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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.57 by dl, Sat Sep 4 11:33:53 2010 UTC vs.
Revision 1.78 by jsr166, Fri Jun 3 14:20:43 2011 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3		* Expert Group and released to the public domain, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		*/
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.io.Serializable;
10		import java.util.Collection;
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 58 | Line 69 | import java.util.WeakHashMap;
69		* rethrown to callers attempting to join them. These exceptions may
70		* additionally include {@link RejectedExecutionException} stemming
71		* from internal resource exhaustion, such as failure to allocate
72	<	* internal task queues.
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:
#	Line 102 | Line 117 | import java.util.WeakHashMap;
117		* result in exceptions or errors, possibly including
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
132		* underlying lightweight task scheduling framework.  Developers
#	Line 116 | 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
#	Line 144 | Line 170 | public abstract class ForkJoinTask<V> im
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. In particular, most
148	<	* join mechanics are in method quietlyJoin, below.
173	>	* in a way that flows well in javadocs.
174		*/
175
176		/*
#	Line 153 | Line 178 | public abstract class ForkJoinTask<V> im
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
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
#	Line 167 | Line 192 | public abstract class ForkJoinTask<V> im
192
193		/** The run status of this task */
194		volatile int status; // accessed directly by pool and workers
170	–
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		/**
177	–	* Table of exceptions thrown by tasks, to enable reporting by
178	–	* callers. Because exceptions are rare, we don't directly keep
179	–	* them with task objects, but instead use a weak ref table.  Note
180	–	* that cancellation exceptions don't appear in the table, but are
181	–	* instead recorded as status values.
182	–	* TODO: Use ConcurrentReferenceHashMap
183	–	*/
184	–	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
185	–	Collections.synchronizedMap
186	–	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
187	–
188	–	// Maintaining completion status
189	–
190	–	/**
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	<	private void setCompletion(int completion) {
208	<	int s;
209	<	while ((s = status) >= 0) {
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	<	break;
214	>	return completion;
215		}
216		}
217		}
218
219		/**
220	<	* Records exception and sets exceptional completion.
221	<	*
222	<	* @return status on exit
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 setExceptionalCompletion(Throwable rex) {
227	<	exceptionMap.put(this, rex);
228	<	setCompletion(EXCEPTIONAL);
226	>	final void tryAwaitDone(long millis) {
227	>	int s;
228	>	try {
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	>	}
237	>	}
238	>	} catch (InterruptedException ie) {
239	>	// caller must check termination
240	>	}
241		}
242
243		/**
244	<	* Blocks a worker thread until completion. Called only by
245	<	* pool. Currently unused -- pool-based waits use timeout
220	<	* version below.
244	>	* Blocks a non-worker-thread until completion.
245	>	* @return status upon completion
246		*/
247	<	final void internalAwaitDone() {
248	<	int s;         // the odd construction reduces lock bias effects
249	<	while ((s = status) >= 0) {
250	<	try {
251	<	synchronized(this) {
252	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
253	<	wait();
247	>	private int externalAwaitDone() {
248	>	int s;
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		}
230	–	} catch (InterruptedException ie) {
231	–	cancelIfTerminating();
264		}
265	+	if (interrupted)
266	+	Thread.currentThread().interrupt();
267		}
268	+	return s;
269		}
270
271		/**
272	<	* Blocks a worker thread until completed or timed out.  Called
238	<	* only by pool.
239	<	*
240	<	* @return status on exit
272	>	* Blocks a non-worker-thread until completion or interruption or timeout.
273		*/
274	<	final int internalAwaitDone(long millis) {
274	>	private int externalInterruptibleAwaitDone(long millis)
275	>	throws InterruptedException {
276		int s;
277	+	if (Thread.interrupted())
278	+	throw new InterruptedException();
279		if ((s = status) >= 0) {
280	<	try {
281	<	synchronized(this) {
282	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
283	<	wait(millis, 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	>	if (millis > 0L)
288	>	break;
289	>	}
290		}
250	–	} catch (InterruptedException ie) {
251	–	cancelIfTerminating();
291		}
253	–	s = status;
292		}
293		return s;
294		}
295
296		/**
297	<	* Blocks a non-worker-thread until completion.
297	>	* Primary execution method for stolen tasks. Unless done, calls
298	>	* exec and records status if completed, but doesn't wait for
299	>	* completion otherwise.
300		*/
301	<	private void externalAwaitDone() {
302	<	int s;
303	<	while ((s = status) >= 0) {
304	<	synchronized(this) {
305	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
306	<	boolean interrupted = false;
307	<	while (status >= 0) {
308	<	try {
309	<	wait();
310	<	} catch (InterruptedException ie) {
311	<	interrupted = true;
312	<	}
313	<	}
314	<	if (interrupted)
315	<	Thread.currentThread().interrupt();
316	<	break;
301	>	final void doExec() {
302	>	if (status >= 0) {
303	>	boolean completed;
304	>	try {
305	>	completed = exec();
306	>	} catch (Throwable rex) {
307	>	setExceptionalCompletion(rex);
308	>	return;
309	>	}
310	>	if (completed)
311	>	setCompletion(NORMAL); // must be outside try block
312	>	}
313	>	}
314	>
315	>	/**
316	>	* Primary mechanics for join, get, quietlyJoin.
317	>	* @return status upon completion
318	>	*/
319	>	private int doJoin() {
320	>	Thread t; ForkJoinWorkerThread w; int s; boolean completed;
321	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
322	>	if ((s = status) < 0)
323	>	return s;
324	>	if ((w = (ForkJoinWorkerThread)t).unpushTask(this)) {
325	>	try {
326	>	completed = exec();
327	>	} catch (Throwable rex) {
328	>	return setExceptionalCompletion(rex);
329		}
330	+	if (completed)
331	+	return setCompletion(NORMAL);
332		}
333	+	return w.joinTask(this);
334		}
335	+	else
336	+	return externalAwaitDone();
337		}
338
339		/**
340	<	* Unless done, calls exec and records status if completed, but
341	<	* doesn't wait for completion otherwise. Primary execution method
285	<	* for ForkJoinWorkerThread.
340	>	* Primary mechanics for invoke, quietlyInvoke.
341	>	* @return status upon completion
342		*/
343	<	final void quietlyExec() {
343	>	private int doInvoke() {
344	>	int s; boolean completed;
345	>	if ((s = status) < 0)
346	>	return s;
347		try {
348	<	if (status < 0 || !exec())
290	<	return;
348	>	completed = exec();
349		} catch (Throwable rex) {
350	<	setExceptionalCompletion(rex);
351	<	return;
350	>	return setExceptionalCompletion(rex);
351	>	}
352	>	if (completed)
353	>	return setCompletion(NORMAL);
354	>	else
355	>	return doJoin();
356	>	}
357	>
358	>	// Exception table support
359	>
360	>	/**
361	>	* Table of exceptions thrown by tasks, to enable reporting by
362	>	* callers. Because exceptions are rare, we don't directly keep
363	>	* them with task objects, but instead use a weak ref table.  Note
364	>	* that cancellation exceptions don't appear in the table, but are
365	>	* instead recorded as status values.
366	>	*
367	>	* Note: These statics are initialized below in static block.
368	>	*/
369	>	private static final ExceptionNode[] exceptionTable;
370	>	private static final ReentrantLock exceptionTableLock;
371	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
372	>
373	>	/**
374	>	* Fixed capacity for exceptionTable.
375	>	*/
376	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
377	>
378	>	/**
379	>	* Key-value nodes for exception table.  The chained hash table
380	>	* uses identity comparisons, full locking, and weak references
381	>	* for keys. The table has a fixed capacity because it only
382	>	* maintains task exceptions long enough for joiners to access
383	>	* them, so should never become very large for sustained
384	>	* periods. However, since we do not know when the last joiner
385	>	* completes, we must use weak references and expunge them. We do
386	>	* so on each operation (hence full locking). Also, some thread in
387	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
388	>	* pool becomes isQuiescent.
389	>	*/
390	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>>{
391	>	final Throwable ex;
392	>	ExceptionNode next;
393	>	final long thrower;  // use id not ref to avoid weak cycles
394	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
395	>	super(task, exceptionTableRefQueue);
396	>	this.ex = ex;
397	>	this.next = next;
398	>	this.thrower = Thread.currentThread().getId();
399	>	}
400	>	}
401	>
402	>	/**
403	>	* Records exception and sets exceptional completion.
404	>	*
405	>	* @return status on exit
406	>	*/
407	>	private int setExceptionalCompletion(Throwable ex) {
408	>	int h = System.identityHashCode(this);
409	>	final ReentrantLock lock = exceptionTableLock;
410	>	lock.lock();
411	>	try {
412	>	expungeStaleExceptions();
413	>	ExceptionNode[] t = exceptionTable;
414	>	int i = h & (t.length - 1);
415	>	for (ExceptionNode e = t[i]; ; e = e.next) {
416	>	if (e == null) {
417	>	t[i] = new ExceptionNode(this, ex, t[i]);
418	>	break;
419	>	}
420	>	if (e.get() == this) // already present
421	>	break;
422	>	}
423	>	} finally {
424	>	lock.unlock();
425	>	}
426	>	return setCompletion(EXCEPTIONAL);
427	>	}
428	>
429	>	/**
430	>	* Removes exception node and clears status
431	>	*/
432	>	private void clearExceptionalCompletion() {
433	>	int h = System.identityHashCode(this);
434	>	final ReentrantLock lock = exceptionTableLock;
435	>	lock.lock();
436	>	try {
437	>	ExceptionNode[] t = exceptionTable;
438	>	int i = h & (t.length - 1);
439	>	ExceptionNode e = t[i];
440	>	ExceptionNode pred = null;
441	>	while (e != null) {
442	>	ExceptionNode next = e.next;
443	>	if (e.get() == this) {
444	>	if (pred == null)
445	>	t[i] = next;
446	>	else
447	>	pred.next = next;
448	>	break;
449	>	}
450	>	pred = e;
451	>	e = next;
452	>	}
453	>	expungeStaleExceptions();
454	>	status = 0;
455	>	} finally {
456	>	lock.unlock();
457	>	}
458	>	}
459	>
460	>	/**
461	>	* Returns a rethrowable exception for the given task, if
462	>	* available. To provide accurate stack traces, if the exception
463	>	* was not thrown by the current thread, we try to create a new
464	>	* exception of the same type as the one thrown, but with the
465	>	* recorded exception as its cause. If there is no such
466	>	* constructor, we instead try to use a no-arg constructor,
467	>	* followed by initCause, to the same effect. If none of these
468	>	* apply, or any fail due to other exceptions, we return the
469	>	* recorded exception, which is still correct, although it may
470	>	* contain a misleading stack trace.
471	>	*
472	>	* @return the exception, or null if none
473	>	*/
474	>	private Throwable getThrowableException() {
475	>	if (status != EXCEPTIONAL)
476	>	return null;
477	>	int h = System.identityHashCode(this);
478	>	ExceptionNode e;
479	>	final ReentrantLock lock = exceptionTableLock;
480	>	lock.lock();
481	>	try {
482	>	expungeStaleExceptions();
483	>	ExceptionNode[] t = exceptionTable;
484	>	e = t[h & (t.length - 1)];
485	>	while (e != null && e.get() != this)
486	>	e = e.next;
487	>	} finally {
488	>	lock.unlock();
489	>	}
490	>	Throwable ex;
491	>	if (e == null || (ex = e.ex) == null)
492	>	return null;
493	>	if (e.thrower != Thread.currentThread().getId()) {
494	>	Class<? extends Throwable> ec = ex.getClass();
495	>	try {
496	>	Constructor<?> noArgCtor = null;
497	>	Constructor<?>[] cs = ec.getConstructors();// public ctors only
498	>	for (int i = 0; i < cs.length; ++i) {
499	>	Constructor<?> c = cs[i];
500	>	Class<?>[] ps = c.getParameterTypes();
501	>	if (ps.length == 0)
502	>	noArgCtor = c;
503	>	else if (ps.length == 1 && ps[0] == Throwable.class)
504	>	return (Throwable)(c.newInstance(ex));
505	>	}
506	>	if (noArgCtor != null) {
507	>	Throwable wx = (Throwable)(noArgCtor.newInstance());
508	>	wx.initCause(ex);
509	>	return wx;
510	>	}
511	>	} catch (Exception ignore) {
512	>	}
513		}
514	<	setCompletion(NORMAL); // must be outside try block
514	>	return ex;
515	>	}
516	>
517	>	/**
518	>	* Poll stale refs and remove them. Call only while holding lock.
519	>	*/
520	>	private static void expungeStaleExceptions() {
521	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
522	>	if (x instanceof ExceptionNode) {
523	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
524	>	ExceptionNode[] t = exceptionTable;
525	>	int i = System.identityHashCode(key) & (t.length - 1);
526	>	ExceptionNode e = t[i];
527	>	ExceptionNode pred = null;
528	>	while (e != null) {
529	>	ExceptionNode next = e.next;
530	>	if (e == x) {
531	>	if (pred == null)
532	>	t[i] = next;
533	>	else
534	>	pred.next = next;
535	>	break;
536	>	}
537	>	pred = e;
538	>	e = next;
539	>	}
540	>	}
541	>	}
542	>	}
543	>
544	>	/**
545	>	* If lock is available, poll stale refs and remove them.
546	>	* Called from ForkJoinPool when pools become quiescent.
547	>	*/
548	>	static final void helpExpungeStaleExceptions() {
549	>	final ReentrantLock lock = exceptionTableLock;
550	>	if (lock.tryLock()) {
551	>	try {
552	>	expungeStaleExceptions();
553	>	} finally {
554	>	lock.unlock();
555	>	}
556	>	}
557	>	}
558	>
559	>	/**
560	>	* Report the result of invoke or join; called only upon
561	>	* non-normal return of internal versions.
562	>	*/
563	>	private V reportResult() {
564	>	int s; Throwable ex;
565	>	if ((s = status) == CANCELLED)
566	>	throw new CancellationException();
567	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
568	>	UNSAFE.throwException(ex);
569	>	return getRawResult();
570		}
571
572		// public methods
#	Line 308 | Line 582 | public abstract class ForkJoinTask<V> im
582		* #isDone} returning {@code true}.
583		*
584		* <p>This method may be invoked only from within {@code
585	<	* ForkJoinTask} computations (as may be determined using method
585	>	* ForkJoinPool} computations (as may be determined using method
586		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
587		* result in exceptions or errors, possibly including {@code
588		* ClassCastException}.
#	Line 322 | Line 596 | public abstract class ForkJoinTask<V> im
596		}
597
598		/**
599	<	* Returns the result of the computation when it {@link #isDone is done}.
600	<	* This method differs from {@link #get()} in that
599	>	* Returns the result of the computation when it {@link #isDone is
600	>	* done}.  This method differs from {@link #get()} in that
601		* abnormal completion results in {@code RuntimeException} or
602	<	* {@code Error}, not {@code ExecutionException}.
602	>	* {@code Error}, not {@code ExecutionException}, and that
603	>	* interrupts of the calling thread do <em>not</em> cause the
604	>	* method to abruptly return by throwing {@code
605	>	* InterruptedException}.
606		*
607		* @return the computed result
608		*/
609		public final V join() {
610	<	quietlyJoin();
611	<	Throwable ex;
612	<	if (status < NORMAL && (ex = getException()) != null)
613	<	UNSAFE.throwException(ex);
337	<	return getRawResult();
610	>	if (doJoin() != NORMAL)
611	>	return reportResult();
612	>	else
613	>	return getRawResult();
614		}
615
616		/**
#	Line 346 | Line 622 | public abstract class ForkJoinTask<V> im
622		* @return the computed result
623		*/
624		public final V invoke() {
625	<	quietlyInvoke();
626	<	Throwable ex;
627	<	if (status < NORMAL && (ex = getException()) != null)
628	<	UNSAFE.throwException(ex);
353	<	return getRawResult();
625	>	if (doInvoke() != NORMAL)
626	>	return reportResult();
627	>	else
628	>	return getRawResult();
629		}
630
631		/**
#	Line 367 | Line 642 | public abstract class ForkJoinTask<V> im
642		* unprocessed.
643		*
644		* <p>This method may be invoked only from within {@code
645	<	* ForkJoinTask} computations (as may be determined using method
645	>	* ForkJoinPool} computations (as may be determined using method
646		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
647		* result in exceptions or errors, possibly including {@code
648		* ClassCastException}.
#	Line 395 | Line 670 | public abstract class ForkJoinTask<V> im
670		* normally or exceptionally, or left unprocessed.
671		*
672		* <p>This method may be invoked only from within {@code
673	<	* ForkJoinTask} computations (as may be determined using method
673	>	* ForkJoinPool} computations (as may be determined using method
674		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
675		* result in exceptions or errors, possibly including {@code
676		* ClassCastException}.
#	Line 414 | Line 689 | public abstract class ForkJoinTask<V> im
689		}
690		else if (i != 0)
691		t.fork();
692	<	else {
693	<	t.quietlyInvoke();
419	<	if (ex == null && t.status < NORMAL)
420	<	ex = t.getException();
421	<	}
692	>	else if (t.doInvoke() < NORMAL && ex == null)
693	>	ex = t.getException();
694		}
695		for (int i = 1; i <= last; ++i) {
696		ForkJoinTask<?> t = tasks[i];
697		if (t != null) {
698		if (ex != null)
699		t.cancel(false);
700	<	else {
701	<	t.quietlyJoin();
430	<	if (ex == null && t.status < NORMAL)
431	<	ex = t.getException();
432	<	}
700	>	else if (t.doJoin() < NORMAL && ex == null)
701	>	ex = t.getException();
702		}
703		}
704		if (ex != null)
#	Line 450 | Line 719 | public abstract class ForkJoinTask<V> im
719		* unprocessed.
720		*
721		* <p>This method may be invoked only from within {@code
722	<	* ForkJoinTask} computations (as may be determined using method
722	>	* ForkJoinPool} computations (as may be determined using method
723		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
724		* result in exceptions or errors, possibly including {@code
725		* ClassCastException}.
#	Line 477 | Line 746 | public abstract class ForkJoinTask<V> im
746		}
747		else if (i != 0)
748		t.fork();
749	<	else {
750	<	t.quietlyInvoke();
482	<	if (ex == null && t.status < NORMAL)
483	<	ex = t.getException();
484	<	}
749	>	else if (t.doInvoke() < NORMAL && ex == null)
750	>	ex = t.getException();
751		}
752		for (int i = 1; i <= last; ++i) {
753		ForkJoinTask<?> t = ts.get(i);
754		if (t != null) {
755		if (ex != null)
756		t.cancel(false);
757	<	else {
758	<	t.quietlyJoin();
493	<	if (ex == null && t.status < NORMAL)
494	<	ex = t.getException();
495	<	}
757	>	else if (t.doJoin() < NORMAL && ex == null)
758	>	ex = t.getException();
759		}
760		}
761		if (ex != null)
#	Line 502 | Line 765 | public abstract class ForkJoinTask<V> im
765
766		/**
767		* Attempts to cancel execution of this task. This attempt will
768	<	* fail if the task has already completed, has already been
769	<	* cancelled, or could not be cancelled for some other reason. If
770	<	* successful, and this task has not started when cancel is
771	<	* called, execution of this task is suppressed, {@link
772	<	* #isCancelled} will report true, and {@link #join} will result
773	<	* in a {@code CancellationException} being thrown.
768	>	* fail if the task has already completed or could not be
769	>	* cancelled for some other reason. If successful, and this task
770	>	* has not started when {@code cancel} is called, execution of
771	>	* this task is suppressed. After this method returns
772	>	* successfully, unless there is an intervening call to {@link
773	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
774	>	* {@link #isDone}, and {@code cancel} will return {@code true}
775	>	* and calls to {@link #join} and related methods will result in
776	>	* {@code CancellationException}.
777		*
778		* <p>This method may be overridden in subclasses, but if so, must
779	<	* still ensure that these minimal properties hold. In particular,
780	<	* the {@code cancel} method itself must not throw exceptions.
779	>	* still ensure that these properties hold. In particular, the
780	>	* {@code cancel} method itself must not throw exceptions.
781		*
782		* <p>This method is designed to be invoked by <em>other</em>
783		* tasks. To terminate the current task, you can just return or
784		* throw an unchecked exception from its computation method, or
785		* invoke {@link #completeExceptionally}.
786		*
787	<	* @param mayInterruptIfRunning this value is ignored in the
788	<	* default implementation because tasks are not
789	<	* cancelled via interruption
787	>	* @param mayInterruptIfRunning this value has no effect in the
788	>	* default implementation because interrupts are not used to
789	>	* control cancellation.
790		*
791		* @return {@code true} if this task is now cancelled
792		*/
793		public boolean cancel(boolean mayInterruptIfRunning) {
794	<	setCompletion(CANCELLED);
529	<	return status == CANCELLED;
794	>	return setCompletion(CANCELLED) == CANCELLED;
795		}
796
797		/**
#	Line 542 | Line 807 | public abstract class ForkJoinTask<V> im
807		}
808		}
809
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	–
810		public final boolean isDone() {
811		return status < 0;
812		}
#	Line 596 | Line 846 | public abstract class ForkJoinTask<V> im
846		int s = status;
847		return ((s >= NORMAL)    ? null :
848		(s == CANCELLED) ? new CancellationException() :
849	<	exceptionMap.get(this));
849	>	getThrowableException());
850		}
851
852		/**
#	Line 621 | Line 871 | public abstract class ForkJoinTask<V> im
871
872		/**
873		* Completes this task, and if not already aborted or cancelled,
874	<	* returning a {@code null} result upon {@code join} and related
875	<	* operations. This method may be used to provide results for
876	<	* asynchronous tasks, or to provide alternative handling for
877	<	* tasks that would not otherwise complete normally. Its use in
878	<	* other situations is discouraged. This method is
879	<	* overridable, but overridden versions must invoke {@code super}
880	<	* implementation to maintain guarantees.
874	>	* returning the given value as the result of subsequent
875	>	* invocations of {@code join} and related operations. This method
876	>	* may be used to provide results for asynchronous tasks, or to
877	>	* provide alternative handling for tasks that would not otherwise
878	>	* complete normally. Its use in other situations is
879	>	* discouraged. This method is overridable, but overridden
880	>	* versions must invoke {@code super} implementation to maintain
881	>	* guarantees.
882		*
883		* @param value the result value for this task
884		*/
#	Line 641 | Line 892 | public abstract class ForkJoinTask<V> im
892		setCompletion(NORMAL);
893		}
894
895	+	/**
896	+	* Waits if necessary for the computation to complete, and then
897	+	* retrieves its result.
898	+	*
899	+	* @return the computed result
900	+	* @throws CancellationException if the computation was cancelled
901	+	* @throws ExecutionException if the computation threw an
902	+	* exception
903	+	* @throws InterruptedException if the current thread is not a
904	+	* member of a ForkJoinPool and was interrupted while waiting
905	+	*/
906		public final V get() throws InterruptedException, ExecutionException {
907	<	quietlyJoin();
908	<	if (Thread.interrupted())
909	<	throw new InterruptedException();
910	<	int s = status;
911	<	if (s < NORMAL) {
912	<	Throwable ex;
913	<	if (s == CANCELLED)
652	<	throw new CancellationException();
653	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
654	<	throw new ExecutionException(ex);
655	<	}
907	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
908	>	doJoin() : externalInterruptibleAwaitDone(0L);
909	>	Throwable ex;
910	>	if (s == CANCELLED)
911	>	throw new CancellationException();
912	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
913	>	throw new ExecutionException(ex);
914		return getRawResult();
915		}
916
917	+	/**
918	+	* Waits if necessary for at most the given time for the computation
919	+	* to complete, and then retrieves its result, if available.
920	+	*
921	+	* @param timeout the maximum time to wait
922	+	* @param unit the time unit of the timeout argument
923	+	* @return the computed result
924	+	* @throws CancellationException if the computation was cancelled
925	+	* @throws ExecutionException if the computation threw an
926	+	* exception
927	+	* @throws InterruptedException if the current thread is not a
928	+	* member of a ForkJoinPool and was interrupted while waiting
929	+	* @throws TimeoutException if the wait timed out
930	+	*/
931		public final V get(long timeout, TimeUnit unit)
932		throws InterruptedException, ExecutionException, TimeoutException {
933		Thread t = Thread.currentThread();
662	–	ForkJoinPool pool;
934		if (t instanceof ForkJoinWorkerThread) {
935		ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
936	<	if (status >= 0 && w.unpushTask(this))
937	<	quietlyExec();
938	<	pool = w.pool;
939	<	}
940	<	else
941	<	pool = null;
942	<	/*
943	<	* Timed wait loop intermixes cases for FJ (pool != null) and
673	<	* non FJ threads. For FJ, decrement pool count but don't try
674	<	* for replacement; increment count on completion. For non-FJ,
675	<	* deal with interrupts. This is messy, but a little less so
676	<	* than is splitting the FJ and nonFJ cases.
677	<	*/
678	<	boolean interrupted = false;
679	<	boolean dec = false; // true if pool count decremented
680	<	long nanos = unit.toNanos(timeout);
681	<	for (;;) {
682	<	if (Thread.interrupted() && pool == null) {
683	<	interrupted = true;
684	<	break;
685	<	}
686	<	int s = status;
687	<	if (s < 0)
688	<	break;
689	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
690	<	long startTime = System.nanoTime();
691	<	long nt; // wait time
692	<	while (status >= 0 &&
693	<	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
694	<	if (pool != null && !dec)
695	<	dec = pool.tryDecrementRunningCount();
696	<	else {
697	<	long ms = nt / 1000000;
698	<	int ns = (int) (nt % 1000000);
699	<	try {
700	<	synchronized(this) {
701	<	if (status >= 0)
702	<	wait(ms, ns);
703	<	}
704	<	} catch (InterruptedException ie) {
705	<	if (pool != null)
706	<	cancelIfTerminating();
707	<	else {
708	<	interrupted = true;
709	<	break;
710	<	}
711	<	}
936	>	long nanos = unit.toNanos(timeout);
937	>	if (status >= 0) {
938	>	boolean completed = false;
939	>	if (w.unpushTask(this)) {
940	>	try {
941	>	completed = exec();
942	>	} catch (Throwable rex) {
943	>	setExceptionalCompletion(rex);
944		}
945		}
946	<	break;
946	>	if (completed)
947	>	setCompletion(NORMAL);
948	>	else if (status >= 0 && nanos > 0)
949	>	w.pool.timedAwaitJoin(this, nanos);
950		}
951		}
952	<	if (pool != null && dec)
953	<	pool.incrementRunningCount();
954	<	if (interrupted)
955	<	throw new InterruptedException();
956	<	int es = status;
957	<	if (es != NORMAL) {
952	>	else {
953	>	long millis = unit.toMillis(timeout);
954	>	if (millis > 0)
955	>	externalInterruptibleAwaitDone(millis);
956	>	}
957	>	int s = status;
958	>	if (s != NORMAL) {
959		Throwable ex;
960	<	if (es == CANCELLED)
960	>	if (s == CANCELLED)
961		throw new CancellationException();
962	<	if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
962	>	if (s != EXCEPTIONAL)
963	>	throw new TimeoutException();
964	>	if ((ex = getThrowableException()) != null)
965		throw new ExecutionException(ex);
728	–	throw new TimeoutException();
966		}
967		return getRawResult();
968		}
#	Line 737 | Line 974 | public abstract class ForkJoinTask<V> im
974		* known to have aborted.
975		*/
976		public final void quietlyJoin() {
977	<	Thread t;
741	<	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
742	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
743	<	if (status >= 0) {
744	<	if (w.unpushTask(this)) {
745	<	boolean completed;
746	<	try {
747	<	completed = exec();
748	<	} catch (Throwable rex) {
749	<	setExceptionalCompletion(rex);
750	<	return;
751	<	}
752	<	if (completed) {
753	<	setCompletion(NORMAL);
754	<	return;
755	<	}
756	<	}
757	<	w.joinTask(this);
758	<	}
759	<	}
760	<	else
761	<	externalAwaitDone();
977	>	doJoin();
978		}
979
980		/**
981		* Commences performing this task and awaits its completion if
982		* necessary, without returning its result or throwing its
983	<	* exception. This method may be useful when processing
768	<	* collections of tasks when some have been cancelled or otherwise
769	<	* known to have aborted.
983	>	* exception.
984		*/
985		public final void quietlyInvoke() {
986	<	if (status >= 0) {
773	<	boolean completed;
774	<	try {
775	<	completed = exec();
776	<	} catch (Throwable rex) {
777	<	setExceptionalCompletion(rex);
778	<	return;
779	<	}
780	<	if (completed)
781	<	setCompletion(NORMAL);
782	<	else
783	<	quietlyJoin();
784	<	}
986	>	doInvoke();
987		}
988
989		/**
#	Line 792 | Line 994 | public abstract class ForkJoinTask<V> im
994		* processed.
995		*
996		* <p>This method may be invoked only from within {@code
997	<	* ForkJoinTask} computations (as may be determined using method
997	>	* ForkJoinPool} computations (as may be determined using method
998		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
999		* result in exceptions or errors, possibly including {@code
1000		* ClassCastException}.
#	Line 811 | Line 1013 | public abstract class ForkJoinTask<V> im
1013		* under any other usage conditions are not guaranteed.
1014		* This method may be useful when executing
1015		* pre-constructed trees of subtasks in loops.
1016	+	*
1017	+	* <p>Upon completion of this method, {@code isDone()} reports
1018	+	* {@code false}, and {@code getException()} reports {@code
1019	+	* null}. However, the value returned by {@code getRawResult} is
1020	+	* unaffected. To clear this value, you can invoke {@code
1021	+	* setRawResult(null)}.
1022		*/
1023		public void reinitialize() {
1024		if (status == EXCEPTIONAL)
1025	<	exceptionMap.remove(this);
1026	<	status = 0;
1025	>	clearExceptionalCompletion();
1026	>	else
1027	>	status = 0;
1028		}
1029
1030		/**
#	Line 832 | Line 1041 | public abstract class ForkJoinTask<V> im
1041		}
1042
1043		/**
1044	<	* Returns {@code true} if the current thread is executing as a
1045	<	* ForkJoinPool computation.
1044	>	* Returns {@code true} if the current thread is a {@link
1045	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1046		*
1047	<	* @return {@code true} if the current thread is executing as a
1048	<	* ForkJoinPool computation, or false otherwise
1047	>	* @return {@code true} if the current thread is a {@link
1048	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1049	>	* or {@code false} otherwise
1050		*/
1051		public static boolean inForkJoinPool() {
1052		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 851 | Line 1061 | public abstract class ForkJoinTask<V> im
1061		* were not, stolen.
1062		*
1063		* <p>This method may be invoked only from within {@code
1064	<	* ForkJoinTask} computations (as may be determined using method
1064	>	* ForkJoinPool} computations (as may be determined using method
1065		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1066		* result in exceptions or errors, possibly including {@code
1067		* ClassCastException}.
#	Line 870 | Line 1080 | public abstract class ForkJoinTask<V> im
1080		* fork other tasks.
1081		*
1082		* <p>This method may be invoked only from within {@code
1083	<	* ForkJoinTask} computations (as may be determined using method
1083	>	* ForkJoinPool} computations (as may be determined using method
1084		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1085		* result in exceptions or errors, possibly including {@code
1086		* ClassCastException}.
#	Line 893 | Line 1103 | public abstract class ForkJoinTask<V> im
1103		* exceeded.
1104		*
1105		* <p>This method may be invoked only from within {@code
1106	<	* ForkJoinTask} computations (as may be determined using method
1106	>	* ForkJoinPool} computations (as may be determined using method
1107		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1108		* result in exceptions or errors, possibly including {@code
1109		* ClassCastException}.
#	Line 951 | Line 1161 | public abstract class ForkJoinTask<V> im
1161		* otherwise.
1162		*
1163		* <p>This method may be invoked only from within {@code
1164	<	* ForkJoinTask} computations (as may be determined using method
1164	>	* ForkJoinPool} computations (as may be determined using method
1165		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1166		* result in exceptions or errors, possibly including {@code
1167		* ClassCastException}.
#	Line 970 | Line 1180 | public abstract class ForkJoinTask<V> im
1180		* be useful otherwise.
1181		*
1182		* <p>This method may be invoked only from within {@code
1183	<	* ForkJoinTask} computations (as may be determined using method
1183	>	* ForkJoinPool} computations (as may be determined using method
1184		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1185		* result in exceptions or errors, possibly including {@code
1186		* ClassCastException}.
#	Line 993 | Line 1203 | public abstract class ForkJoinTask<V> im
1203		* otherwise.
1204		*
1205		* <p>This method may be invoked only from within {@code
1206	<	* ForkJoinTask} computations (as may be determined using method
1206	>	* ForkJoinPool} computations (as may be determined using method
1207		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1208		* result in exceptions or errors, possibly including {@code
1209		* ClassCastException}.
#	Line 1125 | Line 1335 | public abstract class ForkJoinTask<V> im
1335		s.defaultReadObject();
1336		Object ex = s.readObject();
1337		if (ex != null)
1338	<	setExceptionalCompletion((Throwable) ex);
1338	>	setExceptionalCompletion((Throwable)ex);
1339		}
1340
1341		// Unsafe mechanics
1342	<
1343	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1344	<	private static final long statusOffset =
1345	<	objectFieldOffset("status", ForkJoinTask.class);
1346	<
1347	<	private static long objectFieldOffset(String field, Class<?> klazz) {
1342	>	private static final sun.misc.Unsafe UNSAFE;
1343	>	private static final long statusOffset;
1344	>	static {
1345	>	exceptionTableLock = new ReentrantLock();
1346	>	exceptionTableRefQueue = new ReferenceQueue<Object>();
1347	>	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1348		try {
1349	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1350	<	} catch (NoSuchFieldException e) {
1351	<	// Convert Exception to corresponding Error
1352	<	NoSuchFieldError error = new NoSuchFieldError(field);
1353	<	error.initCause(e);
1144	<	throw error;
1349	>	UNSAFE = getUnsafe();
1350	>	statusOffset = UNSAFE.objectFieldOffset
1351	>	(ForkJoinTask.class.getDeclaredField("status"));
1352	>	} catch (Exception e) {
1353	>	throw new Error(e);
1354		}
1355		}
1356

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