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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.63 by dl, Sat Sep 18 12:10:21 2010 UTC vs.
Revision 1.73 by jsr166, Sun Nov 28 21:21:03 2010 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
9		import java.io.Serializable;
10		import java.util.Collection;
11		import java.util.Collections;
#	Line 14 | 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 101 | 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 115 | 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 214 | Line 234 | public abstract class ForkJoinTask<V> im
234		}
235
236		/**
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) {
226	–	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
227	–	wait();
228	–	}
229	–	} catch (InterruptedException ie) {
230	–	cancelIfTerminating();
231	–	}
232	–	}
233	–	}
234	–
235	–	/**
237		* Blocks a worker thread until completed or timed out.  Called
238		* only by pool.
238	–	*
239	–	* @return status on exit
239		*/
240	<	final int internalAwaitDone(long millis) {
241	<	int s;
242	<	if ((s = status) >= 0) {
243	<	try {
240	>	final void internalAwaitDone(long millis, int nanos) {
241	>	int s = status;
242	>	if ((s == 0 &&
243	>	UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL)) ||
244	>	s > 0)  {
245	>	try {     // the odd construction reduces lock bias effects
246		synchronized (this) {
247	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
248	<	wait(millis, 0);
247	>	if (status > 0)
248	>	wait(millis, nanos);
249	>	else
250	>	notifyAll();
251		}
252		} catch (InterruptedException ie) {
253		cancelIfTerminating();
254		}
252	–	s = status;
255		}
254	–	return s;
256		}
257
258		/**
259		* Blocks a non-worker-thread until completion.
260		*/
261		private void externalAwaitDone() {
262	<	int s;
263	<	while ((s = status) >= 0) {
262	>	if (status >= 0) {
263	>	boolean interrupted = false;
264		synchronized (this) {
265	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
266	<	boolean interrupted = false;
267	<	while (status >= 0) {
265	>	for (;;) {
266	>	int s = status;
267	>	if (s == 0)
268	>	UNSAFE.compareAndSwapInt(this, statusOffset,
269	>	0, SIGNAL);
270	>	else if (s < 0) {
271	>	notifyAll();
272	>	break;
273	>	}
274	>	else {
275		try {
276		wait();
277		} catch (InterruptedException ie) {
278		interrupted = true;
279		}
280		}
281	<	if (interrupted)
282	<	Thread.currentThread().interrupt();
283	<	break;
281	>	}
282	>	}
283	>	if (interrupted)
284	>	Thread.currentThread().interrupt();
285	>	}
286	>	}
287	>
288	>	/**
289	>	* Blocks a non-worker-thread until completion or interruption or timeout.
290	>	*/
291	>	private void externalInterruptibleAwaitDone(boolean timed, long nanos)
292	>	throws InterruptedException {
293	>	if (Thread.interrupted())
294	>	throw new InterruptedException();
295	>	if (status >= 0) {
296	>	long startTime = timed ? System.nanoTime() : 0L;
297	>	synchronized (this) {
298	>	for (;;) {
299	>	long nt;
300	>	int s = status;
301	>	if (s == 0)
302	>	UNSAFE.compareAndSwapInt(this, statusOffset,
303	>	0, SIGNAL);
304	>	else if (s < 0) {
305	>	notifyAll();
306	>	break;
307	>	}
308	>	else if (!timed)
309	>	wait();
310	>	else if ((nt = nanos - (System.nanoTime()-startTime)) > 0L)
311	>	wait(nt / 1000000, (int)(nt % 1000000));
312	>	else
313	>	break;
314		}
315		}
316		}
#	Line 307 | Line 345 | public abstract class ForkJoinTask<V> im
345		* #isDone} returning {@code true}.
346		*
347		* <p>This method may be invoked only from within {@code
348	<	* ForkJoinTask} computations (as may be determined using method
348	>	* ForkJoinPool} computations (as may be determined using method
349		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
350		* result in exceptions or errors, possibly including {@code
351		* ClassCastException}.
#	Line 321 | Line 359 | public abstract class ForkJoinTask<V> im
359		}
360
361		/**
362	<	* Returns the result of the computation when it {@link #isDone is done}.
363	<	* This method differs from {@link #get()} in that
362	>	* Returns the result of the computation when it {@link #isDone is
363	>	* done}.  This method differs from {@link #get()} in that
364		* abnormal completion results in {@code RuntimeException} or
365	<	* {@code Error}, not {@code ExecutionException}.
365	>	* {@code Error}, not {@code ExecutionException}, and that
366	>	* interrupts of the calling thread do <em>not</em> cause the
367	>	* method to abruptly return by throwing {@code
368	>	* InterruptedException}.
369		*
370		* @return the computed result
371		*/
#	Line 366 | Line 407 | public abstract class ForkJoinTask<V> im
407		* unprocessed.
408		*
409		* <p>This method may be invoked only from within {@code
410	<	* ForkJoinTask} computations (as may be determined using method
410	>	* ForkJoinPool} computations (as may be determined using method
411		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
412		* result in exceptions or errors, possibly including {@code
413		* ClassCastException}.
#	Line 394 | Line 435 | public abstract class ForkJoinTask<V> im
435		* normally or exceptionally, or left unprocessed.
436		*
437		* <p>This method may be invoked only from within {@code
438	<	* ForkJoinTask} computations (as may be determined using method
438	>	* ForkJoinPool} computations (as may be determined using method
439		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
440		* result in exceptions or errors, possibly including {@code
441		* ClassCastException}.
#	Line 449 | Line 490 | public abstract class ForkJoinTask<V> im
490		* unprocessed.
491		*
492		* <p>This method may be invoked only from within {@code
493	<	* ForkJoinTask} computations (as may be determined using method
493	>	* ForkJoinPool} computations (as may be determined using method
494		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
495		* result in exceptions or errors, possibly including {@code
496		* ClassCastException}.
#	Line 501 | Line 542 | public abstract class ForkJoinTask<V> im
542
543		/**
544		* Attempts to cancel execution of this task. This attempt will
545	<	* fail if the task has already completed, has already been
546	<	* cancelled, or could not be cancelled for some other reason. If
547	<	* successful, and this task has not started when cancel is
548	<	* called, execution of this task is suppressed, {@link
549	<	* #isCancelled} will report true, and {@link #join} will result
550	<	* in a {@code CancellationException} being thrown.
545	>	* fail if the task has already completed or could not be
546	>	* cancelled for some other reason. If successful, and this task
547	>	* has not started when {@code cancel} is called, execution of
548	>	* this task is suppressed. After this method returns
549	>	* successfully, unless there is an intervening call to {@link
550	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
551	>	* {@link #isDone}, and {@code cancel} will return {@code true}
552	>	* and calls to {@link #join} and related methods will result in
553	>	* {@code CancellationException}.
554		*
555		* <p>This method may be overridden in subclasses, but if so, must
556	<	* still ensure that these minimal properties hold. In particular,
557	<	* the {@code cancel} method itself must not throw exceptions.
556	>	* still ensure that these properties hold. In particular, the
557	>	* {@code cancel} method itself must not throw exceptions.
558		*
559		* <p>This method is designed to be invoked by <em>other</em>
560		* tasks. To terminate the current task, you can just return or
561		* throw an unchecked exception from its computation method, or
562		* invoke {@link #completeExceptionally}.
563		*
564	<	* @param mayInterruptIfRunning this value is ignored in the
565	<	* default implementation because tasks are not
566	<	* cancelled via interruption
564	>	* @param mayInterruptIfRunning this value has no effect in the
565	>	* default implementation because interrupts are not used to
566	>	* control cancellation.
567		*
568		* @return {@code true} if this task is now cancelled
569		*/
#	Line 653 | Line 697 | public abstract class ForkJoinTask<V> im
697		* member of a ForkJoinPool and was interrupted while waiting
698		*/
699		public final V get() throws InterruptedException, ExecutionException {
700	<	int s;
701	<	if (Thread.currentThread() instanceof ForkJoinWorkerThread) {
700	>	Thread t = Thread.currentThread();
701	>	if (t instanceof ForkJoinWorkerThread)
702		quietlyJoin();
703	<	s = status;
704	<	}
705	<	else {
706	<	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) {
703	>	else
704	>	externalInterruptibleAwaitDone(false, 0L);
705	>	int s = status;
706	>	if (s != NORMAL) {
707		Throwable ex;
708		if (s == CANCELLED)
709		throw new CancellationException();
#	Line 695 | Line 729 | public abstract class ForkJoinTask<V> im
729		*/
730		public final V get(long timeout, TimeUnit unit)
731		throws InterruptedException, ExecutionException, TimeoutException {
732	+	long nanos = unit.toNanos(timeout);
733		Thread t = Thread.currentThread();
734	<	ForkJoinPool pool;
735	<	if (t instanceof ForkJoinWorkerThread) {
701	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
702	<	if (status >= 0 && w.unpushTask(this))
703	<	quietlyExec();
704	<	pool = w.pool;
705	<	}
734	>	if (t instanceof ForkJoinWorkerThread)
735	>	((ForkJoinWorkerThread)t).joinTask(this, true, nanos);
736		else
737	<	pool = null;
738	<	/*
739	<	* 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
713	<	* than is splitting the FJ and nonFJ cases.
714	<	*/
715	<	boolean interrupted = false;
716	<	boolean dec = false; // true if pool count decremented
717	<	long nanos = unit.toNanos(timeout);
718	<	for (;;) {
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, s, SIGNAL)) {
727	<	long startTime = System.nanoTime();
728	<	long nt; // wait time
729	<	while (status >= 0 &&
730	<	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
731	<	if (pool != null && !dec)
732	<	dec = pool.tryDecrementRunningCount();
733	<	else {
734	<	long ms = nt / 1000000;
735	<	int ns = (int) (nt % 1000000);
736	<	try {
737	<	synchronized (this) {
738	<	if (status >= 0)
739	<	wait(ms, ns);
740	<	}
741	<	} catch (InterruptedException ie) {
742	<	if (pool != null)
743	<	cancelIfTerminating();
744	<	else {
745	<	interrupted = true;
746	<	break;
747	<	}
748	<	}
749	<	}
750	<	}
751	<	break;
752	<	}
753	<	}
754	<	if (pool != null && dec)
755	<	pool.incrementRunningCount();
756	<	if (interrupted)
757	<	throw new InterruptedException();
758	<	int es = status;
759	<	if (es != NORMAL) {
737	>	externalInterruptibleAwaitDone(true, nanos);
738	>	int s = status;
739	>	if (s != NORMAL) {
740		Throwable ex;
741	<	if (es == CANCELLED)
741	>	if (s == CANCELLED)
742		throw new CancellationException();
743	<	if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
743	>	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
744		throw new ExecutionException(ex);
745		throw new TimeoutException();
746		}
#	Line 791 | Line 771 | public abstract class ForkJoinTask<V> im
771		return;
772		}
773		}
774	<	w.joinTask(this);
774	>	w.joinTask(this, false, 0L);
775		}
776		}
777		else
#	Line 827 | Line 807 | public abstract class ForkJoinTask<V> im
807		* processed.
808		*
809		* <p>This method may be invoked only from within {@code
810	<	* ForkJoinTask} computations (as may be determined using method
810	>	* ForkJoinPool} computations (as may be determined using method
811		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
812		* result in exceptions or errors, possibly including {@code
813		* ClassCastException}.
#	Line 846 | Line 826 | public abstract class ForkJoinTask<V> im
826		* under any other usage conditions are not guaranteed.
827		* This method may be useful when executing
828		* pre-constructed trees of subtasks in loops.
829	+	*
830	+	* <p>Upon completion of this method, {@code isDone()} reports
831	+	* {@code false}, and {@code getException()} reports {@code
832	+	* null}. However, the value returned by {@code getRawResult} is
833	+	* unaffected. To clear this value, you can invoke {@code
834	+	* setRawResult(null)}.
835		*/
836		public void reinitialize() {
837		if (status == EXCEPTIONAL)
#	Line 867 | Line 853 | public abstract class ForkJoinTask<V> im
853		}
854
855		/**
856	<	* Returns {@code true} if the current thread is executing as a
857	<	* ForkJoinPool computation.
856	>	* Returns {@code true} if the current thread is a {@link
857	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
858		*
859	<	* @return {@code true} if the current thread is executing as a
860	<	* ForkJoinPool computation, or false otherwise
859	>	* @return {@code true} if the current thread is a {@link
860	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
861	>	* or {@code false} otherwise
862		*/
863		public static boolean inForkJoinPool() {
864		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 886 | Line 873 | public abstract class ForkJoinTask<V> im
873		* were not, stolen.
874		*
875		* <p>This method may be invoked only from within {@code
876	<	* ForkJoinTask} computations (as may be determined using method
876	>	* ForkJoinPool} computations (as may be determined using method
877		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
878		* result in exceptions or errors, possibly including {@code
879		* ClassCastException}.
#	Line 905 | Line 892 | public abstract class ForkJoinTask<V> im
892		* fork other tasks.
893		*
894		* <p>This method may be invoked only from within {@code
895	<	* ForkJoinTask} computations (as may be determined using method
895	>	* ForkJoinPool} computations (as may be determined using method
896		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
897		* result in exceptions or errors, possibly including {@code
898		* ClassCastException}.
#	Line 928 | Line 915 | public abstract class ForkJoinTask<V> im
915		* exceeded.
916		*
917		* <p>This method may be invoked only from within {@code
918	<	* ForkJoinTask} computations (as may be determined using method
918	>	* ForkJoinPool} computations (as may be determined using method
919		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
920		* result in exceptions or errors, possibly including {@code
921		* ClassCastException}.
#	Line 986 | Line 973 | public abstract class ForkJoinTask<V> im
973		* otherwise.
974		*
975		* <p>This method may be invoked only from within {@code
976	<	* ForkJoinTask} computations (as may be determined using method
976	>	* ForkJoinPool} computations (as may be determined using method
977		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
978		* result in exceptions or errors, possibly including {@code
979		* ClassCastException}.
#	Line 1005 | Line 992 | public abstract class ForkJoinTask<V> im
992		* be useful otherwise.
993		*
994		* <p>This method may be invoked only from within {@code
995	<	* ForkJoinTask} computations (as may be determined using method
995	>	* ForkJoinPool} computations (as may be determined using method
996		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
997		* result in exceptions or errors, possibly including {@code
998		* ClassCastException}.
#	Line 1028 | Line 1015 | public abstract class ForkJoinTask<V> im
1015		* otherwise.
1016		*
1017		* <p>This method may be invoked only from within {@code
1018	<	* ForkJoinTask} computations (as may be determined using method
1018	>	* ForkJoinPool} computations (as may be determined using method
1019		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1020		* result in exceptions or errors, possibly including {@code
1021		* ClassCastException}.

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