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Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.1 by dl, Tue Jan 6 14:30:31 2009 UTC vs.
Revision 1.88 by dl, Sun Mar 4 19:47:08 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		import java.io.Serializable;
9	<	import java.util.*;
10	<	import java.util.concurrent.*;
11	<	import java.util.concurrent.atomic.*;
12	<	import sun.misc.Unsafe;
13	<	import java.lang.reflect.*;
9	>	import java.util.Collection;
10	>	import java.util.List;
11	>	import java.util.RandomAccess;
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 ForkJoinPool.  A
27	<	* ForkJoinTask is a thread-like entity that is much lighter weight
28	<	* than a normal thread.  Huge numbers of tasks and subtasks may be
29	<	* hosted by a small number of actual threads in a ForkJoinPool,
30	<	* at the price of some usage limitations.
31	<	*
32	<	* <p> ForkJoinTasks are forms of <tt>Futures</tt> supporting a
33	<	* limited range of use.  The "lightness" of ForkJoinTasks is due to a
34	<	* set of restrictions (that are only partially statically
35	<	* enforceable) reflecting their intended use as computational tasks
36	<	* calculating pure functions or operating on purely isolated objects.
37	<	* The primary coordination mechanisms supported for ForkJoinTasks are
38	<	* <tt>fork</tt>, that arranges asynchronous execution, and
39	<	* <tt>join</tt>, that doesn't proceed until the task's result has
40	<	* been computed. (Cancellation is also supported).  The computation
41	<	* defined in the <tt>compute</tt> method should avoid
42	<	* <tt>synchronized</tt> methods or blocks, and should minimize
43	<	* blocking synchronization apart from joining other tasks or using
44	<	* synchronizers such as Phasers that are advertised to cooperate with
45	<	* fork/join scheduling. Tasks should also not perform blocking IO,
46	<	* and should ideally access variables that are completely independent
47	<	* of those accessed by other running tasks. Minor breaches of these
48	<	* restrictions, for example using shared output streams, may be
49	<	* tolerable in practice, but frequent use may result in poor
50	<	* performance, and the potential to indefinitely stall if the number
51	<	* of threads not waiting for external synchronization becomes
52	<	* exhausted. This usage restriction is in part enforced by not
53	<	* permitting checked exceptions such as IOExceptions to be
26	>	* Abstract base class for tasks that run within a {@link ForkJoinPool}.
27	>	* A {@code ForkJoinTask} is a thread-like entity that is much
28	>	* lighter weight than a normal thread.  Huge numbers of tasks and
29	>	* subtasks may be hosted by a small number of actual threads in a
30	>	* ForkJoinPool, at the price of some usage limitations.
31	>	*
32	>	* <p>A "main" {@code ForkJoinTask} begins execution when submitted
33	>	* to a {@link ForkJoinPool}.  Once started, it will usually in turn
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(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 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	>	* 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 join
60	<	* them. These exceptions may additionally include
61	<	* RejectedExecutionExceptions stemming from internal resource
62	<	* exhaustion such as failure to allocate internal task queues.
63	<	*
64	<	* <p> The <tt>ForkJoinTask</tt> class is not usually directly
65	<	* subclassed.  Instead, you subclass one of the abstract classes that
66	<	* support different styles of fork/join processing.  Normally, a
67	<	* concrete ForkJoinTask subclass declares fields comprising its
68	<	* parameters, established in a constructor, and then defines a
69	<	* <tt>compute</tt> method that somehow uses the control methods
70	<	* supplied by this base class. While these methods have
71	<	* <tt>public</tt> access, some of them may only be called from within
72	<	* other ForkJoinTasks. Attempts to invoke them in other contexts
73	<	* result in exceptions or errors including ClassCastException.  The
74	<	* only way to invoke a "main" driver task is to submit it to a
75	<	* ForkJoinPool. Once started, this will usually in turn start other
76	<	* subtasks.
77	<	*
78	<	* <p>Most base support methods are <tt>final</tt> because their
79	<	* implementations are intrinsically tied to the underlying
80	<	* lightweight task scheduling framework, and so cannot be overridden.
81	<	* Developers creating new basic styles of fork/join processing should
82	<	* minimally implement protected methods <tt>exec</tt>,
83	<	* <tt>setRawResult</tt>, and <tt>getRawResult</tt>, while also
84	<	* introducing an abstract computational method that can be
85	<	* implemented in its subclasses. To support such extensions,
86	<	* instances of ForkJoinTasks maintain an atomically updated
87	<	* <tt>short</tt> representing user-defined control state.  Control
88	<	* state is guaranteed initially to be zero, and to be negative upon
89	<	* completion, but may otherwise be used for any other control
90	<	* purposes, such as maintaining join counts.  The {@link
91	<	* ForkJoinWorkerThread} class supports additional inspection and
92	<	* tuning methods that can be useful when developing extensions.
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:
84	>	* The {@link Future#get} methods support interruptible and/or timed
85	>	* waits for completion and report results using {@code Future}
86	>	* conventions. Method {@link #invoke} is semantically
87	>	* equivalent to {@code fork(); join()} but always attempts to begin
88	>	* execution in the current thread. The "<em>quiet</em>" forms of
89	>	* these methods do not extract results or report exceptions. These
90	>	* may be useful when a set of tasks are being executed, and you need
91	>	* to delay processing of results or exceptions until all complete.
92	>	* Method {@code invokeAll} (available in multiple versions)
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);
106	>	* {@link #isCompletedNormally} is true if a task completed without
107	>	* cancellation or encountering an exception; {@link #isCancelled} is
108	>	* true if the task was cancelled (in which case {@link #getException}
109	>	* returns a {@link java.util.concurrent.CancellationException}); and
110	>	* {@link #isCompletedAbnormally} is true if a task was either
111	>	* cancelled or encountered an exception, in which case {@link
112	>	* #getException} will return either the encountered exception or
113	>	* {@link java.util.concurrent.CancellationException}.
114	>	*
115	>	* <p>The ForkJoinTask class is not usually directly subclassed.
116	>	* Instead, you subclass one of the abstract classes that support a
117	>	* particular style of fork/join processing, typically {@link
118	>	* RecursiveAction} for computations that do not return results, or
119	>	* {@link RecursiveTask} for those that do.  Normally, a concrete
120	>	* ForkJoinTask subclass declares fields comprising its parameters,
121	>	* established in a constructor, and then defines a {@code compute}
122	>	* method that somehow uses the control methods supplied by this base
123	>	* class. While these methods have {@code public} access (to allow
124	>	* instances of different task subclasses to call each other's
125	>	* methods), some of them may only be called from within other
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	>	* {@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>tagged</em> with a {@code
141	>	* short} value using {@link #setForkJoinTaskTag} or {@link
142	>	* #compareAndSetForkJoinTaskTag} and checked using {@link
143	>	* #getForkJoinTaskTag}. The ForkJoinTask implementation does not
144	>	* use these {@code protected} methods or tags for any purpose, but
145	>	* they may be of use in the construction of specialized subclasses.
146	>	* For example, parallel graph traversals can use the supplied methods
147	>	* to avoid revisiting nodes/tasks that have already been processed.
148	>	* Also, completion based designs can use them to record that subtasks
149	>	* have completed. (Method names for tagging are bulky in part to
150	>	* encourage definition of methods that reflect their usage patterns.)
151	>	*
152	>	* <p>Most base support methods are {@code final}, to prevent
153	>	* overriding of implementations that are intrinsically tied to the
154	>	* underlying lightweight task scheduling framework.  Developers
155	>	* creating new basic styles of fork/join processing should minimally
156	>	* implement {@code protected} methods {@link #exec}, {@link
157	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
158	>	* an abstract computational method that can be implemented in its
159	>	* subclasses, possibly relying on other {@code protected} methods
160	>	* provided by this class.
161		*
162		* <p>ForkJoinTasks should perform relatively small amounts of
163	<	* computations, othewise splitting into smaller tasks. As a very
164	<	* rough rule of thumb, a task should perform more than 100 and less
165	<	* than 10000 basic computational steps. If tasks are too big, then
166	<	* parellelism cannot improve throughput. If too small, then memory
167	<	* and internal task maintenance overhead may overwhelm processing.
168	<	*
169	<	* <p>ForkJoinTasks are <tt>Serializable</tt>, which enables them to
170	<	* be used in extensions such as remote execution frameworks. However,
171	<	* it is in general safe to serialize tasks only before or after, but
172	<	* not during execution. Serialization is not relied on during
173	<	* execution itself.
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, 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
173	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
174	>	* of this form, consider using a pool constructed in <em>asyncMode</em>.
175	>	*
176	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
177	>	* used in extensions such as remote execution frameworks. It is
178	>	* sensible to serialize tasks only before or after, but not during,
179	>	* execution. Serialization is not relied on during execution itself.
180	>	*
181	>	* @since 1.7
182	>	* @author Doug Lea
183		*/
184		public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
185	<	/**
186	<	* Status field holding all run status. We pack this into a single
187	<	* int both to minimize footprint overhead and to ensure atomicity
188	<	* (updates are via CAS).
189	<	*
190	<	* Status is initially zero, and takes on nonnegative values until
191	<	* completed, upon which status holds COMPLETED. CANCELLED, or
192	<	* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
193	<	* blocking waits by other threads have SIGNAL_MASK bits set --
194	<	* bit 15 for external (nonFJ) waits, and the rest a count of
195	<	* waiting FJ threads.  (This representation relies on
196	<	* ForkJoinPool max thread limits). Completion of a stolen task
197	<	* with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
198	<	* though suboptimal for some purposes, we use basic builtin
199	<	* wait/notify to take advantage of "monitor inflation" in JVMs
200	<	* that we would otherwise need to emulate to avoid adding further
201	<	* per-task bookkeeping overhead. Note that bits 16-28 are
202	<	* currently unused. Also value 0x80000000 is available as spare
203	<	* completion value.
204	<	*/
205	<	volatile int status; // accessed directy by pool and workers
206	<
207	<	static final int COMPLETION_MASK      = 0xe0000000;
208	<	static final int NORMAL               = 0xe0000000; // == mask
209	<	static final int CANCELLED            = 0xc0000000;
210	<	static final int EXCEPTIONAL          = 0xa0000000;
211	<	static final int SIGNAL_MASK          = 0x0000ffff;
212	<	static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
213	<	static final int EXTERNAL_SIGNAL      = 0x00008000; // top bit of low word
185	>
186	>	/*
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.
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	>	*/
199	>
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	>	*
217	>	* These control bits occupy only (some of) the upper half (16
218	>	* bits) of status field. The lower bits are used for user-defined
219	>	* tags.
220	>	*/
221	>
222	>	/** The run status of this task */
223	>	volatile int status; // accessed directly by pool and workers
224	>	static final int DONE_MASK   = 0xf0000000;  // mask out non-completion bits
225	>	static final int NORMAL      = 0xf0000000;  // must be negative
226	>	static final int CANCELLED   = 0xc0000000;  // must be < NORMAL
227	>	static final int EXCEPTIONAL = 0x80000000;  // must be < CANCELLED
228	>	static final int SIGNAL      = 0x00010000;  // must be >= 1 << 16
229	>	static final int SMASK       = 0x0000ffff;  // short bits for tags
230
231		/**
232	<	* Table of exceptions thrown by tasks, to enable reporting by
233	<	* callers. Because exceptions are rare, we don't directly keep
234	<	* them with task objects, but instead us a weak ref table.  Note
235	<	* that cancellation exceptions don't appear in the table, but are
236	<	* instead recorded as status values.
130	<	* Todo: Use ConcurrentReferenceHashMap
232	>	* Marks completion and wakes up threads waiting to join this
233	>	* task.
234	>	*
235	>	* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
236	>	* @return completion status on exit
237		*/
238	<	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
239	<	Collections.synchronizedMap
240	<	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
241	<
242	<	// within-package utilities
238	>	private int setCompletion(int completion) {
239	>	for (int s;;) {
240	>	if ((s = status) < 0)
241	>	return s;
242	>	if (U.compareAndSwapInt(this, STATUS, s, s | completion)) {
243	>	if ((s >>> 16) != 0)
244	>	synchronized (this) { notifyAll(); }
245	>	return completion;
246	>	}
247	>	}
248	>	}
249
250		/**
251	<	* Get current worker thread, or null if not a worker thread
251	>	* Primary execution method for stolen tasks. Unless done, calls
252	>	* exec and records status if completed, but doesn't wait for
253	>	* completion otherwise.
254	>	*
255	>	* @return status on exit from this method
256		*/
257	<	static ForkJoinWorkerThread getWorker() {
258	<	Thread t = Thread.currentThread();
259	<	return ((t instanceof ForkJoinWorkerThread)?
260	<	(ForkJoinWorkerThread)t : null);
257	>	final int doExec() {
258	>	int s; boolean completed;
259	>	if ((s = status) >= 0) {
260	>	try {
261	>	completed = exec();
262	>	} catch (Throwable rex) {
263	>	return setExceptionalCompletion(rex);
264	>	}
265	>	if (completed)
266	>	s = setCompletion(NORMAL);
267	>	}
268	>	return s;
269		}
270
271		/**
272	<	* Get pool of current worker thread, or null if not a worker thread
272	>	* Tries to set SIGNAL status. Used by ForkJoinPool. Other
273	>	* variants are directly incorporated into externalAwaitDone etc.
274	>	*
275	>	* @return true if successful
276		*/
277	<	static ForkJoinPool getWorkerPool() {
278	<	Thread t = Thread.currentThread();
279	<	return ((t instanceof ForkJoinWorkerThread)?
153	<	((ForkJoinWorkerThread)t).pool : null);
277	>	final boolean trySetSignal() {
278	>	int s;
279	>	return U.compareAndSwapInt(this, STATUS, s = status, s | SIGNAL);
280		}
281
282	<	final boolean casStatus(int cmp, int val) {
283	<	return _unsafe.compareAndSwapInt(this, statusOffset, cmp, val);
282	>	/**
283	>	* Blocks a non-worker-thread until completion.
284	>	* @return status upon completion
285	>	*/
286	>	private int externalAwaitDone() {
287	>	boolean interrupted = false;
288	>	int s;
289	>	while ((s = status) >= 0) {
290	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
291	>	synchronized (this) {
292	>	if (status >= 0) {
293	>	try {
294	>	wait();
295	>	} catch (InterruptedException ie) {
296	>	interrupted = true;
297	>	}
298	>	}
299	>	else
300	>	notifyAll();
301	>	}
302	>	}
303	>	}
304	>	if (interrupted)
305	>	Thread.currentThread().interrupt();
306	>	return s;
307		}
308
309		/**
310	<	* Workaround for not being able to rethrow unchecked exceptions.
310	>	* Blocks a non-worker-thread until completion or interruption.
311		*/
312	<	static void rethrowException(Throwable ex) {
313	<	if (ex != null)
314	<	_unsafe.throwException(ex);
312	>	private int externalInterruptibleAwaitDone() throws InterruptedException {
313	>	int s;
314	>	if (Thread.interrupted())
315	>	throw new InterruptedException();
316	>	while ((s = status) >= 0) {
317	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
318	>	synchronized (this) {
319	>	if (status >= 0)
320	>	wait();
321	>	else
322	>	notifyAll();
323	>	}
324	>	}
325	>	}
326	>	return s;
327		}
328
168	–	// Setting completion status
169	–
329		/**
330	<	* Mark completion and wake up threads waiting to join this task.
331	<	* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
330	>	* Implementation for join, get, quietlyJoin. Directly handles
331	>	* only cases of already-completed, external wait, and
332	>	* unfork+exec.  Others are relayed to ForkJoinPool.awaitJoin.
333	>	*
334	>	* @return status upon completion
335		*/
336	<	final void setCompletion(int completion) {
337	<	ForkJoinPool pool = getWorkerPool();
338	<	if (pool != null) {
339	<	int s; // Clear signal bits while setting completion status
340	<	do;while ((s = status) >= 0 && !casStatus(s, completion));
341	<
342	<	if ((s & SIGNAL_MASK) != 0) {
181	<	if ((s &= INTERNAL_SIGNAL_MASK) != 0)
182	<	pool.updateRunningCount(s);
183	<	synchronized(this) { notifyAll(); }
336	>	private int doJoin() {
337	>	int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
338	>	if ((s = status) >= 0) {
339	>	if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) {
340	>	if (!(w = (wt = (ForkJoinWorkerThread)t).workQueue).
341	>	tryUnpush(this) || (s = doExec()) >= 0)
342	>	s = wt.pool.awaitJoin(w, this);
343		}
344	+	else
345	+	s = externalAwaitDone();
346		}
347	<	else
187	<	externallySetCompletion(completion);
347	>	return s;
348		}
349
350		/**
351	<	* Version of setCompletion for non-FJ threads.  Leaves signal
352	<	* bits for unblocked threads to adjust, and always notifies.
351	>	* Implementation for invoke, quietlyInvoke.
352	>	*
353	>	* @return status upon completion
354		*/
355	<	private void externallySetCompletion(int completion) {
356	<	int s;
357	<	do;while ((s = status) >= 0 &&
358	<	!casStatus(s, (s & SIGNAL_MASK) | completion));
359	<	synchronized(this) { notifyAll(); }
355	>	private int doInvoke() {
356	>	int s; Thread t; ForkJoinWorkerThread wt;
357	>	if ((s = doExec()) >= 0) {
358	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
359	>	s = (wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue,
360	>	this);
361	>	else
362	>	s = externalAwaitDone();
363	>	}
364	>	return s;
365		}
366
367	+	// Exception table support
368	+
369		/**
370	<	* Sets status to indicate normal completion
370	>	* Table of exceptions thrown by tasks, to enable reporting by
371	>	* callers. Because exceptions are rare, we don't directly keep
372	>	* them with task objects, but instead use a weak ref table.  Note
373	>	* that cancellation exceptions don't appear in the table, but are
374	>	* instead recorded as status values.
375	>	*
376	>	* Note: These statics are initialized below in static block.
377		*/
378	<	final void setNormalCompletion() {
379	<	// Try typical fast case -- single CAS, no signal, not already done.
380	<	// Manually expand casStatus to improve chances of inlining it
207	<	if (!_unsafe.compareAndSwapInt(this, statusOffset, 0, NORMAL))
208	<	setCompletion(NORMAL);
209	<	}
378	>	private static final ExceptionNode[] exceptionTable;
379	>	private static final ReentrantLock exceptionTableLock;
380	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
381
382	<	// internal waiting and notification
382	>	/**
383	>	* Fixed capacity for exceptionTable.
384	>	*/
385	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
386
387		/**
388	<	* Performs the actual monitor wait for awaitDone
388	>	* Key-value nodes for exception table.  The chained hash table
389	>	* uses identity comparisons, full locking, and weak references
390	>	* for keys. The table has a fixed capacity because it only
391	>	* maintains task exceptions long enough for joiners to access
392	>	* them, so should never become very large for sustained
393	>	* periods. However, since we do not know when the last joiner
394	>	* completes, we must use weak references and expunge them. We do
395	>	* so on each operation (hence full locking). Also, some thread in
396	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
397	>	* pool becomes isQuiescent.
398		*/
399	<	private void doAwaitDone() {
400	<	// Minimize lock bias and in/de-flation effects by maximizing
401	<	// chances of waiting inside sync
402	<	try {
403	<	while (status >= 0)
404	<	synchronized(this) { if (status >= 0) wait(); }
405	<	} catch (InterruptedException ie) {
406	<	onInterruptedWait();
399	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> {
400	>	final Throwable ex;
401	>	ExceptionNode next;
402	>	final long thrower;  // use id not ref to avoid weak cycles
403	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
404	>	super(task, exceptionTableRefQueue);
405	>	this.ex = ex;
406	>	this.next = next;
407	>	this.thrower = Thread.currentThread().getId();
408		}
409		}
410
411		/**
412	<	* Performs the actual monitor wait for awaitDone
412	>	* Records exception and sets exceptional completion.
413	>	*
414	>	* @return status on exit
415		*/
416	<	private void doAwaitDone(long startTime, long nanos) {
417	<	synchronized(this) {
418	<	try {
419	<	while (status >= 0) {
420	<	long nt = nanos - System.nanoTime() - startTime;
421	<	if (nt <= 0)
422	<	break;
423	<	wait(nt / 1000000, (int)(nt % 1000000));
416	>	private int setExceptionalCompletion(Throwable ex) {
417	>	int h = System.identityHashCode(this);
418	>	final ReentrantLock lock = exceptionTableLock;
419	>	lock.lock();
420	>	try {
421	>	expungeStaleExceptions();
422	>	ExceptionNode[] t = exceptionTable;
423	>	int i = h & (t.length - 1);
424	>	for (ExceptionNode e = t[i]; ; e = e.next) {
425	>	if (e == null) {
426	>	t[i] = new ExceptionNode(this, ex, t[i]);
427	>	break;
428		}
429	<	} catch (InterruptedException ie) {
430	<	onInterruptedWait();
429	>	if (e.get() == this) // already present
430	>	break;
431		}
432	+	} finally {
433	+	lock.unlock();
434		}
435	+	return setCompletion(EXCEPTIONAL);
436		}
437
245	–	// Awaiting completion
246	–
438		/**
439	<	* Sets status to indicate there is joiner, then waits for join,
440	<	* surrounded with pool notifications.
441	<	* @return status upon exit
439	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
440	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
441	>	* exceptions, but if it does anyway, we have no recourse during
442	>	* shutdown, so guard against this case.
443		*/
444	<	final int awaitDone(ForkJoinWorkerThread w, boolean maintainParallelism) {
445	<	ForkJoinPool pool = w == null? null : w.pool;
446	<	int s;
447	<	while ((s = status) >= 0) {
448	<	if (casStatus(s, pool == null? s|EXTERNAL_SIGNAL : s+1)) {
257	<	if (pool == null || !pool.preJoin(this, maintainParallelism))
258	<	doAwaitDone();
259	<	if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
260	<	adjustPoolCountsOnUnblock(pool);
261	<	break;
444	>	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
445	>	if (t != null && t.status >= 0) {
446	>	try {
447	>	t.cancel(false);
448	>	} catch (Throwable ignore) {
449		}
450		}
264	–	return s;
451		}
452
453		/**
454	<	* Timed version of awaitDone
269	<	* @return status upon exit
454	>	* Removes exception node and clears status
455		*/
456	<	final int awaitDone(ForkJoinWorkerThread w, long nanos) {
457	<	ForkJoinPool pool = w == null? null : w.pool;
458	<	int s;
459	<	while ((s = status) >= 0) {
460	<	if (casStatus(s, pool == null? s|EXTERNAL_SIGNAL : s+1)) {
461	<	long startTime = System.nanoTime();
462	<	if (pool == null || !pool.preJoin(this, false))
463	<	doAwaitDone(startTime, nanos);
464	<	if ((s = status) >= 0) {
465	<	adjustPoolCountsOnCancelledWait(pool);
466	<	s = status;
456	>	private void clearExceptionalCompletion() {
457	>	int h = System.identityHashCode(this);
458	>	final ReentrantLock lock = exceptionTableLock;
459	>	lock.lock();
460	>	try {
461	>	ExceptionNode[] t = exceptionTable;
462	>	int i = h & (t.length - 1);
463	>	ExceptionNode e = t[i];
464	>	ExceptionNode pred = null;
465	>	while (e != null) {
466	>	ExceptionNode next = e.next;
467	>	if (e.get() == this) {
468	>	if (pred == null)
469	>	t[i] = next;
470	>	else
471	>	pred.next = next;
472	>	break;
473		}
474	<	if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
475	<	adjustPoolCountsOnUnblock(pool);
285	<	break;
474	>	pred = e;
475	>	e = next;
476		}
477	+	expungeStaleExceptions();
478	+	status = 0;
479	+	} finally {
480	+	lock.unlock();
481		}
288	–	return s;
482		}
483
484		/**
485	<	* Notify pool that thread is unblocked. Called by signalled
486	<	* threads when woken by non-FJ threads (which is atypical).
485	>	* Returns a rethrowable exception for the given task, if
486	>	* available. To provide accurate stack traces, if the exception
487	>	* was not thrown by the current thread, we try to create a new
488	>	* exception of the same type as the one thrown, but with the
489	>	* recorded exception as its cause. If there is no such
490	>	* constructor, we instead try to use a no-arg constructor,
491	>	* followed by initCause, to the same effect. If none of these
492	>	* apply, or any fail due to other exceptions, we return the
493	>	* recorded exception, which is still correct, although it may
494	>	* contain a misleading stack trace.
495	>	*
496	>	* @return the exception, or null if none
497		*/
498	<	private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
499	<	int s;
500	<	do;while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
501	<	if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
502	<	pool.updateRunningCount(s);
498	>	private Throwable getThrowableException() {
499	>	if ((status & DONE_MASK) != EXCEPTIONAL)
500	>	return null;
501	>	int h = System.identityHashCode(this);
502	>	ExceptionNode e;
503	>	final ReentrantLock lock = exceptionTableLock;
504	>	lock.lock();
505	>	try {
506	>	expungeStaleExceptions();
507	>	ExceptionNode[] t = exceptionTable;
508	>	e = t[h & (t.length - 1)];
509	>	while (e != null && e.get() != this)
510	>	e = e.next;
511	>	} finally {
512	>	lock.unlock();
513	>	}
514	>	Throwable ex;
515	>	if (e == null || (ex = e.ex) == null)
516	>	return null;
517	>	if (e.thrower != Thread.currentThread().getId()) {
518	>	Class<? extends Throwable> ec = ex.getClass();
519	>	try {
520	>	Constructor<?> noArgCtor = null;
521	>	Constructor<?>[] cs = ec.getConstructors();// public ctors only
522	>	for (int i = 0; i < cs.length; ++i) {
523	>	Constructor<?> c = cs[i];
524	>	Class<?>[] ps = c.getParameterTypes();
525	>	if (ps.length == 0)
526	>	noArgCtor = c;
527	>	else if (ps.length == 1 && ps[0] == Throwable.class)
528	>	return (Throwable)(c.newInstance(ex));
529	>	}
530	>	if (noArgCtor != null) {
531	>	Throwable wx = (Throwable)(noArgCtor.newInstance());
532	>	wx.initCause(ex);
533	>	return wx;
534	>	}
535	>	} catch (Exception ignore) {
536	>	}
537	>	}
538	>	return ex;
539		}
540
541		/**
542	<	* Notify pool to adjust counts on cancelled or timed out wait
542	>	* Poll stale refs and remove them. Call only while holding lock.
543		*/
544	<	private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
545	<	if (pool != null) {
546	<	int s;
547	<	while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
548	<	if (casStatus(s, s - 1)) {
549	<	pool.updateRunningCount(1);
550	<	break;
544	>	private static void expungeStaleExceptions() {
545	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
546	>	if (x instanceof ExceptionNode) {
547	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
548	>	ExceptionNode[] t = exceptionTable;
549	>	int i = System.identityHashCode(key) & (t.length - 1);
550	>	ExceptionNode e = t[i];
551	>	ExceptionNode pred = null;
552	>	while (e != null) {
553	>	ExceptionNode next = e.next;
554	>	if (e == x) {
555	>	if (pred == null)
556	>	t[i] = next;
557	>	else
558	>	pred.next = next;
559	>	break;
560	>	}
561	>	pred = e;
562	>	e = next;
563		}
564		}
565		}
566		}
567
568	<	private void onInterruptedWait() {
569	<	Thread t = Thread.currentThread();
570	<	if (t instanceof ForkJoinWorkerThread) {
571	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread)t;
572	<	if (w.isTerminating())
573	<	cancelIgnoreExceptions();
574	<	}
324	<	else { // re-interrupt
568	>	/**
569	>	* If lock is available, poll stale refs and remove them.
570	>	* Called from ForkJoinPool when pools become quiescent.
571	>	*/
572	>	static final void helpExpungeStaleExceptions() {
573	>	final ReentrantLock lock = exceptionTableLock;
574	>	if (lock.tryLock()) {
575		try {
576	<	t.interrupt();
577	<	} catch (SecurityException ignore) {
576	>	expungeStaleExceptions();
577	>	} finally {
578	>	lock.unlock();
579		}
580		}
581		}
582
583	<	// Recording and reporting exceptions
584	<
585	<	private void setDoneExceptionally(Throwable rex) {
586	<	exceptionMap.put(this, rex);
587	<	setCompletion(EXCEPTIONAL);
583	>	/**
584	>	* Throws exception, if any, associated with the given status.
585	>	*/
586	>	private void reportException(int s) {
587	>	Throwable ex = ((s == CANCELLED) ?  new CancellationException() :
588	>	(s == EXCEPTIONAL) ? getThrowableException() :
589	>	null);
590	>	if (ex != null)
591	>	U.throwException(ex);
592		}
593
594	+	// public methods
595	+
596		/**
597	<	* Throws the exception associated with status s;
598	<	* @throws the exception
597	>	* Arranges to asynchronously execute this task.  While it is not
598	>	* necessarily enforced, it is a usage error to fork a task more
599	>	* than once unless it has completed and been reinitialized.
600	>	* Subsequent modifications to the state of this task or any data
601	>	* it operates on are not necessarily consistently observable by
602	>	* any thread other than the one executing it unless preceded by a
603	>	* call to {@link #join} or related methods, or a call to {@link
604	>	* #isDone} returning {@code true}.
605	>	*
606	>	* <p>This method may be invoked only from within {@code
607	>	* ForkJoinPool} computations (as may be determined using method
608	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
609	>	* result in exceptions or errors, possibly including {@code
610	>	* ClassCastException}.
611	>	*
612	>	* @return {@code this}, to simplify usage
613		*/
614	<	private void reportException(int s) {
615	<	if ((s &= COMPLETION_MASK) < NORMAL) {
616	<	if (s == CANCELLED)
346	<	throw new CancellationException();
347	<	else
348	<	rethrowException(exceptionMap.get(this));
349	<	}
614	>	public final ForkJoinTask<V> fork() {
615	>	((ForkJoinWorkerThread)Thread.currentThread()).workQueue.push(this);
616	>	return this;
617		}
618
619		/**
620	<	* Returns result or throws exception using j.u.c.Future conventions
621	<	* Only call when isDone known to be true.
620	>	* Returns the result of the computation when it {@link #isDone is
621	>	* done}.  This method differs from {@link #get()} in that
622	>	* abnormal completion results in {@code RuntimeException} or
623	>	* {@code Error}, not {@code ExecutionException}, and that
624	>	* interrupts of the calling thread do <em>not</em> cause the
625	>	* method to abruptly return by throwing {@code
626	>	* InterruptedException}.
627	>	*
628	>	* @return the computed result
629		*/
630	<	private V reportFutureResult()
631	<	throws ExecutionException, InterruptedException {
632	<	int s = status & COMPLETION_MASK;
633	<	if (s < NORMAL) {
360	<	Throwable ex;
361	<	if (s == CANCELLED)
362	<	throw new CancellationException();
363	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
364	<	throw new ExecutionException(ex);
365	<	if (Thread.interrupted())
366	<	throw new InterruptedException();
367	<	}
630	>	public final V join() {
631	>	int s;
632	>	if ((s = doJoin() & DONE_MASK) != NORMAL)
633	>	reportException(s);
634		return getRawResult();
635		}
636
637		/**
638	<	* Returns result or throws exception using j.u.c.Future conventions
639	<	* with timeouts
638	>	* Commences performing this task, awaits its completion if
639	>	* necessary, and returns its result, or throws an (unchecked)
640	>	* {@code RuntimeException} or {@code Error} if the underlying
641	>	* computation did so.
642	>	*
643	>	* @return the computed result
644		*/
645	<	private V reportTimedFutureResult()
646	<	throws InterruptedException, ExecutionException, TimeoutException {
647	<	Throwable ex;
648	<	int s = status & COMPLETION_MASK;
649	<	if (s == NORMAL)
380	<	return getRawResult();
381	<	if (s == CANCELLED)
382	<	throw new CancellationException();
383	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
384	<	throw new ExecutionException(ex);
385	<	if (Thread.interrupted())
386	<	throw new InterruptedException();
387	<	throw new TimeoutException();
645	>	public final V invoke() {
646	>	int s;
647	>	if ((s = doInvoke() & DONE_MASK) != NORMAL)
648	>	reportException(s);
649	>	return getRawResult();
650		}
651
652	<	// internal execution methods
652	>	/**
653	>	* Forks the given tasks, returning when {@code isDone} holds for
654	>	* each task or an (unchecked) exception is encountered, in which
655	>	* case the exception is rethrown. If more than one task
656	>	* encounters an exception, then this method throws any one of
657	>	* these exceptions. If any task encounters an exception, the
658	>	* other may be cancelled. However, the execution status of
659	>	* individual tasks is not guaranteed upon exceptional return. The
660	>	* status of each task may be obtained using {@link
661	>	* #getException()} and related methods to check if they have been
662	>	* cancelled, completed normally or exceptionally, or left
663	>	* unprocessed.
664	>	*
665	>	* <p>This method may be invoked only from within {@code
666	>	* ForkJoinPool} computations (as may be determined using method
667	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
668	>	* result in exceptions or errors, possibly including {@code
669	>	* ClassCastException}.
670	>	*
671	>	* @param t1 the first task
672	>	* @param t2 the second task
673	>	* @throws NullPointerException if any task is null
674	>	*/
675	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
676	>	int s1, s2;
677	>	t2.fork();
678	>	if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL)
679	>	t1.reportException(s1);
680	>	if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
681	>	t2.reportException(s2);
682	>	}
683
684		/**
685	<	* Calls exec, recording completion, and rethrowing exception if
686	<	* encountered. Caller should normally check status before calling
687	<	* @return true if completed normally
685	>	* Forks the given tasks, returning when {@code isDone} holds for
686	>	* each task or an (unchecked) exception is encountered, in which
687	>	* case the exception is rethrown. If more than one task
688	>	* encounters an exception, then this method throws any one of
689	>	* these exceptions. If any task encounters an exception, others
690	>	* may be cancelled. However, the execution status of individual
691	>	* tasks is not guaranteed upon exceptional return. The status of
692	>	* each task may be obtained using {@link #getException()} and
693	>	* related methods to check if they have been cancelled, completed
694	>	* normally or exceptionally, or left unprocessed.
695	>	*
696	>	* <p>This method may be invoked only from within {@code
697	>	* ForkJoinPool} computations (as may be determined using method
698	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
699	>	* result in exceptions or errors, possibly including {@code
700	>	* ClassCastException}.
701	>	*
702	>	* @param tasks the tasks
703	>	* @throws NullPointerException if any task is null
704		*/
705	<	private boolean tryExec() {
706	<	try { // try block must contain only call to exec
707	<	if (!exec())
708	<	return false;
709	<	} catch (Throwable rex) {
710	<	setDoneExceptionally(rex);
711	<	rethrowException(rex);
712	<	return false; // not reached
705	>	public static void invokeAll(ForkJoinTask<?>... tasks) {
706	>	Throwable ex = null;
707	>	int last = tasks.length - 1;
708	>	for (int i = last; i >= 0; --i) {
709	>	ForkJoinTask<?> t = tasks[i];
710	>	if (t == null) {
711	>	if (ex == null)
712	>	ex = new NullPointerException();
713	>	}
714	>	else if (i != 0)
715	>	t.fork();
716	>	else if (t.doInvoke() < NORMAL && ex == null)
717	>	ex = t.getException();
718	>	}
719	>	for (int i = 1; i <= last; ++i) {
720	>	ForkJoinTask<?> t = tasks[i];
721	>	if (t != null) {
722	>	if (ex != null)
723	>	t.cancel(false);
724	>	else if (t.doJoin() < NORMAL)
725	>	ex = t.getException();
726	>	}
727		}
728	<	setNormalCompletion();
729	<	return true;
728	>	if (ex != null)
729	>	U.throwException(ex);
730		}
731
732		/**
733	<	* Main execution method used by worker threads. Invokes
734	<	* base computation unless already complete
733	>	* Forks all tasks in the specified collection, returning when
734	>	* {@code isDone} holds for each task or an (unchecked) exception
735	>	* is encountered, in which case the exception is rethrown. If
736	>	* more than one task encounters an exception, then this method
737	>	* throws any one of these exceptions. If any task encounters an
738	>	* exception, others may be cancelled. However, the execution
739	>	* status of individual tasks is not guaranteed upon exceptional
740	>	* return. The status of each task may be obtained using {@link
741	>	* #getException()} and related methods to check if they have been
742	>	* cancelled, completed normally or exceptionally, or left
743	>	* unprocessed.
744	>	*
745	>	* <p>This method may be invoked only from within {@code
746	>	* ForkJoinPool} computations (as may be determined using method
747	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
748	>	* result in exceptions or errors, possibly including {@code
749	>	* ClassCastException}.
750	>	*
751	>	* @param tasks the collection of tasks
752	>	* @return the tasks argument, to simplify usage
753	>	* @throws NullPointerException if tasks or any element are null
754		*/
755	<	final void quietlyExec() {
756	<	if (status >= 0) {
757	<	try {
758	<	if (!exec())
759	<	return;
760	<	} catch(Throwable rex) {
761	<	setDoneExceptionally(rex);
762	<	return;
755	>	public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
756	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
757	>	invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
758	>	return tasks;
759	>	}
760	>	@SuppressWarnings("unchecked")
761	>	List<? extends ForkJoinTask<?>> ts =
762	>	(List<? extends ForkJoinTask<?>>) tasks;
763	>	Throwable ex = null;
764	>	int last = ts.size() - 1;
765	>	for (int i = last; i >= 0; --i) {
766	>	ForkJoinTask<?> t = ts.get(i);
767	>	if (t == null) {
768	>	if (ex == null)
769	>	ex = new NullPointerException();
770	>	}
771	>	else if (i != 0)
772	>	t.fork();
773	>	else if (t.doInvoke() < NORMAL && ex == null)
774	>	ex = t.getException();
775	>	}
776	>	for (int i = 1; i <= last; ++i) {
777	>	ForkJoinTask<?> t = ts.get(i);
778	>	if (t != null) {
779	>	if (ex != null)
780	>	t.cancel(false);
781	>	else if (t.doJoin() < NORMAL)
782	>	ex = t.getException();
783		}
423	–	setNormalCompletion();
784		}
785	+	if (ex != null)
786	+	U.throwException(ex);
787	+	return tasks;
788		}
789
790		/**
791	<	* Calls exec, recording but not rethrowing exception
792	<	* Caller should normally check status before calling
793	<	* @return true if completed normally
791	>	* Attempts to cancel execution of this task. This attempt will
792	>	* fail if the task has already completed or could not be
793	>	* cancelled for some other reason. If successful, and this task
794	>	* has not started when {@code cancel} is called, execution of
795	>	* this task is suppressed. After this method returns
796	>	* successfully, unless there is an intervening call to {@link
797	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
798	>	* {@link #isDone}, and {@code cancel} will return {@code true}
799	>	* and calls to {@link #join} and related methods will result in
800	>	* {@code CancellationException}.
801	>	*
802	>	* <p>This method may be overridden in subclasses, but if so, must
803	>	* still ensure that these properties hold. In particular, the
804	>	* {@code cancel} method itself must not throw exceptions.
805	>	*
806	>	* <p>This method is designed to be invoked by <em>other</em>
807	>	* tasks. To terminate the current task, you can just return or
808	>	* throw an unchecked exception from its computation method, or
809	>	* invoke {@link #completeExceptionally}.
810	>	*
811	>	* @param mayInterruptIfRunning this value has no effect in the
812	>	* default implementation because interrupts are not used to
813	>	* control cancellation.
814	>	*
815	>	* @return {@code true} if this task is now cancelled
816		*/
817	<	private boolean tryQuietlyInvoke() {
818	<	try {
819	<	if (!exec())
820	<	return false;
821	<	} catch (Throwable rex) {
822	<	setDoneExceptionally(rex);
823	<	return false;
824	<	}
825	<	setNormalCompletion();
826	<	return true;
817	>	public boolean cancel(boolean mayInterruptIfRunning) {
818	>	return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
819	>	}
820	>
821	>	public final boolean isDone() {
822	>	return status < 0;
823	>	}
824	>
825	>	public final boolean isCancelled() {
826	>	return (status & DONE_MASK) == CANCELLED;
827		}
828
829		/**
830	<	* Cancel, ignoring any exceptions it throws
830	>	* Returns {@code true} if this task threw an exception or was cancelled.
831	>	*
832	>	* @return {@code true} if this task threw an exception or was cancelled
833		*/
834	<	final void cancelIgnoreExceptions() {
835	<	try {
449	<	cancel(false);
450	<	} catch(Throwable ignore) {
451	<	}
834	>	public final boolean isCompletedAbnormally() {
835	>	return status < NORMAL;
836		}
837
838	<	// public methods
838	>	/**
839	>	* Returns {@code true} if this task completed without throwing an
840	>	* exception and was not cancelled.
841	>	*
842	>	* @return {@code true} if this task completed without throwing an
843	>	* exception and was not cancelled
844	>	*/
845	>	public final boolean isCompletedNormally() {
846	>	return (status & DONE_MASK) == NORMAL;
847	>	}
848
849		/**
850	<	* Arranges to asynchronously execute this task.  While it is not
851	<	* necessarily enforced, it is a usage error to fork a task more
852	<	* than once unless it has completed and been reinitialized.  This
853	<	* method may be invoked only from within other ForkJoinTask
854	<	* computations. Attempts to invoke in other contexts result in
462	<	* exceptions or errors including ClassCastException.
850	>	* Returns the exception thrown by the base computation, or a
851	>	* {@code CancellationException} if cancelled, or {@code null} if
852	>	* none or if the method has not yet completed.
853	>	*
854	>	* @return the exception, or {@code null} if none
855		*/
856	<	public final void fork() {
857	<	((ForkJoinWorkerThread)(Thread.currentThread())).pushTask(this);
856	>	public final Throwable getException() {
857	>	int s = status & DONE_MASK;
858	>	return ((s >= NORMAL)    ? null :
859	>	(s == CANCELLED) ? new CancellationException() :
860	>	getThrowableException());
861		}
862
863		/**
864	<	* Returns the result of the computation when it is ready.
865	<	* This method differs from <tt>get</tt> in that abnormal
866	<	* completion results in RuntimeExceptions or Errors, not
867	<	* ExecutionExceptions.
864	>	* Completes this task abnormally, and if not already aborted or
865	>	* cancelled, causes it to throw the given exception upon
866	>	* {@code join} and related operations. This method may be used
867	>	* to induce exceptions in asynchronous tasks, or to force
868	>	* completion of tasks that would not otherwise complete.  Its use
869	>	* in other situations is discouraged.  This method is
870	>	* overridable, but overridden versions must invoke {@code super}
871	>	* implementation to maintain guarantees.
872		*
873	<	* @return the computed result
873	>	* @param ex the exception to throw. If this exception is not a
874	>	* {@code RuntimeException} or {@code Error}, the actual exception
875	>	* thrown will be a {@code RuntimeException} with cause {@code ex}.
876		*/
877	<	public final V join() {
878	<	ForkJoinWorkerThread w = getWorker();
879	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryExec())
880	<	reportException(awaitDone(w, true));
480	<	return getRawResult();
877	>	public void completeExceptionally(Throwable ex) {
878	>	setExceptionalCompletion((ex instanceof RuntimeException) ||
879	>	(ex instanceof Error) ? ex :
880	>	new RuntimeException(ex));
881		}
882
883	<	public final V get() throws InterruptedException, ExecutionException {
884	<	ForkJoinWorkerThread w = getWorker();
885	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
886	<	awaitDone(w, true);
887	<	return reportFutureResult();
883	>	/**
884	>	* Completes this task, and if not already aborted or cancelled,
885	>	* returning the given value as the result of subsequent
886	>	* invocations of {@code join} and related operations. This method
887	>	* may be used to provide results for asynchronous tasks, or to
888	>	* provide alternative handling for tasks that would not otherwise
889	>	* complete normally. Its use in other situations is
890	>	* discouraged. This method is overridable, but overridden
891	>	* versions must invoke {@code super} implementation to maintain
892	>	* guarantees.
893	>	*
894	>	* @param value the result value for this task
895	>	*/
896	>	public void complete(V value) {
897	>	try {
898	>	setRawResult(value);
899	>	} catch (Throwable rex) {
900	>	setExceptionalCompletion(rex);
901	>	return;
902	>	}
903	>	setCompletion(NORMAL);
904		}
905
906	<	public final V get(long timeout, TimeUnit unit)
907	<	throws InterruptedException, ExecutionException, TimeoutException {
908	<	ForkJoinWorkerThread w = getWorker();
909	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
910	<	awaitDone(w, unit.toNanos(timeout));
911	<	return reportTimedFutureResult();
906	>	/**
907	>	* Completes this task. The most recent value established by
908	>	* {@link #setRawResult} (or {@code null}) will be returned as the
909	>	* result of subsequent invocations of {@code join} and related
910	>	* operations. This method may be useful when processing sets of
911	>	* tasks when some do not otherwise complete normally. Its use in
912	>	* other situations is discouraged.
913	>	*/
914	>	public final void quietlyComplete() {
915	>	setCompletion(NORMAL);
916		}
917
918		/**
919	<	* Possibly executes other tasks until this task is ready, then
920	<	* returns the result of the computation.  This method may be more
921	<	* efficient than <tt>join</tt>, but is only applicable when there
502	<	* are no potemtial dependencies between continuation of the
503	<	* current task and that of any other task that might be executed
504	<	* while helping. (This usually holds for pure divide-and-conquer
505	<	* tasks).
919	>	* Waits if necessary for the computation to complete, and then
920	>	* retrieves its result.
921	>	*
922		* @return the computed result
923	+	* @throws CancellationException if the computation was cancelled
924	+	* @throws ExecutionException if the computation threw an
925	+	* exception
926	+	* @throws InterruptedException if the current thread is not a
927	+	* member of a ForkJoinPool and was interrupted while waiting
928		*/
929	<	public final V helpJoin() {
930	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread)(Thread.currentThread());
931	<	if (status < 0 || !w.unpushTask(this) || !tryExec())
932	<	reportException(w.helpJoinTask(this));
929	>	public final V get() throws InterruptedException, ExecutionException {
930	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
931	>	doJoin() : externalInterruptibleAwaitDone();
932	>	Throwable ex;
933	>	if ((s &= DONE_MASK) == CANCELLED)
934	>	throw new CancellationException();
935	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
936	>	throw new ExecutionException(ex);
937		return getRawResult();
938		}
939
940		/**
941	<	* Performs this task, awaits its completion if necessary, and
942	<	* return its result.
943	<	* @throws Throwable (a RuntimeException, Error, or unchecked
944	<	* exception) if the underlying computation did so.
941	>	* Waits if necessary for at most the given time for the computation
942	>	* to complete, and then retrieves its result, if available.
943	>	*
944	>	* @param timeout the maximum time to wait
945	>	* @param unit the time unit of the timeout argument
946		* @return the computed result
947	+	* @throws CancellationException if the computation was cancelled
948	+	* @throws ExecutionException if the computation threw an
949	+	* exception
950	+	* @throws InterruptedException if the current thread is not a
951	+	* member of a ForkJoinPool and was interrupted while waiting
952	+	* @throws TimeoutException if the wait timed out
953		*/
954	<	public final V invoke() {
955	<	if (status >= 0 && tryExec())
956	<	return getRawResult();
957	<	else
958	<	return join();
954	>	public final V get(long timeout, TimeUnit unit)
955	>	throws InterruptedException, ExecutionException, TimeoutException {
956	>	if (Thread.interrupted())
957	>	throw new InterruptedException();
958	>	// Messy in part because we measure in nanosecs, but wait in millisecs
959	>	int s; long ns, ms;
960	>	if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) {
961	>	long deadline = System.nanoTime() + ns;
962	>	ForkJoinPool p = null;
963	>	ForkJoinPool.WorkQueue w = null;
964	>	Thread t = Thread.currentThread();
965	>	if (t instanceof ForkJoinWorkerThread) {
966	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
967	>	p = wt.pool;
968	>	w = wt.workQueue;
969	>	s = p.helpJoinOnce(w, this); // no retries on failure
970	>	}
971	>	boolean canBlock = false;
972	>	boolean interrupted = false;
973	>	try {
974	>	while ((s = status) >= 0) {
975	>	if (w != null && w.runState < 0)
976	>	cancelIgnoringExceptions(this);
977	>	else if (!canBlock) {
978	>	if (p == null || p.tryCompensate(this, null))
979	>	canBlock = true;
980	>	}
981	>	else {
982	>	if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
983	>	U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
984	>	synchronized (this) {
985	>	if (status >= 0) {
986	>	try {
987	>	wait(ms);
988	>	} catch (InterruptedException ie) {
989	>	if (p == null)
990	>	interrupted = true;
991	>	}
992	>	}
993	>	else
994	>	notifyAll();
995	>	}
996	>	}
997	>	if ((s = status) < 0 || interrupted ||
998	>	(ns = deadline - System.nanoTime()) <= 0L)
999	>	break;
1000	>	}
1001	>	}
1002	>	} finally {
1003	>	if (p != null && canBlock)
1004	>	p.incrementActiveCount();
1005	>	}
1006	>	if (interrupted)
1007	>	throw new InterruptedException();
1008	>	}
1009	>	if ((s &= DONE_MASK) != NORMAL) {
1010	>	Throwable ex;
1011	>	if (s == CANCELLED)
1012	>	throw new CancellationException();
1013	>	if (s != EXCEPTIONAL)
1014	>	throw new TimeoutException();
1015	>	if ((ex = getThrowableException()) != null)
1016	>	throw new ExecutionException(ex);
1017	>	}
1018	>	return getRawResult();
1019		}
1020
1021		/**
1022	<	* Joins this task, without returning its result or throwing an
1022	>	* Joins this task, without returning its result or throwing its
1023		* exception. This method may be useful when processing
1024		* collections of tasks when some have been cancelled or otherwise
1025		* known to have aborted.
1026		*/
1027		public final void quietlyJoin() {
1028	<	if (status >= 0) {
537	<	ForkJoinWorkerThread w = getWorker();
538	<	if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
539	<	awaitDone(w, true);
540	<	}
1028	>	doJoin();
1029		}
1030
1031		/**
1032	<	* Possibly executes other tasks until this task is ready.
1032	>	* Commences performing this task and awaits its completion if
1033	>	* necessary, without returning its result or throwing its
1034	>	* exception.
1035		*/
1036	<	public final void quietlyHelpJoin() {
1037	<	if (status >= 0) {
548	<	ForkJoinWorkerThread w =
549	<	(ForkJoinWorkerThread)(Thread.currentThread());
550	<	if (!w.unpushTask(this) || !tryQuietlyInvoke())
551	<	w.helpJoinTask(this);
552	<	}
1036	>	public final void quietlyInvoke() {
1037	>	doInvoke();
1038		}
1039
1040		/**
1041	<	* Performs this task and awaits its completion if necessary,
1042	<	* without returning its result or throwing an exception. This
1043	<	* method may be useful when processing collections of tasks when
1044	<	* some have been cancelled or otherwise known to have aborted.
1041	>	* Possibly executes tasks until the pool hosting the current task
1042	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
1043	>	* be of use in designs in which many tasks are forked, but none
1044	>	* are explicitly joined, instead executing them until all are
1045	>	* processed.
1046	>	*
1047	>	* <p>This method may be invoked only from within {@code
1048	>	* ForkJoinPool} computations (as may be determined using method
1049	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1050	>	* result in exceptions or errors, possibly including {@code
1051	>	* ClassCastException}.
1052		*/
1053	<	public final void quietlyInvoke() {
1054	<	if (status >= 0 && !tryQuietlyInvoke())
1055	<	quietlyJoin();
1053	>	public static void helpQuiesce() {
1054	>	ForkJoinWorkerThread wt =
1055	>	(ForkJoinWorkerThread)Thread.currentThread();
1056	>	wt.pool.helpQuiescePool(wt.workQueue);
1057		}
1058
1059		/**
1060	<	* Returns true if the computation performed by this task has
1061	<	* completed (or has been cancelled).
1062	<	* @return true if this computation has completed
1060	>	* Resets the internal bookkeeping state of this task, allowing a
1061	>	* subsequent {@code fork}. This method allows repeated reuse of
1062	>	* this task, but only if reuse occurs when this task has either
1063	>	* never been forked, or has been forked, then completed and all
1064	>	* outstanding joins of this task have also completed. Effects
1065	>	* under any other usage conditions are not guaranteed.
1066	>	* This method may be useful when executing
1067	>	* pre-constructed trees of subtasks in loops.
1068	>	*
1069	>	* <p>Upon completion of this method, {@code isDone()} reports
1070	>	* {@code false}, and {@code getException()} reports {@code
1071	>	* null}. However, the value returned by {@code getRawResult} is
1072	>	* unaffected. To clear this value, you can invoke {@code
1073	>	* setRawResult(null)}.
1074		*/
1075	<	public final boolean isDone() {
1076	<	return status < 0;
1075	>	public void reinitialize() {
1076	>	if ((status & DONE_MASK) == EXCEPTIONAL)
1077	>	clearExceptionalCompletion();
1078	>	else
1079	>	status = 0;
1080		}
1081
1082		/**
1083	<	* Returns true if this task was cancelled.
1084	<	* @return true if this task was cancelled
1083	>	* Returns the pool hosting the current task execution, or null
1084	>	* if this task is executing outside of any ForkJoinPool.
1085	>	*
1086	>	* @see #inForkJoinPool
1087	>	* @return the pool, or {@code null} if none
1088		*/
1089	<	public final boolean isCancelled() {
1090	<	return (status & COMPLETION_MASK) == CANCELLED;
1089	>	public static ForkJoinPool getPool() {
1090	>	Thread t = Thread.currentThread();
1091	>	return (t instanceof ForkJoinWorkerThread) ?
1092	>	((ForkJoinWorkerThread) t).pool : null;
1093		}
1094
1095		/**
1096	<	* Returns true if this task threw an exception or was cancelled
1097	<	* @return true if this task threw an exception or was cancelled
1096	>	* Returns {@code true} if the current thread is a {@link
1097	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1098	>	*
1099	>	* @return {@code true} if the current thread is a {@link
1100	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1101	>	* or {@code false} otherwise
1102		*/
1103	<	public final boolean completedAbnormally() {
1104	<	return (status & COMPLETION_MASK) < NORMAL;
1103	>	public static boolean inForkJoinPool() {
1104	>	return Thread.currentThread() instanceof ForkJoinWorkerThread;
1105		}
1106
1107		/**
1108	<	* Returns the exception thrown by the base computation, or a
1109	<	* CancellationException if cancelled, or null if none or if the
1110	<	* method has not yet completed.
1111	<	* @return the exception, or null if none
1108	>	* Tries to unschedule this task for execution. This method will
1109	>	* typically succeed if this task is the most recently forked task
1110	>	* by the current thread, and has not commenced executing in
1111	>	* another thread.  This method may be useful when arranging
1112	>	* alternative local processing of tasks that could have been, but
1113	>	* were not, stolen.
1114	>	*
1115	>	* <p>This method may be invoked only from within {@code
1116	>	* ForkJoinPool} computations (as may be determined using method
1117	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1118	>	* result in exceptions or errors, possibly including {@code
1119	>	* ClassCastException}.
1120	>	*
1121	>	* @return {@code true} if unforked
1122		*/
1123	<	public final Throwable getException() {
1124	<	int s = status & COMPLETION_MASK;
1125	<	if (s >= NORMAL)
600	<	return null;
601	<	if (s == CANCELLED)
602	<	return new CancellationException();
603	<	return exceptionMap.get(this);
1123	>	public boolean tryUnfork() {
1124	>	return ((ForkJoinWorkerThread)Thread.currentThread())
1125	>	.workQueue.tryUnpush(this);
1126		}
1127
1128		/**
1129	<	* Asserts that the results of this task's computation will not be
1130	<	* used. If a cancellation occurs before this task is processed,
1131	<	* then its <tt>compute</tt> method will not be executed,
1132	<	* <tt>isCancelled</tt> will report true, and <tt>join</tt> will
611	<	* result in a CancellationException being thrown. Otherwise, when
612	<	* cancellation races with completion, there are no guarantees
613	<	* about whether <tt>isCancelled</tt> will report true, whether
614	<	* <tt>join</tt> will return normally or via an exception, or
615	<	* whether these behaviors will remain consistent upon repeated
616	<	* invocation.
1129	>	* Returns an estimate of the number of tasks that have been
1130	>	* forked by the current worker thread but not yet executed. This
1131	>	* value may be useful for heuristic decisions about whether to
1132	>	* fork other tasks.
1133		*
1134	<	* <p>This method may be overridden in subclasses, but if so, must
1135	<	* still ensure that these minimal properties hold. In particular,
1136	<	* the cancel method itself must not throw exceptions.
1134	>	* <p>This method may be invoked only from within {@code
1135	>	* ForkJoinPool} computations (as may be determined using method
1136	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1137	>	* result in exceptions or errors, possibly including {@code
1138	>	* ClassCastException}.
1139		*
1140	<	* <p> This method is designed to be invoked by <em>other</em>
1141	<	* tasks. To terminate the current task, you can just return or
1142	<	* throw an unchecked exception from its computation method, or
1143	<	* invoke <tt>completeExceptionally(someException)</tt>.
1140	>	* @return the number of tasks
1141	>	*/
1142	>	public static int getQueuedTaskCount() {
1143	>	return ((ForkJoinWorkerThread) Thread.currentThread())
1144	>	.workQueue.queueSize();
1145	>	}
1146	>
1147	>	/**
1148	>	* Returns an estimate of how many more locally queued tasks are
1149	>	* held by the current worker thread than there are other worker
1150	>	* threads that might steal them.  This value may be useful for
1151	>	* heuristic decisions about whether to fork other tasks. In many
1152	>	* usages of ForkJoinTasks, at steady state, each worker should
1153	>	* aim to maintain a small constant surplus (for example, 3) of
1154	>	* tasks, and to process computations locally if this threshold is
1155	>	* exceeded.
1156		*
1157	<	* @param mayInterruptIfRunning this value is ignored in the
1158	<	* default implementation because tasks are not in general
1159	<	* cancelled via interruption.
1157	>	* <p>This method may be invoked only from within {@code
1158	>	* ForkJoinPool} computations (as may be determined using method
1159	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1160	>	* result in exceptions or errors, possibly including {@code
1161	>	* ClassCastException}.
1162		*
1163	<	* @return true if this task is now cancelled
1163	>	* @return the surplus number of tasks, which may be negative
1164		*/
1165	<	public boolean cancel(boolean mayInterruptIfRunning) {
1166	<	setCompletion(CANCELLED);
1167	<	return (status & COMPLETION_MASK) == CANCELLED;
1168	<	}
1165	>	public static int getSurplusQueuedTaskCount() {
1166	>	/*
1167	>	* The aim of this method is to return a cheap heuristic guide
1168	>	* for task partitioning when programmers, frameworks, tools,
1169	>	* or languages have little or no idea about task granularity.
1170	>	* In essence by offering this method, we ask users only about
1171	>	* tradeoffs in overhead vs expected throughput and its
1172	>	* variance, rather than how finely to partition tasks.
1173	>	*
1174	>	* In a steady state strict (tree-structured) computation,
1175	>	* each thread makes available for stealing enough tasks for
1176	>	* other threads to remain active. Inductively, if all threads
1177	>	* play by the same rules, each thread should make available
1178	>	* only a constant number of tasks.
1179	>	*
1180	>	* The minimum useful constant is just 1. But using a value of
1181	>	* 1 would require immediate replenishment upon each steal to
1182	>	* maintain enough tasks, which is infeasible.  Further,
1183	>	* partitionings/granularities of offered tasks should
1184	>	* minimize steal rates, which in general means that threads
1185	>	* nearer the top of computation tree should generate more
1186	>	* than those nearer the bottom. In perfect steady state, each
1187	>	* thread is at approximately the same level of computation
1188	>	* tree. However, producing extra tasks amortizes the
1189	>	* uncertainty of progress and diffusion assumptions.
1190	>	*
1191	>	* So, users will want to use values larger, but not much
1192	>	* larger than 1 to both smooth over transient shortages and
1193	>	* hedge against uneven progress; as traded off against the
1194	>	* cost of extra task overhead. We leave the user to pick a
1195	>	* threshold value to compare with the results of this call to
1196	>	* guide decisions, but recommend values such as 3.
1197	>	*
1198	>	* When all threads are active, it is on average OK to
1199	>	* estimate surplus strictly locally. In steady-state, if one
1200	>	* thread is maintaining say 2 surplus tasks, then so are
1201	>	* others. So we can just use estimated queue length.
1202	>	* However, this strategy alone leads to serious mis-estimates
1203	>	* in some non-steady-state conditions (ramp-up, ramp-down,
1204	>	* other stalls). We can detect many of these by further
1205	>	* considering the number of "idle" threads, that are known to
1206	>	* have zero queued tasks, so compensate by a factor of
1207	>	* (#idle/#active) threads.
1208	>	*/
1209	>	ForkJoinWorkerThread wt =
1210	>	(ForkJoinWorkerThread)Thread.currentThread();
1211	>	return wt.workQueue.queueSize() - wt.pool.idlePerActive();
1212	>	}
1213	>
1214	>	// Extension methods
1215	>
1216	>	/**
1217	>	* Returns the result that would be returned by {@link #join}, even
1218	>	* if this task completed abnormally, or {@code null} if this task
1219	>	* is not known to have been completed.  This method is designed
1220	>	* to aid debugging, as well as to support extensions. Its use in
1221	>	* any other context is discouraged.
1222	>	*
1223	>	* @return the result, or {@code null} if not completed
1224	>	*/
1225	>	public abstract V getRawResult();
1226
1227		/**
1228	<	* Completes this task abnormally, and if not already aborted or
1229	<	* cancelled, causes it to throw the given exception upon
1230	<	* <tt>join</tt> and related operations. This method may be used
1231	<	* to induce exceptions in asynchronous tasks, or to force
1232	<	* completion of tasks that would not otherwise complete.  This
644	<	* method is overridable, but overridden versions must invoke
645	<	* <tt>super</tt> implementation to maintain guarantees.
646	<	* @param ex the exception to throw. If this exception is
647	<	* not a RuntimeException or Error, the actual exception thrown
648	<	* will be a RuntimeException with cause ex.
1228	>	* Forces the given value to be returned as a result.  This method
1229	>	* is designed to support extensions, and should not in general be
1230	>	* called otherwise.
1231	>	*
1232	>	* @param value the value
1233		*/
1234	<	public void completeExceptionally(Throwable ex) {
651	<	setDoneExceptionally((ex instanceof RuntimeException) ||
652	<	(ex instanceof Error)? ex :
653	<	new RuntimeException(ex));
654	<	}
1234	>	protected abstract void setRawResult(V value);
1235
1236		/**
1237	<	* Completes this task, and if not already aborted or cancelled,
1238	<	* returning a <tt>null</tt> result upon <tt>join</tt> and related
1239	<	* operations. This method may be used to provide results for
1240	<	* asynchronous tasks, or to provide alternative handling for
1241	<	* tasks that would not otherwise complete normally.
1237	>	* Immediately performs the base action of this task.  This method
1238	>	* is designed to support extensions, and should not in general be
1239	>	* called otherwise. The return value controls whether this task
1240	>	* is considered to be done normally. It may return false in
1241	>	* asynchronous actions that require explicit invocations of
1242	>	* {@link #complete} to become joinable. It may also throw an
1243	>	* (unchecked) exception to indicate abnormal exit.
1244		*
1245	<	* @param value the result value for this task.
1245	>	* @return {@code true} if completed normally
1246		*/
1247	<	public void complete(V value) {
1248	<	try {
1249	<	setRawResult(value);
1250	<	} catch(Throwable rex) {
1251	<	setDoneExceptionally(rex);
1252	<	return;
1253	<	}
1254	<	setNormalCompletion();
1247	>	protected abstract boolean exec();
1248	>
1249	>	/**
1250	>	* Returns, but does not unschedule or execute, a task queued by
1251	>	* the current thread but not yet executed, if one is immediately
1252	>	* available. There is no guarantee that this task will actually
1253	>	* be polled or executed next. Conversely, this method may return
1254	>	* null even if a task exists but cannot be accessed without
1255	>	* contention with other threads.  This method is designed
1256	>	* primarily to support extensions, and is unlikely to be useful
1257	>	* otherwise.
1258	>	*
1259	>	* <p>This method may be invoked only from within {@code
1260	>	* ForkJoinPool} computations (as may be determined using method
1261	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1262	>	* result in exceptions or errors, possibly including {@code
1263	>	* ClassCastException}.
1264	>	*
1265	>	* @return the next task, or {@code null} if none are available
1266	>	*/
1267	>	protected static ForkJoinTask<?> peekNextLocalTask() {
1268	>	return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek();
1269		}
1270
1271		/**
1272	<	* Resets the internal bookkeeping state of this task, allowing a
1273	<	* subsequent <tt>fork</tt>. This method allows repeated reuse of
1274	<	* this task, but only if reuse occurs when this task has either
1275	<	* never been forked, or has been forked, then completed and all
1276	<	* outstanding joins of this task have also completed. Effects
1277	<	* under any other usage conditions are not guaranteed, and are
1278	<	* almost surely wrong. This method may be useful when executing
1279	<	* pre-constructed trees of subtasks in loops.
1272	>	* Unschedules and returns, without executing, the next task
1273	>	* queued by the current thread but not yet executed.  This method
1274	>	* is designed primarily to support extensions, and is unlikely to
1275	>	* be useful otherwise.
1276	>	*
1277	>	* <p>This method may be invoked only from within {@code
1278	>	* ForkJoinPool} computations (as may be determined using method
1279	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1280	>	* result in exceptions or errors, possibly including {@code
1281	>	* ClassCastException}.
1282	>	*
1283	>	* @return the next task, or {@code null} if none are available
1284		*/
1285	<	public void reinitialize() {
1286	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
1287	<	exceptionMap.remove(this);
688	<	status = 0;
1285	>	protected static ForkJoinTask<?> pollNextLocalTask() {
1286	>	return ((ForkJoinWorkerThread) Thread.currentThread())
1287	>	.workQueue.nextLocalTask();
1288		}
1289
1290		/**
1291	<	* Tries to unschedule this task for execution. This method will
1292	<	* typically succeed if this task is the next task that would be
1293	<	* executed by the current thread, and will typically fail (return
1294	<	* false) otherwise. This method may be useful when arranging
1295	<	* faster local processing of tasks that could have been, but were
1296	<	* not, stolen.
1297	<	* @return true if unforked
1291	>	* Unschedules and returns, without executing, the next task
1292	>	* queued by the current thread but not yet executed, if one is
1293	>	* available, or if not available, a task that was forked by some
1294	>	* other thread, if available. Availability may be transient, so a
1295	>	* {@code null} result does not necessarily imply quiescence
1296	>	* of the pool this task is operating in.  This method is designed
1297	>	* primarily to support extensions, and is unlikely to be useful
1298	>	* otherwise.
1299	>	*
1300	>	* <p>This method may be invoked only from within {@code
1301	>	* ForkJoinPool} computations (as may be determined using method
1302	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1303	>	* result in exceptions or errors, possibly including {@code
1304	>	* ClassCastException}.
1305	>	*
1306	>	* @return a task, or {@code null} if none are available
1307		*/
1308	<	public boolean tryUnfork() {
1309	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).unpushTask(this);
1308	>	protected static ForkJoinTask<?> pollTask() {
1309	>	ForkJoinWorkerThread wt =
1310	>	(ForkJoinWorkerThread)Thread.currentThread();
1311	>	return wt.pool.nextTaskFor(wt.workQueue);
1312		}
1313
1314	+	// tag operations
1315	+
1316		/**
1317	<	* Forks both tasks, returning when <tt>isDone</tt> holds for both
1318	<	* of them or an exception is encountered. This method may be
1319	<	* invoked only from within other ForkJoinTask
1320	<	* computations. Attempts to invoke in other contexts result in
709	<	* exceptions or errors including ClassCastException.
710	<	* @param t1 one task
711	<	* @param t2 the other task
712	<	* @throws NullPointerException if t1 or t2 are null
713	<	* @throws RuntimeException or Error if either task did so.
1317	>	* Returns the tag for this task.
1318	>	*
1319	>	* @return the tag for this task
1320	>	* @since 1.8
1321		*/
1322	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
1323	<	t2.fork();
717	<	t1.invoke();
718	<	t2.join();
1322	>	public final short getForkJoinTaskTag() {
1323	>	return (short)status;
1324		}
1325
1326		/**
1327	<	* Forks the given tasks, returning when <tt>isDone</tt> holds for
1328	<	* all of them. If any task encounters an exception, others may be
1329	<	* cancelled.  This method may be invoked only from within other
1330	<	* ForkJoinTask computations. Attempts to invoke in other contexts
1331	<	* result in exceptions or errors including ClassCastException.
727	<	* @param tasks the array of tasks
728	<	* @throws NullPointerException if tasks or any element are null.
729	<	* @throws RuntimeException or Error if any task did so.
1327	>	* Atomically sets the tag value for this task.
1328	>	*
1329	>	* @param tag the tag value
1330	>	* @return the previous value of the tag
1331	>	* @since 1.8
1332		*/
1333	<	public static void invokeAll(ForkJoinTask<?>... tasks) {
1334	<	Throwable ex = null;
1335	<	int last = tasks.length - 1;
1336	<	for (int i = last; i >= 0; --i) {
1337	<	ForkJoinTask<?> t = tasks[i];
736	<	if (t == null) {
737	<	if (ex == null)
738	<	ex = new NullPointerException();
739	<	}
740	<	else if (i != 0)
741	<	t.fork();
742	<	else {
743	<	t.quietlyInvoke();
744	<	if (ex == null)
745	<	ex = t.getException();
746	<	}
1333	>	public final short setForkJoinTaskTag(short tag) {
1334	>	for (int s;;) {
1335	>	if (U.compareAndSwapInt(this, STATUS, s = status,
1336	>	(s & ~SMASK) | (tag & SMASK)))
1337	>	return (short)s;
1338		}
1339	<	for (int i = 1; i <= last; ++i) {
1340	<	ForkJoinTask<?> t = tasks[i];
1341	<	if (t != null) {
1342	<	if (ex != null)
1343	<	t.cancel(false);
1344	<	else {
1345	<	t.quietlyJoin();
1346	<	if (ex == null)
1347	<	ex = t.getException();
1348	<	}
1349	<	}
1339	>	}
1340	>
1341	>	/**
1342	>	* Atomically conditionally sets the tag value for this task.
1343	>	* Among other applications, tags can be used as visit markers
1344	>	* in tasks operating on graphs, as in methods that check: {@code
1345	>	* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1346	>	* before processing, otherwise exiting because the node has
1347	>	* already been visited.
1348	>	*
1349	>	* @param e the expected tag value
1350	>	* @param tag the new tag value
1351	>	* @return true if successful; i.e., the current value was
1352	>	* equal to e and is now tag.
1353	>	* @since 1.8
1354	>	*/
1355	>	public final boolean compareAndSetForkJoinTaskTag(short e, short tag) {
1356	>	for (int s;;) {
1357	>	if ((short)(s = status) != e)
1358	>	return false;
1359	>	if (U.compareAndSwapInt(this, STATUS, s,
1360	>	(s & ~SMASK) | (tag & SMASK)))
1361	>	return true;
1362		}
760	–	if (ex != null)
761	–	rethrowException(ex);
1363		}
1364
1365		/**
1366	<	* Forks all tasks in the collection, returning when
1367	<	* <tt>isDone</tt> holds for all of them. If any task encounters
1368	<	* an exception, others may be cancelled.  This method may be
768	<	* invoked only from within other ForkJoinTask
769	<	* computations. Attempts to invoke in other contexts result in
770	<	* exceptions or errors including ClassCastException.
771	<	* @param tasks the collection of tasks
772	<	* @throws NullPointerException if tasks or any element are null.
773	<	* @throws RuntimeException or Error if any task did so.
1366	>	* Adaptor for Runnables. This implements RunnableFuture
1367	>	* to be compliant with AbstractExecutorService constraints
1368	>	* when used in ForkJoinPool.
1369		*/
1370	<	public static void invokeAll(Collection<? extends ForkJoinTask<?>> tasks) {
1371	<	if (!(tasks instanceof List)) {
1372	<	invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()]));
1373	<	return;
1374	<	}
1375	<	List<? extends ForkJoinTask<?>> ts =
1376	<	(List<? extends ForkJoinTask<?>>)tasks;
1377	<	Throwable ex = null;
783	<	int last = ts.size() - 1;
784	<	for (int i = last; i >= 0; --i) {
785	<	ForkJoinTask<?> t = ts.get(i);
786	<	if (t == null) {
787	<	if (ex == null)
788	<	ex = new NullPointerException();
789	<	}
790	<	else if (i != 0)
791	<	t.fork();
792	<	else {
793	<	t.quietlyInvoke();
794	<	if (ex == null)
795	<	ex = t.getException();
796	<	}
1370	>	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1371	>	implements RunnableFuture<T> {
1372	>	final Runnable runnable;
1373	>	T result;
1374	>	AdaptedRunnable(Runnable runnable, T result) {
1375	>	if (runnable == null) throw new NullPointerException();
1376	>	this.runnable = runnable;
1377	>	this.result = result; // OK to set this even before completion
1378		}
1379	<	for (int i = 1; i <= last; ++i) {
1380	<	ForkJoinTask<?> t = ts.get(i);
1381	<	if (t != null) {
1382	<	if (ex != null)
1383	<	t.cancel(false);
803	<	else {
804	<	t.quietlyJoin();
805	<	if (ex == null)
806	<	ex = t.getException();
807	<	}
808	<	}
809	<	}
810	<	if (ex != null)
811	<	rethrowException(ex);
1379	>	public final T getRawResult() { return result; }
1380	>	public final void setRawResult(T v) { result = v; }
1381	>	public final boolean exec() { runnable.run(); return true; }
1382	>	public final void run() { invoke(); }
1383	>	private static final long serialVersionUID = 5232453952276885070L;
1384		}
1385
1386		/**
1387	<	* Possibly executes tasks until the pool hosting the current task
816	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
817	<	* designs in which many tasks are forked, but none are explicitly
818	<	* joined, instead executing them until all are processed.
1387	>	* Adaptor for Runnables without results
1388		*/
1389	<	public static void helpQuiesce() {
1390	<	((ForkJoinWorkerThread)(Thread.currentThread())).
1391	<	helpQuiescePool();
1389	>	static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1390	>	implements RunnableFuture<Void> {
1391	>	final Runnable runnable;
1392	>	AdaptedRunnableAction(Runnable runnable) {
1393	>	if (runnable == null) throw new NullPointerException();
1394	>	this.runnable = runnable;
1395	>	}
1396	>	public final Void getRawResult() { return null; }
1397	>	public final void setRawResult(Void v) { }
1398	>	public final boolean exec() { runnable.run(); return true; }
1399	>	public final void run() { invoke(); }
1400	>	private static final long serialVersionUID = 5232453952276885070L;
1401		}
1402
1403		/**
1404	<	* Returns a estimate of how many more locally queued tasks are
827	<	* held by the current worker thread than there are other worker
828	<	* threads that might want to steal them.  This value may be
829	<	* useful for heuristic decisions about whether to fork other
830	<	* tasks. In many usages of ForkJoinTasks, at steady state, each
831	<	* worker should aim to maintain a small constant surplus (for
832	<	* example, 3) of tasks, and to process computations locally if
833	<	* this threshold is exceeded.
834	<	* @return the surplus number of tasks, which may be negative
1404	>	* Adaptor for Callables
1405		*/
1406	<	public static int surplus() {
1407	<	return ((ForkJoinWorkerThread)(Thread.currentThread()))
1408	<	.getEstimatedSurplusTaskCount();
1406	>	static final class AdaptedCallable<T> extends ForkJoinTask<T>
1407	>	implements RunnableFuture<T> {
1408	>	final Callable<? extends T> callable;
1409	>	T result;
1410	>	AdaptedCallable(Callable<? extends T> callable) {
1411	>	if (callable == null) throw new NullPointerException();
1412	>	this.callable = callable;
1413	>	}
1414	>	public final T getRawResult() { return result; }
1415	>	public final void setRawResult(T v) { result = v; }
1416	>	public final boolean exec() {
1417	>	try {
1418	>	result = callable.call();
1419	>	return true;
1420	>	} catch (Error err) {
1421	>	throw err;
1422	>	} catch (RuntimeException rex) {
1423	>	throw rex;
1424	>	} catch (Exception ex) {
1425	>	throw new RuntimeException(ex);
1426	>	}
1427	>	}
1428	>	public final void run() { invoke(); }
1429	>	private static final long serialVersionUID = 2838392045355241008L;
1430		}
1431
841	–	// Extension kit
842	–
1432		/**
1433	<	* Returns the result that would be returned by <tt>join</tt>, or
1434	<	* null if this task is not known to have been completed.  This
1435	<	* method is designed to aid debugging, as well as to support
847	<	* extensions. Its use in any other context is discouraged.
1433	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1434	>	* method of the given {@code Runnable} as its action, and returns
1435	>	* a null result upon {@link #join}.
1436		*
1437	<	* @return the result, or null if not completed.
1437	>	* @param runnable the runnable action
1438	>	* @return the task
1439		*/
1440	<	public abstract V getRawResult();
1440	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1441	>	return new AdaptedRunnableAction(runnable);
1442	>	}
1443
1444		/**
1445	<	* Forces the given value to be returned as a result.  This method
1446	<	* is designed to support extensions, and should not in general be
1447	<	* called otherwise.
1445	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1446	>	* method of the given {@code Runnable} as its action, and returns
1447	>	* the given result upon {@link #join}.
1448		*
1449	<	* @param value the value
1449	>	* @param runnable the runnable action
1450	>	* @param result the result upon completion
1451	>	* @return the task
1452		*/
1453	<	protected abstract void setRawResult(V value);
1453	>	public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
1454	>	return new AdaptedRunnable<T>(runnable, result);
1455	>	}
1456
1457		/**
1458	<	* Immediately performs the base action of this task.  This method
1459	<	* is designed to support extensions, and should not in general be
1460	<	* called otherwise. The return value controls whether this task
1461	<	* is considered to be done normally. It may return false in
1462	<	* asynchronous actions that require explicit invocations of
1463	<	* <tt>complete</tt> to become joinable. It may throw exceptions
1464	<	* to indicate abnormal exit.
870	<	* @return true if completed normally
871	<	* @throws Error or RuntimeException if encountered during computation
1458	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1459	>	* method of the given {@code Callable} as its action, and returns
1460	>	* its result upon {@link #join}, translating any checked exceptions
1461	>	* encountered into {@code RuntimeException}.
1462	>	*
1463	>	* @param callable the callable action
1464	>	* @return the task
1465		*/
1466	<	protected abstract boolean exec();
1466	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1467	>	return new AdaptedCallable<T>(callable);
1468	>	}
1469
1470		// Serialization support
1471
1472		private static final long serialVersionUID = -7721805057305804111L;
1473
1474		/**
1475	<	* Save the state to a stream.
1475	>	* Saves this task to a stream (that is, serializes it).
1476		*
1477		* @serialData the current run status and the exception thrown
1478	<	* during execution, or null if none.
884	<	* @param s the stream
1478	>	* during execution, or {@code null} if none
1479		*/
1480		private void writeObject(java.io.ObjectOutputStream s)
1481		throws java.io.IOException {
#	Line 890 | Line 1484 | public abstract class ForkJoinTask<V> im
1484		}
1485
1486		/**
1487	<	* Reconstitute the instance from a stream.
894	<	* @param s the stream
1487	>	* Reconstitutes this task from a stream (that is, deserializes it).
1488		*/
1489		private void readObject(java.io.ObjectInputStream s)
1490		throws java.io.IOException, ClassNotFoundException {
1491		s.defaultReadObject();
899	–	//        status &= ~INTERNAL_SIGNAL_MASK; //  todo: define policy
1492		Object ex = s.readObject();
1493		if (ex != null)
1494	<	setDoneExceptionally((Throwable)ex);
1494	>	setExceptionalCompletion((Throwable)ex);
1495		}
1496
1497	<	// Temporary Unsafe mechanics for preliminary release
1498	<
1499	<	static final Unsafe _unsafe;
908	<	static final long statusOffset;
909	<
1497	>	// Unsafe mechanics
1498	>	private static final sun.misc.Unsafe U;
1499	>	private static final long STATUS;
1500		static {
1501	+	exceptionTableLock = new ReentrantLock();
1502	+	exceptionTableRefQueue = new ReferenceQueue<Object>();
1503	+	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1504		try {
1505	<	if (ForkJoinTask.class.getClassLoader() != null) {
1506	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
914	<	f.setAccessible(true);
915	<	_unsafe = (Unsafe)f.get(null);
916	<	}
917	<	else
918	<	_unsafe = Unsafe.getUnsafe();
919	<	statusOffset = _unsafe.objectFieldOffset
1505	>	U = getUnsafe();
1506	>	STATUS = U.objectFieldOffset
1507		(ForkJoinTask.class.getDeclaredField("status"));
1508	<	} catch (Exception ex) { throw new Error(ex); }
1508	>	} catch (Exception e) {
1509	>	throw new Error(e);
1510	>	}
1511		}
1512
1513	+	/**
1514	+	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1515	+	* Replace with a simple call to Unsafe.getUnsafe when integrating
1516	+	* into a jdk.
1517	+	*
1518	+	* @return a sun.misc.Unsafe
1519	+	*/
1520	+	private static sun.misc.Unsafe getUnsafe() {
1521	+	try {
1522	+	return sun.misc.Unsafe.getUnsafe();
1523	+	} catch (SecurityException se) {
1524	+	try {
1525	+	return java.security.AccessController.doPrivileged
1526	+	(new java.security
1527	+	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1528	+	public sun.misc.Unsafe run() throws Exception {
1529	+	java.lang.reflect.Field f = sun.misc
1530	+	.Unsafe.class.getDeclaredField("theUnsafe");
1531	+	f.setAccessible(true);
1532	+	return (sun.misc.Unsafe) f.get(null);
1533	+	}});
1534	+	} catch (java.security.PrivilegedActionException e) {
1535	+	throw new RuntimeException("Could not initialize intrinsics",
1536	+	e.getCause());
1537	+	}
1538	+	}
1539	+	}
1540		}

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