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root/jsr166/jsr166/src/jsr166y/ForkJoinTask.java

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.27 by dl, Sun Aug 2 11:54:31 2009 UTC vs.
Revision 1.37 by jsr166, Tue Aug 4 20:24:54 2009 UTC

#	Line 12 | Line 12 | import java.io.Serializable;
12		import java.util.Collection;
13		import java.util.Collections;
14		import java.util.List;
15	+	import java.util.RandomAccess;
16		import java.util.Map;
17		import java.util.WeakHashMap;
18
#	Line 22 | Line 23 | import java.util.WeakHashMap;
23		* subtasks may be hosted by a small number of actual threads in a
24		* ForkJoinPool, at the price of some usage limitations.
25		*
26	<	* <p> A "main" ForkJoinTask begins execution when submitted to a
27	<	* {@link ForkJoinPool}. Once started, it will usually in turn start
28	<	* other subtasks.  As indicated by the name of this class, many
29	<	* programs using ForkJoinTasks employ only methods {@code fork} and
30	<	* {@code join}, or derivatives such as {@code invokeAll}.  However,
31	<	* this class also provides a number of other methods that can come
32	<	* into play in advanced usages, as well as extension mechanics that
33	<	* allow support of new forms of fork/join processing.
26	>	* <p>A "main" {@code ForkJoinTask} begins execution when submitted
27	>	* to a {@link ForkJoinPool}.  Once started, it will usually in turn
28	>	* start other subtasks.  As indicated by the name of this class,
29	>	* many programs using {@code ForkJoinTask} employ only methods
30	>	* {@link #fork} and {@link #join}, or derivatives such as {@link
31	>	* #invokeAll}.  However, this class also provides a number of other
32	>	* methods that can come into play in advanced usages, as well as
33	>	* extension mechanics that allow support of new forms of fork/join
34	>	* processing.
35		*
36	<	* <p>A ForkJoinTask is a lightweight form of {@link Future}.  The
37	<	* efficiency of ForkJoinTasks stems from a set of restrictions (that
38	<	* are only partially statically enforceable) reflecting their
39	<	* intended use as computational tasks calculating pure functions or
40	<	* operating on purely isolated objects.  The primary coordination
41	<	* mechanisms are {@link #fork}, that arranges asynchronous execution,
42	<	* and {@link #join}, that doesn't proceed until the task's result has
43	<	* been computed.  Computations should avoid {@code synchronized}
44	<	* methods or blocks, and should minimize other blocking
45	<	* synchronization apart from joining other tasks or using
46	<	* synchronizers such as Phasers that are advertised to cooperate with
47	<	* fork/join scheduling. Tasks should also not perform blocking IO,
48	<	* and should ideally access variables that are completely independent
49	<	* of those accessed by other running tasks. Minor breaches of these
50	<	* restrictions, for example using shared output streams, may be
51	<	* tolerable in practice, but frequent use may result in poor
52	<	* performance, and the potential to indefinitely stall if the number
53	<	* of threads not waiting for IO or other external synchronization
54	<	* becomes exhausted. This usage restriction is in part enforced by
55	<	* not permitting checked exceptions such as {@code IOExceptions}
56	<	* to be thrown. However, computations may still encounter unchecked
57	<	* exceptions, that are rethrown to callers attempting join
58	<	* them. These exceptions may additionally include
59	<	* RejectedExecutionExceptions stemming from internal resource
60	<	* exhaustion such as failure to allocate internal task queues.
36	>	* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
37	>	* The efficiency of {@code ForkJoinTask}s stems from a set of
38	>	* restrictions (that are only partially statically enforceable)
39	>	* reflecting their intended use as computational tasks calculating
40	>	* pure functions or operating on purely isolated objects.  The
41	>	* primary coordination mechanisms are {@link #fork}, that arranges
42	>	* asynchronous execution, and {@link #join}, that doesn't proceed
43	>	* until the task's result has been computed.  Computations should
44	>	* avoid {@code synchronized} methods or blocks, and should minimize
45	>	* other blocking synchronization apart from joining other tasks or
46	>	* using synchronizers such as Phasers that are advertised to
47	>	* cooperate with fork/join scheduling. Tasks should also not perform
48	>	* blocking IO, and should ideally access variables that are
49	>	* completely independent of those accessed by other running
50	>	* tasks. Minor breaches of these restrictions, for example using
51	>	* shared output streams, may be tolerable in practice, but frequent
52	>	* use may result in poor performance, and the potential to
53	>	* indefinitely stall if the number of threads not waiting for IO or
54	>	* other external synchronization becomes exhausted. This usage
55	>	* restriction is in part enforced by not permitting checked
56	>	* exceptions such as {@code IOExceptions} to be thrown. However,
57	>	* computations may still encounter unchecked exceptions, that are
58	>	* rethrown to callers attempting to join them. These exceptions may
59	>	* additionally include RejectedExecutionExceptions stemming from
60	>	* internal resource exhaustion such as failure to allocate internal
61	>	* task queues.
62		*
63		* <p>The primary method for awaiting completion and extracting
64		* results of a task is {@link #join}, but there are several variants:
#	Line 65 | Line 68 | import java.util.WeakHashMap;
68		* execute other tasks while awaiting joins, which is sometimes more
69		* efficient but only applies when all subtasks are known to be
70		* strictly tree-structured. Method {@link #invoke} is semantically
71	<	* equivalent to {@code fork(); join()} but always attempts to
72	<	* begin execution in the current thread. The "<em>quiet</em>" forms
73	<	* of these methods do not extract results or report exceptions. These
71	>	* equivalent to {@code fork(); join()} but always attempts to begin
72	>	* execution in the current thread. The "<em>quiet</em>" forms of
73	>	* these methods do not extract results or report exceptions. These
74		* may be useful when a set of tasks are being executed, and you need
75		* to delay processing of results or exceptions until all complete.
76		* Method {@code invokeAll} (available in multiple versions)
77		* performs the most common form of parallel invocation: forking a set
78		* of tasks and joining them all.
79		*
80	<	* <p> The ForkJoinTask class is not usually directly subclassed.
80	>	* <p>The execution status of tasks may be queried at several levels
81	>	* of detail: {@link #isDone} is true if a task completed in any way
82	>	* (including the case where a task was cancelled without executing);
83	>	* {@link #isCancelled} is true if completion was due to cancellation;
84	>	* {@link #isCompletedNormally} is true if a task completed without
85	>	* cancellation or encountering an exception; {@link
86	>	* #isCompletedExceptionally} is true if if the task encountered an
87	>	* exception (in which case {@link #getException} returns the
88	>	* exception); {@link #isCancelled} is true if the task was cancelled
89	>	* (in which case {@link #getException} returns a {@link
90	>	* java.util.concurrent.CancellationException}); and {@link
91	>	* #isCompletedAbnormally} is true if a task was either cancelled or
92	>	* encountered an exception.
93	>	*
94	>	* <p>The ForkJoinTask class is not usually directly subclassed.
95		* Instead, you subclass one of the abstract classes that support a
96		* particular style of fork/join processing, typically {@link
97		* RecursiveAction} for computations that do not return results, or
#	Line 83 | Line 100 | import java.util.WeakHashMap;
100		* established in a constructor, and then defines a {@code compute}
101		* method that somehow uses the control methods supplied by this base
102		* class. While these methods have {@code public} access (to allow
103	<	* instances of different task subclasses to call each others
103	>	* instances of different task subclasses to call each other's
104		* methods), some of them may only be called from within other
105		* ForkJoinTasks (as may be determined using method {@link
106		* #inForkJoinPool}).  Attempts to invoke them in other contexts
107		* result in exceptions or errors, possibly including
108		* ClassCastException.
109		*
110	<	* <p>Most base support methods are {@code final} because their
111	<	* implementations are intrinsically tied to the underlying
112	<	* lightweight task scheduling framework, and so cannot be overridden.
113	<	* Developers creating new basic styles of fork/join processing should
114	<	* minimally implement {@code protected} methods
115	<	* {@link #exec}, {@link #setRawResult}, and
116	<	* {@link #getRawResult}, while also introducing an abstract
117	<	* computational method that can be implemented in its subclasses,
118	<	* possibly relying on other {@code protected} methods provided
102	<	* by this class.
110	>	* <p>Most base support methods are {@code final}, to prevent
111	>	* overriding of implementations that are intrinsically tied to the
112	>	* underlying lightweight task scheduling framework.  Developers
113	>	* creating new basic styles of fork/join processing should minimally
114	>	* implement {@code protected} methods {@link #exec}, {@link
115	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
116	>	* an abstract computational method that can be implemented in its
117	>	* subclasses, possibly relying on other {@code protected} methods
118	>	* provided by this class.
119		*
120		* <p>ForkJoinTasks should perform relatively small amounts of
121	<	* computations, otherwise splitting into smaller tasks. As a very
122	<	* rough rule of thumb, a task should perform more than 100 and less
123	<	* than 10000 basic computational steps. If tasks are too big, then
124	<	* parallelism cannot improve throughput. If too small, then memory
125	<	* and internal task maintenance overhead may overwhelm processing.
121	>	* computation. Large tasks should be split into smaller subtasks,
122	>	* usually via recursive decomposition. As a very rough rule of thumb,
123	>	* a task should perform more than 100 and less than 10000 basic
124	>	* computational steps. If tasks are too big, then parallelism cannot
125	>	* improve throughput. If too small, then memory and internal task
126	>	* maintenance overhead may overwhelm processing.
127		*
128	<	* <p>This class provides {@code adapt} methods for {@link
129	<	* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
130	<	* may be of use when mixing execution of ForkJoinTasks with other
131	<	* kinds of tasks. When all tasks are of this form, consider using a
132	<	* pool in {@link ForkJoinPool#setAsyncMode}.
128	>	* <p>This class provides {@code adapt} methods for {@link Runnable}
129	>	* and {@link Callable}, that may be of use when mixing execution of
130	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks
131	>	* are of this form, consider using a pool in
132	>	* {@linkplain ForkJoinPool#setAsyncMode async mode}.
133		*
134	<	* <p>ForkJoinTasks are {@code Serializable}, which enables them
135	<	* to be used in extensions such as remote execution frameworks. It is
136	<	* in general sensible to serialize tasks only before or after, but
137	<	* not during execution. Serialization is not relied on during
121	<	* execution itself.
134	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
135	>	* used in extensions such as remote execution frameworks. It is
136	>	* sensible to serialize tasks only before or after, but not during,
137	>	* execution. Serialization is not relied on during execution itself.
138		*
139		* @since 1.7
140		* @author Doug Lea
#	Line 379 | Line 395 | public abstract class ForkJoinTask<V> im
395		* Only call when {@code isDone} known to be true.
396		*/
397		private V reportFutureResult()
398	<	throws ExecutionException, InterruptedException {
398	>	throws InterruptedException, ExecutionException {
399	>	if (Thread.interrupted())
400	>	throw new InterruptedException();
401		int s = status & COMPLETION_MASK;
402		if (s < NORMAL) {
403		Throwable ex;
#	Line 387 | Line 405 | public abstract class ForkJoinTask<V> im
405		throw new CancellationException();
406		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
407		throw new ExecutionException(ex);
390	–	if (Thread.interrupted())
391	–	throw new InterruptedException();
408		}
409		return getRawResult();
410		}
#	Line 399 | Line 415 | public abstract class ForkJoinTask<V> im
415		*/
416		private V reportTimedFutureResult()
417		throws InterruptedException, ExecutionException, TimeoutException {
418	+	if (Thread.interrupted())
419	+	throw new InterruptedException();
420		Throwable ex;
421		int s = status & COMPLETION_MASK;
422		if (s == NORMAL)
423		return getRawResult();
424	<	if (s == CANCELLED)
424	>	else if (s == CANCELLED)
425		throw new CancellationException();
426	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
426	>	else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
427		throw new ExecutionException(ex);
428	<	if (Thread.interrupted())
429	<	throw new InterruptedException();
412	<	throw new TimeoutException();
428	>	else
429	>	throw new TimeoutException();
430		}
431
432		// internal execution methods
#	Line 494 | Line 511 | public abstract class ForkJoinTask<V> im
511		/**
512		* Arranges to asynchronously execute this task.  While it is not
513		* necessarily enforced, it is a usage error to fork a task more
514	<	* than once unless it has completed and been reinitialized.  This
515	<	* method may be invoked only from within ForkJoinTask
516	<	* computations (as may be determined using method {@link
517	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
518	<	* in exceptions or errors, possibly including ClassCastException.
514	>	* than once unless it has completed and been reinitialized.
515	>	*
516	>	* <p>This method may be invoked only from within {@code
517	>	* ForkJoinTask} computations (as may be determined using method
518	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
519	>	* result in exceptions or errors, possibly including {@code
520	>	* ClassCastException}.
521		*
522	<	* @return {@code this}, to simplify usage.
522	>	* @return {@code this}, to simplify usage
523		*/
524		public final ForkJoinTask<V> fork() {
525		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 510 | Line 529 | public abstract class ForkJoinTask<V> im
529
530		/**
531		* Returns the result of the computation when it is ready.
532	<	* This method differs from {@code get} in that abnormal
533	<	* completion results in RuntimeExceptions or Errors, not
534	<	* ExecutionExceptions.
532	>	* This method differs from {@link #get()} in that
533	>	* abnormal completion results in {@code RuntimeException} or
534	>	* {@code Error}, not {@code ExecutionException}.
535		*
536		* @return the computed result
537		*/
#	Line 525 | Line 544 | public abstract class ForkJoinTask<V> im
544
545		/**
546		* Commences performing this task, awaits its completion if
547	<	* necessary, and return its result.
547	>	* necessary, and return its result, or throws an (unchecked)
548	>	* exception if the underlying computation did so.
549		*
530	–	* @throws Throwable (a RuntimeException, Error, or unchecked
531	–	* exception) if the underlying computation did so
550		* @return the computed result
551		*/
552		public final V invoke() {
#	Line 540 | Line 558 | public abstract class ForkJoinTask<V> im
558
559		/**
560		* Forks the given tasks, returning when {@code isDone} holds for
561	<	* each task or an exception is encountered. This method may be
562	<	* invoked only from within ForkJoinTask computations (as may be
563	<	* determined using method {@link #inForkJoinPool}). Attempts to
564	<	* invoke in other contexts result in exceptions or errors,
565	<	* possibly including ClassCastException.
561	>	* each task or an (unchecked) exception is encountered, in which
562	>	* case the exception is rethrown.  If more than one task
563	>	* encounters an exception, then this method throws any one of
564	>	* these exceptions.  The individual status of each task may be
565	>	* checked using {@link #getException()} and related methods.
566	>	*
567	>	* <p>This method may be invoked only from within {@code
568	>	* ForkJoinTask} computations (as may be determined using method
569	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
570	>	* result in exceptions or errors, possibly including {@code
571	>	* ClassCastException}.
572		*
573		* @param t1 the first task
574		* @param t2 the second task
575		* @throws NullPointerException if any task is null
552	–	* @throws RuntimeException or Error if a task did so
576		*/
577	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
577	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
578		t2.fork();
579		t1.invoke();
580		t2.join();
#	Line 559 | Line 582 | public abstract class ForkJoinTask<V> im
582
583		/**
584		* Forks the given tasks, returning when {@code isDone} holds for
585	<	* each task or an exception is encountered. If any task
586	<	* encounters an exception, others may be, but are not guaranteed
587	<	* to be, cancelled.  This method may be invoked only from within
588	<	* ForkJoinTask computations (as may be determined using method
589	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
590	<	* result in exceptions or errors, possibly including
591	<	* ClassCastException.
592	<	*
593	<	* Overloadings of this method exist for the special cases
594	<	* of one to four arguments.
585	>	* each task or an (unchecked) exception is encountered, in which
586	>	* case the exception is rethrown. If any task encounters an
587	>	* exception, others may be, but are not guaranteed to be,
588	>	* cancelled.  If more than one task encounters an exception, then
589	>	* this method throws any one of these exceptions.  The individual
590	>	* status of each task may be checked using {@link #getException()}
591	>	* and related methods.
592	>	*
593	>	* <p>This method may be invoked only from within {@code
594	>	* ForkJoinTask} computations (as may be determined using method
595	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
596	>	* result in exceptions or errors, possibly including {@code
597	>	* ClassCastException}.
598		*
599		* @param tasks the tasks
600	<	* @throws NullPointerException if tasks or any element are null
575	<	* @throws RuntimeException or Error if any task did so
600	>	* @throws NullPointerException if any task is null
601		*/
602		public static void invokeAll(ForkJoinTask<?>... tasks) {
603		Throwable ex = null;
#	Line 608 | Line 633 | public abstract class ForkJoinTask<V> im
633		}
634
635		/**
636	<	* Forks all tasks in the collection, returning when {@code
637	<	* isDone} holds for each task or an exception is encountered. If
638	<	* any task encounters an exception, others may be, but are not
639	<	* guaranteed to be, cancelled.  This method may be invoked only
640	<	* from within ForkJoinTask computations (as may be determined
641	<	* using method {@link #inForkJoinPool}). Attempts to invoke in
642	<	* other contexts result in exceptions or errors, possibly
643	<	* including ClassCastException.
636	>	* Forks all tasks in the specified collection, returning when
637	>	* {@code isDone} holds for each task or an (unchecked) exception
638	>	* is encountered.  If any task encounters an exception, others
639	>	* may be, but are not guaranteed to be, cancelled.  If more than
640	>	* one task encounters an exception, then this method throws any
641	>	* one of these exceptions.  The individual status of each task
642	>	* may be checked using {@link #getException()} and related
643	>	* methods.  The behavior of this operation is undefined if the
644	>	* specified collection is modified while the operation is in
645	>	* progress.
646	>	*
647	>	* <p>This method may be invoked only from within {@code
648	>	* ForkJoinTask} computations (as may be determined using method
649	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
650	>	* result in exceptions or errors, possibly including {@code
651	>	* ClassCastException}.
652		*
653		* @param tasks the collection of tasks
654		* @return the tasks argument, to simplify usage
655		* @throws NullPointerException if tasks or any element are null
623	–	* @throws RuntimeException or Error if any task did so
656		*/
657		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
658	<	if (!(tasks instanceof List<?>)) {
658	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
659		invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
660		return tasks;
661		}
#	Line 664 | Line 696 | public abstract class ForkJoinTask<V> im
696		}
697
698		/**
699	+	* Attempts to cancel execution of this task. This attempt will
700	+	* fail if the task has already completed, has already been
701	+	* cancelled, or could not be cancelled for some other reason. If
702	+	* successful, and this task has not started when cancel is
703	+	* called, execution of this task is suppressed, {@link
704	+	* #isCancelled} will report true, and {@link #join} will result
705	+	* in a {@code CancellationException} being thrown.
706	+	*
707	+	* <p>This method may be overridden in subclasses, but if so, must
708	+	* still ensure that these minimal properties hold. In particular,
709	+	* the {@code cancel} method itself must not throw exceptions.
710	+	*
711	+	* <p>This method is designed to be invoked by <em>other</em>
712	+	* tasks. To terminate the current task, you can just return or
713	+	* throw an unchecked exception from its computation method, or
714	+	* invoke {@link #completeExceptionally}.
715	+	*
716	+	* @param mayInterruptIfRunning this value is ignored in the
717	+	* default implementation because tasks are not
718	+	* cancelled via interruption
719	+	*
720	+	* @return {@code true} if this task is now cancelled
721	+	*/
722	+	public boolean cancel(boolean mayInterruptIfRunning) {
723	+	setCompletion(CANCELLED);
724	+	return (status & COMPLETION_MASK) == CANCELLED;
725	+	}
726	+
727	+	/**
728		* Returns {@code true} if the computation performed by this task
729		* has completed (or has been cancelled).
730		*
#	Line 683 | Line 744 | public abstract class ForkJoinTask<V> im
744		}
745
746		/**
747	<	* Asserts that the results of this task's computation will not be
687	<	* used. If a cancellation occurs before attempting to execute this
688	<	* task, execution will be suppressed, {@link #isCancelled}
689	<	* will report true, and {@link #join} will result in a
690	<	* {@code CancellationException} being thrown. Otherwise, when
691	<	* cancellation races with completion, there are no guarantees
692	<	* about whether {@code isCancelled} will report {@code true},
693	<	* whether {@code join} will return normally or via an exception,
694	<	* or whether these behaviors will remain consistent upon repeated
695	<	* invocation.
696	<	*
697	<	* <p>This method may be overridden in subclasses, but if so, must
698	<	* still ensure that these minimal properties hold. In particular,
699	<	* the cancel method itself must not throw exceptions.
700	<	*
701	<	* <p> This method is designed to be invoked by <em>other</em>
702	<	* tasks. To terminate the current task, you can just return or
703	<	* throw an unchecked exception from its computation method, or
704	<	* invoke {@link #completeExceptionally}.
747	>	* Returns {@code true} if this task threw an exception or was cancelled.
748		*
749	<	* @param mayInterruptIfRunning this value is ignored in the
750	<	* default implementation because tasks are not in general
751	<	* cancelled via interruption
749	>	* @return {@code true} if this task threw an exception or was cancelled
750	>	*/
751	>	public final boolean isCompletedAbnormally() {
752	>	return (status & COMPLETION_MASK) < NORMAL;
753	>	}
754	>
755	>	/**
756	>	* Returns {@code true} if this task completed without throwing an
757	>	* exception and was not cancelled.
758		*
759	<	* @return {@code true} if this task is now cancelled
759	>	* @return {@code true} if this task completed without throwing an
760	>	* exception and was not cancelled
761		*/
762	<	public boolean cancel(boolean mayInterruptIfRunning) {
763	<	setCompletion(CANCELLED);
714	<	return (status & COMPLETION_MASK) == CANCELLED;
762	>	public final boolean isCompletedNormally() {
763	>	return (status & COMPLETION_MASK) == NORMAL;
764		}
765
766		/**
767	<	* Returns {@code true} if this task threw an exception or was cancelled.
767	>	* Returns {@code true} if this task threw an exception.
768		*
769	<	* @return {@code true} if this task threw an exception or was cancelled
769	>	* @return {@code true} if this task threw an exception
770		*/
771	<	public final boolean isCompletedAbnormally() {
772	<	return (status & COMPLETION_MASK) < NORMAL;
771	>	public final boolean isCompletedExceptionally() {
772	>	return (status & COMPLETION_MASK) == EXCEPTIONAL;
773		}
774
775		/**
776		* Returns the exception thrown by the base computation, or a
777	<	* CancellationException if cancelled, or null if none or if the
778	<	* method has not yet completed.
777	>	* {@code CancellationException} if cancelled, or {@code null} if
778	>	* none or if the method has not yet completed.
779		*
780		* @return the exception, or {@code null} if none
781		*/
782		public final Throwable getException() {
783		int s = status & COMPLETION_MASK;
784	<	if (s >= NORMAL)
785	<	return null;
786	<	if (s == CANCELLED)
738	<	return new CancellationException();
739	<	return exceptionMap.get(this);
784	>	return ((s >= NORMAL)    ? null :
785	>	(s == CANCELLED) ? new CancellationException() :
786	>	exceptionMap.get(this));
787		}
788
789		/**
#	Line 804 | Line 851 | public abstract class ForkJoinTask<V> im
851		* there are no potential dependencies between continuation of the
852		* current task and that of any other task that might be executed
853		* while helping. (This usually holds for pure divide-and-conquer
854	<	* tasks). This method may be invoked only from within
855	<	* ForkJoinTask computations (as may be determined using method
856	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
857	<	* result in exceptions or errors, possibly including
858	<	* ClassCastException.
854	>	* tasks).
855	>	*
856	>	* <p>This method may be invoked only from within {@code
857	>	* ForkJoinTask} computations (as may be determined using method
858	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
859	>	* result in exceptions or errors, possibly including {@code
860	>	* ClassCastException}.
861		*
862		* @return the computed result
863		*/
#	Line 821 | Line 870 | public abstract class ForkJoinTask<V> im
870
871		/**
872		* Possibly executes other tasks until this task is ready.  This
873	<	* method may be invoked only from within ForkJoinTask
874	<	* computations (as may be determined using method {@link
875	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
876	<	* in exceptions or errors, possibly including ClassCastException.
873	>	* method may be useful when processing collections of tasks when
874	>	* some have been cancelled or otherwise known to have aborted.
875	>	*
876	>	* <p>This method may be invoked only from within {@code
877	>	* ForkJoinTask} computations (as may be determined using method
878	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
879	>	* result in exceptions or errors, possibly including {@code
880	>	* ClassCastException}.
881		*/
882		public final void quietlyHelpJoin() {
883		if (status >= 0) {
#	Line 863 | Line 916 | public abstract class ForkJoinTask<V> im
916
917		/**
918		* Possibly executes tasks until the pool hosting the current task
919	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
920	<	* designs in which many tasks are forked, but none are explicitly
921	<	* joined, instead executing them until all are processed.  This
922	<	* method may be invoked only from within ForkJoinTask
923	<	* computations (as may be determined using method {@link
924	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
925	<	* in exceptions or errors, possibly including ClassCastException.
919	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
920	>	* be of use in designs in which many tasks are forked, but none
921	>	* are explicitly joined, instead executing them until all are
922	>	* processed.
923	>	*
924	>	* <p>This method may be invoked only from within {@code
925	>	* ForkJoinTask} computations (as may be determined using method
926	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
927	>	* result in exceptions or errors, possibly including {@code
928	>	* ClassCastException}.
929		*/
930		public static void helpQuiesce() {
931		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 882 | Line 938 | public abstract class ForkJoinTask<V> im
938		* this task, but only if reuse occurs when this task has either
939		* never been forked, or has been forked, then completed and all
940		* outstanding joins of this task have also completed. Effects
941	<	* under any other usage conditions are not guaranteed, and are
942	<	* discouraged. This method may be useful when executing
941	>	* under any other usage conditions are not guaranteed.
942	>	* This method may be useful when executing
943		* pre-constructed trees of subtasks in loops.
944		*/
945		public void reinitialize() {
#	Line 922 | Line 978 | public abstract class ForkJoinTask<V> im
978		* by the current thread, and has not commenced executing in
979		* another thread.  This method may be useful when arranging
980		* alternative local processing of tasks that could have been, but
981	<	* were not, stolen. This method may be invoked only from within
982	<	* ForkJoinTask computations (as may be determined using method
983	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
984	<	* result in exceptions or errors, possibly including
985	<	* ClassCastException.
981	>	* were not, stolen.
982	>	*
983	>	* <p>This method may be invoked only from within {@code
984	>	* ForkJoinTask} computations (as may be determined using method
985	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
986	>	* result in exceptions or errors, possibly including {@code
987	>	* ClassCastException}.
988		*
989		* @return {@code true} if unforked
990		*/
#	Line 939 | Line 997 | public abstract class ForkJoinTask<V> im
997		* Returns an estimate of the number of tasks that have been
998		* forked by the current worker thread but not yet executed. This
999		* value may be useful for heuristic decisions about whether to
1000	<	* fork other tasks.  This method may be invoked only from within
1001	<	* ForkJoinTask computations (as may be determined using method
1002	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1003	<	* result in exceptions or errors, possibly including
1004	<	* ClassCastException.
1000	>	* fork other tasks.
1001	>	*
1002	>	* <p>This method may be invoked only from within {@code
1003	>	* ForkJoinTask} computations (as may be determined using method
1004	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1005	>	* result in exceptions or errors, possibly including {@code
1006	>	* ClassCastException}.
1007	>	*
1008		* @return the number of tasks
1009		*/
1010		public static int getQueuedTaskCount() {
#	Line 959 | Line 1020 | public abstract class ForkJoinTask<V> im
1020		* usages of ForkJoinTasks, at steady state, each worker should
1021		* aim to maintain a small constant surplus (for example, 3) of
1022		* tasks, and to process computations locally if this threshold is
1023	<	* exceeded.  This method may be invoked only from within
1024	<	* ForkJoinTask computations (as may be determined using method
1025	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1026	<	* result in exceptions or errors, possibly including
1027	<	* ClassCastException.  *
1023	>	* exceeded.
1024	>	*
1025	>	* <p>This method may be invoked only from within {@code
1026	>	* ForkJoinTask} computations (as may be determined using method
1027	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1028	>	* result in exceptions or errors, possibly including {@code
1029	>	* ClassCastException}.
1030	>	*
1031		* @return the surplus number of tasks, which may be negative
1032		*/
1033		public static int getSurplusQueuedTaskCount() {
#	Line 999 | Line 1063 | public abstract class ForkJoinTask<V> im
1063		* called otherwise. The return value controls whether this task
1064		* is considered to be done normally. It may return false in
1065		* asynchronous actions that require explicit invocations of
1066	<	* {@link #complete} to become joinable. It may throw exceptions
1067	<	* to indicate abnormal exit.
1066	>	* {@link #complete} to become joinable. It may also throw an
1067	>	* (unchecked) exception to indicate abnormal exit.
1068		*
1069		* @return {@code true} if completed normally
1006	–	* @throws Error or RuntimeException if encountered during computation
1070		*/
1071		protected abstract boolean exec();
1072
#	Line 1015 | Line 1078 | public abstract class ForkJoinTask<V> im
1078		* null even if a task exists but cannot be accessed without
1079		* contention with other threads.  This method is designed
1080		* primarily to support extensions, and is unlikely to be useful
1081	<	* otherwise.  This method may be invoked only from within
1082	<	* ForkJoinTask computations (as may be determined using method
1083	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1084	<	* result in exceptions or errors, possibly including
1085	<	* ClassCastException.
1081	>	* otherwise.
1082	>	*
1083	>	* <p>This method may be invoked only from within {@code
1084	>	* ForkJoinTask} computations (as may be determined using method
1085	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1086	>	* result in exceptions or errors, possibly including {@code
1087	>	* ClassCastException}.
1088		*
1089		* @return the next task, or {@code null} if none are available
1090		*/
#	Line 1032 | Line 1097 | public abstract class ForkJoinTask<V> im
1097		* Unschedules and returns, without executing, the next task
1098		* queued by the current thread but not yet executed.  This method
1099		* is designed primarily to support extensions, and is unlikely to
1100	<	* be useful otherwise.  This method may be invoked only from
1101	<	* within ForkJoinTask computations (as may be determined using
1102	<	* method {@link #inForkJoinPool}). Attempts to invoke in other
1103	<	* contexts result in exceptions or errors, possibly including
1104	<	* ClassCastException.
1100	>	* be useful otherwise.
1101	>	*
1102	>	* <p>This method may be invoked only from within {@code
1103	>	* ForkJoinTask} computations (as may be determined using method
1104	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1105	>	* result in exceptions or errors, possibly including {@code
1106	>	* ClassCastException}.
1107		*
1108		* @return the next task, or {@code null} if none are available
1109		*/
#	Line 1053 | Line 1120 | public abstract class ForkJoinTask<V> im
1120		* {@code null} result does not necessarily imply quiescence
1121		* of the pool this task is operating in.  This method is designed
1122		* primarily to support extensions, and is unlikely to be useful
1123	<	* otherwise.  This method may be invoked only from within
1124	<	* ForkJoinTask computations (as may be determined using method
1125	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1126	<	* result in exceptions or errors, possibly including
1127	<	* ClassCastException.
1123	>	* otherwise.
1124	>	*
1125	>	* <p>This method may be invoked only from within {@code
1126	>	* ForkJoinTask} computations (as may be determined using method
1127	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1128	>	* result in exceptions or errors, possibly including {@code
1129	>	* ClassCastException}.
1130		*
1131		* @return a task, or {@code null} if none are available
1132		*/
#	Line 1122 | Line 1191 | public abstract class ForkJoinTask<V> im
1191		}
1192
1193		/**
1194	<	* Returns a new ForkJoinTask that performs the {@code run}
1195	<	* method of the given Runnable as its action, and returns a null
1196	<	* result upon {@code join}.
1194	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1195	>	* method of the given {@code Runnable} as its action, and returns
1196	>	* a null result upon {@link #join}.
1197		*
1198		* @param runnable the runnable action
1199		* @return the task
#	Line 1134 | Line 1203 | public abstract class ForkJoinTask<V> im
1203		}
1204
1205		/**
1206	<	* Returns a new ForkJoinTask that performs the {@code run}
1207	<	* method of the given Runnable as its action, and returns the
1208	<	* given result upon {@code join}.
1206	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1207	>	* method of the given {@code Runnable} as its action, and returns
1208	>	* the given result upon {@link #join}.
1209		*
1210		* @param runnable the runnable action
1211		* @param result the result upon completion
#	Line 1147 | Line 1216 | public abstract class ForkJoinTask<V> im
1216		}
1217
1218		/**
1219	<	* Returns a new ForkJoinTask that performs the {@code call}
1220	<	* method of the given Callable as its action, and returns its
1221	<	* result upon {@code join}, translating any checked
1222	<	* exceptions encountered into {@code RuntimeException}.
1219	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1220	>	* method of the given {@code Callable} as its action, and returns
1221	>	* its result upon {@link #join}, translating any checked exceptions
1222	>	* encountered into {@code RuntimeException}.
1223		*
1224		* @param callable the callable action
1225		* @return the task

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