[ViewVC] Diff of: jsr166/jsr166/src/jsr166y/ForkJoinTask.java

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.24 by jsr166, Mon Jul 27 21:41:53 2009 UTC vs.
Revision 1.92 by dl, Wed Oct 31 12:49:24 2012 UTC

#	Line 1 \| Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3		* Expert Group and released to the public domain, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		*/
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.io.Serializable;
10		import java.util.Collection;
13	–	import java.util.Collections;
11		import java.util.List;
12	<	import java.util.Map;
13	<	import java.util.WeakHashMap;
12	>	import java.util.RandomAccess;
13	>	import java.lang.ref.WeakReference;
14	>	import java.lang.ref.ReferenceQueue;
15	>	import java.util.concurrent.Callable;
16	>	import java.util.concurrent.CancellationException;
17	>	import java.util.concurrent.ExecutionException;
18	>	import java.util.concurrent.Future;
19	>	import java.util.concurrent.RejectedExecutionException;
20	>	import java.util.concurrent.RunnableFuture;
21	>	import java.util.concurrent.TimeUnit;
22	>	import java.util.concurrent.TimeoutException;
23	>	import java.util.concurrent.locks.ReentrantLock;
24	>	import java.lang.reflect.Constructor;
25
26		/**
27	<	* Abstract base class for tasks that run within a {@link
28	<	* ForkJoinPool}. A ForkJoinTask is a thread-like entity that is much
27	>	* Abstract base class for tasks that run within a {@link ForkJoinPool}.
28	>	* A {@code ForkJoinTask} is a thread-like entity that is much
29		* lighter weight than a normal thread. Huge numbers of tasks and
30		* subtasks may be hosted by a small number of actual threads in a
31		* ForkJoinPool, at the price of some usage limitations.
32		*
33	<	* <p> A "main" ForkJoinTask begins execution when submitted to a
34	<	* {@link ForkJoinPool}. Once started, it will usually in turn start
35	<	* other subtasks. As indicated by the name of this class, many
36	<	* programs using ForkJoinTasks employ only methods {@code fork} and
37	<	* {@code join}, or derivatives such as {@code invokeAll}. However,
38	<	* this class also provides a number of other methods that can come
39	<	* into play in advanced usages, as well as extension mechanics that
40	<	* allow support of new forms of fork/join processing.
33	>	* <p>A "main" {@code ForkJoinTask} begins execution when it is
34	>	* explicitly submitted to a {@link ForkJoinPool}, or, if not already
35	>	* engaged in a ForkJoin computation, commenced in the {@link
36	>	* ForkJoinPool#commonPool} via {@link #fork}, {@link #invoke}, or
37	>	* related methods. Once started, it will usually in turn start other
38	>	* subtasks. As indicated by the name of this class, many programs
39	>	* using {@code ForkJoinTask} employ only methods {@link #fork} and
40	>	* {@link #join}, or derivatives such as {@link
41	>	* #invokeAll(ForkJoinTask...) invokeAll}. However, this class also
42	>	* provides a number of other methods that can come into play in
43	>	* advanced usages, as well as extension mechanics that allow support
44	>	* of new forms of fork/join processing.
45	>	*
46	>	* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
47	>	* The efficiency of {@code ForkJoinTask}s stems from a set of
48	>	* restrictions (that are only partially statically enforceable)
49	>	* reflecting their main use as computational tasks calculating pure
50	>	* functions or operating on purely isolated objects. The primary
51	>	* coordination mechanisms are {@link #fork}, that arranges
52	>	* asynchronous execution, and {@link #join}, that doesn't proceed
53	>	* until the task's result has been computed. Computations should
54	>	* ideally avoid {@code synchronized} methods or blocks, and should
55	>	* minimize other blocking synchronization apart from joining other
56	>	* tasks or using synchronizers such as Phasers that are advertised to
57	>	* cooperate with fork/join scheduling. Subdividable tasks should also
58	>	* not perform blocking IO, and should ideally access variables that
59	>	* are completely independent of those accessed by other running
60	>	* tasks. These guidelines are loosely enforced by not permitting
61	>	* checked exceptions such as {@code IOExceptions} to be
62	>	* thrown. However, computations may still encounter unchecked
63	>	* exceptions, that are rethrown to callers attempting to join
64	>	* them. These exceptions may additionally include {@link
65	>	* RejectedExecutionException} stemming from internal resource
66	>	* exhaustion, such as failure to allocate internal task
67	>	* queues. Rethrown exceptions behave in the same way as regular
68	>	* exceptions, but, when possible, contain stack traces (as displayed
69	>	* for example using {@code ex.printStackTrace()}) of both the thread
70	>	* that initiated the computation as well as the thread actually
71	>	* encountering the exception; minimally only the latter.
72		*
73	<	* <p>A ForkJoinTask is a lightweight form of {@link Future}. The
74	<	* efficiency of ForkJoinTasks stems from a set of restrictions (that
75	<	* are only partially statically enforceable) reflecting their
76	<	* intended use as computational tasks calculating pure functions or
77	<	* operating on purely isolated objects. The primary coordination
78	<	* mechanisms are {@link #fork}, that arranges asynchronous execution,
79	<	* and {@link #join}, that doesn't proceed until the task's result has
80	<	* been computed. Computations should avoid {@code synchronized}
81	<	* methods or blocks, and should minimize other blocking
82	<	* synchronization apart from joining other tasks or using
83	<	* synchronizers such as Phasers that are advertised to cooperate with
84	<	* fork/join scheduling. Tasks should also not perform blocking IO,
85	<	* 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 IO or other external synchronization
52	<	* becomes exhausted. This usage restriction is in part enforced by
53	<	* not permitting checked exceptions such as {@code IOExceptions}
54	<	* to be thrown. However, computations may still encounter unchecked
55	<	* exceptions, that are rethrown to callers attempting join
56	<	* them. These exceptions may additionally include
57	<	* RejectedExecutionExceptions stemming from internal resource
58	<	* exhaustion such as failure to allocate internal task queues.
73	>	* <p>It is possible to define and use ForkJoinTasks that may block,
74	>	* but doing do requires three further considerations: (1) Completion
75	>	* of few if any <em>other</em> tasks should be dependent on a task
76	>	* that blocks on external synchronization or IO. Event-style async
77	>	* tasks that are never joined (for example, those subclassing {@link
78	>	* CountedCompleter}) often fall into this category. (2) To minimize
79	>	* resource impact, tasks should be small; ideally performing only the
80	>	* (possibly) blocking action. (3) Unless the {@link
81	>	* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
82	>	* blocked tasks is known to be less than the pool's {@link
83	>	* ForkJoinPool#getParallelism} level, the pool cannot guarantee that
84	>	* enough threads will be available to ensure progress or good
85	>	* performance.
86		*
87		* <p>The primary method for awaiting completion and extracting
88		* results of a task is {@link #join}, but there are several variants:
89		* The {@link Future#get} methods support interruptible and/or timed
90		* waits for completion and report results using {@code Future}
91	<	* conventions. Method {@link #helpJoin} enables callers to actively
92	<	* execute other tasks while awaiting joins, which is sometimes more
93	<	* efficient but only applies when all subtasks are known to be
94	<	* strictly tree-structured. Method {@link #invoke} is semantically
68	<	* equivalent to {@code fork(); join()} but always attempts to
69	<	* begin execution in the current thread. The "<em>quiet</em>" forms
70	<	* of these methods do not extract results or report exceptions. These
91	>	* conventions. Method {@link #invoke} is semantically
92	>	* equivalent to {@code fork(); join()} but always attempts to begin
93	>	* execution in the current thread. The "<em>quiet</em>" forms of
94	>	* these methods do not extract results or report exceptions. These
95		* may be useful when a set of tasks are being executed, and you need
96		* to delay processing of results or exceptions until all complete.
97		* Method {@code invokeAll} (available in multiple versions)
98		* performs the most common form of parallel invocation: forking a set
99		* of tasks and joining them all.
100		*
101	<	* <p> The ForkJoinTask class is not usually directly subclassed.
101	>	* <p>In the most typical usages, a fork-join pair act like a call
102	>	* (fork) and return (join) from a parallel recursive function. As is
103	>	* the case with other forms of recursive calls, returns (joins)
104	>	* should be performed innermost-first. For example, {@code a.fork();
105	>	* b.fork(); b.join(); a.join();} is likely to be substantially more
106	>	* efficient than joining {@code a} before {@code b}.
107	>	*
108	>	* <p>The execution status of tasks may be queried at several levels
109	>	* of detail: {@link #isDone} is true if a task completed in any way
110	>	* (including the case where a task was cancelled without executing);
111	>	* {@link #isCompletedNormally} is true if a task completed without
112	>	* cancellation or encountering an exception; {@link #isCancelled} is
113	>	* true if the task was cancelled (in which case {@link #getException}
114	>	* returns a {@link java.util.concurrent.CancellationException}); and
115	>	* {@link #isCompletedAbnormally} is true if a task was either
116	>	* cancelled or encountered an exception, in which case {@link
117	>	* #getException} will return either the encountered exception or
118	>	* {@link java.util.concurrent.CancellationException}.
119	>	*
120	>	* <p>The ForkJoinTask class is not usually directly subclassed.
121		* Instead, you subclass one of the abstract classes that support a
122	<	* particular style of fork/join processing. Normally, a concrete
123	<	* ForkJoinTask subclass declares fields comprising its parameters,
124	<	* established in a constructor, and then defines a {@code compute}
125	<	* method that somehow uses the control methods supplied by this base
126	<	* class. While these methods have {@code public} access (to allow
127	<	* instances of different task subclasses to call each others
128	<	* methods), some of them may only be called from within other
129	<	* ForkJoinTasks (as may be determined using method {@link
130	<	* #inForkJoinPool}). Attempts to invoke them in other contexts
131	<	* result in exceptions or errors, possibly including
132	<	* ClassCastException.
122	>	* particular style of fork/join processing, typically {@link
123	>	* RecursiveAction} for most computations that do not return results,
124	>	* {@link RecursiveTask} for those that do, and {@link
125	>	* CountedCompleter} for those in which completed actions trigger
126	>	* other actions. Normally, a concrete ForkJoinTask subclass declares
127	>	* fields comprising its parameters, established in a constructor, and
128	>	* then defines a {@code compute} method that somehow uses the control
129	>	* methods supplied by this base class.
130	>	*
131	>	* <p>Method {@link #join} and its variants are appropriate for use
132	>	* only when completion dependencies are acyclic; that is, the
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 short}
141	>	* value using {@link #setForkJoinTaskTag} or {@link
142	>	* #compareAndSetForkJoinTaskTag} and checked using {@link
143	>	* #getForkJoinTaskTag}. The ForkJoinTask implementation does not use
144	>	* these {@code protected} methods or tags for any purpose, but they
145	>	* may be of use in the construction of specialized subclasses. For
146	>	* example, parallel graph traversals can use the supplied methods to
147	>	* avoid revisiting nodes/tasks that have already been processed.
148	>	* (Method names for tagging are bulky in part to encourage definition
149	>	* of methods that reflect their usage patterns.)
150		*
151	<	* <p>Most base support methods are {@code final} because their
152	<	* implementations are intrinsically tied to the underlying
153	<	* lightweight task scheduling framework, and so cannot be overridden.
154	<	* Developers creating new basic styles of fork/join processing should
155	<	* minimally implement {@code protected} methods
156	<	* {@link #exec}, {@link #setRawResult}, and
157	<	* {@link #getRawResult}, while also introducing an abstract
158	<	* computational method that can be implemented in its subclasses,
159	<	* possibly relying on other {@code protected} methods provided
100	<	* by this class.
151	>	* <p>Most base support methods are {@code final}, to prevent
152	>	* overriding of implementations that are intrinsically tied to the
153	>	* underlying lightweight task scheduling framework. Developers
154	>	* creating new basic styles of fork/join processing should minimally
155	>	* implement {@code protected} methods {@link #exec}, {@link
156	>	* #setRawResult}, and {@link #getRawResult}, while also introducing
157	>	* an abstract computational method that can be implemented in its
158	>	* subclasses, possibly relying on other {@code protected} methods
159	>	* provided by this class.
160		*
161		* <p>ForkJoinTasks should perform relatively small amounts of
162	<	* computations, otherwise splitting into smaller tasks. As a very
163	<	* rough rule of thumb, a task should perform more than 100 and less
164	<	* than 10000 basic computational steps. If tasks are too big, then
165	<	* parallelism cannot improve throughput. If too small, then memory
166	<	* and internal task maintenance overhead may overwhelm processing.
162	>	* computation. Large tasks should be split into smaller subtasks,
163	>	* usually via recursive decomposition. As a very rough rule of thumb,
164	>	* a task should perform more than 100 and less than 10000 basic
165	>	* computational steps, and should avoid indefinite looping. If tasks
166	>	* are too big, then parallelism cannot improve throughput. If too
167	>	* small, then memory and internal task maintenance overhead may
168	>	* overwhelm processing.
169		*
170	<	* <p>ForkJoinTasks are {@code Serializable}, which enables them
171	<	* to be used in extensions such as remote execution frameworks. It is
172	<	* in general sensible to serialize tasks only before or after, but
173	<	* not during execution. Serialization is not relied on during
174	<	* execution itself.
170	>	* <p>This class provides {@code adapt} methods for {@link Runnable}
171	>	* and {@link Callable}, that may be of use when mixing execution of
172	>	* {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
173	>	* of this form, consider using a pool constructed in <em>asyncMode</em>.
174	>	*
175	>	* <p>ForkJoinTasks are {@code Serializable}, which enables them to be
176	>	* used in extensions such as remote execution frameworks. It is
177	>	* sensible to serialize tasks only before or after, but not during,
178	>	* execution. Serialization is not relied on during execution itself.
179		*
180		* @since 1.7
181		* @author Doug Lea
182		*/
183		public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
184
185	<	/**
186	<	* Run control status bits packed into a single int to minimize
187	<	* footprint and to ensure atomicity (via CAS). Status is
188	<	* initially zero, and takes on nonnegative values until
189	<	* completed, upon which status holds COMPLETED. CANCELLED, or
190	<	* EXCEPTIONAL, which use the top 3 bits. Tasks undergoing
191	<	* blocking waits by other threads have SIGNAL_MASK bits set --
192	<	* bit 15 for external (nonFJ) waits, and the rest a count of
193	<	* waiting FJ threads. (This representation relies on
194	<	* ForkJoinPool max thread limits). Completion of a stolen task
195	<	* with SIGNAL_MASK bits set awakens waiter via notifyAll. Even
196	<	* though suboptimal for some purposes, we use basic builtin
197	<	* wait/notify to take advantage of "monitor inflation" in JVMs
198	<	* that we would otherwise need to emulate to avoid adding further
199	<	* per-task bookkeeping overhead. Note that bits 16-28 are
200	<	* currently unused. Also value 0x80000000 is available as spare
201	<	* completion value.
202	<	*/
203	<	volatile int status; // accessed directly by pool and workers
204	<
205	<	static final int COMPLETION_MASK = 0xe0000000;
206	<	static final int NORMAL = 0xe0000000; // == mask
207	<	static final int CANCELLED = 0xc0000000;
208	<	static final int EXCEPTIONAL = 0xa0000000;
209	<	static final int SIGNAL_MASK = 0x0000ffff;
210	<	static final int INTERNAL_SIGNAL_MASK = 0x00007fff;
211	<	static final int EXTERNAL_SIGNAL = 0x00008000; // top bit of low word
212	<
213	<	/**
214	<	* Table of exceptions thrown by tasks, to enable reporting by
215	<	* callers. Because exceptions are rare, we don't directly keep
216	<	* them with task objects, but instead use a weak ref table. Note
217	<	* that cancellation exceptions don't appear in the table, but are
218	<	* instead recorded as status values.
154	<	* TODO: Use ConcurrentReferenceHashMap
185	>	/*
186	>	* See the internal documentation of class ForkJoinPool for a
187	>	* general implementation overview. ForkJoinTasks are mainly
188	>	* responsible for maintaining their "status" field amidst relays
189	>	* to methods in ForkJoinWorkerThread and ForkJoinPool.
190	>	*
191	>	* The methods of this class are more-or-less layered into
192	>	* (1) basic status maintenance
193	>	* (2) execution and awaiting completion
194	>	* (3) user-level methods that additionally report results.
195	>	* This is sometimes hard to see because this file orders exported
196	>	* methods in a way that flows well in javadocs.
197	>	*/
198	>
199	>	/*
200	>	* The status field holds run control status bits packed into a
201	>	* single int to minimize footprint and to ensure atomicity (via
202	>	* CAS). Status is initially zero, and takes on nonnegative
203	>	* values until completed, upon which status (anded with
204	>	* DONE_MASK) holds value NORMAL, CANCELLED, or EXCEPTIONAL. Tasks
205	>	* undergoing blocking waits by other threads have the SIGNAL bit
206	>	* set. Completion of a stolen task with SIGNAL set awakens any
207	>	* waiters via notifyAll. Even though suboptimal for some
208	>	* purposes, we use basic builtin wait/notify to take advantage of
209	>	* "monitor inflation" in JVMs that we would otherwise need to
210	>	* emulate to avoid adding further per-task bookkeeping overhead.
211	>	* We want these monitors to be "fat", i.e., not use biasing or
212	>	* thin-lock techniques, so use some odd coding idioms that tend
213	>	* to avoid them, mainly by arranging that every synchronized
214	>	* block performs a wait, notifyAll or both.
215	>	*
216	>	* These control bits occupy only (some of) the upper half (16
217	>	* bits) of status field. The lower bits are used for user-defined
218	>	* tags.
219		*/
156	–	static final Map<ForkJoinTask<?>, Throwable> exceptionMap =
157	–	Collections.synchronizedMap
158	–	(new WeakHashMap<ForkJoinTask<?>, Throwable>());
220
221	<	// within-package utilities
221	>	/** The run status of this task */
222	>	volatile int status; // accessed directly by pool and workers
223	>	static final int DONE_MASK = 0xf0000000; // mask out non-completion bits
224	>	static final int NORMAL = 0xf0000000; // must be negative
225	>	static final int CANCELLED = 0xc0000000; // must be < NORMAL
226	>	static final int EXCEPTIONAL = 0x80000000; // must be < CANCELLED
227	>	static final int SIGNAL = 0x00010000; // must be >= 1 << 16
228	>	static final int SMASK = 0x0000ffff; // short bits for tags
229
230		/**
231	<	* Gets current worker thread, or null if not a worker thread.
231	>	* Marks completion and wakes up threads waiting to join this
232	>	* task.
233	>	*
234	>	* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
235	>	* @return completion status on exit
236		*/
237	<	static ForkJoinWorkerThread getWorker() {
238	<	Thread t = Thread.currentThread();
239	<	return ((t instanceof ForkJoinWorkerThread) ?
240	<	(ForkJoinWorkerThread) t : null);
237	>	private int setCompletion(int completion) {
238	>	for (int s;;) {
239	>	if ((s = status) < 0)
240	>	return s;
241	>	if (U.compareAndSwapInt(this, STATUS, s, s \| completion)) {
242	>	if ((s >>> 16) != 0)
243	>	synchronized (this) { notifyAll(); }
244	>	return completion;
245	>	}
246	>	}
247		}
248
249	<	final boolean casStatus(int cmp, int val) {
250	<	return UNSAFE.compareAndSwapInt(this, statusOffset, cmp, val);
249	>	/**
250	>	* Primary execution method for stolen tasks. Unless done, calls
251	>	* exec and records status if completed, but doesn't wait for
252	>	* completion otherwise.
253	>	*
254	>	* @return status on exit from this method
255	>	*/
256	>	final int doExec() {
257	>	int s; boolean completed;
258	>	if ((s = status) >= 0) {
259	>	try {
260	>	completed = exec();
261	>	} catch (Throwable rex) {
262	>	return setExceptionalCompletion(rex);
263	>	}
264	>	if (completed)
265	>	s = setCompletion(NORMAL);
266	>	}
267	>	return s;
268		}
269
270		/**
271	<	* Workaround for not being able to rethrow unchecked exceptions.
271	>	* Tries to set SIGNAL status unless already completed. Used by
272	>	* ForkJoinPool. Other variants are directly incorporated into
273	>	* externalAwaitDone etc.
274	>	*
275	>	* @return true if successful
276		*/
277	<	static void rethrowException(Throwable ex) {
278	<	if (ex != null)
279	<	UNSAFE.throwException(ex);
277	>	final boolean trySetSignal() {
278	>	int s = status;
279	>	return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s \| SIGNAL);
280		}
281
183	–	// Setting completion status
184	–
282		/**
283	<	* Marks completion and wakes up threads waiting to join this task.
284	<	*
188	<	* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
283	>	* Blocks a non-worker-thread until completion.
284	>	* @return status upon completion
285		*/
286	<	final void setCompletion(int completion) {
287	<	ForkJoinPool pool = getPool();
288	<	if (pool != null) {
289	<	int s; // Clear signal bits while setting completion status
290	<	do {} while ((s = status) >= 0 && !casStatus(s, completion));
291	<
292	<	if ((s & SIGNAL_MASK) != 0) {
293	<	if ((s &= INTERNAL_SIGNAL_MASK) != 0)
294	<	pool.updateRunningCount(s);
295	<	synchronized (this) { notifyAll(); }
286	>	private int externalAwaitDone() {
287	>	int s;
288	>	boolean interrupted = false;
289	>	if ((s = status) >= 0 && ForkJoinPool.tryUnsubmitFromCommonPool(this))
290	>	s = doExec();
291	>	while (s >= 0) {
292	>	if (U.compareAndSwapInt(this, STATUS, s, s \| SIGNAL)) {
293	>	synchronized (this) {
294	>	if (status >= 0) {
295	>	try {
296	>	wait();
297	>	} catch (InterruptedException ie) {
298	>	interrupted = true;
299	>	}
300	>	}
301	>	else
302	>	notifyAll();
303	>	}
304		}
305	+	s = status;
306		}
307	<	else
308	<	externallySetCompletion(completion);
307	>	if (interrupted)
308	>	Thread.currentThread().interrupt();
309	>	return s;
310		}
311
312		/**
313	<	* Version of setCompletion for non-FJ threads. Leaves signal
208	<	* bits for unblocked threads to adjust, and always notifies.
313	>	* Blocks a non-worker-thread until completion or interruption.
314		*/
315	<	private void externallySetCompletion(int completion) {
315	>	private int externalInterruptibleAwaitDone() throws InterruptedException {
316	>	if (Thread.interrupted())
317	>	throw new InterruptedException();
318		int s;
319	<	do {} while ((s = status) >= 0 &&
320	<	!casStatus(s, (s & SIGNAL_MASK) \| completion));
321	<	synchronized (this) { notifyAll(); }
319	>	if ((s = status) >= 0 && ForkJoinPool.tryUnsubmitFromCommonPool(this))
320	>	s = doExec();
321	>	while (s >= 0) {
322	>	if (U.compareAndSwapInt(this, STATUS, s, s \| SIGNAL)) {
323	>	synchronized (this) {
324	>	if (status >= 0)
325	>	wait();
326	>	else
327	>	notifyAll();
328	>	}
329	>	}
330	>	s = status;
331	>	}
332	>	return s;
333		}
334
335		/**
336	<	* Sets status to indicate normal completion.
336	>	* Implementation for join, get, quietlyJoin. Directly handles
337	>	* only cases of already-completed, external wait, and
338	>	* unfork+exec. Others are relayed to ForkJoinPool.awaitJoin.
339	>	*
340	>	* @return status upon completion
341		*/
342	<	final void setNormalCompletion() {
343	<	// Try typical fast case -- single CAS, no signal, not already done.
344	<	// Manually expand casStatus to improve chances of inlining it
345	<	if (!UNSAFE.compareAndSwapInt(this, statusOffset, 0, NORMAL))
346	<	setCompletion(NORMAL);
342	>	private int doJoin() {
343	>	int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
344	>	return (s = status) < 0 ? s :
345	>	((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
346	>	(w = (wt = (ForkJoinWorkerThread)t).workQueue).
347	>	tryUnpush(this) && (s = doExec()) < 0 ? s :
348	>	wt.pool.awaitJoin(w, this) :
349	>	externalAwaitDone();
350		}
351
227	–	// internal waiting and notification
228	–
352		/**
353	<	* Performs the actual monitor wait for awaitDone.
353	>	* Implementation for invoke, quietlyInvoke.
354	>	*
355	>	* @return status upon completion
356		*/
357	<	private void doAwaitDone() {
358	<	// Minimize lock bias and in/de-flation effects by maximizing
359	<	// chances of waiting inside sync
360	<	try {
361	<	while (status >= 0)
362	<	synchronized (this) { if (status >= 0) wait(); }
238	<	} catch (InterruptedException ie) {
239	<	onInterruptedWait();
240	<	}
357	>	private int doInvoke() {
358	>	int s; Thread t; ForkJoinWorkerThread wt;
359	>	return (s = doExec()) < 0 ? s :
360	>	((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
361	>	(wt = (ForkJoinWorkerThread)t).pool.awaitJoin(wt.workQueue, this) :
362	>	externalAwaitDone();
363		}
364
365	+	// Exception table support
366	+
367		/**
368	<	* Performs the actual timed monitor wait for awaitDone.
368	>	* Table of exceptions thrown by tasks, to enable reporting by
369	>	* callers. Because exceptions are rare, we don't directly keep
370	>	* them with task objects, but instead use a weak ref table. Note
371	>	* that cancellation exceptions don't appear in the table, but are
372	>	* instead recorded as status values.
373	>	*
374	>	* Note: These statics are initialized below in static block.
375		*/
376	<	private void doAwaitDone(long startTime, long nanos) {
377	<	synchronized (this) {
378	<	try {
249	<	while (status >= 0) {
250	<	long nt = nanos - System.nanoTime() - startTime;
251	<	if (nt <= 0)
252	<	break;
253	<	wait(nt / 1000000, (int) (nt % 1000000));
254	<	}
255	<	} catch (InterruptedException ie) {
256	<	onInterruptedWait();
257	<	}
258	<	}
259	<	}
376	>	private static final ExceptionNode[] exceptionTable;
377	>	private static final ReentrantLock exceptionTableLock;
378	>	private static final ReferenceQueue<Object> exceptionTableRefQueue;
379
380	<	// Awaiting completion
380	>	/**
381	>	* Fixed capacity for exceptionTable.
382	>	*/
383	>	private static final int EXCEPTION_MAP_CAPACITY = 32;
384
385		/**
386	<	* Sets status to indicate there is joiner, then waits for join,
387	<	* surrounded with pool notifications.
388	<	*
389	<	* @return status upon exit
386	>	* Key-value nodes for exception table. The chained hash table
387	>	* uses identity comparisons, full locking, and weak references
388	>	* for keys. The table has a fixed capacity because it only
389	>	* maintains task exceptions long enough for joiners to access
390	>	* them, so should never become very large for sustained
391	>	* periods. However, since we do not know when the last joiner
392	>	* completes, we must use weak references and expunge them. We do
393	>	* so on each operation (hence full locking). Also, some thread in
394	>	* any ForkJoinPool will call helpExpungeStaleExceptions when its
395	>	* pool becomes isQuiescent.
396		*/
397	<	private int awaitDone(ForkJoinWorkerThread w,
398	<	boolean maintainParallelism) {
399	<	ForkJoinPool pool = (w == null) ? null : w.pool;
400	<	int s;
401	<	while ((s = status) >= 0) {
402	<	if (casStatus(s, (pool == null) ? s\|EXTERNAL_SIGNAL : s+1)) {
403	<	if (pool == null \|\| !pool.preJoin(this, maintainParallelism))
404	<	doAwaitDone();
405	<	if (((s = status) & INTERNAL_SIGNAL_MASK) != 0)
278	<	adjustPoolCountsOnUnblock(pool);
279	<	break;
280	<	}
397	>	static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> {
398	>	final Throwable ex;
399	>	ExceptionNode next;
400	>	final long thrower; // use id not ref to avoid weak cycles
401	>	ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next) {
402	>	super(task, exceptionTableRefQueue);
403	>	this.ex = ex;
404	>	this.next = next;
405	>	this.thrower = Thread.currentThread().getId();
406		}
282	–	return s;
407		}
408
409		/**
410	<	* Timed version of awaitDone
410	>	* Records exception and sets status.
411		*
412	<	* @return status upon exit
412	>	* @return status on exit
413		*/
414	<	private int awaitDone(ForkJoinWorkerThread w, long nanos) {
291	<	ForkJoinPool pool = (w == null) ? null : w.pool;
414	>	final int recordExceptionalCompletion(Throwable ex) {
415		int s;
416	<	while ((s = status) >= 0) {
417	<	if (casStatus(s, (pool == null) ? s\|EXTERNAL_SIGNAL : s+1)) {
418	<	long startTime = System.nanoTime();
419	<	if (pool == null \|\| !pool.preJoin(this, false))
420	<	doAwaitDone(startTime, nanos);
421	<	if ((s = status) >= 0) {
422	<	adjustPoolCountsOnCancelledWait(pool);
423	<	s = status;
416	>	if ((s = status) >= 0) {
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	>	if (e.get() == this) // already present
430	>	break;
431		}
432	<	if (s < 0 && (s & INTERNAL_SIGNAL_MASK) != 0)
433	<	adjustPoolCountsOnUnblock(pool);
304	<	break;
432	>	} finally {
433	>	lock.unlock();
434		}
435	+	s = setCompletion(EXCEPTIONAL);
436		}
437		return s;
438		}
439
440		/**
441	<	* Notifies pool that thread is unblocked. Called by signalled
442	<	* threads when woken by non-FJ threads (which is atypical).
441	>	* Records exception and possibly propagates
442	>	*
443	>	* @return status on exit
444		*/
445	<	private void adjustPoolCountsOnUnblock(ForkJoinPool pool) {
446	<	int s;
447	<	do {} while ((s = status) < 0 && !casStatus(s, s & COMPLETION_MASK));
448	<	if (pool != null && (s &= INTERNAL_SIGNAL_MASK) != 0)
449	<	pool.updateRunningCount(s);
445	>	private int setExceptionalCompletion(Throwable ex) {
446	>	int s = recordExceptionalCompletion(ex);
447	>	if ((s & DONE_MASK) == EXCEPTIONAL)
448	>	internalPropagateException(ex);
449	>	return s;
450		}
451
452		/**
453	<	* Notifies pool to adjust counts on cancelled or timed out wait.
453	>	* Hook for exception propagation support for tasks with completers.
454		*/
455	<	private void adjustPoolCountsOnCancelledWait(ForkJoinPool pool) {
325	<	if (pool != null) {
326	<	int s;
327	<	while ((s = status) >= 0 && (s & INTERNAL_SIGNAL_MASK) != 0) {
328	<	if (casStatus(s, s - 1)) {
329	<	pool.updateRunningCount(1);
330	<	break;
331	<	}
332	<	}
333	<	}
455	>	void internalPropagateException(Throwable ex) {
456		}
457
458		/**
459	<	* Handles interruptions during waits.
459	>	* Cancels, ignoring any exceptions thrown by cancel. Used during
460	>	* worker and pool shutdown. Cancel is spec'ed not to throw any
461	>	* exceptions, but if it does anyway, we have no recourse during
462	>	* shutdown, so guard against this case.
463		*/
464	<	private void onInterruptedWait() {
465	<	ForkJoinWorkerThread w = getWorker();
466	<	if (w == null)
467	<	Thread.currentThread().interrupt(); // re-interrupt
468	<	else if (w.isTerminating())
469	<	cancelIgnoringExceptions();
345	<	// else if FJworker, ignore interrupt
346	<	}
347	<
348	<	// Recording and reporting exceptions
349	<
350	<	private void setDoneExceptionally(Throwable rex) {
351	<	exceptionMap.put(this, rex);
352	<	setCompletion(EXCEPTIONAL);
353	<	}
354	<
355	<	/**
356	<	* Throws the exception associated with status s.
357	<	*
358	<	* @throws the exception
359	<	*/
360	<	private void reportException(int s) {
361	<	if ((s &= COMPLETION_MASK) < NORMAL) {
362	<	if (s == CANCELLED)
363	<	throw new CancellationException();
364	<	else
365	<	rethrowException(exceptionMap.get(this));
464	>	static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
465	>	if (t != null && t.status >= 0) {
466	>	try {
467	>	t.cancel(false);
468	>	} catch (Throwable ignore) {
469	>	}
470		}
471		}
472
473		/**
474	<	* Returns result or throws exception using j.u.c.Future conventions.
371	<	* Only call when {@code isDone} known to be true.
474	>	* Removes exception node and clears status
475		*/
476	<	private V reportFutureResult()
477	<	throws ExecutionException, InterruptedException {
478	<	int s = status & COMPLETION_MASK;
479	<	if (s < NORMAL) {
480	<	Throwable ex;
481	<	if (s == CANCELLED)
482	<	throw new CancellationException();
483	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
484	<	throw new ExecutionException(ex);
485	<	if (Thread.interrupted())
486	<	throw new InterruptedException();
476	>	private void clearExceptionalCompletion() {
477	>	int h = System.identityHashCode(this);
478	>	final ReentrantLock lock = exceptionTableLock;
479	>	lock.lock();
480	>	try {
481	>	ExceptionNode[] t = exceptionTable;
482	>	int i = h & (t.length - 1);
483	>	ExceptionNode e = t[i];
484	>	ExceptionNode pred = null;
485	>	while (e != null) {
486	>	ExceptionNode next = e.next;
487	>	if (e.get() == this) {
488	>	if (pred == null)
489	>	t[i] = next;
490	>	else
491	>	pred.next = next;
492	>	break;
493	>	}
494	>	pred = e;
495	>	e = next;
496	>	}
497	>	expungeStaleExceptions();
498	>	status = 0;
499	>	} finally {
500	>	lock.unlock();
501		}
385	–	return getRawResult();
502		}
503
504		/**
505	<	* Returns result or throws exception using j.u.c.Future conventions
506	<	* with timeouts.
505	>	* Returns a rethrowable exception for the given task, if
506	>	* available. To provide accurate stack traces, if the exception
507	>	* was not thrown by the current thread, we try to create a new
508	>	* exception of the same type as the one thrown, but with the
509	>	* recorded exception as its cause. If there is no such
510	>	* constructor, we instead try to use a no-arg constructor,
511	>	* followed by initCause, to the same effect. If none of these
512	>	* apply, or any fail due to other exceptions, we return the
513	>	* recorded exception, which is still correct, although it may
514	>	* contain a misleading stack trace.
515	>	*
516	>	* @return the exception, or null if none
517		*/
518	<	private V reportTimedFutureResult()
519	<	throws InterruptedException, ExecutionException, TimeoutException {
518	>	private Throwable getThrowableException() {
519	>	if ((status & DONE_MASK) != EXCEPTIONAL)
520	>	return null;
521	>	int h = System.identityHashCode(this);
522	>	ExceptionNode e;
523	>	final ReentrantLock lock = exceptionTableLock;
524	>	lock.lock();
525	>	try {
526	>	expungeStaleExceptions();
527	>	ExceptionNode[] t = exceptionTable;
528	>	e = t[h & (t.length - 1)];
529	>	while (e != null && e.get() != this)
530	>	e = e.next;
531	>	} finally {
532	>	lock.unlock();
533	>	}
534		Throwable ex;
535	<	int s = status & COMPLETION_MASK;
536	<	if (s == NORMAL)
537	<	return getRawResult();
538	<	if (s == CANCELLED)
539	<	throw new CancellationException();
540	<	if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null)
541	<	throw new ExecutionException(ex);
542	<	if (Thread.interrupted())
543	<	throw new InterruptedException();
544	<	throw new TimeoutException();
535	>	if (e == null \|\| (ex = e.ex) == null)
536	>	return null;
537	>	if (false && e.thrower != Thread.currentThread().getId()) {
538	>	Class<? extends Throwable> ec = ex.getClass();
539	>	try {
540	>	Constructor<?> noArgCtor = null;
541	>	Constructor<?>[] cs = ec.getConstructors();// public ctors only
542	>	for (int i = 0; i < cs.length; ++i) {
543	>	Constructor<?> c = cs[i];
544	>	Class<?>[] ps = c.getParameterTypes();
545	>	if (ps.length == 0)
546	>	noArgCtor = c;
547	>	else if (ps.length == 1 && ps[0] == Throwable.class)
548	>	return (Throwable)(c.newInstance(ex));
549	>	}
550	>	if (noArgCtor != null) {
551	>	Throwable wx = (Throwable)(noArgCtor.newInstance());
552	>	wx.initCause(ex);
553	>	return wx;
554	>	}
555	>	} catch (Exception ignore) {
556	>	}
557	>	}
558	>	return ex;
559		}
560
407	–	// internal execution methods
408	–
561		/**
562	<	* Calls exec, recording completion, and rethrowing exception if
411	<	* encountered. Caller should normally check status before calling.
412	<	*
413	<	* @return true if completed normally
562	>	* Poll stale refs and remove them. Call only while holding lock.
563		*/
564	<	private boolean tryExec() {
565	<	try { // try block must contain only call to exec
566	<	if (!exec())
567	<	return false;
568	<	} catch (Throwable rex) {
569	<	setDoneExceptionally(rex);
570	<	rethrowException(rex);
571	<	return false; // not reached
564	>	private static void expungeStaleExceptions() {
565	>	for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
566	>	if (x instanceof ExceptionNode) {
567	>	ForkJoinTask<?> key = ((ExceptionNode)x).get();
568	>	ExceptionNode[] t = exceptionTable;
569	>	int i = System.identityHashCode(key) & (t.length - 1);
570	>	ExceptionNode e = t[i];
571	>	ExceptionNode pred = null;
572	>	while (e != null) {
573	>	ExceptionNode next = e.next;
574	>	if (e == x) {
575	>	if (pred == null)
576	>	t[i] = next;
577	>	else
578	>	pred.next = next;
579	>	break;
580	>	}
581	>	pred = e;
582	>	e = next;
583	>	}
584	>	}
585		}
424	–	setNormalCompletion();
425	–	return true;
586		}
587
588		/**
589	<	* Main execution method used by worker threads. Invokes
590	<	* base computation unless already complete.
589	>	* If lock is available, poll stale refs and remove them.
590	>	* Called from ForkJoinPool when pools become quiescent.
591		*/
592	<	final void quietlyExec() {
593	<	if (status >= 0) {
592	>	static final void helpExpungeStaleExceptions() {
593	>	final ReentrantLock lock = exceptionTableLock;
594	>	if (lock.tryLock()) {
595		try {
596	<	if (!exec())
597	<	return;
598	<	} catch (Throwable rex) {
438	<	setDoneExceptionally(rex);
439	<	return;
596	>	expungeStaleExceptions();
597	>	} finally {
598	>	lock.unlock();
599		}
441	–	setNormalCompletion();
600		}
601		}
602
603		/**
604	<	* Calls exec(), recording but not rethrowing exception.
447	<	* Caller should normally check status before calling.
448	<	*
449	<	* @return true if completed normally
604	>	* A version of "sneaky throw" to relay exceptions
605		*/
606	<	private boolean tryQuietlyInvoke() {
607	<	try {
608	<	if (!exec())
609	<	return false;
610	<	} catch (Throwable rex) {
611	<	setDoneExceptionally(rex);
612	<	return false;
606	>	static void rethrow(final Throwable ex) {
607	>	if (ex != null) {
608	>	if (ex instanceof Error)
609	>	throw (Error)ex;
610	>	if (ex instanceof RuntimeException)
611	>	throw (RuntimeException)ex;
612	>	throw uncheckedThrowable(ex, RuntimeException.class);
613		}
459	–	setNormalCompletion();
460	–	return true;
614		}
615
616		/**
617	<	* Cancels, ignoring any exceptions it throws.
617	>	* The sneaky part of sneaky throw, relying on generics
618	>	* limitations to evade compiler complaints about rethrowing
619	>	* unchecked exceptions
620		*/
621	<	final void cancelIgnoringExceptions() {
622	<	try {
623	<	cancel(false);
469	<	} catch (Throwable ignore) {
470	<	}
621	>	@SuppressWarnings("unchecked") static <T extends Throwable>
622	>	T uncheckedThrowable(final Throwable t, final Class<T> c) {
623	>	return (T)t; // rely on vacuous cast
624		}
625
626		/**
627	<	* Main implementation of helpJoin
627	>	* Throws exception, if any, associated with the given status.
628		*/
629	<	private int busyJoin(ForkJoinWorkerThread w) {
630	<	int s;
631	<	ForkJoinTask<?> t;
632	<	while ((s = status) >= 0 && (t = w.scanWhileJoining(this)) != null)
633	<	t.quietlyExec();
481	<	return (s >= 0) ? awaitDone(w, false) : s; // block if no work
629	>	private void reportException(int s) {
630	>	if (s == CANCELLED)
631	>	throw new CancellationException();
632	>	if (s == EXCEPTIONAL)
633	>	rethrow(getThrowableException());
634		}
635
636		// public methods
637
638		/**
639	<	* Arranges to asynchronously execute this task. While it is not
640	<	* necessarily enforced, it is a usage error to fork a task more
641	<	* than once unless it has completed and been reinitialized. This
642	<	* method may be invoked only from within ForkJoinTask
643	<	* computations (as may be determined using method {@link
644	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
645	<	* in exceptions or errors, possibly including ClassCastException.
639	>	* Arranges to asynchronously execute this task in the pool the
640	>	* current task is running in, if applicable, or using the {@link
641	>	* ForkJoinPool#commonPool} if not {@link #inForkJoinPool}. While
642	>	* it is not necessarily enforced, it is a usage error to fork a
643	>	* task more than once unless it has completed and been
644	>	* reinitialized. Subsequent modifications to the state of this
645	>	* task or any data it operates on are not necessarily
646	>	* consistently observable by any thread other than the one
647	>	* executing it unless preceded by a call to {@link #join} or
648	>	* related methods, or a call to {@link #isDone} returning {@code
649	>	* true}.
650		*
651	<	* @return {@code this}, to simplify usage.
651	>	* @return {@code this}, to simplify usage
652		*/
653		public final ForkJoinTask<V> fork() {
654	<	((ForkJoinWorkerThread) Thread.currentThread())
655	<	.pushTask(this);
654	>	Thread t;
655	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
656	>	((ForkJoinWorkerThread)t).workQueue.push(this);
657	>	else
658	>	ForkJoinPool.submitToCommonPool(this);
659		return this;
660		}
661
662		/**
663	<	* Returns the result of the computation when it is ready.
664	<	* This method differs from {@code get} in that abnormal
665	<	* completion results in RuntimeExceptions or Errors, not
666	<	* ExecutionExceptions.
663	>	* Returns the result of the computation when it {@link #isDone is
664	>	* done}. This method differs from {@link #get()} in that
665	>	* abnormal completion results in {@code RuntimeException} or
666	>	* {@code Error}, not {@code ExecutionException}, and that
667	>	* interrupts of the calling thread do <em>not</em> cause the
668	>	* method to abruptly return by throwing {@code
669	>	* InterruptedException}.
670		*
671		* @return the computed result
672		*/
673		public final V join() {
674	<	ForkJoinWorkerThread w = getWorker();
675	<	if (w == null \|\| status < 0 \|\| !w.unpushTask(this) \|\| !tryExec())
676	<	reportException(awaitDone(w, true));
674	>	int s;
675	>	if ((s = doJoin() & DONE_MASK) != NORMAL)
676	>	reportException(s);
677		return getRawResult();
678		}
679
680		/**
681		* Commences performing this task, awaits its completion if
682	<	* necessary, and return its result.
682	>	* necessary, and returns its result, or throws an (unchecked)
683	>	* {@code RuntimeException} or {@code Error} if the underlying
684	>	* computation did so.
685		*
522	–	* @throws Throwable (a RuntimeException, Error, or unchecked
523	–	* exception) if the underlying computation did so
686		* @return the computed result
687		*/
688		public final V invoke() {
689	<	if (status >= 0 && tryExec())
690	<	return getRawResult();
691	<	else
692	<	return join();
689	>	int s;
690	>	if ((s = doInvoke() & DONE_MASK) != NORMAL)
691	>	reportException(s);
692	>	return getRawResult();
693		}
694
695		/**
696	<	* Forks both tasks, returning when {@code isDone} holds for
697	<	* both of them or an exception is encountered. This method may be
698	<	* invoked only from within ForkJoinTask computations (as may be
699	<	* determined using method {@link #inForkJoinPool}). Attempts to
700	<	* invoke in other contexts result in exceptions or errors,
701	<	* possibly including ClassCastException.
702	<	*
703	<	* @param t1 one task
704	<	* @param t2 the other task
705	<	* @throws NullPointerException if t1 or t2 are null
706	<	* @throws RuntimeException or Error if either task did so
696	>	* Forks the given tasks, returning when {@code isDone} holds for
697	>	* each task or an (unchecked) exception is encountered, in which
698	>	* case the exception is rethrown. If more than one task
699	>	* encounters an exception, then this method throws any one of
700	>	* these exceptions. If any task encounters an exception, the
701	>	* other may be cancelled. However, the execution status of
702	>	* individual tasks is not guaranteed upon exceptional return. The
703	>	* status of each task may be obtained using {@link
704	>	* #getException()} and related methods to check if they have been
705	>	* cancelled, completed normally or exceptionally, or left
706	>	* unprocessed.
707	>	*
708	>	* @param t1 the first task
709	>	* @param t2 the second task
710	>	* @throws NullPointerException if any task is null
711		*/
712	<	public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) {
712	>	public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
713	>	int s1, s2;
714		t2.fork();
715	<	t1.invoke();
716	<	t2.join();
715	>	if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL)
716	>	t1.reportException(s1);
717	>	if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
718	>	t2.reportException(s2);
719		}
720
721		/**
722	<	* Forks the given tasks, returning when {@code isDone} holds
723	<	* for all of them. If any task encounters an exception, others
724	<	* may be cancelled. This method may be invoked only from within
725	<	* ForkJoinTask computations (as may be determined using method
726	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
727	<	* result in exceptions or errors, possibly including
728	<	* ClassCastException.
722	>	* Forks the given tasks, returning when {@code isDone} holds for
723	>	* each task or an (unchecked) exception is encountered, in which
724	>	* case the exception is rethrown. If more than one task
725	>	* encounters an exception, then this method throws any one of
726	>	* these exceptions. If any task encounters an exception, others
727	>	* may be cancelled. However, the execution status of individual
728	>	* tasks is not guaranteed upon exceptional return. The status of
729	>	* each task may be obtained using {@link #getException()} and
730	>	* related methods to check if they have been cancelled, completed
731	>	* normally or exceptionally, or left unprocessed.
732		*
733	<	* @param tasks the array of tasks
734	<	* @throws NullPointerException if tasks or any element are null
563	<	* @throws RuntimeException or Error if any task did so
733	>	* @param tasks the tasks
734	>	* @throws NullPointerException if any task is null
735		*/
736		public static void invokeAll(ForkJoinTask<?>... tasks) {
737		Throwable ex = null;
#	Line 573 \| Line 744 \| public abstract class ForkJoinTask<V> im
744		}
745		else if (i != 0)
746		t.fork();
747	<	else {
748	<	t.quietlyInvoke();
578	<	if (ex == null)
579	<	ex = t.getException();
580	<	}
747	>	else if (t.doInvoke() < NORMAL && ex == null)
748	>	ex = t.getException();
749		}
750		for (int i = 1; i <= last; ++i) {
751		ForkJoinTask<?> t = tasks[i];
752		if (t != null) {
753		if (ex != null)
754		t.cancel(false);
755	<	else {
756	<	t.quietlyJoin();
589	<	if (ex == null)
590	<	ex = t.getException();
591	<	}
755	>	else if (t.doJoin() < NORMAL)
756	>	ex = t.getException();
757		}
758		}
759		if (ex != null)
760	<	rethrowException(ex);
760	>	rethrow(ex);
761		}
762
763		/**
764	<	* Forks all tasks in the collection, returning when
765	<	* {@code isDone} holds for all of them. If any task
766	<	* encounters an exception, others may be cancelled. This method
767	<	* may be invoked only from within ForkJoinTask computations (as
768	<	* may be determined using method {@link
769	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
770	<	* in exceptions or errors, possibly including ClassCastException.
764	>	* Forks all tasks in the specified collection, returning when
765	>	* {@code isDone} holds for each task or an (unchecked) exception
766	>	* is encountered, in which case the exception is rethrown. If
767	>	* more than one task encounters an exception, then this method
768	>	* throws any one of these exceptions. If any task encounters an
769	>	* exception, others may be cancelled. However, the execution
770	>	* status of individual tasks is not guaranteed upon exceptional
771	>	* return. The status of each task may be obtained using {@link
772	>	* #getException()} and related methods to check if they have been
773	>	* cancelled, completed normally or exceptionally, or left
774	>	* unprocessed.
775		*
776		* @param tasks the collection of tasks
777		* @return the tasks argument, to simplify usage
778		* @throws NullPointerException if tasks or any element are null
610	–	* @throws RuntimeException or Error if any task did so
779		*/
780		public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
781	<	if (!(tasks instanceof List<?>)) {
781	>	if (!(tasks instanceof RandomAccess) \|\| !(tasks instanceof List<?>)) {
782		invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
783		return tasks;
784		}
#	Line 627 \| Line 795 \| public abstract class ForkJoinTask<V> im
795		}
796		else if (i != 0)
797		t.fork();
798	<	else {
799	<	t.quietlyInvoke();
632	<	if (ex == null)
633	<	ex = t.getException();
634	<	}
798	>	else if (t.doInvoke() < NORMAL && ex == null)
799	>	ex = t.getException();
800		}
801		for (int i = 1; i <= last; ++i) {
802		ForkJoinTask<?> t = ts.get(i);
803		if (t != null) {
804		if (ex != null)
805		t.cancel(false);
806	<	else {
807	<	t.quietlyJoin();
643	<	if (ex == null)
644	<	ex = t.getException();
645	<	}
806	>	else if (t.doJoin() < NORMAL)
807	>	ex = t.getException();
808		}
809		}
810		if (ex != null)
811	<	rethrowException(ex);
811	>	rethrow(ex);
812		return tasks;
813		}
814
815		/**
816	<	* Returns {@code true} if the computation performed by this task
817	<	* has completed (or has been cancelled).
818	<	*
819	<	* @return {@code true} if this computation has completed
820	<	*/
821	<	public final boolean isDone() {
822	<	return status < 0;
823	<	}
824	<
825	<	/**
664	<	* Returns {@code true} if this task was cancelled.
665	<	*
666	<	* @return {@code true} if this task was cancelled
667	<	*/
668	<	public final boolean isCancelled() {
669	<	return (status & COMPLETION_MASK) == CANCELLED;
670	<	}
671	<
672	<	/**
673	<	* Asserts that the results of this task's computation will not be
674	<	* used. If a cancellation occurs before attempting to execute this
675	<	* task, execution will be suppressed, {@link #isCancelled}
676	<	* will report true, and {@link #join} will result in a
677	<	* {@code CancellationException} being thrown. Otherwise, when
678	<	* cancellation races with completion, there are no guarantees
679	<	* about whether {@code isCancelled} will report {@code true},
680	<	* whether {@code join} will return normally or via an exception,
681	<	* or whether these behaviors will remain consistent upon repeated
682	<	* invocation.
816	>	* Attempts to cancel execution of this task. This attempt will
817	>	* fail if the task has already completed or could not be
818	>	* cancelled for some other reason. If successful, and this task
819	>	* has not started when {@code cancel} is called, execution of
820	>	* this task is suppressed. After this method returns
821	>	* successfully, unless there is an intervening call to {@link
822	>	* #reinitialize}, subsequent calls to {@link #isCancelled},
823	>	* {@link #isDone}, and {@code cancel} will return {@code true}
824	>	* and calls to {@link #join} and related methods will result in
825	>	* {@code CancellationException}.
826		*
827		* <p>This method may be overridden in subclasses, but if so, must
828	<	* still ensure that these minimal properties hold. In particular,
829	<	* the cancel method itself must not throw exceptions.
828	>	* still ensure that these properties hold. In particular, the
829	>	* {@code cancel} method itself must not throw exceptions.
830		*
831	<	* <p> This method is designed to be invoked by <em>other</em>
831	>	* <p>This method is designed to be invoked by <em>other</em>
832		* tasks. To terminate the current task, you can just return or
833		* throw an unchecked exception from its computation method, or
834		* invoke {@link #completeExceptionally}.
835		*
836	<	* @param mayInterruptIfRunning this value is ignored in the
837	<	* default implementation because tasks are not in general
838	<	* cancelled via interruption
836	>	* @param mayInterruptIfRunning this value has no effect in the
837	>	* default implementation because interrupts are not used to
838	>	* control cancellation.
839		*
840		* @return {@code true} if this task is now cancelled
841		*/
842		public boolean cancel(boolean mayInterruptIfRunning) {
843	<	setCompletion(CANCELLED);
844	<	return (status & COMPLETION_MASK) == CANCELLED;
843	>	return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
844	>	}
845	>
846	>	public final boolean isDone() {
847	>	return status < 0;
848	>	}
849	>
850	>	public final boolean isCancelled() {
851	>	return (status & DONE_MASK) == CANCELLED;
852		}
853
854		/**
#	Line 707 \| Line 857 \| public abstract class ForkJoinTask<V> im
857		* @return {@code true} if this task threw an exception or was cancelled
858		*/
859		public final boolean isCompletedAbnormally() {
860	<	return (status & COMPLETION_MASK) < NORMAL;
860	>	return status < NORMAL;
861	>	}
862	>
863	>	/**
864	>	* Returns {@code true} if this task completed without throwing an
865	>	* exception and was not cancelled.
866	>	*
867	>	* @return {@code true} if this task completed without throwing an
868	>	* exception and was not cancelled
869	>	*/
870	>	public final boolean isCompletedNormally() {
871	>	return (status & DONE_MASK) == NORMAL;
872		}
873
874		/**
875		* Returns the exception thrown by the base computation, or a
876	<	* CancellationException if cancelled, or null if none or if the
877	<	* method has not yet completed.
876	>	* {@code CancellationException} if cancelled, or {@code null} if
877	>	* none or if the method has not yet completed.
878		*
879		* @return the exception, or {@code null} if none
880		*/
881		public final Throwable getException() {
882	<	int s = status & COMPLETION_MASK;
883	<	if (s >= NORMAL)
884	<	return null;
885	<	if (s == CANCELLED)
725	<	return new CancellationException();
726	<	return exceptionMap.get(this);
882	>	int s = status & DONE_MASK;
883	>	return ((s >= NORMAL) ? null :
884	>	(s == CANCELLED) ? new CancellationException() :
885	>	getThrowableException());
886		}
887
888		/**
#	Line 732 \| Line 891 \| public abstract class ForkJoinTask<V> im
891		* {@code join} and related operations. This method may be used
892		* to induce exceptions in asynchronous tasks, or to force
893		* completion of tasks that would not otherwise complete. Its use
894	<	* in other situations is likely to be wrong. This method is
894	>	* in other situations is discouraged. This method is
895		* overridable, but overridden versions must invoke {@code super}
896		* implementation to maintain guarantees.
897		*
898	<	* @param ex the exception to throw. If this exception is
899	<	* not a RuntimeException or Error, the actual exception thrown
900	<	* will be a RuntimeException with cause ex.
898	>	* @param ex the exception to throw. If this exception is not a
899	>	* {@code RuntimeException} or {@code Error}, the actual exception
900	>	* thrown will be a {@code RuntimeException} with cause {@code ex}.
901		*/
902		public void completeExceptionally(Throwable ex) {
903	<	setDoneExceptionally((ex instanceof RuntimeException) \|\|
904	<	(ex instanceof Error) ? ex :
905	<	new RuntimeException(ex));
903	>	setExceptionalCompletion((ex instanceof RuntimeException) \|\|
904	>	(ex instanceof Error) ? ex :
905	>	new RuntimeException(ex));
906		}
907
908		/**
909		* Completes this task, and if not already aborted or cancelled,
910	<	* returning a {@code null} result upon {@code join} and related
911	<	* operations. This method may be used to provide results for
912	<	* asynchronous tasks, or to provide alternative handling for
913	<	* tasks that would not otherwise complete normally. Its use in
914	<	* other situations is likely to be wrong. This method is
915	<	* overridable, but overridden versions must invoke {@code super}
916	<	* implementation to maintain guarantees.
910	>	* returning the given value as the result of subsequent
911	>	* invocations of {@code join} and related operations. This method
912	>	* may be used to provide results for asynchronous tasks, or to
913	>	* provide alternative handling for tasks that would not otherwise
914	>	* complete normally. Its use in other situations is
915	>	* discouraged. This method is overridable, but overridden
916	>	* versions must invoke {@code super} implementation to maintain
917	>	* guarantees.
918		*
919		* @param value the result value for this task
920		*/
#	Line 762 \| Line 922 \| public abstract class ForkJoinTask<V> im
922		try {
923		setRawResult(value);
924		} catch (Throwable rex) {
925	<	setDoneExceptionally(rex);
925	>	setExceptionalCompletion(rex);
926		return;
927		}
928	<	setNormalCompletion();
769	<	}
770	<
771	<	public final V get() throws InterruptedException, ExecutionException {
772	<	ForkJoinWorkerThread w = getWorker();
773	<	if (w == null \|\| status < 0 \|\| !w.unpushTask(this) \|\| !tryQuietlyInvoke())
774	<	awaitDone(w, true);
775	<	return reportFutureResult();
928	>	setCompletion(NORMAL);
929		}
930
931	<	public final V get(long timeout, TimeUnit unit)
932	<	throws InterruptedException, ExecutionException, TimeoutException {
933	<	ForkJoinWorkerThread w = getWorker();
934	<	if (w == null \|\| status < 0 \|\| !w.unpushTask(this) \|\| !tryQuietlyInvoke())
935	<	awaitDone(w, unit.toNanos(timeout));
936	<	return reportTimedFutureResult();
931	>	/**
932	>	* Completes this task normally without setting a value. The most
933	>	* recent value established by {@link #setRawResult} (or {@code
934	>	* null} by default) will be returned as the result of subsequent
935	>	* invocations of {@code join} and related operations.
936	>	*
937	>	* @since 1.8
938	>	*/
939	>	public final void quietlyComplete() {
940	>	setCompletion(NORMAL);
941		}
942
943		/**
944	<	* Possibly executes other tasks until this task is ready, then
945	<	* returns the result of the computation. This method may be more
789	<	* efficient than {@code join}, but is only applicable when
790	<	* there are no potential dependencies between continuation of the
791	<	* current task and that of any other task that might be executed
792	<	* while helping. (This usually holds for pure divide-and-conquer
793	<	* tasks). This method may be invoked only from within
794	<	* ForkJoinTask computations (as may be determined using method
795	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
796	<	* result in exceptions or errors, possibly including
797	<	* ClassCastException.
944	>	* Waits if necessary for the computation to complete, and then
945	>	* retrieves its result.
946		*
947		* @return the computed result
948	+	* @throws CancellationException if the computation was cancelled
949	+	* @throws ExecutionException if the computation threw an
950	+	* exception
951	+	* @throws InterruptedException if the current thread is not a
952	+	* member of a ForkJoinPool and was interrupted while waiting
953		*/
954	<	public final V helpJoin() {
955	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) Thread.currentThread();
956	<	if (status < 0 \|\| !w.unpushTask(this) \|\| !tryExec())
957	<	reportException(busyJoin(w));
954	>	public final V get() throws InterruptedException, ExecutionException {
955	>	int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
956	>	doJoin() : externalInterruptibleAwaitDone();
957	>	Throwable ex;
958	>	if ((s &= DONE_MASK) == CANCELLED)
959	>	throw new CancellationException();
960	>	if (s == EXCEPTIONAL && (ex = getThrowableException()) != null)
961	>	throw new ExecutionException(ex);
962		return getRawResult();
963		}
964
965		/**
966	<	* Possibly executes other tasks until this task is ready. This
967	<	* method may be invoked only from within ForkJoinTask
968	<	* computations (as may be determined using method {@link
969	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
970	<	* in exceptions or errors, possibly including ClassCastException.
966	>	* Waits if necessary for at most the given time for the computation
967	>	* to complete, and then retrieves its result, if available.
968	>	*
969	>	* @param timeout the maximum time to wait
970	>	* @param unit the time unit of the timeout argument
971	>	* @return the computed result
972	>	* @throws CancellationException if the computation was cancelled
973	>	* @throws ExecutionException if the computation threw an
974	>	* exception
975	>	* @throws InterruptedException if the current thread is not a
976	>	* member of a ForkJoinPool and was interrupted while waiting
977	>	* @throws TimeoutException if the wait timed out
978		*/
979	<	public final void quietlyHelpJoin() {
980	<	if (status >= 0) {
981	<	ForkJoinWorkerThread w =
982	<	(ForkJoinWorkerThread) Thread.currentThread();
983	<	if (!w.unpushTask(this) \|\| !tryQuietlyInvoke())
984	<	busyJoin(w);
979	>	public final V get(long timeout, TimeUnit unit)
980	>	throws InterruptedException, ExecutionException, TimeoutException {
981	>	if (Thread.interrupted())
982	>	throw new InterruptedException();
983	>	// Messy in part because we measure in nanosecs, but wait in millisecs
984	>	int s; long ns, ms;
985	>	if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) {
986	>	long deadline = System.nanoTime() + ns;
987	>	ForkJoinPool p = null;
988	>	ForkJoinPool.WorkQueue w = null;
989	>	Thread t = Thread.currentThread();
990	>	if (t instanceof ForkJoinWorkerThread) {
991	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
992	>	p = wt.pool;
993	>	w = wt.workQueue;
994	>	s = p.helpJoinOnce(w, this); // no retries on failure
995	>	}
996	>	boolean canBlock = false;
997	>	boolean interrupted = false;
998	>	try {
999	>	while ((s = status) >= 0) {
1000	>	if (w != null && w.runState < 0)
1001	>	cancelIgnoringExceptions(this);
1002	>	else if (!canBlock) {
1003	>	if (p == null \|\| p.tryCompensate(this, null))
1004	>	canBlock = true;
1005	>	}
1006	>	else {
1007	>	if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
1008	>	U.compareAndSwapInt(this, STATUS, s, s \| SIGNAL)) {
1009	>	synchronized (this) {
1010	>	if (status >= 0) {
1011	>	try {
1012	>	wait(ms);
1013	>	} catch (InterruptedException ie) {
1014	>	if (p == null)
1015	>	interrupted = true;
1016	>	}
1017	>	}
1018	>	else
1019	>	notifyAll();
1020	>	}
1021	>	}
1022	>	if ((s = status) < 0 \|\| interrupted \|\|
1023	>	(ns = deadline - System.nanoTime()) <= 0L)
1024	>	break;
1025	>	}
1026	>	}
1027	>	} finally {
1028	>	if (p != null && canBlock)
1029	>	p.incrementActiveCount();
1030	>	}
1031	>	if (interrupted)
1032	>	throw new InterruptedException();
1033		}
1034	+	if ((s &= DONE_MASK) != NORMAL) {
1035	+	Throwable ex;
1036	+	if (s == CANCELLED)
1037	+	throw new CancellationException();
1038	+	if (s != EXCEPTIONAL)
1039	+	throw new TimeoutException();
1040	+	if ((ex = getThrowableException()) != null)
1041	+	throw new ExecutionException(ex);
1042	+	}
1043	+	return getRawResult();
1044		}
1045
1046		/**
1047	<	* Joins this task, without returning its result or throwing an
1047	>	* Joins this task, without returning its result or throwing its
1048		* exception. This method may be useful when processing
1049		* collections of tasks when some have been cancelled or otherwise
1050		* known to have aborted.
1051		*/
1052		public final void quietlyJoin() {
1053	<	if (status >= 0) {
832	<	ForkJoinWorkerThread w = getWorker();
833	<	if (w == null \|\| !w.unpushTask(this) \|\| !tryQuietlyInvoke())
834	<	awaitDone(w, true);
835	<	}
1053	>	doJoin();
1054		}
1055
1056		/**
1057		* Commences performing this task and awaits its completion if
1058	<	* necessary, without returning its result or throwing an
1059	<	* exception. This method may be useful when processing
842	<	* collections of tasks when some have been cancelled or otherwise
843	<	* known to have aborted.
1058	>	* necessary, without returning its result or throwing its
1059	>	* exception.
1060		*/
1061		public final void quietlyInvoke() {
1062	<	if (status >= 0 && !tryQuietlyInvoke())
847	<	quietlyJoin();
1062	>	doInvoke();
1063		}
1064
1065		/**
1066		* Possibly executes tasks until the pool hosting the current task
1067	<	* {@link ForkJoinPool#isQuiescent}. This method may be of use in
1068	<	* designs in which many tasks are forked, but none are explicitly
1069	<	* joined, instead executing them until all are processed.
1067	>	* {@link ForkJoinPool#isQuiescent is quiescent}. This method may
1068	>	* be of use in designs in which many tasks are forked, but none
1069	>	* are explicitly joined, instead executing them until all are
1070	>	* processed.
1071		*/
1072		public static void helpQuiesce() {
1073	<	((ForkJoinWorkerThread) Thread.currentThread())
1074	<	.helpQuiescePool();
1073	>	Thread t;
1074	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
1075	>	ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1076	>	wt.pool.helpQuiescePool(wt.workQueue);
1077	>	}
1078	>	else
1079	>	ForkJoinPool.externalHelpQuiescePool();
1080		}
1081
1082		/**
#	Line 864 \| Line 1085 \| public abstract class ForkJoinTask<V> im
1085		* this task, but only if reuse occurs when this task has either
1086		* never been forked, or has been forked, then completed and all
1087		* outstanding joins of this task have also completed. Effects
1088	<	* under any other usage conditions are not guaranteed, and are
1089	<	* almost surely wrong. This method may be useful when executing
1088	>	* under any other usage conditions are not guaranteed.
1089	>	* This method may be useful when executing
1090		* pre-constructed trees of subtasks in loops.
1091	+	*
1092	+	* <p>Upon completion of this method, {@code isDone()} reports
1093	+	* {@code false}, and {@code getException()} reports {@code
1094	+	* null}. However, the value returned by {@code getRawResult} is
1095	+	* unaffected. To clear this value, you can invoke {@code
1096	+	* setRawResult(null)}.
1097		*/
1098		public void reinitialize() {
1099	<	if ((status & COMPLETION_MASK) == EXCEPTIONAL)
1100	<	exceptionMap.remove(this);
1101	<	status = 0;
1099	>	if ((status & DONE_MASK) == EXCEPTIONAL)
1100	>	clearExceptionalCompletion();
1101	>	else
1102	>	status = 0;
1103		}
1104
1105		/**
1106		* Returns the pool hosting the current task execution, or null
1107		* if this task is executing outside of any ForkJoinPool.
1108		*
1109	+	* @see #inForkJoinPool
1110		* @return the pool, or {@code null} if none
1111		*/
1112		public static ForkJoinPool getPool() {
#	Line 887 \| Line 1116 \| public abstract class ForkJoinTask<V> im
1116		}
1117
1118		/**
1119	<	* Returns {@code true} if the current thread is executing as a
1120	<	* ForkJoinPool computation.
1119	>	* Returns {@code true} if the current thread is a {@link
1120	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1121		*
1122	<	* @return {@code true} if the current thread is executing as a
1123	<	* ForkJoinPool computation, or false otherwise
1122	>	* @return {@code true} if the current thread is a {@link
1123	>	* ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1124	>	* or {@code false} otherwise
1125		*/
1126		public static boolean inForkJoinPool() {
1127		return Thread.currentThread() instanceof ForkJoinWorkerThread;
#	Line 899 \| Line 1129 \| public abstract class ForkJoinTask<V> im
1129
1130		/**
1131		* Tries to unschedule this task for execution. This method will
1132	<	* typically succeed if this task is the most recently forked task
1133	<	* by the current thread, and has not commenced executing in
1134	<	* another thread. This method may be useful when arranging
1135	<	* alternative local processing of tasks that could have been, but
1136	<	* were not, stolen. This method may be invoked only from within
907	<	* ForkJoinTask computations (as may be determined using method
908	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
909	<	* result in exceptions or errors, possibly including
910	<	* ClassCastException.
1132	>	* typically (but is not guaranteed to) succeed if this task is
1133	>	* the most recently forked task by the current thread, and has
1134	>	* not commenced executing in another thread. This method may be
1135	>	* useful when arranging alternative local processing of tasks
1136	>	* that could have been, but were not, stolen.
1137		*
1138		* @return {@code true} if unforked
1139		*/
1140		public boolean tryUnfork() {
1141	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1142	<	.unpushTask(this);
1141	>	Thread t;
1142	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1143	>	((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
1144	>	ForkJoinPool.tryUnsubmitFromCommonPool(this);
1145		}
1146
1147		/**
#	Line 925 \| Line 1153 \| public abstract class ForkJoinTask<V> im
1153		* @return the number of tasks
1154		*/
1155		public static int getQueuedTaskCount() {
1156	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1157	<	.getQueueSize();
1156	>	Thread t;
1157	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1158	>	((ForkJoinWorkerThread)t).workQueue.queueSize() :
1159	>	ForkJoinPool.getEstimatedSubmitterQueueLength();
1160		}
1161
1162		/**
1163		* Returns an estimate of how many more locally queued tasks are
1164		* held by the current worker thread than there are other worker
1165	<	* threads that might steal them. This value may be useful for
1165	>	* threads that might steal them, or zero if this thread is not
1166	>	* operating in a ForkJoinPool. This value may be useful for
1167		* heuristic decisions about whether to fork other tasks. In many
1168		* usages of ForkJoinTasks, at steady state, each worker should
1169		* aim to maintain a small constant surplus (for example, 3) of
#	Line 942 \| Line 1173 \| public abstract class ForkJoinTask<V> im
1173		* @return the surplus number of tasks, which may be negative
1174		*/
1175		public static int getSurplusQueuedTaskCount() {
1176	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1177	<	.getEstimatedSurplusTaskCount();
1176	>	/*
1177	>	* The aim of this method is to return a cheap heuristic guide
1178	>	* for task partitioning when programmers, frameworks, tools,
1179	>	* or languages have little or no idea about task granularity.
1180	>	* In essence by offering this method, we ask users only about
1181	>	* tradeoffs in overhead vs expected throughput and its
1182	>	* variance, rather than how finely to partition tasks.
1183	>	*
1184	>	* In a steady state strict (tree-structured) computation,
1185	>	* each thread makes available for stealing enough tasks for
1186	>	* other threads to remain active. Inductively, if all threads
1187	>	* play by the same rules, each thread should make available
1188	>	* only a constant number of tasks.
1189	>	*
1190	>	* The minimum useful constant is just 1. But using a value of
1191	>	* 1 would require immediate replenishment upon each steal to
1192	>	* maintain enough tasks, which is infeasible. Further,
1193	>	* partitionings/granularities of offered tasks should
1194	>	* minimize steal rates, which in general means that threads
1195	>	* nearer the top of computation tree should generate more
1196	>	* than those nearer the bottom. In perfect steady state, each
1197	>	* thread is at approximately the same level of computation
1198	>	* tree. However, producing extra tasks amortizes the
1199	>	* uncertainty of progress and diffusion assumptions.
1200	>	*
1201	>	* So, users will want to use values larger, but not much
1202	>	* larger than 1 to both smooth over transient shortages and
1203	>	* hedge against uneven progress; as traded off against the
1204	>	* cost of extra task overhead. We leave the user to pick a
1205	>	* threshold value to compare with the results of this call to
1206	>	* guide decisions, but recommend values such as 3.
1207	>	*
1208	>	* When all threads are active, it is on average OK to
1209	>	* estimate surplus strictly locally. In steady-state, if one
1210	>	* thread is maintaining say 2 surplus tasks, then so are
1211	>	* others. So we can just use estimated queue length.
1212	>	* However, this strategy alone leads to serious mis-estimates
1213	>	* in some non-steady-state conditions (ramp-up, ramp-down,
1214	>	* other stalls). We can detect many of these by further
1215	>	* considering the number of "idle" threads, that are known to
1216	>	* have zero queued tasks, so compensate by a factor of
1217	>	* (#idle/#active) threads.
1218	>	*/
1219	>	Thread t; ForkJoinWorkerThread wt;
1220	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1221	>	(wt = (ForkJoinWorkerThread)t).workQueue.queueSize() - wt.pool.idlePerActive() :
1222	>	0;
1223		}
1224
1225		// Extension methods
#	Line 969 \| Line 1245 \| public abstract class ForkJoinTask<V> im
1245		protected abstract void setRawResult(V value);
1246
1247		/**
1248	<	* Immediately performs the base action of this task. This method
1249	<	* is designed to support extensions, and should not in general be
1250	<	* called otherwise. The return value controls whether this task
1251	<	* is considered to be done normally. It may return false in
1248	>	* Immediately performs the base action of this task and returns
1249	>	* true if, upon return from this method, this task is guaranteed
1250	>	* to have completed normally. This method may return false
1251	>	* otherwise, to indicate that this task is not necessarily
1252	>	* complete (or is not known to be complete), for example in
1253		* asynchronous actions that require explicit invocations of
1254	<	* {@link #complete} to become joinable. It may throw exceptions
1255	<	* to indicate abnormal exit.
1254	>	* completion methods. This method may also throw an (unchecked)
1255	>	* exception to indicate abnormal exit. This method is designed to
1256	>	* support extensions, and should not in general be called
1257	>	* otherwise.
1258		*
1259	<	* @return {@code true} if completed normally
981	<	* @throws Error or RuntimeException if encountered during computation
1259	>	* @return {@code true} if this task is known to have completed normally
1260		*/
1261		protected abstract boolean exec();
1262
1263		/**
1264	<	* Returns, but does not unschedule or execute, the task queued by
1265	<	* the current thread but not yet executed, if one is
1266	<	* available. There is no guarantee that this task will actually
1267	<	* be polled or executed next. This method is designed primarily
1268	<	* to support extensions, and is unlikely to be useful otherwise.
1269	<	* This method may be invoked only from within ForkJoinTask
1270	<	* computations (as may be determined using method {@link
1271	<	* #inForkJoinPool}). Attempts to invoke in other contexts result
1272	<	* in exceptions or errors, possibly including ClassCastException.
1264	>	* Returns, but does not unschedule or execute, a task queued by
1265	>	* the current thread but not yet executed, if one is immediately
1266	>	* available and the current thread is operating in a
1267	>	* ForkJoinPool. There is no guarantee that this task will
1268	>	* actually be polled or executed next. Conversely, this method
1269	>	* may return null even if a task exists but cannot be accessed
1270	>	* without contention with other threads. This method is designed
1271	>	* primarily to support extensions, and is unlikely to be useful
1272	>	* otherwise.
1273		*
1274		* @return the next task, or {@code null} if none are available
1275		*/
1276		protected static ForkJoinTask<?> peekNextLocalTask() {
1277	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1278	<	.peekTask();
1277	>	Thread t;
1278	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1279	>	((ForkJoinWorkerThread)t).workQueue.peek() :
1280	>	null;
1281		}
1282
1283		/**
1284		* Unschedules and returns, without executing, the next task
1285	<	* queued by the current thread but not yet executed. This method
1286	<	* is designed primarily to support extensions, and is unlikely to
1287	<	* be useful otherwise. This method may be invoked only from
1288	<	* within ForkJoinTask computations (as may be determined using
1009	<	* method {@link #inForkJoinPool}). Attempts to invoke in other
1010	<	* contexts result in exceptions or errors, possibly including
1011	<	* ClassCastException.
1285	>	* queued by the current thread but not yet executed, if the
1286	>	* current thread is operating in a ForkJoinPool. This method is
1287	>	* designed primarily to support extensions, and is unlikely to be
1288	>	* useful otherwise.
1289		*
1290		* @return the next task, or {@code null} if none are available
1291		*/
1292		protected static ForkJoinTask<?> pollNextLocalTask() {
1293	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1294	<	.pollLocalTask();
1293	>	Thread t;
1294	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1295	>	((ForkJoinWorkerThread)t).workQueue.nextLocalTask() :
1296	>	null;
1297		}
1298
1299		/**
1300	<	* Unschedules and returns, without executing, the next task
1300	>	* If the current thread is operating in a ForkJoinPool,
1301	>	* unschedules and returns, without executing, the next task
1302		* queued by the current thread but not yet executed, if one is
1303		* available, or if not available, a task that was forked by some
1304		* other thread, if available. Availability may be transient, so a
1305	<	* {@code null} result does not necessarily imply quiescence
1306	<	* of the pool this task is operating in. This method is designed
1305	>	* {@code null} result does not necessarily imply quiescence of
1306	>	* the pool this task is operating in. This method is designed
1307		* primarily to support extensions, and is unlikely to be useful
1308	<	* otherwise. This method may be invoked only from within
1029	<	* ForkJoinTask computations (as may be determined using method
1030	<	* {@link #inForkJoinPool}). Attempts to invoke in other contexts
1031	<	* result in exceptions or errors, possibly including
1032	<	* ClassCastException.
1308	>	* otherwise.
1309		*
1310		* @return a task, or {@code null} if none are available
1311		*/
1312		protected static ForkJoinTask<?> pollTask() {
1313	<	return ((ForkJoinWorkerThread) Thread.currentThread())
1314	<	.pollTask();
1313	>	Thread t; ForkJoinWorkerThread wt;
1314	>	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1315	>	(wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) :
1316	>	null;
1317		}
1318
1319	<	// adaptors
1319	>	// tag operations
1320	>
1321	>	/**
1322	>	* Returns the tag for this task.
1323	>	*
1324	>	* @return the tag for this task
1325	>	* @since 1.8
1326	>	*/
1327	>	public final short getForkJoinTaskTag() {
1328	>	return (short)status;
1329	>	}
1330
1331		/**
1332	<	* Returns a new ForkJoinTask that performs the {@code run}
1333	<	* method of the given Runnable as its action, and returns a null
1334	<	* result upon {@code join}.
1332	>	* Atomically sets the tag value for this task.
1333	>	*
1334	>	* @param tag the tag value
1335	>	* @return the previous value of the tag
1336	>	* @since 1.8
1337	>	*/
1338	>	public final short setForkJoinTaskTag(short tag) {
1339	>	for (int s;;) {
1340	>	if (U.compareAndSwapInt(this, STATUS, s = status,
1341	>	(s & ~SMASK) \| (tag & SMASK)))
1342	>	return (short)s;
1343	>	}
1344	>	}
1345	>
1346	>	/**
1347	>	* Atomically conditionally sets the tag value for this task.
1348	>	* Among other applications, tags can be used as visit markers
1349	>	* in tasks operating on graphs, as in methods that check: {@code
1350	>	* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1351	>	* before processing, otherwise exiting because the node has
1352	>	* already been visited.
1353	>	*
1354	>	* @param e the expected tag value
1355	>	* @param tag the new tag value
1356	>	* @return true if successful; i.e., the current value was
1357	>	* equal to e and is now tag.
1358	>	* @since 1.8
1359	>	*/
1360	>	public final boolean compareAndSetForkJoinTaskTag(short e, short tag) {
1361	>	for (int s;;) {
1362	>	if ((short)(s = status) != e)
1363	>	return false;
1364	>	if (U.compareAndSwapInt(this, STATUS, s,
1365	>	(s & ~SMASK) \| (tag & SMASK)))
1366	>	return true;
1367	>	}
1368	>	}
1369	>
1370	>	/**
1371	>	* Adaptor for Runnables. This implements RunnableFuture
1372	>	* to be compliant with AbstractExecutorService constraints
1373	>	* when used in ForkJoinPool.
1374	>	*/
1375	>	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1376	>	implements RunnableFuture<T> {
1377	>	final Runnable runnable;
1378	>	T result;
1379	>	AdaptedRunnable(Runnable runnable, T result) {
1380	>	if (runnable == null) throw new NullPointerException();
1381	>	this.runnable = runnable;
1382	>	this.result = result; // OK to set this even before completion
1383	>	}
1384	>	public final T getRawResult() { return result; }
1385	>	public final void setRawResult(T v) { result = v; }
1386	>	public final boolean exec() { runnable.run(); return true; }
1387	>	public final void run() { invoke(); }
1388	>	private static final long serialVersionUID = 5232453952276885070L;
1389	>	}
1390	>
1391	>	/**
1392	>	* Adaptor for Runnables without results
1393	>	*/
1394	>	static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1395	>	implements RunnableFuture<Void> {
1396	>	final Runnable runnable;
1397	>	AdaptedRunnableAction(Runnable runnable) {
1398	>	if (runnable == null) throw new NullPointerException();
1399	>	this.runnable = runnable;
1400	>	}
1401	>	public final Void getRawResult() { return null; }
1402	>	public final void setRawResult(Void v) { }
1403	>	public final boolean exec() { runnable.run(); return true; }
1404	>	public final void run() { invoke(); }
1405	>	private static final long serialVersionUID = 5232453952276885070L;
1406	>	}
1407	>
1408	>	/**
1409	>	* Adaptor for Callables
1410	>	*/
1411	>	static final class AdaptedCallable<T> extends ForkJoinTask<T>
1412	>	implements RunnableFuture<T> {
1413	>	final Callable<? extends T> callable;
1414	>	T result;
1415	>	AdaptedCallable(Callable<? extends T> callable) {
1416	>	if (callable == null) throw new NullPointerException();
1417	>	this.callable = callable;
1418	>	}
1419	>	public final T getRawResult() { return result; }
1420	>	public final void setRawResult(T v) { result = v; }
1421	>	public final boolean exec() {
1422	>	try {
1423	>	result = callable.call();
1424	>	return true;
1425	>	} catch (Error err) {
1426	>	throw err;
1427	>	} catch (RuntimeException rex) {
1428	>	throw rex;
1429	>	} catch (Exception ex) {
1430	>	throw new RuntimeException(ex);
1431	>	}
1432	>	}
1433	>	public final void run() { invoke(); }
1434	>	private static final long serialVersionUID = 2838392045355241008L;
1435	>	}
1436	>
1437	>	/**
1438	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1439	>	* method of the given {@code Runnable} as its action, and returns
1440	>	* a null result upon {@link #join}.
1441		*
1442		* @param runnable the runnable action
1443		* @return the task
1444		*/
1445	<	public static ForkJoinTask<Void> adapt(Runnable runnable) {
1446	<	return new ForkJoinPool.AdaptedRunnable<Void>(runnable, null);
1445	>	public static ForkJoinTask<?> adapt(Runnable runnable) {
1446	>	return new AdaptedRunnableAction(runnable);
1447		}
1448
1449		/**
1450	<	* Returns a new ForkJoinTask that performs the {@code run}
1451	<	* method of the given Runnable as its action, and returns the
1452	<	* given result upon {@code join}.
1450	>	* Returns a new {@code ForkJoinTask} that performs the {@code run}
1451	>	* method of the given {@code Runnable} as its action, and returns
1452	>	* the given result upon {@link #join}.
1453		*
1454		* @param runnable the runnable action
1455		* @param result the result upon completion
1456		* @return the task
1457		*/
1458		public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
1459	<	return new ForkJoinPool.AdaptedRunnable<T>(runnable, result);
1459	>	return new AdaptedRunnable<T>(runnable, result);
1460		}
1461
1462		/**
1463	<	* Returns a new ForkJoinTask that performs the {@code call}
1464	<	* method of the given Callable as its action, and returns its
1465	<	* result upon {@code join}, translating any checked
1466	<	* exceptions encountered into {@code RuntimeException}.
1463	>	* Returns a new {@code ForkJoinTask} that performs the {@code call}
1464	>	* method of the given {@code Callable} as its action, and returns
1465	>	* its result upon {@link #join}, translating any checked exceptions
1466	>	* encountered into {@code RuntimeException}.
1467		*
1468		* @param callable the callable action
1469		* @return the task
1470		*/
1471	<	public static <T> ForkJoinTask<T> adapt(Callable<T> callable) {
1472	<	return new ForkJoinPool.AdaptedCallable<T>(callable);
1471	>	public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1472	>	return new AdaptedCallable<T>(callable);
1473		}
1474
1475		// Serialization support
#	Line 1083 \| Line 1477 \| public abstract class ForkJoinTask<V> im
1477		private static final long serialVersionUID = -7721805057305804111L;
1478
1479		/**
1480	<	* Save the state to a stream.
1480	>	* Saves this task to a stream (that is, serializes it).
1481		*
1482		* @serialData the current run status and the exception thrown
1483		* during execution, or {@code null} if none
1090	–	* @param s the stream
1484		*/
1485		private void writeObject(java.io.ObjectOutputStream s)
1486		throws java.io.IOException {
#	Line 1096 \| Line 1489 \| public abstract class ForkJoinTask<V> im
1489		}
1490
1491		/**
1492	<	* Reconstitute the instance from a stream.
1100	<	*
1101	<	* @param s the stream
1492	>	* Reconstitutes this task from a stream (that is, deserializes it).
1493		*/
1494		private void readObject(java.io.ObjectInputStream s)
1495		throws java.io.IOException, ClassNotFoundException {
1496		s.defaultReadObject();
1106	–	status &= ~INTERNAL_SIGNAL_MASK; // clear internal signal counts
1107	–	status \|= EXTERNAL_SIGNAL; // conservatively set external signal
1497		Object ex = s.readObject();
1498		if (ex != null)
1499	<	setDoneExceptionally((Throwable) ex);
1499	>	setExceptionalCompletion((Throwable)ex);
1500		}
1501
1502		// Unsafe mechanics
1503	<
1504	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1505	<	private static final long statusOffset =
1506	<	objectFieldOffset("status", ForkJoinTask.class);
1507	<
1508	<	private static long objectFieldOffset(String field, Class<?> klazz) {
1503	>	private static final sun.misc.Unsafe U;
1504	>	private static final long STATUS;
1505	>	static {
1506	>	exceptionTableLock = new ReentrantLock();
1507	>	exceptionTableRefQueue = new ReferenceQueue<Object>();
1508	>	exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1509		try {
1510	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1511	<	} catch (NoSuchFieldException e) {
1512	<	// Convert Exception to corresponding Error
1513	<	NoSuchFieldError error = new NoSuchFieldError(field);
1514	<	error.initCause(e);
1126	<	throw error;
1510	>	U = getUnsafe();
1511	>	STATUS = U.objectFieldOffset
1512	>	(ForkJoinTask.class.getDeclaredField("status"));
1513	>	} catch (Exception e) {
1514	>	throw new Error(e);
1515		}
1516		}
1517

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Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents): Revision 1.24 by jsr166, Mon Jul 27 21:41:53 2009 UTC vs. Revision 1.92 by dl, Wed Oct 31 12:49:24 2012 UTC

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Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.24 by jsr166, Mon Jul 27 21:41:53 2009 UTC vs.
Revision 1.92 by dl, Wed Oct 31 12:49:24 2012 UTC