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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.49 by dl, Wed Jul 7 19:52:31 2010 UTC vs.
Revision 1.86 by dl, Mon Feb 20 18:20:06 2012 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3		* Expert Group and released to the public domain, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		*/
6
7		package jsr166y;
8	–
9	–	import java.util.concurrent.*;
10	–
8		import java.io.Serializable;
9		import java.util.Collection;
13	–	import java.util.Collections;
10		import java.util.List;
11		import java.util.RandomAccess;
12	<	import java.util.Map;
13	<	import java.util.WeakHashMap;
12	>	import java.lang.ref.WeakReference;
13	>	import java.lang.ref.ReferenceQueue;
14	>	import java.util.concurrent.Callable;
15	>	import java.util.concurrent.CancellationException;
16	>	import java.util.concurrent.ExecutionException;
17	>	import java.util.concurrent.Future;
18	>	import java.util.concurrent.RejectedExecutionException;
19	>	import java.util.concurrent.RunnableFuture;
20	>	import java.util.concurrent.TimeUnit;
21	>	import java.util.concurrent.TimeoutException;
22	>	import java.util.concurrent.locks.ReentrantLock;
23	>	import java.lang.reflect.Constructor;
24
25		/**
26		* Abstract base class for tasks that run within a {@link ForkJoinPool}.
#	Line 28 | Line 34 | import java.util.WeakHashMap;
34		* start other subtasks.  As indicated by the name of this class,
35		* many programs using {@code ForkJoinTask} employ only methods
36		* {@link #fork} and {@link #join}, or derivatives such as {@link
37	<	* #invokeAll}.  However, this class also provides a number of other
38	<	* methods that can come into play in advanced usages, as well as
39	<	* extension mechanics that allow support of new forms of fork/join
40	<	* processing.
37	>	* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
38	>	* provides a number of other methods that can come into play in
39	>	* advanced usages, as well as extension mechanics that allow
40	>	* support of new forms of fork/join processing.
41		*
42		* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
43		* The efficiency of {@code ForkJoinTask}s stems from a set of
44		* restrictions (that are only partially statically enforceable)
45	<	* reflecting their intended use as computational tasks calculating
46	<	* pure functions or operating on purely isolated objects.  The
47	<	* primary coordination mechanisms are {@link #fork}, that arranges
45	>	* reflecting their main use as computational tasks calculating pure
46	>	* functions or operating on purely isolated objects.  The primary
47	>	* coordination mechanisms are {@link #fork}, that arranges
48		* asynchronous execution, and {@link #join}, that doesn't proceed
49		* until the task's result has been computed.  Computations should
50	<	* avoid {@code synchronized} methods or blocks, and should minimize
51	<	* other blocking synchronization apart from joining other tasks or
52	<	* using synchronizers such as Phasers that are advertised to
53	<	* cooperate with fork/join scheduling. Tasks should also not perform
54	<	* blocking IO, and should ideally access variables that are
55	<	* completely independent of those accessed by other running
56	<	* tasks. Minor breaches of these restrictions, for example using
57	<	* shared output streams, may be tolerable in practice, but frequent
58	<	* use may result in poor performance, and the potential to
59	<	* indefinitely stall if the number of threads not waiting for IO or
60	<	* other external synchronization becomes exhausted. This usage
61	<	* restriction is in part enforced by not permitting checked
62	<	* exceptions such as {@code IOExceptions} to be thrown. However,
63	<	* computations may still encounter unchecked exceptions, that are
64	<	* rethrown to callers attempting to join them. These exceptions may
65	<	* additionally include {@link RejectedExecutionException} stemming
66	<	* from internal resource exhaustion, such as failure to allocate
67	<	* internal task queues.
50	>	* ideally avoid {@code synchronized} methods or blocks, and should
51	>	* minimize other blocking synchronization apart from joining other
52	>	* tasks or using synchronizers such as Phasers that are advertised to
53	>	* cooperate with fork/join scheduling. Subdividable tasks should also
54	>	* not perform blocking IO, and should ideally access variables that
55	>	* are completely independent of those accessed by other running
56	>	* tasks. These guidelines are loosely enforced by not permitting
57	>	* checked exceptions such as {@code IOExceptions} to be
58	>	* thrown. However, computations may still encounter unchecked
59	>	* exceptions, that are rethrown to callers attempting to join
60	>	* them. These exceptions may additionally include {@link
61	>	* RejectedExecutionException} stemming from internal resource
62	>	* exhaustion, such as failure to allocate internal task
63	>	* queues. Rethrown exceptions behave in the same way as regular
64	>	* exceptions, but, when possible, contain stack traces (as displayed
65	>	* for example using {@code ex.printStackTrace()}) of both the thread
66	>	* that initiated the computation as well as the thread actually
67	>	* encountering the exception; minimally only the latter.
68	>	*
69	>	* <p>It is possible to define and use ForkJoinTasks that may block,
70	>	* but doing do requires three further considerations: (1) Completion
71	>	* of few if any <em>other</em> tasks should be dependent on a task
72	>	* that blocks on external synchronization or IO. Event-style async
73	>	* tasks that are never joined often fall into this category.  (2) To
74	>	* minimize resource impact, tasks should be small; ideally performing
75	>	* only the (possibly) blocking action. (3) Unless the {@link
76	>	* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
77	>	* blocked tasks is known to be less than the pool's {@link
78	>	* ForkJoinPool#getParallelism} level, the pool cannot guarantee that
79	>	* enough threads will be available to ensure progress or good
80	>	* performance.
81		*
82		* <p>The primary method for awaiting completion and extracting
83		* results of a task is {@link #join}, but there are several variants:
#	Line 74 | Line 93 | import java.util.WeakHashMap;
93		* performs the most common form of parallel invocation: forking a set
94		* of tasks and joining them all.
95		*
96	+	* <p>In the most typical usages, a fork-join pair act like a call
97	+	* (fork) and return (join) from a parallel recursive function. As is
98	+	* the case with other forms of recursive calls, returns (joins)
99	+	* should be performed innermost-first. For example, {@code a.fork();
100	+	* b.fork(); b.join(); a.join();} is likely to be substantially more
101	+	* efficient than joining {@code a} before {@code b}.
102	+	*
103		* <p>The execution status of tasks may be queried at several levels
104		* of detail: {@link #isDone} is true if a task completed in any way
105		* (including the case where a task was cancelled without executing);
#	Line 100 | Line 126 | import java.util.WeakHashMap;
126		* ForkJoinTasks (as may be determined using method {@link
127		* #inForkJoinPool}).  Attempts to invoke them in other contexts
128		* result in exceptions or errors, possibly including
129	<	* ClassCastException.
129	>	* {@code ClassCastException}.
130	>	*
131	>	* <p>Method {@link #join} and its variants are appropriate for use
132	>	* only when completion dependencies are acyclic; that is, the
133	>	* parallel computation can be described as a directed acyclic graph
134	>	* (DAG). Otherwise, executions may encounter a form of deadlock as
135	>	* tasks cyclically wait for each other.  However, this framework
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. To support such usages a
140	>	* ForkJoinTask may be atomically <em>marked</em> using {@link
141	>	* #markForkJoinTask} and checked for marking using {@link
142	>	* #isMarkedForkJoinTask}. The ForkJoinTask implementation does not
143	>	* use these {@code protected} methods or marks for any purpose, but
144	>	* they may be of use in the construction of specialized subclasses.
145	>	* For example, parallel graph traversals can use the supplied methods
146	>	* to avoid revisiting nodes/tasks that have already been processed.
147	>	* Also, completion based designs can use them to record that one
148	>	* subtask has completed. (Method names for marking are bulky in part
149	>	* to encourage definition of methods that reflect their usage
150	>	* patterns.)
151		*
152		* <p>Most base support methods are {@code final}, to prevent
153		* overriding of implementations that are intrinsically tied to the
#	Line 116 | Line 163 | import java.util.WeakHashMap;
163		* computation. Large tasks should be split into smaller subtasks,
164		* usually via recursive decomposition. As a very rough rule of thumb,
165		* a task should perform more than 100 and less than 10000 basic
166	<	* computational steps. If tasks are too big, then parallelism cannot
167	<	* improve throughput. If too small, then memory and internal task
168	<	* maintenance overhead may overwhelm processing.
166	>	* computational steps, and should avoid indefinite looping. If tasks
167	>	* are too big, then parallelism cannot improve throughput. If too
168	>	* small, then memory and internal task maintenance overhead may
169	>	* overwhelm processing.
170		*
171		* <p>This class provides {@code adapt} methods for {@link Runnable}
172		* and {@link Callable}, that may be of use when mixing execution of
#	Line 139 | Line 187 | public abstract class ForkJoinTask<V> im
187		* See the internal documentation of class ForkJoinPool for a
188		* general implementation overview.  ForkJoinTasks are mainly
189		* responsible for maintaining their "status" field amidst relays
190	<	* to methods in ForkJoinWorkerThread and ForkJoinPool. The
191	<	* methods of this class are more-or-less layered into (1) basic
192	<	* status maintenance (2) execution and awaiting completion (3)
193	<	* user-level methods that additionally report results. This is
194	<	* sometimes hard to see because this file orders exported methods
195	<	* in a way that flows well in javadocs.
196	<	*/
197	<
150	<	/**
151	<	* Run control status bits packed into a single int to minimize
152	<	* footprint and to ensure atomicity (via CAS).  Status is
153	<	* initially zero, and takes on nonnegative values until
154	<	* completed, upon which status holds value COMPLETED. CANCELLED,
155	<	* or EXCEPTIONAL. Tasks undergoing blocking waits by other
156	<	* threads have the SIGNAL bit set.  Completion of a stolen task
157	<	* with SIGNAL set awakens any waiters via notifyAll. Even though
158	<	* suboptimal for some purposes, we use basic builtin wait/notify
159	<	* to take advantage of "monitor inflation" in JVMs that we would
160	<	* otherwise need to emulate to avoid adding further per-task
161	<	* bookkeeping overhead.  We want these monitors to be "fat",
162	<	* i.e., not use biasing or thin-lock techniques, so use some odd
163	<	* coding idioms that tend to avoid them.
190	>	* to methods in ForkJoinWorkerThread and ForkJoinPool.
191	>	*
192	>	* The methods of this class are more-or-less layered into
193	>	* (1) basic status maintenance
194	>	* (2) execution and awaiting completion
195	>	* (3) user-level methods that additionally report results.
196	>	* This is sometimes hard to see because this file orders exported
197	>	* methods in a way that flows well in javadocs.
198		*/
165	–	volatile int status; // accessed directly by pool and workers
199
200	<	private static final int NORMAL      = -1;
201	<	private static final int CANCELLED   = -2;
202	<	private static final int EXCEPTIONAL = -3;
203	<	private static final int SIGNAL      =  1;
204	<
205	<	/**
206	<	* Table of exceptions thrown by tasks, to enable reporting by
207	<	* callers. Because exceptions are rare, we don't directly keep
208	<	* them with task objects, but instead use a weak ref table.  Note
209	<	* that cancellation exceptions don't appear in the table, but are
210	<	* instead recorded as status values.
211	<	* TODO: Use ConcurrentReferenceHashMap
200	>	/*
201	>	* The status field holds run control status bits packed into a
202	>	* single int to minimize footprint and to ensure atomicity (via
203	>	* CAS).  Status is initially zero, and takes on nonnegative
204	>	* values until completed, upon which status (anded with
205	>	* DONE_MASK) holds value NORMAL, CANCELLED, or EXCEPTIONAL. Tasks
206	>	* undergoing blocking waits by other threads have the SIGNAL bit
207	>	* set.  Completion of a stolen task with SIGNAL set awakens any
208	>	* waiters via notifyAll. Even though suboptimal for some
209	>	* purposes, we use basic builtin wait/notify to take advantage of
210	>	* "monitor inflation" in JVMs that we would otherwise need to
211	>	* emulate to avoid adding further per-task bookkeeping overhead.
212	>	* We want these monitors to be "fat", i.e., not use biasing or
213	>	* thin-lock techniques, so use some odd coding idioms that tend
214	>	* to avoid them, mainly by arranging that every synchronized
215	>	* block performs a wait, notifyAll or both.
216		*/
180	–	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
181	–	Collections.synchronizedMap
182	–	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
217
218	<	// Maintaining completion status
218	>	/** The run status of this task */
219	>	volatile int status; // accessed directly by pool and workers
220	>	static final int DONE_MASK   = 0xf0000000;  // mask out non-completion bits
221	>	static final int NORMAL      = 0xf0000000;  // must be negative
222	>	static final int CANCELLED   = 0xc0000000;  // must be < NORMAL
223	>	static final int EXCEPTIONAL = 0x80000000;  // must be < CANCELLED
224	>	static final int SIGNAL      = 0x00000001;
225	>	static final int MARKED      = 0x00000002;
226
227		/**
228	<	* Marks completion and wakes up threads waiting to join this task,
229	<	* also clearing signal request bits.
228	>	* Marks completion and wakes up threads waiting to join this
229	>	* task. A specialization for NORMAL completion is in method
230	>	* doExec.
231		*
232		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
233	<	* @return status on exit
233	>	* @return completion status on exit
234		*/
235		private int setCompletion(int completion) {
236	<	int s;
237	<	while ((s = status) >= 0) {
238	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
239	<	if (s == SIGNAL)
236	>	for (int s;;) {
237	>	if ((s = status) < 0)
238	>	return s;
239	>	if (U.compareAndSwapInt(this, STATUS, s, s | completion)) {
240	>	if ((s & SIGNAL) != 0)
241		synchronized (this) { notifyAll(); }
242		return completion;
243		}
244		}
245	+	}
246	+
247	+	/**
248	+	* Primary execution method for stolen tasks. Unless done, calls
249	+	* exec and records status if completed, but doesn't wait for
250	+	* completion otherwise.
251	+	*
252	+	* @return status on exit from this method
253	+	*/
254	+	final int doExec() {
255	+	int s; boolean completed;
256	+	if ((s = status) >= 0) {
257	+	try {
258	+	completed = exec();
259	+	} catch (Throwable rex) {
260	+	return setExceptionalCompletion(rex);
261	+	}
262	+	while ((s = status) >= 0 && completed) {
263	+	if (U.compareAndSwapInt(this, STATUS, s, s | NORMAL)) {
264	+	if ((s & SIGNAL) != 0)
265	+	synchronized (this) { notifyAll(); }
266	+	return NORMAL;
267	+	}
268	+	}
269	+	}
270		return s;
271		}
272
273		/**
274	<	* Record exception and set exceptional completion
275	<	* @return status on exit
274	>	* Tries to set SIGNAL status. Used by ForkJoinPool. Other
275	>	* variants are directly incorporated into externalAwaitDone etc.
276	>	*
277	>	* @return true if successful
278		*/
279	<	private int setExceptionalCompletion(Throwable rex) {
280	<	exceptionMap.put(this, rex);
281	<	return setCompletion(EXCEPTIONAL);
279	>	final boolean trySetSignal() {
280	>	int s;
281	>	return U.compareAndSwapInt(this, STATUS, s = status, s | SIGNAL);
282		}
283
284		/**
285	<	* Blocks a worker thread until completion. Called only by pool.
285	>	* Blocks a non-worker-thread until completion.
286	>	* @return status upon completion
287		*/
288	<	final int internalAwaitDone() {
288	>	private int externalAwaitDone() {
289	>	boolean interrupted = false;
290		int s;
291		while ((s = status) >= 0) {
292	<	synchronized(this) {
293	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)) {
294	<	do {
292	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
293	>	synchronized (this) {
294	>	if (status >= 0) {
295		try {
296		wait();
297		} catch (InterruptedException ie) {
298	<	cancelIfTerminating();
298	>	interrupted = true;
299		}
300	<	} while ((s = status) >= 0);
301	<	break;
300	>	}
301	>	else
302	>	notifyAll();
303		}
304		}
305		}
306	+	if (interrupted)
307	+	Thread.currentThread().interrupt();
308		return s;
309		}
310
311		/**
312	<	* Blocks a non-worker-thread until completion.
238	<	* @return status on exit
312	>	* Blocks a non-worker-thread until completion or interruption.
313		*/
314	<	private int externalAwaitDone() {
314	>	private int externalInterruptibleAwaitDone() throws InterruptedException {
315		int s;
316	+	if (Thread.interrupted())
317	+	throw new InterruptedException();
318		while ((s = status) >= 0) {
319	<	synchronized(this) {
320	<	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, SIGNAL)){
321	<	boolean interrupted = false;
322	<	do {
323	<	try {
324	<	wait();
249	<	} catch (InterruptedException ie) {
250	<	interrupted = true;
251	<	}
252	<	} while ((s = status) >= 0);
253	<	if (interrupted)
254	<	Thread.currentThread().interrupt();
255	<	break;
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
331	+
332		/**
333	<	* Unless done, calls exec and records status if completed, but
334	<	* doesn't wait for completion otherwise. Primary execution method
335	<	* for ForkJoinWorkerThread.
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	<	final void tryExec() {
340	<	try {
341	<	if (status < 0 || !exec())
342	<	return;
343	<	} catch (Throwable rex) {
344	<	setExceptionalCompletion(rex);
345	<	return;
339	>	private int doJoin() {
340	>	int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
341	>	if ((s = status) >= 0) {
342	>	if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) {
343	>	if (!(w = (wt = (ForkJoinWorkerThread)t).workQueue).
344	>	tryUnpush(this) || (s = doExec()) >= 0)
345	>	s = wt.pool.awaitJoin(w, this);
346	>	}
347	>	else
348	>	s = externalAwaitDone();
349		}
350	<	setCompletion(NORMAL); // must be outside try block
350	>	return s;
351		}
352
353		/**
354	<	* If not done and this task is next in worker queue, runs it,
355	<	* else waits for it.
354	>	* Implementation for invoke, quietlyInvoke.
355	>	*
356	>	* @return status upon completion
357	>	*/
358	>	private int doInvoke() {
359	>	int s; Thread t; ForkJoinWorkerThread wt;
360	>	if ((s = doExec()) >= 0) {
361	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
362	>	s = (wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue,
363	>	this);
364	>	else
365	>	s = externalAwaitDone();
366	>	}
367	>	return s;
368	>	}
369	>
370	>	// Exception table support
371	>
372	>	/**
373	>	* Table of exceptions thrown by tasks, to enable reporting by
374	>	* callers. Because exceptions are rare, we don't directly keep
375	>	* them with task objects, but instead use a weak ref table.  Note
376	>	* that cancellation exceptions don't appear in the table, but are
377	>	* instead recorded as status values.
378	>	*
379	>	* Note: These statics are initialized below in static block.
380	>	*/
381	>	private static final ExceptionNode[] exceptionTable;
382	>	private static final ReentrantLock exceptionTableLock;
383	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
384	>
385	>	/**
386	>	* Fixed capacity for exceptionTable.
387	>	*/
388	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
389	>
390	>	/**
391	>	* Key-value nodes for exception table.  The chained hash table
392	>	* uses identity comparisons, full locking, and weak references
393	>	* for keys. The table has a fixed capacity because it only
394	>	* maintains task exceptions long enough for joiners to access
395	>	* them, so should never become very large for sustained
396	>	* periods. However, since we do not know when the last joiner
397	>	* completes, we must use weak references and expunge them. We do
398	>	* so on each operation (hence full locking). Also, some thread in
399	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
400	>	* pool becomes isQuiescent.
401	>	*/
402	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> {
403	>	final Throwable ex;
404	>	ExceptionNode next;
405	>	final long thrower;  // use id not ref to avoid weak cycles
406	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
407	>	super(task, exceptionTableRefQueue);
408	>	this.ex = ex;
409	>	this.next = next;
410	>	this.thrower = Thread.currentThread().getId();
411	>	}
412	>	}
413	>
414	>	/**
415	>	* Records exception and sets exceptional completion.
416	>	*
417		* @return status on exit
418		*/
419	<	private int doJoin() {
420	<	int stat;
421	<	if ((stat = status) < 0)
422	<	return stat;
423	<	Thread t = Thread.currentThread();
424	<	ForkJoinWorkerThread w;
425	<	if (t instanceof ForkJoinWorkerThread) {
426	<	if ((w = (ForkJoinWorkerThread) t).unpushTask(this)) {
427	<	boolean completed;
428	<	try {
429	<	completed = exec();
430	<	} catch (Throwable rex) {
295	<	return setExceptionalCompletion(rex);
419	>	private int setExceptionalCompletion(Throwable ex) {
420	>	int h = System.identityHashCode(this);
421	>	final ReentrantLock lock = exceptionTableLock;
422	>	lock.lock();
423	>	try {
424	>	expungeStaleExceptions();
425	>	ExceptionNode[] t = exceptionTable;
426	>	int i = h & (t.length - 1);
427	>	for (ExceptionNode e = t[i]; ; e = e.next) {
428	>	if (e == null) {
429	>	t[i] = new ExceptionNode(this, ex, t[i]);
430	>	break;
431		}
432	<	if (completed)
433	<	return setCompletion(NORMAL);
432	>	if (e.get() == this) // already present
433	>	break;
434		}
435	<	w.joinTask(this);
436	<	return status;
435	>	} finally {
436	>	lock.unlock();
437		}
438	<	return externalAwaitDone();
438	>	return setCompletion(EXCEPTIONAL);
439		}
440
441		/**
442	<	* Unless done, calls exec and records status if completed, or
443	<	* waits for completion otherwise.
444	<	* @return status on exit
442	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
443	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
444	>	* exceptions, but if it does anyway, we have no recourse during
445	>	* shutdown, so guard against this case.
446		*/
447	<	private int doInvoke() {
448	<	int stat;
313	<	if ((stat = status) >= 0) {
314	<	boolean completed;
447	>	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
448	>	if (t != null && t.status >= 0) {
449		try {
450	<	completed = exec();
451	<	} catch (Throwable rex) {
318	<	return setExceptionalCompletion(rex);
450	>	t.cancel(false);
451	>	} catch (Throwable ignore) {
452		}
320	–	if (completed)
321	–	stat = setCompletion(NORMAL);
322	–	else
323	–	stat = doJoin();
453		}
325	–	return stat;
454		}
455
456		/**
457	<	* Returns result or throws exception associated with given status.
330	<	* @param s the status
457	>	* Removes exception node and clears status
458		*/
459	<	private V reportResult(int s) {
459	>	private void clearExceptionalCompletion() {
460	>	int h = System.identityHashCode(this);
461	>	final ReentrantLock lock = exceptionTableLock;
462	>	lock.lock();
463	>	try {
464	>	ExceptionNode[] t = exceptionTable;
465	>	int i = h & (t.length - 1);
466	>	ExceptionNode e = t[i];
467	>	ExceptionNode pred = null;
468	>	while (e != null) {
469	>	ExceptionNode next = e.next;
470	>	if (e.get() == this) {
471	>	if (pred == null)
472	>	t[i] = next;
473	>	else
474	>	pred.next = next;
475	>	break;
476	>	}
477	>	pred = e;
478	>	e = next;
479	>	}
480	>	expungeStaleExceptions();
481	>	status = 0;
482	>	} finally {
483	>	lock.unlock();
484	>	}
485	>	}
486	>
487	>	/**
488	>	* Returns a rethrowable exception for the given task, if
489	>	* available. To provide accurate stack traces, if the exception
490	>	* was not thrown by the current thread, we try to create a new
491	>	* exception of the same type as the one thrown, but with the
492	>	* recorded exception as its cause. If there is no such
493	>	* constructor, we instead try to use a no-arg constructor,
494	>	* followed by initCause, to the same effect. If none of these
495	>	* apply, or any fail due to other exceptions, we return the
496	>	* recorded exception, which is still correct, although it may
497	>	* contain a misleading stack trace.
498	>	*
499	>	* @return the exception, or null if none
500	>	*/
501	>	private Throwable getThrowableException() {
502	>	if ((status & DONE_MASK) != EXCEPTIONAL)
503	>	return null;
504	>	int h = System.identityHashCode(this);
505	>	ExceptionNode e;
506	>	final ReentrantLock lock = exceptionTableLock;
507	>	lock.lock();
508	>	try {
509	>	expungeStaleExceptions();
510	>	ExceptionNode[] t = exceptionTable;
511	>	e = t[h & (t.length - 1)];
512	>	while (e != null && e.get() != this)
513	>	e = e.next;
514	>	} finally {
515	>	lock.unlock();
516	>	}
517		Throwable ex;
518	<	if (s < NORMAL && (ex = getException()) != null)
519	<	UNSAFE.throwException(ex);
520	<	return getRawResult();
518	>	if (e == null || (ex = e.ex) == null)
519	>	return null;
520	>	if (e.thrower != Thread.currentThread().getId()) {
521	>	Class<? extends Throwable> ec = ex.getClass();
522	>	try {
523	>	Constructor<?> noArgCtor = null;
524	>	Constructor<?>[] cs = ec.getConstructors();// public ctors only
525	>	for (int i = 0; i < cs.length; ++i) {
526	>	Constructor<?> c = cs[i];
527	>	Class<?>[] ps = c.getParameterTypes();
528	>	if (ps.length == 0)
529	>	noArgCtor = c;
530	>	else if (ps.length == 1 && ps[0] == Throwable.class)
531	>	return (Throwable)(c.newInstance(ex));
532	>	}
533	>	if (noArgCtor != null) {
534	>	Throwable wx = (Throwable)(noArgCtor.newInstance());
535	>	wx.initCause(ex);
536	>	return wx;
537	>	}
538	>	} catch (Exception ignore) {
539	>	}
540	>	}
541	>	return ex;
542	>	}
543	>
544	>	/**
545	>	* Poll stale refs and remove them. Call only while holding lock.
546	>	*/
547	>	private static void expungeStaleExceptions() {
548	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
549	>	if (x instanceof ExceptionNode) {
550	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
551	>	ExceptionNode[] t = exceptionTable;
552	>	int i = System.identityHashCode(key) & (t.length - 1);
553	>	ExceptionNode e = t[i];
554	>	ExceptionNode pred = null;
555	>	while (e != null) {
556	>	ExceptionNode next = e.next;
557	>	if (e == x) {
558	>	if (pred == null)
559	>	t[i] = next;
560	>	else
561	>	pred.next = next;
562	>	break;
563	>	}
564	>	pred = e;
565	>	e = next;
566	>	}
567	>	}
568	>	}
569	>	}
570	>
571	>	/**
572	>	* If lock is available, poll stale refs and remove them.
573	>	* Called from ForkJoinPool when pools become quiescent.
574	>	*/
575	>	static final void helpExpungeStaleExceptions() {
576	>	final ReentrantLock lock = exceptionTableLock;
577	>	if (lock.tryLock()) {
578	>	try {
579	>	expungeStaleExceptions();
580	>	} finally {
581	>	lock.unlock();
582	>	}
583	>	}
584	>	}
585	>
586	>	/**
587	>	* Throws exception, if any, associated with the given status.
588	>	*/
589	>	private void reportException(int s) {
590	>	Throwable ex = ((s == CANCELLED) ?  new CancellationException() :
591	>	(s == EXCEPTIONAL) ? getThrowableException() :
592	>	null);
593	>	if (ex != null)
594	>	U.throwException(ex);
595		}
596
597		// public methods
#	Line 349 | Line 607 | public abstract class ForkJoinTask<V> im
607		* #isDone} returning {@code true}.
608		*
609		* <p>This method may be invoked only from within {@code
610	<	* ForkJoinTask} computations (as may be determined using method
610	>	* ForkJoinPool} computations (as may be determined using method
611		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
612		* result in exceptions or errors, possibly including {@code
613		* ClassCastException}.
#	Line 357 | Line 615 | public abstract class ForkJoinTask<V> im
615		* @return {@code this}, to simplify usage
616		*/
617		public final ForkJoinTask<V> fork() {
618	<	((ForkJoinWorkerThread) Thread.currentThread())
361	<	.pushTask(this);
618	>	((ForkJoinWorkerThread)Thread.currentThread()).workQueue.push(this);
619		return this;
620		}
621
622		/**
623	<	* Returns the result of the computation when it {@link #isDone is done}.
624	<	* This method differs from {@link #get()} in that
623	>	* Returns the result of the computation when it {@link #isDone is
624	>	* done}.  This method differs from {@link #get()} in that
625		* abnormal completion results in {@code RuntimeException} or
626	<	* {@code Error}, not {@code ExecutionException}.
626	>	* {@code Error}, not {@code ExecutionException}, and that
627	>	* interrupts of the calling thread do <em>not</em> cause the
628	>	* method to abruptly return by throwing {@code
629	>	* InterruptedException}.
630		*
631		* @return the computed result
632		*/
633		public final V join() {
634	<	return reportResult(doJoin());
634	>	int s;
635	>	if ((s = doJoin() & DONE_MASK) != NORMAL)
636	>	reportException(s);
637	>	return getRawResult();
638		}
639
640		/**
641		* Commences performing this task, awaits its completion if
642	<	* necessary, and return its result, or throws an (unchecked)
643	<	* exception if the underlying computation did so.
642	>	* necessary, and returns its result, or throws an (unchecked)
643	>	* {@code RuntimeException} or {@code Error} if the underlying
644	>	* computation did so.
645		*
646		* @return the computed result
647		*/
648		public final V invoke() {
649	<	return reportResult(doInvoke());
649	>	int s;
650	>	if ((s = doInvoke() & DONE_MASK) != NORMAL)
651	>	reportException(s);
652	>	return getRawResult();
653		}
654
655		/**
656		* Forks the given tasks, returning when {@code isDone} holds for
657		* each task or an (unchecked) exception is encountered, in which
658	<	* case the exception is rethrown.  If either task encounters an
659	<	* exception, the other one may be, but is not guaranteed to be,
660	<	* cancelled.  If both tasks throw an exception, then this method
661	<	* throws one of them.  The individual status of each task may be
662	<	* checked using {@link #getException()} and related methods.
658	>	* case the exception is rethrown. If more than one task
659	>	* encounters an exception, then this method throws any one of
660	>	* these exceptions. If any task encounters an exception, the
661	>	* other may be cancelled. However, the execution status of
662	>	* individual tasks is not guaranteed upon exceptional return. The
663	>	* status of each task may be obtained using {@link
664	>	* #getException()} and related methods to check if they have been
665	>	* cancelled, completed normally or exceptionally, or left
666	>	* unprocessed.
667		*
668		* <p>This method may be invoked only from within {@code
669	<	* ForkJoinTask} computations (as may be determined using method
669	>	* ForkJoinPool} computations (as may be determined using method
670		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
671		* result in exceptions or errors, possibly including {@code
672		* ClassCastException}.
#	Line 405 | Line 676 | public abstract class ForkJoinTask<V> im
676		* @throws NullPointerException if any task is null
677		*/
678		public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
679	+	int s1, s2;
680		t2.fork();
681	<	t1.invoke();
682	<	t2.join();
681	>	if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL)
682	>	t1.reportException(s1);
683	>	if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
684	>	t2.reportException(s2);
685		}
686
687		/**
688		* Forks the given tasks, returning when {@code isDone} holds for
689		* each task or an (unchecked) exception is encountered, in which
690	<	* case the exception is rethrown. If any task encounters an
691	<	* exception, others may be, but are not guaranteed to be,
692	<	* cancelled.  If more than one task encounters an exception, then
693	<	* this method throws any one of these exceptions.  The individual
694	<	* status of each task may be checked using {@link #getException()}
695	<	* and related methods.
690	>	* case the exception is rethrown. If more than one task
691	>	* encounters an exception, then this method throws any one of
692	>	* these exceptions. If any task encounters an exception, others
693	>	* may be cancelled. However, the execution status of individual
694	>	* tasks is not guaranteed upon exceptional return. The status of
695	>	* each task may be obtained using {@link #getException()} and
696	>	* related methods to check if they have been cancelled, completed
697	>	* normally or exceptionally, or left unprocessed.
698		*
699		* <p>This method may be invoked only from within {@code
700	<	* ForkJoinTask} computations (as may be determined using method
700	>	* ForkJoinPool} computations (as may be determined using method
701		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
702		* result in exceptions or errors, possibly including {@code
703		* ClassCastException}.
#	Line 448 | Line 724 | public abstract class ForkJoinTask<V> im
724		if (t != null) {
725		if (ex != null)
726		t.cancel(false);
727	<	else if (t.doJoin() < NORMAL && ex == null)
727	>	else if (t.doJoin() < NORMAL)
728		ex = t.getException();
729		}
730		}
731		if (ex != null)
732	<	UNSAFE.throwException(ex);
732	>	U.throwException(ex);
733		}
734
735		/**
736		* Forks all tasks in the specified collection, returning when
737		* {@code isDone} holds for each task or an (unchecked) exception
738	<	* is encountered.  If any task encounters an exception, others
739	<	* may be, but are not guaranteed to be, cancelled.  If more than
740	<	* one task encounters an exception, then this method throws any
741	<	* one of these exceptions.  The individual status of each task
742	<	* may be checked using {@link #getException()} and related
743	<	* methods.  The behavior of this operation is undefined if the
744	<	* specified collection is modified while the operation is in
745	<	* progress.
738	>	* is encountered, in which case the exception is rethrown. If
739	>	* more than one task encounters an exception, then this method
740	>	* throws any one of these exceptions. If any task encounters an
741	>	* exception, others may be cancelled. However, the execution
742	>	* status of individual tasks is not guaranteed upon exceptional
743	>	* return. The status of each task may be obtained using {@link
744	>	* #getException()} and related methods to check if they have been
745	>	* cancelled, completed normally or exceptionally, or left
746	>	* unprocessed.
747		*
748		* <p>This method may be invoked only from within {@code
749	<	* ForkJoinTask} computations (as may be determined using method
749	>	* ForkJoinPool} computations (as may be determined using method
750		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
751		* result in exceptions or errors, possibly including {@code
752		* ClassCastException}.
#	Line 504 | Line 781 | public abstract class ForkJoinTask<V> im
781		if (t != null) {
782		if (ex != null)
783		t.cancel(false);
784	<	else if (t.doJoin() < NORMAL && ex == null)
784	>	else if (t.doJoin() < NORMAL)
785		ex = t.getException();
786		}
787		}
788		if (ex != null)
789	<	UNSAFE.throwException(ex);
789	>	U.throwException(ex);
790		return tasks;
791		}
792
793		/**
794		* Attempts to cancel execution of this task. This attempt will
795	<	* fail if the task has already completed, has already been
796	<	* cancelled, or could not be cancelled for some other reason. If
797	<	* successful, and this task has not started when cancel is
798	<	* called, execution of this task is suppressed, {@link
799	<	* #isCancelled} will report true, and {@link #join} will result
800	<	* in a {@code CancellationException} being thrown.
795	>	* fail if the task has already completed or could not be
796	>	* cancelled for some other reason. If successful, and this task
797	>	* has not started when {@code cancel} is called, execution of
798	>	* this task is suppressed. After this method returns
799	>	* successfully, unless there is an intervening call to {@link
800	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
801	>	* {@link #isDone}, and {@code cancel} will return {@code true}
802	>	* and calls to {@link #join} and related methods will result in
803	>	* {@code CancellationException}.
804		*
805		* <p>This method may be overridden in subclasses, but if so, must
806	<	* still ensure that these minimal properties hold. In particular,
807	<	* the {@code cancel} method itself must not throw exceptions.
806	>	* still ensure that these properties hold. In particular, the
807	>	* {@code cancel} method itself must not throw exceptions.
808		*
809		* <p>This method is designed to be invoked by <em>other</em>
810		* tasks. To terminate the current task, you can just return or
811		* throw an unchecked exception from its computation method, or
812		* invoke {@link #completeExceptionally}.
813		*
814	<	* @param mayInterruptIfRunning this value is ignored in the
815	<	* default implementation because tasks are not
816	<	* cancelled via interruption
814	>	* @param mayInterruptIfRunning this value has no effect in the
815	>	* default implementation because interrupts are not used to
816	>	* control cancellation.
817		*
818		* @return {@code true} if this task is now cancelled
819		*/
820		public boolean cancel(boolean mayInterruptIfRunning) {
821	<	setCompletion(CANCELLED);
542	<	return status == CANCELLED;
543	<	}
544	<
545	<	/**
546	<	* Cancels, ignoring any exceptions it throws. Used during worker
547	<	* and pool shutdown.
548	<	*/
549	<	final void cancelIgnoringExceptions() {
550	<	try {
551	<	cancel(false);
552	<	} catch (Throwable ignore) {
553	<	}
554	<	}
555	<
556	<	/**
557	<	* Cancels ignoring exceptions if worker is terminating
558	<	*/
559	<	private void cancelIfTerminating() {
560	<	Thread t = Thread.currentThread();
561	<	if ((t instanceof ForkJoinWorkerThread) &&
562	<	((ForkJoinWorkerThread) t).isTerminating()) {
563	<	try {
564	<	cancel(false);
565	<	} catch (Throwable ignore) {
566	<	}
567	<	}
821	>	return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
822		}
823
824		public final boolean isDone() {
#	Line 572 | Line 826 | public abstract class ForkJoinTask<V> im
826		}
827
828		public final boolean isCancelled() {
829	<	return status == CANCELLED;
829	>	return (status & DONE_MASK) == CANCELLED;
830		}
831
832		/**
#	Line 592 | Line 846 | public abstract class ForkJoinTask<V> im
846		* exception and was not cancelled
847		*/
848		public final boolean isCompletedNormally() {
849	<	return status == NORMAL;
849	>	return (status & DONE_MASK) == NORMAL;
850		}
851
852		/**
#	Line 603 | Line 857 | public abstract class ForkJoinTask<V> im
857		* @return the exception, or {@code null} if none
858		*/
859		public final Throwable getException() {
860	<	int s = status;
860	>	int s = status & DONE_MASK;
861		return ((s >= NORMAL)    ? null :
862		(s == CANCELLED) ? new CancellationException() :
863	<	exceptionMap.get(this));
863	>	getThrowableException());
864		}
865
866		/**
#	Line 631 | Line 885 | public abstract class ForkJoinTask<V> im
885
886		/**
887		* Completes this task, and if not already aborted or cancelled,
888	<	* returning a {@code null} result upon {@code join} and related
889	<	* operations. This method may be used to provide results for
890	<	* asynchronous tasks, or to provide alternative handling for
891	<	* tasks that would not otherwise complete normally. Its use in
892	<	* other situations is discouraged. This method is
893	<	* overridable, but overridden versions must invoke {@code super}
894	<	* implementation to maintain guarantees.
888	>	* returning the given value as the result of subsequent
889	>	* invocations of {@code join} and related operations. This method
890	>	* may be used to provide results for asynchronous tasks, or to
891	>	* provide alternative handling for tasks that would not otherwise
892	>	* complete normally. Its use in other situations is
893	>	* discouraged. This method is overridable, but overridden
894	>	* versions must invoke {@code super} implementation to maintain
895	>	* guarantees.
896		*
897		* @param value the result value for this task
898		*/
#	Line 651 | Line 906 | public abstract class ForkJoinTask<V> im
906		setCompletion(NORMAL);
907		}
908
909	+	/**
910	+	* Waits if necessary for the computation to complete, and then
911	+	* retrieves its result.
912	+	*
913	+	* @return the computed result
914	+	* @throws CancellationException if the computation was cancelled
915	+	* @throws ExecutionException if the computation threw an
916	+	* exception
917	+	* @throws InterruptedException if the current thread is not a
918	+	* member of a ForkJoinPool and was interrupted while waiting
919	+	*/
920		public final V get() throws InterruptedException, ExecutionException {
921	<	int s = doJoin();
922	<	if (Thread.interrupted())
923	<	throw new InterruptedException();
924	<	if (s < NORMAL) {
925	<	Throwable ex;
926	<	if (s == CANCELLED)
927	<	throw new CancellationException();
662	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
663	<	throw new ExecutionException(ex);
664	<	}
921	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
922	>	doJoin() : externalInterruptibleAwaitDone();
923	>	Throwable ex;
924	>	if ((s &= DONE_MASK) == CANCELLED)
925	>	throw new CancellationException();
926	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
927	>	throw new ExecutionException(ex);
928		return getRawResult();
929		}
930
931	+	/**
932	+	* Waits if necessary for at most the given time for the computation
933	+	* to complete, and then retrieves its result, if available.
934	+	*
935	+	* @param timeout the maximum time to wait
936	+	* @param unit the time unit of the timeout argument
937	+	* @return the computed result
938	+	* @throws CancellationException if the computation was cancelled
939	+	* @throws ExecutionException if the computation threw an
940	+	* exception
941	+	* @throws InterruptedException if the current thread is not a
942	+	* member of a ForkJoinPool and was interrupted while waiting
943	+	* @throws TimeoutException if the wait timed out
944	+	*/
945		public final V get(long timeout, TimeUnit unit)
946		throws InterruptedException, ExecutionException, TimeoutException {
947	<	Thread t = Thread.currentThread();
948	<	ForkJoinPool pool;
949	<	if (t instanceof ForkJoinWorkerThread) {
950	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
951	<	if (status >= 0 && w.unpushTask(this))
952	<	tryExec();
953	<	pool = w.pool;
954	<	}
955	<	else
956	<	pool = null;
957	<	/*
958	<	* Timed wait loop intermixes cases for fj (pool != null) and
959	<	* non FJ threads. For FJ, decrement pool count but don't try
960	<	* for replacement; increment count on completion. For non-FJ,
684	<	* deal with interrupts. This is messy, but a little less so
685	<	* than is splitting the FJ and nonFJ cases.
686	<	*/
687	<	boolean interrupted = false;
688	<	boolean dec = false; // true if pool count decremented
689	<	for (;;) {
690	<	if (Thread.interrupted() && pool == null) {
691	<	interrupted = true;
692	<	break;
947	>	if (Thread.interrupted())
948	>	throw new InterruptedException();
949	>	// Messy in part because we measure in nanosecs, but wait in millisecs
950	>	int s; long ns, ms;
951	>	if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) {
952	>	long deadline = System.nanoTime() + ns;
953	>	ForkJoinPool p = null;
954	>	ForkJoinPool.WorkQueue w = null;
955	>	Thread t = Thread.currentThread();
956	>	if (t instanceof ForkJoinWorkerThread) {
957	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
958	>	p = wt.pool;
959	>	w = wt.workQueue;
960	>	s = p.helpJoinOnce(w, this); // no retries on failure
961		}
962	<	int s = status;
963	<	if (s < 0)
964	<	break;
965	<	if (UNSAFE.compareAndSwapInt(this, statusOffset,
966	<	s, s | SIGNAL)) {
967	<	long startTime = System.nanoTime();
968	<	long nanos = unit.toNanos(timeout);
969	<	long nt; // wait time
970	<	while (status >= 0 &&
971	<	(nt = nanos - (System.nanoTime() - startTime)) > 0) {
704	<	if (pool != null && !dec)
705	<	dec = pool.tryDecrementRunningCount();
962	>	boolean canBlock = false;
963	>	boolean interrupted = false;
964	>	try {
965	>	while ((s = status) >= 0) {
966	>	if (w != null && w.runState < 0)
967	>	cancelIgnoringExceptions(this);
968	>	else if (!canBlock) {
969	>	if (p == null || p.tryCompensate(this, null))
970	>	canBlock = true;
971	>	}
972		else {
973	<	long ms = nt / 1000000;
974	<	int ns = (int) (nt % 1000000);
975	<	try {
976	<	synchronized(this) {
977	<	if (status >= 0)
978	<	wait(ms, ns);
979	<	}
980	<	} catch (InterruptedException ie) {
981	<	if (pool != null)
982	<	cancelIfTerminating();
983	<	else {
984	<	interrupted = true;
985	<	break;
973	>	if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
974	>	U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
975	>	synchronized (this) {
976	>	if (status >= 0) {
977	>	try {
978	>	wait(ms);
979	>	} catch (InterruptedException ie) {
980	>	if (p == null)
981	>	interrupted = true;
982	>	}
983	>	}
984	>	else
985	>	notifyAll();
986		}
987		}
988	+	if ((s = status) < 0 || interrupted ||
989	+	(ns = deadline - System.nanoTime()) <= 0L)
990	+	break;
991		}
992		}
993	<	break;
993	>	} finally {
994	>	if (p != null && canBlock)
995	>	p.incrementActiveCount();
996		}
997	+	if (interrupted)
998	+	throw new InterruptedException();
999		}
1000	<	if (pool != null && dec)
728	<	pool.incrementRunningCount();
729	<	if (interrupted)
730	<	throw new InterruptedException();
731	<	int es = status;
732	<	if (es != NORMAL) {
1000	>	if ((s &= DONE_MASK) != NORMAL) {
1001		Throwable ex;
1002	<	if (es == CANCELLED)
1002	>	if (s == CANCELLED)
1003		throw new CancellationException();
1004	<	if (es == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
1004	>	if (s != EXCEPTIONAL)
1005	>	throw new TimeoutException();
1006	>	if ((ex = getThrowableException()) != null)
1007		throw new ExecutionException(ex);
738	–	throw new TimeoutException();
1008		}
1009		return getRawResult();
1010		}
1011
1012		/**
1013	<	* Joins this task, without returning its result or throwing an
1013	>	* Joins this task, without returning its result or throwing its
1014		* exception. This method may be useful when processing
1015		* collections of tasks when some have been cancelled or otherwise
1016		* known to have aborted.
#	Line 752 | Line 1021 | public abstract class ForkJoinTask<V> im
1021
1022		/**
1023		* Commences performing this task and awaits its completion if
1024	<	* necessary, without returning its result or throwing an
1025	<	* exception. This method may be useful when processing
757	<	* collections of tasks when some have been cancelled or otherwise
758	<	* known to have aborted.
1024	>	* necessary, without returning its result or throwing its
1025	>	* exception.
1026		*/
1027		public final void quietlyInvoke() {
1028		doInvoke();
#	Line 769 | Line 1036 | public abstract class ForkJoinTask<V> im
1036		* processed.
1037		*
1038		* <p>This method may be invoked only from within {@code
1039	<	* ForkJoinTask} computations (as may be determined using method
1039	>	* ForkJoinPool} computations (as may be determined using method
1040		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1041		* result in exceptions or errors, possibly including {@code
1042		* ClassCastException}.
1043		*/
1044		public static void helpQuiesce() {
1045	<	((ForkJoinWorkerThread) Thread.currentThread())
1046	<	.helpQuiescePool();
1045	>	ForkJoinWorkerThread wt =
1046	>	(ForkJoinWorkerThread)Thread.currentThread();
1047	>	wt.pool.helpQuiescePool(wt.workQueue);
1048		}
1049
1050		/**
#	Line 788 | Line 1056 | public abstract class ForkJoinTask<V> im
1056		* under any other usage conditions are not guaranteed.
1057		* This method may be useful when executing
1058		* pre-constructed trees of subtasks in loops.
1059	+	*
1060	+	* <p>Upon completion of this method, {@code isDone()} reports
1061	+	* {@code false}, and {@code getException()} reports {@code
1062	+	* null}. However, the value returned by {@code getRawResult} is
1063	+	* unaffected. To clear this value, you can invoke {@code
1064	+	* setRawResult(null)}.
1065		*/
1066		public void reinitialize() {
1067	<	if (status == EXCEPTIONAL)
1068	<	exceptionMap.remove(this);
1069	<	status = 0;
1067	>	if ((status & DONE_MASK) == EXCEPTIONAL)
1068	>	clearExceptionalCompletion();
1069	>	else
1070	>	status = 0;
1071		}
1072
1073		/**
#	Line 809 | Line 1084 | public abstract class ForkJoinTask<V> im
1084		}
1085
1086		/**
1087	<	* Returns {@code true} if the current thread is executing as a
1088	<	* ForkJoinPool computation.
1087	>	* Returns {@code true} if the current thread is a {@link
1088	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1089		*
1090	<	* @return {@code true} if the current thread is executing as a
1091	<	* ForkJoinPool computation, or false otherwise
1090	>	* @return {@code true} if the current thread is a {@link
1091	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1092	>	* or {@code false} otherwise
1093		*/
1094		public static boolean inForkJoinPool() {
1095		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 828 | Line 1104 | public abstract class ForkJoinTask<V> im
1104		* were not, stolen.
1105		*
1106		* <p>This method may be invoked only from within {@code
1107	<	* ForkJoinTask} computations (as may be determined using method
1107	>	* ForkJoinPool} computations (as may be determined using method
1108		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1109		* result in exceptions or errors, possibly including {@code
1110		* ClassCastException}.
#	Line 836 | Line 1112 | public abstract class ForkJoinTask<V> im
1112		* @return {@code true} if unforked
1113		*/
1114		public boolean tryUnfork() {
1115	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1116	<	.unpushTask(this);
1115	>	return ((ForkJoinWorkerThread)Thread.currentThread())
1116	>	.workQueue.tryUnpush(this);
1117		}
1118
1119		/**
#	Line 847 | Line 1123 | public abstract class ForkJoinTask<V> im
1123		* fork other tasks.
1124		*
1125		* <p>This method may be invoked only from within {@code
1126	<	* ForkJoinTask} computations (as may be determined using method
1126	>	* ForkJoinPool} computations (as may be determined using method
1127		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1128		* result in exceptions or errors, possibly including {@code
1129		* ClassCastException}.
#	Line 856 | Line 1132 | public abstract class ForkJoinTask<V> im
1132		*/
1133		public static int getQueuedTaskCount() {
1134		return ((ForkJoinWorkerThread) Thread.currentThread())
1135	<	.getQueueSize();
1135	>	.workQueue.queueSize();
1136		}
1137
1138		/**
#	Line 870 | Line 1146 | public abstract class ForkJoinTask<V> im
1146		* exceeded.
1147		*
1148		* <p>This method may be invoked only from within {@code
1149	<	* ForkJoinTask} computations (as may be determined using method
1149	>	* ForkJoinPool} computations (as may be determined using method
1150		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1151		* result in exceptions or errors, possibly including {@code
1152		* ClassCastException}.
#	Line 878 | Line 1154 | public abstract class ForkJoinTask<V> im
1154		* @return the surplus number of tasks, which may be negative
1155		*/
1156		public static int getSurplusQueuedTaskCount() {
1157	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1158	<	.getEstimatedSurplusTaskCount();
1157	>	/*
1158	>	* The aim of this method is to return a cheap heuristic guide
1159	>	* for task partitioning when programmers, frameworks, tools,
1160	>	* or languages have little or no idea about task granularity.
1161	>	* In essence by offering this method, we ask users only about
1162	>	* tradeoffs in overhead vs expected throughput and its
1163	>	* variance, rather than how finely to partition tasks.
1164	>	*
1165	>	* In a steady state strict (tree-structured) computation,
1166	>	* each thread makes available for stealing enough tasks for
1167	>	* other threads to remain active. Inductively, if all threads
1168	>	* play by the same rules, each thread should make available
1169	>	* only a constant number of tasks.
1170	>	*
1171	>	* The minimum useful constant is just 1. But using a value of
1172	>	* 1 would require immediate replenishment upon each steal to
1173	>	* maintain enough tasks, which is infeasible.  Further,
1174	>	* partitionings/granularities of offered tasks should
1175	>	* minimize steal rates, which in general means that threads
1176	>	* nearer the top of computation tree should generate more
1177	>	* than those nearer the bottom. In perfect steady state, each
1178	>	* thread is at approximately the same level of computation
1179	>	* tree. However, producing extra tasks amortizes the
1180	>	* uncertainty of progress and diffusion assumptions.
1181	>	*
1182	>	* So, users will want to use values larger, but not much
1183	>	* larger than 1 to both smooth over transient shortages and
1184	>	* hedge against uneven progress; as traded off against the
1185	>	* cost of extra task overhead. We leave the user to pick a
1186	>	* threshold value to compare with the results of this call to
1187	>	* guide decisions, but recommend values such as 3.
1188	>	*
1189	>	* When all threads are active, it is on average OK to
1190	>	* estimate surplus strictly locally. In steady-state, if one
1191	>	* thread is maintaining say 2 surplus tasks, then so are
1192	>	* others. So we can just use estimated queue length.
1193	>	* However, this strategy alone leads to serious mis-estimates
1194	>	* in some non-steady-state conditions (ramp-up, ramp-down,
1195	>	* other stalls). We can detect many of these by further
1196	>	* considering the number of "idle" threads, that are known to
1197	>	* have zero queued tasks, so compensate by a factor of
1198	>	* (#idle/#active) threads.
1199	>	*/
1200	>	ForkJoinWorkerThread wt =
1201	>	(ForkJoinWorkerThread)Thread.currentThread();
1202	>	return wt.workQueue.queueSize() - wt.pool.idlePerActive();
1203		}
1204
1205		// Extension methods
#	Line 928 | Line 1248 | public abstract class ForkJoinTask<V> im
1248		* otherwise.
1249		*
1250		* <p>This method may be invoked only from within {@code
1251	<	* ForkJoinTask} computations (as may be determined using method
1251	>	* ForkJoinPool} computations (as may be determined using method
1252		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1253		* result in exceptions or errors, possibly including {@code
1254		* ClassCastException}.
#	Line 936 | Line 1256 | public abstract class ForkJoinTask<V> im
1256		* @return the next task, or {@code null} if none are available
1257		*/
1258		protected static ForkJoinTask<?> peekNextLocalTask() {
1259	<	return ((ForkJoinWorkerThread) Thread.currentThread())
940	<	.peekTask();
1259	>	return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek();
1260		}
1261
1262		/**
#	Line 947 | Line 1266 | public abstract class ForkJoinTask<V> im
1266		* be useful otherwise.
1267		*
1268		* <p>This method may be invoked only from within {@code
1269	<	* ForkJoinTask} computations (as may be determined using method
1269	>	* ForkJoinPool} computations (as may be determined using method
1270		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1271		* result in exceptions or errors, possibly including {@code
1272		* ClassCastException}.
#	Line 956 | Line 1275 | public abstract class ForkJoinTask<V> im
1275		*/
1276		protected static ForkJoinTask<?> pollNextLocalTask() {
1277		return ((ForkJoinWorkerThread) Thread.currentThread())
1278	<	.pollLocalTask();
1278	>	.workQueue.nextLocalTask();
1279		}
1280
1281		/**
#	Line 970 | Line 1289 | public abstract class ForkJoinTask<V> im
1289		* otherwise.
1290		*
1291		* <p>This method may be invoked only from within {@code
1292	<	* ForkJoinTask} computations (as may be determined using method
1292	>	* ForkJoinPool} computations (as may be determined using method
1293		* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1294		* result in exceptions or errors, possibly including {@code
1295		* ClassCastException}.
#	Line 978 | Line 1297 | public abstract class ForkJoinTask<V> im
1297		* @return a task, or {@code null} if none are available
1298		*/
1299		protected static ForkJoinTask<?> pollTask() {
1300	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1301	<	.pollTask();
1300	>	ForkJoinWorkerThread wt =
1301	>	(ForkJoinWorkerThread)Thread.currentThread();
1302	>	return wt.pool.nextTaskFor(wt.workQueue);
1303	>	}
1304	>
1305	>	// Mark-bit operations
1306	>
1307	>	/**
1308	>	* Returns true if this task is marked.
1309	>	*
1310	>	* @return true if this task is marked
1311	>	* @since 1.8
1312	>	*/
1313	>	public final boolean isMarkedForkJoinTask() {
1314	>	return (status & MARKED) != 0;
1315	>	}
1316	>
1317	>	/**
1318	>	* Atomically sets the mark on this task.
1319	>	*
1320	>	* @return true if this task was previously unmarked
1321	>	* @since 1.8
1322	>	*/
1323	>	public final boolean markForkJoinTask() {
1324	>	for (int s;;) {
1325	>	if (((s = status) & MARKED) != 0)
1326	>	return false;
1327	>	if (U.compareAndSwapInt(this, STATUS, s, s | MARKED))
1328	>	return true;
1329	>	}
1330	>	}
1331	>
1332	>	/**
1333	>	* Atomically clears the mark on this task.
1334	>	*
1335	>	* @return true if this task was previously marked
1336	>	* @since 1.8
1337	>	*/
1338	>	public final boolean unmarkForkJoinTask() {
1339	>	for (int s;;) {
1340	>	if (((s = status) & MARKED) == 0)
1341	>	return false;
1342	>	if (U.compareAndSwapInt(this, STATUS, s, s & ~MARKED))
1343	>	return true;
1344	>	}
1345		}
1346
1347		/**
#	Line 990 | Line 1352 | public abstract class ForkJoinTask<V> im
1352		static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1353		implements RunnableFuture<T> {
1354		final Runnable runnable;
993	–	final T resultOnCompletion;
1355		T result;
1356		AdaptedRunnable(Runnable runnable, T result) {
1357		if (runnable == null) throw new NullPointerException();
1358		this.runnable = runnable;
1359	<	this.resultOnCompletion = result;
1359	>	this.result = result; // OK to set this even before completion
1360		}
1361	<	public T getRawResult() { return result; }
1362	<	public void setRawResult(T v) { result = v; }
1363	<	public boolean exec() {
1364	<	runnable.run();
1365	<	result = resultOnCompletion;
1366	<	return true;
1361	>	public final T getRawResult() { return result; }
1362	>	public final void setRawResult(T v) { result = v; }
1363	>	public final boolean exec() { runnable.run(); return true; }
1364	>	public final void run() { invoke(); }
1365	>	private static final long serialVersionUID = 5232453952276885070L;
1366	>	}
1367	>
1368	>	/**
1369	>	* Adaptor for Runnables without results
1370	>	*/
1371	>	static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1372	>	implements RunnableFuture<Void> {
1373	>	final Runnable runnable;
1374	>	AdaptedRunnableAction(Runnable runnable) {
1375	>	if (runnable == null) throw new NullPointerException();
1376	>	this.runnable = runnable;
1377		}
1378	<	public void run() { invoke(); }
1378	>	public final Void getRawResult() { return null; }
1379	>	public final void setRawResult(Void v) { }
1380	>	public final boolean exec() { runnable.run(); return true; }
1381	>	public final void run() { invoke(); }
1382		private static final long serialVersionUID = 5232453952276885070L;
1383		}
1384
#	Line 1019 | Line 1393 | public abstract class ForkJoinTask<V> im
1393		if (callable == null) throw new NullPointerException();
1394		this.callable = callable;
1395		}
1396	<	public T getRawResult() { return result; }
1397	<	public void setRawResult(T v) { result = v; }
1398	<	public boolean exec() {
1396	>	public final T getRawResult() { return result; }
1397	>	public final void setRawResult(T v) { result = v; }
1398	>	public final boolean exec() {
1399		try {
1400		result = callable.call();
1401		return true;
#	Line 1033 | Line 1407 | public abstract class ForkJoinTask<V> im
1407		throw new RuntimeException(ex);
1408		}
1409		}
1410	<	public void run() { invoke(); }
1410	>	public final void run() { invoke(); }
1411		private static final long serialVersionUID = 2838392045355241008L;
1412		}
1413
#	Line 1046 | Line 1420 | public abstract class ForkJoinTask<V> im
1420		* @return the task
1421		*/
1422		public static ForkJoinTask<?> adapt(Runnable runnable) {
1423	<	return new AdaptedRunnable<Void>(runnable, null);
1423	>	return new AdaptedRunnableAction(runnable);
1424		}
1425
1426		/**
#	Line 1080 | Line 1454 | public abstract class ForkJoinTask<V> im
1454		private static final long serialVersionUID = -7721805057305804111L;
1455
1456		/**
1457	<	* Saves the state to a stream.
1457	>	* Saves this task to a stream (that is, serializes it).
1458		*
1459		* @serialData the current run status and the exception thrown
1460		* during execution, or {@code null} if none
1087	–	* @param s the stream
1461		*/
1462		private void writeObject(java.io.ObjectOutputStream s)
1463		throws java.io.IOException {
#	Line 1093 | Line 1466 | public abstract class ForkJoinTask<V> im
1466		}
1467
1468		/**
1469	<	* Reconstitutes the instance from a stream.
1097	<	*
1098	<	* @param s the stream
1469	>	* Reconstitutes this task from a stream (that is, deserializes it).
1470		*/
1471		private void readObject(java.io.ObjectInputStream s)
1472		throws java.io.IOException, ClassNotFoundException {
1473		s.defaultReadObject();
1474		Object ex = s.readObject();
1475		if (ex != null)
1476	<	setExceptionalCompletion((Throwable) ex);
1106	<	if (status < 0)
1107	<	synchronized (this) { notifyAll(); }
1476	>	setExceptionalCompletion((Throwable)ex);
1477		}
1478
1479		// Unsafe mechanics
1480	<
1481	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1482	<	private static final long statusOffset =
1483	<	objectFieldOffset("status", ForkJoinTask.class);
1484	<
1485	<	private static long objectFieldOffset(String field, Class<?> klazz) {
1480	>	private static final sun.misc.Unsafe U;
1481	>	private static final long STATUS;
1482	>	static {
1483	>	exceptionTableLock = new ReentrantLock();
1484	>	exceptionTableRefQueue = new ReferenceQueue<Object>();
1485	>	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1486		try {
1487	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1488	<	} catch (NoSuchFieldException e) {
1489	<	// Convert Exception to corresponding Error
1490	<	NoSuchFieldError error = new NoSuchFieldError(field);
1491	<	error.initCause(e);
1123	<	throw error;
1487	>	U = getUnsafe();
1488	>	STATUS = U.objectFieldOffset
1489	>	(ForkJoinTask.class.getDeclaredField("status"));
1490	>	} catch (Exception e) {
1491	>	throw new Error(e);
1492		}
1493		}
1494

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