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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.30 by dl, Sun Aug 2 22:28:23 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
#	Line 54 | Line 55 | import java.util.WeakHashMap;
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 join them. These exceptions may
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.
#	Line 85 | Line 86 | import java.util.WeakHashMap;
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
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	>	* 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>This class provides {@code adapt} methods for {@link
115		* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
#	Line 116 | Line 117 | import java.util.WeakHashMap;
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
121	<	* 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		*
125		* @since 1.7
126		* @author Doug Lea
#	Line 496 | 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	<	* @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		*/
509		public final ForkJoinTask<V> fork() {
510		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 512 | 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 541 | Line 543 | public abstract class ForkJoinTask<V> im
543		}
544
545		/**
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		* @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();
#	Line 563 | Line 567 | public abstract class ForkJoinTask<V> im
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.  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
#	Line 610 | Line 613 | public abstract class ForkJoinTask<V> im
613		}
614
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
#	Line 625 | 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 806 | 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 823 | 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 867 | Line 880 | public abstract class ForkJoinTask<V> im
880		* Possibly executes tasks until the pool hosting the current task
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.  This
884	<	* method may be invoked only from within ForkJoinTask
885	<	* computations (as may be determined using method {@link
886	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
887	<	* in exceptions or errors, possibly including ClassCastException.
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 924 | 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 941 | Line 958 | public abstract class ForkJoinTask<V> im
958		* Returns an estimate of the number of tasks that have been
959		* forked by the current worker thread but not yet executed. This
960		* value may be useful for heuristic decisions about whether to
961	<	* fork other tasks.  This method may be invoked only from within
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
965	<	* ClassCastException.
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 961 | Line 981 | public abstract class ForkJoinTask<V> im
981		* usages of ForkJoinTasks, at steady state, each worker should
982		* aim to maintain a small constant surplus (for example, 3) of
983		* tasks, and to process computations locally if this threshold is
984	<	* exceeded.  This method may be invoked only from within
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
988	<	* ClassCastException.
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 1017 | 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 1034 | 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 1055 | 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 1124 | 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
#	Line 1136 | Line 1165 | public abstract class ForkJoinTask<V> im
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 1149 | 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

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