| 15 |
|
* CountedCompleter are similar to those of other completion based |
| 16 |
|
* components (such as {@link java.nio.channels.CompletionHandler}) |
| 17 |
|
* except that multiple <em>pending</em> completions may be necessary |
| 18 |
< |
* to trigger the {@link #onCompletion} action, not just one. Unless |
| 19 |
< |
* initialized otherwise, the {@link #getPendingCount pending count} |
| 20 |
< |
* starts at zero, but may be (atomically) changed using methods |
| 21 |
< |
* {@link #setPendingCount}, {@link #addToPendingCount}, and {@link |
| 22 |
< |
* #compareAndSetPendingCount}. Upon invocation of {@link |
| 18 |
> |
* to trigger the completion action {@link #onCompletion}, not just one. |
| 19 |
> |
* Unless initialized otherwise, the {@linkplain #getPendingCount pending |
| 20 |
> |
* count} starts at zero, but may be (atomically) changed using |
| 21 |
> |
* methods {@link #setPendingCount}, {@link #addToPendingCount}, and |
| 22 |
> |
* {@link #compareAndSetPendingCount}. Upon invocation of {@link |
| 23 |
|
* #tryComplete}, if the pending action count is nonzero, it is |
| 24 |
|
* decremented; otherwise, the completion action is performed, and if |
| 25 |
|
* this completer itself has a completer, the process is continued |
| 126 |
|
* op.apply(array[lo]); |
| 127 |
|
* tryComplete(); |
| 128 |
|
* } |
| 129 |
< |
* } }</pre> |
| 129 |
> |
* }}</pre> |
| 130 |
|
* |
| 131 |
|
* This design can be improved by noticing that in the recursive case, |
| 132 |
|
* the task has nothing to do after forking its right task, so can |
| 133 |
|
* directly invoke its left task before returning. (This is an analog |
| 134 |
|
* of tail recursion removal.) Also, because the task returns upon |
| 135 |
|
* executing its left task (rather than falling through to invoke |
| 136 |
< |
* tryComplete) the pending count is set to one: |
| 136 |
> |
* {@code tryComplete}) the pending count is set to one: |
| 137 |
|
* |
| 138 |
|
* <pre> {@code |
| 139 |
|
* class ForEach<E> ... |
| 183 |
|
* |
| 184 |
|
* <p><b>Searching.</b> A tree of CountedCompleters can search for a |
| 185 |
|
* value or property in different parts of a data structure, and |
| 186 |
< |
* report a result in an {@link java.util.concurrent.AtomicReference} |
| 187 |
< |
* as soon as one is found. The others can poll the result to avoid |
| 188 |
< |
* unnecessary work. (You could additionally {@link #cancel} other |
| 189 |
< |
* tasks, but it is usually simpler and more efficient to just let |
| 190 |
< |
* them notice that the result is set and if so skip further |
| 191 |
< |
* processing.) Illustrating again with an array using full |
| 186 |
> |
* report a result in an {@link |
| 187 |
> |
* java.util.concurrent.atomic.AtomicReference AtomicReference} as |
| 188 |
> |
* soon as one is found. The others can poll the result to avoid |
| 189 |
> |
* unnecessary work. (You could additionally {@linkplain #cancel |
| 190 |
> |
* cancel} other tasks, but it is usually simpler and more efficient |
| 191 |
> |
* to just let them notice that the result is set and if so skip |
| 192 |
> |
* further processing.) Illustrating again with an array using full |
| 193 |
|
* partitioning (again, in practice, leaf tasks will almost always |
| 194 |
|
* process more than one element): |
| 195 |
|
* |
| 278 |
|
* } |
| 279 |
|
* public void onCompletion(CountedCompleter<?> caller) { |
| 280 |
|
* if (caller != this) { |
| 281 |
< |
* MapReducer<E> child = (MapReducer<E>)caller; |
| 282 |
< |
* MapReducer<E> sib = child.sibling; |
| 283 |
< |
* if (sib == null || sib.result == null) |
| 284 |
< |
* result = child.result; |
| 285 |
< |
* else |
| 286 |
< |
* result = reducer.apply(child.result, sib.result); |
| 281 |
> |
* MapReducer<E> child = (MapReducer<E>)caller; |
| 282 |
> |
* MapReducer<E> sib = child.sibling; |
| 283 |
> |
* if (sib == null || sib.result == null) |
| 284 |
> |
* result = child.result; |
| 285 |
> |
* else |
| 286 |
> |
* result = reducer.apply(child.result, sib.result); |
| 287 |
|
* } |
| 288 |
|
* } |
| 289 |
|
* public E getRawResult() { return result; } |
| 292 |
|
* return new MapReducer<E>(null, array, mapper, reducer, |
| 293 |
|
* 0, array.length).invoke(); |
| 294 |
|
* } |
| 295 |
< |
* } }</pre> |
| 295 |
> |
* }}</pre> |
| 296 |
|
* |
| 297 |
|
* Here, method {@code onCompletion} takes a form common to many |
| 298 |
|
* completion designs that combine results. This callback-style method |
| 304 |
|
* distinguishes cases. Most often, when the caller is {@code this}, |
| 305 |
|
* no action is necessary. Otherwise the caller argument can be used |
| 306 |
|
* (usually via a cast) to supply a value (and/or links to other |
| 307 |
< |
* values) to be combined. Asuuming proper use of pending counts, the |
| 307 |
> |
* values) to be combined. Assuming proper use of pending counts, the |
| 308 |
|
* actions inside {@code onCompletion} occur (once) upon completion of |
| 309 |
|
* a task and its subtasks. No additional synchronization is required |
| 310 |
|
* within this method to ensure thread safety of accesses to fields of |
| 389 |
|
* Creates a new CountedCompleter with the given completer |
| 390 |
|
* and initial pending count. |
| 391 |
|
* |
| 392 |
< |
* @param completer this tasks completer, or {@code null} if none |
| 392 |
> |
* @param completer this task's completer, or {@code null} if none |
| 393 |
|
* @param initialPendingCount the initial pending count |
| 394 |
|
*/ |
| 395 |
|
protected CountedCompleter(CountedCompleter<?> completer, |
| 402 |
|
* Creates a new CountedCompleter with the given completer |
| 403 |
|
* and an initial pending count of zero. |
| 404 |
|
* |
| 405 |
< |
* @param completer this tasks completer, or {@code null} if none |
| 405 |
> |
* @param completer this task's completer, or {@code null} if none |
| 406 |
|
*/ |
| 407 |
|
protected CountedCompleter(CountedCompleter<?> completer) { |
| 408 |
|
this.completer = completer; |
| 423 |
|
|
| 424 |
|
/** |
| 425 |
|
* Performs an action when method {@link #tryComplete} is invoked |
| 426 |
< |
* and there are no pending counts, or when the unconditional |
| 426 |
> |
* and the pending count is zero, or when the unconditional |
| 427 |
|
* method {@link #complete} is invoked. By default, this method |
| 428 |
|
* does nothing. You can distinguish cases by checking the |
| 429 |
|
* identity of the given caller argument. If not equal to {@code |
| 451 |
|
* @param caller the task invoking this method (which may |
| 452 |
|
* be this task itself). |
| 453 |
|
* @return true if this exception should be propagated to this |
| 454 |
< |
* tasks completer, if one exists. |
| 454 |
> |
* task's completer, if one exists. |
| 455 |
|
*/ |
| 456 |
|
public boolean onExceptionalCompletion(Throwable ex, CountedCompleter<?> caller) { |
| 457 |
|
return true; |
| 627 |
|
* this task's pending count is non-zero, decrements its pending |
| 628 |
|
* count and returns {@code null}. Otherwise, returns the |
| 629 |
|
* completer. This method can be used as part of a completion |
| 630 |
< |
* traversal loop for homogenous task hierarchies: |
| 630 |
> |
* traversal loop for homogeneous task hierarchies: |
| 631 |
|
* |
| 632 |
|
* <pre> {@code |
| 633 |
|
* for (CountedCompleter<?> c = firstComplete(); |
| 662 |
|
} |
| 663 |
|
|
| 664 |
|
/** |
| 665 |
< |
* Support for FJT exception propagation |
| 665 |
> |
* Supports ForkJoinTask exception propagation. |
| 666 |
|
*/ |
| 667 |
|
void internalPropagateException(Throwable ex) { |
| 668 |
|
CountedCompleter<?> a = this, s = a; |
| 672 |
|
} |
| 673 |
|
|
| 674 |
|
/** |
| 675 |
< |
* Implements execution conventions for CountedCompleters |
| 675 |
> |
* Implements execution conventions for CountedCompleters. |
| 676 |
|
*/ |
| 677 |
|
protected final boolean exec() { |
| 678 |
|
compute(); |
