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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.39 by jsr166, Sun Aug 2 17:55:51 2009 UTC vs.
Revision 1.59 by dl, Fri Jul 23 14:09:17 2010 UTC

#	Line 13 | Line 13 | import java.util.Arrays;
13		import java.util.Collection;
14		import java.util.Collections;
15		import java.util.List;
16	–	import java.util.concurrent.locks.Condition;
16		import java.util.concurrent.locks.LockSupport;
17		import java.util.concurrent.locks.ReentrantLock;
18		import java.util.concurrent.atomic.AtomicInteger;
19	<	import java.util.concurrent.atomic.AtomicLong;
19	>	import java.util.concurrent.CountDownLatch;
20
21		/**
22		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
23		* A {@code ForkJoinPool} provides the entry point for submissions
24	<	* from non-{@code ForkJoinTask}s, as well as management and
25	<	* 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.
24	>	* from non-{@code ForkJoinTask} clients, as well as management and
25	>	* monitoring operations.
26		*
27	<	* <p>{@code ForkJoinPool}s differ from other kinds of {@link
28	<	* Executor}s mainly in that they provide <em>work-stealing</em>: all
29	<	* threads in the pool attempt to find and execute subtasks created by
30	<	* other active tasks (eventually blocking if none exist). This makes
31	<	* them efficient when most tasks spawn other subtasks (as do most
32	<	* {@code ForkJoinTask}s), as well as the mixed execution of some
33	<	* plain {@code Runnable}- or {@code Callable}- based activities along
34	<	* with {@code ForkJoinTask}s. When setting {@linkplain #setAsyncMode
35	<	* 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.
27	>	* <p>A {@code ForkJoinPool} differs from other kinds of {@link
28	>	* ExecutorService} mainly by virtue of employing
29	>	* <em>work-stealing</em>: all threads in the pool attempt to find and
30	>	* execute subtasks created by other active tasks (eventually blocking
31	>	* waiting for work if none exist). This enables efficient processing
32	>	* when most tasks spawn other subtasks (as do most {@code
33	>	* ForkJoinTask}s). When setting <em>asyncMode</em> to true in
34	>	* constructors, {@code ForkJoinPool}s may also be appropriate for use
35	>	* with event-style tasks that are never joined.
36		*
37	<	* <p>A {@code ForkJoinPool} may be constructed with a given
38	<	* parallelism level (target pool size), which it attempts to maintain
39	<	* by dynamically adding, suspending, or resuming threads, even if
40	<	* some tasks are waiting to join others. However, no such adjustments
41	<	* are performed in the face of blocked IO or other unmanaged
42	<	* synchronization. The nested {@link ManagedBlocker} interface
43	<	* enables extension of the kinds of synchronization accommodated.
44	<	* The target parallelism level may also be changed dynamically
45	<	* ({@link #setParallelism}) and thread construction can be limited
53	<	* using methods {@link #setMaximumPoolSize} and/or {@link
54	<	* #setMaintainsParallelism}.
37	>	* <p>A {@code ForkJoinPool} is constructed with a given target
38	>	* parallelism level; by default, equal to the number of available
39	>	* processors. The pool attempts to maintain enough active (or
40	>	* available) threads by dynamically adding, suspending, or resuming
41	>	* internal worker threads, even if some tasks are stalled waiting to
42	>	* join others. However, no such adjustments are guaranteed in the
43	>	* face of blocked IO or other unmanaged synchronization. The nested
44	>	* {@link ManagedBlocker} interface enables extension of the kinds of
45	>	* synchronization accommodated.
46		*
47		* <p>In addition to execution and lifecycle control methods, this
48		* class provides status check methods (for example
#	Line 60 | Line 51 | import java.util.concurrent.atomic.Atomi
51		* {@link #toString} returns indications of pool state in a
52		* convenient form for informal monitoring.
53		*
54	+	* <p> As is the case with other ExecutorServices, there are three
55	+	* main task execution methods summarized in the follwoing
56	+	* table. These are designed to be used by clients not already engaged
57	+	* in fork/join computations in the current pool.  The main forms of
58	+	* these methods accept instances of {@code ForkJoinTask}, but
59	+	* overloaded forms also allow mixed execution of plain {@code
60	+	* Runnable}- or {@code Callable}- based activities as well.  However,
61	+	* tasks that are already executing in a pool should normally
62	+	* <em>NOT</em> use these pool execution methods, but instead use the
63	+	* within-computation forms listed in the table.
64	+	*
65	+	* <table BORDER CELLPADDING=3 CELLSPACING=1>
66	+	*  <tr>
67	+	*    <td></td>
68	+	*    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
69	+	*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
70	+	*  </tr>
71	+	*  <tr>
72	+	*    <td> <b>Arange async execution</td>
73	+	*    <td> {@link #execute(ForkJoinTask)}</td>
74	+	*    <td> {@link ForkJoinTask#fork}</td>
75	+	*  </tr>
76	+	*  <tr>
77	+	*    <td> <b>Await and obtain result</td>
78	+	*    <td> {@link #invoke(ForkJoinTask)}</td>
79	+	*    <td> {@link ForkJoinTask#invoke}</td>
80	+	*  </tr>
81	+	*  <tr>
82	+	*    <td> <b>Arrange exec and obtain Future</td>
83	+	*    <td> {@link #submit(ForkJoinTask)}</td>
84	+	*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
85	+	*  </tr>
86	+	* </table>
87	+	*
88	+	* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
89	+	* used for all parallel task execution in a program or subsystem.
90	+	* Otherwise, use would not usually outweigh the construction and
91	+	* bookkeeping overhead of creating a large set of threads. For
92	+	* example, a common pool could be used for the {@code SortTasks}
93	+	* illustrated in {@link RecursiveAction}. Because {@code
94	+	* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
95	+	* daemon} mode, there is typically no need to explicitly {@link
96	+	* #shutdown} such a pool upon program exit.
97	+	*
98	+	* <pre>
99	+	* static final ForkJoinPool mainPool = new ForkJoinPool();
100	+	* ...
101	+	* public void sort(long[] array) {
102	+	*   mainPool.invoke(new SortTask(array, 0, array.length));
103	+	* }
104	+	* </pre>
105	+	*
106		* <p><b>Implementation notes</b>: This implementation restricts the
107		* maximum number of running threads to 32767. Attempts to create
108	<	* pools with greater than the maximum result in
108	>	* pools with greater than the maximum number result in
109		* {@code IllegalArgumentException}.
110		*
111	+	* <p>This implementation rejects submitted tasks (that is, by throwing
112	+	* {@link RejectedExecutionException}) only when the pool is shut down
113	+	* or internal resources have been exhuasted.
114	+	*
115		* @since 1.7
116		* @author Doug Lea
117		*/
118		public class ForkJoinPool extends AbstractExecutorService {
119
120		/*
121	<	* See the extended comments interspersed below for design,
122	<	* rationale, and walkthroughs.
121	>	* Implementation Overview
122	>	*
123	>	* This class provides the central bookkeeping and control for a
124	>	* set of worker threads: Submissions from non-FJ threads enter
125	>	* into a submission queue. Workers take these tasks and typically
126	>	* split them into subtasks that may be stolen by other workers.
127	>	* The main work-stealing mechanics implemented in class
128	>	* ForkJoinWorkerThread give first priority to processing tasks
129	>	* from their own queues (LIFO or FIFO, depending on mode), then
130	>	* to randomized FIFO steals of tasks in other worker queues, and
131	>	* lastly to new submissions. These mechanics do not consider
132	>	* affinities, loads, cache localities, etc, so rarely provide the
133	>	* best possible performance on a given machine, but portably
134	>	* provide good throughput by averaging over these factors.
135	>	* (Further, even if we did try to use such information, we do not
136	>	* usually have a basis for exploiting it. For example, some sets
137	>	* of tasks profit from cache affinities, but others are harmed by
138	>	* cache pollution effects.)
139	>	*
140	>	* Beyond work-stealing support and essential bookkeeping, the
141	>	* main responsibility of this framework is to arrange tactics for
142	>	* when one worker is waiting to join a task stolen (or always
143	>	* held by) another.  Becauae we are multiplexing many tasks on to
144	>	* a pool of workers, we can't just let them block (as in
145	>	* Thread.join).  We also cannot just reassign the joiner's
146	>	* run-time stack with another and replace it later, which would
147	>	* be a form of "continuation", that even if possible is not
148	>	* necessarily a good idea. Given that the creation costs of most
149	>	* threads on most systems mainly surrounds setting up runtime
150	>	* stacks, thread creation and switching is usually not much more
151	>	* expensive than stack creation and switching, and is more
152	>	* flexible). Instead we combine two tactics:
153	>	*
154	>	*   1. Arranging for the joiner to execute some task that it
155	>	*      would be running if the steal had not occurred.  Method
156	>	*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
157	>	*      links to try to find such a task.
158	>	*
159	>	*   2. Unless there are already enough live threads, creating or
160	>	*      or re-activating a spare thread to compensate for the
161	>	*      (blocked) joiner until it unblocks.  Spares then suspend
162	>	*      at their next opportunity or eventually die if unused for
163	>	*      too long.  See below and the internal documentation
164	>	*      for tryAwaitJoin for more details about compensation
165	>	*      rules.
166	>	*
167	>	* Because the determining existence of conservatively safe
168	>	* helping targets, the availability of already-created spares,
169	>	* and the apparent need to create new spares are all racy and
170	>	* require heuristic guidance, joins (in
171	>	* ForkJoinWorkerThread.joinTask) interleave these options until
172	>	* successful.  Creating a new spare always succeeds, but also
173	>	* increases application footprint, so we try to avoid it, within
174	>	* reason.
175	>	*
176	>	* The ManagedBlocker extension API can't use option (1) so uses a
177	>	* special version of (2) in method awaitBlocker.
178	>	*
179	>	* The main throughput advantages of work-stealing stem from
180	>	* decentralized control -- workers mostly steal tasks from each
181	>	* other. We do not want to negate this by creating bottlenecks
182	>	* implementing other management responsibilities. So we use a
183	>	* collection of techniques that avoid, reduce, or cope well with
184	>	* contention. These entail several instances of bit-packing into
185	>	* CASable fields to maintain only the minimally required
186	>	* atomicity. To enable such packing, we restrict maximum
187	>	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
188	>	* unbalanced increments and decrements) to fit into a 16 bit
189	>	* field, which is far in excess of normal operating range.  Even
190	>	* though updates to some of these bookkeeping fields do sometimes
191	>	* contend with each other, they don't normally cache-contend with
192	>	* updates to others enough to warrant memory padding or
193	>	* isolation. So they are all held as fields of ForkJoinPool
194	>	* objects.  The main capabilities are as follows:
195	>	*
196	>	* 1. Creating and removing workers. Workers are recorded in the
197	>	* "workers" array. This is an array as opposed to some other data
198	>	* structure to support index-based random steals by workers.
199	>	* Updates to the array recording new workers and unrecording
200	>	* terminated ones are protected from each other by a lock
201	>	* (workerLock) but the array is otherwise concurrently readable,
202	>	* and accessed directly by workers. To simplify index-based
203	>	* operations, the array size is always a power of two, and all
204	>	* readers must tolerate null slots. Currently, all worker thread
205	>	* creation is on-demand, triggered by task submissions,
206	>	* replacement of terminated workers, and/or compensation for
207	>	* blocked workers. However, all other support code is set up to
208	>	* work with other policies.
209	>	*
210	>	* 2. Bookkeeping for dynamically adding and removing workers. We
211	>	* aim to approximately maintain the given level of parallelism.
212	>	* When some workers are known to be blocked (on joins or via
213	>	* ManagedBlocker), we may create or resume others to take their
214	>	* place until they unblock (see below). Implementing this
215	>	* requires counts of the number of "running" threads (i.e., those
216	>	* that are neither blocked nor artifically suspended) as well as
217	>	* the total number.  These two values are packed into one field,
218	>	* "workerCounts" because we need accurate snapshots when deciding
219	>	* to create, resume or suspend.  Note however that the
220	>	* correspondance of these counts to reality is not guaranteed. In
221	>	* particular updates for unblocked threads may lag until they
222	>	* actually wake up.
223	>	*
224	>	* 3. Maintaining global run state. The run state of the pool
225	>	* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
226	>	* those in other Executor implementations, as well as a count of
227	>	* "active" workers -- those that are, or soon will be, or
228	>	* recently were executing tasks. The runLevel and active count
229	>	* are packed together in order to correctly trigger shutdown and
230	>	* termination. Without care, active counts can be subject to very
231	>	* high contention.  We substantially reduce this contention by
232	>	* relaxing update rules.  A worker must claim active status
233	>	* prospectively, by activating if it sees that a submitted or
234	>	* stealable task exists (it may find after activating that the
235	>	* task no longer exists). It stays active while processing this
236	>	* task (if it exists) and any other local subtasks it produces,
237	>	* until it cannot find any other tasks. It then tries
238	>	* inactivating (see method preStep), but upon update contention
239	>	* instead scans for more tasks, later retrying inactivation if it
240	>	* doesn't find any.
241	>	*
242	>	* 4. Managing idle workers waiting for tasks. We cannot let
243	>	* workers spin indefinitely scanning for tasks when none are
244	>	* available. On the other hand, we must quickly prod them into
245	>	* action when new tasks are submitted or generated.  We
246	>	* park/unpark these idle workers using an event-count scheme.
247	>	* Field eventCount is incremented upon events that may enable
248	>	* workers that previously could not find a task to now find one:
249	>	* Submission of a new task to the pool, or another worker pushing
250	>	* a task onto a previously empty queue.  (We also use this
251	>	* mechanism for termination and reconfiguration actions that
252	>	* require wakeups of idle workers).  Each worker maintains its
253	>	* last known event count, and blocks when a scan for work did not
254	>	* find a task AND its lastEventCount matches the current
255	>	* eventCount. Waiting idle workers are recorded in a variant of
256	>	* Treiber stack headed by field eventWaiters which, when nonzero,
257	>	* encodes the thread index and count awaited for by the worker
258	>	* thread most recently calling eventSync. This thread in turn has
259	>	* a record (field nextEventWaiter) for the next waiting worker.
260	>	* In addition to allowing simpler decisions about need for
261	>	* wakeup, the event count bits in eventWaiters serve the role of
262	>	* tags to avoid ABA errors in Treiber stacks.  To reduce delays
263	>	* in task diffusion, workers not otherwise occupied may invoke
264	>	* method releaseWaiters, that removes and signals (unparks)
265	>	* workers not waiting on current count. To minimize task
266	>	* production stalls associate with signalling, any worker pushing
267	>	* a task on an empty queue invokes the weaker method signalWork,
268	>	* that only releases idle workers until it detects interference
269	>	* by other threads trying to release, and lets them take
270	>	* over. The net effect is a tree-like diffusion of signals, where
271	>	* released threads (and possibly others) help with unparks.  To
272	>	* further reduce contention effects a bit, failed CASes to
273	>	* increment field eventCount are tolerated without retries.
274	>	* Conceptually they are merged into the same event, which is OK
275	>	* when their only purpose is to enable workers to scan for work.
276	>	*
277	>	* 5. Managing suspension of extra workers. When a worker is about
278	>	* to block waiting for a join (or via ManagedBlockers), we may
279	>	* create a new thread to maintain parallelism level, or at least
280	>	* avoid starvation. Usually, extra threads are needed for only
281	>	* very short periods, yet join dependencies are such that we
282	>	* sometimes need them in bursts. Rather than create new threads
283	>	* each time this happens, we suspend no-longer-needed extra ones
284	>	* as "spares". For most purposes, we don't distinguish "extra"
285	>	* spare threads from normal "core" threads: On each call to
286	>	* preStep (the only point at which we can do this) a worker
287	>	* checks to see if there are now too many running workers, and if
288	>	* so, suspends itself.  Methods tryAwaitJoin and awaitBlocker
289	>	* look for suspended threads to resume before considering
290	>	* creating a new replacement. We don't need a special data
291	>	* structure to maintain spares; simply scanning the workers array
292	>	* looking for worker.isSuspended() is fine because the calling
293	>	* thread is otherwise not doing anything useful anyway; we are at
294	>	* least as happy if after locating a spare, the caller doesn't
295	>	* actually block because the join is ready before we try to
296	>	* adjust and compensate.  Note that this is intrinsically racy.
297	>	* One thread may become a spare at about the same time as another
298	>	* is needlessly being created. We counteract this and related
299	>	* slop in part by requiring resumed spares to immediately recheck
300	>	* (in preStep) to see whether they they should re-suspend. The
301	>	* only effective difference between "extra" and "core" threads is
302	>	* that we allow the "extra" ones to time out and die if they are
303	>	* not resumed within a keep-alive interval of a few seconds. This
304	>	* is implemented mainly within ForkJoinWorkerThread, but requires
305	>	* some coordination (isTrimmed() -- meaning killed while
306	>	* suspended) to correctly maintain pool counts.
307	>	*
308	>	* 6. Deciding when to create new workers. The main dynamic
309	>	* control in this class is deciding when to create extra threads,
310	>	* in methods awaitJoin and awaitBlocker. We always need to create
311	>	* one when the number of running threads would become zero and
312	>	* all workers are busy. However, this is not easy to detect
313	>	* reliably in the presence of transients so we use retries and
314	>	* allow slack (in tryAwaitJoin) to reduce false alarms.  These
315	>	* effectively reduce churn at the price of systematically
316	>	* undershooting target parallelism when many threads are blocked.
317	>	* However, biasing toward undeshooting partially compensates for
318	>	* the above mechanics to suspend extra threads, that normally
319	>	* lead to overshoot because we can only suspend workers
320	>	* in-between top-level actions. It also better copes with the
321	>	* fact that some of the methods in this class tend to never
322	>	* become compiled (but are interpreted), so some components of
323	>	* the entire set of controls might execute many times faster than
324	>	* others. And similarly for cases where the apparent lack of work
325	>	* is just due to GC stalls and other transient system activity.
326	>	*
327	>	* Beware that there is a lot of representation-level coupling
328	>	* among classes ForkJoinPool, ForkJoinWorkerThread, and
329	>	* ForkJoinTask.  For example, direct access to "workers" array by
330	>	* workers, and direct access to ForkJoinTask.status by both
331	>	* ForkJoinPool and ForkJoinWorkerThread.  There is little point
332	>	* trying to reduce this, since any associated future changes in
333	>	* representations will need to be accompanied by algorithmic
334	>	* changes anyway.
335	>	*
336	>	* Style notes: There are lots of inline assignments (of form
337	>	* "while ((local = field) != 0)") which are usually the simplest
338	>	* way to ensure read orderings. Also several occurrences of the
339	>	* unusual "do {} while(!cas...)" which is the simplest way to
340	>	* force an update of a CAS'ed variable. There are also other
341	>	* coding oddities that help some methods perform reasonably even
342	>	* when interpreted (not compiled), at the expense of messiness.
343	>	*
344	>	* The order of declarations in this file is: (1) statics (2)
345	>	* fields (along with constants used when unpacking some of them)
346	>	* (3) internal control methods (4) callbacks and other support
347	>	* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
348	>	* methods (plus a few little helpers).
349		*/
350
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	–
351		/**
352		* Factory for creating new {@link ForkJoinWorkerThread}s.
353		* A {@code ForkJoinWorkerThreadFactory} must be defined and used
#	Line 92 | Line 359 | public class ForkJoinPool extends Abstra
359		* Returns a new worker thread operating in the given pool.
360		*
361		* @param pool the pool this thread works in
362	<	* @throws NullPointerException if pool is null
362	>	* @throws NullPointerException if the pool is null
363		*/
364		public ForkJoinWorkerThread newThread(ForkJoinPool pool);
365		}
#	Line 101 | Line 368 | public class ForkJoinPool extends Abstra
368		* Default ForkJoinWorkerThreadFactory implementation; creates a
369		* new ForkJoinWorkerThread.
370		*/
371	<	static class  DefaultForkJoinWorkerThreadFactory
371	>	static class DefaultForkJoinWorkerThreadFactory
372		implements ForkJoinWorkerThreadFactory {
373		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
374	<	try {
108	<	return new ForkJoinWorkerThread(pool);
109	<	} catch (OutOfMemoryError oom)  {
110	<	return null;
111	<	}
374	>	return new ForkJoinWorkerThread(pool);
375		}
376		}
377
#	Line 144 | Line 407 | public class ForkJoinPool extends Abstra
407		new AtomicInteger();
408
409		/**
410	<	* Array holding all worker threads in the pool. Initialized upon
411	<	* first use. Array size must be a power of two.  Updates and
149	<	* replacements are protected by workerLock, but it is always kept
150	<	* in a consistent enough state to be randomly accessed without
151	<	* locking by workers performing work-stealing.
410	>	* Absolute bound for parallelism level. Twice this number must
411	>	* fit into a 16bit field to enable word-packing for some counts.
412		*/
413	<	volatile ForkJoinWorkerThread[] workers;
413	>	private static final int MAX_THREADS = 0x7fff;
414
415		/**
416	<	* Lock protecting access to workers.
416	>	* Array holding all worker threads in the pool.  Array size must
417	>	* be a power of two.  Updates and replacements are protected by
418	>	* workerLock, but the array is always kept in a consistent enough
419	>	* state to be randomly accessed without locking by workers
420	>	* performing work-stealing, as well as other traversal-based
421	>	* methods in this class. All readers must tolerate that some
422	>	* array slots may be null.
423		*/
424	<	private final ReentrantLock workerLock;
424	>	volatile ForkJoinWorkerThread[] workers;
425
426		/**
427	<	* Condition for awaitTermination.
427	>	* Queue for external submissions.
428		*/
429	<	private final Condition termination;
429	>	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
430
431		/**
432	<	* The uncaught exception handler used when any worker
167	<	* abruptly terminates
432	>	* Lock protecting updates to workers array.
433		*/
434	<	private Thread.UncaughtExceptionHandler ueh;
434	>	private final ReentrantLock workerLock;
435
436		/**
437	<	* Creation factory for worker threads.
437	>	* Latch released upon termination.
438		*/
439	<	private final ForkJoinWorkerThreadFactory factory;
439	>	private final Phaser termination;
440
441		/**
442	<	* Head of stack of threads that were created to maintain
178	<	* parallelism when other threads blocked, but have since
179	<	* suspended when the parallelism level rose.
442	>	* Creation factory for worker threads.
443		*/
444	<	private volatile WaitQueueNode spareStack;
444	>	private final ForkJoinWorkerThreadFactory factory;
445
446		/**
447		* Sum of per-thread steal counts, updated only when threads are
448		* idle or terminating.
449		*/
450	<	private final AtomicLong stealCount;
450	>	private volatile long stealCount;
451
452		/**
453	<	* Queue for external submissions.
453	>	* Encoded record of top of treiber stack of threads waiting for
454	>	* events. The top 32 bits contain the count being waited for. The
455	>	* bottom word contains one plus the pool index of waiting worker
456	>	* thread.
457		*/
458	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
458	>	private volatile long eventWaiters;
459	>
460	>	private static final int  EVENT_COUNT_SHIFT = 32;
461	>	private static final long WAITER_ID_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
462
463		/**
464	<	* Head of Treiber stack for barrier sync. See below for explanation.
464	>	* A counter for events that may wake up worker threads:
465	>	*   - Submission of a new task to the pool
466	>	*   - A worker pushing a task on an empty queue
467	>	*   - termination and reconfiguration
468		*/
469	<	private volatile WaitQueueNode syncStack;
469	>	private volatile int eventCount;
470
471		/**
472	<	* The count for event barrier
473	<	*/
474	<	private volatile long eventCount;
472	>	* Lifecycle control. The low word contains the number of workers
473	>	* that are (probably) executing tasks. This value is atomically
474	>	* incremented before a worker gets a task to run, and decremented
475	>	* when worker has no tasks and cannot find any.  Bits 16-18
476	>	* contain runLevel value. When all are zero, the pool is
477	>	* running. Level transitions are monotonic (running -> shutdown
478	>	* -> terminating -> terminated) so each transition adds a bit.
479	>	* These are bundled together to ensure consistent read for
480	>	* termination checks (i.e., that runLevel is at least SHUTDOWN
481	>	* and active threads is zero).
482	>	*/
483	>	private volatile int runState;
484	>
485	>	// Note: The order among run level values matters.
486	>	private static final int RUNLEVEL_SHIFT     = 16;
487	>	private static final int SHUTDOWN           = 1 << RUNLEVEL_SHIFT;
488	>	private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
489	>	private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
490	>	private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
491	>	private static final int ONE_ACTIVE         = 1; // active update delta
492
493		/**
494	<	* Pool number, just for assigning useful names to worker threads
494	>	* Holds number of total (i.e., created and not yet terminated)
495	>	* and running (i.e., not blocked on joins or other managed sync)
496	>	* threads, packed together to ensure consistent snapshot when
497	>	* making decisions about creating and suspending spare
498	>	* threads. Updated only by CAS. Note that adding a new worker
499	>	* requires incrementing both counts, since workers start off in
500	>	* running state.  This field is also used for memory-fencing
501	>	* configuration parameters.
502		*/
503	<	private final int poolNumber;
503	>	private volatile int workerCounts;
504	>
505	>	private static final int TOTAL_COUNT_SHIFT  = 16;
506	>	private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1;
507	>	private static final int ONE_RUNNING        = 1;
508	>	private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
509
510		/**
511	<	* The maximum allowed pool size
511	>	* The target parallelism level.
512	>	* Accessed directly by ForkJoinWorkerThreads.
513		*/
514	<	private volatile int maxPoolSize;
514	>	final int parallelism;
515
516		/**
517	<	* The desired parallelism level, updated only under workerLock.
517	>	* True if use local fifo, not default lifo, for local polling
518	>	* Read by, and replicated by ForkJoinWorkerThreads
519		*/
520	<	private volatile int parallelism;
520	>	final boolean locallyFifo;
521
522		/**
523	<	* True if use local fifo, not default lifo, for local polling
523	>	* The uncaught exception handler used when any worker abruptly
524	>	* terminates.
525		*/
526	<	private volatile boolean locallyFifo;
526	>	private final Thread.UncaughtExceptionHandler ueh;
527
528		/**
529	<	* Holds number of total (i.e., created and not yet terminated)
226	<	* and running (i.e., not blocked on joins or other managed sync)
227	<	* 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.
529	>	* Pool number, just for assigning useful names to worker threads
530		*/
531	<	private volatile int workerCounts;
531	>	private final int poolNumber;
532
533	<	private static int totalCountOf(int s)           { return s >>> 16;  }
534	<	private static int runningCountOf(int s)         { return s & shortMask; }
237	<	private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
533	>	// Utilities for CASing fields. Note that several of these
534	>	// are manually inlined by callers
535
536		/**
537	<	* 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
537	>	* Increments running count.  Also used by ForkJoinTask.
538		*/
539	<	final void updateRunningCount(int delta) {
540	<	int s;
541	<	do {} while (!casWorkerCounts(s = workerCounts, s + delta));
539	>	final void incrementRunningCount() {
540	>	int c;
541	>	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
542	>	c = workerCounts,
543	>	c + ONE_RUNNING));
544		}
545
546		/**
547	<	* 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
547	>	* Tries to decrement running count unless already zero
548		*/
549	<	private void updateWorkerCount(int delta) {
550	<	int d = delta + (delta << 16); // add to both lo and hi parts
551	<	int s;
552	<	do {} while (!casWorkerCounts(s = workerCounts, s + d));
549	>	final boolean tryDecrementRunningCount() {
550	>	int wc = workerCounts;
551	>	if ((wc & RUNNING_COUNT_MASK) == 0)
552	>	return false;
553	>	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
554	>	wc, wc - ONE_RUNNING);
555		}
556
557		/**
558	<	* Lifecycle control. High word contains runState, low word
266	<	* contains the number of workers that are (probably) executing
267	<	* tasks. This value is atomically incremented before a worker
268	<	* gets a task to run, and decremented when worker has no tasks
269	<	* and cannot find any. These two fields are bundled together to
270	<	* support correct termination triggering.  Note: activeCount
271	<	* CAS'es cheat by assuming active count is in low word, so need
272	<	* to be modified if this changes
558	>	* Tries to increment running count
559		*/
560	<	private volatile int runControl;
561	<
562	<	// RunState values. Order among values matters
563	<	private static final int RUNNING     = 0;
564	<	private static final int SHUTDOWN    = 1;
279	<	private static final int TERMINATING = 2;
280	<	private static final int TERMINATED  = 3;
281	<
282	<	private static int runStateOf(int c)             { return c >>> 16; }
283	<	private static int activeCountOf(int c)          { return c & shortMask; }
284	<	private static int runControlFor(int r, int a)   { return (r << 16) + a; }
560	>	final boolean tryIncrementRunningCount() {
561	>	int wc;
562	>	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
563	>	wc = workerCounts, wc + ONE_RUNNING);
564	>	}
565
566		/**
567		* Tries incrementing active count; fails on contention.
568	<	* Called by workers before/during executing tasks.
568	>	* Called by workers before executing tasks.
569		*
570		* @return true on success
571		*/
572		final boolean tryIncrementActiveCount() {
573	<	int c = runControl;
574	<	return casRunControl(c, c+1);
573	>	int c;
574	>	return UNSAFE.compareAndSwapInt(this, runStateOffset,
575	>	c = runState, c + ONE_ACTIVE);
576		}
577
578		/**
579		* Tries decrementing active count; fails on contention.
580	<	* Possibly triggers termination on success.
300	<	* Called by workers when they can't find tasks.
301	<	*
302	<	* @return true on success
580	>	* Called when workers cannot find tasks to run.
581		*/
582		final boolean tryDecrementActiveCount() {
583	<	int c = runControl;
584	<	int nextc = c - 1;
585	<	if (!casRunControl(c, nextc))
308	<	return false;
309	<	if (canTerminateOnShutdown(nextc))
310	<	terminateOnShutdown();
311	<	return true;
583	>	int c;
584	>	return UNSAFE.compareAndSwapInt(this, runStateOffset,
585	>	c = runState, c - ONE_ACTIVE);
586		}
587
588		/**
589	<	* Returns {@code true} if argument represents zero active count
590	<	* and nonzero runstate, which is the triggering condition for
317	<	* terminating on shutdown.
589	>	* Advances to at least the given level. Returns true if not
590	>	* already in at least the given level.
591		*/
592	<	private static boolean canTerminateOnShutdown(int c) {
593	<	// i.e. least bit is nonzero runState bit
594	<	return ((c & -c) >>> 16) != 0;
592	>	private boolean advanceRunLevel(int level) {
593	>	for (;;) {
594	>	int s = runState;
595	>	if ((s & level) != 0)
596	>	return false;
597	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level))
598	>	return true;
599	>	}
600		}
601
602	+	// workers array maintenance
603	+
604		/**
605	<	* Transition run state to at least the given state. Return true
326	<	* if not already at least given state.
605	>	* Records and returns a workers array index for new worker.
606		*/
607	<	private boolean transitionRunStateTo(int state) {
608	<	for (;;) {
609	<	int c = runControl;
610	<	if (runStateOf(c) >= state)
611	<	return false;
612	<	if (casRunControl(c, runControlFor(state, activeCountOf(c))))
613	<	return true;
607	>	private int recordWorker(ForkJoinWorkerThread w) {
608	>	// Try using slot totalCount-1. If not available, scan and/or resize
609	>	int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1;
610	>	final ReentrantLock lock = this.workerLock;
611	>	lock.lock();
612	>	try {
613	>	ForkJoinWorkerThread[] ws = workers;
614	>	int nws = ws.length;
615	>	if (k < 0 || k >= nws || ws[k] != null) {
616	>	for (k = 0; k < nws && ws[k] != null; ++k)
617	>	;
618	>	if (k == nws)
619	>	ws = Arrays.copyOf(ws, nws << 1);
620	>	}
621	>	ws[k] = w;
622	>	workers = ws; // volatile array write ensures slot visibility
623	>	} finally {
624	>	lock.unlock();
625		}
626	+	return k;
627		}
628
629		/**
630	<	* Controls whether to add spares to maintain parallelism
630	>	* Nulls out record of worker in workers array
631		*/
632	<	private volatile boolean maintainsParallelism;
632	>	private void forgetWorker(ForkJoinWorkerThread w) {
633	>	int idx = w.poolIndex;
634	>	// Locking helps method recordWorker avoid unecessary expansion
635	>	final ReentrantLock lock = this.workerLock;
636	>	lock.lock();
637	>	try {
638	>	ForkJoinWorkerThread[] ws = workers;
639	>	if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify
640	>	ws[idx] = null;
641	>	} finally {
642	>	lock.unlock();
643	>	}
644	>	}
645
646	<	// Constructors
646	>	// adding and removing workers
647
648		/**
649	<	* Creates a ForkJoinPool with a pool size equal to the number of
650	<	* processors available on the system, using the default
651	<	* ForkJoinWorkerThreadFactory.
649	>	* Tries to create and add new worker. Assumes that worker counts
650	>	* are already updated to accommodate the worker, so adjusts on
651	>	* failure.
652		*
653	<	* @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")}
653	>	* @return new worker or null if creation failed
654		*/
655	<	public ForkJoinPool() {
656	<	this(Runtime.getRuntime().availableProcessors(),
657	<	defaultForkJoinWorkerThreadFactory);
655	>	private ForkJoinWorkerThread addWorker() {
656	>	ForkJoinWorkerThread w = null;
657	>	try {
658	>	w = factory.newThread(this);
659	>	} finally { // Adjust on either null or exceptional factory return
660	>	if (w == null) {
661	>	onWorkerCreationFailure();
662	>	return null;
663	>	}
664	>	}
665	>	w.start(recordWorker(w), ueh);
666	>	return w;
667		}
668
669		/**
670	<	* Creates a ForkJoinPool with the indicated parallelism level
362	<	* 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")}
670	>	* Adjusts counts upon failure to create worker
671		*/
672	<	public ForkJoinPool(int parallelism) {
673	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
672	>	private void onWorkerCreationFailure() {
673	>	for (;;) {
674	>	int wc = workerCounts;
675	>	if ((wc >>> TOTAL_COUNT_SHIFT) == 0)
676	>	Thread.yield(); // wait for other counts to settle
677	>	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
678	>	wc - (ONE_RUNNING|ONE_TOTAL)))
679	>	break;
680	>	}
681	>	tryTerminate(false); // in case of failure during shutdown
682		}
683
684		/**
685	<	* Creates a ForkJoinPool with parallelism equal to the number of
686	<	* processors available on the system and using the given
379	<	* ForkJoinWorkerThreadFactory.
685	>	* Creates and/or resumes enough workers to establish target
686	>	* parallelism, giving up if terminating or addWorker fails
687		*
688	<	* @param factory the factory for creating new threads
689	<	* @throws NullPointerException if factory is null
690	<	* @throws SecurityException if a security manager exists and
691	<	*         the caller is not permitted to modify threads
692	<	*         because it does not hold {@link
693	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
694	<	*/
695	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
696	<	this(Runtime.getRuntime().availableProcessors(), factory);
688	>	* TODO: recast this to support lazier creation and automated
689	>	* parallelism maintenance
690	>	*/
691	>	private void ensureEnoughWorkers() {
692	>	while ((runState & TERMINATING) == 0) {
693	>	int pc = parallelism;
694	>	int wc = workerCounts;
695	>	int rc = wc & RUNNING_COUNT_MASK;
696	>	int tc = wc >>> TOTAL_COUNT_SHIFT;
697	>	if (tc < pc) {
698	>	if (UNSAFE.compareAndSwapInt
699	>	(this, workerCountsOffset,
700	>	wc, wc + (ONE_RUNNING|ONE_TOTAL)) &&
701	>	addWorker() == null)
702	>	break;
703	>	}
704	>	else if (tc > pc && rc < pc &&
705	>	tc > (runState & ACTIVE_COUNT_MASK)) {
706	>	ForkJoinWorkerThread spare = null;
707	>	ForkJoinWorkerThread[] ws = workers;
708	>	int nws = ws.length;
709	>	for (int i = 0; i < nws; ++i) {
710	>	ForkJoinWorkerThread w = ws[i];
711	>	if (w != null && w.isSuspended()) {
712	>	if ((workerCounts & RUNNING_COUNT_MASK) > pc)
713	>	return;
714	>	if (w.tryResumeSpare())
715	>	incrementRunningCount();
716	>	break;
717	>	}
718	>	}
719	>	}
720	>	else
721	>	break;
722	>	}
723		}
724
725		/**
726	<	* Creates a ForkJoinPool with the given parallelism and factory.
726	>	* Final callback from terminating worker.  Removes record of
727	>	* worker from array, and adjusts counts. If pool is shutting
728	>	* down, tries to complete terminatation, else possibly replaces
729	>	* the worker.
730		*
731	<	* @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")}
731	>	* @param w the worker
732		*/
733	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
734	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
735	<	throw new IllegalArgumentException();
736	<	if (factory == null)
737	<	throw new NullPointerException();
738	<	checkPermission();
739	<	this.factory = factory;
740	<	this.parallelism = parallelism;
741	<	this.maxPoolSize = MAX_THREADS;
742	<	this.maintainsParallelism = true;
743	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
744	<	this.workerLock = new ReentrantLock();
745	<	this.termination = workerLock.newCondition();
746	<	this.stealCount = new AtomicLong();
747	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
748	<	// worker array and workers are lazily constructed
733	>	final void workerTerminated(ForkJoinWorkerThread w) {
734	>	if (w.active) { // force inactive
735	>	w.active = false;
736	>	do {} while (!tryDecrementActiveCount());
737	>	}
738	>	forgetWorker(w);
739	>
740	>	// Decrement total count, and if was running, running count
741	>	// Spin (waiting for other updates) if either would be negative
742	>	int nr = w.isTrimmed() ? 0 : ONE_RUNNING;
743	>	int unit = ONE_TOTAL + nr;
744	>	for (;;) {
745	>	int wc = workerCounts;
746	>	int rc = wc & RUNNING_COUNT_MASK;
747	>	if (rc - nr < 0 || (wc >>> TOTAL_COUNT_SHIFT) == 0)
748	>	Thread.yield(); // back off if waiting for other updates
749	>	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
750	>	wc, wc - unit))
751	>	break;
752	>	}
753	>
754	>	accumulateStealCount(w); // collect final count
755	>	if (!tryTerminate(false))
756	>	ensureEnoughWorkers();
757		}
758
759	+	// Waiting for and signalling events
760	+
761		/**
762	<	* Creates a new worker thread using factory.
763	<	*
426	<	* @param index the index to assign worker
427	<	* @return new worker, or null of factory failed
762	>	* Releases workers blocked on a count not equal to current count.
763	>	* @return true if any released
764		*/
765	<	private ForkJoinWorkerThread createWorker(int index) {
766	<	Thread.UncaughtExceptionHandler h = ueh;
767	<	ForkJoinWorkerThread w = factory.newThread(this);
768	<	if (w != null) {
769	<	w.poolIndex = index;
770	<	w.setDaemon(true);
771	<	w.setAsyncMode(locallyFifo);
772	<	w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
773	<	if (h != null)
774	<	w.setUncaughtExceptionHandler(h);
765	>	private void releaseWaiters() {
766	>	long top;
767	>	while ((top = eventWaiters) != 0L) {
768	>	ForkJoinWorkerThread[] ws = workers;
769	>	int n = ws.length;
770	>	for (;;) {
771	>	int i = ((int)(top & WAITER_ID_MASK)) - 1;
772	>	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == eventCount)
773	>	return;
774	>	ForkJoinWorkerThread w;
775	>	if (i < n && (w = ws[i]) != null &&
776	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
777	>	top, w.nextWaiter)) {
778	>	LockSupport.unpark(w);
779	>	top = eventWaiters;
780	>	}
781	>	else
782	>	break;      // possibly stale; reread
783	>	}
784		}
440	–	return w;
785		}
786
787		/**
788	<	* Returns a good size for worker array given pool size.
789	<	* Currently requires size to be a power of two.
788	>	* Ensures eventCount on exit is different (mod 2^32) than on
789	>	* entry and wakes up all waiters
790	>	*/
791	>	private void signalEvent() {
792	>	int c;
793	>	do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset,
794	>	c = eventCount, c+1));
795	>	releaseWaiters();
796	>	}
797	>
798	>	/**
799	>	* Advances eventCount and releases waiters until interference by
800	>	* other releasing threads is detected.
801		*/
802	<	private static int arraySizeFor(int poolSize) {
803	<	return (poolSize <= 1) ? 1 :
804	<	(1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
802	>	final void signalWork() {
803	>	int c;
804	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c=eventCount, c+1);
805	>	long top;
806	>	while ((top = eventWaiters) != 0L) {
807	>	int ec = eventCount;
808	>	ForkJoinWorkerThread[] ws = workers;
809	>	int n = ws.length;
810	>	for (;;) {
811	>	int i = ((int)(top & WAITER_ID_MASK)) - 1;
812	>	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
813	>	return;
814	>	ForkJoinWorkerThread w;
815	>	if (i < n && (w = ws[i]) != null &&
816	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
817	>	top, top = w.nextWaiter)) {
818	>	LockSupport.unpark(w);
819	>	if (top != eventWaiters) // let someone else take over
820	>	return;
821	>	}
822	>	else
823	>	break;      // possibly stale; reread
824	>	}
825	>	}
826		}
827
828		/**
829	<	* Creates or resizes array if necessary to hold newLength.
830	<	* Call only under exclusion.
829	>	* If worker is inactive, blocks until terminating or event count
830	>	* advances from last value held by worker; in any case helps
831	>	* release others.
832		*
833	<	* @return the array
833	>	* @param w the calling worker thread
834	>	* @param retries the number of scans by caller failing to find work
835	>	* @return false if now too many threads running
836		*/
837	<	private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
838	<	ForkJoinWorkerThread[] ws = workers;
839	<	if (ws == null)
840	<	return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
841	<	else if (newLength > ws.length)
842	<	return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
843	<	else
844	<	return ws;
837	>	private boolean eventSync(ForkJoinWorkerThread w, int retries) {
838	>	int wec = w.lastEventCount;
839	>	if (retries > 1) { // can only block after 2nd miss
840	>	long nextTop = (((long)wec << EVENT_COUNT_SHIFT) |
841	>	((long)(w.poolIndex + 1)));
842	>	long top;
843	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
844	>	(((int)(top = eventWaiters) & WAITER_ID_MASK) == 0 ||
845	>	(int)(top >>> EVENT_COUNT_SHIFT) == wec) &&
846	>	eventCount == wec) {
847	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
848	>	w.nextWaiter = top, nextTop)) {
849	>	accumulateStealCount(w); // transfer steals while idle
850	>	Thread.interrupted();    // clear/ignore interrupt
851	>	while (eventCount == wec)
852	>	w.doPark();
853	>	break;
854	>	}
855	>	}
856	>	wec = eventCount;
857	>	}
858	>	releaseWaiters();
859	>	int wc = workerCounts;
860	>	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
861	>	w.lastEventCount = wec;
862	>	return true;
863	>	}
864	>	if (wec != w.lastEventCount) // back up if may re-wait
865	>	w.lastEventCount = wec - (wc >>> TOTAL_COUNT_SHIFT);
866	>	return false;
867		}
868
869		/**
870	<	* Tries to shrink workers into smaller array after one or more terminate.
870	>	* Callback from workers invoked upon each top-level action (i.e.,
871	>	* stealing a task or taking a submission and running
872	>	* it). Performs one or both of the following:
873	>	*
874	>	* * If the worker cannot find work, updates its active status to
875	>	* inactive and updates activeCount unless there is contention, in
876	>	* which case it may try again (either in this or a subsequent
877	>	* call).  Additionally, awaits the next task event and/or helps
878	>	* wake up other releasable waiters.
879	>	*
880	>	* * If there are too many running threads, suspends this worker
881	>	* (first forcing inactivation if necessary).  If it is not
882	>	* resumed before a keepAlive elapses, the worker may be "trimmed"
883	>	* -- killed while suspended within suspendAsSpare. Otherwise,
884	>	* upon resume it rechecks to make sure that it is still needed.
885	>	*
886	>	* @param w the worker
887	>	* @param retries the number of scans by caller failing to find work
888	>	* find any (in which case it may block waiting for work).
889		*/
890	<	private void tryShrinkWorkerArray() {
891	<	ForkJoinWorkerThread[] ws = workers;
892	<	if (ws != null) {
893	<	int len = ws.length;
894	<	int last = len - 1;
895	<	while (last >= 0 && ws[last] == null)
896	<	--last;
897	<	int newLength = arraySizeFor(last+1);
898	<	if (newLength < len)
899	<	workers = Arrays.copyOf(ws, newLength);
890	>	final void preStep(ForkJoinWorkerThread w, int retries) {
891	>	boolean active = w.active;
892	>	boolean inactivate = active && retries != 0;
893	>	for (;;) {
894	>	int rs, wc;
895	>	if (inactivate &&
896	>	UNSAFE.compareAndSwapInt(this, runStateOffset,
897	>	rs = runState, rs - ONE_ACTIVE))
898	>	inactivate = active = w.active = false;
899	>	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= parallelism) {
900	>	if (active || eventSync(w, retries))
901	>	break;
902	>	}
903	>	else if (!(inactivate |= active) &&  // must inactivate to suspend
904	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
905	>	wc, wc - ONE_RUNNING) &&
906	>	!w.suspendAsSpare())             // false if trimmed
907	>	break;
908		}
909		}
910
911		/**
912	<	* Initializes workers if necessary.
912	>	* Awaits join of the given task if enough threads, or can resume
913	>	* or create a spare. Fails (in which case the given task might
914	>	* not be done) upon contention or lack of decision about
915	>	* blocking. Returns void because caller must check
916	>	* task status on return anyway.
917	>	*
918	>	* We allow blocking if:
919	>	*
920	>	* 1. There would still be at least as many running threads as
921	>	*    parallelism level if this thread blocks.
922	>	*
923	>	* 2. A spare is resumed to replace this worker. We tolerate
924	>	*    slop in the decision to replace if a spare is found without
925	>	*    first decrementing run count.  This may release too many,
926	>	*    but if so, the superfluous ones will re-suspend via
927	>	*    preStep().
928	>	*
929	>	* 3. After #spares repeated checks, there are no fewer than #spare
930	>	*    threads not running. We allow this slack to avoid hysteresis
931	>	*    and as a hedge against lag/uncertainty of running count
932	>	*    estimates when signalling or unblocking stalls.
933	>	*
934	>	* 4. All existing workers are busy (as rechecked via repeated
935	>	*    retries by caller) and a new spare is created.
936	>	*
937	>	* If none of the above hold, we try to escape out by
938	>	* re-incrementing count and returning to caller, which can retry
939	>	* later.
940	>	*
941	>	* @param joinMe the task to join
942	>	* @param retries if negative, then serve only as a precheck
943	>	*   that the thread can be replaced by a spare. Otherwise,
944	>	*   the number of repeated calls to this method returning busy
945	>	* @return true if the call must be retried because there
946	>	*   none of the blocking checks hold
947		*/
948	<	final void ensureWorkerInitialization() {
949	<	ForkJoinWorkerThread[] ws = workers;
950	<	if (ws == null) {
951	<	final ReentrantLock lock = this.workerLock;
952	<	lock.lock();
953	<	try {
954	<	ws = workers;
955	<	if (ws == null) {
956	<	int ps = parallelism;
957	<	ws = ensureWorkerArrayCapacity(ps);
958	<	for (int i = 0; i < ps; ++i) {
959	<	ForkJoinWorkerThread w = createWorker(i);
948	>	final boolean tryAwaitJoin(ForkJoinTask<?> joinMe, int retries) {
949	>	if (joinMe.status < 0) // precheck for cancellation
950	>	return false;
951	>	if ((runState & TERMINATING) != 0) { // shutting down
952	>	joinMe.cancelIgnoringExceptions();
953	>	return false;
954	>	}
955	>
956	>	int pc = parallelism;
957	>	boolean running = true; // false when running count decremented
958	>	outer:for (;;) {
959	>	int wc = workerCounts;
960	>	int rc = wc & RUNNING_COUNT_MASK;
961	>	int tc = wc >>> TOTAL_COUNT_SHIFT;
962	>	if (running) { // replace with spare or decrement count
963	>	if (rc <= pc && tc > pc &&
964	>	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
965	>	ForkJoinWorkerThread[] ws = workers;
966	>	int nws = ws.length;
967	>	for (int i = 0; i < nws; ++i) { // search for spare
968	>	ForkJoinWorkerThread w = ws[i];
969		if (w != null) {
970	<	ws[i] = w;
971	<	w.start();
972	<	updateWorkerCount(1);
970	>	if (joinMe.status < 0)
971	>	return false;
972	>	if (w.isSuspended()) {
973	>	if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
974	>	w.tryResumeSpare()) {
975	>	running = false;
976	>	break outer;
977	>	}
978	>	continue outer; // rescan
979	>	}
980		}
981		}
982		}
983	<	} finally {
984	<	lock.unlock();
983	>	if (retries < 0 || // < 0 means replacement check only
984	>	rc == 0 || joinMe.status < 0 || workerCounts != wc ||
985	>	!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
986	>	wc, wc - ONE_RUNNING))
987	>	return false; // done or inconsistent or contended
988	>	running = false;
989	>	if (rc > pc)
990	>	break;
991	>	}
992	>	else { // allow blocking if enough threads
993	>	if (rc >= pc || joinMe.status < 0)
994	>	break;
995	>	int sc = tc - pc + 1; // = spare threads, plus the one to add
996	>	if (retries > sc) {
997	>	if (rc > 0 && rc >= pc - sc) // allow slack
998	>	break;
999	>	if (tc < MAX_THREADS &&
1000	>	tc == (runState & ACTIVE_COUNT_MASK) &&
1001	>	workerCounts == wc &&
1002	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1003	>	wc+(ONE_RUNNING|ONE_TOTAL))) {
1004	>	addWorker();
1005	>	break;
1006	>	}
1007	>	}
1008	>	if (workerCounts == wc &&        // back out to allow rescan
1009	>	UNSAFE.compareAndSwapInt (this, workerCountsOffset,
1010	>	wc, wc + ONE_RUNNING)) {
1011	>	releaseWaiters();            // help others progress
1012	>	return true;                 // let caller retry
1013	>	}
1014		}
1015		}
1016	+	// arrive here if can block
1017	+	joinMe.internalAwaitDone();
1018	+	int c;                      // to inline incrementRunningCount
1019	+	do {} while (!UNSAFE.compareAndSwapInt
1020	+	(this, workerCountsOffset,
1021	+	c = workerCounts, c + ONE_RUNNING));
1022	+	return false;
1023		}
1024
1025		/**
1026	<	* Worker creation and startup for threads added via setParallelism.
1026	>	* Same idea as (and shares many code snippets with) tryAwaitJoin,
1027	>	* but self-contained because there are no caller retries.
1028	>	* TODO: Rework to use simpler API.
1029		*/
1030	<	private void createAndStartAddedWorkers() {
1031	<	resumeAllSpares();  // Allow spares to convert to nonspare
1032	<	int ps = parallelism;
1033	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
1034	<	int len = ws.length;
1035	<	// Sweep through slots, to keep lowest indices most populated
1036	<	int k = 0;
1037	<	while (k < len) {
1038	<	if (ws[k] != null) {
1039	<	++k;
1040	<	continue;
1041	<	}
1042	<	int s = workerCounts;
1043	<	int tc = totalCountOf(s);
1044	<	int rc = runningCountOf(s);
1045	<	if (rc >= ps || tc >= ps)
1046	<	break;
1047	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
1048	<	ForkJoinWorkerThread w = createWorker(k);
1049	<	if (w != null) {
1050	<	ws[k++] = w;
1051	<	w.start();
1030	>	final void awaitBlocker(ManagedBlocker blocker)
1031	>	throws InterruptedException {
1032	>	boolean done;
1033	>	if (done = blocker.isReleasable())
1034	>	return;
1035	>	int pc = parallelism;
1036	>	int retries = 0;
1037	>	boolean running = true; // false when running count decremented
1038	>	outer:for (;;) {
1039	>	int wc = workerCounts;
1040	>	int rc = wc & RUNNING_COUNT_MASK;
1041	>	int tc = wc >>> TOTAL_COUNT_SHIFT;
1042	>	if (running) {
1043	>	if (rc <= pc && tc > pc &&
1044	>	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
1045	>	ForkJoinWorkerThread[] ws = workers;
1046	>	int nws = ws.length;
1047	>	for (int i = 0; i < nws; ++i) {
1048	>	ForkJoinWorkerThread w = ws[i];
1049	>	if (w != null) {
1050	>	if (done = blocker.isReleasable())
1051	>	return;
1052	>	if (w.isSuspended()) {
1053	>	if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
1054	>	w.tryResumeSpare()) {
1055	>	running = false;
1056	>	break outer;
1057	>	}
1058	>	continue outer; // rescan
1059	>	}
1060	>	}
1061	>	}
1062		}
1063	<	else {
1064	<	updateWorkerCount(-1); // back out on failed creation
1063	>	if (done = blocker.isReleasable())
1064	>	return;
1065	>	if (rc == 0 || workerCounts != wc ||
1066	>	!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1067	>	wc, wc - ONE_RUNNING))
1068	>	continue;
1069	>	running = false;
1070	>	if (rc > pc)
1071	>	break;
1072	>	}
1073	>	else {
1074	>	if (rc >= pc || (done = blocker.isReleasable()))
1075		break;
1076	+	int sc = tc - pc + 1;
1077	+	if (retries++ > sc) {
1078	+	if (rc > 0 && rc >= pc - sc)
1079	+	break;
1080	+	if (tc < MAX_THREADS &&
1081	+	tc == (runState & ACTIVE_COUNT_MASK) &&
1082	+	workerCounts == wc &&
1083	+	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1084	+	wc+(ONE_RUNNING|ONE_TOTAL))) {
1085	+	addWorker();
1086	+	break;
1087	+	}
1088	+	}
1089	+	Thread.yield();
1090	+	}
1091	+	}
1092	+
1093	+	try {
1094	+	if (!done)
1095	+	do {} while (!blocker.isReleasable() && !blocker.block());
1096	+	} finally {
1097	+	if (!running) {
1098	+	int c;
1099	+	do {} while (!UNSAFE.compareAndSwapInt
1100	+	(this, workerCountsOffset,
1101	+	c = workerCounts, c + ONE_RUNNING));
1102	+	}
1103	+	}
1104	+	}
1105	+
1106	+	/**
1107	+	* Possibly initiates and/or completes termination.
1108	+	*
1109	+	* @param now if true, unconditionally terminate, else only
1110	+	* if shutdown and empty queue and no active workers
1111	+	* @return true if now terminating or terminated
1112	+	*/
1113	+	private boolean tryTerminate(boolean now) {
1114	+	if (now)
1115	+	advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
1116	+	else if (runState < SHUTDOWN ||
1117	+	!submissionQueue.isEmpty() ||
1118	+	(runState & ACTIVE_COUNT_MASK) != 0)
1119	+	return false;
1120	+
1121	+	if (advanceRunLevel(TERMINATING))
1122	+	startTerminating();
1123	+
1124	+	// Finish now if all threads terminated; else in some subsequent call
1125	+	if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1126	+	advanceRunLevel(TERMINATED);
1127	+	termination.arrive();
1128	+	}
1129	+	return true;
1130	+	}
1131	+
1132	+	/**
1133	+	* Actions on transition to TERMINATING
1134	+	*/
1135	+	private void startTerminating() {
1136	+	for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers
1137	+	cancelSubmissions();
1138	+	shutdownWorkers();
1139	+	cancelWorkerTasks();
1140	+	signalEvent();
1141	+	interruptWorkers();
1142	+	}
1143	+	}
1144	+
1145	+	/**
1146	+	* Clear out and cancel submissions, ignoring exceptions
1147	+	*/
1148	+	private void cancelSubmissions() {
1149	+	ForkJoinTask<?> task;
1150	+	while ((task = submissionQueue.poll()) != null) {
1151	+	try {
1152	+	task.cancel(false);
1153	+	} catch (Throwable ignore) {
1154	+	}
1155	+	}
1156	+	}
1157	+
1158	+	/**
1159	+	* Sets all worker run states to at least shutdown,
1160	+	* also resuming suspended workers
1161	+	*/
1162	+	private void shutdownWorkers() {
1163	+	ForkJoinWorkerThread[] ws = workers;
1164	+	int nws = ws.length;
1165	+	for (int i = 0; i < nws; ++i) {
1166	+	ForkJoinWorkerThread w = ws[i];
1167	+	if (w != null)
1168	+	w.shutdown();
1169	+	}
1170	+	}
1171	+
1172	+	/**
1173	+	* Clears out and cancels all locally queued tasks
1174	+	*/
1175	+	private void cancelWorkerTasks() {
1176	+	ForkJoinWorkerThread[] ws = workers;
1177	+	int nws = ws.length;
1178	+	for (int i = 0; i < nws; ++i) {
1179	+	ForkJoinWorkerThread w = ws[i];
1180	+	if (w != null)
1181	+	w.cancelTasks();
1182	+	}
1183	+	}
1184	+
1185	+	/**
1186	+	* Unsticks all workers blocked on joins etc
1187	+	*/
1188	+	private void interruptWorkers() {
1189	+	ForkJoinWorkerThread[] ws = workers;
1190	+	int nws = ws.length;
1191	+	for (int i = 0; i < nws; ++i) {
1192	+	ForkJoinWorkerThread w = ws[i];
1193	+	if (w != null && !w.isTerminated()) {
1194	+	try {
1195	+	w.interrupt();
1196	+	} catch (SecurityException ignore) {
1197		}
1198		}
1199		}
1200		}
1201
1202	+	// misc support for ForkJoinWorkerThread
1203	+
1204	+	/**
1205	+	* Returns pool number
1206	+	*/
1207	+	final int getPoolNumber() {
1208	+	return poolNumber;
1209	+	}
1210	+
1211	+	/**
1212	+	* Accumulates steal count from a worker, clearing
1213	+	* the worker's value
1214	+	*/
1215	+	final void accumulateStealCount(ForkJoinWorkerThread w) {
1216	+	int sc = w.stealCount;
1217	+	if (sc != 0) {
1218	+	long c;
1219	+	w.stealCount = 0;
1220	+	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1221	+	c = stealCount, c + sc));
1222	+	}
1223	+	}
1224	+
1225	+	/**
1226	+	* Returns the approximate (non-atomic) number of idle threads per
1227	+	* active thread.
1228	+	*/
1229	+	final int idlePerActive() {
1230	+	int pc = parallelism; // use parallelism, not rc
1231	+	int ac = runState;    // no mask -- artifically boosts during shutdown
1232	+	// Use exact results for small values, saturate past 4
1233	+	return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1234	+	}
1235	+
1236	+	// Public and protected methods
1237	+
1238	+	// Constructors
1239	+
1240	+	/**
1241	+	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1242	+	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1243	+	* #defaultForkJoinWorkerThreadFactory default thread factory},
1244	+	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1245	+	*
1246	+	* @throws SecurityException if a security manager exists and
1247	+	*         the caller is not permitted to modify threads
1248	+	*         because it does not hold {@link
1249	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1250	+	*/
1251	+	public ForkJoinPool() {
1252	+	this(Runtime.getRuntime().availableProcessors(),
1253	+	defaultForkJoinWorkerThreadFactory, null, false);
1254	+	}
1255	+
1256	+	/**
1257	+	* Creates a {@code ForkJoinPool} with the indicated parallelism
1258	+	* level, the {@linkplain
1259	+	* #defaultForkJoinWorkerThreadFactory default thread factory},
1260	+	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1261	+	*
1262	+	* @param parallelism the parallelism level
1263	+	* @throws IllegalArgumentException if parallelism less than or
1264	+	*         equal to zero, or greater than implementation limit
1265	+	* @throws SecurityException if a security manager exists and
1266	+	*         the caller is not permitted to modify threads
1267	+	*         because it does not hold {@link
1268	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1269	+	*/
1270	+	public ForkJoinPool(int parallelism) {
1271	+	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1272	+	}
1273	+
1274	+	/**
1275	+	* Creates a {@code ForkJoinPool} with the given parameters.
1276	+	*
1277	+	* @param parallelism the parallelism level. For default value,
1278	+	* use {@link java.lang.Runtime#availableProcessors}.
1279	+	* @param factory the factory for creating new threads. For default value,
1280	+	* use {@link #defaultForkJoinWorkerThreadFactory}.
1281	+	* @param handler the handler for internal worker threads that
1282	+	* terminate due to unrecoverable errors encountered while executing
1283	+	* tasks. For default value, use <code>null</code>.
1284	+	* @param asyncMode if true,
1285	+	* establishes local first-in-first-out scheduling mode for forked
1286	+	* tasks that are never joined. This mode may be more appropriate
1287	+	* than default locally stack-based mode in applications in which
1288	+	* worker threads only process event-style asynchronous tasks.
1289	+	* For default value, use <code>false</code>.
1290	+	* @throws IllegalArgumentException if parallelism less than or
1291	+	*         equal to zero, or greater than implementation limit
1292	+	* @throws NullPointerException if the factory is null
1293	+	* @throws SecurityException if a security manager exists and
1294	+	*         the caller is not permitted to modify threads
1295	+	*         because it does not hold {@link
1296	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1297	+	*/
1298	+	public ForkJoinPool(int parallelism,
1299	+	ForkJoinWorkerThreadFactory factory,
1300	+	Thread.UncaughtExceptionHandler handler,
1301	+	boolean asyncMode) {
1302	+	checkPermission();
1303	+	if (factory == null)
1304	+	throw new NullPointerException();
1305	+	if (parallelism <= 0 || parallelism > MAX_THREADS)
1306	+	throw new IllegalArgumentException();
1307	+	this.parallelism = parallelism;
1308	+	this.factory = factory;
1309	+	this.ueh = handler;
1310	+	this.locallyFifo = asyncMode;
1311	+	int arraySize = initialArraySizeFor(parallelism);
1312	+	this.workers = new ForkJoinWorkerThread[arraySize];
1313	+	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1314	+	this.workerLock = new ReentrantLock();
1315	+	this.termination = new Phaser(1);
1316	+	this.poolNumber = poolNumberGenerator.incrementAndGet();
1317	+	}
1318	+
1319	+	/**
1320	+	* Returns initial power of two size for workers array.
1321	+	* @param pc the initial parallelism level
1322	+	*/
1323	+	private static int initialArraySizeFor(int pc) {
1324	+	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1325	+	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1326	+	size |= size >>> 1;
1327	+	size |= size >>> 2;
1328	+	size |= size >>> 4;
1329	+	size |= size >>> 8;
1330	+	return size + 1;
1331	+	}
1332	+
1333		// Execution methods
1334
1335		/**
#	Line 551 | Line 1338 | public class ForkJoinPool extends Abstra
1338		private <T> void doSubmit(ForkJoinTask<T> task) {
1339		if (task == null)
1340		throw new NullPointerException();
1341	<	if (isShutdown())
1341	>	if (runState >= SHUTDOWN)
1342		throw new RejectedExecutionException();
556	–	if (workers == null)
557	–	ensureWorkerInitialization();
1343		submissionQueue.offer(task);
1344	<	signalIdleWorkers();
1344	>	signalEvent();
1345	>	ensureEnoughWorkers();
1346		}
1347
1348		/**
1349		* Performs the given task, returning its result upon completion.
1350	+	* If the caller is already engaged in a fork/join computation in
1351	+	* the current pool, this method is equivalent in effect to
1352	+	* {@link ForkJoinTask#invoke}.
1353		*
1354		* @param task the task
1355		* @return the task's result
1356	<	* @throws NullPointerException if task is null
1357	<	* @throws RejectedExecutionException if pool is shut down
1356	>	* @throws NullPointerException if the task is null
1357	>	* @throws RejectedExecutionException if the task cannot be
1358	>	*         scheduled for execution
1359		*/
1360		public <T> T invoke(ForkJoinTask<T> task) {
1361		doSubmit(task);
#	Line 574 | Line 1364 | public class ForkJoinPool extends Abstra
1364
1365		/**
1366		* Arranges for (asynchronous) execution of the given task.
1367	+	* If the caller is already engaged in a fork/join computation in
1368	+	* the current pool, this method is equivalent in effect to
1369	+	* {@link ForkJoinTask#fork}.
1370		*
1371		* @param task the task
1372	<	* @throws NullPointerException if task is null
1373	<	* @throws RejectedExecutionException if pool is shut down
1372	>	* @throws NullPointerException if the task is null
1373	>	* @throws RejectedExecutionException if the task cannot be
1374	>	*         scheduled for execution
1375		*/
1376		public void execute(ForkJoinTask<?> task) {
1377		doSubmit(task);
#	Line 585 | Line 1379 | public class ForkJoinPool extends Abstra
1379
1380		// AbstractExecutorService methods
1381
1382	+	/**
1383	+	* @throws NullPointerException if the task is null
1384	+	* @throws RejectedExecutionException if the task cannot be
1385	+	*         scheduled for execution
1386	+	*/
1387		public void execute(Runnable task) {
1388		ForkJoinTask<?> job;
1389		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
#	Line 594 | Line 1393 | public class ForkJoinPool extends Abstra
1393		doSubmit(job);
1394		}
1395
1396	+	/**
1397	+	* Submits a ForkJoinTask for execution.
1398	+	* If the caller is already engaged in a fork/join computation in
1399	+	* the current pool, this method is equivalent in effect to
1400	+	* {@link ForkJoinTask#fork}.
1401	+	*
1402	+	* @param task the task to submit
1403	+	* @return the task
1404	+	* @throws NullPointerException if the task is null
1405	+	* @throws RejectedExecutionException if the task cannot be
1406	+	*         scheduled for execution
1407	+	*/
1408	+	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1409	+	doSubmit(task);
1410	+	return task;
1411	+	}
1412	+
1413	+	/**
1414	+	* @throws NullPointerException if the task is null
1415	+	* @throws RejectedExecutionException if the task cannot be
1416	+	*         scheduled for execution
1417	+	*/
1418		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1419		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1420		doSubmit(job);
1421		return job;
1422		}
1423
1424	+	/**
1425	+	* @throws NullPointerException if the task is null
1426	+	* @throws RejectedExecutionException if the task cannot be
1427	+	*         scheduled for execution
1428	+	*/
1429		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1430		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1431		doSubmit(job);
1432		return job;
1433		}
1434
1435	+	/**
1436	+	* @throws NullPointerException if the task is null
1437	+	* @throws RejectedExecutionException if the task cannot be
1438	+	*         scheduled for execution
1439	+	*/
1440		public ForkJoinTask<?> submit(Runnable task) {
1441		ForkJoinTask<?> job;
1442		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
#	Line 617 | Line 1448 | public class ForkJoinPool extends Abstra
1448		}
1449
1450		/**
1451	<	* Submits a ForkJoinTask for execution.
1452	<	*
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
1451	>	* @throws NullPointerException       {@inheritDoc}
1452	>	* @throws RejectedExecutionException {@inheritDoc}
1453		*/
628	–	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
629	–	doSubmit(task);
630	–	return task;
631	–	}
632	–
633	–
1454		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
1455		ArrayList<ForkJoinTask<T>> forkJoinTasks =
1456		new ArrayList<ForkJoinTask<T>>(tasks.size());
#	Line 639 | Line 1459 | public class ForkJoinPool extends Abstra
1459		invoke(new InvokeAll<T>(forkJoinTasks));
1460
1461		@SuppressWarnings({"unchecked", "rawtypes"})
1462	<	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1462	>	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1463		return futures;
1464		}
1465
#	Line 653 | Line 1473 | public class ForkJoinPool extends Abstra
1473		private static final long serialVersionUID = -7914297376763021607L;
1474		}
1475
656	–	// Configuration and status settings and queries
657	–
1476		/**
1477		* Returns the factory used for constructing new workers.
1478		*
#	Line 671 | Line 1489 | public class ForkJoinPool extends Abstra
1489		* @return the handler, or {@code null} if none
1490		*/
1491		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1492	<	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;
683	<	}
684	<
685	<	/**
686	<	* 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.
690	<	*
691	<	* @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();
1492	>	return ueh;
1493		}
1494
1495		/**
1496	<	* Returns the targeted number of worker threads in this pool.
1496	>	* Returns the targeted parallelism level of this pool.
1497		*
1498	<	* @return the targeted number of worker threads in this pool
1498	>	* @return the targeted parallelism level of this pool
1499		*/
1500		public int getParallelism() {
1501		return parallelism;
#	Line 769 | Line 1510 | public class ForkJoinPool extends Abstra
1510		* @return the number of worker threads
1511		*/
1512		public int getPoolSize() {
1513	<	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;
1513	>	return workerCounts >>> TOTAL_COUNT_SHIFT;
1514		}
1515
1516		/**
#	Line 852 | Line 1518 | public class ForkJoinPool extends Abstra
1518		* scheduling mode for forked tasks that are never joined.
1519		*
1520		* @return {@code true} if this pool uses async mode
855	–	* @see #setAsyncMode
1521		*/
1522		public boolean getAsyncMode() {
1523		return locallyFifo;
#	Line 861 | Line 1526 | public class ForkJoinPool extends Abstra
1526		/**
1527		* Returns an estimate of the number of worker threads that are
1528		* not blocked waiting to join tasks or for other managed
1529	<	* synchronization.
1529	>	* synchronization. This method may overestimate the
1530	>	* number of running threads.
1531		*
1532		* @return the number of worker threads
1533		*/
1534		public int getRunningThreadCount() {
1535	<	return runningCountOf(workerCounts);
1535	>	return workerCounts & RUNNING_COUNT_MASK;
1536		}
1537
1538		/**
#	Line 877 | Line 1543 | public class ForkJoinPool extends Abstra
1543		* @return the number of active threads
1544		*/
1545		public int getActiveThreadCount() {
1546	<	return activeCountOf(runControl);
881	<	}
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;
1546	>	return runState & ACTIVE_COUNT_MASK;
1547		}
1548
1549		/**
#	Line 904 | Line 1558 | public class ForkJoinPool extends Abstra
1558		* @return {@code true} if all threads are currently idle
1559		*/
1560		public boolean isQuiescent() {
1561	<	return activeCountOf(runControl) == 0;
1561	>	return (runState & ACTIVE_COUNT_MASK) == 0;
1562		}
1563
1564		/**
#	Line 919 | Line 1573 | public class ForkJoinPool extends Abstra
1573		* @return the number of steals
1574		*/
1575		public long getStealCount() {
1576	<	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);
1576	>	return stealCount;
1577		}
1578
1579		/**
#	Line 945 | Line 1589 | public class ForkJoinPool extends Abstra
1589		public long getQueuedTaskCount() {
1590		long count = 0;
1591		ForkJoinWorkerThread[] ws = workers;
1592	<	if (ws != null) {
1593	<	for (int i = 0; i < ws.length; ++i) {
1594	<	ForkJoinWorkerThread t = ws[i];
1595	<	if (t != null)
1596	<	count += t.getQueueSize();
953	<	}
1592	>	int nws = ws.length;
1593	>	for (int i = 0; i < nws; ++i) {
1594	>	ForkJoinWorkerThread w = ws[i];
1595	>	if (w != null)
1596	>	count += w.getQueueSize();
1597		}
1598		return count;
1599		}
1600
1601		/**
1602	<	* Returns an estimate of the number tasks submitted to this pool
1603	<	* that have not yet begun executing. This method takes time
1602	>	* Returns an estimate of the number of tasks submitted to this
1603	>	* pool that have not yet begun executing.  This method takes time
1604		* proportional to the number of submissions.
1605		*
1606		* @return the number of queued submissions
#	Line 991 | Line 1634 | public class ForkJoinPool extends Abstra
1634		* Removes all available unexecuted submitted and forked tasks
1635		* from scheduling queues and adds them to the given collection,
1636		* without altering their execution status. These may include
1637	<	* artificially generated or wrapped tasks. This method is designed
1638	<	* to be invoked only when the pool is known to be
1637	>	* artificially generated or wrapped tasks. This method is
1638	>	* designed to be invoked only when the pool is known to be
1639		* quiescent. Invocations at other times may not remove all
1640		* tasks. A failure encountered while attempting to add elements
1641		* to collection {@code c} may result in elements being in
#	Line 1007 | Line 1650 | public class ForkJoinPool extends Abstra
1650		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1651		int n = submissionQueue.drainTo(c);
1652		ForkJoinWorkerThread[] ws = workers;
1653	<	if (ws != null) {
1654	<	for (int i = 0; i < ws.length; ++i) {
1655	<	ForkJoinWorkerThread w = ws[i];
1656	<	if (w != null)
1657	<	n += w.drainTasksTo(c);
1015	<	}
1653	>	int nws = ws.length;
1654	>	for (int i = 0; i < nws; ++i) {
1655	>	ForkJoinWorkerThread w = ws[i];
1656	>	if (w != null)
1657	>	n += w.drainTasksTo(c);
1658		}
1659		return n;
1660		}
1661
1662		/**
1663	+	* Returns count of total parks by existing workers.
1664	+	* Used during development only since not meaningful to users.
1665	+	*/
1666	+	private int collectParkCount() {
1667	+	int count = 0;
1668	+	ForkJoinWorkerThread[] ws = workers;
1669	+	int nws = ws.length;
1670	+	for (int i = 0; i < nws; ++i) {
1671	+	ForkJoinWorkerThread w = ws[i];
1672	+	if (w != null)
1673	+	count += w.parkCount;
1674	+	}
1675	+	return count;
1676	+	}
1677	+
1678	+	/**
1679		* Returns a string identifying this pool, as well as its state,
1680		* including indications of run state, parallelism level, and
1681		* worker and task counts.
#	Line 1025 | Line 1683 | public class ForkJoinPool extends Abstra
1683		* @return a string identifying this pool, as well as its state
1684		*/
1685		public String toString() {
1028	–	int ps = parallelism;
1029	–	int wc = workerCounts;
1030	–	int rc = runControl;
1686		long st = getStealCount();
1687		long qt = getQueuedTaskCount();
1688		long qs = getQueuedSubmissionCount();
1689	+	int wc = workerCounts;
1690	+	int tc = wc >>> TOTAL_COUNT_SHIFT;
1691	+	int rc = wc & RUNNING_COUNT_MASK;
1692	+	int pc = parallelism;
1693	+	int rs = runState;
1694	+	int ac = rs & ACTIVE_COUNT_MASK;
1695	+	//        int pk = collectParkCount();
1696		return super.toString() +
1697	<	"[" + runStateToString(runStateOf(rc)) +
1698	<	", parallelism = " + ps +
1699	<	", size = " + totalCountOf(wc) +
1700	<	", active = " + activeCountOf(rc) +
1701	<	", running = " + runningCountOf(wc) +
1697	>	"[" + runLevelToString(rs) +
1698	>	", parallelism = " + pc +
1699	>	", size = " + tc +
1700	>	", active = " + ac +
1701	>	", running = " + rc +
1702		", steals = " + st +
1703		", tasks = " + qt +
1704		", submissions = " + qs +
1705	+	//            ", parks = " + pk +
1706		"]";
1707		}
1708
1709	<	private static String runStateToString(int rs) {
1710	<	switch(rs) {
1711	<	case RUNNING: return "Running";
1712	<	case SHUTDOWN: return "Shutting down";
1713	<	case TERMINATING: return "Terminating";
1051	<	case TERMINATED: return "Terminated";
1052	<	default: throw new Error("Unknown run state");
1053	<	}
1709	>	private static String runLevelToString(int s) {
1710	>	return ((s & TERMINATED) != 0 ? "Terminated" :
1711	>	((s & TERMINATING) != 0 ? "Terminating" :
1712	>	((s & SHUTDOWN) != 0 ? "Shutting down" :
1713	>	"Running")));
1714		}
1715
1056	–	// lifecycle control
1057	–
1716		/**
1717		* Initiates an orderly shutdown in which previously submitted
1718		* tasks are executed, but no new tasks will be accepted.
#	Line 1069 | Line 1727 | public class ForkJoinPool extends Abstra
1727		*/
1728		public void shutdown() {
1729		checkPermission();
1730	<	transitionRunStateTo(SHUTDOWN);
1731	<	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	<	}
1730	>	advanceRunLevel(SHUTDOWN);
1731	>	tryTerminate(false);
1732		}
1733
1734		/**
1735	<	* Attempts to stop all actively executing tasks, and cancels all
1736	<	* waiting tasks.  Tasks that are in the process of being
1737	<	* submitted or executed concurrently during the course of this
1738	<	* method may or may not be rejected. Unlike some other executors,
1739	<	* this method cancels rather than collects non-executed tasks
1740	<	* upon termination, so always returns an empty list. However, you
1741	<	* can use method {@link #drainTasksTo} before invoking this
1742	<	* method to transfer unexecuted tasks to another collection.
1735	>	* Attempts to cancel and/or stop all tasks, and reject all
1736	>	* subsequently submitted tasks.  Tasks that are in the process of
1737	>	* being submitted or executed concurrently during the course of
1738	>	* this method may or may not be rejected. This method cancels
1739	>	* both existing and unexecuted tasks, in order to permit
1740	>	* termination in the presence of task dependencies. So the method
1741	>	* always returns an empty list (unlike the case for some other
1742	>	* Executors).
1743		*
1744		* @return an empty list
1745		* @throws SecurityException if a security manager exists and
#	Line 1106 | Line 1749 | public class ForkJoinPool extends Abstra
1749		*/
1750		public List<Runnable> shutdownNow() {
1751		checkPermission();
1752	<	terminate();
1752	>	tryTerminate(true);
1753		return Collections.emptyList();
1754		}
1755
#	Line 1116 | Line 1759 | public class ForkJoinPool extends Abstra
1759		* @return {@code true} if all tasks have completed following shut down
1760		*/
1761		public boolean isTerminated() {
1762	<	return runStateOf(runControl) == TERMINATED;
1762	>	return runState >= TERMINATED;
1763		}
1764
1765		/**
1766		* Returns {@code true} if the process of termination has
1767	<	* commenced but possibly not yet completed.
1767	>	* commenced but not yet completed.  This method may be useful for
1768	>	* debugging. A return of {@code true} reported a sufficient
1769	>	* period after shutdown may indicate that submitted tasks have
1770	>	* ignored or suppressed interruption, causing this executor not
1771	>	* to properly terminate.
1772		*
1773	<	* @return {@code true} if terminating
1773	>	* @return {@code true} if terminating but not yet terminated
1774		*/
1775		public boolean isTerminating() {
1776	<	return runStateOf(runControl) >= TERMINATING;
1776	>	return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
1777		}
1778
1779		/**
#	Line 1135 | Line 1782 | public class ForkJoinPool extends Abstra
1782		* @return {@code true} if this pool has been shut down
1783		*/
1784		public boolean isShutdown() {
1785	<	return runStateOf(runControl) >= SHUTDOWN;
1785	>	return runState >= SHUTDOWN;
1786		}
1787
1788		/**
#	Line 1151 | Line 1798 | public class ForkJoinPool extends Abstra
1798		*/
1799		public boolean awaitTermination(long timeout, TimeUnit unit)
1800		throws InterruptedException {
1154	–	long nanos = unit.toNanos(timeout);
1155	–	final ReentrantLock lock = this.workerLock;
1156	–	lock.lock();
1157	–	try {
1158	–	for (;;) {
1159	–	if (isTerminated())
1160	–	return true;
1161	–	if (nanos <= 0)
1162	–	return false;
1163	–	nanos = termination.awaitNanos(nanos);
1164	–	}
1165	–	} finally {
1166	–	lock.unlock();
1167	–	}
1168	–	}
1169	–
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();
1801		try {
1802	<	ForkJoinWorkerThread[] ws = workers;
1803	<	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)
1802	>	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1803	>	} catch(TimeoutException ex) {
1804		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	–	}
1805		}
1806		}
1807
#	Line 1742 | Line 1813 | public class ForkJoinPool extends Abstra
1813		* Method {@code isReleasable} must return {@code true} if
1814		* blocking is not necessary. Method {@code block} blocks the
1815		* current thread if necessary (perhaps internally invoking
1816	<	* {@code isReleasable} before actually blocking.).
1816	>	* {@code isReleasable} before actually blocking).
1817		*
1818		* <p>For example, here is a ManagedBlocker based on a
1819		* ReentrantLock:
#	Line 1783 | Line 1854 | public class ForkJoinPool extends Abstra
1854		* Blocks in accord with the given blocker.  If the current thread
1855		* is a {@link ForkJoinWorkerThread}, this method possibly
1856		* arranges for a spare thread to be activated if necessary to
1857	<	* 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.
1857	>	* ensure sufficient parallelism while the current thread is blocked.
1858		*
1859		* <p>If the caller is not a {@link ForkJoinTask}, this method is
1860		* behaviorally equivalent to
#	Line 1804 | Line 1868 | public class ForkJoinPool extends Abstra
1868		* first be expanded to ensure parallelism, and later adjusted.
1869		*
1870		* @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.
1871		* @throws InterruptedException if blocker.block did so
1872		*/
1873	<	public static void managedBlock(ManagedBlocker blocker,
1814	<	boolean maintainParallelism)
1873	>	public static void managedBlock(ManagedBlocker blocker)
1874		throws InterruptedException {
1875		Thread t = Thread.currentThread();
1876	<	ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
1877	<	((ForkJoinWorkerThread) t).pool : null);
1878	<	if (!blocker.isReleasable()) {
1879	<	try {
1821	<	if (pool == null ||
1822	<	!pool.preBlock(blocker, maintainParallelism))
1823	<	awaitBlocker(blocker);
1824	<	} finally {
1825	<	if (pool != null)
1826	<	pool.updateRunningCount(1);
1827	<	}
1876	>	if (t instanceof ForkJoinWorkerThread)
1877	>	((ForkJoinWorkerThread) t).pool.awaitBlocker(blocker);
1878	>	else {
1879	>	do {} while (!blocker.isReleasable() && !blocker.block());
1880		}
1881		}
1882
1831	–	private static void awaitBlocker(ManagedBlocker blocker)
1832	–	throws InterruptedException {
1833	–	do {} while (!blocker.isReleasable() && !blocker.block());
1834	–	}
1835	–
1883		// AbstractExecutorService overrides.  These rely on undocumented
1884		// fact that ForkJoinTask.adapt returns ForkJoinTasks that also
1885		// implement RunnableFuture.
#	Line 1848 | Line 1895 | public class ForkJoinPool extends Abstra
1895		// Unsafe mechanics
1896
1897		private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1851	–	private static final long eventCountOffset =
1852	–	objectFieldOffset("eventCount", ForkJoinPool.class);
1898		private static final long workerCountsOffset =
1899		objectFieldOffset("workerCounts", ForkJoinPool.class);
1900	<	private static final long runControlOffset =
1901	<	objectFieldOffset("runControl", ForkJoinPool.class);
1902	<	private static final long syncStackOffset =
1903	<	objectFieldOffset("syncStack",ForkJoinPool.class);
1904	<	private static final long spareStackOffset =
1905	<	objectFieldOffset("spareStack", ForkJoinPool.class);
1906	<
1907	<	private boolean casEventCount(long cmp, long val) {
1863	<	return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
1864	<	}
1865	<	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	<	}
1900	>	private static final long runStateOffset =
1901	>	objectFieldOffset("runState", ForkJoinPool.class);
1902	>	private static final long eventCountOffset =
1903	>	objectFieldOffset("eventCount", ForkJoinPool.class);
1904	>	private static final long eventWaitersOffset =
1905	>	objectFieldOffset("eventWaiters",ForkJoinPool.class);
1906	>	private static final long stealCountOffset =
1907	>	objectFieldOffset("stealCount",ForkJoinPool.class);
1908
1909		private static long objectFieldOffset(String field, Class<?> klazz) {
1910		try {

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