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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.26 by jsr166, Sat Aug 1 21:17:11 2009 UTC vs.
Revision 1.34 by dl, Tue Aug 4 11:44:33 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 74 | Line 77 | import java.util.WeakHashMap;
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 ForkJoinTask class is not usually directly subclassed.
81		* Instead, you subclass one of the abstract classes that support a
82	<	* particular style of fork/join processing.  Normally, a concrete
82	>	* particular style of fork/join processing, typically {@link
83	>	* RecursiveAction} for computations that do not return results, or
84	>	* {@link RecursiveTask} for those that do.  Normally, a concrete
85		* ForkJoinTask subclass declares fields comprising its parameters,
86		* established in a constructor, and then defines a {@code compute}
87		* method that somehow uses the control methods supplied by this base
88		* class. While these methods have {@code public} access (to allow
89	<	* instances of different task subclasses to call each others
89	>	* instances of different task subclasses to call each other's
90		* methods), some of them may only be called from within other
91		* ForkJoinTasks (as may be determined using method {@link
92		* #inForkJoinPool}).  Attempts to invoke them in other contexts
93		* result in exceptions or errors, possibly including
94		* ClassCastException.
95		*
96	<	* <p>Most base support methods are {@code final} because their
97	<	* implementations are intrinsically tied to the underlying
98	<	* lightweight task scheduling framework, and so cannot be overridden.
99	<	* Developers creating new basic styles of fork/join processing should
100	<	* minimally implement {@code protected} methods
101	<	* {@link #exec}, {@link #setRawResult}, and
102	<	* {@link #getRawResult}, while also introducing an abstract
103	<	* computational method that can be implemented in its subclasses,
104	<	* possibly relying on other {@code protected} methods provided
100	<	* by this class.
96	>	* <p>Most base support methods are {@code final}, to prevent
97	>	* overriding of implementations that are intrinsically tied to the
98	>	* underlying lightweight task scheduling framework.  Developers
99	>	* creating new basic styles of fork/join processing should minimally
100	>	* implement {@code protected} methods {@link #exec}, {@link
101	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
102	>	* an abstract computational method that can be implemented in its
103	>	* subclasses, possibly relying on other {@code protected} methods
104	>	* provided by this class.
105		*
106		* <p>ForkJoinTasks should perform relatively small amounts of
107	<	* computations, otherwise splitting into smaller tasks. As a very
108	<	* rough rule of thumb, a task should perform more than 100 and less
109	<	* than 10000 basic computational steps. If tasks are too big, then
110	<	* parallelism cannot improve throughput. If too small, then memory
111	<	* and internal task maintenance overhead may overwhelm processing.
107	>	* computation. Large tasks should be split into smaller subtasks,
108	>	* usually via recursive decomposition. As a very rough rule of thumb,
109	>	* a task should perform more than 100 and less than 10000 basic
110	>	* computational steps. If tasks are too big, then parallelism cannot
111	>	* improve throughput. If too small, then memory and internal task
112	>	* maintenance overhead may overwhelm processing.
113		*
114	<	* <p>ForkJoinTasks are {@code Serializable}, which enables them
115	<	* to be used in extensions such as remote execution frameworks. It is
116	<	* in general sensible to serialize tasks only before or after, but
117	<	* not during execution. Serialization is not relied on during
118	<	* execution itself.
114	>	* <p>This class provides {@code adapt} methods for {@link
115	>	* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
116	>	* may be of use when mixing execution of ForkJoinTasks with other
117	>	* kinds of tasks. When all tasks are of this form, consider using a
118	>	* pool in {@link ForkJoinPool#setAsyncMode async mode}.
119	>	*
120	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
121	>	* used in extensions such as remote execution frameworks. It is
122	>	* sensible to serialize tasks only before or after, but not during,
123	>	* execution. Serialization is not relied on during execution itself.
124		*
125		* @since 1.7
126		* @author Doug Lea
#	Line 372 | Line 382 | public abstract class ForkJoinTask<V> im
382		*/
383		private V reportFutureResult()
384		throws ExecutionException, InterruptedException {
385	+	if (Thread.interrupted())
386	+	throw new InterruptedException();
387		int s = status & COMPLETION_MASK;
388		if (s < NORMAL) {
389		Throwable ex;
#	Line 379 | Line 391 | public abstract class ForkJoinTask<V> im
391		throw new CancellationException();
392		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
393		throw new ExecutionException(ex);
382	–	if (Thread.interrupted())
383	–	throw new InterruptedException();
394		}
395		return getRawResult();
396		}
#	Line 391 | Line 401 | public abstract class ForkJoinTask<V> im
401		*/
402		private V reportTimedFutureResult()
403		throws InterruptedException, ExecutionException, TimeoutException {
404	+	if (Thread.interrupted())
405	+	throw new InterruptedException();
406		Throwable ex;
407		int s = status & COMPLETION_MASK;
408		if (s == NORMAL)
#	Line 399 | Line 411 | public abstract class ForkJoinTask<V> im
411		throw new CancellationException();
412		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
413		throw new ExecutionException(ex);
402	–	if (Thread.interrupted())
403	–	throw new InterruptedException();
414		throw new TimeoutException();
415		}
416
#	Line 486 | Line 496 | public abstract class ForkJoinTask<V> im
496		/**
497		* Arranges to asynchronously execute this task.  While it is not
498		* necessarily enforced, it is a usage error to fork a task more
499	<	* than once unless it has completed and been reinitialized.  This
500	<	* method may be invoked only from within ForkJoinTask
501	<	* computations (as may be determined using method {@link
502	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
503	<	* in exceptions or errors, possibly including ClassCastException.
499	>	* than once unless it has completed and been reinitialized.
500	>	*
501	>	* <p>This method may be invoked only from within {@code
502	>	* ForkJoinTask} computations (as may be determined using method
503	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
504	>	* result in exceptions or errors, possibly including {@code
505	>	* ClassCastException}.
506		*
507	<	* @return {@code this}, to simplify usage.
507	>	* @return {@code this}, to simplify usage
508		*/
509		public final ForkJoinTask<V> fork() {
510		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 502 | Line 514 | public abstract class ForkJoinTask<V> im
514
515		/**
516		* Returns the result of the computation when it is ready.
517	<	* This method differs from {@code get} in that abnormal
518	<	* completion results in RuntimeExceptions or Errors, not
519	<	* ExecutionExceptions.
517	>	* This method differs from {@link #get()} in that
518	>	* abnormal completion results in {@code RuntimeException} or
519	>	* {@code Error}, not {@code ExecutionException}.
520		*
521		* @return the computed result
522		*/
#	Line 517 | Line 529 | public abstract class ForkJoinTask<V> im
529
530		/**
531		* Commences performing this task, awaits its completion if
532	<	* necessary, and return its result.
532	>	* necessary, and return its result, or throws an (unchecked)
533	>	* exception if the underlying computation did so.
534		*
522	–	* @throws Throwable (a RuntimeException, Error, or unchecked
523	–	* exception) if the underlying computation did so
535		* @return the computed result
536		*/
537		public final V invoke() {
#	Line 531 | Line 542 | public abstract class ForkJoinTask<V> im
542		}
543
544		/**
545	<	* Forks both tasks, returning when {@code isDone} holds for
546	<	* both of them or an exception is encountered. This method may be
547	<	* invoked only from within ForkJoinTask computations (as may be
548	<	* determined using method {@link #inForkJoinPool}). Attempts to
549	<	* invoke in other contexts result in exceptions or errors,
550	<	* possibly including ClassCastException.
551	<	*
552	<	* @param t1 one task
553	<	* @param t2 the other task
554	<	* @throws NullPointerException if t1 or t2 are null
555	<	* @throws RuntimeException or Error if either task did so
545	>	* Forks the given tasks, returning when {@code isDone} holds for
546	>	* each task or an (unchecked) exception is encountered, in which
547	>	* case the exception is rethrown.  If more than one task
548	>	* encounters an exception, then this method throws any one of
549	>	* these exceptions.  The individual status of each task may be
550	>	* checked using {@link #getException()} and related methods.
551	>	*
552	>	* <p>This method may be invoked only from within {@code
553	>	* ForkJoinTask} computations (as may be determined using method
554	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
555	>	* result in exceptions or errors, possibly including {@code
556	>	* ClassCastException}.
557	>	*
558	>	* @param t1 the first task
559	>	* @param t2 the second task
560	>	* @throws NullPointerException if any task is null
561		*/
562	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
562	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
563		t2.fork();
564		t1.invoke();
565		t2.join();
566		}
567
568		/**
569	<	* Forks the given tasks, returning when {@code isDone} holds
570	<	* for all of them. If any task encounters an exception, others
571	<	* may be cancelled.  This method may be invoked only from within
572	<	* ForkJoinTask computations (as may be determined using method
573	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
574	<	* result in exceptions or errors, possibly including
575	<	* ClassCastException.
569	>	* Forks the given tasks, returning when {@code isDone} holds for
570	>	* each task or an (unchecked) exception is encountered, in which
571	>	* case the exception is rethrown. If any task encounters an
572	>	* exception, others may be, but are not guaranteed to be,
573	>	* cancelled.  If more than one task encounters an exception, then
574	>	* this method throws any one of these exceptions.  The individual
575	>	* status of each task may be checked using {@link #getException()}
576	>	* and related methods.
577	>	*
578	>	* <p>This method may be invoked only from within {@code
579	>	* ForkJoinTask} computations (as may be determined using method
580	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
581	>	* result in exceptions or errors, possibly including {@code
582	>	* ClassCastException}.
583		*
584	<	* @param tasks the array of tasks
585	<	* @throws NullPointerException if tasks or any element are null
563	<	* @throws RuntimeException or Error if any task did so
584	>	* @param tasks the tasks
585	>	* @throws NullPointerException if any task is null
586		*/
587		public static void invokeAll(ForkJoinTask<?>... tasks) {
588		Throwable ex = null;
#	Line 596 | Line 618 | public abstract class ForkJoinTask<V> im
618		}
619
620		/**
621	<	* Forks all tasks in the collection, returning when
622	<	* {@code isDone} holds for all of them. If any task
623	<	* encounters an exception, others may be cancelled.  This method
624	<	* may be invoked only from within ForkJoinTask computations (as
625	<	* may be determined using method {@link
626	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
627	<	* in exceptions or errors, possibly including ClassCastException.
621	>	* Forks all tasks in the specified collection, returning when
622	>	* {@code isDone} holds for each task or an (unchecked) exception
623	>	* is encountered.  If any task encounters an exception, others
624	>	* may be, but are not guaranteed to be, cancelled.  If more than
625	>	* one task encounters an exception, then this method throws any
626	>	* one of these exceptions.  The individual status of each task
627	>	* may be checked using {@link #getException()} and related
628	>	* methods.  The behavior of this operation is undefined if the
629	>	* specified collection is modified while the operation is in
630	>	* progress.
631	>	*
632	>	* <p>This method may be invoked only from within {@code
633	>	* ForkJoinTask} computations (as may be determined using method
634	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
635	>	* result in exceptions or errors, possibly including {@code
636	>	* ClassCastException}.
637		*
638		* @param tasks the collection of tasks
639		* @return the tasks argument, to simplify usage
640		* @throws NullPointerException if tasks or any element are null
610	–	* @throws RuntimeException or Error if any task did so
641		*/
642		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
643	<	if (!(tasks instanceof List<?>)) {
643	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
644		invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
645		return tasks;
646		}
#	Line 651 | Line 681 | public abstract class ForkJoinTask<V> im
681		}
682
683		/**
684	+	* Attempts to cancel execution of this task. This attempt will
685	+	* fail if the task has already completed, has already been
686	+	* cancelled, or could not be cancelled for some other reason. If
687	+	* successful, and this task has not started when cancel is
688	+	* called, execution of this task is suppressed, {@link
689	+	* #isCancelled} will report true, and {@link #join} will result
690	+	* in a {@code CancellationException} being thrown.
691	+	*
692	+	* <p>This method may be overridden in subclasses, but if so, must
693	+	* still ensure that these minimal properties hold. In particular,
694	+	* the {@code cancel} method itself must not throw exceptions.
695	+	*
696	+	* <p>This method is designed to be invoked by <em>other</em>
697	+	* tasks. To terminate the current task, you can just return or
698	+	* throw an unchecked exception from its computation method, or
699	+	* invoke {@link #completeExceptionally}.
700	+	*
701	+	* @param mayInterruptIfRunning this value is ignored in the
702	+	* default implementation because tasks are not
703	+	* cancelled via interruption
704	+	*
705	+	* @return {@code true} if this task is now cancelled
706	+	*/
707	+	public boolean cancel(boolean mayInterruptIfRunning) {
708	+	setCompletion(CANCELLED);
709	+	return (status & COMPLETION_MASK) == CANCELLED;
710	+	}
711	+
712	+	/**
713		* Returns {@code true} if the computation performed by this task
714		* has completed (or has been cancelled).
715		*
#	Line 670 | Line 729 | public abstract class ForkJoinTask<V> im
729		}
730
731		/**
732	<	* Asserts that the results of this task's computation will not be
674	<	* used. If a cancellation occurs before attempting to execute this
675	<	* task, execution will be suppressed, {@link #isCancelled}
676	<	* will report true, and {@link #join} will result in a
677	<	* {@code CancellationException} being thrown. Otherwise, when
678	<	* cancellation races with completion, there are no guarantees
679	<	* about whether {@code isCancelled} will report {@code true},
680	<	* whether {@code join} will return normally or via an exception,
681	<	* or whether these behaviors will remain consistent upon repeated
682	<	* invocation.
683	<	*
684	<	* <p>This method may be overridden in subclasses, but if so, must
685	<	* still ensure that these minimal properties hold. In particular,
686	<	* the cancel method itself must not throw exceptions.
687	<	*
688	<	* <p> This method is designed to be invoked by <em>other</em>
689	<	* tasks. To terminate the current task, you can just return or
690	<	* throw an unchecked exception from its computation method, or
691	<	* invoke {@link #completeExceptionally}.
732	>	* Returns {@code true} if this task threw an exception or was cancelled.
733		*
734	<	* @param mayInterruptIfRunning this value is ignored in the
735	<	* default implementation because tasks are not in general
736	<	* cancelled via interruption
734	>	* @return {@code true} if this task threw an exception or was cancelled
735	>	*/
736	>	public final boolean isCompletedAbnormally() {
737	>	return (status & COMPLETION_MASK) < NORMAL;
738	>	}
739	>
740	>	/**
741	>	* Returns {@code true} if this task completed without throwing an
742	>	* exception and was not cancelled.
743		*
744	<	* @return {@code true} if this task is now cancelled
744	>	* @return {@code true} if this task completed without throwing an
745	>	* exception and was not cancelled
746		*/
747	<	public boolean cancel(boolean mayInterruptIfRunning) {
748	<	setCompletion(CANCELLED);
701	<	return (status & COMPLETION_MASK) == CANCELLED;
747	>	public final boolean isCompletedNormally() {
748	>	return (status & COMPLETION_MASK) == NORMAL;
749		}
750
751		/**
752	<	* Returns {@code true} if this task threw an exception or was cancelled.
752	>	* Returns {@code true} if this task threw an exception.
753		*
754	<	* @return {@code true} if this task threw an exception or was cancelled
754	>	* @return {@code true} if this task threw an exception
755		*/
756	<	public final boolean isCompletedAbnormally() {
757	<	return (status & COMPLETION_MASK) < NORMAL;
756	>	public final boolean isCompletedExceptionally() {
757	>	return (status & COMPLETION_MASK) == EXCEPTIONAL;
758		}
759
760		/**
761		* Returns the exception thrown by the base computation, or a
762	<	* CancellationException if cancelled, or null if none or if the
763	<	* method has not yet completed.
762	>	* {@code CancellationException} if cancelled, or {@code null} if
763	>	* none or if the method has not yet completed.
764		*
765		* @return the exception, or {@code null} if none
766		*/
#	Line 732 | Line 779 | public abstract class ForkJoinTask<V> im
779		* {@code join} and related operations. This method may be used
780		* to induce exceptions in asynchronous tasks, or to force
781		* completion of tasks that would not otherwise complete.  Its use
782	<	* in other situations is likely to be wrong.  This method is
782	>	* in other situations is discouraged.  This method is
783		* overridable, but overridden versions must invoke {@code super}
784		* implementation to maintain guarantees.
785		*
#	Line 752 | Line 799 | public abstract class ForkJoinTask<V> im
799		* operations. This method may be used to provide results for
800		* asynchronous tasks, or to provide alternative handling for
801		* tasks that would not otherwise complete normally. Its use in
802	<	* other situations is likely to be wrong. This method is
802	>	* other situations is discouraged. This method is
803		* overridable, but overridden versions must invoke {@code super}
804		* implementation to maintain guarantees.
805		*
#	Line 791 | Line 838 | public abstract class ForkJoinTask<V> im
838		* there are no potential dependencies between continuation of the
839		* current task and that of any other task that might be executed
840		* while helping. (This usually holds for pure divide-and-conquer
841	<	* tasks). This method may be invoked only from within
842	<	* ForkJoinTask computations (as may be determined using method
843	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
844	<	* result in exceptions or errors, possibly including
845	<	* ClassCastException.
841	>	* tasks).
842	>	*
843	>	* <p>This method may be invoked only from within {@code
844	>	* ForkJoinTask} computations (as may be determined using method
845	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
846	>	* result in exceptions or errors, possibly including {@code
847	>	* ClassCastException}.
848		*
849		* @return the computed result
850		*/
#	Line 808 | Line 857 | public abstract class ForkJoinTask<V> im
857
858		/**
859		* Possibly executes other tasks until this task is ready.  This
860	<	* method may be invoked only from within ForkJoinTask
861	<	* computations (as may be determined using method {@link
862	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
863	<	* in exceptions or errors, possibly including ClassCastException.
860	>	* method may be useful when processing collections of tasks when
861	>	* some have been cancelled or otherwise known to have aborted.
862	>	*
863	>	* <p>This method may be invoked only from within {@code
864	>	* ForkJoinTask} computations (as may be determined using method
865	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
866	>	* result in exceptions or errors, possibly including {@code
867	>	* ClassCastException}.
868		*/
869		public final void quietlyHelpJoin() {
870		if (status >= 0) {
#	Line 850 | Line 903 | public abstract class ForkJoinTask<V> im
903
904		/**
905		* Possibly executes tasks until the pool hosting the current task
906	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
907	<	* designs in which many tasks are forked, but none are explicitly
908	<	* joined, instead executing them until all are processed.
906	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
907	>	* be of use in designs in which many tasks are forked, but none
908	>	* are explicitly joined, instead executing them until all are
909	>	* processed.
910	>	*
911	>	* <p>This method may be invoked only from within {@code
912	>	* ForkJoinTask} computations (as may be determined using method
913	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
914	>	* result in exceptions or errors, possibly including {@code
915	>	* ClassCastException}.
916		*/
917		public static void helpQuiesce() {
918		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 865 | Line 925 | public abstract class ForkJoinTask<V> im
925		* this task, but only if reuse occurs when this task has either
926		* never been forked, or has been forked, then completed and all
927		* outstanding joins of this task have also completed. Effects
928	<	* under any other usage conditions are not guaranteed, and are
929	<	* almost surely wrong. This method may be useful when executing
928	>	* under any other usage conditions are not guaranteed.
929	>	* This method may be useful when executing
930		* pre-constructed trees of subtasks in loops.
931		*/
932		public void reinitialize() {
#	Line 879 | Line 939 | public abstract class ForkJoinTask<V> im
939		* Returns the pool hosting the current task execution, or null
940		* if this task is executing outside of any ForkJoinPool.
941		*
942	+	* @see #inForkJoinPool
943		* @return the pool, or {@code null} if none
944		*/
945		public static ForkJoinPool getPool() {
#	Line 904 | Line 965 | public abstract class ForkJoinTask<V> im
965		* by the current thread, and has not commenced executing in
966		* another thread.  This method may be useful when arranging
967		* alternative local processing of tasks that could have been, but
968	<	* were not, stolen. This method may be invoked only from within
969	<	* ForkJoinTask computations (as may be determined using method
970	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
971	<	* result in exceptions or errors, possibly including
972	<	* ClassCastException.
968	>	* were not, stolen.
969	>	*
970	>	* <p>This method may be invoked only from within {@code
971	>	* ForkJoinTask} computations (as may be determined using method
972	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
973	>	* result in exceptions or errors, possibly including {@code
974	>	* ClassCastException}.
975		*
976		* @return {@code true} if unforked
977		*/
#	Line 923 | Line 986 | public abstract class ForkJoinTask<V> im
986		* value may be useful for heuristic decisions about whether to
987		* fork other tasks.
988		*
989	+	* <p>This method may be invoked only from within {@code
990	+	* ForkJoinTask} computations (as may be determined using method
991	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
992	+	* result in exceptions or errors, possibly including {@code
993	+	* ClassCastException}.
994	+	*
995		* @return the number of tasks
996		*/
997		public static int getQueuedTaskCount() {
#	Line 940 | Line 1009 | public abstract class ForkJoinTask<V> im
1009		* tasks, and to process computations locally if this threshold is
1010		* exceeded.
1011		*
1012	+	* <p>This method may be invoked only from within {@code
1013	+	* ForkJoinTask} computations (as may be determined using method
1014	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1015	+	* result in exceptions or errors, possibly including {@code
1016	+	* ClassCastException}.
1017	+	*
1018		* @return the surplus number of tasks, which may be negative
1019		*/
1020		public static int getSurplusQueuedTaskCount() {
#	Line 975 | Line 1050 | public abstract class ForkJoinTask<V> im
1050		* called otherwise. The return value controls whether this task
1051		* is considered to be done normally. It may return false in
1052		* asynchronous actions that require explicit invocations of
1053	<	* {@link #complete} to become joinable. It may throw exceptions
1054	<	* to indicate abnormal exit.
1053	>	* {@link #complete} to become joinable. It may also throw an
1054	>	* (unchecked) exception to indicate abnormal exit.
1055		*
1056		* @return {@code true} if completed normally
982	–	* @throws Error or RuntimeException if encountered during computation
1057		*/
1058		protected abstract boolean exec();
1059
#	Line 991 | Line 1065 | public abstract class ForkJoinTask<V> im
1065		* null even if a task exists but cannot be accessed without
1066		* contention with other threads.  This method is designed
1067		* primarily to support extensions, and is unlikely to be useful
1068	<	* otherwise.  This method may be invoked only from within
1069	<	* ForkJoinTask computations (as may be determined using method
1070	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1071	<	* result in exceptions or errors, possibly including
1072	<	* ClassCastException.
1068	>	* otherwise.
1069	>	*
1070	>	* <p>This method may be invoked only from within {@code
1071	>	* ForkJoinTask} computations (as may be determined using method
1072	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1073	>	* result in exceptions or errors, possibly including {@code
1074	>	* ClassCastException}.
1075		*
1076		* @return the next task, or {@code null} if none are available
1077		*/
#	Line 1008 | Line 1084 | public abstract class ForkJoinTask<V> im
1084		* Unschedules and returns, without executing, the next task
1085		* queued by the current thread but not yet executed.  This method
1086		* is designed primarily to support extensions, and is unlikely to
1087	<	* be useful otherwise.  This method may be invoked only from
1088	<	* within ForkJoinTask computations (as may be determined using
1089	<	* method {@link #inForkJoinPool}). Attempts to invoke in other
1090	<	* contexts result in exceptions or errors, possibly including
1091	<	* ClassCastException.
1087	>	* be useful otherwise.
1088	>	*
1089	>	* <p>This method may be invoked only from within {@code
1090	>	* ForkJoinTask} computations (as may be determined using method
1091	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1092	>	* result in exceptions or errors, possibly including {@code
1093	>	* ClassCastException}.
1094		*
1095		* @return the next task, or {@code null} if none are available
1096		*/
#	Line 1029 | Line 1107 | public abstract class ForkJoinTask<V> im
1107		* {@code null} result does not necessarily imply quiescence
1108		* of the pool this task is operating in.  This method is designed
1109		* primarily to support extensions, and is unlikely to be useful
1110	<	* otherwise.  This method may be invoked only from within
1111	<	* ForkJoinTask computations (as may be determined using method
1112	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1113	<	* result in exceptions or errors, possibly including
1114	<	* ClassCastException.
1110	>	* otherwise.
1111	>	*
1112	>	* <p>This method may be invoked only from within {@code
1113	>	* ForkJoinTask} computations (as may be determined using method
1114	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1115	>	* result in exceptions or errors, possibly including {@code
1116	>	* ClassCastException}.
1117		*
1118		* @return a task, or {@code null} if none are available
1119		*/
#	Line 1073 | Line 1153 | public abstract class ForkJoinTask<V> im
1153		*/
1154		static final class AdaptedCallable<T> extends ForkJoinTask<T>
1155		implements RunnableFuture<T> {
1156	<	final Callable<T> callable;
1156	>	final Callable<? extends T> callable;
1157		T result;
1158	<	AdaptedCallable(Callable<T> callable) {
1158	>	AdaptedCallable(Callable<? extends T> callable) {
1159		if (callable == null) throw new NullPointerException();
1160		this.callable = callable;
1161		}
#	Line 1098 | Line 1178 | public abstract class ForkJoinTask<V> im
1178		}
1179
1180		/**
1181	<	* Returns a new ForkJoinTask that performs the {@code run}
1182	<	* method of the given Runnable as its action, and returns a null
1183	<	* result upon {@code join}.
1181	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1182	>	* method of the given {@code Runnable} as its action, and returns
1183	>	* a null result upon {@link #join}.
1184		*
1185		* @param runnable the runnable action
1186		* @return the task
1187		*/
1188	<	public static ForkJoinTask<Void> adapt(Runnable runnable) {
1188	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1189		return new AdaptedRunnable<Void>(runnable, null);
1190		}
1191
1192		/**
1193	<	* Returns a new ForkJoinTask that performs the {@code run}
1194	<	* method of the given Runnable as its action, and returns the
1195	<	* given result upon {@code join}.
1193	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1194	>	* method of the given {@code Runnable} as its action, and returns
1195	>	* the given result upon {@link #join}.
1196		*
1197		* @param runnable the runnable action
1198		* @param result the result upon completion
#	Line 1123 | Line 1203 | public abstract class ForkJoinTask<V> im
1203		}
1204
1205		/**
1206	<	* Returns a new ForkJoinTask that performs the {@code call}
1207	<	* method of the given Callable as its action, and returns its
1208	<	* result upon {@code join}, translating any checked
1209	<	* exceptions encountered into {@code RuntimeException}.
1206	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1207	>	* method of the given {@code Callable} as its action, and returns
1208	>	* its result upon {@link #join}, translating any checked exceptions
1209	>	* encountered into {@code RuntimeException}.
1210		*
1211		* @param callable the callable action
1212		* @return the task
1213		*/
1214	<	public static <T> ForkJoinTask<T> adapt(Callable<T> callable) {
1214	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1215		return new AdaptedCallable<T>(callable);
1216		}
1217

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