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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.29 by jsr166, Sun Aug 2 17:19:24 2009 UTC vs.
Revision 1.39 by jsr166, Wed Aug 5 00:57:41 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 54 | Line 55 | import java.util.WeakHashMap;
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 join them. These exceptions may
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.
#	Line 67 | 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 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
#	Line 85 | 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
104	<	* 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
123	<	* 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 378 | Line 392 | public abstract class ForkJoinTask<V> im
392
393		/**
394		* Returns result or throws exception using j.u.c.Future conventions.
395	<	* Only call when {@code isDone} known to be true.
395	>	* Only call when {@code isDone} known to be true or thread known
396	>	* to be interrupted.
397		*/
398		private V reportFutureResult()
399	<	throws ExecutionException, InterruptedException {
399	>	throws InterruptedException, ExecutionException {
400	>	if (Thread.interrupted())
401	>	throw new InterruptedException();
402		int s = status & COMPLETION_MASK;
403		if (s < NORMAL) {
404		Throwable ex;
#	Line 389 | Line 406 | public abstract class ForkJoinTask<V> im
406		throw new CancellationException();
407		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
408		throw new ExecutionException(ex);
392	–	if (Thread.interrupted())
393	–	throw new InterruptedException();
409		}
410		return getRawResult();
411		}
#	Line 401 | Line 416 | public abstract class ForkJoinTask<V> im
416		*/
417		private V reportTimedFutureResult()
418		throws InterruptedException, ExecutionException, TimeoutException {
419	+	if (Thread.interrupted())
420	+	throw new InterruptedException();
421		Throwable ex;
422		int s = status & COMPLETION_MASK;
423		if (s == NORMAL)
424		return getRawResult();
425	<	if (s == CANCELLED)
425	>	else if (s == CANCELLED)
426		throw new CancellationException();
427	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
427	>	else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
428		throw new ExecutionException(ex);
429	<	if (Thread.interrupted())
430	<	throw new InterruptedException();
414	<	throw new TimeoutException();
429	>	else
430	>	throw new TimeoutException();
431		}
432
433		// internal execution methods
#	Line 496 | Line 512 | public abstract class ForkJoinTask<V> im
512		/**
513		* Arranges to asynchronously execute this task.  While it is not
514		* necessarily enforced, it is a usage error to fork a task more
515	<	* than once unless it has completed and been reinitialized.  This
516	<	* method may be invoked only from within ForkJoinTask
517	<	* computations (as may be determined using method {@link
518	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
519	<	* in exceptions or errors, possibly including ClassCastException.
515	>	* than once unless it has completed and been reinitialized.
516	>	*
517	>	* <p>This method may be invoked only from within {@code
518	>	* ForkJoinTask} computations (as may be determined using method
519	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
520	>	* result in exceptions or errors, possibly including {@code
521	>	* ClassCastException}.
522		*
523	<	* @return {@code this}, to simplify usage.
523	>	* @return {@code this}, to simplify usage
524		*/
525		public final ForkJoinTask<V> fork() {
526		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 512 | Line 530 | public abstract class ForkJoinTask<V> im
530
531		/**
532		* Returns the result of the computation when it is ready.
533	<	* This method differs from {@code get} in that abnormal
534	<	* completion results in RuntimeExceptions or Errors, not
535	<	* ExecutionExceptions.
533	>	* This method differs from {@link #get()} in that
534	>	* abnormal completion results in {@code RuntimeException} or
535	>	* {@code Error}, not {@code ExecutionException}.
536		*
537		* @return the computed result
538		*/
#	Line 527 | Line 545 | public abstract class ForkJoinTask<V> im
545
546		/**
547		* Commences performing this task, awaits its completion if
548	<	* necessary, and return its result.
548	>	* necessary, and return its result, or throws an (unchecked)
549	>	* exception if the underlying computation did so.
550		*
532	–	* @throws Throwable (a RuntimeException, Error, or unchecked
533	–	* exception) if the underlying computation did so
551		* @return the computed result
552		*/
553		public final V invoke() {
#	Line 542 | Line 559 | public abstract class ForkJoinTask<V> im
559
560		/**
561		* Forks the given tasks, returning when {@code isDone} holds for
562	<	* each task or an exception is encountered. This method may be
563	<	* invoked only from within ForkJoinTask computations (as may be
564	<	* determined using method {@link #inForkJoinPool}). Attempts to
565	<	* invoke in other contexts result in exceptions or errors,
566	<	* possibly including ClassCastException.
562	>	* each task or an (unchecked) exception is encountered, in which
563	>	* case the exception is rethrown.  If either task encounters an
564	>	* exception, the other one may be, but is not guaranteed to be,
565	>	* cancelled.  If both tasks throw an exception, then this method
566	>	* throws one of them.  The individual status of each task may be
567	>	* checked using {@link #getException()} and related methods.
568	>	*
569	>	* <p>This method may be invoked only from within {@code
570	>	* ForkJoinTask} computations (as may be determined using method
571	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
572	>	* result in exceptions or errors, possibly including {@code
573	>	* ClassCastException}.
574		*
575		* @param t1 the first task
576		* @param t2 the second task
577		* @throws NullPointerException if any task is null
554	–	* @throws RuntimeException or Error if a task did so
578		*/
579	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
579	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
580		t2.fork();
581		t1.invoke();
582		t2.join();
#	Line 561 | Line 584 | public abstract class ForkJoinTask<V> im
584
585		/**
586		* Forks the given tasks, returning when {@code isDone} holds for
587	<	* each task or an exception is encountered. If any task
588	<	* encounters an exception, others may be, but are not guaranteed
589	<	* to be, cancelled.  This method may be invoked only from within
590	<	* ForkJoinTask computations (as may be determined using method
591	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
592	<	* result in exceptions or errors, possibly including
593	<	* ClassCastException.
594	<	*
595	<	* Overloadings of this method exist for the special cases
596	<	* of one to four arguments.
587	>	* each task or an (unchecked) exception is encountered, in which
588	>	* case the exception is rethrown. If any task encounters an
589	>	* exception, others may be, but are not guaranteed to be,
590	>	* cancelled.  If more than one task encounters an exception, then
591	>	* this method throws any one of these exceptions.  The individual
592	>	* status of each task may be checked using {@link #getException()}
593	>	* and related methods.
594	>	*
595	>	* <p>This method may be invoked only from within {@code
596	>	* ForkJoinTask} computations (as may be determined using method
597	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
598	>	* result in exceptions or errors, possibly including {@code
599	>	* ClassCastException}.
600		*
601		* @param tasks the tasks
602	<	* @throws NullPointerException if tasks or any element are null
577	<	* @throws RuntimeException or Error if any task did so
602	>	* @throws NullPointerException if any task is null
603		*/
604		public static void invokeAll(ForkJoinTask<?>... tasks) {
605		Throwable ex = null;
#	Line 610 | Line 635 | public abstract class ForkJoinTask<V> im
635		}
636
637		/**
638	<	* Forks all tasks in the collection, returning when {@code
639	<	* isDone} holds for each task or an exception is encountered. If
640	<	* any task encounters an exception, others may be, but are not
641	<	* guaranteed to be, cancelled.  This method may be invoked only
642	<	* from within ForkJoinTask computations (as may be determined
643	<	* using method {@link #inForkJoinPool}). Attempts to invoke in
644	<	* other contexts result in exceptions or errors, possibly
645	<	* including ClassCastException.
638	>	* Forks all tasks in the specified collection, returning when
639	>	* {@code isDone} holds for each task or an (unchecked) exception
640	>	* is encountered.  If any task encounters an exception, others
641	>	* may be, but are not guaranteed to be, cancelled.  If more than
642	>	* one task encounters an exception, then this method throws any
643	>	* one of these exceptions.  The individual status of each task
644	>	* may be checked using {@link #getException()} and related
645	>	* methods.  The behavior of this operation is undefined if the
646	>	* specified collection is modified while the operation is in
647	>	* progress.
648	>	*
649	>	* <p>This method may be invoked only from within {@code
650	>	* ForkJoinTask} computations (as may be determined using method
651	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
652	>	* result in exceptions or errors, possibly including {@code
653	>	* ClassCastException}.
654		*
655		* @param tasks the collection of tasks
656		* @return the tasks argument, to simplify usage
657		* @throws NullPointerException if tasks or any element are null
625	–	* @throws RuntimeException or Error if any task did so
658		*/
659		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
660	<	if (!(tasks instanceof List<?>)) {
660	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
661		invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
662		return tasks;
663		}
#	Line 666 | Line 698 | public abstract class ForkJoinTask<V> im
698		}
699
700		/**
701	<	* Returns {@code true} if the computation performed by this task
702	<	* has completed (or has been cancelled).
703	<	*
704	<	* @return {@code true} if this computation has completed
705	<	*/
706	<	public final boolean isDone() {
707	<	return status < 0;
676	<	}
677	<
678	<	/**
679	<	* Returns {@code true} if this task was cancelled.
680	<	*
681	<	* @return {@code true} if this task was cancelled
682	<	*/
683	<	public final boolean isCancelled() {
684	<	return (status & COMPLETION_MASK) == CANCELLED;
685	<	}
686	<
687	<	/**
688	<	* Asserts that the results of this task's computation will not be
689	<	* used. If a cancellation occurs before attempting to execute this
690	<	* task, execution will be suppressed, {@link #isCancelled}
691	<	* will report true, and {@link #join} will result in a
692	<	* {@code CancellationException} being thrown. Otherwise, when
693	<	* cancellation races with completion, there are no guarantees
694	<	* about whether {@code isCancelled} will report {@code true},
695	<	* whether {@code join} will return normally or via an exception,
696	<	* or whether these behaviors will remain consistent upon repeated
697	<	* invocation.
701	>	* Attempts to cancel execution of this task. This attempt will
702	>	* fail if the task has already completed, has already been
703	>	* cancelled, or could not be cancelled for some other reason. If
704	>	* successful, and this task has not started when cancel is
705	>	* called, execution of this task is suppressed, {@link
706	>	* #isCancelled} will report true, and {@link #join} will result
707	>	* in a {@code CancellationException} being thrown.
708		*
709		* <p>This method may be overridden in subclasses, but if so, must
710		* still ensure that these minimal properties hold. In particular,
#	Line 706 | Line 716 | public abstract class ForkJoinTask<V> im
716		* invoke {@link #completeExceptionally}.
717		*
718		* @param mayInterruptIfRunning this value is ignored in the
719	<	* default implementation because tasks are not in general
719	>	* default implementation because tasks are not
720		* cancelled via interruption
721		*
722		* @return {@code true} if this task is now cancelled
#	Line 717 | Line 727 | public abstract class ForkJoinTask<V> im
727		}
728
729		/**
730	+	* Returns {@code true} if the computation performed by this task
731	+	* has completed (or has been cancelled).
732	+	*
733	+	* @return {@code true} if this computation has completed
734	+	*/
735	+	public final boolean isDone() {
736	+	return status < 0;
737	+	}
738	+
739	+	/**
740	+	* Returns {@code true} if this task was cancelled.
741	+	*
742	+	* @return {@code true} if this task was cancelled
743	+	*/
744	+	public final boolean isCancelled() {
745	+	return (status & COMPLETION_MASK) == CANCELLED;
746	+	}
747	+
748	+	/**
749		* Returns {@code true} if this task threw an exception or was cancelled.
750		*
751		* @return {@code true} if this task threw an exception or was cancelled
#	Line 726 | Line 755 | public abstract class ForkJoinTask<V> im
755		}
756
757		/**
758	+	* Returns {@code true} if this task completed without throwing an
759	+	* exception and was not cancelled.
760	+	*
761	+	* @return {@code true} if this task completed without throwing an
762	+	* exception and was not cancelled
763	+	*/
764	+	public final boolean isCompletedNormally() {
765	+	return (status & COMPLETION_MASK) == NORMAL;
766	+	}
767	+
768	+	/**
769	+	* Returns {@code true} if this task threw an exception.
770	+	*
771	+	* @return {@code true} if this task threw an exception
772	+	*/
773	+	public final boolean isCompletedExceptionally() {
774	+	return (status & COMPLETION_MASK) == EXCEPTIONAL;
775	+	}
776	+
777	+	/**
778		* Returns the exception thrown by the base computation, or a
779		* {@code CancellationException} if cancelled, or {@code null} if
780		* none or if the method has not yet completed.
#	Line 734 | Line 783 | public abstract class ForkJoinTask<V> im
783		*/
784		public final Throwable getException() {
785		int s = status & COMPLETION_MASK;
786	<	if (s >= NORMAL)
787	<	return null;
788	<	if (s == CANCELLED)
740	<	return new CancellationException();
741	<	return exceptionMap.get(this);
786	>	return ((s >= NORMAL)    ? null :
787	>	(s == CANCELLED) ? new CancellationException() :
788	>	exceptionMap.get(this));
789		}
790
791		/**
#	Line 806 | Line 853 | public abstract class ForkJoinTask<V> im
853		* there are no potential dependencies between continuation of the
854		* current task and that of any other task that might be executed
855		* while helping. (This usually holds for pure divide-and-conquer
856	<	* tasks). This method may be invoked only from within
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
860	<	* ClassCastException.
856	>	* tasks).
857	>	*
858	>	* <p>This method may be invoked only from within {@code
859	>	* ForkJoinTask} computations (as may be determined using method
860	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
861	>	* result in exceptions or errors, possibly including {@code
862	>	* ClassCastException}.
863		*
864		* @return the computed result
865		*/
#	Line 823 | Line 872 | public abstract class ForkJoinTask<V> im
872
873		/**
874		* Possibly executes other tasks until this task is ready.  This
875	<	* method may be invoked only from within ForkJoinTask
876	<	* computations (as may be determined using method {@link
877	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
878	<	* in exceptions or errors, possibly including ClassCastException.
875	>	* method may be useful when processing collections of tasks when
876	>	* some have been cancelled or otherwise known to have aborted.
877	>	*
878	>	* <p>This method may be invoked only from within {@code
879	>	* ForkJoinTask} computations (as may be determined using method
880	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
881	>	* result in exceptions or errors, possibly including {@code
882	>	* ClassCastException}.
883		*/
884		public final void quietlyHelpJoin() {
885		if (status >= 0) {
#	Line 865 | Line 918 | public abstract class ForkJoinTask<V> im
918
919		/**
920		* Possibly executes tasks until the pool hosting the current task
921	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
922	<	* designs in which many tasks are forked, but none are explicitly
923	<	* joined, instead executing them until all are processed.  This
924	<	* method may be invoked only from within ForkJoinTask
925	<	* computations (as may be determined using method {@link
926	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
927	<	* in exceptions or errors, possibly including ClassCastException.
921	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
922	>	* be of use in designs in which many tasks are forked, but none
923	>	* are explicitly joined, instead executing them until all are
924	>	* processed.
925	>	*
926	>	* <p>This method may be invoked only from within {@code
927	>	* ForkJoinTask} computations (as may be determined using method
928	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
929	>	* result in exceptions or errors, possibly including {@code
930	>	* ClassCastException}.
931		*/
932		public static void helpQuiesce() {
933		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 884 | Line 940 | public abstract class ForkJoinTask<V> im
940		* this task, but only if reuse occurs when this task has either
941		* never been forked, or has been forked, then completed and all
942		* outstanding joins of this task have also completed. Effects
943	<	* under any other usage conditions are not guaranteed, and are
944	<	* discouraged. This method may be useful when executing
943	>	* under any other usage conditions are not guaranteed.
944	>	* This method may be useful when executing
945		* pre-constructed trees of subtasks in loops.
946		*/
947		public void reinitialize() {
#	Line 924 | Line 980 | public abstract class ForkJoinTask<V> im
980		* by the current thread, and has not commenced executing in
981		* another thread.  This method may be useful when arranging
982		* alternative local processing of tasks that could have been, but
983	<	* were not, stolen. This method may be invoked only from within
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
987	<	* ClassCastException.
983	>	* were not, stolen.
984	>	*
985	>	* <p>This method may be invoked only from within {@code
986	>	* ForkJoinTask} computations (as may be determined using method
987	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
988	>	* result in exceptions or errors, possibly including {@code
989	>	* ClassCastException}.
990		*
991		* @return {@code true} if unforked
992		*/
#	Line 941 | Line 999 | public abstract class ForkJoinTask<V> im
999		* Returns an estimate of the number of tasks that have been
1000		* forked by the current worker thread but not yet executed. This
1001		* value may be useful for heuristic decisions about whether to
1002	<	* fork other tasks.  This method may be invoked only from within
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
1006	<	* ClassCastException.
1002	>	* fork other tasks.
1003	>	*
1004	>	* <p>This method may be invoked only from within {@code
1005	>	* ForkJoinTask} computations (as may be determined using method
1006	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1007	>	* result in exceptions or errors, possibly including {@code
1008	>	* ClassCastException}.
1009	>	*
1010		* @return the number of tasks
1011		*/
1012		public static int getQueuedTaskCount() {
#	Line 961 | Line 1022 | public abstract class ForkJoinTask<V> im
1022		* usages of ForkJoinTasks, at steady state, each worker should
1023		* aim to maintain a small constant surplus (for example, 3) of
1024		* tasks, and to process computations locally if this threshold is
1025	<	* exceeded.  This method may be invoked only from within
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
1029	<	* ClassCastException.  *
1025	>	* exceeded.
1026	>	*
1027	>	* <p>This method may be invoked only from within {@code
1028	>	* ForkJoinTask} computations (as may be determined using method
1029	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1030	>	* result in exceptions or errors, possibly including {@code
1031	>	* ClassCastException}.
1032	>	*
1033		* @return the surplus number of tasks, which may be negative
1034		*/
1035		public static int getSurplusQueuedTaskCount() {
#	Line 1001 | Line 1065 | public abstract class ForkJoinTask<V> im
1065		* called otherwise. The return value controls whether this task
1066		* is considered to be done normally. It may return false in
1067		* asynchronous actions that require explicit invocations of
1068	<	* {@link #complete} to become joinable. It may throw exceptions
1069	<	* to indicate abnormal exit.
1068	>	* {@link #complete} to become joinable. It may also throw an
1069	>	* (unchecked) exception to indicate abnormal exit.
1070		*
1071		* @return {@code true} if completed normally
1008	–	* @throws Error or RuntimeException if encountered during computation
1072		*/
1073		protected abstract boolean exec();
1074
#	Line 1017 | Line 1080 | public abstract class ForkJoinTask<V> im
1080		* null even if a task exists but cannot be accessed without
1081		* contention with other threads.  This method is designed
1082		* primarily to support extensions, and is unlikely to be useful
1083	<	* otherwise.  This method may be invoked only from within
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
1087	<	* ClassCastException.
1083	>	* otherwise.
1084	>	*
1085	>	* <p>This method may be invoked only from within {@code
1086	>	* ForkJoinTask} computations (as may be determined using method
1087	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1088	>	* result in exceptions or errors, possibly including {@code
1089	>	* ClassCastException}.
1090		*
1091		* @return the next task, or {@code null} if none are available
1092		*/
#	Line 1034 | Line 1099 | public abstract class ForkJoinTask<V> im
1099		* Unschedules and returns, without executing, the next task
1100		* queued by the current thread but not yet executed.  This method
1101		* is designed primarily to support extensions, and is unlikely to
1102	<	* be useful otherwise.  This method may be invoked only from
1103	<	* within ForkJoinTask computations (as may be determined using
1104	<	* method {@link #inForkJoinPool}). Attempts to invoke in other
1105	<	* contexts result in exceptions or errors, possibly including
1106	<	* ClassCastException.
1102	>	* be useful otherwise.
1103	>	*
1104	>	* <p>This method may be invoked only from within {@code
1105	>	* ForkJoinTask} computations (as may be determined using method
1106	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1107	>	* result in exceptions or errors, possibly including {@code
1108	>	* ClassCastException}.
1109		*
1110		* @return the next task, or {@code null} if none are available
1111		*/
#	Line 1055 | Line 1122 | public abstract class ForkJoinTask<V> im
1122		* {@code null} result does not necessarily imply quiescence
1123		* of the pool this task is operating in.  This method is designed
1124		* primarily to support extensions, and is unlikely to be useful
1125	<	* otherwise.  This method may be invoked only from within
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
1129	<	* ClassCastException.
1125	>	* otherwise.
1126	>	*
1127	>	* <p>This method may be invoked only from within {@code
1128	>	* ForkJoinTask} computations (as may be determined using method
1129	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1130	>	* result in exceptions or errors, possibly including {@code
1131	>	* ClassCastException}.
1132		*
1133		* @return a task, or {@code null} if none are available
1134		*/
#	Line 1124 | Line 1193 | public abstract class ForkJoinTask<V> im
1193		}
1194
1195		/**
1196	<	* Returns a new ForkJoinTask that performs the {@code run}
1197	<	* method of the given Runnable as its action, and returns a null
1198	<	* result upon {@code join}.
1196	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1197	>	* method of the given {@code Runnable} as its action, and returns
1198	>	* a null result upon {@link #join}.
1199		*
1200		* @param runnable the runnable action
1201		* @return the task
#	Line 1136 | Line 1205 | public abstract class ForkJoinTask<V> im
1205		}
1206
1207		/**
1208	<	* Returns a new ForkJoinTask that performs the {@code run}
1209	<	* method of the given Runnable as its action, and returns the
1210	<	* given result upon {@code join}.
1208	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1209	>	* method of the given {@code Runnable} as its action, and returns
1210	>	* the given result upon {@link #join}.
1211		*
1212		* @param runnable the runnable action
1213		* @param result the result upon completion
#	Line 1149 | Line 1218 | public abstract class ForkJoinTask<V> im
1218		}
1219
1220		/**
1221	<	* Returns a new ForkJoinTask that performs the {@code call}
1222	<	* method of the given Callable as its action, and returns its
1223	<	* result upon {@code join}, translating any checked
1224	<	* exceptions encountered into {@code RuntimeException}.
1221	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1222	>	* method of the given {@code Callable} as its action, and returns
1223	>	* its result upon {@link #join}, translating any checked exceptions
1224	>	* encountered into {@code RuntimeException}.
1225		*
1226		* @param callable the callable action
1227		* @return the task

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