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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.31 by jsr166, Sun Aug 2 22:58:50 2009 UTC vs.
Revision 1.56 by jsr166, Sat Sep 4 00:21:31 2010 UTC

#	Line 12 | Line 12 | import java.io.Serializable;
12		import java.util.Collection;
13		import java.util.Collections;
14		import java.util.List;
15	+	import java.util.RandomAccess;
16		import java.util.Map;
17		import java.util.WeakHashMap;
18
#	Line 54 | Line 55 | import java.util.WeakHashMap;
55		* restriction is in part enforced by not permitting checked
56		* exceptions such as {@code IOExceptions} to be thrown. However,
57		* computations may still encounter unchecked exceptions, that are
58	<	* rethrown to callers attempting join them. These exceptions may
59	<	* additionally include RejectedExecutionExceptions stemming from
60	<	* internal resource exhaustion such as failure to allocate internal
61	<	* task queues.
58	>	* rethrown to callers attempting to join them. These exceptions may
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
70	<	* equivalent to {@code fork(); join()} but always attempts to
71	<	* begin execution in the current thread. The "<em>quiet</em>" forms
72	<	* 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 85 | Line 95 | import java.util.WeakHashMap;
95		* established in a constructor, and then defines a {@code compute}
96		* method that somehow uses the control methods supplied by this base
97		* class. While these methods have {@code public} access (to allow
98	<	* instances of different task subclasses to call each others
98	>	* instances of different task subclasses to call each other's
99		* methods), some of them may only be called from within other
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.
104		*
105	<	* <p>Most base support methods are {@code final} because their
106	<	* implementations are intrinsically tied to the underlying
107	<	* lightweight task scheduling framework, and so cannot be overridden.
108	<	* Developers creating new basic styles of fork/join processing should
109	<	* minimally implement {@code protected} methods
110	<	* {@link #exec}, {@link #setRawResult}, and
111	<	* {@link #getRawResult}, while also introducing an abstract
112	<	* computational method that can be implemented in its subclasses,
113	<	* possibly relying on other {@code protected} methods provided
104	<	* by this class.
105	>	* <p>Most base support methods are {@code final}, to prevent
106	>	* overriding of implementations that are intrinsically tied to the
107	>	* underlying lightweight task scheduling framework.  Developers
108	>	* creating new basic styles of fork/join processing should minimally
109	>	* implement {@code protected} methods {@link #exec}, {@link
110	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
111	>	* an abstract computational method that can be implemented in its
112	>	* subclasses, possibly relying on other {@code protected} methods
113	>	* provided by this class.
114		*
115		* <p>ForkJoinTasks should perform relatively small amounts of
116	<	* computations, otherwise splitting into smaller tasks. As a very
117	<	* rough rule of thumb, a task should perform more than 100 and less
118	<	* than 10000 basic computational steps. If tasks are too big, then
119	<	* parallelism cannot improve throughput. If too small, then memory
120	<	* and internal task maintenance overhead may overwhelm processing.
116	>	* computation. Large tasks should be split into smaller subtasks,
117	>	* usually via recursive decomposition. As a very rough rule of thumb,
118	>	* a task should perform more than 100 and less than 10000 basic
119	>	* computational steps. If tasks are too big, then parallelism cannot
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
117	<	* 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
129	<	* to be used in extensions such as remote execution frameworks. It is
130	<	* in general sensible to serialize tasks only before or after, but
131	<	* not during execution. Serialization is not relied on during
123	<	* execution itself.
128	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
129	>	* used in extensions such as remote execution frameworks. It is
130	>	* sensible to serialize tasks only before or after, but not during,
131	>	* execution. Serialization is not relied on during execution itself.
132		*
133		* @since 1.7
134		* @author Doug Lea
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	>	* COMPLETED. 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	<	}
188	>	// Maintaining completion status
189
190		/**
191	<	* Workaround for not being able to rethrow unchecked exceptions.
192	<	*/
188	<	static void rethrowException(Throwable ex) {
189	<	if (ex != null)
190	<	UNSAFE.throwException(ex);
191	<	}
192	<
193	<	// Setting completion status
194	<
195	<	/**
196	<	* 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);
205		}
206
207		/**
208	<	* Version of setCompletion for non-FJ threads.  Leaves signal
209	<	* bits for unblocked threads to adjust, and always notifies.
210	<	*/
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);
235	<	}
236	<
237	<	// internal waiting and notification
238	<
239	<	/**
240	<	* 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();
231	>	cancelIfTerminating();
232		}
233		}
234		}
235
271	–	// Awaiting completion
272	–
236		/**
237	<	* Sets status to indicate there is joiner, then waits for join,
238	<	* surrounded with pool notifications.
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,
280	<	boolean maintainParallelism) {
281	<	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	<	if (pool == null || !pool.preJoin(this, maintainParallelism))
247	<	doAwaitDone();
248	<	if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
288	<	adjustPoolCountsOnUnblock(pool);
289	<	break;
290	<	}
291	<	}
292	<	return s;
293	<	}
294	<
295	<	/**
296	<	* Timed version of awaitDone
297	<	*
298	<	* @return status upon exit
299	<	*/
300	<	private int awaitDone(ForkJoinWorkerThread w, long nanos) {
301	<	ForkJoinPool pool = (w == null) ? null : w.pool;
302	<	int s;
303	<	while ((s = status) >= 0) {
304	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
305	<	long startTime = System.nanoTime();
306	<	if (pool == null || !pool.preJoin(this, false))
307	<	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	>	* exception if the underlying computation did so.
344		*
534	–	* @throws Throwable (a RuntimeException, Error, or unchecked
535	–	* exception) if the underlying computation did so
345		* @return the computed result
346		*/
347		public final V invoke() {
348	<	if (status >= 0 && tryExec())
349	<	return getRawResult();
350	<	else
351	<	return join();
348	>	quietlyInvoke();
349	>	Throwable ex;
350	>	if (status < NORMAL && (ex = getException()) != null)
351	>	UNSAFE.throwException(ex);
352	>	return getRawResult();
353		}
354
355		/**
356	<	* Forks the given tasks, returning when {@code isDone} holds
357	<	* for each task or an exception is encountered.
356	>	* Forks the given tasks, returning when {@code isDone} holds for
357	>	* each task or an (unchecked) exception is encountered, in which
358	>	* case the exception is rethrown.  If either task encounters an
359	>	* exception, the other one may be, but is not guaranteed to be,
360	>	* cancelled.  If both tasks throw an exception, then this method
361	>	* throws one of them.  The individual status of each task may be
362	>	* checked using {@link #getException()} and related methods.
363		*
364		* <p>This method may be invoked only from within {@code
365		* ForkJoinTask} computations (as may be determined using method
#	Line 555 | Line 370 | public abstract class ForkJoinTask<V> im
370		* @param t1 the first task
371		* @param t2 the second task
372		* @throws NullPointerException if any task is null
558	–	* @throws RuntimeException or Error if a task did so
373		*/
374		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
375		t2.fork();
#	Line 565 | Line 379 | public abstract class ForkJoinTask<V> im
379
380		/**
381		* Forks the given tasks, returning when {@code isDone} holds for
382	<	* each task or an exception is encountered. If any task
383	<	* encounters an exception, others may be, but are not guaranteed
384	<	* to be, cancelled.
382	>	* each task or an (unchecked) exception is encountered, in which
383	>	* case the exception is rethrown. If any task encounters an
384	>	* exception, others may be, but are not guaranteed to be,
385	>	* cancelled.  If more than one task encounters an exception, then
386	>	* this method throws any one of these exceptions.  The individual
387	>	* status of each task may be checked using {@link #getException()}
388	>	* and related methods.
389		*
390		* <p>This method may be invoked only from within {@code
391		* ForkJoinTask} computations (as may be determined using method
#	Line 575 | Line 393 | public abstract class ForkJoinTask<V> im
393		* result in exceptions or errors, possibly including {@code
394		* ClassCastException}.
395		*
578	–	* <p>Overloadings of this method exist for the special cases
579	–	* of one to four arguments.
580	–	*
396		* @param tasks the tasks
397	<	* @throws NullPointerException if tasks or any element are null
583	<	* @throws RuntimeException or Error if any task did so
397	>	* @throws NullPointerException if any task is null
398		*/
399		public static void invokeAll(ForkJoinTask<?>... tasks) {
400		Throwable ex = null;
#	Line 595 | Line 409 | public abstract class ForkJoinTask<V> im
409		t.fork();
410		else {
411		t.quietlyInvoke();
412	<	if (ex == null)
412	>	if (ex == null && t.status < NORMAL)
413		ex = t.getException();
414		}
415		}
#	Line 606 | Line 420 | public abstract class ForkJoinTask<V> im
420		t.cancel(false);
421		else {
422		t.quietlyJoin();
423	<	if (ex == null)
423	>	if (ex == null && t.status < NORMAL)
424		ex = t.getException();
425		}
426		}
427		}
428		if (ex != null)
429	<	rethrowException(ex);
429	>	UNSAFE.throwException(ex);
430		}
431
432		/**
433	<	* Forks all tasks in the collection, returning when {@code
434	<	* isDone} holds for each task or an exception is encountered.
435	<	* If any task encounters an exception, others may be, but are
436	<	* not guaranteed to be, cancelled.
433	>	* Forks all tasks in the specified collection, returning when
434	>	* {@code isDone} holds for each task or an (unchecked) exception
435	>	* is encountered.  If any task encounters an exception, others
436	>	* may be, but are not guaranteed to be, cancelled.  If more than
437	>	* one task encounters an exception, then this method throws any
438	>	* one of these exceptions.  The individual status of each task
439	>	* may be checked using {@link #getException()} and related
440	>	* methods.  The behavior of this operation is undefined if the
441	>	* specified collection is modified while the operation is in
442	>	* progress.
443		*
444		* <p>This method may be invoked only from within {@code
445		* ForkJoinTask} computations (as may be determined using method
#	Line 630 | Line 450 | public abstract class ForkJoinTask<V> im
450		* @param tasks the collection of tasks
451		* @return the tasks argument, to simplify usage
452		* @throws NullPointerException if tasks or any element are null
633	–	* @throws RuntimeException or Error if any task did so
453		*/
454		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
455	<	if (!(tasks instanceof List<?>)) {
455	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
456		invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
457		return tasks;
458		}
#	Line 652 | Line 471 | public abstract class ForkJoinTask<V> im
471		t.fork();
472		else {
473		t.quietlyInvoke();
474	<	if (ex == null)
474	>	if (ex == null && t.status < NORMAL)
475		ex = t.getException();
476		}
477		}
#	Line 663 | Line 482 | public abstract class ForkJoinTask<V> im
482		t.cancel(false);
483		else {
484		t.quietlyJoin();
485	<	if (ex == null)
485	>	if (ex == null && t.status < NORMAL)
486		ex = t.getException();
487		}
488		}
489		}
490		if (ex != null)
491	<	rethrowException(ex);
491	>	UNSAFE.throwException(ex);
492		return tasks;
493		}
494
495		/**
496	<	* Returns {@code true} if the computation performed by this task
497	<	* has completed (or has been cancelled).
498	<	*
499	<	* @return {@code true} if this computation has completed
500	<	*/
501	<	public final boolean isDone() {
502	<	return status < 0;
684	<	}
685	<
686	<	/**
687	<	* Returns {@code true} if this task was cancelled.
688	<	*
689	<	* @return {@code true} if this task was cancelled
690	<	*/
691	<	public final boolean isCancelled() {
692	<	return (status & COMPLETION_MASK) == CANCELLED;
693	<	}
694	<
695	<	/**
696	<	* Asserts that the results of this task's computation will not be
697	<	* used. If a cancellation occurs before attempting to execute this
698	<	* task, execution will be suppressed, {@link #isCancelled}
699	<	* will report true, and {@link #join} will result in a
700	<	* {@code CancellationException} being thrown. Otherwise, when
701	<	* cancellation races with completion, there are no guarantees
702	<	* about whether {@code isCancelled} will report {@code true},
703	<	* whether {@code join} will return normally or via an exception,
704	<	* or whether these behaviors will remain consistent upon repeated
705	<	* invocation.
496	>	* Attempts to cancel execution of this task. This attempt will
497	>	* fail if the task has already completed, has already been
498	>	* cancelled, or could not be cancelled for some other reason. If
499	>	* successful, and this task has not started when cancel is
500	>	* called, execution of this task is suppressed, {@link
501	>	* #isCancelled} will report true, and {@link #join} will result
502	>	* in a {@code CancellationException} being thrown.
503		*
504		* <p>This method may be overridden in subclasses, but if so, must
505		* still ensure that these minimal properties hold. In particular,
#	Line 714 | Line 511 | public abstract class ForkJoinTask<V> im
511		* invoke {@link #completeExceptionally}.
512		*
513		* @param mayInterruptIfRunning this value is ignored in the
514	<	* default implementation because tasks are not in general
514	>	* default implementation because tasks are not
515		* cancelled via interruption
516		*
517		* @return {@code true} if this task is now cancelled
518		*/
519		public boolean cancel(boolean mayInterruptIfRunning) {
520		setCompletion(CANCELLED);
521	<	return (status & COMPLETION_MASK) == CANCELLED;
521	>	return status == CANCELLED;
522	>	}
523	>
524	>	/**
525	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
526	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
527	>	* exceptions, but if it does anyway, we have no recourse during
528	>	* shutdown, so guard against this case.
529	>	*/
530	>	final void cancelIgnoringExceptions() {
531	>	try {
532	>	cancel(false);
533	>	} catch (Throwable ignore) {
534	>	}
535	>	}
536	>
537	>	/**
538	>	* Cancels if current thread is a terminating worker thread,
539	>	* ignoring any exceptions thrown by cancel.
540	>	*/
541	>	final void cancelIfTerminating() {
542	>	Thread t = Thread.currentThread();
543	>	if ((t instanceof ForkJoinWorkerThread) &&
544	>	((ForkJoinWorkerThread) t).isTerminating()) {
545	>	try {
546	>	cancel(false);
547	>	} catch (Throwable ignore) {
548	>	}
549	>	}
550	>	}
551	>
552	>	public final boolean isDone() {
553	>	return status < 0;
554	>	}
555	>
556	>	public final boolean isCancelled() {
557	>	return status == CANCELLED;
558		}
559
560		/**
#	Line 730 | Line 563 | public abstract class ForkJoinTask<V> im
563		* @return {@code true} if this task threw an exception or was cancelled
564		*/
565		public final boolean isCompletedAbnormally() {
566	<	return (status & COMPLETION_MASK) < NORMAL;
566	>	return status < NORMAL;
567	>	}
568	>
569	>	/**
570	>	* Returns {@code true} if this task completed without throwing an
571	>	* exception and was not cancelled.
572	>	*
573	>	* @return {@code true} if this task completed without throwing an
574	>	* exception and was not cancelled
575	>	*/
576	>	public final boolean isCompletedNormally() {
577	>	return status == NORMAL;
578		}
579
580		/**
#	Line 741 | Line 585 | public abstract class ForkJoinTask<V> im
585		* @return the exception, or {@code null} if none
586		*/
587		public final Throwable getException() {
588	<	int s = status & COMPLETION_MASK;
589	<	if (s >= NORMAL)
590	<	return null;
591	<	if (s == CANCELLED)
748	<	return new CancellationException();
749	<	return exceptionMap.get(this);
588	>	int s = status;
589	>	return ((s >= NORMAL)    ? null :
590	>	(s == CANCELLED) ? new CancellationException() :
591	>	exceptionMap.get(this));
592		}
593
594		/**
#	Line 759 | Line 601 | public abstract class ForkJoinTask<V> im
601		* overridable, but overridden versions must invoke {@code super}
602		* implementation to maintain guarantees.
603		*
604	<	* @param ex the exception to throw. If this exception is
605	<	* not a RuntimeException or Error, the actual exception thrown
606	<	* will be a RuntimeException with cause ex.
604	>	* @param ex the exception to throw. If this exception is not a
605	>	* {@code RuntimeException} or {@code Error}, the actual exception
606	>	* thrown will be a {@code RuntimeException} with cause {@code ex}.
607		*/
608		public void completeExceptionally(Throwable ex) {
609	<	setDoneExceptionally((ex instanceof RuntimeException) ||
610	<	(ex instanceof Error) ? ex :
611	<	new RuntimeException(ex));
609	>	setExceptionalCompletion((ex instanceof RuntimeException) ||
610	>	(ex instanceof Error) ? ex :
611	>	new RuntimeException(ex));
612		}
613
614		/**
#	Line 785 | Line 627 | public abstract class ForkJoinTask<V> im
627		try {
628		setRawResult(value);
629		} catch (Throwable rex) {
630	<	setDoneExceptionally(rex);
630	>	setExceptionalCompletion(rex);
631		return;
632		}
633	<	setNormalCompletion();
633	>	setCompletion(NORMAL);
634		}
635
636		public final V get() throws InterruptedException, ExecutionException {
637	<	ForkJoinWorkerThread w = getWorker();
638	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
639	<	awaitDone(w, true);
640	<	return reportFutureResult();
637	>	quietlyJoin();
638	>	if (Thread.interrupted())
639	>	throw new InterruptedException();
640	>	int s = status;
641	>	if (s < NORMAL) {
642	>	Throwable ex;
643	>	if (s == CANCELLED)
644	>	throw new CancellationException();
645	>	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
646	>	throw new ExecutionException(ex);
647	>	}
648	>	return getRawResult();
649		}
650
651		public final V get(long timeout, TimeUnit unit)
652		throws InterruptedException, ExecutionException, TimeoutException {
653	+	Thread t = Thread.currentThread();
654	+	ForkJoinPool pool;
655	+	if (t instanceof ForkJoinWorkerThread) {
656	+	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
657	+	if (status >= 0 && w.unpushTask(this))
658	+	quietlyExec();
659	+	pool = w.pool;
660	+	}
661	+	else
662	+	pool = null;
663	+	/*
664	+	* Timed wait loop intermixes cases for FJ (pool != null) and
665	+	* non FJ threads. For FJ, decrement pool count but don't try
666	+	* for replacement; increment count on completion. For non-FJ,
667	+	* deal with interrupts. This is messy, but a little less so
668	+	* than is splitting the FJ and nonFJ cases.
669	+	*/
670	+	boolean interrupted = false;
671	+	boolean dec = false; // true if pool count decremented
672		long nanos = unit.toNanos(timeout);
673	<	ForkJoinWorkerThread w = getWorker();
674	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
675	<	awaitDone(w, nanos);
676	<	return reportTimedFutureResult();
677	<	}
678	<
679	<	/**
680	<	* Possibly executes other tasks until this task is ready, then
681	<	* returns the result of the computation.  This method may be more
682	<	* efficient than {@code join}, but is only applicable when
683	<	* there are no potential dependencies between continuation of the
684	<	* current task and that of any other task that might be executed
685	<	* while helping. (This usually holds for pure divide-and-conquer
686	<	* tasks).
687	<	*
688	<	* <p>This method may be invoked only from within {@code
689	<	* ForkJoinTask} computations (as may be determined using method
690	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
691	<	* result in exceptions or errors, possibly including {@code
692	<	* ClassCastException}.
693	<	*
694	<	* @return the computed result
695	<	*/
696	<	public final V helpJoin() {
697	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
698	<	if (status < 0 || !w.unpushTask(this) || !tryExec())
699	<	reportException(busyJoin(w));
700	<	return getRawResult();
701	<	}
702	<
703	<	/**
704	<	* Possibly executes other tasks until this task is ready.
705	<	*
706	<	* <p>This method may be invoked only from within {@code
707	<	* ForkJoinTask} computations (as may be determined using method
839	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
840	<	* result in exceptions or errors, possibly including {@code
841	<	* ClassCastException}.
842	<	*/
843	<	public final void quietlyHelpJoin() {
844	<	if (status >= 0) {
845	<	ForkJoinWorkerThread w =
846	<	(ForkJoinWorkerThread) Thread.currentThread();
847	<	if (!w.unpushTask(this) || !tryQuietlyInvoke())
848	<	busyJoin(w);
673	>	for (;;) {
674	>	if (Thread.interrupted() && pool == null) {
675	>	interrupted = true;
676	>	break;
677	>	}
678	>	int s = status;
679	>	if (s < 0)
680	>	break;
681	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
682	>	long startTime = System.nanoTime();
683	>	long nt; // wait time
684	>	while (status >= 0 &&
685	>	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
686	>	if (pool != null && !dec)
687	>	dec = pool.tryDecrementRunningCount();
688	>	else {
689	>	long ms = nt / 1000000;
690	>	int ns = (int) (nt % 1000000);
691	>	try {
692	>	synchronized(this) {
693	>	if (status >= 0)
694	>	wait(ms, ns);
695	>	}
696	>	} catch (InterruptedException ie) {
697	>	if (pool != null)
698	>	cancelIfTerminating();
699	>	else {
700	>	interrupted = true;
701	>	break;
702	>	}
703	>	}
704	>	}
705	>	}
706	>	break;
707	>	}
708		}
709	+	if (pool != null && dec)
710	+	pool.incrementRunningCount();
711	+	if (interrupted)
712	+	throw new InterruptedException();
713	+	int es = status;
714	+	if (es != NORMAL) {
715	+	Throwable ex;
716	+	if (es == CANCELLED)
717	+	throw new CancellationException();
718	+	if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
719	+	throw new ExecutionException(ex);
720	+	throw new TimeoutException();
721	+	}
722	+	return getRawResult();
723		}
724
725		/**
726	<	* Joins this task, without returning its result or throwing an
726	>	* Joins this task, without returning its result or throwing its
727		* exception. This method may be useful when processing
728		* collections of tasks when some have been cancelled or otherwise
729		* known to have aborted.
730		*/
731		public final void quietlyJoin() {
732	<	if (status >= 0) {
733	<	ForkJoinWorkerThread w = getWorker();
734	<	if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
735	<	awaitDone(w, true);
732	>	Thread t;
733	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
734	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
735	>	if (status >= 0) {
736	>	if (w.unpushTask(this)) {
737	>	boolean completed;
738	>	try {
739	>	completed = exec();
740	>	} catch (Throwable rex) {
741	>	setExceptionalCompletion(rex);
742	>	return;
743	>	}
744	>	if (completed) {
745	>	setCompletion(NORMAL);
746	>	return;
747	>	}
748	>	}
749	>	w.joinTask(this);
750	>	}
751		}
752	+	else
753	+	externalAwaitDone();
754		}
755
756		/**
757		* Commences performing this task and awaits its completion if
758	<	* necessary, without returning its result or throwing an
758	>	* necessary, without returning its result or throwing its
759		* exception. This method may be useful when processing
760		* collections of tasks when some have been cancelled or otherwise
761		* known to have aborted.
762		*/
763		public final void quietlyInvoke() {
764	<	if (status >= 0 && !tryQuietlyInvoke())
765	<	quietlyJoin();
764	>	if (status >= 0) {
765	>	boolean completed;
766	>	try {
767	>	completed = exec();
768	>	} catch (Throwable rex) {
769	>	setExceptionalCompletion(rex);
770	>	return;
771	>	}
772	>	if (completed)
773	>	setCompletion(NORMAL);
774	>	else
775	>	quietlyJoin();
776	>	}
777		}
778
779		/**
780		* Possibly executes tasks until the pool hosting the current task
781	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
782	<	* designs in which many tasks are forked, but none are explicitly
783	<	* joined, instead executing them until all are processed.
781	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
782	>	* be of use in designs in which many tasks are forked, but none
783	>	* are explicitly joined, instead executing them until all are
784	>	* processed.
785		*
786		* <p>This method may be invoked only from within {@code
787		* ForkJoinTask} computations (as may be determined using method
#	Line 903 | Line 805 | public abstract class ForkJoinTask<V> im
805		* pre-constructed trees of subtasks in loops.
806		*/
807		public void reinitialize() {
808	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
808	>	if (status == EXCEPTIONAL)
809		exceptionMap.remove(this);
810		status = 0;
811		}
#	Line 1023 | Line 925 | public abstract class ForkJoinTask<V> im
925		* called otherwise. The return value controls whether this task
926		* is considered to be done normally. It may return false in
927		* asynchronous actions that require explicit invocations of
928	<	* {@link #complete} to become joinable. It may throw exceptions
929	<	* to indicate abnormal exit.
928	>	* {@link #complete} to become joinable. It may also throw an
929	>	* (unchecked) exception to indicate abnormal exit.
930		*
931		* @return {@code true} if completed normally
1030	–	* @throws Error or RuntimeException if encountered during computation
932		*/
933		protected abstract boolean exec();
934
#	Line 1194 | Line 1095 | public abstract class ForkJoinTask<V> im
1095		private static final long serialVersionUID = -7721805057305804111L;
1096
1097		/**
1098	<	* Save the state to a stream.
1098	>	* Saves the state to a stream (that is, serializes it).
1099		*
1100		* @serialData the current run status and the exception thrown
1101		* during execution, or {@code null} if none
#	Line 1207 | Line 1108 | public abstract class ForkJoinTask<V> im
1108		}
1109
1110		/**
1111	<	* Reconstitute the instance from a stream.
1111	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1112		*
1113		* @param s the stream
1114		*/
1115		private void readObject(java.io.ObjectInputStream s)
1116		throws java.io.IOException, ClassNotFoundException {
1117		s.defaultReadObject();
1217	–	status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
1218	–	status |= EXTERNAL_SIGNAL; // conservatively set external signal
1118		Object ex = s.readObject();
1119		if (ex != null)
1120	<	setDoneExceptionally((Throwable) ex);
1120	>	setExceptionalCompletion((Throwable) ex);
1121		}
1122
1123		// Unsafe mechanics

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