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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 1.52 by dl, Sat Jul 24 20:28:18 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 151 | Line 147 | public abstract class ForkJoinTask<V> im
147		* in a way that flows well in javadocs.
148		*/
149
150	<	/**
151	<	* Run control status bits packed into a single int to minimize
152	<	* footprint and to ensure atomicity (via CAS).  Status is
153	<	* initially zero, and takes on nonnegative values until
154	<	* completed, upon which status holds COMPLETED. CANCELLED, or
155	<	* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
156	<	* blocking waits by other threads have the SIGNAL bit set.
157	<	*
158	<	* Completion of a stolen task with SIGNAL set awakens any waiters
163	<	* via notifyAll. Even though suboptimal for some purposes, we use
150	>	/*
151	>	* The status field holds run control status bits packed into a
152	>	* single int to minimize footprint and to ensure atomicity (via
153	>	* CAS).  Status is initially zero, and takes on nonnegative
154	>	* values until completed, upon which status holds value
155	>	* COMPLETED. CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
156	>	* waits by other threads have the SIGNAL bit set.  Completion of
157	>	* a stolen task with SIGNAL set awakens any waiters via
158	>	* notifyAll. Even though suboptimal for some purposes, we use
159		* basic builtin wait/notify to take advantage of "monitor
160		* inflation" in JVMs that we would otherwise need to emulate to
161		* avoid adding further per-task bookkeeping overhead.  We want
162		* these monitors to be "fat", i.e., not use biasing or thin-lock
163		* techniques, so use some odd coding idioms that tend to avoid
164		* them.
170	–	*
171	–	* Note that bits 1-28 are currently unused. Also value
172	–	* 0x80000000 is available as spare completion value.
165		*/
166	+
167	+	/** Run status of this task */
168		volatile int status; // accessed directly by pool and workers
169
170	<	private static final int COMPLETION_MASK      = 0xe0000000;
171	<	private static final int NORMAL               = 0xe0000000; // == mask
172	<	private static final int CANCELLED            = 0xc0000000;
173	<	private static final int EXCEPTIONAL          = 0xa0000000;
180	<	private static final int SIGNAL               = 0x00000001;
170	>	private static final int NORMAL      = -1;
171	>	private static final int CANCELLED   = -2;
172	>	private static final int EXCEPTIONAL = -3;
173	>	private static final int SIGNAL      =  1;
174
175		/**
176		* Table of exceptions thrown by tasks, to enable reporting by
#	Line 204 | Line 197 | public abstract class ForkJoinTask<V> im
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;
203		}
#	Line 225 | Line 218 | public abstract class ForkJoinTask<V> im
218		* Blocks a worker thread until completion. Called only by pool.
219		*/
220		final void internalAwaitDone() {
221	<	int s;
221	>	int s;         // the odd construction reduces lock bias effects
222		while ((s = status) >= 0) {
223	<	synchronized(this) {
224	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
225	<	do {
226	<	try {
234	<	wait();
235	<	} catch (InterruptedException ie) {
236	<	cancelIfTerminating();
237	<	}
238	<	} while (status >= 0);
239	<	break;
223	>	try {
224	>	synchronized(this) {
225	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
226	>	wait();
227		}
228	+	} catch (InterruptedException ie) {
229	+	cancelIfTerminating();
230		}
231		}
232		}
#	Line 250 | Line 239 | public abstract class ForkJoinTask<V> im
239		int s;
240		while ((s = status) >= 0) {
241		synchronized(this) {
242	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
242	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
243		boolean interrupted = false;
244	<	do {
244	>	while ((s = status) >= 0) {
245		try {
246		wait();
247		} catch (InterruptedException ie) {
248		interrupted = true;
249		}
250	<	} while ((s = status) >= 0);
250	>	}
251		if (interrupted)
252		Thread.currentThread().interrupt();
253		break;
#	Line 270 | Line 259 | public abstract class ForkJoinTask<V> im
259
260		/**
261		* Unless done, calls exec and records status if completed, but
262	<	* doesn't wait for completion otherwise.
262	>	* doesn't wait for completion otherwise. Primary execution method
263	>	* for ForkJoinWorkerThread.
264		*/
265		final void tryExec() {
266		try {
#	Line 288 | Line 278 | public abstract class ForkJoinTask<V> im
278		* else waits for it.
279		* @return status on exit
280		*/
281	<	private int waitingJoin() {
282	<	int s = status;
283	<	if (s < 0)
284	<	return s;
285	<	Thread t = Thread.currentThread();
286	<	if (t instanceof ForkJoinWorkerThread) {
287	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
288	<	if (w.unpushTask(this)) {
281	>	private int doJoin() {
282	>	int stat;
283	>	Thread t;
284	>	ForkJoinWorkerThread w;
285	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
286	>	if ((stat = status) < 0)
287	>	return stat;
288	>	if ((w = (ForkJoinWorkerThread) t).unpushTask(this)) {
289		boolean completed;
290		try {
291		completed = exec();
#	Line 305 | Line 295 | public abstract class ForkJoinTask<V> im
295		if (completed)
296		return setCompletion(NORMAL);
297		}
298	<	return w.pool.awaitJoin(this);
298	>	return w.joinTask(this);
299		}
300	<	else
311	<	return externalAwaitDone();
300	>	return externalAwaitDone();
301		}
302
303		/**
#	Line 316 | Line 305 | public abstract class ForkJoinTask<V> im
305		* waits for completion otherwise.
306		* @return status on exit
307		*/
308	<	private int waitingInvoke() {
309	<	int s = status;
310	<	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)) {
308	>	private int doInvoke() {
309	>	int stat;
310	>	if ((stat = status) >= 0) {
311		boolean completed;
312		try {
313		completed = exec();
314		} catch (Throwable rex) {
315		return setExceptionalCompletion(rex);
316		}
317	<	if (completed)
352	<	return setCompletion(NORMAL);
317	>	stat = completed ? setCompletion(NORMAL) : doJoin();
318		}
319	<	return w.execWhileJoining(this);
319	>	return stat;
320		}
321
322		/**
#	Line 400 | Line 365 | public abstract class ForkJoinTask<V> im
365		* @return the computed result
366		*/
367		public final V join() {
368	<	return reportResult(waitingJoin());
368	>	return reportResult(doJoin());
369		}
370
371		/**
#	Line 411 | Line 376 | public abstract class ForkJoinTask<V> im
376		* @return the computed result
377		*/
378		public final V invoke() {
379	<	return reportResult(waitingInvoke());
379	>	return reportResult(doInvoke());
380		}
381
382		/**
#	Line 469 | Line 434 | public abstract class ForkJoinTask<V> im
434		}
435		else if (i != 0)
436		t.fork();
437	<	else if (t.waitingInvoke() < NORMAL && ex == null)
437	>	else if (t.doInvoke() < NORMAL && ex == null)
438		ex = t.getException();
439		}
440		for (int i = 1; i <= last; ++i) {
#	Line 477 | Line 442 | public abstract class ForkJoinTask<V> im
442		if (t != null) {
443		if (ex != null)
444		t.cancel(false);
445	<	else if (t.waitingJoin() < NORMAL && ex == null)
445	>	else if (t.doJoin() < NORMAL && ex == null)
446		ex = t.getException();
447		}
448		}
#	Line 525 | Line 490 | public abstract class ForkJoinTask<V> im
490		}
491		else if (i != 0)
492		t.fork();
493	<	else if (t.waitingInvoke() < NORMAL && ex == null)
493	>	else if (t.doInvoke() < NORMAL && ex == null)
494		ex = t.getException();
495		}
496		for (int i = 1; i <= last; ++i) {
#	Line 533 | Line 498 | public abstract class ForkJoinTask<V> im
498		if (t != null) {
499		if (ex != null)
500		t.cancel(false);
501	<	else if (t.waitingJoin() < NORMAL && ex == null)
501	>	else if (t.doJoin() < NORMAL && ex == null)
502		ex = t.getException();
503		}
504		}
#	Line 567 | Line 532 | public abstract class ForkJoinTask<V> im
532		* @return {@code true} if this task is now cancelled
533		*/
534		public boolean cancel(boolean mayInterruptIfRunning) {
535	<	setCompletion(CANCELLED);
571	<	return (status & COMPLETION_MASK) == CANCELLED;
535	>	return setCompletion(CANCELLED) == CANCELLED;
536		}
537
538		/**
539	<	* Cancels, ignoring any exceptions it throws. Used during worker
540	<	* and pool shutdown.
539	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
540	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
541	>	* exceptions, but if it does anyway, we have no recourse during
542	>	* shutdown, so guard against this case.
543		*/
544		final void cancelIgnoringExceptions() {
545		try {
#	Line 585 | Line 551 | public abstract class ForkJoinTask<V> im
551		/**
552		* Cancels ignoring exceptions if worker is terminating
553		*/
554	<	private void cancelIfTerminating() {
554	>	final void cancelIfTerminating() {
555		Thread t = Thread.currentThread();
556		if ((t instanceof ForkJoinWorkerThread) &&
557		((ForkJoinWorkerThread) t).isTerminating()) {
#	Line 601 | Line 567 | public abstract class ForkJoinTask<V> im
567		}
568
569		public final boolean isCancelled() {
570	<	return (status & COMPLETION_MASK) == CANCELLED;
570	>	return status == CANCELLED;
571		}
572
573		/**
#	Line 610 | Line 576 | public abstract class ForkJoinTask<V> im
576		* @return {@code true} if this task threw an exception or was cancelled
577		*/
578		public final boolean isCompletedAbnormally() {
579	<	return (status & COMPLETION_MASK) < NORMAL;
579	>	return status < NORMAL;
580		}
581
582		/**
#	Line 621 | Line 587 | public abstract class ForkJoinTask<V> im
587		* exception and was not cancelled
588		*/
589		public final boolean isCompletedNormally() {
590	<	return (status & COMPLETION_MASK) == NORMAL;
590	>	return status == NORMAL;
591		}
592
593		/**
#	Line 632 | Line 598 | public abstract class ForkJoinTask<V> im
598		* @return the exception, or {@code null} if none
599		*/
600		public final Throwable getException() {
601	<	int s = status & COMPLETION_MASK;
601	>	int s = status;
602		return ((s >= NORMAL)    ? null :
603		(s == CANCELLED) ? new CancellationException() :
604		exceptionMap.get(this));
#	Line 681 | Line 647 | public abstract class ForkJoinTask<V> im
647		}
648
649		public final V get() throws InterruptedException, ExecutionException {
650	<	int s = waitingJoin() & COMPLETION_MASK;
650	>	int s = doJoin();
651		if (Thread.interrupted())
652		throw new InterruptedException();
653		if (s < NORMAL) {
#	Line 707 | Line 673 | public abstract class ForkJoinTask<V> im
673		else
674		pool = null;
675		/*
676	<	* Timed wait loop intermixes cases for fj (pool != null) and
676	>	* Timed wait loop intermixes cases for FJ (pool != null) and
677		* non FJ threads. For FJ, decrement pool count but don't try
678		* for replacement; increment count on completion. For non-FJ,
679		* deal with interrupts. This is messy, but a little less so
#	Line 723 | Line 689 | public abstract class ForkJoinTask<V> im
689		int s = status;
690		if (s < 0)
691		break;
692	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
727	<	s, s | SIGNAL)) {
692	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
693		long startTime = System.nanoTime();
694		long nanos = unit.toNanos(timeout);
695		long nt; // wait time
#	Line 754 | Line 719 | public abstract class ForkJoinTask<V> im
719		}
720		}
721		if (pool != null && dec)
722	<	pool.updateRunningCount(1);
722	>	pool.incrementRunningCount();
723		if (interrupted)
724		throw new InterruptedException();
725	<	int es = status & COMPLETION_MASK;
725	>	int es = status;
726		if (es != NORMAL) {
727		Throwable ex;
728		if (es == CANCELLED)
#	Line 770 | Line 735 | public abstract class ForkJoinTask<V> im
735		}
736
737		/**
773	–	* 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	–	/**
738		* Joins this task, without returning its result or throwing an
739		* exception. This method may be useful when processing
740		* collections of tasks when some have been cancelled or otherwise
741		* known to have aborted.
742		*/
743		public final void quietlyJoin() {
744	<	waitingJoin();
744	>	doJoin();
745		}
746
747		/**
#	Line 824 | Line 752 | public abstract class ForkJoinTask<V> im
752		* known to have aborted.
753		*/
754		public final void quietlyInvoke() {
755	<	waitingInvoke();
755	>	doInvoke();
756		}
757
758		/**
#	Line 856 | Line 784 | public abstract class ForkJoinTask<V> im
784		* pre-constructed trees of subtasks in loops.
785		*/
786		public void reinitialize() {
787	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
787	>	if (status == EXCEPTIONAL)
788		exceptionMap.remove(this);
789		status = 0;
790		}
#	Line 1166 | Line 1094 | public abstract class ForkJoinTask<V> im
1094		private void readObject(java.io.ObjectInputStream s)
1095		throws java.io.IOException, ClassNotFoundException {
1096		s.defaultReadObject();
1169	–	status |= SIGNAL; // conservatively set external signal
1097		Object ex = s.readObject();
1098		if (ex != null)
1099		setExceptionalCompletion((Throwable) ex);

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