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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.27 by jsr166, Sun Jul 26 17:33:37 2009 UTC vs.
Revision 1.44 by dl, Tue Aug 4 11:44:33 2009 UTC

#	Line 20 | Line 20 | import java.util.concurrent.atomic.Atomi
20		import java.util.concurrent.atomic.AtomicLong;
21
22		/**
23	<	* An {@link ExecutorService} for running {@link ForkJoinTask}s.  A
24	<	* 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.
23	>	* An {@link ExecutorService} for running {@link ForkJoinTask}s.
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
35	<	* {@code setAsyncMode}, a ForkJoinPools may also be appropriate for
36	<	* use with fine-grained tasks that are never joined. Otherwise, other
37	<	* ExecutorService implementations are typically more appropriate
38	<	* 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 {@code ManagedBlocker} interface enables extension of
48	<	* the kinds of synchronization accommodated.  The target parallelism
49	<	* level may also be changed dynamically ({@code setParallelism})
50	<	* and thread construction can be limited using methods
51	<	* {@code setMaximumPoolSize} and/or
52	<	* {@code 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
60	<	* {@code getStealCount}) that are intended to aid in developing,
60	>	* {@link #getStealCount}) that are intended to aid in developing,
61		* tuning, and monitoring fork/join applications. Also, method
62	<	* {@code toString} returns indications of pool state in a
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.
86	>	* {@code IllegalArgumentException}.
87		*
88		* @since 1.7
89		* @author Doug Lea
#	Line 81 | Line 102 | public class ForkJoinPool extends Abstra
102		private static final int MAX_THREADS =  0x7FFF;
103
104		/**
105	<	* Factory for creating new ForkJoinWorkerThreads.  A
106	<	* ForkJoinWorkerThreadFactory must be defined and used for
107	<	* ForkJoinWorkerThread subclasses that extend base functionality
108	<	* or initialize threads with different contexts.
105	>	* Factory for creating new {@link ForkJoinWorkerThread}s.
106	>	* A {@code ForkJoinWorkerThreadFactory} must be defined and used
107	>	* for {@code ForkJoinWorkerThread} subclasses that extend base
108	>	* functionality or initialize threads with different contexts.
109		*/
110		public static interface ForkJoinWorkerThreadFactory {
111		/**
#	Line 311 | Line 332 | public class ForkJoinPool extends Abstra
332		}
333
334		/**
335	<	* Returns true if argument represents zero active count and
336	<	* nonzero runstate, which is the triggering condition for
335	>	* Returns {@code true} if argument represents zero active count
336	>	* and nonzero runstate, which is the triggering condition for
337		* terminating on shutdown.
338		*/
339		private static boolean canTerminateOnShutdown(int c) {
#	Line 342 | Line 363 | public class ForkJoinPool extends Abstra
363		// Constructors
364
365		/**
366	<	* Creates a ForkJoinPool with a pool size equal to the number of
367	<	* processors available on the system, using the default
368	<	* ForkJoinWorkerThreadFactory.
366	>	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
367	>	* java.lang.Runtime#availableProcessors}, and using the {@linkplain
368	>	* #defaultForkJoinWorkerThreadFactory default thread factory}.
369		*
370		* @throws SecurityException if a security manager exists and
371		*         the caller is not permitted to modify threads
#	Line 357 | Line 378 | public class ForkJoinPool extends Abstra
378		}
379
380		/**
381	<	* Creates a ForkJoinPool with the indicated parallelism level
382	<	* threads and using the default ForkJoinWorkerThreadFactory.
381	>	* Creates a {@code ForkJoinPool} with the indicated parallelism
382	>	* level and using the {@linkplain
383	>	* #defaultForkJoinWorkerThreadFactory default thread factory}.
384		*
385	<	* @param parallelism the number of worker threads
385	>	* @param parallelism the parallelism level
386		* @throws IllegalArgumentException if parallelism less than or
387		* equal to zero
388		* @throws SecurityException if a security manager exists and
#	Line 373 | Line 395 | public class ForkJoinPool extends Abstra
395		}
396
397		/**
398	<	* Creates a ForkJoinPool with parallelism equal to the number of
399	<	* processors available on the system and using the given
400	<	* ForkJoinWorkerThreadFactory.
398	>	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
399	>	* java.lang.Runtime#availableProcessors}, and using the given
400	>	* thread factory.
401		*
402		* @param factory the factory for creating new threads
403		* @throws NullPointerException if factory is null
#	Line 389 | Line 411 | public class ForkJoinPool extends Abstra
411		}
412
413		/**
414	<	* Creates a ForkJoinPool with the given parallelism and factory.
414	>	* Creates a {@code ForkJoinPool} with the given parallelism and
415	>	* thread factory.
416		*
417	<	* @param parallelism the targeted number of worker threads
417	>	* @param parallelism the parallelism level
418		* @param factory the factory for creating new threads
419		* @throws IllegalArgumentException if parallelism less than or
420		* equal to zero, or greater than implementation limit
#	Line 423 | Line 446 | public class ForkJoinPool extends Abstra
446		* Creates a new worker thread using factory.
447		*
448		* @param index the index to assign worker
449	<	* @return new worker, or null of factory failed
449	>	* @return new worker, or null if factory failed
450		*/
451		private ForkJoinWorkerThread createWorker(int index) {
452		Thread.UncaughtExceptionHandler h = ueh;
#	Line 444 | Line 467 | public class ForkJoinPool extends Abstra
467		* Currently requires size to be a power of two.
468		*/
469		private static int arraySizeFor(int poolSize) {
470	<	return (poolSize <= 1) ? 1 :
471	<	(1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
470	>	if (poolSize <= 1)
471	>	return 1;
472	>	// See Hackers Delight, sec 3.2
473	>	int c = poolSize >= MAX_THREADS ? MAX_THREADS : (poolSize - 1);
474	>	c |= c >>>  1;
475	>	c |= c >>>  2;
476	>	c |= c >>>  4;
477	>	c |= c >>>  8;
478	>	c |= c >>> 16;
479	>	return c + 1;
480		}
481
482		/**
#	Line 578 | Line 609 | public class ForkJoinPool extends Abstra
609		* @throws NullPointerException if task is null
610		* @throws RejectedExecutionException if pool is shut down
611		*/
612	<	public <T> void execute(ForkJoinTask<T> task) {
612	>	public void execute(ForkJoinTask<?> task) {
613		doSubmit(task);
614		}
615
#	Line 589 | Line 620 | public class ForkJoinPool extends Abstra
620		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
621		job = (ForkJoinTask<?>) task;
622		else
623	<	job = new AdaptedRunnable<Void>(task, null);
623	>	job = ForkJoinTask.adapt(task, null);
624		doSubmit(job);
625		}
626
627		public <T> ForkJoinTask<T> submit(Callable<T> task) {
628	<	ForkJoinTask<T> job = new AdaptedCallable<T>(task);
628	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task);
629		doSubmit(job);
630		return job;
631		}
632
633		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
634	<	ForkJoinTask<T> job = new AdaptedRunnable<T>(task, result);
634	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
635		doSubmit(job);
636		return job;
637		}
#	Line 610 | Line 641 | public class ForkJoinPool extends Abstra
641		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
642		job = (ForkJoinTask<?>) task;
643		else
644	<	job = new AdaptedRunnable<Void>(task, null);
644	>	job = ForkJoinTask.adapt(task, null);
645		doSubmit(job);
646		return job;
647		}
#	Line 629 | Line 660 | public class ForkJoinPool extends Abstra
660		return task;
661		}
662
632	–	/**
633	–	* Adaptor for Runnables. This implements RunnableFuture
634	–	* to be compliant with AbstractExecutorService constraints.
635	–	*/
636	–	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
637	–	implements RunnableFuture<T> {
638	–	final Runnable runnable;
639	–	final T resultOnCompletion;
640	–	T result;
641	–	AdaptedRunnable(Runnable runnable, T result) {
642	–	if (runnable == null) throw new NullPointerException();
643	–	this.runnable = runnable;
644	–	this.resultOnCompletion = result;
645	–	}
646	–	public T getRawResult() { return result; }
647	–	public void setRawResult(T v) { result = v; }
648	–	public boolean exec() {
649	–	runnable.run();
650	–	result = resultOnCompletion;
651	–	return true;
652	–	}
653	–	public void run() { invoke(); }
654	–	private static final long serialVersionUID = 5232453952276885070L;
655	–	}
656	–
657	–	/**
658	–	* Adaptor for Callables
659	–	*/
660	–	static final class AdaptedCallable<T> extends ForkJoinTask<T>
661	–	implements RunnableFuture<T> {
662	–	final Callable<T> callable;
663	–	T result;
664	–	AdaptedCallable(Callable<T> callable) {
665	–	if (callable == null) throw new NullPointerException();
666	–	this.callable = callable;
667	–	}
668	–	public T getRawResult() { return result; }
669	–	public void setRawResult(T v) { result = v; }
670	–	public boolean exec() {
671	–	try {
672	–	result = callable.call();
673	–	return true;
674	–	} catch (Error err) {
675	–	throw err;
676	–	} catch (RuntimeException rex) {
677	–	throw rex;
678	–	} catch (Exception ex) {
679	–	throw new RuntimeException(ex);
680	–	}
681	–	}
682	–	public void run() { invoke(); }
683	–	private static final long serialVersionUID = 2838392045355241008L;
684	–	}
663
664		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
665		ArrayList<ForkJoinTask<T>> forkJoinTasks =
666		new ArrayList<ForkJoinTask<T>>(tasks.size());
667		for (Callable<T> task : tasks)
668	<	forkJoinTasks.add(new AdaptedCallable<T>(task));
668	>	forkJoinTasks.add(ForkJoinTask.adapt(task));
669		invoke(new InvokeAll<T>(forkJoinTasks));
670
671		@SuppressWarnings({"unchecked", "rawtypes"})
#	Line 720 | Line 698 | public class ForkJoinPool extends Abstra
698		* Returns the handler for internal worker threads that terminate
699		* due to unrecoverable errors encountered while executing tasks.
700		*
701	<	* @return the handler, or null if none
701	>	* @return the handler, or {@code null} if none
702		*/
703		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
704		Thread.UncaughtExceptionHandler h;
#	Line 741 | Line 719 | public class ForkJoinPool extends Abstra
719		* as handler.
720		*
721		* @param h the new handler
722	<	* @return the old handler, or null if none
722	>	* @return the old handler, or {@code null} if none
723		* @throws SecurityException if a security manager exists and
724		*         the caller is not permitted to modify threads
725		*         because it does not hold {@link
#	Line 789 | Line 767 | public class ForkJoinPool extends Abstra
767		final ReentrantLock lock = this.workerLock;
768		lock.lock();
769		try {
770	<	if (!isTerminating()) {
770	>	if (isProcessingTasks()) {
771		int p = this.parallelism;
772		this.parallelism = parallelism;
773		if (parallelism > p)
#	Line 804 | Line 782 | public class ForkJoinPool extends Abstra
782		}
783
784		/**
785	<	* Returns the targeted number of worker threads in this pool.
785	>	* Returns the targeted parallelism level of this pool.
786		*
787	<	* @return the targeted number of worker threads in this pool
787	>	* @return the targeted parallelism level of this pool
788		*/
789		public int getParallelism() {
790		return parallelism;
#	Line 815 | Line 793 | public class ForkJoinPool extends Abstra
793		/**
794		* Returns the number of worker threads that have started but not
795		* yet terminated.  This result returned by this method may differ
796	<	* from {@code getParallelism} when threads are created to
796	>	* from {@link #getParallelism} when threads are created to
797		* maintain parallelism when others are cooperatively blocked.
798		*
799		* @return the number of worker threads
#	Line 826 | Line 804 | public class ForkJoinPool extends Abstra
804
805		/**
806		* Returns the maximum number of threads allowed to exist in the
807	<	* pool, even if there are insufficient unblocked running threads.
807	>	* pool.  Unless set using {@link #setMaximumPoolSize}, the
808	>	* maximum is an implementation-defined value designed only to
809	>	* prevent runaway growth.
810		*
811		* @return the maximum
812		*/
#	Line 836 | Line 816 | public class ForkJoinPool extends Abstra
816
817		/**
818		* Sets the maximum number of threads allowed to exist in the
819	<	* pool, even if there are insufficient unblocked running threads.
820	<	* Setting this value has no effect on current pool size. It
841	<	* controls construction of new threads.
819	>	* pool.  Setting this value has no effect on current pool
820	>	* size. It controls construction of new threads.
821		*
822	<	* @throws IllegalArgumentException if negative or greater then
822	>	* @throws IllegalArgumentException if negative or greater than
823		* internal implementation limit
824		*/
825		public void setMaximumPoolSize(int newMax) {
#	Line 851 | Line 830 | public class ForkJoinPool extends Abstra
830
831
832		/**
833	<	* Returns true if this pool dynamically maintains its target
834	<	* parallelism level. If false, new threads are added only to
835	<	* avoid possible starvation.
857	<	* This setting is by default true.
833	>	* Returns {@code true} if this pool dynamically maintains its
834	>	* target parallelism level. If false, new threads are added only
835	>	* to avoid possible starvation.  This setting is by default true.
836		*
837	<	* @return true if maintains parallelism
837	>	* @return {@code true} if maintains parallelism
838		*/
839		public boolean getMaintainsParallelism() {
840		return maintainsParallelism;
#	Line 867 | Line 845 | public class ForkJoinPool extends Abstra
845		* parallelism level. If false, new threads are added only to
846		* avoid possible starvation.
847		*
848	<	* @param enable true to maintains parallelism
848	>	* @param enable {@code true} to maintain parallelism
849		*/
850		public void setMaintainsParallelism(boolean enable) {
851		maintainsParallelism = enable;
#	Line 878 | Line 856 | public class ForkJoinPool extends Abstra
856		* tasks that are never joined. This mode may be more appropriate
857		* than default locally stack-based mode in applications in which
858		* worker threads only process asynchronous tasks.  This method is
859	<	* designed to be invoked only when pool is quiescent, and
859	>	* designed to be invoked only when the pool is quiescent, and
860		* typically only before any tasks are submitted. The effects of
861		* invocations at other times may be unpredictable.
862		*
863	<	* @param async if true, use locally FIFO scheduling
863	>	* @param async if {@code true}, use locally FIFO scheduling
864		* @return the previous mode
865	+	* @see #getAsyncMode
866		*/
867		public boolean setAsyncMode(boolean async) {
868		boolean oldMode = locallyFifo;
#	Line 900 | Line 879 | public class ForkJoinPool extends Abstra
879		}
880
881		/**
882	<	* Returns true if this pool uses local first-in-first-out
882	>	* Returns {@code true} if this pool uses local first-in-first-out
883		* scheduling mode for forked tasks that are never joined.
884		*
885	<	* @return true if this pool uses async mode
885	>	* @return {@code true} if this pool uses async mode
886	>	* @see #setAsyncMode
887		*/
888		public boolean getAsyncMode() {
889		return locallyFifo;
#	Line 944 | Line 924 | public class ForkJoinPool extends Abstra
924		}
925
926		/**
927	<	* Returns true if all worker threads are currently idle. An idle
928	<	* worker is one that cannot obtain a task to execute because none
929	<	* are available to steal from other threads, and there are no
930	<	* pending submissions to the pool. This method is conservative;
931	<	* it might not return true immediately upon idleness of all
932	<	* threads, but will eventually become true if threads remain
933	<	* inactive.
927	>	* Returns {@code true} if all worker threads are currently idle.
928	>	* An idle worker is one that cannot obtain a task to execute
929	>	* because none are available to steal from other threads, and
930	>	* there are no pending submissions to the pool. This method is
931	>	* conservative; it might not return {@code true} immediately upon
932	>	* idleness of all threads, but will eventually become true if
933	>	* threads remain inactive.
934		*
935	<	* @return true if all threads are currently idle
935	>	* @return {@code true} if all threads are currently idle
936		*/
937		public boolean isQuiescent() {
938		return activeCountOf(runControl) == 0;
#	Line 1007 | Line 987 | public class ForkJoinPool extends Abstra
987		}
988
989		/**
990	<	* Returns an estimate of the number tasks submitted to this pool
991	<	* that have not yet begun executing. This method takes time
990	>	* Returns an estimate of the number of tasks submitted to this
991	>	* pool that have not yet begun executing.  This method takes time
992		* proportional to the number of submissions.
993		*
994		* @return the number of queued submissions
#	Line 1018 | Line 998 | public class ForkJoinPool extends Abstra
998		}
999
1000		/**
1001	<	* Returns true if there are any tasks submitted to this pool
1002	<	* that have not yet begun executing.
1001	>	* Returns {@code true} if there are any tasks submitted to this
1002	>	* pool that have not yet begun executing.
1003		*
1004		* @return {@code true} if there are any queued submissions
1005		*/
#	Line 1032 | Line 1012 | public class ForkJoinPool extends Abstra
1012		* available.  This method may be useful in extensions to this
1013		* class that re-assign work in systems with multiple pools.
1014		*
1015	<	* @return the next submission, or null if none
1015	>	* @return the next submission, or {@code null} if none
1016		*/
1017		protected ForkJoinTask<?> pollSubmission() {
1018		return submissionQueue.poll();
#	Line 1042 | Line 1022 | public class ForkJoinPool extends Abstra
1022		* Removes all available unexecuted submitted and forked tasks
1023		* from scheduling queues and adds them to the given collection,
1024		* without altering their execution status. These may include
1025	<	* artificially generated or wrapped tasks. This method is designed
1026	<	* to be invoked only when the pool is known to be
1025	>	* artificially generated or wrapped tasks. This method is
1026	>	* designed to be invoked only when the pool is known to be
1027		* quiescent. Invocations at other times may not remove all
1028		* tasks. A failure encountered while attempting to add elements
1029		* to collection {@code c} may result in elements being in
#	Line 1055 | Line 1035 | public class ForkJoinPool extends Abstra
1035		* @param c the collection to transfer elements into
1036		* @return the number of elements transferred
1037		*/
1038	<	protected int drainTasksTo(Collection<ForkJoinTask<?>> c) {
1038	>	protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1039		int n = submissionQueue.drainTo(c);
1040		ForkJoinWorkerThread[] ws = workers;
1041		if (ws != null) {
#	Line 1121 | Line 1101 | public class ForkJoinPool extends Abstra
1101		public void shutdown() {
1102		checkPermission();
1103		transitionRunStateTo(SHUTDOWN);
1104	<	if (canTerminateOnShutdown(runControl))
1104	>	if (canTerminateOnShutdown(runControl)) {
1105	>	if (workers == null) { // shutting down before workers created
1106	>	final ReentrantLock lock = this.workerLock;
1107	>	lock.lock();
1108	>	try {
1109	>	if (workers == null) {
1110	>	terminate();
1111	>	transitionRunStateTo(TERMINATED);
1112	>	termination.signalAll();
1113	>	}
1114	>	} finally {
1115	>	lock.unlock();
1116	>	}
1117	>	}
1118		terminateOnShutdown();
1119	+	}
1120		}
1121
1122		/**
1123	<	* Attempts to stop all actively executing tasks, and cancels all
1124	<	* waiting tasks.  Tasks that are in the process of being
1125	<	* submitted or executed concurrently during the course of this
1126	<	* method may or may not be rejected. Unlike some other executors,
1127	<	* this method cancels rather than collects non-executed tasks
1128	<	* upon termination, so always returns an empty list. However, you
1129	<	* can use method {@code drainTasksTo} before invoking this
1130	<	* method to transfer unexecuted tasks to another collection.
1123	>	* Attempts to cancel and/or stop all tasks, and reject all
1124	>	* subsequently submitted tasks.  Tasks that are in the process of
1125	>	* being submitted or executed concurrently during the course of
1126	>	* this method may or may not be rejected. This method cancels
1127	>	* both existing and unexecuted tasks, in order to permit
1128	>	* termination in the presence of task dependencies. So the method
1129	>	* always returns an empty list (unlike the case for some other
1130	>	* Executors).
1131		*
1132		* @return an empty list
1133		* @throws SecurityException if a security manager exists and
#	Line 1158 | Line 1152 | public class ForkJoinPool extends Abstra
1152
1153		/**
1154		* Returns {@code true} if the process of termination has
1155	<	* commenced but possibly not yet completed.
1155	>	* commenced but not yet completed.  This method may be useful for
1156	>	* debugging. A return of {@code true} reported a sufficient
1157	>	* period after shutdown may indicate that submitted tasks have
1158	>	* ignored or suppressed interruption, causing this executor not
1159	>	* to properly terminate.
1160		*
1161	<	* @return {@code true} if terminating
1161	>	* @return {@code true} if terminating but not yet terminated
1162		*/
1163		public boolean isTerminating() {
1164	<	return runStateOf(runControl) >= TERMINATING;
1164	>	return runStateOf(runControl) == TERMINATING;
1165		}
1166
1167		/**
#	Line 1176 | Line 1174 | public class ForkJoinPool extends Abstra
1174		}
1175
1176		/**
1177	+	* Returns true if pool is not terminating or terminated.
1178	+	* Used internally to suppress execution when terminating.
1179	+	*/
1180	+	final boolean isProcessingTasks() {
1181	+	return runStateOf(runControl) < TERMINATING;
1182	+	}
1183	+
1184	+	/**
1185		* Blocks until all tasks have completed execution after a shutdown
1186		* request, or the timeout occurs, or the current thread is
1187		* interrupted, whichever happens first.
#	Line 1229 | Line 1235 | public class ForkJoinPool extends Abstra
1235		transitionRunStateTo(TERMINATED);
1236		termination.signalAll();
1237		}
1238	<	else if (!isTerminating()) {
1238	>	else if (isProcessingTasks()) {
1239		tryShrinkWorkerArray();
1240		tryResumeSpare(true); // allow replacement
1241		}
#	Line 1470 | Line 1476 | public class ForkJoinPool extends Abstra
1476		final void sync(ForkJoinWorkerThread w) {
1477		updateStealCount(w); // Transfer w's count while it is idle
1478
1479	<	while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
1479	>	while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
1480		long prev = w.lastEventCount;
1481		WaitQueueNode node = null;
1482		WaitQueueNode h;
#	Line 1492 | Line 1498 | public class ForkJoinPool extends Abstra
1498		}
1499
1500		/**
1501	<	* Returns true if worker waiting on sync can proceed:
1501	>	* Returns {@code true} if worker waiting on sync can proceed:
1502		*  - on signal (thread == null)
1503		*  - on event count advance (winning race to notify vs signaller)
1504		*  - on interrupt
#	Line 1500 | Line 1506 | public class ForkJoinPool extends Abstra
1506		* If node was not signalled and event count not advanced on exit,
1507		* then we also help advance event count.
1508		*
1509	<	* @return true if node can be released
1509	>	* @return {@code true} if node can be released
1510		*/
1511		final boolean syncIsReleasable(WaitQueueNode node) {
1512		long prev = node.count;
#	Line 1519 | Line 1525 | public class ForkJoinPool extends Abstra
1525		}
1526
1527		/**
1528	<	* Returns true if a new sync event occurred since last call to
1529	<	* sync or this method, if so, updating caller's count.
1528	>	* Returns {@code true} if a new sync event occurred since last
1529	>	* call to sync or this method, if so, updating caller's count.
1530		*/
1531		final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1532		long lc = w.lastEventCount;
#	Line 1604 | Line 1610 | public class ForkJoinPool extends Abstra
1610		}
1611
1612		/**
1613	<	* Returns true if a spare thread appears to be needed.  If
1614	<	* maintaining parallelism, returns true when the deficit in
1613	>	* Returns {@code true} if a spare thread appears to be needed.
1614	>	* If maintaining parallelism, returns true when the deficit in
1615		* running threads is more than the surplus of total threads, and
1616		* there is apparently some work to do.  This self-limiting rule
1617		* means that the more threads that have already been added, the
#	Line 1675 | Line 1681 | public class ForkJoinPool extends Abstra
1681		for (k = 0; k < len && ws[k] != null; ++k)
1682		;
1683		}
1684	<	if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
1684	>	if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) {
1685		ws[k] = w;
1686		w.start();
1687		}
#	Line 1773 | Line 1779 | public class ForkJoinPool extends Abstra
1779
1780		/**
1781		* Interface for extending managed parallelism for tasks running
1782	<	* in ForkJoinPools. A ManagedBlocker provides two methods.
1783	<	* Method {@code isReleasable} must return true if blocking is not
1784	<	* necessary. Method {@code block} blocks the current thread if
1785	<	* necessary (perhaps internally invoking {@code isReleasable}
1786	<	* before actually blocking.).
1782	>	* in {@link ForkJoinPool}s.
1783	>	*
1784	>	* <p>A {@code ManagedBlocker} provides two methods.
1785	>	* Method {@code isReleasable} must return {@code true} if
1786	>	* blocking is not necessary. Method {@code block} blocks the
1787	>	* current thread if necessary (perhaps internally invoking
1788	>	* {@code isReleasable} before actually blocking).
1789		*
1790		* <p>For example, here is a ManagedBlocker based on a
1791		* ReentrantLock:
#	Line 1801 | Line 1809 | public class ForkJoinPool extends Abstra
1809		* Possibly blocks the current thread, for example waiting for
1810		* a lock or condition.
1811		*
1812	<	* @return true if no additional blocking is necessary (i.e.,
1813	<	* if isReleasable would return true)
1812	>	* @return {@code true} if no additional blocking is necessary
1813	>	* (i.e., if isReleasable would return true)
1814		* @throws InterruptedException if interrupted while waiting
1815		* (the method is not required to do so, but is allowed to)
1816		*/
1817		boolean block() throws InterruptedException;
1818
1819		/**
1820	<	* Returns true if blocking is unnecessary.
1820	>	* Returns {@code true} if blocking is unnecessary.
1821		*/
1822		boolean isReleasable();
1823		}
1824
1825		/**
1826		* Blocks in accord with the given blocker.  If the current thread
1827	<	* is a ForkJoinWorkerThread, this method possibly arranges for a
1828	<	* spare thread to be activated if necessary to ensure parallelism
1829	<	* while the current thread is blocked.  If
1830	<	* {@code maintainParallelism} is true and the pool supports
1831	<	* it ({@link #getMaintainsParallelism}), this method attempts to
1832	<	* maintain the pool's nominal parallelism. Otherwise it activates
1833	<	* a thread only if necessary to avoid complete starvation. This
1834	<	* option may be preferable when blockages use timeouts, or are
1835	<	* almost always brief.
1827	>	* is a {@link ForkJoinWorkerThread}, this method possibly
1828	>	* arranges for a spare thread to be activated if necessary to
1829	>	* ensure parallelism while the current thread is blocked.
1830	>	*
1831	>	* <p>If {@code maintainParallelism} is {@code true} and the pool
1832	>	* supports it ({@link #getMaintainsParallelism}), this method
1833	>	* attempts to maintain the pool's nominal parallelism. Otherwise
1834	>	* it activates a thread only if necessary to avoid complete
1835	>	* starvation. This option may be preferable when blockages use
1836	>	* timeouts, or are almost always brief.
1837		*
1838	<	* <p> If the caller is not a ForkJoinTask, this method is behaviorally
1839	<	* equivalent to
1838	>	* <p>If the caller is not a {@link ForkJoinTask}, this method is
1839	>	* behaviorally equivalent to
1840		*  <pre> {@code
1841		* while (!blocker.isReleasable())
1842		*   if (blocker.block())
1843		*     return;
1844		* }</pre>
1845	<	* If the caller is a ForkJoinTask, then the pool may first
1846	<	* be expanded to ensure parallelism, and later adjusted.
1845	>	*
1846	>	* If the caller is a {@code ForkJoinTask}, then the pool may
1847	>	* first be expanded to ensure parallelism, and later adjusted.
1848		*
1849		* @param blocker the blocker
1850	<	* @param maintainParallelism if true and supported by this pool,
1851	<	* attempt to maintain the pool's nominal parallelism; otherwise
1852	<	* activate a thread only if necessary to avoid complete
1853	<	* starvation.
1850	>	* @param maintainParallelism if {@code true} and supported by
1851	>	* this pool, attempt to maintain the pool's nominal parallelism;
1852	>	* otherwise activate a thread only if necessary to avoid
1853	>	* complete starvation.
1854		* @throws InterruptedException if blocker.block did so
1855		*/
1856		public static void managedBlock(ManagedBlocker blocker,
#	Line 1866 | Line 1876 | public class ForkJoinPool extends Abstra
1876		do {} while (!blocker.isReleasable() && !blocker.block());
1877		}
1878
1879	<	// AbstractExecutorService overrides
1879	>	// AbstractExecutorService overrides.  These rely on undocumented
1880	>	// fact that ForkJoinTask.adapt returns ForkJoinTasks that also
1881	>	// implement RunnableFuture.
1882
1883		protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
1884	<	return new AdaptedRunnable<T>(runnable, value);
1884	>	return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
1885		}
1886
1887		protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
1888	<	return new AdaptedCallable<T>(callable);
1888	>	return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
1889		}
1890
1891		// Unsafe mechanics

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