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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.3 by dl, Wed Jan 7 19:12:36 2009 UTC vs.
Revision 1.10 by jsr166, Tue Jul 21 00:15:13 2009 UTC

#	Line 18 | Line 18 | import java.lang.reflect.*;
18		* lighter weight than a normal thread.  Huge numbers of tasks and
19		* subtasks may be hosted by a small number of actual threads in a
20		* ForkJoinPool, at the price of some usage limitations.
21	<	*
21	>	*
22		* <p> A "main" ForkJoinTask begins execution when submitted to a
23		* {@link ForkJoinPool}. Once started, it will usually in turn start
24		* other subtasks.  As indicated by the name of this class, many
25	<	* programs using ForkJoinTasks employ only methods <code>fork</code>
26	<	* and <code>join</code>, or derivatives such as
27	<	* <code>invokeAll</code>.  However, this class also provides a number
25	>	* programs using ForkJoinTasks employ only methods {@code fork}
26	>	* and {@code join}, or derivatives such as
27	>	* {@code invokeAll}.  However, this class also provides a number
28		* of other methods that can come into play in advanced usages, as
29		* well as extension mechanics that allow support of new forms of
30		* fork/join processing.
31	<	*
31	>	*
32		* <p>A ForkJoinTask is a lightweight form of {@link Future}.  The
33		* efficiency of ForkJoinTasks stems from a set of restrictions (that
34		* are only partially statically enforceable) reflecting their
#	Line 36 | Line 36 | import java.lang.reflect.*;
36		* operating on purely isolated objects.  The primary coordination
37		* mechanisms are {@link #fork}, that arranges asynchronous execution,
38		* and {@link #join}, that doesn't proceed until the task's result has
39	<	* been computed.  Computations should avoid <code>synchronized</code>
39	>	* been computed.  Computations should avoid {@code synchronized}
40		* methods or blocks, and should minimize other blocking
41		* synchronization apart from joining other tasks or using
42		* synchronizers such as Phasers that are advertised to cooperate with
#	Line 48 | Line 48 | import java.lang.reflect.*;
48		* performance, and the potential to indefinitely stall if the number
49		* of threads not waiting for IO or other external synchronization
50		* becomes exhausted. This usage restriction is in part enforced by
51	<	* not permitting checked exceptions such as <code>IOExceptions</code>
51	>	* not permitting checked exceptions such as {@code IOExceptions}
52		* to be thrown. However, computations may still encounter unchecked
53		* exceptions, that are rethrown to callers attempting join
54		* them. These exceptions may additionally include
#	Line 58 | Line 58 | import java.lang.reflect.*;
58		* <p>The primary method for awaiting completion and extracting
59		* results of a task is {@link #join}, but there are several variants:
60		* The {@link Future#get} methods support interruptible and/or timed
61	<	* waits for completion and report results using <code>Future</code>
61	>	* waits for completion and report results using {@code Future}
62		* conventions. Method {@link #helpJoin} enables callers to actively
63		* execute other tasks while awaiting joins, which is sometimes more
64		* efficient but only applies when all subtasks are known to be
65		* strictly tree-structured. Method {@link #invoke} is semantically
66	<	* equivalent to <code>fork(); join()</code> but always attempts to
66	>	* equivalent to {@code fork(); join()} but always attempts to
67		* begin execution in the current thread. The "<em>quiet</em>" forms
68		* of these methods do not extract results or report exceptions. These
69		* may be useful when a set of tasks are being executed, and you need
70		* to delay processing of results or exceptions until all complete.
71	<	* Method <code>invokeAll</code> (available in multiple versions)
71	>	* Method {@code invokeAll} (available in multiple versions)
72		* performs the most common form of parallel invocation: forking a set
73		* of tasks and joining them all.
74		*
#	Line 76 | Line 76 | import java.lang.reflect.*;
76		* Instead, you subclass one of the abstract classes that support a
77		* particular style of fork/join processing.  Normally, a concrete
78		* ForkJoinTask subclass declares fields comprising its parameters,
79	<	* established in a constructor, and then defines a <code>compute</code>
79	>	* established in a constructor, and then defines a {@code compute}
80		* method that somehow uses the control methods supplied by this base
81	<	* class. While these methods have <code>public</code> access (to allow
81	>	* class. While these methods have {@code public} access (to allow
82		* instances of different task subclasses to call each others
83		* methods), some of them may only be called from within other
84		* ForkJoinTasks. Attempts to invoke them in other contexts result in
85	<	* exceptions or errors including ClassCastException.
85	>	* exceptions or errors possibly including ClassCastException.
86		*
87	<	* <p>Most base support methods are <code>final</code> because their
87	>	* <p>Most base support methods are {@code final} because their
88		* implementations are intrinsically tied to the underlying
89		* lightweight task scheduling framework, and so cannot be overridden.
90		* Developers creating new basic styles of fork/join processing should
91	<	* minimally implement <code>protected</code> methods
92	<	* <code>exec</code>, <code>setRawResult</code>, and
93	<	* <code>getRawResult</code>, while also introducing an abstract
91	>	* minimally implement {@code protected} methods
92	>	* {@code exec}, {@code setRawResult}, and
93	>	* {@code getRawResult}, while also introducing an abstract
94		* computational method that can be implemented in its subclasses,
95	<	* possibly relying on other <code>protected</code> methods provided
95	>	* possibly relying on other {@code protected} methods provided
96		* by this class.
97		*
98		* <p>ForkJoinTasks should perform relatively small amounts of
99	<	* computations, othewise splitting into smaller tasks. As a very
99	>	* computations, otherwise splitting into smaller tasks. As a very
100		* rough rule of thumb, a task should perform more than 100 and less
101		* than 10000 basic computational steps. If tasks are too big, then
102	<	* parellelism cannot improve throughput. If too small, then memory
102	>	* parallelism cannot improve throughput. If too small, then memory
103		* and internal task maintenance overhead may overwhelm processing.
104		*
105	<	* <p>ForkJoinTasks are <code>Serializable</code>, which enables them
105	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them
106		* to be used in extensions such as remote execution frameworks. It is
107		* in general sensible to serialize tasks only before or after, but
108		* not during execution. Serialization is not relied on during
#	Line 128 | Line 128 | public abstract class ForkJoinTask<V> im
128		* currently unused. Also value 0x80000000 is available as spare
129		* completion value.
130		*/
131	<	volatile int status; // accessed directy by pool and workers
131	>	volatile int status; // accessed directly by pool and workers
132
133		static final int COMPLETION_MASK      = 0xe0000000;
134		static final int NORMAL               = 0xe0000000; // == mask
#	Line 141 | Line 141 | public abstract class ForkJoinTask<V> im
141		/**
142		* Table of exceptions thrown by tasks, to enable reporting by
143		* callers. Because exceptions are rare, we don't directly keep
144	<	* them with task objects, but instead us a weak ref table.  Note
144	>	* them with task objects, but instead use a weak ref table.  Note
145		* that cancellation exceptions don't appear in the table, but are
146		* instead recorded as status values.
147	<	* Todo: Use ConcurrentReferenceHashMap
147	>	* TODO: Use ConcurrentReferenceHashMap
148		*/
149		static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
150		Collections.synchronizedMap
#	Line 153 | Line 153 | public abstract class ForkJoinTask<V> im
153		// within-package utilities
154
155		/**
156	<	* Get current worker thread, or null if not a worker thread
156	>	* Gets current worker thread, or null if not a worker thread.
157		*/
158		static ForkJoinWorkerThread getWorker() {
159		Thread t = Thread.currentThread();
#	Line 176 | Line 176 | public abstract class ForkJoinTask<V> im
176		// Setting completion status
177
178		/**
179	<	* Mark completion and wake up threads waiting to join this task.
179	>	* Marks completion and wakes up threads waiting to join this task.
180	>	*
181		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
182		*/
183		final void setCompletion(int completion) {
#	Line 255 | Line 256 | public abstract class ForkJoinTask<V> im
256		/**
257		* Sets status to indicate there is joiner, then waits for join,
258		* surrounded with pool notifications.
259	+	*
260		* @return status upon exit
261		*/
262		private int awaitDone(ForkJoinWorkerThread w, boolean maintainParallelism) {
#	Line 297 | Line 299 | public abstract class ForkJoinTask<V> im
299		}
300
301		/**
302	<	* Notify pool that thread is unblocked. Called by signalled
302	>	* Notifies pool that thread is unblocked. Called by signalled
303		* threads when woken by non-FJ threads (which is atypical).
304		*/
305		private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
#	Line 308 | Line 310 | public abstract class ForkJoinTask<V> im
310		}
311
312		/**
313	<	* Notify pool to adjust counts on cancelled or timed out wait
313	>	* Notifies pool to adjust counts on cancelled or timed out wait.
314		*/
315		private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
316		if (pool != null) {
#	Line 323 | Line 325 | public abstract class ForkJoinTask<V> im
325		}
326
327		/**
328	<	* Handle interruptions during waits.
328	>	* Handles interruptions during waits.
329		*/
330		private void onInterruptedWait() {
331		ForkJoinWorkerThread w = getWorker();
#	Line 342 | Line 344 | public abstract class ForkJoinTask<V> im
344		}
345
346		/**
347	<	* Throws the exception associated with status s;
347	>	* Throws the exception associated with status s.
348	>	*
349		* @throws the exception
350		*/
351		private void reportException(int s) {
#	Line 355 | Line 358 | public abstract class ForkJoinTask<V> im
358		}
359
360		/**
361	<	* Returns result or throws exception using j.u.c.Future conventions
361	>	* Returns result or throws exception using j.u.c.Future conventions.
362		* Only call when isDone known to be true.
363		*/
364		private V reportFutureResult()
#	Line 375 | Line 378 | public abstract class ForkJoinTask<V> im
378
379		/**
380		* Returns result or throws exception using j.u.c.Future conventions
381	<	* with timeouts
381	>	* with timeouts.
382		*/
383		private V reportTimedFutureResult()
384		throws InterruptedException, ExecutionException, TimeoutException {
#	Line 396 | Line 399 | public abstract class ForkJoinTask<V> im
399
400		/**
401		* Calls exec, recording completion, and rethrowing exception if
402	<	* encountered. Caller should normally check status before calling
402	>	* encountered. Caller should normally check status before calling.
403	>	*
404		* @return true if completed normally
405		*/
406		private boolean tryExec() {
#	Line 414 | Line 418 | public abstract class ForkJoinTask<V> im
418
419		/**
420		* Main execution method used by worker threads. Invokes
421	<	* base computation unless already complete
421	>	* base computation unless already complete.
422		*/
423		final void quietlyExec() {
424		if (status >= 0) {
#	Line 430 | Line 434 | public abstract class ForkJoinTask<V> im
434		}
435
436		/**
437	<	* Calls exec, recording but not rethrowing exception
438	<	* Caller should normally check status before calling
437	>	* Calls exec(), recording but not rethrowing exception.
438	>	* Caller should normally check status before calling.
439	>	*
440		* @return true if completed normally
441		*/
442		private boolean tryQuietlyInvoke() {
#	Line 447 | Line 452 | public abstract class ForkJoinTask<V> im
452		}
453
454		/**
455	<	* Cancel, ignoring any exceptions it throws
455	>	* Cancels, ignoring any exceptions it throws.
456		*/
457		final void cancelIgnoringExceptions() {
458		try {
#	Line 475 | Line 480 | public abstract class ForkJoinTask<V> im
480		* than once unless it has completed and been reinitialized.  This
481		* method may be invoked only from within ForkJoinTask
482		* computations. Attempts to invoke in other contexts result in
483	<	* exceptions or errors including ClassCastException.
483	>	* exceptions or errors possibly including ClassCastException.
484		*/
485		public final void fork() {
486		((ForkJoinWorkerThread)(Thread.currentThread())).pushTask(this);
#	Line 483 | Line 488 | public abstract class ForkJoinTask<V> im
488
489		/**
490		* Returns the result of the computation when it is ready.
491	<	* This method differs from <code>get</code> in that abnormal
491	>	* This method differs from {@code get} in that abnormal
492		* completion results in RuntimeExceptions or Errors, not
493		* ExecutionExceptions.
494		*
#	Line 499 | Line 504 | public abstract class ForkJoinTask<V> im
504		/**
505		* Commences performing this task, awaits its completion if
506		* necessary, and return its result.
507	+	*
508		* @throws Throwable (a RuntimeException, Error, or unchecked
509	<	* exception) if the underlying computation did so.
509	>	* exception) if the underlying computation did so
510		* @return the computed result
511		*/
512		public final V invoke() {
#	Line 511 | Line 517 | public abstract class ForkJoinTask<V> im
517		}
518
519		/**
520	<	* Forks both tasks, returning when <code>isDone</code> holds for
520	>	* Forks both tasks, returning when {@code isDone} holds for
521		* both of them or an exception is encountered. This method may be
522		* invoked only from within ForkJoinTask computations. Attempts to
523		* invoke in other contexts result in exceptions or errors
524	<	* including ClassCastException.
524	>	* possibly including ClassCastException.
525	>	*
526		* @param t1 one task
527		* @param t2 the other task
528		* @throws NullPointerException if t1 or t2 are null
529	<	* @throws RuntimeException or Error if either task did so.
529	>	* @throws RuntimeException or Error if either task did so
530		*/
531		public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
532		t2.fork();
#	Line 528 | Line 535 | public abstract class ForkJoinTask<V> im
535		}
536
537		/**
538	<	* Forks the given tasks, returning when <code>isDone</code> holds
538	>	* Forks the given tasks, returning when {@code isDone} holds
539		* for all of them. If any task encounters an exception, others
540		* may be cancelled.  This method may be invoked only from within
541		* ForkJoinTask computations. Attempts to invoke in other contexts
542	<	* result in exceptions or errors including ClassCastException.
542	>	* result in exceptions or errors possibly including ClassCastException.
543	>	*
544		* @param tasks the array of tasks
545	<	* @throws NullPointerException if tasks or any element are null.
546	<	* @throws RuntimeException or Error if any task did so.
545	>	* @throws NullPointerException if tasks or any element are null
546	>	* @throws RuntimeException or Error if any task did so
547		*/
548		public static void invokeAll(ForkJoinTask<?>... tasks) {
549		Throwable ex = null;
#	Line 572 | Line 580 | public abstract class ForkJoinTask<V> im
580
581		/**
582		* Forks all tasks in the collection, returning when
583	<	* <code>isDone</code> holds for all of them. If any task
583	>	* {@code isDone} holds for all of them. If any task
584		* encounters an exception, others may be cancelled.  This method
585		* may be invoked only from within ForkJoinTask
586	<	* computations. Attempts to invoke in other contexts resul!t in
587	<	* exceptions or errors including ClassCastException.
586	>	* computations. Attempts to invoke in other contexts result in
587	>	* exceptions or errors possibly including ClassCastException.
588	>	*
589		* @param tasks the collection of tasks
590	<	* @throws NullPointerException if tasks or any element are null.
591	<	* @throws RuntimeException or Error if any task did so.
590	>	* @throws NullPointerException if tasks or any element are null
591	>	* @throws RuntimeException or Error if any task did so
592		*/
593		public static void invokeAll(Collection<? extends ForkJoinTask<?>> tasks) {
594		if (!(tasks instanceof List)) {
#	Line 623 | Line 632 | public abstract class ForkJoinTask<V> im
632		/**
633		* Returns true if the computation performed by this task has
634		* completed (or has been cancelled).
635	+	*
636		* @return true if this computation has completed
637		*/
638		public final boolean isDone() {
#	Line 631 | Line 641 | public abstract class ForkJoinTask<V> im
641
642		/**
643		* Returns true if this task was cancelled.
644	+	*
645		* @return true if this task was cancelled
646		*/
647		public final boolean isCancelled() {
#	Line 639 | Line 650 | public abstract class ForkJoinTask<V> im
650
651		/**
652		* Asserts that the results of this task's computation will not be
653	<	* used. If a cancellation occurs before atempting to execute this
654	<	* task, then execution will be suppressed, <code>isCancelled</code>
655	<	* will report true, and <code>join</code> will result in a
656	<	* <code>CancellationException</code> being thrown. Otherwise, when
653	>	* used. If a cancellation occurs before attempting to execute this
654	>	* task, then execution will be suppressed, {@code isCancelled}
655	>	* will report true, and {@code join} will result in a
656	>	* {@code CancellationException} being thrown. Otherwise, when
657		* cancellation races with completion, there are no guarantees
658	<	* about whether <code>isCancelled</code> will report true, whether
659	<	* <code>join</code> will return normally or via an exception, or
658	>	* about whether {@code isCancelled} will report true, whether
659	>	* {@code join} will return normally or via an exception, or
660		* whether these behaviors will remain consistent upon repeated
661		* invocation.
662		*
#	Line 656 | Line 667 | public abstract class ForkJoinTask<V> im
667		* <p> This method is designed to be invoked by <em>other</em>
668		* tasks. To terminate the current task, you can just return or
669		* throw an unchecked exception from its computation method, or
670	<	* invoke <code>completeExceptionally</code>.
670	>	* invoke {@code completeExceptionally}.
671		*
672		* @param mayInterruptIfRunning this value is ignored in the
673		* default implementation because tasks are not in general
#	Line 670 | Line 681 | public abstract class ForkJoinTask<V> im
681		}
682
683		/**
684	<	* Returns true if this task threw an exception or was cancelled
684	>	* Returns true if this task threw an exception or was cancelled.
685	>	*
686		* @return true if this task threw an exception or was cancelled
687		*/
688		public final boolean isCompletedAbnormally() {
#	Line 681 | Line 693 | public abstract class ForkJoinTask<V> im
693		* Returns the exception thrown by the base computation, or a
694		* CancellationException if cancelled, or null if none or if the
695		* method has not yet completed.
696	+	*
697		* @return the exception, or null if none
698		*/
699		public final Throwable getException() {
#	Line 695 | Line 708 | public abstract class ForkJoinTask<V> im
708		/**
709		* Completes this task abnormally, and if not already aborted or
710		* cancelled, causes it to throw the given exception upon
711	<	* <code>join</code> and related operations. This method may be used
711	>	* {@code join} and related operations. This method may be used
712		* to induce exceptions in asynchronous tasks, or to force
713		* completion of tasks that would not otherwise complete.  Its use
714		* in other situations is likely to be wrong.  This method is
715	<	* overridable, but overridden versions must invoke <code>super</code>
715	>	* overridable, but overridden versions must invoke {@code super}
716		* implementation to maintain guarantees.
717		*
718		* @param ex the exception to throw. If this exception is
#	Line 714 | Line 727 | public abstract class ForkJoinTask<V> im
727
728		/**
729		* Completes this task, and if not already aborted or cancelled,
730	<	* returning a <code>null</code> result upon <code>join</code> and related
730	>	* returning a {@code null} result upon {@code join} and related
731		* operations. This method may be used to provide results for
732		* asynchronous tasks, or to provide alternative handling for
733		* tasks that would not otherwise complete normally. Its use in
734		* other situations is likely to be wrong. This method is
735	<	* overridable, but overridden versions must invoke <code>super</code>
735	>	* overridable, but overridden versions must invoke {@code super}
736		* implementation to maintain guarantees.
737		*
738	<	* @param value the result value for this task.
738	>	* @param value the result value for this task
739		*/
740		public void complete(V value) {
741		try {
#	Line 752 | Line 765 | public abstract class ForkJoinTask<V> im
765		/**
766		* Possibly executes other tasks until this task is ready, then
767		* returns the result of the computation.  This method may be more
768	<	* efficient than <code>join</code>, but is only applicable when
769	<	* there are no potemtial dependencies between continuation of the
768	>	* efficient than {@code join}, but is only applicable when
769	>	* there are no potential dependencies between continuation of the
770		* current task and that of any other task that might be executed
771		* while helping. (This usually holds for pure divide-and-conquer
772		* tasks). This method may be invoked only from within
773		* ForkJoinTask computations. Attempts to invoke in other contexts
774	<	* resul!t in exceptions or errors including ClassCastException.
774	>	* result in exceptions or errors possibly including ClassCastException.
775	>	*
776		* @return the computed result
777		*/
778		public final V helpJoin() {
#	Line 771 | Line 785 | public abstract class ForkJoinTask<V> im
785		/**
786		* Possibly executes other tasks until this task is ready.  This
787		* method may be invoked only from within ForkJoinTask
788	<	* computations. Attempts to invoke in other contexts resul!t in
789	<	* exceptions or errors including ClassCastException.
788	>	* computations. Attempts to invoke in other contexts result in
789	>	* exceptions or errors possibly including ClassCastException.
790		*/
791		public final void quietlyHelpJoin() {
792		if (status >= 0) {
#	Line 822 | Line 836 | public abstract class ForkJoinTask<V> im
836
837		/**
838		* Resets the internal bookkeeping state of this task, allowing a
839	<	* subsequent <code>fork</code>. This method allows repeated reuse of
839	>	* subsequent {@code fork}. This method allows repeated reuse of
840		* this task, but only if reuse occurs when this task has either
841		* never been forked, or has been forked, then completed and all
842		* outstanding joins of this task have also completed. Effects
#	Line 839 | Line 853 | public abstract class ForkJoinTask<V> im
853		/**
854		* Returns the pool hosting the current task execution, or null
855		* if this task is executing outside of any pool.
856	<	* @return the pool, or null if none.
856	>	*
857	>	* @return the pool, or null if none
858		*/
859		public static ForkJoinPool getPool() {
860		Thread t = Thread.currentThread();
#	Line 855 | Line 870 | public abstract class ForkJoinTask<V> im
870		* alternative local processing of tasks that could have been, but
871		* were not, stolen. This method may be invoked only from within
872		* ForkJoinTask computations. Attempts to invoke in other contexts
873	<	* result in exceptions or errors including ClassCastException.
873	>	* result in exceptions or errors possibly including ClassCastException.
874	>	*
875		* @return true if unforked
876		*/
877		public boolean tryUnfork() {
#	Line 867 | Line 883 | public abstract class ForkJoinTask<V> im
883		* forked by the current worker thread but not yet executed. This
884		* value may be useful for heuristic decisions about whether to
885		* fork other tasks.
886	+	*
887		* @return the number of tasks
888		*/
889		public static int getQueuedTaskCount() {
#	Line 875 | Line 892 | public abstract class ForkJoinTask<V> im
892		}
893
894		/**
895	<	* Returns a estimate of how many more locally queued tasks are
895	>	* Returns an estimate of how many more locally queued tasks are
896		* held by the current worker thread than there are other worker
897		* threads that might steal them.  This value may be useful for
898		* heuristic decisions about whether to fork other tasks. In many
#	Line 883 | Line 900 | public abstract class ForkJoinTask<V> im
900		* aim to maintain a small constant surplus (for example, 3) of
901		* tasks, and to process computations locally if this threshold is
902		* exceeded.
903	+	*
904		* @return the surplus number of tasks, which may be negative
905		*/
906		public static int getSurplusQueuedTaskCount() {
#	Line 893 | Line 911 | public abstract class ForkJoinTask<V> im
911		// Extension methods
912
913		/**
914	<	* Returns the result that would be returned by <code>join</code>,
914	>	* Returns the result that would be returned by {@code join},
915		* even if this task completed abnormally, or null if this task is
916		* not known to have been completed.  This method is designed to
917		* aid debugging, as well as to support extensions. Its use in any
918		* other context is discouraged.
919		*
920	<	* @return the result, or null if not completed.
920	>	* @return the result, or null if not completed
921		*/
922		public abstract V getRawResult();
923
#	Line 918 | Line 936 | public abstract class ForkJoinTask<V> im
936		* called otherwise. The return value controls whether this task
937		* is considered to be done normally. It may return false in
938		* asynchronous actions that require explicit invocations of
939	<	* <code>complete</code> to become joinable. It may throw exceptions
939	>	* {@code complete} to become joinable. It may throw exceptions
940		* to indicate abnormal exit.
941	+	*
942		* @return true if completed normally
943		* @throws Error or RuntimeException if encountered during computation
944		*/
945		protected abstract boolean exec();
946
947		/**
948	<	* Returns, but does not unschedule or execute, the task most
949	<	* recently forked by the current thread but not yet executed, if
950	<	* one is available. There is no guarantee that this task will
951	<	* actually be polled or executed next.
952	<	* This method is designed primarily to support extensions,
953	<	* and is unlikely to be useful otherwise.
948	>	* Returns, but does not unschedule or execute, the task queued by
949	>	* the current thread but not yet executed, if one is
950	>	* available. There is no guarantee that this task will actually
951	>	* be polled or executed next.  This method is designed primarily
952	>	* to support extensions, and is unlikely to be useful otherwise.
953	>	* This method may be invoked only from within ForkJoinTask
954	>	* computations. Attempts to invoke in other contexts result in
955	>	* exceptions or errors possibly including ClassCastException.
956		*
957		* @return the next task, or null if none are available
958		*/
#	Line 940 | Line 961 | public abstract class ForkJoinTask<V> im
961		}
962
963		/**
964	<	* Unschedules and returns, without executing, the task most
965	<	* recently forked by the current thread but not yet executed.
966	<	* This method is designed primarily to support extensions,
967	<	* and is unlikely to be useful otherwise.
964	>	* Unschedules and returns, without executing, the next task
965	>	* queued by the current thread but not yet executed.  This method
966	>	* is designed primarily to support extensions, and is unlikely to
967	>	* be useful otherwise.  This method may be invoked only from
968	>	* within ForkJoinTask computations. Attempts to invoke in other
969	>	* contexts result in exceptions or errors possibly including
970	>	* ClassCastException.
971		*
972		* @return the next task, or null if none are available
973		*/
974		protected static ForkJoinTask<?> pollNextLocalTask() {
975	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).popTask();
975	>	return ((ForkJoinWorkerThread)(Thread.currentThread())).pollLocalTask();
976		}
977
978		/**
979	<	* Unschedules and returns, without executing, the task most
980	<	* recently forked by the current thread but not yet executed, if
981	<	* one is available, or if not available, a task that was forked
982	<	* by some other thread, if available. Availability may be
983	<	* transient, so a <code>null</code> result does not necessarily
984	<	* imply quiecence of the pool this task is operating in.
985	<	* This method is designed primarily to support extensions,
986	<	* and is unlikely to be useful otherwise.
987	<	*
979	>	* Unschedules and returns, without executing, the next task
980	>	* queued by the current thread but not yet executed, if one is
981	>	* available, or if not available, a task that was forked by some
982	>	* other thread, if available. Availability may be transient, so a
983	>	* {@code null} result does not necessarily imply quiescence
984	>	* of the pool this task is operating in.  This method is designed
985	>	* primarily to support extensions, and is unlikely to be useful
986	>	* otherwise.  This method may be invoked only from within
987	>	* ForkJoinTask computations. Attempts to invoke in other contexts
988	>	* result in exceptions or errors possibly including
989	>	* ClassCastException.
990	>	*
991		* @return a task, or null if none are available
992		*/
993		protected static ForkJoinTask<?> pollTask() {
994		return ((ForkJoinWorkerThread)(Thread.currentThread())).
995	<	pollLocalOrStolenTask();
995	>	pollTask();
996		}
997
998		// Serialization support
#	Line 976 | Line 1003 | public abstract class ForkJoinTask<V> im
1003		* Save the state to a stream.
1004		*
1005		* @serialData the current run status and the exception thrown
1006	<	* during execution, or null if none.
1006	>	* during execution, or null if none
1007		* @param s the stream
1008		*/
1009		private void writeObject(java.io.ObjectOutputStream s)
#	Line 987 | Line 1014 | public abstract class ForkJoinTask<V> im
1014
1015		/**
1016		* Reconstitute the instance from a stream.
1017	+	*
1018		* @param s the stream
1019		*/
1020		private void readObject(java.io.ObjectInputStream s)
#	Line 1000 | Line 1028 | public abstract class ForkJoinTask<V> im
1028		}
1029
1030		// Temporary Unsafe mechanics for preliminary release
1031	+	private static Unsafe getUnsafe() throws Throwable {
1032	+	try {
1033	+	return Unsafe.getUnsafe();
1034	+	} catch (SecurityException se) {
1035	+	try {
1036	+	return java.security.AccessController.doPrivileged
1037	+	(new java.security.PrivilegedExceptionAction<Unsafe>() {
1038	+	public Unsafe run() throws Exception {
1039	+	return getUnsafePrivileged();
1040	+	}});
1041	+	} catch (java.security.PrivilegedActionException e) {
1042	+	throw e.getCause();
1043	+	}
1044	+	}
1045	+	}
1046	+
1047	+	private static Unsafe getUnsafePrivileged()
1048	+	throws NoSuchFieldException, IllegalAccessException {
1049	+	Field f = Unsafe.class.getDeclaredField("theUnsafe");
1050	+	f.setAccessible(true);
1051	+	return (Unsafe) f.get(null);
1052	+	}
1053	+
1054	+	private static long fieldOffset(String fieldName)
1055	+	throws NoSuchFieldException {
1056	+	return _unsafe.objectFieldOffset
1057	+	(ForkJoinTask.class.getDeclaredField(fieldName));
1058	+	}
1059
1060		static final Unsafe _unsafe;
1061		static final long statusOffset;
1062
1063		static {
1064		try {
1065	<	if (ForkJoinTask.class.getClassLoader() != null) {
1066	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
1067	<	f.setAccessible(true);
1068	<	_unsafe = (Unsafe)f.get(null);
1069	<	}
1014	<	else
1015	<	_unsafe = Unsafe.getUnsafe();
1016	<	statusOffset = _unsafe.objectFieldOffset
1017	<	(ForkJoinTask.class.getDeclaredField("status"));
1018	<	} catch (Exception ex) { throw new Error(ex); }
1065	>	_unsafe = getUnsafe();
1066	>	statusOffset = fieldOffset("status");
1067	>	} catch (Throwable e) {
1068	>	throw new RuntimeException("Could not initialize intrinsics", e);
1069	>	}
1070		}
1071
1072		}

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