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root/jsr166/jsr166/src/jsr166y/ForkJoinTask.java

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.25 by dl, Fri Jul 31 16:27:08 2009 UTC vs.
Revision 1.32 by dl, Mon Aug 3 13:01:15 2009 UTC

#	Line 12 | Line 12 | import java.io.Serializable;
12		import java.util.Collection;
13		import java.util.Collections;
14		import java.util.List;
15	+	import java.util.RandomAccess;
16		import java.util.Map;
17		import java.util.WeakHashMap;
18
19		/**
20	<	* Abstract base class for tasks that run within a {@link
21	<	* ForkJoinPool}.  A ForkJoinTask is a thread-like entity that is much
20	>	* Abstract base class for tasks that run within a {@link ForkJoinPool}.
21	>	* A {@code ForkJoinTask} is a thread-like entity that is much
22		* lighter weight than a normal thread.  Huge numbers of tasks and
23		* subtasks may be hosted by a small number of actual threads in a
24		* ForkJoinPool, at the price of some usage limitations.
25		*
26	<	* <p> A "main" ForkJoinTask begins execution when submitted to a
27	<	* {@link ForkJoinPool}. Once started, it will usually in turn start
28	<	* other subtasks.  As indicated by the name of this class, many
29	<	* programs using ForkJoinTasks employ only methods {@code fork} and
30	<	* {@code join}, or derivatives such as {@code invokeAll}.  However,
31	<	* this class also provides a number of other methods that can come
32	<	* into play in advanced usages, as well as extension mechanics that
33	<	* allow support of new forms of fork/join processing.
26	>	* <p>A "main" {@code ForkJoinTask} begins execution when submitted
27	>	* to a {@link ForkJoinPool}.  Once started, it will usually in turn
28	>	* start other subtasks.  As indicated by the name of this class,
29	>	* many programs using {@code ForkJoinTask} employ only methods
30	>	* {@link #fork} and {@link #join}, or derivatives such as {@link
31	>	* #invokeAll}.  However, this class also provides a number of other
32	>	* methods that can come into play in advanced usages, as well as
33	>	* extension mechanics that allow support of new forms of fork/join
34	>	* processing.
35		*
36	<	* <p>A ForkJoinTask is a lightweight form of {@link Future}.  The
37	<	* efficiency of ForkJoinTasks stems from a set of restrictions (that
38	<	* are only partially statically enforceable) reflecting their
39	<	* intended use as computational tasks calculating pure functions or
40	<	* operating on purely isolated objects.  The primary coordination
41	<	* mechanisms are {@link #fork}, that arranges asynchronous execution,
42	<	* and {@link #join}, that doesn't proceed until the task's result has
43	<	* been computed.  Computations should avoid {@code synchronized}
44	<	* methods or blocks, and should minimize other blocking
45	<	* synchronization apart from joining other tasks or using
46	<	* synchronizers such as Phasers that are advertised to cooperate with
47	<	* fork/join scheduling. Tasks should also not perform blocking IO,
48	<	* and should ideally access variables that are completely independent
49	<	* of those accessed by other running tasks. Minor breaches of these
50	<	* restrictions, for example using shared output streams, may be
51	<	* tolerable in practice, but frequent use may result in poor
52	<	* performance, and the potential to indefinitely stall if the number
53	<	* of threads not waiting for IO or other external synchronization
54	<	* becomes exhausted. This usage restriction is in part enforced by
55	<	* not permitting checked exceptions such as {@code IOExceptions}
56	<	* to be thrown. However, computations may still encounter unchecked
57	<	* exceptions, that are rethrown to callers attempting join
58	<	* them. These exceptions may additionally include
59	<	* RejectedExecutionExceptions stemming from internal resource
60	<	* exhaustion such as failure to allocate internal task queues.
36	>	* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
37	>	* The efficiency of {@code ForkJoinTask}s stems from a set of
38	>	* restrictions (that are only partially statically enforceable)
39	>	* reflecting their intended use as computational tasks calculating
40	>	* pure functions or operating on purely isolated objects.  The
41	>	* primary coordination mechanisms are {@link #fork}, that arranges
42	>	* asynchronous execution, and {@link #join}, that doesn't proceed
43	>	* until the task's result has been computed.  Computations should
44	>	* avoid {@code synchronized} methods or blocks, and should minimize
45	>	* other blocking synchronization apart from joining other tasks or
46	>	* using synchronizers such as Phasers that are advertised to
47	>	* cooperate with fork/join scheduling. Tasks should also not perform
48	>	* blocking IO, and should ideally access variables that are
49	>	* completely independent of those accessed by other running
50	>	* tasks. Minor breaches of these restrictions, for example using
51	>	* shared output streams, may be tolerable in practice, but frequent
52	>	* use may result in poor performance, and the potential to
53	>	* indefinitely stall if the number of threads not waiting for IO or
54	>	* other external synchronization becomes exhausted. This usage
55	>	* restriction is in part enforced by not permitting checked
56	>	* exceptions such as {@code IOExceptions} to be thrown. However,
57	>	* computations may still encounter unchecked exceptions, that are
58	>	* rethrown to callers attempting to join them. These exceptions may
59	>	* additionally include RejectedExecutionExceptions stemming from
60	>	* internal resource exhaustion such as failure to allocate internal
61	>	* task queues.
62		*
63		* <p>The primary method for awaiting completion and extracting
64		* results of a task is {@link #join}, but there are several variants:
#	Line 74 | Line 77 | import java.util.WeakHashMap;
77		* performs the most common form of parallel invocation: forking a set
78		* of tasks and joining them all.
79		*
80	<	* <p> The ForkJoinTask class is not usually directly subclassed.
80	>	* <p>The ForkJoinTask class is not usually directly subclassed.
81		* Instead, you subclass one of the abstract classes that support a
82	<	* particular style of fork/join processing.  Normally, a concrete
82	>	* particular style of fork/join processing, typically {@link
83	>	* RecursiveAction} for computations that do not return results, or
84	>	* {@link RecursiveTask} for those that do.  Normally, a concrete
85		* ForkJoinTask subclass declares fields comprising its parameters,
86		* established in a constructor, and then defines a {@code compute}
87		* method that somehow uses the control methods supplied by this base
88		* 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		* methods), some of them may only be called from within other
91		* ForkJoinTasks (as may be determined using method {@link
92		* #inForkJoinPool}).  Attempts to invoke them in other contexts
93		* result in exceptions or errors, possibly including
94		* ClassCastException.
95		*
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
100	<	* 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	>	* provided by this class.
105		*
106		* <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.
113		*
114	<	* <p>ForkJoinTasks are {@code Serializable}, which enables them
115	<	* to be used in extensions such as remote execution frameworks. It is
116	<	* in general sensible to serialize tasks only before or after, but
117	<	* not during execution. Serialization is not relied on during
118	<	* execution itself.
114	>	* <p>This class provides {@code adapt} methods for {@link
115	>	* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
116	>	* may be of use when mixing execution of ForkJoinTasks with other
117	>	* kinds of tasks. When all tasks are of this form, consider using a
118	>	* pool in {@link ForkJoinPool#setAsyncMode}.
119	>	*
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		*
125		* @since 1.7
126		* @author Doug Lea
#	Line 486 | Line 496 | public abstract class ForkJoinTask<V> im
496		/**
497		* Arranges to asynchronously execute this task.  While it is not
498		* 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	>	* <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.
507	>	* @return {@code this}, to simplify usage
508		*/
509		public final ForkJoinTask<V> fork() {
510		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 502 | Line 514 | public abstract class ForkJoinTask<V> im
514
515		/**
516		* 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		*
521		* @return the computed result
522		*/
#	Line 531 | Line 543 | public abstract class ForkJoinTask<V> im
543		}
544
545		/**
546	<	* Forks both tasks, returning when {@code isDone} holds for
547	<	* both of them 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.
552	<	*
553	<	* @param t1 one task
554	<	* @param t2 the other task
555	<	* @throws NullPointerException if t1 or t2 are null
556	<	* @throws RuntimeException or Error if either task did so
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	>	* @param t1 the first task
556	>	* @param t2 the second task
557	>	* @throws NullPointerException if any task is null
558	>	* @throws RuntimeException or Error if a task did so
559		*/
560	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
560	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
561		t2.fork();
562		t1.invoke();
563		t2.join();
564		}
565
566		/**
567	<	* Forks the given tasks, returning when {@code isDone} holds
568	<	* for all of them. If any task encounters an exception, others
569	<	* may be cancelled.  This method may be invoked only from within
570	<	* ForkJoinTask computations (as may be determined using method
571	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
572	<	* result in exceptions or errors, possibly including
573	<	* ClassCastException.
567	>	* Forks the given tasks, returning when {@code isDone} holds for
568	>	* each task or an exception is encountered. If any task
569	>	* encounters an exception, others may be, but are not guaranteed
570	>	* to be, cancelled.
571	>	*
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 array of tasks
578	>	* @param tasks the tasks
579		* @throws NullPointerException if tasks or any element are null
580		* @throws RuntimeException or Error if any task did so
581		*/
#	Line 596 | Line 613 | public abstract class ForkJoinTask<V> im
613		}
614
615		/**
616	<	* Forks all tasks in the collection, returning when
617	<	* {@code isDone} holds for all of them. If any task
618	<	* encounters an exception, others may be cancelled.  This method
619	<	* may be invoked only from within ForkJoinTask computations (as
620	<	* may be determined using method {@link
621	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
622	<	* in exceptions or errors, possibly 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
#	Line 610 | Line 632 | public abstract class ForkJoinTask<V> im
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		}
#	Line 683 | Line 705 | public abstract class ForkJoinTask<V> im
705		*
706		* <p>This method may be overridden in subclasses, but if so, must
707		* still ensure that these minimal properties hold. In particular,
708	<	* the cancel method itself must not throw exceptions.
708	>	* the {@code cancel} method itself must not throw exceptions.
709		*
710	<	* <p> This method is designed to be invoked by <em>other</em>
710	>	* <p>This method is designed to be invoked by <em>other</em>
711		* tasks. To terminate the current task, you can just return or
712		* throw an unchecked exception from its computation method, or
713		* invoke {@link #completeExceptionally}.
#	Line 712 | Line 734 | public abstract class ForkJoinTask<V> im
734
735		/**
736		* Returns the exception thrown by the base computation, or a
737	<	* CancellationException if cancelled, or null if none or if the
738	<	* method has not yet completed.
737	>	* {@code CancellationException} if cancelled, or {@code null} if
738	>	* none or if the method has not yet completed.
739		*
740		* @return the exception, or {@code null} if none
741		*/
#	Line 732 | Line 754 | public abstract class ForkJoinTask<V> im
754		* {@code join} and related operations. This method may be used
755		* to induce exceptions in asynchronous tasks, or to force
756		* completion of tasks that would not otherwise complete.  Its use
757	<	* in other situations is likely to be wrong.  This method is
757	>	* in other situations is discouraged.  This method is
758		* overridable, but overridden versions must invoke {@code super}
759		* implementation to maintain guarantees.
760		*
#	Line 752 | Line 774 | public abstract class ForkJoinTask<V> im
774		* operations. This method may be used to provide results for
775		* asynchronous tasks, or to provide alternative handling for
776		* tasks that would not otherwise complete normally. Its use in
777	<	* other situations is likely to be wrong. This method is
777	>	* other situations is discouraged. This method is
778		* overridable, but overridden versions must invoke {@code super}
779		* implementation to maintain guarantees.
780		*
#	Line 791 | Line 813 | public abstract class ForkJoinTask<V> im
813		* there are no potential dependencies between continuation of the
814		* current task and that of any other task that might be executed
815		* while helping. (This usually holds for pure divide-and-conquer
816	<	* tasks). This method may be invoked only from within
817	<	* ForkJoinTask computations (as may be determined using method
818	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
819	<	* result in exceptions or errors, possibly including
820	<	* ClassCastException.
816	>	* tasks).
817	>	*
818	>	* <p>This method may be invoked only from within {@code
819	>	* ForkJoinTask} computations (as may be determined using method
820	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
821	>	* result in exceptions or errors, possibly including {@code
822	>	* ClassCastException}.
823		*
824		* @return the computed result
825		*/
#	Line 808 | Line 832 | public abstract class ForkJoinTask<V> im
832
833		/**
834		* Possibly executes other tasks until this task is ready.  This
835	<	* method may be invoked only from within ForkJoinTask
836	<	* computations (as may be determined using method {@link
837	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
838	<	* in exceptions or errors, possibly including ClassCastException.
835	>	* method may be useful when processing collections of tasks when
836	>	* some have been cancelled or otherwise known to have aborted.
837	>	*
838	>	* <p>This method may be invoked only from within {@code
839	>	* ForkJoinTask} computations (as may be determined using method
840	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
841	>	* result in exceptions or errors, possibly including {@code
842	>	* ClassCastException}.
843		*/
844		public final void quietlyHelpJoin() {
845		if (status >= 0) {
#	Line 853 | Line 881 | public abstract class ForkJoinTask<V> im
881		* {@link ForkJoinPool#isQuiescent}. This method may be of use in
882		* designs in which many tasks are forked, but none are explicitly
883		* joined, instead executing them until all are processed.
884	+	*
885	+	* <p>This method may be invoked only from within {@code
886	+	* ForkJoinTask} computations (as may be determined using method
887	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
888	+	* result in exceptions or errors, possibly including {@code
889	+	* ClassCastException}.
890		*/
891		public static void helpQuiesce() {
892		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 865 | Line 899 | public abstract class ForkJoinTask<V> im
899		* this task, but only if reuse occurs when this task has either
900		* never been forked, or has been forked, then completed and all
901		* outstanding joins of this task have also completed. Effects
902	<	* under any other usage conditions are not guaranteed, and are
903	<	* almost surely wrong. This method may be useful when executing
902	>	* under any other usage conditions are not guaranteed.
903	>	* This method may be useful when executing
904		* pre-constructed trees of subtasks in loops.
905		*/
906		public void reinitialize() {
#	Line 879 | Line 913 | public abstract class ForkJoinTask<V> im
913		* Returns the pool hosting the current task execution, or null
914		* if this task is executing outside of any ForkJoinPool.
915		*
916	+	* @see #inForkJoinPool
917		* @return the pool, or {@code null} if none
918		*/
919		public static ForkJoinPool getPool() {
#	Line 904 | Line 939 | public abstract class ForkJoinTask<V> im
939		* by the current thread, and has not commenced executing in
940		* another thread.  This method may be useful when arranging
941		* alternative local processing of tasks that could have been, but
942	<	* were not, stolen. This method may be invoked only from within
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
946	<	* ClassCastException.
942	>	* were not, stolen.
943	>	*
944	>	* <p>This method may be invoked only from within {@code
945	>	* ForkJoinTask} computations (as may be determined using method
946	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
947	>	* result in exceptions or errors, possibly including {@code
948	>	* ClassCastException}.
949		*
950		* @return {@code true} if unforked
951		*/
#	Line 923 | Line 960 | public abstract class ForkJoinTask<V> im
960		* value may be useful for heuristic decisions about whether to
961		* fork other tasks.
962		*
963	+	* <p>This method may be invoked only from within {@code
964	+	* ForkJoinTask} computations (as may be determined using method
965	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
966	+	* result in exceptions or errors, possibly including {@code
967	+	* ClassCastException}.
968	+	*
969		* @return the number of tasks
970		*/
971		public static int getQueuedTaskCount() {
#	Line 940 | Line 983 | public abstract class ForkJoinTask<V> im
983		* tasks, and to process computations locally if this threshold is
984		* exceeded.
985		*
986	+	* <p>This method may be invoked only from within {@code
987	+	* ForkJoinTask} computations (as may be determined using method
988	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
989	+	* result in exceptions or errors, possibly including {@code
990	+	* ClassCastException}.
991	+	*
992		* @return the surplus number of tasks, which may be negative
993		*/
994		public static int getSurplusQueuedTaskCount() {
#	Line 991 | Line 1040 | public abstract class ForkJoinTask<V> im
1040		* null even if a task exists but cannot be accessed without
1041		* contention with other threads.  This method is designed
1042		* primarily to support extensions, and is unlikely to be useful
1043	<	* otherwise.  This method may be invoked only from within
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
1047	<	* ClassCastException.
1043	>	* otherwise.
1044	>	*
1045	>	* <p>This method may be invoked only from within {@code
1046	>	* ForkJoinTask} computations (as may be determined using method
1047	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1048	>	* result in exceptions or errors, possibly including {@code
1049	>	* ClassCastException}.
1050		*
1051		* @return the next task, or {@code null} if none are available
1052		*/
#	Line 1008 | Line 1059 | public abstract class ForkJoinTask<V> im
1059		* Unschedules and returns, without executing, the next task
1060		* queued by the current thread but not yet executed.  This method
1061		* is designed primarily to support extensions, and is unlikely to
1062	<	* be useful otherwise.  This method may be invoked only from
1063	<	* within ForkJoinTask computations (as may be determined using
1064	<	* method {@link #inForkJoinPool}). Attempts to invoke in other
1065	<	* contexts result in exceptions or errors, possibly including
1066	<	* ClassCastException.
1062	>	* be useful otherwise.
1063	>	*
1064	>	* <p>This method may be invoked only from within {@code
1065	>	* ForkJoinTask} computations (as may be determined using method
1066	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1067	>	* result in exceptions or errors, possibly including {@code
1068	>	* ClassCastException}.
1069		*
1070		* @return the next task, or {@code null} if none are available
1071		*/
#	Line 1029 | Line 1082 | public abstract class ForkJoinTask<V> im
1082		* {@code null} result does not necessarily imply quiescence
1083		* of the pool this task is operating in.  This method is designed
1084		* primarily to support extensions, and is unlikely to be useful
1085	<	* otherwise.  This method may be invoked only from within
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
1089	<	* ClassCastException.
1085	>	* otherwise.
1086	>	*
1087	>	* <p>This method may be invoked only from within {@code
1088	>	* ForkJoinTask} computations (as may be determined using method
1089	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1090	>	* result in exceptions or errors, possibly including {@code
1091	>	* ClassCastException}.
1092		*
1093		* @return a task, or {@code null} if none are available
1094		*/
#	Line 1073 | Line 1128 | public abstract class ForkJoinTask<V> im
1128		*/
1129		static final class AdaptedCallable<T> extends ForkJoinTask<T>
1130		implements RunnableFuture<T> {
1131	<	final Callable<T> callable;
1131	>	final Callable<? extends T> callable;
1132		T result;
1133	<	AdaptedCallable(Callable<T> callable) {
1133	>	AdaptedCallable(Callable<? extends T> callable) {
1134		if (callable == null) throw new NullPointerException();
1135		this.callable = callable;
1136		}
#	Line 1098 | Line 1153 | public abstract class ForkJoinTask<V> im
1153		}
1154
1155		/**
1156	<	* Returns a new ForkJoinTask that performs the {@code run}
1157	<	* method of the given Runnable as its action, and returns a null
1158	<	* result upon {@code join}.
1156	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1157	>	* method of the given {@code Runnable} as its action, and returns
1158	>	* a null result upon {@link #join}.
1159		*
1160		* @param runnable the runnable action
1161		* @return the task
1162		*/
1163	<	public static ForkJoinTask<Void> adapt(Runnable runnable) {
1163	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1164		return new AdaptedRunnable<Void>(runnable, null);
1165		}
1166
1167		/**
1168	<	* Returns a new ForkJoinTask that performs the {@code run}
1169	<	* method of the given Runnable as its action, and returns the
1170	<	* given result upon {@code join}.
1168	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1169	>	* method of the given {@code Runnable} as its action, and returns
1170	>	* the given result upon {@link #join}.
1171		*
1172		* @param runnable the runnable action
1173		* @param result the result upon completion
#	Line 1123 | Line 1178 | public abstract class ForkJoinTask<V> im
1178		}
1179
1180		/**
1181	<	* Returns a new ForkJoinTask that performs the {@code call}
1182	<	* method of the given Callable as its action, and returns its
1183	<	* result upon {@code join}, translating any checked
1184	<	* exceptions encountered into {@code RuntimeException}.
1181	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1182	>	* method of the given {@code Callable} as its action, and returns
1183	>	* its result upon {@link #join}, translating any checked exceptions
1184	>	* encountered into {@code RuntimeException}.
1185		*
1186		* @param callable the callable action
1187		* @return the task
1188		*/
1189	<	public static <T> ForkJoinTask<T> adapt(Callable<T> callable) {
1189	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1190		return new AdaptedCallable<T>(callable);
1191		}
1192

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