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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.56 by dl, Thu May 27 16:46:48 2010 UTC vs.
Revision 1.80 by dl, Fri Sep 17 14:24:56 2010 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.util.ArrayList;
10		import java.util.Arrays;
11		import java.util.Collection;
12		import java.util.Collections;
13		import java.util.List;
14	+	import java.util.concurrent.AbstractExecutorService;
15	+	import java.util.concurrent.Callable;
16	+	import java.util.concurrent.ExecutorService;
17	+	import java.util.concurrent.Future;
18	+	import java.util.concurrent.RejectedExecutionException;
19	+	import java.util.concurrent.RunnableFuture;
20	+	import java.util.concurrent.TimeUnit;
21	+	import java.util.concurrent.TimeoutException;
22	+	import java.util.concurrent.atomic.AtomicInteger;
23		import java.util.concurrent.locks.LockSupport;
24		import java.util.concurrent.locks.ReentrantLock;
18	–	import java.util.concurrent.atomic.AtomicInteger;
19	–	import java.util.concurrent.CountDownLatch;
25
26		/**
27		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
28		* A {@code ForkJoinPool} provides the entry point for submissions
29	<	* from non-{@code ForkJoinTask}s, as well as management and
29	>	* from non-{@code ForkJoinTask} clients, as well as management and
30		* monitoring operations.
31		*
32		* <p>A {@code ForkJoinPool} differs from other kinds of {@link
#	Line 30 | Line 35 | import java.util.concurrent.CountDownLat
35		* execute subtasks created by other active tasks (eventually blocking
36		* waiting for work if none exist). This enables efficient processing
37		* when most tasks spawn other subtasks (as do most {@code
38	<	* ForkJoinTask}s). A {@code ForkJoinPool} may also be used for mixed
39	<	* execution of some plain {@code Runnable}- or {@code Callable}-
40	<	* based activities along with {@code ForkJoinTask}s. When setting
36	<	* {@linkplain #setAsyncMode async mode}, a {@code ForkJoinPool} may
37	<	* also be appropriate for use with fine-grained tasks of any form
38	<	* that are never joined. Otherwise, other {@code ExecutorService}
39	<	* implementations are typically more appropriate choices.
38	>	* ForkJoinTask}s). When setting <em>asyncMode</em> to true in
39	>	* constructors, {@code ForkJoinPool}s may also be appropriate for use
40	>	* with event-style tasks that are never joined.
41		*
42		* <p>A {@code ForkJoinPool} is constructed with a given target
43		* parallelism level; by default, equal to the number of available
44	<	* processors. Unless configured otherwise via {@link
45	<	* #setMaintainsParallelism}, the pool attempts to maintain this
46	<	* number of active (or available) threads by dynamically adding,
47	<	* suspending, or resuming internal worker threads, even if some tasks
48	<	* are stalled waiting to join others. However, no such adjustments
49	<	* are performed in the face of blocked IO or other unmanaged
50	<	* synchronization. The nested {@link ManagedBlocker} interface
50	<	* enables extension of the kinds of synchronization accommodated.
51	<	* The target parallelism level may also be changed dynamically
52	<	* ({@link #setParallelism}). The total number of threads may be
53	<	* limited using method {@link #setMaximumPoolSize}, in which case it
54	<	* may become possible for the activities of a pool to stall due to
55	<	* the lack of available threads to process new tasks. When the pool
56	<	* is executing tasks, these and other configuration setting methods
57	<	* may only gradually affect actual pool sizes. It is normally best
58	<	* practice to invoke these methods only when the pool is known to be
59	<	* quiescent.
44	>	* processors. The pool attempts to maintain enough active (or
45	>	* available) threads by dynamically adding, suspending, or resuming
46	>	* internal worker threads, even if some tasks are stalled waiting to
47	>	* join others. However, no such adjustments are guaranteed in the
48	>	* face of blocked IO or other unmanaged synchronization. The nested
49	>	* {@link ManagedBlocker} interface enables extension of the kinds of
50	>	* synchronization accommodated.
51		*
52		* <p>In addition to execution and lifecycle control methods, this
53		* class provides status check methods (for example
#	Line 65 | Line 56 | import java.util.concurrent.CountDownLat
56		* {@link #toString} returns indications of pool state in a
57		* convenient form for informal monitoring.
58		*
59	+	* <p> As is the case with other ExecutorServices, there are three
60	+	* main task execution methods summarized in the following
61	+	* table. These are designed to be used by clients not already engaged
62	+	* in fork/join computations in the current pool.  The main forms of
63	+	* these methods accept instances of {@code ForkJoinTask}, but
64	+	* overloaded forms also allow mixed execution of plain {@code
65	+	* Runnable}- or {@code Callable}- based activities as well.  However,
66	+	* tasks that are already executing in a pool should normally
67	+	* <em>NOT</em> use these pool execution methods, but instead use the
68	+	* within-computation forms listed in the table.
69	+	*
70	+	* <table BORDER CELLPADDING=3 CELLSPACING=1>
71	+	*  <tr>
72	+	*    <td></td>
73	+	*    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
74	+	*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
75	+	*  </tr>
76	+	*  <tr>
77	+	*    <td> <b>Arrange async execution</td>
78	+	*    <td> {@link #execute(ForkJoinTask)}</td>
79	+	*    <td> {@link ForkJoinTask#fork}</td>
80	+	*  </tr>
81	+	*  <tr>
82	+	*    <td> <b>Await and obtain result</td>
83	+	*    <td> {@link #invoke(ForkJoinTask)}</td>
84	+	*    <td> {@link ForkJoinTask#invoke}</td>
85	+	*  </tr>
86	+	*  <tr>
87	+	*    <td> <b>Arrange exec and obtain Future</td>
88	+	*    <td> {@link #submit(ForkJoinTask)}</td>
89	+	*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
90	+	*  </tr>
91	+	* </table>
92	+	*
93		* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
94		* used for all parallel task execution in a program or subsystem.
95		* Otherwise, use would not usually outweigh the construction and
#	Line 89 | Line 114 | import java.util.concurrent.CountDownLat
114		* {@code IllegalArgumentException}.
115		*
116		* <p>This implementation rejects submitted tasks (that is, by throwing
117	<	* {@link RejectedExecutionException}) only when the pool is shut down.
117	>	* {@link RejectedExecutionException}) only when the pool is shut down
118	>	* or internal resources have been exhausted.
119		*
120		* @since 1.7
121		* @author Doug Lea
#	Line 116 | Line 142 | public class ForkJoinPool extends Abstra
142		* of tasks profit from cache affinities, but others are harmed by
143		* cache pollution effects.)
144		*
145	+	* Beyond work-stealing support and essential bookkeeping, the
146	+	* main responsibility of this framework is to take actions when
147	+	* one worker is waiting to join a task stolen (or always held by)
148	+	* another.  Because we are multiplexing many tasks on to a pool
149	+	* of workers, we can't just let them block (as in Thread.join).
150	+	* We also cannot just reassign the joiner's run-time stack with
151	+	* another and replace it later, which would be a form of
152	+	* "continuation", that even if possible is not necessarily a good
153	+	* idea. Given that the creation costs of most threads on most
154	+	* systems mainly surrounds setting up runtime stacks, thread
155	+	* creation and switching is usually not much more expensive than
156	+	* stack creation and switching, and is more flexible). Instead we
157	+	* combine two tactics:
158	+	*
159	+	*   Helping: Arranging for the joiner to execute some task that it
160	+	*      would be running if the steal had not occurred.  Method
161	+	*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
162	+	*      links to try to find such a task.
163	+	*
164	+	*   Compensating: Unless there are already enough live threads,
165	+	*      method helpMaintainParallelism() may create or
166	+	*      re-activate a spare thread to compensate for blocked
167	+	*      joiners until they unblock.
168	+	*
169	+	* It is impossible to keep exactly the target (parallelism)
170	+	* number of threads running at any given time.  Determining
171	+	* existence of conservatively safe helping targets, the
172	+	* availability of already-created spares, and the apparent need
173	+	* to create new spares are all racy and require heuristic
174	+	* guidance, so we rely on multiple retries of each.  Compensation
175	+	* occurs in slow-motion. It is triggered only upon timeouts of
176	+	* Object.wait used for joins. This reduces poor decisions that
177	+	* would otherwise be made when threads are waiting for others
178	+	* that are stalled because of unrelated activities such as
179	+	* garbage collection.
180	+	*
181	+	* The ManagedBlocker extension API can't use helping so relies
182	+	* only on compensation in method awaitBlocker.
183	+	*
184		* The main throughput advantages of work-stealing stem from
185		* decentralized control -- workers mostly steal tasks from each
186		* other. We do not want to negate this by creating bottlenecks
187	<	* implementing the management responsibilities of this class. So
188	<	* we use a collection of techniques that avoid, reduce, or cope
189	<	* well with contention. These entail several instances of
190	<	* bit-packing into CASable fields to maintain only the minimally
191	<	* required atomicity. To enable such packing, we restrict maximum
192	<	* parallelism to (1<<15)-1 (enabling twice this to fit into a 16
193	<	* bit field), which is far in excess of normal operating range.
194	<	* Even though updates to some of these bookkeeping fields do
195	<	* sometimes contend with each other, they don't normally
196	<	* cache-contend with updates to others enough to warrant memory
197	<	* padding or isolation. So they are all held as fields of
198	<	* ForkJoinPool objects.  The main capabilities are as follows:
187	>	* implementing other management responsibilities. So we use a
188	>	* collection of techniques that avoid, reduce, or cope well with
189	>	* contention. These entail several instances of bit-packing into
190	>	* CASable fields to maintain only the minimally required
191	>	* atomicity. To enable such packing, we restrict maximum
192	>	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
193	>	* unbalanced increments and decrements) to fit into a 16 bit
194	>	* field, which is far in excess of normal operating range.  Even
195	>	* though updates to some of these bookkeeping fields do sometimes
196	>	* contend with each other, they don't normally cache-contend with
197	>	* updates to others enough to warrant memory padding or
198	>	* isolation. So they are all held as fields of ForkJoinPool
199	>	* objects.  The main capabilities are as follows:
200		*
201		* 1. Creating and removing workers. Workers are recorded in the
202		* "workers" array. This is an array as opposed to some other data
#	Line 146 | Line 212 | public class ForkJoinPool extends Abstra
212		* blocked workers. However, all other support code is set up to
213		* work with other policies.
214		*
215	+	* To ensure that we do not hold on to worker references that
216	+	* would prevent GC, ALL accesses to workers are via indices into
217	+	* the workers array (which is one source of some of the unusual
218	+	* code constructions here). In essence, the workers array serves
219	+	* as a WeakReference mechanism. Thus for example the event queue
220	+	* stores worker indices, not worker references. Access to the
221	+	* workers in associated methods (for example releaseEventWaiters)
222	+	* must both index-check and null-check the IDs. All such accesses
223	+	* ignore bad IDs by returning out early from what they are doing,
224	+	* since this can only be associated with shutdown, in which case
225	+	* it is OK to give up. On termination, we just clobber these
226	+	* data structures without trying to use them.
227	+	*
228		* 2. Bookkeeping for dynamically adding and removing workers. We
229	<	* maintain a given level of parallelism (or, if
230	<	* maintainsParallelism is false, at least avoid starvation). When
152	<	* some workers are known to be blocked (on joins or via
229	>	* aim to approximately maintain the given level of parallelism.
230	>	* When some workers are known to be blocked (on joins or via
231		* ManagedBlocker), we may create or resume others to take their
232		* place until they unblock (see below). Implementing this
233		* requires counts of the number of "running" threads (i.e., those
234	<	* that are neither blocked nor artifically suspended) as well as
234	>	* that are neither blocked nor artificially suspended) as well as
235		* the total number.  These two values are packed into one field,
236		* "workerCounts" because we need accurate snapshots when deciding
237	<	* to create, resume or suspend.  To support these decisions,
238	<	* updates to spare counts must be prospective (not
239	<	* retrospective).  For example, the running count is decremented
240	<	* before blocking by a thread about to block as a spare, but
163	<	* incremented by the thread about to unblock it. Updates upon
164	<	* resumption ofr threads blocking in awaitJoin or awaitBlocker
165	<	* cannot usually be prospective, so the running count is in
166	<	* general an upper bound of the number of productively running
167	<	* threads Updates to the workerCounts field sometimes transiently
168	<	* encounter a fair amount of contention when join dependencies
169	<	* are such that many threads block or unblock at about the same
170	<	* time. We alleviate this by sometimes bundling updates (for
171	<	* example blocking one thread on join and resuming a spare cancel
172	<	* each other out), and in most other cases performing an
173	<	* alternative action like releasing waiters or locating spares.
237	>	* to create, resume or suspend.  Note however that the
238	>	* correspondence of these counts to reality is not guaranteed. In
239	>	* particular updates for unblocked threads may lag until they
240	>	* actually wake up.
241		*
242		* 3. Maintaining global run state. The run state of the pool
243		* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
#	Line 199 | Line 266 | public class ForkJoinPool extends Abstra
266		* workers that previously could not find a task to now find one:
267		* Submission of a new task to the pool, or another worker pushing
268		* a task onto a previously empty queue.  (We also use this
269	<	* mechanism for termination and reconfiguration actions that
269	>	* mechanism for configuration and termination actions that
270		* require wakeups of idle workers).  Each worker maintains its
271		* last known event count, and blocks when a scan for work did not
272		* find a task AND its lastEventCount matches the current
#	Line 210 | Line 277 | public class ForkJoinPool extends Abstra
277		* a record (field nextEventWaiter) for the next waiting worker.
278		* In addition to allowing simpler decisions about need for
279		* wakeup, the event count bits in eventWaiters serve the role of
280	<	* tags to avoid ABA errors in Treiber stacks.  To reduce delays
281	<	* in task diffusion, workers not otherwise occupied may invoke
282	<	* method releaseWaiters, that removes and signals (unparks)
283	<	* workers not waiting on current count. To minimize task
284	<	* production stalls associate with signalling, any worker pushing
285	<	* a task on an empty queue invokes the weaker method signalWork,
219	<	* that only releases idle workers until it detects interference
220	<	* by other threads trying to release, and lets them take
221	<	* over. The net effect is a tree-like diffusion of signals, where
222	<	* released threads (and possibly others) help with unparks.  To
223	<	* further reduce contention effects a bit, failed CASes to
224	<	* increment field eventCount are tolerated without retries.
280	>	* tags to avoid ABA errors in Treiber stacks. Upon any wakeup,
281	>	* released threads also try to release at most two others.  The
282	>	* net effect is a tree-like diffusion of signals, where released
283	>	* threads (and possibly others) help with unparks.  To further
284	>	* reduce contention effects a bit, failed CASes to increment
285	>	* field eventCount are tolerated without retries in signalWork.
286		* Conceptually they are merged into the same event, which is OK
287		* when their only purpose is to enable workers to scan for work.
288		*
289	<	* 5. Managing suspension of extra workers. When a worker is about
290	<	* to block waiting for a join (or via ManagedBlockers), we may
291	<	* create a new thread to maintain parallelism level, or at least
292	<	* avoid starvation (see below). Usually, extra threads are needed
293	<	* for only very short periods, yet join dependencies are such
294	<	* that we sometimes need them in bursts. Rather than create new
295	<	* threads each time this happens, we suspend no-longer-needed
296	<	* extra ones as "spares". For most purposes, we don't distinguish
297	<	* "extra" spare threads from normal "core" threads: On each call
298	<	* to preStep (the only point at which we can do this) a worker
299	<	* checks to see if there are now too many running workers, and if
300	<	* so, suspends itself.  Methods awaitJoin and awaitBlocker look
301	<	* for suspended threads to resume before considering creating a
302	<	* new replacement. We don't need a special data structure to
303	<	* maintain spares; simply scanning the workers array looking for
304	<	* worker.isSuspended() is fine because the calling thread is
305	<	* otherwise not doing anything useful anyway; we are at least as
306	<	* happy if after locating a spare, the caller doesn't actually
307	<	* block because the join is ready before we try to adjust and
308	<	* compensate.  Note that this is intrinsically racy.  One thread
309	<	* may become a spare at about the same time as another is
310	<	* needlessly being created. We counteract this and related slop
311	<	* in part by requiring resumed spares to immediately recheck (in
312	<	* preStep) to see whether they they should re-suspend. The only
313	<	* effective difference between "extra" and "core" threads is that
314	<	* we allow the "extra" ones to time out and die if they are not
315	<	* resumed within a keep-alive interval of a few seconds. This is
316	<	* implemented mainly within ForkJoinWorkerThread, but requires
317	<	* some coordination (isTrimmed() -- meaning killed while
318	<	* suspended) to correctly maintain pool counts.
319	<	*
320	<	* 6. Deciding when to create new workers. The main dynamic
321	<	* control in this class is deciding when to create extra threads,
322	<	* in methods awaitJoin and awaitBlocker. We always
323	<	* need to create one when the number of running threads becomes
324	<	* zero. But because blocked joins are typically dependent, we
325	<	* don't necessarily need or want one-to-one replacement. Using a
326	<	* one-to-one compensation rule often leads to enough useless
327	<	* overhead creating, suspending, resuming, and/or killing threads
328	<	* to signficantly degrade throughput.  We use a rule reflecting
329	<	* the idea that, the more spare threads you already have, the
330	<	* more evidence you need to create another one. The "evidence"
331	<	* here takes two forms: (1) Using a creation threshold expressed
332	<	* in terms of the current deficit -- target minus running
333	<	* threads. To reduce flickering and drift around target values,
334	<	* the relation is quadratic: adding a spare if (dc*dc)>=(sc*pc)
335	<	* (where dc is deficit, sc is number of spare threads and pc is
336	<	* target parallelism.)  (2) Using a form of adaptive
337	<	* spionning. requiring a number of threshold checks proportional
338	<	* to the number of spare threads.  This effectively reduces churn
339	<	* at the price of systematically undershooting target parallelism
279	<	* when many threads are blocked.  However, biasing toward
280	<	* undeshooting partially compensates for the above mechanics to
281	<	* suspend extra threads, that normally lead to overshoot because
282	<	* we can only suspend workers in-between top-level actions. It
283	<	* also better copes with the fact that some of the methods in
284	<	* this class tend to never become compiled (but are interpreted),
285	<	* so some components of the entire set of controls might execute
286	<	* many times faster than others. And similarly for cases where
287	<	* the apparent lack of work is just due to GC stalls and other
288	<	* transient system activity.
289	<	*
290	<	* 7. Maintaining other configuration parameters and monitoring
291	<	* statistics. Updates to fields controlling parallelism level,
292	<	* max size, etc can only meaningfully take effect for individual
293	<	* threads upon their next top-level actions; i.e., between
294	<	* stealing/running tasks/submission, which are separated by calls
295	<	* to preStep.  Memory ordering for these (assumed infrequent)
296	<	* reconfiguration calls is ensured by using reads and writes to
297	<	* volatile field workerCounts (that must be read in preStep anyway)
298	<	* as "fences" -- user-level reads are preceded by reads of
299	<	* workCounts, and writes are followed by no-op CAS to
300	<	* workerCounts. The values reported by other management and
301	<	* monitoring methods are either computed on demand, or are kept
302	<	* in fields that are only updated when threads are otherwise
303	<	* idle.
289	>	* 5. Managing suspension of extra workers. When a worker notices
290	>	* (usually upon timeout of a wait()) that there are too few
291	>	* running threads, we may create a new thread to maintain
292	>	* parallelism level, or at least avoid starvation. Usually, extra
293	>	* threads are needed for only very short periods, yet join
294	>	* dependencies are such that we sometimes need them in
295	>	* bursts. Rather than create new threads each time this happens,
296	>	* we suspend no-longer-needed extra ones as "spares". For most
297	>	* purposes, we don't distinguish "extra" spare threads from
298	>	* normal "core" threads: On each call to preStep (the only point
299	>	* at which we can do this) a worker checks to see if there are
300	>	* now too many running workers, and if so, suspends itself.
301	>	* Method helpMaintainParallelism looks for suspended threads to
302	>	* resume before considering creating a new replacement. The
303	>	* spares themselves are encoded on another variant of a Treiber
304	>	* Stack, headed at field "spareWaiters".  Note that the use of
305	>	* spares is intrinsically racy.  One thread may become a spare at
306	>	* about the same time as another is needlessly being created. We
307	>	* counteract this and related slop in part by requiring resumed
308	>	* spares to immediately recheck (in preStep) to see whether they
309	>	* should re-suspend.
310	>	*
311	>	* 6. Killing off unneeded workers. A timeout mechanism is used to
312	>	* shed unused workers: The oldest (first) event queue waiter uses
313	>	* a timed rather than hard wait. When this wait times out without
314	>	* a normal wakeup, it tries to shutdown any one (for convenience
315	>	* the newest) other spare or event waiter via
316	>	* tryShutdownUnusedWorker. This eventually reduces the number of
317	>	* worker threads to a minimum of one after a long enough period
318	>	* without use.
319	>	*
320	>	* 7. Deciding when to create new workers. The main dynamic
321	>	* control in this class is deciding when to create extra threads
322	>	* in method helpMaintainParallelism. We would like to keep
323	>	* exactly #parallelism threads running, which is an impossible
324	>	* task. We always need to create one when the number of running
325	>	* threads would become zero and all workers are busy. Beyond
326	>	* this, we must rely on heuristics that work well in the
327	>	* presence of transient phenomena such as GC stalls, dynamic
328	>	* compilation, and wake-up lags. These transients are extremely
329	>	* common -- we are normally trying to fully saturate the CPUs on
330	>	* a machine, so almost any activity other than running tasks
331	>	* impedes accuracy. Our main defense is to allow parallelism to
332	>	* lapse for a while during joins, and use a timeout to see if,
333	>	* after the resulting settling, there is still a need for
334	>	* additional workers.  This also better copes with the fact that
335	>	* some of the methods in this class tend to never become compiled
336	>	* (but are interpreted), so some components of the entire set of
337	>	* controls might execute 100 times faster than others. And
338	>	* similarly for cases where the apparent lack of work is just due
339	>	* to GC stalls and other transient system activity.
340		*
341		* Beware that there is a lot of representation-level coupling
342		* among classes ForkJoinPool, ForkJoinWorkerThread, and
#	Line 313 | Line 349 | public class ForkJoinPool extends Abstra
349		*
350		* Style notes: There are lots of inline assignments (of form
351		* "while ((local = field) != 0)") which are usually the simplest
352	<	* way to ensure read orderings. Also several occurrences of the
353	<	* unusual "do {} while(!cas...)" which is the simplest way to
354	<	* force an update of a CAS'ed variable. There are also a few
355	<	* other coding oddities that help some methods perform reasonably
356	<	* even when interpreted (not compiled).
352	>	* way to ensure the required read orderings (which are sometimes
353	>	* critical). Also several occurrences of the unusual "do {}
354	>	* while (!cas...)" which is the simplest way to force an update of
355	>	* a CAS'ed variable. There are also other coding oddities that
356	>	* help some methods perform reasonably even when interpreted (not
357	>	* compiled), at the expense of some messy constructions that
358	>	* reduce byte code counts.
359		*
360		* The order of declarations in this file is: (1) statics (2)
361		* fields (along with constants used when unpacking some of them)
#	Line 346 | Line 384 | public class ForkJoinPool extends Abstra
384		* Default ForkJoinWorkerThreadFactory implementation; creates a
385		* new ForkJoinWorkerThread.
386		*/
387	<	static class  DefaultForkJoinWorkerThreadFactory
387	>	static class DefaultForkJoinWorkerThreadFactory
388		implements ForkJoinWorkerThreadFactory {
389		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
390		return new ForkJoinWorkerThread(pool);
#	Line 385 | Line 423 | public class ForkJoinPool extends Abstra
423		new AtomicInteger();
424
425		/**
426	<	* Absolute bound for parallelism level. Twice this number must
427	<	* fit into a 16bit field to enable word-packing for some counts.
426	>	* The time to block in a join (see awaitJoin) before checking if
427	>	* a new worker should be (re)started to maintain parallelism
428	>	* level. The value should be short enough to maintain global
429	>	* responsiveness and progress but long enough to avoid
430	>	* counterproductive firings during GC stalls or unrelated system
431	>	* activity, and to not bog down systems with continual re-firings
432	>	* on GCs or legitimately long waits.
433	>	*/
434	>	private static final long JOIN_TIMEOUT_MILLIS = 250L; // 4 per second
435	>
436	>	/**
437	>	* The wakeup interval (in nanoseconds) for the oldest worker
438	>	* waiting for an event to invoke tryShutdownUnusedWorker to
439	>	* shrink the number of workers.  The exact value does not matter
440	>	* too much. It must be short enough to release resources during
441	>	* sustained periods of idleness, but not so short that threads
442	>	* are continually re-created.
443		*/
444	<	private static final int MAX_THREADS = 0x7fff;
444	>	private static final long SHRINK_RATE_NANOS =
445	>	30L * 1000L * 1000L * 1000L; // 2 per minute
446	>
447	>	/**
448	>	* Absolute bound for parallelism level. Twice this number plus
449	>	* one (i.e., 0xfff) must fit into a 16bit field to enable
450	>	* word-packing for some counts and indices.
451	>	*/
452	>	private static final int MAX_WORKERS   = 0x7fff;
453
454		/**
455		* Array holding all worker threads in the pool.  Array size must
#	Line 414 | Line 475 | public class ForkJoinPool extends Abstra
475		/**
476		* Latch released upon termination.
477		*/
478	<	private final CountDownLatch terminationLatch;
478	>	private final Phaser termination;
479
480		/**
481		* Creation factory for worker threads.
#	Line 428 | Line 489 | public class ForkJoinPool extends Abstra
489		private volatile long stealCount;
490
491		/**
492	<	* Encoded record of top of treiber stack of threads waiting for
492	>	* Encoded record of top of Treiber stack of threads waiting for
493		* events. The top 32 bits contain the count being waited for. The
494	<	* bottom word contains one plus the pool index of waiting worker
495	<	* thread.
494	>	* bottom 16 bits contains one plus the pool index of waiting
495	>	* worker thread. (Bits 16-31 are unused.)
496		*/
497		private volatile long eventWaiters;
498
499		private static final int  EVENT_COUNT_SHIFT = 32;
500	<	private static final long WAITER_INDEX_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
500	>	private static final long WAITER_ID_MASK    = (1L << 16) - 1L;
501
502		/**
503		* A counter for events that may wake up worker threads:
504		*   - Submission of a new task to the pool
505		*   - A worker pushing a task on an empty queue
506	<	*   - termination and reconfiguration
506	>	*   - termination
507		*/
508		private volatile int eventCount;
509
510		/**
511	+	* Encoded record of top of Treiber stack of spare threads waiting
512	+	* for resumption. The top 16 bits contain an arbitrary count to
513	+	* avoid ABA effects. The bottom 16bits contains one plus the pool
514	+	* index of waiting worker thread.
515	+	*/
516	+	private volatile int spareWaiters;
517	+
518	+	private static final int SPARE_COUNT_SHIFT = 16;
519	+	private static final int SPARE_ID_MASK     = (1 << 16) - 1;
520	+
521	+	/**
522		* Lifecycle control. The low word contains the number of workers
523		* that are (probably) executing tasks. This value is atomically
524		* incremented before a worker gets a task to run, and decremented
525	<	* when worker has no tasks and cannot find any.  Bits 16-18
525	>	* when a worker has no tasks and cannot find any.  Bits 16-18
526		* contain runLevel value. When all are zero, the pool is
527		* running. Level transitions are monotonic (running -> shutdown
528		* -> terminating -> terminated) so each transition adds a bit.
529		* These are bundled together to ensure consistent read for
530		* termination checks (i.e., that runLevel is at least SHUTDOWN
531		* and active threads is zero).
532	+	*
533	+	* Notes: Most direct CASes are dependent on these bitfield
534	+	* positions.  Also, this field is non-private to enable direct
535	+	* performance-sensitive CASes in ForkJoinWorkerThread.
536		*/
537	<	private volatile int runState;
537	>	volatile int runState;
538
539		// Note: The order among run level values matters.
540		private static final int RUNLEVEL_SHIFT     = 16;
#	Line 466 | Line 542 | public class ForkJoinPool extends Abstra
542		private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
543		private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
544		private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
469	–	private static final int ONE_ACTIVE         = 1; // active update delta
545
546		/**
547		* Holds number of total (i.e., created and not yet terminated)
#	Line 475 | Line 550 | public class ForkJoinPool extends Abstra
550		* making decisions about creating and suspending spare
551		* threads. Updated only by CAS. Note that adding a new worker
552		* requires incrementing both counts, since workers start off in
553	<	* running state.  This field is also used for memory-fencing
479	<	* configuration parameters.
553	>	* running state.
554		*/
555		private volatile int workerCounts;
556
#	Line 485 | Line 559 | public class ForkJoinPool extends Abstra
559		private static final int ONE_RUNNING        = 1;
560		private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
561
488	–	/*
489	–	* Fields parallelism. maxPoolSize, and maintainsParallelism are
490	–	* non-volatile, but external reads/writes use workerCount fences
491	–	* to ensure visability.
492	–	*/
493	–
562		/**
563		* The target parallelism level.
564	+	* Accessed directly by ForkJoinWorkerThreads.
565		*/
566	<	private int parallelism;
498	<
499	<	/**
500	<	* The maximum allowed pool size.
501	<	*/
502	<	private int maxPoolSize;
566	>	final int parallelism;
567
568		/**
569		* True if use local fifo, not default lifo, for local polling
570	<	* Replicated by ForkJoinWorkerThreads
507	<	*/
508	<	private volatile boolean locallyFifo;
509	<
510	<	/**
511	<	* Controls whether to add spares to maintain parallelism
570	>	* Read by, and replicated by ForkJoinWorkerThreads
571		*/
572	<	private boolean maintainsParallelism;
572	>	final boolean locallyFifo;
573
574		/**
575	<	* The uncaught exception handler used when any worker
576	<	* abruptly terminates
575	>	* The uncaught exception handler used when any worker abruptly
576	>	* terminates.
577		*/
578	<	private volatile Thread.UncaughtExceptionHandler ueh;
578	>	private final Thread.UncaughtExceptionHandler ueh;
579
580		/**
581		* Pool number, just for assigning useful names to worker threads
582		*/
583		private final int poolNumber;
584
585	<	// utilities for updating fields
585	>	// Utilities for CASing fields. Note that most of these
586	>	// are usually manually inlined by callers
587
588		/**
589	<	* Adds delta to running count.  Used mainly by ForkJoinTask.
589	>	* Increments running count part of workerCounts
590		*/
591	<	final void updateRunningCount(int delta) {
592	<	int wc;
591	>	final void incrementRunningCount() {
592	>	int c;
593		do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
594	<	wc = workerCounts,
595	<	wc + delta));
594	>	c = workerCounts,
595	>	c + ONE_RUNNING));
596		}
597
598		/**
599	<	* Decrements running count unless already zero
599	>	* Tries to decrement running count unless already zero
600		*/
601		final boolean tryDecrementRunningCount() {
602		int wc = workerCounts;
#	Line 547 | Line 607 | public class ForkJoinPool extends Abstra
607		}
608
609		/**
610	<	* Write fence for user modifications of pool parameters
611	<	* (parallelism. etc).  Note that it doesn't matter if CAS fails.
552	<	*/
553	<	private void workerCountWriteFence() {
554	<	int wc;
555	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
556	<	wc = workerCounts, wc);
557	<	}
558	<
559	<	/**
560	<	* Read fence for external reads of pool parameters
561	<	* (parallelism. maxPoolSize, etc).
562	<	*/
563	<	private void workerCountReadFence() {
564	<	int ignore = workerCounts;
565	<	}
566	<
567	<	/**
568	<	* Tries incrementing active count; fails on contention.
569	<	* Called by workers before executing tasks.
610	>	* Forces decrement of encoded workerCounts, awaiting nonzero if
611	>	* (rarely) necessary when other count updates lag.
612		*
613	<	* @return true on success
613	>	* @param dr -- either zero or ONE_RUNNING
614	>	* @param dt -- either zero or ONE_TOTAL
615		*/
616	<	final boolean tryIncrementActiveCount() {
617	<	int c;
618	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
619	<	c = runState, c + ONE_ACTIVE);
616	>	private void decrementWorkerCounts(int dr, int dt) {
617	>	for (;;) {
618	>	int wc = workerCounts;
619	>	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
620	>	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) {
621	>	if ((runState & TERMINATED) != 0)
622	>	return; // lagging termination on a backout
623	>	Thread.yield();
624	>	}
625	>	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
626	>	wc, wc - (dr + dt)))
627	>	return;
628	>	}
629		}
630
631		/**
#	Line 583 | Line 635 | public class ForkJoinPool extends Abstra
635		final boolean tryDecrementActiveCount() {
636		int c;
637		return UNSAFE.compareAndSwapInt(this, runStateOffset,
638	<	c = runState, c - ONE_ACTIVE);
638	>	c = runState, c - 1);
639		}
640
641		/**
#	Line 612 | Line 664 | public class ForkJoinPool extends Abstra
664		lock.lock();
665		try {
666		ForkJoinWorkerThread[] ws = workers;
667	<	int nws = ws.length;
668	<	if (k < 0 || k >= nws || ws[k] != null) {
669	<	for (k = 0; k < nws && ws[k] != null; ++k)
667	>	int n = ws.length;
668	>	if (k < 0 || k >= n || ws[k] != null) {
669	>	for (k = 0; k < n && ws[k] != null; ++k)
670		;
671	<	if (k == nws)
672	<	ws = Arrays.copyOf(ws, nws << 1);
671	>	if (k == n)
672	>	ws = Arrays.copyOf(ws, n << 1);
673		}
674		ws[k] = w;
675		workers = ws; // volatile array write ensures slot visibility
#	Line 628 | Line 680 | public class ForkJoinPool extends Abstra
680		}
681
682		/**
683	<	* Nulls out record of worker in workers array
683	>	* Nulls out record of worker in workers array.
684		*/
685		private void forgetWorker(ForkJoinWorkerThread w) {
686		int idx = w.poolIndex;
687	<	// Locking helps method recordWorker avoid unecessary expansion
687	>	// Locking helps method recordWorker avoid unnecessary expansion
688		final ReentrantLock lock = this.workerLock;
689		lock.lock();
690		try {
#	Line 644 | Line 696 | public class ForkJoinPool extends Abstra
696		}
697		}
698
647	–	// adding and removing workers
648	–
699		/**
700	<	* Tries to create and add new worker. Assumes that worker counts
701	<	* are already updated to accommodate the worker, so adjusts on
702	<	* failure.
700	>	* Final callback from terminating worker.  Removes record of
701	>	* worker from array, and adjusts counts. If pool is shutting
702	>	* down, tries to complete termination.
703		*
704	<	* @return new worker or null if creation failed
704	>	* @param w the worker
705		*/
706	<	private ForkJoinWorkerThread addWorker() {
707	<	ForkJoinWorkerThread w = null;
708	<	try {
709	<	w = factory.newThread(this);
710	<	} finally { // Adjust on either null or exceptional factory return
711	<	if (w == null) {
662	<	onWorkerCreationFailure();
663	<	return null;
664	<	}
665	<	}
666	<	w.start(recordWorker(w), locallyFifo, ueh);
667	<	return w;
706	>	final void workerTerminated(ForkJoinWorkerThread w) {
707	>	forgetWorker(w);
708	>	decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL);
709	>	while (w.stealCount != 0) // collect final count
710	>	tryAccumulateStealCount(w);
711	>	tryTerminate(false);
712		}
713
714	+	// Waiting for and signalling events
715	+
716		/**
717	<	* Adjusts counts upon failure to create worker
717	>	* Releases workers blocked on a count not equal to current count.
718	>	* Normally called after precheck that eventWaiters isn't zero to
719	>	* avoid wasted array checks. Gives up upon a change in count or
720	>	* upon releasing two workers, letting others take over.
721		*/
722	<	private void onWorkerCreationFailure() {
723	<	for (;;) {
724	<	int wc = workerCounts;
725	<	if ((wc >>> TOTAL_COUNT_SHIFT) > 0 &&
726	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
727	<	wc, wc - (ONE_RUNNING|ONE_TOTAL)))
722	>	private void releaseEventWaiters() {
723	>	ForkJoinWorkerThread[] ws = workers;
724	>	int n = ws.length;
725	>	long h = eventWaiters;
726	>	int ec = eventCount;
727	>	boolean releasedOne = false;
728	>	ForkJoinWorkerThread w; int id;
729	>	while ((id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 &&
730	>	(int)(h >>> EVENT_COUNT_SHIFT) != ec &&
731	>	id < n && (w = ws[id]) != null) {
732	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
733	>	h,  w.nextWaiter)) {
734	>	LockSupport.unpark(w);
735	>	if (releasedOne) // exit on second release
736	>	break;
737	>	releasedOne = true;
738	>	}
739	>	if (eventCount != ec)
740		break;
741	+	h = eventWaiters;
742		}
681	–	tryTerminate(false); // in case of failure during shutdown
743		}
744
745		/**
746	<	* Create enough total workers to establish target parallelism,
747	<	* giving up if terminating or addWorker fails
746	>	* Tries to advance eventCount and releases waiters. Called only
747	>	* from workers.
748		*/
749	<	private void ensureEnoughTotalWorkers() {
750	<	int wc;
751	<	while (((wc = workerCounts) >>> TOTAL_COUNT_SHIFT) < parallelism &&
752	<	runState < TERMINATING) {
753	<	if ((UNSAFE.compareAndSwapInt(this, workerCountsOffset,
693	<	wc, wc + (ONE_RUNNING|ONE_TOTAL)) &&
694	<	addWorker() == null))
695	<	break;
696	<	}
749	>	final void signalWork() {
750	>	int c; // try to increment event count -- CAS failure OK
751	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
752	>	if (eventWaiters != 0L)
753	>	releaseEventWaiters();
754		}
755
756		/**
757	<	* Final callback from terminating worker.  Removes record of
758	<	* worker from array, and adjusts counts. If pool is shutting
702	<	* down, tries to complete terminatation, else possibly replaces
703	<	* the worker.
757	>	* Adds the given worker to event queue and blocks until
758	>	* terminating or event count advances from the given value
759		*
760	<	* @param w the worker
760	>	* @param w the calling worker thread
761	>	* @param ec the count
762		*/
763	<	final void workerTerminated(ForkJoinWorkerThread w) {
764	<	if (w.active) { // force inactive
765	<	w.active = false;
766	<	do {} while (!tryDecrementActiveCount());
767	<	}
768	<	forgetWorker(w);
769	<
770	<	// Decrement total count, and if was running, running count
771	<	// Spin (waiting for other updates) if either would be negative
772	<	int nr = w.isTrimmed() ? 0 : ONE_RUNNING;
717	<	int unit = ONE_TOTAL + nr;
718	<	for (;;) {
719	<	int wc = workerCounts;
720	<	int rc = wc & RUNNING_COUNT_MASK;
721	<	if (rc - nr < 0 || (wc >>> TOTAL_COUNT_SHIFT) == 0)
722	<	Thread.yield(); // back off if waiting for other updates
723	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
724	<	wc, wc - unit))
763	>	private void eventSync(ForkJoinWorkerThread w, int ec) {
764	>	long nh = (((long)ec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
765	>	long h;
766	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
767	>	(((int)((h = eventWaiters) & WAITER_ID_MASK)) == 0 ||
768	>	(int)(h >>> EVENT_COUNT_SHIFT) == ec) &&
769	>	eventCount == ec) {
770	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
771	>	w.nextWaiter = h, nh)) {
772	>	awaitEvent(w, ec);
773		break;
774	+	}
775		}
727	–
728	–	accumulateStealCount(w); // collect final count
729	–	if (!tryTerminate(false))
730	–	ensureEnoughTotalWorkers();
776		}
777
733	–	// Waiting for and signalling events
734	–
778		/**
779	<	* Ensures eventCount on exit is different (mod 2^32) than on
780	<	* entry.  CAS failures are OK -- any change in count suffices.
779	>	* Blocks the given worker (that has already been entered as an
780	>	* event waiter) until terminating or event count advances from
781	>	* the given value. The oldest (first) waiter uses a timed wait to
782	>	* occasionally one-by-one shrink the number of workers (to a
783	>	* minimum of one) if the pool has not been used for extended
784	>	* periods.
785	>	*
786	>	* @param w the calling worker thread
787	>	* @param ec the count
788		*/
789	<	private void advanceEventCount() {
790	<	int c;
791	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
789	>	private void awaitEvent(ForkJoinWorkerThread w, int ec) {
790	>	while (eventCount == ec) {
791	>	if (tryAccumulateStealCount(w)) { // transfer while idle
792	>	boolean untimed = (w.nextWaiter != 0L ||
793	>	(workerCounts & RUNNING_COUNT_MASK) <= 1);
794	>	long startTime = untimed? 0 : System.nanoTime();
795	>	Thread.interrupted();         // clear/ignore interrupt
796	>	if (eventCount != ec || w.isTerminating())
797	>	break;                    // recheck after clear
798	>	if (untimed)
799	>	LockSupport.park(w);
800	>	else {
801	>	LockSupport.parkNanos(w, SHRINK_RATE_NANOS);
802	>	if (eventCount != ec || w.isTerminating())
803	>	break;
804	>	if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS)
805	>	tryShutdownUnusedWorker(ec);
806	>	}
807	>	}
808	>	}
809		}
810
811	+	// Maintaining parallelism
812	+
813		/**
814	<	* Releases workers blocked on a count not equal to current count.
814	>	* Pushes worker onto the spare stack.
815		*/
816	<	final void releaseWaiters() {
817	<	long top;
818	<	int id;
819	<	while ((id = (int)((top = eventWaiters) & WAITER_INDEX_MASK)) > 0 &&
751	<	(int)(top >>> EVENT_COUNT_SHIFT) != eventCount) {
752	<	ForkJoinWorkerThread[] ws = workers;
753	<	ForkJoinWorkerThread w;
754	<	if (ws.length >= id && (w = ws[id - 1]) != null &&
755	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
756	<	top, w.nextWaiter))
757	<	LockSupport.unpark(w);
758	<	}
816	>	final void pushSpare(ForkJoinWorkerThread w) {
817	>	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1);
818	>	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
819	>	w.nextSpare = spareWaiters,ns));
820		}
821
822		/**
823	<	* Advances eventCount and releases waiters until interference by
824	<	* other releasing threads is detected.
823	>	* Tries (once) to resume a spare if the number of running
824	>	* threads is less than target.
825		*/
826	<	final void signalWork() {
827	<	int ec;
828	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, ec=eventCount, ec+1);
829	<	outer:for (;;) {
830	<	long top = eventWaiters;
831	<	ec = eventCount;
832	<	for (;;) {
833	<	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
834	<	int id = (int)(top & WAITER_INDEX_MASK);
835	<	if (id <= 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
836	<	return;
837	<	if ((ws = workers).length < id || (w = ws[id - 1]) == null ||
838	<	!UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
839	<	top, top = w.nextWaiter))
840	<	continue outer;      // possibly stale; reread
826	>	private void tryResumeSpare() {
827	>	int sw, id;
828	>	ForkJoinWorkerThread[] ws = workers;
829	>	int n = ws.length;
830	>	ForkJoinWorkerThread w;
831	>	if ((sw = spareWaiters) != 0 &&
832	>	(id = (sw & SPARE_ID_MASK) - 1) >= 0 &&
833	>	id < n && (w = ws[id]) != null &&
834	>	(workerCounts & RUNNING_COUNT_MASK) < parallelism &&
835	>	spareWaiters == sw &&
836	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
837	>	sw, w.nextSpare)) {
838	>	int c; // increment running count before resume
839	>	do {} while (!UNSAFE.compareAndSwapInt
840	>	(this, workerCountsOffset,
841	>	c = workerCounts, c + ONE_RUNNING));
842	>	if (w.tryUnsuspend())
843		LockSupport.unpark(w);
844	<	if (top != eventWaiters) // let someone else take over
845	<	return;
783	<	}
844	>	else   // back out if w was shutdown
845	>	decrementWorkerCounts(ONE_RUNNING, 0);
846		}
847		}
848
849		/**
850	<	* If worker is inactive, blocks until terminating or event count
851	<	* advances from last value held by worker; in any case helps
852	<	* release others.
853	<	*
854	<	* @param w the calling worker thread
850	>	* Tries to increase the number of running workers if below target
851	>	* parallelism: If a spare exists tries to resume it via
852	>	* tryResumeSpare.  Otherwise, if not enough total workers or all
853	>	* existing workers are busy, adds a new worker. In all cases also
854	>	* helps wake up releasable workers waiting for work.
855		*/
856	<	private void eventSync(ForkJoinWorkerThread w) {
857	<	if (!w.active) {
858	<	int prev = w.lastEventCount;
859	<	long nextTop = (((long)prev << EVENT_COUNT_SHIFT) |
860	<	((long)(w.poolIndex + 1)));
861	<	long top;
862	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
863	<	(((int)(top = eventWaiters) & WAITER_INDEX_MASK) == 0 ||
864	<	(int)(top >>> EVENT_COUNT_SHIFT) == prev) &&
865	<	eventCount == prev) {
866	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
867	<	w.nextWaiter = top, nextTop)) {
868	<	accumulateStealCount(w); // transfer steals while idle
869	<	Thread.interrupted();    // clear/ignore interrupt
870	<	while (eventCount == prev)
871	<	w.doPark();
856	>	private void helpMaintainParallelism() {
857	>	int pc = parallelism;
858	>	int wc, rs, tc;
859	>	while (((wc = workerCounts) & RUNNING_COUNT_MASK) < pc &&
860	>	(rs = runState) < TERMINATING) {
861	>	if (spareWaiters != 0)
862	>	tryResumeSpare();
863	>	else if ((tc = wc >>> TOTAL_COUNT_SHIFT) >= MAX_WORKERS ||
864	>	(tc >= pc && (rs & ACTIVE_COUNT_MASK) != tc))
865	>	break;   // enough total
866	>	else if (runState == rs && workerCounts == wc &&
867	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
868	>	wc + (ONE_RUNNING|ONE_TOTAL))) {
869	>	ForkJoinWorkerThread w = null;
870	>	Throwable fail = null;
871	>	try {
872	>	w = factory.newThread(this);
873	>	} catch (Throwable ex) {
874	>	fail = ex;
875	>	}
876	>	if (w == null) { // null or exceptional factory return
877	>	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
878	>	tryTerminate(false); // handle failure during shutdown
879	>	// If originating from an external caller,
880	>	// propagate exception, else ignore
881	>	if (fail != null && runState < TERMINATING &&
882	>	!(Thread.currentThread() instanceof
883	>	ForkJoinWorkerThread))
884	>	UNSAFE.throwException(fail);
885		break;
886		}
887	+	w.start(recordWorker(w), ueh);
888	+	if ((workerCounts >>> TOTAL_COUNT_SHIFT) >= pc) {
889	+	int c; // advance event count
890	+	UNSAFE.compareAndSwapInt(this, eventCountOffset,
891	+	c = eventCount, c+1);
892	+	break; // add at most one unless total below target
893	+	}
894		}
813	–	w.lastEventCount = eventCount;
895		}
896	<	releaseWaiters();
896	>	if (eventWaiters != 0L)
897	>	releaseEventWaiters();
898		}
899
900		/**
901	<	* Callback from workers invoked upon each top-level action (i.e.,
902	<	* stealing a task or taking a submission and running
903	<	* it). Performs one or both of the following:
904	<	*
905	<	* * If the worker cannot find work, updates its active status to
906	<	* inactive and updates activeCount unless there is contention, in
907	<	* which case it may try again (either in this or a subsequent
826	<	* call).  Additionally, awaits the next task event and/or helps
827	<	* wake up other releasable waiters.
828	<	*
829	<	* * If there are too many running threads, suspends this worker
830	<	* (first forcing inactivation if necessary).  If it is not
831	<	* resumed before a keepAlive elapses, the worker may be "trimmed"
832	<	* -- killed while suspended within suspendAsSpare. Otherwise,
833	<	* upon resume it rechecks to make sure that it is still needed.
901	>	* Callback from the oldest waiter in awaitEvent waking up after a
902	>	* period of non-use. If all workers are idle, tries (once) to
903	>	* shutdown an event waiter or a spare, if one exists. Note that
904	>	* we don't need CAS or locks here because the method is called
905	>	* only from one thread occasionally waking (and even misfires are
906	>	* OK). Note that until the shutdown worker fully terminates,
907	>	* workerCounts will overestimate total count, which is tolerable.
908		*
909	<	* @param w the worker
910	<	* @param worked false if the worker scanned for work but didn't
837	<	* find any (in which case it may block waiting for work).
909	>	* @param ec the event count waited on by caller (to abort
910	>	* attempt if count has since changed).
911		*/
912	<	final void preStep(ForkJoinWorkerThread w, boolean worked) {
913	<	boolean active = w.active;
914	<	boolean inactivate = !worked & active;
915	<	for (;;) {
916	<	if (inactivate) {
917	<	int c = runState;
918	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset,
919	<	c, c - ONE_ACTIVE))
920	<	inactivate = active = w.active = false;
912	>	private void tryShutdownUnusedWorker(int ec) {
913	>	if (runState == 0 && eventCount == ec) { // only trigger if all idle
914	>	ForkJoinWorkerThread[] ws = workers;
915	>	int n = ws.length;
916	>	ForkJoinWorkerThread w = null;
917	>	boolean shutdown = false;
918	>	int sw;
919	>	long h;
920	>	if ((sw = spareWaiters) != 0) { // prefer killing spares
921	>	int id = (sw & SPARE_ID_MASK) - 1;
922	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
923	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
924	>	sw, w.nextSpare))
925	>	shutdown = true;
926		}
927	<	int wc = workerCounts;
928	<	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
929	<	if (!worked)
930	<	eventSync(w);
931	<	return;
927	>	else if ((h = eventWaiters) != 0L) {
928	>	long nh;
929	>	int id = ((int)(h & WAITER_ID_MASK)) - 1;
930	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
931	>	(nh = w.nextWaiter) != 0L && // keep at least one worker
932	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh))
933	>	shutdown = true;
934	>	}
935	>	if (w != null && shutdown) {
936	>	w.shutdown();
937	>	LockSupport.unpark(w);
938		}
855	–	if (!(inactivate |= active) &&  // must inactivate to suspend
856	–	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
857	–	wc, wc - ONE_RUNNING) &&
858	–	!w.suspendAsSpare())        // false if trimmed
859	–	return;
939		}
940	+	releaseEventWaiters(); // in case of interference
941		}
942
943		/**
944	<	* Adjusts counts and creates or resumes compensating threads for
945	<	* a worker blocking on task joinMe.  First tries resuming an
946	<	* existing spare (which usually also avoids any count
867	<	* adjustment), but must then decrement running count to determine
868	<	* whether a new thread is needed. See above for fuller
869	<	* explanation. This code is sprawled out non-modularly mainly
870	<	* because adaptive spinning works best if the entire method is
871	<	* either interpreted or compiled vs having only some pieces of it
872	<	* compiled.
944	>	* Callback from workers invoked upon each top-level action (i.e.,
945	>	* stealing a task or taking a submission and running it).
946	>	* Performs one or more of the following:
947		*
948	<	* @param joinMe the task to join
949	<	* @return task status on exit (to simplify usage by callers)
948	>	* 1. If the worker is active and either did not run a task
949	>	*    or there are too many workers, try to set its active status
950	>	*    to inactive and update activeCount. On contention, we may
951	>	*    try again in this or a subsequent call.
952	>	*
953	>	* 2. If not enough total workers, help create some.
954	>	*
955	>	* 3. If there are too many running workers, suspend this worker
956	>	*    (first forcing inactive if necessary).  If it is not needed,
957	>	*    it may be shutdown while suspended (via
958	>	*    tryShutdownUnusedWorker).  Otherwise, upon resume it
959	>	*    rechecks running thread count and need for event sync.
960	>	*
961	>	* 4. If worker did not run a task, await the next task event via
962	>	*    eventSync if necessary (first forcing inactivation), upon
963	>	*    which the worker may be shutdown via
964	>	*    tryShutdownUnusedWorker.  Otherwise, help release any
965	>	*    existing event waiters that are now releasable,
966	>	*
967	>	* @param w the worker
968	>	* @param ran true if worker ran a task since last call to this method
969		*/
970	<	final int awaitJoin(ForkJoinTask<?> joinMe) {
970	>	final void preStep(ForkJoinWorkerThread w, boolean ran) {
971	>	int wec = w.lastEventCount;
972	>	boolean active = w.active;
973	>	boolean inactivate = false;
974		int pc = parallelism;
975	<	boolean adj = false;        // true when running count adjusted
976	<	int scans = 0;
977	<
978	<	while (joinMe.status >= 0) {
979	<	ForkJoinWorkerThread spare = null;
884	<	if ((workerCounts & RUNNING_COUNT_MASK) < pc) {
885	<	ForkJoinWorkerThread[] ws = workers;
886	<	int nws = ws.length;
887	<	for (int i = 0; i < nws; ++i) {
888	<	ForkJoinWorkerThread w = ws[i];
889	<	if (w != null && w.isSuspended()) {
890	<	spare = w;
891	<	break;
892	<	}
893	<	}
894	<	if (joinMe.status < 0)
895	<	break;
975	>	while (w.runState == 0) {
976	>	int rs = runState;
977	>	if (rs >= TERMINATING) { // propagate shutdown
978	>	w.shutdown();
979	>	break;
980		}
981	+	if ((inactivate || (active && (rs & ACTIVE_COUNT_MASK) >= pc)) &&
982	+	UNSAFE.compareAndSwapInt(this, runStateOffset, rs, rs - 1))
983	+	inactivate = active = w.active = false;
984		int wc = workerCounts;
985	<	int rc = wc & RUNNING_COUNT_MASK;
986	<	int dc = pc - rc;
987	<	if (dc > 0 && spare != null && spare.tryUnsuspend()) {
988	<	if (adj) {
989	<	int c;
990	<	do {} while (!UNSAFE.compareAndSwapInt
904	<	(this, workerCountsOffset,
905	<	c = workerCounts, c + ONE_RUNNING));
906	<	}
907	<	adj = true;
908	<	LockSupport.unpark(spare);
985	>	if ((wc & RUNNING_COUNT_MASK) > pc) {
986	>	if (!(inactivate |= active) && // must inactivate to suspend
987	>	workerCounts == wc &&      // try to suspend as spare
988	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
989	>	wc, wc - ONE_RUNNING))
990	>	w.suspendAsSpare();
991		}
992	<	else if (adj) {
993	<	if (dc <= 0)
992	>	else if ((wc >>> TOTAL_COUNT_SHIFT) < pc)
993	>	helpMaintainParallelism();     // not enough workers
994	>	else if (!ran) {
995	>	long h = eventWaiters;
996	>	int ec = eventCount;
997	>	if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != ec)
998	>	releaseEventWaiters();     // release others before waiting
999	>	else if (ec != wec) {
1000	>	w.lastEventCount = ec;     // no need to wait
1001		break;
913	–	int tc = wc >>> TOTAL_COUNT_SHIFT;
914	–	if (scans > tc) {
915	–	int ts = (tc - pc) * pc;
916	–	if (rc != 0 &&  (dc * dc < ts || !maintainsParallelism))
917	–	break;
918	–	if (scans > ts && tc < maxPoolSize &&
919	–	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
920	–	wc+(ONE_RUNNING|ONE_TOTAL))){
921	–	addWorker();
922	–	break;
923	–	}
1002		}
1003	+	else if (!(inactivate |= active))
1004	+	eventSync(w, wec);         // must inactivate before sync
1005		}
926	–	else if (rc != 0)
927	–	adj = UNSAFE.compareAndSwapInt (this, workerCountsOffset,
928	–	wc, wc - ONE_RUNNING);
929	–	if ((scans++ & 1) == 0)
930	–	releaseWaiters();   // help others progress
1006		else
1007	<	Thread.yield();     // avoid starving productive threads
933	<	}
934	<
935	<	if (adj) {
936	<	joinMe.internalAwaitDone();
937	<	int c;
938	<	do {} while (!UNSAFE.compareAndSwapInt
939	<	(this, workerCountsOffset,
940	<	c = workerCounts, c + ONE_RUNNING));
1007	>	break;
1008		}
942	–	return joinMe.status;
1009		}
1010
1011		/**
1012	<	* Same idea as awaitJoin
1012	>	* Helps and/or blocks awaiting join of the given task.
1013	>	* See above for explanation.
1014	>	*
1015	>	* @param joinMe the task to join
1016	>	* @param worker the current worker thread
1017		*/
1018	<	final void awaitBlocker(ManagedBlocker blocker, boolean maintainPar)
1019	<	throws InterruptedException {
1020	<	maintainPar &= maintainsParallelism;
1021	<	int pc = parallelism;
1022	<	boolean adj = false;        // true when running count adjusted
1023	<	int scans = 0;
954	<	boolean done;
955	<
956	<	for (;;) {
957	<	if (done = blocker.isReleasable())
1018	>	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) {
1019	>	int retries = 2 + (parallelism >> 2); // #helpJoins before blocking
1020	>	while (joinMe.status >= 0) {
1021	>	int wc;
1022	>	worker.helpJoinTask(joinMe);
1023	>	if (joinMe.status < 0)
1024		break;
1025	<	ForkJoinWorkerThread spare = null;
1026	<	if ((workerCounts & RUNNING_COUNT_MASK) < pc) {
1027	<	ForkJoinWorkerThread[] ws = workers;
1028	<	int nws = ws.length;
1029	<	for (int i = 0; i < nws; ++i) {
1030	<	ForkJoinWorkerThread w = ws[i];
1031	<	if (w != null && w.isSuspended()) {
1032	<	spare = w;
1033	<	break;
1034	<	}
1035	<	}
1036	<	if (done = blocker.isReleasable())
1037	<	break;
1038	<	}
1039	<	int wc = workerCounts;
974	<	int rc = wc & RUNNING_COUNT_MASK;
975	<	int dc = pc - rc;
976	<	if (dc > 0 && spare != null && spare.tryUnsuspend()) {
977	<	if (adj) {
978	<	int c;
979	<	do {} while (!UNSAFE.compareAndSwapInt
980	<	(this, workerCountsOffset,
981	<	c = workerCounts, c + ONE_RUNNING));
982	<	}
983	<	adj = true;
984	<	LockSupport.unpark(spare);
985	<	}
986	<	else if (adj) {
987	<	if (dc <= 0)
988	<	break;
989	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
990	<	if (scans > tc) {
991	<	int ts = (tc - pc) * pc;
992	<	if (rc != 0 &&  (dc * dc < ts || !maintainPar))
993	<	break;
994	<	if (scans > ts && tc < maxPoolSize &&
995	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
996	<	wc+(ONE_RUNNING|ONE_TOTAL))){
997	<	addWorker();
998	<	break;
999	<	}
1000	<	}
1001	<	}
1002	<	else if (rc != 0)
1003	<	adj = UNSAFE.compareAndSwapInt (this, workerCountsOffset,
1004	<	wc, wc - ONE_RUNNING);
1005	<	if ((++scans & 1) == 0)
1006	<	releaseWaiters();   // help others progress
1007	<	else
1008	<	Thread.yield();     // avoid starving productive threads
1009	<	}
1010	<
1011	<	try {
1012	<	if (!done)
1013	<	do {} while (!blocker.isReleasable() && !blocker.block());
1014	<	} finally {
1015	<	if (adj) {
1016	<	int c;
1025	>	else if (retries > 0)
1026	>	--retries;
1027	>	else if (((wc = workerCounts) & RUNNING_COUNT_MASK) != 0 &&
1028	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1029	>	wc, wc - ONE_RUNNING)) {
1030	>	int stat, c; long h;
1031	>	while ((stat = joinMe.status) >= 0 &&
1032	>	(h = eventWaiters) != 0L && // help release others
1033	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1034	>	releaseEventWaiters();
1035	>	if (stat >= 0 &&
1036	>	((workerCounts & RUNNING_COUNT_MASK) == 0 ||
1037	>	(stat =
1038	>	joinMe.internalAwaitDone(JOIN_TIMEOUT_MILLIS)) >= 0))
1039	>	helpMaintainParallelism(); // timeout or no running workers
1040		do {} while (!UNSAFE.compareAndSwapInt
1041		(this, workerCountsOffset,
1042		c = workerCounts, c + ONE_RUNNING));
1043	+	if (stat < 0)
1044	+	break;   // else restart
1045		}
1046		}
1047		}
1048
1049		/**
1050	<	* Unless there are not enough other running threads, adjusts
1026	<	* counts and blocks a worker performing helpJoin that cannot find
1027	<	* any work.
1028	<	*
1029	<	* @return true if joinMe now done
1050	>	* Same idea as awaitJoin, but no helping, retries, or timeouts.
1051		*/
1052	<	final boolean tryAwaitBusyJoin(ForkJoinTask<?> joinMe) {
1053	<	int pc = parallelism;
1054	<	outer:for (;;) {
1055	<	releaseWaiters();
1056	<	if ((workerCounts & RUNNING_COUNT_MASK) < pc) {
1057	<	ForkJoinWorkerThread[] ws = workers;
1058	<	int nws = ws.length;
1059	<	for (int i = 0; i < nws; ++i) {
1060	<	ForkJoinWorkerThread w = ws[i];
1061	<	if (w != null && w.isSuspended()) {
1062	<	if (joinMe.status < 0)
1063	<	return true;
1064	<	if ((workerCounts & RUNNING_COUNT_MASK) > pc)
1052	>	final void awaitBlocker(ManagedBlocker blocker)
1053	>	throws InterruptedException {
1054	>	while (!blocker.isReleasable()) {
1055	>	int wc = workerCounts;
1056	>	if ((wc & RUNNING_COUNT_MASK) != 0 &&
1057	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1058	>	wc, wc - ONE_RUNNING)) {
1059	>	try {
1060	>	while (!blocker.isReleasable()) {
1061	>	long h = eventWaiters;
1062	>	if (h != 0L &&
1063	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1064	>	releaseEventWaiters();
1065	>	else if ((workerCounts & RUNNING_COUNT_MASK) == 0 &&
1066	>	runState < TERMINATING)
1067	>	helpMaintainParallelism();
1068	>	else if (blocker.block())
1069		break;
1045	–	if (w.tryUnsuspend()) {
1046	–	LockSupport.unpark(w);
1047	–	break outer;
1048	–	}
1049	–	continue outer;
1070		}
1071	+	} finally {
1072	+	int c;
1073	+	do {} while (!UNSAFE.compareAndSwapInt
1074	+	(this, workerCountsOffset,
1075	+	c = workerCounts, c + ONE_RUNNING));
1076		}
1052	–	}
1053	–	if (joinMe.status < 0)
1054	–	return true;
1055	–	int wc = workerCounts;
1056	–	if ((wc & RUNNING_COUNT_MASK) <= 2 ||
1057	–	(wc >>> TOTAL_COUNT_SHIFT) < pc)
1058	–	return false;  // keep this thread alive
1059	–	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1060	–	wc, wc - ONE_RUNNING))
1077		break;
1078	+	}
1079		}
1063	–
1064	–	joinMe.internalAwaitDone();
1065	–	int c;
1066	–	do {} while (!UNSAFE.compareAndSwapInt
1067	–	(this, workerCountsOffset,
1068	–	c = workerCounts, c + ONE_RUNNING));
1069	–	return true;
1080		}
1081
1082		/**
#	Line 1090 | Line 1100 | public class ForkJoinPool extends Abstra
1100		// Finish now if all threads terminated; else in some subsequent call
1101		if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1102		advanceRunLevel(TERMINATED);
1103	<	terminationLatch.countDown();
1103	>	termination.arrive();
1104		}
1105		return true;
1106		}
1107
1108	+
1109		/**
1110		* Actions on transition to TERMINATING
1111	+	*
1112	+	* Runs up to four passes through workers: (0) shutting down each
1113	+	* (without waking up if parked) to quickly spread notifications
1114	+	* without unnecessary bouncing around event queues etc (1) wake
1115	+	* up and help cancel tasks (2) interrupt (3) mop up races with
1116	+	* interrupted workers
1117		*/
1118		private void startTerminating() {
1119	<	for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers
1120	<	cancelSubmissions();
1121	<	shutdownWorkers();
1122	<	cancelWorkerTasks();
1123	<	advanceEventCount();
1124	<	releaseWaiters();
1125	<	interruptWorkers();
1119	>	cancelSubmissions();
1120	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1121	>	int c; // advance event count
1122	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
1123	>	c = eventCount, c+1);
1124	>	eventWaiters = 0L; // clobber lists
1125	>	spareWaiters = 0;
1126	>	for (ForkJoinWorkerThread w : workers) {
1127	>	if (w != null) {
1128	>	w.shutdown();
1129	>	if (passes > 0 && !w.isTerminated()) {
1130	>	w.cancelTasks();
1131	>	LockSupport.unpark(w);
1132	>	if (passes > 1 && !w.isInterrupted()) {
1133	>	try {
1134	>	w.interrupt();
1135	>	} catch (SecurityException ignore) {
1136	>	}
1137	>	}
1138	>	}
1139	>	}
1140	>	}
1141		}
1142		}
1143
1144		/**
1145	<	* Clear out and cancel submissions, ignoring exceptions
1145	>	* Clears out and cancels submissions, ignoring exceptions.
1146		*/
1147		private void cancelSubmissions() {
1148		ForkJoinTask<?> task;
#	Line 1122 | Line 1154 | public class ForkJoinPool extends Abstra
1154		}
1155		}
1156
1125	–	/**
1126	–	* Sets all worker run states to at least shutdown,
1127	–	* also resuming suspended workers
1128	–	*/
1129	–	private void shutdownWorkers() {
1130	–	ForkJoinWorkerThread[] ws = workers;
1131	–	int nws = ws.length;
1132	–	for (int i = 0; i < nws; ++i) {
1133	–	ForkJoinWorkerThread w = ws[i];
1134	–	if (w != null)
1135	–	w.shutdown();
1136	–	}
1137	–	}
1138	–
1139	–	/**
1140	–	* Clears out and cancels all locally queued tasks
1141	–	*/
1142	–	private void cancelWorkerTasks() {
1143	–	ForkJoinWorkerThread[] ws = workers;
1144	–	int nws = ws.length;
1145	–	for (int i = 0; i < nws; ++i) {
1146	–	ForkJoinWorkerThread w = ws[i];
1147	–	if (w != null)
1148	–	w.cancelTasks();
1149	–	}
1150	–	}
1151	–
1152	–	/**
1153	–	* Unsticks all workers blocked on joins etc
1154	–	*/
1155	–	private void interruptWorkers() {
1156	–	ForkJoinWorkerThread[] ws = workers;
1157	–	int nws = ws.length;
1158	–	for (int i = 0; i < nws; ++i) {
1159	–	ForkJoinWorkerThread w = ws[i];
1160	–	if (w != null && !w.isTerminated()) {
1161	–	try {
1162	–	w.interrupt();
1163	–	} catch (SecurityException ignore) {
1164	–	}
1165	–	}
1166	–	}
1167	–	}
1168	–
1157		// misc support for ForkJoinWorkerThread
1158
1159		/**
1160	<	* Returns pool number
1160	>	* Returns pool number.
1161		*/
1162		final int getPoolNumber() {
1163		return poolNumber;
1164		}
1165
1166		/**
1167	<	* Accumulates steal count from a worker, clearing
1168	<	* the worker's value
1167	>	* Tries to accumulate steal count from a worker, clearing
1168	>	* the worker's value if successful.
1169	>	*
1170	>	* @return true if worker steal count now zero
1171		*/
1172	<	final void accumulateStealCount(ForkJoinWorkerThread w) {
1172	>	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1173		int sc = w.stealCount;
1174	<	if (sc != 0) {
1175	<	long c;
1176	<	w.stealCount = 0;
1177	<	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1178	<	c = stealCount, c + sc));
1174	>	long c = stealCount;
1175	>	// CAS even if zero, for fence effects
1176	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1177	>	if (sc != 0)
1178	>	w.stealCount = 0;
1179	>	return true;
1180		}
1181	+	return sc == 0;
1182		}
1183
1184		/**
#	Line 1194 | Line 1186 | public class ForkJoinPool extends Abstra
1186		* active thread.
1187		*/
1188		final int idlePerActive() {
1189	<	int ac = runState;    // no mask -- artifically boosts during shutdown
1190	<	int pc = parallelism; // use targeted parallelism, not rc
1189	>	int pc = parallelism; // use parallelism, not rc
1190	>	int ac = runState;    // no mask -- artificially boosts during shutdown
1191		// Use exact results for small values, saturate past 4
1192	<	return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1192	>	return ((pc <= ac) ? 0 :
1193	>	(pc >>> 1 <= ac) ? 1 :
1194	>	(pc >>> 2 <= ac) ? 3 :
1195	>	pc >>> 3);
1196		}
1197
1198		// Public and protected methods
#	Line 1206 | Line 1201 | public class ForkJoinPool extends Abstra
1201
1202		/**
1203		* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1204	<	* java.lang.Runtime#availableProcessors}, and using the {@linkplain
1205	<	* #defaultForkJoinWorkerThreadFactory default thread factory}.
1204	>	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1205	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1206	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1207		*
1208		* @throws SecurityException if a security manager exists and
1209		*         the caller is not permitted to modify threads
#	Line 1216 | Line 1212 | public class ForkJoinPool extends Abstra
1212		*/
1213		public ForkJoinPool() {
1214		this(Runtime.getRuntime().availableProcessors(),
1215	<	defaultForkJoinWorkerThreadFactory);
1215	>	defaultForkJoinWorkerThreadFactory, null, false);
1216		}
1217
1218		/**
1219		* Creates a {@code ForkJoinPool} with the indicated parallelism
1220	<	* level and using the {@linkplain
1221	<	* #defaultForkJoinWorkerThreadFactory default thread factory}.
1220	>	* level, the {@linkplain
1221	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1222	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1223		*
1224		* @param parallelism the parallelism level
1225		* @throws IllegalArgumentException if parallelism less than or
#	Line 1233 | Line 1230 | public class ForkJoinPool extends Abstra
1230		*         java.lang.RuntimePermission}{@code ("modifyThread")}
1231		*/
1232		public ForkJoinPool(int parallelism) {
1233	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
1237	<	}
1238	<
1239	<	/**
1240	<	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1241	<	* java.lang.Runtime#availableProcessors}, and using the given
1242	<	* thread factory.
1243	<	*
1244	<	* @param factory the factory for creating new threads
1245	<	* @throws NullPointerException if the factory is null
1246	<	* @throws SecurityException if a security manager exists and
1247	<	*         the caller is not permitted to modify threads
1248	<	*         because it does not hold {@link
1249	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1250	<	*/
1251	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
1252	<	this(Runtime.getRuntime().availableProcessors(), factory);
1233	>	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1234		}
1235
1236		/**
1237	<	* Creates a {@code ForkJoinPool} with the given parallelism and
1257	<	* thread factory.
1237	>	* Creates a {@code ForkJoinPool} with the given parameters.
1238		*
1239	<	* @param parallelism the parallelism level
1240	<	* @param factory the factory for creating new threads
1239	>	* @param parallelism the parallelism level. For default value,
1240	>	* use {@link java.lang.Runtime#availableProcessors}.
1241	>	* @param factory the factory for creating new threads. For default value,
1242	>	* use {@link #defaultForkJoinWorkerThreadFactory}.
1243	>	* @param handler the handler for internal worker threads that
1244	>	* terminate due to unrecoverable errors encountered while executing
1245	>	* tasks. For default value, use {@code null}.
1246	>	* @param asyncMode if true,
1247	>	* establishes local first-in-first-out scheduling mode for forked
1248	>	* tasks that are never joined. This mode may be more appropriate
1249	>	* than default locally stack-based mode in applications in which
1250	>	* worker threads only process event-style asynchronous tasks.
1251	>	* For default value, use {@code false}.
1252		* @throws IllegalArgumentException if parallelism less than or
1253		*         equal to zero, or greater than implementation limit
1254		* @throws NullPointerException if the factory is null
#	Line 1266 | Line 1257 | public class ForkJoinPool extends Abstra
1257		*         because it does not hold {@link
1258		*         java.lang.RuntimePermission}{@code ("modifyThread")}
1259		*/
1260	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
1260	>	public ForkJoinPool(int parallelism,
1261	>	ForkJoinWorkerThreadFactory factory,
1262	>	Thread.UncaughtExceptionHandler handler,
1263	>	boolean asyncMode) {
1264		checkPermission();
1265		if (factory == null)
1266		throw new NullPointerException();
1267	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1267	>	if (parallelism <= 0 || parallelism > MAX_WORKERS)
1268		throw new IllegalArgumentException();
1275	–	this.poolNumber = poolNumberGenerator.incrementAndGet();
1276	–	int arraySize = initialArraySizeFor(parallelism);
1269		this.parallelism = parallelism;
1270		this.factory = factory;
1271	<	this.maxPoolSize = MAX_THREADS;
1272	<	this.maintainsParallelism = true;
1271	>	this.ueh = handler;
1272	>	this.locallyFifo = asyncMode;
1273	>	int arraySize = initialArraySizeFor(parallelism);
1274		this.workers = new ForkJoinWorkerThread[arraySize];
1275		this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1276		this.workerLock = new ReentrantLock();
1277	<	this.terminationLatch = new CountDownLatch(1);
1277	>	this.termination = new Phaser(1);
1278	>	this.poolNumber = poolNumberGenerator.incrementAndGet();
1279		}
1280
1281		/**
#	Line 1289 | Line 1283 | public class ForkJoinPool extends Abstra
1283		* @param pc the initial parallelism level
1284		*/
1285		private static int initialArraySizeFor(int pc) {
1286	<	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1287	<	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1286	>	// If possible, initially allocate enough space for one spare
1287	>	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1288	>	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1289		size |= size >>> 1;
1290		size |= size >>> 2;
1291		size |= size >>> 4;
#	Line 1309 | Line 1304 | public class ForkJoinPool extends Abstra
1304		if (runState >= SHUTDOWN)
1305		throw new RejectedExecutionException();
1306		submissionQueue.offer(task);
1307	<	advanceEventCount();
1308	<	releaseWaiters();
1309	<	ensureEnoughTotalWorkers();
1307	>	int c; // try to increment event count -- CAS failure OK
1308	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
1309	>	helpMaintainParallelism(); // create, start, or resume some workers
1310		}
1311
1312		/**
#	Line 1357 | Line 1352 | public class ForkJoinPool extends Abstra
1352		}
1353
1354		/**
1355	+	* Submits a ForkJoinTask for execution.
1356	+	*
1357	+	* @param task the task to submit
1358	+	* @return the task
1359	+	* @throws NullPointerException if the task is null
1360	+	* @throws RejectedExecutionException if the task cannot be
1361	+	*         scheduled for execution
1362	+	*/
1363	+	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1364	+	doSubmit(task);
1365	+	return task;
1366	+	}
1367	+
1368	+	/**
1369		* @throws NullPointerException if the task is null
1370		* @throws RejectedExecutionException if the task cannot be
1371		*         scheduled for execution
#	Line 1394 | Line 1403 | public class ForkJoinPool extends Abstra
1403		}
1404
1405		/**
1397	–	* Submits a ForkJoinTask for execution.
1398	–	*
1399	–	* @param task the task to submit
1400	–	* @return the task
1401	–	* @throws NullPointerException if the task is null
1402	–	* @throws RejectedExecutionException if the task cannot be
1403	–	*         scheduled for execution
1404	–	*/
1405	–	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1406	–	doSubmit(task);
1407	–	return task;
1408	–	}
1409	–
1410	–	/**
1406		* @throws NullPointerException       {@inheritDoc}
1407		* @throws RejectedExecutionException {@inheritDoc}
1408		*/
#	Line 1449 | Line 1444 | public class ForkJoinPool extends Abstra
1444		* @return the handler, or {@code null} if none
1445		*/
1446		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1452	–	workerCountReadFence();
1447		return ueh;
1448		}
1449
1450		/**
1457	–	* Sets the handler for internal worker threads that terminate due
1458	–	* to unrecoverable errors encountered while executing tasks.
1459	–	* Unless set, the current default or ThreadGroup handler is used
1460	–	* as handler.
1461	–	*
1462	–	* @param h the new handler
1463	–	* @return the old handler, or {@code null} if none
1464	–	* @throws SecurityException if a security manager exists and
1465	–	*         the caller is not permitted to modify threads
1466	–	*         because it does not hold {@link
1467	–	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1468	–	*/
1469	–	public Thread.UncaughtExceptionHandler
1470	–	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
1471	–	checkPermission();
1472	–	Thread.UncaughtExceptionHandler old = ueh;
1473	–	if (h != old) {
1474	–	ueh = h;
1475	–	ForkJoinWorkerThread[] ws = workers;
1476	–	int nws = ws.length;
1477	–	for (int i = 0; i < nws; ++i) {
1478	–	ForkJoinWorkerThread w = ws[i];
1479	–	if (w != null)
1480	–	w.setUncaughtExceptionHandler(h);
1481	–	}
1482	–	}
1483	–	return old;
1484	–	}
1485	–
1486	–	/**
1487	–	* Sets the target parallelism level of this pool.
1488	–	*
1489	–	* @param parallelism the target parallelism
1490	–	* @throws IllegalArgumentException if parallelism less than or
1491	–	* equal to zero or greater than maximum size bounds
1492	–	* @throws SecurityException if a security manager exists and
1493	–	*         the caller is not permitted to modify threads
1494	–	*         because it does not hold {@link
1495	–	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1496	–	*/
1497	–	public void setParallelism(int parallelism) {
1498	–	checkPermission();
1499	–	if (parallelism <= 0 || parallelism > maxPoolSize)
1500	–	throw new IllegalArgumentException();
1501	–	workerCountReadFence();
1502	–	int pc = this.parallelism;
1503	–	if (pc != parallelism) {
1504	–	this.parallelism = parallelism;
1505	–	workerCountWriteFence();
1506	–	// Release spares. If too many, some will die after re-suspend
1507	–	ForkJoinWorkerThread[] ws = workers;
1508	–	int nws = ws.length;
1509	–	for (int i = 0; i < nws; ++i) {
1510	–	ForkJoinWorkerThread w = ws[i];
1511	–	if (w != null && w.tryUnsuspend()) {
1512	–	int c;
1513	–	do {} while (!UNSAFE.compareAndSwapInt
1514	–	(this, workerCountsOffset,
1515	–	c = workerCounts, c + ONE_RUNNING));
1516	–	LockSupport.unpark(w);
1517	–	}
1518	–	}
1519	–	ensureEnoughTotalWorkers();
1520	–	advanceEventCount();
1521	–	releaseWaiters(); // force config recheck by existing workers
1522	–	}
1523	–	}
1524	–
1525	–	/**
1451		* Returns the targeted parallelism level of this pool.
1452		*
1453		* @return the targeted parallelism level of this pool
1454		*/
1455		public int getParallelism() {
1531	–	//        workerCountReadFence(); // inlined below
1532	–	int ignore = workerCounts;
1456		return parallelism;
1457		}
1458
1459		/**
1460		* Returns the number of worker threads that have started but not
1461	<	* yet terminated.  This result returned by this method may differ
1461	>	* yet terminated.  The result returned by this method may differ
1462		* from {@link #getParallelism} when threads are created to
1463		* maintain parallelism when others are cooperatively blocked.
1464		*
#	Line 1546 | Line 1469 | public class ForkJoinPool extends Abstra
1469		}
1470
1471		/**
1549	–	* Returns the maximum number of threads allowed to exist in the
1550	–	* pool. Unless set using {@link #setMaximumPoolSize}, the
1551	–	* maximum is an implementation-defined value designed only to
1552	–	* prevent runaway growth.
1553	–	*
1554	–	* @return the maximum
1555	–	*/
1556	–	public int getMaximumPoolSize() {
1557	–	workerCountReadFence();
1558	–	return maxPoolSize;
1559	–	}
1560	–
1561	–	/**
1562	–	* Sets the maximum number of threads allowed to exist in the
1563	–	* pool. The given value should normally be greater than or equal
1564	–	* to the {@link #getParallelism parallelism} level. Setting this
1565	–	* value has no effect on current pool size. It controls
1566	–	* construction of new threads. The use of this method may cause
1567	–	* tasks that intrinsically require extra threads for dependent
1568	–	* computations to indefinitely stall. If you are instead trying
1569	–	* to minimize internal thread creation, consider setting {@link
1570	–	* #setMaintainsParallelism} as false.
1571	–	*
1572	–	* @throws IllegalArgumentException if negative or greater than
1573	–	* internal implementation limit
1574	–	*/
1575	–	public void setMaximumPoolSize(int newMax) {
1576	–	if (newMax < 0 || newMax > MAX_THREADS)
1577	–	throw new IllegalArgumentException();
1578	–	maxPoolSize = newMax;
1579	–	workerCountWriteFence();
1580	–	}
1581	–
1582	–	/**
1583	–	* Returns {@code true} if this pool dynamically maintains its
1584	–	* target parallelism level. If false, new threads are added only
1585	–	* to avoid possible starvation.  This setting is by default true.
1586	–	*
1587	–	* @return {@code true} if maintains parallelism
1588	–	*/
1589	–	public boolean getMaintainsParallelism() {
1590	–	workerCountReadFence();
1591	–	return maintainsParallelism;
1592	–	}
1593	–
1594	–	/**
1595	–	* Sets whether this pool dynamically maintains its target
1596	–	* parallelism level. If false, new threads are added only to
1597	–	* avoid possible starvation.
1598	–	*
1599	–	* @param enable {@code true} to maintain parallelism
1600	–	*/
1601	–	public void setMaintainsParallelism(boolean enable) {
1602	–	maintainsParallelism = enable;
1603	–	workerCountWriteFence();
1604	–	}
1605	–
1606	–	/**
1607	–	* Establishes local first-in-first-out scheduling mode for forked
1608	–	* tasks that are never joined. This mode may be more appropriate
1609	–	* than default locally stack-based mode in applications in which
1610	–	* worker threads only process asynchronous tasks.  This method is
1611	–	* designed to be invoked only when the pool is quiescent, and
1612	–	* typically only before any tasks are submitted. The effects of
1613	–	* invocations at other times may be unpredictable.
1614	–	*
1615	–	* @param async if {@code true}, use locally FIFO scheduling
1616	–	* @return the previous mode
1617	–	* @see #getAsyncMode
1618	–	*/
1619	–	public boolean setAsyncMode(boolean async) {
1620	–	workerCountReadFence();
1621	–	boolean oldMode = locallyFifo;
1622	–	if (oldMode != async) {
1623	–	locallyFifo = async;
1624	–	workerCountWriteFence();
1625	–	ForkJoinWorkerThread[] ws = workers;
1626	–	int nws = ws.length;
1627	–	for (int i = 0; i < nws; ++i) {
1628	–	ForkJoinWorkerThread w = ws[i];
1629	–	if (w != null)
1630	–	w.setAsyncMode(async);
1631	–	}
1632	–	}
1633	–	return oldMode;
1634	–	}
1635	–
1636	–	/**
1472		* Returns {@code true} if this pool uses local first-in-first-out
1473		* scheduling mode for forked tasks that are never joined.
1474		*
1475		* @return {@code true} if this pool uses async mode
1641	–	* @see #setAsyncMode
1476		*/
1477		public boolean getAsyncMode() {
1644	–	workerCountReadFence();
1478		return locallyFifo;
1479		}
1480
#	Line 1710 | Line 1543 | public class ForkJoinPool extends Abstra
1543		*/
1544		public long getQueuedTaskCount() {
1545		long count = 0;
1546	<	ForkJoinWorkerThread[] ws = workers;
1714	<	int nws = ws.length;
1715	<	for (int i = 0; i < nws; ++i) {
1716	<	ForkJoinWorkerThread w = ws[i];
1546	>	for (ForkJoinWorkerThread w : workers)
1547		if (w != null)
1548		count += w.getQueueSize();
1719	–	}
1549		return count;
1550		}
1551
#	Line 1770 | Line 1599 | public class ForkJoinPool extends Abstra
1599		* @return the number of elements transferred
1600		*/
1601		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1602	<	int n = submissionQueue.drainTo(c);
1603	<	ForkJoinWorkerThread[] ws = workers;
1775	<	int nws = ws.length;
1776	<	for (int i = 0; i < nws; ++i) {
1777	<	ForkJoinWorkerThread w = ws[i];
1602	>	int count = submissionQueue.drainTo(c);
1603	>	for (ForkJoinWorkerThread w : workers)
1604		if (w != null)
1605	<	n += w.drainTasksTo(c);
1606	<	}
1781	<	return n;
1605	>	count += w.drainTasksTo(c);
1606	>	return count;
1607		}
1608
1609		/**
#	Line 1881 | Line 1706 | public class ForkJoinPool extends Abstra
1706		}
1707
1708		/**
1709	+	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1710	+	*/
1711	+	final boolean isAtLeastTerminating() {
1712	+	return runState >= TERMINATING;
1713	+	}
1714	+
1715	+	/**
1716		* Returns {@code true} if this pool has been shut down.
1717		*
1718		* @return {@code true} if this pool has been shut down
#	Line 1902 | Line 1734 | public class ForkJoinPool extends Abstra
1734		*/
1735		public boolean awaitTermination(long timeout, TimeUnit unit)
1736		throws InterruptedException {
1737	<	return terminationLatch.await(timeout, unit);
1737	>	try {
1738	>	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1739	>	} catch (TimeoutException ex) {
1740	>	return false;
1741	>	}
1742		}
1743
1744		/**
1745		* Interface for extending managed parallelism for tasks running
1746		* in {@link ForkJoinPool}s.
1747		*
1748	<	* <p>A {@code ManagedBlocker} provides two methods.
1749	<	* Method {@code isReleasable} must return {@code true} if
1750	<	* blocking is not necessary. Method {@code block} blocks the
1751	<	* current thread if necessary (perhaps internally invoking
1752	<	* {@code isReleasable} before actually blocking).
1748	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1749	>	* {@code isReleasable} must return {@code true} if blocking is
1750	>	* not necessary. Method {@code block} blocks the current thread
1751	>	* if necessary (perhaps internally invoking {@code isReleasable}
1752	>	* before actually blocking). The unusual methods in this API
1753	>	* accommodate synchronizers that may, but don't usually, block
1754	>	* for long periods. Similarly, they allow more efficient internal
1755	>	* handling of cases in which additional workers may be, but
1756	>	* usually are not, needed to ensure sufficient parallelism.
1757	>	* Toward this end, implementations of method {@code isReleasable}
1758	>	* must be amenable to repeated invocation.
1759		*
1760		* <p>For example, here is a ManagedBlocker based on a
1761		* ReentrantLock:
#	Line 1931 | Line 1773 | public class ForkJoinPool extends Abstra
1773		*     return hasLock || (hasLock = lock.tryLock());
1774		*   }
1775		* }}</pre>
1776	+	*
1777	+	* <p>Here is a class that possibly blocks waiting for an
1778	+	* item on a given queue:
1779	+	*  <pre> {@code
1780	+	* class QueueTaker<E> implements ManagedBlocker {
1781	+	*   final BlockingQueue<E> queue;
1782	+	*   volatile E item = null;
1783	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1784	+	*   public boolean block() throws InterruptedException {
1785	+	*     if (item == null)
1786	+	*       item = queue.take();
1787	+	*     return true;
1788	+	*   }
1789	+	*   public boolean isReleasable() {
1790	+	*     return item != null || (item = queue.poll()) != null;
1791	+	*   }
1792	+	*   public E getItem() { // call after pool.managedBlock completes
1793	+	*     return item;
1794	+	*   }
1795	+	* }}</pre>
1796		*/
1797		public static interface ManagedBlocker {
1798		/**
#	Line 1954 | Line 1816 | public class ForkJoinPool extends Abstra
1816		* Blocks in accord with the given blocker.  If the current thread
1817		* is a {@link ForkJoinWorkerThread}, this method possibly
1818		* arranges for a spare thread to be activated if necessary to
1819	<	* ensure parallelism while the current thread is blocked.
1958	<	*
1959	<	* <p>If {@code maintainParallelism} is {@code true} and the pool
1960	<	* supports it ({@link #getMaintainsParallelism}), this method
1961	<	* attempts to maintain the pool's nominal parallelism. Otherwise
1962	<	* it activates a thread only if necessary to avoid complete
1963	<	* starvation. This option may be preferable when blockages use
1964	<	* timeouts, or are almost always brief.
1819	>	* ensure sufficient parallelism while the current thread is blocked.
1820		*
1821		* <p>If the caller is not a {@link ForkJoinTask}, this method is
1822		* behaviorally equivalent to
#	Line 1975 | Line 1830 | public class ForkJoinPool extends Abstra
1830		* first be expanded to ensure parallelism, and later adjusted.
1831		*
1832		* @param blocker the blocker
1978	–	* @param maintainParallelism if {@code true} and supported by
1979	–	* this pool, attempt to maintain the pool's nominal parallelism;
1980	–	* otherwise activate a thread only if necessary to avoid
1981	–	* complete starvation.
1833		* @throws InterruptedException if blocker.block did so
1834		*/
1835	<	public static void managedBlock(ManagedBlocker blocker,
1985	<	boolean maintainParallelism)
1835	>	public static void managedBlock(ManagedBlocker blocker)
1836		throws InterruptedException {
1837		Thread t = Thread.currentThread();
1838	<	if (t instanceof ForkJoinWorkerThread)
1839	<	((ForkJoinWorkerThread) t).pool.
1840	<	awaitBlocker(blocker, maintainParallelism);
1841	<	else
1842	<	awaitBlocker(blocker);
1843	<	}
1844	<
1995	<	/**
1996	<	* Performs Non-FJ blocking
1997	<	*/
1998	<	private static void awaitBlocker(ManagedBlocker blocker)
1999	<	throws InterruptedException {
2000	<	do {} while (!blocker.isReleasable() && !blocker.block());
1838	>	if (t instanceof ForkJoinWorkerThread) {
1839	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1840	>	w.pool.awaitBlocker(blocker);
1841	>	}
1842	>	else {
1843	>	do {} while (!blocker.isReleasable() && !blocker.block());
1844	>	}
1845		}
1846
1847		// AbstractExecutorService overrides.  These rely on undocumented
#	Line 2022 | Line 1866 | public class ForkJoinPool extends Abstra
1866		private static final long eventCountOffset =
1867		objectFieldOffset("eventCount", ForkJoinPool.class);
1868		private static final long eventWaitersOffset =
1869	<	objectFieldOffset("eventWaiters",ForkJoinPool.class);
1869	>	objectFieldOffset("eventWaiters", ForkJoinPool.class);
1870		private static final long stealCountOffset =
1871	<	objectFieldOffset("stealCount",ForkJoinPool.class);
1872	<
1871	>	objectFieldOffset("stealCount", ForkJoinPool.class);
1872	>	private static final long spareWaitersOffset =
1873	>	objectFieldOffset("spareWaiters", ForkJoinPool.class);
1874
1875		private static long objectFieldOffset(String field, Class<?> klazz) {
1876		try {

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