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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.40 by jsr166, Mon Aug 3 00:53:15 2009 UTC vs.
Revision 1.95 by dl, Fri Mar 4 13:29:39 2011 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.util.ArrayList;
10		import java.util.Arrays;
11		import java.util.Collection;
12		import java.util.Collections;
13		import java.util.List;
14	<	import java.util.concurrent.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.  Normally a single {@code ForkJoinPool} is
27	<	* used for a large number of submitted tasks. Otherwise, use would
28	<	* not usually outweigh the construction and bookkeeping overhead of
29	<	* creating a large set of threads.
31	>	* from non-{@code ForkJoinTask} clients, as well as management and
32	>	* monitoring operations.
33		*
34	<	* <p>{@code ForkJoinPool}s differ from other kinds of {@link
35	<	* Executor}s mainly in that they provide <em>work-stealing</em>: all
36	<	* threads in the pool attempt to find and execute subtasks created by
37	<	* other active tasks (eventually blocking if none exist). This makes
38	<	* them efficient when most tasks spawn other subtasks (as do most
39	<	* {@code ForkJoinTask}s), as well as the mixed execution of some
40	<	* plain {@code Runnable}- or {@code Callable}- based activities along
41	<	* with {@code ForkJoinTask}s. When setting {@linkplain #setAsyncMode
42	<	* async mode}, a {@code ForkJoinPool} may also be appropriate for use
40	<	* with fine-grained tasks that are never joined. Otherwise, other
41	<	* {@code ExecutorService} implementations are typically more
42	<	* appropriate choices.
34	>	* <p>A {@code ForkJoinPool} differs from other kinds of {@link
35	>	* ExecutorService} mainly by virtue of employing
36	>	* <em>work-stealing</em>: all threads in the pool attempt to find and
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). 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} may be constructed with a given
45	<	* parallelism level (target pool size), which it attempts to maintain
46	<	* by dynamically adding, suspending, or resuming threads, even if
47	<	* some tasks are waiting to join others. However, no such adjustments
48	<	* are performed in the face of blocked IO or other unmanaged
49	<	* synchronization. The nested {@link ManagedBlocker} interface
50	<	* enables extension of the kinds of synchronization accommodated.
51	<	* The target parallelism level may also be changed dynamically
52	<	* ({@link #setParallelism}) and thread construction can be limited
53	<	* using methods {@link #setMaximumPoolSize} and/or {@link
54	<	* #setMaintainsParallelism}.
44	>	* <p>A {@code ForkJoinPool} is constructed with a given target
45	>	* parallelism level; by default, equal to the number of available
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 60 | 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}
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 explicitly {@link
103	+	* #shutdown} such a pool upon program exit.
104	+	*
105	+	* <pre>
106	+	* static final ForkJoinPool mainPool = new ForkJoinPool();
107	+	* ...
108	+	* public void sort(long[] array) {
109	+	*   mainPool.invoke(new SortTask(array, 0, array.length));
110	+	* }
111	+	* </pre>
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
78	–	/** Mask for packing and unpacking shorts */
79	–	private static final int  shortMask = 0xffff;
80	–
81	–	/** Max pool size -- must be a power of two minus 1 */
82	–	private static final int MAX_THREADS =  0x7FFF;
83	–
338		/**
339		* Factory for creating new {@link ForkJoinWorkerThread}s.
340		* A {@code ForkJoinWorkerThreadFactory} must be defined and used
#	Line 92 | 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 101 | 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 {
108	<	return new ForkJoinWorkerThread(pool);
109	<	} catch (OutOfMemoryError oom)  {
110	<	return null;
111	<	}
361	>	return new ForkJoinWorkerThread(pool);
362		}
363		}
364
#	Line 117 | Line 367 | public class ForkJoinPool extends Abstra
367		* overridden in ForkJoinPool constructors.
368		*/
369		public static final ForkJoinWorkerThreadFactory
370	<	defaultForkJoinWorkerThreadFactory =
121	<	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 =
128	<	new RuntimePermission("modifyThread");
376	>	private static final RuntimePermission modifyThreadPermission;
377
378		/**
379		* If there is a security manager, makes sure caller has
#	Line 140 | Line 388 | public class ForkJoinPool extends Abstra
388		/**
389		* Generator for assigning sequence numbers as pool names.
390		*/
391	<	private static final AtomicInteger poolNumberGenerator =
144	<	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	>	* Array serving as submission queue. Initialized upon construction.
431	>	*/
432	>	private ForkJoinTask<?>[] submissionQueue;
433
434		/**
435	<	* The uncaught exception handler used when any worker
167	<	* abruptly terminates
435	>	* Lock protecting submissions array for addSubmission
436		*/
437	<	private Thread.UncaughtExceptionHandler ueh;
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 174 | 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
179	<	* 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
185	<	* 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
228	<	* making decisions about creating and suspending spare
229	<	* threads. Updated only by CAS.  Note: CASes in
230	<	* updateRunningCount and preJoin assume that running active count
231	<	* 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
241	<	* be called before (with negative arg) and after (with positive)
242	<	* any managed synchronization (i.e., mainly, joins).
243	<	*
244	<	* @param delta the number to add
568	>	* Counter for worker Thread names (unrelated to their poolIndex)
569		*/
570	<	final void updateRunningCount(int delta) {
247	<	int s;
248	<	do {} while (!casWorkerCounts(s = workerCounts, s + delta));
249	<	}
570	>	private volatile int nextWorkerNumber;
571
572		/**
573	<	* Adds delta (which may be negative) to both total and running
253	<	* count.  This must be called upon creation and termination of
254	<	* worker threads.
255	<	*
256	<	* @param delta the number to add
573	>	* The index for the next created worker. Accessed under scanGuard.
574		*/
575	<	private void updateWorkerCount(int delta) {
259	<	int d = delta + (delta << 16); // add to both lo and hi parts
260	<	int s;
261	<	do {} while (!casWorkerCounts(s = workerCounts, s + d));
262	<	}
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
277	<	private static final int RUNNING     = 0;
278	<	private static final int SHUTDOWN    = 1;
279	<	private static final int TERMINATING = 2;
280	<	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.
299	<	* Possibly triggers termination on success.
300	<	* Called by workers when they can't find tasks.
301	<	*
302	<	* @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? 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, possibly
766	>	* terminates worker upon exit.  Otherwise, before blocking,
767	>	* rescans queues to avoid missed signals.  Upon finding work,
768	>	* releases at least one worker (which may be the current
769	>	* worker). Rescans restart upon detected staleness or failure to
770	>	* release due to contention. Note the unusual conventions about
771	>	* Thread.interrupt here and elsewhere: Because interrupts are
772	>	* used solely to alert threads to check termination, which is
773	>	* checked here anyway, we clear status (using Thread.interrupted)
774	>	* before any call to park, so that park does not immediately
775	>	* return due to status being set via some other unrelated call to
776	>	* interrupt in user code.
777	>	*
778	>	* @param w the calling worker
779	>	* @param c the ctl value on entry
780	>	* @return true if waited or another thread was released upon enq
781	>	*/
782	>	private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) {
783	>	int v = w.eventCount;
784	>	w.nextWait = (int)c;                      // w's successor record
785	>	long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
786	>	if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
787	>	long d = ctl; // return true if lost to a deq, to force scan
788	>	return (int)d != (int)c && ((d - c) & AC_MASK) >= 0L;
789	>	}
790	>	for (int sc = w.stealCount; sc != 0;) {   // accumulate stealCount
791	>	long s = stealCount;
792	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s + sc))
793	>	sc = w.stealCount = 0;
794	>	else if (w.eventCount != v)
795	>	return true;                      // update next time
796	>	}
797	>	if (parallelism + (int)(nc >> AC_SHIFT) == 0 &&
798	>	blockedCount == 0 && quiescerCount == 0)
799	>	idleAwaitWork(w, nc, c, v);           // quiescent
800	>	for (boolean rescanned = false;;) {
801	>	if (w.eventCount != v)
802		return true;
803	+	if (!rescanned) {
804	+	int g = scanGuard, m = g & SMASK;
805	+	ForkJoinWorkerThread[] ws = workers;
806	+	if (ws != null && m < ws.length) {
807	+	rescanned = true;
808	+	for (int i = 0; i <= m; ++i) {
809	+	ForkJoinWorkerThread u = ws[i];
810	+	if (u != null) {
811	+	if (u.queueBase != u.queueTop &&
812	+	!tryReleaseWaiter())
813	+	rescanned = false; // contended
814	+	if (w.eventCount != v)
815	+	return true;
816	+	}
817	+	}
818	+	}
819	+	if (scanGuard != g ||              // stale
820	+	(queueBase != queueTop && !tryReleaseWaiter()))
821	+	rescanned = false;
822	+	if (!rescanned)
823	+	Thread.yield();                // reduce contention
824	+	else
825	+	Thread.interrupted();          // clear before park
826	+	}
827	+	else {
828	+	w.parked = true;                   // must recheck
829	+	if (w.eventCount != v) {
830	+	w.parked = false;
831	+	return true;
832	+	}
833	+	LockSupport.park(this);
834	+	rescanned = w.parked = false;
835	+	}
836		}
837		}
838
839		/**
840	<	* Controls whether to add spares to maintain parallelism
841	<	*/
842	<	private volatile boolean maintainsParallelism;
840	>	* If inactivating worker w has caused pool to become
841	>	* quiescent, check for pool termination, and wait for event
842	>	* for up to SHRINK_RATE nanosecs (rescans are unnecessary in
843	>	* this case because quiescence reflects consensus about lack
844	>	* of work). On timeout, if ctl has not changed, terminate the
845	>	* worker. Upon its termination (see deregisterWorker), it may
846	>	* wake up another worker to possibly repeat this process.
847	>	*
848	>	* @param w the calling worker
849	>	* @param currentCtl the ctl value after enqueuing w
850	>	* @param prevCtl the ctl value if w terminated
851	>	* @param v the eventCount w awaits change
852	>	*/
853	>	private void idleAwaitWork(ForkJoinWorkerThread w, long currentCtl,
854	>	long prevCtl, int v) {
855	>	if (w.eventCount == v) {
856	>	if (shutdown)
857	>	tryTerminate(false);
858	>	ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs
859	>	while (ctl == currentCtl) {
860	>	long startTime = System.nanoTime();
861	>	w.parked = true;
862	>	if (w.eventCount == v)             // must recheck
863	>	LockSupport.parkNanos(this, SHRINK_RATE);
864	>	w.parked = false;
865	>	if (w.eventCount != v)
866	>	break;
867	>	else if (System.nanoTime() - startTime < SHRINK_RATE)
868	>	Thread.interrupted();          // spurious wakeup
869	>	else if (UNSAFE.compareAndSwapLong(this, ctlOffset,
870	>	currentCtl, prevCtl)) {
871	>	w.terminate = true;            // restore previous
872	>	w.eventCount = ((int)currentCtl + EC_UNIT) & E_MASK;
873	>	break;
874	>	}
875	>	}
876	>	}
877	>	}
878
879	<	// Constructors
879	>	// Submissions
880
881		/**
882	<	* Creates a ForkJoinPool with a pool size equal to the number of
883	<	* processors available on the system, using the default
348	<	* ForkJoinWorkerThreadFactory.
882	>	* Enqueues the given task in the submissionQueue.  Same idea as
883	>	* ForkJoinWorkerThread.pushTask except for use of submissionLock.
884		*
885	<	* @throws SecurityException if a security manager exists and
351	<	*         the caller is not permitted to modify threads
352	<	*         because it does not hold {@link
353	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
885	>	* @param t the task
886		*/
887	<	public ForkJoinPool() {
888	<	this(Runtime.getRuntime().availableProcessors(),
889	<	defaultForkJoinWorkerThreadFactory);
887	>	private void addSubmission(ForkJoinTask<?> t) {
888	>	final ReentrantLock lock = this.submissionLock;
889	>	lock.lock();
890	>	try {
891	>	ForkJoinTask<?>[] q; int s, m;
892	>	if ((q = submissionQueue) != null) {    // ignore if queue removed
893	>	long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE;
894	>	UNSAFE.putOrderedObject(q, u, t);
895	>	queueTop = s + 1;
896	>	if (s - queueBase == m)
897	>	growSubmissionQueue();
898	>	}
899	>	} finally {
900	>	lock.unlock();
901	>	}
902	>	signalWork();
903		}
904
905	+	//  (pollSubmission is defined below with exported methods)
906	+
907		/**
908	<	* Creates a ForkJoinPool with the indicated parallelism level
909	<	* threads and using the default ForkJoinWorkerThreadFactory.
363	<	*
364	<	* @param parallelism the number of worker threads
365	<	* @throws IllegalArgumentException if parallelism less than or
366	<	* equal to zero
367	<	* @throws SecurityException if a security manager exists and
368	<	*         the caller is not permitted to modify threads
369	<	*         because it does not hold {@link
370	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
908	>	* Creates or doubles submissionQueue array.
909	>	* Basically identical to ForkJoinWorkerThread version.
910		*/
911	<	public ForkJoinPool(int parallelism) {
912	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
911	>	private void growSubmissionQueue() {
912	>	ForkJoinTask<?>[] oldQ = submissionQueue;
913	>	int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY;
914	>	if (size > MAXIMUM_QUEUE_CAPACITY)
915	>	throw new RejectedExecutionException("Queue capacity exceeded");
916	>	if (size < INITIAL_QUEUE_CAPACITY)
917	>	size = INITIAL_QUEUE_CAPACITY;
918	>	ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size];
919	>	int mask = size - 1;
920	>	int top = queueTop;
921	>	int oldMask;
922	>	if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) {
923	>	for (int b = queueBase; b != top; ++b) {
924	>	long u = ((b & oldMask) << ASHIFT) + ABASE;
925	>	Object x = UNSAFE.getObjectVolatile(oldQ, u);
926	>	if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null))
927	>	UNSAFE.putObjectVolatile
928	>	(q, ((b & mask) << ASHIFT) + ABASE, x);
929	>	}
930	>	}
931	>	}
932	>
933	>	// Blocking support
934	>
935	>	/**
936	>	* Tries to increment blockedCount, decrement active count
937	>	* (sometimes implicitly) and possibly release or create a
938	>	* compensating worker in preparation for blocking. Fails
939	>	* on contention or termination.
940	>	*
941	>	* @return true if the caller can block, else should recheck and retry
942	>	*/
943	>	private boolean tryPreBlock() {
944	>	int b = blockedCount;
945	>	if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) {
946	>	int pc = parallelism;
947	>	do {
948	>	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
949	>	int e, ac, tc, rc, i;
950	>	long c = ctl;
951	>	int u = (int)(c >>> 32);
952	>	if ((e = (int)c) < 0) {
953	>	// skip -- terminating
954	>	}
955	>	else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 &&
956	>	(ws = workers) != null &&
957	>	(i = ~e & SMASK) < ws.length &&
958	>	(w = ws[i]) != null) {
959	>	long nc = ((long)(w.nextWait & E_MASK) |
960	>	(c & (AC_MASK|TC_MASK)));
961	>	if (w.eventCount == e &&
962	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
963	>	w.eventCount = (e + EC_UNIT) & E_MASK;
964	>	if (w.parked)
965	>	UNSAFE.unpark(w);
966	>	return true;             // release an idle worker
967	>	}
968	>	}
969	>	else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
970	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
971	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
972	>	return true;             // no compensation needed
973	>	}
974	>	else if (tc + pc < MAX_ID) {
975	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
976	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
977	>	addWorker();
978	>	return true;            // create a replacement
979	>	}
980	>	}
981	>	// try to back out on any failure and let caller retry
982	>	} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
983	>	b = blockedCount, b - 1));
984	>	}
985	>	return false;
986		}
987
988		/**
989	<	* Creates a ForkJoinPool with parallelism equal to the number of
378	<	* processors available on the system and using the given
379	<	* ForkJoinWorkerThreadFactory.
380	<	*
381	<	* @param factory the factory for creating new threads
382	<	* @throws NullPointerException if factory is null
383	<	* @throws SecurityException if a security manager exists and
384	<	*         the caller is not permitted to modify threads
385	<	*         because it does not hold {@link
386	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
989	>	* Decrements blockedCount and increments active count
990		*/
991	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
992	<	this(Runtime.getRuntime().availableProcessors(), factory);
991	>	private void postBlock() {
992	>	long c;
993	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset,  // no mask
994	>	c = ctl, c + AC_UNIT));
995	>	int b;
996	>	do {} while(!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
997	>	b = blockedCount, b - 1));
998		}
999
1000		/**
1001	<	* Creates a ForkJoinPool with the given parallelism and factory.
1001	>	* Possibly blocks waiting for the given task to complete, or
1002	>	* cancels the task if terminating.  Fails to wait if contended.
1003		*
1004	<	* @param parallelism the targeted number of worker threads
396	<	* @param factory the factory for creating new threads
397	<	* @throws IllegalArgumentException if parallelism less than or
398	<	* equal to zero, or greater than implementation limit
399	<	* @throws NullPointerException if factory is null
400	<	* @throws SecurityException if a security manager exists and
401	<	*         the caller is not permitted to modify threads
402	<	*         because it does not hold {@link
403	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1004	>	* @param joinMe the task
1005		*/
1006	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
1007	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1008	<	throw new IllegalArgumentException();
1009	<	if (factory == null)
1010	<	throw new NullPointerException();
1011	<	checkPermission();
1012	<	this.factory = factory;
1013	<	this.parallelism = parallelism;
1014	<	this.maxPoolSize = MAX_THREADS;
1015	<	this.maintainsParallelism = true;
1016	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
416	<	this.workerLock = new ReentrantLock();
417	<	this.termination = workerLock.newCondition();
418	<	this.stealCount = new AtomicLong();
419	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
420	<	// worker array and workers are lazily constructed
1006	>	final void tryAwaitJoin(ForkJoinTask<?> joinMe) {
1007	>	int s;
1008	>	Thread.interrupted(); // clear interrupts before checking termination
1009	>	if (joinMe.status >= 0) {
1010	>	if (tryPreBlock()) {
1011	>	joinMe.tryAwaitDone(0L);
1012	>	postBlock();
1013	>	}
1014	>	else if ((ctl & STOP_BIT) != 0L)
1015	>	joinMe.cancelIgnoringExceptions();
1016	>	}
1017		}
1018
1019		/**
1020	<	* Creates a new worker thread using factory.
1020	>	* Possibly blocks the given worker waiting for joinMe to
1021	>	* complete or timeout
1022		*
1023	<	* @param index the index to assign worker
1024	<	* @return new worker, or null of factory failed
1023	>	* @param joinMe the task
1024	>	* @param millis the wait time for underlying Object.wait
1025		*/
1026	<	private ForkJoinWorkerThread createWorker(int index) {
1027	<	Thread.UncaughtExceptionHandler h = ueh;
1028	<	ForkJoinWorkerThread w = factory.newThread(this);
1029	<	if (w != null) {
1030	<	w.poolIndex = index;
1031	<	w.setDaemon(true);
1032	<	w.setAsyncMode(locallyFifo);
1033	<	w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
1034	<	if (h != null)
1035	<	w.setUncaughtExceptionHandler(h);
1026	>	final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) {
1027	>	while (joinMe.status >= 0) {
1028	>	Thread.interrupted();
1029	>	if ((ctl & STOP_BIT) != 0L) {
1030	>	joinMe.cancelIgnoringExceptions();
1031	>	break;
1032	>	}
1033	>	if (tryPreBlock()) {
1034	>	long last = System.nanoTime();
1035	>	while (joinMe.status >= 0) {
1036	>	long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
1037	>	if (millis <= 0)
1038	>	break;
1039	>	joinMe.tryAwaitDone(millis);
1040	>	if (joinMe.status < 0)
1041	>	break;
1042	>	if ((ctl & STOP_BIT) != 0L) {
1043	>	joinMe.cancelIgnoringExceptions();
1044	>	break;
1045	>	}
1046	>	long now = System.nanoTime();
1047	>	nanos -= now - last;
1048	>	last = now;
1049	>	}
1050	>	postBlock();
1051	>	break;
1052	>	}
1053		}
440	–	return w;
1054		}
1055
1056		/**
1057	<	* Returns a good size for worker array given pool size.
445	<	* Currently requires size to be a power of two.
1057	>	* If necessary, compensates for blocker, and blocks
1058		*/
1059	<	private static int arraySizeFor(int poolSize) {
1060	<	return (poolSize <= 1) ? 1 :
1061	<	(1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
1059	>	private void awaitBlocker(ManagedBlocker blocker)
1060	>	throws InterruptedException {
1061	>	while (!blocker.isReleasable()) {
1062	>	if (tryPreBlock()) {
1063	>	try {
1064	>	do {} while (!blocker.isReleasable() && !blocker.block());
1065	>	} finally {
1066	>	postBlock();
1067	>	}
1068	>	break;
1069	>	}
1070	>	}
1071		}
1072
1073	+	// Creating, registering and deregistring workers
1074	+
1075		/**
1076	<	* Creates or resizes array if necessary to hold newLength.
1077	<	* Call only under exclusion.
455	<	*
456	<	* @return the array
1076	>	* Tries to create and start a worker; minimally rolls back counts
1077	>	* on failure.
1078		*/
1079	<	private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
1080	<	ForkJoinWorkerThread[] ws = workers;
1081	<	if (ws == null)
1082	<	return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
1083	<	else if (newLength > ws.length)
1084	<	return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
1079	>	private void addWorker() {
1080	>	Throwable ex = null;
1081	>	ForkJoinWorkerThread t = null;
1082	>	try {
1083	>	t = factory.newThread(this);
1084	>	} catch (Throwable e) {
1085	>	ex = e;
1086	>	}
1087	>	if (t == null) {  // null or exceptional factory return
1088	>	long c;       // adjust counts
1089	>	do {} while (!UNSAFE.compareAndSwapLong
1090	>	(this, ctlOffset, c = ctl,
1091	>	(((c - AC_UNIT) & AC_MASK) |
1092	>	((c - TC_UNIT) & TC_MASK) |
1093	>	(c & ~(AC_MASK|TC_MASK)))));
1094	>	// Propagate exception if originating from an external caller
1095	>	if (!tryTerminate(false) && ex != null &&
1096	>	!(Thread.currentThread() instanceof ForkJoinWorkerThread))
1097	>	UNSAFE.throwException(ex);
1098	>	}
1099		else
1100	<	return ws;
1100	>	t.start();
1101		}
1102
1103		/**
1104	<	* Tries to shrink workers into smaller array after one or more terminate.
1104	>	* Callback from ForkJoinWorkerThread constructor to assign a
1105	>	* public name
1106		*/
1107	<	private void tryShrinkWorkerArray() {
1108	<	ForkJoinWorkerThread[] ws = workers;
1109	<	if (ws != null) {
1110	<	int len = ws.length;
1111	<	int last = len - 1;
476	<	while (last >= 0 && ws[last] == null)
477	<	--last;
478	<	int newLength = arraySizeFor(last+1);
479	<	if (newLength < len)
480	<	workers = Arrays.copyOf(ws, newLength);
1107	>	final String nextWorkerName() {
1108	>	for (int n;;) {
1109	>	if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset,
1110	>	n = nextWorkerNumber, ++n))
1111	>	return workerNamePrefix + n;
1112		}
1113		}
1114
1115		/**
1116	<	* Initializes workers if necessary.
1116	>	* Callback from ForkJoinWorkerThread constructor to
1117	>	* determine its poolIndex and record in workers array.
1118	>	*
1119	>	* @param w the worker
1120	>	* @return the worker's pool index
1121		*/
1122	<	final void ensureWorkerInitialization() {
1123	<	ForkJoinWorkerThread[] ws = workers;
1124	<	if (ws == null) {
1125	<	final ReentrantLock lock = this.workerLock;
1126	<	lock.lock();
1127	<	try {
1128	<	ws = workers;
1129	<	if (ws == null) {
1130	<	int ps = parallelism;
1131	<	ws = ensureWorkerArrayCapacity(ps);
1132	<	for (int i = 0; i < ps; ++i) {
1133	<	ForkJoinWorkerThread w = createWorker(i);
1134	<	if (w != null) {
1135	<	ws[i] = w;
1136	<	w.start();
1137	<	updateWorkerCount(1);
1122	>	final int registerWorker(ForkJoinWorkerThread w) {
1123	>	/*
1124	>	* In the typical case, a new worker acquires the lock, uses
1125	>	* next available index and returns quickly.  Since we should
1126	>	* not block callers (ultimately from signalWork or
1127	>	* tryPreBlock) waiting for the lock needed to do this, we
1128	>	* instead help release other workers while waiting for the
1129	>	* lock.
1130	>	*/
1131	>	for (int g;;) {
1132	>	ForkJoinWorkerThread[] ws;
1133	>	if (((g = scanGuard) & SG_UNIT) == 0 &&
1134	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1135	>	g, g | SG_UNIT)) {
1136	>	int k = nextWorkerIndex;
1137	>	try {
1138	>	if ((ws = workers) != null) { // ignore on shutdown
1139	>	int n = ws.length;
1140	>	if (k < 0 || k >= n || ws[k] != null) {
1141	>	for (k = 0; k < n && ws[k] != null; ++k)
1142	>	;
1143	>	if (k == n)
1144	>	ws = workers = Arrays.copyOf(ws, n << 1);
1145		}
1146	+	ws[k] = w;
1147	+	nextWorkerIndex = k + 1;
1148	+	int m = g & SMASK;
1149	+	g = k >= m? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1);
1150	+	}
1151	+	} finally {
1152	+	scanGuard = g;
1153	+	}
1154	+	return k;
1155	+	}
1156	+	else if ((ws = workers) != null) { // help release others
1157	+	for (ForkJoinWorkerThread u : ws) {
1158	+	if (u != null && u.queueBase != u.queueTop) {
1159	+	if (tryReleaseWaiter())
1160	+	break;
1161		}
1162		}
1163	+	}
1164	+	}
1165	+	}
1166	+
1167	+	/**
1168	+	* Final callback from terminating worker.  Removes record of
1169	+	* worker from array, and adjusts counts. If pool is shutting
1170	+	* down, tries to complete termination.
1171	+	*
1172	+	* @param w the worker
1173	+	*/
1174	+	final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) {
1175	+	int idx = w.poolIndex;
1176	+	int sc = w.stealCount;
1177	+	int steps = 0;
1178	+	// Remove from array, adjust worker counts and collect steal count.
1179	+	// We can intermix failed removes or adjusts with steal updates
1180	+	do {
1181	+	long s, c;
1182	+	int g;
1183	+	if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 &&
1184	+	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1185	+	g, g |= SG_UNIT)) {
1186	+	ForkJoinWorkerThread[] ws = workers;
1187	+	if (ws != null && idx >= 0 &&
1188	+	idx < ws.length && ws[idx] == w)
1189	+	ws[idx] = null;    // verify
1190	+	nextWorkerIndex = idx;
1191	+	scanGuard = g + SG_UNIT;
1192	+	steps = 1;
1193	+	}
1194	+	if (steps == 1 &&
1195	+	UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1196	+	(((c - AC_UNIT) & AC_MASK) |
1197	+	((c - TC_UNIT) & TC_MASK) |
1198	+	(c & ~(AC_MASK|TC_MASK)))))
1199	+	steps = 2;
1200	+	if (sc != 0 &&
1201	+	UNSAFE.compareAndSwapLong(this, stealCountOffset,
1202	+	s = stealCount, s + sc))
1203	+	sc = 0;
1204	+	} while (steps != 2 || sc != 0);
1205	+	if (!tryTerminate(false)) {
1206	+	if (ex != null)   // possibly replace if died abnormally
1207	+	signalWork();
1208	+	else
1209	+	tryReleaseWaiter();
1210	+	}
1211	+	}
1212	+
1213	+	// Shutdown and termination
1214	+
1215	+	/**
1216	+	* Possibly initiates and/or completes termination.
1217	+	*
1218	+	* @param now if true, unconditionally terminate, else only
1219	+	* if shutdown and empty queue and no active workers
1220	+	* @return true if now terminating or terminated
1221	+	*/
1222	+	private boolean tryTerminate(boolean now) {
1223	+	long c;
1224	+	while (((c = ctl) & STOP_BIT) == 0) {
1225	+	if (!now) {
1226	+	if ((int)(c >> AC_SHIFT) != -parallelism)
1227	+	return false;
1228	+	if (!shutdown || blockedCount != 0 || quiescerCount != 0 ||
1229	+	queueBase != queueTop) {
1230	+	if (ctl == c) // staleness check
1231	+	return false;
1232	+	continue;
1233	+	}
1234	+	}
1235	+	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT))
1236	+	startTerminating();
1237	+	}
1238	+	if ((short)(c >>> TC_SHIFT) == -parallelism) { // signal when 0 workers
1239	+	final ReentrantLock lock = this.submissionLock;
1240	+	lock.lock();
1241	+	try {
1242	+	termination.signalAll();
1243		} finally {
1244		lock.unlock();
1245		}
1246		}
1247	+	return true;
1248		}
1249
1250		/**
1251	<	* Worker creation and startup for threads added via setParallelism.
1252	<	*/
1253	<	private void createAndStartAddedWorkers() {
1254	<	resumeAllSpares();  // Allow spares to convert to nonspare
1255	<	int ps = parallelism;
1256	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
1257	<	int len = ws.length;
1258	<	// Sweep through slots, to keep lowest indices most populated
1259	<	int k = 0;
1260	<	while (k < len) {
1261	<	if (ws[k] != null) {
1262	<	++k;
1263	<	continue;
1251	>	* Runs up to three passes through workers: (0) Setting
1252	>	* termination status for each worker, followed by wakeups up to
1253	>	* queued workers; (1) helping cancel tasks; (2) interrupting
1254	>	* lagging threads (likely in external tasks, but possibly also
1255	>	* blocked in joins).  Each pass repeats previous steps because of
1256	>	* potential lagging thread creation.
1257	>	*/
1258	>	private void startTerminating() {
1259	>	cancelSubmissions();
1260	>	for (int pass = 0; pass < 3; ++pass) {
1261	>	ForkJoinWorkerThread[] ws = workers;
1262	>	if (ws != null) {
1263	>	for (ForkJoinWorkerThread w : ws) {
1264	>	if (w != null) {
1265	>	w.terminate = true;
1266	>	if (pass > 0) {
1267	>	w.cancelTasks();
1268	>	if (pass > 1 && !w.isInterrupted()) {
1269	>	try {
1270	>	w.interrupt();
1271	>	} catch (SecurityException ignore) {
1272	>	}
1273	>	}
1274	>	}
1275	>	}
1276	>	}
1277	>	terminateWaiters();
1278		}
1279	<	int s = workerCounts;
1280	<	int tc = totalCountOf(s);
1281	<	int rc = runningCountOf(s);
1282	<	if (rc >= ps || tc >= ps)
1283	<	break;
1284	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
1285	<	ForkJoinWorkerThread w = createWorker(k);
1286	<	if (w != null) {
1287	<	ws[k++] = w;
1288	<	w.start();
1279	>	}
1280	>	}
1281	>
1282	>	/**
1283	>	* Polls and cancels all submissions. Called only during termination.
1284	>	*/
1285	>	private void cancelSubmissions() {
1286	>	while (queueBase != queueTop) {
1287	>	ForkJoinTask<?> task = pollSubmission();
1288	>	if (task != null) {
1289	>	try {
1290	>	task.cancel(false);
1291	>	} catch (Throwable ignore) {
1292		}
1293	<	else {
1294	<	updateWorkerCount(-1); // back out on failed creation
1295	<	break;
1293	>	}
1294	>	}
1295	>	}
1296	>
1297	>	/**
1298	>	* Tries to set the termination status of waiting workers, and
1299	>	* then wakes them up (after which they will terminate).
1300	>	*/
1301	>	private void terminateWaiters() {
1302	>	ForkJoinWorkerThread[] ws = workers;
1303	>	if (ws != null) {
1304	>	ForkJoinWorkerThread w; long c; int i, e;
1305	>	int n = ws.length;
1306	>	while ((i = ~(e = (int)(c = ctl)) & SMASK) < n &&
1307	>	(w = ws[i]) != null && w.eventCount == (e & E_MASK)) {
1308	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c,
1309	>	(long)(w.nextWait & E_MASK) |
1310	>	((c + AC_UNIT) & AC_MASK) |
1311	>	(c & (TC_MASK|STOP_BIT)))) {
1312	>	w.terminate = true;
1313	>	w.eventCount = e + EC_UNIT;
1314	>	if (w.parked)
1315	>	UNSAFE.unpark(w);
1316		}
1317		}
1318		}
1319		}
1320
1321	<	// Execution methods
1321	>	// misc ForkJoinWorkerThread support
1322
1323		/**
1324	<	* Common code for execute, invoke and submit
1324	>	* Increment or decrement quiescerCount. Needed only to prevent
1325	>	* triggering shutdown if a worker is transiently inactive while
1326	>	* checking quiescence.
1327	>	*
1328	>	* @param delta 1 for increment, -1 for decrement
1329		*/
1330	<	private <T> void doSubmit(ForkJoinTask<T> task) {
1331	<	if (task == null)
1330	>	final void addQuiescerCount(int delta) {
1331	>	int c;
1332	>	do {} while(!UNSAFE.compareAndSwapInt(this, quiescerCountOffset,
1333	>	c = quiescerCount, c + delta));
1334	>	}
1335	>
1336	>	/**
1337	>	* Directly increment or decrement active count without
1338	>	* queuing. This method is used to transiently assert inactivation
1339	>	* while checking quiescence.
1340	>	*
1341	>	* @param delta 1 for increment, -1 for decrement
1342	>	*/
1343	>	final void addActiveCount(int delta) {
1344	>	long d = delta < 0 ? -AC_UNIT : AC_UNIT;
1345	>	long c;
1346	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1347	>	((c + d) & AC_MASK) |
1348	>	(c & ~AC_MASK)));
1349	>	}
1350	>
1351	>	/**
1352	>	* Returns the approximate (non-atomic) number of idle threads per
1353	>	* active thread.
1354	>	*/
1355	>	final int idlePerActive() {
1356	>	// Approximate at powers of two for small values, saturate past 4
1357	>	int p = parallelism;
1358	>	int a = p + (int)(ctl >> AC_SHIFT);
1359	>	return (a > (p >>>= 1) ? 0 :
1360	>	a > (p >>>= 1) ? 1 :
1361	>	a > (p >>>= 1) ? 2 :
1362	>	a > (p >>>= 1) ? 4 :
1363	>	8);
1364	>	}
1365	>
1366	>	// Exported methods
1367	>
1368	>	// Constructors
1369	>
1370	>	/**
1371	>	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1372	>	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1373	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1374	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1375	>	*
1376	>	* @throws SecurityException if a security manager exists and
1377	>	*         the caller is not permitted to modify threads
1378	>	*         because it does not hold {@link
1379	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1380	>	*/
1381	>	public ForkJoinPool() {
1382	>	this(Runtime.getRuntime().availableProcessors(),
1383	>	defaultForkJoinWorkerThreadFactory, null, false);
1384	>	}
1385	>
1386	>	/**
1387	>	* Creates a {@code ForkJoinPool} with the indicated parallelism
1388	>	* level, the {@linkplain
1389	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1390	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1391	>	*
1392	>	* @param parallelism the parallelism level
1393	>	* @throws IllegalArgumentException if parallelism less than or
1394	>	*         equal to zero, or greater than implementation limit
1395	>	* @throws SecurityException if a security manager exists and
1396	>	*         the caller is not permitted to modify threads
1397	>	*         because it does not hold {@link
1398	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1399	>	*/
1400	>	public ForkJoinPool(int parallelism) {
1401	>	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1402	>	}
1403	>
1404	>	/**
1405	>	* Creates a {@code ForkJoinPool} with the given parameters.
1406	>	*
1407	>	* @param parallelism the parallelism level. For default value,
1408	>	* use {@link java.lang.Runtime#availableProcessors}.
1409	>	* @param factory the factory for creating new threads. For default value,
1410	>	* use {@link #defaultForkJoinWorkerThreadFactory}.
1411	>	* @param handler the handler for internal worker threads that
1412	>	* terminate due to unrecoverable errors encountered while executing
1413	>	* tasks. For default value, use {@code null}.
1414	>	* @param asyncMode if true,
1415	>	* establishes local first-in-first-out scheduling mode for forked
1416	>	* tasks that are never joined. This mode may be more appropriate
1417	>	* than default locally stack-based mode in applications in which
1418	>	* worker threads only process event-style asynchronous tasks.
1419	>	* For default value, use {@code false}.
1420	>	* @throws IllegalArgumentException if parallelism less than or
1421	>	*         equal to zero, or greater than implementation limit
1422	>	* @throws NullPointerException if the factory is null
1423	>	* @throws SecurityException if a security manager exists and
1424	>	*         the caller is not permitted to modify threads
1425	>	*         because it does not hold {@link
1426	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1427	>	*/
1428	>	public ForkJoinPool(int parallelism,
1429	>	ForkJoinWorkerThreadFactory factory,
1430	>	Thread.UncaughtExceptionHandler handler,
1431	>	boolean asyncMode) {
1432	>	checkPermission();
1433	>	if (factory == null)
1434		throw new NullPointerException();
1435	<	if (isShutdown())
1436	<	throw new RejectedExecutionException();
1437	<	if (workers == null)
1438	<	ensureWorkerInitialization();
1439	<	submissionQueue.offer(task);
1440	<	signalIdleWorkers();
1435	>	if (parallelism <= 0 || parallelism > MAX_ID)
1436	>	throw new IllegalArgumentException();
1437	>	this.parallelism = parallelism;
1438	>	this.factory = factory;
1439	>	this.ueh = handler;
1440	>	this.locallyFifo = asyncMode;
1441	>	long np = (long)(-parallelism); // offset ctl counts
1442	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
1443	>	this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
1444	>	// initialize workers array with room for 2*parallelism if possible
1445	>	int n = parallelism << 1;
1446	>	if (n >= MAX_ID)
1447	>	n = MAX_ID;
1448	>	else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
1449	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
1450	>	}
1451	>	workers = new ForkJoinWorkerThread[n + 1];
1452	>	this.submissionLock = new ReentrantLock();
1453	>	this.termination = submissionLock.newCondition();
1454	>	StringBuilder sb = new StringBuilder("ForkJoinPool-");
1455	>	sb.append(poolNumberGenerator.incrementAndGet());
1456	>	sb.append("-worker-");
1457	>	this.workerNamePrefix = sb.toString();
1458		}
1459
1460	+	// Execution methods
1461	+
1462		/**
1463		* Performs the given task, returning its result upon completion.
1464	+	* If the computation encounters an unchecked Exception or Error,
1465	+	* it is rethrown as the outcome of this invocation.  Rethrown
1466	+	* exceptions behave in the same way as regular exceptions, but,
1467	+	* when possible, contain stack traces (as displayed for example
1468	+	* using {@code ex.printStackTrace()}) of both the current thread
1469	+	* as well as the thread actually encountering the exception;
1470	+	* minimally only the latter.
1471		*
1472		* @param task the task
1473		* @return the task's result
1474	<	* @throws NullPointerException if task is null
1475	<	* @throws RejectedExecutionException if pool is shut down
1474	>	* @throws NullPointerException if the task is null
1475	>	* @throws RejectedExecutionException if the task cannot be
1476	>	*         scheduled for execution
1477		*/
1478		public <T> T invoke(ForkJoinTask<T> task) {
1479	<	doSubmit(task);
1480	<	return task.join();
1479	>	Thread t = Thread.currentThread();
1480	>	if (task == null)
1481	>	throw new NullPointerException();
1482	>	if (shutdown)
1483	>	throw new RejectedExecutionException();
1484	>	if ((t instanceof ForkJoinWorkerThread) &&
1485	>	((ForkJoinWorkerThread)t).pool == this)
1486	>	return task.invoke();  // bypass submit if in same pool
1487	>	else {
1488	>	addSubmission(task);
1489	>	return task.join();
1490	>	}
1491	>	}
1492	>
1493	>	/**
1494	>	* Unless terminating, forks task if within an ongoing FJ
1495	>	* computation in the current pool, else submits as external task.
1496	>	*/
1497	>	private <T> void forkOrSubmit(ForkJoinTask<T> task) {
1498	>	ForkJoinWorkerThread w;
1499	>	Thread t = Thread.currentThread();
1500	>	if (shutdown)
1501	>	throw new RejectedExecutionException();
1502	>	if ((t instanceof ForkJoinWorkerThread) &&
1503	>	(w = (ForkJoinWorkerThread)t).pool == this)
1504	>	w.pushTask(task);
1505	>	else
1506	>	addSubmission(task);
1507		}
1508
1509		/**
1510		* Arranges for (asynchronous) execution of the given task.
1511		*
1512		* @param task the task
1513	<	* @throws NullPointerException if task is null
1514	<	* @throws RejectedExecutionException if pool is shut down
1513	>	* @throws NullPointerException if the task is null
1514	>	* @throws RejectedExecutionException if the task cannot be
1515	>	*         scheduled for execution
1516		*/
1517		public void execute(ForkJoinTask<?> task) {
1518	<	doSubmit(task);
1518	>	if (task == null)
1519	>	throw new NullPointerException();
1520	>	forkOrSubmit(task);
1521		}
1522
1523		// AbstractExecutorService methods
1524
1525	+	/**
1526	+	* @throws NullPointerException if the task is null
1527	+	* @throws RejectedExecutionException if the task cannot be
1528	+	*         scheduled for execution
1529	+	*/
1530		public void execute(Runnable task) {
1531	+	if (task == null)
1532	+	throw new NullPointerException();
1533		ForkJoinTask<?> job;
1534		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1535		job = (ForkJoinTask<?>) task;
1536		else
1537		job = ForkJoinTask.adapt(task, null);
1538	<	doSubmit(job);
1538	>	forkOrSubmit(job);
1539	>	}
1540	>
1541	>	/**
1542	>	* Submits a ForkJoinTask for execution.
1543	>	*
1544	>	* @param task the task to submit
1545	>	* @return the task
1546	>	* @throws NullPointerException if the task is null
1547	>	* @throws RejectedExecutionException if the task cannot be
1548	>	*         scheduled for execution
1549	>	*/
1550	>	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1551	>	if (task == null)
1552	>	throw new NullPointerException();
1553	>	forkOrSubmit(task);
1554	>	return task;
1555		}
1556
1557	+	/**
1558	+	* @throws NullPointerException if the task is null
1559	+	* @throws RejectedExecutionException if the task cannot be
1560	+	*         scheduled for execution
1561	+	*/
1562		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1563	+	if (task == null)
1564	+	throw new NullPointerException();
1565		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1566	<	doSubmit(job);
1566	>	forkOrSubmit(job);
1567		return job;
1568		}
1569
1570	+	/**
1571	+	* @throws NullPointerException if the task is null
1572	+	* @throws RejectedExecutionException if the task cannot be
1573	+	*         scheduled for execution
1574	+	*/
1575		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1576	+	if (task == null)
1577	+	throw new NullPointerException();
1578		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1579	<	doSubmit(job);
1579	>	forkOrSubmit(job);
1580		return job;
1581		}
1582
1583	+	/**
1584	+	* @throws NullPointerException if the task is null
1585	+	* @throws RejectedExecutionException if the task cannot be
1586	+	*         scheduled for execution
1587	+	*/
1588		public ForkJoinTask<?> submit(Runnable task) {
1589	+	if (task == null)
1590	+	throw new NullPointerException();
1591		ForkJoinTask<?> job;
1592		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1593		job = (ForkJoinTask<?>) task;
1594		else
1595		job = ForkJoinTask.adapt(task, null);
1596	<	doSubmit(job);
1596	>	forkOrSubmit(job);
1597		return job;
1598		}
1599
1600		/**
1601	<	* Submits a ForkJoinTask for execution.
1602	<	*
622	<	* @param task the task to submit
623	<	* @return the task
624	<	* @throws RejectedExecutionException if the task cannot be
625	<	*         scheduled for execution
626	<	* @throws NullPointerException if the task is null
1601	>	* @throws NullPointerException       {@inheritDoc}
1602	>	* @throws RejectedExecutionException {@inheritDoc}
1603		*/
628	–	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
629	–	doSubmit(task);
630	–	return task;
631	–	}
632	–
633	–
1604		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
1605		ArrayList<ForkJoinTask<T>> forkJoinTasks =
1606		new ArrayList<ForkJoinTask<T>>(tasks.size());
#	Line 639 | Line 1609 | public class ForkJoinPool extends Abstra
1609		invoke(new InvokeAll<T>(forkJoinTasks));
1610
1611		@SuppressWarnings({"unchecked", "rawtypes"})
1612	<	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1612	>	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1613		return futures;
1614		}
1615
#	Line 653 | Line 1623 | public class ForkJoinPool extends Abstra
1623		private static final long serialVersionUID = -7914297376763021607L;
1624		}
1625
656	–	// Configuration and status settings and queries
657	–
1626		/**
1627		* Returns the factory used for constructing new workers.
1628		*
#	Line 671 | Line 1639 | public class ForkJoinPool extends Abstra
1639		* @return the handler, or {@code null} if none
1640		*/
1641		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1642	<	Thread.UncaughtExceptionHandler h;
675	<	final ReentrantLock lock = this.workerLock;
676	<	lock.lock();
677	<	try {
678	<	h = ueh;
679	<	} finally {
680	<	lock.unlock();
681	<	}
682	<	return h;
1642	>	return ueh;
1643		}
1644
1645		/**
1646	<	* Sets the handler for internal worker threads that terminate due
687	<	* to unrecoverable errors encountered while executing tasks.
688	<	* Unless set, the current default or ThreadGroup handler is used
689	<	* as handler.
1646	>	* Returns the targeted parallelism level of this pool.
1647		*
1648	<	* @param h the new handler
692	<	* @return the old handler, or {@code null} if none
693	<	* @throws SecurityException if a security manager exists and
694	<	*         the caller is not permitted to modify threads
695	<	*         because it does not hold {@link
696	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
697	<	*/
698	<	public Thread.UncaughtExceptionHandler
699	<	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
700	<	checkPermission();
701	<	Thread.UncaughtExceptionHandler old = null;
702	<	final ReentrantLock lock = this.workerLock;
703	<	lock.lock();
704	<	try {
705	<	old = ueh;
706	<	ueh = h;
707	<	ForkJoinWorkerThread[] ws = workers;
708	<	if (ws != null) {
709	<	for (int i = 0; i < ws.length; ++i) {
710	<	ForkJoinWorkerThread w = ws[i];
711	<	if (w != null)
712	<	w.setUncaughtExceptionHandler(h);
713	<	}
714	<	}
715	<	} finally {
716	<	lock.unlock();
717	<	}
718	<	return old;
719	<	}
720	<
721	<
722	<	/**
723	<	* Sets the target parallelism level of this pool.
724	<	*
725	<	* @param parallelism the target parallelism
726	<	* @throws IllegalArgumentException if parallelism less than or
727	<	* equal to zero or greater than maximum size bounds
728	<	* @throws SecurityException if a security manager exists and
729	<	*         the caller is not permitted to modify threads
730	<	*         because it does not hold {@link
731	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
732	<	*/
733	<	public void setParallelism(int parallelism) {
734	<	checkPermission();
735	<	if (parallelism <= 0 || parallelism > maxPoolSize)
736	<	throw new IllegalArgumentException();
737	<	final ReentrantLock lock = this.workerLock;
738	<	lock.lock();
739	<	try {
740	<	if (!isTerminating()) {
741	<	int p = this.parallelism;
742	<	this.parallelism = parallelism;
743	<	if (parallelism > p)
744	<	createAndStartAddedWorkers();
745	<	else
746	<	trimSpares();
747	<	}
748	<	} finally {
749	<	lock.unlock();
750	<	}
751	<	signalIdleWorkers();
752	<	}
753	<
754	<	/**
755	<	* Returns the targeted number of worker threads in this pool.
756	<	*
757	<	* @return the targeted number of worker threads in this pool
1648	>	* @return the targeted parallelism level of this pool
1649		*/
1650		public int getParallelism() {
1651		return parallelism;
#	Line 762 | Line 1653 | public class ForkJoinPool extends Abstra
1653
1654		/**
1655		* Returns the number of worker threads that have started but not
1656	<	* yet terminated.  This result returned by this method may differ
1656	>	* yet terminated.  The result returned by this method may differ
1657		* from {@link #getParallelism} when threads are created to
1658		* maintain parallelism when others are cooperatively blocked.
1659		*
1660		* @return the number of worker threads
1661		*/
1662		public int getPoolSize() {
1663	<	return totalCountOf(workerCounts);
773	<	}
774	<
775	<	/**
776	<	* Returns the maximum number of threads allowed to exist in the
777	<	* pool, even if there are insufficient unblocked running threads.
778	<	*
779	<	* @return the maximum
780	<	*/
781	<	public int getMaximumPoolSize() {
782	<	return maxPoolSize;
783	<	}
784	<
785	<	/**
786	<	* Sets the maximum number of threads allowed to exist in the
787	<	* pool, even if there are insufficient unblocked running threads.
788	<	* Setting this value has no effect on current pool size. It
789	<	* controls construction of new threads.
790	<	*
791	<	* @throws IllegalArgumentException if negative or greater than
792	<	* internal implementation limit
793	<	*/
794	<	public void setMaximumPoolSize(int newMax) {
795	<	if (newMax < 0 || newMax > MAX_THREADS)
796	<	throw new IllegalArgumentException();
797	<	maxPoolSize = newMax;
798	<	}
799	<
800	<
801	<	/**
802	<	* Returns {@code true} if this pool dynamically maintains its
803	<	* target parallelism level. If false, new threads are added only
804	<	* to avoid possible starvation.  This setting is by default true.
805	<	*
806	<	* @return {@code true} if maintains parallelism
807	<	*/
808	<	public boolean getMaintainsParallelism() {
809	<	return maintainsParallelism;
810	<	}
811	<
812	<	/**
813	<	* Sets whether this pool dynamically maintains its target
814	<	* parallelism level. If false, new threads are added only to
815	<	* avoid possible starvation.
816	<	*
817	<	* @param enable {@code true} to maintain parallelism
818	<	*/
819	<	public void setMaintainsParallelism(boolean enable) {
820	<	maintainsParallelism = enable;
821	<	}
822	<
823	<	/**
824	<	* Establishes local first-in-first-out scheduling mode for forked
825	<	* tasks that are never joined. This mode may be more appropriate
826	<	* than default locally stack-based mode in applications in which
827	<	* worker threads only process asynchronous tasks.  This method is
828	<	* designed to be invoked only when the pool is quiescent, and
829	<	* typically only before any tasks are submitted. The effects of
830	<	* invocations at other times may be unpredictable.
831	<	*
832	<	* @param async if {@code true}, use locally FIFO scheduling
833	<	* @return the previous mode
834	<	* @see #getAsyncMode
835	<	*/
836	<	public boolean setAsyncMode(boolean async) {
837	<	boolean oldMode = locallyFifo;
838	<	locallyFifo = async;
839	<	ForkJoinWorkerThread[] ws = workers;
840	<	if (ws != null) {
841	<	for (int i = 0; i < ws.length; ++i) {
842	<	ForkJoinWorkerThread t = ws[i];
843	<	if (t != null)
844	<	t.setAsyncMode(async);
845	<	}
846	<	}
847	<	return oldMode;
1663	>	return parallelism + (short)(ctl >>> TC_SHIFT);
1664		}
1665
1666		/**
#	Line 852 | Line 1668 | public class ForkJoinPool extends Abstra
1668		* scheduling mode for forked tasks that are never joined.
1669		*
1670		* @return {@code true} if this pool uses async mode
855	–	* @see #setAsyncMode
1671		*/
1672		public boolean getAsyncMode() {
1673		return locallyFifo;
#	Line 861 | Line 1676 | public class ForkJoinPool extends Abstra
1676		/**
1677		* Returns an estimate of the number of worker threads that are
1678		* not blocked waiting to join tasks or for other managed
1679	<	* synchronization.
1679	>	* synchronization. This method may overestimate the
1680	>	* number of running threads.
1681		*
1682		* @return the number of worker threads
1683		*/
1684		public int getRunningThreadCount() {
1685	<	return runningCountOf(workerCounts);
1685	>	int r = parallelism + (int)(ctl >> AC_SHIFT);
1686	>	return r <= 0? 0 : r; // suppress momentarily negative values
1687		}
1688
1689		/**
#	Line 877 | Line 1694 | public class ForkJoinPool extends Abstra
1694		* @return the number of active threads
1695		*/
1696		public int getActiveThreadCount() {
1697	<	return activeCountOf(runControl);
1698	<	}
882	<
883	<	/**
884	<	* Returns an estimate of the number of threads that are currently
885	<	* idle waiting for tasks. This method may underestimate the
886	<	* number of idle threads.
887	<	*
888	<	* @return the number of idle threads
889	<	*/
890	<	final int getIdleThreadCount() {
891	<	int c = runningCountOf(workerCounts) - activeCountOf(runControl);
892	<	return (c <= 0) ? 0 : c;
1697	>	int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount;
1698	>	return r <= 0? 0 : r; // suppress momentarily negative values
1699		}
1700
1701		/**
#	Line 904 | Line 1710 | public class ForkJoinPool extends Abstra
1710		* @return {@code true} if all threads are currently idle
1711		*/
1712		public boolean isQuiescent() {
1713	<	return activeCountOf(runControl) == 0;
1713	>	return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0;
1714		}
1715
1716		/**
#	Line 919 | Line 1725 | public class ForkJoinPool extends Abstra
1725		* @return the number of steals
1726		*/
1727		public long getStealCount() {
1728	<	return stealCount.get();
923	<	}
924	<
925	<	/**
926	<	* Accumulates steal count from a worker.
927	<	* Call only when worker known to be idle.
928	<	*/
929	<	private void updateStealCount(ForkJoinWorkerThread w) {
930	<	int sc = w.getAndClearStealCount();
931	<	if (sc != 0)
932	<	stealCount.addAndGet(sc);
1728	>	return stealCount;
1729		}
1730
1731		/**
#	Line 944 | Line 1740 | public class ForkJoinPool extends Abstra
1740		*/
1741		public long getQueuedTaskCount() {
1742		long count = 0;
1743	<	ForkJoinWorkerThread[] ws = workers;
1744	<	if (ws != null) {
1745	<	for (int i = 0; i < ws.length; ++i) {
1746	<	ForkJoinWorkerThread t = ws[i];
1747	<	if (t != null)
1748	<	count += t.getQueueSize();
953	<	}
1743	>	ForkJoinWorkerThread[] ws;
1744	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1745	>	(ws = workers) != null) {
1746	>	for (ForkJoinWorkerThread w : ws)
1747	>	if (w != null)
1748	>	count -= w.queueBase - w.queueTop; // must read base first
1749		}
1750		return count;
1751		}
1752
1753		/**
1754		* Returns an estimate of the number of tasks submitted to this
1755	<	* pool that have not yet begun executing.  This method takes time
1756	<	* proportional to the number of submissions.
1755	>	* pool that have not yet begun executing.  This method may take
1756	>	* time proportional to the number of submissions.
1757		*
1758		* @return the number of queued submissions
1759		*/
1760		public int getQueuedSubmissionCount() {
1761	<	return submissionQueue.size();
1761	>	return -queueBase + queueTop;
1762		}
1763
1764		/**
#	Line 973 | Line 1768 | public class ForkJoinPool extends Abstra
1768		* @return {@code true} if there are any queued submissions
1769		*/
1770		public boolean hasQueuedSubmissions() {
1771	<	return !submissionQueue.isEmpty();
1771	>	return queueBase != queueTop;
1772		}
1773
1774		/**
#	Line 984 | Line 1779 | public class ForkJoinPool extends Abstra
1779		* @return the next submission, or {@code null} if none
1780		*/
1781		protected ForkJoinTask<?> pollSubmission() {
1782	<	return submissionQueue.poll();
1782	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
1783	>	while ((b = queueBase) != queueTop &&
1784	>	(q = submissionQueue) != null &&
1785	>	(i = (q.length - 1) & b) >= 0) {
1786	>	long u = (i << ASHIFT) + ABASE;
1787	>	if ((t = q[i]) != null &&
1788	>	queueBase == b &&
1789	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1790	>	queueBase = b + 1;
1791	>	return t;
1792	>	}
1793	>	}
1794	>	return null;
1795		}
1796
1797		/**
1798		* Removes all available unexecuted submitted and forked tasks
1799		* from scheduling queues and adds them to the given collection,
1800		* without altering their execution status. These may include
1801	<	* artificially generated or wrapped tasks. This method is designed
1802	<	* to be invoked only when the pool is known to be
1801	>	* artificially generated or wrapped tasks. This method is
1802	>	* designed to be invoked only when the pool is known to be
1803		* quiescent. Invocations at other times may not remove all
1804		* tasks. A failure encountered while attempting to add elements
1805		* to collection {@code c} may result in elements being in
#	Line 1005 | Line 1812 | public class ForkJoinPool extends Abstra
1812		* @return the number of elements transferred
1813		*/
1814		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1815	<	int n = submissionQueue.drainTo(c);
1816	<	ForkJoinWorkerThread[] ws = workers;
1817	<	if (ws != null) {
1818	<	for (int i = 0; i < ws.length; ++i) {
1819	<	ForkJoinWorkerThread w = ws[i];
1820	<	if (w != null)
1014	<	n += w.drainTasksTo(c);
1815	>	int count = 0;
1816	>	while (queueBase != queueTop) {
1817	>	ForkJoinTask<?> t = pollSubmission();
1818	>	if (t != null) {
1819	>	c.add(t);
1820	>	++count;
1821		}
1822		}
1823	<	return n;
1823	>	ForkJoinWorkerThread[] ws;
1824	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1825	>	(ws = workers) != null) {
1826	>	for (ForkJoinWorkerThread w : ws)
1827	>	if (w != null)
1828	>	count += w.drainTasksTo(c);
1829	>	}
1830	>	return count;
1831		}
1832
1833		/**
#	Line 1025 | Line 1838 | public class ForkJoinPool extends Abstra
1838		* @return a string identifying this pool, as well as its state
1839		*/
1840		public String toString() {
1028	–	int ps = parallelism;
1029	–	int wc = workerCounts;
1030	–	int rc = runControl;
1841		long st = getStealCount();
1842		long qt = getQueuedTaskCount();
1843		long qs = getQueuedSubmissionCount();
1844	+	int pc = parallelism;
1845	+	long c = ctl;
1846	+	int tc = pc + (short)(c >>> TC_SHIFT);
1847	+	int rc = pc + (int)(c >> AC_SHIFT);
1848	+	if (rc < 0) // ignore transient negative
1849	+	rc = 0;
1850	+	int ac = rc + blockedCount;
1851	+	String level;
1852	+	if ((c & STOP_BIT) != 0)
1853	+	level = (tc == 0)? "Terminated" : "Terminating";
1854	+	else
1855	+	level = shutdown? "Shutting down" : "Running";
1856		return super.toString() +
1857	<	"[" + runStateToString(runStateOf(rc)) +
1858	<	", parallelism = " + ps +
1859	<	", size = " + totalCountOf(wc) +
1860	<	", active = " + activeCountOf(rc) +
1861	<	", running = " + runningCountOf(wc) +
1857	>	"[" + level +
1858	>	", parallelism = " + pc +
1859	>	", size = " + tc +
1860	>	", active = " + ac +
1861	>	", running = " + rc +
1862		", steals = " + st +
1863		", tasks = " + qt +
1864		", submissions = " + qs +
1865		"]";
1866		}
1867
1046	–	private static String runStateToString(int rs) {
1047	–	switch(rs) {
1048	–	case RUNNING: return "Running";
1049	–	case SHUTDOWN: return "Shutting down";
1050	–	case TERMINATING: return "Terminating";
1051	–	case TERMINATED: return "Terminated";
1052	–	default: throw new Error("Unknown run state");
1053	–	}
1054	–	}
1055	–
1056	–	// lifecycle control
1057	–
1868		/**
1869		* Initiates an orderly shutdown in which previously submitted
1870		* tasks are executed, but no new tasks will be accepted.
#	Line 1069 | Line 1879 | public class ForkJoinPool extends Abstra
1879		*/
1880		public void shutdown() {
1881		checkPermission();
1882	<	transitionRunStateTo(SHUTDOWN);
1883	<	if (canTerminateOnShutdown(runControl)) {
1074	<	if (workers == null) { // shutting down before workers created
1075	<	final ReentrantLock lock = this.workerLock;
1076	<	lock.lock();
1077	<	try {
1078	<	if (workers == null) {
1079	<	terminate();
1080	<	transitionRunStateTo(TERMINATED);
1081	<	termination.signalAll();
1082	<	}
1083	<	} finally {
1084	<	lock.unlock();
1085	<	}
1086	<	}
1087	<	terminateOnShutdown();
1088	<	}
1882	>	shutdown = true;
1883	>	tryTerminate(false);
1884		}
1885
1886		/**
1887	<	* Attempts to stop all actively executing tasks, and cancels all
1888	<	* waiting tasks.  Tasks that are in the process of being
1889	<	* submitted or executed concurrently during the course of this
1890	<	* method may or may not be rejected. Unlike some other executors,
1891	<	* this method cancels rather than collects non-executed tasks
1892	<	* upon termination, so always returns an empty list. However, you
1893	<	* can use method {@link #drainTasksTo} before invoking this
1894	<	* method to transfer unexecuted tasks to another collection.
1887	>	* Attempts to cancel and/or stop all tasks, and reject all
1888	>	* subsequently submitted tasks.  Tasks that are in the process of
1889	>	* being submitted or executed concurrently during the course of
1890	>	* this method may or may not be rejected. This method cancels
1891	>	* both existing and unexecuted tasks, in order to permit
1892	>	* termination in the presence of task dependencies. So the method
1893	>	* always returns an empty list (unlike the case for some other
1894	>	* Executors).
1895		*
1896		* @return an empty list
1897		* @throws SecurityException if a security manager exists and
#	Line 1106 | Line 1901 | public class ForkJoinPool extends Abstra
1901		*/
1902		public List<Runnable> shutdownNow() {
1903		checkPermission();
1904	<	terminate();
1904	>	shutdown = true;
1905	>	tryTerminate(true);
1906		return Collections.emptyList();
1907		}
1908
#	Line 1116 | Line 1912 | public class ForkJoinPool extends Abstra
1912		* @return {@code true} if all tasks have completed following shut down
1913		*/
1914		public boolean isTerminated() {
1915	<	return runStateOf(runControl) == TERMINATED;
1915	>	long c = ctl;
1916	>	return ((c & STOP_BIT) != 0L &&
1917	>	(short)(c >>> TC_SHIFT) == -parallelism);
1918		}
1919
1920		/**
1921		* Returns {@code true} if the process of termination has
1922	<	* commenced but possibly not yet completed.
1922	>	* commenced but not yet completed.  This method may be useful for
1923	>	* debugging. A return of {@code true} reported a sufficient
1924	>	* period after shutdown may indicate that submitted tasks have
1925	>	* ignored or suppressed interruption, or are waiting for IO,
1926	>	* causing this executor not to properly terminate. (See the
1927	>	* advisory notes for class {@link ForkJoinTask} stating that
1928	>	* tasks should not normally entail blocking operations.  But if
1929	>	* they do, they must abort them on interrupt.)
1930		*
1931	<	* @return {@code true} if terminating
1931	>	* @return {@code true} if terminating but not yet terminated
1932		*/
1933		public boolean isTerminating() {
1934	<	return runStateOf(runControl) >= TERMINATING;
1934	>	long c = ctl;
1935	>	return ((c & STOP_BIT) != 0L &&
1936	>	(short)(c >>> TC_SHIFT) != -parallelism);
1937	>	}
1938	>
1939	>	/**
1940	>	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1941	>	*/
1942	>	final boolean isAtLeastTerminating() {
1943	>	return (ctl & STOP_BIT) != 0L;
1944		}
1945
1946		/**
#	Line 1135 | Line 1949 | public class ForkJoinPool extends Abstra
1949		* @return {@code true} if this pool has been shut down
1950		*/
1951		public boolean isShutdown() {
1952	<	return runStateOf(runControl) >= SHUTDOWN;
1952	>	return shutdown;
1953		}
1954
1955		/**
#	Line 1152 | Line 1966 | public class ForkJoinPool extends Abstra
1966		public boolean awaitTermination(long timeout, TimeUnit unit)
1967		throws InterruptedException {
1968		long nanos = unit.toNanos(timeout);
1969	<	final ReentrantLock lock = this.workerLock;
1969	>	final ReentrantLock lock = this.submissionLock;
1970		lock.lock();
1971		try {
1972		for (;;) {
#	Line 1167 | Line 1981 | public class ForkJoinPool extends Abstra
1981		}
1982		}
1983
1170	–	// Shutdown and termination support
1171	–
1172	–	/**
1173	–	* Callback from terminating worker. Nulls out the corresponding
1174	–	* workers slot, and if terminating, tries to terminate; else
1175	–	* tries to shrink workers array.
1176	–	*
1177	–	* @param w the worker
1178	–	*/
1179	–	final void workerTerminated(ForkJoinWorkerThread w) {
1180	–	updateStealCount(w);
1181	–	updateWorkerCount(-1);
1182	–	final ReentrantLock lock = this.workerLock;
1183	–	lock.lock();
1184	–	try {
1185	–	ForkJoinWorkerThread[] ws = workers;
1186	–	if (ws != null) {
1187	–	int idx = w.poolIndex;
1188	–	if (idx >= 0 && idx < ws.length && ws[idx] == w)
1189	–	ws[idx] = null;
1190	–	if (totalCountOf(workerCounts) == 0) {
1191	–	terminate(); // no-op if already terminating
1192	–	transitionRunStateTo(TERMINATED);
1193	–	termination.signalAll();
1194	–	}
1195	–	else if (!isTerminating()) {
1196	–	tryShrinkWorkerArray();
1197	–	tryResumeSpare(true); // allow replacement
1198	–	}
1199	–	}
1200	–	} finally {
1201	–	lock.unlock();
1202	–	}
1203	–	signalIdleWorkers();
1204	–	}
1205	–
1206	–	/**
1207	–	* Initiates termination.
1208	–	*/
1209	–	private void terminate() {
1210	–	if (transitionRunStateTo(TERMINATING)) {
1211	–	stopAllWorkers();
1212	–	resumeAllSpares();
1213	–	signalIdleWorkers();
1214	–	cancelQueuedSubmissions();
1215	–	cancelQueuedWorkerTasks();
1216	–	interruptUnterminatedWorkers();
1217	–	signalIdleWorkers(); // resignal after interrupt
1218	–	}
1219	–	}
1220	–
1221	–	/**
1222	–	* Possibly terminates when on shutdown state.
1223	–	*/
1224	–	private void terminateOnShutdown() {
1225	–	if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
1226	–	terminate();
1227	–	}
1228	–
1229	–	/**
1230	–	* Clears out and cancels submissions.
1231	–	*/
1232	–	private void cancelQueuedSubmissions() {
1233	–	ForkJoinTask<?> task;
1234	–	while ((task = pollSubmission()) != null)
1235	–	task.cancel(false);
1236	–	}
1237	–
1238	–	/**
1239	–	* Cleans out worker queues.
1240	–	*/
1241	–	private void cancelQueuedWorkerTasks() {
1242	–	final ReentrantLock lock = this.workerLock;
1243	–	lock.lock();
1244	–	try {
1245	–	ForkJoinWorkerThread[] ws = workers;
1246	–	if (ws != null) {
1247	–	for (int i = 0; i < ws.length; ++i) {
1248	–	ForkJoinWorkerThread t = ws[i];
1249	–	if (t != null)
1250	–	t.cancelTasks();
1251	–	}
1252	–	}
1253	–	} finally {
1254	–	lock.unlock();
1255	–	}
1256	–	}
1257	–
1258	–	/**
1259	–	* Sets each worker's status to terminating. Requires lock to avoid
1260	–	* conflicts with add/remove.
1261	–	*/
1262	–	private void stopAllWorkers() {
1263	–	final ReentrantLock lock = this.workerLock;
1264	–	lock.lock();
1265	–	try {
1266	–	ForkJoinWorkerThread[] ws = workers;
1267	–	if (ws != null) {
1268	–	for (int i = 0; i < ws.length; ++i) {
1269	–	ForkJoinWorkerThread t = ws[i];
1270	–	if (t != null)
1271	–	t.shutdownNow();
1272	–	}
1273	–	}
1274	–	} finally {
1275	–	lock.unlock();
1276	–	}
1277	–	}
1278	–
1279	–	/**
1280	–	* Interrupts all unterminated workers.  This is not required for
1281	–	* sake of internal control, but may help unstick user code during
1282	–	* shutdown.
1283	–	*/
1284	–	private void interruptUnterminatedWorkers() {
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 && !t.isTerminated()) {
1293	–	try {
1294	–	t.interrupt();
1295	–	} catch (SecurityException ignore) {
1296	–	}
1297	–	}
1298	–	}
1299	–	}
1300	–	} finally {
1301	–	lock.unlock();
1302	–	}
1303	–	}
1304	–
1305	–
1306	–	/*
1307	–	* Nodes for event barrier to manage idle threads.  Queue nodes
1308	–	* are basic Treiber stack nodes, also used for spare stack.
1309	–	*
1310	–	* The event barrier has an event count and a wait queue (actually
1311	–	* a Treiber stack).  Workers are enabled to look for work when
1312	–	* the eventCount is incremented. If they fail to find work, they
1313	–	* may wait for next count. Upon release, threads help others wake
1314	–	* up.
1315	–	*
1316	–	* Synchronization events occur only in enough contexts to
1317	–	* maintain overall liveness:
1318	–	*
1319	–	*   - Submission of a new task to the pool
1320	–	*   - Resizes or other changes to the workers array
1321	–	*   - pool termination
1322	–	*   - A worker pushing a task on an empty queue
1323	–	*
1324	–	* The case of pushing a task occurs often enough, and is heavy
1325	–	* enough compared to simple stack pushes, to require special
1326	–	* handling: Method signalWork returns without advancing count if
1327	–	* the queue appears to be empty.  This would ordinarily result in
1328	–	* races causing some queued waiters not to be woken up. To avoid
1329	–	* this, the first worker enqueued in method sync (see
1330	–	* syncIsReleasable) rescans for tasks after being enqueued, and
1331	–	* helps signal if any are found. This works well because the
1332	–	* worker has nothing better to do, and so might as well help
1333	–	* alleviate the overhead and contention on the threads actually
1334	–	* doing work.  Also, since event counts increments on task
1335	–	* availability exist to maintain liveness (rather than to force
1336	–	* refreshes etc), it is OK for callers to exit early if
1337	–	* contending with another signaller.
1338	–	*/
1339	–	static final class WaitQueueNode {
1340	–	WaitQueueNode next; // only written before enqueued
1341	–	volatile ForkJoinWorkerThread thread; // nulled to cancel wait
1342	–	final long count; // unused for spare stack
1343	–
1344	–	WaitQueueNode(long c, ForkJoinWorkerThread w) {
1345	–	count = c;
1346	–	thread = w;
1347	–	}
1348	–
1349	–	/**
1350	–	* Wakes up waiter, returning false if known to already
1351	–	*/
1352	–	boolean signal() {
1353	–	ForkJoinWorkerThread t = thread;
1354	–	if (t == null)
1355	–	return false;
1356	–	thread = null;
1357	–	LockSupport.unpark(t);
1358	–	return true;
1359	–	}
1360	–
1361	–	/**
1362	–	* Awaits release on sync.
1363	–	*/
1364	–	void awaitSyncRelease(ForkJoinPool p) {
1365	–	while (thread != null && !p.syncIsReleasable(this))
1366	–	LockSupport.park(this);
1367	–	}
1368	–
1369	–	/**
1370	–	* Awaits resumption as spare.
1371	–	*/
1372	–	void awaitSpareRelease() {
1373	–	while (thread != null) {
1374	–	if (!Thread.interrupted())
1375	–	LockSupport.park(this);
1376	–	}
1377	–	}
1378	–	}
1379	–
1380	–	/**
1381	–	* Ensures that no thread is waiting for count to advance from the
1382	–	* current value of eventCount read on entry to this method, by
1383	–	* releasing waiting threads if necessary.
1384	–	*
1385	–	* @return the count
1386	–	*/
1387	–	final long ensureSync() {
1388	–	long c = eventCount;
1389	–	WaitQueueNode q;
1390	–	while ((q = syncStack) != null && q.count < c) {
1391	–	if (casBarrierStack(q, null)) {
1392	–	do {
1393	–	q.signal();
1394	–	} while ((q = q.next) != null);
1395	–	break;
1396	–	}
1397	–	}
1398	–	return c;
1399	–	}
1400	–
1401	–	/**
1402	–	* Increments event count and releases waiting threads.
1403	–	*/
1404	–	private void signalIdleWorkers() {
1405	–	long c;
1406	–	do {} while (!casEventCount(c = eventCount, c+1));
1407	–	ensureSync();
1408	–	}
1409	–
1410	–	/**
1411	–	* Signals threads waiting to poll a task. Because method sync
1412	–	* rechecks availability, it is OK to only proceed if queue
1413	–	* appears to be non-empty, and OK to skip under contention to
1414	–	* increment count (since some other thread succeeded).
1415	–	*/
1416	–	final void signalWork() {
1417	–	long c;
1418	–	WaitQueueNode q;
1419	–	if (syncStack != null &&
1420	–	casEventCount(c = eventCount, c+1) &&
1421	–	(((q = syncStack) != null && q.count <= c) &&
1422	–	(!casBarrierStack(q, q.next) || !q.signal())))
1423	–	ensureSync();
1424	–	}
1425	–
1426	–	/**
1427	–	* Waits until event count advances from last value held by
1428	–	* caller, or if excess threads, caller is resumed as spare, or
1429	–	* caller or pool is terminating. Updates caller's event on exit.
1430	–	*
1431	–	* @param w the calling worker thread
1432	–	*/
1433	–	final void sync(ForkJoinWorkerThread w) {
1434	–	updateStealCount(w); // Transfer w's count while it is idle
1435	–
1436	–	while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
1437	–	long prev = w.lastEventCount;
1438	–	WaitQueueNode node = null;
1439	–	WaitQueueNode h;
1440	–	while (eventCount == prev &&
1441	–	((h = syncStack) == null || h.count == prev)) {
1442	–	if (node == null)
1443	–	node = new WaitQueueNode(prev, w);
1444	–	if (casBarrierStack(node.next = h, node)) {
1445	–	node.awaitSyncRelease(this);
1446	–	break;
1447	–	}
1448	–	}
1449	–	long ec = ensureSync();
1450	–	if (ec != prev) {
1451	–	w.lastEventCount = ec;
1452	–	break;
1453	–	}
1454	–	}
1455	–	}
1456	–
1457	–	/**
1458	–	* Returns {@code true} if worker waiting on sync can proceed:
1459	–	*  - on signal (thread == null)
1460	–	*  - on event count advance (winning race to notify vs signaller)
1461	–	*  - on interrupt
1462	–	*  - if the first queued node, we find work available
1463	–	* If node was not signalled and event count not advanced on exit,
1464	–	* then we also help advance event count.
1465	–	*
1466	–	* @return {@code true} if node can be released
1467	–	*/
1468	–	final boolean syncIsReleasable(WaitQueueNode node) {
1469	–	long prev = node.count;
1470	–	if (!Thread.interrupted() && node.thread != null &&
1471	–	(node.next != null ||
1472	–	!ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
1473	–	eventCount == prev)
1474	–	return false;
1475	–	if (node.thread != null) {
1476	–	node.thread = null;
1477	–	long ec = eventCount;
1478	–	if (prev <= ec) // help signal
1479	–	casEventCount(ec, ec+1);
1480	–	}
1481	–	return true;
1482	–	}
1483	–
1484	–	/**
1485	–	* Returns {@code true} if a new sync event occurred since last
1486	–	* call to sync or this method, if so, updating caller's count.
1487	–	*/
1488	–	final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1489	–	long lc = w.lastEventCount;
1490	–	long ec = ensureSync();
1491	–	if (ec == lc)
1492	–	return false;
1493	–	w.lastEventCount = ec;
1494	–	return true;
1495	–	}
1496	–
1497	–	//  Parallelism maintenance
1498	–
1499	–	/**
1500	–	* Decrements running count; if too low, adds spare.
1501	–	*
1502	–	* Conceptually, all we need to do here is add or resume a
1503	–	* spare thread when one is about to block (and remove or
1504	–	* suspend it later when unblocked -- see suspendIfSpare).
1505	–	* However, implementing this idea requires coping with
1506	–	* several problems: we have imperfect information about the
1507	–	* states of threads. Some count updates can and usually do
1508	–	* lag run state changes, despite arrangements to keep them
1509	–	* accurate (for example, when possible, updating counts
1510	–	* before signalling or resuming), especially when running on
1511	–	* dynamic JVMs that don't optimize the infrequent paths that
1512	–	* update counts. Generating too many threads can make these
1513	–	* problems become worse, because excess threads are more
1514	–	* likely to be context-switched with others, slowing them all
1515	–	* down, especially if there is no work available, so all are
1516	–	* busy scanning or idling.  Also, excess spare threads can
1517	–	* only be suspended or removed when they are idle, not
1518	–	* immediately when they aren't needed. So adding threads will
1519	–	* raise parallelism level for longer than necessary.  Also,
1520	–	* FJ applications often encounter highly transient peaks when
1521	–	* many threads are blocked joining, but for less time than it
1522	–	* takes to create or resume spares.
1523	–	*
1524	–	* @param joinMe if non-null, return early if done
1525	–	* @param maintainParallelism if true, try to stay within
1526	–	* target counts, else create only to avoid starvation
1527	–	* @return true if joinMe known to be done
1528	–	*/
1529	–	final boolean preJoin(ForkJoinTask<?> joinMe,
1530	–	boolean maintainParallelism) {
1531	–	maintainParallelism &= maintainsParallelism; // overrride
1532	–	boolean dec = false;  // true when running count decremented
1533	–	while (spareStack == null || !tryResumeSpare(dec)) {
1534	–	int counts = workerCounts;
1535	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1536	–	// CAS cheat
1537	–	if (!needSpare(counts, maintainParallelism))
1538	–	break;
1539	–	if (joinMe.status < 0)
1540	–	return true;
1541	–	if (tryAddSpare(counts))
1542	–	break;
1543	–	}
1544	–	}
1545	–	return false;
1546	–	}
1547	–
1548	–	/**
1549	–	* Same idea as preJoin
1550	–	*/
1551	–	final boolean preBlock(ManagedBlocker blocker,
1552	–	boolean maintainParallelism) {
1553	–	maintainParallelism &= maintainsParallelism;
1554	–	boolean dec = false;
1555	–	while (spareStack == null || !tryResumeSpare(dec)) {
1556	–	int counts = workerCounts;
1557	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1558	–	if (!needSpare(counts, maintainParallelism))
1559	–	break;
1560	–	if (blocker.isReleasable())
1561	–	return true;
1562	–	if (tryAddSpare(counts))
1563	–	break;
1564	–	}
1565	–	}
1566	–	return false;
1567	–	}
1568	–
1569	–	/**
1570	–	* Returns {@code true} if a spare thread appears to be needed.
1571	–	* If maintaining parallelism, returns true when the deficit in
1572	–	* running threads is more than the surplus of total threads, and
1573	–	* there is apparently some work to do.  This self-limiting rule
1574	–	* means that the more threads that have already been added, the
1575	–	* less parallelism we will tolerate before adding another.
1576	–	*
1577	–	* @param counts current worker counts
1578	–	* @param maintainParallelism try to maintain parallelism
1579	–	*/
1580	–	private boolean needSpare(int counts, boolean maintainParallelism) {
1581	–	int ps = parallelism;
1582	–	int rc = runningCountOf(counts);
1583	–	int tc = totalCountOf(counts);
1584	–	int runningDeficit = ps - rc;
1585	–	int totalSurplus = tc - ps;
1586	–	return (tc < maxPoolSize &&
1587	–	(rc == 0 || totalSurplus < 0 ||
1588	–	(maintainParallelism &&
1589	–	runningDeficit > totalSurplus &&
1590	–	ForkJoinWorkerThread.hasQueuedTasks(workers))));
1591	–	}
1592	–
1593	–	/**
1594	–	* Adds a spare worker if lock available and no more than the
1595	–	* expected numbers of threads exist.
1596	–	*
1597	–	* @return true if successful
1598	–	*/
1599	–	private boolean tryAddSpare(int expectedCounts) {
1600	–	final ReentrantLock lock = this.workerLock;
1601	–	int expectedRunning = runningCountOf(expectedCounts);
1602	–	int expectedTotal = totalCountOf(expectedCounts);
1603	–	boolean success = false;
1604	–	boolean locked = false;
1605	–	// confirm counts while locking; CAS after obtaining lock
1606	–	try {
1607	–	for (;;) {
1608	–	int s = workerCounts;
1609	–	int tc = totalCountOf(s);
1610	–	int rc = runningCountOf(s);
1611	–	if (rc > expectedRunning || tc > expectedTotal)
1612	–	break;
1613	–	if (!locked && !(locked = lock.tryLock()))
1614	–	break;
1615	–	if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
1616	–	createAndStartSpare(tc);
1617	–	success = true;
1618	–	break;
1619	–	}
1620	–	}
1621	–	} finally {
1622	–	if (locked)
1623	–	lock.unlock();
1624	–	}
1625	–	return success;
1626	–	}
1627	–
1628	–	/**
1629	–	* Adds the kth spare worker. On entry, pool counts are already
1630	–	* adjusted to reflect addition.
1631	–	*/
1632	–	private void createAndStartSpare(int k) {
1633	–	ForkJoinWorkerThread w = null;
1634	–	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
1635	–	int len = ws.length;
1636	–	// Probably, we can place at slot k. If not, find empty slot
1637	–	if (k < len && ws[k] != null) {
1638	–	for (k = 0; k < len && ws[k] != null; ++k)
1639	–	;
1640	–	}
1641	–	if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
1642	–	ws[k] = w;
1643	–	w.start();
1644	–	}
1645	–	else
1646	–	updateWorkerCount(-1); // adjust on failure
1647	–	signalIdleWorkers();
1648	–	}
1649	–
1650	–	/**
1651	–	* Suspends calling thread w if there are excess threads.  Called
1652	–	* only from sync.  Spares are enqueued in a Treiber stack using
1653	–	* the same WaitQueueNodes as barriers.  They are resumed mainly
1654	–	* in preJoin, but are also woken on pool events that require all
1655	–	* threads to check run state.
1656	–	*
1657	–	* @param w the caller
1658	–	*/
1659	–	private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1660	–	WaitQueueNode node = null;
1661	–	int s;
1662	–	while (parallelism < runningCountOf(s = workerCounts)) {
1663	–	if (node == null)
1664	–	node = new WaitQueueNode(0, w);
1665	–	if (casWorkerCounts(s, s-1)) { // representation-dependent
1666	–	// push onto stack
1667	–	do {} while (!casSpareStack(node.next = spareStack, node));
1668	–	// block until released by resumeSpare
1669	–	node.awaitSpareRelease();
1670	–	return true;
1671	–	}
1672	–	}
1673	–	return false;
1674	–	}
1675	–
1676	–	/**
1677	–	* Tries to pop and resume a spare thread.
1678	–	*
1679	–	* @param updateCount if true, increment running count on success
1680	–	* @return true if successful
1681	–	*/
1682	–	private boolean tryResumeSpare(boolean updateCount) {
1683	–	WaitQueueNode q;
1684	–	while ((q = spareStack) != null) {
1685	–	if (casSpareStack(q, q.next)) {
1686	–	if (updateCount)
1687	–	updateRunningCount(1);
1688	–	q.signal();
1689	–	return true;
1690	–	}
1691	–	}
1692	–	return false;
1693	–	}
1694	–
1695	–	/**
1696	–	* Pops and resumes all spare threads. Same idea as ensureSync.
1697	–	*
1698	–	* @return true if any spares released
1699	–	*/
1700	–	private boolean resumeAllSpares() {
1701	–	WaitQueueNode q;
1702	–	while ( (q = spareStack) != null) {
1703	–	if (casSpareStack(q, null)) {
1704	–	do {
1705	–	updateRunningCount(1);
1706	–	q.signal();
1707	–	} while ((q = q.next) != null);
1708	–	return true;
1709	–	}
1710	–	}
1711	–	return false;
1712	–	}
1713	–
1714	–	/**
1715	–	* Pops and shuts down excessive spare threads. Call only while
1716	–	* holding lock. This is not guaranteed to eliminate all excess
1717	–	* threads, only those suspended as spares, which are the ones
1718	–	* unlikely to be needed in the future.
1719	–	*/
1720	–	private void trimSpares() {
1721	–	int surplus = totalCountOf(workerCounts) - parallelism;
1722	–	WaitQueueNode q;
1723	–	while (surplus > 0 && (q = spareStack) != null) {
1724	–	if (casSpareStack(q, null)) {
1725	–	do {
1726	–	updateRunningCount(1);
1727	–	ForkJoinWorkerThread w = q.thread;
1728	–	if (w != null && surplus > 0 &&
1729	–	runningCountOf(workerCounts) > 0 && w.shutdown())
1730	–	--surplus;
1731	–	q.signal();
1732	–	} while ((q = q.next) != null);
1733	–	}
1734	–	}
1735	–	}
1736	–
1984		/**
1985		* Interface for extending managed parallelism for tasks running
1986		* in {@link ForkJoinPool}s.
1987		*
1988	<	* <p>A {@code ManagedBlocker} provides two methods.
1989	<	* Method {@code isReleasable} must return {@code true} if
1990	<	* blocking is not necessary. Method {@code block} blocks the
1991	<	* current thread if necessary (perhaps internally invoking
1992	<	* {@code isReleasable} before actually blocking).
1988	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1989	>	* {@code isReleasable} must return {@code true} if blocking is
1990	>	* not necessary. Method {@code block} blocks the current thread
1991	>	* if necessary (perhaps internally invoking {@code isReleasable}
1992	>	* before actually blocking). These actions are performed by any
1993	>	* thread invoking {@link ForkJoinPool#managedBlock}.  The
1994	>	* unusual methods in this API accommodate synchronizers that may,
1995	>	* but don't usually, block for long periods. Similarly, they
1996	>	* allow more efficient internal handling of cases in which
1997	>	* additional workers may be, but usually are not, needed to
1998	>	* ensure sufficient parallelism.  Toward this end,
1999	>	* implementations of method {@code isReleasable} must be amenable
2000	>	* to repeated invocation.
2001		*
2002		* <p>For example, here is a ManagedBlocker based on a
2003		* ReentrantLock:
#	Line 1760 | Line 2015 | public class ForkJoinPool extends Abstra
2015		*     return hasLock || (hasLock = lock.tryLock());
2016		*   }
2017		* }}</pre>
2018	+	*
2019	+	* <p>Here is a class that possibly blocks waiting for an
2020	+	* item on a given queue:
2021	+	*  <pre> {@code
2022	+	* class QueueTaker<E> implements ManagedBlocker {
2023	+	*   final BlockingQueue<E> queue;
2024	+	*   volatile E item = null;
2025	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
2026	+	*   public boolean block() throws InterruptedException {
2027	+	*     if (item == null)
2028	+	*       item = queue.take();
2029	+	*     return true;
2030	+	*   }
2031	+	*   public boolean isReleasable() {
2032	+	*     return item != null || (item = queue.poll()) != null;
2033	+	*   }
2034	+	*   public E getItem() { // call after pool.managedBlock completes
2035	+	*     return item;
2036	+	*   }
2037	+	* }}</pre>
2038		*/
2039		public static interface ManagedBlocker {
2040		/**
#	Line 1783 | Line 2058 | public class ForkJoinPool extends Abstra
2058		* Blocks in accord with the given blocker.  If the current thread
2059		* is a {@link ForkJoinWorkerThread}, this method possibly
2060		* arranges for a spare thread to be activated if necessary to
2061	<	* ensure parallelism while the current thread is blocked.
1787	<	*
1788	<	* <p>If {@code maintainParallelism} is {@code true} and the pool
1789	<	* supports it ({@link #getMaintainsParallelism}), this method
1790	<	* attempts to maintain the pool's nominal parallelism. Otherwise
1791	<	* it activates a thread only if necessary to avoid complete
1792	<	* starvation. This option may be preferable when blockages use
1793	<	* timeouts, or are almost always brief.
2061	>	* ensure sufficient parallelism while the current thread is blocked.
2062		*
2063		* <p>If the caller is not a {@link ForkJoinTask}, this method is
2064		* behaviorally equivalent to
#	Line 1804 | Line 2072 | public class ForkJoinPool extends Abstra
2072		* first be expanded to ensure parallelism, and later adjusted.
2073		*
2074		* @param blocker the blocker
1807	–	* @param maintainParallelism if {@code true} and supported by
1808	–	* this pool, attempt to maintain the pool's nominal parallelism;
1809	–	* otherwise activate a thread only if necessary to avoid
1810	–	* complete starvation.
2075		* @throws InterruptedException if blocker.block did so
2076		*/
2077	<	public static void managedBlock(ManagedBlocker blocker,
1814	<	boolean maintainParallelism)
2077	>	public static void managedBlock(ManagedBlocker blocker)
2078		throws InterruptedException {
2079		Thread t = Thread.currentThread();
2080	<	ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
2081	<	((ForkJoinWorkerThread) t).pool : null);
2082	<	if (!blocker.isReleasable()) {
2083	<	try {
2084	<	if (pool == null ||
2085	<	!pool.preBlock(blocker, maintainParallelism))
1823	<	awaitBlocker(blocker);
1824	<	} finally {
1825	<	if (pool != null)
1826	<	pool.updateRunningCount(1);
1827	<	}
2080	>	if (t instanceof ForkJoinWorkerThread) {
2081	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
2082	>	w.pool.awaitBlocker(blocker);
2083	>	}
2084	>	else {
2085	>	do {} while (!blocker.isReleasable() && !blocker.block());
2086		}
1829	–	}
1830	–
1831	–	private static void awaitBlocker(ManagedBlocker blocker)
1832	–	throws InterruptedException {
1833	–	do {} while (!blocker.isReleasable() && !blocker.block());
2087		}
2088
2089		// AbstractExecutorService overrides.  These rely on undocumented
#	Line 1846 | Line 2099 | public class ForkJoinPool extends Abstra
2099		}
2100
2101		// Unsafe mechanics
2102	<
2103	<	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
2104	<	private static final long eventCountOffset =
2105	<	objectFieldOffset("eventCount", ForkJoinPool.class);
2106	<	private static final long workerCountsOffset =
2107	<	objectFieldOffset("workerCounts", ForkJoinPool.class);
2108	<	private static final long runControlOffset =
2109	<	objectFieldOffset("runControl", ForkJoinPool.class);
2110	<	private static final long syncStackOffset =
2111	<	objectFieldOffset("syncStack",ForkJoinPool.class);
2112	<	private static final long spareStackOffset =
2113	<	objectFieldOffset("spareStack", ForkJoinPool.class);
2114	<
2115	<	private boolean casEventCount(long cmp, long val) {
2116	<	return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
2117	<	}
2118	<	private boolean casWorkerCounts(int cmp, int val) {
1866	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
1867	<	}
1868	<	private boolean casRunControl(int cmp, int val) {
1869	<	return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
1870	<	}
1871	<	private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
1872	<	return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
1873	<	}
1874	<	private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
1875	<	return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
1876	<	}
1877	<
1878	<	private static long objectFieldOffset(String field, Class<?> klazz) {
2102	>	private static final sun.misc.Unsafe UNSAFE;
2103	>	private static final long ctlOffset;
2104	>	private static final long stealCountOffset;
2105	>	private static final long blockedCountOffset;
2106	>	private static final long quiescerCountOffset;
2107	>	private static final long scanGuardOffset;
2108	>	private static final long nextWorkerNumberOffset;
2109	>	private static final long ABASE;
2110	>	private static final int ASHIFT;
2111	>
2112	>	static {
2113	>	poolNumberGenerator = new AtomicInteger();
2114	>	workerSeedGenerator = new Random();
2115	>	modifyThreadPermission = new RuntimePermission("modifyThread");
2116	>	defaultForkJoinWorkerThreadFactory =
2117	>	new DefaultForkJoinWorkerThreadFactory();
2118	>	int s;
2119		try {
2120	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
2121	<	} catch (NoSuchFieldException e) {
2122	<	// Convert Exception to corresponding Error
2123	<	NoSuchFieldError error = new NoSuchFieldError(field);
2124	<	error.initCause(e);
2125	<	throw error;
2126	<	}
2120	>	UNSAFE = getUnsafe();
2121	>	Class k = ForkJoinPool.class;
2122	>	ctlOffset = UNSAFE.objectFieldOffset
2123	>	(k.getDeclaredField("ctl"));
2124	>	stealCountOffset = UNSAFE.objectFieldOffset
2125	>	(k.getDeclaredField("stealCount"));
2126	>	blockedCountOffset = UNSAFE.objectFieldOffset
2127	>	(k.getDeclaredField("blockedCount"));
2128	>	quiescerCountOffset = UNSAFE.objectFieldOffset
2129	>	(k.getDeclaredField("quiescerCount"));
2130	>	scanGuardOffset = UNSAFE.objectFieldOffset
2131	>	(k.getDeclaredField("scanGuard"));
2132	>	nextWorkerNumberOffset = UNSAFE.objectFieldOffset
2133	>	(k.getDeclaredField("nextWorkerNumber"));
2134	>	Class a = ForkJoinTask[].class;
2135	>	ABASE = UNSAFE.arrayBaseOffset(a);
2136	>	s = UNSAFE.arrayIndexScale(a);
2137	>	} catch (Exception e) {
2138	>	throw new Error(e);
2139	>	}
2140	>	if ((s & (s-1)) != 0)
2141	>	throw new Error("data type scale not a power of two");
2142	>	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
2143		}
2144
2145		/**

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