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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.49 by dl, Wed Jul 7 19:52:31 2010 UTC vs.
Revision 1.55 by dl, Sun Aug 29 23:34:46 2010 UTC

#	Line 144 | 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 value COMPLETED. CANCELLED,
156	<	* or EXCEPTIONAL. Tasks undergoing blocking waits by other
157	<	* threads have the SIGNAL bit set.  Completion of a stolen task
158	<	* with SIGNAL set awakens any waiters via notifyAll. Even though
159	<	* suboptimal for some purposes, we use basic builtin wait/notify
160	<	* to take advantage of "monitor inflation" in JVMs that we would
161	<	* otherwise need to emulate to avoid adding further per-task
162	<	* bookkeeping overhead.  We want these monitors to be "fat",
163	<	* i.e., not use biasing or thin-lock techniques, so use some odd
164	<	* coding idioms that tend to avoid them.
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.
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 NORMAL      = -1;
#	Line 188 | Line 192 | public abstract class ForkJoinTask<V> im
192		* also clearing signal request bits.
193		*
194		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
191	–	* @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)
200	>	if (s != 0)
201		synchronized (this) { notifyAll(); }
202	<	return completion;
202	>	break;
203		}
204		}
202	–	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 int internalAwaitDone() {
222	<	int s;
221	>	final void internalAwaitDone() {
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, SIGNAL)) {
226	<	do {
227	<	try {
228	<	wait();
229	<	} catch (InterruptedException ie) {
230	<	cancelIfTerminating();
231	<	}
232	<	} while ((s = status) >= 0);
233	<	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 worker thread until completed or timed out.  Called
237	>	* only by pool.
238	>	*
239	>	* @return status on exit
240	>	*/
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.
238	–	* @return status on exit
259		*/
260	<	private int externalAwaitDone() {
260	>	private void externalAwaitDone() {
261		int s;
262		while ((s = status) >= 0) {
263		synchronized(this) {
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		}
259	–	return s;
279		}
280
281		/**
#	Line 264 | Line 283 | public abstract class ForkJoinTask<V> im
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 275 | Line 294 | public abstract class ForkJoinTask<V> im
294		setCompletion(NORMAL); // must be outside try block
295		}
296
278	–	/**
279	–	* If not done and this task is next in worker queue, runs it,
280	–	* else waits for it.
281	–	* @return status on exit
282	–	*/
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	–	if ((w = (ForkJoinWorkerThread) t).unpushTask(this)) {
291	–	boolean completed;
292	–	try {
293	–	completed = exec();
294	–	} catch (Throwable rex) {
295	–	return setExceptionalCompletion(rex);
296	–	}
297	–	if (completed)
298	–	return setCompletion(NORMAL);
299	–	}
300	–	w.joinTask(this);
301	–	return status;
302	–	}
303	–	return externalAwaitDone();
304	–	}
305	–
306	–	/**
307	–	* Unless done, calls exec and records status if completed, or
308	–	* waits for completion otherwise.
309	–	* @return status on exit
310	–	*/
311	–	private int doInvoke() {
312	–	int stat;
313	–	if ((stat = status) >= 0) {
314	–	boolean completed;
315	–	try {
316	–	completed = exec();
317	–	} catch (Throwable rex) {
318	–	return setExceptionalCompletion(rex);
319	–	}
320	–	if (completed)
321	–	stat = setCompletion(NORMAL);
322	–	else
323	–	stat = doJoin();
324	–	}
325	–	return stat;
326	–	}
327	–
328	–	/**
329	–	* Returns result or throws exception associated with given status.
330	–	* @param s the status
331	–	*/
332	–	private V reportResult(int s) {
333	–	Throwable ex;
334	–	if (s < NORMAL && (ex = getException()) != null)
335	–	UNSAFE.throwException(ex);
336	–	return getRawResult();
337	–	}
338	–
297		// public methods
298
299		/**
#	Line 371 | Line 329 | public abstract class ForkJoinTask<V> im
329		* @return the computed result
330		*/
331		public final V join() {
332	<	return reportResult(doJoin());
332	>	quietlyJoin();
333	>	Throwable ex;
334	>	if (status < NORMAL && (ex = getException()) != null)
335	>	UNSAFE.throwException(ex);
336	>	return getRawResult();
337		}
338
339		/**
#	Line 382 | Line 344 | public abstract class ForkJoinTask<V> im
344		* @return the computed result
345		*/
346		public final V invoke() {
347	<	return reportResult(doInvoke());
347	>	quietlyInvoke();
348	>	Throwable ex;
349	>	if (status < NORMAL && (ex = getException()) != null)
350	>	UNSAFE.throwException(ex);
351	>	return getRawResult();
352		}
353
354		/**
#	Line 440 | Line 406 | public abstract class ForkJoinTask<V> im
406		}
407		else if (i != 0)
408		t.fork();
409	<	else if (t.doInvoke() < 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.doJoin() < 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 496 | Line 468 | public abstract class ForkJoinTask<V> im
468		}
469		else if (i != 0)
470		t.fork();
471	<	else if (t.doInvoke() < 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.doJoin() < 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 543 | Line 521 | public abstract class ForkJoinTask<V> im
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 556 | 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 652 | Line 632 | public abstract class ForkJoinTask<V> im
632		}
633
634		public final V get() throws InterruptedException, ExecutionException {
635	<	int s = doJoin();
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 672 | 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 686 | 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 694 | Line 676 | public abstract class ForkJoinTask<V> im
676		int s = status;
677		if (s < 0)
678		break;
679	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
698	<	s, s | SIGNAL)) {
679	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
680		long startTime = System.nanoTime();
700	–	long nanos = unit.toNanos(timeout);
681		long nt; // wait time
682		while (status >= 0 &&
683		(nt = nanos - (System.nanoTime() - startTime)) > 0) {
#	Line 741 | Line 721 | public abstract class ForkJoinTask<V> im
721		}
722
723		/**
724	<	* 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	<	doJoin();
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	<	doInvoke();
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 1103 | Line 1116 | public abstract class ForkJoinTask<V> im
1116		Object ex = s.readObject();
1117		if (ex != null)
1118		setExceptionalCompletion((Throwable) ex);
1106	–	if (status < 0)
1107	–	synchronized (this) { notifyAll(); }
1119		}
1120
1121		// Unsafe mechanics

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