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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.77 by jsr166, Tue Mar 15 19:47:02 2011 UTC vs.
Revision 1.90 by dl, Sat Apr 21 11:45:20 2012 UTC

#	Line 8 | Line 8 | package jsr166y;
8
9		import java.io.Serializable;
10		import java.util.Collection;
11	–	import java.util.Collections;
11		import java.util.List;
12		import java.util.RandomAccess;
14	–	import java.util.Map;
13		import java.lang.ref.WeakReference;
14		import java.lang.ref.ReferenceQueue;
15		import java.util.concurrent.Callable;
16		import java.util.concurrent.CancellationException;
17		import java.util.concurrent.ExecutionException;
20	–	import java.util.concurrent.Executor;
21	–	import java.util.concurrent.ExecutorService;
18		import java.util.concurrent.Future;
19		import java.util.concurrent.RejectedExecutionException;
20		import java.util.concurrent.RunnableFuture;
#	Line 47 | Line 43 | import java.lang.reflect.Constructor;
43		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
44		* The efficiency of {@code ForkJoinTask}s stems from a set of
45		* restrictions (that are only partially statically enforceable)
46	<	* reflecting their intended use as computational tasks calculating
47	<	* pure functions or operating on purely isolated objects.  The
48	<	* primary coordination mechanisms are {@link #fork}, that arranges
46	>	* reflecting their main use as computational tasks calculating pure
47	>	* functions or operating on purely isolated objects.  The primary
48	>	* coordination mechanisms are {@link #fork}, that arranges
49		* asynchronous execution, and {@link #join}, that doesn't proceed
50		* until the task's result has been computed.  Computations should
51	<	* avoid {@code synchronized} methods or blocks, and should minimize
52	<	* other blocking synchronization apart from joining other tasks or
53	<	* using synchronizers such as Phasers that are advertised to
54	<	* cooperate with fork/join scheduling. Tasks should also not perform
55	<	* blocking IO, and should ideally access variables that are
56	<	* completely independent of those accessed by other running
57	<	* tasks. Minor breaches of these restrictions, for example using
58	<	* shared output streams, may be tolerable in practice, but frequent
59	<	* use may result in poor performance, and the potential to
60	<	* indefinitely stall if the number of threads not waiting for IO or
61	<	* other external synchronization becomes exhausted. This usage
62	<	* restriction is in part enforced by not permitting checked
63	<	* exceptions such as {@code IOExceptions} to be thrown. However,
64	<	* computations may still encounter unchecked exceptions, that are
65	<	* rethrown to callers attempting to join them. These exceptions may
66	<	* additionally include {@link RejectedExecutionException} stemming
67	<	* from internal resource exhaustion, such as failure to allocate
68	<	* internal task queues. Rethrown exceptions behave in the same way as
69	<	* regular exceptions, but, when possible, contain stack traces (as
70	<	* displayed for example using {@code ex.printStackTrace()}) of both
71	<	* the thread that initiated the computation as well as the thread
72	<	* actually encountering the exception; minimally only the latter.
51	>	* ideally avoid {@code synchronized} methods or blocks, and should
52	>	* minimize other blocking synchronization apart from joining other
53	>	* tasks or using synchronizers such as Phasers that are advertised to
54	>	* cooperate with fork/join scheduling. Subdividable tasks should also
55	>	* not perform blocking IO, and should ideally access variables that
56	>	* are completely independent of those accessed by other running
57	>	* tasks. These guidelines are loosely enforced by not permitting
58	>	* checked exceptions such as {@code IOExceptions} to be
59	>	* thrown. However, computations may still encounter unchecked
60	>	* exceptions, that are rethrown to callers attempting to join
61	>	* them. These exceptions may additionally include {@link
62	>	* RejectedExecutionException} stemming from internal resource
63	>	* exhaustion, such as failure to allocate internal task
64	>	* queues. Rethrown exceptions behave in the same way as regular
65	>	* exceptions, but, when possible, contain stack traces (as displayed
66	>	* for example using {@code ex.printStackTrace()}) of both the thread
67	>	* that initiated the computation as well as the thread actually
68	>	* encountering the exception; minimally only the latter.
69	>	*
70	>	* <p>It is possible to define and use ForkJoinTasks that may block,
71	>	* but doing do requires three further considerations: (1) Completion
72	>	* of few if any <em>other</em> tasks should be dependent on a task
73	>	* that blocks on external synchronization or IO. Event-style async
74	>	* tasks that are never joined (for example, those subclassing {@link
75	>	* CountedCompleter}) often fall into this category.  (2) To minimize
76	>	* resource impact, tasks should be small; ideally performing only the
77	>	* (possibly) blocking action. (3) Unless the {@link
78	>	* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
79	>	* blocked tasks is known to be less than the pool's {@link
80	>	* ForkJoinPool#getParallelism} level, the pool cannot guarantee that
81	>	* enough threads will be available to ensure progress or good
82	>	* performance.
83		*
84		* <p>The primary method for awaiting completion and extracting
85		* results of a task is {@link #join}, but there are several variants:
#	Line 89 | Line 95 | import java.lang.reflect.Constructor;
95		* performs the most common form of parallel invocation: forking a set
96		* of tasks and joining them all.
97		*
98	+	* <p>In the most typical usages, a fork-join pair act like a call
99	+	* (fork) and return (join) from a parallel recursive function. As is
100	+	* the case with other forms of recursive calls, returns (joins)
101	+	* should be performed innermost-first. For example, {@code a.fork();
102	+	* b.fork(); b.join(); a.join();} is likely to be substantially more
103	+	* efficient than joining {@code a} before {@code b}.
104	+	*
105		* <p>The execution status of tasks may be queried at several levels
106		* of detail: {@link #isDone} is true if a task completed in any way
107		* (including the case where a task was cancelled without executing);
#	Line 104 | Line 117 | import java.lang.reflect.Constructor;
117		* <p>The ForkJoinTask class is not usually directly subclassed.
118		* Instead, you subclass one of the abstract classes that support a
119		* particular style of fork/join processing, typically {@link
120	<	* RecursiveAction} for computations that do not return results, or
121	<	* {@link RecursiveTask} for those that do.  Normally, a concrete
122	<	* ForkJoinTask subclass declares fields comprising its parameters,
123	<	* established in a constructor, and then defines a {@code compute}
124	<	* method that somehow uses the control methods supplied by this base
125	<	* class. While these methods have {@code public} access (to allow
126	<	* instances of different task subclasses to call each other's
127	<	* methods), some of them may only be called from within other
128	<	* ForkJoinTasks (as may be determined using method {@link
129	<	* #inForkJoinPool}).  Attempts to invoke them in other contexts
130	<	* result in exceptions or errors, possibly including
131	<	* {@code ClassCastException}.
120	>	* RecursiveAction} for most computations that do not return results,
121	>	* {@link RecursiveTask} for those that do, and {@link
122	>	* CountedCompleter} for those in which completed actions trigger
123	>	* other actions.  Normally, a concrete ForkJoinTask subclass declares
124	>	* fields comprising its parameters, established in a constructor, and
125	>	* then defines a {@code compute} method that somehow uses the control
126	>	* methods supplied by this base class. While these methods have
127	>	* {@code public} access (to allow instances of different task
128	>	* subclasses to call each other's methods), some of them may only be
129	>	* called from within other ForkJoinTasks (as may be determined using
130	>	* method {@link #inForkJoinPool}).  Attempts to invoke them in other
131	>	* contexts result in exceptions or errors, possibly including {@code
132	>	* ClassCastException}.
133		*
134		* <p>Method {@link #join} and its variants are appropriate for use
135		* only when completion dependencies are acyclic; that is, the
#	Line 125 | Line 139 | import java.lang.reflect.Constructor;
139		* supports other methods and techniques (for example the use of
140		* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
141		* may be of use in constructing custom subclasses for problems that
142	<	* are not statically structured as DAGs.
142	>	* are not statically structured as DAGs. To support such usages a
143	>	* ForkJoinTask may be atomically <em>tagged</em> with a {@code short}
144	>	* value using {@link #setForkJoinTaskTag} or {@link
145	>	* #compareAndSetForkJoinTaskTag} and checked using {@link
146	>	* #getForkJoinTaskTag}. The ForkJoinTask implementation does not use
147	>	* these {@code protected} methods or tags for any purpose, but they
148	>	* may be of use in the construction of specialized subclasses.  For
149	>	* example, parallel graph traversals can use the supplied methods to
150	>	* avoid revisiting nodes/tasks that have already been processed.
151	>	* (Method names for tagging are bulky in part to encourage definition
152	>	* of methods that reflect their usage patterns.)
153		*
154		* <p>Most base support methods are {@code final}, to prevent
155		* overriding of implementations that are intrinsically tied to the
#	Line 165 | Line 189 | public abstract class ForkJoinTask<V> im
189		* See the internal documentation of class ForkJoinPool for a
190		* general implementation overview.  ForkJoinTasks are mainly
191		* responsible for maintaining their "status" field amidst relays
192	<	* to methods in ForkJoinWorkerThread and ForkJoinPool. The
193	<	* methods of this class are more-or-less layered into (1) basic
194	<	* status maintenance (2) execution and awaiting completion (3)
195	<	* user-level methods that additionally report results. This is
196	<	* sometimes hard to see because this file orders exported methods
197	<	* in a way that flows well in javadocs.
192	>	* to methods in ForkJoinWorkerThread and ForkJoinPool.
193	>	*
194	>	* The methods of this class are more-or-less layered into
195	>	* (1) basic status maintenance
196	>	* (2) execution and awaiting completion
197	>	* (3) user-level methods that additionally report results.
198	>	* This is sometimes hard to see because this file orders exported
199	>	* methods in a way that flows well in javadocs.
200		*/
201
202		/*
203		* The status field holds run control status bits packed into a
204		* single int to minimize footprint and to ensure atomicity (via
205		* CAS).  Status is initially zero, and takes on nonnegative
206	<	* values until completed, upon which status holds value
207	<	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
208	<	* waits by other threads have the SIGNAL bit set.  Completion of
209	<	* a stolen task with SIGNAL set awakens any waiters via
210	<	* notifyAll. Even though suboptimal for some purposes, we use
211	<	* basic builtin wait/notify to take advantage of "monitor
212	<	* inflation" in JVMs that we would otherwise need to emulate to
213	<	* avoid adding further per-task bookkeeping overhead.  We want
214	<	* these monitors to be "fat", i.e., not use biasing or thin-lock
215	<	* techniques, so use some odd coding idioms that tend to avoid
216	<	* them.
206	>	* values until completed, upon which status (anded with
207	>	* DONE_MASK) holds value NORMAL, CANCELLED, or EXCEPTIONAL. Tasks
208	>	* undergoing blocking waits by other threads have the SIGNAL bit
209	>	* set.  Completion of a stolen task with SIGNAL set awakens any
210	>	* waiters via notifyAll. Even though suboptimal for some
211	>	* purposes, we use basic builtin wait/notify to take advantage of
212	>	* "monitor inflation" in JVMs that we would otherwise need to
213	>	* emulate to avoid adding further per-task bookkeeping overhead.
214	>	* We want these monitors to be "fat", i.e., not use biasing or
215	>	* thin-lock techniques, so use some odd coding idioms that tend
216	>	* to avoid them, mainly by arranging that every synchronized
217	>	* block performs a wait, notifyAll or both.
218	>	*
219	>	* These control bits occupy only (some of) the upper half (16
220	>	* bits) of status field. The lower bits are used for user-defined
221	>	* tags.
222		*/
223
224		/** The run status of this task */
225		volatile int status; // accessed directly by pool and workers
226	<	private static final int NORMAL      = -1;
227	<	private static final int CANCELLED   = -2;
228	<	private static final int EXCEPTIONAL = -3;
229	<	private static final int SIGNAL      =  1;
226	>	static final int DONE_MASK   = 0xf0000000;  // mask out non-completion bits
227	>	static final int NORMAL      = 0xf0000000;  // must be negative
228	>	static final int CANCELLED   = 0xc0000000;  // must be < NORMAL
229	>	static final int EXCEPTIONAL = 0x80000000;  // must be < CANCELLED
230	>	static final int SIGNAL      = 0x00010000;  // must be >= 1 << 16
231	>	static final int SMASK       = 0x0000ffff;  // short bits for tags
232
233		/**
234	<	* Marks completion and wakes up threads waiting to join this task,
235	<	* also clearing signal request bits.
234	>	* Marks completion and wakes up threads waiting to join this
235	>	* task.
236		*
237		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
238		* @return completion status on exit
#	Line 208 | Line 241 | public abstract class ForkJoinTask<V> im
241		for (int s;;) {
242		if ((s = status) < 0)
243		return s;
244	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
245	<	if (s != 0)
244	>	if (U.compareAndSwapInt(this, STATUS, s, s | completion)) {
245	>	if ((s >>> 16) != 0)
246		synchronized (this) { notifyAll(); }
247		return completion;
248		}
#	Line 217 | Line 250 | public abstract class ForkJoinTask<V> im
250		}
251
252		/**
253	<	* Tries to block a worker thread until completed or timed out.
254	<	* Uses Object.wait time argument conventions.
255	<	* May fail on contention or interrupt.
253	>	* Primary execution method for stolen tasks. Unless done, calls
254	>	* exec and records status if completed, but doesn't wait for
255	>	* completion otherwise.
256		*
257	<	* @param millis if > 0, wait time.
257	>	* @return status on exit from this method
258		*/
259	<	final void tryAwaitDone(long millis) {
260	<	int s;
261	<	try {
262	<	if (((s = status) > 0 ||
263	<	(s == 0 &&
264	<	UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL))) &&
265	<	status > 0) {
233	<	synchronized (this) {
234	<	if (status > 0)
235	<	wait(millis);
236	<	}
259	>	final int doExec() {
260	>	int s; boolean completed;
261	>	if ((s = status) >= 0) {
262	>	try {
263	>	completed = exec();
264	>	} catch (Throwable rex) {
265	>	return setExceptionalCompletion(rex);
266		}
267	<	} catch (InterruptedException ie) {
268	<	// caller must check termination
267	>	if (completed)
268	>	s = setCompletion(NORMAL);
269		}
270	+	return s;
271	+	}
272	+
273	+	/**
274	+	* Tries to set SIGNAL status unless already completed. Used by
275	+	* ForkJoinPool. Other variants are directly incorporated into
276	+	* externalAwaitDone etc.
277	+	*
278	+	* @return true if successful
279	+	*/
280	+	final boolean trySetSignal() {
281	+	int s = status;
282	+	return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL);
283		}
284
285		/**
#	Line 245 | Line 287 | public abstract class ForkJoinTask<V> im
287		* @return status upon completion
288		*/
289		private int externalAwaitDone() {
290	+	boolean interrupted = false;
291		int s;
292	<	if ((s = status) >= 0) {
293	<	boolean interrupted = false;
294	<	synchronized (this) {
295	<	while ((s = status) >= 0) {
253	<	if (s == 0)
254	<	UNSAFE.compareAndSwapInt(this, statusOffset,
255	<	0, SIGNAL);
256	<	else {
292	>	while ((s = status) >= 0) {
293	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
294	>	synchronized (this) {
295	>	if (status >= 0) {
296		try {
297		wait();
298		} catch (InterruptedException ie) {
299		interrupted = true;
300		}
301		}
302	+	else
303	+	notifyAll();
304		}
305		}
265	–	if (interrupted)
266	–	Thread.currentThread().interrupt();
306		}
307	+	if (interrupted)
308	+	Thread.currentThread().interrupt();
309		return s;
310		}
311
312		/**
313	<	* Blocks a non-worker-thread until completion or interruption or timeout.
313	>	* Blocks a non-worker-thread until completion or interruption.
314		*/
315	<	private int externalInterruptibleAwaitDone(long millis)
275	<	throws InterruptedException {
315	>	private int externalInterruptibleAwaitDone() throws InterruptedException {
316		int s;
317		if (Thread.interrupted())
318		throw new InterruptedException();
319	<	if ((s = status) >= 0) {
320	<	synchronized (this) {
321	<	while ((s = status) >= 0) {
322	<	if (s == 0)
323	<	UNSAFE.compareAndSwapInt(this, statusOffset,
324	<	0, SIGNAL);
325	<	else {
286	<	wait(millis);
287	<	if (millis > 0L)
288	<	break;
289	<	}
319	>	while ((s = status) >= 0) {
320	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
321	>	synchronized (this) {
322	>	if (status >= 0)
323	>	wait();
324	>	else
325	>	notifyAll();
326		}
327		}
328		}
#	Line 294 | Line 330 | public abstract class ForkJoinTask<V> im
330		}
331
332		/**
333	<	* Primary execution method for stolen tasks. Unless done, calls
334	<	* exec and records status if completed, but doesn't wait for
335	<	* completion otherwise.
336	<	*/
301	<	final void doExec() {
302	<	if (status >= 0) {
303	<	boolean completed;
304	<	try {
305	<	completed = exec();
306	<	} catch (Throwable rex) {
307	<	setExceptionalCompletion(rex);
308	<	return;
309	<	}
310	<	if (completed)
311	<	setCompletion(NORMAL); // must be outside try block
312	<	}
313	<	}
314	<
315	<	/**
316	<	* 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 {
326	<	completed = exec();
327	<	} catch (Throwable rex) {
328	<	return setExceptionalCompletion(rex);
329	<	}
330	<	if (completed)
331	<	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
336	<	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)
353	<	return setCompletion(NORMAL);
354	<	else
355	<	return doJoin();
367	>	return s;
368		}
369
370		// Exception table support
#	Line 387 | Line 399 | public abstract class ForkJoinTask<V> im
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;  // use id not ref to avoid weak cycles
#	Line 400 | Line 412 | public abstract class ForkJoinTask<V> im
412		}
413
414		/**
415	<	* Records exception and sets exceptional completion.
415	>	* Records exception and sets status.
416		*
417		* @return status on exit
418		*/
419	<	private int setExceptionalCompletion(Throwable ex) {
420	<	int h = System.identityHashCode(this);
421	<	final ReentrantLock lock = exceptionTableLock;
422	<	lock.lock();
423	<	try {
424	<	expungeStaleExceptions();
425	<	ExceptionNode[] t = exceptionTable;
426	<	int i = h & (t.length - 1);
427	<	for (ExceptionNode e = t[i]; ; e = e.next) {
428	<	if (e == null) {
429	<	t[i] = new ExceptionNode(this, ex, t[i]);
430	<	break;
419	>	final int recordExceptionalCompletion(Throwable ex) {
420	>	int s;
421	>	if ((s = status) >= 0) {
422	>	int h = System.identityHashCode(this);
423	>	final ReentrantLock lock = exceptionTableLock;
424	>	lock.lock();
425	>	try {
426	>	expungeStaleExceptions();
427	>	ExceptionNode[] t = exceptionTable;
428	>	int i = h & (t.length - 1);
429	>	for (ExceptionNode e = t[i]; ; e = e.next) {
430	>	if (e == null) {
431	>	t[i] = new ExceptionNode(this, ex, t[i]);
432	>	break;
433	>	}
434	>	if (e.get() == this) // already present
435	>	break;
436		}
437	<	if (e.get() == this) // already present
438	<	break;
437	>	} finally {
438	>	lock.unlock();
439	>	}
440	>	s = setCompletion(EXCEPTIONAL);
441	>	}
442	>	return s;
443	>	}
444	>
445	>	/**
446	>	* Records exception and possibly propagates
447	>	*
448	>	* @return status on exit
449	>	*/
450	>	private int setExceptionalCompletion(Throwable ex) {
451	>	int s = recordExceptionalCompletion(ex);
452	>	if ((s & DONE_MASK) == EXCEPTIONAL)
453	>	internalPropagateException(ex);
454	>	return s;
455	>	}
456	>
457	>	/**
458	>	* Hook for exception propagation support for tasks with completers.
459	>	*/
460	>	void internalPropagateException(Throwable ex) {
461	>	}
462	>
463	>	/**
464	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
465	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
466	>	* exceptions, but if it does anyway, we have no recourse during
467	>	* shutdown, so guard against this case.
468	>	*/
469	>	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
470	>	if (t != null && t.status >= 0) {
471	>	try {
472	>	t.cancel(false);
473	>	} catch (Throwable ignore) {
474		}
423	–	} finally {
424	–	lock.unlock();
475		}
426	–	return setCompletion(EXCEPTIONAL);
476		}
477
478		/**
#	Line 472 | Line 521 | public abstract class ForkJoinTask<V> im
521		* @return the exception, or null if none
522		*/
523		private Throwable getThrowableException() {
524	<	if (status != EXCEPTIONAL)
524	>	if ((status & DONE_MASK) != EXCEPTIONAL)
525		return null;
526		int h = System.identityHashCode(this);
527		ExceptionNode e;
#	Line 490 | Line 539 | public abstract class ForkJoinTask<V> im
539		Throwable ex;
540		if (e == null || (ex = e.ex) == null)
541		return null;
542	<	if (e.thrower != Thread.currentThread().getId()) {
543	<	Class ec = ex.getClass();
542	>	if (false && e.thrower != Thread.currentThread().getId()) {
543	>	Class<? extends Throwable> ec = ex.getClass();
544		try {
545		Constructor<?> noArgCtor = null;
546		Constructor<?>[] cs = ec.getConstructors();// public ctors only
#	Line 557 | Line 606 | public abstract class ForkJoinTask<V> im
606		}
607
608		/**
609	<	* Report the result of invoke or join; called only upon
561	<	* non-normal return of internal versions.
609	>	* Throws exception, if any, associated with the given status.
610		*/
611	<	private V reportResult() {
612	<	int s; Throwable ex;
613	<	if ((s = status) == CANCELLED)
614	<	throw new CancellationException();
615	<	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
616	<	UNSAFE.throwException(ex);
569	<	return getRawResult();
611	>	private void reportException(int s) {
612	>	Throwable ex = ((s == CANCELLED) ?  new CancellationException() :
613	>	(s == EXCEPTIONAL) ? getThrowableException() :
614	>	null);
615	>	if (ex != null)
616	>	U.throwException(ex);
617		}
618
619		// public methods
#	Line 590 | Line 637 | public abstract class ForkJoinTask<V> im
637		* @return {@code this}, to simplify usage
638		*/
639		public final ForkJoinTask<V> fork() {
640	<	((ForkJoinWorkerThread) Thread.currentThread())
594	<	.pushTask(this);
640	>	((ForkJoinWorkerThread)Thread.currentThread()).workQueue.push(this);
641		return this;
642		}
643
#	Line 607 | Line 653 | public abstract class ForkJoinTask<V> im
653		* @return the computed result
654		*/
655		public final V join() {
656	<	if (doJoin() != NORMAL)
657	<	return reportResult();
658	<	else
659	<	return getRawResult();
656	>	int s;
657	>	if ((s = doJoin() & DONE_MASK) != NORMAL)
658	>	reportException(s);
659	>	return getRawResult();
660		}
661
662		/**
#	Line 622 | Line 668 | public abstract class ForkJoinTask<V> im
668		* @return the computed result
669		*/
670		public final V invoke() {
671	<	if (doInvoke() != NORMAL)
672	<	return reportResult();
673	<	else
674	<	return getRawResult();
671	>	int s;
672	>	if ((s = doInvoke() & DONE_MASK) != NORMAL)
673	>	reportException(s);
674	>	return getRawResult();
675		}
676
677		/**
#	Line 652 | Line 698 | public abstract class ForkJoinTask<V> im
698		* @throws NullPointerException if any task is null
699		*/
700		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
701	+	int s1, s2;
702		t2.fork();
703	<	t1.invoke();
704	<	t2.join();
703	>	if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL)
704	>	t1.reportException(s1);
705	>	if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
706	>	t2.reportException(s2);
707		}
708
709		/**
#	Line 697 | Line 746 | public abstract class ForkJoinTask<V> im
746		if (t != null) {
747		if (ex != null)
748		t.cancel(false);
749	<	else if (t.doJoin() < NORMAL && ex == null)
749	>	else if (t.doJoin() < NORMAL)
750		ex = t.getException();
751		}
752		}
753		if (ex != null)
754	<	UNSAFE.throwException(ex);
754	>	U.throwException(ex);
755		}
756
757		/**
#	Line 754 | Line 803 | public abstract class ForkJoinTask<V> im
803		if (t != null) {
804		if (ex != null)
805		t.cancel(false);
806	<	else if (t.doJoin() < NORMAL && ex == null)
806	>	else if (t.doJoin() < NORMAL)
807		ex = t.getException();
808		}
809		}
810		if (ex != null)
811	<	UNSAFE.throwException(ex);
811	>	U.throwException(ex);
812		return tasks;
813		}
814
#	Line 791 | Line 840 | public abstract class ForkJoinTask<V> im
840		* @return {@code true} if this task is now cancelled
841		*/
842		public boolean cancel(boolean mayInterruptIfRunning) {
843	<	return setCompletion(CANCELLED) == CANCELLED;
795	<	}
796	<
797	<	/**
798	<	* Cancels, ignoring any exceptions thrown by cancel. Used during
799	<	* worker and pool shutdown. Cancel is spec'ed not to throw any
800	<	* exceptions, but if it does anyway, we have no recourse during
801	<	* shutdown, so guard against this case.
802	<	*/
803	<	final void cancelIgnoringExceptions() {
804	<	try {
805	<	cancel(false);
806	<	} catch (Throwable ignore) {
807	<	}
843	>	return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
844		}
845
846		public final boolean isDone() {
#	Line 812 | Line 848 | public abstract class ForkJoinTask<V> im
848		}
849
850		public final boolean isCancelled() {
851	<	return status == CANCELLED;
851	>	return (status & DONE_MASK) == CANCELLED;
852		}
853
854		/**
#	Line 832 | Line 868 | public abstract class ForkJoinTask<V> im
868		* exception and was not cancelled
869		*/
870		public final boolean isCompletedNormally() {
871	<	return status == NORMAL;
871	>	return (status & DONE_MASK) == NORMAL;
872		}
873
874		/**
#	Line 843 | Line 879 | public abstract class ForkJoinTask<V> im
879		* @return the exception, or {@code null} if none
880		*/
881		public final Throwable getException() {
882	<	int s = status;
882	>	int s = status & DONE_MASK;
883		return ((s >= NORMAL)    ? null :
884		(s == CANCELLED) ? new CancellationException() :
885		getThrowableException());
#	Line 893 | Line 929 | public abstract class ForkJoinTask<V> im
929		}
930
931		/**
932	+	* Completes this task normally without setting a value. The most
933	+	* recent value established by {@link #setRawResult} (or {@code
934	+	* null} by default) will be returned as the result of subsequent
935	+	* invocations of {@code join} and related operations.
936	+	*
937	+	* @since 1.8
938	+	*/
939	+	public final void quietlyComplete() {
940	+	setCompletion(NORMAL);
941	+	}
942	+
943	+	/**
944		* Waits if necessary for the computation to complete, and then
945		* retrieves its result.
946		*
#	Line 905 | Line 953 | public abstract class ForkJoinTask<V> im
953		*/
954		public final V get() throws InterruptedException, ExecutionException {
955		int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
956	<	doJoin() : externalInterruptibleAwaitDone(0L);
956	>	doJoin() : externalInterruptibleAwaitDone();
957		Throwable ex;
958	<	if (s == CANCELLED)
958	>	if ((s &= DONE_MASK) == CANCELLED)
959		throw new CancellationException();
960		if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
961		throw new ExecutionException(ex);
#	Line 930 | Line 978 | public abstract class ForkJoinTask<V> im
978		*/
979		public final V get(long timeout, TimeUnit unit)
980		throws InterruptedException, ExecutionException, TimeoutException {
981	<	Thread t = Thread.currentThread();
982	<	if (t instanceof ForkJoinWorkerThread) {
983	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
984	<	long nanos = unit.toNanos(timeout);
985	<	if (status >= 0) {
986	<	boolean completed = false;
987	<	if (w.unpushTask(this)) {
988	<	try {
989	<	completed = exec();
990	<	} catch (Throwable rex) {
991	<	setExceptionalCompletion(rex);
981	>	if (Thread.interrupted())
982	>	throw new InterruptedException();
983	>	// Messy in part because we measure in nanosecs, but wait in millisecs
984	>	int s; long ns, ms;
985	>	if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) {
986	>	long deadline = System.nanoTime() + ns;
987	>	ForkJoinPool p = null;
988	>	ForkJoinPool.WorkQueue w = null;
989	>	Thread t = Thread.currentThread();
990	>	if (t instanceof ForkJoinWorkerThread) {
991	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
992	>	p = wt.pool;
993	>	w = wt.workQueue;
994	>	s = p.helpJoinOnce(w, this); // no retries on failure
995	>	}
996	>	boolean canBlock = false;
997	>	boolean interrupted = false;
998	>	try {
999	>	while ((s = status) >= 0) {
1000	>	if (w != null && w.runState < 0)
1001	>	cancelIgnoringExceptions(this);
1002	>	else if (!canBlock) {
1003	>	if (p == null || p.tryCompensate(this, null))
1004	>	canBlock = true;
1005	>	}
1006	>	else {
1007	>	if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
1008	>	U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
1009	>	synchronized (this) {
1010	>	if (status >= 0) {
1011	>	try {
1012	>	wait(ms);
1013	>	} catch (InterruptedException ie) {
1014	>	if (p == null)
1015	>	interrupted = true;
1016	>	}
1017	>	}
1018	>	else
1019	>	notifyAll();
1020	>	}
1021	>	}
1022	>	if ((s = status) < 0 || interrupted ||
1023	>	(ns = deadline - System.nanoTime()) <= 0L)
1024	>	break;
1025		}
1026		}
1027	<	if (completed)
1028	<	setCompletion(NORMAL);
1029	<	else if (status >= 0 && nanos > 0)
949	<	w.pool.timedAwaitJoin(this, nanos);
1027	>	} finally {
1028	>	if (p != null && canBlock)
1029	>	p.incrementActiveCount();
1030		}
1031	+	if (interrupted)
1032	+	throw new InterruptedException();
1033		}
1034	<	else {
953	<	long millis = unit.toMillis(timeout);
954	<	if (millis > 0)
955	<	externalInterruptibleAwaitDone(millis);
956	<	}
957	<	int s = status;
958	<	if (s != NORMAL) {
1034	>	if ((s &= DONE_MASK) != NORMAL) {
1035		Throwable ex;
1036		if (s == CANCELLED)
1037		throw new CancellationException();
#	Line 1000 | Line 1076 | public abstract class ForkJoinTask<V> im
1076		* ClassCastException}.
1077		*/
1078		public static void helpQuiesce() {
1079	<	((ForkJoinWorkerThread) Thread.currentThread())
1080	<	.helpQuiescePool();
1079	>	ForkJoinWorkerThread wt =
1080	>	(ForkJoinWorkerThread)Thread.currentThread();
1081	>	wt.pool.helpQuiescePool(wt.workQueue);
1082		}
1083
1084		/**
#	Line 1021 | Line 1098 | public abstract class ForkJoinTask<V> im
1098		* setRawResult(null)}.
1099		*/
1100		public void reinitialize() {
1101	<	if (status == EXCEPTIONAL)
1101	>	if ((status & DONE_MASK) == EXCEPTIONAL)
1102		clearExceptionalCompletion();
1103		else
1104		status = 0;
#	Line 1069 | Line 1146 | public abstract class ForkJoinTask<V> im
1146		* @return {@code true} if unforked
1147		*/
1148		public boolean tryUnfork() {
1149	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1150	<	.unpushTask(this);
1149	>	return ((ForkJoinWorkerThread)Thread.currentThread())
1150	>	.workQueue.tryUnpush(this);
1151		}
1152
1153		/**
#	Line 1089 | Line 1166 | public abstract class ForkJoinTask<V> im
1166		*/
1167		public static int getQueuedTaskCount() {
1168		return ((ForkJoinWorkerThread) Thread.currentThread())
1169	<	.getQueueSize();
1169	>	.workQueue.queueSize();
1170		}
1171
1172		/**
#	Line 1111 | Line 1188 | public abstract class ForkJoinTask<V> im
1188		* @return the surplus number of tasks, which may be negative
1189		*/
1190		public static int getSurplusQueuedTaskCount() {
1191	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1192	<	.getEstimatedSurplusTaskCount();
1191	>	/*
1192	>	* The aim of this method is to return a cheap heuristic guide
1193	>	* for task partitioning when programmers, frameworks, tools,
1194	>	* or languages have little or no idea about task granularity.
1195	>	* In essence by offering this method, we ask users only about
1196	>	* tradeoffs in overhead vs expected throughput and its
1197	>	* variance, rather than how finely to partition tasks.
1198	>	*
1199	>	* In a steady state strict (tree-structured) computation,
1200	>	* each thread makes available for stealing enough tasks for
1201	>	* other threads to remain active. Inductively, if all threads
1202	>	* play by the same rules, each thread should make available
1203	>	* only a constant number of tasks.
1204	>	*
1205	>	* The minimum useful constant is just 1. But using a value of
1206	>	* 1 would require immediate replenishment upon each steal to
1207	>	* maintain enough tasks, which is infeasible.  Further,
1208	>	* partitionings/granularities of offered tasks should
1209	>	* minimize steal rates, which in general means that threads
1210	>	* nearer the top of computation tree should generate more
1211	>	* than those nearer the bottom. In perfect steady state, each
1212	>	* thread is at approximately the same level of computation
1213	>	* tree. However, producing extra tasks amortizes the
1214	>	* uncertainty of progress and diffusion assumptions.
1215	>	*
1216	>	* So, users will want to use values larger, but not much
1217	>	* larger than 1 to both smooth over transient shortages and
1218	>	* hedge against uneven progress; as traded off against the
1219	>	* cost of extra task overhead. We leave the user to pick a
1220	>	* threshold value to compare with the results of this call to
1221	>	* guide decisions, but recommend values such as 3.
1222	>	*
1223	>	* When all threads are active, it is on average OK to
1224	>	* estimate surplus strictly locally. In steady-state, if one
1225	>	* thread is maintaining say 2 surplus tasks, then so are
1226	>	* others. So we can just use estimated queue length.
1227	>	* However, this strategy alone leads to serious mis-estimates
1228	>	* in some non-steady-state conditions (ramp-up, ramp-down,
1229	>	* other stalls). We can detect many of these by further
1230	>	* considering the number of "idle" threads, that are known to
1231	>	* have zero queued tasks, so compensate by a factor of
1232	>	* (#idle/#active) threads.
1233	>	*/
1234	>	ForkJoinWorkerThread wt =
1235	>	(ForkJoinWorkerThread)Thread.currentThread();
1236	>	return wt.workQueue.queueSize() - wt.pool.idlePerActive();
1237		}
1238
1239		// Extension methods
#	Line 1138 | Line 1259 | public abstract class ForkJoinTask<V> im
1259		protected abstract void setRawResult(V value);
1260
1261		/**
1262	<	* Immediately performs the base action of this task.  This method
1263	<	* is designed to support extensions, and should not in general be
1264	<	* called otherwise. The return value controls whether this task
1265	<	* is considered to be done normally. It may return false in
1262	>	* Immediately performs the base action of this task and returns
1263	>	* true if, upon return from this method, this task is guaranteed
1264	>	* to have completed normally. This method may return false
1265	>	* otherwise, to indicate that this task is not necessarily
1266	>	* complete (or is not known to be complete), for example in
1267		* asynchronous actions that require explicit invocations of
1268	<	* {@link #complete} to become joinable. It may also throw an
1269	<	* (unchecked) exception to indicate abnormal exit.
1268	>	* completion methods. This method may also throw an (unchecked)
1269	>	* exception to indicate abnormal exit. This method is designed to
1270	>	* support extensions, and should not in general be called
1271	>	* otherwise.
1272		*
1273	<	* @return {@code true} if completed normally
1273	>	* @return {@code true} if this task is known to have completed normally
1274		*/
1275		protected abstract boolean exec();
1276
#	Line 1169 | Line 1293 | public abstract class ForkJoinTask<V> im
1293		* @return the next task, or {@code null} if none are available
1294		*/
1295		protected static ForkJoinTask<?> peekNextLocalTask() {
1296	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1173	<	.peekTask();
1296	>	return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek();
1297		}
1298
1299		/**
#	Line 1189 | Line 1312 | public abstract class ForkJoinTask<V> im
1312		*/
1313		protected static ForkJoinTask<?> pollNextLocalTask() {
1314		return ((ForkJoinWorkerThread) Thread.currentThread())
1315	<	.pollLocalTask();
1315	>	.workQueue.nextLocalTask();
1316		}
1317
1318		/**
#	Line 1211 | Line 1334 | public abstract class ForkJoinTask<V> im
1334		* @return a task, or {@code null} if none are available
1335		*/
1336		protected static ForkJoinTask<?> pollTask() {
1337	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1338	<	.pollTask();
1337	>	ForkJoinWorkerThread wt =
1338	>	(ForkJoinWorkerThread)Thread.currentThread();
1339	>	return wt.pool.nextTaskFor(wt.workQueue);
1340	>	}
1341	>
1342	>	// tag operations
1343	>
1344	>	/**
1345	>	* Returns the tag for this task.
1346	>	*
1347	>	* @return the tag for this task
1348	>	* @since 1.8
1349	>	*/
1350	>	public final short getForkJoinTaskTag() {
1351	>	return (short)status;
1352	>	}
1353	>
1354	>	/**
1355	>	* Atomically sets the tag value for this task.
1356	>	*
1357	>	* @param tag the tag value
1358	>	* @return the previous value of the tag
1359	>	* @since 1.8
1360	>	*/
1361	>	public final short setForkJoinTaskTag(short tag) {
1362	>	for (int s;;) {
1363	>	if (U.compareAndSwapInt(this, STATUS, s = status,
1364	>	(s & ~SMASK) | (tag & SMASK)))
1365	>	return (short)s;
1366	>	}
1367	>	}
1368	>
1369	>	/**
1370	>	* Atomically conditionally sets the tag value for this task.
1371	>	* Among other applications, tags can be used as visit markers
1372	>	* in tasks operating on graphs, as in methods that check: {@code
1373	>	* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1374	>	* before processing, otherwise exiting because the node has
1375	>	* already been visited.
1376	>	*
1377	>	* @param e the expected tag value
1378	>	* @param tag the new tag value
1379	>	* @return true if successful; i.e., the current value was
1380	>	* equal to e and is now tag.
1381	>	* @since 1.8
1382	>	*/
1383	>	public final boolean compareAndSetForkJoinTaskTag(short e, short tag) {
1384	>	for (int s;;) {
1385	>	if ((short)(s = status) != e)
1386	>	return false;
1387	>	if (U.compareAndSwapInt(this, STATUS, s,
1388	>	(s & ~SMASK) | (tag & SMASK)))
1389	>	return true;
1390	>	}
1391		}
1392
1393		/**
#	Line 1223 | Line 1398 | public abstract class ForkJoinTask<V> im
1398		static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1399		implements RunnableFuture<T> {
1400		final Runnable runnable;
1226	–	final T resultOnCompletion;
1401		T result;
1402		AdaptedRunnable(Runnable runnable, T result) {
1403		if (runnable == null) throw new NullPointerException();
1404		this.runnable = runnable;
1405	<	this.resultOnCompletion = result;
1405	>	this.result = result; // OK to set this even before completion
1406		}
1407	<	public T getRawResult() { return result; }
1408	<	public void setRawResult(T v) { result = v; }
1409	<	public boolean exec() {
1410	<	runnable.run();
1411	<	result = resultOnCompletion;
1412	<	return true;
1407	>	public final T getRawResult() { return result; }
1408	>	public final void setRawResult(T v) { result = v; }
1409	>	public final boolean exec() { runnable.run(); return true; }
1410	>	public final void run() { invoke(); }
1411	>	private static final long serialVersionUID = 5232453952276885070L;
1412	>	}
1413	>
1414	>	/**
1415	>	* Adaptor for Runnables without results
1416	>	*/
1417	>	static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1418	>	implements RunnableFuture<Void> {
1419	>	final Runnable runnable;
1420	>	AdaptedRunnableAction(Runnable runnable) {
1421	>	if (runnable == null) throw new NullPointerException();
1422	>	this.runnable = runnable;
1423		}
1424	<	public void run() { invoke(); }
1424	>	public final Void getRawResult() { return null; }
1425	>	public final void setRawResult(Void v) { }
1426	>	public final boolean exec() { runnable.run(); return true; }
1427	>	public final void run() { invoke(); }
1428		private static final long serialVersionUID = 5232453952276885070L;
1429		}
1430
#	Line 1252 | Line 1439 | public abstract class ForkJoinTask<V> im
1439		if (callable == null) throw new NullPointerException();
1440		this.callable = callable;
1441		}
1442	<	public T getRawResult() { return result; }
1443	<	public void setRawResult(T v) { result = v; }
1444	<	public boolean exec() {
1442	>	public final T getRawResult() { return result; }
1443	>	public final void setRawResult(T v) { result = v; }
1444	>	public final boolean exec() {
1445		try {
1446		result = callable.call();
1447		return true;
#	Line 1266 | Line 1453 | public abstract class ForkJoinTask<V> im
1453		throw new RuntimeException(ex);
1454		}
1455		}
1456	<	public void run() { invoke(); }
1456	>	public final void run() { invoke(); }
1457		private static final long serialVersionUID = 2838392045355241008L;
1458		}
1459
#	Line 1279 | Line 1466 | public abstract class ForkJoinTask<V> im
1466		* @return the task
1467		*/
1468		public static ForkJoinTask<?> adapt(Runnable runnable) {
1469	<	return new AdaptedRunnable<Void>(runnable, null);
1469	>	return new AdaptedRunnableAction(runnable);
1470		}
1471
1472		/**
#	Line 1313 | Line 1500 | public abstract class ForkJoinTask<V> im
1500		private static final long serialVersionUID = -7721805057305804111L;
1501
1502		/**
1503	<	* Saves the state to a stream (that is, serializes it).
1503	>	* Saves this task to a stream (that is, serializes it).
1504		*
1505		* @serialData the current run status and the exception thrown
1506		* during execution, or {@code null} if none
1320	–	* @param s the stream
1507		*/
1508		private void writeObject(java.io.ObjectOutputStream s)
1509		throws java.io.IOException {
#	Line 1326 | Line 1512 | public abstract class ForkJoinTask<V> im
1512		}
1513
1514		/**
1515	<	* Reconstitutes the instance from a stream (that is, deserializes it).
1330	<	*
1331	<	* @param s the stream
1515	>	* Reconstitutes this task from a stream (that is, deserializes it).
1516		*/
1517		private void readObject(java.io.ObjectInputStream s)
1518		throws java.io.IOException, ClassNotFoundException {
#	Line 1339 | Line 1523 | public abstract class ForkJoinTask<V> im
1523		}
1524
1525		// Unsafe mechanics
1526	<	private static final sun.misc.Unsafe UNSAFE;
1527	<	private static final long statusOffset;
1526	>	private static final sun.misc.Unsafe U;
1527	>	private static final long STATUS;
1528		static {
1529		exceptionTableLock = new ReentrantLock();
1530		exceptionTableRefQueue = new ReferenceQueue<Object>();
1531		exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1532		try {
1533	<	UNSAFE = getUnsafe();
1534	<	statusOffset = UNSAFE.objectFieldOffset
1533	>	U = getUnsafe();
1534	>	STATUS = U.objectFieldOffset
1535		(ForkJoinTask.class.getDeclaredField("status"));
1536		} catch (Exception e) {
1537		throw new Error(e);

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