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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 1.53 by dl, Wed Aug 11 18:45:12 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.
218		*/
219	<	final int internalAwaitDone() {
220	<	int s;
219	>	final void internalAwaitDone() {
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, SIGNAL)) {
224	<	do {
225	<	try {
224	<	wait();
225	<	} catch (InterruptedException ie) {
226	<	cancelIfTerminating();
227	<	}
228	<	} while ((s = status) >= 0);
229	<	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		}
233	–	return s;
231		}
232
233		/**
234		* Blocks a non-worker-thread until completion.
238	–	* @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, 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		}
259	–	return s;
255		}
256
257		/**
#	Line 264 | Line 259 | public abstract class ForkJoinTask<V> im
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 275 | Line 270 | public abstract class ForkJoinTask<V> im
270		setCompletion(NORMAL); // must be outside try block
271		}
272
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	–
273		// public methods
274
275		/**
#	Line 371 | Line 305 | public abstract class ForkJoinTask<V> im
305		* @return the computed result
306		*/
307		public final V join() {
308	<	return reportResult(doJoin());
308	>	quietlyJoin();
309	>	Throwable ex;
310	>	if (status < NORMAL && (ex = getException()) != null)
311	>	UNSAFE.throwException(ex);
312	>	return getRawResult();
313		}
314
315		/**
#	Line 382 | Line 320 | public abstract class ForkJoinTask<V> im
320		* @return the computed result
321		*/
322		public final V invoke() {
323	<	return reportResult(doInvoke());
323	>	quietlyInvoke();
324	>	Throwable ex;
325	>	if (status < NORMAL && (ex = getException()) != null)
326	>	UNSAFE.throwException(ex);
327	>	return getRawResult();
328		}
329
330		/**
#	Line 440 | Line 382 | public abstract class ForkJoinTask<V> im
382		}
383		else if (i != 0)
384		t.fork();
385	<	else if (t.doInvoke() < 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.doJoin() < 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 496 | Line 444 | public abstract class ForkJoinTask<V> im
444		}
445		else if (i != 0)
446		t.fork();
447	<	else if (t.doInvoke() < 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.doJoin() < 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 543 | Line 497 | public abstract class ForkJoinTask<V> im
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 556 | 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 652 | Line 608 | public abstract class ForkJoinTask<V> im
608		}
609
610		public final V get() throws InterruptedException, ExecutionException {
611	<	int s = doJoin();
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 672 | 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 694 | Line 651 | public abstract class ForkJoinTask<V> im
651		int s = status;
652		if (s < 0)
653		break;
654	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
698	<	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 741 | Line 697 | public abstract class ForkJoinTask<V> im
697		}
698
699		/**
700	<	* 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	<	doJoin();
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	<	doInvoke();
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 1103 | Line 1092 | public abstract class ForkJoinTask<V> im
1092		Object ex = s.readObject();
1093		if (ex != null)
1094		setExceptionalCompletion((Throwable) ex);
1106	–	if (status < 0)
1107	–	synchronized (this) { notifyAll(); }
1095		}
1096
1097		// Unsafe mechanics

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