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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.20 by jsr166, Sun Jul 26 05:55:34 2009 UTC vs.
Revision 1.33 by dl, Tue Aug 4 00:36:45 2009 UTC

#	Line 12 | Line 12 | import java.io.Serializable;
12		import java.util.Collection;
13		import java.util.Collections;
14		import java.util.List;
15	+	import java.util.RandomAccess;
16		import java.util.Map;
17		import java.util.WeakHashMap;
18
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}
30	<	* and {@code join}, or derivatives such as
31	<	* {@code invokeAll}.  However, this class also provides a number
32	<	* of other methods that can come into play in advanced usages, as
33	<	* well as extension mechanics that allow support of new forms of
34	<	* 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 75 | Line 77 | import java.util.WeakHashMap;
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 ForkJoinTask class is not usually directly subclassed.
81		* Instead, you subclass one of the abstract classes that support a
82	<	* particular style of fork/join processing.  Normally, a concrete
82	>	* particular style of fork/join processing, typically {@link
83	>	* RecursiveAction} for computations that do not return results, or
84	>	* {@link RecursiveTask} for those that do.  Normally, a concrete
85		* ForkJoinTask subclass declares fields comprising its parameters,
86		* established in a constructor, and then defines a {@code compute}
87		* method that somehow uses the control methods supplied by this base
88		* class. While these methods have {@code public} access (to allow
89	<	* instances of different task subclasses to call each others
89	>	* instances of different task subclasses to call each other's
90		* methods), some of them may only be called from within other
91		* ForkJoinTasks (as may be determined using method {@link
92		* #inForkJoinPool}).  Attempts to invoke them in other contexts
93		* result in exceptions or errors, possibly including
94		* ClassCastException.
95		*
96	<	* <p>Most base support methods are {@code final} because their
97	<	* implementations are intrinsically tied to the underlying
98	<	* lightweight task scheduling framework, and so cannot be overridden.
99	<	* Developers creating new basic styles of fork/join processing should
100	<	* minimally implement {@code protected} methods
101	<	* {@code exec}, {@code setRawResult}, and
102	<	* {@code getRawResult}, while also introducing an abstract
103	<	* computational method that can be implemented in its subclasses,
104	<	* possibly relying on other {@code protected} methods provided
101	<	* by this class.
96	>	* <p>Most base support methods are {@code final}, to prevent
97	>	* overriding of implementations that are intrinsically tied to the
98	>	* underlying lightweight task scheduling framework.  Developers
99	>	* creating new basic styles of fork/join processing should minimally
100	>	* implement {@code protected} methods {@link #exec}, {@link
101	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
102	>	* an abstract computational method that can be implemented in its
103	>	* subclasses, possibly relying on other {@code protected} methods
104	>	* provided by this class.
105		*
106		* <p>ForkJoinTasks should perform relatively small amounts of
107	<	* computations, otherwise splitting into smaller tasks. As a very
108	<	* rough rule of thumb, a task should perform more than 100 and less
109	<	* than 10000 basic computational steps. If tasks are too big, then
110	<	* parallelism cannot improve throughput. If too small, then memory
111	<	* and internal task maintenance overhead may overwhelm processing.
107	>	* computation. Large tasks should be split into smaller subtasks,
108	>	* usually via recursive decomposition. As a very rough rule of thumb,
109	>	* a task should perform more than 100 and less than 10000 basic
110	>	* computational steps. If tasks are too big, then parallelism cannot
111	>	* improve throughput. If too small, then memory and internal task
112	>	* maintenance overhead may overwhelm processing.
113		*
114	<	* <p>ForkJoinTasks are {@code Serializable}, which enables them
115	<	* to be used in extensions such as remote execution frameworks. It is
116	<	* in general sensible to serialize tasks only before or after, but
117	<	* not during execution. Serialization is not relied on during
118	<	* execution itself.
114	>	* <p>This class provides {@code adapt} methods for {@link
115	>	* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
116	>	* may be of use when mixing execution of ForkJoinTasks with other
117	>	* kinds of tasks. When all tasks are of this form, consider using a
118	>	* pool in {@link ForkJoinPool#setAsyncMode}.
119	>	*
120	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
121	>	* used in extensions such as remote execution frameworks. It is
122	>	* sensible to serialize tasks only before or after, but not during,
123	>	* execution. Serialization is not relied on during execution itself.
124		*
125		* @since 1.7
126		* @author Doug Lea
#	Line 248 | Line 257 | public abstract class ForkJoinTask<V> im
257		synchronized (this) {
258		try {
259		while (status >= 0) {
260	<	long nt = nanos - System.nanoTime() - startTime;
260	>	long nt = nanos - (System.nanoTime() - startTime);
261		if (nt <= 0)
262		break;
263		wait(nt / 1000000, (int) (nt % 1000000));
#	Line 487 | Line 496 | public abstract class ForkJoinTask<V> im
496		/**
497		* Arranges to asynchronously execute this task.  While it is not
498		* necessarily enforced, it is a usage error to fork a task more
499	<	* than once unless it has completed and been reinitialized.  This
500	<	* method may be invoked only from within ForkJoinTask
501	<	* computations (as may be determined using method {@link
502	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
503	<	* in exceptions or errors, possibly including ClassCastException.
499	>	* than once unless it has completed and been reinitialized.
500	>	*
501	>	* <p>This method may be invoked only from within {@code
502	>	* ForkJoinTask} computations (as may be determined using method
503	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
504	>	* result in exceptions or errors, possibly including {@code
505	>	* ClassCastException}.
506		*
507	<	* @return <code>this</code>, to simplify usage.
507	>	* @return {@code this}, to simplify usage
508		*/
509		public final ForkJoinTask<V> fork() {
510		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 503 | Line 514 | public abstract class ForkJoinTask<V> im
514
515		/**
516		* Returns the result of the computation when it is ready.
517	<	* This method differs from {@code get} in that abnormal
518	<	* completion results in RuntimeExceptions or Errors, not
519	<	* ExecutionExceptions.
517	>	* This method differs from {@link #get()} in that
518	>	* abnormal completion results in {@code RuntimeException} or
519	>	* {@code Error}, not {@code ExecutionException}.
520		*
521		* @return the computed result
522		*/
#	Line 532 | Line 543 | public abstract class ForkJoinTask<V> im
543		}
544
545		/**
546	<	* Forks both tasks, returning when {@code isDone} holds for
547	<	* both of them or an exception is encountered. This method may be
548	<	* invoked only from within ForkJoinTask computations (as may be
549	<	* determined using method {@link #inForkJoinPool}). Attempts to
550	<	* invoke in other contexts result in exceptions or errors,
551	<	* possibly including ClassCastException.
552	<	*
553	<	* @param t1 one task
554	<	* @param t2 the other task
555	<	* @throws NullPointerException if t1 or t2 are null
556	<	* @throws RuntimeException or Error if either task did so
546	>	* Forks the given tasks, returning when {@code isDone} holds
547	>	* for each task or an exception is encountered.
548	>	*
549	>	* <p>This method may be invoked only from within {@code
550	>	* ForkJoinTask} computations (as may be determined using method
551	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
552	>	* result in exceptions or errors, possibly including {@code
553	>	* ClassCastException}.
554	>	*
555	>	* @param t1 the first task
556	>	* @param t2 the second task
557	>	* @throws NullPointerException if any task is null
558	>	* @throws RuntimeException or Error if a task did so
559		*/
560	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
560	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
561		t2.fork();
562		t1.invoke();
563		t2.join();
564		}
565
566		/**
567	<	* Forks the given tasks, returning when {@code isDone} holds
568	<	* for all of them. If any task encounters an exception, others
569	<	* may be cancelled.  This method may be invoked only from within
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
573	<	* ClassCastException.
567	>	* Forks the given tasks, returning when {@code isDone} holds for
568	>	* each task or an exception is encountered. If any task
569	>	* encounters an exception, others may be, but are not guaranteed
570	>	* to be, cancelled.
571	>	*
572	>	* <p>This method may be invoked only from within {@code
573	>	* ForkJoinTask} computations (as may be determined using method
574	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
575	>	* result in exceptions or errors, possibly including {@code
576	>	* ClassCastException}.
577		*
578	<	* @param tasks the array of tasks
578	>	* @param tasks the tasks
579		* @throws NullPointerException if tasks or any element are null
580		* @throws RuntimeException or Error if any task did so
581		*/
#	Line 597 | Line 613 | public abstract class ForkJoinTask<V> im
613		}
614
615		/**
616	<	* Forks all tasks in the collection, returning when
617	<	* {@code isDone} holds for all of them. If any task
618	<	* encounters an exception, others may be cancelled.  This method
619	<	* may be invoked only from within ForkJoinTask computations (as
620	<	* may be determined using method {@link
621	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
622	<	* in exceptions or errors, possibly including ClassCastException.
616	>	* Forks all tasks in the specified collection, returning when
617	>	* {@code isDone} holds for each task or an exception is
618	>	* encountered.  If any task encounters an exception, others may
619	>	* be, but are not guaranteed to be, cancelled. The behavior of
620	>	* this operation is undefined if the specified collection is
621	>	* modified while the operation is in progress.
622	>	*
623	>	* <p>This method may be invoked only from within {@code
624	>	* ForkJoinTask} computations (as may be determined using method
625	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
626	>	* result in exceptions or errors, possibly including {@code
627	>	* ClassCastException}.
628		*
629		* @param tasks the collection of tasks
630		* @return the tasks argument, to simplify usage
#	Line 611 | Line 632 | public abstract class ForkJoinTask<V> im
632		* @throws RuntimeException or Error if any task did so
633		*/
634		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
635	<	if (!(tasks instanceof List<?>)) {
635	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
636		invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
637		return tasks;
638		}
#	Line 652 | Line 673 | public abstract class ForkJoinTask<V> im
673		}
674
675		/**
676	<	* Returns true if the computation performed by this task has
677	<	* completed (or has been cancelled).
676	>	* Returns {@code true} if the computation performed by this task
677	>	* has completed (or has been cancelled).
678		*
679	<	* @return true if this computation has completed
679	>	* @return {@code true} if this computation has completed
680		*/
681		public final boolean isDone() {
682		return status < 0;
683		}
684
685		/**
686	<	* Returns true if this task was cancelled.
686	>	* Returns {@code true} if this task was cancelled.
687		*
688	<	* @return true if this task was cancelled
688	>	* @return {@code true} if this task was cancelled
689		*/
690		public final boolean isCancelled() {
691		return (status & COMPLETION_MASK) == CANCELLED;
692		}
693
694		/**
695	<	* Asserts that the results of this task's computation will not be
696	<	* used. If a cancellation occurs before attempting to execute this
697	<	* task, then execution will be suppressed, {@code isCancelled}
698	<	* will report true, and {@code join} will result in a
699	<	* {@code CancellationException} being thrown. Otherwise, when
700	<	* cancellation races with completion, there are no guarantees
701	<	* about whether {@code isCancelled} will report true, whether
681	<	* {@code join} will return normally or via an exception, or
682	<	* whether these behaviors will remain consistent upon repeated
683	<	* invocation.
695	>	* Attempts to cancel execution of this task. This attempt will
696	>	* fail if the task has already completed, has already been
697	>	* cancelled, or could not be cancelled for some other reason. If
698	>	* successful, and this task has not started when cancel is
699	>	* called, execution of this task is suppressed, {@link
700	>	* #isCancelled} will report true, and {@link #join} will result
701	>	* in a {@code CancellationException} being thrown.
702		*
703		* <p>This method may be overridden in subclasses, but if so, must
704		* still ensure that these minimal properties hold. In particular,
705	<	* the cancel method itself must not throw exceptions.
705	>	* the {@code cancel} method itself must not throw exceptions.
706		*
707	<	* <p> This method is designed to be invoked by <em>other</em>
707	>	* <p>This method is designed to be invoked by <em>other</em>
708		* tasks. To terminate the current task, you can just return or
709		* throw an unchecked exception from its computation method, or
710	<	* invoke {@code completeExceptionally}.
710	>	* invoke {@link #completeExceptionally}.
711		*
712		* @param mayInterruptIfRunning this value is ignored in the
713	<	* default implementation because tasks are not in general
713	>	* default implementation because tasks are not
714		* cancelled via interruption
715		*
716	<	* @return true if this task is now cancelled
716	>	* @return {@code true} if this task is now cancelled
717		*/
718		public boolean cancel(boolean mayInterruptIfRunning) {
719		setCompletion(CANCELLED);
#	Line 703 | Line 721 | public abstract class ForkJoinTask<V> im
721		}
722
723		/**
724	<	* Returns true if this task threw an exception or was cancelled.
724	>	* Returns {@code true} if this task threw an exception or was cancelled.
725		*
726	<	* @return true if this task threw an exception or was cancelled
726	>	* @return {@code true} if this task threw an exception or was cancelled
727		*/
728		public final boolean isCompletedAbnormally() {
729		return (status & COMPLETION_MASK) < NORMAL;
#	Line 713 | Line 731 | public abstract class ForkJoinTask<V> im
731
732		/**
733		* Returns the exception thrown by the base computation, or a
734	<	* CancellationException if cancelled, or null if none or if the
735	<	* method has not yet completed.
734	>	* {@code CancellationException} if cancelled, or {@code null} if
735	>	* none or if the method has not yet completed.
736		*
737	<	* @return the exception, or null if none
737	>	* @return the exception, or {@code null} if none
738		*/
739		public final Throwable getException() {
740		int s = status & COMPLETION_MASK;
#	Line 733 | Line 751 | public abstract class ForkJoinTask<V> im
751		* {@code join} and related operations. This method may be used
752		* to induce exceptions in asynchronous tasks, or to force
753		* completion of tasks that would not otherwise complete.  Its use
754	<	* in other situations is likely to be wrong.  This method is
754	>	* in other situations is discouraged.  This method is
755		* overridable, but overridden versions must invoke {@code super}
756		* implementation to maintain guarantees.
757		*
#	Line 753 | Line 771 | public abstract class ForkJoinTask<V> im
771		* operations. This method may be used to provide results for
772		* asynchronous tasks, or to provide alternative handling for
773		* tasks that would not otherwise complete normally. Its use in
774	<	* other situations is likely to be wrong. This method is
774	>	* other situations is discouraged. This method is
775		* overridable, but overridden versions must invoke {@code super}
776		* implementation to maintain guarantees.
777		*
#	Line 778 | Line 796 | public abstract class ForkJoinTask<V> im
796
797		public final V get(long timeout, TimeUnit unit)
798		throws InterruptedException, ExecutionException, TimeoutException {
799	+	long nanos = unit.toNanos(timeout);
800		ForkJoinWorkerThread w = getWorker();
801		if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
802	<	awaitDone(w, unit.toNanos(timeout));
802	>	awaitDone(w, nanos);
803		return reportTimedFutureResult();
804		}
805
#	Line 791 | Line 810 | public abstract class ForkJoinTask<V> im
810		* there are no potential dependencies between continuation of the
811		* current task and that of any other task that might be executed
812		* while helping. (This usually holds for pure divide-and-conquer
813	<	* tasks). This method may be invoked only from within
814	<	* ForkJoinTask computations (as may be determined using method
815	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
816	<	* result in exceptions or errors, possibly including
817	<	* ClassCastException.
813	>	* tasks).
814	>	*
815	>	* <p>This method may be invoked only from within {@code
816	>	* ForkJoinTask} computations (as may be determined using method
817	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
818	>	* result in exceptions or errors, possibly including {@code
819	>	* ClassCastException}.
820		*
821		* @return the computed result
822		*/
#	Line 808 | Line 829 | public abstract class ForkJoinTask<V> im
829
830		/**
831		* Possibly executes other tasks until this task is ready.  This
832	<	* method may be invoked only from within ForkJoinTask
833	<	* computations (as may be determined using method {@link
834	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
835	<	* in exceptions or errors, possibly including ClassCastException.
832	>	* method may be useful when processing collections of tasks when
833	>	* some have been cancelled or otherwise known to have aborted.
834	>	*
835	>	* <p>This method may be invoked only from within {@code
836	>	* ForkJoinTask} computations (as may be determined using method
837	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
838	>	* result in exceptions or errors, possibly including {@code
839	>	* ClassCastException}.
840		*/
841		public final void quietlyHelpJoin() {
842		if (status >= 0) {
#	Line 850 | Line 875 | public abstract class ForkJoinTask<V> im
875
876		/**
877		* Possibly executes tasks until the pool hosting the current task
878	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
879	<	* designs in which many tasks are forked, but none are explicitly
880	<	* joined, instead executing them until all are processed.
878	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
879	>	* be of use in designs in which many tasks are forked, but none
880	>	* are explicitly joined, instead executing them until all are
881	>	* processed.
882	>	*
883	>	* <p>This method may be invoked only from within {@code
884	>	* ForkJoinTask} computations (as may be determined using method
885	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
886	>	* result in exceptions or errors, possibly including {@code
887	>	* ClassCastException}.
888		*/
889		public static void helpQuiesce() {
890		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 865 | Line 897 | public abstract class ForkJoinTask<V> im
897		* this task, but only if reuse occurs when this task has either
898		* never been forked, or has been forked, then completed and all
899		* outstanding joins of this task have also completed. Effects
900	<	* under any other usage conditions are not guaranteed, and are
901	<	* almost surely wrong. This method may be useful when executing
900	>	* under any other usage conditions are not guaranteed.
901	>	* This method may be useful when executing
902		* pre-constructed trees of subtasks in loops.
903		*/
904		public void reinitialize() {
#	Line 879 | Line 911 | public abstract class ForkJoinTask<V> im
911		* Returns the pool hosting the current task execution, or null
912		* if this task is executing outside of any ForkJoinPool.
913		*
914	<	* @return the pool, or null if none
914	>	* @see #inForkJoinPool
915	>	* @return the pool, or {@code null} if none
916		*/
917		public static ForkJoinPool getPool() {
918		Thread t = Thread.currentThread();
#	Line 904 | Line 937 | public abstract class ForkJoinTask<V> im
937		* by the current thread, and has not commenced executing in
938		* another thread.  This method may be useful when arranging
939		* alternative local processing of tasks that could have been, but
940	<	* were not, stolen. This method may be invoked only from within
908	<	* ForkJoinTask computations (as may be determined using method
909	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
910	<	* result in exceptions or errors, possibly including
911	<	* ClassCastException.
940	>	* were not, stolen.
941		*
942	<	* @return true if unforked
942	>	* <p>This method may be invoked only from within {@code
943	>	* ForkJoinTask} computations (as may be determined using method
944	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
945	>	* result in exceptions or errors, possibly including {@code
946	>	* ClassCastException}.
947	>	*
948	>	* @return {@code true} if unforked
949		*/
950		public boolean tryUnfork() {
951		return ((ForkJoinWorkerThread) Thread.currentThread())
#	Line 923 | Line 958 | public abstract class ForkJoinTask<V> im
958		* value may be useful for heuristic decisions about whether to
959		* fork other tasks.
960		*
961	+	* <p>This method may be invoked only from within {@code
962	+	* ForkJoinTask} computations (as may be determined using method
963	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
964	+	* result in exceptions or errors, possibly including {@code
965	+	* ClassCastException}.
966	+	*
967		* @return the number of tasks
968		*/
969		public static int getQueuedTaskCount() {
#	Line 940 | Line 981 | public abstract class ForkJoinTask<V> im
981		* tasks, and to process computations locally if this threshold is
982		* exceeded.
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 the surplus number of tasks, which may be negative
991		*/
992		public static int getSurplusQueuedTaskCount() {
#	Line 950 | Line 997 | public abstract class ForkJoinTask<V> im
997		// Extension methods
998
999		/**
1000	<	* Returns the result that would be returned by {@code join},
1001	<	* even if this task completed abnormally, or null if this task is
1002	<	* not known to have been completed.  This method is designed to
1003	<	* aid debugging, as well as to support extensions. Its use in any
1004	<	* other context is discouraged.
1000	>	* Returns the result that would be returned by {@link #join}, even
1001	>	* if this task completed abnormally, or {@code null} if this task
1002	>	* is not known to have been completed.  This method is designed
1003	>	* to aid debugging, as well as to support extensions. Its use in
1004	>	* any other context is discouraged.
1005		*
1006	<	* @return the result, or null if not completed
1006	>	* @return the result, or {@code null} if not completed
1007		*/
1008		public abstract V getRawResult();
1009
#	Line 975 | Line 1022 | public abstract class ForkJoinTask<V> im
1022		* called otherwise. The return value controls whether this task
1023		* is considered to be done normally. It may return false in
1024		* asynchronous actions that require explicit invocations of
1025	<	* {@code complete} to become joinable. It may throw exceptions
1025	>	* {@link #complete} to become joinable. It may throw exceptions
1026		* to indicate abnormal exit.
1027		*
1028	<	* @return true if completed normally
1028	>	* @return {@code true} if completed normally
1029		* @throws Error or RuntimeException if encountered during computation
1030		*/
1031		protected abstract boolean exec();
1032
1033		/**
1034	<	* Returns, but does not unschedule or execute, the task queued by
1035	<	* the current thread but not yet executed, if one is
1034	>	* Returns, but does not unschedule or execute, a task queued by
1035	>	* the current thread but not yet executed, if one is immediately
1036		* available. There is no guarantee that this task will actually
1037	<	* be polled or executed next.  This method is designed primarily
1038	<	* to support extensions, and is unlikely to be useful otherwise.
1039	<	* This method may be invoked only from within ForkJoinTask
1040	<	* computations (as may be determined using method {@link
1041	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
1042	<	* in exceptions or errors, possibly including ClassCastException.
1037	>	* be polled or executed next. Conversely, this method may return
1038	>	* null even if a task exists but cannot be accessed without
1039	>	* contention with other threads.  This method is designed
1040	>	* primarily to support extensions, and is unlikely to be useful
1041	>	* otherwise.
1042	>	*
1043	>	* <p>This method may be invoked only from within {@code
1044	>	* ForkJoinTask} computations (as may be determined using method
1045	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1046	>	* result in exceptions or errors, possibly including {@code
1047	>	* ClassCastException}.
1048		*
1049	<	* @return the next task, or null if none are available
1049	>	* @return the next task, or {@code null} if none are available
1050		*/
1051		protected static ForkJoinTask<?> peekNextLocalTask() {
1052		return ((ForkJoinWorkerThread) Thread.currentThread())
#	Line 1005 | Line 1057 | public abstract class ForkJoinTask<V> im
1057		* Unschedules and returns, without executing, the next task
1058		* queued by the current thread but not yet executed.  This method
1059		* is designed primarily to support extensions, and is unlikely to
1060	<	* be useful otherwise.  This method may be invoked only from
1009	<	* within ForkJoinTask computations (as may be determined using
1010	<	* method {@link #inForkJoinPool}). Attempts to invoke in other
1011	<	* contexts result in exceptions or errors, possibly including
1012	<	* ClassCastException.
1060	>	* be useful otherwise.
1061		*
1062	<	* @return the next task, or null if none are available
1062	>	* <p>This method may be invoked only from within {@code
1063	>	* ForkJoinTask} computations (as may be determined using method
1064	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1065	>	* result in exceptions or errors, possibly including {@code
1066	>	* ClassCastException}.
1067	>	*
1068	>	* @return the next task, or {@code null} if none are available
1069		*/
1070		protected static ForkJoinTask<?> pollNextLocalTask() {
1071		return ((ForkJoinWorkerThread) Thread.currentThread())
#	Line 1026 | Line 1080 | public abstract class ForkJoinTask<V> im
1080		* {@code null} result does not necessarily imply quiescence
1081		* of the pool this task is operating in.  This method is designed
1082		* primarily to support extensions, and is unlikely to be useful
1083	<	* otherwise.  This method may be invoked only from within
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
1087	<	* ClassCastException.
1083	>	* otherwise.
1084	>	*
1085	>	* <p>This method may be invoked only from within {@code
1086	>	* ForkJoinTask} computations (as may be determined using method
1087	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1088	>	* result in exceptions or errors, possibly including {@code
1089	>	* ClassCastException}.
1090		*
1091	<	* @return a task, or null if none are available
1091	>	* @return a task, or {@code null} if none are available
1092		*/
1093		protected static ForkJoinTask<?> pollTask() {
1094		return ((ForkJoinWorkerThread) Thread.currentThread())
1095		.pollTask();
1096		}
1097
1098	<	// adaptors
1098	>	/**
1099	>	* Adaptor for Runnables. This implements RunnableFuture
1100	>	* to be compliant with AbstractExecutorService constraints
1101	>	* when used in ForkJoinPool.
1102	>	*/
1103	>	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1104	>	implements RunnableFuture<T> {
1105	>	final Runnable runnable;
1106	>	final T resultOnCompletion;
1107	>	T result;
1108	>	AdaptedRunnable(Runnable runnable, T result) {
1109	>	if (runnable == null) throw new NullPointerException();
1110	>	this.runnable = runnable;
1111	>	this.resultOnCompletion = result;
1112	>	}
1113	>	public T getRawResult() { return result; }
1114	>	public void setRawResult(T v) { result = v; }
1115	>	public boolean exec() {
1116	>	runnable.run();
1117	>	result = resultOnCompletion;
1118	>	return true;
1119	>	}
1120	>	public void run() { invoke(); }
1121	>	private static final long serialVersionUID = 5232453952276885070L;
1122	>	}
1123	>
1124	>	/**
1125	>	* Adaptor for Callables
1126	>	*/
1127	>	static final class AdaptedCallable<T> extends ForkJoinTask<T>
1128	>	implements RunnableFuture<T> {
1129	>	final Callable<? extends T> callable;
1130	>	T result;
1131	>	AdaptedCallable(Callable<? extends T> callable) {
1132	>	if (callable == null) throw new NullPointerException();
1133	>	this.callable = callable;
1134	>	}
1135	>	public T getRawResult() { return result; }
1136	>	public void setRawResult(T v) { result = v; }
1137	>	public boolean exec() {
1138	>	try {
1139	>	result = callable.call();
1140	>	return true;
1141	>	} catch (Error err) {
1142	>	throw err;
1143	>	} catch (RuntimeException rex) {
1144	>	throw rex;
1145	>	} catch (Exception ex) {
1146	>	throw new RuntimeException(ex);
1147	>	}
1148	>	}
1149	>	public void run() { invoke(); }
1150	>	private static final long serialVersionUID = 2838392045355241008L;
1151	>	}
1152
1153		/**
1154	<	* Returns a new ForkJoinTask that performs the <code>run</code>
1155	<	* method of the given Runnable as its action, and returns a null
1156	<	* result upon <code>join</code>.
1154	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1155	>	* method of the given {@code Runnable} as its action, and returns
1156	>	* a null result upon {@link #join}.
1157		*
1158		* @param runnable the runnable action
1159		* @return the task
1160		*/
1161	<	public static ForkJoinTask<Void> adapt(Runnable runnable) {
1162	<	return new ForkJoinPool.AdaptedRunnable<Void>(runnable, null);
1161	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1162	>	return new AdaptedRunnable<Void>(runnable, null);
1163		}
1164
1165		/**
1166	<	* Returns a new ForkJoinTask that performs the <code>run</code>
1167	<	* method of the given Runnable as its action, and returns the
1168	<	* given result upon <code>join</code>.
1166	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1167	>	* method of the given {@code Runnable} as its action, and returns
1168	>	* the given result upon {@link #join}.
1169		*
1170		* @param runnable the runnable action
1171		* @param result the result upon completion
1172		* @return the task
1173		*/
1174		public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
1175	<	return new ForkJoinPool.AdaptedRunnable<T>(runnable, result);
1175	>	return new AdaptedRunnable<T>(runnable, result);
1176		}
1177
1178		/**
1179	<	* Returns a new ForkJoinTask that performs the <code>call</code>
1180	<	* method of the given Callable as its action, and returns its
1181	<	* result upon <code>join</code>, translating any checked
1182	<	* exceptions encountered into <code>RuntimeException<code>.
1179	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1180	>	* method of the given {@code Callable} as its action, and returns
1181	>	* its result upon {@link #join}, translating any checked exceptions
1182	>	* encountered into {@code RuntimeException}.
1183		*
1184		* @param callable the callable action
1185		* @return the task
1186		*/
1187	<	public static <T> ForkJoinTask<T> adapt(Callable<T> callable) {
1188	<	return new ForkJoinPool.AdaptedCallable<T>(callable);
1187	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1188	>	return new AdaptedCallable<T>(callable);
1189		}
1190
1191		// Serialization support
#	Line 1087 | Line 1196 | public abstract class ForkJoinTask<V> im
1196		* Save the state to a stream.
1197		*
1198		* @serialData the current run status and the exception thrown
1199	<	* during execution, or null if none
1199	>	* during execution, or {@code null} if none
1200		* @param s the stream
1201		*/
1202		private void writeObject(java.io.ObjectOutputStream s)
#	Line 1111 | Line 1220 | public abstract class ForkJoinTask<V> im
1220		setDoneExceptionally((Throwable) ex);
1221		}
1222
1223	<	// Unsafe mechanics for jsr166y 3rd party package.
1223	>	// Unsafe mechanics
1224	>
1225	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1226	>	private static final long statusOffset =
1227	>	objectFieldOffset("status", ForkJoinTask.class);
1228	>
1229	>	private static long objectFieldOffset(String field, Class<?> klazz) {
1230	>	try {
1231	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1232	>	} catch (NoSuchFieldException e) {
1233	>	// Convert Exception to corresponding Error
1234	>	NoSuchFieldError error = new NoSuchFieldError(field);
1235	>	error.initCause(e);
1236	>	throw error;
1237	>	}
1238	>	}
1239	>
1240	>	/**
1241	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1242	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
1243	>	* into a jdk.
1244	>	*
1245	>	* @return a sun.misc.Unsafe
1246	>	*/
1247		private static sun.misc.Unsafe getUnsafe() {
1248		try {
1249		return sun.misc.Unsafe.getUnsafe();
1250		} catch (SecurityException se) {
1251		try {
1252		return java.security.AccessController.doPrivileged
1253	<	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1253	>	(new java.security
1254	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1255		public sun.misc.Unsafe run() throws Exception {
1256	<	return getUnsafeByReflection();
1256	>	java.lang.reflect.Field f = sun.misc
1257	>	.Unsafe.class.getDeclaredField("theUnsafe");
1258	>	f.setAccessible(true);
1259	>	return (sun.misc.Unsafe) f.get(null);
1260		}});
1261		} catch (java.security.PrivilegedActionException e) {
1262		throw new RuntimeException("Could not initialize intrinsics",
#	Line 1128 | Line 1264 | public abstract class ForkJoinTask<V> im
1264		}
1265		}
1266		}
1131	–
1132	–	private static sun.misc.Unsafe getUnsafeByReflection()
1133	–	throws NoSuchFieldException, IllegalAccessException {
1134	–	java.lang.reflect.Field f =
1135	–	sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
1136	–	f.setAccessible(true);
1137	–	return (sun.misc.Unsafe) f.get(null);
1138	–	}
1139	–
1140	–	private static long fieldOffset(String fieldName, Class<?> klazz) {
1141	–	try {
1142	–	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName));
1143	–	} catch (NoSuchFieldException e) {
1144	–	// Convert Exception to Error
1145	–	NoSuchFieldError error = new NoSuchFieldError(fieldName);
1146	–	error.initCause(e);
1147	–	throw error;
1148	–	}
1149	–	}
1150	–
1151	–	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1152	–	private static final long statusOffset =
1153	–	fieldOffset("status", ForkJoinTask.class);
1154	–
1267		}

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