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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.32 by dl, Mon Aug 3 13:01:15 2009 UTC vs.
Revision 1.58 by dl, Mon Sep 6 11:55:39 2010 UTC

#	Line 56 | Line 56 | import java.util.WeakHashMap;
56		* exceptions such as {@code IOExceptions} to be thrown. However,
57		* computations may still encounter unchecked exceptions, that are
58		* rethrown to callers attempting to join them. These exceptions may
59	<	* additionally include RejectedExecutionExceptions stemming from
60	<	* internal resource exhaustion such as failure to allocate internal
61	<	* task queues.
59	>	* additionally include {@link RejectedExecutionException} stemming
60	>	* from internal resource exhaustion, such as failure to allocate
61	>	* internal task queues.
62		*
63		* <p>The primary method for awaiting completion and extracting
64		* results of a task is {@link #join}, but there are several variants:
65		* The {@link Future#get} methods support interruptible and/or timed
66		* waits for completion and report results using {@code Future}
67	<	* 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
71	<	* equivalent to {@code fork(); join()} but always attempts to
72	<	* begin execution in the current thread. The "<em>quiet</em>" forms
73	<	* of these methods do not extract results or report exceptions. These
67	>	* conventions. Method {@link #invoke} is semantically
68	>	* equivalent to {@code fork(); join()} but always attempts to begin
69	>	* execution in the current thread. The "<em>quiet</em>" forms of
70	>	* these methods do not extract results or report exceptions. These
71		* may be useful when a set of tasks are being executed, and you need
72		* to delay processing of results or exceptions until all complete.
73		* Method {@code invokeAll} (available in multiple versions)
74		* performs the most common form of parallel invocation: forking a set
75		* of tasks and joining them all.
76		*
77	+	* <p>The execution status of tasks may be queried at several levels
78	+	* of detail: {@link #isDone} is true if a task completed in any way
79	+	* (including the case where a task was cancelled without executing);
80	+	* {@link #isCompletedNormally} is true if a task completed without
81	+	* cancellation or encountering an exception; {@link #isCancelled} is
82	+	* true if the task was cancelled (in which case {@link #getException}
83	+	* returns a {@link java.util.concurrent.CancellationException}); and
84	+	* {@link #isCompletedAbnormally} is true if a task was either
85	+	* cancelled or encountered an exception, in which case {@link
86	+	* #getException} will return either the encountered exception or
87	+	* {@link java.util.concurrent.CancellationException}.
88	+	*
89		* <p>The ForkJoinTask class is not usually directly subclassed.
90		* Instead, you subclass one of the abstract classes that support a
91		* particular style of fork/join processing, typically {@link
#	Line 91 | Line 100 | import java.util.WeakHashMap;
100		* ForkJoinTasks (as may be determined using method {@link
101		* #inForkJoinPool}).  Attempts to invoke them in other contexts
102		* result in exceptions or errors, possibly including
103	<	* ClassCastException.
103	>	* {@code ClassCastException}.
104		*
105		* <p>Most base support methods are {@code final}, to prevent
106		* overriding of implementations that are intrinsically tied to the
#	Line 111 | Line 120 | import java.util.WeakHashMap;
120		* improve throughput. If too small, then memory and internal task
121		* maintenance overhead may overwhelm processing.
122		*
123	<	* <p>This class provides {@code adapt} methods for {@link
124	<	* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that
125	<	* may be of use when mixing execution of ForkJoinTasks with other
126	<	* kinds of tasks. When all tasks are of this form, consider using a
118	<	* pool in {@link ForkJoinPool#setAsyncMode}.
123	>	* <p>This class provides {@code adapt} methods for {@link Runnable}
124	>	* and {@link Callable}, that may be of use when mixing execution of
125	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
126	>	* of this form, consider using a pool constructed in <em>asyncMode</em>.
127		*
128		* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
129		* used in extensions such as remote execution frameworks. It is
#	Line 127 | Line 135 | import java.util.WeakHashMap;
135		*/
136		public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
137
138	<	/**
139	<	* Run control status bits packed into a single int to minimize
140	<	* footprint and to ensure atomicity (via CAS).  Status is
141	<	* initially zero, and takes on nonnegative values until
142	<	* completed, upon which status holds COMPLETED. CANCELLED, or
143	<	* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
144	<	* blocking waits by other threads have SIGNAL_MASK bits set --
145	<	* bit 15 for external (nonFJ) waits, and the rest a count of
146	<	* waiting FJ threads.  (This representation relies on
147	<	* ForkJoinPool max thread limits). Completion of a stolen task
148	<	* with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
149	<	* though suboptimal for some purposes, we use basic builtin
150	<	* wait/notify to take advantage of "monitor inflation" in JVMs
151	<	* that we would otherwise need to emulate to avoid adding further
152	<	* per-task bookkeeping overhead. Note that bits 16-28 are
153	<	* currently unused. Also value 0x80000000 is available as spare
154	<	* completion value.
138	>	/*
139	>	* See the internal documentation of class ForkJoinPool for a
140	>	* general implementation overview.  ForkJoinTasks are mainly
141	>	* responsible for maintaining their "status" field amidst relays
142	>	* to methods in ForkJoinWorkerThread and ForkJoinPool. The
143	>	* methods of this class are more-or-less layered into (1) basic
144	>	* status maintenance (2) execution and awaiting completion (3)
145	>	* user-level methods that additionally report results. This is
146	>	* sometimes hard to see because this file orders exported methods
147	>	* in a way that flows well in javadocs. In particular, most
148	>	* join mechanics are in method quietlyJoin, below.
149	>	*/
150	>
151	>	/*
152	>	* The status field holds run control status bits packed into a
153	>	* single int to minimize footprint and to ensure atomicity (via
154	>	* CAS).  Status is initially zero, and takes on nonnegative
155	>	* values until completed, upon which status holds value
156	>	* NORMAL. CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
157	>	* waits by other threads have the SIGNAL bit set.  Completion of
158	>	* a stolen task with SIGNAL set awakens any waiters via
159	>	* notifyAll. Even though suboptimal for some purposes, we use
160	>	* basic builtin wait/notify to take advantage of "monitor
161	>	* inflation" in JVMs that we would otherwise need to emulate to
162	>	* avoid adding further per-task bookkeeping overhead.  We want
163	>	* these monitors to be "fat", i.e., not use biasing or thin-lock
164	>	* techniques, so use some odd coding idioms that tend to avoid
165	>	* them.
166		*/
167	+
168	+	/** The run status of this task */
169		volatile int status; // accessed directly by pool and workers
170
171	<	static final int COMPLETION_MASK      = 0xe0000000;
172	<	static final int NORMAL               = 0xe0000000; // == mask
173	<	static final int CANCELLED            = 0xc0000000;
174	<	static final int EXCEPTIONAL          = 0xa0000000;
154	<	static final int SIGNAL_MASK          = 0x0000ffff;
155	<	static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
156	<	static final int EXTERNAL_SIGNAL      = 0x00008000; // top bit of low word
171	>	private static final int NORMAL      = -1;
172	>	private static final int CANCELLED   = -2;
173	>	private static final int EXCEPTIONAL = -3;
174	>	private static final int SIGNAL      =  1;
175
176		/**
177		* Table of exceptions thrown by tasks, to enable reporting by
#	Line 167 | Line 185 | public abstract class ForkJoinTask<V> im
185		Collections.synchronizedMap
186		(new WeakHashMap<ForkJoinTask<?>, Throwable>());
187
188	<	// within-package utilities
171	<
172	<	/**
173	<	* Gets current worker thread, or null if not a worker thread.
174	<	*/
175	<	static ForkJoinWorkerThread getWorker() {
176	<	Thread t = Thread.currentThread();
177	<	return ((t instanceof ForkJoinWorkerThread) ?
178	<	(ForkJoinWorkerThread) t : null);
179	<	}
180	<
181	<	final boolean casStatus(int cmp, int val) {
182	<	return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val);
183	<	}
184	<
185	<	/**
186	<	* Workaround for not being able to rethrow unchecked exceptions.
187	<	*/
188	<	static void rethrowException(Throwable ex) {
189	<	if (ex != null)
190	<	UNSAFE.throwException(ex);
191	<	}
192	<
193	<	// Setting completion status
188	>	// Maintaining completion status
189
190		/**
191	<	* Marks completion and wakes up threads waiting to join this task.
191	>	* Marks completion and wakes up threads waiting to join this task,
192	>	* also clearing signal request bits.
193		*
194		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
195		*/
196	<	final void setCompletion(int completion) {
197	<	ForkJoinPool pool = getPool();
198	<	if (pool != null) {
199	<	int s; // Clear signal bits while setting completion status
200	<	do {} while ((s = status) >= 0 && !casStatus(s, completion));
201	<
202	<	if ((s & SIGNAL_MASK) != 0) {
207	<	if ((s &= INTERNAL_SIGNAL_MASK) != 0)
208	<	pool.updateRunningCount(s);
209	<	synchronized (this) { notifyAll(); }
196	>	private void setCompletion(int completion) {
197	>	int s;
198	>	while ((s = status) >= 0) {
199	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
200	>	if (s != 0)
201	>	synchronized (this) { notifyAll(); }
202	>	break;
203		}
204		}
212	–	else
213	–	externallySetCompletion(completion);
214	–	}
215	–
216	–	/**
217	–	* Version of setCompletion for non-FJ threads.  Leaves signal
218	–	* bits for unblocked threads to adjust, and always notifies.
219	–	*/
220	–	private void externallySetCompletion(int completion) {
221	–	int s;
222	–	do {} while ((s = status) >= 0 &&
223	–	!casStatus(s, (s & SIGNAL_MASK) | completion));
224	–	synchronized (this) { notifyAll(); }
225	–	}
226	–
227	–	/**
228	–	* Sets status to indicate normal completion.
229	–	*/
230	–	final void setNormalCompletion() {
231	–	// Try typical fast case -- single CAS, no signal, not already done.
232	–	// Manually expand casStatus to improve chances of inlining it
233	–	if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL))
234	–	setCompletion(NORMAL);
205		}
206
237	–	// internal waiting and notification
238	–
207		/**
208	<	* Performs the actual monitor wait for awaitDone.
208	>	* Records exception and sets exceptional completion.
209	>	*
210	>	* @return status on exit
211		*/
212	<	private void doAwaitDone() {
213	<	// Minimize lock bias and in/de-flation effects by maximizing
214	<	// chances of waiting inside sync
245	<	try {
246	<	while (status >= 0)
247	<	synchronized (this) { if (status >= 0) wait(); }
248	<	} catch (InterruptedException ie) {
249	<	onInterruptedWait();
250	<	}
212	>	private void setExceptionalCompletion(Throwable rex) {
213	>	exceptionMap.put(this, rex);
214	>	setCompletion(EXCEPTIONAL);
215		}
216
217		/**
218	<	* Performs the actual timed monitor wait for awaitDone.
218	>	* Blocks a worker thread until completion. Called only by
219	>	* pool. Currently unused -- pool-based waits use timeout
220	>	* version below.
221		*/
222	<	private void doAwaitDone(long startTime, long nanos) {
223	<	synchronized (this) {
222	>	final void internalAwaitDone() {
223	>	int s;         // the odd construction reduces lock bias effects
224	>	while ((s = status) >= 0) {
225		try {
226	<	while (status >= 0) {
227	<	long nt = nanos - (System.nanoTime() - startTime);
228	<	if (nt <= 0)
262	<	break;
263	<	wait(nt / 1000000, (int) (nt % 1000000));
226	>	synchronized(this) {
227	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
228	>	wait();
229		}
230		} catch (InterruptedException ie) {
231	<	onInterruptedWait();
267	<	}
268	<	}
269	<	}
270	<
271	<	// Awaiting completion
272	<
273	<	/**
274	<	* Sets status to indicate there is joiner, then waits for join,
275	<	* surrounded with pool notifications.
276	<	*
277	<	* @return status upon exit
278	<	*/
279	<	private int awaitDone(ForkJoinWorkerThread w,
280	<	boolean maintainParallelism) {
281	<	ForkJoinPool pool = (w == null) ? null : w.pool;
282	<	int s;
283	<	while ((s = status) >= 0) {
284	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
285	<	if (pool == null || !pool.preJoin(this, maintainParallelism))
286	<	doAwaitDone();
287	<	if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
288	<	adjustPoolCountsOnUnblock(pool);
289	<	break;
231	>	cancelIfTerminating();
232		}
233		}
292	–	return s;
234		}
235
236		/**
237	<	* Timed version of awaitDone
237	>	* Blocks a worker thread until completed or timed out.  Called
238	>	* only by pool.
239		*
240	<	* @return status upon exit
240	>	* @return status on exit
241		*/
242	<	private int awaitDone(ForkJoinWorkerThread w, long nanos) {
301	<	ForkJoinPool pool = (w == null) ? null : w.pool;
242	>	final int internalAwaitDone(long millis) {
243		int s;
244	<	while ((s = status) >= 0) {
245	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
246	<	long startTime = System.nanoTime();
247	<	if (pool == null || !pool.preJoin(this, false))
248	<	doAwaitDone(startTime, nanos);
308	<	if ((s = status) >= 0) {
309	<	adjustPoolCountsOnCancelledWait(pool);
310	<	s = status;
244	>	if ((s = status) >= 0) {
245	>	try {
246	>	synchronized(this) {
247	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
248	>	wait(millis, 0);
249		}
250	<	if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
251	<	adjustPoolCountsOnUnblock(pool);
314	<	break;
250	>	} catch (InterruptedException ie) {
251	>	cancelIfTerminating();
252		}
253	+	s = status;
254		}
255		return s;
256		}
257
258		/**
259	<	* Notifies pool that thread is unblocked. Called by signalled
322	<	* threads when woken by non-FJ threads (which is atypical).
259	>	* Blocks a non-worker-thread until completion.
260		*/
261	<	private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
261	>	private void externalAwaitDone() {
262		int s;
263	<	do {} while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
264	<	if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
265	<	pool.updateRunningCount(s);
266	<	}
267	<
268	<	/**
269	<	* Notifies pool to adjust counts on cancelled or timed out wait.
270	<	*/
271	<	private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
272	<	if (pool != null) {
273	<	int s;
274	<	while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
275	<	if (casStatus(s, s - 1)) {
339	<	pool.updateRunningCount(1);
263	>	while ((s = status) >= 0) {
264	>	synchronized(this) {
265	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
266	>	boolean interrupted = false;
267	>	while (status >= 0) {
268	>	try {
269	>	wait();
270	>	} catch (InterruptedException ie) {
271	>	interrupted = true;
272	>	}
273	>	}
274	>	if (interrupted)
275	>	Thread.currentThread().interrupt();
276		break;
277		}
278		}
#	Line 344 | Line 280 | public abstract class ForkJoinTask<V> im
280		}
281
282		/**
283	<	* Handles interruptions during waits.
284	<	*/
285	<	private void onInterruptedWait() {
350	<	ForkJoinWorkerThread w = getWorker();
351	<	if (w == null)
352	<	Thread.currentThread().interrupt(); // re-interrupt
353	<	else if (w.isTerminating())
354	<	cancelIgnoringExceptions();
355	<	// else if FJworker, ignore interrupt
356	<	}
357	<
358	<	// Recording and reporting exceptions
359	<
360	<	private void setDoneExceptionally(Throwable rex) {
361	<	exceptionMap.put(this, rex);
362	<	setCompletion(EXCEPTIONAL);
363	<	}
364	<
365	<	/**
366	<	* Throws the exception associated with status s.
367	<	*
368	<	* @throws the exception
369	<	*/
370	<	private void reportException(int s) {
371	<	if ((s &= COMPLETION_MASK) < NORMAL) {
372	<	if (s == CANCELLED)
373	<	throw new CancellationException();
374	<	else
375	<	rethrowException(exceptionMap.get(this));
376	<	}
377	<	}
378	<
379	<	/**
380	<	* Returns result or throws exception using j.u.c.Future conventions.
381	<	* Only call when {@code isDone} known to be true.
382	<	*/
383	<	private V reportFutureResult()
384	<	throws ExecutionException, InterruptedException {
385	<	int s = status & COMPLETION_MASK;
386	<	if (s < NORMAL) {
387	<	Throwable ex;
388	<	if (s == CANCELLED)
389	<	throw new CancellationException();
390	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
391	<	throw new ExecutionException(ex);
392	<	if (Thread.interrupted())
393	<	throw new InterruptedException();
394	<	}
395	<	return getRawResult();
396	<	}
397	<
398	<	/**
399	<	* Returns result or throws exception using j.u.c.Future conventions
400	<	* with timeouts.
401	<	*/
402	<	private V reportTimedFutureResult()
403	<	throws InterruptedException, ExecutionException, TimeoutException {
404	<	Throwable ex;
405	<	int s = status & COMPLETION_MASK;
406	<	if (s == NORMAL)
407	<	return getRawResult();
408	<	if (s == CANCELLED)
409	<	throw new CancellationException();
410	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
411	<	throw new ExecutionException(ex);
412	<	if (Thread.interrupted())
413	<	throw new InterruptedException();
414	<	throw new TimeoutException();
415	<	}
416	<
417	<	// internal execution methods
418	<
419	<	/**
420	<	* Calls exec, recording completion, and rethrowing exception if
421	<	* encountered. Caller should normally check status before calling.
422	<	*
423	<	* @return true if completed normally
424	<	*/
425	<	private boolean tryExec() {
426	<	try { // try block must contain only call to exec
427	<	if (!exec())
428	<	return false;
429	<	} catch (Throwable rex) {
430	<	setDoneExceptionally(rex);
431	<	rethrowException(rex);
432	<	return false; // not reached
433	<	}
434	<	setNormalCompletion();
435	<	return true;
436	<	}
437	<
438	<	/**
439	<	* Main execution method used by worker threads. Invokes
440	<	* base computation unless already complete.
283	>	* Unless done, calls exec and records status if completed, but
284	>	* doesn't wait for completion otherwise. Primary execution method
285	>	* for ForkJoinWorkerThread.
286		*/
287		final void quietlyExec() {
443	–	if (status >= 0) {
444	–	try {
445	–	if (!exec())
446	–	return;
447	–	} catch (Throwable rex) {
448	–	setDoneExceptionally(rex);
449	–	return;
450	–	}
451	–	setNormalCompletion();
452	–	}
453	–	}
454	–
455	–	/**
456	–	* Calls exec(), recording but not rethrowing exception.
457	–	* Caller should normally check status before calling.
458	–	*
459	–	* @return true if completed normally
460	–	*/
461	–	private boolean tryQuietlyInvoke() {
288		try {
289	<	if (!exec())
290	<	return false;
289	>	if (status < 0 || !exec())
290	>	return;
291		} catch (Throwable rex) {
292	<	setDoneExceptionally(rex);
293	<	return false;
468	<	}
469	<	setNormalCompletion();
470	<	return true;
471	<	}
472	<
473	<	/**
474	<	* Cancels, ignoring any exceptions it throws.
475	<	*/
476	<	final void cancelIgnoringExceptions() {
477	<	try {
478	<	cancel(false);
479	<	} catch (Throwable ignore) {
292	>	setExceptionalCompletion(rex);
293	>	return;
294		}
295	<	}
482	<
483	<	/**
484	<	* Main implementation of helpJoin
485	<	*/
486	<	private int busyJoin(ForkJoinWorkerThread w) {
487	<	int s;
488	<	ForkJoinTask<?> t;
489	<	while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
490	<	t.quietlyExec();
491	<	return (s >= 0) ? awaitDone(w, false) : s; // block if no work
295	>	setCompletion(NORMAL); // must be outside try block
296		}
297
298		// public methods
#	Line 497 | Line 301 | public abstract class ForkJoinTask<V> im
301		* Arranges to asynchronously execute this task.  While it is not
302		* necessarily enforced, it is a usage error to fork a task more
303		* than once unless it has completed and been reinitialized.
304	+	* Subsequent modifications to the state of this task or any data
305	+	* it operates on are not necessarily consistently observable by
306	+	* any thread other than the one executing it unless preceded by a
307	+	* call to {@link #join} or related methods, or a call to {@link
308	+	* #isDone} returning {@code true}.
309		*
310		* <p>This method may be invoked only from within {@code
311		* ForkJoinTask} computations (as may be determined using method
#	Line 513 | Line 322 | public abstract class ForkJoinTask<V> im
322		}
323
324		/**
325	<	* Returns the result of the computation when it is ready.
325	>	* Returns the result of the computation when it {@link #isDone is done}.
326		* This method differs from {@link #get()} in that
327		* abnormal completion results in {@code RuntimeException} or
328		* {@code Error}, not {@code ExecutionException}.
#	Line 521 | Line 330 | public abstract class ForkJoinTask<V> im
330		* @return the computed result
331		*/
332		public final V join() {
333	<	ForkJoinWorkerThread w = getWorker();
334	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryExec())
335	<	reportException(awaitDone(w, true));
333	>	quietlyJoin();
334	>	Throwable ex;
335	>	if (status < NORMAL && (ex = getException()) != null)
336	>	UNSAFE.throwException(ex);
337		return getRawResult();
338		}
339
340		/**
341		* Commences performing this task, awaits its completion if
342	<	* necessary, and return its result.
342	>	* necessary, and returns its result, or throws an (unchecked)
343	>	* {@code RuntimeException} or {@code Error} if the underlying
344	>	* computation did so.
345		*
534	–	* @throws Throwable (a RuntimeException, Error, or unchecked
535	–	* exception) if the underlying computation did so
346		* @return the computed result
347		*/
348		public final V invoke() {
349	<	if (status >= 0 && tryExec())
350	<	return getRawResult();
351	<	else
352	<	return join();
349	>	quietlyInvoke();
350	>	Throwable ex;
351	>	if (status < NORMAL && (ex = getException()) != null)
352	>	UNSAFE.throwException(ex);
353	>	return getRawResult();
354		}
355
356		/**
357	<	* Forks the given tasks, returning when {@code isDone} holds
358	<	* for each task or an exception is encountered.
357	>	* Forks the given tasks, returning when {@code isDone} holds for
358	>	* each task or an (unchecked) exception is encountered, in which
359	>	* case the exception is rethrown. If more than one task
360	>	* encounters an exception, then this method throws any one of
361	>	* these exceptions. If any task encounters an exception, the
362	>	* other may be cancelled. However, the execution status of
363	>	* individual tasks is not guaranteed upon exceptional return. The
364	>	* status of each task may be obtained using {@link
365	>	* #getException()} and related methods to check if they have been
366	>	* cancelled, completed normally or exceptionally, or left
367	>	* unprocessed.
368		*
369		* <p>This method may be invoked only from within {@code
370		* ForkJoinTask} computations (as may be determined using method
#	Line 555 | Line 375 | public abstract class ForkJoinTask<V> im
375		* @param t1 the first task
376		* @param t2 the second task
377		* @throws NullPointerException if any task is null
558	–	* @throws RuntimeException or Error if a task did so
378		*/
379		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
380		t2.fork();
#	Line 565 | Line 384 | public abstract class ForkJoinTask<V> im
384
385		/**
386		* Forks the given tasks, returning when {@code isDone} holds for
387	<	* each task or an exception is encountered. If any task
388	<	* encounters an exception, others may be, but are not guaranteed
389	<	* to be, cancelled.
387	>	* each task or an (unchecked) exception is encountered, in which
388	>	* case the exception is rethrown. If more than one task
389	>	* encounters an exception, then this method throws any one of
390	>	* these exceptions. If any task encounters an exception, others
391	>	* may be cancelled. However, the execution status of individual
392	>	* tasks is not guaranteed upon exceptional return. The status of
393	>	* each task may be obtained using {@link #getException()} and
394	>	* related methods to check if they have been cancelled, completed
395	>	* normally or exceptionally, or left unprocessed.
396		*
397		* <p>This method may be invoked only from within {@code
398		* ForkJoinTask} computations (as may be determined using method
#	Line 576 | Line 401 | public abstract class ForkJoinTask<V> im
401		* ClassCastException}.
402		*
403		* @param tasks the tasks
404	<	* @throws NullPointerException if tasks or any element are null
580	<	* @throws RuntimeException or Error if any task did so
404	>	* @throws NullPointerException if any task is null
405		*/
406		public static void invokeAll(ForkJoinTask<?>... tasks) {
407		Throwable ex = null;
#	Line 592 | Line 416 | public abstract class ForkJoinTask<V> im
416		t.fork();
417		else {
418		t.quietlyInvoke();
419	<	if (ex == null)
419	>	if (ex == null && t.status < NORMAL)
420		ex = t.getException();
421		}
422		}
#	Line 603 | Line 427 | public abstract class ForkJoinTask<V> im
427		t.cancel(false);
428		else {
429		t.quietlyJoin();
430	<	if (ex == null)
430	>	if (ex == null && t.status < NORMAL)
431		ex = t.getException();
432		}
433		}
434		}
435		if (ex != null)
436	<	rethrowException(ex);
436	>	UNSAFE.throwException(ex);
437		}
438
439		/**
440		* Forks all tasks in the specified collection, returning when
441	<	* {@code isDone} holds for each task or an exception is
442	<	* encountered.  If any task encounters an exception, others may
443	<	* be, but are not guaranteed to be, cancelled. The behavior of
444	<	* this operation is undefined if the specified collection is
445	<	* modified while the operation is in progress.
441	>	* {@code isDone} holds for each task or an (unchecked) exception
442	>	* is encountered, in which case the exception is rethrown. If
443	>	* more than one task encounters an exception, then this method
444	>	* throws any one of these exceptions. If any task encounters an
445	>	* exception, others may be cancelled. However, the execution
446	>	* status of individual tasks is not guaranteed upon exceptional
447	>	* return. The status of each task may be obtained using {@link
448	>	* #getException()} and related methods to check if they have been
449	>	* cancelled, completed normally or exceptionally, or left
450	>	* unprocessed.
451		*
452		* <p>This method may be invoked only from within {@code
453		* ForkJoinTask} computations (as may be determined using method
#	Line 629 | Line 458 | public abstract class ForkJoinTask<V> im
458		* @param tasks the collection of tasks
459		* @return the tasks argument, to simplify usage
460		* @throws NullPointerException if tasks or any element are null
632	–	* @throws RuntimeException or Error if any task did so
461		*/
462		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
463		if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
#	Line 651 | Line 479 | public abstract class ForkJoinTask<V> im
479		t.fork();
480		else {
481		t.quietlyInvoke();
482	<	if (ex == null)
482	>	if (ex == null && t.status < NORMAL)
483		ex = t.getException();
484		}
485		}
#	Line 662 | Line 490 | public abstract class ForkJoinTask<V> im
490		t.cancel(false);
491		else {
492		t.quietlyJoin();
493	<	if (ex == null)
493	>	if (ex == null && t.status < NORMAL)
494		ex = t.getException();
495		}
496		}
497		}
498		if (ex != null)
499	<	rethrowException(ex);
499	>	UNSAFE.throwException(ex);
500		return tasks;
501		}
502
503		/**
504	<	* Returns {@code true} if the computation performed by this task
505	<	* has completed (or has been cancelled).
506	<	*
507	<	* @return {@code true} if this computation has completed
508	<	*/
509	<	public final boolean isDone() {
510	<	return status < 0;
683	<	}
684	<
685	<	/**
686	<	* Returns {@code true} if this task was cancelled.
687	<	*
688	<	* @return {@code true} if this task was cancelled
689	<	*/
690	<	public final boolean isCancelled() {
691	<	return (status & COMPLETION_MASK) == CANCELLED;
692	<	}
693	<
694	<	/**
695	<	* Asserts that the results of this task's computation will not be
696	<	* used. If a cancellation occurs before attempting to execute this
697	<	* task, execution will be suppressed, {@link #isCancelled}
698	<	* will report true, and {@link #join} will result in a
699	<	* {@code CancellationException} being thrown. Otherwise, when
700	<	* cancellation races with completion, there are no guarantees
701	<	* about whether {@code isCancelled} will report {@code true},
702	<	* whether {@code join} will return normally or via an exception,
703	<	* or whether these behaviors will remain consistent upon repeated
704	<	* invocation.
504	>	* Attempts to cancel execution of this task. This attempt will
505	>	* fail if the task has already completed, has already been
506	>	* cancelled, or could not be cancelled for some other reason. If
507	>	* successful, and this task has not started when cancel is
508	>	* called, execution of this task is suppressed, {@link
509	>	* #isCancelled} will report true, and {@link #join} will result
510	>	* in a {@code CancellationException} being thrown.
511		*
512		* <p>This method may be overridden in subclasses, but if so, must
513		* still ensure that these minimal properties hold. In particular,
#	Line 713 | Line 519 | public abstract class ForkJoinTask<V> im
519		* invoke {@link #completeExceptionally}.
520		*
521		* @param mayInterruptIfRunning this value is ignored in the
522	<	* default implementation because tasks are not in general
522	>	* default implementation because tasks are not
523		* cancelled via interruption
524		*
525		* @return {@code true} if this task is now cancelled
526		*/
527		public boolean cancel(boolean mayInterruptIfRunning) {
528		setCompletion(CANCELLED);
529	<	return (status & COMPLETION_MASK) == CANCELLED;
529	>	return status == CANCELLED;
530	>	}
531	>
532	>	/**
533	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
534	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
535	>	* exceptions, but if it does anyway, we have no recourse during
536	>	* shutdown, so guard against this case.
537	>	*/
538	>	final void cancelIgnoringExceptions() {
539	>	try {
540	>	cancel(false);
541	>	} catch (Throwable ignore) {
542	>	}
543	>	}
544	>
545	>	/**
546	>	* Cancels if current thread is a terminating worker thread,
547	>	* ignoring any exceptions thrown by cancel.
548	>	*/
549	>	final void cancelIfTerminating() {
550	>	Thread t = Thread.currentThread();
551	>	if ((t instanceof ForkJoinWorkerThread) &&
552	>	((ForkJoinWorkerThread) t).isTerminating()) {
553	>	try {
554	>	cancel(false);
555	>	} catch (Throwable ignore) {
556	>	}
557	>	}
558	>	}
559	>
560	>	public final boolean isDone() {
561	>	return status < 0;
562	>	}
563	>
564	>	public final boolean isCancelled() {
565	>	return status == CANCELLED;
566		}
567
568		/**
#	Line 729 | Line 571 | public abstract class ForkJoinTask<V> im
571		* @return {@code true} if this task threw an exception or was cancelled
572		*/
573		public final boolean isCompletedAbnormally() {
574	<	return (status & COMPLETION_MASK) < NORMAL;
574	>	return status < NORMAL;
575	>	}
576	>
577	>	/**
578	>	* Returns {@code true} if this task completed without throwing an
579	>	* exception and was not cancelled.
580	>	*
581	>	* @return {@code true} if this task completed without throwing an
582	>	* exception and was not cancelled
583	>	*/
584	>	public final boolean isCompletedNormally() {
585	>	return status == NORMAL;
586		}
587
588		/**
#	Line 740 | Line 593 | public abstract class ForkJoinTask<V> im
593		* @return the exception, or {@code null} if none
594		*/
595		public final Throwable getException() {
596	<	int s = status & COMPLETION_MASK;
597	<	if (s >= NORMAL)
598	<	return null;
599	<	if (s == CANCELLED)
747	<	return new CancellationException();
748	<	return exceptionMap.get(this);
596	>	int s = status;
597	>	return ((s >= NORMAL)    ? null :
598	>	(s == CANCELLED) ? new CancellationException() :
599	>	exceptionMap.get(this));
600		}
601
602		/**
#	Line 758 | Line 609 | public abstract class ForkJoinTask<V> im
609		* overridable, but overridden versions must invoke {@code super}
610		* implementation to maintain guarantees.
611		*
612	<	* @param ex the exception to throw. If this exception is
613	<	* not a RuntimeException or Error, the actual exception thrown
614	<	* will be a RuntimeException with cause ex.
612	>	* @param ex the exception to throw. If this exception is not a
613	>	* {@code RuntimeException} or {@code Error}, the actual exception
614	>	* thrown will be a {@code RuntimeException} with cause {@code ex}.
615		*/
616		public void completeExceptionally(Throwable ex) {
617	<	setDoneExceptionally((ex instanceof RuntimeException) ||
618	<	(ex instanceof Error) ? ex :
619	<	new RuntimeException(ex));
617	>	setExceptionalCompletion((ex instanceof RuntimeException) ||
618	>	(ex instanceof Error) ? ex :
619	>	new RuntimeException(ex));
620		}
621
622		/**
623		* Completes this task, and if not already aborted or cancelled,
624	<	* returning a {@code null} result upon {@code join} and related
625	<	* operations. This method may be used to provide results for
626	<	* asynchronous tasks, or to provide alternative handling for
627	<	* tasks that would not otherwise complete normally. Its use in
628	<	* other situations is discouraged. This method is
629	<	* overridable, but overridden versions must invoke {@code super}
630	<	* implementation to maintain guarantees.
624	>	* returning the given value as the result of subsequent
625	>	* invocations of {@code join} and related operations. This method
626	>	* may be used to provide results for asynchronous tasks, or to
627	>	* provide alternative handling for tasks that would not otherwise
628	>	* complete normally. Its use in other situations is
629	>	* discouraged. This method is overridable, but overridden
630	>	* versions must invoke {@code super} implementation to maintain
631	>	* guarantees.
632		*
633		* @param value the result value for this task
634		*/
#	Line 784 | Line 636 | public abstract class ForkJoinTask<V> im
636		try {
637		setRawResult(value);
638		} catch (Throwable rex) {
639	<	setDoneExceptionally(rex);
639	>	setExceptionalCompletion(rex);
640		return;
641		}
642	<	setNormalCompletion();
642	>	setCompletion(NORMAL);
643		}
644
645		public final V get() throws InterruptedException, ExecutionException {
646	<	ForkJoinWorkerThread w = getWorker();
647	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
648	<	awaitDone(w, true);
649	<	return reportFutureResult();
646	>	quietlyJoin();
647	>	if (Thread.interrupted())
648	>	throw new InterruptedException();
649	>	int s = status;
650	>	if (s < NORMAL) {
651	>	Throwable ex;
652	>	if (s == CANCELLED)
653	>	throw new CancellationException();
654	>	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
655	>	throw new ExecutionException(ex);
656	>	}
657	>	return getRawResult();
658		}
659
660		public final V get(long timeout, TimeUnit unit)
661		throws InterruptedException, ExecutionException, TimeoutException {
662	+	Thread t = Thread.currentThread();
663	+	ForkJoinPool pool;
664	+	if (t instanceof ForkJoinWorkerThread) {
665	+	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
666	+	if (status >= 0 && w.unpushTask(this))
667	+	quietlyExec();
668	+	pool = w.pool;
669	+	}
670	+	else
671	+	pool = null;
672	+	/*
673	+	* Timed wait loop intermixes cases for FJ (pool != null) and
674	+	* non FJ threads. For FJ, decrement pool count but don't try
675	+	* for replacement; increment count on completion. For non-FJ,
676	+	* deal with interrupts. This is messy, but a little less so
677	+	* than is splitting the FJ and nonFJ cases.
678	+	*/
679	+	boolean interrupted = false;
680	+	boolean dec = false; // true if pool count decremented
681		long nanos = unit.toNanos(timeout);
682	<	ForkJoinWorkerThread w = getWorker();
683	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
684	<	awaitDone(w, nanos);
685	<	return reportTimedFutureResult();
686	<	}
687	<
688	<	/**
689	<	* Possibly executes other tasks until this task is ready, then
690	<	* returns the result of the computation.  This method may be more
691	<	* efficient than {@code join}, but is only applicable when
692	<	* there are no potential dependencies between continuation of the
693	<	* current task and that of any other task that might be executed
694	<	* while helping. (This usually holds for pure divide-and-conquer
695	<	* tasks).
696	<	*
697	<	* <p>This method may be invoked only from within {@code
698	<	* ForkJoinTask} computations (as may be determined using method
699	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
700	<	* result in exceptions or errors, possibly including {@code
701	<	* ClassCastException}.
702	<	*
703	<	* @return the computed result
704	<	*/
705	<	public final V helpJoin() {
706	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
707	<	if (status < 0 || !w.unpushTask(this) || !tryExec())
708	<	reportException(busyJoin(w));
709	<	return getRawResult();
710	<	}
711	<
712	<	/**
713	<	* Possibly executes other tasks until this task is ready.  This
714	<	* method may be useful when processing collections of tasks when
715	<	* some have been cancelled or otherwise known to have aborted.
716	<	*
717	<	* <p>This method may be invoked only from within {@code
718	<	* ForkJoinTask} 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}.
722	<	*/
723	<	public final void quietlyHelpJoin() {
724	<	if (status >= 0) {
725	<	ForkJoinWorkerThread w =
726	<	(ForkJoinWorkerThread) Thread.currentThread();
727	<	if (!w.unpushTask(this) || !tryQuietlyInvoke())
728	<	busyJoin(w);
682	>	for (;;) {
683	>	if (pool == null && Thread.interrupted()) {
684	>	interrupted = true;
685	>	break;
686	>	}
687	>	int s = status;
688	>	if (s < 0)
689	>	break;
690	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
691	>	long startTime = System.nanoTime();
692	>	long nt; // wait time
693	>	while (status >= 0 &&
694	>	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
695	>	if (pool != null && !dec)
696	>	dec = pool.tryDecrementRunningCount();
697	>	else {
698	>	long ms = nt / 1000000;
699	>	int ns = (int) (nt % 1000000);
700	>	try {
701	>	synchronized(this) {
702	>	if (status >= 0)
703	>	wait(ms, ns);
704	>	}
705	>	} catch (InterruptedException ie) {
706	>	if (pool != null)
707	>	cancelIfTerminating();
708	>	else {
709	>	interrupted = true;
710	>	break;
711	>	}
712	>	}
713	>	}
714	>	}
715	>	break;
716	>	}
717	>	}
718	>	if (pool != null && dec)
719	>	pool.incrementRunningCount();
720	>	if (interrupted)
721	>	throw new InterruptedException();
722	>	int es = status;
723	>	if (es != NORMAL) {
724	>	Throwable ex;
725	>	if (es == CANCELLED)
726	>	throw new CancellationException();
727	>	if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
728	>	throw new ExecutionException(ex);
729	>	throw new TimeoutException();
730		}
731	+	return getRawResult();
732		}
733
734		/**
735	<	* Joins this task, without returning its result or throwing an
735	>	* Joins this task, without returning its result or throwing its
736		* exception. This method may be useful when processing
737		* collections of tasks when some have been cancelled or otherwise
738		* known to have aborted.
739		*/
740		public final void quietlyJoin() {
741	<	if (status >= 0) {
742	<	ForkJoinWorkerThread w = getWorker();
743	<	if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
744	<	awaitDone(w, true);
741	>	Thread t;
742	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
743	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
744	>	if (status >= 0) {
745	>	if (w.unpushTask(this)) {
746	>	boolean completed;
747	>	try {
748	>	completed = exec();
749	>	} catch (Throwable rex) {
750	>	setExceptionalCompletion(rex);
751	>	return;
752	>	}
753	>	if (completed) {
754	>	setCompletion(NORMAL);
755	>	return;
756	>	}
757	>	}
758	>	w.joinTask(this);
759	>	}
760		}
761	+	else
762	+	externalAwaitDone();
763		}
764
765		/**
766		* Commences performing this task and awaits its completion if
767	<	* necessary, without returning its result or throwing an
768	<	* exception. This method may be useful when processing
871	<	* collections of tasks when some have been cancelled or otherwise
872	<	* known to have aborted.
767	>	* necessary, without returning its result or throwing its
768	>	* exception.
769		*/
770		public final void quietlyInvoke() {
771	<	if (status >= 0 && !tryQuietlyInvoke())
772	<	quietlyJoin();
771	>	if (status >= 0) {
772	>	boolean completed;
773	>	try {
774	>	completed = exec();
775	>	} catch (Throwable rex) {
776	>	setExceptionalCompletion(rex);
777	>	return;
778	>	}
779	>	if (completed)
780	>	setCompletion(NORMAL);
781	>	else
782	>	quietlyJoin();
783	>	}
784		}
785
786		/**
787		* Possibly executes tasks until the pool hosting the current task
788	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
789	<	* designs in which many tasks are forked, but none are explicitly
790	<	* joined, instead executing them until all are processed.
788	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
789	>	* be of use in designs in which many tasks are forked, but none
790	>	* are explicitly joined, instead executing them until all are
791	>	* processed.
792		*
793		* <p>This method may be invoked only from within {@code
794		* ForkJoinTask} computations (as may be determined using method
#	Line 904 | Line 812 | public abstract class ForkJoinTask<V> im
812		* pre-constructed trees of subtasks in loops.
813		*/
814		public void reinitialize() {
815	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
815	>	if (status == EXCEPTIONAL)
816		exceptionMap.remove(this);
817		status = 0;
818		}
#	Line 1024 | Line 932 | public abstract class ForkJoinTask<V> im
932		* called otherwise. The return value controls whether this task
933		* is considered to be done normally. It may return false in
934		* asynchronous actions that require explicit invocations of
935	<	* {@link #complete} to become joinable. It may throw exceptions
936	<	* to indicate abnormal exit.
935	>	* {@link #complete} to become joinable. It may also throw an
936	>	* (unchecked) exception to indicate abnormal exit.
937		*
938		* @return {@code true} if completed normally
1031	–	* @throws Error or RuntimeException if encountered during computation
939		*/
940		protected abstract boolean exec();
941
#	Line 1195 | Line 1102 | public abstract class ForkJoinTask<V> im
1102		private static final long serialVersionUID = -7721805057305804111L;
1103
1104		/**
1105	<	* Save the state to a stream.
1105	>	* Saves the state to a stream (that is, serializes it).
1106		*
1107		* @serialData the current run status and the exception thrown
1108		* during execution, or {@code null} if none
#	Line 1208 | Line 1115 | public abstract class ForkJoinTask<V> im
1115		}
1116
1117		/**
1118	<	* Reconstitute the instance from a stream.
1118	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1119		*
1120		* @param s the stream
1121		*/
1122		private void readObject(java.io.ObjectInputStream s)
1123		throws java.io.IOException, ClassNotFoundException {
1124		s.defaultReadObject();
1218	–	status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
1219	–	status |= EXTERNAL_SIGNAL; // conservatively set external signal
1125		Object ex = s.readObject();
1126		if (ex != null)
1127	<	setDoneExceptionally((Throwable) ex);
1127	>	setExceptionalCompletion((Throwable) ex);
1128		}
1129
1130		// Unsafe mechanics

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