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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.40 by dl, Wed Aug 5 11:09:28 2009 UTC vs.
Revision 1.74 by dl, Tue Feb 22 00:39:31 2011 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;
12		import java.util.List;
13		import java.util.RandomAccess;
14		import java.util.Map;
15	<	import java.util.WeakHashMap;
15	>	import java.lang.ref.WeakReference;
16	>	import java.lang.ref.ReferenceQueue;
17	>	import java.util.concurrent.Callable;
18	>	import java.util.concurrent.CancellationException;
19	>	import java.util.concurrent.ExecutionException;
20	>	import java.util.concurrent.Executor;
21	>	import java.util.concurrent.ExecutorService;
22	>	import java.util.concurrent.Future;
23	>	import java.util.concurrent.RejectedExecutionException;
24	>	import java.util.concurrent.RunnableFuture;
25	>	import java.util.concurrent.TimeUnit;
26	>	import java.util.concurrent.TimeoutException;
27	>	import java.util.concurrent.locks.ReentrantLock;
28	>	import java.lang.reflect.Constructor;
29
30		/**
31		* Abstract base class for tasks that run within a {@link ForkJoinPool}.
#	Line 28 | Line 39 | import java.util.WeakHashMap;
39		* start other subtasks.  As indicated by the name of this class,
40		* many programs using {@code ForkJoinTask} employ only methods
41		* {@link #fork} and {@link #join}, or derivatives such as {@link
42	<	* #invokeAll}.  However, this class also provides a number of other
43	<	* methods that can come into play in advanced usages, as well as
44	<	* extension mechanics that allow support of new forms of fork/join
45	<	* processing.
42	>	* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
43	>	* provides a number of other methods that can come into play in
44	>	* advanced usages, as well as extension mechanics that allow
45	>	* support of new forms of fork/join processing.
46		*
47		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
48		* The efficiency of {@code ForkJoinTask}s stems from a set of
#	Line 56 | Line 67 | import java.util.WeakHashMap;
67		* exceptions such as {@code IOExceptions} to be thrown. However,
68		* computations may still encounter unchecked exceptions, that are
69		* rethrown to callers attempting to join them. These exceptions may
70	<	* additionally include RejectedExecutionExceptions stemming from
71	<	* internal resource exhaustion such as failure to allocate internal
72	<	* task queues.
70	>	* additionally include {@link RejectedExecutionException} stemming
71	>	* from internal resource exhaustion, such as failure to allocate
72	>	* internal task queues. Rethrown exceptions behave in the same way as
73	>	* regular exceptions, but, when possible, contain stack traces (as
74	>	* displayed for example using {@code ex.printStackTrace()}) of both
75	>	* the thread that initiated the computation as well as the thread
76	>	* actually encountering the exception; minimally only the latter.
77		*
78		* <p>The primary method for awaiting completion and extracting
79		* results of a task is {@link #join}, but there are several variants:
80		* The {@link Future#get} methods support interruptible and/or timed
81		* waits for completion and report results using {@code Future}
82	<	* 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
82	>	* conventions. Method {@link #invoke} is semantically
83		* equivalent to {@code fork(); join()} but always attempts to begin
84		* execution in the current thread. The "<em>quiet</em>" forms of
85		* these methods do not extract results or report exceptions. These
#	Line 80 | Line 92 | import java.util.WeakHashMap;
92		* <p>The execution status of tasks may be queried at several levels
93		* of detail: {@link #isDone} is true if a task completed in any way
94		* (including the case where a task was cancelled without executing);
83	–	* {@link #isCancelled} is true if completion was due to cancellation;
95		* {@link #isCompletedNormally} is true if a task completed without
96	<	* cancellation or encountering an exception; {@link
97	<	* #isCompletedExceptionally} is true if if the task encountered an
98	<	* exception (in which case {@link #getException} returns the
99	<	* exception); {@link #isCancelled} is true if the task was cancelled
100	<	* (in which case {@link #getException} returns a {@link
101	<	* java.util.concurrent.CancellationException}); and {@link
102	<	* #isCompletedAbnormally} is true if a task was either cancelled or
92	<	* encountered an exception.
96	>	* cancellation or encountering an exception; {@link #isCancelled} is
97	>	* true if the task was cancelled (in which case {@link #getException}
98	>	* returns a {@link java.util.concurrent.CancellationException}); and
99	>	* {@link #isCompletedAbnormally} is true if a task was either
100	>	* cancelled or encountered an exception, in which case {@link
101	>	* #getException} will return either the encountered exception or
102	>	* {@link java.util.concurrent.CancellationException}.
103		*
104		* <p>The ForkJoinTask class is not usually directly subclassed.
105		* Instead, you subclass one of the abstract classes that support a
#	Line 105 | Line 115 | import java.util.WeakHashMap;
115		* ForkJoinTasks (as may be determined using method {@link
116		* #inForkJoinPool}).  Attempts to invoke them in other contexts
117		* result in exceptions or errors, possibly including
118	<	* ClassCastException.
118	>	* {@code ClassCastException}.
119	>	*
120	>	* <p>Method {@link #join} and its variants are appropriate for use
121	>	* only when completion dependencies are acyclic; that is, the
122	>	* parallel computation can be described as a directed acyclic graph
123	>	* (DAG). Otherwise, executions may encounter a form of deadlock as
124	>	* tasks cyclically wait for each other.  However, this framework
125	>	* supports other methods and techniques (for example the use of
126	>	* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
127	>	* may be of use in constructing custom subclasses for problems that
128	>	* are not statically structured as DAGs.
129		*
130		* <p>Most base support methods are {@code final}, to prevent
131		* overriding of implementations that are intrinsically tied to the
#	Line 121 | Line 141 | import java.util.WeakHashMap;
141		* computation. Large tasks should be split into smaller subtasks,
142		* usually via recursive decomposition. As a very rough rule of thumb,
143		* a task should perform more than 100 and less than 10000 basic
144	<	* computational steps. If tasks are too big, then parallelism cannot
145	<	* improve throughput. If too small, then memory and internal task
146	<	* maintenance overhead may overwhelm processing.
144	>	* computational steps, and should avoid indefinite looping. If tasks
145	>	* are too big, then parallelism cannot improve throughput. If too
146	>	* small, then memory and internal task maintenance overhead may
147	>	* overwhelm processing.
148		*
149		* <p>This class provides {@code adapt} methods for {@link Runnable}
150		* and {@link Callable}, that may be of use when mixing execution of
151	<	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks
152	<	* are of this form, consider using a pool in
132	<	* {@linkplain ForkJoinPool#setAsyncMode async mode}.
151	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
152	>	* of this form, consider using a pool constructed in <em>asyncMode</em>.
153		*
154		* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
155		* used in extensions such as remote execution frameworks. It is
#	Line 141 | Line 161 | import java.util.WeakHashMap;
161		*/
162		public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
163
164	<	/**
165	<	* Run control status bits packed into a single int to minimize
166	<	* footprint and to ensure atomicity (via CAS).  Status is
167	<	* initially zero, and takes on nonnegative values until
168	<	* completed, upon which status holds COMPLETED. CANCELLED, or
169	<	* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
170	<	* blocking waits by other threads have SIGNAL_MASK bits set --
171	<	* bit 15 for external (nonFJ) waits, and the rest a count of
172	<	* waiting FJ threads.  (This representation relies on
173	<	* ForkJoinPool max thread limits). Completion of a stolen task
174	<	* with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
175	<	* though suboptimal for some purposes, we use basic builtin
176	<	* wait/notify to take advantage of "monitor inflation" in JVMs
177	<	* that we would otherwise need to emulate to avoid adding further
178	<	* per-task bookkeeping overhead. Note that bits 16-28 are
179	<	* currently unused. Also value 0x80000000 is available as spare
180	<	* completion value.
181	<	*/
182	<	volatile int status; // accessed directly by pool and workers
183	<
184	<	static final int COMPLETION_MASK      = 0xe0000000;
185	<	static final int NORMAL               = 0xe0000000; // == mask
186	<	static final int CANCELLED            = 0xc0000000;
187	<	static final int EXCEPTIONAL          = 0xa0000000;
188	<	static final int SIGNAL_MASK          = 0x0000ffff;
189	<	static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
190	<	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
164	>	/*
165	>	* See the internal documentation of class ForkJoinPool for a
166	>	* general implementation overview.  ForkJoinTasks are mainly
167	>	* responsible for maintaining their "status" field amidst relays
168	>	* to methods in ForkJoinWorkerThread and ForkJoinPool. The
169	>	* methods of this class are more-or-less layered into (1) basic
170	>	* status maintenance (2) execution and awaiting completion (3)
171	>	* user-level methods that additionally report results. This is
172	>	* sometimes hard to see because this file orders exported methods
173	>	* in a way that flows well in javadocs.
174	>	*/
175	>
176	>	/*
177	>	* The status field holds run control status bits packed into a
178	>	* single int to minimize footprint and to ensure atomicity (via
179	>	* CAS).  Status is initially zero, and takes on nonnegative
180	>	* values until completed, upon which status holds value
181	>	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
182	>	* waits by other threads have the SIGNAL bit set.  Completion of
183	>	* a stolen task with SIGNAL set awakens any waiters via
184	>	* notifyAll. Even though suboptimal for some purposes, we use
185	>	* basic builtin wait/notify to take advantage of "monitor
186	>	* inflation" in JVMs that we would otherwise need to emulate to
187	>	* avoid adding further per-task bookkeeping overhead.  We want
188	>	* these monitors to be "fat", i.e., not use biasing or thin-lock
189	>	* techniques, so use some odd coding idioms that tend to avoid
190	>	* them.
191		*/
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	–	}
192
193	<	// Setting completion status
193	>	/** The run status of this task */
194	>	volatile int status; // accessed directly by pool and workers
195	>	private static final int NORMAL      = -1;
196	>	private static final int CANCELLED   = -2;
197	>	private static final int EXCEPTIONAL = -3;
198	>	private static final int SIGNAL      =  1;
199
200		/**
201	<	* Marks completion and wakes up threads waiting to join this task.
201	>	* Marks completion and wakes up threads waiting to join this task,
202	>	* also clearing signal request bits.
203		*
204		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
205	+	* @return completion status on exit
206		*/
207	<	final void setCompletion(int completion) {
208	<	ForkJoinPool pool = getPool();
209	<	if (pool != null) {
210	<	int s; // Clear signal bits while setting completion status
211	<	do {} while ((s = status) >= 0 && !casStatus(s, completion));
212	<
213	<	if ((s & SIGNAL_MASK) != 0) {
214	<	if ((s &= INTERNAL_SIGNAL_MASK) != 0)
222	<	pool.updateRunningCount(s);
223	<	synchronized (this) { notifyAll(); }
207	>	private int setCompletion(int completion) {
208	>	for (int s;;) {
209	>	if ((s = status) < 0)
210	>	return s;
211	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
212	>	if (s != 0)
213	>	synchronized (this) { notifyAll(); }
214	>	return completion;
215		}
216		}
226	–	else
227	–	externallySetCompletion(completion);
217		}
218
219		/**
220	<	* Version of setCompletion for non-FJ threads.  Leaves signal
221	<	* bits for unblocked threads to adjust, and always notifies.
220	>	* Tries to block a worker thread until completed or timed out.
221	>	* Uses Object.wait time argument conventions.
222	>	* May fail on contention or interrupt.
223	>	*
224	>	* @param millis if > 0, wait time.
225		*/
226	<	private void externallySetCompletion(int completion) {
226	>	final void tryAwaitDone(long millis) {
227		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
228		try {
229	<	while (status >= 0)
230	<	synchronized (this) { if (status >= 0) wait(); }
231	<	} catch (InterruptedException ie) {
232	<	onInterruptedWait();
233	<	}
234	<	}
235	<
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));
229	>	if (((s = status) > 0 ||
230	>	(s == 0 &&
231	>	UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL))) &&
232	>	status > 0) {
233	>	synchronized (this) {
234	>	if (status > 0)
235	>	wait(millis);
236		}
279	–	} catch (InterruptedException ie) {
280	–	onInterruptedWait();
237		}
238	+	} catch (InterruptedException ie) {
239	+	// caller must check termination
240		}
241		}
242
285	–	// Awaiting completion
286	–
243		/**
244	<	* Sets status to indicate there is joiner, then waits for join,
245	<	* surrounded with pool notifications.
290	<	*
291	<	* @return status upon exit
244	>	* Blocks a non-worker-thread until completion.
245	>	* @return status upon completion
246		*/
247	<	private int awaitDone(ForkJoinWorkerThread w,
294	<	boolean maintainParallelism) {
295	<	ForkJoinPool pool = (w == null) ? null : w.pool;
247	>	private int externalAwaitDone() {
248		int s;
249	<	while ((s = status) >= 0) {
250	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
251	<	if (pool == null || !pool.preJoin(this, maintainParallelism))
252	<	doAwaitDone();
253	<	if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
254	<	adjustPoolCountsOnUnblock(pool);
255	<	break;
249	>	if ((s = status) >= 0) {
250	>	boolean interrupted = false;
251	>	synchronized (this) {
252	>	while ((s = status) >= 0) {
253	>	if (s == 0)
254	>	UNSAFE.compareAndSwapInt(this, statusOffset,
255	>	0, SIGNAL);
256	>	else {
257	>	try {
258	>	wait();
259	>	} catch (InterruptedException ie) {
260	>	interrupted = true;
261	>	}
262	>	}
263	>	}
264		}
265	+	if (interrupted)
266	+	Thread.currentThread().interrupt();
267		}
268		return s;
269		}
270
271		/**
272	<	* Timed version of awaitDone
311	<	*
312	<	* @return status upon exit
272	>	* Blocks a non-worker-thread until completion or interruption or timeout.
273		*/
274	<	private int awaitDone(ForkJoinWorkerThread w, long nanos) {
275	<	ForkJoinPool pool = (w == null) ? null : w.pool;
274	>	private int externalInterruptibleAwaitDone(long millis)
275	>	throws InterruptedException {
276		int s;
277	<	while ((s = status) >= 0) {
278	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
279	<	long startTime = System.nanoTime();
280	<	if (pool == null || !pool.preJoin(this, false))
281	<	doAwaitDone(startTime, nanos);
282	<	if ((s = status) >= 0) {
283	<	adjustPoolCountsOnCancelledWait(pool);
284	<	s = status;
277	>	if (Thread.interrupted())
278	>	throw new InterruptedException();
279	>	if ((s = status) >= 0) {
280	>	synchronized (this) {
281	>	while ((s = status) >= 0) {
282	>	if (s == 0)
283	>	UNSAFE.compareAndSwapInt(this, statusOffset,
284	>	0, SIGNAL);
285	>	else
286	>	wait(millis);
287		}
326	–	if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
327	–	adjustPoolCountsOnUnblock(pool);
328	–	break;
288		}
289		}
290		return s;
291		}
292
293		/**
294	<	* Notifies pool that thread is unblocked. Called by signalled
295	<	* threads when woken by non-FJ threads (which is atypical).
294	>	* Primary execution method for stolen tasks. Unless done, calls
295	>	* exec and records status if completed, but doesn't wait for
296	>	* completion otherwise.
297		*/
298	<	private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
299	<	int s;
300	<	do {} while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
301	<	if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
302	<	pool.updateRunningCount(s);
298	>	final void doExec() {
299	>	if (status >= 0) {
300	>	boolean completed;
301	>	try {
302	>	completed = exec();
303	>	} catch (Throwable rex) {
304	>	setExceptionalCompletion(rex);
305	>	return;
306	>	}
307	>	if (completed)
308	>	setCompletion(NORMAL); // must be outside try block
309	>	}
310		}
311
312		/**
313	<	* Notifies pool to adjust counts on cancelled or timed out wait.
313	>	* Primary mechanics for join, get, quietlyJoin.
314	>	* @return status upon completion
315		*/
316	<	private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
317	<	if (pool != null) {
318	<	int s;
319	<	while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
320	<	if (casStatus(s, s - 1)) {
321	<	pool.updateRunningCount(1);
322	<	break;
316	>	private int doJoin() {
317	>	Thread t; ForkJoinWorkerThread w; int s; boolean completed;
318	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
319	>	if ((s = status) < 0)
320	>	return s;
321	>	if ((w = (ForkJoinWorkerThread)t).unpushTask(this)) {
322	>	try {
323	>	completed = exec();
324	>	} catch (Throwable rex) {
325	>	return setExceptionalCompletion(rex);
326		}
327	+	if (completed)
328	+	return setCompletion(NORMAL);
329		}
330	+	return w.joinTask(this);
331		}
332	+	else
333	+	return externalAwaitDone();
334		}
335
336		/**
337	<	* Handles interruptions during waits.
337	>	* Primary mechanics for invoke, quietlyInvoke.
338	>	* @return status upon completion
339		*/
340	<	private void onInterruptedWait() {
341	<	ForkJoinWorkerThread w = getWorker();
342	<	if (w == null)
343	<	Thread.currentThread().interrupt(); // re-interrupt
344	<	else if (w.isTerminating())
345	<	cancelIgnoringExceptions();
346	<	// else if FJworker, ignore interrupt
340	>	private int doInvoke() {
341	>	int s; boolean completed;
342	>	if ((s = status) < 0)
343	>	return s;
344	>	try {
345	>	completed = exec();
346	>	} catch (Throwable rex) {
347	>	return setExceptionalCompletion(rex);
348	>	}
349	>	if (completed)
350	>	return setCompletion(NORMAL);
351	>	else
352	>	return doJoin();
353		}
354
355	<	// Recording and reporting exceptions
373	<
374	<	private void setDoneExceptionally(Throwable rex) {
375	<	exceptionMap.put(this, rex);
376	<	setCompletion(EXCEPTIONAL);
377	<	}
355	>	// Exception table support
356
357		/**
358	<	* Throws the exception associated with status s.
358	>	* Table of exceptions thrown by tasks, to enable reporting by
359	>	* callers. Because exceptions are rare, we don't directly keep
360	>	* them with task objects, but instead use a weak ref table.  Note
361	>	* that cancellation exceptions don't appear in the table, but are
362	>	* instead recorded as status values.
363		*
364	<	* @throws the exception
364	>	* Note: These statics are initialized below in static block.
365		*/
366	<	private void reportException(int s) {
367	<	if ((s &= COMPLETION_MASK) < NORMAL) {
368	<	if (s == CANCELLED)
387	<	throw new CancellationException();
388	<	else
389	<	rethrowException(exceptionMap.get(this));
390	<	}
391	<	}
366	>	private static final ExceptionNode[] exceptionTable;
367	>	private static final ReentrantLock exceptionTableLock;
368	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
369
370		/**
371	<	* 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.
371	>	* Fixed capacity for exceptionTable.
372		*/
373	<	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	<	}
373	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
374
375		/**
376	<	* Returns result or throws exception using j.u.c.Future conventions
377	<	* with timeouts.
376	>	* Key-value nodes for exception table.  The chained hash table
377	>	* uses identity comparisons, full locking, and weak references
378	>	* for keys. The table has a fixed capacity because it only
379	>	* maintains task exceptions long enough for joiners to access
380	>	* them, so should never become very large for sustained
381	>	* periods. However, since we do not know when the last joiner
382	>	* completes, we must use weak references and expunge them. We do
383	>	* so on each operation (hence full locking). Also, some thread in
384	>	* any ForkJoinPool will call helpExpunge when its pool becomes
385	>	* isQuiescent.
386		*/
387	<	private V reportTimedFutureResult()
388	<	throws InterruptedException, ExecutionException, TimeoutException {
389	<	if (Thread.interrupted())
390	<	throw new InterruptedException();
391	<	Throwable ex;
392	<	int s = status & COMPLETION_MASK;
393	<	if (s == NORMAL)
394	<	return getRawResult();
395	<	else if (s == CANCELLED)
396	<	throw new CancellationException();
427	<	else if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
428	<	throw new ExecutionException(ex);
429	<	else
430	<	throw new TimeoutException();
387	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>>{
388	>	final Throwable ex;
389	>	ExceptionNode next;
390	>	final long thrower;
391	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
392	>	super(task, exceptionTableRefQueue);
393	>	this.ex = ex;
394	>	this.next = next;
395	>	this.thrower = Thread.currentThread().getId();
396	>	}
397		}
398
433	–	// internal execution methods
434	–
399		/**
400	<	* Calls exec, recording completion, and rethrowing exception if
437	<	* encountered. Caller should normally check status before calling.
400	>	* Records exception and sets exceptional completion.
401		*
402	<	* @return true if completed normally
402	>	* @return status on exit
403		*/
404	<	private boolean tryExec() {
405	<	try { // try block must contain only call to exec
406	<	if (!exec())
407	<	return false;
408	<	} catch (Throwable rex) {
409	<	setDoneExceptionally(rex);
410	<	rethrowException(rex);
411	<	return false; // not reached
404	>	private int setExceptionalCompletion(Throwable ex) {
405	>	int h = System.identityHashCode(this);
406	>	ReentrantLock lock = exceptionTableLock;
407	>	lock.lock();
408	>	try {
409	>	expungeStaleExceptions();
410	>	ExceptionNode[] t = exceptionTable;
411	>	int i = h & (t.length - 1);
412	>	for (ExceptionNode e = t[i]; ; e = e.next) {
413	>	if (e == null) {
414	>	t[i] = new ExceptionNode(this, ex, t[i]);
415	>	break;
416	>	}
417	>	if (e.get() == this) // already present
418	>	break;
419	>	}
420	>	} finally {
421	>	lock.unlock();
422		}
423	<	setNormalCompletion();
451	<	return true;
423	>	return setCompletion(EXCEPTIONAL);
424		}
425
426		/**
427	<	* Main execution method used by worker threads. Invokes
456	<	* base computation unless already complete.
427	>	* Removes exception node and clears status
428		*/
429	<	final void quietlyExec() {
430	<	if (status >= 0) {
429	>	private void clearExceptionalCompletion() {
430	>	int h = System.identityHashCode(this);
431	>	ReentrantLock lock = exceptionTableLock;
432	>	lock.lock();
433	>	try {
434	>	ExceptionNode[] t = exceptionTable;
435	>	int i = h & (t.length - 1);
436	>	ExceptionNode e = t[i];
437	>	ExceptionNode pred = null;
438	>	while (e != null) {
439	>	ExceptionNode next = e.next;
440	>	if (e.get() == this) {
441	>	if (pred == null)
442	>	t[i] = next;
443	>	else
444	>	pred.next = next;
445	>	break;
446	>	}
447	>	pred = e;
448	>	e = next;
449	>	}
450	>	expungeStaleExceptions();
451	>	status = 0;
452	>	} finally {
453	>	lock.unlock();
454	>	}
455	>	}
456	>
457	>	/**
458	>	* Returns a rethrowable exception for the given task, if
459	>	* available. To provide accurate stack traces, if the exception
460	>	* was not thrown by the current thread, we try to create a new
461	>	* exception of the same type as the one thrown, but with the
462	>	* recorded exception as its cause. If there is no such
463	>	* constructor, we instead try to use a no-arg constructor,
464	>	* followed by initCause, to the same effect. If none of these
465	>	* apply, or any fail due to other exceptions, we return the
466	>	* recorded exception, which is still correct, although it may
467	>	* contain a misleading stack trace.
468	>	*
469	>	* @return the exception, or null if none
470	>	*/
471	>	private Throwable getThrowableException() {
472	>	if (status != EXCEPTIONAL)
473	>	return null;
474	>	int h = System.identityHashCode(this);
475	>	ExceptionNode e;
476	>	ReentrantLock lock = exceptionTableLock;
477	>	lock.lock();
478	>	try {
479	>	expungeStaleExceptions();
480	>	ExceptionNode[] t = exceptionTable;
481	>	e = t[h & (t.length - 1)];
482	>	while (e != null && e.get() != this)
483	>	e = e.next;
484	>	} finally {
485	>	lock.unlock();
486	>	}
487	>	Throwable ex;
488	>	if (e == null || (ex = e.ex) == null)
489	>	return null;
490	>	if (e.thrower != Thread.currentThread().getId()) {
491	>	Class ec = ex.getClass();
492		try {
493	<	if (!exec())
494	<	return;
495	<	} catch (Throwable rex) {
496	<	setDoneExceptionally(rex);
497	<	return;
493	>	Constructor<?> noArgCtor = null;
494	>	Constructor<?>[] cs = ec.getConstructors();// public ctors only
495	>	for (int i = 0; i < cs.length; ++i) {
496	>	Constructor<?> c = cs[i];
497	>	Class<?>[] ps = c.getParameterTypes();
498	>	if (ps.length == 0)
499	>	noArgCtor = c;
500	>	else if (ps.length == 1 && ps[0] == Throwable.class)
501	>	return (Throwable)(c.newInstance(ex));
502	>	}
503	>	if (noArgCtor != null) {
504	>	Throwable wx = (Throwable)(noArgCtor.newInstance());
505	>	wx.initCause(ex);
506	>	return wx;
507	>	}
508	>	} catch (Exception ignore) {
509		}
467	–	setNormalCompletion();
510		}
511	+	return ex;
512		}
513
514		/**
515	<	* Calls exec(), recording but not rethrowing exception.
473	<	* Caller should normally check status before calling.
474	<	*
475	<	* @return true if completed normally
515	>	* Poll stale refs and remove them. Call only while holding lock.
516		*/
517	<	private boolean tryQuietlyInvoke() {
518	<	try {
519	<	if (!exec())
520	<	return false;
521	<	} catch (Throwable rex) {
522	<	setDoneExceptionally(rex);
523	<	return false;
517	>	private static void expungeStaleExceptions() {
518	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
519	>	if (x instanceof ExceptionNode) {
520	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
521	>	ExceptionNode[] t = exceptionTable;
522	>	int i = System.identityHashCode(key) & (t.length - 1);
523	>	ExceptionNode e = t[i];
524	>	ExceptionNode pred = null;
525	>	while (e != null) {
526	>	ExceptionNode next = e.next;
527	>	if (e == x) {
528	>	if (pred == null)
529	>	t[i] = next;
530	>	else
531	>	pred.next = next;
532	>	break;
533	>	}
534	>	pred = e;
535	>	e = next;
536	>	}
537	>	}
538		}
485	–	setNormalCompletion();
486	–	return true;
539		}
540
541		/**
542	<	* Cancels, ignoring any exceptions it throws.
542	>	* If lock is available, poll any stale refs and remove them.
543	>	* Called from ForkJoinPool when pools become quiescent.
544		*/
545	<	final void cancelIgnoringExceptions() {
546	<	try {
547	<	cancel(false);
548	<	} catch (Throwable ignore) {
545	>	static final void helpExpungeStaleExceptions() {
546	>	ReentrantLock lock = exceptionTableLock;
547	>	if (lock.tryLock()) {
548	>	try {
549	>	expungeStaleExceptions();
550	>	} finally {
551	>	lock.unlock();
552	>	}
553		}
554		}
555
556		/**
557	<	* Main implementation of helpJoin
557	>	* Report the result of invoke or join; called only upon
558	>	* non-normal return of internal versions.
559		*/
560	<	private int busyJoin(ForkJoinWorkerThread w) {
561	<	int s;
562	<	ForkJoinTask<?> t;
563	<	while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
564	<	t.quietlyExec();
565	<	return (s >= 0) ? awaitDone(w, false) : s; // block if no work
560	>	private V reportResult() {
561	>	int s; Throwable ex;
562	>	if ((s = status) == CANCELLED)
563	>	throw new CancellationException();
564	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
565	>	UNSAFE.throwException(ex);
566	>	return getRawResult();
567		}
568
569		// public methods
#	Line 513 | Line 572 | public abstract class ForkJoinTask<V> im
572		* Arranges to asynchronously execute this task.  While it is not
573		* necessarily enforced, it is a usage error to fork a task more
574		* than once unless it has completed and been reinitialized.
575	+	* Subsequent modifications to the state of this task or any data
576	+	* it operates on are not necessarily consistently observable by
577	+	* any thread other than the one executing it unless preceded by a
578	+	* call to {@link #join} or related methods, or a call to {@link
579	+	* #isDone} returning {@code true}.
580		*
581		* <p>This method may be invoked only from within {@code
582	<	* ForkJoinTask} computations (as may be determined using method
582	>	* ForkJoinPool} computations (as may be determined using method
583		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
584		* result in exceptions or errors, possibly including {@code
585		* ClassCastException}.
#	Line 529 | Line 593 | public abstract class ForkJoinTask<V> im
593		}
594
595		/**
596	<	* Returns the result of the computation when it is ready.
597	<	* This method differs from {@link #get()} in that
596	>	* Returns the result of the computation when it {@link #isDone is
597	>	* done}.  This method differs from {@link #get()} in that
598		* abnormal completion results in {@code RuntimeException} or
599	<	* {@code Error}, not {@code ExecutionException}.
599	>	* {@code Error}, not {@code ExecutionException}, and that
600	>	* interrupts of the calling thread do <em>not</em> cause the
601	>	* method to abruptly return by throwing {@code
602	>	* InterruptedException}.
603		*
604		* @return the computed result
605		*/
606		public final V join() {
607	<	ForkJoinWorkerThread w = getWorker();
608	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryExec())
609	<	reportException(awaitDone(w, true));
610	<	return getRawResult();
607	>	if (doJoin() != NORMAL)
608	>	return reportResult();
609	>	else
610	>	return getRawResult();
611		}
612
613		/**
614		* Commences performing this task, awaits its completion if
615	<	* necessary, and return its result, or throws an (unchecked)
616	<	* exception if the underlying computation did so.
615	>	* necessary, and returns its result, or throws an (unchecked)
616	>	* {@code RuntimeException} or {@code Error} if the underlying
617	>	* computation did so.
618		*
619		* @return the computed result
620		*/
621		public final V invoke() {
622	<	if (status >= 0 && tryExec())
623	<	return getRawResult();
622	>	if (doInvoke() != NORMAL)
623	>	return reportResult();
624		else
625	<	return join();
625	>	return getRawResult();
626		}
627
628		/**
629		* Forks the given tasks, returning when {@code isDone} holds for
630		* each task or an (unchecked) exception is encountered, in which
631	<	* case the exception is rethrown.  If either task encounters an
632	<	* exception, the other one may be, but is not guaranteed to be,
633	<	* cancelled.  If both tasks throw an exception, then this method
634	<	* throws one of them.  The individual status of each task may be
635	<	* checked using {@link #getException()} and related methods.
631	>	* case the exception is rethrown. If more than one task
632	>	* encounters an exception, then this method throws any one of
633	>	* these exceptions. If any task encounters an exception, the
634	>	* other may be cancelled. However, the execution status of
635	>	* individual tasks is not guaranteed upon exceptional return. The
636	>	* status of each task may be obtained using {@link
637	>	* #getException()} and related methods to check if they have been
638	>	* cancelled, completed normally or exceptionally, or left
639	>	* unprocessed.
640		*
641		* <p>This method may be invoked only from within {@code
642	<	* ForkJoinTask} computations (as may be determined using method
642	>	* ForkJoinPool} computations (as may be determined using method
643		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
644		* result in exceptions or errors, possibly including {@code
645		* ClassCastException}.
#	Line 585 | Line 657 | public abstract class ForkJoinTask<V> im
657		/**
658		* Forks the given tasks, returning when {@code isDone} holds for
659		* each task or an (unchecked) exception is encountered, in which
660	<	* case the exception is rethrown. If any task encounters an
661	<	* exception, others may be, but are not guaranteed to be,
662	<	* cancelled.  If more than one task encounters an exception, then
663	<	* this method throws any one of these exceptions.  The individual
664	<	* status of each task may be checked using {@link #getException()}
665	<	* and related methods.
660	>	* case the exception is rethrown. If more than one task
661	>	* encounters an exception, then this method throws any one of
662	>	* these exceptions. If any task encounters an exception, others
663	>	* may be cancelled. However, the execution status of individual
664	>	* tasks is not guaranteed upon exceptional return. The status of
665	>	* each task may be obtained using {@link #getException()} and
666	>	* related methods to check if they have been cancelled, completed
667	>	* normally or exceptionally, or left unprocessed.
668		*
669		* <p>This method may be invoked only from within {@code
670	<	* ForkJoinTask} computations (as may be determined using method
670	>	* ForkJoinPool} computations (as may be determined using method
671		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
672		* result in exceptions or errors, possibly including {@code
673		* ClassCastException}.
#	Line 612 | Line 686 | public abstract class ForkJoinTask<V> im
686		}
687		else if (i != 0)
688		t.fork();
689	<	else {
690	<	t.quietlyInvoke();
617	<	if (ex == null)
618	<	ex = t.getException();
619	<	}
689	>	else if (t.doInvoke() < NORMAL && ex == null)
690	>	ex = t.getException();
691		}
692		for (int i = 1; i <= last; ++i) {
693		ForkJoinTask<?> t = tasks[i];
694		if (t != null) {
695		if (ex != null)
696		t.cancel(false);
697	<	else {
698	<	t.quietlyJoin();
628	<	if (ex == null)
629	<	ex = t.getException();
630	<	}
697	>	else if (t.doJoin() < NORMAL && ex == null)
698	>	ex = t.getException();
699		}
700		}
701		if (ex != null)
702	<	rethrowException(ex);
702	>	UNSAFE.throwException(ex);
703		}
704
705		/**
706		* Forks all tasks in the specified collection, returning when
707		* {@code isDone} holds for each task or an (unchecked) exception
708	<	* is encountered.  If any task encounters an exception, others
709	<	* may be, but are not guaranteed to be, cancelled.  If more than
710	<	* one task encounters an exception, then this method throws any
711	<	* one of these exceptions.  The individual status of each task
712	<	* may be checked using {@link #getException()} and related
713	<	* methods.  The behavior of this operation is undefined if the
714	<	* specified collection is modified while the operation is in
715	<	* progress.
708	>	* is encountered, in which case the exception is rethrown. If
709	>	* more than one task encounters an exception, then this method
710	>	* throws any one of these exceptions. If any task encounters an
711	>	* exception, others may be cancelled. However, the execution
712	>	* status of individual tasks is not guaranteed upon exceptional
713	>	* return. The status of each task may be obtained using {@link
714	>	* #getException()} and related methods to check if they have been
715	>	* cancelled, completed normally or exceptionally, or left
716	>	* unprocessed.
717		*
718		* <p>This method may be invoked only from within {@code
719	<	* ForkJoinTask} computations (as may be determined using method
719	>	* ForkJoinPool} computations (as may be determined using method
720		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
721		* result in exceptions or errors, possibly including {@code
722		* ClassCastException}.
#	Line 674 | Line 743 | public abstract class ForkJoinTask<V> im
743		}
744		else if (i != 0)
745		t.fork();
746	<	else {
747	<	t.quietlyInvoke();
679	<	if (ex == null)
680	<	ex = t.getException();
681	<	}
746	>	else if (t.doInvoke() < NORMAL && ex == null)
747	>	ex = t.getException();
748		}
749		for (int i = 1; i <= last; ++i) {
750		ForkJoinTask<?> t = ts.get(i);
751		if (t != null) {
752		if (ex != null)
753		t.cancel(false);
754	<	else {
755	<	t.quietlyJoin();
690	<	if (ex == null)
691	<	ex = t.getException();
692	<	}
754	>	else if (t.doJoin() < NORMAL && ex == null)
755	>	ex = t.getException();
756		}
757		}
758		if (ex != null)
759	<	rethrowException(ex);
759	>	UNSAFE.throwException(ex);
760		return tasks;
761		}
762
763		/**
764		* Attempts to cancel execution of this task. This attempt will
765	<	* fail if the task has already completed, has already been
766	<	* cancelled, or could not be cancelled for some other reason. If
767	<	* successful, and this task has not started when cancel is
768	<	* called, execution of this task is suppressed, {@link
769	<	* #isCancelled} will report true, and {@link #join} will result
770	<	* in a {@code CancellationException} being thrown.
765	>	* fail if the task has already completed or could not be
766	>	* cancelled for some other reason. If successful, and this task
767	>	* has not started when {@code cancel} is called, execution of
768	>	* this task is suppressed. After this method returns
769	>	* successfully, unless there is an intervening call to {@link
770	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
771	>	* {@link #isDone}, and {@code cancel} will return {@code true}
772	>	* and calls to {@link #join} and related methods will result in
773	>	* {@code CancellationException}.
774		*
775		* <p>This method may be overridden in subclasses, but if so, must
776	<	* still ensure that these minimal properties hold. In particular,
777	<	* the {@code cancel} method itself must not throw exceptions.
776	>	* still ensure that these properties hold. In particular, the
777	>	* {@code cancel} method itself must not throw exceptions.
778		*
779		* <p>This method is designed to be invoked by <em>other</em>
780		* tasks. To terminate the current task, you can just return or
781		* throw an unchecked exception from its computation method, or
782		* invoke {@link #completeExceptionally}.
783		*
784	<	* @param mayInterruptIfRunning this value is ignored in the
785	<	* default implementation because tasks are not
786	<	* cancelled via interruption
784	>	* @param mayInterruptIfRunning this value has no effect in the
785	>	* default implementation because interrupts are not used to
786	>	* control cancellation.
787		*
788		* @return {@code true} if this task is now cancelled
789		*/
790		public boolean cancel(boolean mayInterruptIfRunning) {
791	<	setCompletion(CANCELLED);
792	<	return (status & COMPLETION_MASK) == CANCELLED;
791	>	return setCompletion(CANCELLED) == CANCELLED;
792	>	}
793	>
794	>	/**
795	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
796	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
797	>	* exceptions, but if it does anyway, we have no recourse during
798	>	* shutdown, so guard against this case.
799	>	*/
800	>	final void cancelIgnoringExceptions() {
801	>	try {
802	>	cancel(false);
803	>	} catch (Throwable ignore) {
804	>	}
805		}
806
807		public final boolean isDone() {
#	Line 731 | Line 809 | public abstract class ForkJoinTask<V> im
809		}
810
811		public final boolean isCancelled() {
812	<	return (status & COMPLETION_MASK) == CANCELLED;
812	>	return status == CANCELLED;
813		}
814
815		/**
#	Line 740 | Line 818 | public abstract class ForkJoinTask<V> im
818		* @return {@code true} if this task threw an exception or was cancelled
819		*/
820		public final boolean isCompletedAbnormally() {
821	<	return (status & COMPLETION_MASK) < NORMAL;
821	>	return status < NORMAL;
822		}
823
824		/**
#	Line 751 | Line 829 | public abstract class ForkJoinTask<V> im
829		* exception and was not cancelled
830		*/
831		public final boolean isCompletedNormally() {
832	<	return (status & COMPLETION_MASK) == NORMAL;
755	<	}
756	<
757	<	/**
758	<	* Returns {@code true} if this task threw an exception.
759	<	*
760	<	* @return {@code true} if this task threw an exception
761	<	*/
762	<	public final boolean isCompletedExceptionally() {
763	<	return (status & COMPLETION_MASK) == EXCEPTIONAL;
832	>	return status == NORMAL;
833		}
834
835		/**
#	Line 771 | Line 840 | public abstract class ForkJoinTask<V> im
840		* @return the exception, or {@code null} if none
841		*/
842		public final Throwable getException() {
843	<	int s = status & COMPLETION_MASK;
843	>	int s = status;
844		return ((s >= NORMAL)    ? null :
845		(s == CANCELLED) ? new CancellationException() :
846	<	exceptionMap.get(this));
846	>	getThrowableException());
847		}
848
849		/**
#	Line 787 | Line 856 | public abstract class ForkJoinTask<V> im
856		* overridable, but overridden versions must invoke {@code super}
857		* implementation to maintain guarantees.
858		*
859	<	* @param ex the exception to throw. If this exception is
860	<	* not a RuntimeException or Error, the actual exception thrown
861	<	* will be a RuntimeException with cause ex.
859	>	* @param ex the exception to throw. If this exception is not a
860	>	* {@code RuntimeException} or {@code Error}, the actual exception
861	>	* thrown will be a {@code RuntimeException} with cause {@code ex}.
862		*/
863		public void completeExceptionally(Throwable ex) {
864	<	setDoneExceptionally((ex instanceof RuntimeException) ||
865	<	(ex instanceof Error) ? ex :
866	<	new RuntimeException(ex));
864	>	setExceptionalCompletion((ex instanceof RuntimeException) ||
865	>	(ex instanceof Error) ? ex :
866	>	new RuntimeException(ex));
867		}
868
869		/**
870		* Completes this task, and if not already aborted or cancelled,
871	<	* returning a {@code null} result upon {@code join} and related
872	<	* operations. This method may be used to provide results for
873	<	* asynchronous tasks, or to provide alternative handling for
874	<	* tasks that would not otherwise complete normally. Its use in
875	<	* other situations is discouraged. This method is
876	<	* overridable, but overridden versions must invoke {@code super}
877	<	* implementation to maintain guarantees.
871	>	* returning the given value as the result of subsequent
872	>	* invocations of {@code join} and related operations. This method
873	>	* may be used to provide results for asynchronous tasks, or to
874	>	* provide alternative handling for tasks that would not otherwise
875	>	* complete normally. Its use in other situations is
876	>	* discouraged. This method is overridable, but overridden
877	>	* versions must invoke {@code super} implementation to maintain
878	>	* guarantees.
879		*
880		* @param value the result value for this task
881		*/
#	Line 813 | Line 883 | public abstract class ForkJoinTask<V> im
883		try {
884		setRawResult(value);
885		} catch (Throwable rex) {
886	<	setDoneExceptionally(rex);
886	>	setExceptionalCompletion(rex);
887		return;
888		}
889	<	setNormalCompletion();
820	<	}
821	<
822	<	public final V get() throws InterruptedException, ExecutionException {
823	<	ForkJoinWorkerThread w = getWorker();
824	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
825	<	awaitDone(w, true);
826	<	return reportFutureResult();
827	<	}
828	<
829	<	public final V get(long timeout, TimeUnit unit)
830	<	throws InterruptedException, ExecutionException, TimeoutException {
831	<	long nanos = unit.toNanos(timeout);
832	<	ForkJoinWorkerThread w = getWorker();
833	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
834	<	awaitDone(w, nanos);
835	<	return reportTimedFutureResult();
889	>	setCompletion(NORMAL);
890		}
891
892		/**
893	<	* Possibly executes other tasks until this task is ready, then
894	<	* returns the result of the computation.  This method may be more
841	<	* efficient than {@code join}, but is only applicable when
842	<	* there are no potential dependencies between continuation of the
843	<	* current task and that of any other task that might be executed
844	<	* while helping. (This usually holds for pure divide-and-conquer
845	<	* tasks).
846	<	*
847	<	* <p>This method may be invoked only from within {@code
848	<	* ForkJoinTask} computations (as may be determined using method
849	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
850	<	* result in exceptions or errors, possibly including {@code
851	<	* ClassCastException}.
893	>	* Waits if necessary for the computation to complete, and then
894	>	* retrieves its result.
895		*
896		* @return the computed result
897	+	* @throws CancellationException if the computation was cancelled
898	+	* @throws ExecutionException if the computation threw an
899	+	* exception
900	+	* @throws InterruptedException if the current thread is not a
901	+	* member of a ForkJoinPool and was interrupted while waiting
902		*/
903	<	public final V helpJoin() {
904	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
905	<	if (status < 0 || !w.unpushTask(this) || !tryExec())
906	<	reportException(busyJoin(w));
903	>	public final V get() throws InterruptedException, ExecutionException {
904	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
905	>	doJoin() : externalInterruptibleAwaitDone(0L);
906	>	Throwable ex;
907	>	if (s == CANCELLED)
908	>	throw new CancellationException();
909	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
910	>	throw new ExecutionException(ex);
911		return getRawResult();
912		}
913
914		/**
915	<	* Possibly executes other tasks until this task is ready.  This
916	<	* method may be useful when processing collections of tasks when
865	<	* some have been cancelled or otherwise known to have aborted.
915	>	* Waits if necessary for at most the given time for the computation
916	>	* to complete, and then retrieves its result, if available.
917		*
918	<	* <p>This method may be invoked only from within {@code
919	<	* ForkJoinTask} computations (as may be determined using method
920	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
921	<	* result in exceptions or errors, possibly including {@code
922	<	* ClassCastException}.
918	>	* @param timeout the maximum time to wait
919	>	* @param unit the time unit of the timeout argument
920	>	* @return the computed result
921	>	* @throws CancellationException if the computation was cancelled
922	>	* @throws ExecutionException if the computation threw an
923	>	* exception
924	>	* @throws InterruptedException if the current thread is not a
925	>	* member of a ForkJoinPool and was interrupted while waiting
926	>	* @throws TimeoutException if the wait timed out
927		*/
928	<	public final void quietlyHelpJoin() {
929	<	if (status >= 0) {
930	<	ForkJoinWorkerThread w =
931	<	(ForkJoinWorkerThread) Thread.currentThread();
932	<	if (!w.unpushTask(this) || !tryQuietlyInvoke())
933	<	busyJoin(w);
928	>	public final V get(long timeout, TimeUnit unit)
929	>	throws InterruptedException, ExecutionException, TimeoutException {
930	>	Thread t = Thread.currentThread();
931	>	if (t instanceof ForkJoinWorkerThread) {
932	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
933	>	long nanos = unit.toNanos(timeout);
934	>	if (status >= 0) {
935	>	boolean completed = false;
936	>	if (w.unpushTask(this)) {
937	>	try {
938	>	completed = exec();
939	>	} catch (Throwable rex) {
940	>	setExceptionalCompletion(rex);
941	>	}
942	>	}
943	>	if (completed)
944	>	setCompletion(NORMAL);
945	>	else if (status >= 0 && nanos > 0)
946	>	w.pool.timedAwaitJoin(this, nanos);
947	>	}
948	>	}
949	>	else {
950	>	long millis = unit.toMillis(timeout);
951	>	if (millis > 0)
952	>	externalInterruptibleAwaitDone(millis);
953	>	}
954	>	int s = status;
955	>	if (s != NORMAL) {
956	>	Throwable ex;
957	>	if (s == CANCELLED)
958	>	throw new CancellationException();
959	>	if (s != EXCEPTIONAL)
960	>	throw new TimeoutException();
961	>	if ((ex = getThrowableException()) != null)
962	>	throw new ExecutionException(ex);
963		}
964	+	return getRawResult();
965		}
966
967		/**
968	<	* Joins this task, without returning its result or throwing an
968	>	* Joins this task, without returning its result or throwing its
969		* exception. This method may be useful when processing
970		* collections of tasks when some have been cancelled or otherwise
971		* known to have aborted.
972		*/
973		public final void quietlyJoin() {
974	<	if (status >= 0) {
890	<	ForkJoinWorkerThread w = getWorker();
891	<	if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
892	<	awaitDone(w, true);
893	<	}
974	>	doJoin();
975		}
976
977		/**
978		* Commences performing this task and awaits its completion if
979	<	* necessary, without returning its result or throwing an
980	<	* exception. This method may be useful when processing
900	<	* collections of tasks when some have been cancelled or otherwise
901	<	* known to have aborted.
979	>	* necessary, without returning its result or throwing its
980	>	* exception.
981		*/
982		public final void quietlyInvoke() {
983	<	if (status >= 0 && !tryQuietlyInvoke())
905	<	quietlyJoin();
983	>	doInvoke();
984		}
985
986		/**
#	Line 913 | Line 991 | public abstract class ForkJoinTask<V> im
991		* processed.
992		*
993		* <p>This method may be invoked only from within {@code
994	<	* ForkJoinTask} computations (as may be determined using method
994	>	* ForkJoinPool} computations (as may be determined using method
995		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
996		* result in exceptions or errors, possibly including {@code
997		* ClassCastException}.
#	Line 932 | Line 1010 | public abstract class ForkJoinTask<V> im
1010		* under any other usage conditions are not guaranteed.
1011		* This method may be useful when executing
1012		* pre-constructed trees of subtasks in loops.
1013	+	*
1014	+	* <p>Upon completion of this method, {@code isDone()} reports
1015	+	* {@code false}, and {@code getException()} reports {@code
1016	+	* null}. However, the value returned by {@code getRawResult} is
1017	+	* unaffected. To clear this value, you can invoke {@code
1018	+	* setRawResult(null)}.
1019		*/
1020		public void reinitialize() {
1021	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
1022	<	exceptionMap.remove(this);
1023	<	status = 0;
1021	>	if (status == EXCEPTIONAL)
1022	>	clearExceptionalCompletion();
1023	>	else
1024	>	status = 0;
1025		}
1026
1027		/**
#	Line 953 | Line 1038 | public abstract class ForkJoinTask<V> im
1038		}
1039
1040		/**
1041	<	* Returns {@code true} if the current thread is executing as a
1042	<	* ForkJoinPool computation.
1041	>	* Returns {@code true} if the current thread is a {@link
1042	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1043		*
1044	<	* @return {@code true} if the current thread is executing as a
1045	<	* ForkJoinPool computation, or false otherwise
1044	>	* @return {@code true} if the current thread is a {@link
1045	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1046	>	* or {@code false} otherwise
1047		*/
1048		public static boolean inForkJoinPool() {
1049		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 972 | Line 1058 | public abstract class ForkJoinTask<V> im
1058		* were not, stolen.
1059		*
1060		* <p>This method may be invoked only from within {@code
1061	<	* ForkJoinTask} computations (as may be determined using method
1061	>	* ForkJoinPool} computations (as may be determined using method
1062		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1063		* result in exceptions or errors, possibly including {@code
1064		* ClassCastException}.
#	Line 991 | Line 1077 | public abstract class ForkJoinTask<V> im
1077		* fork other tasks.
1078		*
1079		* <p>This method may be invoked only from within {@code
1080	<	* ForkJoinTask} computations (as may be determined using method
1080	>	* ForkJoinPool} computations (as may be determined using method
1081		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1082		* result in exceptions or errors, possibly including {@code
1083		* ClassCastException}.
#	Line 1014 | Line 1100 | public abstract class ForkJoinTask<V> im
1100		* exceeded.
1101		*
1102		* <p>This method may be invoked only from within {@code
1103	<	* ForkJoinTask} computations (as may be determined using method
1103	>	* ForkJoinPool} computations (as may be determined using method
1104		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1105		* result in exceptions or errors, possibly including {@code
1106		* ClassCastException}.
#	Line 1072 | Line 1158 | public abstract class ForkJoinTask<V> im
1158		* otherwise.
1159		*
1160		* <p>This method may be invoked only from within {@code
1161	<	* ForkJoinTask} computations (as may be determined using method
1161	>	* ForkJoinPool} computations (as may be determined using method
1162		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1163		* result in exceptions or errors, possibly including {@code
1164		* ClassCastException}.
#	Line 1091 | Line 1177 | public abstract class ForkJoinTask<V> im
1177		* be useful otherwise.
1178		*
1179		* <p>This method may be invoked only from within {@code
1180	<	* ForkJoinTask} computations (as may be determined using method
1180	>	* ForkJoinPool} computations (as may be determined using method
1181		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1182		* result in exceptions or errors, possibly including {@code
1183		* ClassCastException}.
#	Line 1114 | Line 1200 | public abstract class ForkJoinTask<V> im
1200		* otherwise.
1201		*
1202		* <p>This method may be invoked only from within {@code
1203	<	* ForkJoinTask} computations (as may be determined using method
1203	>	* ForkJoinPool} computations (as may be determined using method
1204		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1205		* result in exceptions or errors, possibly including {@code
1206		* ClassCastException}.
#	Line 1224 | Line 1310 | public abstract class ForkJoinTask<V> im
1310		private static final long serialVersionUID = -7721805057305804111L;
1311
1312		/**
1313	<	* Save the state to a stream.
1313	>	* Saves the state to a stream (that is, serializes it).
1314		*
1315		* @serialData the current run status and the exception thrown
1316		* during execution, or {@code null} if none
#	Line 1237 | Line 1323 | public abstract class ForkJoinTask<V> im
1323		}
1324
1325		/**
1326	<	* Reconstitute the instance from a stream.
1326	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1327		*
1328		* @param s the stream
1329		*/
1330		private void readObject(java.io.ObjectInputStream s)
1331		throws java.io.IOException, ClassNotFoundException {
1332		s.defaultReadObject();
1247	–	status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
1248	–	status |= EXTERNAL_SIGNAL; // conservatively set external signal
1333		Object ex = s.readObject();
1334		if (ex != null)
1335	<	setDoneExceptionally((Throwable) ex);
1335	>	setExceptionalCompletion((Throwable)ex);
1336		}
1337
1338		// Unsafe mechanics
1339	<
1340	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1341	<	private static final long statusOffset =
1342	<	objectFieldOffset("status", ForkJoinTask.class);
1343	<
1344	<	private static long objectFieldOffset(String field, Class<?> klazz) {
1339	>	private static final sun.misc.Unsafe UNSAFE;
1340	>	private static final long statusOffset;
1341	>	static {
1342	>	exceptionTableLock = new ReentrantLock();
1343	>	exceptionTableRefQueue = new ReferenceQueue<Object>();
1344	>	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1345		try {
1346	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1347	<	} catch (NoSuchFieldException e) {
1348	<	// Convert Exception to corresponding Error
1349	<	NoSuchFieldError error = new NoSuchFieldError(field);
1350	<	error.initCause(e);
1267	<	throw error;
1346	>	UNSAFE = getUnsafe();
1347	>	statusOffset = UNSAFE.objectFieldOffset
1348	>	(ForkJoinTask.class.getDeclaredField("status"));
1349	>	} catch (Exception e) {
1350	>	throw new Error(e);
1351		}
1352		}
1353

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