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 1.57 by dl, Sat Sep 4 11:33:53 2010 UTC vs.
Revision 1.71 by dl, Tue Nov 23 10:51:18 2010 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.io.Serializable;
10		import java.util.Collection;
11		import java.util.Collections;
#	Line 15 | Line 13 | import java.util.List;
13		import java.util.RandomAccess;
14		import java.util.Map;
15		import java.util.WeakHashMap;
16	+	import java.util.concurrent.Callable;
17	+	import java.util.concurrent.CancellationException;
18	+	import java.util.concurrent.ExecutionException;
19	+	import java.util.concurrent.Executor;
20	+	import java.util.concurrent.ExecutorService;
21	+	import java.util.concurrent.Future;
22	+	import java.util.concurrent.RejectedExecutionException;
23	+	import java.util.concurrent.RunnableFuture;
24	+	import java.util.concurrent.TimeUnit;
25	+	import java.util.concurrent.TimeoutException;
26
27		/**
28		* Abstract base class for tasks that run within a {@link ForkJoinPool}.
#	Line 28 | Line 36 | import java.util.WeakHashMap;
36		* start other subtasks.  As indicated by the name of this class,
37		* many programs using {@code ForkJoinTask} employ only methods
38		* {@link #fork} and {@link #join}, or derivatives such as {@link
39	<	* #invokeAll}.  However, this class also provides a number of other
40	<	* methods that can come into play in advanced usages, as well as
41	<	* extension mechanics that allow support of new forms of fork/join
42	<	* processing.
39	>	* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
40	>	* provides a number of other methods that can come into play in
41	>	* advanced usages, as well as extension mechanics that allow
42	>	* support of new forms of fork/join processing.
43		*
44		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
45		* The efficiency of {@code ForkJoinTask}s stems from a set of
#	Line 102 | Line 110 | import java.util.WeakHashMap;
110		* result in exceptions or errors, possibly including
111		* {@code ClassCastException}.
112		*
113	+	* <p>Method {@link #join} and its variants are appropriate for use
114	+	* only when completion dependencies are acyclic; that is, the
115	+	* parallel computation can be described as a directed acyclic graph
116	+	* (DAG). Otherwise, executions may encounter a form of deadlock as
117	+	* tasks cyclically wait for each other.  However, this framework
118	+	* supports other methods and techniques (for example the use of
119	+	* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
120	+	* may be of use in constructing custom subclasses for problems that
121	+	* are not statically structured as DAGs.
122	+	*
123		* <p>Most base support methods are {@code final}, to prevent
124		* overriding of implementations that are intrinsically tied to the
125		* underlying lightweight task scheduling framework.  Developers
#	Line 116 | Line 134 | import java.util.WeakHashMap;
134		* computation. Large tasks should be split into smaller subtasks,
135		* usually via recursive decomposition. As a very rough rule of thumb,
136		* a task should perform more than 100 and less than 10000 basic
137	<	* computational steps. If tasks are too big, then parallelism cannot
138	<	* improve throughput. If too small, then memory and internal task
139	<	* maintenance overhead may overwhelm processing.
137	>	* computational steps, and should avoid indefinite looping. If tasks
138	>	* are too big, then parallelism cannot improve throughput. If too
139	>	* small, then memory and internal task maintenance overhead may
140	>	* overwhelm processing.
141		*
142		* <p>This class provides {@code adapt} methods for {@link Runnable}
143		* and {@link Callable}, that may be of use when mixing execution of
#	Line 153 | Line 172 | public abstract class ForkJoinTask<V> im
172		* single int to minimize footprint and to ensure atomicity (via
173		* CAS).  Status is initially zero, and takes on nonnegative
174		* values until completed, upon which status holds value
175	<	* NORMAL. CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
175	>	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
176		* waits by other threads have the SIGNAL bit set.  Completion of
177		* a stolen task with SIGNAL set awakens any waiters via
178		* notifyAll. Even though suboptimal for some purposes, we use
#	Line 206 | Line 225 | public abstract class ForkJoinTask<V> im
225
226		/**
227		* Records exception and sets exceptional completion.
228	<	*
228	>	*
229		* @return status on exit
230		*/
231		private void setExceptionalCompletion(Throwable rex) {
#	Line 215 | Line 234 | public abstract class ForkJoinTask<V> im
234		}
235
236		/**
237	<	* Blocks a worker thread until completion. Called only by
238	<	* pool. Currently unused -- pool-based waits use timeout
220	<	* version below.
237	>	* Blocks a worker thread until completed or timed out.  Called
238	>	* only by pool.
239		*/
240	<	final void internalAwaitDone() {
241	<	int s;         // the odd construction reduces lock bias effects
242	<	while ((s = status) >= 0) {
243	<	try {
244	<	synchronized(this) {
245	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
246	<	wait();
240	>	final void internalAwaitDone(long millis, int nanos) {
241	>	if (status >= 0) {
242	>	try {     // the odd construction reduces lock bias effects
243	>	synchronized (this) {
244	>	if (status > 0 ||
245	>	UNSAFE.compareAndSwapInt(this, statusOffset,
246	>	0, SIGNAL))
247	>	wait(millis, nanos);
248		}
249		} catch (InterruptedException ie) {
250		cancelIfTerminating();
#	Line 234 | Line 253 | public abstract class ForkJoinTask<V> im
253		}
254
255		/**
256	<	* Blocks a worker thread until completed or timed out.  Called
238	<	* only by pool.
239	<	*
240	<	* @return status on exit
256	>	* Blocks a non-worker-thread until completion.
257		*/
258	<	final int internalAwaitDone(long millis) {
259	<	int s;
260	<	if ((s = status) >= 0) {
261	<	try {
262	<	synchronized(this) {
263	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
264	<	wait(millis, 0);
258	>	private void externalAwaitDone() {
259	>	if (status >= 0) {
260	>	boolean interrupted = false;
261	>	synchronized(this) {
262	>	int s;
263	>	while ((s = status) >= 0) {
264	>	if (s == 0 &&
265	>	!UNSAFE.compareAndSwapInt(this, statusOffset,
266	>	0, SIGNAL))
267	>	continue;
268	>	try {
269	>	wait();
270	>	} catch (InterruptedException ie) {
271	>	interrupted = true;
272	>	}
273		}
250	–	} catch (InterruptedException ie) {
251	–	cancelIfTerminating();
274		}
275	<	s = status;
275	>	if (interrupted)
276	>	Thread.currentThread().interrupt();
277		}
255	–	return s;
278		}
279
280		/**
281	<	* Blocks a non-worker-thread until completion.
281	>	* Blocks a non-worker-thread until completion or interruption or timeout.
282		*/
283	<	private void externalAwaitDone() {
284	<	int s;
285	<	while ((s = status) >= 0) {
283	>	private void externalInterruptibleAwaitDone(boolean timed, long nanos)
284	>	throws InterruptedException {
285	>	if (Thread.interrupted())
286	>	throw new InterruptedException();
287	>	if (status >= 0) {
288	>	long startTime = timed ? System.nanoTime() : 0L;
289		synchronized(this) {
290	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
291	<	boolean interrupted = false;
292	<	while (status >= 0) {
293	<	try {
294	<	wait();
295	<	} catch (InterruptedException ie) {
296	<	interrupted = true;
297	<	}
298	<	}
299	<	if (interrupted)
300	<	Thread.currentThread().interrupt();
301	<	break;
290	>	int s;
291	>	while ((s = status) >= 0) {
292	>	long nt;
293	>	if (s == 0 &&
294	>	!UNSAFE.compareAndSwapInt(this, statusOffset,
295	>	0, SIGNAL))
296	>	continue;
297	>	else if (!timed)
298	>	wait();
299	>	else if ((nt = nanos - (System.nanoTime()-startTime)) > 0L)
300	>	wait(nt / 1000000, (int)(nt % 1000000));
301	>	else
302	>	break;
303		}
304		}
305		}
#	Line 308 | Line 334 | public abstract class ForkJoinTask<V> im
334		* #isDone} returning {@code true}.
335		*
336		* <p>This method may be invoked only from within {@code
337	<	* ForkJoinTask} computations (as may be determined using method
337	>	* ForkJoinPool} computations (as may be determined using method
338		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
339		* result in exceptions or errors, possibly including {@code
340		* ClassCastException}.
#	Line 322 | Line 348 | public abstract class ForkJoinTask<V> im
348		}
349
350		/**
351	<	* Returns the result of the computation when it {@link #isDone is done}.
352	<	* This method differs from {@link #get()} in that
351	>	* Returns the result of the computation when it {@link #isDone is
352	>	* done}.  This method differs from {@link #get()} in that
353		* abnormal completion results in {@code RuntimeException} or
354	<	* {@code Error}, not {@code ExecutionException}.
354	>	* {@code Error}, not {@code ExecutionException}, and that
355	>	* interrupts of the calling thread do <em>not</em> cause the
356	>	* method to abruptly return by throwing {@code
357	>	* InterruptedException}.
358		*
359		* @return the computed result
360		*/
#	Line 367 | Line 396 | public abstract class ForkJoinTask<V> im
396		* unprocessed.
397		*
398		* <p>This method may be invoked only from within {@code
399	<	* ForkJoinTask} computations (as may be determined using method
399	>	* ForkJoinPool} computations (as may be determined using method
400		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
401		* result in exceptions or errors, possibly including {@code
402		* ClassCastException}.
#	Line 395 | Line 424 | public abstract class ForkJoinTask<V> im
424		* normally or exceptionally, or left unprocessed.
425		*
426		* <p>This method may be invoked only from within {@code
427	<	* ForkJoinTask} computations (as may be determined using method
427	>	* ForkJoinPool} computations (as may be determined using method
428		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
429		* result in exceptions or errors, possibly including {@code
430		* ClassCastException}.
#	Line 450 | Line 479 | public abstract class ForkJoinTask<V> im
479		* unprocessed.
480		*
481		* <p>This method may be invoked only from within {@code
482	<	* ForkJoinTask} computations (as may be determined using method
482	>	* ForkJoinPool} computations (as may be determined using method
483		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
484		* result in exceptions or errors, possibly including {@code
485		* ClassCastException}.
#	Line 502 | Line 531 | public abstract class ForkJoinTask<V> im
531
532		/**
533		* Attempts to cancel execution of this task. This attempt will
534	<	* fail if the task has already completed, has already been
535	<	* cancelled, or could not be cancelled for some other reason. If
536	<	* successful, and this task has not started when cancel is
537	<	* called, execution of this task is suppressed, {@link
538	<	* #isCancelled} will report true, and {@link #join} will result
539	<	* in a {@code CancellationException} being thrown.
534	>	* fail if the task has already completed or could not be
535	>	* cancelled for some other reason. If successful, and this task
536	>	* has not started when {@code cancel} is called, execution of
537	>	* this task is suppressed. After this method returns
538	>	* successfully, unless there is an intervening call to {@link
539	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
540	>	* {@link #isDone}, and {@code cancel} will return {@code true}
541	>	* and calls to {@link #join} and related methods will result in
542	>	* {@code CancellationException}.
543		*
544		* <p>This method may be overridden in subclasses, but if so, must
545	<	* still ensure that these minimal properties hold. In particular,
546	<	* the {@code cancel} method itself must not throw exceptions.
545	>	* still ensure that these properties hold. In particular, the
546	>	* {@code cancel} method itself must not throw exceptions.
547		*
548		* <p>This method is designed to be invoked by <em>other</em>
549		* tasks. To terminate the current task, you can just return or
550		* throw an unchecked exception from its computation method, or
551		* invoke {@link #completeExceptionally}.
552		*
553	<	* @param mayInterruptIfRunning this value is ignored in the
554	<	* default implementation because tasks are not
555	<	* cancelled via interruption
553	>	* @param mayInterruptIfRunning this value has no effect in the
554	>	* default implementation because interrupts are not used to
555	>	* control cancellation.
556		*
557		* @return {@code true} if this task is now cancelled
558		*/
#	Line 621 | Line 653 | public abstract class ForkJoinTask<V> im
653
654		/**
655		* Completes this task, and if not already aborted or cancelled,
656	<	* returning a {@code null} result upon {@code join} and related
657	<	* operations. This method may be used to provide results for
658	<	* asynchronous tasks, or to provide alternative handling for
659	<	* tasks that would not otherwise complete normally. Its use in
660	<	* other situations is discouraged. This method is
661	<	* overridable, but overridden versions must invoke {@code super}
662	<	* implementation to maintain guarantees.
656	>	* returning the given value as the result of subsequent
657	>	* invocations of {@code join} and related operations. This method
658	>	* may be used to provide results for asynchronous tasks, or to
659	>	* provide alternative handling for tasks that would not otherwise
660	>	* complete normally. Its use in other situations is
661	>	* discouraged. This method is overridable, but overridden
662	>	* versions must invoke {@code super} implementation to maintain
663	>	* guarantees.
664		*
665		* @param value the result value for this task
666		*/
#	Line 641 | Line 674 | public abstract class ForkJoinTask<V> im
674		setCompletion(NORMAL);
675		}
676
677	+	/**
678	+	* Waits if necessary for the computation to complete, and then
679	+	* retrieves its result.
680	+	*
681	+	* @return the computed result
682	+	* @throws CancellationException if the computation was cancelled
683	+	* @throws ExecutionException if the computation threw an
684	+	* exception
685	+	* @throws InterruptedException if the current thread is not a
686	+	* member of a ForkJoinPool and was interrupted while waiting
687	+	*/
688		public final V get() throws InterruptedException, ExecutionException {
689	<	quietlyJoin();
690	<	if (Thread.interrupted())
691	<	throw new InterruptedException();
689	>	Thread t = Thread.currentThread();
690	>	if (t instanceof ForkJoinWorkerThread)
691	>	quietlyJoin();
692	>	else
693	>	externalInterruptibleAwaitDone(false, 0L);
694		int s = status;
695	<	if (s < NORMAL) {
695	>	if (s != NORMAL) {
696		Throwable ex;
697		if (s == CANCELLED)
698		throw new CancellationException();
#	Line 656 | Line 702 | public abstract class ForkJoinTask<V> im
702		return getRawResult();
703		}
704
705	+	/**
706	+	* Waits if necessary for at most the given time for the computation
707	+	* to complete, and then retrieves its result, if available.
708	+	*
709	+	* @param timeout the maximum time to wait
710	+	* @param unit the time unit of the timeout argument
711	+	* @return the computed result
712	+	* @throws CancellationException if the computation was cancelled
713	+	* @throws ExecutionException if the computation threw an
714	+	* exception
715	+	* @throws InterruptedException if the current thread is not a
716	+	* member of a ForkJoinPool and was interrupted while waiting
717	+	* @throws TimeoutException if the wait timed out
718	+	*/
719		public final V get(long timeout, TimeUnit unit)
720		throws InterruptedException, ExecutionException, TimeoutException {
721	+	long nanos = unit.toNanos(timeout);
722		Thread t = Thread.currentThread();
723	<	ForkJoinPool pool;
724	<	if (t instanceof ForkJoinWorkerThread) {
664	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
665	<	if (status >= 0 && w.unpushTask(this))
666	<	quietlyExec();
667	<	pool = w.pool;
668	<	}
723	>	if (t instanceof ForkJoinWorkerThread)
724	>	((ForkJoinWorkerThread)t).joinTask(this, true, nanos);
725		else
726	<	pool = null;
727	<	/*
728	<	* Timed wait loop intermixes cases for FJ (pool != null) and
673	<	* non FJ threads. For FJ, decrement pool count but don't try
674	<	* for replacement; increment count on completion. For non-FJ,
675	<	* deal with interrupts. This is messy, but a little less so
676	<	* than is splitting the FJ and nonFJ cases.
677	<	*/
678	<	boolean interrupted = false;
679	<	boolean dec = false; // true if pool count decremented
680	<	long nanos = unit.toNanos(timeout);
681	<	for (;;) {
682	<	if (Thread.interrupted() && pool == null) {
683	<	interrupted = true;
684	<	break;
685	<	}
686	<	int s = status;
687	<	if (s < 0)
688	<	break;
689	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
690	<	long startTime = System.nanoTime();
691	<	long nt; // wait time
692	<	while (status >= 0 &&
693	<	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
694	<	if (pool != null && !dec)
695	<	dec = pool.tryDecrementRunningCount();
696	<	else {
697	<	long ms = nt / 1000000;
698	<	int ns = (int) (nt % 1000000);
699	<	try {
700	<	synchronized(this) {
701	<	if (status >= 0)
702	<	wait(ms, ns);
703	<	}
704	<	} catch (InterruptedException ie) {
705	<	if (pool != null)
706	<	cancelIfTerminating();
707	<	else {
708	<	interrupted = true;
709	<	break;
710	<	}
711	<	}
712	<	}
713	<	}
714	<	break;
715	<	}
716	<	}
717	<	if (pool != null && dec)
718	<	pool.incrementRunningCount();
719	<	if (interrupted)
720	<	throw new InterruptedException();
721	<	int es = status;
722	<	if (es != NORMAL) {
726	>	externalInterruptibleAwaitDone(true, nanos);
727	>	int s = status;
728	>	if (s != NORMAL) {
729		Throwable ex;
730	<	if (es == CANCELLED)
730	>	if (s == CANCELLED)
731		throw new CancellationException();
732	<	if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
732	>	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
733		throw new ExecutionException(ex);
734		throw new TimeoutException();
735		}
#	Line 754 | Line 760 | public abstract class ForkJoinTask<V> im
760		return;
761		}
762		}
763	<	w.joinTask(this);
763	>	w.joinTask(this, false, 0L);
764		}
765		}
766		else
#	Line 764 | Line 770 | public abstract class ForkJoinTask<V> im
770		/**
771		* Commences performing this task and awaits its completion if
772		* necessary, without returning its result or throwing its
773	<	* exception. This method may be useful when processing
768	<	* collections of tasks when some have been cancelled or otherwise
769	<	* known to have aborted.
773	>	* exception.
774		*/
775		public final void quietlyInvoke() {
776		if (status >= 0) {
#	Line 792 | Line 796 | public abstract class ForkJoinTask<V> im
796		* processed.
797		*
798		* <p>This method may be invoked only from within {@code
799	<	* ForkJoinTask} computations (as may be determined using method
799	>	* ForkJoinPool} computations (as may be determined using method
800		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
801		* result in exceptions or errors, possibly including {@code
802		* ClassCastException}.
#	Line 811 | Line 815 | public abstract class ForkJoinTask<V> im
815		* under any other usage conditions are not guaranteed.
816		* This method may be useful when executing
817		* pre-constructed trees of subtasks in loops.
818	+	*
819	+	* <p>Upon completion of this method, {@code isDone()} reports
820	+	* {@code false}, and {@code getException()} reports {@code
821	+	* null}. However, the value returned by {@code getRawResult} is
822	+	* unaffected. To clear this value, you can invoke {@code
823	+	* setRawResult(null)}.
824		*/
825		public void reinitialize() {
826		if (status == EXCEPTIONAL)
#	Line 832 | Line 842 | public abstract class ForkJoinTask<V> im
842		}
843
844		/**
845	<	* Returns {@code true} if the current thread is executing as a
846	<	* ForkJoinPool computation.
845	>	* Returns {@code true} if the current thread is a {@link
846	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
847		*
848	<	* @return {@code true} if the current thread is executing as a
849	<	* ForkJoinPool computation, or false otherwise
848	>	* @return {@code true} if the current thread is a {@link
849	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
850	>	* or {@code false} otherwise
851		*/
852		public static boolean inForkJoinPool() {
853		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 851 | Line 862 | public abstract class ForkJoinTask<V> im
862		* were not, stolen.
863		*
864		* <p>This method may be invoked only from within {@code
865	<	* ForkJoinTask} computations (as may be determined using method
865	>	* ForkJoinPool} computations (as may be determined using method
866		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
867		* result in exceptions or errors, possibly including {@code
868		* ClassCastException}.
#	Line 870 | Line 881 | public abstract class ForkJoinTask<V> im
881		* fork other tasks.
882		*
883		* <p>This method may be invoked only from within {@code
884	<	* ForkJoinTask} computations (as may be determined using method
884	>	* ForkJoinPool} computations (as may be determined using method
885		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
886		* result in exceptions or errors, possibly including {@code
887		* ClassCastException}.
#	Line 893 | Line 904 | public abstract class ForkJoinTask<V> im
904		* exceeded.
905		*
906		* <p>This method may be invoked only from within {@code
907	<	* ForkJoinTask} computations (as may be determined using method
907	>	* ForkJoinPool} computations (as may be determined using method
908		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
909		* result in exceptions or errors, possibly including {@code
910		* ClassCastException}.
#	Line 951 | Line 962 | public abstract class ForkJoinTask<V> im
962		* otherwise.
963		*
964		* <p>This method may be invoked only from within {@code
965	<	* ForkJoinTask} computations (as may be determined using method
965	>	* ForkJoinPool} computations (as may be determined using method
966		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
967		* result in exceptions or errors, possibly including {@code
968		* ClassCastException}.
#	Line 970 | Line 981 | public abstract class ForkJoinTask<V> im
981		* be useful otherwise.
982		*
983		* <p>This method may be invoked only from within {@code
984	<	* ForkJoinTask} computations (as may be determined using method
984	>	* ForkJoinPool} computations (as may be determined using method
985		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
986		* result in exceptions or errors, possibly including {@code
987		* ClassCastException}.
#	Line 993 | Line 1004 | public abstract class ForkJoinTask<V> im
1004		* otherwise.
1005		*
1006		* <p>This method may be invoked only from within {@code
1007	<	* ForkJoinTask} computations (as may be determined using method
1007	>	* ForkJoinPool} computations (as may be determined using method
1008		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1009		* result in exceptions or errors, possibly including {@code
1010		* ClassCastException}.

Diff Legend

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