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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.51 by dl, Fri Jul 23 16:49:11 2010 UTC vs.
Revision 1.81 by dl, Thu Jan 26 00:08:13 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.util.concurrent.*;
10	–
8		import java.io.Serializable;
9		import java.util.Collection;
13	–	import java.util.Collections;
10		import java.util.List;
11		import java.util.RandomAccess;
12	<	import java.util.Map;
13	<	import java.util.WeakHashMap;
12	>	import java.lang.ref.WeakReference;
13	>	import java.lang.ref.ReferenceQueue;
14	>	import java.util.concurrent.Callable;
15	>	import java.util.concurrent.CancellationException;
16	>	import java.util.concurrent.ExecutionException;
17	>	import java.util.concurrent.Future;
18	>	import java.util.concurrent.RejectedExecutionException;
19	>	import java.util.concurrent.RunnableFuture;
20	>	import java.util.concurrent.TimeUnit;
21	>	import java.util.concurrent.TimeoutException;
22	>	import java.util.concurrent.locks.ReentrantLock;
23	>	import java.lang.reflect.Constructor;
24
25		/**
26		* Abstract base class for tasks that run within a {@link ForkJoinPool}.
#	Line 28 | Line 34 | import java.util.WeakHashMap;
34		* start other subtasks.  As indicated by the name of this class,
35		* many programs using {@code ForkJoinTask} employ only methods
36		* {@link #fork} and {@link #join}, or derivatives such as {@link
37	<	* #invokeAll}.  However, this class also provides a number of other
38	<	* methods that can come into play in advanced usages, as well as
39	<	* extension mechanics that allow support of new forms of fork/join
40	<	* processing.
37	>	* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
38	>	* provides a number of other methods that can come into play in
39	>	* advanced usages, as well as extension mechanics that allow
40	>	* support of new forms of fork/join processing.
41		*
42		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
43		* The efficiency of {@code ForkJoinTask}s stems from a set of
44		* restrictions (that are only partially statically enforceable)
45	<	* reflecting their intended use as computational tasks calculating
46	<	* pure functions or operating on purely isolated objects.  The
47	<	* primary coordination mechanisms are {@link #fork}, that arranges
45	>	* reflecting their main use as computational tasks calculating pure
46	>	* functions or operating on purely isolated objects.  The primary
47	>	* coordination mechanisms are {@link #fork}, that arranges
48		* asynchronous execution, and {@link #join}, that doesn't proceed
49		* until the task's result has been computed.  Computations should
50	<	* avoid {@code synchronized} methods or blocks, and should minimize
51	<	* other blocking synchronization apart from joining other tasks or
52	<	* using synchronizers such as Phasers that are advertised to
53	<	* cooperate with fork/join scheduling. Tasks should also not perform
54	<	* blocking IO, and should ideally access variables that are
55	<	* completely independent of those accessed by other running
56	<	* tasks. Minor breaches of these restrictions, for example using
57	<	* shared output streams, may be tolerable in practice, but frequent
58	<	* use may result in poor performance, and the potential to
59	<	* indefinitely stall if the number of threads not waiting for IO or
60	<	* other external synchronization becomes exhausted. This usage
61	<	* restriction is in part enforced by not permitting checked
62	<	* exceptions such as {@code IOExceptions} to be thrown. However,
63	<	* computations may still encounter unchecked exceptions, that are
64	<	* rethrown to callers attempting to join them. These exceptions may
65	<	* additionally include {@link RejectedExecutionException} stemming
66	<	* from internal resource exhaustion, such as failure to allocate
67	<	* internal task queues.
50	>	* ideally avoid {@code synchronized} methods or blocks, and should
51	>	* minimize other blocking synchronization apart from joining other
52	>	* tasks or using synchronizers such as Phasers that are advertised to
53	>	* cooperate with fork/join scheduling. Subdividable tasks should also
54	>	* not perform blocking IO, and should ideally access variables that
55	>	* are completely independent of those accessed by other running
56	>	* tasks. These guidelines are loosely enforced by not permitting
57	>	* checked exceptions such as {@code IOExceptions} to be
58	>	* thrown. However, computations may still encounter unchecked
59	>	* exceptions, that are rethrown to callers attempting to join
60	>	* them. These exceptions may additionally include {@link
61	>	* RejectedExecutionException} stemming from internal resource
62	>	* exhaustion, such as failure to allocate internal task
63	>	* queues. Rethrown exceptions behave in the same way as regular
64	>	* exceptions, but, when possible, contain stack traces (as displayed
65	>	* for example using {@code ex.printStackTrace()}) of both the thread
66	>	* that initiated the computation as well as the thread actually
67	>	* encountering the exception; minimally only the latter.
68	>	*
69	>	* <p>It is possible to define and use ForkJoinTasks that may block,
70	>	* but doing do requires three further considerations: (1) Completion
71	>	* of few if any <em>other</em> tasks should be dependent on a task
72	>	* that blocks on external synchronization or IO. Event-style async
73	>	* tasks that are never joined often fall into this category.  (2) To
74	>	* minimize resource impact, tasks should be small; ideally performing
75	>	* only the (possibly) blocking action. (3) Unless the {@link
76	>	* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
77	>	* blocked tasks is known to be less than the pool's {@link
78	>	* ForkJoinPool#getParallelism} level, the pool cannot guarantee that
79	>	* enough threads will be available to ensure progress or good
80	>	* performance.
81		*
82		* <p>The primary method for awaiting completion and extracting
83		* results of a task is {@link #join}, but there are several variants:
#	Line 74 | Line 93 | import java.util.WeakHashMap;
93		* performs the most common form of parallel invocation: forking a set
94		* of tasks and joining them all.
95		*
96	+	* <p>In the most typical usages, a fork-join pair act like a a call
97	+	* (fork) and return (join) from a parallel recursive function. As is
98	+	* the case with other forms of recursive calls, returns (joins)
99	+	* should be performed innermost-first. For example, {@code a.fork();
100	+	* b.fork(); b.join(); a.join();} is likely to be substantially more
101	+	* efficient than joining {@code a} before {@code b}.
102	+	*
103		* <p>The execution status of tasks may be queried at several levels
104		* of detail: {@link #isDone} is true if a task completed in any way
105		* (including the case where a task was cancelled without executing);
#	Line 100 | Line 126 | import java.util.WeakHashMap;
126		* ForkJoinTasks (as may be determined using method {@link
127		* #inForkJoinPool}).  Attempts to invoke them in other contexts
128		* result in exceptions or errors, possibly including
129	<	* ClassCastException.
129	>	* {@code ClassCastException}.
130	>	*
131	>	* <p>Method {@link #join} and its variants are appropriate for use
132	>	* only when completion dependencies are acyclic; that is, the
133	>	* parallel computation can be described as a directed acyclic graph
134	>	* (DAG). Otherwise, executions may encounter a form of deadlock as
135	>	* tasks cyclically wait for each other.  However, this framework
136	>	* supports other methods and techniques (for example the use of
137	>	* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
138	>	* may be of use in constructing custom subclasses for problems that
139	>	* are not statically structured as DAGs. To support such usages a
140	>	* ForkJoinTask may be atomically <em>marked</em> using {@link
141	>	* #markForkJoinTask} and checked for marking using {@link
142	>	* #isMarkedForkJoinTask}. The ForkJoinTask implementation does not
143	>	* use these {@code protected} methods or marks for any purpose, but
144	>	* they may be of use in the construction of specialized subclasses.
145	>	* For example, parallel graph traversals can use the supplied methods
146	>	* to avoid revisiting nodes/tasks that have already been
147	>	* processed. Also, completion based designs can use them to record
148	>	* that one subtask has completed. (Method names for marking are bulky
149	>	* in part to encourage definition of methods that reflect their usage
150	>	* patterns.)
151		*
152		* <p>Most base support methods are {@code final}, to prevent
153		* overriding of implementations that are intrinsically tied to the
#	Line 116 | Line 163 | import java.util.WeakHashMap;
163		* computation. Large tasks should be split into smaller subtasks,
164		* usually via recursive decomposition. As a very rough rule of thumb,
165		* a task should perform more than 100 and less than 10000 basic
166	<	* computational steps. If tasks are too big, then parallelism cannot
167	<	* improve throughput. If too small, then memory and internal task
168	<	* maintenance overhead may overwhelm processing.
166	>	* computational steps, and should avoid indefinite looping. If tasks
167	>	* are too big, then parallelism cannot improve throughput. If too
168	>	* small, then memory and internal task maintenance overhead may
169	>	* overwhelm processing.
170		*
171		* <p>This class provides {@code adapt} methods for {@link Runnable}
172		* and {@link Callable}, that may be of use when mixing execution of
#	Line 139 | Line 187 | public abstract class ForkJoinTask<V> im
187		* See the internal documentation of class ForkJoinPool for a
188		* general implementation overview.  ForkJoinTasks are mainly
189		* responsible for maintaining their "status" field amidst relays
190	<	* to methods in ForkJoinWorkerThread and ForkJoinPool. The
191	<	* methods of this class are more-or-less layered into (1) basic
192	<	* status maintenance (2) execution and awaiting completion (3)
193	<	* user-level methods that additionally report results. This is
194	<	* sometimes hard to see because this file orders exported methods
195	<	* in a way that flows well in javadocs.
190	>	* to methods in ForkJoinWorkerThread and ForkJoinPool.
191	>	*
192	>	* The methods of this class are more-or-less layered into
193	>	* (1) basic status maintenance
194	>	* (2) execution and awaiting completion
195	>	* (3) user-level methods that additionally report results.
196	>	* This is sometimes hard to see because this file orders exported
197	>	* methods in a way that flows well in javadocs.
198	>	*/
199	>
200	>	/**
201	>	* The number of times to try to help join a task without any
202	>	* apparent progress before giving up and blocking. The value is
203	>	* arbitrary but should be large enough to cope with transient
204	>	* stalls (due to GC etc) that can cause helping methods not to be
205	>	* able to proceed because other workers have not progressed to
206	>	* the point where subtasks can be found or taken.
207		*/
208	+	private static final int HELP_RETRIES = 32;
209
210		/*
211		* The status field holds run control status bits packed into a
212		* single int to minimize footprint and to ensure atomicity (via
213		* CAS).  Status is initially zero, and takes on nonnegative
214		* values until completed, upon which status holds value
215	<	* COMPLETED. CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
215	>	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
216		* waits by other threads have the SIGNAL bit set.  Completion of
217		* a stolen task with SIGNAL set awakens any waiters via
218		* notifyAll. Even though suboptimal for some purposes, we use
#	Line 164 | Line 224 | public abstract class ForkJoinTask<V> im
224		* them.
225		*/
226
227	<	/** Run status of this task */
227	>	/** The run status of this task */
228		volatile int status; // accessed directly by pool and workers
229	<
230	<	private static final int NORMAL      = -1;
231	<	private static final int CANCELLED   = -2;
232	<	private static final int EXCEPTIONAL = -3;
233	<	private static final int SIGNAL      =  1;
174	<
175	<	/**
176	<	* Table of exceptions thrown by tasks, to enable reporting by
177	<	* callers. Because exceptions are rare, we don't directly keep
178	<	* them with task objects, but instead use a weak ref table.  Note
179	<	* that cancellation exceptions don't appear in the table, but are
180	<	* instead recorded as status values.
181	<	* TODO: Use ConcurrentReferenceHashMap
182	<	*/
183	<	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
184	<	Collections.synchronizedMap
185	<	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
186	<
187	<	// Maintaining completion status
229	>	static final int NORMAL      = 0xfffffffc;  // negative with low 2 bits 0
230	>	static final int CANCELLED   = 0xfffffff8;  // must be < NORMAL
231	>	static final int EXCEPTIONAL = 0xfffffff4;  // must be < CANCELLED
232	>	static final int SIGNAL      = 0x00000001;
233	>	static final int MARKED      = 0x00000002;
234
235		/**
236	<	* Marks completion and wakes up threads waiting to join this task,
237	<	* also clearing signal request bits.
236	>	* Marks completion and wakes up threads waiting to join this
237	>	* task, also clearing signal request bits. A specialization for
238	>	* NORMAL completion is in method doExec
239		*
240		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
241	<	* @return status on exit
241	>	* @return completion status on exit
242		*/
243		private int setCompletion(int completion) {
244	<	int s;
245	<	while ((s = status) >= 0) {
246	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
247	<	if (s != 0)
244	>	for (int s;;) {
245	>	if ((s = status) < 0)
246	>	return s;
247	>	if (U.compareAndSwapInt(this, STATUS, s, (s & ~SIGNAL)|completion)) {
248	>	if ((s & SIGNAL) != 0)
249		synchronized (this) { notifyAll(); }
250		return completion;
251		}
252		}
205	–	return s;
206	–	}
207	–
208	–	/**
209	–	* Record exception and set exceptional completion
210	–	* @return status on exit
211	–	*/
212	–	private int setExceptionalCompletion(Throwable rex) {
213	–	exceptionMap.put(this, rex);
214	–	return setCompletion(EXCEPTIONAL);
253		}
254
255		/**
256	<	* Blocks a worker thread until completion. Called only by pool.
257	<	*/
258	<	final void internalAwaitDone() {
259	<	int s;         // the odd construction reduces lock bias effects
260	<	while ((s = status) >= 0) {
256	>	* Primary execution method for stolen tasks. Unless done, calls
257	>	* exec and records status if completed, but doesn't wait for
258	>	* completion otherwise.
259	>	*
260	>	* @return status on exit from this method
261	>	*/
262	>	final int doExec() {
263	>	int s; boolean completed;
264	>	if ((s = status) >= 0) {
265		try {
266	<	synchronized(this) {
267	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
268	<	wait();
266	>	completed = exec();
267	>	} catch (Throwable rex) {
268	>	return setExceptionalCompletion(rex);
269	>	}
270	>	while ((s = status) >= 0 && completed) {
271	>	if (U.compareAndSwapInt(this, STATUS, s, (s & ~SIGNAL)|NORMAL)) {
272	>	if ((s & SIGNAL) != 0)
273	>	synchronized (this) { notifyAll(); }
274	>	return NORMAL;
275		}
228	–	} catch (InterruptedException ie) {
229	–	cancelIfTerminating();
276		}
277		}
278	+	return s;
279		}
280
281		/**
282		* Blocks a non-worker-thread until completion.
283	<	* @return status on exit
283	>	* @return status upon completion
284		*/
285		private int externalAwaitDone() {
286		int s;
287	<	while ((s = status) >= 0) {
288	<	synchronized(this) {
289	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
290	<	boolean interrupted = false;
291	<	while ((s = status) >= 0) {
287	>	if ((s = status) >= 0) {
288	>	boolean interrupted = false;
289	>	synchronized (this) {
290	>	while ((s = status) >= 0) {
291	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
292		try {
293		wait();
294		} catch (InterruptedException ie) {
295		interrupted = true;
296		}
297		}
251	–	if (interrupted)
252	–	Thread.currentThread().interrupt();
253	–	break;
298		}
299		}
300	+	if (interrupted)
301	+	Thread.currentThread().interrupt();
302		}
303		return s;
304		}
305
306		/**
307	<	* Unless done, calls exec and records status if completed, but
262	<	* doesn't wait for completion otherwise. Primary execution method
263	<	* for ForkJoinWorkerThread.
307	>	* Blocks a non-worker-thread until completion or interruption or timeout.
308		*/
309	<	final void tryExec() {
310	<	try {
311	<	if (status < 0 || !exec())
312	<	return;
313	<	} catch (Throwable rex) {
314	<	setExceptionalCompletion(rex);
315	<	return;
309	>	private int externalInterruptibleAwaitDone(long millis)
310	>	throws InterruptedException {
311	>	int s;
312	>	if (Thread.interrupted())
313	>	throw new InterruptedException();
314	>	if ((s = status) >= 0) {
315	>	synchronized (this) {
316	>	while ((s = status) >= 0) {
317	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
318	>	wait(millis);
319	>	if (millis > 0L)
320	>	break;
321	>	}
322	>	}
323	>	}
324		}
325	<	setCompletion(NORMAL); // must be outside try block
325	>	return s;
326		}
327
328	+
329		/**
330	<	* If not done and this task is next in worker queue, runs it,
331	<	* else waits for it.
332	<	* @return status on exit
330	>	* Implementation for join, get, quietlyJoin. Directly handles
331	>	* only cases of already-completed, external wait, and
332	>	* unfork+exec.  Others are relayed to awaitJoin.
333	>	*
334	>	* @return status upon completion
335		*/
336		private int doJoin() {
337	<	int stat;
338	<	if ((stat = status) < 0)
339	<	return stat;
340	<	Thread t = Thread.currentThread();
341	<	ForkJoinWorkerThread w;
342	<	if (t instanceof ForkJoinWorkerThread) {
343	<	if ((w = (ForkJoinWorkerThread) t).unpushTask(this)) {
344	<	boolean completed;
337	>	int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
338	>	if ((s = status) >= 0) {
339	>	if (!((t = Thread.currentThread()) instanceof ForkJoinWorkerThread))
340	>	s = externalAwaitDone();
341	>	else if (!(w = (wt = (ForkJoinWorkerThread)t).workQueue).
342	>	tryUnpush(this) || (s = doExec()) >= 0)
343	>	s = awaitJoin(w, wt.pool);
344	>	}
345	>	return s;
346	>	}
347	>
348	>	/**
349	>	* Helps and/or blocks until joined.
350	>	*
351	>	* @param w the joiner
352	>	* @param p the pool
353	>	* @return status upon completion
354	>	*/
355	>	private int awaitJoin(ForkJoinPool.WorkQueue w, ForkJoinPool p) {
356	>	int s;
357	>	ForkJoinTask<?> prevJoin = w.currentJoin;
358	>	w.currentJoin = this;
359	>	for (int k = HELP_RETRIES; (s = status) >= 0;) {
360	>	if ((w.queueSize() > 0) ?
361	>	w.tryRemoveAndExec(this) :        // self-help
362	>	p.tryHelpStealer(w, this))        // help process tasks
363	>	k = HELP_RETRIES;                 // reset if made progress
364	>	else if ((s = status) < 0)            // recheck
365	>	break;
366	>	else if (--k > 0) {
367	>	if ((k & 3) == 1)
368	>	Thread.yield();               // occasionally yield
369	>	}
370	>	else if (k == 0)
371	>	p.tryPollForAndExec(w, this);     // uncommon self-help case
372	>	else if (p.tryCompensate()) {         // true if can block
373		try {
374	<	completed = exec();
375	<	} catch (Throwable rex) {
376	<	return setExceptionalCompletion(rex);
374	>	int ss = status;
375	>	if (ss >= 0 &&                // assert need signal
376	>	U.compareAndSwapInt(this, STATUS, ss, ss | SIGNAL)) {
377	>	synchronized (this) {
378	>	if (status >= 0)      // block
379	>	wait();
380	>	}
381	>	}
382	>	} catch (InterruptedException ignore) {
383	>	} finally {
384	>	p.incrementActiveCount();     // re-activate
385		}
295	–	if (completed)
296	–	return setCompletion(NORMAL);
386		}
298	–	return w.joinTask(this);
387		}
388	<	return externalAwaitDone();
388	>	w.currentJoin = prevJoin;
389	>	return s;
390		}
391
392		/**
393	<	* Unless done, calls exec and records status if completed, or
394	<	* waits for completion otherwise.
395	<	* @return status on exit
393	>	* Implementation for invoke, quietlyInvoke.
394	>	*
395	>	* @return status upon completion
396		*/
397		private int doInvoke() {
398	<	int stat;
399	<	if ((stat = status) >= 0) {
400	<	boolean completed;
398	>	int s;
399	>	if ((s = doExec()) < 0)
400	>	return s;
401	>	else
402	>	return doJoin();
403	>	}
404	>
405	>	// Exception table support
406	>
407	>	/**
408	>	* Table of exceptions thrown by tasks, to enable reporting by
409	>	* callers. Because exceptions are rare, we don't directly keep
410	>	* them with task objects, but instead use a weak ref table.  Note
411	>	* that cancellation exceptions don't appear in the table, but are
412	>	* instead recorded as status values.
413	>	*
414	>	* Note: These statics are initialized below in static block.
415	>	*/
416	>	private static final ExceptionNode[] exceptionTable;
417	>	private static final ReentrantLock exceptionTableLock;
418	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
419	>
420	>	/**
421	>	* Fixed capacity for exceptionTable.
422	>	*/
423	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
424	>
425	>	/**
426	>	* Key-value nodes for exception table.  The chained hash table
427	>	* uses identity comparisons, full locking, and weak references
428	>	* for keys. The table has a fixed capacity because it only
429	>	* maintains task exceptions long enough for joiners to access
430	>	* them, so should never become very large for sustained
431	>	* periods. However, since we do not know when the last joiner
432	>	* completes, we must use weak references and expunge them. We do
433	>	* so on each operation (hence full locking). Also, some thread in
434	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
435	>	* pool becomes isQuiescent.
436	>	*/
437	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>>{
438	>	final Throwable ex;
439	>	ExceptionNode next;
440	>	final long thrower;  // use id not ref to avoid weak cycles
441	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
442	>	super(task, exceptionTableRefQueue);
443	>	this.ex = ex;
444	>	this.next = next;
445	>	this.thrower = Thread.currentThread().getId();
446	>	}
447	>	}
448	>
449	>	/**
450	>	* Records exception and sets exceptional completion.
451	>	*
452	>	* @return status on exit
453	>	*/
454	>	private int setExceptionalCompletion(Throwable ex) {
455	>	int h = System.identityHashCode(this);
456	>	final ReentrantLock lock = exceptionTableLock;
457	>	lock.lock();
458	>	try {
459	>	expungeStaleExceptions();
460	>	ExceptionNode[] t = exceptionTable;
461	>	int i = h & (t.length - 1);
462	>	for (ExceptionNode e = t[i]; ; e = e.next) {
463	>	if (e == null) {
464	>	t[i] = new ExceptionNode(this, ex, t[i]);
465	>	break;
466	>	}
467	>	if (e.get() == this) // already present
468	>	break;
469	>	}
470	>	} finally {
471	>	lock.unlock();
472	>	}
473	>	return setCompletion(EXCEPTIONAL);
474	>	}
475	>
476	>	/**
477	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
478	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
479	>	* exceptions, but if it does anyway, we have no recourse during
480	>	* shutdown, so guard against this case.
481	>	*/
482	>	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
483	>	if (t != null && t.status >= 0) {
484		try {
485	<	completed = exec();
486	<	} catch (Throwable rex) {
315	<	return setExceptionalCompletion(rex);
485	>	t.cancel(false);
486	>	} catch (Throwable ignore) {
487		}
317	–	stat = completed ? setCompletion(NORMAL) : doJoin();
488		}
319	–	return stat;
489		}
490
491		/**
492	<	* Returns result or throws exception associated with given status.
324	<	* @param s the status
492	>	* Removes exception node and clears status
493		*/
494	<	private V reportResult(int s) {
494	>	private void clearExceptionalCompletion() {
495	>	int h = System.identityHashCode(this);
496	>	final ReentrantLock lock = exceptionTableLock;
497	>	lock.lock();
498	>	try {
499	>	ExceptionNode[] t = exceptionTable;
500	>	int i = h & (t.length - 1);
501	>	ExceptionNode e = t[i];
502	>	ExceptionNode pred = null;
503	>	while (e != null) {
504	>	ExceptionNode next = e.next;
505	>	if (e.get() == this) {
506	>	if (pred == null)
507	>	t[i] = next;
508	>	else
509	>	pred.next = next;
510	>	break;
511	>	}
512	>	pred = e;
513	>	e = next;
514	>	}
515	>	expungeStaleExceptions();
516	>	status = 0;
517	>	} finally {
518	>	lock.unlock();
519	>	}
520	>	}
521	>
522	>	/**
523	>	* Returns a rethrowable exception for the given task, if
524	>	* available. To provide accurate stack traces, if the exception
525	>	* was not thrown by the current thread, we try to create a new
526	>	* exception of the same type as the one thrown, but with the
527	>	* recorded exception as its cause. If there is no such
528	>	* constructor, we instead try to use a no-arg constructor,
529	>	* followed by initCause, to the same effect. If none of these
530	>	* apply, or any fail due to other exceptions, we return the
531	>	* recorded exception, which is still correct, although it may
532	>	* contain a misleading stack trace.
533	>	*
534	>	* @return the exception, or null if none
535	>	*/
536	>	private Throwable getThrowableException() {
537	>	if (status != EXCEPTIONAL)
538	>	return null;
539	>	int h = System.identityHashCode(this);
540	>	ExceptionNode e;
541	>	final ReentrantLock lock = exceptionTableLock;
542	>	lock.lock();
543	>	try {
544	>	expungeStaleExceptions();
545	>	ExceptionNode[] t = exceptionTable;
546	>	e = t[h & (t.length - 1)];
547	>	while (e != null && e.get() != this)
548	>	e = e.next;
549	>	} finally {
550	>	lock.unlock();
551	>	}
552		Throwable ex;
553	<	if (s < NORMAL && (ex = getException()) != null)
554	<	UNSAFE.throwException(ex);
553	>	if (e == null || (ex = e.ex) == null)
554	>	return null;
555	>	if (e.thrower != Thread.currentThread().getId()) {
556	>	Class<? extends Throwable> ec = ex.getClass();
557	>	try {
558	>	Constructor<?> noArgCtor = null;
559	>	Constructor<?>[] cs = ec.getConstructors();// public ctors only
560	>	for (int i = 0; i < cs.length; ++i) {
561	>	Constructor<?> c = cs[i];
562	>	Class<?>[] ps = c.getParameterTypes();
563	>	if (ps.length == 0)
564	>	noArgCtor = c;
565	>	else if (ps.length == 1 && ps[0] == Throwable.class)
566	>	return (Throwable)(c.newInstance(ex));
567	>	}
568	>	if (noArgCtor != null) {
569	>	Throwable wx = (Throwable)(noArgCtor.newInstance());
570	>	wx.initCause(ex);
571	>	return wx;
572	>	}
573	>	} catch (Exception ignore) {
574	>	}
575	>	}
576	>	return ex;
577	>	}
578	>
579	>	/**
580	>	* Poll stale refs and remove them. Call only while holding lock.
581	>	*/
582	>	private static void expungeStaleExceptions() {
583	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
584	>	if (x instanceof ExceptionNode) {
585	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
586	>	ExceptionNode[] t = exceptionTable;
587	>	int i = System.identityHashCode(key) & (t.length - 1);
588	>	ExceptionNode e = t[i];
589	>	ExceptionNode pred = null;
590	>	while (e != null) {
591	>	ExceptionNode next = e.next;
592	>	if (e == x) {
593	>	if (pred == null)
594	>	t[i] = next;
595	>	else
596	>	pred.next = next;
597	>	break;
598	>	}
599	>	pred = e;
600	>	e = next;
601	>	}
602	>	}
603	>	}
604	>	}
605	>
606	>	/**
607	>	* If lock is available, poll stale refs and remove them.
608	>	* Called from ForkJoinPool when pools become quiescent.
609	>	*/
610	>	static final void helpExpungeStaleExceptions() {
611	>	final ReentrantLock lock = exceptionTableLock;
612	>	if (lock.tryLock()) {
613	>	try {
614	>	expungeStaleExceptions();
615	>	} finally {
616	>	lock.unlock();
617	>	}
618	>	}
619	>	}
620	>
621	>	/**
622	>	* Report the result of invoke or join; called only upon
623	>	* non-normal return of internal versions.
624	>	*/
625	>	private V reportResult() {
626	>	int s; Throwable ex;
627	>	if ((s = status) == CANCELLED)
628	>	throw new CancellationException();
629	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
630	>	U.throwException(ex);
631		return getRawResult();
632		}
633
#	Line 343 | Line 644 | public abstract class ForkJoinTask<V> im
644		* #isDone} returning {@code true}.
645		*
646		* <p>This method may be invoked only from within {@code
647	<	* ForkJoinTask} computations (as may be determined using method
647	>	* ForkJoinPool} computations (as may be determined using method
648		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
649		* result in exceptions or errors, possibly including {@code
650		* ClassCastException}.
#	Line 351 | Line 652 | public abstract class ForkJoinTask<V> im
652		* @return {@code this}, to simplify usage
653		*/
654		public final ForkJoinTask<V> fork() {
655	<	((ForkJoinWorkerThread) Thread.currentThread())
656	<	.pushTask(this);
655	>	ForkJoinWorkerThread wt;
656	>	(wt = (ForkJoinWorkerThread)Thread.currentThread()).
657	>	workQueue.push(this, wt.pool);
658		return this;
659		}
660
661		/**
662	<	* Returns the result of the computation when it {@link #isDone is done}.
663	<	* This method differs from {@link #get()} in that
662	>	* Returns the result of the computation when it {@link #isDone is
663	>	* done}.  This method differs from {@link #get()} in that
664		* abnormal completion results in {@code RuntimeException} or
665	<	* {@code Error}, not {@code ExecutionException}.
665	>	* {@code Error}, not {@code ExecutionException}, and that
666	>	* interrupts of the calling thread do <em>not</em> cause the
667	>	* method to abruptly return by throwing {@code
668	>	* InterruptedException}.
669		*
670		* @return the computed result
671		*/
672		public final V join() {
673	<	return reportResult(doJoin());
673	>	if (doJoin() != NORMAL)
674	>	return reportResult();
675	>	else
676	>	return getRawResult();
677		}
678
679		/**
680		* Commences performing this task, awaits its completion if
681	<	* necessary, and return its result, or throws an (unchecked)
682	<	* exception if the underlying computation did so.
681	>	* necessary, and returns its result, or throws an (unchecked)
682	>	* {@code RuntimeException} or {@code Error} if the underlying
683	>	* computation did so.
684		*
685		* @return the computed result
686		*/
687		public final V invoke() {
688	<	return reportResult(doInvoke());
688	>	if (doInvoke() != NORMAL)
689	>	return reportResult();
690	>	else
691	>	return getRawResult();
692		}
693
694		/**
695		* Forks the given tasks, returning when {@code isDone} holds for
696		* each task or an (unchecked) exception is encountered, in which
697	<	* case the exception is rethrown.  If either task encounters an
698	<	* exception, the other one may be, but is not guaranteed to be,
699	<	* cancelled.  If both tasks throw an exception, then this method
700	<	* throws one of them.  The individual status of each task may be
701	<	* checked using {@link #getException()} and related methods.
697	>	* case the exception is rethrown. If more than one task
698	>	* encounters an exception, then this method throws any one of
699	>	* these exceptions. If any task encounters an exception, the
700	>	* other may be cancelled. However, the execution status of
701	>	* individual tasks is not guaranteed upon exceptional return. The
702	>	* status of each task may be obtained using {@link
703	>	* #getException()} and related methods to check if they have been
704	>	* cancelled, completed normally or exceptionally, or left
705	>	* unprocessed.
706		*
707		* <p>This method may be invoked only from within {@code
708	<	* ForkJoinTask} computations (as may be determined using method
708	>	* ForkJoinPool} computations (as may be determined using method
709		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
710		* result in exceptions or errors, possibly including {@code
711		* ClassCastException}.
#	Line 407 | Line 723 | public abstract class ForkJoinTask<V> im
723		/**
724		* Forks the given tasks, returning when {@code isDone} holds for
725		* each task or an (unchecked) exception is encountered, in which
726	<	* case the exception is rethrown. If any task encounters an
727	<	* exception, others may be, but are not guaranteed to be,
728	<	* cancelled.  If more than one task encounters an exception, then
729	<	* this method throws any one of these exceptions.  The individual
730	<	* status of each task may be checked using {@link #getException()}
731	<	* and related methods.
726	>	* case the exception is rethrown. If more than one task
727	>	* encounters an exception, then this method throws any one of
728	>	* these exceptions. If any task encounters an exception, others
729	>	* may be cancelled. However, the execution status of individual
730	>	* tasks is not guaranteed upon exceptional return. The status of
731	>	* each task may be obtained using {@link #getException()} and
732	>	* related methods to check if they have been cancelled, completed
733	>	* normally or exceptionally, or left unprocessed.
734		*
735		* <p>This method may be invoked only from within {@code
736	<	* ForkJoinTask} computations (as may be determined using method
736	>	* ForkJoinPool} computations (as may be determined using method
737		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
738		* result in exceptions or errors, possibly including {@code
739		* ClassCastException}.
#	Line 442 | Line 760 | public abstract class ForkJoinTask<V> im
760		if (t != null) {
761		if (ex != null)
762		t.cancel(false);
763	<	else if (t.doJoin() < NORMAL && ex == null)
763	>	else if (t.doJoin() < NORMAL)
764		ex = t.getException();
765		}
766		}
767		if (ex != null)
768	<	UNSAFE.throwException(ex);
768	>	U.throwException(ex);
769		}
770
771		/**
772		* Forks all tasks in the specified collection, returning when
773		* {@code isDone} holds for each task or an (unchecked) exception
774	<	* is encountered.  If any task encounters an exception, others
775	<	* may be, but are not guaranteed to be, cancelled.  If more than
776	<	* one task encounters an exception, then this method throws any
777	<	* one of these exceptions.  The individual status of each task
778	<	* may be checked using {@link #getException()} and related
779	<	* methods.  The behavior of this operation is undefined if the
780	<	* specified collection is modified while the operation is in
781	<	* progress.
774	>	* is encountered, in which case the exception is rethrown. If
775	>	* more than one task encounters an exception, then this method
776	>	* throws any one of these exceptions. If any task encounters an
777	>	* exception, others may be cancelled. However, the execution
778	>	* status of individual tasks is not guaranteed upon exceptional
779	>	* return. The status of each task may be obtained using {@link
780	>	* #getException()} and related methods to check if they have been
781	>	* cancelled, completed normally or exceptionally, or left
782	>	* unprocessed.
783		*
784		* <p>This method may be invoked only from within {@code
785	<	* ForkJoinTask} computations (as may be determined using method
785	>	* ForkJoinPool} computations (as may be determined using method
786		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
787		* result in exceptions or errors, possibly including {@code
788		* ClassCastException}.
#	Line 498 | Line 817 | public abstract class ForkJoinTask<V> im
817		if (t != null) {
818		if (ex != null)
819		t.cancel(false);
820	<	else if (t.doJoin() < NORMAL && ex == null)
820	>	else if (t.doJoin() < NORMAL)
821		ex = t.getException();
822		}
823		}
824		if (ex != null)
825	<	UNSAFE.throwException(ex);
825	>	U.throwException(ex);
826		return tasks;
827		}
828
829		/**
830		* Attempts to cancel execution of this task. This attempt will
831	<	* fail if the task has already completed, has already been
832	<	* cancelled, or could not be cancelled for some other reason. If
833	<	* successful, and this task has not started when cancel is
834	<	* called, execution of this task is suppressed, {@link
835	<	* #isCancelled} will report true, and {@link #join} will result
836	<	* in a {@code CancellationException} being thrown.
831	>	* fail if the task has already completed or could not be
832	>	* cancelled for some other reason. If successful, and this task
833	>	* has not started when {@code cancel} is called, execution of
834	>	* this task is suppressed. After this method returns
835	>	* successfully, unless there is an intervening call to {@link
836	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
837	>	* {@link #isDone}, and {@code cancel} will return {@code true}
838	>	* and calls to {@link #join} and related methods will result in
839	>	* {@code CancellationException}.
840		*
841		* <p>This method may be overridden in subclasses, but if so, must
842	<	* still ensure that these minimal properties hold. In particular,
843	<	* the {@code cancel} method itself must not throw exceptions.
842	>	* still ensure that these properties hold. In particular, the
843	>	* {@code cancel} method itself must not throw exceptions.
844		*
845		* <p>This method is designed to be invoked by <em>other</em>
846		* tasks. To terminate the current task, you can just return or
847		* throw an unchecked exception from its computation method, or
848		* invoke {@link #completeExceptionally}.
849		*
850	<	* @param mayInterruptIfRunning this value is ignored in the
851	<	* default implementation because tasks are not
852	<	* cancelled via interruption
850	>	* @param mayInterruptIfRunning this value has no effect in the
851	>	* default implementation because interrupts are not used to
852	>	* control cancellation.
853		*
854		* @return {@code true} if this task is now cancelled
855		*/
#	Line 535 | Line 857 | public abstract class ForkJoinTask<V> im
857		return setCompletion(CANCELLED) == CANCELLED;
858		}
859
538	–	/**
539	–	* Cancels, ignoring any exceptions it throws. Used during worker
540	–	* and pool shutdown.
541	–	*/
542	–	final void cancelIgnoringExceptions() {
543	–	try {
544	–	cancel(false);
545	–	} catch (Throwable ignore) {
546	–	}
547	–	}
548	–
549	–	/**
550	–	* Cancels ignoring exceptions if worker is terminating
551	–	*/
552	–	final void cancelIfTerminating() {
553	–	Thread t = Thread.currentThread();
554	–	if ((t instanceof ForkJoinWorkerThread) &&
555	–	((ForkJoinWorkerThread) t).isTerminating()) {
556	–	try {
557	–	cancel(false);
558	–	} catch (Throwable ignore) {
559	–	}
560	–	}
561	–	}
562	–
860		public final boolean isDone() {
861		return status < 0;
862		}
#	Line 599 | Line 896 | public abstract class ForkJoinTask<V> im
896		int s = status;
897		return ((s >= NORMAL)    ? null :
898		(s == CANCELLED) ? new CancellationException() :
899	<	exceptionMap.get(this));
899	>	getThrowableException());
900		}
901
902		/**
#	Line 624 | Line 921 | public abstract class ForkJoinTask<V> im
921
922		/**
923		* Completes this task, and if not already aborted or cancelled,
924	<	* returning a {@code null} result upon {@code join} and related
925	<	* operations. This method may be used to provide results for
926	<	* asynchronous tasks, or to provide alternative handling for
927	<	* tasks that would not otherwise complete normally. Its use in
928	<	* other situations is discouraged. This method is
929	<	* overridable, but overridden versions must invoke {@code super}
930	<	* implementation to maintain guarantees.
924	>	* returning the given value as the result of subsequent
925	>	* invocations of {@code join} and related operations. This method
926	>	* may be used to provide results for asynchronous tasks, or to
927	>	* provide alternative handling for tasks that would not otherwise
928	>	* complete normally. Its use in other situations is
929	>	* discouraged. This method is overridable, but overridden
930	>	* versions must invoke {@code super} implementation to maintain
931	>	* guarantees.
932		*
933		* @param value the result value for this task
934		*/
#	Line 644 | Line 942 | public abstract class ForkJoinTask<V> im
942		setCompletion(NORMAL);
943		}
944
945	+	/**
946	+	* Waits if necessary for the computation to complete, and then
947	+	* retrieves its result.
948	+	*
949	+	* @return the computed result
950	+	* @throws CancellationException if the computation was cancelled
951	+	* @throws ExecutionException if the computation threw an
952	+	* exception
953	+	* @throws InterruptedException if the current thread is not a
954	+	* member of a ForkJoinPool and was interrupted while waiting
955	+	*/
956		public final V get() throws InterruptedException, ExecutionException {
957	<	int s = doJoin();
958	<	if (Thread.interrupted())
959	<	throw new InterruptedException();
960	<	if (s < NORMAL) {
961	<	Throwable ex;
962	<	if (s == CANCELLED)
963	<	throw new CancellationException();
655	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
656	<	throw new ExecutionException(ex);
657	<	}
957	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
958	>	doJoin() : externalInterruptibleAwaitDone(0L);
959	>	Throwable ex;
960	>	if (s == CANCELLED)
961	>	throw new CancellationException();
962	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
963	>	throw new ExecutionException(ex);
964		return getRawResult();
965		}
966
967	+	/**
968	+	* Waits if necessary for at most the given time for the computation
969	+	* to complete, and then retrieves its result, if available.
970	+	*
971	+	* @param timeout the maximum time to wait
972	+	* @param unit the time unit of the timeout argument
973	+	* @return the computed result
974	+	* @throws CancellationException if the computation was cancelled
975	+	* @throws ExecutionException if the computation threw an
976	+	* exception
977	+	* @throws InterruptedException if the current thread is not a
978	+	* member of a ForkJoinPool and was interrupted while waiting
979	+	* @throws TimeoutException if the wait timed out
980	+	*/
981		public final V get(long timeout, TimeUnit unit)
982		throws InterruptedException, ExecutionException, TimeoutException {
983	+	// Messy in part because we measure in nanos, but wait in millis
984	+	int s; long millis, nanos;
985		Thread t = Thread.currentThread();
986	<	ForkJoinPool pool;
987	<	if (t instanceof ForkJoinWorkerThread) {
988	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
989	<	if (status >= 0 && w.unpushTask(this))
990	<	tryExec();
991	<	pool = w.pool;
992	<	}
993	<	else
994	<	pool = null;
995	<	/*
996	<	* Timed wait loop intermixes cases for fj (pool != null) and
997	<	* non FJ threads. For FJ, decrement pool count but don't try
998	<	* for replacement; increment count on completion. For non-FJ,
999	<	* deal with interrupts. This is messy, but a little less so
1000	<	* than is splitting the FJ and nonFJ cases.
1001	<	*/
1002	<	boolean interrupted = false;
1003	<	boolean dec = false; // true if pool count decremented
1004	<	for (;;) {
1005	<	if (Thread.interrupted() && pool == null) {
684	<	interrupted = true;
685	<	break;
686	<	}
687	<	int s = status;
688	<	if (s < 0)
689	<	break;
690	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
691	<	s, s | SIGNAL)) {
692	<	long startTime = System.nanoTime();
693	<	long nanos = unit.toNanos(timeout);
694	<	long nt; // wait time
695	<	while (status >= 0 &&
696	<	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
697	<	if (pool != null && !dec)
698	<	dec = pool.tryDecrementRunningCount();
986	>	if (!(t instanceof ForkJoinWorkerThread)) {
987	>	if ((millis = unit.toMillis(timeout)) > 0L)
988	>	s = externalInterruptibleAwaitDone(millis);
989	>	else
990	>	s = status;
991	>	}
992	>	else if ((s = status) >= 0 && (nanos = unit.toNanos(timeout)) > 0L) {
993	>	long deadline = System.nanoTime() + nanos;
994	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
995	>	ForkJoinPool.WorkQueue w = wt.workQueue;
996	>	ForkJoinPool p = wt.pool;
997	>	if (w.tryUnpush(this))
998	>	doExec();
999	>	boolean blocking = false;
1000	>	try {
1001	>	while ((s = status) >= 0) {
1002	>	if (w.runState < 0)
1003	>	cancelIgnoringExceptions(this);
1004	>	else if (!blocking)
1005	>	blocking = p.tryCompensate();
1006		else {
1007	<	long ms = nt / 1000000;
1008	<	int ns = (int) (nt % 1000000);
1009	<	try {
1010	<	synchronized(this) {
1011	<	if (status >= 0)
1012	<	wait(ms, ns);
1013	<	}
1014	<	} catch (InterruptedException ie) {
1015	<	if (pool != null)
709	<	cancelIfTerminating();
710	<	else {
711	<	interrupted = true;
712	<	break;
1007	>	millis = TimeUnit.NANOSECONDS.toMillis(nanos);
1008	>	if (millis > 0L &&
1009	>	U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
1010	>	try {
1011	>	synchronized (this) {
1012	>	if (status >= 0)
1013	>	wait(millis);
1014	>	}
1015	>	} catch (InterruptedException ie) {
1016		}
1017		}
1018	+	if ((s = status) < 0 ||
1019	+	(nanos = deadline - System.nanoTime()) <= 0L)
1020	+	break;
1021		}
1022		}
1023	<	break;
1023	>	} finally {
1024	>	if (blocking)
1025	>	p.incrementActiveCount();
1026		}
1027		}
1028	<	if (pool != null && dec)
721	<	pool.incrementRunningCount();
722	<	if (interrupted)
723	<	throw new InterruptedException();
724	<	int es = status;
725	<	if (es != NORMAL) {
1028	>	if (s != NORMAL) {
1029		Throwable ex;
1030	<	if (es == CANCELLED)
1030	>	if (s == CANCELLED)
1031		throw new CancellationException();
1032	<	if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
1032	>	if (s != EXCEPTIONAL)
1033	>	throw new TimeoutException();
1034	>	if ((ex = getThrowableException()) != null)
1035		throw new ExecutionException(ex);
731	–	throw new TimeoutException();
1036		}
1037		return getRawResult();
1038		}
1039
1040		/**
1041	<	* Joins this task, without returning its result or throwing an
1041	>	* Joins this task, without returning its result or throwing its
1042		* exception. This method may be useful when processing
1043		* collections of tasks when some have been cancelled or otherwise
1044		* known to have aborted.
#	Line 745 | Line 1049 | public abstract class ForkJoinTask<V> im
1049
1050		/**
1051		* Commences performing this task and awaits its completion if
1052	<	* necessary, without returning its result or throwing an
1053	<	* exception. This method may be useful when processing
750	<	* collections of tasks when some have been cancelled or otherwise
751	<	* known to have aborted.
1052	>	* necessary, without returning its result or throwing its
1053	>	* exception.
1054		*/
1055		public final void quietlyInvoke() {
1056		doInvoke();
#	Line 762 | Line 1064 | public abstract class ForkJoinTask<V> im
1064		* processed.
1065		*
1066		* <p>This method may be invoked only from within {@code
1067	<	* ForkJoinTask} computations (as may be determined using method
1067	>	* ForkJoinPool} computations (as may be determined using method
1068		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1069		* result in exceptions or errors, possibly including {@code
1070		* ClassCastException}.
1071		*/
1072		public static void helpQuiesce() {
1073	<	((ForkJoinWorkerThread) Thread.currentThread())
1074	<	.helpQuiescePool();
1073	>	ForkJoinWorkerThread w =
1074	>	(ForkJoinWorkerThread)Thread.currentThread();
1075	>	w.pool.helpQuiescePool(w.workQueue);
1076		}
1077
1078		/**
#	Line 781 | Line 1084 | public abstract class ForkJoinTask<V> im
1084		* under any other usage conditions are not guaranteed.
1085		* This method may be useful when executing
1086		* pre-constructed trees of subtasks in loops.
1087	+	*
1088	+	* <p>Upon completion of this method, {@code isDone()} reports
1089	+	* {@code false}, and {@code getException()} reports {@code
1090	+	* null}. However, the value returned by {@code getRawResult} is
1091	+	* unaffected. To clear this value, you can invoke {@code
1092	+	* setRawResult(null)}.
1093		*/
1094		public void reinitialize() {
1095		if (status == EXCEPTIONAL)
1096	<	exceptionMap.remove(this);
1097	<	status = 0;
1096	>	clearExceptionalCompletion();
1097	>	else
1098	>	status = 0;
1099		}
1100
1101		/**
#	Line 802 | Line 1112 | public abstract class ForkJoinTask<V> im
1112		}
1113
1114		/**
1115	<	* Returns {@code true} if the current thread is executing as a
1116	<	* ForkJoinPool computation.
1115	>	* Returns {@code true} if the current thread is a {@link
1116	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1117		*
1118	<	* @return {@code true} if the current thread is executing as a
1119	<	* ForkJoinPool computation, or false otherwise
1118	>	* @return {@code true} if the current thread is a {@link
1119	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1120	>	* or {@code false} otherwise
1121		*/
1122		public static boolean inForkJoinPool() {
1123		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 821 | Line 1132 | public abstract class ForkJoinTask<V> im
1132		* were not, stolen.
1133		*
1134		* <p>This method may be invoked only from within {@code
1135	<	* ForkJoinTask} computations (as may be determined using method
1135	>	* ForkJoinPool} computations (as may be determined using method
1136		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1137		* result in exceptions or errors, possibly including {@code
1138		* ClassCastException}.
#	Line 829 | Line 1140 | public abstract class ForkJoinTask<V> im
1140		* @return {@code true} if unforked
1141		*/
1142		public boolean tryUnfork() {
1143	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1144	<	.unpushTask(this);
1143	>	return ((ForkJoinWorkerThread)Thread.currentThread())
1144	>	.workQueue.tryUnpush(this);
1145		}
1146
1147		/**
#	Line 840 | Line 1151 | public abstract class ForkJoinTask<V> im
1151		* fork other tasks.
1152		*
1153		* <p>This method may be invoked only from within {@code
1154	<	* ForkJoinTask} computations (as may be determined using method
1154	>	* ForkJoinPool} computations (as may be determined using method
1155		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1156		* result in exceptions or errors, possibly including {@code
1157		* ClassCastException}.
#	Line 849 | Line 1160 | public abstract class ForkJoinTask<V> im
1160		*/
1161		public static int getQueuedTaskCount() {
1162		return ((ForkJoinWorkerThread) Thread.currentThread())
1163	<	.getQueueSize();
1163	>	.workQueue.queueSize();
1164		}
1165
1166		/**
#	Line 863 | Line 1174 | public abstract class ForkJoinTask<V> im
1174		* exceeded.
1175		*
1176		* <p>This method may be invoked only from within {@code
1177	<	* ForkJoinTask} computations (as may be determined using method
1177	>	* ForkJoinPool} computations (as may be determined using method
1178		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1179		* result in exceptions or errors, possibly including {@code
1180		* ClassCastException}.
#	Line 871 | Line 1182 | public abstract class ForkJoinTask<V> im
1182		* @return the surplus number of tasks, which may be negative
1183		*/
1184		public static int getSurplusQueuedTaskCount() {
1185	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1186	<	.getEstimatedSurplusTaskCount();
1185	>	/*
1186	>	* The aim of this method is to return a cheap heuristic guide
1187	>	* for task partitioning when programmers, frameworks, tools,
1188	>	* or languages have little or no idea about task granularity.
1189	>	* In essence by offering this method, we ask users only about
1190	>	* tradeoffs in overhead vs expected throughput and its
1191	>	* variance, rather than how finely to partition tasks.
1192	>	*
1193	>	* In a steady state strict (tree-structured) computation,
1194	>	* each thread makes available for stealing enough tasks for
1195	>	* other threads to remain active. Inductively, if all threads
1196	>	* play by the same rules, each thread should make available
1197	>	* only a constant number of tasks.
1198	>	*
1199	>	* The minimum useful constant is just 1. But using a value of
1200	>	* 1 would require immediate replenishment upon each steal to
1201	>	* maintain enough tasks, which is infeasible.  Further,
1202	>	* partitionings/granularities of offered tasks should
1203	>	* minimize steal rates, which in general means that threads
1204	>	* nearer the top of computation tree should generate more
1205	>	* than those nearer the bottom. In perfect steady state, each
1206	>	* thread is at approximately the same level of computation
1207	>	* tree. However, producing extra tasks amortizes the
1208	>	* uncertainty of progress and diffusion assumptions.
1209	>	*
1210	>	* So, users will want to use values larger, but not much
1211	>	* larger than 1 to both smooth over transient shortages and
1212	>	* hedge against uneven progress; as traded off against the
1213	>	* cost of extra task overhead. We leave the user to pick a
1214	>	* threshold value to compare with the results of this call to
1215	>	* guide decisions, but recommend values such as 3.
1216	>	*
1217	>	* When all threads are active, it is on average OK to
1218	>	* estimate surplus strictly locally. In steady-state, if one
1219	>	* thread is maintaining say 2 surplus tasks, then so are
1220	>	* others. So we can just use estimated queue length.
1221	>	* However, this strategy alone leads to serious mis-estimates
1222	>	* in some non-steady-state conditions (ramp-up, ramp-down,
1223	>	* other stalls). We can detect many of these by further
1224	>	* considering the number of "idle" threads, that are known to
1225	>	* have zero queued tasks, so compensate by a factor of
1226	>	* (#idle/#active) threads.
1227	>	*/
1228	>	ForkJoinWorkerThread w =
1229	>	(ForkJoinWorkerThread)Thread.currentThread();
1230	>	return w.workQueue.queueSize() - w.pool.idlePerActive();
1231		}
1232
1233		// Extension methods
#	Line 921 | Line 1276 | public abstract class ForkJoinTask<V> im
1276		* otherwise.
1277		*
1278		* <p>This method may be invoked only from within {@code
1279	<	* ForkJoinTask} computations (as may be determined using method
1279	>	* ForkJoinPool} computations (as may be determined using method
1280		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1281		* result in exceptions or errors, possibly including {@code
1282		* ClassCastException}.
#	Line 929 | Line 1284 | public abstract class ForkJoinTask<V> im
1284		* @return the next task, or {@code null} if none are available
1285		*/
1286		protected static ForkJoinTask<?> peekNextLocalTask() {
1287	<	return ((ForkJoinWorkerThread) Thread.currentThread())
933	<	.peekTask();
1287	>	return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek();
1288		}
1289
1290		/**
#	Line 940 | Line 1294 | public abstract class ForkJoinTask<V> im
1294		* be useful otherwise.
1295		*
1296		* <p>This method may be invoked only from within {@code
1297	<	* ForkJoinTask} computations (as may be determined using method
1297	>	* ForkJoinPool} computations (as may be determined using method
1298		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1299		* result in exceptions or errors, possibly including {@code
1300		* ClassCastException}.
#	Line 949 | Line 1303 | public abstract class ForkJoinTask<V> im
1303		*/
1304		protected static ForkJoinTask<?> pollNextLocalTask() {
1305		return ((ForkJoinWorkerThread) Thread.currentThread())
1306	<	.pollLocalTask();
1306	>	.workQueue.nextLocalTask();
1307		}
1308
1309		/**
#	Line 963 | Line 1317 | public abstract class ForkJoinTask<V> im
1317		* otherwise.
1318		*
1319		* <p>This method may be invoked only from within {@code
1320	<	* ForkJoinTask} computations (as may be determined using method
1320	>	* ForkJoinPool} computations (as may be determined using method
1321		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1322		* result in exceptions or errors, possibly including {@code
1323		* ClassCastException}.
#	Line 971 | Line 1325 | public abstract class ForkJoinTask<V> im
1325		* @return a task, or {@code null} if none are available
1326		*/
1327		protected static ForkJoinTask<?> pollTask() {
1328	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1329	<	.pollTask();
1328	>	ForkJoinWorkerThread w =
1329	>	(ForkJoinWorkerThread)Thread.currentThread();
1330	>	return w.pool.nextTaskFor(w.workQueue);
1331	>	}
1332	>
1333	>	// Mark-bit operations
1334	>
1335	>	/**
1336	>	* Returns true if this task is marked.
1337	>	*
1338	>	* @return true if this task is marked
1339	>	* @since 1.8
1340	>	*/
1341	>	public final boolean isMarkedForkJoinTask() {
1342	>	return (status & MARKED) != 0;
1343	>	}
1344	>
1345	>	/**
1346	>	* Atomically sets the mark on this task.
1347	>	*
1348	>	* @return true if this task was previously unmarked
1349	>	* @since 1.8
1350	>	*/
1351	>	public final boolean markForkJoinTask() {
1352	>	for (int s;;) {
1353	>	if (((s = status) & MARKED) != 0)
1354	>	return false;
1355	>	if (U.compareAndSwapInt(this, STATUS, s, s | MARKED))
1356	>	return true;
1357	>	}
1358	>	}
1359	>
1360	>	/**
1361	>	* Atomically clears the mark on this task.
1362	>	*
1363	>	* @return true if this task was previously marked
1364	>	* @since 1.8
1365	>	*/
1366	>	public final boolean unmarkForkJoinTask() {
1367	>	for (int s;;) {
1368	>	if (((s = status) & MARKED) == 0)
1369	>	return false;
1370	>	if (U.compareAndSwapInt(this, STATUS, s, s & ~MARKED))
1371	>	return true;
1372	>	}
1373		}
1374
1375		/**
#	Line 1073 | Line 1470 | public abstract class ForkJoinTask<V> im
1470		private static final long serialVersionUID = -7721805057305804111L;
1471
1472		/**
1473	<	* Saves the state to a stream.
1473	>	* Saves this task to a stream (that is, serializes it).
1474		*
1475		* @serialData the current run status and the exception thrown
1476		* during execution, or {@code null} if none
1080	–	* @param s the stream
1477		*/
1478		private void writeObject(java.io.ObjectOutputStream s)
1479		throws java.io.IOException {
#	Line 1086 | Line 1482 | public abstract class ForkJoinTask<V> im
1482		}
1483
1484		/**
1485	<	* Reconstitutes the instance from a stream.
1090	<	*
1091	<	* @param s the stream
1485	>	* Reconstitutes this task from a stream (that is, deserializes it).
1486		*/
1487		private void readObject(java.io.ObjectInputStream s)
1488		throws java.io.IOException, ClassNotFoundException {
1489		s.defaultReadObject();
1490		Object ex = s.readObject();
1491		if (ex != null)
1492	<	setExceptionalCompletion((Throwable) ex);
1492	>	setExceptionalCompletion((Throwable)ex);
1493		}
1494
1495		// Unsafe mechanics
1496	<
1497	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1498	<	private static final long statusOffset =
1499	<	objectFieldOffset("status", ForkJoinTask.class);
1500	<
1501	<	private static long objectFieldOffset(String field, Class<?> klazz) {
1496	>	private static final sun.misc.Unsafe U;
1497	>	private static final long STATUS;
1498	>	static {
1499	>	exceptionTableLock = new ReentrantLock();
1500	>	exceptionTableRefQueue = new ReferenceQueue<Object>();
1501	>	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1502		try {
1503	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1504	<	} catch (NoSuchFieldException e) {
1505	<	// Convert Exception to corresponding Error
1506	<	NoSuchFieldError error = new NoSuchFieldError(field);
1507	<	error.initCause(e);
1114	<	throw error;
1503	>	U = getUnsafe();
1504	>	STATUS = U.objectFieldOffset
1505	>	(ForkJoinTask.class.getDeclaredField("status"));
1506	>	} catch (Exception e) {
1507	>	throw new Error(e);
1508		}
1509		}
1510

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