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Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.42 by dl, Mon Aug 3 13:01:15 2009 UTC vs.
Revision 1.102 by jsr166, Thu Apr 14 01:17:58 2011 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;
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.TimeoutException;
23	>	import java.util.concurrent.atomic.AtomicInteger;
24		import java.util.concurrent.locks.LockSupport;
25		import java.util.concurrent.locks.ReentrantLock;
26	<	import java.util.concurrent.atomic.AtomicInteger;
20	<	import java.util.concurrent.atomic.AtomicLong;
26	>	import java.util.concurrent.locks.Condition;
27
28		/**
29		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
30		* A {@code ForkJoinPool} provides the entry point for submissions
31	<	* from non-{@code ForkJoinTask}s, as well as management and
32	<	* monitoring operations.
31	>	* from non-{@code ForkJoinTask} clients, as well as management and
32	>	* monitoring operations.
33		*
34		* <p>A {@code ForkJoinPool} differs from other kinds of {@link
35		* ExecutorService} mainly by virtue of employing
#	Line 31 | Line 37 | import java.util.concurrent.atomic.Atomi
37		* execute subtasks created by other active tasks (eventually blocking
38		* waiting for work if none exist). This enables efficient processing
39		* when most tasks spawn other subtasks (as do most {@code
40	<	* ForkJoinTask}s). A {@code ForkJoinPool} may also be used for mixed
41	<	* execution of some plain {@code Runnable}- or {@code Callable}-
42	<	* based activities along with {@code ForkJoinTask}s. When setting
37	<	* {@linkplain #setAsyncMode async mode}, a {@code ForkJoinPool} may
38	<	* 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.
40	>	* ForkJoinTask}s). When setting <em>asyncMode</em> to true in
41	>	* constructors, {@code ForkJoinPool}s may also be appropriate for use
42	>	* with event-style tasks that are never joined.
43		*
44		* <p>A {@code ForkJoinPool} is constructed with a given target
45		* parallelism level; by default, equal to the number of available
46	<	* processors. Unless configured otherwise via {@link
47	<	* #setMaintainsParallelism}, the pool attempts to maintain this
48	<	* number of active (or available) threads by dynamically adding,
49	<	* suspending, or resuming internal worker threads, even if some tasks
50	<	* are waiting to join others. However, no such adjustments are
51	<	* performed in the face of blocked IO or other unmanaged
52	<	* 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.
46	>	* processors. The pool attempts to maintain enough active (or
47	>	* available) threads by dynamically adding, suspending, or resuming
48	>	* internal worker threads, even if some tasks are stalled waiting to
49	>	* join others. However, no such adjustments are guaranteed in the
50	>	* face of blocked IO or other unmanaged synchronization. The nested
51	>	* {@link ManagedBlocker} interface enables extension of the kinds of
52	>	* synchronization accommodated.
53		*
54		* <p>In addition to execution and lifecycle control methods, this
55		* class provides status check methods (for example
#	Line 62 | Line 58 | import java.util.concurrent.atomic.Atomi
58		* {@link #toString} returns indications of pool state in a
59		* convenient form for informal monitoring.
60		*
61	+	* <p> As is the case with other ExecutorServices, there are three
62	+	* main task execution methods summarized in the following
63	+	* table. These are designed to be used by clients not already engaged
64	+	* in fork/join computations in the current pool.  The main forms of
65	+	* these methods accept instances of {@code ForkJoinTask}, but
66	+	* overloaded forms also allow mixed execution of plain {@code
67	+	* Runnable}- or {@code Callable}- based activities as well.  However,
68	+	* tasks that are already executing in a pool should normally
69	+	* <em>NOT</em> use these pool execution methods, but instead use the
70	+	* within-computation forms listed in the table.
71	+	*
72	+	* <table BORDER CELLPADDING=3 CELLSPACING=1>
73	+	*  <tr>
74	+	*    <td></td>
75	+	*    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
76	+	*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
77	+	*  </tr>
78	+	*  <tr>
79	+	*    <td> <b>Arrange async execution</td>
80	+	*    <td> {@link #execute(ForkJoinTask)}</td>
81	+	*    <td> {@link ForkJoinTask#fork}</td>
82	+	*  </tr>
83	+	*  <tr>
84	+	*    <td> <b>Await and obtain result</td>
85	+	*    <td> {@link #invoke(ForkJoinTask)}</td>
86	+	*    <td> {@link ForkJoinTask#invoke}</td>
87	+	*  </tr>
88	+	*  <tr>
89	+	*    <td> <b>Arrange exec and obtain Future</td>
90	+	*    <td> {@link #submit(ForkJoinTask)}</td>
91	+	*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
92	+	*  </tr>
93	+	* </table>
94	+	*
95		* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
96		* used for all parallel task execution in a program or subsystem.
97		* Otherwise, use would not usually outweigh the construction and
98		* bookkeeping overhead of creating a large set of threads. For
99	<	* example a common pool could be used for the {@code SortTasks}
99	>	* example, a common pool could be used for the {@code SortTasks}
100		* illustrated in {@link RecursiveAction}. Because {@code
101		* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
102	<	* daemon} mode, there is typically no need to explictly {@link
102	>	* daemon} mode, there is typically no need to explicitly {@link
103		* #shutdown} such a pool upon program exit.
104		*
105		* <pre>
#	Line 82 | Line 112 | import java.util.concurrent.atomic.Atomi
112		*
113		* <p><b>Implementation notes</b>: This implementation restricts the
114		* maximum number of running threads to 32767. Attempts to create
115	<	* pools with greater than the maximum result in
115	>	* pools with greater than the maximum number result in
116		* {@code IllegalArgumentException}.
117		*
118	+	* <p>This implementation rejects submitted tasks (that is, by throwing
119	+	* {@link RejectedExecutionException}) only when the pool is shut down
120	+	* or internal resources have been exhausted.
121	+	*
122		* @since 1.7
123		* @author Doug Lea
124		*/
125		public class ForkJoinPool extends AbstractExecutorService {
126
127		/*
128	<	* See the extended comments interspersed below for design,
129	<	* rationale, and walkthroughs.
128	>	* Implementation Overview
129	>	*
130	>	* This class provides the central bookkeeping and control for a
131	>	* set of worker threads: Submissions from non-FJ threads enter
132	>	* into a submission queue. Workers take these tasks and typically
133	>	* split them into subtasks that may be stolen by other workers.
134	>	* Preference rules give first priority to processing tasks from
135	>	* their own queues (LIFO or FIFO, depending on mode), then to
136	>	* randomized FIFO steals of tasks in other worker queues, and
137	>	* lastly to new submissions.
138	>	*
139	>	* The main throughput advantages of work-stealing stem from
140	>	* decentralized control -- workers mostly take tasks from
141	>	* themselves or each other. We cannot negate this in the
142	>	* implementation of other management responsibilities. The main
143	>	* tactic for avoiding bottlenecks is packing nearly all
144	>	* essentially atomic control state into a single 64bit volatile
145	>	* variable ("ctl"). This variable is read on the order of 10-100
146	>	* times as often as it is modified (always via CAS). (There is
147	>	* some additional control state, for example variable "shutdown"
148	>	* for which we can cope with uncoordinated updates.)  This
149	>	* streamlines synchronization and control at the expense of messy
150	>	* constructions needed to repack status bits upon updates.
151	>	* Updates tend not to contend with each other except during
152	>	* bursts while submitted tasks begin or end.  In some cases when
153	>	* they do contend, threads can instead do something else
154	>	* (usually, scan for tasks) until contention subsides.
155	>	*
156	>	* To enable packing, we restrict maximum parallelism to (1<<15)-1
157	>	* (which is far in excess of normal operating range) to allow
158	>	* ids, counts, and their negations (used for thresholding) to fit
159	>	* into 16bit fields.
160	>	*
161	>	* Recording Workers.  Workers are recorded in the "workers" array
162	>	* that is created upon pool construction and expanded if (rarely)
163	>	* necessary.  This is an array as opposed to some other data
164	>	* structure to support index-based random steals by workers.
165	>	* Updates to the array recording new workers and unrecording
166	>	* terminated ones are protected from each other by a seqLock
167	>	* (scanGuard) but the array is otherwise concurrently readable,
168	>	* and accessed directly by workers. To simplify index-based
169	>	* operations, the array size is always a power of two, and all
170	>	* readers must tolerate null slots. To avoid flailing during
171	>	* start-up, the array is presized to hold twice #parallelism
172	>	* workers (which is unlikely to need further resizing during
173	>	* execution). But to avoid dealing with so many null slots,
174	>	* variable scanGuard includes a mask for the nearest power of two
175	>	* that contains all current workers.  All worker thread creation
176	>	* is on-demand, triggered by task submissions, replacement of
177	>	* terminated workers, and/or compensation for blocked
178	>	* workers. However, all other support code is set up to work with
179	>	* other policies.  To ensure that we do not hold on to worker
180	>	* references that would prevent GC, ALL accesses to workers are
181	>	* via indices into the workers array (which is one source of some
182	>	* of the messy code constructions here). In essence, the workers
183	>	* array serves as a weak reference mechanism. Thus for example
184	>	* the wait queue field of ctl stores worker indices, not worker
185	>	* references.  Access to the workers in associated methods (for
186	>	* example signalWork) must both index-check and null-check the
187	>	* IDs. All such accesses ignore bad IDs by returning out early
188	>	* from what they are doing, since this can only be associated
189	>	* with termination, in which case it is OK to give up.
190	>	*
191	>	* All uses of the workers array, as well as queue arrays, check
192	>	* that the array is non-null (even if previously non-null). This
193	>	* allows nulling during termination, which is currently not
194	>	* necessary, but remains an option for resource-revocation-based
195	>	* shutdown schemes.
196	>	*
197	>	* Wait Queuing. Unlike HPC work-stealing frameworks, we cannot
198	>	* let workers spin indefinitely scanning for tasks when none can
199	>	* be found immediately, and we cannot start/resume workers unless
200	>	* there appear to be tasks available.  On the other hand, we must
201	>	* quickly prod them into action when new tasks are submitted or
202	>	* generated.  We park/unpark workers after placing in an event
203	>	* wait queue when they cannot find work. This "queue" is actually
204	>	* a simple Treiber stack, headed by the "id" field of ctl, plus a
205	>	* 15bit counter value to both wake up waiters (by advancing their
206	>	* count) and avoid ABA effects. Successors are held in worker
207	>	* field "nextWait".  Queuing deals with several intrinsic races,
208	>	* mainly that a task-producing thread can miss seeing (and
209	>	* signalling) another thread that gave up looking for work but
210	>	* has not yet entered the wait queue. We solve this by requiring
211	>	* a full sweep of all workers both before (in scan()) and after
212	>	* (in tryAwaitWork()) a newly waiting worker is added to the wait
213	>	* queue. During a rescan, the worker might release some other
214	>	* queued worker rather than itself, which has the same net
215	>	* effect. Because enqueued workers may actually be rescanning
216	>	* rather than waiting, we set and clear the "parked" field of
217	>	* ForkJoinWorkerThread to reduce unnecessary calls to unpark.
218	>	* (Use of the parked field requires a secondary recheck to avoid
219	>	* missed signals.)
220	>	*
221	>	* Signalling.  We create or wake up workers only when there
222	>	* appears to be at least one task they might be able to find and
223	>	* execute.  When a submission is added or another worker adds a
224	>	* task to a queue that previously had two or fewer tasks, they
225	>	* signal waiting workers (or trigger creation of new ones if
226	>	* fewer than the given parallelism level -- see signalWork).
227	>	* These primary signals are buttressed by signals during rescans
228	>	* as well as those performed when a worker steals a task and
229	>	* notices that there are more tasks too; together these cover the
230	>	* signals needed in cases when more than two tasks are pushed
231	>	* but untaken.
232	>	*
233	>	* Trimming workers. To release resources after periods of lack of
234	>	* use, a worker starting to wait when the pool is quiescent will
235	>	* time out and terminate if the pool has remained quiescent for
236	>	* SHRINK_RATE nanosecs. This will slowly propagate, eventually
237	>	* terminating all workers after long periods of non-use.
238	>	*
239	>	* Submissions. External submissions are maintained in an
240	>	* array-based queue that is structured identically to
241	>	* ForkJoinWorkerThread queues except for the use of
242	>	* submissionLock in method addSubmission. Unlike the case for
243	>	* worker queues, multiple external threads can add new
244	>	* submissions, so adding requires a lock.
245	>	*
246	>	* Compensation. Beyond work-stealing support and lifecycle
247	>	* control, the main responsibility of this framework is to take
248	>	* actions when one worker is waiting to join a task stolen (or
249	>	* always held by) another.  Because we are multiplexing many
250	>	* tasks on to a pool of workers, we can't just let them block (as
251	>	* in Thread.join).  We also cannot just reassign the joiner's
252	>	* run-time stack with another and replace it later, which would
253	>	* be a form of "continuation", that even if possible is not
254	>	* necessarily a good idea since we sometimes need both an
255	>	* unblocked task and its continuation to progress. Instead we
256	>	* combine two tactics:
257	>	*
258	>	*   Helping: Arranging for the joiner to execute some task that it
259	>	*      would be running if the steal had not occurred.  Method
260	>	*      ForkJoinWorkerThread.joinTask tracks joining->stealing
261	>	*      links to try to find such a task.
262	>	*
263	>	*   Compensating: Unless there are already enough live threads,
264	>	*      method tryPreBlock() may create or re-activate a spare
265	>	*      thread to compensate for blocked joiners until they
266	>	*      unblock.
267	>	*
268	>	* The ManagedBlocker extension API can't use helping so relies
269	>	* only on compensation in method awaitBlocker.
270	>	*
271	>	* It is impossible to keep exactly the target parallelism number
272	>	* of threads running at any given time.  Determining the
273	>	* existence of conservatively safe helping targets, the
274	>	* availability of already-created spares, and the apparent need
275	>	* to create new spares are all racy and require heuristic
276	>	* guidance, so we rely on multiple retries of each.  Currently,
277	>	* in keeping with on-demand signalling policy, we compensate only
278	>	* if blocking would leave less than one active (non-waiting,
279	>	* non-blocked) worker. Additionally, to avoid some false alarms
280	>	* due to GC, lagging counters, system activity, etc, compensated
281	>	* blocking for joins is only attempted after rechecks stabilize
282	>	* (retries are interspersed with Thread.yield, for good
283	>	* citizenship).  The variable blockedCount, incremented before
284	>	* blocking and decremented after, is sometimes needed to
285	>	* distinguish cases of waiting for work vs blocking on joins or
286	>	* other managed sync. Both cases are equivalent for most pool
287	>	* control, so we can update non-atomically. (Additionally,
288	>	* contention on blockedCount alleviates some contention on ctl).
289	>	*
290	>	* Shutdown and Termination. A call to shutdownNow atomically sets
291	>	* the ctl stop bit and then (non-atomically) sets each workers
292	>	* "terminate" status, cancels all unprocessed tasks, and wakes up
293	>	* all waiting workers.  Detecting whether termination should
294	>	* commence after a non-abrupt shutdown() call requires more work
295	>	* and bookkeeping. We need consensus about quiesence (i.e., that
296	>	* there is no more work) which is reflected in active counts so
297	>	* long as there are no current blockers, as well as possible
298	>	* re-evaluations during independent changes in blocking or
299	>	* quiescing workers.
300	>	*
301	>	* Style notes: There is a lot of representation-level coupling
302	>	* among classes ForkJoinPool, ForkJoinWorkerThread, and
303	>	* ForkJoinTask.  Most fields of ForkJoinWorkerThread maintain
304	>	* data structures managed by ForkJoinPool, so are directly
305	>	* accessed.  Conversely we allow access to "workers" array by
306	>	* workers, and direct access to ForkJoinTask.status by both
307	>	* ForkJoinPool and ForkJoinWorkerThread.  There is little point
308	>	* trying to reduce this, since any associated future changes in
309	>	* representations will need to be accompanied by algorithmic
310	>	* changes anyway. All together, these low-level implementation
311	>	* choices produce as much as a factor of 4 performance
312	>	* improvement compared to naive implementations, and enable the
313	>	* processing of billions of tasks per second, at the expense of
314	>	* some ugliness.
315	>	*
316	>	* Methods signalWork() and scan() are the main bottlenecks so are
317	>	* especially heavily micro-optimized/mangled.  There are lots of
318	>	* inline assignments (of form "while ((local = field) != 0)")
319	>	* which are usually the simplest way to ensure the required read
320	>	* orderings (which are sometimes critical). This leads to a
321	>	* "C"-like style of listing declarations of these locals at the
322	>	* heads of methods or blocks.  There are several occurrences of
323	>	* the unusual "do {} while (!cas...)"  which is the simplest way
324	>	* to force an update of a CAS'ed variable. There are also other
325	>	* coding oddities that help some methods perform reasonably even
326	>	* when interpreted (not compiled).
327	>	*
328	>	* The order of declarations in this file is: (1) declarations of
329	>	* statics (2) fields (along with constants used when unpacking
330	>	* some of them), listed in an order that tends to reduce
331	>	* contention among them a bit under most JVMs.  (3) internal
332	>	* control methods (4) callbacks and other support for
333	>	* ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
334	>	* methods (plus a few little helpers). (6) static block
335	>	* initializing all statics in a minimally dependent order.
336		*/
337
98	–	/** Mask for packing and unpacking shorts */
99	–	private static final int  shortMask = 0xffff;
100	–
101	–	/** Max pool size -- must be a power of two minus 1 */
102	–	private static final int MAX_THREADS =  0x7FFF;
103	–
338		/**
339		* Factory for creating new {@link ForkJoinWorkerThread}s.
340		* A {@code ForkJoinWorkerThreadFactory} must be defined and used
#	Line 112 | Line 346 | public class ForkJoinPool extends Abstra
346		* Returns a new worker thread operating in the given pool.
347		*
348		* @param pool the pool this thread works in
349	<	* @throws NullPointerException if pool is null
349	>	* @throws NullPointerException if the pool is null
350		*/
351		public ForkJoinWorkerThread newThread(ForkJoinPool pool);
352		}
#	Line 121 | Line 355 | public class ForkJoinPool extends Abstra
355		* Default ForkJoinWorkerThreadFactory implementation; creates a
356		* new ForkJoinWorkerThread.
357		*/
358	<	static class  DefaultForkJoinWorkerThreadFactory
358	>	static class DefaultForkJoinWorkerThreadFactory
359		implements ForkJoinWorkerThreadFactory {
360		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
361	<	try {
128	<	return new ForkJoinWorkerThread(pool);
129	<	} catch (OutOfMemoryError oom)  {
130	<	return null;
131	<	}
361	>	return new ForkJoinWorkerThread(pool);
362		}
363		}
364
#	Line 137 | Line 367 | public class ForkJoinPool extends Abstra
367		* overridden in ForkJoinPool constructors.
368		*/
369		public static final ForkJoinWorkerThreadFactory
370	<	defaultForkJoinWorkerThreadFactory =
141	<	new DefaultForkJoinWorkerThreadFactory();
370	>	defaultForkJoinWorkerThreadFactory;
371
372		/**
373		* Permission required for callers of methods that may start or
374		* kill threads.
375		*/
376	<	private static final RuntimePermission modifyThreadPermission =
148	<	new RuntimePermission("modifyThread");
376	>	private static final RuntimePermission modifyThreadPermission;
377
378		/**
379		* If there is a security manager, makes sure caller has
#	Line 160 | Line 388 | public class ForkJoinPool extends Abstra
388		/**
389		* Generator for assigning sequence numbers as pool names.
390		*/
391	<	private static final AtomicInteger poolNumberGenerator =
164	<	new AtomicInteger();
391	>	private static final AtomicInteger poolNumberGenerator;
392
393		/**
394	<	* Array holding all worker threads in the pool. Initialized upon
395	<	* first use. Array size must be a power of two.  Updates and
396	<	* replacements are protected by workerLock, but it is always kept
397	<	* in a consistent enough state to be randomly accessed without
398	<	* locking by workers performing work-stealing.
394	>	* Generator for initial random seeds for worker victim
395	>	* selection. This is used only to create initial seeds. Random
396	>	* steals use a cheaper xorshift generator per steal attempt. We
397	>	* don't expect much contention on seedGenerator, so just use a
398	>	* plain Random.
399		*/
400	<	volatile ForkJoinWorkerThread[] workers;
400	>	static final Random workerSeedGenerator;
401
402		/**
403	<	* Lock protecting access to workers.
403	>	* Array holding all worker threads in the pool.  Initialized upon
404	>	* construction. Array size must be a power of two.  Updates and
405	>	* replacements are protected by scanGuard, but the array is
406	>	* always kept in a consistent enough state to be randomly
407	>	* accessed without locking by workers performing work-stealing,
408	>	* as well as other traversal-based methods in this class, so long
409	>	* as reads memory-acquire by first reading ctl. All readers must
410	>	* tolerate that some array slots may be null.
411		*/
412	<	private final ReentrantLock workerLock;
412	>	ForkJoinWorkerThread[] workers;
413
414		/**
415	<	* Condition for awaitTermination.
415	>	* Initial size for submission queue array. Must be a power of
416	>	* two.  In many applications, these always stay small so we use a
417	>	* small initial cap.
418		*/
419	<	private final Condition termination;
419	>	private static final int INITIAL_QUEUE_CAPACITY = 8;
420	>
421	>	/**
422	>	* Maximum size for submission queue array. Must be a power of two
423	>	* less than or equal to 1 << (31 - width of array entry) to
424	>	* ensure lack of index wraparound, but is capped at a lower
425	>	* value to help users trap runaway computations.
426	>	*/
427	>	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 24; // 16M
428
429		/**
430	<	* The uncaught exception handler used when any worker
187	<	* abruptly terminates
430	>	* Array serving as submission queue. Initialized upon construction.
431		*/
432	<	private Thread.UncaughtExceptionHandler ueh;
432	>	private ForkJoinTask<?>[] submissionQueue;
433	>
434	>	/**
435	>	* Lock protecting submissions array for addSubmission
436	>	*/
437	>	private final ReentrantLock submissionLock;
438	>
439	>	/**
440	>	* Condition for awaitTermination, using submissionLock for
441	>	* convenience.
442	>	*/
443	>	private final Condition termination;
444
445		/**
446		* Creation factory for worker threads.
#	Line 194 | Line 448 | public class ForkJoinPool extends Abstra
448		private final ForkJoinWorkerThreadFactory factory;
449
450		/**
451	<	* Head of stack of threads that were created to maintain
452	<	* parallelism when other threads blocked, but have since
199	<	* suspended when the parallelism level rose.
451	>	* The uncaught exception handler used when any worker abruptly
452	>	* terminates.
453		*/
454	<	private volatile WaitQueueNode spareStack;
454	>	final Thread.UncaughtExceptionHandler ueh;
455
456		/**
457	<	* Sum of per-thread steal counts, updated only when threads are
205	<	* idle or terminating.
457	>	* Prefix for assigning names to worker threads
458		*/
459	<	private final AtomicLong stealCount;
459	>	private final String workerNamePrefix;
460
461		/**
462	<	* Queue for external submissions.
462	>	* Sum of per-thread steal counts, updated only when threads are
463	>	* idle or terminating.
464		*/
465	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
465	>	private volatile long stealCount;
466
467		/**
468	<	* Head of Treiber stack for barrier sync. See below for explanation.
468	>	* Main pool control -- a long packed with:
469	>	* AC: Number of active running workers minus target parallelism (16 bits)
470	>	* TC: Number of total workers minus target parallelism (16bits)
471	>	* ST: true if pool is terminating (1 bit)
472	>	* EC: the wait count of top waiting thread (15 bits)
473	>	* ID: ~poolIndex of top of Treiber stack of waiting threads (16 bits)
474	>	*
475	>	* When convenient, we can extract the upper 32 bits of counts and
476	>	* the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
477	>	* (int)ctl.  The ec field is never accessed alone, but always
478	>	* together with id and st. The offsets of counts by the target
479	>	* parallelism and the positionings of fields makes it possible to
480	>	* perform the most common checks via sign tests of fields: When
481	>	* ac is negative, there are not enough active workers, when tc is
482	>	* negative, there are not enough total workers, when id is
483	>	* negative, there is at least one waiting worker, and when e is
484	>	* negative, the pool is terminating.  To deal with these possibly
485	>	* negative fields, we use casts in and out of "short" and/or
486	>	* signed shifts to maintain signedness.
487		*/
488	<	private volatile WaitQueueNode syncStack;
488	>	volatile long ctl;
489	>
490	>	// bit positions/shifts for fields
491	>	private static final int  AC_SHIFT   = 48;
492	>	private static final int  TC_SHIFT   = 32;
493	>	private static final int  ST_SHIFT   = 31;
494	>	private static final int  EC_SHIFT   = 16;
495	>
496	>	// bounds
497	>	private static final int  MAX_ID     = 0x7fff;  // max poolIndex
498	>	private static final int  SMASK      = 0xffff;  // mask short bits
499	>	private static final int  SHORT_SIGN = 1 << 15;
500	>	private static final int  INT_SIGN   = 1 << 31;
501	>
502	>	// masks
503	>	private static final long STOP_BIT   = 0x0001L << ST_SHIFT;
504	>	private static final long AC_MASK    = ((long)SMASK) << AC_SHIFT;
505	>	private static final long TC_MASK    = ((long)SMASK) << TC_SHIFT;
506	>
507	>	// units for incrementing and decrementing
508	>	private static final long TC_UNIT    = 1L << TC_SHIFT;
509	>	private static final long AC_UNIT    = 1L << AC_SHIFT;
510	>
511	>	// masks and units for dealing with u = (int)(ctl >>> 32)
512	>	private static final int  UAC_SHIFT  = AC_SHIFT - 32;
513	>	private static final int  UTC_SHIFT  = TC_SHIFT - 32;
514	>	private static final int  UAC_MASK   = SMASK << UAC_SHIFT;
515	>	private static final int  UTC_MASK   = SMASK << UTC_SHIFT;
516	>	private static final int  UAC_UNIT   = 1 << UAC_SHIFT;
517	>	private static final int  UTC_UNIT   = 1 << UTC_SHIFT;
518	>
519	>	// masks and units for dealing with e = (int)ctl
520	>	private static final int  E_MASK     = 0x7fffffff; // no STOP_BIT
521	>	private static final int  EC_UNIT    = 1 << EC_SHIFT;
522
523		/**
524	<	* The count for event barrier
524	>	* The target parallelism level.
525		*/
526	<	private volatile long eventCount;
526	>	final int parallelism;
527
528		/**
529	<	* Pool number, just for assigning useful names to worker threads
529	>	* Index (mod submission queue length) of next element to take
530	>	* from submission queue. Usage is identical to that for
531	>	* per-worker queues -- see ForkJoinWorkerThread internal
532	>	* documentation.
533		*/
534	<	private final int poolNumber;
534	>	volatile int queueBase;
535
536		/**
537	<	* The maximum allowed pool size
537	>	* Index (mod submission queue length) of next element to add
538	>	* in submission queue. Usage is identical to that for
539	>	* per-worker queues -- see ForkJoinWorkerThread internal
540	>	* documentation.
541		*/
542	<	private volatile int maxPoolSize;
542	>	int queueTop;
543
544		/**
545	<	* The desired parallelism level, updated only under workerLock.
545	>	* True when shutdown() has been called.
546		*/
547	<	private volatile int parallelism;
547	>	volatile boolean shutdown;
548
549		/**
550		* True if use local fifo, not default lifo, for local polling
551	+	* Read by, and replicated by ForkJoinWorkerThreads
552		*/
553	<	private volatile boolean locallyFifo;
553	>	final boolean locallyFifo;
554
555		/**
556	<	* Holds number of total (i.e., created and not yet terminated)
557	<	* and running (i.e., not blocked on joins or other managed sync)
558	<	* threads, packed into one int to ensure consistent snapshot when
248	<	* making decisions about creating and suspending spare
249	<	* threads. Updated only by CAS.  Note: CASes in
250	<	* updateRunningCount and preJoin assume that running active count
251	<	* is in low word, so need to be modified if this changes.
556	>	* The number of threads in ForkJoinWorkerThreads.helpQuiescePool.
557	>	* When non-zero, suppresses automatic shutdown when active
558	>	* counts become zero.
559		*/
560	<	private volatile int workerCounts;
560	>	volatile int quiescerCount;
561
562	<	private static int totalCountOf(int s)           { return s >>> 16;  }
563	<	private static int runningCountOf(int s)         { return s & shortMask; }
564	<	private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
562	>	/**
563	>	* The number of threads blocked in join.
564	>	*/
565	>	volatile int blockedCount;
566
567		/**
568	<	* Adds delta (which may be negative) to running count.  This must
261	<	* be called before (with negative arg) and after (with positive)
262	<	* any managed synchronization (i.e., mainly, joins).
263	<	*
264	<	* @param delta the number to add
568	>	* Counter for worker Thread names (unrelated to their poolIndex)
569		*/
570	<	final void updateRunningCount(int delta) {
267	<	int s;
268	<	do {} while (!casWorkerCounts(s = workerCounts, s + delta));
269	<	}
570	>	private volatile int nextWorkerNumber;
571
572		/**
573	<	* Adds delta (which may be negative) to both total and running
273	<	* count.  This must be called upon creation and termination of
274	<	* worker threads.
275	<	*
276	<	* @param delta the number to add
573	>	* The index for the next created worker. Accessed under scanGuard.
574		*/
575	<	private void updateWorkerCount(int delta) {
279	<	int d = delta + (delta << 16); // add to both lo and hi parts
280	<	int s;
281	<	do {} while (!casWorkerCounts(s = workerCounts, s + d));
282	<	}
575	>	private int nextWorkerIndex;
576
577		/**
578	<	* Lifecycle control. High word contains runState, low word
579	<	* contains the number of workers that are (probably) executing
580	<	* tasks. This value is atomically incremented before a worker
581	<	* gets a task to run, and decremented when worker has no tasks
582	<	* and cannot find any. These two fields are bundled together to
583	<	* support correct termination triggering.  Note: activeCount
584	<	* CAS'es cheat by assuming active count is in low word, so need
585	<	* to be modified if this changes
578	>	* SeqLock and index masking for updates to workers array.  Locked
579	>	* when SG_UNIT is set. Unlocking clears bit by adding
580	>	* SG_UNIT. Staleness of read-only operations can be checked by
581	>	* comparing scanGuard to value before the reads. The low 16 bits
582	>	* (i.e, anding with SMASK) hold (the smallest power of two
583	>	* covering all worker indices, minus one, and is used to avoid
584	>	* dealing with large numbers of null slots when the workers array
585	>	* is overallocated.
586		*/
587	<	private volatile int runControl;
587	>	volatile int scanGuard;
588
589	<	// RunState values. Order among values matters
297	<	private static final int RUNNING     = 0;
298	<	private static final int SHUTDOWN    = 1;
299	<	private static final int TERMINATING = 2;
300	<	private static final int TERMINATED  = 3;
589	>	private static final int SG_UNIT = 1 << 16;
590
591	<	private static int runStateOf(int c)             { return c >>> 16; }
592	<	private static int activeCountOf(int c)          { return c & shortMask; }
593	<	private static int runControlFor(int r, int a)   { return (r << 16) + a; }
591	>	/**
592	>	* The wakeup interval (in nanoseconds) for a worker waiting for a
593	>	* task when the pool is quiescent to instead try to shrink the
594	>	* number of workers.  The exact value does not matter too
595	>	* much. It must be short enough to release resources during
596	>	* sustained periods of idleness, but not so short that threads
597	>	* are continually re-created.
598	>	*/
599	>	private static final long SHRINK_RATE =
600	>	4L * 1000L * 1000L * 1000L; // 4 seconds
601
602		/**
603	<	* Tries incrementing active count; fails on contention.
604	<	* Called by workers before/during executing tasks.
603	>	* Top-level loop for worker threads: On each step: if the
604	>	* previous step swept through all queues and found no tasks, or
605	>	* there are excess threads, then possibly blocks. Otherwise,
606	>	* scans for and, if found, executes a task. Returns when pool
607	>	* and/or worker terminate.
608		*
609	<	* @return true on success
609	>	* @param w the worker
610		*/
611	<	final boolean tryIncrementActiveCount() {
612	<	int c = runControl;
613	<	return casRunControl(c, c+1);
611	>	final void work(ForkJoinWorkerThread w) {
612	>	boolean swept = false;                // true on empty scans
613	>	long c;
614	>	while (!w.terminate && (int)(c = ctl) >= 0) {
615	>	int a;                            // active count
616	>	if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0)
617	>	swept = scan(w, a);
618	>	else if (tryAwaitWork(w, c))
619	>	swept = false;
620	>	}
621		}
622
623	+	// Signalling
624	+
625		/**
626	<	* Tries decrementing active count; fails on contention.
319	<	* Possibly triggers termination on success.
320	<	* Called by workers when they can't find tasks.
321	<	*
322	<	* @return true on success
626	>	* Wakes up or creates a worker.
627		*/
628	<	final boolean tryDecrementActiveCount() {
629	<	int c = runControl;
630	<	int nextc = c - 1;
631	<	if (!casRunControl(c, nextc))
632	<	return false;
633	<	if (canTerminateOnShutdown(nextc))
634	<	terminateOnShutdown();
635	<	return true;
628	>	final void signalWork() {
629	>	/*
630	>	* The while condition is true if: (there is are too few total
631	>	* workers OR there is at least one waiter) AND (there are too
632	>	* few active workers OR the pool is terminating).  The value
633	>	* of e distinguishes the remaining cases: zero (no waiters)
634	>	* for create, negative if terminating (in which case do
635	>	* nothing), else release a waiter. The secondary checks for
636	>	* release (non-null array etc) can fail if the pool begins
637	>	* terminating after the test, and don't impose any added cost
638	>	* because JVMs must perform null and bounds checks anyway.
639	>	*/
640	>	long c; int e, u;
641	>	while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) &
642	>	(INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN) && e >= 0) {
643	>	if (e > 0) {                         // release a waiting worker
644	>	int i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
645	>	if ((ws = workers) == null ||
646	>	(i = ~e & SMASK) >= ws.length ||
647	>	(w = ws[i]) == null)
648	>	break;
649	>	long nc = (((long)(w.nextWait & E_MASK)) |
650	>	((long)(u + UAC_UNIT) << 32));
651	>	if (w.eventCount == e &&
652	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
653	>	w.eventCount = (e + EC_UNIT) & E_MASK;
654	>	if (w.parked)
655	>	UNSAFE.unpark(w);
656	>	break;
657	>	}
658	>	}
659	>	else if (UNSAFE.compareAndSwapLong
660	>	(this, ctlOffset, c,
661	>	(long)(((u + UTC_UNIT) & UTC_MASK) |
662	>	((u + UAC_UNIT) & UAC_MASK)) << 32)) {
663	>	addWorker();
664	>	break;
665	>	}
666	>	}
667		}
668
669		/**
670	<	* Returns {@code true} if argument represents zero active count
671	<	* and nonzero runstate, which is the triggering condition for
672	<	* terminating on shutdown.
670	>	* Variant of signalWork to help release waiters on rescans.
671	>	* Tries once to release a waiter if active count < 0.
672	>	*
673	>	* @return false if failed due to contention, else true
674		*/
675	<	private static boolean canTerminateOnShutdown(int c) {
676	<	// i.e. least bit is nonzero runState bit
677	<	return ((c & -c) >>> 16) != 0;
675	>	private boolean tryReleaseWaiter() {
676	>	long c; int e, i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
677	>	if ((e = (int)(c = ctl)) > 0 &&
678	>	(int)(c >> AC_SHIFT) < 0 &&
679	>	(ws = workers) != null &&
680	>	(i = ~e & SMASK) < ws.length &&
681	>	(w = ws[i]) != null) {
682	>	long nc = ((long)(w.nextWait & E_MASK) |
683	>	((c + AC_UNIT) & (AC_MASK|TC_MASK)));
684	>	if (w.eventCount != e ||
685	>	!UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
686	>	return false;
687	>	w.eventCount = (e + EC_UNIT) & E_MASK;
688	>	if (w.parked)
689	>	UNSAFE.unpark(w);
690	>	}
691	>	return true;
692		}
693
694	+	// Scanning for tasks
695	+
696		/**
697	<	* Transition run state to at least the given state. Return true
698	<	* if not already at least given state.
697	>	* Scans for and, if found, executes one task. Scans start at a
698	>	* random index of workers array, and randomly select the first
699	>	* (2*#workers)-1 probes, and then, if all empty, resort to 2
700	>	* circular sweeps, which is necessary to check quiescence. and
701	>	* taking a submission only if no stealable tasks were found.  The
702	>	* steal code inside the loop is a specialized form of
703	>	* ForkJoinWorkerThread.deqTask, followed bookkeeping to support
704	>	* helpJoinTask and signal propagation. The code for submission
705	>	* queues is almost identical. On each steal, the worker completes
706	>	* not only the task, but also all local tasks that this task may
707	>	* have generated. On detecting staleness or contention when
708	>	* trying to take a task, this method returns without finishing
709	>	* sweep, which allows global state rechecks before retry.
710	>	*
711	>	* @param w the worker
712	>	* @param a the number of active workers
713	>	* @return true if swept all queues without finding a task
714		*/
715	<	private boolean transitionRunStateTo(int state) {
716	<	for (;;) {
717	<	int c = runControl;
718	<	if (runStateOf(c) >= state)
715	>	private boolean scan(ForkJoinWorkerThread w, int a) {
716	>	int g = scanGuard; // mask 0 avoids useless scans if only one active
717	>	int m = (parallelism == 1 - a && blockedCount == 0) ? 0 : g & SMASK;
718	>	ForkJoinWorkerThread[] ws = workers;
719	>	if (ws == null || ws.length <= m)         // staleness check
720	>	return false;
721	>	for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) {
722	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
723	>	ForkJoinWorkerThread v = ws[k & m];
724	>	if (v != null && (b = v.queueBase) != v.queueTop &&
725	>	(q = v.queue) != null && (i = (q.length - 1) & b) >= 0) {
726	>	long u = (i << ASHIFT) + ABASE;
727	>	if ((t = q[i]) != null && v.queueBase == b &&
728	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
729	>	int d = (v.queueBase = b + 1) - v.queueTop;
730	>	v.stealHint = w.poolIndex;
731	>	if (d != 0)
732	>	signalWork();             // propagate if nonempty
733	>	w.execTask(t);
734	>	}
735	>	r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5);
736	>	return false;                     // store next seed
737	>	}
738	>	else if (j < 0) {                     // xorshift
739	>	r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
740	>	}
741	>	else
742	>	++k;
743	>	}
744	>	if (scanGuard != g)                       // staleness check
745	>	return false;
746	>	else {                                    // try to take submission
747	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
748	>	if ((b = queueBase) != queueTop &&
749	>	(q = submissionQueue) != null &&
750	>	(i = (q.length - 1) & b) >= 0) {
751	>	long u = (i << ASHIFT) + ABASE;
752	>	if ((t = q[i]) != null && queueBase == b &&
753	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
754	>	queueBase = b + 1;
755	>	w.execTask(t);
756	>	}
757		return false;
758	<	if (casRunControl(c, runControlFor(state, activeCountOf(c))))
758	>	}
759	>	return true;                         // all queues empty
760	>	}
761	>	}
762	>
763	>	/**
764	>	* Tries to enqueue worker w in wait queue and await change in
765	>	* worker's eventCount.  If the pool is quiescent and there is
766	>	* more than one worker, possibly terminates worker upon exit.
767	>	* Otherwise, before blocking, rescans queues to avoid missed
768	>	* signals.  Upon finding work, releases at least one worker
769	>	* (which may be the current worker). Rescans restart upon
770	>	* detected staleness or failure to release due to
771	>	* contention. Note the unusual conventions about Thread.interrupt
772	>	* here and elsewhere: Because interrupts are used solely to alert
773	>	* threads to check termination, which is checked here anyway, we
774	>	* clear status (using Thread.interrupted) before any call to
775	>	* park, so that park does not immediately return due to status
776	>	* being set via some other unrelated call to interrupt in user
777	>	* code.
778	>	*
779	>	* @param w the calling worker
780	>	* @param c the ctl value on entry
781	>	* @return true if waited or another thread was released upon enq
782	>	*/
783	>	private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) {
784	>	int v = w.eventCount;
785	>	w.nextWait = (int)c;                      // w's successor record
786	>	long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
787	>	if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
788	>	long d = ctl; // return true if lost to a deq, to force scan
789	>	return (int)d != (int)c && ((d - c) & AC_MASK) >= 0L;
790	>	}
791	>	for (int sc = w.stealCount; sc != 0;) {   // accumulate stealCount
792	>	long s = stealCount;
793	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s + sc))
794	>	sc = w.stealCount = 0;
795	>	else if (w.eventCount != v)
796	>	return true;                      // update next time
797	>	}
798	>	if ((!shutdown || !tryTerminate(false)) &&
799	>	(int)c != 0 && parallelism + (int)(nc >> AC_SHIFT) == 0 &&
800	>	blockedCount == 0 && quiescerCount == 0)
801	>	idleAwaitWork(w, nc, c, v);           // quiescent
802	>	for (boolean rescanned = false;;) {
803	>	if (w.eventCount != v)
804		return true;
805	+	if (!rescanned) {
806	+	int g = scanGuard, m = g & SMASK;
807	+	ForkJoinWorkerThread[] ws = workers;
808	+	if (ws != null && m < ws.length) {
809	+	rescanned = true;
810	+	for (int i = 0; i <= m; ++i) {
811	+	ForkJoinWorkerThread u = ws[i];
812	+	if (u != null) {
813	+	if (u.queueBase != u.queueTop &&
814	+	!tryReleaseWaiter())
815	+	rescanned = false; // contended
816	+	if (w.eventCount != v)
817	+	return true;
818	+	}
819	+	}
820	+	}
821	+	if (scanGuard != g ||              // stale
822	+	(queueBase != queueTop && !tryReleaseWaiter()))
823	+	rescanned = false;
824	+	if (!rescanned)
825	+	Thread.yield();                // reduce contention
826	+	else
827	+	Thread.interrupted();          // clear before park
828	+	}
829	+	else {
830	+	w.parked = true;                   // must recheck
831	+	if (w.eventCount != v) {
832	+	w.parked = false;
833	+	return true;
834	+	}
835	+	LockSupport.park(this);
836	+	rescanned = w.parked = false;
837	+	}
838		}
839		}
840
841		/**
842	<	* Controls whether to add spares to maintain parallelism
843	<	*/
844	<	private volatile boolean maintainsParallelism;
842	>	* If inactivating worker w has caused pool to become
843	>	* quiescent, check for pool termination, and wait for event
844	>	* for up to SHRINK_RATE nanosecs (rescans are unnecessary in
845	>	* this case because quiescence reflects consensus about lack
846	>	* of work). On timeout, if ctl has not changed, terminate the
847	>	* worker. Upon its termination (see deregisterWorker), it may
848	>	* wake up another worker to possibly repeat this process.
849	>	*
850	>	* @param w the calling worker
851	>	* @param currentCtl the ctl value after enqueuing w
852	>	* @param prevCtl the ctl value if w terminated
853	>	* @param v the eventCount w awaits change
854	>	*/
855	>	private void idleAwaitWork(ForkJoinWorkerThread w, long currentCtl,
856	>	long prevCtl, int v) {
857	>	if (w.eventCount == v) {
858	>	if (shutdown)
859	>	tryTerminate(false);
860	>	ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs
861	>	while (ctl == currentCtl) {
862	>	long startTime = System.nanoTime();
863	>	w.parked = true;
864	>	if (w.eventCount == v)             // must recheck
865	>	LockSupport.parkNanos(this, SHRINK_RATE);
866	>	w.parked = false;
867	>	if (w.eventCount != v)
868	>	break;
869	>	else if (System.nanoTime() - startTime <
870	>	SHRINK_RATE - (SHRINK_RATE / 10)) // timing slop
871	>	Thread.interrupted();          // spurious wakeup
872	>	else if (UNSAFE.compareAndSwapLong(this, ctlOffset,
873	>	currentCtl, prevCtl)) {
874	>	w.terminate = true;            // restore previous
875	>	w.eventCount = ((int)currentCtl + EC_UNIT) & E_MASK;
876	>	break;
877	>	}
878	>	}
879	>	}
880	>	}
881
882	<	// Constructors
882	>	// Submissions
883
884		/**
885	<	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
886	<	* java.lang.Runtime#availableProcessors}, and using the {@linkplain
368	<	* #defaultForkJoinWorkerThreadFactory default thread factory}.
885	>	* Enqueues the given task in the submissionQueue.  Same idea as
886	>	* ForkJoinWorkerThread.pushTask except for use of submissionLock.
887		*
888	<	* @throws SecurityException if a security manager exists and
371	<	*         the caller is not permitted to modify threads
372	<	*         because it does not hold {@link
373	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
888	>	* @param t the task
889		*/
890	<	public ForkJoinPool() {
891	<	this(Runtime.getRuntime().availableProcessors(),
892	<	defaultForkJoinWorkerThreadFactory);
890	>	private void addSubmission(ForkJoinTask<?> t) {
891	>	final ReentrantLock lock = this.submissionLock;
892	>	lock.lock();
893	>	try {
894	>	ForkJoinTask<?>[] q; int s, m;
895	>	if ((q = submissionQueue) != null) {    // ignore if queue removed
896	>	long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE;
897	>	UNSAFE.putOrderedObject(q, u, t);
898	>	queueTop = s + 1;
899	>	if (s - queueBase == m)
900	>	growSubmissionQueue();
901	>	}
902	>	} finally {
903	>	lock.unlock();
904	>	}
905	>	signalWork();
906		}
907
908	+	//  (pollSubmission is defined below with exported methods)
909	+
910		/**
911	<	* Creates a {@code ForkJoinPool} with the indicated parallelism
912	<	* level and using the {@linkplain
383	<	* #defaultForkJoinWorkerThreadFactory default thread factory}.
384	<	*
385	<	* @param parallelism the parallelism level
386	<	* @throws IllegalArgumentException if parallelism less than or
387	<	* equal to zero
388	<	* @throws SecurityException if a security manager exists and
389	<	*         the caller is not permitted to modify threads
390	<	*         because it does not hold {@link
391	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
911	>	* Creates or doubles submissionQueue array.
912	>	* Basically identical to ForkJoinWorkerThread version.
913		*/
914	<	public ForkJoinPool(int parallelism) {
915	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
914	>	private void growSubmissionQueue() {
915	>	ForkJoinTask<?>[] oldQ = submissionQueue;
916	>	int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY;
917	>	if (size > MAXIMUM_QUEUE_CAPACITY)
918	>	throw new RejectedExecutionException("Queue capacity exceeded");
919	>	if (size < INITIAL_QUEUE_CAPACITY)
920	>	size = INITIAL_QUEUE_CAPACITY;
921	>	ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size];
922	>	int mask = size - 1;
923	>	int top = queueTop;
924	>	int oldMask;
925	>	if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) {
926	>	for (int b = queueBase; b != top; ++b) {
927	>	long u = ((b & oldMask) << ASHIFT) + ABASE;
928	>	Object x = UNSAFE.getObjectVolatile(oldQ, u);
929	>	if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null))
930	>	UNSAFE.putObjectVolatile
931	>	(q, ((b & mask) << ASHIFT) + ABASE, x);
932	>	}
933	>	}
934	>	}
935	>
936	>	// Blocking support
937	>
938	>	/**
939	>	* Tries to increment blockedCount, decrement active count
940	>	* (sometimes implicitly) and possibly release or create a
941	>	* compensating worker in preparation for blocking. Fails
942	>	* on contention or termination.
943	>	*
944	>	* @return true if the caller can block, else should recheck and retry
945	>	*/
946	>	private boolean tryPreBlock() {
947	>	int b = blockedCount;
948	>	if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) {
949	>	int pc = parallelism;
950	>	do {
951	>	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
952	>	int e, ac, tc, rc, i;
953	>	long c = ctl;
954	>	int u = (int)(c >>> 32);
955	>	if ((e = (int)c) < 0) {
956	>	// skip -- terminating
957	>	}
958	>	else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 &&
959	>	(ws = workers) != null &&
960	>	(i = ~e & SMASK) < ws.length &&
961	>	(w = ws[i]) != null) {
962	>	long nc = ((long)(w.nextWait & E_MASK) |
963	>	(c & (AC_MASK|TC_MASK)));
964	>	if (w.eventCount == e &&
965	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
966	>	w.eventCount = (e + EC_UNIT) & E_MASK;
967	>	if (w.parked)
968	>	UNSAFE.unpark(w);
969	>	return true;             // release an idle worker
970	>	}
971	>	}
972	>	else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
973	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
974	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
975	>	return true;             // no compensation needed
976	>	}
977	>	else if (tc + pc < MAX_ID) {
978	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
979	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
980	>	addWorker();
981	>	return true;            // create a replacement
982	>	}
983	>	}
984	>	// try to back out on any failure and let caller retry
985	>	} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
986	>	b = blockedCount, b - 1));
987	>	}
988	>	return false;
989		}
990
991		/**
992	<	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
399	<	* java.lang.Runtime#availableProcessors}, and using the given
400	<	* thread factory.
401	<	*
402	<	* @param factory the factory for creating new threads
403	<	* @throws NullPointerException if factory is null
404	<	* @throws SecurityException if a security manager exists and
405	<	*         the caller is not permitted to modify threads
406	<	*         because it does not hold {@link
407	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
992	>	* Decrements blockedCount and increments active count
993		*/
994	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
995	<	this(Runtime.getRuntime().availableProcessors(), factory);
994	>	private void postBlock() {
995	>	long c;
996	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset,  // no mask
997	>	c = ctl, c + AC_UNIT));
998	>	int b;
999	>	do {} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
1000	>	b = blockedCount, b - 1));
1001		}
1002
1003		/**
1004	<	* Creates a {@code ForkJoinPool} with the given parallelism and
1005	<	* thread factory.
1004	>	* Possibly blocks waiting for the given task to complete, or
1005	>	* cancels the task if terminating.  Fails to wait if contended.
1006		*
1007	<	* @param parallelism the parallelism level
418	<	* @param factory the factory for creating new threads
419	<	* @throws IllegalArgumentException if parallelism less than or
420	<	* equal to zero, or greater than implementation limit
421	<	* @throws NullPointerException if factory is null
422	<	* @throws SecurityException if a security manager exists and
423	<	*         the caller is not permitted to modify threads
424	<	*         because it does not hold {@link
425	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1007	>	* @param joinMe the task
1008		*/
1009	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
1010	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1011	<	throw new IllegalArgumentException();
1012	<	if (factory == null)
1013	<	throw new NullPointerException();
1014	<	checkPermission();
1015	<	this.factory = factory;
1016	<	this.parallelism = parallelism;
1017	<	this.maxPoolSize = MAX_THREADS;
1018	<	this.maintainsParallelism = true;
1019	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
438	<	this.workerLock = new ReentrantLock();
439	<	this.termination = workerLock.newCondition();
440	<	this.stealCount = new AtomicLong();
441	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
442	<	// worker array and workers are lazily constructed
1009	>	final void tryAwaitJoin(ForkJoinTask<?> joinMe) {
1010	>	int s;
1011	>	Thread.interrupted(); // clear interrupts before checking termination
1012	>	if (joinMe.status >= 0) {
1013	>	if (tryPreBlock()) {
1014	>	joinMe.tryAwaitDone(0L);
1015	>	postBlock();
1016	>	}
1017	>	else if ((ctl & STOP_BIT) != 0L)
1018	>	joinMe.cancelIgnoringExceptions();
1019	>	}
1020		}
1021
1022		/**
1023	<	* Creates a new worker thread using factory.
1023	>	* Possibly blocks the given worker waiting for joinMe to
1024	>	* complete or timeout
1025		*
1026	<	* @param index the index to assign worker
1027	<	* @return new worker, or null if factory failed
1026	>	* @param joinMe the task
1027	>	* @param millis the wait time for underlying Object.wait
1028		*/
1029	<	private ForkJoinWorkerThread createWorker(int index) {
1030	<	Thread.UncaughtExceptionHandler h = ueh;
1031	<	ForkJoinWorkerThread w = factory.newThread(this);
1032	<	if (w != null) {
1033	<	w.poolIndex = index;
1034	<	w.setDaemon(true);
1035	<	w.setAsyncMode(locallyFifo);
1036	<	w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
1037	<	if (h != null)
1038	<	w.setUncaughtExceptionHandler(h);
1029	>	final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) {
1030	>	while (joinMe.status >= 0) {
1031	>	Thread.interrupted();
1032	>	if ((ctl & STOP_BIT) != 0L) {
1033	>	joinMe.cancelIgnoringExceptions();
1034	>	break;
1035	>	}
1036	>	if (tryPreBlock()) {
1037	>	long last = System.nanoTime();
1038	>	while (joinMe.status >= 0) {
1039	>	long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
1040	>	if (millis <= 0)
1041	>	break;
1042	>	joinMe.tryAwaitDone(millis);
1043	>	if (joinMe.status < 0)
1044	>	break;
1045	>	if ((ctl & STOP_BIT) != 0L) {
1046	>	joinMe.cancelIgnoringExceptions();
1047	>	break;
1048	>	}
1049	>	long now = System.nanoTime();
1050	>	nanos -= now - last;
1051	>	last = now;
1052	>	}
1053	>	postBlock();
1054	>	break;
1055	>	}
1056		}
462	–	return w;
1057		}
1058
1059		/**
1060	<	* Returns a good size for worker array given pool size.
467	<	* Currently requires size to be a power of two.
1060	>	* If necessary, compensates for blocker, and blocks
1061		*/
1062	<	private static int arraySizeFor(int poolSize) {
1063	<	if (poolSize <= 1)
1064	<	return 1;
1065	<	// See Hackers Delight, sec 3.2
1066	<	int c = poolSize >= MAX_THREADS ? MAX_THREADS : (poolSize - 1);
1067	<	c |= c >>>  1;
1068	<	c |= c >>>  2;
1069	<	c |= c >>>  4;
1070	<	c |= c >>>  8;
1071	<	c |= c >>> 16;
1072	<	return c + 1;
1062	>	private void awaitBlocker(ManagedBlocker blocker)
1063	>	throws InterruptedException {
1064	>	while (!blocker.isReleasable()) {
1065	>	if (tryPreBlock()) {
1066	>	try {
1067	>	do {} while (!blocker.isReleasable() && !blocker.block());
1068	>	} finally {
1069	>	postBlock();
1070	>	}
1071	>	break;
1072	>	}
1073	>	}
1074		}
1075
1076	+	// Creating, registering and deregistring workers
1077	+
1078		/**
1079	<	* Creates or resizes array if necessary to hold newLength.
1080	<	* Call only under exclusion.
485	<	*
486	<	* @return the array
1079	>	* Tries to create and start a worker; minimally rolls back counts
1080	>	* on failure.
1081		*/
1082	<	private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
1083	<	ForkJoinWorkerThread[] ws = workers;
1084	<	if (ws == null)
1085	<	return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
1086	<	else if (newLength > ws.length)
1087	<	return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
1082	>	private void addWorker() {
1083	>	Throwable ex = null;
1084	>	ForkJoinWorkerThread t = null;
1085	>	try {
1086	>	t = factory.newThread(this);
1087	>	} catch (Throwable e) {
1088	>	ex = e;
1089	>	}
1090	>	if (t == null) {  // null or exceptional factory return
1091	>	long c;       // adjust counts
1092	>	do {} while (!UNSAFE.compareAndSwapLong
1093	>	(this, ctlOffset, c = ctl,
1094	>	(((c - AC_UNIT) & AC_MASK) |
1095	>	((c - TC_UNIT) & TC_MASK) |
1096	>	(c & ~(AC_MASK|TC_MASK)))));
1097	>	// Propagate exception if originating from an external caller
1098	>	if (!tryTerminate(false) && ex != null &&
1099	>	!(Thread.currentThread() instanceof ForkJoinWorkerThread))
1100	>	UNSAFE.throwException(ex);
1101	>	}
1102		else
1103	<	return ws;
1103	>	t.start();
1104		}
1105
1106		/**
1107	<	* Tries to shrink workers into smaller array after one or more terminate.
1107	>	* Callback from ForkJoinWorkerThread constructor to assign a
1108	>	* public name
1109		*/
1110	<	private void tryShrinkWorkerArray() {
1111	<	ForkJoinWorkerThread[] ws = workers;
1112	<	if (ws != null) {
1113	<	int len = ws.length;
1114	<	int last = len - 1;
506	<	while (last >= 0 && ws[last] == null)
507	<	--last;
508	<	int newLength = arraySizeFor(last+1);
509	<	if (newLength < len)
510	<	workers = Arrays.copyOf(ws, newLength);
1110	>	final String nextWorkerName() {
1111	>	for (int n;;) {
1112	>	if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset,
1113	>	n = nextWorkerNumber, ++n))
1114	>	return workerNamePrefix + n;
1115		}
1116		}
1117
1118		/**
1119	<	* Initializes workers if necessary.
1119	>	* Callback from ForkJoinWorkerThread constructor to
1120	>	* determine its poolIndex and record in workers array.
1121	>	*
1122	>	* @param w the worker
1123	>	* @return the worker's pool index
1124		*/
1125	<	final void ensureWorkerInitialization() {
1126	<	ForkJoinWorkerThread[] ws = workers;
1127	<	if (ws == null) {
1128	<	final ReentrantLock lock = this.workerLock;
1129	<	lock.lock();
1130	<	try {
1131	<	ws = workers;
1132	<	if (ws == null) {
1133	<	int ps = parallelism;
1134	<	ws = ensureWorkerArrayCapacity(ps);
1135	<	for (int i = 0; i < ps; ++i) {
1136	<	ForkJoinWorkerThread w = createWorker(i);
1137	<	if (w != null) {
1138	<	ws[i] = w;
1139	<	w.start();
1140	<	updateWorkerCount(1);
1125	>	final int registerWorker(ForkJoinWorkerThread w) {
1126	>	/*
1127	>	* In the typical case, a new worker acquires the lock, uses
1128	>	* next available index and returns quickly.  Since we should
1129	>	* not block callers (ultimately from signalWork or
1130	>	* tryPreBlock) waiting for the lock needed to do this, we
1131	>	* instead help release other workers while waiting for the
1132	>	* lock.
1133	>	*/
1134	>	for (int g;;) {
1135	>	ForkJoinWorkerThread[] ws;
1136	>	if (((g = scanGuard) & SG_UNIT) == 0 &&
1137	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1138	>	g, g | SG_UNIT)) {
1139	>	int k = nextWorkerIndex;
1140	>	try {
1141	>	if ((ws = workers) != null) { // ignore on shutdown
1142	>	int n = ws.length;
1143	>	if (k < 0 || k >= n || ws[k] != null) {
1144	>	for (k = 0; k < n && ws[k] != null; ++k)
1145	>	;
1146	>	if (k == n)
1147	>	ws = workers = Arrays.copyOf(ws, n << 1);
1148		}
1149	+	ws[k] = w;
1150	+	nextWorkerIndex = k + 1;
1151	+	int m = g & SMASK;
1152	+	g = (k > m) ? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1);
1153	+	}
1154	+	} finally {
1155	+	scanGuard = g;
1156	+	}
1157	+	return k;
1158	+	}
1159	+	else if ((ws = workers) != null) { // help release others
1160	+	for (ForkJoinWorkerThread u : ws) {
1161	+	if (u != null && u.queueBase != u.queueTop) {
1162	+	if (tryReleaseWaiter())
1163	+	break;
1164		}
1165		}
1166	+	}
1167	+	}
1168	+	}
1169	+
1170	+	/**
1171	+	* Final callback from terminating worker.  Removes record of
1172	+	* worker from array, and adjusts counts. If pool is shutting
1173	+	* down, tries to complete termination.
1174	+	*
1175	+	* @param w the worker
1176	+	*/
1177	+	final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) {
1178	+	int idx = w.poolIndex;
1179	+	int sc = w.stealCount;
1180	+	int steps = 0;
1181	+	// Remove from array, adjust worker counts and collect steal count.
1182	+	// We can intermix failed removes or adjusts with steal updates
1183	+	do {
1184	+	long s, c;
1185	+	int g;
1186	+	if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 &&
1187	+	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1188	+	g, g |= SG_UNIT)) {
1189	+	ForkJoinWorkerThread[] ws = workers;
1190	+	if (ws != null && idx >= 0 &&
1191	+	idx < ws.length && ws[idx] == w)
1192	+	ws[idx] = null;    // verify
1193	+	nextWorkerIndex = idx;
1194	+	scanGuard = g + SG_UNIT;
1195	+	steps = 1;
1196	+	}
1197	+	if (steps == 1 &&
1198	+	UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1199	+	(((c - AC_UNIT) & AC_MASK) |
1200	+	((c - TC_UNIT) & TC_MASK) |
1201	+	(c & ~(AC_MASK|TC_MASK)))))
1202	+	steps = 2;
1203	+	if (sc != 0 &&
1204	+	UNSAFE.compareAndSwapLong(this, stealCountOffset,
1205	+	s = stealCount, s + sc))
1206	+	sc = 0;
1207	+	} while (steps != 2 || sc != 0);
1208	+	if (!tryTerminate(false)) {
1209	+	if (ex != null)   // possibly replace if died abnormally
1210	+	signalWork();
1211	+	else
1212	+	tryReleaseWaiter();
1213	+	}
1214	+	}
1215	+
1216	+	// Shutdown and termination
1217	+
1218	+	/**
1219	+	* Possibly initiates and/or completes termination.
1220	+	*
1221	+	* @param now if true, unconditionally terminate, else only
1222	+	* if shutdown and empty queue and no active workers
1223	+	* @return true if now terminating or terminated
1224	+	*/
1225	+	private boolean tryTerminate(boolean now) {
1226	+	long c;
1227	+	while (((c = ctl) & STOP_BIT) == 0) {
1228	+	if (!now) {
1229	+	if ((int)(c >> AC_SHIFT) != -parallelism)
1230	+	return false;
1231	+	if (!shutdown || blockedCount != 0 || quiescerCount != 0 ||
1232	+	queueBase != queueTop) {
1233	+	if (ctl == c) // staleness check
1234	+	return false;
1235	+	continue;
1236	+	}
1237	+	}
1238	+	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT))
1239	+	startTerminating();
1240	+	}
1241	+	if ((short)(c >>> TC_SHIFT) == -parallelism) { // signal when 0 workers
1242	+	final ReentrantLock lock = this.submissionLock;
1243	+	lock.lock();
1244	+	try {
1245	+	termination.signalAll();
1246		} finally {
1247		lock.unlock();
1248		}
1249		}
1250	+	return true;
1251		}
1252
1253		/**
1254	<	* Worker creation and startup for threads added via setParallelism.
1255	<	*/
1256	<	private void createAndStartAddedWorkers() {
1257	<	resumeAllSpares();  // Allow spares to convert to nonspare
1258	<	int ps = parallelism;
1259	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
1260	<	int len = ws.length;
1261	<	// Sweep through slots, to keep lowest indices most populated
1262	<	int k = 0;
1263	<	while (k < len) {
1264	<	if (ws[k] != null) {
1265	<	++k;
1266	<	continue;
1254	>	* Runs up to three passes through workers: (0) Setting
1255	>	* termination status for each worker, followed by wakeups up to
1256	>	* queued workers; (1) helping cancel tasks; (2) interrupting
1257	>	* lagging threads (likely in external tasks, but possibly also
1258	>	* blocked in joins).  Each pass repeats previous steps because of
1259	>	* potential lagging thread creation.
1260	>	*/
1261	>	private void startTerminating() {
1262	>	cancelSubmissions();
1263	>	for (int pass = 0; pass < 3; ++pass) {
1264	>	ForkJoinWorkerThread[] ws = workers;
1265	>	if (ws != null) {
1266	>	for (ForkJoinWorkerThread w : ws) {
1267	>	if (w != null) {
1268	>	w.terminate = true;
1269	>	if (pass > 0) {
1270	>	w.cancelTasks();
1271	>	if (pass > 1 && !w.isInterrupted()) {
1272	>	try {
1273	>	w.interrupt();
1274	>	} catch (SecurityException ignore) {
1275	>	}
1276	>	}
1277	>	}
1278	>	}
1279	>	}
1280	>	terminateWaiters();
1281		}
1282	<	int s = workerCounts;
1283	<	int tc = totalCountOf(s);
1284	<	int rc = runningCountOf(s);
1285	<	if (rc >= ps || tc >= ps)
1286	<	break;
1287	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
1288	<	ForkJoinWorkerThread w = createWorker(k);
1289	<	if (w != null) {
1290	<	ws[k++] = w;
1291	<	w.start();
1282	>	}
1283	>	}
1284	>
1285	>	/**
1286	>	* Polls and cancels all submissions. Called only during termination.
1287	>	*/
1288	>	private void cancelSubmissions() {
1289	>	while (queueBase != queueTop) {
1290	>	ForkJoinTask<?> task = pollSubmission();
1291	>	if (task != null) {
1292	>	try {
1293	>	task.cancel(false);
1294	>	} catch (Throwable ignore) {
1295		}
1296	<	else {
1297	<	updateWorkerCount(-1); // back out on failed creation
1298	<	break;
1296	>	}
1297	>	}
1298	>	}
1299	>
1300	>	/**
1301	>	* Tries to set the termination status of waiting workers, and
1302	>	* then wakes them up (after which they will terminate).
1303	>	*/
1304	>	private void terminateWaiters() {
1305	>	ForkJoinWorkerThread[] ws = workers;
1306	>	if (ws != null) {
1307	>	ForkJoinWorkerThread w; long c; int i, e;
1308	>	int n = ws.length;
1309	>	while ((i = ~(e = (int)(c = ctl)) & SMASK) < n &&
1310	>	(w = ws[i]) != null && w.eventCount == (e & E_MASK)) {
1311	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c,
1312	>	(long)(w.nextWait & E_MASK) |
1313	>	((c + AC_UNIT) & AC_MASK) |
1314	>	(c & (TC_MASK|STOP_BIT)))) {
1315	>	w.terminate = true;
1316	>	w.eventCount = e + EC_UNIT;
1317	>	if (w.parked)
1318	>	UNSAFE.unpark(w);
1319		}
1320		}
1321		}
1322		}
1323
1324	<	// Execution methods
1324	>	// misc ForkJoinWorkerThread support
1325
1326		/**
1327	<	* Common code for execute, invoke and submit
1327	>	* Increment or decrement quiescerCount. Needed only to prevent
1328	>	* triggering shutdown if a worker is transiently inactive while
1329	>	* checking quiescence.
1330	>	*
1331	>	* @param delta 1 for increment, -1 for decrement
1332		*/
1333	<	private <T> void doSubmit(ForkJoinTask<T> task) {
1334	<	if (task == null)
1333	>	final void addQuiescerCount(int delta) {
1334	>	int c;
1335	>	do {} while (!UNSAFE.compareAndSwapInt(this, quiescerCountOffset,
1336	>	c = quiescerCount, c + delta));
1337	>	}
1338	>
1339	>	/**
1340	>	* Directly increment or decrement active count without
1341	>	* queuing. This method is used to transiently assert inactivation
1342	>	* while checking quiescence.
1343	>	*
1344	>	* @param delta 1 for increment, -1 for decrement
1345	>	*/
1346	>	final void addActiveCount(int delta) {
1347	>	long d = delta < 0 ? -AC_UNIT : AC_UNIT;
1348	>	long c;
1349	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1350	>	((c + d) & AC_MASK) |
1351	>	(c & ~AC_MASK)));
1352	>	}
1353	>
1354	>	/**
1355	>	* Returns the approximate (non-atomic) number of idle threads per
1356	>	* active thread.
1357	>	*/
1358	>	final int idlePerActive() {
1359	>	// Approximate at powers of two for small values, saturate past 4
1360	>	int p = parallelism;
1361	>	int a = p + (int)(ctl >> AC_SHIFT);
1362	>	return (a > (p >>>= 1) ? 0 :
1363	>	a > (p >>>= 1) ? 1 :
1364	>	a > (p >>>= 1) ? 2 :
1365	>	a > (p >>>= 1) ? 4 :
1366	>	8);
1367	>	}
1368	>
1369	>	// Exported methods
1370	>
1371	>	// Constructors
1372	>
1373	>	/**
1374	>	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1375	>	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1376	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1377	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1378	>	*
1379	>	* @throws SecurityException if a security manager exists and
1380	>	*         the caller is not permitted to modify threads
1381	>	*         because it does not hold {@link
1382	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1383	>	*/
1384	>	public ForkJoinPool() {
1385	>	this(Runtime.getRuntime().availableProcessors(),
1386	>	defaultForkJoinWorkerThreadFactory, null, false);
1387	>	}
1388	>
1389	>	/**
1390	>	* Creates a {@code ForkJoinPool} with the indicated parallelism
1391	>	* level, the {@linkplain
1392	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1393	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1394	>	*
1395	>	* @param parallelism the parallelism level
1396	>	* @throws IllegalArgumentException if parallelism less than or
1397	>	*         equal to zero, or greater than implementation limit
1398	>	* @throws SecurityException if a security manager exists and
1399	>	*         the caller is not permitted to modify threads
1400	>	*         because it does not hold {@link
1401	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1402	>	*/
1403	>	public ForkJoinPool(int parallelism) {
1404	>	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1405	>	}
1406	>
1407	>	/**
1408	>	* Creates a {@code ForkJoinPool} with the given parameters.
1409	>	*
1410	>	* @param parallelism the parallelism level. For default value,
1411	>	* use {@link java.lang.Runtime#availableProcessors}.
1412	>	* @param factory the factory for creating new threads. For default value,
1413	>	* use {@link #defaultForkJoinWorkerThreadFactory}.
1414	>	* @param handler the handler for internal worker threads that
1415	>	* terminate due to unrecoverable errors encountered while executing
1416	>	* tasks. For default value, use {@code null}.
1417	>	* @param asyncMode if true,
1418	>	* establishes local first-in-first-out scheduling mode for forked
1419	>	* tasks that are never joined. This mode may be more appropriate
1420	>	* than default locally stack-based mode in applications in which
1421	>	* worker threads only process event-style asynchronous tasks.
1422	>	* For default value, use {@code false}.
1423	>	* @throws IllegalArgumentException if parallelism less than or
1424	>	*         equal to zero, or greater than implementation limit
1425	>	* @throws NullPointerException if the factory is null
1426	>	* @throws SecurityException if a security manager exists and
1427	>	*         the caller is not permitted to modify threads
1428	>	*         because it does not hold {@link
1429	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1430	>	*/
1431	>	public ForkJoinPool(int parallelism,
1432	>	ForkJoinWorkerThreadFactory factory,
1433	>	Thread.UncaughtExceptionHandler handler,
1434	>	boolean asyncMode) {
1435	>	checkPermission();
1436	>	if (factory == null)
1437		throw new NullPointerException();
1438	<	if (isShutdown())
1439	<	throw new RejectedExecutionException();
1440	<	if (workers == null)
1441	<	ensureWorkerInitialization();
1442	<	submissionQueue.offer(task);
1443	<	signalIdleWorkers();
1438	>	if (parallelism <= 0 || parallelism > MAX_ID)
1439	>	throw new IllegalArgumentException();
1440	>	this.parallelism = parallelism;
1441	>	this.factory = factory;
1442	>	this.ueh = handler;
1443	>	this.locallyFifo = asyncMode;
1444	>	long np = (long)(-parallelism); // offset ctl counts
1445	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
1446	>	this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
1447	>	// initialize workers array with room for 2*parallelism if possible
1448	>	int n = parallelism << 1;
1449	>	if (n >= MAX_ID)
1450	>	n = MAX_ID;
1451	>	else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
1452	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
1453	>	}
1454	>	workers = new ForkJoinWorkerThread[n + 1];
1455	>	this.submissionLock = new ReentrantLock();
1456	>	this.termination = submissionLock.newCondition();
1457	>	StringBuilder sb = new StringBuilder("ForkJoinPool-");
1458	>	sb.append(poolNumberGenerator.incrementAndGet());
1459	>	sb.append("-worker-");
1460	>	this.workerNamePrefix = sb.toString();
1461		}
1462
1463	+	// Execution methods
1464	+
1465		/**
1466		* Performs the given task, returning its result upon completion.
1467	+	* If the computation encounters an unchecked Exception or Error,
1468	+	* it is rethrown as the outcome of this invocation.  Rethrown
1469	+	* exceptions behave in the same way as regular exceptions, but,
1470	+	* when possible, contain stack traces (as displayed for example
1471	+	* using {@code ex.printStackTrace()}) of both the current thread
1472	+	* as well as the thread actually encountering the exception;
1473	+	* minimally only the latter.
1474		*
1475		* @param task the task
1476		* @return the task's result
1477	<	* @throws NullPointerException if task is null
1478	<	* @throws RejectedExecutionException if pool is shut down
1477	>	* @throws NullPointerException if the task is null
1478	>	* @throws RejectedExecutionException if the task cannot be
1479	>	*         scheduled for execution
1480		*/
1481		public <T> T invoke(ForkJoinTask<T> task) {
1482	<	doSubmit(task);
1483	<	return task.join();
1482	>	Thread t = Thread.currentThread();
1483	>	if (task == null)
1484	>	throw new NullPointerException();
1485	>	if (shutdown)
1486	>	throw new RejectedExecutionException();
1487	>	if ((t instanceof ForkJoinWorkerThread) &&
1488	>	((ForkJoinWorkerThread)t).pool == this)
1489	>	return task.invoke();  // bypass submit if in same pool
1490	>	else {
1491	>	addSubmission(task);
1492	>	return task.join();
1493	>	}
1494	>	}
1495	>
1496	>	/**
1497	>	* Unless terminating, forks task if within an ongoing FJ
1498	>	* computation in the current pool, else submits as external task.
1499	>	*/
1500	>	private <T> void forkOrSubmit(ForkJoinTask<T> task) {
1501	>	ForkJoinWorkerThread w;
1502	>	Thread t = Thread.currentThread();
1503	>	if (shutdown)
1504	>	throw new RejectedExecutionException();
1505	>	if ((t instanceof ForkJoinWorkerThread) &&
1506	>	(w = (ForkJoinWorkerThread)t).pool == this)
1507	>	w.pushTask(task);
1508	>	else
1509	>	addSubmission(task);
1510		}
1511
1512		/**
1513		* Arranges for (asynchronous) execution of the given task.
1514		*
1515		* @param task the task
1516	<	* @throws NullPointerException if task is null
1517	<	* @throws RejectedExecutionException if pool is shut down
1516	>	* @throws NullPointerException if the task is null
1517	>	* @throws RejectedExecutionException if the task cannot be
1518	>	*         scheduled for execution
1519		*/
1520		public void execute(ForkJoinTask<?> task) {
1521	<	doSubmit(task);
1521	>	if (task == null)
1522	>	throw new NullPointerException();
1523	>	forkOrSubmit(task);
1524		}
1525
1526		// AbstractExecutorService methods
1527
1528	+	/**
1529	+	* @throws NullPointerException if the task is null
1530	+	* @throws RejectedExecutionException if the task cannot be
1531	+	*         scheduled for execution
1532	+	*/
1533		public void execute(Runnable task) {
1534	+	if (task == null)
1535	+	throw new NullPointerException();
1536		ForkJoinTask<?> job;
1537		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1538		job = (ForkJoinTask<?>) task;
1539		else
1540		job = ForkJoinTask.adapt(task, null);
1541	<	doSubmit(job);
1541	>	forkOrSubmit(job);
1542	>	}
1543	>
1544	>	/**
1545	>	* Submits a ForkJoinTask for execution.
1546	>	*
1547	>	* @param task the task to submit
1548	>	* @return the task
1549	>	* @throws NullPointerException if the task is null
1550	>	* @throws RejectedExecutionException if the task cannot be
1551	>	*         scheduled for execution
1552	>	*/
1553	>	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1554	>	if (task == null)
1555	>	throw new NullPointerException();
1556	>	forkOrSubmit(task);
1557	>	return task;
1558		}
1559
1560	+	/**
1561	+	* @throws NullPointerException if the task is null
1562	+	* @throws RejectedExecutionException if the task cannot be
1563	+	*         scheduled for execution
1564	+	*/
1565		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1566	+	if (task == null)
1567	+	throw new NullPointerException();
1568		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1569	<	doSubmit(job);
1569	>	forkOrSubmit(job);
1570		return job;
1571		}
1572
1573	+	/**
1574	+	* @throws NullPointerException if the task is null
1575	+	* @throws RejectedExecutionException if the task cannot be
1576	+	*         scheduled for execution
1577	+	*/
1578		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1579	+	if (task == null)
1580	+	throw new NullPointerException();
1581		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1582	<	doSubmit(job);
1582	>	forkOrSubmit(job);
1583		return job;
1584		}
1585
1586	+	/**
1587	+	* @throws NullPointerException if the task is null
1588	+	* @throws RejectedExecutionException if the task cannot be
1589	+	*         scheduled for execution
1590	+	*/
1591		public ForkJoinTask<?> submit(Runnable task) {
1592	+	if (task == null)
1593	+	throw new NullPointerException();
1594		ForkJoinTask<?> job;
1595		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1596		job = (ForkJoinTask<?>) task;
1597		else
1598		job = ForkJoinTask.adapt(task, null);
1599	<	doSubmit(job);
1599	>	forkOrSubmit(job);
1600		return job;
1601		}
1602
1603		/**
1604	<	* Submits a ForkJoinTask for execution.
1605	<	*
652	<	* @param task the task to submit
653	<	* @return the task
654	<	* @throws RejectedExecutionException if the task cannot be
655	<	*         scheduled for execution
656	<	* @throws NullPointerException if the task is null
1604	>	* @throws NullPointerException       {@inheritDoc}
1605	>	* @throws RejectedExecutionException {@inheritDoc}
1606		*/
658	–	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
659	–	doSubmit(task);
660	–	return task;
661	–	}
662	–
663	–
1607		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
1608		ArrayList<ForkJoinTask<T>> forkJoinTasks =
1609		new ArrayList<ForkJoinTask<T>>(tasks.size());
#	Line 669 | Line 1612 | public class ForkJoinPool extends Abstra
1612		invoke(new InvokeAll<T>(forkJoinTasks));
1613
1614		@SuppressWarnings({"unchecked", "rawtypes"})
1615	<	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1615	>	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1616		return futures;
1617		}
1618
#	Line 683 | Line 1626 | public class ForkJoinPool extends Abstra
1626		private static final long serialVersionUID = -7914297376763021607L;
1627		}
1628
686	–	// Configuration and status settings and queries
687	–
1629		/**
1630		* Returns the factory used for constructing new workers.
1631		*
#	Line 701 | Line 1642 | public class ForkJoinPool extends Abstra
1642		* @return the handler, or {@code null} if none
1643		*/
1644		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1645	<	Thread.UncaughtExceptionHandler h;
705	<	final ReentrantLock lock = this.workerLock;
706	<	lock.lock();
707	<	try {
708	<	h = ueh;
709	<	} finally {
710	<	lock.unlock();
711	<	}
712	<	return h;
713	<	}
714	<
715	<	/**
716	<	* Sets the handler for internal worker threads that terminate due
717	<	* to unrecoverable errors encountered while executing tasks.
718	<	* Unless set, the current default or ThreadGroup handler is used
719	<	* as handler.
720	<	*
721	<	* @param h the new handler
722	<	* @return the old handler, or {@code null} if none
723	<	* @throws SecurityException if a security manager exists and
724	<	*         the caller is not permitted to modify threads
725	<	*         because it does not hold {@link
726	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
727	<	*/
728	<	public Thread.UncaughtExceptionHandler
729	<	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
730	<	checkPermission();
731	<	Thread.UncaughtExceptionHandler old = null;
732	<	final ReentrantLock lock = this.workerLock;
733	<	lock.lock();
734	<	try {
735	<	old = ueh;
736	<	ueh = h;
737	<	ForkJoinWorkerThread[] ws = workers;
738	<	if (ws != null) {
739	<	for (int i = 0; i < ws.length; ++i) {
740	<	ForkJoinWorkerThread w = ws[i];
741	<	if (w != null)
742	<	w.setUncaughtExceptionHandler(h);
743	<	}
744	<	}
745	<	} finally {
746	<	lock.unlock();
747	<	}
748	<	return old;
749	<	}
750	<
751	<
752	<	/**
753	<	* Sets the target parallelism level of this pool.
754	<	*
755	<	* @param parallelism the target parallelism
756	<	* @throws IllegalArgumentException if parallelism less than or
757	<	* equal to zero or greater than maximum size bounds
758	<	* @throws SecurityException if a security manager exists and
759	<	*         the caller is not permitted to modify threads
760	<	*         because it does not hold {@link
761	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
762	<	*/
763	<	public void setParallelism(int parallelism) {
764	<	checkPermission();
765	<	if (parallelism <= 0 || parallelism > maxPoolSize)
766	<	throw new IllegalArgumentException();
767	<	final ReentrantLock lock = this.workerLock;
768	<	lock.lock();
769	<	try {
770	<	if (isProcessingTasks()) {
771	<	int p = this.parallelism;
772	<	this.parallelism = parallelism;
773	<	if (parallelism > p)
774	<	createAndStartAddedWorkers();
775	<	else
776	<	trimSpares();
777	<	}
778	<	} finally {
779	<	lock.unlock();
780	<	}
781	<	signalIdleWorkers();
1645	>	return ueh;
1646		}
1647
1648		/**
#	Line 792 | Line 1656 | public class ForkJoinPool extends Abstra
1656
1657		/**
1658		* Returns the number of worker threads that have started but not
1659	<	* yet terminated.  This result returned by this method may differ
1659	>	* yet terminated.  The result returned by this method may differ
1660		* from {@link #getParallelism} when threads are created to
1661		* maintain parallelism when others are cooperatively blocked.
1662		*
1663		* @return the number of worker threads
1664		*/
1665		public int getPoolSize() {
1666	<	return totalCountOf(workerCounts);
803	<	}
804	<
805	<	/**
806	<	* Returns the maximum number of threads allowed to exist in the
807	<	* pool.  Unless set using {@link #setMaximumPoolSize}, the
808	<	* maximum is an implementation-defined value designed only to
809	<	* prevent runaway growth.
810	<	*
811	<	* @return the maximum
812	<	*/
813	<	public int getMaximumPoolSize() {
814	<	return maxPoolSize;
815	<	}
816	<
817	<	/**
818	<	* Sets the maximum number of threads allowed to exist in the
819	<	* pool.  Setting this value has no effect on current pool
820	<	* size. It controls construction of new threads.
821	<	*
822	<	* @throws IllegalArgumentException if negative or greater than
823	<	* internal implementation limit
824	<	*/
825	<	public void setMaximumPoolSize(int newMax) {
826	<	if (newMax < 0 || newMax > MAX_THREADS)
827	<	throw new IllegalArgumentException();
828	<	maxPoolSize = newMax;
829	<	}
830	<
831	<
832	<	/**
833	<	* Returns {@code true} if this pool dynamically maintains its
834	<	* target parallelism level. If false, new threads are added only
835	<	* to avoid possible starvation.  This setting is by default true.
836	<	*
837	<	* @return {@code true} if maintains parallelism
838	<	*/
839	<	public boolean getMaintainsParallelism() {
840	<	return maintainsParallelism;
841	<	}
842	<
843	<	/**
844	<	* Sets whether this pool dynamically maintains its target
845	<	* parallelism level. If false, new threads are added only to
846	<	* avoid possible starvation.
847	<	*
848	<	* @param enable {@code true} to maintain parallelism
849	<	*/
850	<	public void setMaintainsParallelism(boolean enable) {
851	<	maintainsParallelism = enable;
852	<	}
853	<
854	<	/**
855	<	* Establishes local first-in-first-out scheduling mode for forked
856	<	* tasks that are never joined. This mode may be more appropriate
857	<	* than default locally stack-based mode in applications in which
858	<	* worker threads only process asynchronous tasks.  This method is
859	<	* designed to be invoked only when the pool is quiescent, and
860	<	* typically only before any tasks are submitted. The effects of
861	<	* invocations at other times may be unpredictable.
862	<	*
863	<	* @param async if {@code true}, use locally FIFO scheduling
864	<	* @return the previous mode
865	<	* @see #getAsyncMode
866	<	*/
867	<	public boolean setAsyncMode(boolean async) {
868	<	boolean oldMode = locallyFifo;
869	<	locallyFifo = async;
870	<	ForkJoinWorkerThread[] ws = workers;
871	<	if (ws != null) {
872	<	for (int i = 0; i < ws.length; ++i) {
873	<	ForkJoinWorkerThread t = ws[i];
874	<	if (t != null)
875	<	t.setAsyncMode(async);
876	<	}
877	<	}
878	<	return oldMode;
1666	>	return parallelism + (short)(ctl >>> TC_SHIFT);
1667		}
1668
1669		/**
#	Line 883 | Line 1671 | public class ForkJoinPool extends Abstra
1671		* scheduling mode for forked tasks that are never joined.
1672		*
1673		* @return {@code true} if this pool uses async mode
886	–	* @see #setAsyncMode
1674		*/
1675		public boolean getAsyncMode() {
1676		return locallyFifo;
#	Line 892 | Line 1679 | public class ForkJoinPool extends Abstra
1679		/**
1680		* Returns an estimate of the number of worker threads that are
1681		* not blocked waiting to join tasks or for other managed
1682	<	* synchronization.
1682	>	* synchronization. This method may overestimate the
1683	>	* number of running threads.
1684		*
1685		* @return the number of worker threads
1686		*/
1687		public int getRunningThreadCount() {
1688	<	return runningCountOf(workerCounts);
1688	>	int r = parallelism + (int)(ctl >> AC_SHIFT);
1689	>	return (r <= 0) ? 0 : r; // suppress momentarily negative values
1690		}
1691
1692		/**
#	Line 908 | Line 1697 | public class ForkJoinPool extends Abstra
1697		* @return the number of active threads
1698		*/
1699		public int getActiveThreadCount() {
1700	<	return activeCountOf(runControl);
1701	<	}
913	<
914	<	/**
915	<	* Returns an estimate of the number of threads that are currently
916	<	* idle waiting for tasks. This method may underestimate the
917	<	* number of idle threads.
918	<	*
919	<	* @return the number of idle threads
920	<	*/
921	<	final int getIdleThreadCount() {
922	<	int c = runningCountOf(workerCounts) - activeCountOf(runControl);
923	<	return (c <= 0) ? 0 : c;
1700	>	int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount;
1701	>	return (r <= 0) ? 0 : r; // suppress momentarily negative values
1702		}
1703
1704		/**
#	Line 935 | Line 1713 | public class ForkJoinPool extends Abstra
1713		* @return {@code true} if all threads are currently idle
1714		*/
1715		public boolean isQuiescent() {
1716	<	return activeCountOf(runControl) == 0;
1716	>	return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0;
1717		}
1718
1719		/**
#	Line 950 | Line 1728 | public class ForkJoinPool extends Abstra
1728		* @return the number of steals
1729		*/
1730		public long getStealCount() {
1731	<	return stealCount.get();
954	<	}
955	<
956	<	/**
957	<	* Accumulates steal count from a worker.
958	<	* Call only when worker known to be idle.
959	<	*/
960	<	private void updateStealCount(ForkJoinWorkerThread w) {
961	<	int sc = w.getAndClearStealCount();
962	<	if (sc != 0)
963	<	stealCount.addAndGet(sc);
1731	>	return stealCount;
1732		}
1733
1734		/**
#	Line 975 | Line 1743 | public class ForkJoinPool extends Abstra
1743		*/
1744		public long getQueuedTaskCount() {
1745		long count = 0;
1746	<	ForkJoinWorkerThread[] ws = workers;
1747	<	if (ws != null) {
1748	<	for (int i = 0; i < ws.length; ++i) {
1749	<	ForkJoinWorkerThread t = ws[i];
1750	<	if (t != null)
1751	<	count += t.getQueueSize();
984	<	}
1746	>	ForkJoinWorkerThread[] ws;
1747	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1748	>	(ws = workers) != null) {
1749	>	for (ForkJoinWorkerThread w : ws)
1750	>	if (w != null)
1751	>	count -= w.queueBase - w.queueTop; // must read base first
1752		}
1753		return count;
1754		}
1755
1756		/**
1757		* Returns an estimate of the number of tasks submitted to this
1758	<	* pool that have not yet begun executing.  This method takes time
1759	<	* proportional to the number of submissions.
1758	>	* pool that have not yet begun executing.  This method may take
1759	>	* time proportional to the number of submissions.
1760		*
1761		* @return the number of queued submissions
1762		*/
1763		public int getQueuedSubmissionCount() {
1764	<	return submissionQueue.size();
1764	>	return -queueBase + queueTop;
1765		}
1766
1767		/**
#	Line 1004 | Line 1771 | public class ForkJoinPool extends Abstra
1771		* @return {@code true} if there are any queued submissions
1772		*/
1773		public boolean hasQueuedSubmissions() {
1774	<	return !submissionQueue.isEmpty();
1774	>	return queueBase != queueTop;
1775		}
1776
1777		/**
#	Line 1015 | Line 1782 | public class ForkJoinPool extends Abstra
1782		* @return the next submission, or {@code null} if none
1783		*/
1784		protected ForkJoinTask<?> pollSubmission() {
1785	<	return submissionQueue.poll();
1785	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
1786	>	while ((b = queueBase) != queueTop &&
1787	>	(q = submissionQueue) != null &&
1788	>	(i = (q.length - 1) & b) >= 0) {
1789	>	long u = (i << ASHIFT) + ABASE;
1790	>	if ((t = q[i]) != null &&
1791	>	queueBase == b &&
1792	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1793	>	queueBase = b + 1;
1794	>	return t;
1795	>	}
1796	>	}
1797	>	return null;
1798		}
1799
1800		/**
#	Line 1036 | Line 1815 | public class ForkJoinPool extends Abstra
1815		* @return the number of elements transferred
1816		*/
1817		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1818	<	int n = submissionQueue.drainTo(c);
1819	<	ForkJoinWorkerThread[] ws = workers;
1820	<	if (ws != null) {
1821	<	for (int i = 0; i < ws.length; ++i) {
1822	<	ForkJoinWorkerThread w = ws[i];
1823	<	if (w != null)
1045	<	n += w.drainTasksTo(c);
1818	>	int count = 0;
1819	>	while (queueBase != queueTop) {
1820	>	ForkJoinTask<?> t = pollSubmission();
1821	>	if (t != null) {
1822	>	c.add(t);
1823	>	++count;
1824		}
1825		}
1826	<	return n;
1826	>	ForkJoinWorkerThread[] ws;
1827	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1828	>	(ws = workers) != null) {
1829	>	for (ForkJoinWorkerThread w : ws)
1830	>	if (w != null)
1831	>	count += w.drainTasksTo(c);
1832	>	}
1833	>	return count;
1834		}
1835
1836		/**
#	Line 1056 | Line 1841 | public class ForkJoinPool extends Abstra
1841		* @return a string identifying this pool, as well as its state
1842		*/
1843		public String toString() {
1059	–	int ps = parallelism;
1060	–	int wc = workerCounts;
1061	–	int rc = runControl;
1844		long st = getStealCount();
1845		long qt = getQueuedTaskCount();
1846		long qs = getQueuedSubmissionCount();
1847	+	int pc = parallelism;
1848	+	long c = ctl;
1849	+	int tc = pc + (short)(c >>> TC_SHIFT);
1850	+	int rc = pc + (int)(c >> AC_SHIFT);
1851	+	if (rc < 0) // ignore transient negative
1852	+	rc = 0;
1853	+	int ac = rc + blockedCount;
1854	+	String level;
1855	+	if ((c & STOP_BIT) != 0)
1856	+	level = (tc == 0) ? "Terminated" : "Terminating";
1857	+	else
1858	+	level = shutdown ? "Shutting down" : "Running";
1859		return super.toString() +
1860	<	"[" + runStateToString(runStateOf(rc)) +
1861	<	", parallelism = " + ps +
1862	<	", size = " + totalCountOf(wc) +
1863	<	", active = " + activeCountOf(rc) +
1864	<	", running = " + runningCountOf(wc) +
1860	>	"[" + level +
1861	>	", parallelism = " + pc +
1862	>	", size = " + tc +
1863	>	", active = " + ac +
1864	>	", running = " + rc +
1865		", steals = " + st +
1866		", tasks = " + qt +
1867		", submissions = " + qs +
1868		"]";
1869		}
1870
1077	–	private static String runStateToString(int rs) {
1078	–	switch(rs) {
1079	–	case RUNNING: return "Running";
1080	–	case SHUTDOWN: return "Shutting down";
1081	–	case TERMINATING: return "Terminating";
1082	–	case TERMINATED: return "Terminated";
1083	–	default: throw new Error("Unknown run state");
1084	–	}
1085	–	}
1086	–
1087	–	// lifecycle control
1088	–
1871		/**
1872		* Initiates an orderly shutdown in which previously submitted
1873		* tasks are executed, but no new tasks will be accepted.
#	Line 1100 | Line 1882 | public class ForkJoinPool extends Abstra
1882		*/
1883		public void shutdown() {
1884		checkPermission();
1885	<	transitionRunStateTo(SHUTDOWN);
1886	<	if (canTerminateOnShutdown(runControl)) {
1105	<	if (workers == null) { // shutting down before workers created
1106	<	final ReentrantLock lock = this.workerLock;
1107	<	lock.lock();
1108	<	try {
1109	<	if (workers == null) {
1110	<	terminate();
1111	<	transitionRunStateTo(TERMINATED);
1112	<	termination.signalAll();
1113	<	}
1114	<	} finally {
1115	<	lock.unlock();
1116	<	}
1117	<	}
1118	<	terminateOnShutdown();
1119	<	}
1885	>	shutdown = true;
1886	>	tryTerminate(false);
1887		}
1888
1889		/**
#	Line 1137 | Line 1904 | public class ForkJoinPool extends Abstra
1904		*/
1905		public List<Runnable> shutdownNow() {
1906		checkPermission();
1907	<	terminate();
1907	>	shutdown = true;
1908	>	tryTerminate(true);
1909		return Collections.emptyList();
1910		}
1911
#	Line 1147 | Line 1915 | public class ForkJoinPool extends Abstra
1915		* @return {@code true} if all tasks have completed following shut down
1916		*/
1917		public boolean isTerminated() {
1918	<	return runStateOf(runControl) == TERMINATED;
1918	>	long c = ctl;
1919	>	return ((c & STOP_BIT) != 0L &&
1920	>	(short)(c >>> TC_SHIFT) == -parallelism);
1921		}
1922
1923		/**
#	Line 1155 | Line 1925 | public class ForkJoinPool extends Abstra
1925		* commenced but not yet completed.  This method may be useful for
1926		* debugging. A return of {@code true} reported a sufficient
1927		* period after shutdown may indicate that submitted tasks have
1928	<	* ignored or suppressed interruption, causing this executor not
1929	<	* to properly terminate.
1928	>	* ignored or suppressed interruption, or are waiting for IO,
1929	>	* causing this executor not to properly terminate. (See the
1930	>	* advisory notes for class {@link ForkJoinTask} stating that
1931	>	* tasks should not normally entail blocking operations.  But if
1932	>	* they do, they must abort them on interrupt.)
1933		*
1934		* @return {@code true} if terminating but not yet terminated
1935		*/
1936		public boolean isTerminating() {
1937	<	return runStateOf(runControl) == TERMINATING;
1937	>	long c = ctl;
1938	>	return ((c & STOP_BIT) != 0L &&
1939	>	(short)(c >>> TC_SHIFT) != -parallelism);
1940		}
1941
1942		/**
1943	<	* Returns {@code true} if this pool has been shut down.
1169	<	*
1170	<	* @return {@code true} if this pool has been shut down
1943	>	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1944		*/
1945	<	public boolean isShutdown() {
1946	<	return runStateOf(runControl) >= SHUTDOWN;
1945	>	final boolean isAtLeastTerminating() {
1946	>	return (ctl & STOP_BIT) != 0L;
1947		}
1948
1949		/**
1950	<	* Returns true if pool is not terminating or terminated.
1951	<	* Used internally to suppress execution when terminating.
1950	>	* Returns {@code true} if this pool has been shut down.
1951	>	*
1952	>	* @return {@code true} if this pool has been shut down
1953		*/
1954	<	final boolean isProcessingTasks() {
1955	<	return runStateOf(runControl) < TERMINATING;
1954	>	public boolean isShutdown() {
1955	>	return shutdown;
1956		}
1957
1958		/**
#	Line 1195 | Line 1969 | public class ForkJoinPool extends Abstra
1969		public boolean awaitTermination(long timeout, TimeUnit unit)
1970		throws InterruptedException {
1971		long nanos = unit.toNanos(timeout);
1972	<	final ReentrantLock lock = this.workerLock;
1972	>	final ReentrantLock lock = this.submissionLock;
1973		lock.lock();
1974		try {
1975		for (;;) {
#	Line 1210 | Line 1984 | public class ForkJoinPool extends Abstra
1984		}
1985		}
1986
1213	–	// Shutdown and termination support
1214	–
1215	–	/**
1216	–	* Callback from terminating worker. Nulls out the corresponding
1217	–	* workers slot, and if terminating, tries to terminate; else
1218	–	* tries to shrink workers array.
1219	–	*
1220	–	* @param w the worker
1221	–	*/
1222	–	final void workerTerminated(ForkJoinWorkerThread w) {
1223	–	updateStealCount(w);
1224	–	updateWorkerCount(-1);
1225	–	final ReentrantLock lock = this.workerLock;
1226	–	lock.lock();
1227	–	try {
1228	–	ForkJoinWorkerThread[] ws = workers;
1229	–	if (ws != null) {
1230	–	int idx = w.poolIndex;
1231	–	if (idx >= 0 && idx < ws.length && ws[idx] == w)
1232	–	ws[idx] = null;
1233	–	if (totalCountOf(workerCounts) == 0) {
1234	–	terminate(); // no-op if already terminating
1235	–	transitionRunStateTo(TERMINATED);
1236	–	termination.signalAll();
1237	–	}
1238	–	else if (isProcessingTasks()) {
1239	–	tryShrinkWorkerArray();
1240	–	tryResumeSpare(true); // allow replacement
1241	–	}
1242	–	}
1243	–	} finally {
1244	–	lock.unlock();
1245	–	}
1246	–	signalIdleWorkers();
1247	–	}
1248	–
1249	–	/**
1250	–	* Initiates termination.
1251	–	*/
1252	–	private void terminate() {
1253	–	if (transitionRunStateTo(TERMINATING)) {
1254	–	stopAllWorkers();
1255	–	resumeAllSpares();
1256	–	signalIdleWorkers();
1257	–	cancelQueuedSubmissions();
1258	–	cancelQueuedWorkerTasks();
1259	–	interruptUnterminatedWorkers();
1260	–	signalIdleWorkers(); // resignal after interrupt
1261	–	}
1262	–	}
1263	–
1264	–	/**
1265	–	* Possibly terminates when on shutdown state.
1266	–	*/
1267	–	private void terminateOnShutdown() {
1268	–	if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
1269	–	terminate();
1270	–	}
1271	–
1272	–	/**
1273	–	* Clears out and cancels submissions.
1274	–	*/
1275	–	private void cancelQueuedSubmissions() {
1276	–	ForkJoinTask<?> task;
1277	–	while ((task = pollSubmission()) != null)
1278	–	task.cancel(false);
1279	–	}
1280	–
1281	–	/**
1282	–	* Cleans out worker queues.
1283	–	*/
1284	–	private void cancelQueuedWorkerTasks() {
1285	–	final ReentrantLock lock = this.workerLock;
1286	–	lock.lock();
1287	–	try {
1288	–	ForkJoinWorkerThread[] ws = workers;
1289	–	if (ws != null) {
1290	–	for (int i = 0; i < ws.length; ++i) {
1291	–	ForkJoinWorkerThread t = ws[i];
1292	–	if (t != null)
1293	–	t.cancelTasks();
1294	–	}
1295	–	}
1296	–	} finally {
1297	–	lock.unlock();
1298	–	}
1299	–	}
1300	–
1301	–	/**
1302	–	* Sets each worker's status to terminating. Requires lock to avoid
1303	–	* conflicts with add/remove.
1304	–	*/
1305	–	private void stopAllWorkers() {
1306	–	final ReentrantLock lock = this.workerLock;
1307	–	lock.lock();
1308	–	try {
1309	–	ForkJoinWorkerThread[] ws = workers;
1310	–	if (ws != null) {
1311	–	for (int i = 0; i < ws.length; ++i) {
1312	–	ForkJoinWorkerThread t = ws[i];
1313	–	if (t != null)
1314	–	t.shutdownNow();
1315	–	}
1316	–	}
1317	–	} finally {
1318	–	lock.unlock();
1319	–	}
1320	–	}
1321	–
1322	–	/**
1323	–	* Interrupts all unterminated workers.  This is not required for
1324	–	* sake of internal control, but may help unstick user code during
1325	–	* shutdown.
1326	–	*/
1327	–	private void interruptUnterminatedWorkers() {
1328	–	final ReentrantLock lock = this.workerLock;
1329	–	lock.lock();
1330	–	try {
1331	–	ForkJoinWorkerThread[] ws = workers;
1332	–	if (ws != null) {
1333	–	for (int i = 0; i < ws.length; ++i) {
1334	–	ForkJoinWorkerThread t = ws[i];
1335	–	if (t != null && !t.isTerminated()) {
1336	–	try {
1337	–	t.interrupt();
1338	–	} catch (SecurityException ignore) {
1339	–	}
1340	–	}
1341	–	}
1342	–	}
1343	–	} finally {
1344	–	lock.unlock();
1345	–	}
1346	–	}
1347	–
1348	–
1349	–	/*
1350	–	* Nodes for event barrier to manage idle threads.  Queue nodes
1351	–	* are basic Treiber stack nodes, also used for spare stack.
1352	–	*
1353	–	* The event barrier has an event count and a wait queue (actually
1354	–	* a Treiber stack).  Workers are enabled to look for work when
1355	–	* the eventCount is incremented. If they fail to find work, they
1356	–	* may wait for next count. Upon release, threads help others wake
1357	–	* up.
1358	–	*
1359	–	* Synchronization events occur only in enough contexts to
1360	–	* maintain overall liveness:
1361	–	*
1362	–	*   - Submission of a new task to the pool
1363	–	*   - Resizes or other changes to the workers array
1364	–	*   - pool termination
1365	–	*   - A worker pushing a task on an empty queue
1366	–	*
1367	–	* The case of pushing a task occurs often enough, and is heavy
1368	–	* enough compared to simple stack pushes, to require special
1369	–	* handling: Method signalWork returns without advancing count if
1370	–	* the queue appears to be empty.  This would ordinarily result in
1371	–	* races causing some queued waiters not to be woken up. To avoid
1372	–	* this, the first worker enqueued in method sync (see
1373	–	* syncIsReleasable) rescans for tasks after being enqueued, and
1374	–	* helps signal if any are found. This works well because the
1375	–	* worker has nothing better to do, and so might as well help
1376	–	* alleviate the overhead and contention on the threads actually
1377	–	* doing work.  Also, since event counts increments on task
1378	–	* availability exist to maintain liveness (rather than to force
1379	–	* refreshes etc), it is OK for callers to exit early if
1380	–	* contending with another signaller.
1381	–	*/
1382	–	static final class WaitQueueNode {
1383	–	WaitQueueNode next; // only written before enqueued
1384	–	volatile ForkJoinWorkerThread thread; // nulled to cancel wait
1385	–	final long count; // unused for spare stack
1386	–
1387	–	WaitQueueNode(long c, ForkJoinWorkerThread w) {
1388	–	count = c;
1389	–	thread = w;
1390	–	}
1391	–
1392	–	/**
1393	–	* Wakes up waiter, returning false if known to already
1394	–	*/
1395	–	boolean signal() {
1396	–	ForkJoinWorkerThread t = thread;
1397	–	if (t == null)
1398	–	return false;
1399	–	thread = null;
1400	–	LockSupport.unpark(t);
1401	–	return true;
1402	–	}
1403	–
1404	–	/**
1405	–	* Awaits release on sync.
1406	–	*/
1407	–	void awaitSyncRelease(ForkJoinPool p) {
1408	–	while (thread != null && !p.syncIsReleasable(this))
1409	–	LockSupport.park(this);
1410	–	}
1411	–
1412	–	/**
1413	–	* Awaits resumption as spare.
1414	–	*/
1415	–	void awaitSpareRelease() {
1416	–	while (thread != null) {
1417	–	if (!Thread.interrupted())
1418	–	LockSupport.park(this);
1419	–	}
1420	–	}
1421	–	}
1422	–
1423	–	/**
1424	–	* Ensures that no thread is waiting for count to advance from the
1425	–	* current value of eventCount read on entry to this method, by
1426	–	* releasing waiting threads if necessary.
1427	–	*
1428	–	* @return the count
1429	–	*/
1430	–	final long ensureSync() {
1431	–	long c = eventCount;
1432	–	WaitQueueNode q;
1433	–	while ((q = syncStack) != null && q.count < c) {
1434	–	if (casBarrierStack(q, null)) {
1435	–	do {
1436	–	q.signal();
1437	–	} while ((q = q.next) != null);
1438	–	break;
1439	–	}
1440	–	}
1441	–	return c;
1442	–	}
1443	–
1444	–	/**
1445	–	* Increments event count and releases waiting threads.
1446	–	*/
1447	–	private void signalIdleWorkers() {
1448	–	long c;
1449	–	do {} while (!casEventCount(c = eventCount, c+1));
1450	–	ensureSync();
1451	–	}
1452	–
1453	–	/**
1454	–	* Signals threads waiting to poll a task. Because method sync
1455	–	* rechecks availability, it is OK to only proceed if queue
1456	–	* appears to be non-empty, and OK to skip under contention to
1457	–	* increment count (since some other thread succeeded).
1458	–	*/
1459	–	final void signalWork() {
1460	–	long c;
1461	–	WaitQueueNode q;
1462	–	if (syncStack != null &&
1463	–	casEventCount(c = eventCount, c+1) &&
1464	–	(((q = syncStack) != null && q.count <= c) &&
1465	–	(!casBarrierStack(q, q.next) || !q.signal())))
1466	–	ensureSync();
1467	–	}
1468	–
1469	–	/**
1470	–	* Waits until event count advances from last value held by
1471	–	* caller, or if excess threads, caller is resumed as spare, or
1472	–	* caller or pool is terminating. Updates caller's event on exit.
1473	–	*
1474	–	* @param w the calling worker thread
1475	–	*/
1476	–	final void sync(ForkJoinWorkerThread w) {
1477	–	updateStealCount(w); // Transfer w's count while it is idle
1478	–
1479	–	while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
1480	–	long prev = w.lastEventCount;
1481	–	WaitQueueNode node = null;
1482	–	WaitQueueNode h;
1483	–	while (eventCount == prev &&
1484	–	((h = syncStack) == null || h.count == prev)) {
1485	–	if (node == null)
1486	–	node = new WaitQueueNode(prev, w);
1487	–	if (casBarrierStack(node.next = h, node)) {
1488	–	node.awaitSyncRelease(this);
1489	–	break;
1490	–	}
1491	–	}
1492	–	long ec = ensureSync();
1493	–	if (ec != prev) {
1494	–	w.lastEventCount = ec;
1495	–	break;
1496	–	}
1497	–	}
1498	–	}
1499	–
1500	–	/**
1501	–	* Returns {@code true} if worker waiting on sync can proceed:
1502	–	*  - on signal (thread == null)
1503	–	*  - on event count advance (winning race to notify vs signaller)
1504	–	*  - on interrupt
1505	–	*  - if the first queued node, we find work available
1506	–	* If node was not signalled and event count not advanced on exit,
1507	–	* then we also help advance event count.
1508	–	*
1509	–	* @return {@code true} if node can be released
1510	–	*/
1511	–	final boolean syncIsReleasable(WaitQueueNode node) {
1512	–	long prev = node.count;
1513	–	if (!Thread.interrupted() && node.thread != null &&
1514	–	(node.next != null ||
1515	–	!ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
1516	–	eventCount == prev)
1517	–	return false;
1518	–	if (node.thread != null) {
1519	–	node.thread = null;
1520	–	long ec = eventCount;
1521	–	if (prev <= ec) // help signal
1522	–	casEventCount(ec, ec+1);
1523	–	}
1524	–	return true;
1525	–	}
1526	–
1527	–	/**
1528	–	* Returns {@code true} if a new sync event occurred since last
1529	–	* call to sync or this method, if so, updating caller's count.
1530	–	*/
1531	–	final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1532	–	long lc = w.lastEventCount;
1533	–	long ec = ensureSync();
1534	–	if (ec == lc)
1535	–	return false;
1536	–	w.lastEventCount = ec;
1537	–	return true;
1538	–	}
1539	–
1540	–	//  Parallelism maintenance
1541	–
1542	–	/**
1543	–	* Decrements running count; if too low, adds spare.
1544	–	*
1545	–	* Conceptually, all we need to do here is add or resume a
1546	–	* spare thread when one is about to block (and remove or
1547	–	* suspend it later when unblocked -- see suspendIfSpare).
1548	–	* However, implementing this idea requires coping with
1549	–	* several problems: we have imperfect information about the
1550	–	* states of threads. Some count updates can and usually do
1551	–	* lag run state changes, despite arrangements to keep them
1552	–	* accurate (for example, when possible, updating counts
1553	–	* before signalling or resuming), especially when running on
1554	–	* dynamic JVMs that don't optimize the infrequent paths that
1555	–	* update counts. Generating too many threads can make these
1556	–	* problems become worse, because excess threads are more
1557	–	* likely to be context-switched with others, slowing them all
1558	–	* down, especially if there is no work available, so all are
1559	–	* busy scanning or idling.  Also, excess spare threads can
1560	–	* only be suspended or removed when they are idle, not
1561	–	* immediately when they aren't needed. So adding threads will
1562	–	* raise parallelism level for longer than necessary.  Also,
1563	–	* FJ applications often encounter highly transient peaks when
1564	–	* many threads are blocked joining, but for less time than it
1565	–	* takes to create or resume spares.
1566	–	*
1567	–	* @param joinMe if non-null, return early if done
1568	–	* @param maintainParallelism if true, try to stay within
1569	–	* target counts, else create only to avoid starvation
1570	–	* @return true if joinMe known to be done
1571	–	*/
1572	–	final boolean preJoin(ForkJoinTask<?> joinMe,
1573	–	boolean maintainParallelism) {
1574	–	maintainParallelism &= maintainsParallelism; // overrride
1575	–	boolean dec = false;  // true when running count decremented
1576	–	while (spareStack == null || !tryResumeSpare(dec)) {
1577	–	int counts = workerCounts;
1578	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1579	–	// CAS cheat
1580	–	if (!needSpare(counts, maintainParallelism))
1581	–	break;
1582	–	if (joinMe.status < 0)
1583	–	return true;
1584	–	if (tryAddSpare(counts))
1585	–	break;
1586	–	}
1587	–	}
1588	–	return false;
1589	–	}
1590	–
1591	–	/**
1592	–	* Same idea as preJoin
1593	–	*/
1594	–	final boolean preBlock(ManagedBlocker blocker,
1595	–	boolean maintainParallelism) {
1596	–	maintainParallelism &= maintainsParallelism;
1597	–	boolean dec = false;
1598	–	while (spareStack == null || !tryResumeSpare(dec)) {
1599	–	int counts = workerCounts;
1600	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1601	–	if (!needSpare(counts, maintainParallelism))
1602	–	break;
1603	–	if (blocker.isReleasable())
1604	–	return true;
1605	–	if (tryAddSpare(counts))
1606	–	break;
1607	–	}
1608	–	}
1609	–	return false;
1610	–	}
1611	–
1612	–	/**
1613	–	* Returns {@code true} if a spare thread appears to be needed.
1614	–	* If maintaining parallelism, returns true when the deficit in
1615	–	* running threads is more than the surplus of total threads, and
1616	–	* there is apparently some work to do.  This self-limiting rule
1617	–	* means that the more threads that have already been added, the
1618	–	* less parallelism we will tolerate before adding another.
1619	–	*
1620	–	* @param counts current worker counts
1621	–	* @param maintainParallelism try to maintain parallelism
1622	–	*/
1623	–	private boolean needSpare(int counts, boolean maintainParallelism) {
1624	–	int ps = parallelism;
1625	–	int rc = runningCountOf(counts);
1626	–	int tc = totalCountOf(counts);
1627	–	int runningDeficit = ps - rc;
1628	–	int totalSurplus = tc - ps;
1629	–	return (tc < maxPoolSize &&
1630	–	(rc == 0 || totalSurplus < 0 ||
1631	–	(maintainParallelism &&
1632	–	runningDeficit > totalSurplus &&
1633	–	ForkJoinWorkerThread.hasQueuedTasks(workers))));
1634	–	}
1635	–
1636	–	/**
1637	–	* Adds a spare worker if lock available and no more than the
1638	–	* expected numbers of threads exist.
1639	–	*
1640	–	* @return true if successful
1641	–	*/
1642	–	private boolean tryAddSpare(int expectedCounts) {
1643	–	final ReentrantLock lock = this.workerLock;
1644	–	int expectedRunning = runningCountOf(expectedCounts);
1645	–	int expectedTotal = totalCountOf(expectedCounts);
1646	–	boolean success = false;
1647	–	boolean locked = false;
1648	–	// confirm counts while locking; CAS after obtaining lock
1649	–	try {
1650	–	for (;;) {
1651	–	int s = workerCounts;
1652	–	int tc = totalCountOf(s);
1653	–	int rc = runningCountOf(s);
1654	–	if (rc > expectedRunning || tc > expectedTotal)
1655	–	break;
1656	–	if (!locked && !(locked = lock.tryLock()))
1657	–	break;
1658	–	if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
1659	–	createAndStartSpare(tc);
1660	–	success = true;
1661	–	break;
1662	–	}
1663	–	}
1664	–	} finally {
1665	–	if (locked)
1666	–	lock.unlock();
1667	–	}
1668	–	return success;
1669	–	}
1670	–
1671	–	/**
1672	–	* Adds the kth spare worker. On entry, pool counts are already
1673	–	* adjusted to reflect addition.
1674	–	*/
1675	–	private void createAndStartSpare(int k) {
1676	–	ForkJoinWorkerThread w = null;
1677	–	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
1678	–	int len = ws.length;
1679	–	// Probably, we can place at slot k. If not, find empty slot
1680	–	if (k < len && ws[k] != null) {
1681	–	for (k = 0; k < len && ws[k] != null; ++k)
1682	–	;
1683	–	}
1684	–	if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) {
1685	–	ws[k] = w;
1686	–	w.start();
1687	–	}
1688	–	else
1689	–	updateWorkerCount(-1); // adjust on failure
1690	–	signalIdleWorkers();
1691	–	}
1692	–
1693	–	/**
1694	–	* Suspends calling thread w if there are excess threads.  Called
1695	–	* only from sync.  Spares are enqueued in a Treiber stack using
1696	–	* the same WaitQueueNodes as barriers.  They are resumed mainly
1697	–	* in preJoin, but are also woken on pool events that require all
1698	–	* threads to check run state.
1699	–	*
1700	–	* @param w the caller
1701	–	*/
1702	–	private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1703	–	WaitQueueNode node = null;
1704	–	int s;
1705	–	while (parallelism < runningCountOf(s = workerCounts)) {
1706	–	if (node == null)
1707	–	node = new WaitQueueNode(0, w);
1708	–	if (casWorkerCounts(s, s-1)) { // representation-dependent
1709	–	// push onto stack
1710	–	do {} while (!casSpareStack(node.next = spareStack, node));
1711	–	// block until released by resumeSpare
1712	–	node.awaitSpareRelease();
1713	–	return true;
1714	–	}
1715	–	}
1716	–	return false;
1717	–	}
1718	–
1719	–	/**
1720	–	* Tries to pop and resume a spare thread.
1721	–	*
1722	–	* @param updateCount if true, increment running count on success
1723	–	* @return true if successful
1724	–	*/
1725	–	private boolean tryResumeSpare(boolean updateCount) {
1726	–	WaitQueueNode q;
1727	–	while ((q = spareStack) != null) {
1728	–	if (casSpareStack(q, q.next)) {
1729	–	if (updateCount)
1730	–	updateRunningCount(1);
1731	–	q.signal();
1732	–	return true;
1733	–	}
1734	–	}
1735	–	return false;
1736	–	}
1737	–
1738	–	/**
1739	–	* Pops and resumes all spare threads. Same idea as ensureSync.
1740	–	*
1741	–	* @return true if any spares released
1742	–	*/
1743	–	private boolean resumeAllSpares() {
1744	–	WaitQueueNode q;
1745	–	while ( (q = spareStack) != null) {
1746	–	if (casSpareStack(q, null)) {
1747	–	do {
1748	–	updateRunningCount(1);
1749	–	q.signal();
1750	–	} while ((q = q.next) != null);
1751	–	return true;
1752	–	}
1753	–	}
1754	–	return false;
1755	–	}
1756	–
1757	–	/**
1758	–	* Pops and shuts down excessive spare threads. Call only while
1759	–	* holding lock. This is not guaranteed to eliminate all excess
1760	–	* threads, only those suspended as spares, which are the ones
1761	–	* unlikely to be needed in the future.
1762	–	*/
1763	–	private void trimSpares() {
1764	–	int surplus = totalCountOf(workerCounts) - parallelism;
1765	–	WaitQueueNode q;
1766	–	while (surplus > 0 && (q = spareStack) != null) {
1767	–	if (casSpareStack(q, null)) {
1768	–	do {
1769	–	updateRunningCount(1);
1770	–	ForkJoinWorkerThread w = q.thread;
1771	–	if (w != null && surplus > 0 &&
1772	–	runningCountOf(workerCounts) > 0 && w.shutdown())
1773	–	--surplus;
1774	–	q.signal();
1775	–	} while ((q = q.next) != null);
1776	–	}
1777	–	}
1778	–	}
1779	–
1987		/**
1988		* Interface for extending managed parallelism for tasks running
1989		* in {@link ForkJoinPool}s.
1990		*
1991	<	* <p>A {@code ManagedBlocker} provides two methods.
1992	<	* Method {@code isReleasable} must return {@code true} if
1993	<	* blocking is not necessary. Method {@code block} blocks the
1994	<	* current thread if necessary (perhaps internally invoking
1995	<	* {@code isReleasable} before actually blocking).
1991	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1992	>	* {@code isReleasable} must return {@code true} if blocking is
1993	>	* not necessary. Method {@code block} blocks the current thread
1994	>	* if necessary (perhaps internally invoking {@code isReleasable}
1995	>	* before actually blocking). These actions are performed by any
1996	>	* thread invoking {@link ForkJoinPool#managedBlock}.  The
1997	>	* unusual methods in this API accommodate synchronizers that may,
1998	>	* but don't usually, block for long periods. Similarly, they
1999	>	* allow more efficient internal handling of cases in which
2000	>	* additional workers may be, but usually are not, needed to
2001	>	* ensure sufficient parallelism.  Toward this end,
2002	>	* implementations of method {@code isReleasable} must be amenable
2003	>	* to repeated invocation.
2004		*
2005		* <p>For example, here is a ManagedBlocker based on a
2006		* ReentrantLock:
#	Line 1803 | Line 2018 | public class ForkJoinPool extends Abstra
2018		*     return hasLock || (hasLock = lock.tryLock());
2019		*   }
2020		* }}</pre>
2021	+	*
2022	+	* <p>Here is a class that possibly blocks waiting for an
2023	+	* item on a given queue:
2024	+	*  <pre> {@code
2025	+	* class QueueTaker<E> implements ManagedBlocker {
2026	+	*   final BlockingQueue<E> queue;
2027	+	*   volatile E item = null;
2028	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
2029	+	*   public boolean block() throws InterruptedException {
2030	+	*     if (item == null)
2031	+	*       item = queue.take();
2032	+	*     return true;
2033	+	*   }
2034	+	*   public boolean isReleasable() {
2035	+	*     return item != null || (item = queue.poll()) != null;
2036	+	*   }
2037	+	*   public E getItem() { // call after pool.managedBlock completes
2038	+	*     return item;
2039	+	*   }
2040	+	* }}</pre>
2041		*/
2042		public static interface ManagedBlocker {
2043		/**
#	Line 1826 | Line 2061 | public class ForkJoinPool extends Abstra
2061		* Blocks in accord with the given blocker.  If the current thread
2062		* is a {@link ForkJoinWorkerThread}, this method possibly
2063		* arranges for a spare thread to be activated if necessary to
2064	<	* ensure parallelism while the current thread is blocked.
1830	<	*
1831	<	* <p>If {@code maintainParallelism} is {@code true} and the pool
1832	<	* supports it ({@link #getMaintainsParallelism}), this method
1833	<	* attempts to maintain the pool's nominal parallelism. Otherwise
1834	<	* it activates a thread only if necessary to avoid complete
1835	<	* starvation. This option may be preferable when blockages use
1836	<	* timeouts, or are almost always brief.
2064	>	* ensure sufficient parallelism while the current thread is blocked.
2065		*
2066		* <p>If the caller is not a {@link ForkJoinTask}, this method is
2067		* behaviorally equivalent to
#	Line 1847 | Line 2075 | public class ForkJoinPool extends Abstra
2075		* first be expanded to ensure parallelism, and later adjusted.
2076		*
2077		* @param blocker the blocker
1850	–	* @param maintainParallelism if {@code true} and supported by
1851	–	* this pool, attempt to maintain the pool's nominal parallelism;
1852	–	* otherwise activate a thread only if necessary to avoid
1853	–	* complete starvation.
2078		* @throws InterruptedException if blocker.block did so
2079		*/
2080	<	public static void managedBlock(ManagedBlocker blocker,
1857	<	boolean maintainParallelism)
2080	>	public static void managedBlock(ManagedBlocker blocker)
2081		throws InterruptedException {
2082		Thread t = Thread.currentThread();
2083	<	ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
2084	<	((ForkJoinWorkerThread) t).pool : null);
2085	<	if (!blocker.isReleasable()) {
2086	<	try {
2087	<	if (pool == null ||
2088	<	!pool.preBlock(blocker, maintainParallelism))
1866	<	awaitBlocker(blocker);
1867	<	} finally {
1868	<	if (pool != null)
1869	<	pool.updateRunningCount(1);
1870	<	}
2083	>	if (t instanceof ForkJoinWorkerThread) {
2084	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
2085	>	w.pool.awaitBlocker(blocker);
2086	>	}
2087	>	else {
2088	>	do {} while (!blocker.isReleasable() && !blocker.block());
2089		}
1872	–	}
1873	–
1874	–	private static void awaitBlocker(ManagedBlocker blocker)
1875	–	throws InterruptedException {
1876	–	do {} while (!blocker.isReleasable() && !blocker.block());
2090		}
2091
2092		// AbstractExecutorService overrides.  These rely on undocumented
#	Line 1889 | Line 2102 | public class ForkJoinPool extends Abstra
2102		}
2103
2104		// Unsafe mechanics
2105	<
2106	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
2107	<	private static final long eventCountOffset =
2108	<	objectFieldOffset("eventCount", ForkJoinPool.class);
2109	<	private static final long workerCountsOffset =
2110	<	objectFieldOffset("workerCounts", ForkJoinPool.class);
2111	<	private static final long runControlOffset =
2112	<	objectFieldOffset("runControl", ForkJoinPool.class);
2113	<	private static final long syncStackOffset =
2114	<	objectFieldOffset("syncStack",ForkJoinPool.class);
2115	<	private static final long spareStackOffset =
2116	<	objectFieldOffset("spareStack", ForkJoinPool.class);
2117	<
2118	<	private boolean casEventCount(long cmp, long val) {
2119	<	return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
2120	<	}
2121	<	private boolean casWorkerCounts(int cmp, int val) {
1909	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
1910	<	}
1911	<	private boolean casRunControl(int cmp, int val) {
1912	<	return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
1913	<	}
1914	<	private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
1915	<	return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
1916	<	}
1917	<	private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
1918	<	return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
1919	<	}
1920	<
1921	<	private static long objectFieldOffset(String field, Class<?> klazz) {
2105	>	private static final sun.misc.Unsafe UNSAFE;
2106	>	private static final long ctlOffset;
2107	>	private static final long stealCountOffset;
2108	>	private static final long blockedCountOffset;
2109	>	private static final long quiescerCountOffset;
2110	>	private static final long scanGuardOffset;
2111	>	private static final long nextWorkerNumberOffset;
2112	>	private static final long ABASE;
2113	>	private static final int ASHIFT;
2114	>
2115	>	static {
2116	>	poolNumberGenerator = new AtomicInteger();
2117	>	workerSeedGenerator = new Random();
2118	>	modifyThreadPermission = new RuntimePermission("modifyThread");
2119	>	defaultForkJoinWorkerThreadFactory =
2120	>	new DefaultForkJoinWorkerThreadFactory();
2121	>	int s;
2122		try {
2123	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
2124	<	} catch (NoSuchFieldException e) {
2125	<	// Convert Exception to corresponding Error
2126	<	NoSuchFieldError error = new NoSuchFieldError(field);
2127	<	error.initCause(e);
2128	<	throw error;
2129	<	}
2123	>	UNSAFE = getUnsafe();
2124	>	Class k = ForkJoinPool.class;
2125	>	ctlOffset = UNSAFE.objectFieldOffset
2126	>	(k.getDeclaredField("ctl"));
2127	>	stealCountOffset = UNSAFE.objectFieldOffset
2128	>	(k.getDeclaredField("stealCount"));
2129	>	blockedCountOffset = UNSAFE.objectFieldOffset
2130	>	(k.getDeclaredField("blockedCount"));
2131	>	quiescerCountOffset = UNSAFE.objectFieldOffset
2132	>	(k.getDeclaredField("quiescerCount"));
2133	>	scanGuardOffset = UNSAFE.objectFieldOffset
2134	>	(k.getDeclaredField("scanGuard"));
2135	>	nextWorkerNumberOffset = UNSAFE.objectFieldOffset
2136	>	(k.getDeclaredField("nextWorkerNumber"));
2137	>	Class a = ForkJoinTask[].class;
2138	>	ABASE = UNSAFE.arrayBaseOffset(a);
2139	>	s = UNSAFE.arrayIndexScale(a);
2140	>	} catch (Exception e) {
2141	>	throw new Error(e);
2142	>	}
2143	>	if ((s & (s-1)) != 0)
2144	>	throw new Error("data type scale not a power of two");
2145	>	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
2146		}
2147
2148		/**

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