| 5 |
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*/ |
| 6 |
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|
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package jsr166e; |
| 8 |
– |
|
| 8 |
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/** |
| 9 |
< |
* A resultless {@link ForkJoinTask} with a completion action |
| 9 |
> |
* A {@link ForkJoinTask} with a completion action |
| 10 |
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* performed when triggered and there are no remaining pending |
| 11 |
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* actions. Uses of CountedCompleter are similar to those of other |
| 12 |
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* completion based components (such as {@link |
| 21 |
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* decremented; otherwise, the completion action is performed, and if |
| 22 |
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* this completer itself has a completer, the process is continued |
| 23 |
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* with its completer. As is the case with related synchronization |
| 24 |
< |
* components such as {@link Phaser} and {@link |
| 25 |
< |
* java.util.concurrent.Semaphore} these methods affect only internal |
| 26 |
< |
* counts; they do not establish any further internal bookkeeping. In |
| 27 |
< |
* particular, the identities of pending tasks are not maintained. As |
| 28 |
< |
* illustrated below, you can create subclasses that do record some or |
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< |
* all pended tasks or their results when needed. |
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> |
* components such as {@link java.util.concurrent.Phaser Phaser} and |
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> |
* {@link java.util.concurrent.Semaphore Semaphore}, these methods |
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> |
* affect only internal counts; they do not establish any further |
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> |
* internal bookkeeping. In particular, the identities of pending |
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> |
* tasks are not maintained. As illustrated below, you can create |
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> |
* subclasses that do record some or all pending tasks or their |
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> |
* results when needed. |
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* |
| 32 |
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* <p>A concrete CountedCompleter class must define method {@link |
| 33 |
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* #compute}, that should, in almost all use cases, invoke {@code |
| 36 |
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* normal completion, and method {@link #onExceptionalCompletion} to |
| 37 |
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* perform an action upon any exception. |
| 38 |
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* |
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+ |
* <p>CountedCompleters most often do not bear results, in which case |
| 40 |
+ |
* they are normally declared as {@code CountedCompleter<Void>}, and |
| 41 |
+ |
* will always return {@code null} as a result value. In other cases, |
| 42 |
+ |
* you should override method {@link #getRawResult} to provide a |
| 43 |
+ |
* result from {@code join(), invoke()}, and related methods. (Method |
| 44 |
+ |
* {@link #setRawResult} by default plays no role in CountedCompleters |
| 45 |
+ |
* but may be overridden for example to maintain fields holding result |
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+ |
* data.) |
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+ |
* |
| 48 |
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* <p>A CountedCompleter that does not itself have a completer (i.e., |
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* one for which {@link #getCompleter} returns {@code null}) can be |
| 50 |
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* used as a regular ForkJoinTask with this added functionality. |
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* <p><b>Parallel recursive decomposition.</b> CountedCompleters may |
| 65 |
|
* be arranged in trees similar to those often used with {@link |
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|
* RecursiveAction}s, although the constructions involved in setting |
| 67 |
< |
* them up typically vary. Even though they entail a bit more |
| 67 |
> |
* them up typically vary. Here, the completer of each task is its |
| 68 |
> |
* parent in the computation tree. Even though they entail a bit more |
| 69 |
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* bookkeeping, CountedCompleters may be better choices when applying |
| 70 |
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* a possibly time-consuming operation (that cannot be further |
| 71 |
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* subdivided) to each element of an array or collection; especially |
| 90 |
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* <pre> {@code |
| 91 |
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* class MyOperation<E> { void apply(E e) { ... } } |
| 92 |
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* |
| 93 |
< |
* class ForEach<E> extends CountedCompleter { |
| 93 |
> |
* class ForEach<E> extends CountedCompleter<Void> { |
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* |
| 95 |
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* public static <E> void forEach(ForkJoinPool pool, E[] array, MyOperation<E> op) { |
| 96 |
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* pool.invoke(new ForEach<E>(null, array, op, 0, array.length)); |
| 97 |
|
* } |
| 98 |
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* |
| 99 |
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* final E[] array; final MyOperation<E> op; final int lo, hi; |
| 100 |
< |
* ForEach(CountedCompleter p, E[] array, MyOperation<E> op, int lo, int hi) { |
| 100 |
> |
* ForEach(CountedCompleter<?> p, E[] array, MyOperation<E> op, int lo, int hi) { |
| 101 |
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* super(p); |
| 102 |
|
* this.array = array; this.op = op; this.lo = lo; this.hi = hi; |
| 103 |
|
* } |
| 141 |
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* |
| 142 |
|
* As a further improvement, notice that the left task need not even |
| 143 |
|
* exist. Instead of creating a new one, we can iterate using the |
| 144 |
< |
* original task, and add a pending count for each fork: |
| 144 |
> |
* original task, and add a pending count for each fork. Additionally, |
| 145 |
> |
* this version uses {@code helpComplete} to streamline assistance in |
| 146 |
> |
* the execution of forked tasks. |
| 147 |
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* |
| 148 |
|
* <pre> {@code |
| 149 |
|
* class ForEach<E> ... |
| 157 |
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* } |
| 158 |
|
* if (h > l) |
| 159 |
|
* op.apply(array[l]); |
| 160 |
< |
* tryComplete(); |
| 160 |
> |
* helpComplete(); |
| 161 |
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* } |
| 162 |
|
* }</pre> |
| 163 |
|
* |
| 174 |
|
* and reductions are all of type {@code E}), one way to do this in |
| 175 |
|
* divide and conquer designs is to have each subtask record its |
| 176 |
|
* sibling, so that it can be accessed in method {@code onCompletion}. |
| 177 |
< |
* For clarity, this class uses explicit left and right subtasks, but |
| 178 |
< |
* variants of other streamlinings seen in the above example may also |
| 179 |
< |
* apply. |
| 177 |
> |
* This technique applies to reductions in which the order of |
| 178 |
> |
* combining left and right results does not matter; ordered |
| 179 |
> |
* reductions require explicit left/right designations. Variants of |
| 180 |
> |
* other streamlinings seen in the above examples may also apply. |
| 181 |
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* |
| 182 |
|
* <pre> {@code |
| 183 |
|
* class MyMapper<E> { E apply(E v) { ... } } |
| 184 |
|
* class MyReducer<E> { E apply(E x, E y) { ... } } |
| 185 |
< |
* class MapReducer<E> extends CountedCompleter { |
| 185 |
> |
* class MapReducer<E> extends CountedCompleter<E> { |
| 186 |
|
* final E[] array; final MyMapper<E> mapper; |
| 187 |
|
* final MyReducer<E> reducer; final int lo, hi; |
| 188 |
< |
* MapReducer sibling; |
| 188 |
> |
* MapReducer<E> sibling; |
| 189 |
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* E result; |
| 190 |
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* MapReducer(CountedCompleter p, E[] array, MyMapper<E> mapper, |
| 191 |
|
* MyReducer<E> reducer, int lo, int hi) { |
| 220 |
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* result = reducer.apply(child.result, sib.result); |
| 221 |
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* } |
| 222 |
|
* } |
| 223 |
+ |
* public E getRawResult() { return result; } |
| 224 |
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* |
| 225 |
|
* public static <E> E mapReduce(ForkJoinPool pool, E[] array, |
| 226 |
|
* MyMapper<E> mapper, MyReducer<E> reducer) { |
| 227 |
< |
* MapReducer<E> mr = new MapReducer<E>(null, array, mapper, |
| 228 |
< |
* reducer, 0, array.length); |
| 215 |
< |
* pool.invoke(mr); |
| 216 |
< |
* return mr.result; |
| 227 |
> |
* return pool.invoke(new MapReducer<E>(null, array, mapper, |
| 228 |
> |
* reducer, 0, array.length)); |
| 229 |
|
* } |
| 230 |
|
* } }</pre> |
| 231 |
|
* |
| 235 |
|
* triggers another async task. For example: |
| 236 |
|
* |
| 237 |
|
* <pre> {@code |
| 238 |
< |
* class HeaderBuilder extends CountedCompleter { ... } |
| 239 |
< |
* class BodyBuilder extends CountedCompleter { ... } |
| 240 |
< |
* class PacketSender extends CountedCompleter { |
| 238 |
> |
* class HeaderBuilder extends CountedCompleter<...> { ... } |
| 239 |
> |
* class BodyBuilder extends CountedCompleter<...> { ... } |
| 240 |
> |
* class PacketSender extends CountedCompleter<...> { |
| 241 |
|
* PacketSender(...) { super(null, 1); ... } // trigger on second completion |
| 242 |
|
* public void compute() { } // never called |
| 243 |
< |
* public void onCompletion(CountedCompleter caller) { sendPacket(); } |
| 243 |
> |
* public void onCompletion(CountedCompleter<?> caller) { sendPacket(); } |
| 244 |
|
* } |
| 245 |
|
* // sample use: |
| 246 |
|
* PacketSender p = new PacketSender(); |
| 251 |
|
* @since 1.8 |
| 252 |
|
* @author Doug Lea |
| 253 |
|
*/ |
| 254 |
< |
public abstract class CountedCompleter extends ForkJoinTask<Void> { |
| 254 |
> |
public abstract class CountedCompleter<T> extends ForkJoinTask<T> { |
| 255 |
|
private static final long serialVersionUID = 5232453752276485070L; |
| 256 |
|
|
| 257 |
|
/** This task's completer, or null if none */ |
| 258 |
< |
final CountedCompleter completer; |
| 258 |
> |
final CountedCompleter<?> completer; |
| 259 |
|
/** The number of pending tasks until completion */ |
| 260 |
|
volatile int pending; |
| 261 |
|
|
| 266 |
|
* @param completer this tasks completer, or {@code null} if none |
| 267 |
|
* @param initialPendingCount the initial pending count |
| 268 |
|
*/ |
| 269 |
< |
protected CountedCompleter(CountedCompleter completer, |
| 269 |
> |
protected CountedCompleter(CountedCompleter<?> completer, |
| 270 |
|
int initialPendingCount) { |
| 271 |
|
this.completer = completer; |
| 272 |
|
this.pending = initialPendingCount; |
| 278 |
|
* |
| 279 |
|
* @param completer this tasks completer, or {@code null} if none |
| 280 |
|
*/ |
| 281 |
< |
protected CountedCompleter(CountedCompleter completer) { |
| 281 |
> |
protected CountedCompleter(CountedCompleter<?> completer) { |
| 282 |
|
this.completer = completer; |
| 283 |
|
} |
| 284 |
|
|
| 304 |
|
* @param caller the task invoking this method (which may |
| 305 |
|
* be this task itself). |
| 306 |
|
*/ |
| 307 |
< |
public void onCompletion(CountedCompleter caller) { |
| 307 |
> |
public void onCompletion(CountedCompleter<?> caller) { |
| 308 |
|
} |
| 309 |
|
|
| 310 |
|
/** |
| 324 |
|
* @return true if this exception should be propagated to this |
| 325 |
|
* tasks completer, if one exists. |
| 326 |
|
*/ |
| 327 |
< |
public boolean onExceptionalCompletion(Throwable ex, CountedCompleter caller) { |
| 327 |
> |
public boolean onExceptionalCompletion(Throwable ex, CountedCompleter<?> caller) { |
| 328 |
|
return true; |
| 329 |
|
} |
| 330 |
|
|
| 334 |
|
* |
| 335 |
|
* @return the completer |
| 336 |
|
*/ |
| 337 |
< |
public final CountedCompleter getCompleter() { |
| 337 |
> |
public final CountedCompleter<?> getCompleter() { |
| 338 |
|
return completer; |
| 339 |
|
} |
| 340 |
|
|
| 379 |
|
} |
| 380 |
|
|
| 381 |
|
/** |
| 382 |
+ |
* Returns the root of the current computation; i.e., this |
| 383 |
+ |
* task if it has no completer, else its completer's root. |
| 384 |
+ |
* |
| 385 |
+ |
* @return the root of the current computation |
| 386 |
+ |
*/ |
| 387 |
+ |
public final CountedCompleter<?> getRoot() { |
| 388 |
+ |
CountedCompleter<?> a = this, p; |
| 389 |
+ |
while ((p = a.completer) != null) |
| 390 |
+ |
a = p; |
| 391 |
+ |
return a; |
| 392 |
+ |
} |
| 393 |
+ |
|
| 394 |
+ |
/** |
| 395 |
|
* If the pending count is nonzero, decrements the count; |
| 396 |
|
* otherwise invokes {@link #onCompletion} and then similarly |
| 397 |
|
* tries to complete this task's completer, if one exists, |
| 398 |
|
* else marks this task as complete. |
| 399 |
|
*/ |
| 400 |
|
public final void tryComplete() { |
| 401 |
< |
CountedCompleter a = this, s = a; |
| 401 |
> |
CountedCompleter<?> a = this, s = a; |
| 402 |
|
for (int c;;) { |
| 403 |
|
if ((c = a.pending) == 0) { |
| 404 |
|
a.onCompletion(s); |
| 413 |
|
} |
| 414 |
|
|
| 415 |
|
/** |
| 416 |
+ |
* Identical to {@link #tryComplete}, but may additionally execute |
| 417 |
+ |
* other tasks within the current computation (i.e., those |
| 418 |
+ |
* with the same {@link #getRoot}. |
| 419 |
+ |
*/ |
| 420 |
+ |
public final void helpComplete() { |
| 421 |
+ |
CountedCompleter<?> a = this, s = a; |
| 422 |
+ |
for (int c;;) { |
| 423 |
+ |
if ((c = a.pending) == 0) { |
| 424 |
+ |
a.onCompletion(s); |
| 425 |
+ |
if ((a = (s = a).completer) == null) { |
| 426 |
+ |
s.quietlyComplete(); |
| 427 |
+ |
return; |
| 428 |
+ |
} |
| 429 |
+ |
} |
| 430 |
+ |
else if (U.compareAndSwapInt(a, PENDING, c, c - 1)) { |
| 431 |
+ |
CountedCompleter<?> root = a.getRoot(); |
| 432 |
+ |
Thread thread = Thread.currentThread(); |
| 433 |
+ |
ForkJoinPool.WorkQueue wq = |
| 434 |
+ |
(thread instanceof ForkJoinWorkerThread)? |
| 435 |
+ |
((ForkJoinWorkerThread)thread).workQueue : null; |
| 436 |
+ |
ForkJoinTask<?> t; |
| 437 |
+ |
while ((t = (wq != null) ? wq.popCC(root) : |
| 438 |
+ |
ForkJoinPool.popCCFromCommonPool(root)) != null) { |
| 439 |
+ |
t.doExec(); |
| 440 |
+ |
if (root.isDone()) |
| 441 |
+ |
break; |
| 442 |
+ |
} |
| 443 |
+ |
return; |
| 444 |
+ |
} |
| 445 |
+ |
} |
| 446 |
+ |
} |
| 447 |
+ |
|
| 448 |
+ |
/** |
| 449 |
|
* Regardless of pending count, invokes {@link #onCompletion}, |
| 450 |
< |
* marks this task as complete with a {@code null} return value, |
| 451 |
< |
* and further triggers {@link #tryComplete} on this task's |
| 452 |
< |
* completer, if one exists. This method may be useful when |
| 453 |
< |
* forcing completion as soon as any one (versus all) of several |
| 454 |
< |
* subtask results are obtained. |
| 450 |
> |
* marks this task as complete and further triggers {@link |
| 451 |
> |
* #tryComplete} on this task's completer, if one exists. This |
| 452 |
> |
* method may be useful when forcing completion as soon as any one |
| 453 |
> |
* (versus all) of several subtask results are obtained. The |
| 454 |
> |
* given rawResult is used as an argument to {@link #setRawResult} |
| 455 |
> |
* before marking this task as complete; its value is meaningful |
| 456 |
> |
* only for classes overriding {@code setRawResult}. |
| 457 |
|
* |
| 458 |
< |
* @param mustBeNull the {@code null} completion value |
| 458 |
> |
* @param rawResult the raw result |
| 459 |
|
*/ |
| 460 |
< |
public void complete(Void mustBeNull) { |
| 461 |
< |
CountedCompleter p; |
| 460 |
> |
public void complete(T rawResult) { |
| 461 |
> |
CountedCompleter<?> p; |
| 462 |
|
onCompletion(this); |
| 463 |
+ |
setRawResult(rawResult); |
| 464 |
|
quietlyComplete(); |
| 465 |
|
if ((p = completer) != null) |
| 466 |
|
p.tryComplete(); |
| 470 |
|
* Support for FJT exception propagation |
| 471 |
|
*/ |
| 472 |
|
void internalPropagateException(Throwable ex) { |
| 473 |
< |
CountedCompleter a = this, s = a; |
| 473 |
> |
CountedCompleter<?> a = this, s = a; |
| 474 |
|
while (a.onExceptionalCompletion(ex, s) && |
| 475 |
|
(a = (s = a).completer) != null && a.status >= 0) |
| 476 |
|
a.recordExceptionalCompletion(ex); |
| 485 |
|
} |
| 486 |
|
|
| 487 |
|
/** |
| 488 |
< |
* Always returns {@code null}. |
| 488 |
> |
* Returns the result of the computation. By default |
| 489 |
> |
* returns {@code null}, which is appropriate for {@code Void} |
| 490 |
> |
* actions, but in other cases should be overridden. |
| 491 |
|
* |
| 492 |
< |
* @return {@code null} always |
| 492 |
> |
* @return the result of the computation |
| 493 |
|
*/ |
| 494 |
< |
public final Void getRawResult() { return null; } |
| 494 |
> |
public T getRawResult() { return null; } |
| 495 |
|
|
| 496 |
|
/** |
| 497 |
< |
* Requires null completion value. |
| 497 |
> |
* A method that result-bearing CountedCompleters may optionally |
| 498 |
> |
* use to help maintain result data. By default, does nothing. |
| 499 |
|
*/ |
| 500 |
< |
protected final void setRawResult(Void mustBeNull) { } |
| 500 |
> |
protected void setRawResult(T t) { } |
| 501 |
|
|
| 502 |
|
// Unsafe mechanics |
| 503 |
|
private static final sun.misc.Unsafe U; |
| 512 |
|
} |
| 513 |
|
} |
| 514 |
|
|
| 451 |
– |
|
| 515 |
|
/** |
| 516 |
|
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
| 517 |
|
* Replace with a simple call to Unsafe.getUnsafe when integrating |
