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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.74 by dl, Tue Feb 22 00:39:31 2011 UTC vs.
Revision 1.81 by dl, Thu Jan 26 00:08:13 2012 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3		* Expert Group and released to the public domain, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		*/
6
7		package jsr166y;
8	–
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;
14	–	import java.util.Map;
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;
20	–	import java.util.concurrent.Executor;
21	–	import java.util.concurrent.ExecutorService;
17		import java.util.concurrent.Future;
18		import java.util.concurrent.RejectedExecutionException;
19		import java.util.concurrent.RunnableFuture;
#	Line 47 | Line 42 | import java.lang.reflect.Constructor;
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. Rethrown exceptions behave in the same way as
68	<	* regular exceptions, but, when possible, contain stack traces (as
69	<	* displayed for example using {@code ex.printStackTrace()}) of both
70	<	* the thread that initiated the computation as well as the thread
71	<	* actually encountering the exception; minimally only the latter.
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 89 | Line 93 | import java.lang.reflect.Constructor;
93		* performs the most common form of parallel invocation: forking a set
94		* of tasks and joining them all.
95		*
96	+	* <p>In the most typical usages, a fork-join pair act like a a call
97	+	* (fork) and return (join) from a parallel recursive function. As is
98	+	* the case with other forms of recursive calls, returns (joins)
99	+	* should be performed innermost-first. For example, {@code a.fork();
100	+	* b.fork(); b.join(); a.join();} is likely to be substantially more
101	+	* efficient than joining {@code a} before {@code b}.
102	+	*
103		* <p>The execution status of tasks may be queried at several levels
104		* of detail: {@link #isDone} is true if a task completed in any way
105		* (including the case where a task was cancelled without executing);
#	Line 125 | Line 136 | import java.lang.reflect.Constructor;
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
147	>	* processed. Also, completion based designs can use them to record
148	>	* that one subtask has completed. (Method names for marking are bulky
149	>	* in part to encourage definition of methods that reflect their usage
150	>	* patterns.)
151		*
152		* <p>Most base support methods are {@code final}, to prevent
153		* overriding of implementations that are intrinsically tied to the
#	Line 165 | Line 187 | public abstract class ForkJoinTask<V> im
187		* See the internal documentation of class ForkJoinPool for a
188		* general implementation overview.  ForkJoinTasks are mainly
189		* responsible for maintaining their "status" field amidst relays
190	<	* to methods in ForkJoinWorkerThread and ForkJoinPool. The
191	<	* methods of this class are more-or-less layered into (1) basic
192	<	* status maintenance (2) execution and awaiting completion (3)
193	<	* user-level methods that additionally report results. This is
194	<	* sometimes hard to see because this file orders exported methods
195	<	* in a way that flows well in javadocs.
190	>	* to methods in ForkJoinWorkerThread and ForkJoinPool.
191	>	*
192	>	* The methods of this class are more-or-less layered into
193	>	* (1) basic status maintenance
194	>	* (2) execution and awaiting completion
195	>	* (3) user-level methods that additionally report results.
196	>	* This is sometimes hard to see because this file orders exported
197	>	* methods in a way that flows well in javadocs.
198	>	*/
199	>
200	>	/**
201	>	* The number of times to try to help join a task without any
202	>	* apparent progress before giving up and blocking. The value is
203	>	* arbitrary but should be large enough to cope with transient
204	>	* stalls (due to GC etc) that can cause helping methods not to be
205	>	* able to proceed because other workers have not progressed to
206	>	* the point where subtasks can be found or taken.
207		*/
208	+	private static final int HELP_RETRIES = 32;
209
210		/*
211		* The status field holds run control status bits packed into a
#	Line 192 | 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	<	private static final int NORMAL      = -1;
230	<	private static final int CANCELLED   = -2;
231	<	private static final int EXCEPTIONAL = -3;
232	<	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	<	* Marks completion and wakes up threads waiting to join this task,
237	<	* also clearing signal request bits.
236	>	* Marks completion and wakes up threads waiting to join this
237	>	* task, also clearing signal request bits. A specialization for
238	>	* NORMAL completion is in method doExec
239		*
240		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
241		* @return completion status on exit
#	Line 208 | Line 244 | public abstract class ForkJoinTask<V> im
244		for (int s;;) {
245		if ((s = status) < 0)
246		return s;
247	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
248	<	if (s != 0)
247	>	if (U.compareAndSwapInt(this, STATUS, s, (s & ~SIGNAL)|completion)) {
248	>	if ((s & SIGNAL) != 0)
249		synchronized (this) { notifyAll(); }
250		return completion;
251		}
#	Line 217 | Line 253 | public abstract class ForkJoinTask<V> im
253		}
254
255		/**
256	<	* Tries to block a worker thread until completed or timed out.
257	<	* Uses Object.wait time argument conventions.
258	<	* May fail on contention or interrupt.
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	<	* @param millis if > 0, wait time.
260	>	* @return status on exit from this method
261		*/
262	<	final void tryAwaitDone(long millis) {
263	<	int s;
264	<	try {
265	<	if (((s = status) > 0 ||
266	<	(s == 0 &&
267	<	UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL))) &&
268	<	status > 0) {
269	<	synchronized (this) {
270	<	if (status > 0)
271	<	wait(millis);
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		}
276		}
238	–	} catch (InterruptedException ie) {
239	–	// caller must check termination
277		}
278	+	return s;
279		}
280
281		/**
#	Line 250 | Line 288 | public abstract class ForkJoinTask<V> im
288		boolean interrupted = false;
289		synchronized (this) {
290		while ((s = status) >= 0) {
291	<	if (s == 0)
254	<	UNSAFE.compareAndSwapInt(this, statusOffset,
255	<	0, SIGNAL);
256	<	else {
291	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
292		try {
293		wait();
294		} catch (InterruptedException ie) {
#	Line 279 | Line 314 | public abstract class ForkJoinTask<V> im
314		if ((s = status) >= 0) {
315		synchronized (this) {
316		while ((s = status) >= 0) {
317	<	if (s == 0)
283	<	UNSAFE.compareAndSwapInt(this, statusOffset,
284	<	0, SIGNAL);
285	<	else
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	<	* Primary execution method for stolen tasks. Unless done, calls
331	<	* exec and records status if completed, but doesn't wait for
332	<	* completion otherwise.
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	<	final void doExec() {
337	<	if (status >= 0) {
338	<	boolean completed;
339	<	try {
340	<	completed = exec();
341	<	} catch (Throwable rex) {
342	<	setExceptionalCompletion(rex);
343	<	return;
306	<	}
307	<	if (completed)
308	<	setCompletion(NORMAL); // must be outside try block
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	<	* Primary mechanics for join, get, quietlyJoin.
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 doJoin() {
356	<	Thread t; ForkJoinWorkerThread w; int s; boolean completed;
357	<	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
358	<	if ((s = status) < 0)
359	<	return s;
360	<	if ((w = (ForkJoinWorkerThread)t).unpushTask(this)) {
355	>	private int awaitJoin(ForkJoinPool.WorkQueue w, ForkJoinPool p) {
356	>	int s;
357	>	ForkJoinTask<?> prevJoin = w.currentJoin;
358	>	w.currentJoin = this;
359	>	for (int k = HELP_RETRIES; (s = status) >= 0;) {
360	>	if ((w.queueSize() > 0) ?
361	>	w.tryRemoveAndExec(this) :        // self-help
362	>	p.tryHelpStealer(w, this))        // help process tasks
363	>	k = HELP_RETRIES;                 // reset if made progress
364	>	else if ((s = status) < 0)            // recheck
365	>	break;
366	>	else if (--k > 0) {
367	>	if ((k & 3) == 1)
368	>	Thread.yield();               // occasionally yield
369	>	}
370	>	else if (k == 0)
371	>	p.tryPollForAndExec(w, this);     // uncommon self-help case
372	>	else if (p.tryCompensate()) {         // true if can block
373		try {
374	<	completed = exec();
375	<	} catch (Throwable rex) {
376	<	return setExceptionalCompletion(rex);
374	>	int ss = status;
375	>	if (ss >= 0 &&                // assert need signal
376	>	U.compareAndSwapInt(this, STATUS, ss, ss | SIGNAL)) {
377	>	synchronized (this) {
378	>	if (status >= 0)      // block
379	>	wait();
380	>	}
381	>	}
382	>	} catch (InterruptedException ignore) {
383	>	} finally {
384	>	p.incrementActiveCount();     // re-activate
385		}
327	–	if (completed)
328	–	return setCompletion(NORMAL);
386		}
330	–	return w.joinTask(this);
387		}
388	<	else
389	<	return externalAwaitDone();
388	>	w.currentJoin = prevJoin;
389	>	return s;
390		}
391
392		/**
393	<	* Primary mechanics for invoke, quietlyInvoke.
393	>	* Implementation for invoke, quietlyInvoke.
394	>	*
395		* @return status upon completion
396		*/
397		private int doInvoke() {
398	<	int s; boolean completed;
399	<	if ((s = status) < 0)
398	>	int s;
399	>	if ((s = doExec()) < 0)
400		return s;
344	–	try {
345	–	completed = exec();
346	–	} catch (Throwable rex) {
347	–	return setExceptionalCompletion(rex);
348	–	}
349	–	if (completed)
350	–	return setCompletion(NORMAL);
401		else
402		return doJoin();
403		}
#	Line 381 | Line 431 | public abstract class ForkJoinTask<V> im
431		* periods. However, since we do not know when the last joiner
432		* completes, we must use weak references and expunge them. We do
433		* so on each operation (hence full locking). Also, some thread in
434	<	* any ForkJoinPool will call helpExpunge when its pool becomes
435	<	* isQuiescent.
434	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
435	>	* pool becomes isQuiescent.
436		*/
437		static final class ExceptionNode extends WeakReference<ForkJoinTask<?>>{
438		final Throwable ex;
439		ExceptionNode next;
440	<	final long thrower;
440	>	final long thrower;  // use id not ref to avoid weak cycles
441		ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
442		super(task, exceptionTableRefQueue);
443		this.ex = ex;
#	Line 403 | Line 453 | public abstract class ForkJoinTask<V> im
453		*/
454		private int setExceptionalCompletion(Throwable ex) {
455		int h = System.identityHashCode(this);
456	<	ReentrantLock lock = exceptionTableLock;
456	>	final ReentrantLock lock = exceptionTableLock;
457		lock.lock();
458		try {
459		expungeStaleExceptions();
#	Line 424 | Line 474 | public abstract class ForkJoinTask<V> im
474		}
475
476		/**
477	+	* Cancels, ignoring any exceptions thrown by cancel. Used during
478	+	* worker and pool shutdown. Cancel is spec'ed not to throw any
479	+	* exceptions, but if it does anyway, we have no recourse during
480	+	* shutdown, so guard against this case.
481	+	*/
482	+	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
483	+	if (t != null && t.status >= 0) {
484	+	try {
485	+	t.cancel(false);
486	+	} catch (Throwable ignore) {
487	+	}
488	+	}
489	+	}
490	+
491	+	/**
492		* Removes exception node and clears status
493		*/
494		private void clearExceptionalCompletion() {
495		int h = System.identityHashCode(this);
496	<	ReentrantLock lock = exceptionTableLock;
496	>	final ReentrantLock lock = exceptionTableLock;
497		lock.lock();
498		try {
499		ExceptionNode[] t = exceptionTable;
#	Line 473 | Line 538 | public abstract class ForkJoinTask<V> im
538		return null;
539		int h = System.identityHashCode(this);
540		ExceptionNode e;
541	<	ReentrantLock lock = exceptionTableLock;
541	>	final ReentrantLock lock = exceptionTableLock;
542		lock.lock();
543		try {
544		expungeStaleExceptions();
#	Line 488 | Line 553 | public abstract class ForkJoinTask<V> im
553		if (e == null || (ex = e.ex) == null)
554		return null;
555		if (e.thrower != Thread.currentThread().getId()) {
556	<	Class ec = ex.getClass();
556	>	Class<? extends Throwable> ec = ex.getClass();
557		try {
558		Constructor<?> noArgCtor = null;
559		Constructor<?>[] cs = ec.getConstructors();// public ctors only
#	Line 539 | Line 604 | public abstract class ForkJoinTask<V> im
604		}
605
606		/**
607	<	* If lock is available, poll any stale refs and remove them.
607	>	* If lock is available, poll stale refs and remove them.
608		* Called from ForkJoinPool when pools become quiescent.
609		*/
610		static final void helpExpungeStaleExceptions() {
611	<	ReentrantLock lock = exceptionTableLock;
611	>	final ReentrantLock lock = exceptionTableLock;
612		if (lock.tryLock()) {
613		try {
614		expungeStaleExceptions();
#	Line 562 | Line 627 | public abstract class ForkJoinTask<V> im
627		if ((s = status) == CANCELLED)
628		throw new CancellationException();
629		if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
630	<	UNSAFE.throwException(ex);
630	>	U.throwException(ex);
631		return getRawResult();
632		}
633
#	Line 587 | Line 652 | public abstract class ForkJoinTask<V> im
652		* @return {@code this}, to simplify usage
653		*/
654		public final ForkJoinTask<V> fork() {
655	<	((ForkJoinWorkerThread) Thread.currentThread())
656	<	.pushTask(this);
655	>	ForkJoinWorkerThread wt;
656	>	(wt = (ForkJoinWorkerThread)Thread.currentThread()).
657	>	workQueue.push(this, wt.pool);
658		return this;
659		}
660
#	Line 694 | Line 760 | public abstract class ForkJoinTask<V> im
760		if (t != null) {
761		if (ex != null)
762		t.cancel(false);
763	<	else if (t.doJoin() < NORMAL && ex == null)
763	>	else if (t.doJoin() < NORMAL)
764		ex = t.getException();
765		}
766		}
767		if (ex != null)
768	<	UNSAFE.throwException(ex);
768	>	U.throwException(ex);
769		}
770
771		/**
#	Line 751 | Line 817 | public abstract class ForkJoinTask<V> im
817		if (t != null) {
818		if (ex != null)
819		t.cancel(false);
820	<	else if (t.doJoin() < NORMAL && ex == null)
820	>	else if (t.doJoin() < NORMAL)
821		ex = t.getException();
822		}
823		}
824		if (ex != null)
825	<	UNSAFE.throwException(ex);
825	>	U.throwException(ex);
826		return tasks;
827		}
828
#	Line 791 | Line 857 | public abstract class ForkJoinTask<V> im
857		return setCompletion(CANCELLED) == CANCELLED;
858		}
859
794	–	/**
795	–	* Cancels, ignoring any exceptions thrown by cancel. Used during
796	–	* worker and pool shutdown. Cancel is spec'ed not to throw any
797	–	* exceptions, but if it does anyway, we have no recourse during
798	–	* shutdown, so guard against this case.
799	–	*/
800	–	final void cancelIgnoringExceptions() {
801	–	try {
802	–	cancel(false);
803	–	} catch (Throwable ignore) {
804	–	}
805	–	}
806	–
860		public final boolean isDone() {
861		return status < 0;
862		}
#	Line 927 | Line 980 | public abstract class ForkJoinTask<V> im
980		*/
981		public final V get(long timeout, TimeUnit unit)
982		throws InterruptedException, ExecutionException, TimeoutException {
983	+	// Messy in part because we measure in nanos, but wait in millis
984	+	int s; long millis, nanos;
985		Thread t = Thread.currentThread();
986	<	if (t instanceof ForkJoinWorkerThread) {
987	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
988	<	long nanos = unit.toNanos(timeout);
989	<	if (status >= 0) {
990	<	boolean completed = false;
991	<	if (w.unpushTask(this)) {
992	<	try {
993	<	completed = exec();
994	<	} catch (Throwable rex) {
995	<	setExceptionalCompletion(rex);
986	>	if (!(t instanceof ForkJoinWorkerThread)) {
987	>	if ((millis = unit.toMillis(timeout)) > 0L)
988	>	s = externalInterruptibleAwaitDone(millis);
989	>	else
990	>	s = status;
991	>	}
992	>	else if ((s = status) >= 0 && (nanos = unit.toNanos(timeout)) > 0L) {
993	>	long deadline = System.nanoTime() + nanos;
994	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
995	>	ForkJoinPool.WorkQueue w = wt.workQueue;
996	>	ForkJoinPool p = wt.pool;
997	>	if (w.tryUnpush(this))
998	>	doExec();
999	>	boolean blocking = false;
1000	>	try {
1001	>	while ((s = status) >= 0) {
1002	>	if (w.runState < 0)
1003	>	cancelIgnoringExceptions(this);
1004	>	else if (!blocking)
1005	>	blocking = p.tryCompensate();
1006	>	else {
1007	>	millis = TimeUnit.NANOSECONDS.toMillis(nanos);
1008	>	if (millis > 0L &&
1009	>	U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
1010	>	try {
1011	>	synchronized (this) {
1012	>	if (status >= 0)
1013	>	wait(millis);
1014	>	}
1015	>	} catch (InterruptedException ie) {
1016	>	}
1017	>	}
1018	>	if ((s = status) < 0 ||
1019	>	(nanos = deadline - System.nanoTime()) <= 0L)
1020	>	break;
1021		}
1022		}
1023	<	if (completed)
1024	<	setCompletion(NORMAL);
1025	<	else if (status >= 0 && nanos > 0)
946	<	w.pool.timedAwaitJoin(this, nanos);
1023	>	} finally {
1024	>	if (blocking)
1025	>	p.incrementActiveCount();
1026		}
1027		}
949	–	else {
950	–	long millis = unit.toMillis(timeout);
951	–	if (millis > 0)
952	–	externalInterruptibleAwaitDone(millis);
953	–	}
954	–	int s = status;
1028		if (s != NORMAL) {
1029		Throwable ex;
1030		if (s == CANCELLED)
#	Line 997 | Line 1070 | public abstract class ForkJoinTask<V> im
1070		* ClassCastException}.
1071		*/
1072		public static void helpQuiesce() {
1073	<	((ForkJoinWorkerThread) Thread.currentThread())
1074	<	.helpQuiescePool();
1073	>	ForkJoinWorkerThread w =
1074	>	(ForkJoinWorkerThread)Thread.currentThread();
1075	>	w.pool.helpQuiescePool(w.workQueue);
1076		}
1077
1078		/**
#	Line 1066 | Line 1140 | public abstract class ForkJoinTask<V> im
1140		* @return {@code true} if unforked
1141		*/
1142		public boolean tryUnfork() {
1143	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1144	<	.unpushTask(this);
1143	>	return ((ForkJoinWorkerThread)Thread.currentThread())
1144	>	.workQueue.tryUnpush(this);
1145		}
1146
1147		/**
#	Line 1086 | Line 1160 | public abstract class ForkJoinTask<V> im
1160		*/
1161		public static int getQueuedTaskCount() {
1162		return ((ForkJoinWorkerThread) Thread.currentThread())
1163	<	.getQueueSize();
1163	>	.workQueue.queueSize();
1164		}
1165
1166		/**
#	Line 1108 | Line 1182 | public abstract class ForkJoinTask<V> im
1182		* @return the surplus number of tasks, which may be negative
1183		*/
1184		public static int getSurplusQueuedTaskCount() {
1185	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1186	<	.getEstimatedSurplusTaskCount();
1185	>	/*
1186	>	* The aim of this method is to return a cheap heuristic guide
1187	>	* for task partitioning when programmers, frameworks, tools,
1188	>	* or languages have little or no idea about task granularity.
1189	>	* In essence by offering this method, we ask users only about
1190	>	* tradeoffs in overhead vs expected throughput and its
1191	>	* variance, rather than how finely to partition tasks.
1192	>	*
1193	>	* In a steady state strict (tree-structured) computation,
1194	>	* each thread makes available for stealing enough tasks for
1195	>	* other threads to remain active. Inductively, if all threads
1196	>	* play by the same rules, each thread should make available
1197	>	* only a constant number of tasks.
1198	>	*
1199	>	* The minimum useful constant is just 1. But using a value of
1200	>	* 1 would require immediate replenishment upon each steal to
1201	>	* maintain enough tasks, which is infeasible.  Further,
1202	>	* partitionings/granularities of offered tasks should
1203	>	* minimize steal rates, which in general means that threads
1204	>	* nearer the top of computation tree should generate more
1205	>	* than those nearer the bottom. In perfect steady state, each
1206	>	* thread is at approximately the same level of computation
1207	>	* tree. However, producing extra tasks amortizes the
1208	>	* uncertainty of progress and diffusion assumptions.
1209	>	*
1210	>	* So, users will want to use values larger, but not much
1211	>	* larger than 1 to both smooth over transient shortages and
1212	>	* hedge against uneven progress; as traded off against the
1213	>	* cost of extra task overhead. We leave the user to pick a
1214	>	* threshold value to compare with the results of this call to
1215	>	* guide decisions, but recommend values such as 3.
1216	>	*
1217	>	* When all threads are active, it is on average OK to
1218	>	* estimate surplus strictly locally. In steady-state, if one
1219	>	* thread is maintaining say 2 surplus tasks, then so are
1220	>	* others. So we can just use estimated queue length.
1221	>	* However, this strategy alone leads to serious mis-estimates
1222	>	* in some non-steady-state conditions (ramp-up, ramp-down,
1223	>	* other stalls). We can detect many of these by further
1224	>	* considering the number of "idle" threads, that are known to
1225	>	* have zero queued tasks, so compensate by a factor of
1226	>	* (#idle/#active) threads.
1227	>	*/
1228	>	ForkJoinWorkerThread w =
1229	>	(ForkJoinWorkerThread)Thread.currentThread();
1230	>	return w.workQueue.queueSize() - w.pool.idlePerActive();
1231		}
1232
1233		// Extension methods
#	Line 1166 | Line 1284 | public abstract class ForkJoinTask<V> im
1284		* @return the next task, or {@code null} if none are available
1285		*/
1286		protected static ForkJoinTask<?> peekNextLocalTask() {
1287	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1170	<	.peekTask();
1287	>	return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek();
1288		}
1289
1290		/**
#	Line 1186 | Line 1303 | public abstract class ForkJoinTask<V> im
1303		*/
1304		protected static ForkJoinTask<?> pollNextLocalTask() {
1305		return ((ForkJoinWorkerThread) Thread.currentThread())
1306	<	.pollLocalTask();
1306	>	.workQueue.nextLocalTask();
1307		}
1308
1309		/**
#	Line 1208 | Line 1325 | public abstract class ForkJoinTask<V> im
1325		* @return a task, or {@code null} if none are available
1326		*/
1327		protected static ForkJoinTask<?> pollTask() {
1328	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1329	<	.pollTask();
1328	>	ForkJoinWorkerThread w =
1329	>	(ForkJoinWorkerThread)Thread.currentThread();
1330	>	return w.pool.nextTaskFor(w.workQueue);
1331	>	}
1332	>
1333	>	// Mark-bit operations
1334	>
1335	>	/**
1336	>	* Returns true if this task is marked.
1337	>	*
1338	>	* @return true if this task is marked
1339	>	* @since 1.8
1340	>	*/
1341	>	public final boolean isMarkedForkJoinTask() {
1342	>	return (status & MARKED) != 0;
1343	>	}
1344	>
1345	>	/**
1346	>	* Atomically sets the mark on this task.
1347	>	*
1348	>	* @return true if this task was previously unmarked
1349	>	* @since 1.8
1350	>	*/
1351	>	public final boolean markForkJoinTask() {
1352	>	for (int s;;) {
1353	>	if (((s = status) & MARKED) != 0)
1354	>	return false;
1355	>	if (U.compareAndSwapInt(this, STATUS, s, s | MARKED))
1356	>	return true;
1357	>	}
1358	>	}
1359	>
1360	>	/**
1361	>	* Atomically clears the mark on this task.
1362	>	*
1363	>	* @return true if this task was previously marked
1364	>	* @since 1.8
1365	>	*/
1366	>	public final boolean unmarkForkJoinTask() {
1367	>	for (int s;;) {
1368	>	if (((s = status) & MARKED) == 0)
1369	>	return false;
1370	>	if (U.compareAndSwapInt(this, STATUS, s, s & ~MARKED))
1371	>	return true;
1372	>	}
1373		}
1374
1375		/**
#	Line 1310 | Line 1470 | public abstract class ForkJoinTask<V> im
1470		private static final long serialVersionUID = -7721805057305804111L;
1471
1472		/**
1473	<	* Saves the state to a stream (that is, serializes it).
1473	>	* Saves this task to a stream (that is, serializes it).
1474		*
1475		* @serialData the current run status and the exception thrown
1476		* during execution, or {@code null} if none
1317	–	* @param s the stream
1477		*/
1478		private void writeObject(java.io.ObjectOutputStream s)
1479		throws java.io.IOException {
#	Line 1323 | Line 1482 | public abstract class ForkJoinTask<V> im
1482		}
1483
1484		/**
1485	<	* Reconstitutes the instance from a stream (that is, deserializes it).
1327	<	*
1328	<	* @param s the stream
1485	>	* Reconstitutes this task from a stream (that is, deserializes it).
1486		*/
1487		private void readObject(java.io.ObjectInputStream s)
1488		throws java.io.IOException, ClassNotFoundException {
#	Line 1336 | Line 1493 | public abstract class ForkJoinTask<V> im
1493		}
1494
1495		// Unsafe mechanics
1496	<	private static final sun.misc.Unsafe UNSAFE;
1497	<	private static final long statusOffset;
1496	>	private static final sun.misc.Unsafe U;
1497	>	private static final long STATUS;
1498		static {
1499		exceptionTableLock = new ReentrantLock();
1500		exceptionTableRefQueue = new ReferenceQueue<Object>();
1501		exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1502		try {
1503	<	UNSAFE = getUnsafe();
1504	<	statusOffset = UNSAFE.objectFieldOffset
1503	>	U = getUnsafe();
1504	>	STATUS = U.objectFieldOffset
1505		(ForkJoinTask.class.getDeclaredField("status"));
1506		} catch (Exception e) {
1507		throw new Error(e);

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