| 5 |
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*/ |
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package jsr166y; |
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+ |
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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; |
| 71 |
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* but doing do requires three further considerations: (1) Completion |
| 72 |
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* of few if any <em>other</em> tasks should be dependent on a task |
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* that blocks on external synchronization or IO. Event-style async |
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< |
* tasks that are never joined often fall into this category. (2) To |
| 75 |
< |
* minimize resource impact, tasks should be small; ideally performing |
| 76 |
< |
* only the (possibly) blocking action. (3) Unless the {@link |
| 74 |
> |
* tasks that are never joined (for example, those subclassing {@link |
| 75 |
> |
* CountedCompleter}) often fall into this category. (2) To minimize |
| 76 |
> |
* resource impact, tasks should be small; ideally performing only the |
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> |
* (possibly) blocking action. (3) Unless the {@link |
| 78 |
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* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly |
| 79 |
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* blocked tasks is known to be less than the pool's {@link |
| 80 |
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* ForkJoinPool#getParallelism} level, the pool cannot guarantee that |
| 117 |
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* <p>The ForkJoinTask class is not usually directly subclassed. |
| 118 |
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* Instead, you subclass one of the abstract classes that support a |
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* particular style of fork/join processing, typically {@link |
| 120 |
< |
* RecursiveAction} for computations that do not return results, or |
| 121 |
< |
* {@link RecursiveTask} for those that do. Normally, a concrete |
| 122 |
< |
* ForkJoinTask subclass declares fields comprising its parameters, |
| 123 |
< |
* established in a constructor, and then defines a {@code compute} |
| 124 |
< |
* method that somehow uses the control methods supplied by this base |
| 125 |
< |
* class. While these methods have {@code public} access (to allow |
| 126 |
< |
* instances of different task subclasses to call each other's |
| 127 |
< |
* methods), some of them may only be called from within other |
| 128 |
< |
* ForkJoinTasks (as may be determined using method {@link |
| 129 |
< |
* #inForkJoinPool}). Attempts to invoke them in other contexts |
| 130 |
< |
* result in exceptions or errors, possibly including |
| 131 |
< |
* {@code ClassCastException}. |
| 120 |
> |
* RecursiveAction} for most computations that do not return results, |
| 121 |
> |
* {@link RecursiveTask} for those that do, and {@link |
| 122 |
> |
* CountedCompleter} for those in which completed actions trigger |
| 123 |
> |
* other actions. Normally, a concrete ForkJoinTask subclass declares |
| 124 |
> |
* fields comprising its parameters, established in a constructor, and |
| 125 |
> |
* then defines a {@code compute} method that somehow uses the control |
| 126 |
> |
* 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}. |
| 133 |
|
* |
| 134 |
|
* <p>Method {@link #join} and its variants are appropriate for use |
| 135 |
|
* only when completion dependencies are acyclic; that is, the |
| 140 |
|
* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that |
| 141 |
|
* may be of use in constructing custom subclasses for problems that |
| 142 |
|
* are not statically structured as DAGs. To support such usages a |
| 143 |
< |
* ForkJoinTask may be atomically <em>marked</em> using {@link |
| 144 |
< |
* #markForkJoinTask} and checked for marking using {@link |
| 145 |
< |
* #isMarkedForkJoinTask}. The ForkJoinTask implementation does not |
| 146 |
< |
* use these {@code protected} methods or marks for any purpose, but |
| 147 |
< |
* they may be of use in the construction of specialized subclasses. |
| 148 |
< |
* For example, parallel graph traversals can use the supplied methods |
| 149 |
< |
* to avoid revisiting nodes/tasks that have already been processed. |
| 150 |
< |
* Also, completion based designs can use them to record that one |
| 151 |
< |
* subtask has completed. (Method names for marking are bulky in part |
| 152 |
< |
* to encourage definition of methods that reflect their usage |
| 150 |
< |
* patterns.) |
| 143 |
> |
* ForkJoinTask may be atomically <em>tagged</em> with a {@code short} |
| 144 |
> |
* value using {@link #setForkJoinTaskTag} or {@link |
| 145 |
> |
* #compareAndSetForkJoinTaskTag} and checked using {@link |
| 146 |
> |
* #getForkJoinTaskTag}. The ForkJoinTask implementation does not use |
| 147 |
> |
* these {@code protected} methods or tags for any purpose, but they |
| 148 |
> |
* may be of use in the construction of specialized subclasses. For |
| 149 |
> |
* example, parallel graph traversals can use the supplied methods to |
| 150 |
> |
* avoid revisiting nodes/tasks that have already been processed. |
| 151 |
> |
* (Method names for tagging are bulky in part to encourage definition |
| 152 |
> |
* of methods that reflect their usage patterns.) |
| 153 |
|
* |
| 154 |
|
* <p>Most base support methods are {@code final}, to prevent |
| 155 |
|
* overriding of implementations that are intrinsically tied to the |
| 215 |
|
* thin-lock techniques, so use some odd coding idioms that tend |
| 216 |
|
* to avoid them, mainly by arranging that every synchronized |
| 217 |
|
* block performs a wait, notifyAll or both. |
| 218 |
+ |
* |
| 219 |
+ |
* These control bits occupy only (some of) the upper half (16 |
| 220 |
+ |
* bits) of status field. The lower bits are used for user-defined |
| 221 |
+ |
* tags. |
| 222 |
|
*/ |
| 223 |
|
|
| 224 |
|
/** The run status of this task */ |
| 227 |
|
static final int NORMAL = 0xf0000000; // must be negative |
| 228 |
|
static final int CANCELLED = 0xc0000000; // must be < NORMAL |
| 229 |
|
static final int EXCEPTIONAL = 0x80000000; // must be < CANCELLED |
| 230 |
< |
static final int SIGNAL = 0x00000001; |
| 231 |
< |
static final int MARKED = 0x00000002; |
| 230 |
> |
static final int SIGNAL = 0x00010000; // must be >= 1 << 16 |
| 231 |
> |
static final int SMASK = 0x0000ffff; // short bits for tags |
| 232 |
|
|
| 233 |
|
/** |
| 234 |
|
* Marks completion and wakes up threads waiting to join this |
| 235 |
< |
* task. A specialization for NORMAL completion is in method |
| 230 |
< |
* doExec. |
| 235 |
> |
* task. |
| 236 |
|
* |
| 237 |
|
* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL |
| 238 |
|
* @return completion status on exit |
| 242 |
|
if ((s = status) < 0) |
| 243 |
|
return s; |
| 244 |
|
if (U.compareAndSwapInt(this, STATUS, s, s | completion)) { |
| 245 |
< |
if ((s & SIGNAL) != 0) |
| 245 |
> |
if ((s >>> 16) != 0) |
| 246 |
|
synchronized (this) { notifyAll(); } |
| 247 |
|
return completion; |
| 248 |
|
} |
| 264 |
|
} catch (Throwable rex) { |
| 265 |
|
return setExceptionalCompletion(rex); |
| 266 |
|
} |
| 267 |
< |
while ((s = status) >= 0 && completed) { |
| 268 |
< |
if (U.compareAndSwapInt(this, STATUS, s, s | NORMAL)) { |
| 264 |
< |
if ((s & SIGNAL) != 0) |
| 265 |
< |
synchronized (this) { notifyAll(); } |
| 266 |
< |
return NORMAL; |
| 267 |
< |
} |
| 268 |
< |
} |
| 267 |
> |
if (completed) |
| 268 |
> |
s = setCompletion(NORMAL); |
| 269 |
|
} |
| 270 |
|
return s; |
| 271 |
|
} |
| 272 |
|
|
| 273 |
|
/** |
| 274 |
< |
* Tries to set SIGNAL status. Used by ForkJoinPool. Other |
| 275 |
< |
* variants are directly incorporated into externalAwaitDone etc. |
| 274 |
> |
* Tries to set SIGNAL status unless already completed. Used by |
| 275 |
> |
* ForkJoinPool. Other variants are directly incorporated into |
| 276 |
> |
* externalAwaitDone etc. |
| 277 |
|
* |
| 278 |
|
* @return true if successful |
| 279 |
|
*/ |
| 280 |
|
final boolean trySetSignal() { |
| 281 |
< |
int s; |
| 282 |
< |
return U.compareAndSwapInt(this, STATUS, s = status, s | SIGNAL); |
| 281 |
> |
int s = status; |
| 282 |
> |
return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL); |
| 283 |
|
} |
| 284 |
|
|
| 285 |
|
/** |
| 329 |
|
return s; |
| 330 |
|
} |
| 331 |
|
|
| 331 |
– |
|
| 332 |
|
/** |
| 333 |
|
* Implementation for join, get, quietlyJoin. Directly handles |
| 334 |
|
* only cases of already-completed, external wait, and |
| 412 |
|
} |
| 413 |
|
|
| 414 |
|
/** |
| 415 |
< |
* Records exception and sets exceptional completion. |
| 415 |
> |
* Records exception and sets status. |
| 416 |
|
* |
| 417 |
|
* @return status on exit |
| 418 |
|
*/ |
| 419 |
< |
private int setExceptionalCompletion(Throwable ex) { |
| 420 |
< |
int h = System.identityHashCode(this); |
| 421 |
< |
final ReentrantLock lock = exceptionTableLock; |
| 422 |
< |
lock.lock(); |
| 423 |
< |
try { |
| 424 |
< |
expungeStaleExceptions(); |
| 425 |
< |
ExceptionNode[] t = exceptionTable; |
| 426 |
< |
int i = h & (t.length - 1); |
| 427 |
< |
for (ExceptionNode e = t[i]; ; e = e.next) { |
| 428 |
< |
if (e == null) { |
| 429 |
< |
t[i] = new ExceptionNode(this, ex, t[i]); |
| 430 |
< |
break; |
| 419 |
> |
final int recordExceptionalCompletion(Throwable ex) { |
| 420 |
> |
int s; |
| 421 |
> |
if ((s = status) >= 0) { |
| 422 |
> |
int h = System.identityHashCode(this); |
| 423 |
> |
final ReentrantLock lock = exceptionTableLock; |
| 424 |
> |
lock.lock(); |
| 425 |
> |
try { |
| 426 |
> |
expungeStaleExceptions(); |
| 427 |
> |
ExceptionNode[] t = exceptionTable; |
| 428 |
> |
int i = h & (t.length - 1); |
| 429 |
> |
for (ExceptionNode e = t[i]; ; e = e.next) { |
| 430 |
> |
if (e == null) { |
| 431 |
> |
t[i] = new ExceptionNode(this, ex, t[i]); |
| 432 |
> |
break; |
| 433 |
> |
} |
| 434 |
> |
if (e.get() == this) // already present |
| 435 |
> |
break; |
| 436 |
|
} |
| 437 |
< |
if (e.get() == this) // already present |
| 438 |
< |
break; |
| 437 |
> |
} finally { |
| 438 |
> |
lock.unlock(); |
| 439 |
|
} |
| 440 |
< |
} finally { |
| 436 |
< |
lock.unlock(); |
| 440 |
> |
s = setCompletion(EXCEPTIONAL); |
| 441 |
|
} |
| 442 |
< |
return setCompletion(EXCEPTIONAL); |
| 442 |
> |
return s; |
| 443 |
> |
} |
| 444 |
> |
|
| 445 |
> |
/** |
| 446 |
> |
* Records exception and possibly propagates |
| 447 |
> |
* |
| 448 |
> |
* @return status on exit |
| 449 |
> |
*/ |
| 450 |
> |
private int setExceptionalCompletion(Throwable ex) { |
| 451 |
> |
int s = recordExceptionalCompletion(ex); |
| 452 |
> |
if ((s & DONE_MASK) == EXCEPTIONAL) |
| 453 |
> |
internalPropagateException(ex); |
| 454 |
> |
return s; |
| 455 |
> |
} |
| 456 |
> |
|
| 457 |
> |
/** |
| 458 |
> |
* Hook for exception propagation support for tasks with completers. |
| 459 |
> |
*/ |
| 460 |
> |
void internalPropagateException(Throwable ex) { |
| 461 |
|
} |
| 462 |
|
|
| 463 |
|
/** |
| 539 |
|
Throwable ex; |
| 540 |
|
if (e == null || (ex = e.ex) == null) |
| 541 |
|
return null; |
| 542 |
< |
if (e.thrower != Thread.currentThread().getId()) { |
| 542 |
> |
if (false && e.thrower != Thread.currentThread().getId()) { |
| 543 |
|
Class<? extends Throwable> ec = ex.getClass(); |
| 544 |
|
try { |
| 545 |
|
Constructor<?> noArgCtor = null; |
| 929 |
|
} |
| 930 |
|
|
| 931 |
|
/** |
| 932 |
+ |
* Completes this task normally without setting a value. The most |
| 933 |
+ |
* recent value established by {@link #setRawResult} (or {@code |
| 934 |
+ |
* null} by default) will be returned as the result of subsequent |
| 935 |
+ |
* invocations of {@code join} and related operations. |
| 936 |
+ |
* |
| 937 |
+ |
* @since 1.8 |
| 938 |
+ |
*/ |
| 939 |
+ |
public final void quietlyComplete() { |
| 940 |
+ |
setCompletion(NORMAL); |
| 941 |
+ |
} |
| 942 |
+ |
|
| 943 |
+ |
/** |
| 944 |
|
* Waits if necessary for the computation to complete, and then |
| 945 |
|
* retrieves its result. |
| 946 |
|
* |
| 1259 |
|
protected abstract void setRawResult(V value); |
| 1260 |
|
|
| 1261 |
|
/** |
| 1262 |
< |
* Immediately performs the base action of this task. This method |
| 1263 |
< |
* is designed to support extensions, and should not in general be |
| 1264 |
< |
* called otherwise. The return value controls whether this task |
| 1265 |
< |
* is considered to be done normally. It may return false in |
| 1262 |
> |
* Immediately performs the base action of this task and returns |
| 1263 |
> |
* true if, upon return from this method, this task is guaranteed |
| 1264 |
> |
* to have completed normally. This method may return false |
| 1265 |
> |
* otherwise, to indicate that this task is not necessarily |
| 1266 |
> |
* complete (or is not known to be complete), for example in |
| 1267 |
|
* asynchronous actions that require explicit invocations of |
| 1268 |
< |
* {@link #complete} to become joinable. It may also throw an |
| 1269 |
< |
* (unchecked) exception to indicate abnormal exit. |
| 1268 |
> |
* completion methods. This method may also throw an (unchecked) |
| 1269 |
> |
* exception to indicate abnormal exit. This method is designed to |
| 1270 |
> |
* support extensions, and should not in general be called |
| 1271 |
> |
* otherwise. |
| 1272 |
|
* |
| 1273 |
< |
* @return {@code true} if completed normally |
| 1273 |
> |
* @return {@code true} if this task is known to have completed normally |
| 1274 |
|
*/ |
| 1275 |
|
protected abstract boolean exec(); |
| 1276 |
|
|
| 1339 |
|
return wt.pool.nextTaskFor(wt.workQueue); |
| 1340 |
|
} |
| 1341 |
|
|
| 1342 |
< |
// Mark-bit operations |
| 1342 |
> |
// tag operations |
| 1343 |
|
|
| 1344 |
|
/** |
| 1345 |
< |
* Returns true if this task is marked. |
| 1345 |
> |
* Returns the tag for this task. |
| 1346 |
|
* |
| 1347 |
< |
* @return true if this task is marked |
| 1347 |
> |
* @return the tag for this task |
| 1348 |
|
* @since 1.8 |
| 1349 |
|
*/ |
| 1350 |
< |
public final boolean isMarkedForkJoinTask() { |
| 1351 |
< |
return (status & MARKED) != 0; |
| 1350 |
> |
public final short getForkJoinTaskTag() { |
| 1351 |
> |
return (short)status; |
| 1352 |
|
} |
| 1353 |
|
|
| 1354 |
|
/** |
| 1355 |
< |
* Atomically sets the mark on this task. |
| 1355 |
> |
* Atomically sets the tag value for this task. |
| 1356 |
|
* |
| 1357 |
< |
* @return true if this task was previously unmarked |
| 1357 |
> |
* @param tag the tag value |
| 1358 |
> |
* @return the previous value of the tag |
| 1359 |
|
* @since 1.8 |
| 1360 |
|
*/ |
| 1361 |
< |
public final boolean markForkJoinTask() { |
| 1361 |
> |
public final short setForkJoinTaskTag(short tag) { |
| 1362 |
|
for (int s;;) { |
| 1363 |
< |
if (((s = status) & MARKED) != 0) |
| 1364 |
< |
return false; |
| 1365 |
< |
if (U.compareAndSwapInt(this, STATUS, s, s | MARKED)) |
| 1328 |
< |
return true; |
| 1363 |
> |
if (U.compareAndSwapInt(this, STATUS, s = status, |
| 1364 |
> |
(s & ~SMASK) | (tag & SMASK))) |
| 1365 |
> |
return (short)s; |
| 1366 |
|
} |
| 1367 |
|
} |
| 1368 |
|
|
| 1369 |
|
/** |
| 1370 |
< |
* Atomically clears the mark on this task. |
| 1370 |
> |
* Atomically conditionally sets the tag value for this task. |
| 1371 |
> |
* Among other applications, tags can be used as visit markers |
| 1372 |
> |
* in tasks operating on graphs, as in methods that check: {@code |
| 1373 |
> |
* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))} |
| 1374 |
> |
* before processing, otherwise exiting because the node has |
| 1375 |
> |
* already been visited. |
| 1376 |
|
* |
| 1377 |
< |
* @return true if this task was previously marked |
| 1377 |
> |
* @param e the expected tag value |
| 1378 |
> |
* @param tag the new tag value |
| 1379 |
> |
* @return true if successful; i.e., the current value was |
| 1380 |
> |
* equal to e and is now tag. |
| 1381 |
|
* @since 1.8 |
| 1382 |
|
*/ |
| 1383 |
< |
public final boolean unmarkForkJoinTask() { |
| 1383 |
> |
public final boolean compareAndSetForkJoinTaskTag(short e, short tag) { |
| 1384 |
|
for (int s;;) { |
| 1385 |
< |
if (((s = status) & MARKED) == 0) |
| 1385 |
> |
if ((short)(s = status) != e) |
| 1386 |
|
return false; |
| 1387 |
< |
if (U.compareAndSwapInt(this, STATUS, s, s & ~MARKED)) |
| 1387 |
> |
if (U.compareAndSwapInt(this, STATUS, s, |
| 1388 |
> |
(s & ~SMASK) | (tag & SMASK))) |
| 1389 |
|
return true; |
| 1390 |
|
} |
| 1391 |
|
} |
