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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.24 by jsr166, Mon Jul 27 21:41:53 2009 UTC vs.
Revision 1.27 by dl, Sun Aug 2 11:54:31 2009 UTC

#	Line 16 | Line 16 | import java.util.Map;
16		import java.util.WeakHashMap;
17
18		/**
19	<	* Abstract base class for tasks that run within a {@link
20	<	* ForkJoinPool}.  A ForkJoinTask is a thread-like entity that is much
19	>	* Abstract base class for tasks that run within a {@link ForkJoinPool}.
20	>	* A {@code ForkJoinTask} is a thread-like entity that is much
21		* lighter weight than a normal thread.  Huge numbers of tasks and
22		* subtasks may be hosted by a small number of actual threads in a
23		* ForkJoinPool, at the price of some usage limitations.
#	Line 76 | Line 76 | import java.util.WeakHashMap;
76		*
77		* <p> The ForkJoinTask class is not usually directly subclassed.
78		* Instead, you subclass one of the abstract classes that support a
79	<	* particular style of fork/join processing.  Normally, a concrete
79	>	* particular style of fork/join processing, typically {@link
80	>	* RecursiveAction} for computations that do not return results, or
81	>	* {@link RecursiveTask} for those that do.  Normally, a concrete
82		* ForkJoinTask subclass declares fields comprising its parameters,
83		* established in a constructor, and then defines a {@code compute}
84		* method that somehow uses the control methods supplied by this base
#	Line 106 | Line 108 | import java.util.WeakHashMap;
108		* parallelism cannot improve throughput. If too small, then memory
109		* and internal task maintenance overhead may overwhelm processing.
110		*
111	+	* <p>This class provides {@code adapt} methods for {@link
112	+	* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
113	+	* may be of use when mixing execution of ForkJoinTasks with other
114	+	* kinds of tasks. When all tasks are of this form, consider using a
115	+	* pool in {@link ForkJoinPool#setAsyncMode}.
116	+	*
117		* <p>ForkJoinTasks are {@code Serializable}, which enables them
118		* to be used in extensions such as remote execution frameworks. It is
119		* in general sensible to serialize tasks only before or after, but
#	Line 247 | Line 255 | public abstract class ForkJoinTask<V> im
255		synchronized (this) {
256		try {
257		while (status >= 0) {
258	<	long nt = nanos - System.nanoTime() - startTime;
258	>	long nt = nanos - (System.nanoTime() - startTime);
259		if (nt <= 0)
260		break;
261		wait(nt / 1000000, (int) (nt % 1000000));
#	Line 531 | Line 539 | public abstract class ForkJoinTask<V> im
539		}
540
541		/**
542	<	* Forks both tasks, returning when {@code isDone} holds for
543	<	* both of them or an exception is encountered. This method may be
542	>	* Forks the given tasks, returning when {@code isDone} holds for
543	>	* each task or an exception is encountered. This method may be
544		* invoked only from within ForkJoinTask computations (as may be
545		* determined using method {@link #inForkJoinPool}). Attempts to
546		* invoke in other contexts result in exceptions or errors,
547		* possibly including ClassCastException.
548		*
549	<	* @param t1 one task
550	<	* @param t2 the other task
551	<	* @throws NullPointerException if t1 or t2 are null
552	<	* @throws RuntimeException or Error if either task did so
549	>	* @param t1 the first task
550	>	* @param t2 the second task
551	>	* @throws NullPointerException if any task is null
552	>	* @throws RuntimeException or Error if a task did so
553		*/
554		public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
555		t2.fork();
#	Line 550 | Line 558 | public abstract class ForkJoinTask<V> im
558		}
559
560		/**
561	<	* Forks the given tasks, returning when {@code isDone} holds
562	<	* for all of them. If any task encounters an exception, others
563	<	* may be cancelled.  This method may be invoked only from within
561	>	* Forks the given tasks, returning when {@code isDone} holds for
562	>	* each task or an exception is encountered. If any task
563	>	* encounters an exception, others may be, but are not guaranteed
564	>	* to be, cancelled.  This method may be invoked only from within
565		* ForkJoinTask computations (as may be determined using method
566		* {@link #inForkJoinPool}). Attempts to invoke in other contexts
567		* result in exceptions or errors, possibly including
568		* ClassCastException.
569		*
570	<	* @param tasks the array of tasks
570	>	* Overloadings of this method exist for the special cases
571	>	* of one to four arguments.
572	>	*
573	>	* @param tasks the tasks
574		* @throws NullPointerException if tasks or any element are null
575		* @throws RuntimeException or Error if any task did so
576		*/
#	Line 596 | Line 608 | public abstract class ForkJoinTask<V> im
608		}
609
610		/**
611	<	* Forks all tasks in the collection, returning when
612	<	* {@code isDone} holds for all of them. If any task
613	<	* encounters an exception, others may be cancelled.  This method
614	<	* may be invoked only from within ForkJoinTask computations (as
615	<	* may be determined using method {@link
616	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
617	<	* in exceptions or errors, possibly including ClassCastException.
611	>	* Forks all tasks in the collection, returning when {@code
612	>	* isDone} holds for each task or an exception is encountered. If
613	>	* any task encounters an exception, others may be, but are not
614	>	* guaranteed to be, cancelled.  This method may be invoked only
615	>	* from within ForkJoinTask computations (as may be determined
616	>	* using method {@link #inForkJoinPool}). Attempts to invoke in
617	>	* other contexts result in exceptions or errors, possibly
618	>	* including ClassCastException.
619		*
620		* @param tasks the collection of tasks
621		* @return the tasks argument, to simplify usage
#	Line 732 | Line 745 | public abstract class ForkJoinTask<V> im
745		* {@code join} and related operations. This method may be used
746		* to induce exceptions in asynchronous tasks, or to force
747		* completion of tasks that would not otherwise complete.  Its use
748	<	* in other situations is likely to be wrong.  This method is
748	>	* in other situations is discouraged.  This method is
749		* overridable, but overridden versions must invoke {@code super}
750		* implementation to maintain guarantees.
751		*
#	Line 752 | Line 765 | public abstract class ForkJoinTask<V> im
765		* operations. This method may be used to provide results for
766		* asynchronous tasks, or to provide alternative handling for
767		* tasks that would not otherwise complete normally. Its use in
768	<	* other situations is likely to be wrong. This method is
768	>	* other situations is discouraged. This method is
769		* overridable, but overridden versions must invoke {@code super}
770		* implementation to maintain guarantees.
771		*
#	Line 777 | Line 790 | public abstract class ForkJoinTask<V> im
790
791		public final V get(long timeout, TimeUnit unit)
792		throws InterruptedException, ExecutionException, TimeoutException {
793	+	long nanos = unit.toNanos(timeout);
794		ForkJoinWorkerThread w = getWorker();
795		if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
796	<	awaitDone(w, unit.toNanos(timeout));
796	>	awaitDone(w, nanos);
797		return reportTimedFutureResult();
798		}
799
#	Line 851 | Line 865 | public abstract class ForkJoinTask<V> im
865		* Possibly executes tasks until the pool hosting the current task
866		* {@link ForkJoinPool#isQuiescent}. This method may be of use in
867		* designs in which many tasks are forked, but none are explicitly
868	<	* joined, instead executing them until all are processed.
868	>	* joined, instead executing them until all are processed.  This
869	>	* method may be invoked only from within ForkJoinTask
870	>	* computations (as may be determined using method {@link
871	>	* #inForkJoinPool}). Attempts to invoke in other contexts result
872	>	* in exceptions or errors, possibly including ClassCastException.
873		*/
874		public static void helpQuiesce() {
875		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 865 | Line 883 | public abstract class ForkJoinTask<V> im
883		* never been forked, or has been forked, then completed and all
884		* outstanding joins of this task have also completed. Effects
885		* under any other usage conditions are not guaranteed, and are
886	<	* almost surely wrong. This method may be useful when executing
886	>	* discouraged. This method may be useful when executing
887		* pre-constructed trees of subtasks in loops.
888		*/
889		public void reinitialize() {
#	Line 878 | Line 896 | public abstract class ForkJoinTask<V> im
896		* Returns the pool hosting the current task execution, or null
897		* if this task is executing outside of any ForkJoinPool.
898		*
899	+	* @see #inForkJoinPool
900		* @return the pool, or {@code null} if none
901		*/
902		public static ForkJoinPool getPool() {
#	Line 920 | Line 939 | public abstract class ForkJoinTask<V> im
939		* Returns an estimate of the number of tasks that have been
940		* forked by the current worker thread but not yet executed. This
941		* value may be useful for heuristic decisions about whether to
942	<	* fork other tasks.
943	<	*
942	>	* fork other tasks.  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.
947		* @return the number of tasks
948		*/
949		public static int getQueuedTaskCount() {
#	Line 937 | Line 959 | public abstract class ForkJoinTask<V> im
959		* usages of ForkJoinTasks, at steady state, each worker should
960		* aim to maintain a small constant surplus (for example, 3) of
961		* tasks, and to process computations locally if this threshold is
962	<	* exceeded.
963	<	*
962	>	* exceeded.  This method may be invoked only from within
963	>	* ForkJoinTask computations (as may be determined using method
964	>	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
965	>	* result in exceptions or errors, possibly including
966	>	* ClassCastException.  *
967		* @return the surplus number of tasks, which may be negative
968		*/
969		public static int getSurplusQueuedTaskCount() {
#	Line 983 | Line 1008 | public abstract class ForkJoinTask<V> im
1008		protected abstract boolean exec();
1009
1010		/**
1011	<	* Returns, but does not unschedule or execute, the task queued by
1012	<	* the current thread but not yet executed, if one is
1011	>	* Returns, but does not unschedule or execute, a task queued by
1012	>	* the current thread but not yet executed, if one is immediately
1013		* available. There is no guarantee that this task will actually
1014	<	* be polled or executed next.  This method is designed primarily
1015	<	* to support extensions, and is unlikely to be useful otherwise.
1016	<	* This method may be invoked only from within ForkJoinTask
1017	<	* computations (as may be determined using method {@link
1018	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
1019	<	* in exceptions or errors, possibly including ClassCastException.
1014	>	* be polled or executed next. Conversely, this method may return
1015	>	* null even if a task exists but cannot be accessed without
1016	>	* contention with other threads.  This method is designed
1017	>	* primarily to support extensions, and is unlikely to be useful
1018	>	* otherwise.  This method may be invoked only from within
1019	>	* ForkJoinTask computations (as may be determined using method
1020	>	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1021	>	* result in exceptions or errors, possibly including
1022	>	* ClassCastException.
1023		*
1024		* @return the next task, or {@code null} if none are available
1025		*/
#	Line 1038 | Line 1066 | public abstract class ForkJoinTask<V> im
1066		.pollTask();
1067		}
1068
1069	<	// adaptors
1069	>	/**
1070	>	* Adaptor for Runnables. This implements RunnableFuture
1071	>	* to be compliant with AbstractExecutorService constraints
1072	>	* when used in ForkJoinPool.
1073	>	*/
1074	>	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1075	>	implements RunnableFuture<T> {
1076	>	final Runnable runnable;
1077	>	final T resultOnCompletion;
1078	>	T result;
1079	>	AdaptedRunnable(Runnable runnable, T result) {
1080	>	if (runnable == null) throw new NullPointerException();
1081	>	this.runnable = runnable;
1082	>	this.resultOnCompletion = result;
1083	>	}
1084	>	public T getRawResult() { return result; }
1085	>	public void setRawResult(T v) { result = v; }
1086	>	public boolean exec() {
1087	>	runnable.run();
1088	>	result = resultOnCompletion;
1089	>	return true;
1090	>	}
1091	>	public void run() { invoke(); }
1092	>	private static final long serialVersionUID = 5232453952276885070L;
1093	>	}
1094	>
1095	>	/**
1096	>	* Adaptor for Callables
1097	>	*/
1098	>	static final class AdaptedCallable<T> extends ForkJoinTask<T>
1099	>	implements RunnableFuture<T> {
1100	>	final Callable<? extends T> callable;
1101	>	T result;
1102	>	AdaptedCallable(Callable<? extends T> callable) {
1103	>	if (callable == null) throw new NullPointerException();
1104	>	this.callable = callable;
1105	>	}
1106	>	public T getRawResult() { return result; }
1107	>	public void setRawResult(T v) { result = v; }
1108	>	public boolean exec() {
1109	>	try {
1110	>	result = callable.call();
1111	>	return true;
1112	>	} catch (Error err) {
1113	>	throw err;
1114	>	} catch (RuntimeException rex) {
1115	>	throw rex;
1116	>	} catch (Exception ex) {
1117	>	throw new RuntimeException(ex);
1118	>	}
1119	>	}
1120	>	public void run() { invoke(); }
1121	>	private static final long serialVersionUID = 2838392045355241008L;
1122	>	}
1123
1124		/**
1125		* Returns a new ForkJoinTask that performs the {@code run}
#	Line 1048 | Line 1129 | public abstract class ForkJoinTask<V> im
1129		* @param runnable the runnable action
1130		* @return the task
1131		*/
1132	<	public static ForkJoinTask<Void> adapt(Runnable runnable) {
1133	<	return new ForkJoinPool.AdaptedRunnable<Void>(runnable, null);
1132	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1133	>	return new AdaptedRunnable<Void>(runnable, null);
1134		}
1135
1136		/**
#	Line 1062 | Line 1143 | public abstract class ForkJoinTask<V> im
1143		* @return the task
1144		*/
1145		public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
1146	<	return new ForkJoinPool.AdaptedRunnable<T>(runnable, result);
1146	>	return new AdaptedRunnable<T>(runnable, result);
1147		}
1148
1149		/**
#	Line 1074 | Line 1155 | public abstract class ForkJoinTask<V> im
1155		* @param callable the callable action
1156		* @return the task
1157		*/
1158	<	public static <T> ForkJoinTask<T> adapt(Callable<T> callable) {
1159	<	return new ForkJoinPool.AdaptedCallable<T>(callable);
1158	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1159	>	return new AdaptedCallable<T>(callable);
1160		}
1161
1162		// Serialization support

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