110 |
|
* result in exceptions or errors, possibly including |
111 |
|
* {@code ClassCastException}. |
112 |
|
* |
113 |
+ |
* <p>Method {@link #join} and its variants are appropriate for use |
114 |
+ |
* only when completion dependencies are acyclic; that is, the |
115 |
+ |
* parallel computation can be described as a directed acyclic graph |
116 |
+ |
* (DAG). Otherwise, executions may encounter a form of deadlock as |
117 |
+ |
* tasks cyclically wait for each other. However, this framework |
118 |
+ |
* supports other methods and techniques (for example the use of |
119 |
+ |
* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that |
120 |
+ |
* may be of use in constructing custom subclasses for problems that |
121 |
+ |
* are not statically structured as DAGs. |
122 |
+ |
* |
123 |
|
* <p>Most base support methods are {@code final}, to prevent |
124 |
|
* overriding of implementations that are intrinsically tied to the |
125 |
|
* underlying lightweight task scheduling framework. Developers |
134 |
|
* computation. Large tasks should be split into smaller subtasks, |
135 |
|
* usually via recursive decomposition. As a very rough rule of thumb, |
136 |
|
* a task should perform more than 100 and less than 10000 basic |
137 |
< |
* computational steps. If tasks are too big, then parallelism cannot |
138 |
< |
* improve throughput. If too small, then memory and internal task |
139 |
< |
* maintenance overhead may overwhelm processing. |
137 |
> |
* computational steps, and should avoid indefinite looping. If tasks |
138 |
> |
* are too big, then parallelism cannot improve throughput. If too |
139 |
> |
* small, then memory and internal task maintenance overhead may |
140 |
> |
* overwhelm processing. |
141 |
|
* |
142 |
|
* <p>This class provides {@code adapt} methods for {@link Runnable} |
143 |
|
* and {@link Callable}, that may be of use when mixing execution of |
234 |
|
} |
235 |
|
|
236 |
|
/** |
226 |
– |
* Blocks a worker thread until completion. Called only by |
227 |
– |
* pool. Currently unused -- pool-based waits use timeout |
228 |
– |
* version below. |
229 |
– |
*/ |
230 |
– |
final void internalAwaitDone() { |
231 |
– |
int s; // the odd construction reduces lock bias effects |
232 |
– |
while ((s = status) >= 0) { |
233 |
– |
try { |
234 |
– |
synchronized (this) { |
235 |
– |
if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL)) |
236 |
– |
wait(); |
237 |
– |
} |
238 |
– |
} catch (InterruptedException ie) { |
239 |
– |
cancelIfTerminating(); |
240 |
– |
} |
241 |
– |
} |
242 |
– |
} |
243 |
– |
|
244 |
– |
/** |
237 |
|
* Blocks a worker thread until completed or timed out. Called |
238 |
|
* only by pool. |
247 |
– |
* |
248 |
– |
* @return status on exit |
239 |
|
*/ |
240 |
< |
final int internalAwaitDone(long millis, int nanos) { |
241 |
< |
int s; |
242 |
< |
if ((s = status) >= 0) { |
243 |
< |
try { |
240 |
> |
final void internalAwaitDone(long millis, int nanos) { |
241 |
> |
int s = status; |
242 |
> |
if ((s == 0 && |
243 |
> |
UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL)) || |
244 |
> |
s > 0) { |
245 |
> |
try { // the odd construction reduces lock bias effects |
246 |
|
synchronized (this) { |
247 |
< |
if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL)) |
247 |
> |
if (status > 0) |
248 |
|
wait(millis, nanos); |
249 |
+ |
else |
250 |
+ |
notifyAll(); |
251 |
|
} |
252 |
|
} catch (InterruptedException ie) { |
253 |
|
cancelIfTerminating(); |
254 |
|
} |
261 |
– |
s = status; |
255 |
|
} |
263 |
– |
return s; |
256 |
|
} |
257 |
|
|
258 |
|
/** |
259 |
|
* Blocks a non-worker-thread until completion. |
260 |
|
*/ |
261 |
|
private void externalAwaitDone() { |
262 |
< |
int s; |
263 |
< |
while ((s = status) >= 0) { |
262 |
> |
if (status >= 0) { |
263 |
> |
boolean interrupted = false; |
264 |
|
synchronized (this) { |
265 |
< |
if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) { |
266 |
< |
boolean interrupted = false; |
267 |
< |
while (status >= 0) { |
265 |
> |
for (;;) { |
266 |
> |
int s = status; |
267 |
> |
if (s == 0) |
268 |
> |
UNSAFE.compareAndSwapInt(this, statusOffset, |
269 |
> |
0, SIGNAL); |
270 |
> |
else if (s < 0) { |
271 |
> |
notifyAll(); |
272 |
> |
break; |
273 |
> |
} |
274 |
> |
else { |
275 |
|
try { |
276 |
|
wait(); |
277 |
|
} catch (InterruptedException ie) { |
278 |
|
interrupted = true; |
279 |
|
} |
280 |
|
} |
281 |
< |
if (interrupted) |
282 |
< |
Thread.currentThread().interrupt(); |
283 |
< |
break; |
281 |
> |
} |
282 |
> |
} |
283 |
> |
if (interrupted) |
284 |
> |
Thread.currentThread().interrupt(); |
285 |
> |
} |
286 |
> |
} |
287 |
> |
|
288 |
> |
/** |
289 |
> |
* Blocks a non-worker-thread until completion or interruption or timeout. |
290 |
> |
*/ |
291 |
> |
private void externalInterruptibleAwaitDone(boolean timed, long nanos) |
292 |
> |
throws InterruptedException { |
293 |
> |
if (Thread.interrupted()) |
294 |
> |
throw new InterruptedException(); |
295 |
> |
if (status >= 0) { |
296 |
> |
long startTime = timed ? System.nanoTime() : 0L; |
297 |
> |
synchronized (this) { |
298 |
> |
for (;;) { |
299 |
> |
long nt; |
300 |
> |
int s = status; |
301 |
> |
if (s == 0) |
302 |
> |
UNSAFE.compareAndSwapInt(this, statusOffset, |
303 |
> |
0, SIGNAL); |
304 |
> |
else if (s < 0) { |
305 |
> |
notifyAll(); |
306 |
> |
break; |
307 |
> |
} |
308 |
> |
else if (!timed) |
309 |
> |
wait(); |
310 |
> |
else if ((nt = nanos - (System.nanoTime()-startTime)) > 0L) |
311 |
> |
wait(nt / 1000000, (int)(nt % 1000000)); |
312 |
> |
else |
313 |
> |
break; |
314 |
|
} |
315 |
|
} |
316 |
|
} |
345 |
|
* #isDone} returning {@code true}. |
346 |
|
* |
347 |
|
* <p>This method may be invoked only from within {@code |
348 |
< |
* ForkJoinTask} computations (as may be determined using method |
348 |
> |
* ForkJoinPool} computations (as may be determined using method |
349 |
|
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
350 |
|
* result in exceptions or errors, possibly including {@code |
351 |
|
* ClassCastException}. |
359 |
|
} |
360 |
|
|
361 |
|
/** |
362 |
< |
* Returns the result of the computation when it {@link #isDone is done}. |
363 |
< |
* This method differs from {@link #get()} in that |
362 |
> |
* Returns the result of the computation when it {@link #isDone is |
363 |
> |
* done}. This method differs from {@link #get()} in that |
364 |
|
* abnormal completion results in {@code RuntimeException} or |
365 |
< |
* {@code Error}, not {@code ExecutionException}. |
365 |
> |
* {@code Error}, not {@code ExecutionException}, and that |
366 |
> |
* interrupts of the calling thread do <em>not</em> cause the |
367 |
> |
* method to abruptly return by throwing {@code |
368 |
> |
* InterruptedException}. |
369 |
|
* |
370 |
|
* @return the computed result |
371 |
|
*/ |
407 |
|
* unprocessed. |
408 |
|
* |
409 |
|
* <p>This method may be invoked only from within {@code |
410 |
< |
* ForkJoinTask} computations (as may be determined using method |
410 |
> |
* ForkJoinPool} computations (as may be determined using method |
411 |
|
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
412 |
|
* result in exceptions or errors, possibly including {@code |
413 |
|
* ClassCastException}. |
435 |
|
* normally or exceptionally, or left unprocessed. |
436 |
|
* |
437 |
|
* <p>This method may be invoked only from within {@code |
438 |
< |
* ForkJoinTask} computations (as may be determined using method |
438 |
> |
* ForkJoinPool} computations (as may be determined using method |
439 |
|
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
440 |
|
* result in exceptions or errors, possibly including {@code |
441 |
|
* ClassCastException}. |
490 |
|
* unprocessed. |
491 |
|
* |
492 |
|
* <p>This method may be invoked only from within {@code |
493 |
< |
* ForkJoinTask} computations (as may be determined using method |
493 |
> |
* ForkJoinPool} computations (as may be determined using method |
494 |
|
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
495 |
|
* result in exceptions or errors, possibly including {@code |
496 |
|
* ClassCastException}. |
542 |
|
|
543 |
|
/** |
544 |
|
* Attempts to cancel execution of this task. This attempt will |
545 |
< |
* fail if the task has already completed, has already been |
546 |
< |
* cancelled, or could not be cancelled for some other reason. If |
547 |
< |
* successful, and this task has not started when cancel is |
548 |
< |
* called, execution of this task is suppressed, {@link |
549 |
< |
* #isCancelled} will report true, and {@link #join} will result |
550 |
< |
* in a {@code CancellationException} being thrown. |
545 |
> |
* fail if the task has already completed or could not be |
546 |
> |
* cancelled for some other reason. If successful, and this task |
547 |
> |
* has not started when {@code cancel} is called, execution of |
548 |
> |
* this task is suppressed. After this method returns |
549 |
> |
* successfully, unless there is an intervening call to {@link |
550 |
> |
* #reinitialize}, subsequent calls to {@link #isCancelled}, |
551 |
> |
* {@link #isDone}, and {@code cancel} will return {@code true} |
552 |
> |
* and calls to {@link #join} and related methods will result in |
553 |
> |
* {@code CancellationException}. |
554 |
|
* |
555 |
|
* <p>This method may be overridden in subclasses, but if so, must |
556 |
< |
* still ensure that these minimal properties hold. In particular, |
557 |
< |
* the {@code cancel} method itself must not throw exceptions. |
556 |
> |
* still ensure that these properties hold. In particular, the |
557 |
> |
* {@code cancel} method itself must not throw exceptions. |
558 |
|
* |
559 |
|
* <p>This method is designed to be invoked by <em>other</em> |
560 |
|
* tasks. To terminate the current task, you can just return or |
561 |
|
* throw an unchecked exception from its computation method, or |
562 |
|
* invoke {@link #completeExceptionally}. |
563 |
|
* |
564 |
< |
* @param mayInterruptIfRunning this value is ignored in the |
565 |
< |
* default implementation because tasks are not |
566 |
< |
* cancelled via interruption |
564 |
> |
* @param mayInterruptIfRunning this value has no effect in the |
565 |
> |
* default implementation because interrupts are not used to |
566 |
> |
* control cancellation. |
567 |
|
* |
568 |
|
* @return {@code true} if this task is now cancelled |
569 |
|
*/ |
697 |
|
* member of a ForkJoinPool and was interrupted while waiting |
698 |
|
*/ |
699 |
|
public final V get() throws InterruptedException, ExecutionException { |
700 |
< |
int s; |
701 |
< |
if (Thread.currentThread() instanceof ForkJoinWorkerThread) { |
700 |
> |
Thread t = Thread.currentThread(); |
701 |
> |
if (t instanceof ForkJoinWorkerThread) |
702 |
|
quietlyJoin(); |
703 |
< |
s = status; |
704 |
< |
} |
705 |
< |
else { |
706 |
< |
while ((s = status) >= 0) { |
672 |
< |
synchronized (this) { // interruptible form of awaitDone |
673 |
< |
if (UNSAFE.compareAndSwapInt(this, statusOffset, |
674 |
< |
s, SIGNAL)) { |
675 |
< |
while (status >= 0) |
676 |
< |
wait(); |
677 |
< |
} |
678 |
< |
} |
679 |
< |
} |
680 |
< |
} |
681 |
< |
if (s < NORMAL) { |
703 |
> |
else |
704 |
> |
externalInterruptibleAwaitDone(false, 0L); |
705 |
> |
int s = status; |
706 |
> |
if (s != NORMAL) { |
707 |
|
Throwable ex; |
708 |
|
if (s == CANCELLED) |
709 |
|
throw new CancellationException(); |
730 |
|
public final V get(long timeout, TimeUnit unit) |
731 |
|
throws InterruptedException, ExecutionException, TimeoutException { |
732 |
|
long nanos = unit.toNanos(timeout); |
733 |
< |
if (status >= 0) { |
734 |
< |
Thread t = Thread.currentThread(); |
735 |
< |
if (t instanceof ForkJoinWorkerThread) { |
736 |
< |
ForkJoinWorkerThread w = (ForkJoinWorkerThread) t; |
737 |
< |
boolean completed = false; // timed variant of quietlyJoin |
738 |
< |
if (w.unpushTask(this)) { |
739 |
< |
try { |
715 |
< |
completed = exec(); |
716 |
< |
} catch (Throwable rex) { |
717 |
< |
setExceptionalCompletion(rex); |
718 |
< |
} |
719 |
< |
} |
720 |
< |
if (completed) |
721 |
< |
setCompletion(NORMAL); |
722 |
< |
else if (status >= 0) |
723 |
< |
w.joinTask(this, true, nanos); |
724 |
< |
} |
725 |
< |
else if (Thread.interrupted()) |
726 |
< |
throw new InterruptedException(); |
727 |
< |
else { |
728 |
< |
long startTime = System.nanoTime(); |
729 |
< |
int s; long nt; |
730 |
< |
while ((s = status) >= 0 && |
731 |
< |
(nt = nanos - (System.nanoTime() - startTime)) > 0) { |
732 |
< |
if (UNSAFE.compareAndSwapInt(this, statusOffset, s, |
733 |
< |
SIGNAL)) { |
734 |
< |
long ms = nt / 1000000; |
735 |
< |
int ns = (int) (nt % 1000000); |
736 |
< |
synchronized (this) { |
737 |
< |
if (status >= 0) |
738 |
< |
wait(ms, ns); // exit on IE throw |
739 |
< |
} |
740 |
< |
} |
741 |
< |
} |
742 |
< |
} |
743 |
< |
} |
744 |
< |
int es = status; |
745 |
< |
if (es != NORMAL) { |
733 |
> |
Thread t = Thread.currentThread(); |
734 |
> |
if (t instanceof ForkJoinWorkerThread) |
735 |
> |
((ForkJoinWorkerThread)t).joinTask(this, true, nanos); |
736 |
> |
else |
737 |
> |
externalInterruptibleAwaitDone(true, nanos); |
738 |
> |
int s = status; |
739 |
> |
if (s != NORMAL) { |
740 |
|
Throwable ex; |
741 |
< |
if (es == CANCELLED) |
741 |
> |
if (s == CANCELLED) |
742 |
|
throw new CancellationException(); |
743 |
< |
if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) |
743 |
> |
if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) |
744 |
|
throw new ExecutionException(ex); |
745 |
|
throw new TimeoutException(); |
746 |
|
} |
807 |
|
* processed. |
808 |
|
* |
809 |
|
* <p>This method may be invoked only from within {@code |
810 |
< |
* ForkJoinTask} computations (as may be determined using method |
810 |
> |
* ForkJoinPool} computations (as may be determined using method |
811 |
|
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
812 |
|
* result in exceptions or errors, possibly including {@code |
813 |
|
* ClassCastException}. |
853 |
|
} |
854 |
|
|
855 |
|
/** |
856 |
< |
* Returns {@code true} if the current thread is executing as a |
857 |
< |
* ForkJoinPool computation. |
856 |
> |
* Returns {@code true} if the current thread is a {@link |
857 |
> |
* ForkJoinWorkerThread} executing as a ForkJoinPool computation. |
858 |
|
* |
859 |
< |
* @return {@code true} if the current thread is executing as a |
860 |
< |
* ForkJoinPool computation, or false otherwise |
859 |
> |
* @return {@code true} if the current thread is a {@link |
860 |
> |
* ForkJoinWorkerThread} executing as a ForkJoinPool computation, |
861 |
> |
* or {@code false} otherwise |
862 |
|
*/ |
863 |
|
public static boolean inForkJoinPool() { |
864 |
|
return Thread.currentThread() instanceof ForkJoinWorkerThread; |
873 |
|
* were not, stolen. |
874 |
|
* |
875 |
|
* <p>This method may be invoked only from within {@code |
876 |
< |
* ForkJoinTask} computations (as may be determined using method |
876 |
> |
* ForkJoinPool} computations (as may be determined using method |
877 |
|
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
878 |
|
* result in exceptions or errors, possibly including {@code |
879 |
|
* ClassCastException}. |
892 |
|
* fork other tasks. |
893 |
|
* |
894 |
|
* <p>This method may be invoked only from within {@code |
895 |
< |
* ForkJoinTask} computations (as may be determined using method |
895 |
> |
* ForkJoinPool} computations (as may be determined using method |
896 |
|
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
897 |
|
* result in exceptions or errors, possibly including {@code |
898 |
|
* ClassCastException}. |
915 |
|
* exceeded. |
916 |
|
* |
917 |
|
* <p>This method may be invoked only from within {@code |
918 |
< |
* ForkJoinTask} computations (as may be determined using method |
918 |
> |
* ForkJoinPool} computations (as may be determined using method |
919 |
|
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
920 |
|
* result in exceptions or errors, possibly including {@code |
921 |
|
* ClassCastException}. |
973 |
|
* otherwise. |
974 |
|
* |
975 |
|
* <p>This method may be invoked only from within {@code |
976 |
< |
* ForkJoinTask} computations (as may be determined using method |
976 |
> |
* ForkJoinPool} computations (as may be determined using method |
977 |
|
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
978 |
|
* result in exceptions or errors, possibly including {@code |
979 |
|
* ClassCastException}. |
992 |
|
* be useful otherwise. |
993 |
|
* |
994 |
|
* <p>This method may be invoked only from within {@code |
995 |
< |
* ForkJoinTask} computations (as may be determined using method |
995 |
> |
* ForkJoinPool} computations (as may be determined using method |
996 |
|
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
997 |
|
* result in exceptions or errors, possibly including {@code |
998 |
|
* ClassCastException}. |
1015 |
|
* otherwise. |
1016 |
|
* |
1017 |
|
* <p>This method may be invoked only from within {@code |
1018 |
< |
* ForkJoinTask} computations (as may be determined using method |
1018 |
> |
* ForkJoinPool} computations (as may be determined using method |
1019 |
|
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1020 |
|
* result in exceptions or errors, possibly including {@code |
1021 |
|
* ClassCastException}. |