ViewVC Help

View File | Revision Log | Show Annotations | Download File | Root Listing

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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.31 by jsr166, Sun Aug 2 22:58:50 2009 UTC vs.
Revision 1.35 by dl, Tue Aug 4 12:41:27 2009 UTC

#	Line 12 | Line 12 | import java.io.Serializable;
12		import java.util.Collection;
13		import java.util.Collections;
14		import java.util.List;
15	+	import java.util.RandomAccess;
16		import java.util.Map;
17		import java.util.WeakHashMap;
18
#	Line 54 | Line 55 | import java.util.WeakHashMap;
55		* restriction is in part enforced by not permitting checked
56		* exceptions such as {@code IOExceptions} to be thrown. However,
57		* computations may still encounter unchecked exceptions, that are
58	<	* rethrown to callers attempting join them. These exceptions may
58	>	* rethrown to callers attempting to join them. These exceptions may
59		* additionally include RejectedExecutionExceptions stemming from
60		* internal resource exhaustion such as failure to allocate internal
61		* task queues.
#	Line 67 | 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 #isCancelled} is true if completion was due to cancellation;
84	+	* {@link #isCompletedNormally} is true if a task completed without
85	+	* cancellation or encountering an exception; {@link
86	+	* #isCompletedExceptionally} is true if if the task encountered an
87	+	* exception (in which case {@link #getException} returns the
88	+	* exception); {@link #isCancelled} is true if the task was cancelled
89	+	* (in which case {@link #getException} returns a {@link
90	+	* java.util.concurrent.CancellationException}; and {@link
91	+	* #isCompletedAbnormally} is true if a task was either cancelled or
92	+	* encountered an exception.
93	+	*
94		* <p>The ForkJoinTask class is not usually directly subclassed.
95		* Instead, you subclass one of the abstract classes that support a
96		* particular style of fork/join processing, typically {@link
#	Line 85 | Line 100 | import java.util.WeakHashMap;
100		* established in a constructor, and then defines a {@code compute}
101		* method that somehow uses the control methods supplied by this base
102		* class. While these methods have {@code public} access (to allow
103	<	* instances of different task subclasses to call each others
103	>	* instances of different task subclasses to call each other's
104		* methods), some of them may only be called from within other
105		* ForkJoinTasks (as may be determined using method {@link
106		* #inForkJoinPool}).  Attempts to invoke them in other contexts
107		* result in exceptions or errors, possibly including
108		* ClassCastException.
109		*
110	<	* <p>Most base support methods are {@code final} because their
111	<	* implementations are intrinsically tied to the underlying
112	<	* lightweight task scheduling framework, and so cannot be overridden.
113	<	* Developers creating new basic styles of fork/join processing should
114	<	* minimally implement {@code protected} methods
115	<	* {@link #exec}, {@link #setRawResult}, and
116	<	* {@link #getRawResult}, while also introducing an abstract
117	<	* computational method that can be implemented in its subclasses,
118	<	* possibly relying on other {@code protected} methods provided
104	<	* by this class.
110	>	* <p>Most base support methods are {@code final}, to prevent
111	>	* overriding of implementations that are intrinsically tied to the
112	>	* underlying lightweight task scheduling framework.  Developers
113	>	* creating new basic styles of fork/join processing should minimally
114	>	* implement {@code protected} methods {@link #exec}, {@link
115	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
116	>	* an abstract computational method that can be implemented in its
117	>	* subclasses, possibly relying on other {@code protected} methods
118	>	* provided by this class.
119		*
120		* <p>ForkJoinTasks should perform relatively small amounts of
121	<	* computations, otherwise splitting into smaller tasks. As a very
122	<	* rough rule of thumb, a task should perform more than 100 and less
123	<	* than 10000 basic computational steps. If tasks are too big, then
124	<	* parallelism cannot improve throughput. If too small, then memory
125	<	* and internal task maintenance overhead may overwhelm processing.
121	>	* computation. Large tasks should be split into smaller subtasks,
122	>	* usually via recursive decomposition. As a very rough rule of thumb,
123	>	* a task should perform more than 100 and less than 10000 basic
124	>	* computational steps. If tasks are too big, then parallelism cannot
125	>	* improve throughput. If too small, then memory and internal task
126	>	* maintenance overhead may overwhelm processing.
127		*
128		* <p>This class provides {@code adapt} methods for {@link
129		* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
130		* may be of use when mixing execution of ForkJoinTasks with other
131		* kinds of tasks. When all tasks are of this form, consider using a
132	<	* pool in {@link ForkJoinPool#setAsyncMode}.
132	>	* pool in {@link ForkJoinPool#setAsyncMode async mode}.
133		*
134	<	* <p>ForkJoinTasks are {@code Serializable}, which enables them
135	<	* to be used in extensions such as remote execution frameworks. It is
136	<	* in general sensible to serialize tasks only before or after, but
137	<	* not during execution. Serialization is not relied on during
123	<	* execution itself.
134	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
135	>	* used in extensions such as remote execution frameworks. It is
136	>	* sensible to serialize tasks only before or after, but not during,
137	>	* execution. Serialization is not relied on during execution itself.
138		*
139		* @since 1.7
140		* @author Doug Lea
#	Line 382 | Line 396 | public abstract class ForkJoinTask<V> im
396		*/
397		private V reportFutureResult()
398		throws ExecutionException, InterruptedException {
399	+	if (Thread.interrupted())
400	+	throw new InterruptedException();
401		int s = status & COMPLETION_MASK;
402		if (s < NORMAL) {
403		Throwable ex;
#	Line 389 | Line 405 | public abstract class ForkJoinTask<V> im
405		throw new CancellationException();
406		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
407		throw new ExecutionException(ex);
392	–	if (Thread.interrupted())
393	–	throw new InterruptedException();
408		}
409		return getRawResult();
410		}
#	Line 401 | Line 415 | public abstract class ForkJoinTask<V> im
415		*/
416		private V reportTimedFutureResult()
417		throws InterruptedException, ExecutionException, TimeoutException {
418	+	if (Thread.interrupted())
419	+	throw new InterruptedException();
420		Throwable ex;
421		int s = status & COMPLETION_MASK;
422		if (s == NORMAL)
#	Line 409 | Line 425 | public abstract class ForkJoinTask<V> im
425		throw new CancellationException();
426		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
427		throw new ExecutionException(ex);
412	–	if (Thread.interrupted())
413	–	throw new InterruptedException();
428		throw new TimeoutException();
429		}
430
#	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 more than one task
562	>	* encounters an exception, then this method throws any one of
563	>	* these exceptions.  The individual status of each task may be
564	>	* checked using {@link #getException()} and related methods.
565		*
566		* <p>This method may be invoked only from within {@code
567		* ForkJoinTask} computations (as may be determined using method
#	Line 555 | Line 572 | public abstract class ForkJoinTask<V> im
572		* @param t1 the first task
573		* @param t2 the second task
574		* @throws NullPointerException if any task is null
558	–	* @throws RuntimeException or Error if a task did so
575		*/
576		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
577		t2.fork();
#	Line 565 | Line 581 | public abstract class ForkJoinTask<V> im
581
582		/**
583		* Forks the given tasks, returning when {@code isDone} holds for
584	<	* each task or an exception is encountered. If any task
585	<	* encounters an exception, others may be, but are not guaranteed
586	<	* to be, cancelled.
584	>	* each task or an (unchecked) exception is encountered, in which
585	>	* case the exception is rethrown. If any task encounters an
586	>	* exception, others may be, but are not guaranteed to be,
587	>	* cancelled.  If more than one task encounters an exception, then
588	>	* this method throws any one of these exceptions.  The individual
589	>	* status of each task may be checked using {@link #getException()}
590	>	* and related methods.
591		*
592		* <p>This method may be invoked only from within {@code
593		* ForkJoinTask} computations (as may be determined using method
#	Line 575 | Line 595 | public abstract class ForkJoinTask<V> im
595		* result in exceptions or errors, possibly including {@code
596		* ClassCastException}.
597		*
578	–	* <p>Overloadings of this method exist for the special cases
579	–	* of one to four arguments.
580	–	*
598		* @param tasks the tasks
599	<	* @throws NullPointerException if tasks or any element are null
583	<	* @throws RuntimeException or Error if any task did so
599	>	* @throws NullPointerException if any task is null
600		*/
601		public static void invokeAll(ForkJoinTask<?>... tasks) {
602		Throwable ex = null;
#	Line 616 | Line 632 | public abstract class ForkJoinTask<V> im
632		}
633
634		/**
635	<	* Forks all tasks in the collection, returning when {@code
636	<	* isDone} holds for each task or an exception is encountered.
637	<	* If any task encounters an exception, others may be, but are
638	<	* not guaranteed to be, cancelled.
635	>	* Forks all tasks in the specified collection, returning when
636	>	* {@code isDone} holds for each task or an (unchecked) exception
637	>	* is encountered.  If any task encounters an exception, others
638	>	* may be, but are not guaranteed to be, cancelled.  If more than
639	>	* one task encounters an exception, then this method throws any
640	>	* one of these exceptions.  The individual status of each task
641	>	* may be checked using {@link #getException()} and related
642	>	* methods.  The behavior of this operation is undefined if the
643	>	* specified collection is modified while the operation is in
644	>	* progress.
645		*
646		* <p>This method may be invoked only from within {@code
647		* ForkJoinTask} computations (as may be determined using method
#	Line 630 | Line 652 | public abstract class ForkJoinTask<V> im
652		* @param tasks the collection of tasks
653		* @return the tasks argument, to simplify usage
654		* @throws NullPointerException if tasks or any element are null
633	–	* @throws RuntimeException or Error if any task did so
655		*/
656		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
657	<	if (!(tasks instanceof List<?>)) {
657	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
658		invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
659		return tasks;
660		}
#	Line 674 | Line 695 | public abstract class ForkJoinTask<V> im
695		}
696
697		/**
698	<	* Returns {@code true} if the computation performed by this task
699	<	* has completed (or has been cancelled).
700	<	*
701	<	* @return {@code true} if this computation has completed
702	<	*/
703	<	public final boolean isDone() {
704	<	return status < 0;
684	<	}
685	<
686	<	/**
687	<	* Returns {@code true} if this task was cancelled.
688	<	*
689	<	* @return {@code true} if this task was cancelled
690	<	*/
691	<	public final boolean isCancelled() {
692	<	return (status & COMPLETION_MASK) == CANCELLED;
693	<	}
694	<
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, 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 {@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.
698	>	* Attempts to cancel execution of this task. This attempt will
699	>	* fail if the task has already completed, has already been
700	>	* cancelled, or could not be cancelled for some other reason. If
701	>	* successful, and this task has not started when cancel is
702	>	* called, execution of this task is suppressed, {@link
703	>	* #isCancelled} will report true, and {@link #join} will result
704	>	* in a {@code CancellationException} being thrown.
705		*
706		* <p>This method may be overridden in subclasses, but if so, must
707		* still ensure that these minimal properties hold. In particular,
#	Line 714 | Line 713 | public abstract class ForkJoinTask<V> im
713		* invoke {@link #completeExceptionally}.
714		*
715		* @param mayInterruptIfRunning this value is ignored in the
716	<	* default implementation because tasks are not in general
716	>	* default implementation because tasks are not
717		* cancelled via interruption
718		*
719		* @return {@code true} if this task is now cancelled
#	Line 725 | Line 724 | public abstract class ForkJoinTask<V> im
724		}
725
726		/**
727	+	* Returns {@code true} if the computation performed by this task
728	+	* has completed (or has been cancelled).
729	+	*
730	+	* @return {@code true} if this computation has completed
731	+	*/
732	+	public final boolean isDone() {
733	+	return status < 0;
734	+	}
735	+
736	+	/**
737	+	* Returns {@code true} if this task was cancelled.
738	+	*
739	+	* @return {@code true} if this task was cancelled
740	+	*/
741	+	public final boolean isCancelled() {
742	+	return (status & COMPLETION_MASK) == CANCELLED;
743	+	}
744	+
745	+	/**
746		* Returns {@code true} if this task threw an exception or was cancelled.
747		*
748		* @return {@code true} if this task threw an exception or was cancelled
#	Line 734 | Line 752 | public abstract class ForkJoinTask<V> im
752		}
753
754		/**
755	+	* Returns {@code true} if this task completed without throwing an
756	+	* exception and was not cancelled.
757	+	*
758	+	* @return {@code true} if this task completed without throwing an
759	+	* exception and was not cancelled
760	+	*/
761	+	public final boolean isCompletedNormally() {
762	+	return (status & COMPLETION_MASK) == NORMAL;
763	+	}
764	+
765	+	/**
766	+	* Returns {@code true} if this task threw an exception.
767	+	*
768	+	* @return {@code true} if this task threw an exception
769	+	*/
770	+	public final boolean isCompletedExceptionally() {
771	+	return (status & COMPLETION_MASK) == EXCEPTIONAL;
772	+	}
773	+
774	+	/**
775		* Returns the exception thrown by the base computation, or a
776		* {@code CancellationException} if cancelled, or {@code null} if
777		* none or if the method has not yet completed.
#	Line 832 | Line 870 | public abstract class ForkJoinTask<V> im
870		}
871
872		/**
873	<	* Possibly executes other tasks until this task is ready.
873	>	* Possibly executes other tasks until this task is ready.  This
874	>	* method may be useful when processing collections of tasks when
875	>	* some have been cancelled or otherwise known to have aborted.
876		*
877		* <p>This method may be invoked only from within {@code
878		* ForkJoinTask} computations (as may be determined using method
#	Line 877 | Line 917 | public abstract class ForkJoinTask<V> im
917
918		/**
919		* Possibly executes tasks until the pool hosting the current task
920	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
921	<	* designs in which many tasks are forked, but none are explicitly
922	<	* joined, instead executing them until all are processed.
920	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
921	>	* be of use in designs in which many tasks are forked, but none
922	>	* are explicitly joined, instead executing them until all are
923	>	* processed.
924		*
925		* <p>This method may be invoked only from within {@code
926		* ForkJoinTask} computations (as may be determined using method
#	Line 1023 | Line 1064 | public abstract class ForkJoinTask<V> im
1064		* called otherwise. The return value controls whether this task
1065		* is considered to be done normally. It may return false in
1066		* asynchronous actions that require explicit invocations of
1067	<	* {@link #complete} to become joinable. It may throw exceptions
1068	<	* to indicate abnormal exit.
1067	>	* {@link #complete} to become joinable. It may also throw an
1068	>	* (unchecked) exception to indicate abnormal exit.
1069		*
1070		* @return {@code true} if completed normally
1030	–	* @throws Error or RuntimeException if encountered during computation
1071		*/
1072		protected abstract boolean exec();
1073

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines