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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.49 by dl, Wed Jul 7 19:52:31 2010 UTC vs.
Revision 1.79 by jsr166, Fri Jun 10 18:10:53 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;
13	–	import java.util.Collections;
11		import java.util.List;
12		import java.util.RandomAccess;
13	<	import java.util.Map;
14	<	import java.util.WeakHashMap;
13	>	import java.lang.ref.WeakReference;
14	>	import java.lang.ref.ReferenceQueue;
15	>	import java.util.concurrent.Callable;
16	>	import java.util.concurrent.CancellationException;
17	>	import java.util.concurrent.ExecutionException;
18	>	import java.util.concurrent.Future;
19	>	import java.util.concurrent.RejectedExecutionException;
20	>	import java.util.concurrent.RunnableFuture;
21	>	import java.util.concurrent.TimeUnit;
22	>	import java.util.concurrent.TimeoutException;
23	>	import java.util.concurrent.locks.ReentrantLock;
24	>	import java.lang.reflect.Constructor;
25
26		/**
27		* Abstract base class for tasks that run within a {@link ForkJoinPool}.
#	Line 28 | Line 35 | import java.util.WeakHashMap;
35		* start other subtasks.  As indicated by the name of this class,
36		* many programs using {@code ForkJoinTask} employ only methods
37		* {@link #fork} and {@link #join}, or derivatives such as {@link
38	<	* #invokeAll}.  However, this class also provides a number of other
39	<	* methods that can come into play in advanced usages, as well as
40	<	* extension mechanics that allow support of new forms of fork/join
41	<	* processing.
38	>	* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
39	>	* provides a number of other methods that can come into play in
40	>	* advanced usages, as well as extension mechanics that allow
41	>	* support of new forms of fork/join processing.
42		*
43		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
44		* The efficiency of {@code ForkJoinTask}s stems from a set of
#	Line 58 | Line 65 | import java.util.WeakHashMap;
65		* rethrown to callers attempting to join them. These exceptions may
66		* additionally include {@link RejectedExecutionException} stemming
67		* from internal resource exhaustion, such as failure to allocate
68	<	* internal task queues.
68	>	* internal task queues. Rethrown exceptions behave in the same way as
69	>	* regular exceptions, but, when possible, contain stack traces (as
70	>	* displayed for example using {@code ex.printStackTrace()}) of both
71	>	* the thread that initiated the computation as well as the thread
72	>	* actually encountering the exception; minimally only the latter.
73		*
74		* <p>The primary method for awaiting completion and extracting
75		* results of a task is {@link #join}, but there are several variants:
#	Line 100 | Line 111 | import java.util.WeakHashMap;
111		* ForkJoinTasks (as may be determined using method {@link
112		* #inForkJoinPool}).  Attempts to invoke them in other contexts
113		* result in exceptions or errors, possibly including
114	<	* ClassCastException.
114	>	* {@code ClassCastException}.
115	>	*
116	>	* <p>Method {@link #join} and its variants are appropriate for use
117	>	* only when completion dependencies are acyclic; that is, the
118	>	* parallel computation can be described as a directed acyclic graph
119	>	* (DAG). Otherwise, executions may encounter a form of deadlock as
120	>	* tasks cyclically wait for each other.  However, this framework
121	>	* supports other methods and techniques (for example the use of
122	>	* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
123	>	* may be of use in constructing custom subclasses for problems that
124	>	* are not statically structured as DAGs.
125		*
126		* <p>Most base support methods are {@code final}, to prevent
127		* overriding of implementations that are intrinsically tied to the
#	Line 116 | Line 137 | import java.util.WeakHashMap;
137		* computation. Large tasks should be split into smaller subtasks,
138		* usually via recursive decomposition. As a very rough rule of thumb,
139		* a task should perform more than 100 and less than 10000 basic
140	<	* computational steps. If tasks are too big, then parallelism cannot
141	<	* improve throughput. If too small, then memory and internal task
142	<	* maintenance overhead may overwhelm processing.
140	>	* computational steps, and should avoid indefinite looping. If tasks
141	>	* are too big, then parallelism cannot improve throughput. If too
142	>	* small, then memory and internal task maintenance overhead may
143	>	* overwhelm processing.
144		*
145		* <p>This class provides {@code adapt} methods for {@link Runnable}
146		* and {@link Callable}, that may be of use when mixing execution of
#	Line 147 | Line 169 | public abstract class ForkJoinTask<V> im
169		* in a way that flows well in javadocs.
170		*/
171
172	<	/**
173	<	* Run control status bits packed into a single int to minimize
174	<	* footprint and to ensure atomicity (via CAS).  Status is
175	<	* initially zero, and takes on nonnegative values until
176	<	* completed, upon which status holds value COMPLETED. CANCELLED,
177	<	* or EXCEPTIONAL. Tasks undergoing blocking waits by other
178	<	* threads have the SIGNAL bit set.  Completion of a stolen task
179	<	* with SIGNAL set awakens any waiters via notifyAll. Even though
180	<	* suboptimal for some purposes, we use basic builtin wait/notify
181	<	* to take advantage of "monitor inflation" in JVMs that we would
182	<	* otherwise need to emulate to avoid adding further per-task
183	<	* bookkeeping overhead.  We want these monitors to be "fat",
184	<	* i.e., not use biasing or thin-lock techniques, so use some odd
185	<	* coding idioms that tend to avoid them.
172	>	/*
173	>	* The status field holds run control status bits packed into a
174	>	* single int to minimize footprint and to ensure atomicity (via
175	>	* CAS).  Status is initially zero, and takes on nonnegative
176	>	* values until completed, upon which status holds value
177	>	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
178	>	* waits by other threads have the SIGNAL bit set.  Completion of
179	>	* a stolen task with SIGNAL set awakens any waiters via
180	>	* notifyAll. Even though suboptimal for some purposes, we use
181	>	* basic builtin wait/notify to take advantage of "monitor
182	>	* inflation" in JVMs that we would otherwise need to emulate to
183	>	* avoid adding further per-task bookkeeping overhead.  We want
184	>	* these monitors to be "fat", i.e., not use biasing or thin-lock
185	>	* techniques, so use some odd coding idioms that tend to avoid
186	>	* them.
187		*/
165	–	volatile int status; // accessed directly by pool and workers
188
189	+	/** The run status of this task */
190	+	volatile int status; // accessed directly by pool and workers
191		private static final int NORMAL      = -1;
192		private static final int CANCELLED   = -2;
193		private static final int EXCEPTIONAL = -3;
194		private static final int SIGNAL      =  1;
195
196		/**
173	–	* Table of exceptions thrown by tasks, to enable reporting by
174	–	* callers. Because exceptions are rare, we don't directly keep
175	–	* them with task objects, but instead use a weak ref table.  Note
176	–	* that cancellation exceptions don't appear in the table, but are
177	–	* instead recorded as status values.
178	–	* TODO: Use ConcurrentReferenceHashMap
179	–	*/
180	–	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
181	–	Collections.synchronizedMap
182	–	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
183	–
184	–	// Maintaining completion status
185	–
186	–	/**
197		* Marks completion and wakes up threads waiting to join this task,
198		* also clearing signal request bits.
199		*
200		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
201	<	* @return status on exit
201	>	* @return completion status on exit
202		*/
203		private int setCompletion(int completion) {
204	<	int s;
205	<	while ((s = status) >= 0) {
204	>	for (int s;;) {
205	>	if ((s = status) < 0)
206	>	return s;
207		if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
208	<	if (s == SIGNAL)
208	>	if (s != 0)
209		synchronized (this) { notifyAll(); }
210		return completion;
211		}
212		}
202	–	return s;
213		}
214
215		/**
216	<	* Record exception and set exceptional completion
217	<	* @return status on exit
216	>	* Tries to block a worker thread until completed or timed out.
217	>	* Uses Object.wait time argument conventions.
218	>	* May fail on contention or interrupt.
219	>	*
220	>	* @param millis if > 0, wait time.
221		*/
222	<	private int setExceptionalCompletion(Throwable rex) {
223	<	exceptionMap.put(this, rex);
224	<	return setCompletion(EXCEPTIONAL);
222	>	final void tryAwaitDone(long millis) {
223	>	int s;
224	>	try {
225	>	if (((s = status) > 0 ||
226	>	(s == 0 &&
227	>	UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL))) &&
228	>	status > 0) {
229	>	synchronized (this) {
230	>	if (status > 0)
231	>	wait(millis);
232	>	}
233	>	}
234	>	} catch (InterruptedException ie) {
235	>	// caller must check termination
236	>	}
237		}
238
239		/**
240	<	* Blocks a worker thread until completion. Called only by pool.
240	>	* Blocks a non-worker-thread until completion.
241	>	* @return status upon completion
242		*/
243	<	final int internalAwaitDone() {
243	>	private int externalAwaitDone() {
244		int s;
245	<	while ((s = status) >= 0) {
246	<	synchronized(this) {
247	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
248	<	do {
245	>	if ((s = status) >= 0) {
246	>	boolean interrupted = false;
247	>	synchronized (this) {
248	>	while ((s = status) >= 0) {
249	>	if (s == 0)
250	>	UNSAFE.compareAndSwapInt(this, statusOffset,
251	>	0, SIGNAL);
252	>	else {
253		try {
254		wait();
255		} catch (InterruptedException ie) {
256	<	cancelIfTerminating();
256	>	interrupted = true;
257		}
258	<	} while ((s = status) >= 0);
229	<	break;
258	>	}
259		}
260		}
261	+	if (interrupted)
262	+	Thread.currentThread().interrupt();
263		}
264		return s;
265		}
266
267		/**
268	<	* Blocks a non-worker-thread until completion.
238	<	* @return status on exit
268	>	* Blocks a non-worker-thread until completion or interruption or timeout.
269		*/
270	<	private int externalAwaitDone() {
270	>	private int externalInterruptibleAwaitDone(long millis)
271	>	throws InterruptedException {
272		int s;
273	<	while ((s = status) >= 0) {
274	<	synchronized(this) {
275	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
276	<	boolean interrupted = false;
277	<	do {
278	<	try {
279	<	wait();
280	<	} catch (InterruptedException ie) {
281	<	interrupted = true;
282	<	}
283	<	} while ((s = status) >= 0);
284	<	if (interrupted)
285	<	Thread.currentThread().interrupt();
255	<	break;
273	>	if (Thread.interrupted())
274	>	throw new InterruptedException();
275	>	if ((s = status) >= 0) {
276	>	synchronized (this) {
277	>	while ((s = status) >= 0) {
278	>	if (s == 0)
279	>	UNSAFE.compareAndSwapInt(this, statusOffset,
280	>	0, SIGNAL);
281	>	else {
282	>	wait(millis);
283	>	if (millis > 0L)
284	>	break;
285	>	}
286		}
287		}
288		}
#	Line 260 | Line 290 | public abstract class ForkJoinTask<V> im
290		}
291
292		/**
293	<	* Unless done, calls exec and records status if completed, but
294	<	* doesn't wait for completion otherwise. Primary execution method
295	<	* for ForkJoinWorkerThread.
293	>	* Primary execution method for stolen tasks. Unless done, calls
294	>	* exec and records status if completed, but doesn't wait for
295	>	* completion otherwise.
296		*/
297	<	final void tryExec() {
298	<	try {
299	<	if (status < 0 || !exec())
297	>	final void doExec() {
298	>	if (status >= 0) {
299	>	boolean completed;
300	>	try {
301	>	completed = exec();
302	>	} catch (Throwable rex) {
303	>	setExceptionalCompletion(rex);
304		return;
305	<	} catch (Throwable rex) {
306	<	setExceptionalCompletion(rex);
307	<	return;
305	>	}
306	>	if (completed)
307	>	setCompletion(NORMAL); // must be outside try block
308		}
275	–	setCompletion(NORMAL); // must be outside try block
309		}
310
311		/**
312	<	* If not done and this task is next in worker queue, runs it,
313	<	* else waits for it.
281	<	* @return status on exit
312	>	* Primary mechanics for join, get, quietlyJoin.
313	>	* @return status upon completion
314		*/
315		private int doJoin() {
316	<	int stat;
317	<	if ((stat = status) < 0)
318	<	return stat;
319	<	Thread t = Thread.currentThread();
320	<	ForkJoinWorkerThread w;
289	<	if (t instanceof ForkJoinWorkerThread) {
290	<	if ((w = (ForkJoinWorkerThread) t).unpushTask(this)) {
291	<	boolean completed;
316	>	Thread t; ForkJoinWorkerThread w; int s; boolean completed;
317	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
318	>	if ((s = status) < 0)
319	>	return s;
320	>	if ((w = (ForkJoinWorkerThread)t).unpushTask(this)) {
321		try {
322		completed = exec();
323		} catch (Throwable rex) {
#	Line 297 | Line 326 | public abstract class ForkJoinTask<V> im
326		if (completed)
327		return setCompletion(NORMAL);
328		}
329	<	w.joinTask(this);
301	<	return status;
329	>	return w.joinTask(this);
330		}
331	<	return externalAwaitDone();
331	>	else
332	>	return externalAwaitDone();
333		}
334
335		/**
336	<	* Unless done, calls exec and records status if completed, or
337	<	* waits for completion otherwise.
309	<	* @return status on exit
336	>	* Primary mechanics for invoke, quietlyInvoke.
337	>	* @return status upon completion
338		*/
339		private int doInvoke() {
340	<	int stat;
341	<	if ((stat = status) >= 0) {
342	<	boolean completed;
343	<	try {
344	<	completed = exec();
345	<	} catch (Throwable rex) {
346	<	return setExceptionalCompletion(rex);
340	>	int s; boolean completed;
341	>	if ((s = status) < 0)
342	>	return s;
343	>	try {
344	>	completed = exec();
345	>	} catch (Throwable rex) {
346	>	return setExceptionalCompletion(rex);
347	>	}
348	>	if (completed)
349	>	return setCompletion(NORMAL);
350	>	else
351	>	return doJoin();
352	>	}
353	>
354	>	// Exception table support
355	>
356	>	/**
357	>	* Table of exceptions thrown by tasks, to enable reporting by
358	>	* callers. Because exceptions are rare, we don't directly keep
359	>	* them with task objects, but instead use a weak ref table.  Note
360	>	* that cancellation exceptions don't appear in the table, but are
361	>	* instead recorded as status values.
362	>	*
363	>	* Note: These statics are initialized below in static block.
364	>	*/
365	>	private static final ExceptionNode[] exceptionTable;
366	>	private static final ReentrantLock exceptionTableLock;
367	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
368	>
369	>	/**
370	>	* Fixed capacity for exceptionTable.
371	>	*/
372	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
373	>
374	>	/**
375	>	* Key-value nodes for exception table.  The chained hash table
376	>	* uses identity comparisons, full locking, and weak references
377	>	* for keys. The table has a fixed capacity because it only
378	>	* maintains task exceptions long enough for joiners to access
379	>	* them, so should never become very large for sustained
380	>	* periods. However, since we do not know when the last joiner
381	>	* completes, we must use weak references and expunge them. We do
382	>	* so on each operation (hence full locking). Also, some thread in
383	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
384	>	* pool becomes isQuiescent.
385	>	*/
386	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>>{
387	>	final Throwable ex;
388	>	ExceptionNode next;
389	>	final long thrower;  // use id not ref to avoid weak cycles
390	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
391	>	super(task, exceptionTableRefQueue);
392	>	this.ex = ex;
393	>	this.next = next;
394	>	this.thrower = Thread.currentThread().getId();
395	>	}
396	>	}
397	>
398	>	/**
399	>	* Records exception and sets exceptional completion.
400	>	*
401	>	* @return status on exit
402	>	*/
403	>	private int setExceptionalCompletion(Throwable ex) {
404	>	int h = System.identityHashCode(this);
405	>	final ReentrantLock lock = exceptionTableLock;
406	>	lock.lock();
407	>	try {
408	>	expungeStaleExceptions();
409	>	ExceptionNode[] t = exceptionTable;
410	>	int i = h & (t.length - 1);
411	>	for (ExceptionNode e = t[i]; ; e = e.next) {
412	>	if (e == null) {
413	>	t[i] = new ExceptionNode(this, ex, t[i]);
414	>	break;
415	>	}
416	>	if (e.get() == this) // already present
417	>	break;
418		}
419	<	if (completed)
420	<	stat = setCompletion(NORMAL);
322	<	else
323	<	stat = doJoin();
419	>	} finally {
420	>	lock.unlock();
421		}
422	<	return stat;
422	>	return setCompletion(EXCEPTIONAL);
423		}
424
425		/**
426	<	* Returns result or throws exception associated with given status.
330	<	* @param s the status
426	>	* Removes exception node and clears status
427		*/
428	<	private V reportResult(int s) {
428	>	private void clearExceptionalCompletion() {
429	>	int h = System.identityHashCode(this);
430	>	final ReentrantLock lock = exceptionTableLock;
431	>	lock.lock();
432	>	try {
433	>	ExceptionNode[] t = exceptionTable;
434	>	int i = h & (t.length - 1);
435	>	ExceptionNode e = t[i];
436	>	ExceptionNode pred = null;
437	>	while (e != null) {
438	>	ExceptionNode next = e.next;
439	>	if (e.get() == this) {
440	>	if (pred == null)
441	>	t[i] = next;
442	>	else
443	>	pred.next = next;
444	>	break;
445	>	}
446	>	pred = e;
447	>	e = next;
448	>	}
449	>	expungeStaleExceptions();
450	>	status = 0;
451	>	} finally {
452	>	lock.unlock();
453	>	}
454	>	}
455	>
456	>	/**
457	>	* Returns a rethrowable exception for the given task, if
458	>	* available. To provide accurate stack traces, if the exception
459	>	* was not thrown by the current thread, we try to create a new
460	>	* exception of the same type as the one thrown, but with the
461	>	* recorded exception as its cause. If there is no such
462	>	* constructor, we instead try to use a no-arg constructor,
463	>	* followed by initCause, to the same effect. If none of these
464	>	* apply, or any fail due to other exceptions, we return the
465	>	* recorded exception, which is still correct, although it may
466	>	* contain a misleading stack trace.
467	>	*
468	>	* @return the exception, or null if none
469	>	*/
470	>	private Throwable getThrowableException() {
471	>	if (status != EXCEPTIONAL)
472	>	return null;
473	>	int h = System.identityHashCode(this);
474	>	ExceptionNode e;
475	>	final ReentrantLock lock = exceptionTableLock;
476	>	lock.lock();
477	>	try {
478	>	expungeStaleExceptions();
479	>	ExceptionNode[] t = exceptionTable;
480	>	e = t[h & (t.length - 1)];
481	>	while (e != null && e.get() != this)
482	>	e = e.next;
483	>	} finally {
484	>	lock.unlock();
485	>	}
486		Throwable ex;
487	<	if (s < NORMAL && (ex = getException()) != null)
487	>	if (e == null || (ex = e.ex) == null)
488	>	return null;
489	>	if (e.thrower != Thread.currentThread().getId()) {
490	>	Class<? extends Throwable> ec = ex.getClass();
491	>	try {
492	>	Constructor<?> noArgCtor = null;
493	>	Constructor<?>[] cs = ec.getConstructors();// public ctors only
494	>	for (int i = 0; i < cs.length; ++i) {
495	>	Constructor<?> c = cs[i];
496	>	Class<?>[] ps = c.getParameterTypes();
497	>	if (ps.length == 0)
498	>	noArgCtor = c;
499	>	else if (ps.length == 1 && ps[0] == Throwable.class)
500	>	return (Throwable)(c.newInstance(ex));
501	>	}
502	>	if (noArgCtor != null) {
503	>	Throwable wx = (Throwable)(noArgCtor.newInstance());
504	>	wx.initCause(ex);
505	>	return wx;
506	>	}
507	>	} catch (Exception ignore) {
508	>	}
509	>	}
510	>	return ex;
511	>	}
512	>
513	>	/**
514	>	* Poll stale refs and remove them. Call only while holding lock.
515	>	*/
516	>	private static void expungeStaleExceptions() {
517	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
518	>	if (x instanceof ExceptionNode) {
519	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
520	>	ExceptionNode[] t = exceptionTable;
521	>	int i = System.identityHashCode(key) & (t.length - 1);
522	>	ExceptionNode e = t[i];
523	>	ExceptionNode pred = null;
524	>	while (e != null) {
525	>	ExceptionNode next = e.next;
526	>	if (e == x) {
527	>	if (pred == null)
528	>	t[i] = next;
529	>	else
530	>	pred.next = next;
531	>	break;
532	>	}
533	>	pred = e;
534	>	e = next;
535	>	}
536	>	}
537	>	}
538	>	}
539	>
540	>	/**
541	>	* If lock is available, poll stale refs and remove them.
542	>	* Called from ForkJoinPool when pools become quiescent.
543	>	*/
544	>	static final void helpExpungeStaleExceptions() {
545	>	final ReentrantLock lock = exceptionTableLock;
546	>	if (lock.tryLock()) {
547	>	try {
548	>	expungeStaleExceptions();
549	>	} finally {
550	>	lock.unlock();
551	>	}
552	>	}
553	>	}
554	>
555	>	/**
556	>	* Report the result of invoke or join; called only upon
557	>	* non-normal return of internal versions.
558	>	*/
559	>	private V reportResult() {
560	>	int s; Throwable ex;
561	>	if ((s = status) == CANCELLED)
562	>	throw new CancellationException();
563	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
564		UNSAFE.throwException(ex);
565		return getRawResult();
566		}
#	Line 349 | Line 578 | public abstract class ForkJoinTask<V> im
578		* #isDone} returning {@code true}.
579		*
580		* <p>This method may be invoked only from within {@code
581	<	* ForkJoinTask} computations (as may be determined using method
581	>	* ForkJoinPool} computations (as may be determined using method
582		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
583		* result in exceptions or errors, possibly including {@code
584		* ClassCastException}.
#	Line 363 | Line 592 | public abstract class ForkJoinTask<V> im
592		}
593
594		/**
595	<	* Returns the result of the computation when it {@link #isDone is done}.
596	<	* This method differs from {@link #get()} in that
595	>	* Returns the result of the computation when it {@link #isDone is
596	>	* done}.  This method differs from {@link #get()} in that
597		* abnormal completion results in {@code RuntimeException} or
598	<	* {@code Error}, not {@code ExecutionException}.
598	>	* {@code Error}, not {@code ExecutionException}, and that
599	>	* interrupts of the calling thread do <em>not</em> cause the
600	>	* method to abruptly return by throwing {@code
601	>	* InterruptedException}.
602		*
603		* @return the computed result
604		*/
605		public final V join() {
606	<	return reportResult(doJoin());
606	>	if (doJoin() != NORMAL)
607	>	return reportResult();
608	>	else
609	>	return getRawResult();
610		}
611
612		/**
613		* Commences performing this task, awaits its completion if
614	<	* necessary, and return its result, or throws an (unchecked)
615	<	* exception if the underlying computation did so.
614	>	* necessary, and returns its result, or throws an (unchecked)
615	>	* {@code RuntimeException} or {@code Error} if the underlying
616	>	* computation did so.
617		*
618		* @return the computed result
619		*/
620		public final V invoke() {
621	<	return reportResult(doInvoke());
621	>	if (doInvoke() != NORMAL)
622	>	return reportResult();
623	>	else
624	>	return getRawResult();
625		}
626
627		/**
628		* Forks the given tasks, returning when {@code isDone} holds for
629		* each task or an (unchecked) exception is encountered, in which
630	<	* case the exception is rethrown.  If either task encounters an
631	<	* exception, the other one may be, but is not guaranteed to be,
632	<	* cancelled.  If both tasks throw an exception, then this method
633	<	* throws one of them.  The individual status of each task may be
634	<	* checked using {@link #getException()} and related methods.
630	>	* case the exception is rethrown. If more than one task
631	>	* encounters an exception, then this method throws any one of
632	>	* these exceptions. If any task encounters an exception, the
633	>	* other may be cancelled. However, the execution status of
634	>	* individual tasks is not guaranteed upon exceptional return. The
635	>	* status of each task may be obtained using {@link
636	>	* #getException()} and related methods to check if they have been
637	>	* cancelled, completed normally or exceptionally, or left
638	>	* unprocessed.
639		*
640		* <p>This method may be invoked only from within {@code
641	<	* ForkJoinTask} computations (as may be determined using method
641	>	* ForkJoinPool} computations (as may be determined using method
642		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
643		* result in exceptions or errors, possibly including {@code
644		* ClassCastException}.
#	Line 413 | Line 656 | public abstract class ForkJoinTask<V> im
656		/**
657		* Forks the given tasks, returning when {@code isDone} holds for
658		* each task or an (unchecked) exception is encountered, in which
659	<	* case the exception is rethrown. If any task encounters an
660	<	* exception, others may be, but are not guaranteed to be,
661	<	* cancelled.  If more than one task encounters an exception, then
662	<	* this method throws any one of these exceptions.  The individual
663	<	* status of each task may be checked using {@link #getException()}
664	<	* and related methods.
659	>	* case the exception is rethrown. If more than one task
660	>	* encounters an exception, then this method throws any one of
661	>	* these exceptions. If any task encounters an exception, others
662	>	* may be cancelled. However, the execution status of individual
663	>	* tasks is not guaranteed upon exceptional return. The status of
664	>	* each task may be obtained using {@link #getException()} and
665	>	* related methods to check if they have been cancelled, completed
666	>	* normally or exceptionally, or left unprocessed.
667		*
668		* <p>This method may be invoked only from within {@code
669	<	* ForkJoinTask} computations (as may be determined using method
669	>	* ForkJoinPool} computations (as may be determined using method
670		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
671		* result in exceptions or errors, possibly including {@code
672		* ClassCastException}.
#	Line 459 | Line 704 | public abstract class ForkJoinTask<V> im
704		/**
705		* Forks all tasks in the specified collection, returning when
706		* {@code isDone} holds for each task or an (unchecked) exception
707	<	* is encountered.  If any task encounters an exception, others
708	<	* may be, but are not guaranteed to be, cancelled.  If more than
709	<	* one task encounters an exception, then this method throws any
710	<	* one of these exceptions.  The individual status of each task
711	<	* may be checked using {@link #getException()} and related
712	<	* methods.  The behavior of this operation is undefined if the
713	<	* specified collection is modified while the operation is in
714	<	* progress.
707	>	* is encountered, in which case the exception is rethrown. If
708	>	* more than one task encounters an exception, then this method
709	>	* throws any one of these exceptions. If any task encounters an
710	>	* exception, others may be cancelled. However, the execution
711	>	* status of individual tasks is not guaranteed upon exceptional
712	>	* return. The status of each task may be obtained using {@link
713	>	* #getException()} and related methods to check if they have been
714	>	* cancelled, completed normally or exceptionally, or left
715	>	* unprocessed.
716		*
717		* <p>This method may be invoked only from within {@code
718	<	* ForkJoinTask} computations (as may be determined using method
718	>	* ForkJoinPool} computations (as may be determined using method
719		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
720		* result in exceptions or errors, possibly including {@code
721		* ClassCastException}.
#	Line 515 | Line 761 | public abstract class ForkJoinTask<V> im
761
762		/**
763		* Attempts to cancel execution of this task. This attempt will
764	<	* fail if the task has already completed, has already been
765	<	* cancelled, or could not be cancelled for some other reason. If
766	<	* successful, and this task has not started when cancel is
767	<	* called, execution of this task is suppressed, {@link
768	<	* #isCancelled} will report true, and {@link #join} will result
769	<	* in a {@code CancellationException} being thrown.
764	>	* fail if the task has already completed or could not be
765	>	* cancelled for some other reason. If successful, and this task
766	>	* has not started when {@code cancel} is called, execution of
767	>	* this task is suppressed. After this method returns
768	>	* successfully, unless there is an intervening call to {@link
769	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
770	>	* {@link #isDone}, and {@code cancel} will return {@code true}
771	>	* and calls to {@link #join} and related methods will result in
772	>	* {@code CancellationException}.
773		*
774		* <p>This method may be overridden in subclasses, but if so, must
775	<	* still ensure that these minimal properties hold. In particular,
776	<	* the {@code cancel} method itself must not throw exceptions.
775	>	* still ensure that these properties hold. In particular, the
776	>	* {@code cancel} method itself must not throw exceptions.
777		*
778		* <p>This method is designed to be invoked by <em>other</em>
779		* tasks. To terminate the current task, you can just return or
780		* throw an unchecked exception from its computation method, or
781		* invoke {@link #completeExceptionally}.
782		*
783	<	* @param mayInterruptIfRunning this value is ignored in the
784	<	* default implementation because tasks are not
785	<	* cancelled via interruption
783	>	* @param mayInterruptIfRunning this value has no effect in the
784	>	* default implementation because interrupts are not used to
785	>	* control cancellation.
786		*
787		* @return {@code true} if this task is now cancelled
788		*/
789		public boolean cancel(boolean mayInterruptIfRunning) {
790	<	setCompletion(CANCELLED);
542	<	return status == CANCELLED;
790	>	return setCompletion(CANCELLED) == CANCELLED;
791		}
792
793		/**
794	<	* Cancels, ignoring any exceptions it throws. Used during worker
795	<	* and pool shutdown.
794	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
795	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
796	>	* exceptions, but if it does anyway, we have no recourse during
797	>	* shutdown, so guard against this case.
798		*/
799		final void cancelIgnoringExceptions() {
800		try {
#	Line 553 | Line 803 | public abstract class ForkJoinTask<V> im
803		}
804		}
805
556	–	/**
557	–	* Cancels ignoring exceptions if worker is terminating
558	–	*/
559	–	private void cancelIfTerminating() {
560	–	Thread t = Thread.currentThread();
561	–	if ((t instanceof ForkJoinWorkerThread) &&
562	–	((ForkJoinWorkerThread) t).isTerminating()) {
563	–	try {
564	–	cancel(false);
565	–	} catch (Throwable ignore) {
566	–	}
567	–	}
568	–	}
569	–
806		public final boolean isDone() {
807		return status < 0;
808		}
#	Line 606 | Line 842 | public abstract class ForkJoinTask<V> im
842		int s = status;
843		return ((s >= NORMAL)    ? null :
844		(s == CANCELLED) ? new CancellationException() :
845	<	exceptionMap.get(this));
845	>	getThrowableException());
846		}
847
848		/**
#	Line 631 | Line 867 | public abstract class ForkJoinTask<V> im
867
868		/**
869		* Completes this task, and if not already aborted or cancelled,
870	<	* returning a {@code null} result upon {@code join} and related
871	<	* operations. This method may be used to provide results for
872	<	* asynchronous tasks, or to provide alternative handling for
873	<	* tasks that would not otherwise complete normally. Its use in
874	<	* other situations is discouraged. This method is
875	<	* overridable, but overridden versions must invoke {@code super}
876	<	* implementation to maintain guarantees.
870	>	* returning the given value as the result of subsequent
871	>	* invocations of {@code join} and related operations. This method
872	>	* may be used to provide results for asynchronous tasks, or to
873	>	* provide alternative handling for tasks that would not otherwise
874	>	* complete normally. Its use in other situations is
875	>	* discouraged. This method is overridable, but overridden
876	>	* versions must invoke {@code super} implementation to maintain
877	>	* guarantees.
878		*
879		* @param value the result value for this task
880		*/
#	Line 651 | Line 888 | public abstract class ForkJoinTask<V> im
888		setCompletion(NORMAL);
889		}
890
891	+	/**
892	+	* Waits if necessary for the computation to complete, and then
893	+	* retrieves its result.
894	+	*
895	+	* @return the computed result
896	+	* @throws CancellationException if the computation was cancelled
897	+	* @throws ExecutionException if the computation threw an
898	+	* exception
899	+	* @throws InterruptedException if the current thread is not a
900	+	* member of a ForkJoinPool and was interrupted while waiting
901	+	*/
902		public final V get() throws InterruptedException, ExecutionException {
903	<	int s = doJoin();
904	<	if (Thread.interrupted())
905	<	throw new InterruptedException();
906	<	if (s < NORMAL) {
907	<	Throwable ex;
908	<	if (s == CANCELLED)
909	<	throw new CancellationException();
662	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
663	<	throw new ExecutionException(ex);
664	<	}
903	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
904	>	doJoin() : externalInterruptibleAwaitDone(0L);
905	>	Throwable ex;
906	>	if (s == CANCELLED)
907	>	throw new CancellationException();
908	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
909	>	throw new ExecutionException(ex);
910		return getRawResult();
911		}
912
913	+	/**
914	+	* Waits if necessary for at most the given time for the computation
915	+	* to complete, and then retrieves its result, if available.
916	+	*
917	+	* @param timeout the maximum time to wait
918	+	* @param unit the time unit of the timeout argument
919	+	* @return the computed result
920	+	* @throws CancellationException if the computation was cancelled
921	+	* @throws ExecutionException if the computation threw an
922	+	* exception
923	+	* @throws InterruptedException if the current thread is not a
924	+	* member of a ForkJoinPool and was interrupted while waiting
925	+	* @throws TimeoutException if the wait timed out
926	+	*/
927		public final V get(long timeout, TimeUnit unit)
928		throws InterruptedException, ExecutionException, TimeoutException {
929		Thread t = Thread.currentThread();
671	–	ForkJoinPool pool;
930		if (t instanceof ForkJoinWorkerThread) {
931		ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
932	<	if (status >= 0 && w.unpushTask(this))
933	<	tryExec();
934	<	pool = w.pool;
935	<	}
936	<	else
937	<	pool = null;
938	<	/*
939	<	* Timed wait loop intermixes cases for fj (pool != null) and
682	<	* non FJ threads. For FJ, decrement pool count but don't try
683	<	* for replacement; increment count on completion. For non-FJ,
684	<	* deal with interrupts. This is messy, but a little less so
685	<	* than is splitting the FJ and nonFJ cases.
686	<	*/
687	<	boolean interrupted = false;
688	<	boolean dec = false; // true if pool count decremented
689	<	for (;;) {
690	<	if (Thread.interrupted() && pool == null) {
691	<	interrupted = true;
692	<	break;
693	<	}
694	<	int s = status;
695	<	if (s < 0)
696	<	break;
697	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
698	<	s, s | SIGNAL)) {
699	<	long startTime = System.nanoTime();
700	<	long nanos = unit.toNanos(timeout);
701	<	long nt; // wait time
702	<	while (status >= 0 &&
703	<	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
704	<	if (pool != null && !dec)
705	<	dec = pool.tryDecrementRunningCount();
706	<	else {
707	<	long ms = nt / 1000000;
708	<	int ns = (int) (nt % 1000000);
709	<	try {
710	<	synchronized(this) {
711	<	if (status >= 0)
712	<	wait(ms, ns);
713	<	}
714	<	} catch (InterruptedException ie) {
715	<	if (pool != null)
716	<	cancelIfTerminating();
717	<	else {
718	<	interrupted = true;
719	<	break;
720	<	}
721	<	}
932	>	long nanos = unit.toNanos(timeout);
933	>	if (status >= 0) {
934	>	boolean completed = false;
935	>	if (w.unpushTask(this)) {
936	>	try {
937	>	completed = exec();
938	>	} catch (Throwable rex) {
939	>	setExceptionalCompletion(rex);
940		}
941		}
942	<	break;
942	>	if (completed)
943	>	setCompletion(NORMAL);
944	>	else if (status >= 0 && nanos > 0)
945	>	w.pool.timedAwaitJoin(this, nanos);
946		}
947		}
948	<	if (pool != null && dec)
949	<	pool.incrementRunningCount();
950	<	if (interrupted)
951	<	throw new InterruptedException();
952	<	int es = status;
953	<	if (es != NORMAL) {
948	>	else {
949	>	long millis = unit.toMillis(timeout);
950	>	if (millis > 0)
951	>	externalInterruptibleAwaitDone(millis);
952	>	}
953	>	int s = status;
954	>	if (s != NORMAL) {
955		Throwable ex;
956	<	if (es == CANCELLED)
956	>	if (s == CANCELLED)
957		throw new CancellationException();
958	<	if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
958	>	if (s != EXCEPTIONAL)
959	>	throw new TimeoutException();
960	>	if ((ex = getThrowableException()) != null)
961		throw new ExecutionException(ex);
738	–	throw new TimeoutException();
962		}
963		return getRawResult();
964		}
965
966		/**
967	<	* Joins this task, without returning its result or throwing an
967	>	* Joins this task, without returning its result or throwing its
968		* exception. This method may be useful when processing
969		* collections of tasks when some have been cancelled or otherwise
970		* known to have aborted.
#	Line 752 | Line 975 | public abstract class ForkJoinTask<V> im
975
976		/**
977		* Commences performing this task and awaits its completion if
978	<	* necessary, without returning its result or throwing an
979	<	* exception. This method may be useful when processing
757	<	* collections of tasks when some have been cancelled or otherwise
758	<	* known to have aborted.
978	>	* necessary, without returning its result or throwing its
979	>	* exception.
980		*/
981		public final void quietlyInvoke() {
982		doInvoke();
#	Line 769 | Line 990 | public abstract class ForkJoinTask<V> im
990		* processed.
991		*
992		* <p>This method may be invoked only from within {@code
993	<	* ForkJoinTask} computations (as may be determined using method
993	>	* ForkJoinPool} computations (as may be determined using method
994		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
995		* result in exceptions or errors, possibly including {@code
996		* ClassCastException}.
#	Line 788 | Line 1009 | public abstract class ForkJoinTask<V> im
1009		* under any other usage conditions are not guaranteed.
1010		* This method may be useful when executing
1011		* pre-constructed trees of subtasks in loops.
1012	+	*
1013	+	* <p>Upon completion of this method, {@code isDone()} reports
1014	+	* {@code false}, and {@code getException()} reports {@code
1015	+	* null}. However, the value returned by {@code getRawResult} is
1016	+	* unaffected. To clear this value, you can invoke {@code
1017	+	* setRawResult(null)}.
1018		*/
1019		public void reinitialize() {
1020		if (status == EXCEPTIONAL)
1021	<	exceptionMap.remove(this);
1022	<	status = 0;
1021	>	clearExceptionalCompletion();
1022	>	else
1023	>	status = 0;
1024		}
1025
1026		/**
#	Line 809 | Line 1037 | public abstract class ForkJoinTask<V> im
1037		}
1038
1039		/**
1040	<	* Returns {@code true} if the current thread is executing as a
1041	<	* ForkJoinPool computation.
1040	>	* Returns {@code true} if the current thread is a {@link
1041	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1042		*
1043	<	* @return {@code true} if the current thread is executing as a
1044	<	* ForkJoinPool computation, or false otherwise
1043	>	* @return {@code true} if the current thread is a {@link
1044	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1045	>	* or {@code false} otherwise
1046		*/
1047		public static boolean inForkJoinPool() {
1048		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 828 | Line 1057 | public abstract class ForkJoinTask<V> im
1057		* were not, stolen.
1058		*
1059		* <p>This method may be invoked only from within {@code
1060	<	* ForkJoinTask} computations (as may be determined using method
1060	>	* ForkJoinPool} computations (as may be determined using method
1061		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1062		* result in exceptions or errors, possibly including {@code
1063		* ClassCastException}.
#	Line 847 | Line 1076 | public abstract class ForkJoinTask<V> im
1076		* fork other tasks.
1077		*
1078		* <p>This method may be invoked only from within {@code
1079	<	* ForkJoinTask} computations (as may be determined using method
1079	>	* ForkJoinPool} computations (as may be determined using method
1080		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1081		* result in exceptions or errors, possibly including {@code
1082		* ClassCastException}.
#	Line 870 | Line 1099 | public abstract class ForkJoinTask<V> im
1099		* exceeded.
1100		*
1101		* <p>This method may be invoked only from within {@code
1102	<	* ForkJoinTask} computations (as may be determined using method
1102	>	* ForkJoinPool} computations (as may be determined using method
1103		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1104		* result in exceptions or errors, possibly including {@code
1105		* ClassCastException}.
#	Line 928 | Line 1157 | public abstract class ForkJoinTask<V> im
1157		* otherwise.
1158		*
1159		* <p>This method may be invoked only from within {@code
1160	<	* ForkJoinTask} computations (as may be determined using method
1160	>	* ForkJoinPool} computations (as may be determined using method
1161		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1162		* result in exceptions or errors, possibly including {@code
1163		* ClassCastException}.
#	Line 947 | Line 1176 | public abstract class ForkJoinTask<V> im
1176		* be useful otherwise.
1177		*
1178		* <p>This method may be invoked only from within {@code
1179	<	* ForkJoinTask} computations (as may be determined using method
1179	>	* ForkJoinPool} computations (as may be determined using method
1180		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1181		* result in exceptions or errors, possibly including {@code
1182		* ClassCastException}.
#	Line 970 | Line 1199 | public abstract class ForkJoinTask<V> im
1199		* otherwise.
1200		*
1201		* <p>This method may be invoked only from within {@code
1202	<	* ForkJoinTask} computations (as may be determined using method
1202	>	* ForkJoinPool} computations (as may be determined using method
1203		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1204		* result in exceptions or errors, possibly including {@code
1205		* ClassCastException}.
#	Line 1080 | Line 1309 | public abstract class ForkJoinTask<V> im
1309		private static final long serialVersionUID = -7721805057305804111L;
1310
1311		/**
1312	<	* Saves the state to a stream.
1312	>	* Saves the state to a stream (that is, serializes it).
1313		*
1314		* @serialData the current run status and the exception thrown
1315		* during execution, or {@code null} if none
#	Line 1093 | Line 1322 | public abstract class ForkJoinTask<V> im
1322		}
1323
1324		/**
1325	<	* Reconstitutes the instance from a stream.
1325	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1326		*
1327		* @param s the stream
1328		*/
#	Line 1102 | Line 1331 | public abstract class ForkJoinTask<V> im
1331		s.defaultReadObject();
1332		Object ex = s.readObject();
1333		if (ex != null)
1334	<	setExceptionalCompletion((Throwable) ex);
1106	<	if (status < 0)
1107	<	synchronized (this) { notifyAll(); }
1334	>	setExceptionalCompletion((Throwable)ex);
1335		}
1336
1337		// Unsafe mechanics
1338	<
1339	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1340	<	private static final long statusOffset =
1341	<	objectFieldOffset("status", ForkJoinTask.class);
1342	<
1343	<	private static long objectFieldOffset(String field, Class<?> klazz) {
1338	>	private static final sun.misc.Unsafe UNSAFE;
1339	>	private static final long statusOffset;
1340	>	static {
1341	>	exceptionTableLock = new ReentrantLock();
1342	>	exceptionTableRefQueue = new ReferenceQueue<Object>();
1343	>	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1344		try {
1345	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1346	<	} catch (NoSuchFieldException e) {
1347	<	// Convert Exception to corresponding Error
1348	<	NoSuchFieldError error = new NoSuchFieldError(field);
1349	<	error.initCause(e);
1123	<	throw error;
1345	>	UNSAFE = getUnsafe();
1346	>	statusOffset = UNSAFE.objectFieldOffset
1347	>	(ForkJoinTask.class.getDeclaredField("status"));
1348	>	} catch (Exception e) {
1349	>	throw new Error(e);
1350		}
1351		}
1352

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