5 |
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*/ |
6 |
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|
7 |
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package jsr166y; |
8 |
+ |
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9 |
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import java.io.Serializable; |
10 |
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import java.util.Collection; |
11 |
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import java.util.List; |
30 |
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* subtasks may be hosted by a small number of actual threads in a |
31 |
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* ForkJoinPool, at the price of some usage limitations. |
32 |
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* |
33 |
< |
* <p>A "main" {@code ForkJoinTask} begins execution when submitted |
34 |
< |
* to a {@link ForkJoinPool}. Once started, it will usually in turn |
35 |
< |
* start other subtasks. As indicated by the name of this class, |
36 |
< |
* many programs using {@code ForkJoinTask} employ only methods |
37 |
< |
* {@link #fork} and {@link #join}, or derivatives such as {@link |
33 |
> |
* <p>A "main" {@code ForkJoinTask} begins execution when it is |
34 |
> |
* explicitly submitted to a {@link ForkJoinPool}, or, if not already |
35 |
> |
* engaged in a ForkJoin computation, commenced in the {@link |
36 |
> |
* ForkJoinPool#commonPool} via {@link #fork}, {@link #invoke}, or |
37 |
> |
* related methods. Once started, it will usually in turn start other |
38 |
> |
* subtasks. As indicated by the name of this class, many programs |
39 |
> |
* using {@code ForkJoinTask} employ only methods {@link #fork} and |
40 |
> |
* {@link #join}, or derivatives such as {@link |
41 |
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* #invokeAll(ForkJoinTask...) invokeAll}. However, this class also |
42 |
|
* provides a number of other methods that can come into play in |
43 |
< |
* advanced usages, as well as extension mechanics that allow |
44 |
< |
* support of new forms of fork/join processing. |
43 |
> |
* advanced usages, as well as extension mechanics that allow support |
44 |
> |
* of new forms of fork/join processing. |
45 |
|
* |
46 |
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* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}. |
47 |
|
* The efficiency of {@code ForkJoinTask}s stems from a set of |
74 |
|
* but doing do requires three further considerations: (1) Completion |
75 |
|
* of few if any <em>other</em> tasks should be dependent on a task |
76 |
|
* that blocks on external synchronization or IO. Event-style async |
77 |
< |
* tasks that are never joined often fall into this category. (2) To |
78 |
< |
* minimize resource impact, tasks should be small; ideally performing |
79 |
< |
* only the (possibly) blocking action. (3) Unless the {@link |
77 |
> |
* tasks that are never joined (for example, those subclassing {@link |
78 |
> |
* CountedCompleter}) often fall into this category. (2) To minimize |
79 |
> |
* resource impact, tasks should be small; ideally performing only the |
80 |
> |
* (possibly) blocking action. (3) Unless the {@link |
81 |
|
* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly |
82 |
|
* blocked tasks is known to be less than the pool's {@link |
83 |
|
* ForkJoinPool#getParallelism} level, the pool cannot guarantee that |
120 |
|
* <p>The ForkJoinTask class is not usually directly subclassed. |
121 |
|
* Instead, you subclass one of the abstract classes that support a |
122 |
|
* particular style of fork/join processing, typically {@link |
123 |
< |
* RecursiveAction} for computations that do not return results, or |
124 |
< |
* {@link RecursiveTask} for those that do. Normally, a concrete |
125 |
< |
* ForkJoinTask subclass declares fields comprising its parameters, |
126 |
< |
* established in a constructor, and then defines a {@code compute} |
127 |
< |
* method that somehow uses the control methods supplied by this base |
128 |
< |
* class. While these methods have {@code public} access (to allow |
129 |
< |
* instances of different task subclasses to call each other's |
125 |
< |
* methods), some of them may only be called from within other |
126 |
< |
* ForkJoinTasks (as may be determined using method {@link |
127 |
< |
* #inForkJoinPool}). Attempts to invoke them in other contexts |
128 |
< |
* result in exceptions or errors, possibly including |
129 |
< |
* {@code ClassCastException}. |
123 |
> |
* RecursiveAction} for most computations that do not return results, |
124 |
> |
* {@link RecursiveTask} for those that do, and {@link |
125 |
> |
* CountedCompleter} for those in which completed actions trigger |
126 |
> |
* other actions. Normally, a concrete ForkJoinTask subclass declares |
127 |
> |
* fields comprising its parameters, established in a constructor, and |
128 |
> |
* then defines a {@code compute} method that somehow uses the control |
129 |
> |
* methods supplied by this base class. |
130 |
|
* |
131 |
|
* <p>Method {@link #join} and its variants are appropriate for use |
132 |
|
* only when completion dependencies are acyclic; that is, the |
137 |
|
* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that |
138 |
|
* may be of use in constructing custom subclasses for problems that |
139 |
|
* are not statically structured as DAGs. To support such usages a |
140 |
< |
* ForkJoinTask may be atomically <em>tagged</em> with a {@code |
141 |
< |
* short} value using {@link #setForkJoinTaskTag} or {@link |
140 |
> |
* ForkJoinTask may be atomically <em>tagged</em> with a {@code short} |
141 |
> |
* value using {@link #setForkJoinTaskTag} or {@link |
142 |
|
* #compareAndSetForkJoinTaskTag} and checked using {@link |
143 |
< |
* #getForkJoinTaskTag}. The ForkJoinTask implementation does not |
144 |
< |
* use these {@code protected} methods or tags for any purpose, but |
145 |
< |
* they may be of use in the construction of specialized subclasses. |
146 |
< |
* For example, parallel graph traversals can use the supplied methods |
147 |
< |
* to avoid revisiting nodes/tasks that have already been processed. |
148 |
< |
* Also, completion based designs can use them to record that subtasks |
149 |
< |
* have completed. (Method names for tagging are bulky in part to |
150 |
< |
* encourage definition of methods that reflect their usage patterns.) |
143 |
> |
* #getForkJoinTaskTag}. The ForkJoinTask implementation does not use |
144 |
> |
* these {@code protected} methods or tags for any purpose, but they |
145 |
> |
* may be of use in the construction of specialized subclasses. For |
146 |
> |
* example, parallel graph traversals can use the supplied methods to |
147 |
> |
* avoid revisiting nodes/tasks that have already been processed. |
148 |
> |
* (Method names for tagging are bulky in part to encourage definition |
149 |
> |
* of methods that reflect their usage patterns.) |
150 |
|
* |
151 |
|
* <p>Most base support methods are {@code final}, to prevent |
152 |
|
* overriding of implementations that are intrinsically tied to the |
268 |
|
} |
269 |
|
|
270 |
|
/** |
271 |
< |
* Tries to set SIGNAL status. Used by ForkJoinPool. Other |
272 |
< |
* variants are directly incorporated into externalAwaitDone etc. |
271 |
> |
* Tries to set SIGNAL status unless already completed. Used by |
272 |
> |
* ForkJoinPool. Other variants are directly incorporated into |
273 |
> |
* externalAwaitDone etc. |
274 |
|
* |
275 |
|
* @return true if successful |
276 |
|
*/ |
277 |
|
final boolean trySetSignal() { |
278 |
< |
int s; |
279 |
< |
return U.compareAndSwapInt(this, STATUS, s = status, s | SIGNAL); |
278 |
> |
int s = status; |
279 |
> |
return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL); |
280 |
|
} |
281 |
|
|
282 |
|
/** |
284 |
|
* @return status upon completion |
285 |
|
*/ |
286 |
|
private int externalAwaitDone() { |
287 |
– |
boolean interrupted = false; |
287 |
|
int s; |
288 |
< |
while ((s = status) >= 0) { |
288 |
> |
boolean interrupted = false; |
289 |
> |
if ((s = status) >= 0 && ForkJoinPool.tryUnsubmitFromCommonPool(this)) |
290 |
> |
s = doExec(); |
291 |
> |
while (s >= 0) { |
292 |
|
if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { |
293 |
|
synchronized (this) { |
294 |
|
if (status >= 0) { |
302 |
|
notifyAll(); |
303 |
|
} |
304 |
|
} |
305 |
+ |
s = status; |
306 |
|
} |
307 |
|
if (interrupted) |
308 |
|
Thread.currentThread().interrupt(); |
313 |
|
* Blocks a non-worker-thread until completion or interruption. |
314 |
|
*/ |
315 |
|
private int externalInterruptibleAwaitDone() throws InterruptedException { |
313 |
– |
int s; |
316 |
|
if (Thread.interrupted()) |
317 |
|
throw new InterruptedException(); |
318 |
< |
while ((s = status) >= 0) { |
318 |
> |
int s; |
319 |
> |
if ((s = status) >= 0 && ForkJoinPool.tryUnsubmitFromCommonPool(this)) |
320 |
> |
s = doExec(); |
321 |
> |
while (s >= 0) { |
322 |
|
if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) { |
323 |
|
synchronized (this) { |
324 |
|
if (status >= 0) |
327 |
|
notifyAll(); |
328 |
|
} |
329 |
|
} |
330 |
+ |
s = status; |
331 |
|
} |
332 |
|
return s; |
333 |
|
} |
341 |
|
*/ |
342 |
|
private int doJoin() { |
343 |
|
int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w; |
344 |
< |
if ((s = status) >= 0) { |
345 |
< |
if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) { |
346 |
< |
if (!(w = (wt = (ForkJoinWorkerThread)t).workQueue). |
347 |
< |
tryUnpush(this) || (s = doExec()) >= 0) |
348 |
< |
s = wt.pool.awaitJoin(w, this); |
349 |
< |
} |
344 |
< |
else |
345 |
< |
s = externalAwaitDone(); |
346 |
< |
} |
347 |
< |
return s; |
344 |
> |
return (s = status) < 0 ? s : |
345 |
> |
((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
346 |
> |
(w = (wt = (ForkJoinWorkerThread)t).workQueue). |
347 |
> |
tryUnpush(this) && (s = doExec()) < 0 ? s : |
348 |
> |
wt.pool.awaitJoin(w, this) : |
349 |
> |
externalAwaitDone(); |
350 |
|
} |
351 |
|
|
352 |
|
/** |
356 |
|
*/ |
357 |
|
private int doInvoke() { |
358 |
|
int s; Thread t; ForkJoinWorkerThread wt; |
359 |
< |
if ((s = doExec()) >= 0) { |
360 |
< |
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) |
361 |
< |
s = (wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue, |
362 |
< |
this); |
361 |
< |
else |
362 |
< |
s = externalAwaitDone(); |
363 |
< |
} |
364 |
< |
return s; |
359 |
> |
return (s = doExec()) < 0 ? s : |
360 |
> |
((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
361 |
> |
(wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue, this) : |
362 |
> |
externalAwaitDone(); |
363 |
|
} |
364 |
|
|
365 |
|
// Exception table support |
407 |
|
} |
408 |
|
|
409 |
|
/** |
410 |
< |
* Records exception and sets exceptional completion. |
410 |
> |
* Records exception and sets status. |
411 |
|
* |
412 |
|
* @return status on exit |
413 |
|
*/ |
414 |
< |
private int setExceptionalCompletion(Throwable ex) { |
415 |
< |
int h = System.identityHashCode(this); |
416 |
< |
final ReentrantLock lock = exceptionTableLock; |
417 |
< |
lock.lock(); |
418 |
< |
try { |
419 |
< |
expungeStaleExceptions(); |
420 |
< |
ExceptionNode[] t = exceptionTable; |
421 |
< |
int i = h & (t.length - 1); |
422 |
< |
for (ExceptionNode e = t[i]; ; e = e.next) { |
423 |
< |
if (e == null) { |
424 |
< |
t[i] = new ExceptionNode(this, ex, t[i]); |
425 |
< |
break; |
414 |
> |
final int recordExceptionalCompletion(Throwable ex) { |
415 |
> |
int s; |
416 |
> |
if ((s = status) >= 0) { |
417 |
> |
int h = System.identityHashCode(this); |
418 |
> |
final ReentrantLock lock = exceptionTableLock; |
419 |
> |
lock.lock(); |
420 |
> |
try { |
421 |
> |
expungeStaleExceptions(); |
422 |
> |
ExceptionNode[] t = exceptionTable; |
423 |
> |
int i = h & (t.length - 1); |
424 |
> |
for (ExceptionNode e = t[i]; ; e = e.next) { |
425 |
> |
if (e == null) { |
426 |
> |
t[i] = new ExceptionNode(this, ex, t[i]); |
427 |
> |
break; |
428 |
> |
} |
429 |
> |
if (e.get() == this) // already present |
430 |
> |
break; |
431 |
|
} |
432 |
< |
if (e.get() == this) // already present |
433 |
< |
break; |
432 |
> |
} finally { |
433 |
> |
lock.unlock(); |
434 |
|
} |
435 |
< |
} finally { |
433 |
< |
lock.unlock(); |
435 |
> |
s = setCompletion(EXCEPTIONAL); |
436 |
|
} |
437 |
< |
return setCompletion(EXCEPTIONAL); |
437 |
> |
return s; |
438 |
> |
} |
439 |
> |
|
440 |
> |
/** |
441 |
> |
* Records exception and possibly propagates |
442 |
> |
* |
443 |
> |
* @return status on exit |
444 |
> |
*/ |
445 |
> |
private int setExceptionalCompletion(Throwable ex) { |
446 |
> |
int s = recordExceptionalCompletion(ex); |
447 |
> |
if ((s & DONE_MASK) == EXCEPTIONAL) |
448 |
> |
internalPropagateException(ex); |
449 |
> |
return s; |
450 |
> |
} |
451 |
> |
|
452 |
> |
/** |
453 |
> |
* Hook for exception propagation support for tasks with completers. |
454 |
> |
*/ |
455 |
> |
void internalPropagateException(Throwable ex) { |
456 |
|
} |
457 |
|
|
458 |
|
/** |
534 |
|
Throwable ex; |
535 |
|
if (e == null || (ex = e.ex) == null) |
536 |
|
return null; |
537 |
< |
if (e.thrower != Thread.currentThread().getId()) { |
537 |
> |
if (false && e.thrower != Thread.currentThread().getId()) { |
538 |
|
Class<? extends Throwable> ec = ex.getClass(); |
539 |
|
try { |
540 |
|
Constructor<?> noArgCtor = null; |
614 |
|
// public methods |
615 |
|
|
616 |
|
/** |
617 |
< |
* Arranges to asynchronously execute this task. While it is not |
618 |
< |
* necessarily enforced, it is a usage error to fork a task more |
619 |
< |
* than once unless it has completed and been reinitialized. |
620 |
< |
* Subsequent modifications to the state of this task or any data |
621 |
< |
* it operates on are not necessarily consistently observable by |
622 |
< |
* any thread other than the one executing it unless preceded by a |
623 |
< |
* call to {@link #join} or related methods, or a call to {@link |
624 |
< |
* #isDone} returning {@code true}. |
625 |
< |
* |
626 |
< |
* <p>This method may be invoked only from within {@code |
627 |
< |
* ForkJoinPool} computations (as may be determined using method |
608 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
609 |
< |
* result in exceptions or errors, possibly including {@code |
610 |
< |
* ClassCastException}. |
617 |
> |
* Arranges to asynchronously execute this task in the pool the |
618 |
> |
* current task is running in, if applicable, or using the {@link |
619 |
> |
* ForkJoinPool#commonPool} if not {@link #inForkJoinPool}. While |
620 |
> |
* it is not necessarily enforced, it is a usage error to fork a |
621 |
> |
* task more than once unless it has completed and been |
622 |
> |
* reinitialized. Subsequent modifications to the state of this |
623 |
> |
* task or any data it operates on are not necessarily |
624 |
> |
* consistently observable by any thread other than the one |
625 |
> |
* executing it unless preceded by a call to {@link #join} or |
626 |
> |
* related methods, or a call to {@link #isDone} returning {@code |
627 |
> |
* true}. |
628 |
|
* |
629 |
|
* @return {@code this}, to simplify usage |
630 |
|
*/ |
631 |
|
public final ForkJoinTask<V> fork() { |
632 |
< |
((ForkJoinWorkerThread)Thread.currentThread()).workQueue.push(this); |
632 |
> |
Thread t; |
633 |
> |
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) |
634 |
> |
((ForkJoinWorkerThread)t).workQueue.push(this); |
635 |
> |
else |
636 |
> |
ForkJoinPool.submitToCommonPool(this); |
637 |
|
return this; |
638 |
|
} |
639 |
|
|
683 |
|
* cancelled, completed normally or exceptionally, or left |
684 |
|
* unprocessed. |
685 |
|
* |
665 |
– |
* <p>This method may be invoked only from within {@code |
666 |
– |
* ForkJoinPool} computations (as may be determined using method |
667 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
668 |
– |
* result in exceptions or errors, possibly including {@code |
669 |
– |
* ClassCastException}. |
670 |
– |
* |
686 |
|
* @param t1 the first task |
687 |
|
* @param t2 the second task |
688 |
|
* @throws NullPointerException if any task is null |
708 |
|
* related methods to check if they have been cancelled, completed |
709 |
|
* normally or exceptionally, or left unprocessed. |
710 |
|
* |
696 |
– |
* <p>This method may be invoked only from within {@code |
697 |
– |
* ForkJoinPool} computations (as may be determined using method |
698 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
699 |
– |
* result in exceptions or errors, possibly including {@code |
700 |
– |
* ClassCastException}. |
701 |
– |
* |
711 |
|
* @param tasks the tasks |
712 |
|
* @throws NullPointerException if any task is null |
713 |
|
*/ |
751 |
|
* cancelled, completed normally or exceptionally, or left |
752 |
|
* unprocessed. |
753 |
|
* |
745 |
– |
* <p>This method may be invoked only from within {@code |
746 |
– |
* ForkJoinPool} computations (as may be determined using method |
747 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
748 |
– |
* result in exceptions or errors, possibly including {@code |
749 |
– |
* ClassCastException}. |
750 |
– |
* |
754 |
|
* @param tasks the collection of tasks |
755 |
|
* @return the tasks argument, to simplify usage |
756 |
|
* @throws NullPointerException if tasks or any element are null |
907 |
|
} |
908 |
|
|
909 |
|
/** |
910 |
< |
* Completes this task. The most recent value established by |
911 |
< |
* {@link #setRawResult} (or {@code null}) will be returned as the |
912 |
< |
* result of subsequent invocations of {@code join} and related |
913 |
< |
* operations. This method may be useful when processing sets of |
914 |
< |
* tasks when some do not otherwise complete normally. Its use in |
915 |
< |
* other situations is discouraged. |
910 |
> |
* Completes this task normally without setting a value. The most |
911 |
> |
* recent value established by {@link #setRawResult} (or {@code |
912 |
> |
* null} by default) will be returned as the result of subsequent |
913 |
> |
* invocations of {@code join} and related operations. |
914 |
> |
* |
915 |
> |
* @since 1.8 |
916 |
|
*/ |
917 |
|
public final void quietlyComplete() { |
918 |
|
setCompletion(NORMAL); |
1046 |
|
* be of use in designs in which many tasks are forked, but none |
1047 |
|
* are explicitly joined, instead executing them until all are |
1048 |
|
* processed. |
1046 |
– |
* |
1047 |
– |
* <p>This method may be invoked only from within {@code |
1048 |
– |
* ForkJoinPool} computations (as may be determined using method |
1049 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1050 |
– |
* result in exceptions or errors, possibly including {@code |
1051 |
– |
* ClassCastException}. |
1049 |
|
*/ |
1050 |
|
public static void helpQuiesce() { |
1051 |
< |
ForkJoinWorkerThread wt = |
1052 |
< |
(ForkJoinWorkerThread)Thread.currentThread(); |
1053 |
< |
wt.pool.helpQuiescePool(wt.workQueue); |
1051 |
> |
Thread t; |
1052 |
> |
if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) { |
1053 |
> |
ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t; |
1054 |
> |
wt.pool.helpQuiescePool(wt.workQueue); |
1055 |
> |
} |
1056 |
> |
else |
1057 |
> |
ForkJoinPool.externalHelpQuiescePool(); |
1058 |
|
} |
1059 |
|
|
1060 |
|
/** |
1107 |
|
|
1108 |
|
/** |
1109 |
|
* Tries to unschedule this task for execution. This method will |
1110 |
< |
* typically succeed if this task is the most recently forked task |
1111 |
< |
* by the current thread, and has not commenced executing in |
1112 |
< |
* another thread. This method may be useful when arranging |
1113 |
< |
* alternative local processing of tasks that could have been, but |
1114 |
< |
* were not, stolen. |
1114 |
< |
* |
1115 |
< |
* <p>This method may be invoked only from within {@code |
1116 |
< |
* ForkJoinPool} computations (as may be determined using method |
1117 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1118 |
< |
* result in exceptions or errors, possibly including {@code |
1119 |
< |
* ClassCastException}. |
1110 |
> |
* typically (but is not guaranteed to) succeed if this task is |
1111 |
> |
* the most recently forked task by the current thread, and has |
1112 |
> |
* not commenced executing in another thread. This method may be |
1113 |
> |
* useful when arranging alternative local processing of tasks |
1114 |
> |
* that could have been, but were not, stolen. |
1115 |
|
* |
1116 |
|
* @return {@code true} if unforked |
1117 |
|
*/ |
1118 |
|
public boolean tryUnfork() { |
1119 |
< |
return ((ForkJoinWorkerThread)Thread.currentThread()) |
1120 |
< |
.workQueue.tryUnpush(this); |
1119 |
> |
Thread t; |
1120 |
> |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1121 |
> |
((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) : |
1122 |
> |
ForkJoinPool.tryUnsubmitFromCommonPool(this); |
1123 |
|
} |
1124 |
|
|
1125 |
|
/** |
1128 |
|
* value may be useful for heuristic decisions about whether to |
1129 |
|
* fork other tasks. |
1130 |
|
* |
1134 |
– |
* <p>This method may be invoked only from within {@code |
1135 |
– |
* ForkJoinPool} computations (as may be determined using method |
1136 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1137 |
– |
* result in exceptions or errors, possibly including {@code |
1138 |
– |
* ClassCastException}. |
1139 |
– |
* |
1131 |
|
* @return the number of tasks |
1132 |
|
*/ |
1133 |
|
public static int getQueuedTaskCount() { |
1134 |
< |
return ((ForkJoinWorkerThread) Thread.currentThread()) |
1135 |
< |
.workQueue.queueSize(); |
1134 |
> |
Thread t; |
1135 |
> |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1136 |
> |
((ForkJoinWorkerThread)t).workQueue.queueSize() : |
1137 |
> |
ForkJoinPool.getEstimatedSubmitterQueueLength(); |
1138 |
|
} |
1139 |
|
|
1140 |
|
/** |
1141 |
|
* Returns an estimate of how many more locally queued tasks are |
1142 |
|
* held by the current worker thread than there are other worker |
1143 |
< |
* threads that might steal them. This value may be useful for |
1143 |
> |
* threads that might steal them, or zero if this thread is not |
1144 |
> |
* operating in a ForkJoinPool. This value may be useful for |
1145 |
|
* heuristic decisions about whether to fork other tasks. In many |
1146 |
|
* usages of ForkJoinTasks, at steady state, each worker should |
1147 |
|
* aim to maintain a small constant surplus (for example, 3) of |
1148 |
|
* tasks, and to process computations locally if this threshold is |
1149 |
|
* exceeded. |
1150 |
|
* |
1157 |
– |
* <p>This method may be invoked only from within {@code |
1158 |
– |
* ForkJoinPool} computations (as may be determined using method |
1159 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1160 |
– |
* result in exceptions or errors, possibly including {@code |
1161 |
– |
* ClassCastException}. |
1162 |
– |
* |
1151 |
|
* @return the surplus number of tasks, which may be negative |
1152 |
|
*/ |
1153 |
|
public static int getSurplusQueuedTaskCount() { |
1194 |
|
* have zero queued tasks, so compensate by a factor of |
1195 |
|
* (#idle/#active) threads. |
1196 |
|
*/ |
1197 |
< |
ForkJoinWorkerThread wt = |
1198 |
< |
(ForkJoinWorkerThread)Thread.currentThread(); |
1199 |
< |
return wt.workQueue.queueSize() - wt.pool.idlePerActive(); |
1197 |
> |
Thread t; ForkJoinWorkerThread wt; |
1198 |
> |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1199 |
> |
(wt = (ForkJoinWorkerThread)t).workQueue.queueSize() - wt.pool.idlePerActive() : |
1200 |
> |
0; |
1201 |
|
} |
1202 |
|
|
1203 |
|
// Extension methods |
1223 |
|
protected abstract void setRawResult(V value); |
1224 |
|
|
1225 |
|
/** |
1226 |
< |
* Immediately performs the base action of this task. This method |
1227 |
< |
* is designed to support extensions, and should not in general be |
1228 |
< |
* called otherwise. The return value controls whether this task |
1229 |
< |
* is considered to be done normally. It may return false in |
1226 |
> |
* Immediately performs the base action of this task and returns |
1227 |
> |
* true if, upon return from this method, this task is guaranteed |
1228 |
> |
* to have completed normally. This method may return false |
1229 |
> |
* otherwise, to indicate that this task is not necessarily |
1230 |
> |
* complete (or is not known to be complete), for example in |
1231 |
|
* asynchronous actions that require explicit invocations of |
1232 |
< |
* {@link #complete} to become joinable. It may also throw an |
1233 |
< |
* (unchecked) exception to indicate abnormal exit. |
1232 |
> |
* completion methods. This method may also throw an (unchecked) |
1233 |
> |
* exception to indicate abnormal exit. This method is designed to |
1234 |
> |
* support extensions, and should not in general be called |
1235 |
> |
* otherwise. |
1236 |
|
* |
1237 |
< |
* @return {@code true} if completed normally |
1237 |
> |
* @return {@code true} if this task is known to have completed normally |
1238 |
|
*/ |
1239 |
|
protected abstract boolean exec(); |
1240 |
|
|
1241 |
|
/** |
1242 |
|
* Returns, but does not unschedule or execute, a task queued by |
1243 |
|
* the current thread but not yet executed, if one is immediately |
1244 |
< |
* available. There is no guarantee that this task will actually |
1245 |
< |
* be polled or executed next. Conversely, this method may return |
1246 |
< |
* null even if a task exists but cannot be accessed without |
1247 |
< |
* contention with other threads. This method is designed |
1244 |
> |
* available and the current thread is operating in a |
1245 |
> |
* ForkJoinPool. There is no guarantee that this task will |
1246 |
> |
* actually be polled or executed next. Conversely, this method |
1247 |
> |
* may return null even if a task exists but cannot be accessed |
1248 |
> |
* without contention with other threads. This method is designed |
1249 |
|
* primarily to support extensions, and is unlikely to be useful |
1250 |
|
* otherwise. |
1251 |
|
* |
1259 |
– |
* <p>This method may be invoked only from within {@code |
1260 |
– |
* ForkJoinPool} computations (as may be determined using method |
1261 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1262 |
– |
* result in exceptions or errors, possibly including {@code |
1263 |
– |
* ClassCastException}. |
1264 |
– |
* |
1252 |
|
* @return the next task, or {@code null} if none are available |
1253 |
|
*/ |
1254 |
|
protected static ForkJoinTask<?> peekNextLocalTask() { |
1255 |
< |
return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek(); |
1255 |
> |
Thread t; |
1256 |
> |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1257 |
> |
((ForkJoinWorkerThread)t).workQueue.peek() : |
1258 |
> |
null; |
1259 |
|
} |
1260 |
|
|
1261 |
|
/** |
1262 |
|
* Unschedules and returns, without executing, the next task |
1263 |
< |
* queued by the current thread but not yet executed. This method |
1264 |
< |
* is designed primarily to support extensions, and is unlikely to |
1265 |
< |
* be useful otherwise. |
1266 |
< |
* |
1277 |
< |
* <p>This method may be invoked only from within {@code |
1278 |
< |
* ForkJoinPool} computations (as may be determined using method |
1279 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1280 |
< |
* result in exceptions or errors, possibly including {@code |
1281 |
< |
* ClassCastException}. |
1263 |
> |
* queued by the current thread but not yet executed, if the |
1264 |
> |
* current thread is operating in a ForkJoinPool. This method is |
1265 |
> |
* designed primarily to support extensions, and is unlikely to be |
1266 |
> |
* useful otherwise. |
1267 |
|
* |
1268 |
|
* @return the next task, or {@code null} if none are available |
1269 |
|
*/ |
1270 |
|
protected static ForkJoinTask<?> pollNextLocalTask() { |
1271 |
< |
return ((ForkJoinWorkerThread) Thread.currentThread()) |
1272 |
< |
.workQueue.nextLocalTask(); |
1271 |
> |
Thread t; |
1272 |
> |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1273 |
> |
((ForkJoinWorkerThread)t).workQueue.nextLocalTask() : |
1274 |
> |
null; |
1275 |
|
} |
1276 |
|
|
1277 |
|
/** |
1278 |
< |
* Unschedules and returns, without executing, the next task |
1278 |
> |
* If the current thread is operating in a ForkJoinPool, |
1279 |
> |
* unschedules and returns, without executing, the next task |
1280 |
|
* queued by the current thread but not yet executed, if one is |
1281 |
|
* available, or if not available, a task that was forked by some |
1282 |
|
* other thread, if available. Availability may be transient, so a |
1283 |
< |
* {@code null} result does not necessarily imply quiescence |
1284 |
< |
* of the pool this task is operating in. This method is designed |
1283 |
> |
* {@code null} result does not necessarily imply quiescence of |
1284 |
> |
* the pool this task is operating in. This method is designed |
1285 |
|
* primarily to support extensions, and is unlikely to be useful |
1286 |
|
* otherwise. |
1287 |
|
* |
1300 |
– |
* <p>This method may be invoked only from within {@code |
1301 |
– |
* ForkJoinPool} computations (as may be determined using method |
1302 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1303 |
– |
* result in exceptions or errors, possibly including {@code |
1304 |
– |
* ClassCastException}. |
1305 |
– |
* |
1288 |
|
* @return a task, or {@code null} if none are available |
1289 |
|
*/ |
1290 |
|
protected static ForkJoinTask<?> pollTask() { |
1291 |
< |
ForkJoinWorkerThread wt = |
1292 |
< |
(ForkJoinWorkerThread)Thread.currentThread(); |
1293 |
< |
return wt.pool.nextTaskFor(wt.workQueue); |
1291 |
> |
Thread t; ForkJoinWorkerThread wt; |
1292 |
> |
return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ? |
1293 |
> |
(wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) : |
1294 |
> |
null; |
1295 |
|
} |
1296 |
|
|
1297 |
|
// tag operations |
1324 |
|
/** |
1325 |
|
* Atomically conditionally sets the tag value for this task. |
1326 |
|
* Among other applications, tags can be used as visit markers |
1327 |
< |
* in tasks operating on graphs, as in mathods that check: {@code |
1327 |
> |
* in tasks operating on graphs, as in methods that check: {@code |
1328 |
|
* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))} |
1329 |
|
* before processing, otherwise exiting because the node has |
1330 |
|
* already been visited. |