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Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.75 by dl, Tue Feb 22 10:50:51 2011 UTC vs.
Revision 1.96 by dl, Wed Dec 19 00:02:59 2012 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3		* Expert Group and released to the public domain, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		*/
6
7		package jsr166y;
8
9		import java.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 34 | Line 30 | import java.lang.reflect.Constructor;
30		* subtasks may be hosted by a small number of actual threads in a
31		* ForkJoinPool, at the price of some usage limitations.
32		*
33	<	* <p>A "main" {@code ForkJoinTask} begins execution when submitted
34	<	* to a {@link ForkJoinPool}.  Once started, it will usually in turn
35	<	* start other subtasks.  As indicated by the name of this class,
36	<	* many programs using {@code ForkJoinTask} employ only methods
37	<	* {@link #fork} and {@link #join}, or derivatives such as {@link
33	>	* <p>A "main" {@code ForkJoinTask} begins execution when it is
34	>	* explicitly submitted to a {@link ForkJoinPool}, or, if not already
35	>	* engaged in a ForkJoin computation, commenced in the {@link
36	>	* ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or
37	>	* related methods.  Once started, it will usually in turn start other
38	>	* subtasks.  As indicated by the name of this class, many programs
39	>	* using {@code ForkJoinTask} employ only methods {@link #fork} and
40	>	* {@link #join}, or derivatives such as {@link
41		* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
42		* provides a number of other methods that can come into play in
43	<	* advanced usages, as well as extension mechanics that allow
44	<	* support of new forms of fork/join processing.
43	>	* advanced usages, as well as extension mechanics that allow support
44	>	* of new forms of fork/join processing.
45		*
46		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
47		* The efficiency of {@code ForkJoinTask}s stems from a set of
48		* restrictions (that are only partially statically enforceable)
49	<	* reflecting their intended use as computational tasks calculating
50	<	* pure functions or operating on purely isolated objects.  The
51	<	* primary coordination mechanisms are {@link #fork}, that arranges
49	>	* reflecting their main use as computational tasks calculating pure
50	>	* functions or operating on purely isolated objects.  The primary
51	>	* coordination mechanisms are {@link #fork}, that arranges
52		* asynchronous execution, and {@link #join}, that doesn't proceed
53		* until the task's result has been computed.  Computations should
54	<	* avoid {@code synchronized} methods or blocks, and should minimize
55	<	* other blocking synchronization apart from joining other tasks or
56	<	* using synchronizers such as Phasers that are advertised to
57	<	* cooperate with fork/join scheduling. Tasks should also not perform
58	<	* blocking IO, and should ideally access variables that are
59	<	* completely independent of those accessed by other running
60	<	* tasks. Minor breaches of these restrictions, for example using
61	<	* shared output streams, may be tolerable in practice, but frequent
62	<	* use may result in poor performance, and the potential to
63	<	* indefinitely stall if the number of threads not waiting for IO or
64	<	* other external synchronization becomes exhausted. This usage
65	<	* restriction is in part enforced by not permitting checked
66	<	* exceptions such as {@code IOExceptions} to be thrown. However,
67	<	* computations may still encounter unchecked exceptions, that are
68	<	* rethrown to callers attempting to join them. These exceptions may
69	<	* additionally include {@link RejectedExecutionException} stemming
70	<	* from internal resource exhaustion, such as failure to allocate
71	<	* internal task queues. Rethrown exceptions behave in the same way as
72	<	* regular exceptions, but, when possible, contain stack traces (as
73	<	* displayed for example using {@code ex.printStackTrace()}) of both
74	<	* the thread that initiated the computation as well as the thread
75	<	* actually encountering the exception; minimally only the latter.
54	>	* ideally avoid {@code synchronized} methods or blocks, and should
55	>	* minimize other blocking synchronization apart from joining other
56	>	* tasks or using synchronizers such as Phasers that are advertised to
57	>	* cooperate with fork/join scheduling. Subdividable tasks should also
58	>	* not perform blocking I/O, and should ideally access variables that
59	>	* are completely independent of those accessed by other running
60	>	* tasks. These guidelines are loosely enforced by not permitting
61	>	* checked exceptions such as {@code IOExceptions} to be
62	>	* thrown. However, computations may still encounter unchecked
63	>	* exceptions, that are rethrown to callers attempting to join
64	>	* them. These exceptions may additionally include {@link
65	>	* RejectedExecutionException} stemming from internal resource
66	>	* exhaustion, such as failure to allocate internal task
67	>	* queues. Rethrown exceptions behave in the same way as regular
68	>	* exceptions, but, when possible, contain stack traces (as displayed
69	>	* for example using {@code ex.printStackTrace()}) of both the thread
70	>	* that initiated the computation as well as the thread actually
71	>	* encountering the exception; minimally only the latter.
72	>	*
73	>	* <p>It is possible to define and use ForkJoinTasks that may block,
74	>	* but doing do requires three further considerations: (1) Completion
75	>	* of few if any <em>other</em> tasks should be dependent on a task
76	>	* that blocks on external synchronization or I/O. Event-style async
77	>	* tasks that are never joined (for example, those subclassing {@link
78	>	* CountedCompleter}) often fall into this category.  (2) To minimize
79	>	* resource impact, tasks should be small; ideally performing only the
80	>	* (possibly) blocking action. (3) Unless the {@link
81	>	* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
82	>	* blocked tasks is known to be less than the pool's {@link
83	>	* ForkJoinPool#getParallelism} level, the pool cannot guarantee that
84	>	* enough threads will be available to ensure progress or good
85	>	* performance.
86		*
87		* <p>The primary method for awaiting completion and extracting
88		* results of a task is {@link #join}, but there are several variants:
#	Line 89 | Line 98 | import java.lang.reflect.Constructor;
98		* performs the most common form of parallel invocation: forking a set
99		* of tasks and joining them all.
100		*
101	+	* <p>In the most typical usages, a fork-join pair act like a call
102	+	* (fork) and return (join) from a parallel recursive function. As is
103	+	* the case with other forms of recursive calls, returns (joins)
104	+	* should be performed innermost-first. For example, {@code a.fork();
105	+	* b.fork(); b.join(); a.join();} is likely to be substantially more
106	+	* efficient than joining {@code a} before {@code b}.
107	+	*
108		* <p>The execution status of tasks may be queried at several levels
109		* of detail: {@link #isDone} is true if a task completed in any way
110		* (including the case where a task was cancelled without executing);
#	Line 104 | Line 120 | import java.lang.reflect.Constructor;
120		* <p>The ForkJoinTask class is not usually directly subclassed.
121		* Instead, you subclass one of the abstract classes that support a
122		* particular style of fork/join processing, typically {@link
123	<	* RecursiveAction} for computations that do not return results, or
124	<	* {@link RecursiveTask} for those that do.  Normally, a concrete
125	<	* ForkJoinTask subclass declares fields comprising its parameters,
126	<	* established in a constructor, and then defines a {@code compute}
127	<	* method that somehow uses the control methods supplied by this base
128	<	* class. While these methods have {@code public} access (to allow
129	<	* instances of different task subclasses to call each other's
114	<	* methods), some of them may only be called from within other
115	<	* ForkJoinTasks (as may be determined using method {@link
116	<	* #inForkJoinPool}).  Attempts to invoke them in other contexts
117	<	* result in exceptions or errors, possibly including
118	<	* {@code ClassCastException}.
123	>	* RecursiveAction} for most computations that do not return results,
124	>	* {@link RecursiveTask} for those that do, and {@link
125	>	* CountedCompleter} for those in which completed actions trigger
126	>	* other actions.  Normally, a concrete ForkJoinTask subclass declares
127	>	* fields comprising its parameters, established in a constructor, and
128	>	* then defines a {@code compute} method that somehow uses the control
129	>	* methods supplied by this base class.
130		*
131		* <p>Method {@link #join} and its variants are appropriate for use
132		* only when completion dependencies are acyclic; that is, the
#	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>tagged</em> with a {@code short}
141	>	* value using {@link #setForkJoinTaskTag} or {@link
142	>	* #compareAndSetForkJoinTaskTag} and checked using {@link
143	>	* #getForkJoinTaskTag}. The ForkJoinTask implementation does not use
144	>	* these {@code protected} methods or tags for any purpose, but they
145	>	* may be of use in the construction of specialized subclasses.  For
146	>	* example, parallel graph traversals can use the supplied methods to
147	>	* avoid revisiting nodes/tasks that have already been processed.
148	>	* (Method names for tagging are bulky in part to encourage definition
149	>	* of methods that reflect their usage patterns.)
150		*
151		* <p>Most base support methods are {@code final}, to prevent
152		* overriding of implementations that are intrinsically tied to the
#	Line 165 | Line 186 | public abstract class ForkJoinTask<V> im
186		* See the internal documentation of class ForkJoinPool for a
187		* general implementation overview.  ForkJoinTasks are mainly
188		* responsible for maintaining their "status" field amidst relays
189	<	* to methods in ForkJoinWorkerThread and ForkJoinPool. The
190	<	* methods of this class are more-or-less layered into (1) basic
191	<	* status maintenance (2) execution and awaiting completion (3)
192	<	* user-level methods that additionally report results. This is
193	<	* sometimes hard to see because this file orders exported methods
194	<	* in a way that flows well in javadocs.
189	>	* to methods in ForkJoinWorkerThread and ForkJoinPool.
190	>	*
191	>	* The methods of this class are more-or-less layered into
192	>	* (1) basic status maintenance
193	>	* (2) execution and awaiting completion
194	>	* (3) user-level methods that additionally report results.
195	>	* This is sometimes hard to see because this file orders exported
196	>	* methods in a way that flows well in javadocs.
197		*/
198
199		/*
200		* The status field holds run control status bits packed into a
201		* single int to minimize footprint and to ensure atomicity (via
202		* CAS).  Status is initially zero, and takes on nonnegative
203	<	* values until completed, upon which status holds value
204	<	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
205	<	* waits by other threads have the SIGNAL bit set.  Completion of
206	<	* a stolen task with SIGNAL set awakens any waiters via
207	<	* notifyAll. Even though suboptimal for some purposes, we use
208	<	* basic builtin wait/notify to take advantage of "monitor
209	<	* inflation" in JVMs that we would otherwise need to emulate to
210	<	* avoid adding further per-task bookkeeping overhead.  We want
211	<	* these monitors to be "fat", i.e., not use biasing or thin-lock
212	<	* techniques, so use some odd coding idioms that tend to avoid
213	<	* them.
203	>	* values until completed, upon which status (anded with
204	>	* DONE_MASK) holds value NORMAL, CANCELLED, or EXCEPTIONAL. Tasks
205	>	* undergoing blocking waits by other threads have the SIGNAL bit
206	>	* set.  Completion of a stolen task with SIGNAL set awakens any
207	>	* waiters via notifyAll. Even though suboptimal for some
208	>	* purposes, we use basic builtin wait/notify to take advantage of
209	>	* "monitor inflation" in JVMs that we would otherwise need to
210	>	* emulate to avoid adding further per-task bookkeeping overhead.
211	>	* We want these monitors to be "fat", i.e., not use biasing or
212	>	* thin-lock techniques, so use some odd coding idioms that tend
213	>	* to avoid them, mainly by arranging that every synchronized
214	>	* block performs a wait, notifyAll or both.
215	>	*
216	>	* These control bits occupy only (some of) the upper half (16
217	>	* bits) of status field. The lower bits are used for user-defined
218	>	* tags.
219		*/
220
221		/** The run status of this task */
222		volatile int status; // accessed directly by pool and workers
223	<	private static final int NORMAL      = -1;
224	<	private static final int CANCELLED   = -2;
225	<	private static final int EXCEPTIONAL = -3;
226	<	private static final int SIGNAL      =  1;
223	>	static final int DONE_MASK   = 0xf0000000;  // mask out non-completion bits
224	>	static final int NORMAL      = 0xf0000000;  // must be negative
225	>	static final int CANCELLED   = 0xc0000000;  // must be < NORMAL
226	>	static final int EXCEPTIONAL = 0x80000000;  // must be < CANCELLED
227	>	static final int SIGNAL      = 0x00010000;  // must be >= 1 << 16
228	>	static final int SMASK       = 0x0000ffff;  // short bits for tags
229
230		/**
231	<	* Marks completion and wakes up threads waiting to join this task,
232	<	* also clearing signal request bits.
231	>	* Marks completion and wakes up threads waiting to join this
232	>	* task.
233		*
234		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
235		* @return completion status on exit
#	Line 208 | Line 238 | public abstract class ForkJoinTask<V> im
238		for (int s;;) {
239		if ((s = status) < 0)
240		return s;
241	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
242	<	if (s != 0)
241	>	if (U.compareAndSwapInt(this, STATUS, s, s | completion)) {
242	>	if ((s >>> 16) != 0)
243		synchronized (this) { notifyAll(); }
244		return completion;
245		}
#	Line 217 | Line 247 | public abstract class ForkJoinTask<V> im
247		}
248
249		/**
250	<	* Tries to block a worker thread until completed or timed out.
251	<	* Uses Object.wait time argument conventions.
252	<	* May fail on contention or interrupt.
250	>	* Primary execution method for stolen tasks. Unless done, calls
251	>	* exec and records status if completed, but doesn't wait for
252	>	* completion otherwise.
253		*
254	<	* @param millis if > 0, wait time.
254	>	* @return status on exit from this method
255		*/
256	<	final void tryAwaitDone(long millis) {
257	<	int s;
258	<	try {
259	<	if (((s = status) > 0 ||
260	<	(s == 0 &&
261	<	UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL))) &&
262	<	status > 0) {
233	<	synchronized (this) {
234	<	if (status > 0)
235	<	wait(millis);
236	<	}
256	>	final int doExec() {
257	>	int s; boolean completed;
258	>	if ((s = status) >= 0) {
259	>	try {
260	>	completed = exec();
261	>	} catch (Throwable rex) {
262	>	return setExceptionalCompletion(rex);
263		}
264	<	} catch (InterruptedException ie) {
265	<	// caller must check termination
264	>	if (completed)
265	>	s = setCompletion(NORMAL);
266		}
267	+	return s;
268	+	}
269	+
270	+	/**
271	+	* Tries to set SIGNAL status unless already completed. Used by
272	+	* ForkJoinPool. Other variants are directly incorporated into
273	+	* externalAwaitDone etc.
274	+	*
275	+	* @return true if successful
276	+	*/
277	+	final boolean trySetSignal() {
278	+	int s = status;
279	+	return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL);
280		}
281
282		/**
#	Line 246 | Line 285 | public abstract class ForkJoinTask<V> im
285		*/
286		private int externalAwaitDone() {
287		int s;
288	<	if ((s = status) >= 0) {
289	<	boolean interrupted = false;
290	<	synchronized (this) {
291	<	while ((s = status) >= 0) {
292	<	if (s == 0)
293	<	UNSAFE.compareAndSwapInt(this, statusOffset,
255	<	0, SIGNAL);
256	<	else {
288	>	ForkJoinPool.externalHelpJoin(this);
289	>	boolean interrupted = false;
290	>	while ((s = status) >= 0) {
291	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
292	>	synchronized (this) {
293	>	if (status >= 0) {
294		try {
295		wait();
296		} catch (InterruptedException ie) {
297		interrupted = true;
298		}
299		}
300	+	else
301	+	notifyAll();
302		}
303		}
265	–	if (interrupted)
266	–	Thread.currentThread().interrupt();
304		}
305	+	if (interrupted)
306	+	Thread.currentThread().interrupt();
307		return s;
308		}
309
310		/**
311	<	* Blocks a non-worker-thread until completion or interruption or timeout.
311	>	* Blocks a non-worker-thread until completion or interruption.
312		*/
313	<	private int externalInterruptibleAwaitDone(long millis)
275	<	throws InterruptedException {
313	>	private int externalInterruptibleAwaitDone() throws InterruptedException {
314		int s;
315		if (Thread.interrupted())
316		throw new InterruptedException();
317	<	if ((s = status) >= 0) {
318	<	synchronized (this) {
319	<	while ((s = status) >= 0) {
320	<	if (s == 0)
321	<	UNSAFE.compareAndSwapInt(this, statusOffset,
322	<	0, SIGNAL);
323	<	else {
324	<	wait(millis);
287	<	if (millis > 0L)
288	<	break;
289	<	}
317	>	ForkJoinPool.externalHelpJoin(this);
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	>	notifyAll();
325		}
326		}
327		}
328		return s;
329		}
330
296	–	/**
297	–	* Primary execution method for stolen tasks. Unless done, calls
298	–	* exec and records status if completed, but doesn't wait for
299	–	* completion otherwise.
300	–	*/
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	–	}
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 {
346	<	completed = exec();
327	<	} catch (Throwable rex) {
328	<	return setExceptionalCompletion(rex);
329	<	}
330	<	if (completed)
331	<	return setCompletion(NORMAL);
332	<	}
333	<	return w.joinTask(this);
334	<	}
335	<	else
336	<	return externalAwaitDone();
340	>	int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
341	>	return (s = status) < 0 ? s :
342	>	((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
343	>	(w = (wt = (ForkJoinWorkerThread)t).workQueue).
344	>	tryUnpush(this) && (s = doExec()) < 0 ? s :
345	>	wt.pool.awaitJoin(w, this) :
346	>	externalAwaitDone();
347		}
348
349		/**
350	<	* Primary mechanics for invoke, quietlyInvoke.
350	>	* Implementation for invoke, quietlyInvoke.
351	>	*
352		* @return status upon completion
353		*/
354		private int doInvoke() {
355	<	int s; boolean completed;
356	<	if ((s = status) < 0)
357	<	return s;
358	<	try {
359	<	completed = exec();
349	<	} catch (Throwable rex) {
350	<	return setExceptionalCompletion(rex);
351	<	}
352	<	if (completed)
353	<	return setCompletion(NORMAL);
354	<	else
355	<	return doJoin();
355	>	int s; Thread t; ForkJoinWorkerThread wt;
356	>	return (s = doExec()) < 0 ? s :
357	>	((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
358	>	(wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue, this) :
359	>	externalAwaitDone();
360		}
361
362		// Exception table support
#	Line 384 | Line 388 | public abstract class ForkJoinTask<V> im
388		* periods. However, since we do not know when the last joiner
389		* completes, we must use weak references and expunge them. We do
390		* so on each operation (hence full locking). Also, some thread in
391	<	* any ForkJoinPool will call helpExpunge when its pool becomes
392	<	* isQuiescent.
391	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
392	>	* pool becomes isQuiescent.
393		*/
394	<	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>>{
394	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> {
395		final Throwable ex;
396		ExceptionNode next;
397	<	final long thrower;
397	>	final long thrower;  // use id not ref to avoid weak cycles
398		ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
399		super(task, exceptionTableRefQueue);
400		this.ex = ex;
#	Line 400 | Line 404 | public abstract class ForkJoinTask<V> im
404		}
405
406		/**
407	<	* Records exception and sets exceptional completion.
407	>	* Records exception and sets status.
408		*
409		* @return status on exit
410		*/
411	<	private int setExceptionalCompletion(Throwable ex) {
412	<	int h = System.identityHashCode(this);
413	<	ReentrantLock lock = exceptionTableLock;
414	<	lock.lock();
415	<	try {
416	<	expungeStaleExceptions();
417	<	ExceptionNode[] t = exceptionTable;
418	<	int i = h & (t.length - 1);
419	<	for (ExceptionNode e = t[i]; ; e = e.next) {
420	<	if (e == null) {
421	<	t[i] = new ExceptionNode(this, ex, t[i]);
422	<	break;
411	>	final int recordExceptionalCompletion(Throwable ex) {
412	>	int s;
413	>	if ((s = status) >= 0) {
414	>	int h = System.identityHashCode(this);
415	>	final ReentrantLock lock = exceptionTableLock;
416	>	lock.lock();
417	>	try {
418	>	expungeStaleExceptions();
419	>	ExceptionNode[] t = exceptionTable;
420	>	int i = h & (t.length - 1);
421	>	for (ExceptionNode e = t[i]; ; e = e.next) {
422	>	if (e == null) {
423	>	t[i] = new ExceptionNode(this, ex, t[i]);
424	>	break;
425	>	}
426	>	if (e.get() == this) // already present
427	>	break;
428		}
429	<	if (e.get() == this) // already present
430	<	break;
429	>	} finally {
430	>	lock.unlock();
431	>	}
432	>	s = setCompletion(EXCEPTIONAL);
433	>	}
434	>	return s;
435	>	}
436	>
437	>	/**
438	>	* Records exception and possibly propagates
439	>	*
440	>	* @return status on exit
441	>	*/
442	>	private int setExceptionalCompletion(Throwable ex) {
443	>	int s = recordExceptionalCompletion(ex);
444	>	if ((s & DONE_MASK) == EXCEPTIONAL)
445	>	internalPropagateException(ex);
446	>	return s;
447	>	}
448	>
449	>	/**
450	>	* Hook for exception propagation support for tasks with completers.
451	>	*/
452	>	void internalPropagateException(Throwable ex) {
453	>	}
454	>
455	>	/**
456	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
457	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
458	>	* exceptions, but if it does anyway, we have no recourse during
459	>	* shutdown, so guard against this case.
460	>	*/
461	>	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
462	>	if (t != null && t.status >= 0) {
463	>	try {
464	>	t.cancel(false);
465	>	} catch (Throwable ignore) {
466		}
423	–	} finally {
424	–	lock.unlock();
467		}
426	–	return setCompletion(EXCEPTIONAL);
468		}
469
470		/**
#	Line 431 | Line 472 | public abstract class ForkJoinTask<V> im
472		*/
473		private void clearExceptionalCompletion() {
474		int h = System.identityHashCode(this);
475	<	ReentrantLock lock = exceptionTableLock;
475	>	final ReentrantLock lock = exceptionTableLock;
476		lock.lock();
477		try {
478		ExceptionNode[] t = exceptionTable;
#	Line 472 | Line 513 | public abstract class ForkJoinTask<V> im
513		* @return the exception, or null if none
514		*/
515		private Throwable getThrowableException() {
516	<	if (status != EXCEPTIONAL)
516	>	if ((status & DONE_MASK) != EXCEPTIONAL)
517		return null;
518		int h = System.identityHashCode(this);
519		ExceptionNode e;
520	<	ReentrantLock lock = exceptionTableLock;
520	>	final ReentrantLock lock = exceptionTableLock;
521		lock.lock();
522		try {
523		expungeStaleExceptions();
#	Line 490 | Line 531 | public abstract class ForkJoinTask<V> im
531		Throwable ex;
532		if (e == null || (ex = e.ex) == null)
533		return null;
534	<	if (e.thrower != Thread.currentThread().getId()) {
535	<	Class ec = ex.getClass();
534	>	if (false && e.thrower != Thread.currentThread().getId()) {
535	>	Class<? extends Throwable> ec = ex.getClass();
536		try {
537		Constructor<?> noArgCtor = null;
538		Constructor<?>[] cs = ec.getConstructors();// public ctors only
#	Line 542 | Line 583 | public abstract class ForkJoinTask<V> im
583		}
584
585		/**
586	<	* If lock is available, poll any stale refs and remove them.
586	>	* If lock is available, poll stale refs and remove them.
587		* Called from ForkJoinPool when pools become quiescent.
588		*/
589		static final void helpExpungeStaleExceptions() {
590	<	ReentrantLock lock = exceptionTableLock;
590	>	final ReentrantLock lock = exceptionTableLock;
591		if (lock.tryLock()) {
592		try {
593		expungeStaleExceptions();
#	Line 557 | Line 598 | public abstract class ForkJoinTask<V> im
598		}
599
600		/**
601	<	* Report the result of invoke or join; called only upon
602	<	* non-normal return of internal versions.
601	>	* A version of "sneaky throw" to relay exceptions
602	>	*/
603	>	static void rethrow(final Throwable ex) {
604	>	if (ex != null) {
605	>	if (ex instanceof Error)
606	>	throw (Error)ex;
607	>	if (ex instanceof RuntimeException)
608	>	throw (RuntimeException)ex;
609	>	throw uncheckedThrowable(ex, RuntimeException.class);
610	>	}
611	>	}
612	>
613	>	/**
614	>	* The sneaky part of sneaky throw, relying on generics
615	>	* limitations to evade compiler complaints about rethrowing
616	>	* unchecked exceptions
617	>	*/
618	>	@SuppressWarnings("unchecked") static <T extends Throwable>
619	>	T uncheckedThrowable(final Throwable t, final Class<T> c) {
620	>	return (T)t; // rely on vacuous cast
621	>	}
622	>
623	>	/**
624	>	* Throws exception, if any, associated with the given status.
625		*/
626	<	private V reportResult() {
627	<	int s; Throwable ex;
565	<	if ((s = status) == CANCELLED)
626	>	private void reportException(int s) {
627	>	if (s == CANCELLED)
628		throw new CancellationException();
629	<	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
630	<	UNSAFE.throwException(ex);
569	<	return getRawResult();
629	>	if (s == EXCEPTIONAL)
630	>	rethrow(getThrowableException());
631		}
632
633		// public methods
634
635		/**
636	<	* Arranges to asynchronously execute this task.  While it is not
637	<	* necessarily enforced, it is a usage error to fork a task more
638	<	* than once unless it has completed and been reinitialized.
639	<	* Subsequent modifications to the state of this task or any data
640	<	* it operates on are not necessarily consistently observable by
641	<	* any thread other than the one executing it unless preceded by a
642	<	* call to {@link #join} or related methods, or a call to {@link
643	<	* #isDone} returning {@code true}.
644	<	*
645	<	* <p>This method may be invoked only from within {@code
646	<	* ForkJoinPool} computations (as may be determined using method
586	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
587	<	* result in exceptions or errors, possibly including {@code
588	<	* ClassCastException}.
636	>	* Arranges to asynchronously execute this task in the pool the
637	>	* current task is running in, if applicable, or using the {@link
638	>	* ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}.  While
639	>	* it is not necessarily enforced, it is a usage error to fork a
640	>	* task more than once unless it has completed and been
641	>	* reinitialized.  Subsequent modifications to the state of this
642	>	* task or any data it operates on are not necessarily
643	>	* consistently observable by any thread other than the one
644	>	* executing it unless preceded by a call to {@link #join} or
645	>	* related methods, or a call to {@link #isDone} returning {@code
646	>	* true}.
647		*
648		* @return {@code this}, to simplify usage
649		*/
650		public final ForkJoinTask<V> fork() {
651	<	((ForkJoinWorkerThread) Thread.currentThread())
652	<	.pushTask(this);
651	>	Thread t;
652	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
653	>	((ForkJoinWorkerThread)t).workQueue.push(this);
654	>	else
655	>	ForkJoinPool.commonPool.externalPush(this);
656		return this;
657		}
658
#	Line 607 | Line 668 | public abstract class ForkJoinTask<V> im
668		* @return the computed result
669		*/
670		public final V join() {
671	<	if (doJoin() != NORMAL)
672	<	return reportResult();
673	<	else
674	<	return getRawResult();
671	>	int s;
672	>	if ((s = doJoin() & DONE_MASK) != NORMAL)
673	>	reportException(s);
674	>	return getRawResult();
675		}
676
677		/**
#	Line 622 | Line 683 | public abstract class ForkJoinTask<V> im
683		* @return the computed result
684		*/
685		public final V invoke() {
686	<	if (doInvoke() != NORMAL)
687	<	return reportResult();
688	<	else
689	<	return getRawResult();
686	>	int s;
687	>	if ((s = doInvoke() & DONE_MASK) != NORMAL)
688	>	reportException(s);
689	>	return getRawResult();
690		}
691
692		/**
#	Line 641 | Line 702 | public abstract class ForkJoinTask<V> im
702		* cancelled, completed normally or exceptionally, or left
703		* unprocessed.
704		*
644	–	* <p>This method may be invoked only from within {@code
645	–	* ForkJoinPool} computations (as may be determined using method
646	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
647	–	* result in exceptions or errors, possibly including {@code
648	–	* ClassCastException}.
649	–	*
705		* @param t1 the first task
706		* @param t2 the second task
707		* @throws NullPointerException if any task is null
708		*/
709		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
710	+	int s1, s2;
711		t2.fork();
712	<	t1.invoke();
713	<	t2.join();
712	>	if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL)
713	>	t1.reportException(s1);
714	>	if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
715	>	t2.reportException(s2);
716		}
717
718		/**
#	Line 669 | Line 727 | public abstract class ForkJoinTask<V> im
727		* related methods to check if they have been cancelled, completed
728		* normally or exceptionally, or left unprocessed.
729		*
672	–	* <p>This method may be invoked only from within {@code
673	–	* ForkJoinPool} computations (as may be determined using method
674	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
675	–	* result in exceptions or errors, possibly including {@code
676	–	* ClassCastException}.
677	–	*
730		* @param tasks the tasks
731		* @throws NullPointerException if any task is null
732		*/
#	Line 697 | Line 749 | public abstract class ForkJoinTask<V> im
749		if (t != null) {
750		if (ex != null)
751		t.cancel(false);
752	<	else if (t.doJoin() < NORMAL && ex == null)
752	>	else if (t.doJoin() < NORMAL)
753		ex = t.getException();
754		}
755		}
756		if (ex != null)
757	<	UNSAFE.throwException(ex);
757	>	rethrow(ex);
758		}
759
760		/**
#	Line 718 | Line 770 | public abstract class ForkJoinTask<V> im
770		* cancelled, completed normally or exceptionally, or left
771		* unprocessed.
772		*
721	–	* <p>This method may be invoked only from within {@code
722	–	* ForkJoinPool} computations (as may be determined using method
723	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
724	–	* result in exceptions or errors, possibly including {@code
725	–	* ClassCastException}.
726	–	*
773		* @param tasks the collection of tasks
774		* @return the tasks argument, to simplify usage
775		* @throws NullPointerException if tasks or any element are null
#	Line 754 | Line 800 | public abstract class ForkJoinTask<V> im
800		if (t != null) {
801		if (ex != null)
802		t.cancel(false);
803	<	else if (t.doJoin() < NORMAL && ex == null)
803	>	else if (t.doJoin() < NORMAL)
804		ex = t.getException();
805		}
806		}
807		if (ex != null)
808	<	UNSAFE.throwException(ex);
808	>	rethrow(ex);
809		return tasks;
810		}
811
#	Line 791 | Line 837 | public abstract class ForkJoinTask<V> im
837		* @return {@code true} if this task is now cancelled
838		*/
839		public boolean cancel(boolean mayInterruptIfRunning) {
840	<	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	<	}
840	>	return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
841		}
842
843		public final boolean isDone() {
#	Line 812 | Line 845 | public abstract class ForkJoinTask<V> im
845		}
846
847		public final boolean isCancelled() {
848	<	return status == CANCELLED;
848	>	return (status & DONE_MASK) == CANCELLED;
849		}
850
851		/**
#	Line 832 | Line 865 | public abstract class ForkJoinTask<V> im
865		* exception and was not cancelled
866		*/
867		public final boolean isCompletedNormally() {
868	<	return status == NORMAL;
868	>	return (status & DONE_MASK) == NORMAL;
869		}
870
871		/**
#	Line 843 | Line 876 | public abstract class ForkJoinTask<V> im
876		* @return the exception, or {@code null} if none
877		*/
878		public final Throwable getException() {
879	<	int s = status;
879	>	int s = status & DONE_MASK;
880		return ((s >= NORMAL)    ? null :
881		(s == CANCELLED) ? new CancellationException() :
882		getThrowableException());
#	Line 893 | Line 926 | public abstract class ForkJoinTask<V> im
926		}
927
928		/**
929	+	* Completes this task normally without setting a value. The most
930	+	* recent value established by {@link #setRawResult} (or {@code
931	+	* null} by default) will be returned as the result of subsequent
932	+	* invocations of {@code join} and related operations.
933	+	*
934	+	* @since 1.8
935	+	*/
936	+	public final void quietlyComplete() {
937	+	setCompletion(NORMAL);
938	+	}
939	+
940	+	/**
941		* Waits if necessary for the computation to complete, and then
942		* retrieves its result.
943		*
#	Line 905 | Line 950 | public abstract class ForkJoinTask<V> im
950		*/
951		public final V get() throws InterruptedException, ExecutionException {
952		int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
953	<	doJoin() : externalInterruptibleAwaitDone(0L);
953	>	doJoin() : externalInterruptibleAwaitDone();
954		Throwable ex;
955	<	if (s == CANCELLED)
955	>	if ((s &= DONE_MASK) == CANCELLED)
956		throw new CancellationException();
957		if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
958		throw new ExecutionException(ex);
#	Line 930 | Line 975 | public abstract class ForkJoinTask<V> im
975		*/
976		public final V get(long timeout, TimeUnit unit)
977		throws InterruptedException, ExecutionException, TimeoutException {
978	<	Thread t = Thread.currentThread();
979	<	if (t instanceof ForkJoinWorkerThread) {
980	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
981	<	long nanos = unit.toNanos(timeout);
982	<	if (status >= 0) {
983	<	boolean completed = false;
984	<	if (w.unpushTask(this)) {
985	<	try {
986	<	completed = exec();
987	<	} catch (Throwable rex) {
988	<	setExceptionalCompletion(rex);
978	>	if (Thread.interrupted())
979	>	throw new InterruptedException();
980	>	// Messy in part because we measure in nanosecs, but wait in millisecs
981	>	int s; long ms;
982	>	long ns = unit.toNanos(timeout);
983	>	if ((s = status) >= 0 && ns > 0L) {
984	>	long deadline = System.nanoTime() + ns;
985	>	ForkJoinPool p = null;
986	>	ForkJoinPool.WorkQueue w = null;
987	>	Thread t = Thread.currentThread();
988	>	if (t instanceof ForkJoinWorkerThread) {
989	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
990	>	p = wt.pool;
991	>	w = wt.workQueue;
992	>	p.helpJoinOnce(w, this); // no retries on failure
993	>	}
994	>	else
995	>	ForkJoinPool.externalHelpJoin(this);
996	>	boolean canBlock = false;
997	>	boolean interrupted = false;
998	>	try {
999	>	while ((s = status) >= 0) {
1000	>	if (w != null && w.qlock < 0)
1001	>	cancelIgnoringExceptions(this);
1002	>	else if (!canBlock) {
1003	>	if (p == null || p.tryCompensate())
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 992 | Line 1068 | public abstract class ForkJoinTask<V> im
1068		* be of use in designs in which many tasks are forked, but none
1069		* are explicitly joined, instead executing them until all are
1070		* processed.
995	–	*
996	–	* <p>This method may be invoked only from within {@code
997	–	* ForkJoinPool} computations (as may be determined using method
998	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
999	–	* result in exceptions or errors, possibly including {@code
1000	–	* ClassCastException}.
1071		*/
1072		public static void helpQuiesce() {
1073	<	((ForkJoinWorkerThread) Thread.currentThread())
1074	<	.helpQuiescePool();
1073	>	Thread t;
1074	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
1075	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1076	>	wt.pool.helpQuiescePool(wt.workQueue);
1077	>	}
1078	>	else
1079	>	ForkJoinPool.externalHelpQuiescePool();
1080		}
1081
1082		/**
#	Line 1021 | Line 1096 | public abstract class ForkJoinTask<V> im
1096		* setRawResult(null)}.
1097		*/
1098		public void reinitialize() {
1099	<	if (status == EXCEPTIONAL)
1099	>	if ((status & DONE_MASK) == EXCEPTIONAL)
1100		clearExceptionalCompletion();
1101		else
1102		status = 0;
#	Line 1054 | Line 1129 | public abstract class ForkJoinTask<V> im
1129
1130		/**
1131		* Tries to unschedule this task for execution. This method will
1132	<	* typically succeed if this task is the most recently forked task
1133	<	* by the current thread, and has not commenced executing in
1134	<	* another thread.  This method may be useful when arranging
1135	<	* alternative local processing of tasks that could have been, but
1136	<	* were not, stolen.
1062	<	*
1063	<	* <p>This method may be invoked only from within {@code
1064	<	* ForkJoinPool} computations (as may be determined using method
1065	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1066	<	* result in exceptions or errors, possibly including {@code
1067	<	* ClassCastException}.
1132	>	* typically (but is not guaranteed to) succeed if this task is
1133	>	* the most recently forked task by the current thread, and has
1134	>	* not commenced executing in another thread.  This method may be
1135	>	* useful when arranging alternative local processing of tasks
1136	>	* that could have been, but were not, stolen.
1137		*
1138		* @return {@code true} if unforked
1139		*/
1140		public boolean tryUnfork() {
1141	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1142	<	.unpushTask(this);
1141	>	Thread t;
1142	>	return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1143	>	((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
1144	>	ForkJoinPool.tryExternalUnpush(this));
1145		}
1146
1147		/**
#	Line 1079 | Line 1150 | public abstract class ForkJoinTask<V> im
1150		* value may be useful for heuristic decisions about whether to
1151		* fork other tasks.
1152		*
1082	–	* <p>This method may be invoked only from within {@code
1083	–	* ForkJoinPool} computations (as may be determined using method
1084	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1085	–	* result in exceptions or errors, possibly including {@code
1086	–	* ClassCastException}.
1087	–	*
1153		* @return the number of tasks
1154		*/
1155		public static int getQueuedTaskCount() {
1156	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1157	<	.getQueueSize();
1156	>	Thread t; ForkJoinPool.WorkQueue q;
1157	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1158	>	q = ((ForkJoinWorkerThread)t).workQueue;
1159	>	else
1160	>	q = ForkJoinPool.commonSubmitterQueue();
1161	>	return (q == null) ? 0 : q.queueSize();
1162		}
1163
1164		/**
1165		* Returns an estimate of how many more locally queued tasks are
1166		* held by the current worker thread than there are other worker
1167	<	* threads that might steal them.  This value may be useful for
1167	>	* threads that might steal them, or zero if this thread is not
1168	>	* operating in a ForkJoinPool. This value may be useful for
1169		* heuristic decisions about whether to fork other tasks. In many
1170		* usages of ForkJoinTasks, at steady state, each worker should
1171		* aim to maintain a small constant surplus (for example, 3) of
1172		* tasks, and to process computations locally if this threshold is
1173		* exceeded.
1174		*
1105	–	* <p>This method may be invoked only from within {@code
1106	–	* ForkJoinPool} computations (as may be determined using method
1107	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1108	–	* result in exceptions or errors, possibly including {@code
1109	–	* ClassCastException}.
1110	–	*
1175		* @return the surplus number of tasks, which may be negative
1176		*/
1177		public static int getSurplusQueuedTaskCount() {
1178	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1115	<	.getEstimatedSurplusTaskCount();
1178	>	return ForkJoinPool.getSurplusQueuedTaskCount();
1179		}
1180
1181		// Extension methods
#	Line 1138 | Line 1201 | public abstract class ForkJoinTask<V> im
1201		protected abstract void setRawResult(V value);
1202
1203		/**
1204	<	* Immediately performs the base action of this task.  This method
1205	<	* is designed to support extensions, and should not in general be
1206	<	* called otherwise. The return value controls whether this task
1207	<	* is considered to be done normally. It may return false in
1204	>	* Immediately performs the base action of this task and returns
1205	>	* true if, upon return from this method, this task is guaranteed
1206	>	* to have completed normally. This method may return false
1207	>	* otherwise, to indicate that this task is not necessarily
1208	>	* complete (or is not known to be complete), for example in
1209		* asynchronous actions that require explicit invocations of
1210	<	* {@link #complete} to become joinable. It may also throw an
1211	<	* (unchecked) exception to indicate abnormal exit.
1210	>	* completion methods. This method may also throw an (unchecked)
1211	>	* exception to indicate abnormal exit. This method is designed to
1212	>	* support extensions, and should not in general be called
1213	>	* otherwise.
1214		*
1215	<	* @return {@code true} if completed normally
1215	>	* @return {@code true} if this task is known to have completed normally
1216		*/
1217		protected abstract boolean exec();
1218
#	Line 1160 | Line 1226 | public abstract class ForkJoinTask<V> im
1226		* primarily to support extensions, and is unlikely to be useful
1227		* otherwise.
1228		*
1163	–	* <p>This method may be invoked only from within {@code
1164	–	* ForkJoinPool} computations (as may be determined using method
1165	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1166	–	* result in exceptions or errors, possibly including {@code
1167	–	* ClassCastException}.
1168	–	*
1229		* @return the next task, or {@code null} if none are available
1230		*/
1231		protected static ForkJoinTask<?> peekNextLocalTask() {
1232	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1233	<	.peekTask();
1232	>	Thread t; ForkJoinPool.WorkQueue q;
1233	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1234	>	q = ((ForkJoinWorkerThread)t).workQueue;
1235	>	else
1236	>	q = ForkJoinPool.commonSubmitterQueue();
1237	>	return (q == null) ? null : q.peek();
1238		}
1239
1240		/**
1241		* Unschedules and returns, without executing, the next task
1242	<	* queued by the current thread but not yet executed.  This method
1243	<	* is designed primarily to support extensions, and is unlikely to
1244	<	* be useful otherwise.
1245	<	*
1182	<	* <p>This method may be invoked only from within {@code
1183	<	* ForkJoinPool} computations (as may be determined using method
1184	<	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1185	<	* result in exceptions or errors, possibly including {@code
1186	<	* ClassCastException}.
1242	>	* queued by the current thread but not yet executed, if the
1243	>	* current thread is operating in a ForkJoinPool.  This method is
1244	>	* designed primarily to support extensions, and is unlikely to be
1245	>	* useful otherwise.
1246		*
1247		* @return the next task, or {@code null} if none are available
1248		*/
1249		protected static ForkJoinTask<?> pollNextLocalTask() {
1250	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1251	<	.pollLocalTask();
1250	>	Thread t;
1251	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1252	>	((ForkJoinWorkerThread)t).workQueue.nextLocalTask() :
1253	>	null;
1254		}
1255
1256		/**
1257	<	* Unschedules and returns, without executing, the next task
1257	>	* If the current thread is operating in a ForkJoinPool,
1258	>	* unschedules and returns, without executing, the next task
1259		* queued by the current thread but not yet executed, if one is
1260		* available, or if not available, a task that was forked by some
1261		* other thread, if available. Availability may be transient, so a
1262	<	* {@code null} result does not necessarily imply quiescence
1263	<	* of the pool this task is operating in.  This method is designed
1262	>	* {@code null} result does not necessarily imply quiescence of
1263	>	* the pool this task is operating in.  This method is designed
1264		* primarily to support extensions, and is unlikely to be useful
1265		* otherwise.
1266		*
1205	–	* <p>This method may be invoked only from within {@code
1206	–	* ForkJoinPool} computations (as may be determined using method
1207	–	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1208	–	* result in exceptions or errors, possibly including {@code
1209	–	* ClassCastException}.
1210	–	*
1267		* @return a task, or {@code null} if none are available
1268		*/
1269		protected static ForkJoinTask<?> pollTask() {
1270	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1271	<	.pollTask();
1270	>	Thread t; ForkJoinWorkerThread wt;
1271	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1272	>	(wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) :
1273	>	null;
1274	>	}
1275	>
1276	>	// tag operations
1277	>
1278	>	/**
1279	>	* Returns the tag for this task.
1280	>	*
1281	>	* @return the tag for this task
1282	>	* @since 1.8
1283	>	*/
1284	>	public final short getForkJoinTaskTag() {
1285	>	return (short)status;
1286	>	}
1287	>
1288	>	/**
1289	>	* Atomically sets the tag value for this task.
1290	>	*
1291	>	* @param tag the tag value
1292	>	* @return the previous value of the tag
1293	>	* @since 1.8
1294	>	*/
1295	>	public final short setForkJoinTaskTag(short tag) {
1296	>	for (int s;;) {
1297	>	if (U.compareAndSwapInt(this, STATUS, s = status,
1298	>	(s & ~SMASK) | (tag & SMASK)))
1299	>	return (short)s;
1300	>	}
1301	>	}
1302	>
1303	>	/**
1304	>	* Atomically conditionally sets the tag value for this task.
1305	>	* Among other applications, tags can be used as visit markers
1306	>	* in tasks operating on graphs, as in methods that check: {@code
1307	>	* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1308	>	* before processing, otherwise exiting because the node has
1309	>	* already been visited.
1310	>	*
1311	>	* @param e the expected tag value
1312	>	* @param tag the new tag value
1313	>	* @return true if successful; i.e., the current value was
1314	>	* equal to e and is now tag.
1315	>	* @since 1.8
1316	>	*/
1317	>	public final boolean compareAndSetForkJoinTaskTag(short e, short tag) {
1318	>	for (int s;;) {
1319	>	if ((short)(s = status) != e)
1320	>	return false;
1321	>	if (U.compareAndSwapInt(this, STATUS, s,
1322	>	(s & ~SMASK) | (tag & SMASK)))
1323	>	return true;
1324	>	}
1325		}
1326
1327		/**
#	Line 1223 | Line 1332 | public abstract class ForkJoinTask<V> im
1332		static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1333		implements RunnableFuture<T> {
1334		final Runnable runnable;
1226	–	final T resultOnCompletion;
1335		T result;
1336		AdaptedRunnable(Runnable runnable, T result) {
1337		if (runnable == null) throw new NullPointerException();
1338		this.runnable = runnable;
1339	<	this.resultOnCompletion = result;
1339	>	this.result = result; // OK to set this even before completion
1340		}
1341	<	public T getRawResult() { return result; }
1342	<	public void setRawResult(T v) { result = v; }
1343	<	public boolean exec() {
1344	<	runnable.run();
1345	<	result = resultOnCompletion;
1346	<	return true;
1341	>	public final T getRawResult() { return result; }
1342	>	public final void setRawResult(T v) { result = v; }
1343	>	public final boolean exec() { runnable.run(); return true; }
1344	>	public final void run() { invoke(); }
1345	>	private static final long serialVersionUID = 5232453952276885070L;
1346	>	}
1347	>
1348	>	/**
1349	>	* Adaptor for Runnables without results
1350	>	*/
1351	>	static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1352	>	implements RunnableFuture<Void> {
1353	>	final Runnable runnable;
1354	>	AdaptedRunnableAction(Runnable runnable) {
1355	>	if (runnable == null) throw new NullPointerException();
1356	>	this.runnable = runnable;
1357		}
1358	<	public void run() { invoke(); }
1358	>	public final Void getRawResult() { return null; }
1359	>	public final void setRawResult(Void v) { }
1360	>	public final boolean exec() { runnable.run(); return true; }
1361	>	public final void run() { invoke(); }
1362		private static final long serialVersionUID = 5232453952276885070L;
1363		}
1364
#	Line 1252 | Line 1373 | public abstract class ForkJoinTask<V> im
1373		if (callable == null) throw new NullPointerException();
1374		this.callable = callable;
1375		}
1376	<	public T getRawResult() { return result; }
1377	<	public void setRawResult(T v) { result = v; }
1378	<	public boolean exec() {
1376	>	public final T getRawResult() { return result; }
1377	>	public final void setRawResult(T v) { result = v; }
1378	>	public final boolean exec() {
1379		try {
1380		result = callable.call();
1381		return true;
#	Line 1266 | Line 1387 | public abstract class ForkJoinTask<V> im
1387		throw new RuntimeException(ex);
1388		}
1389		}
1390	<	public void run() { invoke(); }
1390	>	public final void run() { invoke(); }
1391		private static final long serialVersionUID = 2838392045355241008L;
1392		}
1393
#	Line 1279 | Line 1400 | public abstract class ForkJoinTask<V> im
1400		* @return the task
1401		*/
1402		public static ForkJoinTask<?> adapt(Runnable runnable) {
1403	<	return new AdaptedRunnable<Void>(runnable, null);
1403	>	return new AdaptedRunnableAction(runnable);
1404		}
1405
1406		/**
#	Line 1313 | Line 1434 | public abstract class ForkJoinTask<V> im
1434		private static final long serialVersionUID = -7721805057305804111L;
1435
1436		/**
1437	<	* Saves the state to a stream (that is, serializes it).
1437	>	* Saves this task to a stream (that is, serializes it).
1438		*
1439		* @serialData the current run status and the exception thrown
1440		* during execution, or {@code null} if none
1320	–	* @param s the stream
1441		*/
1442		private void writeObject(java.io.ObjectOutputStream s)
1443		throws java.io.IOException {
#	Line 1326 | Line 1446 | public abstract class ForkJoinTask<V> im
1446		}
1447
1448		/**
1449	<	* Reconstitutes the instance from a stream (that is, deserializes it).
1330	<	*
1331	<	* @param s the stream
1449	>	* Reconstitutes this task from a stream (that is, deserializes it).
1450		*/
1451		private void readObject(java.io.ObjectInputStream s)
1452		throws java.io.IOException, ClassNotFoundException {
#	Line 1339 | Line 1457 | public abstract class ForkJoinTask<V> im
1457		}
1458
1459		// Unsafe mechanics
1460	<	private static final sun.misc.Unsafe UNSAFE;
1461	<	private static final long statusOffset;
1460	>	private static final sun.misc.Unsafe U;
1461	>	private static final long STATUS;
1462	>
1463		static {
1464		exceptionTableLock = new ReentrantLock();
1465		exceptionTableRefQueue = new ReferenceQueue<Object>();
1466		exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1467		try {
1468	<	UNSAFE = getUnsafe();
1469	<	statusOffset = UNSAFE.objectFieldOffset
1470	<	(ForkJoinTask.class.getDeclaredField("status"));
1468	>	U = getUnsafe();
1469	>	Class<?> k = ForkJoinTask.class;
1470	>	STATUS = U.objectFieldOffset
1471	>	(k.getDeclaredField("status"));
1472		} catch (Exception e) {
1473		throw new Error(e);
1474		}

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