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root/jsr166/jsr166/src/jsr166y/ForkJoinPool.java

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.40 by jsr166, Mon Aug 3 00:53:15 2009 UTC vs.
Revision 1.74 by jsr166, Tue Sep 7 06:32:45 2010 UTC

#	Line 7 | Line 7
7		package jsr166y;
8
9		import java.util.concurrent.*;
10	–
10		import java.util.ArrayList;
11		import java.util.Arrays;
12		import java.util.Collection;
13		import java.util.Collections;
14		import java.util.List;
16	–	import java.util.concurrent.locks.Condition;
15		import java.util.concurrent.locks.LockSupport;
16		import java.util.concurrent.locks.ReentrantLock;
17		import java.util.concurrent.atomic.AtomicInteger;
18	<	import java.util.concurrent.atomic.AtomicLong;
18	>	import java.util.concurrent.CountDownLatch;
19
20		/**
21		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
22		* A {@code ForkJoinPool} provides the entry point for submissions
23	<	* from non-{@code ForkJoinTask}s, as well as management and
24	<	* monitoring operations.  Normally a single {@code ForkJoinPool} is
27	<	* used for a large number of submitted tasks. Otherwise, use would
28	<	* not usually outweigh the construction and bookkeeping overhead of
29	<	* creating a large set of threads.
23	>	* from non-{@code ForkJoinTask} clients, as well as management and
24	>	* monitoring operations.
25		*
26	<	* <p>{@code ForkJoinPool}s differ from other kinds of {@link
27	<	* Executor}s mainly in that they provide <em>work-stealing</em>: all
28	<	* threads in the pool attempt to find and execute subtasks created by
29	<	* other active tasks (eventually blocking if none exist). This makes
30	<	* them efficient when most tasks spawn other subtasks (as do most
31	<	* {@code ForkJoinTask}s), as well as the mixed execution of some
32	<	* plain {@code Runnable}- or {@code Callable}- based activities along
33	<	* with {@code ForkJoinTask}s. When setting {@linkplain #setAsyncMode
34	<	* async mode}, a {@code ForkJoinPool} may also be appropriate for use
40	<	* with fine-grained tasks that are never joined. Otherwise, other
41	<	* {@code ExecutorService} implementations are typically more
42	<	* appropriate choices.
26	>	* <p>A {@code ForkJoinPool} differs from other kinds of {@link
27	>	* ExecutorService} mainly by virtue of employing
28	>	* <em>work-stealing</em>: all threads in the pool attempt to find and
29	>	* execute subtasks created by other active tasks (eventually blocking
30	>	* waiting for work if none exist). This enables efficient processing
31	>	* when most tasks spawn other subtasks (as do most {@code
32	>	* ForkJoinTask}s). When setting <em>asyncMode</em> to true in
33	>	* constructors, {@code ForkJoinPool}s may also be appropriate for use
34	>	* with event-style tasks that are never joined.
35		*
36	<	* <p>A {@code ForkJoinPool} may be constructed with a given
37	<	* parallelism level (target pool size), which it attempts to maintain
38	<	* by dynamically adding, suspending, or resuming threads, even if
39	<	* some tasks are waiting to join others. However, no such adjustments
40	<	* are performed in the face of blocked IO or other unmanaged
41	<	* synchronization. The nested {@link ManagedBlocker} interface
42	<	* enables extension of the kinds of synchronization accommodated.
43	<	* The target parallelism level may also be changed dynamically
44	<	* ({@link #setParallelism}) and thread construction can be limited
53	<	* using methods {@link #setMaximumPoolSize} and/or {@link
54	<	* #setMaintainsParallelism}.
36	>	* <p>A {@code ForkJoinPool} is constructed with a given target
37	>	* parallelism level; by default, equal to the number of available
38	>	* processors. The pool attempts to maintain enough active (or
39	>	* available) threads by dynamically adding, suspending, or resuming
40	>	* internal worker threads, even if some tasks are stalled waiting to
41	>	* join others. However, no such adjustments are guaranteed in the
42	>	* face of blocked IO or other unmanaged synchronization. The nested
43	>	* {@link ManagedBlocker} interface enables extension of the kinds of
44	>	* synchronization accommodated.
45		*
46		* <p>In addition to execution and lifecycle control methods, this
47		* class provides status check methods (for example
#	Line 60 | Line 50 | import java.util.concurrent.atomic.Atomi
50		* {@link #toString} returns indications of pool state in a
51		* convenient form for informal monitoring.
52		*
53	+	* <p> As is the case with other ExecutorServices, there are three
54	+	* main task execution methods summarized in the following
55	+	* table. These are designed to be used by clients not already engaged
56	+	* in fork/join computations in the current pool.  The main forms of
57	+	* these methods accept instances of {@code ForkJoinTask}, but
58	+	* overloaded forms also allow mixed execution of plain {@code
59	+	* Runnable}- or {@code Callable}- based activities as well.  However,
60	+	* tasks that are already executing in a pool should normally
61	+	* <em>NOT</em> use these pool execution methods, but instead use the
62	+	* within-computation forms listed in the table.
63	+	*
64	+	* <table BORDER CELLPADDING=3 CELLSPACING=1>
65	+	*  <tr>
66	+	*    <td></td>
67	+	*    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
68	+	*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
69	+	*  </tr>
70	+	*  <tr>
71	+	*    <td> <b>Arrange async execution</td>
72	+	*    <td> {@link #execute(ForkJoinTask)}</td>
73	+	*    <td> {@link ForkJoinTask#fork}</td>
74	+	*  </tr>
75	+	*  <tr>
76	+	*    <td> <b>Await and obtain result</td>
77	+	*    <td> {@link #invoke(ForkJoinTask)}</td>
78	+	*    <td> {@link ForkJoinTask#invoke}</td>
79	+	*  </tr>
80	+	*  <tr>
81	+	*    <td> <b>Arrange exec and obtain Future</td>
82	+	*    <td> {@link #submit(ForkJoinTask)}</td>
83	+	*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
84	+	*  </tr>
85	+	* </table>
86	+	*
87	+	* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
88	+	* used for all parallel task execution in a program or subsystem.
89	+	* Otherwise, use would not usually outweigh the construction and
90	+	* bookkeeping overhead of creating a large set of threads. For
91	+	* example, a common pool could be used for the {@code SortTasks}
92	+	* illustrated in {@link RecursiveAction}. Because {@code
93	+	* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
94	+	* daemon} mode, there is typically no need to explicitly {@link
95	+	* #shutdown} such a pool upon program exit.
96	+	*
97	+	* <pre>
98	+	* static final ForkJoinPool mainPool = new ForkJoinPool();
99	+	* ...
100	+	* public void sort(long[] array) {
101	+	*   mainPool.invoke(new SortTask(array, 0, array.length));
102	+	* }
103	+	* </pre>
104	+	*
105		* <p><b>Implementation notes</b>: This implementation restricts the
106		* maximum number of running threads to 32767. Attempts to create
107	<	* pools with greater than the maximum result in
107	>	* pools with greater than the maximum number result in
108		* {@code IllegalArgumentException}.
109		*
110	+	* <p>This implementation rejects submitted tasks (that is, by throwing
111	+	* {@link RejectedExecutionException}) only when the pool is shut down
112	+	* or internal resources have been exhausted.
113	+	*
114		* @since 1.7
115		* @author Doug Lea
116		*/
117		public class ForkJoinPool extends AbstractExecutorService {
118
119		/*
120	<	* See the extended comments interspersed below for design,
121	<	* rationale, and walkthroughs.
120	>	* Implementation Overview
121	>	*
122	>	* This class provides the central bookkeeping and control for a
123	>	* set of worker threads: Submissions from non-FJ threads enter
124	>	* into a submission queue. Workers take these tasks and typically
125	>	* split them into subtasks that may be stolen by other workers.
126	>	* The main work-stealing mechanics implemented in class
127	>	* ForkJoinWorkerThread give first priority to processing tasks
128	>	* from their own queues (LIFO or FIFO, depending on mode), then
129	>	* to randomized FIFO steals of tasks in other worker queues, and
130	>	* lastly to new submissions. These mechanics do not consider
131	>	* affinities, loads, cache localities, etc, so rarely provide the
132	>	* best possible performance on a given machine, but portably
133	>	* provide good throughput by averaging over these factors.
134	>	* (Further, even if we did try to use such information, we do not
135	>	* usually have a basis for exploiting it. For example, some sets
136	>	* of tasks profit from cache affinities, but others are harmed by
137	>	* cache pollution effects.)
138	>	*
139	>	* Beyond work-stealing support and essential bookkeeping, the
140	>	* main responsibility of this framework is to take actions when
141	>	* one worker is waiting to join a task stolen (or always held by)
142	>	* another.  Because we are multiplexing many tasks on to a pool
143	>	* of workers, we can't just let them block (as in Thread.join).
144	>	* We also cannot just reassign the joiner's run-time stack with
145	>	* another and replace it later, which would be a form of
146	>	* "continuation", that even if possible is not necessarily a good
147	>	* idea. Given that the creation costs of most threads on most
148	>	* systems mainly surrounds setting up runtime stacks, thread
149	>	* creation and switching is usually not much more expensive than
150	>	* stack creation and switching, and is more flexible). Instead we
151	>	* combine two tactics:
152	>	*
153	>	*   Helping: Arranging for the joiner to execute some task that it
154	>	*      would be running if the steal had not occurred.  Method
155	>	*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
156	>	*      links to try to find such a task.
157	>	*
158	>	*   Compensating: Unless there are already enough live threads,
159	>	*      method helpMaintainParallelism() may create or
160	>	*      re-activate a spare thread to compensate for blocked
161	>	*      joiners until they unblock.
162	>	*
163	>	* It is impossible to keep exactly the target (parallelism)
164	>	* number of threads running at any given time.  Determining
165	>	* existence of conservatively safe helping targets, the
166	>	* availability of already-created spares, and the apparent need
167	>	* to create new spares are all racy and require heuristic
168	>	* guidance, so we rely on multiple retries of each.  Compensation
169	>	* occurs in slow-motion. It is triggered only upon timeouts of
170	>	* Object.wait used for joins. This reduces poor decisions that
171	>	* would otherwise be made when threads are waiting for others
172	>	* that are stalled because of unrelated activities such as
173	>	* garbage collection.
174	>	*
175	>	* The ManagedBlocker extension API can't use helping so relies
176	>	* only on compensation in method awaitBlocker.
177	>	*
178	>	* The main throughput advantages of work-stealing stem from
179	>	* decentralized control -- workers mostly steal tasks from each
180	>	* other. We do not want to negate this by creating bottlenecks
181	>	* implementing other management responsibilities. So we use a
182	>	* collection of techniques that avoid, reduce, or cope well with
183	>	* contention. These entail several instances of bit-packing into
184	>	* CASable fields to maintain only the minimally required
185	>	* atomicity. To enable such packing, we restrict maximum
186	>	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
187	>	* unbalanced increments and decrements) to fit into a 16 bit
188	>	* field, which is far in excess of normal operating range.  Even
189	>	* though updates to some of these bookkeeping fields do sometimes
190	>	* contend with each other, they don't normally cache-contend with
191	>	* updates to others enough to warrant memory padding or
192	>	* isolation. So they are all held as fields of ForkJoinPool
193	>	* objects.  The main capabilities are as follows:
194	>	*
195	>	* 1. Creating and removing workers. Workers are recorded in the
196	>	* "workers" array. This is an array as opposed to some other data
197	>	* structure to support index-based random steals by workers.
198	>	* Updates to the array recording new workers and unrecording
199	>	* terminated ones are protected from each other by a lock
200	>	* (workerLock) but the array is otherwise concurrently readable,
201	>	* and accessed directly by workers. To simplify index-based
202	>	* operations, the array size is always a power of two, and all
203	>	* readers must tolerate null slots. Currently, all worker thread
204	>	* creation is on-demand, triggered by task submissions,
205	>	* replacement of terminated workers, and/or compensation for
206	>	* blocked workers. However, all other support code is set up to
207	>	* work with other policies.
208	>	*
209	>	* To ensure that we do not hold on to worker references that
210	>	* would prevent GC, ALL accesses to workers are via indices into
211	>	* the workers array (which is one source of some of the unusual
212	>	* code constructions here). In essence, the workers array serves
213	>	* as a WeakReference mechanism. Thus for example the event queue
214	>	* stores worker indices, not worker references. Access to the
215	>	* workers in associated methods (for example releaseEventWaiters)
216	>	* must both index-check and null-check the IDs. All such accesses
217	>	* ignore bad IDs by returning out early from what they are doing,
218	>	* since this can only be associated with shutdown, in which case
219	>	* it is OK to give up. On termination, we just clobber these
220	>	* data structures without trying to use them.
221	>	*
222	>	* 2. Bookkeeping for dynamically adding and removing workers. We
223	>	* aim to approximately maintain the given level of parallelism.
224	>	* When some workers are known to be blocked (on joins or via
225	>	* ManagedBlocker), we may create or resume others to take their
226	>	* place until they unblock (see below). Implementing this
227	>	* requires counts of the number of "running" threads (i.e., those
228	>	* that are neither blocked nor artificially suspended) as well as
229	>	* the total number.  These two values are packed into one field,
230	>	* "workerCounts" because we need accurate snapshots when deciding
231	>	* to create, resume or suspend.  Note however that the
232	>	* correspondence of these counts to reality is not guaranteed. In
233	>	* particular updates for unblocked threads may lag until they
234	>	* actually wake up.
235	>	*
236	>	* 3. Maintaining global run state. The run state of the pool
237	>	* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
238	>	* those in other Executor implementations, as well as a count of
239	>	* "active" workers -- those that are, or soon will be, or
240	>	* recently were executing tasks. The runLevel and active count
241	>	* are packed together in order to correctly trigger shutdown and
242	>	* termination. Without care, active counts can be subject to very
243	>	* high contention.  We substantially reduce this contention by
244	>	* relaxing update rules.  A worker must claim active status
245	>	* prospectively, by activating if it sees that a submitted or
246	>	* stealable task exists (it may find after activating that the
247	>	* task no longer exists). It stays active while processing this
248	>	* task (if it exists) and any other local subtasks it produces,
249	>	* until it cannot find any other tasks. It then tries
250	>	* inactivating (see method preStep), but upon update contention
251	>	* instead scans for more tasks, later retrying inactivation if it
252	>	* doesn't find any.
253	>	*
254	>	* 4. Managing idle workers waiting for tasks. We cannot let
255	>	* workers spin indefinitely scanning for tasks when none are
256	>	* available. On the other hand, we must quickly prod them into
257	>	* action when new tasks are submitted or generated.  We
258	>	* park/unpark these idle workers using an event-count scheme.
259	>	* Field eventCount is incremented upon events that may enable
260	>	* workers that previously could not find a task to now find one:
261	>	* Submission of a new task to the pool, or another worker pushing
262	>	* a task onto a previously empty queue.  (We also use this
263	>	* mechanism for configuration and termination actions that
264	>	* require wakeups of idle workers).  Each worker maintains its
265	>	* last known event count, and blocks when a scan for work did not
266	>	* find a task AND its lastEventCount matches the current
267	>	* eventCount. Waiting idle workers are recorded in a variant of
268	>	* Treiber stack headed by field eventWaiters which, when nonzero,
269	>	* encodes the thread index and count awaited for by the worker
270	>	* thread most recently calling eventSync. This thread in turn has
271	>	* a record (field nextEventWaiter) for the next waiting worker.
272	>	* In addition to allowing simpler decisions about need for
273	>	* wakeup, the event count bits in eventWaiters serve the role of
274	>	* tags to avoid ABA errors in Treiber stacks. Upon any wakeup,
275	>	* released threads also try to release at most two others.  The
276	>	* net effect is a tree-like diffusion of signals, where released
277	>	* threads (and possibly others) help with unparks.  To further
278	>	* reduce contention effects a bit, failed CASes to increment
279	>	* field eventCount are tolerated without retries in signalWork.
280	>	* Conceptually they are merged into the same event, which is OK
281	>	* when their only purpose is to enable workers to scan for work.
282	>	*
283	>	* 5. Managing suspension of extra workers. When a worker notices
284	>	* (usually upon timeout of a wait()) that there are too few
285	>	* running threads, we may create a new thread to maintain
286	>	* parallelism level, or at least avoid starvation. Usually, extra
287	>	* threads are needed for only very short periods, yet join
288	>	* dependencies are such that we sometimes need them in
289	>	* bursts. Rather than create new threads each time this happens,
290	>	* we suspend no-longer-needed extra ones as "spares". For most
291	>	* purposes, we don't distinguish "extra" spare threads from
292	>	* normal "core" threads: On each call to preStep (the only point
293	>	* at which we can do this) a worker checks to see if there are
294	>	* now too many running workers, and if so, suspends itself.
295	>	* Method helpMaintainParallelism looks for suspended threads to
296	>	* resume before considering creating a new replacement. The
297	>	* spares themselves are encoded on another variant of a Treiber
298	>	* Stack, headed at field "spareWaiters".  Note that the use of
299	>	* spares is intrinsically racy.  One thread may become a spare at
300	>	* about the same time as another is needlessly being created. We
301	>	* counteract this and related slop in part by requiring resumed
302	>	* spares to immediately recheck (in preStep) to see whether they
303	>	* should re-suspend.
304	>	*
305	>	* 6. Killing off unneeded workers. A timeout mechanism is used to
306	>	* shed unused workers: The oldest (first) event queue waiter uses
307	>	* a timed rather than hard wait. When this wait times out without
308	>	* a normal wakeup, it tries to shutdown any one (for convenience
309	>	* the newest) other spare or event waiter via
310	>	* tryShutdownUnusedWorker. This eventually reduces the number of
311	>	* worker threads to a minimum of one after a long enough period
312	>	* without use.
313	>	*
314	>	* 7. Deciding when to create new workers. The main dynamic
315	>	* control in this class is deciding when to create extra threads
316	>	* in method helpMaintainParallelism. We would like to keep
317	>	* exactly #parallelism threads running, which is an impossible
318	>	* task. We always need to create one when the number of running
319	>	* threads would become zero and all workers are busy. Beyond
320	>	* this, we must rely on heuristics that work well in the
321	>	* presence of transient phenomena such as GC stalls, dynamic
322	>	* compilation, and wake-up lags. These transients are extremely
323	>	* common -- we are normally trying to fully saturate the CPUs on
324	>	* a machine, so almost any activity other than running tasks
325	>	* impedes accuracy. Our main defense is to allow parallelism to
326	>	* lapse for a while during joins, and use a timeout to see if,
327	>	* after the resulting settling, there is still a need for
328	>	* additional workers.  This also better copes with the fact that
329	>	* some of the methods in this class tend to never become compiled
330	>	* (but are interpreted), so some components of the entire set of
331	>	* controls might execute 100 times faster than others. And
332	>	* similarly for cases where the apparent lack of work is just due
333	>	* to GC stalls and other transient system activity.
334	>	*
335	>	* Beware that there is a lot of representation-level coupling
336	>	* among classes ForkJoinPool, ForkJoinWorkerThread, and
337	>	* ForkJoinTask.  For example, direct access to "workers" array by
338	>	* workers, and direct access to ForkJoinTask.status by both
339	>	* ForkJoinPool and ForkJoinWorkerThread.  There is little point
340	>	* trying to reduce this, since any associated future changes in
341	>	* representations will need to be accompanied by algorithmic
342	>	* changes anyway.
343	>	*
344	>	* Style notes: There are lots of inline assignments (of form
345	>	* "while ((local = field) != 0)") which are usually the simplest
346	>	* way to ensure the required read orderings (which are sometimes
347	>	* critical). Also several occurrences of the unusual "do {}
348	>	* while (!cas...)" which is the simplest way to force an update of
349	>	* a CAS'ed variable. There are also other coding oddities that
350	>	* help some methods perform reasonably even when interpreted (not
351	>	* compiled), at the expense of some messy constructions that
352	>	* reduce byte code counts.
353	>	*
354	>	* The order of declarations in this file is: (1) statics (2)
355	>	* fields (along with constants used when unpacking some of them)
356	>	* (3) internal control methods (4) callbacks and other support
357	>	* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
358	>	* methods (plus a few little helpers).
359		*/
360
78	–	/** Mask for packing and unpacking shorts */
79	–	private static final int  shortMask = 0xffff;
80	–
81	–	/** Max pool size -- must be a power of two minus 1 */
82	–	private static final int MAX_THREADS =  0x7FFF;
83	–
361		/**
362		* Factory for creating new {@link ForkJoinWorkerThread}s.
363		* A {@code ForkJoinWorkerThreadFactory} must be defined and used
#	Line 92 | Line 369 | public class ForkJoinPool extends Abstra
369		* Returns a new worker thread operating in the given pool.
370		*
371		* @param pool the pool this thread works in
372	<	* @throws NullPointerException if pool is null
372	>	* @throws NullPointerException if the pool is null
373		*/
374		public ForkJoinWorkerThread newThread(ForkJoinPool pool);
375		}
#	Line 101 | Line 378 | public class ForkJoinPool extends Abstra
378		* Default ForkJoinWorkerThreadFactory implementation; creates a
379		* new ForkJoinWorkerThread.
380		*/
381	<	static class  DefaultForkJoinWorkerThreadFactory
381	>	static class DefaultForkJoinWorkerThreadFactory
382		implements ForkJoinWorkerThreadFactory {
383		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
384	<	try {
108	<	return new ForkJoinWorkerThread(pool);
109	<	} catch (OutOfMemoryError oom)  {
110	<	return null;
111	<	}
384	>	return new ForkJoinWorkerThread(pool);
385		}
386		}
387
#	Line 144 | Line 417 | public class ForkJoinPool extends Abstra
417		new AtomicInteger();
418
419		/**
420	<	* Array holding all worker threads in the pool. Initialized upon
421	<	* first use. Array size must be a power of two.  Updates and
422	<	* replacements are protected by workerLock, but it is always kept
423	<	* in a consistent enough state to be randomly accessed without
424	<	* locking by workers performing work-stealing.
420	>	* The time to block in a join (see awaitJoin) before checking if
421	>	* a new worker should be (re)started to maintain parallelism
422	>	* level. The value should be short enough to maintain global
423	>	* responsiveness and progress but long enough to avoid
424	>	* counterproductive firings during GC stalls or unrelated system
425	>	* activity, and to not bog down systems with continual re-firings
426	>	* on GCs or legitimately long waits.
427		*/
428	<	volatile ForkJoinWorkerThread[] workers;
428	>	private static final long JOIN_TIMEOUT_MILLIS = 250L; // 4 per second
429
430		/**
431	<	* Lock protecting access to workers.
431	>	* The wakeup interval (in nanoseconds) for the oldest worker
432	>	* waiting for an event invokes tryShutdownUnusedWorker to shrink
433	>	* the number of workers.  The exact value does not matter too
434	>	* much, but should be long enough to slowly release resources
435	>	* during long periods without use without disrupting normal use.
436		*/
437	<	private final ReentrantLock workerLock;
437	>	private static final long SHRINK_RATE_NANOS =
438	>	30L * 1000L * 1000L * 1000L; // 2 per minute
439
440		/**
441	<	* Condition for awaitTermination.
441	>	* Absolute bound for parallelism level. Twice this number plus
442	>	* one (i.e., 0xfff) must fit into a 16bit field to enable
443	>	* word-packing for some counts and indices.
444		*/
445	<	private final Condition termination;
445	>	private static final int MAX_WORKERS   = 0x7fff;
446
447		/**
448	<	* The uncaught exception handler used when any worker
449	<	* abruptly terminates
448	>	* Array holding all worker threads in the pool.  Array size must
449	>	* be a power of two.  Updates and replacements are protected by
450	>	* workerLock, but the array is always kept in a consistent enough
451	>	* state to be randomly accessed without locking by workers
452	>	* performing work-stealing, as well as other traversal-based
453	>	* methods in this class. All readers must tolerate that some
454	>	* array slots may be null.
455		*/
456	<	private Thread.UncaughtExceptionHandler ueh;
456	>	volatile ForkJoinWorkerThread[] workers;
457
458		/**
459	<	* Creation factory for worker threads.
459	>	* Queue for external submissions.
460		*/
461	<	private final ForkJoinWorkerThreadFactory factory;
461	>	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
462
463		/**
464	<	* Head of stack of threads that were created to maintain
178	<	* parallelism when other threads blocked, but have since
179	<	* suspended when the parallelism level rose.
464	>	* Lock protecting updates to workers array.
465		*/
466	<	private volatile WaitQueueNode spareStack;
466	>	private final ReentrantLock workerLock;
467
468		/**
469	<	* Sum of per-thread steal counts, updated only when threads are
185	<	* idle or terminating.
469	>	* Latch released upon termination.
470		*/
471	<	private final AtomicLong stealCount;
471	>	private final Phaser termination;
472
473		/**
474	<	* Queue for external submissions.
474	>	* Creation factory for worker threads.
475		*/
476	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
476	>	private final ForkJoinWorkerThreadFactory factory;
477
478		/**
479	<	* Head of Treiber stack for barrier sync. See below for explanation.
479	>	* Sum of per-thread steal counts, updated only when threads are
480	>	* idle or terminating.
481		*/
482	<	private volatile WaitQueueNode syncStack;
482	>	private volatile long stealCount;
483
484		/**
485	<	* The count for event barrier
485	>	* Encoded record of top of Treiber stack of threads waiting for
486	>	* events. The top 32 bits contain the count being waited for. The
487	>	* bottom 16 bits contains one plus the pool index of waiting
488	>	* worker thread. (Bits 16-31 are unused.)
489		*/
490	<	private volatile long eventCount;
490	>	private volatile long eventWaiters;
491
492	<	/**
493	<	* Pool number, just for assigning useful names to worker threads
206	<	*/
207	<	private final int poolNumber;
492	>	private static final int  EVENT_COUNT_SHIFT = 32;
493	>	private static final long WAITER_ID_MASK    = (1L << 16) - 1L;
494
495		/**
496	<	* The maximum allowed pool size
496	>	* A counter for events that may wake up worker threads:
497	>	*   - Submission of a new task to the pool
498	>	*   - A worker pushing a task on an empty queue
499	>	*   - termination
500		*/
501	<	private volatile int maxPoolSize;
501	>	private volatile int eventCount;
502
503		/**
504	<	* The desired parallelism level, updated only under workerLock.
504	>	* Encoded record of top of Treiber stack of spare threads waiting
505	>	* for resumption. The top 16 bits contain an arbitrary count to
506	>	* avoid ABA effects. The bottom 16bits contains one plus the pool
507	>	* index of waiting worker thread.
508		*/
509	<	private volatile int parallelism;
509	>	private volatile int spareWaiters;
510	>
511	>	private static final int SPARE_COUNT_SHIFT = 16;
512	>	private static final int SPARE_ID_MASK     = (1 << 16) - 1;
513
514		/**
515	<	* True if use local fifo, not default lifo, for local polling
515	>	* Lifecycle control. The low word contains the number of workers
516	>	* that are (probably) executing tasks. This value is atomically
517	>	* incremented before a worker gets a task to run, and decremented
518	>	* when worker has no tasks and cannot find any.  Bits 16-18
519	>	* contain runLevel value. When all are zero, the pool is
520	>	* running. Level transitions are monotonic (running -> shutdown
521	>	* -> terminating -> terminated) so each transition adds a bit.
522	>	* These are bundled together to ensure consistent read for
523	>	* termination checks (i.e., that runLevel is at least SHUTDOWN
524	>	* and active threads is zero).
525	>	*
526	>	* Notes: Most direct CASes are dependent on these bitfield
527	>	* positions.  Also, this field is non-private to enable direct
528	>	* performance-sensitive CASes in ForkJoinWorkerThread.
529		*/
530	<	private volatile boolean locallyFifo;
530	>	volatile int runState;
531	>
532	>	// Note: The order among run level values matters.
533	>	private static final int RUNLEVEL_SHIFT     = 16;
534	>	private static final int SHUTDOWN           = 1 << RUNLEVEL_SHIFT;
535	>	private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
536	>	private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
537	>	private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
538
539		/**
540		* Holds number of total (i.e., created and not yet terminated)
541		* and running (i.e., not blocked on joins or other managed sync)
542	<	* threads, packed into one int to ensure consistent snapshot when
542	>	* threads, packed together to ensure consistent snapshot when
543		* making decisions about creating and suspending spare
544	<	* threads. Updated only by CAS.  Note: CASes in
545	<	* updateRunningCount and preJoin assume that running active count
546	<	* is in low word, so need to be modified if this changes.
544	>	* threads. Updated only by CAS. Note that adding a new worker
545	>	* requires incrementing both counts, since workers start off in
546	>	* running state.
547		*/
548		private volatile int workerCounts;
549
550	<	private static int totalCountOf(int s)           { return s >>> 16;  }
551	<	private static int runningCountOf(int s)         { return s & shortMask; }
552	<	private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
550	>	private static final int TOTAL_COUNT_SHIFT  = 16;
551	>	private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1;
552	>	private static final int ONE_RUNNING        = 1;
553	>	private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
554
555		/**
556	<	* Adds delta (which may be negative) to running count.  This must
557	<	* be called before (with negative arg) and after (with positive)
242	<	* any managed synchronization (i.e., mainly, joins).
243	<	*
244	<	* @param delta the number to add
556	>	* The target parallelism level.
557	>	* Accessed directly by ForkJoinWorkerThreads.
558		*/
559	<	final void updateRunningCount(int delta) {
247	<	int s;
248	<	do {} while (!casWorkerCounts(s = workerCounts, s + delta));
249	<	}
559	>	final int parallelism;
560
561		/**
562	<	* Adds delta (which may be negative) to both total and running
563	<	* count.  This must be called upon creation and termination of
254	<	* worker threads.
255	<	*
256	<	* @param delta the number to add
562	>	* True if use local fifo, not default lifo, for local polling
563	>	* Read by, and replicated by ForkJoinWorkerThreads
564		*/
565	<	private void updateWorkerCount(int delta) {
259	<	int d = delta + (delta << 16); // add to both lo and hi parts
260	<	int s;
261	<	do {} while (!casWorkerCounts(s = workerCounts, s + d));
262	<	}
565	>	final boolean locallyFifo;
566
567		/**
568	<	* Lifecycle control. High word contains runState, low word
569	<	* contains the number of workers that are (probably) executing
267	<	* tasks. This value is atomically incremented before a worker
268	<	* gets a task to run, and decremented when worker has no tasks
269	<	* and cannot find any. These two fields are bundled together to
270	<	* support correct termination triggering.  Note: activeCount
271	<	* CAS'es cheat by assuming active count is in low word, so need
272	<	* to be modified if this changes
568	>	* The uncaught exception handler used when any worker abruptly
569	>	* terminates.
570		*/
571	<	private volatile int runControl;
571	>	private final Thread.UncaughtExceptionHandler ueh;
572
573	<	// RunState values. Order among values matters
574	<	private static final int RUNNING     = 0;
575	<	private static final int SHUTDOWN    = 1;
576	<	private static final int TERMINATING = 2;
280	<	private static final int TERMINATED  = 3;
573	>	/**
574	>	* Pool number, just for assigning useful names to worker threads
575	>	*/
576	>	private final int poolNumber;
577
578	<	private static int runStateOf(int c)             { return c >>> 16; }
579	<	private static int activeCountOf(int c)          { return c & shortMask; }
284	<	private static int runControlFor(int r, int a)   { return (r << 16) + a; }
578	>	// Utilities for CASing fields. Note that most of these
579	>	// are usually manually inlined by callers
580
581		/**
582	<	* Tries incrementing active count; fails on contention.
288	<	* Called by workers before/during executing tasks.
289	<	*
290	<	* @return true on success
582	>	* Increments running count part of workerCounts
583		*/
584	<	final boolean tryIncrementActiveCount() {
585	<	int c = runControl;
586	<	return casRunControl(c, c+1);
584	>	final void incrementRunningCount() {
585	>	int c;
586	>	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
587	>	c = workerCounts,
588	>	c + ONE_RUNNING));
589		}
590
591		/**
592	<	* Tries decrementing active count; fails on contention.
299	<	* Possibly triggers termination on success.
300	<	* Called by workers when they can't find tasks.
301	<	*
302	<	* @return true on success
592	>	* Tries to decrement running count unless already zero
593		*/
594	<	final boolean tryDecrementActiveCount() {
595	<	int c = runControl;
596	<	int nextc = c - 1;
307	<	if (!casRunControl(c, nextc))
594	>	final boolean tryDecrementRunningCount() {
595	>	int wc = workerCounts;
596	>	if ((wc & RUNNING_COUNT_MASK) == 0)
597		return false;
598	<	if (canTerminateOnShutdown(nextc))
599	<	terminateOnShutdown();
311	<	return true;
598	>	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
599	>	wc, wc - ONE_RUNNING);
600		}
601
602		/**
603	<	* Returns {@code true} if argument represents zero active count
604	<	* and nonzero runstate, which is the triggering condition for
605	<	* terminating on shutdown.
603	>	* Forces decrement of encoded workerCounts, awaiting nonzero if
604	>	* (rarely) necessary when other count updates lag.
605	>	*
606	>	* @param dr -- either zero or ONE_RUNNING
607	>	* @param dt == either zero or ONE_TOTAL
608		*/
609	<	private static boolean canTerminateOnShutdown(int c) {
610	<	// i.e. least bit is nonzero runState bit
611	<	return ((c & -c) >>> 16) != 0;
609	>	private void decrementWorkerCounts(int dr, int dt) {
610	>	for (;;) {
611	>	int wc = workerCounts;
612	>	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
613	>	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) {
614	>	if ((runState & TERMINATED) != 0)
615	>	return; // lagging termination on a backout
616	>	Thread.yield();
617	>	}
618	>	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
619	>	wc, wc - (dr + dt)))
620	>	return;
621	>	}
622	>	}
623	>
624	>	/**
625	>	* Tries decrementing active count; fails on contention.
626	>	* Called when workers cannot find tasks to run.
627	>	*/
628	>	final boolean tryDecrementActiveCount() {
629	>	int c;
630	>	return UNSAFE.compareAndSwapInt(this, runStateOffset,
631	>	c = runState, c - 1);
632		}
633
634		/**
635	<	* Transition run state to at least the given state. Return true
636	<	* if not already at least given state.
635	>	* Advances to at least the given level. Returns true if not
636	>	* already in at least the given level.
637		*/
638	<	private boolean transitionRunStateTo(int state) {
638	>	private boolean advanceRunLevel(int level) {
639		for (;;) {
640	<	int c = runControl;
641	<	if (runStateOf(c) >= state)
640	>	int s = runState;
641	>	if ((s & level) != 0)
642		return false;
643	<	if (casRunControl(c, runControlFor(state, activeCountOf(c))))
643	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level))
644		return true;
645		}
646		}
647
648	+	// workers array maintenance
649	+
650		/**
651	<	* Controls whether to add spares to maintain parallelism
651	>	* Records and returns a workers array index for new worker.
652		*/
653	<	private volatile boolean maintainsParallelism;
653	>	private int recordWorker(ForkJoinWorkerThread w) {
654	>	// Try using slot totalCount-1. If not available, scan and/or resize
655	>	int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1;
656	>	final ReentrantLock lock = this.workerLock;
657	>	lock.lock();
658	>	try {
659	>	ForkJoinWorkerThread[] ws = workers;
660	>	int n = ws.length;
661	>	if (k < 0 || k >= n || ws[k] != null) {
662	>	for (k = 0; k < n && ws[k] != null; ++k)
663	>	;
664	>	if (k == n)
665	>	ws = Arrays.copyOf(ws, n << 1);
666	>	}
667	>	ws[k] = w;
668	>	workers = ws; // volatile array write ensures slot visibility
669	>	} finally {
670	>	lock.unlock();
671	>	}
672	>	return k;
673	>	}
674
675	<	// Constructors
675	>	/**
676	>	* Nulls out record of worker in workers array.
677	>	*/
678	>	private void forgetWorker(ForkJoinWorkerThread w) {
679	>	int idx = w.poolIndex;
680	>	// Locking helps method recordWorker avoid unnecessary expansion
681	>	final ReentrantLock lock = this.workerLock;
682	>	lock.lock();
683	>	try {
684	>	ForkJoinWorkerThread[] ws = workers;
685	>	if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify
686	>	ws[idx] = null;
687	>	} finally {
688	>	lock.unlock();
689	>	}
690	>	}
691
692		/**
693	<	* Creates a ForkJoinPool with a pool size equal to the number of
694	<	* processors available on the system, using the default
695	<	* ForkJoinWorkerThreadFactory.
693	>	* Final callback from terminating worker.  Removes record of
694	>	* worker from array, and adjusts counts. If pool is shutting
695	>	* down, tries to complete termination.
696		*
697	<	* @throws SecurityException if a security manager exists and
351	<	*         the caller is not permitted to modify threads
352	<	*         because it does not hold {@link
353	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
697	>	* @param w the worker
698		*/
699	<	public ForkJoinPool() {
700	<	this(Runtime.getRuntime().availableProcessors(),
701	<	defaultForkJoinWorkerThreadFactory);
699	>	final void workerTerminated(ForkJoinWorkerThread w) {
700	>	forgetWorker(w);
701	>	decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL);
702	>	while (w.stealCount != 0) // collect final count
703	>	tryAccumulateStealCount(w);
704	>	tryTerminate(false);
705		}
706
707	+	// Waiting for and signalling events
708	+
709		/**
710	<	* Creates a ForkJoinPool with the indicated parallelism level
711	<	* threads and using the default ForkJoinWorkerThreadFactory.
712	<	*
713	<	* @param parallelism the number of worker threads
365	<	* @throws IllegalArgumentException if parallelism less than or
366	<	* equal to zero
367	<	* @throws SecurityException if a security manager exists and
368	<	*         the caller is not permitted to modify threads
369	<	*         because it does not hold {@link
370	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
710	>	* Releases workers blocked on a count not equal to current count.
711	>	* Normally called after precheck that eventWaiters isn't zero to
712	>	* avoid wasted array checks. Gives up upon a change in count or
713	>	* upon releasing two workers, letting others take over.
714		*/
715	<	public ForkJoinPool(int parallelism) {
716	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
715	>	private void releaseEventWaiters() {
716	>	ForkJoinWorkerThread[] ws = workers;
717	>	int n = ws.length;
718	>	long h = eventWaiters;
719	>	int ec = eventCount;
720	>	boolean releasedOne = false;
721	>	ForkJoinWorkerThread w; int id;
722	>	while ((id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 &&
723	>	(int)(h >>> EVENT_COUNT_SHIFT) != ec &&
724	>	id < n && (w = ws[id]) != null) {
725	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
726	>	h,  w.nextWaiter)) {
727	>	LockSupport.unpark(w);
728	>	if (releasedOne) // exit on second release
729	>	break;
730	>	releasedOne = true;
731	>	}
732	>	if (eventCount != ec)
733	>	break;
734	>	h = eventWaiters;
735	>	}
736		}
737
738		/**
739	<	* Creates a ForkJoinPool with parallelism equal to the number of
740	<	* processors available on the system and using the given
379	<	* ForkJoinWorkerThreadFactory.
380	<	*
381	<	* @param factory the factory for creating new threads
382	<	* @throws NullPointerException if factory is null
383	<	* @throws SecurityException if a security manager exists and
384	<	*         the caller is not permitted to modify threads
385	<	*         because it does not hold {@link
386	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
739	>	* Tries to advance eventCount and releases waiters. Called only
740	>	* from workers.
741		*/
742	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
743	<	this(Runtime.getRuntime().availableProcessors(), factory);
742	>	final void signalWork() {
743	>	int c; // try to increment event count -- CAS failure OK
744	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
745	>	if (eventWaiters != 0L)
746	>	releaseEventWaiters();
747		}
748
749		/**
750	<	* Creates a ForkJoinPool with the given parallelism and factory.
750	>	* Adds the given worker to event queue and blocks until
751	>	* terminating or event count advances from the given value
752		*
753	<	* @param parallelism the targeted number of worker threads
754	<	* @param factory the factory for creating new threads
397	<	* @throws IllegalArgumentException if parallelism less than or
398	<	* equal to zero, or greater than implementation limit
399	<	* @throws NullPointerException if factory is null
400	<	* @throws SecurityException if a security manager exists and
401	<	*         the caller is not permitted to modify threads
402	<	*         because it does not hold {@link
403	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
753	>	* @param w the calling worker thread
754	>	* @param ec the count
755		*/
756	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
757	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
758	<	throw new IllegalArgumentException();
759	<	if (factory == null)
760	<	throw new NullPointerException();
761	<	checkPermission();
762	<	this.factory = factory;
763	<	this.parallelism = parallelism;
764	<	this.maxPoolSize = MAX_THREADS;
765	<	this.maintainsParallelism = true;
766	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
767	<	this.workerLock = new ReentrantLock();
768	<	this.termination = workerLock.newCondition();
418	<	this.stealCount = new AtomicLong();
419	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
420	<	// worker array and workers are lazily constructed
756	>	private void eventSync(ForkJoinWorkerThread w, int ec) {
757	>	long nh = (((long)ec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
758	>	long h;
759	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
760	>	(((int)((h = eventWaiters) & WAITER_ID_MASK)) == 0 ||
761	>	(int)(h >>> EVENT_COUNT_SHIFT) == ec) &&
762	>	eventCount == ec) {
763	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
764	>	w.nextWaiter = h, nh)) {
765	>	awaitEvent(w, ec);
766	>	break;
767	>	}
768	>	}
769		}
770
771		/**
772	<	* Creates a new worker thread using factory.
772	>	* Blocks the given worker (that has already been entered as an
773	>	* event waiter) until terminating or event count advances from
774	>	* the given value. The oldest (first) waiter uses a timed wait to
775	>	* occasionally one-by-one shrink the number of workers (to a
776	>	* minimum of one) if the pool has not been used for extended
777	>	* periods.
778		*
779	<	* @param index the index to assign worker
780	<	* @return new worker, or null of factory failed
779	>	* @param w the calling worker thread
780	>	* @param ec the count
781		*/
782	<	private ForkJoinWorkerThread createWorker(int index) {
783	<	Thread.UncaughtExceptionHandler h = ueh;
784	<	ForkJoinWorkerThread w = factory.newThread(this);
785	<	if (w != null) {
786	<	w.poolIndex = index;
787	<	w.setDaemon(true);
788	<	w.setAsyncMode(locallyFifo);
789	<	w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
790	<	if (h != null)
791	<	w.setUncaughtExceptionHandler(h);
782	>	private void awaitEvent(ForkJoinWorkerThread w, int ec) {
783	>	while (eventCount == ec) {
784	>	if (tryAccumulateStealCount(w)) { // transfer while idle
785	>	boolean untimed = (w.nextWaiter != 0L ||
786	>	(workerCounts & RUNNING_COUNT_MASK) <= 1);
787	>	long startTime = untimed? 0 : System.nanoTime();
788	>	Thread.interrupted();         // clear/ignore interrupt
789	>	if (eventCount != ec || w.runState != 0 ||
790	>	runState >= TERMINATING)  // recheck after clear
791	>	break;
792	>	if (untimed)
793	>	LockSupport.park(w);
794	>	else {
795	>	LockSupport.parkNanos(w, SHRINK_RATE_NANOS);
796	>	if (eventCount != ec || w.runState != 0 ||
797	>	runState >= TERMINATING)
798	>	break;
799	>	if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS)
800	>	tryShutdownUnusedWorker(ec);
801	>	}
802	>	}
803		}
440	–	return w;
804		}
805
806	+	// Maintaining parallelism
807	+
808		/**
809	<	* Returns a good size for worker array given pool size.
445	<	* Currently requires size to be a power of two.
809	>	* Pushes worker onto the spare stack.
810		*/
811	<	private static int arraySizeFor(int poolSize) {
812	<	return (poolSize <= 1) ? 1 :
813	<	(1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
811	>	final void pushSpare(ForkJoinWorkerThread w) {
812	>	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1);
813	>	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
814	>	w.nextSpare = spareWaiters,ns));
815		}
816
817		/**
818	<	* Creates or resizes array if necessary to hold newLength.
819	<	* Call only under exclusion.
455	<	*
456	<	* @return the array
818	>	* Tries (once) to resume a spare if the number of running
819	>	* threads is less than target.
820		*/
821	<	private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
821	>	private void tryResumeSpare() {
822	>	int sw, id;
823		ForkJoinWorkerThread[] ws = workers;
824	<	if (ws == null)
825	<	return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
826	<	else if (newLength > ws.length)
827	<	return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
828	<	else
829	<	return ws;
824	>	int n = ws.length;
825	>	ForkJoinWorkerThread w;
826	>	if ((sw = spareWaiters) != 0 &&
827	>	(id = (sw & SPARE_ID_MASK) - 1) >= 0 &&
828	>	id < n && (w = ws[id]) != null &&
829	>	(workerCounts & RUNNING_COUNT_MASK) < parallelism &&
830	>	spareWaiters == sw &&
831	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
832	>	sw, w.nextSpare)) {
833	>	int c; // increment running count before resume
834	>	do {} while (!UNSAFE.compareAndSwapInt
835	>	(this, workerCountsOffset,
836	>	c = workerCounts, c + ONE_RUNNING));
837	>	if (w.tryUnsuspend())
838	>	LockSupport.unpark(w);
839	>	else   // back out if w was shutdown
840	>	decrementWorkerCounts(ONE_RUNNING, 0);
841	>	}
842		}
843
844		/**
845	<	* Tries to shrink workers into smaller array after one or more terminate.
846	<	*/
847	<	private void tryShrinkWorkerArray() {
848	<	ForkJoinWorkerThread[] ws = workers;
849	<	if (ws != null) {
850	<	int len = ws.length;
851	<	int last = len - 1;
852	<	while (last >= 0 && ws[last] == null)
853	<	--last;
854	<	int newLength = arraySizeFor(last+1);
855	<	if (newLength < len)
856	<	workers = Arrays.copyOf(ws, newLength);
845	>	* Tries to increase the number of running workers if below target
846	>	* parallelism: If a spare exists tries to resume it via
847	>	* tryResumeSpare.  Otherwise, if not enough total workers or all
848	>	* existing workers are busy, adds a new worker. In all cases also
849	>	* helps wake up releasable workers waiting for work.
850	>	*/
851	>	private void helpMaintainParallelism() {
852	>	int pc = parallelism;
853	>	int wc, rs, tc;
854	>	while (((wc = workerCounts) & RUNNING_COUNT_MASK) < pc &&
855	>	(rs = runState) < TERMINATING) {
856	>	if (spareWaiters != 0)
857	>	tryResumeSpare();
858	>	else if ((tc = wc >>> TOTAL_COUNT_SHIFT) >= MAX_WORKERS ||
859	>	(tc >= pc && (rs & ACTIVE_COUNT_MASK) != tc))
860	>	break;   // enough total
861	>	else if (runState == rs && workerCounts == wc &&
862	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
863	>	wc + (ONE_RUNNING|ONE_TOTAL))) {
864	>	ForkJoinWorkerThread w = null;
865	>	try {
866	>	w = factory.newThread(this);
867	>	} finally { // adjust on null or exceptional factory return
868	>	if (w == null) {
869	>	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
870	>	tryTerminate(false); // handle failure during shutdown
871	>	}
872	>	}
873	>	if (w == null)
874	>	break;
875	>	w.start(recordWorker(w), ueh);
876	>	if ((workerCounts >>> TOTAL_COUNT_SHIFT) >= pc) {
877	>	int c; // advance event count
878	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
879	>	c = eventCount, c+1);
880	>	break; // add at most one unless total below target
881	>	}
882	>	}
883		}
884	+	if (eventWaiters != 0L)
885	+	releaseEventWaiters();
886		}
887
888		/**
889	<	* Initializes workers if necessary.
889	>	* Callback from the oldest waiter in awaitEvent waking up after a
890	>	* period of non-use. If all workers are idle, tries (once) to
891	>	* shutdown an event waiter or a spare, if one exists. Note that
892	>	* we don't need CAS or locks here because the method is called
893	>	* only from one thread occasionally waking (and even misfires are
894	>	* OK). Note that until the shutdown worker fully terminates,
895	>	* workerCounts will overestimate total count, which is tolerable.
896	>	*
897	>	* @param ec the event count waited on by caller (to abort
898	>	* attempt if count has since changed).
899		*/
900	<	final void ensureWorkerInitialization() {
901	<	ForkJoinWorkerThread[] ws = workers;
902	<	if (ws == null) {
903	<	final ReentrantLock lock = this.workerLock;
904	<	lock.lock();
905	<	try {
906	<	ws = workers;
907	<	if (ws == null) {
908	<	int ps = parallelism;
909	<	ws = ensureWorkerArrayCapacity(ps);
910	<	for (int i = 0; i < ps; ++i) {
911	<	ForkJoinWorkerThread w = createWorker(i);
912	<	if (w != null) {
913	<	ws[i] = w;
914	<	w.start();
915	<	updateWorkerCount(1);
916	<	}
917	<	}
900	>	private void tryShutdownUnusedWorker(int ec) {
901	>	if (runState == 0 && eventCount == ec) { // only trigger if all idle
902	>	ForkJoinWorkerThread[] ws = workers;
903	>	int n = ws.length;
904	>	ForkJoinWorkerThread w = null;
905	>	boolean shutdown = false;
906	>	int sw;
907	>	long h;
908	>	if ((sw = spareWaiters) != 0) { // prefer killing spares
909	>	int id = (sw & SPARE_ID_MASK) - 1;
910	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
911	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
912	>	sw, w.nextSpare))
913	>	shutdown = true;
914	>	}
915	>	else if ((h = eventWaiters) != 0L) {
916	>	long nh;
917	>	int id = ((int)(h & WAITER_ID_MASK)) - 1;
918	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
919	>	(nh = w.nextWaiter) != 0L && // keep at least one worker
920	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh))
921	>	shutdown = true;
922	>	}
923	>	if (w != null && shutdown) {
924	>	w.shutdown();
925	>	LockSupport.unpark(w);
926	>	}
927	>	}
928	>	releaseEventWaiters(); // in case of interference
929	>	}
930	>
931	>	/**
932	>	* Callback from workers invoked upon each top-level action (i.e.,
933	>	* stealing a task or taking a submission and running it).
934	>	* Performs one or more of the following:
935	>	*
936	>	* 1. If the worker is active and either did not run a task
937	>	*    or there are too many workers, try to set its active status
938	>	*    to inactive and update activeCount. On contention, we may
939	>	*    try again in this or a subsequent call.
940	>	*
941	>	* 2. If not enough total workers, help create some.
942	>	*
943	>	* 3. If there are too many running workers, suspend this worker
944	>	*    (first forcing inactive if necessary).  If it is not needed,
945	>	*    it may be shutdown while suspended (via
946	>	*    tryShutdownUnusedWorker).  Otherwise, upon resume it
947	>	*    rechecks running thread count and need for event sync.
948	>	*
949	>	* 4. If worker did not run a task, await the next task event via
950	>	*    eventSync if necessary (first forcing inactivation), upon
951	>	*    which the worker may be shutdown via
952	>	*    tryShutdownUnusedWorker.  Otherwise, help release any
953	>	*    existing event waiters that are now releasable,
954	>	*
955	>	* @param w the worker
956	>	* @param ran true if worker ran a task since last call to this method
957	>	*/
958	>	final void preStep(ForkJoinWorkerThread w, boolean ran) {
959	>	int wec = w.lastEventCount;
960	>	boolean active = w.active;
961	>	boolean inactivate = false;
962	>	int pc = parallelism;
963	>	int rs;
964	>	while (w.runState == 0 && (rs = runState) < TERMINATING) {
965	>	if ((inactivate || (active && (rs & ACTIVE_COUNT_MASK) >= pc)) &&
966	>	UNSAFE.compareAndSwapInt(this, runStateOffset, rs, rs - 1))
967	>	inactivate = active = w.active = false;
968	>	int wc = workerCounts;
969	>	if ((wc & RUNNING_COUNT_MASK) > pc) {
970	>	if (!(inactivate |= active) && // must inactivate to suspend
971	>	workerCounts == wc &&      // try to suspend as spare
972	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
973	>	wc, wc - ONE_RUNNING))
974	>	w.suspendAsSpare();
975	>	}
976	>	else if ((wc >>> TOTAL_COUNT_SHIFT) < pc)
977	>	helpMaintainParallelism();     // not enough workers
978	>	else if (!ran) {
979	>	long h = eventWaiters;
980	>	int ec = eventCount;
981	>	if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != ec)
982	>	releaseEventWaiters();     // release others before waiting
983	>	else if (ec != wec) {
984	>	w.lastEventCount = ec;     // no need to wait
985	>	break;
986		}
987	<	} finally {
988	<	lock.unlock();
987	>	else if (!(inactivate |= active))
988	>	eventSync(w, wec);         // must inactivate before sync
989		}
990	+	else
991	+	break;
992		}
993		}
994
995		/**
996	<	* Worker creation and startup for threads added via setParallelism.
996	>	* Helps and/or blocks awaiting join of the given task.
997	>	* See above for explanation.
998	>	*
999	>	* @param joinMe the task to join
1000	>	* @param worker the current worker thread
1001		*/
1002	<	private void createAndStartAddedWorkers() {
1003	<	resumeAllSpares();  // Allow spares to convert to nonspare
1004	<	int ps = parallelism;
1005	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
1006	<	int len = ws.length;
1007	<	// Sweep through slots, to keep lowest indices most populated
1008	<	int k = 0;
1009	<	while (k < len) {
1010	<	if (ws[k] != null) {
1011	<	++k;
1012	<	continue;
1002	>	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) {
1003	>	int retries = 2 + (parallelism >> 2); // #helpJoins before blocking
1004	>	while (joinMe.status >= 0) {
1005	>	int wc;
1006	>	worker.helpJoinTask(joinMe);
1007	>	if (joinMe.status < 0)
1008	>	break;
1009	>	else if (retries > 0)
1010	>	--retries;
1011	>	else if (((wc = workerCounts) & RUNNING_COUNT_MASK) != 0 &&
1012	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1013	>	wc, wc - ONE_RUNNING)) {
1014	>	int stat, c; long h;
1015	>	while ((stat = joinMe.status) >= 0 &&
1016	>	(h = eventWaiters) != 0L && // help release others
1017	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1018	>	releaseEventWaiters();
1019	>	if (stat >= 0 &&
1020	>	((workerCounts & RUNNING_COUNT_MASK) == 0 ||
1021	>	(stat =
1022	>	joinMe.internalAwaitDone(JOIN_TIMEOUT_MILLIS)) >= 0))
1023	>	helpMaintainParallelism(); // timeout or no running workers
1024	>	do {} while (!UNSAFE.compareAndSwapInt
1025	>	(this, workerCountsOffset,
1026	>	c = workerCounts, c + ONE_RUNNING));
1027	>	if (stat < 0)
1028	>	break;   // else restart
1029		}
1030	<	int s = workerCounts;
1031	<	int tc = totalCountOf(s);
1032	<	int rc = runningCountOf(s);
1033	<	if (rc >= ps || tc >= ps)
1030	>	}
1031	>	}
1032	>
1033	>	/**
1034	>	* Same idea as awaitJoin, but no helping, retries, or timeouts.
1035	>	*/
1036	>	final void awaitBlocker(ManagedBlocker blocker)
1037	>	throws InterruptedException {
1038	>	while (!blocker.isReleasable()) {
1039	>	int wc = workerCounts;
1040	>	if ((wc & RUNNING_COUNT_MASK) != 0 &&
1041	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1042	>	wc, wc - ONE_RUNNING)) {
1043	>	try {
1044	>	while (!blocker.isReleasable()) {
1045	>	long h = eventWaiters;
1046	>	if (h != 0L &&
1047	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1048	>	releaseEventWaiters();
1049	>	else if ((workerCounts & RUNNING_COUNT_MASK) == 0 &&
1050	>	runState < TERMINATING)
1051	>	helpMaintainParallelism();
1052	>	else if (blocker.block())
1053	>	break;
1054	>	}
1055	>	} finally {
1056	>	int c;
1057	>	do {} while (!UNSAFE.compareAndSwapInt
1058	>	(this, workerCountsOffset,
1059	>	c = workerCounts, c + ONE_RUNNING));
1060	>	}
1061		break;
1062	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
1063	<	ForkJoinWorkerThread w = createWorker(k);
1062	>	}
1063	>	}
1064	>	}
1065	>
1066	>	/**
1067	>	* Possibly initiates and/or completes termination.
1068	>	*
1069	>	* @param now if true, unconditionally terminate, else only
1070	>	* if shutdown and empty queue and no active workers
1071	>	* @return true if now terminating or terminated
1072	>	*/
1073	>	private boolean tryTerminate(boolean now) {
1074	>	if (now)
1075	>	advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
1076	>	else if (runState < SHUTDOWN ||
1077	>	!submissionQueue.isEmpty() ||
1078	>	(runState & ACTIVE_COUNT_MASK) != 0)
1079	>	return false;
1080	>
1081	>	if (advanceRunLevel(TERMINATING))
1082	>	startTerminating();
1083	>
1084	>	// Finish now if all threads terminated; else in some subsequent call
1085	>	if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1086	>	advanceRunLevel(TERMINATED);
1087	>	termination.arrive();
1088	>	}
1089	>	return true;
1090	>	}
1091	>
1092	>	/**
1093	>	* Actions on transition to TERMINATING
1094	>	*
1095	>	* Runs up to four passes through workers: (0) shutting down each
1096	>	* (without waking up if parked) to quickly spread notifications
1097	>	* without unnecessary bouncing around event queues etc (1) wake
1098	>	* up and help cancel tasks (2) interrupt (3) mop up races with
1099	>	* interrupted workers
1100	>	*/
1101	>	private void startTerminating() {
1102	>	cancelSubmissions();
1103	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1104	>	int c; // advance event count
1105	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
1106	>	c = eventCount, c+1);
1107	>	eventWaiters = 0L; // clobber lists
1108	>	spareWaiters = 0;
1109	>	for (ForkJoinWorkerThread w : workers) {
1110		if (w != null) {
1111	<	ws[k++] = w;
1112	<	w.start();
1113	<	}
1114	<	else {
1115	<	updateWorkerCount(-1); // back out on failed creation
1116	<	break;
1111	>	w.shutdown();
1112	>	if (passes > 0 && !w.isTerminated()) {
1113	>	w.cancelTasks();
1114	>	LockSupport.unpark(w);
1115	>	if (passes > 1) {
1116	>	try {
1117	>	w.interrupt();
1118	>	} catch (SecurityException ignore) {
1119	>	}
1120	>	}
1121	>	}
1122		}
1123		}
1124		}
1125		}
1126
1127	+	/**
1128	+	* Clears out and cancels submissions, ignoring exceptions.
1129	+	*/
1130	+	private void cancelSubmissions() {
1131	+	ForkJoinTask<?> task;
1132	+	while ((task = submissionQueue.poll()) != null) {
1133	+	try {
1134	+	task.cancel(false);
1135	+	} catch (Throwable ignore) {
1136	+	}
1137	+	}
1138	+	}
1139	+
1140	+	// misc support for ForkJoinWorkerThread
1141	+
1142	+	/**
1143	+	* Returns pool number.
1144	+	*/
1145	+	final int getPoolNumber() {
1146	+	return poolNumber;
1147	+	}
1148	+
1149	+	/**
1150	+	* Tries to accumulate steal count from a worker, clearing
1151	+	* the worker's value if successful.
1152	+	*
1153	+	* @return true if worker steal count now zero
1154	+	*/
1155	+	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1156	+	int sc = w.stealCount;
1157	+	long c = stealCount;
1158	+	// CAS even if zero, for fence effects
1159	+	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1160	+	if (sc != 0)
1161	+	w.stealCount = 0;
1162	+	return true;
1163	+	}
1164	+	return sc == 0;
1165	+	}
1166	+
1167	+	/**
1168	+	* Returns the approximate (non-atomic) number of idle threads per
1169	+	* active thread.
1170	+	*/
1171	+	final int idlePerActive() {
1172	+	int pc = parallelism; // use parallelism, not rc
1173	+	int ac = runState;    // no mask -- artificially boosts during shutdown
1174	+	// Use exact results for small values, saturate past 4
1175	+	return ((pc <= ac) ? 0 :
1176	+	(pc >>> 1 <= ac) ? 1 :
1177	+	(pc >>> 2 <= ac) ? 3 :
1178	+	pc >>> 3);
1179	+	}
1180	+
1181	+	// Public and protected methods
1182	+
1183	+	// Constructors
1184	+
1185	+	/**
1186	+	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1187	+	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1188	+	* #defaultForkJoinWorkerThreadFactory default thread factory},
1189	+	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1190	+	*
1191	+	* @throws SecurityException if a security manager exists and
1192	+	*         the caller is not permitted to modify threads
1193	+	*         because it does not hold {@link
1194	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1195	+	*/
1196	+	public ForkJoinPool() {
1197	+	this(Runtime.getRuntime().availableProcessors(),
1198	+	defaultForkJoinWorkerThreadFactory, null, false);
1199	+	}
1200	+
1201	+	/**
1202	+	* Creates a {@code ForkJoinPool} with the indicated parallelism
1203	+	* level, the {@linkplain
1204	+	* #defaultForkJoinWorkerThreadFactory default thread factory},
1205	+	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1206	+	*
1207	+	* @param parallelism the parallelism level
1208	+	* @throws IllegalArgumentException if parallelism less than or
1209	+	*         equal to zero, or greater than implementation limit
1210	+	* @throws SecurityException if a security manager exists and
1211	+	*         the caller is not permitted to modify threads
1212	+	*         because it does not hold {@link
1213	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1214	+	*/
1215	+	public ForkJoinPool(int parallelism) {
1216	+	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1217	+	}
1218	+
1219	+	/**
1220	+	* Creates a {@code ForkJoinPool} with the given parameters.
1221	+	*
1222	+	* @param parallelism the parallelism level. For default value,
1223	+	* use {@link java.lang.Runtime#availableProcessors}.
1224	+	* @param factory the factory for creating new threads. For default value,
1225	+	* use {@link #defaultForkJoinWorkerThreadFactory}.
1226	+	* @param handler the handler for internal worker threads that
1227	+	* terminate due to unrecoverable errors encountered while executing
1228	+	* tasks. For default value, use {@code null}.
1229	+	* @param asyncMode if true,
1230	+	* establishes local first-in-first-out scheduling mode for forked
1231	+	* tasks that are never joined. This mode may be more appropriate
1232	+	* than default locally stack-based mode in applications in which
1233	+	* worker threads only process event-style asynchronous tasks.
1234	+	* For default value, use {@code false}.
1235	+	* @throws IllegalArgumentException if parallelism less than or
1236	+	*         equal to zero, or greater than implementation limit
1237	+	* @throws NullPointerException if the factory is null
1238	+	* @throws SecurityException if a security manager exists and
1239	+	*         the caller is not permitted to modify threads
1240	+	*         because it does not hold {@link
1241	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1242	+	*/
1243	+	public ForkJoinPool(int parallelism,
1244	+	ForkJoinWorkerThreadFactory factory,
1245	+	Thread.UncaughtExceptionHandler handler,
1246	+	boolean asyncMode) {
1247	+	checkPermission();
1248	+	if (factory == null)
1249	+	throw new NullPointerException();
1250	+	if (parallelism <= 0 || parallelism > MAX_WORKERS)
1251	+	throw new IllegalArgumentException();
1252	+	this.parallelism = parallelism;
1253	+	this.factory = factory;
1254	+	this.ueh = handler;
1255	+	this.locallyFifo = asyncMode;
1256	+	int arraySize = initialArraySizeFor(parallelism);
1257	+	this.workers = new ForkJoinWorkerThread[arraySize];
1258	+	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1259	+	this.workerLock = new ReentrantLock();
1260	+	this.termination = new Phaser(1);
1261	+	this.poolNumber = poolNumberGenerator.incrementAndGet();
1262	+	}
1263	+
1264	+	/**
1265	+	* Returns initial power of two size for workers array.
1266	+	* @param pc the initial parallelism level
1267	+	*/
1268	+	private static int initialArraySizeFor(int pc) {
1269	+	// If possible, initially allocate enough space for one spare
1270	+	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1271	+	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1272	+	size |= size >>> 1;
1273	+	size |= size >>> 2;
1274	+	size |= size >>> 4;
1275	+	size |= size >>> 8;
1276	+	return size + 1;
1277	+	}
1278	+
1279		// Execution methods
1280
1281		/**
#	Line 551 | Line 1284 | public class ForkJoinPool extends Abstra
1284		private <T> void doSubmit(ForkJoinTask<T> task) {
1285		if (task == null)
1286		throw new NullPointerException();
1287	<	if (isShutdown())
1287	>	if (runState >= SHUTDOWN)
1288		throw new RejectedExecutionException();
556	–	if (workers == null)
557	–	ensureWorkerInitialization();
1289		submissionQueue.offer(task);
1290	<	signalIdleWorkers();
1290	>	int c; // try to increment event count -- CAS failure OK
1291	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
1292	>	helpMaintainParallelism(); // create, start, or resume some workers
1293		}
1294
1295		/**
#	Line 564 | Line 1297 | public class ForkJoinPool extends Abstra
1297		*
1298		* @param task the task
1299		* @return the task's result
1300	<	* @throws NullPointerException if task is null
1301	<	* @throws RejectedExecutionException if pool is shut down
1300	>	* @throws NullPointerException if the task is null
1301	>	* @throws RejectedExecutionException if the task cannot be
1302	>	*         scheduled for execution
1303		*/
1304		public <T> T invoke(ForkJoinTask<T> task) {
1305		doSubmit(task);
#	Line 576 | Line 1310 | public class ForkJoinPool extends Abstra
1310		* Arranges for (asynchronous) execution of the given task.
1311		*
1312		* @param task the task
1313	<	* @throws NullPointerException if task is null
1314	<	* @throws RejectedExecutionException if pool is shut down
1313	>	* @throws NullPointerException if the task is null
1314	>	* @throws RejectedExecutionException if the task cannot be
1315	>	*         scheduled for execution
1316		*/
1317		public void execute(ForkJoinTask<?> task) {
1318		doSubmit(task);
#	Line 585 | Line 1320 | public class ForkJoinPool extends Abstra
1320
1321		// AbstractExecutorService methods
1322
1323	+	/**
1324	+	* @throws NullPointerException if the task is null
1325	+	* @throws RejectedExecutionException if the task cannot be
1326	+	*         scheduled for execution
1327	+	*/
1328		public void execute(Runnable task) {
1329		ForkJoinTask<?> job;
1330		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
#	Line 594 | Line 1334 | public class ForkJoinPool extends Abstra
1334		doSubmit(job);
1335		}
1336
1337	+	/**
1338	+	* Submits a ForkJoinTask for execution.
1339	+	*
1340	+	* @param task the task to submit
1341	+	* @return the task
1342	+	* @throws NullPointerException if the task is null
1343	+	* @throws RejectedExecutionException if the task cannot be
1344	+	*         scheduled for execution
1345	+	*/
1346	+	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1347	+	doSubmit(task);
1348	+	return task;
1349	+	}
1350	+
1351	+	/**
1352	+	* @throws NullPointerException if the task is null
1353	+	* @throws RejectedExecutionException if the task cannot be
1354	+	*         scheduled for execution
1355	+	*/
1356		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1357		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1358		doSubmit(job);
1359		return job;
1360		}
1361
1362	+	/**
1363	+	* @throws NullPointerException if the task is null
1364	+	* @throws RejectedExecutionException if the task cannot be
1365	+	*         scheduled for execution
1366	+	*/
1367		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1368		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1369		doSubmit(job);
1370		return job;
1371		}
1372
1373	+	/**
1374	+	* @throws NullPointerException if the task is null
1375	+	* @throws RejectedExecutionException if the task cannot be
1376	+	*         scheduled for execution
1377	+	*/
1378		public ForkJoinTask<?> submit(Runnable task) {
1379		ForkJoinTask<?> job;
1380		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
#	Line 617 | Line 1386 | public class ForkJoinPool extends Abstra
1386		}
1387
1388		/**
1389	<	* Submits a ForkJoinTask for execution.
1390	<	*
622	<	* @param task the task to submit
623	<	* @return the task
624	<	* @throws RejectedExecutionException if the task cannot be
625	<	*         scheduled for execution
626	<	* @throws NullPointerException if the task is null
1389	>	* @throws NullPointerException       {@inheritDoc}
1390	>	* @throws RejectedExecutionException {@inheritDoc}
1391		*/
628	–	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
629	–	doSubmit(task);
630	–	return task;
631	–	}
632	–
633	–
1392		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
1393		ArrayList<ForkJoinTask<T>> forkJoinTasks =
1394		new ArrayList<ForkJoinTask<T>>(tasks.size());
#	Line 639 | Line 1397 | public class ForkJoinPool extends Abstra
1397		invoke(new InvokeAll<T>(forkJoinTasks));
1398
1399		@SuppressWarnings({"unchecked", "rawtypes"})
1400	<	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1400	>	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1401		return futures;
1402		}
1403
#	Line 653 | Line 1411 | public class ForkJoinPool extends Abstra
1411		private static final long serialVersionUID = -7914297376763021607L;
1412		}
1413
656	–	// Configuration and status settings and queries
657	–
1414		/**
1415		* Returns the factory used for constructing new workers.
1416		*
#	Line 671 | Line 1427 | public class ForkJoinPool extends Abstra
1427		* @return the handler, or {@code null} if none
1428		*/
1429		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1430	<	Thread.UncaughtExceptionHandler h;
675	<	final ReentrantLock lock = this.workerLock;
676	<	lock.lock();
677	<	try {
678	<	h = ueh;
679	<	} finally {
680	<	lock.unlock();
681	<	}
682	<	return h;
683	<	}
684	<
685	<	/**
686	<	* Sets the handler for internal worker threads that terminate due
687	<	* to unrecoverable errors encountered while executing tasks.
688	<	* Unless set, the current default or ThreadGroup handler is used
689	<	* as handler.
690	<	*
691	<	* @param h the new handler
692	<	* @return the old handler, or {@code null} if none
693	<	* @throws SecurityException if a security manager exists and
694	<	*         the caller is not permitted to modify threads
695	<	*         because it does not hold {@link
696	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
697	<	*/
698	<	public Thread.UncaughtExceptionHandler
699	<	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
700	<	checkPermission();
701	<	Thread.UncaughtExceptionHandler old = null;
702	<	final ReentrantLock lock = this.workerLock;
703	<	lock.lock();
704	<	try {
705	<	old = ueh;
706	<	ueh = h;
707	<	ForkJoinWorkerThread[] ws = workers;
708	<	if (ws != null) {
709	<	for (int i = 0; i < ws.length; ++i) {
710	<	ForkJoinWorkerThread w = ws[i];
711	<	if (w != null)
712	<	w.setUncaughtExceptionHandler(h);
713	<	}
714	<	}
715	<	} finally {
716	<	lock.unlock();
717	<	}
718	<	return old;
719	<	}
720	<
721	<
722	<	/**
723	<	* Sets the target parallelism level of this pool.
724	<	*
725	<	* @param parallelism the target parallelism
726	<	* @throws IllegalArgumentException if parallelism less than or
727	<	* equal to zero or greater than maximum size bounds
728	<	* @throws SecurityException if a security manager exists and
729	<	*         the caller is not permitted to modify threads
730	<	*         because it does not hold {@link
731	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
732	<	*/
733	<	public void setParallelism(int parallelism) {
734	<	checkPermission();
735	<	if (parallelism <= 0 || parallelism > maxPoolSize)
736	<	throw new IllegalArgumentException();
737	<	final ReentrantLock lock = this.workerLock;
738	<	lock.lock();
739	<	try {
740	<	if (!isTerminating()) {
741	<	int p = this.parallelism;
742	<	this.parallelism = parallelism;
743	<	if (parallelism > p)
744	<	createAndStartAddedWorkers();
745	<	else
746	<	trimSpares();
747	<	}
748	<	} finally {
749	<	lock.unlock();
750	<	}
751	<	signalIdleWorkers();
1430	>	return ueh;
1431		}
1432
1433		/**
1434	<	* Returns the targeted number of worker threads in this pool.
1434	>	* Returns the targeted parallelism level of this pool.
1435		*
1436	<	* @return the targeted number of worker threads in this pool
1436	>	* @return the targeted parallelism level of this pool
1437		*/
1438		public int getParallelism() {
1439		return parallelism;
#	Line 769 | Line 1448 | public class ForkJoinPool extends Abstra
1448		* @return the number of worker threads
1449		*/
1450		public int getPoolSize() {
1451	<	return totalCountOf(workerCounts);
773	<	}
774	<
775	<	/**
776	<	* Returns the maximum number of threads allowed to exist in the
777	<	* pool, even if there are insufficient unblocked running threads.
778	<	*
779	<	* @return the maximum
780	<	*/
781	<	public int getMaximumPoolSize() {
782	<	return maxPoolSize;
783	<	}
784	<
785	<	/**
786	<	* Sets the maximum number of threads allowed to exist in the
787	<	* pool, even if there are insufficient unblocked running threads.
788	<	* Setting this value has no effect on current pool size. It
789	<	* controls construction of new threads.
790	<	*
791	<	* @throws IllegalArgumentException if negative or greater than
792	<	* internal implementation limit
793	<	*/
794	<	public void setMaximumPoolSize(int newMax) {
795	<	if (newMax < 0 || newMax > MAX_THREADS)
796	<	throw new IllegalArgumentException();
797	<	maxPoolSize = newMax;
798	<	}
799	<
800	<
801	<	/**
802	<	* Returns {@code true} if this pool dynamically maintains its
803	<	* target parallelism level. If false, new threads are added only
804	<	* to avoid possible starvation.  This setting is by default true.
805	<	*
806	<	* @return {@code true} if maintains parallelism
807	<	*/
808	<	public boolean getMaintainsParallelism() {
809	<	return maintainsParallelism;
810	<	}
811	<
812	<	/**
813	<	* Sets whether this pool dynamically maintains its target
814	<	* parallelism level. If false, new threads are added only to
815	<	* avoid possible starvation.
816	<	*
817	<	* @param enable {@code true} to maintain parallelism
818	<	*/
819	<	public void setMaintainsParallelism(boolean enable) {
820	<	maintainsParallelism = enable;
821	<	}
822	<
823	<	/**
824	<	* Establishes local first-in-first-out scheduling mode for forked
825	<	* tasks that are never joined. This mode may be more appropriate
826	<	* than default locally stack-based mode in applications in which
827	<	* worker threads only process asynchronous tasks.  This method is
828	<	* designed to be invoked only when the pool is quiescent, and
829	<	* typically only before any tasks are submitted. The effects of
830	<	* invocations at other times may be unpredictable.
831	<	*
832	<	* @param async if {@code true}, use locally FIFO scheduling
833	<	* @return the previous mode
834	<	* @see #getAsyncMode
835	<	*/
836	<	public boolean setAsyncMode(boolean async) {
837	<	boolean oldMode = locallyFifo;
838	<	locallyFifo = async;
839	<	ForkJoinWorkerThread[] ws = workers;
840	<	if (ws != null) {
841	<	for (int i = 0; i < ws.length; ++i) {
842	<	ForkJoinWorkerThread t = ws[i];
843	<	if (t != null)
844	<	t.setAsyncMode(async);
845	<	}
846	<	}
847	<	return oldMode;
1451	>	return workerCounts >>> TOTAL_COUNT_SHIFT;
1452		}
1453
1454		/**
#	Line 852 | Line 1456 | public class ForkJoinPool extends Abstra
1456		* scheduling mode for forked tasks that are never joined.
1457		*
1458		* @return {@code true} if this pool uses async mode
855	–	* @see #setAsyncMode
1459		*/
1460		public boolean getAsyncMode() {
1461		return locallyFifo;
#	Line 861 | Line 1464 | public class ForkJoinPool extends Abstra
1464		/**
1465		* Returns an estimate of the number of worker threads that are
1466		* not blocked waiting to join tasks or for other managed
1467	<	* synchronization.
1467	>	* synchronization. This method may overestimate the
1468	>	* number of running threads.
1469		*
1470		* @return the number of worker threads
1471		*/
1472		public int getRunningThreadCount() {
1473	<	return runningCountOf(workerCounts);
1473	>	return workerCounts & RUNNING_COUNT_MASK;
1474		}
1475
1476		/**
#	Line 877 | Line 1481 | public class ForkJoinPool extends Abstra
1481		* @return the number of active threads
1482		*/
1483		public int getActiveThreadCount() {
1484	<	return activeCountOf(runControl);
881	<	}
882	<
883	<	/**
884	<	* Returns an estimate of the number of threads that are currently
885	<	* idle waiting for tasks. This method may underestimate the
886	<	* number of idle threads.
887	<	*
888	<	* @return the number of idle threads
889	<	*/
890	<	final int getIdleThreadCount() {
891	<	int c = runningCountOf(workerCounts) - activeCountOf(runControl);
892	<	return (c <= 0) ? 0 : c;
1484	>	return runState & ACTIVE_COUNT_MASK;
1485		}
1486
1487		/**
#	Line 904 | Line 1496 | public class ForkJoinPool extends Abstra
1496		* @return {@code true} if all threads are currently idle
1497		*/
1498		public boolean isQuiescent() {
1499	<	return activeCountOf(runControl) == 0;
1499	>	return (runState & ACTIVE_COUNT_MASK) == 0;
1500		}
1501
1502		/**
#	Line 919 | Line 1511 | public class ForkJoinPool extends Abstra
1511		* @return the number of steals
1512		*/
1513		public long getStealCount() {
1514	<	return stealCount.get();
923	<	}
924	<
925	<	/**
926	<	* Accumulates steal count from a worker.
927	<	* Call only when worker known to be idle.
928	<	*/
929	<	private void updateStealCount(ForkJoinWorkerThread w) {
930	<	int sc = w.getAndClearStealCount();
931	<	if (sc != 0)
932	<	stealCount.addAndGet(sc);
1514	>	return stealCount;
1515		}
1516
1517		/**
#	Line 944 | Line 1526 | public class ForkJoinPool extends Abstra
1526		*/
1527		public long getQueuedTaskCount() {
1528		long count = 0;
1529	<	ForkJoinWorkerThread[] ws = workers;
1530	<	if (ws != null) {
1531	<	for (int i = 0; i < ws.length; ++i) {
950	<	ForkJoinWorkerThread t = ws[i];
951	<	if (t != null)
952	<	count += t.getQueueSize();
953	<	}
954	<	}
1529	>	for (ForkJoinWorkerThread w : workers)
1530	>	if (w != null)
1531	>	count += w.getQueueSize();
1532		return count;
1533		}
1534
#	Line 991 | Line 1568 | public class ForkJoinPool extends Abstra
1568		* Removes all available unexecuted submitted and forked tasks
1569		* from scheduling queues and adds them to the given collection,
1570		* without altering their execution status. These may include
1571	<	* artificially generated or wrapped tasks. This method is designed
1572	<	* to be invoked only when the pool is known to be
1571	>	* artificially generated or wrapped tasks. This method is
1572	>	* designed to be invoked only when the pool is known to be
1573		* quiescent. Invocations at other times may not remove all
1574		* tasks. A failure encountered while attempting to add elements
1575		* to collection {@code c} may result in elements being in
#	Line 1005 | Line 1582 | public class ForkJoinPool extends Abstra
1582		* @return the number of elements transferred
1583		*/
1584		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1585	<	int n = submissionQueue.drainTo(c);
1586	<	ForkJoinWorkerThread[] ws = workers;
1587	<	if (ws != null) {
1588	<	for (int i = 0; i < ws.length; ++i) {
1589	<	ForkJoinWorkerThread w = ws[i];
1013	<	if (w != null)
1014	<	n += w.drainTasksTo(c);
1015	<	}
1016	<	}
1017	<	return n;
1585	>	int count = submissionQueue.drainTo(c);
1586	>	for (ForkJoinWorkerThread w : workers)
1587	>	if (w != null)
1588	>	count += w.drainTasksTo(c);
1589	>	return count;
1590		}
1591
1592		/**
#	Line 1025 | Line 1597 | public class ForkJoinPool extends Abstra
1597		* @return a string identifying this pool, as well as its state
1598		*/
1599		public String toString() {
1028	–	int ps = parallelism;
1029	–	int wc = workerCounts;
1030	–	int rc = runControl;
1600		long st = getStealCount();
1601		long qt = getQueuedTaskCount();
1602		long qs = getQueuedSubmissionCount();
1603	+	int wc = workerCounts;
1604	+	int tc = wc >>> TOTAL_COUNT_SHIFT;
1605	+	int rc = wc & RUNNING_COUNT_MASK;
1606	+	int pc = parallelism;
1607	+	int rs = runState;
1608	+	int ac = rs & ACTIVE_COUNT_MASK;
1609		return super.toString() +
1610	<	"[" + runStateToString(runStateOf(rc)) +
1611	<	", parallelism = " + ps +
1612	<	", size = " + totalCountOf(wc) +
1613	<	", active = " + activeCountOf(rc) +
1614	<	", running = " + runningCountOf(wc) +
1610	>	"[" + runLevelToString(rs) +
1611	>	", parallelism = " + pc +
1612	>	", size = " + tc +
1613	>	", active = " + ac +
1614	>	", running = " + rc +
1615		", steals = " + st +
1616		", tasks = " + qt +
1617		", submissions = " + qs +
1618		"]";
1619		}
1620
1621	<	private static String runStateToString(int rs) {
1622	<	switch(rs) {
1623	<	case RUNNING: return "Running";
1624	<	case SHUTDOWN: return "Shutting down";
1625	<	case TERMINATING: return "Terminating";
1051	<	case TERMINATED: return "Terminated";
1052	<	default: throw new Error("Unknown run state");
1053	<	}
1621	>	private static String runLevelToString(int s) {
1622	>	return ((s & TERMINATED) != 0 ? "Terminated" :
1623	>	((s & TERMINATING) != 0 ? "Terminating" :
1624	>	((s & SHUTDOWN) != 0 ? "Shutting down" :
1625	>	"Running")));
1626		}
1627
1056	–	// lifecycle control
1057	–
1628		/**
1629		* Initiates an orderly shutdown in which previously submitted
1630		* tasks are executed, but no new tasks will be accepted.
#	Line 1069 | Line 1639 | public class ForkJoinPool extends Abstra
1639		*/
1640		public void shutdown() {
1641		checkPermission();
1642	<	transitionRunStateTo(SHUTDOWN);
1643	<	if (canTerminateOnShutdown(runControl)) {
1074	<	if (workers == null) { // shutting down before workers created
1075	<	final ReentrantLock lock = this.workerLock;
1076	<	lock.lock();
1077	<	try {
1078	<	if (workers == null) {
1079	<	terminate();
1080	<	transitionRunStateTo(TERMINATED);
1081	<	termination.signalAll();
1082	<	}
1083	<	} finally {
1084	<	lock.unlock();
1085	<	}
1086	<	}
1087	<	terminateOnShutdown();
1088	<	}
1642	>	advanceRunLevel(SHUTDOWN);
1643	>	tryTerminate(false);
1644		}
1645
1646		/**
1647	<	* Attempts to stop all actively executing tasks, and cancels all
1648	<	* waiting tasks.  Tasks that are in the process of being
1649	<	* submitted or executed concurrently during the course of this
1650	<	* method may or may not be rejected. Unlike some other executors,
1651	<	* this method cancels rather than collects non-executed tasks
1652	<	* upon termination, so always returns an empty list. However, you
1653	<	* can use method {@link #drainTasksTo} before invoking this
1654	<	* method to transfer unexecuted tasks to another collection.
1647	>	* Attempts to cancel and/or stop all tasks, and reject all
1648	>	* subsequently submitted tasks.  Tasks that are in the process of
1649	>	* being submitted or executed concurrently during the course of
1650	>	* this method may or may not be rejected. This method cancels
1651	>	* both existing and unexecuted tasks, in order to permit
1652	>	* termination in the presence of task dependencies. So the method
1653	>	* always returns an empty list (unlike the case for some other
1654	>	* Executors).
1655		*
1656		* @return an empty list
1657		* @throws SecurityException if a security manager exists and
#	Line 1106 | Line 1661 | public class ForkJoinPool extends Abstra
1661		*/
1662		public List<Runnable> shutdownNow() {
1663		checkPermission();
1664	<	terminate();
1664	>	tryTerminate(true);
1665		return Collections.emptyList();
1666		}
1667
#	Line 1116 | Line 1671 | public class ForkJoinPool extends Abstra
1671		* @return {@code true} if all tasks have completed following shut down
1672		*/
1673		public boolean isTerminated() {
1674	<	return runStateOf(runControl) == TERMINATED;
1674	>	return runState >= TERMINATED;
1675		}
1676
1677		/**
1678		* Returns {@code true} if the process of termination has
1679	<	* commenced but possibly not yet completed.
1679	>	* commenced but not yet completed.  This method may be useful for
1680	>	* debugging. A return of {@code true} reported a sufficient
1681	>	* period after shutdown may indicate that submitted tasks have
1682	>	* ignored or suppressed interruption, causing this executor not
1683	>	* to properly terminate.
1684		*
1685	<	* @return {@code true} if terminating
1685	>	* @return {@code true} if terminating but not yet terminated
1686		*/
1687		public boolean isTerminating() {
1688	<	return runStateOf(runControl) >= TERMINATING;
1688	>	return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
1689		}
1690
1691		/**
#	Line 1135 | Line 1694 | public class ForkJoinPool extends Abstra
1694		* @return {@code true} if this pool has been shut down
1695		*/
1696		public boolean isShutdown() {
1697	<	return runStateOf(runControl) >= SHUTDOWN;
1697	>	return runState >= SHUTDOWN;
1698		}
1699
1700		/**
#	Line 1151 | Line 1710 | public class ForkJoinPool extends Abstra
1710		*/
1711		public boolean awaitTermination(long timeout, TimeUnit unit)
1712		throws InterruptedException {
1154	–	long nanos = unit.toNanos(timeout);
1155	–	final ReentrantLock lock = this.workerLock;
1156	–	lock.lock();
1157	–	try {
1158	–	for (;;) {
1159	–	if (isTerminated())
1160	–	return true;
1161	–	if (nanos <= 0)
1162	–	return false;
1163	–	nanos = termination.awaitNanos(nanos);
1164	–	}
1165	–	} finally {
1166	–	lock.unlock();
1167	–	}
1168	–	}
1169	–
1170	–	// Shutdown and termination support
1171	–
1172	–	/**
1173	–	* Callback from terminating worker. Nulls out the corresponding
1174	–	* workers slot, and if terminating, tries to terminate; else
1175	–	* tries to shrink workers array.
1176	–	*
1177	–	* @param w the worker
1178	–	*/
1179	–	final void workerTerminated(ForkJoinWorkerThread w) {
1180	–	updateStealCount(w);
1181	–	updateWorkerCount(-1);
1182	–	final ReentrantLock lock = this.workerLock;
1183	–	lock.lock();
1184	–	try {
1185	–	ForkJoinWorkerThread[] ws = workers;
1186	–	if (ws != null) {
1187	–	int idx = w.poolIndex;
1188	–	if (idx >= 0 && idx < ws.length && ws[idx] == w)
1189	–	ws[idx] = null;
1190	–	if (totalCountOf(workerCounts) == 0) {
1191	–	terminate(); // no-op if already terminating
1192	–	transitionRunStateTo(TERMINATED);
1193	–	termination.signalAll();
1194	–	}
1195	–	else if (!isTerminating()) {
1196	–	tryShrinkWorkerArray();
1197	–	tryResumeSpare(true); // allow replacement
1198	–	}
1199	–	}
1200	–	} finally {
1201	–	lock.unlock();
1202	–	}
1203	–	signalIdleWorkers();
1204	–	}
1205	–
1206	–	/**
1207	–	* Initiates termination.
1208	–	*/
1209	–	private void terminate() {
1210	–	if (transitionRunStateTo(TERMINATING)) {
1211	–	stopAllWorkers();
1212	–	resumeAllSpares();
1213	–	signalIdleWorkers();
1214	–	cancelQueuedSubmissions();
1215	–	cancelQueuedWorkerTasks();
1216	–	interruptUnterminatedWorkers();
1217	–	signalIdleWorkers(); // resignal after interrupt
1218	–	}
1219	–	}
1220	–
1221	–	/**
1222	–	* Possibly terminates when on shutdown state.
1223	–	*/
1224	–	private void terminateOnShutdown() {
1225	–	if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
1226	–	terminate();
1227	–	}
1228	–
1229	–	/**
1230	–	* Clears out and cancels submissions.
1231	–	*/
1232	–	private void cancelQueuedSubmissions() {
1233	–	ForkJoinTask<?> task;
1234	–	while ((task = pollSubmission()) != null)
1235	–	task.cancel(false);
1236	–	}
1237	–
1238	–	/**
1239	–	* Cleans out worker queues.
1240	–	*/
1241	–	private void cancelQueuedWorkerTasks() {
1242	–	final ReentrantLock lock = this.workerLock;
1243	–	lock.lock();
1713		try {
1714	<	ForkJoinWorkerThread[] ws = workers;
1715	<	if (ws != null) {
1247	<	for (int i = 0; i < ws.length; ++i) {
1248	<	ForkJoinWorkerThread t = ws[i];
1249	<	if (t != null)
1250	<	t.cancelTasks();
1251	<	}
1252	<	}
1253	<	} finally {
1254	<	lock.unlock();
1255	<	}
1256	<	}
1257	<
1258	<	/**
1259	<	* Sets each worker's status to terminating. Requires lock to avoid
1260	<	* conflicts with add/remove.
1261	<	*/
1262	<	private void stopAllWorkers() {
1263	<	final ReentrantLock lock = this.workerLock;
1264	<	lock.lock();
1265	<	try {
1266	<	ForkJoinWorkerThread[] ws = workers;
1267	<	if (ws != null) {
1268	<	for (int i = 0; i < ws.length; ++i) {
1269	<	ForkJoinWorkerThread t = ws[i];
1270	<	if (t != null)
1271	<	t.shutdownNow();
1272	<	}
1273	<	}
1274	<	} finally {
1275	<	lock.unlock();
1276	<	}
1277	<	}
1278	<
1279	<	/**
1280	<	* Interrupts all unterminated workers.  This is not required for
1281	<	* sake of internal control, but may help unstick user code during
1282	<	* shutdown.
1283	<	*/
1284	<	private void interruptUnterminatedWorkers() {
1285	<	final ReentrantLock lock = this.workerLock;
1286	<	lock.lock();
1287	<	try {
1288	<	ForkJoinWorkerThread[] ws = workers;
1289	<	if (ws != null) {
1290	<	for (int i = 0; i < ws.length; ++i) {
1291	<	ForkJoinWorkerThread t = ws[i];
1292	<	if (t != null && !t.isTerminated()) {
1293	<	try {
1294	<	t.interrupt();
1295	<	} catch (SecurityException ignore) {
1296	<	}
1297	<	}
1298	<	}
1299	<	}
1300	<	} finally {
1301	<	lock.unlock();
1302	<	}
1303	<	}
1304	<
1305	<
1306	<	/*
1307	<	* Nodes for event barrier to manage idle threads.  Queue nodes
1308	<	* are basic Treiber stack nodes, also used for spare stack.
1309	<	*
1310	<	* The event barrier has an event count and a wait queue (actually
1311	<	* a Treiber stack).  Workers are enabled to look for work when
1312	<	* the eventCount is incremented. If they fail to find work, they
1313	<	* may wait for next count. Upon release, threads help others wake
1314	<	* up.
1315	<	*
1316	<	* Synchronization events occur only in enough contexts to
1317	<	* maintain overall liveness:
1318	<	*
1319	<	*   - Submission of a new task to the pool
1320	<	*   - Resizes or other changes to the workers array
1321	<	*   - pool termination
1322	<	*   - A worker pushing a task on an empty queue
1323	<	*
1324	<	* The case of pushing a task occurs often enough, and is heavy
1325	<	* enough compared to simple stack pushes, to require special
1326	<	* handling: Method signalWork returns without advancing count if
1327	<	* the queue appears to be empty.  This would ordinarily result in
1328	<	* races causing some queued waiters not to be woken up. To avoid
1329	<	* this, the first worker enqueued in method sync (see
1330	<	* syncIsReleasable) rescans for tasks after being enqueued, and
1331	<	* helps signal if any are found. This works well because the
1332	<	* worker has nothing better to do, and so might as well help
1333	<	* alleviate the overhead and contention on the threads actually
1334	<	* doing work.  Also, since event counts increments on task
1335	<	* availability exist to maintain liveness (rather than to force
1336	<	* refreshes etc), it is OK for callers to exit early if
1337	<	* contending with another signaller.
1338	<	*/
1339	<	static final class WaitQueueNode {
1340	<	WaitQueueNode next; // only written before enqueued
1341	<	volatile ForkJoinWorkerThread thread; // nulled to cancel wait
1342	<	final long count; // unused for spare stack
1343	<
1344	<	WaitQueueNode(long c, ForkJoinWorkerThread w) {
1345	<	count = c;
1346	<	thread = w;
1347	<	}
1348	<
1349	<	/**
1350	<	* Wakes up waiter, returning false if known to already
1351	<	*/
1352	<	boolean signal() {
1353	<	ForkJoinWorkerThread t = thread;
1354	<	if (t == null)
1355	<	return false;
1356	<	thread = null;
1357	<	LockSupport.unpark(t);
1358	<	return true;
1359	<	}
1360	<
1361	<	/**
1362	<	* Awaits release on sync.
1363	<	*/
1364	<	void awaitSyncRelease(ForkJoinPool p) {
1365	<	while (thread != null && !p.syncIsReleasable(this))
1366	<	LockSupport.park(this);
1367	<	}
1368	<
1369	<	/**
1370	<	* Awaits resumption as spare.
1371	<	*/
1372	<	void awaitSpareRelease() {
1373	<	while (thread != null) {
1374	<	if (!Thread.interrupted())
1375	<	LockSupport.park(this);
1376	<	}
1377	<	}
1378	<	}
1379	<
1380	<	/**
1381	<	* Ensures that no thread is waiting for count to advance from the
1382	<	* current value of eventCount read on entry to this method, by
1383	<	* releasing waiting threads if necessary.
1384	<	*
1385	<	* @return the count
1386	<	*/
1387	<	final long ensureSync() {
1388	<	long c = eventCount;
1389	<	WaitQueueNode q;
1390	<	while ((q = syncStack) != null && q.count < c) {
1391	<	if (casBarrierStack(q, null)) {
1392	<	do {
1393	<	q.signal();
1394	<	} while ((q = q.next) != null);
1395	<	break;
1396	<	}
1397	<	}
1398	<	return c;
1399	<	}
1400	<
1401	<	/**
1402	<	* Increments event count and releases waiting threads.
1403	<	*/
1404	<	private void signalIdleWorkers() {
1405	<	long c;
1406	<	do {} while (!casEventCount(c = eventCount, c+1));
1407	<	ensureSync();
1408	<	}
1409	<
1410	<	/**
1411	<	* Signals threads waiting to poll a task. Because method sync
1412	<	* rechecks availability, it is OK to only proceed if queue
1413	<	* appears to be non-empty, and OK to skip under contention to
1414	<	* increment count (since some other thread succeeded).
1415	<	*/
1416	<	final void signalWork() {
1417	<	long c;
1418	<	WaitQueueNode q;
1419	<	if (syncStack != null &&
1420	<	casEventCount(c = eventCount, c+1) &&
1421	<	(((q = syncStack) != null && q.count <= c) &&
1422	<	(!casBarrierStack(q, q.next) || !q.signal())))
1423	<	ensureSync();
1424	<	}
1425	<
1426	<	/**
1427	<	* Waits until event count advances from last value held by
1428	<	* caller, or if excess threads, caller is resumed as spare, or
1429	<	* caller or pool is terminating. Updates caller's event on exit.
1430	<	*
1431	<	* @param w the calling worker thread
1432	<	*/
1433	<	final void sync(ForkJoinWorkerThread w) {
1434	<	updateStealCount(w); // Transfer w's count while it is idle
1435	<
1436	<	while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
1437	<	long prev = w.lastEventCount;
1438	<	WaitQueueNode node = null;
1439	<	WaitQueueNode h;
1440	<	while (eventCount == prev &&
1441	<	((h = syncStack) == null || h.count == prev)) {
1442	<	if (node == null)
1443	<	node = new WaitQueueNode(prev, w);
1444	<	if (casBarrierStack(node.next = h, node)) {
1445	<	node.awaitSyncRelease(this);
1446	<	break;
1447	<	}
1448	<	}
1449	<	long ec = ensureSync();
1450	<	if (ec != prev) {
1451	<	w.lastEventCount = ec;
1452	<	break;
1453	<	}
1454	<	}
1455	<	}
1456	<
1457	<	/**
1458	<	* Returns {@code true} if worker waiting on sync can proceed:
1459	<	*  - on signal (thread == null)
1460	<	*  - on event count advance (winning race to notify vs signaller)
1461	<	*  - on interrupt
1462	<	*  - if the first queued node, we find work available
1463	<	* If node was not signalled and event count not advanced on exit,
1464	<	* then we also help advance event count.
1465	<	*
1466	<	* @return {@code true} if node can be released
1467	<	*/
1468	<	final boolean syncIsReleasable(WaitQueueNode node) {
1469	<	long prev = node.count;
1470	<	if (!Thread.interrupted() && node.thread != null &&
1471	<	(node.next != null ||
1472	<	!ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
1473	<	eventCount == prev)
1474	<	return false;
1475	<	if (node.thread != null) {
1476	<	node.thread = null;
1477	<	long ec = eventCount;
1478	<	if (prev <= ec) // help signal
1479	<	casEventCount(ec, ec+1);
1480	<	}
1481	<	return true;
1482	<	}
1483	<
1484	<	/**
1485	<	* Returns {@code true} if a new sync event occurred since last
1486	<	* call to sync or this method, if so, updating caller's count.
1487	<	*/
1488	<	final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1489	<	long lc = w.lastEventCount;
1490	<	long ec = ensureSync();
1491	<	if (ec == lc)
1714	>	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1715	>	} catch (TimeoutException ex) {
1716		return false;
1493	–	w.lastEventCount = ec;
1494	–	return true;
1495	–	}
1496	–
1497	–	//  Parallelism maintenance
1498	–
1499	–	/**
1500	–	* Decrements running count; if too low, adds spare.
1501	–	*
1502	–	* Conceptually, all we need to do here is add or resume a
1503	–	* spare thread when one is about to block (and remove or
1504	–	* suspend it later when unblocked -- see suspendIfSpare).
1505	–	* However, implementing this idea requires coping with
1506	–	* several problems: we have imperfect information about the
1507	–	* states of threads. Some count updates can and usually do
1508	–	* lag run state changes, despite arrangements to keep them
1509	–	* accurate (for example, when possible, updating counts
1510	–	* before signalling or resuming), especially when running on
1511	–	* dynamic JVMs that don't optimize the infrequent paths that
1512	–	* update counts. Generating too many threads can make these
1513	–	* problems become worse, because excess threads are more
1514	–	* likely to be context-switched with others, slowing them all
1515	–	* down, especially if there is no work available, so all are
1516	–	* busy scanning or idling.  Also, excess spare threads can
1517	–	* only be suspended or removed when they are idle, not
1518	–	* immediately when they aren't needed. So adding threads will
1519	–	* raise parallelism level for longer than necessary.  Also,
1520	–	* FJ applications often encounter highly transient peaks when
1521	–	* many threads are blocked joining, but for less time than it
1522	–	* takes to create or resume spares.
1523	–	*
1524	–	* @param joinMe if non-null, return early if done
1525	–	* @param maintainParallelism if true, try to stay within
1526	–	* target counts, else create only to avoid starvation
1527	–	* @return true if joinMe known to be done
1528	–	*/
1529	–	final boolean preJoin(ForkJoinTask<?> joinMe,
1530	–	boolean maintainParallelism) {
1531	–	maintainParallelism &= maintainsParallelism; // overrride
1532	–	boolean dec = false;  // true when running count decremented
1533	–	while (spareStack == null || !tryResumeSpare(dec)) {
1534	–	int counts = workerCounts;
1535	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1536	–	// CAS cheat
1537	–	if (!needSpare(counts, maintainParallelism))
1538	–	break;
1539	–	if (joinMe.status < 0)
1540	–	return true;
1541	–	if (tryAddSpare(counts))
1542	–	break;
1543	–	}
1544	–	}
1545	–	return false;
1546	–	}
1547	–
1548	–	/**
1549	–	* Same idea as preJoin
1550	–	*/
1551	–	final boolean preBlock(ManagedBlocker blocker,
1552	–	boolean maintainParallelism) {
1553	–	maintainParallelism &= maintainsParallelism;
1554	–	boolean dec = false;
1555	–	while (spareStack == null || !tryResumeSpare(dec)) {
1556	–	int counts = workerCounts;
1557	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1558	–	if (!needSpare(counts, maintainParallelism))
1559	–	break;
1560	–	if (blocker.isReleasable())
1561	–	return true;
1562	–	if (tryAddSpare(counts))
1563	–	break;
1564	–	}
1565	–	}
1566	–	return false;
1567	–	}
1568	–
1569	–	/**
1570	–	* Returns {@code true} if a spare thread appears to be needed.
1571	–	* If maintaining parallelism, returns true when the deficit in
1572	–	* running threads is more than the surplus of total threads, and
1573	–	* there is apparently some work to do.  This self-limiting rule
1574	–	* means that the more threads that have already been added, the
1575	–	* less parallelism we will tolerate before adding another.
1576	–	*
1577	–	* @param counts current worker counts
1578	–	* @param maintainParallelism try to maintain parallelism
1579	–	*/
1580	–	private boolean needSpare(int counts, boolean maintainParallelism) {
1581	–	int ps = parallelism;
1582	–	int rc = runningCountOf(counts);
1583	–	int tc = totalCountOf(counts);
1584	–	int runningDeficit = ps - rc;
1585	–	int totalSurplus = tc - ps;
1586	–	return (tc < maxPoolSize &&
1587	–	(rc == 0 || totalSurplus < 0 ||
1588	–	(maintainParallelism &&
1589	–	runningDeficit > totalSurplus &&
1590	–	ForkJoinWorkerThread.hasQueuedTasks(workers))));
1591	–	}
1592	–
1593	–	/**
1594	–	* Adds a spare worker if lock available and no more than the
1595	–	* expected numbers of threads exist.
1596	–	*
1597	–	* @return true if successful
1598	–	*/
1599	–	private boolean tryAddSpare(int expectedCounts) {
1600	–	final ReentrantLock lock = this.workerLock;
1601	–	int expectedRunning = runningCountOf(expectedCounts);
1602	–	int expectedTotal = totalCountOf(expectedCounts);
1603	–	boolean success = false;
1604	–	boolean locked = false;
1605	–	// confirm counts while locking; CAS after obtaining lock
1606	–	try {
1607	–	for (;;) {
1608	–	int s = workerCounts;
1609	–	int tc = totalCountOf(s);
1610	–	int rc = runningCountOf(s);
1611	–	if (rc > expectedRunning || tc > expectedTotal)
1612	–	break;
1613	–	if (!locked && !(locked = lock.tryLock()))
1614	–	break;
1615	–	if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
1616	–	createAndStartSpare(tc);
1617	–	success = true;
1618	–	break;
1619	–	}
1620	–	}
1621	–	} finally {
1622	–	if (locked)
1623	–	lock.unlock();
1624	–	}
1625	–	return success;
1626	–	}
1627	–
1628	–	/**
1629	–	* Adds the kth spare worker. On entry, pool counts are already
1630	–	* adjusted to reflect addition.
1631	–	*/
1632	–	private void createAndStartSpare(int k) {
1633	–	ForkJoinWorkerThread w = null;
1634	–	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
1635	–	int len = ws.length;
1636	–	// Probably, we can place at slot k. If not, find empty slot
1637	–	if (k < len && ws[k] != null) {
1638	–	for (k = 0; k < len && ws[k] != null; ++k)
1639	–	;
1640	–	}
1641	–	if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
1642	–	ws[k] = w;
1643	–	w.start();
1644	–	}
1645	–	else
1646	–	updateWorkerCount(-1); // adjust on failure
1647	–	signalIdleWorkers();
1648	–	}
1649	–
1650	–	/**
1651	–	* Suspends calling thread w if there are excess threads.  Called
1652	–	* only from sync.  Spares are enqueued in a Treiber stack using
1653	–	* the same WaitQueueNodes as barriers.  They are resumed mainly
1654	–	* in preJoin, but are also woken on pool events that require all
1655	–	* threads to check run state.
1656	–	*
1657	–	* @param w the caller
1658	–	*/
1659	–	private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1660	–	WaitQueueNode node = null;
1661	–	int s;
1662	–	while (parallelism < runningCountOf(s = workerCounts)) {
1663	–	if (node == null)
1664	–	node = new WaitQueueNode(0, w);
1665	–	if (casWorkerCounts(s, s-1)) { // representation-dependent
1666	–	// push onto stack
1667	–	do {} while (!casSpareStack(node.next = spareStack, node));
1668	–	// block until released by resumeSpare
1669	–	node.awaitSpareRelease();
1670	–	return true;
1671	–	}
1672	–	}
1673	–	return false;
1674	–	}
1675	–
1676	–	/**
1677	–	* Tries to pop and resume a spare thread.
1678	–	*
1679	–	* @param updateCount if true, increment running count on success
1680	–	* @return true if successful
1681	–	*/
1682	–	private boolean tryResumeSpare(boolean updateCount) {
1683	–	WaitQueueNode q;
1684	–	while ((q = spareStack) != null) {
1685	–	if (casSpareStack(q, q.next)) {
1686	–	if (updateCount)
1687	–	updateRunningCount(1);
1688	–	q.signal();
1689	–	return true;
1690	–	}
1691	–	}
1692	–	return false;
1693	–	}
1694	–
1695	–	/**
1696	–	* Pops and resumes all spare threads. Same idea as ensureSync.
1697	–	*
1698	–	* @return true if any spares released
1699	–	*/
1700	–	private boolean resumeAllSpares() {
1701	–	WaitQueueNode q;
1702	–	while ( (q = spareStack) != null) {
1703	–	if (casSpareStack(q, null)) {
1704	–	do {
1705	–	updateRunningCount(1);
1706	–	q.signal();
1707	–	} while ((q = q.next) != null);
1708	–	return true;
1709	–	}
1710	–	}
1711	–	return false;
1712	–	}
1713	–
1714	–	/**
1715	–	* Pops and shuts down excessive spare threads. Call only while
1716	–	* holding lock. This is not guaranteed to eliminate all excess
1717	–	* threads, only those suspended as spares, which are the ones
1718	–	* unlikely to be needed in the future.
1719	–	*/
1720	–	private void trimSpares() {
1721	–	int surplus = totalCountOf(workerCounts) - parallelism;
1722	–	WaitQueueNode q;
1723	–	while (surplus > 0 && (q = spareStack) != null) {
1724	–	if (casSpareStack(q, null)) {
1725	–	do {
1726	–	updateRunningCount(1);
1727	–	ForkJoinWorkerThread w = q.thread;
1728	–	if (w != null && surplus > 0 &&
1729	–	runningCountOf(workerCounts) > 0 && w.shutdown())
1730	–	--surplus;
1731	–	q.signal();
1732	–	} while ((q = q.next) != null);
1733	–	}
1717		}
1718		}
1719
#	Line 1738 | Line 1721 | public class ForkJoinPool extends Abstra
1721		* Interface for extending managed parallelism for tasks running
1722		* in {@link ForkJoinPool}s.
1723		*
1724	<	* <p>A {@code ManagedBlocker} provides two methods.
1725	<	* Method {@code isReleasable} must return {@code true} if
1726	<	* blocking is not necessary. Method {@code block} blocks the
1727	<	* current thread if necessary (perhaps internally invoking
1728	<	* {@code isReleasable} before actually blocking).
1724	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1725	>	* {@code isReleasable} must return {@code true} if blocking is
1726	>	* not necessary. Method {@code block} blocks the current thread
1727	>	* if necessary (perhaps internally invoking {@code isReleasable}
1728	>	* before actually blocking). The unusual methods in this API
1729	>	* accommodate synchronizers that may, but don't usually, block
1730	>	* for long periods. Similarly, they allow more efficient internal
1731	>	* handling of cases in which additional workers may be, but
1732	>	* usually are not, needed to ensure sufficient parallelism.
1733	>	* Toward this end, implementations of method {@code isReleasable}
1734	>	* must be amenable to repeated invocation.
1735		*
1736		* <p>For example, here is a ManagedBlocker based on a
1737		* ReentrantLock:
#	Line 1760 | Line 1749 | public class ForkJoinPool extends Abstra
1749		*     return hasLock || (hasLock = lock.tryLock());
1750		*   }
1751		* }}</pre>
1752	+	*
1753	+	* <p>Here is a class that possibly blocks waiting for an
1754	+	* item on a given queue:
1755	+	*  <pre> {@code
1756	+	* class QueueTaker<E> implements ManagedBlocker {
1757	+	*   final BlockingQueue<E> queue;
1758	+	*   volatile E item = null;
1759	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1760	+	*   public boolean block() throws InterruptedException {
1761	+	*     if (item == null)
1762	+	*       item = queue.take();
1763	+	*     return true;
1764	+	*   }
1765	+	*   public boolean isReleasable() {
1766	+	*     return item != null || (item = queue.poll()) != null;
1767	+	*   }
1768	+	*   public E getItem() { // call after pool.managedBlock completes
1769	+	*     return item;
1770	+	*   }
1771	+	* }}</pre>
1772		*/
1773		public static interface ManagedBlocker {
1774		/**
#	Line 1783 | Line 1792 | public class ForkJoinPool extends Abstra
1792		* Blocks in accord with the given blocker.  If the current thread
1793		* is a {@link ForkJoinWorkerThread}, this method possibly
1794		* arranges for a spare thread to be activated if necessary to
1795	<	* ensure parallelism while the current thread is blocked.
1787	<	*
1788	<	* <p>If {@code maintainParallelism} is {@code true} and the pool
1789	<	* supports it ({@link #getMaintainsParallelism}), this method
1790	<	* attempts to maintain the pool's nominal parallelism. Otherwise
1791	<	* it activates a thread only if necessary to avoid complete
1792	<	* starvation. This option may be preferable when blockages use
1793	<	* timeouts, or are almost always brief.
1795	>	* ensure sufficient parallelism while the current thread is blocked.
1796		*
1797		* <p>If the caller is not a {@link ForkJoinTask}, this method is
1798		* behaviorally equivalent to
#	Line 1804 | Line 1806 | public class ForkJoinPool extends Abstra
1806		* first be expanded to ensure parallelism, and later adjusted.
1807		*
1808		* @param blocker the blocker
1807	–	* @param maintainParallelism if {@code true} and supported by
1808	–	* this pool, attempt to maintain the pool's nominal parallelism;
1809	–	* otherwise activate a thread only if necessary to avoid
1810	–	* complete starvation.
1809		* @throws InterruptedException if blocker.block did so
1810		*/
1811	<	public static void managedBlock(ManagedBlocker blocker,
1814	<	boolean maintainParallelism)
1811	>	public static void managedBlock(ManagedBlocker blocker)
1812		throws InterruptedException {
1813		Thread t = Thread.currentThread();
1814	<	ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
1815	<	((ForkJoinWorkerThread) t).pool : null);
1816	<	if (!blocker.isReleasable()) {
1817	<	try {
1818	<	if (pool == null ||
1819	<	!pool.preBlock(blocker, maintainParallelism))
1823	<	awaitBlocker(blocker);
1824	<	} finally {
1825	<	if (pool != null)
1826	<	pool.updateRunningCount(1);
1827	<	}
1814	>	if (t instanceof ForkJoinWorkerThread) {
1815	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1816	>	w.pool.awaitBlocker(blocker);
1817	>	}
1818	>	else {
1819	>	do {} while (!blocker.isReleasable() && !blocker.block());
1820		}
1829	–	}
1830	–
1831	–	private static void awaitBlocker(ManagedBlocker blocker)
1832	–	throws InterruptedException {
1833	–	do {} while (!blocker.isReleasable() && !blocker.block());
1821		}
1822
1823		// AbstractExecutorService overrides.  These rely on undocumented
#	Line 1848 | Line 1835 | public class ForkJoinPool extends Abstra
1835		// Unsafe mechanics
1836
1837		private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1851	–	private static final long eventCountOffset =
1852	–	objectFieldOffset("eventCount", ForkJoinPool.class);
1838		private static final long workerCountsOffset =
1839		objectFieldOffset("workerCounts", ForkJoinPool.class);
1840	<	private static final long runControlOffset =
1841	<	objectFieldOffset("runControl", ForkJoinPool.class);
1842	<	private static final long syncStackOffset =
1843	<	objectFieldOffset("syncStack",ForkJoinPool.class);
1844	<	private static final long spareStackOffset =
1845	<	objectFieldOffset("spareStack", ForkJoinPool.class);
1846	<
1847	<	private boolean casEventCount(long cmp, long val) {
1848	<	return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
1849	<	}
1865	<	private boolean casWorkerCounts(int cmp, int val) {
1866	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
1867	<	}
1868	<	private boolean casRunControl(int cmp, int val) {
1869	<	return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
1870	<	}
1871	<	private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
1872	<	return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
1873	<	}
1874	<	private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
1875	<	return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
1876	<	}
1840	>	private static final long runStateOffset =
1841	>	objectFieldOffset("runState", ForkJoinPool.class);
1842	>	private static final long eventCountOffset =
1843	>	objectFieldOffset("eventCount", ForkJoinPool.class);
1844	>	private static final long eventWaitersOffset =
1845	>	objectFieldOffset("eventWaiters",ForkJoinPool.class);
1846	>	private static final long stealCountOffset =
1847	>	objectFieldOffset("stealCount",ForkJoinPool.class);
1848	>	private static final long spareWaitersOffset =
1849	>	objectFieldOffset("spareWaiters",ForkJoinPool.class);
1850
1851		private static long objectFieldOffset(String field, Class<?> klazz) {
1852		try {

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