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Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.7 by jsr166, Mon Jul 20 21:45:06 2009 UTC vs.
Revision 1.136 by dl, Mon Oct 29 17:23:34 2012 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3		* Expert Group and released to the public domain, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		*/
6
7		package jsr166y;
8	<	import java.util.*;
9	<	import java.util.concurrent.*;
10	<	import java.util.concurrent.locks.*;
11	<	import java.util.concurrent.atomic.*;
12	<	import sun.misc.Unsafe;
13	<	import java.lang.reflect.*;
8	>
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.Random;
15	>	import java.util.concurrent.AbstractExecutorService;
16	>	import java.util.concurrent.Callable;
17	>	import java.util.concurrent.ExecutorService;
18	>	import java.util.concurrent.Future;
19	>	import java.util.concurrent.RejectedExecutionException;
20	>	import java.util.concurrent.RunnableFuture;
21	>	import java.util.concurrent.TimeUnit;
22	>	import java.util.concurrent.atomic.AtomicInteger;
23	>	import java.util.concurrent.atomic.AtomicLong;
24	>	import java.util.concurrent.locks.AbstractQueuedSynchronizer;
25	>	import java.util.concurrent.locks.Condition;
26
27		/**
28	<	* An {@link ExecutorService} for running {@link ForkJoinTask}s.  A
29	<	* ForkJoinPool provides the entry point for submissions from
30	<	* non-ForkJoinTasks, as well as management and monitoring operations.
31	<	* Normally a single ForkJoinPool is used for a large number of
32	<	* submitted tasks. Otherwise, use would not usually outweigh the
33	<	* construction and bookkeeping overhead of creating a large set of
34	<	* threads.
28	>	* An {@link ExecutorService} for running {@link ForkJoinTask}s.
29	>	* A {@code ForkJoinPool} provides the entry point for submissions
30	>	* from non-{@code ForkJoinTask} clients, as well as management and
31	>	* monitoring operations.
32	>	*
33	>	* <p>A {@code ForkJoinPool} differs from other kinds of {@link
34	>	* ExecutorService} mainly by virtue of employing
35	>	* <em>work-stealing</em>: all threads in the pool attempt to find and
36	>	* execute tasks submitted to the pool and/or created by other active
37	>	* tasks (eventually blocking waiting for work if none exist). This
38	>	* enables efficient processing when most tasks spawn other subtasks
39	>	* (as do most {@code ForkJoinTask}s), as well as when many small
40	>	* tasks are submitted to the pool from external clients.  Especially
41	>	* when setting <em>asyncMode</em> to true in constructors, {@code
42	>	* ForkJoinPool}s may also be appropriate for use with event-style
43	>	* tasks that are never joined.
44		*
45	<	* <p>ForkJoinPools differ from other kinds of Executors mainly in
46	<	* that they provide <em>work-stealing</em>: all threads in the pool
47	<	* attempt to find and execute subtasks created by other active tasks
48	<	* (eventually blocking if none exist). This makes them efficient when
49	<	* most tasks spawn other subtasks (as do most ForkJoinTasks), as well
50	<	* as the mixed execution of some plain Runnable- or Callable- based
51	<	* activities along with ForkJoinTasks. When setting
52	<	* <tt>setAsyncMode</tt>, a ForkJoinPools may also be appropriate for
53	<	* use with fine-grained tasks that are never joined. Otherwise, other
54	<	* ExecutorService implementations are typically more appropriate
34	<	* choices.
45	>	* <p>A static {@link #commonPool} is available and appropriate for
46	>	* most applications. The common pool is used by any ForkJoinTask that
47	>	* is not explicitly submitted to a specified pool. Using the common
48	>	* pool normally reduces resource usage (its threads are slowly
49	>	* reclaimed during periods of non-use, and reinstated upon subsequent
50	>	* use).  The common pool is by default constructed with default
51	>	* parameters, but these may be controlled by setting any or all of
52	>	* the three properties {@code
53	>	* java.util.concurrent.ForkJoinPool.common.{parallelism,
54	>	* threadFactory, exceptionHandler}}.
55		*
56	<	* <p>A ForkJoinPool may be constructed with a given parallelism level
57	<	* (target pool size), which it attempts to maintain by dynamically
58	<	* adding, suspending, or resuming threads, even if some tasks are
59	<	* waiting to join others. However, no such adjustments are performed
60	<	* in the face of blocked IO or other unmanaged synchronization. The
61	<	* nested <code>ManagedBlocker</code> interface enables extension of
62	<	* the kinds of synchronization accommodated.  The target parallelism
63	<	* level may also be changed dynamically (<code>setParallelism</code>)
64	<	* and thread construction can be limited using methods
65	<	* <code>setMaximumPoolSize</code> and/or
46	<	* <code>setMaintainsParallelism</code>.
56	>	* <p>For applications that require separate or custom pools, a {@code
57	>	* ForkJoinPool} may be constructed with a given target parallelism
58	>	* level; by default, equal to the number of available processors. The
59	>	* pool attempts to maintain enough active (or available) threads by
60	>	* dynamically adding, suspending, or resuming internal worker
61	>	* threads, even if some tasks are stalled waiting to join
62	>	* others. However, no such adjustments are guaranteed in the face of
63	>	* blocked IO or other unmanaged synchronization. The nested {@link
64	>	* ManagedBlocker} interface enables extension of the kinds of
65	>	* synchronization accommodated.
66		*
67		* <p>In addition to execution and lifecycle control methods, this
68		* class provides status check methods (for example
69	<	* <code>getStealCount</code>) that are intended to aid in developing,
69	>	* {@link #getStealCount}) that are intended to aid in developing,
70		* tuning, and monitoring fork/join applications. Also, method
71	<	* <code>toString</code> returns indications of pool state in a
71	>	* {@link #toString} returns indications of pool state in a
72		* convenient form for informal monitoring.
73		*
74	+	* <p> As is the case with other ExecutorServices, there are three
75	+	* main task execution methods summarized in the following table.
76	+	* These are designed to be used primarily by clients not already
77	+	* engaged in fork/join computations in the current pool.  The main
78	+	* forms of these methods accept instances of {@code ForkJoinTask},
79	+	* but overloaded forms also allow mixed execution of plain {@code
80	+	* Runnable}- or {@code Callable}- based activities as well.  However,
81	+	* tasks that are already executing in a pool should normally instead
82	+	* use the within-computation forms listed in the table unless using
83	+	* async event-style tasks that are not usually joined, in which case
84	+	* there is little difference among choice of methods.
85	+	*
86	+	* <table BORDER CELLPADDING=3 CELLSPACING=1>
87	+	*  <tr>
88	+	*    <td></td>
89	+	*    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
90	+	*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
91	+	*  </tr>
92	+	*  <tr>
93	+	*    <td> <b>Arrange async execution</td>
94	+	*    <td> {@link #execute(ForkJoinTask)}</td>
95	+	*    <td> {@link ForkJoinTask#fork}</td>
96	+	*  </tr>
97	+	*  <tr>
98	+	*    <td> <b>Await and obtain result</td>
99	+	*    <td> {@link #invoke(ForkJoinTask)}</td>
100	+	*    <td> {@link ForkJoinTask#invoke}</td>
101	+	*  </tr>
102	+	*  <tr>
103	+	*    <td> <b>Arrange exec and obtain Future</td>
104	+	*    <td> {@link #submit(ForkJoinTask)}</td>
105	+	*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
106	+	*  </tr>
107	+	* </table>
108	+	*
109		* <p><b>Implementation notes</b>: This implementation restricts the
110		* maximum number of running threads to 32767. Attempts to create
111	<	* pools with greater than the maximum result in
112	<	* IllegalArgumentExceptions.
111	>	* pools with greater than the maximum number result in
112	>	* {@code IllegalArgumentException}.
113	>	*
114	>	* <p>This implementation rejects submitted tasks (that is, by throwing
115	>	* {@link RejectedExecutionException}) only when the pool is shut down
116	>	* or internal resources have been exhausted.
117	>	*
118	>	* @since 1.7
119	>	* @author Doug Lea
120		*/
121		public class ForkJoinPool extends AbstractExecutorService {
122
123		/*
124	<	* See the extended comments interspersed below for design,
125	<	* rationale, and walkthroughs.
124	>	* Implementation Overview
125	>	*
126	>	* This class and its nested classes provide the main
127	>	* functionality and control for a set of worker threads:
128	>	* Submissions from non-FJ threads enter into submission queues.
129	>	* Workers take these tasks and typically split them into subtasks
130	>	* that may be stolen by other workers.  Preference rules give
131	>	* first priority to processing tasks from their own queues (LIFO
132	>	* or FIFO, depending on mode), then to randomized FIFO steals of
133	>	* tasks in other queues.
134	>	*
135	>	* WorkQueues
136	>	* ==========
137	>	*
138	>	* Most operations occur within work-stealing queues (in nested
139	>	* class WorkQueue).  These are special forms of Deques that
140	>	* support only three of the four possible end-operations -- push,
141	>	* pop, and poll (aka steal), under the further constraints that
142	>	* push and pop are called only from the owning thread (or, as
143	>	* extended here, under a lock), while poll may be called from
144	>	* other threads.  (If you are unfamiliar with them, you probably
145	>	* want to read Herlihy and Shavit's book "The Art of
146	>	* Multiprocessor programming", chapter 16 describing these in
147	>	* more detail before proceeding.)  The main work-stealing queue
148	>	* design is roughly similar to those in the papers "Dynamic
149	>	* Circular Work-Stealing Deque" by Chase and Lev, SPAA 2005
150	>	* (http://research.sun.com/scalable/pubs/index.html) and
151	>	* "Idempotent work stealing" by Michael, Saraswat, and Vechev,
152	>	* PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186).
153	>	* The main differences ultimately stem from GC requirements that
154	>	* we null out taken slots as soon as we can, to maintain as small
155	>	* a footprint as possible even in programs generating huge
156	>	* numbers of tasks. To accomplish this, we shift the CAS
157	>	* arbitrating pop vs poll (steal) from being on the indices
158	>	* ("base" and "top") to the slots themselves.  So, both a
159	>	* successful pop and poll mainly entail a CAS of a slot from
160	>	* non-null to null.  Because we rely on CASes of references, we
161	>	* do not need tag bits on base or top.  They are simple ints as
162	>	* used in any circular array-based queue (see for example
163	>	* ArrayDeque).  Updates to the indices must still be ordered in a
164	>	* way that guarantees that top == base means the queue is empty,
165	>	* but otherwise may err on the side of possibly making the queue
166	>	* appear nonempty when a push, pop, or poll have not fully
167	>	* committed. Note that this means that the poll operation,
168	>	* considered individually, is not wait-free. One thief cannot
169	>	* successfully continue until another in-progress one (or, if
170	>	* previously empty, a push) completes.  However, in the
171	>	* aggregate, we ensure at least probabilistic non-blockingness.
172	>	* If an attempted steal fails, a thief always chooses a different
173	>	* random victim target to try next. So, in order for one thief to
174	>	* progress, it suffices for any in-progress poll or new push on
175	>	* any empty queue to complete. (This is why we normally use
176	>	* method pollAt and its variants that try once at the apparent
177	>	* base index, else consider alternative actions, rather than
178	>	* method poll.)
179	>	*
180	>	* This approach also enables support of a user mode in which local
181	>	* task processing is in FIFO, not LIFO order, simply by using
182	>	* poll rather than pop.  This can be useful in message-passing
183	>	* frameworks in which tasks are never joined.  However neither
184	>	* mode considers affinities, loads, cache localities, etc, so
185	>	* rarely provide the best possible performance on a given
186	>	* machine, but portably provide good throughput by averaging over
187	>	* these factors.  (Further, even if we did try to use such
188	>	* information, we do not usually have a basis for exploiting it.
189	>	* For example, some sets of tasks profit from cache affinities,
190	>	* but others are harmed by cache pollution effects.)
191	>	*
192	>	* WorkQueues are also used in a similar way for tasks submitted
193	>	* to the pool. We cannot mix these tasks in the same queues used
194	>	* for work-stealing (this would contaminate lifo/fifo
195	>	* processing). Instead, we loosely associate submission queues
196	>	* with submitting threads, using a form of hashing.  The
197	>	* ThreadLocal Submitter class contains a value initially used as
198	>	* a hash code for choosing existing queues, but may be randomly
199	>	* repositioned upon contention with other submitters.  In
200	>	* essence, submitters act like workers except that they never
201	>	* take tasks, and they are multiplexed on to a finite number of
202	>	* shared work queues. However, classes are set up so that future
203	>	* extensions could allow submitters to optionally help perform
204	>	* tasks as well. Insertion of tasks in shared mode requires a
205	>	* lock (mainly to protect in the case of resizing) but we use
206	>	* only a simple spinlock (using bits in field runState), because
207	>	* submitters encountering a busy queue move on to try or create
208	>	* other queues -- they block only when creating and registering
209	>	* new queues.
210	>	*
211	>	* Management
212	>	* ==========
213	>	*
214	>	* The main throughput advantages of work-stealing stem from
215	>	* decentralized control -- workers mostly take tasks from
216	>	* themselves or each other. We cannot negate this in the
217	>	* implementation of other management responsibilities. The main
218	>	* tactic for avoiding bottlenecks is packing nearly all
219	>	* essentially atomic control state into two volatile variables
220	>	* that are by far most often read (not written) as status and
221	>	* consistency checks.
222	>	*
223	>	* Field "ctl" contains 64 bits holding all the information needed
224	>	* to atomically decide to add, inactivate, enqueue (on an event
225	>	* queue), dequeue, and/or re-activate workers.  To enable this
226	>	* packing, we restrict maximum parallelism to (1<<15)-1 (which is
227	>	* far in excess of normal operating range) to allow ids, counts,
228	>	* and their negations (used for thresholding) to fit into 16bit
229	>	* fields.
230	>	*
231	>	* Field "runState" contains 32 bits needed to register and
232	>	* deregister WorkQueues, as well as to enable shutdown. It is
233	>	* only modified under a lock (normally briefly held, but
234	>	* occasionally protecting allocations and resizings) but even
235	>	* when locked remains available to check consistency.
236	>	*
237	>	* Recording WorkQueues.  WorkQueues are recorded in the
238	>	* "workQueues" array that is created upon first use and expanded
239	>	* if necessary.  Updates to the array while recording new workers
240	>	* and unrecording terminated ones are protected from each other
241	>	* by a lock but the array is otherwise concurrently readable, and
242	>	* accessed directly.  To simplify index-based operations, the
243	>	* array size is always a power of two, and all readers must
244	>	* tolerate null slots. Shared (submission) queues are at even
245	>	* indices, worker queues at odd indices. Grouping them together
246	>	* in this way simplifies and speeds up task scanning.
247	>	*
248	>	* All worker thread creation is on-demand, triggered by task
249	>	* submissions, replacement of terminated workers, and/or
250	>	* compensation for blocked workers. However, all other support
251	>	* code is set up to work with other policies.  To ensure that we
252	>	* do not hold on to worker references that would prevent GC, ALL
253	>	* accesses to workQueues are via indices into the workQueues
254	>	* array (which is one source of some of the messy code
255	>	* constructions here). In essence, the workQueues array serves as
256	>	* a weak reference mechanism. Thus for example the wait queue
257	>	* field of ctl stores indices, not references.  Access to the
258	>	* workQueues in associated methods (for example signalWork) must
259	>	* both index-check and null-check the IDs. All such accesses
260	>	* ignore bad IDs by returning out early from what they are doing,
261	>	* since this can only be associated with termination, in which
262	>	* case it is OK to give up.  All uses of the workQueues array
263	>	* also check that it is non-null (even if previously
264	>	* non-null). This allows nulling during termination, which is
265	>	* currently not necessary, but remains an option for
266	>	* resource-revocation-based shutdown schemes. It also helps
267	>	* reduce JIT issuance of uncommon-trap code, which tends to
268	>	* unnecessarily complicate control flow in some methods.
269	>	*
270	>	* Event Queuing. Unlike HPC work-stealing frameworks, we cannot
271	>	* let workers spin indefinitely scanning for tasks when none can
272	>	* be found immediately, and we cannot start/resume workers unless
273	>	* there appear to be tasks available.  On the other hand, we must
274	>	* quickly prod them into action when new tasks are submitted or
275	>	* generated. In many usages, ramp-up time to activate workers is
276	>	* the main limiting factor in overall performance (this is
277	>	* compounded at program start-up by JIT compilation and
278	>	* allocation). So we try to streamline this as much as possible.
279	>	* We park/unpark workers after placing in an event wait queue
280	>	* when they cannot find work. This "queue" is actually a simple
281	>	* Treiber stack, headed by the "id" field of ctl, plus a 15bit
282	>	* counter value (that reflects the number of times a worker has
283	>	* been inactivated) to avoid ABA effects (we need only as many
284	>	* version numbers as worker threads). Successors are held in
285	>	* field WorkQueue.nextWait.  Queuing deals with several intrinsic
286	>	* races, mainly that a task-producing thread can miss seeing (and
287	>	* signalling) another thread that gave up looking for work but
288	>	* has not yet entered the wait queue. We solve this by requiring
289	>	* a full sweep of all workers (via repeated calls to method
290	>	* scan()) both before and after a newly waiting worker is added
291	>	* to the wait queue. During a rescan, the worker might release
292	>	* some other queued worker rather than itself, which has the same
293	>	* net effect. Because enqueued workers may actually be rescanning
294	>	* rather than waiting, we set and clear the "parker" field of
295	>	* WorkQueues to reduce unnecessary calls to unpark.  (This
296	>	* requires a secondary recheck to avoid missed signals.)  Note
297	>	* the unusual conventions about Thread.interrupts surrounding
298	>	* parking and other blocking: Because interrupts are used solely
299	>	* to alert threads to check termination, which is checked anyway
300	>	* upon blocking, we clear status (using Thread.interrupted)
301	>	* before any call to park, so that park does not immediately
302	>	* return due to status being set via some other unrelated call to
303	>	* interrupt in user code.
304	>	*
305	>	* Signalling.  We create or wake up workers only when there
306	>	* appears to be at least one task they might be able to find and
307	>	* execute.  When a submission is added or another worker adds a
308	>	* task to a queue that previously had fewer than two tasks, they
309	>	* signal waiting workers (or trigger creation of new ones if
310	>	* fewer than the given parallelism level -- see signalWork).
311	>	* These primary signals are buttressed by signals during rescans;
312	>	* together these cover the signals needed in cases when more
313	>	* tasks are pushed but untaken, and improve performance compared
314	>	* to having one thread wake up all workers.
315	>	*
316	>	* Trimming workers. To release resources after periods of lack of
317	>	* use, a worker starting to wait when the pool is quiescent will
318	>	* time out and terminate if the pool has remained quiescent for a
319	>	* given period -- a short period if there are more threads than
320	>	* parallelism, longer as the number of threads decreases. This
321	>	* will slowly propagate, eventually terminating all workers after
322	>	* periods of non-use.
323	>	*
324	>	* Shutdown and Termination. A call to shutdownNow atomically sets
325	>	* a runState bit and then (non-atomically) sets each worker's
326	>	* runState status, cancels all unprocessed tasks, and wakes up
327	>	* all waiting workers.  Detecting whether termination should
328	>	* commence after a non-abrupt shutdown() call requires more work
329	>	* and bookkeeping. We need consensus about quiescence (i.e., that
330	>	* there is no more work). The active count provides a primary
331	>	* indication but non-abrupt shutdown still requires a rechecking
332	>	* scan for any workers that are inactive but not queued.
333	>	*
334	>	* Joining Tasks
335	>	* =============
336	>	*
337	>	* Any of several actions may be taken when one worker is waiting
338	>	* to join a task stolen (or always held) by another.  Because we
339	>	* are multiplexing many tasks on to a pool of workers, we can't
340	>	* just let them block (as in Thread.join).  We also cannot just
341	>	* reassign the joiner's run-time stack with another and replace
342	>	* it later, which would be a form of "continuation", that even if
343	>	* possible is not necessarily a good idea since we sometimes need
344	>	* both an unblocked task and its continuation to progress.
345	>	* Instead we combine two tactics:
346	>	*
347	>	*   Helping: Arranging for the joiner to execute some task that it
348	>	*      would be running if the steal had not occurred.
349	>	*
350	>	*   Compensating: Unless there are already enough live threads,
351	>	*      method tryCompensate() may create or re-activate a spare
352	>	*      thread to compensate for blocked joiners until they unblock.
353	>	*
354	>	* A third form (implemented in tryRemoveAndExec and
355	>	* tryPollForAndExec) amounts to helping a hypothetical
356	>	* compensator: If we can readily tell that a possible action of a
357	>	* compensator is to steal and execute the task being joined, the
358	>	* joining thread can do so directly, without the need for a
359	>	* compensation thread (although at the expense of larger run-time
360	>	* stacks, but the tradeoff is typically worthwhile).
361	>	*
362	>	* The ManagedBlocker extension API can't use helping so relies
363	>	* only on compensation in method awaitBlocker.
364	>	*
365	>	* The algorithm in tryHelpStealer entails a form of "linear"
366	>	* helping: Each worker records (in field currentSteal) the most
367	>	* recent task it stole from some other worker. Plus, it records
368	>	* (in field currentJoin) the task it is currently actively
369	>	* joining. Method tryHelpStealer uses these markers to try to
370	>	* find a worker to help (i.e., steal back a task from and execute
371	>	* it) that could hasten completion of the actively joined task.
372	>	* In essence, the joiner executes a task that would be on its own
373	>	* local deque had the to-be-joined task not been stolen. This may
374	>	* be seen as a conservative variant of the approach in Wagner &
375	>	* Calder "Leapfrogging: a portable technique for implementing
376	>	* efficient futures" SIGPLAN Notices, 1993
377	>	* (http://portal.acm.org/citation.cfm?id=155354). It differs in
378	>	* that: (1) We only maintain dependency links across workers upon
379	>	* steals, rather than use per-task bookkeeping.  This sometimes
380	>	* requires a linear scan of workQueues array to locate stealers,
381	>	* but often doesn't because stealers leave hints (that may become
382	>	* stale/wrong) of where to locate them.  A stealHint is only a
383	>	* hint because a worker might have had multiple steals and the
384	>	* hint records only one of them (usually the most current).
385	>	* Hinting isolates cost to when it is needed, rather than adding
386	>	* to per-task overhead.  (2) It is "shallow", ignoring nesting
387	>	* and potentially cyclic mutual steals.  (3) It is intentionally
388	>	* racy: field currentJoin is updated only while actively joining,
389	>	* which means that we miss links in the chain during long-lived
390	>	* tasks, GC stalls etc (which is OK since blocking in such cases
391	>	* is usually a good idea).  (4) We bound the number of attempts
392	>	* to find work (see MAX_HELP) and fall back to suspending the
393	>	* worker and if necessary replacing it with another.
394	>	*
395	>	* It is impossible to keep exactly the target parallelism number
396	>	* of threads running at any given time.  Determining the
397	>	* existence of conservatively safe helping targets, the
398	>	* availability of already-created spares, and the apparent need
399	>	* to create new spares are all racy, so we rely on multiple
400	>	* retries of each.  Compensation in the apparent absence of
401	>	* helping opportunities is challenging to control on JVMs, where
402	>	* GC and other activities can stall progress of tasks that in
403	>	* turn stall out many other dependent tasks, without us being
404	>	* able to determine whether they will ever require compensation.
405	>	* Even though work-stealing otherwise encounters little
406	>	* degradation in the presence of more threads than cores,
407	>	* aggressively adding new threads in such cases entails risk of
408	>	* unwanted positive feedback control loops in which more threads
409	>	* cause more dependent stalls (as well as delayed progress of
410	>	* unblocked threads to the point that we know they are available)
411	>	* leading to more situations requiring more threads, and so
412	>	* on. This aspect of control can be seen as an (analytically
413	>	* intractable) game with an opponent that may choose the worst
414	>	* (for us) active thread to stall at any time.  We take several
415	>	* precautions to bound losses (and thus bound gains), mainly in
416	>	* methods tryCompensate and awaitJoin: (1) We only try
417	>	* compensation after attempting enough helping steps (measured
418	>	* via counting and timing) that we have already consumed the
419	>	* estimated cost of creating and activating a new thread.  (2) We
420	>	* allow up to 50% of threads to be blocked before initially
421	>	* adding any others, and unless completely saturated, check that
422	>	* some work is available for a new worker before adding. Also, we
423	>	* create up to only 50% more threads until entering a mode that
424	>	* only adds a thread if all others are possibly blocked.  All
425	>	* together, this means that we might be half as fast to react,
426	>	* and create half as many threads as possible in the ideal case,
427	>	* but present vastly fewer anomalies in all other cases compared
428	>	* to both more aggressive and more conservative alternatives.
429	>	*
430	>	* Style notes: There is a lot of representation-level coupling
431	>	* among classes ForkJoinPool, ForkJoinWorkerThread, and
432	>	* ForkJoinTask.  The fields of WorkQueue maintain data structures
433	>	* managed by ForkJoinPool, so are directly accessed.  There is
434	>	* little point trying to reduce this, since any associated future
435	>	* changes in representations will need to be accompanied by
436	>	* algorithmic changes anyway. Several methods intrinsically
437	>	* sprawl because they must accumulate sets of consistent reads of
438	>	* volatiles held in local variables.  Methods signalWork() and
439	>	* scan() are the main bottlenecks, so are especially heavily
440	>	* micro-optimized/mangled.  There are lots of inline assignments
441	>	* (of form "while ((local = field) != 0)") which are usually the
442	>	* simplest way to ensure the required read orderings (which are
443	>	* sometimes critical). This leads to a "C"-like style of listing
444	>	* declarations of these locals at the heads of methods or blocks.
445	>	* There are several occurrences of the unusual "do {} while
446	>	* (!cas...)"  which is the simplest way to force an update of a
447	>	* CAS'ed variable. There are also other coding oddities that help
448	>	* some methods perform reasonably even when interpreted (not
449	>	* compiled).
450	>	*
451	>	* The order of declarations in this file is:
452	>	* (1) Static utility functions
453	>	* (2) Nested (static) classes
454	>	* (3) Static fields
455	>	* (4) Fields, along with constants used when unpacking some of them
456	>	* (5) Internal control methods
457	>	* (6) Callbacks and other support for ForkJoinTask methods
458	>	* (7) Exported methods
459	>	* (8) Static block initializing statics in minimally dependent order
460		*/
461
462	<	/** Mask for packing and unpacking shorts */
463	<	private static final int  shortMask = 0xffff;
462	>	// Static utilities
463	>
464	>	/**
465	>	* If there is a security manager, makes sure caller has
466	>	* permission to modify threads.
467	>	*/
468	>	private static void checkPermission() {
469	>	SecurityManager security = System.getSecurityManager();
470	>	if (security != null)
471	>	security.checkPermission(modifyThreadPermission);
472	>	}
473
474	<	/** Max pool size -- must be a power of two minus 1 */
71	<	private static final int MAX_THREADS =  0x7FFF;
474	>	// Nested classes
475
476		/**
477	<	* Factory for creating new ForkJoinWorkerThreads.  A
478	<	* ForkJoinWorkerThreadFactory must be defined and used for
479	<	* ForkJoinWorkerThread subclasses that extend base functionality
480	<	* or initialize threads with different contexts.
477	>	* Factory for creating new {@link ForkJoinWorkerThread}s.
478	>	* A {@code ForkJoinWorkerThreadFactory} must be defined and used
479	>	* for {@code ForkJoinWorkerThread} subclasses that extend base
480	>	* functionality or initialize threads with different contexts.
481		*/
482		public static interface ForkJoinWorkerThreadFactory {
483		/**
484		* Returns a new worker thread operating in the given pool.
485		*
486		* @param pool the pool this thread works in
487	<	* @throws NullPointerException if pool is null;
487	>	* @throws NullPointerException if the pool is null
488		*/
489		public ForkJoinWorkerThread newThread(ForkJoinPool pool);
490		}
491
492		/**
493	<	* Default ForkJoinWorkerThreadFactory implementation, creates a
493	>	* Default ForkJoinWorkerThreadFactory implementation; creates a
494		* new ForkJoinWorkerThread.
495		*/
496	<	static class  DefaultForkJoinWorkerThreadFactory
496	>	static class DefaultForkJoinWorkerThreadFactory
497		implements ForkJoinWorkerThreadFactory {
498		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
499	<	try {
500	<	return new ForkJoinWorkerThread(pool);
501	<	} catch (OutOfMemoryError oom)  {
499	>	return new ForkJoinWorkerThread(pool);
500	>	}
501	>	}
502	>
503	>	/**
504	>	* Class for artificial tasks that are used to replace the target
505	>	* of local joins if they are removed from an interior queue slot
506	>	* in WorkQueue.tryRemoveAndExec. We don't need the proxy to
507	>	* actually do anything beyond having a unique identity.
508	>	*/
509	>	static final class EmptyTask extends ForkJoinTask<Void> {
510	>	EmptyTask() { status = ForkJoinTask.NORMAL; } // force done
511	>	public final Void getRawResult() { return null; }
512	>	public final void setRawResult(Void x) {}
513	>	public final boolean exec() { return true; }
514	>	}
515	>
516	>	/**
517	>	* Queues supporting work-stealing as well as external task
518	>	* submission. See above for main rationale and algorithms.
519	>	* Implementation relies heavily on "Unsafe" intrinsics
520	>	* and selective use of "volatile":
521	>	*
522	>	* Field "base" is the index (mod array.length) of the least valid
523	>	* queue slot, which is always the next position to steal (poll)
524	>	* from if nonempty. Reads and writes require volatile orderings
525	>	* but not CAS, because updates are only performed after slot
526	>	* CASes.
527	>	*
528	>	* Field "top" is the index (mod array.length) of the next queue
529	>	* slot to push to or pop from. It is written only by owner thread
530	>	* for push, or under lock for trySharedPush, and accessed by
531	>	* other threads only after reading (volatile) base.  Both top and
532	>	* base are allowed to wrap around on overflow, but (top - base)
533	>	* (or more commonly -(base - top) to force volatile read of base
534	>	* before top) still estimates size.
535	>	*
536	>	* The array slots are read and written using the emulation of
537	>	* volatiles/atomics provided by Unsafe. Insertions must in
538	>	* general use putOrderedObject as a form of releasing store to
539	>	* ensure that all writes to the task object are ordered before
540	>	* its publication in the queue. (Although we can avoid one case
541	>	* of this when locked in trySharedPush.) All removals entail a
542	>	* CAS to null.  The array is always a power of two. To ensure
543	>	* safety of Unsafe array operations, all accesses perform
544	>	* explicit null checks and implicit bounds checks via
545	>	* power-of-two masking.
546	>	*
547	>	* In addition to basic queuing support, this class contains
548	>	* fields described elsewhere to control execution. It turns out
549	>	* to work better memory-layout-wise to include them in this
550	>	* class rather than a separate class.
551	>	*
552	>	* Performance on most platforms is very sensitive to placement of
553	>	* instances of both WorkQueues and their arrays -- we absolutely
554	>	* do not want multiple WorkQueue instances or multiple queue
555	>	* arrays sharing cache lines. (It would be best for queue objects
556	>	* and their arrays to share, but there is nothing available to
557	>	* help arrange that).  Unfortunately, because they are recorded
558	>	* in a common array, WorkQueue instances are often moved to be
559	>	* adjacent by garbage collectors. To reduce impact, we use field
560	>	* padding that works OK on common platforms; this effectively
561	>	* trades off slightly slower average field access for the sake of
562	>	* avoiding really bad worst-case access. (Until better JVM
563	>	* support is in place, this padding is dependent on transient
564	>	* properties of JVM field layout rules.)  We also take care in
565	>	* allocating, sizing and resizing the array. Non-shared queue
566	>	* arrays are initialized (via method growArray) by workers before
567	>	* use. Others are allocated on first use.
568	>	*/
569	>	static final class WorkQueue {
570	>	/**
571	>	* Capacity of work-stealing queue array upon initialization.
572	>	* Must be a power of two; at least 4, but should be larger to
573	>	* reduce or eliminate cacheline sharing among queues.
574	>	* Currently, it is much larger, as a partial workaround for
575	>	* the fact that JVMs often place arrays in locations that
576	>	* share GC bookkeeping (especially cardmarks) such that
577	>	* per-write accesses encounter serious memory contention.
578	>	*/
579	>	static final int INITIAL_QUEUE_CAPACITY = 1 << 13;
580	>
581	>	/**
582	>	* Maximum size for queue arrays. Must be a power of two less
583	>	* than or equal to 1 << (31 - width of array entry) to ensure
584	>	* lack of wraparound of index calculations, but defined to a
585	>	* value a bit less than this to help users trap runaway
586	>	* programs before saturating systems.
587	>	*/
588	>	static final int MAXIMUM_QUEUE_CAPACITY = 1 << 26; // 64M
589	>
590	>	volatile long totalSteals; // cumulative number of steals
591	>	int seed;                  // for random scanning; initialize nonzero
592	>	volatile int eventCount;   // encoded inactivation count; < 0 if inactive
593	>	int nextWait;              // encoded record of next event waiter
594	>	int rescans;               // remaining scans until block
595	>	int nsteals;               // top-level task executions since last idle
596	>	final int mode;            // lifo, fifo, or shared
597	>	int poolIndex;             // index of this queue in pool (or 0)
598	>	int stealHint;             // index of most recent known stealer
599	>	volatile int runState;     // 1: locked, -1: terminate; else 0
600	>	volatile int base;         // index of next slot for poll
601	>	int top;                   // index of next slot for push
602	>	ForkJoinTask<?>[] array;   // the elements (initially unallocated)
603	>	final ForkJoinPool pool;   // the containing pool (may be null)
604	>	final ForkJoinWorkerThread owner; // owning thread or null if shared
605	>	volatile Thread parker;    // == owner during call to park; else null
606	>	volatile ForkJoinTask<?> currentJoin;  // task being joined in awaitJoin
607	>	ForkJoinTask<?> currentSteal; // current non-local task being executed
608	>	// Heuristic padding to ameliorate unfortunate memory placements
609	>	Object p00, p01, p02, p03, p04, p05, p06, p07;
610	>	Object p08, p09, p0a, p0b, p0c, p0d, p0e;
611	>
612	>	WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner, int mode) {
613	>	this.mode = mode;
614	>	this.pool = pool;
615	>	this.owner = owner;
616	>	// Place indices in the center of array (that is not yet allocated)
617	>	base = top = INITIAL_QUEUE_CAPACITY >>> 1;
618	>	}
619	>
620	>	/**
621	>	* Returns the approximate number of tasks in the queue.
622	>	*/
623	>	final int queueSize() {
624	>	int n = base - top;       // non-owner callers must read base first
625	>	return (n >= 0) ? 0 : -n; // ignore transient negative
626	>	}
627	>
628	>	/**
629	>	* Provides a more accurate estimate of whether this queue has
630	>	* any tasks than does queueSize, by checking whether a
631	>	* near-empty queue has at least one unclaimed task.
632	>	*/
633	>	final boolean isEmpty() {
634	>	ForkJoinTask<?>[] a; int m, s;
635	>	int n = base - (s = top);
636	>	return (n >= 0 ||
637	>	(n == -1 &&
638	>	((a = array) == null ||
639	>	(m = a.length - 1) < 0 ||
640	>	U.getObjectVolatile
641	>	(a, ((m & (s - 1)) << ASHIFT) + ABASE) == null)));
642	>	}
643	>
644	>	/**
645	>	* Pushes a task. Call only by owner in unshared queues.
646	>	*
647	>	* @param task the task. Caller must ensure non-null.
648	>	* @throw RejectedExecutionException if array cannot be resized
649	>	*/
650	>	final void push(ForkJoinTask<?> task) {
651	>	ForkJoinTask<?>[] a; ForkJoinPool p;
652	>	int s = top, m, n;
653	>	if ((a = array) != null) {    // ignore if queue removed
654	>	U.putOrderedObject
655	>	(a, (((m = a.length - 1) & s) << ASHIFT) + ABASE, task);
656	>	if ((n = (top = s + 1) - base) <= 2) {
657	>	if ((p = pool) != null)
658	>	p.signalWork();
659	>	}
660	>	else if (n >= m)
661	>	growArray(true);
662	>	}
663	>	}
664	>
665	>	/**
666	>	* Pushes a task if lock is free and array is either big
667	>	* enough or can be resized to be big enough.
668	>	*
669	>	* @param task the task. Caller must ensure non-null.
670	>	* @return true if submitted
671	>	*/
672	>	final boolean trySharedPush(ForkJoinTask<?> task) {
673	>	boolean submitted = false;
674	>	if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
675	>	ForkJoinTask<?>[] a = array;
676	>	int s = top;
677	>	try {
678	>	if ((a != null && a.length > s + 1 - base) ||
679	>	(a = growArray(false)) != null) { // must presize
680	>	int j = (((a.length - 1) & s) << ASHIFT) + ABASE;
681	>	U.putObject(a, (long)j, task);    // don't need "ordered"
682	>	top = s + 1;
683	>	submitted = true;
684	>	}
685	>	} finally {
686	>	runState = 0;                         // unlock
687	>	}
688	>	}
689	>	return submitted;
690	>	}
691	>
692	>	/**
693	>	* Takes next task, if one exists, in LIFO order.  Call only
694	>	* by owner in unshared queues. (We do not have a shared
695	>	* version of this method because it is never needed.)
696	>	*/
697	>	final ForkJoinTask<?> pop() {
698	>	ForkJoinTask<?>[] a; ForkJoinTask<?> t; int m;
699	>	if ((a = array) != null && (m = a.length - 1) >= 0) {
700	>	for (int s; (s = top - 1) - base >= 0;) {
701	>	long j = ((m & s) << ASHIFT) + ABASE;
702	>	if ((t = (ForkJoinTask<?>)U.getObject(a, j)) == null)
703	>	break;
704	>	if (U.compareAndSwapObject(a, j, t, null)) {
705	>	top = s;
706	>	return t;
707	>	}
708	>	}
709	>	}
710	>	return null;
711	>	}
712	>
713	>	/**
714	>	* Takes a task in FIFO order if b is base of queue and a task
715	>	* can be claimed without contention. Specialized versions
716	>	* appear in ForkJoinPool methods scan and tryHelpStealer.
717	>	*/
718	>	final ForkJoinTask<?> pollAt(int b) {
719	>	ForkJoinTask<?> t; ForkJoinTask<?>[] a;
720	>	if ((a = array) != null) {
721	>	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
722	>	if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null &&
723	>	base == b &&
724	>	U.compareAndSwapObject(a, j, t, null)) {
725	>	base = b + 1;
726	>	return t;
727	>	}
728	>	}
729	>	return null;
730	>	}
731	>
732	>	/**
733	>	* Takes next task, if one exists, in FIFO order.
734	>	*/
735	>	final ForkJoinTask<?> poll() {
736	>	ForkJoinTask<?>[] a; int b; ForkJoinTask<?> t;
737	>	while ((b = base) - top < 0 && (a = array) != null) {
738	>	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
739	>	t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
740	>	if (t != null) {
741	>	if (base == b &&
742	>	U.compareAndSwapObject(a, j, t, null)) {
743	>	base = b + 1;
744	>	return t;
745	>	}
746	>	}
747	>	else if (base == b) {
748	>	if (b + 1 == top)
749	>	break;
750	>	Thread.yield(); // wait for lagging update
751	>	}
752	>	}
753	>	return null;
754	>	}
755	>
756	>	/**
757	>	* Takes next task, if one exists, in order specified by mode.
758	>	*/
759	>	final ForkJoinTask<?> nextLocalTask() {
760	>	return mode == 0 ? pop() : poll();
761	>	}
762	>
763	>	/**
764	>	* Returns next task, if one exists, in order specified by mode.
765	>	*/
766	>	final ForkJoinTask<?> peek() {
767	>	ForkJoinTask<?>[] a = array; int m;
768	>	if (a == null || (m = a.length - 1) < 0)
769	>	return null;
770	>	int i = mode == 0 ? top - 1 : base;
771	>	int j = ((i & m) << ASHIFT) + ABASE;
772	>	return (ForkJoinTask<?>)U.getObjectVolatile(a, j);
773	>	}
774	>
775	>	/**
776	>	* Pops the given task only if it is at the current top.
777	>	*/
778	>	final boolean tryUnpush(ForkJoinTask<?> t) {
779	>	ForkJoinTask<?>[] a; int s;
780	>	if ((a = array) != null && (s = top) != base &&
781	>	U.compareAndSwapObject
782	>	(a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) {
783	>	top = s;
784	>	return true;
785	>	}
786	>	return false;
787	>	}
788	>
789	>	/**
790	>	* Version of tryUnpush for shared queues; called by non-FJ
791	>	* submitters after prechecking that task probably exists.
792	>	*/
793	>	final boolean trySharedUnpush(ForkJoinTask<?> t) {
794	>	boolean success = false;
795	>	if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
796	>	try {
797	>	ForkJoinTask<?>[] a; int s;
798	>	if ((a = array) != null && (s = top) != base &&
799	>	U.compareAndSwapObject
800	>	(a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) {
801	>	top = s;
802	>	success = true;
803	>	}
804	>	} finally {
805	>	runState = 0;                         // unlock
806	>	}
807	>	}
808	>	return success;
809	>	}
810	>
811	>	/**
812	>	* Polls the given task only if it is at the current base.
813	>	*/
814	>	final boolean pollFor(ForkJoinTask<?> task) {
815	>	ForkJoinTask<?>[] a; int b;
816	>	if ((b = base) - top < 0 && (a = array) != null) {
817	>	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
818	>	if (U.getObjectVolatile(a, j) == task && base == b &&
819	>	U.compareAndSwapObject(a, j, task, null)) {
820	>	base = b + 1;
821	>	return true;
822	>	}
823	>	}
824	>	return false;
825	>	}
826	>
827	>	/**
828	>	* Initializes or doubles the capacity of array. Call either
829	>	* by owner or with lock held -- it is OK for base, but not
830	>	* top, to move while resizings are in progress.
831	>	*
832	>	* @param rejectOnFailure if true, throw exception if capacity
833	>	* exceeded (relayed ultimately to user); else return null.
834	>	*/
835	>	final ForkJoinTask<?>[] growArray(boolean rejectOnFailure) {
836	>	ForkJoinTask<?>[] oldA = array;
837	>	int size = oldA != null ? oldA.length << 1 : INITIAL_QUEUE_CAPACITY;
838	>	if (size <= MAXIMUM_QUEUE_CAPACITY) {
839	>	int oldMask, t, b;
840	>	ForkJoinTask<?>[] a = array = new ForkJoinTask<?>[size];
841	>	if (oldA != null && (oldMask = oldA.length - 1) >= 0 &&
842	>	(t = top) - (b = base) > 0) {
843	>	int mask = size - 1;
844	>	do {
845	>	ForkJoinTask<?> x;
846	>	int oldj = ((b & oldMask) << ASHIFT) + ABASE;
847	>	int j    = ((b &    mask) << ASHIFT) + ABASE;
848	>	x = (ForkJoinTask<?>)U.getObjectVolatile(oldA, oldj);
849	>	if (x != null &&
850	>	U.compareAndSwapObject(oldA, oldj, x, null))
851	>	U.putObjectVolatile(a, j, x);
852	>	} while (++b != t);
853	>	}
854	>	return a;
855	>	}
856	>	else if (!rejectOnFailure)
857		return null;
858	+	else
859	+	throw new RejectedExecutionException("Queue capacity exceeded");
860	+	}
861	+
862	+	/**
863	+	* Removes and cancels all known tasks, ignoring any exceptions.
864	+	*/
865	+	final void cancelAll() {
866	+	ForkJoinTask.cancelIgnoringExceptions(currentJoin);
867	+	ForkJoinTask.cancelIgnoringExceptions(currentSteal);
868	+	for (ForkJoinTask<?> t; (t = poll()) != null; )
869	+	ForkJoinTask.cancelIgnoringExceptions(t);
870	+	}
871	+
872	+	/**
873	+	* Computes next value for random probes.  Scans don't require
874	+	* a very high quality generator, but also not a crummy one.
875	+	* Marsaglia xor-shift is cheap and works well enough.  Note:
876	+	* This is manually inlined in its usages in ForkJoinPool to
877	+	* avoid writes inside busy scan loops.
878	+	*/
879	+	final int nextSeed() {
880	+	int r = seed;
881	+	r ^= r << 13;
882	+	r ^= r >>> 17;
883	+	return seed = r ^= r << 5;
884	+	}
885	+
886	+	// Execution methods
887	+
888	+	/**
889	+	* Pops and runs tasks until empty.
890	+	*/
891	+	private void popAndExecAll() {
892	+	// A bit faster than repeated pop calls
893	+	ForkJoinTask<?>[] a; int m, s; long j; ForkJoinTask<?> t;
894	+	while ((a = array) != null && (m = a.length - 1) >= 0 &&
895	+	(s = top - 1) - base >= 0 &&
896	+	(t = ((ForkJoinTask<?>)
897	+	U.getObject(a, j = ((m & s) << ASHIFT) + ABASE)))
898	+	!= null) {
899	+	if (U.compareAndSwapObject(a, j, t, null)) {
900	+	top = s;
901	+	t.doExec();
902	+	}
903	+	}
904	+	}
905	+
906	+	/**
907	+	* Polls and runs tasks until empty.
908	+	*/
909	+	private void pollAndExecAll() {
910	+	for (ForkJoinTask<?> t; (t = poll()) != null;)
911	+	t.doExec();
912	+	}
913	+
914	+	/**
915	+	* If present, removes from queue and executes the given task, or
916	+	* any other cancelled task. Returns (true) immediately on any CAS
917	+	* or consistency check failure so caller can retry.
918	+	*
919	+	* @return 0 if no progress can be made, else positive
920	+	* (this unusual convention simplifies use with tryHelpStealer.)
921	+	*/
922	+	final int tryRemoveAndExec(ForkJoinTask<?> task) {
923	+	int stat = 1;
924	+	boolean removed = false, empty = true;
925	+	ForkJoinTask<?>[] a; int m, s, b, n;
926	+	if ((a = array) != null && (m = a.length - 1) >= 0 &&
927	+	(n = (s = top) - (b = base)) > 0) {
928	+	for (ForkJoinTask<?> t;;) {           // traverse from s to b
929	+	int j = ((--s & m) << ASHIFT) + ABASE;
930	+	t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
931	+	if (t == null)                    // inconsistent length
932	+	break;
933	+	else if (t == task) {
934	+	if (s + 1 == top) {           // pop
935	+	if (!U.compareAndSwapObject(a, j, task, null))
936	+	break;
937	+	top = s;
938	+	removed = true;
939	+	}
940	+	else if (base == b)           // replace with proxy
941	+	removed = U.compareAndSwapObject(a, j, task,
942	+	new EmptyTask());
943	+	break;
944	+	}
945	+	else if (t.status >= 0)
946	+	empty = false;
947	+	else if (s + 1 == top) {          // pop and throw away
948	+	if (U.compareAndSwapObject(a, j, t, null))
949	+	top = s;
950	+	break;
951	+	}
952	+	if (--n == 0) {
953	+	if (!empty && base == b)
954	+	stat = 0;
955	+	break;
956	+	}
957	+	}
958	+	}
959	+	if (removed)
960	+	task.doExec();
961	+	return stat;
962	+	}
963	+
964	+	/**
965	+	* Executes a top-level task and any local tasks remaining
966	+	* after execution.
967	+	*/
968	+	final void runTask(ForkJoinTask<?> t) {
969	+	if (t != null) {
970	+	currentSteal = t;
971	+	t.doExec();
972	+	if (top != base) {       // process remaining local tasks
973	+	if (mode == 0)
974	+	popAndExecAll();
975	+	else
976	+	pollAndExecAll();
977	+	}
978	+	++nsteals;
979	+	currentSteal = null;
980	+	}
981	+	}
982	+
983	+	/**
984	+	* Executes a non-top-level (stolen) task.
985	+	*/
986	+	final void runSubtask(ForkJoinTask<?> t) {
987	+	if (t != null) {
988	+	ForkJoinTask<?> ps = currentSteal;
989	+	currentSteal = t;
990	+	t.doExec();
991	+	currentSteal = ps;
992	+	}
993	+	}
994	+
995	+	/**
996	+	* Returns true if owned and not known to be blocked.
997	+	*/
998	+	final boolean isApparentlyUnblocked() {
999	+	Thread wt; Thread.State s;
1000	+	return (eventCount >= 0 &&
1001	+	(wt = owner) != null &&
1002	+	(s = wt.getState()) != Thread.State.BLOCKED &&
1003	+	s != Thread.State.WAITING &&
1004	+	s != Thread.State.TIMED_WAITING);
1005	+	}
1006	+
1007	+	/**
1008	+	* If this owned and is not already interrupted, try to
1009	+	* interrupt and/or unpark, ignoring exceptions.
1010	+	*/
1011	+	final void interruptOwner() {
1012	+	Thread wt, p;
1013	+	if ((wt = owner) != null && !wt.isInterrupted()) {
1014	+	try {
1015	+	wt.interrupt();
1016	+	} catch (SecurityException ignore) {
1017	+	}
1018		}
1019	+	if ((p = parker) != null)
1020	+	U.unpark(p);
1021	+	}
1022	+
1023	+	// Unsafe mechanics
1024	+	private static final sun.misc.Unsafe U;
1025	+	private static final long RUNSTATE;
1026	+	private static final int ABASE;
1027	+	private static final int ASHIFT;
1028	+	static {
1029	+	int s;
1030	+	try {
1031	+	U = getUnsafe();
1032	+	Class<?> k = WorkQueue.class;
1033	+	Class<?> ak = ForkJoinTask[].class;
1034	+	RUNSTATE = U.objectFieldOffset
1035	+	(k.getDeclaredField("runState"));
1036	+	ABASE = U.arrayBaseOffset(ak);
1037	+	s = U.arrayIndexScale(ak);
1038	+	} catch (Exception e) {
1039	+	throw new Error(e);
1040	+	}
1041	+	if ((s & (s-1)) != 0)
1042	+	throw new Error("data type scale not a power of two");
1043	+	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
1044	+	}
1045	+	}
1046	+
1047	+	/**
1048	+	* Per-thread records for threads that submit to pools. Currently
1049	+	* holds only pseudo-random seed / index that is used to choose
1050	+	* submission queues in method doSubmit. In the future, this may
1051	+	* also incorporate a means to implement different task rejection
1052	+	* and resubmission policies.
1053	+	*
1054	+	* Seeds for submitters and workers/workQueues work in basically
1055	+	* the same way but are initialized and updated using slightly
1056	+	* different mechanics. Both are initialized using the same
1057	+	* approach as in class ThreadLocal, where successive values are
1058	+	* unlikely to collide with previous values. This is done during
1059	+	* registration for workers, but requires a separate AtomicInteger
1060	+	* for submitters. Seeds are then randomly modified upon
1061	+	* collisions using xorshifts, which requires a non-zero seed.
1062	+	*/
1063	+	static final class Submitter {
1064	+	int seed;
1065	+	Submitter() {
1066	+	int s = nextSubmitterSeed.getAndAdd(SEED_INCREMENT);
1067	+	seed = (s == 0) ? 1 : s; // ensure non-zero
1068		}
1069		}
1070
1071	+	/** ThreadLocal class for Submitters */
1072	+	static final class ThreadSubmitter extends ThreadLocal<Submitter> {
1073	+	public Submitter initialValue() { return new Submitter(); }
1074	+	}
1075	+
1076	+	// static fields (initialized in static initializer below)
1077	+
1078		/**
1079		* Creates a new ForkJoinWorkerThread. This factory is used unless
1080		* overridden in ForkJoinPool constructors.
1081		*/
1082		public static final ForkJoinWorkerThreadFactory
1083	<	defaultForkJoinWorkerThreadFactory =
1084	<	new DefaultForkJoinWorkerThreadFactory();
1083	>	defaultForkJoinWorkerThreadFactory;
1084	>
1085	>
1086	>	/** Property prefix for constructing common pool */
1087	>	private static final String propPrefix =
1088	>	"java.util.concurrent.ForkJoinPool.common.";
1089
1090		/**
1091	<	* Permission required for callers of methods that may start or
1092	<	* kill threads.
1091	>	* Common (static) pool. Non-null for public use unless a static
1092	>	* construction exception, but internal usages must null-check on
1093	>	* use.
1094		*/
1095	<	private static final RuntimePermission modifyThreadPermission =
117	<	new RuntimePermission("modifyThread");
1095	>	static final ForkJoinPool commonPool;
1096
1097		/**
1098	<	* If there is a security manager, makes sure caller has
121	<	* permission to modify threads.
1098	>	* Common pool parallelism. Must equal commonPool.parallelism.
1099		*/
1100	<	private static void checkPermission() {
124	<	SecurityManager security = System.getSecurityManager();
125	<	if (security != null)
126	<	security.checkPermission(modifyThreadPermission);
127	<	}
1100	>	static final int commonPoolParallelism;
1101
1102		/**
1103		* Generator for assigning sequence numbers as pool names.
1104		*/
1105	<	private static final AtomicInteger poolNumberGenerator =
133	<	new AtomicInteger();
1105	>	private static final AtomicInteger poolNumberGenerator;
1106
1107		/**
1108	<	* Array holding all worker threads in the pool. Initialized upon
1109	<	* first use. Array size must be a power of two.  Updates and
138	<	* replacements are protected by workerLock, but it is always kept
139	<	* in a consistent enough state to be randomly accessed without
140	<	* locking by workers performing work-stealing.
1108	>	* Generator for initial hashes/seeds for submitters. Accessed by
1109	>	* Submitter class constructor.
1110		*/
1111	<	volatile ForkJoinWorkerThread[] workers;
1111	>	static final AtomicInteger nextSubmitterSeed;
1112
1113		/**
1114	<	* Lock protecting access to workers.
1114	>	* Permission required for callers of methods that may start or
1115	>	* kill threads.
1116		*/
1117	<	private final ReentrantLock workerLock;
1117	>	private static final RuntimePermission modifyThreadPermission;
1118
1119		/**
1120	<	* Condition for awaitTermination.
1120	>	* Per-thread submission bookkeeping. Shared across all pools
1121	>	* to reduce ThreadLocal pollution and because random motion
1122	>	* to avoid contention in one pool is likely to hold for others.
1123		*/
1124	<	private final Condition termination;
1124	>	private static final ThreadSubmitter submitters;
1125
1126	<	/**
155	<	* The uncaught exception handler used when any worker
156	<	* abrupty terminates
157	<	*/
158	<	private Thread.UncaughtExceptionHandler ueh;
1126	>	// static constants
1127
1128		/**
1129	<	* Creation factory for worker threads.
1129	>	* Initial timeout value (in nanoseconds) for the thread triggering
1130	>	* quiescence to park waiting for new work. On timeout, the thread
1131	>	* will instead try to shrink the number of workers.
1132		*/
1133	<	private final ForkJoinWorkerThreadFactory factory;
1133	>	private static final long IDLE_TIMEOUT      = 1000L * 1000L * 1000L; // 1sec
1134
1135		/**
1136	<	* Head of stack of threads that were created to maintain
167	<	* parallelism when other threads blocked, but have since
168	<	* suspended when the parallelism level rose.
1136	>	* Timeout value when there are more threads than parallelism level
1137		*/
1138	<	private volatile WaitQueueNode spareStack;
1138	>	private static final long FAST_IDLE_TIMEOUT =  100L * 1000L * 1000L;
1139
1140		/**
1141	<	* Sum of per-thread steal counts, updated only when threads are
1142	<	* idle or terminating.
1141	>	* The maximum stolen->joining link depth allowed in method
1142	>	* tryHelpStealer.  Must be a power of two. This value also
1143	>	* controls the maximum number of times to try to help join a task
1144	>	* without any apparent progress or change in pool state before
1145	>	* giving up and blocking (see awaitJoin).  Depths for legitimate
1146	>	* chains are unbounded, but we use a fixed constant to avoid
1147	>	* (otherwise unchecked) cycles and to bound staleness of
1148	>	* traversal parameters at the expense of sometimes blocking when
1149	>	* we could be helping.
1150		*/
1151	<	private final AtomicLong stealCount;
1151	>	private static final int MAX_HELP = 64;
1152
1153		/**
1154	<	* Queue for external submissions.
1154	>	* Secondary time-based bound (in nanosecs) for helping attempts
1155	>	* before trying compensated blocking in awaitJoin. Used in
1156	>	* conjunction with MAX_HELP to reduce variance due to different
1157	>	* polling rates associated with different helping options. The
1158	>	* value should roughly approximate the time required to create
1159	>	* and/or activate a worker thread.
1160		*/
1161	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
1161	>	private static final long COMPENSATION_DELAY = 1L << 18; // ~0.25 millisec
1162
1163		/**
1164	<	* Head of Treiber stack for barrier sync. See below for explanation
1164	>	* Increment for seed generators. See class ThreadLocal for
1165	>	* explanation.
1166		*/
1167	<	private volatile WaitQueueNode syncStack;
1167	>	private static final int SEED_INCREMENT = 0x61c88647;
1168
1169		/**
1170	<	* The count for event barrier
1170	>	* Bits and masks for control variables
1171	>	*
1172	>	* Field ctl is a long packed with:
1173	>	* AC: Number of active running workers minus target parallelism (16 bits)
1174	>	* TC: Number of total workers minus target parallelism (16 bits)
1175	>	* ST: true if pool is terminating (1 bit)
1176	>	* EC: the wait count of top waiting thread (15 bits)
1177	>	* ID: poolIndex of top of Treiber stack of waiters (16 bits)
1178	>	*
1179	>	* When convenient, we can extract the upper 32 bits of counts and
1180	>	* the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
1181	>	* (int)ctl.  The ec field is never accessed alone, but always
1182	>	* together with id and st. The offsets of counts by the target
1183	>	* parallelism and the positionings of fields makes it possible to
1184	>	* perform the most common checks via sign tests of fields: When
1185	>	* ac is negative, there are not enough active workers, when tc is
1186	>	* negative, there are not enough total workers, and when e is
1187	>	* negative, the pool is terminating.  To deal with these possibly
1188	>	* negative fields, we use casts in and out of "short" and/or
1189	>	* signed shifts to maintain signedness.
1190	>	*
1191	>	* When a thread is queued (inactivated), its eventCount field is
1192	>	* set negative, which is the only way to tell if a worker is
1193	>	* prevented from executing tasks, even though it must continue to
1194	>	* scan for them to avoid queuing races. Note however that
1195	>	* eventCount updates lag releases so usage requires care.
1196	>	*
1197	>	* Field runState is an int packed with:
1198	>	* SHUTDOWN: true if shutdown is enabled (1 bit)
1199	>	* SEQ:  a sequence number updated upon (de)registering workers (30 bits)
1200	>	* INIT: set true after workQueues array construction (1 bit)
1201	>	*
1202	>	* The sequence number enables simple consistency checks:
1203	>	* Staleness of read-only operations on the workQueues array can
1204	>	* be checked by comparing runState before vs after the reads.
1205		*/
191	–	private volatile long eventCount;
1206
1207	<	/**
1208	<	* Pool number, just for assigning useful names to worker threads
1209	<	*/
1210	<	private final int poolNumber;
1207	>	// bit positions/shifts for fields
1208	>	private static final int  AC_SHIFT   = 48;
1209	>	private static final int  TC_SHIFT   = 32;
1210	>	private static final int  ST_SHIFT   = 31;
1211	>	private static final int  EC_SHIFT   = 16;
1212
1213	<	/**
1214	<	* The maximum allowed pool size
1215	<	*/
1216	<	private volatile int maxPoolSize;
1213	>	// bounds
1214	>	private static final int  SMASK      = 0xffff;  // short bits
1215	>	private static final int  MAX_CAP    = 0x7fff;  // max #workers - 1
1216	>	private static final int  SQMASK     = 0xfffe;  // even short bits
1217	>	private static final int  SHORT_SIGN = 1 << 15;
1218	>	private static final int  INT_SIGN   = 1 << 31;
1219	>
1220	>	// masks
1221	>	private static final long STOP_BIT   = 0x0001L << ST_SHIFT;
1222	>	private static final long AC_MASK    = ((long)SMASK) << AC_SHIFT;
1223	>	private static final long TC_MASK    = ((long)SMASK) << TC_SHIFT;
1224	>
1225	>	// units for incrementing and decrementing
1226	>	private static final long TC_UNIT    = 1L << TC_SHIFT;
1227	>	private static final long AC_UNIT    = 1L << AC_SHIFT;
1228	>
1229	>	// masks and units for dealing with u = (int)(ctl >>> 32)
1230	>	private static final int  UAC_SHIFT  = AC_SHIFT - 32;
1231	>	private static final int  UTC_SHIFT  = TC_SHIFT - 32;
1232	>	private static final int  UAC_MASK   = SMASK << UAC_SHIFT;
1233	>	private static final int  UTC_MASK   = SMASK << UTC_SHIFT;
1234	>	private static final int  UAC_UNIT   = 1 << UAC_SHIFT;
1235	>	private static final int  UTC_UNIT   = 1 << UTC_SHIFT;
1236	>
1237	>	// masks and units for dealing with e = (int)ctl
1238	>	private static final int E_MASK      = 0x7fffffff; // no STOP_BIT
1239	>	private static final int E_SEQ       = 1 << EC_SHIFT;
1240	>
1241	>	// runState bits
1242	>	private static final int SHUTDOWN    = 1 << 31;
1243	>
1244	>	// access mode for WorkQueue
1245	>	static final int LIFO_QUEUE          =  0;
1246	>	static final int FIFO_QUEUE          =  1;
1247	>	static final int SHARED_QUEUE        = -1;
1248	>
1249	>	// Instance fields
1250	>
1251	>	/*
1252	>	* Field layout order in this class tends to matter more than one
1253	>	* would like. Runtime layout order is only loosely related to
1254	>	* declaration order and may differ across JVMs, but the following
1255	>	* empirically works OK on current JVMs.
1256	>	*/
1257	>
1258	>	volatile long stealCount;                  // collects worker counts
1259	>	volatile long ctl;                         // main pool control
1260	>	final int parallelism;                     // parallelism level
1261	>	final int localMode;                       // per-worker scheduling mode
1262	>	volatile int nextWorkerNumber;             // to create worker name string
1263	>	final int submitMask;                      // submit queue index bound
1264	>	int nextSeed;                              // for initializing worker seeds
1265	>	volatile int mainLock;                     // spinlock for array updates
1266	>	volatile int runState;                     // shutdown status and seq
1267	>	WorkQueue[] workQueues;                    // main registry
1268	>	final ForkJoinWorkerThreadFactory factory; // factory for new workers
1269	>	final Thread.UncaughtExceptionHandler ueh; // per-worker UEH
1270	>	final String workerNamePrefix;             // to create worker name string
1271	>
1272	>	/*
1273	>	* Mechanics for main lock protecting worker array updates.  Uses
1274	>	* the same strategy as ConcurrentHashMap bins -- a spinLock for
1275	>	* normal cases, but falling back to builtin lock when (rarely)
1276	>	* needed.  See internal ConcurrentHashMap documentation for
1277	>	* explanation.
1278	>	*/
1279	>
1280	>	static final int LOCK_WAITING = 2; // bit to indicate need for signal
1281	>	static final int MAX_LOCK_SPINS = 1 << 8;
1282	>
1283	>	private void tryAwaitMainLock() {
1284	>	int spins = MAX_LOCK_SPINS, r = 0, h;
1285	>	while (((h = mainLock) & 1) != 0) {
1286	>	if (r == 0)
1287	>	r = ThreadLocalRandom.current().nextInt(); // randomize spins
1288	>	else if (spins >= 0) {
1289	>	r ^= r << 1; r ^= r >>> 3; r ^= r << 10; // xorshift
1290	>	if (r >= 0)
1291	>	--spins;
1292	>	}
1293	>	else if (U.compareAndSwapInt(this, MAINLOCK, h, h | LOCK_WAITING)) {
1294	>	synchronized (this) {
1295	>	if ((mainLock & LOCK_WAITING) != 0) {
1296	>	try {
1297	>	wait();
1298	>	} catch (InterruptedException ie) {
1299	>	Thread.currentThread().interrupt();
1300	>	}
1301	>	}
1302	>	else
1303	>	notifyAll(); // possibly won race vs signaller
1304	>	}
1305	>	break;
1306	>	}
1307	>	}
1308	>	}
1309	>
1310	>	//  Creating, registering, and deregistering workers
1311
1312		/**
1313	<	* The desired parallelism level, updated only under workerLock.
1313	>	* Tries to create and start a worker
1314		*/
1315	<	private volatile int parallelism;
1315	>	private void addWorker() {
1316	>	Throwable ex = null;
1317	>	ForkJoinWorkerThread wt = null;
1318	>	try {
1319	>	if ((wt = factory.newThread(this)) != null) {
1320	>	wt.start();
1321	>	return;
1322	>	}
1323	>	} catch (Throwable e) {
1324	>	ex = e;
1325	>	}
1326	>	deregisterWorker(wt, ex); // adjust counts etc on failure
1327	>	}
1328
1329		/**
1330	<	* True if use local fifo, not default lifo, for local polling
1330	>	* Callback from ForkJoinWorkerThread constructor to assign a
1331	>	* public name. This must be separate from registerWorker because
1332	>	* it is called during the "super" constructor call in
1333	>	* ForkJoinWorkerThread.
1334		*/
1335	<	private volatile boolean locallyFifo;
1335	>	final String nextWorkerName() {
1336	>	int n;
1337	>	do {} while(!U.compareAndSwapInt(this, NEXTWORKERNUMBER,
1338	>	n = nextWorkerNumber, ++n));
1339	>	return workerNamePrefix.concat(Integer.toString(n));
1340	>	}
1341
1342		/**
1343	<	* Holds number of total (i.e., created and not yet terminated)
1344	<	* and running (i.e., not blocked on joins or other managed sync)
1345	<	* threads, packed into one int to ensure consistent snapshot when
1346	<	* making decisions about creating and suspending spare
1347	<	* threads. Updated only by CAS.  Note: CASes in
1348	<	* updateRunningCount and preJoin running active count is in low
1349	<	* word, so need to be modified if this changes
1343	>	* Callback from ForkJoinWorkerThread constructor to establish its
1344	>	* poolIndex and record its WorkQueue. To avoid scanning bias due
1345	>	* to packing entries in front of the workQueues array, we treat
1346	>	* the array as a simple power-of-two hash table using per-thread
1347	>	* seed as hash, expanding as needed.
1348	>	*
1349	>	* @param w the worker's queue
1350		*/
1351	<	private volatile int workerCounts;
1351	>	final void registerWorker(WorkQueue w) {
1352	>	while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
1353	>	tryAwaitMainLock();
1354	>	try {
1355	>	WorkQueue[] ws;
1356	>	if ((ws = workQueues) == null)
1357	>	ws = workQueues = new WorkQueue[submitMask + 1];
1358	>	if (w != null) {
1359	>	int rs, n =  ws.length, m = n - 1;
1360	>	int s = nextSeed += SEED_INCREMENT; // rarely-colliding sequence
1361	>	w.seed = (s == 0) ? 1 : s;          // ensure non-zero seed
1362	>	int r = (s << 1) | 1;               // use odd-numbered indices
1363	>	if (ws[r &= m] != null) {           // collision
1364	>	int probes = 0;                 // step by approx half size
1365	>	int step = (n <= 4) ? 2 : ((n >>> 1) & SQMASK) + 2;
1366	>	while (ws[r = (r + step) & m] != null) {
1367	>	if (++probes >= n) {
1368	>	workQueues = ws = Arrays.copyOf(ws, n <<= 1);
1369	>	m = n - 1;
1370	>	probes = 0;
1371	>	}
1372	>	}
1373	>	}
1374	>	w.eventCount = w.poolIndex = r;     // establish before recording
1375	>	ws[r] = w;                          // also update seq
1376	>	runState = ((rs = runState) & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN);
1377	>	}
1378	>	} finally {
1379	>	if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
1380	>	mainLock = 0;
1381	>	synchronized (this) { notifyAll(); };
1382	>	}
1383	>	}
1384
1385	<	private static int totalCountOf(int s)           { return s >>> 16;  }
225	<	private static int runningCountOf(int s)         { return s & shortMask; }
226	<	private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
1385	>	}
1386
1387		/**
1388	<	* Add delta (which may be negative) to running count.  This must
1389	<	* be called before (with negative arg) and after (with positive)
1390	<	* any managed synchronization (i.e., mainly, joins)
1391	<	* @param delta the number to add
1388	>	* Final callback from terminating worker, as well as upon failure
1389	>	* to construct or start a worker in addWorker.  Removes record of
1390	>	* worker from array, and adjusts counts. If pool is shutting
1391	>	* down, tries to complete termination.
1392	>	*
1393	>	* @param wt the worker thread or null if addWorker failed
1394	>	* @param ex the exception causing failure, or null if none
1395		*/
1396	<	final void updateRunningCount(int delta) {
1397	<	int s;
1398	<	do;while (!casWorkerCounts(s = workerCounts, s + delta));
1396	>	final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
1397	>	WorkQueue w = null;
1398	>	if (wt != null && (w = wt.workQueue) != null) {
1399	>	w.runState = -1;                // ensure runState is set
1400	>	long steals = w.totalSteals + w.nsteals, sc;
1401	>	do {} while(!U.compareAndSwapLong(this, STEALCOUNT,
1402	>	sc = stealCount, sc + steals));
1403	>	int idx = w.poolIndex;
1404	>	while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
1405	>	tryAwaitMainLock();
1406	>	try {
1407	>	WorkQueue[] ws = workQueues;
1408	>	if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w)
1409	>	ws[idx] = null;
1410	>	} finally {
1411	>	if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
1412	>	mainLock = 0;
1413	>	synchronized (this) { notifyAll(); };
1414	>	}
1415	>	}
1416	>	}
1417	>
1418	>	long c;                             // adjust ctl counts
1419	>	do {} while (!U.compareAndSwapLong
1420	>	(this, CTL, c = ctl, (((c - AC_UNIT) & AC_MASK) |
1421	>	((c - TC_UNIT) & TC_MASK) |
1422	>	(c & ~(AC_MASK|TC_MASK)))));
1423	>
1424	>	if (!tryTerminate(false, false) && w != null) {
1425	>	w.cancelAll();                  // cancel remaining tasks
1426	>	if (w.array != null)            // suppress signal if never ran
1427	>	signalWork();               // wake up or create replacement
1428	>	if (ex == null)                 // help clean refs on way out
1429	>	ForkJoinTask.helpExpungeStaleExceptions();
1430	>	}
1431	>
1432	>	if (ex != null)                     // rethrow
1433	>	U.throwException(ex);
1434	>	}
1435	>
1436	>	// Submissions
1437	>
1438	>	/**
1439	>	* Unless shutting down, adds the given task to a submission queue
1440	>	* at submitter's current queue index (modulo submission
1441	>	* range). If no queue exists at the index, one is created.  If
1442	>	* the queue is busy, another index is randomly chosen. The
1443	>	* submitMask bounds the effective number of queues to the
1444	>	* (nearest power of two for) parallelism level.
1445	>	*
1446	>	* @param task the task. Caller must ensure non-null.
1447	>	*/
1448	>	private void doSubmit(ForkJoinTask<?> task) {
1449	>	Submitter s = submitters.get();
1450	>	for (int r = s.seed, m = submitMask;;) {
1451	>	WorkQueue[] ws; WorkQueue q;
1452	>	int k = r & m & SQMASK;          // use only even indices
1453	>	if (runState < 0)
1454	>	throw new RejectedExecutionException(); // shutting down
1455	>	else if ((ws = workQueues) == null || ws.length <= k) {
1456	>	while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
1457	>	tryAwaitMainLock();
1458	>	try {
1459	>	if (workQueues == null)
1460	>	workQueues = new WorkQueue[submitMask + 1];
1461	>	} finally {
1462	>	if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
1463	>	mainLock = 0;
1464	>	synchronized (this) { notifyAll(); };
1465	>	}
1466	>	}
1467	>	}
1468	>	else if ((q = ws[k]) == null) {  // create new queue
1469	>	WorkQueue nq = new WorkQueue(this, null, SHARED_QUEUE);
1470	>	while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
1471	>	tryAwaitMainLock();
1472	>	try {
1473	>	int rs = runState;       // to update seq
1474	>	if (ws == workQueues && ws[k] == null) {
1475	>	ws[k] = nq;
1476	>	runState = ((rs & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN));
1477	>	}
1478	>	} finally {
1479	>	if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
1480	>	mainLock = 0;
1481	>	synchronized (this) { notifyAll(); };
1482	>	}
1483	>	}
1484	>	}
1485	>	else if (q.trySharedPush(task)) {
1486	>	signalWork();
1487	>	return;
1488	>	}
1489	>	else if (m > 1) {                // move to a different index
1490	>	r ^= r << 13;                // same xorshift as WorkQueues
1491	>	r ^= r >>> 17;
1492	>	s.seed = r ^= r << 5;
1493	>	}
1494	>	else
1495	>	Thread.yield();              // yield if no alternatives
1496	>	}
1497		}
1498
1499		/**
1500	<	* Add delta (which may be negative) to both total and running
241	<	* count.  This must be called upon creation and termination of
242	<	* worker threads.
243	<	* @param delta the number to add
1500	>	* Submits the given (non-null) task to the common pool, if possible.
1501		*/
1502	<	private void updateWorkerCount(int delta) {
1503	<	int d = delta + (delta << 16); // add to both lo and hi parts
1504	<	int s;
1505	<	do;while (!casWorkerCounts(s = workerCounts, s + d));
1502	>	static void submitToCommonPool(ForkJoinTask<?> task) {
1503	>	ForkJoinPool p;
1504	>	if ((p = commonPool) == null)
1505	>	throw new RejectedExecutionException("Common Pool Unavailable");
1506	>	p.doSubmit(task);
1507		}
1508
1509		/**
1510	<	* Lifecycle control. High word contains runState, low word
1511	<	* contains the number of workers that are (probably) executing
1512	<	* tasks. This value is atomically incremented before a worker
1513	<	* gets a task to run, and decremented when worker has no tasks
1514	<	* and cannot find any. These two fields are bundled together to
1515	<	* support correct termination triggering.  Note: activeCount
1516	<	* CAS'es cheat by assuming active count is in low word, so need
259	<	* to be modified if this changes
1510	>	* Returns true if the given task was submitted to common pool
1511	>	* and has not yet commenced execution, and is available for
1512	>	* removal according to execution policies; if so removing the
1513	>	* submission from the pool.
1514	>	*
1515	>	* @param task the task
1516	>	* @return true if successful
1517		*/
1518	<	private volatile int runControl;
1519	<
1520	<	// RunState values. Order among values matters
1521	<	private static final int RUNNING     = 0;
1522	<	private static final int SHUTDOWN    = 1;
1523	<	private static final int TERMINATING = 2;
1524	<	private static final int TERMINATED  = 3;
1518	>	static boolean tryUnsubmitFromCommonPool(ForkJoinTask<?> task) {
1519	>	// Peek, looking for task and eligibility before
1520	>	// using trySharedUnpush to actually take it under lock
1521	>	ForkJoinPool p; WorkQueue[] ws; WorkQueue q;
1522	>	ForkJoinTask<?>[] a; int t, s, n;
1523	>	int k = submitters.get().seed & SQMASK;
1524	>	return ((p = commonPool) != null &&
1525	>	(ws = p.workQueues) != null &&
1526	>	ws.length > (k &= p.submitMask) &&
1527	>	(q = ws[k]) != null &&
1528	>	(a = q.array) != null &&
1529	>	(n = (t = q.top) - q.base) > 0 &&
1530	>	(n > 1 || (int)(p.ctl >> AC_SHIFT) < 0) &&
1531	>	(s = t - 1) >= 0 && s < a.length && a[s] == task &&
1532	>	q.trySharedUnpush(task));
1533	>	}
1534
1535	<	private static int runStateOf(int c)             { return c >>> 16; }
270	<	private static int activeCountOf(int c)          { return c & shortMask; }
271	<	private static int runControlFor(int r, int a)   { return (r << 16) + a; }
1535	>	// Maintaining ctl counts
1536
1537		/**
1538	<	* Try incrementing active count; fail on contention. Called by
275	<	* workers before/during executing tasks.
276	<	* @return true on success;
1538	>	* Increments active count; mainly called upon return from blocking.
1539		*/
1540	<	final boolean tryIncrementActiveCount() {
1541	<	int c = runControl;
1542	<	return casRunControl(c, c+1);
1540	>	final void incrementActiveCount() {
1541	>	long c;
1542	>	do {} while (!U.compareAndSwapLong(this, CTL, c = ctl, c + AC_UNIT));
1543		}
1544
1545		/**
1546	<	* Try decrementing active count; fail on contention.
285	<	* Possibly trigger termination on success
286	<	* Called by workers when they can't find tasks.
287	<	* @return true on success
1546	>	* Tries to create one or activate one or more workers if too few are active.
1547		*/
1548	<	final boolean tryDecrementActiveCount() {
1549	<	int c = runControl;
1550	<	int nextc = c - 1;
1551	<	if (!casRunControl(c, nextc))
1552	<	return false;
1553	<	if (canTerminateOnShutdown(nextc))
1554	<	terminateOnShutdown();
1555	<	return true;
1548	>	final void signalWork() {
1549	>	long c; int u;
1550	>	while ((u = (int)((c = ctl) >>> 32)) < 0) {     // too few active
1551	>	WorkQueue[] ws = workQueues; int e, i; WorkQueue w; Thread p;
1552	>	if ((e = (int)c) > 0) {                     // at least one waiting
1553	>	if (ws != null && (i = e & SMASK) < ws.length &&
1554	>	(w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) {
1555	>	long nc = (((long)(w.nextWait & E_MASK)) |
1556	>	((long)(u + UAC_UNIT) << 32));
1557	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1558	>	w.eventCount = (e + E_SEQ) & E_MASK;
1559	>	if ((p = w.parker) != null)
1560	>	U.unpark(p);                // activate and release
1561	>	break;
1562	>	}
1563	>	}
1564	>	else
1565	>	break;
1566	>	}
1567	>	else if (e == 0 && (u & SHORT_SIGN) != 0) { // too few total
1568	>	long nc = (long)(((u + UTC_UNIT) & UTC_MASK) |
1569	>	((u + UAC_UNIT) & UAC_MASK)) << 32;
1570	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1571	>	addWorker();
1572	>	break;
1573	>	}
1574	>	}
1575	>	else
1576	>	break;
1577	>	}
1578		}
1579
1580	+	// Scanning for tasks
1581	+
1582		/**
1583	<	* Return true if argument represents zero active count and
301	<	* nonzero runstate, which is the triggering condition for
302	<	* terminating on shutdown.
1583	>	* Top-level runloop for workers, called by ForkJoinWorkerThread.run.
1584		*/
1585	<	private static boolean canTerminateOnShutdown(int c) {
1586	<	return ((c & -c) >>> 16) != 0; // i.e. least bit is nonzero runState bit
1585	>	final void runWorker(WorkQueue w) {
1586	>	w.growArray(false);         // initialize queue array in this thread
1587	>	do { w.runTask(scan(w)); } while (w.runState >= 0);
1588	>	}
1589	>
1590	>	/**
1591	>	* Scans for and, if found, returns one task, else possibly
1592	>	* inactivates the worker. This method operates on single reads of
1593	>	* volatile state and is designed to be re-invoked continuously,
1594	>	* in part because it returns upon detecting inconsistencies,
1595	>	* contention, or state changes that indicate possible success on
1596	>	* re-invocation.
1597	>	*
1598	>	* The scan searches for tasks across a random permutation of
1599	>	* queues (starting at a random index and stepping by a random
1600	>	* relative prime, checking each at least once).  The scan
1601	>	* terminates upon either finding a non-empty queue, or completing
1602	>	* the sweep. If the worker is not inactivated, it takes and
1603	>	* returns a task from this queue.  On failure to find a task, we
1604	>	* take one of the following actions, after which the caller will
1605	>	* retry calling this method unless terminated.
1606	>	*
1607	>	* * If pool is terminating, terminate the worker.
1608	>	*
1609	>	* * If not a complete sweep, try to release a waiting worker.  If
1610	>	* the scan terminated because the worker is inactivated, then the
1611	>	* released worker will often be the calling worker, and it can
1612	>	* succeed obtaining a task on the next call. Or maybe it is
1613	>	* another worker, but with same net effect. Releasing in other
1614	>	* cases as well ensures that we have enough workers running.
1615	>	*
1616	>	* * If not already enqueued, try to inactivate and enqueue the
1617	>	* worker on wait queue. Or, if inactivating has caused the pool
1618	>	* to be quiescent, relay to idleAwaitWork to check for
1619	>	* termination and possibly shrink pool.
1620	>	*
1621	>	* * If already inactive, and the caller has run a task since the
1622	>	* last empty scan, return (to allow rescan) unless others are
1623	>	* also inactivated.  Field WorkQueue.rescans counts down on each
1624	>	* scan to ensure eventual inactivation and blocking.
1625	>	*
1626	>	* * If already enqueued and none of the above apply, park
1627	>	* awaiting signal,
1628	>	*
1629	>	* @param w the worker (via its WorkQueue)
1630	>	* @return a task or null if none found
1631	>	*/
1632	>	private final ForkJoinTask<?> scan(WorkQueue w) {
1633	>	WorkQueue[] ws;                       // first update random seed
1634	>	int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
1635	>	int rs = runState, m;                 // volatile read order matters
1636	>	if ((ws = workQueues) != null && (m = ws.length - 1) > 0) {
1637	>	int ec = w.eventCount;            // ec is negative if inactive
1638	>	int step = (r >>> 16) | 1;        // relative prime
1639	>	for (int j = (m + 1) << 2; ; r += step) {
1640	>	WorkQueue q; ForkJoinTask<?> t; ForkJoinTask<?>[] a; int b;
1641	>	if ((q = ws[r & m]) != null && (b = q.base) - q.top < 0 &&
1642	>	(a = q.array) != null) {  // probably nonempty
1643	>	int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
1644	>	t = (ForkJoinTask<?>)U.getObjectVolatile(a, i);
1645	>	if (q.base == b && ec >= 0 && t != null &&
1646	>	U.compareAndSwapObject(a, i, t, null)) {
1647	>	if (q.top - (q.base = b + 1) > 0)
1648	>	signalWork();    // help pushes signal
1649	>	return t;
1650	>	}
1651	>	else if (ec < 0 || j <= m) {
1652	>	rs = 0;               // mark scan as imcomplete
1653	>	break;                // caller can retry after release
1654	>	}
1655	>	}
1656	>	if (--j < 0)
1657	>	break;
1658	>	}
1659	>
1660	>	long c = ctl; int e = (int)c, a = (int)(c >> AC_SHIFT), nr, ns;
1661	>	if (e < 0)                        // decode ctl on empty scan
1662	>	w.runState = -1;              // pool is terminating
1663	>	else if (rs == 0 || rs != runState) { // incomplete scan
1664	>	WorkQueue v; Thread p;        // try to release a waiter
1665	>	if (e > 0 && a < 0 && w.eventCount == ec &&
1666	>	(v = ws[e & m]) != null && v.eventCount == (e | INT_SIGN)) {
1667	>	long nc = ((long)(v.nextWait & E_MASK) |
1668	>	((c + AC_UNIT) & (AC_MASK|TC_MASK)));
1669	>	if (ctl == c && U.compareAndSwapLong(this, CTL, c, nc)) {
1670	>	v.eventCount = (e + E_SEQ) & E_MASK;
1671	>	if ((p = v.parker) != null)
1672	>	U.unpark(p);
1673	>	}
1674	>	}
1675	>	}
1676	>	else if (ec >= 0) {               // try to enqueue/inactivate
1677	>	long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
1678	>	w.nextWait = e;
1679	>	w.eventCount = ec | INT_SIGN; // mark as inactive
1680	>	if (ctl != c || !U.compareAndSwapLong(this, CTL, c, nc))
1681	>	w.eventCount = ec;        // unmark on CAS failure
1682	>	else {
1683	>	if ((ns = w.nsteals) != 0) {
1684	>	w.nsteals = 0;        // set rescans if ran task
1685	>	w.rescans = (a > 0) ? 0 : a + parallelism;
1686	>	w.totalSteals += ns;
1687	>	}
1688	>	if (a == 1 - parallelism) // quiescent
1689	>	idleAwaitWork(w, nc, c);
1690	>	}
1691	>	}
1692	>	else if (w.eventCount < 0) {      // already queued
1693	>	int ac = a + parallelism;
1694	>	if ((nr = w.rescans) > 0)     // continue rescanning
1695	>	w.rescans = (ac < nr) ? ac : nr - 1;
1696	>	else if (((w.seed >>> 16) & ac) == 0) { // randomize park
1697	>	Thread.interrupted();     // clear status
1698	>	Thread wt = Thread.currentThread();
1699	>	U.putObject(wt, PARKBLOCKER, this);
1700	>	w.parker = wt;            // emulate LockSupport.park
1701	>	if (w.eventCount < 0)     // recheck
1702	>	U.park(false, 0L);
1703	>	w.parker = null;
1704	>	U.putObject(wt, PARKBLOCKER, null);
1705	>	}
1706	>	}
1707	>	}
1708	>	return null;
1709		}
1710
1711		/**
1712	<	* Transition run state to at least the given state. Return true
1713	<	* if not already at least given state.
1714	<	*/
1715	<	private boolean transitionRunStateTo(int state) {
1716	<	for (;;) {
1717	<	int c = runControl;
1718	<	if (runStateOf(c) >= state)
1719	<	return false;
1720	<	if (casRunControl(c, runControlFor(state, activeCountOf(c))))
1721	<	return true;
1712	>	* If inactivating worker w has caused the pool to become
1713	>	* quiescent, checks for pool termination, and, so long as this is
1714	>	* not the only worker, waits for event for up to a given
1715	>	* duration.  On timeout, if ctl has not changed, terminates the
1716	>	* worker, which will in turn wake up another worker to possibly
1717	>	* repeat this process.
1718	>	*
1719	>	* @param w the calling worker
1720	>	* @param currentCtl the ctl value triggering possible quiescence
1721	>	* @param prevCtl the ctl value to restore if thread is terminated
1722	>	*/
1723	>	private void idleAwaitWork(WorkQueue w, long currentCtl, long prevCtl) {
1724	>	if (w.eventCount < 0 && !tryTerminate(false, false) &&
1725	>	(int)prevCtl != 0 && !hasQueuedSubmissions() && ctl == currentCtl) {
1726	>	int dc = -(short)(currentCtl >>> TC_SHIFT);
1727	>	long parkTime = dc < 0 ? FAST_IDLE_TIMEOUT: (dc + 1) * IDLE_TIMEOUT;
1728	>	long deadline = System.nanoTime() + parkTime - 100000L; // 1ms slop
1729	>	Thread wt = Thread.currentThread();
1730	>	while (ctl == currentCtl) {
1731	>	Thread.interrupted();  // timed variant of version in scan()
1732	>	U.putObject(wt, PARKBLOCKER, this);
1733	>	w.parker = wt;
1734	>	if (ctl == currentCtl)
1735	>	U.park(false, parkTime);
1736	>	w.parker = null;
1737	>	U.putObject(wt, PARKBLOCKER, null);
1738	>	if (ctl != currentCtl)
1739	>	break;
1740	>	if (deadline - System.nanoTime() <= 0L &&
1741	>	U.compareAndSwapLong(this, CTL, currentCtl, prevCtl)) {
1742	>	w.eventCount = (w.eventCount + E_SEQ) | E_MASK;
1743	>	w.runState = -1;   // shrink
1744	>	break;
1745	>	}
1746	>	}
1747		}
1748		}
1749
1750		/**
1751	<	* Controls whether to add spares to maintain parallelism
1752	<	*/
1753	<	private volatile boolean maintainsParallelism;
1754	<
1755	<	// Constructors
1751	>	* Tries to locate and execute tasks for a stealer of the given
1752	>	* task, or in turn one of its stealers, Traces currentSteal ->
1753	>	* currentJoin links looking for a thread working on a descendant
1754	>	* of the given task and with a non-empty queue to steal back and
1755	>	* execute tasks from. The first call to this method upon a
1756	>	* waiting join will often entail scanning/search, (which is OK
1757	>	* because the joiner has nothing better to do), but this method
1758	>	* leaves hints in workers to speed up subsequent calls. The
1759	>	* implementation is very branchy to cope with potential
1760	>	* inconsistencies or loops encountering chains that are stale,
1761	>	* unknown, or so long that they are likely cyclic.
1762	>	*
1763	>	* @param joiner the joining worker
1764	>	* @param task the task to join
1765	>	* @return 0 if no progress can be made, negative if task
1766	>	* known complete, else positive
1767	>	*/
1768	>	private int tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
1769	>	int stat = 0, steps = 0;                    // bound to avoid cycles
1770	>	if (joiner != null && task != null) {       // hoist null checks
1771	>	restart: for (;;) {
1772	>	ForkJoinTask<?> subtask = task;     // current target
1773	>	for (WorkQueue j = joiner, v;;) {   // v is stealer of subtask
1774	>	WorkQueue[] ws; int m, s, h;
1775	>	if ((s = task.status) < 0) {
1776	>	stat = s;
1777	>	break restart;
1778	>	}
1779	>	if ((ws = workQueues) == null || (m = ws.length - 1) <= 0)
1780	>	break restart;              // shutting down
1781	>	if ((v = ws[h = (j.stealHint | 1) & m]) == null ||
1782	>	v.currentSteal != subtask) {
1783	>	for (int origin = h;;) {    // find stealer
1784	>	if (((h = (h + 2) & m) & 15) == 1 &&
1785	>	(subtask.status < 0 || j.currentJoin != subtask))
1786	>	continue restart;   // occasional staleness check
1787	>	if ((v = ws[h]) != null &&
1788	>	v.currentSteal == subtask) {
1789	>	j.stealHint = h;    // save hint
1790	>	break;
1791	>	}
1792	>	if (h == origin)
1793	>	break restart;      // cannot find stealer
1794	>	}
1795	>	}
1796	>	for (;;) { // help stealer or descend to its stealer
1797	>	ForkJoinTask[] a;  int b;
1798	>	if (subtask.status < 0)     // surround probes with
1799	>	continue restart;       //   consistency checks
1800	>	if ((b = v.base) - v.top < 0 && (a = v.array) != null) {
1801	>	int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
1802	>	ForkJoinTask<?> t =
1803	>	(ForkJoinTask<?>)U.getObjectVolatile(a, i);
1804	>	if (subtask.status < 0 || j.currentJoin != subtask ||
1805	>	v.currentSteal != subtask)
1806	>	continue restart;   // stale
1807	>	stat = 1;               // apparent progress
1808	>	if (t != null && v.base == b &&
1809	>	U.compareAndSwapObject(a, i, t, null)) {
1810	>	v.base = b + 1;     // help stealer
1811	>	joiner.runSubtask(t);
1812	>	}
1813	>	else if (v.base == b && ++steps == MAX_HELP)
1814	>	break restart;      // v apparently stalled
1815	>	}
1816	>	else {                      // empty -- try to descend
1817	>	ForkJoinTask<?> next = v.currentJoin;
1818	>	if (subtask.status < 0 || j.currentJoin != subtask ||
1819	>	v.currentSteal != subtask)
1820	>	continue restart;   // stale
1821	>	else if (next == null || ++steps == MAX_HELP)
1822	>	break restart;      // dead-end or maybe cyclic
1823	>	else {
1824	>	subtask = next;
1825	>	j = v;
1826	>	break;
1827	>	}
1828	>	}
1829	>	}
1830	>	}
1831	>	}
1832	>	}
1833	>	return stat;
1834	>	}
1835
1836		/**
1837	<	* Creates a ForkJoinPool with a pool size equal to the number of
1838	<	* processors available on the system and using the default
1839	<	* ForkJoinWorkerThreadFactory,
1840	<	* @throws SecurityException if a security manager exists and
334	<	*         the caller is not permitted to modify threads
335	<	*         because it does not hold {@link
336	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
1837	>	* If task is at base of some steal queue, steals and executes it.
1838	>	*
1839	>	* @param joiner the joining worker
1840	>	* @param task the task
1841		*/
1842	<	public ForkJoinPool() {
1843	<	this(Runtime.getRuntime().availableProcessors(),
1844	<	defaultForkJoinWorkerThreadFactory);
1842	>	private void tryPollForAndExec(WorkQueue joiner, ForkJoinTask<?> task) {
1843	>	WorkQueue[] ws;
1844	>	if ((ws = workQueues) != null) {
1845	>	for (int j = 1; j < ws.length && task.status >= 0; j += 2) {
1846	>	WorkQueue q = ws[j];
1847	>	if (q != null && q.pollFor(task)) {
1848	>	joiner.runSubtask(task);
1849	>	break;
1850	>	}
1851	>	}
1852	>	}
1853		}
1854
1855		/**
1856	<	* Creates a ForkJoinPool with the indicated parellelism level
1857	<	* threads, and using the default ForkJoinWorkerThreadFactory,
1858	<	* @param parallelism the number of worker threads
1859	<	* @throws IllegalArgumentException if parallelism less than or
1860	<	* equal to zero
1861	<	* @throws SecurityException if a security manager exists and
1862	<	*         the caller is not permitted to modify threads
1863	<	*         because it does not hold {@link
1864	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
1865	<	*/
1866	<	public ForkJoinPool(int parallelism) {
1867	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
1856	>	* Tries to decrement active count (sometimes implicitly) and
1857	>	* possibly release or create a compensating worker in preparation
1858	>	* for blocking. Fails on contention or termination. Otherwise,
1859	>	* adds a new thread if no idle workers are available and either
1860	>	* pool would become completely starved or: (at least half
1861	>	* starved, and fewer than 50% spares exist, and there is at least
1862	>	* one task apparently available). Even though the availability
1863	>	* check requires a full scan, it is worthwhile in reducing false
1864	>	* alarms.
1865	>	*
1866	>	* @param task if non-null, a task being waited for
1867	>	* @param blocker if non-null, a blocker being waited for
1868	>	* @return true if the caller can block, else should recheck and retry
1869	>	*/
1870	>	final boolean tryCompensate(ForkJoinTask<?> task, ManagedBlocker blocker) {
1871	>	int pc = parallelism, e;
1872	>	long c = ctl;
1873	>	WorkQueue[] ws = workQueues;
1874	>	if ((e = (int)c) >= 0 && ws != null) {
1875	>	int u, a, ac, hc;
1876	>	int tc = (short)((u = (int)(c >>> 32)) >>> UTC_SHIFT) + pc;
1877	>	boolean replace = false;
1878	>	if ((a = u >> UAC_SHIFT) <= 0) {
1879	>	if ((ac = a + pc) <= 1)
1880	>	replace = true;
1881	>	else if ((e > 0 || (task != null &&
1882	>	ac <= (hc = pc >>> 1) && tc < pc + hc))) {
1883	>	WorkQueue w;
1884	>	for (int j = 0; j < ws.length; ++j) {
1885	>	if ((w = ws[j]) != null && !w.isEmpty()) {
1886	>	replace = true;
1887	>	break;   // in compensation range and tasks available
1888	>	}
1889	>	}
1890	>	}
1891	>	}
1892	>	if ((task == null || task.status >= 0) && // recheck need to block
1893	>	(blocker == null || !blocker.isReleasable()) && ctl == c) {
1894	>	if (!replace) {          // no compensation
1895	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
1896	>	if (U.compareAndSwapLong(this, CTL, c, nc))
1897	>	return true;
1898	>	}
1899	>	else if (e != 0) {       // release an idle worker
1900	>	WorkQueue w; Thread p; int i;
1901	>	if ((i = e & SMASK) < ws.length && (w = ws[i]) != null) {
1902	>	long nc = ((long)(w.nextWait & E_MASK) |
1903	>	(c & (AC_MASK|TC_MASK)));
1904	>	if (w.eventCount == (e | INT_SIGN) &&
1905	>	U.compareAndSwapLong(this, CTL, c, nc)) {
1906	>	w.eventCount = (e + E_SEQ) & E_MASK;
1907	>	if ((p = w.parker) != null)
1908	>	U.unpark(p);
1909	>	return true;
1910	>	}
1911	>	}
1912	>	}
1913	>	else if (tc < MAX_CAP) { // create replacement
1914	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
1915	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1916	>	addWorker();
1917	>	return true;
1918	>	}
1919	>	}
1920	>	}
1921	>	}
1922	>	return false;
1923		}
1924
1925		/**
1926	<	* Creates a ForkJoinPool with parallelism equal to the number of
1927	<	* processors available on the system and using the given
1928	<	* ForkJoinWorkerThreadFactory,
1929	<	* @param factory the factory for creating new threads
1930	<	* @throws NullPointerException if factory is null
364	<	* @throws SecurityException if a security manager exists and
365	<	*         the caller is not permitted to modify threads
366	<	*         because it does not hold {@link
367	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
1926	>	* Helps and/or blocks until the given task is done.
1927	>	*
1928	>	* @param joiner the joining worker
1929	>	* @param task the task
1930	>	* @return task status on exit
1931		*/
1932	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
1933	<	this(Runtime.getRuntime().availableProcessors(), factory);
1932	>	final int awaitJoin(WorkQueue joiner, ForkJoinTask<?> task) {
1933	>	int s;
1934	>	if ((s = task.status) >= 0) {
1935	>	ForkJoinTask<?> prevJoin = joiner.currentJoin;
1936	>	joiner.currentJoin = task;
1937	>	long startTime = 0L;
1938	>	for (int k = 0;;) {
1939	>	if ((s = (joiner.isEmpty() ?           // try to help
1940	>	tryHelpStealer(joiner, task) :
1941	>	joiner.tryRemoveAndExec(task))) == 0 &&
1942	>	(s = task.status) >= 0) {
1943	>	if (k == 0) {
1944	>	startTime = System.nanoTime();
1945	>	tryPollForAndExec(joiner, task); // check uncommon case
1946	>	}
1947	>	else if ((k & (MAX_HELP - 1)) == 0 &&
1948	>	System.nanoTime() - startTime >=
1949	>	COMPENSATION_DELAY &&
1950	>	tryCompensate(task, null)) {
1951	>	if (task.trySetSignal()) {
1952	>	synchronized (task) {
1953	>	if (task.status >= 0) {
1954	>	try {                // see ForkJoinTask
1955	>	task.wait();     //  for explanation
1956	>	} catch (InterruptedException ie) {
1957	>	}
1958	>	}
1959	>	else
1960	>	task.notifyAll();
1961	>	}
1962	>	}
1963	>	long c;                          // re-activate
1964	>	do {} while (!U.compareAndSwapLong
1965	>	(this, CTL, c = ctl, c + AC_UNIT));
1966	>	}
1967	>	}
1968	>	if (s < 0 || (s = task.status) < 0) {
1969	>	joiner.currentJoin = prevJoin;
1970	>	break;
1971	>	}
1972	>	else if ((k++ & (MAX_HELP - 1)) == MAX_HELP >>> 1)
1973	>	Thread.yield();                     // for politeness
1974	>	}
1975	>	}
1976	>	return s;
1977		}
1978
1979		/**
1980	<	* Creates a ForkJoinPool with the given parallelism and factory.
1980	>	* Stripped-down variant of awaitJoin used by timed joins. Tries
1981	>	* to help join only while there is continuous progress. (Caller
1982	>	* will then enter a timed wait.)
1983		*
1984	<	* @param parallelism the targeted number of worker threads
1985	<	* @param factory the factory for creating new threads
1986	<	* @throws IllegalArgumentException if parallelism less than or
379	<	* equal to zero, or greater than implementation limit.
380	<	* @throws NullPointerException if factory is null
381	<	* @throws SecurityException if a security manager exists and
382	<	*         the caller is not permitted to modify threads
383	<	*         because it does not hold {@link
384	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
1984	>	* @param joiner the joining worker
1985	>	* @param task the task
1986	>	* @return task status on exit
1987		*/
1988	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
1989	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1990	<	throw new IllegalArgumentException();
1991	<	if (factory == null)
1992	<	throw new NullPointerException();
1993	<	checkPermission();
1994	<	this.factory = factory;
1995	<	this.parallelism = parallelism;
394	<	this.maxPoolSize = MAX_THREADS;
395	<	this.maintainsParallelism = true;
396	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
397	<	this.workerLock = new ReentrantLock();
398	<	this.termination = workerLock.newCondition();
399	<	this.stealCount = new AtomicLong();
400	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
401	<	// worker array and workers are lazily constructed
1988	>	final int helpJoinOnce(WorkQueue joiner, ForkJoinTask<?> task) {
1989	>	int s;
1990	>	while ((s = task.status) >= 0 &&
1991	>	(joiner.isEmpty() ?
1992	>	tryHelpStealer(joiner, task) :
1993	>	joiner.tryRemoveAndExec(task)) != 0)
1994	>	;
1995	>	return s;
1996		}
1997
1998		/**
1999	<	* Create new worker using factory.
2000	<	* @param index the index to assign worker
2001	<	* @return new worker, or null of factory failed
2002	<	*/
2003	<	private ForkJoinWorkerThread createWorker(int index) {
2004	<	Thread.UncaughtExceptionHandler h = ueh;
2005	<	ForkJoinWorkerThread w = factory.newThread(this);
2006	<	if (w != null) {
2007	<	w.poolIndex = index;
2008	<	w.setDaemon(true);
2009	<	w.setAsyncMode(locallyFifo);
2010	<	w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
2011	<	if (h != null)
2012	<	w.setUncaughtExceptionHandler(h);
1999	>	* Returns a (probably) non-empty steal queue, if one is found
2000	>	* during a random, then cyclic scan, else null.  This method must
2001	>	* be retried by caller if, by the time it tries to use the queue,
2002	>	* it is empty.
2003	>	*/
2004	>	private WorkQueue findNonEmptyStealQueue(WorkQueue w) {
2005	>	// Similar to loop in scan(), but ignoring submissions
2006	>	int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
2007	>	int step = (r >>> 16) | 1;
2008	>	for (WorkQueue[] ws;;) {
2009	>	int rs = runState, m;
2010	>	if ((ws = workQueues) == null || (m = ws.length - 1) < 1)
2011	>	return null;
2012	>	for (int j = (m + 1) << 2; ; r += step) {
2013	>	WorkQueue q = ws[((r << 1) | 1) & m];
2014	>	if (q != null && !q.isEmpty())
2015	>	return q;
2016	>	else if (--j < 0) {
2017	>	if (runState == rs)
2018	>	return null;
2019	>	break;
2020	>	}
2021	>	}
2022	>	}
2023	>	}
2024	>
2025	>	/**
2026	>	* Runs tasks until {@code isQuiescent()}. We piggyback on
2027	>	* active count ctl maintenance, but rather than blocking
2028	>	* when tasks cannot be found, we rescan until all others cannot
2029	>	* find tasks either.
2030	>	*/
2031	>	final void helpQuiescePool(WorkQueue w) {
2032	>	for (boolean active = true;;) {
2033	>	ForkJoinTask<?> localTask; // exhaust local queue
2034	>	while ((localTask = w.nextLocalTask()) != null)
2035	>	localTask.doExec();
2036	>	WorkQueue q = findNonEmptyStealQueue(w);
2037	>	if (q != null) {
2038	>	ForkJoinTask<?> t; int b;
2039	>	if (!active) {      // re-establish active count
2040	>	long c;
2041	>	active = true;
2042	>	do {} while (!U.compareAndSwapLong
2043	>	(this, CTL, c = ctl, c + AC_UNIT));
2044	>	}
2045	>	if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
2046	>	w.runSubtask(t);
2047	>	}
2048	>	else {
2049	>	long c;
2050	>	if (active) {       // decrement active count without queuing
2051	>	active = false;
2052	>	do {} while (!U.compareAndSwapLong
2053	>	(this, CTL, c = ctl, c -= AC_UNIT));
2054	>	}
2055	>	else
2056	>	c = ctl;        // re-increment on exit
2057	>	if ((int)(c >> AC_SHIFT) + parallelism == 0) {
2058	>	do {} while (!U.compareAndSwapLong
2059	>	(this, CTL, c = ctl, c + AC_UNIT));
2060	>	break;
2061	>	}
2062	>	}
2063		}
420	–	return w;
2064		}
2065
2066		/**
2067	<	* Return a good size for worker array given pool size.
425	<	* Currently requires size to be a power of two.
2067	>	* Restricted version of helpQuiescePool for non-FJ callers
2068		*/
2069	<	private static int arraySizeFor(int ps) {
2070	<	return ps <= 1? 1 : (1 << (32 - Integer.numberOfLeadingZeros(ps-1)));
2069	>	static void externalHelpQuiescePool() {
2070	>	ForkJoinPool p; WorkQueue[] ws; WorkQueue w, q;
2071	>	ForkJoinTask<?> t; int b;
2072	>	int k = submitters.get().seed & SQMASK;
2073	>	if ((p = commonPool) != null &&
2074	>	(ws = p.workQueues) != null &&
2075	>	ws.length > (k &= p.submitMask) &&
2076	>	(w = ws[k]) != null &&
2077	>	(q = p.findNonEmptyStealQueue(w)) != null &&
2078	>	(b = q.base) - q.top < 0 &&
2079	>	(t = q.pollAt(b)) != null)
2080	>	t.doExec();
2081		}
2082
2083		/**
2084	<	* Create or resize array if necessary to hold newLength.
2085	<	* Call only under exlusion or lock
2086	<	* @return the array
2084	>	* Gets and removes a local or stolen task for the given worker.
2085	>	*
2086	>	* @return a task, if available
2087	>	*/
2088	>	final ForkJoinTask<?> nextTaskFor(WorkQueue w) {
2089	>	for (ForkJoinTask<?> t;;) {
2090	>	WorkQueue q; int b;
2091	>	if ((t = w.nextLocalTask()) != null)
2092	>	return t;
2093	>	if ((q = findNonEmptyStealQueue(w)) == null)
2094	>	return null;
2095	>	if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
2096	>	return t;
2097	>	}
2098	>	}
2099	>
2100	>	/**
2101	>	* Returns the approximate (non-atomic) number of idle threads per
2102	>	* active thread to offset steal queue size for method
2103	>	* ForkJoinTask.getSurplusQueuedTaskCount().
2104		*/
2105	<	private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
2106	<	ForkJoinWorkerThread[] ws = workers;
2107	<	if (ws == null)
2108	<	return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
2109	<	else if (newLength > ws.length)
2110	<	return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
2111	<	else
2112	<	return ws;
2105	>	final int idlePerActive() {
2106	>	// Approximate at powers of two for small values, saturate past 4
2107	>	int p = parallelism;
2108	>	int a = p + (int)(ctl >> AC_SHIFT);
2109	>	return (a > (p >>>= 1) ? 0 :
2110	>	a > (p >>>= 1) ? 1 :
2111	>	a > (p >>>= 1) ? 2 :
2112	>	a > (p >>>= 1) ? 4 :
2113	>	8);
2114		}
2115
2116		/**
2117	<	* Try to shrink workers into smaller array after one or more terminate
2117	>	* Returns approximate submission queue length for the given caller
2118		*/
2119	<	private void tryShrinkWorkerArray() {
2120	<	ForkJoinWorkerThread[] ws = workers;
2121	<	if (ws != null) {
2122	<	int len = ws.length;
2123	<	int last = len - 1;
2124	<	while (last >= 0 && ws[last] == null)
2125	<	--last;
2126	<	int newLength = arraySizeFor(last+1);
2127	<	if (newLength < len)
458	<	workers = Arrays.copyOf(ws, newLength);
459	<	}
2119	>	static int getEstimatedSubmitterQueueLength() {
2120	>	ForkJoinPool p; WorkQueue[] ws; WorkQueue q;
2121	>	int k = submitters.get().seed & SQMASK;
2122	>	return ((p = commonPool) != null &&
2123	>	p.runState >= 0 &&
2124	>	(ws = p.workQueues) != null &&
2125	>	ws.length > (k &= p.submitMask) &&
2126	>	(q = ws[k]) != null) ?
2127	>	q.queueSize() : 0;
2128		}
2129
2130	+	//  Termination
2131	+
2132		/**
2133	<	* Initialize workers if necessary
2133	>	* Possibly initiates and/or completes termination.  The caller
2134	>	* triggering termination runs three passes through workQueues:
2135	>	* (0) Setting termination status, followed by wakeups of queued
2136	>	* workers; (1) cancelling all tasks; (2) interrupting lagging
2137	>	* threads (likely in external tasks, but possibly also blocked in
2138	>	* joins).  Each pass repeats previous steps because of potential
2139	>	* lagging thread creation.
2140	>	*
2141	>	* @param now if true, unconditionally terminate, else only
2142	>	* if no work and no active workers
2143	>	* @param enable if true, enable shutdown when next possible
2144	>	* @return true if now terminating or terminated
2145		*/
2146	<	final void ensureWorkerInitialization() {
2147	<	ForkJoinWorkerThread[] ws = workers;
2148	<	if (ws == null) {
2149	<	final ReentrantLock lock = this.workerLock;
2150	<	lock.lock();
2151	<	try {
2152	<	ws = workers;
2153	<	if (ws == null) {
2154	<	int ps = parallelism;
2155	<	ws = ensureWorkerArrayCapacity(ps);
2156	<	for (int i = 0; i < ps; ++i) {
2157	<	ForkJoinWorkerThread w = createWorker(i);
2158	<	if (w != null) {
2159	<	ws[i] = w;
2160	<	w.start();
2161	<	updateWorkerCount(1);
2146	>	private boolean tryTerminate(boolean now, boolean enable) {
2147	>	for (long c;;) {
2148	>	if (((c = ctl) & STOP_BIT) != 0) {      // already terminating
2149	>	if ((short)(c >>> TC_SHIFT) == -parallelism) {
2150	>	synchronized(this) {
2151	>	notifyAll();                // signal when 0 workers
2152	>	}
2153	>	}
2154	>	return true;
2155	>	}
2156	>	if (runState >= 0) {                    // not yet enabled
2157	>	if (!enable)
2158	>	return false;
2159	>	while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
2160	>	tryAwaitMainLock();
2161	>	try {
2162	>	runState |= SHUTDOWN;
2163	>	} finally {
2164	>	if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
2165	>	mainLock = 0;
2166	>	synchronized (this) { notifyAll(); };
2167	>	}
2168	>	}
2169	>	}
2170	>	if (!now) {                             // check if idle & no tasks
2171	>	if ((int)(c >> AC_SHIFT) != -parallelism ||
2172	>	hasQueuedSubmissions())
2173	>	return false;
2174	>	// Check for unqueued inactive workers. One pass suffices.
2175	>	WorkQueue[] ws = workQueues; WorkQueue w;
2176	>	if (ws != null) {
2177	>	for (int i = 1; i < ws.length; i += 2) {
2178	>	if ((w = ws[i]) != null && w.eventCount >= 0)
2179	>	return false;
2180	>	}
2181	>	}
2182	>	}
2183	>	if (U.compareAndSwapLong(this, CTL, c, c | STOP_BIT)) {
2184	>	for (int pass = 0; pass < 3; ++pass) {
2185	>	WorkQueue[] ws = workQueues;
2186	>	if (ws != null) {
2187	>	WorkQueue w;
2188	>	int n = ws.length;
2189	>	for (int i = 0; i < n; ++i) {
2190	>	if ((w = ws[i]) != null) {
2191	>	w.runState = -1;
2192	>	if (pass > 0) {
2193	>	w.cancelAll();
2194	>	if (pass > 1)
2195	>	w.interruptOwner();
2196	>	}
2197	>	}
2198	>	}
2199	>	// Wake up workers parked on event queue
2200	>	int i, e; long cc; Thread p;
2201	>	while ((e = (int)(cc = ctl) & E_MASK) != 0 &&
2202	>	(i = e & SMASK) < n &&
2203	>	(w = ws[i]) != null) {
2204	>	long nc = ((long)(w.nextWait & E_MASK) |
2205	>	((cc + AC_UNIT) & AC_MASK) |
2206	>	(cc & (TC_MASK|STOP_BIT)));
2207	>	if (w.eventCount == (e | INT_SIGN) &&
2208	>	U.compareAndSwapLong(this, CTL, cc, nc)) {
2209	>	w.eventCount = (e + E_SEQ) & E_MASK;
2210	>	w.runState = -1;
2211	>	if ((p = w.parker) != null)
2212	>	U.unpark(p);
2213	>	}
2214		}
2215		}
2216		}
484	–	} finally {
485	–	lock.unlock();
2217		}
2218		}
2219		}
2220
2221	+	// Exported methods
2222	+
2223	+	// Constructors
2224	+
2225		/**
2226	<	* Worker creation and startup for threads added via setParallelism.
2226	>	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
2227	>	* java.lang.Runtime#availableProcessors}, using the {@linkplain
2228	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
2229	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
2230	>	*
2231	>	* @throws SecurityException if a security manager exists and
2232	>	*         the caller is not permitted to modify threads
2233	>	*         because it does not hold {@link
2234	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
2235		*/
2236	<	private void createAndStartAddedWorkers() {
2237	<	resumeAllSpares();  // Allow spares to convert to nonspare
2238	<	int ps = parallelism;
496	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
497	<	int len = ws.length;
498	<	// Sweep through slots, to keep lowest indices most populated
499	<	int k = 0;
500	<	while (k < len) {
501	<	if (ws[k] != null) {
502	<	++k;
503	<	continue;
504	<	}
505	<	int s = workerCounts;
506	<	int tc = totalCountOf(s);
507	<	int rc = runningCountOf(s);
508	<	if (rc >= ps || tc >= ps)
509	<	break;
510	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
511	<	ForkJoinWorkerThread w = createWorker(k);
512	<	if (w != null) {
513	<	ws[k++] = w;
514	<	w.start();
515	<	}
516	<	else {
517	<	updateWorkerCount(-1); // back out on failed creation
518	<	break;
519	<	}
520	<	}
521	<	}
2236	>	public ForkJoinPool() {
2237	>	this(Runtime.getRuntime().availableProcessors(),
2238	>	defaultForkJoinWorkerThreadFactory, null, false);
2239		}
2240
2241	<	// Execution methods
2241	>	/**
2242	>	* Creates a {@code ForkJoinPool} with the indicated parallelism
2243	>	* level, the {@linkplain
2244	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
2245	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
2246	>	*
2247	>	* @param parallelism the parallelism level
2248	>	* @throws IllegalArgumentException if parallelism less than or
2249	>	*         equal to zero, or greater than implementation limit
2250	>	* @throws SecurityException if a security manager exists and
2251	>	*         the caller is not permitted to modify threads
2252	>	*         because it does not hold {@link
2253	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
2254	>	*/
2255	>	public ForkJoinPool(int parallelism) {
2256	>	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
2257	>	}
2258	>
2259	>	/**
2260	>	* Creates a {@code ForkJoinPool} with the given parameters.
2261	>	*
2262	>	* @param parallelism the parallelism level. For default value,
2263	>	* use {@link java.lang.Runtime#availableProcessors}.
2264	>	* @param factory the factory for creating new threads. For default value,
2265	>	* use {@link #defaultForkJoinWorkerThreadFactory}.
2266	>	* @param handler the handler for internal worker threads that
2267	>	* terminate due to unrecoverable errors encountered while executing
2268	>	* tasks. For default value, use {@code null}.
2269	>	* @param asyncMode if true,
2270	>	* establishes local first-in-first-out scheduling mode for forked
2271	>	* tasks that are never joined. This mode may be more appropriate
2272	>	* than default locally stack-based mode in applications in which
2273	>	* worker threads only process event-style asynchronous tasks.
2274	>	* For default value, use {@code false}.
2275	>	* @throws IllegalArgumentException if parallelism less than or
2276	>	*         equal to zero, or greater than implementation limit
2277	>	* @throws NullPointerException if the factory is null
2278	>	* @throws SecurityException if a security manager exists and
2279	>	*         the caller is not permitted to modify threads
2280	>	*         because it does not hold {@link
2281	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
2282	>	*/
2283	>	public ForkJoinPool(int parallelism,
2284	>	ForkJoinWorkerThreadFactory factory,
2285	>	Thread.UncaughtExceptionHandler handler,
2286	>	boolean asyncMode) {
2287	>	checkPermission();
2288	>	if (factory == null)
2289	>	throw new NullPointerException();
2290	>	if (parallelism <= 0 || parallelism > MAX_CAP)
2291	>	throw new IllegalArgumentException();
2292	>	this.parallelism = parallelism;
2293	>	this.factory = factory;
2294	>	this.ueh = handler;
2295	>	this.localMode = asyncMode ? FIFO_QUEUE : LIFO_QUEUE;
2296	>	long np = (long)(-parallelism); // offset ctl counts
2297	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
2298	>	// Use nearest power 2 for workQueues size. See Hackers Delight sec 3.2.
2299	>	int n = parallelism - 1;
2300	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16;
2301	>	this.submitMask = ((n + 1) << 1) - 1;
2302	>	int pn = poolNumberGenerator.incrementAndGet();
2303	>	StringBuilder sb = new StringBuilder("ForkJoinPool-");
2304	>	sb.append(Integer.toString(pn));
2305	>	sb.append("-worker-");
2306	>	this.workerNamePrefix = sb.toString();
2307	>	this.runState = 1;              // set init flag
2308	>	}
2309
2310		/**
2311	<	* Common code for execute, invoke and submit
2311	>	* Constructor for common pool, suitable only for static initialization.
2312	>	* Basically the same as above, but uses smallest possible initial footprint.
2313	>	*/
2314	>	ForkJoinPool(int parallelism, int submitMask,
2315	>	ForkJoinWorkerThreadFactory factory,
2316	>	Thread.UncaughtExceptionHandler handler) {
2317	>	this.factory = factory;
2318	>	this.ueh = handler;
2319	>	this.submitMask = submitMask;
2320	>	this.parallelism = parallelism;
2321	>	long np = (long)(-parallelism);
2322	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
2323	>	this.localMode = LIFO_QUEUE;
2324	>	this.workerNamePrefix = "ForkJoinPool.commonPool-worker-";
2325	>	this.runState = 1;
2326	>	}
2327	>
2328	>	/**
2329	>	* Returns the common pool instance.
2330	>	*
2331	>	* @return the common pool instance
2332		*/
2333	<	private <T> void doSubmit(ForkJoinTask<T> task) {
2334	<	if (isShutdown())
2335	<	throw new RejectedExecutionException();
2336	<	if (workers == null)
2337	<	ensureWorkerInitialization();
534	<	submissionQueue.offer(task);
535	<	signalIdleWorkers();
2333	>	public static ForkJoinPool commonPool() {
2334	>	ForkJoinPool p;
2335	>	if ((p = commonPool) == null)
2336	>	throw new Error("Common Pool Unavailable");
2337	>	return p;
2338		}
2339
2340	+	// Execution methods
2341	+
2342		/**
2343	<	* Performs the given task; returning its result upon completion
2343	>	* Performs the given task, returning its result upon completion.
2344	>	* If the computation encounters an unchecked Exception or Error,
2345	>	* it is rethrown as the outcome of this invocation.  Rethrown
2346	>	* exceptions behave in the same way as regular exceptions, but,
2347	>	* when possible, contain stack traces (as displayed for example
2348	>	* using {@code ex.printStackTrace()}) of both the current thread
2349	>	* as well as the thread actually encountering the exception;
2350	>	* minimally only the latter.
2351	>	*
2352		* @param task the task
2353		* @return the task's result
2354	<	* @throws NullPointerException if task is null
2355	<	* @throws RejectedExecutionException if pool is shut down
2354	>	* @throws NullPointerException if the task is null
2355	>	* @throws RejectedExecutionException if the task cannot be
2356	>	*         scheduled for execution
2357		*/
2358		public <T> T invoke(ForkJoinTask<T> task) {
2359	+	if (task == null)
2360	+	throw new NullPointerException();
2361		doSubmit(task);
2362		return task.join();
2363		}
2364
2365		/**
2366		* Arranges for (asynchronous) execution of the given task.
2367	+	*
2368		* @param task the task
2369	<	* @throws NullPointerException if task is null
2370	<	* @throws RejectedExecutionException if pool is shut down
2369	>	* @throws NullPointerException if the task is null
2370	>	* @throws RejectedExecutionException if the task cannot be
2371	>	*         scheduled for execution
2372		*/
2373	<	public <T> void execute(ForkJoinTask<T> task) {
2373	>	public void execute(ForkJoinTask<?> task) {
2374	>	if (task == null)
2375	>	throw new NullPointerException();
2376		doSubmit(task);
2377		}
2378
2379		// AbstractExecutorService methods
2380
2381	+	/**
2382	+	* @throws NullPointerException if the task is null
2383	+	* @throws RejectedExecutionException if the task cannot be
2384	+	*         scheduled for execution
2385	+	*/
2386		public void execute(Runnable task) {
2387	<	doSubmit(new AdaptedRunnable<Void>(task, null));
2387	>	if (task == null)
2388	>	throw new NullPointerException();
2389	>	ForkJoinTask<?> job;
2390	>	if (task instanceof ForkJoinTask<?>) // avoid re-wrap
2391	>	job = (ForkJoinTask<?>) task;
2392	>	else
2393	>	job = new ForkJoinTask.AdaptedRunnableAction(task);
2394	>	doSubmit(job);
2395	>	}
2396	>
2397	>	/**
2398	>	* Submits a ForkJoinTask for execution.
2399	>	*
2400	>	* @param task the task to submit
2401	>	* @return the task
2402	>	* @throws NullPointerException if the task is null
2403	>	* @throws RejectedExecutionException if the task cannot be
2404	>	*         scheduled for execution
2405	>	*/
2406	>	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
2407	>	if (task == null)
2408	>	throw new NullPointerException();
2409	>	doSubmit(task);
2410	>	return task;
2411		}
2412
2413	+	/**
2414	+	* @throws NullPointerException if the task is null
2415	+	* @throws RejectedExecutionException if the task cannot be
2416	+	*         scheduled for execution
2417	+	*/
2418		public <T> ForkJoinTask<T> submit(Callable<T> task) {
2419	<	ForkJoinTask<T> job = new AdaptedCallable<T>(task);
2419	>	ForkJoinTask<T> job = new ForkJoinTask.AdaptedCallable<T>(task);
2420		doSubmit(job);
2421		return job;
2422		}
2423
2424	+	/**
2425	+	* @throws NullPointerException if the task is null
2426	+	* @throws RejectedExecutionException if the task cannot be
2427	+	*         scheduled for execution
2428	+	*/
2429		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
2430	<	ForkJoinTask<T> job = new AdaptedRunnable<T>(task, result);
2430	>	ForkJoinTask<T> job = new ForkJoinTask.AdaptedRunnable<T>(task, result);
2431		doSubmit(job);
2432		return job;
2433		}
2434
2435	+	/**
2436	+	* @throws NullPointerException if the task is null
2437	+	* @throws RejectedExecutionException if the task cannot be
2438	+	*         scheduled for execution
2439	+	*/
2440		public ForkJoinTask<?> submit(Runnable task) {
2441	<	ForkJoinTask<Void> job = new AdaptedRunnable<Void>(task, null);
2441	>	if (task == null)
2442	>	throw new NullPointerException();
2443	>	ForkJoinTask<?> job;
2444	>	if (task instanceof ForkJoinTask<?>) // avoid re-wrap
2445	>	job = (ForkJoinTask<?>) task;
2446	>	else
2447	>	job = new ForkJoinTask.AdaptedRunnableAction(task);
2448		doSubmit(job);
2449		return job;
2450		}
2451
2452		/**
2453	<	* Adaptor for Runnables. This implements RunnableFuture
2454	<	* to be compliant with AbstractExecutorService constraints
2453	>	* @throws NullPointerException       {@inheritDoc}
2454	>	* @throws RejectedExecutionException {@inheritDoc}
2455		*/
588	–	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
589	–	implements RunnableFuture<T> {
590	–	final Runnable runnable;
591	–	final T resultOnCompletion;
592	–	T result;
593	–	AdaptedRunnable(Runnable runnable, T result) {
594	–	if (runnable == null) throw new NullPointerException();
595	–	this.runnable = runnable;
596	–	this.resultOnCompletion = result;
597	–	}
598	–	public T getRawResult() { return result; }
599	–	public void setRawResult(T v) { result = v; }
600	–	public boolean exec() {
601	–	runnable.run();
602	–	result = resultOnCompletion;
603	–	return true;
604	–	}
605	–	public void run() { invoke(); }
606	–	}
607	–
608	–	/**
609	–	* Adaptor for Callables
610	–	*/
611	–	static final class AdaptedCallable<T> extends ForkJoinTask<T>
612	–	implements RunnableFuture<T> {
613	–	final Callable<T> callable;
614	–	T result;
615	–	AdaptedCallable(Callable<T> callable) {
616	–	if (callable == null) throw new NullPointerException();
617	–	this.callable = callable;
618	–	}
619	–	public T getRawResult() { return result; }
620	–	public void setRawResult(T v) { result = v; }
621	–	public boolean exec() {
622	–	try {
623	–	result = callable.call();
624	–	return true;
625	–	} catch (Error err) {
626	–	throw err;
627	–	} catch (RuntimeException rex) {
628	–	throw rex;
629	–	} catch (Exception ex) {
630	–	throw new RuntimeException(ex);
631	–	}
632	–	}
633	–	public void run() { invoke(); }
634	–	}
635	–
2456		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
2457	<	ArrayList<ForkJoinTask<T>> ts =
2458	<	new ArrayList<ForkJoinTask<T>>(tasks.size());
2459	<	for (Callable<T> c : tasks)
2460	<	ts.add(new AdaptedCallable<T>(c));
2461	<	invoke(new InvokeAll<T>(ts));
2462	<	return (List<Future<T>>)(List)ts;
2463	<	}
2457	>	// In previous versions of this class, this method constructed
2458	>	// a task to run ForkJoinTask.invokeAll, but now external
2459	>	// invocation of multiple tasks is at least as efficient.
2460	>	List<ForkJoinTask<T>> fs = new ArrayList<ForkJoinTask<T>>(tasks.size());
2461	>	// Workaround needed because method wasn't declared with
2462	>	// wildcards in return type but should have been.
2463	>	@SuppressWarnings({"unchecked", "rawtypes"})
2464	>	List<Future<T>> futures = (List<Future<T>>) (List) fs;
2465
2466	<	static final class InvokeAll<T> extends RecursiveAction {
2467	<	final ArrayList<ForkJoinTask<T>> tasks;
2468	<	InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; }
2469	<	public void compute() {
2470	<	try { invokeAll(tasks); } catch(Exception ignore) {}
2466	>	boolean done = false;
2467	>	try {
2468	>	for (Callable<T> t : tasks) {
2469	>	ForkJoinTask<T> f = new ForkJoinTask.AdaptedCallable<T>(t);
2470	>	doSubmit(f);
2471	>	fs.add(f);
2472	>	}
2473	>	for (ForkJoinTask<T> f : fs)
2474	>	f.quietlyJoin();
2475	>	done = true;
2476	>	return futures;
2477	>	} finally {
2478	>	if (!done)
2479	>	for (ForkJoinTask<T> f : fs)
2480	>	f.cancel(false);
2481		}
2482		}
2483
653	–	// Configuration and status settings and queries
654	–
2484		/**
2485	<	* Returns the factory used for constructing new workers
2485	>	* Returns the factory used for constructing new workers.
2486		*
2487		* @return the factory used for constructing new workers
2488		*/
#	Line 664 | Line 2493 | public class ForkJoinPool extends Abstra
2493		/**
2494		* Returns the handler for internal worker threads that terminate
2495		* due to unrecoverable errors encountered while executing tasks.
2496	<	* @return the handler, or null if none
2496	>	*
2497	>	* @return the handler, or {@code null} if none
2498		*/
2499		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
2500	<	Thread.UncaughtExceptionHandler h;
671	<	final ReentrantLock lock = this.workerLock;
672	<	lock.lock();
673	<	try {
674	<	h = ueh;
675	<	} finally {
676	<	lock.unlock();
677	<	}
678	<	return h;
2500	>	return ueh;
2501		}
2502
2503		/**
2504	<	* Sets the handler for internal worker threads that terminate due
683	<	* to unrecoverable errors encountered while executing tasks.
684	<	* Unless set, the current default or ThreadGroup handler is used
685	<	* as handler.
2504	>	* Returns the targeted parallelism level of this pool.
2505		*
2506	<	* @param h the new handler
688	<	* @return the old handler, or null if none
689	<	* @throws SecurityException if a security manager exists and
690	<	*         the caller is not permitted to modify threads
691	<	*         because it does not hold {@link
692	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
693	<	*/
694	<	public Thread.UncaughtExceptionHandler
695	<	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
696	<	checkPermission();
697	<	Thread.UncaughtExceptionHandler old = null;
698	<	final ReentrantLock lock = this.workerLock;
699	<	lock.lock();
700	<	try {
701	<	old = ueh;
702	<	ueh = h;
703	<	ForkJoinWorkerThread[] ws = workers;
704	<	if (ws != null) {
705	<	for (int i = 0; i < ws.length; ++i) {
706	<	ForkJoinWorkerThread w = ws[i];
707	<	if (w != null)
708	<	w.setUncaughtExceptionHandler(h);
709	<	}
710	<	}
711	<	} finally {
712	<	lock.unlock();
713	<	}
714	<	return old;
715	<	}
716	<
717	<
718	<	/**
719	<	* Sets the target paralleism level of this pool.
720	<	* @param parallelism the target parallelism
721	<	* @throws IllegalArgumentException if parallelism less than or
722	<	* equal to zero or greater than maximum size bounds.
723	<	* @throws SecurityException if a security manager exists and
724	<	*         the caller is not permitted to modify threads
725	<	*         because it does not hold {@link
726	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
2506	>	* @return the targeted parallelism level of this pool
2507		*/
2508	<	public void setParallelism(int parallelism) {
2509	<	checkPermission();
730	<	if (parallelism <= 0 || parallelism > maxPoolSize)
731	<	throw new IllegalArgumentException();
732	<	final ReentrantLock lock = this.workerLock;
733	<	lock.lock();
734	<	try {
735	<	if (!isTerminating()) {
736	<	int p = this.parallelism;
737	<	this.parallelism = parallelism;
738	<	if (parallelism > p)
739	<	createAndStartAddedWorkers();
740	<	else
741	<	trimSpares();
742	<	}
743	<	} finally {
744	<	lock.unlock();
745	<	}
746	<	signalIdleWorkers();
2508	>	public int getParallelism() {
2509	>	return parallelism;
2510		}
2511
2512		/**
2513	<	* Returns the targeted number of worker threads in this pool.
2513	>	* Returns the targeted parallelism level of the common pool.
2514		*
2515	<	* @return the targeted number of worker threads in this pool
2515	>	* @return the targeted parallelism level of the common pool
2516		*/
2517	<	public int getParallelism() {
2518	<	return parallelism;
2517	>	public static int getCommonPoolParallelism() {
2518	>	return commonPoolParallelism;
2519		}
2520
2521		/**
2522		* Returns the number of worker threads that have started but not
2523	<	* yet terminated.  This result returned by this method may differ
2524	<	* from <code>getParallelism</code> when threads are created to
2523	>	* yet terminated.  The result returned by this method may differ
2524	>	* from {@link #getParallelism} when threads are created to
2525		* maintain parallelism when others are cooperatively blocked.
2526		*
2527		* @return the number of worker threads
2528		*/
2529		public int getPoolSize() {
2530	<	return totalCountOf(workerCounts);
768	<	}
769	<
770	<	/**
771	<	* Returns the maximum number of threads allowed to exist in the
772	<	* pool, even if there are insufficient unblocked running threads.
773	<	* @return the maximum
774	<	*/
775	<	public int getMaximumPoolSize() {
776	<	return maxPoolSize;
777	<	}
778	<
779	<	/**
780	<	* Sets the maximum number of threads allowed to exist in the
781	<	* pool, even if there are insufficient unblocked running threads.
782	<	* Setting this value has no effect on current pool size. It
783	<	* controls construction of new threads.
784	<	* @throws IllegalArgumentException if negative or greater then
785	<	* internal implementation limit.
786	<	*/
787	<	public void setMaximumPoolSize(int newMax) {
788	<	if (newMax < 0 || newMax > MAX_THREADS)
789	<	throw new IllegalArgumentException();
790	<	maxPoolSize = newMax;
791	<	}
792	<
793	<
794	<	/**
795	<	* Returns true if this pool dynamically maintains its target
796	<	* parallelism level. If false, new threads are added only to
797	<	* avoid possible starvation.
798	<	* This setting is by default true;
799	<	* @return true if maintains parallelism
800	<	*/
801	<	public boolean getMaintainsParallelism() {
802	<	return maintainsParallelism;
803	<	}
804	<
805	<	/**
806	<	* Sets whether this pool dynamically maintains its target
807	<	* parallelism level. If false, new threads are added only to
808	<	* avoid possible starvation.
809	<	* @param enable true to maintains parallelism
810	<	*/
811	<	public void setMaintainsParallelism(boolean enable) {
812	<	maintainsParallelism = enable;
2530	>	return parallelism + (short)(ctl >>> TC_SHIFT);
2531		}
2532
2533		/**
2534	<	* Establishes local first-in-first-out scheduling mode for forked
817	<	* tasks that are never joined. This mode may be more appropriate
818	<	* than default locally stack-based mode in applications in which
819	<	* worker threads only process asynchronous tasks.  This method is
820	<	* designed to be invoked only when pool is quiescent, and
821	<	* typically only before any tasks are submitted. The effects of
822	<	* invocations at ather times may be unpredictable.
823	<	*
824	<	* @param async if true, use locally FIFO scheduling
825	<	* @return the previous mode.
826	<	*/
827	<	public boolean setAsyncMode(boolean async) {
828	<	boolean oldMode = locallyFifo;
829	<	locallyFifo = async;
830	<	ForkJoinWorkerThread[] ws = workers;
831	<	if (ws != null) {
832	<	for (int i = 0; i < ws.length; ++i) {
833	<	ForkJoinWorkerThread t = ws[i];
834	<	if (t != null)
835	<	t.setAsyncMode(async);
836	<	}
837	<	}
838	<	return oldMode;
839	<	}
840	<
841	<	/**
842	<	* Returns true if this pool uses local first-in-first-out
2534	>	* Returns {@code true} if this pool uses local first-in-first-out
2535		* scheduling mode for forked tasks that are never joined.
2536		*
2537	<	* @return true if this pool uses async mode.
2537	>	* @return {@code true} if this pool uses async mode
2538		*/
2539		public boolean getAsyncMode() {
2540	<	return locallyFifo;
2540	>	return localMode != 0;
2541		}
2542
2543		/**
2544		* Returns an estimate of the number of worker threads that are
2545		* not blocked waiting to join tasks or for other managed
2546	<	* synchronization.
2546	>	* synchronization. This method may overestimate the
2547	>	* number of running threads.
2548		*
2549		* @return the number of worker threads
2550		*/
2551		public int getRunningThreadCount() {
2552	<	return runningCountOf(workerCounts);
2552	>	int rc = 0;
2553	>	WorkQueue[] ws; WorkQueue w;
2554	>	if ((ws = workQueues) != null) {
2555	>	for (int i = 1; i < ws.length; i += 2) {
2556	>	if ((w = ws[i]) != null && w.isApparentlyUnblocked())
2557	>	++rc;
2558	>	}
2559	>	}
2560	>	return rc;
2561		}
2562
2563		/**
2564		* Returns an estimate of the number of threads that are currently
2565		* stealing or executing tasks. This method may overestimate the
2566		* number of active threads.
2567	<	* @return the number of active threads.
2567	>	*
2568	>	* @return the number of active threads
2569		*/
2570		public int getActiveThreadCount() {
2571	<	return activeCountOf(runControl);
2571	>	int r = parallelism + (int)(ctl >> AC_SHIFT);
2572	>	return (r <= 0) ? 0 : r; // suppress momentarily negative values
2573		}
2574
2575		/**
2576	<	* Returns an estimate of the number of threads that are currently
2577	<	* idle waiting for tasks. This method may underestimate the
2578	<	* number of idle threads.
2579	<	* @return the number of idle threads.
2580	<	*/
2581	<	final int getIdleThreadCount() {
2582	<	int c = runningCountOf(workerCounts) - activeCountOf(runControl);
2583	<	return (c <= 0)? 0 : c;
2584	<	}
882	<
883	<	/**
884	<	* Returns true if all worker threads are currently idle. An idle
885	<	* worker is one that cannot obtain a task to execute because none
886	<	* are available to steal from other threads, and there are no
887	<	* pending submissions to the pool. This method is conservative:
888	<	* It might not return true immediately upon idleness of all
889	<	* threads, but will eventually become true if threads remain
890	<	* inactive.
891	<	* @return true if all threads are currently idle
2576	>	* Returns {@code true} if all worker threads are currently idle.
2577	>	* An idle worker is one that cannot obtain a task to execute
2578	>	* because none are available to steal from other threads, and
2579	>	* there are no pending submissions to the pool. This method is
2580	>	* conservative; it might not return {@code true} immediately upon
2581	>	* idleness of all threads, but will eventually become true if
2582	>	* threads remain inactive.
2583	>	*
2584	>	* @return {@code true} if all threads are currently idle
2585		*/
2586		public boolean isQuiescent() {
2587	<	return activeCountOf(runControl) == 0;
2587	>	return (int)(ctl >> AC_SHIFT) + parallelism == 0;
2588		}
2589
2590		/**
#	Line 899 | Line 2592 | public class ForkJoinPool extends Abstra
2592		* one thread's work queue by another. The reported value
2593		* underestimates the actual total number of steals when the pool
2594		* is not quiescent. This value may be useful for monitoring and
2595	<	* tuning fork/join programs: In general, steal counts should be
2595	>	* tuning fork/join programs: in general, steal counts should be
2596		* high enough to keep threads busy, but low enough to avoid
2597		* overhead and contention across threads.
2598	<	* @return the number of steals.
2598	>	*
2599	>	* @return the number of steals
2600		*/
2601		public long getStealCount() {
2602	<	return stealCount.get();
2603	<	}
2604	<
2605	<	/**
2606	<	* Accumulate steal count from a worker. Call only
2607	<	* when worker known to be idle.
2608	<	*/
2609	<	private void updateStealCount(ForkJoinWorkerThread w) {
2610	<	int sc = w.getAndClearStealCount();
917	<	if (sc != 0)
918	<	stealCount.addAndGet(sc);
2602	>	long count = stealCount;
2603	>	WorkQueue[] ws; WorkQueue w;
2604	>	if ((ws = workQueues) != null) {
2605	>	for (int i = 1; i < ws.length; i += 2) {
2606	>	if ((w = ws[i]) != null)
2607	>	count += w.totalSteals;
2608	>	}
2609	>	}
2610	>	return count;
2611		}
2612
2613		/**
#	Line 925 | Line 2617 | public class ForkJoinPool extends Abstra
2617		* an approximation, obtained by iterating across all threads in
2618		* the pool. This method may be useful for tuning task
2619		* granularities.
2620	<	* @return the number of queued tasks.
2620	>	*
2621	>	* @return the number of queued tasks
2622		*/
2623		public long getQueuedTaskCount() {
2624		long count = 0;
2625	<	ForkJoinWorkerThread[] ws = workers;
2626	<	if (ws != null) {
2627	<	for (int i = 0; i < ws.length; ++i) {
2628	<	ForkJoinWorkerThread t = ws[i];
2629	<	if (t != null)
937	<	count += t.getQueueSize();
2625	>	WorkQueue[] ws; WorkQueue w;
2626	>	if ((ws = workQueues) != null) {
2627	>	for (int i = 1; i < ws.length; i += 2) {
2628	>	if ((w = ws[i]) != null)
2629	>	count += w.queueSize();
2630		}
2631		}
2632		return count;
2633		}
2634
2635		/**
2636	<	* Returns an estimate of the number tasks submitted to this pool
2637	<	* that have not yet begun executing. This method takes time
2638	<	* proportional to the number of submissions.
2639	<	* @return the number of queued submissions.
2636	>	* Returns an estimate of the number of tasks submitted to this
2637	>	* pool that have not yet begun executing.  This method may take
2638	>	* time proportional to the number of submissions.
2639	>	*
2640	>	* @return the number of queued submissions
2641		*/
2642		public int getQueuedSubmissionCount() {
2643	<	return submissionQueue.size();
2643	>	int count = 0;
2644	>	WorkQueue[] ws; WorkQueue w;
2645	>	if ((ws = workQueues) != null) {
2646	>	for (int i = 0; i < ws.length; i += 2) {
2647	>	if ((w = ws[i]) != null)
2648	>	count += w.queueSize();
2649	>	}
2650	>	}
2651	>	return count;
2652		}
2653
2654		/**
2655	<	* Returns true if there are any tasks submitted to this pool
2656	<	* that have not yet begun executing.
2657	<	* @return <code>true</code> if there are any queued submissions.
2655	>	* Returns {@code true} if there are any tasks submitted to this
2656	>	* pool that have not yet begun executing.
2657	>	*
2658	>	* @return {@code true} if there are any queued submissions
2659		*/
2660		public boolean hasQueuedSubmissions() {
2661	<	return !submissionQueue.isEmpty();
2661	>	WorkQueue[] ws; WorkQueue w;
2662	>	if ((ws = workQueues) != null) {
2663	>	for (int i = 0; i < ws.length; i += 2) {
2664	>	if ((w = ws[i]) != null && !w.isEmpty())
2665	>	return true;
2666	>	}
2667	>	}
2668	>	return false;
2669		}
2670
2671		/**
2672		* Removes and returns the next unexecuted submission if one is
2673		* available.  This method may be useful in extensions to this
2674		* class that re-assign work in systems with multiple pools.
2675	<	* @return the next submission, or null if none
2675	>	*
2676	>	* @return the next submission, or {@code null} if none
2677		*/
2678		protected ForkJoinTask<?> pollSubmission() {
2679	<	return submissionQueue.poll();
2679	>	WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t;
2680	>	if ((ws = workQueues) != null) {
2681	>	for (int i = 0; i < ws.length; i += 2) {
2682	>	if ((w = ws[i]) != null && (t = w.poll()) != null)
2683	>	return t;
2684	>	}
2685	>	}
2686	>	return null;
2687		}
2688
2689		/**
2690		* Removes all available unexecuted submitted and forked tasks
2691		* from scheduling queues and adds them to the given collection,
2692		* without altering their execution status. These may include
2693	<	* artifically generated or wrapped tasks. This method id designed
2694	<	* to be invoked only when the pool is known to be
2693	>	* artificially generated or wrapped tasks. This method is
2694	>	* designed to be invoked only when the pool is known to be
2695		* quiescent. Invocations at other times may not remove all
2696		* tasks. A failure encountered while attempting to add elements
2697	<	* to collection <tt>c</tt> may result in elements being in
2697	>	* to collection {@code c} may result in elements being in
2698		* neither, either or both collections when the associated
2699		* exception is thrown.  The behavior of this operation is
2700		* undefined if the specified collection is modified while the
2701		* operation is in progress.
2702	+	*
2703		* @param c the collection to transfer elements into
2704		* @return the number of elements transferred
2705		*/
2706	<	protected int drainTasksTo(Collection<ForkJoinTask<?>> c) {
2707	<	int n = submissionQueue.drainTo(c);
2708	<	ForkJoinWorkerThread[] ws = workers;
2709	<	if (ws != null) {
2706	>	protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
2707	>	int count = 0;
2708	>	WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t;
2709	>	if ((ws = workQueues) != null) {
2710		for (int i = 0; i < ws.length; ++i) {
2711	<	ForkJoinWorkerThread w = ws[i];
2712	<	if (w != null)
2713	<	n += w.drainTasksTo(c);
2711	>	if ((w = ws[i]) != null) {
2712	>	while ((t = w.poll()) != null) {
2713	>	c.add(t);
2714	>	++count;
2715	>	}
2716	>	}
2717		}
2718		}
2719	<	return n;
2719	>	return count;
2720		}
2721
2722		/**
#	Line 1006 | Line 2727 | public class ForkJoinPool extends Abstra
2727		* @return a string identifying this pool, as well as its state
2728		*/
2729		public String toString() {
2730	<	int ps = parallelism;
2731	<	int wc = workerCounts;
2732	<	int rc = runControl;
2733	<	long st = getStealCount();
2734	<	long qt = getQueuedTaskCount();
2735	<	long qs = getQueuedSubmissionCount();
2730	>	// Use a single pass through workQueues to collect counts
2731	>	long qt = 0L, qs = 0L; int rc = 0;
2732	>	long st = stealCount;
2733	>	long c = ctl;
2734	>	WorkQueue[] ws; WorkQueue w;
2735	>	if ((ws = workQueues) != null) {
2736	>	for (int i = 0; i < ws.length; ++i) {
2737	>	if ((w = ws[i]) != null) {
2738	>	int size = w.queueSize();
2739	>	if ((i & 1) == 0)
2740	>	qs += size;
2741	>	else {
2742	>	qt += size;
2743	>	st += w.totalSteals;
2744	>	if (w.isApparentlyUnblocked())
2745	>	++rc;
2746	>	}
2747	>	}
2748	>	}
2749	>	}
2750	>	int pc = parallelism;
2751	>	int tc = pc + (short)(c >>> TC_SHIFT);
2752	>	int ac = pc + (int)(c >> AC_SHIFT);
2753	>	if (ac < 0) // ignore transient negative
2754	>	ac = 0;
2755	>	String level;
2756	>	if ((c & STOP_BIT) != 0)
2757	>	level = (tc == 0) ? "Terminated" : "Terminating";
2758	>	else
2759	>	level = runState < 0 ? "Shutting down" : "Running";
2760		return super.toString() +
2761	<	"[" + runStateToString(runStateOf(rc)) +
2762	<	", parallelism = " + ps +
2763	<	", size = " + totalCountOf(wc) +
2764	<	", active = " + activeCountOf(rc) +
2765	<	", running = " + runningCountOf(wc) +
2761	>	"[" + level +
2762	>	", parallelism = " + pc +
2763	>	", size = " + tc +
2764	>	", active = " + ac +
2765	>	", running = " + rc +
2766		", steals = " + st +
2767		", tasks = " + qt +
2768		", submissions = " + qs +
2769		"]";
2770		}
2771
1027	–	private static String runStateToString(int rs) {
1028	–	switch(rs) {
1029	–	case RUNNING: return "Running";
1030	–	case SHUTDOWN: return "Shutting down";
1031	–	case TERMINATING: return "Terminating";
1032	–	case TERMINATED: return "Terminated";
1033	–	default: throw new Error("Unknown run state");
1034	–	}
1035	–	}
1036	–
1037	–	// lifecycle control
1038	–
2772		/**
2773	<	* Initiates an orderly shutdown in which previously submitted
2774	<	* tasks are executed, but no new tasks will be accepted.
2775	<	* Invocation has no additional effect if already shut down.
2776	<	* Tasks that are in the process of being submitted concurrently
2777	<	* during the course of this method may or may not be rejected.
2773	>	* Possibly initiates an orderly shutdown in which previously
2774	>	* submitted tasks are executed, but no new tasks will be
2775	>	* accepted. Invocation has no effect on execution state if this
2776	>	* is the {@link #commonPool}, and no additional effect if
2777	>	* already shut down.  Tasks that are in the process of being
2778	>	* submitted concurrently during the course of this method may or
2779	>	* may not be rejected.
2780	>	*
2781		* @throws SecurityException if a security manager exists and
2782		*         the caller is not permitted to modify threads
2783		*         because it does not hold {@link
2784	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
2784	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
2785		*/
2786		public void shutdown() {
2787		checkPermission();
2788	<	transitionRunStateTo(SHUTDOWN);
2789	<	if (canTerminateOnShutdown(runControl))
1054	<	terminateOnShutdown();
2788	>	if (this != commonPool)
2789	>	tryTerminate(false, true);
2790		}
2791
2792		/**
2793	<	* Attempts to stop all actively executing tasks, and cancels all
2794	<	* waiting tasks.  Tasks that are in the process of being
2795	<	* submitted or executed concurrently during the course of this
2796	<	* method may or may not be rejected. Unlike some other executors,
2797	<	* this method cancels rather than collects non-executed tasks
2798	<	* upon termination, so always returns an empty list. However, you
2799	<	* can use method <code>drainTasksTo</code> before invoking this
2800	<	* method to transfer unexecuted tasks to another collection.
2793	>	* Possibly attempts to cancel and/or stop all tasks, and reject
2794	>	* all subsequently submitted tasks.  Invocation has no effect on
2795	>	* execution state if this is the {@link #commonPool}, and no
2796	>	* additional effect if already shut down. Otherwise, tasks that
2797	>	* are in the process of being submitted or executed concurrently
2798	>	* during the course of this method may or may not be
2799	>	* rejected. This method cancels both existing and unexecuted
2800	>	* tasks, in order to permit termination in the presence of task
2801	>	* dependencies. So the method always returns an empty list
2802	>	* (unlike the case for some other Executors).
2803	>	*
2804		* @return an empty list
2805		* @throws SecurityException if a security manager exists and
2806		*         the caller is not permitted to modify threads
2807		*         because it does not hold {@link
2808	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
2808	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
2809		*/
2810		public List<Runnable> shutdownNow() {
2811		checkPermission();
2812	<	terminate();
2812	>	if (this != commonPool)
2813	>	tryTerminate(true, true);
2814		return Collections.emptyList();
2815		}
2816
2817		/**
2818	<	* Returns <code>true</code> if all tasks have completed following shut down.
2818	>	* Returns {@code true} if all tasks have completed following shut down.
2819		*
2820	<	* @return <code>true</code> if all tasks have completed following shut down
2820	>	* @return {@code true} if all tasks have completed following shut down
2821		*/
2822		public boolean isTerminated() {
2823	<	return runStateOf(runControl) == TERMINATED;
2823	>	long c = ctl;
2824	>	return ((c & STOP_BIT) != 0L &&
2825	>	(short)(c >>> TC_SHIFT) == -parallelism);
2826		}
2827
2828		/**
2829	<	* Returns <code>true</code> if the process of termination has
2830	<	* commenced but possibly not yet completed.
2829	>	* Returns {@code true} if the process of termination has
2830	>	* commenced but not yet completed.  This method may be useful for
2831	>	* debugging. A return of {@code true} reported a sufficient
2832	>	* period after shutdown may indicate that submitted tasks have
2833	>	* ignored or suppressed interruption, or are waiting for IO,
2834	>	* causing this executor not to properly terminate. (See the
2835	>	* advisory notes for class {@link ForkJoinTask} stating that
2836	>	* tasks should not normally entail blocking operations.  But if
2837	>	* they do, they must abort them on interrupt.)
2838		*
2839	<	* @return <code>true</code> if terminating
2839	>	* @return {@code true} if terminating but not yet terminated
2840		*/
2841		public boolean isTerminating() {
2842	<	return runStateOf(runControl) >= TERMINATING;
2842	>	long c = ctl;
2843	>	return ((c & STOP_BIT) != 0L &&
2844	>	(short)(c >>> TC_SHIFT) != -parallelism);
2845		}
2846
2847		/**
2848	<	* Returns <code>true</code> if this pool has been shut down.
2848	>	* Returns {@code true} if this pool has been shut down.
2849		*
2850	<	* @return <code>true</code> if this pool has been shut down
2850	>	* @return {@code true} if this pool has been shut down
2851		*/
2852		public boolean isShutdown() {
2853	<	return runStateOf(runControl) >= SHUTDOWN;
2853	>	return runState < 0;
2854		}
2855
2856		/**
#	Line 1110 | Line 2860 | public class ForkJoinPool extends Abstra
2860		*
2861		* @param timeout the maximum time to wait
2862		* @param unit the time unit of the timeout argument
2863	<	* @return <code>true</code> if this executor terminated and
2864	<	*         <code>false</code> if the timeout elapsed before termination
2863	>	* @return {@code true} if this executor terminated and
2864	>	*         {@code false} if the timeout elapsed before termination
2865		* @throws InterruptedException if interrupted while waiting
2866		*/
2867		public boolean awaitTermination(long timeout, TimeUnit unit)
2868		throws InterruptedException {
2869		long nanos = unit.toNanos(timeout);
2870	<	final ReentrantLock lock = this.workerLock;
1121	<	lock.lock();
1122	<	try {
1123	<	for (;;) {
1124	<	if (isTerminated())
1125	<	return true;
1126	<	if (nanos <= 0)
1127	<	return false;
1128	<	nanos = termination.awaitNanos(nanos);
1129	<	}
1130	<	} finally {
1131	<	lock.unlock();
1132	<	}
1133	<	}
1134	<
1135	<	// Shutdown and termination support
1136	<
1137	<	/**
1138	<	* Callback from terminating worker. Null out the corresponding
1139	<	* workers slot, and if terminating, try to terminate, else try to
1140	<	* shrink workers array.
1141	<	* @param w the worker
1142	<	*/
1143	<	final void workerTerminated(ForkJoinWorkerThread w) {
1144	<	updateStealCount(w);
1145	<	updateWorkerCount(-1);
1146	<	final ReentrantLock lock = this.workerLock;
1147	<	lock.lock();
1148	<	try {
1149	<	ForkJoinWorkerThread[] ws = workers;
1150	<	if (ws != null) {
1151	<	int idx = w.poolIndex;
1152	<	if (idx >= 0 && idx < ws.length && ws[idx] == w)
1153	<	ws[idx] = null;
1154	<	if (totalCountOf(workerCounts) == 0) {
1155	<	terminate(); // no-op if already terminating
1156	<	transitionRunStateTo(TERMINATED);
1157	<	termination.signalAll();
1158	<	}
1159	<	else if (!isTerminating()) {
1160	<	tryShrinkWorkerArray();
1161	<	tryResumeSpare(true); // allow replacement
1162	<	}
1163	<	}
1164	<	} finally {
1165	<	lock.unlock();
1166	<	}
1167	<	signalIdleWorkers();
1168	<	}
1169	<
1170	<	/**
1171	<	* Initiate termination.
1172	<	*/
1173	<	private void terminate() {
1174	<	if (transitionRunStateTo(TERMINATING)) {
1175	<	stopAllWorkers();
1176	<	resumeAllSpares();
1177	<	signalIdleWorkers();
1178	<	cancelQueuedSubmissions();
1179	<	cancelQueuedWorkerTasks();
1180	<	interruptUnterminatedWorkers();
1181	<	signalIdleWorkers(); // resignal after interrupt
1182	<	}
1183	<	}
1184	<
1185	<	/**
1186	<	* Possibly terminate when on shutdown state
1187	<	*/
1188	<	private void terminateOnShutdown() {
1189	<	if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
1190	<	terminate();
1191	<	}
1192	<
1193	<	/**
1194	<	* Clear out and cancel submissions
1195	<	*/
1196	<	private void cancelQueuedSubmissions() {
1197	<	ForkJoinTask<?> task;
1198	<	while ((task = pollSubmission()) != null)
1199	<	task.cancel(false);
1200	<	}
1201	<
1202	<	/**
1203	<	* Clean out worker queues.
1204	<	*/
1205	<	private void cancelQueuedWorkerTasks() {
1206	<	final ReentrantLock lock = this.workerLock;
1207	<	lock.lock();
1208	<	try {
1209	<	ForkJoinWorkerThread[] ws = workers;
1210	<	if (ws != null) {
1211	<	for (int i = 0; i < ws.length; ++i) {
1212	<	ForkJoinWorkerThread t = ws[i];
1213	<	if (t != null)
1214	<	t.cancelTasks();
1215	<	}
1216	<	}
1217	<	} finally {
1218	<	lock.unlock();
1219	<	}
1220	<	}
1221	<
1222	<	/**
1223	<	* Set each worker's status to terminating. Requires lock to avoid
1224	<	* conflicts with add/remove
1225	<	*/
1226	<	private void stopAllWorkers() {
1227	<	final ReentrantLock lock = this.workerLock;
1228	<	lock.lock();
1229	<	try {
1230	<	ForkJoinWorkerThread[] ws = workers;
1231	<	if (ws != null) {
1232	<	for (int i = 0; i < ws.length; ++i) {
1233	<	ForkJoinWorkerThread t = ws[i];
1234	<	if (t != null)
1235	<	t.shutdownNow();
1236	<	}
1237	<	}
1238	<	} finally {
1239	<	lock.unlock();
1240	<	}
1241	<	}
1242	<
1243	<	/**
1244	<	* Interrupt all unterminated workers.  This is not required for
1245	<	* sake of internal control, but may help unstick user code during
1246	<	* shutdown.
1247	<	*/
1248	<	private void interruptUnterminatedWorkers() {
1249	<	final ReentrantLock lock = this.workerLock;
1250	<	lock.lock();
1251	<	try {
1252	<	ForkJoinWorkerThread[] ws = workers;
1253	<	if (ws != null) {
1254	<	for (int i = 0; i < ws.length; ++i) {
1255	<	ForkJoinWorkerThread t = ws[i];
1256	<	if (t != null && !t.isTerminated()) {
1257	<	try {
1258	<	t.interrupt();
1259	<	} catch (SecurityException ignore) {
1260	<	}
1261	<	}
1262	<	}
1263	<	}
1264	<	} finally {
1265	<	lock.unlock();
1266	<	}
1267	<	}
1268	<
1269	<
1270	<	/*
1271	<	* Nodes for event barrier to manage idle threads.  Queue nodes
1272	<	* are basic Treiber stack nodes, also used for spare stack.
1273	<	*
1274	<	* The event barrier has an event count and a wait queue (actually
1275	<	* a Treiber stack).  Workers are enabled to look for work when
1276	<	* the eventCount is incremented. If they fail to find work, they
1277	<	* may wait for next count. Upon release, threads help others wake
1278	<	* up.
1279	<	*
1280	<	* Synchronization events occur only in enough contexts to
1281	<	* maintain overall liveness:
1282	<	*
1283	<	*   - Submission of a new task to the pool
1284	<	*   - Resizes or other changes to the workers array
1285	<	*   - pool termination
1286	<	*   - A worker pushing a task on an empty queue
1287	<	*
1288	<	* The case of pushing a task occurs often enough, and is heavy
1289	<	* enough compared to simple stack pushes, to require special
1290	<	* handling: Method signalWork returns without advancing count if
1291	<	* the queue appears to be empty.  This would ordinarily result in
1292	<	* races causing some queued waiters not to be woken up. To avoid
1293	<	* this, the first worker enqueued in method sync (see
1294	<	* syncIsReleasable) rescans for tasks after being enqueued, and
1295	<	* helps signal if any are found. This works well because the
1296	<	* worker has nothing better to do, and so might as well help
1297	<	* alleviate the overhead and contention on the threads actually
1298	<	* doing work.  Also, since event counts increments on task
1299	<	* availability exist to maintain liveness (rather than to force
1300	<	* refreshes etc), it is OK for callers to exit early if
1301	<	* contending with another signaller.
1302	<	*/
1303	<	static final class WaitQueueNode {
1304	<	WaitQueueNode next; // only written before enqueued
1305	<	volatile ForkJoinWorkerThread thread; // nulled to cancel wait
1306	<	final long count; // unused for spare stack
1307	<
1308	<	WaitQueueNode(long c, ForkJoinWorkerThread w) {
1309	<	count = c;
1310	<	thread = w;
1311	<	}
1312	<
1313	<	/**
1314	<	* Wake up waiter, returning false if known to already
1315	<	*/
1316	<	boolean signal() {
1317	<	ForkJoinWorkerThread t = thread;
1318	<	if (t == null)
1319	<	return false;
1320	<	thread = null;
1321	<	LockSupport.unpark(t);
2870	>	if (isTerminated())
2871		return true;
2872	<	}
2873	<
2874	<	/**
2875	<	* Await release on sync
2876	<	*/
2877	<	void awaitSyncRelease(ForkJoinPool p) {
2878	<	while (thread != null && !p.syncIsReleasable(this))
1330	<	LockSupport.park(this);
1331	<	}
1332	<
1333	<	/**
1334	<	* Await resumption as spare
1335	<	*/
1336	<	void awaitSpareRelease() {
1337	<	while (thread != null) {
1338	<	if (!Thread.interrupted())
1339	<	LockSupport.park(this);
1340	<	}
1341	<	}
1342	<	}
1343	<
1344	<	/**
1345	<	* Ensures that no thread is waiting for count to advance from the
1346	<	* current value of eventCount read on entry to this method, by
1347	<	* releasing waiting threads if necessary.
1348	<	* @return the count
1349	<	*/
1350	<	final long ensureSync() {
1351	<	long c = eventCount;
1352	<	WaitQueueNode q;
1353	<	while ((q = syncStack) != null && q.count < c) {
1354	<	if (casBarrierStack(q, null)) {
1355	<	do {
1356	<	q.signal();
1357	<	} while ((q = q.next) != null);
1358	<	break;
1359	<	}
1360	<	}
1361	<	return c;
1362	<	}
1363	<
1364	<	/**
1365	<	* Increments event count and releases waiting threads.
1366	<	*/
1367	<	private void signalIdleWorkers() {
1368	<	long c;
1369	<	do;while (!casEventCount(c = eventCount, c+1));
1370	<	ensureSync();
1371	<	}
1372	<
1373	<	/**
1374	<	* Signal threads waiting to poll a task. Because method sync
1375	<	* rechecks availability, it is OK to only proceed if queue
1376	<	* appears to be non-empty, and OK to skip under contention to
1377	<	* increment count (since some other thread succeeded).
1378	<	*/
1379	<	final void signalWork() {
1380	<	long c;
1381	<	WaitQueueNode q;
1382	<	if (syncStack != null &&
1383	<	casEventCount(c = eventCount, c+1) &&
1384	<	(((q = syncStack) != null && q.count <= c) &&
1385	<	(!casBarrierStack(q, q.next) || !q.signal())))
1386	<	ensureSync();
1387	<	}
1388	<
1389	<	/**
1390	<	* Waits until event count advances from last value held by
1391	<	* caller, or if excess threads, caller is resumed as spare, or
1392	<	* caller or pool is terminating. Updates caller's event on exit.
1393	<	* @param w the calling worker thread
1394	<	*/
1395	<	final void sync(ForkJoinWorkerThread w) {
1396	<	updateStealCount(w); // Transfer w's count while it is idle
1397	<
1398	<	while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
1399	<	long prev = w.lastEventCount;
1400	<	WaitQueueNode node = null;
1401	<	WaitQueueNode h;
1402	<	while (eventCount == prev &&
1403	<	((h = syncStack) == null || h.count == prev)) {
1404	<	if (node == null)
1405	<	node = new WaitQueueNode(prev, w);
1406	<	if (casBarrierStack(node.next = h, node)) {
1407	<	node.awaitSyncRelease(this);
1408	<	break;
1409	<	}
1410	<	}
1411	<	long ec = ensureSync();
1412	<	if (ec != prev) {
1413	<	w.lastEventCount = ec;
1414	<	break;
1415	<	}
1416	<	}
1417	<	}
1418	<
1419	<	/**
1420	<	* Returns true if worker waiting on sync can proceed:
1421	<	*  - on signal (thread == null)
1422	<	*  - on event count advance (winning race to notify vs signaller)
1423	<	*  - on Interrupt
1424	<	*  - if the first queued node, we find work available
1425	<	* If node was not signalled and event count not advanced on exit,
1426	<	* then we also help advance event count.
1427	<	* @return true if node can be released
1428	<	*/
1429	<	final boolean syncIsReleasable(WaitQueueNode node) {
1430	<	long prev = node.count;
1431	<	if (!Thread.interrupted() && node.thread != null &&
1432	<	(node.next != null ||
1433	<	!ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
1434	<	eventCount == prev)
1435	<	return false;
1436	<	if (node.thread != null) {
1437	<	node.thread = null;
1438	<	long ec = eventCount;
1439	<	if (prev <= ec) // help signal
1440	<	casEventCount(ec, ec+1);
1441	<	}
1442	<	return true;
1443	<	}
1444	<
1445	<	/**
1446	<	* Returns true if a new sync event occurred since last call to
1447	<	* sync or this method, if so, updating caller's count.
1448	<	*/
1449	<	final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1450	<	long lc = w.lastEventCount;
1451	<	long ec = ensureSync();
1452	<	if (ec == lc)
1453	<	return false;
1454	<	w.lastEventCount = ec;
1455	<	return true;
1456	<	}
1457	<
1458	<	//  Parallelism maintenance
1459	<
1460	<	/**
1461	<	* Decrement running count; if too low, add spare.
1462	<	*
1463	<	* Conceptually, all we need to do here is add or resume a
1464	<	* spare thread when one is about to block (and remove or
1465	<	* suspend it later when unblocked -- see suspendIfSpare).
1466	<	* However, implementing this idea requires coping with
1467	<	* several problems: We have imperfect information about the
1468	<	* states of threads. Some count updates can and usually do
1469	<	* lag run state changes, despite arrangements to keep them
1470	<	* accurate (for example, when possible, updating counts
1471	<	* before signalling or resuming), especially when running on
1472	<	* dynamic JVMs that don't optimize the infrequent paths that
1473	<	* update counts. Generating too many threads can make these
1474	<	* problems become worse, because excess threads are more
1475	<	* likely to be context-switched with others, slowing them all
1476	<	* down, especially if there is no work available, so all are
1477	<	* busy scanning or idling.  Also, excess spare threads can
1478	<	* only be suspended or removed when they are idle, not
1479	<	* immediately when they aren't needed. So adding threads will
1480	<	* raise parallelism level for longer than necessary.  Also,
1481	<	* FJ applications often enounter highly transient peaks when
1482	<	* many threads are blocked joining, but for less time than it
1483	<	* takes to create or resume spares.
1484	<	*
1485	<	* @param joinMe if non-null, return early if done
1486	<	* @param maintainParallelism if true, try to stay within
1487	<	* target counts, else create only to avoid starvation
1488	<	* @return true if joinMe known to be done
1489	<	*/
1490	<	final boolean preJoin(ForkJoinTask<?> joinMe, boolean maintainParallelism) {
1491	<	maintainParallelism &= maintainsParallelism; // overrride
1492	<	boolean dec = false;  // true when running count decremented
1493	<	while (spareStack == null || !tryResumeSpare(dec)) {
1494	<	int counts = workerCounts;
1495	<	if (dec || (dec = casWorkerCounts(counts, --counts))) { // CAS cheat
1496	<	if (!needSpare(counts, maintainParallelism))
1497	<	break;
1498	<	if (joinMe.status < 0)
1499	<	return true;
1500	<	if (tryAddSpare(counts))
1501	<	break;
1502	<	}
1503	<	}
1504	<	return false;
1505	<	}
1506	<
1507	<	/**
1508	<	* Same idea as preJoin
1509	<	*/
1510	<	final boolean preBlock(ManagedBlocker blocker, boolean maintainParallelism){
1511	<	maintainParallelism &= maintainsParallelism;
1512	<	boolean dec = false;
1513	<	while (spareStack == null || !tryResumeSpare(dec)) {
1514	<	int counts = workerCounts;
1515	<	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1516	<	if (!needSpare(counts, maintainParallelism))
1517	<	break;
1518	<	if (blocker.isReleasable())
1519	<	return true;
1520	<	if (tryAddSpare(counts))
1521	<	break;
1522	<	}
1523	<	}
1524	<	return false;
1525	<	}
1526	<
1527	<	/**
1528	<	* Returns true if a spare thread appears to be needed.  If
1529	<	* maintaining parallelism, returns true when the deficit in
1530	<	* running threads is more than the surplus of total threads, and
1531	<	* there is apparently some work to do.  This self-limiting rule
1532	<	* means that the more threads that have already been added, the
1533	<	* less parallelism we will tolerate before adding another.
1534	<	* @param counts current worker counts
1535	<	* @param maintainParallelism try to maintain parallelism
1536	<	*/
1537	<	private boolean needSpare(int counts, boolean maintainParallelism) {
1538	<	int ps = parallelism;
1539	<	int rc = runningCountOf(counts);
1540	<	int tc = totalCountOf(counts);
1541	<	int runningDeficit = ps - rc;
1542	<	int totalSurplus = tc - ps;
1543	<	return (tc < maxPoolSize &&
1544	<	(rc == 0 || totalSurplus < 0 ||
1545	<	(maintainParallelism &&
1546	<	runningDeficit > totalSurplus &&
1547	<	ForkJoinWorkerThread.hasQueuedTasks(workers))));
1548	<	}
1549	<
1550	<	/**
1551	<	* Add a spare worker if lock available and no more than the
1552	<	* expected numbers of threads exist
1553	<	* @return true if successful
1554	<	*/
1555	<	private boolean tryAddSpare(int expectedCounts) {
1556	<	final ReentrantLock lock = this.workerLock;
1557	<	int expectedRunning = runningCountOf(expectedCounts);
1558	<	int expectedTotal = totalCountOf(expectedCounts);
1559	<	boolean success = false;
1560	<	boolean locked = false;
1561	<	// confirm counts while locking; CAS after obtaining lock
1562	<	try {
1563	<	for (;;) {
1564	<	int s = workerCounts;
1565	<	int tc = totalCountOf(s);
1566	<	int rc = runningCountOf(s);
1567	<	if (rc > expectedRunning || tc > expectedTotal)
2872	>	long startTime = System.nanoTime();
2873	>	boolean terminated = false;
2874	>	synchronized(this) {
2875	>	for (long waitTime = nanos, millis = 0L;;) {
2876	>	if (terminated = isTerminated() ||
2877	>	waitTime <= 0L ||
2878	>	(millis = unit.toMillis(waitTime)) <= 0L)
2879		break;
2880	<	if (!locked && !(locked = lock.tryLock()))
2881	<	break;
1571	<	if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
1572	<	createAndStartSpare(tc);
1573	<	success = true;
1574	<	break;
1575	<	}
1576	<	}
1577	<	} finally {
1578	<	if (locked)
1579	<	lock.unlock();
1580	<	}
1581	<	return success;
1582	<	}
1583	<
1584	<	/**
1585	<	* Add the kth spare worker. On entry, pool coounts are already
1586	<	* adjusted to reflect addition.
1587	<	*/
1588	<	private void createAndStartSpare(int k) {
1589	<	ForkJoinWorkerThread w = null;
1590	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
1591	<	int len = ws.length;
1592	<	// Probably, we can place at slot k. If not, find empty slot
1593	<	if (k < len && ws[k] != null) {
1594	<	for (k = 0; k < len && ws[k] != null; ++k)
1595	<	;
1596	<	}
1597	<	if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
1598	<	ws[k] = w;
1599	<	w.start();
1600	<	}
1601	<	else
1602	<	updateWorkerCount(-1); // adjust on failure
1603	<	signalIdleWorkers();
1604	<	}
1605	<
1606	<	/**
1607	<	* Suspend calling thread w if there are excess threads.  Called
1608	<	* only from sync.  Spares are enqueued in a Treiber stack
1609	<	* using the same WaitQueueNodes as barriers.  They are resumed
1610	<	* mainly in preJoin, but are also woken on pool events that
1611	<	* require all threads to check run state.
1612	<	* @param w the caller
1613	<	*/
1614	<	private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1615	<	WaitQueueNode node = null;
1616	<	int s;
1617	<	while (parallelism < runningCountOf(s = workerCounts)) {
1618	<	if (node == null)
1619	<	node = new WaitQueueNode(0, w);
1620	<	if (casWorkerCounts(s, s-1)) { // representation-dependent
1621	<	// push onto stack
1622	<	do;while (!casSpareStack(node.next = spareStack, node));
1623	<	// block until released by resumeSpare
1624	<	node.awaitSpareRelease();
1625	<	return true;
1626	<	}
1627	<	}
1628	<	return false;
1629	<	}
1630	<
1631	<	/**
1632	<	* Try to pop and resume a spare thread.
1633	<	* @param updateCount if true, increment running count on success
1634	<	* @return true if successful
1635	<	*/
1636	<	private boolean tryResumeSpare(boolean updateCount) {
1637	<	WaitQueueNode q;
1638	<	while ((q = spareStack) != null) {
1639	<	if (casSpareStack(q, q.next)) {
1640	<	if (updateCount)
1641	<	updateRunningCount(1);
1642	<	q.signal();
1643	<	return true;
1644	<	}
1645	<	}
1646	<	return false;
1647	<	}
1648	<
1649	<	/**
1650	<	* Pop and resume all spare threads. Same idea as ensureSync.
1651	<	* @return true if any spares released
1652	<	*/
1653	<	private boolean resumeAllSpares() {
1654	<	WaitQueueNode q;
1655	<	while ( (q = spareStack) != null) {
1656	<	if (casSpareStack(q, null)) {
1657	<	do {
1658	<	updateRunningCount(1);
1659	<	q.signal();
1660	<	} while ((q = q.next) != null);
1661	<	return true;
1662	<	}
1663	<	}
1664	<	return false;
1665	<	}
1666	<
1667	<	/**
1668	<	* Pop and shutdown excessive spare threads. Call only while
1669	<	* holding lock. This is not guaranteed to eliminate all excess
1670	<	* threads, only those suspended as spares, which are the ones
1671	<	* unlikely to be needed in the future.
1672	<	*/
1673	<	private void trimSpares() {
1674	<	int surplus = totalCountOf(workerCounts) - parallelism;
1675	<	WaitQueueNode q;
1676	<	while (surplus > 0 && (q = spareStack) != null) {
1677	<	if (casSpareStack(q, null)) {
1678	<	do {
1679	<	updateRunningCount(1);
1680	<	ForkJoinWorkerThread w = q.thread;
1681	<	if (w != null && surplus > 0 &&
1682	<	runningCountOf(workerCounts) > 0 && w.shutdown())
1683	<	--surplus;
1684	<	q.signal();
1685	<	} while ((q = q.next) != null);
2880	>	wait(millis);
2881	>	waitTime = nanos - (System.nanoTime() - startTime);
2882		}
2883		}
2884	+	return terminated;
2885		}
2886
2887		/**
2888		* Interface for extending managed parallelism for tasks running
2889	<	* in ForkJoinPools. A ManagedBlocker provides two methods.
2890	<	* Method <code>isReleasable</code> must return true if blocking is not
2891	<	* necessary. Method <code>block</code> blocks the current thread
2892	<	* if necessary (perhaps internally invoking isReleasable before
2893	<	* actually blocking.).
2889	>	* in {@link ForkJoinPool}s.
2890	>	*
2891	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
2892	>	* {@code isReleasable} must return {@code true} if blocking is
2893	>	* not necessary. Method {@code block} blocks the current thread
2894	>	* if necessary (perhaps internally invoking {@code isReleasable}
2895	>	* before actually blocking). These actions are performed by any
2896	>	* thread invoking {@link ForkJoinPool#managedBlock}.  The
2897	>	* unusual methods in this API accommodate synchronizers that may,
2898	>	* but don't usually, block for long periods. Similarly, they
2899	>	* allow more efficient internal handling of cases in which
2900	>	* additional workers may be, but usually are not, needed to
2901	>	* ensure sufficient parallelism.  Toward this end,
2902	>	* implementations of method {@code isReleasable} must be amenable
2903	>	* to repeated invocation.
2904	>	*
2905		* <p>For example, here is a ManagedBlocker based on a
2906		* ReentrantLock:
2907	<	* <pre>
2908	<	*   class ManagedLocker implements ManagedBlocker {
2909	<	*     final ReentrantLock lock;
2910	<	*     boolean hasLock = false;
2911	<	*     ManagedLocker(ReentrantLock lock) { this.lock = lock; }
2912	<	*     public boolean block() {
2913	<	*        if (!hasLock)
2914	<	*           lock.lock();
2915	<	*        return true;
2916	<	*     }
2917	<	*     public boolean isReleasable() {
2918	<	*        return hasLock || (hasLock = lock.tryLock());
1711	<	*     }
2907	>	*  <pre> {@code
2908	>	* class ManagedLocker implements ManagedBlocker {
2909	>	*   final ReentrantLock lock;
2910	>	*   boolean hasLock = false;
2911	>	*   ManagedLocker(ReentrantLock lock) { this.lock = lock; }
2912	>	*   public boolean block() {
2913	>	*     if (!hasLock)
2914	>	*       lock.lock();
2915	>	*     return true;
2916	>	*   }
2917	>	*   public boolean isReleasable() {
2918	>	*     return hasLock || (hasLock = lock.tryLock());
2919		*   }
2920	<	* </pre>
2920	>	* }}</pre>
2921	>	*
2922	>	* <p>Here is a class that possibly blocks waiting for an
2923	>	* item on a given queue:
2924	>	*  <pre> {@code
2925	>	* class QueueTaker<E> implements ManagedBlocker {
2926	>	*   final BlockingQueue<E> queue;
2927	>	*   volatile E item = null;
2928	>	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
2929	>	*   public boolean block() throws InterruptedException {
2930	>	*     if (item == null)
2931	>	*       item = queue.take();
2932	>	*     return true;
2933	>	*   }
2934	>	*   public boolean isReleasable() {
2935	>	*     return item != null || (item = queue.poll()) != null;
2936	>	*   }
2937	>	*   public E getItem() { // call after pool.managedBlock completes
2938	>	*     return item;
2939	>	*   }
2940	>	* }}</pre>
2941		*/
2942		public static interface ManagedBlocker {
2943		/**
2944		* Possibly blocks the current thread, for example waiting for
2945		* a lock or condition.
2946	<	* @return true if no additional blocking is necessary (i.e.,
2947	<	* if isReleasable would return true).
2946	>	*
2947	>	* @return {@code true} if no additional blocking is necessary
2948	>	* (i.e., if isReleasable would return true)
2949		* @throws InterruptedException if interrupted while waiting
2950	<	* (the method is not required to do so, but is allowe to).
2950	>	* (the method is not required to do so, but is allowed to)
2951		*/
2952		boolean block() throws InterruptedException;
2953
2954		/**
2955	<	* Returns true if blocking is unnecessary.
2955	>	* Returns {@code true} if blocking is unnecessary.
2956		*/
2957		boolean isReleasable();
2958		}
2959
2960		/**
2961		* Blocks in accord with the given blocker.  If the current thread
2962	<	* is a ForkJoinWorkerThread, this method possibly arranges for a
2963	<	* spare thread to be activated if necessary to ensure parallelism
2964	<	* while the current thread is blocked.  If
2965	<	* <code>maintainParallelism</code> is true and the pool supports
2966	<	* it ({@link #getMaintainsParallelism}), this method attempts to
2967	<	* maintain the pool's nominal parallelism. Otherwise if activates
2968	<	* a thread only if necessary to avoid complete starvation. This
2969	<	* option may be preferable when blockages use timeouts, or are
2970	<	* almost always brief.
2971	<	*
2972	<	* <p> If the caller is not a ForkJoinTask, this method is behaviorally
2973	<	* equivalent to
2974	<	* <pre>
2975	<	*   while (!blocker.isReleasable())
1748	<	*      if (blocker.block())
1749	<	*         return;
1750	<	* </pre>
1751	<	* If the caller is a ForkJoinTask, then the pool may first
1752	<	* be expanded to ensure parallelism, and later adjusted.
2962	>	* is a {@link ForkJoinWorkerThread}, this method possibly
2963	>	* arranges for a spare thread to be activated if necessary to
2964	>	* ensure sufficient parallelism while the current thread is blocked.
2965	>	*
2966	>	* <p>If the caller is not a {@link ForkJoinTask}, this method is
2967	>	* behaviorally equivalent to
2968	>	*  <pre> {@code
2969	>	* while (!blocker.isReleasable())
2970	>	*   if (blocker.block())
2971	>	*     return;
2972	>	* }</pre>
2973	>	*
2974	>	* If the caller is a {@code ForkJoinTask}, then the pool may
2975	>	* first be expanded to ensure parallelism, and later adjusted.
2976		*
2977		* @param blocker the blocker
2978	<	* @param maintainParallelism if true and supported by this pool,
1756	<	* attempt to maintain the pool's nominal parallelism; otherwise
1757	<	* activate a thread only if necessary to avoid complete
1758	<	* starvation.
1759	<	* @throws InterruptedException if blocker.block did so.
2978	>	* @throws InterruptedException if blocker.block did so
2979		*/
2980	<	public static void managedBlock(ManagedBlocker blocker,
1762	<	boolean maintainParallelism)
2980	>	public static void managedBlock(ManagedBlocker blocker)
2981		throws InterruptedException {
2982		Thread t = Thread.currentThread();
2983	<	ForkJoinPool pool = (t instanceof ForkJoinWorkerThread?
2984	<	((ForkJoinWorkerThread)t).pool : null);
2985	<	if (!blocker.isReleasable()) {
2986	<	try {
2987	<	if (pool == null ||
2988	<	!pool.preBlock(blocker, maintainParallelism))
2989	<	awaitBlocker(blocker);
2990	<	} finally {
2991	<	if (pool != null)
2992	<	pool.updateRunningCount(1);
2983	>	ForkJoinPool p = ((t instanceof ForkJoinWorkerThread) ?
2984	>	((ForkJoinWorkerThread)t).pool : null);
2985	>	while (!blocker.isReleasable()) {
2986	>	if (p == null || p.tryCompensate(null, blocker)) {
2987	>	try {
2988	>	do {} while (!blocker.isReleasable() && !blocker.block());
2989	>	} finally {
2990	>	if (p != null)
2991	>	p.incrementActiveCount();
2992	>	}
2993	>	break;
2994		}
2995		}
2996		}
2997
2998	<	private static void awaitBlocker(ManagedBlocker blocker)
2999	<	throws InterruptedException {
3000	<	do;while (!blocker.isReleasable() && !blocker.block());
1782	<	}
1783	<
1784	<	// AbstractExecutorService overrides
2998	>	// AbstractExecutorService overrides.  These rely on undocumented
2999	>	// fact that ForkJoinTask.adapt returns ForkJoinTasks that also
3000	>	// implement RunnableFuture.
3001
3002		protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
3003	<	return new AdaptedRunnable(runnable, value);
3003	>	return new ForkJoinTask.AdaptedRunnable<T>(runnable, value);
3004		}
3005
3006		protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
3007	<	return new AdaptedCallable(callable);
3007	>	return new ForkJoinTask.AdaptedCallable<T>(callable);
3008		}
3009
3010	+	// Unsafe mechanics
3011	+	private static final sun.misc.Unsafe U;
3012	+	private static final long CTL;
3013	+	private static final long PARKBLOCKER;
3014	+	private static final int ABASE;
3015	+	private static final int ASHIFT;
3016	+	private static final long NEXTWORKERNUMBER;
3017	+	private static final long STEALCOUNT;
3018	+	private static final long MAINLOCK;
3019
3020	<	// Temporary Unsafe mechanics for preliminary release
3021	<	private static Unsafe getUnsafe() throws Throwable {
3020	>	static {
3021	>	poolNumberGenerator = new AtomicInteger();
3022	>	nextSubmitterSeed = new AtomicInteger(0x55555555);
3023	>	modifyThreadPermission = new RuntimePermission("modifyThread");
3024	>	defaultForkJoinWorkerThreadFactory =
3025	>	new DefaultForkJoinWorkerThreadFactory();
3026	>	submitters = new ThreadSubmitter();
3027	>	int s;
3028		try {
3029	<	return Unsafe.getUnsafe();
3029	>	U = getUnsafe();
3030	>	Class<?> k = ForkJoinPool.class;
3031	>	Class<?> ak = ForkJoinTask[].class;
3032	>	CTL = U.objectFieldOffset
3033	>	(k.getDeclaredField("ctl"));
3034	>	NEXTWORKERNUMBER = U.objectFieldOffset
3035	>	(k.getDeclaredField("nextWorkerNumber"));
3036	>	STEALCOUNT = U.objectFieldOffset
3037	>	(k.getDeclaredField("stealCount"));
3038	>	MAINLOCK = U.objectFieldOffset
3039	>	(k.getDeclaredField("mainLock"));
3040	>	Class<?> tk = Thread.class;
3041	>	PARKBLOCKER = U.objectFieldOffset
3042	>	(tk.getDeclaredField("parkBlocker"));
3043	>	ABASE = U.arrayBaseOffset(ak);
3044	>	s = U.arrayIndexScale(ak);
3045	>	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
3046	>	} catch (Exception e) {
3047	>	throw new Error(e);
3048	>	}
3049	>	if ((s & (s-1)) != 0)
3050	>	throw new Error("data type scale not a power of two");
3051	>	try { // Establish common pool
3052	>	String pp = System.getProperty(propPrefix + "parallelism");
3053	>	String fp = System.getProperty(propPrefix + "threadFactory");
3054	>	String up = System.getProperty(propPrefix + "exceptionHandler");
3055	>	ForkJoinWorkerThreadFactory fac = (fp == null) ?
3056	>	defaultForkJoinWorkerThreadFactory :
3057	>	((ForkJoinWorkerThreadFactory)ClassLoader.
3058	>	getSystemClassLoader().loadClass(fp).newInstance());
3059	>	Thread.UncaughtExceptionHandler ueh = (up == null)? null :
3060	>	((Thread.UncaughtExceptionHandler)ClassLoader.
3061	>	getSystemClassLoader().loadClass(up).newInstance());
3062	>	int par;
3063	>	if ((pp == null || (par = Integer.parseInt(pp)) <= 0))
3064	>	par = Runtime.getRuntime().availableProcessors();
3065	>	if (par > MAX_CAP)
3066	>	par = MAX_CAP;
3067	>	commonPoolParallelism = par;
3068	>	int n = par - 1; // precompute submit mask
3069	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4;
3070	>	n |= n >>> 8; n |= n >>> 16;
3071	>	int mask = ((n + 1) << 1) - 1;
3072	>	commonPool = new ForkJoinPool(par, mask, fac, ueh);
3073	>	} catch (Exception e) {
3074	>	throw new Error(e);
3075	>	}
3076	>	}
3077	>
3078	>	/**
3079	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
3080	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
3081	>	* into a jdk.
3082	>	*
3083	>	* @return a sun.misc.Unsafe
3084	>	*/
3085	>	private static sun.misc.Unsafe getUnsafe() {
3086	>	try {
3087	>	return sun.misc.Unsafe.getUnsafe();
3088		} catch (SecurityException se) {
3089		try {
3090		return java.security.AccessController.doPrivileged
3091	<	(new java.security.PrivilegedExceptionAction<Unsafe>() {
3092	<	public Unsafe run() throws Exception {
3093	<	return getUnsafePrivileged();
3091	>	(new java.security
3092	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
3093	>	public sun.misc.Unsafe run() throws Exception {
3094	>	java.lang.reflect.Field f = sun.misc
3095	>	.Unsafe.class.getDeclaredField("theUnsafe");
3096	>	f.setAccessible(true);
3097	>	return (sun.misc.Unsafe) f.get(null);
3098		}});
3099		} catch (java.security.PrivilegedActionException e) {
3100	<	throw e.getCause();
3100	>	throw new RuntimeException("Could not initialize intrinsics",
3101	>	e.getCause());
3102		}
3103		}
3104		}
3105
1812	–	private static Unsafe getUnsafePrivileged()
1813	–	throws NoSuchFieldException, IllegalAccessException {
1814	–	Field f = Unsafe.class.getDeclaredField("theUnsafe");
1815	–	f.setAccessible(true);
1816	–	return (Unsafe) f.get(null);
1817	–	}
1818	–
1819	–	private static long fieldOffset(String fieldName)
1820	–	throws NoSuchFieldException {
1821	–	return _unsafe.objectFieldOffset
1822	–	(ForkJoinPool.class.getDeclaredField(fieldName));
1823	–	}
1824	–
1825	–	static final Unsafe _unsafe;
1826	–	static final long eventCountOffset;
1827	–	static final long workerCountsOffset;
1828	–	static final long runControlOffset;
1829	–	static final long syncStackOffset;
1830	–	static final long spareStackOffset;
1831	–
1832	–	static {
1833	–	try {
1834	–	_unsafe = getUnsafe();
1835	–	eventCountOffset = fieldOffset("eventCount");
1836	–	workerCountsOffset = fieldOffset("workerCounts");
1837	–	runControlOffset = fieldOffset("runControl");
1838	–	syncStackOffset = fieldOffset("syncStack");
1839	–	spareStackOffset = fieldOffset("spareStack");
1840	–	} catch (Throwable e) {
1841	–	throw new RuntimeException("Could not initialize intrinsics", e);
1842	–	}
1843	–	}
1844	–
1845	–	private boolean casEventCount(long cmp, long val) {
1846	–	return _unsafe.compareAndSwapLong(this, eventCountOffset, cmp, val);
1847	–	}
1848	–	private boolean casWorkerCounts(int cmp, int val) {
1849	–	return _unsafe.compareAndSwapInt(this, workerCountsOffset, cmp, val);
1850	–	}
1851	–	private boolean casRunControl(int cmp, int val) {
1852	–	return _unsafe.compareAndSwapInt(this, runControlOffset, cmp, val);
1853	–	}
1854	–	private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
1855	–	return _unsafe.compareAndSwapObject(this, spareStackOffset, cmp, val);
1856	–	}
1857	–	private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
1858	–	return _unsafe.compareAndSwapObject(this, syncStackOffset, cmp, val);
1859	–	}
3106		}

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