ViewVC Help

View File | Revision Log | Show Annotations | Download File | Root Listing

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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.48 by dl, Thu May 27 16:46:48 2010 UTC vs.
Revision 1.56 by jsr166, Sat Sep 4 00:21:31 2010 UTC

#	Line 64 | Line 64 | import java.util.WeakHashMap;
64		* results of a task is {@link #join}, but there are several variants:
65		* The {@link Future#get} methods support interruptible and/or timed
66		* waits for completion and report results using {@code Future}
67	<	* conventions. Method {@link #helpJoin} enables callers to actively
68	<	* execute other tasks while awaiting joins, which is sometimes more
69	<	* efficient but only applies when all subtasks are known to be
70	<	* strictly tree-structured. Method {@link #invoke} is semantically
67	>	* conventions. Method {@link #invoke} is semantically
68		* equivalent to {@code fork(); join()} but always attempts to begin
69		* execution in the current thread. The "<em>quiet</em>" forms of
70		* these methods do not extract results or report exceptions. These
#	Line 125 | Line 122 | import java.util.WeakHashMap;
122		*
123		* <p>This class provides {@code adapt} methods for {@link Runnable}
124		* and {@link Callable}, that may be of use when mixing execution of
125	<	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks
126	<	* are of this form, consider using a pool in
130	<	* {@linkplain ForkJoinPool#setAsyncMode async mode}.
125	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
126	>	* of this form, consider using a pool constructed in <em>asyncMode</em>.
127		*
128		* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
129		* used in extensions such as remote execution frameworks. It is
#	Line 148 | 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 COMPLETED. CANCELLED, or
156	<	* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
157	<	* blocking waits by other threads have the SIGNAL bit set.
158	<	*
159	<	* Completion of a stolen task with SIGNAL set awakens any waiters
163	<	* via notifyAll. Even though suboptimal for some purposes, we use
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	>	* COMPLETED. 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.
170	–	*
171	–	* Note that bits 1-28 are currently unused. Also value
172	–	* 0x80000000 is available as spare completion value.
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 COMPLETION_MASK      = 0xe0000000;
172	<	private static final int NORMAL               = 0xe0000000; // == mask
173	<	private static final int CANCELLED            = 0xc0000000;
174	<	private static final int EXCEPTIONAL          = 0xa0000000;
180	<	private static final int SIGNAL               = 0x00000001;
171	>	private static final int NORMAL      = -1;
172	>	private static final int CANCELLED   = -2;
173	>	private static final int EXCEPTIONAL = -3;
174	>	private static final int SIGNAL      =  1;
175
176		/**
177		* Table of exceptions thrown by tasks, to enable reporting by
#	Line 198 | Line 192 | public abstract class ForkJoinTask<V> im
192		* also clearing signal request bits.
193		*
194		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
201	–	* @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) != 0)
200	>	if (s != 0)
201		synchronized (this) { notifyAll(); }
202	<	return completion;
202	>	break;
203		}
204		}
212	–	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 void internalAwaitDone() {
223	<	int s;
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, s|SIGNAL)){
227	<	do {
228	<	try {
234	<	wait();
235	<	} catch (InterruptedException ie) {
236	<	cancelIfTerminating();
237	<	}
238	<	} while (status >= 0);
239	<	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 non-worker-thread until completion.
237	>	* Blocks a worker thread until completed or timed out.  Called
238	>	* only by pool.
239	>	*
240		* @return status on exit
241		*/
242	<	private int externalAwaitDone() {
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.
260	>	*/
261	>	private void externalAwaitDone() {
262		int s;
263		while ((s = status) >= 0) {
264		synchronized(this) {
265	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
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		}
268	–	return s;
280		}
281
282		/**
283		* Unless done, calls exec and records status if completed, but
284	<	* doesn't wait for completion otherwise.
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 283 | Line 295 | public abstract class ForkJoinTask<V> im
295		setCompletion(NORMAL); // must be outside try block
296		}
297
286	–	/**
287	–	* If not done and this task is next in worker queue, runs it,
288	–	* else waits for it.
289	–	* @return status on exit
290	–	*/
291	–	private int waitingJoin() {
292	–	int s = status;
293	–	if (s < 0)
294	–	return s;
295	–	Thread t = Thread.currentThread();
296	–	if (t instanceof ForkJoinWorkerThread) {
297	–	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
298	–	if (w.unpushTask(this)) {
299	–	boolean completed;
300	–	try {
301	–	completed = exec();
302	–	} catch (Throwable rex) {
303	–	return setExceptionalCompletion(rex);
304	–	}
305	–	if (completed)
306	–	return setCompletion(NORMAL);
307	–	}
308	–	return w.pool.awaitJoin(this);
309	–	}
310	–	else
311	–	return externalAwaitDone();
312	–	}
313	–
314	–	/**
315	–	* Unless done, calls exec and records status if completed, or
316	–	* waits for completion otherwise.
317	–	* @return status on exit
318	–	*/
319	–	private int waitingInvoke() {
320	–	int s = status;
321	–	if (s < 0)
322	–	return s;
323	–	boolean completed;
324	–	try {
325	–	completed = exec();
326	–	} catch (Throwable rex) {
327	–	return setExceptionalCompletion(rex);
328	–	}
329	–	if (completed)
330	–	return setCompletion(NORMAL);
331	–	return waitingJoin();
332	–	}
333	–
334	–	/**
335	–	* If this task is next in worker queue, runs it, else processes other
336	–	* tasks until complete.
337	–	* @return status on exit
338	–	*/
339	–	private int busyJoin() {
340	–	int s = status;
341	–	if (s < 0)
342	–	return s;
343	–	ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
344	–	if (w.unpushTask(this)) {
345	–	boolean completed;
346	–	try {
347	–	completed = exec();
348	–	} catch (Throwable rex) {
349	–	return setExceptionalCompletion(rex);
350	–	}
351	–	if (completed)
352	–	return setCompletion(NORMAL);
353	–	}
354	–	return w.execWhileJoining(this);
355	–	}
356	–
357	–	/**
358	–	* Returns result or throws exception associated with given status.
359	–	* @param s the status
360	–	*/
361	–	private V reportResult(int s) {
362	–	Throwable ex;
363	–	if (s < NORMAL && (ex = getException()) != null)
364	–	UNSAFE.throwException(ex);
365	–	return getRawResult();
366	–	}
367	–
298		// public methods
299
300		/**
#	Line 400 | Line 330 | public abstract class ForkJoinTask<V> im
330		* @return the computed result
331		*/
332		public final V join() {
333	<	return reportResult(waitingJoin());
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)
342	>	* necessary, and returns its result, or throws an (unchecked)
343		* exception if the underlying computation did so.
344		*
345		* @return the computed result
346		*/
347		public final V invoke() {
348	<	return reportResult(waitingInvoke());
348	>	quietlyInvoke();
349	>	Throwable ex;
350	>	if (status < NORMAL && (ex = getException()) != null)
351	>	UNSAFE.throwException(ex);
352	>	return getRawResult();
353		}
354
355		/**
#	Line 469 | Line 407 | public abstract class ForkJoinTask<V> im
407		}
408		else if (i != 0)
409		t.fork();
410	<	else if (t.waitingInvoke() < NORMAL && ex == null)
411	<	ex = t.getException();
410	>	else {
411	>	t.quietlyInvoke();
412	>	if (ex == null && t.status < NORMAL)
413	>	ex = t.getException();
414	>	}
415		}
416		for (int i = 1; i <= last; ++i) {
417		ForkJoinTask<?> t = tasks[i];
418		if (t != null) {
419		if (ex != null)
420		t.cancel(false);
421	<	else if (t.waitingJoin() < NORMAL && ex == null)
422	<	ex = t.getException();
421	>	else {
422	>	t.quietlyJoin();
423	>	if (ex == null && t.status < NORMAL)
424	>	ex = t.getException();
425	>	}
426		}
427		}
428		if (ex != null)
#	Line 525 | Line 469 | public abstract class ForkJoinTask<V> im
469		}
470		else if (i != 0)
471		t.fork();
472	<	else if (t.waitingInvoke() < NORMAL && ex == null)
473	<	ex = t.getException();
472	>	else {
473	>	t.quietlyInvoke();
474	>	if (ex == null && t.status < NORMAL)
475	>	ex = t.getException();
476	>	}
477		}
478		for (int i = 1; i <= last; ++i) {
479		ForkJoinTask<?> t = ts.get(i);
480		if (t != null) {
481		if (ex != null)
482		t.cancel(false);
483	<	else if (t.waitingJoin() < NORMAL && ex == null)
484	<	ex = t.getException();
483	>	else {
484	>	t.quietlyJoin();
485	>	if (ex == null && t.status < NORMAL)
486	>	ex = t.getException();
487	>	}
488		}
489		}
490		if (ex != null)
#	Line 568 | Line 518 | public abstract class ForkJoinTask<V> im
518		*/
519		public boolean cancel(boolean mayInterruptIfRunning) {
520		setCompletion(CANCELLED);
521	<	return (status & COMPLETION_MASK) == CANCELLED;
521	>	return status == CANCELLED;
522		}
523
524		/**
525	<	* Cancels, ignoring any exceptions it throws. Used during worker
526	<	* and pool shutdown.
525	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
526	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
527	>	* exceptions, but if it does anyway, we have no recourse during
528	>	* shutdown, so guard against this case.
529		*/
530		final void cancelIgnoringExceptions() {
531		try {
#	Line 583 | Line 535 | public abstract class ForkJoinTask<V> im
535		}
536
537		/**
538	<	* Cancels ignoring exceptions if worker is terminating
538	>	* Cancels if current thread is a terminating worker thread,
539	>	* ignoring any exceptions thrown by cancel.
540		*/
541	<	private void cancelIfTerminating() {
541	>	final void cancelIfTerminating() {
542		Thread t = Thread.currentThread();
543		if ((t instanceof ForkJoinWorkerThread) &&
544		((ForkJoinWorkerThread) t).isTerminating()) {
#	Line 601 | Line 554 | public abstract class ForkJoinTask<V> im
554		}
555
556		public final boolean isCancelled() {
557	<	return (status & COMPLETION_MASK) == CANCELLED;
557	>	return status == CANCELLED;
558		}
559
560		/**
#	Line 610 | Line 563 | public abstract class ForkJoinTask<V> im
563		* @return {@code true} if this task threw an exception or was cancelled
564		*/
565		public final boolean isCompletedAbnormally() {
566	<	return (status & COMPLETION_MASK) < NORMAL;
566	>	return status < NORMAL;
567		}
568
569		/**
#	Line 621 | Line 574 | public abstract class ForkJoinTask<V> im
574		* exception and was not cancelled
575		*/
576		public final boolean isCompletedNormally() {
577	<	return (status & COMPLETION_MASK) == NORMAL;
577	>	return status == NORMAL;
578		}
579
580		/**
#	Line 632 | Line 585 | public abstract class ForkJoinTask<V> im
585		* @return the exception, or {@code null} if none
586		*/
587		public final Throwable getException() {
588	<	int s = status & COMPLETION_MASK;
588	>	int s = status;
589		return ((s >= NORMAL)    ? null :
590		(s == CANCELLED) ? new CancellationException() :
591		exceptionMap.get(this));
#	Line 681 | Line 634 | public abstract class ForkJoinTask<V> im
634		}
635
636		public final V get() throws InterruptedException, ExecutionException {
637	<	int s = waitingJoin() & COMPLETION_MASK;
637	>	quietlyJoin();
638		if (Thread.interrupted())
639		throw new InterruptedException();
640	+	int s = status;
641		if (s < NORMAL) {
642		Throwable ex;
643		if (s == CANCELLED)
#	Line 701 | Line 655 | public abstract class ForkJoinTask<V> im
655		if (t instanceof ForkJoinWorkerThread) {
656		ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
657		if (status >= 0 && w.unpushTask(this))
658	<	tryExec();
658	>	quietlyExec();
659		pool = w.pool;
660		}
661		else
662		pool = null;
663		/*
664	<	* Timed wait loop intermixes cases for fj (pool != null) and
664	>	* Timed wait loop intermixes cases for FJ (pool != null) and
665		* non FJ threads. For FJ, decrement pool count but don't try
666		* for replacement; increment count on completion. For non-FJ,
667		* deal with interrupts. This is messy, but a little less so
#	Line 715 | Line 669 | public abstract class ForkJoinTask<V> im
669		*/
670		boolean interrupted = false;
671		boolean dec = false; // true if pool count decremented
672	+	long nanos = unit.toNanos(timeout);
673		for (;;) {
674		if (Thread.interrupted() && pool == null) {
675		interrupted = true;
#	Line 723 | Line 678 | public abstract class ForkJoinTask<V> im
678		int s = status;
679		if (s < 0)
680		break;
681	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
727	<	s, s | SIGNAL)) {
681	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
682		long startTime = System.nanoTime();
729	–	long nanos = unit.toNanos(timeout);
683		long nt; // wait time
684		while (status >= 0 &&
685		(nt = nanos - (System.nanoTime() - startTime)) > 0) {
#	Line 754 | Line 707 | public abstract class ForkJoinTask<V> im
707		}
708		}
709		if (pool != null && dec)
710	<	pool.updateRunningCount(1);
710	>	pool.incrementRunningCount();
711		if (interrupted)
712		throw new InterruptedException();
713	<	int es = status & COMPLETION_MASK;
713	>	int es = status;
714		if (es != NORMAL) {
715		Throwable ex;
716		if (es == CANCELLED)
#	Line 770 | Line 723 | public abstract class ForkJoinTask<V> im
723		}
724
725		/**
726	<	* Possibly executes other tasks until this task {@link #isDone is
774	<	* done}, then returns the result of the computation.  This method
775	<	* may be more efficient than {@code join}, but is only applicable
776	<	* when there are no potential dependencies between continuation
777	<	* of the current task and that of any other task that might be
778	<	* executed while helping. (This usually holds for pure
779	<	* divide-and-conquer tasks).
780	<	*
781	<	* <p>This method may be invoked only from within {@code
782	<	* ForkJoinTask} computations (as may be determined using method
783	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
784	<	* result in exceptions or errors, possibly including {@code
785	<	* ClassCastException}.
786	<	*
787	<	* @return the computed result
788	<	*/
789	<	public final V helpJoin() {
790	<	return reportResult(busyJoin());
791	<	}
792	<
793	<	/**
794	<	* Possibly executes other tasks until this task {@link #isDone is
795	<	* done}.  This method may be useful when processing collections
796	<	* of tasks when some have been cancelled or otherwise known to
797	<	* have aborted.
798	<	*
799	<	* <p>This method may be invoked only from within {@code
800	<	* ForkJoinTask} computations (as may be determined using method
801	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
802	<	* result in exceptions or errors, possibly including {@code
803	<	* ClassCastException}.
804	<	*/
805	<	public final void quietlyHelpJoin() {
806	<	busyJoin();
807	<	}
808	<
809	<	/**
810	<	* Joins this task, without returning its result or throwing an
726	>	* Joins this task, without returning its result or throwing its
727		* exception. This method may be useful when processing
728		* collections of tasks when some have been cancelled or otherwise
729		* known to have aborted.
730		*/
731		public final void quietlyJoin() {
732	<	waitingJoin();
732	>	Thread t;
733	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
734	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
735	>	if (status >= 0) {
736	>	if (w.unpushTask(this)) {
737	>	boolean completed;
738	>	try {
739	>	completed = exec();
740	>	} catch (Throwable rex) {
741	>	setExceptionalCompletion(rex);
742	>	return;
743	>	}
744	>	if (completed) {
745	>	setCompletion(NORMAL);
746	>	return;
747	>	}
748	>	}
749	>	w.joinTask(this);
750	>	}
751	>	}
752	>	else
753	>	externalAwaitDone();
754		}
755
756		/**
757		* Commences performing this task and awaits its completion if
758	<	* necessary, without returning its result or throwing an
758	>	* necessary, without returning its result or throwing its
759		* exception. This method may be useful when processing
760		* collections of tasks when some have been cancelled or otherwise
761		* known to have aborted.
762		*/
763		public final void quietlyInvoke() {
764	<	waitingInvoke();
764	>	if (status >= 0) {
765	>	boolean completed;
766	>	try {
767	>	completed = exec();
768	>	} catch (Throwable rex) {
769	>	setExceptionalCompletion(rex);
770	>	return;
771	>	}
772	>	if (completed)
773	>	setCompletion(NORMAL);
774	>	else
775	>	quietlyJoin();
776	>	}
777		}
778
779		/**
#	Line 856 | Line 805 | public abstract class ForkJoinTask<V> im
805		* pre-constructed trees of subtasks in loops.
806		*/
807		public void reinitialize() {
808	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
808	>	if (status == EXCEPTIONAL)
809		exceptionMap.remove(this);
810		status = 0;
811		}
#	Line 1146 | Line 1095 | public abstract class ForkJoinTask<V> im
1095		private static final long serialVersionUID = -7721805057305804111L;
1096
1097		/**
1098	<	* Saves the state to a stream.
1098	>	* Saves the state to a stream (that is, serializes it).
1099		*
1100		* @serialData the current run status and the exception thrown
1101		* during execution, or {@code null} if none
#	Line 1159 | Line 1108 | public abstract class ForkJoinTask<V> im
1108		}
1109
1110		/**
1111	<	* Reconstitutes the instance from a stream.
1111	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1112		*
1113		* @param s the stream
1114		*/
1115		private void readObject(java.io.ObjectInputStream s)
1116		throws java.io.IOException, ClassNotFoundException {
1117		s.defaultReadObject();
1169	–	status |= SIGNAL; // conservatively set external signal
1118		Object ex = s.readObject();
1119		if (ex != null)
1120		setExceptionalCompletion((Throwable) ex);

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines