ViewVC Help

View File | Revision Log | Show Annotations | Download File | Root Listing

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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.27 by dl, Sun Aug 2 11:54:31 2009 UTC vs.
Revision 1.41 by dl, Wed Aug 5 23:37:32 2009 UTC

#	Line 12 | Line 12 | import java.io.Serializable;
12		import java.util.Collection;
13		import java.util.Collections;
14		import java.util.List;
15	+	import java.util.RandomAccess;
16		import java.util.Map;
17		import java.util.WeakHashMap;
18
#	Line 22 | Line 23 | import java.util.WeakHashMap;
23		* subtasks may be hosted by a small number of actual threads in a
24		* ForkJoinPool, at the price of some usage limitations.
25		*
26	<	* <p> A "main" ForkJoinTask begins execution when submitted to a
27	<	* {@link ForkJoinPool}. Once started, it will usually in turn start
28	<	* other subtasks.  As indicated by the name of this class, many
29	<	* programs using ForkJoinTasks employ only methods {@code fork} and
30	<	* {@code join}, or derivatives such as {@code invokeAll}.  However,
31	<	* this class also provides a number of other methods that can come
32	<	* into play in advanced usages, as well as extension mechanics that
33	<	* allow support of new forms of fork/join processing.
26	>	* <p>A "main" {@code ForkJoinTask} begins execution when submitted
27	>	* to a {@link ForkJoinPool}.  Once started, it will usually in turn
28	>	* start other subtasks.  As indicated by the name of this class,
29	>	* many programs using {@code ForkJoinTask} employ only methods
30	>	* {@link #fork} and {@link #join}, or derivatives such as {@link
31	>	* #invokeAll}.  However, this class also provides a number of other
32	>	* methods that can come into play in advanced usages, as well as
33	>	* extension mechanics that allow support of new forms of fork/join
34	>	* processing.
35		*
36	<	* <p>A ForkJoinTask is a lightweight form of {@link Future}.  The
37	<	* efficiency of ForkJoinTasks stems from a set of restrictions (that
38	<	* are only partially statically enforceable) reflecting their
39	<	* intended use as computational tasks calculating pure functions or
40	<	* operating on purely isolated objects.  The primary coordination
41	<	* mechanisms are {@link #fork}, that arranges asynchronous execution,
42	<	* and {@link #join}, that doesn't proceed until the task's result has
43	<	* been computed.  Computations should avoid {@code synchronized}
44	<	* methods or blocks, and should minimize other blocking
45	<	* synchronization apart from joining other tasks or using
46	<	* synchronizers such as Phasers that are advertised to cooperate with
47	<	* fork/join scheduling. Tasks should also not perform blocking IO,
48	<	* and should ideally access variables that are completely independent
49	<	* of those accessed by other running tasks. Minor breaches of these
50	<	* restrictions, for example using shared output streams, may be
51	<	* tolerable in practice, but frequent use may result in poor
52	<	* performance, and the potential to indefinitely stall if the number
53	<	* of threads not waiting for IO or other external synchronization
54	<	* becomes exhausted. This usage restriction is in part enforced by
55	<	* not permitting checked exceptions such as {@code IOExceptions}
56	<	* to be thrown. However, computations may still encounter unchecked
57	<	* exceptions, that are rethrown to callers attempting join
58	<	* them. These exceptions may additionally include
59	<	* RejectedExecutionExceptions stemming from internal resource
60	<	* exhaustion such as failure to allocate internal task queues.
36	>	* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
37	>	* The efficiency of {@code ForkJoinTask}s stems from a set of
38	>	* restrictions (that are only partially statically enforceable)
39	>	* reflecting their intended use as computational tasks calculating
40	>	* pure functions or operating on purely isolated objects.  The
41	>	* primary coordination mechanisms are {@link #fork}, that arranges
42	>	* asynchronous execution, and {@link #join}, that doesn't proceed
43	>	* until the task's result has been computed.  Computations should
44	>	* avoid {@code synchronized} methods or blocks, and should minimize
45	>	* other blocking synchronization apart from joining other tasks or
46	>	* using synchronizers such as Phasers that are advertised to
47	>	* cooperate with fork/join scheduling. Tasks should also not perform
48	>	* blocking IO, and should ideally access variables that are
49	>	* completely independent of those accessed by other running
50	>	* tasks. Minor breaches of these restrictions, for example using
51	>	* shared output streams, may be tolerable in practice, but frequent
52	>	* use may result in poor performance, and the potential to
53	>	* indefinitely stall if the number of threads not waiting for IO or
54	>	* other external synchronization becomes exhausted. This usage
55	>	* restriction is in part enforced by not permitting checked
56	>	* exceptions such as {@code IOExceptions} to be thrown. However,
57	>	* computations may still encounter unchecked exceptions, that are
58	>	* rethrown to callers attempting to join them. These exceptions may
59	>	* additionally include RejectedExecutionExceptions stemming from
60	>	* internal resource exhaustion such as failure to allocate internal
61	>	* task queues.
62		*
63		* <p>The primary method for awaiting completion and extracting
64		* results of a task is {@link #join}, but there are several variants:
#	Line 65 | Line 68 | import java.util.WeakHashMap;
68		* execute other tasks while awaiting joins, which is sometimes more
69		* efficient but only applies when all subtasks are known to be
70		* strictly tree-structured. Method {@link #invoke} is semantically
71	<	* equivalent to {@code fork(); join()} but always attempts to
72	<	* begin execution in the current thread. The "<em>quiet</em>" forms
73	<	* of these methods do not extract results or report exceptions. These
71	>	* equivalent to {@code fork(); join()} but always attempts to begin
72	>	* execution in the current thread. The "<em>quiet</em>" forms of
73	>	* these methods do not extract results or report exceptions. These
74		* may be useful when a set of tasks are being executed, and you need
75		* to delay processing of results or exceptions until all complete.
76		* Method {@code invokeAll} (available in multiple versions)
77		* performs the most common form of parallel invocation: forking a set
78		* of tasks and joining them all.
79		*
80	<	* <p> The ForkJoinTask class is not usually directly subclassed.
80	>	* <p>The execution status of tasks may be queried at several levels
81	>	* of detail: {@link #isDone} is true if a task completed in any way
82	>	* (including the case where a task was cancelled without executing);
83	>	* {@link #isCancelled} is true if completion was due to cancellation;
84	>	* {@link #isCompletedNormally} is true if a task completed without
85	>	* cancellation or encountering an exception; {@link
86	>	* #isCompletedExceptionally} is true if if the task encountered an
87	>	* exception (in which case {@link #getException} returns the
88	>	* exception); {@link #isCancelled} is true if the task was cancelled
89	>	* (in which case {@link #getException} returns a {@link
90	>	* java.util.concurrent.CancellationException}); and {@link
91	>	* #isCompletedAbnormally} is true if a task was either cancelled or
92	>	* encountered an exception.
93	>	*
94	>	* <p>The ForkJoinTask class is not usually directly subclassed.
95		* Instead, you subclass one of the abstract classes that support a
96		* particular style of fork/join processing, typically {@link
97		* RecursiveAction} for computations that do not return results, or
#	Line 83 | Line 100 | import java.util.WeakHashMap;
100		* established in a constructor, and then defines a {@code compute}
101		* method that somehow uses the control methods supplied by this base
102		* class. While these methods have {@code public} access (to allow
103	<	* instances of different task subclasses to call each others
103	>	* instances of different task subclasses to call each other's
104		* methods), some of them may only be called from within other
105		* ForkJoinTasks (as may be determined using method {@link
106		* #inForkJoinPool}).  Attempts to invoke them in other contexts
107		* result in exceptions or errors, possibly including
108		* ClassCastException.
109		*
110	<	* <p>Most base support methods are {@code final} because their
111	<	* implementations are intrinsically tied to the underlying
112	<	* lightweight task scheduling framework, and so cannot be overridden.
113	<	* Developers creating new basic styles of fork/join processing should
114	<	* minimally implement {@code protected} methods
115	<	* {@link #exec}, {@link #setRawResult}, and
116	<	* {@link #getRawResult}, while also introducing an abstract
117	<	* computational method that can be implemented in its subclasses,
118	<	* possibly relying on other {@code protected} methods provided
102	<	* by this class.
110	>	* <p>Most base support methods are {@code final}, to prevent
111	>	* overriding of implementations that are intrinsically tied to the
112	>	* underlying lightweight task scheduling framework.  Developers
113	>	* creating new basic styles of fork/join processing should minimally
114	>	* implement {@code protected} methods {@link #exec}, {@link
115	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
116	>	* an abstract computational method that can be implemented in its
117	>	* subclasses, possibly relying on other {@code protected} methods
118	>	* provided by this class.
119		*
120		* <p>ForkJoinTasks should perform relatively small amounts of
121	<	* computations, otherwise splitting into smaller tasks. As a very
122	<	* rough rule of thumb, a task should perform more than 100 and less
123	<	* than 10000 basic computational steps. If tasks are too big, then
124	<	* parallelism cannot improve throughput. If too small, then memory
125	<	* and internal task maintenance overhead may overwhelm processing.
121	>	* computation. Large tasks should be split into smaller subtasks,
122	>	* usually via recursive decomposition. As a very rough rule of thumb,
123	>	* a task should perform more than 100 and less than 10000 basic
124	>	* computational steps. If tasks are too big, then parallelism cannot
125	>	* improve throughput. If too small, then memory and internal task
126	>	* maintenance overhead may overwhelm processing.
127		*
128	<	* <p>This class provides {@code adapt} methods for {@link
129	<	* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
130	<	* may be of use when mixing execution of ForkJoinTasks with other
131	<	* kinds of tasks. When all tasks are of this form, consider using a
132	<	* pool in {@link ForkJoinPool#setAsyncMode}.
128	>	* <p>This class provides {@code adapt} methods for {@link Runnable}
129	>	* and {@link Callable}, that may be of use when mixing execution of
130	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks
131	>	* are of this form, consider using a pool in
132	>	* {@linkplain ForkJoinPool#setAsyncMode async mode}.
133		*
134	<	* <p>ForkJoinTasks are {@code Serializable}, which enables them
135	<	* to be used in extensions such as remote execution frameworks. It is
136	<	* in general sensible to serialize tasks only before or after, but
137	<	* not during execution. Serialization is not relied on during
121	<	* execution itself.
134	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
135	>	* used in extensions such as remote execution frameworks. It is
136	>	* sensible to serialize tasks only before or after, but not during,
137	>	* execution. Serialization is not relied on during execution itself.
138		*
139		* @since 1.7
140		* @author Doug Lea
#	Line 376 | 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 387 | 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);
390	–	if (Thread.interrupted())
391	–	throw new InterruptedException();
409		}
410		return getRawResult();
411		}
#	Line 399 | 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();
412	<	throw new TimeoutException();
429	>	else
430	>	throw new TimeoutException();
431		}
432
433		// internal execution methods
#	Line 494 | 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 509 | Line 529 | public abstract class ForkJoinTask<V> im
529		}
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.
532	>	* Returns the result of the computation when it {@link #isDone is done}.
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 525 | 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		*
530	–	* @throws Throwable (a RuntimeException, Error, or unchecked
531	–	* exception) if the underlying computation did so
551		* @return the computed result
552		*/
553		public final V invoke() {
#	Line 540 | 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
552	–	* @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 559 | 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
575	<	* @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 608 | 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
623	–	* @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 664 | 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;
674	<	}
675	<
676	<	/**
677	<	* Returns {@code true} if this task was cancelled.
678	<	*
679	<	* @return {@code true} if this task was cancelled
680	<	*/
681	<	public final boolean isCancelled() {
682	<	return (status & COMPLETION_MASK) == CANCELLED;
683	<	}
684	<
685	<	/**
686	<	* Asserts that the results of this task's computation will not be
687	<	* used. If a cancellation occurs before attempting to execute this
688	<	* task, execution will be suppressed, {@link #isCancelled}
689	<	* will report true, and {@link #join} will result in a
690	<	* {@code CancellationException} being thrown. Otherwise, when
691	<	* cancellation races with completion, there are no guarantees
692	<	* about whether {@code isCancelled} will report {@code true},
693	<	* whether {@code join} will return normally or via an exception,
694	<	* or whether these behaviors will remain consistent upon repeated
695	<	* invocation.
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,
711	<	* the cancel method itself must not throw exceptions.
711	>	* the {@code cancel} method itself must not throw exceptions.
712		*
713	<	* <p> This method is designed to be invoked by <em>other</em>
713	>	* <p>This method is designed to be invoked by <em>other</em>
714		* tasks. To terminate the current task, you can just return or
715		* throw an unchecked exception from its computation method, or
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 714 | Line 726 | public abstract class ForkJoinTask<V> im
726		return (status & COMPLETION_MASK) == CANCELLED;
727		}
728
729	+	public final boolean isDone() {
730	+	return status < 0;
731	+	}
732	+
733	+	public final boolean isCancelled() {
734	+	return (status & COMPLETION_MASK) == CANCELLED;
735	+	}
736	+
737		/**
738		* Returns {@code true} if this task threw an exception or was cancelled.
739		*
#	Line 724 | Line 744 | public abstract class ForkJoinTask<V> im
744		}
745
746		/**
747	+	* Returns {@code true} if this task completed without throwing an
748	+	* exception and was not cancelled.
749	+	*
750	+	* @return {@code true} if this task completed without throwing an
751	+	* exception and was not cancelled
752	+	*/
753	+	public final boolean isCompletedNormally() {
754	+	return (status & COMPLETION_MASK) == NORMAL;
755	+	}
756	+
757	+	/**
758	+	* Returns {@code true} if this task threw an exception.
759	+	*
760	+	* @return {@code true} if this task threw an exception
761	+	*/
762	+	public final boolean isCompletedExceptionally() {
763	+	return (status & COMPLETION_MASK) == EXCEPTIONAL;
764	+	}
765	+
766	+	/**
767		* Returns the exception thrown by the base computation, or a
768	<	* CancellationException if cancelled, or null if none or if the
769	<	* method has not yet completed.
768	>	* {@code CancellationException} if cancelled, or {@code null} if
769	>	* none or if the method has not yet completed.
770		*
771		* @return the exception, or {@code null} if none
772		*/
773		public final Throwable getException() {
774		int s = status & COMPLETION_MASK;
775	<	if (s >= NORMAL)
776	<	return null;
777	<	if (s == CANCELLED)
738	<	return new CancellationException();
739	<	return exceptionMap.get(this);
775	>	return ((s >= NORMAL)    ? null :
776	>	(s == CANCELLED) ? new CancellationException() :
777	>	exceptionMap.get(this));
778		}
779
780		/**
#	Line 798 | Line 836 | public abstract class ForkJoinTask<V> im
836		}
837
838		/**
839	<	* Possibly executes other tasks until this task is ready, then
840	<	* returns the result of the computation.  This method may be more
841	<	* efficient than {@code join}, but is only applicable when
842	<	* there are no potential dependencies between continuation of the
843	<	* current task and that of any other task that might be executed
844	<	* while helping. (This usually holds for pure divide-and-conquer
845	<	* tasks). This method may be invoked only from within
846	<	* ForkJoinTask computations (as may be determined using method
847	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
848	<	* result in exceptions or errors, possibly including
849	<	* ClassCastException.
839	>	* Possibly executes other tasks until this task {@link #isDone is
840	>	* done}, then returns the result of the computation.  This method
841	>	* may be more efficient than {@code join}, but is only applicable
842	>	* when there are no potential dependencies between continuation
843	>	* of the current task and that of any other task that might be
844	>	* executed while helping. (This usually holds for pure
845	>	* divide-and-conquer tasks).
846	>	*
847	>	* <p>This method may be invoked only from within {@code
848	>	* ForkJoinTask} computations (as may be determined using method
849	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
850	>	* result in exceptions or errors, possibly including {@code
851	>	* ClassCastException}.
852		*
853		* @return the computed result
854		*/
#	Line 820 | Line 860 | public abstract class ForkJoinTask<V> im
860		}
861
862		/**
863	<	* Possibly executes other tasks until this task is ready.  This
864	<	* method may be invoked only from within ForkJoinTask
865	<	* computations (as may be determined using method {@link
866	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
867	<	* in exceptions or errors, possibly including ClassCastException.
863	>	* Possibly executes other tasks until this task {@link #isDone is
864	>	* done}.  This method may be useful when processing collections
865	>	* of tasks when some have been cancelled or otherwise known to
866	>	* have aborted.
867	>	*
868	>	* <p>This method may be invoked only from within {@code
869	>	* ForkJoinTask} computations (as may be determined using method
870	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
871	>	* result in exceptions or errors, possibly including {@code
872	>	* ClassCastException}.
873		*/
874		public final void quietlyHelpJoin() {
875		if (status >= 0) {
#	Line 863 | Line 908 | public abstract class ForkJoinTask<V> im
908
909		/**
910		* Possibly executes tasks until the pool hosting the current task
911	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
912	<	* designs in which many tasks are forked, but none are explicitly
913	<	* joined, instead executing them until all are processed.  This
914	<	* method may be invoked only from within ForkJoinTask
915	<	* computations (as may be determined using method {@link
916	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
917	<	* in exceptions or errors, possibly including ClassCastException.
911	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
912	>	* be of use in designs in which many tasks are forked, but none
913	>	* are explicitly joined, instead executing them until all are
914	>	* processed.
915	>	*
916	>	* <p>This method may be invoked only from within {@code
917	>	* ForkJoinTask} computations (as may be determined using method
918	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
919	>	* result in exceptions or errors, possibly including {@code
920	>	* ClassCastException}.
921		*/
922		public static void helpQuiesce() {
923		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 882 | Line 930 | public abstract class ForkJoinTask<V> im
930		* this task, but only if reuse occurs when this task has either
931		* never been forked, or has been forked, then completed and all
932		* outstanding joins of this task have also completed. Effects
933	<	* under any other usage conditions are not guaranteed, and are
934	<	* discouraged. This method may be useful when executing
933	>	* under any other usage conditions are not guaranteed.
934	>	* This method may be useful when executing
935		* pre-constructed trees of subtasks in loops.
936		*/
937		public void reinitialize() {
#	Line 922 | Line 970 | public abstract class ForkJoinTask<V> im
970		* by the current thread, and has not commenced executing in
971		* another thread.  This method may be useful when arranging
972		* alternative local processing of tasks that could have been, but
973	<	* were not, stolen. This method may be invoked only from within
974	<	* ForkJoinTask computations (as may be determined using method
975	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
976	<	* result in exceptions or errors, possibly including
977	<	* ClassCastException.
973	>	* were not, stolen.
974	>	*
975	>	* <p>This method may be invoked only from within {@code
976	>	* ForkJoinTask} computations (as may be determined using method
977	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
978	>	* result in exceptions or errors, possibly including {@code
979	>	* ClassCastException}.
980		*
981		* @return {@code true} if unforked
982		*/
#	Line 939 | Line 989 | public abstract class ForkJoinTask<V> im
989		* Returns an estimate of the number of tasks that have been
990		* forked by the current worker thread but not yet executed. This
991		* value may be useful for heuristic decisions about whether to
992	<	* fork other tasks.  This method may be invoked only from within
993	<	* ForkJoinTask computations (as may be determined using method
994	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
995	<	* result in exceptions or errors, possibly including
996	<	* ClassCastException.
992	>	* fork other tasks.
993	>	*
994	>	* <p>This method may be invoked only from within {@code
995	>	* ForkJoinTask} computations (as may be determined using method
996	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
997	>	* result in exceptions or errors, possibly including {@code
998	>	* ClassCastException}.
999	>	*
1000		* @return the number of tasks
1001		*/
1002		public static int getQueuedTaskCount() {
#	Line 959 | Line 1012 | public abstract class ForkJoinTask<V> im
1012		* usages of ForkJoinTasks, at steady state, each worker should
1013		* aim to maintain a small constant surplus (for example, 3) of
1014		* tasks, and to process computations locally if this threshold is
1015	<	* exceeded.  This method may be invoked only from within
1016	<	* ForkJoinTask computations (as may be determined using method
1017	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1018	<	* result in exceptions or errors, possibly including
1019	<	* ClassCastException.  *
1015	>	* exceeded.
1016	>	*
1017	>	* <p>This method may be invoked only from within {@code
1018	>	* ForkJoinTask} computations (as may be determined using method
1019	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1020	>	* result in exceptions or errors, possibly including {@code
1021	>	* ClassCastException}.
1022	>	*
1023		* @return the surplus number of tasks, which may be negative
1024		*/
1025		public static int getSurplusQueuedTaskCount() {
#	Line 999 | Line 1055 | public abstract class ForkJoinTask<V> im
1055		* called otherwise. The return value controls whether this task
1056		* is considered to be done normally. It may return false in
1057		* asynchronous actions that require explicit invocations of
1058	<	* {@link #complete} to become joinable. It may throw exceptions
1059	<	* to indicate abnormal exit.
1058	>	* {@link #complete} to become joinable. It may also throw an
1059	>	* (unchecked) exception to indicate abnormal exit.
1060		*
1061		* @return {@code true} if completed normally
1006	–	* @throws Error or RuntimeException if encountered during computation
1062		*/
1063		protected abstract boolean exec();
1064
#	Line 1015 | Line 1070 | public abstract class ForkJoinTask<V> im
1070		* null even if a task exists but cannot be accessed without
1071		* contention with other threads.  This method is designed
1072		* primarily to support extensions, and is unlikely to be useful
1073	<	* otherwise.  This method may be invoked only from within
1074	<	* ForkJoinTask computations (as may be determined using method
1075	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1076	<	* result in exceptions or errors, possibly including
1077	<	* ClassCastException.
1073	>	* otherwise.
1074	>	*
1075	>	* <p>This method may be invoked only from within {@code
1076	>	* ForkJoinTask} computations (as may be determined using method
1077	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1078	>	* result in exceptions or errors, possibly including {@code
1079	>	* ClassCastException}.
1080		*
1081		* @return the next task, or {@code null} if none are available
1082		*/
#	Line 1032 | Line 1089 | public abstract class ForkJoinTask<V> im
1089		* Unschedules and returns, without executing, the next task
1090		* queued by the current thread but not yet executed.  This method
1091		* is designed primarily to support extensions, and is unlikely to
1092	<	* be useful otherwise.  This method may be invoked only from
1093	<	* within ForkJoinTask computations (as may be determined using
1094	<	* method {@link #inForkJoinPool}). Attempts to invoke in other
1095	<	* contexts result in exceptions or errors, possibly including
1096	<	* ClassCastException.
1092	>	* be useful otherwise.
1093	>	*
1094	>	* <p>This method may be invoked only from within {@code
1095	>	* ForkJoinTask} computations (as may be determined using method
1096	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1097	>	* result in exceptions or errors, possibly including {@code
1098	>	* ClassCastException}.
1099		*
1100		* @return the next task, or {@code null} if none are available
1101		*/
#	Line 1053 | Line 1112 | public abstract class ForkJoinTask<V> im
1112		* {@code null} result does not necessarily imply quiescence
1113		* of the pool this task is operating in.  This method is designed
1114		* primarily to support extensions, and is unlikely to be useful
1115	<	* otherwise.  This method may be invoked only from within
1116	<	* ForkJoinTask computations (as may be determined using method
1117	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1118	<	* result in exceptions or errors, possibly including
1119	<	* ClassCastException.
1115	>	* otherwise.
1116	>	*
1117	>	* <p>This method may be invoked only from within {@code
1118	>	* ForkJoinTask} computations (as may be determined using method
1119	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1120	>	* result in exceptions or errors, possibly including {@code
1121	>	* ClassCastException}.
1122		*
1123		* @return a task, or {@code null} if none are available
1124		*/
#	Line 1122 | Line 1183 | public abstract class ForkJoinTask<V> im
1183		}
1184
1185		/**
1186	<	* Returns a new ForkJoinTask that performs the {@code run}
1187	<	* method of the given Runnable as its action, and returns a null
1188	<	* result upon {@code join}.
1186	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1187	>	* method of the given {@code Runnable} as its action, and returns
1188	>	* a null result upon {@link #join}.
1189		*
1190		* @param runnable the runnable action
1191		* @return the task
#	Line 1134 | Line 1195 | public abstract class ForkJoinTask<V> im
1195		}
1196
1197		/**
1198	<	* Returns a new ForkJoinTask that performs the {@code run}
1199	<	* method of the given Runnable as its action, and returns the
1200	<	* given result upon {@code join}.
1198	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1199	>	* method of the given {@code Runnable} as its action, and returns
1200	>	* the given result upon {@link #join}.
1201		*
1202		* @param runnable the runnable action
1203		* @param result the result upon completion
#	Line 1147 | Line 1208 | public abstract class ForkJoinTask<V> im
1208		}
1209
1210		/**
1211	<	* Returns a new ForkJoinTask that performs the {@code call}
1212	<	* method of the given Callable as its action, and returns its
1213	<	* result upon {@code join}, translating any checked
1214	<	* exceptions encountered into {@code RuntimeException}.
1211	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1212	>	* method of the given {@code Callable} as its action, and returns
1213	>	* its result upon {@link #join}, translating any checked exceptions
1214	>	* encountered into {@code RuntimeException}.
1215		*
1216		* @param callable the callable action
1217		* @return the task

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines