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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.45 by jsr166, Thu Oct 22 08:19:44 2009 UTC vs.
Revision 1.69 by dl, Mon Nov 22 12:24:34 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 125 | Line 140 | import java.util.WeakHashMap;
140		*
141		* <p>This class provides {@code adapt} methods for {@link Runnable}
142		* and {@link Callable}, that may be of use when mixing execution of
143	<	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks
144	<	* are of this form, consider using a pool in
130	<	* {@linkplain ForkJoinPool#setAsyncMode async mode}.
143	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
144	>	* of this form, consider using a pool constructed in <em>asyncMode</em>.
145		*
146		* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
147		* used in extensions such as remote execution frameworks. It is
#	Line 139 | Line 153 | import java.util.WeakHashMap;
153		*/
154		public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
155
156	<	/**
157	<	* Run control status bits packed into a single int to minimize
158	<	* footprint and to ensure atomicity (via CAS).  Status is
159	<	* initially zero, and takes on nonnegative values until
160	<	* completed, upon which status holds COMPLETED. CANCELLED, or
161	<	* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
162	<	* blocking waits by other threads have SIGNAL_MASK bits set --
163	<	* bit 15 for external (nonFJ) waits, and the rest a count of
164	<	* waiting FJ threads.  (This representation relies on
165	<	* ForkJoinPool max thread limits). Completion of a stolen task
166	<	* with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
167	<	* though suboptimal for some purposes, we use basic builtin
168	<	* wait/notify to take advantage of "monitor inflation" in JVMs
169	<	* that we would otherwise need to emulate to avoid adding further
170	<	* per-task bookkeeping overhead. Note that bits 16-28 are
171	<	* currently unused. Also value 0x80000000 is available as spare
172	<	* completion value.
156	>	/*
157	>	* See the internal documentation of class ForkJoinPool for a
158	>	* general implementation overview.  ForkJoinTasks are mainly
159	>	* responsible for maintaining their "status" field amidst relays
160	>	* to methods in ForkJoinWorkerThread and ForkJoinPool. The
161	>	* methods of this class are more-or-less layered into (1) basic
162	>	* status maintenance (2) execution and awaiting completion (3)
163	>	* user-level methods that additionally report results. This is
164	>	* sometimes hard to see because this file orders exported methods
165	>	* in a way that flows well in javadocs. In particular, most
166	>	* join mechanics are in method quietlyJoin, below.
167	>	*/
168	>
169	>	/*
170	>	* The status field holds run control status bits packed into a
171	>	* single int to minimize footprint and to ensure atomicity (via
172	>	* CAS).  Status is initially zero, and takes on nonnegative
173	>	* values until completed, upon which status holds value
174	>	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
175	>	* waits by other threads have the SIGNAL bit set.  Completion of
176	>	* a stolen task with SIGNAL set awakens any waiters via
177	>	* notifyAll. Even though suboptimal for some purposes, we use
178	>	* basic builtin wait/notify to take advantage of "monitor
179	>	* inflation" in JVMs that we would otherwise need to emulate to
180	>	* avoid adding further per-task bookkeeping overhead.  We want
181	>	* these monitors to be "fat", i.e., not use biasing or thin-lock
182	>	* techniques, so use some odd coding idioms that tend to avoid
183	>	* them.
184		*/
185	+
186	+	/** The run status of this task */
187		volatile int status; // accessed directly by pool and workers
188
189	<	static final int COMPLETION_MASK      = 0xe0000000;
190	<	static final int NORMAL               = 0xe0000000; // == mask
191	<	static final int CANCELLED            = 0xc0000000;
192	<	static final int EXCEPTIONAL          = 0xa0000000;
166	<	static final int SIGNAL_MASK          = 0x0000ffff;
167	<	static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
168	<	static final int EXTERNAL_SIGNAL      = 0x00008000; // top bit of low word
189	>	private static final int NORMAL      = -1;
190	>	private static final int CANCELLED   = -2;
191	>	private static final int EXCEPTIONAL = -3;
192	>	private static final int SIGNAL      =  1;
193
194		/**
195		* Table of exceptions thrown by tasks, to enable reporting by
#	Line 179 | Line 203 | public abstract class ForkJoinTask<V> im
203		Collections.synchronizedMap
204		(new WeakHashMap<ForkJoinTask<?>, Throwable>());
205
206	<	// within-package utilities
183	<
184	<	/**
185	<	* Gets current worker thread, or null if not a worker thread.
186	<	*/
187	<	static ForkJoinWorkerThread getWorker() {
188	<	Thread t = Thread.currentThread();
189	<	return ((t instanceof ForkJoinWorkerThread) ?
190	<	(ForkJoinWorkerThread) t : null);
191	<	}
192	<
193	<	final boolean casStatus(int cmp, int val) {
194	<	return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val);
195	<	}
196	<
197	<	/**
198	<	* Workaround for not being able to rethrow unchecked exceptions.
199	<	*/
200	<	static void rethrowException(Throwable ex) {
201	<	if (ex != null)
202	<	UNSAFE.throwException(ex);
203	<	}
204	<
205	<	// Setting completion status
206	>	// Maintaining completion status
207
208		/**
209	<	* Marks completion and wakes up threads waiting to join this task.
209	>	* Marks completion and wakes up threads waiting to join this task,
210	>	* also clearing signal request bits.
211		*
212		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
213		*/
214	<	final void setCompletion(int completion) {
215	<	ForkJoinPool pool = getPool();
216	<	if (pool != null) {
217	<	int s; // Clear signal bits while setting completion status
218	<	do {} while ((s = status) >= 0 && !casStatus(s, completion));
219	<
220	<	if ((s & SIGNAL_MASK) != 0) {
219	<	if ((s &= INTERNAL_SIGNAL_MASK) != 0)
220	<	pool.updateRunningCount(s);
221	<	synchronized (this) { notifyAll(); }
214	>	private void setCompletion(int completion) {
215	>	int s;
216	>	while ((s = status) >= 0) {
217	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
218	>	if (s != 0)
219	>	synchronized (this) { notifyAll(); }
220	>	break;
221		}
222		}
224	–	else
225	–	externallySetCompletion(completion);
226	–	}
227	–
228	–	/**
229	–	* Version of setCompletion for non-FJ threads.  Leaves signal
230	–	* bits for unblocked threads to adjust, and always notifies.
231	–	*/
232	–	private void externallySetCompletion(int completion) {
233	–	int s;
234	–	do {} while ((s = status) >= 0 &&
235	–	!casStatus(s, (s & SIGNAL_MASK) | completion));
236	–	synchronized (this) { notifyAll(); }
237	–	}
238	–
239	–	/**
240	–	* Sets status to indicate normal completion.
241	–	*/
242	–	final void setNormalCompletion() {
243	–	// Try typical fast case -- single CAS, no signal, not already done.
244	–	// Manually expand casStatus to improve chances of inlining it
245	–	if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL))
246	–	setCompletion(NORMAL);
223		}
224
249	–	// internal waiting and notification
250	–
225		/**
226	<	* Performs the actual monitor wait for awaitDone.
226	>	* Records exception and sets exceptional completion.
227	>	*
228	>	* @return status on exit
229		*/
230	<	private void doAwaitDone() {
231	<	// Minimize lock bias and in/de-flation effects by maximizing
232	<	// chances of waiting inside sync
257	<	try {
258	<	while (status >= 0)
259	<	synchronized (this) { if (status >= 0) wait(); }
260	<	} catch (InterruptedException ie) {
261	<	onInterruptedWait();
262	<	}
230	>	private void setExceptionalCompletion(Throwable rex) {
231	>	exceptionMap.put(this, rex);
232	>	setCompletion(EXCEPTIONAL);
233		}
234
235		/**
236	<	* Performs the actual timed monitor wait for awaitDone.
236	>	* Blocks a worker thread until completion. Called only by
237	>	* pool. Currently unused -- pool-based waits use timeout
238	>	* version below.
239		*/
240	<	private void doAwaitDone(long startTime, long nanos) {
241	<	synchronized (this) {
240	>	final void internalAwaitDone() {
241	>	int s;         // the odd construction reduces lock bias effects
242	>	while ((s = status) >= 0) {
243		try {
244	<	while (status >= 0) {
245	<	long nt = nanos - (System.nanoTime() - startTime);
246	<	if (nt <= 0)
274	<	break;
275	<	wait(nt / 1000000, (int) (nt % 1000000));
244	>	synchronized (this) {
245	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
246	>	wait();
247		}
248		} catch (InterruptedException ie) {
249	<	onInterruptedWait();
279	<	}
280	<	}
281	<	}
282	<
283	<	// Awaiting completion
284	<
285	<	/**
286	<	* Sets status to indicate there is joiner, then waits for join,
287	<	* surrounded with pool notifications.
288	<	*
289	<	* @return status upon exit
290	<	*/
291	<	private int awaitDone(ForkJoinWorkerThread w,
292	<	boolean maintainParallelism) {
293	<	ForkJoinPool pool = (w == null) ? null : w.pool;
294	<	int s;
295	<	while ((s = status) >= 0) {
296	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
297	<	if (pool == null || !pool.preJoin(this, maintainParallelism))
298	<	doAwaitDone();
299	<	if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
300	<	adjustPoolCountsOnUnblock(pool);
301	<	break;
249	>	cancelIfTerminating();
250		}
251		}
304	–	return s;
252		}
253
254		/**
255	<	* Timed version of awaitDone
255	>	* Blocks a worker thread until completed or timed out.  Called
256	>	* only by pool.
257		*
258	<	* @return status upon exit
258	>	* @return status on exit
259		*/
260	<	private int awaitDone(ForkJoinWorkerThread w, long nanos) {
313	<	ForkJoinPool pool = (w == null) ? null : w.pool;
260	>	final int internalAwaitDone(long millis, int nanos) {
261		int s;
262	<	while ((s = status) >= 0) {
263	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
264	<	long startTime = System.nanoTime();
265	<	if (pool == null || !pool.preJoin(this, false))
266	<	doAwaitDone(startTime, nanos);
320	<	if ((s = status) >= 0) {
321	<	adjustPoolCountsOnCancelledWait(pool);
322	<	s = status;
262	>	if ((s = status) >= 0) {
263	>	try {
264	>	synchronized (this) {
265	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
266	>	wait(millis, nanos);
267		}
268	<	if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
269	<	adjustPoolCountsOnUnblock(pool);
326	<	break;
268	>	} catch (InterruptedException ie) {
269	>	cancelIfTerminating();
270		}
271	+	s = status;
272		}
273		return s;
274		}
275
276		/**
277	<	* Notifies pool that thread is unblocked. Called by signalled
334	<	* threads when woken by non-FJ threads (which is atypical).
277	>	* Blocks a non-worker-thread until completion.
278		*/
279	<	private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
279	>	private void externalAwaitDone() {
280		int s;
281	<	do {} while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
282	<	if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
283	<	pool.updateRunningCount(s);
284	<	}
285	<
286	<	/**
287	<	* Notifies pool to adjust counts on cancelled or timed out wait.
288	<	*/
289	<	private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
290	<	if (pool != null) {
291	<	int s;
292	<	while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
293	<	if (casStatus(s, s - 1)) {
351	<	pool.updateRunningCount(1);
281	>	while ((s = status) >= 0) {
282	>	synchronized (this) {
283	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
284	>	boolean interrupted = false;
285	>	while (status >= 0) {
286	>	try {
287	>	wait();
288	>	} catch (InterruptedException ie) {
289	>	interrupted = true;
290	>	}
291	>	}
292	>	if (interrupted)
293	>	Thread.currentThread().interrupt();
294		break;
295		}
296		}
#	Line 356 | Line 298 | public abstract class ForkJoinTask<V> im
298		}
299
300		/**
301	<	* Handles interruptions during waits.
302	<	*/
303	<	private void onInterruptedWait() {
362	<	ForkJoinWorkerThread w = getWorker();
363	<	if (w == null)
364	<	Thread.currentThread().interrupt(); // re-interrupt
365	<	else if (w.isTerminating())
366	<	cancelIgnoringExceptions();
367	<	// else if FJworker, ignore interrupt
368	<	}
369	<
370	<	// Recording and reporting exceptions
371	<
372	<	private void setDoneExceptionally(Throwable rex) {
373	<	exceptionMap.put(this, rex);
374	<	setCompletion(EXCEPTIONAL);
375	<	}
376	<
377	<	/**
378	<	* Throws the exception associated with status s.
379	<	*
380	<	* @throws the exception
381	<	*/
382	<	private void reportException(int s) {
383	<	if ((s &= COMPLETION_MASK) < NORMAL) {
384	<	if (s == CANCELLED)
385	<	throw new CancellationException();
386	<	else
387	<	rethrowException(exceptionMap.get(this));
388	<	}
389	<	}
390	<
391	<	/**
392	<	* Returns result or throws exception using j.u.c.Future conventions.
393	<	* Only call when {@code isDone} known to be true or thread known
394	<	* to be interrupted.
395	<	*/
396	<	private V reportFutureResult()
397	<	throws InterruptedException, ExecutionException {
398	<	if (Thread.interrupted())
399	<	throw new InterruptedException();
400	<	int s = status & COMPLETION_MASK;
401	<	if (s < NORMAL) {
402	<	Throwable ex;
403	<	if (s == CANCELLED)
404	<	throw new CancellationException();
405	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
406	<	throw new ExecutionException(ex);
407	<	}
408	<	return getRawResult();
409	<	}
410	<
411	<	/**
412	<	* Returns result or throws exception using j.u.c.Future conventions
413	<	* with timeouts.
414	<	*/
415	<	private V reportTimedFutureResult()
416	<	throws InterruptedException, ExecutionException, TimeoutException {
417	<	if (Thread.interrupted())
418	<	throw new InterruptedException();
419	<	Throwable ex;
420	<	int s = status & COMPLETION_MASK;
421	<	if (s == NORMAL)
422	<	return getRawResult();
423	<	else if (s == CANCELLED)
424	<	throw new CancellationException();
425	<	else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
426	<	throw new ExecutionException(ex);
427	<	else
428	<	throw new TimeoutException();
429	<	}
430	<
431	<	// internal execution methods
432	<
433	<	/**
434	<	* Calls exec, recording completion, and rethrowing exception if
435	<	* encountered. Caller should normally check status before calling.
436	<	*
437	<	* @return true if completed normally
438	<	*/
439	<	private boolean tryExec() {
440	<	try { // try block must contain only call to exec
441	<	if (!exec())
442	<	return false;
443	<	} catch (Throwable rex) {
444	<	setDoneExceptionally(rex);
445	<	rethrowException(rex);
446	<	return false; // not reached
447	<	}
448	<	setNormalCompletion();
449	<	return true;
450	<	}
451	<
452	<	/**
453	<	* Main execution method used by worker threads. Invokes
454	<	* base computation unless already complete.
301	>	* Unless done, calls exec and records status if completed, but
302	>	* doesn't wait for completion otherwise. Primary execution method
303	>	* for ForkJoinWorkerThread.
304		*/
305		final void quietlyExec() {
457	–	if (status >= 0) {
458	–	try {
459	–	if (!exec())
460	–	return;
461	–	} catch (Throwable rex) {
462	–	setDoneExceptionally(rex);
463	–	return;
464	–	}
465	–	setNormalCompletion();
466	–	}
467	–	}
468	–
469	–	/**
470	–	* Calls exec(), recording but not rethrowing exception.
471	–	* Caller should normally check status before calling.
472	–	*
473	–	* @return true if completed normally
474	–	*/
475	–	private boolean tryQuietlyInvoke() {
306		try {
307	<	if (!exec())
308	<	return false;
307	>	if (status < 0 || !exec())
308	>	return;
309		} catch (Throwable rex) {
310	<	setDoneExceptionally(rex);
311	<	return false;
482	<	}
483	<	setNormalCompletion();
484	<	return true;
485	<	}
486	<
487	<	/**
488	<	* Cancels, ignoring any exceptions it throws.
489	<	*/
490	<	final void cancelIgnoringExceptions() {
491	<	try {
492	<	cancel(false);
493	<	} catch (Throwable ignore) {
310	>	setExceptionalCompletion(rex);
311	>	return;
312		}
313	<	}
496	<
497	<	/**
498	<	* Main implementation of helpJoin
499	<	*/
500	<	private int busyJoin(ForkJoinWorkerThread w) {
501	<	int s;
502	<	ForkJoinTask<?> t;
503	<	while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
504	<	t.quietlyExec();
505	<	return (s >= 0) ? awaitDone(w, false) : s; // block if no work
313	>	setCompletion(NORMAL); // must be outside try block
314		}
315
316		// public methods
#	Line 532 | Line 340 | public abstract class ForkJoinTask<V> im
340		}
341
342		/**
343	<	* Returns the result of the computation when it {@link #isDone is done}.
344	<	* This method differs from {@link #get()} in that
343	>	* Returns the result of the computation when it {@link #isDone is
344	>	* done}.  This method differs from {@link #get()} in that
345		* abnormal completion results in {@code RuntimeException} or
346	<	* {@code Error}, not {@code ExecutionException}.
346	>	* {@code Error}, not {@code ExecutionException}, and that
347	>	* interrupts of the calling thread do <em>not</em> cause the
348	>	* method to abruptly return by throwing {@code
349	>	* InterruptedException}.
350		*
351		* @return the computed result
352		*/
353		public final V join() {
354	<	ForkJoinWorkerThread w = getWorker();
355	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryExec())
356	<	reportException(awaitDone(w, true));
354	>	quietlyJoin();
355	>	Throwable ex;
356	>	if (status < NORMAL && (ex = getException()) != null)
357	>	UNSAFE.throwException(ex);
358		return getRawResult();
359		}
360
361		/**
362		* Commences performing this task, awaits its completion if
363	<	* necessary, and return its result, or throws an (unchecked)
364	<	* exception if the underlying computation did so.
363	>	* necessary, and returns its result, or throws an (unchecked)
364	>	* {@code RuntimeException} or {@code Error} if the underlying
365	>	* computation did so.
366		*
367		* @return the computed result
368		*/
369		public final V invoke() {
370	<	if (status >= 0 && tryExec())
371	<	return getRawResult();
372	<	else
373	<	return join();
370	>	quietlyInvoke();
371	>	Throwable ex;
372	>	if (status < NORMAL && (ex = getException()) != null)
373	>	UNSAFE.throwException(ex);
374	>	return getRawResult();
375		}
376
377		/**
378		* Forks the given tasks, returning when {@code isDone} holds for
379		* each task or an (unchecked) exception is encountered, in which
380	<	* case the exception is rethrown.  If either task encounters an
381	<	* exception, the other one may be, but is not guaranteed to be,
382	<	* cancelled.  If both tasks throw an exception, then this method
383	<	* throws one of them.  The individual status of each task may be
384	<	* checked using {@link #getException()} and related methods.
380	>	* case the exception is rethrown. If more than one task
381	>	* encounters an exception, then this method throws any one of
382	>	* these exceptions. If any task encounters an exception, the
383	>	* other may be cancelled. However, the execution status of
384	>	* individual tasks is not guaranteed upon exceptional return. The
385	>	* status of each task may be obtained using {@link
386	>	* #getException()} and related methods to check if they have been
387	>	* cancelled, completed normally or exceptionally, or left
388	>	* unprocessed.
389		*
390		* <p>This method may be invoked only from within {@code
391	<	* ForkJoinTask} computations (as may be determined using method
391	>	* ForkJoinPool} computations (as may be determined using method
392		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
393		* result in exceptions or errors, possibly including {@code
394		* ClassCastException}.
#	Line 588 | Line 406 | public abstract class ForkJoinTask<V> im
406		/**
407		* Forks the given tasks, returning when {@code isDone} holds for
408		* each task or an (unchecked) exception is encountered, in which
409	<	* case the exception is rethrown. If any task encounters an
410	<	* exception, others may be, but are not guaranteed to be,
411	<	* cancelled.  If more than one task encounters an exception, then
412	<	* this method throws any one of these exceptions.  The individual
413	<	* status of each task may be checked using {@link #getException()}
414	<	* and related methods.
409	>	* case the exception is rethrown. If more than one task
410	>	* encounters an exception, then this method throws any one of
411	>	* these exceptions. If any task encounters an exception, others
412	>	* may be cancelled. However, the execution status of individual
413	>	* tasks is not guaranteed upon exceptional return. The status of
414	>	* each task may be obtained using {@link #getException()} and
415	>	* related methods to check if they have been cancelled, completed
416	>	* normally or exceptionally, or left unprocessed.
417		*
418		* <p>This method may be invoked only from within {@code
419	<	* ForkJoinTask} computations (as may be determined using method
419	>	* ForkJoinPool} computations (as may be determined using method
420		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
421		* result in exceptions or errors, possibly including {@code
422		* ClassCastException}.
#	Line 617 | Line 437 | public abstract class ForkJoinTask<V> im
437		t.fork();
438		else {
439		t.quietlyInvoke();
440	<	if (ex == null)
440	>	if (ex == null && t.status < NORMAL)
441		ex = t.getException();
442		}
443		}
#	Line 628 | Line 448 | public abstract class ForkJoinTask<V> im
448		t.cancel(false);
449		else {
450		t.quietlyJoin();
451	<	if (ex == null)
451	>	if (ex == null && t.status < NORMAL)
452		ex = t.getException();
453		}
454		}
455		}
456		if (ex != null)
457	<	rethrowException(ex);
457	>	UNSAFE.throwException(ex);
458		}
459
460		/**
461		* Forks all tasks in the specified collection, returning when
462		* {@code isDone} holds for each task or an (unchecked) exception
463	<	* is encountered.  If any task encounters an exception, others
464	<	* may be, but are not guaranteed to be, cancelled.  If more than
465	<	* one task encounters an exception, then this method throws any
466	<	* one of these exceptions.  The individual status of each task
467	<	* may be checked using {@link #getException()} and related
468	<	* methods.  The behavior of this operation is undefined if the
469	<	* specified collection is modified while the operation is in
470	<	* progress.
463	>	* is encountered, in which case the exception is rethrown. If
464	>	* more than one task encounters an exception, then this method
465	>	* throws any one of these exceptions. If any task encounters an
466	>	* exception, others may be cancelled. However, the execution
467	>	* status of individual tasks is not guaranteed upon exceptional
468	>	* return. The status of each task may be obtained using {@link
469	>	* #getException()} and related methods to check if they have been
470	>	* cancelled, completed normally or exceptionally, or left
471	>	* unprocessed.
472		*
473		* <p>This method may be invoked only from within {@code
474	<	* ForkJoinTask} computations (as may be determined using method
474	>	* ForkJoinPool} computations (as may be determined using method
475		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
476		* result in exceptions or errors, possibly including {@code
477		* ClassCastException}.
#	Line 679 | Line 500 | public abstract class ForkJoinTask<V> im
500		t.fork();
501		else {
502		t.quietlyInvoke();
503	<	if (ex == null)
503	>	if (ex == null && t.status < NORMAL)
504		ex = t.getException();
505		}
506		}
#	Line 690 | Line 511 | public abstract class ForkJoinTask<V> im
511		t.cancel(false);
512		else {
513		t.quietlyJoin();
514	<	if (ex == null)
514	>	if (ex == null && t.status < NORMAL)
515		ex = t.getException();
516		}
517		}
518		}
519		if (ex != null)
520	<	rethrowException(ex);
520	>	UNSAFE.throwException(ex);
521		return tasks;
522		}
523
524		/**
525		* Attempts to cancel execution of this task. This attempt will
526	<	* fail if the task has already completed, has already been
527	<	* cancelled, or could not be cancelled for some other reason. If
528	<	* successful, and this task has not started when cancel is
529	<	* called, execution of this task is suppressed, {@link
530	<	* #isCancelled} will report true, and {@link #join} will result
531	<	* in a {@code CancellationException} being thrown.
526	>	* fail if the task has already completed or could not be
527	>	* cancelled for some other reason. If successful, and this task
528	>	* has not started when {@code cancel} is called, execution of
529	>	* this task is suppressed. After this method returns
530	>	* successfully, unless there is an intervening call to {@link
531	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
532	>	* {@link #isDone}, and {@code cancel} will return {@code true}
533	>	* and calls to {@link #join} and related methods will result in
534	>	* {@code CancellationException}.
535		*
536		* <p>This method may be overridden in subclasses, but if so, must
537	<	* still ensure that these minimal properties hold. In particular,
538	<	* the {@code cancel} method itself must not throw exceptions.
537	>	* still ensure that these properties hold. In particular, the
538	>	* {@code cancel} method itself must not throw exceptions.
539		*
540		* <p>This method is designed to be invoked by <em>other</em>
541		* tasks. To terminate the current task, you can just return or
542		* throw an unchecked exception from its computation method, or
543		* invoke {@link #completeExceptionally}.
544		*
545	<	* @param mayInterruptIfRunning this value is ignored in the
546	<	* default implementation because tasks are not
547	<	* cancelled via interruption
545	>	* @param mayInterruptIfRunning this value has no effect in the
546	>	* default implementation because interrupts are not used to
547	>	* control cancellation.
548		*
549		* @return {@code true} if this task is now cancelled
550		*/
551		public boolean cancel(boolean mayInterruptIfRunning) {
552		setCompletion(CANCELLED);
553	<	return (status & COMPLETION_MASK) == CANCELLED;
553	>	return status == CANCELLED;
554	>	}
555	>
556	>	/**
557	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
558	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
559	>	* exceptions, but if it does anyway, we have no recourse during
560	>	* shutdown, so guard against this case.
561	>	*/
562	>	final void cancelIgnoringExceptions() {
563	>	try {
564	>	cancel(false);
565	>	} catch (Throwable ignore) {
566	>	}
567	>	}
568	>
569	>	/**
570	>	* Cancels if current thread is a terminating worker thread,
571	>	* ignoring any exceptions thrown by cancel.
572	>	*/
573	>	final void cancelIfTerminating() {
574	>	Thread t = Thread.currentThread();
575	>	if ((t instanceof ForkJoinWorkerThread) &&
576	>	((ForkJoinWorkerThread) t).isTerminating()) {
577	>	try {
578	>	cancel(false);
579	>	} catch (Throwable ignore) {
580	>	}
581	>	}
582		}
583
584		public final boolean isDone() {
#	Line 734 | Line 586 | public abstract class ForkJoinTask<V> im
586		}
587
588		public final boolean isCancelled() {
589	<	return (status & COMPLETION_MASK) == CANCELLED;
589	>	return status == CANCELLED;
590		}
591
592		/**
#	Line 743 | Line 595 | public abstract class ForkJoinTask<V> im
595		* @return {@code true} if this task threw an exception or was cancelled
596		*/
597		public final boolean isCompletedAbnormally() {
598	<	return (status & COMPLETION_MASK) < NORMAL;
598	>	return status < NORMAL;
599		}
600
601		/**
#	Line 754 | Line 606 | public abstract class ForkJoinTask<V> im
606		* exception and was not cancelled
607		*/
608		public final boolean isCompletedNormally() {
609	<	return (status & COMPLETION_MASK) == NORMAL;
609	>	return status == NORMAL;
610		}
611
612		/**
#	Line 765 | Line 617 | public abstract class ForkJoinTask<V> im
617		* @return the exception, or {@code null} if none
618		*/
619		public final Throwable getException() {
620	<	int s = status & COMPLETION_MASK;
620	>	int s = status;
621		return ((s >= NORMAL)    ? null :
622		(s == CANCELLED) ? new CancellationException() :
623		exceptionMap.get(this));
#	Line 786 | Line 638 | public abstract class ForkJoinTask<V> im
638		* thrown will be a {@code RuntimeException} with cause {@code ex}.
639		*/
640		public void completeExceptionally(Throwable ex) {
641	<	setDoneExceptionally((ex instanceof RuntimeException) ||
642	<	(ex instanceof Error) ? ex :
643	<	new RuntimeException(ex));
641	>	setExceptionalCompletion((ex instanceof RuntimeException) ||
642	>	(ex instanceof Error) ? ex :
643	>	new RuntimeException(ex));
644		}
645
646		/**
647		* Completes this task, and if not already aborted or cancelled,
648	<	* returning a {@code null} result upon {@code join} and related
649	<	* operations. This method may be used to provide results for
650	<	* asynchronous tasks, or to provide alternative handling for
651	<	* tasks that would not otherwise complete normally. Its use in
652	<	* other situations is discouraged. This method is
653	<	* overridable, but overridden versions must invoke {@code super}
654	<	* implementation to maintain guarantees.
648	>	* returning the given value as the result of subsequent
649	>	* invocations of {@code join} and related operations. This method
650	>	* may be used to provide results for asynchronous tasks, or to
651	>	* provide alternative handling for tasks that would not otherwise
652	>	* complete normally. Its use in other situations is
653	>	* discouraged. This method is overridable, but overridden
654	>	* versions must invoke {@code super} implementation to maintain
655	>	* guarantees.
656		*
657		* @param value the result value for this task
658		*/
#	Line 807 | Line 660 | public abstract class ForkJoinTask<V> im
660		try {
661		setRawResult(value);
662		} catch (Throwable rex) {
663	<	setDoneExceptionally(rex);
663	>	setExceptionalCompletion(rex);
664		return;
665		}
666	<	setNormalCompletion();
814	<	}
815	<
816	<	public final V get() throws InterruptedException, ExecutionException {
817	<	ForkJoinWorkerThread w = getWorker();
818	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
819	<	awaitDone(w, true);
820	<	return reportFutureResult();
821	<	}
822	<
823	<	public final V get(long timeout, TimeUnit unit)
824	<	throws InterruptedException, ExecutionException, TimeoutException {
825	<	long nanos = unit.toNanos(timeout);
826	<	ForkJoinWorkerThread w = getWorker();
827	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
828	<	awaitDone(w, nanos);
829	<	return reportTimedFutureResult();
666	>	setCompletion(NORMAL);
667		}
668
669		/**
670	<	* Possibly executes other tasks until this task {@link #isDone is
671	<	* done}, then returns the result of the computation.  This method
835	<	* may be more efficient than {@code join}, but is only applicable
836	<	* when there are no potential dependencies between continuation
837	<	* of the current task and that of any other task that might be
838	<	* executed while helping. (This usually holds for pure
839	<	* divide-and-conquer tasks).
840	<	*
841	<	* <p>This method may be invoked only from within {@code
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 {@code
845	<	* ClassCastException}.
670	>	* Waits if necessary for the computation to complete, and then
671	>	* retrieves its result.
672		*
673		* @return the computed result
674	+	* @throws CancellationException if the computation was cancelled
675	+	* @throws ExecutionException if the computation threw an
676	+	* exception
677	+	* @throws InterruptedException if the current thread is not a
678	+	* member of a ForkJoinPool and was interrupted while waiting
679		*/
680	<	public final V helpJoin() {
681	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
682	<	if (status < 0 || !w.unpushTask(this) || !tryExec())
683	<	reportException(busyJoin(w));
680	>	public final V get() throws InterruptedException, ExecutionException {
681	>	int s;
682	>	if (Thread.currentThread() instanceof ForkJoinWorkerThread) {
683	>	quietlyJoin();
684	>	s = status;
685	>	}
686	>	else {
687	>	while ((s = status) >= 0) {
688	>	synchronized (this) { // interruptible form of awaitDone
689	>	if (UNSAFE.compareAndSwapInt(this, statusOffset,
690	>	s, SIGNAL)) {
691	>	while (status >= 0)
692	>	wait();
693	>	}
694	>	}
695	>	}
696	>	}
697	>	if (s < NORMAL) {
698	>	Throwable ex;
699	>	if (s == CANCELLED)
700	>	throw new CancellationException();
701	>	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
702	>	throw new ExecutionException(ex);
703	>	}
704		return getRawResult();
705		}
706
707		/**
708	<	* Possibly executes other tasks until this task {@link #isDone is
709	<	* done}.  This method may be useful when processing collections
859	<	* of tasks when some have been cancelled or otherwise known to
860	<	* have aborted.
708	>	* Waits if necessary for at most the given time for the computation
709	>	* to complete, and then retrieves its result, if available.
710		*
711	<	* <p>This method may be invoked only from within {@code
712	<	* ForkJoinTask} computations (as may be determined using method
713	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
714	<	* result in exceptions or errors, possibly including {@code
715	<	* ClassCastException}.
711	>	* @param timeout the maximum time to wait
712	>	* @param unit the time unit of the timeout argument
713	>	* @return the computed result
714	>	* @throws CancellationException if the computation was cancelled
715	>	* @throws ExecutionException if the computation threw an
716	>	* exception
717	>	* @throws InterruptedException if the current thread is not a
718	>	* member of a ForkJoinPool and was interrupted while waiting
719	>	* @throws TimeoutException if the wait timed out
720		*/
721	<	public final void quietlyHelpJoin() {
721	>	public final V get(long timeout, TimeUnit unit)
722	>	throws InterruptedException, ExecutionException, TimeoutException {
723	>	long nanos = unit.toNanos(timeout);
724		if (status >= 0) {
725	<	ForkJoinWorkerThread w =
726	<	(ForkJoinWorkerThread) Thread.currentThread();
727	<	if (!w.unpushTask(this) || !tryQuietlyInvoke())
728	<	busyJoin(w);
725	>	Thread t = Thread.currentThread();
726	>	if (t instanceof ForkJoinWorkerThread) {
727	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
728	>	boolean completed = false; // timed variant of quietlyJoin
729	>	if (w.unpushTask(this)) {
730	>	try {
731	>	completed = exec();
732	>	} catch (Throwable rex) {
733	>	setExceptionalCompletion(rex);
734	>	}
735	>	}
736	>	if (completed)
737	>	setCompletion(NORMAL);
738	>	else if (status >= 0)
739	>	w.joinTask(this, true, nanos);
740	>	}
741	>	else if (Thread.interrupted())
742	>	throw new InterruptedException();
743	>	else {
744	>	long startTime = System.nanoTime();
745	>	int s; long nt;
746	>	while ((s = status) >= 0 &&
747	>	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
748	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,
749	>	SIGNAL)) {
750	>	long ms = nt / 1000000;
751	>	int ns = (int) (nt % 1000000);
752	>	synchronized (this) {
753	>	if (status >= 0)
754	>	wait(ms, ns); // exit on IE throw
755	>	}
756	>	}
757	>	}
758	>	}
759		}
760	+	int es = status;
761	+	if (es != NORMAL) {
762	+	Throwable ex;
763	+	if (es == CANCELLED)
764	+	throw new CancellationException();
765	+	if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
766	+	throw new ExecutionException(ex);
767	+	throw new TimeoutException();
768	+	}
769	+	return getRawResult();
770		}
771
772		/**
773	<	* Joins this task, without returning its result or throwing an
773	>	* Joins this task, without returning its result or throwing its
774		* exception. This method may be useful when processing
775		* collections of tasks when some have been cancelled or otherwise
776		* known to have aborted.
777		*/
778		public final void quietlyJoin() {
779	<	if (status >= 0) {
780	<	ForkJoinWorkerThread w = getWorker();
781	<	if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
782	<	awaitDone(w, true);
779	>	Thread t;
780	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
781	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
782	>	if (status >= 0) {
783	>	if (w.unpushTask(this)) {
784	>	boolean completed;
785	>	try {
786	>	completed = exec();
787	>	} catch (Throwable rex) {
788	>	setExceptionalCompletion(rex);
789	>	return;
790	>	}
791	>	if (completed) {
792	>	setCompletion(NORMAL);
793	>	return;
794	>	}
795	>	}
796	>	w.joinTask(this, false, 0L);
797	>	}
798		}
799	+	else
800	+	externalAwaitDone();
801		}
802
803		/**
804		* Commences performing this task and awaits its completion if
805	<	* necessary, without returning its result or throwing an
806	<	* exception. This method may be useful when processing
895	<	* collections of tasks when some have been cancelled or otherwise
896	<	* known to have aborted.
805	>	* necessary, without returning its result or throwing its
806	>	* exception.
807		*/
808		public final void quietlyInvoke() {
809	<	if (status >= 0 && !tryQuietlyInvoke())
810	<	quietlyJoin();
809	>	if (status >= 0) {
810	>	boolean completed;
811	>	try {
812	>	completed = exec();
813	>	} catch (Throwable rex) {
814	>	setExceptionalCompletion(rex);
815	>	return;
816	>	}
817	>	if (completed)
818	>	setCompletion(NORMAL);
819	>	else
820	>	quietlyJoin();
821	>	}
822		}
823
824		/**
#	Line 908 | Line 829 | public abstract class ForkJoinTask<V> im
829		* processed.
830		*
831		* <p>This method may be invoked only from within {@code
832	<	* ForkJoinTask} computations (as may be determined using method
832	>	* ForkJoinPool} computations (as may be determined using method
833		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
834		* result in exceptions or errors, possibly including {@code
835		* ClassCastException}.
#	Line 927 | Line 848 | public abstract class ForkJoinTask<V> im
848		* under any other usage conditions are not guaranteed.
849		* This method may be useful when executing
850		* pre-constructed trees of subtasks in loops.
851	+	*
852	+	* <p>Upon completion of this method, {@code isDone()} reports
853	+	* {@code false}, and {@code getException()} reports {@code
854	+	* null}. However, the value returned by {@code getRawResult} is
855	+	* unaffected. To clear this value, you can invoke {@code
856	+	* setRawResult(null)}.
857		*/
858		public void reinitialize() {
859	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
859	>	if (status == EXCEPTIONAL)
860		exceptionMap.remove(this);
861		status = 0;
862		}
#	Line 967 | Line 894 | public abstract class ForkJoinTask<V> im
894		* were not, stolen.
895		*
896		* <p>This method may be invoked only from within {@code
897	<	* ForkJoinTask} computations (as may be determined using method
897	>	* ForkJoinPool} computations (as may be determined using method
898		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
899		* result in exceptions or errors, possibly including {@code
900		* ClassCastException}.
#	Line 986 | Line 913 | public abstract class ForkJoinTask<V> im
913		* fork other tasks.
914		*
915		* <p>This method may be invoked only from within {@code
916	<	* ForkJoinTask} computations (as may be determined using method
916	>	* ForkJoinPool} computations (as may be determined using method
917		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
918		* result in exceptions or errors, possibly including {@code
919		* ClassCastException}.
#	Line 1009 | Line 936 | public abstract class ForkJoinTask<V> im
936		* exceeded.
937		*
938		* <p>This method may be invoked only from within {@code
939	<	* ForkJoinTask} computations (as may be determined using method
939	>	* ForkJoinPool} computations (as may be determined using method
940		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
941		* result in exceptions or errors, possibly including {@code
942		* ClassCastException}.
#	Line 1067 | Line 994 | public abstract class ForkJoinTask<V> im
994		* otherwise.
995		*
996		* <p>This method may be invoked only from within {@code
997	<	* ForkJoinTask} computations (as may be determined using method
997	>	* ForkJoinPool} computations (as may be determined using method
998		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
999		* result in exceptions or errors, possibly including {@code
1000		* ClassCastException}.
#	Line 1086 | Line 1013 | public abstract class ForkJoinTask<V> im
1013		* be useful otherwise.
1014		*
1015		* <p>This method may be invoked only from within {@code
1016	<	* ForkJoinTask} computations (as may be determined using method
1016	>	* ForkJoinPool} computations (as may be determined using method
1017		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1018		* result in exceptions or errors, possibly including {@code
1019		* ClassCastException}.
#	Line 1109 | Line 1036 | public abstract class ForkJoinTask<V> im
1036		* otherwise.
1037		*
1038		* <p>This method may be invoked only from within {@code
1039	<	* ForkJoinTask} computations (as may be determined using method
1039	>	* ForkJoinPool} computations (as may be determined using method
1040		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1041		* result in exceptions or errors, possibly including {@code
1042		* ClassCastException}.
#	Line 1219 | Line 1146 | public abstract class ForkJoinTask<V> im
1146		private static final long serialVersionUID = -7721805057305804111L;
1147
1148		/**
1149	<	* Saves the state to a stream.
1149	>	* Saves the state to a stream (that is, serializes it).
1150		*
1151		* @serialData the current run status and the exception thrown
1152		* during execution, or {@code null} if none
#	Line 1232 | Line 1159 | public abstract class ForkJoinTask<V> im
1159		}
1160
1161		/**
1162	<	* Reconstitutes the instance from a stream.
1162	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1163		*
1164		* @param s the stream
1165		*/
1166		private void readObject(java.io.ObjectInputStream s)
1167		throws java.io.IOException, ClassNotFoundException {
1168		s.defaultReadObject();
1242	–	status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
1243	–	status |= EXTERNAL_SIGNAL; // conservatively set external signal
1169		Object ex = s.readObject();
1170		if (ex != null)
1171	<	setDoneExceptionally((Throwable) ex);
1171	>	setExceptionalCompletion((Throwable) ex);
1172		}
1173
1174		// Unsafe mechanics

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