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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.47 by dl, Sun Apr 18 12:51:18 2010 UTC vs.
Revision 1.70 by dl, Tue Nov 23 00:10:39 2010 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.io.Serializable;
10		import java.util.Collection;
11		import java.util.Collections;
#	Line 15 | Line 13 | import java.util.List;
13		import java.util.RandomAccess;
14		import java.util.Map;
15		import java.util.WeakHashMap;
16	+	import java.util.concurrent.Callable;
17	+	import java.util.concurrent.CancellationException;
18	+	import java.util.concurrent.ExecutionException;
19	+	import java.util.concurrent.Executor;
20	+	import java.util.concurrent.ExecutorService;
21	+	import java.util.concurrent.Future;
22	+	import java.util.concurrent.RejectedExecutionException;
23	+	import java.util.concurrent.RunnableFuture;
24	+	import java.util.concurrent.TimeUnit;
25	+	import java.util.concurrent.TimeoutException;
26
27		/**
28		* Abstract base class for tasks that run within a {@link ForkJoinPool}.
#	Line 28 | Line 36 | import java.util.WeakHashMap;
36		* start other subtasks.  As indicated by the name of this class,
37		* many programs using {@code ForkJoinTask} employ only methods
38		* {@link #fork} and {@link #join}, or derivatives such as {@link
39	<	* #invokeAll}.  However, this class also provides a number of other
40	<	* methods that can come into play in advanced usages, as well as
41	<	* extension mechanics that allow support of new forms of fork/join
42	<	* processing.
39	>	* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
40	>	* provides a number of other methods that can come into play in
41	>	* advanced usages, as well as extension mechanics that allow
42	>	* support of new forms of fork/join processing.
43		*
44		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
45		* The efficiency of {@code ForkJoinTask}s stems from a set of
#	Line 64 | Line 72 | import java.util.WeakHashMap;
72		* results of a task is {@link #join}, but there are several variants:
73		* The {@link Future#get} methods support interruptible and/or timed
74		* waits for completion and report results using {@code Future}
75	<	* 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
75	>	* conventions. Method {@link #invoke} is semantically
76		* equivalent to {@code fork(); join()} but always attempts to begin
77		* execution in the current thread. The "<em>quiet</em>" forms of
78		* these methods do not extract results or report exceptions. These
#	Line 103 | Line 108 | import java.util.WeakHashMap;
108		* ForkJoinTasks (as may be determined using method {@link
109		* #inForkJoinPool}).  Attempts to invoke them in other contexts
110		* result in exceptions or errors, possibly including
111	<	* ClassCastException.
111	>	* {@code ClassCastException}.
112	>	*
113	>	* <p>Method {@link #join} and its variants are appropriate for use
114	>	* only when completion dependencies are acyclic; that is, the
115	>	* parallel computation can be described as a directed acyclic graph
116	>	* (DAG). Otherwise, executions may encounter a form of deadlock as
117	>	* tasks cyclically wait for each other.  However, this framework
118	>	* supports other methods and techniques (for example the use of
119	>	* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
120	>	* may be of use in constructing custom subclasses for problems that
121	>	* are not statically structured as DAGs.
122		*
123		* <p>Most base support methods are {@code final}, to prevent
124		* overriding of implementations that are intrinsically tied to the
#	Line 119 | Line 134 | import java.util.WeakHashMap;
134		* computation. Large tasks should be split into smaller subtasks,
135		* usually via recursive decomposition. As a very rough rule of thumb,
136		* a task should perform more than 100 and less than 10000 basic
137	<	* computational steps. If tasks are too big, then parallelism cannot
138	<	* improve throughput. If too small, then memory and internal task
139	<	* maintenance overhead may overwhelm processing.
137	>	* computational steps, and should avoid indefinite looping. If tasks
138	>	* are too big, then parallelism cannot improve throughput. If too
139	>	* small, then memory and internal task maintenance overhead may
140	>	* overwhelm processing.
141		*
142		* <p>This class provides {@code adapt} methods for {@link Runnable}
143		* and {@link Callable}, that may be of use when mixing execution of
144	<	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks
145	<	* are of this form, consider using a pool in
130	<	* {@linkplain ForkJoinPool#setAsyncMode async mode}.
144	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
145	>	* of this form, consider using a pool constructed in <em>asyncMode</em>.
146		*
147		* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
148		* used in extensions such as remote execution frameworks. It is
#	Line 148 | Line 163 | public abstract class ForkJoinTask<V> im
163		* status maintenance (2) execution and awaiting completion (3)
164		* user-level methods that additionally report results. This is
165		* sometimes hard to see because this file orders exported methods
166	<	* in a way that flows well in javadocs.
166	>	* in a way that flows well in javadocs. In particular, most
167	>	* join mechanics are in method quietlyJoin, below.
168		*/
169
170	<	/**
171	<	* Run control status bits packed into a single int to minimize
172	<	* footprint and to ensure atomicity (via CAS).  Status is
173	<	* initially zero, and takes on nonnegative values until
174	<	* completed, upon which status holds COMPLETED. CANCELLED, or
175	<	* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
176	<	* blocking waits by other threads have SIGNAL_MASK bits set --
177	<	* bit 15 for external (nonFJ) waits, and the rest a count of
178	<	* waiting FJ threads.  (This representation relies on
179	<	* ForkJoinPool max thread limits). Signal counts are not directly
180	<	* incremented by ForkJoinTask methods, but instead via a call to
181	<	* requestSignal within ForkJoinPool.preJoin, once their need is
182	<	* established.
183	<	*
184	<	* Completion of a stolen task with SIGNAL_MASK bits set awakens
169	<	* any waiters via notifyAll. Even though suboptimal for some
170	<	* purposes, we use basic builtin wait/notify to take advantage of
171	<	* "monitor inflation" in JVMs that we would otherwise need to
172	<	* emulate to avoid adding further per-task bookkeeping overhead.
173	<	* We want these monitors to be "fat", i.e., not use biasing or
174	<	* thin-lock techniques, so use some odd coding idioms that tend
175	<	* to avoid them.
176	<	*
177	<	* Note that bits 16-28 are currently unused. Also value
178	<	* 0x80000000 is available as spare completion value.
170	>	/*
171	>	* The status field holds run control status bits packed into a
172	>	* single int to minimize footprint and to ensure atomicity (via
173	>	* CAS).  Status is initially zero, and takes on nonnegative
174	>	* values until completed, upon which status holds value
175	>	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
176	>	* waits by other threads have the SIGNAL bit set.  Completion of
177	>	* a stolen task with SIGNAL set awakens any waiters via
178	>	* notifyAll. Even though suboptimal for some purposes, we use
179	>	* basic builtin wait/notify to take advantage of "monitor
180	>	* inflation" in JVMs that we would otherwise need to emulate to
181	>	* avoid adding further per-task bookkeeping overhead.  We want
182	>	* these monitors to be "fat", i.e., not use biasing or thin-lock
183	>	* techniques, so use some odd coding idioms that tend to avoid
184	>	* them.
185		*/
186	+
187	+	/** The run status of this task */
188		volatile int status; // accessed directly by pool and workers
189
190	<	private static final int COMPLETION_MASK      = 0xe0000000;
191	<	private static final int NORMAL               = 0xe0000000; // == mask
192	<	private static final int CANCELLED            = 0xc0000000;
193	<	private static final int EXCEPTIONAL          = 0xa0000000;
186	<	private static final int SIGNAL_MASK          = 0x0000ffff;
187	<	private static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
188	<	private static final int EXTERNAL_SIGNAL      = 0x00008000;
190	>	private static final int NORMAL      = -1;
191	>	private static final int CANCELLED   = -2;
192	>	private static final int EXCEPTIONAL = -3;
193	>	private static final int SIGNAL      =  1;
194
195		/**
196		* Table of exceptions thrown by tasks, to enable reporting by
#	Line 211 | Line 216 | public abstract class ForkJoinTask<V> im
216		int s;
217		while ((s = status) >= 0) {
218		if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
219	<	if ((s & SIGNAL_MASK) != 0) {
215	<	Thread t = Thread.currentThread();
216	<	if (t instanceof ForkJoinWorkerThread)
217	<	((ForkJoinWorkerThread) t).pool.updateRunningCount
218	<	(s & INTERNAL_SIGNAL_MASK);
219	>	if (s != 0)
220		synchronized (this) { notifyAll(); }
221	<	}
221	<	return;
221	>	break;
222		}
223		}
224		}
225
226		/**
227	<	* Record exception and set exceptional completion
227	>	* Records exception and sets exceptional completion.
228	>	*
229	>	* @return status on exit
230		*/
231	<	private void setDoneExceptionally(Throwable rex) {
231	>	private void setExceptionalCompletion(Throwable rex) {
232		exceptionMap.put(this, rex);
233		setCompletion(EXCEPTIONAL);
234		}
235
236		/**
237	<	* Main internal execution method: Unless done, calls exec and
238	<	* records completion.
237	<	*
238	<	* @return true if ran and completed normally
237	>	* Blocks a worker thread until completed or timed out.  Called
238	>	* only by pool.
239		*/
240	<	final boolean tryExec() {
241	<	try {
242	<	if (status < 0 || !exec())
243	<	return false;
244	<	} catch (Throwable rex) {
245	<	setDoneExceptionally(rex);
246	<	return false;
247	<	}
248	<	setCompletion(NORMAL); // must be outside try block
249	<	return true;
250	<	}
251	<
252	<	/**
253	<	* Increments internal signal count (thus requesting signal upon
254	<	* completion) unless already done.  Call only once per join.
255	<	* Used by ForkJoinPool.preJoin.
256	<	*
257	<	* @return status
258	<	*/
259	<	final int requestSignal() {
260	<	int s;
261	<	do {} while ((s = status) >= 0 &&
262	<	!UNSAFE.compareAndSwapInt(this, statusOffset, s, s + 1));
263	<	return s;
264	<	}
265	<
266	<	/**
267	<	* Sets external signal request unless already done.
268	<	*
269	<	* @return status
270	<	*/
271	<	private int requestExternalSignal() {
272	<	int s;
273	<	do {} while ((s = status) >= 0 &&
274	<	!UNSAFE.compareAndSwapInt(this, statusOffset,
275	<	s, s | EXTERNAL_SIGNAL));
276	<	return s;
277	<	}
278	<
279	<	/*
280	<	* Awaiting completion. The four versions, internal vs external X
281	<	* untimed vs timed, have the same overall structure but differ
282	<	* from each other enough to defy simple integration.
283	<	*/
284	<
285	<	/**
286	<	* Blocks a worker until this task is done, also maintaining pool
287	<	* and signal counts
288	<	*/
289	<	private void awaitDone(ForkJoinWorkerThread w) {
240	>	final void internalAwaitDone(long millis, int nanos) {
241		if (status >= 0) {
242	<	w.pool.preJoin(this);
243	<	while (status >= 0) {
244	<	try { // minimize lock scope
245	<	synchronized(this) {
246	<	if (status >= 0)
247	<	wait();
297	<	else { // help release; also helps avoid lock-biasing
298	<	notifyAll();
299	<	break;
300	<	}
301	<	}
302	<	} catch (InterruptedException ie) {
303	<	cancelIfTerminating();
242	>	try {     // the odd construction reduces lock bias effects
243	>	synchronized (this) {
244	>	if (status > 0 ||
245	>	UNSAFE.compareAndSwapInt(this, statusOffset,
246	>	0, SIGNAL))
247	>	wait(millis, nanos);
248		}
249	+	} catch (InterruptedException ie) {
250	+	cancelIfTerminating();
251		}
252		}
253		}
254
255		/**
256	<	* Blocks a non-ForkJoin thread until this task is done.
256	>	* Blocks a non-worker-thread until completion.
257		*/
258		private void externalAwaitDone() {
313	–	if (requestExternalSignal() >= 0) {
314	–	boolean interrupted = false;
315	–	while (status >= 0) {
316	–	try {
317	–	synchronized(this) {
318	–	if (status >= 0)
319	–	wait();
320	–	else {
321	–	notifyAll();
322	–	break;
323	–	}
324	–	}
325	–	} catch (InterruptedException ie) {
326	–	interrupted = true;
327	–	}
328	–	}
329	–	if (interrupted)
330	–	Thread.currentThread().interrupt();
331	–	}
332	–	}
333	–
334	–	/**
335	–	* Blocks a worker until this task is done or timeout elapses
336	–	*/
337	–	private void timedAwaitDone(ForkJoinWorkerThread w, long nanos) {
259		if (status >= 0) {
260	<	long startTime = System.nanoTime();
261	<	ForkJoinPool pool = w.pool;
262	<	pool.preJoin(this);
263	<	while (status >= 0) {
264	<	long nt = nanos - (System.nanoTime() - startTime);
265	<	if (nt > 0) {
266	<	long ms = nt / 1000000;
267	<	int ns = (int) (nt % 1000000);
260	>	boolean interrupted = false;
261	>	synchronized(this) {
262	>	int s;
263	>	while ((s = status) >= 0) {
264	>	if (s == 0 &&
265	>	!UNSAFE.compareAndSwapInt(this, statusOffset,
266	>	0, SIGNAL))
267	>	continue;
268		try {
269	<	synchronized(this) { if (status >= 0) wait(ms, ns); }
269	>	wait();
270		} catch (InterruptedException ie) {
271	<	cancelIfTerminating();
271	>	interrupted = true;
272		}
273		}
353	–	else {
354	–	int s; // adjust running count on timeout
355	–	while ((s = status) >= 0 &&
356	–	(s & INTERNAL_SIGNAL_MASK) != 0) {
357	–	if (UNSAFE.compareAndSwapInt(this, statusOffset,
358	–	s, s - 1)) {
359	–	pool.updateRunningCount(1);
360	–	break;
361	–	}
362	–	}
363	–	break;
364	–	}
365	–	}
366	–	}
367	–	}
368	–
369	–	/**
370	–	* Blocks a non-ForkJoin thread until this task is done or timeout elapses
371	–	*/
372	–	private void externalTimedAwaitDone(long nanos) {
373	–	if (requestExternalSignal() >= 0) {
374	–	long startTime = System.nanoTime();
375	–	boolean interrupted = false;
376	–	while (status >= 0) {
377	–	long nt = nanos - (System.nanoTime() - startTime);
378	–	if (nt <= 0)
379	–	break;
380	–	long ms = nt / 1000000;
381	–	int ns = (int) (nt % 1000000);
382	–	try {
383	–	synchronized(this) { if (status >= 0) wait(ms, ns); }
384	–	} catch (InterruptedException ie) {
385	–	interrupted = true;
386	–	}
274		}
275		if (interrupted)
276		Thread.currentThread().interrupt();
277		}
278		}
279
393	–	// reporting results
394	–
395	–	/**
396	–	* Returns result or throws the exception associated with status.
397	–	* Uses Unsafe as a workaround for javac not allowing rethrow of
398	–	* unchecked exceptions.
399	–	*/
400	–	private V reportResult() {
401	–	if ((status & COMPLETION_MASK) < NORMAL) {
402	–	Throwable ex = getException();
403	–	if (ex != null)
404	–	UNSAFE.throwException(ex);
405	–	}
406	–	return getRawResult();
407	–	}
408	–
280		/**
281	<	* Returns result or throws exception using j.u.c.Future conventions.
411	<	* Only call when {@code isDone} known to be true or thread known
412	<	* to be interrupted.
281	>	* Blocks a non-worker-thread until completion or interruption or timeout
282		*/
283	<	private V reportFutureResult()
284	<	throws InterruptedException, ExecutionException {
283	>	private void externalInterruptibleAwaitDone(boolean timed, long nanos)
284	>	throws InterruptedException {
285		if (Thread.interrupted())
286		throw new InterruptedException();
287	<	int s = status & COMPLETION_MASK;
288	<	if (s < NORMAL) {
289	<	Throwable ex;
290	<	if (s == CANCELLED)
291	<	throw new CancellationException();
292	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
293	<	throw new ExecutionException(ex);
287	>	if (status >= 0) {
288	>	long startTime = timed ? System.nanoTime() : 0L;
289	>	synchronized(this) {
290	>	int s;
291	>	while ((s = status) >= 0) {
292	>	long nt;
293	>	if (s == 0 &&
294	>	!UNSAFE.compareAndSwapInt(this, statusOffset,
295	>	0, SIGNAL))
296	>	continue;
297	>	else if (!timed)
298	>	wait();
299	>	else if ((nt = nanos - (System.nanoTime()-startTime)) > 0L)
300	>	wait(nt / 1000000, (int)(nt % 1000000));
301	>	else
302	>	break;
303	>	}
304	>	}
305		}
426	–	return getRawResult();
306		}
307
308		/**
309	<	* Returns result or throws exception using j.u.c.Future conventions
310	<	* with timeouts.
309	>	* Unless done, calls exec and records status if completed, but
310	>	* doesn't wait for completion otherwise. Primary execution method
311	>	* for ForkJoinWorkerThread.
312		*/
313	<	private V reportTimedFutureResult()
314	<	throws InterruptedException, ExecutionException, TimeoutException {
315	<	if (Thread.interrupted())
316	<	throw new InterruptedException();
317	<	Throwable ex;
318	<	int s = status & COMPLETION_MASK;
319	<	if (s == NORMAL)
320	<	return getRawResult();
321	<	else if (s == CANCELLED)
442	<	throw new CancellationException();
443	<	else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
444	<	throw new ExecutionException(ex);
445	<	else
446	<	throw new TimeoutException();
313	>	final void quietlyExec() {
314	>	try {
315	>	if (status < 0 || !exec())
316	>	return;
317	>	} catch (Throwable rex) {
318	>	setExceptionalCompletion(rex);
319	>	return;
320	>	}
321	>	setCompletion(NORMAL); // must be outside try block
322		}
323
324		// public methods
#	Line 459 | Line 334 | public abstract class ForkJoinTask<V> im
334		* #isDone} returning {@code true}.
335		*
336		* <p>This method may be invoked only from within {@code
337	<	* ForkJoinTask} computations (as may be determined using method
337	>	* ForkJoinPool} computations (as may be determined using method
338		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
339		* result in exceptions or errors, possibly including {@code
340		* ClassCastException}.
#	Line 473 | Line 348 | public abstract class ForkJoinTask<V> im
348		}
349
350		/**
351	<	* Returns the result of the computation when it {@link #isDone is done}.
352	<	* This method differs from {@link #get()} in that
351	>	* Returns the result of the computation when it {@link #isDone is
352	>	* done}.  This method differs from {@link #get()} in that
353		* abnormal completion results in {@code RuntimeException} or
354	<	* {@code Error}, not {@code ExecutionException}.
354	>	* {@code Error}, not {@code ExecutionException}, and that
355	>	* interrupts of the calling thread do <em>not</em> cause the
356	>	* method to abruptly return by throwing {@code
357	>	* InterruptedException}.
358		*
359		* @return the computed result
360		*/
361		public final V join() {
362		quietlyJoin();
363	<	return reportResult();
363	>	Throwable ex;
364	>	if (status < NORMAL && (ex = getException()) != null)
365	>	UNSAFE.throwException(ex);
366	>	return getRawResult();
367		}
368
369		/**
370		* Commences performing this task, awaits its completion if
371	<	* necessary, and return its result, or throws an (unchecked)
372	<	* exception if the underlying computation did so.
371	>	* necessary, and returns its result, or throws an (unchecked)
372	>	* {@code RuntimeException} or {@code Error} if the underlying
373	>	* computation did so.
374		*
375		* @return the computed result
376		*/
377		public final V invoke() {
378	<	if (!tryExec())
379	<	quietlyJoin();
380	<	return reportResult();
378	>	quietlyInvoke();
379	>	Throwable ex;
380	>	if (status < NORMAL && (ex = getException()) != null)
381	>	UNSAFE.throwException(ex);
382	>	return getRawResult();
383		}
384
385		/**
386		* Forks the given tasks, returning when {@code isDone} holds for
387		* each task or an (unchecked) exception is encountered, in which
388	<	* case the exception is rethrown.  If either task encounters an
389	<	* exception, the other one may be, but is not guaranteed to be,
390	<	* cancelled.  If both tasks throw an exception, then this method
391	<	* throws one of them.  The individual status of each task may be
392	<	* checked using {@link #getException()} and related methods.
388	>	* case the exception is rethrown. If more than one task
389	>	* encounters an exception, then this method throws any one of
390	>	* these exceptions. If any task encounters an exception, the
391	>	* other may be cancelled. However, the execution status of
392	>	* individual tasks is not guaranteed upon exceptional return. The
393	>	* status of each task may be obtained using {@link
394	>	* #getException()} and related methods to check if they have been
395	>	* cancelled, completed normally or exceptionally, or left
396	>	* unprocessed.
397		*
398		* <p>This method may be invoked only from within {@code
399	<	* ForkJoinTask} computations (as may be determined using method
399	>	* ForkJoinPool} computations (as may be determined using method
400		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
401		* result in exceptions or errors, possibly including {@code
402		* ClassCastException}.
#	Line 526 | Line 414 | public abstract class ForkJoinTask<V> im
414		/**
415		* Forks the given tasks, returning when {@code isDone} holds for
416		* each task or an (unchecked) exception is encountered, in which
417	<	* case the exception is rethrown. If any task encounters an
418	<	* exception, others may be, but are not guaranteed to be,
419	<	* cancelled.  If more than one task encounters an exception, then
420	<	* this method throws any one of these exceptions.  The individual
421	<	* status of each task may be checked using {@link #getException()}
422	<	* and related methods.
417	>	* case the exception is rethrown. If more than one task
418	>	* encounters an exception, then this method throws any one of
419	>	* these exceptions. If any task encounters an exception, others
420	>	* may be cancelled. However, the execution status of individual
421	>	* tasks is not guaranteed upon exceptional return. The status of
422	>	* each task may be obtained using {@link #getException()} and
423	>	* related methods to check if they have been cancelled, completed
424	>	* normally or exceptionally, or left unprocessed.
425		*
426		* <p>This method may be invoked only from within {@code
427	<	* ForkJoinTask} computations (as may be determined using method
427	>	* ForkJoinPool} computations (as may be determined using method
428		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
429		* result in exceptions or errors, possibly including {@code
430		* ClassCastException}.
#	Line 555 | Line 445 | public abstract class ForkJoinTask<V> im
445		t.fork();
446		else {
447		t.quietlyInvoke();
448	<	if (ex == null)
448	>	if (ex == null && t.status < NORMAL)
449		ex = t.getException();
450		}
451		}
#	Line 566 | Line 456 | public abstract class ForkJoinTask<V> im
456		t.cancel(false);
457		else {
458		t.quietlyJoin();
459	<	if (ex == null)
459	>	if (ex == null && t.status < NORMAL)
460		ex = t.getException();
461		}
462		}
#	Line 578 | Line 468 | public abstract class ForkJoinTask<V> im
468		/**
469		* Forks all tasks in the specified collection, returning when
470		* {@code isDone} holds for each task or an (unchecked) exception
471	<	* is encountered.  If any task encounters an exception, others
472	<	* may be, but are not guaranteed to be, cancelled.  If more than
473	<	* one task encounters an exception, then this method throws any
474	<	* one of these exceptions.  The individual status of each task
475	<	* may be checked using {@link #getException()} and related
476	<	* methods.  The behavior of this operation is undefined if the
477	<	* specified collection is modified while the operation is in
478	<	* progress.
471	>	* is encountered, in which case the exception is rethrown. If
472	>	* more than one task encounters an exception, then this method
473	>	* throws any one of these exceptions. If any task encounters an
474	>	* exception, others may be cancelled. However, the execution
475	>	* status of individual tasks is not guaranteed upon exceptional
476	>	* return. The status of each task may be obtained using {@link
477	>	* #getException()} and related methods to check if they have been
478	>	* cancelled, completed normally or exceptionally, or left
479	>	* unprocessed.
480		*
481		* <p>This method may be invoked only from within {@code
482	<	* ForkJoinTask} computations (as may be determined using method
482	>	* ForkJoinPool} computations (as may be determined using method
483		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
484		* result in exceptions or errors, possibly including {@code
485		* ClassCastException}.
#	Line 617 | Line 508 | public abstract class ForkJoinTask<V> im
508		t.fork();
509		else {
510		t.quietlyInvoke();
511	<	if (ex == null)
511	>	if (ex == null && t.status < NORMAL)
512		ex = t.getException();
513		}
514		}
#	Line 628 | Line 519 | public abstract class ForkJoinTask<V> im
519		t.cancel(false);
520		else {
521		t.quietlyJoin();
522	<	if (ex == null)
522	>	if (ex == null && t.status < NORMAL)
523		ex = t.getException();
524		}
525		}
#	Line 640 | Line 531 | public abstract class ForkJoinTask<V> im
531
532		/**
533		* Attempts to cancel execution of this task. This attempt will
534	<	* fail if the task has already completed, has already been
535	<	* cancelled, or could not be cancelled for some other reason. If
536	<	* successful, and this task has not started when cancel is
537	<	* called, execution of this task is suppressed, {@link
538	<	* #isCancelled} will report true, and {@link #join} will result
539	<	* in a {@code CancellationException} being thrown.
534	>	* fail if the task has already completed or could not be
535	>	* cancelled for some other reason. If successful, and this task
536	>	* has not started when {@code cancel} is called, execution of
537	>	* this task is suppressed. After this method returns
538	>	* successfully, unless there is an intervening call to {@link
539	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
540	>	* {@link #isDone}, and {@code cancel} will return {@code true}
541	>	* and calls to {@link #join} and related methods will result in
542	>	* {@code CancellationException}.
543		*
544		* <p>This method may be overridden in subclasses, but if so, must
545	<	* still ensure that these minimal properties hold. In particular,
546	<	* the {@code cancel} method itself must not throw exceptions.
545	>	* still ensure that these properties hold. In particular, the
546	>	* {@code cancel} method itself must not throw exceptions.
547		*
548		* <p>This method is designed to be invoked by <em>other</em>
549		* tasks. To terminate the current task, you can just return or
550		* throw an unchecked exception from its computation method, or
551		* invoke {@link #completeExceptionally}.
552		*
553	<	* @param mayInterruptIfRunning this value is ignored in the
554	<	* default implementation because tasks are not
555	<	* cancelled via interruption
553	>	* @param mayInterruptIfRunning this value has no effect in the
554	>	* default implementation because interrupts are not used to
555	>	* control cancellation.
556		*
557		* @return {@code true} if this task is now cancelled
558		*/
559		public boolean cancel(boolean mayInterruptIfRunning) {
560		setCompletion(CANCELLED);
561	<	return (status & COMPLETION_MASK) == CANCELLED;
561	>	return status == CANCELLED;
562		}
563
564		/**
565	<	* Cancels, ignoring any exceptions it throws. Used during worker
566	<	* and pool shutdown.
565	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
566	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
567	>	* exceptions, but if it does anyway, we have no recourse during
568	>	* shutdown, so guard against this case.
569		*/
570		final void cancelIgnoringExceptions() {
571		try {
#	Line 679 | Line 575 | public abstract class ForkJoinTask<V> im
575		}
576
577		/**
578	<	* Cancels ignoring exceptions if worker is terminating
578	>	* Cancels if current thread is a terminating worker thread,
579	>	* ignoring any exceptions thrown by cancel.
580		*/
581	<	private void cancelIfTerminating() {
581	>	final void cancelIfTerminating() {
582		Thread t = Thread.currentThread();
583		if ((t instanceof ForkJoinWorkerThread) &&
584		((ForkJoinWorkerThread) t).isTerminating()) {
#	Line 697 | Line 594 | public abstract class ForkJoinTask<V> im
594		}
595
596		public final boolean isCancelled() {
597	<	return (status & COMPLETION_MASK) == CANCELLED;
597	>	return status == CANCELLED;
598		}
599
600		/**
#	Line 706 | Line 603 | public abstract class ForkJoinTask<V> im
603		* @return {@code true} if this task threw an exception or was cancelled
604		*/
605		public final boolean isCompletedAbnormally() {
606	<	return (status & COMPLETION_MASK) < NORMAL;
606	>	return status < NORMAL;
607		}
608
609		/**
#	Line 717 | Line 614 | public abstract class ForkJoinTask<V> im
614		* exception and was not cancelled
615		*/
616		public final boolean isCompletedNormally() {
617	<	return (status & COMPLETION_MASK) == NORMAL;
617	>	return status == NORMAL;
618		}
619
620		/**
#	Line 728 | Line 625 | public abstract class ForkJoinTask<V> im
625		* @return the exception, or {@code null} if none
626		*/
627		public final Throwable getException() {
628	<	int s = status & COMPLETION_MASK;
628	>	int s = status;
629		return ((s >= NORMAL)    ? null :
630		(s == CANCELLED) ? new CancellationException() :
631		exceptionMap.get(this));
#	Line 749 | Line 646 | public abstract class ForkJoinTask<V> im
646		* thrown will be a {@code RuntimeException} with cause {@code ex}.
647		*/
648		public void completeExceptionally(Throwable ex) {
649	<	setDoneExceptionally((ex instanceof RuntimeException) ||
650	<	(ex instanceof Error) ? ex :
651	<	new RuntimeException(ex));
649	>	setExceptionalCompletion((ex instanceof RuntimeException) ||
650	>	(ex instanceof Error) ? ex :
651	>	new RuntimeException(ex));
652		}
653
654		/**
655		* Completes this task, and if not already aborted or cancelled,
656	<	* returning a {@code null} result upon {@code join} and related
657	<	* operations. This method may be used to provide results for
658	<	* asynchronous tasks, or to provide alternative handling for
659	<	* tasks that would not otherwise complete normally. Its use in
660	<	* other situations is discouraged. This method is
661	<	* overridable, but overridden versions must invoke {@code super}
662	<	* implementation to maintain guarantees.
656	>	* returning the given value as the result of subsequent
657	>	* invocations of {@code join} and related operations. This method
658	>	* may be used to provide results for asynchronous tasks, or to
659	>	* provide alternative handling for tasks that would not otherwise
660	>	* complete normally. Its use in other situations is
661	>	* discouraged. This method is overridable, but overridden
662	>	* versions must invoke {@code super} implementation to maintain
663	>	* guarantees.
664		*
665		* @param value the result value for this task
666		*/
#	Line 770 | Line 668 | public abstract class ForkJoinTask<V> im
668		try {
669		setRawResult(value);
670		} catch (Throwable rex) {
671	<	setDoneExceptionally(rex);
671	>	setExceptionalCompletion(rex);
672		return;
673		}
674		setCompletion(NORMAL);
675		}
676
779	–	public final V get() throws InterruptedException, ExecutionException {
780	–	quietlyJoin();
781	–	return reportFutureResult();
782	–	}
783	–
784	–	public final V get(long timeout, TimeUnit unit)
785	–	throws InterruptedException, ExecutionException, TimeoutException {
786	–	long nanos = unit.toNanos(timeout);
787	–	Thread t = Thread.currentThread();
788	–	if (t instanceof ForkJoinWorkerThread) {
789	–	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
790	–	if (!w.unpushTask(this) || !tryExec())
791	–	timedAwaitDone(w, nanos);
792	–	}
793	–	else
794	–	externalTimedAwaitDone(nanos);
795	–	return reportTimedFutureResult();
796	–	}
797	–
677		/**
678	<	* Possibly executes other tasks until this task {@link #isDone is
679	<	* done}, then returns the result of the computation.  This method
801	<	* may be more efficient than {@code join}, but is only applicable
802	<	* when there are no potential dependencies between continuation
803	<	* of the current task and that of any other task that might be
804	<	* executed while helping. (This usually holds for pure
805	<	* divide-and-conquer tasks).
806	<	*
807	<	* <p>This method may be invoked only from within {@code
808	<	* ForkJoinTask} computations (as may be determined using method
809	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
810	<	* result in exceptions or errors, possibly including {@code
811	<	* ClassCastException}.
678	>	* Waits if necessary for the computation to complete, and then
679	>	* retrieves its result.
680		*
681		* @return the computed result
682	+	* @throws CancellationException if the computation was cancelled
683	+	* @throws ExecutionException if the computation threw an
684	+	* exception
685	+	* @throws InterruptedException if the current thread is not a
686	+	* member of a ForkJoinPool and was interrupted while waiting
687		*/
688	<	public final V helpJoin() {
689	<	quietlyHelpJoin();
690	<	return reportResult();
688	>	public final V get() throws InterruptedException, ExecutionException {
689	>	Thread t = Thread.currentThread();
690	>	if (t instanceof ForkJoinWorkerThread)
691	>	quietlyJoin();
692	>	else
693	>	externalInterruptibleAwaitDone(false, 0L);
694	>	int s = status;
695	>	if (s != NORMAL) {
696	>	Throwable ex;
697	>	if (s == CANCELLED)
698	>	throw new CancellationException();
699	>	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
700	>	throw new ExecutionException(ex);
701	>	}
702	>	return getRawResult();
703		}
704
705		/**
706	<	* Possibly executes other tasks until this task {@link #isDone is
707	<	* done}.  This method may be useful when processing collections
823	<	* of tasks when some have been cancelled or otherwise known to
824	<	* have aborted.
706	>	* Waits if necessary for at most the given time for the computation
707	>	* to complete, and then retrieves its result, if available.
708		*
709	<	* <p>This method may be invoked only from within {@code
710	<	* ForkJoinTask} computations (as may be determined using method
711	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
712	<	* result in exceptions or errors, possibly including {@code
713	<	* ClassCastException}.
709	>	* @param timeout the maximum time to wait
710	>	* @param unit the time unit of the timeout argument
711	>	* @return the computed result
712	>	* @throws CancellationException if the computation was cancelled
713	>	* @throws ExecutionException if the computation threw an
714	>	* exception
715	>	* @throws InterruptedException if the current thread is not a
716	>	* member of a ForkJoinPool and was interrupted while waiting
717	>	* @throws TimeoutException if the wait timed out
718		*/
719	<	public final void quietlyHelpJoin() {
720	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
721	<	if (!w.unpushTask(this) || !tryExec()) {
722	<	for (;;) {
723	<	ForkJoinTask<?> t;
724	<	if (status < 0)
725	<	return;
726	<	else if ((t = w.scanWhileJoining(this)) != null)
727	<	t.tryExec();
728	<	else if (status < 0)
729	<	return;
730	<	else if (w.pool.preBlockHelpingJoin(this)) {
731	<	while (status >= 0) { // variant of awaitDone
732	<	try {
733	<	synchronized(this) {
734	<	if (status >= 0)
848	<	wait();
849	<	else {
850	<	notifyAll();
851	<	break;
852	<	}
853	<	}
854	<	} catch (InterruptedException ie) {
855	<	cancelIfTerminating();
856	<	}
857	<	}
858	<	return;
859	<	}
860	<	}
719	>	public final V get(long timeout, TimeUnit unit)
720	>	throws InterruptedException, ExecutionException, TimeoutException {
721	>	long nanos = unit.toNanos(timeout);
722	>	Thread t = Thread.currentThread();
723	>	if (t instanceof ForkJoinWorkerThread)
724	>	((ForkJoinWorkerThread)t).joinTask(this, true, nanos);
725	>	else
726	>	externalInterruptibleAwaitDone(true, nanos);
727	>	int s = status;
728	>	if (s != NORMAL) {
729	>	Throwable ex;
730	>	if (s == CANCELLED)
731	>	throw new CancellationException();
732	>	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
733	>	throw new ExecutionException(ex);
734	>	throw new TimeoutException();
735		}
736	+	return getRawResult();
737		}
738
739		/**
740	<	* Joins this task, without returning its result or throwing an
740	>	* Joins this task, without returning its result or throwing its
741		* exception. This method may be useful when processing
742		* collections of tasks when some have been cancelled or otherwise
743		* known to have aborted.
744		*/
745		public final void quietlyJoin() {
746	<	Thread t = Thread.currentThread();
747	<	if (t instanceof ForkJoinWorkerThread) {
746	>	Thread t;
747	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
748		ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
749	<	if (!w.unpushTask(this) || !tryExec())
750	<	awaitDone(w);
749	>	if (status >= 0) {
750	>	if (w.unpushTask(this)) {
751	>	boolean completed;
752	>	try {
753	>	completed = exec();
754	>	} catch (Throwable rex) {
755	>	setExceptionalCompletion(rex);
756	>	return;
757	>	}
758	>	if (completed) {
759	>	setCompletion(NORMAL);
760	>	return;
761	>	}
762	>	}
763	>	w.joinTask(this, false, 0L);
764	>	}
765		}
766		else
767		externalAwaitDone();
#	Line 880 | Line 769 | public abstract class ForkJoinTask<V> im
769
770		/**
771		* Commences performing this task and awaits its completion if
772	<	* necessary, without returning its result or throwing an
773	<	* exception. This method may be useful when processing
885	<	* collections of tasks when some have been cancelled or otherwise
886	<	* known to have aborted.
772	>	* necessary, without returning its result or throwing its
773	>	* exception.
774		*/
775		public final void quietlyInvoke() {
776	<	if (!tryExec())
777	<	quietlyJoin();
776	>	if (status >= 0) {
777	>	boolean completed;
778	>	try {
779	>	completed = exec();
780	>	} catch (Throwable rex) {
781	>	setExceptionalCompletion(rex);
782	>	return;
783	>	}
784	>	if (completed)
785	>	setCompletion(NORMAL);
786	>	else
787	>	quietlyJoin();
788	>	}
789		}
790
791		/**
#	Line 898 | Line 796 | public abstract class ForkJoinTask<V> im
796		* processed.
797		*
798		* <p>This method may be invoked only from within {@code
799	<	* ForkJoinTask} computations (as may be determined using method
799	>	* ForkJoinPool} computations (as may be determined using method
800		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
801		* result in exceptions or errors, possibly including {@code
802		* ClassCastException}.
#	Line 917 | Line 815 | public abstract class ForkJoinTask<V> im
815		* under any other usage conditions are not guaranteed.
816		* This method may be useful when executing
817		* pre-constructed trees of subtasks in loops.
818	+	*
819	+	* <p>Upon completion of this method, {@code isDone()} reports
820	+	* {@code false}, and {@code getException()} reports {@code
821	+	* null}. However, the value returned by {@code getRawResult} is
822	+	* unaffected. To clear this value, you can invoke {@code
823	+	* setRawResult(null)}.
824		*/
825		public void reinitialize() {
826	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
826	>	if (status == EXCEPTIONAL)
827		exceptionMap.remove(this);
828		status = 0;
829		}
#	Line 957 | Line 861 | public abstract class ForkJoinTask<V> im
861		* were not, stolen.
862		*
863		* <p>This method may be invoked only from within {@code
864	<	* ForkJoinTask} computations (as may be determined using method
864	>	* ForkJoinPool} computations (as may be determined using method
865		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
866		* result in exceptions or errors, possibly including {@code
867		* ClassCastException}.
#	Line 976 | Line 880 | public abstract class ForkJoinTask<V> im
880		* fork other tasks.
881		*
882		* <p>This method may be invoked only from within {@code
883	<	* ForkJoinTask} computations (as may be determined using method
883	>	* ForkJoinPool} computations (as may be determined using method
884		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
885		* result in exceptions or errors, possibly including {@code
886		* ClassCastException}.
#	Line 999 | Line 903 | public abstract class ForkJoinTask<V> im
903		* exceeded.
904		*
905		* <p>This method may be invoked only from within {@code
906	<	* ForkJoinTask} computations (as may be determined using method
906	>	* ForkJoinPool} 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}.
#	Line 1057 | Line 961 | public abstract class ForkJoinTask<V> im
961		* otherwise.
962		*
963		* <p>This method may be invoked only from within {@code
964	<	* ForkJoinTask} computations (as may be determined using method
964	>	* ForkJoinPool} computations (as may be determined using method
965		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
966		* result in exceptions or errors, possibly including {@code
967		* ClassCastException}.
#	Line 1076 | Line 980 | public abstract class ForkJoinTask<V> im
980		* be useful otherwise.
981		*
982		* <p>This method may be invoked only from within {@code
983	<	* ForkJoinTask} computations (as may be determined using method
983	>	* ForkJoinPool} computations (as may be determined using method
984		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
985		* result in exceptions or errors, possibly including {@code
986		* ClassCastException}.
#	Line 1099 | Line 1003 | public abstract class ForkJoinTask<V> im
1003		* otherwise.
1004		*
1005		* <p>This method may be invoked only from within {@code
1006	<	* ForkJoinTask} computations (as may be determined using method
1006	>	* ForkJoinPool} computations (as may be determined using method
1007		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1008		* result in exceptions or errors, possibly including {@code
1009		* ClassCastException}.
#	Line 1209 | Line 1113 | public abstract class ForkJoinTask<V> im
1113		private static final long serialVersionUID = -7721805057305804111L;
1114
1115		/**
1116	<	* Saves the state to a stream.
1116	>	* Saves the state to a stream (that is, serializes it).
1117		*
1118		* @serialData the current run status and the exception thrown
1119		* during execution, or {@code null} if none
#	Line 1222 | Line 1126 | public abstract class ForkJoinTask<V> im
1126		}
1127
1128		/**
1129	<	* Reconstitutes the instance from a stream.
1129	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1130		*
1131		* @param s the stream
1132		*/
1133		private void readObject(java.io.ObjectInputStream s)
1134		throws java.io.IOException, ClassNotFoundException {
1135		s.defaultReadObject();
1232	–	status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
1233	–	status |= EXTERNAL_SIGNAL; // conservatively set external signal
1136		Object ex = s.readObject();
1137		if (ex != null)
1138	<	setDoneExceptionally((Throwable) ex);
1138	>	setExceptionalCompletion((Throwable) ex);
1139		}
1140
1141		// Unsafe mechanics

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