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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.1 by dl, Tue Jan 6 14:30:31 2009 UTC vs.
Revision 1.11 by jsr166, Tue Jul 21 18:11:44 2009 UTC

#	Line 13 | Line 13 | import sun.misc.Unsafe;
13		import java.lang.reflect.*;
14
15		/**
16	<	* Abstract base class for tasks that run within a ForkJoinPool.  A
17	<	* ForkJoinTask is a thread-like entity that is much lighter weight
18	<	* than a normal thread.  Huge numbers of tasks and subtasks may be
19	<	* hosted by a small number of actual threads in a ForkJoinPool,
20	<	* at the price of some usage limitations.
16	>	* Abstract base class for tasks that run within a {@link
17	>	* ForkJoinPool}.  A ForkJoinTask is a thread-like entity that is much
18	>	* lighter weight than a normal thread.  Huge numbers of tasks and
19	>	* subtasks may be hosted by a small number of actual threads in a
20	>	* ForkJoinPool, at the price of some usage limitations.
21		*
22	<	* <p> ForkJoinTasks are forms of <tt>Futures</tt> supporting a
23	<	* limited range of use.  The "lightness" of ForkJoinTasks is due to a
24	<	* set of restrictions (that are only partially statically
25	<	* enforceable) reflecting their intended use as computational tasks
26	<	* calculating pure functions or operating on purely isolated objects.
27	<	* The primary coordination mechanisms supported for ForkJoinTasks are
28	<	* <tt>fork</tt>, that arranges asynchronous execution, and
29	<	* <tt>join</tt>, that doesn't proceed until the task's result has
30	<	* been computed. (Cancellation is also supported).  The computation
31	<	* defined in the <tt>compute</tt> method should avoid
32	<	* <tt>synchronized</tt> methods or blocks, and should minimize
33	<	* blocking synchronization apart from joining other tasks or using
22	>	* <p> A "main" ForkJoinTask begins execution when submitted to a
23	>	* {@link ForkJoinPool}. Once started, it will usually in turn start
24	>	* other subtasks.  As indicated by the name of this class, many
25	>	* programs using ForkJoinTasks employ only methods {@code fork}
26	>	* and {@code join}, or derivatives such as
27	>	* {@code invokeAll}.  However, this class also provides a number
28	>	* of other methods that can come into play in advanced usages, as
29	>	* well as extension mechanics that allow support of new forms of
30	>	* fork/join processing.
31	>	*
32	>	* <p>A ForkJoinTask is a lightweight form of {@link Future}.  The
33	>	* efficiency of ForkJoinTasks stems from a set of restrictions (that
34	>	* are only partially statically enforceable) reflecting their
35	>	* intended use as computational tasks calculating pure functions or
36	>	* operating on purely isolated objects.  The primary coordination
37	>	* mechanisms are {@link #fork}, that arranges asynchronous execution,
38	>	* and {@link #join}, that doesn't proceed until the task's result has
39	>	* been computed.  Computations should avoid {@code synchronized}
40	>	* methods or blocks, and should minimize other blocking
41	>	* synchronization apart from joining other tasks or using
42		* synchronizers such as Phasers that are advertised to cooperate with
43		* fork/join scheduling. Tasks should also not perform blocking IO,
44		* and should ideally access variables that are completely independent
#	Line 38 | Line 46 | import java.lang.reflect.*;
46		* restrictions, for example using shared output streams, may be
47		* tolerable in practice, but frequent use may result in poor
48		* performance, and the potential to indefinitely stall if the number
49	<	* of threads not waiting for external synchronization becomes
50	<	* exhausted. This usage restriction is in part enforced by not
51	<	* permitting checked exceptions such as IOExceptions to be
52	<	* thrown. However, computations may still encounter unchecked
49	>	* of threads not waiting for IO or other external synchronization
50	>	* becomes exhausted. This usage restriction is in part enforced by
51	>	* not permitting checked exceptions such as {@code IOExceptions}
52	>	* to be thrown. However, computations may still encounter unchecked
53		* exceptions, that are rethrown to callers attempting join
54		* them. These exceptions may additionally include
55		* RejectedExecutionExceptions stemming from internal resource
56		* exhaustion such as failure to allocate internal task queues.
57		*
58	<	* <p> The <tt>ForkJoinTask</tt> class is not usually directly
59	<	* subclassed.  Instead, you subclass one of the abstract classes that
60	<	* support different styles of fork/join processing.  Normally, a
61	<	* concrete ForkJoinTask subclass declares fields comprising its
62	<	* parameters, established in a constructor, and then defines a
63	<	* <tt>compute</tt> method that somehow uses the control methods
64	<	* supplied by this base class. While these methods have
65	<	* <tt>public</tt> access, some of them may only be called from within
66	<	* other ForkJoinTasks. Attempts to invoke them in other contexts
67	<	* result in exceptions or errors including ClassCastException.  The
68	<	* only way to invoke a "main" driver task is to submit it to a
69	<	* ForkJoinPool. Once started, this will usually in turn start other
70	<	* subtasks.
58	>	* <p>The primary method for awaiting completion and extracting
59	>	* results of a task is {@link #join}, but there are several variants:
60	>	* The {@link Future#get} methods support interruptible and/or timed
61	>	* waits for completion and report results using {@code Future}
62	>	* conventions. Method {@link #helpJoin} enables callers to actively
63	>	* execute other tasks while awaiting joins, which is sometimes more
64	>	* efficient but only applies when all subtasks are known to be
65	>	* strictly tree-structured. Method {@link #invoke} is semantically
66	>	* equivalent to {@code fork(); join()} but always attempts to
67	>	* begin execution in the current thread. The "<em>quiet</em>" forms
68	>	* of these methods do not extract results or report exceptions. These
69	>	* may be useful when a set of tasks are being executed, and you need
70	>	* to delay processing of results or exceptions until all complete.
71	>	* Method {@code invokeAll} (available in multiple versions)
72	>	* performs the most common form of parallel invocation: forking a set
73	>	* of tasks and joining them all.
74	>	*
75	>	* <p> The ForkJoinTask class is not usually directly subclassed.
76	>	* Instead, you subclass one of the abstract classes that support a
77	>	* particular style of fork/join processing.  Normally, a concrete
78	>	* ForkJoinTask subclass declares fields comprising its parameters,
79	>	* established in a constructor, and then defines a {@code compute}
80	>	* method that somehow uses the control methods supplied by this base
81	>	* class. While these methods have {@code public} access (to allow
82	>	* instances of different task subclasses to call each others
83	>	* methods), some of them may only be called from within other
84	>	* ForkJoinTasks. Attempts to invoke them in other contexts result in
85	>	* exceptions or errors possibly including ClassCastException.
86		*
87	<	* <p>Most base support methods are <tt>final</tt> because their
87	>	* <p>Most base support methods are {@code final} because their
88		* implementations are intrinsically tied to the underlying
89		* lightweight task scheduling framework, and so cannot be overridden.
90		* Developers creating new basic styles of fork/join processing should
91	<	* minimally implement protected methods <tt>exec</tt>,
92	<	* <tt>setRawResult</tt>, and <tt>getRawResult</tt>, while also
93	<	* introducing an abstract computational method that can be
94	<	* implemented in its subclasses. To support such extensions,
95	<	* instances of ForkJoinTasks maintain an atomically updated
96	<	* <tt>short</tt> representing user-defined control state.  Control
74	<	* state is guaranteed initially to be zero, and to be negative upon
75	<	* completion, but may otherwise be used for any other control
76	<	* purposes, such as maintaining join counts.  The {@link
77	<	* ForkJoinWorkerThread} class supports additional inspection and
78	<	* tuning methods that can be useful when developing extensions.
91	>	* minimally implement {@code protected} methods
92	>	* {@code exec}, {@code setRawResult}, and
93	>	* {@code getRawResult}, while also introducing an abstract
94	>	* computational method that can be implemented in its subclasses,
95	>	* possibly relying on other {@code protected} methods provided
96	>	* by this class.
97		*
98		* <p>ForkJoinTasks should perform relatively small amounts of
99	<	* computations, othewise splitting into smaller tasks. As a very
99	>	* computations, otherwise splitting into smaller tasks. As a very
100		* rough rule of thumb, a task should perform more than 100 and less
101		* than 10000 basic computational steps. If tasks are too big, then
102	<	* parellelism cannot improve throughput. If too small, then memory
102	>	* parallelism cannot improve throughput. If too small, then memory
103		* and internal task maintenance overhead may overwhelm processing.
104		*
105	<	* <p>ForkJoinTasks are <tt>Serializable</tt>, which enables them to
106	<	* be used in extensions such as remote execution frameworks. However,
107	<	* it is in general safe to serialize tasks only before or after, but
105	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them
106	>	* to be used in extensions such as remote execution frameworks. It is
107	>	* in general sensible to serialize tasks only before or after, but
108		* not during execution. Serialization is not relied on during
109		* execution itself.
110		*/
111		public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
112	+
113		/**
114	<	* Status field holding all run status. We pack this into a single
115	<	* int both to minimize footprint overhead and to ensure atomicity
116	<	* (updates are via CAS).
98	<	*
99	<	* Status is initially zero, and takes on nonnegative values until
114	>	* Run control status bits packed into a single int to minimize
115	>	* footprint and to ensure atomicity (via CAS).  Status is
116	>	* initially zero, and takes on nonnegative values until
117		* completed, upon which status holds COMPLETED. CANCELLED, or
118		* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
119		* blocking waits by other threads have SIGNAL_MASK bits set --
#	Line 111 | Line 128 | public abstract class ForkJoinTask<V> im
128		* currently unused. Also value 0x80000000 is available as spare
129		* completion value.
130		*/
131	<	volatile int status; // accessed directy by pool and workers
131	>	volatile int status; // accessed directly by pool and workers
132
133		static final int COMPLETION_MASK      = 0xe0000000;
134		static final int NORMAL               = 0xe0000000; // == mask
#	Line 124 | Line 141 | public abstract class ForkJoinTask<V> im
141		/**
142		* Table of exceptions thrown by tasks, to enable reporting by
143		* callers. Because exceptions are rare, we don't directly keep
144	<	* them with task objects, but instead us a weak ref table.  Note
144	>	* them with task objects, but instead use a weak ref table.  Note
145		* that cancellation exceptions don't appear in the table, but are
146		* instead recorded as status values.
147	<	* Todo: Use ConcurrentReferenceHashMap
147	>	* TODO: Use ConcurrentReferenceHashMap
148		*/
149		static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
150		Collections.synchronizedMap
#	Line 136 | Line 153 | public abstract class ForkJoinTask<V> im
153		// within-package utilities
154
155		/**
156	<	* Get current worker thread, or null if not a worker thread
156	>	* Gets current worker thread, or null if not a worker thread.
157		*/
158		static ForkJoinWorkerThread getWorker() {
159		Thread t = Thread.currentThread();
#	Line 144 | Line 161 | public abstract class ForkJoinTask<V> im
161		(ForkJoinWorkerThread)t : null);
162		}
163
147	–	/**
148	–	* Get pool of current worker thread, or null if not a worker thread
149	–	*/
150	–	static ForkJoinPool getWorkerPool() {
151	–	Thread t = Thread.currentThread();
152	–	return ((t instanceof ForkJoinWorkerThread)?
153	–	((ForkJoinWorkerThread)t).pool : null);
154	–	}
155	–
164		final boolean casStatus(int cmp, int val) {
165	<	return _unsafe.compareAndSwapInt(this, statusOffset, cmp, val);
165	>	return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val);
166		}
167
168		/**
#	Line 162 | Line 170 | public abstract class ForkJoinTask<V> im
170		*/
171		static void rethrowException(Throwable ex) {
172		if (ex != null)
173	<	_unsafe.throwException(ex);
173	>	UNSAFE.throwException(ex);
174		}
175
176		// Setting completion status
177
178		/**
179	<	* Mark completion and wake up threads waiting to join this task.
179	>	* Marks completion and wakes up threads waiting to join this task.
180	>	*
181		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
182		*/
183		final void setCompletion(int completion) {
184	<	ForkJoinPool pool = getWorkerPool();
184	>	ForkJoinPool pool = getPool();
185		if (pool != null) {
186		int s; // Clear signal bits while setting completion status
187		do;while ((s = status) >= 0 && !casStatus(s, completion));
#	Line 204 | Line 213 | public abstract class ForkJoinTask<V> im
213		final void setNormalCompletion() {
214		// Try typical fast case -- single CAS, no signal, not already done.
215		// Manually expand casStatus to improve chances of inlining it
216	<	if (!_unsafe.compareAndSwapInt(this, statusOffset, 0, NORMAL))
216	>	if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL))
217		setCompletion(NORMAL);
218		}
219
#	Line 247 | Line 256 | public abstract class ForkJoinTask<V> im
256		/**
257		* Sets status to indicate there is joiner, then waits for join,
258		* surrounded with pool notifications.
259	+	*
260		* @return status upon exit
261		*/
262	<	final int awaitDone(ForkJoinWorkerThread w, boolean maintainParallelism) {
262	>	private int awaitDone(ForkJoinWorkerThread w, boolean maintainParallelism) {
263		ForkJoinPool pool = w == null? null : w.pool;
264		int s;
265		while ((s = status) >= 0) {
#	Line 268 | Line 278 | public abstract class ForkJoinTask<V> im
278		* Timed version of awaitDone
279		* @return status upon exit
280		*/
281	<	final int awaitDone(ForkJoinWorkerThread w, long nanos) {
281	>	private int awaitDone(ForkJoinWorkerThread w, long nanos) {
282		ForkJoinPool pool = w == null? null : w.pool;
283		int s;
284		while ((s = status) >= 0) {
#	Line 289 | Line 299 | public abstract class ForkJoinTask<V> im
299		}
300
301		/**
302	<	* Notify pool that thread is unblocked. Called by signalled
302	>	* Notifies pool that thread is unblocked. Called by signalled
303		* threads when woken by non-FJ threads (which is atypical).
304		*/
305		private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
#	Line 300 | Line 310 | public abstract class ForkJoinTask<V> im
310		}
311
312		/**
313	<	* Notify pool to adjust counts on cancelled or timed out wait
313	>	* Notifies pool to adjust counts on cancelled or timed out wait.
314		*/
315		private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
316		if (pool != null) {
#	Line 314 | Line 324 | public abstract class ForkJoinTask<V> im
324		}
325		}
326
327	+	/**
328	+	* Handles interruptions during waits.
329	+	*/
330		private void onInterruptedWait() {
331	<	Thread t = Thread.currentThread();
332	<	if (t instanceof ForkJoinWorkerThread) {
333	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread)t;
334	<	if (w.isTerminating())
335	<	cancelIgnoreExceptions();
336	<	}
324	<	else { // re-interrupt
325	<	try {
326	<	t.interrupt();
327	<	} catch (SecurityException ignore) {
328	<	}
329	<	}
331	>	ForkJoinWorkerThread w = getWorker();
332	>	if (w == null)
333	>	Thread.currentThread().interrupt(); // re-interrupt
334	>	else if (w.isTerminating())
335	>	cancelIgnoringExceptions();
336	>	// else if FJworker, ignore interrupt
337		}
338
339		// Recording and reporting exceptions
#	Line 337 | Line 344 | public abstract class ForkJoinTask<V> im
344		}
345
346		/**
347	<	* Throws the exception associated with status s;
347	>	* Throws the exception associated with status s.
348	>	*
349		* @throws the exception
350		*/
351		private void reportException(int s) {
#	Line 350 | Line 358 | public abstract class ForkJoinTask<V> im
358		}
359
360		/**
361	<	* Returns result or throws exception using j.u.c.Future conventions
361	>	* Returns result or throws exception using j.u.c.Future conventions.
362		* Only call when isDone known to be true.
363		*/
364		private V reportFutureResult()
#	Line 370 | Line 378 | public abstract class ForkJoinTask<V> im
378
379		/**
380		* Returns result or throws exception using j.u.c.Future conventions
381	<	* with timeouts
381	>	* with timeouts.
382		*/
383		private V reportTimedFutureResult()
384		throws InterruptedException, ExecutionException, TimeoutException {
#	Line 391 | Line 399 | public abstract class ForkJoinTask<V> im
399
400		/**
401		* Calls exec, recording completion, and rethrowing exception if
402	<	* encountered. Caller should normally check status before calling
402	>	* encountered. Caller should normally check status before calling.
403	>	*
404		* @return true if completed normally
405		*/
406		private boolean tryExec() {
#	Line 409 | Line 418 | public abstract class ForkJoinTask<V> im
418
419		/**
420		* Main execution method used by worker threads. Invokes
421	<	* base computation unless already complete
421	>	* base computation unless already complete.
422		*/
423		final void quietlyExec() {
424		if (status >= 0) {
#	Line 425 | Line 434 | public abstract class ForkJoinTask<V> im
434		}
435
436		/**
437	<	* Calls exec, recording but not rethrowing exception
438	<	* Caller should normally check status before calling
437	>	* Calls exec(), recording but not rethrowing exception.
438	>	* Caller should normally check status before calling.
439	>	*
440		* @return true if completed normally
441		*/
442		private boolean tryQuietlyInvoke() {
#	Line 442 | Line 452 | public abstract class ForkJoinTask<V> im
452		}
453
454		/**
455	<	* Cancel, ignoring any exceptions it throws
455	>	* Cancels, ignoring any exceptions it throws.
456		*/
457	<	final void cancelIgnoreExceptions() {
457	>	final void cancelIgnoringExceptions() {
458		try {
459		cancel(false);
460		} catch(Throwable ignore) {
461		}
462		}
463
464	+	/**
465	+	* Main implementation of helpJoin
466	+	*/
467	+	private int busyJoin(ForkJoinWorkerThread w) {
468	+	int s;
469	+	ForkJoinTask<?> t;
470	+	while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
471	+	t.quietlyExec();
472	+	return (s >= 0)? awaitDone(w, false) : s; // block if no work
473	+	}
474	+
475		// public methods
476
477		/**
478		* Arranges to asynchronously execute this task.  While it is not
479		* necessarily enforced, it is a usage error to fork a task more
480		* than once unless it has completed and been reinitialized.  This
481	<	* method may be invoked only from within other ForkJoinTask
481	>	* method may be invoked only from within ForkJoinTask
482		* computations. Attempts to invoke in other contexts result in
483	<	* exceptions or errors including ClassCastException.
483	>	* exceptions or errors possibly including ClassCastException.
484		*/
485		public final void fork() {
486		((ForkJoinWorkerThread)(Thread.currentThread())).pushTask(this);
#	Line 467 | Line 488 | public abstract class ForkJoinTask<V> im
488
489		/**
490		* Returns the result of the computation when it is ready.
491	<	* This method differs from <tt>get</tt> in that abnormal
491	>	* This method differs from {@code get} in that abnormal
492		* completion results in RuntimeExceptions or Errors, not
493		* ExecutionExceptions.
494		*
#	Line 480 | Line 501 | public abstract class ForkJoinTask<V> im
501		return getRawResult();
502		}
503
483	–	public final V get() throws InterruptedException, ExecutionException {
484	–	ForkJoinWorkerThread w = getWorker();
485	–	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
486	–	awaitDone(w, true);
487	–	return reportFutureResult();
488	–	}
489	–
490	–	public final V get(long timeout, TimeUnit unit)
491	–	throws InterruptedException, ExecutionException, TimeoutException {
492	–	ForkJoinWorkerThread w = getWorker();
493	–	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
494	–	awaitDone(w, unit.toNanos(timeout));
495	–	return reportTimedFutureResult();
496	–	}
497	–
504		/**
505	<	* Possibly executes other tasks until this task is ready, then
506	<	* returns the result of the computation.  This method may be more
507	<	* efficient than <tt>join</tt>, but is only applicable when there
502	<	* are no potemtial dependencies between continuation of the
503	<	* current task and that of any other task that might be executed
504	<	* while helping. (This usually holds for pure divide-and-conquer
505	<	* tasks).
506	<	* @return the computed result
507	<	*/
508	<	public final V helpJoin() {
509	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread)(Thread.currentThread());
510	<	if (status < 0 || !w.unpushTask(this) || !tryExec())
511	<	reportException(w.helpJoinTask(this));
512	<	return getRawResult();
513	<	}
514	<
515	<	/**
516	<	* Performs this task, awaits its completion if necessary, and
517	<	* return its result.
505	>	* Commences performing this task, awaits its completion if
506	>	* necessary, and return its result.
507	>	*
508		* @throws Throwable (a RuntimeException, Error, or unchecked
509	<	* exception) if the underlying computation did so.
509	>	* exception) if the underlying computation did so
510		* @return the computed result
511		*/
512		public final V invoke() {
#	Line 527 | Line 517 | public abstract class ForkJoinTask<V> im
517		}
518
519		/**
520	<	* Joins this task, without returning its result or throwing an
521	<	* exception. This method may be useful when processing
522	<	* collections of tasks when some have been cancelled or otherwise
523	<	* known to have aborted.
520	>	* Forks both tasks, returning when {@code isDone} holds for
521	>	* both of them or an exception is encountered. This method may be
522	>	* invoked only from within ForkJoinTask computations. Attempts to
523	>	* invoke in other contexts result in exceptions or errors
524	>	* possibly including ClassCastException.
525	>	*
526	>	* @param t1 one task
527	>	* @param t2 the other task
528	>	* @throws NullPointerException if t1 or t2 are null
529	>	* @throws RuntimeException or Error if either task did so
530		*/
531	<	public final void quietlyJoin() {
532	<	if (status >= 0) {
533	<	ForkJoinWorkerThread w = getWorker();
534	<	if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
539	<	awaitDone(w, true);
540	<	}
531	>	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
532	>	t2.fork();
533	>	t1.invoke();
534	>	t2.join();
535		}
536
537		/**
538	<	* Possibly executes other tasks until this task is ready.
538	>	* Forks the given tasks, returning when {@code isDone} holds
539	>	* for all of them. If any task encounters an exception, others
540	>	* may be cancelled.  This method may be invoked only from within
541	>	* ForkJoinTask computations. Attempts to invoke in other contexts
542	>	* result in exceptions or errors possibly including ClassCastException.
543	>	*
544	>	* @param tasks the array of tasks
545	>	* @throws NullPointerException if tasks or any element are null
546	>	* @throws RuntimeException or Error if any task did so
547		*/
548	<	public final void quietlyHelpJoin() {
549	<	if (status >= 0) {
550	<	ForkJoinWorkerThread w =
551	<	(ForkJoinWorkerThread)(Thread.currentThread());
552	<	if (!w.unpushTask(this) || !tryQuietlyInvoke())
553	<	w.helpJoinTask(this);
548	>	public static void invokeAll(ForkJoinTask<?>... tasks) {
549	>	Throwable ex = null;
550	>	int last = tasks.length - 1;
551	>	for (int i = last; i >= 0; --i) {
552	>	ForkJoinTask<?> t = tasks[i];
553	>	if (t == null) {
554	>	if (ex == null)
555	>	ex = new NullPointerException();
556	>	}
557	>	else if (i != 0)
558	>	t.fork();
559	>	else {
560	>	t.quietlyInvoke();
561	>	if (ex == null)
562	>	ex = t.getException();
563	>	}
564		}
565	+	for (int i = 1; i <= last; ++i) {
566	+	ForkJoinTask<?> t = tasks[i];
567	+	if (t != null) {
568	+	if (ex != null)
569	+	t.cancel(false);
570	+	else {
571	+	t.quietlyJoin();
572	+	if (ex == null)
573	+	ex = t.getException();
574	+	}
575	+	}
576	+	}
577	+	if (ex != null)
578	+	rethrowException(ex);
579		}
580
581		/**
582	<	* Performs this task and awaits its completion if necessary,
583	<	* without returning its result or throwing an exception. This
584	<	* method may be useful when processing collections of tasks when
585	<	* some have been cancelled or otherwise known to have aborted.
582	>	* Forks all tasks in the collection, returning when
583	>	* {@code isDone} holds for all of them. If any task
584	>	* encounters an exception, others may be cancelled.  This method
585	>	* may be invoked only from within ForkJoinTask
586	>	* computations. Attempts to invoke in other contexts result in
587	>	* exceptions or errors possibly including ClassCastException.
588	>	*
589	>	* @param tasks the collection of tasks
590	>	* @throws NullPointerException if tasks or any element are null
591	>	* @throws RuntimeException or Error if any task did so
592		*/
593	<	public final void quietlyInvoke() {
594	<	if (status >= 0 && !tryQuietlyInvoke())
595	<	quietlyJoin();
593	>	public static void invokeAll(Collection<? extends ForkJoinTask<?>> tasks) {
594	>	if (!(tasks instanceof List)) {
595	>	invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()]));
596	>	return;
597	>	}
598	>	List<? extends ForkJoinTask<?>> ts =
599	>	(List<? extends ForkJoinTask<?>>)tasks;
600	>	Throwable ex = null;
601	>	int last = ts.size() - 1;
602	>	for (int i = last; i >= 0; --i) {
603	>	ForkJoinTask<?> t = ts.get(i);
604	>	if (t == null) {
605	>	if (ex == null)
606	>	ex = new NullPointerException();
607	>	}
608	>	else if (i != 0)
609	>	t.fork();
610	>	else {
611	>	t.quietlyInvoke();
612	>	if (ex == null)
613	>	ex = t.getException();
614	>	}
615	>	}
616	>	for (int i = 1; i <= last; ++i) {
617	>	ForkJoinTask<?> t = ts.get(i);
618	>	if (t != null) {
619	>	if (ex != null)
620	>	t.cancel(false);
621	>	else {
622	>	t.quietlyJoin();
623	>	if (ex == null)
624	>	ex = t.getException();
625	>	}
626	>	}
627	>	}
628	>	if (ex != null)
629	>	rethrowException(ex);
630		}
631
632		/**
633		* Returns true if the computation performed by this task has
634		* completed (or has been cancelled).
635	+	*
636		* @return true if this computation has completed
637		*/
638		public final boolean isDone() {
#	Line 574 | Line 641 | public abstract class ForkJoinTask<V> im
641
642		/**
643		* Returns true if this task was cancelled.
644	+	*
645		* @return true if this task was cancelled
646		*/
647		public final boolean isCancelled() {
#	Line 581 | Line 649 | public abstract class ForkJoinTask<V> im
649		}
650
651		/**
584	–	* Returns true if this task threw an exception or was cancelled
585	–	* @return true if this task threw an exception or was cancelled
586	–	*/
587	–	public final boolean completedAbnormally() {
588	–	return (status & COMPLETION_MASK) < NORMAL;
589	–	}
590	–
591	–	/**
592	–	* Returns the exception thrown by the base computation, or a
593	–	* CancellationException if cancelled, or null if none or if the
594	–	* method has not yet completed.
595	–	* @return the exception, or null if none
596	–	*/
597	–	public final Throwable getException() {
598	–	int s = status & COMPLETION_MASK;
599	–	if (s >= NORMAL)
600	–	return null;
601	–	if (s == CANCELLED)
602	–	return new CancellationException();
603	–	return exceptionMap.get(this);
604	–	}
605	–
606	–	/**
652		* Asserts that the results of this task's computation will not be
653	<	* used. If a cancellation occurs before this task is processed,
654	<	* then its <tt>compute</tt> method will not be executed,
655	<	* <tt>isCancelled</tt> will report true, and <tt>join</tt> will
656	<	* result in a CancellationException being thrown. Otherwise, when
653	>	* used. If a cancellation occurs before attempting to execute this
654	>	* task, then execution will be suppressed, {@code isCancelled}
655	>	* will report true, and {@code join} will result in a
656	>	* {@code CancellationException} being thrown. Otherwise, when
657		* cancellation races with completion, there are no guarantees
658	<	* about whether <tt>isCancelled</tt> will report true, whether
659	<	* <tt>join</tt> will return normally or via an exception, or
658	>	* about whether {@code isCancelled} will report true, whether
659	>	* {@code join} will return normally or via an exception, or
660		* whether these behaviors will remain consistent upon repeated
661		* invocation.
662		*
#	Line 622 | Line 667 | public abstract class ForkJoinTask<V> im
667		* <p> This method is designed to be invoked by <em>other</em>
668		* tasks. To terminate the current task, you can just return or
669		* throw an unchecked exception from its computation method, or
670	<	* invoke <tt>completeExceptionally(someException)</tt>.
670	>	* invoke {@code completeExceptionally}.
671		*
672		* @param mayInterruptIfRunning this value is ignored in the
673		* default implementation because tasks are not in general
#	Line 636 | Line 681 | public abstract class ForkJoinTask<V> im
681		}
682
683		/**
684	+	* Returns true if this task threw an exception or was cancelled.
685	+	*
686	+	* @return true if this task threw an exception or was cancelled
687	+	*/
688	+	public final boolean isCompletedAbnormally() {
689	+	return (status & COMPLETION_MASK) < NORMAL;
690	+	}
691	+
692	+	/**
693	+	* Returns the exception thrown by the base computation, or a
694	+	* CancellationException if cancelled, or null if none or if the
695	+	* method has not yet completed.
696	+	*
697	+	* @return the exception, or null if none
698	+	*/
699	+	public final Throwable getException() {
700	+	int s = status & COMPLETION_MASK;
701	+	if (s >= NORMAL)
702	+	return null;
703	+	if (s == CANCELLED)
704	+	return new CancellationException();
705	+	return exceptionMap.get(this);
706	+	}
707	+
708	+	/**
709		* Completes this task abnormally, and if not already aborted or
710		* cancelled, causes it to throw the given exception upon
711	<	* <tt>join</tt> and related operations. This method may be used
711	>	* {@code join} and related operations. This method may be used
712		* to induce exceptions in asynchronous tasks, or to force
713	<	* completion of tasks that would not otherwise complete.  This
714	<	* method is overridable, but overridden versions must invoke
715	<	* <tt>super</tt> implementation to maintain guarantees.
713	>	* completion of tasks that would not otherwise complete.  Its use
714	>	* in other situations is likely to be wrong.  This method is
715	>	* overridable, but overridden versions must invoke {@code super}
716	>	* implementation to maintain guarantees.
717	>	*
718		* @param ex the exception to throw. If this exception is
719		* not a RuntimeException or Error, the actual exception thrown
720		* will be a RuntimeException with cause ex.
#	Line 655 | Line 727 | public abstract class ForkJoinTask<V> im
727
728		/**
729		* Completes this task, and if not already aborted or cancelled,
730	<	* returning a <tt>null</tt> result upon <tt>join</tt> and related
730	>	* returning a {@code null} result upon {@code join} and related
731		* operations. This method may be used to provide results for
732		* asynchronous tasks, or to provide alternative handling for
733	<	* tasks that would not otherwise complete normally.
733	>	* tasks that would not otherwise complete normally. Its use in
734	>	* other situations is likely to be wrong. This method is
735	>	* overridable, but overridden versions must invoke {@code super}
736	>	* implementation to maintain guarantees.
737		*
738	<	* @param value the result value for this task.
738	>	* @param value the result value for this task
739		*/
740		public void complete(V value) {
741		try {
#	Line 672 | Line 747 | public abstract class ForkJoinTask<V> im
747		setNormalCompletion();
748		}
749
750	<	/**
751	<	* Resets the internal bookkeeping state of this task, allowing a
752	<	* subsequent <tt>fork</tt>. This method allows repeated reuse of
753	<	* this task, but only if reuse occurs when this task has either
754	<	* never been forked, or has been forked, then completed and all
755	<	* outstanding joins of this task have also completed. Effects
756	<	* under any other usage conditions are not guaranteed, and are
757	<	* almost surely wrong. This method may be useful when executing
758	<	* pre-constructed trees of subtasks in loops.
759	<	*/
760	<	public void reinitialize() {
761	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
762	<	exceptionMap.remove(this);
688	<	status = 0;
750	>	public final V get() throws InterruptedException, ExecutionException {
751	>	ForkJoinWorkerThread w = getWorker();
752	>	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
753	>	awaitDone(w, true);
754	>	return reportFutureResult();
755	>	}
756	>
757	>	public final V get(long timeout, TimeUnit unit)
758	>	throws InterruptedException, ExecutionException, TimeoutException {
759	>	ForkJoinWorkerThread w = getWorker();
760	>	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
761	>	awaitDone(w, unit.toNanos(timeout));
762	>	return reportTimedFutureResult();
763		}
764
765		/**
766	<	* Tries to unschedule this task for execution. This method will
767	<	* typically succeed if this task is the next task that would be
768	<	* executed by the current thread, and will typically fail (return
769	<	* false) otherwise. This method may be useful when arranging
770	<	* faster local processing of tasks that could have been, but were
771	<	* not, stolen.
772	<	* @return true if unforked
766	>	* Possibly executes other tasks until this task is ready, then
767	>	* returns the result of the computation.  This method may be more
768	>	* efficient than {@code join}, but is only applicable when
769	>	* there are no potential dependencies between continuation of the
770	>	* current task and that of any other task that might be executed
771	>	* while helping. (This usually holds for pure divide-and-conquer
772	>	* tasks). This method may be invoked only from within
773	>	* ForkJoinTask computations. Attempts to invoke in other contexts
774	>	* result in exceptions or errors possibly including ClassCastException.
775	>	*
776	>	* @return the computed result
777		*/
778	<	public boolean tryUnfork() {
779	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).unpushTask(this);
778	>	public final V helpJoin() {
779	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread)(Thread.currentThread());
780	>	if (status < 0 || !w.unpushTask(this) || !tryExec())
781	>	reportException(busyJoin(w));
782	>	return getRawResult();
783		}
784
785		/**
786	<	* Forks both tasks, returning when <tt>isDone</tt> holds for both
787	<	* of them or an exception is encountered. This method may be
707	<	* invoked only from within other ForkJoinTask
786	>	* Possibly executes other tasks until this task is ready.  This
787	>	* method may be invoked only from within ForkJoinTask
788		* computations. Attempts to invoke in other contexts result in
789	<	* exceptions or errors including ClassCastException.
710	<	* @param t1 one task
711	<	* @param t2 the other task
712	<	* @throws NullPointerException if t1 or t2 are null
713	<	* @throws RuntimeException or Error if either task did so.
789	>	* exceptions or errors possibly including ClassCastException.
790		*/
791	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
792	<	t2.fork();
793	<	t1.invoke();
794	<	t2.join();
791	>	public final void quietlyHelpJoin() {
792	>	if (status >= 0) {
793	>	ForkJoinWorkerThread w =
794	>	(ForkJoinWorkerThread)(Thread.currentThread());
795	>	if (!w.unpushTask(this) || !tryQuietlyInvoke())
796	>	busyJoin(w);
797	>	}
798		}
799
800		/**
801	<	* Forks the given tasks, returning when <tt>isDone</tt> holds for
802	<	* all of them. If any task encounters an exception, others may be
803	<	* cancelled.  This method may be invoked only from within other
804	<	* ForkJoinTask computations. Attempts to invoke in other contexts
726	<	* result in exceptions or errors including ClassCastException.
727	<	* @param tasks the array of tasks
728	<	* @throws NullPointerException if tasks or any element are null.
729	<	* @throws RuntimeException or Error if any task did so.
801	>	* Joins this task, without returning its result or throwing an
802	>	* exception. This method may be useful when processing
803	>	* collections of tasks when some have been cancelled or otherwise
804	>	* known to have aborted.
805		*/
806	<	public static void invokeAll(ForkJoinTask<?>... tasks) {
807	<	Throwable ex = null;
808	<	int last = tasks.length - 1;
809	<	for (int i = last; i >= 0; --i) {
810	<	ForkJoinTask<?> t = tasks[i];
736	<	if (t == null) {
737	<	if (ex == null)
738	<	ex = new NullPointerException();
739	<	}
740	<	else if (i != 0)
741	<	t.fork();
742	<	else {
743	<	t.quietlyInvoke();
744	<	if (ex == null)
745	<	ex = t.getException();
746	<	}
747	<	}
748	<	for (int i = 1; i <= last; ++i) {
749	<	ForkJoinTask<?> t = tasks[i];
750	<	if (t != null) {
751	<	if (ex != null)
752	<	t.cancel(false);
753	<	else {
754	<	t.quietlyJoin();
755	<	if (ex == null)
756	<	ex = t.getException();
757	<	}
758	<	}
806	>	public final void quietlyJoin() {
807	>	if (status >= 0) {
808	>	ForkJoinWorkerThread w = getWorker();
809	>	if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
810	>	awaitDone(w, true);
811		}
760	–	if (ex != null)
761	–	rethrowException(ex);
812		}
813
814		/**
815	<	* Forks all tasks in the collection, returning when
816	<	* <tt>isDone</tt> holds for all of them. If any task encounters
817	<	* an exception, others may be cancelled.  This method may be
818	<	* invoked only from within other ForkJoinTask
819	<	* computations. Attempts to invoke in other contexts result in
770	<	* exceptions or errors including ClassCastException.
771	<	* @param tasks the collection of tasks
772	<	* @throws NullPointerException if tasks or any element are null.
773	<	* @throws RuntimeException or Error if any task did so.
815	>	* Commences performing this task and awaits its completion if
816	>	* necessary, without returning its result or throwing an
817	>	* exception. This method may be useful when processing
818	>	* collections of tasks when some have been cancelled or otherwise
819	>	* known to have aborted.
820		*/
821	<	public static void invokeAll(Collection<? extends ForkJoinTask<?>> tasks) {
822	<	if (!(tasks instanceof List)) {
823	<	invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()]));
778	<	return;
779	<	}
780	<	List<? extends ForkJoinTask<?>> ts =
781	<	(List<? extends ForkJoinTask<?>>)tasks;
782	<	Throwable ex = null;
783	<	int last = ts.size() - 1;
784	<	for (int i = last; i >= 0; --i) {
785	<	ForkJoinTask<?> t = ts.get(i);
786	<	if (t == null) {
787	<	if (ex == null)
788	<	ex = new NullPointerException();
789	<	}
790	<	else if (i != 0)
791	<	t.fork();
792	<	else {
793	<	t.quietlyInvoke();
794	<	if (ex == null)
795	<	ex = t.getException();
796	<	}
797	<	}
798	<	for (int i = 1; i <= last; ++i) {
799	<	ForkJoinTask<?> t = ts.get(i);
800	<	if (t != null) {
801	<	if (ex != null)
802	<	t.cancel(false);
803	<	else {
804	<	t.quietlyJoin();
805	<	if (ex == null)
806	<	ex = t.getException();
807	<	}
808	<	}
809	<	}
810	<	if (ex != null)
811	<	rethrowException(ex);
821	>	public final void quietlyInvoke() {
822	>	if (status >= 0 && !tryQuietlyInvoke())
823	>	quietlyJoin();
824		}
825
826		/**
#	Line 823 | Line 835 | public abstract class ForkJoinTask<V> im
835		}
836
837		/**
838	<	* Returns a estimate of how many more locally queued tasks are
838	>	* Resets the internal bookkeeping state of this task, allowing a
839	>	* subsequent {@code fork}. This method allows repeated reuse of
840	>	* this task, but only if reuse occurs when this task has either
841	>	* never been forked, or has been forked, then completed and all
842	>	* outstanding joins of this task have also completed. Effects
843	>	* under any other usage conditions are not guaranteed, and are
844	>	* almost surely wrong. This method may be useful when executing
845	>	* pre-constructed trees of subtasks in loops.
846	>	*/
847	>	public void reinitialize() {
848	>	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
849	>	exceptionMap.remove(this);
850	>	status = 0;
851	>	}
852	>
853	>	/**
854	>	* Returns the pool hosting the current task execution, or null
855	>	* if this task is executing outside of any pool.
856	>	*
857	>	* @return the pool, or null if none
858	>	*/
859	>	public static ForkJoinPool getPool() {
860	>	Thread t = Thread.currentThread();
861	>	return ((t instanceof ForkJoinWorkerThread)?
862	>	((ForkJoinWorkerThread)t).pool : null);
863	>	}
864	>
865	>	/**
866	>	* Tries to unschedule this task for execution. This method will
867	>	* typically succeed if this task is the most recently forked task
868	>	* by the current thread, and has not commenced executing in
869	>	* another thread.  This method may be useful when arranging
870	>	* alternative local processing of tasks that could have been, but
871	>	* were not, stolen. This method may be invoked only from within
872	>	* ForkJoinTask computations. Attempts to invoke in other contexts
873	>	* result in exceptions or errors possibly including ClassCastException.
874	>	*
875	>	* @return true if unforked
876	>	*/
877	>	public boolean tryUnfork() {
878	>	return ((ForkJoinWorkerThread)(Thread.currentThread())).unpushTask(this);
879	>	}
880	>
881	>	/**
882	>	* Returns an estimate of the number of tasks that have been
883	>	* forked by the current worker thread but not yet executed. This
884	>	* value may be useful for heuristic decisions about whether to
885	>	* fork other tasks.
886	>	*
887	>	* @return the number of tasks
888	>	*/
889	>	public static int getQueuedTaskCount() {
890	>	return ((ForkJoinWorkerThread)(Thread.currentThread())).
891	>	getQueueSize();
892	>	}
893	>
894	>	/**
895	>	* Returns an estimate of how many more locally queued tasks are
896		* held by the current worker thread than there are other worker
897	<	* threads that might want to steal them.  This value may be
898	<	* useful for heuristic decisions about whether to fork other
899	<	* tasks. In many usages of ForkJoinTasks, at steady state, each
900	<	* worker should aim to maintain a small constant surplus (for
901	<	* example, 3) of tasks, and to process computations locally if
902	<	* this threshold is exceeded.
897	>	* threads that might steal them.  This value may be useful for
898	>	* heuristic decisions about whether to fork other tasks. In many
899	>	* usages of ForkJoinTasks, at steady state, each worker should
900	>	* aim to maintain a small constant surplus (for example, 3) of
901	>	* tasks, and to process computations locally if this threshold is
902	>	* exceeded.
903	>	*
904		* @return the surplus number of tasks, which may be negative
905		*/
906	<	public static int surplus() {
906	>	public static int getSurplusQueuedTaskCount() {
907		return ((ForkJoinWorkerThread)(Thread.currentThread()))
908		.getEstimatedSurplusTaskCount();
909		}
910
911	<	// Extension kit
911	>	// Extension methods
912
913		/**
914	<	* Returns the result that would be returned by <tt>join</tt>, or
915	<	* null if this task is not known to have been completed.  This
916	<	* method is designed to aid debugging, as well as to support
917	<	* extensions. Its use in any other context is discouraged.
914	>	* Returns the result that would be returned by {@code join},
915	>	* even if this task completed abnormally, or null if this task is
916	>	* not known to have been completed.  This method is designed to
917	>	* aid debugging, as well as to support extensions. Its use in any
918	>	* other context is discouraged.
919		*
920	<	* @return the result, or null if not completed.
920	>	* @return the result, or null if not completed
921		*/
922		public abstract V getRawResult();
923
#	Line 865 | Line 936 | public abstract class ForkJoinTask<V> im
936		* called otherwise. The return value controls whether this task
937		* is considered to be done normally. It may return false in
938		* asynchronous actions that require explicit invocations of
939	<	* <tt>complete</tt> to become joinable. It may throw exceptions
939	>	* {@code complete} to become joinable. It may throw exceptions
940		* to indicate abnormal exit.
941	+	*
942		* @return true if completed normally
943		* @throws Error or RuntimeException if encountered during computation
944		*/
945		protected abstract boolean exec();
946
947	+	/**
948	+	* Returns, but does not unschedule or execute, the task queued by
949	+	* the current thread but not yet executed, if one is
950	+	* available. There is no guarantee that this task will actually
951	+	* be polled or executed next.  This method is designed primarily
952	+	* to support extensions, and is unlikely to be useful otherwise.
953	+	* This method may be invoked only from within ForkJoinTask
954	+	* computations. Attempts to invoke in other contexts result in
955	+	* exceptions or errors possibly including ClassCastException.
956	+	*
957	+	* @return the next task, or null if none are available
958	+	*/
959	+	protected static ForkJoinTask<?> peekNextLocalTask() {
960	+	return ((ForkJoinWorkerThread)(Thread.currentThread())).peekTask();
961	+	}
962	+
963	+	/**
964	+	* Unschedules and returns, without executing, the next task
965	+	* queued by the current thread but not yet executed.  This method
966	+	* is designed primarily to support extensions, and is unlikely to
967	+	* be useful otherwise.  This method may be invoked only from
968	+	* within ForkJoinTask computations. Attempts to invoke in other
969	+	* contexts result in exceptions or errors possibly including
970	+	* ClassCastException.
971	+	*
972	+	* @return the next task, or null if none are available
973	+	*/
974	+	protected static ForkJoinTask<?> pollNextLocalTask() {
975	+	return ((ForkJoinWorkerThread)(Thread.currentThread())).pollLocalTask();
976	+	}
977	+
978	+	/**
979	+	* Unschedules and returns, without executing, the next task
980	+	* queued by the current thread but not yet executed, if one is
981	+	* available, or if not available, a task that was forked by some
982	+	* other thread, if available. Availability may be transient, so a
983	+	* {@code null} result does not necessarily imply quiescence
984	+	* of the pool this task is operating in.  This method is designed
985	+	* primarily to support extensions, and is unlikely to be useful
986	+	* otherwise.  This method may be invoked only from within
987	+	* ForkJoinTask computations. Attempts to invoke in other contexts
988	+	* result in exceptions or errors possibly including
989	+	* ClassCastException.
990	+	*
991	+	* @return a task, or null if none are available
992	+	*/
993	+	protected static ForkJoinTask<?> pollTask() {
994	+	return ((ForkJoinWorkerThread)(Thread.currentThread())).
995	+	pollTask();
996	+	}
997	+
998		// Serialization support
999
1000		private static final long serialVersionUID = -7721805057305804111L;
#	Line 880 | Line 1003 | public abstract class ForkJoinTask<V> im
1003		* Save the state to a stream.
1004		*
1005		* @serialData the current run status and the exception thrown
1006	<	* during execution, or null if none.
1006	>	* during execution, or null if none
1007		* @param s the stream
1008		*/
1009		private void writeObject(java.io.ObjectOutputStream s)
#	Line 891 | Line 1014 | public abstract class ForkJoinTask<V> im
1014
1015		/**
1016		* Reconstitute the instance from a stream.
1017	+	*
1018		* @param s the stream
1019		*/
1020		private void readObject(java.io.ObjectInputStream s)
1021		throws java.io.IOException, ClassNotFoundException {
1022		s.defaultReadObject();
1023	<	//        status &= ~INTERNAL_SIGNAL_MASK; //  todo: define policy
1023	>	status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
1024	>	status |= EXTERNAL_SIGNAL; // conservatively set external signal
1025		Object ex = s.readObject();
1026		if (ex != null)
1027		setDoneExceptionally((Throwable)ex);
1028		}
1029
1030		// Temporary Unsafe mechanics for preliminary release
1031	+	private static Unsafe getUnsafe() throws Throwable {
1032	+	try {
1033	+	return Unsafe.getUnsafe();
1034	+	} catch (SecurityException se) {
1035	+	try {
1036	+	return java.security.AccessController.doPrivileged
1037	+	(new java.security.PrivilegedExceptionAction<Unsafe>() {
1038	+	public Unsafe run() throws Exception {
1039	+	return getUnsafePrivileged();
1040	+	}});
1041	+	} catch (java.security.PrivilegedActionException e) {
1042	+	throw e.getCause();
1043	+	}
1044	+	}
1045	+	}
1046
1047	<	static final Unsafe _unsafe;
1047	>	private static Unsafe getUnsafePrivileged()
1048	>	throws NoSuchFieldException, IllegalAccessException {
1049	>	Field f = Unsafe.class.getDeclaredField("theUnsafe");
1050	>	f.setAccessible(true);
1051	>	return (Unsafe) f.get(null);
1052	>	}
1053	>
1054	>	private static long fieldOffset(String fieldName)
1055	>	throws NoSuchFieldException {
1056	>	return UNSAFE.objectFieldOffset
1057	>	(ForkJoinTask.class.getDeclaredField(fieldName));
1058	>	}
1059	>
1060	>	static final Unsafe UNSAFE;
1061		static final long statusOffset;
1062
1063		static {
1064		try {
1065	<	if (ForkJoinTask.class.getClassLoader() != null) {
1066	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
1067	<	f.setAccessible(true);
1068	<	_unsafe = (Unsafe)f.get(null);
1069	<	}
917	<	else
918	<	_unsafe = Unsafe.getUnsafe();
919	<	statusOffset = _unsafe.objectFieldOffset
920	<	(ForkJoinTask.class.getDeclaredField("status"));
921	<	} catch (Exception ex) { throw new Error(ex); }
1065	>	UNSAFE = getUnsafe();
1066	>	statusOffset = fieldOffset("status");
1067	>	} catch (Throwable e) {
1068	>	throw new RuntimeException("Could not initialize intrinsics", e);
1069	>	}
1070		}
1071
1072		}

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