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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.46 by dl, Mon Apr 5 15:52:26 2010 UTC vs.
Revision 1.72 by dl, Wed Nov 24 10:50:38 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
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
237	>	* Blocks a worker thread until completed or timed out.  Called
238	>	* only by pool.
239		*/
240	<	private void awaitDone(ForkJoinWorkerThread w) {
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();
248	<	else { // help release; also helps avoid lock-biasing
249	<	notifyAll();
250	<	break;
300	<	}
301	<	}
302	<	} catch (InterruptedException ie) {
303	<	cancelIfTerminating();
240	>	final void internalAwaitDone(long millis, int nanos) {
241	>	int s = status;
242	>	if ((s == 0 &&
243	>	UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL)) ||
244	>	s > 0)  {
245	>	try {     // the odd construction reduces lock bias effects
246	>	synchronized (this) {
247	>	if (status > 0)
248	>	wait(millis, nanos);
249	>	else
250	>	notifyAll();
251		}
252	+	} catch (InterruptedException ie) {
253	+	cancelIfTerminating();
254		}
255		}
256		}
257
258		/**
259	<	* Blocks a non-ForkJoin thread until this task is done.
259	>	* Blocks a non-worker-thread until completion.
260		*/
261		private void externalAwaitDone() {
262	<	if (requestExternalSignal() >= 0) {
262	>	if (status >= 0) {
263		boolean interrupted = false;
264	<	while (status >= 0) {
265	<	try {
266	<	synchronized(this) {
267	<	if (status >= 0)
268	<	wait();
269	<	else {
270	<	notifyAll();
271	<	break;
264	>	synchronized(this) {
265	>	for (;;) {
266	>	int s = status;
267	>	if (s == 0)
268	>	UNSAFE.compareAndSwapInt(this, statusOffset,
269	>	0, SIGNAL);
270	>	else if (s < 0) {
271	>	notifyAll();
272	>	break;
273	>	}
274	>	else {
275	>	try {
276	>	wait();
277	>	} catch (InterruptedException ie) {
278	>	interrupted = true;
279		}
280		}
325	–	} catch (InterruptedException ie) {
326	–	interrupted = true;
281		}
282		}
283		if (interrupted)
#	Line 332 | Line 286 | public abstract class ForkJoinTask<V> im
286		}
287
288		/**
289	<	* Blocks a worker until this task is done or timeout elapses
289	>	* Blocks a non-worker-thread until completion or interruption or timeout.
290		*/
291	<	private void timedAwaitDone(ForkJoinWorkerThread w, long nanos) {
291	>	private void externalInterruptibleAwaitDone(boolean timed, long nanos)
292	>	throws InterruptedException {
293	>	if (Thread.interrupted())
294	>	throw new InterruptedException();
295		if (status >= 0) {
296	<	long startTime = System.nanoTime();
297	<	ForkJoinPool pool = w.pool;
298	<	pool.preJoin(this);
299	<	while (status >= 0) {
300	<	long nt = nanos - (System.nanoTime() - startTime);
301	<	if (nt > 0) {
302	<	long ms = nt / 1000000;
303	<	int ns = (int) (nt % 1000000);
304	<	try {
305	<	synchronized(this) { if (status >= 0) wait(ms, ns); }
306	<	} catch (InterruptedException ie) {
350	<	cancelIfTerminating();
351	<	}
352	<	}
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	<	}
296	>	long startTime = timed ? System.nanoTime() : 0L;
297	>	synchronized(this) {
298	>	for (;;) {
299	>	long nt;
300	>	int s = status;
301	>	if (s == 0)
302	>	UNSAFE.compareAndSwapInt(this, statusOffset,
303	>	0, SIGNAL);
304	>	else if (s < 0) {
305	>	notifyAll();
306	>	break;
307		}
308	<	break;
309	<	}
310	<	}
311	<	}
312	<	}
313	<
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;
308	>	else if (!timed)
309	>	wait();
310	>	else if ((nt = nanos - (System.nanoTime()-startTime)) > 0L)
311	>	wait(nt / 1000000, (int)(nt % 1000000));
312	>	else
313	>	break;
314		}
315		}
388	–	if (interrupted)
389	–	Thread.currentThread().interrupt();
390	–	}
391	–	}
392	–
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);
316		}
406	–	return getRawResult();
317		}
318
319		/**
320	<	* Returns result or throws exception using j.u.c.Future conventions.
321	<	* Only call when {@code isDone} known to be true or thread known
322	<	* to be interrupted.
320	>	* Unless done, calls exec and records status if completed, but
321	>	* doesn't wait for completion otherwise. Primary execution method
322	>	* for ForkJoinWorkerThread.
323		*/
324	<	private V reportFutureResult()
325	<	throws InterruptedException, ExecutionException {
326	<	if (Thread.interrupted())
327	<	throw new InterruptedException();
328	<	int s = status & COMPLETION_MASK;
329	<	if (s < NORMAL) {
330	<	Throwable ex;
421	<	if (s == CANCELLED)
422	<	throw new CancellationException();
423	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
424	<	throw new ExecutionException(ex);
324	>	final void quietlyExec() {
325	>	try {
326	>	if (status < 0 || !exec())
327	>	return;
328	>	} catch (Throwable rex) {
329	>	setExceptionalCompletion(rex);
330	>	return;
331		}
332	<	return getRawResult();
427	<	}
428	<
429	<	/**
430	<	* Returns result or throws exception using j.u.c.Future conventions
431	<	* with timeouts.
432	<	*/
433	<	private V reportTimedFutureResult()
434	<	throws InterruptedException, ExecutionException, TimeoutException {
435	<	if (Thread.interrupted())
436	<	throw new InterruptedException();
437	<	Throwable ex;
438	<	int s = status & COMPLETION_MASK;
439	<	if (s == NORMAL)
440	<	return getRawResult();
441	<	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();
332	>	setCompletion(NORMAL); // must be outside try block
333		}
334
335		// public methods
#	Line 459 | Line 345 | public abstract class ForkJoinTask<V> im
345		* #isDone} returning {@code true}.
346		*
347		* <p>This method may be invoked only from within {@code
348	<	* ForkJoinTask} computations (as may be determined using method
348	>	* ForkJoinPool} computations (as may be determined using method
349		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
350		* result in exceptions or errors, possibly including {@code
351		* ClassCastException}.
#	Line 473 | Line 359 | public abstract class ForkJoinTask<V> im
359		}
360
361		/**
362	<	* Returns the result of the computation when it {@link #isDone is done}.
363	<	* This method differs from {@link #get()} in that
362	>	* Returns the result of the computation when it {@link #isDone is
363	>	* done}.  This method differs from {@link #get()} in that
364		* abnormal completion results in {@code RuntimeException} or
365	<	* {@code Error}, not {@code ExecutionException}.
365	>	* {@code Error}, not {@code ExecutionException}, and that
366	>	* interrupts of the calling thread do <em>not</em> cause the
367	>	* method to abruptly return by throwing {@code
368	>	* InterruptedException}.
369		*
370		* @return the computed result
371		*/
372		public final V join() {
373		quietlyJoin();
374	<	return reportResult();
374	>	Throwable ex;
375	>	if (status < NORMAL && (ex = getException()) != null)
376	>	UNSAFE.throwException(ex);
377	>	return getRawResult();
378		}
379
380		/**
381		* Commences performing this task, awaits its completion if
382	<	* necessary, and return its result, or throws an (unchecked)
383	<	* exception if the underlying computation did so.
382	>	* necessary, and returns its result, or throws an (unchecked)
383	>	* {@code RuntimeException} or {@code Error} if the underlying
384	>	* computation did so.
385		*
386		* @return the computed result
387		*/
388		public final V invoke() {
389	<	if (!tryExec())
390	<	quietlyJoin();
391	<	return reportResult();
389	>	quietlyInvoke();
390	>	Throwable ex;
391	>	if (status < NORMAL && (ex = getException()) != null)
392	>	UNSAFE.throwException(ex);
393	>	return getRawResult();
394		}
395
396		/**
397		* Forks the given tasks, returning when {@code isDone} holds for
398		* each task or an (unchecked) exception is encountered, in which
399	<	* case the exception is rethrown.  If either task encounters an
400	<	* exception, the other one may be, but is not guaranteed to be,
401	<	* cancelled.  If both tasks throw an exception, then this method
402	<	* throws one of them.  The individual status of each task may be
403	<	* checked using {@link #getException()} and related methods.
399	>	* case the exception is rethrown. If more than one task
400	>	* encounters an exception, then this method throws any one of
401	>	* these exceptions. If any task encounters an exception, the
402	>	* other may be cancelled. However, the execution status of
403	>	* individual tasks is not guaranteed upon exceptional return. The
404	>	* status of each task may be obtained using {@link
405	>	* #getException()} and related methods to check if they have been
406	>	* cancelled, completed normally or exceptionally, or left
407	>	* unprocessed.
408		*
409		* <p>This method may be invoked only from within {@code
410	<	* ForkJoinTask} computations (as may be determined using method
410	>	* ForkJoinPool} computations (as may be determined using method
411		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
412		* result in exceptions or errors, possibly including {@code
413		* ClassCastException}.
#	Line 526 | Line 425 | public abstract class ForkJoinTask<V> im
425		/**
426		* Forks the given tasks, returning when {@code isDone} holds for
427		* each task or an (unchecked) exception is encountered, in which
428	<	* case the exception is rethrown. If any task encounters an
429	<	* exception, others may be, but are not guaranteed to be,
430	<	* cancelled.  If more than one task encounters an exception, then
431	<	* this method throws any one of these exceptions.  The individual
432	<	* status of each task may be checked using {@link #getException()}
433	<	* and related methods.
428	>	* case the exception is rethrown. If more than one task
429	>	* encounters an exception, then this method throws any one of
430	>	* these exceptions. If any task encounters an exception, others
431	>	* may be cancelled. However, the execution status of individual
432	>	* tasks is not guaranteed upon exceptional return. The status of
433	>	* each task may be obtained using {@link #getException()} and
434	>	* related methods to check if they have been cancelled, completed
435	>	* normally or exceptionally, or left unprocessed.
436		*
437		* <p>This method may be invoked only from within {@code
438	<	* ForkJoinTask} computations (as may be determined using method
438	>	* ForkJoinPool} computations (as may be determined using method
439		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
440		* result in exceptions or errors, possibly including {@code
441		* ClassCastException}.
#	Line 555 | Line 456 | public abstract class ForkJoinTask<V> im
456		t.fork();
457		else {
458		t.quietlyInvoke();
459	<	if (ex == null)
459	>	if (ex == null && t.status < NORMAL)
460		ex = t.getException();
461		}
462		}
#	Line 566 | Line 467 | public abstract class ForkJoinTask<V> im
467		t.cancel(false);
468		else {
469		t.quietlyJoin();
470	<	if (ex == null)
470	>	if (ex == null && t.status < NORMAL)
471		ex = t.getException();
472		}
473		}
#	Line 578 | Line 479 | public abstract class ForkJoinTask<V> im
479		/**
480		* Forks all tasks in the specified collection, returning when
481		* {@code isDone} holds for each task or an (unchecked) exception
482	<	* is encountered.  If any task encounters an exception, others
483	<	* may be, but are not guaranteed to be, cancelled.  If more than
484	<	* one task encounters an exception, then this method throws any
485	<	* one of these exceptions.  The individual status of each task
486	<	* may be checked using {@link #getException()} and related
487	<	* methods.  The behavior of this operation is undefined if the
488	<	* specified collection is modified while the operation is in
489	<	* progress.
482	>	* is encountered, in which case the exception is rethrown. If
483	>	* more than one task encounters an exception, then this method
484	>	* throws any one of these exceptions. If any task encounters an
485	>	* exception, others may be cancelled. However, the execution
486	>	* status of individual tasks is not guaranteed upon exceptional
487	>	* return. The status of each task may be obtained using {@link
488	>	* #getException()} and related methods to check if they have been
489	>	* cancelled, completed normally or exceptionally, or left
490	>	* unprocessed.
491		*
492		* <p>This method may be invoked only from within {@code
493	<	* ForkJoinTask} computations (as may be determined using method
493	>	* ForkJoinPool} computations (as may be determined using method
494		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
495		* result in exceptions or errors, possibly including {@code
496		* ClassCastException}.
#	Line 617 | Line 519 | public abstract class ForkJoinTask<V> im
519		t.fork();
520		else {
521		t.quietlyInvoke();
522	<	if (ex == null)
522	>	if (ex == null && t.status < NORMAL)
523		ex = t.getException();
524		}
525		}
#	Line 628 | Line 530 | public abstract class ForkJoinTask<V> im
530		t.cancel(false);
531		else {
532		t.quietlyJoin();
533	<	if (ex == null)
533	>	if (ex == null && t.status < NORMAL)
534		ex = t.getException();
535		}
536		}
#	Line 640 | Line 542 | public abstract class ForkJoinTask<V> im
542
543		/**
544		* Attempts to cancel execution of this task. This attempt will
545	<	* fail if the task has already completed, has already been
546	<	* cancelled, or could not be cancelled for some other reason. If
547	<	* successful, and this task has not started when cancel is
548	<	* called, execution of this task is suppressed, {@link
549	<	* #isCancelled} will report true, and {@link #join} will result
550	<	* in a {@code CancellationException} being thrown.
545	>	* fail if the task has already completed or could not be
546	>	* cancelled for some other reason. If successful, and this task
547	>	* has not started when {@code cancel} is called, execution of
548	>	* this task is suppressed. After this method returns
549	>	* successfully, unless there is an intervening call to {@link
550	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
551	>	* {@link #isDone}, and {@code cancel} will return {@code true}
552	>	* and calls to {@link #join} and related methods will result in
553	>	* {@code CancellationException}.
554		*
555		* <p>This method may be overridden in subclasses, but if so, must
556	<	* still ensure that these minimal properties hold. In particular,
557	<	* the {@code cancel} method itself must not throw exceptions.
556	>	* still ensure that these properties hold. In particular, the
557	>	* {@code cancel} method itself must not throw exceptions.
558		*
559		* <p>This method is designed to be invoked by <em>other</em>
560		* tasks. To terminate the current task, you can just return or
561		* throw an unchecked exception from its computation method, or
562		* invoke {@link #completeExceptionally}.
563		*
564	<	* @param mayInterruptIfRunning this value is ignored in the
565	<	* default implementation because tasks are not
566	<	* cancelled via interruption
564	>	* @param mayInterruptIfRunning this value has no effect in the
565	>	* default implementation because interrupts are not used to
566	>	* control cancellation.
567		*
568		* @return {@code true} if this task is now cancelled
569		*/
570		public boolean cancel(boolean mayInterruptIfRunning) {
571		setCompletion(CANCELLED);
572	<	return (status & COMPLETION_MASK) == CANCELLED;
572	>	return status == CANCELLED;
573		}
574
575		/**
576	<	* Cancels, ignoring any exceptions it throws. Used during worker
577	<	* and pool shutdown.
576	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
577	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
578	>	* exceptions, but if it does anyway, we have no recourse during
579	>	* shutdown, so guard against this case.
580		*/
581		final void cancelIgnoringExceptions() {
582		try {
#	Line 679 | Line 586 | public abstract class ForkJoinTask<V> im
586		}
587
588		/**
589	<	* Cancels ignoring exceptions if worker is terminating
589	>	* Cancels if current thread is a terminating worker thread,
590	>	* ignoring any exceptions thrown by cancel.
591		*/
592	<	private void cancelIfTerminating() {
592	>	final void cancelIfTerminating() {
593		Thread t = Thread.currentThread();
594		if ((t instanceof ForkJoinWorkerThread) &&
595	<	((ForkJoinWorkerThread) t).isTerminating()) {
595	>	((ForkJoinWorkerThread) t).isTerminating()) {
596		try {
597		cancel(false);
598		} catch (Throwable ignore) {
#	Line 697 | Line 605 | public abstract class ForkJoinTask<V> im
605		}
606
607		public final boolean isCancelled() {
608	<	return (status & COMPLETION_MASK) == CANCELLED;
608	>	return status == CANCELLED;
609		}
610
611		/**
#	Line 706 | Line 614 | public abstract class ForkJoinTask<V> im
614		* @return {@code true} if this task threw an exception or was cancelled
615		*/
616		public final boolean isCompletedAbnormally() {
617	<	return (status & COMPLETION_MASK) < NORMAL;
617	>	return status < NORMAL;
618		}
619
620		/**
#	Line 717 | Line 625 | public abstract class ForkJoinTask<V> im
625		* exception and was not cancelled
626		*/
627		public final boolean isCompletedNormally() {
628	<	return (status & COMPLETION_MASK) == NORMAL;
628	>	return status == NORMAL;
629		}
630
631		/**
#	Line 728 | Line 636 | public abstract class ForkJoinTask<V> im
636		* @return the exception, or {@code null} if none
637		*/
638		public final Throwable getException() {
639	<	int s = status & COMPLETION_MASK;
639	>	int s = status;
640		return ((s >= NORMAL)    ? null :
641		(s == CANCELLED) ? new CancellationException() :
642		exceptionMap.get(this));
#	Line 749 | Line 657 | public abstract class ForkJoinTask<V> im
657		* thrown will be a {@code RuntimeException} with cause {@code ex}.
658		*/
659		public void completeExceptionally(Throwable ex) {
660	<	setDoneExceptionally((ex instanceof RuntimeException) ||
661	<	(ex instanceof Error) ? ex :
662	<	new RuntimeException(ex));
660	>	setExceptionalCompletion((ex instanceof RuntimeException) ||
661	>	(ex instanceof Error) ? ex :
662	>	new RuntimeException(ex));
663		}
664
665		/**
666		* Completes this task, and if not already aborted or cancelled,
667	<	* returning a {@code null} result upon {@code join} and related
668	<	* operations. This method may be used to provide results for
669	<	* asynchronous tasks, or to provide alternative handling for
670	<	* tasks that would not otherwise complete normally. Its use in
671	<	* other situations is discouraged. This method is
672	<	* overridable, but overridden versions must invoke {@code super}
673	<	* implementation to maintain guarantees.
667	>	* returning the given value as the result of subsequent
668	>	* invocations of {@code join} and related operations. This method
669	>	* may be used to provide results for asynchronous tasks, or to
670	>	* provide alternative handling for tasks that would not otherwise
671	>	* complete normally. Its use in other situations is
672	>	* discouraged. This method is overridable, but overridden
673	>	* versions must invoke {@code super} implementation to maintain
674	>	* guarantees.
675		*
676		* @param value the result value for this task
677		*/
#	Line 770 | Line 679 | public abstract class ForkJoinTask<V> im
679		try {
680		setRawResult(value);
681		} catch (Throwable rex) {
682	<	setDoneExceptionally(rex);
682	>	setExceptionalCompletion(rex);
683		return;
684		}
685		setCompletion(NORMAL);
686		}
687
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	–
688		/**
689	<	* Possibly executes other tasks until this task {@link #isDone is
690	<	* 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}.
689	>	* Waits if necessary for the computation to complete, and then
690	>	* retrieves its result.
691		*
692		* @return the computed result
693	+	* @throws CancellationException if the computation was cancelled
694	+	* @throws ExecutionException if the computation threw an
695	+	* exception
696	+	* @throws InterruptedException if the current thread is not a
697	+	* member of a ForkJoinPool and was interrupted while waiting
698		*/
699	<	public final V helpJoin() {
700	<	quietlyHelpJoin();
701	<	return reportResult();
699	>	public final V get() throws InterruptedException, ExecutionException {
700	>	Thread t = Thread.currentThread();
701	>	if (t instanceof ForkJoinWorkerThread)
702	>	quietlyJoin();
703	>	else
704	>	externalInterruptibleAwaitDone(false, 0L);
705	>	int s = status;
706	>	if (s != NORMAL) {
707	>	Throwable ex;
708	>	if (s == CANCELLED)
709	>	throw new CancellationException();
710	>	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
711	>	throw new ExecutionException(ex);
712	>	}
713	>	return getRawResult();
714		}
715
716		/**
717	<	* Possibly executes other tasks until this task {@link #isDone is
718	<	* done}.  This method may be useful when processing collections
823	<	* of tasks when some have been cancelled or otherwise known to
824	<	* have aborted.
717	>	* Waits if necessary for at most the given time for the computation
718	>	* to complete, and then retrieves its result, if available.
719		*
720	<	* <p>This method may be invoked only from within {@code
721	<	* ForkJoinTask} computations (as may be determined using method
722	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
723	<	* result in exceptions or errors, possibly including {@code
724	<	* ClassCastException}.
720	>	* @param timeout the maximum time to wait
721	>	* @param unit the time unit of the timeout argument
722	>	* @return the computed result
723	>	* @throws CancellationException if the computation was cancelled
724	>	* @throws ExecutionException if the computation threw an
725	>	* exception
726	>	* @throws InterruptedException if the current thread is not a
727	>	* member of a ForkJoinPool and was interrupted while waiting
728	>	* @throws TimeoutException if the wait timed out
729		*/
730	<	public final void quietlyHelpJoin() {
731	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
732	<	if (!w.unpushTask(this) || !tryExec()) {
733	<	while (status >= 0) {
734	<	ForkJoinTask<?> t = w.scanWhileJoining(this);
735	<	if (t == null) {
736	<	if (status >= 0)
737	<	awaitDone(w);
738	<	break;
739	<	}
740	<	t.tryExec();
741	<	}
730	>	public final V get(long timeout, TimeUnit unit)
731	>	throws InterruptedException, ExecutionException, TimeoutException {
732	>	long nanos = unit.toNanos(timeout);
733	>	Thread t = Thread.currentThread();
734	>	if (t instanceof ForkJoinWorkerThread)
735	>	((ForkJoinWorkerThread)t).joinTask(this, true, nanos);
736	>	else
737	>	externalInterruptibleAwaitDone(true, nanos);
738	>	int s = status;
739	>	if (s != NORMAL) {
740	>	Throwable ex;
741	>	if (s == CANCELLED)
742	>	throw new CancellationException();
743	>	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
744	>	throw new ExecutionException(ex);
745	>	throw new TimeoutException();
746		}
747	+	return getRawResult();
748		}
749
750		/**
751	<	* Joins this task, without returning its result or throwing an
751	>	* Joins this task, without returning its result or throwing its
752		* exception. This method may be useful when processing
753		* collections of tasks when some have been cancelled or otherwise
754		* known to have aborted.
755		*/
756		public final void quietlyJoin() {
757	<	Thread t = Thread.currentThread();
758	<	if (t instanceof ForkJoinWorkerThread) {
757	>	Thread t;
758	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
759		ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
760	<	if (!w.unpushTask(this) || !tryExec())
761	<	awaitDone(w);
760	>	if (status >= 0) {
761	>	if (w.unpushTask(this)) {
762	>	boolean completed;
763	>	try {
764	>	completed = exec();
765	>	} catch (Throwable rex) {
766	>	setExceptionalCompletion(rex);
767	>	return;
768	>	}
769	>	if (completed) {
770	>	setCompletion(NORMAL);
771	>	return;
772	>	}
773	>	}
774	>	w.joinTask(this, false, 0L);
775	>	}
776		}
777		else
778		externalAwaitDone();
#	Line 863 | Line 780 | public abstract class ForkJoinTask<V> im
780
781		/**
782		* Commences performing this task and awaits its completion if
783	<	* necessary, without returning its result or throwing an
784	<	* exception. This method may be useful when processing
868	<	* collections of tasks when some have been cancelled or otherwise
869	<	* known to have aborted.
783	>	* necessary, without returning its result or throwing its
784	>	* exception.
785		*/
786		public final void quietlyInvoke() {
787	<	if (!tryExec())
788	<	quietlyJoin();
787	>	if (status >= 0) {
788	>	boolean completed;
789	>	try {
790	>	completed = exec();
791	>	} catch (Throwable rex) {
792	>	setExceptionalCompletion(rex);
793	>	return;
794	>	}
795	>	if (completed)
796	>	setCompletion(NORMAL);
797	>	else
798	>	quietlyJoin();
799	>	}
800		}
801
802		/**
#	Line 881 | Line 807 | public abstract class ForkJoinTask<V> im
807		* processed.
808		*
809		* <p>This method may be invoked only from within {@code
810	<	* ForkJoinTask} computations (as may be determined using method
810	>	* ForkJoinPool} computations (as may be determined using method
811		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
812		* result in exceptions or errors, possibly including {@code
813		* ClassCastException}.
#	Line 900 | Line 826 | public abstract class ForkJoinTask<V> im
826		* under any other usage conditions are not guaranteed.
827		* This method may be useful when executing
828		* pre-constructed trees of subtasks in loops.
829	+	*
830	+	* <p>Upon completion of this method, {@code isDone()} reports
831	+	* {@code false}, and {@code getException()} reports {@code
832	+	* null}. However, the value returned by {@code getRawResult} is
833	+	* unaffected. To clear this value, you can invoke {@code
834	+	* setRawResult(null)}.
835		*/
836		public void reinitialize() {
837	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
837	>	if (status == EXCEPTIONAL)
838		exceptionMap.remove(this);
839		status = 0;
840		}
#	Line 921 | Line 853 | public abstract class ForkJoinTask<V> im
853		}
854
855		/**
856	<	* Returns {@code true} if the current thread is executing as a
857	<	* ForkJoinPool computation.
856	>	* Returns {@code true} if the current thread is a {@link
857	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
858		*
859	<	* @return {@code true} if the current thread is executing as a
860	<	* ForkJoinPool computation, or false otherwise
859	>	* @return {@code true} if the current thread is a {@link
860	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
861	>	* or {@code false} otherwise
862		*/
863		public static boolean inForkJoinPool() {
864		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 940 | Line 873 | public abstract class ForkJoinTask<V> im
873		* were not, stolen.
874		*
875		* <p>This method may be invoked only from within {@code
876	<	* ForkJoinTask} computations (as may be determined using method
876	>	* ForkJoinPool} computations (as may be determined using method
877		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
878		* result in exceptions or errors, possibly including {@code
879		* ClassCastException}.
#	Line 959 | Line 892 | public abstract class ForkJoinTask<V> im
892		* fork other tasks.
893		*
894		* <p>This method may be invoked only from within {@code
895	<	* ForkJoinTask} computations (as may be determined using method
895	>	* ForkJoinPool} computations (as may be determined using method
896		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
897		* result in exceptions or errors, possibly including {@code
898		* ClassCastException}.
#	Line 982 | Line 915 | public abstract class ForkJoinTask<V> im
915		* exceeded.
916		*
917		* <p>This method may be invoked only from within {@code
918	<	* ForkJoinTask} computations (as may be determined using method
918	>	* ForkJoinPool} computations (as may be determined using method
919		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
920		* result in exceptions or errors, possibly including {@code
921		* ClassCastException}.
#	Line 1040 | Line 973 | public abstract class ForkJoinTask<V> im
973		* otherwise.
974		*
975		* <p>This method may be invoked only from within {@code
976	<	* ForkJoinTask} computations (as may be determined using method
976	>	* ForkJoinPool} computations (as may be determined using method
977		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
978		* result in exceptions or errors, possibly including {@code
979		* ClassCastException}.
#	Line 1059 | Line 992 | public abstract class ForkJoinTask<V> im
992		* be useful otherwise.
993		*
994		* <p>This method may be invoked only from within {@code
995	<	* ForkJoinTask} computations (as may be determined using method
995	>	* ForkJoinPool} computations (as may be determined using method
996		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
997		* result in exceptions or errors, possibly including {@code
998		* ClassCastException}.
#	Line 1082 | Line 1015 | public abstract class ForkJoinTask<V> im
1015		* otherwise.
1016		*
1017		* <p>This method may be invoked only from within {@code
1018	<	* ForkJoinTask} computations (as may be determined using method
1018	>	* ForkJoinPool} computations (as may be determined using method
1019		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1020		* result in exceptions or errors, possibly including {@code
1021		* ClassCastException}.
#	Line 1192 | Line 1125 | public abstract class ForkJoinTask<V> im
1125		private static final long serialVersionUID = -7721805057305804111L;
1126
1127		/**
1128	<	* Saves the state to a stream.
1128	>	* Saves the state to a stream (that is, serializes it).
1129		*
1130		* @serialData the current run status and the exception thrown
1131		* during execution, or {@code null} if none
#	Line 1205 | Line 1138 | public abstract class ForkJoinTask<V> im
1138		}
1139
1140		/**
1141	<	* Reconstitutes the instance from a stream.
1141	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1142		*
1143		* @param s the stream
1144		*/
1145		private void readObject(java.io.ObjectInputStream s)
1146		throws java.io.IOException, ClassNotFoundException {
1147		s.defaultReadObject();
1215	–	status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
1216	–	status |= EXTERNAL_SIGNAL; // conservatively set external signal
1148		Object ex = s.readObject();
1149		if (ex != null)
1150	<	setDoneExceptionally((Throwable) ex);
1150	>	setExceptionalCompletion((Throwable) ex);
1151		}
1152
1153		// Unsafe mechanics

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