** + * Runs up to three passes through workers: (0) Setting + * termination status for each worker, followed by wakeups up to + * queued workers; (1) helping cancel tasks; (2) interrupting + * lagging threads (likely in external tasks, but possibly also + * blocked in joins). Each pass repeats previous steps because of + * potential lagging thread creation. + */ + private void startTerminating() { + cancelSubmissions(); + for (int pass = 0; pass < 3; ++pass) { + ForkJoinWorkerThread[] ws = workers; + if (ws != null) { + for (ForkJoinWorkerThread w : ws) { + if (w != null) { + w.terminate = true; + if (pass > 0) { + w.cancelTasks(); + if (pass > 1 && !w.isInterrupted()) { + try { + w.interrupt(); + } catch (SecurityException ignore) { + } + } + } + } + } + terminateWaiters(); + } + } + } + + /** + * Polls and cancels all submissions. Called only during termination. + */ + private void cancelSubmissions() { + while (queueBase != queueTop) { + ForkJoinTask<?> task = pollSubmission(); + if (task != null) { + try { + task.cancel(false); + } catch (Throwable ignore) { + } + } + } + } + + /** + * Tries to set the termination status of waiting workers, and + * then wakes them up (after which they will terminate). + */ + private void terminateWaiters() { + ForkJoinWorkerThread[] ws = workers; + if (ws != null) { + ForkJoinWorkerThread w; long c; int i, e; + int n = ws.length; + while ((i = ~(e = (int)(c = ctl)) & SMASK) < n && + (w = ws[i]) != null && w.eventCount == (e & E_MASK)) { + if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, + (long)(w.nextWait & E_MASK) | + ((c + AC_UNIT) & AC_MASK) | + (c & (TC_MASK|STOP_BIT)))) { + w.terminate = true; + w.eventCount = e + EC_UNIT; + if (w.parked) + UNSAFE.unpark(w); + } + } + } + } + + // misc ForkJoinWorkerThread support + + /** + * Increments or decrements quiescerCount. Needed only to prevent + * triggering shutdown if a worker is transiently inactive while + * checking quiescence. + * + * @param delta 1 for increment, -1 for decrement + */ + final void addQuiescerCount(int delta) { + int c; + do {} while (!UNSAFE.compareAndSwapInt(this, quiescerCountOffset, + c = quiescerCount, c + delta)); + } + + /** + * Directly increments or decrements active count without queuing. + * This method is used to transiently assert inactivation while + * checking quiescence. + * + * @param delta 1 for increment, -1 for decrement + */ + final void addActiveCount(int delta) { + long d = (long)delta << AC_SHIFT; + long c; + do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, + c = ctl, c + d)); + } + + /** + * Returns the approximate (non-atomic) number of idle threads per + * active thread. + */ + final int idlePerActive() { + // Approximate at powers of two for small values, saturate past 4 + int p = parallelism; + int a = p + (int)(ctl >> AC_SHIFT); + return (a > (p >>>= 1) ? 0 : + a > (p >>>= 1) ? 1 : + a > (p >>>= 1) ? 2 : + a > (p >>>= 1) ? 4 : + 8); + } + + // Exported methods + + // Constructors + + /** + * Creates a {@code ForkJoinPool} with parallelism equal to {@link + * java.lang.Runtime#availableProcessors}, using the {@linkplain + * #defaultForkJoinWorkerThreadFactory default thread factory}, + * no UncaughtExceptionHandler, and non-async LIFO processing mode. + */ + public ForkJoinPool() { + this(Runtime.getRuntime().availableProcessors(), + defaultForkJoinWorkerThreadFactory, null, false); + } + + /** + * Creates a {@code ForkJoinPool} with the indicated parallelism + * level, the {@linkplain + * #defaultForkJoinWorkerThreadFactory default thread factory}, + * no UncaughtExceptionHandler, and non-async LIFO processing mode. + * + * @param parallelism the parallelism level + * @throws IllegalArgumentException if parallelism less than or + * equal to zero, or greater than implementation limit + */ + public ForkJoinPool(int parallelism) { + this(parallelism, defaultForkJoinWorkerThreadFactory, null, false); + } + + /** + * Creates a {@code ForkJoinPool} with the given parameters. + * + * @param parallelism the parallelism level. For default value, + * use {@link java.lang.Runtime#availableProcessors}. + * @param factory the factory for creating new threads. For default value, + * use {@link #defaultForkJoinWorkerThreadFactory}. + * @param handler the handler for internal worker threads that + * terminate due to unrecoverable errors encountered while executing + * tasks. For default value, use {@code null}. + * @param asyncMode if true, + * establishes local first-in-first-out scheduling mode for forked + * tasks that are never joined. This mode may be more appropriate + * than default locally stack-based mode in applications in which + * worker threads only process event-style asynchronous tasks. + * For default value, use {@code false}. + * @throws IllegalArgumentException if parallelism less than or + * equal to zero, or greater than implementation limit + * @throws NullPointerException if the factory is null + */ + public ForkJoinPool(int parallelism, + ForkJoinWorkerThreadFactory factory, + Thread.UncaughtExceptionHandler handler, + boolean asyncMode) { + checkPermission(); + if (factory == null) + throw new NullPointerException(); + if (parallelism <= 0 || parallelism > MAX_ID) + throw new IllegalArgumentException(); + this.parallelism = parallelism; + this.factory = factory; + this.ueh = handler; + this.locallyFifo = asyncMode; + long np = (long)(-parallelism); // offset ctl counts + this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK); + this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY]; + // initialize workers array with room for 2*parallelism if possible + int n = parallelism << 1; + if (n >= MAX_ID) + n = MAX_ID; + else { // See Hackers Delight, sec 3.2, where n < (1 << 16) + n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; + } + workers = new ForkJoinWorkerThread[n + 1]; + this.submissionLock = new ReentrantLock(); + this.termination = submissionLock.newCondition(); + StringBuilder sb = new StringBuilder("ForkJoinPool-"); + sb.append(poolNumberGenerator.incrementAndGet()); + sb.append("-worker-"); + this.workerNamePrefix = sb.toString(); + } + + // Execution methods + + /** + * Performs the given task, returning its result upon completion. + * If the computation encounters an unchecked Exception or Error, + * it is rethrown as the outcome of this invocation. Rethrown + * exceptions behave in the same way as regular exceptions, but, + * when possible, contain stack traces (as displayed for example + * using {@code ex.printStackTrace()}) of both the current thread + * as well as the thread actually encountering the exception; + * minimally only the latter. + * + * @param task the task + * @return the task's result + * @throws NullPointerException if the task is null + * @throws RejectedExecutionException if the task cannot be + * scheduled for execution + */ + public <T> T invoke(ForkJoinTask<T> task) { + Thread t = Thread.currentThread(); + if (task == null) + throw new NullPointerException(); + if (shutdown) + throw new RejectedExecutionException(); + if ((t instanceof ForkJoinWorkerThread) && + ((ForkJoinWorkerThread)t).pool == this) + return task.invoke(); // bypass submit if in same pool + else { + addSubmission(task); + return task.join(); + } + } + + /** + * Unless terminating, forks task if within an ongoing FJ + * computation in the current pool, else submits as external task. + */ + private <T> void forkOrSubmit(ForkJoinTask<T> task) { + ForkJoinWorkerThread w; + Thread t = Thread.currentThread(); + if (shutdown) + throw new RejectedExecutionException(); + if ((t instanceof ForkJoinWorkerThread) && + (w = (ForkJoinWorkerThread)t).pool == this) + w.pushTask(task); + else + addSubmission(task); + } + + /** + * Arranges for (asynchronous) execution of the given task. + * + * @param task the task + * @throws NullPointerException if the task is null + * @throws RejectedExecutionException if the task cannot be + * scheduled for execution + */ + public void execute(ForkJoinTask<?> task) { + if (task == null) + throw new NullPointerException(); + forkOrSubmit(task); + } + + // AbstractExecutorService methods + + /** + * @throws NullPointerException if the task is null + * @throws RejectedExecutionException if the task cannot be + * scheduled for execution + */ + public void execute(Runnable task) { + if (task == null) + throw new NullPointerException(); + ForkJoinTask<?> job; + if (task instanceof ForkJoinTask<?>) // avoid re-wrap + job = (ForkJoinTask<?>) task; + else + job = ForkJoinTask.adapt(task, null); + forkOrSubmit(job); + } + + /** + * Submits a ForkJoinTask for execution. + * + * @param task the task to submit + * @return the task + * @throws NullPointerException if the task is null + * @throws RejectedExecutionException if the task cannot be + * scheduled for execution + */ + public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) { + if (task == null) + throw new NullPointerException(); + forkOrSubmit(task); + return task; + } + + /** + * @throws NullPointerException if the task is null + * @throws RejectedExecutionException if the task cannot be + * scheduled for execution + */ + public <T> ForkJoinTask<T> submit(Callable<T> task) { + if (task == null) + throw new NullPointerException(); + ForkJoinTask<T> job = ForkJoinTask.adapt(task); + forkOrSubmit(job); + return job; + } + + /** + * @throws NullPointerException if the task is null + * @throws RejectedExecutionException if the task cannot be + * scheduled for execution + */ + public <T> ForkJoinTask<T> submit(Runnable task, T result) { + if (task == null) + throw new NullPointerException(); + ForkJoinTask<T> job = ForkJoinTask.adapt(task, result); + forkOrSubmit(job); + return job; + } + + /** + * @throws NullPointerException if the task is null + * @throws RejectedExecutionException if the task cannot be + * scheduled for execution + */ + public ForkJoinTask<?> submit(Runnable task) { + if (task == null) + throw new NullPointerException(); + ForkJoinTask<?> job; + if (task instanceof ForkJoinTask<?>) // avoid re-wrap + job = (ForkJoinTask<?>) task; + else + job = ForkJoinTask.adapt(task, null); + forkOrSubmit(job); + return job; + } + + /** + * @throws NullPointerException {@inheritDoc} + * @throws RejectedExecutionException {@inheritDoc} + */ + public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) { + ArrayList<ForkJoinTask<T>> forkJoinTasks = + new ArrayList<ForkJoinTask<T>>(tasks.size()); + for (Callable<T> task : tasks) + forkJoinTasks.add(ForkJoinTask.adapt(task)); + invoke(new InvokeAll<T>(forkJoinTasks)); + + @SuppressWarnings({"unchecked", "rawtypes"}) + List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks; + return futures; + } + + static final class InvokeAll<T> extends RecursiveAction { + final ArrayList<ForkJoinTask<T>> tasks; + InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; } + public void compute() { + try { invokeAll(tasks); } + catch (Exception ignore) {} + } + private static final long serialVersionUID = -7914297376763021607L; + } + + /** + * Returns the factory used for constructing new workers. + * + * @return the factory used for constructing new workers + */ + public ForkJoinWorkerThreadFactory getFactory() { + return factory; + } + + /** + * Returns the handler for internal worker threads that terminate + * due to unrecoverable errors encountered while executing tasks. + * + * @return the handler, or {@code null} if none + */ + public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { + return ueh; + } + + /** + * Returns the targeted parallelism level of this pool. + * + * @return the targeted parallelism level of this pool + */ + public int getParallelism() { + return parallelism; + } + + /** + * Returns the number of worker threads that have started but not + * yet terminated. The result returned by this method may differ + * from {@link #getParallelism} when threads are created to + * maintain parallelism when others are cooperatively blocked. + * + * @return the number of worker threads + */ + public int getPoolSize() { + return parallelism + (short)(ctl >>> TC_SHIFT); + } + + /** + * Returns {@code true} if this pool uses local first-in-first-out + * scheduling mode for forked tasks that are never joined. + * + * @return {@code true} if this pool uses async mode + */ + public boolean getAsyncMode() { + return locallyFifo; + } + + /** + * Returns an estimate of the number of worker threads that are + * not blocked waiting to join tasks or for other managed + * synchronization. This method may overestimate the + * number of running threads. + * + * @return the number of worker threads + */ + public int getRunningThreadCount() { + int r = parallelism + (int)(ctl >> AC_SHIFT); + return (r <= 0) ? 0 : r; // suppress momentarily negative values + } + + /** + * Returns an estimate of the number of threads that are currently + * stealing or executing tasks. This method may overestimate the + * number of active threads. + * + * @return the number of active threads + */ + public int getActiveThreadCount() { + int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount; + return (r <= 0) ? 0 : r; // suppress momentarily negative values + } + + /** + * Returns {@code true} if all worker threads are currently idle. + * An idle worker is one that cannot obtain a task to execute + * because none are available to steal from other threads, and + * there are no pending submissions to the pool. This method is + * conservative; it might not return {@code true} immediately upon + * idleness of all threads, but will eventually become true if + * threads remain inactive. + * + * @return {@code true} if all threads are currently idle + */ + public boolean isQuiescent() { + return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0; + } + + /** + * Returns an estimate of the total number of tasks stolen from + * one thread's work queue by another. The reported value + * underestimates the actual total number of steals when the pool + * is not quiescent. This value may be useful for monitoring and + * tuning fork/join programs: in general, steal counts should be + * high enough to keep threads busy, but low enough to avoid + * overhead and contention across threads. + * + * @return the number of steals + */ + public long getStealCount() { + return stealCount; + } + + /** + * Returns an estimate of the total number of tasks currently held + * in queues by worker threads (but not including tasks submitted + * to the pool that have not begun executing). This value is only + * an approximation, obtained by iterating across all threads in + * the pool. This method may be useful for tuning task + * granularities. + * + * @return the number of queued tasks + */ + public long getQueuedTaskCount() { + long count = 0; + ForkJoinWorkerThread[] ws; + if ((short)(ctl >>> TC_SHIFT) > -parallelism && + (ws = workers) != null) { + for (ForkJoinWorkerThread w : ws) + if (w != null) + count -= w.queueBase - w.queueTop; // must read base first + } + return count; + } + + /** + * Returns an estimate of the number of tasks submitted to this + * pool that have not yet begun executing. This method may take + * time proportional to the number of submissions. + * + * @return the number of queued submissions + */ + public int getQueuedSubmissionCount() { + return -queueBase + queueTop; + } + + /** + * Returns {@code true} if there are any tasks submitted to this + * pool that have not yet begun executing. + * + * @return {@code true} if there are any queued submissions + */ + public boolean hasQueuedSubmissions() { + return queueBase != queueTop; + } + + /** + * Removes and returns the next unexecuted submission if one is + * available. This method may be useful in extensions to this + * class that re-assign work in systems with multiple pools. + * + * @return the next submission, or {@code null} if none + */ + protected ForkJoinTask<?> pollSubmission() { + ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i; + while ((b = queueBase) != queueTop && + (q = submissionQueue) != null && + (i = (q.length - 1) & b) >= 0) { + long u = (i << ASHIFT) + ABASE; + if ((t = q[i]) != null && + queueBase == b && + UNSAFE.compareAndSwapObject(q, u, t, null)) { + queueBase = b + 1; + return t; + } + } + return null; + } + + /** + * Removes all available unexecuted submitted and forked tasks + * from scheduling queues and adds them to the given collection, + * without altering their execution status. These may include + * artificially generated or wrapped tasks. This method is + * designed to be invoked only when the pool is known to be + * quiescent. Invocations at other times may not remove all + * tasks. A failure encountered while attempting to add elements + * to collection {@code c} may result in elements being in + * neither, either or both collections when the associated + * exception is thrown. The behavior of this operation is + * undefined if the specified collection is modified while the + * operation is in progress. + * + * @param c the collection to transfer elements into + * @return the number of elements transferred + */ + protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { + int count = 0; + while (queueBase != queueTop) { + ForkJoinTask<?> t = pollSubmission(); + if (t != null) { + c.add(t); + ++count; + } + } + ForkJoinWorkerThread[] ws; + if ((short)(ctl >>> TC_SHIFT) > -parallelism && + (ws = workers) != null) { + for (ForkJoinWorkerThread w : ws) + if (w != null) + count += w.drainTasksTo(c); + } + return count; + } + + /** + * Returns a string identifying this pool, as well as its state, + * including indications of run state, parallelism level, and + * worker and task counts. + * + * @return a string identifying this pool, as well as its state + */ + public String toString() { + long st = getStealCount(); + long qt = getQueuedTaskCount(); + long qs = getQueuedSubmissionCount(); + int pc = parallelism; + long c = ctl; + int tc = pc + (short)(c >>> TC_SHIFT); + int rc = pc + (int)(c >> AC_SHIFT); + if (rc < 0) // ignore transient negative + rc = 0; + int ac = rc + blockedCount; + String level; + if ((c & STOP_BIT) != 0) + level = (tc == 0) ? "Terminated" : "Terminating"; + else + level = shutdown ? "Shutting down" : "Running"; + return super.toString() + + "[" + level + + ", parallelism = " + pc + + ", size = " + tc + + ", active = " + ac + + ", running = " + rc + + ", steals = " + st + + ", tasks = " + qt + + ", submissions = " + qs + + "]"; + } + + /** + * Initiates an orderly shutdown in which previously submitted + * tasks are executed, but no new tasks will be accepted. + * Invocation has no additional effect if 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. + */ + public void shutdown() { + checkPermission(); + shutdown = true; + tryTerminate(false); + } + + /** + * Attempts to cancel and/or stop all tasks, and reject all + * subsequently submitted tasks. Tasks that are in the process of + * being submitted or executed concurrently during the course of + * this method may or may not be rejected. This method cancels + * both existing and unexecuted tasks, in order to permit + * termination in the presence of task dependencies. So the method + * always returns an empty list (unlike the case for some other + * Executors). + * + * @return an empty list + */ + public List<Runnable> shutdownNow() { + checkPermission(); + shutdown = true; + tryTerminate(true); + return Collections.emptyList(); + } + + /** + * Returns {@code true} if all tasks have completed following shut down. + * + * @return {@code true} if all tasks have completed following shut down + */ + public boolean isTerminated() { + long c = ctl; + return ((c & STOP_BIT) != 0L && + (short)(c >>> TC_SHIFT) == -parallelism); + } + + /** + * Returns {@code true} if the process of termination has + * commenced but not yet completed. This method may be useful for + * debugging. A return of {@code true} reported a sufficient + * period after shutdown may indicate that submitted tasks have + * ignored or suppressed interruption, or are waiting for IO, + * causing this executor not to properly terminate. (See the + * advisory notes for class {@link ForkJoinTask} stating that + * tasks should not normally entail blocking operations. But if + * they do, they must abort them on interrupt.) + * + * @return {@code true} if terminating but not yet terminated + */ + public boolean isTerminating() { + long c = ctl; + return ((c & STOP_BIT) != 0L && + (short)(c >>> TC_SHIFT) != -parallelism); + } + + /** + * Returns true if terminating or terminated. Used by ForkJoinWorkerThread. + */ + final boolean isAtLeastTerminating() { + return (ctl & STOP_BIT) != 0L; + } + + /** + * Returns {@code true} if this pool has been shut down. + * + * @return {@code true} if this pool has been shut down + */ + public boolean isShutdown() { + return shutdown; + } + + /** + * Blocks until all tasks have completed execution after a shutdown + * request, or the timeout occurs, or the current thread is + * interrupted, whichever happens first. + * + * @param timeout the maximum time to wait + * @param unit the time unit of the timeout argument + * @return {@code true} if this executor terminated and + * {@code false} if the timeout elapsed before termination + * @throws InterruptedException if interrupted while waiting + */ + public boolean awaitTermination(long timeout, TimeUnit unit) + throws InterruptedException { + long nanos = unit.toNanos(timeout); + final ReentrantLock lock = this.submissionLock; + lock.lock(); + try { + for (;;) { + if (isTerminated()) + return true; + if (nanos <= 0) + return false; + nanos = termination.awaitNanos(nanos); + } + } finally { + lock.unlock(); + } + } + + /** + * Interface for extending managed parallelism for tasks running + * in {@link ForkJoinPool}s. + * + * <p>A {@code ManagedBlocker} provides two methods. Method + * {@code isReleasable} must return {@code true} if blocking is + * 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 + * 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, + * implementations of method {@code isReleasable} must be amenable + * to repeated invocation. + * + * <p>For example, here is a ManagedBlocker based on a + * ReentrantLock: + * <pre> {@code + * class ManagedLocker implements ManagedBlocker { + * final ReentrantLock lock; + * boolean hasLock = false; + * ManagedLocker(ReentrantLock lock) { this.lock = lock; } + * public boolean block() { + * if (!hasLock) + * lock.lock(); + * return true; + * } + * public boolean isReleasable() { + * return hasLock || (hasLock = lock.tryLock()); + * } + * }}</pre> + * + * <p>Here is a class that possibly blocks waiting for an + * item on a given queue: + * <pre> {@code + * class QueueTaker<E> implements ManagedBlocker { + * final BlockingQueue<E> queue; + * volatile E item = null; + * QueueTaker(BlockingQueue<E> q) { this.queue = q; } + * public boolean block() throws InterruptedException { + * if (item == null) + * item = queue.take(); + * return true; + * } + * public boolean isReleasable() { + * return item != null || (item = queue.poll()) != null; + * } + * public E getItem() { // call after pool.managedBlock completes + * return item; + * } + * }}</pre> + */ + public static interface ManagedBlocker { + /** + * Possibly blocks the current thread, for example waiting for + * a lock or condition. + * + * @return {@code true} if no additional blocking is necessary + * (i.e., if isReleasable would return true) + * @throws InterruptedException if interrupted while waiting + * (the method is not required to do so, but is allowed to) + */ + boolean block() throws InterruptedException; + + /** + * Returns {@code true} if blocking is unnecessary. + */ + boolean isReleasable(); + } + + /** + * Blocks in accord with the given blocker. If the current thread + * is a {@link ForkJoinWorkerThread}, this method possibly + * arranges for a spare thread to be activated if necessary to + * ensure sufficient parallelism while the current thread is blocked. + * + * <p>If the caller is not a {@link ForkJoinTask}, this method is + * behaviorally equivalent to + * <pre> {@code + * while (!blocker.isReleasable()) + * if (blocker.block()) + * return; + * }</pre> + * + * If the caller is a {@code ForkJoinTask}, then the pool may + * first be expanded to ensure parallelism, and later adjusted. + * + * @param blocker the blocker + * @throws InterruptedException if blocker.block did so + */ + public static void managedBlock(ManagedBlocker blocker) + throws InterruptedException { + Thread t = Thread.currentThread(); + if (t instanceof ForkJoinWorkerThread) { + ForkJoinWorkerThread w = (ForkJoinWorkerThread) t; + w.pool.awaitBlocker(blocker); + } + else { + do {} while (!blocker.isReleasable() && !blocker.block()); + } + } + + // AbstractExecutorService overrides. These rely on undocumented + // fact that ForkJoinTask.adapt returns ForkJoinTasks that also + // implement RunnableFuture. + + protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) { + return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value); + } + + protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) { + return (RunnableFuture<T>) ForkJoinTask.adapt(callable); + } + + // Unsafe mechanics + private static final sun.misc.Unsafe UNSAFE; + private static final long ctlOffset; + private static final long stealCountOffset; + private static final long blockedCountOffset; + private static final long quiescerCountOffset; + private static final long scanGuardOffset; + private static final long nextWorkerNumberOffset; + private static final long ABASE; + private static final int ASHIFT; + + static { + poolNumberGenerator = new AtomicInteger(); + workerSeedGenerator = new Random(); + modifyThreadPermission = new RuntimePermission("modifyThread"); + defaultForkJoinWorkerThreadFactory = + new DefaultForkJoinWorkerThreadFactory(); + try { + UNSAFE = sun.misc.Unsafe.getUnsafe(); + Class<?> k = ForkJoinPool.class; + ctlOffset = UNSAFE.objectFieldOffset + (k.getDeclaredField("ctl")); + stealCountOffset = UNSAFE.objectFieldOffset + (k.getDeclaredField("stealCount")); + blockedCountOffset = UNSAFE.objectFieldOffset + (k.getDeclaredField("blockedCount")); + quiescerCountOffset = UNSAFE.objectFieldOffset + (k.getDeclaredField("quiescerCount")); + scanGuardOffset = UNSAFE.objectFieldOffset + (k.getDeclaredField("scanGuard")); + nextWorkerNumberOffset = UNSAFE.objectFieldOffset + (k.getDeclaredField("nextWorkerNumber")); + } catch (Exception e) { + throw new Error(e); + } + Class<?> a = ForkJoinTask[].class; + ABASE = UNSAFE.arrayBaseOffset(a); + int s = UNSAFE.arrayIndexScale(a); + if ((s & (s-1)) != 0) + throw new Error("data type scale not a power of two"); + ASHIFT = 31 - Integer.numberOfLeadingZeros(s); + } + +} |