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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.25 by dl, Fri Jul 31 16:27:08 2009 UTC vs.
Revision 1.72 by dl, Wed Nov 24 10:50:38 2010 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.io.Serializable;
10		import java.util.Collection;
11		import java.util.Collections;
12		import java.util.List;
13	+	import java.util.RandomAccess;
14		import java.util.Map;
15		import java.util.WeakHashMap;
16	+	import java.util.concurrent.Callable;
17	+	import java.util.concurrent.CancellationException;
18	+	import java.util.concurrent.ExecutionException;
19	+	import java.util.concurrent.Executor;
20	+	import java.util.concurrent.ExecutorService;
21	+	import java.util.concurrent.Future;
22	+	import java.util.concurrent.RejectedExecutionException;
23	+	import java.util.concurrent.RunnableFuture;
24	+	import java.util.concurrent.TimeUnit;
25	+	import java.util.concurrent.TimeoutException;
26
27		/**
28	<	* Abstract base class for tasks that run within a {@link
29	<	* ForkJoinPool}.  A ForkJoinTask is a thread-like entity that is much
28	>	* Abstract base class for tasks that run within a {@link ForkJoinPool}.
29	>	* A {@code ForkJoinTask} is a thread-like entity that is much
30		* lighter weight than a normal thread.  Huge numbers of tasks and
31		* subtasks may be hosted by a small number of actual threads in a
32		* ForkJoinPool, at the price of some usage limitations.
33		*
34	<	* <p> A "main" ForkJoinTask begins execution when submitted to a
35	<	* {@link ForkJoinPool}. Once started, it will usually in turn start
36	<	* other subtasks.  As indicated by the name of this class, many
37	<	* programs using ForkJoinTasks employ only methods {@code fork} and
38	<	* {@code join}, or derivatives such as {@code invokeAll}.  However,
39	<	* this class also provides a number of other methods that can come
40	<	* into play in advanced usages, as well as extension mechanics that
41	<	* allow support of new forms of fork/join processing.
34	>	* <p>A "main" {@code ForkJoinTask} begins execution when submitted
35	>	* to a {@link ForkJoinPool}.  Once started, it will usually in turn
36	>	* start other subtasks.  As indicated by the name of this class,
37	>	* many programs using {@code ForkJoinTask} employ only methods
38	>	* {@link #fork} and {@link #join}, or derivatives such as {@link
39	>	* #invokeAll(ForkJoinTask...) invokeAll}.  However, this class also
40	>	* provides a number of other methods that can come into play in
41	>	* advanced usages, as well as extension mechanics that allow
42	>	* support of new forms of fork/join processing.
43		*
44	<	* <p>A ForkJoinTask is a lightweight form of {@link Future}.  The
45	<	* efficiency of ForkJoinTasks stems from a set of restrictions (that
46	<	* are only partially statically enforceable) reflecting their
47	<	* intended use as computational tasks calculating pure functions or
48	<	* operating on purely isolated objects.  The primary coordination
49	<	* mechanisms are {@link #fork}, that arranges asynchronous execution,
50	<	* and {@link #join}, that doesn't proceed until the task's result has
51	<	* been computed.  Computations should avoid {@code synchronized}
52	<	* methods or blocks, and should minimize other blocking
53	<	* synchronization apart from joining other tasks or using
54	<	* synchronizers such as Phasers that are advertised to cooperate with
55	<	* fork/join scheduling. Tasks should also not perform blocking IO,
56	<	* and should ideally access variables that are completely independent
57	<	* of those accessed by other running tasks. Minor breaches of these
58	<	* restrictions, for example using shared output streams, may be
59	<	* tolerable in practice, but frequent use may result in poor
60	<	* performance, and the potential to indefinitely stall if the number
61	<	* of threads not waiting for IO or other external synchronization
62	<	* becomes exhausted. This usage restriction is in part enforced by
63	<	* not permitting checked exceptions such as {@code IOExceptions}
64	<	* to be thrown. However, computations may still encounter unchecked
65	<	* exceptions, that are rethrown to callers attempting join
66	<	* them. These exceptions may additionally include
67	<	* RejectedExecutionExceptions stemming from internal resource
68	<	* exhaustion such as failure to allocate internal task queues.
44	>	* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
45	>	* The efficiency of {@code ForkJoinTask}s stems from a set of
46	>	* restrictions (that are only partially statically enforceable)
47	>	* reflecting their intended use as computational tasks calculating
48	>	* pure functions or operating on purely isolated objects.  The
49	>	* primary coordination mechanisms are {@link #fork}, that arranges
50	>	* asynchronous execution, and {@link #join}, that doesn't proceed
51	>	* until the task's result has been computed.  Computations should
52	>	* avoid {@code synchronized} methods or blocks, and should minimize
53	>	* other blocking synchronization apart from joining other tasks or
54	>	* using synchronizers such as Phasers that are advertised to
55	>	* cooperate with fork/join scheduling. Tasks should also not perform
56	>	* blocking IO, and should ideally access variables that are
57	>	* completely independent of those accessed by other running
58	>	* tasks. Minor breaches of these restrictions, for example using
59	>	* shared output streams, may be tolerable in practice, but frequent
60	>	* use may result in poor performance, and the potential to
61	>	* indefinitely stall if the number of threads not waiting for IO or
62	>	* other external synchronization becomes exhausted. This usage
63	>	* restriction is in part enforced by not permitting checked
64	>	* exceptions such as {@code IOExceptions} to be thrown. However,
65	>	* computations may still encounter unchecked exceptions, that are
66	>	* rethrown to callers attempting to join them. These exceptions may
67	>	* additionally include {@link RejectedExecutionException} stemming
68	>	* from internal resource exhaustion, such as failure to allocate
69	>	* internal task queues.
70		*
71		* <p>The primary method for awaiting completion and extracting
72		* results of a task is {@link #join}, but there are several variants:
73		* The {@link Future#get} methods support interruptible and/or timed
74		* waits for completion and report results using {@code Future}
75	<	* conventions. Method {@link #helpJoin} enables callers to actively
76	<	* execute other tasks while awaiting joins, which is sometimes more
77	<	* efficient but only applies when all subtasks are known to be
78	<	* strictly tree-structured. Method {@link #invoke} is semantically
68	<	* equivalent to {@code fork(); join()} but always attempts to
69	<	* begin execution in the current thread. The "<em>quiet</em>" forms
70	<	* of these methods do not extract results or report exceptions. These
75	>	* conventions. Method {@link #invoke} is semantically
76	>	* equivalent to {@code fork(); join()} but always attempts to begin
77	>	* execution in the current thread. The "<em>quiet</em>" forms of
78	>	* these methods do not extract results or report exceptions. These
79		* may be useful when a set of tasks are being executed, and you need
80		* to delay processing of results or exceptions until all complete.
81		* Method {@code invokeAll} (available in multiple versions)
82		* performs the most common form of parallel invocation: forking a set
83		* of tasks and joining them all.
84		*
85	<	* <p> The ForkJoinTask class is not usually directly subclassed.
85	>	* <p>The execution status of tasks may be queried at several levels
86	>	* of detail: {@link #isDone} is true if a task completed in any way
87	>	* (including the case where a task was cancelled without executing);
88	>	* {@link #isCompletedNormally} is true if a task completed without
89	>	* cancellation or encountering an exception; {@link #isCancelled} is
90	>	* true if the task was cancelled (in which case {@link #getException}
91	>	* returns a {@link java.util.concurrent.CancellationException}); and
92	>	* {@link #isCompletedAbnormally} is true if a task was either
93	>	* cancelled or encountered an exception, in which case {@link
94	>	* #getException} will return either the encountered exception or
95	>	* {@link java.util.concurrent.CancellationException}.
96	>	*
97	>	* <p>The ForkJoinTask class is not usually directly subclassed.
98		* Instead, you subclass one of the abstract classes that support a
99	<	* particular style of fork/join processing.  Normally, a concrete
99	>	* particular style of fork/join processing, typically {@link
100	>	* RecursiveAction} for computations that do not return results, or
101	>	* {@link RecursiveTask} for those that do.  Normally, a concrete
102		* ForkJoinTask subclass declares fields comprising its parameters,
103		* established in a constructor, and then defines a {@code compute}
104		* method that somehow uses the control methods supplied by this base
105		* class. While these methods have {@code public} access (to allow
106	<	* instances of different task subclasses to call each others
106	>	* instances of different task subclasses to call each other's
107		* methods), some of them may only be called from within other
108		* ForkJoinTasks (as may be determined using method {@link
109		* #inForkJoinPool}).  Attempts to invoke them in other contexts
110		* result in exceptions or errors, possibly including
111	<	* ClassCastException.
111	>	* {@code ClassCastException}.
112		*
113	<	* <p>Most base support methods are {@code final} because their
114	<	* implementations are intrinsically tied to the underlying
115	<	* lightweight task scheduling framework, and so cannot be overridden.
116	<	* Developers creating new basic styles of fork/join processing should
117	<	* minimally implement {@code protected} methods
118	<	* {@link #exec}, {@link #setRawResult}, and
119	<	* {@link #getRawResult}, while also introducing an abstract
120	<	* computational method that can be implemented in its subclasses,
121	<	* possibly relying on other {@code protected} methods provided
122	<	* by this class.
113	>	* <p>Method {@link #join} and its variants are appropriate for use
114	>	* only when completion dependencies are acyclic; that is, the
115	>	* parallel computation can be described as a directed acyclic graph
116	>	* (DAG). Otherwise, executions may encounter a form of deadlock as
117	>	* tasks cyclically wait for each other.  However, this framework
118	>	* supports other methods and techniques (for example the use of
119	>	* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
120	>	* may be of use in constructing custom subclasses for problems that
121	>	* are not statically structured as DAGs.
122	>	*
123	>	* <p>Most base support methods are {@code final}, to prevent
124	>	* overriding of implementations that are intrinsically tied to the
125	>	* underlying lightweight task scheduling framework.  Developers
126	>	* creating new basic styles of fork/join processing should minimally
127	>	* implement {@code protected} methods {@link #exec}, {@link
128	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
129	>	* an abstract computational method that can be implemented in its
130	>	* subclasses, possibly relying on other {@code protected} methods
131	>	* provided by this class.
132		*
133		* <p>ForkJoinTasks should perform relatively small amounts of
134	<	* computations, otherwise splitting into smaller tasks. As a very
135	<	* rough rule of thumb, a task should perform more than 100 and less
136	<	* than 10000 basic computational steps. If tasks are too big, then
137	<	* parallelism cannot improve throughput. If too small, then memory
138	<	* and internal task maintenance overhead may overwhelm processing.
134	>	* computation. Large tasks should be split into smaller subtasks,
135	>	* usually via recursive decomposition. As a very rough rule of thumb,
136	>	* a task should perform more than 100 and less than 10000 basic
137	>	* computational steps, and should avoid indefinite looping. If tasks
138	>	* are too big, then parallelism cannot improve throughput. If too
139	>	* small, then memory and internal task maintenance overhead may
140	>	* overwhelm processing.
141	>	*
142	>	* <p>This class provides {@code adapt} methods for {@link Runnable}
143	>	* and {@link Callable}, that may be of use when mixing execution of
144	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
145	>	* of this form, consider using a pool constructed in <em>asyncMode</em>.
146		*
147	<	* <p>ForkJoinTasks are {@code Serializable}, which enables them
148	<	* to be used in extensions such as remote execution frameworks. It is
149	<	* in general sensible to serialize tasks only before or after, but
150	<	* not during execution. Serialization is not relied on during
113	<	* execution itself.
147	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
148	>	* used in extensions such as remote execution frameworks. It is
149	>	* sensible to serialize tasks only before or after, but not during,
150	>	* execution. Serialization is not relied on during execution itself.
151		*
152		* @since 1.7
153		* @author Doug Lea
154		*/
155		public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
156
157	<	/**
158	<	* Run control status bits packed into a single int to minimize
159	<	* footprint and to ensure atomicity (via CAS).  Status is
160	<	* initially zero, and takes on nonnegative values until
161	<	* completed, upon which status holds COMPLETED. CANCELLED, or
162	<	* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
163	<	* blocking waits by other threads have SIGNAL_MASK bits set --
164	<	* bit 15 for external (nonFJ) waits, and the rest a count of
165	<	* waiting FJ threads.  (This representation relies on
166	<	* ForkJoinPool max thread limits). Completion of a stolen task
167	<	* with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
168	<	* though suboptimal for some purposes, we use basic builtin
169	<	* wait/notify to take advantage of "monitor inflation" in JVMs
170	<	* that we would otherwise need to emulate to avoid adding further
171	<	* per-task bookkeeping overhead. Note that bits 16-28 are
172	<	* currently unused. Also value 0x80000000 is available as spare
173	<	* completion value.
157	>	/*
158	>	* See the internal documentation of class ForkJoinPool for a
159	>	* general implementation overview.  ForkJoinTasks are mainly
160	>	* responsible for maintaining their "status" field amidst relays
161	>	* to methods in ForkJoinWorkerThread and ForkJoinPool. The
162	>	* methods of this class are more-or-less layered into (1) basic
163	>	* status maintenance (2) execution and awaiting completion (3)
164	>	* user-level methods that additionally report results. This is
165	>	* sometimes hard to see because this file orders exported methods
166	>	* in a way that flows well in javadocs. In particular, most
167	>	* join mechanics are in method quietlyJoin, below.
168	>	*/
169	>
170	>	/*
171	>	* The status field holds run control status bits packed into a
172	>	* single int to minimize footprint and to ensure atomicity (via
173	>	* CAS).  Status is initially zero, and takes on nonnegative
174	>	* values until completed, upon which status holds value
175	>	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
176	>	* waits by other threads have the SIGNAL bit set.  Completion of
177	>	* a stolen task with SIGNAL set awakens any waiters via
178	>	* notifyAll. Even though suboptimal for some purposes, we use
179	>	* basic builtin wait/notify to take advantage of "monitor
180	>	* inflation" in JVMs that we would otherwise need to emulate to
181	>	* avoid adding further per-task bookkeeping overhead.  We want
182	>	* these monitors to be "fat", i.e., not use biasing or thin-lock
183	>	* techniques, so use some odd coding idioms that tend to avoid
184	>	* them.
185		*/
186	+
187	+	/** The run status of this task */
188		volatile int status; // accessed directly by pool and workers
189
190	<	static final int COMPLETION_MASK      = 0xe0000000;
191	<	static final int NORMAL               = 0xe0000000; // == mask
192	<	static final int CANCELLED            = 0xc0000000;
193	<	static final int EXCEPTIONAL          = 0xa0000000;
144	<	static final int SIGNAL_MASK          = 0x0000ffff;
145	<	static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
146	<	static final int EXTERNAL_SIGNAL      = 0x00008000; // top bit of low word
190	>	private static final int NORMAL      = -1;
191	>	private static final int CANCELLED   = -2;
192	>	private static final int EXCEPTIONAL = -3;
193	>	private static final int SIGNAL      =  1;
194
195		/**
196		* Table of exceptions thrown by tasks, to enable reporting by
#	Line 157 | Line 204 | public abstract class ForkJoinTask<V> im
204		Collections.synchronizedMap
205		(new WeakHashMap<ForkJoinTask<?>, Throwable>());
206
207	<	// within-package utilities
161	<
162	<	/**
163	<	* Gets current worker thread, or null if not a worker thread.
164	<	*/
165	<	static ForkJoinWorkerThread getWorker() {
166	<	Thread t = Thread.currentThread();
167	<	return ((t instanceof ForkJoinWorkerThread) ?
168	<	(ForkJoinWorkerThread) t : null);
169	<	}
170	<
171	<	final boolean casStatus(int cmp, int val) {
172	<	return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val);
173	<	}
207	>	// Maintaining completion status
208
209		/**
210	<	* Workaround for not being able to rethrow unchecked exceptions.
211	<	*/
178	<	static void rethrowException(Throwable ex) {
179	<	if (ex != null)
180	<	UNSAFE.throwException(ex);
181	<	}
182	<
183	<	// Setting completion status
184	<
185	<	/**
186	<	* Marks completion and wakes up threads waiting to join this task.
210	>	* Marks completion and wakes up threads waiting to join this task,
211	>	* also clearing signal request bits.
212		*
213		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
214		*/
215	<	final void setCompletion(int completion) {
191	<	ForkJoinPool pool = getPool();
192	<	if (pool != null) {
193	<	int s; // Clear signal bits while setting completion status
194	<	do {} while ((s = status) >= 0 && !casStatus(s, completion));
195	<
196	<	if ((s & SIGNAL_MASK) != 0) {
197	<	if ((s &= INTERNAL_SIGNAL_MASK) != 0)
198	<	pool.updateRunningCount(s);
199	<	synchronized (this) { notifyAll(); }
200	<	}
201	<	}
202	<	else
203	<	externallySetCompletion(completion);
204	<	}
205	<
206	<	/**
207	<	* Version of setCompletion for non-FJ threads.  Leaves signal
208	<	* bits for unblocked threads to adjust, and always notifies.
209	<	*/
210	<	private void externallySetCompletion(int completion) {
211	<	int s;
212	<	do {} while ((s = status) >= 0 &&
213	<	!casStatus(s, (s & SIGNAL_MASK) | completion));
214	<	synchronized (this) { notifyAll(); }
215	<	}
216	<
217	<	/**
218	<	* Sets status to indicate normal completion.
219	<	*/
220	<	final void setNormalCompletion() {
221	<	// Try typical fast case -- single CAS, no signal, not already done.
222	<	// Manually expand casStatus to improve chances of inlining it
223	<	if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL))
224	<	setCompletion(NORMAL);
225	<	}
226	<
227	<	// internal waiting and notification
228	<
229	<	/**
230	<	* Performs the actual monitor wait for awaitDone.
231	<	*/
232	<	private void doAwaitDone() {
233	<	// Minimize lock bias and in/de-flation effects by maximizing
234	<	// chances of waiting inside sync
235	<	try {
236	<	while (status >= 0)
237	<	synchronized (this) { if (status >= 0) wait(); }
238	<	} catch (InterruptedException ie) {
239	<	onInterruptedWait();
240	<	}
241	<	}
242	<
243	<	/**
244	<	* Performs the actual timed monitor wait for awaitDone.
245	<	*/
246	<	private void doAwaitDone(long startTime, long nanos) {
247	<	synchronized (this) {
248	<	try {
249	<	while (status >= 0) {
250	<	long nt = nanos - (System.nanoTime() - startTime);
251	<	if (nt <= 0)
252	<	break;
253	<	wait(nt / 1000000, (int) (nt % 1000000));
254	<	}
255	<	} catch (InterruptedException ie) {
256	<	onInterruptedWait();
257	<	}
258	<	}
259	<	}
260	<
261	<	// Awaiting completion
262	<
263	<	/**
264	<	* Sets status to indicate there is joiner, then waits for join,
265	<	* surrounded with pool notifications.
266	<	*
267	<	* @return status upon exit
268	<	*/
269	<	private int awaitDone(ForkJoinWorkerThread w,
270	<	boolean maintainParallelism) {
271	<	ForkJoinPool pool = (w == null) ? null : w.pool;
215	>	private void setCompletion(int completion) {
216		int s;
217		while ((s = status) >= 0) {
218	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
219	<	if (pool == null || !pool.preJoin(this, maintainParallelism))
220	<	doAwaitDone();
277	<	if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
278	<	adjustPoolCountsOnUnblock(pool);
218	>	if (UNSAFE.compareAndSwapInt(this, statusOffset, s, completion)) {
219	>	if (s != 0)
220	>	synchronized (this) { notifyAll(); }
221		break;
222		}
223		}
282	–	return s;
224		}
225
226		/**
227	<	* Timed version of awaitDone
227	>	* Records exception and sets exceptional completion.
228		*
229	<	* @return status upon exit
229	>	* @return status on exit
230		*/
231	<	private int awaitDone(ForkJoinWorkerThread w, long nanos) {
291	<	ForkJoinPool pool = (w == null) ? null : w.pool;
292	<	int s;
293	<	while ((s = status) >= 0) {
294	<	if (casStatus(s, (pool == null) ? s|EXTERNAL_SIGNAL : s+1)) {
295	<	long startTime = System.nanoTime();
296	<	if (pool == null || !pool.preJoin(this, false))
297	<	doAwaitDone(startTime, nanos);
298	<	if ((s = status) >= 0) {
299	<	adjustPoolCountsOnCancelledWait(pool);
300	<	s = status;
301	<	}
302	<	if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
303	<	adjustPoolCountsOnUnblock(pool);
304	<	break;
305	<	}
306	<	}
307	<	return s;
308	<	}
309	<
310	<	/**
311	<	* Notifies pool that thread is unblocked. Called by signalled
312	<	* threads when woken by non-FJ threads (which is atypical).
313	<	*/
314	<	private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
315	<	int s;
316	<	do {} while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
317	<	if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
318	<	pool.updateRunningCount(s);
319	<	}
320	<
321	<	/**
322	<	* Notifies pool to adjust counts on cancelled or timed out wait.
323	<	*/
324	<	private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
325	<	if (pool != null) {
326	<	int s;
327	<	while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
328	<	if (casStatus(s, s - 1)) {
329	<	pool.updateRunningCount(1);
330	<	break;
331	<	}
332	<	}
333	<	}
334	<	}
335	<
336	<	/**
337	<	* Handles interruptions during waits.
338	<	*/
339	<	private void onInterruptedWait() {
340	<	ForkJoinWorkerThread w = getWorker();
341	<	if (w == null)
342	<	Thread.currentThread().interrupt(); // re-interrupt
343	<	else if (w.isTerminating())
344	<	cancelIgnoringExceptions();
345	<	// else if FJworker, ignore interrupt
346	<	}
347	<
348	<	// Recording and reporting exceptions
349	<
350	<	private void setDoneExceptionally(Throwable rex) {
231	>	private void setExceptionalCompletion(Throwable rex) {
232		exceptionMap.put(this, rex);
233		setCompletion(EXCEPTIONAL);
234		}
235
236		/**
237	<	* Throws the exception associated with status s.
238	<	*
358	<	* @throws the exception
237	>	* Blocks a worker thread until completed or timed out.  Called
238	>	* only by pool.
239		*/
240	<	private void reportException(int s) {
241	<	if ((s &= COMPLETION_MASK) < NORMAL) {
242	<	if (s == CANCELLED)
243	<	throw new CancellationException();
244	<	else
245	<	rethrowException(exceptionMap.get(this));
240	>	final void internalAwaitDone(long millis, int nanos) {
241	>	int s = status;
242	>	if ((s == 0 &&
243	>	UNSAFE.compareAndSwapInt(this, statusOffset, 0, SIGNAL)) ||
244	>	s > 0)  {
245	>	try {     // the odd construction reduces lock bias effects
246	>	synchronized (this) {
247	>	if (status > 0)
248	>	wait(millis, nanos);
249	>	else
250	>	notifyAll();
251	>	}
252	>	} catch (InterruptedException ie) {
253	>	cancelIfTerminating();
254	>	}
255		}
256		}
257
258		/**
259	<	* Returns result or throws exception using j.u.c.Future conventions.
371	<	* Only call when {@code isDone} known to be true.
259	>	* Blocks a non-worker-thread until completion.
260		*/
261	<	private V reportFutureResult()
262	<	throws ExecutionException, InterruptedException {
263	<	int s = status & COMPLETION_MASK;
264	<	if (s < NORMAL) {
265	<	Throwable ex;
266	<	if (s == CANCELLED)
267	<	throw new CancellationException();
268	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
269	<	throw new ExecutionException(ex);
270	<	if (Thread.interrupted())
271	<	throw new InterruptedException();
261	>	private void externalAwaitDone() {
262	>	if (status >= 0) {
263	>	boolean interrupted = false;
264	>	synchronized(this) {
265	>	for (;;) {
266	>	int s = status;
267	>	if (s == 0)
268	>	UNSAFE.compareAndSwapInt(this, statusOffset,
269	>	0, SIGNAL);
270	>	else if (s < 0) {
271	>	notifyAll();
272	>	break;
273	>	}
274	>	else {
275	>	try {
276	>	wait();
277	>	} catch (InterruptedException ie) {
278	>	interrupted = true;
279	>	}
280	>	}
281	>	}
282	>	}
283	>	if (interrupted)
284	>	Thread.currentThread().interrupt();
285		}
385	–	return getRawResult();
286		}
287
288		/**
289	<	* Returns result or throws exception using j.u.c.Future conventions
390	<	* with timeouts.
289	>	* Blocks a non-worker-thread until completion or interruption or timeout.
290		*/
291	<	private V reportTimedFutureResult()
292	<	throws InterruptedException, ExecutionException, TimeoutException {
394	<	Throwable ex;
395	<	int s = status & COMPLETION_MASK;
396	<	if (s == NORMAL)
397	<	return getRawResult();
398	<	if (s == CANCELLED)
399	<	throw new CancellationException();
400	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
401	<	throw new ExecutionException(ex);
291	>	private void externalInterruptibleAwaitDone(boolean timed, long nanos)
292	>	throws InterruptedException {
293		if (Thread.interrupted())
294		throw new InterruptedException();
404	–	throw new TimeoutException();
405	–	}
406	–
407	–	// internal execution methods
408	–
409	–	/**
410	–	* Calls exec, recording completion, and rethrowing exception if
411	–	* encountered. Caller should normally check status before calling.
412	–	*
413	–	* @return true if completed normally
414	–	*/
415	–	private boolean tryExec() {
416	–	try { // try block must contain only call to exec
417	–	if (!exec())
418	–	return false;
419	–	} catch (Throwable rex) {
420	–	setDoneExceptionally(rex);
421	–	rethrowException(rex);
422	–	return false; // not reached
423	–	}
424	–	setNormalCompletion();
425	–	return true;
426	–	}
427	–
428	–	/**
429	–	* Main execution method used by worker threads. Invokes
430	–	* base computation unless already complete.
431	–	*/
432	–	final void quietlyExec() {
295		if (status >= 0) {
296	<	try {
297	<	if (!exec())
298	<	return;
299	<	} catch (Throwable rex) {
300	<	setDoneExceptionally(rex);
301	<	return;
296	>	long startTime = timed ? System.nanoTime() : 0L;
297	>	synchronized(this) {
298	>	for (;;) {
299	>	long nt;
300	>	int s = status;
301	>	if (s == 0)
302	>	UNSAFE.compareAndSwapInt(this, statusOffset,
303	>	0, SIGNAL);
304	>	else if (s < 0) {
305	>	notifyAll();
306	>	break;
307	>	}
308	>	else if (!timed)
309	>	wait();
310	>	else if ((nt = nanos - (System.nanoTime()-startTime)) > 0L)
311	>	wait(nt / 1000000, (int)(nt % 1000000));
312	>	else
313	>	break;
314	>	}
315		}
441	–	setNormalCompletion();
316		}
317		}
318
319		/**
320	<	* Calls exec(), recording but not rethrowing exception.
321	<	* Caller should normally check status before calling.
322	<	*
449	<	* @return true if completed normally
320	>	* Unless done, calls exec and records status if completed, but
321	>	* doesn't wait for completion otherwise. Primary execution method
322	>	* for ForkJoinWorkerThread.
323		*/
324	<	private boolean tryQuietlyInvoke() {
324	>	final void quietlyExec() {
325		try {
326	<	if (!exec())
327	<	return false;
326	>	if (status < 0 || !exec())
327	>	return;
328		} catch (Throwable rex) {
329	<	setDoneExceptionally(rex);
330	<	return false;
458	<	}
459	<	setNormalCompletion();
460	<	return true;
461	<	}
462	<
463	<	/**
464	<	* Cancels, ignoring any exceptions it throws.
465	<	*/
466	<	final void cancelIgnoringExceptions() {
467	<	try {
468	<	cancel(false);
469	<	} catch (Throwable ignore) {
329	>	setExceptionalCompletion(rex);
330	>	return;
331		}
332	<	}
472	<
473	<	/**
474	<	* Main implementation of helpJoin
475	<	*/
476	<	private int busyJoin(ForkJoinWorkerThread w) {
477	<	int s;
478	<	ForkJoinTask<?> t;
479	<	while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
480	<	t.quietlyExec();
481	<	return (s >= 0) ? awaitDone(w, false) : s; // block if no work
332	>	setCompletion(NORMAL); // must be outside try block
333		}
334
335		// public methods
#	Line 486 | Line 337 | public abstract class ForkJoinTask<V> im
337		/**
338		* Arranges to asynchronously execute this task.  While it is not
339		* necessarily enforced, it is a usage error to fork a task more
340	<	* than once unless it has completed and been reinitialized.  This
341	<	* method may be invoked only from within ForkJoinTask
342	<	* computations (as may be determined using method {@link
343	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
344	<	* in exceptions or errors, possibly including ClassCastException.
340	>	* than once unless it has completed and been reinitialized.
341	>	* Subsequent modifications to the state of this task or any data
342	>	* it operates on are not necessarily consistently observable by
343	>	* any thread other than the one executing it unless preceded by a
344	>	* call to {@link #join} or related methods, or a call to {@link
345	>	* #isDone} returning {@code true}.
346	>	*
347	>	* <p>This method may be invoked only from within {@code
348	>	* ForkJoinPool} computations (as may be determined using method
349	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
350	>	* result in exceptions or errors, possibly including {@code
351	>	* ClassCastException}.
352		*
353	<	* @return {@code this}, to simplify usage.
353	>	* @return {@code this}, to simplify usage
354		*/
355		public final ForkJoinTask<V> fork() {
356		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 501 | Line 359 | public abstract class ForkJoinTask<V> im
359		}
360
361		/**
362	<	* Returns the result of the computation when it is ready.
363	<	* This method differs from {@code get} in that abnormal
364	<	* completion results in RuntimeExceptions or Errors, not
365	<	* ExecutionExceptions.
362	>	* Returns the result of the computation when it {@link #isDone is
363	>	* done}.  This method differs from {@link #get()} in that
364	>	* abnormal completion results in {@code RuntimeException} or
365	>	* {@code Error}, not {@code ExecutionException}, and that
366	>	* interrupts of the calling thread do <em>not</em> cause the
367	>	* method to abruptly return by throwing {@code
368	>	* InterruptedException}.
369		*
370		* @return the computed result
371		*/
372		public final V join() {
373	<	ForkJoinWorkerThread w = getWorker();
374	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryExec())
375	<	reportException(awaitDone(w, true));
373	>	quietlyJoin();
374	>	Throwable ex;
375	>	if (status < NORMAL && (ex = getException()) != null)
376	>	UNSAFE.throwException(ex);
377		return getRawResult();
378		}
379
380		/**
381		* Commences performing this task, awaits its completion if
382	<	* necessary, and return its result.
382	>	* necessary, and returns its result, or throws an (unchecked)
383	>	* {@code RuntimeException} or {@code Error} if the underlying
384	>	* computation did so.
385		*
522	–	* @throws Throwable (a RuntimeException, Error, or unchecked
523	–	* exception) if the underlying computation did so
386		* @return the computed result
387		*/
388		public final V invoke() {
389	<	if (status >= 0 && tryExec())
390	<	return getRawResult();
391	<	else
392	<	return join();
389	>	quietlyInvoke();
390	>	Throwable ex;
391	>	if (status < NORMAL && (ex = getException()) != null)
392	>	UNSAFE.throwException(ex);
393	>	return getRawResult();
394		}
395
396		/**
397	<	* Forks both tasks, returning when {@code isDone} holds for
398	<	* both of them or an exception is encountered. This method may be
399	<	* invoked only from within ForkJoinTask computations (as may be
400	<	* determined using method {@link #inForkJoinPool}). Attempts to
401	<	* invoke in other contexts result in exceptions or errors,
402	<	* possibly including ClassCastException.
403	<	*
404	<	* @param t1 one task
405	<	* @param t2 the other task
406	<	* @throws NullPointerException if t1 or t2 are null
407	<	* @throws RuntimeException or Error if either task did so
397	>	* Forks the given tasks, returning when {@code isDone} holds for
398	>	* each task or an (unchecked) exception is encountered, in which
399	>	* case the exception is rethrown. If more than one task
400	>	* encounters an exception, then this method throws any one of
401	>	* these exceptions. If any task encounters an exception, the
402	>	* other may be cancelled. However, the execution status of
403	>	* individual tasks is not guaranteed upon exceptional return. The
404	>	* status of each task may be obtained using {@link
405	>	* #getException()} and related methods to check if they have been
406	>	* cancelled, completed normally or exceptionally, or left
407	>	* unprocessed.
408	>	*
409	>	* <p>This method may be invoked only from within {@code
410	>	* ForkJoinPool} computations (as may be determined using method
411	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
412	>	* result in exceptions or errors, possibly including {@code
413	>	* ClassCastException}.
414	>	*
415	>	* @param t1 the first task
416	>	* @param t2 the second task
417	>	* @throws NullPointerException if any task is null
418		*/
419	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
419	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
420		t2.fork();
421		t1.invoke();
422		t2.join();
423		}
424
425		/**
426	<	* Forks the given tasks, returning when {@code isDone} holds
427	<	* for all of them. If any task encounters an exception, others
428	<	* may be cancelled.  This method may be invoked only from within
429	<	* ForkJoinTask computations (as may be determined using method
430	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
431	<	* result in exceptions or errors, possibly including
432	<	* ClassCastException.
426	>	* Forks the given tasks, returning when {@code isDone} holds for
427	>	* each task or an (unchecked) exception is encountered, in which
428	>	* case the exception is rethrown. If more than one task
429	>	* encounters an exception, then this method throws any one of
430	>	* these exceptions. If any task encounters an exception, others
431	>	* may be cancelled. However, the execution status of individual
432	>	* tasks is not guaranteed upon exceptional return. The status of
433	>	* each task may be obtained using {@link #getException()} and
434	>	* related methods to check if they have been cancelled, completed
435	>	* normally or exceptionally, or left unprocessed.
436	>	*
437	>	* <p>This method may be invoked only from within {@code
438	>	* ForkJoinPool} computations (as may be determined using method
439	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
440	>	* result in exceptions or errors, possibly including {@code
441	>	* ClassCastException}.
442		*
443	<	* @param tasks the array of tasks
444	<	* @throws NullPointerException if tasks or any element are null
563	<	* @throws RuntimeException or Error if any task did so
443	>	* @param tasks the tasks
444	>	* @throws NullPointerException if any task is null
445		*/
446		public static void invokeAll(ForkJoinTask<?>... tasks) {
447		Throwable ex = null;
#	Line 575 | Line 456 | public abstract class ForkJoinTask<V> im
456		t.fork();
457		else {
458		t.quietlyInvoke();
459	<	if (ex == null)
459	>	if (ex == null && t.status < NORMAL)
460		ex = t.getException();
461		}
462		}
#	Line 586 | Line 467 | public abstract class ForkJoinTask<V> im
467		t.cancel(false);
468		else {
469		t.quietlyJoin();
470	<	if (ex == null)
470	>	if (ex == null && t.status < NORMAL)
471		ex = t.getException();
472		}
473		}
474		}
475		if (ex != null)
476	<	rethrowException(ex);
476	>	UNSAFE.throwException(ex);
477		}
478
479		/**
480	<	* Forks all tasks in the collection, returning when
481	<	* {@code isDone} holds for all of them. If any task
482	<	* encounters an exception, others may be cancelled.  This method
483	<	* may be invoked only from within ForkJoinTask computations (as
484	<	* may be determined using method {@link
485	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
486	<	* in exceptions or errors, possibly including ClassCastException.
480	>	* Forks all tasks in the specified collection, returning when
481	>	* {@code isDone} holds for each task or an (unchecked) exception
482	>	* is encountered, in which case the exception is rethrown. If
483	>	* more than one task encounters an exception, then this method
484	>	* throws any one of these exceptions. If any task encounters an
485	>	* exception, others may be cancelled. However, the execution
486	>	* status of individual tasks is not guaranteed upon exceptional
487	>	* return. The status of each task may be obtained using {@link
488	>	* #getException()} and related methods to check if they have been
489	>	* cancelled, completed normally or exceptionally, or left
490	>	* unprocessed.
491	>	*
492	>	* <p>This method may be invoked only from within {@code
493	>	* ForkJoinPool} computations (as may be determined using method
494	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
495	>	* result in exceptions or errors, possibly including {@code
496	>	* ClassCastException}.
497		*
498		* @param tasks the collection of tasks
499		* @return the tasks argument, to simplify usage
500		* @throws NullPointerException if tasks or any element are null
610	–	* @throws RuntimeException or Error if any task did so
501		*/
502		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
503	<	if (!(tasks instanceof List<?>)) {
503	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
504		invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
505		return tasks;
506		}
#	Line 629 | Line 519 | public abstract class ForkJoinTask<V> im
519		t.fork();
520		else {
521		t.quietlyInvoke();
522	<	if (ex == null)
522	>	if (ex == null && t.status < NORMAL)
523		ex = t.getException();
524		}
525		}
#	Line 640 | Line 530 | public abstract class ForkJoinTask<V> im
530		t.cancel(false);
531		else {
532		t.quietlyJoin();
533	<	if (ex == null)
533	>	if (ex == null && t.status < NORMAL)
534		ex = t.getException();
535		}
536		}
537		}
538		if (ex != null)
539	<	rethrowException(ex);
539	>	UNSAFE.throwException(ex);
540		return tasks;
541		}
542
543		/**
544	<	* Returns {@code true} if the computation performed by this task
545	<	* has completed (or has been cancelled).
546	<	*
547	<	* @return {@code true} if this computation has completed
548	<	*/
549	<	public final boolean isDone() {
550	<	return status < 0;
551	<	}
552	<
553	<	/**
664	<	* Returns {@code true} if this task was cancelled.
665	<	*
666	<	* @return {@code true} if this task was cancelled
667	<	*/
668	<	public final boolean isCancelled() {
669	<	return (status & COMPLETION_MASK) == CANCELLED;
670	<	}
671	<
672	<	/**
673	<	* Asserts that the results of this task's computation will not be
674	<	* used. If a cancellation occurs before attempting to execute this
675	<	* task, execution will be suppressed, {@link #isCancelled}
676	<	* will report true, and {@link #join} will result in a
677	<	* {@code CancellationException} being thrown. Otherwise, when
678	<	* cancellation races with completion, there are no guarantees
679	<	* about whether {@code isCancelled} will report {@code true},
680	<	* whether {@code join} will return normally or via an exception,
681	<	* or whether these behaviors will remain consistent upon repeated
682	<	* invocation.
544	>	* Attempts to cancel execution of this task. This attempt will
545	>	* fail if the task has already completed or could not be
546	>	* cancelled for some other reason. If successful, and this task
547	>	* has not started when {@code cancel} is called, execution of
548	>	* this task is suppressed. After this method returns
549	>	* successfully, unless there is an intervening call to {@link
550	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
551	>	* {@link #isDone}, and {@code cancel} will return {@code true}
552	>	* and calls to {@link #join} and related methods will result in
553	>	* {@code CancellationException}.
554		*
555		* <p>This method may be overridden in subclasses, but if so, must
556	<	* still ensure that these minimal properties hold. In particular,
557	<	* the cancel method itself must not throw exceptions.
556	>	* still ensure that these properties hold. In particular, the
557	>	* {@code cancel} method itself must not throw exceptions.
558		*
559	<	* <p> This method is designed to be invoked by <em>other</em>
559	>	* <p>This method is designed to be invoked by <em>other</em>
560		* tasks. To terminate the current task, you can just return or
561		* throw an unchecked exception from its computation method, or
562		* invoke {@link #completeExceptionally}.
563		*
564	<	* @param mayInterruptIfRunning this value is ignored in the
565	<	* default implementation because tasks are not in general
566	<	* cancelled via interruption
564	>	* @param mayInterruptIfRunning this value has no effect in the
565	>	* default implementation because interrupts are not used to
566	>	* control cancellation.
567		*
568		* @return {@code true} if this task is now cancelled
569		*/
570		public boolean cancel(boolean mayInterruptIfRunning) {
571		setCompletion(CANCELLED);
572	<	return (status & COMPLETION_MASK) == CANCELLED;
572	>	return status == CANCELLED;
573	>	}
574	>
575	>	/**
576	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
577	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
578	>	* exceptions, but if it does anyway, we have no recourse during
579	>	* shutdown, so guard against this case.
580	>	*/
581	>	final void cancelIgnoringExceptions() {
582	>	try {
583	>	cancel(false);
584	>	} catch (Throwable ignore) {
585	>	}
586	>	}
587	>
588	>	/**
589	>	* Cancels if current thread is a terminating worker thread,
590	>	* ignoring any exceptions thrown by cancel.
591	>	*/
592	>	final void cancelIfTerminating() {
593	>	Thread t = Thread.currentThread();
594	>	if ((t instanceof ForkJoinWorkerThread) &&
595	>	((ForkJoinWorkerThread) t).isTerminating()) {
596	>	try {
597	>	cancel(false);
598	>	} catch (Throwable ignore) {
599	>	}
600	>	}
601	>	}
602	>
603	>	public final boolean isDone() {
604	>	return status < 0;
605	>	}
606	>
607	>	public final boolean isCancelled() {
608	>	return status == CANCELLED;
609		}
610
611		/**
#	Line 707 | Line 614 | public abstract class ForkJoinTask<V> im
614		* @return {@code true} if this task threw an exception or was cancelled
615		*/
616		public final boolean isCompletedAbnormally() {
617	<	return (status & COMPLETION_MASK) < NORMAL;
617	>	return status < NORMAL;
618	>	}
619	>
620	>	/**
621	>	* Returns {@code true} if this task completed without throwing an
622	>	* exception and was not cancelled.
623	>	*
624	>	* @return {@code true} if this task completed without throwing an
625	>	* exception and was not cancelled
626	>	*/
627	>	public final boolean isCompletedNormally() {
628	>	return status == NORMAL;
629		}
630
631		/**
632		* Returns the exception thrown by the base computation, or a
633	<	* CancellationException if cancelled, or null if none or if the
634	<	* method has not yet completed.
633	>	* {@code CancellationException} if cancelled, or {@code null} if
634	>	* none or if the method has not yet completed.
635		*
636		* @return the exception, or {@code null} if none
637		*/
638		public final Throwable getException() {
639	<	int s = status & COMPLETION_MASK;
640	<	if (s >= NORMAL)
641	<	return null;
642	<	if (s == CANCELLED)
725	<	return new CancellationException();
726	<	return exceptionMap.get(this);
639	>	int s = status;
640	>	return ((s >= NORMAL)    ? null :
641	>	(s == CANCELLED) ? new CancellationException() :
642	>	exceptionMap.get(this));
643		}
644
645		/**
#	Line 732 | Line 648 | public abstract class ForkJoinTask<V> im
648		* {@code join} and related operations. This method may be used
649		* to induce exceptions in asynchronous tasks, or to force
650		* completion of tasks that would not otherwise complete.  Its use
651	<	* in other situations is likely to be wrong.  This method is
651	>	* in other situations is discouraged.  This method is
652		* overridable, but overridden versions must invoke {@code super}
653		* implementation to maintain guarantees.
654		*
655	<	* @param ex the exception to throw. If this exception is
656	<	* not a RuntimeException or Error, the actual exception thrown
657	<	* will be a RuntimeException with cause ex.
655	>	* @param ex the exception to throw. If this exception is not a
656	>	* {@code RuntimeException} or {@code Error}, the actual exception
657	>	* thrown will be a {@code RuntimeException} with cause {@code ex}.
658		*/
659		public void completeExceptionally(Throwable ex) {
660	<	setDoneExceptionally((ex instanceof RuntimeException) ||
661	<	(ex instanceof Error) ? ex :
662	<	new RuntimeException(ex));
660	>	setExceptionalCompletion((ex instanceof RuntimeException) ||
661	>	(ex instanceof Error) ? ex :
662	>	new RuntimeException(ex));
663		}
664
665		/**
666		* Completes this task, and if not already aborted or cancelled,
667	<	* returning a {@code null} result upon {@code join} and related
668	<	* operations. This method may be used to provide results for
669	<	* asynchronous tasks, or to provide alternative handling for
670	<	* tasks that would not otherwise complete normally. Its use in
671	<	* other situations is likely to be wrong. This method is
672	<	* overridable, but overridden versions must invoke {@code super}
673	<	* implementation to maintain guarantees.
667	>	* returning the given value as the result of subsequent
668	>	* invocations of {@code join} and related operations. This method
669	>	* may be used to provide results for asynchronous tasks, or to
670	>	* provide alternative handling for tasks that would not otherwise
671	>	* complete normally. Its use in other situations is
672	>	* discouraged. This method is overridable, but overridden
673	>	* versions must invoke {@code super} implementation to maintain
674	>	* guarantees.
675		*
676		* @param value the result value for this task
677		*/
#	Line 762 | Line 679 | public abstract class ForkJoinTask<V> im
679		try {
680		setRawResult(value);
681		} catch (Throwable rex) {
682	<	setDoneExceptionally(rex);
682	>	setExceptionalCompletion(rex);
683		return;
684		}
685	<	setNormalCompletion();
769	<	}
770	<
771	<	public final V get() throws InterruptedException, ExecutionException {
772	<	ForkJoinWorkerThread w = getWorker();
773	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
774	<	awaitDone(w, true);
775	<	return reportFutureResult();
776	<	}
777	<
778	<	public final V get(long timeout, TimeUnit unit)
779	<	throws InterruptedException, ExecutionException, TimeoutException {
780	<	long nanos = unit.toNanos(timeout);
781	<	ForkJoinWorkerThread w = getWorker();
782	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
783	<	awaitDone(w, nanos);
784	<	return reportTimedFutureResult();
685	>	setCompletion(NORMAL);
686		}
687
688		/**
689	<	* Possibly executes other tasks until this task is ready, then
690	<	* returns the result of the computation.  This method may be more
790	<	* efficient than {@code join}, but is only applicable when
791	<	* there are no potential dependencies between continuation of the
792	<	* current task and that of any other task that might be executed
793	<	* while helping. (This usually holds for pure divide-and-conquer
794	<	* tasks). This method may be invoked only from within
795	<	* ForkJoinTask computations (as may be determined using method
796	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
797	<	* result in exceptions or errors, possibly including
798	<	* ClassCastException.
689	>	* Waits if necessary for the computation to complete, and then
690	>	* retrieves its result.
691		*
692		* @return the computed result
693	+	* @throws CancellationException if the computation was cancelled
694	+	* @throws ExecutionException if the computation threw an
695	+	* exception
696	+	* @throws InterruptedException if the current thread is not a
697	+	* member of a ForkJoinPool and was interrupted while waiting
698		*/
699	<	public final V helpJoin() {
700	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
701	<	if (status < 0 || !w.unpushTask(this) || !tryExec())
702	<	reportException(busyJoin(w));
699	>	public final V get() throws InterruptedException, ExecutionException {
700	>	Thread t = Thread.currentThread();
701	>	if (t instanceof ForkJoinWorkerThread)
702	>	quietlyJoin();
703	>	else
704	>	externalInterruptibleAwaitDone(false, 0L);
705	>	int s = status;
706	>	if (s != NORMAL) {
707	>	Throwable ex;
708	>	if (s == CANCELLED)
709	>	throw new CancellationException();
710	>	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
711	>	throw new ExecutionException(ex);
712	>	}
713		return getRawResult();
714		}
715
716		/**
717	<	* Possibly executes other tasks until this task is ready.  This
718	<	* method may be invoked only from within ForkJoinTask
719	<	* computations (as may be determined using method {@link
720	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
721	<	* in exceptions or errors, possibly including ClassCastException.
717	>	* Waits if necessary for at most the given time for the computation
718	>	* to complete, and then retrieves its result, if available.
719	>	*
720	>	* @param timeout the maximum time to wait
721	>	* @param unit the time unit of the timeout argument
722	>	* @return the computed result
723	>	* @throws CancellationException if the computation was cancelled
724	>	* @throws ExecutionException if the computation threw an
725	>	* exception
726	>	* @throws InterruptedException if the current thread is not a
727	>	* member of a ForkJoinPool and was interrupted while waiting
728	>	* @throws TimeoutException if the wait timed out
729		*/
730	<	public final void quietlyHelpJoin() {
731	<	if (status >= 0) {
732	<	ForkJoinWorkerThread w =
733	<	(ForkJoinWorkerThread) Thread.currentThread();
734	<	if (!w.unpushTask(this) || !tryQuietlyInvoke())
735	<	busyJoin(w);
730	>	public final V get(long timeout, TimeUnit unit)
731	>	throws InterruptedException, ExecutionException, TimeoutException {
732	>	long nanos = unit.toNanos(timeout);
733	>	Thread t = Thread.currentThread();
734	>	if (t instanceof ForkJoinWorkerThread)
735	>	((ForkJoinWorkerThread)t).joinTask(this, true, nanos);
736	>	else
737	>	externalInterruptibleAwaitDone(true, nanos);
738	>	int s = status;
739	>	if (s != NORMAL) {
740	>	Throwable ex;
741	>	if (s == CANCELLED)
742	>	throw new CancellationException();
743	>	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
744	>	throw new ExecutionException(ex);
745	>	throw new TimeoutException();
746		}
747	+	return getRawResult();
748		}
749
750		/**
751	<	* Joins this task, without returning its result or throwing an
751	>	* Joins this task, without returning its result or throwing its
752		* exception. This method may be useful when processing
753		* collections of tasks when some have been cancelled or otherwise
754		* known to have aborted.
755		*/
756		public final void quietlyJoin() {
757	<	if (status >= 0) {
758	<	ForkJoinWorkerThread w = getWorker();
759	<	if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
760	<	awaitDone(w, true);
757	>	Thread t;
758	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
759	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
760	>	if (status >= 0) {
761	>	if (w.unpushTask(this)) {
762	>	boolean completed;
763	>	try {
764	>	completed = exec();
765	>	} catch (Throwable rex) {
766	>	setExceptionalCompletion(rex);
767	>	return;
768	>	}
769	>	if (completed) {
770	>	setCompletion(NORMAL);
771	>	return;
772	>	}
773	>	}
774	>	w.joinTask(this, false, 0L);
775	>	}
776		}
777	+	else
778	+	externalAwaitDone();
779		}
780
781		/**
782		* Commences performing this task and awaits its completion if
783	<	* necessary, without returning its result or throwing an
784	<	* exception. This method may be useful when processing
843	<	* collections of tasks when some have been cancelled or otherwise
844	<	* known to have aborted.
783	>	* necessary, without returning its result or throwing its
784	>	* exception.
785		*/
786		public final void quietlyInvoke() {
787	<	if (status >= 0 && !tryQuietlyInvoke())
788	<	quietlyJoin();
787	>	if (status >= 0) {
788	>	boolean completed;
789	>	try {
790	>	completed = exec();
791	>	} catch (Throwable rex) {
792	>	setExceptionalCompletion(rex);
793	>	return;
794	>	}
795	>	if (completed)
796	>	setCompletion(NORMAL);
797	>	else
798	>	quietlyJoin();
799	>	}
800		}
801
802		/**
803		* Possibly executes tasks until the pool hosting the current task
804	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
805	<	* designs in which many tasks are forked, but none are explicitly
806	<	* joined, instead executing them until all are processed.
804	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
805	>	* be of use in designs in which many tasks are forked, but none
806	>	* are explicitly joined, instead executing them until all are
807	>	* processed.
808	>	*
809	>	* <p>This method may be invoked only from within {@code
810	>	* ForkJoinPool} computations (as may be determined using method
811	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
812	>	* result in exceptions or errors, possibly including {@code
813	>	* ClassCastException}.
814		*/
815		public static void helpQuiesce() {
816		((ForkJoinWorkerThread) Thread.currentThread())
#	Line 865 | Line 823 | public abstract class ForkJoinTask<V> im
823		* this task, but only if reuse occurs when this task has either
824		* never been forked, or has been forked, then completed and all
825		* outstanding joins of this task have also completed. Effects
826	<	* under any other usage conditions are not guaranteed, and are
827	<	* almost surely wrong. This method may be useful when executing
826	>	* under any other usage conditions are not guaranteed.
827	>	* This method may be useful when executing
828		* pre-constructed trees of subtasks in loops.
829	+	*
830	+	* <p>Upon completion of this method, {@code isDone()} reports
831	+	* {@code false}, and {@code getException()} reports {@code
832	+	* null}. However, the value returned by {@code getRawResult} is
833	+	* unaffected. To clear this value, you can invoke {@code
834	+	* setRawResult(null)}.
835		*/
836		public void reinitialize() {
837	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
837	>	if (status == EXCEPTIONAL)
838		exceptionMap.remove(this);
839		status = 0;
840		}
#	Line 879 | Line 843 | public abstract class ForkJoinTask<V> im
843		* Returns the pool hosting the current task execution, or null
844		* if this task is executing outside of any ForkJoinPool.
845		*
846	+	* @see #inForkJoinPool
847		* @return the pool, or {@code null} if none
848		*/
849		public static ForkJoinPool getPool() {
#	Line 888 | Line 853 | public abstract class ForkJoinTask<V> im
853		}
854
855		/**
856	<	* Returns {@code true} if the current thread is executing as a
857	<	* ForkJoinPool computation.
856	>	* Returns {@code true} if the current thread is a {@link
857	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
858		*
859	<	* @return {@code true} if the current thread is executing as a
860	<	* ForkJoinPool computation, or false otherwise
859	>	* @return {@code true} if the current thread is a {@link
860	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
861	>	* or {@code false} otherwise
862		*/
863		public static boolean inForkJoinPool() {
864		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 904 | Line 870 | public abstract class ForkJoinTask<V> im
870		* by the current thread, and has not commenced executing in
871		* another thread.  This method may be useful when arranging
872		* alternative local processing of tasks that could have been, but
873	<	* were not, stolen. This method may be invoked only from within
874	<	* ForkJoinTask computations (as may be determined using method
875	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
876	<	* result in exceptions or errors, possibly including
877	<	* ClassCastException.
873	>	* were not, stolen.
874	>	*
875	>	* <p>This method may be invoked only from within {@code
876	>	* ForkJoinPool} computations (as may be determined using method
877	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
878	>	* result in exceptions or errors, possibly including {@code
879	>	* ClassCastException}.
880		*
881		* @return {@code true} if unforked
882		*/
#	Line 923 | Line 891 | public abstract class ForkJoinTask<V> im
891		* value may be useful for heuristic decisions about whether to
892		* fork other tasks.
893		*
894	+	* <p>This method may be invoked only from within {@code
895	+	* ForkJoinPool} computations (as may be determined using method
896	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
897	+	* result in exceptions or errors, possibly including {@code
898	+	* ClassCastException}.
899	+	*
900		* @return the number of tasks
901		*/
902		public static int getQueuedTaskCount() {
#	Line 940 | Line 914 | public abstract class ForkJoinTask<V> im
914		* tasks, and to process computations locally if this threshold is
915		* exceeded.
916		*
917	+	* <p>This method may be invoked only from within {@code
918	+	* ForkJoinPool} computations (as may be determined using method
919	+	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
920	+	* result in exceptions or errors, possibly including {@code
921	+	* ClassCastException}.
922	+	*
923		* @return the surplus number of tasks, which may be negative
924		*/
925		public static int getSurplusQueuedTaskCount() {
#	Line 975 | Line 955 | public abstract class ForkJoinTask<V> im
955		* called otherwise. The return value controls whether this task
956		* is considered to be done normally. It may return false in
957		* asynchronous actions that require explicit invocations of
958	<	* {@link #complete} to become joinable. It may throw exceptions
959	<	* to indicate abnormal exit.
958	>	* {@link #complete} to become joinable. It may also throw an
959	>	* (unchecked) exception to indicate abnormal exit.
960		*
961		* @return {@code true} if completed normally
982	–	* @throws Error or RuntimeException if encountered during computation
962		*/
963		protected abstract boolean exec();
964
#	Line 991 | Line 970 | public abstract class ForkJoinTask<V> im
970		* null even if a task exists but cannot be accessed without
971		* contention with other threads.  This method is designed
972		* primarily to support extensions, and is unlikely to be useful
973	<	* otherwise.  This method may be invoked only from within
974	<	* ForkJoinTask computations (as may be determined using method
975	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
976	<	* result in exceptions or errors, possibly including
977	<	* ClassCastException.
973	>	* otherwise.
974	>	*
975	>	* <p>This method may be invoked only from within {@code
976	>	* ForkJoinPool} computations (as may be determined using method
977	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
978	>	* result in exceptions or errors, possibly including {@code
979	>	* ClassCastException}.
980		*
981		* @return the next task, or {@code null} if none are available
982		*/
#	Line 1008 | Line 989 | public abstract class ForkJoinTask<V> im
989		* Unschedules and returns, without executing, the next task
990		* queued by the current thread but not yet executed.  This method
991		* is designed primarily to support extensions, and is unlikely to
992	<	* be useful otherwise.  This method may be invoked only from
993	<	* within ForkJoinTask computations (as may be determined using
994	<	* method {@link #inForkJoinPool}). Attempts to invoke in other
995	<	* contexts result in exceptions or errors, possibly including
996	<	* ClassCastException.
992	>	* be useful otherwise.
993	>	*
994	>	* <p>This method may be invoked only from within {@code
995	>	* ForkJoinPool} computations (as may be determined using method
996	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
997	>	* result in exceptions or errors, possibly including {@code
998	>	* ClassCastException}.
999		*
1000		* @return the next task, or {@code null} if none are available
1001		*/
#	Line 1029 | Line 1012 | public abstract class ForkJoinTask<V> im
1012		* {@code null} result does not necessarily imply quiescence
1013		* of the pool this task is operating in.  This method is designed
1014		* primarily to support extensions, and is unlikely to be useful
1015	<	* otherwise.  This method may be invoked only from within
1016	<	* ForkJoinTask computations (as may be determined using method
1017	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1018	<	* result in exceptions or errors, possibly including
1019	<	* ClassCastException.
1015	>	* otherwise.
1016	>	*
1017	>	* <p>This method may be invoked only from within {@code
1018	>	* ForkJoinPool} computations (as may be determined using method
1019	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1020	>	* result in exceptions or errors, possibly including {@code
1021	>	* ClassCastException}.
1022		*
1023		* @return a task, or {@code null} if none are available
1024		*/
#	Line 1073 | Line 1058 | public abstract class ForkJoinTask<V> im
1058		*/
1059		static final class AdaptedCallable<T> extends ForkJoinTask<T>
1060		implements RunnableFuture<T> {
1061	<	final Callable<T> callable;
1061	>	final Callable<? extends T> callable;
1062		T result;
1063	<	AdaptedCallable(Callable<T> callable) {
1063	>	AdaptedCallable(Callable<? extends T> callable) {
1064		if (callable == null) throw new NullPointerException();
1065		this.callable = callable;
1066		}
#	Line 1098 | Line 1083 | public abstract class ForkJoinTask<V> im
1083		}
1084
1085		/**
1086	<	* Returns a new ForkJoinTask that performs the {@code run}
1087	<	* method of the given Runnable as its action, and returns a null
1088	<	* result upon {@code join}.
1086	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1087	>	* method of the given {@code Runnable} as its action, and returns
1088	>	* a null result upon {@link #join}.
1089		*
1090		* @param runnable the runnable action
1091		* @return the task
1092		*/
1093	<	public static ForkJoinTask<Void> adapt(Runnable runnable) {
1093	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1094		return new AdaptedRunnable<Void>(runnable, null);
1095		}
1096
1097		/**
1098	<	* Returns a new ForkJoinTask that performs the {@code run}
1099	<	* method of the given Runnable as its action, and returns the
1100	<	* given result upon {@code join}.
1098	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1099	>	* method of the given {@code Runnable} as its action, and returns
1100	>	* the given result upon {@link #join}.
1101		*
1102		* @param runnable the runnable action
1103		* @param result the result upon completion
#	Line 1123 | Line 1108 | public abstract class ForkJoinTask<V> im
1108		}
1109
1110		/**
1111	<	* Returns a new ForkJoinTask that performs the {@code call}
1112	<	* method of the given Callable as its action, and returns its
1113	<	* result upon {@code join}, translating any checked
1114	<	* exceptions encountered into {@code RuntimeException}.
1111	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1112	>	* method of the given {@code Callable} as its action, and returns
1113	>	* its result upon {@link #join}, translating any checked exceptions
1114	>	* encountered into {@code RuntimeException}.
1115		*
1116		* @param callable the callable action
1117		* @return the task
1118		*/
1119	<	public static <T> ForkJoinTask<T> adapt(Callable<T> callable) {
1119	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1120		return new AdaptedCallable<T>(callable);
1121		}
1122
#	Line 1140 | Line 1125 | public abstract class ForkJoinTask<V> im
1125		private static final long serialVersionUID = -7721805057305804111L;
1126
1127		/**
1128	<	* Save the state to a stream.
1128	>	* Saves the state to a stream (that is, serializes it).
1129		*
1130		* @serialData the current run status and the exception thrown
1131		* during execution, or {@code null} if none
#	Line 1153 | Line 1138 | public abstract class ForkJoinTask<V> im
1138		}
1139
1140		/**
1141	<	* Reconstitute the instance from a stream.
1141	>	* Reconstitutes the instance from a stream (that is, deserializes it).
1142		*
1143		* @param s the stream
1144		*/
1145		private void readObject(java.io.ObjectInputStream s)
1146		throws java.io.IOException, ClassNotFoundException {
1147		s.defaultReadObject();
1163	–	status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
1164	–	status |= EXTERNAL_SIGNAL; // conservatively set external signal
1148		Object ex = s.readObject();
1149		if (ex != null)
1150	<	setDoneExceptionally((Throwable) ex);
1150	>	setExceptionalCompletion((Throwable) ex);
1151		}
1152
1153		// Unsafe mechanics

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