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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.33 by dl, Fri Jul 31 16:27:08 2009 UTC vs.
Revision 1.51 by dl, Fri Dec 4 15:46:38 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 81 | Line 105 | public class ForkJoinPool extends Abstra
105		private static final int MAX_THREADS =  0x7FFF;
106
107		/**
108	<	* Factory for creating new ForkJoinWorkerThreads.  A
109	<	* ForkJoinWorkerThreadFactory must be defined and used for
110	<	* ForkJoinWorkerThread subclasses that extend base functionality
111	<	* or initialize threads with different contexts.
108	>	* Factory for creating new {@link ForkJoinWorkerThread}s.
109	>	* A {@code ForkJoinWorkerThreadFactory} must be defined and used
110	>	* for {@code ForkJoinWorkerThread} subclasses that extend base
111	>	* functionality or initialize threads with different contexts.
112		*/
113		public static interface ForkJoinWorkerThreadFactory {
114		/**
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 492 | Line 526 | public class ForkJoinPool extends Abstra
526		ws = workers;
527		if (ws == null) {
528		int ps = parallelism;
529	+	updateWorkerCount(ps);
530		ws = ensureWorkerArrayCapacity(ps);
531		for (int i = 0; i < ps; ++i) {
532		ForkJoinWorkerThread w = createWorker(i);
533		if (w != null) {
534		ws[i] = w;
535		w.start();
501	–	updateWorkerCount(1);
536		}
537	+	else
538	+	updateWorkerCount(-1);
539		}
540		}
541		} finally {
#	Line 563 | Line 599 | public class ForkJoinPool extends Abstra
599		*
600		* @param task the task
601		* @return the task's result
602	<	* @throws NullPointerException if task is null
603	<	* @throws RejectedExecutionException if pool is shut down
602	>	* @throws NullPointerException if the task is null
603	>	* @throws RejectedExecutionException if the task cannot be
604	>	*         scheduled for execution
605		*/
606		public <T> T invoke(ForkJoinTask<T> task) {
607		doSubmit(task);
#	Line 575 | Line 612 | public class ForkJoinPool extends Abstra
612		* Arranges for (asynchronous) execution of the given task.
613		*
614		* @param task the task
615	<	* @throws NullPointerException if task is null
616	<	* @throws RejectedExecutionException if pool is shut down
615	>	* @throws NullPointerException if the task is null
616	>	* @throws RejectedExecutionException if the task cannot be
617	>	*         scheduled for execution
618		*/
619	<	public <T> void execute(ForkJoinTask<T> task) {
619	>	public void execute(ForkJoinTask<?> task) {
620		doSubmit(task);
621		}
622
623		// AbstractExecutorService methods
624
625	+	/**
626	+	* @throws NullPointerException if the task is null
627	+	* @throws RejectedExecutionException if the task cannot be
628	+	*         scheduled for execution
629	+	*/
630		public void execute(Runnable task) {
631		ForkJoinTask<?> job;
632		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
#	Line 593 | Line 636 | public class ForkJoinPool extends Abstra
636		doSubmit(job);
637		}
638
639	+	/**
640	+	* @throws NullPointerException if the task is null
641	+	* @throws RejectedExecutionException if the task cannot be
642	+	*         scheduled for execution
643	+	*/
644		public <T> ForkJoinTask<T> submit(Callable<T> task) {
645		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
646		doSubmit(job);
647		return job;
648		}
649
650	+	/**
651	+	* @throws NullPointerException if the task is null
652	+	* @throws RejectedExecutionException if the task cannot be
653	+	*         scheduled for execution
654	+	*/
655		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
656		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
657		doSubmit(job);
658		return job;
659		}
660
661	+	/**
662	+	* @throws NullPointerException if the task is null
663	+	* @throws RejectedExecutionException if the task cannot be
664	+	*         scheduled for execution
665	+	*/
666		public ForkJoinTask<?> submit(Runnable task) {
667		ForkJoinTask<?> job;
668		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
#	Line 620 | Line 678 | public class ForkJoinPool extends Abstra
678		*
679		* @param task the task to submit
680		* @return the task
681	+	* @throws NullPointerException if the task is null
682		* @throws RejectedExecutionException if the task cannot be
683		*         scheduled for execution
625	–	* @throws NullPointerException if the task is null
684		*/
685		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
686		doSubmit(task);
#	Line 630 | Line 688 | public class ForkJoinPool extends Abstra
688		}
689
690
691	+	/**
692	+	* @throws NullPointerException       {@inheritDoc}
693	+	* @throws RejectedExecutionException {@inheritDoc}
694	+	*/
695		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
696		ArrayList<ForkJoinTask<T>> forkJoinTasks =
697		new ArrayList<ForkJoinTask<T>>(tasks.size());
#	Line 736 | Line 798 | public class ForkJoinPool extends Abstra
798		final ReentrantLock lock = this.workerLock;
799		lock.lock();
800		try {
801	<	if (!isTerminating()) {
801	>	if (isProcessingTasks()) {
802		int p = this.parallelism;
803		this.parallelism = parallelism;
804	<	if (parallelism > p)
805	<	createAndStartAddedWorkers();
806	<	else
807	<	trimSpares();
804	>	if (workers != null) {
805	>	if (parallelism > p)
806	>	createAndStartAddedWorkers();
807	>	else
808	>	trimSpares();
809	>	}
810		}
811		} finally {
812		lock.unlock();
#	Line 751 | Line 815 | public class ForkJoinPool extends Abstra
815		}
816
817		/**
818	<	* Returns the targeted number of worker threads in this pool.
818	>	* Returns the targeted parallelism level of this pool.
819		*
820	<	* @return the targeted number of worker threads in this pool
820	>	* @return the targeted parallelism level of this pool
821		*/
822		public int getParallelism() {
823		return parallelism;
#	Line 773 | Line 837 | public class ForkJoinPool extends Abstra
837
838		/**
839		* Returns the maximum number of threads allowed to exist in the
840	<	* pool, even if there are insufficient unblocked running threads.
840	>	* pool. Unless set using {@link #setMaximumPoolSize}, the
841	>	* maximum is an implementation-defined value designed only to
842	>	* prevent runaway growth.
843		*
844		* @return the maximum
845		*/
#	Line 783 | Line 849 | public class ForkJoinPool extends Abstra
849
850		/**
851		* Sets the maximum number of threads allowed to exist in the
852	<	* pool, even if there are insufficient unblocked running threads.
853	<	* Setting this value has no effect on current pool size. It
854	<	* controls construction of new threads.
852	>	* pool. The given value should normally be greater than or equal
853	>	* to the {@link #getParallelism parallelism} level. Setting this
854	>	* value has no effect on current pool size. It controls
855	>	* construction of new threads.
856		*
857	<	* @throws IllegalArgumentException if negative or greater then
857	>	* @throws IllegalArgumentException if negative or greater than
858		* internal implementation limit
859		*/
860		public void setMaximumPoolSize(int newMax) {
#	Line 955 | Line 1022 | public class ForkJoinPool extends Abstra
1022		}
1023
1024		/**
1025	<	* Returns an estimate of the number tasks submitted to this pool
1026	<	* that have not yet begun executing. This method takes time
1025	>	* Returns an estimate of the number of tasks submitted to this
1026	>	* pool that have not yet begun executing.  This method takes time
1027		* proportional to the number of submissions.
1028		*
1029		* @return the number of queued submissions
#	Line 990 | Line 1057 | public class ForkJoinPool extends Abstra
1057		* Removes all available unexecuted submitted and forked tasks
1058		* from scheduling queues and adds them to the given collection,
1059		* without altering their execution status. These may include
1060	<	* artificially generated or wrapped tasks. This method is designed
1061	<	* to be invoked only when the pool is known to be
1060	>	* artificially generated or wrapped tasks. This method is
1061	>	* designed to be invoked only when the pool is known to be
1062		* quiescent. Invocations at other times may not remove all
1063		* tasks. A failure encountered while attempting to add elements
1064		* to collection {@code c} may result in elements being in
#	Line 1043 | Line 1110 | public class ForkJoinPool extends Abstra
1110		}
1111
1112		private static String runStateToString(int rs) {
1113	<	switch(rs) {
1113	>	switch (rs) {
1114		case RUNNING: return "Running";
1115		case SHUTDOWN: return "Shutting down";
1116		case TERMINATING: return "Terminating";
#	Line 1088 | Line 1155 | public class ForkJoinPool extends Abstra
1155		}
1156
1157		/**
1158	<	* Attempts to stop all actively executing tasks, and cancels all
1159	<	* waiting tasks.  Tasks that are in the process of being
1160	<	* submitted or executed concurrently during the course of this
1161	<	* method may or may not be rejected. Unlike some other executors,
1162	<	* this method cancels rather than collects non-executed tasks
1163	<	* upon termination, so always returns an empty list. However, you
1164	<	* can use method {@link #drainTasksTo} before invoking this
1165	<	* method to transfer unexecuted tasks to another collection.
1158	>	* Attempts to cancel and/or stop all tasks, and reject all
1159	>	* subsequently submitted tasks.  Tasks that are in the process of
1160	>	* being submitted or executed concurrently during the course of
1161	>	* this method may or may not be rejected. This method cancels
1162	>	* both existing and unexecuted tasks, in order to permit
1163	>	* termination in the presence of task dependencies. So the method
1164	>	* always returns an empty list (unlike the case for some other
1165	>	* Executors).
1166		*
1167		* @return an empty list
1168		* @throws SecurityException if a security manager exists and
#	Line 1120 | Line 1187 | public class ForkJoinPool extends Abstra
1187
1188		/**
1189		* Returns {@code true} if the process of termination has
1190	<	* commenced but possibly not yet completed.
1190	>	* commenced but not yet completed.  This method may be useful for
1191	>	* debugging. A return of {@code true} reported a sufficient
1192	>	* period after shutdown may indicate that submitted tasks have
1193	>	* ignored or suppressed interruption, causing this executor not
1194	>	* to properly terminate.
1195		*
1196	<	* @return {@code true} if terminating
1196	>	* @return {@code true} if terminating but not yet terminated
1197		*/
1198		public boolean isTerminating() {
1199	<	return runStateOf(runControl) >= TERMINATING;
1199	>	return runStateOf(runControl) == TERMINATING;
1200		}
1201
1202		/**
#	Line 1138 | Line 1209 | public class ForkJoinPool extends Abstra
1209		}
1210
1211		/**
1212	+	* Returns true if pool is not terminating or terminated.
1213	+	* Used internally to suppress execution when terminating.
1214	+	*/
1215	+	final boolean isProcessingTasks() {
1216	+	return runStateOf(runControl) < TERMINATING;
1217	+	}
1218	+
1219	+	/**
1220		* Blocks until all tasks have completed execution after a shutdown
1221		* request, or the timeout occurs, or the current thread is
1222		* interrupted, whichever happens first.
#	Line 1191 | Line 1270 | public class ForkJoinPool extends Abstra
1270		transitionRunStateTo(TERMINATED);
1271		termination.signalAll();
1272		}
1273	<	else if (!isTerminating()) {
1273	>	else if (isProcessingTasks()) {
1274		tryShrinkWorkerArray();
1275		tryResumeSpare(true); // allow replacement
1276		}
#	Line 1301 | Line 1380 | public class ForkJoinPool extends Abstra
1380		}
1381		}
1382
1304	–
1383		/*
1384		* Nodes for event barrier to manage idle threads.  Queue nodes
1385		* are basic Treiber stack nodes, also used for spare stack.
#	Line 1325 | Line 1403 | public class ForkJoinPool extends Abstra
1403		* handling: Method signalWork returns without advancing count if
1404		* the queue appears to be empty.  This would ordinarily result in
1405		* races causing some queued waiters not to be woken up. To avoid
1406	<	* this, the first worker enqueued in method sync (see
1407	<	* syncIsReleasable) rescans for tasks after being enqueued, and
1408	<	* helps signal if any are found. This works well because the
1409	<	* worker has nothing better to do, and so might as well help
1410	<	* alleviate the overhead and contention on the threads actually
1411	<	* doing work.  Also, since event counts increments on task
1412	<	* availability exist to maintain liveness (rather than to force
1413	<	* refreshes etc), it is OK for callers to exit early if
1336	<	* contending with another signaller.
1406	>	* this, the first worker enqueued in method sync rescans for
1407	>	* tasks after being enqueued, and helps signal if any are
1408	>	* found. This works well because the worker has nothing better to
1409	>	* do, and so might as well help alleviate the overhead and
1410	>	* contention on the threads actually doing work.  Also, since
1411	>	* event counts increments on task availability exist to maintain
1412	>	* liveness (rather than to force refreshes etc), it is OK for
1413	>	* callers to exit early if contending with another signaller.
1414		*/
1415		static final class WaitQueueNode {
1416		WaitQueueNode next; // only written before enqueued
#	Line 1346 | Line 1423 | public class ForkJoinPool extends Abstra
1423		}
1424
1425		/**
1426	<	* Wakes up waiter, returning false if known to already
1426	>	* Wakes up waiter, returning false if known to already be awake
1427		*/
1428		boolean signal() {
1429		ForkJoinWorkerThread t = thread;
#	Line 1356 | Line 1433 | public class ForkJoinPool extends Abstra
1433		LockSupport.unpark(t);
1434		return true;
1435		}
1359	–
1360	–	/**
1361	–	* Awaits release on sync.
1362	–	*/
1363	–	void awaitSyncRelease(ForkJoinPool p) {
1364	–	while (thread != null && !p.syncIsReleasable(this))
1365	–	LockSupport.park(this);
1366	–	}
1367	–
1368	–	/**
1369	–	* Awaits resumption as spare.
1370	–	*/
1371	–	void awaitSpareRelease() {
1372	–	while (thread != null) {
1373	–	if (!Thread.interrupted())
1374	–	LockSupport.park(this);
1375	–	}
1376	–	}
1436		}
1437
1438		/**
1439		* Ensures that no thread is waiting for count to advance from the
1440		* current value of eventCount read on entry to this method, by
1441		* releasing waiting threads if necessary.
1383	–	*
1384	–	* @return the count
1442		*/
1443	<	final long ensureSync() {
1443	>	final void ensureSync() {
1444		long c = eventCount;
1445		WaitQueueNode q;
1446		while ((q = syncStack) != null && q.count < c) {
#	Line 1394 | Line 1451 | public class ForkJoinPool extends Abstra
1451		break;
1452		}
1453		}
1397	–	return c;
1454		}
1455
1456		/**
#	Line 1409 | Line 1465 | public class ForkJoinPool extends Abstra
1465		/**
1466		* Signals threads waiting to poll a task. Because method sync
1467		* rechecks availability, it is OK to only proceed if queue
1468	<	* appears to be non-empty, and OK to skip under contention to
1469	<	* increment count (since some other thread succeeded).
1468	>	* appears to be non-empty, and OK if CAS to increment count
1469	>	* fails (since some other thread succeeded).
1470		*/
1471		final void signalWork() {
1472	<	long c;
1473	<	WaitQueueNode q;
1474	<	if (syncStack != null &&
1475	<	casEventCount(c = eventCount, c+1) &&
1476	<	(((q = syncStack) != null && q.count <= c) &&
1477	<	(!casBarrierStack(q, q.next) || !q.signal())))
1478	<	ensureSync();
1472	>	if (syncStack != null) {
1473	>	long c;
1474	>	casEventCount(c = eventCount, c+1);
1475	>	WaitQueueNode q = syncStack;
1476	>	if (q != null && q.count <= c &&
1477	>	(!casBarrierStack(q, q.next) || !q.signal()))
1478	>	ensureSync();
1479	>	}
1480		}
1481
1482		/**
#	Line 1432 | Line 1489 | public class ForkJoinPool extends Abstra
1489		final void sync(ForkJoinWorkerThread w) {
1490		updateStealCount(w); // Transfer w's count while it is idle
1491
1492	<	while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
1492	>	if (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
1493		long prev = w.lastEventCount;
1494		WaitQueueNode node = null;
1495		WaitQueueNode h;
1496	<	while (eventCount == prev &&
1496	>	long ec;
1497	>	while ((ec = eventCount) == prev &&
1498		((h = syncStack) == null || h.count == prev)) {
1499		if (node == null)
1500		node = new WaitQueueNode(prev, w);
1501		if (casBarrierStack(node.next = h, node)) {
1502	<	node.awaitSyncRelease(this);
1502	>	if (!Thread.interrupted() &&
1503	>	node.thread != null &&
1504	>	eventCount == prev &&
1505	>	(h != null || // cover signalWork race
1506	>	(!ForkJoinWorkerThread.hasQueuedTasks(workers) &&
1507	>	eventCount == prev)))
1508	>	LockSupport.park(this);
1509	>	ec = eventCount;
1510	>	if (node.thread != null) {
1511	>	node.thread = null;
1512	>	if (ec == prev)
1513	>	casEventCount(prev, prev + 1); // help signal
1514	>	}
1515		break;
1516		}
1517		}
1518	<	long ec = ensureSync();
1519	<	if (ec != prev) {
1450	<	w.lastEventCount = ec;
1451	<	break;
1452	<	}
1453	<	}
1454	<	}
1455	<
1456	<	/**
1457	<	* Returns {@code true} if worker waiting on sync can proceed:
1458	<	*  - on signal (thread == null)
1459	<	*  - on event count advance (winning race to notify vs signaller)
1460	<	*  - on interrupt
1461	<	*  - if the first queued node, we find work available
1462	<	* If node was not signalled and event count not advanced on exit,
1463	<	* then we also help advance event count.
1464	<	*
1465	<	* @return {@code true} if node can be released
1466	<	*/
1467	<	final boolean syncIsReleasable(WaitQueueNode node) {
1468	<	long prev = node.count;
1469	<	if (!Thread.interrupted() && node.thread != null &&
1470	<	(node.next != null ||
1471	<	!ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
1472	<	eventCount == prev)
1473	<	return false;
1474	<	if (node.thread != null) {
1475	<	node.thread = null;
1476	<	long ec = eventCount;
1477	<	if (prev <= ec) // help signal
1478	<	casEventCount(ec, ec+1);
1518	>	w.lastEventCount = ec;
1519	>	ensureSync();
1520		}
1480	–	return true;
1521		}
1522
1523		/**
#	Line 1486 | Line 1526 | public class ForkJoinPool extends Abstra
1526		*/
1527		final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1528		long lc = w.lastEventCount;
1529	<	long ec = ensureSync();
1530	<	if (ec == lc)
1531	<	return false;
1532	<	w.lastEventCount = ec;
1533	<	return true;
1529	>	long ec = eventCount;
1530	>	if (lc != ec)
1531	>	w.lastEventCount = ec;
1532	>	ensureSync();
1533	>	return lc != ec || lc != eventCount;
1534		}
1535
1536		//  Parallelism maintenance
#	Line 1532 | Line 1572 | public class ForkJoinPool extends Abstra
1572		while (spareStack == null || !tryResumeSpare(dec)) {
1573		int counts = workerCounts;
1574		if (dec || (dec = casWorkerCounts(counts, --counts))) {
1535	–	// CAS cheat
1575		if (!needSpare(counts, maintainParallelism))
1576		break;
1577		if (joinMe.status < 0)
#	Line 1637 | Line 1676 | public class ForkJoinPool extends Abstra
1676		for (k = 0; k < len && ws[k] != null; ++k)
1677		;
1678		}
1679	<	if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
1679	>	if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) {
1680		ws[k] = w;
1681		w.start();
1682		}
#	Line 1657 | Line 1696 | public class ForkJoinPool extends Abstra
1696		*/
1697		private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1698		WaitQueueNode node = null;
1699	<	int s;
1700	<	while (parallelism < runningCountOf(s = workerCounts)) {
1699	>	for (;;) {
1700	>	int p = parallelism;
1701	>	int s = workerCounts;
1702	>	int r = runningCountOf(s);
1703	>	int t = totalCountOf(s);
1704	>	// use t as bound if r transiently out of sync
1705	>	if (t <= p || r <= p)
1706	>	return false; // not a spare
1707		if (node == null)
1708		node = new WaitQueueNode(0, w);
1709	<	if (casWorkerCounts(s, s-1)) { // representation-dependent
1710	<	// push onto stack
1666	<	do {} while (!casSpareStack(node.next = spareStack, node));
1667	<	// block until released by resumeSpare
1668	<	node.awaitSpareRelease();
1669	<	return true;
1670	<	}
1709	>	if (casWorkerCounts(s, workerCountsFor(t, r - 1)))
1710	>	break;
1711		}
1712	<	return false;
1712	>	// push onto stack
1713	>	do {} while (!casSpareStack(node.next = spareStack, node));
1714	>	// block until released by resumeSpare
1715	>	while (!Thread.interrupted() && node.thread != null)
1716	>	LockSupport.park(this);
1717	>	return true;
1718		}
1719
1720		/**
#	Line 1735 | Line 1780 | public class ForkJoinPool extends Abstra
1780
1781		/**
1782		* Interface for extending managed parallelism for tasks running
1783	<	* in ForkJoinPools. A ManagedBlocker provides two methods.
1783	>	* in {@link ForkJoinPool}s.
1784	>	*
1785	>	* <p>A {@code ManagedBlocker} provides two methods.
1786		* Method {@code isReleasable} must return {@code true} if
1787		* blocking is not necessary. Method {@code block} blocks the
1788		* current thread if necessary (perhaps internally invoking
1789	<	* {@code isReleasable} before actually blocking.).
1789	>	* {@code isReleasable} before actually blocking).
1790		*
1791		* <p>For example, here is a ManagedBlocker based on a
1792		* ReentrantLock:
#	Line 1778 | Line 1825 | public class ForkJoinPool extends Abstra
1825
1826		/**
1827		* Blocks in accord with the given blocker.  If the current thread
1828	<	* is a ForkJoinWorkerThread, this method possibly arranges for a
1829	<	* spare thread to be activated if necessary to ensure parallelism
1830	<	* while the current thread is blocked.  If
1831	<	* {@code maintainParallelism} is {@code true} and the pool supports
1832	<	* it ({@link #getMaintainsParallelism}), this method attempts to
1833	<	* maintain the pool's nominal parallelism. Otherwise it activates
1834	<	* a thread only if necessary to avoid complete starvation. This
1835	<	* option may be preferable when blockages use timeouts, or are
1836	<	* almost always brief.
1828	>	* is a {@link ForkJoinWorkerThread}, this method possibly
1829	>	* arranges for a spare thread to be activated if necessary to
1830	>	* ensure parallelism while the current thread is blocked.
1831	>	*
1832	>	* <p>If {@code maintainParallelism} is {@code true} and the pool
1833	>	* supports it ({@link #getMaintainsParallelism}), this method
1834	>	* attempts to maintain the pool's nominal parallelism. Otherwise
1835	>	* it activates a thread only if necessary to avoid complete
1836	>	* starvation. This option may be preferable when blockages use
1837	>	* timeouts, or are almost always brief.
1838		*
1839	<	* <p> If the caller is not a ForkJoinTask, this method is behaviorally
1840	<	* equivalent to
1839	>	* <p>If the caller is not a {@link ForkJoinTask}, this method is
1840	>	* behaviorally equivalent to
1841		*  <pre> {@code
1842		* while (!blocker.isReleasable())
1843		*   if (blocker.block())
1844		*     return;
1845		* }</pre>
1846	<	* If the caller is a ForkJoinTask, then the pool may first
1847	<	* be expanded to ensure parallelism, and later adjusted.
1846	>	*
1847	>	* If the caller is a {@code ForkJoinTask}, then the pool may
1848	>	* first be expanded to ensure parallelism, and later adjusted.
1849		*
1850		* @param blocker the blocker
1851		* @param maintainParallelism if {@code true} and supported by
#	Line 1833 | Line 1882 | public class ForkJoinPool extends Abstra
1882		// implement RunnableFuture.
1883
1884		protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
1885	<	return (RunnableFuture<T>)ForkJoinTask.adapt(runnable, value);
1885	>	return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
1886		}
1887
1888		protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
1889	<	return (RunnableFuture<T>)ForkJoinTask.adapt(callable);
1889	>	return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
1890		}
1891
1892		// Unsafe mechanics

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