| 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 |
| 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 stalled waiting to join others. However, no such adjustments |
| 49 |
|
* are 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 explicitly {@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 ForkJoinPool with a pool size equal to the number of |
| 367 |
< |
* processors available on the system, using the default |
| 368 |
< |
* ForkJoinWorkerThreadFactory. |
| 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 ForkJoinPool with the indicated parallelism level |
| 382 |
< |
* threads and using the default ForkJoinWorkerThreadFactory. |
| 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 ForkJoinPool with parallelism equal to the number of |
| 399 |
< |
* processors available on the system and using the given |
| 400 |
< |
* ForkJoinWorkerThreadFactory. |
| 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 |
| 411 |
|
} |
| 412 |
|
|
| 413 |
|
/** |
| 414 |
< |
* Creates a ForkJoinPool with the given parallelism and factory. |
| 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 |
| 446 |
|
* Creates a new worker thread using factory. |
| 447 |
|
* |
| 448 |
|
* @param index the index to assign worker |
| 449 |
< |
* @return new worker, or null of factory failed |
| 449 |
> |
* @return new worker, or null if factory failed |
| 450 |
|
*/ |
| 451 |
|
private ForkJoinWorkerThread createWorker(int index) { |
| 452 |
|
Thread.UncaughtExceptionHandler h = ueh; |
| 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 |
| 821 |
< |
* controls construction of new threads. |
| 819 |
> |
* pool. The given value should normally be greater than or equal |
| 820 |
> |
* to the {@link #getParallelism parallelism} level. Setting this |
| 821 |
> |
* value has no effect on current pool size. It controls |
| 822 |
> |
* construction of new threads. |
| 823 |
|
* |
| 824 |
|
* @throws IllegalArgumentException if negative or greater than |
| 825 |
|
* internal implementation limit |
| 989 |
|
} |
| 990 |
|
|
| 991 |
|
/** |
| 992 |
< |
* Returns an estimate of the number tasks submitted to this pool |
| 993 |
< |
* that have not yet begun executing. This method takes time |
| 992 |
> |
* Returns an estimate of the number of tasks submitted to this |
| 993 |
> |
* pool that have not yet begun executing. This method takes time |
| 994 |
|
* proportional to the number of submissions. |
| 995 |
|
* |
| 996 |
|
* @return the number of queued submissions |
| 1024 |
|
* Removes all available unexecuted submitted and forked tasks |
| 1025 |
|
* from scheduling queues and adds them to the given collection, |
| 1026 |
|
* without altering their execution status. These may include |
| 1027 |
< |
* artificially generated or wrapped tasks. This method is designed |
| 1028 |
< |
* to be invoked only when the pool is known to be |
| 1027 |
> |
* artificially generated or wrapped tasks. This method is |
| 1028 |
> |
* designed to be invoked only when the pool is known to be |
| 1029 |
|
* quiescent. Invocations at other times may not remove all |
| 1030 |
|
* tasks. A failure encountered while attempting to add elements |
| 1031 |
|
* to collection {@code c} may result in elements being in |
| 1122 |
|
} |
| 1123 |
|
|
| 1124 |
|
/** |
| 1125 |
< |
* Attempts to stop all actively executing tasks, and cancels all |
| 1126 |
< |
* waiting tasks. Tasks that are in the process of being |
| 1127 |
< |
* submitted or executed concurrently during the course of this |
| 1128 |
< |
* method may or may not be rejected. Unlike some other executors, |
| 1129 |
< |
* this method cancels rather than collects non-executed tasks |
| 1130 |
< |
* upon termination, so always returns an empty list. However, you |
| 1131 |
< |
* can use method {@link #drainTasksTo} before invoking this |
| 1132 |
< |
* method to transfer unexecuted tasks to another collection. |
| 1125 |
> |
* Attempts to cancel and/or stop all tasks, and reject all |
| 1126 |
> |
* subsequently submitted tasks. Tasks that are in the process of |
| 1127 |
> |
* being submitted or executed concurrently during the course of |
| 1128 |
> |
* this method may or may not be rejected. This method cancels |
| 1129 |
> |
* both existing and unexecuted tasks, in order to permit |
| 1130 |
> |
* termination in the presence of task dependencies. So the method |
| 1131 |
> |
* always returns an empty list (unlike the case for some other |
| 1132 |
> |
* Executors). |
| 1133 |
|
* |
| 1134 |
|
* @return an empty list |
| 1135 |
|
* @throws SecurityException if a security manager exists and |
| 1154 |
|
|
| 1155 |
|
/** |
| 1156 |
|
* Returns {@code true} if the process of termination has |
| 1157 |
< |
* commenced but possibly not yet completed. |
| 1157 |
> |
* commenced but not yet completed. This method may be useful for |
| 1158 |
> |
* debugging. A return of {@code true} reported a sufficient |
| 1159 |
> |
* period after shutdown may indicate that submitted tasks have |
| 1160 |
> |
* ignored or suppressed interruption, causing this executor not |
| 1161 |
> |
* to properly terminate. |
| 1162 |
|
* |
| 1163 |
< |
* @return {@code true} if terminating |
| 1163 |
> |
* @return {@code true} if terminating but not yet terminated |
| 1164 |
|
*/ |
| 1165 |
|
public boolean isTerminating() { |
| 1166 |
< |
return runStateOf(runControl) >= TERMINATING; |
| 1166 |
> |
return runStateOf(runControl) == TERMINATING; |
| 1167 |
|
} |
| 1168 |
|
|
| 1169 |
|
/** |
| 1176 |
|
} |
| 1177 |
|
|
| 1178 |
|
/** |
| 1179 |
+ |
* Returns true if pool is not terminating or terminated. |
| 1180 |
+ |
* Used internally to suppress execution when terminating. |
| 1181 |
+ |
*/ |
| 1182 |
+ |
final boolean isProcessingTasks() { |
| 1183 |
+ |
return runStateOf(runControl) < TERMINATING; |
| 1184 |
+ |
} |
| 1185 |
+ |
|
| 1186 |
+ |
/** |
| 1187 |
|
* Blocks until all tasks have completed execution after a shutdown |
| 1188 |
|
* request, or the timeout occurs, or the current thread is |
| 1189 |
|
* interrupted, whichever happens first. |
| 1237 |
|
transitionRunStateTo(TERMINATED); |
| 1238 |
|
termination.signalAll(); |
| 1239 |
|
} |
| 1240 |
< |
else if (!isTerminating()) { |
| 1240 |
> |
else if (isProcessingTasks()) { |
| 1241 |
|
tryShrinkWorkerArray(); |
| 1242 |
|
tryResumeSpare(true); // allow replacement |
| 1243 |
|
} |
| 1478 |
|
final void sync(ForkJoinWorkerThread w) { |
| 1479 |
|
updateStealCount(w); // Transfer w's count while it is idle |
| 1480 |
|
|
| 1481 |
< |
while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) { |
| 1481 |
> |
while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) { |
| 1482 |
|
long prev = w.lastEventCount; |
| 1483 |
|
WaitQueueNode node = null; |
| 1484 |
|
WaitQueueNode h; |
| 1683 |
|
for (k = 0; k < len && ws[k] != null; ++k) |
| 1684 |
|
; |
| 1685 |
|
} |
| 1686 |
< |
if (k < len && !isTerminating() && (w = createWorker(k)) != null) { |
| 1686 |
> |
if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) { |
| 1687 |
|
ws[k] = w; |
| 1688 |
|
w.start(); |
| 1689 |
|
} |
| 1787 |
|
* Method {@code isReleasable} must return {@code true} if |
| 1788 |
|
* blocking is not necessary. Method {@code block} blocks the |
| 1789 |
|
* current thread if necessary (perhaps internally invoking |
| 1790 |
< |
* {@code isReleasable} before actually blocking.). |
| 1790 |
> |
* {@code isReleasable} before actually blocking). |
| 1791 |
|
* |
| 1792 |
|
* <p>For example, here is a ManagedBlocker based on a |
| 1793 |
|
* ReentrantLock: |
