30 |
|
* subtasks may be hosted by a small number of actual threads in a |
31 |
|
* ForkJoinPool, at the price of some usage limitations. |
32 |
|
* |
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 |
|
* #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 |
|
* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}. |
47 |
|
* The efficiency of {@code ForkJoinTask}s stems from a set of |
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. While these methods have |
127 |
< |
* {@code public} access (to allow instances of different task |
128 |
< |
* subclasses to call each other's methods), some of them may only be |
129 |
< |
* called from within other ForkJoinTasks (as may be determined using |
130 |
< |
* method {@link #inForkJoinPool}). Attempts to invoke them in other |
131 |
< |
* contexts result in exceptions or errors, possibly including {@code |
132 |
< |
* ClassCastException}. |
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 |
284 |
|
* @return status upon completion |
285 |
|
*/ |
286 |
|
private int externalAwaitDone() { |
290 |
– |
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 { |
316 |
– |
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 |
< |
} |
347 |
< |
else |
348 |
< |
s = externalAwaitDone(); |
349 |
< |
} |
350 |
< |
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); |
364 |
< |
else |
365 |
< |
s = externalAwaitDone(); |
366 |
< |
} |
367 |
< |
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 |
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 |
633 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
634 |
< |
* result in exceptions or errors, possibly including {@code |
635 |
< |
* 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 |
|
* |
690 |
– |
* <p>This method may be invoked only from within {@code |
691 |
– |
* ForkJoinPool} computations (as may be determined using method |
692 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
693 |
– |
* result in exceptions or errors, possibly including {@code |
694 |
– |
* ClassCastException}. |
695 |
– |
* |
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 |
|
* |
721 |
– |
* <p>This method may be invoked only from within {@code |
722 |
– |
* ForkJoinPool} computations (as may be determined using method |
723 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
724 |
– |
* result in exceptions or errors, possibly including {@code |
725 |
– |
* ClassCastException}. |
726 |
– |
* |
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 |
|
* |
770 |
– |
* <p>This method may be invoked only from within {@code |
771 |
– |
* ForkJoinPool} computations (as may be determined using method |
772 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
773 |
– |
* result in exceptions or errors, possibly including {@code |
774 |
– |
* ClassCastException}. |
775 |
– |
* |
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 |
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. |
1071 |
– |
* |
1072 |
– |
* <p>This method may be invoked only from within {@code |
1073 |
– |
* ForkJoinPool} computations (as may be determined using method |
1074 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1075 |
– |
* result in exceptions or errors, possibly including {@code |
1076 |
– |
* 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. |
1139 |
< |
* |
1140 |
< |
* <p>This method may be invoked only from within {@code |
1141 |
< |
* ForkJoinPool} computations (as may be determined using method |
1142 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1143 |
< |
* result in exceptions or errors, possibly including {@code |
1144 |
< |
* 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 |
|
* |
1159 |
– |
* <p>This method may be invoked only from within {@code |
1160 |
– |
* ForkJoinPool} computations (as may be determined using method |
1161 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1162 |
– |
* result in exceptions or errors, possibly including {@code |
1163 |
– |
* ClassCastException}. |
1164 |
– |
* |
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 |
|
* |
1182 |
– |
* <p>This method may be invoked only from within {@code |
1183 |
– |
* ForkJoinPool} computations (as may be determined using method |
1184 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1185 |
– |
* result in exceptions or errors, possibly including {@code |
1186 |
– |
* ClassCastException}. |
1187 |
– |
* |
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 |
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 |
|
* |
1287 |
– |
* <p>This method may be invoked only from within {@code |
1288 |
– |
* ForkJoinPool} computations (as may be determined using method |
1289 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1290 |
– |
* result in exceptions or errors, possibly including {@code |
1291 |
– |
* ClassCastException}. |
1292 |
– |
* |
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 |
< |
* |
1305 |
< |
* <p>This method may be invoked only from within {@code |
1306 |
< |
* ForkJoinPool} computations (as may be determined using method |
1307 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1308 |
< |
* result in exceptions or errors, possibly including {@code |
1309 |
< |
* 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 |
|
* |
1328 |
– |
* <p>This method may be invoked only from within {@code |
1329 |
– |
* ForkJoinPool} computations (as may be determined using method |
1330 |
– |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1331 |
– |
* result in exceptions or errors, possibly including {@code |
1332 |
– |
* ClassCastException}. |
1333 |
– |
* |
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 |