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root/jsr166/jsr166/src/jsr166y/ForkJoinPool.java

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.37 by dl, Sun Aug 2 11:54:31 2009 UTC vs.
Revision 1.48 by jsr166, Thu Aug 6 06:41:34 2009 UTC

#	Line 21 | Line 21 | import java.util.concurrent.atomic.Atomi
21
22		/**
23		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
24	<	* A ForkJoinPool provides the entry point for submissions from
25	<	* non-ForkJoinTasks, as well as management and monitoring operations.
26	<	* Normally a single ForkJoinPool is used for a large number of
27	<	* submitted tasks. Otherwise, use would not usually outweigh the
28	<	* construction and bookkeeping overhead of creating a large set of
29	<	* threads.
24	>	* A {@code ForkJoinPool} provides the entry point for submissions
25	>	* from non-{@code ForkJoinTask}s, as well as management and
26	>	* monitoring operations.
27		*
28	<	* <p>ForkJoinPools differ from other kinds of Executors mainly in
29	<	* that they provide <em>work-stealing</em>: all threads in the pool
30	<	* attempt to find and execute subtasks created by other active tasks
31	<	* (eventually blocking if none exist). This makes them efficient when
32	<	* most tasks spawn other subtasks (as do most ForkJoinTasks), as well
33	<	* as the mixed execution of some plain Runnable- or Callable- based
34	<	* activities along with ForkJoinTasks. When setting {@linkplain
35	<	* #setAsyncMode async mode}, a ForkJoinPool may also be appropriate
36	<	* for use with fine-grained tasks that are never joined. Otherwise,
37	<	* other ExecutorService implementations are typically more
38	<	* appropriate choices.
28	>	* <p>A {@code ForkJoinPool} differs from other kinds of {@link
29	>	* ExecutorService} mainly by virtue of employing
30	>	* <em>work-stealing</em>: all threads in the pool attempt to find and
31	>	* execute subtasks created by other active tasks (eventually blocking
32	>	* waiting for work if none exist). This enables efficient processing
33	>	* when most tasks spawn other subtasks (as do most {@code
34	>	* ForkJoinTask}s). A {@code ForkJoinPool} may also be used for mixed
35	>	* execution of some plain {@code Runnable}- or {@code Callable}-
36	>	* based activities along with {@code ForkJoinTask}s. When setting
37	>	* {@linkplain #setAsyncMode async mode}, a {@code ForkJoinPool} may
38	>	* also be appropriate for use with fine-grained tasks of any form
39	>	* that are never joined. Otherwise, other {@code ExecutorService}
40	>	* implementations are typically more appropriate choices.
41		*
42	<	* <p>A ForkJoinPool may be constructed with a given parallelism level
43	<	* (target pool size), which it attempts to maintain by dynamically
44	<	* adding, suspending, or resuming threads, even if some tasks are
45	<	* waiting to join others. However, no such adjustments are performed
46	<	* in the face of blocked IO or other unmanaged synchronization. The
47	<	* nested {@link ManagedBlocker} interface enables extension of
48	<	* the kinds of synchronization accommodated.  The target parallelism
49	<	* level may also be changed dynamically ({@link #setParallelism})
50	<	* and thread construction can be limited using methods
51	<	* {@link #setMaximumPoolSize} and/or
52	<	* {@link #setMaintainsParallelism}.
42	>	* <p>A {@code ForkJoinPool} is constructed with a given target
43	>	* parallelism level; by default, equal to the number of available
44	>	* processors. Unless configured otherwise via {@link
45	>	* #setMaintainsParallelism}, the pool attempts to maintain this
46	>	* number of active (or available) threads by dynamically adding,
47	>	* suspending, or resuming internal worker threads, even if some tasks
48	>	* are stalled waiting to join others. However, no such adjustments
49	>	* are performed in the face of blocked IO or other unmanaged
50	>	* synchronization. The nested {@link ManagedBlocker} interface
51	>	* enables extension of the kinds of synchronization accommodated.
52	>	* The target parallelism level may also be changed dynamically
53	>	* ({@link #setParallelism}). The total number of threads may be
54	>	* limited using method {@link #setMaximumPoolSize}, in which case it
55	>	* may become possible for the activities of a pool to stall due to
56	>	* the lack of available threads to process new tasks.
57		*
58		* <p>In addition to execution and lifecycle control methods, this
59		* class provides status check methods (for example
#	Line 59 | Line 62 | import java.util.concurrent.atomic.Atomi
62		* {@link #toString} returns indications of pool state in a
63		* convenient form for informal monitoring.
64		*
65	+	* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
66	+	* used for all parallel task execution in a program or subsystem.
67	+	* Otherwise, use would not usually outweigh the construction and
68	+	* bookkeeping overhead of creating a large set of threads. For
69	+	* example, a common pool could be used for the {@code SortTasks}
70	+	* illustrated in {@link RecursiveAction}. Because {@code
71	+	* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
72	+	* daemon} mode, there is typically no need to explicitly {@link
73	+	* #shutdown} such a pool upon program exit.
74	+	*
75	+	* <pre>
76	+	* static final ForkJoinPool mainPool = new ForkJoinPool();
77	+	* ...
78	+	* public void sort(long[] array) {
79	+	*   mainPool.invoke(new SortTask(array, 0, array.length));
80	+	* }
81	+	* </pre>
82	+	*
83		* <p><b>Implementation notes</b>: This implementation restricts the
84		* maximum number of running threads to 32767. Attempts to create
85	<	* pools with greater than the maximum result in
86	<	* IllegalArgumentExceptions.
85	>	* pools with greater than the maximum number result in
86	>	* {@code IllegalArgumentException}.
87	>	*
88	>	* <p>This implementation rejects submitted tasks (that is, by throwing
89	>	* {@link RejectedExecutionException}) only when the pool is shut down.
90		*
91		* @since 1.7
92		* @author Doug Lea
#	Line 91 | Line 115 | public class ForkJoinPool extends Abstra
115		* Returns a new worker thread operating in the given pool.
116		*
117		* @param pool the pool this thread works in
118	<	* @throws NullPointerException if pool is null
118	>	* @throws NullPointerException if the pool is null
119		*/
120		public ForkJoinWorkerThread newThread(ForkJoinPool pool);
121		}
#	Line 342 | Line 366 | public class ForkJoinPool extends Abstra
366		// Constructors
367
368		/**
369	<	* Creates a ForkJoinPool with a pool size equal to the number of
370	<	* processors available on the system, using the default
371	<	* ForkJoinWorkerThreadFactory.
369	>	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
370	>	* java.lang.Runtime#availableProcessors}, and using the {@linkplain
371	>	* #defaultForkJoinWorkerThreadFactory default thread factory}.
372		*
373		* @throws SecurityException if a security manager exists and
374		*         the caller is not permitted to modify threads
#	Line 357 | Line 381 | public class ForkJoinPool extends Abstra
381		}
382
383		/**
384	<	* Creates a ForkJoinPool with the indicated parallelism level
385	<	* threads and using the default ForkJoinWorkerThreadFactory.
384	>	* Creates a {@code ForkJoinPool} with the indicated parallelism
385	>	* level and using the {@linkplain
386	>	* #defaultForkJoinWorkerThreadFactory default thread factory}.
387		*
388	<	* @param parallelism the number of worker threads
388	>	* @param parallelism the parallelism level
389		* @throws IllegalArgumentException if parallelism less than or
390	<	* equal to zero
390	>	*         equal to zero, or greater than implementation limit
391		* @throws SecurityException if a security manager exists and
392		*         the caller is not permitted to modify threads
393		*         because it does not hold {@link
#	Line 373 | Line 398 | public class ForkJoinPool extends Abstra
398		}
399
400		/**
401	<	* Creates a ForkJoinPool with parallelism equal to the number of
402	<	* processors available on the system and using the given
403	<	* ForkJoinWorkerThreadFactory.
401	>	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
402	>	* java.lang.Runtime#availableProcessors}, and using the given
403	>	* thread factory.
404		*
405		* @param factory the factory for creating new threads
406	<	* @throws NullPointerException if factory is null
406	>	* @throws NullPointerException if the factory is null
407		* @throws SecurityException if a security manager exists and
408		*         the caller is not permitted to modify threads
409		*         because it does not hold {@link
#	Line 389 | Line 414 | public class ForkJoinPool extends Abstra
414		}
415
416		/**
417	<	* Creates a ForkJoinPool with the given parallelism and factory.
417	>	* Creates a {@code ForkJoinPool} with the given parallelism and
418	>	* thread factory.
419		*
420	<	* @param parallelism the targeted number of worker threads
420	>	* @param parallelism the parallelism level
421		* @param factory the factory for creating new threads
422		* @throws IllegalArgumentException if parallelism less than or
423	<	* equal to zero, or greater than implementation limit
424	<	* @throws NullPointerException if factory is null
423	>	*         equal to zero, or greater than implementation limit
424	>	* @throws NullPointerException if the factory is null
425		* @throws SecurityException if a security manager exists and
426		*         the caller is not permitted to modify threads
427		*         because it does not hold {@link
#	Line 423 | Line 449 | public class ForkJoinPool extends Abstra
449		* Creates a new worker thread using factory.
450		*
451		* @param index the index to assign worker
452	<	* @return new worker, or null of factory failed
452	>	* @return new worker, or null if factory failed
453		*/
454		private ForkJoinWorkerThread createWorker(int index) {
455		Thread.UncaughtExceptionHandler h = ueh;
#	Line 444 | Line 470 | public class ForkJoinPool extends Abstra
470		* Currently requires size to be a power of two.
471		*/
472		private static int arraySizeFor(int poolSize) {
473	<	return (poolSize <= 1) ? 1 :
474	<	(1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
473	>	if (poolSize <= 1)
474	>	return 1;
475	>	// See Hackers Delight, sec 3.2
476	>	int c = poolSize >= MAX_THREADS ? MAX_THREADS : (poolSize - 1);
477	>	c |= c >>>  1;
478	>	c |= c >>>  2;
479	>	c |= c >>>  4;
480	>	c |= c >>>  8;
481	>	c |= c >>> 16;
482	>	return c + 1;
483		}
484
485		/**
#	Line 563 | Line 597 | public class ForkJoinPool extends Abstra
597		*
598		* @param task the task
599		* @return the task's result
600	<	* @throws NullPointerException if task is null
601	<	* @throws RejectedExecutionException if pool is shut down
600	>	* @throws NullPointerException if the task is null
601	>	* @throws RejectedExecutionException if the task cannot be
602	>	*         scheduled for execution
603		*/
604		public <T> T invoke(ForkJoinTask<T> task) {
605		doSubmit(task);
#	Line 575 | Line 610 | public class ForkJoinPool extends Abstra
610		* Arranges for (asynchronous) execution of the given task.
611		*
612		* @param task the task
613	<	* @throws NullPointerException if task is null
614	<	* @throws RejectedExecutionException if pool is shut down
613	>	* @throws NullPointerException if the task is null
614	>	* @throws RejectedExecutionException if the task cannot be
615	>	*         scheduled for execution
616		*/
617		public void execute(ForkJoinTask<?> task) {
618		doSubmit(task);
#	Line 584 | Line 620 | public class ForkJoinPool extends Abstra
620
621		// AbstractExecutorService methods
622
623	+	/**
624	+	* @throws NullPointerException if the task is null
625	+	* @throws RejectedExecutionException if the task cannot be
626	+	*         scheduled for execution
627	+	*/
628		public void execute(Runnable task) {
629		ForkJoinTask<?> job;
630		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
#	Line 593 | Line 634 | public class ForkJoinPool extends Abstra
634		doSubmit(job);
635		}
636
637	+	/**
638	+	* @throws NullPointerException if the task is null
639	+	* @throws RejectedExecutionException if the task cannot be
640	+	*         scheduled for execution
641	+	*/
642		public <T> ForkJoinTask<T> submit(Callable<T> task) {
643		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
644		doSubmit(job);
645		return job;
646		}
647
648	+	/**
649	+	* @throws NullPointerException if the task is null
650	+	* @throws RejectedExecutionException if the task cannot be
651	+	*         scheduled for execution
652	+	*/
653		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
654		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
655		doSubmit(job);
656		return job;
657		}
658
659	+	/**
660	+	* @throws NullPointerException if the task is null
661	+	* @throws RejectedExecutionException if the task cannot be
662	+	*         scheduled for execution
663	+	*/
664		public ForkJoinTask<?> submit(Runnable task) {
665		ForkJoinTask<?> job;
666		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
#	Line 620 | Line 676 | public class ForkJoinPool extends Abstra
676		*
677		* @param task the task to submit
678		* @return the task
679	+	* @throws NullPointerException if the task is null
680		* @throws RejectedExecutionException if the task cannot be
681		*         scheduled for execution
625	–	* @throws NullPointerException if the task is null
682		*/
683		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
684		doSubmit(task);
#	Line 630 | Line 686 | public class ForkJoinPool extends Abstra
686		}
687
688
689	+	/**
690	+	* @throws NullPointerException       {@inheritDoc}
691	+	* @throws RejectedExecutionException {@inheritDoc}
692	+	*/
693		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
694		ArrayList<ForkJoinTask<T>> forkJoinTasks =
695		new ArrayList<ForkJoinTask<T>>(tasks.size());
#	Line 736 | Line 796 | public class ForkJoinPool extends Abstra
796		final ReentrantLock lock = this.workerLock;
797		lock.lock();
798		try {
799	<	if (!isTerminating()) {
799	>	if (isProcessingTasks()) {
800		int p = this.parallelism;
801		this.parallelism = parallelism;
802		if (parallelism > p)
#	Line 751 | Line 811 | public class ForkJoinPool extends Abstra
811		}
812
813		/**
814	<	* Returns the targeted number of worker threads in this pool.
814	>	* Returns the targeted parallelism level of this pool.
815		*
816	<	* @return the targeted number of worker threads in this pool
816	>	* @return the targeted parallelism level of this pool
817		*/
818		public int getParallelism() {
819		return parallelism;
#	Line 773 | Line 833 | public class ForkJoinPool extends Abstra
833
834		/**
835		* Returns the maximum number of threads allowed to exist in the
836	<	* pool, even if there are insufficient unblocked running threads.
836	>	* pool. Unless set using {@link #setMaximumPoolSize}, the
837	>	* maximum is an implementation-defined value designed only to
838	>	* prevent runaway growth.
839		*
840		* @return the maximum
841		*/
#	Line 783 | Line 845 | public class ForkJoinPool extends Abstra
845
846		/**
847		* Sets the maximum number of threads allowed to exist in the
848	<	* pool, even if there are insufficient unblocked running threads.
849	<	* Setting this value has no effect on current pool size. It
850	<	* controls construction of new threads.
848	>	* pool. The given value should normally be greater than or equal
849	>	* to the {@link #getParallelism parallelism} level. Setting this
850	>	* value has no effect on current pool size. It controls
851	>	* construction of new threads.
852		*
853		* @throws IllegalArgumentException if negative or greater than
854		* internal implementation limit
#	Line 955 | Line 1018 | public class ForkJoinPool extends Abstra
1018		}
1019
1020		/**
1021	<	* Returns an estimate of the number tasks submitted to this pool
1022	<	* that have not yet begun executing. This method takes time
1021	>	* Returns an estimate of the number of tasks submitted to this
1022	>	* pool that have not yet begun executing.  This method takes time
1023		* proportional to the number of submissions.
1024		*
1025		* @return the number of queued submissions
#	Line 990 | Line 1053 | public class ForkJoinPool extends Abstra
1053		* Removes all available unexecuted submitted and forked tasks
1054		* from scheduling queues and adds them to the given collection,
1055		* without altering their execution status. These may include
1056	<	* artificially generated or wrapped tasks. This method is designed
1057	<	* to be invoked only when the pool is known to be
1056	>	* artificially generated or wrapped tasks. This method is
1057	>	* designed to be invoked only when the pool is known to be
1058		* quiescent. Invocations at other times may not remove all
1059		* tasks. A failure encountered while attempting to add elements
1060		* to collection {@code c} may result in elements being in
#	Line 1088 | Line 1151 | public class ForkJoinPool extends Abstra
1151		}
1152
1153		/**
1154	<	* Attempts to stop all actively executing tasks, and cancels all
1155	<	* waiting tasks.  Tasks that are in the process of being
1156	<	* submitted or executed concurrently during the course of this
1157	<	* method may or may not be rejected. Unlike some other executors,
1158	<	* this method cancels rather than collects non-executed tasks
1159	<	* upon termination, so always returns an empty list. However, you
1160	<	* can use method {@link #drainTasksTo} before invoking this
1161	<	* method to transfer unexecuted tasks to another collection.
1154	>	* Attempts to cancel and/or stop all tasks, and reject all
1155	>	* subsequently submitted tasks.  Tasks that are in the process of
1156	>	* being submitted or executed concurrently during the course of
1157	>	* this method may or may not be rejected. This method cancels
1158	>	* both existing and unexecuted tasks, in order to permit
1159	>	* termination in the presence of task dependencies. So the method
1160	>	* always returns an empty list (unlike the case for some other
1161	>	* Executors).
1162		*
1163		* @return an empty list
1164		* @throws SecurityException if a security manager exists and
#	Line 1120 | Line 1183 | public class ForkJoinPool extends Abstra
1183
1184		/**
1185		* Returns {@code true} if the process of termination has
1186	<	* commenced but possibly not yet completed.
1186	>	* commenced but not yet completed.  This method may be useful for
1187	>	* debugging. A return of {@code true} reported a sufficient
1188	>	* period after shutdown may indicate that submitted tasks have
1189	>	* ignored or suppressed interruption, causing this executor not
1190	>	* to properly terminate.
1191		*
1192	<	* @return {@code true} if terminating
1192	>	* @return {@code true} if terminating but not yet terminated
1193		*/
1194		public boolean isTerminating() {
1195	<	return runStateOf(runControl) >= TERMINATING;
1195	>	return runStateOf(runControl) == TERMINATING;
1196		}
1197
1198		/**
#	Line 1138 | Line 1205 | public class ForkJoinPool extends Abstra
1205		}
1206
1207		/**
1208	+	* Returns true if pool is not terminating or terminated.
1209	+	* Used internally to suppress execution when terminating.
1210	+	*/
1211	+	final boolean isProcessingTasks() {
1212	+	return runStateOf(runControl) < TERMINATING;
1213	+	}
1214	+
1215	+	/**
1216		* Blocks until all tasks have completed execution after a shutdown
1217		* request, or the timeout occurs, or the current thread is
1218		* interrupted, whichever happens first.
#	Line 1191 | Line 1266 | public class ForkJoinPool extends Abstra
1266		transitionRunStateTo(TERMINATED);
1267		termination.signalAll();
1268		}
1269	<	else if (!isTerminating()) {
1269	>	else if (isProcessingTasks()) {
1270		tryShrinkWorkerArray();
1271		tryResumeSpare(true); // allow replacement
1272		}
#	Line 1432 | Line 1507 | public class ForkJoinPool extends Abstra
1507		final void sync(ForkJoinWorkerThread w) {
1508		updateStealCount(w); // Transfer w's count while it is idle
1509
1510	<	while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
1510	>	while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
1511		long prev = w.lastEventCount;
1512		WaitQueueNode node = null;
1513		WaitQueueNode h;
#	Line 1532 | Line 1607 | public class ForkJoinPool extends Abstra
1607		while (spareStack == null || !tryResumeSpare(dec)) {
1608		int counts = workerCounts;
1609		if (dec || (dec = casWorkerCounts(counts, --counts))) {
1535	–	// CAS cheat
1610		if (!needSpare(counts, maintainParallelism))
1611		break;
1612		if (joinMe.status < 0)
#	Line 1637 | Line 1711 | public class ForkJoinPool extends Abstra
1711		for (k = 0; k < len && ws[k] != null; ++k)
1712		;
1713		}
1714	<	if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
1714	>	if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) {
1715		ws[k] = w;
1716		w.start();
1717		}
#	Line 1741 | Line 1815 | public class ForkJoinPool extends Abstra
1815		* Method {@code isReleasable} must return {@code true} if
1816		* blocking is not necessary. Method {@code block} blocks the
1817		* current thread if necessary (perhaps internally invoking
1818	<	* {@code isReleasable} before actually blocking.).
1818	>	* {@code isReleasable} before actually blocking).
1819		*
1820		* <p>For example, here is a ManagedBlocker based on a
1821		* ReentrantLock:
#	Line 1780 | Line 1854 | public class ForkJoinPool extends Abstra
1854
1855		/**
1856		* Blocks in accord with the given blocker.  If the current thread
1857	<	* is a ForkJoinWorkerThread, this method possibly arranges for a
1858	<	* spare thread to be activated if necessary to ensure parallelism
1859	<	* while the current thread is blocked.  If
1860	<	* {@code maintainParallelism} is {@code true} and the pool supports
1861	<	* it ({@link #getMaintainsParallelism}), this method attempts to
1862	<	* maintain the pool's nominal parallelism. Otherwise it activates
1863	<	* a thread only if necessary to avoid complete starvation. This
1864	<	* option may be preferable when blockages use timeouts, or are
1865	<	* almost always brief.
1857	>	* is a {@link ForkJoinWorkerThread}, this method possibly
1858	>	* arranges for a spare thread to be activated if necessary to
1859	>	* ensure parallelism while the current thread is blocked.
1860	>	*
1861	>	* <p>If {@code maintainParallelism} is {@code true} and the pool
1862	>	* supports it ({@link #getMaintainsParallelism}), this method
1863	>	* attempts to maintain the pool's nominal parallelism. Otherwise
1864	>	* it activates a thread only if necessary to avoid complete
1865	>	* starvation. This option may be preferable when blockages use
1866	>	* timeouts, or are almost always brief.
1867		*
1868	<	* <p> If the caller is not a ForkJoinTask, this method is behaviorally
1869	<	* equivalent to
1868	>	* <p>If the caller is not a {@link ForkJoinTask}, this method is
1869	>	* behaviorally equivalent to
1870		*  <pre> {@code
1871		* while (!blocker.isReleasable())
1872		*   if (blocker.block())
1873		*     return;
1874		* }</pre>
1875	<	* If the caller is a ForkJoinTask, then the pool may first
1876	<	* be expanded to ensure parallelism, and later adjusted.
1875	>	*
1876	>	* If the caller is a {@code ForkJoinTask}, then the pool may
1877	>	* first be expanded to ensure parallelism, and later adjusted.
1878		*
1879		* @param blocker the blocker
1880		* @param maintainParallelism if {@code true} and supported by

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