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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 1.53 by dl, Wed Aug 11 18:45:12 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
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.
218		*/
219		final void internalAwaitDone() {
220	<	int s;
220	>	int s;         // the odd construction reduces lock bias effects
221		while ((s = status) >= 0) {
222	<	synchronized(this) {
223	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
224	<	do {
225	<	try {
234	<	wait();
235	<	} catch (InterruptedException ie) {
236	<	cancelIfTerminating();
237	<	}
238	<	} while (status >= 0);
239	<	break;
222	>	try {
223	>	synchronized(this) {
224	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
225	>	wait();
226		}
227	+	} catch (InterruptedException ie) {
228	+	cancelIfTerminating();
229		}
230		}
231		}
232
233		/**
234		* Blocks a non-worker-thread until completion.
247	–	* @return status on exit
235		*/
236	<	private int externalAwaitDone() {
236	>	private void externalAwaitDone() {
237		int s;
238		while ((s = status) >= 0) {
239		synchronized(this) {
240	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
240	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
241		boolean interrupted = false;
242	<	do {
242	>	while (status >= 0) {
243		try {
244		wait();
245		} catch (InterruptedException ie) {
246		interrupted = true;
247		}
248	<	} while ((s = status) >= 0);
248	>	}
249		if (interrupted)
250		Thread.currentThread().interrupt();
251		break;
252		}
253		}
254		}
268	–	return s;
255		}
256
257		/**
258		* Unless done, calls exec and records status if completed, but
259	<	* doesn't wait for completion otherwise.
259	>	* doesn't wait for completion otherwise. Primary execution method
260	>	* for ForkJoinWorkerThread.
261		*/
262	<	final void tryExec() {
262	>	final void quietlyExec() {
263		try {
264		if (status < 0 || !exec())
265		return;
#	Line 283 | Line 270 | public abstract class ForkJoinTask<V> im
270		setCompletion(NORMAL); // must be outside try block
271		}
272
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	–
273		// public methods
274
275		/**
#	Line 400 | Line 305 | public abstract class ForkJoinTask<V> im
305		* @return the computed result
306		*/
307		public final V join() {
308	<	return reportResult(waitingJoin());
308	>	quietlyJoin();
309	>	Throwable ex;
310	>	if (status < NORMAL && (ex = getException()) != null)
311	>	UNSAFE.throwException(ex);
312	>	return getRawResult();
313		}
314
315		/**
#	Line 411 | Line 320 | public abstract class ForkJoinTask<V> im
320		* @return the computed result
321		*/
322		public final V invoke() {
323	<	return reportResult(waitingInvoke());
323	>	quietlyInvoke();
324	>	Throwable ex;
325	>	if (status < NORMAL && (ex = getException()) != null)
326	>	UNSAFE.throwException(ex);
327	>	return getRawResult();
328		}
329
330		/**
#	Line 469 | Line 382 | public abstract class ForkJoinTask<V> im
382		}
383		else if (i != 0)
384		t.fork();
385	<	else if (t.waitingInvoke() < NORMAL && ex == null)
386	<	ex = t.getException();
385	>	else {
386	>	t.quietlyInvoke();
387	>	if (ex == null && t.status < NORMAL)
388	>	ex = t.getException();
389	>	}
390		}
391		for (int i = 1; i <= last; ++i) {
392		ForkJoinTask<?> t = tasks[i];
393		if (t != null) {
394		if (ex != null)
395		t.cancel(false);
396	<	else if (t.waitingJoin() < NORMAL && ex == null)
397	<	ex = t.getException();
396	>	else {
397	>	t.quietlyJoin();
398	>	if (ex == null && t.status < NORMAL)
399	>	ex = t.getException();
400	>	}
401		}
402		}
403		if (ex != null)
#	Line 525 | Line 444 | public abstract class ForkJoinTask<V> im
444		}
445		else if (i != 0)
446		t.fork();
447	<	else if (t.waitingInvoke() < NORMAL && ex == null)
448	<	ex = t.getException();
447	>	else {
448	>	t.quietlyInvoke();
449	>	if (ex == null && t.status < NORMAL)
450	>	ex = t.getException();
451	>	}
452		}
453		for (int i = 1; i <= last; ++i) {
454		ForkJoinTask<?> t = ts.get(i);
455		if (t != null) {
456		if (ex != null)
457		t.cancel(false);
458	<	else if (t.waitingJoin() < NORMAL && ex == null)
459	<	ex = t.getException();
458	>	else {
459	>	t.quietlyJoin();
460	>	if (ex == null && t.status < NORMAL)
461	>	ex = t.getException();
462	>	}
463		}
464		}
465		if (ex != null)
#	Line 568 | Line 493 | public abstract class ForkJoinTask<V> im
493		*/
494		public boolean cancel(boolean mayInterruptIfRunning) {
495		setCompletion(CANCELLED);
496	<	return (status & COMPLETION_MASK) == CANCELLED;
496	>	return status == CANCELLED;
497		}
498
499		/**
500	<	* Cancels, ignoring any exceptions it throws. Used during worker
501	<	* and pool shutdown.
500	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
501	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
502	>	* exceptions, but if it does anyway, we have no recourse during
503	>	* shutdown, so guard against this case.
504		*/
505		final void cancelIgnoringExceptions() {
506		try {
#	Line 585 | Line 512 | public abstract class ForkJoinTask<V> im
512		/**
513		* Cancels ignoring exceptions if worker is terminating
514		*/
515	<	private void cancelIfTerminating() {
515	>	final void cancelIfTerminating() {
516		Thread t = Thread.currentThread();
517		if ((t instanceof ForkJoinWorkerThread) &&
518		((ForkJoinWorkerThread) t).isTerminating()) {
#	Line 601 | Line 528 | public abstract class ForkJoinTask<V> im
528		}
529
530		public final boolean isCancelled() {
531	<	return (status & COMPLETION_MASK) == CANCELLED;
531	>	return status == CANCELLED;
532		}
533
534		/**
#	Line 610 | Line 537 | public abstract class ForkJoinTask<V> im
537		* @return {@code true} if this task threw an exception or was cancelled
538		*/
539		public final boolean isCompletedAbnormally() {
540	<	return (status & COMPLETION_MASK) < NORMAL;
540	>	return status < NORMAL;
541		}
542
543		/**
#	Line 621 | Line 548 | public abstract class ForkJoinTask<V> im
548		* exception and was not cancelled
549		*/
550		public final boolean isCompletedNormally() {
551	<	return (status & COMPLETION_MASK) == NORMAL;
551	>	return status == NORMAL;
552		}
553
554		/**
#	Line 632 | Line 559 | public abstract class ForkJoinTask<V> im
559		* @return the exception, or {@code null} if none
560		*/
561		public final Throwable getException() {
562	<	int s = status & COMPLETION_MASK;
562	>	int s = status;
563		return ((s >= NORMAL)    ? null :
564		(s == CANCELLED) ? new CancellationException() :
565		exceptionMap.get(this));
#	Line 681 | Line 608 | public abstract class ForkJoinTask<V> im
608		}
609
610		public final V get() throws InterruptedException, ExecutionException {
611	<	int s = waitingJoin() & COMPLETION_MASK;
611	>	quietlyJoin();
612		if (Thread.interrupted())
613		throw new InterruptedException();
614	+	int s = status;
615		if (s < NORMAL) {
616		Throwable ex;
617		if (s == CANCELLED)
#	Line 701 | Line 629 | public abstract class ForkJoinTask<V> im
629		if (t instanceof ForkJoinWorkerThread) {
630		ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
631		if (status >= 0 && w.unpushTask(this))
632	<	tryExec();
632	>	quietlyExec();
633		pool = w.pool;
634		}
635		else
636		pool = null;
637		/*
638	<	* Timed wait loop intermixes cases for fj (pool != null) and
638	>	* Timed wait loop intermixes cases for FJ (pool != null) and
639		* non FJ threads. For FJ, decrement pool count but don't try
640		* for replacement; increment count on completion. For non-FJ,
641		* deal with interrupts. This is messy, but a little less so
#	Line 723 | Line 651 | public abstract class ForkJoinTask<V> im
651		int s = status;
652		if (s < 0)
653		break;
654	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
727	<	s, s | SIGNAL)) {
654	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
655		long startTime = System.nanoTime();
656		long nanos = unit.toNanos(timeout);
657		long nt; // wait time
#	Line 754 | Line 681 | public abstract class ForkJoinTask<V> im
681		}
682		}
683		if (pool != null && dec)
684	<	pool.updateRunningCount(1);
684	>	pool.incrementRunningCount();
685		if (interrupted)
686		throw new InterruptedException();
687	<	int es = status & COMPLETION_MASK;
687	>	int es = status;
688		if (es != NORMAL) {
689		Throwable ex;
690		if (es == CANCELLED)
#	Line 770 | Line 697 | public abstract class ForkJoinTask<V> im
697		}
698
699		/**
700	<	* 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
700	>	* Joins this task, without returning its result or throwing its
701		* exception. This method may be useful when processing
702		* collections of tasks when some have been cancelled or otherwise
703		* known to have aborted.
704		*/
705		public final void quietlyJoin() {
706	<	waitingJoin();
706	>	Thread t;
707	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
708	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
709	>	if (status >= 0) {
710	>	if (w.unpushTask(this)) {
711	>	boolean completed;
712	>	try {
713	>	completed = exec();
714	>	} catch (Throwable rex) {
715	>	setExceptionalCompletion(rex);
716	>	return;
717	>	}
718	>	if (completed) {
719	>	setCompletion(NORMAL);
720	>	return;
721	>	}
722	>	}
723	>	w.joinTask(this);
724	>	}
725	>	}
726	>	else
727	>	externalAwaitDone();
728		}
729
730		/**
731		* Commences performing this task and awaits its completion if
732	<	* necessary, without returning its result or throwing an
732	>	* necessary, without returning its result or throwing its
733		* exception. This method may be useful when processing
734		* collections of tasks when some have been cancelled or otherwise
735		* known to have aborted.
736		*/
737		public final void quietlyInvoke() {
738	<	waitingInvoke();
738	>	if (status >= 0) {
739	>	boolean completed;
740	>	try {
741	>	completed = exec();
742	>	} catch (Throwable rex) {
743	>	setExceptionalCompletion(rex);
744	>	return;
745	>	}
746	>	if (completed)
747	>	setCompletion(NORMAL);
748	>	else
749	>	quietlyJoin();
750	>	}
751		}
752
753		/**
#	Line 856 | Line 779 | public abstract class ForkJoinTask<V> im
779		* pre-constructed trees of subtasks in loops.
780		*/
781		public void reinitialize() {
782	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
782	>	if (status == EXCEPTIONAL)
783		exceptionMap.remove(this);
784		status = 0;
785		}
#	Line 1166 | Line 1089 | public abstract class ForkJoinTask<V> im
1089		private void readObject(java.io.ObjectInputStream s)
1090		throws java.io.IOException, ClassNotFoundException {
1091		s.defaultReadObject();
1169	–	status |= SIGNAL; // conservatively set external signal
1092		Object ex = s.readObject();
1093		if (ex != null)
1094		setExceptionalCompletion((Throwable) ex);

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