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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.51 by dl, Fri Jul 23 16:49:11 2010 UTC vs.
Revision 1.64 by jsr166, Mon Sep 20 20:42:37 2010 UTC

#	Line 7 | Line 7
7		package jsr166y;
8
9		import java.util.concurrent.*;
10	–
10		import java.io.Serializable;
11		import java.util.Collection;
12		import java.util.Collections;
#	Line 28 | Line 27 | import java.util.WeakHashMap;
27		* start other subtasks.  As indicated by the name of this class,
28		* many programs using {@code ForkJoinTask} employ only methods
29		* {@link #fork} and {@link #join}, or derivatives such as {@link
30	<	* #invokeAll}.  However, this class also provides a number of other
31	<	* methods that can come into play in advanced usages, as well as
32	<	* extension mechanics that allow support of new forms of fork/join
33	<	* processing.
30	>	* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
31	>	* provides a number of other methods that can come into play in
32	>	* advanced usages, as well as extension mechanics that allow
33	>	* support of new forms of fork/join processing.
34		*
35		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
36		* The efficiency of {@code ForkJoinTask}s stems from a set of
#	Line 100 | Line 99 | import java.util.WeakHashMap;
99		* ForkJoinTasks (as may be determined using method {@link
100		* #inForkJoinPool}).  Attempts to invoke them in other contexts
101		* result in exceptions or errors, possibly including
102	<	* ClassCastException.
102	>	* {@code ClassCastException}.
103		*
104		* <p>Most base support methods are {@code final}, to prevent
105		* overriding of implementations that are intrinsically tied to the
#	Line 144 | Line 143 | public abstract class ForkJoinTask<V> im
143		* status maintenance (2) execution and awaiting completion (3)
144		* user-level methods that additionally report results. This is
145		* sometimes hard to see because this file orders exported methods
146	<	* in a way that flows well in javadocs.
146	>	* in a way that flows well in javadocs. In particular, most
147	>	* join mechanics are in method quietlyJoin, below.
148		*/
149
150		/*
#	Line 152 | Line 152 | public abstract class ForkJoinTask<V> im
152		* single int to minimize footprint and to ensure atomicity (via
153		* CAS).  Status is initially zero, and takes on nonnegative
154		* values until completed, upon which status holds value
155	<	* COMPLETED. CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
155	>	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
156		* waits by other threads have the SIGNAL bit set.  Completion of
157		* a stolen task with SIGNAL set awakens any waiters via
158		* notifyAll. Even though suboptimal for some purposes, we use
#	Line 164 | Line 164 | public abstract class ForkJoinTask<V> im
164		* them.
165		*/
166
167	<	/** Run status of this task */
167	>	/** The run status of this task */
168		volatile int status; // accessed directly by pool and workers
169
170		private static final int NORMAL      = -1;
#	Line 191 | Line 191 | public abstract class ForkJoinTask<V> im
191		* also clearing signal request bits.
192		*
193		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
194	–	* @return status on exit
194		*/
195	<	private int setCompletion(int completion) {
195	>	private void setCompletion(int completion) {
196		int s;
197		while ((s = status) >= 0) {
198		if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
199		if (s != 0)
200		synchronized (this) { notifyAll(); }
201	<	return completion;
201	>	break;
202		}
203		}
205	–	return s;
204		}
205
206		/**
207	<	* Record exception and set exceptional completion
207	>	* Records exception and sets exceptional completion.
208	>	*
209		* @return status on exit
210		*/
211	<	private int setExceptionalCompletion(Throwable rex) {
211	>	private void setExceptionalCompletion(Throwable rex) {
212		exceptionMap.put(this, rex);
213	<	return setCompletion(EXCEPTIONAL);
213	>	setCompletion(EXCEPTIONAL);
214		}
215
216		/**
217	<	* Blocks a worker thread until completion. Called only by pool.
217	>	* Blocks a worker thread until completion. Called only by
218	>	* pool. Currently unused -- pool-based waits use timeout
219	>	* version below.
220		*/
221		final void internalAwaitDone() {
222		int s;         // the odd construction reduces lock bias effects
223		while ((s = status) >= 0) {
224		try {
225	<	synchronized(this) {
225	>	synchronized (this) {
226		if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
227		wait();
228		}
#	Line 232 | Line 233 | public abstract class ForkJoinTask<V> im
233		}
234
235		/**
236	<	* Blocks a non-worker-thread until completion.
236	>	* Blocks a worker thread until completed or timed out.  Called
237	>	* only by pool.
238	>	*
239		* @return status on exit
240		*/
241	<	private int externalAwaitDone() {
241	>	final int internalAwaitDone(long millis) {
242	>	int s;
243	>	if ((s = status) >= 0) {
244	>	try {
245	>	synchronized (this) {
246	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
247	>	wait(millis, 0);
248	>	}
249	>	} catch (InterruptedException ie) {
250	>	cancelIfTerminating();
251	>	}
252	>	s = status;
253	>	}
254	>	return s;
255	>	}
256	>
257	>	/**
258	>	* Blocks a non-worker-thread until completion.
259	>	*/
260	>	private void externalAwaitDone() {
261		int s;
262		while ((s = status) >= 0) {
263	<	synchronized(this) {
263	>	synchronized (this) {
264		if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
265		boolean interrupted = false;
266	<	while ((s = status) >= 0) {
266	>	while (status >= 0) {
267		try {
268		wait();
269		} catch (InterruptedException ie) {
#	Line 254 | Line 276 | public abstract class ForkJoinTask<V> im
276		}
277		}
278		}
257	–	return s;
279		}
280
281		/**
#	Line 262 | Line 283 | public abstract class ForkJoinTask<V> im
283		* doesn't wait for completion otherwise. Primary execution method
284		* for ForkJoinWorkerThread.
285		*/
286	<	final void tryExec() {
286	>	final void quietlyExec() {
287		try {
288		if (status < 0 || !exec())
289		return;
#	Line 273 | Line 294 | public abstract class ForkJoinTask<V> im
294		setCompletion(NORMAL); // must be outside try block
295		}
296
276	–	/**
277	–	* If not done and this task is next in worker queue, runs it,
278	–	* else waits for it.
279	–	* @return status on exit
280	–	*/
281	–	private int doJoin() {
282	–	int stat;
283	–	if ((stat = status) < 0)
284	–	return stat;
285	–	Thread t = Thread.currentThread();
286	–	ForkJoinWorkerThread w;
287	–	if (t instanceof ForkJoinWorkerThread) {
288	–	if ((w = (ForkJoinWorkerThread) t).unpushTask(this)) {
289	–	boolean completed;
290	–	try {
291	–	completed = exec();
292	–	} catch (Throwable rex) {
293	–	return setExceptionalCompletion(rex);
294	–	}
295	–	if (completed)
296	–	return setCompletion(NORMAL);
297	–	}
298	–	return w.joinTask(this);
299	–	}
300	–	return externalAwaitDone();
301	–	}
302	–
303	–	/**
304	–	* Unless done, calls exec and records status if completed, or
305	–	* waits for completion otherwise.
306	–	* @return status on exit
307	–	*/
308	–	private int doInvoke() {
309	–	int stat;
310	–	if ((stat = status) >= 0) {
311	–	boolean completed;
312	–	try {
313	–	completed = exec();
314	–	} catch (Throwable rex) {
315	–	return setExceptionalCompletion(rex);
316	–	}
317	–	stat = completed ? setCompletion(NORMAL) : doJoin();
318	–	}
319	–	return stat;
320	–	}
321	–
322	–	/**
323	–	* Returns result or throws exception associated with given status.
324	–	* @param s the status
325	–	*/
326	–	private V reportResult(int s) {
327	–	Throwable ex;
328	–	if (s < NORMAL && (ex = getException()) != null)
329	–	UNSAFE.throwException(ex);
330	–	return getRawResult();
331	–	}
332	–
297		// public methods
298
299		/**
#	Line 365 | Line 329 | public abstract class ForkJoinTask<V> im
329		* @return the computed result
330		*/
331		public final V join() {
332	<	return reportResult(doJoin());
332	>	quietlyJoin();
333	>	Throwable ex;
334	>	if (status < NORMAL && (ex = getException()) != null)
335	>	UNSAFE.throwException(ex);
336	>	return getRawResult();
337		}
338
339		/**
340		* Commences performing this task, awaits its completion if
341	<	* necessary, and return its result, or throws an (unchecked)
342	<	* exception if the underlying computation did so.
341	>	* necessary, and returns its result, or throws an (unchecked)
342	>	* {@code RuntimeException} or {@code Error} if the underlying
343	>	* computation did so.
344		*
345		* @return the computed result
346		*/
347		public final V invoke() {
348	<	return reportResult(doInvoke());
348	>	quietlyInvoke();
349	>	Throwable ex;
350	>	if (status < NORMAL && (ex = getException()) != null)
351	>	UNSAFE.throwException(ex);
352	>	return getRawResult();
353		}
354
355		/**
356		* Forks the given tasks, returning when {@code isDone} holds for
357		* each task or an (unchecked) exception is encountered, in which
358	<	* case the exception is rethrown.  If either task encounters an
359	<	* exception, the other one may be, but is not guaranteed to be,
360	<	* cancelled.  If both tasks throw an exception, then this method
361	<	* throws one of them.  The individual status of each task may be
362	<	* checked using {@link #getException()} and related methods.
358	>	* case the exception is rethrown. If more than one task
359	>	* encounters an exception, then this method throws any one of
360	>	* these exceptions. If any task encounters an exception, the
361	>	* other may be cancelled. However, the execution status of
362	>	* individual tasks is not guaranteed upon exceptional return. The
363	>	* status of each task may be obtained using {@link
364	>	* #getException()} and related methods to check if they have been
365	>	* cancelled, completed normally or exceptionally, or left
366	>	* unprocessed.
367		*
368		* <p>This method may be invoked only from within {@code
369		* ForkJoinTask} computations (as may be determined using method
#	Line 407 | Line 384 | public abstract class ForkJoinTask<V> im
384		/**
385		* Forks the given tasks, returning when {@code isDone} holds for
386		* each task or an (unchecked) exception is encountered, in which
387	<	* case the exception is rethrown. If any task encounters an
388	<	* exception, others may be, but are not guaranteed to be,
389	<	* cancelled.  If more than one task encounters an exception, then
390	<	* this method throws any one of these exceptions.  The individual
391	<	* status of each task may be checked using {@link #getException()}
392	<	* and related methods.
387	>	* case the exception is rethrown. If more than one task
388	>	* encounters an exception, then this method throws any one of
389	>	* these exceptions. If any task encounters an exception, others
390	>	* may be cancelled. However, the execution status of individual
391	>	* tasks is not guaranteed upon exceptional return. The status of
392	>	* each task may be obtained using {@link #getException()} and
393	>	* related methods to check if they have been cancelled, completed
394	>	* normally or exceptionally, or left unprocessed.
395		*
396		* <p>This method may be invoked only from within {@code
397		* ForkJoinTask} computations (as may be determined using method
#	Line 434 | Line 413 | public abstract class ForkJoinTask<V> im
413		}
414		else if (i != 0)
415		t.fork();
416	<	else if (t.doInvoke() < NORMAL && ex == null)
417	<	ex = t.getException();
416	>	else {
417	>	t.quietlyInvoke();
418	>	if (ex == null && t.status < NORMAL)
419	>	ex = t.getException();
420	>	}
421		}
422		for (int i = 1; i <= last; ++i) {
423		ForkJoinTask<?> t = tasks[i];
424		if (t != null) {
425		if (ex != null)
426		t.cancel(false);
427	<	else if (t.doJoin() < NORMAL && ex == null)
428	<	ex = t.getException();
427	>	else {
428	>	t.quietlyJoin();
429	>	if (ex == null && t.status < NORMAL)
430	>	ex = t.getException();
431	>	}
432		}
433		}
434		if (ex != null)
#	Line 453 | Line 438 | public abstract class ForkJoinTask<V> im
438		/**
439		* Forks all tasks in the specified collection, returning when
440		* {@code isDone} holds for each task or an (unchecked) exception
441	<	* is encountered.  If any task encounters an exception, others
442	<	* may be, but are not guaranteed to be, cancelled.  If more than
443	<	* one task encounters an exception, then this method throws any
444	<	* one of these exceptions.  The individual status of each task
445	<	* may be checked using {@link #getException()} and related
446	<	* methods.  The behavior of this operation is undefined if the
447	<	* specified collection is modified while the operation is in
448	<	* progress.
441	>	* is encountered, in which case the exception is rethrown. If
442	>	* more than one task encounters an exception, then this method
443	>	* throws any one of these exceptions. If any task encounters an
444	>	* exception, others may be cancelled. However, the execution
445	>	* status of individual tasks is not guaranteed upon exceptional
446	>	* return. The status of each task may be obtained using {@link
447	>	* #getException()} and related methods to check if they have been
448	>	* cancelled, completed normally or exceptionally, or left
449	>	* unprocessed.
450		*
451		* <p>This method may be invoked only from within {@code
452		* ForkJoinTask} computations (as may be determined using method
#	Line 490 | Line 476 | public abstract class ForkJoinTask<V> im
476		}
477		else if (i != 0)
478		t.fork();
479	<	else if (t.doInvoke() < NORMAL && ex == null)
480	<	ex = t.getException();
479	>	else {
480	>	t.quietlyInvoke();
481	>	if (ex == null && t.status < NORMAL)
482	>	ex = t.getException();
483	>	}
484		}
485		for (int i = 1; i <= last; ++i) {
486		ForkJoinTask<?> t = ts.get(i);
487		if (t != null) {
488		if (ex != null)
489		t.cancel(false);
490	<	else if (t.doJoin() < NORMAL && ex == null)
491	<	ex = t.getException();
490	>	else {
491	>	t.quietlyJoin();
492	>	if (ex == null && t.status < NORMAL)
493	>	ex = t.getException();
494	>	}
495		}
496		}
497		if (ex != null)
#	Line 532 | Line 524 | public abstract class ForkJoinTask<V> im
524		* @return {@code true} if this task is now cancelled
525		*/
526		public boolean cancel(boolean mayInterruptIfRunning) {
527	<	return setCompletion(CANCELLED) == CANCELLED;
527	>	setCompletion(CANCELLED);
528	>	return status == CANCELLED;
529		}
530
531		/**
532	<	* Cancels, ignoring any exceptions it throws. Used during worker
533	<	* and pool shutdown.
532	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
533	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
534	>	* exceptions, but if it does anyway, we have no recourse during
535	>	* shutdown, so guard against this case.
536		*/
537		final void cancelIgnoringExceptions() {
538		try {
#	Line 547 | Line 542 | public abstract class ForkJoinTask<V> im
542		}
543
544		/**
545	<	* Cancels ignoring exceptions if worker is terminating
545	>	* Cancels if current thread is a terminating worker thread,
546	>	* ignoring any exceptions thrown by cancel.
547		*/
548		final void cancelIfTerminating() {
549		Thread t = Thread.currentThread();
#	Line 624 | Line 620 | public abstract class ForkJoinTask<V> im
620
621		/**
622		* Completes this task, and if not already aborted or cancelled,
623	<	* returning a {@code null} result upon {@code join} and related
624	<	* operations. This method may be used to provide results for
625	<	* asynchronous tasks, or to provide alternative handling for
626	<	* tasks that would not otherwise complete normally. Its use in
627	<	* other situations is discouraged. This method is
628	<	* overridable, but overridden versions must invoke {@code super}
629	<	* implementation to maintain guarantees.
623	>	* returning the given value as the result of subsequent
624	>	* invocations of {@code join} and related operations. This method
625	>	* may be used to provide results for asynchronous tasks, or to
626	>	* provide alternative handling for tasks that would not otherwise
627	>	* complete normally. Its use in other situations is
628	>	* discouraged. This method is overridable, but overridden
629	>	* versions must invoke {@code super} implementation to maintain
630	>	* guarantees.
631		*
632		* @param value the result value for this task
633		*/
#	Line 644 | Line 641 | public abstract class ForkJoinTask<V> im
641		setCompletion(NORMAL);
642		}
643
644	+	/**
645	+	* Waits if necessary for the computation to complete, and then
646	+	* retrieves its result.
647	+	*
648	+	* @return the computed result
649	+	* @throws CancellationException if the computation was cancelled
650	+	* @throws ExecutionException if the computation threw an
651	+	* exception
652	+	* @throws InterruptedException if the current thread is not a
653	+	* member of a ForkJoinPool and was interrupted while waiting
654	+	*/
655		public final V get() throws InterruptedException, ExecutionException {
656	<	int s = doJoin();
657	<	if (Thread.interrupted())
658	<	throw new InterruptedException();
656	>	int s;
657	>	if (Thread.currentThread() instanceof ForkJoinWorkerThread) {
658	>	quietlyJoin();
659	>	s = status;
660	>	}
661	>	else {
662	>	while ((s = status) >= 0) {
663	>	synchronized (this) { // interruptible form of awaitDone
664	>	if (UNSAFE.compareAndSwapInt(this, statusOffset,
665	>	s, SIGNAL)) {
666	>	while (status >= 0)
667	>	wait();
668	>	}
669	>	}
670	>	}
671	>	}
672		if (s < NORMAL) {
673		Throwable ex;
674		if (s == CANCELLED)
#	Line 658 | Line 679 | public abstract class ForkJoinTask<V> im
679		return getRawResult();
680		}
681
682	+	/**
683	+	* Waits if necessary for at most the given time for the computation
684	+	* to complete, and then retrieves its result, if available.
685	+	*
686	+	* @param timeout the maximum time to wait
687	+	* @param unit the time unit of the timeout argument
688	+	* @return the computed result
689	+	* @throws CancellationException if the computation was cancelled
690	+	* @throws ExecutionException if the computation threw an
691	+	* exception
692	+	* @throws InterruptedException if the current thread is not a
693	+	* member of a ForkJoinPool and was interrupted while waiting
694	+	* @throws TimeoutException if the wait timed out
695	+	*/
696		public final V get(long timeout, TimeUnit unit)
697		throws InterruptedException, ExecutionException, TimeoutException {
698		Thread t = Thread.currentThread();
#	Line 665 | Line 700 | public abstract class ForkJoinTask<V> im
700		if (t instanceof ForkJoinWorkerThread) {
701		ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
702		if (status >= 0 && w.unpushTask(this))
703	<	tryExec();
703	>	quietlyExec();
704		pool = w.pool;
705		}
706		else
707		pool = null;
708		/*
709	<	* Timed wait loop intermixes cases for fj (pool != null) and
709	>	* Timed wait loop intermixes cases for FJ (pool != null) and
710		* non FJ threads. For FJ, decrement pool count but don't try
711		* for replacement; increment count on completion. For non-FJ,
712		* deal with interrupts. This is messy, but a little less so
#	Line 679 | Line 714 | public abstract class ForkJoinTask<V> im
714		*/
715		boolean interrupted = false;
716		boolean dec = false; // true if pool count decremented
717	+	long nanos = unit.toNanos(timeout);
718		for (;;) {
719	<	if (Thread.interrupted() && pool == null) {
719	>	if (pool == null && Thread.interrupted()) {
720		interrupted = true;
721		break;
722		}
723		int s = status;
724		if (s < 0)
725		break;
726	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
691	<	s, s | SIGNAL)) {
726	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
727		long startTime = System.nanoTime();
693	–	long nanos = unit.toNanos(timeout);
728		long nt; // wait time
729		while (status >= 0 &&
730		(nt = nanos - (System.nanoTime() - startTime)) > 0) {
#	Line 700 | Line 734 | public abstract class ForkJoinTask<V> im
734		long ms = nt / 1000000;
735		int ns = (int) (nt % 1000000);
736		try {
737	<	synchronized(this) {
737	>	synchronized (this) {
738		if (status >= 0)
739		wait(ms, ns);
740		}
#	Line 734 | Line 768 | public abstract class ForkJoinTask<V> im
768		}
769
770		/**
771	<	* Joins this task, without returning its result or throwing an
771	>	* Joins this task, without returning its result or throwing its
772		* exception. This method may be useful when processing
773		* collections of tasks when some have been cancelled or otherwise
774		* known to have aborted.
775		*/
776		public final void quietlyJoin() {
777	<	doJoin();
777	>	Thread t;
778	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
779	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
780	>	if (status >= 0) {
781	>	if (w.unpushTask(this)) {
782	>	boolean completed;
783	>	try {
784	>	completed = exec();
785	>	} catch (Throwable rex) {
786	>	setExceptionalCompletion(rex);
787	>	return;
788	>	}
789	>	if (completed) {
790	>	setCompletion(NORMAL);
791	>	return;
792	>	}
793	>	}
794	>	w.joinTask(this);
795	>	}
796	>	}
797	>	else
798	>	externalAwaitDone();
799		}
800
801		/**
802		* Commences performing this task and awaits its completion if
803	<	* necessary, without returning its result or throwing an
804	<	* exception. This method may be useful when processing
750	<	* collections of tasks when some have been cancelled or otherwise
751	<	* known to have aborted.
803	>	* necessary, without returning its result or throwing its
804	>	* exception.
805		*/
806		public final void quietlyInvoke() {
807	<	doInvoke();
807	>	if (status >= 0) {
808	>	boolean completed;
809	>	try {
810	>	completed = exec();
811	>	} catch (Throwable rex) {
812	>	setExceptionalCompletion(rex);
813	>	return;
814	>	}
815	>	if (completed)
816	>	setCompletion(NORMAL);
817	>	else
818	>	quietlyJoin();
819	>	}
820		}
821
822		/**
#	Line 1073 | Line 1138 | public abstract class ForkJoinTask<V> im
1138		private static final long serialVersionUID = -7721805057305804111L;
1139
1140		/**
1141	<	* Saves the state to a stream.
1141	>	* Saves the state to a stream (that is, serializes it).
1142		*
1143		* @serialData the current run status and the exception thrown
1144		* during execution, or {@code null} if none
#	Line 1086 | Line 1151 | public abstract class ForkJoinTask<V> im
1151		}
1152
1153		/**
1154	<	* Reconstitutes the instance from a stream.
1154	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1155		*
1156		* @param s the stream
1157		*/

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