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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 1.31 by jsr166, Sun Aug 2 22:58:50 2009 UTC

#	Line 16 | Line 16 | import java.util.Map;
16		import java.util.WeakHashMap;
17
18		/**
19	<	* Abstract base class for tasks that run within a {@link
20	<	* ForkJoinPool}.  A ForkJoinTask is a thread-like entity that is much
19	>	* Abstract base class for tasks that run within a {@link ForkJoinPool}.
20	>	* A {@code ForkJoinTask} is a thread-like entity that is much
21		* lighter weight than a normal thread.  Huge numbers of tasks and
22		* subtasks may be hosted by a small number of actual threads in a
23		* ForkJoinPool, at the price of some usage limitations.
24		*
25	<	* <p> A "main" ForkJoinTask begins execution when submitted to a
26	<	* {@link ForkJoinPool}. Once started, it will usually in turn start
27	<	* other subtasks.  As indicated by the name of this class, many
28	<	* programs using ForkJoinTasks employ only methods {@code fork}
29	<	* and {@code join}, or derivatives such as
30	<	* {@code invokeAll}.  However, this class also provides a number
31	<	* of other methods that can come into play in advanced usages, as
32	<	* well as extension mechanics that allow support of new forms of
33	<	* fork/join processing.
25	>	* <p>A "main" {@code ForkJoinTask} begins execution when submitted
26	>	* to a {@link ForkJoinPool}.  Once started, it will usually in turn
27	>	* start other subtasks.  As indicated by the name of this class,
28	>	* many programs using {@code ForkJoinTask} employ only methods
29	>	* {@link #fork} and {@link #join}, or derivatives such as {@link
30	>	* #invokeAll}.  However, this class also provides a number of other
31	>	* methods that can come into play in advanced usages, as well as
32	>	* extension mechanics that allow support of new forms of fork/join
33	>	* processing.
34		*
35	<	* <p>A ForkJoinTask is a lightweight form of {@link Future}.  The
36	<	* efficiency of ForkJoinTasks stems from a set of restrictions (that
37	<	* are only partially statically enforceable) reflecting their
38	<	* intended use as computational tasks calculating pure functions or
39	<	* operating on purely isolated objects.  The primary coordination
40	<	* mechanisms are {@link #fork}, that arranges asynchronous execution,
41	<	* and {@link #join}, that doesn't proceed until the task's result has
42	<	* been computed.  Computations should avoid {@code synchronized}
43	<	* methods or blocks, and should minimize other blocking
44	<	* synchronization apart from joining other tasks or using
45	<	* synchronizers such as Phasers that are advertised to cooperate with
46	<	* fork/join scheduling. Tasks should also not perform blocking IO,
47	<	* and should ideally access variables that are completely independent
48	<	* of those accessed by other running tasks. Minor breaches of these
49	<	* restrictions, for example using shared output streams, may be
50	<	* tolerable in practice, but frequent use may result in poor
51	<	* performance, and the potential to indefinitely stall if the number
52	<	* of threads not waiting for IO or other external synchronization
53	<	* becomes exhausted. This usage restriction is in part enforced by
54	<	* not permitting checked exceptions such as {@code IOExceptions}
55	<	* to be thrown. However, computations may still encounter unchecked
56	<	* exceptions, that are rethrown to callers attempting join
57	<	* them. These exceptions may additionally include
58	<	* RejectedExecutionExceptions stemming from internal resource
59	<	* exhaustion such as failure to allocate internal task queues.
35	>	* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
36	>	* The efficiency of {@code ForkJoinTask}s stems from a set of
37	>	* restrictions (that are only partially statically enforceable)
38	>	* reflecting their intended use as computational tasks calculating
39	>	* pure functions or operating on purely isolated objects.  The
40	>	* primary coordination mechanisms are {@link #fork}, that arranges
41	>	* asynchronous execution, and {@link #join}, that doesn't proceed
42	>	* until the task's result has been computed.  Computations should
43	>	* avoid {@code synchronized} methods or blocks, and should minimize
44	>	* other blocking synchronization apart from joining other tasks or
45	>	* using synchronizers such as Phasers that are advertised to
46	>	* cooperate with fork/join scheduling. Tasks should also not perform
47	>	* blocking IO, and should ideally access variables that are
48	>	* completely independent of those accessed by other running
49	>	* tasks. Minor breaches of these restrictions, for example using
50	>	* shared output streams, may be tolerable in practice, but frequent
51	>	* use may result in poor performance, and the potential to
52	>	* indefinitely stall if the number of threads not waiting for IO or
53	>	* other external synchronization becomes exhausted. This usage
54	>	* restriction is in part enforced by not permitting checked
55	>	* exceptions such as {@code IOExceptions} to be thrown. However,
56	>	* computations may still encounter unchecked exceptions, that are
57	>	* rethrown to callers attempting join them. These exceptions may
58	>	* additionally include RejectedExecutionExceptions stemming from
59	>	* internal resource exhaustion such as failure to allocate internal
60	>	* task queues.
61		*
62		* <p>The primary method for awaiting completion and extracting
63		* results of a task is {@link #join}, but there are several variants:
#	Line 75 | Line 76 | import java.util.WeakHashMap;
76		* performs the most common form of parallel invocation: forking a set
77		* of tasks and joining them all.
78		*
79	<	* <p> The ForkJoinTask class is not usually directly subclassed.
79	>	* <p>The ForkJoinTask class is not usually directly subclassed.
80		* Instead, you subclass one of the abstract classes that support a
81	<	* particular style of fork/join processing.  Normally, a concrete
81	>	* particular style of fork/join processing, typically {@link
82	>	* RecursiveAction} for computations that do not return results, or
83	>	* {@link RecursiveTask} for those that do.  Normally, a concrete
84		* ForkJoinTask subclass declares fields comprising its parameters,
85		* established in a constructor, and then defines a {@code compute}
86		* method that somehow uses the control methods supplied by this base
#	Line 94 | Line 97 | import java.util.WeakHashMap;
97		* lightweight task scheduling framework, and so cannot be overridden.
98		* Developers creating new basic styles of fork/join processing should
99		* minimally implement {@code protected} methods
100	<	* {@code exec}, {@code setRawResult}, and
101	<	* {@code getRawResult}, while also introducing an abstract
100	>	* {@link #exec}, {@link #setRawResult}, and
101	>	* {@link #getRawResult}, while also introducing an abstract
102		* computational method that can be implemented in its subclasses,
103		* possibly relying on other {@code protected} methods provided
104		* by this class.
#	Line 107 | Line 110 | import java.util.WeakHashMap;
110		* parallelism cannot improve throughput. If too small, then memory
111		* and internal task maintenance overhead may overwhelm processing.
112		*
113	+	* <p>This class provides {@code adapt} methods for {@link
114	+	* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
115	+	* may be of use when mixing execution of ForkJoinTasks with other
116	+	* kinds of tasks. When all tasks are of this form, consider using a
117	+	* pool in {@link ForkJoinPool#setAsyncMode}.
118	+	*
119		* <p>ForkJoinTasks are {@code Serializable}, which enables them
120		* to be used in extensions such as remote execution frameworks. It is
121		* in general sensible to serialize tasks only before or after, but
#	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	>	* <p>Overloadings of this method exist for the special cases
579	>	* of one to four arguments.
580		*
581	<	* @param tasks the array of tasks
581	>	* @param tasks the tasks
582		* @throws NullPointerException if tasks or any element are null
583		* @throws RuntimeException or Error if any task did so
584		*/
#	Line 597 | Line 616 | public abstract class ForkJoinTask<V> im
616		}
617
618		/**
619	<	* Forks all tasks in the collection, returning when
620	<	* {@code isDone} holds for all of them. If any task
621	<	* encounters an exception, others may be cancelled.  This method
622	<	* may be invoked only from within ForkJoinTask computations (as
623	<	* may be determined using method {@link
624	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
625	<	* in exceptions or errors, possibly including ClassCastException.
619	>	* Forks all tasks in the collection, returning when {@code
620	>	* isDone} holds for each task or an exception is encountered.
621	>	* If any task encounters an exception, others may be, but are
622	>	* not guaranteed to be, cancelled.
623	>	*
624	>	* <p>This method may be invoked only from within {@code
625	>	* ForkJoinTask} computations (as may be determined using method
626	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
627	>	* result in exceptions or errors, possibly including {@code
628	>	* ClassCastException}.
629		*
630		* @param tasks the collection of tasks
631		* @return the tasks argument, to simplify usage
#	Line 652 | Line 674 | public abstract class ForkJoinTask<V> im
674		}
675
676		/**
677	<	* Returns true if the computation performed by this task has
678	<	* completed (or has been cancelled).
677	>	* Returns {@code true} if the computation performed by this task
678	>	* has completed (or has been cancelled).
679		*
680	<	* @return true if this computation has completed
680	>	* @return {@code true} if this computation has completed
681		*/
682		public final boolean isDone() {
683		return status < 0;
684		}
685
686		/**
687	<	* Returns true if this task was cancelled.
687	>	* Returns {@code true} if this task was cancelled.
688		*
689	<	* @return true if this task was cancelled
689	>	* @return {@code true} if this task was cancelled
690		*/
691		public final boolean isCancelled() {
692		return (status & COMPLETION_MASK) == CANCELLED;
#	Line 673 | Line 695 | public abstract class ForkJoinTask<V> im
695		/**
696		* Asserts that the results of this task's computation will not be
697		* used. If a cancellation occurs before attempting to execute this
698	<	* task, then execution will be suppressed, {@code isCancelled}
699	<	* will report true, and {@code join} will result in a
698	>	* task, execution will be suppressed, {@link #isCancelled}
699	>	* will report true, and {@link #join} will result in a
700		* {@code CancellationException} being thrown. Otherwise, when
701		* cancellation races with completion, there are no guarantees
702	<	* about whether {@code isCancelled} will report true, whether
703	<	* {@code join} will return normally or via an exception, or
704	<	* whether these behaviors will remain consistent upon repeated
702	>	* about whether {@code isCancelled} will report {@code true},
703	>	* whether {@code join} will return normally or via an exception,
704	>	* or whether these behaviors will remain consistent upon repeated
705		* invocation.
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 {@code completeExceptionally}.
714	>	* invoke {@link #completeExceptionally}.
715		*
716		* @param mayInterruptIfRunning this value is ignored in the
717		* default implementation because tasks are not in general
718		* cancelled via interruption
719		*
720	<	* @return true if this task is now cancelled
720	>	* @return {@code true} if this task is now cancelled
721		*/
722		public boolean cancel(boolean mayInterruptIfRunning) {
723		setCompletion(CANCELLED);
#	Line 703 | Line 725 | public abstract class ForkJoinTask<V> im
725		}
726
727		/**
728	<	* Returns true if this task threw an exception or was cancelled.
728	>	* Returns {@code true} if this task threw an exception or was cancelled.
729		*
730	<	* @return true if this task threw an exception or was cancelled
730	>	* @return {@code true} if this task threw an exception or was cancelled
731		*/
732		public final boolean isCompletedAbnormally() {
733		return (status & COMPLETION_MASK) < NORMAL;
#	Line 713 | Line 735 | public abstract class ForkJoinTask<V> im
735
736		/**
737		* Returns the exception thrown by the base computation, or a
738	<	* CancellationException if cancelled, or null if none or if the
739	<	* method has not yet completed.
738	>	* {@code CancellationException} if cancelled, or {@code null} if
739	>	* none or if the method has not yet completed.
740		*
741	<	* @return the exception, or null if none
741	>	* @return the exception, or {@code null} if none
742		*/
743		public final Throwable getException() {
744		int s = status & COMPLETION_MASK;
#	Line 733 | Line 755 | public abstract class ForkJoinTask<V> im
755		* {@code join} and related operations. This method may be used
756		* to induce exceptions in asynchronous tasks, or to force
757		* completion of tasks that would not otherwise complete.  Its use
758	<	* in other situations is likely to be wrong.  This method is
758	>	* in other situations is discouraged.  This method is
759		* overridable, but overridden versions must invoke {@code super}
760		* implementation to maintain guarantees.
761		*
#	Line 753 | Line 775 | public abstract class ForkJoinTask<V> im
775		* operations. This method may be used to provide results for
776		* asynchronous tasks, or to provide alternative handling for
777		* tasks that would not otherwise complete normally. Its use in
778	<	* other situations is likely to be wrong. This method is
778	>	* other situations is discouraged. This method is
779		* overridable, but overridden versions must invoke {@code super}
780		* implementation to maintain guarantees.
781		*
#	Line 778 | Line 800 | public abstract class ForkJoinTask<V> im
800
801		public final V get(long timeout, TimeUnit unit)
802		throws InterruptedException, ExecutionException, TimeoutException {
803	+	long nanos = unit.toNanos(timeout);
804		ForkJoinWorkerThread w = getWorker();
805		if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
806	<	awaitDone(w, unit.toNanos(timeout));
806	>	awaitDone(w, nanos);
807		return reportTimedFutureResult();
808		}
809
#	Line 791 | Line 814 | public abstract class ForkJoinTask<V> im
814		* there are no potential dependencies between continuation of the
815		* current task and that of any other task that might be executed
816		* while helping. (This usually holds for pure divide-and-conquer
817	<	* tasks). This method may be invoked only from within
818	<	* ForkJoinTask computations (as may be determined using method
819	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
820	<	* result in exceptions or errors, possibly including
821	<	* ClassCastException.
817	>	* tasks).
818	>	*
819	>	* <p>This method may be invoked only from within {@code
820	>	* ForkJoinTask} computations (as may be determined using method
821	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
822	>	* result in exceptions or errors, possibly including {@code
823	>	* ClassCastException}.
824		*
825		* @return the computed result
826		*/
#	Line 807 | Line 832 | public abstract class ForkJoinTask<V> im
832		}
833
834		/**
835	<	* Possibly executes other tasks until this task is ready.  This
836	<	* method may be invoked only from within ForkJoinTask
837	<	* computations (as may be determined using method {@link
838	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
839	<	* in exceptions or errors, possibly including ClassCastException.
835	>	* Possibly executes other tasks until this task is ready.
836	>	*
837	>	* <p>This method may be invoked only from within {@code
838	>	* ForkJoinTask} computations (as may be determined using method
839	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
840	>	* result in exceptions or errors, possibly including {@code
841	>	* ClassCastException}.
842		*/
843		public final void quietlyHelpJoin() {
844		if (status >= 0) {
#	Line 853 | Line 880 | public abstract class ForkJoinTask<V> im
880		* {@link ForkJoinPool#isQuiescent}. This method may be of use in
881		* designs in which many tasks are forked, but none are explicitly
882		* joined, instead executing them until all are processed.
883	+	*
884	+	* <p>This method may be invoked only from within {@code
885	+	* ForkJoinTask} computations (as may be determined using method
886	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
887	+	* result in exceptions or errors, possibly including {@code
888	+	* ClassCastException}.
889		*/
890		public static void helpQuiesce() {
891		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 865 | Line 898 | public abstract class ForkJoinTask<V> im
898		* this task, but only if reuse occurs when this task has either
899		* never been forked, or has been forked, then completed and all
900		* outstanding joins of this task have also completed. Effects
901	<	* under any other usage conditions are not guaranteed, and are
902	<	* almost surely wrong. This method may be useful when executing
901	>	* under any other usage conditions are not guaranteed.
902	>	* This method may be useful when executing
903		* pre-constructed trees of subtasks in loops.
904		*/
905		public void reinitialize() {
#	Line 879 | Line 912 | public abstract class ForkJoinTask<V> im
912		* Returns the pool hosting the current task execution, or null
913		* if this task is executing outside of any ForkJoinPool.
914		*
915	<	* @return the pool, or null if none
915	>	* @see #inForkJoinPool
916	>	* @return the pool, or {@code null} if none
917		*/
918		public static ForkJoinPool getPool() {
919		Thread t = Thread.currentThread();
#	Line 904 | Line 938 | public abstract class ForkJoinTask<V> im
938		* by the current thread, and has not commenced executing in
939		* another thread.  This method may be useful when arranging
940		* alternative local processing of tasks that could have been, but
941	<	* were not, stolen. This method may be invoked only from within
942	<	* ForkJoinTask computations (as may be determined using method
943	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
944	<	* result in exceptions or errors, possibly including
945	<	* ClassCastException.
941	>	* were not, stolen.
942	>	*
943	>	* <p>This method may be invoked only from within {@code
944	>	* ForkJoinTask} computations (as may be determined using method
945	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
946	>	* result in exceptions or errors, possibly including {@code
947	>	* ClassCastException}.
948		*
949	<	* @return true if unforked
949	>	* @return {@code true} if unforked
950		*/
951		public boolean tryUnfork() {
952		return ((ForkJoinWorkerThread) Thread.currentThread())
#	Line 923 | Line 959 | public abstract class ForkJoinTask<V> im
959		* value may be useful for heuristic decisions about whether to
960		* fork other tasks.
961		*
962	+	* <p>This method may be invoked only from within {@code
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 {@code
966	+	* ClassCastException}.
967	+	*
968		* @return the number of tasks
969		*/
970		public static int getQueuedTaskCount() {
#	Line 940 | Line 982 | public abstract class ForkJoinTask<V> im
982		* tasks, and to process computations locally if this threshold is
983		* exceeded.
984		*
985	+	* <p>This method may be invoked only from within {@code
986	+	* ForkJoinTask} computations (as may be determined using method
987	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
988	+	* result in exceptions or errors, possibly including {@code
989	+	* ClassCastException}.
990	+	*
991		* @return the surplus number of tasks, which may be negative
992		*/
993		public static int getSurplusQueuedTaskCount() {
#	Line 950 | Line 998 | public abstract class ForkJoinTask<V> im
998		// Extension methods
999
1000		/**
1001	<	* Returns the result that would be returned by {@code join},
1002	<	* even if this task completed abnormally, or null if this task is
1003	<	* not known to have been completed.  This method is designed to
1004	<	* aid debugging, as well as to support extensions. Its use in any
1005	<	* other context is discouraged.
1001	>	* Returns the result that would be returned by {@link #join}, even
1002	>	* if this task completed abnormally, or {@code null} if this task
1003	>	* is not known to have been completed.  This method is designed
1004	>	* to aid debugging, as well as to support extensions. Its use in
1005	>	* any other context is discouraged.
1006		*
1007	<	* @return the result, or null if not completed
1007	>	* @return the result, or {@code null} if not completed
1008		*/
1009		public abstract V getRawResult();
1010
#	Line 975 | Line 1023 | public abstract class ForkJoinTask<V> im
1023		* called otherwise. The return value controls whether this task
1024		* is considered to be done normally. It may return false in
1025		* asynchronous actions that require explicit invocations of
1026	<	* {@code complete} to become joinable. It may throw exceptions
1026	>	* {@link #complete} to become joinable. It may throw exceptions
1027		* to indicate abnormal exit.
1028		*
1029	<	* @return true if completed normally
1029	>	* @return {@code true} if completed normally
1030		* @throws Error or RuntimeException if encountered during computation
1031		*/
1032		protected abstract boolean exec();
1033
1034		/**
1035	<	* Returns, but does not unschedule or execute, the task queued by
1036	<	* the current thread but not yet executed, if one is
1035	>	* Returns, but does not unschedule or execute, a task queued by
1036	>	* the current thread but not yet executed, if one is immediately
1037		* available. There is no guarantee that this task will actually
1038	<	* be polled or executed next.  This method is designed primarily
1039	<	* to support extensions, and is unlikely to be useful otherwise.
1040	<	* This method may be invoked only from within ForkJoinTask
1041	<	* computations (as may be determined using method {@link
1042	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
1043	<	* in exceptions or errors, possibly including ClassCastException.
1038	>	* be polled or executed next. Conversely, this method may return
1039	>	* null even if a task exists but cannot be accessed without
1040	>	* contention with other threads.  This method is designed
1041	>	* primarily to support extensions, and is unlikely to be useful
1042	>	* otherwise.
1043	>	*
1044	>	* <p>This method may be invoked only from within {@code
1045	>	* ForkJoinTask} computations (as may be determined using method
1046	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1047	>	* result in exceptions or errors, possibly including {@code
1048	>	* ClassCastException}.
1049		*
1050	<	* @return the next task, or null if none are available
1050	>	* @return the next task, or {@code null} if none are available
1051		*/
1052		protected static ForkJoinTask<?> peekNextLocalTask() {
1053		return ((ForkJoinWorkerThread) Thread.currentThread())
#	Line 1005 | Line 1058 | public abstract class ForkJoinTask<V> im
1058		* Unschedules and returns, without executing, the next task
1059		* queued by the current thread but not yet executed.  This method
1060		* is designed primarily to support extensions, and is unlikely to
1061	<	* 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.
1061	>	* be useful otherwise.
1062		*
1063	<	* @return the next task, or null if none are available
1063	>	* <p>This method may be invoked only from within {@code
1064	>	* ForkJoinTask} computations (as may be determined using method
1065	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1066	>	* result in exceptions or errors, possibly including {@code
1067	>	* ClassCastException}.
1068	>	*
1069	>	* @return the next task, or {@code null} if none are available
1070		*/
1071		protected static ForkJoinTask<?> pollNextLocalTask() {
1072		return ((ForkJoinWorkerThread) Thread.currentThread())
#	Line 1026 | Line 1081 | public abstract class ForkJoinTask<V> im
1081		* {@code null} result does not necessarily imply quiescence
1082		* of the pool this task is operating in.  This method is designed
1083		* primarily to support extensions, and is unlikely to be useful
1084	<	* otherwise.  This method may be invoked only from within
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
1088	<	* ClassCastException.
1084	>	* otherwise.
1085	>	*
1086	>	* <p>This method may be invoked only from within {@code
1087	>	* ForkJoinTask} computations (as may be determined using method
1088	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1089	>	* result in exceptions or errors, possibly including {@code
1090	>	* ClassCastException}.
1091		*
1092	<	* @return a task, or null if none are available
1092	>	* @return a task, or {@code null} if none are available
1093		*/
1094		protected static ForkJoinTask<?> pollTask() {
1095		return ((ForkJoinWorkerThread) Thread.currentThread())
1096		.pollTask();
1097		}
1098
1099	<	// adaptors
1099	>	/**
1100	>	* Adaptor for Runnables. This implements RunnableFuture
1101	>	* to be compliant with AbstractExecutorService constraints
1102	>	* when used in ForkJoinPool.
1103	>	*/
1104	>	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1105	>	implements RunnableFuture<T> {
1106	>	final Runnable runnable;
1107	>	final T resultOnCompletion;
1108	>	T result;
1109	>	AdaptedRunnable(Runnable runnable, T result) {
1110	>	if (runnable == null) throw new NullPointerException();
1111	>	this.runnable = runnable;
1112	>	this.resultOnCompletion = result;
1113	>	}
1114	>	public T getRawResult() { return result; }
1115	>	public void setRawResult(T v) { result = v; }
1116	>	public boolean exec() {
1117	>	runnable.run();
1118	>	result = resultOnCompletion;
1119	>	return true;
1120	>	}
1121	>	public void run() { invoke(); }
1122	>	private static final long serialVersionUID = 5232453952276885070L;
1123	>	}
1124
1125		/**
1126	<	* Returns a new ForkJoinTask that performs the <code>run</code>
1127	<	* method of the given Runnable as its action, and returns a null
1128	<	* result upon <code>join</code>.
1126	>	* Adaptor for Callables
1127	>	*/
1128	>	static final class AdaptedCallable<T> extends ForkJoinTask<T>
1129	>	implements RunnableFuture<T> {
1130	>	final Callable<? extends T> callable;
1131	>	T result;
1132	>	AdaptedCallable(Callable<? extends T> callable) {
1133	>	if (callable == null) throw new NullPointerException();
1134	>	this.callable = callable;
1135	>	}
1136	>	public T getRawResult() { return result; }
1137	>	public void setRawResult(T v) { result = v; }
1138	>	public boolean exec() {
1139	>	try {
1140	>	result = callable.call();
1141	>	return true;
1142	>	} catch (Error err) {
1143	>	throw err;
1144	>	} catch (RuntimeException rex) {
1145	>	throw rex;
1146	>	} catch (Exception ex) {
1147	>	throw new RuntimeException(ex);
1148	>	}
1149	>	}
1150	>	public void run() { invoke(); }
1151	>	private static final long serialVersionUID = 2838392045355241008L;
1152	>	}
1153	>
1154	>	/**
1155	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1156	>	* method of the given {@code Runnable} as its action, and returns
1157	>	* a null result upon {@link #join}.
1158		*
1159		* @param runnable the runnable action
1160		* @return the task
1161		*/
1162	<	public static ForkJoinTask<Void> adapt(Runnable runnable) {
1163	<	return new ForkJoinPool.AdaptedRunnable<Void>(runnable, null);
1162	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1163	>	return new AdaptedRunnable<Void>(runnable, null);
1164		}
1165
1166		/**
1167	<	* Returns a new ForkJoinTask that performs the <code>run</code>
1168	<	* method of the given Runnable as its action, and returns the
1169	<	* given result upon <code>join</code>.
1167	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1168	>	* method of the given {@code Runnable} as its action, and returns
1169	>	* the given result upon {@link #join}.
1170		*
1171		* @param runnable the runnable action
1172		* @param result the result upon completion
1173		* @return the task
1174		*/
1175		public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
1176	<	return new ForkJoinPool.AdaptedRunnable<T>(runnable, result);
1176	>	return new AdaptedRunnable<T>(runnable, result);
1177		}
1178
1179		/**
1180	<	* Returns a new ForkJoinTask that performs the <code>call</code>
1181	<	* method of the given Callable as its action, and returns its
1182	<	* result upon <code>join</code>, translating any checked
1183	<	* exceptions encountered into <code>RuntimeException<code>.
1180	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1181	>	* method of the given {@code Callable} as its action, and returns
1182	>	* its result upon {@link #join}, translating any checked exceptions
1183	>	* encountered into {@code RuntimeException}.
1184		*
1185		* @param callable the callable action
1186		* @return the task
1187		*/
1188	<	public static <T> ForkJoinTask<T> adapt(Callable<T> callable) {
1189	<	return new ForkJoinPool.AdaptedCallable<T>(callable);
1188	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1189	>	return new AdaptedCallable<T>(callable);
1190		}
1191
1192		// Serialization support
#	Line 1087 | Line 1197 | public abstract class ForkJoinTask<V> im
1197		* Save the state to a stream.
1198		*
1199		* @serialData the current run status and the exception thrown
1200	<	* during execution, or null if none
1200	>	* during execution, or {@code null} if none
1201		* @param s the stream
1202		*/
1203		private void writeObject(java.io.ObjectOutputStream s)
#	Line 1111 | Line 1221 | public abstract class ForkJoinTask<V> im
1221		setDoneExceptionally((Throwable) ex);
1222		}
1223
1224	<	// Unsafe mechanics for jsr166y 3rd party package.
1224	>	// Unsafe mechanics
1225	>
1226	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1227	>	private static final long statusOffset =
1228	>	objectFieldOffset("status", ForkJoinTask.class);
1229	>
1230	>	private static long objectFieldOffset(String field, Class<?> klazz) {
1231	>	try {
1232	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1233	>	} catch (NoSuchFieldException e) {
1234	>	// Convert Exception to corresponding Error
1235	>	NoSuchFieldError error = new NoSuchFieldError(field);
1236	>	error.initCause(e);
1237	>	throw error;
1238	>	}
1239	>	}
1240	>
1241	>	/**
1242	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1243	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
1244	>	* into a jdk.
1245	>	*
1246	>	* @return a sun.misc.Unsafe
1247	>	*/
1248		private static sun.misc.Unsafe getUnsafe() {
1249		try {
1250		return sun.misc.Unsafe.getUnsafe();
1251		} catch (SecurityException se) {
1252		try {
1253		return java.security.AccessController.doPrivileged
1254	<	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1254	>	(new java.security
1255	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1256		public sun.misc.Unsafe run() throws Exception {
1257	<	return getUnsafeByReflection();
1257	>	java.lang.reflect.Field f = sun.misc
1258	>	.Unsafe.class.getDeclaredField("theUnsafe");
1259	>	f.setAccessible(true);
1260	>	return (sun.misc.Unsafe) f.get(null);
1261		}});
1262		} catch (java.security.PrivilegedActionException e) {
1263		throw new RuntimeException("Could not initialize intrinsics",
#	Line 1128 | Line 1265 | public abstract class ForkJoinTask<V> im
1265		}
1266		}
1267		}
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	–
1268		}

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