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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 1.49 by dl, Wed Jul 7 19:52:31 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 155 | Line 151 | public abstract class ForkJoinTask<V> im
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
159	<	* via 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
168	<	* techniques, so use some odd coding idioms that tend to avoid
169	<	* them.
170	<	*
171	<	* Note that bits 1-28 are currently unused. Also value
172	<	* 0x80000000 is available as spare completion value.
154	>	* completed, upon which status holds value COMPLETED. CANCELLED,
155	>	* or EXCEPTIONAL. Tasks undergoing blocking waits by other
156	>	* threads have the SIGNAL bit set.  Completion of a stolen task
157	>	* with SIGNAL set awakens any waiters via notifyAll. Even though
158	>	* suboptimal for some purposes, we use basic builtin wait/notify
159	>	* to take advantage of "monitor inflation" in JVMs that we would
160	>	* otherwise need to emulate to avoid adding further per-task
161	>	* bookkeeping overhead.  We want these monitors to be "fat",
162	>	* i.e., not use biasing or thin-lock techniques, so use some odd
163	>	* coding idioms that tend to avoid them.
164		*/
165		volatile int status; // accessed directly by pool and workers
166
167	<	private static final int COMPLETION_MASK      = 0xe0000000;
168	<	private static final int NORMAL               = 0xe0000000; // == mask
169	<	private static final int CANCELLED            = 0xc0000000;
170	<	private static final int EXCEPTIONAL          = 0xa0000000;
180	<	private static final int SIGNAL               = 0x00000001;
167	>	private static final int NORMAL      = -1;
168	>	private static final int CANCELLED   = -2;
169	>	private static final int EXCEPTIONAL = -3;
170	>	private static final int SIGNAL      =  1;
171
172		/**
173		* Table of exceptions thrown by tasks, to enable reporting by
#	Line 204 | Line 194 | public abstract class ForkJoinTask<V> im
194		int s;
195		while ((s = status) >= 0) {
196		if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
197	<	if ((s & SIGNAL) != 0)
197	>	if (s == SIGNAL)
198		synchronized (this) { notifyAll(); }
199		return completion;
200		}
#	Line 224 | Line 214 | public abstract class ForkJoinTask<V> im
214		/**
215		* Blocks a worker thread until completion. Called only by pool.
216		*/
217	<	final void internalAwaitDone() {
217	>	final int internalAwaitDone() {
218		int s;
219		while ((s = status) >= 0) {
220		synchronized(this) {
221	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
221	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
222		do {
223		try {
224		wait();
225		} catch (InterruptedException ie) {
226		cancelIfTerminating();
227		}
228	<	} while (status >= 0);
228	>	} while ((s = status) >= 0);
229		break;
230		}
231		}
232		}
233	+	return s;
234		}
235
236		/**
#	Line 250 | Line 241 | public abstract class ForkJoinTask<V> im
241		int s;
242		while ((s = status) >= 0) {
243		synchronized(this) {
244	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, s|SIGNAL)){
244	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
245		boolean interrupted = false;
246		do {
247		try {
#	Line 270 | Line 261 | public abstract class ForkJoinTask<V> im
261
262		/**
263		* Unless done, calls exec and records status if completed, but
264	<	* doesn't wait for completion otherwise.
264	>	* doesn't wait for completion otherwise. Primary execution method
265	>	* for ForkJoinWorkerThread.
266		*/
267		final void tryExec() {
268		try {
#	Line 288 | Line 280 | public abstract class ForkJoinTask<V> im
280		* else waits for it.
281		* @return status on exit
282		*/
283	<	private int waitingJoin() {
284	<	int s = status;
285	<	if (s < 0)
286	<	return s;
283	>	private int doJoin() {
284	>	int stat;
285	>	if ((stat = status) < 0)
286	>	return stat;
287		Thread t = Thread.currentThread();
288	+	ForkJoinWorkerThread w;
289		if (t instanceof ForkJoinWorkerThread) {
290	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
298	<	if (w.unpushTask(this)) {
290	>	if ((w = (ForkJoinWorkerThread) t).unpushTask(this)) {
291		boolean completed;
292		try {
293		completed = exec();
#	Line 305 | Line 297 | public abstract class ForkJoinTask<V> im
297		if (completed)
298		return setCompletion(NORMAL);
299		}
300	<	return w.pool.awaitJoin(this);
300	>	w.joinTask(this);
301	>	return status;
302		}
303	<	else
311	<	return externalAwaitDone();
303	>	return externalAwaitDone();
304		}
305
306		/**
#	Line 316 | Line 308 | public abstract class ForkJoinTask<V> im
308		* waits for completion otherwise.
309		* @return status on exit
310		*/
311	<	private int waitingInvoke() {
312	<	int s = status;
313	<	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)) {
311	>	private int doInvoke() {
312	>	int stat;
313	>	if ((stat = status) >= 0) {
314		boolean completed;
315		try {
316		completed = exec();
#	Line 349 | Line 318 | public abstract class ForkJoinTask<V> im
318		return setExceptionalCompletion(rex);
319		}
320		if (completed)
321	<	return setCompletion(NORMAL);
321	>	stat = setCompletion(NORMAL);
322	>	else
323	>	stat = doJoin();
324		}
325	<	return w.execWhileJoining(this);
325	>	return stat;
326		}
327
328		/**
#	Line 400 | Line 371 | public abstract class ForkJoinTask<V> im
371		* @return the computed result
372		*/
373		public final V join() {
374	<	return reportResult(waitingJoin());
374	>	return reportResult(doJoin());
375		}
376
377		/**
#	Line 411 | Line 382 | public abstract class ForkJoinTask<V> im
382		* @return the computed result
383		*/
384		public final V invoke() {
385	<	return reportResult(waitingInvoke());
385	>	return reportResult(doInvoke());
386		}
387
388		/**
#	Line 469 | Line 440 | public abstract class ForkJoinTask<V> im
440		}
441		else if (i != 0)
442		t.fork();
443	<	else if (t.waitingInvoke() < NORMAL && ex == null)
443	>	else if (t.doInvoke() < NORMAL && ex == null)
444		ex = t.getException();
445		}
446		for (int i = 1; i <= last; ++i) {
#	Line 477 | Line 448 | public abstract class ForkJoinTask<V> im
448		if (t != null) {
449		if (ex != null)
450		t.cancel(false);
451	<	else if (t.waitingJoin() < NORMAL && ex == null)
451	>	else if (t.doJoin() < NORMAL && ex == null)
452		ex = t.getException();
453		}
454		}
#	Line 525 | Line 496 | public abstract class ForkJoinTask<V> im
496		}
497		else if (i != 0)
498		t.fork();
499	<	else if (t.waitingInvoke() < NORMAL && ex == null)
499	>	else if (t.doInvoke() < NORMAL && ex == null)
500		ex = t.getException();
501		}
502		for (int i = 1; i <= last; ++i) {
#	Line 533 | Line 504 | public abstract class ForkJoinTask<V> im
504		if (t != null) {
505		if (ex != null)
506		t.cancel(false);
507	<	else if (t.waitingJoin() < NORMAL && ex == null)
507	>	else if (t.doJoin() < NORMAL && ex == null)
508		ex = t.getException();
509		}
510		}
#	Line 568 | Line 539 | public abstract class ForkJoinTask<V> im
539		*/
540		public boolean cancel(boolean mayInterruptIfRunning) {
541		setCompletion(CANCELLED);
542	<	return (status & COMPLETION_MASK) == CANCELLED;
542	>	return status == CANCELLED;
543		}
544
545		/**
#	Line 601 | Line 572 | public abstract class ForkJoinTask<V> im
572		}
573
574		public final boolean isCancelled() {
575	<	return (status & COMPLETION_MASK) == CANCELLED;
575	>	return status == CANCELLED;
576		}
577
578		/**
#	Line 610 | Line 581 | public abstract class ForkJoinTask<V> im
581		* @return {@code true} if this task threw an exception or was cancelled
582		*/
583		public final boolean isCompletedAbnormally() {
584	<	return (status & COMPLETION_MASK) < NORMAL;
584	>	return status < NORMAL;
585		}
586
587		/**
#	Line 621 | Line 592 | public abstract class ForkJoinTask<V> im
592		* exception and was not cancelled
593		*/
594		public final boolean isCompletedNormally() {
595	<	return (status & COMPLETION_MASK) == NORMAL;
595	>	return status == NORMAL;
596		}
597
598		/**
#	Line 632 | Line 603 | public abstract class ForkJoinTask<V> im
603		* @return the exception, or {@code null} if none
604		*/
605		public final Throwable getException() {
606	<	int s = status & COMPLETION_MASK;
606	>	int s = status;
607		return ((s >= NORMAL)    ? null :
608		(s == CANCELLED) ? new CancellationException() :
609		exceptionMap.get(this));
#	Line 681 | Line 652 | public abstract class ForkJoinTask<V> im
652		}
653
654		public final V get() throws InterruptedException, ExecutionException {
655	<	int s = waitingJoin() & COMPLETION_MASK;
655	>	int s = doJoin();
656		if (Thread.interrupted())
657		throw new InterruptedException();
658		if (s < NORMAL) {
#	Line 754 | Line 725 | public abstract class ForkJoinTask<V> im
725		}
726		}
727		if (pool != null && dec)
728	<	pool.updateRunningCount(1);
728	>	pool.incrementRunningCount();
729		if (interrupted)
730		throw new InterruptedException();
731	<	int es = status & COMPLETION_MASK;
731	>	int es = status;
732		if (es != NORMAL) {
733		Throwable ex;
734		if (es == CANCELLED)
#	Line 770 | Line 741 | public abstract class ForkJoinTask<V> im
741		}
742
743		/**
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	–	/**
744		* Joins this task, without returning its result or throwing an
745		* exception. This method may be useful when processing
746		* collections of tasks when some have been cancelled or otherwise
747		* known to have aborted.
748		*/
749		public final void quietlyJoin() {
750	<	waitingJoin();
750	>	doJoin();
751		}
752
753		/**
#	Line 824 | Line 758 | public abstract class ForkJoinTask<V> im
758		* known to have aborted.
759		*/
760		public final void quietlyInvoke() {
761	<	waitingInvoke();
761	>	doInvoke();
762		}
763
764		/**
#	Line 856 | Line 790 | public abstract class ForkJoinTask<V> im
790		* pre-constructed trees of subtasks in loops.
791		*/
792		public void reinitialize() {
793	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
793	>	if (status == EXCEPTIONAL)
794		exceptionMap.remove(this);
795		status = 0;
796		}
#	Line 1166 | Line 1100 | public abstract class ForkJoinTask<V> im
1100		private void readObject(java.io.ObjectInputStream s)
1101		throws java.io.IOException, ClassNotFoundException {
1102		s.defaultReadObject();
1169	–	status |= SIGNAL; // conservatively set external signal
1103		Object ex = s.readObject();
1104		if (ex != null)
1105		setExceptionalCompletion((Throwable) ex);
1106	+	if (status < 0)
1107	+	synchronized (this) { notifyAll(); }
1108		}
1109
1110		// Unsafe mechanics

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