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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.90 by dl, Sat Apr 21 11:45:20 2012 UTC vs.
Revision 1.100 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 287 | Line 284 | public abstract class ForkJoinTask<V> im
284		* @return status upon completion
285		*/
286		private int externalAwaitDone() {
290	–	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 316 | 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 329 | Line 328 | public abstract class ForkJoinTask<V> im
328		return s;
329		}
330
331	+
332		/**
333		* Implementation for join, get, quietlyJoin. Directly handles
334		* only cases of already-completed, external wait, and
#	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 443 | Line 435 | public abstract class ForkJoinTask<V> im
435		}
436
437		/**
438	<	* Records exception and possibly propagates
438	>	* Records exception and possibly propagates.
439		*
440		* @return status on exit
441		*/
#	Line 476 | Line 468 | public abstract class ForkJoinTask<V> im
468		}
469
470		/**
471	<	* Removes exception node and clears status
471	>	* Removes exception node and clears status.
472		*/
473		private void clearExceptionalCompletion() {
474		int h = System.identityHashCode(this);
#	Line 606 | 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)
616	<	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
633	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
634	<	* result in exceptions or errors, possibly including {@code
635	<	* 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 687 | Line 703 | public abstract class ForkJoinTask<V> im
703		* cancelled, completed normally or exceptionally, or left
704		* unprocessed.
705		*
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	–	*
706		* @param t1 the first task
707		* @param t2 the second task
708		* @throws NullPointerException if any task is null
#	Line 718 | 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		*
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	–	*
731		* @param tasks the tasks
732		* @throws NullPointerException if any task is null
733		*/
#	Line 751 | 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 767 | Line 771 | public abstract class ForkJoinTask<V> im
771		* cancelled, completed normally or exceptionally, or left
772		* unprocessed.
773		*
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	–	*
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 808 | 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 981 | 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 991 | 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 1068 | 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.
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}.
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 1131 | 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.
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}.
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 1156 | Line 1151 | public abstract class ForkJoinTask<V> im
1151		* value may be useful for heuristic decisions about whether to
1152		* fork other tasks.
1153		*
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	–	*
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		*
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	–	*
1176		* @return the surplus number of tasks, which may be negative
1177		*/
1178		public static int getSurplusQueuedTaskCount() {
1179	<	/*
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();
1179	>	return ForkJoinPool.getSurplusQueuedTaskCount();
1180		}
1181
1182		// Extension methods
#	Line 1284 | Line 1227 | public abstract class ForkJoinTask<V> im
1227		* primarily to support extensions, and is unlikely to be useful
1228		* otherwise.
1229		*
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	–	*
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	<	*
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}.
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		*
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	–	*
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		// tag operations
#	Line 1525 | 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 1548 | 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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