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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 1.43 by dl, Wed Aug 19 11:24:58 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 497 | Line 511 | public abstract class ForkJoinTask<V> im
511		* Arranges to asynchronously execute this task.  While it is not
512		* necessarily enforced, it is a usage error to fork a task more
513		* than once unless it has completed and been reinitialized.
514	+	* Subsequent modifications to the state of this task or any data
515	+	* it operates on are not necessarily consistently observable by
516	+	* any thread other than the one executing it unless preceded by a
517	+	* call to {@link #join} or related methods, or a call to {@link
518	+	* #isDone} returning {@code true}.
519		*
520		* <p>This method may be invoked only from within {@code
521		* ForkJoinTask} computations (as may be determined using method
#	Line 513 | Line 532 | public abstract class ForkJoinTask<V> im
532		}
533
534		/**
535	<	* Returns the result of the computation when it is ready.
535	>	* Returns the result of the computation when it {@link #isDone is done}.
536		* This method differs from {@link #get()} in that
537		* abnormal completion results in {@code RuntimeException} or
538		* {@code Error}, not {@code ExecutionException}.
#	Line 529 | Line 548 | public abstract class ForkJoinTask<V> im
548
549		/**
550		* Commences performing this task, awaits its completion if
551	<	* necessary, and return its result.
551	>	* necessary, and return its result, or throws an (unchecked)
552	>	* exception if the underlying computation did so.
553		*
534	–	* @throws Throwable (a RuntimeException, Error, or unchecked
535	–	* exception) if the underlying computation did so
554		* @return the computed result
555		*/
556		public final V invoke() {
#	Line 543 | Line 561 | public abstract class ForkJoinTask<V> im
561		}
562
563		/**
564	<	* Forks the given tasks, returning when {@code isDone} holds
565	<	* for each task or an exception is encountered.
564	>	* Forks the given tasks, returning when {@code isDone} holds for
565	>	* each task or an (unchecked) exception is encountered, in which
566	>	* case the exception is rethrown.  If either task encounters an
567	>	* exception, the other one may be, but is not guaranteed to be,
568	>	* cancelled.  If both tasks throw an exception, then this method
569	>	* throws one of them.  The individual status of each task may be
570	>	* checked using {@link #getException()} and related methods.
571		*
572		* <p>This method may be invoked only from within {@code
573		* ForkJoinTask} computations (as may be determined using method
#	Line 555 | Line 578 | public abstract class ForkJoinTask<V> im
578		* @param t1 the first task
579		* @param t2 the second task
580		* @throws NullPointerException if any task is null
558	–	* @throws RuntimeException or Error if a task did so
581		*/
582		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
583		t2.fork();
#	Line 565 | Line 587 | public abstract class ForkJoinTask<V> im
587
588		/**
589		* Forks the given tasks, returning when {@code isDone} holds for
590	<	* each task or an exception is encountered. If any task
591	<	* encounters an exception, others may be, but are not guaranteed
592	<	* to be, cancelled.
590	>	* each task or an (unchecked) exception is encountered, in which
591	>	* case the exception is rethrown. If any task encounters an
592	>	* exception, others may be, but are not guaranteed to be,
593	>	* cancelled.  If more than one task encounters an exception, then
594	>	* this method throws any one of these exceptions.  The individual
595	>	* status of each task may be checked using {@link #getException()}
596	>	* and related methods.
597		*
598		* <p>This method may be invoked only from within {@code
599		* ForkJoinTask} computations (as may be determined using method
#	Line 576 | Line 602 | public abstract class ForkJoinTask<V> im
602		* ClassCastException}.
603		*
604		* @param tasks the tasks
605	<	* @throws NullPointerException if tasks or any element are null
580	<	* @throws RuntimeException or Error if any task did so
605	>	* @throws NullPointerException if any task is null
606		*/
607		public static void invokeAll(ForkJoinTask<?>... tasks) {
608		Throwable ex = null;
#	Line 614 | Line 639 | public abstract class ForkJoinTask<V> im
639
640		/**
641		* Forks all tasks in the specified collection, returning when
642	<	* {@code isDone} holds for each task or an exception is
643	<	* encountered.  If any task encounters an exception, others may
644	<	* be, but are not guaranteed to be, cancelled. The behavior of
645	<	* this operation is undefined if the specified collection is
646	<	* modified while the operation is in progress.
642	>	* {@code isDone} holds for each task or an (unchecked) exception
643	>	* is encountered.  If any task encounters an exception, others
644	>	* may be, but are not guaranteed to be, cancelled.  If more than
645	>	* one task encounters an exception, then this method throws any
646	>	* one of these exceptions.  The individual status of each task
647	>	* may be checked using {@link #getException()} and related
648	>	* methods.  The behavior of this operation is undefined if the
649	>	* specified collection is modified while the operation is in
650	>	* progress.
651		*
652		* <p>This method may be invoked only from within {@code
653		* ForkJoinTask} computations (as may be determined using method
#	Line 629 | Line 658 | public abstract class ForkJoinTask<V> im
658		* @param tasks the collection of tasks
659		* @return the tasks argument, to simplify usage
660		* @throws NullPointerException if tasks or any element are null
632	–	* @throws RuntimeException or Error if any task did so
661		*/
662		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
663		if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
#	Line 673 | Line 701 | public abstract class ForkJoinTask<V> im
701		}
702
703		/**
704	<	* Returns {@code true} if the computation performed by this task
705	<	* has completed (or has been cancelled).
706	<	*
707	<	* @return {@code true} if this computation has completed
708	<	*/
709	<	public final boolean isDone() {
710	<	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.
704	>	* Attempts to cancel execution of this task. This attempt will
705	>	* fail if the task has already completed, has already been
706	>	* cancelled, or could not be cancelled for some other reason. If
707	>	* successful, and this task has not started when cancel is
708	>	* called, execution of this task is suppressed, {@link
709	>	* #isCancelled} will report true, and {@link #join} will result
710	>	* in a {@code CancellationException} being thrown.
711		*
712		* <p>This method may be overridden in subclasses, but if so, must
713		* still ensure that these minimal properties hold. In particular,
#	Line 713 | Line 719 | public abstract class ForkJoinTask<V> im
719		* invoke {@link #completeExceptionally}.
720		*
721		* @param mayInterruptIfRunning this value is ignored in the
722	<	* default implementation because tasks are not in general
722	>	* default implementation because tasks are not
723		* cancelled via interruption
724		*
725		* @return {@code true} if this task is now cancelled
#	Line 723 | Line 729 | public abstract class ForkJoinTask<V> im
729		return (status & COMPLETION_MASK) == CANCELLED;
730		}
731
732	+	public final boolean isDone() {
733	+	return status < 0;
734	+	}
735	+
736	+	public final boolean isCancelled() {
737	+	return (status & COMPLETION_MASK) == CANCELLED;
738	+	}
739	+
740		/**
741		* Returns {@code true} if this task threw an exception or was cancelled.
742		*
#	Line 733 | Line 747 | public abstract class ForkJoinTask<V> im
747		}
748
749		/**
750	+	* Returns {@code true} if this task completed without throwing an
751	+	* exception and was not cancelled.
752	+	*
753	+	* @return {@code true} if this task completed without throwing an
754	+	* exception and was not cancelled
755	+	*/
756	+	public final boolean isCompletedNormally() {
757	+	return (status & COMPLETION_MASK) == NORMAL;
758	+	}
759	+
760	+	/**
761		* Returns the exception thrown by the base computation, or a
762		* {@code CancellationException} if cancelled, or {@code null} if
763		* none or if the method has not yet completed.
#	Line 741 | Line 766 | public abstract class ForkJoinTask<V> im
766		*/
767		public final Throwable getException() {
768		int s = status & COMPLETION_MASK;
769	<	if (s >= NORMAL)
770	<	return null;
771	<	if (s == CANCELLED)
747	<	return new CancellationException();
748	<	return exceptionMap.get(this);
769	>	return ((s >= NORMAL)    ? null :
770	>	(s == CANCELLED) ? new CancellationException() :
771	>	exceptionMap.get(this));
772		}
773
774		/**
#	Line 807 | Line 830 | public abstract class ForkJoinTask<V> im
830		}
831
832		/**
833	<	* Possibly executes other tasks until this task is ready, then
834	<	* returns the result of the computation.  This method may be more
835	<	* efficient than {@code join}, but is only applicable when
836	<	* there are no potential dependencies between continuation of the
837	<	* current task and that of any other task that might be executed
838	<	* while helping. (This usually holds for pure divide-and-conquer
839	<	* tasks).
833	>	* Possibly executes other tasks until this task {@link #isDone is
834	>	* done}, then returns the result of the computation.  This method
835	>	* may be more efficient than {@code join}, but is only applicable
836	>	* when there are no potential dependencies between continuation
837	>	* of the current task and that of any other task that might be
838	>	* executed while helping. (This usually holds for pure
839	>	* divide-and-conquer tasks).
840		*
841		* <p>This method may be invoked only from within {@code
842		* ForkJoinTask} computations (as may be determined using method
#	Line 831 | Line 854 | public abstract class ForkJoinTask<V> im
854		}
855
856		/**
857	<	* Possibly executes other tasks until this task is ready.  This
858	<	* method may be useful when processing collections of tasks when
859	<	* some have been cancelled or otherwise known to have aborted.
857	>	* Possibly executes other tasks until this task {@link #isDone is
858	>	* done}.  This method may be useful when processing collections
859	>	* of tasks when some have been cancelled or otherwise known to
860	>	* have aborted.
861		*
862		* <p>This method may be invoked only from within {@code
863		* ForkJoinTask} computations (as may be determined using method
#	Line 878 | Line 902 | public abstract class ForkJoinTask<V> im
902
903		/**
904		* Possibly executes tasks until the pool hosting the current task
905	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
906	<	* designs in which many tasks are forked, but none are explicitly
907	<	* joined, instead executing them until all are processed.
905	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
906	>	* be of use in designs in which many tasks are forked, but none
907	>	* are explicitly joined, instead executing them until all are
908	>	* processed.
909		*
910		* <p>This method may be invoked only from within {@code
911		* ForkJoinTask} computations (as may be determined using method
#	Line 1024 | Line 1049 | public abstract class ForkJoinTask<V> im
1049		* called otherwise. The return value controls whether this task
1050		* is considered to be done normally. It may return false in
1051		* asynchronous actions that require explicit invocations of
1052	<	* {@link #complete} to become joinable. It may throw exceptions
1053	<	* to indicate abnormal exit.
1052	>	* {@link #complete} to become joinable. It may also throw an
1053	>	* (unchecked) exception to indicate abnormal exit.
1054		*
1055		* @return {@code true} if completed normally
1031	–	* @throws Error or RuntimeException if encountered during computation
1056		*/
1057		protected abstract boolean exec();
1058

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