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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 1.100 by jsr166, Tue Feb 5 17:09:54 2013 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 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 387 | Line 391 | public abstract class ForkJoinTask<V> im
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;  // use id not ref to avoid weak cycles
#	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	<	final 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		/**
471	<	* Removes exception node and clears status
471	>	* Removes exception node and clears status.
472		*/
473		private void clearExceptionalCompletion() {
474		int h = System.identityHashCode(this);
#	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;
#	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 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	>	ForkJoinTask.<RuntimeException>uncheckedThrow(ex);
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	<	private V reportResult() {
619	<	int s; Throwable ex;
620	<	if ((s = status) == CANCELLED)
618	>	@SuppressWarnings("unchecked") static <T extends Throwable>
619	>	void uncheckedThrow(Throwable t) throws T {
620	>	if (t != null)
621	>	throw (T)t; // rely on vacuous cast
622	>	}
623	>
624	>	/**
625	>	* Throws exception, if any, associated with the given status.
626	>	*/
627	>	private void reportException(int s) {
628	>	if (s == CANCELLED)
629		throw new CancellationException();
630	<	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
631	<	UNSAFE.throwException(ex);
569	<	return getRawResult();
630	>	if (s == EXCEPTIONAL)
631	>	rethrow(getThrowableException());
632		}
633
634		// public methods
635
636		/**
637	<	* Arranges to asynchronously execute this task.  While it is not
638	<	* necessarily enforced, it is a usage error to fork a task more
639	<	* than once unless it has completed and been reinitialized.
640	<	* Subsequent modifications to the state of this task or any data
641	<	* it operates on are not necessarily consistently observable by
642	<	* any thread other than the one executing it unless preceded by a
643	<	* call to {@link #join} or related methods, or a call to {@link
644	<	* #isDone} returning {@code true}.
645	<	*
646	<	* <p>This method may be invoked only from within {@code
647	<	* 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}.
637	>	* Arranges to asynchronously execute this task in the pool the
638	>	* current task is running in, if applicable, or using the {@link
639	>	* ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}.  While
640	>	* it is not necessarily enforced, it is a usage error to fork a
641	>	* task more than once unless it has completed and been
642	>	* reinitialized.  Subsequent modifications to the state of this
643	>	* task or any data it operates on are not necessarily
644	>	* consistently observable by any thread other than the one
645	>	* executing it unless preceded by a call to {@link #join} or
646	>	* related methods, or a call to {@link #isDone} returning {@code
647	>	* true}.
648		*
649		* @return {@code this}, to simplify usage
650		*/
651		public final ForkJoinTask<V> fork() {
652	<	((ForkJoinWorkerThread) Thread.currentThread())
653	<	.pushTask(this);
652	>	Thread t;
653	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
654	>	((ForkJoinWorkerThread)t).workQueue.push(this);
655	>	else
656	>	ForkJoinPool.common.externalPush(this);
657		return this;
658		}
659
#	Line 607 | Line 669 | public abstract class ForkJoinTask<V> im
669		* @return the computed result
670		*/
671		public final V join() {
672	<	if (doJoin() != NORMAL)
673	<	return reportResult();
674	<	else
675	<	return getRawResult();
672	>	int s;
673	>	if ((s = doJoin() & DONE_MASK) != NORMAL)
674	>	reportException(s);
675	>	return getRawResult();
676		}
677
678		/**
#	Line 622 | Line 684 | public abstract class ForkJoinTask<V> im
684		* @return the computed result
685		*/
686		public final V invoke() {
687	<	if (doInvoke() != NORMAL)
688	<	return reportResult();
689	<	else
690	<	return getRawResult();
687	>	int s;
688	>	if ((s = doInvoke() & DONE_MASK) != NORMAL)
689	>	reportException(s);
690	>	return getRawResult();
691		}
692
693		/**
#	Line 641 | Line 703 | public abstract class ForkJoinTask<V> im
703		* cancelled, completed normally or exceptionally, or left
704		* unprocessed.
705		*
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	–	*
706		* @param t1 the first task
707		* @param t2 the second task
708		* @throws NullPointerException if any task is null
709		*/
710		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
711	+	int s1, s2;
712		t2.fork();
713	<	t1.invoke();
714	<	t2.join();
713	>	if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL)
714	>	t1.reportException(s1);
715	>	if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
716	>	t2.reportException(s2);
717		}
718
719		/**
#	Line 669 | Line 728 | public abstract class ForkJoinTask<V> im
728		* related methods to check if they have been cancelled, completed
729		* normally or exceptionally, or left unprocessed.
730		*
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	–	*
731		* @param tasks the tasks
732		* @throws NullPointerException if any task is null
733		*/
#	Line 697 | Line 750 | public abstract class ForkJoinTask<V> im
750		if (t != null) {
751		if (ex != null)
752		t.cancel(false);
753	<	else if (t.doJoin() < NORMAL && ex == null)
753	>	else if (t.doJoin() < NORMAL)
754		ex = t.getException();
755		}
756		}
757		if (ex != null)
758	<	UNSAFE.throwException(ex);
758	>	rethrow(ex);
759		}
760
761		/**
#	Line 718 | Line 771 | public abstract class ForkJoinTask<V> im
771		* cancelled, completed normally or exceptionally, or left
772		* unprocessed.
773		*
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	–	*
774		* @param tasks the collection of tasks
775		* @return the tasks argument, to simplify usage
776		* @throws NullPointerException if tasks or any element are null
#	Line 754 | Line 801 | public abstract class ForkJoinTask<V> im
801		if (t != null) {
802		if (ex != null)
803		t.cancel(false);
804	<	else if (t.doJoin() < NORMAL && ex == null)
804	>	else if (t.doJoin() < NORMAL)
805		ex = t.getException();
806		}
807		}
808		if (ex != null)
809	<	UNSAFE.throwException(ex);
809	>	rethrow(ex);
810		return tasks;
811		}
812
#	Line 791 | Line 838 | public abstract class ForkJoinTask<V> im
838		* @return {@code true} if this task is now cancelled
839		*/
840		public boolean cancel(boolean mayInterruptIfRunning) {
841	<	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	<	}
841	>	return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
842		}
843
844		public final boolean isDone() {
#	Line 812 | Line 846 | public abstract class ForkJoinTask<V> im
846		}
847
848		public final boolean isCancelled() {
849	<	return status == CANCELLED;
849	>	return (status & DONE_MASK) == CANCELLED;
850		}
851
852		/**
#	Line 832 | Line 866 | public abstract class ForkJoinTask<V> im
866		* exception and was not cancelled
867		*/
868		public final boolean isCompletedNormally() {
869	<	return status == NORMAL;
869	>	return (status & DONE_MASK) == NORMAL;
870		}
871
872		/**
#	Line 843 | Line 877 | public abstract class ForkJoinTask<V> im
877		* @return the exception, or {@code null} if none
878		*/
879		public final Throwable getException() {
880	<	int s = status;
880	>	int s = status & DONE_MASK;
881		return ((s >= NORMAL)    ? null :
882		(s == CANCELLED) ? new CancellationException() :
883		getThrowableException());
#	Line 893 | Line 927 | public abstract class ForkJoinTask<V> im
927		}
928
929		/**
930	+	* Completes this task normally without setting a value. The most
931	+	* recent value established by {@link #setRawResult} (or {@code
932	+	* null} by default) will be returned as the result of subsequent
933	+	* invocations of {@code join} and related operations.
934	+	*
935	+	* @since 1.8
936	+	*/
937	+	public final void quietlyComplete() {
938	+	setCompletion(NORMAL);
939	+	}
940	+
941	+	/**
942		* Waits if necessary for the computation to complete, and then
943		* retrieves its result.
944		*
#	Line 905 | Line 951 | public abstract class ForkJoinTask<V> im
951		*/
952		public final V get() throws InterruptedException, ExecutionException {
953		int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
954	<	doJoin() : externalInterruptibleAwaitDone(0L);
954	>	doJoin() : externalInterruptibleAwaitDone();
955		Throwable ex;
956	<	if (s == CANCELLED)
956	>	if ((s &= DONE_MASK) == CANCELLED)
957		throw new CancellationException();
958		if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
959		throw new ExecutionException(ex);
#	Line 930 | Line 976 | public abstract class ForkJoinTask<V> im
976		*/
977		public final V get(long timeout, TimeUnit unit)
978		throws InterruptedException, ExecutionException, TimeoutException {
979	<	Thread t = Thread.currentThread();
980	<	if (t instanceof ForkJoinWorkerThread) {
981	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
982	<	long nanos = unit.toNanos(timeout);
983	<	if (status >= 0) {
984	<	boolean completed = false;
985	<	if (w.unpushTask(this)) {
986	<	try {
987	<	completed = exec();
988	<	} catch (Throwable rex) {
989	<	setExceptionalCompletion(rex);
979	>	if (Thread.interrupted())
980	>	throw new InterruptedException();
981	>	// Messy in part because we measure in nanosecs, but wait in millisecs
982	>	int s; long ms;
983	>	long ns = unit.toNanos(timeout);
984	>	if ((s = status) >= 0 && ns > 0L) {
985	>	long deadline = System.nanoTime() + ns;
986	>	ForkJoinPool p = null;
987	>	ForkJoinPool.WorkQueue w = null;
988	>	Thread t = Thread.currentThread();
989	>	if (t instanceof ForkJoinWorkerThread) {
990	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
991	>	p = wt.pool;
992	>	w = wt.workQueue;
993	>	p.helpJoinOnce(w, this); // no retries on failure
994	>	}
995	>	else
996	>	ForkJoinPool.externalHelpJoin(this);
997	>	boolean canBlock = false;
998	>	boolean interrupted = false;
999	>	try {
1000	>	while ((s = status) >= 0) {
1001	>	if (w != null && w.qlock < 0)
1002	>	cancelIgnoringExceptions(this);
1003	>	else if (!canBlock) {
1004	>	if (p == null || p.tryCompensate())
1005	>	canBlock = true;
1006	>	}
1007	>	else {
1008	>	if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
1009	>	U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
1010	>	synchronized (this) {
1011	>	if (status >= 0) {
1012	>	try {
1013	>	wait(ms);
1014	>	} catch (InterruptedException ie) {
1015	>	if (p == null)
1016	>	interrupted = true;
1017	>	}
1018	>	}
1019	>	else
1020	>	notifyAll();
1021	>	}
1022	>	}
1023	>	if ((s = status) < 0 || interrupted ||
1024	>	(ns = deadline - System.nanoTime()) <= 0L)
1025	>	break;
1026		}
1027		}
1028	<	if (completed)
1029	<	setCompletion(NORMAL);
1030	<	else if (status >= 0 && nanos > 0)
949	<	w.pool.timedAwaitJoin(this, nanos);
1028	>	} finally {
1029	>	if (p != null && canBlock)
1030	>	p.incrementActiveCount();
1031		}
1032	+	if (interrupted)
1033	+	throw new InterruptedException();
1034		}
1035	<	else {
953	<	long millis = unit.toMillis(timeout);
954	<	if (millis > 0)
955	<	externalInterruptibleAwaitDone(millis);
956	<	}
957	<	int s = status;
958	<	if (s != NORMAL) {
1035	>	if ((s &= DONE_MASK) != NORMAL) {
1036		Throwable ex;
1037		if (s == CANCELLED)
1038		throw new CancellationException();
#	Line 992 | Line 1069 | public abstract class ForkJoinTask<V> im
1069		* be of use in designs in which many tasks are forked, but none
1070		* are explicitly joined, instead executing them until all are
1071		* 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}.
1072		*/
1073		public static void helpQuiesce() {
1074	<	((ForkJoinWorkerThread) Thread.currentThread())
1075	<	.helpQuiescePool();
1074	>	Thread t;
1075	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
1076	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1077	>	wt.pool.helpQuiescePool(wt.workQueue);
1078	>	}
1079	>	else
1080	>	ForkJoinPool.quiesceCommonPool();
1081		}
1082
1083		/**
#	Line 1021 | Line 1097 | public abstract class ForkJoinTask<V> im
1097		* setRawResult(null)}.
1098		*/
1099		public void reinitialize() {
1100	<	if (status == EXCEPTIONAL)
1100	>	if ((status & DONE_MASK) == EXCEPTIONAL)
1101		clearExceptionalCompletion();
1102		else
1103		status = 0;
#	Line 1054 | Line 1130 | public abstract class ForkJoinTask<V> im
1130
1131		/**
1132		* Tries to unschedule this task for execution. This method will
1133	<	* typically succeed if this task is the most recently forked task
1134	<	* by the current thread, and has not commenced executing in
1135	<	* another thread.  This method may be useful when arranging
1136	<	* alternative local processing of tasks that could have been, but
1137	<	* 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}.
1133	>	* typically (but is not guaranteed to) succeed if this task is
1134	>	* the most recently forked task by the current thread, and has
1135	>	* not commenced executing in another thread.  This method may be
1136	>	* useful when arranging alternative local processing of tasks
1137	>	* that could have been, but were not, stolen.
1138		*
1139		* @return {@code true} if unforked
1140		*/
1141		public boolean tryUnfork() {
1142	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1143	<	.unpushTask(this);
1142	>	Thread t;
1143	>	return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1144	>	((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
1145	>	ForkJoinPool.tryExternalUnpush(this));
1146		}
1147
1148		/**
#	Line 1079 | Line 1151 | public abstract class ForkJoinTask<V> im
1151		* value may be useful for heuristic decisions about whether to
1152		* fork other tasks.
1153		*
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	–	*
1154		* @return the number of tasks
1155		*/
1156		public static int getQueuedTaskCount() {
1157	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1158	<	.getQueueSize();
1157	>	Thread t; ForkJoinPool.WorkQueue q;
1158	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1159	>	q = ((ForkJoinWorkerThread)t).workQueue;
1160	>	else
1161	>	q = ForkJoinPool.commonSubmitterQueue();
1162	>	return (q == null) ? 0 : q.queueSize();
1163		}
1164
1165		/**
1166		* Returns an estimate of how many more locally queued tasks are
1167		* held by the current worker thread than there are other worker
1168	<	* threads that might steal them.  This value may be useful for
1168	>	* threads that might steal them, or zero if this thread is not
1169	>	* operating in a ForkJoinPool. This value may be useful for
1170		* heuristic decisions about whether to fork other tasks. In many
1171		* usages of ForkJoinTasks, at steady state, each worker should
1172		* aim to maintain a small constant surplus (for example, 3) of
1173		* tasks, and to process computations locally if this threshold is
1174		* exceeded.
1175		*
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	–	*
1176		* @return the surplus number of tasks, which may be negative
1177		*/
1178		public static int getSurplusQueuedTaskCount() {
1179	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1115	<	.getEstimatedSurplusTaskCount();
1179	>	return ForkJoinPool.getSurplusQueuedTaskCount();
1180		}
1181
1182		// Extension methods
#	Line 1138 | Line 1202 | public abstract class ForkJoinTask<V> im
1202		protected abstract void setRawResult(V value);
1203
1204		/**
1205	<	* Immediately performs the base action of this task.  This method
1206	<	* is designed to support extensions, and should not in general be
1207	<	* called otherwise. The return value controls whether this task
1208	<	* is considered to be done normally. It may return false in
1205	>	* Immediately performs the base action of this task and returns
1206	>	* true if, upon return from this method, this task is guaranteed
1207	>	* to have completed normally. This method may return false
1208	>	* otherwise, to indicate that this task is not necessarily
1209	>	* complete (or is not known to be complete), for example in
1210		* asynchronous actions that require explicit invocations of
1211	<	* {@link #complete} to become joinable. It may also throw an
1212	<	* (unchecked) exception to indicate abnormal exit.
1211	>	* completion methods. This method may also throw an (unchecked)
1212	>	* exception to indicate abnormal exit. This method is designed to
1213	>	* support extensions, and should not in general be called
1214	>	* otherwise.
1215		*
1216	<	* @return {@code true} if completed normally
1216	>	* @return {@code true} if this task is known to have completed normally
1217		*/
1218		protected abstract boolean exec();
1219
#	Line 1160 | Line 1227 | public abstract class ForkJoinTask<V> im
1227		* primarily to support extensions, and is unlikely to be useful
1228		* otherwise.
1229		*
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	–	*
1230		* @return the next task, or {@code null} if none are available
1231		*/
1232		protected static ForkJoinTask<?> peekNextLocalTask() {
1233	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1234	<	.peekTask();
1233	>	Thread t; ForkJoinPool.WorkQueue q;
1234	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1235	>	q = ((ForkJoinWorkerThread)t).workQueue;
1236	>	else
1237	>	q = ForkJoinPool.commonSubmitterQueue();
1238	>	return (q == null) ? null : q.peek();
1239		}
1240
1241		/**
1242		* Unschedules and returns, without executing, the next task
1243	<	* queued by the current thread but not yet executed.  This method
1244	<	* is designed primarily to support extensions, and is unlikely to
1245	<	* be useful otherwise.
1246	<	*
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}.
1243	>	* queued by the current thread but not yet executed, if the
1244	>	* current thread is operating in a ForkJoinPool.  This method is
1245	>	* designed primarily to support extensions, and is unlikely to be
1246	>	* useful otherwise.
1247		*
1248		* @return the next task, or {@code null} if none are available
1249		*/
1250		protected static ForkJoinTask<?> pollNextLocalTask() {
1251	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1252	<	.pollLocalTask();
1251	>	Thread t;
1252	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1253	>	((ForkJoinWorkerThread)t).workQueue.nextLocalTask() :
1254	>	null;
1255		}
1256
1257		/**
1258	<	* Unschedules and returns, without executing, the next task
1258	>	* If the current thread is operating in a ForkJoinPool,
1259	>	* unschedules and returns, without executing, the next task
1260		* queued by the current thread but not yet executed, if one is
1261		* available, or if not available, a task that was forked by some
1262		* other thread, if available. Availability may be transient, so a
1263	<	* {@code null} result does not necessarily imply quiescence
1264	<	* of the pool this task is operating in.  This method is designed
1263	>	* {@code null} result does not necessarily imply quiescence of
1264	>	* the pool this task is operating in.  This method is designed
1265		* primarily to support extensions, and is unlikely to be useful
1266		* otherwise.
1267		*
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	–	*
1268		* @return a task, or {@code null} if none are available
1269		*/
1270		protected static ForkJoinTask<?> pollTask() {
1271	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1272	<	.pollTask();
1271	>	Thread t; ForkJoinWorkerThread wt;
1272	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1273	>	(wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) :
1274	>	null;
1275	>	}
1276	>
1277	>	// tag operations
1278	>
1279	>	/**
1280	>	* Returns the tag for this task.
1281	>	*
1282	>	* @return the tag for this task
1283	>	* @since 1.8
1284	>	*/
1285	>	public final short getForkJoinTaskTag() {
1286	>	return (short)status;
1287	>	}
1288	>
1289	>	/**
1290	>	* Atomically sets the tag value for this task.
1291	>	*
1292	>	* @param tag the tag value
1293	>	* @return the previous value of the tag
1294	>	* @since 1.8
1295	>	*/
1296	>	public final short setForkJoinTaskTag(short tag) {
1297	>	for (int s;;) {
1298	>	if (U.compareAndSwapInt(this, STATUS, s = status,
1299	>	(s & ~SMASK) | (tag & SMASK)))
1300	>	return (short)s;
1301	>	}
1302	>	}
1303	>
1304	>	/**
1305	>	* Atomically conditionally sets the tag value for this task.
1306	>	* Among other applications, tags can be used as visit markers
1307	>	* in tasks operating on graphs, as in methods that check: {@code
1308	>	* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1309	>	* before processing, otherwise exiting because the node has
1310	>	* already been visited.
1311	>	*
1312	>	* @param e the expected tag value
1313	>	* @param tag the new tag value
1314	>	* @return true if successful; i.e., the current value was
1315	>	* equal to e and is now tag.
1316	>	* @since 1.8
1317	>	*/
1318	>	public final boolean compareAndSetForkJoinTaskTag(short e, short tag) {
1319	>	for (int s;;) {
1320	>	if ((short)(s = status) != e)
1321	>	return false;
1322	>	if (U.compareAndSwapInt(this, STATUS, s,
1323	>	(s & ~SMASK) | (tag & SMASK)))
1324	>	return true;
1325	>	}
1326		}
1327
1328		/**
#	Line 1223 | Line 1333 | public abstract class ForkJoinTask<V> im
1333		static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1334		implements RunnableFuture<T> {
1335		final Runnable runnable;
1226	–	final T resultOnCompletion;
1336		T result;
1337		AdaptedRunnable(Runnable runnable, T result) {
1338		if (runnable == null) throw new NullPointerException();
1339		this.runnable = runnable;
1340	<	this.resultOnCompletion = result;
1340	>	this.result = result; // OK to set this even before completion
1341		}
1342	<	public T getRawResult() { return result; }
1343	<	public void setRawResult(T v) { result = v; }
1344	<	public boolean exec() {
1345	<	runnable.run();
1346	<	result = resultOnCompletion;
1347	<	return true;
1342	>	public final T getRawResult() { return result; }
1343	>	public final void setRawResult(T v) { result = v; }
1344	>	public final boolean exec() { runnable.run(); return true; }
1345	>	public final void run() { invoke(); }
1346	>	private static final long serialVersionUID = 5232453952276885070L;
1347	>	}
1348	>
1349	>	/**
1350	>	* Adaptor for Runnables without results
1351	>	*/
1352	>	static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1353	>	implements RunnableFuture<Void> {
1354	>	final Runnable runnable;
1355	>	AdaptedRunnableAction(Runnable runnable) {
1356	>	if (runnable == null) throw new NullPointerException();
1357	>	this.runnable = runnable;
1358		}
1359	<	public void run() { invoke(); }
1359	>	public final Void getRawResult() { return null; }
1360	>	public final void setRawResult(Void v) { }
1361	>	public final boolean exec() { runnable.run(); return true; }
1362	>	public final void run() { invoke(); }
1363		private static final long serialVersionUID = 5232453952276885070L;
1364		}
1365
#	Line 1252 | Line 1374 | public abstract class ForkJoinTask<V> im
1374		if (callable == null) throw new NullPointerException();
1375		this.callable = callable;
1376		}
1377	<	public T getRawResult() { return result; }
1378	<	public void setRawResult(T v) { result = v; }
1379	<	public boolean exec() {
1377	>	public final T getRawResult() { return result; }
1378	>	public final void setRawResult(T v) { result = v; }
1379	>	public final boolean exec() {
1380		try {
1381		result = callable.call();
1382		return true;
#	Line 1266 | Line 1388 | public abstract class ForkJoinTask<V> im
1388		throw new RuntimeException(ex);
1389		}
1390		}
1391	<	public void run() { invoke(); }
1391	>	public final void run() { invoke(); }
1392		private static final long serialVersionUID = 2838392045355241008L;
1393		}
1394
#	Line 1279 | Line 1401 | public abstract class ForkJoinTask<V> im
1401		* @return the task
1402		*/
1403		public static ForkJoinTask<?> adapt(Runnable runnable) {
1404	<	return new AdaptedRunnable<Void>(runnable, null);
1404	>	return new AdaptedRunnableAction(runnable);
1405		}
1406
1407		/**
#	Line 1313 | Line 1435 | public abstract class ForkJoinTask<V> im
1435		private static final long serialVersionUID = -7721805057305804111L;
1436
1437		/**
1438	<	* Saves the state to a stream (that is, serializes it).
1438	>	* Saves this task to a stream (that is, serializes it).
1439		*
1440		* @serialData the current run status and the exception thrown
1441		* during execution, or {@code null} if none
1320	–	* @param s the stream
1442		*/
1443		private void writeObject(java.io.ObjectOutputStream s)
1444		throws java.io.IOException {
#	Line 1326 | Line 1447 | public abstract class ForkJoinTask<V> im
1447		}
1448
1449		/**
1450	<	* Reconstitutes the instance from a stream (that is, deserializes it).
1330	<	*
1331	<	* @param s the stream
1450	>	* Reconstitutes this task from a stream (that is, deserializes it).
1451		*/
1452		private void readObject(java.io.ObjectInputStream s)
1453		throws java.io.IOException, ClassNotFoundException {
#	Line 1339 | Line 1458 | public abstract class ForkJoinTask<V> im
1458		}
1459
1460		// Unsafe mechanics
1461	<	private static final sun.misc.Unsafe UNSAFE;
1462	<	private static final long statusOffset;
1461	>	private static final sun.misc.Unsafe U;
1462	>	private static final long STATUS;
1463	>
1464		static {
1465		exceptionTableLock = new ReentrantLock();
1466		exceptionTableRefQueue = new ReferenceQueue<Object>();
1467		exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1468		try {
1469	<	UNSAFE = getUnsafe();
1470	<	statusOffset = UNSAFE.objectFieldOffset
1471	<	(ForkJoinTask.class.getDeclaredField("status"));
1469	>	U = getUnsafe();
1470	>	Class<?> k = ForkJoinTask.class;
1471	>	STATUS = U.objectFieldOffset
1472	>	(k.getDeclaredField("status"));
1473		} catch (Exception e) {
1474		throw new Error(e);
1475		}
#	Line 1364 | Line 1485 | public abstract class ForkJoinTask<V> im
1485		private static sun.misc.Unsafe getUnsafe() {
1486		try {
1487		return sun.misc.Unsafe.getUnsafe();
1488	<	} catch (SecurityException se) {
1489	<	try {
1490	<	return java.security.AccessController.doPrivileged
1491	<	(new java.security
1492	<	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1493	<	public sun.misc.Unsafe run() throws Exception {
1494	<	java.lang.reflect.Field f = sun.misc
1495	<	.Unsafe.class.getDeclaredField("theUnsafe");
1496	<	f.setAccessible(true);
1497	<	return (sun.misc.Unsafe) f.get(null);
1498	<	}});
1499	<	} catch (java.security.PrivilegedActionException e) {
1500	<	throw new RuntimeException("Could not initialize intrinsics",
1501	<	e.getCause());
1502	<	}
1488	>	} catch (SecurityException tryReflectionInstead) {}
1489	>	try {
1490	>	return java.security.AccessController.doPrivileged
1491	>	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1492	>	public sun.misc.Unsafe run() throws Exception {
1493	>	Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
1494	>	for (java.lang.reflect.Field f : k.getDeclaredFields()) {
1495	>	f.setAccessible(true);
1496	>	Object x = f.get(null);
1497	>	if (k.isInstance(x))
1498	>	return k.cast(x);
1499	>	}
1500	>	throw new NoSuchFieldError("the Unsafe");
1501	>	}});
1502	>	} catch (java.security.PrivilegedActionException e) {
1503	>	throw new RuntimeException("Could not initialize intrinsics",
1504	>	e.getCause());
1505		}
1506		}
1507		}

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