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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.51 by dl, Fri Jul 23 16:49:11 2010 UTC vs.
Revision 1.74 by dl, Tue Feb 22 00:39:31 2011 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.io.Serializable;
10		import java.util.Collection;
11		import java.util.Collections;
12		import java.util.List;
13		import java.util.RandomAccess;
14		import java.util.Map;
15	<	import java.util.WeakHashMap;
15	>	import java.lang.ref.WeakReference;
16	>	import java.lang.ref.ReferenceQueue;
17	>	import java.util.concurrent.Callable;
18	>	import java.util.concurrent.CancellationException;
19	>	import java.util.concurrent.ExecutionException;
20	>	import java.util.concurrent.Executor;
21	>	import java.util.concurrent.ExecutorService;
22	>	import java.util.concurrent.Future;
23	>	import java.util.concurrent.RejectedExecutionException;
24	>	import java.util.concurrent.RunnableFuture;
25	>	import java.util.concurrent.TimeUnit;
26	>	import java.util.concurrent.TimeoutException;
27	>	import java.util.concurrent.locks.ReentrantLock;
28	>	import java.lang.reflect.Constructor;
29
30		/**
31		* Abstract base class for tasks that run within a {@link ForkJoinPool}.
#	Line 28 | Line 39 | import java.util.WeakHashMap;
39		* start other subtasks.  As indicated by the name of this class,
40		* many programs using {@code ForkJoinTask} employ only methods
41		* {@link #fork} and {@link #join}, or derivatives such as {@link
42	<	* #invokeAll}.  However, this class also provides a number of other
43	<	* methods that can come into play in advanced usages, as well as
44	<	* extension mechanics that allow support of new forms of fork/join
45	<	* processing.
42	>	* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
43	>	* provides a number of other methods that can come into play in
44	>	* advanced usages, as well as extension mechanics that allow
45	>	* support of new forms of fork/join processing.
46		*
47		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
48		* The efficiency of {@code ForkJoinTask}s stems from a set of
#	Line 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 100 | Line 115 | import java.util.WeakHashMap;
115		* ForkJoinTasks (as may be determined using method {@link
116		* #inForkJoinPool}).  Attempts to invoke them in other contexts
117		* result in exceptions or errors, possibly including
118	<	* ClassCastException.
118	>	* {@code ClassCastException}.
119	>	*
120	>	* <p>Method {@link #join} and its variants are appropriate for use
121	>	* only when completion dependencies are acyclic; that is, the
122	>	* parallel computation can be described as a directed acyclic graph
123	>	* (DAG). Otherwise, executions may encounter a form of deadlock as
124	>	* tasks cyclically wait for each other.  However, this framework
125	>	* supports other methods and techniques (for example the use of
126	>	* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
127	>	* may be of use in constructing custom subclasses for problems that
128	>	* are not statically structured as DAGs.
129		*
130		* <p>Most base support methods are {@code final}, to prevent
131		* overriding of implementations that are intrinsically tied to the
#	Line 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 152 | 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	<	* COMPLETED. 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 164 | Line 190 | public abstract class ForkJoinTask<V> im
190		* them.
191		*/
192
193	<	/** Run status of this task */
193	>	/** The run status of this task */
194		volatile int status; // accessed directly by pool and workers
169	–
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		/**
176	–	* Table of exceptions thrown by tasks, to enable reporting by
177	–	* callers. Because exceptions are rare, we don't directly keep
178	–	* them with task objects, but instead use a weak ref table.  Note
179	–	* that cancellation exceptions don't appear in the table, but are
180	–	* instead recorded as status values.
181	–	* TODO: Use ConcurrentReferenceHashMap
182	–	*/
183	–	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
184	–	Collections.synchronizedMap
185	–	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
186	–
187	–	// Maintaining completion status
188	–
189	–	/**
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 status on exit
205	>	* @return completion status on exit
206		*/
207		private int setCompletion(int completion) {
208	<	int s;
209	<	while ((s = status) >= 0) {
208	>	for (int s;;) {
209	>	if ((s = status) < 0)
210	>	return s;
211		if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
212		if (s != 0)
213		synchronized (this) { notifyAll(); }
214		return completion;
215		}
216		}
205	–	return s;
217		}
218
219		/**
220	<	* Record exception and set exceptional completion
221	<	* @return status on exit
222	<	*/
223	<	private int setExceptionalCompletion(Throwable rex) {
224	<	exceptionMap.put(this, rex);
214	<	return setCompletion(EXCEPTIONAL);
215	<	}
216	<
217	<	/**
218	<	* Blocks a worker thread until completion. Called only by pool.
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	<	final void internalAwaitDone() {
227	<	int s;         // the odd construction reduces lock bias effects
228	<	while ((s = status) >= 0) {
229	<	try {
230	<	synchronized(this) {
231	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
232	<	wait();
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		}
228	–	} catch (InterruptedException ie) {
229	–	cancelIfTerminating();
237		}
238	+	} catch (InterruptedException ie) {
239	+	// caller must check termination
240		}
241		}
242
243		/**
244		* Blocks a non-worker-thread until completion.
245	<	* @return status on exit
245	>	* @return status upon completion
246		*/
247		private int externalAwaitDone() {
248		int s;
249	<	while ((s = status) >= 0) {
250	<	synchronized(this) {
251	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
252	<	boolean interrupted = false;
253	<	while ((s = status) >= 0) {
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		}
251	–	if (interrupted)
252	–	Thread.currentThread().interrupt();
253	–	break;
263		}
264		}
265	+	if (interrupted)
266	+	Thread.currentThread().interrupt();
267		}
268		return s;
269		}
270
271		/**
272	<	* Unless done, calls exec and records status if completed, but
262	<	* doesn't wait for completion otherwise. Primary execution method
263	<	* for ForkJoinWorkerThread.
272	>	* Blocks a non-worker-thread until completion or interruption or timeout.
273		*/
274	<	final void tryExec() {
275	<	try {
276	<	if (status < 0 || !exec())
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	>	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	>	}
288	>	}
289	>	}
290	>	return s;
291	>	}
292	>
293	>	/**
294	>	* Primary execution method for stolen tasks. Unless done, calls
295	>	* exec and records status if completed, but doesn't wait for
296	>	* completion otherwise.
297	>	*/
298	>	final void doExec() {
299	>	if (status >= 0) {
300	>	boolean completed;
301	>	try {
302	>	completed = exec();
303	>	} catch (Throwable rex) {
304	>	setExceptionalCompletion(rex);
305		return;
306	<	} catch (Throwable rex) {
307	<	setExceptionalCompletion(rex);
308	<	return;
306	>	}
307	>	if (completed)
308	>	setCompletion(NORMAL); // must be outside try block
309		}
273	–	setCompletion(NORMAL); // must be outside try block
310		}
311
312		/**
313	<	* If not done and this task is next in worker queue, runs it,
314	<	* else waits for it.
279	<	* @return status on exit
313	>	* Primary mechanics for join, get, quietlyJoin.
314	>	* @return status upon completion
315		*/
316		private int doJoin() {
317	<	int stat;
318	<	if ((stat = status) < 0)
319	<	return stat;
320	<	Thread t = Thread.currentThread();
321	<	ForkJoinWorkerThread w;
287	<	if (t instanceof ForkJoinWorkerThread) {
288	<	if ((w = (ForkJoinWorkerThread) t).unpushTask(this)) {
289	<	boolean completed;
317	>	Thread t; ForkJoinWorkerThread w; int s; boolean completed;
318	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
319	>	if ((s = status) < 0)
320	>	return s;
321	>	if ((w = (ForkJoinWorkerThread)t).unpushTask(this)) {
322		try {
323		completed = exec();
324		} catch (Throwable rex) {
#	Line 297 | Line 329 | public abstract class ForkJoinTask<V> im
329		}
330		return w.joinTask(this);
331		}
332	<	return externalAwaitDone();
332	>	else
333	>	return externalAwaitDone();
334		}
335
336		/**
337	<	* Unless done, calls exec and records status if completed, or
338	<	* waits for completion otherwise.
306	<	* @return status on exit
337	>	* Primary mechanics for invoke, quietlyInvoke.
338	>	* @return status upon completion
339		*/
340		private int doInvoke() {
341	<	int stat;
342	<	if ((stat = status) >= 0) {
343	<	boolean completed;
344	<	try {
345	<	completed = exec();
346	<	} catch (Throwable rex) {
347	<	return setExceptionalCompletion(rex);
341	>	int s; boolean completed;
342	>	if ((s = status) < 0)
343	>	return s;
344	>	try {
345	>	completed = exec();
346	>	} catch (Throwable rex) {
347	>	return setExceptionalCompletion(rex);
348	>	}
349	>	if (completed)
350	>	return setCompletion(NORMAL);
351	>	else
352	>	return doJoin();
353	>	}
354	>
355	>	// Exception table support
356	>
357	>	/**
358	>	* Table of exceptions thrown by tasks, to enable reporting by
359	>	* callers. Because exceptions are rare, we don't directly keep
360	>	* them with task objects, but instead use a weak ref table.  Note
361	>	* that cancellation exceptions don't appear in the table, but are
362	>	* instead recorded as status values.
363	>	*
364	>	* Note: These statics are initialized below in static block.
365	>	*/
366	>	private static final ExceptionNode[] exceptionTable;
367	>	private static final ReentrantLock exceptionTableLock;
368	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
369	>
370	>	/**
371	>	* Fixed capacity for exceptionTable.
372	>	*/
373	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
374	>
375	>	/**
376	>	* Key-value nodes for exception table.  The chained hash table
377	>	* uses identity comparisons, full locking, and weak references
378	>	* for keys. The table has a fixed capacity because it only
379	>	* maintains task exceptions long enough for joiners to access
380	>	* them, so should never become very large for sustained
381	>	* periods. However, since we do not know when the last joiner
382	>	* completes, we must use weak references and expunge them. We do
383	>	* so on each operation (hence full locking). Also, some thread in
384	>	* any ForkJoinPool will call helpExpunge when its pool becomes
385	>	* isQuiescent.
386	>	*/
387	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>>{
388	>	final Throwable ex;
389	>	ExceptionNode next;
390	>	final long thrower;
391	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
392	>	super(task, exceptionTableRefQueue);
393	>	this.ex = ex;
394	>	this.next = next;
395	>	this.thrower = Thread.currentThread().getId();
396	>	}
397	>	}
398	>
399	>	/**
400	>	* Records exception and sets exceptional completion.
401	>	*
402	>	* @return status on exit
403	>	*/
404	>	private int setExceptionalCompletion(Throwable ex) {
405	>	int h = System.identityHashCode(this);
406	>	ReentrantLock lock = exceptionTableLock;
407	>	lock.lock();
408	>	try {
409	>	expungeStaleExceptions();
410	>	ExceptionNode[] t = exceptionTable;
411	>	int i = h & (t.length - 1);
412	>	for (ExceptionNode e = t[i]; ; e = e.next) {
413	>	if (e == null) {
414	>	t[i] = new ExceptionNode(this, ex, t[i]);
415	>	break;
416	>	}
417	>	if (e.get() == this) // already present
418	>	break;
419		}
420	<	stat = completed ? setCompletion(NORMAL) : doJoin();
420	>	} finally {
421	>	lock.unlock();
422		}
423	<	return stat;
423	>	return setCompletion(EXCEPTIONAL);
424		}
425
426		/**
427	<	* Returns result or throws exception associated with given status.
324	<	* @param s the status
427	>	* Removes exception node and clears status
428		*/
429	<	private V reportResult(int s) {
429	>	private void clearExceptionalCompletion() {
430	>	int h = System.identityHashCode(this);
431	>	ReentrantLock lock = exceptionTableLock;
432	>	lock.lock();
433	>	try {
434	>	ExceptionNode[] t = exceptionTable;
435	>	int i = h & (t.length - 1);
436	>	ExceptionNode e = t[i];
437	>	ExceptionNode pred = null;
438	>	while (e != null) {
439	>	ExceptionNode next = e.next;
440	>	if (e.get() == this) {
441	>	if (pred == null)
442	>	t[i] = next;
443	>	else
444	>	pred.next = next;
445	>	break;
446	>	}
447	>	pred = e;
448	>	e = next;
449	>	}
450	>	expungeStaleExceptions();
451	>	status = 0;
452	>	} finally {
453	>	lock.unlock();
454	>	}
455	>	}
456	>
457	>	/**
458	>	* Returns a rethrowable exception for the given task, if
459	>	* available. To provide accurate stack traces, if the exception
460	>	* was not thrown by the current thread, we try to create a new
461	>	* exception of the same type as the one thrown, but with the
462	>	* recorded exception as its cause. If there is no such
463	>	* constructor, we instead try to use a no-arg constructor,
464	>	* followed by initCause, to the same effect. If none of these
465	>	* apply, or any fail due to other exceptions, we return the
466	>	* recorded exception, which is still correct, although it may
467	>	* contain a misleading stack trace.
468	>	*
469	>	* @return the exception, or null if none
470	>	*/
471	>	private Throwable getThrowableException() {
472	>	if (status != EXCEPTIONAL)
473	>	return null;
474	>	int h = System.identityHashCode(this);
475	>	ExceptionNode e;
476	>	ReentrantLock lock = exceptionTableLock;
477	>	lock.lock();
478	>	try {
479	>	expungeStaleExceptions();
480	>	ExceptionNode[] t = exceptionTable;
481	>	e = t[h & (t.length - 1)];
482	>	while (e != null && e.get() != this)
483	>	e = e.next;
484	>	} finally {
485	>	lock.unlock();
486	>	}
487		Throwable ex;
488	<	if (s < NORMAL && (ex = getException()) != null)
488	>	if (e == null || (ex = e.ex) == null)
489	>	return null;
490	>	if (e.thrower != Thread.currentThread().getId()) {
491	>	Class ec = ex.getClass();
492	>	try {
493	>	Constructor<?> noArgCtor = null;
494	>	Constructor<?>[] cs = ec.getConstructors();// public ctors only
495	>	for (int i = 0; i < cs.length; ++i) {
496	>	Constructor<?> c = cs[i];
497	>	Class<?>[] ps = c.getParameterTypes();
498	>	if (ps.length == 0)
499	>	noArgCtor = c;
500	>	else if (ps.length == 1 && ps[0] == Throwable.class)
501	>	return (Throwable)(c.newInstance(ex));
502	>	}
503	>	if (noArgCtor != null) {
504	>	Throwable wx = (Throwable)(noArgCtor.newInstance());
505	>	wx.initCause(ex);
506	>	return wx;
507	>	}
508	>	} catch (Exception ignore) {
509	>	}
510	>	}
511	>	return ex;
512	>	}
513	>
514	>	/**
515	>	* Poll stale refs and remove them. Call only while holding lock.
516	>	*/
517	>	private static void expungeStaleExceptions() {
518	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
519	>	if (x instanceof ExceptionNode) {
520	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
521	>	ExceptionNode[] t = exceptionTable;
522	>	int i = System.identityHashCode(key) & (t.length - 1);
523	>	ExceptionNode e = t[i];
524	>	ExceptionNode pred = null;
525	>	while (e != null) {
526	>	ExceptionNode next = e.next;
527	>	if (e == x) {
528	>	if (pred == null)
529	>	t[i] = next;
530	>	else
531	>	pred.next = next;
532	>	break;
533	>	}
534	>	pred = e;
535	>	e = next;
536	>	}
537	>	}
538	>	}
539	>	}
540	>
541	>	/**
542	>	* If lock is available, poll any stale refs and remove them.
543	>	* Called from ForkJoinPool when pools become quiescent.
544	>	*/
545	>	static final void helpExpungeStaleExceptions() {
546	>	ReentrantLock lock = exceptionTableLock;
547	>	if (lock.tryLock()) {
548	>	try {
549	>	expungeStaleExceptions();
550	>	} finally {
551	>	lock.unlock();
552	>	}
553	>	}
554	>	}
555	>
556	>	/**
557	>	* Report the result of invoke or join; called only upon
558	>	* non-normal return of internal versions.
559	>	*/
560	>	private V reportResult() {
561	>	int s; Throwable ex;
562	>	if ((s = status) == CANCELLED)
563	>	throw new CancellationException();
564	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
565		UNSAFE.throwException(ex);
566		return getRawResult();
567		}
#	Line 343 | Line 579 | public abstract class ForkJoinTask<V> im
579		* #isDone} returning {@code true}.
580		*
581		* <p>This method may be invoked only from within {@code
582	<	* ForkJoinTask} computations (as may be determined using method
582	>	* ForkJoinPool} computations (as may be determined using method
583		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
584		* result in exceptions or errors, possibly including {@code
585		* ClassCastException}.
#	Line 357 | Line 593 | public abstract class ForkJoinTask<V> im
593		}
594
595		/**
596	<	* Returns the result of the computation when it {@link #isDone is done}.
597	<	* This method differs from {@link #get()} in that
596	>	* Returns the result of the computation when it {@link #isDone is
597	>	* done}.  This method differs from {@link #get()} in that
598		* abnormal completion results in {@code RuntimeException} or
599	<	* {@code Error}, not {@code ExecutionException}.
599	>	* {@code Error}, not {@code ExecutionException}, and that
600	>	* interrupts of the calling thread do <em>not</em> cause the
601	>	* method to abruptly return by throwing {@code
602	>	* InterruptedException}.
603		*
604		* @return the computed result
605		*/
606		public final V join() {
607	<	return reportResult(doJoin());
607	>	if (doJoin() != NORMAL)
608	>	return reportResult();
609	>	else
610	>	return getRawResult();
611		}
612
613		/**
614		* Commences performing this task, awaits its completion if
615	<	* necessary, and return its result, or throws an (unchecked)
616	<	* exception if the underlying computation did so.
615	>	* necessary, and returns its result, or throws an (unchecked)
616	>	* {@code RuntimeException} or {@code Error} if the underlying
617	>	* computation did so.
618		*
619		* @return the computed result
620		*/
621		public final V invoke() {
622	<	return reportResult(doInvoke());
622	>	if (doInvoke() != NORMAL)
623	>	return reportResult();
624	>	else
625	>	return getRawResult();
626		}
627
628		/**
629		* Forks the given tasks, returning when {@code isDone} holds for
630		* each task or an (unchecked) exception is encountered, in which
631	<	* case the exception is rethrown.  If either task encounters an
632	<	* exception, the other one may be, but is not guaranteed to be,
633	<	* cancelled.  If both tasks throw an exception, then this method
634	<	* throws one of them.  The individual status of each task may be
635	<	* checked using {@link #getException()} and related methods.
631	>	* case the exception is rethrown. If more than one task
632	>	* encounters an exception, then this method throws any one of
633	>	* these exceptions. If any task encounters an exception, the
634	>	* other may be cancelled. However, the execution status of
635	>	* individual tasks is not guaranteed upon exceptional return. The
636	>	* status of each task may be obtained using {@link
637	>	* #getException()} and related methods to check if they have been
638	>	* cancelled, completed normally or exceptionally, or left
639	>	* unprocessed.
640		*
641		* <p>This method may be invoked only from within {@code
642	<	* ForkJoinTask} computations (as may be determined using method
642	>	* ForkJoinPool} computations (as may be determined using method
643		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
644		* result in exceptions or errors, possibly including {@code
645		* ClassCastException}.
#	Line 407 | Line 657 | public abstract class ForkJoinTask<V> im
657		/**
658		* Forks the given tasks, returning when {@code isDone} holds for
659		* each task or an (unchecked) exception is encountered, in which
660	<	* case the exception is rethrown. If any task encounters an
661	<	* exception, others may be, but are not guaranteed to be,
662	<	* cancelled.  If more than one task encounters an exception, then
663	<	* this method throws any one of these exceptions.  The individual
664	<	* status of each task may be checked using {@link #getException()}
665	<	* and related methods.
660	>	* case the exception is rethrown. If more than one task
661	>	* encounters an exception, then this method throws any one of
662	>	* these exceptions. If any task encounters an exception, others
663	>	* may be cancelled. However, the execution status of individual
664	>	* tasks is not guaranteed upon exceptional return. The status of
665	>	* each task may be obtained using {@link #getException()} and
666	>	* related methods to check if they have been cancelled, completed
667	>	* normally or exceptionally, or left unprocessed.
668		*
669		* <p>This method may be invoked only from within {@code
670	<	* ForkJoinTask} computations (as may be determined using method
670	>	* ForkJoinPool} computations (as may be determined using method
671		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
672		* result in exceptions or errors, possibly including {@code
673		* ClassCastException}.
#	Line 453 | Line 705 | public abstract class ForkJoinTask<V> im
705		/**
706		* Forks all tasks in the specified collection, returning when
707		* {@code isDone} holds for each task or an (unchecked) exception
708	<	* is encountered.  If any task encounters an exception, others
709	<	* may be, but are not guaranteed to be, cancelled.  If more than
710	<	* one task encounters an exception, then this method throws any
711	<	* one of these exceptions.  The individual status of each task
712	<	* may be checked using {@link #getException()} and related
713	<	* methods.  The behavior of this operation is undefined if the
714	<	* specified collection is modified while the operation is in
715	<	* progress.
708	>	* is encountered, in which case the exception is rethrown. If
709	>	* more than one task encounters an exception, then this method
710	>	* throws any one of these exceptions. If any task encounters an
711	>	* exception, others may be cancelled. However, the execution
712	>	* status of individual tasks is not guaranteed upon exceptional
713	>	* return. The status of each task may be obtained using {@link
714	>	* #getException()} and related methods to check if they have been
715	>	* cancelled, completed normally or exceptionally, or left
716	>	* unprocessed.
717		*
718		* <p>This method may be invoked only from within {@code
719	<	* ForkJoinTask} computations (as may be determined using method
719	>	* ForkJoinPool} computations (as may be determined using method
720		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
721		* result in exceptions or errors, possibly including {@code
722		* ClassCastException}.
#	Line 509 | Line 762 | public abstract class ForkJoinTask<V> im
762
763		/**
764		* Attempts to cancel execution of this task. This attempt will
765	<	* fail if the task has already completed, has already been
766	<	* cancelled, or could not be cancelled for some other reason. If
767	<	* successful, and this task has not started when cancel is
768	<	* called, execution of this task is suppressed, {@link
769	<	* #isCancelled} will report true, and {@link #join} will result
770	<	* in a {@code CancellationException} being thrown.
765	>	* fail if the task has already completed or could not be
766	>	* cancelled for some other reason. If successful, and this task
767	>	* has not started when {@code cancel} is called, execution of
768	>	* this task is suppressed. After this method returns
769	>	* successfully, unless there is an intervening call to {@link
770	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
771	>	* {@link #isDone}, and {@code cancel} will return {@code true}
772	>	* and calls to {@link #join} and related methods will result in
773	>	* {@code CancellationException}.
774		*
775		* <p>This method may be overridden in subclasses, but if so, must
776	<	* still ensure that these minimal properties hold. In particular,
777	<	* the {@code cancel} method itself must not throw exceptions.
776	>	* still ensure that these properties hold. In particular, the
777	>	* {@code cancel} method itself must not throw exceptions.
778		*
779		* <p>This method is designed to be invoked by <em>other</em>
780		* tasks. To terminate the current task, you can just return or
781		* throw an unchecked exception from its computation method, or
782		* invoke {@link #completeExceptionally}.
783		*
784	<	* @param mayInterruptIfRunning this value is ignored in the
785	<	* default implementation because tasks are not
786	<	* cancelled via interruption
784	>	* @param mayInterruptIfRunning this value has no effect in the
785	>	* default implementation because interrupts are not used to
786	>	* control cancellation.
787		*
788		* @return {@code true} if this task is now cancelled
789		*/
#	Line 536 | Line 792 | public abstract class ForkJoinTask<V> im
792		}
793
794		/**
795	<	* Cancels, ignoring any exceptions it throws. Used during worker
796	<	* and pool shutdown.
795	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
796	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
797	>	* exceptions, but if it does anyway, we have no recourse during
798	>	* shutdown, so guard against this case.
799		*/
800		final void cancelIgnoringExceptions() {
801		try {
#	Line 546 | Line 804 | public abstract class ForkJoinTask<V> im
804		}
805		}
806
549	–	/**
550	–	* Cancels ignoring exceptions if worker is terminating
551	–	*/
552	–	final void cancelIfTerminating() {
553	–	Thread t = Thread.currentThread();
554	–	if ((t instanceof ForkJoinWorkerThread) &&
555	–	((ForkJoinWorkerThread) t).isTerminating()) {
556	–	try {
557	–	cancel(false);
558	–	} catch (Throwable ignore) {
559	–	}
560	–	}
561	–	}
562	–
807		public final boolean isDone() {
808		return status < 0;
809		}
#	Line 599 | Line 843 | public abstract class ForkJoinTask<V> im
843		int s = status;
844		return ((s >= NORMAL)    ? null :
845		(s == CANCELLED) ? new CancellationException() :
846	<	exceptionMap.get(this));
846	>	getThrowableException());
847		}
848
849		/**
#	Line 624 | Line 868 | public abstract class ForkJoinTask<V> im
868
869		/**
870		* Completes this task, and if not already aborted or cancelled,
871	<	* returning a {@code null} result upon {@code join} and related
872	<	* operations. This method may be used to provide results for
873	<	* asynchronous tasks, or to provide alternative handling for
874	<	* tasks that would not otherwise complete normally. Its use in
875	<	* other situations is discouraged. This method is
876	<	* overridable, but overridden versions must invoke {@code super}
877	<	* implementation to maintain guarantees.
871	>	* returning the given value as the result of subsequent
872	>	* invocations of {@code join} and related operations. This method
873	>	* may be used to provide results for asynchronous tasks, or to
874	>	* provide alternative handling for tasks that would not otherwise
875	>	* complete normally. Its use in other situations is
876	>	* discouraged. This method is overridable, but overridden
877	>	* versions must invoke {@code super} implementation to maintain
878	>	* guarantees.
879		*
880		* @param value the result value for this task
881		*/
#	Line 644 | Line 889 | public abstract class ForkJoinTask<V> im
889		setCompletion(NORMAL);
890		}
891
892	+	/**
893	+	* Waits if necessary for the computation to complete, and then
894	+	* retrieves its result.
895	+	*
896	+	* @return the computed result
897	+	* @throws CancellationException if the computation was cancelled
898	+	* @throws ExecutionException if the computation threw an
899	+	* exception
900	+	* @throws InterruptedException if the current thread is not a
901	+	* member of a ForkJoinPool and was interrupted while waiting
902	+	*/
903		public final V get() throws InterruptedException, ExecutionException {
904	<	int s = doJoin();
905	<	if (Thread.interrupted())
906	<	throw new InterruptedException();
907	<	if (s < NORMAL) {
908	<	Throwable ex;
909	<	if (s == CANCELLED)
910	<	throw new CancellationException();
655	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
656	<	throw new ExecutionException(ex);
657	<	}
904	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
905	>	doJoin() : externalInterruptibleAwaitDone(0L);
906	>	Throwable ex;
907	>	if (s == CANCELLED)
908	>	throw new CancellationException();
909	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
910	>	throw new ExecutionException(ex);
911		return getRawResult();
912		}
913
914	+	/**
915	+	* Waits if necessary for at most the given time for the computation
916	+	* to complete, and then retrieves its result, if available.
917	+	*
918	+	* @param timeout the maximum time to wait
919	+	* @param unit the time unit of the timeout argument
920	+	* @return the computed result
921	+	* @throws CancellationException if the computation was cancelled
922	+	* @throws ExecutionException if the computation threw an
923	+	* exception
924	+	* @throws InterruptedException if the current thread is not a
925	+	* member of a ForkJoinPool and was interrupted while waiting
926	+	* @throws TimeoutException if the wait timed out
927	+	*/
928		public final V get(long timeout, TimeUnit unit)
929		throws InterruptedException, ExecutionException, TimeoutException {
930		Thread t = Thread.currentThread();
664	–	ForkJoinPool pool;
931		if (t instanceof ForkJoinWorkerThread) {
932		ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
933	<	if (status >= 0 && w.unpushTask(this))
934	<	tryExec();
935	<	pool = w.pool;
936	<	}
937	<	else
938	<	pool = null;
939	<	/*
940	<	* Timed wait loop intermixes cases for fj (pool != null) and
675	<	* non FJ threads. For FJ, decrement pool count but don't try
676	<	* for replacement; increment count on completion. For non-FJ,
677	<	* deal with interrupts. This is messy, but a little less so
678	<	* than is splitting the FJ and nonFJ cases.
679	<	*/
680	<	boolean interrupted = false;
681	<	boolean dec = false; // true if pool count decremented
682	<	for (;;) {
683	<	if (Thread.interrupted() && pool == null) {
684	<	interrupted = true;
685	<	break;
686	<	}
687	<	int s = status;
688	<	if (s < 0)
689	<	break;
690	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
691	<	s, s | SIGNAL)) {
692	<	long startTime = System.nanoTime();
693	<	long nanos = unit.toNanos(timeout);
694	<	long nt; // wait time
695	<	while (status >= 0 &&
696	<	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
697	<	if (pool != null && !dec)
698	<	dec = pool.tryDecrementRunningCount();
699	<	else {
700	<	long ms = nt / 1000000;
701	<	int ns = (int) (nt % 1000000);
702	<	try {
703	<	synchronized(this) {
704	<	if (status >= 0)
705	<	wait(ms, ns);
706	<	}
707	<	} catch (InterruptedException ie) {
708	<	if (pool != null)
709	<	cancelIfTerminating();
710	<	else {
711	<	interrupted = true;
712	<	break;
713	<	}
714	<	}
933	>	long nanos = unit.toNanos(timeout);
934	>	if (status >= 0) {
935	>	boolean completed = false;
936	>	if (w.unpushTask(this)) {
937	>	try {
938	>	completed = exec();
939	>	} catch (Throwable rex) {
940	>	setExceptionalCompletion(rex);
941		}
942		}
943	<	break;
943	>	if (completed)
944	>	setCompletion(NORMAL);
945	>	else if (status >= 0 && nanos > 0)
946	>	w.pool.timedAwaitJoin(this, nanos);
947		}
948		}
949	<	if (pool != null && dec)
950	<	pool.incrementRunningCount();
951	<	if (interrupted)
952	<	throw new InterruptedException();
953	<	int es = status;
954	<	if (es != NORMAL) {
949	>	else {
950	>	long millis = unit.toMillis(timeout);
951	>	if (millis > 0)
952	>	externalInterruptibleAwaitDone(millis);
953	>	}
954	>	int s = status;
955	>	if (s != NORMAL) {
956		Throwable ex;
957	<	if (es == CANCELLED)
957	>	if (s == CANCELLED)
958		throw new CancellationException();
959	<	if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
959	>	if (s != EXCEPTIONAL)
960	>	throw new TimeoutException();
961	>	if ((ex = getThrowableException()) != null)
962		throw new ExecutionException(ex);
731	–	throw new TimeoutException();
963		}
964		return getRawResult();
965		}
966
967		/**
968	<	* Joins this task, without returning its result or throwing an
968	>	* Joins this task, without returning its result or throwing its
969		* exception. This method may be useful when processing
970		* collections of tasks when some have been cancelled or otherwise
971		* known to have aborted.
#	Line 745 | Line 976 | public abstract class ForkJoinTask<V> im
976
977		/**
978		* Commences performing this task and awaits its completion if
979	<	* necessary, without returning its result or throwing an
980	<	* exception. This method may be useful when processing
750	<	* collections of tasks when some have been cancelled or otherwise
751	<	* known to have aborted.
979	>	* necessary, without returning its result or throwing its
980	>	* exception.
981		*/
982		public final void quietlyInvoke() {
983		doInvoke();
#	Line 762 | Line 991 | public abstract class ForkJoinTask<V> im
991		* processed.
992		*
993		* <p>This method may be invoked only from within {@code
994	<	* ForkJoinTask} computations (as may be determined using method
994	>	* ForkJoinPool} computations (as may be determined using method
995		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
996		* result in exceptions or errors, possibly including {@code
997		* ClassCastException}.
#	Line 781 | Line 1010 | public abstract class ForkJoinTask<V> im
1010		* under any other usage conditions are not guaranteed.
1011		* This method may be useful when executing
1012		* pre-constructed trees of subtasks in loops.
1013	+	*
1014	+	* <p>Upon completion of this method, {@code isDone()} reports
1015	+	* {@code false}, and {@code getException()} reports {@code
1016	+	* null}. However, the value returned by {@code getRawResult} is
1017	+	* unaffected. To clear this value, you can invoke {@code
1018	+	* setRawResult(null)}.
1019		*/
1020		public void reinitialize() {
1021		if (status == EXCEPTIONAL)
1022	<	exceptionMap.remove(this);
1023	<	status = 0;
1022	>	clearExceptionalCompletion();
1023	>	else
1024	>	status = 0;
1025		}
1026
1027		/**
#	Line 802 | Line 1038 | public abstract class ForkJoinTask<V> im
1038		}
1039
1040		/**
1041	<	* Returns {@code true} if the current thread is executing as a
1042	<	* ForkJoinPool computation.
1041	>	* Returns {@code true} if the current thread is a {@link
1042	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1043		*
1044	<	* @return {@code true} if the current thread is executing as a
1045	<	* ForkJoinPool computation, or false otherwise
1044	>	* @return {@code true} if the current thread is a {@link
1045	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1046	>	* or {@code false} otherwise
1047		*/
1048		public static boolean inForkJoinPool() {
1049		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 821 | Line 1058 | public abstract class ForkJoinTask<V> im
1058		* were not, stolen.
1059		*
1060		* <p>This method may be invoked only from within {@code
1061	<	* ForkJoinTask} computations (as may be determined using method
1061	>	* ForkJoinPool} computations (as may be determined using method
1062		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1063		* result in exceptions or errors, possibly including {@code
1064		* ClassCastException}.
#	Line 840 | Line 1077 | public abstract class ForkJoinTask<V> im
1077		* fork other tasks.
1078		*
1079		* <p>This method may be invoked only from within {@code
1080	<	* ForkJoinTask} computations (as may be determined using method
1080	>	* ForkJoinPool} computations (as may be determined using method
1081		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1082		* result in exceptions or errors, possibly including {@code
1083		* ClassCastException}.
#	Line 863 | Line 1100 | public abstract class ForkJoinTask<V> im
1100		* exceeded.
1101		*
1102		* <p>This method may be invoked only from within {@code
1103	<	* ForkJoinTask} computations (as may be determined using method
1103	>	* ForkJoinPool} computations (as may be determined using method
1104		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1105		* result in exceptions or errors, possibly including {@code
1106		* ClassCastException}.
#	Line 921 | Line 1158 | public abstract class ForkJoinTask<V> im
1158		* otherwise.
1159		*
1160		* <p>This method may be invoked only from within {@code
1161	<	* ForkJoinTask} computations (as may be determined using method
1161	>	* ForkJoinPool} computations (as may be determined using method
1162		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1163		* result in exceptions or errors, possibly including {@code
1164		* ClassCastException}.
#	Line 940 | Line 1177 | public abstract class ForkJoinTask<V> im
1177		* be useful otherwise.
1178		*
1179		* <p>This method may be invoked only from within {@code
1180	<	* ForkJoinTask} computations (as may be determined using method
1180	>	* ForkJoinPool} computations (as may be determined using method
1181		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1182		* result in exceptions or errors, possibly including {@code
1183		* ClassCastException}.
#	Line 963 | Line 1200 | public abstract class ForkJoinTask<V> im
1200		* otherwise.
1201		*
1202		* <p>This method may be invoked only from within {@code
1203	<	* ForkJoinTask} computations (as may be determined using method
1203	>	* ForkJoinPool} computations (as may be determined using method
1204		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1205		* result in exceptions or errors, possibly including {@code
1206		* ClassCastException}.
#	Line 1073 | Line 1310 | public abstract class ForkJoinTask<V> im
1310		private static final long serialVersionUID = -7721805057305804111L;
1311
1312		/**
1313	<	* Saves the state to a stream.
1313	>	* Saves the state to a stream (that is, serializes it).
1314		*
1315		* @serialData the current run status and the exception thrown
1316		* during execution, or {@code null} if none
#	Line 1086 | Line 1323 | public abstract class ForkJoinTask<V> im
1323		}
1324
1325		/**
1326	<	* Reconstitutes the instance from a stream.
1326	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1327		*
1328		* @param s the stream
1329		*/
#	Line 1095 | Line 1332 | public abstract class ForkJoinTask<V> im
1332		s.defaultReadObject();
1333		Object ex = s.readObject();
1334		if (ex != null)
1335	<	setExceptionalCompletion((Throwable) ex);
1335	>	setExceptionalCompletion((Throwable)ex);
1336		}
1337
1338		// Unsafe mechanics
1339	<
1340	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1341	<	private static final long statusOffset =
1342	<	objectFieldOffset("status", ForkJoinTask.class);
1343	<
1344	<	private static long objectFieldOffset(String field, Class<?> klazz) {
1339	>	private static final sun.misc.Unsafe UNSAFE;
1340	>	private static final long statusOffset;
1341	>	static {
1342	>	exceptionTableLock = new ReentrantLock();
1343	>	exceptionTableRefQueue = new ReferenceQueue<Object>();
1344	>	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1345		try {
1346	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1347	<	} catch (NoSuchFieldException e) {
1348	<	// Convert Exception to corresponding Error
1349	<	NoSuchFieldError error = new NoSuchFieldError(field);
1350	<	error.initCause(e);
1114	<	throw error;
1346	>	UNSAFE = getUnsafe();
1347	>	statusOffset = UNSAFE.objectFieldOffset
1348	>	(ForkJoinTask.class.getDeclaredField("status"));
1349	>	} catch (Exception e) {
1350	>	throw new Error(e);
1351		}
1352		}
1353

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