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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.86 by dl, Mon Feb 20 18:20:06 2012 UTC vs.
Revision 1.99 by jsr166, Wed Jan 9 02:51:37 2013 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	+
9		import java.io.Serializable;
10		import java.util.Collection;
11		import java.util.List;
#	Line 29 | Line 30 | import java.lang.reflect.Constructor;
30		* subtasks may be hosted by a small number of actual threads in a
31		* ForkJoinPool, at the price of some usage limitations.
32		*
33	<	* <p>A "main" {@code ForkJoinTask} begins execution when submitted
34	<	* to a {@link ForkJoinPool}.  Once started, it will usually in turn
35	<	* start other subtasks.  As indicated by the name of this class,
36	<	* many programs using {@code ForkJoinTask} employ only methods
37	<	* {@link #fork} and {@link #join}, or derivatives such as {@link
33	>	* <p>A "main" {@code ForkJoinTask} begins execution when it is
34	>	* explicitly submitted to a {@link ForkJoinPool}, or, if not already
35	>	* engaged in a ForkJoin computation, commenced in the {@link
36	>	* ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or
37	>	* related methods.  Once started, it will usually in turn start other
38	>	* subtasks.  As indicated by the name of this class, many programs
39	>	* using {@code ForkJoinTask} employ only methods {@link #fork} and
40	>	* {@link #join}, or derivatives such as {@link
41		* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
42		* provides a number of other methods that can come into play in
43	<	* advanced usages, as well as extension mechanics that allow
44	<	* support of new forms of fork/join processing.
43	>	* advanced usages, as well as extension mechanics that allow support
44	>	* of new forms of fork/join processing.
45		*
46		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
47		* The efficiency of {@code ForkJoinTask}s stems from a set of
#	Line 51 | Line 55 | import java.lang.reflect.Constructor;
55		* minimize other blocking synchronization apart from joining other
56		* tasks or using synchronizers such as Phasers that are advertised to
57		* cooperate with fork/join scheduling. Subdividable tasks should also
58	<	* not perform blocking IO, and should ideally access variables that
58	>	* not perform blocking I/O, and should ideally access variables that
59		* are completely independent of those accessed by other running
60		* tasks. These guidelines are loosely enforced by not permitting
61		* checked exceptions such as {@code IOExceptions} to be
#	Line 69 | Line 73 | import java.lang.reflect.Constructor;
73		* <p>It is possible to define and use ForkJoinTasks that may block,
74		* but doing do requires three further considerations: (1) Completion
75		* of few if any <em>other</em> tasks should be dependent on a task
76	<	* that blocks on external synchronization or IO. Event-style async
77	<	* tasks that are never joined often fall into this category.  (2) To
78	<	* minimize resource impact, tasks should be small; ideally performing
79	<	* only the (possibly) blocking action. (3) Unless the {@link
76	>	* that blocks on external synchronization or I/O. Event-style async
77	>	* tasks that are never joined (for example, those subclassing {@link
78	>	* CountedCompleter}) often fall into this category.  (2) To minimize
79	>	* resource impact, tasks should be small; ideally performing only the
80	>	* (possibly) blocking action. (3) Unless the {@link
81		* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
82		* blocked tasks is known to be less than the pool's {@link
83		* ForkJoinPool#getParallelism} level, the pool cannot guarantee that
#	Line 115 | Line 120 | import java.lang.reflect.Constructor;
120		* <p>The ForkJoinTask class is not usually directly subclassed.
121		* Instead, you subclass one of the abstract classes that support a
122		* particular style of fork/join processing, typically {@link
123	<	* RecursiveAction} for computations that do not return results, or
124	<	* {@link RecursiveTask} for those that do.  Normally, a concrete
125	<	* ForkJoinTask subclass declares fields comprising its parameters,
126	<	* established in a constructor, and then defines a {@code compute}
127	<	* method that somehow uses the control methods supplied by this base
128	<	* class. While these methods have {@code public} access (to allow
129	<	* instances of different task subclasses to call each other's
125	<	* methods), some of them may only be called from within other
126	<	* ForkJoinTasks (as may be determined using method {@link
127	<	* #inForkJoinPool}).  Attempts to invoke them in other contexts
128	<	* result in exceptions or errors, possibly including
129	<	* {@code ClassCastException}.
123	>	* RecursiveAction} for most computations that do not return results,
124	>	* {@link RecursiveTask} for those that do, and {@link
125	>	* CountedCompleter} for those in which completed actions trigger
126	>	* other actions.  Normally, a concrete ForkJoinTask subclass declares
127	>	* fields comprising its parameters, established in a constructor, and
128	>	* then defines a {@code compute} method that somehow uses the control
129	>	* methods supplied by this base class.
130		*
131		* <p>Method {@link #join} and its variants are appropriate for use
132		* only when completion dependencies are acyclic; that is, the
#	Line 137 | Line 137 | import java.lang.reflect.Constructor;
137		* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
138		* may be of use in constructing custom subclasses for problems that
139		* are not statically structured as DAGs. To support such usages a
140	<	* ForkJoinTask may be atomically <em>marked</em> using {@link
141	<	* #markForkJoinTask} and checked for marking using {@link
142	<	* #isMarkedForkJoinTask}. The ForkJoinTask implementation does not
143	<	* use these {@code protected} methods or marks for any purpose, but
144	<	* they may be of use in the construction of specialized subclasses.
145	<	* For example, parallel graph traversals can use the supplied methods
146	<	* to avoid revisiting nodes/tasks that have already been processed.
147	<	* Also, completion based designs can use them to record that one
148	<	* subtask has completed. (Method names for marking are bulky in part
149	<	* to encourage definition of methods that reflect their usage
150	<	* patterns.)
140	>	* ForkJoinTask may be atomically <em>tagged</em> with a {@code short}
141	>	* value using {@link #setForkJoinTaskTag} or {@link
142	>	* #compareAndSetForkJoinTaskTag} and checked using {@link
143	>	* #getForkJoinTaskTag}. The ForkJoinTask implementation does not use
144	>	* these {@code protected} methods or tags for any purpose, but they
145	>	* may be of use in the construction of specialized subclasses.  For
146	>	* example, parallel graph traversals can use the supplied methods to
147	>	* avoid revisiting nodes/tasks that have already been processed.
148	>	* (Method names for tagging are bulky in part to encourage definition
149	>	* of methods that reflect their usage patterns.)
150		*
151		* <p>Most base support methods are {@code final}, to prevent
152		* overriding of implementations that are intrinsically tied to the
#	Line 213 | Line 212 | public abstract class ForkJoinTask<V> im
212		* thin-lock techniques, so use some odd coding idioms that tend
213		* to avoid them, mainly by arranging that every synchronized
214		* block performs a wait, notifyAll or both.
215	+	*
216	+	* These control bits occupy only (some of) the upper half (16
217	+	* bits) of status field. The lower bits are used for user-defined
218	+	* tags.
219		*/
220
221		/** The run status of this task */
#	Line 221 | Line 224 | public abstract class ForkJoinTask<V> im
224		static final int NORMAL      = 0xf0000000;  // must be negative
225		static final int CANCELLED   = 0xc0000000;  // must be < NORMAL
226		static final int EXCEPTIONAL = 0x80000000;  // must be < CANCELLED
227	<	static final int SIGNAL      = 0x00000001;
228	<	static final int MARKED      = 0x00000002;
227	>	static final int SIGNAL      = 0x00010000;  // must be >= 1 << 16
228	>	static final int SMASK       = 0x0000ffff;  // short bits for tags
229
230		/**
231		* Marks completion and wakes up threads waiting to join this
232	<	* task. A specialization for NORMAL completion is in method
230	<	* doExec.
232	>	* task.
233		*
234		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
235		* @return completion status on exit
#	Line 237 | Line 239 | public abstract class ForkJoinTask<V> im
239		if ((s = status) < 0)
240		return s;
241		if (U.compareAndSwapInt(this, STATUS, s, s | completion)) {
242	<	if ((s & SIGNAL) != 0)
242	>	if ((s >>> 16) != 0)
243		synchronized (this) { notifyAll(); }
244		return completion;
245		}
#	Line 259 | Line 261 | public abstract class ForkJoinTask<V> im
261		} catch (Throwable rex) {
262		return setExceptionalCompletion(rex);
263		}
264	<	while ((s = status) >= 0 && completed) {
265	<	if (U.compareAndSwapInt(this, STATUS, s, s | NORMAL)) {
264	<	if ((s & SIGNAL) != 0)
265	<	synchronized (this) { notifyAll(); }
266	<	return NORMAL;
267	<	}
268	<	}
264	>	if (completed)
265	>	s = setCompletion(NORMAL);
266		}
267		return s;
268		}
269
270		/**
271	<	* Tries to set SIGNAL status. Used by ForkJoinPool. Other
272	<	* variants are directly incorporated into externalAwaitDone etc.
271	>	* Tries to set SIGNAL status unless already completed. Used by
272	>	* ForkJoinPool. Other variants are directly incorporated into
273	>	* externalAwaitDone etc.
274		*
275		* @return true if successful
276		*/
277		final boolean trySetSignal() {
278	<	int s;
279	<	return U.compareAndSwapInt(this, STATUS, s = status, s | SIGNAL);
278	>	int s = status;
279	>	return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL);
280		}
281
282		/**
#	Line 286 | Line 284 | public abstract class ForkJoinTask<V> im
284		* @return status upon completion
285		*/
286		private int externalAwaitDone() {
289	–	boolean interrupted = false;
287		int s;
288	+	ForkJoinPool.externalHelpJoin(this);
289	+	boolean interrupted = false;
290		while ((s = status) >= 0) {
291		if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
292		synchronized (this) {
#	Line 315 | Line 314 | public abstract class ForkJoinTask<V> im
314		int s;
315		if (Thread.interrupted())
316		throw new InterruptedException();
317	+	ForkJoinPool.externalHelpJoin(this);
318		while ((s = status) >= 0) {
319		if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
320		synchronized (this) {
#	Line 338 | Line 338 | public abstract class ForkJoinTask<V> im
338		*/
339		private int doJoin() {
340		int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
341	<	if ((s = status) >= 0) {
342	<	if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) {
343	<	if (!(w = (wt = (ForkJoinWorkerThread)t).workQueue).
344	<	tryUnpush(this) || (s = doExec()) >= 0)
345	<	s = wt.pool.awaitJoin(w, this);
346	<	}
347	<	else
348	<	s = externalAwaitDone();
349	<	}
350	<	return s;
341	>	return (s = status) < 0 ? s :
342	>	((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
343	>	(w = (wt = (ForkJoinWorkerThread)t).workQueue).
344	>	tryUnpush(this) && (s = doExec()) < 0 ? s :
345	>	wt.pool.awaitJoin(w, this) :
346	>	externalAwaitDone();
347		}
348
349		/**
#	Line 357 | Line 353 | public abstract class ForkJoinTask<V> im
353		*/
354		private int doInvoke() {
355		int s; Thread t; ForkJoinWorkerThread wt;
356	<	if ((s = doExec()) >= 0) {
357	<	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
358	<	s = (wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue,
359	<	this);
364	<	else
365	<	s = externalAwaitDone();
366	<	}
367	<	return s;
356	>	return (s = doExec()) < 0 ? s :
357	>	((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
358	>	(wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue, this) :
359	>	externalAwaitDone();
360		}
361
362		// Exception table support
#	Line 412 | Line 404 | public abstract class ForkJoinTask<V> im
404		}
405
406		/**
407	<	* Records exception and sets exceptional completion.
407	>	* Records exception and sets status.
408		*
409		* @return status on exit
410		*/
411	<	private int setExceptionalCompletion(Throwable ex) {
412	<	int h = System.identityHashCode(this);
413	<	final ReentrantLock lock = exceptionTableLock;
414	<	lock.lock();
415	<	try {
416	<	expungeStaleExceptions();
417	<	ExceptionNode[] t = exceptionTable;
418	<	int i = h & (t.length - 1);
419	<	for (ExceptionNode e = t[i]; ; e = e.next) {
420	<	if (e == null) {
421	<	t[i] = new ExceptionNode(this, ex, t[i]);
422	<	break;
411	>	final int recordExceptionalCompletion(Throwable ex) {
412	>	int s;
413	>	if ((s = status) >= 0) {
414	>	int h = System.identityHashCode(this);
415	>	final ReentrantLock lock = exceptionTableLock;
416	>	lock.lock();
417	>	try {
418	>	expungeStaleExceptions();
419	>	ExceptionNode[] t = exceptionTable;
420	>	int i = h & (t.length - 1);
421	>	for (ExceptionNode e = t[i]; ; e = e.next) {
422	>	if (e == null) {
423	>	t[i] = new ExceptionNode(this, ex, t[i]);
424	>	break;
425	>	}
426	>	if (e.get() == this) // already present
427	>	break;
428		}
429	<	if (e.get() == this) // already present
430	<	break;
429	>	} finally {
430	>	lock.unlock();
431		}
432	<	} finally {
436	<	lock.unlock();
432	>	s = setCompletion(EXCEPTIONAL);
433		}
434	<	return setCompletion(EXCEPTIONAL);
434	>	return s;
435	>	}
436	>
437	>	/**
438	>	* Records exception and possibly propagates.
439	>	*
440	>	* @return status on exit
441	>	*/
442	>	private int setExceptionalCompletion(Throwable ex) {
443	>	int s = recordExceptionalCompletion(ex);
444	>	if ((s & DONE_MASK) == EXCEPTIONAL)
445	>	internalPropagateException(ex);
446	>	return s;
447	>	}
448	>
449	>	/**
450	>	* Hook for exception propagation support for tasks with completers.
451	>	*/
452	>	void internalPropagateException(Throwable ex) {
453		}
454
455		/**
#	Line 517 | Line 531 | public abstract class ForkJoinTask<V> im
531		Throwable ex;
532		if (e == null || (ex = e.ex) == null)
533		return null;
534	<	if (e.thrower != Thread.currentThread().getId()) {
534	>	if (false && e.thrower != Thread.currentThread().getId()) {
535		Class<? extends Throwable> ec = ex.getClass();
536		try {
537		Constructor<?> noArgCtor = null;
#	Line 584 | Line 598 | public abstract class ForkJoinTask<V> im
598		}
599
600		/**
601	+	* A version of "sneaky throw" to relay exceptions
602	+	*/
603	+	static void rethrow(final Throwable ex) {
604	+	if (ex != null) {
605	+	if (ex instanceof Error)
606	+	throw (Error)ex;
607	+	if (ex instanceof RuntimeException)
608	+	throw (RuntimeException)ex;
609	+	ForkJoinTask.<RuntimeException>uncheckedThrow(ex);
610	+	}
611	+	}
612	+
613	+	/**
614	+	* The sneaky part of sneaky throw, relying on generics
615	+	* limitations to evade compiler complaints about rethrowing
616	+	* unchecked exceptions
617	+	*/
618	+	@SuppressWarnings("unchecked") static <T extends Throwable>
619	+	void uncheckedThrow(Throwable t) throws T {
620	+	if (t != null)
621	+	throw (T)t; // rely on vacuous cast
622	+	}
623	+
624	+	/**
625		* Throws exception, if any, associated with the given status.
626		*/
627		private void reportException(int s) {
628	<	Throwable ex = ((s == CANCELLED) ?  new CancellationException() :
629	<	(s == EXCEPTIONAL) ? getThrowableException() :
630	<	null);
631	<	if (ex != null)
594	<	U.throwException(ex);
628	>	if (s == CANCELLED)
629	>	throw new CancellationException();
630	>	if (s == EXCEPTIONAL)
631	>	rethrow(getThrowableException());
632		}
633
634		// public methods
635
636		/**
637	<	* Arranges to asynchronously execute this task.  While it is not
638	<	* necessarily enforced, it is a usage error to fork a task more
639	<	* than once unless it has completed and been reinitialized.
640	<	* Subsequent modifications to the state of this task or any data
641	<	* it operates on are not necessarily consistently observable by
642	<	* any thread other than the one executing it unless preceded by a
643	<	* call to {@link #join} or related methods, or a call to {@link
644	<	* #isDone} returning {@code true}.
645	<	*
646	<	* <p>This method may be invoked only from within {@code
647	<	* ForkJoinPool} computations (as may be determined using method
611	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
612	<	* result in exceptions or errors, possibly including {@code
613	<	* ClassCastException}.
637	>	* Arranges to asynchronously execute this task in the pool the
638	>	* current task is running in, if applicable, or using the {@link
639	>	* ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}.  While
640	>	* it is not necessarily enforced, it is a usage error to fork a
641	>	* task more than once unless it has completed and been
642	>	* reinitialized.  Subsequent modifications to the state of this
643	>	* task or any data it operates on are not necessarily
644	>	* consistently observable by any thread other than the one
645	>	* executing it unless preceded by a call to {@link #join} or
646	>	* related methods, or a call to {@link #isDone} returning {@code
647	>	* true}.
648		*
649		* @return {@code this}, to simplify usage
650		*/
651		public final ForkJoinTask<V> fork() {
652	<	((ForkJoinWorkerThread)Thread.currentThread()).workQueue.push(this);
652	>	Thread t;
653	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
654	>	((ForkJoinWorkerThread)t).workQueue.push(this);
655	>	else
656	>	ForkJoinPool.common.externalPush(this);
657		return this;
658		}
659
#	Line 665 | Line 703 | public abstract class ForkJoinTask<V> im
703		* cancelled, completed normally or exceptionally, or left
704		* unprocessed.
705		*
668	–	* <p>This method may be invoked only from within {@code
669	–	* ForkJoinPool} computations (as may be determined using method
670	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
671	–	* result in exceptions or errors, possibly including {@code
672	–	* ClassCastException}.
673	–	*
706		* @param t1 the first task
707		* @param t2 the second task
708		* @throws NullPointerException if any task is null
#	Line 696 | Line 728 | public abstract class ForkJoinTask<V> im
728		* related methods to check if they have been cancelled, completed
729		* normally or exceptionally, or left unprocessed.
730		*
699	–	* <p>This method may be invoked only from within {@code
700	–	* ForkJoinPool} computations (as may be determined using method
701	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
702	–	* result in exceptions or errors, possibly including {@code
703	–	* ClassCastException}.
704	–	*
731		* @param tasks the tasks
732		* @throws NullPointerException if any task is null
733		*/
#	Line 729 | Line 755 | public abstract class ForkJoinTask<V> im
755		}
756		}
757		if (ex != null)
758	<	U.throwException(ex);
758	>	rethrow(ex);
759		}
760
761		/**
#	Line 745 | Line 771 | public abstract class ForkJoinTask<V> im
771		* cancelled, completed normally or exceptionally, or left
772		* unprocessed.
773		*
748	–	* <p>This method may be invoked only from within {@code
749	–	* ForkJoinPool} computations (as may be determined using method
750	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
751	–	* result in exceptions or errors, possibly including {@code
752	–	* ClassCastException}.
753	–	*
774		* @param tasks the collection of tasks
775		* @return the tasks argument, to simplify usage
776		* @throws NullPointerException if tasks or any element are null
#	Line 786 | Line 806 | public abstract class ForkJoinTask<V> im
806		}
807		}
808		if (ex != null)
809	<	U.throwException(ex);
809	>	rethrow(ex);
810		return tasks;
811		}
812
#	Line 907 | Line 927 | public abstract class ForkJoinTask<V> im
927		}
928
929		/**
930	+	* Completes this task normally without setting a value. The most
931	+	* recent value established by {@link #setRawResult} (or {@code
932	+	* null} by default) will be returned as the result of subsequent
933	+	* invocations of {@code join} and related operations.
934	+	*
935	+	* @since 1.8
936	+	*/
937	+	public final void quietlyComplete() {
938	+	setCompletion(NORMAL);
939	+	}
940	+
941	+	/**
942		* Waits if necessary for the computation to complete, and then
943		* retrieves its result.
944		*
#	Line 947 | Line 979 | public abstract class ForkJoinTask<V> im
979		if (Thread.interrupted())
980		throw new InterruptedException();
981		// Messy in part because we measure in nanosecs, but wait in millisecs
982	<	int s; long ns, ms;
983	<	if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) {
982	>	int s; long ms;
983	>	long ns = unit.toNanos(timeout);
984	>	if ((s = status) >= 0 && ns > 0L) {
985		long deadline = System.nanoTime() + ns;
986		ForkJoinPool p = null;
987		ForkJoinPool.WorkQueue w = null;
#	Line 957 | Line 990 | public abstract class ForkJoinTask<V> im
990		ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
991		p = wt.pool;
992		w = wt.workQueue;
993	<	s = p.helpJoinOnce(w, this); // no retries on failure
993	>	p.helpJoinOnce(w, this); // no retries on failure
994		}
995	+	else
996	+	ForkJoinPool.externalHelpJoin(this);
997		boolean canBlock = false;
998		boolean interrupted = false;
999		try {
1000		while ((s = status) >= 0) {
1001	<	if (w != null && w.runState < 0)
1001	>	if (w != null && w.qlock < 0)
1002		cancelIgnoringExceptions(this);
1003		else if (!canBlock) {
1004	<	if (p == null || p.tryCompensate(this, null))
1004	>	if (p == null || p.tryCompensate())
1005		canBlock = true;
1006		}
1007		else {
#	Line 1034 | Line 1069 | public abstract class ForkJoinTask<V> im
1069		* be of use in designs in which many tasks are forked, but none
1070		* are explicitly joined, instead executing them until all are
1071		* processed.
1037	–	*
1038	–	* <p>This method may be invoked only from within {@code
1039	–	* ForkJoinPool} computations (as may be determined using method
1040	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1041	–	* result in exceptions or errors, possibly including {@code
1042	–	* ClassCastException}.
1072		*/
1073		public static void helpQuiesce() {
1074	<	ForkJoinWorkerThread wt =
1075	<	(ForkJoinWorkerThread)Thread.currentThread();
1076	<	wt.pool.helpQuiescePool(wt.workQueue);
1074	>	Thread t;
1075	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
1076	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1077	>	wt.pool.helpQuiescePool(wt.workQueue);
1078	>	}
1079	>	else
1080	>	ForkJoinPool.quiesceCommonPool();
1081		}
1082
1083		/**
#	Line 1097 | Line 1130 | public abstract class ForkJoinTask<V> im
1130
1131		/**
1132		* Tries to unschedule this task for execution. This method will
1133	<	* typically succeed if this task is the most recently forked task
1134	<	* by the current thread, and has not commenced executing in
1135	<	* another thread.  This method may be useful when arranging
1136	<	* alternative local processing of tasks that could have been, but
1137	<	* were not, stolen.
1105	<	*
1106	<	* <p>This method may be invoked only from within {@code
1107	<	* ForkJoinPool} computations (as may be determined using method
1108	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1109	<	* result in exceptions or errors, possibly including {@code
1110	<	* ClassCastException}.
1133	>	* typically (but is not guaranteed to) succeed if this task is
1134	>	* the most recently forked task by the current thread, and has
1135	>	* not commenced executing in another thread.  This method may be
1136	>	* useful when arranging alternative local processing of tasks
1137	>	* that could have been, but were not, stolen.
1138		*
1139		* @return {@code true} if unforked
1140		*/
1141		public boolean tryUnfork() {
1142	<	return ((ForkJoinWorkerThread)Thread.currentThread())
1143	<	.workQueue.tryUnpush(this);
1142	>	Thread t;
1143	>	return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1144	>	((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
1145	>	ForkJoinPool.tryExternalUnpush(this));
1146		}
1147
1148		/**
#	Line 1122 | Line 1151 | public abstract class ForkJoinTask<V> im
1151		* value may be useful for heuristic decisions about whether to
1152		* fork other tasks.
1153		*
1125	–	* <p>This method may be invoked only from within {@code
1126	–	* ForkJoinPool} computations (as may be determined using method
1127	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1128	–	* result in exceptions or errors, possibly including {@code
1129	–	* ClassCastException}.
1130	–	*
1154		* @return the number of tasks
1155		*/
1156		public static int getQueuedTaskCount() {
1157	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1158	<	.workQueue.queueSize();
1157	>	Thread t; ForkJoinPool.WorkQueue q;
1158	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1159	>	q = ((ForkJoinWorkerThread)t).workQueue;
1160	>	else
1161	>	q = ForkJoinPool.commonSubmitterQueue();
1162	>	return (q == null) ? 0 : q.queueSize();
1163		}
1164
1165		/**
1166		* Returns an estimate of how many more locally queued tasks are
1167		* held by the current worker thread than there are other worker
1168	<	* threads that might steal them.  This value may be useful for
1168	>	* threads that might steal them, or zero if this thread is not
1169	>	* operating in a ForkJoinPool. This value may be useful for
1170		* heuristic decisions about whether to fork other tasks. In many
1171		* usages of ForkJoinTasks, at steady state, each worker should
1172		* aim to maintain a small constant surplus (for example, 3) of
1173		* tasks, and to process computations locally if this threshold is
1174		* exceeded.
1175		*
1148	–	* <p>This method may be invoked only from within {@code
1149	–	* ForkJoinPool} computations (as may be determined using method
1150	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1151	–	* result in exceptions or errors, possibly including {@code
1152	–	* ClassCastException}.
1153	–	*
1176		* @return the surplus number of tasks, which may be negative
1177		*/
1178		public static int getSurplusQueuedTaskCount() {
1179	<	/*
1158	<	* The aim of this method is to return a cheap heuristic guide
1159	<	* for task partitioning when programmers, frameworks, tools,
1160	<	* or languages have little or no idea about task granularity.
1161	<	* In essence by offering this method, we ask users only about
1162	<	* tradeoffs in overhead vs expected throughput and its
1163	<	* variance, rather than how finely to partition tasks.
1164	<	*
1165	<	* In a steady state strict (tree-structured) computation,
1166	<	* each thread makes available for stealing enough tasks for
1167	<	* other threads to remain active. Inductively, if all threads
1168	<	* play by the same rules, each thread should make available
1169	<	* only a constant number of tasks.
1170	<	*
1171	<	* The minimum useful constant is just 1. But using a value of
1172	<	* 1 would require immediate replenishment upon each steal to
1173	<	* maintain enough tasks, which is infeasible.  Further,
1174	<	* partitionings/granularities of offered tasks should
1175	<	* minimize steal rates, which in general means that threads
1176	<	* nearer the top of computation tree should generate more
1177	<	* than those nearer the bottom. In perfect steady state, each
1178	<	* thread is at approximately the same level of computation
1179	<	* tree. However, producing extra tasks amortizes the
1180	<	* uncertainty of progress and diffusion assumptions.
1181	<	*
1182	<	* So, users will want to use values larger, but not much
1183	<	* larger than 1 to both smooth over transient shortages and
1184	<	* hedge against uneven progress; as traded off against the
1185	<	* cost of extra task overhead. We leave the user to pick a
1186	<	* threshold value to compare with the results of this call to
1187	<	* guide decisions, but recommend values such as 3.
1188	<	*
1189	<	* When all threads are active, it is on average OK to
1190	<	* estimate surplus strictly locally. In steady-state, if one
1191	<	* thread is maintaining say 2 surplus tasks, then so are
1192	<	* others. So we can just use estimated queue length.
1193	<	* However, this strategy alone leads to serious mis-estimates
1194	<	* in some non-steady-state conditions (ramp-up, ramp-down,
1195	<	* other stalls). We can detect many of these by further
1196	<	* considering the number of "idle" threads, that are known to
1197	<	* have zero queued tasks, so compensate by a factor of
1198	<	* (#idle/#active) threads.
1199	<	*/
1200	<	ForkJoinWorkerThread wt =
1201	<	(ForkJoinWorkerThread)Thread.currentThread();
1202	<	return wt.workQueue.queueSize() - wt.pool.idlePerActive();
1179	>	return ForkJoinPool.getSurplusQueuedTaskCount();
1180		}
1181
1182		// Extension methods
#	Line 1225 | Line 1202 | public abstract class ForkJoinTask<V> im
1202		protected abstract void setRawResult(V value);
1203
1204		/**
1205	<	* Immediately performs the base action of this task.  This method
1206	<	* is designed to support extensions, and should not in general be
1207	<	* called otherwise. The return value controls whether this task
1208	<	* is considered to be done normally. It may return false in
1205	>	* Immediately performs the base action of this task and returns
1206	>	* true if, upon return from this method, this task is guaranteed
1207	>	* to have completed normally. This method may return false
1208	>	* otherwise, to indicate that this task is not necessarily
1209	>	* complete (or is not known to be complete), for example in
1210		* asynchronous actions that require explicit invocations of
1211	<	* {@link #complete} to become joinable. It may also throw an
1212	<	* (unchecked) exception to indicate abnormal exit.
1211	>	* completion methods. This method may also throw an (unchecked)
1212	>	* exception to indicate abnormal exit. This method is designed to
1213	>	* support extensions, and should not in general be called
1214	>	* otherwise.
1215		*
1216	<	* @return {@code true} if completed normally
1216	>	* @return {@code true} if this task is known to have completed normally
1217		*/
1218		protected abstract boolean exec();
1219
#	Line 1247 | Line 1227 | public abstract class ForkJoinTask<V> im
1227		* primarily to support extensions, and is unlikely to be useful
1228		* otherwise.
1229		*
1250	–	* <p>This method may be invoked only from within {@code
1251	–	* ForkJoinPool} computations (as may be determined using method
1252	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1253	–	* result in exceptions or errors, possibly including {@code
1254	–	* ClassCastException}.
1255	–	*
1230		* @return the next task, or {@code null} if none are available
1231		*/
1232		protected static ForkJoinTask<?> peekNextLocalTask() {
1233	<	return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek();
1233	>	Thread t; ForkJoinPool.WorkQueue q;
1234	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1235	>	q = ((ForkJoinWorkerThread)t).workQueue;
1236	>	else
1237	>	q = ForkJoinPool.commonSubmitterQueue();
1238	>	return (q == null) ? null : q.peek();
1239		}
1240
1241		/**
1242		* Unschedules and returns, without executing, the next task
1243	<	* queued by the current thread but not yet executed.  This method
1244	<	* is designed primarily to support extensions, and is unlikely to
1245	<	* be useful otherwise.
1246	<	*
1268	<	* <p>This method may be invoked only from within {@code
1269	<	* ForkJoinPool} computations (as may be determined using method
1270	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1271	<	* result in exceptions or errors, possibly including {@code
1272	<	* ClassCastException}.
1243	>	* queued by the current thread but not yet executed, if the
1244	>	* current thread is operating in a ForkJoinPool.  This method is
1245	>	* designed primarily to support extensions, and is unlikely to be
1246	>	* useful otherwise.
1247		*
1248		* @return the next task, or {@code null} if none are available
1249		*/
1250		protected static ForkJoinTask<?> pollNextLocalTask() {
1251	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1252	<	.workQueue.nextLocalTask();
1251	>	Thread t;
1252	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1253	>	((ForkJoinWorkerThread)t).workQueue.nextLocalTask() :
1254	>	null;
1255		}
1256
1257		/**
1258	<	* Unschedules and returns, without executing, the next task
1258	>	* If the current thread is operating in a ForkJoinPool,
1259	>	* unschedules and returns, without executing, the next task
1260		* queued by the current thread but not yet executed, if one is
1261		* available, or if not available, a task that was forked by some
1262		* other thread, if available. Availability may be transient, so a
1263	<	* {@code null} result does not necessarily imply quiescence
1264	<	* of the pool this task is operating in.  This method is designed
1263	>	* {@code null} result does not necessarily imply quiescence of
1264	>	* the pool this task is operating in.  This method is designed
1265		* primarily to support extensions, and is unlikely to be useful
1266		* otherwise.
1267		*
1291	–	* <p>This method may be invoked only from within {@code
1292	–	* ForkJoinPool} computations (as may be determined using method
1293	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1294	–	* result in exceptions or errors, possibly including {@code
1295	–	* ClassCastException}.
1296	–	*
1268		* @return a task, or {@code null} if none are available
1269		*/
1270		protected static ForkJoinTask<?> pollTask() {
1271	<	ForkJoinWorkerThread wt =
1272	<	(ForkJoinWorkerThread)Thread.currentThread();
1273	<	return wt.pool.nextTaskFor(wt.workQueue);
1271	>	Thread t; ForkJoinWorkerThread wt;
1272	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1273	>	(wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) :
1274	>	null;
1275		}
1276
1277	<	// Mark-bit operations
1277	>	// tag operations
1278
1279		/**
1280	<	* Returns true if this task is marked.
1280	>	* Returns the tag for this task.
1281		*
1282	<	* @return true if this task is marked
1282	>	* @return the tag for this task
1283		* @since 1.8
1284		*/
1285	<	public final boolean isMarkedForkJoinTask() {
1286	<	return (status & MARKED) != 0;
1285	>	public final short getForkJoinTaskTag() {
1286	>	return (short)status;
1287		}
1288
1289		/**
1290	<	* Atomically sets the mark on this task.
1290	>	* Atomically sets the tag value for this task.
1291		*
1292	<	* @return true if this task was previously unmarked
1292	>	* @param tag the tag value
1293	>	* @return the previous value of the tag
1294		* @since 1.8
1295		*/
1296	<	public final boolean markForkJoinTask() {
1296	>	public final short setForkJoinTaskTag(short tag) {
1297		for (int s;;) {
1298	<	if (((s = status) & MARKED) != 0)
1299	<	return false;
1300	<	if (U.compareAndSwapInt(this, STATUS, s, s | MARKED))
1328	<	return true;
1298	>	if (U.compareAndSwapInt(this, STATUS, s = status,
1299	>	(s & ~SMASK) | (tag & SMASK)))
1300	>	return (short)s;
1301		}
1302		}
1303
1304		/**
1305	<	* Atomically clears the mark on this task.
1305	>	* Atomically conditionally sets the tag value for this task.
1306	>	* Among other applications, tags can be used as visit markers
1307	>	* in tasks operating on graphs, as in methods that check: {@code
1308	>	* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1309	>	* before processing, otherwise exiting because the node has
1310	>	* already been visited.
1311		*
1312	<	* @return true if this task was previously marked
1312	>	* @param e the expected tag value
1313	>	* @param tag the new tag value
1314	>	* @return true if successful; i.e., the current value was
1315	>	* equal to e and is now tag.
1316		* @since 1.8
1317		*/
1318	<	public final boolean unmarkForkJoinTask() {
1318	>	public final boolean compareAndSetForkJoinTaskTag(short e, short tag) {
1319		for (int s;;) {
1320	<	if (((s = status) & MARKED) == 0)
1320	>	if ((short)(s = status) != e)
1321		return false;
1322	<	if (U.compareAndSwapInt(this, STATUS, s, s & ~MARKED))
1322	>	if (U.compareAndSwapInt(this, STATUS, s,
1323	>	(s & ~SMASK) | (tag & SMASK)))
1324		return true;
1325		}
1326		}
#	Line 1479 | Line 1460 | public abstract class ForkJoinTask<V> im
1460		// Unsafe mechanics
1461		private static final sun.misc.Unsafe U;
1462		private static final long STATUS;
1463	+
1464		static {
1465		exceptionTableLock = new ReentrantLock();
1466		exceptionTableRefQueue = new ReferenceQueue<Object>();
1467		exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1468		try {
1469		U = getUnsafe();
1470	+	Class<?> k = ForkJoinTask.class;
1471		STATUS = U.objectFieldOffset
1472	<	(ForkJoinTask.class.getDeclaredField("status"));
1472	>	(k.getDeclaredField("status"));
1473		} catch (Exception e) {
1474		throw new Error(e);
1475		}
#	Line 1502 | Line 1485 | public abstract class ForkJoinTask<V> im
1485		private static sun.misc.Unsafe getUnsafe() {
1486		try {
1487		return sun.misc.Unsafe.getUnsafe();
1488	<	} catch (SecurityException se) {
1489	<	try {
1490	<	return java.security.AccessController.doPrivileged
1491	<	(new java.security
1492	<	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1493	<	public sun.misc.Unsafe run() throws Exception {
1494	<	java.lang.reflect.Field f = sun.misc
1495	<	.Unsafe.class.getDeclaredField("theUnsafe");
1496	<	f.setAccessible(true);
1497	<	return (sun.misc.Unsafe) f.get(null);
1498	<	}});
1499	<	} catch (java.security.PrivilegedActionException e) {
1500	<	throw new RuntimeException("Could not initialize intrinsics",
1501	<	e.getCause());
1502	<	}
1488	>	} catch (SecurityException tryReflectionInstead) {}
1489	>	try {
1490	>	return java.security.AccessController.doPrivileged
1491	>	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1492	>	public sun.misc.Unsafe run() throws Exception {
1493	>	Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
1494	>	for (java.lang.reflect.Field f : k.getDeclaredFields()) {
1495	>	f.setAccessible(true);
1496	>	Object x = f.get(null);
1497	>	if (k.isInstance(x))
1498	>	return k.cast(x);
1499	>	}
1500	>	throw new NoSuchFieldError("the Unsafe");
1501	>	}});
1502	>	} catch (java.security.PrivilegedActionException e) {
1503	>	throw new RuntimeException("Could not initialize intrinsics",
1504	>	e.getCause());
1505		}
1506		}
1507		}

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