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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.24 by jsr166, Mon Jul 27 21:41:53 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
19		/**
20	<	* Abstract base class for tasks that run within a {@link
21	<	* ForkJoinPool}.  A ForkJoinTask is a thread-like entity that is much
20	>	* Abstract base class for tasks that run within a {@link ForkJoinPool}.
21	>	* A {@code ForkJoinTask} is a thread-like entity that is much
22		* lighter weight than a normal thread.  Huge numbers of tasks and
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 #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.  Normally, a concrete
94	>	* particular style of fork/join processing, typically {@link
95	>	* RecursiveAction} for computations that do not return results, or
96	>	* {@link RecursiveTask} for those that do.  Normally, a concrete
97		* ForkJoinTask subclass declares fields comprising its parameters,
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
100	<	* 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 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
113	<	* 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 247 | Line 269 | public abstract class ForkJoinTask<V> im
269		synchronized (this) {
270		try {
271		while (status >= 0) {
272	<	long nt = nanos - System.nanoTime() - startTime;
272	>	long nt = nanos - (System.nanoTime() - startTime);
273		if (nt <= 0)
274		break;
275		wait(nt / 1000000, (int) (nt % 1000000));
#	Line 368 | 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 379 | 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);
382	–	if (Thread.interrupted())
383	–	throw new InterruptedException();
407		}
408		return getRawResult();
409		}
#	Line 391 | 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();
404	<	throw new TimeoutException();
427	>	else
428	>	throw new TimeoutException();
429		}
430
431		// internal execution methods
#	Line 486 | 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 501 | 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 517 | 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		*
522	–	* @throws Throwable (a RuntimeException, Error, or unchecked
523	–	* exception) if the underlying computation did so
549		* @return the computed result
550		*/
551		public final V invoke() {
#	Line 531 | Line 556 | public abstract class ForkJoinTask<V> im
556		}
557
558		/**
559	<	* Forks both tasks, returning when {@code isDone} holds for
560	<	* both of them 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.
565	<	*
566	<	* @param t1 one task
567	<	* @param t2 the other task
568	<	* @throws NullPointerException if t1 or t2 are null
569	<	* @throws RuntimeException or Error if either task did so
559	>	* Forks the given tasks, returning when {@code isDone} holds for
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
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();
581		}
582
583		/**
584	<	* Forks the given tasks, returning when {@code isDone} holds
585	<	* for all of them. If any task encounters an exception, others
586	<	* may be cancelled.  This method may be invoked only from within
587	<	* ForkJoinTask computations (as may be determined using method
588	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
589	<	* result in exceptions or errors, possibly including
590	<	* ClassCastException.
584	>	* Forks the given tasks, returning when {@code isDone} holds for
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 array of tasks
600	<	* @throws NullPointerException if tasks or any element are null
563	<	* @throws RuntimeException or Error if any task did so
599	>	* @param tasks the tasks
600	>	* @throws NullPointerException if any task is null
601		*/
602		public static void invokeAll(ForkJoinTask<?>... tasks) {
603		Throwable ex = null;
#	Line 596 | Line 633 | public abstract class ForkJoinTask<V> im
633		}
634
635		/**
636	<	* Forks all tasks in the collection, returning when
637	<	* {@code isDone} holds for all of them. If any task
638	<	* encounters an exception, others may be cancelled.  This method
639	<	* may be invoked only from within ForkJoinTask computations (as
640	<	* may be determined using method {@link
641	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
642	<	* in exceptions or errors, possibly 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
610	–	* @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 651 | 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;
661	<	}
662	<
663	<	/**
664	<	* Returns {@code true} if this task was cancelled.
665	<	*
666	<	* @return {@code true} if this task was cancelled
667	<	*/
668	<	public final boolean isCancelled() {
669	<	return (status & COMPLETION_MASK) == CANCELLED;
670	<	}
671	<
672	<	/**
673	<	* Asserts that the results of this task's computation will not be
674	<	* used. If a cancellation occurs before attempting to execute this
675	<	* task, execution will be suppressed, {@link #isCancelled}
676	<	* will report true, and {@link #join} will result in a
677	<	* {@code CancellationException} being thrown. Otherwise, when
678	<	* cancellation races with completion, there are no guarantees
679	<	* about whether {@code isCancelled} will report {@code true},
680	<	* whether {@code join} will return normally or via an exception,
681	<	* or whether these behaviors will remain consistent upon repeated
682	<	* invocation.
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,
709	<	* the cancel method itself must not throw exceptions.
709	>	* the {@code cancel} method itself must not throw exceptions.
710		*
711	<	* <p> This method is designed to be invoked by <em>other</em>
711	>	* <p>This method is designed to be invoked by <em>other</em>
712		* tasks. To terminate the current task, you can just return or
713		* throw an unchecked exception from its computation method, or
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 701 | 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 711 | 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	<	* CancellationException if cancelled, or null if none or if the
758	<	* method has not yet completed.
757	>	* {@code CancellationException} if cancelled, or {@code null} if
758	>	* none or if the method has not yet completed.
759		*
760		* @return the exception, or {@code null} if none
761		*/
762		public final Throwable getException() {
763		int s = status & COMPLETION_MASK;
764	<	if (s >= NORMAL)
765	<	return null;
766	<	if (s == CANCELLED)
725	<	return new CancellationException();
726	<	return exceptionMap.get(this);
764	>	return ((s >= NORMAL)    ? null :
765	>	(s == CANCELLED) ? new CancellationException() :
766	>	exceptionMap.get(this));
767		}
768
769		/**
#	Line 732 | Line 772 | public abstract class ForkJoinTask<V> im
772		* {@code join} and related operations. This method may be used
773		* to induce exceptions in asynchronous tasks, or to force
774		* completion of tasks that would not otherwise complete.  Its use
775	<	* in other situations is likely to be wrong.  This method is
775	>	* in other situations is discouraged.  This method is
776		* overridable, but overridden versions must invoke {@code super}
777		* implementation to maintain guarantees.
778		*
#	Line 752 | Line 792 | public abstract class ForkJoinTask<V> im
792		* operations. This method may be used to provide results for
793		* asynchronous tasks, or to provide alternative handling for
794		* tasks that would not otherwise complete normally. Its use in
795	<	* other situations is likely to be wrong. This method is
795	>	* other situations is discouraged. This method is
796		* overridable, but overridden versions must invoke {@code super}
797		* implementation to maintain guarantees.
798		*
#	Line 777 | Line 817 | public abstract class ForkJoinTask<V> im
817
818		public final V get(long timeout, TimeUnit unit)
819		throws InterruptedException, ExecutionException, TimeoutException {
820	+	long nanos = unit.toNanos(timeout);
821		ForkJoinWorkerThread w = getWorker();
822		if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
823	<	awaitDone(w, unit.toNanos(timeout));
823	>	awaitDone(w, nanos);
824		return reportTimedFutureResult();
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 806 | 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 849 | 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.
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 864 | Line 919 | public abstract class ForkJoinTask<V> im
919		* this task, but only if reuse occurs when this task has either
920		* never been forked, or has been forked, then completed and all
921		* outstanding joins of this task have also completed. Effects
922	<	* under any other usage conditions are not guaranteed, and are
923	<	* almost surely wrong. This method may be useful when executing
922	>	* under any other usage conditions are not guaranteed.
923	>	* This method may be useful when executing
924		* pre-constructed trees of subtasks in loops.
925		*/
926		public void reinitialize() {
#	Line 878 | Line 933 | public abstract class ForkJoinTask<V> im
933		* Returns the pool hosting the current task execution, or null
934		* if this task is executing outside of any ForkJoinPool.
935		*
936	+	* @see #inForkJoinPool
937		* @return the pool, or {@code null} if none
938		*/
939		public static ForkJoinPool getPool() {
#	Line 903 | 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 922 | Line 980 | public abstract class ForkJoinTask<V> im
980		* value may be useful for heuristic decisions about whether to
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 939 | Line 1003 | public abstract class ForkJoinTask<V> im
1003		* tasks, and to process computations locally if this threshold is
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 974 | 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
981	–	* @throws Error or RuntimeException if encountered during computation
1051		*/
1052		protected abstract boolean exec();
1053
1054		/**
1055	<	* Returns, but does not unschedule or execute, the task queued by
1056	<	* the current thread but not yet executed, if one is
1055	>	* Returns, but does not unschedule or execute, a task queued by
1056	>	* the current thread but not yet executed, if one is immediately
1057		* available. There is no guarantee that this task will actually
1058	<	* be polled or executed next.  This method is designed primarily
1059	<	* to support extensions, and is unlikely to be useful otherwise.
1060	<	* This method may be invoked only from within ForkJoinTask
1061	<	* computations (as may be determined using method {@link
1062	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
1063	<	* in exceptions or errors, possibly including ClassCastException.
1058	>	* be polled or executed next. Conversely, this method may return
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.
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 1004 | 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 1025 | 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 1038 | Line 1116 | public abstract class ForkJoinTask<V> im
1116		.pollTask();
1117		}
1118
1119	<	// adaptors
1119	>	/**
1120	>	* Adaptor for Runnables. This implements RunnableFuture
1121	>	* to be compliant with AbstractExecutorService constraints
1122	>	* when used in ForkJoinPool.
1123	>	*/
1124	>	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1125	>	implements RunnableFuture<T> {
1126	>	final Runnable runnable;
1127	>	final T resultOnCompletion;
1128	>	T result;
1129	>	AdaptedRunnable(Runnable runnable, T result) {
1130	>	if (runnable == null) throw new NullPointerException();
1131	>	this.runnable = runnable;
1132	>	this.resultOnCompletion = result;
1133	>	}
1134	>	public T getRawResult() { return result; }
1135	>	public void setRawResult(T v) { result = v; }
1136	>	public boolean exec() {
1137	>	runnable.run();
1138	>	result = resultOnCompletion;
1139	>	return true;
1140	>	}
1141	>	public void run() { invoke(); }
1142	>	private static final long serialVersionUID = 5232453952276885070L;
1143	>	}
1144	>
1145	>	/**
1146	>	* Adaptor for Callables
1147	>	*/
1148	>	static final class AdaptedCallable<T> extends ForkJoinTask<T>
1149	>	implements RunnableFuture<T> {
1150	>	final Callable<? extends T> callable;
1151	>	T result;
1152	>	AdaptedCallable(Callable<? extends T> callable) {
1153	>	if (callable == null) throw new NullPointerException();
1154	>	this.callable = callable;
1155	>	}
1156	>	public T getRawResult() { return result; }
1157	>	public void setRawResult(T v) { result = v; }
1158	>	public boolean exec() {
1159	>	try {
1160	>	result = callable.call();
1161	>	return true;
1162	>	} catch (Error err) {
1163	>	throw err;
1164	>	} catch (RuntimeException rex) {
1165	>	throw rex;
1166	>	} catch (Exception ex) {
1167	>	throw new RuntimeException(ex);
1168	>	}
1169	>	}
1170	>	public void run() { invoke(); }
1171	>	private static final long serialVersionUID = 2838392045355241008L;
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
1181		*/
1182	<	public static ForkJoinTask<Void> adapt(Runnable runnable) {
1183	<	return new ForkJoinPool.AdaptedRunnable<Void>(runnable, null);
1182	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1183	>	return new AdaptedRunnable<Void>(runnable, null);
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
1193		* @return the task
1194		*/
1195		public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
1196	<	return new ForkJoinPool.AdaptedRunnable<T>(runnable, result);
1196	>	return new AdaptedRunnable<T>(runnable, result);
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
1207		*/
1208	<	public static <T> ForkJoinTask<T> adapt(Callable<T> callable) {
1209	<	return new ForkJoinPool.AdaptedCallable<T>(callable);
1208	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1209	>	return new AdaptedCallable<T>(callable);
1210		}
1211
1212		// Serialization support

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