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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.6 by dl, Thu Jul 16 15:32:34 2009 UTC vs.
Revision 1.42 by dl, Thu Aug 6 23:08:50 2009 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	<	import java.io.Serializable;
9	<	import java.util.*;
8	>
9		import java.util.concurrent.*;
10	<	import java.util.concurrent.atomic.*;
11	<	import sun.misc.Unsafe;
12	<	import java.lang.reflect.*;
10	>
11	>	import java.io.Serializable;
12	>	import java.util.Collection;
13	>	import java.util.Collections;
14	>	import java.util.List;
15	>	import java.util.RandomAccess;
16	>	import java.util.Map;
17	>	import java.util.WeakHashMap;
18
19		/**
20	<	* Abstract base class for tasks that run within a {@link
21	<	* ForkJoinPool}.  A ForkJoinTask is a thread-like entity that is much
20	>	* Abstract base class for tasks that run within a {@link ForkJoinPool}.
21	>	* A {@code ForkJoinTask} is a thread-like entity that is much
22		* lighter weight than a normal thread.  Huge numbers of tasks and
23		* subtasks may be hosted by a small number of actual threads in a
24		* ForkJoinPool, at the price of some usage limitations.
25		*
26	<	* <p> A "main" ForkJoinTask begins execution when submitted to a
27	<	* {@link ForkJoinPool}. Once started, it will usually in turn start
28	<	* other subtasks.  As indicated by the name of this class, many
29	<	* programs using ForkJoinTasks employ only methods <code>fork</code>
30	<	* and <code>join</code>, or derivatives such as
31	<	* <code>invokeAll</code>.  However, this class also provides a number
32	<	* of other methods that can come into play in advanced usages, as
33	<	* well as extension mechanics that allow support of new forms of
34	<	* fork/join processing.
26	>	* <p>A "main" {@code ForkJoinTask} begins execution when submitted
27	>	* to a {@link ForkJoinPool}.  Once started, it will usually in turn
28	>	* start other subtasks.  As indicated by the name of this class,
29	>	* many programs using {@code ForkJoinTask} employ only methods
30	>	* {@link #fork} and {@link #join}, or derivatives such as {@link
31	>	* #invokeAll}.  However, this class also provides a number of other
32	>	* methods that can come into play in advanced usages, as well as
33	>	* extension mechanics that allow support of new forms of fork/join
34	>	* processing.
35		*
36	<	* <p>A ForkJoinTask is a lightweight form of {@link Future}.  The
37	<	* efficiency of ForkJoinTasks stems from a set of restrictions (that
38	<	* are only partially statically enforceable) reflecting their
39	<	* intended use as computational tasks calculating pure functions or
40	<	* operating on purely isolated objects.  The primary coordination
41	<	* mechanisms are {@link #fork}, that arranges asynchronous execution,
42	<	* and {@link #join}, that doesn't proceed until the task's result has
43	<	* been computed.  Computations should avoid <code>synchronized</code>
44	<	* methods or blocks, and should minimize other blocking
45	<	* synchronization apart from joining other tasks or using
46	<	* synchronizers such as Phasers that are advertised to cooperate with
47	<	* fork/join scheduling. Tasks should also not perform blocking IO,
48	<	* and should ideally access variables that are completely independent
49	<	* of those accessed by other running tasks. Minor breaches of these
50	<	* restrictions, for example using shared output streams, may be
51	<	* tolerable in practice, but frequent use may result in poor
52	<	* performance, and the potential to indefinitely stall if the number
53	<	* of threads not waiting for IO or other external synchronization
54	<	* becomes exhausted. This usage restriction is in part enforced by
55	<	* not permitting checked exceptions such as <code>IOExceptions</code>
56	<	* to be thrown. However, computations may still encounter unchecked
57	<	* exceptions, that are rethrown to callers attempting join
58	<	* them. These exceptions may additionally include
59	<	* RejectedExecutionExceptions stemming from internal resource
60	<	* exhaustion such as failure to allocate internal task queues.
36	>	* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
37	>	* The efficiency of {@code ForkJoinTask}s stems from a set of
38	>	* restrictions (that are only partially statically enforceable)
39	>	* reflecting their intended use as computational tasks calculating
40	>	* pure functions or operating on purely isolated objects.  The
41	>	* primary coordination mechanisms are {@link #fork}, that arranges
42	>	* asynchronous execution, and {@link #join}, that doesn't proceed
43	>	* until the task's result has been computed.  Computations should
44	>	* avoid {@code synchronized} methods or blocks, and should minimize
45	>	* other blocking synchronization apart from joining other tasks or
46	>	* using synchronizers such as Phasers that are advertised to
47	>	* cooperate with fork/join scheduling. Tasks should also not perform
48	>	* blocking IO, and should ideally access variables that are
49	>	* completely independent of those accessed by other running
50	>	* tasks. Minor breaches of these restrictions, for example using
51	>	* shared output streams, may be tolerable in practice, but frequent
52	>	* use may result in poor performance, and the potential to
53	>	* indefinitely stall if the number of threads not waiting for IO or
54	>	* other external synchronization becomes exhausted. This usage
55	>	* restriction is in part enforced by not permitting checked
56	>	* exceptions such as {@code IOExceptions} to be thrown. However,
57	>	* computations may still encounter unchecked exceptions, that are
58	>	* rethrown to callers attempting to join them. These exceptions may
59	>	* additionally include RejectedExecutionExceptions stemming from
60	>	* internal resource exhaustion such as failure to allocate internal
61	>	* task queues.
62		*
63		* <p>The primary method for awaiting completion and extracting
64		* results of a task is {@link #join}, but there are several variants:
65		* The {@link Future#get} methods support interruptible and/or timed
66	<	* waits for completion and report results using <code>Future</code>
66	>	* waits for completion and report results using {@code Future}
67		* conventions. Method {@link #helpJoin} enables callers to actively
68		* execute other tasks while awaiting joins, which is sometimes more
69		* efficient but only applies when all subtasks are known to be
70		* strictly tree-structured. Method {@link #invoke} is semantically
71	<	* equivalent to <code>fork(); join()</code> but always attempts to
72	<	* begin execution in the current thread. The "<em>quiet</em>" forms
73	<	* of these methods do not extract results or report exceptions. These
71	>	* equivalent to {@code fork(); join()} but always attempts to begin
72	>	* execution in the current thread. The "<em>quiet</em>" forms of
73	>	* these methods do not extract results or report exceptions. These
74		* may be useful when a set of tasks are being executed, and you need
75		* to delay processing of results or exceptions until all complete.
76	<	* Method <code>invokeAll</code> (available in multiple versions)
76	>	* Method {@code invokeAll} (available in multiple versions)
77		* performs the most common form of parallel invocation: forking a set
78		* of tasks and joining them all.
79		*
80	<	* <p> The ForkJoinTask class is not usually directly subclassed.
80	>	* <p>The execution status of tasks may be queried at several levels
81	>	* of detail: {@link #isDone} is true if a task completed in any way
82	>	* (including the case where a task was cancelled without executing);
83	>	* {@link #isCompletedNormally} is true if a task completed without
84	>	* cancellation or encountering an exception; {@link #isCancelled} is
85	>	* true if the task was cancelled (in which case {@link #getException}
86	>	* returns a {@link java.util.concurrent.CancellationException}); and
87	>	* {@link #isCompletedAbnormally} is true if a task was either
88	>	* cancelled or encountered an exception, in which case {@link
89	>	* #getException} will return either the encountered exception or
90	>	* {@link java.util.concurrent.CancellationException}.
91	>	*
92	>	* <p>The ForkJoinTask class is not usually directly subclassed.
93		* Instead, you subclass one of the abstract classes that support a
94	<	* particular style of fork/join processing.  Normally, a concrete
94	>	* particular style of fork/join processing, typically {@link
95	>	* RecursiveAction} for computations that do not return results, or
96	>	* {@link RecursiveTask} for those that do.  Normally, a concrete
97		* ForkJoinTask subclass declares fields comprising its parameters,
98	<	* established in a constructor, and then defines a <code>compute</code>
98	>	* established in a constructor, and then defines a {@code compute}
99		* method that somehow uses the control methods supplied by this base
100	<	* class. While these methods have <code>public</code> access (to allow
101	<	* instances of different task subclasses to call each others
100	>	* class. While these methods have {@code public} access (to allow
101	>	* instances of different task subclasses to call each other's
102		* methods), some of them may only be called from within other
103	<	* ForkJoinTasks. Attempts to invoke them in other contexts result in
104	<	* exceptions or errors possibly including ClassCastException.
103	>	* ForkJoinTasks (as may be determined using method {@link
104	>	* #inForkJoinPool}).  Attempts to invoke them in other contexts
105	>	* result in exceptions or errors, possibly including
106	>	* ClassCastException.
107		*
108	<	* <p>Most base support methods are <code>final</code> because their
109	<	* implementations are intrinsically tied to the underlying
110	<	* lightweight task scheduling framework, and so cannot be overridden.
111	<	* Developers creating new basic styles of fork/join processing should
112	<	* minimally implement <code>protected</code> methods
113	<	* <code>exec</code>, <code>setRawResult</code>, and
114	<	* <code>getRawResult</code>, while also introducing an abstract
115	<	* computational method that can be implemented in its subclasses,
116	<	* possibly relying on other <code>protected</code> methods provided
96	<	* by this class.
108	>	* <p>Most base support methods are {@code final}, to prevent
109	>	* overriding of implementations that are intrinsically tied to the
110	>	* underlying lightweight task scheduling framework.  Developers
111	>	* creating new basic styles of fork/join processing should minimally
112	>	* implement {@code protected} methods {@link #exec}, {@link
113	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
114	>	* an abstract computational method that can be implemented in its
115	>	* subclasses, possibly relying on other {@code protected} methods
116	>	* provided by this class.
117		*
118		* <p>ForkJoinTasks should perform relatively small amounts of
119	<	* computations, othewise splitting into smaller tasks. As a very
120	<	* rough rule of thumb, a task should perform more than 100 and less
121	<	* than 10000 basic computational steps. If tasks are too big, then
122	<	* parellelism cannot improve throughput. If too small, then memory
123	<	* and internal task maintenance overhead may overwhelm processing.
119	>	* computation. Large tasks should be split into smaller subtasks,
120	>	* usually via recursive decomposition. As a very rough rule of thumb,
121	>	* a task should perform more than 100 and less than 10000 basic
122	>	* computational steps. If tasks are too big, then parallelism cannot
123	>	* improve throughput. If too small, then memory and internal task
124	>	* maintenance overhead may overwhelm processing.
125	>	*
126	>	* <p>This class provides {@code adapt} methods for {@link Runnable}
127	>	* and {@link Callable}, that may be of use when mixing execution of
128	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks
129	>	* are of this form, consider using a pool in
130	>	* {@linkplain ForkJoinPool#setAsyncMode async mode}.
131		*
132	<	* <p>ForkJoinTasks are <code>Serializable</code>, which enables them
133	<	* to be used in extensions such as remote execution frameworks. It is
134	<	* in general sensible to serialize tasks only before or after, but
135	<	* not during execution. Serialization is not relied on during
136	<	* execution itself.
132	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
133	>	* used in extensions such as remote execution frameworks. It is
134	>	* sensible to serialize tasks only before or after, but not during,
135	>	* execution. Serialization is not relied on during execution itself.
136	>	*
137	>	* @since 1.7
138	>	* @author Doug Lea
139		*/
140		public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
141
#	Line 128 | Line 157 | public abstract class ForkJoinTask<V> im
157		* currently unused. Also value 0x80000000 is available as spare
158		* completion value.
159		*/
160	<	volatile int status; // accessed directy by pool and workers
160	>	volatile int status; // accessed directly by pool and workers
161
162		static final int COMPLETION_MASK      = 0xe0000000;
163		static final int NORMAL               = 0xe0000000; // == mask
#	Line 141 | Line 170 | public abstract class ForkJoinTask<V> im
170		/**
171		* Table of exceptions thrown by tasks, to enable reporting by
172		* callers. Because exceptions are rare, we don't directly keep
173	<	* them with task objects, but instead us a weak ref table.  Note
173	>	* them with task objects, but instead use a weak ref table.  Note
174		* that cancellation exceptions don't appear in the table, but are
175		* instead recorded as status values.
176	<	* Todo: Use ConcurrentReferenceHashMap
176	>	* TODO: Use ConcurrentReferenceHashMap
177		*/
178		static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
179		Collections.synchronizedMap
#	Line 153 | Line 182 | public abstract class ForkJoinTask<V> im
182		// within-package utilities
183
184		/**
185	<	* Get current worker thread, or null if not a worker thread
185	>	* Gets current worker thread, or null if not a worker thread.
186		*/
187		static ForkJoinWorkerThread getWorker() {
188		Thread t = Thread.currentThread();
189	<	return ((t instanceof ForkJoinWorkerThread)?
190	<	(ForkJoinWorkerThread)t : null);
189	>	return ((t instanceof ForkJoinWorkerThread) ?
190	>	(ForkJoinWorkerThread) t : null);
191		}
192
193		final boolean casStatus(int cmp, int val) {
194	<	return _unsafe.compareAndSwapInt(this, statusOffset, cmp, val);
194	>	return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val);
195		}
196
197		/**
#	Line 170 | Line 199 | public abstract class ForkJoinTask<V> im
199		*/
200		static void rethrowException(Throwable ex) {
201		if (ex != null)
202	<	_unsafe.throwException(ex);
202	>	UNSAFE.throwException(ex);
203		}
204
205		// Setting completion status
206
207		/**
208	<	* Mark completion and wake up threads waiting to join this task.
208	>	* Marks completion and wakes up threads waiting to join this task.
209	>	*
210		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
211		*/
212		final void setCompletion(int completion) {
213		ForkJoinPool pool = getPool();
214		if (pool != null) {
215		int s; // Clear signal bits while setting completion status
216	<	do;while ((s = status) >= 0 && !casStatus(s, completion));
216	>	do {} while ((s = status) >= 0 && !casStatus(s, completion));
217
218		if ((s & SIGNAL_MASK) != 0) {
219		if ((s &= INTERNAL_SIGNAL_MASK) != 0)
220		pool.updateRunningCount(s);
221	<	synchronized(this) { notifyAll(); }
221	>	synchronized (this) { notifyAll(); }
222		}
223		}
224		else
#	Line 201 | Line 231 | public abstract class ForkJoinTask<V> im
231		*/
232		private void externallySetCompletion(int completion) {
233		int s;
234	<	do;while ((s = status) >= 0 &&
235	<	!casStatus(s, (s & SIGNAL_MASK) | completion));
236	<	synchronized(this) { notifyAll(); }
234	>	do {} while ((s = status) >= 0 &&
235	>	!casStatus(s, (s & SIGNAL_MASK) | completion));
236	>	synchronized (this) { notifyAll(); }
237		}
238
239		/**
240	<	* Sets status to indicate normal completion
240	>	* Sets status to indicate normal completion.
241		*/
242		final void setNormalCompletion() {
243		// Try typical fast case -- single CAS, no signal, not already done.
244		// Manually expand casStatus to improve chances of inlining it
245	<	if (!_unsafe.compareAndSwapInt(this, statusOffset, 0, NORMAL))
245	>	if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL))
246		setCompletion(NORMAL);
247		}
248
249		// internal waiting and notification
250
251		/**
252	<	* Performs the actual monitor wait for awaitDone
252	>	* Performs the actual monitor wait for awaitDone.
253		*/
254		private void doAwaitDone() {
255		// Minimize lock bias and in/de-flation effects by maximizing
256		// chances of waiting inside sync
257		try {
258		while (status >= 0)
259	<	synchronized(this) { if (status >= 0) wait(); }
259	>	synchronized (this) { if (status >= 0) wait(); }
260		} catch (InterruptedException ie) {
261		onInterruptedWait();
262		}
263		}
264
265		/**
266	<	* Performs the actual monitor wait for awaitDone
266	>	* Performs the actual timed monitor wait for awaitDone.
267		*/
268		private void doAwaitDone(long startTime, long nanos) {
269	<	synchronized(this) {
269	>	synchronized (this) {
270		try {
271		while (status >= 0) {
272	<	long nt = nanos - System.nanoTime() - startTime;
272	>	long nt = nanos - (System.nanoTime() - startTime);
273		if (nt <= 0)
274		break;
275	<	wait(nt / 1000000, (int)(nt % 1000000));
275	>	wait(nt / 1000000, (int) (nt % 1000000));
276		}
277		} catch (InterruptedException ie) {
278		onInterruptedWait();
#	Line 255 | Line 285 | public abstract class ForkJoinTask<V> im
285		/**
286		* Sets status to indicate there is joiner, then waits for join,
287		* surrounded with pool notifications.
288	+	*
289		* @return status upon exit
290		*/
291	<	private int awaitDone(ForkJoinWorkerThread w, boolean maintainParallelism) {
292	<	ForkJoinPool pool = w == null? null : w.pool;
291	>	private int awaitDone(ForkJoinWorkerThread w,
292	>	boolean maintainParallelism) {
293	>	ForkJoinPool pool = (w == null) ? null : w.pool;
294		int s;
295		while ((s = status) >= 0) {
296	<	if (casStatus(s, pool == null? s|EXTERNAL_SIGNAL : s+1)) {
296	>	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
297		if (pool == null || !pool.preJoin(this, maintainParallelism))
298		doAwaitDone();
299		if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
#	Line 274 | Line 306 | public abstract class ForkJoinTask<V> im
306
307		/**
308		* Timed version of awaitDone
309	+	*
310		* @return status upon exit
311		*/
312		private int awaitDone(ForkJoinWorkerThread w, long nanos) {
313	<	ForkJoinPool pool = w == null? null : w.pool;
313	>	ForkJoinPool pool = (w == null) ? null : w.pool;
314		int s;
315		while ((s = status) >= 0) {
316	<	if (casStatus(s, pool == null? s|EXTERNAL_SIGNAL : s+1)) {
316	>	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
317		long startTime = System.nanoTime();
318		if (pool == null || !pool.preJoin(this, false))
319		doAwaitDone(startTime, nanos);
#	Line 297 | Line 330 | public abstract class ForkJoinTask<V> im
330		}
331
332		/**
333	<	* Notify pool that thread is unblocked. Called by signalled
333	>	* Notifies pool that thread is unblocked. Called by signalled
334		* threads when woken by non-FJ threads (which is atypical).
335		*/
336		private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
337		int s;
338	<	do;while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
338	>	do {} while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
339		if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
340		pool.updateRunningCount(s);
341		}
342
343		/**
344	<	* Notify pool to adjust counts on cancelled or timed out wait
344	>	* Notifies pool to adjust counts on cancelled or timed out wait.
345		*/
346		private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
347		if (pool != null) {
#	Line 323 | Line 356 | public abstract class ForkJoinTask<V> im
356		}
357
358		/**
359	<	* Handle interruptions during waits.
359	>	* Handles interruptions during waits.
360		*/
361		private void onInterruptedWait() {
362		ForkJoinWorkerThread w = getWorker();
#	Line 342 | Line 375 | public abstract class ForkJoinTask<V> im
375		}
376
377		/**
378	<	* Throws the exception associated with status s;
378	>	* Throws the exception associated with status s.
379	>	*
380		* @throws the exception
381		*/
382		private void reportException(int s) {
#	Line 355 | Line 389 | public abstract class ForkJoinTask<V> im
389		}
390
391		/**
392	<	* Returns result or throws exception using j.u.c.Future conventions
393	<	* Only call when isDone known to be true.
392	>	* Returns result or throws exception using j.u.c.Future conventions.
393	>	* Only call when {@code isDone} known to be true or thread known
394	>	* to be interrupted.
395		*/
396		private V reportFutureResult()
397	<	throws ExecutionException, InterruptedException {
397	>	throws InterruptedException, ExecutionException {
398	>	if (Thread.interrupted())
399	>	throw new InterruptedException();
400		int s = status & COMPLETION_MASK;
401		if (s < NORMAL) {
402		Throwable ex;
#	Line 367 | Line 404 | public abstract class ForkJoinTask<V> im
404		throw new CancellationException();
405		if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
406		throw new ExecutionException(ex);
370	–	if (Thread.interrupted())
371	–	throw new InterruptedException();
407		}
408		return getRawResult();
409		}
410
411		/**
412		* Returns result or throws exception using j.u.c.Future conventions
413	<	* with timeouts
413	>	* with timeouts.
414		*/
415		private V reportTimedFutureResult()
416		throws InterruptedException, ExecutionException, TimeoutException {
417	+	if (Thread.interrupted())
418	+	throw new InterruptedException();
419		Throwable ex;
420		int s = status & COMPLETION_MASK;
421		if (s == NORMAL)
422		return getRawResult();
423	<	if (s == CANCELLED)
423	>	else if (s == CANCELLED)
424		throw new CancellationException();
425	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
425	>	else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
426		throw new ExecutionException(ex);
427	<	if (Thread.interrupted())
428	<	throw new InterruptedException();
392	<	throw new TimeoutException();
427	>	else
428	>	throw new TimeoutException();
429		}
430
431		// internal execution methods
432
433		/**
434		* Calls exec, recording completion, and rethrowing exception if
435	<	* encountered. Caller should normally check status before calling
435	>	* encountered. Caller should normally check status before calling.
436	>	*
437		* @return true if completed normally
438		*/
439		private boolean tryExec() {
#	Line 414 | Line 451 | public abstract class ForkJoinTask<V> im
451
452		/**
453		* Main execution method used by worker threads. Invokes
454	<	* base computation unless already complete
454	>	* base computation unless already complete.
455		*/
456		final void quietlyExec() {
457		if (status >= 0) {
458		try {
459		if (!exec())
460		return;
461	<	} catch(Throwable rex) {
461	>	} catch (Throwable rex) {
462		setDoneExceptionally(rex);
463		return;
464		}
#	Line 430 | Line 467 | public abstract class ForkJoinTask<V> im
467		}
468
469		/**
470	<	* Calls exec, recording but not rethrowing exception
471	<	* Caller should normally check status before calling
470	>	* Calls exec(), recording but not rethrowing exception.
471	>	* Caller should normally check status before calling.
472	>	*
473		* @return true if completed normally
474		*/
475		private boolean tryQuietlyInvoke() {
#	Line 447 | Line 485 | public abstract class ForkJoinTask<V> im
485		}
486
487		/**
488	<	* Cancel, ignoring any exceptions it throws
488	>	* Cancels, ignoring any exceptions it throws.
489		*/
490		final void cancelIgnoringExceptions() {
491		try {
492		cancel(false);
493	<	} catch(Throwable ignore) {
493	>	} catch (Throwable ignore) {
494		}
495		}
496
#	Line 464 | Line 502 | public abstract class ForkJoinTask<V> im
502		ForkJoinTask<?> t;
503		while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
504		t.quietlyExec();
505	<	return (s >= 0)? awaitDone(w, false) : s; // block if no work
505	>	return (s >= 0) ? awaitDone(w, false) : s; // block if no work
506		}
507
508		// public methods
#	Line 472 | Line 510 | public abstract class ForkJoinTask<V> im
510		/**
511		* Arranges to asynchronously execute this task.  While it is not
512		* necessarily enforced, it is a usage error to fork a task more
513	<	* than once unless it has completed and been reinitialized.  This
514	<	* method may be invoked only from within ForkJoinTask
515	<	* computations. Attempts to invoke in other contexts result in
516	<	* exceptions or errors possibly including ClassCastException.
513	>	* than once unless it has completed and been reinitialized.
514	>	*
515	>	* <p>This method may be invoked only from within {@code
516	>	* ForkJoinTask} computations (as may be determined using method
517	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
518	>	* result in exceptions or errors, possibly including {@code
519	>	* ClassCastException}.
520	>	*
521	>	* @return {@code this}, to simplify usage
522		*/
523	<	public final void fork() {
524	<	((ForkJoinWorkerThread)(Thread.currentThread())).pushTask(this);
523	>	public final ForkJoinTask<V> fork() {
524	>	((ForkJoinWorkerThread) Thread.currentThread())
525	>	.pushTask(this);
526	>	return this;
527		}
528
529		/**
530	<	* Returns the result of the computation when it is ready.
531	<	* This method differs from <code>get</code> in that abnormal
532	<	* completion results in RuntimeExceptions or Errors, not
533	<	* ExecutionExceptions.
530	>	* Returns the result of the computation when it {@link #isDone is done}.
531	>	* This method differs from {@link #get()} in that
532	>	* abnormal completion results in {@code RuntimeException} or
533	>	* {@code Error}, not {@code ExecutionException}.
534		*
535		* @return the computed result
536		*/
#	Line 498 | Line 543 | public abstract class ForkJoinTask<V> im
543
544		/**
545		* Commences performing this task, awaits its completion if
546	<	* necessary, and return its result.
547	<	* @throws Throwable (a RuntimeException, Error, or unchecked
548	<	* exception) if the underlying computation did so.
546	>	* necessary, and return its result, or throws an (unchecked)
547	>	* exception if the underlying computation did so.
548	>	*
549		* @return the computed result
550		*/
551		public final V invoke() {
#	Line 511 | Line 556 | public abstract class ForkJoinTask<V> im
556		}
557
558		/**
559	<	* Forks both tasks, returning when <code>isDone</code> holds for
560	<	* both of them or an exception is encountered. This method may be
561	<	* invoked only from within ForkJoinTask computations. Attempts to
562	<	* invoke in other contexts result in exceptions or errors
563	<	* possibly including ClassCastException.
564	<	* @param t1 one task
565	<	* @param t2 the other task
566	<	* @throws NullPointerException if t1 or t2 are null
567	<	* @throws RuntimeException or Error if either task did so.
559	>	* Forks the given tasks, returning when {@code isDone} holds for
560	>	* each task or an (unchecked) exception is encountered, in which
561	>	* case the exception is rethrown.  If either task encounters an
562	>	* exception, the other one may be, but is not guaranteed to be,
563	>	* cancelled.  If both tasks throw an exception, then this method
564	>	* throws one of them.  The individual status of each task may be
565	>	* checked using {@link #getException()} and related methods.
566	>	*
567	>	* <p>This method may be invoked only from within {@code
568	>	* ForkJoinTask} computations (as may be determined using method
569	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
570	>	* result in exceptions or errors, possibly including {@code
571	>	* ClassCastException}.
572	>	*
573	>	* @param t1 the first task
574	>	* @param t2 the second task
575	>	* @throws NullPointerException if any task is null
576		*/
577	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
577	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
578		t2.fork();
579		t1.invoke();
580		t2.join();
581		}
582
583		/**
584	<	* Forks the given tasks, returning when <code>isDone</code> holds
585	<	* for all of them. If any task encounters an exception, others
586	<	* may be cancelled.  This method may be invoked only from within
587	<	* ForkJoinTask computations. Attempts to invoke in other contexts
588	<	* result in exceptions or errors possibly including ClassCastException.
589	<	* @param tasks the array of tasks
590	<	* @throws NullPointerException if tasks or any element are null.
591	<	* @throws RuntimeException or Error if any task did so.
584	>	* Forks the given tasks, returning when {@code isDone} holds for
585	>	* each task or an (unchecked) exception is encountered, in which
586	>	* case the exception is rethrown. If any task encounters an
587	>	* exception, others may be, but are not guaranteed to be,
588	>	* cancelled.  If more than one task encounters an exception, then
589	>	* this method throws any one of these exceptions.  The individual
590	>	* status of each task may be checked using {@link #getException()}
591	>	* and related methods.
592	>	*
593	>	* <p>This method may be invoked only from within {@code
594	>	* ForkJoinTask} computations (as may be determined using method
595	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
596	>	* result in exceptions or errors, possibly including {@code
597	>	* ClassCastException}.
598	>	*
599	>	* @param tasks the tasks
600	>	* @throws NullPointerException if any task is null
601		*/
602		public static void invokeAll(ForkJoinTask<?>... tasks) {
603		Throwable ex = null;
#	Line 571 | Line 633 | public abstract class ForkJoinTask<V> im
633		}
634
635		/**
636	<	* Forks all tasks in the collection, returning when
637	<	* <code>isDone</code> holds for all of them. If any task
638	<	* encounters an exception, others may be cancelled.  This method
639	<	* may be invoked only from within ForkJoinTask
640	<	* computations. Attempts to invoke in other contexts resul!t in
641	<	* exceptions or errors possibly including ClassCastException.
636	>	* Forks all tasks in the specified collection, returning when
637	>	* {@code isDone} holds for each task or an (unchecked) exception
638	>	* is encountered.  If any task encounters an exception, others
639	>	* may be, but are not guaranteed to be, cancelled.  If more than
640	>	* one task encounters an exception, then this method throws any
641	>	* one of these exceptions.  The individual status of each task
642	>	* may be checked using {@link #getException()} and related
643	>	* methods.  The behavior of this operation is undefined if the
644	>	* specified collection is modified while the operation is in
645	>	* progress.
646	>	*
647	>	* <p>This method may be invoked only from within {@code
648	>	* ForkJoinTask} computations (as may be determined using method
649	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
650	>	* result in exceptions or errors, possibly including {@code
651	>	* ClassCastException}.
652	>	*
653		* @param tasks the collection of tasks
654	<	* @throws NullPointerException if tasks or any element are null.
655	<	* @throws RuntimeException or Error if any task did so.
654	>	* @return the tasks argument, to simplify usage
655	>	* @throws NullPointerException if tasks or any element are null
656		*/
657	<	public static void invokeAll(Collection<? extends ForkJoinTask<?>> tasks) {
658	<	if (!(tasks instanceof List)) {
659	<	invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()]));
660	<	return;
657	>	public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
658	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
659	>	invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
660	>	return tasks;
661		}
662	+	@SuppressWarnings("unchecked")
663		List<? extends ForkJoinTask<?>> ts =
664	<	(List<? extends ForkJoinTask<?>>)tasks;
664	>	(List<? extends ForkJoinTask<?>>) tasks;
665		Throwable ex = null;
666		int last = ts.size() - 1;
667		for (int i = last; i >= 0; --i) {
#	Line 618 | Line 692 | public abstract class ForkJoinTask<V> im
692		}
693		if (ex != null)
694		rethrowException(ex);
695	+	return tasks;
696		}
697
698		/**
699	<	* Returns true if the computation performed by this task has
700	<	* completed (or has been cancelled).
701	<	* @return true if this computation has completed
702	<	*/
703	<	public final boolean isDone() {
704	<	return status < 0;
705	<	}
631	<
632	<	/**
633	<	* Returns true if this task was cancelled.
634	<	* @return true if this task was cancelled
635	<	*/
636	<	public final boolean isCancelled() {
637	<	return (status & COMPLETION_MASK) == CANCELLED;
638	<	}
639	<
640	<	/**
641	<	* Asserts that the results of this task's computation will not be
642	<	* used. If a cancellation occurs before atempting to execute this
643	<	* task, then execution will be suppressed, <code>isCancelled</code>
644	<	* will report true, and <code>join</code> will result in a
645	<	* <code>CancellationException</code> being thrown. Otherwise, when
646	<	* cancellation races with completion, there are no guarantees
647	<	* about whether <code>isCancelled</code> will report true, whether
648	<	* <code>join</code> will return normally or via an exception, or
649	<	* whether these behaviors will remain consistent upon repeated
650	<	* invocation.
699	>	* Attempts to cancel execution of this task. This attempt will
700	>	* fail if the task has already completed, has already been
701	>	* cancelled, or could not be cancelled for some other reason. If
702	>	* successful, and this task has not started when cancel is
703	>	* called, execution of this task is suppressed, {@link
704	>	* #isCancelled} will report true, and {@link #join} will result
705	>	* in a {@code CancellationException} being thrown.
706		*
707		* <p>This method may be overridden in subclasses, but if so, must
708		* still ensure that these minimal properties hold. In particular,
709	<	* the cancel method itself must not throw exceptions.
709	>	* the {@code cancel} method itself must not throw exceptions.
710		*
711	<	* <p> This method is designed to be invoked by <em>other</em>
711	>	* <p>This method is designed to be invoked by <em>other</em>
712		* tasks. To terminate the current task, you can just return or
713		* throw an unchecked exception from its computation method, or
714	<	* invoke <code>completeExceptionally</code>.
714	>	* invoke {@link #completeExceptionally}.
715		*
716		* @param mayInterruptIfRunning this value is ignored in the
717	<	* default implementation because tasks are not in general
718	<	* cancelled via interruption.
717	>	* default implementation because tasks are not
718	>	* cancelled via interruption
719		*
720	<	* @return true if this task is now cancelled
720	>	* @return {@code true} if this task is now cancelled
721		*/
722		public boolean cancel(boolean mayInterruptIfRunning) {
723		setCompletion(CANCELLED);
724		return (status & COMPLETION_MASK) == CANCELLED;
725		}
726
727	+	public final boolean isDone() {
728	+	return status < 0;
729	+	}
730	+
731	+	public final boolean isCancelled() {
732	+	return (status & COMPLETION_MASK) == CANCELLED;
733	+	}
734	+
735		/**
736	<	* Returns true if this task threw an exception or was cancelled
737	<	* @return true if this task threw an exception or was cancelled
736	>	* Returns {@code true} if this task threw an exception or was cancelled.
737	>	*
738	>	* @return {@code true} if this task threw an exception or was cancelled
739		*/
740		public final boolean isCompletedAbnormally() {
741		return (status & COMPLETION_MASK) < NORMAL;
742		}
743
744		/**
745	+	* Returns {@code true} if this task completed without throwing an
746	+	* exception and was not cancelled.
747	+	*
748	+	* @return {@code true} if this task completed without throwing an
749	+	* exception and was not cancelled
750	+	*/
751	+	public final boolean isCompletedNormally() {
752	+	return (status & COMPLETION_MASK) == NORMAL;
753	+	}
754	+
755	+	/**
756		* Returns the exception thrown by the base computation, or a
757	<	* CancellationException if cancelled, or null if none or if the
758	<	* method has not yet completed.
759	<	* @return the exception, or null if none
757	>	* {@code CancellationException} if cancelled, or {@code null} if
758	>	* none or if the method has not yet completed.
759	>	*
760	>	* @return the exception, or {@code null} if none
761		*/
762		public final Throwable getException() {
763		int s = status & COMPLETION_MASK;
764	<	if (s >= NORMAL)
765	<	return null;
766	<	if (s == CANCELLED)
691	<	return new CancellationException();
692	<	return exceptionMap.get(this);
764	>	return ((s >= NORMAL)    ? null :
765	>	(s == CANCELLED) ? new CancellationException() :
766	>	exceptionMap.get(this));
767		}
768
769		/**
770		* Completes this task abnormally, and if not already aborted or
771		* cancelled, causes it to throw the given exception upon
772	<	* <code>join</code> and related operations. This method may be used
772	>	* {@code join} and related operations. This method may be used
773		* to induce exceptions in asynchronous tasks, or to force
774		* completion of tasks that would not otherwise complete.  Its use
775	<	* in other situations is likely to be wrong.  This method is
776	<	* overridable, but overridden versions must invoke <code>super</code>
775	>	* in other situations is discouraged.  This method is
776	>	* overridable, but overridden versions must invoke {@code super}
777		* implementation to maintain guarantees.
778		*
779		* @param ex the exception to throw. If this exception is
#	Line 708 | Line 782 | public abstract class ForkJoinTask<V> im
782		*/
783		public void completeExceptionally(Throwable ex) {
784		setDoneExceptionally((ex instanceof RuntimeException) ||
785	<	(ex instanceof Error)? ex :
785	>	(ex instanceof Error) ? ex :
786		new RuntimeException(ex));
787		}
788
789		/**
790		* Completes this task, and if not already aborted or cancelled,
791	<	* returning a <code>null</code> result upon <code>join</code> and related
791	>	* returning a {@code null} result upon {@code join} and related
792		* operations. This method may be used to provide results for
793		* asynchronous tasks, or to provide alternative handling for
794		* tasks that would not otherwise complete normally. Its use in
795	<	* other situations is likely to be wrong. This method is
796	<	* overridable, but overridden versions must invoke <code>super</code>
795	>	* other situations is discouraged. This method is
796	>	* overridable, but overridden versions must invoke {@code super}
797		* implementation to maintain guarantees.
798		*
799	<	* @param value the result value for this task.
799	>	* @param value the result value for this task
800		*/
801		public void complete(V value) {
802		try {
803		setRawResult(value);
804	<	} catch(Throwable rex) {
804	>	} catch (Throwable rex) {
805		setDoneExceptionally(rex);
806		return;
807		}
#	Line 743 | Line 817 | public abstract class ForkJoinTask<V> im
817
818		public final V get(long timeout, TimeUnit unit)
819		throws InterruptedException, ExecutionException, TimeoutException {
820	+	long nanos = unit.toNanos(timeout);
821		ForkJoinWorkerThread w = getWorker();
822		if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
823	<	awaitDone(w, unit.toNanos(timeout));
823	>	awaitDone(w, nanos);
824		return reportTimedFutureResult();
825		}
826
827		/**
828	<	* Possibly executes other tasks until this task is ready, then
829	<	* returns the result of the computation.  This method may be more
830	<	* efficient than <code>join</code>, but is only applicable when
831	<	* there are no potemtial dependencies between continuation of the
832	<	* current task and that of any other task that might be executed
833	<	* while helping. (This usually holds for pure divide-and-conquer
834	<	* tasks). This method may be invoked only from within
835	<	* ForkJoinTask computations. Attempts to invoke in other contexts
836	<	* resul!t in exceptions or errors possibly including ClassCastException.
828	>	* Possibly executes other tasks until this task {@link #isDone is
829	>	* done}, then returns the result of the computation.  This method
830	>	* may be more efficient than {@code join}, but is only applicable
831	>	* when there are no potential dependencies between continuation
832	>	* of the current task and that of any other task that might be
833	>	* executed while helping. (This usually holds for pure
834	>	* divide-and-conquer tasks).
835	>	*
836	>	* <p>This method may be invoked only from within {@code
837	>	* ForkJoinTask} computations (as may be determined using method
838	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
839	>	* result in exceptions or errors, possibly including {@code
840	>	* ClassCastException}.
841	>	*
842		* @return the computed result
843		*/
844		public final V helpJoin() {
845	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread)(Thread.currentThread());
845	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
846		if (status < 0 || !w.unpushTask(this) || !tryExec())
847		reportException(busyJoin(w));
848		return getRawResult();
849		}
850
851		/**
852	<	* Possibly executes other tasks until this task is ready.  This
853	<	* method may be invoked only from within ForkJoinTask
854	<	* computations. Attempts to invoke in other contexts resul!t in
855	<	* exceptions or errors possibly including ClassCastException.
852	>	* Possibly executes other tasks until this task {@link #isDone is
853	>	* done}.  This method may be useful when processing collections
854	>	* of tasks when some have been cancelled or otherwise known to
855	>	* have aborted.
856	>	*
857	>	* <p>This method may be invoked only from within {@code
858	>	* ForkJoinTask} computations (as may be determined using method
859	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
860	>	* result in exceptions or errors, possibly including {@code
861	>	* ClassCastException}.
862		*/
863		public final void quietlyHelpJoin() {
864		if (status >= 0) {
865		ForkJoinWorkerThread w =
866	<	(ForkJoinWorkerThread)(Thread.currentThread());
866	>	(ForkJoinWorkerThread) Thread.currentThread();
867		if (!w.unpushTask(this) || !tryQuietlyInvoke())
868		busyJoin(w);
869		}
#	Line 811 | Line 897 | public abstract class ForkJoinTask<V> im
897
898		/**
899		* Possibly executes tasks until the pool hosting the current task
900	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
901	<	* designs in which many tasks are forked, but none are explicitly
902	<	* joined, instead executing them until all are processed.
900	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
901	>	* be of use in designs in which many tasks are forked, but none
902	>	* are explicitly joined, instead executing them until all are
903	>	* processed.
904	>	*
905	>	* <p>This method may be invoked only from within {@code
906	>	* ForkJoinTask} computations (as may be determined using method
907	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
908	>	* result in exceptions or errors, possibly including {@code
909	>	* ClassCastException}.
910		*/
911		public static void helpQuiesce() {
912	<	((ForkJoinWorkerThread)(Thread.currentThread())).
913	<	helpQuiescePool();
912	>	((ForkJoinWorkerThread) Thread.currentThread())
913	>	.helpQuiescePool();
914		}
915
916		/**
917		* Resets the internal bookkeeping state of this task, allowing a
918	<	* subsequent <code>fork</code>. This method allows repeated reuse of
918	>	* subsequent {@code fork}. This method allows repeated reuse of
919		* this task, but only if reuse occurs when this task has either
920		* never been forked, or has been forked, then completed and all
921		* outstanding joins of this task have also completed. Effects
922	<	* under any other usage conditions are not guaranteed, and are
923	<	* almost surely wrong. This method may be useful when executing
922	>	* under any other usage conditions are not guaranteed.
923	>	* This method may be useful when executing
924		* pre-constructed trees of subtasks in loops.
925		*/
926		public void reinitialize() {
#	Line 838 | Line 931 | public abstract class ForkJoinTask<V> im
931
932		/**
933		* Returns the pool hosting the current task execution, or null
934	<	* if this task is executing outside of any pool.
935	<	* @return the pool, or null if none.
934	>	* if this task is executing outside of any ForkJoinPool.
935	>	*
936	>	* @see #inForkJoinPool
937	>	* @return the pool, or {@code null} if none
938		*/
939		public static ForkJoinPool getPool() {
940		Thread t = Thread.currentThread();
941	<	return ((t instanceof ForkJoinWorkerThread)?
942	<	((ForkJoinWorkerThread)t).pool : null);
941	>	return (t instanceof ForkJoinWorkerThread) ?
942	>	((ForkJoinWorkerThread) t).pool : null;
943	>	}
944	>
945	>	/**
946	>	* Returns {@code true} if the current thread is executing as a
947	>	* ForkJoinPool computation.
948	>	*
949	>	* @return {@code true} if the current thread is executing as a
950	>	* ForkJoinPool computation, or false otherwise
951	>	*/
952	>	public static boolean inForkJoinPool() {
953	>	return Thread.currentThread() instanceof ForkJoinWorkerThread;
954		}
955
956		/**
#	Line 853 | Line 959 | public abstract class ForkJoinTask<V> im
959		* by the current thread, and has not commenced executing in
960		* another thread.  This method may be useful when arranging
961		* alternative local processing of tasks that could have been, but
962	<	* were not, stolen. This method may be invoked only from within
963	<	* ForkJoinTask computations. Attempts to invoke in other contexts
964	<	* result in exceptions or errors possibly including ClassCastException.
965	<	* @return true if unforked
962	>	* were not, stolen.
963	>	*
964	>	* <p>This method may be invoked only from within {@code
965	>	* ForkJoinTask} computations (as may be determined using method
966	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
967	>	* result in exceptions or errors, possibly including {@code
968	>	* ClassCastException}.
969	>	*
970	>	* @return {@code true} if unforked
971		*/
972		public boolean tryUnfork() {
973	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).unpushTask(this);
973	>	return ((ForkJoinWorkerThread) Thread.currentThread())
974	>	.unpushTask(this);
975		}
976
977		/**
#	Line 867 | Line 979 | public abstract class ForkJoinTask<V> im
979		* forked by the current worker thread but not yet executed. This
980		* value may be useful for heuristic decisions about whether to
981		* fork other tasks.
982	+	*
983	+	* <p>This method may be invoked only from within {@code
984	+	* ForkJoinTask} computations (as may be determined using method
985	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
986	+	* result in exceptions or errors, possibly including {@code
987	+	* ClassCastException}.
988	+	*
989		* @return the number of tasks
990		*/
991		public static int getQueuedTaskCount() {
992	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
993	<	getQueueSize();
992	>	return ((ForkJoinWorkerThread) Thread.currentThread())
993	>	.getQueueSize();
994		}
995
996		/**
997	<	* Returns a estimate of how many more locally queued tasks are
997	>	* Returns an estimate of how many more locally queued tasks are
998		* held by the current worker thread than there are other worker
999		* threads that might steal them.  This value may be useful for
1000		* heuristic decisions about whether to fork other tasks. In many
#	Line 883 | Line 1002 | public abstract class ForkJoinTask<V> im
1002		* aim to maintain a small constant surplus (for example, 3) of
1003		* tasks, and to process computations locally if this threshold is
1004		* exceeded.
1005	+	*
1006	+	* <p>This method may be invoked only from within {@code
1007	+	* ForkJoinTask} computations (as may be determined using method
1008	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1009	+	* result in exceptions or errors, possibly including {@code
1010	+	* ClassCastException}.
1011	+	*
1012		* @return the surplus number of tasks, which may be negative
1013		*/
1014		public static int getSurplusQueuedTaskCount() {
1015	<	return ((ForkJoinWorkerThread)(Thread.currentThread()))
1015	>	return ((ForkJoinWorkerThread) Thread.currentThread())
1016		.getEstimatedSurplusTaskCount();
1017		}
1018
1019		// Extension methods
1020
1021		/**
1022	<	* Returns the result that would be returned by <code>join</code>,
1023	<	* even if this task completed abnormally, or null if this task is
1024	<	* not known to have been completed.  This method is designed to
1025	<	* aid debugging, as well as to support extensions. Its use in any
1026	<	* other context is discouraged.
1022	>	* Returns the result that would be returned by {@link #join}, even
1023	>	* if this task completed abnormally, or {@code null} if this task
1024	>	* is not known to have been completed.  This method is designed
1025	>	* to aid debugging, as well as to support extensions. Its use in
1026	>	* any other context is discouraged.
1027		*
1028	<	* @return the result, or null if not completed.
1028	>	* @return the result, or {@code null} if not completed
1029		*/
1030		public abstract V getRawResult();
1031
#	Line 918 | Line 1044 | public abstract class ForkJoinTask<V> im
1044		* called otherwise. The return value controls whether this task
1045		* is considered to be done normally. It may return false in
1046		* asynchronous actions that require explicit invocations of
1047	<	* <code>complete</code> to become joinable. It may throw exceptions
1048	<	* to indicate abnormal exit.
1049	<	* @return true if completed normally
1050	<	* @throws Error or RuntimeException if encountered during computation
1047	>	* {@link #complete} to become joinable. It may also throw an
1048	>	* (unchecked) exception to indicate abnormal exit.
1049	>	*
1050	>	* @return {@code true} if completed normally
1051		*/
1052		protected abstract boolean exec();
1053
1054		/**
1055	<	* Returns, but does not unschedule or execute, the task queued by
1056	<	* the current thread but not yet executed, if one is
1055	>	* Returns, but does not unschedule or execute, a task queued by
1056	>	* the current thread but not yet executed, if one is immediately
1057		* available. There is no guarantee that this task will actually
1058	<	* be polled or executed next.  This method is designed primarily
1059	<	* to support extensions, and is unlikely to be useful otherwise.
1060	<	* This method may be invoked only from within ForkJoinTask
1061	<	* computations. Attempts to invoke in other contexts result in
1062	<	* exceptions or errors possibly including ClassCastException.
1058	>	* be polled or executed next. Conversely, this method may return
1059	>	* null even if a task exists but cannot be accessed without
1060	>	* contention with other threads.  This method is designed
1061	>	* primarily to support extensions, and is unlikely to be useful
1062	>	* otherwise.
1063	>	*
1064	>	* <p>This method may be invoked only from within {@code
1065	>	* ForkJoinTask} computations (as may be determined using method
1066	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1067	>	* result in exceptions or errors, possibly including {@code
1068	>	* ClassCastException}.
1069		*
1070	<	* @return the next task, or null if none are available
1070	>	* @return the next task, or {@code null} if none are available
1071		*/
1072		protected static ForkJoinTask<?> peekNextLocalTask() {
1073	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).peekTask();
1073	>	return ((ForkJoinWorkerThread) Thread.currentThread())
1074	>	.peekTask();
1075		}
1076
1077		/**
1078		* Unschedules and returns, without executing, the next task
1079		* queued by the current thread but not yet executed.  This method
1080		* is designed primarily to support extensions, and is unlikely to
1081	<	* be useful otherwise.  This method may be invoked only from
949	<	* within ForkJoinTask computations. Attempts to invoke in other
950	<	* contexts result in exceptions or errors possibly including
951	<	* ClassCastException.
1081	>	* be useful otherwise.
1082		*
1083	<	* @return the next task, or null if none are available
1083	>	* <p>This method may be invoked only from within {@code
1084	>	* ForkJoinTask} computations (as may be determined using method
1085	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1086	>	* result in exceptions or errors, possibly including {@code
1087	>	* ClassCastException}.
1088	>	*
1089	>	* @return the next task, or {@code null} if none are available
1090		*/
1091		protected static ForkJoinTask<?> pollNextLocalTask() {
1092	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).pollLocalTask();
1092	>	return ((ForkJoinWorkerThread) Thread.currentThread())
1093	>	.pollLocalTask();
1094		}
1095	<
1095	>
1096		/**
1097		* Unschedules and returns, without executing, the next task
1098		* queued by the current thread but not yet executed, if one is
1099		* available, or if not available, a task that was forked by some
1100		* other thread, if available. Availability may be transient, so a
1101	<	* <code>null</code> result does not necessarily imply quiecence
1101	>	* {@code null} result does not necessarily imply quiescence
1102		* of the pool this task is operating in.  This method is designed
1103		* primarily to support extensions, and is unlikely to be useful
1104	<	* otherwise.  This method may be invoked only from within
968	<	* ForkJoinTask computations. Attempts to invoke in other contexts
969	<	* result in exceptions or errors possibly including
970	<	* ClassCastException.
1104	>	* otherwise.
1105		*
1106	<	* @return a task, or null if none are available
1106	>	* <p>This method may be invoked only from within {@code
1107	>	* ForkJoinTask} computations (as may be determined using method
1108	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1109	>	* result in exceptions or errors, possibly including {@code
1110	>	* ClassCastException}.
1111	>	*
1112	>	* @return a task, or {@code null} if none are available
1113		*/
1114		protected static ForkJoinTask<?> pollTask() {
1115	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
1116	<	pollTask();
1115	>	return ((ForkJoinWorkerThread) Thread.currentThread())
1116	>	.pollTask();
1117	>	}
1118	>
1119	>	/**
1120	>	* Adaptor for Runnables. This implements RunnableFuture
1121	>	* to be compliant with AbstractExecutorService constraints
1122	>	* when used in ForkJoinPool.
1123	>	*/
1124	>	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1125	>	implements RunnableFuture<T> {
1126	>	final Runnable runnable;
1127	>	final T resultOnCompletion;
1128	>	T result;
1129	>	AdaptedRunnable(Runnable runnable, T result) {
1130	>	if (runnable == null) throw new NullPointerException();
1131	>	this.runnable = runnable;
1132	>	this.resultOnCompletion = result;
1133	>	}
1134	>	public T getRawResult() { return result; }
1135	>	public void setRawResult(T v) { result = v; }
1136	>	public boolean exec() {
1137	>	runnable.run();
1138	>	result = resultOnCompletion;
1139	>	return true;
1140	>	}
1141	>	public void run() { invoke(); }
1142	>	private static final long serialVersionUID = 5232453952276885070L;
1143	>	}
1144	>
1145	>	/**
1146	>	* Adaptor for Callables
1147	>	*/
1148	>	static final class AdaptedCallable<T> extends ForkJoinTask<T>
1149	>	implements RunnableFuture<T> {
1150	>	final Callable<? extends T> callable;
1151	>	T result;
1152	>	AdaptedCallable(Callable<? extends T> callable) {
1153	>	if (callable == null) throw new NullPointerException();
1154	>	this.callable = callable;
1155	>	}
1156	>	public T getRawResult() { return result; }
1157	>	public void setRawResult(T v) { result = v; }
1158	>	public boolean exec() {
1159	>	try {
1160	>	result = callable.call();
1161	>	return true;
1162	>	} catch (Error err) {
1163	>	throw err;
1164	>	} catch (RuntimeException rex) {
1165	>	throw rex;
1166	>	} catch (Exception ex) {
1167	>	throw new RuntimeException(ex);
1168	>	}
1169	>	}
1170	>	public void run() { invoke(); }
1171	>	private static final long serialVersionUID = 2838392045355241008L;
1172	>	}
1173	>
1174	>	/**
1175	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1176	>	* method of the given {@code Runnable} as its action, and returns
1177	>	* a null result upon {@link #join}.
1178	>	*
1179	>	* @param runnable the runnable action
1180	>	* @return the task
1181	>	*/
1182	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1183	>	return new AdaptedRunnable<Void>(runnable, null);
1184	>	}
1185	>
1186	>	/**
1187	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1188	>	* method of the given {@code Runnable} as its action, and returns
1189	>	* the given result upon {@link #join}.
1190	>	*
1191	>	* @param runnable the runnable action
1192	>	* @param result the result upon completion
1193	>	* @return the task
1194	>	*/
1195	>	public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
1196	>	return new AdaptedRunnable<T>(runnable, result);
1197	>	}
1198	>
1199	>	/**
1200	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1201	>	* method of the given {@code Callable} as its action, and returns
1202	>	* its result upon {@link #join}, translating any checked exceptions
1203	>	* encountered into {@code RuntimeException}.
1204	>	*
1205	>	* @param callable the callable action
1206	>	* @return the task
1207	>	*/
1208	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1209	>	return new AdaptedCallable<T>(callable);
1210		}
1211
1212		// Serialization support
#	Line 984 | Line 1217 | public abstract class ForkJoinTask<V> im
1217		* Save the state to a stream.
1218		*
1219		* @serialData the current run status and the exception thrown
1220	<	* during execution, or null if none.
1220	>	* during execution, or {@code null} if none
1221		* @param s the stream
1222		*/
1223		private void writeObject(java.io.ObjectOutputStream s)
#	Line 995 | Line 1228 | public abstract class ForkJoinTask<V> im
1228
1229		/**
1230		* Reconstitute the instance from a stream.
1231	+	*
1232		* @param s the stream
1233		*/
1234		private void readObject(java.io.ObjectInputStream s)
#	Line 1004 | Line 1238 | public abstract class ForkJoinTask<V> im
1238		status |= EXTERNAL_SIGNAL; // conservatively set external signal
1239		Object ex = s.readObject();
1240		if (ex != null)
1241	<	setDoneExceptionally((Throwable)ex);
1241	>	setDoneExceptionally((Throwable) ex);
1242		}
1243
1244	<	// Temporary Unsafe mechanics for preliminary release
1245	<	private static Unsafe getUnsafe() throws Throwable {
1244	>	// Unsafe mechanics
1245	>
1246	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1247	>	private static final long statusOffset =
1248	>	objectFieldOffset("status", ForkJoinTask.class);
1249	>
1250	>	private static long objectFieldOffset(String field, Class<?> klazz) {
1251		try {
1252	<	return Unsafe.getUnsafe();
1252	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1253	>	} catch (NoSuchFieldException e) {
1254	>	// Convert Exception to corresponding Error
1255	>	NoSuchFieldError error = new NoSuchFieldError(field);
1256	>	error.initCause(e);
1257	>	throw error;
1258	>	}
1259	>	}
1260	>
1261	>	/**
1262	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1263	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
1264	>	* into a jdk.
1265	>	*
1266	>	* @return a sun.misc.Unsafe
1267	>	*/
1268	>	private static sun.misc.Unsafe getUnsafe() {
1269	>	try {
1270	>	return sun.misc.Unsafe.getUnsafe();
1271		} catch (SecurityException se) {
1272		try {
1273		return java.security.AccessController.doPrivileged
1274	<	(new java.security.PrivilegedExceptionAction<Unsafe>() {
1275	<	public Unsafe run() throws Exception {
1276	<	return getUnsafePrivileged();
1274	>	(new java.security
1275	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1276	>	public sun.misc.Unsafe run() throws Exception {
1277	>	java.lang.reflect.Field f = sun.misc
1278	>	.Unsafe.class.getDeclaredField("theUnsafe");
1279	>	f.setAccessible(true);
1280	>	return (sun.misc.Unsafe) f.get(null);
1281		}});
1282		} catch (java.security.PrivilegedActionException e) {
1283	<	throw e.getCause();
1283	>	throw new RuntimeException("Could not initialize intrinsics",
1284	>	e.getCause());
1285		}
1286		}
1287		}
1026	–
1027	–	private static Unsafe getUnsafePrivileged()
1028	–	throws NoSuchFieldException, IllegalAccessException {
1029	–	Field f = Unsafe.class.getDeclaredField("theUnsafe");
1030	–	f.setAccessible(true);
1031	–	return (Unsafe) f.get(null);
1032	–	}
1033	–
1034	–	private static long fieldOffset(String fieldName)
1035	–	throws NoSuchFieldException {
1036	–	return _unsafe.objectFieldOffset
1037	–	(ForkJoinTask.class.getDeclaredField(fieldName));
1038	–	}
1039	–
1040	–	static final Unsafe _unsafe;
1041	–	static final long statusOffset;
1042	–
1043	–	static {
1044	–	try {
1045	–	_unsafe = getUnsafe();
1046	–	statusOffset = fieldOffset("status");
1047	–	} catch (Throwable e) {
1048	–	throw new RuntimeException("Could not initialize intrinsics", e);
1049	–	}
1050	–	}
1051	–
1288		}

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