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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 1.55 by dl, Sun Aug 29 23:34:46 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.
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;
222	>	int s;         // the odd construction reduces lock bias effects
223		while ((s = status) >= 0) {
224	<	synchronized(this) {
225	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
226	<	do {
227	<	try {
234	<	wait();
235	<	} catch (InterruptedException ie) {
236	<	cancelIfTerminating();
237	<	}
238	<	} while (status >= 0);
239	<	break;
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		/**
236	<	* Blocks a non-worker-thread until completion.
236	>	* Blocks a worker thread until completed or timed out.  Called
237	>	* only by pool.
238	>	*
239		* @return status on exit
240		*/
241	<	private int externalAwaitDone() {
241	>	final int internalAwaitDone(long millis) {
242	>	int s;
243	>	if ((s = status) >= 0) {
244	>	try {
245	>	synchronized(this) {
246	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
247	>	wait(millis, 0);
248	>	}
249	>	} catch (InterruptedException ie) {
250	>	cancelIfTerminating();
251	>	}
252	>	s = status;
253	>	}
254	>	return s;
255	>	}
256	>
257	>	/**
258	>	* Blocks a non-worker-thread until completion.
259	>	*/
260	>	private void externalAwaitDone() {
261		int s;
262		while ((s = status) >= 0) {
263		synchronized(this) {
264	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
264	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
265		boolean interrupted = false;
266	<	do {
266	>	while (status >= 0) {
267		try {
268		wait();
269		} catch (InterruptedException ie) {
270		interrupted = true;
271		}
272	<	} while ((s = status) >= 0);
272	>	}
273		if (interrupted)
274		Thread.currentThread().interrupt();
275		break;
276		}
277		}
278		}
268	–	return s;
279		}
280
281		/**
282		* Unless done, calls exec and records status if completed, but
283	<	* doesn't wait for completion otherwise.
283	>	* doesn't wait for completion otherwise. Primary execution method
284	>	* for ForkJoinWorkerThread.
285		*/
286	<	final void tryExec() {
286	>	final void quietlyExec() {
287		try {
288		if (status < 0 || !exec())
289		return;
#	Line 283 | Line 294 | public abstract class ForkJoinTask<V> im
294		setCompletion(NORMAL); // must be outside try block
295		}
296
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	–
297		// public methods
298
299		/**
#	Line 400 | Line 329 | public abstract class ForkJoinTask<V> im
329		* @return the computed result
330		*/
331		public final V join() {
332	<	return reportResult(waitingJoin());
332	>	quietlyJoin();
333	>	Throwable ex;
334	>	if (status < NORMAL && (ex = getException()) != null)
335	>	UNSAFE.throwException(ex);
336	>	return getRawResult();
337		}
338
339		/**
#	Line 411 | Line 344 | public abstract class ForkJoinTask<V> im
344		* @return the computed result
345		*/
346		public final V invoke() {
347	<	return reportResult(waitingInvoke());
347	>	quietlyInvoke();
348	>	Throwable ex;
349	>	if (status < NORMAL && (ex = getException()) != null)
350	>	UNSAFE.throwException(ex);
351	>	return getRawResult();
352		}
353
354		/**
#	Line 469 | Line 406 | public abstract class ForkJoinTask<V> im
406		}
407		else if (i != 0)
408		t.fork();
409	<	else if (t.waitingInvoke() < NORMAL && ex == null)
410	<	ex = t.getException();
409	>	else {
410	>	t.quietlyInvoke();
411	>	if (ex == null && t.status < NORMAL)
412	>	ex = t.getException();
413	>	}
414		}
415		for (int i = 1; i <= last; ++i) {
416		ForkJoinTask<?> t = tasks[i];
417		if (t != null) {
418		if (ex != null)
419		t.cancel(false);
420	<	else if (t.waitingJoin() < NORMAL && ex == null)
421	<	ex = t.getException();
420	>	else {
421	>	t.quietlyJoin();
422	>	if (ex == null && t.status < NORMAL)
423	>	ex = t.getException();
424	>	}
425		}
426		}
427		if (ex != null)
#	Line 525 | Line 468 | public abstract class ForkJoinTask<V> im
468		}
469		else if (i != 0)
470		t.fork();
471	<	else if (t.waitingInvoke() < NORMAL && ex == null)
472	<	ex = t.getException();
471	>	else {
472	>	t.quietlyInvoke();
473	>	if (ex == null && t.status < NORMAL)
474	>	ex = t.getException();
475	>	}
476		}
477		for (int i = 1; i <= last; ++i) {
478		ForkJoinTask<?> t = ts.get(i);
479		if (t != null) {
480		if (ex != null)
481		t.cancel(false);
482	<	else if (t.waitingJoin() < NORMAL && ex == null)
483	<	ex = t.getException();
482	>	else {
483	>	t.quietlyJoin();
484	>	if (ex == null && t.status < NORMAL)
485	>	ex = t.getException();
486	>	}
487		}
488		}
489		if (ex != null)
#	Line 568 | Line 517 | public abstract class ForkJoinTask<V> im
517		*/
518		public boolean cancel(boolean mayInterruptIfRunning) {
519		setCompletion(CANCELLED);
520	<	return (status & COMPLETION_MASK) == CANCELLED;
520	>	return status == CANCELLED;
521		}
522
523		/**
524	<	* Cancels, ignoring any exceptions it throws. Used during worker
525	<	* and pool shutdown.
524	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
525	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
526	>	* exceptions, but if it does anyway, we have no recourse during
527	>	* shutdown, so guard against this case.
528		*/
529		final void cancelIgnoringExceptions() {
530		try {
#	Line 585 | Line 536 | public abstract class ForkJoinTask<V> im
536		/**
537		* Cancels ignoring exceptions if worker is terminating
538		*/
539	<	private void cancelIfTerminating() {
539	>	final void cancelIfTerminating() {
540		Thread t = Thread.currentThread();
541		if ((t instanceof ForkJoinWorkerThread) &&
542		((ForkJoinWorkerThread) t).isTerminating()) {
#	Line 601 | Line 552 | public abstract class ForkJoinTask<V> im
552		}
553
554		public final boolean isCancelled() {
555	<	return (status & COMPLETION_MASK) == CANCELLED;
555	>	return status == CANCELLED;
556		}
557
558		/**
#	Line 610 | Line 561 | public abstract class ForkJoinTask<V> im
561		* @return {@code true} if this task threw an exception or was cancelled
562		*/
563		public final boolean isCompletedAbnormally() {
564	<	return (status & COMPLETION_MASK) < NORMAL;
564	>	return status < NORMAL;
565		}
566
567		/**
#	Line 621 | Line 572 | public abstract class ForkJoinTask<V> im
572		* exception and was not cancelled
573		*/
574		public final boolean isCompletedNormally() {
575	<	return (status & COMPLETION_MASK) == NORMAL;
575	>	return status == NORMAL;
576		}
577
578		/**
#	Line 632 | Line 583 | public abstract class ForkJoinTask<V> im
583		* @return the exception, or {@code null} if none
584		*/
585		public final Throwable getException() {
586	<	int s = status & COMPLETION_MASK;
586	>	int s = status;
587		return ((s >= NORMAL)    ? null :
588		(s == CANCELLED) ? new CancellationException() :
589		exceptionMap.get(this));
#	Line 681 | Line 632 | public abstract class ForkJoinTask<V> im
632		}
633
634		public final V get() throws InterruptedException, ExecutionException {
635	<	int s = waitingJoin() & COMPLETION_MASK;
635	>	quietlyJoin();
636		if (Thread.interrupted())
637		throw new InterruptedException();
638	+	int s = status;
639		if (s < NORMAL) {
640		Throwable ex;
641		if (s == CANCELLED)
#	Line 701 | Line 653 | public abstract class ForkJoinTask<V> im
653		if (t instanceof ForkJoinWorkerThread) {
654		ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
655		if (status >= 0 && w.unpushTask(this))
656	<	tryExec();
656	>	quietlyExec();
657		pool = w.pool;
658		}
659		else
660		pool = null;
661		/*
662	<	* Timed wait loop intermixes cases for fj (pool != null) and
662	>	* Timed wait loop intermixes cases for FJ (pool != null) and
663		* non FJ threads. For FJ, decrement pool count but don't try
664		* for replacement; increment count on completion. For non-FJ,
665		* deal with interrupts. This is messy, but a little less so
#	Line 715 | Line 667 | public abstract class ForkJoinTask<V> im
667		*/
668		boolean interrupted = false;
669		boolean dec = false; // true if pool count decremented
670	+	long nanos = unit.toNanos(timeout);
671		for (;;) {
672		if (Thread.interrupted() && pool == null) {
673		interrupted = true;
#	Line 723 | Line 676 | public abstract class ForkJoinTask<V> im
676		int s = status;
677		if (s < 0)
678		break;
679	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
727	<	s, s | SIGNAL)) {
679	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
680		long startTime = System.nanoTime();
729	–	long nanos = unit.toNanos(timeout);
681		long nt; // wait time
682		while (status >= 0 &&
683		(nt = nanos - (System.nanoTime() - startTime)) > 0) {
#	Line 754 | Line 705 | public abstract class ForkJoinTask<V> im
705		}
706		}
707		if (pool != null && dec)
708	<	pool.updateRunningCount(1);
708	>	pool.incrementRunningCount();
709		if (interrupted)
710		throw new InterruptedException();
711	<	int es = status & COMPLETION_MASK;
711	>	int es = status;
712		if (es != NORMAL) {
713		Throwable ex;
714		if (es == CANCELLED)
#	Line 770 | Line 721 | public abstract class ForkJoinTask<V> im
721		}
722
723		/**
724	<	* 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
724	>	* Joins this task, without returning its result or throwing its
725		* exception. This method may be useful when processing
726		* collections of tasks when some have been cancelled or otherwise
727		* known to have aborted.
728		*/
729		public final void quietlyJoin() {
730	<	waitingJoin();
730	>	Thread t;
731	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
732	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
733	>	if (status >= 0) {
734	>	if (w.unpushTask(this)) {
735	>	boolean completed;
736	>	try {
737	>	completed = exec();
738	>	} catch (Throwable rex) {
739	>	setExceptionalCompletion(rex);
740	>	return;
741	>	}
742	>	if (completed) {
743	>	setCompletion(NORMAL);
744	>	return;
745	>	}
746	>	}
747	>	w.joinTask(this);
748	>	}
749	>	}
750	>	else
751	>	externalAwaitDone();
752		}
753
754		/**
755		* Commences performing this task and awaits its completion if
756	<	* necessary, without returning its result or throwing an
756	>	* necessary, without returning its result or throwing its
757		* exception. This method may be useful when processing
758		* collections of tasks when some have been cancelled or otherwise
759		* known to have aborted.
760		*/
761		public final void quietlyInvoke() {
762	<	waitingInvoke();
762	>	if (status >= 0) {
763	>	boolean completed;
764	>	try {
765	>	completed = exec();
766	>	} catch (Throwable rex) {
767	>	setExceptionalCompletion(rex);
768	>	return;
769	>	}
770	>	if (completed)
771	>	setCompletion(NORMAL);
772	>	else
773	>	quietlyJoin();
774	>	}
775		}
776
777		/**
#	Line 856 | Line 803 | public abstract class ForkJoinTask<V> im
803		* pre-constructed trees of subtasks in loops.
804		*/
805		public void reinitialize() {
806	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
806	>	if (status == EXCEPTIONAL)
807		exceptionMap.remove(this);
808		status = 0;
809		}
#	Line 1166 | Line 1113 | public abstract class ForkJoinTask<V> im
1113		private void readObject(java.io.ObjectInputStream s)
1114		throws java.io.IOException, ClassNotFoundException {
1115		s.defaultReadObject();
1169	–	status |= SIGNAL; // conservatively set external signal
1116		Object ex = s.readObject();
1117		if (ex != null)
1118		setExceptionalCompletion((Throwable) ex);

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