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Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.49 by jsr166, Mon Nov 16 04:57:09 2009 UTC vs.
Revision 1.120 by jsr166, Tue Jan 31 01:32:25 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.Condition;
15	<	import java.util.concurrent.locks.LockSupport;
16	<	import java.util.concurrent.locks.ReentrantLock;
14	>	import java.util.Random;
15	>	import java.util.concurrent.AbstractExecutorService;
16	>	import java.util.concurrent.Callable;
17	>	import java.util.concurrent.ExecutorService;
18	>	import java.util.concurrent.Future;
19	>	import java.util.concurrent.RejectedExecutionException;
20	>	import java.util.concurrent.RunnableFuture;
21	>	import java.util.concurrent.TimeUnit;
22		import java.util.concurrent.atomic.AtomicInteger;
23		import java.util.concurrent.atomic.AtomicLong;
24	+	import java.util.concurrent.locks.AbstractQueuedSynchronizer;
25	+	import java.util.concurrent.locks.Condition;
26
27		/**
28		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
29		* A {@code ForkJoinPool} provides the entry point for submissions
30	<	* from non-{@code ForkJoinTask}s, as well as management and
30	>	* from non-{@code ForkJoinTask} clients, as well as management and
31		* monitoring operations.
32		*
33		* <p>A {@code ForkJoinPool} differs from other kinds of {@link
34		* ExecutorService} mainly by virtue of employing
35		* <em>work-stealing</em>: all threads in the pool attempt to find and
36	<	* execute subtasks created by other active tasks (eventually blocking
37	<	* waiting for work if none exist). This enables efficient processing
38	<	* when most tasks spawn other subtasks (as do most {@code
39	<	* ForkJoinTask}s). A {@code ForkJoinPool} may also be used for mixed
40	<	* execution of some plain {@code Runnable}- or {@code Callable}-
41	<	* based activities along with {@code ForkJoinTask}s. When setting
42	<	* {@linkplain #setAsyncMode async mode}, a {@code ForkJoinPool} may
43	<	* also be appropriate for use with fine-grained tasks of any form
39	<	* that are never joined. Otherwise, other {@code ExecutorService}
40	<	* implementations are typically more appropriate choices.
36	>	* execute tasks submitted to the pool and/or created by other active
37	>	* tasks (eventually blocking waiting for work if none exist). This
38	>	* enables efficient processing when most tasks spawn other subtasks
39	>	* (as do most {@code ForkJoinTask}s), as well as when many small
40	>	* tasks are submitted to the pool from external clients.  Especially
41	>	* when setting <em>asyncMode</em> to true in constructors, {@code
42	>	* ForkJoinPool}s may also be appropriate for use with event-style
43	>	* tasks that are never joined.
44		*
45		* <p>A {@code ForkJoinPool} is constructed with a given target
46		* parallelism level; by default, equal to the number of available
47	<	* processors. Unless configured otherwise via {@link
48	<	* #setMaintainsParallelism}, the pool attempts to maintain this
49	<	* number of active (or available) threads by dynamically adding,
50	<	* suspending, or resuming internal worker threads, even if some tasks
51	<	* are stalled waiting to join others. However, no such adjustments
52	<	* are performed in the face of blocked IO or other unmanaged
53	<	* synchronization. The nested {@link ManagedBlocker} interface
51	<	* enables extension of the kinds of synchronization accommodated.
52	<	* The target parallelism level may also be changed dynamically
53	<	* ({@link #setParallelism}). The total number of threads may be
54	<	* limited using method {@link #setMaximumPoolSize}, in which case it
55	<	* may become possible for the activities of a pool to stall due to
56	<	* the lack of available threads to process new tasks.
47	>	* processors. The pool attempts to maintain enough active (or
48	>	* available) threads by dynamically adding, suspending, or resuming
49	>	* internal worker threads, even if some tasks are stalled waiting to
50	>	* join others. However, no such adjustments are guaranteed in the
51	>	* face of blocked IO or other unmanaged synchronization. The nested
52	>	* {@link ManagedBlocker} interface enables extension of the kinds of
53	>	* synchronization accommodated.
54		*
55		* <p>In addition to execution and lifecycle control methods, this
56		* class provides status check methods (for example
#	Line 62 | Line 59 | import java.util.concurrent.atomic.Atomi
59		* {@link #toString} returns indications of pool state in a
60		* convenient form for informal monitoring.
61		*
62	+	* <p> As is the case with other ExecutorServices, there are three
63	+	* main task execution methods summarized in the following table.
64	+	* These are designed to be used primarily by clients not already
65	+	* engaged in fork/join computations in the current pool.  The main
66	+	* forms of these methods accept instances of {@code ForkJoinTask},
67	+	* but overloaded forms also allow mixed execution of plain {@code
68	+	* Runnable}- or {@code Callable}- based activities as well.  However,
69	+	* tasks that are already executing in a pool should normally instead
70	+	* use the within-computation forms listed in the table unless using
71	+	* async event-style tasks that are not usually joined, in which case
72	+	* there is little difference among choice of methods.
73	+	*
74	+	* <table BORDER CELLPADDING=3 CELLSPACING=1>
75	+	*  <tr>
76	+	*    <td></td>
77	+	*    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
78	+	*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
79	+	*  </tr>
80	+	*  <tr>
81	+	*    <td> <b>Arrange async execution</td>
82	+	*    <td> {@link #execute(ForkJoinTask)}</td>
83	+	*    <td> {@link ForkJoinTask#fork}</td>
84	+	*  </tr>
85	+	*  <tr>
86	+	*    <td> <b>Await and obtain result</td>
87	+	*    <td> {@link #invoke(ForkJoinTask)}</td>
88	+	*    <td> {@link ForkJoinTask#invoke}</td>
89	+	*  </tr>
90	+	*  <tr>
91	+	*    <td> <b>Arrange exec and obtain Future</td>
92	+	*    <td> {@link #submit(ForkJoinTask)}</td>
93	+	*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
94	+	*  </tr>
95	+	* </table>
96	+	*
97		* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
98		* used for all parallel task execution in a program or subsystem.
99		* Otherwise, use would not usually outweigh the construction and
#	Line 72 | Line 104 | import java.util.concurrent.atomic.Atomi
104		* daemon} mode, there is typically no need to explicitly {@link
105		* #shutdown} such a pool upon program exit.
106		*
107	<	* <pre>
107	>	*  <pre> {@code
108		* static final ForkJoinPool mainPool = new ForkJoinPool();
109		* ...
110		* public void sort(long[] array) {
111		*   mainPool.invoke(new SortTask(array, 0, array.length));
112	<	* }
81	<	* </pre>
112	>	* }}</pre>
113		*
114		* <p><b>Implementation notes</b>: This implementation restricts the
115		* maximum number of running threads to 32767. Attempts to create
#	Line 86 | Line 117 | import java.util.concurrent.atomic.Atomi
117		* {@code IllegalArgumentException}.
118		*
119		* <p>This implementation rejects submitted tasks (that is, by throwing
120	<	* {@link RejectedExecutionException}) only when the pool is shut down.
120	>	* {@link RejectedExecutionException}) only when the pool is shut down
121	>	* or internal resources have been exhausted.
122		*
123		* @since 1.7
124		* @author Doug Lea
#	Line 94 | Line 126 | import java.util.concurrent.atomic.Atomi
126		public class ForkJoinPool extends AbstractExecutorService {
127
128		/*
129	<	* See the extended comments interspersed below for design,
130	<	* rationale, and walkthroughs.
131	<	*/
129	>	* Implementation Overview
130	>	*
131	>	* This class and its nested classes provide the main
132	>	* functionality and control for a set of worker threads:
133	>	* Submissions from non-FJ threads enter into submission queues.
134	>	* Workers take these tasks and typically split them into subtasks
135	>	* that may be stolen by other workers.  Preference rules give
136	>	* first priority to processing tasks from their own queues (LIFO
137	>	* or FIFO, depending on mode), then to randomized FIFO steals of
138	>	* tasks in other queues.
139	>	*
140	>	* WorkQueues
141	>	* ==========
142	>	*
143	>	* Most operations occur within work-stealing queues (in nested
144	>	* class WorkQueue).  These are special forms of Deques that
145	>	* support only three of the four possible end-operations -- push,
146	>	* pop, and poll (aka steal), under the further constraints that
147	>	* push and pop are called only from the owning thread (or, as
148	>	* extended here, under a lock), while poll may be called from
149	>	* other threads.  (If you are unfamiliar with them, you probably
150	>	* want to read Herlihy and Shavit's book "The Art of
151	>	* Multiprocessor programming", chapter 16 describing these in
152	>	* more detail before proceeding.)  The main work-stealing queue
153	>	* design is roughly similar to those in the papers "Dynamic
154	>	* Circular Work-Stealing Deque" by Chase and Lev, SPAA 2005
155	>	* (http://research.sun.com/scalable/pubs/index.html) and
156	>	* "Idempotent work stealing" by Michael, Saraswat, and Vechev,
157	>	* PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186).
158	>	* The main differences ultimately stem from GC requirements that
159	>	* we null out taken slots as soon as we can, to maintain as small
160	>	* a footprint as possible even in programs generating huge
161	>	* numbers of tasks. To accomplish this, we shift the CAS
162	>	* arbitrating pop vs poll (steal) from being on the indices
163	>	* ("base" and "top") to the slots themselves.  So, both a
164	>	* successful pop and poll mainly entail a CAS of a slot from
165	>	* non-null to null.  Because we rely on CASes of references, we
166	>	* do not need tag bits on base or top.  They are simple ints as
167	>	* used in any circular array-based queue (see for example
168	>	* ArrayDeque).  Updates to the indices must still be ordered in a
169	>	* way that guarantees that top == base means the queue is empty,
170	>	* but otherwise may err on the side of possibly making the queue
171	>	* appear nonempty when a push, pop, or poll have not fully
172	>	* committed. Note that this means that the poll operation,
173	>	* considered individually, is not wait-free. One thief cannot
174	>	* successfully continue until another in-progress one (or, if
175	>	* previously empty, a push) completes.  However, in the
176	>	* aggregate, we ensure at least probabilistic non-blockingness.
177	>	* If an attempted steal fails, a thief always chooses a different
178	>	* random victim target to try next. So, in order for one thief to
179	>	* progress, it suffices for any in-progress poll or new push on
180	>	* any empty queue to complete.
181	>	*
182	>	* This approach also enables support of a user mode in which local
183	>	* task processing is in FIFO, not LIFO order, simply by using
184	>	* poll rather than pop.  This can be useful in message-passing
185	>	* frameworks in which tasks are never joined.  However neither
186	>	* mode considers affinities, loads, cache localities, etc, so
187	>	* rarely provide the best possible performance on a given
188	>	* machine, but portably provide good throughput by averaging over
189	>	* these factors.  (Further, even if we did try to use such
190	>	* information, we do not usually have a basis for exploiting it.
191	>	* For example, some sets of tasks profit from cache affinities,
192	>	* but others are harmed by cache pollution effects.)
193	>	*
194	>	* WorkQueues are also used in a similar way for tasks submitted
195	>	* to the pool. We cannot mix these tasks in the same queues used
196	>	* for work-stealing (this would contaminate lifo/fifo
197	>	* processing). Instead, we loosely associate submission queues
198	>	* with submitting threads, using a form of hashing.  The
199	>	* ThreadLocal Submitter class contains a value initially used as
200	>	* a hash code for choosing existing queues, but may be randomly
201	>	* repositioned upon contention with other submitters.  In
202	>	* essence, submitters act like workers except that they never
203	>	* take tasks, and they are multiplexed on to a finite number of
204	>	* shared work queues. However, classes are set up so that future
205	>	* extensions could allow submitters to optionally help perform
206	>	* tasks as well. Insertion of tasks in shared mode requires a
207	>	* lock (mainly to protect in the case of resizing) but we use
208	>	* only a simple spinlock (using bits in field runState), because
209	>	* submitters encountering a busy queue move on to try or create
210	>	* other queues, so never block.
211	>	*
212	>	* Management
213	>	* ==========
214	>	*
215	>	* The main throughput advantages of work-stealing stem from
216	>	* decentralized control -- workers mostly take tasks from
217	>	* themselves or each other. We cannot negate this in the
218	>	* implementation of other management responsibilities. The main
219	>	* tactic for avoiding bottlenecks is packing nearly all
220	>	* essentially atomic control state into two volatile variables
221	>	* that are by far most often read (not written) as status and
222	>	* consistency checks.
223	>	*
224	>	* Field "ctl" contains 64 bits holding all the information needed
225	>	* to atomically decide to add, inactivate, enqueue (on an event
226	>	* queue), dequeue, and/or re-activate workers.  To enable this
227	>	* packing, we restrict maximum parallelism to (1<<15)-1 (which is
228	>	* far in excess of normal operating range) to allow ids, counts,
229	>	* and their negations (used for thresholding) to fit into 16bit
230	>	* fields.
231	>	*
232	>	* Field "runState" contains 32 bits needed to register and
233	>	* deregister WorkQueues, as well as to enable shutdown. It is
234	>	* only modified under a lock (normally briefly held, but
235	>	* occasionally protecting allocations and resizings) but even
236	>	* when locked remains available to check consistency. An
237	>	* auxiliary field "growHints", also only modified under lock,
238	>	* contains a candidate index for the next WorkQueue and
239	>	* a mask for submission queue indices.
240	>	*
241	>	* Recording WorkQueues.  WorkQueues are recorded in the
242	>	* "workQueues" array that is created upon pool construction and
243	>	* expanded if necessary.  Updates to the array while recording
244	>	* new workers and unrecording terminated ones are protected from
245	>	* each other by a lock but the array is otherwise concurrently
246	>	* readable, and accessed directly.  To simplify index-based
247	>	* operations, the array size is always a power of two, and all
248	>	* readers must tolerate null slots. Shared (submission) queues
249	>	* are at even indices, worker queues at odd indices. Grouping
250	>	* them together in this way simplifies and speeds up task
251	>	* scanning. To avoid flailing during start-up, the array is
252	>	* presized to hold twice #parallelism workers (which is unlikely
253	>	* to need further resizing during execution). But to avoid
254	>	* dealing with so many null slots, variable runState includes a
255	>	* mask for the nearest power of two that contains all currently
256	>	* used indices.
257	>	*
258	>	* All worker thread creation is on-demand, triggered by task
259	>	* submissions, replacement of terminated workers, and/or
260	>	* compensation for blocked workers. However, all other support
261	>	* code is set up to work with other policies.  To ensure that we
262	>	* do not hold on to worker references that would prevent GC, ALL
263	>	* accesses to workQueues are via indices into the workQueues
264	>	* array (which is one source of some of the messy code
265	>	* constructions here). In essence, the workQueues array serves as
266	>	* a weak reference mechanism. Thus for example the wait queue
267	>	* field of ctl stores indices, not references.  Access to the
268	>	* workQueues in associated methods (for example signalWork) must
269	>	* both index-check and null-check the IDs. All such accesses
270	>	* ignore bad IDs by returning out early from what they are doing,
271	>	* since this can only be associated with termination, in which
272	>	* case it is OK to give up.  All uses of the workQueues array
273	>	* also check that it is non-null (even if previously
274	>	* non-null). This allows nulling during termination, which is
275	>	* currently not necessary, but remains an option for
276	>	* resource-revocation-based shutdown schemes. It also helps
277	>	* reduce JIT issuance of uncommon-trap code, which tends to
278	>	* unnecessarily complicate control flow in some methods.
279	>	*
280	>	* Event Queuing. Unlike HPC work-stealing frameworks, we cannot
281	>	* let workers spin indefinitely scanning for tasks when none can
282	>	* be found immediately, and we cannot start/resume workers unless
283	>	* there appear to be tasks available.  On the other hand, we must
284	>	* quickly prod them into action when new tasks are submitted or
285	>	* generated. In many usages, ramp-up time to activate workers is
286	>	* the main limiting factor in overall performance (this is
287	>	* compounded at program start-up by JIT compilation and
288	>	* allocation). So we try to streamline this as much as possible.
289	>	* We park/unpark workers after placing in an event wait queue
290	>	* when they cannot find work. This "queue" is actually a simple
291	>	* Treiber stack, headed by the "id" field of ctl, plus a 15bit
292	>	* counter value (that reflects the number of times a worker has
293	>	* been inactivated) to avoid ABA effects (we need only as many
294	>	* version numbers as worker threads). Successors are held in
295	>	* field WorkQueue.nextWait.  Queuing deals with several intrinsic
296	>	* races, mainly that a task-producing thread can miss seeing (and
297	>	* signalling) another thread that gave up looking for work but
298	>	* has not yet entered the wait queue. We solve this by requiring
299	>	* a full sweep of all workers (via repeated calls to method
300	>	* scan()) both before and after a newly waiting worker is added
301	>	* to the wait queue. During a rescan, the worker might release
302	>	* some other queued worker rather than itself, which has the same
303	>	* net effect. Because enqueued workers may actually be rescanning
304	>	* rather than waiting, we set and clear the "parker" field of
305	>	* WorkQueues to reduce unnecessary calls to unpark.  (This
306	>	* requires a secondary recheck to avoid missed signals.)  Note
307	>	* the unusual conventions about Thread.interrupts surrounding
308	>	* parking and other blocking: Because interrupts are used solely
309	>	* to alert threads to check termination, which is checked anyway
310	>	* upon blocking, we clear status (using Thread.interrupted)
311	>	* before any call to park, so that park does not immediately
312	>	* return due to status being set via some other unrelated call to
313	>	* interrupt in user code.
314	>	*
315	>	* Signalling.  We create or wake up workers only when there
316	>	* appears to be at least one task they might be able to find and
317	>	* execute.  When a submission is added or another worker adds a
318	>	* task to a queue that previously had fewer than two tasks, they
319	>	* signal waiting workers (or trigger creation of new ones if
320	>	* fewer than the given parallelism level -- see signalWork).
321	>	* These primary signals are buttressed by signals during rescans;
322	>	* together these cover the signals needed in cases when more
323	>	* tasks are pushed but untaken, and improve performance compared
324	>	* to having one thread wake up all workers.
325	>	*
326	>	* Trimming workers. To release resources after periods of lack of
327	>	* use, a worker starting to wait when the pool is quiescent will
328	>	* time out and terminate if the pool has remained quiescent for
329	>	* SHRINK_RATE nanosecs. This will slowly propagate, eventually
330	>	* terminating all workers after long periods of non-use.
331	>	*
332	>	* Shutdown and Termination. A call to shutdownNow atomically sets
333	>	* a runState bit and then (non-atomically) sets each worker's
334	>	* runState status, cancels all unprocessed tasks, and wakes up
335	>	* all waiting workers.  Detecting whether termination should
336	>	* commence after a non-abrupt shutdown() call requires more work
337	>	* and bookkeeping. We need consensus about quiescence (i.e., that
338	>	* there is no more work). The active count provides a primary
339	>	* indication but non-abrupt shutdown still requires a rechecking
340	>	* scan for any workers that are inactive but not queued.
341	>	*
342	>	* Joining Tasks
343	>	* =============
344	>	*
345	>	* Any of several actions may be taken when one worker is waiting
346	>	* to join a task stolen (or always held) by another.  Because we
347	>	* are multiplexing many tasks on to a pool of workers, we can't
348	>	* just let them block (as in Thread.join).  We also cannot just
349	>	* reassign the joiner's run-time stack with another and replace
350	>	* it later, which would be a form of "continuation", that even if
351	>	* possible is not necessarily a good idea since we sometimes need
352	>	* both an unblocked task and its continuation to progress.
353	>	* Instead we combine two tactics:
354	>	*
355	>	*   Helping: Arranging for the joiner to execute some task that it
356	>	*      would be running if the steal had not occurred.
357	>	*
358	>	*   Compensating: Unless there are already enough live threads,
359	>	*      method tryCompensate() may create or re-activate a spare
360	>	*      thread to compensate for blocked joiners until they unblock.
361	>	*
362	>	* A third form (implemented in tryRemoveAndExec and
363	>	* tryPollForAndExec) amounts to helping a hypothetical
364	>	* compensator: If we can readily tell that a possible action of a
365	>	* compensator is to steal and execute the task being joined, the
366	>	* joining thread can do so directly, without the need for a
367	>	* compensation thread (although at the expense of larger run-time
368	>	* stacks, but the tradeoff is typically worthwhile).
369	>	*
370	>	* The ManagedBlocker extension API can't use helping so relies
371	>	* only on compensation in method awaitBlocker.
372	>	*
373	>	* The algorithm in tryHelpStealer entails a form of "linear"
374	>	* helping: Each worker records (in field currentSteal) the most
375	>	* recent task it stole from some other worker. Plus, it records
376	>	* (in field currentJoin) the task it is currently actively
377	>	* joining. Method tryHelpStealer uses these markers to try to
378	>	* find a worker to help (i.e., steal back a task from and execute
379	>	* it) that could hasten completion of the actively joined task.
380	>	* In essence, the joiner executes a task that would be on its own
381	>	* local deque had the to-be-joined task not been stolen. This may
382	>	* be seen as a conservative variant of the approach in Wagner &
383	>	* Calder "Leapfrogging: a portable technique for implementing
384	>	* efficient futures" SIGPLAN Notices, 1993
385	>	* (http://portal.acm.org/citation.cfm?id=155354). It differs in
386	>	* that: (1) We only maintain dependency links across workers upon
387	>	* steals, rather than use per-task bookkeeping.  This sometimes
388	>	* requires a linear scan of workQueues array to locate stealers, but
389	>	* often doesn't because stealers leave hints (that may become
390	>	* stale/wrong) of where to locate them.  A stealHint is only a
391	>	* hint because a worker might have had multiple steals and the
392	>	* hint records only one of them (usually the most current).
393	>	* Hinting isolates cost to when it is needed, rather than adding
394	>	* to per-task overhead.  (2) It is "shallow", ignoring nesting
395	>	* and potentially cyclic mutual steals.  (3) It is intentionally
396	>	* racy: field currentJoin is updated only while actively joining,
397	>	* which means that we miss links in the chain during long-lived
398	>	* tasks, GC stalls etc (which is OK since blocking in such cases
399	>	* is usually a good idea).  (4) We bound the number of attempts
400	>	* to find work (see MAX_HELP_DEPTH) and fall back to suspending
401	>	* the worker and if necessary replacing it with another.
402	>	*
403	>	* It is impossible to keep exactly the target parallelism number
404	>	* of threads running at any given time.  Determining the
405	>	* existence of conservatively safe helping targets, the
406	>	* availability of already-created spares, and the apparent need
407	>	* to create new spares are all racy, so we rely on multiple
408	>	* retries of each.  Currently, in keeping with on-demand
409	>	* signalling policy, we compensate only if blocking would leave
410	>	* less than one active (non-waiting, non-blocked) worker.
411	>	* Additionally, to avoid some false alarms due to GC, lagging
412	>	* counters, system activity, etc, compensated blocking for joins
413	>	* is only attempted after rechecks stabilize in
414	>	* ForkJoinTask.awaitJoin. (Retries are interspersed with
415	>	* Thread.yield, for good citizenship.)
416	>	*
417	>	* Style notes: There is a lot of representation-level coupling
418	>	* among classes ForkJoinPool, ForkJoinWorkerThread, and
419	>	* ForkJoinTask.  The fields of WorkQueue maintain data structures
420	>	* managed by ForkJoinPool, so are directly accessed.  There is
421	>	* little point trying to reduce this, since any associated future
422	>	* changes in representations will need to be accompanied by
423	>	* algorithmic changes anyway. Several methods intrinsically
424	>	* sprawl because they must accumulate sets of consistent reads of
425	>	* volatiles held in local variables.  Methods signalWork() and
426	>	* scan() are the main bottlenecks, so are especially heavily
427	>	* micro-optimized/mangled.  There are lots of inline assignments
428	>	* (of form "while ((local = field) != 0)") which are usually the
429	>	* simplest way to ensure the required read orderings (which are
430	>	* sometimes critical). This leads to a "C"-like style of listing
431	>	* declarations of these locals at the heads of methods or blocks.
432	>	* There are several occurrences of the unusual "do {} while
433	>	* (!cas...)"  which is the simplest way to force an update of a
434	>	* CAS'ed variable. There are also other coding oddities that help
435	>	* some methods perform reasonably even when interpreted (not
436	>	* compiled).
437	>	*
438	>	* The order of declarations in this file is:
439	>	* (1) Static utility functions
440	>	* (2) Nested (static) classes
441	>	* (3) Static fields
442	>	* (4) Fields, along with constants used when unpacking some of them
443	>	* (5) Internal control methods
444	>	* (6) Callbacks and other support for ForkJoinTask methods
445	>	* (7) Exported methods
446	>	* (8) Static block initializing statics in minimally dependent order
447	>	*/
448	>
449	>	// Static utilities
450	>
451	>	/**
452	>	* Computes an initial hash code (also serving as a non-zero
453	>	* random seed) for a thread id. This method is expected to
454	>	* provide higher-quality hash codes than using method hashCode().
455	>	*/
456	>	static final int hashId(long id) {
457	>	int h = (int)id ^ (int)(id >>> 32); // Use MurmurHash of thread id
458	>	h ^= h >>> 16; h *= 0x85ebca6b;
459	>	h ^= h >>> 13; h *= 0xc2b2ae35;
460	>	h ^= h >>> 16;
461	>	return (h == 0)? 1 : h; // ensure nonzero
462	>	}
463
464	<	/** Mask for packing and unpacking shorts */
465	<	private static final int  shortMask = 0xffff;
464	>	/**
465	>	* If there is a security manager, makes sure caller has
466	>	* permission to modify threads.
467	>	*/
468	>	private static void checkPermission() {
469	>	SecurityManager security = System.getSecurityManager();
470	>	if (security != null)
471	>	security.checkPermission(modifyThreadPermission);
472	>	}
473
474	<	/** Max pool size -- must be a power of two minus 1 */
105	<	private static final int MAX_THREADS =  0x7FFF;
474	>	// Nested classes
475
476		/**
477		* Factory for creating new {@link ForkJoinWorkerThread}s.
#	Line 124 | Line 493 | public class ForkJoinPool extends Abstra
493		* Default ForkJoinWorkerThreadFactory implementation; creates a
494		* new ForkJoinWorkerThread.
495		*/
496	<	static class  DefaultForkJoinWorkerThreadFactory
496	>	static class DefaultForkJoinWorkerThreadFactory
497		implements ForkJoinWorkerThreadFactory {
498		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
499	<	try {
131	<	return new ForkJoinWorkerThread(pool);
132	<	} catch (OutOfMemoryError oom)  {
133	<	return null;
134	<	}
499	>	return new ForkJoinWorkerThread(pool);
500		}
501		}
502
503		/**
504	<	* Creates a new ForkJoinWorkerThread. This factory is used unless
505	<	* overridden in ForkJoinPool constructors.
504	>	* A simple non-reentrant lock used for exclusion when managing
505	>	* queues and workers. We use a custom lock so that we can readily
506	>	* probe lock state in constructions that check among alternative
507	>	* actions. The lock is normally only very briefly held, and
508	>	* sometimes treated as a spinlock, but other usages block to
509	>	* reduce overall contention in those cases where locked code
510	>	* bodies perform allocation/resizing.
511		*/
512	<	public static final ForkJoinWorkerThreadFactory
513	<	defaultForkJoinWorkerThreadFactory =
514	<	new DefaultForkJoinWorkerThreadFactory();
515	<
516	<	/**
517	<	* Permission required for callers of methods that may start or
518	<	* kill threads.
512	>	static final class Mutex extends AbstractQueuedSynchronizer {
513	>	public final boolean tryAcquire(int ignore) {
514	>	return compareAndSetState(0, 1);
515	>	}
516	>	public final boolean tryRelease(int ignore) {
517	>	setState(0);
518	>	return true;
519	>	}
520	>	public final void lock() { acquire(0); }
521	>	public final void unlock() { release(0); }
522	>	public final boolean isHeldExclusively() { return getState() == 1; }
523	>	public final Condition newCondition() { return new ConditionObject(); }
524	>	}
525	>
526	>	/**
527	>	* Class for artificial tasks that are used to replace the target
528	>	* of local joins if they are removed from an interior queue slot
529	>	* in WorkQueue.tryRemoveAndExec. We don't need the proxy to
530	>	* actually do anything beyond having a unique identity.
531	>	*/
532	>	static final class EmptyTask extends ForkJoinTask<Void> {
533	>	EmptyTask() { status = ForkJoinTask.NORMAL; } // force done
534	>	public final Void getRawResult() { return null; }
535	>	public final void setRawResult(Void x) {}
536	>	public final boolean exec() { return true; }
537	>	}
538	>
539	>	/**
540	>	* Queues supporting work-stealing as well as external task
541	>	* submission. See above for main rationale and algorithms.
542	>	* Implementation relies heavily on "Unsafe" intrinsics
543	>	* and selective use of "volatile":
544	>	*
545	>	* Field "base" is the index (mod array.length) of the least valid
546	>	* queue slot, which is always the next position to steal (poll)
547	>	* from if nonempty. Reads and writes require volatile orderings
548	>	* but not CAS, because updates are only performed after slot
549	>	* CASes.
550	>	*
551	>	* Field "top" is the index (mod array.length) of the next queue
552	>	* slot to push to or pop from. It is written only by owner thread
553	>	* for push, or under lock for trySharedPush, and accessed by
554	>	* other threads only after reading (volatile) base.  Both top and
555	>	* base are allowed to wrap around on overflow, but (top - base)
556	>	* (or more commonly -(base - top) to force volatile read of base
557	>	* before top) still estimates size.
558	>	*
559	>	* The array slots are read and written using the emulation of
560	>	* volatiles/atomics provided by Unsafe. Insertions must in
561	>	* general use putOrderedObject as a form of releasing store to
562	>	* ensure that all writes to the task object are ordered before
563	>	* its publication in the queue. (Although we can avoid one case
564	>	* of this when locked in trySharedPush.) All removals entail a
565	>	* CAS to null.  The array is always a power of two. To ensure
566	>	* safety of Unsafe array operations, all accesses perform
567	>	* explicit null checks and implicit bounds checks via
568	>	* power-of-two masking.
569	>	*
570	>	* In addition to basic queuing support, this class contains
571	>	* fields described elsewhere to control execution. It turns out
572	>	* to work better memory-layout-wise to include them in this
573	>	* class rather than a separate class.
574	>	*
575	>	* Performance on most platforms is very sensitive to placement of
576	>	* instances of both WorkQueues and their arrays -- we absolutely
577	>	* do not want multiple WorkQueue instances or multiple queue
578	>	* arrays sharing cache lines. (It would be best for queue objects
579	>	* and their arrays to share, but there is nothing available to
580	>	* help arrange that).  Unfortunately, because they are recorded
581	>	* in a common array, WorkQueue instances are often moved to be
582	>	* adjacent by garbage collectors. To reduce impact, we use field
583	>	* padding that works OK on common platforms; this effectively
584	>	* trades off slightly slower average field access for the sake of
585	>	* avoiding really bad worst-case access. (Until better JVM
586	>	* support is in place, this padding is dependent on transient
587	>	* properties of JVM field layout rules.)  We also take care in
588	>	* allocating, sizing and resizing the array. Non-shared queue
589	>	* arrays are initialized (via method growArray) by workers before
590	>	* use. Others are allocated on first use.
591		*/
592	<	private static final RuntimePermission modifyThreadPermission =
593	<	new RuntimePermission("modifyThread");
592	>	static final class WorkQueue {
593	>	/**
594	>	* Capacity of work-stealing queue array upon initialization.
595	>	* Must be a power of two; at least 4, but set larger to
596	>	* reduce cacheline sharing among queues.
597	>	*/
598	>	static final int INITIAL_QUEUE_CAPACITY = 1 << 8;
599
600	<	/**
601	<	* If there is a security manager, makes sure caller has
602	<	* permission to modify threads.
603	<	*/
604	<	private static void checkPermission() {
605	<	SecurityManager security = System.getSecurityManager();
606	<	if (security != null)
607	<	security.checkPermission(modifyThreadPermission);
600	>	/**
601	>	* Maximum size for queue arrays. Must be a power of two less
602	>	* than or equal to 1 << (31 - width of array entry) to ensure
603	>	* lack of wraparound of index calculations, but defined to a
604	>	* value a bit less than this to help users trap runaway
605	>	* programs before saturating systems.
606	>	*/
607	>	static final int MAXIMUM_QUEUE_CAPACITY = 1 << 26; // 64M
608	>
609	>	volatile long totalSteals; // cumulative number of steals
610	>	int seed;                  // for random scanning; initialize nonzero
611	>	volatile int eventCount;   // encoded inactivation count; < 0 if inactive
612	>	int nextWait;              // encoded record of next event waiter
613	>	int rescans;               // remaining scans until block
614	>	int nsteals;               // top-level task executions since last idle
615	>	final int mode;            // lifo, fifo, or shared
616	>	int poolIndex;             // index of this queue in pool (or 0)
617	>	int stealHint;             // index of most recent known stealer
618	>	volatile int runState;     // 1: locked, -1: terminate; else 0
619	>	volatile int base;         // index of next slot for poll
620	>	int top;                   // index of next slot for push
621	>	ForkJoinTask<?>[] array;   // the elements (initially unallocated)
622	>	final ForkJoinWorkerThread owner; // owning thread or null if shared
623	>	volatile Thread parker;    // == owner during call to park; else null
624	>	ForkJoinTask<?> currentJoin;  // task being joined in awaitJoin
625	>	ForkJoinTask<?> currentSteal; // current non-local task being executed
626	>	// Heuristic padding to ameliorate unfortunate memory placements
627	>	Object p00, p01, p02, p03, p04, p05, p06, p07, p08, p09, p0a;
628	>
629	>	WorkQueue(ForkJoinWorkerThread owner, int mode) {
630	>	this.owner = owner;
631	>	this.mode = mode;
632	>	// Place indices in the center of array (that is not yet allocated)
633	>	base = top = INITIAL_QUEUE_CAPACITY >>> 1;
634	>	}
635	>
636	>	/**
637	>	* Returns number of tasks in the queue.
638	>	*/
639	>	final int queueSize() {
640	>	int n = base - top; // non-owner callers must read base first
641	>	return (n >= 0) ? 0 : -n;
642	>	}
643	>
644	>	/**
645	>	* Pushes a task. Call only by owner in unshared queues.
646	>	*
647	>	* @param task the task. Caller must ensure non-null.
648	>	* @param p if non-null, pool to signal if necessary
649	>	* @throw RejectedExecutionException if array cannot be resized
650	>	*/
651	>	final void push(ForkJoinTask<?> task, ForkJoinPool p) {
652	>	ForkJoinTask<?>[] a;
653	>	int s = top, m, n;
654	>	if ((a = array) != null) {    // ignore if queue removed
655	>	U.putOrderedObject
656	>	(a, (((m = a.length - 1) & s) << ASHIFT) + ABASE, task);
657	>	if ((n = (top = s + 1) - base) <= 2) {
658	>	if (p != null)
659	>	p.signalWork();
660	>	}
661	>	else if (n >= m)
662	>	growArray(true);
663	>	}
664	>	}
665	>
666	>	/**
667	>	* Pushes a task if lock is free and array is either big
668	>	* enough or can be resized to be big enough.
669	>	*
670	>	* @param task the task. Caller must ensure non-null.
671	>	* @return true if submitted
672	>	*/
673	>	final boolean trySharedPush(ForkJoinTask<?> task) {
674	>	boolean submitted = false;
675	>	if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
676	>	ForkJoinTask<?>[] a = array;
677	>	int s = top;
678	>	try {
679	>	if ((a != null && a.length > s + 1 - base) ||
680	>	(a = growArray(false)) != null) { // must presize
681	>	int j = (((a.length - 1) & s) << ASHIFT) + ABASE;
682	>	U.putObject(a, (long)j, task);    // don't need "ordered"
683	>	top = s + 1;
684	>	submitted = true;
685	>	}
686	>	} finally {
687	>	runState = 0;                         // unlock
688	>	}
689	>	}
690	>	return submitted;
691	>	}
692	>
693	>	/**
694	>	* Takes next task, if one exists, in FIFO order.
695	>	*/
696	>	final ForkJoinTask<?> poll() {
697	>	ForkJoinTask<?>[] a; int b; ForkJoinTask<?> t;
698	>	while ((b = base) - top < 0 && (a = array) != null) {
699	>	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
700	>	if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null &&
701	>	base == b &&
702	>	U.compareAndSwapObject(a, j, t, null)) {
703	>	base = b + 1;
704	>	return t;
705	>	}
706	>	}
707	>	return null;
708	>	}
709	>
710	>	/**
711	>	* Takes next task, if one exists, in LIFO order.  Call only
712	>	* by owner in unshared queues. (We do not have a shared
713	>	* version of this method because it is never needed.)
714	>	*/
715	>	final ForkJoinTask<?> pop() {
716	>	ForkJoinTask<?> t; int m;
717	>	ForkJoinTask<?>[] a = array;
718	>	if (a != null && (m = a.length - 1) >= 0) {
719	>	for (int s; (s = top - 1) - base >= 0;) {
720	>	int j = ((m & s) << ASHIFT) + ABASE;
721	>	if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) == null)
722	>	break;
723	>	if (U.compareAndSwapObject(a, j, t, null)) {
724	>	top = s;
725	>	return t;
726	>	}
727	>	}
728	>	}
729	>	return null;
730	>	}
731	>
732	>	/**
733	>	* Takes next task, if one exists, in order specified by mode.
734	>	*/
735	>	final ForkJoinTask<?> nextLocalTask() {
736	>	return mode == 0 ? pop() : poll();
737	>	}
738	>
739	>	/**
740	>	* Returns next task, if one exists, in order specified by mode.
741	>	*/
742	>	final ForkJoinTask<?> peek() {
743	>	ForkJoinTask<?>[] a = array; int m;
744	>	if (a == null || (m = a.length - 1) < 0)
745	>	return null;
746	>	int i = mode == 0 ? top - 1 : base;
747	>	int j = ((i & m) << ASHIFT) + ABASE;
748	>	return (ForkJoinTask<?>)U.getObjectVolatile(a, j);
749	>	}
750	>
751	>	/**
752	>	* Returns task at index b if b is current base of queue.
753	>	*/
754	>	final ForkJoinTask<?> pollAt(int b) {
755	>	ForkJoinTask<?> t; ForkJoinTask<?>[] a;
756	>	if ((a = array) != null) {
757	>	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
758	>	if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null &&
759	>	base == b &&
760	>	U.compareAndSwapObject(a, j, t, null)) {
761	>	base = b + 1;
762	>	return t;
763	>	}
764	>	}
765	>	return null;
766	>	}
767	>
768	>	/**
769	>	* Pops the given task only if it is at the current top.
770	>	*/
771	>	final boolean tryUnpush(ForkJoinTask<?> t) {
772	>	ForkJoinTask<?>[] a; int s;
773	>	if ((a = array) != null && (s = top) != base &&
774	>	U.compareAndSwapObject
775	>	(a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) {
776	>	top = s;
777	>	return true;
778	>	}
779	>	return false;
780	>	}
781	>
782	>	/**
783	>	* Polls the given task only if it is at the current base.
784	>	*/
785	>	final boolean pollFor(ForkJoinTask<?> task) {
786	>	ForkJoinTask<?>[] a; int b;
787	>	if ((b = base) - top < 0 && (a = array) != null) {
788	>	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
789	>	if (U.getObjectVolatile(a, j) == task && base == b &&
790	>	U.compareAndSwapObject(a, j, task, null)) {
791	>	base = b + 1;
792	>	return true;
793	>	}
794	>	}
795	>	return false;
796	>	}
797	>
798	>	/**
799	>	* If present, removes from queue and executes the given task, or
800	>	* any other cancelled task. Returns (true) immediately on any CAS
801	>	* or consistency check failure so caller can retry.
802	>	*
803	>	* @return false if no progress can be made
804	>	*/
805	>	final boolean tryRemoveAndExec(ForkJoinTask<?> task) {
806	>	boolean removed = false, empty = true, progress = true;
807	>	ForkJoinTask<?>[] a; int m, s, b, n;
808	>	if ((a = array) != null && (m = a.length - 1) >= 0 &&
809	>	(n = (s = top) - (b = base)) > 0) {
810	>	for (ForkJoinTask<?> t;;) {           // traverse from s to b
811	>	int j = ((--s & m) << ASHIFT) + ABASE;
812	>	t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
813	>	if (t == null)                    // inconsistent length
814	>	break;
815	>	else if (t == task) {
816	>	if (s + 1 == top) {           // pop
817	>	if (!U.compareAndSwapObject(a, j, task, null))
818	>	break;
819	>	top = s;
820	>	removed = true;
821	>	}
822	>	else if (base == b)           // replace with proxy
823	>	removed = U.compareAndSwapObject(a, j, task,
824	>	new EmptyTask());
825	>	break;
826	>	}
827	>	else if (t.status >= 0)
828	>	empty = false;
829	>	else if (s + 1 == top) {          // pop and throw away
830	>	if (U.compareAndSwapObject(a, j, t, null))
831	>	top = s;
832	>	break;
833	>	}
834	>	if (--n == 0) {
835	>	if (!empty && base == b)
836	>	progress = false;
837	>	break;
838	>	}
839	>	}
840	>	}
841	>	if (removed)
842	>	task.doExec();
843	>	return progress;
844	>	}
845	>
846	>	/**
847	>	* Initializes or doubles the capacity of array. Call either
848	>	* by owner or with lock held -- it is OK for base, but not
849	>	* top, to move while resizings are in progress.
850	>	*
851	>	* @param rejectOnFailure if true, throw exception if capacity
852	>	* exceeded (relayed ultimately to user); else return null.
853	>	*/
854	>	final ForkJoinTask<?>[] growArray(boolean rejectOnFailure) {
855	>	ForkJoinTask<?>[] oldA = array;
856	>	int size = oldA != null ? oldA.length << 1 : INITIAL_QUEUE_CAPACITY;
857	>	if (size <= MAXIMUM_QUEUE_CAPACITY) {
858	>	int oldMask, t, b;
859	>	ForkJoinTask<?>[] a = array = new ForkJoinTask<?>[size];
860	>	if (oldA != null && (oldMask = oldA.length - 1) >= 0 &&
861	>	(t = top) - (b = base) > 0) {
862	>	int mask = size - 1;
863	>	do {
864	>	ForkJoinTask<?> x;
865	>	int oldj = ((b & oldMask) << ASHIFT) + ABASE;
866	>	int j    = ((b &    mask) << ASHIFT) + ABASE;
867	>	x = (ForkJoinTask<?>)U.getObjectVolatile(oldA, oldj);
868	>	if (x != null &&
869	>	U.compareAndSwapObject(oldA, oldj, x, null))
870	>	U.putObjectVolatile(a, j, x);
871	>	} while (++b != t);
872	>	}
873	>	return a;
874	>	}
875	>	else if (!rejectOnFailure)
876	>	return null;
877	>	else
878	>	throw new RejectedExecutionException("Queue capacity exceeded");
879	>	}
880	>
881	>	/**
882	>	* Removes and cancels all known tasks, ignoring any exceptions.
883	>	*/
884	>	final void cancelAll() {
885	>	ForkJoinTask.cancelIgnoringExceptions(currentJoin);
886	>	ForkJoinTask.cancelIgnoringExceptions(currentSteal);
887	>	for (ForkJoinTask<?> t; (t = poll()) != null; )
888	>	ForkJoinTask.cancelIgnoringExceptions(t);
889	>	}
890	>
891	>	/**
892	>	* Computes next value for random probes.  Scans don't require
893	>	* a very high quality generator, but also not a crummy one.
894	>	* Marsaglia xor-shift is cheap and works well enough.  Note:
895	>	* This is manually inlined in several usages in ForkJoinPool
896	>	* to avoid writes inside busy scan loops.
897	>	*/
898	>	final int nextSeed() {
899	>	int r = seed;
900	>	r ^= r << 13;
901	>	r ^= r >>> 17;
902	>	return seed = r ^= r << 5;
903	>	}
904	>
905	>	// Execution methods
906	>
907	>	/**
908	>	* Removes and runs tasks until empty, using local mode
909	>	* ordering.
910	>	*/
911	>	final void runLocalTasks() {
912	>	if (base - top < 0) {
913	>	for (ForkJoinTask<?> t; (t = nextLocalTask()) != null; )
914	>	t.doExec();
915	>	}
916	>	}
917	>
918	>	/**
919	>	* Executes a top-level task and any local tasks remaining
920	>	* after execution.
921	>	*
922	>	* @return true unless terminating
923	>	*/
924	>	final boolean runTask(ForkJoinTask<?> t) {
925	>	boolean alive = true;
926	>	if (t != null) {
927	>	currentSteal = t;
928	>	t.doExec();
929	>	runLocalTasks();
930	>	++nsteals;
931	>	currentSteal = null;
932	>	}
933	>	else if (runState < 0)            // terminating
934	>	alive = false;
935	>	return alive;
936	>	}
937	>
938	>	/**
939	>	* Executes a non-top-level (stolen) task.
940	>	*/
941	>	final void runSubtask(ForkJoinTask<?> t) {
942	>	if (t != null) {
943	>	ForkJoinTask<?> ps = currentSteal;
944	>	currentSteal = t;
945	>	t.doExec();
946	>	currentSteal = ps;
947	>	}
948	>	}
949	>
950	>	/**
951	>	* Returns true if owned and not known to be blocked.
952	>	*/
953	>	final boolean isApparentlyUnblocked() {
954	>	Thread wt; Thread.State s;
955	>	return (eventCount >= 0 &&
956	>	(wt = owner) != null &&
957	>	(s = wt.getState()) != Thread.State.BLOCKED &&
958	>	s != Thread.State.WAITING &&
959	>	s != Thread.State.TIMED_WAITING);
960	>	}
961	>
962	>	/**
963	>	* If this owned and is not already interrupted, try to
964	>	* interrupt and/or unpark, ignoring exceptions.
965	>	*/
966	>	final void interruptOwner() {
967	>	Thread wt, p;
968	>	if ((wt = owner) != null && !wt.isInterrupted()) {
969	>	try {
970	>	wt.interrupt();
971	>	} catch (SecurityException ignore) {
972	>	}
973	>	}
974	>	if ((p = parker) != null)
975	>	U.unpark(p);
976	>	}
977	>
978	>	// Unsafe mechanics
979	>	private static final sun.misc.Unsafe U;
980	>	private static final long RUNSTATE;
981	>	private static final int ABASE;
982	>	private static final int ASHIFT;
983	>	static {
984	>	int s;
985	>	try {
986	>	U = getUnsafe();
987	>	Class<?> k = WorkQueue.class;
988	>	Class<?> ak = ForkJoinTask[].class;
989	>	RUNSTATE = U.objectFieldOffset
990	>	(k.getDeclaredField("runState"));
991	>	ABASE = U.arrayBaseOffset(ak);
992	>	s = U.arrayIndexScale(ak);
993	>	} catch (Exception e) {
994	>	throw new Error(e);
995	>	}
996	>	if ((s & (s-1)) != 0)
997	>	throw new Error("data type scale not a power of two");
998	>	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
999	>	}
1000		}
1001
1002		/**
1003	<	* Generator for assigning sequence numbers as pool names.
1003	>	* Per-thread records for threads that submit to pools. Currently
1004	>	* holds only pseudo-random seed / index that is used to choose
1005	>	* submission queues in method doSubmit. In the future, this may
1006	>	* also incorporate a means to implement different task rejection
1007	>	* and resubmission policies.
1008		*/
1009	<	private static final AtomicInteger poolNumberGenerator =
1010	<	new AtomicInteger();
1009	>	static final class Submitter {
1010	>	int seed;
1011	>	Submitter() { seed = hashId(Thread.currentThread().getId()); }
1012	>	}
1013
1014	<	/**
1015	<	* Array holding all worker threads in the pool. Initialized upon
1016	<	* first use. Array size must be a power of two.  Updates and
1017	<	* replacements are protected by workerLock, but it is always kept
173	<	* in a consistent enough state to be randomly accessed without
174	<	* locking by workers performing work-stealing.
175	<	*/
176	<	volatile ForkJoinWorkerThread[] workers;
1014	>	/** ThreadLocal class for Submitters */
1015	>	static final class ThreadSubmitter extends ThreadLocal<Submitter> {
1016	>	public Submitter initialValue() { return new Submitter(); }
1017	>	}
1018
1019	<	/**
179	<	* Lock protecting access to workers.
180	<	*/
181	<	private final ReentrantLock workerLock;
1019	>	// static fields (initialized in static initializer below)
1020
1021		/**
1022	<	* Condition for awaitTermination.
1022	>	* Creates a new ForkJoinWorkerThread. This factory is used unless
1023	>	* overridden in ForkJoinPool constructors.
1024		*/
1025	<	private final Condition termination;
1025	>	public static final ForkJoinWorkerThreadFactory
1026	>	defaultForkJoinWorkerThreadFactory;
1027
1028		/**
1029	<	* The uncaught exception handler used when any worker
190	<	* abruptly terminates
1029	>	* Generator for assigning sequence numbers as pool names.
1030		*/
1031	<	private Thread.UncaughtExceptionHandler ueh;
1031	>	private static final AtomicInteger poolNumberGenerator;
1032
1033		/**
1034	<	* Creation factory for worker threads.
1034	>	* Permission required for callers of methods that may start or
1035	>	* kill threads.
1036		*/
1037	<	private final ForkJoinWorkerThreadFactory factory;
1037	>	private static final RuntimePermission modifyThreadPermission;
1038
1039		/**
1040	<	* Head of stack of threads that were created to maintain
1041	<	* parallelism when other threads blocked, but have since
1042	<	* suspended when the parallelism level rose.
1043	<	*/
1044	<	private volatile WaitQueueNode spareStack;
1040	>	* Per-thread submission bookeeping. Shared across all pools
1041	>	* to reduce ThreadLocal pollution and because random motion
1042	>	* to avoid contention in one pool is likely to hold for others.
1043	>	*/
1044	>	private static final ThreadSubmitter submitters;
1045	>
1046	>	// static constants
1047	>
1048	>	/**
1049	>	* The wakeup interval (in nanoseconds) for a worker waiting for a
1050	>	* task when the pool is quiescent to instead try to shrink the
1051	>	* number of workers.  The exact value does not matter too
1052	>	* much. It must be short enough to release resources during
1053	>	* sustained periods of idleness, but not so short that threads
1054	>	* are continually re-created.
1055	>	*/
1056	>	private static final long SHRINK_RATE =
1057	>	4L * 1000L * 1000L * 1000L; // 4 seconds
1058	>
1059	>	/**
1060	>	* The timeout value for attempted shrinkage, includes
1061	>	* some slop to cope with system timer imprecision.
1062	>	*/
1063	>	private static final long SHRINK_TIMEOUT = SHRINK_RATE - (SHRINK_RATE / 10);
1064	>
1065	>	/**
1066	>	* The maximum stolen->joining link depth allowed in tryHelpStealer.
1067	>	* Depths for legitimate chains are unbounded, but we use a fixed
1068	>	* constant to avoid (otherwise unchecked) cycles and to bound
1069	>	* staleness of traversal parameters at the expense of sometimes
1070	>	* blocking when we could be helping.
1071	>	*/
1072	>	private static final int MAX_HELP_DEPTH = 16;
1073	>
1074	>	/**
1075	>	* Bits and masks for control variables
1076	>	*
1077	>	* Field ctl is a long packed with:
1078	>	* AC: Number of active running workers minus target parallelism (16 bits)
1079	>	* TC: Number of total workers minus target parallelism (16 bits)
1080	>	* ST: true if pool is terminating (1 bit)
1081	>	* EC: the wait count of top waiting thread (15 bits)
1082	>	* ID: poolIndex of top of Treiber stack of waiters (16 bits)
1083	>	*
1084	>	* When convenient, we can extract the upper 32 bits of counts and
1085	>	* the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
1086	>	* (int)ctl.  The ec field is never accessed alone, but always
1087	>	* together with id and st. The offsets of counts by the target
1088	>	* parallelism and the positionings of fields makes it possible to
1089	>	* perform the most common checks via sign tests of fields: When
1090	>	* ac is negative, there are not enough active workers, when tc is
1091	>	* negative, there are not enough total workers, and when e is
1092	>	* negative, the pool is terminating.  To deal with these possibly
1093	>	* negative fields, we use casts in and out of "short" and/or
1094	>	* signed shifts to maintain signedness.
1095	>	*
1096	>	* When a thread is queued (inactivated), its eventCount field is
1097	>	* set negative, which is the only way to tell if a worker is
1098	>	* prevented from executing tasks, even though it must continue to
1099	>	* scan for them to avoid queuing races. Note however that
1100	>	* eventCount updates lag releases so usage requires care.
1101	>	*
1102	>	* Field runState is an int packed with:
1103	>	* SHUTDOWN: true if shutdown is enabled (1 bit)
1104	>	* SEQ:  a sequence number updated upon (de)registering workers (15 bits)
1105	>	* MASK: mask (power of 2 - 1) covering all registered poolIndexes (16 bits)
1106	>	*
1107	>	* The combination of mask and sequence number enables simple
1108	>	* consistency checks: Staleness of read-only operations on the
1109	>	* workQueues array can be checked by comparing runState before vs
1110	>	* after the reads. The low 16 bits (i.e, anding with SMASK) hold
1111	>	* the smallest power of two covering all indices, minus
1112	>	* one.
1113	>	*/
1114	>
1115	>	// bit positions/shifts for fields
1116	>	private static final int  AC_SHIFT   = 48;
1117	>	private static final int  TC_SHIFT   = 32;
1118	>	private static final int  ST_SHIFT   = 31;
1119	>	private static final int  EC_SHIFT   = 16;
1120	>
1121	>	// bounds
1122	>	private static final int  POOL_MAX   = 0x7fff;  // max #workers - 1
1123	>	private static final int  SMASK      = 0xffff;  // short bits
1124	>	private static final int  SQMASK     = 0xfffe;  // even short bits
1125	>	private static final int  SHORT_SIGN = 1 << 15;
1126	>	private static final int  INT_SIGN   = 1 << 31;
1127	>
1128	>	// masks
1129	>	private static final long STOP_BIT   = 0x0001L << ST_SHIFT;
1130	>	private static final long AC_MASK    = ((long)SMASK) << AC_SHIFT;
1131	>	private static final long TC_MASK    = ((long)SMASK) << TC_SHIFT;
1132	>
1133	>	// units for incrementing and decrementing
1134	>	private static final long TC_UNIT    = 1L << TC_SHIFT;
1135	>	private static final long AC_UNIT    = 1L << AC_SHIFT;
1136	>
1137	>	// masks and units for dealing with u = (int)(ctl >>> 32)
1138	>	private static final int  UAC_SHIFT  = AC_SHIFT - 32;
1139	>	private static final int  UTC_SHIFT  = TC_SHIFT - 32;
1140	>	private static final int  UAC_MASK   = SMASK << UAC_SHIFT;
1141	>	private static final int  UTC_MASK   = SMASK << UTC_SHIFT;
1142	>	private static final int  UAC_UNIT   = 1 << UAC_SHIFT;
1143	>	private static final int  UTC_UNIT   = 1 << UTC_SHIFT;
1144	>
1145	>	// masks and units for dealing with e = (int)ctl
1146	>	private static final int E_MASK      = 0x7fffffff; // no STOP_BIT
1147	>	private static final int E_SEQ       = 1 << EC_SHIFT;
1148	>
1149	>	// runState bits
1150	>	private static final int SHUTDOWN    = 1 << 31;
1151	>	private static final int RS_SEQ      = 1 << 16;
1152	>	private static final int RS_SEQ_MASK = 0x7fff0000;
1153	>
1154	>	// access mode for WorkQueue
1155	>	static final int LIFO_QUEUE          =  0;
1156	>	static final int FIFO_QUEUE          =  1;
1157	>	static final int SHARED_QUEUE        = -1;
1158
1159	<	/**
1160	<	* Sum of per-thread steal counts, updated only when threads are
1161	<	* idle or terminating.
1162	<	*/
1163	<	private final AtomicLong stealCount;
1159	>	// Instance fields
1160	>
1161	>	/*
1162	>	* Field layout order in this class tends to matter more than one
1163	>	* would like. Runtime layout order is only loosely related to
1164	>	* declaration order and may differ across JVMs, but the following
1165	>	* empirically works OK on current JVMs.
1166	>	*/
1167	>
1168	>	volatile long ctl;                         // main pool control
1169	>	final int parallelism;                     // parallelism level
1170	>	final int localMode;                       // per-worker scheduling mode
1171	>	int growHints;                             // for expanding indices/ranges
1172	>	volatile int runState;                     // shutdown status, seq, and mask
1173	>	WorkQueue[] workQueues;                    // main registry
1174	>	final Mutex lock;                          // for registration
1175	>	final Condition termination;               // for awaitTermination
1176	>	final ForkJoinWorkerThreadFactory factory; // factory for new workers
1177	>	final Thread.UncaughtExceptionHandler ueh; // per-worker UEH
1178	>	final AtomicLong stealCount;               // collect counts when terminated
1179	>	final AtomicInteger nextWorkerNumber;      // to create worker name string
1180	>	final String workerNamePrefix;             // to create worker name string
1181	>
1182	>	//  Creating, registering, deregistering and running workers
1183	>
1184	>	/**
1185	>	* Tries to create and start a worker
1186	>	*/
1187	>	private void addWorker() {
1188	>	Throwable ex = null;
1189	>	ForkJoinWorkerThread wt = null;
1190	>	try {
1191	>	if ((wt = factory.newThread(this)) != null) {
1192	>	wt.start();
1193	>	return;
1194	>	}
1195	>	} catch (Throwable e) {
1196	>	ex = e;
1197	>	}
1198	>	deregisterWorker(wt, ex); // adjust counts etc on failure
1199	>	}
1200
1201		/**
1202	<	* Queue for external submissions.
1202	>	* Callback from ForkJoinWorkerThread constructor to assign a
1203	>	* public name. This must be separate from registerWorker because
1204	>	* it is called during the "super" constructor call in
1205	>	* ForkJoinWorkerThread.
1206		*/
1207	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
1207	>	final String nextWorkerName() {
1208	>	return workerNamePrefix.concat
1209	>	(Integer.toString(nextWorkerNumber.addAndGet(1)));
1210	>	}
1211
1212		/**
1213	<	* Head of Treiber stack for barrier sync. See below for explanation.
1213	>	* Callback from ForkJoinWorkerThread constructor to establish and
1214	>	* record its WorkQueue.
1215	>	*
1216	>	* @param wt the worker thread
1217		*/
1218	<	private volatile WaitQueueNode syncStack;
1218	>	final void registerWorker(ForkJoinWorkerThread wt) {
1219	>	WorkQueue w = wt.workQueue;
1220	>	Mutex lock = this.lock;
1221	>	lock.lock();
1222	>	try {
1223	>	int g = growHints, k = g & SMASK;
1224	>	WorkQueue[] ws = workQueues;
1225	>	if (ws != null) {                       // ignore on shutdown
1226	>	int n = ws.length;
1227	>	if ((k & 1) == 0 || k >= n || ws[k] != null) {
1228	>	for (k = 1; k < n && ws[k] != null; k += 2)
1229	>	;                           // workers are at odd indices
1230	>	if (k >= n)                     // resize
1231	>	workQueues = ws = Arrays.copyOf(ws, n << 1);
1232	>	}
1233	>	w.eventCount = w.poolIndex = k;     // establish before recording
1234	>	ws[k] = w;
1235	>	growHints = (g & ~SMASK) | ((k + 2) & SMASK);
1236	>	int rs = runState;
1237	>	int m = rs & SMASK;                 // recalculate runState mask
1238	>	if (k > m)
1239	>	m = (m << 1) + 1;
1240	>	runState = (rs & SHUTDOWN) | ((rs + RS_SEQ) & RS_SEQ_MASK) | m;
1241	>	}
1242	>	} finally {
1243	>	lock.unlock();
1244	>	}
1245	>	}
1246
1247		/**
1248	<	* The count for event barrier
1249	<	*/
1250	<	private volatile long eventCount;
1248	>	* Final callback from terminating worker, as well as upon failure
1249	>	* to construct or start a worker in addWorker.  Removes record of
1250	>	* worker from array, and adjusts counts. If pool is shutting
1251	>	* down, tries to complete termination.
1252	>	*
1253	>	* @param wt the worker thread or null if addWorker failed
1254	>	* @param ex the exception causing failure, or null if none
1255	>	*/
1256	>	final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
1257	>	WorkQueue w = null;
1258	>	if (wt != null && (w = wt.workQueue) != null) {
1259	>	w.runState = -1;                // ensure runState is set
1260	>	stealCount.getAndAdd(w.totalSteals + w.nsteals);
1261	>	int idx = w.poolIndex;
1262	>	Mutex lock = this.lock;
1263	>	lock.lock();
1264	>	try {                           // remove record from array
1265	>	WorkQueue[] ws = workQueues;
1266	>	if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w) {
1267	>	ws[idx] = null;
1268	>	growHints = (growHints & ~SMASK) | idx;
1269	>	}
1270	>	} finally {
1271	>	lock.unlock();
1272	>	}
1273	>	}
1274	>
1275	>	long c;                             // adjust ctl counts
1276	>	do {} while (!U.compareAndSwapLong
1277	>	(this, CTL, c = ctl, (((c - AC_UNIT) & AC_MASK) |
1278	>	((c - TC_UNIT) & TC_MASK) |
1279	>	(c & ~(AC_MASK|TC_MASK)))));
1280	>
1281	>	if (!tryTerminate(false, false) && w != null) {
1282	>	w.cancelAll();                  // cancel remaining tasks
1283	>	if (w.array != null)            // suppress signal if never ran
1284	>	signalWork();               // wake up or create replacement
1285	>	if (ex == null)                 // help clean refs on way out
1286	>	ForkJoinTask.helpExpungeStaleExceptions();
1287	>	}
1288	>
1289	>	if (ex != null)                     // rethrow
1290	>	U.throwException(ex);
1291	>	}
1292
1293		/**
1294	<	* Pool number, just for assigning useful names to worker threads
1294	>	* Top-level runloop for workers, called by ForkJoinWorkerThread.run.
1295		*/
1296	<	private final int poolNumber;
1296	>	final void runWorker(ForkJoinWorkerThread wt) {
1297	>	// Initialize queue array and seed in this thread
1298	>	WorkQueue w = wt.workQueue;
1299	>	w.growArray(false);
1300	>	w.seed = hashId(Thread.currentThread().getId());
1301	>
1302	>	do {} while (w.runTask(scan(w)));
1303	>	}
1304	>
1305	>	// Submissions
1306
1307		/**
1308	<	* The maximum allowed pool size
1308	>	* Unless shutting down, adds the given task to a submission queue
1309	>	* at submitter's current queue index (modulo submission
1310	>	* range). If no queue exists at the index, one is created unless
1311	>	* pool lock is busy.  If the queue and/or lock are busy, another
1312	>	* index is randomly chosen. The mask in growHints controls the
1313	>	* effective index range of queues considered. The mask is
1314	>	* expanded, up to the current workerQueue mask, upon any detected
1315	>	* contention but otherwise remains small to avoid needlessly
1316	>	* creating queues when there is no contention.
1317		*/
1318	<	private volatile int maxPoolSize;
1318	>	private void doSubmit(ForkJoinTask<?> task) {
1319	>	if (task == null)
1320	>	throw new NullPointerException();
1321	>	Submitter s = submitters.get();
1322	>	for (int r = s.seed, m = growHints >>> 16;;) {
1323	>	WorkQueue[] ws; WorkQueue q; Mutex lk;
1324	>	int k = r & m & SQMASK;          // use only even indices
1325	>	if (runState < 0 || (ws = workQueues) == null || ws.length <= k)
1326	>	throw new RejectedExecutionException(); // shutting down
1327	>	if ((q = ws[k]) == null && (lk = lock).tryAcquire(0)) {
1328	>	try {                        // try to create new queue
1329	>	if (ws == workQueues && (q = ws[k]) == null) {
1330	>	int rs;              // update runState seq
1331	>	ws[k] = q = new WorkQueue(null, SHARED_QUEUE);
1332	>	runState = (((rs = runState) & SHUTDOWN) |
1333	>	((rs + RS_SEQ) & ~SHUTDOWN));
1334	>	}
1335	>	} finally {
1336	>	lk.unlock();
1337	>	}
1338	>	}
1339	>	if (q != null) {
1340	>	if (q.trySharedPush(task)) {
1341	>	signalWork();
1342	>	return;
1343	>	}
1344	>	else if (m < parallelism - 1 && m < (runState & SMASK)) {
1345	>	Mutex lock = this.lock;
1346	>	lock.lock();             // block until lock free
1347	>	int g = growHints;
1348	>	if (g >>> 16 == m)       // expand range
1349	>	growHints = (((m << 1) + 1) << 16) | (g & SMASK);
1350	>	lock.unlock();           // no need for try/finally
1351	>	}
1352	>	else if ((r & m) == 0)
1353	>	Thread.yield();          // occasionally yield if busy
1354	>	}
1355	>	if (m == (m = growHints >>> 16)) {
1356	>	r ^= r << 13;                // update seed unless new range
1357	>	r ^= r >>> 17;               // same xorshift as WorkQueues
1358	>	s.seed = r ^= r << 5;
1359	>	}
1360	>	}
1361	>	}
1362	>
1363	>	// Maintaining ctl counts
1364
1365		/**
1366	<	* The desired parallelism level, updated only under workerLock.
1366	>	* Increments active count; mainly called upon return from blocking.
1367		*/
1368	<	private volatile int parallelism;
1368	>	final void incrementActiveCount() {
1369	>	long c;
1370	>	do {} while (!U.compareAndSwapLong(this, CTL, c = ctl, c + AC_UNIT));
1371	>	}
1372
1373		/**
1374	<	* True if use local fifo, not default lifo, for local polling
1374	>	* Tries to activate or create a worker if too few are active.
1375		*/
1376	<	private volatile boolean locallyFifo;
1376	>	final void signalWork() {
1377	>	long c; int u;
1378	>	while ((u = (int)((c = ctl) >>> 32)) < 0) {     // too few active
1379	>	WorkQueue[] ws = workQueues; int e, i; WorkQueue w; Thread p;
1380	>	if ((e = (int)c) > 0) {                     // at least one waiting
1381	>	if (ws != null && (i = e & SMASK) < ws.length &&
1382	>	(w = ws[i]) != null && w.eventCount == (e | INT_SIGN)) {
1383	>	long nc = (((long)(w.nextWait & E_MASK)) |
1384	>	((long)(u + UAC_UNIT) << 32));
1385	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1386	>	w.eventCount = (e + E_SEQ) & E_MASK;
1387	>	if ((p = w.parker) != null)
1388	>	U.unpark(p);                // activate and release
1389	>	break;
1390	>	}
1391	>	}
1392	>	else
1393	>	break;
1394	>	}
1395	>	else if (e == 0 && (u & SHORT_SIGN) != 0) { // too few total
1396	>	long nc = (long)(((u + UTC_UNIT) & UTC_MASK) |
1397	>	((u + UAC_UNIT) & UAC_MASK)) << 32;
1398	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1399	>	addWorker();
1400	>	break;
1401	>	}
1402	>	}
1403	>	else
1404	>	break;
1405	>	}
1406	>	}
1407
1408		/**
1409	<	* Holds number of total (i.e., created and not yet terminated)
1410	<	* and running (i.e., not blocked on joins or other managed sync)
1411	<	* threads, packed into one int to ensure consistent snapshot when
1412	<	* making decisions about creating and suspending spare
1413	<	* threads. Updated only by CAS.  Note: CASes in
1414	<	* updateRunningCount and preJoin assume that running active count
1415	<	* is in low word, so need to be modified if this changes.
1416	<	*/
1417	<	private volatile int workerCounts;
1409	>	* Tries to decrement active count (sometimes implicitly) and
1410	>	* possibly release or create a compensating worker in preparation
1411	>	* for blocking. Fails on contention or termination.
1412	>	*
1413	>	* @return true if the caller can block, else should recheck and retry
1414	>	*/
1415	>	final boolean tryCompensate() {
1416	>	WorkQueue w; Thread p;
1417	>	int pc = parallelism, e, u, ac, tc, i;
1418	>	long c = ctl;
1419	>	WorkQueue[] ws = workQueues;
1420	>	if ((e = (int)c) >= 0) {
1421	>	if ((ac = ((u = (int)(c >>> 32)) >> UAC_SHIFT)) <= 0 &&
1422	>	e != 0 && ws != null && (i = e & SMASK) < ws.length &&
1423	>	(w = ws[i]) != null) {
1424	>	long nc = (long)(w.nextWait & E_MASK) | (c & (AC_MASK|TC_MASK));
1425	>	if (w.eventCount == (e | INT_SIGN) &&
1426	>	U.compareAndSwapLong(this, CTL, c, nc)) {
1427	>	w.eventCount = (e + E_SEQ) & E_MASK;
1428	>	if ((p = w.parker) != null)
1429	>	U.unpark(p);
1430	>	return true;             // release an idle worker
1431	>	}
1432	>	}
1433	>	else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
1434	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
1435	>	if (U.compareAndSwapLong(this, CTL, c, nc))
1436	>	return true;             // no compensation needed
1437	>	}
1438	>	else if (tc + pc < POOL_MAX) {
1439	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
1440	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1441	>	addWorker();
1442	>	return true;             // create replacement
1443	>	}
1444	>	}
1445	>	}
1446	>	return false;
1447	>	}
1448
1449	<	private static int totalCountOf(int s)           { return s >>> 16;  }
259	<	private static int runningCountOf(int s)         { return s & shortMask; }
260	<	private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
1449	>	// Scanning for tasks
1450
1451		/**
1452	<	* Adds delta (which may be negative) to running count.  This must
1453	<	* be called before (with negative arg) and after (with positive)
1454	<	* any managed synchronization (i.e., mainly, joins).
1455	<	*
1456	<	* @param delta the number to add
1457	<	*/
1458	<	final void updateRunningCount(int delta) {
1459	<	int s;
1460	<	do {} while (!casWorkerCounts(s = workerCounts, s + delta));
1452	>	* Scans for and, if found, returns one task, else possibly
1453	>	* inactivates the worker. This method operates on single reads of
1454	>	* volatile state and is designed to be re-invoked continuously in
1455	>	* part because it returns upon detecting inconsistencies,
1456	>	* contention, or state changes that indicate possible success on
1457	>	* re-invocation.
1458	>	*
1459	>	* The scan searches for tasks across queues, randomly selecting
1460	>	* the first #queues probes, favoring steals over submissions
1461	>	* (by exploiting even/odd indexing), and then performing a
1462	>	* circular sweep of all queues.  The scan terminates upon either
1463	>	* finding a non-empty queue, or completing a full sweep. If the
1464	>	* worker is not inactivated, it takes and returns a task from
1465	>	* this queue.  On failure to find a task, we take one of the
1466	>	* following actions, after which the caller will retry calling
1467	>	* this method unless terminated.
1468	>	*
1469	>	* * If pool is terminating, terminate the worker.
1470	>	*
1471	>	* * If not a complete sweep, try to release a waiting worker.  If
1472	>	* the scan terminated because the worker is inactivated, then the
1473	>	* released worker will often be the calling worker, and it can
1474	>	* succeed obtaining a task on the next call. Or maybe it is
1475	>	* another worker, but with same net effect. Releasing in other
1476	>	* cases as well ensures that we have enough workers running.
1477	>	*
1478	>	* * If the caller has run a task since the last empty scan,
1479	>	* return (to allow rescan) if other workers are not also yet
1480	>	* enqueued.  Field WorkQueue.rescans counts down on each scan to
1481	>	* ensure eventual inactivation and blocking.
1482	>	*
1483	>	* * If not already enqueued, try to inactivate and enqueue the
1484	>	* worker on wait queue.
1485	>	*
1486	>	* * If already enqueued and none of the above apply, either park
1487	>	* awaiting signal, or if this is the most recent waiter and pool
1488	>	* is quiescent, relay to idleAwaitWork to check for termination
1489	>	* and possibly shrink pool.
1490	>	*
1491	>	* @param w the worker (via its WorkQueue)
1492	>	* @return a task or null of none found
1493	>	*/
1494	>	private final ForkJoinTask<?> scan(WorkQueue w) {
1495	>	boolean swept = false;               // true after full empty scan
1496	>	WorkQueue[] ws;                      // volatile read order matters
1497	>	int r = w.seed, ec = w.eventCount;   // ec is negative if inactive
1498	>	int rs = runState, m = rs & SMASK;
1499	>	if ((ws = workQueues) != null && ws.length > m) { // consistency check
1500	>	for (int k = 0, j = -1 - m; ; ++j) {
1501	>	WorkQueue q; int b;
1502	>	if (j < 0) {                 // random probes while j negative
1503	>	r ^= r << 13; r ^= r >>> 17; k = (r ^= r << 5) | (j & 1);
1504	>	}                            // worker (not submit) for odd j
1505	>	else                         // cyclic scan when j >= 0
1506	>	k += 7;                  // step 7 reduces array packing bias
1507	>	if ((q = ws[k & m]) != null && (b = q.base) - q.top < 0) {
1508	>	ForkJoinTask<?> t = (ec >= 0) ? q.pollAt(b) : null;
1509	>	w.seed = r;              // save seed for next scan
1510	>	if (t != null)
1511	>	return t;
1512	>	break;
1513	>	}
1514	>	else if (j - m > m) {
1515	>	if (rs == runState)      // staleness check
1516	>	swept = true;
1517	>	break;
1518	>	}
1519	>	}
1520	>
1521	>	// Decode ctl on empty scan
1522	>	long c = ctl; int e = (int)c, a = (int)(c >> AC_SHIFT), nr, ns;
1523	>	if (e < 0)                       // pool is terminating
1524	>	w.runState = -1;
1525	>	else if (!swept) {               // try to release a waiter
1526	>	WorkQueue v; Thread p;
1527	>	if (e > 0 && a < 0 && (v = ws[e & m]) != null &&
1528	>	v.eventCount == (e | INT_SIGN)) {
1529	>	long nc = ((long)(v.nextWait & E_MASK) |
1530	>	((c + AC_UNIT) & (AC_MASK|TC_MASK)));
1531	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1532	>	v.eventCount = (e + E_SEQ) & E_MASK;
1533	>	if ((p = v.parker) != null)
1534	>	U.unpark(p);
1535	>	}
1536	>	}
1537	>	}
1538	>	else if ((nr = w.rescans) > 0) { // continue rescanning
1539	>	int ac = a + parallelism;
1540	>	if (((w.rescans = (ac < nr) ? ac : nr - 1) & 3) == 0 &&
1541	>	w.eventCount == ec)
1542	>	Thread.yield();          // occasionally yield
1543	>	}
1544	>	else if (ec >= 0) {              // try to enqueue
1545	>	long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
1546	>	w.nextWait = e;
1547	>	w.eventCount = ec | INT_SIGN;// mark as inactive
1548	>	if (!U.compareAndSwapLong(this, CTL, c, nc))
1549	>	w.eventCount = ec;       // unmark on CAS failure
1550	>	else if ((ns = w.nsteals) != 0) {
1551	>	w.nsteals = 0;           // set rescans if ran task
1552	>	w.rescans = a + parallelism;
1553	>	w.totalSteals += ns;
1554	>	}
1555	>	}
1556	>	else{                            // already queued
1557	>	if (parallelism == -a)
1558	>	idleAwaitWork(w);        // quiescent
1559	>	if (w.eventCount == ec) {
1560	>	Thread.interrupted();    // clear status
1561	>	ForkJoinWorkerThread wt = w.owner;
1562	>	U.putObject(wt, PARKBLOCKER, this);
1563	>	w.parker = wt;           // emulate LockSupport.park
1564	>	if (w.eventCount == ec)  // recheck
1565	>	U.park(false, 0L);   // block
1566	>	w.parker = null;
1567	>	U.putObject(wt, PARKBLOCKER, null);
1568	>	}
1569	>	}
1570	>	}
1571	>	return null;
1572		}
1573
1574		/**
1575	<	* Adds delta (which may be negative) to both total and running
1576	<	* count.  This must be called upon creation and termination of
1577	<	* worker threads.
1578	<	*
1579	<	* @param delta the number to add
1580	<	*/
1581	<	private void updateWorkerCount(int delta) {
1582	<	int d = delta + (delta << 16); // add to both lo and hi parts
1583	<	int s;
1584	<	do {} while (!casWorkerCounts(s = workerCounts, s + d));
1575	>	* If inactivating worker w has caused pool to become quiescent,
1576	>	* checks for pool termination, and, so long as this is not the
1577	>	* only worker, waits for event for up to SHRINK_RATE nanosecs.
1578	>	* On timeout, if ctl has not changed, terminates the worker,
1579	>	* which will in turn wake up another worker to possibly repeat
1580	>	* this process.
1581	>	*
1582	>	* @param w the calling worker
1583	>	*/
1584	>	private void idleAwaitWork(WorkQueue w) {
1585	>	long c; int nw, ec;
1586	>	if (!tryTerminate(false, false) &&
1587	>	(int)((c = ctl) >> AC_SHIFT) + parallelism == 0 &&
1588	>	(ec = w.eventCount) == ((int)c | INT_SIGN) &&
1589	>	(nw = w.nextWait) != 0) {
1590	>	long nc = ((long)(nw & E_MASK) | // ctl to restore on timeout
1591	>	((c + AC_UNIT) & AC_MASK) | (c & TC_MASK));
1592	>	ForkJoinWorkerThread wt = w.owner;
1593	>	while (ctl == c) {
1594	>	long startTime = System.nanoTime();
1595	>	Thread.interrupted();  // timed variant of version in scan()
1596	>	U.putObject(wt, PARKBLOCKER, this);
1597	>	w.parker = wt;
1598	>	if (ctl == c)
1599	>	U.park(false, SHRINK_RATE);
1600	>	w.parker = null;
1601	>	U.putObject(wt, PARKBLOCKER, null);
1602	>	if (ctl != c)
1603	>	break;
1604	>	if (System.nanoTime() - startTime >= SHRINK_TIMEOUT &&
1605	>	U.compareAndSwapLong(this, CTL, c, nc)) {
1606	>	w.eventCount = (ec + E_SEQ) | E_MASK;
1607	>	w.runState = -1;          // shrink
1608	>	break;
1609	>	}
1610	>	}
1611	>	}
1612		}
1613
1614		/**
1615	<	* Lifecycle control. High word contains runState, low word
1616	<	* contains the number of workers that are (probably) executing
1617	<	* tasks. This value is atomically incremented before a worker
1618	<	* gets a task to run, and decremented when worker has no tasks
1619	<	* and cannot find any. These two fields are bundled together to
1620	<	* support correct termination triggering.  Note: activeCount
1621	<	* CAS'es cheat by assuming active count is in low word, so need
1622	<	* to be modified if this changes
1623	<	*/
1624	<	private volatile int runControl;
1625	<
1626	<	// RunState values. Order among values matters
1627	<	private static final int RUNNING     = 0;
1628	<	private static final int SHUTDOWN    = 1;
1629	<	private static final int TERMINATING = 2;
1630	<	private static final int TERMINATED  = 3;
1615	>	* Tries to locate and execute tasks for a stealer of the given
1616	>	* task, or in turn one of its stealers, Traces currentSteal ->
1617	>	* currentJoin links looking for a thread working on a descendant
1618	>	* of the given task and with a non-empty queue to steal back and
1619	>	* execute tasks from. The first call to this method upon a
1620	>	* waiting join will often entail scanning/search, (which is OK
1621	>	* because the joiner has nothing better to do), but this method
1622	>	* leaves hints in workers to speed up subsequent calls. The
1623	>	* implementation is very branchy to cope with potential
1624	>	* inconsistencies or loops encountering chains that are stale,
1625	>	* unknown, or of length greater than MAX_HELP_DEPTH links.  All
1626	>	* of these cases are dealt with by just retrying by caller.
1627	>	*
1628	>	* @param joiner the joining worker
1629	>	* @param task the task to join
1630	>	* @return true if found or ran a task (and so is immediately retryable)
1631	>	*/
1632	>	final boolean tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
1633	>	ForkJoinTask<?> subtask;    // current target
1634	>	boolean progress = false;
1635	>	int depth = 0;              // current chain depth
1636	>	int m = runState & SMASK;
1637	>	WorkQueue[] ws = workQueues;
1638	>
1639	>	if (ws != null && ws.length > m && (subtask = task).status >= 0) {
1640	>	outer:for (WorkQueue j = joiner;;) {
1641	>	// Try to find the stealer of subtask, by first using hint
1642	>	WorkQueue stealer = null;
1643	>	WorkQueue v = ws[j.stealHint & m];
1644	>	if (v != null && v.currentSteal == subtask)
1645	>	stealer = v;
1646	>	else {
1647	>	for (int i = 1; i <= m; i += 2) {
1648	>	if ((v = ws[i]) != null && v.currentSteal == subtask) {
1649	>	stealer = v;
1650	>	j.stealHint = i; // save hint
1651	>	break;
1652	>	}
1653	>	}
1654	>	if (stealer == null)
1655	>	break;
1656	>	}
1657
1658	<	private static int runStateOf(int c)             { return c >>> 16; }
1659	<	private static int activeCountOf(int c)          { return c & shortMask; }
1660	<	private static int runControlFor(int r, int a)   { return (r << 16) + a; }
1658	>	for (WorkQueue q = stealer;;) { // Try to help stealer
1659	>	ForkJoinTask<?> t; int b;
1660	>	if (task.status < 0)
1661	>	break outer;
1662	>	if ((b = q.base) - q.top < 0) {
1663	>	progress = true;
1664	>	if (subtask.status < 0)
1665	>	break outer;               // stale
1666	>	if ((t = q.pollAt(b)) != null) {
1667	>	stealer.stealHint = joiner.poolIndex;
1668	>	joiner.runSubtask(t);
1669	>	}
1670	>	}
1671	>	else { // empty - try to descend to find stealer's stealer
1672	>	ForkJoinTask<?> next = stealer.currentJoin;
1673	>	if (++depth == MAX_HELP_DEPTH || subtask.status < 0 ||
1674	>	next == null || next == subtask)
1675	>	break outer;  // max depth, stale, dead-end, cyclic
1676	>	subtask = next;
1677	>	j = stealer;
1678	>	break;
1679	>	}
1680	>	}
1681	>	}
1682	>	}
1683	>	return progress;
1684	>	}
1685
1686		/**
1687	<	* Tries incrementing active count; fails on contention.
311	<	* Called by workers before/during executing tasks.
1687	>	* If task is at base of some steal queue, steals and executes it.
1688		*
1689	<	* @return true on success
1689	>	* @param joiner the joining worker
1690	>	* @param task the task
1691		*/
1692	<	final boolean tryIncrementActiveCount() {
1693	<	int c = runControl;
1694	<	return casRunControl(c, c+1);
1692	>	final void tryPollForAndExec(WorkQueue joiner, ForkJoinTask<?> task) {
1693	>	WorkQueue[] ws;
1694	>	int m = runState & SMASK;
1695	>	if ((ws = workQueues) != null && ws.length > m) {
1696	>	for (int j = 1; j <= m && task.status >= 0; j += 2) {
1697	>	WorkQueue q = ws[j];
1698	>	if (q != null && q.pollFor(task)) {
1699	>	joiner.runSubtask(task);
1700	>	break;
1701	>	}
1702	>	}
1703	>	}
1704		}
1705
1706		/**
1707	<	* Tries decrementing active count; fails on contention.
1708	<	* Possibly triggers termination on success.
1709	<	* Called by workers when they can't find tasks.
1710	<	*
1711	<	* @return true on success
1712	<	*/
1713	<	final boolean tryDecrementActiveCount() {
1714	<	int c = runControl;
1715	<	int nextc = c - 1;
1716	<	if (!casRunControl(c, nextc))
1717	<	return false;
1718	<	if (canTerminateOnShutdown(nextc))
1719	<	terminateOnShutdown();
1720	<	return true;
1707	>	* Returns a non-empty steal queue, if one is found during a random,
1708	>	* then cyclic scan, else null.  This method must be retried by
1709	>	* caller if, by the time it tries to use the queue, it is empty.
1710	>	*/
1711	>	private WorkQueue findNonEmptyStealQueue(WorkQueue w) {
1712	>	int r = w.seed;    // Same idea as scan(), but ignoring submissions
1713	>	for (WorkQueue[] ws;;) {
1714	>	int m = runState & SMASK;
1715	>	if ((ws = workQueues) == null)
1716	>	return null;
1717	>	if (ws.length > m) {
1718	>	WorkQueue q;
1719	>	for (int k = 0, j = -1 - m;; ++j) {
1720	>	if (j < 0) {
1721	>	r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
1722	>	}
1723	>	else
1724	>	k += 7;
1725	>	if ((q = ws[(k | 1) & m]) != null && q.base - q.top < 0) {
1726	>	w.seed = r;
1727	>	return q;
1728	>	}
1729	>	else if (j - m > m)
1730	>	return null;
1731	>	}
1732	>	}
1733	>	}
1734		}
1735
1736		/**
1737	<	* Returns {@code true} if argument represents zero active count
1738	<	* and nonzero runstate, which is the triggering condition for
1739	<	* terminating on shutdown.
1740	<	*/
1741	<	private static boolean canTerminateOnShutdown(int c) {
1742	<	// i.e. least bit is nonzero runState bit
1743	<	return ((c & -c) >>> 16) != 0;
1737	>	* Runs tasks until {@code isQuiescent()}. We piggyback on
1738	>	* active count ctl maintenance, but rather than blocking
1739	>	* when tasks cannot be found, we rescan until all others cannot
1740	>	* find tasks either.
1741	>	*/
1742	>	final void helpQuiescePool(WorkQueue w) {
1743	>	for (boolean active = true;;) {
1744	>	w.runLocalTasks();      // exhaust local queue
1745	>	WorkQueue q = findNonEmptyStealQueue(w);
1746	>	if (q != null) {
1747	>	ForkJoinTask<?> t;
1748	>	if (!active) {      // re-establish active count
1749	>	long c;
1750	>	active = true;
1751	>	do {} while (!U.compareAndSwapLong
1752	>	(this, CTL, c = ctl, c + AC_UNIT));
1753	>	}
1754	>	if ((t = q.poll()) != null)
1755	>	w.runSubtask(t);
1756	>	}
1757	>	else {
1758	>	long c;
1759	>	if (active) {       // decrement active count without queuing
1760	>	active = false;
1761	>	do {} while (!U.compareAndSwapLong
1762	>	(this, CTL, c = ctl, c -= AC_UNIT));
1763	>	}
1764	>	else
1765	>	c = ctl;        // re-increment on exit
1766	>	if ((int)(c >> AC_SHIFT) + parallelism == 0) {
1767	>	do {} while (!U.compareAndSwapLong
1768	>	(this, CTL, c = ctl, c + AC_UNIT));
1769	>	break;
1770	>	}
1771	>	}
1772	>	}
1773		}
1774
1775		/**
1776	<	* Transition run state to at least the given state. Return true
1777	<	* if not already at least given state.
1776	>	* Gets and removes a local or stolen task for the given worker.
1777	>	*
1778	>	* @return a task, if available
1779		*/
1780	<	private boolean transitionRunStateTo(int state) {
1781	<	for (;;) {
1782	<	int c = runControl;
1783	<	if (runStateOf(c) >= state)
1784	<	return false;
1785	<	if (casRunControl(c, runControlFor(state, activeCountOf(c))))
1786	<	return true;
1780	>	final ForkJoinTask<?> nextTaskFor(WorkQueue w) {
1781	>	for (ForkJoinTask<?> t;;) {
1782	>	WorkQueue q;
1783	>	if ((t = w.nextLocalTask()) != null)
1784	>	return t;
1785	>	if ((q = findNonEmptyStealQueue(w)) == null)
1786	>	return null;
1787	>	if ((t = q.poll()) != null)
1788	>	return t;
1789		}
1790		}
1791
1792		/**
1793	<	* Controls whether to add spares to maintain parallelism
1794	<	*/
1795	<	private volatile boolean maintainsParallelism;
1793	>	* Returns the approximate (non-atomic) number of idle threads per
1794	>	* active thread to offset steal queue size for method
1795	>	* ForkJoinTask.getSurplusQueuedTaskCount().
1796	>	*/
1797	>	final int idlePerActive() {
1798	>	// Approximate at powers of two for small values, saturate past 4
1799	>	int p = parallelism;
1800	>	int a = p + (int)(ctl >> AC_SHIFT);
1801	>	return (a > (p >>>= 1) ? 0 :
1802	>	a > (p >>>= 1) ? 1 :
1803	>	a > (p >>>= 1) ? 2 :
1804	>	a > (p >>>= 1) ? 4 :
1805	>	8);
1806	>	}
1807	>
1808	>	//  Termination
1809	>
1810	>	/**
1811	>	* Possibly initiates and/or completes termination.  The caller
1812	>	* triggering termination runs three passes through workQueues:
1813	>	* (0) Setting termination status, followed by wakeups of queued
1814	>	* workers; (1) cancelling all tasks; (2) interrupting lagging
1815	>	* threads (likely in external tasks, but possibly also blocked in
1816	>	* joins).  Each pass repeats previous steps because of potential
1817	>	* lagging thread creation.
1818	>	*
1819	>	* @param now if true, unconditionally terminate, else only
1820	>	* if no work and no active workers
1821	>	* @param enable if true, enable shutdown when next possible
1822	>	* @return true if now terminating or terminated
1823	>	*/
1824	>	private boolean tryTerminate(boolean now, boolean enable) {
1825	>	Mutex lock = this.lock;
1826	>	for (long c;;) {
1827	>	if (((c = ctl) & STOP_BIT) != 0) {      // already terminating
1828	>	if ((short)(c >>> TC_SHIFT) == -parallelism) {
1829	>	lock.lock();                    // don't need try/finally
1830	>	termination.signalAll();        // signal when 0 workers
1831	>	lock.unlock();
1832	>	}
1833	>	return true;
1834	>	}
1835	>	if (runState >= 0) {                    // not yet enabled
1836	>	if (!enable)
1837	>	return false;
1838	>	lock.lock();
1839	>	runState |= SHUTDOWN;
1840	>	lock.unlock();
1841	>	}
1842	>	if (!now) {                             // check if idle & no tasks
1843	>	if ((int)(c >> AC_SHIFT) != -parallelism ||
1844	>	hasQueuedSubmissions())
1845	>	return false;
1846	>	// Check for unqueued inactive workers. One pass suffices.
1847	>	WorkQueue[] ws = workQueues; WorkQueue w;
1848	>	if (ws != null) {
1849	>	for (int i = 1; i < ws.length; i += 2) {
1850	>	if ((w = ws[i]) != null && w.eventCount >= 0)
1851	>	return false;
1852	>	}
1853	>	}
1854	>	}
1855	>	if (U.compareAndSwapLong(this, CTL, c, c | STOP_BIT)) {
1856	>	for (int pass = 0; pass < 3; ++pass) {
1857	>	WorkQueue[] ws = workQueues;
1858	>	if (ws != null) {
1859	>	WorkQueue w;
1860	>	int n = ws.length;
1861	>	for (int i = 0; i < n; ++i) {
1862	>	if ((w = ws[i]) != null) {
1863	>	w.runState = -1;
1864	>	if (pass > 0) {
1865	>	w.cancelAll();
1866	>	if (pass > 1)
1867	>	w.interruptOwner();
1868	>	}
1869	>	}
1870	>	}
1871	>	// Wake up workers parked on event queue
1872	>	int i, e; long cc; Thread p;
1873	>	while ((e = (int)(cc = ctl) & E_MASK) != 0 &&
1874	>	(i = e & SMASK) < n &&
1875	>	(w = ws[i]) != null) {
1876	>	long nc = ((long)(w.nextWait & E_MASK) |
1877	>	((cc + AC_UNIT) & AC_MASK) |
1878	>	(cc & (TC_MASK|STOP_BIT)));
1879	>	if (w.eventCount == (e | INT_SIGN) &&
1880	>	U.compareAndSwapLong(this, CTL, cc, nc)) {
1881	>	w.eventCount = (e + E_SEQ) & E_MASK;
1882	>	w.runState = -1;
1883	>	if ((p = w.parker) != null)
1884	>	U.unpark(p);
1885	>	}
1886	>	}
1887	>	}
1888	>	}
1889	>	}
1890	>	}
1891	>	}
1892	>
1893	>	// Exported methods
1894
1895		// Constructors
1896
1897		/**
1898		* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1899	<	* java.lang.Runtime#availableProcessors}, and using the {@linkplain
1900	<	* #defaultForkJoinWorkerThreadFactory default thread factory}.
1899	>	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1900	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1901	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1902		*
1903		* @throws SecurityException if a security manager exists and
1904		*         the caller is not permitted to modify threads
#	Line 377 | Line 1907 | public class ForkJoinPool extends Abstra
1907		*/
1908		public ForkJoinPool() {
1909		this(Runtime.getRuntime().availableProcessors(),
1910	<	defaultForkJoinWorkerThreadFactory);
1910	>	defaultForkJoinWorkerThreadFactory, null, false);
1911		}
1912
1913		/**
1914		* Creates a {@code ForkJoinPool} with the indicated parallelism
1915	<	* level and using the {@linkplain
1916	<	* #defaultForkJoinWorkerThreadFactory default thread factory}.
1915	>	* level, the {@linkplain
1916	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1917	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1918		*
1919		* @param parallelism the parallelism level
1920		* @throws IllegalArgumentException if parallelism less than or
#	Line 394 | Line 1925 | public class ForkJoinPool extends Abstra
1925		*         java.lang.RuntimePermission}{@code ("modifyThread")}
1926		*/
1927		public ForkJoinPool(int parallelism) {
1928	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
1928	>	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1929		}
1930
1931		/**
1932	<	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
402	<	* java.lang.Runtime#availableProcessors}, and using the given
403	<	* thread factory.
404	<	*
405	<	* @param factory the factory for creating new threads
406	<	* @throws NullPointerException if the factory is null
407	<	* @throws SecurityException if a security manager exists and
408	<	*         the caller is not permitted to modify threads
409	<	*         because it does not hold {@link
410	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
411	<	*/
412	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
413	<	this(Runtime.getRuntime().availableProcessors(), factory);
414	<	}
415	<
416	<	/**
417	<	* Creates a {@code ForkJoinPool} with the given parallelism and
418	<	* thread factory.
1932	>	* Creates a {@code ForkJoinPool} with the given parameters.
1933		*
1934	<	* @param parallelism the parallelism level
1935	<	* @param factory the factory for creating new threads
1934	>	* @param parallelism the parallelism level. For default value,
1935	>	* use {@link java.lang.Runtime#availableProcessors}.
1936	>	* @param factory the factory for creating new threads. For default value,
1937	>	* use {@link #defaultForkJoinWorkerThreadFactory}.
1938	>	* @param handler the handler for internal worker threads that
1939	>	* terminate due to unrecoverable errors encountered while executing
1940	>	* tasks. For default value, use {@code null}.
1941	>	* @param asyncMode if true,
1942	>	* establishes local first-in-first-out scheduling mode for forked
1943	>	* tasks that are never joined. This mode may be more appropriate
1944	>	* than default locally stack-based mode in applications in which
1945	>	* worker threads only process event-style asynchronous tasks.
1946	>	* For default value, use {@code false}.
1947		* @throws IllegalArgumentException if parallelism less than or
1948		*         equal to zero, or greater than implementation limit
1949		* @throws NullPointerException if the factory is null
#	Line 427 | Line 1952 | public class ForkJoinPool extends Abstra
1952		*         because it does not hold {@link
1953		*         java.lang.RuntimePermission}{@code ("modifyThread")}
1954		*/
1955	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
1956	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1957	<	throw new IllegalArgumentException();
1955	>	public ForkJoinPool(int parallelism,
1956	>	ForkJoinWorkerThreadFactory factory,
1957	>	Thread.UncaughtExceptionHandler handler,
1958	>	boolean asyncMode) {
1959	>	checkPermission();
1960		if (factory == null)
1961		throw new NullPointerException();
1962	<	checkPermission();
1963	<	this.factory = factory;
1962	>	if (parallelism <= 0 || parallelism > POOL_MAX)
1963	>	throw new IllegalArgumentException();
1964		this.parallelism = parallelism;
1965	<	this.maxPoolSize = MAX_THREADS;
1966	<	this.maintainsParallelism = true;
1967	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
1968	<	this.workerLock = new ReentrantLock();
1969	<	this.termination = workerLock.newCondition();
1970	<	this.stealCount = new AtomicLong();
1971	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1972	<	// worker array and workers are lazily constructed
1973	<	}
1974	<
1975	<	/**
1976	<	* Creates a new worker thread using factory.
450	<	*
451	<	* @param index the index to assign worker
452	<	* @return new worker, or null if factory failed
453	<	*/
454	<	private ForkJoinWorkerThread createWorker(int index) {
455	<	Thread.UncaughtExceptionHandler h = ueh;
456	<	ForkJoinWorkerThread w = factory.newThread(this);
457	<	if (w != null) {
458	<	w.poolIndex = index;
459	<	w.setDaemon(true);
460	<	w.setAsyncMode(locallyFifo);
461	<	w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
462	<	if (h != null)
463	<	w.setUncaughtExceptionHandler(h);
464	<	}
465	<	return w;
466	<	}
467	<
468	<	/**
469	<	* Returns a good size for worker array given pool size.
470	<	* Currently requires size to be a power of two.
471	<	*/
472	<	private static int arraySizeFor(int poolSize) {
473	<	if (poolSize <= 1)
474	<	return 1;
475	<	// See Hackers Delight, sec 3.2
476	<	int c = poolSize >= MAX_THREADS ? MAX_THREADS : (poolSize - 1);
477	<	c |= c >>>  1;
478	<	c |= c >>>  2;
479	<	c |= c >>>  4;
480	<	c |= c >>>  8;
481	<	c |= c >>> 16;
482	<	return c + 1;
483	<	}
484	<
485	<	/**
486	<	* Creates or resizes array if necessary to hold newLength.
487	<	* Call only under exclusion.
488	<	*
489	<	* @return the array
490	<	*/
491	<	private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
492	<	ForkJoinWorkerThread[] ws = workers;
493	<	if (ws == null)
494	<	return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
495	<	else if (newLength > ws.length)
496	<	return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
497	<	else
498	<	return ws;
499	<	}
500	<
501	<	/**
502	<	* Tries to shrink workers into smaller array after one or more terminate.
503	<	*/
504	<	private void tryShrinkWorkerArray() {
505	<	ForkJoinWorkerThread[] ws = workers;
506	<	if (ws != null) {
507	<	int len = ws.length;
508	<	int last = len - 1;
509	<	while (last >= 0 && ws[last] == null)
510	<	--last;
511	<	int newLength = arraySizeFor(last+1);
512	<	if (newLength < len)
513	<	workers = Arrays.copyOf(ws, newLength);
514	<	}
515	<	}
516	<
517	<	/**
518	<	* Initializes workers if necessary.
519	<	*/
520	<	final void ensureWorkerInitialization() {
521	<	ForkJoinWorkerThread[] ws = workers;
522	<	if (ws == null) {
523	<	final ReentrantLock lock = this.workerLock;
524	<	lock.lock();
525	<	try {
526	<	ws = workers;
527	<	if (ws == null) {
528	<	int ps = parallelism;
529	<	ws = ensureWorkerArrayCapacity(ps);
530	<	for (int i = 0; i < ps; ++i) {
531	<	ForkJoinWorkerThread w = createWorker(i);
532	<	if (w != null) {
533	<	ws[i] = w;
534	<	w.start();
535	<	updateWorkerCount(1);
536	<	}
537	<	}
538	<	}
539	<	} finally {
540	<	lock.unlock();
541	<	}
542	<	}
543	<	}
544	<
545	<	/**
546	<	* Worker creation and startup for threads added via setParallelism.
547	<	*/
548	<	private void createAndStartAddedWorkers() {
549	<	resumeAllSpares();  // Allow spares to convert to nonspare
550	<	int ps = parallelism;
551	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
552	<	int len = ws.length;
553	<	// Sweep through slots, to keep lowest indices most populated
554	<	int k = 0;
555	<	while (k < len) {
556	<	if (ws[k] != null) {
557	<	++k;
558	<	continue;
559	<	}
560	<	int s = workerCounts;
561	<	int tc = totalCountOf(s);
562	<	int rc = runningCountOf(s);
563	<	if (rc >= ps || tc >= ps)
564	<	break;
565	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
566	<	ForkJoinWorkerThread w = createWorker(k);
567	<	if (w != null) {
568	<	ws[k++] = w;
569	<	w.start();
570	<	}
571	<	else {
572	<	updateWorkerCount(-1); // back out on failed creation
573	<	break;
574	<	}
575	<	}
1965	>	this.factory = factory;
1966	>	this.ueh = handler;
1967	>	this.localMode = asyncMode ? FIFO_QUEUE : LIFO_QUEUE;
1968	>	this.growHints = 1;
1969	>	long np = (long)(-parallelism); // offset ctl counts
1970	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
1971	>	// initialize workQueues array with room for 2*parallelism if possible
1972	>	int n = parallelism << 1;
1973	>	if (n >= POOL_MAX)
1974	>	n = POOL_MAX;
1975	>	else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
1976	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
1977		}
1978	+	this.workQueues = new WorkQueue[(n + 1) << 1]; // #slots = 2 * #workers
1979	+	this.termination = (this.lock = new Mutex()).newCondition();
1980	+	this.stealCount = new AtomicLong();
1981	+	this.nextWorkerNumber = new AtomicInteger();
1982	+	StringBuilder sb = new StringBuilder("ForkJoinPool-");
1983	+	sb.append(poolNumberGenerator.incrementAndGet());
1984	+	sb.append("-worker-");
1985	+	this.workerNamePrefix = sb.toString();
1986		}
1987
1988		// Execution methods
1989
1990		/**
582	–	* Common code for execute, invoke and submit
583	–	*/
584	–	private <T> void doSubmit(ForkJoinTask<T> task) {
585	–	if (task == null)
586	–	throw new NullPointerException();
587	–	if (isShutdown())
588	–	throw new RejectedExecutionException();
589	–	if (workers == null)
590	–	ensureWorkerInitialization();
591	–	submissionQueue.offer(task);
592	–	signalIdleWorkers();
593	–	}
594	–
595	–	/**
1991		* Performs the given task, returning its result upon completion.
1992	+	* If the computation encounters an unchecked Exception or Error,
1993	+	* it is rethrown as the outcome of this invocation.  Rethrown
1994	+	* exceptions behave in the same way as regular exceptions, but,
1995	+	* when possible, contain stack traces (as displayed for example
1996	+	* using {@code ex.printStackTrace()}) of both the current thread
1997	+	* as well as the thread actually encountering the exception;
1998	+	* minimally only the latter.
1999		*
2000		* @param task the task
2001		* @return the task's result
#	Line 626 | Line 2028 | public class ForkJoinPool extends Abstra
2028		*         scheduled for execution
2029		*/
2030		public void execute(Runnable task) {
2031	+	if (task == null)
2032	+	throw new NullPointerException();
2033		ForkJoinTask<?> job;
2034		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
2035		job = (ForkJoinTask<?>) task;
#	Line 635 | Line 2039 | public class ForkJoinPool extends Abstra
2039		}
2040
2041		/**
2042	+	* Submits a ForkJoinTask for execution.
2043	+	*
2044	+	* @param task the task to submit
2045	+	* @return the task
2046	+	* @throws NullPointerException if the task is null
2047	+	* @throws RejectedExecutionException if the task cannot be
2048	+	*         scheduled for execution
2049	+	*/
2050	+	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
2051	+	doSubmit(task);
2052	+	return task;
2053	+	}
2054	+
2055	+	/**
2056		* @throws NullPointerException if the task is null
2057		* @throws RejectedExecutionException if the task cannot be
2058		*         scheduled for execution
2059		*/
2060		public <T> ForkJoinTask<T> submit(Callable<T> task) {
2061	+	if (task == null)
2062	+	throw new NullPointerException();
2063		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
2064		doSubmit(job);
2065		return job;
#	Line 651 | Line 2071 | public class ForkJoinPool extends Abstra
2071		*         scheduled for execution
2072		*/
2073		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
2074	+	if (task == null)
2075	+	throw new NullPointerException();
2076		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
2077		doSubmit(job);
2078		return job;
#	Line 662 | Line 2084 | public class ForkJoinPool extends Abstra
2084		*         scheduled for execution
2085		*/
2086		public ForkJoinTask<?> submit(Runnable task) {
2087	+	if (task == null)
2088	+	throw new NullPointerException();
2089		ForkJoinTask<?> job;
2090		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
2091		job = (ForkJoinTask<?>) task;
#	Line 672 | Line 2096 | public class ForkJoinPool extends Abstra
2096		}
2097
2098		/**
675	–	* Submits a ForkJoinTask for execution.
676	–	*
677	–	* @param task the task to submit
678	–	* @return the task
679	–	* @throws NullPointerException if the task is null
680	–	* @throws RejectedExecutionException if the task cannot be
681	–	*         scheduled for execution
682	–	*/
683	–	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
684	–	doSubmit(task);
685	–	return task;
686	–	}
687	–
688	–
689	–	/**
2099		* @throws NullPointerException       {@inheritDoc}
2100		* @throws RejectedExecutionException {@inheritDoc}
2101		*/
2102		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
2103	<	ArrayList<ForkJoinTask<T>> forkJoinTasks =
2104	<	new ArrayList<ForkJoinTask<T>>(tasks.size());
2105	<	for (Callable<T> task : tasks)
2106	<	forkJoinTasks.add(ForkJoinTask.adapt(task));
2107	<	invoke(new InvokeAll<T>(forkJoinTasks));
2108	<
2103	>	// In previous versions of this class, this method constructed
2104	>	// a task to run ForkJoinTask.invokeAll, but now external
2105	>	// invocation of multiple tasks is at least as efficient.
2106	>	List<ForkJoinTask<T>> fs = new ArrayList<ForkJoinTask<T>>(tasks.size());
2107	>	// Workaround needed because method wasn't declared with
2108	>	// wildcards in return type but should have been.
2109		@SuppressWarnings({"unchecked", "rawtypes"})
2110	<	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
702	<	return futures;
703	<	}
2110	>	List<Future<T>> futures = (List<Future<T>>) (List) fs;
2111
2112	<	static final class InvokeAll<T> extends RecursiveAction {
2113	<	final ArrayList<ForkJoinTask<T>> tasks;
2114	<	InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; }
2115	<	public void compute() {
2116	<	try { invokeAll(tasks); }
2117	<	catch (Exception ignore) {}
2112	>	boolean done = false;
2113	>	try {
2114	>	for (Callable<T> t : tasks) {
2115	>	ForkJoinTask<T> f = ForkJoinTask.adapt(t);
2116	>	doSubmit(f);
2117	>	fs.add(f);
2118	>	}
2119	>	for (ForkJoinTask<T> f : fs)
2120	>	f.quietlyJoin();
2121	>	done = true;
2122	>	return futures;
2123	>	} finally {
2124	>	if (!done)
2125	>	for (ForkJoinTask<T> f : fs)
2126	>	f.cancel(false);
2127		}
712	–	private static final long serialVersionUID = -7914297376763021607L;
2128		}
2129
715	–	// Configuration and status settings and queries
716	–
2130		/**
2131		* Returns the factory used for constructing new workers.
2132		*
#	Line 730 | Line 2143 | public class ForkJoinPool extends Abstra
2143		* @return the handler, or {@code null} if none
2144		*/
2145		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
2146	<	Thread.UncaughtExceptionHandler h;
734	<	final ReentrantLock lock = this.workerLock;
735	<	lock.lock();
736	<	try {
737	<	h = ueh;
738	<	} finally {
739	<	lock.unlock();
740	<	}
741	<	return h;
742	<	}
743	<
744	<	/**
745	<	* Sets the handler for internal worker threads that terminate due
746	<	* to unrecoverable errors encountered while executing tasks.
747	<	* Unless set, the current default or ThreadGroup handler is used
748	<	* as handler.
749	<	*
750	<	* @param h the new handler
751	<	* @return the old handler, or {@code null} if none
752	<	* @throws SecurityException if a security manager exists and
753	<	*         the caller is not permitted to modify threads
754	<	*         because it does not hold {@link
755	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
756	<	*/
757	<	public Thread.UncaughtExceptionHandler
758	<	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
759	<	checkPermission();
760	<	Thread.UncaughtExceptionHandler old = null;
761	<	final ReentrantLock lock = this.workerLock;
762	<	lock.lock();
763	<	try {
764	<	old = ueh;
765	<	ueh = h;
766	<	ForkJoinWorkerThread[] ws = workers;
767	<	if (ws != null) {
768	<	for (int i = 0; i < ws.length; ++i) {
769	<	ForkJoinWorkerThread w = ws[i];
770	<	if (w != null)
771	<	w.setUncaughtExceptionHandler(h);
772	<	}
773	<	}
774	<	} finally {
775	<	lock.unlock();
776	<	}
777	<	return old;
778	<	}
779	<
780	<
781	<	/**
782	<	* Sets the target parallelism level of this pool.
783	<	*
784	<	* @param parallelism the target parallelism
785	<	* @throws IllegalArgumentException if parallelism less than or
786	<	* equal to zero or greater than maximum size bounds
787	<	* @throws SecurityException if a security manager exists and
788	<	*         the caller is not permitted to modify threads
789	<	*         because it does not hold {@link
790	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
791	<	*/
792	<	public void setParallelism(int parallelism) {
793	<	checkPermission();
794	<	if (parallelism <= 0 || parallelism > maxPoolSize)
795	<	throw new IllegalArgumentException();
796	<	final ReentrantLock lock = this.workerLock;
797	<	lock.lock();
798	<	try {
799	<	if (isProcessingTasks()) {
800	<	int p = this.parallelism;
801	<	this.parallelism = parallelism;
802	<	if (parallelism > p)
803	<	createAndStartAddedWorkers();
804	<	else
805	<	trimSpares();
806	<	}
807	<	} finally {
808	<	lock.unlock();
809	<	}
810	<	signalIdleWorkers();
2146	>	return ueh;
2147		}
2148
2149		/**
#	Line 821 | Line 2157 | public class ForkJoinPool extends Abstra
2157
2158		/**
2159		* Returns the number of worker threads that have started but not
2160	<	* yet terminated.  This result returned by this method may differ
2160	>	* yet terminated.  The result returned by this method may differ
2161		* from {@link #getParallelism} when threads are created to
2162		* maintain parallelism when others are cooperatively blocked.
2163		*
2164		* @return the number of worker threads
2165		*/
2166		public int getPoolSize() {
2167	<	return totalCountOf(workerCounts);
832	<	}
833	<
834	<	/**
835	<	* Returns the maximum number of threads allowed to exist in the
836	<	* pool. Unless set using {@link #setMaximumPoolSize}, the
837	<	* maximum is an implementation-defined value designed only to
838	<	* prevent runaway growth.
839	<	*
840	<	* @return the maximum
841	<	*/
842	<	public int getMaximumPoolSize() {
843	<	return maxPoolSize;
844	<	}
845	<
846	<	/**
847	<	* Sets the maximum number of threads allowed to exist in the
848	<	* pool. The given value should normally be greater than or equal
849	<	* to the {@link #getParallelism parallelism} level. Setting this
850	<	* value has no effect on current pool size. It controls
851	<	* construction of new threads.
852	<	*
853	<	* @throws IllegalArgumentException if negative or greater than
854	<	* internal implementation limit
855	<	*/
856	<	public void setMaximumPoolSize(int newMax) {
857	<	if (newMax < 0 || newMax > MAX_THREADS)
858	<	throw new IllegalArgumentException();
859	<	maxPoolSize = newMax;
860	<	}
861	<
862	<
863	<	/**
864	<	* Returns {@code true} if this pool dynamically maintains its
865	<	* target parallelism level. If false, new threads are added only
866	<	* to avoid possible starvation.  This setting is by default true.
867	<	*
868	<	* @return {@code true} if maintains parallelism
869	<	*/
870	<	public boolean getMaintainsParallelism() {
871	<	return maintainsParallelism;
872	<	}
873	<
874	<	/**
875	<	* Sets whether this pool dynamically maintains its target
876	<	* parallelism level. If false, new threads are added only to
877	<	* avoid possible starvation.
878	<	*
879	<	* @param enable {@code true} to maintain parallelism
880	<	*/
881	<	public void setMaintainsParallelism(boolean enable) {
882	<	maintainsParallelism = enable;
883	<	}
884	<
885	<	/**
886	<	* Establishes local first-in-first-out scheduling mode for forked
887	<	* tasks that are never joined. This mode may be more appropriate
888	<	* than default locally stack-based mode in applications in which
889	<	* worker threads only process asynchronous tasks.  This method is
890	<	* designed to be invoked only when the pool is quiescent, and
891	<	* typically only before any tasks are submitted. The effects of
892	<	* invocations at other times may be unpredictable.
893	<	*
894	<	* @param async if {@code true}, use locally FIFO scheduling
895	<	* @return the previous mode
896	<	* @see #getAsyncMode
897	<	*/
898	<	public boolean setAsyncMode(boolean async) {
899	<	boolean oldMode = locallyFifo;
900	<	locallyFifo = async;
901	<	ForkJoinWorkerThread[] ws = workers;
902	<	if (ws != null) {
903	<	for (int i = 0; i < ws.length; ++i) {
904	<	ForkJoinWorkerThread t = ws[i];
905	<	if (t != null)
906	<	t.setAsyncMode(async);
907	<	}
908	<	}
909	<	return oldMode;
2167	>	return parallelism + (short)(ctl >>> TC_SHIFT);
2168		}
2169
2170		/**
#	Line 914 | Line 2172 | public class ForkJoinPool extends Abstra
2172		* scheduling mode for forked tasks that are never joined.
2173		*
2174		* @return {@code true} if this pool uses async mode
917	–	* @see #setAsyncMode
2175		*/
2176		public boolean getAsyncMode() {
2177	<	return locallyFifo;
2177	>	return localMode != 0;
2178		}
2179
2180		/**
2181		* Returns an estimate of the number of worker threads that are
2182		* not blocked waiting to join tasks or for other managed
2183	<	* synchronization.
2183	>	* synchronization. This method may overestimate the
2184	>	* number of running threads.
2185		*
2186		* @return the number of worker threads
2187		*/
2188		public int getRunningThreadCount() {
2189	<	return runningCountOf(workerCounts);
2189	>	int rc = 0;
2190	>	WorkQueue[] ws; WorkQueue w;
2191	>	if ((ws = workQueues) != null) {
2192	>	for (int i = 1; i < ws.length; i += 2) {
2193	>	if ((w = ws[i]) != null && w.isApparentlyUnblocked())
2194	>	++rc;
2195	>	}
2196	>	}
2197	>	return rc;
2198		}
2199
2200		/**
#	Line 939 | Line 2205 | public class ForkJoinPool extends Abstra
2205		* @return the number of active threads
2206		*/
2207		public int getActiveThreadCount() {
2208	<	return activeCountOf(runControl);
2209	<	}
944	<
945	<	/**
946	<	* Returns an estimate of the number of threads that are currently
947	<	* idle waiting for tasks. This method may underestimate the
948	<	* number of idle threads.
949	<	*
950	<	* @return the number of idle threads
951	<	*/
952	<	final int getIdleThreadCount() {
953	<	int c = runningCountOf(workerCounts) - activeCountOf(runControl);
954	<	return (c <= 0) ? 0 : c;
2208	>	int r = parallelism + (int)(ctl >> AC_SHIFT);
2209	>	return (r <= 0) ? 0 : r; // suppress momentarily negative values
2210		}
2211
2212		/**
#	Line 966 | Line 2221 | public class ForkJoinPool extends Abstra
2221		* @return {@code true} if all threads are currently idle
2222		*/
2223		public boolean isQuiescent() {
2224	<	return activeCountOf(runControl) == 0;
2224	>	return (int)(ctl >> AC_SHIFT) + parallelism == 0;
2225		}
2226
2227		/**
#	Line 981 | Line 2236 | public class ForkJoinPool extends Abstra
2236		* @return the number of steals
2237		*/
2238		public long getStealCount() {
2239	<	return stealCount.get();
2240	<	}
2241	<
2242	<	/**
2243	<	* Accumulates steal count from a worker.
2244	<	* Call only when worker known to be idle.
2245	<	*/
2246	<	private void updateStealCount(ForkJoinWorkerThread w) {
2247	<	int sc = w.getAndClearStealCount();
993	<	if (sc != 0)
994	<	stealCount.addAndGet(sc);
2239	>	long count = stealCount.get();
2240	>	WorkQueue[] ws; WorkQueue w;
2241	>	if ((ws = workQueues) != null) {
2242	>	for (int i = 1; i < ws.length; i += 2) {
2243	>	if ((w = ws[i]) != null)
2244	>	count += w.totalSteals;
2245	>	}
2246	>	}
2247	>	return count;
2248		}
2249
2250		/**
#	Line 1006 | Line 2259 | public class ForkJoinPool extends Abstra
2259		*/
2260		public long getQueuedTaskCount() {
2261		long count = 0;
2262	<	ForkJoinWorkerThread[] ws = workers;
2263	<	if (ws != null) {
2264	<	for (int i = 0; i < ws.length; ++i) {
2265	<	ForkJoinWorkerThread t = ws[i];
2266	<	if (t != null)
1014	<	count += t.getQueueSize();
2262	>	WorkQueue[] ws; WorkQueue w;
2263	>	if ((ws = workQueues) != null) {
2264	>	for (int i = 1; i < ws.length; i += 2) {
2265	>	if ((w = ws[i]) != null)
2266	>	count += w.queueSize();
2267		}
2268		}
2269		return count;
#	Line 1019 | Line 2271 | public class ForkJoinPool extends Abstra
2271
2272		/**
2273		* Returns an estimate of the number of tasks submitted to this
2274	<	* pool that have not yet begun executing.  This method takes time
2275	<	* proportional to the number of submissions.
2274	>	* pool that have not yet begun executing.  This method may take
2275	>	* time proportional to the number of submissions.
2276		*
2277		* @return the number of queued submissions
2278		*/
2279		public int getQueuedSubmissionCount() {
2280	<	return submissionQueue.size();
2280	>	int count = 0;
2281	>	WorkQueue[] ws; WorkQueue w;
2282	>	if ((ws = workQueues) != null) {
2283	>	for (int i = 0; i < ws.length; i += 2) {
2284	>	if ((w = ws[i]) != null)
2285	>	count += w.queueSize();
2286	>	}
2287	>	}
2288	>	return count;
2289		}
2290
2291		/**
#	Line 1035 | Line 2295 | public class ForkJoinPool extends Abstra
2295		* @return {@code true} if there are any queued submissions
2296		*/
2297		public boolean hasQueuedSubmissions() {
2298	<	return !submissionQueue.isEmpty();
2298	>	WorkQueue[] ws; WorkQueue w;
2299	>	if ((ws = workQueues) != null) {
2300	>	for (int i = 0; i < ws.length; i += 2) {
2301	>	if ((w = ws[i]) != null && w.queueSize() != 0)
2302	>	return true;
2303	>	}
2304	>	}
2305	>	return false;
2306		}
2307
2308		/**
#	Line 1046 | Line 2313 | public class ForkJoinPool extends Abstra
2313		* @return the next submission, or {@code null} if none
2314		*/
2315		protected ForkJoinTask<?> pollSubmission() {
2316	<	return submissionQueue.poll();
2316	>	WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t;
2317	>	if ((ws = workQueues) != null) {
2318	>	for (int i = 0; i < ws.length; i += 2) {
2319	>	if ((w = ws[i]) != null && (t = w.poll()) != null)
2320	>	return t;
2321	>	}
2322	>	}
2323	>	return null;
2324		}
2325
2326		/**
#	Line 1067 | Line 2341 | public class ForkJoinPool extends Abstra
2341		* @return the number of elements transferred
2342		*/
2343		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
2344	<	int n = submissionQueue.drainTo(c);
2345	<	ForkJoinWorkerThread[] ws = workers;
2346	<	if (ws != null) {
2344	>	int count = 0;
2345	>	WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t;
2346	>	if ((ws = workQueues) != null) {
2347		for (int i = 0; i < ws.length; ++i) {
2348	<	ForkJoinWorkerThread w = ws[i];
2349	<	if (w != null)
2350	<	n += w.drainTasksTo(c);
2348	>	if ((w = ws[i]) != null) {
2349	>	while ((t = w.poll()) != null) {
2350	>	c.add(t);
2351	>	++count;
2352	>	}
2353	>	}
2354		}
2355		}
2356	<	return n;
2356	>	return count;
2357		}
2358
2359		/**
#	Line 1087 | Line 2364 | public class ForkJoinPool extends Abstra
2364		* @return a string identifying this pool, as well as its state
2365		*/
2366		public String toString() {
2367	<	int ps = parallelism;
2368	<	int wc = workerCounts;
2369	<	int rc = runControl;
2370	<	long st = getStealCount();
2371	<	long qt = getQueuedTaskCount();
2372	<	long qs = getQueuedSubmissionCount();
2367	>	// Use a single pass through workQueues to collect counts
2368	>	long qt = 0L, qs = 0L; int rc = 0;
2369	>	long st = stealCount.get();
2370	>	long c = ctl;
2371	>	WorkQueue[] ws; WorkQueue w;
2372	>	if ((ws = workQueues) != null) {
2373	>	for (int i = 0; i < ws.length; ++i) {
2374	>	if ((w = ws[i]) != null) {
2375	>	int size = w.queueSize();
2376	>	if ((i & 1) == 0)
2377	>	qs += size;
2378	>	else {
2379	>	qt += size;
2380	>	st += w.totalSteals;
2381	>	if (w.isApparentlyUnblocked())
2382	>	++rc;
2383	>	}
2384	>	}
2385	>	}
2386	>	}
2387	>	int pc = parallelism;
2388	>	int tc = pc + (short)(c >>> TC_SHIFT);
2389	>	int ac = pc + (int)(c >> AC_SHIFT);
2390	>	if (ac < 0) // ignore transient negative
2391	>	ac = 0;
2392	>	String level;
2393	>	if ((c & STOP_BIT) != 0)
2394	>	level = (tc == 0) ? "Terminated" : "Terminating";
2395	>	else
2396	>	level = runState < 0 ? "Shutting down" : "Running";
2397		return super.toString() +
2398	<	"[" + runStateToString(runStateOf(rc)) +
2399	<	", parallelism = " + ps +
2400	<	", size = " + totalCountOf(wc) +
2401	<	", active = " + activeCountOf(rc) +
2402	<	", running = " + runningCountOf(wc) +
2398	>	"[" + level +
2399	>	", parallelism = " + pc +
2400	>	", size = " + tc +
2401	>	", active = " + ac +
2402	>	", running = " + rc +
2403		", steals = " + st +
2404		", tasks = " + qt +
2405		", submissions = " + qs +
2406		"]";
2407		}
2408
1108	–	private static String runStateToString(int rs) {
1109	–	switch (rs) {
1110	–	case RUNNING: return "Running";
1111	–	case SHUTDOWN: return "Shutting down";
1112	–	case TERMINATING: return "Terminating";
1113	–	case TERMINATED: return "Terminated";
1114	–	default: throw new Error("Unknown run state");
1115	–	}
1116	–	}
1117	–
1118	–	// lifecycle control
1119	–
2409		/**
2410		* Initiates an orderly shutdown in which previously submitted
2411		* tasks are executed, but no new tasks will be accepted.
#	Line 1131 | Line 2420 | public class ForkJoinPool extends Abstra
2420		*/
2421		public void shutdown() {
2422		checkPermission();
2423	<	transitionRunStateTo(SHUTDOWN);
1135	<	if (canTerminateOnShutdown(runControl)) {
1136	<	if (workers == null) { // shutting down before workers created
1137	<	final ReentrantLock lock = this.workerLock;
1138	<	lock.lock();
1139	<	try {
1140	<	if (workers == null) {
1141	<	terminate();
1142	<	transitionRunStateTo(TERMINATED);
1143	<	termination.signalAll();
1144	<	}
1145	<	} finally {
1146	<	lock.unlock();
1147	<	}
1148	<	}
1149	<	terminateOnShutdown();
1150	<	}
2423	>	tryTerminate(false, true);
2424		}
2425
2426		/**
#	Line 1168 | Line 2441 | public class ForkJoinPool extends Abstra
2441		*/
2442		public List<Runnable> shutdownNow() {
2443		checkPermission();
2444	<	terminate();
2444	>	tryTerminate(true, true);
2445		return Collections.emptyList();
2446		}
2447
#	Line 1178 | Line 2451 | public class ForkJoinPool extends Abstra
2451		* @return {@code true} if all tasks have completed following shut down
2452		*/
2453		public boolean isTerminated() {
2454	<	return runStateOf(runControl) == TERMINATED;
2454	>	long c = ctl;
2455	>	return ((c & STOP_BIT) != 0L &&
2456	>	(short)(c >>> TC_SHIFT) == -parallelism);
2457		}
2458
2459		/**
#	Line 1186 | Line 2461 | public class ForkJoinPool extends Abstra
2461		* commenced but not yet completed.  This method may be useful for
2462		* debugging. A return of {@code true} reported a sufficient
2463		* period after shutdown may indicate that submitted tasks have
2464	<	* ignored or suppressed interruption, causing this executor not
2465	<	* to properly terminate.
2464	>	* ignored or suppressed interruption, or are waiting for IO,
2465	>	* causing this executor not to properly terminate. (See the
2466	>	* advisory notes for class {@link ForkJoinTask} stating that
2467	>	* tasks should not normally entail blocking operations.  But if
2468	>	* they do, they must abort them on interrupt.)
2469		*
2470		* @return {@code true} if terminating but not yet terminated
2471		*/
2472		public boolean isTerminating() {
2473	<	return runStateOf(runControl) == TERMINATING;
2473	>	long c = ctl;
2474	>	return ((c & STOP_BIT) != 0L &&
2475	>	(short)(c >>> TC_SHIFT) != -parallelism);
2476		}
2477
2478		/**
#	Line 1201 | Line 2481 | public class ForkJoinPool extends Abstra
2481		* @return {@code true} if this pool has been shut down
2482		*/
2483		public boolean isShutdown() {
2484	<	return runStateOf(runControl) >= SHUTDOWN;
1205	<	}
1206	<
1207	<	/**
1208	<	* Returns true if pool is not terminating or terminated.
1209	<	* Used internally to suppress execution when terminating.
1210	<	*/
1211	<	final boolean isProcessingTasks() {
1212	<	return runStateOf(runControl) < TERMINATING;
2484	>	return runState < 0;
2485		}
2486
2487		/**
#	Line 1226 | Line 2498 | public class ForkJoinPool extends Abstra
2498		public boolean awaitTermination(long timeout, TimeUnit unit)
2499		throws InterruptedException {
2500		long nanos = unit.toNanos(timeout);
2501	<	final ReentrantLock lock = this.workerLock;
2501	>	final Mutex lock = this.lock;
2502		lock.lock();
2503		try {
2504		for (;;) {
#	Line 1241 | Line 2513 | public class ForkJoinPool extends Abstra
2513		}
2514		}
2515
1244	–	// Shutdown and termination support
1245	–
1246	–	/**
1247	–	* Callback from terminating worker. Nulls out the corresponding
1248	–	* workers slot, and if terminating, tries to terminate; else
1249	–	* tries to shrink workers array.
1250	–	*
1251	–	* @param w the worker
1252	–	*/
1253	–	final void workerTerminated(ForkJoinWorkerThread w) {
1254	–	updateStealCount(w);
1255	–	updateWorkerCount(-1);
1256	–	final ReentrantLock lock = this.workerLock;
1257	–	lock.lock();
1258	–	try {
1259	–	ForkJoinWorkerThread[] ws = workers;
1260	–	if (ws != null) {
1261	–	int idx = w.poolIndex;
1262	–	if (idx >= 0 && idx < ws.length && ws[idx] == w)
1263	–	ws[idx] = null;
1264	–	if (totalCountOf(workerCounts) == 0) {
1265	–	terminate(); // no-op if already terminating
1266	–	transitionRunStateTo(TERMINATED);
1267	–	termination.signalAll();
1268	–	}
1269	–	else if (isProcessingTasks()) {
1270	–	tryShrinkWorkerArray();
1271	–	tryResumeSpare(true); // allow replacement
1272	–	}
1273	–	}
1274	–	} finally {
1275	–	lock.unlock();
1276	–	}
1277	–	signalIdleWorkers();
1278	–	}
1279	–
1280	–	/**
1281	–	* Initiates termination.
1282	–	*/
1283	–	private void terminate() {
1284	–	if (transitionRunStateTo(TERMINATING)) {
1285	–	stopAllWorkers();
1286	–	resumeAllSpares();
1287	–	signalIdleWorkers();
1288	–	cancelQueuedSubmissions();
1289	–	cancelQueuedWorkerTasks();
1290	–	interruptUnterminatedWorkers();
1291	–	signalIdleWorkers(); // resignal after interrupt
1292	–	}
1293	–	}
1294	–
1295	–	/**
1296	–	* Possibly terminates when on shutdown state.
1297	–	*/
1298	–	private void terminateOnShutdown() {
1299	–	if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
1300	–	terminate();
1301	–	}
1302	–
1303	–	/**
1304	–	* Clears out and cancels submissions.
1305	–	*/
1306	–	private void cancelQueuedSubmissions() {
1307	–	ForkJoinTask<?> task;
1308	–	while ((task = pollSubmission()) != null)
1309	–	task.cancel(false);
1310	–	}
1311	–
1312	–	/**
1313	–	* Cleans out worker queues.
1314	–	*/
1315	–	private void cancelQueuedWorkerTasks() {
1316	–	final ReentrantLock lock = this.workerLock;
1317	–	lock.lock();
1318	–	try {
1319	–	ForkJoinWorkerThread[] ws = workers;
1320	–	if (ws != null) {
1321	–	for (int i = 0; i < ws.length; ++i) {
1322	–	ForkJoinWorkerThread t = ws[i];
1323	–	if (t != null)
1324	–	t.cancelTasks();
1325	–	}
1326	–	}
1327	–	} finally {
1328	–	lock.unlock();
1329	–	}
1330	–	}
1331	–
1332	–	/**
1333	–	* Sets each worker's status to terminating. Requires lock to avoid
1334	–	* conflicts with add/remove.
1335	–	*/
1336	–	private void stopAllWorkers() {
1337	–	final ReentrantLock lock = this.workerLock;
1338	–	lock.lock();
1339	–	try {
1340	–	ForkJoinWorkerThread[] ws = workers;
1341	–	if (ws != null) {
1342	–	for (int i = 0; i < ws.length; ++i) {
1343	–	ForkJoinWorkerThread t = ws[i];
1344	–	if (t != null)
1345	–	t.shutdownNow();
1346	–	}
1347	–	}
1348	–	} finally {
1349	–	lock.unlock();
1350	–	}
1351	–	}
1352	–
1353	–	/**
1354	–	* Interrupts all unterminated workers.  This is not required for
1355	–	* sake of internal control, but may help unstick user code during
1356	–	* shutdown.
1357	–	*/
1358	–	private void interruptUnterminatedWorkers() {
1359	–	final ReentrantLock lock = this.workerLock;
1360	–	lock.lock();
1361	–	try {
1362	–	ForkJoinWorkerThread[] ws = workers;
1363	–	if (ws != null) {
1364	–	for (int i = 0; i < ws.length; ++i) {
1365	–	ForkJoinWorkerThread t = ws[i];
1366	–	if (t != null && !t.isTerminated()) {
1367	–	try {
1368	–	t.interrupt();
1369	–	} catch (SecurityException ignore) {
1370	–	}
1371	–	}
1372	–	}
1373	–	}
1374	–	} finally {
1375	–	lock.unlock();
1376	–	}
1377	–	}
1378	–
1379	–
1380	–	/*
1381	–	* Nodes for event barrier to manage idle threads.  Queue nodes
1382	–	* are basic Treiber stack nodes, also used for spare stack.
1383	–	*
1384	–	* The event barrier has an event count and a wait queue (actually
1385	–	* a Treiber stack).  Workers are enabled to look for work when
1386	–	* the eventCount is incremented. If they fail to find work, they
1387	–	* may wait for next count. Upon release, threads help others wake
1388	–	* up.
1389	–	*
1390	–	* Synchronization events occur only in enough contexts to
1391	–	* maintain overall liveness:
1392	–	*
1393	–	*   - Submission of a new task to the pool
1394	–	*   - Resizes or other changes to the workers array
1395	–	*   - pool termination
1396	–	*   - A worker pushing a task on an empty queue
1397	–	*
1398	–	* The case of pushing a task occurs often enough, and is heavy
1399	–	* enough compared to simple stack pushes, to require special
1400	–	* handling: Method signalWork returns without advancing count if
1401	–	* the queue appears to be empty.  This would ordinarily result in
1402	–	* races causing some queued waiters not to be woken up. To avoid
1403	–	* this, the first worker enqueued in method sync (see
1404	–	* syncIsReleasable) rescans for tasks after being enqueued, and
1405	–	* helps signal if any are found. This works well because the
1406	–	* worker has nothing better to do, and so might as well help
1407	–	* alleviate the overhead and contention on the threads actually
1408	–	* doing work.  Also, since event counts increments on task
1409	–	* availability exist to maintain liveness (rather than to force
1410	–	* refreshes etc), it is OK for callers to exit early if
1411	–	* contending with another signaller.
1412	–	*/
1413	–	static final class WaitQueueNode {
1414	–	WaitQueueNode next; // only written before enqueued
1415	–	volatile ForkJoinWorkerThread thread; // nulled to cancel wait
1416	–	final long count; // unused for spare stack
1417	–
1418	–	WaitQueueNode(long c, ForkJoinWorkerThread w) {
1419	–	count = c;
1420	–	thread = w;
1421	–	}
1422	–
1423	–	/**
1424	–	* Wakes up waiter, returning false if known to already
1425	–	*/
1426	–	boolean signal() {
1427	–	ForkJoinWorkerThread t = thread;
1428	–	if (t == null)
1429	–	return false;
1430	–	thread = null;
1431	–	LockSupport.unpark(t);
1432	–	return true;
1433	–	}
1434	–
1435	–	/**
1436	–	* Awaits release on sync.
1437	–	*/
1438	–	void awaitSyncRelease(ForkJoinPool p) {
1439	–	while (thread != null && !p.syncIsReleasable(this))
1440	–	LockSupport.park(this);
1441	–	}
1442	–
1443	–	/**
1444	–	* Awaits resumption as spare.
1445	–	*/
1446	–	void awaitSpareRelease() {
1447	–	while (thread != null) {
1448	–	if (!Thread.interrupted())
1449	–	LockSupport.park(this);
1450	–	}
1451	–	}
1452	–	}
1453	–
1454	–	/**
1455	–	* Ensures that no thread is waiting for count to advance from the
1456	–	* current value of eventCount read on entry to this method, by
1457	–	* releasing waiting threads if necessary.
1458	–	*
1459	–	* @return the count
1460	–	*/
1461	–	final long ensureSync() {
1462	–	long c = eventCount;
1463	–	WaitQueueNode q;
1464	–	while ((q = syncStack) != null && q.count < c) {
1465	–	if (casBarrierStack(q, null)) {
1466	–	do {
1467	–	q.signal();
1468	–	} while ((q = q.next) != null);
1469	–	break;
1470	–	}
1471	–	}
1472	–	return c;
1473	–	}
1474	–
1475	–	/**
1476	–	* Increments event count and releases waiting threads.
1477	–	*/
1478	–	private void signalIdleWorkers() {
1479	–	long c;
1480	–	do {} while (!casEventCount(c = eventCount, c+1));
1481	–	ensureSync();
1482	–	}
1483	–
1484	–	/**
1485	–	* Signals threads waiting to poll a task. Because method sync
1486	–	* rechecks availability, it is OK to only proceed if queue
1487	–	* appears to be non-empty, and OK to skip under contention to
1488	–	* increment count (since some other thread succeeded).
1489	–	*/
1490	–	final void signalWork() {
1491	–	long c;
1492	–	WaitQueueNode q;
1493	–	if (syncStack != null &&
1494	–	casEventCount(c = eventCount, c+1) &&
1495	–	(((q = syncStack) != null && q.count <= c) &&
1496	–	(!casBarrierStack(q, q.next) || !q.signal())))
1497	–	ensureSync();
1498	–	}
1499	–
1500	–	/**
1501	–	* Waits until event count advances from last value held by
1502	–	* caller, or if excess threads, caller is resumed as spare, or
1503	–	* caller or pool is terminating. Updates caller's event on exit.
1504	–	*
1505	–	* @param w the calling worker thread
1506	–	*/
1507	–	final void sync(ForkJoinWorkerThread w) {
1508	–	updateStealCount(w); // Transfer w's count while it is idle
1509	–
1510	–	while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
1511	–	long prev = w.lastEventCount;
1512	–	WaitQueueNode node = null;
1513	–	WaitQueueNode h;
1514	–	while (eventCount == prev &&
1515	–	((h = syncStack) == null || h.count == prev)) {
1516	–	if (node == null)
1517	–	node = new WaitQueueNode(prev, w);
1518	–	if (casBarrierStack(node.next = h, node)) {
1519	–	node.awaitSyncRelease(this);
1520	–	break;
1521	–	}
1522	–	}
1523	–	long ec = ensureSync();
1524	–	if (ec != prev) {
1525	–	w.lastEventCount = ec;
1526	–	break;
1527	–	}
1528	–	}
1529	–	}
1530	–
1531	–	/**
1532	–	* Returns {@code true} if worker waiting on sync can proceed:
1533	–	*  - on signal (thread == null)
1534	–	*  - on event count advance (winning race to notify vs signaller)
1535	–	*  - on interrupt
1536	–	*  - if the first queued node, we find work available
1537	–	* If node was not signalled and event count not advanced on exit,
1538	–	* then we also help advance event count.
1539	–	*
1540	–	* @return {@code true} if node can be released
1541	–	*/
1542	–	final boolean syncIsReleasable(WaitQueueNode node) {
1543	–	long prev = node.count;
1544	–	if (!Thread.interrupted() && node.thread != null &&
1545	–	(node.next != null ||
1546	–	!ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
1547	–	eventCount == prev)
1548	–	return false;
1549	–	if (node.thread != null) {
1550	–	node.thread = null;
1551	–	long ec = eventCount;
1552	–	if (prev <= ec) // help signal
1553	–	casEventCount(ec, ec+1);
1554	–	}
1555	–	return true;
1556	–	}
1557	–
1558	–	/**
1559	–	* Returns {@code true} if a new sync event occurred since last
1560	–	* call to sync or this method, if so, updating caller's count.
1561	–	*/
1562	–	final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1563	–	long lc = w.lastEventCount;
1564	–	long ec = ensureSync();
1565	–	if (ec == lc)
1566	–	return false;
1567	–	w.lastEventCount = ec;
1568	–	return true;
1569	–	}
1570	–
1571	–	//  Parallelism maintenance
1572	–
1573	–	/**
1574	–	* Decrements running count; if too low, adds spare.
1575	–	*
1576	–	* Conceptually, all we need to do here is add or resume a
1577	–	* spare thread when one is about to block (and remove or
1578	–	* suspend it later when unblocked -- see suspendIfSpare).
1579	–	* However, implementing this idea requires coping with
1580	–	* several problems: we have imperfect information about the
1581	–	* states of threads. Some count updates can and usually do
1582	–	* lag run state changes, despite arrangements to keep them
1583	–	* accurate (for example, when possible, updating counts
1584	–	* before signalling or resuming), especially when running on
1585	–	* dynamic JVMs that don't optimize the infrequent paths that
1586	–	* update counts. Generating too many threads can make these
1587	–	* problems become worse, because excess threads are more
1588	–	* likely to be context-switched with others, slowing them all
1589	–	* down, especially if there is no work available, so all are
1590	–	* busy scanning or idling.  Also, excess spare threads can
1591	–	* only be suspended or removed when they are idle, not
1592	–	* immediately when they aren't needed. So adding threads will
1593	–	* raise parallelism level for longer than necessary.  Also,
1594	–	* FJ applications often encounter highly transient peaks when
1595	–	* many threads are blocked joining, but for less time than it
1596	–	* takes to create or resume spares.
1597	–	*
1598	–	* @param joinMe if non-null, return early if done
1599	–	* @param maintainParallelism if true, try to stay within
1600	–	* target counts, else create only to avoid starvation
1601	–	* @return true if joinMe known to be done
1602	–	*/
1603	–	final boolean preJoin(ForkJoinTask<?> joinMe,
1604	–	boolean maintainParallelism) {
1605	–	maintainParallelism &= maintainsParallelism; // overrride
1606	–	boolean dec = false;  // true when running count decremented
1607	–	while (spareStack == null || !tryResumeSpare(dec)) {
1608	–	int counts = workerCounts;
1609	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1610	–	if (!needSpare(counts, maintainParallelism))
1611	–	break;
1612	–	if (joinMe.status < 0)
1613	–	return true;
1614	–	if (tryAddSpare(counts))
1615	–	break;
1616	–	}
1617	–	}
1618	–	return false;
1619	–	}
1620	–
1621	–	/**
1622	–	* Same idea as preJoin
1623	–	*/
1624	–	final boolean preBlock(ManagedBlocker blocker,
1625	–	boolean maintainParallelism) {
1626	–	maintainParallelism &= maintainsParallelism;
1627	–	boolean dec = false;
1628	–	while (spareStack == null || !tryResumeSpare(dec)) {
1629	–	int counts = workerCounts;
1630	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1631	–	if (!needSpare(counts, maintainParallelism))
1632	–	break;
1633	–	if (blocker.isReleasable())
1634	–	return true;
1635	–	if (tryAddSpare(counts))
1636	–	break;
1637	–	}
1638	–	}
1639	–	return false;
1640	–	}
1641	–
1642	–	/**
1643	–	* Returns {@code true} if a spare thread appears to be needed.
1644	–	* If maintaining parallelism, returns true when the deficit in
1645	–	* running threads is more than the surplus of total threads, and
1646	–	* there is apparently some work to do.  This self-limiting rule
1647	–	* means that the more threads that have already been added, the
1648	–	* less parallelism we will tolerate before adding another.
1649	–	*
1650	–	* @param counts current worker counts
1651	–	* @param maintainParallelism try to maintain parallelism
1652	–	*/
1653	–	private boolean needSpare(int counts, boolean maintainParallelism) {
1654	–	int ps = parallelism;
1655	–	int rc = runningCountOf(counts);
1656	–	int tc = totalCountOf(counts);
1657	–	int runningDeficit = ps - rc;
1658	–	int totalSurplus = tc - ps;
1659	–	return (tc < maxPoolSize &&
1660	–	(rc == 0 || totalSurplus < 0 ||
1661	–	(maintainParallelism &&
1662	–	runningDeficit > totalSurplus &&
1663	–	ForkJoinWorkerThread.hasQueuedTasks(workers))));
1664	–	}
1665	–
1666	–	/**
1667	–	* Adds a spare worker if lock available and no more than the
1668	–	* expected numbers of threads exist.
1669	–	*
1670	–	* @return true if successful
1671	–	*/
1672	–	private boolean tryAddSpare(int expectedCounts) {
1673	–	final ReentrantLock lock = this.workerLock;
1674	–	int expectedRunning = runningCountOf(expectedCounts);
1675	–	int expectedTotal = totalCountOf(expectedCounts);
1676	–	boolean success = false;
1677	–	boolean locked = false;
1678	–	// confirm counts while locking; CAS after obtaining lock
1679	–	try {
1680	–	for (;;) {
1681	–	int s = workerCounts;
1682	–	int tc = totalCountOf(s);
1683	–	int rc = runningCountOf(s);
1684	–	if (rc > expectedRunning || tc > expectedTotal)
1685	–	break;
1686	–	if (!locked && !(locked = lock.tryLock()))
1687	–	break;
1688	–	if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
1689	–	createAndStartSpare(tc);
1690	–	success = true;
1691	–	break;
1692	–	}
1693	–	}
1694	–	} finally {
1695	–	if (locked)
1696	–	lock.unlock();
1697	–	}
1698	–	return success;
1699	–	}
1700	–
1701	–	/**
1702	–	* Adds the kth spare worker. On entry, pool counts are already
1703	–	* adjusted to reflect addition.
1704	–	*/
1705	–	private void createAndStartSpare(int k) {
1706	–	ForkJoinWorkerThread w = null;
1707	–	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
1708	–	int len = ws.length;
1709	–	// Probably, we can place at slot k. If not, find empty slot
1710	–	if (k < len && ws[k] != null) {
1711	–	for (k = 0; k < len && ws[k] != null; ++k)
1712	–	;
1713	–	}
1714	–	if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) {
1715	–	ws[k] = w;
1716	–	w.start();
1717	–	}
1718	–	else
1719	–	updateWorkerCount(-1); // adjust on failure
1720	–	signalIdleWorkers();
1721	–	}
1722	–
1723	–	/**
1724	–	* Suspends calling thread w if there are excess threads.  Called
1725	–	* only from sync.  Spares are enqueued in a Treiber stack using
1726	–	* the same WaitQueueNodes as barriers.  They are resumed mainly
1727	–	* in preJoin, but are also woken on pool events that require all
1728	–	* threads to check run state.
1729	–	*
1730	–	* @param w the caller
1731	–	*/
1732	–	private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1733	–	WaitQueueNode node = null;
1734	–	int s;
1735	–	while (parallelism < runningCountOf(s = workerCounts)) {
1736	–	if (node == null)
1737	–	node = new WaitQueueNode(0, w);
1738	–	if (casWorkerCounts(s, s-1)) { // representation-dependent
1739	–	// push onto stack
1740	–	do {} while (!casSpareStack(node.next = spareStack, node));
1741	–	// block until released by resumeSpare
1742	–	node.awaitSpareRelease();
1743	–	return true;
1744	–	}
1745	–	}
1746	–	return false;
1747	–	}
1748	–
1749	–	/**
1750	–	* Tries to pop and resume a spare thread.
1751	–	*
1752	–	* @param updateCount if true, increment running count on success
1753	–	* @return true if successful
1754	–	*/
1755	–	private boolean tryResumeSpare(boolean updateCount) {
1756	–	WaitQueueNode q;
1757	–	while ((q = spareStack) != null) {
1758	–	if (casSpareStack(q, q.next)) {
1759	–	if (updateCount)
1760	–	updateRunningCount(1);
1761	–	q.signal();
1762	–	return true;
1763	–	}
1764	–	}
1765	–	return false;
1766	–	}
1767	–
1768	–	/**
1769	–	* Pops and resumes all spare threads. Same idea as ensureSync.
1770	–	*
1771	–	* @return true if any spares released
1772	–	*/
1773	–	private boolean resumeAllSpares() {
1774	–	WaitQueueNode q;
1775	–	while ( (q = spareStack) != null) {
1776	–	if (casSpareStack(q, null)) {
1777	–	do {
1778	–	updateRunningCount(1);
1779	–	q.signal();
1780	–	} while ((q = q.next) != null);
1781	–	return true;
1782	–	}
1783	–	}
1784	–	return false;
1785	–	}
1786	–
1787	–	/**
1788	–	* Pops and shuts down excessive spare threads. Call only while
1789	–	* holding lock. This is not guaranteed to eliminate all excess
1790	–	* threads, only those suspended as spares, which are the ones
1791	–	* unlikely to be needed in the future.
1792	–	*/
1793	–	private void trimSpares() {
1794	–	int surplus = totalCountOf(workerCounts) - parallelism;
1795	–	WaitQueueNode q;
1796	–	while (surplus > 0 && (q = spareStack) != null) {
1797	–	if (casSpareStack(q, null)) {
1798	–	do {
1799	–	updateRunningCount(1);
1800	–	ForkJoinWorkerThread w = q.thread;
1801	–	if (w != null && surplus > 0 &&
1802	–	runningCountOf(workerCounts) > 0 && w.shutdown())
1803	–	--surplus;
1804	–	q.signal();
1805	–	} while ((q = q.next) != null);
1806	–	}
1807	–	}
1808	–	}
1809	–
2516		/**
2517		* Interface for extending managed parallelism for tasks running
2518		* in {@link ForkJoinPool}s.
2519		*
2520	<	* <p>A {@code ManagedBlocker} provides two methods.
2521	<	* Method {@code isReleasable} must return {@code true} if
2522	<	* blocking is not necessary. Method {@code block} blocks the
2523	<	* current thread if necessary (perhaps internally invoking
2524	<	* {@code isReleasable} before actually blocking).
2520	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
2521	>	* {@code isReleasable} must return {@code true} if blocking is
2522	>	* not necessary. Method {@code block} blocks the current thread
2523	>	* if necessary (perhaps internally invoking {@code isReleasable}
2524	>	* before actually blocking). These actions are performed by any
2525	>	* thread invoking {@link ForkJoinPool#managedBlock}.  The
2526	>	* unusual methods in this API accommodate synchronizers that may,
2527	>	* but don't usually, block for long periods. Similarly, they
2528	>	* allow more efficient internal handling of cases in which
2529	>	* additional workers may be, but usually are not, needed to
2530	>	* ensure sufficient parallelism.  Toward this end,
2531	>	* implementations of method {@code isReleasable} must be amenable
2532	>	* to repeated invocation.
2533		*
2534		* <p>For example, here is a ManagedBlocker based on a
2535		* ReentrantLock:
#	Line 1833 | Line 2547 | public class ForkJoinPool extends Abstra
2547		*     return hasLock || (hasLock = lock.tryLock());
2548		*   }
2549		* }}</pre>
2550	+	*
2551	+	* <p>Here is a class that possibly blocks waiting for an
2552	+	* item on a given queue:
2553	+	*  <pre> {@code
2554	+	* class QueueTaker<E> implements ManagedBlocker {
2555	+	*   final BlockingQueue<E> queue;
2556	+	*   volatile E item = null;
2557	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
2558	+	*   public boolean block() throws InterruptedException {
2559	+	*     if (item == null)
2560	+	*       item = queue.take();
2561	+	*     return true;
2562	+	*   }
2563	+	*   public boolean isReleasable() {
2564	+	*     return item != null || (item = queue.poll()) != null;
2565	+	*   }
2566	+	*   public E getItem() { // call after pool.managedBlock completes
2567	+	*     return item;
2568	+	*   }
2569	+	* }}</pre>
2570		*/
2571		public static interface ManagedBlocker {
2572		/**
#	Line 1856 | Line 2590 | public class ForkJoinPool extends Abstra
2590		* Blocks in accord with the given blocker.  If the current thread
2591		* is a {@link ForkJoinWorkerThread}, this method possibly
2592		* arranges for a spare thread to be activated if necessary to
2593	<	* ensure parallelism while the current thread is blocked.
1860	<	*
1861	<	* <p>If {@code maintainParallelism} is {@code true} and the pool
1862	<	* supports it ({@link #getMaintainsParallelism}), this method
1863	<	* attempts to maintain the pool's nominal parallelism. Otherwise
1864	<	* it activates a thread only if necessary to avoid complete
1865	<	* starvation. This option may be preferable when blockages use
1866	<	* timeouts, or are almost always brief.
2593	>	* ensure sufficient parallelism while the current thread is blocked.
2594		*
2595		* <p>If the caller is not a {@link ForkJoinTask}, this method is
2596		* behaviorally equivalent to
#	Line 1877 | Line 2604 | public class ForkJoinPool extends Abstra
2604		* first be expanded to ensure parallelism, and later adjusted.
2605		*
2606		* @param blocker the blocker
1880	–	* @param maintainParallelism if {@code true} and supported by
1881	–	* this pool, attempt to maintain the pool's nominal parallelism;
1882	–	* otherwise activate a thread only if necessary to avoid
1883	–	* complete starvation.
2607		* @throws InterruptedException if blocker.block did so
2608		*/
2609	<	public static void managedBlock(ManagedBlocker blocker,
1887	<	boolean maintainParallelism)
2609	>	public static void managedBlock(ManagedBlocker blocker)
2610		throws InterruptedException {
2611		Thread t = Thread.currentThread();
2612	<	ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
2613	<	((ForkJoinWorkerThread) t).pool : null);
2614	<	if (!blocker.isReleasable()) {
2615	<	try {
2616	<	if (pool == null ||
2617	<	!pool.preBlock(blocker, maintainParallelism))
2618	<	awaitBlocker(blocker);
2619	<	} finally {
2620	<	if (pool != null)
2621	<	pool.updateRunningCount(1);
2612	>	ForkJoinPool p = ((t instanceof ForkJoinWorkerThread) ?
2613	>	((ForkJoinWorkerThread)t).pool : null);
2614	>	while (!blocker.isReleasable()) {
2615	>	if (p == null || p.tryCompensate()) {
2616	>	try {
2617	>	do {} while (!blocker.isReleasable() && !blocker.block());
2618	>	} finally {
2619	>	if (p != null)
2620	>	p.incrementActiveCount();
2621	>	}
2622	>	break;
2623		}
2624		}
2625		}
2626
1904	–	private static void awaitBlocker(ManagedBlocker blocker)
1905	–	throws InterruptedException {
1906	–	do {} while (!blocker.isReleasable() && !blocker.block());
1907	–	}
1908	–
2627		// AbstractExecutorService overrides.  These rely on undocumented
2628		// fact that ForkJoinTask.adapt returns ForkJoinTasks that also
2629		// implement RunnableFuture.
#	Line 1919 | Line 2637 | public class ForkJoinPool extends Abstra
2637		}
2638
2639		// Unsafe mechanics
2640	<
2641	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
2642	<	private static final long eventCountOffset =
2643	<	objectFieldOffset("eventCount", ForkJoinPool.class);
2644	<	private static final long workerCountsOffset =
2645	<	objectFieldOffset("workerCounts", ForkJoinPool.class);
2646	<	private static final long runControlOffset =
2647	<	objectFieldOffset("runControl", ForkJoinPool.class);
2648	<	private static final long syncStackOffset =
2649	<	objectFieldOffset("syncStack",ForkJoinPool.class);
1932	<	private static final long spareStackOffset =
1933	<	objectFieldOffset("spareStack", ForkJoinPool.class);
1934	<
1935	<	private boolean casEventCount(long cmp, long val) {
1936	<	return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
1937	<	}
1938	<	private boolean casWorkerCounts(int cmp, int val) {
1939	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
1940	<	}
1941	<	private boolean casRunControl(int cmp, int val) {
1942	<	return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
1943	<	}
1944	<	private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
1945	<	return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
1946	<	}
1947	<	private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
1948	<	return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
1949	<	}
1950	<
1951	<	private static long objectFieldOffset(String field, Class<?> klazz) {
2640	>	private static final sun.misc.Unsafe U;
2641	>	private static final long CTL;
2642	>	private static final long PARKBLOCKER;
2643	>
2644	>	static {
2645	>	poolNumberGenerator = new AtomicInteger();
2646	>	modifyThreadPermission = new RuntimePermission("modifyThread");
2647	>	defaultForkJoinWorkerThreadFactory =
2648	>	new DefaultForkJoinWorkerThreadFactory();
2649	>	submitters = new ThreadSubmitter();
2650		try {
2651	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
2652	<	} catch (NoSuchFieldException e) {
2653	<	// Convert Exception to corresponding Error
2654	<	NoSuchFieldError error = new NoSuchFieldError(field);
2655	<	error.initCause(e);
2656	<	throw error;
2651	>	U = getUnsafe();
2652	>	Class<?> k = ForkJoinPool.class;
2653	>	CTL = U.objectFieldOffset
2654	>	(k.getDeclaredField("ctl"));
2655	>	Class<?> tk = Thread.class;
2656	>	PARKBLOCKER = U.objectFieldOffset
2657	>	(tk.getDeclaredField("parkBlocker"));
2658	>	} catch (Exception e) {
2659	>	throw new Error(e);
2660		}
2661		}
2662
#	Line 1986 | Line 2687 | public class ForkJoinPool extends Abstra
2687		}
2688		}
2689		}
2690	+
2691		}

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