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Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.64 by jsr166, Mon Sep 20 20:42:37 2010 UTC vs.
Revision 1.90 by dl, Sat Apr 21 11:45:20 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.*;
9		import java.io.Serializable;
10		import java.util.Collection;
12	–	import java.util.Collections;
11		import java.util.List;
12		import java.util.RandomAccess;
13	<	import java.util.Map;
14	<	import java.util.WeakHashMap;
13	>	import java.lang.ref.WeakReference;
14	>	import java.lang.ref.ReferenceQueue;
15	>	import java.util.concurrent.Callable;
16	>	import java.util.concurrent.CancellationException;
17	>	import java.util.concurrent.ExecutionException;
18	>	import java.util.concurrent.Future;
19	>	import java.util.concurrent.RejectedExecutionException;
20	>	import java.util.concurrent.RunnableFuture;
21	>	import java.util.concurrent.TimeUnit;
22	>	import java.util.concurrent.TimeoutException;
23	>	import java.util.concurrent.locks.ReentrantLock;
24	>	import java.lang.reflect.Constructor;
25
26		/**
27		* Abstract base class for tasks that run within a {@link ForkJoinPool}.
#	Line 35 | Line 43 | import java.util.WeakHashMap;
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 (for example, those subclassing {@link
75	>	* CountedCompleter}) often fall into this category.  (2) To minimize
76	>	* resource impact, tasks should be small; ideally performing only the
77	>	* (possibly) blocking action. (3) Unless the {@link
78	>	* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
79	>	* blocked tasks is known to be less than the pool's {@link
80	>	* ForkJoinPool#getParallelism} level, the pool cannot guarantee that
81	>	* enough threads will be available to ensure progress or good
82	>	* performance.
83		*
84		* <p>The primary method for awaiting completion and extracting
85		* results of a task is {@link #join}, but there are several variants:
#	Line 73 | Line 95 | import java.util.WeakHashMap;
95		* performs the most common form of parallel invocation: forking a set
96		* of tasks and joining them all.
97		*
98	+	* <p>In the most typical usages, a fork-join pair act like a call
99	+	* (fork) and return (join) from a parallel recursive function. As is
100	+	* the case with other forms of recursive calls, returns (joins)
101	+	* should be performed innermost-first. For example, {@code a.fork();
102	+	* b.fork(); b.join(); a.join();} is likely to be substantially more
103	+	* efficient than joining {@code a} before {@code b}.
104	+	*
105		* <p>The execution status of tasks may be queried at several levels
106		* of detail: {@link #isDone} is true if a task completed in any way
107		* (including the case where a task was cancelled without executing);
#	Line 88 | Line 117 | import java.util.WeakHashMap;
117		* <p>The ForkJoinTask class is not usually directly subclassed.
118		* Instead, you subclass one of the abstract classes that support a
119		* particular style of fork/join processing, typically {@link
120	<	* RecursiveAction} for computations that do not return results, or
121	<	* {@link RecursiveTask} for those that do.  Normally, a concrete
122	<	* ForkJoinTask subclass declares fields comprising its parameters,
123	<	* established in a constructor, and then defines a {@code compute}
124	<	* method that somehow uses the control methods supplied by this base
125	<	* class. While these methods have {@code public} access (to allow
126	<	* instances of different task subclasses to call each other's
127	<	* methods), some of them may only be called from within other
128	<	* ForkJoinTasks (as may be determined using method {@link
129	<	* #inForkJoinPool}).  Attempts to invoke them in other contexts
130	<	* result in exceptions or errors, possibly including
131	<	* {@code ClassCastException}.
120	>	* RecursiveAction} for most computations that do not return results,
121	>	* {@link RecursiveTask} for those that do, and {@link
122	>	* CountedCompleter} for those in which completed actions trigger
123	>	* other actions.  Normally, a concrete ForkJoinTask subclass declares
124	>	* fields comprising its parameters, established in a constructor, and
125	>	* then defines a {@code compute} method that somehow uses the control
126	>	* methods supplied by this base class. While these methods have
127	>	* {@code public} access (to allow instances of different task
128	>	* subclasses to call each other's methods), some of them may only be
129	>	* called from within other ForkJoinTasks (as may be determined using
130	>	* method {@link #inForkJoinPool}).  Attempts to invoke them in other
131	>	* contexts result in exceptions or errors, possibly including {@code
132	>	* ClassCastException}.
133	>	*
134	>	* <p>Method {@link #join} and its variants are appropriate for use
135	>	* only when completion dependencies are acyclic; that is, the
136	>	* parallel computation can be described as a directed acyclic graph
137	>	* (DAG). Otherwise, executions may encounter a form of deadlock as
138	>	* tasks cyclically wait for each other.  However, this framework
139	>	* supports other methods and techniques (for example the use of
140	>	* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
141	>	* may be of use in constructing custom subclasses for problems that
142	>	* are not statically structured as DAGs. To support such usages a
143	>	* ForkJoinTask may be atomically <em>tagged</em> with a {@code short}
144	>	* value using {@link #setForkJoinTaskTag} or {@link
145	>	* #compareAndSetForkJoinTaskTag} and checked using {@link
146	>	* #getForkJoinTaskTag}. The ForkJoinTask implementation does not use
147	>	* these {@code protected} methods or tags for any purpose, but they
148	>	* may be of use in the construction of specialized subclasses.  For
149	>	* example, parallel graph traversals can use the supplied methods to
150	>	* avoid revisiting nodes/tasks that have already been processed.
151	>	* (Method names for tagging are bulky in part to encourage definition
152	>	* 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 115 | Line 165 | import java.util.WeakHashMap;
165		* computation. Large tasks should be split into smaller subtasks,
166		* usually via recursive decomposition. As a very rough rule of thumb,
167		* a task should perform more than 100 and less than 10000 basic
168	<	* computational steps. If tasks are too big, then parallelism cannot
169	<	* improve throughput. If too small, then memory and internal task
170	<	* maintenance overhead may overwhelm processing.
168	>	* computational steps, and should avoid indefinite looping. If tasks
169	>	* are too big, then parallelism cannot improve throughput. If too
170	>	* small, then memory and internal task maintenance overhead may
171	>	* overwhelm processing.
172		*
173		* <p>This class provides {@code adapt} methods for {@link Runnable}
174		* and {@link Callable}, that may be of use when mixing execution of
#	Line 138 | 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	+	/**
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	<	private static final int NORMAL      = -1;
313	<	private static final int CANCELLED   = -2;
314	<	private static final int EXCEPTIONAL = -3;
315	<	private static final int SIGNAL      =  1;
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 178 | 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	>	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	<	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
184	<	Collections.synchronizedMap
185	<	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
388	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
389
390	<	// Maintaining completion status
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,
191	<	* also clearing signal request bits.
415	>	* Records exception and sets status.
416		*
417	<	* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
417	>	* @return status on exit
418		*/
419	<	private void setCompletion(int completion) {
419	>	final int recordExceptionalCompletion(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	+	return s;
443		}
444
445		/**
446	<	* Records exception and sets exceptional completion.
446	>	* Records exception and possibly propagates
447		*
448		* @return status on exit
449		*/
450	<	private void setExceptionalCompletion(Throwable rex) {
451	<	exceptionMap.put(this, rex);
452	<	setCompletion(EXCEPTIONAL);
450	>	private int setExceptionalCompletion(Throwable ex) {
451	>	int s = recordExceptionalCompletion(ex);
452	>	if ((s & DONE_MASK) == EXCEPTIONAL)
453	>	internalPropagateException(ex);
454	>	return s;
455		}
456
457		/**
458	<	* Blocks a worker thread until completion. Called only by
218	<	* pool. Currently unused -- pool-based waits use timeout
219	<	* version below.
458	>	* Hook for exception propagation support for tasks with completers.
459		*/
460	<	final void internalAwaitDone() {
461	<	int s;         // the odd construction reduces lock bias effects
462	<	while ((s = status) >= 0) {
460	>	void internalPropagateException(Throwable ex) {
461	>	}
462	>
463	>	/**
464	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
465	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
466	>	* exceptions, but if it does anyway, we have no recourse during
467	>	* shutdown, so guard against this case.
468	>	*/
469	>	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
470	>	if (t != null && t.status >= 0) {
471		try {
472	<	synchronized (this) {
473	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
227	<	wait();
228	<	}
229	<	} catch (InterruptedException ie) {
230	<	cancelIfTerminating();
472	>	t.cancel(false);
473	>	} catch (Throwable ignore) {
474		}
475		}
476		}
477
478		/**
479	<	* Blocks a worker thread until completed or timed out.  Called
237	<	* only by pool.
238	<	*
239	<	* @return status on exit
479	>	* Removes exception node and clears status
480		*/
481	<	final int internalAwaitDone(long millis) {
482	<	int s;
483	<	if ((s = status) >= 0) {
481	>	private void clearExceptionalCompletion() {
482	>	int h = System.identityHashCode(this);
483	>	final ReentrantLock lock = exceptionTableLock;
484	>	lock.lock();
485	>	try {
486	>	ExceptionNode[] t = exceptionTable;
487	>	int i = h & (t.length - 1);
488	>	ExceptionNode e = t[i];
489	>	ExceptionNode pred = null;
490	>	while (e != null) {
491	>	ExceptionNode next = e.next;
492	>	if (e.get() == this) {
493	>	if (pred == null)
494	>	t[i] = next;
495	>	else
496	>	pred.next = next;
497	>	break;
498	>	}
499	>	pred = e;
500	>	e = next;
501	>	}
502	>	expungeStaleExceptions();
503	>	status = 0;
504	>	} finally {
505	>	lock.unlock();
506	>	}
507	>	}
508	>
509	>	/**
510	>	* Returns a rethrowable exception for the given task, if
511	>	* available. To provide accurate stack traces, if the exception
512	>	* was not thrown by the current thread, we try to create a new
513	>	* exception of the same type as the one thrown, but with the
514	>	* recorded exception as its cause. If there is no such
515	>	* constructor, we instead try to use a no-arg constructor,
516	>	* followed by initCause, to the same effect. If none of these
517	>	* apply, or any fail due to other exceptions, we return the
518	>	* recorded exception, which is still correct, although it may
519	>	* contain a misleading stack trace.
520	>	*
521	>	* @return the exception, or null if none
522	>	*/
523	>	private Throwable getThrowableException() {
524	>	if ((status & DONE_MASK) != EXCEPTIONAL)
525	>	return null;
526	>	int h = System.identityHashCode(this);
527	>	ExceptionNode e;
528	>	final ReentrantLock lock = exceptionTableLock;
529	>	lock.lock();
530	>	try {
531	>	expungeStaleExceptions();
532	>	ExceptionNode[] t = exceptionTable;
533	>	e = t[h & (t.length - 1)];
534	>	while (e != null && e.get() != this)
535	>	e = e.next;
536	>	} finally {
537	>	lock.unlock();
538	>	}
539	>	Throwable ex;
540	>	if (e == null || (ex = e.ex) == null)
541	>	return null;
542	>	if (false && e.thrower != Thread.currentThread().getId()) {
543	>	Class<? extends Throwable> ec = ex.getClass();
544		try {
545	<	synchronized (this) {
546	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s,SIGNAL))
547	<	wait(millis, 0);
545	>	Constructor<?> noArgCtor = null;
546	>	Constructor<?>[] cs = ec.getConstructors();// public ctors only
547	>	for (int i = 0; i < cs.length; ++i) {
548	>	Constructor<?> c = cs[i];
549	>	Class<?>[] ps = c.getParameterTypes();
550	>	if (ps.length == 0)
551	>	noArgCtor = c;
552	>	else if (ps.length == 1 && ps[0] == Throwable.class)
553	>	return (Throwable)(c.newInstance(ex));
554	>	}
555	>	if (noArgCtor != null) {
556	>	Throwable wx = (Throwable)(noArgCtor.newInstance());
557	>	wx.initCause(ex);
558	>	return wx;
559		}
560	<	} catch (InterruptedException ie) {
250	<	cancelIfTerminating();
560	>	} catch (Exception ignore) {
561		}
252	–	s = status;
562		}
563	<	return s;
563	>	return ex;
564		}
565
566		/**
567	<	* Blocks a non-worker-thread until completion.
567	>	* Poll stale refs and remove them. Call only while holding lock.
568		*/
569	<	private void externalAwaitDone() {
570	<	int s;
571	<	while ((s = status) >= 0) {
572	<	synchronized (this) {
573	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
574	<	boolean interrupted = false;
575	<	while (status >= 0) {
576	<	try {
577	<	wait();
578	<	} catch (InterruptedException ie) {
579	<	interrupted = true;
580	<	}
569	>	private static void expungeStaleExceptions() {
570	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
571	>	if (x instanceof ExceptionNode) {
572	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
573	>	ExceptionNode[] t = exceptionTable;
574	>	int i = System.identityHashCode(key) & (t.length - 1);
575	>	ExceptionNode e = t[i];
576	>	ExceptionNode pred = null;
577	>	while (e != null) {
578	>	ExceptionNode next = e.next;
579	>	if (e == x) {
580	>	if (pred == null)
581	>	t[i] = next;
582	>	else
583	>	pred.next = next;
584	>	break;
585		}
586	<	if (interrupted)
587	<	Thread.currentThread().interrupt();
275	<	break;
586	>	pred = e;
587	>	e = next;
588		}
589		}
590		}
591		}
592
593		/**
594	<	* Unless done, calls exec and records status if completed, but
595	<	* doesn't wait for completion otherwise. Primary execution method
284	<	* for ForkJoinWorkerThread.
594	>	* If lock is available, poll stale refs and remove them.
595	>	* Called from ForkJoinPool when pools become quiescent.
596		*/
597	<	final void quietlyExec() {
598	<	try {
599	<	if (status < 0 || !exec())
600	<	return;
601	<	} catch (Throwable rex) {
602	<	setExceptionalCompletion(rex);
603	<	return;
597	>	static final void helpExpungeStaleExceptions() {
598	>	final ReentrantLock lock = exceptionTableLock;
599	>	if (lock.tryLock()) {
600	>	try {
601	>	expungeStaleExceptions();
602	>	} finally {
603	>	lock.unlock();
604	>	}
605		}
606	<	setCompletion(NORMAL); // must be outside try block
606	>	}
607	>
608	>	/**
609	>	* Throws exception, if any, associated with the given status.
610	>	*/
611	>	private void reportException(int s) {
612	>	Throwable ex = ((s == CANCELLED) ?  new CancellationException() :
613	>	(s == EXCEPTIONAL) ? getThrowableException() :
614	>	null);
615	>	if (ex != null)
616	>	U.throwException(ex);
617		}
618
619		// public methods
#	Line 307 | Line 629 | public abstract class ForkJoinTask<V> im
629		* #isDone} returning {@code true}.
630		*
631		* <p>This method may be invoked only from within {@code
632	<	* ForkJoinTask} computations (as may be determined using method
632	>	* ForkJoinPool} computations (as may be determined using method
633		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
634		* result in exceptions or errors, possibly including {@code
635		* ClassCastException}.
#	Line 315 | Line 637 | public abstract class ForkJoinTask<V> im
637		* @return {@code this}, to simplify usage
638		*/
639		public final ForkJoinTask<V> fork() {
640	<	((ForkJoinWorkerThread) Thread.currentThread())
319	<	.pushTask(this);
640	>	((ForkJoinWorkerThread)Thread.currentThread()).workQueue.push(this);
641		return this;
642		}
643
644		/**
645	<	* Returns the result of the computation when it {@link #isDone is done}.
646	<	* This method differs from {@link #get()} in that
645	>	* Returns the result of the computation when it {@link #isDone is
646	>	* done}.  This method differs from {@link #get()} in that
647		* abnormal completion results in {@code RuntimeException} or
648	<	* {@code Error}, not {@code ExecutionException}.
648	>	* {@code Error}, not {@code ExecutionException}, and that
649	>	* interrupts of the calling thread do <em>not</em> cause the
650	>	* method to abruptly return by throwing {@code
651	>	* InterruptedException}.
652		*
653		* @return the computed result
654		*/
655		public final V join() {
656	<	quietlyJoin();
657	<	Throwable ex;
658	<	if (status < NORMAL && (ex = getException()) != null)
335	<	UNSAFE.throwException(ex);
656	>	int s;
657	>	if ((s = doJoin() & DONE_MASK) != NORMAL)
658	>	reportException(s);
659		return getRawResult();
660		}
661
#	Line 345 | Line 668 | public abstract class ForkJoinTask<V> im
668		* @return the computed result
669		*/
670		public final V invoke() {
671	<	quietlyInvoke();
672	<	Throwable ex;
673	<	if (status < NORMAL && (ex = getException()) != null)
351	<	UNSAFE.throwException(ex);
671	>	int s;
672	>	if ((s = doInvoke() & DONE_MASK) != NORMAL)
673	>	reportException(s);
674		return getRawResult();
675		}
676
#	Line 366 | Line 688 | public abstract class ForkJoinTask<V> im
688		* unprocessed.
689		*
690		* <p>This method may be invoked only from within {@code
691	<	* ForkJoinTask} computations (as may be determined using method
691	>	* ForkJoinPool} computations (as may be determined using method
692		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
693		* result in exceptions or errors, possibly including {@code
694		* ClassCastException}.
#	Line 376 | Line 698 | public abstract class ForkJoinTask<V> im
698		* @throws NullPointerException if any task is null
699		*/
700		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
701	+	int s1, s2;
702		t2.fork();
703	<	t1.invoke();
704	<	t2.join();
703	>	if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL)
704	>	t1.reportException(s1);
705	>	if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
706	>	t2.reportException(s2);
707		}
708
709		/**
#	Line 394 | Line 719 | public abstract class ForkJoinTask<V> im
719		* normally or exceptionally, or left unprocessed.
720		*
721		* <p>This method may be invoked only from within {@code
722	<	* ForkJoinTask} computations (as may be determined using method
722	>	* ForkJoinPool} computations (as may be determined using method
723		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
724		* result in exceptions or errors, possibly including {@code
725		* ClassCastException}.
#	Line 413 | Line 738 | public abstract class ForkJoinTask<V> im
738		}
739		else if (i != 0)
740		t.fork();
741	<	else {
742	<	t.quietlyInvoke();
418	<	if (ex == null && t.status < NORMAL)
419	<	ex = t.getException();
420	<	}
741	>	else if (t.doInvoke() < NORMAL && ex == null)
742	>	ex = t.getException();
743		}
744		for (int i = 1; i <= last; ++i) {
745		ForkJoinTask<?> t = tasks[i];
746		if (t != null) {
747		if (ex != null)
748		t.cancel(false);
749	<	else {
750	<	t.quietlyJoin();
429	<	if (ex == null && t.status < NORMAL)
430	<	ex = t.getException();
431	<	}
749	>	else if (t.doJoin() < NORMAL)
750	>	ex = t.getException();
751		}
752		}
753		if (ex != null)
754	<	UNSAFE.throwException(ex);
754	>	U.throwException(ex);
755		}
756
757		/**
#	Line 449 | Line 768 | public abstract class ForkJoinTask<V> im
768		* unprocessed.
769		*
770		* <p>This method may be invoked only from within {@code
771	<	* ForkJoinTask} computations (as may be determined using method
771	>	* ForkJoinPool} computations (as may be determined using method
772		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
773		* result in exceptions or errors, possibly including {@code
774		* ClassCastException}.
#	Line 476 | Line 795 | public abstract class ForkJoinTask<V> im
795		}
796		else if (i != 0)
797		t.fork();
798	<	else {
799	<	t.quietlyInvoke();
481	<	if (ex == null && t.status < NORMAL)
482	<	ex = t.getException();
483	<	}
798	>	else if (t.doInvoke() < NORMAL && ex == null)
799	>	ex = t.getException();
800		}
801		for (int i = 1; i <= last; ++i) {
802		ForkJoinTask<?> t = ts.get(i);
803		if (t != null) {
804		if (ex != null)
805		t.cancel(false);
806	<	else {
807	<	t.quietlyJoin();
492	<	if (ex == null && t.status < NORMAL)
493	<	ex = t.getException();
494	<	}
806	>	else if (t.doJoin() < NORMAL)
807	>	ex = t.getException();
808		}
809		}
810		if (ex != null)
811	<	UNSAFE.throwException(ex);
811	>	U.throwException(ex);
812		return tasks;
813		}
814
815		/**
816		* Attempts to cancel execution of this task. This attempt will
817	<	* fail if the task has already completed, has already been
818	<	* cancelled, or could not be cancelled for some other reason. If
819	<	* successful, and this task has not started when cancel is
820	<	* called, execution of this task is suppressed, {@link
821	<	* #isCancelled} will report true, and {@link #join} will result
822	<	* in a {@code CancellationException} being thrown.
817	>	* fail if the task has already completed or could not be
818	>	* cancelled for some other reason. If successful, and this task
819	>	* has not started when {@code cancel} is called, execution of
820	>	* this task is suppressed. After this method returns
821	>	* successfully, unless there is an intervening call to {@link
822	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
823	>	* {@link #isDone}, and {@code cancel} will return {@code true}
824	>	* and calls to {@link #join} and related methods will result in
825	>	* {@code CancellationException}.
826		*
827		* <p>This method may be overridden in subclasses, but if so, must
828	<	* still ensure that these minimal properties hold. In particular,
829	<	* the {@code cancel} method itself must not throw exceptions.
828	>	* still ensure that these properties hold. In particular, the
829	>	* {@code cancel} method itself must not throw exceptions.
830		*
831		* <p>This method is designed to be invoked by <em>other</em>
832		* tasks. To terminate the current task, you can just return or
833		* throw an unchecked exception from its computation method, or
834		* invoke {@link #completeExceptionally}.
835		*
836	<	* @param mayInterruptIfRunning this value is ignored in the
837	<	* default implementation because tasks are not
838	<	* cancelled via interruption
836	>	* @param mayInterruptIfRunning this value has no effect in the
837	>	* default implementation because interrupts are not used to
838	>	* control cancellation.
839		*
840		* @return {@code true} if this task is now cancelled
841		*/
842		public boolean cancel(boolean mayInterruptIfRunning) {
843	<	setCompletion(CANCELLED);
528	<	return status == CANCELLED;
529	<	}
530	<
531	<	/**
532	<	* Cancels, ignoring any exceptions thrown by cancel. Used during
533	<	* worker and pool shutdown. Cancel is spec'ed not to throw any
534	<	* exceptions, but if it does anyway, we have no recourse during
535	<	* shutdown, so guard against this case.
536	<	*/
537	<	final void cancelIgnoringExceptions() {
538	<	try {
539	<	cancel(false);
540	<	} catch (Throwable ignore) {
541	<	}
542	<	}
543	<
544	<	/**
545	<	* Cancels if current thread is a terminating worker thread,
546	<	* ignoring any exceptions thrown by cancel.
547	<	*/
548	<	final void cancelIfTerminating() {
549	<	Thread t = Thread.currentThread();
550	<	if ((t instanceof ForkJoinWorkerThread) &&
551	<	((ForkJoinWorkerThread) t).isTerminating()) {
552	<	try {
553	<	cancel(false);
554	<	} catch (Throwable ignore) {
555	<	}
556	<	}
843	>	return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
844		}
845
846		public final boolean isDone() {
#	Line 561 | Line 848 | public abstract class ForkJoinTask<V> im
848		}
849
850		public final boolean isCancelled() {
851	<	return status == CANCELLED;
851	>	return (status & DONE_MASK) == CANCELLED;
852		}
853
854		/**
#	Line 581 | Line 868 | public abstract class ForkJoinTask<V> im
868		* exception and was not cancelled
869		*/
870		public final boolean isCompletedNormally() {
871	<	return status == NORMAL;
871	>	return (status & DONE_MASK) == NORMAL;
872		}
873
874		/**
#	Line 592 | Line 879 | public abstract class ForkJoinTask<V> im
879		* @return the exception, or {@code null} if none
880		*/
881		public final Throwable getException() {
882	<	int s = status;
882	>	int s = status & DONE_MASK;
883		return ((s >= NORMAL)    ? null :
884		(s == CANCELLED) ? new CancellationException() :
885	<	exceptionMap.get(this));
885	>	getThrowableException());
886		}
887
888		/**
#	Line 642 | Line 929 | public abstract class ForkJoinTask<V> im
929		}
930
931		/**
932	+	* Completes this task normally without setting a value. The most
933	+	* recent value established by {@link #setRawResult} (or {@code
934	+	* null} by default) will be returned as the result of subsequent
935	+	* invocations of {@code join} and related operations.
936	+	*
937	+	* @since 1.8
938	+	*/
939	+	public final void quietlyComplete() {
940	+	setCompletion(NORMAL);
941	+	}
942	+
943	+	/**
944		* Waits if necessary for the computation to complete, and then
945		* retrieves its result.
946		*
#	Line 653 | Line 952 | public abstract class ForkJoinTask<V> im
952		* member of a ForkJoinPool and was interrupted while waiting
953		*/
954		public final V get() throws InterruptedException, ExecutionException {
955	<	int s;
956	<	if (Thread.currentThread() instanceof ForkJoinWorkerThread) {
957	<	quietlyJoin();
958	<	s = status;
959	<	}
960	<	else {
961	<	while ((s = status) >= 0) {
663	<	synchronized (this) { // interruptible form of awaitDone
664	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
665	<	s, SIGNAL)) {
666	<	while (status >= 0)
667	<	wait();
668	<	}
669	<	}
670	<	}
671	<	}
672	<	if (s < NORMAL) {
673	<	Throwable ex;
674	<	if (s == CANCELLED)
675	<	throw new CancellationException();
676	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
677	<	throw new ExecutionException(ex);
678	<	}
955	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
956	>	doJoin() : externalInterruptibleAwaitDone();
957	>	Throwable ex;
958	>	if ((s &= DONE_MASK) == CANCELLED)
959	>	throw new CancellationException();
960	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
961	>	throw new ExecutionException(ex);
962		return getRawResult();
963		}
964
#	Line 695 | Line 978 | public abstract class ForkJoinTask<V> im
978		*/
979		public final V get(long timeout, TimeUnit unit)
980		throws InterruptedException, ExecutionException, TimeoutException {
981	<	Thread t = Thread.currentThread();
982	<	ForkJoinPool pool;
983	<	if (t instanceof ForkJoinWorkerThread) {
984	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
985	<	if (status >= 0 && w.unpushTask(this))
986	<	quietlyExec();
987	<	pool = w.pool;
988	<	}
989	<	else
990	<	pool = null;
991	<	/*
992	<	* Timed wait loop intermixes cases for FJ (pool != null) and
993	<	* non FJ threads. For FJ, decrement pool count but don't try
994	<	* for replacement; increment count on completion. For non-FJ,
712	<	* deal with interrupts. This is messy, but a little less so
713	<	* than is splitting the FJ and nonFJ cases.
714	<	*/
715	<	boolean interrupted = false;
716	<	boolean dec = false; // true if pool count decremented
717	<	long nanos = unit.toNanos(timeout);
718	<	for (;;) {
719	<	if (pool == null && Thread.interrupted()) {
720	<	interrupted = true;
721	<	break;
981	>	if (Thread.interrupted())
982	>	throw new InterruptedException();
983	>	// Messy in part because we measure in nanosecs, but wait in millisecs
984	>	int s; long ns, ms;
985	>	if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) {
986	>	long deadline = System.nanoTime() + ns;
987	>	ForkJoinPool p = null;
988	>	ForkJoinPool.WorkQueue w = null;
989	>	Thread t = Thread.currentThread();
990	>	if (t instanceof ForkJoinWorkerThread) {
991	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
992	>	p = wt.pool;
993	>	w = wt.workQueue;
994	>	s = p.helpJoinOnce(w, this); // no retries on failure
995		}
996	<	int s = status;
997	<	if (s < 0)
998	<	break;
999	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
1000	<	long startTime = System.nanoTime();
1001	<	long nt; // wait time
1002	<	while (status >= 0 &&
1003	<	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
1004	<	if (pool != null && !dec)
1005	<	dec = pool.tryDecrementRunningCount();
996	>	boolean canBlock = false;
997	>	boolean interrupted = false;
998	>	try {
999	>	while ((s = status) >= 0) {
1000	>	if (w != null && w.runState < 0)
1001	>	cancelIgnoringExceptions(this);
1002	>	else if (!canBlock) {
1003	>	if (p == null || p.tryCompensate(this, null))
1004	>	canBlock = true;
1005	>	}
1006		else {
1007	<	long ms = nt / 1000000;
1008	<	int ns = (int) (nt % 1000000);
736	<	try {
1007	>	if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
1008	>	U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
1009		synchronized (this) {
1010	<	if (status >= 0)
1011	<	wait(ms, ns);
1012	<	}
1013	<	} catch (InterruptedException ie) {
1014	<	if (pool != null)
1015	<	cancelIfTerminating();
1016	<	else {
1017	<	interrupted = true;
1018	<	break;
1010	>	if (status >= 0) {
1011	>	try {
1012	>	wait(ms);
1013	>	} catch (InterruptedException ie) {
1014	>	if (p == null)
1015	>	interrupted = true;
1016	>	}
1017	>	}
1018	>	else
1019	>	notifyAll();
1020		}
1021		}
1022	+	if ((s = status) < 0 || interrupted ||
1023	+	(ns = deadline - System.nanoTime()) <= 0L)
1024	+	break;
1025		}
1026		}
1027	<	break;
1027	>	} finally {
1028	>	if (p != null && canBlock)
1029	>	p.incrementActiveCount();
1030		}
1031	+	if (interrupted)
1032	+	throw new InterruptedException();
1033		}
1034	<	if (pool != null && dec)
755	<	pool.incrementRunningCount();
756	<	if (interrupted)
757	<	throw new InterruptedException();
758	<	int es = status;
759	<	if (es != NORMAL) {
1034	>	if ((s &= DONE_MASK) != NORMAL) {
1035		Throwable ex;
1036	<	if (es == CANCELLED)
1036	>	if (s == CANCELLED)
1037		throw new CancellationException();
1038	<	if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
1038	>	if (s != EXCEPTIONAL)
1039	>	throw new TimeoutException();
1040	>	if ((ex = getThrowableException()) != null)
1041		throw new ExecutionException(ex);
765	–	throw new TimeoutException();
1042		}
1043		return getRawResult();
1044		}
#	Line 774 | Line 1050 | public abstract class ForkJoinTask<V> im
1050		* known to have aborted.
1051		*/
1052		public final void quietlyJoin() {
1053	<	Thread t;
778	<	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
779	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
780	<	if (status >= 0) {
781	<	if (w.unpushTask(this)) {
782	<	boolean completed;
783	<	try {
784	<	completed = exec();
785	<	} catch (Throwable rex) {
786	<	setExceptionalCompletion(rex);
787	<	return;
788	<	}
789	<	if (completed) {
790	<	setCompletion(NORMAL);
791	<	return;
792	<	}
793	<	}
794	<	w.joinTask(this);
795	<	}
796	<	}
797	<	else
798	<	externalAwaitDone();
1053	>	doJoin();
1054		}
1055
1056		/**
#	Line 804 | Line 1059 | public abstract class ForkJoinTask<V> im
1059		* exception.
1060		*/
1061		public final void quietlyInvoke() {
1062	<	if (status >= 0) {
808	<	boolean completed;
809	<	try {
810	<	completed = exec();
811	<	} catch (Throwable rex) {
812	<	setExceptionalCompletion(rex);
813	<	return;
814	<	}
815	<	if (completed)
816	<	setCompletion(NORMAL);
817	<	else
818	<	quietlyJoin();
819	<	}
1062	>	doInvoke();
1063		}
1064
1065		/**
#	Line 827 | Line 1070 | public abstract class ForkJoinTask<V> im
1070		* processed.
1071		*
1072		* <p>This method may be invoked only from within {@code
1073	<	* ForkJoinTask} computations (as may be determined using method
1073	>	* ForkJoinPool} computations (as may be determined using method
1074		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1075		* result in exceptions or errors, possibly including {@code
1076		* ClassCastException}.
1077		*/
1078		public static void helpQuiesce() {
1079	<	((ForkJoinWorkerThread) Thread.currentThread())
1080	<	.helpQuiescePool();
1079	>	ForkJoinWorkerThread wt =
1080	>	(ForkJoinWorkerThread)Thread.currentThread();
1081	>	wt.pool.helpQuiescePool(wt.workQueue);
1082		}
1083
1084		/**
#	Line 846 | Line 1090 | public abstract class ForkJoinTask<V> im
1090		* under any other usage conditions are not guaranteed.
1091		* This method may be useful when executing
1092		* pre-constructed trees of subtasks in loops.
1093	+	*
1094	+	* <p>Upon completion of this method, {@code isDone()} reports
1095	+	* {@code false}, and {@code getException()} reports {@code
1096	+	* null}. However, the value returned by {@code getRawResult} is
1097	+	* unaffected. To clear this value, you can invoke {@code
1098	+	* setRawResult(null)}.
1099		*/
1100		public void reinitialize() {
1101	<	if (status == EXCEPTIONAL)
1102	<	exceptionMap.remove(this);
1103	<	status = 0;
1101	>	if ((status & DONE_MASK) == EXCEPTIONAL)
1102	>	clearExceptionalCompletion();
1103	>	else
1104	>	status = 0;
1105		}
1106
1107		/**
#	Line 867 | Line 1118 | public abstract class ForkJoinTask<V> im
1118		}
1119
1120		/**
1121	<	* Returns {@code true} if the current thread is executing as a
1122	<	* ForkJoinPool computation.
1121	>	* Returns {@code true} if the current thread is a {@link
1122	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1123		*
1124	<	* @return {@code true} if the current thread is executing as a
1125	<	* ForkJoinPool computation, or false otherwise
1124	>	* @return {@code true} if the current thread is a {@link
1125	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1126	>	* or {@code false} otherwise
1127		*/
1128		public static boolean inForkJoinPool() {
1129		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 886 | Line 1138 | public abstract class ForkJoinTask<V> im
1138		* were not, stolen.
1139		*
1140		* <p>This method may be invoked only from within {@code
1141	<	* ForkJoinTask} computations (as may be determined using method
1141	>	* ForkJoinPool} computations (as may be determined using method
1142		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1143		* result in exceptions or errors, possibly including {@code
1144		* ClassCastException}.
#	Line 894 | Line 1146 | public abstract class ForkJoinTask<V> im
1146		* @return {@code true} if unforked
1147		*/
1148		public boolean tryUnfork() {
1149	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1150	<	.unpushTask(this);
1149	>	return ((ForkJoinWorkerThread)Thread.currentThread())
1150	>	.workQueue.tryUnpush(this);
1151		}
1152
1153		/**
#	Line 905 | Line 1157 | public abstract class ForkJoinTask<V> im
1157		* fork other tasks.
1158		*
1159		* <p>This method may be invoked only from within {@code
1160	<	* ForkJoinTask} computations (as may be determined using method
1160	>	* ForkJoinPool} computations (as may be determined using method
1161		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1162		* result in exceptions or errors, possibly including {@code
1163		* ClassCastException}.
#	Line 914 | Line 1166 | public abstract class ForkJoinTask<V> im
1166		*/
1167		public static int getQueuedTaskCount() {
1168		return ((ForkJoinWorkerThread) Thread.currentThread())
1169	<	.getQueueSize();
1169	>	.workQueue.queueSize();
1170		}
1171
1172		/**
#	Line 928 | Line 1180 | public abstract class ForkJoinTask<V> im
1180		* exceeded.
1181		*
1182		* <p>This method may be invoked only from within {@code
1183	<	* ForkJoinTask} computations (as may be determined using method
1183	>	* ForkJoinPool} computations (as may be determined using method
1184		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1185		* result in exceptions or errors, possibly including {@code
1186		* ClassCastException}.
#	Line 936 | Line 1188 | public abstract class ForkJoinTask<V> im
1188		* @return the surplus number of tasks, which may be negative
1189		*/
1190		public static int getSurplusQueuedTaskCount() {
1191	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1192	<	.getEstimatedSurplusTaskCount();
1191	>	/*
1192	>	* The aim of this method is to return a cheap heuristic guide
1193	>	* for task partitioning when programmers, frameworks, tools,
1194	>	* or languages have little or no idea about task granularity.
1195	>	* In essence by offering this method, we ask users only about
1196	>	* tradeoffs in overhead vs expected throughput and its
1197	>	* variance, rather than how finely to partition tasks.
1198	>	*
1199	>	* In a steady state strict (tree-structured) computation,
1200	>	* each thread makes available for stealing enough tasks for
1201	>	* other threads to remain active. Inductively, if all threads
1202	>	* play by the same rules, each thread should make available
1203	>	* only a constant number of tasks.
1204	>	*
1205	>	* The minimum useful constant is just 1. But using a value of
1206	>	* 1 would require immediate replenishment upon each steal to
1207	>	* maintain enough tasks, which is infeasible.  Further,
1208	>	* partitionings/granularities of offered tasks should
1209	>	* minimize steal rates, which in general means that threads
1210	>	* nearer the top of computation tree should generate more
1211	>	* than those nearer the bottom. In perfect steady state, each
1212	>	* thread is at approximately the same level of computation
1213	>	* tree. However, producing extra tasks amortizes the
1214	>	* uncertainty of progress and diffusion assumptions.
1215	>	*
1216	>	* So, users will want to use values larger, but not much
1217	>	* larger than 1 to both smooth over transient shortages and
1218	>	* hedge against uneven progress; as traded off against the
1219	>	* cost of extra task overhead. We leave the user to pick a
1220	>	* threshold value to compare with the results of this call to
1221	>	* guide decisions, but recommend values such as 3.
1222	>	*
1223	>	* When all threads are active, it is on average OK to
1224	>	* estimate surplus strictly locally. In steady-state, if one
1225	>	* thread is maintaining say 2 surplus tasks, then so are
1226	>	* others. So we can just use estimated queue length.
1227	>	* However, this strategy alone leads to serious mis-estimates
1228	>	* in some non-steady-state conditions (ramp-up, ramp-down,
1229	>	* other stalls). We can detect many of these by further
1230	>	* considering the number of "idle" threads, that are known to
1231	>	* have zero queued tasks, so compensate by a factor of
1232	>	* (#idle/#active) threads.
1233	>	*/
1234	>	ForkJoinWorkerThread wt =
1235	>	(ForkJoinWorkerThread)Thread.currentThread();
1236	>	return wt.workQueue.queueSize() - wt.pool.idlePerActive();
1237		}
1238
1239		// Extension methods
#	Line 963 | Line 1259 | public abstract class ForkJoinTask<V> im
1259		protected abstract void setRawResult(V value);
1260
1261		/**
1262	<	* Immediately performs the base action of this task.  This method
1263	<	* is designed to support extensions, and should not in general be
1264	<	* called otherwise. The return value controls whether this task
1265	<	* is considered to be done normally. It may return false in
1262	>	* Immediately performs the base action of this task and returns
1263	>	* true if, upon return from this method, this task is guaranteed
1264	>	* to have completed normally. This method may return false
1265	>	* otherwise, to indicate that this task is not necessarily
1266	>	* complete (or is not known to be complete), for example in
1267		* asynchronous actions that require explicit invocations of
1268	<	* {@link #complete} to become joinable. It may also throw an
1269	<	* (unchecked) exception to indicate abnormal exit.
1268	>	* completion methods. This method may also throw an (unchecked)
1269	>	* exception to indicate abnormal exit. This method is designed to
1270	>	* support extensions, and should not in general be called
1271	>	* otherwise.
1272		*
1273	<	* @return {@code true} if completed normally
1273	>	* @return {@code true} if this task is known to have completed normally
1274		*/
1275		protected abstract boolean exec();
1276
#	Line 986 | Line 1285 | public abstract class ForkJoinTask<V> im
1285		* otherwise.
1286		*
1287		* <p>This method may be invoked only from within {@code
1288	<	* ForkJoinTask} computations (as may be determined using method
1288	>	* ForkJoinPool} computations (as may be determined using method
1289		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1290		* result in exceptions or errors, possibly including {@code
1291		* ClassCastException}.
#	Line 994 | Line 1293 | public abstract class ForkJoinTask<V> im
1293		* @return the next task, or {@code null} if none are available
1294		*/
1295		protected static ForkJoinTask<?> peekNextLocalTask() {
1296	<	return ((ForkJoinWorkerThread) Thread.currentThread())
998	<	.peekTask();
1296	>	return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek();
1297		}
1298
1299		/**
#	Line 1005 | Line 1303 | public abstract class ForkJoinTask<V> im
1303		* be useful otherwise.
1304		*
1305		* <p>This method may be invoked only from within {@code
1306	<	* ForkJoinTask} computations (as may be determined using method
1306	>	* ForkJoinPool} computations (as may be determined using method
1307		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1308		* result in exceptions or errors, possibly including {@code
1309		* ClassCastException}.
#	Line 1014 | Line 1312 | public abstract class ForkJoinTask<V> im
1312		*/
1313		protected static ForkJoinTask<?> pollNextLocalTask() {
1314		return ((ForkJoinWorkerThread) Thread.currentThread())
1315	<	.pollLocalTask();
1315	>	.workQueue.nextLocalTask();
1316		}
1317
1318		/**
#	Line 1028 | Line 1326 | public abstract class ForkJoinTask<V> im
1326		* otherwise.
1327		*
1328		* <p>This method may be invoked only from within {@code
1329	<	* ForkJoinTask} computations (as may be determined using method
1329	>	* ForkJoinPool} computations (as may be determined using method
1330		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1331		* result in exceptions or errors, possibly including {@code
1332		* ClassCastException}.
#	Line 1036 | Line 1334 | public abstract class ForkJoinTask<V> im
1334		* @return a task, or {@code null} if none are available
1335		*/
1336		protected static ForkJoinTask<?> pollTask() {
1337	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1338	<	.pollTask();
1337	>	ForkJoinWorkerThread wt =
1338	>	(ForkJoinWorkerThread)Thread.currentThread();
1339	>	return wt.pool.nextTaskFor(wt.workQueue);
1340	>	}
1341	>
1342	>	// tag operations
1343	>
1344	>	/**
1345	>	* Returns the tag for this task.
1346	>	*
1347	>	* @return the tag for this task
1348	>	* @since 1.8
1349	>	*/
1350	>	public final short getForkJoinTaskTag() {
1351	>	return (short)status;
1352	>	}
1353	>
1354	>	/**
1355	>	* Atomically sets the tag value for this task.
1356	>	*
1357	>	* @param tag the tag value
1358	>	* @return the previous value of the tag
1359	>	* @since 1.8
1360	>	*/
1361	>	public final short setForkJoinTaskTag(short tag) {
1362	>	for (int s;;) {
1363	>	if (U.compareAndSwapInt(this, STATUS, s = status,
1364	>	(s & ~SMASK) | (tag & SMASK)))
1365	>	return (short)s;
1366	>	}
1367	>	}
1368	>
1369	>	/**
1370	>	* Atomically conditionally sets the tag value for this task.
1371	>	* Among other applications, tags can be used as visit markers
1372	>	* in tasks operating on graphs, as in methods that check: {@code
1373	>	* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1374	>	* before processing, otherwise exiting because the node has
1375	>	* already been visited.
1376	>	*
1377	>	* @param e the expected tag value
1378	>	* @param tag the new tag value
1379	>	* @return true if successful; i.e., the current value was
1380	>	* equal to e and is now tag.
1381	>	* @since 1.8
1382	>	*/
1383	>	public final boolean compareAndSetForkJoinTaskTag(short e, short tag) {
1384	>	for (int s;;) {
1385	>	if ((short)(s = status) != e)
1386	>	return false;
1387	>	if (U.compareAndSwapInt(this, STATUS, s,
1388	>	(s & ~SMASK) | (tag & SMASK)))
1389	>	return true;
1390	>	}
1391		}
1392
1393		/**
#	Line 1048 | Line 1398 | public abstract class ForkJoinTask<V> im
1398		static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1399		implements RunnableFuture<T> {
1400		final Runnable runnable;
1051	–	final T resultOnCompletion;
1401		T result;
1402		AdaptedRunnable(Runnable runnable, T result) {
1403		if (runnable == null) throw new NullPointerException();
1404		this.runnable = runnable;
1405	<	this.resultOnCompletion = result;
1405	>	this.result = result; // OK to set this even before completion
1406		}
1407	<	public T getRawResult() { return result; }
1408	<	public void setRawResult(T v) { result = v; }
1409	<	public boolean exec() {
1410	<	runnable.run();
1411	<	result = resultOnCompletion;
1412	<	return true;
1407	>	public final T getRawResult() { return result; }
1408	>	public final void setRawResult(T v) { result = v; }
1409	>	public final boolean exec() { runnable.run(); return true; }
1410	>	public final void run() { invoke(); }
1411	>	private static final long serialVersionUID = 5232453952276885070L;
1412	>	}
1413	>
1414	>	/**
1415	>	* Adaptor for Runnables without results
1416	>	*/
1417	>	static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1418	>	implements RunnableFuture<Void> {
1419	>	final Runnable runnable;
1420	>	AdaptedRunnableAction(Runnable runnable) {
1421	>	if (runnable == null) throw new NullPointerException();
1422	>	this.runnable = runnable;
1423		}
1424	<	public void run() { invoke(); }
1424	>	public final Void getRawResult() { return null; }
1425	>	public final void setRawResult(Void v) { }
1426	>	public final boolean exec() { runnable.run(); return true; }
1427	>	public final void run() { invoke(); }
1428		private static final long serialVersionUID = 5232453952276885070L;
1429		}
1430
#	Line 1077 | Line 1439 | public abstract class ForkJoinTask<V> im
1439		if (callable == null) throw new NullPointerException();
1440		this.callable = callable;
1441		}
1442	<	public T getRawResult() { return result; }
1443	<	public void setRawResult(T v) { result = v; }
1444	<	public boolean exec() {
1442	>	public final T getRawResult() { return result; }
1443	>	public final void setRawResult(T v) { result = v; }
1444	>	public final boolean exec() {
1445		try {
1446		result = callable.call();
1447		return true;
#	Line 1091 | Line 1453 | public abstract class ForkJoinTask<V> im
1453		throw new RuntimeException(ex);
1454		}
1455		}
1456	<	public void run() { invoke(); }
1456	>	public final void run() { invoke(); }
1457		private static final long serialVersionUID = 2838392045355241008L;
1458		}
1459
#	Line 1104 | Line 1466 | public abstract class ForkJoinTask<V> im
1466		* @return the task
1467		*/
1468		public static ForkJoinTask<?> adapt(Runnable runnable) {
1469	<	return new AdaptedRunnable<Void>(runnable, null);
1469	>	return new AdaptedRunnableAction(runnable);
1470		}
1471
1472		/**
#	Line 1138 | Line 1500 | public abstract class ForkJoinTask<V> im
1500		private static final long serialVersionUID = -7721805057305804111L;
1501
1502		/**
1503	<	* Saves the state to a stream (that is, serializes it).
1503	>	* Saves this task to a stream (that is, serializes it).
1504		*
1505		* @serialData the current run status and the exception thrown
1506		* during execution, or {@code null} if none
1145	–	* @param s the stream
1507		*/
1508		private void writeObject(java.io.ObjectOutputStream s)
1509		throws java.io.IOException {
#	Line 1151 | Line 1512 | public abstract class ForkJoinTask<V> im
1512		}
1513
1514		/**
1515	<	* Reconstitutes the instance from a stream (that is, deserializes it).
1155	<	*
1156	<	* @param s the stream
1515	>	* Reconstitutes this task from a stream (that is, deserializes it).
1516		*/
1517		private void readObject(java.io.ObjectInputStream s)
1518		throws java.io.IOException, ClassNotFoundException {
1519		s.defaultReadObject();
1520		Object ex = s.readObject();
1521		if (ex != null)
1522	<	setExceptionalCompletion((Throwable) ex);
1522	>	setExceptionalCompletion((Throwable)ex);
1523		}
1524
1525		// Unsafe mechanics
1526	<
1527	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1528	<	private static final long statusOffset =
1529	<	objectFieldOffset("status", ForkJoinTask.class);
1530	<
1531	<	private static long objectFieldOffset(String field, Class<?> klazz) {
1526	>	private static final sun.misc.Unsafe U;
1527	>	private static final long STATUS;
1528	>	static {
1529	>	exceptionTableLock = new ReentrantLock();
1530	>	exceptionTableRefQueue = new ReferenceQueue<Object>();
1531	>	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1532		try {
1533	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1534	<	} catch (NoSuchFieldException e) {
1535	<	// Convert Exception to corresponding Error
1536	<	NoSuchFieldError error = new NoSuchFieldError(field);
1537	<	error.initCause(e);
1179	<	throw error;
1533	>	U = getUnsafe();
1534	>	STATUS = U.objectFieldOffset
1535	>	(ForkJoinTask.class.getDeclaredField("status"));
1536	>	} catch (Exception e) {
1537	>	throw new Error(e);
1538		}
1539		}
1540

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