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Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.74 by dl, Tue Feb 22 00:39:31 2011 UTC vs.
Revision 1.86 by dl, Mon Feb 20 18:20:06 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 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 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 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 status field holds run control status bits packed into a
202		* single int to minimize footprint and to ensure atomicity (via
203		* CAS).  Status is initially zero, and takes on nonnegative
204	<	* values until completed, upon which status holds value
205	<	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
206	<	* waits by other threads have the SIGNAL bit set.  Completion of
207	<	* a stolen task with SIGNAL set awakens any waiters via
208	<	* notifyAll. Even though suboptimal for some purposes, we use
209	<	* basic builtin wait/notify to take advantage of "monitor
210	<	* inflation" in JVMs that we would otherwise need to emulate to
211	<	* avoid adding further per-task bookkeeping overhead.  We want
212	<	* these monitors to be "fat", i.e., not use biasing or thin-lock
213	<	* techniques, so use some odd coding idioms that tend to avoid
214	<	* them.
204	>	* values until completed, upon which status (anded with
205	>	* DONE_MASK) holds value NORMAL, CANCELLED, or EXCEPTIONAL. Tasks
206	>	* undergoing blocking waits by other threads have the SIGNAL bit
207	>	* set.  Completion of a stolen task with SIGNAL set awakens any
208	>	* waiters via notifyAll. Even though suboptimal for some
209	>	* purposes, we use basic builtin wait/notify to take advantage of
210	>	* "monitor inflation" in JVMs that we would otherwise need to
211	>	* emulate to avoid adding further per-task bookkeeping overhead.
212	>	* We want these monitors to be "fat", i.e., not use biasing or
213	>	* thin-lock techniques, so use some odd coding idioms that tend
214	>	* to avoid them, mainly by arranging that every synchronized
215	>	* block performs a wait, notifyAll or both.
216		*/
217
218		/** The run status of this task */
219		volatile int status; // accessed directly by pool and workers
220	<	private static final int NORMAL      = -1;
221	<	private static final int CANCELLED   = -2;
222	<	private static final int EXCEPTIONAL = -3;
223	<	private static final int SIGNAL      =  1;
220	>	static final int DONE_MASK   = 0xf0000000;  // mask out non-completion bits
221	>	static final int NORMAL      = 0xf0000000;  // must be negative
222	>	static final int CANCELLED   = 0xc0000000;  // must be < NORMAL
223	>	static final int EXCEPTIONAL = 0x80000000;  // must be < CANCELLED
224	>	static final int SIGNAL      = 0x00000001;
225	>	static final int MARKED      = 0x00000002;
226
227		/**
228	<	* Marks completion and wakes up threads waiting to join this task,
229	<	* also clearing signal request bits.
228	>	* Marks completion and wakes up threads waiting to join this
229	>	* task. A specialization for NORMAL completion is in method
230	>	* doExec.
231		*
232		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
233		* @return completion status on exit
#	Line 208 | Line 236 | public abstract class ForkJoinTask<V> im
236		for (int s;;) {
237		if ((s = status) < 0)
238		return s;
239	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
240	<	if (s != 0)
239	>	if (U.compareAndSwapInt(this, STATUS, s, s | completion)) {
240	>	if ((s & SIGNAL) != 0)
241		synchronized (this) { notifyAll(); }
242		return completion;
243		}
#	Line 217 | Line 245 | public abstract class ForkJoinTask<V> im
245		}
246
247		/**
248	<	* Tries to block a worker thread until completed or timed out.
249	<	* Uses Object.wait time argument conventions.
250	<	* May fail on contention or interrupt.
248	>	* Primary execution method for stolen tasks. Unless done, calls
249	>	* exec and records status if completed, but doesn't wait for
250	>	* completion otherwise.
251		*
252	<	* @param millis if > 0, wait time.
252	>	* @return status on exit from this method
253		*/
254	<	final void tryAwaitDone(long millis) {
255	<	int s;
256	<	try {
257	<	if (((s = status) > 0 ||
258	<	(s == 0 &&
259	<	UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL))) &&
260	<	status > 0) {
261	<	synchronized (this) {
262	<	if (status > 0)
263	<	wait(millis);
254	>	final int doExec() {
255	>	int s; boolean completed;
256	>	if ((s = status) >= 0) {
257	>	try {
258	>	completed = exec();
259	>	} catch (Throwable rex) {
260	>	return setExceptionalCompletion(rex);
261	>	}
262	>	while ((s = status) >= 0 && completed) {
263	>	if (U.compareAndSwapInt(this, STATUS, s, s | NORMAL)) {
264	>	if ((s & SIGNAL) != 0)
265	>	synchronized (this) { notifyAll(); }
266	>	return NORMAL;
267		}
268		}
238	–	} catch (InterruptedException ie) {
239	–	// caller must check termination
269		}
270	+	return s;
271	+	}
272	+
273	+	/**
274	+	* Tries to set SIGNAL status. Used by ForkJoinPool. Other
275	+	* variants are directly incorporated into externalAwaitDone etc.
276	+	*
277	+	* @return true if successful
278	+	*/
279	+	final boolean trySetSignal() {
280	+	int s;
281	+	return U.compareAndSwapInt(this, STATUS, s = status, s | SIGNAL);
282		}
283
284		/**
#	Line 245 | Line 286 | public abstract class ForkJoinTask<V> im
286		* @return status upon completion
287		*/
288		private int externalAwaitDone() {
289	+	boolean interrupted = false;
290		int s;
291	<	if ((s = status) >= 0) {
292	<	boolean interrupted = false;
293	<	synchronized (this) {
294	<	while ((s = status) >= 0) {
253	<	if (s == 0)
254	<	UNSAFE.compareAndSwapInt(this, statusOffset,
255	<	0, SIGNAL);
256	<	else {
291	>	while ((s = status) >= 0) {
292	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
293	>	synchronized (this) {
294	>	if (status >= 0) {
295		try {
296		wait();
297		} catch (InterruptedException ie) {
298		interrupted = true;
299		}
300		}
301	+	else
302	+	notifyAll();
303		}
304		}
265	–	if (interrupted)
266	–	Thread.currentThread().interrupt();
305		}
306	+	if (interrupted)
307	+	Thread.currentThread().interrupt();
308		return s;
309		}
310
311		/**
312	<	* Blocks a non-worker-thread until completion or interruption or timeout.
312	>	* Blocks a non-worker-thread until completion or interruption.
313		*/
314	<	private int externalInterruptibleAwaitDone(long millis)
275	<	throws InterruptedException {
314	>	private int externalInterruptibleAwaitDone() throws InterruptedException {
315		int s;
316		if (Thread.interrupted())
317		throw new InterruptedException();
318	<	if ((s = status) >= 0) {
319	<	synchronized (this) {
320	<	while ((s = status) >= 0) {
321	<	if (s == 0)
322	<	UNSAFE.compareAndSwapInt(this, statusOffset,
284	<	0, SIGNAL);
318	>	while ((s = status) >= 0) {
319	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
320	>	synchronized (this) {
321	>	if (status >= 0)
322	>	wait();
323		else
324	<	wait(millis);
324	>	notifyAll();
325		}
326		}
327		}
328		return s;
329		}
330
293	–	/**
294	–	* Primary execution method for stolen tasks. Unless done, calls
295	–	* exec and records status if completed, but doesn't wait for
296	–	* completion otherwise.
297	–	*/
298	–	final void doExec() {
299	–	if (status >= 0) {
300	–	boolean completed;
301	–	try {
302	–	completed = exec();
303	–	} catch (Throwable rex) {
304	–	setExceptionalCompletion(rex);
305	–	return;
306	–	}
307	–	if (completed)
308	–	setCompletion(NORMAL); // must be outside try block
309	–	}
310	–	}
331
332		/**
333	<	* Primary mechanics for join, get, quietlyJoin.
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	<	Thread t; ForkJoinWorkerThread w; int s; boolean completed;
341	<	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
342	<	if ((s = status) < 0)
343	<	return s;
344	<	if ((w = (ForkJoinWorkerThread)t).unpushTask(this)) {
345	<	try {
323	<	completed = exec();
324	<	} catch (Throwable rex) {
325	<	return setExceptionalCompletion(rex);
326	<	}
327	<	if (completed)
328	<	return setCompletion(NORMAL);
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	<	return w.joinTask(this);
347	>	else
348	>	s = externalAwaitDone();
349		}
350	<	else
333	<	return externalAwaitDone();
350	>	return s;
351		}
352
353		/**
354	<	* Primary mechanics for invoke, quietlyInvoke.
354	>	* Implementation for invoke, quietlyInvoke.
355	>	*
356		* @return status upon completion
357		*/
358		private int doInvoke() {
359	<	int s; boolean completed;
360	<	if ((s = status) < 0)
361	<	return s;
362	<	try {
363	<	completed = exec();
364	<	} catch (Throwable rex) {
365	<	return setExceptionalCompletion(rex);
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	<	if (completed)
350	<	return setCompletion(NORMAL);
351	<	else
352	<	return doJoin();
367	>	return s;
368		}
369
370		// Exception table support
#	Line 381 | Line 396 | public abstract class ForkJoinTask<V> im
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 helpExpunge when its pool becomes
400	<	* isQuiescent.
399	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
400	>	* pool becomes isQuiescent.
401		*/
402	<	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>>{
402	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> {
403		final Throwable ex;
404		ExceptionNode next;
405	<	final long thrower;
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;
#	Line 403 | Line 418 | public abstract class ForkJoinTask<V> im
418		*/
419		private int setExceptionalCompletion(Throwable ex) {
420		int h = System.identityHashCode(this);
421	<	ReentrantLock lock = exceptionTableLock;
421	>	final ReentrantLock lock = exceptionTableLock;
422		lock.lock();
423		try {
424		expungeStaleExceptions();
#	Line 424 | Line 439 | public abstract class ForkJoinTask<V> im
439		}
440
441		/**
442	+	* Cancels, ignoring any exceptions thrown by cancel. Used during
443	+	* worker and pool shutdown. Cancel is spec'ed not to throw any
444	+	* exceptions, but if it does anyway, we have no recourse during
445	+	* shutdown, so guard against this case.
446	+	*/
447	+	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
448	+	if (t != null && t.status >= 0) {
449	+	try {
450	+	t.cancel(false);
451	+	} catch (Throwable ignore) {
452	+	}
453	+	}
454	+	}
455	+
456	+	/**
457		* Removes exception node and clears status
458		*/
459		private void clearExceptionalCompletion() {
460		int h = System.identityHashCode(this);
461	<	ReentrantLock lock = exceptionTableLock;
461	>	final ReentrantLock lock = exceptionTableLock;
462		lock.lock();
463		try {
464		ExceptionNode[] t = exceptionTable;
#	Line 469 | Line 499 | public abstract class ForkJoinTask<V> im
499		* @return the exception, or null if none
500		*/
501		private Throwable getThrowableException() {
502	<	if (status != EXCEPTIONAL)
502	>	if ((status & DONE_MASK) != EXCEPTIONAL)
503		return null;
504		int h = System.identityHashCode(this);
505		ExceptionNode e;
506	<	ReentrantLock lock = exceptionTableLock;
506	>	final ReentrantLock lock = exceptionTableLock;
507		lock.lock();
508		try {
509		expungeStaleExceptions();
#	Line 488 | Line 518 | public abstract class ForkJoinTask<V> im
518		if (e == null || (ex = e.ex) == null)
519		return null;
520		if (e.thrower != Thread.currentThread().getId()) {
521	<	Class ec = ex.getClass();
521	>	Class<? extends Throwable> ec = ex.getClass();
522		try {
523		Constructor<?> noArgCtor = null;
524		Constructor<?>[] cs = ec.getConstructors();// public ctors only
#	Line 539 | Line 569 | public abstract class ForkJoinTask<V> im
569		}
570
571		/**
572	<	* If lock is available, poll any stale refs and remove them.
572	>	* If lock is available, poll stale refs and remove them.
573		* Called from ForkJoinPool when pools become quiescent.
574		*/
575		static final void helpExpungeStaleExceptions() {
576	<	ReentrantLock lock = exceptionTableLock;
576	>	final ReentrantLock lock = exceptionTableLock;
577		if (lock.tryLock()) {
578		try {
579		expungeStaleExceptions();
#	Line 554 | Line 584 | public abstract class ForkJoinTask<V> im
584		}
585
586		/**
587	<	* Report the result of invoke or join; called only upon
558	<	* non-normal return of internal versions.
587	>	* Throws exception, if any, associated with the given status.
588		*/
589	<	private V reportResult() {
590	<	int s; Throwable ex;
591	<	if ((s = status) == CANCELLED)
592	<	throw new CancellationException();
593	<	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
594	<	UNSAFE.throwException(ex);
566	<	return getRawResult();
589	>	private void reportException(int s) {
590	>	Throwable ex = ((s == CANCELLED) ?  new CancellationException() :
591	>	(s == EXCEPTIONAL) ? getThrowableException() :
592	>	null);
593	>	if (ex != null)
594	>	U.throwException(ex);
595		}
596
597		// public methods
#	Line 587 | Line 615 | public abstract class ForkJoinTask<V> im
615		* @return {@code this}, to simplify usage
616		*/
617		public final ForkJoinTask<V> fork() {
618	<	((ForkJoinWorkerThread) Thread.currentThread())
591	<	.pushTask(this);
618	>	((ForkJoinWorkerThread)Thread.currentThread()).workQueue.push(this);
619		return this;
620		}
621
#	Line 604 | Line 631 | public abstract class ForkJoinTask<V> im
631		* @return the computed result
632		*/
633		public final V join() {
634	<	if (doJoin() != NORMAL)
635	<	return reportResult();
636	<	else
637	<	return getRawResult();
634	>	int s;
635	>	if ((s = doJoin() & DONE_MASK) != NORMAL)
636	>	reportException(s);
637	>	return getRawResult();
638		}
639
640		/**
#	Line 619 | Line 646 | public abstract class ForkJoinTask<V> im
646		* @return the computed result
647		*/
648		public final V invoke() {
649	<	if (doInvoke() != NORMAL)
650	<	return reportResult();
651	<	else
652	<	return getRawResult();
649	>	int s;
650	>	if ((s = doInvoke() & DONE_MASK) != NORMAL)
651	>	reportException(s);
652	>	return getRawResult();
653		}
654
655		/**
#	Line 649 | Line 676 | public abstract class ForkJoinTask<V> im
676		* @throws NullPointerException if any task is null
677		*/
678		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
679	+	int s1, s2;
680		t2.fork();
681	<	t1.invoke();
682	<	t2.join();
681	>	if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL)
682	>	t1.reportException(s1);
683	>	if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
684	>	t2.reportException(s2);
685		}
686
687		/**
#	Line 694 | Line 724 | public abstract class ForkJoinTask<V> im
724		if (t != null) {
725		if (ex != null)
726		t.cancel(false);
727	<	else if (t.doJoin() < NORMAL && ex == null)
727	>	else if (t.doJoin() < NORMAL)
728		ex = t.getException();
729		}
730		}
731		if (ex != null)
732	<	UNSAFE.throwException(ex);
732	>	U.throwException(ex);
733		}
734
735		/**
#	Line 751 | Line 781 | public abstract class ForkJoinTask<V> im
781		if (t != null) {
782		if (ex != null)
783		t.cancel(false);
784	<	else if (t.doJoin() < NORMAL && ex == null)
784	>	else if (t.doJoin() < NORMAL)
785		ex = t.getException();
786		}
787		}
788		if (ex != null)
789	<	UNSAFE.throwException(ex);
789	>	U.throwException(ex);
790		return tasks;
791		}
792
#	Line 788 | Line 818 | public abstract class ForkJoinTask<V> im
818		* @return {@code true} if this task is now cancelled
819		*/
820		public boolean cancel(boolean mayInterruptIfRunning) {
821	<	return setCompletion(CANCELLED) == CANCELLED;
792	<	}
793	<
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	<	}
821	>	return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
822		}
823
824		public final boolean isDone() {
#	Line 809 | Line 826 | public abstract class ForkJoinTask<V> im
826		}
827
828		public final boolean isCancelled() {
829	<	return status == CANCELLED;
829	>	return (status & DONE_MASK) == CANCELLED;
830		}
831
832		/**
#	Line 829 | Line 846 | public abstract class ForkJoinTask<V> im
846		* exception and was not cancelled
847		*/
848		public final boolean isCompletedNormally() {
849	<	return status == NORMAL;
849	>	return (status & DONE_MASK) == NORMAL;
850		}
851
852		/**
#	Line 840 | Line 857 | public abstract class ForkJoinTask<V> im
857		* @return the exception, or {@code null} if none
858		*/
859		public final Throwable getException() {
860	<	int s = status;
860	>	int s = status & DONE_MASK;
861		return ((s >= NORMAL)    ? null :
862		(s == CANCELLED) ? new CancellationException() :
863		getThrowableException());
#	Line 902 | Line 919 | public abstract class ForkJoinTask<V> im
919		*/
920		public final V get() throws InterruptedException, ExecutionException {
921		int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
922	<	doJoin() : externalInterruptibleAwaitDone(0L);
922	>	doJoin() : externalInterruptibleAwaitDone();
923		Throwable ex;
924	<	if (s == CANCELLED)
924	>	if ((s &= DONE_MASK) == CANCELLED)
925		throw new CancellationException();
926		if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
927		throw new ExecutionException(ex);
#	Line 927 | Line 944 | public abstract class ForkJoinTask<V> im
944		*/
945		public final V get(long timeout, TimeUnit unit)
946		throws InterruptedException, ExecutionException, TimeoutException {
947	<	Thread t = Thread.currentThread();
948	<	if (t instanceof ForkJoinWorkerThread) {
949	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
950	<	long nanos = unit.toNanos(timeout);
951	<	if (status >= 0) {
952	<	boolean completed = false;
953	<	if (w.unpushTask(this)) {
954	<	try {
955	<	completed = exec();
956	<	} catch (Throwable rex) {
957	<	setExceptionalCompletion(rex);
947	>	if (Thread.interrupted())
948	>	throw new InterruptedException();
949	>	// Messy in part because we measure in nanosecs, but wait in millisecs
950	>	int s; long ns, ms;
951	>	if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) {
952	>	long deadline = System.nanoTime() + ns;
953	>	ForkJoinPool p = null;
954	>	ForkJoinPool.WorkQueue w = null;
955	>	Thread t = Thread.currentThread();
956	>	if (t instanceof ForkJoinWorkerThread) {
957	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
958	>	p = wt.pool;
959	>	w = wt.workQueue;
960	>	s = p.helpJoinOnce(w, this); // no retries on failure
961	>	}
962	>	boolean canBlock = false;
963	>	boolean interrupted = false;
964	>	try {
965	>	while ((s = status) >= 0) {
966	>	if (w != null && w.runState < 0)
967	>	cancelIgnoringExceptions(this);
968	>	else if (!canBlock) {
969	>	if (p == null || p.tryCompensate(this, null))
970	>	canBlock = true;
971	>	}
972	>	else {
973	>	if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
974	>	U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
975	>	synchronized (this) {
976	>	if (status >= 0) {
977	>	try {
978	>	wait(ms);
979	>	} catch (InterruptedException ie) {
980	>	if (p == null)
981	>	interrupted = true;
982	>	}
983	>	}
984	>	else
985	>	notifyAll();
986	>	}
987	>	}
988	>	if ((s = status) < 0 || interrupted ||
989	>	(ns = deadline - System.nanoTime()) <= 0L)
990	>	break;
991		}
992		}
993	<	if (completed)
994	<	setCompletion(NORMAL);
995	<	else if (status >= 0 && nanos > 0)
946	<	w.pool.timedAwaitJoin(this, nanos);
993	>	} finally {
994	>	if (p != null && canBlock)
995	>	p.incrementActiveCount();
996		}
997	+	if (interrupted)
998	+	throw new InterruptedException();
999		}
1000	<	else {
950	<	long millis = unit.toMillis(timeout);
951	<	if (millis > 0)
952	<	externalInterruptibleAwaitDone(millis);
953	<	}
954	<	int s = status;
955	<	if (s != NORMAL) {
1000	>	if ((s &= DONE_MASK) != NORMAL) {
1001		Throwable ex;
1002		if (s == CANCELLED)
1003		throw new CancellationException();
#	Line 997 | Line 1042 | public abstract class ForkJoinTask<V> im
1042		* ClassCastException}.
1043		*/
1044		public static void helpQuiesce() {
1045	<	((ForkJoinWorkerThread) Thread.currentThread())
1046	<	.helpQuiescePool();
1045	>	ForkJoinWorkerThread wt =
1046	>	(ForkJoinWorkerThread)Thread.currentThread();
1047	>	wt.pool.helpQuiescePool(wt.workQueue);
1048		}
1049
1050		/**
#	Line 1018 | Line 1064 | public abstract class ForkJoinTask<V> im
1064		* setRawResult(null)}.
1065		*/
1066		public void reinitialize() {
1067	<	if (status == EXCEPTIONAL)
1067	>	if ((status & DONE_MASK) == EXCEPTIONAL)
1068		clearExceptionalCompletion();
1069		else
1070		status = 0;
#	Line 1066 | Line 1112 | public abstract class ForkJoinTask<V> im
1112		* @return {@code true} if unforked
1113		*/
1114		public boolean tryUnfork() {
1115	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1116	<	.unpushTask(this);
1115	>	return ((ForkJoinWorkerThread)Thread.currentThread())
1116	>	.workQueue.tryUnpush(this);
1117		}
1118
1119		/**
#	Line 1086 | Line 1132 | public abstract class ForkJoinTask<V> im
1132		*/
1133		public static int getQueuedTaskCount() {
1134		return ((ForkJoinWorkerThread) Thread.currentThread())
1135	<	.getQueueSize();
1135	>	.workQueue.queueSize();
1136		}
1137
1138		/**
#	Line 1108 | Line 1154 | public abstract class ForkJoinTask<V> im
1154		* @return the surplus number of tasks, which may be negative
1155		*/
1156		public static int getSurplusQueuedTaskCount() {
1157	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1158	<	.getEstimatedSurplusTaskCount();
1157	>	/*
1158	>	* The aim of this method is to return a cheap heuristic guide
1159	>	* for task partitioning when programmers, frameworks, tools,
1160	>	* or languages have little or no idea about task granularity.
1161	>	* In essence by offering this method, we ask users only about
1162	>	* tradeoffs in overhead vs expected throughput and its
1163	>	* variance, rather than how finely to partition tasks.
1164	>	*
1165	>	* In a steady state strict (tree-structured) computation,
1166	>	* each thread makes available for stealing enough tasks for
1167	>	* other threads to remain active. Inductively, if all threads
1168	>	* play by the same rules, each thread should make available
1169	>	* only a constant number of tasks.
1170	>	*
1171	>	* The minimum useful constant is just 1. But using a value of
1172	>	* 1 would require immediate replenishment upon each steal to
1173	>	* maintain enough tasks, which is infeasible.  Further,
1174	>	* partitionings/granularities of offered tasks should
1175	>	* minimize steal rates, which in general means that threads
1176	>	* nearer the top of computation tree should generate more
1177	>	* than those nearer the bottom. In perfect steady state, each
1178	>	* thread is at approximately the same level of computation
1179	>	* tree. However, producing extra tasks amortizes the
1180	>	* uncertainty of progress and diffusion assumptions.
1181	>	*
1182	>	* So, users will want to use values larger, but not much
1183	>	* larger than 1 to both smooth over transient shortages and
1184	>	* hedge against uneven progress; as traded off against the
1185	>	* cost of extra task overhead. We leave the user to pick a
1186	>	* threshold value to compare with the results of this call to
1187	>	* guide decisions, but recommend values such as 3.
1188	>	*
1189	>	* When all threads are active, it is on average OK to
1190	>	* estimate surplus strictly locally. In steady-state, if one
1191	>	* thread is maintaining say 2 surplus tasks, then so are
1192	>	* others. So we can just use estimated queue length.
1193	>	* However, this strategy alone leads to serious mis-estimates
1194	>	* in some non-steady-state conditions (ramp-up, ramp-down,
1195	>	* other stalls). We can detect many of these by further
1196	>	* considering the number of "idle" threads, that are known to
1197	>	* have zero queued tasks, so compensate by a factor of
1198	>	* (#idle/#active) threads.
1199	>	*/
1200	>	ForkJoinWorkerThread wt =
1201	>	(ForkJoinWorkerThread)Thread.currentThread();
1202	>	return wt.workQueue.queueSize() - wt.pool.idlePerActive();
1203		}
1204
1205		// Extension methods
#	Line 1166 | Line 1256 | public abstract class ForkJoinTask<V> im
1256		* @return the next task, or {@code null} if none are available
1257		*/
1258		protected static ForkJoinTask<?> peekNextLocalTask() {
1259	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1170	<	.peekTask();
1259	>	return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek();
1260		}
1261
1262		/**
#	Line 1186 | Line 1275 | public abstract class ForkJoinTask<V> im
1275		*/
1276		protected static ForkJoinTask<?> pollNextLocalTask() {
1277		return ((ForkJoinWorkerThread) Thread.currentThread())
1278	<	.pollLocalTask();
1278	>	.workQueue.nextLocalTask();
1279		}
1280
1281		/**
#	Line 1208 | Line 1297 | public abstract class ForkJoinTask<V> im
1297		* @return a task, or {@code null} if none are available
1298		*/
1299		protected static ForkJoinTask<?> pollTask() {
1300	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1301	<	.pollTask();
1300	>	ForkJoinWorkerThread wt =
1301	>	(ForkJoinWorkerThread)Thread.currentThread();
1302	>	return wt.pool.nextTaskFor(wt.workQueue);
1303	>	}
1304	>
1305	>	// Mark-bit operations
1306	>
1307	>	/**
1308	>	* Returns true if this task is marked.
1309	>	*
1310	>	* @return true if this task is marked
1311	>	* @since 1.8
1312	>	*/
1313	>	public final boolean isMarkedForkJoinTask() {
1314	>	return (status & MARKED) != 0;
1315	>	}
1316	>
1317	>	/**
1318	>	* Atomically sets the mark on this task.
1319	>	*
1320	>	* @return true if this task was previously unmarked
1321	>	* @since 1.8
1322	>	*/
1323	>	public final boolean markForkJoinTask() {
1324	>	for (int s;;) {
1325	>	if (((s = status) & MARKED) != 0)
1326	>	return false;
1327	>	if (U.compareAndSwapInt(this, STATUS, s, s | MARKED))
1328	>	return true;
1329	>	}
1330	>	}
1331	>
1332	>	/**
1333	>	* Atomically clears the mark on this task.
1334	>	*
1335	>	* @return true if this task was previously marked
1336	>	* @since 1.8
1337	>	*/
1338	>	public final boolean unmarkForkJoinTask() {
1339	>	for (int s;;) {
1340	>	if (((s = status) & MARKED) == 0)
1341	>	return false;
1342	>	if (U.compareAndSwapInt(this, STATUS, s, s & ~MARKED))
1343	>	return true;
1344	>	}
1345		}
1346
1347		/**
#	Line 1220 | Line 1352 | public abstract class ForkJoinTask<V> im
1352		static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1353		implements RunnableFuture<T> {
1354		final Runnable runnable;
1223	–	final T resultOnCompletion;
1355		T result;
1356		AdaptedRunnable(Runnable runnable, T result) {
1357		if (runnable == null) throw new NullPointerException();
1358		this.runnable = runnable;
1359	<	this.resultOnCompletion = result;
1359	>	this.result = result; // OK to set this even before completion
1360		}
1361	<	public T getRawResult() { return result; }
1362	<	public void setRawResult(T v) { result = v; }
1363	<	public boolean exec() {
1364	<	runnable.run();
1365	<	result = resultOnCompletion;
1366	<	return true;
1361	>	public final T getRawResult() { return result; }
1362	>	public final void setRawResult(T v) { result = v; }
1363	>	public final boolean exec() { runnable.run(); return true; }
1364	>	public final void run() { invoke(); }
1365	>	private static final long serialVersionUID = 5232453952276885070L;
1366	>	}
1367	>
1368	>	/**
1369	>	* Adaptor for Runnables without results
1370	>	*/
1371	>	static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1372	>	implements RunnableFuture<Void> {
1373	>	final Runnable runnable;
1374	>	AdaptedRunnableAction(Runnable runnable) {
1375	>	if (runnable == null) throw new NullPointerException();
1376	>	this.runnable = runnable;
1377		}
1378	<	public void run() { invoke(); }
1378	>	public final Void getRawResult() { return null; }
1379	>	public final void setRawResult(Void v) { }
1380	>	public final boolean exec() { runnable.run(); return true; }
1381	>	public final void run() { invoke(); }
1382		private static final long serialVersionUID = 5232453952276885070L;
1383		}
1384
#	Line 1249 | Line 1393 | public abstract class ForkJoinTask<V> im
1393		if (callable == null) throw new NullPointerException();
1394		this.callable = callable;
1395		}
1396	<	public T getRawResult() { return result; }
1397	<	public void setRawResult(T v) { result = v; }
1398	<	public boolean exec() {
1396	>	public final T getRawResult() { return result; }
1397	>	public final void setRawResult(T v) { result = v; }
1398	>	public final boolean exec() {
1399		try {
1400		result = callable.call();
1401		return true;
#	Line 1263 | Line 1407 | public abstract class ForkJoinTask<V> im
1407		throw new RuntimeException(ex);
1408		}
1409		}
1410	<	public void run() { invoke(); }
1410	>	public final void run() { invoke(); }
1411		private static final long serialVersionUID = 2838392045355241008L;
1412		}
1413
#	Line 1276 | Line 1420 | public abstract class ForkJoinTask<V> im
1420		* @return the task
1421		*/
1422		public static ForkJoinTask<?> adapt(Runnable runnable) {
1423	<	return new AdaptedRunnable<Void>(runnable, null);
1423	>	return new AdaptedRunnableAction(runnable);
1424		}
1425
1426		/**
#	Line 1310 | Line 1454 | public abstract class ForkJoinTask<V> im
1454		private static final long serialVersionUID = -7721805057305804111L;
1455
1456		/**
1457	<	* Saves the state to a stream (that is, serializes it).
1457	>	* Saves this task to a stream (that is, serializes it).
1458		*
1459		* @serialData the current run status and the exception thrown
1460		* during execution, or {@code null} if none
1317	–	* @param s the stream
1461		*/
1462		private void writeObject(java.io.ObjectOutputStream s)
1463		throws java.io.IOException {
#	Line 1323 | Line 1466 | public abstract class ForkJoinTask<V> im
1466		}
1467
1468		/**
1469	<	* Reconstitutes the instance from a stream (that is, deserializes it).
1327	<	*
1328	<	* @param s the stream
1469	>	* Reconstitutes this task from a stream (that is, deserializes it).
1470		*/
1471		private void readObject(java.io.ObjectInputStream s)
1472		throws java.io.IOException, ClassNotFoundException {
#	Line 1336 | Line 1477 | public abstract class ForkJoinTask<V> im
1477		}
1478
1479		// Unsafe mechanics
1480	<	private static final sun.misc.Unsafe UNSAFE;
1481	<	private static final long statusOffset;
1480	>	private static final sun.misc.Unsafe U;
1481	>	private static final long STATUS;
1482		static {
1483		exceptionTableLock = new ReentrantLock();
1484		exceptionTableRefQueue = new ReferenceQueue<Object>();
1485		exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1486		try {
1487	<	UNSAFE = getUnsafe();
1488	<	statusOffset = UNSAFE.objectFieldOffset
1487	>	U = getUnsafe();
1488	>	STATUS = U.objectFieldOffset
1489		(ForkJoinTask.class.getDeclaredField("status"));
1490		} catch (Exception e) {
1491		throw new Error(e);

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