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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.54 by dl, Wed Aug 11 19:44:30 2010 UTC vs.
Revision 1.66 by dl, Sun Oct 24 19:37:26 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 100 | Line 108 | import java.util.WeakHashMap;
108		* ForkJoinTasks (as may be determined using method {@link
109		* #inForkJoinPool}).  Attempts to invoke them in other contexts
110		* result in exceptions or errors, possibly including
111	<	* ClassCastException.
111	>	* {@code ClassCastException}.
112		*
113		* <p>Most base support methods are {@code final}, to prevent
114		* overriding of implementations that are intrinsically tied to the
#	Line 153 | Line 161 | public abstract class ForkJoinTask<V> im
161		* single int to minimize footprint and to ensure atomicity (via
162		* CAS).  Status is initially zero, and takes on nonnegative
163		* values until completed, upon which status holds value
164	<	* COMPLETED. CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
164	>	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
165		* waits by other threads have the SIGNAL bit set.  Completion of
166		* a stolen task with SIGNAL set awakens any waiters via
167		* notifyAll. Even though suboptimal for some purposes, we use
#	Line 205 | Line 213 | public abstract class ForkJoinTask<V> im
213		}
214
215		/**
216	<	* Record exception and set exceptional completion
216	>	* Records exception and sets exceptional completion.
217	>	*
218		* @return status on exit
219		*/
220		private void setExceptionalCompletion(Throwable rex) {
#	Line 214 | Line 223 | public abstract class ForkJoinTask<V> im
223		}
224
225		/**
226	<	* Blocks a worker thread until completion. Called only by pool.
226	>	* Blocks a worker thread until completion. Called only by
227	>	* pool. Currently unused -- pool-based waits use timeout
228	>	* version below.
229		*/
230		final void internalAwaitDone() {
231		int s;         // the odd construction reduces lock bias effects
232		while ((s = status) >= 0) {
233		try {
234	<	synchronized(this) {
234	>	synchronized (this) {
235		if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
236		wait();
237		}
#	Line 231 | Line 242 | public abstract class ForkJoinTask<V> im
242		}
243
244		/**
245	+	* Blocks a worker thread until completed or timed out.  Called
246	+	* only by pool.
247	+	*
248	+	* @return status on exit
249	+	*/
250	+	final int internalAwaitDone(long millis, int nanos) {
251	+	int s;
252	+	if ((s = status) >= 0) {
253	+	try {
254	+	synchronized (this) {
255	+	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
256	+	wait(millis, nanos);
257	+	}
258	+	} catch (InterruptedException ie) {
259	+	cancelIfTerminating();
260	+	}
261	+	s = status;
262	+	}
263	+	return s;
264	+	}
265	+
266	+	/**
267		* Blocks a non-worker-thread until completion.
268		*/
269		private void externalAwaitDone() {
270		int s;
271		while ((s = status) >= 0) {
272	<	synchronized(this) {
273	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
272	>	synchronized (this) {
273	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
274		boolean interrupted = false;
275		while (status >= 0) {
276		try {
#	Line 314 | Line 347 | public abstract class ForkJoinTask<V> im
347
348		/**
349		* Commences performing this task, awaits its completion if
350	<	* necessary, and return its result, or throws an (unchecked)
351	<	* exception if the underlying computation did so.
350	>	* necessary, and returns its result, or throws an (unchecked)
351	>	* {@code RuntimeException} or {@code Error} if the underlying
352	>	* computation did so.
353		*
354		* @return the computed result
355		*/
#	Line 330 | Line 364 | public abstract class ForkJoinTask<V> im
364		/**
365		* Forks the given tasks, returning when {@code isDone} holds for
366		* each task or an (unchecked) exception is encountered, in which
367	<	* case the exception is rethrown.  If either task encounters an
368	<	* exception, the other one may be, but is not guaranteed to be,
369	<	* cancelled.  If both tasks throw an exception, then this method
370	<	* throws one of them.  The individual status of each task may be
371	<	* checked using {@link #getException()} and related methods.
367	>	* case the exception is rethrown. If more than one task
368	>	* encounters an exception, then this method throws any one of
369	>	* these exceptions. If any task encounters an exception, the
370	>	* other may be cancelled. However, the execution status of
371	>	* individual tasks is not guaranteed upon exceptional return. The
372	>	* status of each task may be obtained using {@link
373	>	* #getException()} and related methods to check if they have been
374	>	* cancelled, completed normally or exceptionally, or left
375	>	* unprocessed.
376		*
377		* <p>This method may be invoked only from within {@code
378		* ForkJoinTask} computations (as may be determined using method
#	Line 355 | Line 393 | public abstract class ForkJoinTask<V> im
393		/**
394		* Forks the given tasks, returning when {@code isDone} holds for
395		* each task or an (unchecked) exception is encountered, in which
396	<	* case the exception is rethrown. If any task encounters an
397	<	* exception, others may be, but are not guaranteed to be,
398	<	* cancelled.  If more than one task encounters an exception, then
399	<	* this method throws any one of these exceptions.  The individual
400	<	* status of each task may be checked using {@link #getException()}
401	<	* and related methods.
396	>	* case the exception is rethrown. If more than one task
397	>	* encounters an exception, then this method throws any one of
398	>	* these exceptions. If any task encounters an exception, others
399	>	* may be cancelled. However, the execution status of individual
400	>	* tasks is not guaranteed upon exceptional return. The status of
401	>	* each task may be obtained using {@link #getException()} and
402	>	* related methods to check if they have been cancelled, completed
403	>	* normally or exceptionally, or left unprocessed.
404		*
405		* <p>This method may be invoked only from within {@code
406		* ForkJoinTask} computations (as may be determined using method
#	Line 407 | Line 447 | public abstract class ForkJoinTask<V> im
447		/**
448		* Forks all tasks in the specified collection, returning when
449		* {@code isDone} holds for each task or an (unchecked) exception
450	<	* is encountered.  If any task encounters an exception, others
451	<	* may be, but are not guaranteed to be, cancelled.  If more than
452	<	* one task encounters an exception, then this method throws any
453	<	* one of these exceptions.  The individual status of each task
454	<	* may be checked using {@link #getException()} and related
455	<	* methods.  The behavior of this operation is undefined if the
456	<	* specified collection is modified while the operation is in
457	<	* progress.
450	>	* is encountered, in which case the exception is rethrown. If
451	>	* more than one task encounters an exception, then this method
452	>	* throws any one of these exceptions. If any task encounters an
453	>	* exception, others may be cancelled. However, the execution
454	>	* status of individual tasks is not guaranteed upon exceptional
455	>	* return. The status of each task may be obtained using {@link
456	>	* #getException()} and related methods to check if they have been
457	>	* cancelled, completed normally or exceptionally, or left
458	>	* unprocessed.
459		*
460		* <p>This method may be invoked only from within {@code
461		* ForkJoinTask} computations (as may be determined using method
#	Line 510 | Line 551 | public abstract class ForkJoinTask<V> im
551		}
552
553		/**
554	<	* Cancels ignoring exceptions if worker is terminating
554	>	* Cancels if current thread is a terminating worker thread,
555	>	* ignoring any exceptions thrown by cancel.
556		*/
557		final void cancelIfTerminating() {
558		Thread t = Thread.currentThread();
#	Line 587 | Line 629 | public abstract class ForkJoinTask<V> im
629
630		/**
631		* Completes this task, and if not already aborted or cancelled,
632	<	* returning a {@code null} result upon {@code join} and related
633	<	* operations. This method may be used to provide results for
634	<	* asynchronous tasks, or to provide alternative handling for
635	<	* tasks that would not otherwise complete normally. Its use in
636	<	* other situations is discouraged. This method is
637	<	* overridable, but overridden versions must invoke {@code super}
638	<	* implementation to maintain guarantees.
632	>	* returning the given value as the result of subsequent
633	>	* invocations of {@code join} and related operations. This method
634	>	* may be used to provide results for asynchronous tasks, or to
635	>	* provide alternative handling for tasks that would not otherwise
636	>	* complete normally. Its use in other situations is
637	>	* discouraged. This method is overridable, but overridden
638	>	* versions must invoke {@code super} implementation to maintain
639	>	* guarantees.
640		*
641		* @param value the result value for this task
642		*/
#	Line 607 | Line 650 | public abstract class ForkJoinTask<V> im
650		setCompletion(NORMAL);
651		}
652
653	+	/**
654	+	* Waits if necessary for the computation to complete, and then
655	+	* retrieves its result.
656	+	*
657	+	* @return the computed result
658	+	* @throws CancellationException if the computation was cancelled
659	+	* @throws ExecutionException if the computation threw an
660	+	* exception
661	+	* @throws InterruptedException if the current thread is not a
662	+	* member of a ForkJoinPool and was interrupted while waiting
663	+	*/
664		public final V get() throws InterruptedException, ExecutionException {
665	<	quietlyJoin();
666	<	if (Thread.interrupted())
667	<	throw new InterruptedException();
668	<	int s = status;
665	>	int s;
666	>	if (Thread.currentThread() instanceof ForkJoinWorkerThread) {
667	>	quietlyJoin();
668	>	s = status;
669	>	}
670	>	else {
671	>	while ((s = status) >= 0) {
672	>	synchronized (this) { // interruptible form of awaitDone
673	>	if (UNSAFE.compareAndSwapInt(this, statusOffset,
674	>	s, SIGNAL)) {
675	>	while (status >= 0)
676	>	wait();
677	>	}
678	>	}
679	>	}
680	>	}
681		if (s < NORMAL) {
682		Throwable ex;
683		if (s == CANCELLED)
#	Line 622 | Line 688 | public abstract class ForkJoinTask<V> im
688		return getRawResult();
689		}
690
691	+	/**
692	+	* Waits if necessary for at most the given time for the computation
693	+	* to complete, and then retrieves its result, if available.
694	+	*
695	+	* @param timeout the maximum time to wait
696	+	* @param unit the time unit of the timeout argument
697	+	* @return the computed result
698	+	* @throws CancellationException if the computation was cancelled
699	+	* @throws ExecutionException if the computation threw an
700	+	* exception
701	+	* @throws InterruptedException if the current thread is not a
702	+	* member of a ForkJoinPool and was interrupted while waiting
703	+	* @throws TimeoutException if the wait timed out
704	+	*/
705		public final V get(long timeout, TimeUnit unit)
706		throws InterruptedException, ExecutionException, TimeoutException {
627	–	Thread t = Thread.currentThread();
628	–	ForkJoinPool pool;
629	–	if (t instanceof ForkJoinWorkerThread) {
630	–	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
631	–	if (status >= 0 && w.unpushTask(this))
632	–	quietlyExec();
633	–	pool = w.pool;
634	–	}
635	–	else
636	–	pool = null;
637	–	/*
638	–	* Timed wait loop intermixes cases for FJ (pool != null) and
639	–	* non FJ threads. For FJ, decrement pool count but don't try
640	–	* for replacement; increment count on completion. For non-FJ,
641	–	* deal with interrupts. This is messy, but a little less so
642	–	* than is splitting the FJ and nonFJ cases.
643	–	*/
644	–	boolean interrupted = false;
645	–	boolean dec = false; // true if pool count decremented
707		long nanos = unit.toNanos(timeout);
708	<	for (;;) {
709	<	if (Thread.interrupted() && pool == null) {
710	<	interrupted = true;
711	<	break;
708	>	if (status >= 0) {
709	>	Thread t = Thread.currentThread();
710	>	if (t instanceof ForkJoinWorkerThread) {
711	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
712	>	boolean completed = false; // timed variant of quietlyJoin
713	>	if (w.unpushTask(this)) {
714	>	try {
715	>	completed = exec();
716	>	} catch (Throwable rex) {
717	>	setExceptionalCompletion(rex);
718	>	}
719	>	}
720	>	if (completed)
721	>	setCompletion(NORMAL);
722	>	else if (status >= 0)
723	>	w.joinTask(this, true, nanos);
724		}
725	<	int s = status;
726	<	if (s < 0)
727	<	break;
655	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
725	>	else if (Thread.interrupted())
726	>	throw new InterruptedException();
727	>	else {
728		long startTime = System.nanoTime();
729	<	long nt; // wait time
730	<	while (status >= 0 &&
729	>	int s; long nt;
730	>	while ((s = status) >= 0 &&
731		(nt = nanos - (System.nanoTime() - startTime)) > 0) {
732	<	if (pool != null && !dec)
733	<	dec = pool.tryDecrementRunningCount();
662	<	else {
732	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,
733	>	SIGNAL)) {
734		long ms = nt / 1000000;
735		int ns = (int) (nt % 1000000);
736	<	try {
737	<	synchronized(this) {
738	<	if (status >= 0)
668	<	wait(ms, ns);
669	<	}
670	<	} catch (InterruptedException ie) {
671	<	if (pool != null)
672	<	cancelIfTerminating();
673	<	else {
674	<	interrupted = true;
675	<	break;
676	<	}
736	>	synchronized (this) {
737	>	if (status >= 0)
738	>	wait(ms, ns); // exit on IE throw
739		}
740		}
741		}
680	–	break;
742		}
743		}
683	–	if (pool != null && dec)
684	–	pool.incrementRunningCount();
685	–	if (interrupted)
686	–	throw new InterruptedException();
744		int es = status;
745		if (es != NORMAL) {
746		Throwable ex;
#	Line 720 | Line 777 | public abstract class ForkJoinTask<V> im
777		return;
778		}
779		}
780	<	w.joinTask(this);
780	>	w.joinTask(this, false, 0L);
781		}
782		}
783		else
#	Line 730 | Line 787 | public abstract class ForkJoinTask<V> im
787		/**
788		* Commences performing this task and awaits its completion if
789		* necessary, without returning its result or throwing its
790	<	* exception. This method may be useful when processing
734	<	* collections of tasks when some have been cancelled or otherwise
735	<	* known to have aborted.
790	>	* exception.
791		*/
792		public final void quietlyInvoke() {
793		if (status >= 0) {
#	Line 1069 | Line 1124 | public abstract class ForkJoinTask<V> im
1124		private static final long serialVersionUID = -7721805057305804111L;
1125
1126		/**
1127	<	* Saves the state to a stream.
1127	>	* Saves the state to a stream (that is, serializes it).
1128		*
1129		* @serialData the current run status and the exception thrown
1130		* during execution, or {@code null} if none
#	Line 1082 | Line 1137 | public abstract class ForkJoinTask<V> im
1137		}
1138
1139		/**
1140	<	* Reconstitutes the instance from a stream.
1140	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1141		*
1142		* @param s the stream
1143		*/

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