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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.49 by dl, Wed Jul 7 19:52:31 2010 UTC vs.
Revision 1.62 by dl, Fri Sep 17 14:24:56 2010 UTC

#	Line 28 | Line 28 | import java.util.WeakHashMap;
28		* start other subtasks.  As indicated by the name of this class,
29		* many programs using {@code ForkJoinTask} employ only methods
30		* {@link #fork} and {@link #join}, or derivatives such as {@link
31	<	* #invokeAll}.  However, this class also provides a number of other
32	<	* methods that can come into play in advanced usages, as well as
33	<	* extension mechanics that allow support of new forms of fork/join
34	<	* processing.
31	>	* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
32	>	* provides a number of other methods that can come into play in
33	>	* advanced usages, as well as extension mechanics that allow
34	>	* support of new forms of fork/join processing.
35		*
36		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
37		* The efficiency of {@code ForkJoinTask}s stems from a set of
#	Line 100 | Line 100 | import java.util.WeakHashMap;
100		* ForkJoinTasks (as may be determined using method {@link
101		* #inForkJoinPool}).  Attempts to invoke them in other contexts
102		* result in exceptions or errors, possibly including
103	<	* ClassCastException.
103	>	* {@code ClassCastException}.
104		*
105		* <p>Most base support methods are {@code final}, to prevent
106		* overriding of implementations that are intrinsically tied to the
#	Line 144 | Line 144 | public abstract class ForkJoinTask<V> im
144		* status maintenance (2) execution and awaiting completion (3)
145		* user-level methods that additionally report results. This is
146		* sometimes hard to see because this file orders exported methods
147	<	* in a way that flows well in javadocs.
147	>	* in a way that flows well in javadocs. In particular, most
148	>	* join mechanics are in method quietlyJoin, below.
149		*/
150
151	<	/**
152	<	* Run control status bits packed into a single int to minimize
153	<	* footprint and to ensure atomicity (via CAS).  Status is
154	<	* initially zero, and takes on nonnegative values until
155	<	* completed, upon which status holds value COMPLETED. CANCELLED,
156	<	* or EXCEPTIONAL. Tasks undergoing blocking waits by other
157	<	* threads have the SIGNAL bit set.  Completion of a stolen task
158	<	* with SIGNAL set awakens any waiters via notifyAll. Even though
159	<	* suboptimal for some purposes, we use basic builtin wait/notify
160	<	* to take advantage of "monitor inflation" in JVMs that we would
161	<	* otherwise need to emulate to avoid adding further per-task
162	<	* bookkeeping overhead.  We want these monitors to be "fat",
163	<	* i.e., not use biasing or thin-lock techniques, so use some odd
164	<	* coding idioms that tend to avoid them.
151	>	/*
152	>	* The status field holds run control status bits packed into a
153	>	* single int to minimize footprint and to ensure atomicity (via
154	>	* CAS).  Status is initially zero, and takes on nonnegative
155	>	* values until completed, upon which status holds value
156	>	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
157	>	* waits by other threads have the SIGNAL bit set.  Completion of
158	>	* a stolen task with SIGNAL set awakens any waiters via
159	>	* notifyAll. Even though suboptimal for some purposes, we use
160	>	* basic builtin wait/notify to take advantage of "monitor
161	>	* inflation" in JVMs that we would otherwise need to emulate to
162	>	* avoid adding further per-task bookkeeping overhead.  We want
163	>	* these monitors to be "fat", i.e., not use biasing or thin-lock
164	>	* techniques, so use some odd coding idioms that tend to avoid
165	>	* them.
166		*/
167	+
168	+	/** The run status of this task */
169		volatile int status; // accessed directly by pool and workers
170
171		private static final int NORMAL      = -1;
#	Line 188 | Line 192 | public abstract class ForkJoinTask<V> im
192		* also clearing signal request bits.
193		*
194		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
191	–	* @return status on exit
195		*/
196	<	private int setCompletion(int completion) {
196	>	private void setCompletion(int completion) {
197		int s;
198		while ((s = status) >= 0) {
199		if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
200	<	if (s == SIGNAL)
200	>	if (s != 0)
201		synchronized (this) { notifyAll(); }
202	<	return completion;
202	>	break;
203		}
204		}
202	–	return s;
205		}
206
207		/**
208	<	* Record exception and set exceptional completion
208	>	* Records exception and sets exceptional completion.
209	>	*
210		* @return status on exit
211		*/
212	<	private int setExceptionalCompletion(Throwable rex) {
212	>	private void setExceptionalCompletion(Throwable rex) {
213		exceptionMap.put(this, rex);
214	<	return setCompletion(EXCEPTIONAL);
214	>	setCompletion(EXCEPTIONAL);
215		}
216
217		/**
218	<	* Blocks a worker thread until completion. Called only by pool.
218	>	* Blocks a worker thread until completion. Called only by
219	>	* pool. Currently unused -- pool-based waits use timeout
220	>	* version below.
221		*/
222	<	final int internalAwaitDone() {
223	<	int s;
222	>	final void internalAwaitDone() {
223	>	int s;         // the odd construction reduces lock bias effects
224		while ((s = status) >= 0) {
225	<	synchronized(this) {
226	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
227	<	do {
228	<	try {
224	<	wait();
225	<	} catch (InterruptedException ie) {
226	<	cancelIfTerminating();
227	<	}
228	<	} while ((s = status) >= 0);
229	<	break;
225	>	try {
226	>	synchronized (this) {
227	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
228	>	wait();
229		}
230	+	} catch (InterruptedException ie) {
231	+	cancelIfTerminating();
232		}
233		}
234	+	}
235	+
236	+	/**
237	+	* Blocks a worker thread until completed or timed out.  Called
238	+	* only by pool.
239	+	*
240	+	* @return status on exit
241	+	*/
242	+	final int internalAwaitDone(long millis) {
243	+	int s;
244	+	if ((s = status) >= 0) {
245	+	try {
246	+	synchronized (this) {
247	+	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
248	+	wait(millis, 0);
249	+	}
250	+	} catch (InterruptedException ie) {
251	+	cancelIfTerminating();
252	+	}
253	+	s = status;
254	+	}
255		return s;
256		}
257
258		/**
259		* Blocks a non-worker-thread until completion.
238	–	* @return status on exit
260		*/
261	<	private int externalAwaitDone() {
261	>	private void externalAwaitDone() {
262		int s;
263		while ((s = status) >= 0) {
264	<	synchronized(this) {
264	>	synchronized (this) {
265		if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
266		boolean interrupted = false;
267	<	do {
267	>	while (status >= 0) {
268		try {
269		wait();
270		} catch (InterruptedException ie) {
271		interrupted = true;
272		}
273	<	} while ((s = status) >= 0);
273	>	}
274		if (interrupted)
275		Thread.currentThread().interrupt();
276		break;
277		}
278		}
279		}
259	–	return s;
280		}
281
282		/**
#	Line 264 | Line 284 | public abstract class ForkJoinTask<V> im
284		* doesn't wait for completion otherwise. Primary execution method
285		* for ForkJoinWorkerThread.
286		*/
287	<	final void tryExec() {
287	>	final void quietlyExec() {
288		try {
289		if (status < 0 || !exec())
290		return;
#	Line 275 | Line 295 | public abstract class ForkJoinTask<V> im
295		setCompletion(NORMAL); // must be outside try block
296		}
297
278	–	/**
279	–	* If not done and this task is next in worker queue, runs it,
280	–	* else waits for it.
281	–	* @return status on exit
282	–	*/
283	–	private int doJoin() {
284	–	int stat;
285	–	if ((stat = status) < 0)
286	–	return stat;
287	–	Thread t = Thread.currentThread();
288	–	ForkJoinWorkerThread w;
289	–	if (t instanceof ForkJoinWorkerThread) {
290	–	if ((w = (ForkJoinWorkerThread) t).unpushTask(this)) {
291	–	boolean completed;
292	–	try {
293	–	completed = exec();
294	–	} catch (Throwable rex) {
295	–	return setExceptionalCompletion(rex);
296	–	}
297	–	if (completed)
298	–	return setCompletion(NORMAL);
299	–	}
300	–	w.joinTask(this);
301	–	return status;
302	–	}
303	–	return externalAwaitDone();
304	–	}
305	–
306	–	/**
307	–	* Unless done, calls exec and records status if completed, or
308	–	* waits for completion otherwise.
309	–	* @return status on exit
310	–	*/
311	–	private int doInvoke() {
312	–	int stat;
313	–	if ((stat = status) >= 0) {
314	–	boolean completed;
315	–	try {
316	–	completed = exec();
317	–	} catch (Throwable rex) {
318	–	return setExceptionalCompletion(rex);
319	–	}
320	–	if (completed)
321	–	stat = setCompletion(NORMAL);
322	–	else
323	–	stat = doJoin();
324	–	}
325	–	return stat;
326	–	}
327	–
328	–	/**
329	–	* Returns result or throws exception associated with given status.
330	–	* @param s the status
331	–	*/
332	–	private V reportResult(int s) {
333	–	Throwable ex;
334	–	if (s < NORMAL && (ex = getException()) != null)
335	–	UNSAFE.throwException(ex);
336	–	return getRawResult();
337	–	}
338	–
298		// public methods
299
300		/**
#	Line 371 | Line 330 | public abstract class ForkJoinTask<V> im
330		* @return the computed result
331		*/
332		public final V join() {
333	<	return reportResult(doJoin());
333	>	quietlyJoin();
334	>	Throwable ex;
335	>	if (status < NORMAL && (ex = getException()) != null)
336	>	UNSAFE.throwException(ex);
337	>	return getRawResult();
338		}
339
340		/**
341		* Commences performing this task, awaits its completion if
342	<	* necessary, and return its result, or throws an (unchecked)
343	<	* exception if the underlying computation did so.
342	>	* necessary, and returns its result, or throws an (unchecked)
343	>	* {@code RuntimeException} or {@code Error} if the underlying
344	>	* computation did so.
345		*
346		* @return the computed result
347		*/
348		public final V invoke() {
349	<	return reportResult(doInvoke());
349	>	quietlyInvoke();
350	>	Throwable ex;
351	>	if (status < NORMAL && (ex = getException()) != null)
352	>	UNSAFE.throwException(ex);
353	>	return getRawResult();
354		}
355
356		/**
357		* Forks the given tasks, returning when {@code isDone} holds for
358		* each task or an (unchecked) exception is encountered, in which
359	<	* case the exception is rethrown.  If either task encounters an
360	<	* exception, the other one may be, but is not guaranteed to be,
361	<	* cancelled.  If both tasks throw an exception, then this method
362	<	* throws one of them.  The individual status of each task may be
363	<	* checked using {@link #getException()} and related methods.
359	>	* case the exception is rethrown. If more than one task
360	>	* encounters an exception, then this method throws any one of
361	>	* these exceptions. If any task encounters an exception, the
362	>	* other may be cancelled. However, the execution status of
363	>	* individual tasks is not guaranteed upon exceptional return. The
364	>	* status of each task may be obtained using {@link
365	>	* #getException()} and related methods to check if they have been
366	>	* cancelled, completed normally or exceptionally, or left
367	>	* unprocessed.
368		*
369		* <p>This method may be invoked only from within {@code
370		* ForkJoinTask} computations (as may be determined using method
#	Line 413 | Line 385 | public abstract class ForkJoinTask<V> im
385		/**
386		* Forks the given tasks, returning when {@code isDone} holds for
387		* each task or an (unchecked) exception is encountered, in which
388	<	* case the exception is rethrown. If any task encounters an
389	<	* exception, others may be, but are not guaranteed to be,
390	<	* cancelled.  If more than one task encounters an exception, then
391	<	* this method throws any one of these exceptions.  The individual
392	<	* status of each task may be checked using {@link #getException()}
393	<	* and related methods.
388	>	* case the exception is rethrown. If more than one task
389	>	* encounters an exception, then this method throws any one of
390	>	* these exceptions. If any task encounters an exception, others
391	>	* may be cancelled. However, the execution status of individual
392	>	* tasks is not guaranteed upon exceptional return. The status of
393	>	* each task may be obtained using {@link #getException()} and
394	>	* related methods to check if they have been cancelled, completed
395	>	* normally or exceptionally, or left unprocessed.
396		*
397		* <p>This method may be invoked only from within {@code
398		* ForkJoinTask} computations (as may be determined using method
#	Line 440 | Line 414 | public abstract class ForkJoinTask<V> im
414		}
415		else if (i != 0)
416		t.fork();
417	<	else if (t.doInvoke() < NORMAL && ex == null)
418	<	ex = t.getException();
417	>	else {
418	>	t.quietlyInvoke();
419	>	if (ex == null && t.status < NORMAL)
420	>	ex = t.getException();
421	>	}
422		}
423		for (int i = 1; i <= last; ++i) {
424		ForkJoinTask<?> t = tasks[i];
425		if (t != null) {
426		if (ex != null)
427		t.cancel(false);
428	<	else if (t.doJoin() < NORMAL && ex == null)
429	<	ex = t.getException();
428	>	else {
429	>	t.quietlyJoin();
430	>	if (ex == null && t.status < NORMAL)
431	>	ex = t.getException();
432	>	}
433		}
434		}
435		if (ex != null)
#	Line 459 | Line 439 | public abstract class ForkJoinTask<V> im
439		/**
440		* Forks all tasks in the specified collection, returning when
441		* {@code isDone} holds for each task or an (unchecked) exception
442	<	* is encountered.  If any task encounters an exception, others
443	<	* may be, but are not guaranteed to be, cancelled.  If more than
444	<	* one task encounters an exception, then this method throws any
445	<	* one of these exceptions.  The individual status of each task
446	<	* may be checked using {@link #getException()} and related
447	<	* methods.  The behavior of this operation is undefined if the
448	<	* specified collection is modified while the operation is in
449	<	* progress.
442	>	* is encountered, in which case the exception is rethrown. If
443	>	* more than one task encounters an exception, then this method
444	>	* throws any one of these exceptions. If any task encounters an
445	>	* exception, others may be cancelled. However, the execution
446	>	* status of individual tasks is not guaranteed upon exceptional
447	>	* return. The status of each task may be obtained using {@link
448	>	* #getException()} and related methods to check if they have been
449	>	* cancelled, completed normally or exceptionally, or left
450	>	* unprocessed.
451		*
452		* <p>This method may be invoked only from within {@code
453		* ForkJoinTask} computations (as may be determined using method
#	Line 496 | Line 477 | public abstract class ForkJoinTask<V> im
477		}
478		else if (i != 0)
479		t.fork();
480	<	else if (t.doInvoke() < NORMAL && ex == null)
481	<	ex = t.getException();
480	>	else {
481	>	t.quietlyInvoke();
482	>	if (ex == null && t.status < NORMAL)
483	>	ex = t.getException();
484	>	}
485		}
486		for (int i = 1; i <= last; ++i) {
487		ForkJoinTask<?> t = ts.get(i);
488		if (t != null) {
489		if (ex != null)
490		t.cancel(false);
491	<	else if (t.doJoin() < NORMAL && ex == null)
492	<	ex = t.getException();
491	>	else {
492	>	t.quietlyJoin();
493	>	if (ex == null && t.status < NORMAL)
494	>	ex = t.getException();
495	>	}
496		}
497		}
498		if (ex != null)
#	Line 543 | Line 530 | public abstract class ForkJoinTask<V> im
530		}
531
532		/**
533	<	* Cancels, ignoring any exceptions it throws. Used during worker
534	<	* and pool shutdown.
533	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
534	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
535	>	* exceptions, but if it does anyway, we have no recourse during
536	>	* shutdown, so guard against this case.
537		*/
538		final void cancelIgnoringExceptions() {
539		try {
#	Line 554 | Line 543 | public abstract class ForkJoinTask<V> im
543		}
544
545		/**
546	<	* Cancels ignoring exceptions if worker is terminating
546	>	* Cancels if current thread is a terminating worker thread,
547	>	* ignoring any exceptions thrown by cancel.
548		*/
549	<	private void cancelIfTerminating() {
549	>	final void cancelIfTerminating() {
550		Thread t = Thread.currentThread();
551		if ((t instanceof ForkJoinWorkerThread) &&
552		((ForkJoinWorkerThread) t).isTerminating()) {
#	Line 631 | Line 621 | public abstract class ForkJoinTask<V> im
621
622		/**
623		* Completes this task, and if not already aborted or cancelled,
624	<	* returning a {@code null} result upon {@code join} and related
625	<	* operations. This method may be used to provide results for
626	<	* asynchronous tasks, or to provide alternative handling for
627	<	* tasks that would not otherwise complete normally. Its use in
628	<	* other situations is discouraged. This method is
629	<	* overridable, but overridden versions must invoke {@code super}
630	<	* implementation to maintain guarantees.
624	>	* returning the given value as the result of subsequent
625	>	* invocations of {@code join} and related operations. This method
626	>	* may be used to provide results for asynchronous tasks, or to
627	>	* provide alternative handling for tasks that would not otherwise
628	>	* complete normally. Its use in other situations is
629	>	* discouraged. This method is overridable, but overridden
630	>	* versions must invoke {@code super} implementation to maintain
631	>	* guarantees.
632		*
633		* @param value the result value for this task
634		*/
#	Line 651 | Line 642 | public abstract class ForkJoinTask<V> im
642		setCompletion(NORMAL);
643		}
644
645	+	/**
646	+	* @throws CancellationException {@inheritDoc}
647	+	*/
648		public final V get() throws InterruptedException, ExecutionException {
649	<	int s = doJoin();
650	<	if (Thread.interrupted())
651	<	throw new InterruptedException();
649	>	int s;
650	>	if (Thread.currentThread() instanceof ForkJoinWorkerThread) {
651	>	quietlyJoin();
652	>	s = status;
653	>	}
654	>	else {
655	>	while ((s = status) >= 0) {
656	>	synchronized (this) { // interruptible form of awaitDone
657	>	if (UNSAFE.compareAndSwapInt(this, statusOffset,
658	>	s, SIGNAL)) {
659	>	while (status >= 0)
660	>	wait();
661	>	}
662	>	}
663	>	}
664	>	}
665		if (s < NORMAL) {
666		Throwable ex;
667		if (s == CANCELLED)
#	Line 665 | Line 672 | public abstract class ForkJoinTask<V> im
672		return getRawResult();
673		}
674
675	+	/**
676	+	* @throws CancellationException {@inheritDoc}
677	+	*/
678		public final V get(long timeout, TimeUnit unit)
679		throws InterruptedException, ExecutionException, TimeoutException {
680		Thread t = Thread.currentThread();
#	Line 672 | Line 682 | public abstract class ForkJoinTask<V> im
682		if (t instanceof ForkJoinWorkerThread) {
683		ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
684		if (status >= 0 && w.unpushTask(this))
685	<	tryExec();
685	>	quietlyExec();
686		pool = w.pool;
687		}
688		else
689		pool = null;
690		/*
691	<	* Timed wait loop intermixes cases for fj (pool != null) and
691	>	* Timed wait loop intermixes cases for FJ (pool != null) and
692		* non FJ threads. For FJ, decrement pool count but don't try
693		* for replacement; increment count on completion. For non-FJ,
694		* deal with interrupts. This is messy, but a little less so
#	Line 686 | Line 696 | public abstract class ForkJoinTask<V> im
696		*/
697		boolean interrupted = false;
698		boolean dec = false; // true if pool count decremented
699	+	long nanos = unit.toNanos(timeout);
700		for (;;) {
701	<	if (Thread.interrupted() && pool == null) {
701	>	if (pool == null && Thread.interrupted()) {
702		interrupted = true;
703		break;
704		}
705		int s = status;
706		if (s < 0)
707		break;
708	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
698	<	s, s | SIGNAL)) {
708	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
709		long startTime = System.nanoTime();
700	–	long nanos = unit.toNanos(timeout);
710		long nt; // wait time
711		while (status >= 0 &&
712		(nt = nanos - (System.nanoTime() - startTime)) > 0) {
#	Line 707 | Line 716 | public abstract class ForkJoinTask<V> im
716		long ms = nt / 1000000;
717		int ns = (int) (nt % 1000000);
718		try {
719	<	synchronized(this) {
719	>	synchronized (this) {
720		if (status >= 0)
721		wait(ms, ns);
722		}
#	Line 741 | Line 750 | public abstract class ForkJoinTask<V> im
750		}
751
752		/**
753	<	* Joins this task, without returning its result or throwing an
753	>	* Joins this task, without returning its result or throwing its
754		* exception. This method may be useful when processing
755		* collections of tasks when some have been cancelled or otherwise
756		* known to have aborted.
757		*/
758		public final void quietlyJoin() {
759	<	doJoin();
759	>	Thread t;
760	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
761	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
762	>	if (status >= 0) {
763	>	if (w.unpushTask(this)) {
764	>	boolean completed;
765	>	try {
766	>	completed = exec();
767	>	} catch (Throwable rex) {
768	>	setExceptionalCompletion(rex);
769	>	return;
770	>	}
771	>	if (completed) {
772	>	setCompletion(NORMAL);
773	>	return;
774	>	}
775	>	}
776	>	w.joinTask(this);
777	>	}
778	>	}
779	>	else
780	>	externalAwaitDone();
781		}
782
783		/**
784		* Commences performing this task and awaits its completion if
785	<	* necessary, without returning its result or throwing an
786	<	* exception. This method may be useful when processing
757	<	* collections of tasks when some have been cancelled or otherwise
758	<	* known to have aborted.
785	>	* necessary, without returning its result or throwing its
786	>	* exception.
787		*/
788		public final void quietlyInvoke() {
789	<	doInvoke();
789	>	if (status >= 0) {
790	>	boolean completed;
791	>	try {
792	>	completed = exec();
793	>	} catch (Throwable rex) {
794	>	setExceptionalCompletion(rex);
795	>	return;
796	>	}
797	>	if (completed)
798	>	setCompletion(NORMAL);
799	>	else
800	>	quietlyJoin();
801	>	}
802		}
803
804		/**
#	Line 1080 | Line 1120 | public abstract class ForkJoinTask<V> im
1120		private static final long serialVersionUID = -7721805057305804111L;
1121
1122		/**
1123	<	* Saves the state to a stream.
1123	>	* Saves the state to a stream (that is, serializes it).
1124		*
1125		* @serialData the current run status and the exception thrown
1126		* during execution, or {@code null} if none
#	Line 1093 | Line 1133 | public abstract class ForkJoinTask<V> im
1133		}
1134
1135		/**
1136	<	* Reconstitutes the instance from a stream.
1136	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1137		*
1138		* @param s the stream
1139		*/
#	Line 1103 | Line 1143 | public abstract class ForkJoinTask<V> im
1143		Object ex = s.readObject();
1144		if (ex != null)
1145		setExceptionalCompletion((Throwable) ex);
1106	–	if (status < 0)
1107	–	synchronized (this) { notifyAll(); }
1146		}
1147
1148		// Unsafe mechanics

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