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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.29 by jsr166, Sun Aug 2 17:19:24 2009 UTC vs.
Revision 1.55 by dl, Sun Aug 29 23:34:46 2010 UTC

#	Line 12 | Line 12 | 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
#	Line 54 | Line 55 | import java.util.WeakHashMap;
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 join them. These exceptions may
59	<	* additionally include RejectedExecutionExceptions stemming from
60	<	* internal resource exhaustion such as failure to allocate internal
61	<	* task queues.
58	>	* rethrown to callers attempting to join them. These exceptions may
59	>	* additionally include {@link RejectedExecutionException} stemming
60	>	* from internal resource exhaustion, such as failure to allocate
61	>	* internal 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}
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
70	<	* equivalent to {@code fork(); join()} but always attempts to
71	<	* begin execution in the current thread. The "<em>quiet</em>" forms
72	<	* of these methods do not extract results or report exceptions. These
67	>	* conventions. Method {@link #invoke} is semantically
68	>	* equivalent to {@code fork(); join()} but always attempts to begin
69	>	* execution in the current thread. The "<em>quiet</em>" forms of
70	>	* these methods do not extract results or report exceptions. These
71		* may be useful when a set of tasks are being executed, and you need
72		* to delay processing of results or exceptions until all complete.
73		* Method {@code invokeAll} (available in multiple versions)
74		* performs the most common form of parallel invocation: forking a set
75		* of tasks and joining them all.
76		*
77	+	* <p>The execution status of tasks may be queried at several levels
78	+	* of detail: {@link #isDone} is true if a task completed in any way
79	+	* (including the case where a task was cancelled without executing);
80	+	* {@link #isCompletedNormally} is true if a task completed without
81	+	* cancellation or encountering an exception; {@link #isCancelled} is
82	+	* true if the task was cancelled (in which case {@link #getException}
83	+	* returns a {@link java.util.concurrent.CancellationException}); and
84	+	* {@link #isCompletedAbnormally} is true if a task was either
85	+	* cancelled or encountered an exception, in which case {@link
86	+	* #getException} will return either the encountered exception or
87	+	* {@link java.util.concurrent.CancellationException}.
88	+	*
89		* <p>The ForkJoinTask class is not usually directly subclassed.
90		* Instead, you subclass one of the abstract classes that support a
91		* particular style of fork/join processing, typically {@link
#	Line 85 | Line 95 | import java.util.WeakHashMap;
95		* established in a constructor, and then defines a {@code compute}
96		* method that somehow uses the control methods supplied by this base
97		* class. While these methods have {@code public} access (to allow
98	<	* instances of different task subclasses to call each others
98	>	* instances of different task subclasses to call each other's
99		* methods), some of them may only be called from within other
100		* ForkJoinTasks (as may be determined using method {@link
101		* #inForkJoinPool}).  Attempts to invoke them in other contexts
102		* result in exceptions or errors, possibly including
103		* ClassCastException.
104		*
105	<	* <p>Most base support methods are {@code final} because their
106	<	* implementations are intrinsically tied to the underlying
107	<	* lightweight task scheduling framework, and so cannot be overridden.
108	<	* Developers creating new basic styles of fork/join processing should
109	<	* minimally implement {@code protected} methods
110	<	* {@link #exec}, {@link #setRawResult}, and
111	<	* {@link #getRawResult}, while also introducing an abstract
112	<	* computational method that can be implemented in its subclasses,
113	<	* possibly relying on other {@code protected} methods provided
104	<	* by this class.
105	>	* <p>Most base support methods are {@code final}, to prevent
106	>	* overriding of implementations that are intrinsically tied to the
107	>	* underlying lightweight task scheduling framework.  Developers
108	>	* creating new basic styles of fork/join processing should minimally
109	>	* implement {@code protected} methods {@link #exec}, {@link
110	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
111	>	* an abstract computational method that can be implemented in its
112	>	* subclasses, possibly relying on other {@code protected} methods
113	>	* provided by this class.
114		*
115		* <p>ForkJoinTasks should perform relatively small amounts of
116	<	* computations, otherwise splitting into smaller tasks. As a very
117	<	* rough rule of thumb, a task should perform more than 100 and less
118	<	* than 10000 basic computational steps. If tasks are too big, then
119	<	* parallelism cannot improve throughput. If too small, then memory
120	<	* and internal task maintenance overhead may overwhelm processing.
116	>	* computation. Large tasks should be split into smaller subtasks,
117	>	* usually via recursive decomposition. As a very rough rule of thumb,
118	>	* a task should perform more than 100 and less than 10000 basic
119	>	* computational steps. If tasks are too big, then parallelism cannot
120	>	* improve throughput. If too small, then memory and internal task
121	>	* maintenance overhead may overwhelm processing.
122		*
123	<	* <p>This class provides {@code adapt} methods for {@link
124	<	* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
125	<	* may be of use when mixing execution of ForkJoinTasks with other
126	<	* kinds of tasks. When all tasks are of this form, consider using a
117	<	* pool in {@link ForkJoinPool#setAsyncMode}.
123	>	* <p>This class provides {@code adapt} methods for {@link Runnable}
124	>	* and {@link Callable}, that may be of use when mixing execution of
125	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
126	>	* of this form, consider using a pool constructed in <em>asyncMode</em>.
127		*
128	<	* <p>ForkJoinTasks are {@code Serializable}, which enables them
129	<	* to be used in extensions such as remote execution frameworks. It is
130	<	* in general sensible to serialize tasks only before or after, but
131	<	* not during execution. Serialization is not relied on during
123	<	* execution itself.
128	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
129	>	* used in extensions such as remote execution frameworks. It is
130	>	* sensible to serialize tasks only before or after, but not during,
131	>	* execution. Serialization is not relied on during execution itself.
132		*
133		* @since 1.7
134		* @author Doug Lea
135		*/
136		public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
137
138	<	/**
139	<	* Run control status bits packed into a single int to minimize
140	<	* footprint and to ensure atomicity (via CAS).  Status is
141	<	* initially zero, and takes on nonnegative values until
142	<	* completed, upon which status holds COMPLETED. CANCELLED, or
143	<	* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
144	<	* blocking waits by other threads have SIGNAL_MASK bits set --
145	<	* bit 15 for external (nonFJ) waits, and the rest a count of
146	<	* waiting FJ threads.  (This representation relies on
147	<	* ForkJoinPool max thread limits). Completion of a stolen task
148	<	* with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
149	<	* though suboptimal for some purposes, we use basic builtin
150	<	* wait/notify to take advantage of "monitor inflation" in JVMs
151	<	* that we would otherwise need to emulate to avoid adding further
152	<	* per-task bookkeeping overhead. Note that bits 16-28 are
153	<	* currently unused. Also value 0x80000000 is available as spare
154	<	* completion value.
138	>	/*
139	>	* See the internal documentation of class ForkJoinPool for a
140	>	* general implementation overview.  ForkJoinTasks are mainly
141	>	* responsible for maintaining their "status" field amidst relays
142	>	* to methods in ForkJoinWorkerThread and ForkJoinPool. The
143	>	* methods of this class are more-or-less layered into (1) basic
144	>	* status maintenance (2) execution and awaiting completion (3)
145	>	* user-level methods that additionally report results. This is
146	>	* sometimes hard to see because this file orders exported methods
147	>	* in a way that flows well in javadocs. In particular, most
148	>	* join mechanics are in method quietlyJoin, below.
149	>	*/
150	>
151	>	/*
152	>	* The status field holds run control status bits packed into a
153	>	* single int to minimize footprint and to ensure atomicity (via
154	>	* CAS).  Status is initially zero, and takes on nonnegative
155	>	* values until completed, upon which status holds value
156	>	* COMPLETED. CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
157	>	* waits by other threads have the SIGNAL bit set.  Completion of
158	>	* a stolen task with SIGNAL set awakens any waiters via
159	>	* notifyAll. Even though suboptimal for some purposes, we use
160	>	* basic builtin wait/notify to take advantage of "monitor
161	>	* inflation" in JVMs that we would otherwise need to emulate to
162	>	* avoid adding further per-task bookkeeping overhead.  We want
163	>	* these monitors to be "fat", i.e., not use biasing or thin-lock
164	>	* techniques, so use some odd coding idioms that tend to avoid
165	>	* them.
166		*/
167	+
168	+	/** The run status of this task */
169		volatile int status; // accessed directly by pool and workers
170
171	<	static final int COMPLETION_MASK      = 0xe0000000;
172	<	static final int NORMAL               = 0xe0000000; // == mask
173	<	static final int CANCELLED            = 0xc0000000;
174	<	static final int EXCEPTIONAL          = 0xa0000000;
154	<	static final int SIGNAL_MASK          = 0x0000ffff;
155	<	static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
156	<	static final int EXTERNAL_SIGNAL      = 0x00008000; // top bit of low word
171	>	private static final int NORMAL      = -1;
172	>	private static final int CANCELLED   = -2;
173	>	private static final int EXCEPTIONAL = -3;
174	>	private static final int SIGNAL      =  1;
175
176		/**
177		* Table of exceptions thrown by tasks, to enable reporting by
#	Line 167 | Line 185 | public abstract class ForkJoinTask<V> im
185		Collections.synchronizedMap
186		(new WeakHashMap<ForkJoinTask<?>, Throwable>());
187
188	<	// within-package utilities
171	<
172	<	/**
173	<	* Gets current worker thread, or null if not a worker thread.
174	<	*/
175	<	static ForkJoinWorkerThread getWorker() {
176	<	Thread t = Thread.currentThread();
177	<	return ((t instanceof ForkJoinWorkerThread) ?
178	<	(ForkJoinWorkerThread) t : null);
179	<	}
180	<
181	<	final boolean casStatus(int cmp, int val) {
182	<	return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val);
183	<	}
188	>	// Maintaining completion status
189
190		/**
191	<	* Workaround for not being able to rethrow unchecked exceptions.
192	<	*/
188	<	static void rethrowException(Throwable ex) {
189	<	if (ex != null)
190	<	UNSAFE.throwException(ex);
191	<	}
192	<
193	<	// Setting completion status
194	<
195	<	/**
196	<	* Marks completion and wakes up threads waiting to join this task.
191	>	* Marks completion and wakes up threads waiting to join this task,
192	>	* also clearing signal request bits.
193		*
194		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
195		*/
196	<	final void setCompletion(int completion) {
197	<	ForkJoinPool pool = getPool();
198	<	if (pool != null) {
199	<	int s; // Clear signal bits while setting completion status
200	<	do {} while ((s = status) >= 0 && !casStatus(s, completion));
201	<
202	<	if ((s & SIGNAL_MASK) != 0) {
207	<	if ((s &= INTERNAL_SIGNAL_MASK) != 0)
208	<	pool.updateRunningCount(s);
209	<	synchronized (this) { notifyAll(); }
196	>	private void setCompletion(int completion) {
197	>	int s;
198	>	while ((s = status) >= 0) {
199	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
200	>	if (s != 0)
201	>	synchronized (this) { notifyAll(); }
202	>	break;
203		}
204		}
212	–	else
213	–	externallySetCompletion(completion);
205		}
206
207		/**
208	<	* Version of setCompletion for non-FJ threads.  Leaves signal
209	<	* bits for unblocked threads to adjust, and always notifies.
219	<	*/
220	<	private void externallySetCompletion(int completion) {
221	<	int s;
222	<	do {} while ((s = status) >= 0 &&
223	<	!casStatus(s, (s & SIGNAL_MASK) | completion));
224	<	synchronized (this) { notifyAll(); }
225	<	}
226	<
227	<	/**
228	<	* Sets status to indicate normal completion.
229	<	*/
230	<	final void setNormalCompletion() {
231	<	// Try typical fast case -- single CAS, no signal, not already done.
232	<	// Manually expand casStatus to improve chances of inlining it
233	<	if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL))
234	<	setCompletion(NORMAL);
235	<	}
236	<
237	<	// internal waiting and notification
238	<
239	<	/**
240	<	* Performs the actual monitor wait for awaitDone.
208	>	* Record exception and set exceptional completion
209	>	* @return status on exit
210		*/
211	<	private void doAwaitDone() {
212	<	// Minimize lock bias and in/de-flation effects by maximizing
213	<	// chances of waiting inside sync
245	<	try {
246	<	while (status >= 0)
247	<	synchronized (this) { if (status >= 0) wait(); }
248	<	} catch (InterruptedException ie) {
249	<	onInterruptedWait();
250	<	}
211	>	private void setExceptionalCompletion(Throwable rex) {
212	>	exceptionMap.put(this, rex);
213	>	setCompletion(EXCEPTIONAL);
214		}
215
216		/**
217	<	* Performs the actual timed monitor wait for awaitDone.
217	>	* Blocks a worker thread until completion. Called only by
218	>	* pool. Currently unused -- pool-based waits use timeout
219	>	* version below.
220		*/
221	<	private void doAwaitDone(long startTime, long nanos) {
222	<	synchronized (this) {
221	>	final void internalAwaitDone() {
222	>	int s;         // the odd construction reduces lock bias effects
223	>	while ((s = status) >= 0) {
224		try {
225	<	while (status >= 0) {
226	<	long nt = nanos - (System.nanoTime() - startTime);
227	<	if (nt <= 0)
262	<	break;
263	<	wait(nt / 1000000, (int) (nt % 1000000));
225	>	synchronized(this) {
226	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
227	>	wait();
228		}
229		} catch (InterruptedException ie) {
230	<	onInterruptedWait();
267	<	}
268	<	}
269	<	}
270	<
271	<	// Awaiting completion
272	<
273	<	/**
274	<	* Sets status to indicate there is joiner, then waits for join,
275	<	* surrounded with pool notifications.
276	<	*
277	<	* @return status upon exit
278	<	*/
279	<	private int awaitDone(ForkJoinWorkerThread w,
280	<	boolean maintainParallelism) {
281	<	ForkJoinPool pool = (w == null) ? null : w.pool;
282	<	int s;
283	<	while ((s = status) >= 0) {
284	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
285	<	if (pool == null || !pool.preJoin(this, maintainParallelism))
286	<	doAwaitDone();
287	<	if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
288	<	adjustPoolCountsOnUnblock(pool);
289	<	break;
230	>	cancelIfTerminating();
231		}
232		}
292	–	return s;
233		}
234
235		/**
236	<	* Timed version of awaitDone
236	>	* Blocks a worker thread until completed or timed out.  Called
237	>	* only by pool.
238		*
239	<	* @return status upon exit
239	>	* @return status on exit
240		*/
241	<	private int awaitDone(ForkJoinWorkerThread w, long nanos) {
301	<	ForkJoinPool pool = (w == null) ? null : w.pool;
241	>	final int internalAwaitDone(long millis) {
242		int s;
243	<	while ((s = status) >= 0) {
244	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
245	<	long startTime = System.nanoTime();
246	<	if (pool == null || !pool.preJoin(this, false))
247	<	doAwaitDone(startTime, nanos);
308	<	if ((s = status) >= 0) {
309	<	adjustPoolCountsOnCancelledWait(pool);
310	<	s = status;
243	>	if ((s = status) >= 0) {
244	>	try {
245	>	synchronized(this) {
246	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
247	>	wait(millis, 0);
248		}
249	<	if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
250	<	adjustPoolCountsOnUnblock(pool);
314	<	break;
249	>	} catch (InterruptedException ie) {
250	>	cancelIfTerminating();
251		}
252	+	s = status;
253		}
254		return s;
255		}
256
257		/**
258	<	* Notifies pool that thread is unblocked. Called by signalled
322	<	* threads when woken by non-FJ threads (which is atypical).
258	>	* Blocks a non-worker-thread until completion.
259		*/
260	<	private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
260	>	private void externalAwaitDone() {
261		int s;
262	<	do {} while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
263	<	if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
264	<	pool.updateRunningCount(s);
265	<	}
266	<
267	<	/**
268	<	* Notifies pool to adjust counts on cancelled or timed out wait.
269	<	*/
270	<	private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
271	<	if (pool != null) {
272	<	int s;
273	<	while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
274	<	if (casStatus(s, s - 1)) {
339	<	pool.updateRunningCount(1);
262	>	while ((s = status) >= 0) {
263	>	synchronized(this) {
264	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
265	>	boolean interrupted = false;
266	>	while (status >= 0) {
267	>	try {
268	>	wait();
269	>	} catch (InterruptedException ie) {
270	>	interrupted = true;
271	>	}
272	>	}
273	>	if (interrupted)
274	>	Thread.currentThread().interrupt();
275		break;
276		}
277		}
#	Line 344 | Line 279 | public abstract class ForkJoinTask<V> im
279		}
280
281		/**
282	<	* Handles interruptions during waits.
283	<	*/
284	<	private void onInterruptedWait() {
350	<	ForkJoinWorkerThread w = getWorker();
351	<	if (w == null)
352	<	Thread.currentThread().interrupt(); // re-interrupt
353	<	else if (w.isTerminating())
354	<	cancelIgnoringExceptions();
355	<	// else if FJworker, ignore interrupt
356	<	}
357	<
358	<	// Recording and reporting exceptions
359	<
360	<	private void setDoneExceptionally(Throwable rex) {
361	<	exceptionMap.put(this, rex);
362	<	setCompletion(EXCEPTIONAL);
363	<	}
364	<
365	<	/**
366	<	* Throws the exception associated with status s.
367	<	*
368	<	* @throws the exception
369	<	*/
370	<	private void reportException(int s) {
371	<	if ((s &= COMPLETION_MASK) < NORMAL) {
372	<	if (s == CANCELLED)
373	<	throw new CancellationException();
374	<	else
375	<	rethrowException(exceptionMap.get(this));
376	<	}
377	<	}
378	<
379	<	/**
380	<	* Returns result or throws exception using j.u.c.Future conventions.
381	<	* Only call when {@code isDone} known to be true.
382	<	*/
383	<	private V reportFutureResult()
384	<	throws ExecutionException, InterruptedException {
385	<	int s = status & COMPLETION_MASK;
386	<	if (s < NORMAL) {
387	<	Throwable ex;
388	<	if (s == CANCELLED)
389	<	throw new CancellationException();
390	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
391	<	throw new ExecutionException(ex);
392	<	if (Thread.interrupted())
393	<	throw new InterruptedException();
394	<	}
395	<	return getRawResult();
396	<	}
397	<
398	<	/**
399	<	* Returns result or throws exception using j.u.c.Future conventions
400	<	* with timeouts.
401	<	*/
402	<	private V reportTimedFutureResult()
403	<	throws InterruptedException, ExecutionException, TimeoutException {
404	<	Throwable ex;
405	<	int s = status & COMPLETION_MASK;
406	<	if (s == NORMAL)
407	<	return getRawResult();
408	<	if (s == CANCELLED)
409	<	throw new CancellationException();
410	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
411	<	throw new ExecutionException(ex);
412	<	if (Thread.interrupted())
413	<	throw new InterruptedException();
414	<	throw new TimeoutException();
415	<	}
416	<
417	<	// internal execution methods
418	<
419	<	/**
420	<	* Calls exec, recording completion, and rethrowing exception if
421	<	* encountered. Caller should normally check status before calling.
422	<	*
423	<	* @return true if completed normally
424	<	*/
425	<	private boolean tryExec() {
426	<	try { // try block must contain only call to exec
427	<	if (!exec())
428	<	return false;
429	<	} catch (Throwable rex) {
430	<	setDoneExceptionally(rex);
431	<	rethrowException(rex);
432	<	return false; // not reached
433	<	}
434	<	setNormalCompletion();
435	<	return true;
436	<	}
437	<
438	<	/**
439	<	* Main execution method used by worker threads. Invokes
440	<	* base computation unless already complete.
282	>	* Unless done, calls exec and records status if completed, but
283	>	* doesn't wait for completion otherwise. Primary execution method
284	>	* for ForkJoinWorkerThread.
285		*/
286		final void quietlyExec() {
443	–	if (status >= 0) {
444	–	try {
445	–	if (!exec())
446	–	return;
447	–	} catch (Throwable rex) {
448	–	setDoneExceptionally(rex);
449	–	return;
450	–	}
451	–	setNormalCompletion();
452	–	}
453	–	}
454	–
455	–	/**
456	–	* Calls exec(), recording but not rethrowing exception.
457	–	* Caller should normally check status before calling.
458	–	*
459	–	* @return true if completed normally
460	–	*/
461	–	private boolean tryQuietlyInvoke() {
287		try {
288	<	if (!exec())
289	<	return false;
288	>	if (status < 0 || !exec())
289	>	return;
290		} catch (Throwable rex) {
291	<	setDoneExceptionally(rex);
292	<	return false;
468	<	}
469	<	setNormalCompletion();
470	<	return true;
471	<	}
472	<
473	<	/**
474	<	* Cancels, ignoring any exceptions it throws.
475	<	*/
476	<	final void cancelIgnoringExceptions() {
477	<	try {
478	<	cancel(false);
479	<	} catch (Throwable ignore) {
291	>	setExceptionalCompletion(rex);
292	>	return;
293		}
294	<	}
482	<
483	<	/**
484	<	* Main implementation of helpJoin
485	<	*/
486	<	private int busyJoin(ForkJoinWorkerThread w) {
487	<	int s;
488	<	ForkJoinTask<?> t;
489	<	while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
490	<	t.quietlyExec();
491	<	return (s >= 0) ? awaitDone(w, false) : s; // block if no work
294	>	setCompletion(NORMAL); // must be outside try block
295		}
296
297		// public methods
#	Line 496 | Line 299 | public abstract class ForkJoinTask<V> im
299		/**
300		* Arranges to asynchronously execute this task.  While it is not
301		* necessarily enforced, it is a usage error to fork a task more
302	<	* than once unless it has completed and been reinitialized.  This
303	<	* method may be invoked only from within ForkJoinTask
304	<	* computations (as may be determined using method {@link
305	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
306	<	* in exceptions or errors, possibly including ClassCastException.
302	>	* than once unless it has completed and been reinitialized.
303	>	* Subsequent modifications to the state of this task or any data
304	>	* it operates on are not necessarily consistently observable by
305	>	* any thread other than the one executing it unless preceded by a
306	>	* call to {@link #join} or related methods, or a call to {@link
307	>	* #isDone} returning {@code true}.
308	>	*
309	>	* <p>This method may be invoked only from within {@code
310	>	* ForkJoinTask} computations (as may be determined using method
311	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
312	>	* result in exceptions or errors, possibly including {@code
313	>	* ClassCastException}.
314		*
315	<	* @return {@code this}, to simplify usage.
315	>	* @return {@code this}, to simplify usage
316		*/
317		public final ForkJoinTask<V> fork() {
318		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 511 | Line 321 | public abstract class ForkJoinTask<V> im
321		}
322
323		/**
324	<	* Returns the result of the computation when it is ready.
325	<	* This method differs from {@code get} in that abnormal
326	<	* completion results in RuntimeExceptions or Errors, not
327	<	* ExecutionExceptions.
324	>	* Returns the result of the computation when it {@link #isDone is done}.
325	>	* This method differs from {@link #get()} in that
326	>	* abnormal completion results in {@code RuntimeException} or
327	>	* {@code Error}, not {@code ExecutionException}.
328		*
329		* @return the computed result
330		*/
331		public final V join() {
332	<	ForkJoinWorkerThread w = getWorker();
333	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryExec())
334	<	reportException(awaitDone(w, true));
332	>	quietlyJoin();
333	>	Throwable ex;
334	>	if (status < NORMAL && (ex = getException()) != null)
335	>	UNSAFE.throwException(ex);
336		return getRawResult();
337		}
338
339		/**
340		* Commences performing this task, awaits its completion if
341	<	* necessary, and return its result.
341	>	* necessary, and return its result, or throws an (unchecked)
342	>	* exception if the underlying computation did so.
343		*
532	–	* @throws Throwable (a RuntimeException, Error, or unchecked
533	–	* exception) if the underlying computation did so
344		* @return the computed result
345		*/
346		public final V invoke() {
347	<	if (status >= 0 && tryExec())
348	<	return getRawResult();
349	<	else
350	<	return join();
347	>	quietlyInvoke();
348	>	Throwable ex;
349	>	if (status < NORMAL && (ex = getException()) != null)
350	>	UNSAFE.throwException(ex);
351	>	return getRawResult();
352		}
353
354		/**
355		* Forks the given tasks, returning when {@code isDone} holds for
356	<	* each task or an exception is encountered. This method may be
357	<	* invoked only from within ForkJoinTask computations (as may be
358	<	* determined using method {@link #inForkJoinPool}). Attempts to
359	<	* invoke in other contexts result in exceptions or errors,
360	<	* possibly including ClassCastException.
356	>	* each task or an (unchecked) exception is encountered, in which
357	>	* case the exception is rethrown.  If either task encounters an
358	>	* exception, the other one may be, but is not guaranteed to be,
359	>	* cancelled.  If both tasks throw an exception, then this method
360	>	* throws one of them.  The individual status of each task may be
361	>	* checked using {@link #getException()} and related methods.
362	>	*
363	>	* <p>This method may be invoked only from within {@code
364	>	* ForkJoinTask} computations (as may be determined using method
365	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
366	>	* result in exceptions or errors, possibly including {@code
367	>	* ClassCastException}.
368		*
369		* @param t1 the first task
370		* @param t2 the second task
371		* @throws NullPointerException if any task is null
554	–	* @throws RuntimeException or Error if a task did so
372		*/
373	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
373	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
374		t2.fork();
375		t1.invoke();
376		t2.join();
#	Line 561 | Line 378 | public abstract class ForkJoinTask<V> im
378
379		/**
380		* Forks the given tasks, returning when {@code isDone} holds for
381	<	* each task or an exception is encountered. If any task
382	<	* encounters an exception, others may be, but are not guaranteed
383	<	* to be, cancelled.  This method may be invoked only from within
384	<	* ForkJoinTask computations (as may be determined using method
385	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
386	<	* result in exceptions or errors, possibly including
387	<	* ClassCastException.
388	<	*
389	<	* Overloadings of this method exist for the special cases
390	<	* of one to four arguments.
381	>	* each task or an (unchecked) exception is encountered, in which
382	>	* case the exception is rethrown. If any task encounters an
383	>	* exception, others may be, but are not guaranteed to be,
384	>	* cancelled.  If more than one task encounters an exception, then
385	>	* this method throws any one of these exceptions.  The individual
386	>	* status of each task may be checked using {@link #getException()}
387	>	* and related methods.
388	>	*
389	>	* <p>This method may be invoked only from within {@code
390	>	* ForkJoinTask} computations (as may be determined using method
391	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
392	>	* result in exceptions or errors, possibly including {@code
393	>	* ClassCastException}.
394		*
395		* @param tasks the tasks
396	<	* @throws NullPointerException if tasks or any element are null
577	<	* @throws RuntimeException or Error if any task did so
396	>	* @throws NullPointerException if any task is null
397		*/
398		public static void invokeAll(ForkJoinTask<?>... tasks) {
399		Throwable ex = null;
#	Line 589 | Line 408 | public abstract class ForkJoinTask<V> im
408		t.fork();
409		else {
410		t.quietlyInvoke();
411	<	if (ex == null)
411	>	if (ex == null && t.status < NORMAL)
412		ex = t.getException();
413		}
414		}
#	Line 600 | Line 419 | public abstract class ForkJoinTask<V> im
419		t.cancel(false);
420		else {
421		t.quietlyJoin();
422	<	if (ex == null)
422	>	if (ex == null && t.status < NORMAL)
423		ex = t.getException();
424		}
425		}
426		}
427		if (ex != null)
428	<	rethrowException(ex);
428	>	UNSAFE.throwException(ex);
429		}
430
431		/**
432	<	* Forks all tasks in the collection, returning when {@code
433	<	* isDone} holds for each task or an exception is encountered. If
434	<	* any task encounters an exception, others may be, but are not
435	<	* guaranteed to be, cancelled.  This method may be invoked only
436	<	* from within ForkJoinTask computations (as may be determined
437	<	* using method {@link #inForkJoinPool}). Attempts to invoke in
438	<	* other contexts result in exceptions or errors, possibly
439	<	* including ClassCastException.
432	>	* Forks all tasks in the specified collection, returning when
433	>	* {@code isDone} holds for each task or an (unchecked) exception
434	>	* is encountered.  If any task encounters an exception, others
435	>	* may be, but are not guaranteed to be, cancelled.  If more than
436	>	* one task encounters an exception, then this method throws any
437	>	* one of these exceptions.  The individual status of each task
438	>	* may be checked using {@link #getException()} and related
439	>	* methods.  The behavior of this operation is undefined if the
440	>	* specified collection is modified while the operation is in
441	>	* progress.
442	>	*
443	>	* <p>This method may be invoked only from within {@code
444	>	* ForkJoinTask} computations (as may be determined using method
445	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
446	>	* result in exceptions or errors, possibly including {@code
447	>	* ClassCastException}.
448		*
449		* @param tasks the collection of tasks
450		* @return the tasks argument, to simplify usage
451		* @throws NullPointerException if tasks or any element are null
625	–	* @throws RuntimeException or Error if any task did so
452		*/
453		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
454	<	if (!(tasks instanceof List<?>)) {
454	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
455		invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
456		return tasks;
457		}
#	Line 644 | Line 470 | public abstract class ForkJoinTask<V> im
470		t.fork();
471		else {
472		t.quietlyInvoke();
473	<	if (ex == null)
473	>	if (ex == null && t.status < NORMAL)
474		ex = t.getException();
475		}
476		}
#	Line 655 | Line 481 | public abstract class ForkJoinTask<V> im
481		t.cancel(false);
482		else {
483		t.quietlyJoin();
484	<	if (ex == null)
484	>	if (ex == null && t.status < NORMAL)
485		ex = t.getException();
486		}
487		}
488		}
489		if (ex != null)
490	<	rethrowException(ex);
490	>	UNSAFE.throwException(ex);
491		return tasks;
492		}
493
494		/**
495	<	* Returns {@code true} if the computation performed by this task
496	<	* has completed (or has been cancelled).
497	<	*
498	<	* @return {@code true} if this computation has completed
499	<	*/
500	<	public final boolean isDone() {
501	<	return status < 0;
676	<	}
677	<
678	<	/**
679	<	* Returns {@code true} if this task was cancelled.
680	<	*
681	<	* @return {@code true} if this task was cancelled
682	<	*/
683	<	public final boolean isCancelled() {
684	<	return (status & COMPLETION_MASK) == CANCELLED;
685	<	}
686	<
687	<	/**
688	<	* Asserts that the results of this task's computation will not be
689	<	* used. If a cancellation occurs before attempting to execute this
690	<	* task, execution will be suppressed, {@link #isCancelled}
691	<	* will report true, and {@link #join} will result in a
692	<	* {@code CancellationException} being thrown. Otherwise, when
693	<	* cancellation races with completion, there are no guarantees
694	<	* about whether {@code isCancelled} will report {@code true},
695	<	* whether {@code join} will return normally or via an exception,
696	<	* or whether these behaviors will remain consistent upon repeated
697	<	* invocation.
495	>	* Attempts to cancel execution of this task. This attempt will
496	>	* fail if the task has already completed, has already been
497	>	* cancelled, or could not be cancelled for some other reason. If
498	>	* successful, and this task has not started when cancel is
499	>	* called, execution of this task is suppressed, {@link
500	>	* #isCancelled} will report true, and {@link #join} will result
501	>	* in a {@code CancellationException} being thrown.
502		*
503		* <p>This method may be overridden in subclasses, but if so, must
504		* still ensure that these minimal properties hold. In particular,
#	Line 706 | Line 510 | public abstract class ForkJoinTask<V> im
510		* invoke {@link #completeExceptionally}.
511		*
512		* @param mayInterruptIfRunning this value is ignored in the
513	<	* default implementation because tasks are not in general
513	>	* default implementation because tasks are not
514		* cancelled via interruption
515		*
516		* @return {@code true} if this task is now cancelled
517		*/
518		public boolean cancel(boolean mayInterruptIfRunning) {
519		setCompletion(CANCELLED);
520	<	return (status & COMPLETION_MASK) == CANCELLED;
520	>	return status == CANCELLED;
521	>	}
522	>
523	>	/**
524	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
525	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
526	>	* exceptions, but if it does anyway, we have no recourse during
527	>	* shutdown, so guard against this case.
528	>	*/
529	>	final void cancelIgnoringExceptions() {
530	>	try {
531	>	cancel(false);
532	>	} catch (Throwable ignore) {
533	>	}
534	>	}
535	>
536	>	/**
537	>	* Cancels ignoring exceptions if worker is terminating
538	>	*/
539	>	final void cancelIfTerminating() {
540	>	Thread t = Thread.currentThread();
541	>	if ((t instanceof ForkJoinWorkerThread) &&
542	>	((ForkJoinWorkerThread) t).isTerminating()) {
543	>	try {
544	>	cancel(false);
545	>	} catch (Throwable ignore) {
546	>	}
547	>	}
548	>	}
549	>
550	>	public final boolean isDone() {
551	>	return status < 0;
552	>	}
553	>
554	>	public final boolean isCancelled() {
555	>	return status == CANCELLED;
556		}
557
558		/**
#	Line 722 | Line 561 | public abstract class ForkJoinTask<V> im
561		* @return {@code true} if this task threw an exception or was cancelled
562		*/
563		public final boolean isCompletedAbnormally() {
564	<	return (status & COMPLETION_MASK) < NORMAL;
564	>	return status < NORMAL;
565	>	}
566	>
567	>	/**
568	>	* Returns {@code true} if this task completed without throwing an
569	>	* exception and was not cancelled.
570	>	*
571	>	* @return {@code true} if this task completed without throwing an
572	>	* exception and was not cancelled
573	>	*/
574	>	public final boolean isCompletedNormally() {
575	>	return status == NORMAL;
576		}
577
578		/**
#	Line 733 | Line 583 | public abstract class ForkJoinTask<V> im
583		* @return the exception, or {@code null} if none
584		*/
585		public final Throwable getException() {
586	<	int s = status & COMPLETION_MASK;
587	<	if (s >= NORMAL)
588	<	return null;
589	<	if (s == CANCELLED)
740	<	return new CancellationException();
741	<	return exceptionMap.get(this);
586	>	int s = status;
587	>	return ((s >= NORMAL)    ? null :
588	>	(s == CANCELLED) ? new CancellationException() :
589	>	exceptionMap.get(this));
590		}
591
592		/**
#	Line 751 | Line 599 | public abstract class ForkJoinTask<V> im
599		* overridable, but overridden versions must invoke {@code super}
600		* implementation to maintain guarantees.
601		*
602	<	* @param ex the exception to throw. If this exception is
603	<	* not a RuntimeException or Error, the actual exception thrown
604	<	* will be a RuntimeException with cause ex.
602	>	* @param ex the exception to throw. If this exception is not a
603	>	* {@code RuntimeException} or {@code Error}, the actual exception
604	>	* thrown will be a {@code RuntimeException} with cause {@code ex}.
605		*/
606		public void completeExceptionally(Throwable ex) {
607	<	setDoneExceptionally((ex instanceof RuntimeException) ||
608	<	(ex instanceof Error) ? ex :
609	<	new RuntimeException(ex));
607	>	setExceptionalCompletion((ex instanceof RuntimeException) ||
608	>	(ex instanceof Error) ? ex :
609	>	new RuntimeException(ex));
610		}
611
612		/**
#	Line 777 | Line 625 | public abstract class ForkJoinTask<V> im
625		try {
626		setRawResult(value);
627		} catch (Throwable rex) {
628	<	setDoneExceptionally(rex);
628	>	setExceptionalCompletion(rex);
629		return;
630		}
631	<	setNormalCompletion();
631	>	setCompletion(NORMAL);
632		}
633
634		public final V get() throws InterruptedException, ExecutionException {
635	<	ForkJoinWorkerThread w = getWorker();
636	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
637	<	awaitDone(w, true);
638	<	return reportFutureResult();
635	>	quietlyJoin();
636	>	if (Thread.interrupted())
637	>	throw new InterruptedException();
638	>	int s = status;
639	>	if (s < NORMAL) {
640	>	Throwable ex;
641	>	if (s == CANCELLED)
642	>	throw new CancellationException();
643	>	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
644	>	throw new ExecutionException(ex);
645	>	}
646	>	return getRawResult();
647		}
648
649		public final V get(long timeout, TimeUnit unit)
650		throws InterruptedException, ExecutionException, TimeoutException {
651	+	Thread t = Thread.currentThread();
652	+	ForkJoinPool pool;
653	+	if (t instanceof ForkJoinWorkerThread) {
654	+	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
655	+	if (status >= 0 && w.unpushTask(this))
656	+	quietlyExec();
657	+	pool = w.pool;
658	+	}
659	+	else
660	+	pool = null;
661	+	/*
662	+	* Timed wait loop intermixes cases for FJ (pool != null) and
663	+	* non FJ threads. For FJ, decrement pool count but don't try
664	+	* for replacement; increment count on completion. For non-FJ,
665	+	* deal with interrupts. This is messy, but a little less so
666	+	* than is splitting the FJ and nonFJ cases.
667	+	*/
668	+	boolean interrupted = false;
669	+	boolean dec = false; // true if pool count decremented
670		long nanos = unit.toNanos(timeout);
671	<	ForkJoinWorkerThread w = getWorker();
672	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
673	<	awaitDone(w, nanos);
674	<	return reportTimedFutureResult();
675	<	}
676	<
677	<	/**
678	<	* Possibly executes other tasks until this task is ready, then
679	<	* returns the result of the computation.  This method may be more
680	<	* efficient than {@code join}, but is only applicable when
681	<	* there are no potential dependencies between continuation of the
682	<	* current task and that of any other task that might be executed
683	<	* while helping. (This usually holds for pure divide-and-conquer
684	<	* tasks). This method may be invoked only from within
685	<	* ForkJoinTask computations (as may be determined using method
686	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
687	<	* result in exceptions or errors, possibly including
688	<	* ClassCastException.
689	<	*
690	<	* @return the computed result
691	<	*/
692	<	public final V helpJoin() {
693	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
694	<	if (status < 0 || !w.unpushTask(this) || !tryExec())
695	<	reportException(busyJoin(w));
696	<	return getRawResult();
697	<	}
698	<
699	<	/**
700	<	* Possibly executes other tasks until this task is ready.  This
701	<	* method may be invoked only from within ForkJoinTask
702	<	* computations (as may be determined using method {@link
703	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
704	<	* in exceptions or errors, possibly including ClassCastException.
705	<	*/
831	<	public final void quietlyHelpJoin() {
832	<	if (status >= 0) {
833	<	ForkJoinWorkerThread w =
834	<	(ForkJoinWorkerThread) Thread.currentThread();
835	<	if (!w.unpushTask(this) || !tryQuietlyInvoke())
836	<	busyJoin(w);
671	>	for (;;) {
672	>	if (Thread.interrupted() && pool == null) {
673	>	interrupted = true;
674	>	break;
675	>	}
676	>	int s = status;
677	>	if (s < 0)
678	>	break;
679	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
680	>	long startTime = System.nanoTime();
681	>	long nt; // wait time
682	>	while (status >= 0 &&
683	>	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
684	>	if (pool != null && !dec)
685	>	dec = pool.tryDecrementRunningCount();
686	>	else {
687	>	long ms = nt / 1000000;
688	>	int ns = (int) (nt % 1000000);
689	>	try {
690	>	synchronized(this) {
691	>	if (status >= 0)
692	>	wait(ms, ns);
693	>	}
694	>	} catch (InterruptedException ie) {
695	>	if (pool != null)
696	>	cancelIfTerminating();
697	>	else {
698	>	interrupted = true;
699	>	break;
700	>	}
701	>	}
702	>	}
703	>	}
704	>	break;
705	>	}
706		}
707	+	if (pool != null && dec)
708	+	pool.incrementRunningCount();
709	+	if (interrupted)
710	+	throw new InterruptedException();
711	+	int es = status;
712	+	if (es != NORMAL) {
713	+	Throwable ex;
714	+	if (es == CANCELLED)
715	+	throw new CancellationException();
716	+	if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
717	+	throw new ExecutionException(ex);
718	+	throw new TimeoutException();
719	+	}
720	+	return getRawResult();
721		}
722
723		/**
724	<	* Joins this task, without returning its result or throwing an
724	>	* Joins this task, without returning its result or throwing its
725		* exception. This method may be useful when processing
726		* collections of tasks when some have been cancelled or otherwise
727		* known to have aborted.
728		*/
729		public final void quietlyJoin() {
730	<	if (status >= 0) {
731	<	ForkJoinWorkerThread w = getWorker();
732	<	if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
733	<	awaitDone(w, true);
730	>	Thread t;
731	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
732	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
733	>	if (status >= 0) {
734	>	if (w.unpushTask(this)) {
735	>	boolean completed;
736	>	try {
737	>	completed = exec();
738	>	} catch (Throwable rex) {
739	>	setExceptionalCompletion(rex);
740	>	return;
741	>	}
742	>	if (completed) {
743	>	setCompletion(NORMAL);
744	>	return;
745	>	}
746	>	}
747	>	w.joinTask(this);
748	>	}
749		}
750	+	else
751	+	externalAwaitDone();
752		}
753
754		/**
755		* Commences performing this task and awaits its completion if
756	<	* necessary, without returning its result or throwing an
756	>	* necessary, without returning its result or throwing its
757		* exception. This method may be useful when processing
758		* collections of tasks when some have been cancelled or otherwise
759		* known to have aborted.
760		*/
761		public final void quietlyInvoke() {
762	<	if (status >= 0 && !tryQuietlyInvoke())
763	<	quietlyJoin();
762	>	if (status >= 0) {
763	>	boolean completed;
764	>	try {
765	>	completed = exec();
766	>	} catch (Throwable rex) {
767	>	setExceptionalCompletion(rex);
768	>	return;
769	>	}
770	>	if (completed)
771	>	setCompletion(NORMAL);
772	>	else
773	>	quietlyJoin();
774	>	}
775		}
776
777		/**
778		* Possibly executes tasks until the pool hosting the current task
779	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
780	<	* designs in which many tasks are forked, but none are explicitly
781	<	* joined, instead executing them until all are processed.  This
782	<	* method may be invoked only from within ForkJoinTask
783	<	* computations (as may be determined using method {@link
784	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
785	<	* in exceptions or errors, possibly including ClassCastException.
779	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
780	>	* be of use in designs in which many tasks are forked, but none
781	>	* are explicitly joined, instead executing them until all are
782	>	* processed.
783	>	*
784	>	* <p>This method may be invoked only from within {@code
785	>	* ForkJoinTask} computations (as may be determined using method
786	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
787	>	* result in exceptions or errors, possibly including {@code
788	>	* ClassCastException}.
789		*/
790		public static void helpQuiesce() {
791		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 884 | Line 798 | public abstract class ForkJoinTask<V> im
798		* this task, but only if reuse occurs when this task has either
799		* never been forked, or has been forked, then completed and all
800		* outstanding joins of this task have also completed. Effects
801	<	* under any other usage conditions are not guaranteed, and are
802	<	* discouraged. This method may be useful when executing
801	>	* under any other usage conditions are not guaranteed.
802	>	* This method may be useful when executing
803		* pre-constructed trees of subtasks in loops.
804		*/
805		public void reinitialize() {
806	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
806	>	if (status == EXCEPTIONAL)
807		exceptionMap.remove(this);
808		status = 0;
809		}
#	Line 924 | Line 838 | public abstract class ForkJoinTask<V> im
838		* by the current thread, and has not commenced executing in
839		* another thread.  This method may be useful when arranging
840		* alternative local processing of tasks that could have been, but
841	<	* were not, stolen. This method may be invoked only from within
842	<	* ForkJoinTask computations (as may be determined using method
843	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
844	<	* result in exceptions or errors, possibly including
845	<	* ClassCastException.
841	>	* were not, stolen.
842	>	*
843	>	* <p>This method may be invoked only from within {@code
844	>	* ForkJoinTask} computations (as may be determined using method
845	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
846	>	* result in exceptions or errors, possibly including {@code
847	>	* ClassCastException}.
848		*
849		* @return {@code true} if unforked
850		*/
#	Line 941 | Line 857 | public abstract class ForkJoinTask<V> im
857		* Returns an estimate of the number of tasks that have been
858		* forked by the current worker thread but not yet executed. This
859		* value may be useful for heuristic decisions about whether to
860	<	* fork other tasks.  This method may be invoked only from within
861	<	* ForkJoinTask computations (as may be determined using method
862	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
863	<	* result in exceptions or errors, possibly including
864	<	* ClassCastException.
860	>	* fork other tasks.
861	>	*
862	>	* <p>This method may be invoked only from within {@code
863	>	* ForkJoinTask} computations (as may be determined using method
864	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
865	>	* result in exceptions or errors, possibly including {@code
866	>	* ClassCastException}.
867	>	*
868		* @return the number of tasks
869		*/
870		public static int getQueuedTaskCount() {
#	Line 961 | Line 880 | public abstract class ForkJoinTask<V> im
880		* usages of ForkJoinTasks, at steady state, each worker should
881		* aim to maintain a small constant surplus (for example, 3) of
882		* tasks, and to process computations locally if this threshold is
883	<	* exceeded.  This method may be invoked only from within
884	<	* ForkJoinTask computations (as may be determined using method
885	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
886	<	* result in exceptions or errors, possibly including
887	<	* ClassCastException.  *
883	>	* exceeded.
884	>	*
885	>	* <p>This method may be invoked only from within {@code
886	>	* ForkJoinTask} computations (as may be determined using method
887	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
888	>	* result in exceptions or errors, possibly including {@code
889	>	* ClassCastException}.
890	>	*
891		* @return the surplus number of tasks, which may be negative
892		*/
893		public static int getSurplusQueuedTaskCount() {
#	Line 1001 | Line 923 | public abstract class ForkJoinTask<V> im
923		* called otherwise. The return value controls whether this task
924		* is considered to be done normally. It may return false in
925		* asynchronous actions that require explicit invocations of
926	<	* {@link #complete} to become joinable. It may throw exceptions
927	<	* to indicate abnormal exit.
926	>	* {@link #complete} to become joinable. It may also throw an
927	>	* (unchecked) exception to indicate abnormal exit.
928		*
929		* @return {@code true} if completed normally
1008	–	* @throws Error or RuntimeException if encountered during computation
930		*/
931		protected abstract boolean exec();
932
#	Line 1017 | Line 938 | public abstract class ForkJoinTask<V> im
938		* null even if a task exists but cannot be accessed without
939		* contention with other threads.  This method is designed
940		* primarily to support extensions, and is unlikely to be useful
941	<	* otherwise.  This method may be invoked only from within
942	<	* ForkJoinTask computations (as may be determined using method
943	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
944	<	* result in exceptions or errors, possibly including
945	<	* ClassCastException.
941	>	* otherwise.
942	>	*
943	>	* <p>This method may be invoked only from within {@code
944	>	* ForkJoinTask} computations (as may be determined using method
945	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
946	>	* result in exceptions or errors, possibly including {@code
947	>	* ClassCastException}.
948		*
949		* @return the next task, or {@code null} if none are available
950		*/
#	Line 1034 | Line 957 | public abstract class ForkJoinTask<V> im
957		* Unschedules and returns, without executing, the next task
958		* queued by the current thread but not yet executed.  This method
959		* is designed primarily to support extensions, and is unlikely to
960	<	* be useful otherwise.  This method may be invoked only from
961	<	* within ForkJoinTask computations (as may be determined using
962	<	* method {@link #inForkJoinPool}). Attempts to invoke in other
963	<	* contexts result in exceptions or errors, possibly including
964	<	* ClassCastException.
960	>	* be useful otherwise.
961	>	*
962	>	* <p>This method may be invoked only from within {@code
963	>	* ForkJoinTask} computations (as may be determined using method
964	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
965	>	* result in exceptions or errors, possibly including {@code
966	>	* ClassCastException}.
967		*
968		* @return the next task, or {@code null} if none are available
969		*/
#	Line 1055 | Line 980 | public abstract class ForkJoinTask<V> im
980		* {@code null} result does not necessarily imply quiescence
981		* of the pool this task is operating in.  This method is designed
982		* primarily to support extensions, and is unlikely to be useful
983	<	* otherwise.  This method may be invoked only from within
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
987	<	* ClassCastException.
983	>	* otherwise.
984	>	*
985	>	* <p>This method may be invoked only from within {@code
986	>	* ForkJoinTask} computations (as may be determined using method
987	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
988	>	* result in exceptions or errors, possibly including {@code
989	>	* ClassCastException}.
990		*
991		* @return a task, or {@code null} if none are available
992		*/
#	Line 1124 | Line 1051 | public abstract class ForkJoinTask<V> im
1051		}
1052
1053		/**
1054	<	* Returns a new ForkJoinTask that performs the {@code run}
1055	<	* method of the given Runnable as its action, and returns a null
1056	<	* result upon {@code join}.
1054	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1055	>	* method of the given {@code Runnable} as its action, and returns
1056	>	* a null result upon {@link #join}.
1057		*
1058		* @param runnable the runnable action
1059		* @return the task
#	Line 1136 | Line 1063 | public abstract class ForkJoinTask<V> im
1063		}
1064
1065		/**
1066	<	* Returns a new ForkJoinTask that performs the {@code run}
1067	<	* method of the given Runnable as its action, and returns the
1068	<	* given result upon {@code join}.
1066	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1067	>	* method of the given {@code Runnable} as its action, and returns
1068	>	* the given result upon {@link #join}.
1069		*
1070		* @param runnable the runnable action
1071		* @param result the result upon completion
#	Line 1149 | Line 1076 | public abstract class ForkJoinTask<V> im
1076		}
1077
1078		/**
1079	<	* Returns a new ForkJoinTask that performs the {@code call}
1080	<	* method of the given Callable as its action, and returns its
1081	<	* result upon {@code join}, translating any checked
1082	<	* exceptions encountered into {@code RuntimeException}.
1079	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1080	>	* method of the given {@code Callable} as its action, and returns
1081	>	* its result upon {@link #join}, translating any checked exceptions
1082	>	* encountered into {@code RuntimeException}.
1083		*
1084		* @param callable the callable action
1085		* @return the task
#	Line 1166 | Line 1093 | public abstract class ForkJoinTask<V> im
1093		private static final long serialVersionUID = -7721805057305804111L;
1094
1095		/**
1096	<	* Save the state to a stream.
1096	>	* Saves the state to a stream.
1097		*
1098		* @serialData the current run status and the exception thrown
1099		* during execution, or {@code null} if none
#	Line 1179 | Line 1106 | public abstract class ForkJoinTask<V> im
1106		}
1107
1108		/**
1109	<	* Reconstitute the instance from a stream.
1109	>	* Reconstitutes the instance from a stream.
1110		*
1111		* @param s the stream
1112		*/
1113		private void readObject(java.io.ObjectInputStream s)
1114		throws java.io.IOException, ClassNotFoundException {
1115		s.defaultReadObject();
1189	–	status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
1190	–	status |= EXTERNAL_SIGNAL; // conservatively set external signal
1116		Object ex = s.readObject();
1117		if (ex != null)
1118	<	setDoneExceptionally((Throwable) ex);
1118	>	setExceptionalCompletion((Throwable) ex);
1119		}
1120
1121		// Unsafe mechanics

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