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

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.1 by dl, Tue Jan 6 14:30:31 2009 UTC vs.
Revision 1.82 by dl, Thu Jan 26 18:15:12 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 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>marked</em> using {@link
141	>	* #markForkJoinTask} and checked for marking using {@link
142	>	* #isMarkedForkJoinTask}. The ForkJoinTask implementation does not
143	>	* use these {@code protected} methods or marks for any purpose, but
144	>	* they may be of use in the construction of specialized subclasses.
145	>	* For example, parallel graph traversals can use the supplied methods
146	>	* to avoid revisiting nodes/tasks that have already been
147	>	* processed. Also, completion based designs can use them to record
148	>	* that one subtask has completed. (Method names for marking are bulky
149	>	* in part to encourage definition of methods that reflect their usage
150	>	* patterns.)
151	>	*
152	>	* <p>Most base support methods are {@code final}, to prevent
153	>	* overriding of implementations that are intrinsically tied to the
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 {
94	–	/**
95	–	* Status field holding all run status. We pack this into a single
96	–	* int both to minimize footprint overhead and to ensure atomicity
97	–	* (updates are via CAS).
98	–	*
99	–	* Status is initially zero, and takes on nonnegative values until
100	–	* completed, upon which status holds COMPLETED. CANCELLED, or
101	–	* EXCEPTIONAL, which use the top 3 bits.  Tasks undergoing
102	–	* blocking waits by other threads have SIGNAL_MASK bits set --
103	–	* bit 15 for external (nonFJ) waits, and the rest a count of
104	–	* waiting FJ threads.  (This representation relies on
105	–	* ForkJoinPool max thread limits). Completion of a stolen task
106	–	* with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
107	–	* though suboptimal for some purposes, we use basic builtin
108	–	* wait/notify to take advantage of "monitor inflation" in JVMs
109	–	* that we would otherwise need to emulate to avoid adding further
110	–	* per-task bookkeeping overhead. Note that bits 16-28 are
111	–	* currently unused. Also value 0x80000000 is available as spare
112	–	* completion value.
113	–	*/
114	–	volatile int status; // accessed directy by pool and workers
115	–
116	–	static final int COMPLETION_MASK      = 0xe0000000;
117	–	static final int NORMAL               = 0xe0000000; // == mask
118	–	static final int CANCELLED            = 0xc0000000;
119	–	static final int EXCEPTIONAL          = 0xa0000000;
120	–	static final int SIGNAL_MASK          = 0x0000ffff;
121	–	static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
122	–	static final int EXTERNAL_SIGNAL      = 0x00008000; // top bit of low word
185
186	<	/**
187	<	* Table of exceptions thrown by tasks, to enable reporting by
188	<	* callers. Because exceptions are rare, we don't directly keep
189	<	* them with task objects, but instead us a weak ref table.  Note
190	<	* that cancellation exceptions don't appear in the table, but are
191	<	* instead recorded as status values.
192	<	* Todo: Use ConcurrentReferenceHashMap
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		*/
132	–	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
133	–	Collections.synchronizedMap
134	–	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
135	–
136	–	// within-package utilities
199
200		/**
201	<	* Get current worker thread, or null if not a worker thread
201	>	* The number of times to try to help join a task without any
202	>	* apparent progress before giving up and blocking. The value is
203	>	* arbitrary but should be large enough to cope with transient
204	>	* stalls (due to GC etc) that can cause helping methods not to be
205	>	* able to proceed because other workers have not progressed to
206	>	* the point where subtasks can be found or taken.
207	>	*/
208	>	private static final int HELP_RETRIES = 32;
209	>
210	>	/*
211	>	* The status field holds run control status bits packed into a
212	>	* single int to minimize footprint and to ensure atomicity (via
213	>	* CAS).  Status is initially zero, and takes on nonnegative
214	>	* values until completed, upon which status holds value
215	>	* NORMAL, CANCELLED, or EXCEPTIONAL. Tasks undergoing blocking
216	>	* waits by other threads have the SIGNAL bit set.  Completion of
217	>	* a stolen task with SIGNAL set awakens any waiters via
218	>	* notifyAll. Even though suboptimal for some purposes, we use
219	>	* basic builtin wait/notify to take advantage of "monitor
220	>	* inflation" in JVMs that we would otherwise need to emulate to
221	>	* avoid adding further per-task bookkeeping overhead.  We want
222	>	* these monitors to be "fat", i.e., not use biasing or thin-lock
223	>	* techniques, so use some odd coding idioms that tend to avoid
224	>	* them.
225	>	*/
226	>
227	>	/** The run status of this task */
228	>	volatile int status; // accessed directly by pool and workers
229	>	static final int NORMAL      = 0xfffffffc;  // negative with low 2 bits 0
230	>	static final int CANCELLED   = 0xfffffff8;  // must be < NORMAL
231	>	static final int EXCEPTIONAL = 0xfffffff4;  // must be < CANCELLED
232	>	static final int SIGNAL      = 0x00000001;
233	>	static final int MARKED      = 0x00000002;
234	>
235	>	/**
236	>	* Marks completion and wakes up threads waiting to join this
237	>	* task, also clearing signal request bits. A specialization for
238	>	* NORMAL completion is in method doExec
239	>	*
240	>	* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
241	>	* @return completion status on exit
242		*/
243	<	static ForkJoinWorkerThread getWorker() {
244	<	Thread t = Thread.currentThread();
245	<	return ((t instanceof ForkJoinWorkerThread)?
246	<	(ForkJoinWorkerThread)t : null);
243	>	private int setCompletion(int completion) {
244	>	for (int s;;) {
245	>	if ((s = status) < 0)
246	>	return s;
247	>	if (U.compareAndSwapInt(this, STATUS, s, (s & ~SIGNAL)|completion)) {
248	>	if ((s & SIGNAL) != 0)
249	>	synchronized (this) { notifyAll(); }
250	>	return completion;
251	>	}
252	>	}
253		}
254
255		/**
256	<	* Get pool of current worker thread, or null if not a worker thread
256	>	* Primary execution method for stolen tasks. Unless done, calls
257	>	* exec and records status if completed, but doesn't wait for
258	>	* completion otherwise.
259	>	*
260	>	* @return status on exit from this method
261		*/
262	<	static ForkJoinPool getWorkerPool() {
263	<	Thread t = Thread.currentThread();
264	<	return ((t instanceof ForkJoinWorkerThread)?
265	<	((ForkJoinWorkerThread)t).pool : null);
262	>	final int doExec() {
263	>	int s; boolean completed;
264	>	if ((s = status) >= 0) {
265	>	try {
266	>	completed = exec();
267	>	} catch (Throwable rex) {
268	>	return setExceptionalCompletion(rex);
269	>	}
270	>	while ((s = status) >= 0 && completed) {
271	>	if (U.compareAndSwapInt(this, STATUS, s, (s & ~SIGNAL)|NORMAL)) {
272	>	if ((s & SIGNAL) != 0)
273	>	synchronized (this) { notifyAll(); }
274	>	return NORMAL;
275	>	}
276	>	}
277	>	}
278	>	return s;
279		}
280
281	<	final boolean casStatus(int cmp, int val) {
282	<	return _unsafe.compareAndSwapInt(this, statusOffset, cmp, val);
281	>	/**
282	>	* Blocks a non-worker-thread until completion.
283	>	* @return status upon completion
284	>	*/
285	>	private int externalAwaitDone() {
286	>	int s;
287	>	if ((s = status) >= 0) {
288	>	boolean interrupted = false;
289	>	synchronized (this) {
290	>	while ((s = status) >= 0) {
291	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
292	>	try {
293	>	wait();
294	>	} catch (InterruptedException ie) {
295	>	interrupted = true;
296	>	}
297	>	}
298	>	}
299	>	}
300	>	if (interrupted)
301	>	Thread.currentThread().interrupt();
302	>	}
303	>	return s;
304		}
305
306		/**
307	<	* Workaround for not being able to rethrow unchecked exceptions.
307	>	* Blocks a non-worker-thread until completion or interruption or timeout.
308		*/
309	<	static void rethrowException(Throwable ex) {
310	<	if (ex != null)
311	<	_unsafe.throwException(ex);
309	>	private int externalInterruptibleAwaitDone(long millis)
310	>	throws InterruptedException {
311	>	int s;
312	>	if (Thread.interrupted())
313	>	throw new InterruptedException();
314	>	if ((s = status) >= 0) {
315	>	synchronized (this) {
316	>	while ((s = status) >= 0) {
317	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
318	>	wait(millis);
319	>	if (millis > 0L)
320	>	break;
321	>	}
322	>	}
323	>	}
324	>	}
325	>	return s;
326		}
327
168	–	// Setting completion status
328
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 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) {
343	<	if ((s &= INTERNAL_SIGNAL_MASK) != 0)
182	<	pool.updateRunningCount(s);
183	<	synchronized(this) { notifyAll(); }
184	<	}
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	>	s = externalAwaitDone();
341	>	else if (!(w = (wt = (ForkJoinWorkerThread)t).workQueue).
342	>	tryUnpush(this) || (s = doExec()) >= 0)
343	>	s = awaitJoin(w, wt.pool);
344		}
345	<	else
187	<	externallySetCompletion(completion);
345	>	return s;
346		}
347
348		/**
349	<	* Version of setCompletion for non-FJ threads.  Leaves signal
350	<	* bits for unblocked threads to adjust, and always notifies.
349	>	* Helps and/or blocks until joined.
350	>	*
351	>	* @param w the joiner
352	>	* @param p the pool
353	>	* @return status upon completion
354		*/
355	<	private void externallySetCompletion(int completion) {
355	>	private int awaitJoin(ForkJoinPool.WorkQueue w, ForkJoinPool p) {
356		int s;
357	<	do;while ((s = status) >= 0 &&
358	<	!casStatus(s, (s & SIGNAL_MASK) | completion));
359	<	synchronized(this) { notifyAll(); }
357	>	ForkJoinTask<?> prevJoin = w.currentJoin;
358	>	w.currentJoin = this;
359	>	for (int k = HELP_RETRIES; (s = status) >= 0;) {
360	>	if ((w.queueSize() > 0) ?
361	>	w.tryRemoveAndExec(this) :        // self-help
362	>	p.tryHelpStealer(w, this))        // help process tasks
363	>	k = HELP_RETRIES;                 // reset if made progress
364	>	else if ((s = status) < 0)            // recheck
365	>	break;
366	>	else if (--k > 0) {
367	>	if ((k & 3) == 1)
368	>	Thread.yield();               // occasionally yield
369	>	}
370	>	else if (k == 0)
371	>	p.tryPollForAndExec(w, this);     // uncommon self-help case
372	>	else if (p.tryCompensate()) {         // true if can block
373	>	try {
374	>	int ss = status;
375	>	if (ss >= 0 &&                // assert need signal
376	>	U.compareAndSwapInt(this, STATUS, ss, ss | SIGNAL)) {
377	>	synchronized (this) {
378	>	if (status >= 0)      // block
379	>	wait();
380	>	}
381	>	}
382	>	} catch (InterruptedException ignore) {
383	>	} finally {
384	>	p.incrementActiveCount();     // re-activate
385	>	}
386	>	}
387	>	}
388	>	w.currentJoin = prevJoin;
389	>	return s;
390		}
391
392		/**
393	<	* Sets status to indicate normal completion
393	>	* Implementation for invoke, quietlyInvoke.
394	>	*
395	>	* @return status upon completion
396		*/
397	<	final void setNormalCompletion() {
398	<	// Try typical fast case -- single CAS, no signal, not already done.
399	<	// Manually expand casStatus to improve chances of inlining it
400	<	if (!_unsafe.compareAndSwapInt(this, statusOffset, 0, NORMAL))
401	<	setCompletion(NORMAL);
397	>	private int doInvoke() {
398	>	int s; Thread t;
399	>	if ((s = doExec()) >= 0) {
400	>	if (!((t = Thread.currentThread()) instanceof ForkJoinWorkerThread))
401	>	s = externalAwaitDone();
402	>	else {
403	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
404	>	s = awaitJoin(wt.workQueue, wt.pool);
405	>	}
406	>	}
407	>	return s;
408		}
409
410	<	// internal waiting and notification
410	>	// Exception table support
411
412		/**
413	<	* Performs the actual monitor wait for awaitDone
413	>	* Table of exceptions thrown by tasks, to enable reporting by
414	>	* callers. Because exceptions are rare, we don't directly keep
415	>	* them with task objects, but instead use a weak ref table.  Note
416	>	* that cancellation exceptions don't appear in the table, but are
417	>	* instead recorded as status values.
418	>	*
419	>	* Note: These statics are initialized below in static block.
420		*/
421	<	private void doAwaitDone() {
422	<	// Minimize lock bias and in/de-flation effects by maximizing
423	<	// chances of waiting inside sync
424	<	try {
425	<	while (status >= 0)
426	<	synchronized(this) { if (status >= 0) wait(); }
427	<	} catch (InterruptedException ie) {
428	<	onInterruptedWait();
421	>	private static final ExceptionNode[] exceptionTable;
422	>	private static final ReentrantLock exceptionTableLock;
423	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
424	>
425	>	/**
426	>	* Fixed capacity for exceptionTable.
427	>	*/
428	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
429	>
430	>	/**
431	>	* Key-value nodes for exception table.  The chained hash table
432	>	* uses identity comparisons, full locking, and weak references
433	>	* for keys. The table has a fixed capacity because it only
434	>	* maintains task exceptions long enough for joiners to access
435	>	* them, so should never become very large for sustained
436	>	* periods. However, since we do not know when the last joiner
437	>	* completes, we must use weak references and expunge them. We do
438	>	* so on each operation (hence full locking). Also, some thread in
439	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
440	>	* pool becomes isQuiescent.
441	>	*/
442	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>>{
443	>	final Throwable ex;
444	>	ExceptionNode next;
445	>	final long thrower;  // use id not ref to avoid weak cycles
446	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
447	>	super(task, exceptionTableRefQueue);
448	>	this.ex = ex;
449	>	this.next = next;
450	>	this.thrower = Thread.currentThread().getId();
451		}
452		}
453
454		/**
455	<	* Performs the actual monitor wait for awaitDone
455	>	* Records exception and sets exceptional completion.
456	>	*
457	>	* @return status on exit
458		*/
459	<	private void doAwaitDone(long startTime, long nanos) {
460	<	synchronized(this) {
461	<	try {
462	<	while (status >= 0) {
463	<	long nt = nanos - System.nanoTime() - startTime;
464	<	if (nt <= 0)
465	<	break;
466	<	wait(nt / 1000000, (int)(nt % 1000000));
459	>	private int setExceptionalCompletion(Throwable ex) {
460	>	int h = System.identityHashCode(this);
461	>	final ReentrantLock lock = exceptionTableLock;
462	>	lock.lock();
463	>	try {
464	>	expungeStaleExceptions();
465	>	ExceptionNode[] t = exceptionTable;
466	>	int i = h & (t.length - 1);
467	>	for (ExceptionNode e = t[i]; ; e = e.next) {
468	>	if (e == null) {
469	>	t[i] = new ExceptionNode(this, ex, t[i]);
470	>	break;
471		}
472	<	} catch (InterruptedException ie) {
473	<	onInterruptedWait();
472	>	if (e.get() == this) // already present
473	>	break;
474		}
475	+	} finally {
476	+	lock.unlock();
477		}
478	+	return setCompletion(EXCEPTIONAL);
479		}
480
245	–	// Awaiting completion
246	–
481		/**
482	<	* Sets status to indicate there is joiner, then waits for join,
483	<	* surrounded with pool notifications.
484	<	* @return status upon exit
482	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
483	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
484	>	* exceptions, but if it does anyway, we have no recourse during
485	>	* shutdown, so guard against this case.
486		*/
487	<	final int awaitDone(ForkJoinWorkerThread w, boolean maintainParallelism) {
488	<	ForkJoinPool pool = w == null? null : w.pool;
489	<	int s;
490	<	while ((s = status) >= 0) {
491	<	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;
487	>	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
488	>	if (t != null && t.status >= 0) {
489	>	try {
490	>	t.cancel(false);
491	>	} catch (Throwable ignore) {
492		}
493		}
264	–	return s;
494		}
495
496		/**
497	<	* Timed version of awaitDone
269	<	* @return status upon exit
497	>	* Removes exception node and clears status
498		*/
499	<	final int awaitDone(ForkJoinWorkerThread w, long nanos) {
500	<	ForkJoinPool pool = w == null? null : w.pool;
501	<	int s;
502	<	while ((s = status) >= 0) {
503	<	if (casStatus(s, pool == null? s|EXTERNAL_SIGNAL : s+1)) {
504	<	long startTime = System.nanoTime();
505	<	if (pool == null || !pool.preJoin(this, false))
506	<	doAwaitDone(startTime, nanos);
507	<	if ((s = status) >= 0) {
508	<	adjustPoolCountsOnCancelledWait(pool);
509	<	s = status;
499	>	private void clearExceptionalCompletion() {
500	>	int h = System.identityHashCode(this);
501	>	final ReentrantLock lock = exceptionTableLock;
502	>	lock.lock();
503	>	try {
504	>	ExceptionNode[] t = exceptionTable;
505	>	int i = h & (t.length - 1);
506	>	ExceptionNode e = t[i];
507	>	ExceptionNode pred = null;
508	>	while (e != null) {
509	>	ExceptionNode next = e.next;
510	>	if (e.get() == this) {
511	>	if (pred == null)
512	>	t[i] = next;
513	>	else
514	>	pred.next = next;
515	>	break;
516		}
517	<	if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
518	<	adjustPoolCountsOnUnblock(pool);
285	<	break;
517	>	pred = e;
518	>	e = next;
519		}
520	+	expungeStaleExceptions();
521	+	status = 0;
522	+	} finally {
523	+	lock.unlock();
524		}
288	–	return s;
525		}
526
527		/**
528	<	* Notify pool that thread is unblocked. Called by signalled
529	<	* threads when woken by non-FJ threads (which is atypical).
528	>	* Returns a rethrowable exception for the given task, if
529	>	* available. To provide accurate stack traces, if the exception
530	>	* was not thrown by the current thread, we try to create a new
531	>	* exception of the same type as the one thrown, but with the
532	>	* recorded exception as its cause. If there is no such
533	>	* constructor, we instead try to use a no-arg constructor,
534	>	* followed by initCause, to the same effect. If none of these
535	>	* apply, or any fail due to other exceptions, we return the
536	>	* recorded exception, which is still correct, although it may
537	>	* contain a misleading stack trace.
538	>	*
539	>	* @return the exception, or null if none
540		*/
541	<	private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
542	<	int s;
543	<	do;while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
544	<	if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
545	<	pool.updateRunningCount(s);
541	>	private Throwable getThrowableException() {
542	>	if (status != EXCEPTIONAL)
543	>	return null;
544	>	int h = System.identityHashCode(this);
545	>	ExceptionNode e;
546	>	final ReentrantLock lock = exceptionTableLock;
547	>	lock.lock();
548	>	try {
549	>	expungeStaleExceptions();
550	>	ExceptionNode[] t = exceptionTable;
551	>	e = t[h & (t.length - 1)];
552	>	while (e != null && e.get() != this)
553	>	e = e.next;
554	>	} finally {
555	>	lock.unlock();
556	>	}
557	>	Throwable ex;
558	>	if (e == null || (ex = e.ex) == null)
559	>	return null;
560	>	if (e.thrower != Thread.currentThread().getId()) {
561	>	Class<? extends Throwable> ec = ex.getClass();
562	>	try {
563	>	Constructor<?> noArgCtor = null;
564	>	Constructor<?>[] cs = ec.getConstructors();// public ctors only
565	>	for (int i = 0; i < cs.length; ++i) {
566	>	Constructor<?> c = cs[i];
567	>	Class<?>[] ps = c.getParameterTypes();
568	>	if (ps.length == 0)
569	>	noArgCtor = c;
570	>	else if (ps.length == 1 && ps[0] == Throwable.class)
571	>	return (Throwable)(c.newInstance(ex));
572	>	}
573	>	if (noArgCtor != null) {
574	>	Throwable wx = (Throwable)(noArgCtor.newInstance());
575	>	wx.initCause(ex);
576	>	return wx;
577	>	}
578	>	} catch (Exception ignore) {
579	>	}
580	>	}
581	>	return ex;
582		}
583
584		/**
585	<	* Notify pool to adjust counts on cancelled or timed out wait
585	>	* Poll stale refs and remove them. Call only while holding lock.
586		*/
587	<	private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
588	<	if (pool != null) {
589	<	int s;
590	<	while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
591	<	if (casStatus(s, s - 1)) {
592	<	pool.updateRunningCount(1);
593	<	break;
587	>	private static void expungeStaleExceptions() {
588	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
589	>	if (x instanceof ExceptionNode) {
590	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
591	>	ExceptionNode[] t = exceptionTable;
592	>	int i = System.identityHashCode(key) & (t.length - 1);
593	>	ExceptionNode e = t[i];
594	>	ExceptionNode pred = null;
595	>	while (e != null) {
596	>	ExceptionNode next = e.next;
597	>	if (e == x) {
598	>	if (pred == null)
599	>	t[i] = next;
600	>	else
601	>	pred.next = next;
602	>	break;
603	>	}
604	>	pred = e;
605	>	e = next;
606		}
607		}
608		}
609		}
610
611	<	private void onInterruptedWait() {
612	<	Thread t = Thread.currentThread();
613	<	if (t instanceof ForkJoinWorkerThread) {
614	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread)t;
615	<	if (w.isTerminating())
616	<	cancelIgnoreExceptions();
617	<	}
324	<	else { // re-interrupt
611	>	/**
612	>	* If lock is available, poll stale refs and remove them.
613	>	* Called from ForkJoinPool when pools become quiescent.
614	>	*/
615	>	static final void helpExpungeStaleExceptions() {
616	>	final ReentrantLock lock = exceptionTableLock;
617	>	if (lock.tryLock()) {
618		try {
619	<	t.interrupt();
620	<	} catch (SecurityException ignore) {
619	>	expungeStaleExceptions();
620	>	} finally {
621	>	lock.unlock();
622		}
623		}
624		}
625
626	<	// Recording and reporting exceptions
627	<
628	<	private void setDoneExceptionally(Throwable rex) {
629	<	exceptionMap.put(this, rex);
630	<	setCompletion(EXCEPTIONAL);
626	>	/**
627	>	* Report the result of invoke or join; called only upon
628	>	* non-normal return of internal versions.
629	>	*/
630	>	private V reportResult() {
631	>	int s; Throwable ex;
632	>	if ((s = status) == CANCELLED)
633	>	throw new CancellationException();
634	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
635	>	U.throwException(ex);
636	>	return getRawResult();
637		}
638
639	+	// public methods
640	+
641		/**
642	<	* Throws the exception associated with status s;
643	<	* @throws the exception
642	>	* Arranges to asynchronously execute this task.  While it is not
643	>	* necessarily enforced, it is a usage error to fork a task more
644	>	* than once unless it has completed and been reinitialized.
645	>	* Subsequent modifications to the state of this task or any data
646	>	* it operates on are not necessarily consistently observable by
647	>	* any thread other than the one executing it unless preceded by a
648	>	* call to {@link #join} or related methods, or a call to {@link
649	>	* #isDone} returning {@code true}.
650	>	*
651	>	* <p>This method may be invoked only from within {@code
652	>	* ForkJoinPool} computations (as may be determined using method
653	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
654	>	* result in exceptions or errors, possibly including {@code
655	>	* ClassCastException}.
656	>	*
657	>	* @return {@code this}, to simplify usage
658		*/
659	<	private void reportException(int s) {
660	<	if ((s &= COMPLETION_MASK) < NORMAL) {
661	<	if (s == CANCELLED)
662	<	throw new CancellationException();
663	<	else
348	<	rethrowException(exceptionMap.get(this));
349	<	}
659	>	public final ForkJoinTask<V> fork() {
660	>	ForkJoinWorkerThread wt;
661	>	(wt = (ForkJoinWorkerThread)Thread.currentThread()).
662	>	workQueue.push(this, wt.pool);
663	>	return this;
664		}
665
666		/**
667	<	* Returns result or throws exception using j.u.c.Future conventions
668	<	* Only call when isDone known to be true.
667	>	* Returns the result of the computation when it {@link #isDone is
668	>	* done}.  This method differs from {@link #get()} in that
669	>	* abnormal completion results in {@code RuntimeException} or
670	>	* {@code Error}, not {@code ExecutionException}, and that
671	>	* interrupts of the calling thread do <em>not</em> cause the
672	>	* method to abruptly return by throwing {@code
673	>	* InterruptedException}.
674	>	*
675	>	* @return the computed result
676		*/
677	<	private V reportFutureResult()
678	<	throws ExecutionException, InterruptedException {
679	<	int s = status & COMPLETION_MASK;
680	<	if (s < NORMAL) {
681	<	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	<	}
368	<	return getRawResult();
677	>	public final V join() {
678	>	if (doJoin() != NORMAL)
679	>	return reportResult();
680	>	else
681	>	return getRawResult();
682		}
683
684		/**
685	<	* Returns result or throws exception using j.u.c.Future conventions
686	<	* with timeouts
685	>	* Commences performing this task, awaits its completion if
686	>	* necessary, and returns its result, or throws an (unchecked)
687	>	* {@code RuntimeException} or {@code Error} if the underlying
688	>	* computation did so.
689	>	*
690	>	* @return the computed result
691		*/
692	<	private V reportTimedFutureResult()
693	<	throws InterruptedException, ExecutionException, TimeoutException {
694	<	Throwable ex;
695	<	int s = status & COMPLETION_MASK;
379	<	if (s == NORMAL)
692	>	public final V invoke() {
693	>	if (doInvoke() != NORMAL)
694	>	return reportResult();
695	>	else
696		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();
697		}
698
390	–	// internal execution methods
391	–
699		/**
700	<	* Calls exec, recording completion, and rethrowing exception if
701	<	* encountered. Caller should normally check status before calling
702	<	* @return true if completed normally
700	>	* Forks the given tasks, returning when {@code isDone} holds for
701	>	* each task or an (unchecked) exception is encountered, in which
702	>	* case the exception is rethrown. If more than one task
703	>	* encounters an exception, then this method throws any one of
704	>	* these exceptions. If any task encounters an exception, the
705	>	* other may be cancelled. However, the execution status of
706	>	* individual tasks is not guaranteed upon exceptional return. The
707	>	* status of each task may be obtained using {@link
708	>	* #getException()} and related methods to check if they have been
709	>	* cancelled, completed normally or exceptionally, or left
710	>	* unprocessed.
711	>	*
712	>	* <p>This method may be invoked only from within {@code
713	>	* ForkJoinPool} computations (as may be determined using method
714	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
715	>	* result in exceptions or errors, possibly including {@code
716	>	* ClassCastException}.
717	>	*
718	>	* @param t1 the first task
719	>	* @param t2 the second task
720	>	* @throws NullPointerException if any task is null
721		*/
722	<	private boolean tryExec() {
723	<	try { // try block must contain only call to exec
724	<	if (!exec())
725	<	return false;
401	<	} catch (Throwable rex) {
402	<	setDoneExceptionally(rex);
403	<	rethrowException(rex);
404	<	return false; // not reached
405	<	}
406	<	setNormalCompletion();
407	<	return true;
722	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
723	>	t2.fork();
724	>	t1.invoke();
725	>	t2.join();
726		}
727
728		/**
729	<	* Main execution method used by worker threads. Invokes
730	<	* base computation unless already complete
729	>	* Forks the given tasks, returning when {@code isDone} holds for
730	>	* each task or an (unchecked) exception is encountered, in which
731	>	* case the exception is rethrown. If more than one task
732	>	* encounters an exception, then this method throws any one of
733	>	* these exceptions. If any task encounters an exception, others
734	>	* may be cancelled. However, the execution status of individual
735	>	* tasks is not guaranteed upon exceptional return. The status of
736	>	* each task may be obtained using {@link #getException()} and
737	>	* related methods to check if they have been cancelled, completed
738	>	* normally or exceptionally, or left unprocessed.
739	>	*
740	>	* <p>This method may be invoked only from within {@code
741	>	* ForkJoinPool} computations (as may be determined using method
742	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
743	>	* result in exceptions or errors, possibly including {@code
744	>	* ClassCastException}.
745	>	*
746	>	* @param tasks the tasks
747	>	* @throws NullPointerException if any task is null
748		*/
749	<	final void quietlyExec() {
750	<	if (status >= 0) {
751	<	try {
752	<	if (!exec())
753	<	return;
754	<	} catch(Throwable rex) {
755	<	setDoneExceptionally(rex);
756	<	return;
749	>	public static void invokeAll(ForkJoinTask<?>... tasks) {
750	>	Throwable ex = null;
751	>	int last = tasks.length - 1;
752	>	for (int i = last; i >= 0; --i) {
753	>	ForkJoinTask<?> t = tasks[i];
754	>	if (t == null) {
755	>	if (ex == null)
756	>	ex = new NullPointerException();
757	>	}
758	>	else if (i != 0)
759	>	t.fork();
760	>	else if (t.doInvoke() < NORMAL && ex == null)
761	>	ex = t.getException();
762	>	}
763	>	for (int i = 1; i <= last; ++i) {
764	>	ForkJoinTask<?> t = tasks[i];
765	>	if (t != null) {
766	>	if (ex != null)
767	>	t.cancel(false);
768	>	else if (t.doJoin() < NORMAL)
769	>	ex = t.getException();
770		}
423	–	setNormalCompletion();
771		}
772	+	if (ex != null)
773	+	U.throwException(ex);
774		}
775
776		/**
777	<	* Calls exec, recording but not rethrowing exception
778	<	* Caller should normally check status before calling
779	<	* @return true if completed normally
777	>	* Forks all tasks in the specified collection, returning when
778	>	* {@code isDone} holds for each task or an (unchecked) exception
779	>	* is encountered, in which case the exception is rethrown. If
780	>	* more than one task encounters an exception, then this method
781	>	* throws any one of these exceptions. If any task encounters an
782	>	* exception, others may be cancelled. However, the execution
783	>	* status of individual tasks is not guaranteed upon exceptional
784	>	* return. The status of each task may be obtained using {@link
785	>	* #getException()} and related methods to check if they have been
786	>	* cancelled, completed normally or exceptionally, or left
787	>	* unprocessed.
788	>	*
789	>	* <p>This method may be invoked only from within {@code
790	>	* ForkJoinPool} computations (as may be determined using method
791	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
792	>	* result in exceptions or errors, possibly including {@code
793	>	* ClassCastException}.
794	>	*
795	>	* @param tasks the collection of tasks
796	>	* @return the tasks argument, to simplify usage
797	>	* @throws NullPointerException if tasks or any element are null
798		*/
799	<	private boolean tryQuietlyInvoke() {
800	<	try {
801	<	if (!exec())
802	<	return false;
803	<	} catch (Throwable rex) {
804	<	setDoneExceptionally(rex);
805	<	return false;
799	>	public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
800	>	if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
801	>	invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
802	>	return tasks;
803	>	}
804	>	@SuppressWarnings("unchecked")
805	>	List<? extends ForkJoinTask<?>> ts =
806	>	(List<? extends ForkJoinTask<?>>) tasks;
807	>	Throwable ex = null;
808	>	int last = ts.size() - 1;
809	>	for (int i = last; i >= 0; --i) {
810	>	ForkJoinTask<?> t = ts.get(i);
811	>	if (t == null) {
812	>	if (ex == null)
813	>	ex = new NullPointerException();
814	>	}
815	>	else if (i != 0)
816	>	t.fork();
817	>	else if (t.doInvoke() < NORMAL && ex == null)
818	>	ex = t.getException();
819	>	}
820	>	for (int i = 1; i <= last; ++i) {
821	>	ForkJoinTask<?> t = ts.get(i);
822	>	if (t != null) {
823	>	if (ex != null)
824	>	t.cancel(false);
825	>	else if (t.doJoin() < NORMAL)
826	>	ex = t.getException();
827	>	}
828		}
829	<	setNormalCompletion();
830	<	return true;
829	>	if (ex != null)
830	>	U.throwException(ex);
831	>	return tasks;
832		}
833
834		/**
835	<	* Cancel, ignoring any exceptions it throws
835	>	* Attempts to cancel execution of this task. This attempt will
836	>	* fail if the task has already completed or could not be
837	>	* cancelled for some other reason. If successful, and this task
838	>	* has not started when {@code cancel} is called, execution of
839	>	* this task is suppressed. After this method returns
840	>	* successfully, unless there is an intervening call to {@link
841	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
842	>	* {@link #isDone}, and {@code cancel} will return {@code true}
843	>	* and calls to {@link #join} and related methods will result in
844	>	* {@code CancellationException}.
845	>	*
846	>	* <p>This method may be overridden in subclasses, but if so, must
847	>	* still ensure that these properties hold. In particular, the
848	>	* {@code cancel} method itself must not throw exceptions.
849	>	*
850	>	* <p>This method is designed to be invoked by <em>other</em>
851	>	* tasks. To terminate the current task, you can just return or
852	>	* throw an unchecked exception from its computation method, or
853	>	* invoke {@link #completeExceptionally}.
854	>	*
855	>	* @param mayInterruptIfRunning this value has no effect in the
856	>	* default implementation because interrupts are not used to
857	>	* control cancellation.
858	>	*
859	>	* @return {@code true} if this task is now cancelled
860		*/
861	<	final void cancelIgnoreExceptions() {
862	<	try {
449	<	cancel(false);
450	<	} catch(Throwable ignore) {
451	<	}
861	>	public boolean cancel(boolean mayInterruptIfRunning) {
862	>	return setCompletion(CANCELLED) == CANCELLED;
863		}
864
865	<	// public methods
865	>	public final boolean isDone() {
866	>	return status < 0;
867	>	}
868	>
869	>	public final boolean isCancelled() {
870	>	return status == CANCELLED;
871	>	}
872
873		/**
874	<	* Arranges to asynchronously execute this task.  While it is not
875	<	* necessarily enforced, it is a usage error to fork a task more
876	<	* than once unless it has completed and been reinitialized.  This
460	<	* method may be invoked only from within other ForkJoinTask
461	<	* computations. Attempts to invoke in other contexts result in
462	<	* exceptions or errors including ClassCastException.
874	>	* Returns {@code true} if this task threw an exception or was cancelled.
875	>	*
876	>	* @return {@code true} if this task threw an exception or was cancelled
877		*/
878	<	public final void fork() {
879	<	((ForkJoinWorkerThread)(Thread.currentThread())).pushTask(this);
878	>	public final boolean isCompletedAbnormally() {
879	>	return status < NORMAL;
880		}
881
882		/**
883	<	* Returns the result of the computation when it is ready.
884	<	* This method differs from <tt>get</tt> in that abnormal
471	<	* completion results in RuntimeExceptions or Errors, not
472	<	* ExecutionExceptions.
883	>	* Returns {@code true} if this task completed without throwing an
884	>	* exception and was not cancelled.
885		*
886	<	* @return the computed result
886	>	* @return {@code true} if this task completed without throwing an
887	>	* exception and was not cancelled
888		*/
889	<	public final V join() {
890	<	ForkJoinWorkerThread w = getWorker();
478	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryExec())
479	<	reportException(awaitDone(w, true));
480	<	return getRawResult();
889	>	public final boolean isCompletedNormally() {
890	>	return status == NORMAL;
891		}
892
893	<	public final V get() throws InterruptedException, ExecutionException {
894	<	ForkJoinWorkerThread w = getWorker();
895	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
896	<	awaitDone(w, true);
897	<	return reportFutureResult();
893	>	/**
894	>	* Returns the exception thrown by the base computation, or a
895	>	* {@code CancellationException} if cancelled, or {@code null} if
896	>	* none or if the method has not yet completed.
897	>	*
898	>	* @return the exception, or {@code null} if none
899	>	*/
900	>	public final Throwable getException() {
901	>	int s = status;
902	>	return ((s >= NORMAL)    ? null :
903	>	(s == CANCELLED) ? new CancellationException() :
904	>	getThrowableException());
905		}
906
907	<	public final V get(long timeout, TimeUnit unit)
908	<	throws InterruptedException, ExecutionException, TimeoutException {
909	<	ForkJoinWorkerThread w = getWorker();
910	<	if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke())
911	<	awaitDone(w, unit.toNanos(timeout));
912	<	return reportTimedFutureResult();
907	>	/**
908	>	* Completes this task abnormally, and if not already aborted or
909	>	* cancelled, causes it to throw the given exception upon
910	>	* {@code join} and related operations. This method may be used
911	>	* to induce exceptions in asynchronous tasks, or to force
912	>	* completion of tasks that would not otherwise complete.  Its use
913	>	* in other situations is discouraged.  This method is
914	>	* overridable, but overridden versions must invoke {@code super}
915	>	* implementation to maintain guarantees.
916	>	*
917	>	* @param ex the exception to throw. If this exception is not a
918	>	* {@code RuntimeException} or {@code Error}, the actual exception
919	>	* thrown will be a {@code RuntimeException} with cause {@code ex}.
920	>	*/
921	>	public void completeExceptionally(Throwable ex) {
922	>	setExceptionalCompletion((ex instanceof RuntimeException) ||
923	>	(ex instanceof Error) ? ex :
924	>	new RuntimeException(ex));
925	>	}
926	>
927	>	/**
928	>	* Completes this task, and if not already aborted or cancelled,
929	>	* returning the given value as the result of subsequent
930	>	* invocations of {@code join} and related operations. This method
931	>	* may be used to provide results for asynchronous tasks, or to
932	>	* provide alternative handling for tasks that would not otherwise
933	>	* complete normally. Its use in other situations is
934	>	* discouraged. This method is overridable, but overridden
935	>	* versions must invoke {@code super} implementation to maintain
936	>	* guarantees.
937	>	*
938	>	* @param value the result value for this task
939	>	*/
940	>	public void complete(V value) {
941	>	try {
942	>	setRawResult(value);
943	>	} catch (Throwable rex) {
944	>	setExceptionalCompletion(rex);
945	>	return;
946	>	}
947	>	setCompletion(NORMAL);
948		}
949
950		/**
951	<	* Possibly executes other tasks until this task is ready, then
952	<	* returns the result of the computation.  This method may be more
953	<	* 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).
951	>	* Waits if necessary for the computation to complete, and then
952	>	* retrieves its result.
953	>	*
954		* @return the computed result
955	+	* @throws CancellationException if the computation was cancelled
956	+	* @throws ExecutionException if the computation threw an
957	+	* exception
958	+	* @throws InterruptedException if the current thread is not a
959	+	* member of a ForkJoinPool and was interrupted while waiting
960		*/
961	<	public final V helpJoin() {
962	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread)(Thread.currentThread());
963	<	if (status < 0 || !w.unpushTask(this) || !tryExec())
964	<	reportException(w.helpJoinTask(this));
961	>	public final V get() throws InterruptedException, ExecutionException {
962	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
963	>	doJoin() : externalInterruptibleAwaitDone(0L);
964	>	Throwable ex;
965	>	if (s == CANCELLED)
966	>	throw new CancellationException();
967	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
968	>	throw new ExecutionException(ex);
969		return getRawResult();
970		}
971
972		/**
973	<	* Performs this task, awaits its completion if necessary, and
974	<	* return its result.
975	<	* @throws Throwable (a RuntimeException, Error, or unchecked
976	<	* exception) if the underlying computation did so.
973	>	* Waits if necessary for at most the given time for the computation
974	>	* to complete, and then retrieves its result, if available.
975	>	*
976	>	* @param timeout the maximum time to wait
977	>	* @param unit the time unit of the timeout argument
978		* @return the computed result
979	+	* @throws CancellationException if the computation was cancelled
980	+	* @throws ExecutionException if the computation threw an
981	+	* exception
982	+	* @throws InterruptedException if the current thread is not a
983	+	* member of a ForkJoinPool and was interrupted while waiting
984	+	* @throws TimeoutException if the wait timed out
985		*/
986	<	public final V invoke() {
987	<	if (status >= 0 && tryExec())
988	<	return getRawResult();
989	<	else
990	<	return join();
986	>	public final V get(long timeout, TimeUnit unit)
987	>	throws InterruptedException, ExecutionException, TimeoutException {
988	>	// Messy in part because we measure in nanos, but wait in millis
989	>	int s; long millis, nanos;
990	>	Thread t = Thread.currentThread();
991	>	if (!(t instanceof ForkJoinWorkerThread)) {
992	>	if ((millis = unit.toMillis(timeout)) > 0L)
993	>	s = externalInterruptibleAwaitDone(millis);
994	>	else
995	>	s = status;
996	>	}
997	>	else if ((s = status) >= 0 && (nanos = unit.toNanos(timeout)) > 0L) {
998	>	long deadline = System.nanoTime() + nanos;
999	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1000	>	ForkJoinPool.WorkQueue w = wt.workQueue;
1001	>	ForkJoinPool p = wt.pool;
1002	>	if (w.tryUnpush(this))
1003	>	doExec();
1004	>	boolean blocking = false;
1005	>	try {
1006	>	while ((s = status) >= 0) {
1007	>	if (w.runState < 0)
1008	>	cancelIgnoringExceptions(this);
1009	>	else if (!blocking)
1010	>	blocking = p.tryCompensate();
1011	>	else {
1012	>	millis = TimeUnit.NANOSECONDS.toMillis(nanos);
1013	>	if (millis > 0L &&
1014	>	U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
1015	>	try {
1016	>	synchronized (this) {
1017	>	if (status >= 0)
1018	>	wait(millis);
1019	>	}
1020	>	} catch (InterruptedException ie) {
1021	>	}
1022	>	}
1023	>	if ((s = status) < 0 ||
1024	>	(nanos = deadline - System.nanoTime()) <= 0L)
1025	>	break;
1026	>	}
1027	>	}
1028	>	} finally {
1029	>	if (blocking)
1030	>	p.incrementActiveCount();
1031	>	}
1032	>	}
1033	>	if (s != NORMAL) {
1034	>	Throwable ex;
1035	>	if (s == CANCELLED)
1036	>	throw new CancellationException();
1037	>	if (s != EXCEPTIONAL)
1038	>	throw new TimeoutException();
1039	>	if ((ex = getThrowableException()) != null)
1040	>	throw new ExecutionException(ex);
1041	>	}
1042	>	return getRawResult();
1043		}
1044
1045		/**
1046	<	* Joins this task, without returning its result or throwing an
1046	>	* Joins this task, without returning its result or throwing its
1047		* exception. This method may be useful when processing
1048		* collections of tasks when some have been cancelled or otherwise
1049		* known to have aborted.
1050		*/
1051		public final void quietlyJoin() {
1052	<	if (status >= 0) {
537	<	ForkJoinWorkerThread w = getWorker();
538	<	if (w == null || !w.unpushTask(this) || !tryQuietlyInvoke())
539	<	awaitDone(w, true);
540	<	}
1052	>	doJoin();
1053		}
1054
1055		/**
1056	<	* Possibly executes other tasks until this task is ready.
1056	>	* Commences performing this task and awaits its completion if
1057	>	* necessary, without returning its result or throwing its
1058	>	* exception.
1059		*/
1060	<	public final void quietlyHelpJoin() {
1061	<	if (status >= 0) {
548	<	ForkJoinWorkerThread w =
549	<	(ForkJoinWorkerThread)(Thread.currentThread());
550	<	if (!w.unpushTask(this) || !tryQuietlyInvoke())
551	<	w.helpJoinTask(this);
552	<	}
1060	>	public final void quietlyInvoke() {
1061	>	doInvoke();
1062		}
1063
1064		/**
1065	<	* Performs this task and awaits its completion if necessary,
1066	<	* without returning its result or throwing an exception. This
1067	<	* method may be useful when processing collections of tasks when
1068	<	* some have been cancelled or otherwise known to have aborted.
1065	>	* Possibly executes tasks until the pool hosting the current task
1066	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
1067	>	* be of use in designs in which many tasks are forked, but none
1068	>	* are explicitly joined, instead executing them until all are
1069	>	* processed.
1070	>	*
1071	>	* <p>This method may be invoked only from within {@code
1072	>	* ForkJoinPool} computations (as may be determined using method
1073	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1074	>	* result in exceptions or errors, possibly including {@code
1075	>	* ClassCastException}.
1076		*/
1077	<	public final void quietlyInvoke() {
1078	<	if (status >= 0 && !tryQuietlyInvoke())
1079	<	quietlyJoin();
1077	>	public static void helpQuiesce() {
1078	>	ForkJoinWorkerThread wt =
1079	>	(ForkJoinWorkerThread)Thread.currentThread();
1080	>	wt.pool.helpQuiescePool(wt.workQueue);
1081		}
1082
1083		/**
1084	<	* Returns true if the computation performed by this task has
1085	<	* completed (or has been cancelled).
1086	<	* @return true if this computation has completed
1084	>	* Resets the internal bookkeeping state of this task, allowing a
1085	>	* subsequent {@code fork}. This method allows repeated reuse of
1086	>	* this task, but only if reuse occurs when this task has either
1087	>	* never been forked, or has been forked, then completed and all
1088	>	* outstanding joins of this task have also completed. Effects
1089	>	* under any other usage conditions are not guaranteed.
1090	>	* This method may be useful when executing
1091	>	* pre-constructed trees of subtasks in loops.
1092	>	*
1093	>	* <p>Upon completion of this method, {@code isDone()} reports
1094	>	* {@code false}, and {@code getException()} reports {@code
1095	>	* null}. However, the value returned by {@code getRawResult} is
1096	>	* unaffected. To clear this value, you can invoke {@code
1097	>	* setRawResult(null)}.
1098		*/
1099	<	public final boolean isDone() {
1100	<	return status < 0;
1099	>	public void reinitialize() {
1100	>	if (status == EXCEPTIONAL)
1101	>	clearExceptionalCompletion();
1102	>	else
1103	>	status = 0;
1104		}
1105
1106		/**
1107	<	* Returns true if this task was cancelled.
1108	<	* @return true if this task was cancelled
1107	>	* Returns the pool hosting the current task execution, or null
1108	>	* if this task is executing outside of any ForkJoinPool.
1109	>	*
1110	>	* @see #inForkJoinPool
1111	>	* @return the pool, or {@code null} if none
1112		*/
1113	<	public final boolean isCancelled() {
1114	<	return (status & COMPLETION_MASK) == CANCELLED;
1113	>	public static ForkJoinPool getPool() {
1114	>	Thread t = Thread.currentThread();
1115	>	return (t instanceof ForkJoinWorkerThread) ?
1116	>	((ForkJoinWorkerThread) t).pool : null;
1117		}
1118
1119		/**
1120	<	* Returns true if this task threw an exception or was cancelled
1121	<	* @return true if this task threw an exception or was cancelled
1120	>	* Returns {@code true} if the current thread is a {@link
1121	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1122	>	*
1123	>	* @return {@code true} if the current thread is a {@link
1124	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1125	>	* or {@code false} otherwise
1126		*/
1127	<	public final boolean completedAbnormally() {
1128	<	return (status & COMPLETION_MASK) < NORMAL;
1127	>	public static boolean inForkJoinPool() {
1128	>	return Thread.currentThread() instanceof ForkJoinWorkerThread;
1129		}
1130
1131		/**
1132	<	* Returns the exception thrown by the base computation, or a
1133	<	* CancellationException if cancelled, or null if none or if the
1134	<	* method has not yet completed.
1135	<	* @return the exception, or null if none
1132	>	* Tries to unschedule this task for execution. This method will
1133	>	* typically succeed if this task is the most recently forked task
1134	>	* by the current thread, and has not commenced executing in
1135	>	* another thread.  This method may be useful when arranging
1136	>	* alternative local processing of tasks that could have been, but
1137	>	* were not, stolen.
1138	>	*
1139	>	* <p>This method may be invoked only from within {@code
1140	>	* ForkJoinPool} computations (as may be determined using method
1141	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1142	>	* result in exceptions or errors, possibly including {@code
1143	>	* ClassCastException}.
1144	>	*
1145	>	* @return {@code true} if unforked
1146		*/
1147	<	public final Throwable getException() {
1148	<	int s = status & COMPLETION_MASK;
1149	<	if (s >= NORMAL)
600	<	return null;
601	<	if (s == CANCELLED)
602	<	return new CancellationException();
603	<	return exceptionMap.get(this);
1147	>	public boolean tryUnfork() {
1148	>	return ((ForkJoinWorkerThread)Thread.currentThread())
1149	>	.workQueue.tryUnpush(this);
1150		}
1151
1152		/**
1153	<	* Asserts that the results of this task's computation will not be
1154	<	* used. If a cancellation occurs before this task is processed,
1155	<	* then its <tt>compute</tt> method will not be executed,
1156	<	* <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.
1153	>	* Returns an estimate of the number of tasks that have been
1154	>	* forked by the current worker thread but not yet executed. This
1155	>	* value may be useful for heuristic decisions about whether to
1156	>	* fork other tasks.
1157		*
1158	<	* <p>This method may be overridden in subclasses, but if so, must
1159	<	* still ensure that these minimal properties hold. In particular,
1160	<	* the cancel method itself must not throw exceptions.
1158	>	* <p>This method may be invoked only from within {@code
1159	>	* ForkJoinPool} computations (as may be determined using method
1160	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1161	>	* result in exceptions or errors, possibly including {@code
1162	>	* ClassCastException}.
1163		*
1164	<	* <p> This method is designed to be invoked by <em>other</em>
1165	<	* tasks. To terminate the current task, you can just return or
1166	<	* throw an unchecked exception from its computation method, or
1167	<	* invoke <tt>completeExceptionally(someException)</tt>.
1164	>	* @return the number of tasks
1165	>	*/
1166	>	public static int getQueuedTaskCount() {
1167	>	return ((ForkJoinWorkerThread) Thread.currentThread())
1168	>	.workQueue.queueSize();
1169	>	}
1170	>
1171	>	/**
1172	>	* Returns an estimate of how many more locally queued tasks are
1173	>	* held by the current worker thread than there are other worker
1174	>	* threads that might steal them.  This value may be useful for
1175	>	* heuristic decisions about whether to fork other tasks. In many
1176	>	* usages of ForkJoinTasks, at steady state, each worker should
1177	>	* aim to maintain a small constant surplus (for example, 3) of
1178	>	* tasks, and to process computations locally if this threshold is
1179	>	* exceeded.
1180	>	*
1181	>	* <p>This method may be invoked only from within {@code
1182	>	* ForkJoinPool} computations (as may be determined using method
1183	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1184	>	* result in exceptions or errors, possibly including {@code
1185	>	* ClassCastException}.
1186		*
1187	<	* @param mayInterruptIfRunning this value is ignored in the
1188	<	* default implementation because tasks are not in general
1189	<	* cancelled via interruption.
1187	>	* @return the surplus number of tasks, which may be negative
1188	>	*/
1189	>	public static int getSurplusQueuedTaskCount() {
1190	>	/*
1191	>	* The aim of this method is to return a cheap heuristic guide
1192	>	* for task partitioning when programmers, frameworks, tools,
1193	>	* or languages have little or no idea about task granularity.
1194	>	* In essence by offering this method, we ask users only about
1195	>	* tradeoffs in overhead vs expected throughput and its
1196	>	* variance, rather than how finely to partition tasks.
1197	>	*
1198	>	* In a steady state strict (tree-structured) computation,
1199	>	* each thread makes available for stealing enough tasks for
1200	>	* other threads to remain active. Inductively, if all threads
1201	>	* play by the same rules, each thread should make available
1202	>	* only a constant number of tasks.
1203	>	*
1204	>	* The minimum useful constant is just 1. But using a value of
1205	>	* 1 would require immediate replenishment upon each steal to
1206	>	* maintain enough tasks, which is infeasible.  Further,
1207	>	* partitionings/granularities of offered tasks should
1208	>	* minimize steal rates, which in general means that threads
1209	>	* nearer the top of computation tree should generate more
1210	>	* than those nearer the bottom. In perfect steady state, each
1211	>	* thread is at approximately the same level of computation
1212	>	* tree. However, producing extra tasks amortizes the
1213	>	* uncertainty of progress and diffusion assumptions.
1214	>	*
1215	>	* So, users will want to use values larger, but not much
1216	>	* larger than 1 to both smooth over transient shortages and
1217	>	* hedge against uneven progress; as traded off against the
1218	>	* cost of extra task overhead. We leave the user to pick a
1219	>	* threshold value to compare with the results of this call to
1220	>	* guide decisions, but recommend values such as 3.
1221	>	*
1222	>	* When all threads are active, it is on average OK to
1223	>	* estimate surplus strictly locally. In steady-state, if one
1224	>	* thread is maintaining say 2 surplus tasks, then so are
1225	>	* others. So we can just use estimated queue length.
1226	>	* However, this strategy alone leads to serious mis-estimates
1227	>	* in some non-steady-state conditions (ramp-up, ramp-down,
1228	>	* other stalls). We can detect many of these by further
1229	>	* considering the number of "idle" threads, that are known to
1230	>	* have zero queued tasks, so compensate by a factor of
1231	>	* (#idle/#active) threads.
1232	>	*/
1233	>	ForkJoinWorkerThread wt =
1234	>	(ForkJoinWorkerThread)Thread.currentThread();
1235	>	return wt.workQueue.queueSize() - wt.pool.idlePerActive();
1236	>	}
1237	>
1238	>	// Extension methods
1239	>
1240	>	/**
1241	>	* Returns the result that would be returned by {@link #join}, even
1242	>	* if this task completed abnormally, or {@code null} if this task
1243	>	* is not known to have been completed.  This method is designed
1244	>	* to aid debugging, as well as to support extensions. Its use in
1245	>	* any other context is discouraged.
1246		*
1247	<	* @return true if this task is now cancelled
1247	>	* @return the result, or {@code null} if not completed
1248		*/
1249	<	public boolean cancel(boolean mayInterruptIfRunning) {
634	<	setCompletion(CANCELLED);
635	<	return (status & COMPLETION_MASK) == CANCELLED;
636	<	}
1249	>	public abstract V getRawResult();
1250
1251		/**
1252	<	* Completes this task abnormally, and if not already aborted or
1253	<	* cancelled, causes it to throw the given exception upon
1254	<	* <tt>join</tt> and related operations. This method may be used
1255	<	* to induce exceptions in asynchronous tasks, or to force
1256	<	* 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.
1252	>	* Forces the given value to be returned as a result.  This method
1253	>	* is designed to support extensions, and should not in general be
1254	>	* called otherwise.
1255	>	*
1256	>	* @param value the value
1257		*/
1258	<	public void completeExceptionally(Throwable ex) {
651	<	setDoneExceptionally((ex instanceof RuntimeException) ||
652	<	(ex instanceof Error)? ex :
653	<	new RuntimeException(ex));
654	<	}
1258	>	protected abstract void setRawResult(V value);
1259
1260		/**
1261	<	* Completes this task, and if not already aborted or cancelled,
1262	<	* returning a <tt>null</tt> result upon <tt>join</tt> and related
1263	<	* operations. This method may be used to provide results for
1264	<	* asynchronous tasks, or to provide alternative handling for
1265	<	* tasks that would not otherwise complete normally.
1261	>	* Immediately performs the base action of this task.  This method
1262	>	* is designed to support extensions, and should not in general be
1263	>	* called otherwise. The return value controls whether this task
1264	>	* is considered to be done normally. It may return false in
1265	>	* asynchronous actions that require explicit invocations of
1266	>	* {@link #complete} to become joinable. It may also throw an
1267	>	* (unchecked) exception to indicate abnormal exit.
1268		*
1269	<	* @param value the result value for this task.
1269	>	* @return {@code true} if completed normally
1270		*/
1271	<	public void complete(V value) {
1272	<	try {
1273	<	setRawResult(value);
1274	<	} catch(Throwable rex) {
1275	<	setDoneExceptionally(rex);
1276	<	return;
1277	<	}
1278	<	setNormalCompletion();
1271	>	protected abstract boolean exec();
1272	>
1273	>	/**
1274	>	* Returns, but does not unschedule or execute, a task queued by
1275	>	* the current thread but not yet executed, if one is immediately
1276	>	* available. There is no guarantee that this task will actually
1277	>	* be polled or executed next. Conversely, this method may return
1278	>	* null even if a task exists but cannot be accessed without
1279	>	* contention with other threads.  This method is designed
1280	>	* primarily to support extensions, and is unlikely to be useful
1281	>	* otherwise.
1282	>	*
1283	>	* <p>This method may be invoked only from within {@code
1284	>	* ForkJoinPool} computations (as may be determined using method
1285	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1286	>	* result in exceptions or errors, possibly including {@code
1287	>	* ClassCastException}.
1288	>	*
1289	>	* @return the next task, or {@code null} if none are available
1290	>	*/
1291	>	protected static ForkJoinTask<?> peekNextLocalTask() {
1292	>	return ((ForkJoinWorkerThread) Thread.currentThread()).workQueue.peek();
1293		}
1294
1295		/**
1296	<	* Resets the internal bookkeeping state of this task, allowing a
1297	<	* subsequent <tt>fork</tt>. This method allows repeated reuse of
1298	<	* this task, but only if reuse occurs when this task has either
1299	<	* never been forked, or has been forked, then completed and all
1300	<	* outstanding joins of this task have also completed. Effects
1301	<	* under any other usage conditions are not guaranteed, and are
1302	<	* almost surely wrong. This method may be useful when executing
1303	<	* pre-constructed trees of subtasks in loops.
1296	>	* Unschedules and returns, without executing, the next task
1297	>	* queued by the current thread but not yet executed.  This method
1298	>	* is designed primarily to support extensions, and is unlikely to
1299	>	* be useful otherwise.
1300	>	*
1301	>	* <p>This method may be invoked only from within {@code
1302	>	* ForkJoinPool} computations (as may be determined using method
1303	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1304	>	* result in exceptions or errors, possibly including {@code
1305	>	* ClassCastException}.
1306	>	*
1307	>	* @return the next task, or {@code null} if none are available
1308		*/
1309	<	public void reinitialize() {
1310	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
1311	<	exceptionMap.remove(this);
688	<	status = 0;
1309	>	protected static ForkJoinTask<?> pollNextLocalTask() {
1310	>	return ((ForkJoinWorkerThread) Thread.currentThread())
1311	>	.workQueue.nextLocalTask();
1312		}
1313
1314		/**
1315	<	* Tries to unschedule this task for execution. This method will
1316	<	* typically succeed if this task is the next task that would be
1317	<	* executed by the current thread, and will typically fail (return
1318	<	* false) otherwise. This method may be useful when arranging
1319	<	* faster local processing of tasks that could have been, but were
1320	<	* not, stolen.
1321	<	* @return true if unforked
1315	>	* Unschedules and returns, without executing, the next task
1316	>	* queued by the current thread but not yet executed, if one is
1317	>	* available, or if not available, a task that was forked by some
1318	>	* other thread, if available. Availability may be transient, so a
1319	>	* {@code null} result does not necessarily imply quiescence
1320	>	* of the pool this task is operating in.  This method is designed
1321	>	* primarily to support extensions, and is unlikely to be useful
1322	>	* otherwise.
1323	>	*
1324	>	* <p>This method may be invoked only from within {@code
1325	>	* ForkJoinPool} computations (as may be determined using method
1326	>	* {@link #inForkJoinPool}).  Attempts to invoke in other contexts
1327	>	* result in exceptions or errors, possibly including {@code
1328	>	* ClassCastException}.
1329	>	*
1330	>	* @return a task, or {@code null} if none are available
1331		*/
1332	<	public boolean tryUnfork() {
1333	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).unpushTask(this);
1332	>	protected static ForkJoinTask<?> pollTask() {
1333	>	ForkJoinWorkerThread wt =
1334	>	(ForkJoinWorkerThread)Thread.currentThread();
1335	>	return wt.pool.nextTaskFor(wt.workQueue);
1336		}
1337
1338	+	// Mark-bit operations
1339	+
1340		/**
1341	<	* Forks both tasks, returning when <tt>isDone</tt> holds for both
1342	<	* of them or an exception is encountered. This method may be
1343	<	* invoked only from within other ForkJoinTask
1344	<	* 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.
1341	>	* Returns true if this task is marked.
1342	>	*
1343	>	* @return true if this task is marked
1344	>	* @since 1.8
1345		*/
1346	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
1347	<	t2.fork();
717	<	t1.invoke();
718	<	t2.join();
1346	>	public final boolean isMarkedForkJoinTask() {
1347	>	return (status & MARKED) != 0;
1348		}
1349
1350		/**
1351	<	* Forks the given tasks, returning when <tt>isDone</tt> holds for
1352	<	* all of them. If any task encounters an exception, others may be
1353	<	* cancelled.  This method may be invoked only from within other
1354	<	* ForkJoinTask computations. Attempts to invoke in other contexts
726	<	* 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.
1351	>	* Atomically sets the mark on this task.
1352	>	*
1353	>	* @return true if this task was previously unmarked
1354	>	* @since 1.8
1355		*/
1356	<	public static void invokeAll(ForkJoinTask<?>... tasks) {
1357	<	Throwable ex = null;
1358	<	int last = tasks.length - 1;
1359	<	for (int i = last; i >= 0; --i) {
1360	<	ForkJoinTask<?> t = tasks[i];
1361	<	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	<	}
747	<	}
748	<	for (int i = 1; i <= last; ++i) {
749	<	ForkJoinTask<?> t = tasks[i];
750	<	if (t != null) {
751	<	if (ex != null)
752	<	t.cancel(false);
753	<	else {
754	<	t.quietlyJoin();
755	<	if (ex == null)
756	<	ex = t.getException();
757	<	}
758	<	}
1356	>	public final boolean markForkJoinTask() {
1357	>	for (int s;;) {
1358	>	if (((s = status) & MARKED) != 0)
1359	>	return false;
1360	>	if (U.compareAndSwapInt(this, STATUS, s, s | MARKED))
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
1369	<	* 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	>	* Atomically clears the mark on this task.
1367	>	*
1368	>	* @return true if this task was previously marked
1369	>	* @since 1.8
1370		*/
1371	<	public static void invokeAll(Collection<? extends ForkJoinTask<?>> tasks) {
1372	<	if (!(tasks instanceof List)) {
1373	<	invokeAll(tasks.toArray(new ForkJoinTask[tasks.size()]));
1374	<	return;
1375	<	}
1376	<	List<? extends ForkJoinTask<?>> ts =
781	<	(List<? extends ForkJoinTask<?>>)tasks;
782	<	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	<	}
797	<	}
798	<	for (int i = 1; i <= last; ++i) {
799	<	ForkJoinTask<?> t = ts.get(i);
800	<	if (t != null) {
801	<	if (ex != null)
802	<	t.cancel(false);
803	<	else {
804	<	t.quietlyJoin();
805	<	if (ex == null)
806	<	ex = t.getException();
807	<	}
808	<	}
1371	>	public final boolean unmarkForkJoinTask() {
1372	>	for (int s;;) {
1373	>	if (((s = status) & MARKED) == 0)
1374	>	return false;
1375	>	if (U.compareAndSwapInt(this, STATUS, s, s & ~MARKED))
1376	>	return true;
1377		}
810	–	if (ex != null)
811	–	rethrowException(ex);
1378		}
1379
1380		/**
1381	<	* Possibly executes tasks until the pool hosting the current task
1382	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
1383	<	* designs in which many tasks are forked, but none are explicitly
818	<	* joined, instead executing them until all are processed.
1381	>	* Adaptor for Runnables. This implements RunnableFuture
1382	>	* to be compliant with AbstractExecutorService constraints
1383	>	* when used in ForkJoinPool.
1384		*/
1385	<	public static void helpQuiesce() {
1386	<	((ForkJoinWorkerThread)(Thread.currentThread())).
1387	<	helpQuiescePool();
1385	>	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1386	>	implements RunnableFuture<T> {
1387	>	final Runnable runnable;
1388	>	final T resultOnCompletion;
1389	>	T result;
1390	>	AdaptedRunnable(Runnable runnable, T result) {
1391	>	if (runnable == null) throw new NullPointerException();
1392	>	this.runnable = runnable;
1393	>	this.resultOnCompletion = result;
1394	>	}
1395	>	public T getRawResult() { return result; }
1396	>	public void setRawResult(T v) { result = v; }
1397	>	public boolean exec() {
1398	>	runnable.run();
1399	>	result = resultOnCompletion;
1400	>	return true;
1401	>	}
1402	>	public void run() { invoke(); }
1403	>	private static final long serialVersionUID = 5232453952276885070L;
1404		}
1405
1406		/**
1407	<	* 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
1407	>	* Adaptor for Callables
1408		*/
1409	<	public static int surplus() {
1410	<	return ((ForkJoinWorkerThread)(Thread.currentThread()))
1411	<	.getEstimatedSurplusTaskCount();
1409	>	static final class AdaptedCallable<T> extends ForkJoinTask<T>
1410	>	implements RunnableFuture<T> {
1411	>	final Callable<? extends T> callable;
1412	>	T result;
1413	>	AdaptedCallable(Callable<? extends T> callable) {
1414	>	if (callable == null) throw new NullPointerException();
1415	>	this.callable = callable;
1416	>	}
1417	>	public T getRawResult() { return result; }
1418	>	public void setRawResult(T v) { result = v; }
1419	>	public boolean exec() {
1420	>	try {
1421	>	result = callable.call();
1422	>	return true;
1423	>	} catch (Error err) {
1424	>	throw err;
1425	>	} catch (RuntimeException rex) {
1426	>	throw rex;
1427	>	} catch (Exception ex) {
1428	>	throw new RuntimeException(ex);
1429	>	}
1430	>	}
1431	>	public void run() { invoke(); }
1432	>	private static final long serialVersionUID = 2838392045355241008L;
1433		}
1434
841	–	// Extension kit
842	–
1435		/**
1436	<	* Returns the result that would be returned by <tt>join</tt>, or
1437	<	* null if this task is not known to have been completed.  This
1438	<	* method is designed to aid debugging, as well as to support
847	<	* extensions. Its use in any other context is discouraged.
1436	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1437	>	* method of the given {@code Runnable} as its action, and returns
1438	>	* a null result upon {@link #join}.
1439		*
1440	<	* @return the result, or null if not completed.
1440	>	* @param runnable the runnable action
1441	>	* @return the task
1442		*/
1443	<	public abstract V getRawResult();
1443	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1444	>	return new AdaptedRunnable<Void>(runnable, null);
1445	>	}
1446
1447		/**
1448	<	* Forces the given value to be returned as a result.  This method
1449	<	* is designed to support extensions, and should not in general be
1450	<	* called otherwise.
1448	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1449	>	* method of the given {@code Runnable} as its action, and returns
1450	>	* the given result upon {@link #join}.
1451		*
1452	<	* @param value the value
1452	>	* @param runnable the runnable action
1453	>	* @param result the result upon completion
1454	>	* @return the task
1455		*/
1456	<	protected abstract void setRawResult(V value);
1456	>	public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
1457	>	return new AdaptedRunnable<T>(runnable, result);
1458	>	}
1459
1460		/**
1461	<	* Immediately performs the base action of this task.  This method
1462	<	* is designed to support extensions, and should not in general be
1463	<	* called otherwise. The return value controls whether this task
1464	<	* is considered to be done normally. It may return false in
1465	<	* asynchronous actions that require explicit invocations of
1466	<	* <tt>complete</tt> to become joinable. It may throw exceptions
1467	<	* to indicate abnormal exit.
870	<	* @return true if completed normally
871	<	* @throws Error or RuntimeException if encountered during computation
1461	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1462	>	* method of the given {@code Callable} as its action, and returns
1463	>	* its result upon {@link #join}, translating any checked exceptions
1464	>	* encountered into {@code RuntimeException}.
1465	>	*
1466	>	* @param callable the callable action
1467	>	* @return the task
1468		*/
1469	<	protected abstract boolean exec();
1469	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1470	>	return new AdaptedCallable<T>(callable);
1471	>	}
1472
1473		// Serialization support
1474
1475		private static final long serialVersionUID = -7721805057305804111L;
1476
1477		/**
1478	<	* Save the state to a stream.
1478	>	* Saves this task to a stream (that is, serializes it).
1479		*
1480		* @serialData the current run status and the exception thrown
1481	<	* during execution, or null if none.
884	<	* @param s the stream
1481	>	* during execution, or {@code null} if none
1482		*/
1483		private void writeObject(java.io.ObjectOutputStream s)
1484		throws java.io.IOException {
#	Line 890 | Line 1487 | public abstract class ForkJoinTask<V> im
1487		}
1488
1489		/**
1490	<	* Reconstitute the instance from a stream.
894	<	* @param s the stream
1490	>	* Reconstitutes this task from a stream (that is, deserializes it).
1491		*/
1492		private void readObject(java.io.ObjectInputStream s)
1493		throws java.io.IOException, ClassNotFoundException {
1494		s.defaultReadObject();
899	–	//        status &= ~INTERNAL_SIGNAL_MASK; //  todo: define policy
1495		Object ex = s.readObject();
1496		if (ex != null)
1497	<	setDoneExceptionally((Throwable)ex);
1497	>	setExceptionalCompletion((Throwable)ex);
1498		}
1499
1500	<	// Temporary Unsafe mechanics for preliminary release
1501	<
1502	<	static final Unsafe _unsafe;
908	<	static final long statusOffset;
909	<
1500	>	// Unsafe mechanics
1501	>	private static final sun.misc.Unsafe U;
1502	>	private static final long STATUS;
1503		static {
1504	+	exceptionTableLock = new ReentrantLock();
1505	+	exceptionTableRefQueue = new ReferenceQueue<Object>();
1506	+	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1507		try {
1508	<	if (ForkJoinTask.class.getClassLoader() != null) {
1509	<	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
1508	>	U = getUnsafe();
1509	>	STATUS = U.objectFieldOffset
1510		(ForkJoinTask.class.getDeclaredField("status"));
1511	<	} catch (Exception ex) { throw new Error(ex); }
1511	>	} catch (Exception e) {
1512	>	throw new Error(e);
1513	>	}
1514		}
1515
1516	+	/**
1517	+	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1518	+	* Replace with a simple call to Unsafe.getUnsafe when integrating
1519	+	* into a jdk.
1520	+	*
1521	+	* @return a sun.misc.Unsafe
1522	+	*/
1523	+	private static sun.misc.Unsafe getUnsafe() {
1524	+	try {
1525	+	return sun.misc.Unsafe.getUnsafe();
1526	+	} catch (SecurityException se) {
1527	+	try {
1528	+	return java.security.AccessController.doPrivileged
1529	+	(new java.security
1530	+	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1531	+	public sun.misc.Unsafe run() throws Exception {
1532	+	java.lang.reflect.Field f = sun.misc
1533	+	.Unsafe.class.getDeclaredField("theUnsafe");
1534	+	f.setAccessible(true);
1535	+	return (sun.misc.Unsafe) f.get(null);
1536	+	}});
1537	+	} catch (java.security.PrivilegedActionException e) {
1538	+	throw new RuntimeException("Could not initialize intrinsics",
1539	+	e.getCause());
1540	+	}
1541	+	}
1542	+	}
1543		}

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