12 |
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import java.util.Collection; |
13 |
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import java.util.Collections; |
14 |
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import java.util.List; |
15 |
+ |
import java.util.RandomAccess; |
16 |
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import java.util.Map; |
17 |
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import java.util.WeakHashMap; |
18 |
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|
55 |
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* restriction is in part enforced by not permitting checked |
56 |
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* exceptions such as {@code IOExceptions} to be thrown. However, |
57 |
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* computations may still encounter unchecked exceptions, that are |
58 |
< |
* rethrown to callers attempting join them. These exceptions may |
58 |
> |
* rethrown to callers attempting to join them. These exceptions may |
59 |
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* additionally include RejectedExecutionExceptions stemming from |
60 |
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* internal resource exhaustion such as failure to allocate internal |
61 |
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* task queues. |
68 |
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* execute other tasks while awaiting joins, which is sometimes more |
69 |
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* efficient but only applies when all subtasks are known to be |
70 |
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* strictly tree-structured. Method {@link #invoke} is semantically |
71 |
< |
* equivalent to {@code fork(); join()} but always attempts to |
72 |
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* begin execution in the current thread. The "<em>quiet</em>" forms |
73 |
< |
* of these methods do not extract results or report exceptions. These |
71 |
> |
* equivalent to {@code fork(); join()} but always attempts to begin |
72 |
> |
* execution in the current thread. The "<em>quiet</em>" forms of |
73 |
> |
* these methods do not extract results or report exceptions. These |
74 |
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* may be useful when a set of tasks are being executed, and you need |
75 |
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* to delay processing of results or exceptions until all complete. |
76 |
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* Method {@code invokeAll} (available in multiple versions) |
77 |
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* performs the most common form of parallel invocation: forking a set |
78 |
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* of tasks and joining them all. |
79 |
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* |
80 |
+ |
* <p>The execution status of tasks may be queried at several levels |
81 |
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* of detail: {@link #isDone} is true if a task completed in any way |
82 |
+ |
* (including the case where a task was cancelled without executing); |
83 |
+ |
* {@link #isCancelled} is true if completion was due to cancellation; |
84 |
+ |
* {@link #isCompletedNormally} is true if a task completed without |
85 |
+ |
* cancellation or encountering an exception; {@link |
86 |
+ |
* #isCompletedExceptionally} is true if if the task encountered an |
87 |
+ |
* exception (in which case {@link #getException} returns the |
88 |
+ |
* exception); {@link #isCancelled} is true if the task was cancelled |
89 |
+ |
* (in which case {@link #getException} returns a {@link |
90 |
+ |
* java.util.concurrent.CancellationException}); and {@link |
91 |
+ |
* #isCompletedAbnormally} is true if a task was either cancelled or |
92 |
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* encountered an exception. |
93 |
+ |
* |
94 |
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* <p>The ForkJoinTask class is not usually directly subclassed. |
95 |
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* Instead, you subclass one of the abstract classes that support a |
96 |
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* particular style of fork/join processing, typically {@link |
100 |
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* established in a constructor, and then defines a {@code compute} |
101 |
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* method that somehow uses the control methods supplied by this base |
102 |
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* class. While these methods have {@code public} access (to allow |
103 |
< |
* instances of different task subclasses to call each others |
103 |
> |
* instances of different task subclasses to call each other's |
104 |
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* methods), some of them may only be called from within other |
105 |
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* ForkJoinTasks (as may be determined using method {@link |
106 |
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* #inForkJoinPool}). Attempts to invoke them in other contexts |
107 |
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* result in exceptions or errors, possibly including |
108 |
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* ClassCastException. |
109 |
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* |
110 |
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* <p>Most base support methods are {@code final} because their |
111 |
< |
* implementations are intrinsically tied to the underlying |
112 |
< |
* lightweight task scheduling framework, and so cannot be overridden. |
113 |
< |
* Developers creating new basic styles of fork/join processing should |
114 |
< |
* minimally implement {@code protected} methods |
115 |
< |
* {@link #exec}, {@link #setRawResult}, and |
116 |
< |
* {@link #getRawResult}, while also introducing an abstract |
117 |
< |
* computational method that can be implemented in its subclasses, |
118 |
< |
* possibly relying on other {@code protected} methods provided |
104 |
< |
* by this class. |
110 |
> |
* <p>Most base support methods are {@code final}, to prevent |
111 |
> |
* overriding of implementations that are intrinsically tied to the |
112 |
> |
* underlying lightweight task scheduling framework. Developers |
113 |
> |
* creating new basic styles of fork/join processing should minimally |
114 |
> |
* implement {@code protected} methods {@link #exec}, {@link |
115 |
> |
* #setRawResult}, and {@link #getRawResult}, while also introducing |
116 |
> |
* an abstract computational method that can be implemented in its |
117 |
> |
* subclasses, possibly relying on other {@code protected} methods |
118 |
> |
* provided by this class. |
119 |
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* |
120 |
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* <p>ForkJoinTasks should perform relatively small amounts of |
121 |
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* computations, otherwise splitting into smaller tasks. As a very |
122 |
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* rough rule of thumb, a task should perform more than 100 and less |
123 |
< |
* than 10000 basic computational steps. If tasks are too big, then |
124 |
< |
* parallelism cannot improve throughput. If too small, then memory |
125 |
< |
* and internal task maintenance overhead may overwhelm processing. |
121 |
> |
* computation. Large tasks should be split into smaller subtasks, |
122 |
> |
* usually via recursive decomposition. As a very rough rule of thumb, |
123 |
> |
* a task should perform more than 100 and less than 10000 basic |
124 |
> |
* computational steps. If tasks are too big, then parallelism cannot |
125 |
> |
* improve throughput. If too small, then memory and internal task |
126 |
> |
* maintenance overhead may overwhelm processing. |
127 |
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* |
128 |
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* <p>This class provides {@code adapt} methods for {@link |
129 |
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* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that |
130 |
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* may be of use when mixing execution of ForkJoinTasks with other |
131 |
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* kinds of tasks. When all tasks are of this form, consider using a |
132 |
< |
* pool in {@link ForkJoinPool#setAsyncMode}. |
132 |
> |
* pool in {@link ForkJoinPool#setAsyncMode async mode}. |
133 |
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* |
134 |
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* <p>ForkJoinTasks are {@code Serializable}, which enables them |
135 |
< |
* to be used in extensions such as remote execution frameworks. It is |
136 |
< |
* in general sensible to serialize tasks only before or after, but |
137 |
< |
* not during execution. Serialization is not relied on during |
123 |
< |
* execution itself. |
134 |
> |
* <p>ForkJoinTasks are {@code Serializable}, which enables them to be |
135 |
> |
* used in extensions such as remote execution frameworks. It is |
136 |
> |
* sensible to serialize tasks only before or after, but not during, |
137 |
> |
* execution. Serialization is not relied on during execution itself. |
138 |
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* |
139 |
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* @since 1.7 |
140 |
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* @author Doug Lea |
396 |
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*/ |
397 |
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private V reportFutureResult() |
398 |
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throws ExecutionException, InterruptedException { |
399 |
+ |
if (Thread.interrupted()) |
400 |
+ |
throw new InterruptedException(); |
401 |
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int s = status & COMPLETION_MASK; |
402 |
|
if (s < NORMAL) { |
403 |
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Throwable ex; |
405 |
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throw new CancellationException(); |
406 |
|
if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) |
407 |
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throw new ExecutionException(ex); |
392 |
– |
if (Thread.interrupted()) |
393 |
– |
throw new InterruptedException(); |
408 |
|
} |
409 |
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return getRawResult(); |
410 |
|
} |
415 |
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*/ |
416 |
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private V reportTimedFutureResult() |
417 |
|
throws InterruptedException, ExecutionException, TimeoutException { |
418 |
+ |
if (Thread.interrupted()) |
419 |
+ |
throw new InterruptedException(); |
420 |
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Throwable ex; |
421 |
|
int s = status & COMPLETION_MASK; |
422 |
|
if (s == NORMAL) |
425 |
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throw new CancellationException(); |
426 |
|
if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) |
427 |
|
throw new ExecutionException(ex); |
412 |
– |
if (Thread.interrupted()) |
413 |
– |
throw new InterruptedException(); |
428 |
|
throw new TimeoutException(); |
429 |
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} |
430 |
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|
543 |
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|
544 |
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/** |
545 |
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* Commences performing this task, awaits its completion if |
546 |
< |
* necessary, and return its result. |
546 |
> |
* necessary, and return its result, or throws an (unchecked) |
547 |
> |
* exception if the underlying computation did so. |
548 |
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* |
534 |
– |
* @throws Throwable (a RuntimeException, Error, or unchecked |
535 |
– |
* exception) if the underlying computation did so |
549 |
|
* @return the computed result |
550 |
|
*/ |
551 |
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public final V invoke() { |
556 |
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} |
557 |
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|
558 |
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/** |
559 |
< |
* Forks the given tasks, returning when {@code isDone} holds |
560 |
< |
* for each task or an exception is encountered. |
559 |
> |
* Forks the given tasks, returning when {@code isDone} holds for |
560 |
> |
* each task or an (unchecked) exception is encountered, in which |
561 |
> |
* case the exception is rethrown. If more than one task |
562 |
> |
* encounters an exception, then this method throws any one of |
563 |
> |
* these exceptions. The individual status of each task may be |
564 |
> |
* checked using {@link #getException()} and related methods. |
565 |
|
* |
566 |
|
* <p>This method may be invoked only from within {@code |
567 |
|
* ForkJoinTask} computations (as may be determined using method |
572 |
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* @param t1 the first task |
573 |
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* @param t2 the second task |
574 |
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* @throws NullPointerException if any task is null |
558 |
– |
* @throws RuntimeException or Error if a task did so |
575 |
|
*/ |
576 |
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public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) { |
577 |
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t2.fork(); |
581 |
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|
582 |
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/** |
583 |
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* Forks the given tasks, returning when {@code isDone} holds for |
584 |
< |
* each task or an exception is encountered. If any task |
585 |
< |
* encounters an exception, others may be, but are not guaranteed |
586 |
< |
* to be, cancelled. |
584 |
> |
* each task or an (unchecked) exception is encountered, in which |
585 |
> |
* case the exception is rethrown. If any task encounters an |
586 |
> |
* exception, others may be, but are not guaranteed to be, |
587 |
> |
* cancelled. If more than one task encounters an exception, then |
588 |
> |
* this method throws any one of these exceptions. The individual |
589 |
> |
* status of each task may be checked using {@link #getException()} |
590 |
> |
* and related methods. |
591 |
|
* |
592 |
|
* <p>This method may be invoked only from within {@code |
593 |
|
* ForkJoinTask} computations (as may be determined using method |
595 |
|
* result in exceptions or errors, possibly including {@code |
596 |
|
* ClassCastException}. |
597 |
|
* |
578 |
– |
* <p>Overloadings of this method exist for the special cases |
579 |
– |
* of one to four arguments. |
580 |
– |
* |
598 |
|
* @param tasks the tasks |
599 |
< |
* @throws NullPointerException if tasks or any element are null |
583 |
< |
* @throws RuntimeException or Error if any task did so |
599 |
> |
* @throws NullPointerException if any task is null |
600 |
|
*/ |
601 |
|
public static void invokeAll(ForkJoinTask<?>... tasks) { |
602 |
|
Throwable ex = null; |
632 |
|
} |
633 |
|
|
634 |
|
/** |
635 |
< |
* Forks all tasks in the collection, returning when {@code |
636 |
< |
* isDone} holds for each task or an exception is encountered. |
637 |
< |
* If any task encounters an exception, others may be, but are |
638 |
< |
* not guaranteed to be, cancelled. |
635 |
> |
* Forks all tasks in the specified collection, returning when |
636 |
> |
* {@code isDone} holds for each task or an (unchecked) exception |
637 |
> |
* is encountered. If any task encounters an exception, others |
638 |
> |
* may be, but are not guaranteed to be, cancelled. If more than |
639 |
> |
* one task encounters an exception, then this method throws any |
640 |
> |
* one of these exceptions. The individual status of each task |
641 |
> |
* may be checked using {@link #getException()} and related |
642 |
> |
* methods. The behavior of this operation is undefined if the |
643 |
> |
* specified collection is modified while the operation is in |
644 |
> |
* progress. |
645 |
|
* |
646 |
|
* <p>This method may be invoked only from within {@code |
647 |
|
* ForkJoinTask} computations (as may be determined using method |
652 |
|
* @param tasks the collection of tasks |
653 |
|
* @return the tasks argument, to simplify usage |
654 |
|
* @throws NullPointerException if tasks or any element are null |
633 |
– |
* @throws RuntimeException or Error if any task did so |
655 |
|
*/ |
656 |
|
public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) { |
657 |
< |
if (!(tasks instanceof List<?>)) { |
657 |
> |
if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) { |
658 |
|
invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()])); |
659 |
|
return tasks; |
660 |
|
} |
695 |
|
} |
696 |
|
|
697 |
|
/** |
698 |
< |
* Returns {@code true} if the computation performed by this task |
699 |
< |
* has completed (or has been cancelled). |
700 |
< |
* |
701 |
< |
* @return {@code true} if this computation has completed |
702 |
< |
*/ |
703 |
< |
public final boolean isDone() { |
704 |
< |
return status < 0; |
684 |
< |
} |
685 |
< |
|
686 |
< |
/** |
687 |
< |
* Returns {@code true} if this task was cancelled. |
688 |
< |
* |
689 |
< |
* @return {@code true} if this task was cancelled |
690 |
< |
*/ |
691 |
< |
public final boolean isCancelled() { |
692 |
< |
return (status & COMPLETION_MASK) == CANCELLED; |
693 |
< |
} |
694 |
< |
|
695 |
< |
/** |
696 |
< |
* Asserts that the results of this task's computation will not be |
697 |
< |
* used. If a cancellation occurs before attempting to execute this |
698 |
< |
* task, execution will be suppressed, {@link #isCancelled} |
699 |
< |
* will report true, and {@link #join} will result in a |
700 |
< |
* {@code CancellationException} being thrown. Otherwise, when |
701 |
< |
* cancellation races with completion, there are no guarantees |
702 |
< |
* about whether {@code isCancelled} will report {@code true}, |
703 |
< |
* whether {@code join} will return normally or via an exception, |
704 |
< |
* or whether these behaviors will remain consistent upon repeated |
705 |
< |
* invocation. |
698 |
> |
* Attempts to cancel execution of this task. This attempt will |
699 |
> |
* fail if the task has already completed, has already been |
700 |
> |
* cancelled, or could not be cancelled for some other reason. If |
701 |
> |
* successful, and this task has not started when cancel is |
702 |
> |
* called, execution of this task is suppressed, {@link |
703 |
> |
* #isCancelled} will report true, and {@link #join} will result |
704 |
> |
* in a {@code CancellationException} being thrown. |
705 |
|
* |
706 |
|
* <p>This method may be overridden in subclasses, but if so, must |
707 |
|
* still ensure that these minimal properties hold. In particular, |
713 |
|
* invoke {@link #completeExceptionally}. |
714 |
|
* |
715 |
|
* @param mayInterruptIfRunning this value is ignored in the |
716 |
< |
* default implementation because tasks are not in general |
716 |
> |
* default implementation because tasks are not |
717 |
|
* cancelled via interruption |
718 |
|
* |
719 |
|
* @return {@code true} if this task is now cancelled |
724 |
|
} |
725 |
|
|
726 |
|
/** |
727 |
+ |
* Returns {@code true} if the computation performed by this task |
728 |
+ |
* has completed (or has been cancelled). |
729 |
+ |
* |
730 |
+ |
* @return {@code true} if this computation has completed |
731 |
+ |
*/ |
732 |
+ |
public final boolean isDone() { |
733 |
+ |
return status < 0; |
734 |
+ |
} |
735 |
+ |
|
736 |
+ |
/** |
737 |
+ |
* Returns {@code true} if this task was cancelled. |
738 |
+ |
* |
739 |
+ |
* @return {@code true} if this task was cancelled |
740 |
+ |
*/ |
741 |
+ |
public final boolean isCancelled() { |
742 |
+ |
return (status & COMPLETION_MASK) == CANCELLED; |
743 |
+ |
} |
744 |
+ |
|
745 |
+ |
/** |
746 |
|
* Returns {@code true} if this task threw an exception or was cancelled. |
747 |
|
* |
748 |
|
* @return {@code true} if this task threw an exception or was cancelled |
752 |
|
} |
753 |
|
|
754 |
|
/** |
755 |
+ |
* Returns {@code true} if this task completed without throwing an |
756 |
+ |
* exception and was not cancelled. |
757 |
+ |
* |
758 |
+ |
* @return {@code true} if this task completed without throwing an |
759 |
+ |
* exception and was not cancelled |
760 |
+ |
*/ |
761 |
+ |
public final boolean isCompletedNormally() { |
762 |
+ |
return (status & COMPLETION_MASK) == NORMAL; |
763 |
+ |
} |
764 |
+ |
|
765 |
+ |
/** |
766 |
+ |
* Returns {@code true} if this task threw an exception. |
767 |
+ |
* |
768 |
+ |
* @return {@code true} if this task threw an exception |
769 |
+ |
*/ |
770 |
+ |
public final boolean isCompletedExceptionally() { |
771 |
+ |
return (status & COMPLETION_MASK) == EXCEPTIONAL; |
772 |
+ |
} |
773 |
+ |
|
774 |
+ |
/** |
775 |
|
* Returns the exception thrown by the base computation, or a |
776 |
|
* {@code CancellationException} if cancelled, or {@code null} if |
777 |
|
* none or if the method has not yet completed. |
870 |
|
} |
871 |
|
|
872 |
|
/** |
873 |
< |
* Possibly executes other tasks until this task is ready. |
873 |
> |
* Possibly executes other tasks until this task is ready. This |
874 |
> |
* method may be useful when processing collections of tasks when |
875 |
> |
* some have been cancelled or otherwise known to have aborted. |
876 |
|
* |
877 |
|
* <p>This method may be invoked only from within {@code |
878 |
|
* ForkJoinTask} computations (as may be determined using method |
917 |
|
|
918 |
|
/** |
919 |
|
* Possibly executes tasks until the pool hosting the current task |
920 |
< |
* {@link ForkJoinPool#isQuiescent}. This method may be of use in |
921 |
< |
* designs in which many tasks are forked, but none are explicitly |
922 |
< |
* joined, instead executing them until all are processed. |
920 |
> |
* {@link ForkJoinPool#isQuiescent is quiescent}. This method may |
921 |
> |
* be of use in designs in which many tasks are forked, but none |
922 |
> |
* are explicitly joined, instead executing them until all are |
923 |
> |
* processed. |
924 |
|
* |
925 |
|
* <p>This method may be invoked only from within {@code |
926 |
|
* ForkJoinTask} computations (as may be determined using method |
1064 |
|
* called otherwise. The return value controls whether this task |
1065 |
|
* is considered to be done normally. It may return false in |
1066 |
|
* asynchronous actions that require explicit invocations of |
1067 |
< |
* {@link #complete} to become joinable. It may throw exceptions |
1068 |
< |
* to indicate abnormal exit. |
1067 |
> |
* {@link #complete} to become joinable. It may also throw an |
1068 |
> |
* (unchecked) exception to indicate abnormal exit. |
1069 |
|
* |
1070 |
|
* @return {@code true} if completed normally |
1030 |
– |
* @throws Error or RuntimeException if encountered during computation |
1071 |
|
*/ |
1072 |
|
protected abstract boolean exec(); |
1073 |
|
|