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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.32 by dl, Mon Aug 3 13:01:15 2009 UTC vs.
Revision 1.42 by dl, Thu Aug 6 23:08:50 2009 UTC

#	Line 68 | Line 68 | import java.util.WeakHashMap;
68		* execute other tasks while awaiting joins, which is sometimes more
69		* efficient but only applies when all subtasks are known to be
70		* strictly tree-structured. Method {@link #invoke} is semantically
71	<	* equivalent to {@code fork(); join()} but always attempts to
72	<	* begin execution in the current thread. The "<em>quiet</em>" forms
73	<	* of these methods do not extract results or report exceptions. These
71	>	* equivalent to {@code fork(); join()} but always attempts to begin
72	>	* execution in the current thread. The "<em>quiet</em>" forms of
73	>	* these methods do not extract results or report exceptions. These
74		* may be useful when a set of tasks are being executed, and you need
75		* to delay processing of results or exceptions until all complete.
76		* Method {@code invokeAll} (available in multiple versions)
77		* performs the most common form of parallel invocation: forking a set
78		* of tasks and joining them all.
79		*
80	+	* <p>The execution status of tasks may be queried at several levels
81	+	* of detail: {@link #isDone} is true if a task completed in any way
82	+	* (including the case where a task was cancelled without executing);
83	+	* {@link #isCompletedNormally} is true if a task completed without
84	+	* cancellation or encountering an exception; {@link #isCancelled} is
85	+	* true if the task was cancelled (in which case {@link #getException}
86	+	* returns a {@link java.util.concurrent.CancellationException}); and
87	+	* {@link #isCompletedAbnormally} is true if a task was either
88	+	* cancelled or encountered an exception, in which case {@link
89	+	* #getException} will return either the encountered exception or
90	+	* {@link java.util.concurrent.CancellationException}.
91	+	*
92		* <p>The ForkJoinTask class is not usually directly subclassed.
93		* Instead, you subclass one of the abstract classes that support a
94		* particular style of fork/join processing, typically {@link
#	Line 111 | Line 123 | import java.util.WeakHashMap;
123		* improve throughput. If too small, then memory and internal task
124		* maintenance overhead may overwhelm processing.
125		*
126	<	* <p>This class provides {@code adapt} methods for {@link
127	<	* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
128	<	* may be of use when mixing execution of ForkJoinTasks with other
129	<	* kinds of tasks. When all tasks are of this form, consider using a
130	<	* pool in {@link ForkJoinPool#setAsyncMode}.
126	>	* <p>This class provides {@code adapt} methods for {@link Runnable}
127	>	* and {@link Callable}, that may be of use when mixing execution of
128	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks
129	>	* are of this form, consider using a pool in
130	>	* {@linkplain ForkJoinPool#setAsyncMode async mode}.
131		*
132		* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
133		* used in extensions such as remote execution frameworks. It is
#	Line 378 | Line 390 | public abstract class ForkJoinTask<V> im
390
391		/**
392		* Returns result or throws exception using j.u.c.Future conventions.
393	<	* Only call when {@code isDone} known to be true.
393	>	* Only call when {@code isDone} known to be true or thread known
394	>	* to be interrupted.
395		*/
396		private V reportFutureResult()
397	<	throws ExecutionException, InterruptedException {
397	>	throws InterruptedException, ExecutionException {
398	>	if (Thread.interrupted())
399	>	throw new InterruptedException();
400		int s = status & COMPLETION_MASK;
401		if (s < NORMAL) {
402		Throwable ex;
#	Line 389 | Line 404 | public abstract class ForkJoinTask<V> im
404		throw new CancellationException();
405		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
406		throw new ExecutionException(ex);
392	–	if (Thread.interrupted())
393	–	throw new InterruptedException();
407		}
408		return getRawResult();
409		}
#	Line 401 | Line 414 | public abstract class ForkJoinTask<V> im
414		*/
415		private V reportTimedFutureResult()
416		throws InterruptedException, ExecutionException, TimeoutException {
417	+	if (Thread.interrupted())
418	+	throw new InterruptedException();
419		Throwable ex;
420		int s = status & COMPLETION_MASK;
421		if (s == NORMAL)
422		return getRawResult();
423	<	if (s == CANCELLED)
423	>	else if (s == CANCELLED)
424		throw new CancellationException();
425	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
425	>	else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
426		throw new ExecutionException(ex);
427	<	if (Thread.interrupted())
428	<	throw new InterruptedException();
414	<	throw new TimeoutException();
427	>	else
428	>	throw new TimeoutException();
429		}
430
431		// internal execution methods
#	Line 513 | Line 527 | public abstract class ForkJoinTask<V> im
527		}
528
529		/**
530	<	* Returns the result of the computation when it is ready.
530	>	* Returns the result of the computation when it {@link #isDone is done}.
531		* This method differs from {@link #get()} in that
532		* abnormal completion results in {@code RuntimeException} or
533		* {@code Error}, not {@code ExecutionException}.
#	Line 529 | Line 543 | public abstract class ForkJoinTask<V> im
543
544		/**
545		* Commences performing this task, awaits its completion if
546	<	* necessary, and return its result.
546	>	* necessary, and return its result, or throws an (unchecked)
547	>	* exception if the underlying computation did so.
548		*
534	–	* @throws Throwable (a RuntimeException, Error, or unchecked
535	–	* exception) if the underlying computation did so
549		* @return the computed result
550		*/
551		public final V invoke() {
#	Line 543 | Line 556 | public abstract class ForkJoinTask<V> im
556		}
557
558		/**
559	<	* Forks the given tasks, returning when {@code isDone} holds
560	<	* for each task or an exception is encountered.
559	>	* Forks the given tasks, returning when {@code isDone} holds for
560	>	* each task or an (unchecked) exception is encountered, in which
561	>	* case the exception is rethrown.  If either task encounters an
562	>	* exception, the other one may be, but is not guaranteed to be,
563	>	* cancelled.  If both tasks throw an exception, then this method
564	>	* throws one of them.  The individual status of each task may be
565	>	* checked using {@link #getException()} and related methods.
566		*
567		* <p>This method may be invoked only from within {@code
568		* ForkJoinTask} computations (as may be determined using method
#	Line 555 | Line 573 | public abstract class ForkJoinTask<V> im
573		* @param t1 the first task
574		* @param t2 the second task
575		* @throws NullPointerException if any task is null
558	–	* @throws RuntimeException or Error if a task did so
576		*/
577		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
578		t2.fork();
#	Line 565 | Line 582 | public abstract class ForkJoinTask<V> im
582
583		/**
584		* Forks the given tasks, returning when {@code isDone} holds for
585	<	* each task or an exception is encountered. If any task
586	<	* encounters an exception, others may be, but are not guaranteed
587	<	* to be, cancelled.
585	>	* each task or an (unchecked) exception is encountered, in which
586	>	* case the exception is rethrown. If any task encounters an
587	>	* exception, others may be, but are not guaranteed to be,
588	>	* cancelled.  If more than one task encounters an exception, then
589	>	* this method throws any one of these exceptions.  The individual
590	>	* status of each task may be checked using {@link #getException()}
591	>	* and related methods.
592		*
593		* <p>This method may be invoked only from within {@code
594		* ForkJoinTask} computations (as may be determined using method
#	Line 576 | Line 597 | public abstract class ForkJoinTask<V> im
597		* ClassCastException}.
598		*
599		* @param tasks the tasks
600	<	* @throws NullPointerException if tasks or any element are null
580	<	* @throws RuntimeException or Error if any task did so
600	>	* @throws NullPointerException if any task is null
601		*/
602		public static void invokeAll(ForkJoinTask<?>... tasks) {
603		Throwable ex = null;
#	Line 614 | Line 634 | public abstract class ForkJoinTask<V> im
634
635		/**
636		* Forks all tasks in the specified collection, returning when
637	<	* {@code isDone} holds for each task or an exception is
638	<	* encountered.  If any task encounters an exception, others may
639	<	* be, but are not guaranteed to be, cancelled. The behavior of
640	<	* this operation is undefined if the specified collection is
641	<	* modified while the operation is in progress.
637	>	* {@code isDone} holds for each task or an (unchecked) exception
638	>	* is encountered.  If any task encounters an exception, others
639	>	* may be, but are not guaranteed to be, cancelled.  If more than
640	>	* one task encounters an exception, then this method throws any
641	>	* one of these exceptions.  The individual status of each task
642	>	* may be checked using {@link #getException()} and related
643	>	* methods.  The behavior of this operation is undefined if the
644	>	* specified collection is modified while the operation is in
645	>	* progress.
646		*
647		* <p>This method may be invoked only from within {@code
648		* ForkJoinTask} computations (as may be determined using method
#	Line 629 | Line 653 | public abstract class ForkJoinTask<V> im
653		* @param tasks the collection of tasks
654		* @return the tasks argument, to simplify usage
655		* @throws NullPointerException if tasks or any element are null
632	–	* @throws RuntimeException or Error if any task did so
656		*/
657		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
658		if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
#	Line 673 | Line 696 | public abstract class ForkJoinTask<V> im
696		}
697
698		/**
699	<	* Returns {@code true} if the computation performed by this task
700	<	* has completed (or has been cancelled).
701	<	*
702	<	* @return {@code true} if this computation has completed
703	<	*/
704	<	public final boolean isDone() {
705	<	return status < 0;
683	<	}
684	<
685	<	/**
686	<	* Returns {@code true} if this task was cancelled.
687	<	*
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, execution will be suppressed, {@link #isCancelled}
698	<	* will report true, and {@link #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 {@code true},
702	<	* whether {@code join} will return normally or via an exception,
703	<	* or whether these behaviors will remain consistent upon repeated
704	<	* invocation.
699	>	* Attempts to cancel execution of this task. This attempt will
700	>	* fail if the task has already completed, has already been
701	>	* cancelled, or could not be cancelled for some other reason. If
702	>	* successful, and this task has not started when cancel is
703	>	* called, execution of this task is suppressed, {@link
704	>	* #isCancelled} will report true, and {@link #join} will result
705	>	* in a {@code CancellationException} being thrown.
706		*
707		* <p>This method may be overridden in subclasses, but if so, must
708		* still ensure that these minimal properties hold. In particular,
#	Line 713 | Line 714 | public abstract class ForkJoinTask<V> im
714		* invoke {@link #completeExceptionally}.
715		*
716		* @param mayInterruptIfRunning this value is ignored in the
717	<	* default implementation because tasks are not in general
717	>	* default implementation because tasks are not
718		* cancelled via interruption
719		*
720		* @return {@code true} if this task is now cancelled
#	Line 723 | Line 724 | public abstract class ForkJoinTask<V> im
724		return (status & COMPLETION_MASK) == CANCELLED;
725		}
726
727	+	public final boolean isDone() {
728	+	return status < 0;
729	+	}
730	+
731	+	public final boolean isCancelled() {
732	+	return (status & COMPLETION_MASK) == CANCELLED;
733	+	}
734	+
735		/**
736		* Returns {@code true} if this task threw an exception or was cancelled.
737		*
#	Line 733 | Line 742 | public abstract class ForkJoinTask<V> im
742		}
743
744		/**
745	+	* Returns {@code true} if this task completed without throwing an
746	+	* exception and was not cancelled.
747	+	*
748	+	* @return {@code true} if this task completed without throwing an
749	+	* exception and was not cancelled
750	+	*/
751	+	public final boolean isCompletedNormally() {
752	+	return (status & COMPLETION_MASK) == NORMAL;
753	+	}
754	+
755	+	/**
756		* Returns the exception thrown by the base computation, or a
757		* {@code CancellationException} if cancelled, or {@code null} if
758		* none or if the method has not yet completed.
#	Line 741 | Line 761 | public abstract class ForkJoinTask<V> im
761		*/
762		public final Throwable getException() {
763		int s = status & COMPLETION_MASK;
764	<	if (s >= NORMAL)
765	<	return null;
766	<	if (s == CANCELLED)
747	<	return new CancellationException();
748	<	return exceptionMap.get(this);
764	>	return ((s >= NORMAL)    ? null :
765	>	(s == CANCELLED) ? new CancellationException() :
766	>	exceptionMap.get(this));
767		}
768
769		/**
#	Line 807 | Line 825 | public abstract class ForkJoinTask<V> im
825		}
826
827		/**
828	<	* Possibly executes other tasks until this task is ready, then
829	<	* returns the result of the computation.  This method may be more
830	<	* efficient than {@code join}, but is only applicable when
831	<	* there are no potential dependencies between continuation of the
832	<	* current task and that of any other task that might be executed
833	<	* while helping. (This usually holds for pure divide-and-conquer
834	<	* tasks).
828	>	* Possibly executes other tasks until this task {@link #isDone is
829	>	* done}, then returns the result of the computation.  This method
830	>	* may be more efficient than {@code join}, but is only applicable
831	>	* when there are no potential dependencies between continuation
832	>	* of the current task and that of any other task that might be
833	>	* executed while helping. (This usually holds for pure
834	>	* divide-and-conquer tasks).
835		*
836		* <p>This method may be invoked only from within {@code
837		* ForkJoinTask} computations (as may be determined using method
#	Line 831 | Line 849 | public abstract class ForkJoinTask<V> im
849		}
850
851		/**
852	<	* Possibly executes other tasks until this task is ready.  This
853	<	* method may be useful when processing collections of tasks when
854	<	* some have been cancelled or otherwise known to have aborted.
852	>	* Possibly executes other tasks until this task {@link #isDone is
853	>	* done}.  This method may be useful when processing collections
854	>	* of tasks when some have been cancelled or otherwise known to
855	>	* have aborted.
856		*
857		* <p>This method may be invoked only from within {@code
858		* ForkJoinTask} computations (as may be determined using method
#	Line 878 | Line 897 | public abstract class ForkJoinTask<V> im
897
898		/**
899		* Possibly executes tasks until the pool hosting the current task
900	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
901	<	* designs in which many tasks are forked, but none are explicitly
902	<	* joined, instead executing them until all are processed.
900	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
901	>	* be of use in designs in which many tasks are forked, but none
902	>	* are explicitly joined, instead executing them until all are
903	>	* processed.
904		*
905		* <p>This method may be invoked only from within {@code
906		* ForkJoinTask} computations (as may be determined using method
#	Line 1024 | Line 1044 | public abstract class ForkJoinTask<V> im
1044		* called otherwise. The return value controls whether this task
1045		* is considered to be done normally. It may return false in
1046		* asynchronous actions that require explicit invocations of
1047	<	* {@link #complete} to become joinable. It may throw exceptions
1048	<	* to indicate abnormal exit.
1047	>	* {@link #complete} to become joinable. It may also throw an
1048	>	* (unchecked) exception to indicate abnormal exit.
1049		*
1050		* @return {@code true} if completed normally
1031	–	* @throws Error or RuntimeException if encountered during computation
1051		*/
1052		protected abstract boolean exec();
1053

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