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. |
86 |
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* established in a constructor, and then defines a {@code compute} |
87 |
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* method that somehow uses the control methods supplied by this base |
88 |
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* class. While these methods have {@code public} access (to allow |
89 |
< |
* instances of different task subclasses to call each others |
89 |
> |
* instances of different task subclasses to call each other's |
90 |
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* methods), some of them may only be called from within other |
91 |
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* ForkJoinTasks (as may be determined using method {@link |
92 |
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* #inForkJoinPool}). Attempts to invoke them in other contexts |
93 |
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* result in exceptions or errors, possibly including |
94 |
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* ClassCastException. |
95 |
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* |
96 |
< |
* <p>Most base support methods are {@code final} because their |
97 |
< |
* implementations are intrinsically tied to the underlying |
98 |
< |
* lightweight task scheduling framework, and so cannot be overridden. |
99 |
< |
* Developers creating new basic styles of fork/join processing should |
100 |
< |
* minimally implement {@code protected} methods |
101 |
< |
* {@link #exec}, {@link #setRawResult}, and |
102 |
< |
* {@link #getRawResult}, while also introducing an abstract |
103 |
< |
* computational method that can be implemented in its subclasses, |
104 |
< |
* possibly relying on other {@code protected} methods provided |
104 |
< |
* by this class. |
96 |
> |
* <p>Most base support methods are {@code final}, to prevent |
97 |
> |
* overriding of implementations that are intrinsically tied to the |
98 |
> |
* underlying lightweight task scheduling framework. Developers |
99 |
> |
* creating new basic styles of fork/join processing should minimally |
100 |
> |
* implement {@code protected} methods {@link #exec}, {@link |
101 |
> |
* #setRawResult}, and {@link #getRawResult}, while also introducing |
102 |
> |
* an abstract computational method that can be implemented in its |
103 |
> |
* subclasses, possibly relying on other {@code protected} methods |
104 |
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* provided by this class. |
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* |
106 |
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* <p>ForkJoinTasks should perform relatively small amounts of |
107 |
< |
* computations, otherwise splitting into smaller tasks. As a very |
108 |
< |
* rough rule of thumb, a task should perform more than 100 and less |
109 |
< |
* than 10000 basic computational steps. If tasks are too big, then |
110 |
< |
* parallelism cannot improve throughput. If too small, then memory |
111 |
< |
* and internal task maintenance overhead may overwhelm processing. |
107 |
> |
* computation. Large tasks should be split into smaller subtasks, |
108 |
> |
* usually via recursive decomposition. As a very rough rule of thumb, |
109 |
> |
* a task should perform more than 100 and less than 10000 basic |
110 |
> |
* computational steps. If tasks are too big, then parallelism cannot |
111 |
> |
* improve throughput. If too small, then memory and internal task |
112 |
> |
* maintenance overhead may overwhelm processing. |
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* |
114 |
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* <p>This class provides {@code adapt} methods for {@link |
115 |
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* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that |
117 |
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* kinds of tasks. When all tasks are of this form, consider using a |
118 |
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* pool in {@link ForkJoinPool#setAsyncMode}. |
119 |
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* |
120 |
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* <p>ForkJoinTasks are {@code Serializable}, which enables them |
121 |
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* to be used in extensions such as remote execution frameworks. It is |
122 |
< |
* in general sensible to serialize tasks only before or after, but |
123 |
< |
* not during execution. Serialization is not relied on during |
123 |
< |
* execution itself. |
120 |
> |
* <p>ForkJoinTasks are {@code Serializable}, which enables them to be |
121 |
> |
* used in extensions such as remote execution frameworks. It is |
122 |
> |
* sensible to serialize tasks only before or after, but not during, |
123 |
> |
* execution. Serialization is not relied on during execution itself. |
124 |
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* |
125 |
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* @since 1.7 |
126 |
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* @author Doug Lea |
496 |
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/** |
497 |
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* Arranges to asynchronously execute this task. While it is not |
498 |
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* necessarily enforced, it is a usage error to fork a task more |
499 |
< |
* than once unless it has completed and been reinitialized. This |
500 |
< |
* method may be invoked only from within ForkJoinTask |
501 |
< |
* computations (as may be determined using method {@link |
502 |
< |
* #inForkJoinPool}). Attempts to invoke in other contexts result |
503 |
< |
* in exceptions or errors, possibly including ClassCastException. |
499 |
> |
* than once unless it has completed and been reinitialized. |
500 |
|
* |
501 |
< |
* @return {@code this}, to simplify usage. |
501 |
> |
* <p>This method may be invoked only from within {@code |
502 |
> |
* ForkJoinTask} computations (as may be determined using method |
503 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
504 |
> |
* result in exceptions or errors, possibly including {@code |
505 |
> |
* ClassCastException}. |
506 |
> |
* |
507 |
> |
* @return {@code this}, to simplify usage |
508 |
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*/ |
509 |
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public final ForkJoinTask<V> fork() { |
510 |
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((ForkJoinWorkerThread) Thread.currentThread()) |
514 |
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|
515 |
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/** |
516 |
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* Returns the result of the computation when it is ready. |
517 |
< |
* This method differs from {@code get} in that abnormal |
518 |
< |
* completion results in RuntimeExceptions or Errors, not |
519 |
< |
* ExecutionExceptions. |
517 |
> |
* This method differs from {@link #get()} in that |
518 |
> |
* abnormal completion results in {@code RuntimeException} or |
519 |
> |
* {@code Error}, not {@code ExecutionException}. |
520 |
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* |
521 |
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* @return the computed result |
522 |
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*/ |
543 |
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} |
544 |
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|
545 |
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/** |
546 |
< |
* Forks the given tasks, returning when {@code isDone} holds for |
547 |
< |
* each task or an exception is encountered. This method may be |
548 |
< |
* invoked only from within ForkJoinTask computations (as may be |
549 |
< |
* determined using method {@link #inForkJoinPool}). Attempts to |
550 |
< |
* invoke in other contexts result in exceptions or errors, |
551 |
< |
* possibly including ClassCastException. |
546 |
> |
* Forks the given tasks, returning when {@code isDone} holds |
547 |
> |
* for each task or an exception is encountered. |
548 |
> |
* |
549 |
> |
* <p>This method may be invoked only from within {@code |
550 |
> |
* ForkJoinTask} computations (as may be determined using method |
551 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
552 |
> |
* result in exceptions or errors, possibly including {@code |
553 |
> |
* ClassCastException}. |
554 |
|
* |
555 |
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* @param t1 the first task |
556 |
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* @param t2 the second task |
557 |
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* @throws NullPointerException if any task is null |
558 |
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* @throws RuntimeException or Error if a task did so |
559 |
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*/ |
560 |
< |
public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) { |
560 |
> |
public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) { |
561 |
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t2.fork(); |
562 |
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t1.invoke(); |
563 |
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t2.join(); |
567 |
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* Forks the given tasks, returning when {@code isDone} holds for |
568 |
|
* each task or an exception is encountered. If any task |
569 |
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* encounters an exception, others may be, but are not guaranteed |
570 |
< |
* to be, cancelled. This method may be invoked only from within |
567 |
< |
* ForkJoinTask computations (as may be determined using method |
568 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
569 |
< |
* result in exceptions or errors, possibly including |
570 |
< |
* ClassCastException. |
570 |
> |
* to be, cancelled. |
571 |
|
* |
572 |
< |
* Overloadings of this method exist for the special cases |
573 |
< |
* of one to four arguments. |
572 |
> |
* <p>This method may be invoked only from within {@code |
573 |
> |
* ForkJoinTask} computations (as may be determined using method |
574 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
575 |
> |
* result in exceptions or errors, possibly including {@code |
576 |
> |
* ClassCastException}. |
577 |
|
* |
578 |
|
* @param tasks the tasks |
579 |
|
* @throws NullPointerException if tasks or any element are null |
613 |
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} |
614 |
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|
615 |
|
/** |
616 |
< |
* Forks all tasks in the collection, returning when {@code |
617 |
< |
* isDone} holds for each task or an exception is encountered. If |
618 |
< |
* any task encounters an exception, others may be, but are not |
619 |
< |
* guaranteed to be, cancelled. This method may be invoked only |
620 |
< |
* from within ForkJoinTask computations (as may be determined |
621 |
< |
* using method {@link #inForkJoinPool}). Attempts to invoke in |
622 |
< |
* other contexts result in exceptions or errors, possibly |
623 |
< |
* including ClassCastException. |
616 |
> |
* Forks all tasks in the specified collection, returning when |
617 |
> |
* {@code isDone} holds for each task or an exception is |
618 |
> |
* encountered. If any task encounters an exception, others may |
619 |
> |
* be, but are not guaranteed to be, cancelled. The behavior of |
620 |
> |
* this operation is undefined if the specified collection is |
621 |
> |
* modified while the operation is in progress. |
622 |
> |
* |
623 |
> |
* <p>This method may be invoked only from within {@code |
624 |
> |
* ForkJoinTask} computations (as may be determined using method |
625 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
626 |
> |
* result in exceptions or errors, possibly including {@code |
627 |
> |
* ClassCastException}. |
628 |
|
* |
629 |
|
* @param tasks the collection of tasks |
630 |
|
* @return the tasks argument, to simplify usage |
632 |
|
* @throws RuntimeException or Error if any task did so |
633 |
|
*/ |
634 |
|
public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) { |
635 |
< |
if (!(tasks instanceof List<?>)) { |
635 |
> |
if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) { |
636 |
|
invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()])); |
637 |
|
return tasks; |
638 |
|
} |
692 |
|
} |
693 |
|
|
694 |
|
/** |
695 |
< |
* Asserts that the results of this task's computation will not be |
696 |
< |
* used. If a cancellation occurs before attempting to execute this |
697 |
< |
* task, execution will be suppressed, {@link #isCancelled} |
698 |
< |
* will report true, and {@link #join} will result in a |
699 |
< |
* {@code CancellationException} being thrown. Otherwise, when |
700 |
< |
* cancellation races with completion, there are no guarantees |
701 |
< |
* about whether {@code isCancelled} will report {@code true}, |
695 |
< |
* whether {@code join} will return normally or via an exception, |
696 |
< |
* or whether these behaviors will remain consistent upon repeated |
697 |
< |
* invocation. |
695 |
> |
* Attempts to cancel execution of this task. This attempt will |
696 |
> |
* fail if the task has already completed, has already been |
697 |
> |
* cancelled, or could not be cancelled for some other reason. If |
698 |
> |
* successful, and this task has not started when cancel is |
699 |
> |
* called, execution of this task is suppressed, {@link |
700 |
> |
* #isCancelled} will report true, and {@link #join} will result |
701 |
> |
* in a {@code CancellationException} being thrown. |
702 |
|
* |
703 |
|
* <p>This method may be overridden in subclasses, but if so, must |
704 |
|
* still ensure that these minimal properties hold. In particular, |
710 |
|
* invoke {@link #completeExceptionally}. |
711 |
|
* |
712 |
|
* @param mayInterruptIfRunning this value is ignored in the |
713 |
< |
* default implementation because tasks are not in general |
713 |
> |
* default implementation because tasks are not |
714 |
|
* cancelled via interruption |
715 |
|
* |
716 |
|
* @return {@code true} if this task is now cancelled |
810 |
|
* there are no potential dependencies between continuation of the |
811 |
|
* current task and that of any other task that might be executed |
812 |
|
* while helping. (This usually holds for pure divide-and-conquer |
813 |
< |
* tasks). This method may be invoked only from within |
814 |
< |
* ForkJoinTask computations (as may be determined using method |
815 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
816 |
< |
* result in exceptions or errors, possibly including |
817 |
< |
* ClassCastException. |
813 |
> |
* tasks). |
814 |
> |
* |
815 |
> |
* <p>This method may be invoked only from within {@code |
816 |
> |
* ForkJoinTask} computations (as may be determined using method |
817 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
818 |
> |
* result in exceptions or errors, possibly including {@code |
819 |
> |
* ClassCastException}. |
820 |
|
* |
821 |
|
* @return the computed result |
822 |
|
*/ |
829 |
|
|
830 |
|
/** |
831 |
|
* Possibly executes other tasks until this task is ready. This |
832 |
< |
* method may be invoked only from within ForkJoinTask |
833 |
< |
* computations (as may be determined using method {@link |
834 |
< |
* #inForkJoinPool}). Attempts to invoke in other contexts result |
835 |
< |
* in exceptions or errors, possibly including ClassCastException. |
832 |
> |
* method may be useful when processing collections of tasks when |
833 |
> |
* some have been cancelled or otherwise known to have aborted. |
834 |
> |
* |
835 |
> |
* <p>This method may be invoked only from within {@code |
836 |
> |
* ForkJoinTask} computations (as may be determined using method |
837 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
838 |
> |
* result in exceptions or errors, possibly including {@code |
839 |
> |
* ClassCastException}. |
840 |
|
*/ |
841 |
|
public final void quietlyHelpJoin() { |
842 |
|
if (status >= 0) { |
875 |
|
|
876 |
|
/** |
877 |
|
* Possibly executes tasks until the pool hosting the current task |
878 |
< |
* {@link ForkJoinPool#isQuiescent}. This method may be of use in |
879 |
< |
* designs in which many tasks are forked, but none are explicitly |
880 |
< |
* joined, instead executing them until all are processed. This |
881 |
< |
* method may be invoked only from within ForkJoinTask |
882 |
< |
* computations (as may be determined using method {@link |
883 |
< |
* #inForkJoinPool}). Attempts to invoke in other contexts result |
884 |
< |
* in exceptions or errors, possibly including ClassCastException. |
878 |
> |
* {@link ForkJoinPool#isQuiescent is quiescent}. This method may |
879 |
> |
* be of use in designs in which many tasks are forked, but none |
880 |
> |
* are explicitly joined, instead executing them until all are |
881 |
> |
* processed. |
882 |
> |
* |
883 |
> |
* <p>This method may be invoked only from within {@code |
884 |
> |
* ForkJoinTask} computations (as may be determined using method |
885 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
886 |
> |
* result in exceptions or errors, possibly including {@code |
887 |
> |
* ClassCastException}. |
888 |
|
*/ |
889 |
|
public static void helpQuiesce() { |
890 |
|
((ForkJoinWorkerThread) Thread.currentThread()) |
937 |
|
* by the current thread, and has not commenced executing in |
938 |
|
* another thread. This method may be useful when arranging |
939 |
|
* alternative local processing of tasks that could have been, but |
940 |
< |
* were not, stolen. This method may be invoked only from within |
941 |
< |
* ForkJoinTask computations (as may be determined using method |
942 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
943 |
< |
* result in exceptions or errors, possibly including |
944 |
< |
* ClassCastException. |
940 |
> |
* were not, stolen. |
941 |
> |
* |
942 |
> |
* <p>This method may be invoked only from within {@code |
943 |
> |
* ForkJoinTask} computations (as may be determined using method |
944 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
945 |
> |
* result in exceptions or errors, possibly including {@code |
946 |
> |
* ClassCastException}. |
947 |
|
* |
948 |
|
* @return {@code true} if unforked |
949 |
|
*/ |
956 |
|
* Returns an estimate of the number of tasks that have been |
957 |
|
* forked by the current worker thread but not yet executed. This |
958 |
|
* value may be useful for heuristic decisions about whether to |
959 |
< |
* fork other tasks. This method may be invoked only from within |
960 |
< |
* ForkJoinTask computations (as may be determined using method |
961 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
962 |
< |
* result in exceptions or errors, possibly including |
963 |
< |
* ClassCastException. |
959 |
> |
* fork other tasks. |
960 |
> |
* |
961 |
> |
* <p>This method may be invoked only from within {@code |
962 |
> |
* ForkJoinTask} computations (as may be determined using method |
963 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
964 |
> |
* result in exceptions or errors, possibly including {@code |
965 |
> |
* ClassCastException}. |
966 |
> |
* |
967 |
|
* @return the number of tasks |
968 |
|
*/ |
969 |
|
public static int getQueuedTaskCount() { |
979 |
|
* usages of ForkJoinTasks, at steady state, each worker should |
980 |
|
* aim to maintain a small constant surplus (for example, 3) of |
981 |
|
* tasks, and to process computations locally if this threshold is |
982 |
< |
* exceeded. This method may be invoked only from within |
983 |
< |
* ForkJoinTask computations (as may be determined using method |
984 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
985 |
< |
* result in exceptions or errors, possibly including |
986 |
< |
* ClassCastException. |
982 |
> |
* exceeded. |
983 |
> |
* |
984 |
> |
* <p>This method may be invoked only from within {@code |
985 |
> |
* ForkJoinTask} computations (as may be determined using method |
986 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
987 |
> |
* result in exceptions or errors, possibly including {@code |
988 |
> |
* ClassCastException}. |
989 |
> |
* |
990 |
|
* @return the surplus number of tasks, which may be negative |
991 |
|
*/ |
992 |
|
public static int getSurplusQueuedTaskCount() { |
1038 |
|
* null even if a task exists but cannot be accessed without |
1039 |
|
* contention with other threads. This method is designed |
1040 |
|
* primarily to support extensions, and is unlikely to be useful |
1041 |
< |
* otherwise. This method may be invoked only from within |
1042 |
< |
* ForkJoinTask computations (as may be determined using method |
1043 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1044 |
< |
* result in exceptions or errors, possibly including |
1045 |
< |
* ClassCastException. |
1041 |
> |
* otherwise. |
1042 |
> |
* |
1043 |
> |
* <p>This method may be invoked only from within {@code |
1044 |
> |
* ForkJoinTask} computations (as may be determined using method |
1045 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1046 |
> |
* result in exceptions or errors, possibly including {@code |
1047 |
> |
* ClassCastException}. |
1048 |
|
* |
1049 |
|
* @return the next task, or {@code null} if none are available |
1050 |
|
*/ |
1057 |
|
* Unschedules and returns, without executing, the next task |
1058 |
|
* queued by the current thread but not yet executed. This method |
1059 |
|
* is designed primarily to support extensions, and is unlikely to |
1060 |
< |
* be useful otherwise. This method may be invoked only from |
1061 |
< |
* within ForkJoinTask computations (as may be determined using |
1062 |
< |
* method {@link #inForkJoinPool}). Attempts to invoke in other |
1063 |
< |
* contexts result in exceptions or errors, possibly including |
1064 |
< |
* ClassCastException. |
1060 |
> |
* be useful otherwise. |
1061 |
> |
* |
1062 |
> |
* <p>This method may be invoked only from within {@code |
1063 |
> |
* ForkJoinTask} computations (as may be determined using method |
1064 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1065 |
> |
* result in exceptions or errors, possibly including {@code |
1066 |
> |
* ClassCastException}. |
1067 |
|
* |
1068 |
|
* @return the next task, or {@code null} if none are available |
1069 |
|
*/ |
1080 |
|
* {@code null} result does not necessarily imply quiescence |
1081 |
|
* of the pool this task is operating in. This method is designed |
1082 |
|
* primarily to support extensions, and is unlikely to be useful |
1083 |
< |
* otherwise. This method may be invoked only from within |
1084 |
< |
* ForkJoinTask computations (as may be determined using method |
1085 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1086 |
< |
* result in exceptions or errors, possibly including |
1087 |
< |
* ClassCastException. |
1083 |
> |
* otherwise. |
1084 |
> |
* |
1085 |
> |
* <p>This method may be invoked only from within {@code |
1086 |
> |
* ForkJoinTask} computations (as may be determined using method |
1087 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1088 |
> |
* result in exceptions or errors, possibly including {@code |
1089 |
> |
* ClassCastException}. |
1090 |
|
* |
1091 |
|
* @return a task, or {@code null} if none are available |
1092 |
|
*/ |
1151 |
|
} |
1152 |
|
|
1153 |
|
/** |
1154 |
< |
* Returns a new ForkJoinTask that performs the {@code run} |
1155 |
< |
* method of the given Runnable as its action, and returns a null |
1156 |
< |
* result upon {@code join}. |
1154 |
> |
* Returns a new {@code ForkJoinTask} that performs the {@code run} |
1155 |
> |
* method of the given {@code Runnable} as its action, and returns |
1156 |
> |
* a null result upon {@link #join}. |
1157 |
|
* |
1158 |
|
* @param runnable the runnable action |
1159 |
|
* @return the task |
1163 |
|
} |
1164 |
|
|
1165 |
|
/** |
1166 |
< |
* Returns a new ForkJoinTask that performs the {@code run} |
1167 |
< |
* method of the given Runnable as its action, and returns the |
1168 |
< |
* given result upon {@code join}. |
1166 |
> |
* Returns a new {@code ForkJoinTask} that performs the {@code run} |
1167 |
> |
* method of the given {@code Runnable} as its action, and returns |
1168 |
> |
* the given result upon {@link #join}. |
1169 |
|
* |
1170 |
|
* @param runnable the runnable action |
1171 |
|
* @param result the result upon completion |
1176 |
|
} |
1177 |
|
|
1178 |
|
/** |
1179 |
< |
* Returns a new ForkJoinTask that performs the {@code call} |
1180 |
< |
* method of the given Callable as its action, and returns its |
1181 |
< |
* result upon {@code join}, translating any checked |
1182 |
< |
* exceptions encountered into {@code RuntimeException}. |
1179 |
> |
* Returns a new {@code ForkJoinTask} that performs the {@code call} |
1180 |
> |
* method of the given {@code Callable} as its action, and returns |
1181 |
> |
* its result upon {@link #join}, translating any checked exceptions |
1182 |
> |
* encountered into {@code RuntimeException}. |
1183 |
|
* |
1184 |
|
* @param callable the callable action |
1185 |
|
* @return the task |