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Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.39 by jsr166, Wed Aug 5 00:57:41 2009 UTC vs.
Revision 1.79 by jsr166, Fri Jun 10 18:10:53 2011 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3		* Expert Group and released to the public domain, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		*/
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.io.Serializable;
10		import java.util.Collection;
13	–	import java.util.Collections;
11		import java.util.List;
12		import java.util.RandomAccess;
13	<	import java.util.Map;
14	<	import java.util.WeakHashMap;
13	>	import java.lang.ref.WeakReference;
14	>	import java.lang.ref.ReferenceQueue;
15	>	import java.util.concurrent.Callable;
16	>	import java.util.concurrent.CancellationException;
17	>	import java.util.concurrent.ExecutionException;
18	>	import java.util.concurrent.Future;
19	>	import java.util.concurrent.RejectedExecutionException;
20	>	import java.util.concurrent.RunnableFuture;
21	>	import java.util.concurrent.TimeUnit;
22	>	import java.util.concurrent.TimeoutException;
23	>	import java.util.concurrent.locks.ReentrantLock;
24	>	import java.lang.reflect.Constructor;
25
26		/**
27		* Abstract base class for tasks that run within a {@link ForkJoinPool}.
#	Line 28 | Line 35 | import java.util.WeakHashMap;
35		* start other subtasks.  As indicated by the name of this class,
36		* many programs using {@code ForkJoinTask} employ only methods
37		* {@link #fork} and {@link #join}, or derivatives such as {@link
38	<	* #invokeAll}.  However, this class also provides a number of other
39	<	* methods that can come into play in advanced usages, as well as
40	<	* extension mechanics that allow support of new forms of fork/join
41	<	* processing.
38	>	* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
39	>	* provides a number of other methods that can come into play in
40	>	* advanced usages, as well as extension mechanics that allow
41	>	* support of new forms of fork/join processing.
42		*
43		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
44		* The efficiency of {@code ForkJoinTask}s stems from a set of
#	Line 56 | Line 63 | import java.util.WeakHashMap;
63		* exceptions such as {@code IOExceptions} to be thrown. However,
64		* computations may still encounter unchecked exceptions, that are
65		* rethrown to callers attempting to join them. These exceptions may
66	<	* additionally include RejectedExecutionExceptions stemming from
67	<	* internal resource exhaustion such as failure to allocate internal
68	<	* task queues.
66	>	* additionally include {@link RejectedExecutionException} stemming
67	>	* from internal resource exhaustion, such as failure to allocate
68	>	* internal task queues. Rethrown exceptions behave in the same way as
69	>	* regular exceptions, but, when possible, contain stack traces (as
70	>	* displayed for example using {@code ex.printStackTrace()}) of both
71	>	* the thread that initiated the computation as well as the thread
72	>	* actually encountering the exception; minimally only the latter.
73		*
74		* <p>The primary method for awaiting completion and extracting
75		* results of a task is {@link #join}, but there are several variants:
76		* The {@link Future#get} methods support interruptible and/or timed
77		* waits for completion and report results using {@code Future}
78	<	* 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
78	>	* conventions. Method {@link #invoke} is semantically
79		* equivalent to {@code fork(); join()} but always attempts to begin
80		* execution in the current thread. The "<em>quiet</em>" forms of
81		* these methods do not extract results or report exceptions. These
#	Line 80 | Line 88 | import java.util.WeakHashMap;
88		* <p>The execution status of tasks may be queried at several levels
89		* of detail: {@link #isDone} is true if a task completed in any way
90		* (including the case where a task was cancelled without executing);
83	–	* {@link #isCancelled} is true if completion was due to cancellation;
91		* {@link #isCompletedNormally} is true if a task completed without
92	<	* cancellation or encountering an exception; {@link
93	<	* #isCompletedExceptionally} is true if if the task encountered an
94	<	* exception (in which case {@link #getException} returns the
95	<	* exception); {@link #isCancelled} is true if the task was cancelled
96	<	* (in which case {@link #getException} returns a {@link
97	<	* java.util.concurrent.CancellationException}); and {@link
98	<	* #isCompletedAbnormally} is true if a task was either cancelled or
92	<	* encountered an exception.
92	>	* cancellation or encountering an exception; {@link #isCancelled} is
93	>	* true if the task was cancelled (in which case {@link #getException}
94	>	* returns a {@link java.util.concurrent.CancellationException}); and
95	>	* {@link #isCompletedAbnormally} is true if a task was either
96	>	* cancelled or encountered an exception, in which case {@link
97	>	* #getException} will return either the encountered exception or
98	>	* {@link java.util.concurrent.CancellationException}.
99		*
100		* <p>The ForkJoinTask class is not usually directly subclassed.
101		* Instead, you subclass one of the abstract classes that support a
#	Line 105 | Line 111 | import java.util.WeakHashMap;
111		* ForkJoinTasks (as may be determined using method {@link
112		* #inForkJoinPool}).  Attempts to invoke them in other contexts
113		* result in exceptions or errors, possibly including
114	<	* ClassCastException.
114	>	* {@code ClassCastException}.
115	>	*
116	>	* <p>Method {@link #join} and its variants are appropriate for use
117	>	* only when completion dependencies are acyclic; that is, the
118	>	* parallel computation can be described as a directed acyclic graph
119	>	* (DAG). Otherwise, executions may encounter a form of deadlock as
120	>	* tasks cyclically wait for each other.  However, this framework
121	>	* supports other methods and techniques (for example the use of
122	>	* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
123	>	* may be of use in constructing custom subclasses for problems that
124	>	* are not statically structured as DAGs.
125		*
126		* <p>Most base support methods are {@code final}, to prevent
127		* overriding of implementations that are intrinsically tied to the
#	Line 121 | Line 137 | import java.util.WeakHashMap;
137		* computation. Large tasks should be split into smaller subtasks,
138		* usually via recursive decomposition. As a very rough rule of thumb,
139		* a task should perform more than 100 and less than 10000 basic
140	<	* computational steps. If tasks are too big, then parallelism cannot
141	<	* improve throughput. If too small, then memory and internal task
142	<	* maintenance overhead may overwhelm processing.
140	>	* computational steps, and should avoid indefinite looping. If tasks
141	>	* are too big, then parallelism cannot improve throughput. If too
142	>	* small, then memory and internal task maintenance overhead may
143	>	* overwhelm processing.
144		*
145		* <p>This class provides {@code adapt} methods for {@link Runnable}
146		* and {@link Callable}, that may be of use when mixing execution of
147	<	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks
148	<	* are of this form, consider using a pool in
132	<	* {@linkplain ForkJoinPool#setAsyncMode async mode}.
147	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
148	>	* of this form, consider using a pool constructed in <em>asyncMode</em>.
149		*
150		* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
151		* used in extensions such as remote execution frameworks. It is
#	Line 141 | Line 157 | import java.util.WeakHashMap;
157		*/
158		public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
159
160	<	/**
161	<	* Run control status bits packed into a single int to minimize
162	<	* footprint and to ensure atomicity (via CAS).  Status is
163	<	* initially zero, and takes on nonnegative values until
164	<	* completed, upon which status holds COMPLETED. CANCELLED, or
165	<	* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
166	<	* blocking waits by other threads have SIGNAL_MASK bits set --
167	<	* bit 15 for external (nonFJ) waits, and the rest a count of
168	<	* waiting FJ threads.  (This representation relies on
169	<	* ForkJoinPool max thread limits). Completion of a stolen task
170	<	* with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
171	<	* though suboptimal for some purposes, we use basic builtin
172	<	* wait/notify to take advantage of "monitor inflation" in JVMs
173	<	* that we would otherwise need to emulate to avoid adding further
174	<	* per-task bookkeeping overhead. Note that bits 16-28 are
175	<	* currently unused. Also value 0x80000000 is available as spare
176	<	* completion value.
177	<	*/
178	<	volatile int status; // accessed directly by pool and workers
179	<
180	<	static final int COMPLETION_MASK      = 0xe0000000;
181	<	static final int NORMAL               = 0xe0000000; // == mask
182	<	static final int CANCELLED            = 0xc0000000;
183	<	static final int EXCEPTIONAL          = 0xa0000000;
184	<	static final int SIGNAL_MASK          = 0x0000ffff;
185	<	static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
186	<	static final int EXTERNAL_SIGNAL      = 0x00008000; // top bit of low word
171	<
172	<	/**
173	<	* Table of exceptions thrown by tasks, to enable reporting by
174	<	* callers. Because exceptions are rare, we don't directly keep
175	<	* them with task objects, but instead use a weak ref table.  Note
176	<	* that cancellation exceptions don't appear in the table, but are
177	<	* instead recorded as status values.
178	<	* TODO: Use ConcurrentReferenceHashMap
160	>	/*
161	>	* See the internal documentation of class ForkJoinPool for a
162	>	* general implementation overview.  ForkJoinTasks are mainly
163	>	* responsible for maintaining their "status" field amidst relays
164	>	* to methods in ForkJoinWorkerThread and ForkJoinPool. The
165	>	* methods of this class are more-or-less layered into (1) basic
166	>	* status maintenance (2) execution and awaiting completion (3)
167	>	* user-level methods that additionally report results. This is
168	>	* sometimes hard to see because this file orders exported methods
169	>	* in a way that flows well in javadocs.
170	>	*/
171	>
172	>	/*
173	>	* The status field holds run control status bits packed into a
174	>	* single int to minimize footprint and to ensure atomicity (via
175	>	* CAS).  Status is initially zero, and takes on nonnegative
176	>	* values until completed, upon which status holds value
177	>	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
178	>	* waits by other threads have the SIGNAL bit set.  Completion of
179	>	* a stolen task with SIGNAL set awakens any waiters via
180	>	* notifyAll. Even though suboptimal for some purposes, we use
181	>	* basic builtin wait/notify to take advantage of "monitor
182	>	* inflation" in JVMs that we would otherwise need to emulate to
183	>	* avoid adding further per-task bookkeeping overhead.  We want
184	>	* these monitors to be "fat", i.e., not use biasing or thin-lock
185	>	* techniques, so use some odd coding idioms that tend to avoid
186	>	* them.
187		*/
180	–	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
181	–	Collections.synchronizedMap
182	–	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
183	–
184	–	// within-package utilities
185	–
186	–	/**
187	–	* Gets current worker thread, or null if not a worker thread.
188	–	*/
189	–	static ForkJoinWorkerThread getWorker() {
190	–	Thread t = Thread.currentThread();
191	–	return ((t instanceof ForkJoinWorkerThread) ?
192	–	(ForkJoinWorkerThread) t : null);
193	–	}
194	–
195	–	final boolean casStatus(int cmp, int val) {
196	–	return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val);
197	–	}
198	–
199	–	/**
200	–	* Workaround for not being able to rethrow unchecked exceptions.
201	–	*/
202	–	static void rethrowException(Throwable ex) {
203	–	if (ex != null)
204	–	UNSAFE.throwException(ex);
205	–	}
188
189	<	// Setting completion status
189	>	/** The run status of this task */
190	>	volatile int status; // accessed directly by pool and workers
191	>	private static final int NORMAL      = -1;
192	>	private static final int CANCELLED   = -2;
193	>	private static final int EXCEPTIONAL = -3;
194	>	private static final int SIGNAL      =  1;
195
196		/**
197	<	* Marks completion and wakes up threads waiting to join this task.
197	>	* Marks completion and wakes up threads waiting to join this task,
198	>	* also clearing signal request bits.
199		*
200		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
201	+	* @return completion status on exit
202		*/
203	<	final void setCompletion(int completion) {
204	<	ForkJoinPool pool = getPool();
205	<	if (pool != null) {
206	<	int s; // Clear signal bits while setting completion status
207	<	do {} while ((s = status) >= 0 && !casStatus(s, completion));
208	<
209	<	if ((s & SIGNAL_MASK) != 0) {
210	<	if ((s &= INTERNAL_SIGNAL_MASK) != 0)
222	<	pool.updateRunningCount(s);
223	<	synchronized (this) { notifyAll(); }
203	>	private int setCompletion(int completion) {
204	>	for (int s;;) {
205	>	if ((s = status) < 0)
206	>	return s;
207	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
208	>	if (s != 0)
209	>	synchronized (this) { notifyAll(); }
210	>	return completion;
211		}
212		}
226	–	else
227	–	externallySetCompletion(completion);
213		}
214
215		/**
216	<	* Version of setCompletion for non-FJ threads.  Leaves signal
217	<	* bits for unblocked threads to adjust, and always notifies.
216	>	* Tries to block a worker thread until completed or timed out.
217	>	* Uses Object.wait time argument conventions.
218	>	* May fail on contention or interrupt.
219	>	*
220	>	* @param millis if > 0, wait time.
221		*/
222	<	private void externallySetCompletion(int completion) {
222	>	final void tryAwaitDone(long millis) {
223		int s;
236	–	do {} while ((s = status) >= 0 &&
237	–	!casStatus(s, (s & SIGNAL_MASK) | completion));
238	–	synchronized (this) { notifyAll(); }
239	–	}
240	–
241	–	/**
242	–	* Sets status to indicate normal completion.
243	–	*/
244	–	final void setNormalCompletion() {
245	–	// Try typical fast case -- single CAS, no signal, not already done.
246	–	// Manually expand casStatus to improve chances of inlining it
247	–	if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL))
248	–	setCompletion(NORMAL);
249	–	}
250	–
251	–	// internal waiting and notification
252	–
253	–	/**
254	–	* Performs the actual monitor wait for awaitDone.
255	–	*/
256	–	private void doAwaitDone() {
257	–	// Minimize lock bias and in/de-flation effects by maximizing
258	–	// chances of waiting inside sync
224		try {
225	<	while (status >= 0)
226	<	synchronized (this) { if (status >= 0) wait(); }
227	<	} catch (InterruptedException ie) {
228	<	onInterruptedWait();
229	<	}
230	<	}
231	<
267	<	/**
268	<	* Performs the actual timed monitor wait for awaitDone.
269	<	*/
270	<	private void doAwaitDone(long startTime, long nanos) {
271	<	synchronized (this) {
272	<	try {
273	<	while (status >= 0) {
274	<	long nt = nanos - (System.nanoTime() - startTime);
275	<	if (nt <= 0)
276	<	break;
277	<	wait(nt / 1000000, (int) (nt % 1000000));
225	>	if (((s = status) > 0 ||
226	>	(s == 0 &&
227	>	UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL))) &&
228	>	status > 0) {
229	>	synchronized (this) {
230	>	if (status > 0)
231	>	wait(millis);
232		}
279	–	} catch (InterruptedException ie) {
280	–	onInterruptedWait();
233		}
234	+	} catch (InterruptedException ie) {
235	+	// caller must check termination
236		}
237		}
238
285	–	// Awaiting completion
286	–
239		/**
240	<	* Sets status to indicate there is joiner, then waits for join,
241	<	* surrounded with pool notifications.
290	<	*
291	<	* @return status upon exit
240	>	* Blocks a non-worker-thread until completion.
241	>	* @return status upon completion
242		*/
243	<	private int awaitDone(ForkJoinWorkerThread w,
294	<	boolean maintainParallelism) {
295	<	ForkJoinPool pool = (w == null) ? null : w.pool;
243	>	private int externalAwaitDone() {
244		int s;
245	<	while ((s = status) >= 0) {
246	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
247	<	if (pool == null || !pool.preJoin(this, maintainParallelism))
248	<	doAwaitDone();
249	<	if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
250	<	adjustPoolCountsOnUnblock(pool);
251	<	break;
245	>	if ((s = status) >= 0) {
246	>	boolean interrupted = false;
247	>	synchronized (this) {
248	>	while ((s = status) >= 0) {
249	>	if (s == 0)
250	>	UNSAFE.compareAndSwapInt(this, statusOffset,
251	>	0, SIGNAL);
252	>	else {
253	>	try {
254	>	wait();
255	>	} catch (InterruptedException ie) {
256	>	interrupted = true;
257	>	}
258	>	}
259	>	}
260		}
261	+	if (interrupted)
262	+	Thread.currentThread().interrupt();
263		}
264		return s;
265		}
266
267		/**
268	<	* Timed version of awaitDone
311	<	*
312	<	* @return status upon exit
268	>	* Blocks a non-worker-thread until completion or interruption or timeout.
269		*/
270	<	private int awaitDone(ForkJoinWorkerThread w, long nanos) {
271	<	ForkJoinPool pool = (w == null) ? null : w.pool;
270	>	private int externalInterruptibleAwaitDone(long millis)
271	>	throws InterruptedException {
272		int s;
273	<	while ((s = status) >= 0) {
274	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
275	<	long startTime = System.nanoTime();
276	<	if (pool == null || !pool.preJoin(this, false))
277	<	doAwaitDone(startTime, nanos);
278	<	if ((s = status) >= 0) {
279	<	adjustPoolCountsOnCancelledWait(pool);
280	<	s = status;
273	>	if (Thread.interrupted())
274	>	throw new InterruptedException();
275	>	if ((s = status) >= 0) {
276	>	synchronized (this) {
277	>	while ((s = status) >= 0) {
278	>	if (s == 0)
279	>	UNSAFE.compareAndSwapInt(this, statusOffset,
280	>	0, SIGNAL);
281	>	else {
282	>	wait(millis);
283	>	if (millis > 0L)
284	>	break;
285	>	}
286		}
326	–	if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
327	–	adjustPoolCountsOnUnblock(pool);
328	–	break;
287		}
288		}
289		return s;
290		}
291
292		/**
293	<	* Notifies pool that thread is unblocked. Called by signalled
294	<	* threads when woken by non-FJ threads (which is atypical).
293	>	* Primary execution method for stolen tasks. Unless done, calls
294	>	* exec and records status if completed, but doesn't wait for
295	>	* completion otherwise.
296		*/
297	<	private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
298	<	int s;
299	<	do {} while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
300	<	if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
301	<	pool.updateRunningCount(s);
297	>	final void doExec() {
298	>	if (status >= 0) {
299	>	boolean completed;
300	>	try {
301	>	completed = exec();
302	>	} catch (Throwable rex) {
303	>	setExceptionalCompletion(rex);
304	>	return;
305	>	}
306	>	if (completed)
307	>	setCompletion(NORMAL); // must be outside try block
308	>	}
309		}
310
311		/**
312	<	* Notifies pool to adjust counts on cancelled or timed out wait.
312	>	* Primary mechanics for join, get, quietlyJoin.
313	>	* @return status upon completion
314		*/
315	<	private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
316	<	if (pool != null) {
317	<	int s;
318	<	while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
319	<	if (casStatus(s, s - 1)) {
320	<	pool.updateRunningCount(1);
321	<	break;
315	>	private int doJoin() {
316	>	Thread t; ForkJoinWorkerThread w; int s; boolean completed;
317	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
318	>	if ((s = status) < 0)
319	>	return s;
320	>	if ((w = (ForkJoinWorkerThread)t).unpushTask(this)) {
321	>	try {
322	>	completed = exec();
323	>	} catch (Throwable rex) {
324	>	return setExceptionalCompletion(rex);
325		}
326	+	if (completed)
327	+	return setCompletion(NORMAL);
328		}
329	+	return w.joinTask(this);
330		}
331	+	else
332	+	return externalAwaitDone();
333		}
334
335		/**
336	<	* Handles interruptions during waits.
336	>	* Primary mechanics for invoke, quietlyInvoke.
337	>	* @return status upon completion
338		*/
339	<	private void onInterruptedWait() {
340	<	ForkJoinWorkerThread w = getWorker();
341	<	if (w == null)
342	<	Thread.currentThread().interrupt(); // re-interrupt
343	<	else if (w.isTerminating())
344	<	cancelIgnoringExceptions();
345	<	// else if FJworker, ignore interrupt
339	>	private int doInvoke() {
340	>	int s; boolean completed;
341	>	if ((s = status) < 0)
342	>	return s;
343	>	try {
344	>	completed = exec();
345	>	} catch (Throwable rex) {
346	>	return setExceptionalCompletion(rex);
347	>	}
348	>	if (completed)
349	>	return setCompletion(NORMAL);
350	>	else
351	>	return doJoin();
352		}
353
354	<	// Recording and reporting exceptions
373	<
374	<	private void setDoneExceptionally(Throwable rex) {
375	<	exceptionMap.put(this, rex);
376	<	setCompletion(EXCEPTIONAL);
377	<	}
354	>	// Exception table support
355
356		/**
357	<	* Throws the exception associated with status s.
357	>	* Table of exceptions thrown by tasks, to enable reporting by
358	>	* callers. Because exceptions are rare, we don't directly keep
359	>	* them with task objects, but instead use a weak ref table.  Note
360	>	* that cancellation exceptions don't appear in the table, but are
361	>	* instead recorded as status values.
362		*
363	<	* @throws the exception
363	>	* Note: These statics are initialized below in static block.
364		*/
365	<	private void reportException(int s) {
366	<	if ((s &= COMPLETION_MASK) < NORMAL) {
367	<	if (s == CANCELLED)
387	<	throw new CancellationException();
388	<	else
389	<	rethrowException(exceptionMap.get(this));
390	<	}
391	<	}
365	>	private static final ExceptionNode[] exceptionTable;
366	>	private static final ReentrantLock exceptionTableLock;
367	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
368
369		/**
370	<	* Returns result or throws exception using j.u.c.Future conventions.
395	<	* Only call when {@code isDone} known to be true or thread known
396	<	* to be interrupted.
370	>	* Fixed capacity for exceptionTable.
371		*/
372	<	private V reportFutureResult()
399	<	throws InterruptedException, ExecutionException {
400	<	if (Thread.interrupted())
401	<	throw new InterruptedException();
402	<	int s = status & COMPLETION_MASK;
403	<	if (s < NORMAL) {
404	<	Throwable ex;
405	<	if (s == CANCELLED)
406	<	throw new CancellationException();
407	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
408	<	throw new ExecutionException(ex);
409	<	}
410	<	return getRawResult();
411	<	}
372	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
373
374		/**
375	<	* Returns result or throws exception using j.u.c.Future conventions
376	<	* with timeouts.
375	>	* Key-value nodes for exception table.  The chained hash table
376	>	* uses identity comparisons, full locking, and weak references
377	>	* for keys. The table has a fixed capacity because it only
378	>	* maintains task exceptions long enough for joiners to access
379	>	* them, so should never become very large for sustained
380	>	* periods. However, since we do not know when the last joiner
381	>	* completes, we must use weak references and expunge them. We do
382	>	* so on each operation (hence full locking). Also, some thread in
383	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
384	>	* pool becomes isQuiescent.
385		*/
386	<	private V reportTimedFutureResult()
387	<	throws InterruptedException, ExecutionException, TimeoutException {
388	<	if (Thread.interrupted())
389	<	throw new InterruptedException();
390	<	Throwable ex;
391	<	int s = status & COMPLETION_MASK;
392	<	if (s == NORMAL)
393	<	return getRawResult();
394	<	else if (s == CANCELLED)
395	<	throw new CancellationException();
427	<	else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
428	<	throw new ExecutionException(ex);
429	<	else
430	<	throw new TimeoutException();
386	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>>{
387	>	final Throwable ex;
388	>	ExceptionNode next;
389	>	final long thrower;  // use id not ref to avoid weak cycles
390	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
391	>	super(task, exceptionTableRefQueue);
392	>	this.ex = ex;
393	>	this.next = next;
394	>	this.thrower = Thread.currentThread().getId();
395	>	}
396		}
397
433	–	// internal execution methods
434	–
398		/**
399	<	* Calls exec, recording completion, and rethrowing exception if
437	<	* encountered. Caller should normally check status before calling.
399	>	* Records exception and sets exceptional completion.
400		*
401	<	* @return true if completed normally
401	>	* @return status on exit
402		*/
403	<	private boolean tryExec() {
404	<	try { // try block must contain only call to exec
405	<	if (!exec())
406	<	return false;
407	<	} catch (Throwable rex) {
408	<	setDoneExceptionally(rex);
409	<	rethrowException(rex);
410	<	return false; // not reached
403	>	private int setExceptionalCompletion(Throwable ex) {
404	>	int h = System.identityHashCode(this);
405	>	final ReentrantLock lock = exceptionTableLock;
406	>	lock.lock();
407	>	try {
408	>	expungeStaleExceptions();
409	>	ExceptionNode[] t = exceptionTable;
410	>	int i = h & (t.length - 1);
411	>	for (ExceptionNode e = t[i]; ; e = e.next) {
412	>	if (e == null) {
413	>	t[i] = new ExceptionNode(this, ex, t[i]);
414	>	break;
415	>	}
416	>	if (e.get() == this) // already present
417	>	break;
418	>	}
419	>	} finally {
420	>	lock.unlock();
421		}
422	<	setNormalCompletion();
451	<	return true;
422	>	return setCompletion(EXCEPTIONAL);
423		}
424
425		/**
426	<	* Main execution method used by worker threads. Invokes
456	<	* base computation unless already complete.
426	>	* Removes exception node and clears status
427		*/
428	<	final void quietlyExec() {
429	<	if (status >= 0) {
428	>	private void clearExceptionalCompletion() {
429	>	int h = System.identityHashCode(this);
430	>	final ReentrantLock lock = exceptionTableLock;
431	>	lock.lock();
432	>	try {
433	>	ExceptionNode[] t = exceptionTable;
434	>	int i = h & (t.length - 1);
435	>	ExceptionNode e = t[i];
436	>	ExceptionNode pred = null;
437	>	while (e != null) {
438	>	ExceptionNode next = e.next;
439	>	if (e.get() == this) {
440	>	if (pred == null)
441	>	t[i] = next;
442	>	else
443	>	pred.next = next;
444	>	break;
445	>	}
446	>	pred = e;
447	>	e = next;
448	>	}
449	>	expungeStaleExceptions();
450	>	status = 0;
451	>	} finally {
452	>	lock.unlock();
453	>	}
454	>	}
455	>
456	>	/**
457	>	* Returns a rethrowable exception for the given task, if
458	>	* available. To provide accurate stack traces, if the exception
459	>	* was not thrown by the current thread, we try to create a new
460	>	* exception of the same type as the one thrown, but with the
461	>	* recorded exception as its cause. If there is no such
462	>	* constructor, we instead try to use a no-arg constructor,
463	>	* followed by initCause, to the same effect. If none of these
464	>	* apply, or any fail due to other exceptions, we return the
465	>	* recorded exception, which is still correct, although it may
466	>	* contain a misleading stack trace.
467	>	*
468	>	* @return the exception, or null if none
469	>	*/
470	>	private Throwable getThrowableException() {
471	>	if (status != EXCEPTIONAL)
472	>	return null;
473	>	int h = System.identityHashCode(this);
474	>	ExceptionNode e;
475	>	final ReentrantLock lock = exceptionTableLock;
476	>	lock.lock();
477	>	try {
478	>	expungeStaleExceptions();
479	>	ExceptionNode[] t = exceptionTable;
480	>	e = t[h & (t.length - 1)];
481	>	while (e != null && e.get() != this)
482	>	e = e.next;
483	>	} finally {
484	>	lock.unlock();
485	>	}
486	>	Throwable ex;
487	>	if (e == null || (ex = e.ex) == null)
488	>	return null;
489	>	if (e.thrower != Thread.currentThread().getId()) {
490	>	Class<? extends Throwable> ec = ex.getClass();
491		try {
492	<	if (!exec())
493	<	return;
494	<	} catch (Throwable rex) {
495	<	setDoneExceptionally(rex);
496	<	return;
492	>	Constructor<?> noArgCtor = null;
493	>	Constructor<?>[] cs = ec.getConstructors();// public ctors only
494	>	for (int i = 0; i < cs.length; ++i) {
495	>	Constructor<?> c = cs[i];
496	>	Class<?>[] ps = c.getParameterTypes();
497	>	if (ps.length == 0)
498	>	noArgCtor = c;
499	>	else if (ps.length == 1 && ps[0] == Throwable.class)
500	>	return (Throwable)(c.newInstance(ex));
501	>	}
502	>	if (noArgCtor != null) {
503	>	Throwable wx = (Throwable)(noArgCtor.newInstance());
504	>	wx.initCause(ex);
505	>	return wx;
506	>	}
507	>	} catch (Exception ignore) {
508		}
467	–	setNormalCompletion();
509		}
510	+	return ex;
511		}
512
513		/**
514	<	* Calls exec(), recording but not rethrowing exception.
473	<	* Caller should normally check status before calling.
474	<	*
475	<	* @return true if completed normally
514	>	* Poll stale refs and remove them. Call only while holding lock.
515		*/
516	<	private boolean tryQuietlyInvoke() {
517	<	try {
518	<	if (!exec())
519	<	return false;
520	<	} catch (Throwable rex) {
521	<	setDoneExceptionally(rex);
522	<	return false;
516	>	private static void expungeStaleExceptions() {
517	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
518	>	if (x instanceof ExceptionNode) {
519	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
520	>	ExceptionNode[] t = exceptionTable;
521	>	int i = System.identityHashCode(key) & (t.length - 1);
522	>	ExceptionNode e = t[i];
523	>	ExceptionNode pred = null;
524	>	while (e != null) {
525	>	ExceptionNode next = e.next;
526	>	if (e == x) {
527	>	if (pred == null)
528	>	t[i] = next;
529	>	else
530	>	pred.next = next;
531	>	break;
532	>	}
533	>	pred = e;
534	>	e = next;
535	>	}
536	>	}
537		}
485	–	setNormalCompletion();
486	–	return true;
538		}
539
540		/**
541	<	* Cancels, ignoring any exceptions it throws.
541	>	* If lock is available, poll stale refs and remove them.
542	>	* Called from ForkJoinPool when pools become quiescent.
543		*/
544	<	final void cancelIgnoringExceptions() {
545	<	try {
546	<	cancel(false);
547	<	} catch (Throwable ignore) {
544	>	static final void helpExpungeStaleExceptions() {
545	>	final ReentrantLock lock = exceptionTableLock;
546	>	if (lock.tryLock()) {
547	>	try {
548	>	expungeStaleExceptions();
549	>	} finally {
550	>	lock.unlock();
551	>	}
552		}
553		}
554
555		/**
556	<	* Main implementation of helpJoin
556	>	* Report the result of invoke or join; called only upon
557	>	* non-normal return of internal versions.
558		*/
559	<	private int busyJoin(ForkJoinWorkerThread w) {
560	<	int s;
561	<	ForkJoinTask<?> t;
562	<	while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
563	<	t.quietlyExec();
564	<	return (s >= 0) ? awaitDone(w, false) : s; // block if no work
559	>	private V reportResult() {
560	>	int s; Throwable ex;
561	>	if ((s = status) == CANCELLED)
562	>	throw new CancellationException();
563	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
564	>	UNSAFE.throwException(ex);
565	>	return getRawResult();
566		}
567
568		// public methods
#	Line 513 | Line 571 | public abstract class ForkJoinTask<V> im
571		* Arranges to asynchronously execute this task.  While it is not
572		* necessarily enforced, it is a usage error to fork a task more
573		* than once unless it has completed and been reinitialized.
574	+	* Subsequent modifications to the state of this task or any data
575	+	* it operates on are not necessarily consistently observable by
576	+	* any thread other than the one executing it unless preceded by a
577	+	* call to {@link #join} or related methods, or a call to {@link
578	+	* #isDone} returning {@code true}.
579		*
580		* <p>This method may be invoked only from within {@code
581	<	* ForkJoinTask} computations (as may be determined using method
581	>	* ForkJoinPool} computations (as may be determined using method
582		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
583		* result in exceptions or errors, possibly including {@code
584		* ClassCastException}.
#	Line 529 | Line 592 | public abstract class ForkJoinTask<V> im
592		}
593
594		/**
595	<	* Returns the result of the computation when it is ready.
596	<	* This method differs from {@link #get()} in that
595	>	* Returns the result of the computation when it {@link #isDone is
596	>	* done}.  This method differs from {@link #get()} in that
597		* abnormal completion results in {@code RuntimeException} or
598	<	* {@code Error}, not {@code ExecutionException}.
598	>	* {@code Error}, not {@code ExecutionException}, and that
599	>	* interrupts of the calling thread do <em>not</em> cause the
600	>	* method to abruptly return by throwing {@code
601	>	* InterruptedException}.
602		*
603		* @return the computed result
604		*/
605		public final V join() {
606	<	ForkJoinWorkerThread w = getWorker();
607	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryExec())
608	<	reportException(awaitDone(w, true));
609	<	return getRawResult();
606	>	if (doJoin() != NORMAL)
607	>	return reportResult();
608	>	else
609	>	return getRawResult();
610		}
611
612		/**
613		* Commences performing this task, awaits its completion if
614	<	* necessary, and return its result, or throws an (unchecked)
615	<	* exception if the underlying computation did so.
614	>	* necessary, and returns its result, or throws an (unchecked)
615	>	* {@code RuntimeException} or {@code Error} if the underlying
616	>	* computation did so.
617		*
618		* @return the computed result
619		*/
620		public final V invoke() {
621	<	if (status >= 0 && tryExec())
622	<	return getRawResult();
621	>	if (doInvoke() != NORMAL)
622	>	return reportResult();
623		else
624	<	return join();
624	>	return getRawResult();
625		}
626
627		/**
628		* Forks the given tasks, returning when {@code isDone} holds for
629		* each task or an (unchecked) exception is encountered, in which
630	<	* case the exception is rethrown.  If either task encounters an
631	<	* exception, the other one may be, but is not guaranteed to be,
632	<	* cancelled.  If both tasks throw an exception, then this method
633	<	* throws one of them.  The individual status of each task may be
634	<	* checked using {@link #getException()} and related methods.
630	>	* case the exception is rethrown. If more than one task
631	>	* encounters an exception, then this method throws any one of
632	>	* these exceptions. If any task encounters an exception, the
633	>	* other may be cancelled. However, the execution status of
634	>	* individual tasks is not guaranteed upon exceptional return. The
635	>	* status of each task may be obtained using {@link
636	>	* #getException()} and related methods to check if they have been
637	>	* cancelled, completed normally or exceptionally, or left
638	>	* unprocessed.
639		*
640		* <p>This method may be invoked only from within {@code
641	<	* ForkJoinTask} computations (as may be determined using method
641	>	* ForkJoinPool} computations (as may be determined using method
642		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
643		* result in exceptions or errors, possibly including {@code
644		* ClassCastException}.
#	Line 585 | Line 656 | public abstract class ForkJoinTask<V> im
656		/**
657		* Forks the given tasks, returning when {@code isDone} holds for
658		* each task or an (unchecked) exception is encountered, in which
659	<	* case the exception is rethrown. If any task encounters an
660	<	* exception, others may be, but are not guaranteed to be,
661	<	* cancelled.  If more than one task encounters an exception, then
662	<	* this method throws any one of these exceptions.  The individual
663	<	* status of each task may be checked using {@link #getException()}
664	<	* and related methods.
659	>	* case the exception is rethrown. If more than one task
660	>	* encounters an exception, then this method throws any one of
661	>	* these exceptions. If any task encounters an exception, others
662	>	* may be cancelled. However, the execution status of individual
663	>	* tasks is not guaranteed upon exceptional return. The status of
664	>	* each task may be obtained using {@link #getException()} and
665	>	* related methods to check if they have been cancelled, completed
666	>	* normally or exceptionally, or left unprocessed.
667		*
668		* <p>This method may be invoked only from within {@code
669	<	* ForkJoinTask} computations (as may be determined using method
669	>	* ForkJoinPool} computations (as may be determined using method
670		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
671		* result in exceptions or errors, possibly including {@code
672		* ClassCastException}.
#	Line 612 | Line 685 | public abstract class ForkJoinTask<V> im
685		}
686		else if (i != 0)
687		t.fork();
688	<	else {
689	<	t.quietlyInvoke();
617	<	if (ex == null)
618	<	ex = t.getException();
619	<	}
688	>	else if (t.doInvoke() < NORMAL && ex == null)
689	>	ex = t.getException();
690		}
691		for (int i = 1; i <= last; ++i) {
692		ForkJoinTask<?> t = tasks[i];
693		if (t != null) {
694		if (ex != null)
695		t.cancel(false);
696	<	else {
697	<	t.quietlyJoin();
628	<	if (ex == null)
629	<	ex = t.getException();
630	<	}
696	>	else if (t.doJoin() < NORMAL && ex == null)
697	>	ex = t.getException();
698		}
699		}
700		if (ex != null)
701	<	rethrowException(ex);
701	>	UNSAFE.throwException(ex);
702		}
703
704		/**
705		* Forks all tasks in the specified collection, returning when
706		* {@code isDone} holds for each task or an (unchecked) exception
707	<	* is encountered.  If any task encounters an exception, others
708	<	* may be, but are not guaranteed to be, cancelled.  If more than
709	<	* one task encounters an exception, then this method throws any
710	<	* one of these exceptions.  The individual status of each task
711	<	* may be checked using {@link #getException()} and related
712	<	* methods.  The behavior of this operation is undefined if the
713	<	* specified collection is modified while the operation is in
714	<	* progress.
707	>	* is encountered, in which case the exception is rethrown. If
708	>	* more than one task encounters an exception, then this method
709	>	* throws any one of these exceptions. If any task encounters an
710	>	* exception, others may be cancelled. However, the execution
711	>	* status of individual tasks is not guaranteed upon exceptional
712	>	* return. The status of each task may be obtained using {@link
713	>	* #getException()} and related methods to check if they have been
714	>	* cancelled, completed normally or exceptionally, or left
715	>	* unprocessed.
716		*
717		* <p>This method may be invoked only from within {@code
718	<	* ForkJoinTask} computations (as may be determined using method
718	>	* ForkJoinPool} computations (as may be determined using method
719		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
720		* result in exceptions or errors, possibly including {@code
721		* ClassCastException}.
#	Line 674 | Line 742 | public abstract class ForkJoinTask<V> im
742		}
743		else if (i != 0)
744		t.fork();
745	<	else {
746	<	t.quietlyInvoke();
679	<	if (ex == null)
680	<	ex = t.getException();
681	<	}
745	>	else if (t.doInvoke() < NORMAL && ex == null)
746	>	ex = t.getException();
747		}
748		for (int i = 1; i <= last; ++i) {
749		ForkJoinTask<?> t = ts.get(i);
750		if (t != null) {
751		if (ex != null)
752		t.cancel(false);
753	<	else {
754	<	t.quietlyJoin();
690	<	if (ex == null)
691	<	ex = t.getException();
692	<	}
753	>	else if (t.doJoin() < NORMAL && ex == null)
754	>	ex = t.getException();
755		}
756		}
757		if (ex != null)
758	<	rethrowException(ex);
758	>	UNSAFE.throwException(ex);
759		return tasks;
760		}
761
762		/**
763		* Attempts to cancel execution of this task. This attempt will
764	<	* fail if the task has already completed, has already been
765	<	* cancelled, or could not be cancelled for some other reason. If
766	<	* successful, and this task has not started when cancel is
767	<	* called, execution of this task is suppressed, {@link
768	<	* #isCancelled} will report true, and {@link #join} will result
769	<	* in a {@code CancellationException} being thrown.
764	>	* fail if the task has already completed or could not be
765	>	* cancelled for some other reason. If successful, and this task
766	>	* has not started when {@code cancel} is called, execution of
767	>	* this task is suppressed. After this method returns
768	>	* successfully, unless there is an intervening call to {@link
769	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
770	>	* {@link #isDone}, and {@code cancel} will return {@code true}
771	>	* and calls to {@link #join} and related methods will result in
772	>	* {@code CancellationException}.
773		*
774		* <p>This method may be overridden in subclasses, but if so, must
775	<	* still ensure that these minimal properties hold. In particular,
776	<	* the {@code cancel} method itself must not throw exceptions.
775	>	* still ensure that these properties hold. In particular, the
776	>	* {@code cancel} method itself must not throw exceptions.
777		*
778		* <p>This method is designed to be invoked by <em>other</em>
779		* tasks. To terminate the current task, you can just return or
780		* throw an unchecked exception from its computation method, or
781		* invoke {@link #completeExceptionally}.
782		*
783	<	* @param mayInterruptIfRunning this value is ignored in the
784	<	* default implementation because tasks are not
785	<	* cancelled via interruption
783	>	* @param mayInterruptIfRunning this value has no effect in the
784	>	* default implementation because interrupts are not used to
785	>	* control cancellation.
786		*
787		* @return {@code true} if this task is now cancelled
788		*/
789		public boolean cancel(boolean mayInterruptIfRunning) {
790	<	setCompletion(CANCELLED);
726	<	return (status & COMPLETION_MASK) == CANCELLED;
790	>	return setCompletion(CANCELLED) == CANCELLED;
791		}
792
793		/**
794	<	* Returns {@code true} if the computation performed by this task
795	<	* has completed (or has been cancelled).
796	<	*
797	<	* @return {@code true} if this computation has completed
794	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
795	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
796	>	* exceptions, but if it does anyway, we have no recourse during
797	>	* shutdown, so guard against this case.
798		*/
799	+	final void cancelIgnoringExceptions() {
800	+	try {
801	+	cancel(false);
802	+	} catch (Throwable ignore) {
803	+	}
804	+	}
805	+
806		public final boolean isDone() {
807		return status < 0;
808		}
809
739	–	/**
740	–	* Returns {@code true} if this task was cancelled.
741	–	*
742	–	* @return {@code true} if this task was cancelled
743	–	*/
810		public final boolean isCancelled() {
811	<	return (status & COMPLETION_MASK) == CANCELLED;
811	>	return status == CANCELLED;
812		}
813
814		/**
#	Line 751 | Line 817 | public abstract class ForkJoinTask<V> im
817		* @return {@code true} if this task threw an exception or was cancelled
818		*/
819		public final boolean isCompletedAbnormally() {
820	<	return (status & COMPLETION_MASK) < NORMAL;
820	>	return status < NORMAL;
821		}
822
823		/**
#	Line 762 | Line 828 | public abstract class ForkJoinTask<V> im
828		* exception and was not cancelled
829		*/
830		public final boolean isCompletedNormally() {
831	<	return (status & COMPLETION_MASK) == NORMAL;
766	<	}
767	<
768	<	/**
769	<	* Returns {@code true} if this task threw an exception.
770	<	*
771	<	* @return {@code true} if this task threw an exception
772	<	*/
773	<	public final boolean isCompletedExceptionally() {
774	<	return (status & COMPLETION_MASK) == EXCEPTIONAL;
831	>	return status == NORMAL;
832		}
833
834		/**
#	Line 782 | Line 839 | public abstract class ForkJoinTask<V> im
839		* @return the exception, or {@code null} if none
840		*/
841		public final Throwable getException() {
842	<	int s = status & COMPLETION_MASK;
842	>	int s = status;
843		return ((s >= NORMAL)    ? null :
844		(s == CANCELLED) ? new CancellationException() :
845	<	exceptionMap.get(this));
845	>	getThrowableException());
846		}
847
848		/**
#	Line 798 | Line 855 | public abstract class ForkJoinTask<V> im
855		* overridable, but overridden versions must invoke {@code super}
856		* implementation to maintain guarantees.
857		*
858	<	* @param ex the exception to throw. If this exception is
859	<	* not a RuntimeException or Error, the actual exception thrown
860	<	* will be a RuntimeException with cause ex.
858	>	* @param ex the exception to throw. If this exception is not a
859	>	* {@code RuntimeException} or {@code Error}, the actual exception
860	>	* thrown will be a {@code RuntimeException} with cause {@code ex}.
861		*/
862		public void completeExceptionally(Throwable ex) {
863	<	setDoneExceptionally((ex instanceof RuntimeException) ||
864	<	(ex instanceof Error) ? ex :
865	<	new RuntimeException(ex));
863	>	setExceptionalCompletion((ex instanceof RuntimeException) ||
864	>	(ex instanceof Error) ? ex :
865	>	new RuntimeException(ex));
866		}
867
868		/**
869		* Completes this task, and if not already aborted or cancelled,
870	<	* returning a {@code null} result upon {@code join} and related
871	<	* operations. This method may be used to provide results for
872	<	* asynchronous tasks, or to provide alternative handling for
873	<	* tasks that would not otherwise complete normally. Its use in
874	<	* other situations is discouraged. This method is
875	<	* overridable, but overridden versions must invoke {@code super}
876	<	* implementation to maintain guarantees.
870	>	* returning the given value as the result of subsequent
871	>	* invocations of {@code join} and related operations. This method
872	>	* may be used to provide results for asynchronous tasks, or to
873	>	* provide alternative handling for tasks that would not otherwise
874	>	* complete normally. Its use in other situations is
875	>	* discouraged. This method is overridable, but overridden
876	>	* versions must invoke {@code super} implementation to maintain
877	>	* guarantees.
878		*
879		* @param value the result value for this task
880		*/
#	Line 824 | Line 882 | public abstract class ForkJoinTask<V> im
882		try {
883		setRawResult(value);
884		} catch (Throwable rex) {
885	<	setDoneExceptionally(rex);
885	>	setExceptionalCompletion(rex);
886		return;
887		}
888	<	setNormalCompletion();
831	<	}
832	<
833	<	public final V get() throws InterruptedException, ExecutionException {
834	<	ForkJoinWorkerThread w = getWorker();
835	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
836	<	awaitDone(w, true);
837	<	return reportFutureResult();
838	<	}
839	<
840	<	public final V get(long timeout, TimeUnit unit)
841	<	throws InterruptedException, ExecutionException, TimeoutException {
842	<	long nanos = unit.toNanos(timeout);
843	<	ForkJoinWorkerThread w = getWorker();
844	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
845	<	awaitDone(w, nanos);
846	<	return reportTimedFutureResult();
888	>	setCompletion(NORMAL);
889		}
890
891		/**
892	<	* Possibly executes other tasks until this task is ready, then
893	<	* returns the result of the computation.  This method may be more
852	<	* efficient than {@code join}, but is only applicable when
853	<	* there are no potential dependencies between continuation of the
854	<	* current task and that of any other task that might be executed
855	<	* while helping. (This usually holds for pure divide-and-conquer
856	<	* tasks).
857	<	*
858	<	* <p>This method may be invoked only from within {@code
859	<	* ForkJoinTask} computations (as may be determined using method
860	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
861	<	* result in exceptions or errors, possibly including {@code
862	<	* ClassCastException}.
892	>	* Waits if necessary for the computation to complete, and then
893	>	* retrieves its result.
894		*
895		* @return the computed result
896	+	* @throws CancellationException if the computation was cancelled
897	+	* @throws ExecutionException if the computation threw an
898	+	* exception
899	+	* @throws InterruptedException if the current thread is not a
900	+	* member of a ForkJoinPool and was interrupted while waiting
901		*/
902	<	public final V helpJoin() {
903	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
904	<	if (status < 0 || !w.unpushTask(this) || !tryExec())
905	<	reportException(busyJoin(w));
902	>	public final V get() throws InterruptedException, ExecutionException {
903	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
904	>	doJoin() : externalInterruptibleAwaitDone(0L);
905	>	Throwable ex;
906	>	if (s == CANCELLED)
907	>	throw new CancellationException();
908	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
909	>	throw new ExecutionException(ex);
910		return getRawResult();
911		}
912
913		/**
914	<	* Possibly executes other tasks until this task is ready.  This
915	<	* method may be useful when processing collections of tasks when
876	<	* some have been cancelled or otherwise known to have aborted.
914	>	* Waits if necessary for at most the given time for the computation
915	>	* to complete, and then retrieves its result, if available.
916		*
917	<	* <p>This method may be invoked only from within {@code
918	<	* ForkJoinTask} 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}.
917	>	* @param timeout the maximum time to wait
918	>	* @param unit the time unit of the timeout argument
919	>	* @return the computed result
920	>	* @throws CancellationException if the computation was cancelled
921	>	* @throws ExecutionException if the computation threw an
922	>	* exception
923	>	* @throws InterruptedException if the current thread is not a
924	>	* member of a ForkJoinPool and was interrupted while waiting
925	>	* @throws TimeoutException if the wait timed out
926		*/
927	<	public final void quietlyHelpJoin() {
928	<	if (status >= 0) {
929	<	ForkJoinWorkerThread w =
930	<	(ForkJoinWorkerThread) Thread.currentThread();
931	<	if (!w.unpushTask(this) || !tryQuietlyInvoke())
932	<	busyJoin(w);
927	>	public final V get(long timeout, TimeUnit unit)
928	>	throws InterruptedException, ExecutionException, TimeoutException {
929	>	Thread t = Thread.currentThread();
930	>	if (t instanceof ForkJoinWorkerThread) {
931	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
932	>	long nanos = unit.toNanos(timeout);
933	>	if (status >= 0) {
934	>	boolean completed = false;
935	>	if (w.unpushTask(this)) {
936	>	try {
937	>	completed = exec();
938	>	} catch (Throwable rex) {
939	>	setExceptionalCompletion(rex);
940	>	}
941	>	}
942	>	if (completed)
943	>	setCompletion(NORMAL);
944	>	else if (status >= 0 && nanos > 0)
945	>	w.pool.timedAwaitJoin(this, nanos);
946	>	}
947	>	}
948	>	else {
949	>	long millis = unit.toMillis(timeout);
950	>	if (millis > 0)
951	>	externalInterruptibleAwaitDone(millis);
952	>	}
953	>	int s = status;
954	>	if (s != NORMAL) {
955	>	Throwable ex;
956	>	if (s == CANCELLED)
957	>	throw new CancellationException();
958	>	if (s != EXCEPTIONAL)
959	>	throw new TimeoutException();
960	>	if ((ex = getThrowableException()) != null)
961	>	throw new ExecutionException(ex);
962		}
963	+	return getRawResult();
964		}
965
966		/**
967	<	* Joins this task, without returning its result or throwing an
967	>	* Joins this task, without returning its result or throwing its
968		* exception. This method may be useful when processing
969		* collections of tasks when some have been cancelled or otherwise
970		* known to have aborted.
971		*/
972		public final void quietlyJoin() {
973	<	if (status >= 0) {
901	<	ForkJoinWorkerThread w = getWorker();
902	<	if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
903	<	awaitDone(w, true);
904	<	}
973	>	doJoin();
974		}
975
976		/**
977		* Commences performing this task and awaits its completion if
978	<	* necessary, without returning its result or throwing an
979	<	* exception. This method may be useful when processing
911	<	* collections of tasks when some have been cancelled or otherwise
912	<	* known to have aborted.
978	>	* necessary, without returning its result or throwing its
979	>	* exception.
980		*/
981		public final void quietlyInvoke() {
982	<	if (status >= 0 && !tryQuietlyInvoke())
916	<	quietlyJoin();
982	>	doInvoke();
983		}
984
985		/**
#	Line 924 | Line 990 | public abstract class ForkJoinTask<V> im
990		* processed.
991		*
992		* <p>This method may be invoked only from within {@code
993	<	* ForkJoinTask} computations (as may be determined using method
993	>	* ForkJoinPool} computations (as may be determined using method
994		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
995		* result in exceptions or errors, possibly including {@code
996		* ClassCastException}.
#	Line 943 | Line 1009 | public abstract class ForkJoinTask<V> im
1009		* under any other usage conditions are not guaranteed.
1010		* This method may be useful when executing
1011		* pre-constructed trees of subtasks in loops.
1012	+	*
1013	+	* <p>Upon completion of this method, {@code isDone()} reports
1014	+	* {@code false}, and {@code getException()} reports {@code
1015	+	* null}. However, the value returned by {@code getRawResult} is
1016	+	* unaffected. To clear this value, you can invoke {@code
1017	+	* setRawResult(null)}.
1018		*/
1019		public void reinitialize() {
1020	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
1021	<	exceptionMap.remove(this);
1022	<	status = 0;
1020	>	if (status == EXCEPTIONAL)
1021	>	clearExceptionalCompletion();
1022	>	else
1023	>	status = 0;
1024		}
1025
1026		/**
#	Line 964 | Line 1037 | public abstract class ForkJoinTask<V> im
1037		}
1038
1039		/**
1040	<	* Returns {@code true} if the current thread is executing as a
1041	<	* ForkJoinPool computation.
1040	>	* Returns {@code true} if the current thread is a {@link
1041	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1042		*
1043	<	* @return {@code true} if the current thread is executing as a
1044	<	* ForkJoinPool computation, or false otherwise
1043	>	* @return {@code true} if the current thread is a {@link
1044	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1045	>	* or {@code false} otherwise
1046		*/
1047		public static boolean inForkJoinPool() {
1048		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 983 | Line 1057 | public abstract class ForkJoinTask<V> im
1057		* were not, stolen.
1058		*
1059		* <p>This method may be invoked only from within {@code
1060	<	* ForkJoinTask} computations (as may be determined using method
1060	>	* ForkJoinPool} computations (as may be determined using method
1061		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1062		* result in exceptions or errors, possibly including {@code
1063		* ClassCastException}.
#	Line 1002 | Line 1076 | public abstract class ForkJoinTask<V> im
1076		* fork other tasks.
1077		*
1078		* <p>This method may be invoked only from within {@code
1079	<	* ForkJoinTask} computations (as may be determined using method
1079	>	* ForkJoinPool} computations (as may be determined using method
1080		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1081		* result in exceptions or errors, possibly including {@code
1082		* ClassCastException}.
#	Line 1025 | Line 1099 | public abstract class ForkJoinTask<V> im
1099		* exceeded.
1100		*
1101		* <p>This method may be invoked only from within {@code
1102	<	* ForkJoinTask} computations (as may be determined using method
1102	>	* ForkJoinPool} computations (as may be determined using method
1103		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1104		* result in exceptions or errors, possibly including {@code
1105		* ClassCastException}.
#	Line 1083 | Line 1157 | public abstract class ForkJoinTask<V> im
1157		* otherwise.
1158		*
1159		* <p>This method may be invoked only from within {@code
1160	<	* ForkJoinTask} computations (as may be determined using method
1160	>	* ForkJoinPool} computations (as may be determined using method
1161		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1162		* result in exceptions or errors, possibly including {@code
1163		* ClassCastException}.
#	Line 1102 | Line 1176 | public abstract class ForkJoinTask<V> im
1176		* be useful otherwise.
1177		*
1178		* <p>This method may be invoked only from within {@code
1179	<	* ForkJoinTask} computations (as may be determined using method
1179	>	* ForkJoinPool} computations (as may be determined using method
1180		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1181		* result in exceptions or errors, possibly including {@code
1182		* ClassCastException}.
#	Line 1125 | Line 1199 | public abstract class ForkJoinTask<V> im
1199		* otherwise.
1200		*
1201		* <p>This method may be invoked only from within {@code
1202	<	* ForkJoinTask} computations (as may be determined using method
1202	>	* ForkJoinPool} computations (as may be determined using method
1203		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1204		* result in exceptions or errors, possibly including {@code
1205		* ClassCastException}.
#	Line 1235 | Line 1309 | public abstract class ForkJoinTask<V> im
1309		private static final long serialVersionUID = -7721805057305804111L;
1310
1311		/**
1312	<	* Save the state to a stream.
1312	>	* Saves the state to a stream (that is, serializes it).
1313		*
1314		* @serialData the current run status and the exception thrown
1315		* during execution, or {@code null} if none
#	Line 1248 | Line 1322 | public abstract class ForkJoinTask<V> im
1322		}
1323
1324		/**
1325	<	* Reconstitute the instance from a stream.
1325	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1326		*
1327		* @param s the stream
1328		*/
1329		private void readObject(java.io.ObjectInputStream s)
1330		throws java.io.IOException, ClassNotFoundException {
1331		s.defaultReadObject();
1258	–	status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
1259	–	status |= EXTERNAL_SIGNAL; // conservatively set external signal
1332		Object ex = s.readObject();
1333		if (ex != null)
1334	<	setDoneExceptionally((Throwable) ex);
1334	>	setExceptionalCompletion((Throwable)ex);
1335		}
1336
1337		// Unsafe mechanics
1338	<
1339	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1340	<	private static final long statusOffset =
1341	<	objectFieldOffset("status", ForkJoinTask.class);
1342	<
1343	<	private static long objectFieldOffset(String field, Class<?> klazz) {
1338	>	private static final sun.misc.Unsafe UNSAFE;
1339	>	private static final long statusOffset;
1340	>	static {
1341	>	exceptionTableLock = new ReentrantLock();
1342	>	exceptionTableRefQueue = new ReferenceQueue<Object>();
1343	>	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1344		try {
1345	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1346	<	} catch (NoSuchFieldException e) {
1347	<	// Convert Exception to corresponding Error
1348	<	NoSuchFieldError error = new NoSuchFieldError(field);
1349	<	error.initCause(e);
1278	<	throw error;
1345	>	UNSAFE = getUnsafe();
1346	>	statusOffset = UNSAFE.objectFieldOffset
1347	>	(ForkJoinTask.class.getDeclaredField("status"));
1348	>	} catch (Exception e) {
1349	>	throw new Error(e);
1350		}
1351		}
1352

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