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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.25 by dl, Fri Jul 31 16:27:08 2009 UTC vs.
Revision 1.35 by dl, Tue Aug 4 12:41:27 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 #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.  Normally, a concrete
96	>	* particular style of fork/join processing, typically {@link
97	>	* RecursiveAction} for computations that do not return results, or
98	>	* {@link RecursiveTask} for those that do.  Normally, a concrete
99		* ForkJoinTask subclass declares fields comprising its parameters,
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
100	<	* 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 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
113	<	* 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 372 | Line 396 | public abstract class ForkJoinTask<V> im
396		*/
397		private V reportFutureResult()
398		throws ExecutionException, InterruptedException {
399	+	if (Thread.interrupted())
400	+	throw new InterruptedException();
401		int s = status & COMPLETION_MASK;
402		if (s < NORMAL) {
403		Throwable ex;
#	Line 379 | Line 405 | public abstract class ForkJoinTask<V> im
405		throw new CancellationException();
406		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
407		throw new ExecutionException(ex);
382	–	if (Thread.interrupted())
383	–	throw new InterruptedException();
408		}
409		return getRawResult();
410		}
#	Line 391 | Line 415 | public abstract class ForkJoinTask<V> im
415		*/
416		private V reportTimedFutureResult()
417		throws InterruptedException, ExecutionException, TimeoutException {
418	+	if (Thread.interrupted())
419	+	throw new InterruptedException();
420		Throwable ex;
421		int s = status & COMPLETION_MASK;
422		if (s == NORMAL)
#	Line 399 | Line 425 | public abstract class ForkJoinTask<V> im
425		throw new CancellationException();
426		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
427		throw new ExecutionException(ex);
402	–	if (Thread.interrupted())
403	–	throw new InterruptedException();
428		throw new TimeoutException();
429		}
430
#	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
490	<	* method may be invoked only from within ForkJoinTask
491	<	* computations (as may be determined using method {@link
492	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
493	<	* in exceptions or errors, possibly including ClassCastException.
513	>	* than once unless it has completed and been reinitialized.
514		*
515	<	* @return {@code this}, to simplify usage.
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
522		*/
523		public final ForkJoinTask<V> fork() {
524		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 502 | Line 528 | public abstract class ForkJoinTask<V> im
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.
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 more than one task
562	>	* encounters an exception, then this method throws any one of
563	>	* these exceptions.  The individual status of each task may be
564	>	* checked using {@link #getException()} and related methods.
565	>	*
566	>	* <p>This method may be invoked only from within {@code
567	>	* ForkJoinTask} computations (as may be determined using method
568	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
569	>	* result in exceptions or errors, possibly including {@code
570	>	* ClassCastException}.
571	>	*
572	>	* @param t1 the first task
573	>	* @param t2 the second task
574	>	* @throws NullPointerException if any task is null
575		*/
576	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
576	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
577		t2.fork();
578		t1.invoke();
579		t2.join();
580		}
581
582		/**
583	<	* Forks the given tasks, returning when {@code isDone} holds
584	<	* for all of them. If any task encounters an exception, others
585	<	* may be cancelled.  This method may be invoked only from within
586	<	* ForkJoinTask computations (as may be determined using method
587	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
588	<	* result in exceptions or errors, possibly including
589	<	* ClassCastException.
583	>	* Forks the given tasks, returning when {@code isDone} holds for
584	>	* each task or an (unchecked) exception is encountered, in which
585	>	* case the exception is rethrown. If any task encounters an
586	>	* exception, others may be, but are not guaranteed to be,
587	>	* cancelled.  If more than one task encounters an exception, then
588	>	* this method throws any one of these exceptions.  The individual
589	>	* status of each task may be checked using {@link #getException()}
590	>	* and related methods.
591	>	*
592	>	* <p>This method may be invoked only from within {@code
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 {@code
596	>	* ClassCastException}.
597		*
598	<	* @param tasks the array of tasks
599	<	* @throws NullPointerException if tasks or any element are null
563	<	* @throws RuntimeException or Error if any task did so
598	>	* @param tasks the tasks
599	>	* @throws NullPointerException if any task is null
600		*/
601		public static void invokeAll(ForkJoinTask<?>... tasks) {
602		Throwable ex = null;
#	Line 596 | Line 632 | public abstract class ForkJoinTask<V> im
632		}
633
634		/**
635	<	* Forks all tasks in the collection, returning when
636	<	* {@code isDone} holds for all of them. If any task
637	<	* encounters an exception, others may be cancelled.  This method
638	<	* may be invoked only from within ForkJoinTask computations (as
639	<	* may be determined using method {@link
640	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
641	<	* in exceptions or errors, possibly including ClassCastException.
635	>	* Forks all tasks in the specified collection, returning when
636	>	* {@code isDone} holds for each task or an (unchecked) exception
637	>	* is encountered.  If any task encounters an exception, others
638	>	* may be, but are not guaranteed to be, cancelled.  If more than
639	>	* one task encounters an exception, then this method throws any
640	>	* one of these exceptions.  The individual status of each task
641	>	* may be checked using {@link #getException()} and related
642	>	* methods.  The behavior of this operation is undefined if the
643	>	* specified collection is modified while the operation is in
644	>	* progress.
645	>	*
646	>	* <p>This method may be invoked only from within {@code
647	>	* ForkJoinTask} computations (as may be determined using method
648	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
649	>	* result in exceptions or errors, possibly including {@code
650	>	* ClassCastException}.
651		*
652		* @param tasks the collection of tasks
653		* @return the tasks argument, to simplify usage
654		* @throws NullPointerException if tasks or any element are null
610	–	* @throws RuntimeException or Error if any task did so
655		*/
656		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
657	<	if (!(tasks instanceof List<?>)) {
657	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
658		invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
659		return tasks;
660		}
#	Line 651 | Line 695 | public abstract class ForkJoinTask<V> im
695		}
696
697		/**
698	+	* Attempts to cancel execution of this task. This attempt will
699	+	* fail if the task has already completed, has already been
700	+	* cancelled, or could not be cancelled for some other reason. If
701	+	* successful, and this task has not started when cancel is
702	+	* called, execution of this task is suppressed, {@link
703	+	* #isCancelled} will report true, and {@link #join} will result
704	+	* in a {@code CancellationException} being thrown.
705	+	*
706	+	* <p>This method may be overridden in subclasses, but if so, must
707	+	* still ensure that these minimal properties hold. In particular,
708	+	* the {@code cancel} method itself must not throw exceptions.
709	+	*
710	+	* <p>This method is designed to be invoked by <em>other</em>
711	+	* tasks. To terminate the current task, you can just return or
712	+	* throw an unchecked exception from its computation method, or
713	+	* invoke {@link #completeExceptionally}.
714	+	*
715	+	* @param mayInterruptIfRunning this value is ignored in the
716	+	* default implementation because tasks are not
717	+	* cancelled via interruption
718	+	*
719	+	* @return {@code true} if this task is now cancelled
720	+	*/
721	+	public boolean cancel(boolean mayInterruptIfRunning) {
722	+	setCompletion(CANCELLED);
723	+	return (status & COMPLETION_MASK) == CANCELLED;
724	+	}
725	+
726	+	/**
727		* Returns {@code true} if the computation performed by this task
728		* has completed (or has been cancelled).
729		*
#	Line 670 | Line 743 | public abstract class ForkJoinTask<V> im
743		}
744
745		/**
746	<	* 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.
683	<	*
684	<	* <p>This method may be overridden in subclasses, but if so, must
685	<	* still ensure that these minimal properties hold. In particular,
686	<	* the cancel method itself must not throw exceptions.
687	<	*
688	<	* <p> This method is designed to be invoked by <em>other</em>
689	<	* tasks. To terminate the current task, you can just return or
690	<	* throw an unchecked exception from its computation method, or
691	<	* invoke {@link #completeExceptionally}.
746	>	* Returns {@code true} if this task threw an exception or was cancelled.
747		*
748	<	* @param mayInterruptIfRunning this value is ignored in the
749	<	* default implementation because tasks are not in general
750	<	* cancelled via interruption
748	>	* @return {@code true} if this task threw an exception or was cancelled
749	>	*/
750	>	public final boolean isCompletedAbnormally() {
751	>	return (status & COMPLETION_MASK) < NORMAL;
752	>	}
753	>
754	>	/**
755	>	* Returns {@code true} if this task completed without throwing an
756	>	* exception and was not cancelled.
757		*
758	<	* @return {@code true} if this task is now cancelled
758	>	* @return {@code true} if this task completed without throwing an
759	>	* exception and was not cancelled
760		*/
761	<	public boolean cancel(boolean mayInterruptIfRunning) {
762	<	setCompletion(CANCELLED);
701	<	return (status & COMPLETION_MASK) == CANCELLED;
761	>	public final boolean isCompletedNormally() {
762	>	return (status & COMPLETION_MASK) == NORMAL;
763		}
764
765		/**
766	<	* Returns {@code true} if this task threw an exception or was cancelled.
766	>	* Returns {@code true} if this task threw an exception.
767		*
768	<	* @return {@code true} if this task threw an exception or was cancelled
768	>	* @return {@code true} if this task threw an exception
769		*/
770	<	public final boolean isCompletedAbnormally() {
771	<	return (status & COMPLETION_MASK) < NORMAL;
770	>	public final boolean isCompletedExceptionally() {
771	>	return (status & COMPLETION_MASK) == EXCEPTIONAL;
772		}
773
774		/**
775		* Returns the exception thrown by the base computation, or a
776	<	* CancellationException if cancelled, or null if none or if the
777	<	* method has not yet completed.
776	>	* {@code CancellationException} if cancelled, or {@code null} if
777	>	* none or if the method has not yet completed.
778		*
779		* @return the exception, or {@code null} if none
780		*/
#	Line 732 | Line 793 | public abstract class ForkJoinTask<V> im
793		* {@code join} and related operations. This method may be used
794		* to induce exceptions in asynchronous tasks, or to force
795		* completion of tasks that would not otherwise complete.  Its use
796	<	* in other situations is likely to be wrong.  This method is
796	>	* in other situations is discouraged.  This method is
797		* overridable, but overridden versions must invoke {@code super}
798		* implementation to maintain guarantees.
799		*
#	Line 752 | Line 813 | public abstract class ForkJoinTask<V> im
813		* operations. This method may be used to provide results for
814		* asynchronous tasks, or to provide alternative handling for
815		* tasks that would not otherwise complete normally. Its use in
816	<	* other situations is likely to be wrong. This method is
816	>	* other situations is discouraged. This method is
817		* overridable, but overridden versions must invoke {@code super}
818		* implementation to maintain guarantees.
819		*
#	Line 791 | Line 852 | public abstract class ForkJoinTask<V> im
852		* there are no potential dependencies between continuation of the
853		* current task and that of any other task that might be executed
854		* while helping. (This usually holds for pure divide-and-conquer
855	<	* tasks). This method may be invoked only from within
856	<	* ForkJoinTask computations (as may be determined using method
857	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
858	<	* result in exceptions or errors, possibly including
859	<	* ClassCastException.
855	>	* tasks).
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		* @return the computed result
864		*/
#	Line 808 | Line 871 | public abstract class ForkJoinTask<V> im
871
872		/**
873		* Possibly executes other tasks until this task is ready.  This
874	<	* method may be invoked only from within ForkJoinTask
875	<	* computations (as may be determined using method {@link
876	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
877	<	* in exceptions or errors, possibly including ClassCastException.
874	>	* method may be useful when processing collections of tasks when
875	>	* some have been cancelled or otherwise known to have aborted.
876	>	*
877	>	* <p>This method may be invoked only from within {@code
878	>	* ForkJoinTask} computations (as may be determined using method
879	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
880	>	* result in exceptions or errors, possibly including {@code
881	>	* ClassCastException}.
882		*/
883		public final void quietlyHelpJoin() {
884		if (status >= 0) {
#	Line 850 | Line 917 | public abstract class ForkJoinTask<V> im
917
918		/**
919		* Possibly executes tasks until the pool hosting the current task
920	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
921	<	* designs in which many tasks are forked, but none are explicitly
922	<	* joined, instead executing them until all are processed.
920	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
921	>	* be of use in designs in which many tasks are forked, but none
922	>	* are explicitly joined, instead executing them until all are
923	>	* processed.
924	>	*
925	>	* <p>This method may be invoked only from within {@code
926	>	* ForkJoinTask} computations (as may be determined using method
927	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
928	>	* result in exceptions or errors, possibly including {@code
929	>	* ClassCastException}.
930		*/
931		public static void helpQuiesce() {
932		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 865 | Line 939 | public abstract class ForkJoinTask<V> im
939		* this task, but only if reuse occurs when this task has either
940		* never been forked, or has been forked, then completed and all
941		* outstanding joins of this task have also completed. Effects
942	<	* under any other usage conditions are not guaranteed, and are
943	<	* almost surely wrong. This method may be useful when executing
942	>	* under any other usage conditions are not guaranteed.
943	>	* This method may be useful when executing
944		* pre-constructed trees of subtasks in loops.
945		*/
946		public void reinitialize() {
#	Line 879 | Line 953 | public abstract class ForkJoinTask<V> im
953		* Returns the pool hosting the current task execution, or null
954		* if this task is executing outside of any ForkJoinPool.
955		*
956	+	* @see #inForkJoinPool
957		* @return the pool, or {@code null} if none
958		*/
959		public static ForkJoinPool getPool() {
#	Line 904 | Line 979 | public abstract class ForkJoinTask<V> im
979		* by the current thread, and has not commenced executing in
980		* another thread.  This method may be useful when arranging
981		* alternative local processing of tasks that could have been, but
982	<	* were not, stolen. This method may be invoked only from within
983	<	* ForkJoinTask computations (as may be determined using method
984	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
985	<	* result in exceptions or errors, possibly including
986	<	* ClassCastException.
982	>	* were not, stolen.
983	>	*
984	>	* <p>This method may be invoked only from within {@code
985	>	* ForkJoinTask} computations (as may be determined using method
986	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
987	>	* result in exceptions or errors, possibly including {@code
988	>	* ClassCastException}.
989		*
990		* @return {@code true} if unforked
991		*/
#	Line 923 | Line 1000 | public abstract class ForkJoinTask<V> im
1000		* value may be useful for heuristic decisions about whether to
1001		* fork other tasks.
1002		*
1003	+	* <p>This method may be invoked only from within {@code
1004	+	* ForkJoinTask} computations (as may be determined using method
1005	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1006	+	* result in exceptions or errors, possibly including {@code
1007	+	* ClassCastException}.
1008	+	*
1009		* @return the number of tasks
1010		*/
1011		public static int getQueuedTaskCount() {
#	Line 940 | Line 1023 | public abstract class ForkJoinTask<V> im
1023		* tasks, and to process computations locally if this threshold is
1024		* exceeded.
1025		*
1026	+	* <p>This method may be invoked only from within {@code
1027	+	* ForkJoinTask} computations (as may be determined using method
1028	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1029	+	* result in exceptions or errors, possibly including {@code
1030	+	* ClassCastException}.
1031	+	*
1032		* @return the surplus number of tasks, which may be negative
1033		*/
1034		public static int getSurplusQueuedTaskCount() {
#	Line 975 | Line 1064 | public abstract class ForkJoinTask<V> im
1064		* called otherwise. The return value controls whether this task
1065		* is considered to be done normally. It may return false in
1066		* asynchronous actions that require explicit invocations of
1067	<	* {@link #complete} to become joinable. It may throw exceptions
1068	<	* to indicate abnormal exit.
1067	>	* {@link #complete} to become joinable. It may also throw an
1068	>	* (unchecked) exception to indicate abnormal exit.
1069		*
1070		* @return {@code true} if completed normally
982	–	* @throws Error or RuntimeException if encountered during computation
1071		*/
1072		protected abstract boolean exec();
1073
#	Line 991 | Line 1079 | public abstract class ForkJoinTask<V> im
1079		* null even if a task exists but cannot be accessed without
1080		* contention with other threads.  This method is designed
1081		* primarily to support extensions, and is unlikely to be useful
1082	<	* otherwise.  This method may be invoked only from within
1083	<	* ForkJoinTask computations (as may be determined using method
1084	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1085	<	* result in exceptions or errors, possibly including
1086	<	* ClassCastException.
1082	>	* otherwise.
1083	>	*
1084	>	* <p>This method may be invoked only from within {@code
1085	>	* ForkJoinTask} computations (as may be determined using method
1086	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1087	>	* result in exceptions or errors, possibly including {@code
1088	>	* ClassCastException}.
1089		*
1090		* @return the next task, or {@code null} if none are available
1091		*/
#	Line 1008 | Line 1098 | public abstract class ForkJoinTask<V> im
1098		* Unschedules and returns, without executing, the next task
1099		* queued by the current thread but not yet executed.  This method
1100		* is designed primarily to support extensions, and is unlikely to
1101	<	* be useful otherwise.  This method may be invoked only from
1102	<	* within ForkJoinTask computations (as may be determined using
1103	<	* method {@link #inForkJoinPool}). Attempts to invoke in other
1104	<	* contexts result in exceptions or errors, possibly including
1105	<	* ClassCastException.
1101	>	* be useful otherwise.
1102	>	*
1103	>	* <p>This method may be invoked only from within {@code
1104	>	* ForkJoinTask} computations (as may be determined using method
1105	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1106	>	* result in exceptions or errors, possibly including {@code
1107	>	* ClassCastException}.
1108		*
1109		* @return the next task, or {@code null} if none are available
1110		*/
#	Line 1029 | Line 1121 | public abstract class ForkJoinTask<V> im
1121		* {@code null} result does not necessarily imply quiescence
1122		* of the pool this task is operating in.  This method is designed
1123		* primarily to support extensions, and is unlikely to be useful
1124	<	* otherwise.  This method may be invoked only from within
1125	<	* ForkJoinTask computations (as may be determined using method
1126	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1127	<	* result in exceptions or errors, possibly including
1128	<	* ClassCastException.
1124	>	* otherwise.
1125	>	*
1126	>	* <p>This method may be invoked only from within {@code
1127	>	* ForkJoinTask} computations (as may be determined using method
1128	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1129	>	* result in exceptions or errors, possibly including {@code
1130	>	* ClassCastException}.
1131		*
1132		* @return a task, or {@code null} if none are available
1133		*/
#	Line 1073 | Line 1167 | public abstract class ForkJoinTask<V> im
1167		*/
1168		static final class AdaptedCallable<T> extends ForkJoinTask<T>
1169		implements RunnableFuture<T> {
1170	<	final Callable<T> callable;
1170	>	final Callable<? extends T> callable;
1171		T result;
1172	<	AdaptedCallable(Callable<T> callable) {
1172	>	AdaptedCallable(Callable<? extends T> callable) {
1173		if (callable == null) throw new NullPointerException();
1174		this.callable = callable;
1175		}
#	Line 1098 | Line 1192 | public abstract class ForkJoinTask<V> im
1192		}
1193
1194		/**
1195	<	* Returns a new ForkJoinTask that performs the {@code run}
1196	<	* method of the given Runnable as its action, and returns a null
1197	<	* result upon {@code join}.
1195	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1196	>	* method of the given {@code Runnable} as its action, and returns
1197	>	* a null result upon {@link #join}.
1198		*
1199		* @param runnable the runnable action
1200		* @return the task
1201		*/
1202	<	public static ForkJoinTask<Void> adapt(Runnable runnable) {
1202	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1203		return new AdaptedRunnable<Void>(runnable, null);
1204		}
1205
1206		/**
1207	<	* Returns a new ForkJoinTask that performs the {@code run}
1208	<	* method of the given Runnable as its action, and returns the
1209	<	* given result upon {@code join}.
1207	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1208	>	* method of the given {@code Runnable} as its action, and returns
1209	>	* the given result upon {@link #join}.
1210		*
1211		* @param runnable the runnable action
1212		* @param result the result upon completion
#	Line 1123 | Line 1217 | public abstract class ForkJoinTask<V> im
1217		}
1218
1219		/**
1220	<	* Returns a new ForkJoinTask that performs the {@code call}
1221	<	* method of the given Callable as its action, and returns its
1222	<	* result upon {@code join}, translating any checked
1223	<	* exceptions encountered into {@code RuntimeException}.
1220	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1221	>	* method of the given {@code Callable} as its action, and returns
1222	>	* its result upon {@link #join}, translating any checked exceptions
1223	>	* encountered into {@code RuntimeException}.
1224		*
1225		* @param callable the callable action
1226		* @return the task
1227		*/
1228	<	public static <T> ForkJoinTask<T> adapt(Callable<T> callable) {
1228	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1229		return new AdaptedCallable<T>(callable);
1230		}
1231

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