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Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.67 by jsr166, Wed Sep 1 03:32:03 2010 UTC vs.
Revision 1.140 by dl, Wed Nov 14 17:20:37 2012 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3		* Expert Group and released to the public domain, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		*/
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.util.ArrayList;
10		import java.util.Arrays;
11		import java.util.Collection;
12		import java.util.Collections;
13		import java.util.List;
14	<	import java.util.concurrent.locks.LockSupport;
15	<	import java.util.concurrent.locks.ReentrantLock;
16	<	import java.util.concurrent.atomic.AtomicInteger;
17	<	import java.util.concurrent.CountDownLatch;
14	>	import java.util.concurrent.AbstractExecutorService;
15	>	import java.util.concurrent.Callable;
16	>	import java.util.concurrent.ExecutorService;
17	>	import java.util.concurrent.Future;
18	>	import java.util.concurrent.RejectedExecutionException;
19	>	import java.util.concurrent.RunnableFuture;
20	>	import java.util.concurrent.TimeUnit;
21
22		/**
23		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
#	Line 27 | Line 28 | import java.util.concurrent.CountDownLat
28		* <p>A {@code ForkJoinPool} differs from other kinds of {@link
29		* ExecutorService} mainly by virtue of employing
30		* <em>work-stealing</em>: all threads in the pool attempt to find and
31	<	* execute subtasks created by other active tasks (eventually blocking
32	<	* waiting for work if none exist). This enables efficient processing
33	<	* when most tasks spawn other subtasks (as do most {@code
34	<	* ForkJoinTask}s). When setting <em>asyncMode</em> to true in
35	<	* constructors, {@code ForkJoinPool}s may also be appropriate for use
36	<	* with event-style tasks that are never joined.
31	>	* execute tasks submitted to the pool and/or created by other active
32	>	* tasks (eventually blocking waiting for work if none exist). This
33	>	* enables efficient processing when most tasks spawn other subtasks
34	>	* (as do most {@code ForkJoinTask}s), as well as when many small
35	>	* tasks are submitted to the pool from external clients.  Especially
36	>	* when setting <em>asyncMode</em> to true in constructors, {@code
37	>	* ForkJoinPool}s may also be appropriate for use with event-style
38	>	* tasks that are never joined.
39	>	*
40	>	* <p>A static {@link #commonPool} is available and appropriate for
41	>	* most applications. The common pool is used by any ForkJoinTask that
42	>	* is not explicitly submitted to a specified pool. Using the common
43	>	* pool normally reduces resource usage (its threads are slowly
44	>	* reclaimed during periods of non-use, and reinstated upon subsequent
45	>	* use).
46		*
47	<	* <p>A {@code ForkJoinPool} is constructed with a given target
48	<	* parallelism level; by default, equal to the number of available
49	<	* processors. The pool attempts to maintain enough active (or
50	<	* available) threads by dynamically adding, suspending, or resuming
51	<	* internal worker threads, even if some tasks are stalled waiting to
52	<	* join others. However, no such adjustments are guaranteed in the
53	<	* face of blocked IO or other unmanaged synchronization. The nested
54	<	* {@link ManagedBlocker} interface enables extension of the kinds of
47	>	* <p>For applications that require separate or custom pools, a {@code
48	>	* ForkJoinPool} may be constructed with a given target parallelism
49	>	* level; by default, equal to the number of available processors. The
50	>	* pool attempts to maintain enough active (or available) threads by
51	>	* dynamically adding, suspending, or resuming internal worker
52	>	* threads, even if some tasks are stalled waiting to join
53	>	* others. However, no such adjustments are guaranteed in the face of
54	>	* blocked IO or other unmanaged synchronization. The nested {@link
55	>	* ManagedBlocker} interface enables extension of the kinds of
56		* synchronization accommodated.
57		*
58		* <p>In addition to execution and lifecycle control methods, this
#	Line 52 | Line 63 | import java.util.concurrent.CountDownLat
63		* convenient form for informal monitoring.
64		*
65		* <p> As is the case with other ExecutorServices, there are three
66	<	* main task execution methods summarized in the following
67	<	* table. These are designed to be used by clients not already engaged
68	<	* in fork/join computations in the current pool.  The main forms of
69	<	* these methods accept instances of {@code ForkJoinTask}, but
70	<	* overloaded forms also allow mixed execution of plain {@code
66	>	* main task execution methods summarized in the following table.
67	>	* These are designed to be used primarily by clients not already
68	>	* engaged in fork/join computations in the current pool.  The main
69	>	* forms of these methods accept instances of {@code ForkJoinTask},
70	>	* but overloaded forms also allow mixed execution of plain {@code
71		* Runnable}- or {@code Callable}- based activities as well.  However,
72	<	* tasks that are already executing in a pool should normally
73	<	* <em>NOT</em> use these pool execution methods, but instead use the
74	<	* within-computation forms listed in the table.
72	>	* tasks that are already executing in a pool should normally instead
73	>	* use the within-computation forms listed in the table unless using
74	>	* async event-style tasks that are not usually joined, in which case
75	>	* there is little difference among choice of methods.
76		*
77		* <table BORDER CELLPADDING=3 CELLSPACING=1>
78		*  <tr>
#	Line 85 | Line 97 | import java.util.concurrent.CountDownLat
97		*  </tr>
98		* </table>
99		*
100	<	* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
101	<	* used for all parallel task execution in a program or subsystem.
102	<	* Otherwise, use would not usually outweigh the construction and
103	<	* bookkeeping overhead of creating a large set of threads. For
104	<	* example, a common pool could be used for the {@code SortTasks}
105	<	* illustrated in {@link RecursiveAction}. Because {@code
106	<	* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
107	<	* daemon} mode, there is typically no need to explicitly {@link
108	<	* #shutdown} such a pool upon program exit.
97	<	*
98	<	* <pre>
99	<	* static final ForkJoinPool mainPool = new ForkJoinPool();
100	<	* ...
101	<	* public void sort(long[] array) {
102	<	*   mainPool.invoke(new SortTask(array, 0, array.length));
103	<	* }
104	<	* </pre>
100	>	* <p>The common pool is by default constructed with default
101	>	* parameters, but these may be controlled by setting three {@link
102	>	* System#getProperty properties} with prefix {@code
103	>	* java.util.concurrent.ForkJoinPool.common}: {@code parallelism} --
104	>	* an integer greater than zero, {@code threadFactory} -- the class
105	>	* name of a {@link ForkJoinWorkerThreadFactory}, and {@code
106	>	* exceptionHandler} -- the class name of a {@link
107	>	* Thread.UncaughtExceptionHandler}. Upon any error in establishing
108	>	* these settings, default parameters are used.
109		*
110		* <p><b>Implementation notes</b>: This implementation restricts the
111		* maximum number of running threads to 32767. Attempts to create
#	Line 120 | Line 124 | public class ForkJoinPool extends Abstra
124		/*
125		* Implementation Overview
126		*
127	<	* This class provides the central bookkeeping and control for a
128	<	* set of worker threads: Submissions from non-FJ threads enter
129	<	* into a submission queue. Workers take these tasks and typically
130	<	* split them into subtasks that may be stolen by other workers.
131	<	* The main work-stealing mechanics implemented in class
132	<	* ForkJoinWorkerThread give first priority to processing tasks
133	<	* from their own queues (LIFO or FIFO, depending on mode), then
134	<	* to randomized FIFO steals of tasks in other worker queues, and
135	<	* lastly to new submissions. These mechanics do not consider
136	<	* affinities, loads, cache localities, etc, so rarely provide the
137	<	* best possible performance on a given machine, but portably
138	<	* provide good throughput by averaging over these factors.
139	<	* (Further, even if we did try to use such information, we do not
140	<	* usually have a basis for exploiting it. For example, some sets
141	<	* of tasks profit from cache affinities, but others are harmed by
142	<	* cache pollution effects.)
143	<	*
144	<	* Beyond work-stealing support and essential bookkeeping, the
145	<	* main responsibility of this framework is to take actions when
146	<	* one worker is waiting to join a task stolen (or always held by)
147	<	* another.  Because we are multiplexing many tasks on to a pool
148	<	* of workers, we can't just let them block (as in Thread.join).
149	<	* We also cannot just reassign the joiner's run-time stack with
150	<	* another and replace it later, which would be a form of
151	<	* "continuation", that even if possible is not necessarily a good
152	<	* idea. Given that the creation costs of most threads on most
153	<	* systems mainly surrounds setting up runtime stacks, thread
154	<	* creation and switching is usually not much more expensive than
155	<	* stack creation and switching, and is more flexible). Instead we
156	<	* combine two tactics:
127	>	* This class and its nested classes provide the main
128	>	* functionality and control for a set of worker threads:
129	>	* Submissions from non-FJ threads enter into submission queues.
130	>	* Workers take these tasks and typically split them into subtasks
131	>	* that may be stolen by other workers.  Preference rules give
132	>	* first priority to processing tasks from their own queues (LIFO
133	>	* or FIFO, depending on mode), then to randomized FIFO steals of
134	>	* tasks in other queues.
135	>	*
136	>	* WorkQueues
137	>	* ==========
138	>	*
139	>	* Most operations occur within work-stealing queues (in nested
140	>	* class WorkQueue).  These are special forms of Deques that
141	>	* support only three of the four possible end-operations -- push,
142	>	* pop, and poll (aka steal), under the further constraints that
143	>	* push and pop are called only from the owning thread (or, as
144	>	* extended here, under a lock), while poll may be called from
145	>	* other threads.  (If you are unfamiliar with them, you probably
146	>	* want to read Herlihy and Shavit's book "The Art of
147	>	* Multiprocessor programming", chapter 16 describing these in
148	>	* more detail before proceeding.)  The main work-stealing queue
149	>	* design is roughly similar to those in the papers "Dynamic
150	>	* Circular Work-Stealing Deque" by Chase and Lev, SPAA 2005
151	>	* (http://research.sun.com/scalable/pubs/index.html) and
152	>	* "Idempotent work stealing" by Michael, Saraswat, and Vechev,
153	>	* PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186).
154	>	* The main differences ultimately stem from GC requirements that
155	>	* we null out taken slots as soon as we can, to maintain as small
156	>	* a footprint as possible even in programs generating huge
157	>	* numbers of tasks. To accomplish this, we shift the CAS
158	>	* arbitrating pop vs poll (steal) from being on the indices
159	>	* ("base" and "top") to the slots themselves.  So, both a
160	>	* successful pop and poll mainly entail a CAS of a slot from
161	>	* non-null to null.  Because we rely on CASes of references, we
162	>	* do not need tag bits on base or top.  They are simple ints as
163	>	* used in any circular array-based queue (see for example
164	>	* ArrayDeque).  Updates to the indices must still be ordered in a
165	>	* way that guarantees that top == base means the queue is empty,
166	>	* but otherwise may err on the side of possibly making the queue
167	>	* appear nonempty when a push, pop, or poll have not fully
168	>	* committed. Note that this means that the poll operation,
169	>	* considered individually, is not wait-free. One thief cannot
170	>	* successfully continue until another in-progress one (or, if
171	>	* previously empty, a push) completes.  However, in the
172	>	* aggregate, we ensure at least probabilistic non-blockingness.
173	>	* If an attempted steal fails, a thief always chooses a different
174	>	* random victim target to try next. So, in order for one thief to
175	>	* progress, it suffices for any in-progress poll or new push on
176	>	* any empty queue to complete. (This is why we normally use
177	>	* method pollAt and its variants that try once at the apparent
178	>	* base index, else consider alternative actions, rather than
179	>	* method poll.)
180	>	*
181	>	* This approach also enables support of a user mode in which local
182	>	* task processing is in FIFO, not LIFO order, simply by using
183	>	* poll rather than pop.  This can be useful in message-passing
184	>	* frameworks in which tasks are never joined.  However neither
185	>	* mode considers affinities, loads, cache localities, etc, so
186	>	* rarely provide the best possible performance on a given
187	>	* machine, but portably provide good throughput by averaging over
188	>	* these factors.  (Further, even if we did try to use such
189	>	* information, we do not usually have a basis for exploiting it.
190	>	* For example, some sets of tasks profit from cache affinities,
191	>	* but others are harmed by cache pollution effects.)
192	>	*
193	>	* WorkQueues are also used in a similar way for tasks submitted
194	>	* to the pool. We cannot mix these tasks in the same queues used
195	>	* for work-stealing (this would contaminate lifo/fifo
196	>	* processing). Instead, we randomly associate submission queues
197	>	* with submitting threads, using a form of hashing.  The
198	>	* ThreadLocal Submitter class contains a value initially used as
199	>	* a hash code for choosing existing queues, but may be randomly
200	>	* repositioned upon contention with other submitters.  In
201	>	* essence, submitters act like workers except that they are
202	>	* restricted to executing local tasks that they submitted (or in
203	>	* the case of CountedCompleters, others with the same root task).
204	>	* However, because most shared/external queue operations are more
205	>	* expensive than internal, and because, at steady state, external
206	>	* submitters will compete for CPU with workers, ForkJoinTask.join
207	>	* and related methods disable them from repeatedly helping to
208	>	* process tasks if all workers are active.  Insertion of tasks in
209	>	* shared mode requires a lock (mainly to protect in the case of
210	>	* resizing) but we use only a simple spinlock (using bits in
211	>	* field qlock), because submitters encountering a busy queue move
212	>	* on to try or create other queues -- they block only when
213	>	* creating and registering new queues.
214	>	*
215	>	* Management
216	>	* ==========
217	>	*
218	>	* The main throughput advantages of work-stealing stem from
219	>	* decentralized control -- workers mostly take tasks from
220	>	* themselves or each other. We cannot negate this in the
221	>	* implementation of other management responsibilities. The main
222	>	* tactic for avoiding bottlenecks is packing nearly all
223	>	* essentially atomic control state into two volatile variables
224	>	* that are by far most often read (not written) as status and
225	>	* consistency checks.
226	>	*
227	>	* Field "ctl" contains 64 bits holding all the information needed
228	>	* to atomically decide to add, inactivate, enqueue (on an event
229	>	* queue), dequeue, and/or re-activate workers.  To enable this
230	>	* packing, we restrict maximum parallelism to (1<<15)-1 (which is
231	>	* far in excess of normal operating range) to allow ids, counts,
232	>	* and their negations (used for thresholding) to fit into 16bit
233	>	* fields.
234	>	*
235	>	* Field "plock" is a form of sequence lock with a saturating
236	>	* shutdown bit (similarly for per-queue "qlocks"), mainly
237	>	* protecting updates to the workQueues array, as well as to
238	>	* enable shutdown.  When used as a lock, it is normally only very
239	>	* briefly held, so is nearly always available after at most a
240	>	* brief spin, but we use a monitor-based backup strategy to
241	>	* blocking when needed.
242	>	*
243	>	* Recording WorkQueues.  WorkQueues are recorded in the
244	>	* "workQueues" array that is created upon first use and expanded
245	>	* if necessary.  Updates to the array while recording new workers
246	>	* and unrecording terminated ones are protected from each other
247	>	* by a lock but the array is otherwise concurrently readable, and
248	>	* accessed directly.  To simplify index-based operations, the
249	>	* array size is always a power of two, and all readers must
250	>	* tolerate null slots. Worker queues are at odd indices Shared
251	>	* (submission) queues are at even indices, up to a maximum of 64
252	>	* slots, to limit growth even if array needs to expand to add
253	>	* more workers. Grouping them together in this way simplifies and
254	>	* speeds up task scanning.
255	>	*
256	>	* All worker thread creation is on-demand, triggered by task
257	>	* submissions, replacement of terminated workers, and/or
258	>	* compensation for blocked workers. However, all other support
259	>	* code is set up to work with other policies.  To ensure that we
260	>	* do not hold on to worker references that would prevent GC, ALL
261	>	* accesses to workQueues are via indices into the workQueues
262	>	* array (which is one source of some of the messy code
263	>	* constructions here). In essence, the workQueues array serves as
264	>	* a weak reference mechanism. Thus for example the wait queue
265	>	* field of ctl stores indices, not references.  Access to the
266	>	* workQueues in associated methods (for example signalWork) must
267	>	* both index-check and null-check the IDs. All such accesses
268	>	* ignore bad IDs by returning out early from what they are doing,
269	>	* since this can only be associated with termination, in which
270	>	* case it is OK to give up.  All uses of the workQueues array
271	>	* also check that it is non-null (even if previously
272	>	* non-null). This allows nulling during termination, which is
273	>	* currently not necessary, but remains an option for
274	>	* resource-revocation-based shutdown schemes. It also helps
275	>	* reduce JIT issuance of uncommon-trap code, which tends to
276	>	* unnecessarily complicate control flow in some methods.
277	>	*
278	>	* Event Queuing. Unlike HPC work-stealing frameworks, we cannot
279	>	* let workers spin indefinitely scanning for tasks when none can
280	>	* be found immediately, and we cannot start/resume workers unless
281	>	* there appear to be tasks available.  On the other hand, we must
282	>	* quickly prod them into action when new tasks are submitted or
283	>	* generated. In many usages, ramp-up time to activate workers is
284	>	* the main limiting factor in overall performance (this is
285	>	* compounded at program start-up by JIT compilation and
286	>	* allocation). So we try to streamline this as much as possible.
287	>	* We park/unpark workers after placing in an event wait queue
288	>	* when they cannot find work. This "queue" is actually a simple
289	>	* Treiber stack, headed by the "id" field of ctl, plus a 15bit
290	>	* counter value (that reflects the number of times a worker has
291	>	* been inactivated) to avoid ABA effects (we need only as many
292	>	* version numbers as worker threads). Successors are held in
293	>	* field WorkQueue.nextWait.  Queuing deals with several intrinsic
294	>	* races, mainly that a task-producing thread can miss seeing (and
295	>	* signalling) another thread that gave up looking for work but
296	>	* has not yet entered the wait queue. We solve this by requiring
297	>	* a full sweep of all workers (via repeated calls to method
298	>	* scan()) both before and after a newly waiting worker is added
299	>	* to the wait queue. During a rescan, the worker might release
300	>	* some other queued worker rather than itself, which has the same
301	>	* net effect. Because enqueued workers may actually be rescanning
302	>	* rather than waiting, we set and clear the "parker" field of
303	>	* WorkQueues to reduce unnecessary calls to unpark.  (This
304	>	* requires a secondary recheck to avoid missed signals.)  Note
305	>	* the unusual conventions about Thread.interrupts surrounding
306	>	* parking and other blocking: Because interrupts are used solely
307	>	* to alert threads to check termination, which is checked anyway
308	>	* upon blocking, we clear status (using Thread.interrupted)
309	>	* before any call to park, so that park does not immediately
310	>	* return due to status being set via some other unrelated call to
311	>	* interrupt in user code.
312	>	*
313	>	* Signalling.  We create or wake up workers only when there
314	>	* appears to be at least one task they might be able to find and
315	>	* execute. However, many other threads may notice the same task
316	>	* and each signal to wake up a thread that might take it. So in
317	>	* general, pools will be over-signalled.  When a submission is
318	>	* added or another worker adds a task to a queue that is
319	>	* apparently empty, they signal waiting workers (or trigger
320	>	* creation of new ones if fewer than the given parallelism level
321	>	* -- see signalWork).  These primary signals are buttressed by
322	>	* signals whenever other threads scan for work or do not have a
323	>	* task to process. On most platforms, signalling (unpark)
324	>	* overhead time is noticeably long, and the time between
325	>	* signalling a thread and it actually making progress can be very
326	>	* noticeably long, so it is worth offloading these delays from
327	>	* critical paths as much as possible.
328	>	*
329	>	* Trimming workers. To release resources after periods of lack of
330	>	* use, a worker starting to wait when the pool is quiescent will
331	>	* time out and terminate if the pool has remained quiescent for a
332	>	* given period -- a short period if there are more threads than
333	>	* parallelism, longer as the number of threads decreases. This
334	>	* will slowly propagate, eventually terminating all workers after
335	>	* periods of non-use.
336	>	*
337	>	* Shutdown and Termination. A call to shutdownNow atomically sets
338	>	* a plock bit and then (non-atomically) sets each worker's
339	>	* qlock status, cancels all unprocessed tasks, and wakes up
340	>	* all waiting workers.  Detecting whether termination should
341	>	* commence after a non-abrupt shutdown() call requires more work
342	>	* and bookkeeping. We need consensus about quiescence (i.e., that
343	>	* there is no more work). The active count provides a primary
344	>	* indication but non-abrupt shutdown still requires a rechecking
345	>	* scan for any workers that are inactive but not queued.
346	>	*
347	>	* Joining Tasks
348	>	* =============
349	>	*
350	>	* Any of several actions may be taken when one worker is waiting
351	>	* to join a task stolen (or always held) by another.  Because we
352	>	* are multiplexing many tasks on to a pool of workers, we can't
353	>	* just let them block (as in Thread.join).  We also cannot just
354	>	* reassign the joiner's run-time stack with another and replace
355	>	* it later, which would be a form of "continuation", that even if
356	>	* possible is not necessarily a good idea since we sometimes need
357	>	* both an unblocked task and its continuation to progress.
358	>	* Instead we combine two tactics:
359		*
360		*   Helping: Arranging for the joiner to execute some task that it
361	<	*      would be running if the steal had not occurred.  Method
156	<	*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
157	<	*      links to try to find such a task.
361	>	*      would be running if the steal had not occurred.
362		*
363		*   Compensating: Unless there are already enough live threads,
364	<	*      method helpMaintainParallelism() may create or or
365	<	*      re-activate a spare thread to compensate for blocked
162	<	*      joiners until they unblock.
364	>	*      method tryCompensate() may create or re-activate a spare
365	>	*      thread to compensate for blocked joiners until they unblock.
366		*
367	<	* It is impossible to keep exactly the target (parallelism)
368	<	* number of threads running at any given time.  Determining
369	<	* existence of conservatively safe helping targets, the
370	<	* availability of already-created spares, and the apparent need
371	<	* to create new spares are all racy and require heuristic
372	<	* guidance, so we rely on multiple retries of each.  Compensation
373	<	* occurs in slow-motion. It is triggered only upon timeouts of
171	<	* Object.wait used for joins. This reduces poor decisions that
172	<	* would otherwise be made when threads are waiting for others
173	<	* that are stalled because of unrelated activities such as
174	<	* garbage collection.
367	>	* A third form (implemented in tryRemoveAndExec) amounts to
368	>	* helping a hypothetical compensator: If we can readily tell that
369	>	* a possible action of a compensator is to steal and execute the
370	>	* task being joined, the joining thread can do so directly,
371	>	* without the need for a compensation thread (although at the
372	>	* expense of larger run-time stacks, but the tradeoff is
373	>	* typically worthwhile).
374		*
375		* The ManagedBlocker extension API can't use helping so relies
376		* only on compensation in method awaitBlocker.
377		*
378	<	* The main throughput advantages of work-stealing stem from
379	<	* decentralized control -- workers mostly steal tasks from each
380	<	* other. We do not want to negate this by creating bottlenecks
381	<	* implementing other management responsibilities. So we use a
382	<	* collection of techniques that avoid, reduce, or cope well with
383	<	* contention. These entail several instances of bit-packing into
384	<	* CASable fields to maintain only the minimally required
385	<	* atomicity. To enable such packing, we restrict maximum
386	<	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
387	<	* unbalanced increments and decrements) to fit into a 16 bit
388	<	* field, which is far in excess of normal operating range.  Even
389	<	* though updates to some of these bookkeeping fields do sometimes
390	<	* contend with each other, they don't normally cache-contend with
391	<	* updates to others enough to warrant memory padding or
392	<	* isolation. So they are all held as fields of ForkJoinPool
393	<	* objects.  The main capabilities are as follows:
394	<	*
395	<	* 1. Creating and removing workers. Workers are recorded in the
396	<	* "workers" array. This is an array as opposed to some other data
397	<	* structure to support index-based random steals by workers.
398	<	* Updates to the array recording new workers and unrecording
399	<	* terminated ones are protected from each other by a lock
400	<	* (workerLock) but the array is otherwise concurrently readable,
401	<	* and accessed directly by workers. To simplify index-based
402	<	* operations, the array size is always a power of two, and all
403	<	* readers must tolerate null slots. Currently, all worker thread
404	<	* creation is on-demand, triggered by task submissions,
405	<	* replacement of terminated workers, and/or compensation for
406	<	* blocked workers. However, all other support code is set up to
407	<	* work with other policies.
408	<	*
409	<	* To ensure that we do not hold on to worker references that
410	<	* would prevent GC, ALL accesses to workers are via indices into
411	<	* the workers array (which is one source of some of the unusual
412	<	* code constructions here). In essence, the workers array serves
413	<	* as a WeakReference mechanism. Thus for example the event queue
414	<	* stores worker indices, not worker references. Access to the
415	<	* workers in associated methods (for example releaseEventWaiters)
416	<	* must both index-check and null-check the IDs. All such accesses
417	<	* ignore bad IDs by returning out early from what they are doing,
418	<	* since this can only be associated with shutdown, in which case
419	<	* it is OK to give up. On termination, we just clobber these
420	<	* data structures without trying to use them.
421	<	*
422	<	* 2. Bookkeeping for dynamically adding and removing workers. We
423	<	* aim to approximately maintain the given level of parallelism.
424	<	* When some workers are known to be blocked (on joins or via
425	<	* ManagedBlocker), we may create or resume others to take their
426	<	* place until they unblock (see below). Implementing this
427	<	* requires counts of the number of "running" threads (i.e., those
428	<	* that are neither blocked nor artificially suspended) as well as
429	<	* the total number.  These two values are packed into one field,
430	<	* "workerCounts" because we need accurate snapshots when deciding
431	<	* to create, resume or suspend.  Note however that the
432	<	* correspondence of these counts to reality is not guaranteed. In
433	<	* particular updates for unblocked threads may lag until they
434	<	* actually wake up.
435	<	*
436	<	* 3. Maintaining global run state. The run state of the pool
437	<	* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
438	<	* those in other Executor implementations, as well as a count of
439	<	* "active" workers -- those that are, or soon will be, or
440	<	* recently were executing tasks. The runLevel and active count
441	<	* are packed together in order to correctly trigger shutdown and
442	<	* termination. Without care, active counts can be subject to very
443	<	* high contention.  We substantially reduce this contention by
444	<	* relaxing update rules.  A worker must claim active status
445	<	* prospectively, by activating if it sees that a submitted or
446	<	* stealable task exists (it may find after activating that the
447	<	* task no longer exists). It stays active while processing this
448	<	* task (if it exists) and any other local subtasks it produces,
449	<	* until it cannot find any other tasks. It then tries
450	<	* inactivating (see method preStep), but upon update contention
451	<	* instead scans for more tasks, later retrying inactivation if it
452	<	* doesn't find any.
453	<	*
454	<	* 4. Managing idle workers waiting for tasks. We cannot let
455	<	* workers spin indefinitely scanning for tasks when none are
456	<	* available. On the other hand, we must quickly prod them into
457	<	* action when new tasks are submitted or generated.  We
458	<	* park/unpark these idle workers using an event-count scheme.
459	<	* Field eventCount is incremented upon events that may enable
460	<	* workers that previously could not find a task to now find one:
461	<	* Submission of a new task to the pool, or another worker pushing
462	<	* a task onto a previously empty queue.  (We also use this
463	<	* mechanism for configuration and termination actions that
265	<	* require wakeups of idle workers).  Each worker maintains its
266	<	* last known event count, and blocks when a scan for work did not
267	<	* find a task AND its lastEventCount matches the current
268	<	* eventCount. Waiting idle workers are recorded in a variant of
269	<	* Treiber stack headed by field eventWaiters which, when nonzero,
270	<	* encodes the thread index and count awaited for by the worker
271	<	* thread most recently calling eventSync. This thread in turn has
272	<	* a record (field nextEventWaiter) for the next waiting worker.
273	<	* In addition to allowing simpler decisions about need for
274	<	* wakeup, the event count bits in eventWaiters serve the role of
275	<	* tags to avoid ABA errors in Treiber stacks. Upon any wakeup,
276	<	* released threads also try to release at most two others.  The
277	<	* net effect is a tree-like diffusion of signals, where released
278	<	* threads (and possibly others) help with unparks.  To further
279	<	* reduce contention effects a bit, failed CASes to increment
280	<	* field eventCount are tolerated without retries in signalWork.
281	<	* Conceptually they are merged into the same event, which is OK
282	<	* when their only purpose is to enable workers to scan for work.
283	<	*
284	<	* 5. Managing suspension of extra workers. When a worker notices
285	<	* (usually upon timeout of a wait()) that there are too few
286	<	* running threads, we may create a new thread to maintain
287	<	* parallelism level, or at least avoid starvation. Usually, extra
288	<	* threads are needed for only very short periods, yet join
289	<	* dependencies are such that we sometimes need them in
290	<	* bursts. Rather than create new threads each time this happens,
291	<	* we suspend no-longer-needed extra ones as "spares". For most
292	<	* purposes, we don't distinguish "extra" spare threads from
293	<	* normal "core" threads: On each call to preStep (the only point
294	<	* at which we can do this) a worker checks to see if there are
295	<	* now too many running workers, and if so, suspends itself.
296	<	* Method helpMaintainParallelism looks for suspended threads to
297	<	* resume before considering creating a new replacement. The
298	<	* spares themselves are encoded on another variant of a Treiber
299	<	* Stack, headed at field "spareWaiters".  Note that the use of
300	<	* spares is intrinsically racy.  One thread may become a spare at
301	<	* about the same time as another is needlessly being created. We
302	<	* counteract this and related slop in part by requiring resumed
303	<	* spares to immediately recheck (in preStep) to see whether they
304	<	* they should re-suspend.
305	<	*
306	<	* 6. Killing off unneeded workers. A timeout mechanism is used to
307	<	* shed unused workers: The oldest (first) event queue waiter uses
308	<	* a timed rather than hard wait. When this wait times out without
309	<	* a normal wakeup, it tries to shutdown any one (for convenience
310	<	* the newest) other spare or event waiter via
311	<	* tryShutdownUnusedWorker. This eventually reduces the number of
312	<	* worker threads to a minimum of one after a long enough period
313	<	* without use.
314	<	*
315	<	* 7. Deciding when to create new workers. The main dynamic
316	<	* control in this class is deciding when to create extra threads
317	<	* in method helpMaintainParallelism. We would like to keep
318	<	* exactly #parallelism threads running, which is an impossible
319	<	* task. We always need to create one when the number of running
320	<	* threads would become zero and all workers are busy. Beyond
321	<	* this, we must rely on heuristics that work well in the the
322	<	* presence of transients phenomena such as GC stalls, dynamic
323	<	* compilation, and wake-up lags. These transients are extremely
324	<	* common -- we are normally trying to fully saturate the CPUs on
325	<	* a machine, so almost any activity other than running tasks
326	<	* impedes accuracy. Our main defense is to allow parallelism to
327	<	* lapse for a while during joins, and use a timeout to see if,
328	<	* after the resulting settling, there is still a need for
329	<	* additional workers.  This also better copes with the fact that
330	<	* some of the methods in this class tend to never become compiled
331	<	* (but are interpreted), so some components of the entire set of
332	<	* controls might execute 100 times faster than others. And
333	<	* similarly for cases where the apparent lack of work is just due
334	<	* to GC stalls and other transient system activity.
335	<	*
336	<	* Beware that there is a lot of representation-level coupling
337	<	* among classes ForkJoinPool, ForkJoinWorkerThread, and
338	<	* ForkJoinTask.  For example, direct access to "workers" array by
339	<	* workers, and direct access to ForkJoinTask.status by both
340	<	* ForkJoinPool and ForkJoinWorkerThread.  There is little point
378	>	* The algorithm in tryHelpStealer entails a form of "linear"
379	>	* helping: Each worker records (in field currentSteal) the most
380	>	* recent task it stole from some other worker. Plus, it records
381	>	* (in field currentJoin) the task it is currently actively
382	>	* joining. Method tryHelpStealer uses these markers to try to
383	>	* find a worker to help (i.e., steal back a task from and execute
384	>	* it) that could hasten completion of the actively joined task.
385	>	* In essence, the joiner executes a task that would be on its own
386	>	* local deque had the to-be-joined task not been stolen. This may
387	>	* be seen as a conservative variant of the approach in Wagner &
388	>	* Calder "Leapfrogging: a portable technique for implementing
389	>	* efficient futures" SIGPLAN Notices, 1993
390	>	* (http://portal.acm.org/citation.cfm?id=155354). It differs in
391	>	* that: (1) We only maintain dependency links across workers upon
392	>	* steals, rather than use per-task bookkeeping.  This sometimes
393	>	* requires a linear scan of workQueues array to locate stealers,
394	>	* but often doesn't because stealers leave hints (that may become
395	>	* stale/wrong) of where to locate them.  A stealHint is only a
396	>	* hint because a worker might have had multiple steals and the
397	>	* hint records only one of them (usually the most current).
398	>	* Hinting isolates cost to when it is needed, rather than adding
399	>	* to per-task overhead.  (2) It is "shallow", ignoring nesting
400	>	* and potentially cyclic mutual steals.  (3) It is intentionally
401	>	* racy: field currentJoin is updated only while actively joining,
402	>	* which means that we miss links in the chain during long-lived
403	>	* tasks, GC stalls etc (which is OK since blocking in such cases
404	>	* is usually a good idea).  (4) We bound the number of attempts
405	>	* to find work (see MAX_HELP) and fall back to suspending the
406	>	* worker and if necessary replacing it with another.
407	>	*
408	>	* Helping actions for CountedCompleters are much simpler: Method
409	>	* helpComplete can take and execute any task with the same root
410	>	* as the task being waited on. However, this still entails some
411	>	* traversal of completer chains, so is less efficient than using
412	>	* CountedCompleters without explicit joins.
413	>	*
414	>	* It is impossible to keep exactly the target parallelism number
415	>	* of threads running at any given time.  Determining the
416	>	* existence of conservatively safe helping targets, the
417	>	* availability of already-created spares, and the apparent need
418	>	* to create new spares are all racy, so we rely on multiple
419	>	* retries of each.  Compensation in the apparent absence of
420	>	* helping opportunities is challenging to control on JVMs, where
421	>	* GC and other activities can stall progress of tasks that in
422	>	* turn stall out many other dependent tasks, without us being
423	>	* able to determine whether they will ever require compensation.
424	>	* Even though work-stealing otherwise encounters little
425	>	* degradation in the presence of more threads than cores,
426	>	* aggressively adding new threads in such cases entails risk of
427	>	* unwanted positive feedback control loops in which more threads
428	>	* cause more dependent stalls (as well as delayed progress of
429	>	* unblocked threads to the point that we know they are available)
430	>	* leading to more situations requiring more threads, and so
431	>	* on. This aspect of control can be seen as an (analytically
432	>	* intractable) game with an opponent that may choose the worst
433	>	* (for us) active thread to stall at any time.  We take several
434	>	* precautions to bound losses (and thus bound gains), mainly in
435	>	* methods tryCompensate and awaitJoin.
436	>	*
437	>	* Common Pool
438	>	* ===========
439	>	*
440	>	* The static commonPool always exists after static
441	>	* initialization.  Since it (or any other created pool) need
442	>	* never be used, we minimize initial construction overhead and
443	>	* footprint to the setup of about a dozen fields, with no nested
444	>	* allocation. Most bootstrapping occurs within method
445	>	* fullExternalPush during the first submission to the pool.
446	>	*
447	>	* When external threads submit to the common pool, they can
448	>	* perform some subtask processing (see externalHelpJoin and
449	>	* related methods).  We do not need to record whether these
450	>	* submissions are to the common pool -- if not, externalHelpJoin
451	>	* returns quicky (at the most helping to signal some common pool
452	>	* workers). These submitters would otherwise be blocked waiting
453	>	* for completion, so the extra effort (with liberally sprinkled
454	>	* task status checks) in inapplicable cases amounts to an odd
455	>	* form of limited spin-wait before blocking in ForkJoinTask.join.
456	>	*
457	>	* Style notes
458	>	* ===========
459	>	*
460	>	* There is a lot of representation-level coupling among classes
461	>	* ForkJoinPool, ForkJoinWorkerThread, and ForkJoinTask.  The
462	>	* fields of WorkQueue maintain data structures managed by
463	>	* ForkJoinPool, so are directly accessed.  There is little point
464		* trying to reduce this, since any associated future changes in
465		* representations will need to be accompanied by algorithmic
466	<	* changes anyway.
467	<	*
468	<	* Style notes: There are lots of inline assignments (of form
469	<	* "while ((local = field) != 0)") which are usually the simplest
470	<	* way to ensure the required read orderings (which are sometimes
471	<	* critical). Also several occurrences of the unusual "do {}
472	<	* while(!cas...)" which is the simplest way to force an update of
473	<	* a CAS'ed variable. There are also other coding oddities that
474	<	* help some methods perform reasonably even when interpreted (not
475	<	* compiled), at the expense of some messy constructions that
476	<	* reduce byte code counts.
477	<	*
478	<	* The order of declarations in this file is: (1) statics (2)
479	<	* fields (along with constants used when unpacking some of them)
480	<	* (3) internal control methods (4) callbacks and other support
481	<	* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
482	<	* methods (plus a few little helpers).
466	>	* changes anyway. Several methods intrinsically sprawl because
467	>	* they must accumulate sets of consistent reads of volatiles held
468	>	* in local variables.  Methods signalWork() and scan() are the
469	>	* main bottlenecks, so are especially heavily
470	>	* micro-optimized/mangled.  There are lots of inline assignments
471	>	* (of form "while ((local = field) != 0)") which are usually the
472	>	* simplest way to ensure the required read orderings (which are
473	>	* sometimes critical). This leads to a "C"-like style of listing
474	>	* declarations of these locals at the heads of methods or blocks.
475	>	* There are several occurrences of the unusual "do {} while
476	>	* (!cas...)"  which is the simplest way to force an update of a
477	>	* CAS'ed variable. There are also other coding oddities (including
478	>	* several unnecessary-looking hoisted null checks) that help
479	>	* some methods perform reasonably even when interpreted (not
480	>	* compiled).
481	>	*
482	>	* The order of declarations in this file is:
483	>	* (1) Static utility functions
484	>	* (2) Nested (static) classes
485	>	* (3) Static fields
486	>	* (4) Fields, along with constants used when unpacking some of them
487	>	* (5) Internal control methods
488	>	* (6) Callbacks and other support for ForkJoinTask methods
489	>	* (7) Exported methods
490	>	* (8) Static block initializing statics in minimally dependent order
491		*/
492
493	+	// Static utilities
494	+
495	+	/**
496	+	* If there is a security manager, makes sure caller has
497	+	* permission to modify threads.
498	+	*/
499	+	private static void checkPermission() {
500	+	SecurityManager security = System.getSecurityManager();
501	+	if (security != null)
502	+	security.checkPermission(modifyThreadPermission);
503	+	}
504	+
505	+	// Nested classes
506	+
507		/**
508		* Factory for creating new {@link ForkJoinWorkerThread}s.
509		* A {@code ForkJoinWorkerThreadFactory} must be defined and used
#	Line 387 | Line 532 | public class ForkJoinPool extends Abstra
532		}
533
534		/**
535	<	* Creates a new ForkJoinWorkerThread. This factory is used unless
536	<	* overridden in ForkJoinPool constructors.
535	>	* Class for artificial tasks that are used to replace the target
536	>	* of local joins if they are removed from an interior queue slot
537	>	* in WorkQueue.tryRemoveAndExec. We don't need the proxy to
538	>	* actually do anything beyond having a unique identity.
539	>	*/
540	>	static final class EmptyTask extends ForkJoinTask<Void> {
541	>	private static final long serialVersionUID = -7721805057305804111L;
542	>	EmptyTask() { status = ForkJoinTask.NORMAL; } // force done
543	>	public final Void getRawResult() { return null; }
544	>	public final void setRawResult(Void x) {}
545	>	public final boolean exec() { return true; }
546	>	}
547	>
548	>	/**
549	>	* Queues supporting work-stealing as well as external task
550	>	* submission. See above for main rationale and algorithms.
551	>	* Implementation relies heavily on "Unsafe" intrinsics
552	>	* and selective use of "volatile":
553	>	*
554	>	* Field "base" is the index (mod array.length) of the least valid
555	>	* queue slot, which is always the next position to steal (poll)
556	>	* from if nonempty. Reads and writes require volatile orderings
557	>	* but not CAS, because updates are only performed after slot
558	>	* CASes.
559	>	*
560	>	* Field "top" is the index (mod array.length) of the next queue
561	>	* slot to push to or pop from. It is written only by owner thread
562	>	* for push, or under lock for external/shared push, and accessed
563	>	* by other threads only after reading (volatile) base.  Both top
564	>	* and base are allowed to wrap around on overflow, but (top -
565	>	* base) (or more commonly -(base - top) to force volatile read of
566	>	* base before top) still estimates size. The lock ("qlock") is
567	>	* forced to -1 on termination, causing all further lock attempts
568	>	* to fail. (Note: we don't need CAS for termination state because
569	>	* upon pool shutdown, all shared-queues will stop being used
570	>	* anyway.)  Nearly all lock bodies are set up so that exceptions
571	>	* within lock bodies are "impossible" (modulo JVM errors that
572	>	* would cause failure anyway.)
573	>	*
574	>	* The array slots are read and written using the emulation of
575	>	* volatiles/atomics provided by Unsafe. Insertions must in
576	>	* general use putOrderedObject as a form of releasing store to
577	>	* ensure that all writes to the task object are ordered before
578	>	* its publication in the queue.  All removals entail a CAS to
579	>	* null.  The array is always a power of two. To ensure safety of
580	>	* Unsafe array operations, all accesses perform explicit null
581	>	* checks and implicit bounds checks via power-of-two masking.
582	>	*
583	>	* In addition to basic queuing support, this class contains
584	>	* fields described elsewhere to control execution. It turns out
585	>	* to work better memory-layout-wise to include them in this class
586	>	* rather than a separate class.
587	>	*
588	>	* Performance on most platforms is very sensitive to placement of
589	>	* instances of both WorkQueues and their arrays -- we absolutely
590	>	* do not want multiple WorkQueue instances or multiple queue
591	>	* arrays sharing cache lines. (It would be best for queue objects
592	>	* and their arrays to share, but there is nothing available to
593	>	* help arrange that).  Unfortunately, because they are recorded
594	>	* in a common array, WorkQueue instances are often moved to be
595	>	* adjacent by garbage collectors. To reduce impact, we use field
596	>	* padding that works OK on common platforms; this effectively
597	>	* trades off slightly slower average field access for the sake of
598	>	* avoiding really bad worst-case access. (Until better JVM
599	>	* support is in place, this padding is dependent on transient
600	>	* properties of JVM field layout rules.)  We also take care in
601	>	* allocating, sizing and resizing the array. Non-shared queue
602	>	* arrays are initialized by workers before use. Others are
603	>	* allocated on first use.
604		*/
605	<	public static final ForkJoinWorkerThreadFactory
606	<	defaultForkJoinWorkerThreadFactory =
607	<	new DefaultForkJoinWorkerThreadFactory();
605	>	static final class WorkQueue {
606	>	/**
607	>	* Capacity of work-stealing queue array upon initialization.
608	>	* Must be a power of two; at least 4, but should be larger to
609	>	* reduce or eliminate cacheline sharing among queues.
610	>	* Currently, it is much larger, as a partial workaround for
611	>	* the fact that JVMs often place arrays in locations that
612	>	* share GC bookkeeping (especially cardmarks) such that
613	>	* per-write accesses encounter serious memory contention.
614	>	*/
615	>	static final int INITIAL_QUEUE_CAPACITY = 1 << 13;
616
617	<	/**
618	<	* Permission required for callers of methods that may start or
619	<	* kill threads.
620	<	*/
621	<	private static final RuntimePermission modifyThreadPermission =
622	<	new RuntimePermission("modifyThread");
617	>	/**
618	>	* Maximum size for queue arrays. Must be a power of two less
619	>	* than or equal to 1 << (31 - width of array entry) to ensure
620	>	* lack of wraparound of index calculations, but defined to a
621	>	* value a bit less than this to help users trap runaway
622	>	* programs before saturating systems.
623	>	*/
624	>	static final int MAXIMUM_QUEUE_CAPACITY = 1 << 26; // 64M
625
626	<	/**
627	<	* If there is a security manager, makes sure caller has
628	<	* permission to modify threads.
629	<	*/
630	<	private static void checkPermission() {
631	<	SecurityManager security = System.getSecurityManager();
632	<	if (security != null)
633	<	security.checkPermission(modifyThreadPermission);
626	>	int seed;                  // for random scanning; initialize nonzero
627	>	volatile int eventCount;   // encoded inactivation count; < 0 if inactive
628	>	int nextWait;              // encoded record of next event waiter
629	>	final int mode;            // lifo, fifo, or shared
630	>	int nsteals;               // cumulative number of steals
631	>	int poolIndex;             // index of this queue in pool (or 0)
632	>	int stealHint;             // index of most recent known stealer
633	>	volatile int qlock;        // 1: locked, -1: terminate; else 0
634	>	volatile int base;         // index of next slot for poll
635	>	int top;                   // index of next slot for push
636	>	ForkJoinTask<?>[] array;   // the elements (initially unallocated)
637	>	final ForkJoinPool pool;   // the containing pool (may be null)
638	>	final ForkJoinWorkerThread owner; // owning thread or null if shared
639	>	volatile Thread parker;    // == owner during call to park; else null
640	>	volatile ForkJoinTask<?> currentJoin;  // task being joined in awaitJoin
641	>	ForkJoinTask<?> currentSteal; // current non-local task being executed
642	>	// Heuristic padding to ameliorate unfortunate memory placements
643	>	Object p00, p01, p02, p03, p04, p05, p06, p07;
644	>	Object p08, p09, p0a, p0b, p0c, p0d, p0e;
645	>
646	>	WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner, int mode) {
647	>	this.mode = mode;
648	>	this.pool = pool;
649	>	this.owner = owner;
650	>	// Place indices in the center of array (that is not yet allocated)
651	>	base = top = INITIAL_QUEUE_CAPACITY >>> 1;
652	>	}
653	>
654	>	/**
655	>	* Pushes a task. Call only by owner in unshared queues.
656	>	* Cases needing resizing or rejection are relyaed to fullPush
657	>	* (that also handles shared queues).
658	>	*
659	>	* @param task the task. Caller must ensure non-null.
660	>	* @throw RejectedExecutionException if array cannot be resized
661	>	*/
662	>	final void push(ForkJoinTask<?> task) {
663	>	ForkJoinPool p; ForkJoinTask<?>[] a;
664	>	int s = top, n;
665	>	if ((a = array) != null && a.length > (n = s + 1 - base)) {
666	>	U.putOrderedObject
667	>	(a, (((a.length - 1) & s) << ASHIFT) + ABASE, task);
668	>	top = s + 1;
669	>	if (n <= 1 && (p = pool) != null)
670	>	p.signalWork(this, 1);
671	>	}
672	>	else
673	>	fullPush(task, true);
674	>	}
675	>
676	>	/**
677	>	* Pushes a task if lock is free and array is either big
678	>	* enough or can be resized to be big enough. Note: a
679	>	* specialization of a common fast path of this method is in
680	>	* ForkJoinPool.externalPush. When called from a FJWT queue,
681	>	* this can fail only if the pool has been shut down or
682	>	* an out of memory error.
683	>	*
684	>	* @param task the task. Caller must ensure non-null.
685	>	* @param owned if true, throw RJE on failure
686	>	*/
687	>	final boolean fullPush(ForkJoinTask<?> task, boolean owned) {
688	>	ForkJoinPool p; ForkJoinTask<?>[] a;
689	>	if (owned) {
690	>	if (qlock < 0) // must be shutting down
691	>	throw new RejectedExecutionException();
692	>	}
693	>	else if (!U.compareAndSwapInt(this, QLOCK, 0, 1))
694	>	return false;
695	>	try {
696	>	int s = top, oldLen, len;
697	>	if ((a = array) == null)
698	>	a = array = new ForkJoinTask<?>[len=INITIAL_QUEUE_CAPACITY];
699	>	else if ((oldLen = a.length) > s + 1 - base)
700	>	len = oldLen;
701	>	else if ((len = oldLen << 1) > MAXIMUM_QUEUE_CAPACITY)
702	>	throw new RejectedExecutionException("Capacity exceeded");
703	>	else {
704	>	int oldMask, b;
705	>	ForkJoinTask<?>[] oldA = a;
706	>	a = array = new ForkJoinTask<?>[len];
707	>	if ((oldMask = oldLen - 1) >= 0 && s - (b = base) > 0) {
708	>	int mask = len - 1;
709	>	do {
710	>	ForkJoinTask<?> x;
711	>	int oldj = ((b & oldMask) << ASHIFT) + ABASE;
712	>	int j    = ((b &    mask) << ASHIFT) + ABASE;
713	>	x = (ForkJoinTask<?>)
714	>	U.getObjectVolatile(oldA, oldj);
715	>	if (x != null &&
716	>	U.compareAndSwapObject(oldA, oldj, x, null))
717	>	U.putObjectVolatile(a, j, x);
718	>	} while (++b != s);
719	>	}
720	>	}
721	>	U.putOrderedObject
722	>	(a, (((len - 1) & s) << ASHIFT) + ABASE, task);
723	>	top = s + 1;
724	>	} finally {
725	>	if (!owned)
726	>	qlock = 0;
727	>	}
728	>	if ((p = pool) != null)
729	>	p.signalWork(this, 1);
730	>	return true;
731	>	}
732	>
733	>	/**
734	>	* Takes next task, if one exists, in LIFO order.  Call only
735	>	* by owner in unshared queues.
736	>	*/
737	>	final ForkJoinTask<?> pop() {
738	>	ForkJoinTask<?>[] a; ForkJoinTask<?> t; int m;
739	>	if ((a = array) != null && (m = a.length - 1) >= 0) {
740	>	for (int s; (s = top - 1) - base >= 0;) {
741	>	long j = ((m & s) << ASHIFT) + ABASE;
742	>	if ((t = (ForkJoinTask<?>)U.getObject(a, j)) == null)
743	>	break;
744	>	if (U.compareAndSwapObject(a, j, t, null)) {
745	>	top = s;
746	>	return t;
747	>	}
748	>	}
749	>	}
750	>	return null;
751	>	}
752	>
753	>	/**
754	>	* Takes a task in FIFO order if b is base of queue and a task
755	>	* can be claimed without contention. Specialized versions
756	>	* appear in ForkJoinPool methods scan and tryHelpStealer.
757	>	*/
758	>	final ForkJoinTask<?> pollAt(int b) {
759	>	ForkJoinTask<?> t; ForkJoinTask<?>[] a;
760	>	if ((a = array) != null) {
761	>	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
762	>	if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null &&
763	>	base == b &&
764	>	U.compareAndSwapObject(a, j, t, null)) {
765	>	base = b + 1;
766	>	return t;
767	>	}
768	>	}
769	>	return null;
770	>	}
771	>
772	>	/**
773	>	* Takes next task, if one exists, in FIFO order.
774	>	*/
775	>	final ForkJoinTask<?> poll() {
776	>	ForkJoinTask<?>[] a; int b; ForkJoinTask<?> t;
777	>	while ((b = base) - top < 0 && (a = array) != null) {
778	>	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
779	>	t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
780	>	if (t != null) {
781	>	if (base == b &&
782	>	U.compareAndSwapObject(a, j, t, null)) {
783	>	base = b + 1;
784	>	return t;
785	>	}
786	>	}
787	>	else if (base == b) {
788	>	if (b + 1 == top)
789	>	break;
790	>	Thread.yield(); // wait for lagging update (very rare)
791	>	}
792	>	}
793	>	return null;
794	>	}
795	>
796	>	/**
797	>	* Takes next task, if one exists, in order specified by mode.
798	>	*/
799	>	final ForkJoinTask<?> nextLocalTask() {
800	>	return mode == 0 ? pop() : poll();
801	>	}
802	>
803	>	/**
804	>	* Returns next task, if one exists, in order specified by mode.
805	>	*/
806	>	final ForkJoinTask<?> peek() {
807	>	ForkJoinTask<?>[] a = array; int m;
808	>	if (a == null || (m = a.length - 1) < 0)
809	>	return null;
810	>	int i = mode == 0 ? top - 1 : base;
811	>	int j = ((i & m) << ASHIFT) + ABASE;
812	>	return (ForkJoinTask<?>)U.getObjectVolatile(a, j);
813	>	}
814	>
815	>	/**
816	>	* Pops the given task only if it is at the current top.
817	>	* (A shared version is available only via FJP.tryExternalUnpush)
818	>	*/
819	>	final boolean tryUnpush(ForkJoinTask<?> t) {
820	>	ForkJoinTask<?>[] a; int s;
821	>	if ((a = array) != null && (s = top) != base &&
822	>	U.compareAndSwapObject
823	>	(a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) {
824	>	top = s;
825	>	return true;
826	>	}
827	>	return false;
828	>	}
829	>
830	>	/**
831	>	* Removes and cancels all known tasks, ignoring any exceptions.
832	>	*/
833	>	final void cancelAll() {
834	>	ForkJoinTask.cancelIgnoringExceptions(currentJoin);
835	>	ForkJoinTask.cancelIgnoringExceptions(currentSteal);
836	>	for (ForkJoinTask<?> t; (t = poll()) != null; )
837	>	ForkJoinTask.cancelIgnoringExceptions(t);
838	>	}
839	>
840	>	/**
841	>	* Computes next value for random probes.  Scans don't require
842	>	* a very high quality generator, but also not a crummy one.
843	>	* Marsaglia xor-shift is cheap and works well enough.  Note:
844	>	* This is manually inlined in its usages in ForkJoinPool to
845	>	* avoid writes inside busy scan loops.
846	>	*/
847	>	final int nextSeed() {
848	>	int r = seed;
849	>	r ^= r << 13;
850	>	r ^= r >>> 17;
851	>	return seed = r ^= r << 5;
852	>	}
853	>
854	>	/**
855	>	* Provides a more accurate estimate of size than (top - base)
856	>	* by ordering reads and checking whether a near-empty queue
857	>	* has at least one unclaimed task.
858	>	*/
859	>	final int queueSize() {
860	>	ForkJoinTask<?>[] a; int k, s, n;
861	>	return ((n = base - (s = top)) < 0 &&
862	>	(n != -1 ||
863	>	((a = array) != null && (k = a.length) > 0 &&
864	>	U.getObject
865	>	(a, (long)((((k - 1) & (s - 1)) << ASHIFT) + ABASE)) != null))) ?
866	>	-n : 0;
867	>	}
868	>
869	>	// Specialized execution methods
870	>
871	>	/**
872	>	* Pops and runs tasks until empty.
873	>	*/
874	>	private void popAndExecAll() {
875	>	// A bit faster than repeated pop calls
876	>	ForkJoinTask<?>[] a; int m, s; long j; ForkJoinTask<?> t;
877	>	while ((a = array) != null && (m = a.length - 1) >= 0 &&
878	>	(s = top - 1) - base >= 0 &&
879	>	(t = ((ForkJoinTask<?>)
880	>	U.getObject(a, j = ((m & s) << ASHIFT) + ABASE)))
881	>	!= null) {
882	>	if (U.compareAndSwapObject(a, j, t, null)) {
883	>	top = s;
884	>	t.doExec();
885	>	}
886	>	}
887	>	}
888	>
889	>	/**
890	>	* Polls and runs tasks until empty.
891	>	*/
892	>	private void pollAndExecAll() {
893	>	for (ForkJoinTask<?> t; (t = poll()) != null;)
894	>	t.doExec();
895	>	}
896	>
897	>	/**
898	>	* If present, removes from queue and executes the given task,
899	>	* or any other cancelled task. Returns (true) on any CAS
900	>	* or consistency check failure so caller can retry.
901	>	*
902	>	* @return false if no progress can be made, else true;
903	>	*/
904	>	final boolean tryRemoveAndExec(ForkJoinTask<?> task) {
905	>	boolean stat = true, removed = false, empty = true;
906	>	ForkJoinTask<?>[] a; int m, s, b, n;
907	>	if ((a = array) != null && (m = a.length - 1) >= 0 &&
908	>	(n = (s = top) - (b = base)) > 0) {
909	>	for (ForkJoinTask<?> t;;) {           // traverse from s to b
910	>	int j = ((--s & m) << ASHIFT) + ABASE;
911	>	t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
912	>	if (t == null)                    // inconsistent length
913	>	break;
914	>	else if (t == task) {
915	>	if (s + 1 == top) {           // pop
916	>	if (!U.compareAndSwapObject(a, j, task, null))
917	>	break;
918	>	top = s;
919	>	removed = true;
920	>	}
921	>	else if (base == b)           // replace with proxy
922	>	removed = U.compareAndSwapObject(a, j, task,
923	>	new EmptyTask());
924	>	break;
925	>	}
926	>	else if (t.status >= 0)
927	>	empty = false;
928	>	else if (s + 1 == top) {          // pop and throw away
929	>	if (U.compareAndSwapObject(a, j, t, null))
930	>	top = s;
931	>	break;
932	>	}
933	>	if (--n == 0) {
934	>	if (!empty && base == b)
935	>	stat = false;
936	>	break;
937	>	}
938	>	}
939	>	}
940	>	if (removed)
941	>	task.doExec();
942	>	return stat;
943	>	}
944	>
945	>	/**
946	>	* Polls for and executes the given task or any other task in
947	>	* its CountedCompleter computation
948	>	*/
949	>	final boolean pollAndExecCC(ForkJoinTask<?> root) {
950	>	ForkJoinTask<?>[] a; int b; Object o;
951	>	outer: while ((b = base) - top < 0 && (a = array) != null) {
952	>	long j = (((a.length - 1) & b) << ASHIFT) + ABASE;
953	>	if ((o = U.getObject(a, j)) == null ||
954	>	!(o instanceof CountedCompleter))
955	>	break;
956	>	for (CountedCompleter<?> t = (CountedCompleter<?>)o, r = t;;) {
957	>	if (r == root) {
958	>	if (base == b &&
959	>	U.compareAndSwapObject(a, j, t, null)) {
960	>	base = b + 1;
961	>	t.doExec();
962	>	return true;
963	>	}
964	>	else
965	>	break; // restart
966	>	}
967	>	if ((r = r.completer) == null)
968	>	break outer; // not part of root computation
969	>	}
970	>	}
971	>	return false;
972	>	}
973	>
974	>	/**
975	>	* Executes a top-level task and any local tasks remaining
976	>	* after execution.
977	>	*/
978	>	final void runTask(ForkJoinTask<?> t) {
979	>	if (t != null) {
980	>	(currentSteal = t).doExec();
981	>	currentSteal = null;
982	>	if (++nsteals < 0) {     // spill on overflow
983	>	ForkJoinPool p;
984	>	if ((p = pool) != null)
985	>	p.collectStealCount(this);
986	>	}
987	>	if (top != base) {       // process remaining local tasks
988	>	if (mode == 0)
989	>	popAndExecAll();
990	>	else
991	>	pollAndExecAll();
992	>	}
993	>	}
994	>	}
995	>
996	>	/**
997	>	* Executes a non-top-level (stolen) task.
998	>	*/
999	>	final void runSubtask(ForkJoinTask<?> t) {
1000	>	if (t != null) {
1001	>	ForkJoinTask<?> ps = currentSteal;
1002	>	(currentSteal = t).doExec();
1003	>	currentSteal = ps;
1004	>	}
1005	>	}
1006	>
1007	>	/**
1008	>	* Returns true if owned and not known to be blocked.
1009	>	*/
1010	>	final boolean isApparentlyUnblocked() {
1011	>	Thread wt; Thread.State s;
1012	>	return (eventCount >= 0 &&
1013	>	(wt = owner) != null &&
1014	>	(s = wt.getState()) != Thread.State.BLOCKED &&
1015	>	s != Thread.State.WAITING &&
1016	>	s != Thread.State.TIMED_WAITING);
1017	>	}
1018	>
1019	>	/**
1020	>	* If this owned and is not already interrupted, try to
1021	>	* interrupt and/or unpark, ignoring exceptions.
1022	>	*/
1023	>	final void interruptOwner() {
1024	>	Thread wt, p;
1025	>	if ((wt = owner) != null && !wt.isInterrupted()) {
1026	>	try {
1027	>	wt.interrupt();
1028	>	} catch (SecurityException ignore) {
1029	>	}
1030	>	}
1031	>	if ((p = parker) != null)
1032	>	U.unpark(p);
1033	>	}
1034	>
1035	>	// Unsafe mechanics
1036	>	private static final sun.misc.Unsafe U;
1037	>	private static final long QLOCK;
1038	>	private static final int ABASE;
1039	>	private static final int ASHIFT;
1040	>	static {
1041	>	int s;
1042	>	try {
1043	>	U = getUnsafe();
1044	>	Class<?> k = WorkQueue.class;
1045	>	Class<?> ak = ForkJoinTask[].class;
1046	>	QLOCK = U.objectFieldOffset
1047	>	(k.getDeclaredField("qlock"));
1048	>	ABASE = U.arrayBaseOffset(ak);
1049	>	s = U.arrayIndexScale(ak);
1050	>	} catch (Exception e) {
1051	>	throw new Error(e);
1052	>	}
1053	>	if ((s & (s-1)) != 0)
1054	>	throw new Error("data type scale not a power of two");
1055	>	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
1056	>	}
1057		}
1058
1059		/**
1060	<	* Generator for assigning sequence numbers as pool names.
1060	>	* Per-thread records for threads that submit to pools. Currently
1061	>	* holds only pseudo-random seed / index that is used to choose
1062	>	* submission queues in method externalPush. In the future, this may
1063	>	* also incorporate a means to implement different task rejection
1064	>	* and resubmission policies.
1065	>	*
1066	>	* Seeds for submitters and workers/workQueues work in basically
1067	>	* the same way but are initialized and updated using slightly
1068	>	* different mechanics. Both are initialized using the same
1069	>	* approach as in class ThreadLocal, where successive values are
1070	>	* unlikely to collide with previous values. Seeds are then
1071	>	* randomly modified upon collisions using xorshifts, which
1072	>	* requires a non-zero seed.
1073		*/
1074	<	private static final AtomicInteger poolNumberGenerator =
1075	<	new AtomicInteger();
1074	>	static final class Submitter {
1075	>	int seed;
1076	>	Submitter(int s) { seed = s; }
1077	>	}
1078
1079	<	/**
1080	<	* The time to block in a join (see awaitJoin) before checking if
1081	<	* a new worker should be (re)started to maintain parallelism
1082	<	* level. The value should be short enough to maintain global
1083	<	* responsiveness and progress but long enough to avoid
425	<	* counterproductive firings during GC stalls or unrelated system
426	<	* activity, and to not bog down systems with continual re-firings
427	<	* on GCs or legitimately long waits.
428	<	*/
429	<	private static final long JOIN_TIMEOUT_MILLIS = 250L; // 4 per second
1079	>	/** Property prefix for constructing common pool */
1080	>	private static final String propPrefix =
1081	>	"java.util.concurrent.ForkJoinPool.common.";
1082	>
1083	>	// static fields (initialized in static initializer below)
1084
1085		/**
1086	<	* The wakeup interval (in nanoseconds) for the oldest worker
1087	<	* worker waiting for an event invokes tryShutdownUnusedWorker to shrink
434	<	* the number of workers.  The exact value does not matter too
435	<	* much, but should be long enough to slowly release resources
436	<	* during long periods without use without disrupting normal use.
1086	>	* Creates a new ForkJoinWorkerThread. This factory is used unless
1087	>	* overridden in ForkJoinPool constructors.
1088		*/
1089	<	private static final long SHRINK_RATE_NANOS =
1090	<	30L * 1000L * 1000L * 1000L; // 2 per minute
1089	>	public static final ForkJoinWorkerThreadFactory
1090	>	defaultForkJoinWorkerThreadFactory;
1091
1092		/**
1093	<	* Absolute bound for parallelism level. Twice this number plus
1094	<	* one (i.e., 0xfff) must fit into a 16bit field to enable
1095	<	* word-packing for some counts and indices.
1093	>	* Common (static) pool. Non-null for public use unless a static
1094	>	* construction exception, but internal usages null-check on use
1095	>	* to paranoically avoid potential initialization circularities
1096	>	* as well as to simplify generated code.
1097		*/
1098	<	private static final int MAX_WORKERS   = 0x7fff;
1098	>	static final ForkJoinPool commonPool;
1099
1100		/**
1101	<	* Array holding all worker threads in the pool.  Array size must
1102	<	* be a power of two.  Updates and replacements are protected by
451	<	* workerLock, but the array is always kept in a consistent enough
452	<	* state to be randomly accessed without locking by workers
453	<	* performing work-stealing, as well as other traversal-based
454	<	* methods in this class. All readers must tolerate that some
455	<	* array slots may be null.
1101	>	* Permission required for callers of methods that may start or
1102	>	* kill threads.
1103		*/
1104	<	volatile ForkJoinWorkerThread[] workers;
1104	>	private static final RuntimePermission modifyThreadPermission;
1105
1106		/**
1107	<	* Queue for external submissions.
1107	>	* Per-thread submission bookkeeping. Shared across all pools
1108	>	* to reduce ThreadLocal pollution and because random motion
1109	>	* to avoid contention in one pool is likely to hold for others.
1110	>	* Lazily initialized on first submission (but null-checked
1111	>	* in other contexts to avoid unnecessary initialization).
1112		*/
1113	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
1113	>	static final ThreadLocal<Submitter> submitters;
1114
1115		/**
1116	<	* Lock protecting updates to workers array.
1116	>	* Common pool parallelism. Must equal commonPool.parallelism.
1117		*/
1118	<	private final ReentrantLock workerLock;
1118	>	static final int commonPoolParallelism;
1119
1120		/**
1121	<	* Latch released upon termination.
1121	>	* Sequence number for creating workerNamePrefix.
1122		*/
1123	<	private final Phaser termination;
1123	>	private static int poolNumberSequence;
1124
1125		/**
1126	<	* Creation factory for worker threads.
1126	>	* Return the next sequence number. We don't expect this to
1127	>	* ever contend so use simple builtin sync.
1128		*/
1129	<	private final ForkJoinWorkerThreadFactory factory;
1129	>	private static final synchronized int nextPoolId() {
1130	>	return ++poolNumberSequence;
1131	>	}
1132	>
1133	>	// static constants
1134
1135		/**
1136	<	* Sum of per-thread steal counts, updated only when threads are
1137	<	* idle or terminating.
1136	>	* Initial timeout value (in nanoseconds) for the thread
1137	>	* triggering quiescence to park waiting for new work. On timeout,
1138	>	* the thread will instead try to shrink the number of
1139	>	* workers. The value should be large enough to avoid overly
1140	>	* aggressive shrinkage during most transient stalls (long GCs
1141	>	* etc).
1142		*/
1143	<	private volatile long stealCount;
1143	>	private static final long IDLE_TIMEOUT      = 2000L * 1000L * 1000L; // 2sec
1144
1145		/**
1146	<	* Encoded record of top of Treiber stack of threads waiting for
487	<	* events. The top 32 bits contain the count being waited for. The
488	<	* bottom 16 bits contains one plus the pool index of waiting
489	<	* worker thread. (Bits 16-31 are unused.)
1146	>	* Timeout value when there are more threads than parallelism level
1147		*/
1148	<	private volatile long eventWaiters;
492	<
493	<	private static final int  EVENT_COUNT_SHIFT = 32;
494	<	private static final long WAITER_ID_MASK    = (1L << 16) - 1L;
1148	>	private static final long FAST_IDLE_TIMEOUT =  200L * 1000L * 1000L;
1149
1150		/**
1151	<	* A counter for events that may wake up worker threads:
1152	<	*   - Submission of a new task to the pool
1153	<	*   - A worker pushing a task on an empty queue
1154	<	*   - termination
1151	>	* The maximum stolen->joining link depth allowed in method
1152	>	* tryHelpStealer.  Must be a power of two.  Depths for legitimate
1153	>	* chains are unbounded, but we use a fixed constant to avoid
1154	>	* (otherwise unchecked) cycles and to bound staleness of
1155	>	* traversal parameters at the expense of sometimes blocking when
1156	>	* we could be helping.
1157		*/
1158	<	private volatile int eventCount;
1158	>	private static final int MAX_HELP = 64;
1159
1160		/**
1161	<	* Encoded record of top of Treiber stack of spare threads waiting
1162	<	* for resumption. The top 16 bits contain an arbitrary count to
507	<	* avoid ABA effects. The bottom 16bits contains one plus the pool
508	<	* index of waiting worker thread.
1161	>	* Increment for seed generators. See class ThreadLocal for
1162	>	* explanation.
1163		*/
1164	<	private volatile int spareWaiters;
511	<
512	<	private static final int SPARE_COUNT_SHIFT = 16;
513	<	private static final int SPARE_ID_MASK     = (1 << 16) - 1;
1164	>	private static final int SEED_INCREMENT = 0x61c88647;
1165
1166		/**
1167	<	* Lifecycle control. The low word contains the number of workers
1168	<	* that are (probably) executing tasks. This value is atomically
1169	<	* incremented before a worker gets a task to run, and decremented
1170	<	* when worker has no tasks and cannot find any.  Bits 16-18
1171	<	* contain runLevel value. When all are zero, the pool is
1172	<	* running. Level transitions are monotonic (running -> shutdown
1173	<	* -> terminating -> terminated) so each transition adds a bit.
1174	<	* These are bundled together to ensure consistent read for
1175	<	* termination checks (i.e., that runLevel is at least SHUTDOWN
1176	<	* and active threads is zero).
1167	>	* Bits and masks for control variables
1168	>	*
1169	>	* Field ctl is a long packed with:
1170	>	* AC: Number of active running workers minus target parallelism (16 bits)
1171	>	* TC: Number of total workers minus target parallelism (16 bits)
1172	>	* ST: true if pool is terminating (1 bit)
1173	>	* EC: the wait count of top waiting thread (15 bits)
1174	>	* ID: poolIndex of top of Treiber stack of waiters (16 bits)
1175	>	*
1176	>	* When convenient, we can extract the upper 32 bits of counts and
1177	>	* the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
1178	>	* (int)ctl.  The ec field is never accessed alone, but always
1179	>	* together with id and st. The offsets of counts by the target
1180	>	* parallelism and the positionings of fields makes it possible to
1181	>	* perform the most common checks via sign tests of fields: When
1182	>	* ac is negative, there are not enough active workers, when tc is
1183	>	* negative, there are not enough total workers, and when e is
1184	>	* negative, the pool is terminating.  To deal with these possibly
1185	>	* negative fields, we use casts in and out of "short" and/or
1186	>	* signed shifts to maintain signedness.
1187		*
1188	<	* Notes: Most direct CASes are dependent on these bitfield
1189	<	* positions.  Also, this field is non-private to enable direct
1190	<	* performance-sensitive CASes in ForkJoinWorkerThread.
1188	>	* When a thread is queued (inactivated), its eventCount field is
1189	>	* set negative, which is the only way to tell if a worker is
1190	>	* prevented from executing tasks, even though it must continue to
1191	>	* scan for them to avoid queuing races. Note however that
1192	>	* eventCount updates lag releases so usage requires care.
1193	>	*
1194	>	* Field plock is an int packed with:
1195	>	* SHUTDOWN: true if shutdown is enabled (1 bit)
1196	>	* SEQ:  a sequence lock, with PL_LOCK bit set if locked (30 bits)
1197	>	* SIGNAL: set when threads may be waiting on the lock (1 bit)
1198	>	*
1199	>	* The sequence number enables simple consistency checks:
1200	>	* Staleness of read-only operations on the workQueues array can
1201	>	* be checked by comparing plock before vs after the reads.
1202		*/
531	–	volatile int runState;
1203
1204	<	// Note: The order among run level values matters.
1205	<	private static final int RUNLEVEL_SHIFT     = 16;
1206	<	private static final int SHUTDOWN           = 1 << RUNLEVEL_SHIFT;
1207	<	private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
1208	<	private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
538	<	private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
1204	>	// bit positions/shifts for fields
1205	>	private static final int  AC_SHIFT   = 48;
1206	>	private static final int  TC_SHIFT   = 32;
1207	>	private static final int  ST_SHIFT   = 31;
1208	>	private static final int  EC_SHIFT   = 16;
1209
1210	<	/**
1211	<	* Holds number of total (i.e., created and not yet terminated)
1212	<	* and running (i.e., not blocked on joins or other managed sync)
1213	<	* threads, packed together to ensure consistent snapshot when
1214	<	* making decisions about creating and suspending spare
1215	<	* threads. Updated only by CAS. Note that adding a new worker
1216	<	* requires incrementing both counts, since workers start off in
547	<	* running state.
548	<	*/
549	<	private volatile int workerCounts;
1210	>	// bounds
1211	>	private static final int  SMASK      = 0xffff;  // short bits
1212	>	private static final int  MAX_CAP    = 0x7fff;  // max #workers - 1
1213	>	private static final int  EVENMASK   = 0xfffe;  // even short bits
1214	>	private static final int  SQMASK     = 0x007e;  // max 64 (even) slots
1215	>	private static final int  SHORT_SIGN = 1 << 15;
1216	>	private static final int  INT_SIGN   = 1 << 31;
1217
1218	<	private static final int TOTAL_COUNT_SHIFT  = 16;
1219	<	private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1;
1220	<	private static final int ONE_RUNNING        = 1;
1221	<	private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
1218	>	// masks
1219	>	private static final long STOP_BIT   = 0x0001L << ST_SHIFT;
1220	>	private static final long AC_MASK    = ((long)SMASK) << AC_SHIFT;
1221	>	private static final long TC_MASK    = ((long)SMASK) << TC_SHIFT;
1222
1223	<	/**
1224	<	* The target parallelism level.
1225	<	* Accessed directly by ForkJoinWorkerThreads.
559	<	*/
560	<	final int parallelism;
1223	>	// units for incrementing and decrementing
1224	>	private static final long TC_UNIT    = 1L << TC_SHIFT;
1225	>	private static final long AC_UNIT    = 1L << AC_SHIFT;
1226
1227	<	/**
1228	<	* True if use local fifo, not default lifo, for local polling
1229	<	* Read by, and replicated by ForkJoinWorkerThreads
1230	<	*/
1231	<	final boolean locallyFifo;
1227	>	// masks and units for dealing with u = (int)(ctl >>> 32)
1228	>	private static final int  UAC_SHIFT  = AC_SHIFT - 32;
1229	>	private static final int  UTC_SHIFT  = TC_SHIFT - 32;
1230	>	private static final int  UAC_MASK   = SMASK << UAC_SHIFT;
1231	>	private static final int  UTC_MASK   = SMASK << UTC_SHIFT;
1232	>	private static final int  UAC_UNIT   = 1 << UAC_SHIFT;
1233	>	private static final int  UTC_UNIT   = 1 << UTC_SHIFT;
1234
1235	<	/**
1236	<	* The uncaught exception handler used when any worker abruptly
1237	<	* terminates.
571	<	*/
572	<	private final Thread.UncaughtExceptionHandler ueh;
1235	>	// masks and units for dealing with e = (int)ctl
1236	>	private static final int E_MASK      = 0x7fffffff; // no STOP_BIT
1237	>	private static final int E_SEQ       = 1 << EC_SHIFT;
1238
1239	<	/**
1240	<	* Pool number, just for assigning useful names to worker threads
1241	<	*/
1242	<	private final int poolNumber;
1239	>	// plock bits
1240	>	private static final int SHUTDOWN    = 1 << 31;
1241	>	private static final int PL_LOCK     = 2;
1242	>	private static final int PL_SIGNAL   = 1;
1243	>	private static final int PL_SPINS    = 1 << 8;
1244
1245	<	// Utilities for CASing fields. Note that most of these
1246	<	// are usually manually inlined by callers
1245	>	// access mode for WorkQueue
1246	>	static final int LIFO_QUEUE          =  0;
1247	>	static final int FIFO_QUEUE          =  1;
1248	>	static final int SHARED_QUEUE        = -1;
1249
1250	<	/**
583	<	* Increments running count part of workerCounts
584	<	*/
585	<	final void incrementRunningCount() {
586	<	int c;
587	<	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
588	<	c = workerCounts,
589	<	c + ONE_RUNNING));
590	<	}
1250	>	// Instance fields
1251
1252	<	/**
1253	<	* Tries to decrement running count unless already zero
1254	<	*/
1255	<	final boolean tryDecrementRunningCount() {
1256	<	int wc = workerCounts;
1257	<	if ((wc & RUNNING_COUNT_MASK) == 0)
1258	<	return false;
1259	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1260	<	wc, wc - ONE_RUNNING);
1261	<	}
1252	>	/*
1253	>	* Field layout order in this class tends to matter more than one
1254	>	* would like. Runtime layout order is only loosely related to
1255	>	* declaration order and may differ across JVMs, but the following
1256	>	* empirically works OK on current JVMs.
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 indexSeed;                    // worker/submitter index seed
1263	>	volatile int plock;                        // shutdown status and seqLock
1264	>	WorkQueue[] workQueues;                    // main registry
1265	>	final ForkJoinWorkerThreadFactory factory; // factory for new workers
1266	>	final Thread.UncaughtExceptionHandler ueh; // per-worker UEH
1267	>	final String workerNamePrefix;             // to create worker name string
1268
1269	<	/**
1270	<	* Forces decrement of encoded workerCounts, awaiting nonzero if
1271	<	* (rarely) necessary when other count updates lag.
1272	<	*
1273	<	* @param dr -- either zero or ONE_RUNNING
1274	<	* @param dt == either zero or ONE_TOTAL
1269	>	/*
1270	>	* Acquires the plock lock to protect worker array and related
1271	>	* updates. This method is called only if an initial CAS on plock
1272	>	* fails. This acts as a spinLock for normal cases, but falls back
1273	>	* to builtin monitor to block when (rarely) needed. This would be
1274	>	* a terrible idea for a highly contended lock, but works fine as
1275	>	* a more conservative alternative to a pure spinlock.  See
1276	>	* internal ConcurrentHashMap documentation for further
1277	>	* explanation of nearly the same construction.
1278		*/
1279	<	private void decrementWorkerCounts(int dr, int dt) {
1279	>	private int acquirePlock() {
1280	>	int spins = PL_SPINS, r = 0, ps, nps;
1281		for (;;) {
1282	<	int wc = workerCounts;
1283	<	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
1284	<	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) {
1285	<	if ((runState & TERMINATED) != 0)
1286	<	return; // lagging termination on a backout
1287	<	Thread.yield();
1282	>	if (((ps = plock) & PL_LOCK) == 0 &&
1283	>	U.compareAndSwapInt(this, PLOCK, ps, nps = ps + PL_LOCK))
1284	>	return nps;
1285	>	else if (r == 0)
1286	>	r = ThreadLocalRandom.current().nextInt(); // randomize spins
1287	>	else if (spins >= 0) {
1288	>	r ^= r << 1; r ^= r >>> 3; r ^= r << 10; // xorshift
1289	>	if (r >= 0)
1290	>	--spins;
1291	>	}
1292	>	else if (U.compareAndSwapInt(this, PLOCK, ps, ps | PL_SIGNAL)) {
1293	>	synchronized(this) {
1294	>	if ((plock & PL_SIGNAL) != 0) {
1295	>	try {
1296	>	wait();
1297	>	} catch (InterruptedException ie) {
1298	>	try {
1299	>	Thread.currentThread().interrupt();
1300	>	} catch (SecurityException ignore) {
1301	>	}
1302	>	}
1303	>	}
1304	>	else
1305	>	notifyAll();
1306	>	}
1307		}
619	–	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
620	–	wc, wc - (dr + dt)))
621	–	return;
1308		}
1309		}
1310
1311		/**
1312	<	* Tries decrementing active count; fails on contention.
1313	<	* Called when workers cannot find tasks to run.
1312	>	* Unlocks and signals any thread waiting for plock. Called only
1313	>	* when CAS of seq value for unlock fails.
1314		*/
1315	<	final boolean tryDecrementActiveCount() {
1316	<	int c;
1317	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
1318	<	c = runState, c - 1);
1315	>	private void releasePlock(int ps) {
1316	>	plock = ps;
1317	>	synchronized(this) { notifyAll(); }
1318	>	}
1319	>
1320	>	//  Registering and deregistering workers
1321	>
1322	>	/**
1323	>	* Callback from ForkJoinWorkerThread constructor to establish its
1324	>	* poolIndex and record its WorkQueue. To avoid scanning bias due
1325	>	* to packing entries in front of the workQueues array, we treat
1326	>	* the array as a simple power-of-two hash table using per-thread
1327	>	* seed as hash, expanding as needed.
1328	>	*
1329	>	* @param w the worker's queue
1330	>	*/
1331	>	final void registerWorker(WorkQueue w) {
1332	>	int s, ps; // generate a rarely colliding candidate index seed
1333	>	do {} while (!U.compareAndSwapInt(this, INDEXSEED,
1334	>	s = indexSeed, s += SEED_INCREMENT) ||
1335	>	s == 0); // skip 0
1336	>	if (((ps = plock) & PL_LOCK) != 0 ||
1337	>	!U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
1338	>	ps = acquirePlock();
1339	>	int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
1340	>	try {
1341	>	WorkQueue[] ws;
1342	>	if (w != null && (ws = workQueues) != null) {
1343	>	w.seed = s;
1344	>	int n = ws.length, m = n - 1;
1345	>	int r = (s << 1) | 1;               // use odd-numbered indices
1346	>	if (ws[r &= m] != null) {           // collision
1347	>	int probes = 0;                 // step by approx half size
1348	>	int step = (n <= 4) ? 2 : ((n >>> 1) & EVENMASK) + 2;
1349	>	while (ws[r = (r + step) & m] != null) {
1350	>	if (++probes >= n) {
1351	>	workQueues = ws = Arrays.copyOf(ws, n <<= 1);
1352	>	m = n - 1;
1353	>	probes = 0;
1354	>	}
1355	>	}
1356	>	}
1357	>	w.eventCount = w.poolIndex = r;     // establish before recording
1358	>	ws[r] = w;
1359	>	}
1360	>	} finally {
1361	>	if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
1362	>	releasePlock(nps);
1363	>	}
1364		}
1365
1366		/**
1367	<	* Advances to at least the given level. Returns true if not
1368	<	* already in at least the given level.
1369	<	*/
1370	<	private boolean advanceRunLevel(int level) {
1371	<	for (;;) {
1372	<	int s = runState;
1373	<	if ((s & level) != 0)
1374	<	return false;
1375	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level))
1376	<	return true;
1367	>	* Final callback from terminating worker, as well as upon failure
1368	>	* to construct or start a worker.  Removes record of worker from
1369	>	* array, and adjusts counts. If pool is shutting down, tries to
1370	>	* complete termination.
1371	>	*
1372	>	* @param wt the worker thread or null if construction failed
1373	>	* @param ex the exception causing failure, or null if none
1374	>	*/
1375	>	final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
1376	>	WorkQueue w = null;
1377	>	if (wt != null && (w = wt.workQueue) != null) {
1378	>	int ps;
1379	>	collectStealCount(w);
1380	>	w.qlock = -1;                // ensure set
1381	>	if (((ps = plock) & PL_LOCK) != 0 ||
1382	>	!U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
1383	>	ps = acquirePlock();
1384	>	int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
1385	>	try {
1386	>	int idx = w.poolIndex;
1387	>	WorkQueue[] ws = workQueues;
1388	>	if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w)
1389	>	ws[idx] = null;
1390	>	} finally {
1391	>	if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
1392	>	releasePlock(nps);
1393	>	}
1394		}
647	–	}
1395
1396	<	// workers array maintenance
1396	>	long c;                             // adjust ctl counts
1397	>	do {} while (!U.compareAndSwapLong
1398	>	(this, CTL, c = ctl, (((c - AC_UNIT) & AC_MASK) |
1399	>	((c - TC_UNIT) & TC_MASK) |
1400	>	(c & ~(AC_MASK|TC_MASK)))));
1401	>
1402	>	if (!tryTerminate(false, false) && w != null) {
1403	>	w.cancelAll();                  // cancel remaining tasks
1404	>	if (w.array != null)            // suppress signal if never ran
1405	>	signalWork(null, 1);        // wake up or create replacement
1406	>	if (ex == null)                 // help clean refs on way out
1407	>	ForkJoinTask.helpExpungeStaleExceptions();
1408	>	}
1409	>
1410	>	if (ex != null)                     // rethrow
1411	>	ForkJoinTask.rethrow(ex);
1412	>	}
1413
1414		/**
1415	<	* Records and returns a workers array index for new worker.
1416	<	*/
1417	<	private int recordWorker(ForkJoinWorkerThread w) {
1418	<	// Try using slot totalCount-1. If not available, scan and/or resize
1419	<	int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1;
1420	<	final ReentrantLock lock = this.workerLock;
1421	<	lock.lock();
1422	<	try {
1423	<	ForkJoinWorkerThread[] ws = workers;
1424	<	int n = ws.length;
1425	<	if (k < 0 || k >= n || ws[k] != null) {
1426	<	for (k = 0; k < n && ws[k] != null; ++k)
1427	<	;
1428	<	if (k == n)
1429	<	ws = Arrays.copyOf(ws, n << 1);
1415	>	* Collect worker steal count into total. Called on termination
1416	>	* and upon int overflow of local count. (There is a possible race
1417	>	* in the latter case vs any caller of getStealCount, which can
1418	>	* make its results less accurate than usual.)
1419	>	*/
1420	>	final void collectStealCount(WorkQueue w) {
1421	>	if (w != null) {
1422	>	long sc;
1423	>	int ns = w.nsteals;
1424	>	w.nsteals = 0; // handle overflow
1425	>	long steals = (ns >= 0) ? ns : 1L + (long)(Integer.MAX_VALUE);
1426	>	do {} while (!U.compareAndSwapLong(this, STEALCOUNT,
1427	>	sc = stealCount, sc + steals));
1428	>	}
1429	>	}
1430	>
1431	>	// Submissions
1432	>
1433	>	/**
1434	>	* Unless shutting down, adds the given task to a submission queue
1435	>	* at submitter's current queue index (modulo submission
1436	>	* range). Only the most common path is directly handled in this
1437	>	* method. All others are relayed to fullExternalPush.
1438	>	*
1439	>	* @param task the task. Caller must ensure non-null.
1440	>	*/
1441	>	final void externalPush(ForkJoinTask<?> task) {
1442	>	WorkQueue[] ws; WorkQueue q; Submitter z; int m; ForkJoinTask<?>[] a;
1443	>	if ((z = submitters.get()) != null && plock > 0 &&
1444	>	(ws = workQueues) != null && (m = (ws.length - 1)) >= 0 &&
1445	>	(q = ws[m & z.seed & SQMASK]) != null &&
1446	>	U.compareAndSwapInt(q, QLOCK, 0, 1)) { // lock
1447	>	int s = q.top, n;
1448	>	if ((a = q.array) != null && a.length > (n = s + 1 - q.base)) {
1449	>	U.putObject(a, (long)(((a.length - 1) & s) << ASHIFT) + ABASE,
1450	>	task);
1451	>	q.top = s + 1;                     // push on to deque
1452	>	q.qlock = 0;
1453	>	if (n <= 1)
1454	>	signalWork(q, 1);
1455	>	return;
1456		}
1457	<	ws[k] = w;
669	<	workers = ws; // volatile array write ensures slot visibility
670	<	} finally {
671	<	lock.unlock();
1457	>	q.qlock = 0;
1458		}
1459	<	return k;
1459	>	fullExternalPush(task);
1460		}
1461
1462		/**
1463	<	* Nulls out record of worker in workers array
1464	<	*/
1465	<	private void forgetWorker(ForkJoinWorkerThread w) {
1466	<	int idx = w.poolIndex;
1467	<	// Locking helps method recordWorker avoid unnecessary expansion
1468	<	final ReentrantLock lock = this.workerLock;
1469	<	lock.lock();
1470	<	try {
1471	<	ForkJoinWorkerThread[] ws = workers;
1472	<	if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify
1473	<	ws[idx] = null;
1474	<	} finally {
1475	<	lock.unlock();
1463	>	* Full version of externalPush. This method is called, among
1464	>	* other times, upon the first submission of the first task to the
1465	>	* pool, so must perform secondary initialization: creating
1466	>	* workQueue array and setting plock to a valid value. It also
1467	>	* detects first submission by an external thread by looking up
1468	>	* its ThreadLocal, and creates a new shared queue if the one at
1469	>	* index if empty or contended. The lock bodies must be
1470	>	* exception-free (so no try/finally) so we optimistically
1471	>	* allocate new queues/arrays outside the locks and throw them
1472	>	* away if (very rarely) not needed. Note that the plock seq value
1473	>	* can eventually wrap around zero, but if so harmlessly fails to
1474	>	* reinitialize.
1475	>	*/
1476	>	private void fullExternalPush(ForkJoinTask<?> task) {
1477	>	for (Submitter z = null;;) {
1478	>	WorkQueue[] ws; WorkQueue q; int ps, m, r, s;
1479	>	if ((ps = plock) < 0)
1480	>	throw new RejectedExecutionException();
1481	>	else if ((ws = workQueues) == null || (m = ws.length - 1) < 0) {
1482	>	int n = parallelism - 1; n |= n >>> 1; n |= n >>> 2;
1483	>	n |= n >>> 4; n |= n >>> 8; n |= n >>> 16;
1484	>	WorkQueue[] nws = new WorkQueue[(n + 1) << 1]; // power of two
1485	>	if ((ps & PL_LOCK) != 0 ||
1486	>	!U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
1487	>	ps = acquirePlock();
1488	>	if ((ws = workQueues) == null)
1489	>	workQueues = nws;
1490	>	int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
1491	>	if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
1492	>	releasePlock(nps);
1493	>	}
1494	>	else if (z == null && (z = submitters.get()) == null) {
1495	>	if (U.compareAndSwapInt(this, INDEXSEED,
1496	>	s = indexSeed, s += SEED_INCREMENT) &&
1497	>	s != 0) // skip 0
1498	>	submitters.set(z = new Submitter(s));
1499	>	}
1500	>	else {
1501	>	int k = (r = z.seed) & m & SQMASK;
1502	>	if ((q = ws[k]) == null && (ps & PL_LOCK) == 0) {
1503	>	(q = new WorkQueue(this, null, SHARED_QUEUE)).poolIndex = k;
1504	>	if (((ps = plock) & PL_LOCK) != 0 ||
1505	>	!U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
1506	>	ps = acquirePlock();
1507	>	WorkQueue w = null;
1508	>	if ((ws = workQueues) != null && k < ws.length &&
1509	>	(w = ws[k]) == null)
1510	>	ws[k] = q;
1511	>	else
1512	>	q = w;
1513	>	int nps = (ps & SHUTDOWN) | ((ps + PL_LOCK) & ~SHUTDOWN);
1514	>	if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
1515	>	releasePlock(nps);
1516	>	}
1517	>	if (q != null && q.qlock == 0 && q.fullPush(task, false))
1518	>	return;
1519	>	r ^= r << 13;                // same xorshift as WorkQueues
1520	>	r ^= r >>> 17;
1521	>	z.seed = r ^= r << 5;        // move to a different index
1522	>	}
1523		}
1524		}
1525
1526	+	// Maintaining ctl counts
1527	+
1528		/**
1529	<	* Final callback from terminating worker.  Removes record of
695	<	* worker from array, and adjusts counts. If pool is shutting
696	<	* down, tries to complete termination.
697	<	*
698	<	* @param w the worker
1529	>	* Increments active count; mainly called upon return from blocking.
1530		*/
1531	<	final void workerTerminated(ForkJoinWorkerThread w) {
1532	<	forgetWorker(w);
1533	<	decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL);
703	<	while (w.stealCount != 0) // collect final count
704	<	tryAccumulateStealCount(w);
705	<	tryTerminate(false);
1531	>	final void incrementActiveCount() {
1532	>	long c;
1533	>	do {} while (!U.compareAndSwapLong(this, CTL, c = ctl, c + AC_UNIT));
1534		}
1535
708	–	// Waiting for and signalling events
709	–
1536		/**
1537	<	* Releases workers blocked on a count not equal to current count.
1538	<	* Normally called after precheck that eventWaiters isn't zero to
1539	<	* avoid wasted array checks. Gives up upon a change in count or
1540	<	* upon releasing two workers, letting others take over.
1541	<	*/
1542	<	private void releaseEventWaiters() {
1543	<	ForkJoinWorkerThread[] ws = workers;
1544	<	int n = ws.length;
1545	<	long h = eventWaiters;
1546	<	int ec = eventCount;
1547	<	boolean releasedOne = false;
1548	<	ForkJoinWorkerThread w; int id;
1549	<	while ((id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 &&
1550	<	(int)(h >>> EVENT_COUNT_SHIFT) != ec &&
1551	<	id < n && (w = ws[id]) != null) {
1552	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
1553	<	h,  w.nextWaiter)) {
1554	<	LockSupport.unpark(w);
1555	<	if (releasedOne) // exit on second release
1537	>	* Tries to create (at most one) or activate (possibly several)
1538	>	* workers if too few are active. On contention failure, continues
1539	>	* until at least one worker is signalled or the given queue is
1540	>	* empty or all workers are active.
1541	>	*
1542	>	* @param q if non-null, the queue holding tasks to be signalled
1543	>	* @param signals the target number of signals.
1544	>	*/
1545	>	final void signalWork(WorkQueue q, int signals) {
1546	>	long c; int e, u, i; WorkQueue[] ws; WorkQueue w; Thread p;
1547	>	while ((u = (int)((c = ctl) >>> 32)) < 0) {
1548	>	if ((e = (int)c) > 0) {
1549	>	if ((ws = workQueues) != null && ws.length > (i = e & SMASK) &&
1550	>	(w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) {
1551	>	long nc = (((long)(w.nextWait & E_MASK)) |
1552	>	((long)(u + UAC_UNIT) << 32));
1553	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1554	>	w.eventCount = (e + E_SEQ) & E_MASK;
1555	>	if ((p = w.parker) != null)
1556	>	U.unpark(p);
1557	>	if (--signals <= 0)
1558	>	break;
1559	>	}
1560	>	else
1561	>	signals = 1;
1562	>	if ((q != null && q.queueSize() == 0))
1563	>	break;
1564	>	}
1565	>	else
1566	>	break;
1567	>	}
1568	>	else if (e == 0 && (u & SHORT_SIGN) != 0) {
1569	>	long nc = (long)(((u + UTC_UNIT) & UTC_MASK) |
1570	>	((u + UAC_UNIT) & UAC_MASK)) << 32;
1571	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1572	>	ForkJoinWorkerThread wt = null;
1573	>	Throwable ex = null;
1574	>	boolean started = false;
1575	>	try {
1576	>	ForkJoinWorkerThreadFactory fac;
1577	>	if ((fac = factory) != null &&
1578	>	(wt = fac.newThread(this)) != null) {
1579	>	wt.start();
1580	>	started = true;
1581	>	}
1582	>	} catch (Throwable rex) {
1583	>	ex = rex;
1584	>	}
1585	>	if (!started)
1586	>	deregisterWorker(wt, ex); // adjust counts on failure
1587		break;
1588	<	releasedOne = true;
1588	>	}
1589		}
1590	<	if (eventCount != ec)
1590	>	else
1591		break;
735	–	h = eventWaiters;
1592		}
1593		}
1594
1595	+	// Scanning for tasks
1596	+
1597		/**
1598	<	* Tries to advance eventCount and releases waiters. Called only
741	<	* from workers.
1598	>	* Top-level runloop for workers, called by ForkJoinWorkerThread.run.
1599		*/
1600	<	final void signalWork() {
1601	<	int c; // try to increment event count -- CAS failure OK
1602	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
1603	<	if (eventWaiters != 0L)
747	<	releaseEventWaiters();
1600	>	final void runWorker(WorkQueue w) {
1601	>	// initialize queue array in this thread
1602	>	w.array = new ForkJoinTask<?>[WorkQueue.INITIAL_QUEUE_CAPACITY];
1603	>	do { w.runTask(scan(w)); } while (w.qlock >= 0);
1604		}
1605
1606		/**
1607	<	* Adds the given worker to event queue and blocks until
1608	<	* terminating or event count advances from the given value
1609	<	*
1610	<	* @param w the calling worker thread
1611	<	* @param ec the count
1612	<	*/
1613	<	private void eventSync(ForkJoinWorkerThread w, int ec) {
1614	<	long nh = (((long)ec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
1615	<	long h;
1616	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
1617	<	(((int)((h = eventWaiters) & WAITER_ID_MASK)) == 0 ||
1618	<	(int)(h >>> EVENT_COUNT_SHIFT) == ec) &&
1619	<	eventCount == ec) {
1620	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
1621	<	w.nextWaiter = h, nh)) {
1622	<	awaitEvent(w, ec);
1623	<	break;
1607	>	* Scans for and, if found, returns one task, else possibly
1608	>	* inactivates the worker. This method operates on single reads of
1609	>	* volatile state and is designed to be re-invoked continuously,
1610	>	* in part because it returns upon detecting inconsistencies,
1611	>	* contention, or state changes that indicate possible success on
1612	>	* re-invocation.
1613	>	*
1614	>	* The scan searches for tasks across a random permutation of
1615	>	* queues (starting at a random index and stepping by a random
1616	>	* relative prime, checking each at least once).  The scan
1617	>	* terminates upon either finding a non-empty queue, or completing
1618	>	* the sweep. If the worker is not inactivated, it takes and
1619	>	* returns a task from this queue. Otherwise, if not activated, it
1620	>	* signals workers (that may include itself) and returns so caller
1621	>	* can retry. Also returns for trtry if the worker array may have
1622	>	* changed during an empty scan.  On failure to find a task, we
1623	>	* take one of the following actions, after which the caller will
1624	>	* retry calling this method unless terminated.
1625	>	*
1626	>	* * If pool is terminating, terminate the worker.
1627	>	*
1628	>	* * If not already enqueued, try to inactivate and enqueue the
1629	>	* worker on wait queue. Or, if inactivating has caused the pool
1630	>	* to be quiescent, relay to idleAwaitWork to check for
1631	>	* termination and possibly shrink pool.
1632	>	*
1633	>	* * If already enqueued and none of the above apply, possibly
1634	>	* (with 1/2 probablility) park awaiting signal, else lingering to
1635	>	* help scan and signal.
1636	>	*
1637	>	* @param w the worker (via its WorkQueue)
1638	>	* @return a task or null if none found
1639	>	*/
1640	>	private final ForkJoinTask<?> scan(WorkQueue w) {
1641	>	WorkQueue[] ws; WorkQueue q;           // first update random seed
1642	>	int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
1643	>	int ps = plock, m;                     // volatile read order matters
1644	>	if ((ws = workQueues) != null && (m = ws.length - 1) > 0) {
1645	>	int ec = w.eventCount;             // ec is negative if inactive
1646	>	int step = (r >>> 16) | 1;         // relatively prime
1647	>	for (int j = (m + 1) << 2;  ; --j, r += step) {
1648	>	ForkJoinTask<?> t; ForkJoinTask<?>[] a; int b, n;
1649	>	if ((q = ws[r & m]) != null && (b = q.base) - q.top < 0 &&
1650	>	(a = q.array) != null) {   // probably nonempty
1651	>	int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
1652	>	t = (ForkJoinTask<?>)U.getObjectVolatile(a, i);
1653	>	if (q.base == b && ec >= 0 && t != null &&
1654	>	U.compareAndSwapObject(a, i, t, null)) {
1655	>	if ((n = q.top - (q.base = b + 1)) > 0)
1656	>	signalWork(q, n);
1657	>	return t;              // taken
1658	>	}
1659	>	if (j < m || (ec < 0 && (ec = w.eventCount) < 0)) {
1660	>	if ((n = q.queueSize() - 1) > 0)
1661	>	signalWork(q, n);
1662	>	break;                 // let caller retry after signal
1663	>	}
1664	>	}
1665	>	else if (j < 0) {              // end of scan
1666	>	long c = ctl; int e;
1667	>	if (plock != ps)           // incomplete sweep
1668	>	break;
1669	>	if ((e = (int)c) < 0)      // pool is terminating
1670	>	w.qlock = -1;
1671	>	else if (ec >= 0) {        // try to enqueue/inactivate
1672	>	long nc = ((long)ec |
1673	>	((c - AC_UNIT) & (AC_MASK|TC_MASK)));
1674	>	w.nextWait = e;
1675	>	w.eventCount = ec | INT_SIGN; // mark as inactive
1676	>	if (ctl != c ||
1677	>	!U.compareAndSwapLong(this, CTL, c, nc))
1678	>	w.eventCount = ec; // unmark on CAS failure
1679	>	else if ((int)(c >> AC_SHIFT) == 1 - parallelism)
1680	>	idleAwaitWork(w, nc, c);  // quiescent
1681	>	}
1682	>	else if (w.seed >= 0 && w.eventCount < 0) {
1683	>	Thread wt = Thread.currentThread();
1684	>	Thread.interrupted();  // clear status
1685	>	U.putObject(wt, PARKBLOCKER, this);
1686	>	w.parker = wt;         // emulate LockSupport.park
1687	>	if (w.eventCount < 0)  // recheck
1688	>	U.park(false, 0L);
1689	>	w.parker = null;
1690	>	U.putObject(wt, PARKBLOCKER, null);
1691	>	}
1692	>	break;
1693	>	}
1694		}
1695		}
1696	+	return null;
1697		}
1698
1699		/**
1700	<	* Blocks the given worker (that has already been entered as an
1701	<	* event waiter) until terminating or event count advances from
1702	<	* the given value. The oldest (first) waiter uses a timed wait to
1703	<	* occasionally one-by-one shrink the number of workers (to a
1704	<	* minimum of one) if the pool has not been used for extended
1705	<	* periods.
1706	<	*
1707	<	* @param w the calling worker thread
1708	<	* @param ec the count
1709	<	*/
1710	<	private void awaitEvent(ForkJoinWorkerThread w, int ec) {
1711	<	while (eventCount == ec) {
1712	<	if (tryAccumulateStealCount(w)) { // transfer while idle
1713	<	boolean untimed = (w.nextWaiter != 0L ||
1714	<	(workerCounts & RUNNING_COUNT_MASK) <= 1);
1715	<	long startTime = untimed? 0 : System.nanoTime();
1716	<	Thread.interrupted();         // clear/ignore interrupt
1717	<	if (eventCount != ec || w.runState != 0 ||
1718	<	runState >= TERMINATING)  // recheck after clear
1700	>	* If inactivating worker w has caused the pool to become
1701	>	* quiescent, checks for pool termination, and, so long as this is
1702	>	* not the only worker, waits for event for up to a given
1703	>	* duration.  On timeout, if ctl has not changed, terminates the
1704	>	* worker, which will in turn wake up another worker to possibly
1705	>	* repeat this process.
1706	>	*
1707	>	* @param w the calling worker
1708	>	* @param currentCtl the ctl value triggering possible quiescence
1709	>	* @param prevCtl the ctl value to restore if thread is terminated
1710	>	*/
1711	>	private void idleAwaitWork(WorkQueue w, long currentCtl, long prevCtl) {
1712	>	if (w.eventCount < 0 &&
1713	>	(this == commonPool || !tryTerminate(false, false)) &&
1714	>	(int)prevCtl != 0) {
1715	>	int dc = -(short)(currentCtl >>> TC_SHIFT);
1716	>	long parkTime = dc < 0 ? FAST_IDLE_TIMEOUT: (dc + 1) * IDLE_TIMEOUT;
1717	>	long deadline = System.nanoTime() + parkTime - 100000L; // 1ms slop
1718	>	Thread wt = Thread.currentThread();
1719	>	while (ctl == currentCtl) {
1720	>	Thread.interrupted();  // timed variant of version in scan()
1721	>	U.putObject(wt, PARKBLOCKER, this);
1722	>	w.parker = wt;
1723	>	if (ctl == currentCtl)
1724	>	U.park(false, parkTime);
1725	>	w.parker = null;
1726	>	U.putObject(wt, PARKBLOCKER, null);
1727	>	if (ctl != currentCtl)
1728	>	break;
1729	>	if (deadline - System.nanoTime() <= 0L &&
1730	>	U.compareAndSwapLong(this, CTL, currentCtl, prevCtl)) {
1731	>	w.eventCount = (w.eventCount + E_SEQ) | E_MASK;
1732	>	w.qlock = -1;   // shrink
1733		break;
793	–	if (untimed)
794	–	LockSupport.park(w);
795	–	else {
796	–	LockSupport.parkNanos(w, SHRINK_RATE_NANOS);
797	–	if (eventCount != ec || w.runState != 0 ||
798	–	runState >= TERMINATING)
799	–	break;
800	–	if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS)
801	–	tryShutdownUnusedWorker(ec);
1734		}
1735		}
1736		}
1737		}
1738
807	–	// Maintaining parallelism
808	–
1739		/**
1740	<	* Pushes worker onto the spare stack
1740	>	* Scans through queues looking for work while joining a task;
1741	>	* if any are present, signals.
1742	>	*
1743	>	* @param task to return early if done
1744	>	* @param origin an index to start scan
1745		*/
1746	<	final void pushSpare(ForkJoinWorkerThread w) {
1747	<	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1);
1748	<	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
1749	<	w.nextSpare = spareWaiters,ns));
1746	>	final int helpSignal(ForkJoinTask<?> task, int origin) {
1747	>	WorkQueue[] ws; WorkQueue q; int m, n, s;
1748	>	if (task != null && (ws = workQueues) != null &&
1749	>	(m = ws.length - 1) >= 0) {
1750	>	for (int i = 0; i <= m; ++i) {
1751	>	if ((s = task.status) < 0)
1752	>	return s;
1753	>	if ((q = ws[(i + origin) & m]) != null &&
1754	>	(n = q.queueSize()) > 0) {
1755	>	signalWork(q, n);
1756	>	if ((int)(ctl >> AC_SHIFT) >= 0)
1757	>	break;
1758	>	}
1759	>	}
1760	>	}
1761	>	return 0;
1762		}
1763
1764		/**
1765	<	* Tries (once) to resume a spare if the number of running
1766	<	* threads is less than target.
1767	<	*/
1768	<	private void tryResumeSpare() {
1769	<	int sw, id;
1770	<	ForkJoinWorkerThread[] ws = workers;
1771	<	int n = ws.length;
1772	<	ForkJoinWorkerThread w;
1773	<	if ((sw = spareWaiters) != 0 &&
1774	<	(id = (sw & SPARE_ID_MASK) - 1) >= 0 &&
1775	<	id < n && (w = ws[id]) != null &&
1776	<	(workerCounts & RUNNING_COUNT_MASK) < parallelism &&
1777	<	spareWaiters == sw &&
1778	<	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
1779	<	sw, w.nextSpare)) {
1780	<	int c; // increment running count before resume
1781	<	do {} while(!UNSAFE.compareAndSwapInt
1782	<	(this, workerCountsOffset,
1783	<	c = workerCounts, c + ONE_RUNNING));
1784	<	if (w.tryUnsuspend())
1785	<	LockSupport.unpark(w);
1786	<	else   // back out if w was shutdown
1787	<	decrementWorkerCounts(ONE_RUNNING, 0);
1765	>	* Tries to locate and execute tasks for a stealer of the given
1766	>	* task, or in turn one of its stealers, Traces currentSteal ->
1767	>	* currentJoin links looking for a thread working on a descendant
1768	>	* of the given task and with a non-empty queue to steal back and
1769	>	* execute tasks from. The first call to this method upon a
1770	>	* waiting join will often entail scanning/search, (which is OK
1771	>	* because the joiner has nothing better to do), but this method
1772	>	* leaves hints in workers to speed up subsequent calls. The
1773	>	* implementation is very branchy to cope with potential
1774	>	* inconsistencies or loops encountering chains that are stale,
1775	>	* unknown, or so long that they are likely cyclic.
1776	>	*
1777	>	* @param joiner the joining worker
1778	>	* @param task the task to join
1779	>	* @return 0 if no progress can be made, negative if task
1780	>	* known complete, else positive
1781	>	*/
1782	>	private int tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
1783	>	int stat = 0, steps = 0;                    // bound to avoid cycles
1784	>	if (joiner != null && task != null) {       // hoist null checks
1785	>	restart: for (;;) {
1786	>	ForkJoinTask<?> subtask = task;     // current target
1787	>	for (WorkQueue j = joiner, v;;) {   // v is stealer of subtask
1788	>	WorkQueue[] ws; int m, s, h;
1789	>	if ((s = task.status) < 0) {
1790	>	stat = s;
1791	>	break restart;
1792	>	}
1793	>	if ((ws = workQueues) == null || (m = ws.length - 1) <= 0)
1794	>	break restart;              // shutting down
1795	>	if ((v = ws[h = (j.stealHint | 1) & m]) == null ||
1796	>	v.currentSteal != subtask) {
1797	>	for (int origin = h;;) {    // find stealer
1798	>	if (((h = (h + 2) & m) & 15) == 1 &&
1799	>	(subtask.status < 0 || j.currentJoin != subtask))
1800	>	continue restart;   // occasional staleness check
1801	>	if ((v = ws[h]) != null &&
1802	>	v.currentSteal == subtask) {
1803	>	j.stealHint = h;    // save hint
1804	>	break;
1805	>	}
1806	>	if (h == origin)
1807	>	break restart;      // cannot find stealer
1808	>	}
1809	>	}
1810	>	for (;;) { // help stealer or descend to its stealer
1811	>	ForkJoinTask[] a;  int b;
1812	>	if (subtask.status < 0)     // surround probes with
1813	>	continue restart;       //   consistency checks
1814	>	if ((b = v.base) - v.top < 0 && (a = v.array) != null) {
1815	>	int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
1816	>	ForkJoinTask<?> t =
1817	>	(ForkJoinTask<?>)U.getObjectVolatile(a, i);
1818	>	if (subtask.status < 0 || j.currentJoin != subtask ||
1819	>	v.currentSteal != subtask)
1820	>	continue restart;   // stale
1821	>	stat = 1;               // apparent progress
1822	>	if (t != null && v.base == b &&
1823	>	U.compareAndSwapObject(a, i, t, null)) {
1824	>	v.base = b + 1;     // help stealer
1825	>	joiner.runSubtask(t);
1826	>	}
1827	>	else if (v.base == b && ++steps == MAX_HELP)
1828	>	break restart;      // v apparently stalled
1829	>	}
1830	>	else {                      // empty -- try to descend
1831	>	ForkJoinTask<?> next = v.currentJoin;
1832	>	if (subtask.status < 0 || j.currentJoin != subtask ||
1833	>	v.currentSteal != subtask)
1834	>	continue restart;   // stale
1835	>	else if (next == null || ++steps == MAX_HELP)
1836	>	break restart;      // dead-end or maybe cyclic
1837	>	else {
1838	>	subtask = next;
1839	>	j = v;
1840	>	break;
1841	>	}
1842	>	}
1843	>	}
1844	>	}
1845	>	}
1846		}
1847	+	return stat;
1848		}
1849
1850		/**
1851	<	* Tries to increase the number of running workers if below target
1852	<	* parallelism: If a spare exists tries to resume it via
1853	<	* tryResumeSpare.  Otherwise, if not enough total workers or all
1854	<	* existing workers are busy, adds a new worker. In all cases also
1855	<	* helps wake up releasable workers waiting for work.
1851	>	* Analog of tryHelpStealer for CountedCompleters. Tries to steal
1852	>	* and run tasks within the target's computation
1853	>	*
1854	>	* @param task the task to join
1855	>	* @param mode if shared, exit upon completing any task
1856	>	* if all workers are active
1857	>	*
1858		*/
1859	<	private void helpMaintainParallelism() {
1860	<	int pc = parallelism;
1861	<	int wc, rs, tc;
1862	<	while (((wc = workerCounts) & RUNNING_COUNT_MASK) < pc &&
1863	<	(rs = runState) < TERMINATING) {
1864	<	if (spareWaiters != 0)
1865	<	tryResumeSpare();
1866	<	else if ((tc = wc >>> TOTAL_COUNT_SHIFT) >= MAX_WORKERS ||
1867	<	(tc >= pc && (rs & ACTIVE_COUNT_MASK) != tc))
1868	<	break;   // enough total
1869	<	else if (runState == rs && workerCounts == wc &&
863	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
864	<	wc + (ONE_RUNNING|ONE_TOTAL))) {
865	<	ForkJoinWorkerThread w = null;
866	<	try {
867	<	w = factory.newThread(this);
868	<	} finally { // adjust on null or exceptional factory return
869	<	if (w == null) {
870	<	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
871	<	tryTerminate(false); // handle failure during shutdown
872	<	}
1859	>	private int helpComplete(ForkJoinTask<?> task, int mode) {
1860	>	WorkQueue[] ws; WorkQueue q; int m, n, s;
1861	>	if (task != null && (ws = workQueues) != null &&
1862	>	(m = ws.length - 1) >= 0) {
1863	>	for (int j = 1, origin = j;;) {
1864	>	if ((s = task.status) < 0)
1865	>	return s;
1866	>	if ((q = ws[j & m]) != null && q.pollAndExecCC(task)) {
1867	>	origin = j;
1868	>	if (mode == SHARED_QUEUE && (int)(ctl >> AC_SHIFT) >= 0)
1869	>	break;
1870		}
1871	<	if (w == null)
1871	>	else if ((j = (j + 2) & m) == origin)
1872		break;
876	–	w.start(recordWorker(w), ueh);
877	–	if ((workerCounts >>> TOTAL_COUNT_SHIFT) >= pc) {
878	–	int c; // advance event count
879	–	UNSAFE.compareAndSwapInt(this, eventCountOffset,
880	–	c = eventCount, c+1);
881	–	break; // add at most one unless total below target
882	–	}
883	–	}
884	–	}
885	–	if (eventWaiters != 0L)
886	–	releaseEventWaiters();
887	–	}
888	–
889	–	/**
890	–	* Callback from the oldest waiter in awaitEvent waking up after a
891	–	* period of non-use. If all workers are idle, tries (once) to
892	–	* shutdown an event waiter or a spare, if one exists. Note that
893	–	* we don't need CAS or locks here because the method is called
894	–	* only from one thread occasionally waking (and even misfires are
895	–	* OK). Note that until the shutdown worker fully terminates,
896	–	* workerCounts will overestimate total count, which is tolerable.
897	–	*
898	–	* @param ec the event count waited on by caller (to abort
899	–	* attempt if count has since changed).
900	–	*/
901	–	private void tryShutdownUnusedWorker(int ec) {
902	–	if (runState == 0 && eventCount == ec) { // only trigger if all idle
903	–	ForkJoinWorkerThread[] ws = workers;
904	–	int n = ws.length;
905	–	ForkJoinWorkerThread w = null;
906	–	boolean shutdown = false;
907	–	int sw;
908	–	long h;
909	–	if ((sw = spareWaiters) != 0) { // prefer killing spares
910	–	int id = (sw & SPARE_ID_MASK) - 1;
911	–	if (id >= 0 && id < n && (w = ws[id]) != null &&
912	–	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
913	–	sw, w.nextSpare))
914	–	shutdown = true;
915	–	}
916	–	else if ((h = eventWaiters) != 0L) {
917	–	long nh;
918	–	int id = ((int)(h & WAITER_ID_MASK)) - 1;
919	–	if (id >= 0 && id < n && (w = ws[id]) != null &&
920	–	(nh = w.nextWaiter) != 0L && // keep at least one worker
921	–	UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh))
922	–	shutdown = true;
923	–	}
924	–	if (w != null && shutdown) {
925	–	w.shutdown();
926	–	LockSupport.unpark(w);
927	–	}
928	–	}
929	–	releaseEventWaiters(); // in case of interference
930	–	}
931	–
932	–	/**
933	–	* Callback from workers invoked upon each top-level action (i.e.,
934	–	* stealing a task or taking a submission and running it).
935	–	* Performs one or more of the following:
936	–	*
937	–	* 1. If the worker is active and either did not run a task
938	–	*    or there are too many workers, try to set its active status
939	–	*    to inactive and update activeCount. On contention, we may
940	–	*    try again in this or a subsequent call.
941	–	*
942	–	* 2. If not enough total workers, help create some.
943	–	*
944	–	* 3. If there are too many running workers, suspend this worker
945	–	*    (first forcing inactive if necessary).  If it is not needed,
946	–	*    it may be shutdown while suspended (via
947	–	*    tryShutdownUnusedWorker).  Otherwise, upon resume it
948	–	*    rechecks running thread count and need for event sync.
949	–	*
950	–	* 4. If worker did not run a task, await the next task event via
951	–	*    eventSync if necessary (first forcing inactivation), upon
952	–	*    which the worker may be shutdown via
953	–	*    tryShutdownUnusedWorker.  Otherwise, help release any
954	–	*    existing event waiters that are now releasable,
955	–	*
956	–	* @param w the worker
957	–	* @param ran true if worker ran a task since last call to this method
958	–	*/
959	–	final void preStep(ForkJoinWorkerThread w, boolean ran) {
960	–	int wec = w.lastEventCount;
961	–	boolean active = w.active;
962	–	boolean inactivate = false;
963	–	int pc = parallelism;
964	–	int rs;
965	–	while (w.runState == 0 && (rs = runState) < TERMINATING) {
966	–	if ((inactivate || (active && (rs & ACTIVE_COUNT_MASK) >= pc)) &&
967	–	UNSAFE.compareAndSwapInt(this, runStateOffset, rs, rs - 1))
968	–	inactivate = active = w.active = false;
969	–	int wc = workerCounts;
970	–	if ((wc & RUNNING_COUNT_MASK) > pc) {
971	–	if (!(inactivate |= active) && // must inactivate to suspend
972	–	workerCounts == wc &&      // try to suspend as spare
973	–	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
974	–	wc, wc - ONE_RUNNING))
975	–	w.suspendAsSpare();
976	–	}
977	–	else if ((wc >>> TOTAL_COUNT_SHIFT) < pc)
978	–	helpMaintainParallelism();     // not enough workers
979	–	else if (!ran) {
980	–	long h = eventWaiters;
981	–	int ec = eventCount;
982	–	if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != ec)
983	–	releaseEventWaiters();     // release others before waiting
984	–	else if (ec != wec) {
985	–	w.lastEventCount = ec;     // no need to wait
986	–	break;
987	–	}
988	–	else if (!(inactivate |= active))
989	–	eventSync(w, wec);         // must inactivate before sync
1873		}
991	–	else
992	–	break;
1874		}
1875	+	return 0;
1876		}
1877
1878		/**
1879	<	* Helps and/or blocks awaiting join of the given task.
1880	<	* See above for explanation.
1881	<	*
1882	<	* @param joinMe the task to join
1883	<	* @param worker the current worker thread
1884	<	*/
1885	<	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) {
1886	<	int retries = 2 + (parallelism >> 2); // #helpJoins before blocking
1887	<	while (joinMe.status >= 0) {
1888	<	int wc;
1889	<	worker.helpJoinTask(joinMe);
1890	<	if (joinMe.status < 0)
1891	<	break;
1892	<	else if (retries > 0)
1893	<	--retries;
1894	<	else if (((wc = workerCounts) & RUNNING_COUNT_MASK) != 0 &&
1895	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1896	<	wc, wc - ONE_RUNNING)) {
1897	<	int stat, c; long h;
1898	<	while ((stat = joinMe.status) >= 0 &&
1899	<	(h = eventWaiters) != 0L && // help release others
1900	<	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1901	<	releaseEventWaiters();
1902	<	if (stat >= 0 &&
1903	<	((workerCounts & RUNNING_COUNT_MASK) == 0 ||
1904	<	(stat =
1905	<	joinMe.internalAwaitDone(JOIN_TIMEOUT_MILLIS)) >= 0))
1906	<	helpMaintainParallelism(); // timeout or no running workers
1907	<	do {} while (!UNSAFE.compareAndSwapInt
1908	<	(this, workerCountsOffset,
1909	<	c = workerCounts, c + ONE_RUNNING));
1910	<	if (stat < 0)
1911	<	break;   // else restart
1879	>	* Tries to decrement active count (sometimes implicitly) and
1880	>	* possibly release or create a compensating worker in preparation
1881	>	* for blocking. Fails on contention or termination. Otherwise,
1882	>	* adds a new thread if no idle workers are available and pool
1883	>	* may become starved.
1884	>	*/
1885	>	final boolean tryCompensate() {
1886	>	int pc = parallelism, e, u, i, tc; long c;
1887	>	WorkQueue[] ws; WorkQueue w; Thread p;
1888	>	if ((e = (int)(c = ctl)) >= 0 && (ws = workQueues) != null) {
1889	>	if (e != 0 && (i = e & SMASK) < ws.length &&
1890	>	(w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) {
1891	>	long nc = ((long)(w.nextWait & E_MASK) |
1892	>	(c & (AC_MASK|TC_MASK)));
1893	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1894	>	w.eventCount = (e + E_SEQ) & E_MASK;
1895	>	if ((p = w.parker) != null)
1896	>	U.unpark(p);
1897	>	return true;   // replace with idle worker
1898	>	}
1899	>	}
1900	>	else if ((short)((u = (int)(c >>> 32)) >>> UTC_SHIFT) >= 0 &&
1901	>	(u >> UAC_SHIFT) + pc > 1) {
1902	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
1903	>	if (U.compareAndSwapLong(this, CTL, c, nc))
1904	>	return true;    // no compensation
1905	>	}
1906	>	else if ((tc = u + pc) < MAX_CAP) {
1907	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
1908	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1909	>	Throwable ex = null;
1910	>	ForkJoinWorkerThread wt = null;
1911	>	try {
1912	>	ForkJoinWorkerThreadFactory fac;
1913	>	if ((fac = factory) != null &&
1914	>	(wt = fac.newThread(this)) != null) {
1915	>	wt.start();
1916	>	return true;
1917	>	}
1918	>	} catch (Throwable rex) {
1919	>	ex = rex;
1920	>	}
1921	>	deregisterWorker(wt, ex); // adjust counts etc
1922	>	}
1923		}
1924		}
1925	+	return false;
1926		}
1927
1928		/**
1929	<	* Same idea as awaitJoin, but no helping, retries, or timeouts.
1929	>	* Helps and/or blocks until the given task is done.
1930	>	*
1931	>	* @param joiner the joining worker
1932	>	* @param task the task
1933	>	* @return task status on exit
1934		*/
1935	<	final void awaitBlocker(ManagedBlocker blocker)
1936	<	throws InterruptedException {
1937	<	while (!blocker.isReleasable()) {
1938	<	int wc = workerCounts;
1939	<	if ((wc & RUNNING_COUNT_MASK) != 0 &&
1940	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1941	<	wc, wc - ONE_RUNNING)) {
1942	<	try {
1943	<	while (!blocker.isReleasable()) {
1944	<	long h = eventWaiters;
1945	<	if (h != 0L &&
1946	<	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1947	<	releaseEventWaiters();
1948	<	else if ((workerCounts & RUNNING_COUNT_MASK) == 0 &&
1949	<	runState < TERMINATING)
1950	<	helpMaintainParallelism();
1951	<	else if (blocker.block())
1952	<	break;
1935	>	final int awaitJoin(WorkQueue joiner, ForkJoinTask<?> task) {
1936	>	int s = 0;
1937	>	if (joiner != null && task != null && (s = task.status) >= 0) {
1938	>	ForkJoinTask<?> prevJoin = joiner.currentJoin;
1939	>	joiner.currentJoin = task;
1940	>	do {} while ((s = task.status) >= 0 &&
1941	>	joiner.queueSize() > 0 &&
1942	>	joiner.tryRemoveAndExec(task)); // process local tasks
1943	>	if (s >= 0 && (s = task.status) >= 0 &&
1944	>	(s = helpSignal(task, joiner.poolIndex)) >= 0 &&
1945	>	(task instanceof CountedCompleter))
1946	>	s = helpComplete(task, LIFO_QUEUE);
1947	>	while (s >= 0 && (s = task.status) >= 0) {
1948	>	if ((joiner.queueSize() > 0 ||           // try helping
1949	>	(s = tryHelpStealer(joiner, task)) == 0) &&
1950	>	(s = task.status) >= 0 && tryCompensate()) {
1951	>	if (task.trySetSignal() && (s = task.status) >= 0) {
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	<	} finally {
1964	<	int c;
1965	<	do {} while (!UNSAFE.compareAndSwapInt
1059	<	(this, workerCountsOffset,
1060	<	c = workerCounts, c + ONE_RUNNING));
1963	>	long c;                          // re-activate
1964	>	do {} while (!U.compareAndSwapLong
1965	>	(this, CTL, c = ctl, c + AC_UNIT));
1966		}
1062	–	break;
1967		}
1968	+	joiner.currentJoin = prevJoin;
1969		}
1970	+	return s;
1971		}
1972
1973		/**
1974	<	* Possibly initiates and/or completes termination.
1974	>	* Stripped-down variant of awaitJoin used by timed joins. Tries
1975	>	* to help join only while there is continuous progress. (Caller
1976	>	* will then enter a timed wait.)
1977		*
1978	<	* @param now if true, unconditionally terminate, else only
1979	<	* if shutdown and empty queue and no active workers
1072	<	* @return true if now terminating or terminated
1978	>	* @param joiner the joining worker
1979	>	* @param task the task
1980		*/
1981	<	private boolean tryTerminate(boolean now) {
1982	<	if (now)
1983	<	advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
1984	<	else if (runState < SHUTDOWN ||
1985	<	!submissionQueue.isEmpty() ||
1986	<	(runState & ACTIVE_COUNT_MASK) != 0)
1987	<	return false;
1981	>	final void helpJoinOnce(WorkQueue joiner, ForkJoinTask<?> task) {
1982	>	int s;
1983	>	if (joiner != null && task != null && (s = task.status) >= 0) {
1984	>	ForkJoinTask<?> prevJoin = joiner.currentJoin;
1985	>	joiner.currentJoin = task;
1986	>	do {} while ((s = task.status) >= 0 &&
1987	>	joiner.queueSize() > 0 &&
1988	>	joiner.tryRemoveAndExec(task));
1989	>	if (s >= 0 && (s = task.status) >= 0 &&
1990	>	(s = helpSignal(task, joiner.poolIndex)) >= 0 &&
1991	>	(task instanceof CountedCompleter))
1992	>	s = helpComplete(task, LIFO_QUEUE);
1993	>	if (s >= 0 && joiner.queueSize() == 0) {
1994	>	do {} while (task.status >= 0 &&
1995	>	tryHelpStealer(joiner, task) > 0);
1996	>	}
1997	>	joiner.currentJoin = prevJoin;
1998	>	}
1999	>	}
2000
2001	<	if (advanceRunLevel(TERMINATING))
2002	<	startTerminating();
2001	>	/**
2002	>	* Returns a (probably) non-empty steal queue, if one is found
2003	>	* during a random, then cyclic scan, else null.  This method must
2004	>	* be retried by caller if, by the time it tries to use the queue,
2005	>	* it is empty.
2006	>	* @param r a (random) seed for scanning
2007	>	*/
2008	>	private WorkQueue findNonEmptyStealQueue(int r) {
2009	>	int step = (r >>> 16) | 1;
2010	>	for (WorkQueue[] ws;;) {
2011	>	int ps = plock, m;
2012	>	if ((ws = workQueues) == null || (m = ws.length - 1) < 1)
2013	>	return null;
2014	>	for (int j = (m + 1) << 2; ; r += step) {
2015	>	WorkQueue q = ws[((r << 1) | 1) & m];
2016	>	if (q != null && q.queueSize() > 0)
2017	>	return q;
2018	>	else if (--j < 0) {
2019	>	if (plock == ps)
2020	>	return null;
2021	>	break;
2022	>	}
2023	>	}
2024	>	}
2025	>	}
2026
2027	<	// Finish now if all threads terminated; else in some subsequent call
2028	<	if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
2029	<	advanceRunLevel(TERMINATED);
2030	<	termination.arrive();
2031	<	}
2032	<	return true;
2027	>	/**
2028	>	* Runs tasks until {@code isQuiescent()}. We piggyback on
2029	>	* active count ctl maintenance, but rather than blocking
2030	>	* when tasks cannot be found, we rescan until all others cannot
2031	>	* find tasks either.
2032	>	*/
2033	>	final void helpQuiescePool(WorkQueue w) {
2034	>	for (boolean active = true;;) {
2035	>	ForkJoinTask<?> localTask; // exhaust local queue
2036	>	while ((localTask = w.nextLocalTask()) != null)
2037	>	localTask.doExec();
2038	>	// Similar to loop in scan(), but ignoring submissions
2039	>	WorkQueue q = findNonEmptyStealQueue(w.nextSeed());
2040	>	if (q != null) {
2041	>	ForkJoinTask<?> t; int b;
2042	>	if (!active) {      // re-establish active count
2043	>	long c;
2044	>	active = true;
2045	>	do {} while (!U.compareAndSwapLong
2046	>	(this, CTL, c = ctl, c + AC_UNIT));
2047	>	}
2048	>	if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
2049	>	w.runSubtask(t);
2050	>	}
2051	>	else {
2052	>	long c;
2053	>	if (active) {       // decrement active count without queuing
2054	>	active = false;
2055	>	do {} while (!U.compareAndSwapLong
2056	>	(this, CTL, c = ctl, c -= AC_UNIT));
2057	>	}
2058	>	else
2059	>	c = ctl;        // re-increment on exit
2060	>	if ((int)(c >> AC_SHIFT) + parallelism == 0) {
2061	>	do {} while (!U.compareAndSwapLong
2062	>	(this, CTL, c = ctl, c + AC_UNIT));
2063	>	break;
2064	>	}
2065	>	}
2066	>	}
2067		}
2068
2069		/**
2070	<	* Actions on transition to TERMINATING
2071	<	*
2072	<	* Runs up to four passes through workers: (0) shutting down each
2073	<	* (without waking up if parked) to quickly spread notifications
2074	<	* without unnecessary bouncing around event queues etc (1) wake
2075	<	* up and help cancel tasks (2) interrupt (3) mop up races with
2076	<	* interrupted workers
2077	<	*/
2078	<	private void startTerminating() {
2079	<	cancelSubmissions();
2080	<	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
2081	<	int c; // advance event count
2082	<	UNSAFE.compareAndSwapInt(this, eventCountOffset,
2083	<	c = eventCount, c+1);
2084	<	eventWaiters = 0L; // clobber lists
2085	<	spareWaiters = 0;
2086	<	ForkJoinWorkerThread[] ws = workers;
2087	<	int n = ws.length;
2088	<	for (int i = 0; i < n; ++i) {
2089	<	ForkJoinWorkerThread w = ws[i];
2090	<	if (w != null) {
2091	<	w.shutdown();
2092	<	if (passes > 0 && !w.isTerminated()) {
2093	<	w.cancelTasks();
2094	<	LockSupport.unpark(w);
2095	<	if (passes > 1) {
2096	<	try {
2097	<	w.interrupt();
2098	<	} catch (SecurityException ignore) {
2070	>	* Gets and removes a local or stolen task for the given worker.
2071	>	*
2072	>	* @return a task, if available
2073	>	*/
2074	>	final ForkJoinTask<?> nextTaskFor(WorkQueue w) {
2075	>	for (ForkJoinTask<?> t;;) {
2076	>	WorkQueue q; int b;
2077	>	if ((t = w.nextLocalTask()) != null)
2078	>	return t;
2079	>	if ((q = findNonEmptyStealQueue(w.nextSeed())) == null)
2080	>	return null;
2081	>	if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
2082	>	return t;
2083	>	}
2084	>	}
2085	>
2086	>	/**
2087	>	* Returns a cheap heuristic guide for task partitioning when
2088	>	* programmers, frameworks, tools, or languages have little or no
2089	>	* idea about task granularity.  In essence by offering this
2090	>	* method, we ask users only about tradeoffs in overhead vs
2091	>	* expected throughput and its variance, rather than how finely to
2092	>	* partition tasks.
2093	>	*
2094	>	* In a steady state strict (tree-structured) computation, each
2095	>	* thread makes available for stealing enough tasks for other
2096	>	* threads to remain active. Inductively, if all threads play by
2097	>	* the same rules, each thread should make available only a
2098	>	* constant number of tasks.
2099	>	*
2100	>	* The minimum useful constant is just 1. But using a value of 1
2101	>	* would require immediate replenishment upon each steal to
2102	>	* maintain enough tasks, which is infeasible.  Further,
2103	>	* partitionings/granularities of offered tasks should minimize
2104	>	* steal rates, which in general means that threads nearer the top
2105	>	* of computation tree should generate more than those nearer the
2106	>	* bottom. In perfect steady state, each thread is at
2107	>	* approximately the same level of computation tree. However,
2108	>	* producing extra tasks amortizes the uncertainty of progress and
2109	>	* diffusion assumptions.
2110	>	*
2111	>	* So, users will want to use values larger, but not much larger
2112	>	* than 1 to both smooth over transient shortages and hedge
2113	>	* against uneven progress; as traded off against the cost of
2114	>	* extra task overhead. We leave the user to pick a threshold
2115	>	* value to compare with the results of this call to guide
2116	>	* decisions, but recommend values such as 3.
2117	>	*
2118	>	* When all threads are active, it is on average OK to estimate
2119	>	* surplus strictly locally. In steady-state, if one thread is
2120	>	* maintaining say 2 surplus tasks, then so are others. So we can
2121	>	* just use estimated queue length.  However, this strategy alone
2122	>	* leads to serious mis-estimates in some non-steady-state
2123	>	* conditions (ramp-up, ramp-down, other stalls). We can detect
2124	>	* many of these by further considering the number of "idle"
2125	>	* threads, that are known to have zero queued tasks, so
2126	>	* compensate by a factor of (#idle/#active) threads.
2127	>	*
2128	>	* Note: The approximation of #busy workers as #active workers is
2129	>	* not very good under current signalling scheme, and should be
2130	>	* improved.
2131	>	*/
2132	>	static int getSurplusQueuedTaskCount() {
2133	>	Thread t; ForkJoinWorkerThread wt; ForkJoinPool pool; WorkQueue q;
2134	>	if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)) {
2135	>	int b = (q = (wt = (ForkJoinWorkerThread)t).workQueue).base;
2136	>	int p = (pool = wt.pool).parallelism;
2137	>	int a = (int)(pool.ctl >> AC_SHIFT) + p;
2138	>	return q.top - b - (a > (p >>>= 1) ? 0 :
2139	>	a > (p >>>= 1) ? 1 :
2140	>	a > (p >>>= 1) ? 2 :
2141	>	a > (p >>>= 1) ? 4 :
2142	>	8);
2143	>	}
2144	>	return 0;
2145	>	}
2146	>
2147	>	//  Termination
2148	>
2149	>	/**
2150	>	* Possibly initiates and/or completes termination.  The caller
2151	>	* triggering termination runs three passes through workQueues:
2152	>	* (0) Setting termination status, followed by wakeups of queued
2153	>	* workers; (1) cancelling all tasks; (2) interrupting lagging
2154	>	* threads (likely in external tasks, but possibly also blocked in
2155	>	* joins).  Each pass repeats previous steps because of potential
2156	>	* lagging thread creation.
2157	>	*
2158	>	* @param now if true, unconditionally terminate, else only
2159	>	* if no work and no active workers
2160	>	* @param enable if true, enable shutdown when next possible
2161	>	* @return true if now terminating or terminated
2162	>	*/
2163	>	private boolean tryTerminate(boolean now, boolean enable) {
2164	>	if (this == commonPool)                     // cannot shut down
2165	>	return false;
2166	>	for (long c;;) {
2167	>	if (((c = ctl) & STOP_BIT) != 0) {      // already terminating
2168	>	if ((short)(c >>> TC_SHIFT) == -parallelism) {
2169	>	synchronized (this) {
2170	>	notifyAll();                // signal when 0 workers
2171	>	}
2172	>	}
2173	>	return true;
2174	>	}
2175	>	if (plock >= 0) {                       // not yet enabled
2176	>	int ps;
2177	>	if (!enable)
2178	>	return false;
2179	>	if (((ps = plock) & PL_LOCK) != 0 ||
2180	>	!U.compareAndSwapInt(this, PLOCK, ps, ps += PL_LOCK))
2181	>	ps = acquirePlock();
2182	>	int nps = SHUTDOWN;
2183	>	if (!U.compareAndSwapInt(this, PLOCK, ps, nps))
2184	>	releasePlock(nps);
2185	>	}
2186	>	if (!now) {                             // check if idle & no tasks
2187	>	if ((int)(c >> AC_SHIFT) != -parallelism ||
2188	>	hasQueuedSubmissions())
2189	>	return false;
2190	>	// Check for unqueued inactive workers. One pass suffices.
2191	>	WorkQueue[] ws = workQueues; WorkQueue w;
2192	>	if (ws != null) {
2193	>	for (int i = 1; i < ws.length; i += 2) {
2194	>	if ((w = ws[i]) != null && w.eventCount >= 0)
2195	>	return false;
2196	>	}
2197	>	}
2198	>	}
2199	>	if (U.compareAndSwapLong(this, CTL, c, c | STOP_BIT)) {
2200	>	for (int pass = 0; pass < 3; ++pass) {
2201	>	WorkQueue[] ws = workQueues;
2202	>	if (ws != null) {
2203	>	WorkQueue w;
2204	>	int n = ws.length;
2205	>	for (int i = 0; i < n; ++i) {
2206	>	if ((w = ws[i]) != null) {
2207	>	w.qlock = -1;
2208	>	if (pass > 0) {
2209	>	w.cancelAll();
2210	>	if (pass > 1)
2211	>	w.interruptOwner();
2212	>	}
2213	>	}
2214	>	}
2215	>	// Wake up workers parked on event queue
2216	>	int i, e; long cc; Thread p;
2217	>	while ((e = (int)(cc = ctl) & E_MASK) != 0 &&
2218	>	(i = e & SMASK) < n &&
2219	>	(w = ws[i]) != null) {
2220	>	long nc = ((long)(w.nextWait & E_MASK) |
2221	>	((cc + AC_UNIT) & AC_MASK) |
2222	>	(cc & (TC_MASK|STOP_BIT)));
2223	>	if (w.eventCount == (e | INT_SIGN) &&
2224	>	U.compareAndSwapLong(this, CTL, cc, nc)) {
2225	>	w.eventCount = (e + E_SEQ) & E_MASK;
2226	>	w.qlock = -1;
2227	>	if ((p = w.parker) != null)
2228	>	U.unpark(p);
2229		}
2230		}
2231		}
#	Line 1128 | Line 2234 | public class ForkJoinPool extends Abstra
2234		}
2235		}
2236
2237	+	// external operations on common pool
2238	+
2239		/**
2240	<	* Clear out and cancel submissions, ignoring exceptions
2240	>	* Returns common pool queue for a thread that has submitted at
2241	>	* least one task.
2242		*/
2243	<	private void cancelSubmissions() {
2244	<	ForkJoinTask<?> task;
2245	<	while ((task = submissionQueue.poll()) != null) {
2246	<	try {
2247	<	task.cancel(false);
2248	<	} catch (Throwable ignore) {
2243	>	static WorkQueue commonSubmitterQueue() {
2244	>	ForkJoinPool p; WorkQueue[] ws; int m; Submitter z;
2245	>	return ((z = submitters.get()) != null &&
2246	>	(p = commonPool) != null &&
2247	>	(ws = p.workQueues) != null &&
2248	>	(m = ws.length - 1) >= 0) ?
2249	>	ws[m & z.seed & SQMASK] : null;
2250	>	}
2251	>
2252	>	/**
2253	>	* Tries to pop the given task from submitter's queue in common pool.
2254	>	*/
2255	>	static boolean tryExternalUnpush(ForkJoinTask<?> t) {
2256	>	ForkJoinPool p; WorkQueue[] ws; WorkQueue q; Submitter z;
2257	>	ForkJoinTask<?>[] a;  int m, s; long j;
2258	>	if ((z = submitters.get()) != null &&
2259	>	(p = commonPool) != null &&
2260	>	(ws = p.workQueues) != null &&
2261	>	(m = ws.length - 1) >= 0 &&
2262	>	(q = ws[m & z.seed & SQMASK]) != null &&
2263	>	(s = q.top) != q.base &&
2264	>	(a = q.array) != null &&
2265	>	U.getObjectVolatile
2266	>	(a, j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE) == t &&
2267	>	U.compareAndSwapInt(q, QLOCK, 0, 1)) {
2268	>	if (q.array == a && q.top == s && // recheck
2269	>	U.compareAndSwapObject(a, j, t, null)) {
2270	>	q.top = s - 1;
2271	>	q.qlock = 0;
2272	>	return true;
2273		}
2274	+	q.qlock = 0;
2275		}
2276	+	return false;
2277		}
2278
1144	–	// misc support for ForkJoinWorkerThread
1145	–
2279		/**
2280	<	* Returns pool number
2281	<	*/
2282	<	final int getPoolNumber() {
2283	<	return poolNumber;
2280	>	* Tries to pop and run local tasks within the same computation
2281	>	* as the given root. On failure, tries to help complete from
2282	>	* other queues via helpComplete.
2283	>	*/
2284	>	private void externalHelpComplete(WorkQueue q, ForkJoinTask<?> root) {
2285	>	ForkJoinTask<?>[] a; int m;
2286	>	if (q != null && (a = q.array) != null && (m = (a.length - 1)) >= 0 &&
2287	>	root != null && root.status >= 0) {
2288	>	for (;;) {
2289	>	int s; Object o; CountedCompleter<?> task = null;
2290	>	if ((s = q.top) - q.base > 0) {
2291	>	long j = ((m & (s - 1)) << ASHIFT) + ABASE;
2292	>	if ((o = U.getObject(a, j)) != null &&
2293	>	(o instanceof CountedCompleter)) {
2294	>	CountedCompleter<?> t = (CountedCompleter<?>)o, r = t;
2295	>	do {
2296	>	if (r == root) {
2297	>	if (U.compareAndSwapInt(q, QLOCK, 0, 1)) {
2298	>	if (q.array == a && q.top == s &&
2299	>	U.compareAndSwapObject(a, j, t, null)) {
2300	>	q.top = s - 1;
2301	>	task = t;
2302	>	}
2303	>	q.qlock = 0;
2304	>	}
2305	>	break;
2306	>	}
2307	>	} while((r = r.completer) != null);
2308	>	}
2309	>	}
2310	>	if (task != null)
2311	>	task.doExec();
2312	>	if (root.status < 0 || (int)(ctl >> AC_SHIFT) >= 0)
2313	>	break;
2314	>	if (task == null) {
2315	>	if (helpSignal(root, q.poolIndex) >= 0)
2316	>	helpComplete(root, SHARED_QUEUE);
2317	>	break;
2318	>	}
2319	>	}
2320	>	}
2321		}
2322
2323		/**
2324	<	* Tries to accumulates steal count from a worker, clearing
2325	<	* the worker's value.
1156	<	*
1157	<	* @return true if worker steal count now zero
2324	>	* Tries to help execute or signal availability of the given task
2325	>	* from submitter's queue in common pool.
2326		*/
2327	<	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
2328	<	int sc = w.stealCount;
2329	<	long c = stealCount;
2330	<	// CAS even if zero, for fence effects
2331	<	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
2332	<	if (sc != 0)
2333	<	w.stealCount = 0;
2334	<	return true;
2327	>	static void externalHelpJoin(ForkJoinTask<?> t) {
2328	>	// Some hard-to-avoid overlap with tryExternalUnpush
2329	>	ForkJoinPool p; WorkQueue[] ws; WorkQueue q, w; Submitter z;
2330	>	ForkJoinTask<?>[] a;  int m, s, n; long j;
2331	>	if (t != null && t.status >= 0 &&
2332	>	(z = submitters.get()) != null &&
2333	>	(p = commonPool) != null &&
2334	>	(ws = p.workQueues) != null &&
2335	>	(m = ws.length - 1) >= 0 &&
2336	>	(q = ws[m & z.seed & SQMASK]) != null &&
2337	>	(a = q.array) != null) {
2338	>	if ((s = q.top) != q.base &&
2339	>	U.getObjectVolatile
2340	>	(a, j = (((a.length - 1) & (s - 1)) << ASHIFT) + ABASE) == t &&
2341	>	U.compareAndSwapInt(q, QLOCK, 0, 1)) {
2342	>	if (q.array == a && q.top == s &&
2343	>	U.compareAndSwapObject(a, j, t, null)) {
2344	>	q.top = s - 1;
2345	>	q.qlock = 0;
2346	>	t.doExec();
2347	>	}
2348	>	else
2349	>	q.qlock = 0;
2350	>	}
2351	>	if (t.status >= 0) {
2352	>	if (t instanceof CountedCompleter)
2353	>	p.externalHelpComplete(q, t);
2354	>	else
2355	>	p.helpSignal(t, q.poolIndex);
2356	>	}
2357		}
1168	–	return sc == 0;
2358		}
2359
2360		/**
2361	<	* Returns the approximate (non-atomic) number of idle threads per
1173	<	* active thread.
2361	>	* Restricted version of helpQuiescePool for external callers
2362		*/
2363	<	final int idlePerActive() {
2364	<	int pc = parallelism; // use parallelism, not rc
2365	<	int ac = runState;    // no mask -- artificially boosts during shutdown
2366	<	// Use exact results for small values, saturate past 4
2367	<	return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
2363	>	static void externalHelpQuiescePool() {
2364	>	ForkJoinPool p; ForkJoinTask<?> t; WorkQueue q; int b;
2365	>	int r = ThreadLocalRandom.current().nextInt();
2366	>	if ((p = commonPool) != null &&
2367	>	(q = p.findNonEmptyStealQueue(r)) != null &&
2368	>	(b = q.base) - q.top < 0 &&
2369	>	(t = q.pollAt(b)) != null)
2370	>	t.doExec();
2371		}
2372
2373	<	// Public and protected methods
2373	>	// Exported methods
2374
2375		// Constructors
2376
#	Line 1226 | Line 2417 | public class ForkJoinPool extends Abstra
2417		* use {@link #defaultForkJoinWorkerThreadFactory}.
2418		* @param handler the handler for internal worker threads that
2419		* terminate due to unrecoverable errors encountered while executing
2420	<	* tasks. For default value, use <code>null</code>.
2420	>	* tasks. For default value, use {@code null}.
2421		* @param asyncMode if true,
2422		* establishes local first-in-first-out scheduling mode for forked
2423		* tasks that are never joined. This mode may be more appropriate
2424		* than default locally stack-based mode in applications in which
2425		* worker threads only process event-style asynchronous tasks.
2426	<	* For default value, use <code>false</code>.
2426	>	* For default value, use {@code false}.
2427		* @throws IllegalArgumentException if parallelism less than or
2428		*         equal to zero, or greater than implementation limit
2429		* @throws NullPointerException if the factory is null
#	Line 1248 | Line 2439 | public class ForkJoinPool extends Abstra
2439		checkPermission();
2440		if (factory == null)
2441		throw new NullPointerException();
2442	<	if (parallelism <= 0 || parallelism > MAX_WORKERS)
2442	>	if (parallelism <= 0 || parallelism > MAX_CAP)
2443		throw new IllegalArgumentException();
2444		this.parallelism = parallelism;
2445		this.factory = factory;
2446		this.ueh = handler;
2447	<	this.locallyFifo = asyncMode;
2448	<	int arraySize = initialArraySizeFor(parallelism);
2449	<	this.workers = new ForkJoinWorkerThread[arraySize];
2450	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
2451	<	this.workerLock = new ReentrantLock();
2452	<	this.termination = new Phaser(1);
2453	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
2447	>	this.localMode = asyncMode ? FIFO_QUEUE : LIFO_QUEUE;
2448	>	long np = (long)(-parallelism); // offset ctl counts
2449	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
2450	>	int pn = nextPoolId();
2451	>	StringBuilder sb = new StringBuilder("ForkJoinPool-");
2452	>	sb.append(Integer.toString(pn));
2453	>	sb.append("-worker-");
2454	>	this.workerNamePrefix = sb.toString();
2455		}
2456
2457		/**
2458	<	* Returns initial power of two size for workers array.
2459	<	* @param pc the initial parallelism level
2460	<	*/
2461	<	private static int initialArraySizeFor(int pc) {
2462	<	// If possible, initially allocate enough space for one spare
2463	<	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
2464	<	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
2465	<	size |= size >>> 1;
2466	<	size |= size >>> 2;
2467	<	size |= size >>> 4;
2468	<	size |= size >>> 8;
2469	<	return size + 1;
2458	>	* Constructor for common pool, suitable only for static initialization.
2459	>	* Basically the same as above, but uses smallest possible initial footprint.
2460	>	*/
2461	>	ForkJoinPool(int parallelism, long ctl,
2462	>	ForkJoinWorkerThreadFactory factory,
2463	>	Thread.UncaughtExceptionHandler handler) {
2464	>	this.parallelism = parallelism;
2465	>	this.ctl = ctl;
2466	>	this.factory = factory;
2467	>	this.ueh = handler;
2468	>	this.localMode = LIFO_QUEUE;
2469	>	this.workerNamePrefix = "ForkJoinPool.commonPool-worker-";
2470		}
2471
1280	–	// Execution methods
1281	–
2472		/**
2473	<	* Common code for execute, invoke and submit
2473	>	* Returns the common pool instance.
2474	>	*
2475	>	* @return the common pool instance
2476		*/
2477	<	private <T> void doSubmit(ForkJoinTask<T> task) {
2478	<	if (task == null)
1287	<	throw new NullPointerException();
1288	<	if (runState >= SHUTDOWN)
1289	<	throw new RejectedExecutionException();
1290	<	submissionQueue.offer(task);
1291	<	int c; // try to increment event count -- CAS failure OK
1292	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
1293	<	helpMaintainParallelism(); // create, start, or resume some workers
2477	>	public static ForkJoinPool commonPool() {
2478	>	return commonPool; // cannot be null (if so, a static init error)
2479		}
2480
2481	+	// Execution methods
2482	+
2483		/**
2484		* Performs the given task, returning its result upon completion.
2485	+	* If the computation encounters an unchecked Exception or Error,
2486	+	* it is rethrown as the outcome of this invocation.  Rethrown
2487	+	* exceptions behave in the same way as regular exceptions, but,
2488	+	* when possible, contain stack traces (as displayed for example
2489	+	* using {@code ex.printStackTrace()}) of both the current thread
2490	+	* as well as the thread actually encountering the exception;
2491	+	* minimally only the latter.
2492		*
2493		* @param task the task
2494		* @return the task's result
#	Line 1303 | Line 2497 | public class ForkJoinPool extends Abstra
2497		*         scheduled for execution
2498		*/
2499		public <T> T invoke(ForkJoinTask<T> task) {
2500	<	doSubmit(task);
2500	>	if (task == null)
2501	>	throw new NullPointerException();
2502	>	externalPush(task);
2503		return task.join();
2504		}
2505
#	Line 1316 | Line 2512 | public class ForkJoinPool extends Abstra
2512		*         scheduled for execution
2513		*/
2514		public void execute(ForkJoinTask<?> task) {
2515	<	doSubmit(task);
2515	>	if (task == null)
2516	>	throw new NullPointerException();
2517	>	externalPush(task);
2518		}
2519
2520		// AbstractExecutorService methods
#	Line 1327 | Line 2525 | public class ForkJoinPool extends Abstra
2525		*         scheduled for execution
2526		*/
2527		public void execute(Runnable task) {
2528	+	if (task == null)
2529	+	throw new NullPointerException();
2530		ForkJoinTask<?> job;
2531		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
2532		job = (ForkJoinTask<?>) task;
2533		else
2534	<	job = ForkJoinTask.adapt(task, null);
2535	<	doSubmit(job);
2534	>	job = new ForkJoinTask.AdaptedRunnableAction(task);
2535	>	externalPush(job);
2536		}
2537
2538		/**
#	Line 1345 | Line 2545 | public class ForkJoinPool extends Abstra
2545		*         scheduled for execution
2546		*/
2547		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
2548	<	doSubmit(task);
2548	>	if (task == null)
2549	>	throw new NullPointerException();
2550	>	externalPush(task);
2551		return task;
2552		}
2553
#	Line 1355 | Line 2557 | public class ForkJoinPool extends Abstra
2557		*         scheduled for execution
2558		*/
2559		public <T> ForkJoinTask<T> submit(Callable<T> task) {
2560	<	ForkJoinTask<T> job = ForkJoinTask.adapt(task);
2561	<	doSubmit(job);
2560	>	ForkJoinTask<T> job = new ForkJoinTask.AdaptedCallable<T>(task);
2561	>	externalPush(job);
2562		return job;
2563		}
2564
#	Line 1366 | Line 2568 | public class ForkJoinPool extends Abstra
2568		*         scheduled for execution
2569		*/
2570		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
2571	<	ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
2572	<	doSubmit(job);
2571	>	ForkJoinTask<T> job = new ForkJoinTask.AdaptedRunnable<T>(task, result);
2572	>	externalPush(job);
2573		return job;
2574		}
2575
#	Line 1377 | Line 2579 | public class ForkJoinPool extends Abstra
2579		*         scheduled for execution
2580		*/
2581		public ForkJoinTask<?> submit(Runnable task) {
2582	+	if (task == null)
2583	+	throw new NullPointerException();
2584		ForkJoinTask<?> job;
2585		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
2586		job = (ForkJoinTask<?>) task;
2587		else
2588	<	job = ForkJoinTask.adapt(task, null);
2589	<	doSubmit(job);
2588	>	job = new ForkJoinTask.AdaptedRunnableAction(task);
2589	>	externalPush(job);
2590		return job;
2591		}
2592
#	Line 1391 | Line 2595 | public class ForkJoinPool extends Abstra
2595		* @throws RejectedExecutionException {@inheritDoc}
2596		*/
2597		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
2598	<	ArrayList<ForkJoinTask<T>> forkJoinTasks =
2599	<	new ArrayList<ForkJoinTask<T>>(tasks.size());
2600	<	for (Callable<T> task : tasks)
2601	<	forkJoinTasks.add(ForkJoinTask.adapt(task));
2602	<	invoke(new InvokeAll<T>(forkJoinTasks));
2603	<
2598	>	// In previous versions of this class, this method constructed
2599	>	// a task to run ForkJoinTask.invokeAll, but now external
2600	>	// invocation of multiple tasks is at least as efficient.
2601	>	List<ForkJoinTask<T>> fs = new ArrayList<ForkJoinTask<T>>(tasks.size());
2602	>	// Workaround needed because method wasn't declared with
2603	>	// wildcards in return type but should have been.
2604		@SuppressWarnings({"unchecked", "rawtypes"})
2605	<	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1402	<	return futures;
1403	<	}
2605	>	List<Future<T>> futures = (List<Future<T>>) (List) fs;
2606
2607	<	static final class InvokeAll<T> extends RecursiveAction {
2608	<	final ArrayList<ForkJoinTask<T>> tasks;
2609	<	InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; }
2610	<	public void compute() {
2611	<	try { invokeAll(tasks); }
2612	<	catch (Exception ignore) {}
2607	>	boolean done = false;
2608	>	try {
2609	>	for (Callable<T> t : tasks) {
2610	>	ForkJoinTask<T> f = new ForkJoinTask.AdaptedCallable<T>(t);
2611	>	externalPush(f);
2612	>	fs.add(f);
2613	>	}
2614	>	for (ForkJoinTask<T> f : fs)
2615	>	f.quietlyJoin();
2616	>	done = true;
2617	>	return futures;
2618	>	} finally {
2619	>	if (!done)
2620	>	for (ForkJoinTask<T> f : fs)
2621	>	f.cancel(false);
2622		}
1412	–	private static final long serialVersionUID = -7914297376763021607L;
2623		}
2624
2625		/**
#	Line 1441 | Line 2651 | public class ForkJoinPool extends Abstra
2651		}
2652
2653		/**
2654	+	* Returns the targeted parallelism level of the common pool.
2655	+	*
2656	+	* @return the targeted parallelism level of the common pool
2657	+	*/
2658	+	public static int getCommonPoolParallelism() {
2659	+	return commonPoolParallelism;
2660	+	}
2661	+
2662	+	/**
2663		* Returns the number of worker threads that have started but not
2664	<	* yet terminated.  This result returned by this method may differ
2664	>	* yet terminated.  The result returned by this method may differ
2665		* from {@link #getParallelism} when threads are created to
2666		* maintain parallelism when others are cooperatively blocked.
2667		*
2668		* @return the number of worker threads
2669		*/
2670		public int getPoolSize() {
2671	<	return workerCounts >>> TOTAL_COUNT_SHIFT;
2671	>	return parallelism + (short)(ctl >>> TC_SHIFT);
2672		}
2673
2674		/**
#	Line 1459 | Line 2678 | public class ForkJoinPool extends Abstra
2678		* @return {@code true} if this pool uses async mode
2679		*/
2680		public boolean getAsyncMode() {
2681	<	return locallyFifo;
2681	>	return localMode != 0;
2682		}
2683
2684		/**
#	Line 1471 | Line 2690 | public class ForkJoinPool extends Abstra
2690		* @return the number of worker threads
2691		*/
2692		public int getRunningThreadCount() {
2693	<	return workerCounts & RUNNING_COUNT_MASK;
2693	>	int rc = 0;
2694	>	WorkQueue[] ws; WorkQueue w;
2695	>	if ((ws = workQueues) != null) {
2696	>	for (int i = 1; i < ws.length; i += 2) {
2697	>	if ((w = ws[i]) != null && w.isApparentlyUnblocked())
2698	>	++rc;
2699	>	}
2700	>	}
2701	>	return rc;
2702		}
2703
2704		/**
#	Line 1482 | Line 2709 | public class ForkJoinPool extends Abstra
2709		* @return the number of active threads
2710		*/
2711		public int getActiveThreadCount() {
2712	<	return runState & ACTIVE_COUNT_MASK;
2712	>	int r = parallelism + (int)(ctl >> AC_SHIFT);
2713	>	return (r <= 0) ? 0 : r; // suppress momentarily negative values
2714		}
2715
2716		/**
#	Line 1497 | Line 2725 | public class ForkJoinPool extends Abstra
2725		* @return {@code true} if all threads are currently idle
2726		*/
2727		public boolean isQuiescent() {
2728	<	return (runState & ACTIVE_COUNT_MASK) == 0;
2728	>	return (int)(ctl >> AC_SHIFT) + parallelism == 0;
2729		}
2730
2731		/**
#	Line 1512 | Line 2740 | public class ForkJoinPool extends Abstra
2740		* @return the number of steals
2741		*/
2742		public long getStealCount() {
2743	<	return stealCount;
2743	>	long count = stealCount;
2744	>	WorkQueue[] ws; WorkQueue w;
2745	>	if ((ws = workQueues) != null) {
2746	>	for (int i = 1; i < ws.length; i += 2) {
2747	>	if ((w = ws[i]) != null)
2748	>	count += w.nsteals;
2749	>	}
2750	>	}
2751	>	return count;
2752		}
2753
2754		/**
#	Line 1527 | Line 2763 | public class ForkJoinPool extends Abstra
2763		*/
2764		public long getQueuedTaskCount() {
2765		long count = 0;
2766	<	ForkJoinWorkerThread[] ws = workers;
2767	<	int n = ws.length;
2768	<	for (int i = 0; i < n; ++i) {
2769	<	ForkJoinWorkerThread w = ws[i];
2770	<	if (w != null)
2771	<	count += w.getQueueSize();
2766	>	WorkQueue[] ws; WorkQueue w;
2767	>	if ((ws = workQueues) != null) {
2768	>	for (int i = 1; i < ws.length; i += 2) {
2769	>	if ((w = ws[i]) != null)
2770	>	count += w.queueSize();
2771	>	}
2772		}
2773		return count;
2774		}
2775
2776		/**
2777		* Returns an estimate of the number of tasks submitted to this
2778	<	* pool that have not yet begun executing.  This method takes time
2779	<	* proportional to the number of submissions.
2778	>	* pool that have not yet begun executing.  This method may take
2779	>	* time proportional to the number of submissions.
2780		*
2781		* @return the number of queued submissions
2782		*/
2783		public int getQueuedSubmissionCount() {
2784	<	return submissionQueue.size();
2784	>	int count = 0;
2785	>	WorkQueue[] ws; WorkQueue w;
2786	>	if ((ws = workQueues) != null) {
2787	>	for (int i = 0; i < ws.length; i += 2) {
2788	>	if ((w = ws[i]) != null)
2789	>	count += w.queueSize();
2790	>	}
2791	>	}
2792	>	return count;
2793		}
2794
2795		/**
#	Line 1555 | Line 2799 | public class ForkJoinPool extends Abstra
2799		* @return {@code true} if there are any queued submissions
2800		*/
2801		public boolean hasQueuedSubmissions() {
2802	<	return !submissionQueue.isEmpty();
2802	>	WorkQueue[] ws; WorkQueue w;
2803	>	if ((ws = workQueues) != null) {
2804	>	for (int i = 0; i < ws.length; i += 2) {
2805	>	if ((w = ws[i]) != null && w.queueSize() != 0)
2806	>	return true;
2807	>	}
2808	>	}
2809	>	return false;
2810		}
2811
2812		/**
#	Line 1566 | Line 2817 | public class ForkJoinPool extends Abstra
2817		* @return the next submission, or {@code null} if none
2818		*/
2819		protected ForkJoinTask<?> pollSubmission() {
2820	<	return submissionQueue.poll();
2820	>	WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t;
2821	>	if ((ws = workQueues) != null) {
2822	>	for (int i = 0; i < ws.length; i += 2) {
2823	>	if ((w = ws[i]) != null && (t = w.poll()) != null)
2824	>	return t;
2825	>	}
2826	>	}
2827	>	return null;
2828		}
2829
2830		/**
#	Line 1587 | Line 2845 | public class ForkJoinPool extends Abstra
2845		* @return the number of elements transferred
2846		*/
2847		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
2848	<	int count = submissionQueue.drainTo(c);
2849	<	ForkJoinWorkerThread[] ws = workers;
2850	<	int n = ws.length;
2851	<	for (int i = 0; i < n; ++i) {
2852	<	ForkJoinWorkerThread w = ws[i];
2853	<	if (w != null)
2854	<	count += w.drainTasksTo(c);
2848	>	int count = 0;
2849	>	WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t;
2850	>	if ((ws = workQueues) != null) {
2851	>	for (int i = 0; i < ws.length; ++i) {
2852	>	if ((w = ws[i]) != null) {
2853	>	while ((t = w.poll()) != null) {
2854	>	c.add(t);
2855	>	++count;
2856	>	}
2857	>	}
2858	>	}
2859		}
2860		return count;
2861		}
#	Line 1606 | Line 2868 | public class ForkJoinPool extends Abstra
2868		* @return a string identifying this pool, as well as its state
2869		*/
2870		public String toString() {
2871	<	long st = getStealCount();
2872	<	long qt = getQueuedTaskCount();
2873	<	long qs = getQueuedSubmissionCount();
2874	<	int wc = workerCounts;
2875	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
2876	<	int rc = wc & RUNNING_COUNT_MASK;
2871	>	// Use a single pass through workQueues to collect counts
2872	>	long qt = 0L, qs = 0L; int rc = 0;
2873	>	long st = stealCount;
2874	>	long c = ctl;
2875	>	WorkQueue[] ws; WorkQueue w;
2876	>	if ((ws = workQueues) != null) {
2877	>	for (int i = 0; i < ws.length; ++i) {
2878	>	if ((w = ws[i]) != null) {
2879	>	int size = w.queueSize();
2880	>	if ((i & 1) == 0)
2881	>	qs += size;
2882	>	else {
2883	>	qt += size;
2884	>	st += w.nsteals;
2885	>	if (w.isApparentlyUnblocked())
2886	>	++rc;
2887	>	}
2888	>	}
2889	>	}
2890	>	}
2891		int pc = parallelism;
2892	<	int rs = runState;
2893	<	int ac = rs & ACTIVE_COUNT_MASK;
2892	>	int tc = pc + (short)(c >>> TC_SHIFT);
2893	>	int ac = pc + (int)(c >> AC_SHIFT);
2894	>	if (ac < 0) // ignore transient negative
2895	>	ac = 0;
2896	>	String level;
2897	>	if ((c & STOP_BIT) != 0)
2898	>	level = (tc == 0) ? "Terminated" : "Terminating";
2899	>	else
2900	>	level = plock < 0 ? "Shutting down" : "Running";
2901		return super.toString() +
2902	<	"[" + runLevelToString(rs) +
2902	>	"[" + level +
2903		", parallelism = " + pc +
2904		", size = " + tc +
2905		", active = " + ac +
#	Line 1627 | Line 2910 | public class ForkJoinPool extends Abstra
2910		"]";
2911		}
2912
1630	–	private static String runLevelToString(int s) {
1631	–	return ((s & TERMINATED) != 0 ? "Terminated" :
1632	–	((s & TERMINATING) != 0 ? "Terminating" :
1633	–	((s & SHUTDOWN) != 0 ? "Shutting down" :
1634	–	"Running")));
1635	–	}
1636	–
2913		/**
2914	<	* Initiates an orderly shutdown in which previously submitted
2915	<	* tasks are executed, but no new tasks will be accepted.
2916	<	* Invocation has no additional effect if already shut down.
2917	<	* Tasks that are in the process of being submitted concurrently
2918	<	* during the course of this method may or may not be rejected.
2914	>	* Possibly initiates an orderly shutdown in which previously
2915	>	* submitted tasks are executed, but no new tasks will be
2916	>	* accepted. Invocation has no effect on execution state if this
2917	>	* is the {@link #commonPool}, and no additional effect if
2918	>	* already shut down.  Tasks that are in the process of being
2919	>	* submitted concurrently during the course of this method may or
2920	>	* may not be rejected.
2921		*
2922		* @throws SecurityException if a security manager exists and
2923		*         the caller is not permitted to modify threads
#	Line 1648 | Line 2926 | public class ForkJoinPool extends Abstra
2926		*/
2927		public void shutdown() {
2928		checkPermission();
2929	<	advanceRunLevel(SHUTDOWN);
1652	<	tryTerminate(false);
2929	>	tryTerminate(false, true);
2930		}
2931
2932		/**
2933	<	* Attempts to cancel and/or stop all tasks, and reject all
2934	<	* subsequently submitted tasks.  Tasks that are in the process of
2935	<	* being submitted or executed concurrently during the course of
2936	<	* this method may or may not be rejected. This method cancels
2937	<	* both existing and unexecuted tasks, in order to permit
2938	<	* termination in the presence of task dependencies. So the method
2939	<	* always returns an empty list (unlike the case for some other
2940	<	* Executors).
2933	>	* Possibly attempts to cancel and/or stop all tasks, and reject
2934	>	* all subsequently submitted tasks.  Invocation has no effect on
2935	>	* execution state if this is the {@link #commonPool}, and no
2936	>	* additional effect if already shut down. Otherwise, tasks that
2937	>	* are in the process of being submitted or executed concurrently
2938	>	* during the course of this method may or may not be
2939	>	* rejected. This method cancels both existing and unexecuted
2940	>	* tasks, in order to permit termination in the presence of task
2941	>	* dependencies. So the method always returns an empty list
2942	>	* (unlike the case for some other Executors).
2943		*
2944		* @return an empty list
2945		* @throws SecurityException if a security manager exists and
#	Line 1670 | Line 2949 | public class ForkJoinPool extends Abstra
2949		*/
2950		public List<Runnable> shutdownNow() {
2951		checkPermission();
2952	<	tryTerminate(true);
2952	>	tryTerminate(true, true);
2953		return Collections.emptyList();
2954		}
2955
#	Line 1680 | Line 2959 | public class ForkJoinPool extends Abstra
2959		* @return {@code true} if all tasks have completed following shut down
2960		*/
2961		public boolean isTerminated() {
2962	<	return runState >= TERMINATED;
2962	>	long c = ctl;
2963	>	return ((c & STOP_BIT) != 0L &&
2964	>	(short)(c >>> TC_SHIFT) == -parallelism);
2965		}
2966
2967		/**
#	Line 1688 | Line 2969 | public class ForkJoinPool extends Abstra
2969		* commenced but not yet completed.  This method may be useful for
2970		* debugging. A return of {@code true} reported a sufficient
2971		* period after shutdown may indicate that submitted tasks have
2972	<	* ignored or suppressed interruption, causing this executor not
2973	<	* to properly terminate.
2972	>	* ignored or suppressed interruption, or are waiting for IO,
2973	>	* causing this executor not to properly terminate. (See the
2974	>	* advisory notes for class {@link ForkJoinTask} stating that
2975	>	* tasks should not normally entail blocking operations.  But if
2976	>	* they do, they must abort them on interrupt.)
2977		*
2978		* @return {@code true} if terminating but not yet terminated
2979		*/
2980		public boolean isTerminating() {
2981	<	return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
2981	>	long c = ctl;
2982	>	return ((c & STOP_BIT) != 0L &&
2983	>	(short)(c >>> TC_SHIFT) != -parallelism);
2984		}
2985
2986		/**
#	Line 1703 | Line 2989 | public class ForkJoinPool extends Abstra
2989		* @return {@code true} if this pool has been shut down
2990		*/
2991		public boolean isShutdown() {
2992	<	return runState >= SHUTDOWN;
2992	>	return plock < 0;
2993		}
2994
2995		/**
2996	<	* Blocks until all tasks have completed execution after a shutdown
2997	<	* request, or the timeout occurs, or the current thread is
2998	<	* interrupted, whichever happens first.
2996	>	* Blocks until all tasks have completed execution after a
2997	>	* shutdown request, or the timeout occurs, or the current thread
2998	>	* is interrupted, whichever happens first. Note that the {@link
2999	>	* #commonPool()} never terminates until program shutdown so
3000	>	* this method will always time out.
3001		*
3002		* @param timeout the maximum time to wait
3003		* @param unit the time unit of the timeout argument
#	Line 1719 | Line 3007 | public class ForkJoinPool extends Abstra
3007		*/
3008		public boolean awaitTermination(long timeout, TimeUnit unit)
3009		throws InterruptedException {
3010	<	try {
3011	<	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
3012	<	} catch(TimeoutException ex) {
3013	<	return false;
3010	>	long nanos = unit.toNanos(timeout);
3011	>	if (isTerminated())
3012	>	return true;
3013	>	long startTime = System.nanoTime();
3014	>	boolean terminated = false;
3015	>	synchronized (this) {
3016	>	for (long waitTime = nanos, millis = 0L;;) {
3017	>	if (terminated = isTerminated() ||
3018	>	waitTime <= 0L ||
3019	>	(millis = unit.toMillis(waitTime)) <= 0L)
3020	>	break;
3021	>	wait(millis);
3022	>	waitTime = nanos - (System.nanoTime() - startTime);
3023	>	}
3024		}
3025	+	return terminated;
3026		}
3027
3028		/**
#	Line 1734 | Line 3033 | public class ForkJoinPool extends Abstra
3033		* {@code isReleasable} must return {@code true} if blocking is
3034		* not necessary. Method {@code block} blocks the current thread
3035		* if necessary (perhaps internally invoking {@code isReleasable}
3036	<	* before actually blocking). The unusual methods in this API
3037	<	* accommodate synchronizers that may, but don't usually, block
3038	<	* for long periods. Similarly, they allow more efficient internal
3039	<	* handling of cases in which additional workers may be, but
3040	<	* usually are not, needed to ensure sufficient parallelism.
3041	<	* Toward this end, implementations of method {@code isReleasable}
3042	<	* must be amenable to repeated invocation.
3036	>	* before actually blocking). These actions are performed by any
3037	>	* thread invoking {@link ForkJoinPool#managedBlock}.  The
3038	>	* unusual methods in this API accommodate synchronizers that may,
3039	>	* but don't usually, block for long periods. Similarly, they
3040	>	* allow more efficient internal handling of cases in which
3041	>	* additional workers may be, but usually are not, needed to
3042	>	* ensure sufficient parallelism.  Toward this end,
3043	>	* implementations of method {@code isReleasable} must be amenable
3044	>	* to repeated invocation.
3045		*
3046		* <p>For example, here is a ManagedBlocker based on a
3047		* ReentrantLock:
#	Line 1821 | Line 3122 | public class ForkJoinPool extends Abstra
3122		throws InterruptedException {
3123		Thread t = Thread.currentThread();
3124		if (t instanceof ForkJoinWorkerThread) {
3125	<	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
3126	<	w.pool.awaitBlocker(blocker);
3125	>	ForkJoinPool p = ((ForkJoinWorkerThread)t).pool;
3126	>	while (!blocker.isReleasable()) { // variant of helpSignal
3127	>	WorkQueue[] ws; WorkQueue q; int m, n;
3128	>	if ((ws = p.workQueues) != null && (m = ws.length - 1) >= 0) {
3129	>	for (int i = 0; i <= m; ++i) {
3130	>	if (blocker.isReleasable())
3131	>	return;
3132	>	if ((q = ws[i]) != null && (n = q.queueSize()) > 0) {
3133	>	p.signalWork(q, n);
3134	>	if ((int)(p.ctl >> AC_SHIFT) >= 0)
3135	>	break;
3136	>	}
3137	>	}
3138	>	}
3139	>	if (p.tryCompensate()) {
3140	>	try {
3141	>	do {} while (!blocker.isReleasable() &&
3142	>	!blocker.block());
3143	>	} finally {
3144	>	p.incrementActiveCount();
3145	>	}
3146	>	break;
3147	>	}
3148	>	}
3149		}
3150		else {
3151	<	do {} while (!blocker.isReleasable() && !blocker.block());
3151	>	do {} while (!blocker.isReleasable() &&
3152	>	!blocker.block());
3153		}
3154		}
3155
#	Line 1834 | Line 3158 | public class ForkJoinPool extends Abstra
3158		// implement RunnableFuture.
3159
3160		protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
3161	<	return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
3161	>	return new ForkJoinTask.AdaptedRunnable<T>(runnable, value);
3162		}
3163
3164		protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
3165	<	return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
3165	>	return new ForkJoinTask.AdaptedCallable<T>(callable);
3166		}
3167
3168		// Unsafe mechanics
3169	<
3170	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
3171	<	private static final long workerCountsOffset =
3172	<	objectFieldOffset("workerCounts", ForkJoinPool.class);
3173	<	private static final long runStateOffset =
3174	<	objectFieldOffset("runState", ForkJoinPool.class);
3175	<	private static final long eventCountOffset =
3176	<	objectFieldOffset("eventCount", ForkJoinPool.class);
3177	<	private static final long eventWaitersOffset =
3178	<	objectFieldOffset("eventWaiters",ForkJoinPool.class);
3179	<	private static final long stealCountOffset =
3180	<	objectFieldOffset("stealCount",ForkJoinPool.class);
3181	<	private static final long spareWaitersOffset =
3182	<	objectFieldOffset("spareWaiters",ForkJoinPool.class);
3183	<
3184	<	private static long objectFieldOffset(String field, Class<?> klazz) {
3169	>	private static final sun.misc.Unsafe U;
3170	>	private static final long CTL;
3171	>	private static final long PARKBLOCKER;
3172	>	private static final int ABASE;
3173	>	private static final int ASHIFT;
3174	>	private static final long STEALCOUNT;
3175	>	private static final long PLOCK;
3176	>	private static final long INDEXSEED;
3177	>	private static final long QLOCK;
3178	>
3179	>	static {
3180	>	// Establish common pool parameters
3181	>	// TBD: limit or report ignored exceptions?
3182	>
3183	>	int par = 0;
3184	>	ForkJoinWorkerThreadFactory fac = null;
3185	>	Thread.UncaughtExceptionHandler handler = null;
3186		try {
3187	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
3188	<	} catch (NoSuchFieldException e) {
3189	<	// Convert Exception to corresponding Error
3190	<	NoSuchFieldError error = new NoSuchFieldError(field);
3191	<	error.initCause(e);
3192	<	throw error;
3187	>	String pp = System.getProperty(propPrefix + "parallelism");
3188	>	String hp = System.getProperty(propPrefix + "exceptionHandler");
3189	>	String fp = System.getProperty(propPrefix + "threadFactory");
3190	>	if (fp != null)
3191	>	fac = ((ForkJoinWorkerThreadFactory)ClassLoader.
3192	>	getSystemClassLoader().loadClass(fp).newInstance());
3193	>	if (hp != null)
3194	>	handler = ((Thread.UncaughtExceptionHandler)ClassLoader.
3195	>	getSystemClassLoader().loadClass(hp).newInstance());
3196	>	if (pp != null)
3197	>	par = Integer.parseInt(pp);
3198	>	} catch(Exception ignore) {
3199		}
3200	+
3201	+	int s; // initialize field offsets for CAS etc
3202	+	try {
3203	+	U = getUnsafe();
3204	+	Class<?> k = ForkJoinPool.class;
3205	+	CTL = U.objectFieldOffset
3206	+	(k.getDeclaredField("ctl"));
3207	+	STEALCOUNT = U.objectFieldOffset
3208	+	(k.getDeclaredField("stealCount"));
3209	+	PLOCK = U.objectFieldOffset
3210	+	(k.getDeclaredField("plock"));
3211	+	INDEXSEED = U.objectFieldOffset
3212	+	(k.getDeclaredField("indexSeed"));
3213	+	Class<?> tk = Thread.class;
3214	+	PARKBLOCKER = U.objectFieldOffset
3215	+	(tk.getDeclaredField("parkBlocker"));
3216	+	Class<?> wk = WorkQueue.class;
3217	+	QLOCK = U.objectFieldOffset
3218	+	(wk.getDeclaredField("qlock"));
3219	+	Class<?> ak = ForkJoinTask[].class;
3220	+	ABASE = U.arrayBaseOffset(ak);
3221	+	s = U.arrayIndexScale(ak);
3222	+	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
3223	+	} catch (Exception e) {
3224	+	throw new Error(e);
3225	+	}
3226	+	if ((s & (s-1)) != 0)
3227	+	throw new Error("data type scale not a power of two");
3228	+
3229	+	/*
3230	+	* For extra caution, computations to set up pool state are
3231	+	* here; the constructor just assigns these values to fields.
3232	+	*/
3233	+	ForkJoinWorkerThreadFactory defaultFac =
3234	+	defaultForkJoinWorkerThreadFactory =
3235	+	new DefaultForkJoinWorkerThreadFactory();
3236	+	if (fac == null)
3237	+	fac = defaultFac;
3238	+	if (par <= 0)
3239	+	par = Runtime.getRuntime().availableProcessors();
3240	+	if (par > MAX_CAP)
3241	+	par = MAX_CAP;
3242	+	long np = (long)(-par); // precompute initial ctl value
3243	+	long ct = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
3244	+
3245	+	commonPoolParallelism = par;
3246	+	commonPool = new ForkJoinPool(par, ct, fac, handler);
3247	+	modifyThreadPermission = new RuntimePermission("modifyThread");
3248	+	submitters = new ThreadLocal<Submitter>();
3249		}
3250
3251		/**
#	Line 1895 | Line 3275 | public class ForkJoinPool extends Abstra
3275		}
3276		}
3277		}
3278	+
3279		}

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