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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.66 by dl, Sun Oct 24 19:37:26 2010 UTC vs.
Revision 1.70 by dl, Tue Nov 23 00:10:39 2010 UTC

#	Line 110 | Line 110 | import java.util.concurrent.TimeoutExcep
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 124 | Line 134 | import java.util.concurrent.TimeoutExcep
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 223 | 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
228	<	* 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) {
233	<	try {
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 (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
245	<	wait();
244	>	if (status > 0 ||
245	>	UNSAFE.compareAndSwapInt(this, statusOffset,
246	>	0, SIGNAL))
247	>	wait(millis, nanos);
248		}
249		} catch (InterruptedException ie) {
250		cancelIfTerminating();
#	Line 242 | Line 253 | public abstract class ForkJoinTask<V> im
253		}
254
255		/**
256	<	* Blocks a worker thread until completed or timed out.  Called
246	<	* only by pool.
247	<	*
248	<	* @return status on exit
256	>	* Blocks a non-worker-thread until completion.
257		*/
258	<	final int internalAwaitDone(long millis, int nanos) {
259	<	int s;
260	<	if ((s = status) >= 0) {
261	<	try {
262	<	synchronized (this) {
263	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
264	<	wait(millis, nanos);
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		}
258	–	} catch (InterruptedException ie) {
259	–	cancelIfTerminating();
274		}
275	<	s = status;
275	>	if (interrupted)
276	>	Thread.currentThread().interrupt();
277		}
263	–	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) {
286	<	synchronized (this) {
287	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
288	<	boolean interrupted = false;
289	<	while (status >= 0) {
290	<	try {
291	<	wait();
292	<	} catch (InterruptedException ie) {
293	<	interrupted = true;
294	<	}
295	<	}
296	<	if (interrupted)
297	<	Thread.currentThread().interrupt();
298	<	break;
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	>	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 316 | 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 330 | 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 375 | 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 403 | 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 458 | 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 510 | 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 662 | Line 686 | public abstract class ForkJoinTask<V> im
686		* member of a ForkJoinPool and was interrupted while waiting
687		*/
688		public final V get() throws InterruptedException, ExecutionException {
689	<	int s;
690	<	if (Thread.currentThread() instanceof ForkJoinWorkerThread) {
689	>	Thread t = Thread.currentThread();
690	>	if (t instanceof ForkJoinWorkerThread)
691		quietlyJoin();
692	<	s = status;
693	<	}
694	<	else {
695	<	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) {
692	>	else
693	>	externalInterruptibleAwaitDone(false, 0L);
694	>	int s = status;
695	>	if (s != NORMAL) {
696		Throwable ex;
697		if (s == CANCELLED)
698		throw new CancellationException();
#	Line 705 | Line 719 | public abstract class ForkJoinTask<V> im
719		public final V get(long timeout, TimeUnit unit)
720		throws InterruptedException, ExecutionException, TimeoutException {
721		long nanos = unit.toNanos(timeout);
722	<	if (status >= 0) {
723	<	Thread t = Thread.currentThread();
724	<	if (t instanceof ForkJoinWorkerThread) {
725	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
726	<	boolean completed = false; // timed variant of quietlyJoin
727	<	if (w.unpushTask(this)) {
728	<	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	<	else if (Thread.interrupted())
726	<	throw new InterruptedException();
727	<	else {
728	<	long startTime = System.nanoTime();
729	<	int s; long nt;
730	<	while ((s = status) >= 0 &&
731	<	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
732	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,
733	<	SIGNAL)) {
734	<	long ms = nt / 1000000;
735	<	int ns = (int) (nt % 1000000);
736	<	synchronized (this) {
737	<	if (status >= 0)
738	<	wait(ms, ns); // exit on IE throw
739	<	}
740	<	}
741	<	}
742	<	}
743	<	}
744	<	int es = status;
745	<	if (es != NORMAL) {
722	>	Thread t = Thread.currentThread();
723	>	if (t instanceof ForkJoinWorkerThread)
724	>	((ForkJoinWorkerThread)t).joinTask(this, true, nanos);
725	>	else
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 813 | 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 832 | 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 872 | Line 861 | public abstract class ForkJoinTask<V> im
861		* were not, stolen.
862		*
863		* <p>This method may be invoked only from within {@code
864	<	* ForkJoinTask} computations (as may be determined using method
864	>	* ForkJoinPool} computations (as may be determined using method
865		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
866		* result in exceptions or errors, possibly including {@code
867		* ClassCastException}.
#	Line 891 | Line 880 | public abstract class ForkJoinTask<V> im
880		* fork other tasks.
881		*
882		* <p>This method may be invoked only from within {@code
883	<	* ForkJoinTask} computations (as may be determined using method
883	>	* ForkJoinPool} computations (as may be determined using method
884		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
885		* result in exceptions or errors, possibly including {@code
886		* ClassCastException}.
#	Line 914 | Line 903 | public abstract class ForkJoinTask<V> im
903		* exceeded.
904		*
905		* <p>This method may be invoked only from within {@code
906	<	* ForkJoinTask} computations (as may be determined using method
906	>	* ForkJoinPool} computations (as may be determined using method
907		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
908		* result in exceptions or errors, possibly including {@code
909		* ClassCastException}.
#	Line 972 | Line 961 | public abstract class ForkJoinTask<V> im
961		* otherwise.
962		*
963		* <p>This method may be invoked only from within {@code
964	<	* ForkJoinTask} computations (as may be determined using method
964	>	* ForkJoinPool} computations (as may be determined using method
965		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
966		* result in exceptions or errors, possibly including {@code
967		* ClassCastException}.
#	Line 991 | Line 980 | public abstract class ForkJoinTask<V> im
980		* be useful otherwise.
981		*
982		* <p>This method may be invoked only from within {@code
983	<	* ForkJoinTask} computations (as may be determined using method
983	>	* ForkJoinPool} computations (as may be determined using method
984		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
985		* result in exceptions or errors, possibly including {@code
986		* ClassCastException}.
#	Line 1014 | Line 1003 | public abstract class ForkJoinTask<V> im
1003		* otherwise.
1004		*
1005		* <p>This method may be invoked only from within {@code
1006	<	* ForkJoinTask} computations (as may be determined using method
1006	>	* ForkJoinPool} computations (as may be determined using method
1007		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1008		* result in exceptions or errors, possibly including {@code
1009		* ClassCastException}.

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