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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.71 by dl, Tue Nov 23 10:51:18 2010 UTC vs.
Revision 1.85 by jsr166, Tue Jan 31 01:51:13 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	–
8		import java.io.Serializable;
9		import java.util.Collection;
11	–	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;
19	–	import java.util.concurrent.Executor;
20	–	import java.util.concurrent.ExecutorService;
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 44 | Line 42 | import java.util.concurrent.TimeoutExcep
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 82 | Line 93 | import java.util.concurrent.TimeoutExcep
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 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 118 | Line 136 | import java.util.concurrent.TimeoutExcep
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.
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 processed.
147	>	* Also, completion based designs can use them to record that one
148	>	* subtask has completed. (Method names for marking are bulky in part
149	>	* 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 158 | 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. In particular, most
196	<	* join mechanics are in method quietlyJoin, below.
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
#	Line 186 | Line 226 | public abstract class ForkJoinTask<V> im
226
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;
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	<	* Table of exceptions thrown by tasks, to enable reporting by
237	<	* callers. Because exceptions are rare, we don't directly keep
238	<	* them with task objects, but instead use a weak ref table.  Note
199	<	* that cancellation exceptions don't appear in the table, but are
200	<	* instead recorded as status values.
201	<	* TODO: Use ConcurrentReferenceHashMap
202	<	*/
203	<	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
204	<	Collections.synchronizedMap
205	<	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
206	<
207	<	// Maintaining completion status
208	<
209	<	/**
210	<	* Marks completion and wakes up threads waiting to join this task,
211	<	* 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 completion status on exit
242		*/
243	<	private void setCompletion(int completion) {
244	<	int s;
245	<	while ((s = status) >= 0) {
246	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
247	<	if (s != 0)
243	>	private int setCompletion(int completion) {
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	<	break;
250	>	return completion;
251		}
252		}
253		}
254
255		/**
256	<	* Records exception and sets exceptional completion.
257	<	*
258	<	* @return status on exit
259	<	*/
260	<	private void setExceptionalCompletion(Throwable rex) {
261	<	exceptionMap.put(this, rex);
262	<	setCompletion(EXCEPTIONAL);
263	<	}
264	<
265	<	/**
266	<	* Blocks a worker thread until completed or timed out.  Called
267	<	* only by pool.
268	<	*/
269	<	final void internalAwaitDone(long millis, int nanos) {
270	<	if (status >= 0) {
271	<	try {     // the odd construction reduces lock bias effects
272	<	synchronized (this) {
273	<	if (status > 0 ||
274	<	UNSAFE.compareAndSwapInt(this, statusOffset,
246	<	0, SIGNAL))
247	<	wait(millis, nanos);
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	>	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		}
249	–	} catch (InterruptedException ie) {
250	–	cancelIfTerminating();
276		}
277		}
278	+	return s;
279		}
280
281		/**
282		* Blocks a non-worker-thread until completion.
283	+	* @return status upon completion
284		*/
285	<	private void externalAwaitDone() {
286	<	if (status >= 0) {
285	>	private int externalAwaitDone() {
286	>	int s;
287	>	if ((s = status) >= 0) {
288		boolean interrupted = false;
289	<	synchronized(this) {
262	<	int s;
289	>	synchronized (this) {
290		while ((s = status) >= 0) {
291	<	if (s == 0 &&
292	<	!UNSAFE.compareAndSwapInt(this, statusOffset,
293	<	0, SIGNAL))
294	<	continue;
295	<	try {
296	<	wait();
270	<	} catch (InterruptedException ie) {
271	<	interrupted = true;
291	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
292	>	try {
293	>	wait();
294	>	} catch (InterruptedException ie) {
295	>	interrupted = true;
296	>	}
297		}
298		}
299		}
300		if (interrupted)
301		Thread.currentThread().interrupt();
302		}
303	+	return s;
304		}
305
306		/**
307		* Blocks a non-worker-thread until completion or interruption or timeout.
308		*/
309	<	private void externalInterruptibleAwaitDone(boolean timed, long nanos)
309	>	private int externalInterruptibleAwaitDone(long millis)
310		throws InterruptedException {
311	+	int s;
312		if (Thread.interrupted())
313		throw new InterruptedException();
314	<	if (status >= 0) {
315	<	long startTime = timed ? System.nanoTime() : 0L;
289	<	synchronized(this) {
290	<	int s;
314	>	if ((s = status) >= 0) {
315	>	synchronized (this) {
316		while ((s = status) >= 0) {
317	<	long nt;
318	<	if (s == 0 &&
319	<	!UNSAFE.compareAndSwapInt(this, statusOffset,
320	<	0, SIGNAL))
321	<	continue;
322	<	else if (!timed)
323	<	wait();
324	<	else if ((nt = nanos - (System.nanoTime()-startTime)) > 0L)
325	<	wait(nt / 1000000, (int)(nt % 1000000));
317	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
318	>	wait(millis);
319	>	if (millis > 0L)
320	>	break;
321	>	}
322	>	}
323	>	}
324	>	}
325	>	return s;
326	>	}
327	>
328	>
329	>	/**
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 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	>	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	>	}
386	>	}
387	>	}
388	>	w.currentJoin = prevJoin;
389	>	return s;
390	>	}
391	>
392	>	/**
393	>	* Implementation for invoke, quietlyInvoke.
394	>	*
395	>	* @return status upon completion
396	>	*/
397	>	private int doInvoke() {
398	>	int s; Thread t;
399	>	if ((s = doExec()) >= 0) {
400	>	if (!((t = Thread.currentThread()) instanceof ForkJoinWorkerThread))
401	>	s = externalAwaitDone();
402	>	else {
403	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
404	>	s = awaitJoin(wt.workQueue, wt.pool);
405	>	}
406	>	}
407	>	return s;
408	>	}
409	>
410	>	// Exception table support
411	>
412	>	/**
413	>	* Table of exceptions thrown by tasks, to enable reporting by
414	>	* callers. Because exceptions are rare, we don't directly keep
415	>	* them with task objects, but instead use a weak ref table.  Note
416	>	* that cancellation exceptions don't appear in the table, but are
417	>	* instead recorded as status values.
418	>	*
419	>	* Note: These statics are initialized below in static block.
420	>	*/
421	>	private static final ExceptionNode[] exceptionTable;
422	>	private static final ReentrantLock exceptionTableLock;
423	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
424	>
425	>	/**
426	>	* Fixed capacity for exceptionTable.
427	>	*/
428	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
429	>
430	>	/**
431	>	* Key-value nodes for exception table.  The chained hash table
432	>	* uses identity comparisons, full locking, and weak references
433	>	* for keys. The table has a fixed capacity because it only
434	>	* maintains task exceptions long enough for joiners to access
435	>	* them, so should never become very large for sustained
436	>	* periods. However, since we do not know when the last joiner
437	>	* completes, we must use weak references and expunge them. We do
438	>	* so on each operation (hence full locking). Also, some thread in
439	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
440	>	* pool becomes isQuiescent.
441	>	*/
442	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> {
443	>	final Throwable ex;
444	>	ExceptionNode next;
445	>	final long thrower;  // use id not ref to avoid weak cycles
446	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
447	>	super(task, exceptionTableRefQueue);
448	>	this.ex = ex;
449	>	this.next = next;
450	>	this.thrower = Thread.currentThread().getId();
451	>	}
452	>	}
453	>
454	>	/**
455	>	* Records exception and sets exceptional completion.
456	>	*
457	>	* @return status on exit
458	>	*/
459	>	private int setExceptionalCompletion(Throwable ex) {
460	>	int h = System.identityHashCode(this);
461	>	final ReentrantLock lock = exceptionTableLock;
462	>	lock.lock();
463	>	try {
464	>	expungeStaleExceptions();
465	>	ExceptionNode[] t = exceptionTable;
466	>	int i = h & (t.length - 1);
467	>	for (ExceptionNode e = t[i]; ; e = e.next) {
468	>	if (e == null) {
469	>	t[i] = new ExceptionNode(this, ex, t[i]);
470	>	break;
471	>	}
472	>	if (e.get() == this) // already present
473	>	break;
474	>	}
475	>	} finally {
476	>	lock.unlock();
477	>	}
478	>	return setCompletion(EXCEPTIONAL);
479	>	}
480	>
481	>	/**
482	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
483	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
484	>	* exceptions, but if it does anyway, we have no recourse during
485	>	* shutdown, so guard against this case.
486	>	*/
487	>	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
488	>	if (t != null && t.status >= 0) {
489	>	try {
490	>	t.cancel(false);
491	>	} catch (Throwable ignore) {
492	>	}
493	>	}
494	>	}
495	>
496	>	/**
497	>	* Removes exception node and clears status
498	>	*/
499	>	private void clearExceptionalCompletion() {
500	>	int h = System.identityHashCode(this);
501	>	final ReentrantLock lock = exceptionTableLock;
502	>	lock.lock();
503	>	try {
504	>	ExceptionNode[] t = exceptionTable;
505	>	int i = h & (t.length - 1);
506	>	ExceptionNode e = t[i];
507	>	ExceptionNode pred = null;
508	>	while (e != null) {
509	>	ExceptionNode next = e.next;
510	>	if (e.get() == this) {
511	>	if (pred == null)
512	>	t[i] = next;
513		else
514	+	pred.next = next;
515	+	break;
516	+	}
517	+	pred = e;
518	+	e = next;
519	+	}
520	+	expungeStaleExceptions();
521	+	status = 0;
522	+	} finally {
523	+	lock.unlock();
524	+	}
525	+	}
526	+
527	+	/**
528	+	* Returns a rethrowable exception for the given task, if
529	+	* available. To provide accurate stack traces, if the exception
530	+	* was not thrown by the current thread, we try to create a new
531	+	* exception of the same type as the one thrown, but with the
532	+	* recorded exception as its cause. If there is no such
533	+	* constructor, we instead try to use a no-arg constructor,
534	+	* followed by initCause, to the same effect. If none of these
535	+	* apply, or any fail due to other exceptions, we return the
536	+	* recorded exception, which is still correct, although it may
537	+	* contain a misleading stack trace.
538	+	*
539	+	* @return the exception, or null if none
540	+	*/
541	+	private Throwable getThrowableException() {
542	+	if (status != EXCEPTIONAL)
543	+	return null;
544	+	int h = System.identityHashCode(this);
545	+	ExceptionNode e;
546	+	final ReentrantLock lock = exceptionTableLock;
547	+	lock.lock();
548	+	try {
549	+	expungeStaleExceptions();
550	+	ExceptionNode[] t = exceptionTable;
551	+	e = t[h & (t.length - 1)];
552	+	while (e != null && e.get() != this)
553	+	e = e.next;
554	+	} finally {
555	+	lock.unlock();
556	+	}
557	+	Throwable ex;
558	+	if (e == null || (ex = e.ex) == null)
559	+	return null;
560	+	if (e.thrower != Thread.currentThread().getId()) {
561	+	Class<? extends Throwable> ec = ex.getClass();
562	+	try {
563	+	Constructor<?> noArgCtor = null;
564	+	Constructor<?>[] cs = ec.getConstructors();// public ctors only
565	+	for (int i = 0; i < cs.length; ++i) {
566	+	Constructor<?> c = cs[i];
567	+	Class<?>[] ps = c.getParameterTypes();
568	+	if (ps.length == 0)
569	+	noArgCtor = c;
570	+	else if (ps.length == 1 && ps[0] == Throwable.class)
571	+	return (Throwable)(c.newInstance(ex));
572	+	}
573	+	if (noArgCtor != null) {
574	+	Throwable wx = (Throwable)(noArgCtor.newInstance());
575	+	wx.initCause(ex);
576	+	return wx;
577	+	}
578	+	} catch (Exception ignore) {
579	+	}
580	+	}
581	+	return ex;
582	+	}
583	+
584	+	/**
585	+	* Poll stale refs and remove them. Call only while holding lock.
586	+	*/
587	+	private static void expungeStaleExceptions() {
588	+	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
589	+	if (x instanceof ExceptionNode) {
590	+	ForkJoinTask<?> key = ((ExceptionNode)x).get();
591	+	ExceptionNode[] t = exceptionTable;
592	+	int i = System.identityHashCode(key) & (t.length - 1);
593	+	ExceptionNode e = t[i];
594	+	ExceptionNode pred = null;
595	+	while (e != null) {
596	+	ExceptionNode next = e.next;
597	+	if (e == x) {
598	+	if (pred == null)
599	+	t[i] = next;
600	+	else
601	+	pred.next = next;
602		break;
603	+	}
604	+	pred = e;
605	+	e = next;
606		}
607		}
608		}
609		}
610
611		/**
612	<	* Unless done, calls exec and records status if completed, but
613	<	* doesn't wait for completion otherwise. Primary execution method
311	<	* for ForkJoinWorkerThread.
612	>	* If lock is available, poll stale refs and remove them.
613	>	* Called from ForkJoinPool when pools become quiescent.
614		*/
615	<	final void quietlyExec() {
616	<	try {
617	<	if (status < 0 || !exec())
618	<	return;
619	<	} catch (Throwable rex) {
620	<	setExceptionalCompletion(rex);
621	<	return;
615	>	static final void helpExpungeStaleExceptions() {
616	>	final ReentrantLock lock = exceptionTableLock;
617	>	if (lock.tryLock()) {
618	>	try {
619	>	expungeStaleExceptions();
620	>	} finally {
621	>	lock.unlock();
622	>	}
623		}
624	<	setCompletion(NORMAL); // must be outside try block
624	>	}
625	>
626	>	/**
627	>	* Report the result of invoke or join; called only upon
628	>	* non-normal return of internal versions.
629	>	*/
630	>	private V reportResult() {
631	>	int s; Throwable ex;
632	>	if ((s = status) == CANCELLED)
633	>	throw new CancellationException();
634	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
635	>	U.throwException(ex);
636	>	return getRawResult();
637		}
638
639		// public methods
#	Line 342 | Line 657 | public abstract class ForkJoinTask<V> im
657		* @return {@code this}, to simplify usage
658		*/
659		public final ForkJoinTask<V> fork() {
660	<	((ForkJoinWorkerThread) Thread.currentThread())
661	<	.pushTask(this);
660	>	ForkJoinWorkerThread wt;
661	>	(wt = (ForkJoinWorkerThread)Thread.currentThread()).
662	>	workQueue.push(this, wt.pool);
663		return this;
664		}
665
#	Line 359 | Line 675 | public abstract class ForkJoinTask<V> im
675		* @return the computed result
676		*/
677		public final V join() {
678	<	quietlyJoin();
679	<	Throwable ex;
680	<	if (status < NORMAL && (ex = getException()) != null)
681	<	UNSAFE.throwException(ex);
366	<	return getRawResult();
678	>	if (doJoin() != NORMAL)
679	>	return reportResult();
680	>	else
681	>	return getRawResult();
682		}
683
684		/**
#	Line 375 | Line 690 | public abstract class ForkJoinTask<V> im
690		* @return the computed result
691		*/
692		public final V invoke() {
693	<	quietlyInvoke();
694	<	Throwable ex;
695	<	if (status < NORMAL && (ex = getException()) != null)
696	<	UNSAFE.throwException(ex);
382	<	return getRawResult();
693	>	if (doInvoke() != NORMAL)
694	>	return reportResult();
695	>	else
696	>	return getRawResult();
697		}
698
699		/**
#	Line 443 | Line 757 | public abstract class ForkJoinTask<V> im
757		}
758		else if (i != 0)
759		t.fork();
760	<	else {
761	<	t.quietlyInvoke();
448	<	if (ex == null && t.status < NORMAL)
449	<	ex = t.getException();
450	<	}
760	>	else if (t.doInvoke() < NORMAL && ex == null)
761	>	ex = t.getException();
762		}
763		for (int i = 1; i <= last; ++i) {
764		ForkJoinTask<?> t = tasks[i];
765		if (t != null) {
766		if (ex != null)
767		t.cancel(false);
768	<	else {
769	<	t.quietlyJoin();
459	<	if (ex == null && t.status < NORMAL)
460	<	ex = t.getException();
461	<	}
768	>	else if (t.doJoin() < NORMAL)
769	>	ex = t.getException();
770		}
771		}
772		if (ex != null)
773	<	UNSAFE.throwException(ex);
773	>	U.throwException(ex);
774		}
775
776		/**
#	Line 506 | Line 814 | public abstract class ForkJoinTask<V> im
814		}
815		else if (i != 0)
816		t.fork();
817	<	else {
818	<	t.quietlyInvoke();
511	<	if (ex == null && t.status < NORMAL)
512	<	ex = t.getException();
513	<	}
817	>	else if (t.doInvoke() < NORMAL && ex == null)
818	>	ex = t.getException();
819		}
820		for (int i = 1; i <= last; ++i) {
821		ForkJoinTask<?> t = ts.get(i);
822		if (t != null) {
823		if (ex != null)
824		t.cancel(false);
825	<	else {
826	<	t.quietlyJoin();
522	<	if (ex == null && t.status < NORMAL)
523	<	ex = t.getException();
524	<	}
825	>	else if (t.doJoin() < NORMAL)
826	>	ex = t.getException();
827		}
828		}
829		if (ex != null)
830	<	UNSAFE.throwException(ex);
830	>	U.throwException(ex);
831		return tasks;
832		}
833
#	Line 557 | Line 859 | public abstract class ForkJoinTask<V> im
859		* @return {@code true} if this task is now cancelled
860		*/
861		public boolean cancel(boolean mayInterruptIfRunning) {
862	<	setCompletion(CANCELLED);
561	<	return status == CANCELLED;
562	<	}
563	<
564	<	/**
565	<	* Cancels, ignoring any exceptions thrown by cancel. Used during
566	<	* worker and pool shutdown. Cancel is spec'ed not to throw any
567	<	* exceptions, but if it does anyway, we have no recourse during
568	<	* shutdown, so guard against this case.
569	<	*/
570	<	final void cancelIgnoringExceptions() {
571	<	try {
572	<	cancel(false);
573	<	} catch (Throwable ignore) {
574	<	}
575	<	}
576	<
577	<	/**
578	<	* Cancels if current thread is a terminating worker thread,
579	<	* ignoring any exceptions thrown by cancel.
580	<	*/
581	<	final void cancelIfTerminating() {
582	<	Thread t = Thread.currentThread();
583	<	if ((t instanceof ForkJoinWorkerThread) &&
584	<	((ForkJoinWorkerThread) t).isTerminating()) {
585	<	try {
586	<	cancel(false);
587	<	} catch (Throwable ignore) {
588	<	}
589	<	}
862	>	return setCompletion(CANCELLED) == CANCELLED;
863		}
864
865		public final boolean isDone() {
#	Line 628 | Line 901 | public abstract class ForkJoinTask<V> im
901		int s = status;
902		return ((s >= NORMAL)    ? null :
903		(s == CANCELLED) ? new CancellationException() :
904	<	exceptionMap.get(this));
904	>	getThrowableException());
905		}
906
907		/**
#	Line 686 | Line 959 | public abstract class ForkJoinTask<V> im
959		* member of a ForkJoinPool and was interrupted while waiting
960		*/
961		public final V get() throws InterruptedException, ExecutionException {
962	<	Thread t = Thread.currentThread();
963	<	if (t instanceof ForkJoinWorkerThread)
964	<	quietlyJoin();
965	<	else
966	<	externalInterruptibleAwaitDone(false, 0L);
967	<	int s = status;
968	<	if (s != NORMAL) {
696	<	Throwable ex;
697	<	if (s == CANCELLED)
698	<	throw new CancellationException();
699	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
700	<	throw new ExecutionException(ex);
701	<	}
962	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
963	>	doJoin() : externalInterruptibleAwaitDone(0L);
964	>	Throwable ex;
965	>	if (s == CANCELLED)
966	>	throw new CancellationException();
967	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
968	>	throw new ExecutionException(ex);
969		return getRawResult();
970		}
971
#	Line 718 | Line 985 | public abstract class ForkJoinTask<V> im
985		*/
986		public final V get(long timeout, TimeUnit unit)
987		throws InterruptedException, ExecutionException, TimeoutException {
988	<	long nanos = unit.toNanos(timeout);
988	>	// Messy in part because we measure in nanos, but wait in millis
989	>	int s; long millis, nanos;
990		Thread t = Thread.currentThread();
991	<	if (t instanceof ForkJoinWorkerThread)
992	<	((ForkJoinWorkerThread)t).joinTask(this, true, nanos);
993	<	else
994	<	externalInterruptibleAwaitDone(true, nanos);
995	<	int s = status;
991	>	if (!(t instanceof ForkJoinWorkerThread)) {
992	>	if ((millis = unit.toMillis(timeout)) > 0L)
993	>	s = externalInterruptibleAwaitDone(millis);
994	>	else
995	>	s = status;
996	>	}
997	>	else if ((s = status) >= 0 && (nanos = unit.toNanos(timeout)) > 0L) {
998	>	long deadline = System.nanoTime() + nanos;
999	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1000	>	ForkJoinPool.WorkQueue w = wt.workQueue;
1001	>	ForkJoinPool p = wt.pool;
1002	>	if (w.tryUnpush(this))
1003	>	doExec();
1004	>	boolean blocking = false;
1005	>	try {
1006	>	while ((s = status) >= 0) {
1007	>	if (w.runState < 0)
1008	>	cancelIgnoringExceptions(this);
1009	>	else if (!blocking)
1010	>	blocking = p.tryCompensate();
1011	>	else {
1012	>	millis = TimeUnit.NANOSECONDS.toMillis(nanos);
1013	>	if (millis > 0L &&
1014	>	U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
1015	>	try {
1016	>	synchronized (this) {
1017	>	if (status >= 0)
1018	>	wait(millis);
1019	>	}
1020	>	} catch (InterruptedException ie) {
1021	>	}
1022	>	}
1023	>	if ((s = status) < 0 ||
1024	>	(nanos = deadline - System.nanoTime()) <= 0L)
1025	>	break;
1026	>	}
1027	>	}
1028	>	} finally {
1029	>	if (blocking)
1030	>	p.incrementActiveCount();
1031	>	}
1032	>	}
1033		if (s != NORMAL) {
1034		Throwable ex;
1035		if (s == CANCELLED)
1036		throw new CancellationException();
1037	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
1037	>	if (s != EXCEPTIONAL)
1038	>	throw new TimeoutException();
1039	>	if ((ex = getThrowableException()) != null)
1040		throw new ExecutionException(ex);
734	–	throw new TimeoutException();
1041		}
1042		return getRawResult();
1043		}
#	Line 743 | Line 1049 | public abstract class ForkJoinTask<V> im
1049		* known to have aborted.
1050		*/
1051		public final void quietlyJoin() {
1052	<	Thread t;
747	<	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
748	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
749	<	if (status >= 0) {
750	<	if (w.unpushTask(this)) {
751	<	boolean completed;
752	<	try {
753	<	completed = exec();
754	<	} catch (Throwable rex) {
755	<	setExceptionalCompletion(rex);
756	<	return;
757	<	}
758	<	if (completed) {
759	<	setCompletion(NORMAL);
760	<	return;
761	<	}
762	<	}
763	<	w.joinTask(this, false, 0L);
764	<	}
765	<	}
766	<	else
767	<	externalAwaitDone();
1052	>	doJoin();
1053		}
1054
1055		/**
#	Line 773 | Line 1058 | public abstract class ForkJoinTask<V> im
1058		* exception.
1059		*/
1060		public final void quietlyInvoke() {
1061	<	if (status >= 0) {
777	<	boolean completed;
778	<	try {
779	<	completed = exec();
780	<	} catch (Throwable rex) {
781	<	setExceptionalCompletion(rex);
782	<	return;
783	<	}
784	<	if (completed)
785	<	setCompletion(NORMAL);
786	<	else
787	<	quietlyJoin();
788	<	}
1061	>	doInvoke();
1062		}
1063
1064		/**
#	Line 802 | Line 1075 | public abstract class ForkJoinTask<V> im
1075		* ClassCastException}.
1076		*/
1077		public static void helpQuiesce() {
1078	<	((ForkJoinWorkerThread) Thread.currentThread())
1079	<	.helpQuiescePool();
1078	>	ForkJoinWorkerThread wt =
1079	>	(ForkJoinWorkerThread)Thread.currentThread();
1080	>	wt.pool.helpQuiescePool(wt.workQueue);
1081		}
1082
1083		/**
#	Line 824 | Line 1098 | public abstract class ForkJoinTask<V> im
1098		*/
1099		public void reinitialize() {
1100		if (status == EXCEPTIONAL)
1101	<	exceptionMap.remove(this);
1102	<	status = 0;
1101	>	clearExceptionalCompletion();
1102	>	else
1103	>	status = 0;
1104		}
1105
1106		/**
#	Line 870 | Line 1145 | public abstract class ForkJoinTask<V> im
1145		* @return {@code true} if unforked
1146		*/
1147		public boolean tryUnfork() {
1148	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1149	<	.unpushTask(this);
1148	>	return ((ForkJoinWorkerThread)Thread.currentThread())
1149	>	.workQueue.tryUnpush(this);
1150		}
1151
1152		/**
#	Line 890 | Line 1165 | public abstract class ForkJoinTask<V> im
1165		*/
1166		public static int getQueuedTaskCount() {
1167		return ((ForkJoinWorkerThread) Thread.currentThread())
1168	<	.getQueueSize();
1168	>	.workQueue.queueSize();
1169		}
1170
1171		/**
#	Line 912 | Line 1187 | public abstract class ForkJoinTask<V> im
1187		* @return the surplus number of tasks, which may be negative
1188		*/
1189		public static int getSurplusQueuedTaskCount() {
1190	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1191	<	.getEstimatedSurplusTaskCount();
1190	>	/*
1191	>	* The aim of this method is to return a cheap heuristic guide
1192	>	* for task partitioning when programmers, frameworks, tools,
1193	>	* or languages have little or no idea about task granularity.
1194	>	* In essence by offering this method, we ask users only about
1195	>	* tradeoffs in overhead vs expected throughput and its
1196	>	* variance, rather than how finely to partition tasks.
1197	>	*
1198	>	* In a steady state strict (tree-structured) computation,
1199	>	* each thread makes available for stealing enough tasks for
1200	>	* other threads to remain active. Inductively, if all threads
1201	>	* play by the same rules, each thread should make available
1202	>	* only a constant number of tasks.
1203	>	*
1204	>	* The minimum useful constant is just 1. But using a value of
1205	>	* 1 would require immediate replenishment upon each steal to
1206	>	* maintain enough tasks, which is infeasible.  Further,
1207	>	* partitionings/granularities of offered tasks should
1208	>	* minimize steal rates, which in general means that threads
1209	>	* nearer the top of computation tree should generate more
1210	>	* than those nearer the bottom. In perfect steady state, each
1211	>	* thread is at approximately the same level of computation
1212	>	* tree. However, producing extra tasks amortizes the
1213	>	* uncertainty of progress and diffusion assumptions.
1214	>	*
1215	>	* So, users will want to use values larger, but not much
1216	>	* larger than 1 to both smooth over transient shortages and
1217	>	* hedge against uneven progress; as traded off against the
1218	>	* cost of extra task overhead. We leave the user to pick a
1219	>	* threshold value to compare with the results of this call to
1220	>	* guide decisions, but recommend values such as 3.
1221	>	*
1222	>	* When all threads are active, it is on average OK to
1223	>	* estimate surplus strictly locally. In steady-state, if one
1224	>	* thread is maintaining say 2 surplus tasks, then so are
1225	>	* others. So we can just use estimated queue length.
1226	>	* However, this strategy alone leads to serious mis-estimates
1227	>	* in some non-steady-state conditions (ramp-up, ramp-down,
1228	>	* other stalls). We can detect many of these by further
1229	>	* considering the number of "idle" threads, that are known to
1230	>	* have zero queued tasks, so compensate by a factor of
1231	>	* (#idle/#active) threads.
1232	>	*/
1233	>	ForkJoinWorkerThread wt =
1234	>	(ForkJoinWorkerThread)Thread.currentThread();
1235	>	return wt.workQueue.queueSize() - wt.pool.idlePerActive();
1236		}
1237
1238		// Extension methods
#	Line 970 | Line 1289 | public abstract class ForkJoinTask<V> im
1289		* @return the next task, or {@code null} if none are available
1290		*/
1291		protected static ForkJoinTask<?> peekNextLocalTask() {
1292	<	return ((ForkJoinWorkerThread) Thread.currentThread())
974	<	.peekTask();
1292	>	return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek();
1293		}
1294
1295		/**
#	Line 990 | Line 1308 | public abstract class ForkJoinTask<V> im
1308		*/
1309		protected static ForkJoinTask<?> pollNextLocalTask() {
1310		return ((ForkJoinWorkerThread) Thread.currentThread())
1311	<	.pollLocalTask();
1311	>	.workQueue.nextLocalTask();
1312		}
1313
1314		/**
#	Line 1012 | Line 1330 | public abstract class ForkJoinTask<V> im
1330		* @return a task, or {@code null} if none are available
1331		*/
1332		protected static ForkJoinTask<?> pollTask() {
1333	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1334	<	.pollTask();
1333	>	ForkJoinWorkerThread wt =
1334	>	(ForkJoinWorkerThread)Thread.currentThread();
1335	>	return wt.pool.nextTaskFor(wt.workQueue);
1336	>	}
1337	>
1338	>	// Mark-bit operations
1339	>
1340	>	/**
1341	>	* Returns true if this task is marked.
1342	>	*
1343	>	* @return true if this task is marked
1344	>	* @since 1.8
1345	>	*/
1346	>	public final boolean isMarkedForkJoinTask() {
1347	>	return (status & MARKED) != 0;
1348	>	}
1349	>
1350	>	/**
1351	>	* Atomically sets the mark on this task.
1352	>	*
1353	>	* @return true if this task was previously unmarked
1354	>	* @since 1.8
1355	>	*/
1356	>	public final boolean markForkJoinTask() {
1357	>	for (int s;;) {
1358	>	if (((s = status) & MARKED) != 0)
1359	>	return false;
1360	>	if (U.compareAndSwapInt(this, STATUS, s, s | MARKED))
1361	>	return true;
1362	>	}
1363	>	}
1364	>
1365	>	/**
1366	>	* Atomically clears the mark on this task.
1367	>	*
1368	>	* @return true if this task was previously marked
1369	>	* @since 1.8
1370	>	*/
1371	>	public final boolean unmarkForkJoinTask() {
1372	>	for (int s;;) {
1373	>	if (((s = status) & MARKED) == 0)
1374	>	return false;
1375	>	if (U.compareAndSwapInt(this, STATUS, s, s & ~MARKED))
1376	>	return true;
1377	>	}
1378		}
1379
1380		/**
#	Line 1114 | Line 1475 | public abstract class ForkJoinTask<V> im
1475		private static final long serialVersionUID = -7721805057305804111L;
1476
1477		/**
1478	<	* Saves the state to a stream (that is, serializes it).
1478	>	* Saves this task to a stream (that is, serializes it).
1479		*
1480		* @serialData the current run status and the exception thrown
1481		* during execution, or {@code null} if none
1121	–	* @param s the stream
1482		*/
1483		private void writeObject(java.io.ObjectOutputStream s)
1484		throws java.io.IOException {
#	Line 1127 | Line 1487 | public abstract class ForkJoinTask<V> im
1487		}
1488
1489		/**
1490	<	* Reconstitutes the instance from a stream (that is, deserializes it).
1131	<	*
1132	<	* @param s the stream
1490	>	* Reconstitutes this task from a stream (that is, deserializes it).
1491		*/
1492		private void readObject(java.io.ObjectInputStream s)
1493		throws java.io.IOException, ClassNotFoundException {
1494		s.defaultReadObject();
1495		Object ex = s.readObject();
1496		if (ex != null)
1497	<	setExceptionalCompletion((Throwable) ex);
1497	>	setExceptionalCompletion((Throwable)ex);
1498		}
1499
1500		// Unsafe mechanics
1501	<
1502	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1503	<	private static final long statusOffset =
1504	<	objectFieldOffset("status", ForkJoinTask.class);
1505	<
1506	<	private static long objectFieldOffset(String field, Class<?> klazz) {
1501	>	private static final sun.misc.Unsafe U;
1502	>	private static final long STATUS;
1503	>	static {
1504	>	exceptionTableLock = new ReentrantLock();
1505	>	exceptionTableRefQueue = new ReferenceQueue<Object>();
1506	>	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1507		try {
1508	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1509	<	} catch (NoSuchFieldException e) {
1510	<	// Convert Exception to corresponding Error
1511	<	NoSuchFieldError error = new NoSuchFieldError(field);
1512	<	error.initCause(e);
1155	<	throw error;
1508	>	U = getUnsafe();
1509	>	STATUS = U.objectFieldOffset
1510	>	(ForkJoinTask.class.getDeclaredField("status"));
1511	>	} catch (Exception e) {
1512	>	throw new Error(e);
1513		}
1514		}
1515

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