| 8 |
|
|
| 9 |
|
/** |
| 10 |
|
* A {@link ForkJoinTask} with a completion action performed when |
| 11 |
< |
* triggered and there are no remaining pending |
| 12 |
< |
* actions. CountedCompleters are in general more robust in the |
| 11 |
> |
* triggered and there are no remaining pending actions. |
| 12 |
> |
* CountedCompleters are in general more robust in the |
| 13 |
|
* presence of subtask stalls and blockage than are other forms of |
| 14 |
|
* ForkJoinTasks, but are less intuitive to program. Uses of |
| 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(CountedCompleter)}, |
| 19 |
> |
* not just one. |
| 20 |
> |
* Unless initialized otherwise, the {@linkplain #getPendingCount pending |
| 21 |
> |
* count} starts at zero, but may be (atomically) changed using |
| 22 |
> |
* methods {@link #setPendingCount}, {@link #addToPendingCount}, and |
| 23 |
> |
* {@link #compareAndSetPendingCount}. Upon invocation of {@link |
| 24 |
|
* #tryComplete}, if the pending action count is nonzero, it is |
| 25 |
|
* decremented; otherwise, the completion action is performed, and if |
| 26 |
|
* this completer itself has a completer, the process is continued |
| 41 |
|
* <p>A concrete CountedCompleter class must define method {@link |
| 42 |
|
* #compute}, that should in most cases (as illustrated below), invoke |
| 43 |
|
* {@code tryComplete()} once before returning. The class may also |
| 44 |
< |
* optionally override method {@link #onCompletion} to perform an |
| 45 |
< |
* action upon normal completion, and method {@link |
| 46 |
< |
* #onExceptionalCompletion} to perform an action upon any exception. |
| 44 |
> |
* optionally override method {@link #onCompletion(CountedCompleter)} |
| 45 |
> |
* to perform an action upon normal completion, and method |
| 46 |
> |
* {@link #onExceptionalCompletion(Throwable, CountedCompleter)} to |
| 47 |
> |
* perform an action upon any exception. |
| 48 |
|
* |
| 49 |
|
* <p>CountedCompleters most often do not bear results, in which case |
| 50 |
|
* they are normally declared as {@code CountedCompleter<Void>}, and |
| 65 |
|
* only as an internal helper for other computations, so its own task |
| 66 |
|
* status (as reported in methods such as {@link ForkJoinTask#isDone}) |
| 67 |
|
* is arbitrary; this status changes only upon explicit invocations of |
| 68 |
< |
* {@link #complete}, {@link ForkJoinTask#cancel}, {@link |
| 69 |
< |
* ForkJoinTask#completeExceptionally} or upon exceptional completion |
| 70 |
< |
* of method {@code compute}. Upon any exceptional completion, the |
| 71 |
< |
* exception may be relayed to a task's completer (and its completer, |
| 72 |
< |
* and so on), if one exists and it has not otherwise already |
| 73 |
< |
* completed. Similarly, cancelling an internal CountedCompleter has |
| 74 |
< |
* only a local effect on that completer, so is not often useful. |
| 68 |
> |
* {@link #complete}, {@link ForkJoinTask#cancel}, |
| 69 |
> |
* {@link ForkJoinTask#completeExceptionally(Throwable)} or upon |
| 70 |
> |
* exceptional completion of method {@code compute}. Upon any |
| 71 |
> |
* exceptional completion, the exception may be relayed to a task's |
| 72 |
> |
* completer (and its completer, and so on), if one exists and it has |
| 73 |
> |
* not otherwise already completed. Similarly, cancelling an internal |
| 74 |
> |
* CountedCompleter has only a local effect on that completer, so is |
| 75 |
> |
* not often useful. |
| 76 |
|
* |
| 77 |
|
* <p><b>Sample Usages.</b> |
| 78 |
|
* |
| 99 |
|
* improve load balancing. In the recursive case, the second of each |
| 100 |
|
* pair of subtasks to finish triggers completion of its parent |
| 101 |
|
* (because no result combination is performed, the default no-op |
| 102 |
< |
* implementation of method {@code onCompletion} is not overridden). A |
| 103 |
< |
* static utility method sets up the base task and invokes it |
| 102 |
> |
* implementation of method {@code onCompletion} is not overridden). |
| 103 |
> |
* A static utility method sets up the base task and invokes it |
| 104 |
|
* (here, implicitly using the {@link ForkJoinPool#commonPool()}). |
| 105 |
|
* |
| 106 |
|
* <pre> {@code |
| 155 |
|
* } |
| 156 |
|
* }</pre> |
| 157 |
|
* |
| 158 |
< |
* As a further improvement, notice that the left task need not even |
| 159 |
< |
* exist. Instead of creating a new one, we can iterate using the |
| 160 |
< |
* original task, and add a pending count for each fork. Additionally, |
| 161 |
< |
* because no task in this tree implements an {@link #onCompletion} |
| 162 |
< |
* method, {@code tryComplete()} can be replaced with {@link |
| 160 |
< |
* #propagateCompletion}. |
| 158 |
> |
* As a further improvement, notice that the left task need not even exist. |
| 159 |
> |
* Instead of creating a new one, we can iterate using the original task, |
| 160 |
> |
* and add a pending count for each fork. Additionally, because no task |
| 161 |
> |
* in this tree implements an {@link #onCompletion(CountedCompleter)} method, |
| 162 |
> |
* {@code tryComplete()} can be replaced with {@link #propagateCompletion}. |
| 163 |
|
* |
| 164 |
|
* <pre> {@code |
| 165 |
|
* class ForEach<E> ... |
| 237 |
|
* |
| 238 |
|
* <p><b>Recording subtasks.</b> CountedCompleter tasks that combine |
| 239 |
|
* results of multiple subtasks usually need to access these results |
| 240 |
< |
* in method {@link #onCompletion}. As illustrated in the following |
| 240 |
> |
* in method {@link #onCompletion(CountedCompleter)}. As illustrated in the following |
| 241 |
|
* class (that performs a simplified form of map-reduce where mappings |
| 242 |
|
* and reductions are all of type {@code E}), one way to do this in |
| 243 |
|
* divide and conquer designs is to have each subtask record its |
| 338 |
|
* while (h - l >= 2) { |
| 339 |
|
* int mid = (l + h) >>> 1; |
| 340 |
|
* addToPendingCount(1); |
| 341 |
< |
* (forks = new MapReducer(this, array, mapper, reducer, mid, h, forks)).fork; |
| 341 |
> |
* (forks = new MapReducer(this, array, mapper, reducer, mid, h, forks)).fork(); |
| 342 |
|
* h = mid; |
| 343 |
|
* } |
| 344 |
|
* if (h > l) |
| 359 |
|
* |
| 360 |
|
* <p><b>Triggers.</b> Some CountedCompleters are themselves never |
| 361 |
|
* forked, but instead serve as bits of plumbing in other designs; |
| 362 |
< |
* including those in which the completion of one of more async tasks |
| 362 |
> |
* including those in which the completion of one or more async tasks |
| 363 |
|
* triggers another async task. For example: |
| 364 |
|
* |
| 365 |
|
* <pre> {@code |
| 439 |
|
} |
| 440 |
|
|
| 441 |
|
/** |
| 442 |
< |
* Performs an action when method {@link #completeExceptionally} |
| 443 |
< |
* is invoked or method {@link #compute} throws an exception, and |
| 444 |
< |
* this task has not otherwise already completed normally. On |
| 445 |
< |
* entry to this method, this task {@link |
| 446 |
< |
* ForkJoinTask#isCompletedAbnormally}. The return value of this |
| 447 |
< |
* method controls further propagation: If {@code true} and this |
| 448 |
< |
* task has a completer, then this completer is also completed |
| 449 |
< |
* exceptionally. The default implementation of this method does |
| 450 |
< |
* nothing except return {@code true}. |
| 442 |
> |
* Performs an action when method {@link |
| 443 |
> |
* #completeExceptionally(Throwable)} is invoked or method {@link |
| 444 |
> |
* #compute} throws an exception, and this task has not already |
| 445 |
> |
* otherwise completed normally. On entry to this method, this task |
| 446 |
> |
* {@link ForkJoinTask#isCompletedAbnormally}. The return value |
| 447 |
> |
* of this method controls further propagation: If {@code true} |
| 448 |
> |
* and this task has a completer that has not completed, then that |
| 449 |
> |
* completer is also completed exceptionally, with the same |
| 450 |
> |
* exception as this completer. The default implementation of |
| 451 |
> |
* this method does nothing except return {@code true}. |
| 452 |
|
* |
| 453 |
|
* @param ex the exception |
| 454 |
|
* @param caller the task invoking this method (which may |
| 455 |
|
* be this task itself) |
| 456 |
< |
* @return true if this exception should be propagated to this |
| 456 |
> |
* @return {@code true} if this exception should be propagated to this |
| 457 |
|
* task's completer, if one exists |
| 458 |
|
*/ |
| 459 |
|
public boolean onExceptionalCompletion(Throwable ex, CountedCompleter<?> caller) { |
| 494 |
|
* @param delta the value to add |
| 495 |
|
*/ |
| 496 |
|
public final void addToPendingCount(int delta) { |
| 497 |
< |
int c; // note: can replace with intrinsic in jdk8 |
| 497 |
> |
int c; |
| 498 |
|
do {} while (!U.compareAndSwapInt(this, PENDING, c = pending, c+delta)); |
| 499 |
|
} |
| 500 |
|
|
| 504 |
|
* |
| 505 |
|
* @param expected the expected value |
| 506 |
|
* @param count the new value |
| 507 |
< |
* @return true if successful |
| 507 |
> |
* @return {@code true} if successful |
| 508 |
|
*/ |
| 509 |
|
public final boolean compareAndSetPendingCount(int expected, int count) { |
| 510 |
|
return U.compareAndSwapInt(this, PENDING, expected, count); |
| 538 |
|
|
| 539 |
|
/** |
| 540 |
|
* If the pending count is nonzero, decrements the count; |
| 541 |
< |
* otherwise invokes {@link #onCompletion} and then similarly |
| 542 |
< |
* tries to complete this task's completer, if one exists, |
| 543 |
< |
* else marks this task as complete. |
| 541 |
> |
* otherwise invokes {@link #onCompletion(CountedCompleter)} |
| 542 |
> |
* and then similarly tries to complete this task's completer, |
| 543 |
> |
* if one exists, else marks this task as complete. |
| 544 |
|
*/ |
| 545 |
|
public final void tryComplete() { |
| 546 |
|
CountedCompleter<?> a = this, s = a; |
| 559 |
|
|
| 560 |
|
/** |
| 561 |
|
* Equivalent to {@link #tryComplete} but does not invoke {@link |
| 562 |
< |
* #onCompletion} along the completion path: If the pending count |
| 563 |
< |
* is nonzero, decrements the count; otherwise, similarly tries to |
| 564 |
< |
* complete this task's completer, if one exists, else marks this |
| 565 |
< |
* task as complete. This method may be useful in cases where |
| 566 |
< |
* {@code onCompletion} should not, or need not, be invoked for |
| 567 |
< |
* each completer in a computation. |
| 562 |
> |
* #onCompletion(CountedCompleter)} along the completion path: |
| 563 |
> |
* If the pending count is nonzero, decrements the count; |
| 564 |
> |
* otherwise, similarly tries to complete this task's completer, if |
| 565 |
> |
* one exists, else marks this task as complete. This method may be |
| 566 |
> |
* useful in cases where {@code onCompletion} should not, or need |
| 567 |
> |
* not, be invoked for each completer in a computation. |
| 568 |
|
*/ |
| 569 |
|
public final void propagateCompletion() { |
| 570 |
|
CountedCompleter<?> a = this, s = a; |
| 581 |
|
} |
| 582 |
|
|
| 583 |
|
/** |
| 584 |
< |
* Regardless of pending count, invokes {@link #onCompletion}, |
| 585 |
< |
* marks this task as complete and further triggers {@link |
| 586 |
< |
* #tryComplete} on this task's completer, if one exists. The |
| 587 |
< |
* given rawResult is used as an argument to {@link #setRawResult} |
| 588 |
< |
* before invoking {@link #onCompletion} or marking this task as |
| 589 |
< |
* complete; its value is meaningful only for classes overriding |
| 590 |
< |
* {@code setRawResult}. |
| 584 |
> |
* Regardless of pending count, invokes |
| 585 |
> |
* {@link #onCompletion(CountedCompleter)}, marks this task as |
| 586 |
> |
* complete and further triggers {@link #tryComplete} on this |
| 587 |
> |
* task's completer, if one exists. The given rawResult is |
| 588 |
> |
* used as an argument to {@link #setRawResult} before invoking |
| 589 |
> |
* {@link #onCompletion(CountedCompleter)} or marking this task |
| 590 |
> |
* as complete; its value is meaningful only for classes |
| 591 |
> |
* overriding {@code setRawResult}. This method does not modify |
| 592 |
> |
* the pending count. |
| 593 |
|
* |
| 594 |
|
* <p>This method may be useful when forcing completion as soon as |
| 595 |
|
* any one (versus all) of several subtask results are obtained. |
| 629 |
|
/** |
| 630 |
|
* If this task does not have a completer, invokes {@link |
| 631 |
|
* ForkJoinTask#quietlyComplete} and returns {@code null}. Or, if |
| 632 |
< |
* this task's pending count is non-zero, decrements its pending |
| 633 |
< |
* count and returns {@code null}. Otherwise, returns the |
| 632 |
> |
* the completer's pending count is non-zero, decrements that |
| 633 |
> |
* pending count and returns {@code null}. Otherwise, returns the |
| 634 |
|
* completer. This method can be used as part of a completion |
| 635 |
|
* traversal loop for homogeneous task hierarchies: |
| 636 |
|
* |
| 672 |
|
void internalPropagateException(Throwable ex) { |
| 673 |
|
CountedCompleter<?> a = this, s = a; |
| 674 |
|
while (a.onExceptionalCompletion(ex, s) && |
| 675 |
< |
(a = (s = a).completer) != null && a.status >= 0) |
| 676 |
< |
a.recordExceptionalCompletion(ex); |
| 675 |
> |
(a = (s = a).completer) != null && a.status >= 0 && |
| 676 |
> |
a.recordExceptionalCompletion(ex) == EXCEPTIONAL) |
| 677 |
> |
; |
| 678 |
|
} |
| 679 |
|
|
| 680 |
|
/** |
