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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.30 by dl, Sun Aug 2 22:28:23 2009 UTC vs.
Revision 1.42 by dl, Thu Aug 6 23:08:50 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 #isCompletedNormally} is true if a task completed without
84	+	* cancellation or encountering an exception; {@link #isCancelled} is
85	+	* true if the task was cancelled (in which case {@link #getException}
86	+	* returns a {@link java.util.concurrent.CancellationException}); and
87	+	* {@link #isCompletedAbnormally} is true if a task was either
88	+	* cancelled or encountered an exception, in which case {@link
89	+	* #getException} will return either the encountered exception or
90	+	* {@link java.util.concurrent.CancellationException}.
91	+	*
92		* <p>The ForkJoinTask class is not usually directly subclassed.
93		* Instead, you subclass one of the abstract classes that support a
94		* particular style of fork/join processing, typically {@link
#	Line 85 | Line 98 | import java.util.WeakHashMap;
98		* established in a constructor, and then defines a {@code compute}
99		* method that somehow uses the control methods supplied by this base
100		* class. While these methods have {@code public} access (to allow
101	<	* instances of different task subclasses to call each others
101	>	* instances of different task subclasses to call each other's
102		* methods), some of them may only be called from within other
103		* ForkJoinTasks (as may be determined using method {@link
104		* #inForkJoinPool}).  Attempts to invoke them in other contexts
105		* result in exceptions or errors, possibly including
106		* ClassCastException.
107		*
108	<	* <p>Most base support methods are {@code final} because their
109	<	* implementations are intrinsically tied to the underlying
110	<	* lightweight task scheduling framework, and so cannot be overridden.
111	<	* Developers creating new basic styles of fork/join processing should
112	<	* minimally implement {@code protected} methods
113	<	* {@link #exec}, {@link #setRawResult}, and
114	<	* {@link #getRawResult}, while also introducing an abstract
115	<	* computational method that can be implemented in its subclasses,
116	<	* possibly relying on other {@code protected} methods provided
104	<	* by this class.
108	>	* <p>Most base support methods are {@code final}, to prevent
109	>	* overriding of implementations that are intrinsically tied to the
110	>	* underlying lightweight task scheduling framework.  Developers
111	>	* creating new basic styles of fork/join processing should minimally
112	>	* implement {@code protected} methods {@link #exec}, {@link
113	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
114	>	* an abstract computational method that can be implemented in its
115	>	* subclasses, possibly relying on other {@code protected} methods
116	>	* provided by this class.
117		*
118		* <p>ForkJoinTasks should perform relatively small amounts of
119	<	* computations, otherwise splitting into smaller tasks. As a very
120	<	* rough rule of thumb, a task should perform more than 100 and less
121	<	* than 10000 basic computational steps. If tasks are too big, then
122	<	* parallelism cannot improve throughput. If too small, then memory
123	<	* and internal task maintenance overhead may overwhelm processing.
119	>	* computation. Large tasks should be split into smaller subtasks,
120	>	* usually via recursive decomposition. As a very rough rule of thumb,
121	>	* a task should perform more than 100 and less than 10000 basic
122	>	* computational steps. If tasks are too big, then parallelism cannot
123	>	* improve throughput. If too small, then memory and internal task
124	>	* maintenance overhead may overwhelm processing.
125		*
126	<	* <p>This class provides {@code adapt} methods for {@link
127	<	* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
128	<	* may be of use when mixing execution of ForkJoinTasks with other
129	<	* kinds of tasks. When all tasks are of this form, consider using a
130	<	* pool in {@link ForkJoinPool#setAsyncMode}.
126	>	* <p>This class provides {@code adapt} methods for {@link Runnable}
127	>	* and {@link Callable}, that may be of use when mixing execution of
128	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks
129	>	* are of this form, consider using a pool in
130	>	* {@linkplain ForkJoinPool#setAsyncMode async mode}.
131		*
132	<	* <p>ForkJoinTasks are {@code Serializable}, which enables them
133	<	* to be used in extensions such as remote execution frameworks. It is
134	<	* in general sensible to serialize tasks only before or after, but
135	<	* not during execution. Serialization is not relied on during
123	<	* execution itself.
132	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
133	>	* used in extensions such as remote execution frameworks. It is
134	>	* sensible to serialize tasks only before or after, but not during,
135	>	* execution. Serialization is not relied on during execution itself.
136		*
137		* @since 1.7
138		* @author Doug Lea
#	Line 378 | Line 390 | public abstract class ForkJoinTask<V> im
390
391		/**
392		* Returns result or throws exception using j.u.c.Future conventions.
393	<	* Only call when {@code isDone} known to be true.
393	>	* Only call when {@code isDone} known to be true or thread known
394	>	* to be interrupted.
395		*/
396		private V reportFutureResult()
397	<	throws ExecutionException, InterruptedException {
397	>	throws InterruptedException, ExecutionException {
398	>	if (Thread.interrupted())
399	>	throw new InterruptedException();
400		int s = status & COMPLETION_MASK;
401		if (s < NORMAL) {
402		Throwable ex;
#	Line 389 | Line 404 | public abstract class ForkJoinTask<V> im
404		throw new CancellationException();
405		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
406		throw new ExecutionException(ex);
392	–	if (Thread.interrupted())
393	–	throw new InterruptedException();
407		}
408		return getRawResult();
409		}
#	Line 401 | Line 414 | public abstract class ForkJoinTask<V> im
414		*/
415		private V reportTimedFutureResult()
416		throws InterruptedException, ExecutionException, TimeoutException {
417	+	if (Thread.interrupted())
418	+	throw new InterruptedException();
419		Throwable ex;
420		int s = status & COMPLETION_MASK;
421		if (s == NORMAL)
422		return getRawResult();
423	<	if (s == CANCELLED)
423	>	else if (s == CANCELLED)
424		throw new CancellationException();
425	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
425	>	else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
426		throw new ExecutionException(ex);
427	<	if (Thread.interrupted())
428	<	throw new InterruptedException();
414	<	throw new TimeoutException();
427	>	else
428	>	throw new TimeoutException();
429		}
430
431		// internal execution methods
#	Line 496 | Line 510 | public abstract class ForkJoinTask<V> im
510		/**
511		* Arranges to asynchronously execute this task.  While it is not
512		* necessarily enforced, it is a usage error to fork a task more
513	<	* than once unless it has completed and been reinitialized.  This
514	<	* method may be invoked only from within ForkJoinTask
515	<	* computations (as may be determined using method {@link
516	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
517	<	* in exceptions or errors, possibly including ClassCastException.
513	>	* than once unless it has completed and been reinitialized.
514	>	*
515	>	* <p>This method may be invoked only from within {@code
516	>	* ForkJoinTask} computations (as may be determined using method
517	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
518	>	* result in exceptions or errors, possibly including {@code
519	>	* ClassCastException}.
520		*
521	<	* @return {@code this}, to simplify usage.
521	>	* @return {@code this}, to simplify usage
522		*/
523		public final ForkJoinTask<V> fork() {
524		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 511 | Line 527 | public abstract class ForkJoinTask<V> im
527		}
528
529		/**
530	<	* Returns the result of the computation when it is ready.
531	<	* This method differs from {@code get} in that abnormal
532	<	* completion results in RuntimeExceptions or Errors, not
533	<	* ExecutionExceptions.
530	>	* Returns the result of the computation when it {@link #isDone is done}.
531	>	* This method differs from {@link #get()} in that
532	>	* abnormal completion results in {@code RuntimeException} or
533	>	* {@code Error}, not {@code ExecutionException}.
534		*
535		* @return the computed result
536		*/
#	Line 527 | Line 543 | public abstract class ForkJoinTask<V> im
543
544		/**
545		* Commences performing this task, awaits its completion if
546	<	* necessary, and return its result.
546	>	* necessary, and return its result, or throws an (unchecked)
547	>	* exception if the underlying computation did so.
548		*
532	–	* @throws Throwable (a RuntimeException, Error, or unchecked
533	–	* exception) if the underlying computation did so
549		* @return the computed result
550		*/
551		public final V invoke() {
#	Line 542 | Line 557 | public abstract class ForkJoinTask<V> im
557
558		/**
559		* Forks the given tasks, returning when {@code isDone} holds for
560	<	* each task or an exception is encountered. This method may be
561	<	* invoked only from within ForkJoinTask computations (as may be
562	<	* determined using method {@link #inForkJoinPool}). Attempts to
563	<	* invoke in other contexts result in exceptions or errors,
564	<	* possibly including ClassCastException.
560	>	* each task or an (unchecked) exception is encountered, in which
561	>	* case the exception is rethrown.  If either task encounters an
562	>	* exception, the other one may be, but is not guaranteed to be,
563	>	* cancelled.  If both tasks throw an exception, then this method
564	>	* throws one of them.  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
554	–	* @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 561 | 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
577	<	* @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 610 | 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
625	–	* @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 666 | Line 696 | public abstract class ForkJoinTask<V> im
696		}
697
698		/**
699	<	* Returns {@code true} if the computation performed by this task
700	<	* has completed (or has been cancelled).
701	<	*
702	<	* @return {@code true} if this computation has completed
703	<	*/
704	<	public final boolean isDone() {
705	<	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.
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,
#	Line 706 | Line 714 | public abstract class ForkJoinTask<V> im
714		* invoke {@link #completeExceptionally}.
715		*
716		* @param mayInterruptIfRunning this value is ignored in the
717	<	* default implementation because tasks are not in general
717	>	* default implementation because tasks are not
718		* cancelled via interruption
719		*
720		* @return {@code true} if this task is now cancelled
#	Line 716 | Line 724 | public abstract class ForkJoinTask<V> im
724		return (status & COMPLETION_MASK) == CANCELLED;
725		}
726
727	+	public final boolean isDone() {
728	+	return status < 0;
729	+	}
730	+
731	+	public final boolean isCancelled() {
732	+	return (status & COMPLETION_MASK) == CANCELLED;
733	+	}
734	+
735		/**
736		* Returns {@code true} if this task threw an exception or was cancelled.
737		*
#	Line 726 | Line 742 | public abstract class ForkJoinTask<V> im
742		}
743
744		/**
745	+	* Returns {@code true} if this task completed without throwing an
746	+	* exception and was not cancelled.
747	+	*
748	+	* @return {@code true} if this task completed without throwing an
749	+	* exception and was not cancelled
750	+	*/
751	+	public final boolean isCompletedNormally() {
752	+	return (status & COMPLETION_MASK) == NORMAL;
753	+	}
754	+
755	+	/**
756		* Returns the exception thrown by the base computation, or a
757		* {@code CancellationException} if cancelled, or {@code null} if
758		* none or if the method has not yet completed.
#	Line 734 | Line 761 | public abstract class ForkJoinTask<V> im
761		*/
762		public final Throwable getException() {
763		int s = status & COMPLETION_MASK;
764	<	if (s >= NORMAL)
765	<	return null;
766	<	if (s == CANCELLED)
740	<	return new CancellationException();
741	<	return exceptionMap.get(this);
764	>	return ((s >= NORMAL)    ? null :
765	>	(s == CANCELLED) ? new CancellationException() :
766	>	exceptionMap.get(this));
767		}
768
769		/**
#	Line 800 | Line 825 | public abstract class ForkJoinTask<V> im
825		}
826
827		/**
828	<	* Possibly executes other tasks until this task is ready, then
829	<	* returns the result of the computation.  This method may be more
830	<	* efficient than {@code join}, but is only applicable when
831	<	* there are no potential dependencies between continuation of the
832	<	* current task and that of any other task that might be executed
833	<	* while helping. (This usually holds for pure divide-and-conquer
834	<	* tasks). This method may be invoked only from within
835	<	* ForkJoinTask computations (as may be determined using method
836	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
837	<	* result in exceptions or errors, possibly including
838	<	* ClassCastException.
828	>	* Possibly executes other tasks until this task {@link #isDone is
829	>	* done}, then returns the result of the computation.  This method
830	>	* may be more efficient than {@code join}, but is only applicable
831	>	* when there are no potential dependencies between continuation
832	>	* of the current task and that of any other task that might be
833	>	* executed while helping. (This usually holds for pure
834	>	* divide-and-conquer tasks).
835	>	*
836	>	* <p>This method may be invoked only from within {@code
837	>	* ForkJoinTask} computations (as may be determined using method
838	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
839	>	* result in exceptions or errors, possibly including {@code
840	>	* ClassCastException}.
841		*
842		* @return the computed result
843		*/
#	Line 822 | Line 849 | public abstract class ForkJoinTask<V> im
849		}
850
851		/**
852	<	* Possibly executes other tasks until this task is ready.  This
853	<	* method may be invoked only from within ForkJoinTask
854	<	* computations (as may be determined using method {@link
855	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
856	<	* in exceptions or errors, possibly including ClassCastException.
852	>	* Possibly executes other tasks until this task {@link #isDone is
853	>	* done}.  This method may be useful when processing collections
854	>	* of tasks when some have been cancelled or otherwise known to
855	>	* have aborted.
856	>	*
857	>	* <p>This method may be invoked only from within {@code
858	>	* ForkJoinTask} computations (as may be determined using method
859	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
860	>	* result in exceptions or errors, possibly including {@code
861	>	* ClassCastException}.
862		*/
863		public final void quietlyHelpJoin() {
864		if (status >= 0) {
#	Line 865 | Line 897 | public abstract class ForkJoinTask<V> im
897
898		/**
899		* Possibly executes tasks until the pool hosting the current task
900	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
901	<	* designs in which many tasks are forked, but none are explicitly
902	<	* joined, instead executing them until all are processed.  This
903	<	* method may be invoked only from within ForkJoinTask
904	<	* computations (as may be determined using method {@link
905	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
906	<	* in exceptions or errors, possibly including ClassCastException.
900	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
901	>	* be of use in designs in which many tasks are forked, but none
902	>	* are explicitly joined, instead executing them until all are
903	>	* processed.
904	>	*
905	>	* <p>This method may be invoked only from within {@code
906	>	* ForkJoinTask} computations (as may be determined using method
907	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
908	>	* result in exceptions or errors, possibly including {@code
909	>	* ClassCastException}.
910		*/
911		public static void helpQuiesce() {
912		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 924 | Line 959 | public abstract class ForkJoinTask<V> im
959		* by the current thread, and has not commenced executing in
960		* another thread.  This method may be useful when arranging
961		* alternative local processing of tasks that could have been, but
962	<	* were not, stolen. This method may be invoked only from within
963	<	* ForkJoinTask computations (as may be determined using method
964	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
965	<	* result in exceptions or errors, possibly including
966	<	* ClassCastException.
962	>	* were not, stolen.
963	>	*
964	>	* <p>This method may be invoked only from within {@code
965	>	* ForkJoinTask} computations (as may be determined using method
966	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
967	>	* result in exceptions or errors, possibly including {@code
968	>	* ClassCastException}.
969		*
970		* @return {@code true} if unforked
971		*/
#	Line 941 | Line 978 | public abstract class ForkJoinTask<V> im
978		* Returns an estimate of the number of tasks that have been
979		* forked by the current worker thread but not yet executed. This
980		* value may be useful for heuristic decisions about whether to
981	<	* fork other tasks.  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	>	* fork other tasks.
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 the number of tasks
990		*/
991		public static int getQueuedTaskCount() {
#	Line 961 | Line 1001 | public abstract class ForkJoinTask<V> im
1001		* usages of ForkJoinTasks, at steady state, each worker should
1002		* aim to maintain a small constant surplus (for example, 3) of
1003		* tasks, and to process computations locally if this threshold is
1004	<	* exceeded.  This method may be invoked only from within
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
1008	<	* ClassCastException.
1004	>	* exceeded.
1005	>	*
1006	>	* <p>This method may be invoked only from within {@code
1007	>	* ForkJoinTask} computations (as may be determined using method
1008	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1009	>	* result in exceptions or errors, possibly including {@code
1010	>	* ClassCastException}.
1011	>	*
1012		* @return the surplus number of tasks, which may be negative
1013		*/
1014		public static int getSurplusQueuedTaskCount() {
#	Line 1001 | Line 1044 | public abstract class ForkJoinTask<V> im
1044		* called otherwise. The return value controls whether this task
1045		* is considered to be done normally. It may return false in
1046		* asynchronous actions that require explicit invocations of
1047	<	* {@link #complete} to become joinable. It may throw exceptions
1048	<	* to indicate abnormal exit.
1047	>	* {@link #complete} to become joinable. It may also throw an
1048	>	* (unchecked) exception to indicate abnormal exit.
1049		*
1050		* @return {@code true} if completed normally
1008	–	* @throws Error or RuntimeException if encountered during computation
1051		*/
1052		protected abstract boolean exec();
1053
#	Line 1017 | Line 1059 | public abstract class ForkJoinTask<V> im
1059		* null even if a task exists but cannot be accessed without
1060		* contention with other threads.  This method is designed
1061		* primarily to support extensions, and is unlikely to be useful
1062	<	* otherwise.  This method may be invoked only from within
1063	<	* ForkJoinTask computations (as may be determined using method
1064	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1065	<	* result in exceptions or errors, possibly including
1066	<	* ClassCastException.
1062	>	* otherwise.
1063	>	*
1064	>	* <p>This method may be invoked only from within {@code
1065	>	* ForkJoinTask} computations (as may be determined using method
1066	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1067	>	* result in exceptions or errors, possibly including {@code
1068	>	* ClassCastException}.
1069		*
1070		* @return the next task, or {@code null} if none are available
1071		*/
#	Line 1034 | Line 1078 | public abstract class ForkJoinTask<V> im
1078		* Unschedules and returns, without executing, the next task
1079		* queued by the current thread but not yet executed.  This method
1080		* is designed primarily to support extensions, and is unlikely to
1081	<	* be useful otherwise.  This method may be invoked only from
1082	<	* within ForkJoinTask computations (as may be determined using
1083	<	* method {@link #inForkJoinPool}). Attempts to invoke in other
1084	<	* contexts result in exceptions or errors, possibly including
1085	<	* ClassCastException.
1081	>	* be useful 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 1055 | Line 1101 | public abstract class ForkJoinTask<V> im
1101		* {@code null} result does not necessarily imply quiescence
1102		* of the pool this task is operating in.  This method is designed
1103		* primarily to support extensions, and is unlikely to be useful
1104	<	* otherwise.  This method may be invoked only from within
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
1108	<	* ClassCastException.
1104	>	* otherwise.
1105	>	*
1106	>	* <p>This method may be invoked only from within {@code
1107	>	* ForkJoinTask} computations (as may be determined using method
1108	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1109	>	* result in exceptions or errors, possibly including {@code
1110	>	* ClassCastException}.
1111		*
1112		* @return a task, or {@code null} if none are available
1113		*/
#	Line 1124 | Line 1172 | public abstract class ForkJoinTask<V> im
1172		}
1173
1174		/**
1175	<	* Returns a new ForkJoinTask that performs the {@code run}
1176	<	* method of the given Runnable as its action, and returns a null
1177	<	* result upon {@code join}.
1175	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1176	>	* method of the given {@code Runnable} as its action, and returns
1177	>	* a null result upon {@link #join}.
1178		*
1179		* @param runnable the runnable action
1180		* @return the task
#	Line 1136 | Line 1184 | public abstract class ForkJoinTask<V> im
1184		}
1185
1186		/**
1187	<	* Returns a new ForkJoinTask that performs the {@code run}
1188	<	* method of the given Runnable as its action, and returns the
1189	<	* given result upon {@code join}.
1187	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1188	>	* method of the given {@code Runnable} as its action, and returns
1189	>	* the given result upon {@link #join}.
1190		*
1191		* @param runnable the runnable action
1192		* @param result the result upon completion
#	Line 1149 | Line 1197 | public abstract class ForkJoinTask<V> im
1197		}
1198
1199		/**
1200	<	* Returns a new ForkJoinTask that performs the {@code call}
1201	<	* method of the given Callable as its action, and returns its
1202	<	* result upon {@code join}, translating any checked
1203	<	* exceptions encountered into {@code RuntimeException}.
1200	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1201	>	* method of the given {@code Callable} as its action, and returns
1202	>	* its result upon {@link #join}, translating any checked exceptions
1203	>	* encountered into {@code RuntimeException}.
1204		*
1205		* @param callable the callable action
1206		* @return the task

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