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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.70 by dl, Tue Nov 23 00:10:39 2010 UTC vs.
Revision 1.89 by dl, Mon Apr 9 13:11:44 2012 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.io.Serializable;
10		import java.util.Collection;
11	–	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;
19	–	import java.util.concurrent.Executor;
20	–	import java.util.concurrent.ExecutorService;
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 44 | Line 43 | import java.util.concurrent.TimeoutExcep
43		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
44		* The efficiency of {@code ForkJoinTask}s stems from a set of
45		* restrictions (that are only partially statically enforceable)
46	<	* reflecting their intended use as computational tasks calculating
47	<	* pure functions or operating on purely isolated objects.  The
48	<	* primary coordination mechanisms are {@link #fork}, that arranges
46	>	* reflecting their main use as computational tasks calculating pure
47	>	* functions or operating on purely isolated objects.  The primary
48	>	* coordination mechanisms are {@link #fork}, that arranges
49		* asynchronous execution, and {@link #join}, that doesn't proceed
50		* until the task's result has been computed.  Computations should
51	<	* avoid {@code synchronized} methods or blocks, and should minimize
52	<	* other blocking synchronization apart from joining other tasks or
53	<	* using synchronizers such as Phasers that are advertised to
54	<	* cooperate with fork/join scheduling. Tasks should also not perform
55	<	* blocking IO, and should ideally access variables that are
56	<	* completely independent of those accessed by other running
57	<	* tasks. Minor breaches of these restrictions, for example using
58	<	* shared output streams, may be tolerable in practice, but frequent
59	<	* use may result in poor performance, and the potential to
60	<	* indefinitely stall if the number of threads not waiting for IO or
61	<	* other external synchronization becomes exhausted. This usage
62	<	* restriction is in part enforced by not permitting checked
63	<	* exceptions such as {@code IOExceptions} to be thrown. However,
64	<	* computations may still encounter unchecked exceptions, that are
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.
51	>	* ideally avoid {@code synchronized} methods or blocks, and should
52	>	* minimize other blocking synchronization apart from joining other
53	>	* tasks or using synchronizers such as Phasers that are advertised to
54	>	* cooperate with fork/join scheduling. Subdividable tasks should also
55	>	* not perform blocking IO, and should ideally access variables that
56	>	* are completely independent of those accessed by other running
57	>	* tasks. These guidelines are loosely enforced by not permitting
58	>	* checked exceptions such as {@code IOExceptions} to be
59	>	* thrown. However, computations may still encounter unchecked
60	>	* exceptions, that are rethrown to callers attempting to join
61	>	* them. These exceptions may additionally include {@link
62	>	* RejectedExecutionException} stemming from internal resource
63	>	* exhaustion, such as failure to allocate internal task
64	>	* queues. Rethrown exceptions behave in the same way as regular
65	>	* exceptions, but, when possible, contain stack traces (as displayed
66	>	* for example using {@code ex.printStackTrace()}) of both the thread
67	>	* that initiated the computation as well as the thread actually
68	>	* encountering the exception; minimally only the latter.
69	>	*
70	>	* <p>It is possible to define and use ForkJoinTasks that may block,
71	>	* but doing do requires three further considerations: (1) Completion
72	>	* of few if any <em>other</em> tasks should be dependent on a task
73	>	* that blocks on external synchronization or IO. Event-style async
74	>	* tasks that are never joined often fall into this category.  (2) To
75	>	* minimize resource impact, tasks should be small; ideally performing
76	>	* only the (possibly) blocking action. (3) Unless the {@link
77	>	* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
78	>	* blocked tasks is known to be less than the pool's {@link
79	>	* ForkJoinPool#getParallelism} level, the pool cannot guarantee that
80	>	* enough threads will be available to ensure progress or good
81	>	* performance.
82		*
83		* <p>The primary method for awaiting completion and extracting
84		* results of a task is {@link #join}, but there are several variants:
#	Line 82 | Line 94 | import java.util.concurrent.TimeoutExcep
94		* performs the most common form of parallel invocation: forking a set
95		* of tasks and joining them all.
96		*
97	+	* <p>In the most typical usages, a fork-join pair act like a call
98	+	* (fork) and return (join) from a parallel recursive function. As is
99	+	* the case with other forms of recursive calls, returns (joins)
100	+	* should be performed innermost-first. For example, {@code a.fork();
101	+	* b.fork(); b.join(); a.join();} is likely to be substantially more
102	+	* efficient than joining {@code a} before {@code b}.
103	+	*
104		* <p>The execution status of tasks may be queried at several levels
105		* of detail: {@link #isDone} is true if a task completed in any way
106		* (including the case where a task was cancelled without executing);
#	Line 97 | Line 116 | import java.util.concurrent.TimeoutExcep
116		* <p>The ForkJoinTask class is not usually directly subclassed.
117		* Instead, you subclass one of the abstract classes that support a
118		* particular style of fork/join processing, typically {@link
119	<	* RecursiveAction} for computations that do not return results, or
120	<	* {@link RecursiveTask} for those that do.  Normally, a concrete
121	<	* ForkJoinTask subclass declares fields comprising its parameters,
122	<	* established in a constructor, and then defines a {@code compute}
123	<	* method that somehow uses the control methods supplied by this base
124	<	* class. While these methods have {@code public} access (to allow
125	<	* instances of different task subclasses to call each other's
126	<	* methods), some of them may only be called from within other
127	<	* ForkJoinTasks (as may be determined using method {@link
128	<	* #inForkJoinPool}).  Attempts to invoke them in other contexts
129	<	* result in exceptions or errors, possibly including
130	<	* {@code ClassCastException}.
119	>	* RecursiveAction} for most computations that do not return results,
120	>	* {@link RecursiveTask} for those that do, and {@link
121	>	* CountedCompleter} for those in which completed actions trigger
122	>	* other actions.  Normally, a concrete ForkJoinTask subclass declares
123	>	* fields comprising its parameters, established in a constructor, and
124	>	* then defines a {@code compute} method that somehow uses the control
125	>	* methods supplied by this base class. While these methods have
126	>	* {@code public} access (to allow instances of different task
127	>	* subclasses to call each other's methods), some of them may only be
128	>	* called from within other ForkJoinTasks (as may be determined using
129	>	* method {@link #inForkJoinPool}).  Attempts to invoke them in other
130	>	* contexts result in exceptions or errors, possibly including {@code
131	>	* ClassCastException}.
132		*
133		* <p>Method {@link #join} and its variants are appropriate for use
134		* only when completion dependencies are acyclic; that is, the
#	Line 118 | Line 138 | import java.util.concurrent.TimeoutExcep
138		* supports other methods and techniques (for example the use of
139		* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
140		* may be of use in constructing custom subclasses for problems that
141	<	* are not statically structured as DAGs.
141	>	* are not statically structured as DAGs. To support such usages a
142	>	* ForkJoinTask may be atomically <em>tagged</em> with a {@code
143	>	* short} value using {@link #setForkJoinTaskTag} or {@link
144	>	* #compareAndSetForkJoinTaskTag} and checked using {@link
145	>	* #getForkJoinTaskTag}. The ForkJoinTask implementation does not
146	>	* use these {@code protected} methods or tags for any purpose, but
147	>	* they may be of use in the construction of specialized subclasses.
148	>	* For example, parallel graph traversals can use the supplied methods
149	>	* to avoid revisiting nodes/tasks that have already been processed.
150	>	* Also, completion based designs can use them to record that subtasks
151	>	* have completed. (Method names for tagging are bulky in part to
152	>	* encourage definition of methods that reflect their usage patterns.)
153		*
154		* <p>Most base support methods are {@code final}, to prevent
155		* overriding of implementations that are intrinsically tied to the
#	Line 158 | Line 189 | public abstract class ForkJoinTask<V> im
189		* See the internal documentation of class ForkJoinPool for a
190		* general implementation overview.  ForkJoinTasks are mainly
191		* responsible for maintaining their "status" field amidst relays
192	<	* to methods in ForkJoinWorkerThread and ForkJoinPool. The
193	<	* methods of this class are more-or-less layered into (1) basic
194	<	* status maintenance (2) execution and awaiting completion (3)
195	<	* user-level methods that additionally report results. This is
196	<	* sometimes hard to see because this file orders exported methods
197	<	* in a way that flows well in javadocs. In particular, most
198	<	* join mechanics are in method quietlyJoin, below.
192	>	* to methods in ForkJoinWorkerThread and ForkJoinPool.
193	>	*
194	>	* The methods of this class are more-or-less layered into
195	>	* (1) basic status maintenance
196	>	* (2) execution and awaiting completion
197	>	* (3) user-level methods that additionally report results.
198	>	* This is sometimes hard to see because this file orders exported
199	>	* methods in a way that flows well in javadocs.
200		*/
201
202		/*
203		* The status field holds run control status bits packed into a
204		* single int to minimize footprint and to ensure atomicity (via
205		* CAS).  Status is initially zero, and takes on nonnegative
206	<	* values until completed, upon which status holds value
207	<	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
208	<	* waits by other threads have the SIGNAL bit set.  Completion of
209	<	* a stolen task with SIGNAL set awakens any waiters via
210	<	* notifyAll. Even though suboptimal for some purposes, we use
211	<	* basic builtin wait/notify to take advantage of "monitor
212	<	* inflation" in JVMs that we would otherwise need to emulate to
213	<	* avoid adding further per-task bookkeeping overhead.  We want
214	<	* these monitors to be "fat", i.e., not use biasing or thin-lock
215	<	* techniques, so use some odd coding idioms that tend to avoid
216	<	* them.
206	>	* values until completed, upon which status (anded with
207	>	* DONE_MASK) holds value NORMAL, CANCELLED, or EXCEPTIONAL. Tasks
208	>	* undergoing blocking waits by other threads have the SIGNAL bit
209	>	* set.  Completion of a stolen task with SIGNAL set awakens any
210	>	* waiters via notifyAll. Even though suboptimal for some
211	>	* purposes, we use basic builtin wait/notify to take advantage of
212	>	* "monitor inflation" in JVMs that we would otherwise need to
213	>	* emulate to avoid adding further per-task bookkeeping overhead.
214	>	* We want these monitors to be "fat", i.e., not use biasing or
215	>	* thin-lock techniques, so use some odd coding idioms that tend
216	>	* to avoid them, mainly by arranging that every synchronized
217	>	* block performs a wait, notifyAll or both.
218	>	*
219	>	* These control bits occupy only (some of) the upper half (16
220	>	* bits) of status field. The lower bits are used for user-defined
221	>	* tags.
222		*/
223
224		/** The run status of this task */
225		volatile int status; // accessed directly by pool and workers
226	+	static final int DONE_MASK   = 0xf0000000;  // mask out non-completion bits
227	+	static final int NORMAL      = 0xf0000000;  // must be negative
228	+	static final int CANCELLED   = 0xc0000000;  // must be < NORMAL
229	+	static final int EXCEPTIONAL = 0x80000000;  // must be < CANCELLED
230	+	static final int SIGNAL      = 0x00010000;  // must be >= 1 << 16
231	+	static final int SMASK       = 0x0000ffff;  // short bits for tags
232	+
233	+	/**
234	+	* Marks completion and wakes up threads waiting to join this
235	+	* task.
236	+	*
237	+	* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
238	+	* @return completion status on exit
239	+	*/
240	+	private int setCompletion(int completion) {
241	+	for (int s;;) {
242	+	if ((s = status) < 0)
243	+	return s;
244	+	if (U.compareAndSwapInt(this, STATUS, s, s | completion)) {
245	+	if ((s >>> 16) != 0)
246	+	synchronized (this) { notifyAll(); }
247	+	return completion;
248	+	}
249	+	}
250	+	}
251
252	<	private static final int NORMAL      = -1;
253	<	private static final int CANCELLED   = -2;
254	<	private static final int EXCEPTIONAL = -3;
255	<	private static final int SIGNAL      =  1;
252	>	/**
253	>	* Primary execution method for stolen tasks. Unless done, calls
254	>	* exec and records status if completed, but doesn't wait for
255	>	* completion otherwise.
256	>	*
257	>	* @return status on exit from this method
258	>	*/
259	>	final int doExec() {
260	>	int s; boolean completed;
261	>	if ((s = status) >= 0) {
262	>	try {
263	>	completed = exec();
264	>	} catch (Throwable rex) {
265	>	return setExceptionalCompletion(rex);
266	>	}
267	>	if (completed)
268	>	s = setCompletion(NORMAL);
269	>	}
270	>	return s;
271	>	}
272	>
273	>	/**
274	>	* Tries to set SIGNAL status unless already completed. Used by
275	>	* ForkJoinPool. Other variants are directly incorporated into
276	>	* externalAwaitDone etc.
277	>	*
278	>	* @return true if successful
279	>	*/
280	>	final boolean trySetSignal() {
281	>	int s = status;
282	>	return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL);
283	>	}
284	>
285	>	/**
286	>	* Blocks a non-worker-thread until completion.
287	>	* @return status upon completion
288	>	*/
289	>	private int externalAwaitDone() {
290	>	boolean interrupted = false;
291	>	int s;
292	>	while ((s = status) >= 0) {
293	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
294	>	synchronized (this) {
295	>	if (status >= 0) {
296	>	try {
297	>	wait();
298	>	} catch (InterruptedException ie) {
299	>	interrupted = true;
300	>	}
301	>	}
302	>	else
303	>	notifyAll();
304	>	}
305	>	}
306	>	}
307	>	if (interrupted)
308	>	Thread.currentThread().interrupt();
309	>	return s;
310	>	}
311	>
312	>	/**
313	>	* Blocks a non-worker-thread until completion or interruption.
314	>	*/
315	>	private int externalInterruptibleAwaitDone() throws InterruptedException {
316	>	int s;
317	>	if (Thread.interrupted())
318	>	throw new InterruptedException();
319	>	while ((s = status) >= 0) {
320	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
321	>	synchronized (this) {
322	>	if (status >= 0)
323	>	wait();
324	>	else
325	>	notifyAll();
326	>	}
327	>	}
328	>	}
329	>	return s;
330	>	}
331	>
332	>	/**
333	>	* Implementation for join, get, quietlyJoin. Directly handles
334	>	* only cases of already-completed, external wait, and
335	>	* unfork+exec.  Others are relayed to ForkJoinPool.awaitJoin.
336	>	*
337	>	* @return status upon completion
338	>	*/
339	>	private int doJoin() {
340	>	int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
341	>	if ((s = status) >= 0) {
342	>	if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) {
343	>	if (!(w = (wt = (ForkJoinWorkerThread)t).workQueue).
344	>	tryUnpush(this) || (s = doExec()) >= 0)
345	>	s = wt.pool.awaitJoin(w, this);
346	>	}
347	>	else
348	>	s = externalAwaitDone();
349	>	}
350	>	return s;
351	>	}
352	>
353	>	/**
354	>	* Implementation for invoke, quietlyInvoke.
355	>	*
356	>	* @return status upon completion
357	>	*/
358	>	private int doInvoke() {
359	>	int s; Thread t; ForkJoinWorkerThread wt;
360	>	if ((s = doExec()) >= 0) {
361	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
362	>	s = (wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue,
363	>	this);
364	>	else
365	>	s = externalAwaitDone();
366	>	}
367	>	return s;
368	>	}
369	>
370	>	// Exception table support
371
372		/**
373		* Table of exceptions thrown by tasks, to enable reporting by
#	Line 198 | Line 375 | public abstract class ForkJoinTask<V> im
375		* them with task objects, but instead use a weak ref table.  Note
376		* that cancellation exceptions don't appear in the table, but are
377		* instead recorded as status values.
378	<	* TODO: Use ConcurrentReferenceHashMap
378	>	*
379	>	* Note: These statics are initialized below in static block.
380		*/
381	<	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
382	<	Collections.synchronizedMap
383	<	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
384	<
385	<	// Maintaining completion status
381	>	private static final ExceptionNode[] exceptionTable;
382	>	private static final ReentrantLock exceptionTableLock;
383	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
384	>
385	>	/**
386	>	* Fixed capacity for exceptionTable.
387	>	*/
388	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
389	>
390	>	/**
391	>	* Key-value nodes for exception table.  The chained hash table
392	>	* uses identity comparisons, full locking, and weak references
393	>	* for keys. The table has a fixed capacity because it only
394	>	* maintains task exceptions long enough for joiners to access
395	>	* them, so should never become very large for sustained
396	>	* periods. However, since we do not know when the last joiner
397	>	* completes, we must use weak references and expunge them. We do
398	>	* so on each operation (hence full locking). Also, some thread in
399	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
400	>	* pool becomes isQuiescent.
401	>	*/
402	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> {
403	>	final Throwable ex;
404	>	ExceptionNode next;
405	>	final long thrower;  // use id not ref to avoid weak cycles
406	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
407	>	super(task, exceptionTableRefQueue);
408	>	this.ex = ex;
409	>	this.next = next;
410	>	this.thrower = Thread.currentThread().getId();
411	>	}
412	>	}
413
414		/**
415	<	* Marks completion and wakes up threads waiting to join this task,
211	<	* also clearing signal request bits.
415	>	* Records exception and sets exceptional completion.
416		*
417	<	* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
417	>	* @return status on exit
418		*/
419	<	private void setCompletion(int completion) {
419	>	private int setExceptionalCompletion(Throwable ex) {
420		int s;
421	<	while ((s = status) >= 0) {
422	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
423	<	if (s != 0)
424	<	synchronized (this) { notifyAll(); }
425	<	break;
421	>	if ((s = status) >= 0) {
422	>	int h = System.identityHashCode(this);
423	>	final ReentrantLock lock = exceptionTableLock;
424	>	lock.lock();
425	>	try {
426	>	expungeStaleExceptions();
427	>	ExceptionNode[] t = exceptionTable;
428	>	int i = h & (t.length - 1);
429	>	for (ExceptionNode e = t[i]; ; e = e.next) {
430	>	if (e == null) {
431	>	t[i] = new ExceptionNode(this, ex, t[i]);
432	>	break;
433	>	}
434	>	if (e.get() == this) // already present
435	>	break;
436	>	}
437	>	} finally {
438	>	lock.unlock();
439		}
440	+	s = setCompletion(EXCEPTIONAL);
441		}
442	+	ForkJoinTask<?> p = internalGetCompleter(); // propagate
443	+	if (p != null && p.status >= 0)
444	+	p.setExceptionalCompletion(ex);
445	+	return s;
446		}
447
448		/**
449	<	* Records exception and sets exceptional completion.
228	<	*
229	<	* @return status on exit
449	>	* Exception propagation support for tasks with completers.
450		*/
451	<	private void setExceptionalCompletion(Throwable rex) {
452	<	exceptionMap.put(this, rex);
233	<	setCompletion(EXCEPTIONAL);
451	>	ForkJoinTask<?> internalGetCompleter() {
452	>	return null;
453		}
454
455		/**
456	<	* Blocks a worker thread until completed or timed out.  Called
457	<	* only by pool.
456	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
457	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
458	>	* exceptions, but if it does anyway, we have no recourse during
459	>	* shutdown, so guard against this case.
460		*/
461	<	final void internalAwaitDone(long millis, int nanos) {
462	<	if (status >= 0) {
463	<	try {     // the odd construction reduces lock bias effects
464	<	synchronized (this) {
465	<	if (status > 0 ||
245	<	UNSAFE.compareAndSwapInt(this, statusOffset,
246	<	0, SIGNAL))
247	<	wait(millis, nanos);
248	<	}
249	<	} catch (InterruptedException ie) {
250	<	cancelIfTerminating();
461	>	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
462	>	if (t != null && t.status >= 0) {
463	>	try {
464	>	t.cancel(false);
465	>	} catch (Throwable ignore) {
466		}
467		}
468		}
469
470		/**
471	<	* Blocks a non-worker-thread until completion.
471	>	* Removes exception node and clears status
472		*/
473	<	private void externalAwaitDone() {
474	<	if (status >= 0) {
475	<	boolean interrupted = false;
476	<	synchronized(this) {
477	<	int s;
478	<	while ((s = status) >= 0) {
479	<	if (s == 0 &&
480	<	!UNSAFE.compareAndSwapInt(this, statusOffset,
481	<	0, SIGNAL))
482	<	continue;
483	<	try {
484	<	wait();
485	<	} catch (InterruptedException ie) {
486	<	interrupted = true;
487	<	}
473	>	private void clearExceptionalCompletion() {
474	>	int h = System.identityHashCode(this);
475	>	final ReentrantLock lock = exceptionTableLock;
476	>	lock.lock();
477	>	try {
478	>	ExceptionNode[] t = exceptionTable;
479	>	int i = h & (t.length - 1);
480	>	ExceptionNode e = t[i];
481	>	ExceptionNode pred = null;
482	>	while (e != null) {
483	>	ExceptionNode next = e.next;
484	>	if (e.get() == this) {
485	>	if (pred == null)
486	>	t[i] = next;
487	>	else
488	>	pred.next = next;
489	>	break;
490		}
491	+	pred = e;
492	+	e = next;
493	+	}
494	+	expungeStaleExceptions();
495	+	status = 0;
496	+	} finally {
497	+	lock.unlock();
498	+	}
499	+	}
500	+
501	+	/**
502	+	* Returns a rethrowable exception for the given task, if
503	+	* available. To provide accurate stack traces, if the exception
504	+	* was not thrown by the current thread, we try to create a new
505	+	* exception of the same type as the one thrown, but with the
506	+	* recorded exception as its cause. If there is no such
507	+	* constructor, we instead try to use a no-arg constructor,
508	+	* followed by initCause, to the same effect. If none of these
509	+	* apply, or any fail due to other exceptions, we return the
510	+	* recorded exception, which is still correct, although it may
511	+	* contain a misleading stack trace.
512	+	*
513	+	* @return the exception, or null if none
514	+	*/
515	+	private Throwable getThrowableException() {
516	+	if ((status & DONE_MASK) != EXCEPTIONAL)
517	+	return null;
518	+	int h = System.identityHashCode(this);
519	+	ExceptionNode e;
520	+	final ReentrantLock lock = exceptionTableLock;
521	+	lock.lock();
522	+	try {
523	+	expungeStaleExceptions();
524	+	ExceptionNode[] t = exceptionTable;
525	+	e = t[h & (t.length - 1)];
526	+	while (e != null && e.get() != this)
527	+	e = e.next;
528	+	} finally {
529	+	lock.unlock();
530	+	}
531	+	Throwable ex;
532	+	if (e == null || (ex = e.ex) == null)
533	+	return null;
534	+	if (false && e.thrower != Thread.currentThread().getId()) {
535	+	Class<? extends Throwable> ec = ex.getClass();
536	+	try {
537	+	Constructor<?> noArgCtor = null;
538	+	Constructor<?>[] cs = ec.getConstructors();// public ctors only
539	+	for (int i = 0; i < cs.length; ++i) {
540	+	Constructor<?> c = cs[i];
541	+	Class<?>[] ps = c.getParameterTypes();
542	+	if (ps.length == 0)
543	+	noArgCtor = c;
544	+	else if (ps.length == 1 && ps[0] == Throwable.class)
545	+	return (Throwable)(c.newInstance(ex));
546	+	}
547	+	if (noArgCtor != null) {
548	+	Throwable wx = (Throwable)(noArgCtor.newInstance());
549	+	wx.initCause(ex);
550	+	return wx;
551	+	}
552	+	} catch (Exception ignore) {
553		}
275	–	if (interrupted)
276	–	Thread.currentThread().interrupt();
554		}
555	+	return ex;
556		}
557
558		/**
559	<	* Blocks a non-worker-thread until completion or interruption or timeout
559	>	* Poll stale refs and remove them. Call only while holding lock.
560		*/
561	<	private void externalInterruptibleAwaitDone(boolean timed, long nanos)
562	<	throws InterruptedException {
563	<	if (Thread.interrupted())
564	<	throw new InterruptedException();
565	<	if (status >= 0) {
566	<	long startTime = timed ? System.nanoTime() : 0L;
567	<	synchronized(this) {
568	<	int s;
569	<	while ((s = status) >= 0) {
570	<	long nt;
571	<	if (s == 0 &&
572	<	!UNSAFE.compareAndSwapInt(this, statusOffset,
573	<	0, SIGNAL))
574	<	continue;
575	<	else if (!timed)
298	<	wait();
299	<	else if ((nt = nanos - (System.nanoTime()-startTime)) > 0L)
300	<	wait(nt / 1000000, (int)(nt % 1000000));
301	<	else
561	>	private static void expungeStaleExceptions() {
562	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
563	>	if (x instanceof ExceptionNode) {
564	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
565	>	ExceptionNode[] t = exceptionTable;
566	>	int i = System.identityHashCode(key) & (t.length - 1);
567	>	ExceptionNode e = t[i];
568	>	ExceptionNode pred = null;
569	>	while (e != null) {
570	>	ExceptionNode next = e.next;
571	>	if (e == x) {
572	>	if (pred == null)
573	>	t[i] = next;
574	>	else
575	>	pred.next = next;
576		break;
577	+	}
578	+	pred = e;
579	+	e = next;
580		}
581		}
582		}
583		}
584
585		/**
586	<	* Unless done, calls exec and records status if completed, but
587	<	* doesn't wait for completion otherwise. Primary execution method
311	<	* for ForkJoinWorkerThread.
586	>	* If lock is available, poll stale refs and remove them.
587	>	* Called from ForkJoinPool when pools become quiescent.
588		*/
589	<	final void quietlyExec() {
590	<	try {
591	<	if (status < 0 || !exec())
592	<	return;
593	<	} catch (Throwable rex) {
594	<	setExceptionalCompletion(rex);
595	<	return;
589	>	static final void helpExpungeStaleExceptions() {
590	>	final ReentrantLock lock = exceptionTableLock;
591	>	if (lock.tryLock()) {
592	>	try {
593	>	expungeStaleExceptions();
594	>	} finally {
595	>	lock.unlock();
596	>	}
597		}
598	<	setCompletion(NORMAL); // must be outside try block
598	>	}
599	>
600	>	/**
601	>	* Throws exception, if any, associated with the given status.
602	>	*/
603	>	private void reportException(int s) {
604	>	Throwable ex = ((s == CANCELLED) ?  new CancellationException() :
605	>	(s == EXCEPTIONAL) ? getThrowableException() :
606	>	null);
607	>	if (ex != null)
608	>	U.throwException(ex);
609		}
610
611		// public methods
#	Line 342 | Line 629 | public abstract class ForkJoinTask<V> im
629		* @return {@code this}, to simplify usage
630		*/
631		public final ForkJoinTask<V> fork() {
632	<	((ForkJoinWorkerThread) Thread.currentThread())
346	<	.pushTask(this);
632	>	((ForkJoinWorkerThread)Thread.currentThread()).workQueue.push(this);
633		return this;
634		}
635
#	Line 359 | Line 645 | public abstract class ForkJoinTask<V> im
645		* @return the computed result
646		*/
647		public final V join() {
648	<	quietlyJoin();
649	<	Throwable ex;
650	<	if (status < NORMAL && (ex = getException()) != null)
365	<	UNSAFE.throwException(ex);
648	>	int s;
649	>	if ((s = doJoin() & DONE_MASK) != NORMAL)
650	>	reportException(s);
651		return getRawResult();
652		}
653
#	Line 375 | Line 660 | public abstract class ForkJoinTask<V> im
660		* @return the computed result
661		*/
662		public final V invoke() {
663	<	quietlyInvoke();
664	<	Throwable ex;
665	<	if (status < NORMAL && (ex = getException()) != null)
381	<	UNSAFE.throwException(ex);
663	>	int s;
664	>	if ((s = doInvoke() & DONE_MASK) != NORMAL)
665	>	reportException(s);
666		return getRawResult();
667		}
668
#	Line 406 | Line 690 | public abstract class ForkJoinTask<V> im
690		* @throws NullPointerException if any task is null
691		*/
692		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
693	+	int s1, s2;
694		t2.fork();
695	<	t1.invoke();
696	<	t2.join();
695	>	if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL)
696	>	t1.reportException(s1);
697	>	if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
698	>	t2.reportException(s2);
699		}
700
701		/**
#	Line 443 | Line 730 | public abstract class ForkJoinTask<V> im
730		}
731		else if (i != 0)
732		t.fork();
733	<	else {
734	<	t.quietlyInvoke();
448	<	if (ex == null && t.status < NORMAL)
449	<	ex = t.getException();
450	<	}
733	>	else if (t.doInvoke() < NORMAL && ex == null)
734	>	ex = t.getException();
735		}
736		for (int i = 1; i <= last; ++i) {
737		ForkJoinTask<?> t = tasks[i];
738		if (t != null) {
739		if (ex != null)
740		t.cancel(false);
741	<	else {
742	<	t.quietlyJoin();
459	<	if (ex == null && t.status < NORMAL)
460	<	ex = t.getException();
461	<	}
741	>	else if (t.doJoin() < NORMAL)
742	>	ex = t.getException();
743		}
744		}
745		if (ex != null)
746	<	UNSAFE.throwException(ex);
746	>	U.throwException(ex);
747		}
748
749		/**
#	Line 506 | Line 787 | public abstract class ForkJoinTask<V> im
787		}
788		else if (i != 0)
789		t.fork();
790	<	else {
791	<	t.quietlyInvoke();
511	<	if (ex == null && t.status < NORMAL)
512	<	ex = t.getException();
513	<	}
790	>	else if (t.doInvoke() < NORMAL && ex == null)
791	>	ex = t.getException();
792		}
793		for (int i = 1; i <= last; ++i) {
794		ForkJoinTask<?> t = ts.get(i);
795		if (t != null) {
796		if (ex != null)
797		t.cancel(false);
798	<	else {
799	<	t.quietlyJoin();
522	<	if (ex == null && t.status < NORMAL)
523	<	ex = t.getException();
524	<	}
798	>	else if (t.doJoin() < NORMAL)
799	>	ex = t.getException();
800		}
801		}
802		if (ex != null)
803	<	UNSAFE.throwException(ex);
803	>	U.throwException(ex);
804		return tasks;
805		}
806
#	Line 557 | Line 832 | public abstract class ForkJoinTask<V> im
832		* @return {@code true} if this task is now cancelled
833		*/
834		public boolean cancel(boolean mayInterruptIfRunning) {
835	<	setCompletion(CANCELLED);
561	<	return status == CANCELLED;
562	<	}
563	<
564	<	/**
565	<	* Cancels, ignoring any exceptions thrown by cancel. Used during
566	<	* worker and pool shutdown. Cancel is spec'ed not to throw any
567	<	* exceptions, but if it does anyway, we have no recourse during
568	<	* shutdown, so guard against this case.
569	<	*/
570	<	final void cancelIgnoringExceptions() {
571	<	try {
572	<	cancel(false);
573	<	} catch (Throwable ignore) {
574	<	}
575	<	}
576	<
577	<	/**
578	<	* Cancels if current thread is a terminating worker thread,
579	<	* ignoring any exceptions thrown by cancel.
580	<	*/
581	<	final void cancelIfTerminating() {
582	<	Thread t = Thread.currentThread();
583	<	if ((t instanceof ForkJoinWorkerThread) &&
584	<	((ForkJoinWorkerThread) t).isTerminating()) {
585	<	try {
586	<	cancel(false);
587	<	} catch (Throwable ignore) {
588	<	}
589	<	}
835	>	return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
836		}
837
838		public final boolean isDone() {
#	Line 594 | Line 840 | public abstract class ForkJoinTask<V> im
840		}
841
842		public final boolean isCancelled() {
843	<	return status == CANCELLED;
843	>	return (status & DONE_MASK) == CANCELLED;
844		}
845
846		/**
#	Line 614 | Line 860 | public abstract class ForkJoinTask<V> im
860		* exception and was not cancelled
861		*/
862		public final boolean isCompletedNormally() {
863	<	return status == NORMAL;
863	>	return (status & DONE_MASK) == NORMAL;
864		}
865
866		/**
#	Line 625 | Line 871 | public abstract class ForkJoinTask<V> im
871		* @return the exception, or {@code null} if none
872		*/
873		public final Throwable getException() {
874	<	int s = status;
874	>	int s = status & DONE_MASK;
875		return ((s >= NORMAL)    ? null :
876		(s == CANCELLED) ? new CancellationException() :
877	<	exceptionMap.get(this));
877	>	getThrowableException());
878		}
879
880		/**
#	Line 675 | Line 921 | public abstract class ForkJoinTask<V> im
921		}
922
923		/**
924	+	* Completes this task normally without setting a value. The most
925	+	* recent value established by {@link #setRawResult} (or {@code
926	+	* null} by default) will be returned as the result of subsequent
927	+	* invocations of {@code join} and related operations.
928	+	*
929	+	* @since 1.8
930	+	*/
931	+	public final void quietlyComplete() {
932	+	setCompletion(NORMAL);
933	+	}
934	+
935	+	/**
936		* Waits if necessary for the computation to complete, and then
937		* retrieves its result.
938		*
#	Line 686 | Line 944 | public abstract class ForkJoinTask<V> im
944		* member of a ForkJoinPool and was interrupted while waiting
945		*/
946		public final V get() throws InterruptedException, ExecutionException {
947	<	Thread t = Thread.currentThread();
948	<	if (t instanceof ForkJoinWorkerThread)
949	<	quietlyJoin();
950	<	else
951	<	externalInterruptibleAwaitDone(false, 0L);
952	<	int s = status;
953	<	if (s != NORMAL) {
696	<	Throwable ex;
697	<	if (s == CANCELLED)
698	<	throw new CancellationException();
699	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
700	<	throw new ExecutionException(ex);
701	<	}
947	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
948	>	doJoin() : externalInterruptibleAwaitDone();
949	>	Throwable ex;
950	>	if ((s &= DONE_MASK) == CANCELLED)
951	>	throw new CancellationException();
952	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
953	>	throw new ExecutionException(ex);
954		return getRawResult();
955		}
956
#	Line 718 | Line 970 | public abstract class ForkJoinTask<V> im
970		*/
971		public final V get(long timeout, TimeUnit unit)
972		throws InterruptedException, ExecutionException, TimeoutException {
973	<	long nanos = unit.toNanos(timeout);
974	<	Thread t = Thread.currentThread();
975	<	if (t instanceof ForkJoinWorkerThread)
976	<	((ForkJoinWorkerThread)t).joinTask(this, true, nanos);
977	<	else
978	<	externalInterruptibleAwaitDone(true, nanos);
979	<	int s = status;
980	<	if (s != NORMAL) {
973	>	if (Thread.interrupted())
974	>	throw new InterruptedException();
975	>	// Messy in part because we measure in nanosecs, but wait in millisecs
976	>	int s; long ns, ms;
977	>	if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) {
978	>	long deadline = System.nanoTime() + ns;
979	>	ForkJoinPool p = null;
980	>	ForkJoinPool.WorkQueue w = null;
981	>	Thread t = Thread.currentThread();
982	>	if (t instanceof ForkJoinWorkerThread) {
983	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
984	>	p = wt.pool;
985	>	w = wt.workQueue;
986	>	s = p.helpJoinOnce(w, this); // no retries on failure
987	>	}
988	>	boolean canBlock = false;
989	>	boolean interrupted = false;
990	>	try {
991	>	while ((s = status) >= 0) {
992	>	if (w != null && w.runState < 0)
993	>	cancelIgnoringExceptions(this);
994	>	else if (!canBlock) {
995	>	if (p == null || p.tryCompensate(this, null))
996	>	canBlock = true;
997	>	}
998	>	else {
999	>	if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
1000	>	U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
1001	>	synchronized (this) {
1002	>	if (status >= 0) {
1003	>	try {
1004	>	wait(ms);
1005	>	} catch (InterruptedException ie) {
1006	>	if (p == null)
1007	>	interrupted = true;
1008	>	}
1009	>	}
1010	>	else
1011	>	notifyAll();
1012	>	}
1013	>	}
1014	>	if ((s = status) < 0 || interrupted ||
1015	>	(ns = deadline - System.nanoTime()) <= 0L)
1016	>	break;
1017	>	}
1018	>	}
1019	>	} finally {
1020	>	if (p != null && canBlock)
1021	>	p.incrementActiveCount();
1022	>	}
1023	>	if (interrupted)
1024	>	throw new InterruptedException();
1025	>	}
1026	>	if ((s &= DONE_MASK) != NORMAL) {
1027		Throwable ex;
1028		if (s == CANCELLED)
1029		throw new CancellationException();
1030	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
1030	>	if (s != EXCEPTIONAL)
1031	>	throw new TimeoutException();
1032	>	if ((ex = getThrowableException()) != null)
1033		throw new ExecutionException(ex);
734	–	throw new TimeoutException();
1034		}
1035		return getRawResult();
1036		}
#	Line 743 | Line 1042 | public abstract class ForkJoinTask<V> im
1042		* known to have aborted.
1043		*/
1044		public final void quietlyJoin() {
1045	<	Thread t;
747	<	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
748	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
749	<	if (status >= 0) {
750	<	if (w.unpushTask(this)) {
751	<	boolean completed;
752	<	try {
753	<	completed = exec();
754	<	} catch (Throwable rex) {
755	<	setExceptionalCompletion(rex);
756	<	return;
757	<	}
758	<	if (completed) {
759	<	setCompletion(NORMAL);
760	<	return;
761	<	}
762	<	}
763	<	w.joinTask(this, false, 0L);
764	<	}
765	<	}
766	<	else
767	<	externalAwaitDone();
1045	>	doJoin();
1046		}
1047
1048		/**
#	Line 773 | Line 1051 | public abstract class ForkJoinTask<V> im
1051		* exception.
1052		*/
1053		public final void quietlyInvoke() {
1054	<	if (status >= 0) {
777	<	boolean completed;
778	<	try {
779	<	completed = exec();
780	<	} catch (Throwable rex) {
781	<	setExceptionalCompletion(rex);
782	<	return;
783	<	}
784	<	if (completed)
785	<	setCompletion(NORMAL);
786	<	else
787	<	quietlyJoin();
788	<	}
1054	>	doInvoke();
1055		}
1056
1057		/**
#	Line 802 | Line 1068 | public abstract class ForkJoinTask<V> im
1068		* ClassCastException}.
1069		*/
1070		public static void helpQuiesce() {
1071	<	((ForkJoinWorkerThread) Thread.currentThread())
1072	<	.helpQuiescePool();
1071	>	ForkJoinWorkerThread wt =
1072	>	(ForkJoinWorkerThread)Thread.currentThread();
1073	>	wt.pool.helpQuiescePool(wt.workQueue);
1074		}
1075
1076		/**
#	Line 823 | Line 1090 | public abstract class ForkJoinTask<V> im
1090		* setRawResult(null)}.
1091		*/
1092		public void reinitialize() {
1093	<	if (status == EXCEPTIONAL)
1094	<	exceptionMap.remove(this);
1095	<	status = 0;
1093	>	if ((status & DONE_MASK) == EXCEPTIONAL)
1094	>	clearExceptionalCompletion();
1095	>	else
1096	>	status = 0;
1097		}
1098
1099		/**
#	Line 842 | Line 1110 | public abstract class ForkJoinTask<V> im
1110		}
1111
1112		/**
1113	<	* Returns {@code true} if the current thread is executing as a
1114	<	* ForkJoinPool computation.
1113	>	* Returns {@code true} if the current thread is a {@link
1114	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1115		*
1116	<	* @return {@code true} if the current thread is executing as a
1117	<	* ForkJoinPool computation, or false otherwise
1116	>	* @return {@code true} if the current thread is a {@link
1117	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1118	>	* or {@code false} otherwise
1119		*/
1120		public static boolean inForkJoinPool() {
1121		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 869 | Line 1138 | public abstract class ForkJoinTask<V> im
1138		* @return {@code true} if unforked
1139		*/
1140		public boolean tryUnfork() {
1141	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1142	<	.unpushTask(this);
1141	>	return ((ForkJoinWorkerThread)Thread.currentThread())
1142	>	.workQueue.tryUnpush(this);
1143		}
1144
1145		/**
#	Line 889 | Line 1158 | public abstract class ForkJoinTask<V> im
1158		*/
1159		public static int getQueuedTaskCount() {
1160		return ((ForkJoinWorkerThread) Thread.currentThread())
1161	<	.getQueueSize();
1161	>	.workQueue.queueSize();
1162		}
1163
1164		/**
#	Line 911 | Line 1180 | public abstract class ForkJoinTask<V> im
1180		* @return the surplus number of tasks, which may be negative
1181		*/
1182		public static int getSurplusQueuedTaskCount() {
1183	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1184	<	.getEstimatedSurplusTaskCount();
1183	>	/*
1184	>	* The aim of this method is to return a cheap heuristic guide
1185	>	* for task partitioning when programmers, frameworks, tools,
1186	>	* or languages have little or no idea about task granularity.
1187	>	* In essence by offering this method, we ask users only about
1188	>	* tradeoffs in overhead vs expected throughput and its
1189	>	* variance, rather than how finely to partition tasks.
1190	>	*
1191	>	* In a steady state strict (tree-structured) computation,
1192	>	* each thread makes available for stealing enough tasks for
1193	>	* other threads to remain active. Inductively, if all threads
1194	>	* play by the same rules, each thread should make available
1195	>	* only a constant number of tasks.
1196	>	*
1197	>	* The minimum useful constant is just 1. But using a value of
1198	>	* 1 would require immediate replenishment upon each steal to
1199	>	* maintain enough tasks, which is infeasible.  Further,
1200	>	* partitionings/granularities of offered tasks should
1201	>	* minimize steal rates, which in general means that threads
1202	>	* nearer the top of computation tree should generate more
1203	>	* than those nearer the bottom. In perfect steady state, each
1204	>	* thread is at approximately the same level of computation
1205	>	* tree. However, producing extra tasks amortizes the
1206	>	* uncertainty of progress and diffusion assumptions.
1207	>	*
1208	>	* So, users will want to use values larger, but not much
1209	>	* larger than 1 to both smooth over transient shortages and
1210	>	* hedge against uneven progress; as traded off against the
1211	>	* cost of extra task overhead. We leave the user to pick a
1212	>	* threshold value to compare with the results of this call to
1213	>	* guide decisions, but recommend values such as 3.
1214	>	*
1215	>	* When all threads are active, it is on average OK to
1216	>	* estimate surplus strictly locally. In steady-state, if one
1217	>	* thread is maintaining say 2 surplus tasks, then so are
1218	>	* others. So we can just use estimated queue length.
1219	>	* However, this strategy alone leads to serious mis-estimates
1220	>	* in some non-steady-state conditions (ramp-up, ramp-down,
1221	>	* other stalls). We can detect many of these by further
1222	>	* considering the number of "idle" threads, that are known to
1223	>	* have zero queued tasks, so compensate by a factor of
1224	>	* (#idle/#active) threads.
1225	>	*/
1226	>	ForkJoinWorkerThread wt =
1227	>	(ForkJoinWorkerThread)Thread.currentThread();
1228	>	return wt.workQueue.queueSize() - wt.pool.idlePerActive();
1229		}
1230
1231		// Extension methods
#	Line 938 | Line 1251 | public abstract class ForkJoinTask<V> im
1251		protected abstract void setRawResult(V value);
1252
1253		/**
1254	<	* Immediately performs the base action of this task.  This method
1255	<	* is designed to support extensions, and should not in general be
1256	<	* called otherwise. The return value controls whether this task
1257	<	* is considered to be done normally. It may return false in
1254	>	* Immediately performs the base action of this task and returns
1255	>	* true if, upon return from this method, this task is guaranteed
1256	>	* to have completed normally. This method may return false
1257	>	* otherwise, to indicate that this task is not necessarily
1258	>	* complete (or is not known to be complete), for example in
1259		* asynchronous actions that require explicit invocations of
1260	<	* {@link #complete} to become joinable. It may also throw an
1261	<	* (unchecked) exception to indicate abnormal exit.
1260	>	* completion methods. This method may also throw an (unchecked)
1261	>	* exception to indicate abnormal exit. This method is designed to
1262	>	* support extensions, and should not in general be called
1263	>	* otherwise.
1264		*
1265	<	* @return {@code true} if completed normally
1265	>	* @return {@code true} if this task is known to have completed normally
1266		*/
1267		protected abstract boolean exec();
1268
#	Line 969 | Line 1285 | public abstract class ForkJoinTask<V> im
1285		* @return the next task, or {@code null} if none are available
1286		*/
1287		protected static ForkJoinTask<?> peekNextLocalTask() {
1288	<	return ((ForkJoinWorkerThread) Thread.currentThread())
973	<	.peekTask();
1288	>	return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek();
1289		}
1290
1291		/**
#	Line 989 | Line 1304 | public abstract class ForkJoinTask<V> im
1304		*/
1305		protected static ForkJoinTask<?> pollNextLocalTask() {
1306		return ((ForkJoinWorkerThread) Thread.currentThread())
1307	<	.pollLocalTask();
1307	>	.workQueue.nextLocalTask();
1308		}
1309
1310		/**
#	Line 1011 | Line 1326 | public abstract class ForkJoinTask<V> im
1326		* @return a task, or {@code null} if none are available
1327		*/
1328		protected static ForkJoinTask<?> pollTask() {
1329	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1330	<	.pollTask();
1329	>	ForkJoinWorkerThread wt =
1330	>	(ForkJoinWorkerThread)Thread.currentThread();
1331	>	return wt.pool.nextTaskFor(wt.workQueue);
1332	>	}
1333	>
1334	>	// tag operations
1335	>
1336	>	/**
1337	>	* Returns the tag for this task.
1338	>	*
1339	>	* @return the tag for this task
1340	>	* @since 1.8
1341	>	*/
1342	>	public final short getForkJoinTaskTag() {
1343	>	return (short)status;
1344	>	}
1345	>
1346	>	/**
1347	>	* Atomically sets the tag value for this task.
1348	>	*
1349	>	* @param tag the tag value
1350	>	* @return the previous value of the tag
1351	>	* @since 1.8
1352	>	*/
1353	>	public final short setForkJoinTaskTag(short tag) {
1354	>	for (int s;;) {
1355	>	if (U.compareAndSwapInt(this, STATUS, s = status,
1356	>	(s & ~SMASK) | (tag & SMASK)))
1357	>	return (short)s;
1358	>	}
1359	>	}
1360	>
1361	>	/**
1362	>	* Atomically conditionally sets the tag value for this task.
1363	>	* Among other applications, tags can be used as visit markers
1364	>	* in tasks operating on graphs, as in methods that check: {@code
1365	>	* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1366	>	* before processing, otherwise exiting because the node has
1367	>	* already been visited.
1368	>	*
1369	>	* @param e the expected tag value
1370	>	* @param tag the new tag value
1371	>	* @return true if successful; i.e., the current value was
1372	>	* equal to e and is now tag.
1373	>	* @since 1.8
1374	>	*/
1375	>	public final boolean compareAndSetForkJoinTaskTag(short e, short tag) {
1376	>	for (int s;;) {
1377	>	if ((short)(s = status) != e)
1378	>	return false;
1379	>	if (U.compareAndSwapInt(this, STATUS, s,
1380	>	(s & ~SMASK) | (tag & SMASK)))
1381	>	return true;
1382	>	}
1383		}
1384
1385		/**
#	Line 1023 | Line 1390 | public abstract class ForkJoinTask<V> im
1390		static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1391		implements RunnableFuture<T> {
1392		final Runnable runnable;
1026	–	final T resultOnCompletion;
1393		T result;
1394		AdaptedRunnable(Runnable runnable, T result) {
1395		if (runnable == null) throw new NullPointerException();
1396		this.runnable = runnable;
1397	<	this.resultOnCompletion = result;
1397	>	this.result = result; // OK to set this even before completion
1398		}
1399	<	public T getRawResult() { return result; }
1400	<	public void setRawResult(T v) { result = v; }
1401	<	public boolean exec() {
1402	<	runnable.run();
1403	<	result = resultOnCompletion;
1404	<	return true;
1399	>	public final T getRawResult() { return result; }
1400	>	public final void setRawResult(T v) { result = v; }
1401	>	public final boolean exec() { runnable.run(); return true; }
1402	>	public final void run() { invoke(); }
1403	>	private static final long serialVersionUID = 5232453952276885070L;
1404	>	}
1405	>
1406	>	/**
1407	>	* Adaptor for Runnables without results
1408	>	*/
1409	>	static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1410	>	implements RunnableFuture<Void> {
1411	>	final Runnable runnable;
1412	>	AdaptedRunnableAction(Runnable runnable) {
1413	>	if (runnable == null) throw new NullPointerException();
1414	>	this.runnable = runnable;
1415		}
1416	<	public void run() { invoke(); }
1416	>	public final Void getRawResult() { return null; }
1417	>	public final void setRawResult(Void v) { }
1418	>	public final boolean exec() { runnable.run(); return true; }
1419	>	public final void run() { invoke(); }
1420		private static final long serialVersionUID = 5232453952276885070L;
1421		}
1422
#	Line 1052 | Line 1431 | public abstract class ForkJoinTask<V> im
1431		if (callable == null) throw new NullPointerException();
1432		this.callable = callable;
1433		}
1434	<	public T getRawResult() { return result; }
1435	<	public void setRawResult(T v) { result = v; }
1436	<	public boolean exec() {
1434	>	public final T getRawResult() { return result; }
1435	>	public final void setRawResult(T v) { result = v; }
1436	>	public final boolean exec() {
1437		try {
1438		result = callable.call();
1439		return true;
#	Line 1066 | Line 1445 | public abstract class ForkJoinTask<V> im
1445		throw new RuntimeException(ex);
1446		}
1447		}
1448	<	public void run() { invoke(); }
1448	>	public final void run() { invoke(); }
1449		private static final long serialVersionUID = 2838392045355241008L;
1450		}
1451
#	Line 1079 | Line 1458 | public abstract class ForkJoinTask<V> im
1458		* @return the task
1459		*/
1460		public static ForkJoinTask<?> adapt(Runnable runnable) {
1461	<	return new AdaptedRunnable<Void>(runnable, null);
1461	>	return new AdaptedRunnableAction(runnable);
1462		}
1463
1464		/**
#	Line 1113 | Line 1492 | public abstract class ForkJoinTask<V> im
1492		private static final long serialVersionUID = -7721805057305804111L;
1493
1494		/**
1495	<	* Saves the state to a stream (that is, serializes it).
1495	>	* Saves this task to a stream (that is, serializes it).
1496		*
1497		* @serialData the current run status and the exception thrown
1498		* during execution, or {@code null} if none
1120	–	* @param s the stream
1499		*/
1500		private void writeObject(java.io.ObjectOutputStream s)
1501		throws java.io.IOException {
#	Line 1126 | Line 1504 | public abstract class ForkJoinTask<V> im
1504		}
1505
1506		/**
1507	<	* Reconstitutes the instance from a stream (that is, deserializes it).
1130	<	*
1131	<	* @param s the stream
1507	>	* Reconstitutes this task from a stream (that is, deserializes it).
1508		*/
1509		private void readObject(java.io.ObjectInputStream s)
1510		throws java.io.IOException, ClassNotFoundException {
1511		s.defaultReadObject();
1512		Object ex = s.readObject();
1513		if (ex != null)
1514	<	setExceptionalCompletion((Throwable) ex);
1514	>	setExceptionalCompletion((Throwable)ex);
1515		}
1516
1517		// Unsafe mechanics
1518	<
1519	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1520	<	private static final long statusOffset =
1521	<	objectFieldOffset("status", ForkJoinTask.class);
1522	<
1523	<	private static long objectFieldOffset(String field, Class<?> klazz) {
1518	>	private static final sun.misc.Unsafe U;
1519	>	private static final long STATUS;
1520	>	static {
1521	>	exceptionTableLock = new ReentrantLock();
1522	>	exceptionTableRefQueue = new ReferenceQueue<Object>();
1523	>	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1524		try {
1525	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1526	<	} catch (NoSuchFieldException e) {
1527	<	// Convert Exception to corresponding Error
1528	<	NoSuchFieldError error = new NoSuchFieldError(field);
1529	<	error.initCause(e);
1154	<	throw error;
1525	>	U = getUnsafe();
1526	>	STATUS = U.objectFieldOffset
1527	>	(ForkJoinTask.class.getDeclaredField("status"));
1528	>	} catch (Exception e) {
1529	>	throw new Error(e);
1530		}
1531		}
1532

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