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root/jsr166/jsr166/src/jsr166e/ForkJoinTask.java

Comparing jsr166/src/jsr166e/ForkJoinTask.java (file contents):
Revision 1.1 by dl, Mon Aug 13 15:52:33 2012 UTC vs.
Revision 1.12 by jsr166, Tue Feb 5 17:09:54 2013 UTC

#	Line 30 | 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 52 | 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 70 | 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
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
#	Line 123 | Line 126 | import java.lang.reflect.Constructor;
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. While these methods have
127	<	* {@code public} access (to allow instances of different task
128	<	* subclasses to call each other's methods), some of them may only be
129	<	* called from within other ForkJoinTasks (as may be determined using
130	<	* method {@link #inForkJoinPool}).  Attempts to invoke them in other
131	<	* contexts result in exceptions or errors, possibly including {@code
132	<	* ClassCastException}.
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 134 | import java.lang.reflect.Constructor;
134		* (DAG). Otherwise, executions may encounter a form of deadlock as
135		* tasks cyclically wait for each other.  However, this framework
136		* supports other methods and techniques (for example the use of
137	<	* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
137	>	* {@link java.util.concurrent.Phaser}, {@link #helpQuiesce}, and
138	>	* {@link #complete}) that
139		* may be of use in constructing custom subclasses for problems that
140		* are not statically structured as DAGs. To support such usages a
141		* ForkJoinTask may be atomically <em>tagged</em> with a {@code short}
#	Line 287 | Line 285 | public abstract class ForkJoinTask<V> im
285		* @return status upon completion
286		*/
287		private int externalAwaitDone() {
290	–	boolean interrupted = false;
288		int s;
289	+	ForkJoinPool.externalHelpJoin(this);
290	+	boolean interrupted = false;
291		while ((s = status) >= 0) {
292		if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
293		synchronized (this) {
#	Line 316 | Line 315 | public abstract class ForkJoinTask<V> im
315		int s;
316		if (Thread.interrupted())
317		throw new InterruptedException();
318	+	ForkJoinPool.externalHelpJoin(this);
319		while ((s = status) >= 0) {
320		if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
321		synchronized (this) {
#	Line 329 | Line 329 | public abstract class ForkJoinTask<V> im
329		return s;
330		}
331
332	+
333		/**
334		* Implementation for join, get, quietlyJoin. Directly handles
335		* only cases of already-completed, external wait, and
#	Line 338 | Line 339 | public abstract class ForkJoinTask<V> im
339		*/
340		private int doJoin() {
341		int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
342	<	if ((s = status) >= 0) {
343	<	if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) {
344	<	if (!(w = (wt = (ForkJoinWorkerThread)t).workQueue).
345	<	tryUnpush(this) || (s = doExec()) >= 0)
346	<	s = wt.pool.awaitJoin(w, this);
347	<	}
347	<	else
348	<	s = externalAwaitDone();
349	<	}
350	<	return s;
342	>	return (s = status) < 0 ? s :
343	>	((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
344	>	(w = (wt = (ForkJoinWorkerThread)t).workQueue).
345	>	tryUnpush(this) && (s = doExec()) < 0 ? s :
346	>	wt.pool.awaitJoin(w, this) :
347	>	externalAwaitDone();
348		}
349
350		/**
#	Line 357 | Line 354 | public abstract class ForkJoinTask<V> im
354		*/
355		private int doInvoke() {
356		int s; Thread t; ForkJoinWorkerThread wt;
357	<	if ((s = doExec()) >= 0) {
358	<	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
359	<	s = (wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue,
360	<	this);
364	<	else
365	<	s = externalAwaitDone();
366	<	}
367	<	return s;
357	>	return (s = doExec()) < 0 ? s :
358	>	((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
359	>	(wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue, this) :
360	>	externalAwaitDone();
361		}
362
363		// Exception table support
#	Line 443 | Line 436 | public abstract class ForkJoinTask<V> im
436		}
437
438		/**
439	<	* Records exception and possibly propagates
439	>	* Records exception and possibly propagates.
440		*
441		* @return status on exit
442		*/
#	Line 476 | Line 469 | public abstract class ForkJoinTask<V> im
469		}
470
471		/**
472	<	* Removes exception node and clears status
472	>	* Removes exception node and clears status.
473		*/
474		private void clearExceptionalCompletion() {
475		int h = System.identityHashCode(this);
#	Line 606 | Line 599 | public abstract class ForkJoinTask<V> im
599		}
600
601		/**
602	+	* A version of "sneaky throw" to relay exceptions
603	+	*/
604	+	static void rethrow(final Throwable ex) {
605	+	if (ex != null) {
606	+	if (ex instanceof Error)
607	+	throw (Error)ex;
608	+	if (ex instanceof RuntimeException)
609	+	throw (RuntimeException)ex;
610	+	ForkJoinTask.<RuntimeException>uncheckedThrow(ex);
611	+	}
612	+	}
613	+
614	+	/**
615	+	* The sneaky part of sneaky throw, relying on generics
616	+	* limitations to evade compiler complaints about rethrowing
617	+	* unchecked exceptions
618	+	*/
619	+	@SuppressWarnings("unchecked") static <T extends Throwable>
620	+	void uncheckedThrow(Throwable t) throws T {
621	+	if (t != null)
622	+	throw (T)t; // rely on vacuous cast
623	+	}
624	+
625	+	/**
626		* Throws exception, if any, associated with the given status.
627		*/
628		private void reportException(int s) {
629	<	Throwable ex = ((s == CANCELLED) ?  new CancellationException() :
630	<	(s == EXCEPTIONAL) ? getThrowableException() :
631	<	null);
632	<	if (ex != null)
616	<	U.throwException(ex);
629	>	if (s == CANCELLED)
630	>	throw new CancellationException();
631	>	if (s == EXCEPTIONAL)
632	>	rethrow(getThrowableException());
633		}
634
635		// public methods
636
637		/**
638	<	* Arranges to asynchronously execute this task.  While it is not
639	<	* necessarily enforced, it is a usage error to fork a task more
640	<	* than once unless it has completed and been reinitialized.
641	<	* Subsequent modifications to the state of this task or any data
642	<	* it operates on are not necessarily consistently observable by
643	<	* any thread other than the one executing it unless preceded by a
644	<	* call to {@link #join} or related methods, or a call to {@link
645	<	* #isDone} returning {@code true}.
646	<	*
647	<	* <p>This method may be invoked only from within {@code
648	<	* ForkJoinPool} computations (as may be determined using method
633	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
634	<	* result in exceptions or errors, possibly including {@code
635	<	* ClassCastException}.
638	>	* Arranges to asynchronously execute this task in the pool the
639	>	* current task is running in, if applicable, or using the {@link
640	>	* ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}.  While
641	>	* it is not necessarily enforced, it is a usage error to fork a
642	>	* task more than once unless it has completed and been
643	>	* reinitialized.  Subsequent modifications to the state of this
644	>	* task or any data it operates on are not necessarily
645	>	* consistently observable by any thread other than the one
646	>	* executing it unless preceded by a call to {@link #join} or
647	>	* related methods, or a call to {@link #isDone} returning {@code
648	>	* true}.
649		*
650		* @return {@code this}, to simplify usage
651		*/
652		public final ForkJoinTask<V> fork() {
653	<	((ForkJoinWorkerThread)Thread.currentThread()).workQueue.push(this);
653	>	Thread t;
654	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
655	>	((ForkJoinWorkerThread)t).workQueue.push(this);
656	>	else
657	>	ForkJoinPool.common.externalPush(this);
658		return this;
659		}
660
#	Line 687 | Line 704 | public abstract class ForkJoinTask<V> im
704		* cancelled, completed normally or exceptionally, or left
705		* unprocessed.
706		*
690	–	* <p>This method may be invoked only from within {@code
691	–	* ForkJoinPool} computations (as may be determined using method
692	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
693	–	* result in exceptions or errors, possibly including {@code
694	–	* ClassCastException}.
695	–	*
707		* @param t1 the first task
708		* @param t2 the second task
709		* @throws NullPointerException if any task is null
#	Line 718 | Line 729 | public abstract class ForkJoinTask<V> im
729		* related methods to check if they have been cancelled, completed
730		* normally or exceptionally, or left unprocessed.
731		*
721	–	* <p>This method may be invoked only from within {@code
722	–	* ForkJoinPool} computations (as may be determined using method
723	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
724	–	* result in exceptions or errors, possibly including {@code
725	–	* ClassCastException}.
726	–	*
732		* @param tasks the tasks
733		* @throws NullPointerException if any task is null
734		*/
#	Line 751 | Line 756 | public abstract class ForkJoinTask<V> im
756		}
757		}
758		if (ex != null)
759	<	U.throwException(ex);
759	>	rethrow(ex);
760		}
761
762		/**
#	Line 767 | Line 772 | public abstract class ForkJoinTask<V> im
772		* cancelled, completed normally or exceptionally, or left
773		* unprocessed.
774		*
770	–	* <p>This method may be invoked only from within {@code
771	–	* ForkJoinPool} computations (as may be determined using method
772	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
773	–	* result in exceptions or errors, possibly including {@code
774	–	* ClassCastException}.
775	–	*
775		* @param tasks the collection of tasks
776		* @return the tasks argument, to simplify usage
777		* @throws NullPointerException if tasks or any element are null
#	Line 808 | Line 807 | public abstract class ForkJoinTask<V> im
807		}
808		}
809		if (ex != null)
810	<	U.throwException(ex);
810	>	rethrow(ex);
811		return tasks;
812		}
813
#	Line 981 | Line 980 | public abstract class ForkJoinTask<V> im
980		if (Thread.interrupted())
981		throw new InterruptedException();
982		// Messy in part because we measure in nanosecs, but wait in millisecs
983	<	int s; long ns, ms;
984	<	if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) {
983	>	int s; long ms;
984	>	long ns = unit.toNanos(timeout);
985	>	if ((s = status) >= 0 && ns > 0L) {
986		long deadline = System.nanoTime() + ns;
987		ForkJoinPool p = null;
988		ForkJoinPool.WorkQueue w = null;
#	Line 991 | Line 991 | public abstract class ForkJoinTask<V> im
991		ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
992		p = wt.pool;
993		w = wt.workQueue;
994	<	s = p.helpJoinOnce(w, this); // no retries on failure
994	>	p.helpJoinOnce(w, this); // no retries on failure
995		}
996	+	else
997	+	ForkJoinPool.externalHelpJoin(this);
998		boolean canBlock = false;
999		boolean interrupted = false;
1000		try {
1001		while ((s = status) >= 0) {
1002	<	if (w != null && w.runState < 0)
1002	>	if (w != null && w.qlock < 0)
1003		cancelIgnoringExceptions(this);
1004		else if (!canBlock) {
1005	<	if (p == null || p.tryCompensate(this, null))
1005	>	if (p == null || p.tryCompensate())
1006		canBlock = true;
1007		}
1008		else {
#	Line 1068 | Line 1070 | public abstract class ForkJoinTask<V> im
1070		* be of use in designs in which many tasks are forked, but none
1071		* are explicitly joined, instead executing them until all are
1072		* processed.
1071	–	*
1072	–	* <p>This method may be invoked only from within {@code
1073	–	* ForkJoinPool} computations (as may be determined using method
1074	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1075	–	* result in exceptions or errors, possibly including {@code
1076	–	* ClassCastException}.
1073		*/
1074		public static void helpQuiesce() {
1075	<	ForkJoinWorkerThread wt =
1076	<	(ForkJoinWorkerThread)Thread.currentThread();
1077	<	wt.pool.helpQuiescePool(wt.workQueue);
1075	>	Thread t;
1076	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
1077	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1078	>	wt.pool.helpQuiescePool(wt.workQueue);
1079	>	}
1080	>	else
1081	>	ForkJoinPool.quiesceCommonPool();
1082		}
1083
1084		/**
#	Line 1131 | Line 1131 | public abstract class ForkJoinTask<V> im
1131
1132		/**
1133		* Tries to unschedule this task for execution. This method will
1134	<	* typically succeed if this task is the most recently forked task
1135	<	* by the current thread, and has not commenced executing in
1136	<	* another thread.  This method may be useful when arranging
1137	<	* alternative local processing of tasks that could have been, but
1138	<	* were not, stolen.
1139	<	*
1140	<	* <p>This method may be invoked only from within {@code
1141	<	* ForkJoinPool} computations (as may be determined using method
1142	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1143	<	* result in exceptions or errors, possibly including {@code
1144	<	* ClassCastException}.
1134	>	* typically (but is not guaranteed to) succeed if this task is
1135	>	* the most recently forked task by the current thread, and has
1136	>	* not commenced executing in another thread.  This method may be
1137	>	* useful when arranging alternative local processing of tasks
1138	>	* that could have been, but were not, stolen.
1139		*
1140		* @return {@code true} if unforked
1141		*/
1142		public boolean tryUnfork() {
1143	<	return ((ForkJoinWorkerThread)Thread.currentThread())
1144	<	.workQueue.tryUnpush(this);
1143	>	Thread t;
1144	>	return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1145	>	((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
1146	>	ForkJoinPool.tryExternalUnpush(this));
1147		}
1148
1149		/**
#	Line 1156 | Line 1152 | public abstract class ForkJoinTask<V> im
1152		* value may be useful for heuristic decisions about whether to
1153		* fork other tasks.
1154		*
1159	–	* <p>This method may be invoked only from within {@code
1160	–	* ForkJoinPool} computations (as may be determined using method
1161	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1162	–	* result in exceptions or errors, possibly including {@code
1163	–	* ClassCastException}.
1164	–	*
1155		* @return the number of tasks
1156		*/
1157		public static int getQueuedTaskCount() {
1158	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1159	<	.workQueue.queueSize();
1158	>	Thread t; ForkJoinPool.WorkQueue q;
1159	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1160	>	q = ((ForkJoinWorkerThread)t).workQueue;
1161	>	else
1162	>	q = ForkJoinPool.commonSubmitterQueue();
1163	>	return (q == null) ? 0 : q.queueSize();
1164		}
1165
1166		/**
1167		* Returns an estimate of how many more locally queued tasks are
1168		* held by the current worker thread than there are other worker
1169	<	* threads that might steal them.  This value may be useful for
1169	>	* threads that might steal them, or zero if this thread is not
1170	>	* operating in a ForkJoinPool. This value may be useful for
1171		* heuristic decisions about whether to fork other tasks. In many
1172		* usages of ForkJoinTasks, at steady state, each worker should
1173		* aim to maintain a small constant surplus (for example, 3) of
1174		* tasks, and to process computations locally if this threshold is
1175		* exceeded.
1176		*
1182	–	* <p>This method may be invoked only from within {@code
1183	–	* ForkJoinPool} computations (as may be determined using method
1184	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1185	–	* result in exceptions or errors, possibly including {@code
1186	–	* ClassCastException}.
1187	–	*
1177		* @return the surplus number of tasks, which may be negative
1178		*/
1179		public static int getSurplusQueuedTaskCount() {
1180	<	/*
1192	<	* The aim of this method is to return a cheap heuristic guide
1193	<	* for task partitioning when programmers, frameworks, tools,
1194	<	* or languages have little or no idea about task granularity.
1195	<	* In essence by offering this method, we ask users only about
1196	<	* tradeoffs in overhead vs expected throughput and its
1197	<	* variance, rather than how finely to partition tasks.
1198	<	*
1199	<	* In a steady state strict (tree-structured) computation,
1200	<	* each thread makes available for stealing enough tasks for
1201	<	* other threads to remain active. Inductively, if all threads
1202	<	* play by the same rules, each thread should make available
1203	<	* only a constant number of tasks.
1204	<	*
1205	<	* The minimum useful constant is just 1. But using a value of
1206	<	* 1 would require immediate replenishment upon each steal to
1207	<	* maintain enough tasks, which is infeasible.  Further,
1208	<	* partitionings/granularities of offered tasks should
1209	<	* minimize steal rates, which in general means that threads
1210	<	* nearer the top of computation tree should generate more
1211	<	* than those nearer the bottom. In perfect steady state, each
1212	<	* thread is at approximately the same level of computation
1213	<	* tree. However, producing extra tasks amortizes the
1214	<	* uncertainty of progress and diffusion assumptions.
1215	<	*
1216	<	* So, users will want to use values larger, but not much
1217	<	* larger than 1 to both smooth over transient shortages and
1218	<	* hedge against uneven progress; as traded off against the
1219	<	* cost of extra task overhead. We leave the user to pick a
1220	<	* threshold value to compare with the results of this call to
1221	<	* guide decisions, but recommend values such as 3.
1222	<	*
1223	<	* When all threads are active, it is on average OK to
1224	<	* estimate surplus strictly locally. In steady-state, if one
1225	<	* thread is maintaining say 2 surplus tasks, then so are
1226	<	* others. So we can just use estimated queue length.
1227	<	* However, this strategy alone leads to serious mis-estimates
1228	<	* in some non-steady-state conditions (ramp-up, ramp-down,
1229	<	* other stalls). We can detect many of these by further
1230	<	* considering the number of "idle" threads, that are known to
1231	<	* have zero queued tasks, so compensate by a factor of
1232	<	* (#idle/#active) threads.
1233	<	*/
1234	<	ForkJoinWorkerThread wt =
1235	<	(ForkJoinWorkerThread)Thread.currentThread();
1236	<	return wt.workQueue.queueSize() - wt.pool.idlePerActive();
1180	>	return ForkJoinPool.getSurplusQueuedTaskCount();
1181		}
1182
1183		// Extension methods
#	Line 1284 | Line 1228 | public abstract class ForkJoinTask<V> im
1228		* primarily to support extensions, and is unlikely to be useful
1229		* otherwise.
1230		*
1287	–	* <p>This method may be invoked only from within {@code
1288	–	* ForkJoinPool} computations (as may be determined using method
1289	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1290	–	* result in exceptions or errors, possibly including {@code
1291	–	* ClassCastException}.
1292	–	*
1231		* @return the next task, or {@code null} if none are available
1232		*/
1233		protected static ForkJoinTask<?> peekNextLocalTask() {
1234	<	return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek();
1234	>	Thread t; ForkJoinPool.WorkQueue q;
1235	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1236	>	q = ((ForkJoinWorkerThread)t).workQueue;
1237	>	else
1238	>	q = ForkJoinPool.commonSubmitterQueue();
1239	>	return (q == null) ? null : q.peek();
1240		}
1241
1242		/**
1243		* Unschedules and returns, without executing, the next task
1244	<	* queued by the current thread but not yet executed.  This method
1245	<	* is designed primarily to support extensions, and is unlikely to
1246	<	* be useful otherwise.
1247	<	*
1305	<	* <p>This method may be invoked only from within {@code
1306	<	* ForkJoinPool} computations (as may be determined using method
1307	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1308	<	* result in exceptions or errors, possibly including {@code
1309	<	* ClassCastException}.
1244	>	* queued by the current thread but not yet executed, if the
1245	>	* current thread is operating in a ForkJoinPool.  This method is
1246	>	* designed primarily to support extensions, and is unlikely to be
1247	>	* useful otherwise.
1248		*
1249		* @return the next task, or {@code null} if none are available
1250		*/
1251		protected static ForkJoinTask<?> pollNextLocalTask() {
1252	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1253	<	.workQueue.nextLocalTask();
1252	>	Thread t;
1253	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1254	>	((ForkJoinWorkerThread)t).workQueue.nextLocalTask() :
1255	>	null;
1256		}
1257
1258		/**
1259	<	* Unschedules and returns, without executing, the next task
1259	>	* If the current thread is operating in a ForkJoinPool,
1260	>	* unschedules and returns, without executing, the next task
1261		* queued by the current thread but not yet executed, if one is
1262		* available, or if not available, a task that was forked by some
1263		* other thread, if available. Availability may be transient, so a
1264	<	* {@code null} result does not necessarily imply quiescence
1265	<	* of the pool this task is operating in.  This method is designed
1264	>	* {@code null} result does not necessarily imply quiescence of
1265	>	* the pool this task is operating in.  This method is designed
1266		* primarily to support extensions, and is unlikely to be useful
1267		* otherwise.
1268		*
1328	–	* <p>This method may be invoked only from within {@code
1329	–	* ForkJoinPool} computations (as may be determined using method
1330	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1331	–	* result in exceptions or errors, possibly including {@code
1332	–	* ClassCastException}.
1333	–	*
1269		* @return a task, or {@code null} if none are available
1270		*/
1271		protected static ForkJoinTask<?> pollTask() {
1272	<	ForkJoinWorkerThread wt =
1273	<	(ForkJoinWorkerThread)Thread.currentThread();
1274	<	return wt.pool.nextTaskFor(wt.workQueue);
1272	>	Thread t; ForkJoinWorkerThread wt;
1273	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1274	>	(wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) :
1275	>	null;
1276		}
1277
1278		// tag operations
#	Line 1525 | Line 1461 | public abstract class ForkJoinTask<V> im
1461		// Unsafe mechanics
1462		private static final sun.misc.Unsafe U;
1463		private static final long STATUS;
1464	+
1465		static {
1466		exceptionTableLock = new ReentrantLock();
1467		exceptionTableRefQueue = new ReferenceQueue<Object>();
1468		exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1469		try {
1470		U = getUnsafe();
1471	+	Class<?> k = ForkJoinTask.class;
1472		STATUS = U.objectFieldOffset
1473	<	(ForkJoinTask.class.getDeclaredField("status"));
1473	>	(k.getDeclaredField("status"));
1474		} catch (Exception e) {
1475		throw new Error(e);
1476		}
#	Line 1548 | Line 1486 | public abstract class ForkJoinTask<V> im
1486		private static sun.misc.Unsafe getUnsafe() {
1487		try {
1488		return sun.misc.Unsafe.getUnsafe();
1489	<	} catch (SecurityException se) {
1490	<	try {
1491	<	return java.security.AccessController.doPrivileged
1492	<	(new java.security
1493	<	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1494	<	public sun.misc.Unsafe run() throws Exception {
1495	<	java.lang.reflect.Field f = sun.misc
1496	<	.Unsafe.class.getDeclaredField("theUnsafe");
1497	<	f.setAccessible(true);
1498	<	return (sun.misc.Unsafe) f.get(null);
1499	<	}});
1500	<	} catch (java.security.PrivilegedActionException e) {
1501	<	throw new RuntimeException("Could not initialize intrinsics",
1502	<	e.getCause());
1503	<	}
1489	>	} catch (SecurityException tryReflectionInstead) {}
1490	>	try {
1491	>	return java.security.AccessController.doPrivileged
1492	>	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1493	>	public sun.misc.Unsafe run() throws Exception {
1494	>	Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
1495	>	for (java.lang.reflect.Field f : k.getDeclaredFields()) {
1496	>	f.setAccessible(true);
1497	>	Object x = f.get(null);
1498	>	if (k.isInstance(x))
1499	>	return k.cast(x);
1500	>	}
1501	>	throw new NoSuchFieldError("the Unsafe");
1502	>	}});
1503	>	} catch (java.security.PrivilegedActionException e) {
1504	>	throw new RuntimeException("Could not initialize intrinsics",
1505	>	e.getCause());
1506		}
1507		}
1508		}

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