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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.28 by jsr166, Sun Aug 2 17:02:06 2009 UTC vs.
Revision 1.44 by jsr166, Wed Aug 19 17:44:45 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
59	<	* additionally include RejectedExecutionExceptions stemming from
60	<	* internal resource exhaustion such as failure to allocate internal
61	<	* task queues.
58	>	* rethrown to callers attempting to join them. These exceptions may
59	>	* additionally include {@link RejectedExecutionException} stemming
60	>	* from internal resource exhaustion, such as failure to allocate
61	>	* internal 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 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	>	* Subsequent modifications to the state of this task or any data
515	>	* it operates on are not necessarily consistently observable by
516	>	* any thread other than the one executing it unless preceded by a
517	>	* call to {@link #join} or related methods, or a call to {@link
518	>	* #isDone} returning {@code true}.
519	>	*
520	>	* <p>This method may be invoked only from within {@code
521	>	* ForkJoinTask} computations (as may be determined using method
522	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
523	>	* result in exceptions or errors, possibly including {@code
524	>	* ClassCastException}.
525		*
526	<	* @return {@code this}, to simplify usage.
526	>	* @return {@code this}, to simplify usage
527		*/
528		public final ForkJoinTask<V> fork() {
529		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 511 | Line 532 | public abstract class ForkJoinTask<V> im
532		}
533
534		/**
535	<	* Returns the result of the computation when it is ready.
536	<	* This method differs from {@code get} in that abnormal
537	<	* completion results in RuntimeExceptions or Errors, not
538	<	* ExecutionExceptions.
535	>	* Returns the result of the computation when it {@link #isDone is done}.
536	>	* This method differs from {@link #get()} in that
537	>	* abnormal completion results in {@code RuntimeException} or
538	>	* {@code Error}, not {@code ExecutionException}.
539		*
540		* @return the computed result
541		*/
#	Line 527 | Line 548 | public abstract class ForkJoinTask<V> im
548
549		/**
550		* Commences performing this task, awaits its completion if
551	<	* necessary, and return its result.
551	>	* necessary, and return its result, or throws an (unchecked)
552	>	* exception if the underlying computation did so.
553		*
532	–	* @throws Throwable (a RuntimeException, Error, or unchecked
533	–	* exception) if the underlying computation did so
554		* @return the computed result
555		*/
556		public final V invoke() {
#	Line 542 | Line 562 | public abstract class ForkJoinTask<V> im
562
563		/**
564		* Forks the given tasks, returning when {@code isDone} holds for
565	<	* each task or an exception is encountered. This method may be
566	<	* invoked only from within ForkJoinTask computations (as may be
567	<	* determined using method {@link #inForkJoinPool}). Attempts to
568	<	* invoke in other contexts result in exceptions or errors,
569	<	* possibly including ClassCastException.
565	>	* each task or an (unchecked) exception is encountered, in which
566	>	* case the exception is rethrown.  If either task encounters an
567	>	* exception, the other one may be, but is not guaranteed to be,
568	>	* cancelled.  If both tasks throw an exception, then this method
569	>	* throws one of them.  The individual status of each task may be
570	>	* checked using {@link #getException()} and related methods.
571	>	*
572	>	* <p>This method may be invoked only from within {@code
573	>	* ForkJoinTask} computations (as may be determined using method
574	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
575	>	* result in exceptions or errors, possibly including {@code
576	>	* ClassCastException}.
577		*
578		* @param t1 the first task
579		* @param t2 the second task
580		* @throws NullPointerException if any task is null
554	–	* @throws RuntimeException or Error if a task did so
581		*/
582	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
582	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
583		t2.fork();
584		t1.invoke();
585		t2.join();
#	Line 561 | Line 587 | public abstract class ForkJoinTask<V> im
587
588		/**
589		* Forks the given tasks, returning when {@code isDone} holds for
590	<	* each task or an exception is encountered. If any task
591	<	* encounters an exception, others may be, but are not guaranteed
592	<	* to be, cancelled.  This method may be invoked only from within
593	<	* ForkJoinTask computations (as may be determined using method
594	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
595	<	* result in exceptions or errors, possibly including
596	<	* ClassCastException.
597	<	*
598	<	* Overloadings of this method exist for the special cases
599	<	* of one to four arguments.
590	>	* each task or an (unchecked) exception is encountered, in which
591	>	* case the exception is rethrown. If any task encounters an
592	>	* exception, others may be, but are not guaranteed to be,
593	>	* cancelled.  If more than one task encounters an exception, then
594	>	* this method throws any one of these exceptions.  The individual
595	>	* status of each task may be checked using {@link #getException()}
596	>	* and related methods.
597	>	*
598	>	* <p>This method may be invoked only from within {@code
599	>	* ForkJoinTask} computations (as may be determined using method
600	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
601	>	* result in exceptions or errors, possibly including {@code
602	>	* ClassCastException}.
603		*
604		* @param tasks the tasks
605	<	* @throws NullPointerException if tasks or any element are null
577	<	* @throws RuntimeException or Error if any task did so
605	>	* @throws NullPointerException if any task is null
606		*/
607		public static void invokeAll(ForkJoinTask<?>... tasks) {
608		Throwable ex = null;
#	Line 610 | Line 638 | public abstract class ForkJoinTask<V> im
638		}
639
640		/**
641	<	* Forks all tasks in the collection, returning when {@code
642	<	* isDone} holds for each task or an exception is encountered. If
643	<	* any task encounters an exception, others may be, but are not
644	<	* guaranteed to be, cancelled.  This method may be invoked only
645	<	* from within ForkJoinTask computations (as may be determined
646	<	* using method {@link #inForkJoinPool}). Attempts to invoke in
647	<	* other contexts result in exceptions or errors, possibly
648	<	* including ClassCastException.
641	>	* Forks all tasks in the specified collection, returning when
642	>	* {@code isDone} holds for each task or an (unchecked) exception
643	>	* is encountered.  If any task encounters an exception, others
644	>	* may be, but are not guaranteed to be, cancelled.  If more than
645	>	* one task encounters an exception, then this method throws any
646	>	* one of these exceptions.  The individual status of each task
647	>	* may be checked using {@link #getException()} and related
648	>	* methods.  The behavior of this operation is undefined if the
649	>	* specified collection is modified while the operation is in
650	>	* progress.
651	>	*
652	>	* <p>This method may be invoked only from within {@code
653	>	* ForkJoinTask} computations (as may be determined using method
654	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
655	>	* result in exceptions or errors, possibly including {@code
656	>	* ClassCastException}.
657		*
658		* @param tasks the collection of tasks
659		* @return the tasks argument, to simplify usage
660		* @throws NullPointerException if tasks or any element are null
625	–	* @throws RuntimeException or Error if any task did so
661		*/
662		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
663	<	if (!(tasks instanceof List<?>)) {
663	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
664		invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
665		return tasks;
666		}
#	Line 666 | Line 701 | public abstract class ForkJoinTask<V> im
701		}
702
703		/**
704	<	* Returns {@code true} if the computation performed by this task
705	<	* has completed (or has been cancelled).
706	<	*
707	<	* @return {@code true} if this computation has completed
708	<	*/
709	<	public final boolean isDone() {
710	<	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.
704	>	* Attempts to cancel execution of this task. This attempt will
705	>	* fail if the task has already completed, has already been
706	>	* cancelled, or could not be cancelled for some other reason. If
707	>	* successful, and this task has not started when cancel is
708	>	* called, execution of this task is suppressed, {@link
709	>	* #isCancelled} will report true, and {@link #join} will result
710	>	* in a {@code CancellationException} being thrown.
711		*
712		* <p>This method may be overridden in subclasses, but if so, must
713		* still ensure that these minimal properties hold. In particular,
714	<	* the cancel method itself must not throw exceptions.
714	>	* the {@code cancel} method itself must not throw exceptions.
715		*
716		* <p>This method is designed to be invoked by <em>other</em>
717		* tasks. To terminate the current task, you can just return or
#	Line 706 | Line 719 | public abstract class ForkJoinTask<V> im
719		* invoke {@link #completeExceptionally}.
720		*
721		* @param mayInterruptIfRunning this value is ignored in the
722	<	* default implementation because tasks are not in general
722	>	* default implementation because tasks are not
723		* cancelled via interruption
724		*
725		* @return {@code true} if this task is now cancelled
#	Line 716 | Line 729 | public abstract class ForkJoinTask<V> im
729		return (status & COMPLETION_MASK) == CANCELLED;
730		}
731
732	+	public final boolean isDone() {
733	+	return status < 0;
734	+	}
735	+
736	+	public final boolean isCancelled() {
737	+	return (status & COMPLETION_MASK) == CANCELLED;
738	+	}
739	+
740		/**
741		* Returns {@code true} if this task threw an exception or was cancelled.
742		*
#	Line 726 | Line 747 | public abstract class ForkJoinTask<V> im
747		}
748
749		/**
750	+	* Returns {@code true} if this task completed without throwing an
751	+	* exception and was not cancelled.
752	+	*
753	+	* @return {@code true} if this task completed without throwing an
754	+	* exception and was not cancelled
755	+	*/
756	+	public final boolean isCompletedNormally() {
757	+	return (status & COMPLETION_MASK) == NORMAL;
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		*/
767		public final Throwable getException() {
768		int s = status & COMPLETION_MASK;
769	<	if (s >= NORMAL)
770	<	return null;
771	<	if (s == CANCELLED)
740	<	return new CancellationException();
741	<	return exceptionMap.get(this);
769	>	return ((s >= NORMAL)    ? null :
770	>	(s == CANCELLED) ? new CancellationException() :
771	>	exceptionMap.get(this));
772		}
773
774		/**
#	Line 751 | Line 781 | public abstract class ForkJoinTask<V> im
781		* overridable, but overridden versions must invoke {@code super}
782		* implementation to maintain guarantees.
783		*
784	<	* @param ex the exception to throw. If this exception is
785	<	* not a RuntimeException or Error, the actual exception thrown
786	<	* will be a RuntimeException with cause ex.
784	>	* @param ex the exception to throw. If this exception is not a
785	>	* {@code RuntimeException} or {@code Error}, the actual exception
786	>	* thrown will be a {@code RuntimeException} with cause {@code ex}.
787		*/
788		public void completeExceptionally(Throwable ex) {
789		setDoneExceptionally((ex instanceof RuntimeException) ||
#	Line 800 | Line 830 | public abstract class ForkJoinTask<V> im
830		}
831
832		/**
833	<	* Possibly executes other tasks until this task is ready, then
834	<	* returns the result of the computation.  This method may be more
835	<	* efficient than {@code join}, but is only applicable when
836	<	* there are no potential dependencies between continuation of the
837	<	* current task and that of any other task that might be executed
838	<	* while helping. (This usually holds for pure divide-and-conquer
839	<	* tasks). This method may be invoked only from within
840	<	* ForkJoinTask computations (as may be determined using method
841	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
842	<	* result in exceptions or errors, possibly including
843	<	* ClassCastException.
833	>	* Possibly executes other tasks until this task {@link #isDone is
834	>	* done}, then returns the result of the computation.  This method
835	>	* may be more efficient than {@code join}, but is only applicable
836	>	* when there are no potential dependencies between continuation
837	>	* of the current task and that of any other task that might be
838	>	* executed while helping. (This usually holds for pure
839	>	* divide-and-conquer tasks).
840	>	*
841	>	* <p>This method may be invoked only from within {@code
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 {@code
845	>	* ClassCastException}.
846		*
847		* @return the computed result
848		*/
#	Line 822 | Line 854 | public abstract class ForkJoinTask<V> im
854		}
855
856		/**
857	<	* Possibly executes other tasks until this task is ready.  This
858	<	* method may be invoked only from within ForkJoinTask
859	<	* computations (as may be determined using method {@link
860	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
861	<	* in exceptions or errors, possibly including ClassCastException.
857	>	* Possibly executes other tasks until this task {@link #isDone is
858	>	* done}.  This method may be useful when processing collections
859	>	* of tasks when some have been cancelled or otherwise known to
860	>	* have aborted.
861	>	*
862	>	* <p>This method may be invoked only from within {@code
863	>	* ForkJoinTask} computations (as may be determined using method
864	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
865	>	* result in exceptions or errors, possibly including {@code
866	>	* ClassCastException}.
867		*/
868		public final void quietlyHelpJoin() {
869		if (status >= 0) {
#	Line 865 | Line 902 | public abstract class ForkJoinTask<V> im
902
903		/**
904		* Possibly executes tasks until the pool hosting the current task
905	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
906	<	* designs in which many tasks are forked, but none are explicitly
907	<	* joined, instead executing them until all are processed.  This
908	<	* method may be invoked only from within ForkJoinTask
909	<	* computations (as may be determined using method {@link
910	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
911	<	* in exceptions or errors, possibly including ClassCastException.
905	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
906	>	* be of use in designs in which many tasks are forked, but none
907	>	* are explicitly joined, instead executing them until all are
908	>	* processed.
909	>	*
910	>	* <p>This method may be invoked only from within {@code
911	>	* ForkJoinTask} computations (as may be determined using method
912	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
913	>	* result in exceptions or errors, possibly including {@code
914	>	* ClassCastException}.
915		*/
916		public static void helpQuiesce() {
917		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 884 | Line 924 | public abstract class ForkJoinTask<V> im
924		* this task, but only if reuse occurs when this task has either
925		* never been forked, or has been forked, then completed and all
926		* outstanding joins of this task have also completed. Effects
927	<	* under any other usage conditions are not guaranteed, and are
928	<	* discouraged. This method may be useful when executing
927	>	* under any other usage conditions are not guaranteed.
928	>	* This method may be useful when executing
929		* pre-constructed trees of subtasks in loops.
930		*/
931		public void reinitialize() {
#	Line 924 | Line 964 | public abstract class ForkJoinTask<V> im
964		* by the current thread, and has not commenced executing in
965		* another thread.  This method may be useful when arranging
966		* alternative local processing of tasks that could have been, but
967	<	* were not, stolen. This method may be invoked only from within
968	<	* ForkJoinTask computations (as may be determined using method
969	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
970	<	* result in exceptions or errors, possibly including
971	<	* ClassCastException.
967	>	* were not, stolen.
968	>	*
969	>	* <p>This method may be invoked only from within {@code
970	>	* ForkJoinTask} computations (as may be determined using method
971	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
972	>	* result in exceptions or errors, possibly including {@code
973	>	* ClassCastException}.
974		*
975		* @return {@code true} if unforked
976		*/
#	Line 941 | Line 983 | public abstract class ForkJoinTask<V> im
983		* Returns an estimate of the number of tasks that have been
984		* forked by the current worker thread but not yet executed. This
985		* value may be useful for heuristic decisions about whether to
986	<	* fork other tasks.  This method may be invoked only from within
987	<	* ForkJoinTask computations (as may be determined using method
988	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
989	<	* result in exceptions or errors, possibly including
990	<	* ClassCastException.
986	>	* fork other tasks.
987	>	*
988	>	* <p>This method may be invoked only from within {@code
989	>	* ForkJoinTask} computations (as may be determined using method
990	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
991	>	* result in exceptions or errors, possibly including {@code
992	>	* ClassCastException}.
993	>	*
994		* @return the number of tasks
995		*/
996		public static int getQueuedTaskCount() {
#	Line 961 | Line 1006 | public abstract class ForkJoinTask<V> im
1006		* usages of ForkJoinTasks, at steady state, each worker should
1007		* aim to maintain a small constant surplus (for example, 3) of
1008		* tasks, and to process computations locally if this threshold is
1009	<	* exceeded.  This method may be invoked only from within
1010	<	* ForkJoinTask computations (as may be determined using method
1011	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1012	<	* result in exceptions or errors, possibly including
1013	<	* ClassCastException.  *
1009	>	* exceeded.
1010	>	*
1011	>	* <p>This method may be invoked only from within {@code
1012	>	* ForkJoinTask} computations (as may be determined using method
1013	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1014	>	* result in exceptions or errors, possibly including {@code
1015	>	* ClassCastException}.
1016	>	*
1017		* @return the surplus number of tasks, which may be negative
1018		*/
1019		public static int getSurplusQueuedTaskCount() {
#	Line 1001 | Line 1049 | public abstract class ForkJoinTask<V> im
1049		* called otherwise. The return value controls whether this task
1050		* is considered to be done normally. It may return false in
1051		* asynchronous actions that require explicit invocations of
1052	<	* {@link #complete} to become joinable. It may throw exceptions
1053	<	* to indicate abnormal exit.
1052	>	* {@link #complete} to become joinable. It may also throw an
1053	>	* (unchecked) exception to indicate abnormal exit.
1054		*
1055		* @return {@code true} if completed normally
1008	–	* @throws Error or RuntimeException if encountered during computation
1056		*/
1057		protected abstract boolean exec();
1058
#	Line 1017 | Line 1064 | public abstract class ForkJoinTask<V> im
1064		* null even if a task exists but cannot be accessed without
1065		* contention with other threads.  This method is designed
1066		* primarily to support extensions, and is unlikely to be useful
1067	<	* otherwise.  This method may be invoked only from within
1068	<	* ForkJoinTask computations (as may be determined using method
1069	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1070	<	* result in exceptions or errors, possibly including
1071	<	* ClassCastException.
1067	>	* otherwise.
1068	>	*
1069	>	* <p>This method may be invoked only from within {@code
1070	>	* ForkJoinTask} computations (as may be determined using method
1071	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1072	>	* result in exceptions or errors, possibly including {@code
1073	>	* ClassCastException}.
1074		*
1075		* @return the next task, or {@code null} if none are available
1076		*/
#	Line 1034 | Line 1083 | public abstract class ForkJoinTask<V> im
1083		* Unschedules and returns, without executing, the next task
1084		* queued by the current thread but not yet executed.  This method
1085		* is designed primarily to support extensions, and is unlikely to
1086	<	* be useful otherwise.  This method may be invoked only from
1087	<	* within ForkJoinTask computations (as may be determined using
1088	<	* method {@link #inForkJoinPool}). Attempts to invoke in other
1089	<	* contexts result in exceptions or errors, possibly including
1090	<	* ClassCastException.
1086	>	* be useful otherwise.
1087	>	*
1088	>	* <p>This method may be invoked only from within {@code
1089	>	* ForkJoinTask} computations (as may be determined using method
1090	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1091	>	* result in exceptions or errors, possibly including {@code
1092	>	* ClassCastException}.
1093		*
1094		* @return the next task, or {@code null} if none are available
1095		*/
#	Line 1055 | Line 1106 | public abstract class ForkJoinTask<V> im
1106		* {@code null} result does not necessarily imply quiescence
1107		* of the pool this task is operating in.  This method is designed
1108		* primarily to support extensions, and is unlikely to be useful
1109	<	* otherwise.  This method may be invoked only from within
1110	<	* ForkJoinTask computations (as may be determined using method
1111	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1112	<	* result in exceptions or errors, possibly including
1113	<	* ClassCastException.
1109	>	* otherwise.
1110	>	*
1111	>	* <p>This method may be invoked only from within {@code
1112	>	* ForkJoinTask} computations (as may be determined using method
1113	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1114	>	* result in exceptions or errors, possibly including {@code
1115	>	* ClassCastException}.
1116		*
1117		* @return a task, or {@code null} if none are available
1118		*/
#	Line 1124 | Line 1177 | public abstract class ForkJoinTask<V> im
1177		}
1178
1179		/**
1180	<	* Returns a new ForkJoinTask that performs the {@code run}
1181	<	* method of the given Runnable as its action, and returns a null
1182	<	* result upon {@code join}.
1180	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1181	>	* method of the given {@code Runnable} as its action, and returns
1182	>	* a null result upon {@link #join}.
1183		*
1184		* @param runnable the runnable action
1185		* @return the task
#	Line 1136 | Line 1189 | public abstract class ForkJoinTask<V> im
1189		}
1190
1191		/**
1192	<	* Returns a new ForkJoinTask that performs the {@code run}
1193	<	* method of the given Runnable as its action, and returns the
1194	<	* given result upon {@code join}.
1192	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1193	>	* method of the given {@code Runnable} as its action, and returns
1194	>	* the given result upon {@link #join}.
1195		*
1196		* @param runnable the runnable action
1197		* @param result the result upon completion
#	Line 1149 | Line 1202 | public abstract class ForkJoinTask<V> im
1202		}
1203
1204		/**
1205	<	* Returns a new ForkJoinTask that performs the {@code call}
1206	<	* method of the given Callable as its action, and returns its
1207	<	* result upon {@code join}, translating any checked
1208	<	* exceptions encountered into {@code RuntimeException}.
1205	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1206	>	* method of the given {@code Callable} as its action, and returns
1207	>	* its result upon {@link #join}, translating any checked exceptions
1208	>	* encountered into {@code RuntimeException}.
1209		*
1210		* @param callable the callable action
1211		* @return the task

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