23 |
|
* An {@link ExecutorService} for running {@link ForkJoinTask}s. |
24 |
|
* A {@code ForkJoinPool} provides the entry point for submissions |
25 |
|
* from non-{@code ForkJoinTask}s, as well as management and |
26 |
< |
* monitoring operations. Normally a single {@code ForkJoinPool} is |
27 |
< |
* used for a large number of submitted tasks. Otherwise, use would |
28 |
< |
* not usually outweigh the construction and bookkeeping overhead of |
29 |
< |
* creating a large set of threads. |
26 |
> |
* monitoring operations. |
27 |
|
* |
28 |
< |
* <p>{@code ForkJoinPool}s differ from other kinds of {@link |
29 |
< |
* Executor}s mainly in that they provide <em>work-stealing</em>: all |
30 |
< |
* threads in the pool attempt to find and execute subtasks created by |
31 |
< |
* other active tasks (eventually blocking if none exist). This makes |
32 |
< |
* them efficient when most tasks spawn other subtasks (as do most |
33 |
< |
* {@code ForkJoinTask}s), as well as the mixed execution of some |
34 |
< |
* plain {@code Runnable}- or {@code Callable}- based activities along |
35 |
< |
* with {@code ForkJoinTask}s. When setting {@linkplain #setAsyncMode |
36 |
< |
* async mode}, a {@code ForkJoinPool} may also be appropriate for use |
37 |
< |
* with fine-grained tasks that are never joined. Otherwise, other |
38 |
< |
* {@code ExecutorService} implementations are typically more |
39 |
< |
* appropriate choices. |
28 |
> |
* <p>A {@code ForkJoinPool} differs from other kinds of {@link |
29 |
> |
* ExecutorService} mainly by virtue of employing |
30 |
> |
* <em>work-stealing</em>: all threads in the pool attempt to find and |
31 |
> |
* execute subtasks created by other active tasks (eventually blocking |
32 |
> |
* waiting for work if none exist). This enables efficient processing |
33 |
> |
* when most tasks spawn other subtasks (as do most {@code |
34 |
> |
* ForkJoinTask}s). A {@code ForkJoinPool} may also be used for mixed |
35 |
> |
* execution of some plain {@code Runnable}- or {@code Callable}- |
36 |
> |
* based activities along with {@code ForkJoinTask}s. When setting |
37 |
> |
* {@linkplain #setAsyncMode async mode}, a {@code ForkJoinPool} may |
38 |
> |
* also be appropriate for use with fine-grained tasks of any form |
39 |
> |
* that are never joined. Otherwise, other {@code ExecutorService} |
40 |
> |
* implementations are typically more appropriate choices. |
41 |
|
* |
42 |
< |
* <p>A {@code ForkJoinPool} may be constructed with a given |
43 |
< |
* parallelism level (target pool size), which it attempts to maintain |
44 |
< |
* by dynamically adding, suspending, or resuming threads, even if |
45 |
< |
* some tasks are waiting to join others. However, no such adjustments |
46 |
< |
* are performed in the face of blocked IO or other unmanaged |
42 |
> |
* <p>A {@code ForkJoinPool} is constructed with a given target |
43 |
> |
* parallelism level; by default, equal to the number of available |
44 |
> |
* processors. Unless configured otherwise via {@link |
45 |
> |
* #setMaintainsParallelism}, the pool attempts to maintain this |
46 |
> |
* number of active (or available) threads by dynamically adding, |
47 |
> |
* suspending, or resuming internal worker threads, even if some tasks |
48 |
> |
* are waiting to join others. However, no such adjustments are |
49 |
> |
* performed in the face of blocked IO or other unmanaged |
50 |
|
* synchronization. The nested {@link ManagedBlocker} interface |
51 |
|
* enables extension of the kinds of synchronization accommodated. |
52 |
|
* The target parallelism level may also be changed dynamically |
53 |
< |
* ({@link #setParallelism}) and thread construction can be limited |
54 |
< |
* using methods {@link #setMaximumPoolSize} and/or {@link |
55 |
< |
* #setMaintainsParallelism}. |
53 |
> |
* ({@link #setParallelism}). The total number of threads may be |
54 |
> |
* limited using method {@link #setMaximumPoolSize}, in which case it |
55 |
> |
* may become possible for the activities of a pool to stall due to |
56 |
> |
* the lack of available threads to process new tasks. |
57 |
|
* |
58 |
|
* <p>In addition to execution and lifecycle control methods, this |
59 |
|
* class provides status check methods (for example |
62 |
|
* {@link #toString} returns indications of pool state in a |
63 |
|
* convenient form for informal monitoring. |
64 |
|
* |
65 |
+ |
* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is |
66 |
+ |
* used for all parallel task execution in a program or subsystem. |
67 |
+ |
* Otherwise, use would not usually outweigh the construction and |
68 |
+ |
* bookkeeping overhead of creating a large set of threads. For |
69 |
+ |
* example a common pool could be used for the {@code SortTasks} |
70 |
+ |
* illustrated in {@link RecursiveAction}. Because {@code |
71 |
+ |
* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon |
72 |
+ |
* daemon} mode, there is typically no need to explictly {@link |
73 |
+ |
* #shutdown} such a pool upon program exit. |
74 |
+ |
* |
75 |
+ |
* <pre> |
76 |
+ |
* static final ForkJoinPool mainPool = new ForkJoinPool(); |
77 |
+ |
* ... |
78 |
+ |
* public void sort(long[] array) { |
79 |
+ |
* mainPool.invoke(new SortTask(array, 0, array.length)); |
80 |
+ |
* } |
81 |
+ |
* </pre> |
82 |
+ |
* |
83 |
|
* <p><b>Implementation notes</b>: This implementation restricts the |
84 |
|
* maximum number of running threads to 32767. Attempts to create |
85 |
|
* pools with greater than the maximum result in |
363 |
|
// Constructors |
364 |
|
|
365 |
|
/** |
366 |
< |
* Creates a {@code ForkJoinPool} with a pool size equal to the |
367 |
< |
* number of processors available on the system, using the |
368 |
< |
* {@linkplain #defaultForkJoinWorkerThreadFactory default thread factory}. |
366 |
> |
* Creates a {@code ForkJoinPool} with parallelism equal to {@link |
367 |
> |
* java.lang.Runtime#availableProcessors}, and using the {@linkplain |
368 |
> |
* #defaultForkJoinWorkerThreadFactory default thread factory}. |
369 |
|
* |
370 |
|
* @throws SecurityException if a security manager exists and |
371 |
|
* the caller is not permitted to modify threads |
378 |
|
} |
379 |
|
|
380 |
|
/** |
381 |
< |
* Creates a {@code ForkJoinPool} with the indicated parallelism level |
382 |
< |
* threads and using the |
383 |
< |
* {@linkplain #defaultForkJoinWorkerThreadFactory default thread factory}. |
381 |
> |
* Creates a {@code ForkJoinPool} with the indicated parallelism |
382 |
> |
* level and using the {@linkplain |
383 |
> |
* #defaultForkJoinWorkerThreadFactory default thread factory}. |
384 |
|
* |
385 |
< |
* @param parallelism the number of worker threads |
385 |
> |
* @param parallelism the parallelism level |
386 |
|
* @throws IllegalArgumentException if parallelism less than or |
387 |
|
* equal to zero |
388 |
|
* @throws SecurityException if a security manager exists and |
395 |
|
} |
396 |
|
|
397 |
|
/** |
398 |
< |
* Creates a {@code ForkJoinPool} with parallelism equal to the |
399 |
< |
* number of processors available on the system and using the |
400 |
< |
* given thread factory. |
398 |
> |
* Creates a {@code ForkJoinPool} with parallelism equal to {@link |
399 |
> |
* java.lang.Runtime#availableProcessors}, and using the given |
400 |
> |
* thread factory. |
401 |
|
* |
402 |
|
* @param factory the factory for creating new threads |
403 |
|
* @throws NullPointerException if factory is null |
414 |
|
* Creates a {@code ForkJoinPool} with the given parallelism and |
415 |
|
* thread factory. |
416 |
|
* |
417 |
< |
* @param parallelism the targeted number of worker threads |
417 |
> |
* @param parallelism the parallelism level |
418 |
|
* @param factory the factory for creating new threads |
419 |
|
* @throws IllegalArgumentException if parallelism less than or |
420 |
|
* equal to zero, or greater than implementation limit |
467 |
|
* Currently requires size to be a power of two. |
468 |
|
*/ |
469 |
|
private static int arraySizeFor(int poolSize) { |
470 |
< |
return (poolSize <= 1) ? 1 : |
471 |
< |
(1 << (32 - Integer.numberOfLeadingZeros(poolSize-1))); |
470 |
> |
if (poolSize <= 1) |
471 |
> |
return 1; |
472 |
> |
// See Hackers Delight, sec 3.2 |
473 |
> |
int c = poolSize >= MAX_THREADS ? MAX_THREADS : (poolSize - 1); |
474 |
> |
c |= c >>> 1; |
475 |
> |
c |= c >>> 2; |
476 |
> |
c |= c >>> 4; |
477 |
> |
c |= c >>> 8; |
478 |
> |
c |= c >>> 16; |
479 |
> |
return c + 1; |
480 |
|
} |
481 |
|
|
482 |
|
/** |
767 |
|
final ReentrantLock lock = this.workerLock; |
768 |
|
lock.lock(); |
769 |
|
try { |
770 |
< |
if (!isTerminating()) { |
770 |
> |
if (isProcessingTasks()) { |
771 |
|
int p = this.parallelism; |
772 |
|
this.parallelism = parallelism; |
773 |
|
if (parallelism > p) |
782 |
|
} |
783 |
|
|
784 |
|
/** |
785 |
< |
* Returns the targeted number of worker threads in this pool. |
785 |
> |
* Returns the targeted parallelism level of this pool. |
786 |
|
* |
787 |
< |
* @return the targeted number of worker threads in this pool |
787 |
> |
* @return the targeted parallelism level of this pool |
788 |
|
*/ |
789 |
|
public int getParallelism() { |
790 |
|
return parallelism; |
804 |
|
|
805 |
|
/** |
806 |
|
* Returns the maximum number of threads allowed to exist in the |
807 |
< |
* pool, even if there are insufficient unblocked running threads. |
807 |
> |
* pool. Unless set using {@link #setMaximumPoolSize}, the |
808 |
> |
* maximum is an implementation-defined value designed only to |
809 |
> |
* prevent runaway growth. |
810 |
|
* |
811 |
|
* @return the maximum |
812 |
|
*/ |
816 |
|
|
817 |
|
/** |
818 |
|
* Sets the maximum number of threads allowed to exist in the |
819 |
< |
* pool, even if there are insufficient unblocked running threads. |
820 |
< |
* Setting this value has no effect on current pool size. It |
791 |
< |
* controls construction of new threads. |
819 |
> |
* pool. Setting this value has no effect on current pool |
820 |
> |
* size. It controls construction of new threads. |
821 |
|
* |
822 |
|
* @throws IllegalArgumentException if negative or greater than |
823 |
|
* internal implementation limit |
1120 |
|
} |
1121 |
|
|
1122 |
|
/** |
1123 |
< |
* Attempts to stop all actively executing tasks, and cancels all |
1124 |
< |
* waiting tasks. Tasks that are in the process of being |
1125 |
< |
* submitted or executed concurrently during the course of this |
1126 |
< |
* method may or may not be rejected. Unlike some other executors, |
1127 |
< |
* this method cancels rather than collects non-executed tasks |
1128 |
< |
* upon termination, so always returns an empty list. However, you |
1129 |
< |
* can use method {@link #drainTasksTo} before invoking this |
1130 |
< |
* method to transfer unexecuted tasks to another collection. |
1123 |
> |
* Attempts to cancel and/or stop all tasks, and reject all |
1124 |
> |
* subsequently submitted tasks. Tasks that are in the process of |
1125 |
> |
* being submitted or executed concurrently during the course of |
1126 |
> |
* this method may or may not be rejected. This method cancels |
1127 |
> |
* both existing and unexecuted tasks, in order to permit |
1128 |
> |
* termination in the presence of task dependencies. So the method |
1129 |
> |
* always returns an empty list (unlike the case for some other |
1130 |
> |
* Executors). |
1131 |
|
* |
1132 |
|
* @return an empty list |
1133 |
|
* @throws SecurityException if a security manager exists and |
1152 |
|
|
1153 |
|
/** |
1154 |
|
* Returns {@code true} if the process of termination has |
1155 |
< |
* commenced but possibly not yet completed. |
1155 |
> |
* commenced but not yet completed. This method may be useful for |
1156 |
> |
* debugging. A return of {@code true} reported a sufficient |
1157 |
> |
* period after shutdown may indicate that submitted tasks have |
1158 |
> |
* ignored or suppressed interruption, causing this executor not |
1159 |
> |
* to properly terminate. |
1160 |
|
* |
1161 |
< |
* @return {@code true} if terminating |
1161 |
> |
* @return {@code true} if terminating but not yet terminated |
1162 |
|
*/ |
1163 |
|
public boolean isTerminating() { |
1164 |
< |
return runStateOf(runControl) >= TERMINATING; |
1164 |
> |
return runStateOf(runControl) == TERMINATING; |
1165 |
|
} |
1166 |
|
|
1167 |
|
/** |
1174 |
|
} |
1175 |
|
|
1176 |
|
/** |
1177 |
+ |
* Returns true if pool is not terminating or terminated. |
1178 |
+ |
* Used internally to suppress execution when terminating. |
1179 |
+ |
*/ |
1180 |
+ |
final boolean isProcessingTasks() { |
1181 |
+ |
return runStateOf(runControl) < TERMINATING; |
1182 |
+ |
} |
1183 |
+ |
|
1184 |
+ |
/** |
1185 |
|
* Blocks until all tasks have completed execution after a shutdown |
1186 |
|
* request, or the timeout occurs, or the current thread is |
1187 |
|
* interrupted, whichever happens first. |
1235 |
|
transitionRunStateTo(TERMINATED); |
1236 |
|
termination.signalAll(); |
1237 |
|
} |
1238 |
< |
else if (!isTerminating()) { |
1238 |
> |
else if (isProcessingTasks()) { |
1239 |
|
tryShrinkWorkerArray(); |
1240 |
|
tryResumeSpare(true); // allow replacement |
1241 |
|
} |
1476 |
|
final void sync(ForkJoinWorkerThread w) { |
1477 |
|
updateStealCount(w); // Transfer w's count while it is idle |
1478 |
|
|
1479 |
< |
while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) { |
1479 |
> |
while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) { |
1480 |
|
long prev = w.lastEventCount; |
1481 |
|
WaitQueueNode node = null; |
1482 |
|
WaitQueueNode h; |
1681 |
|
for (k = 0; k < len && ws[k] != null; ++k) |
1682 |
|
; |
1683 |
|
} |
1684 |
< |
if (k < len && !isTerminating() && (w = createWorker(k)) != null) { |
1684 |
> |
if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) { |
1685 |
|
ws[k] = w; |
1686 |
|
w.start(); |
1687 |
|
} |