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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.29 by jsr166, Mon Jul 27 21:41:53 2009 UTC vs.
Revision 1.53 by dl, Mon Apr 5 15:52:26 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 ForkJoinPool provides the entry point for submissions from
24	<	* non-ForkJoinTasks, as well as management and monitoring operations.
25	<	* Normally a single ForkJoinPool is used for a large number of
27	<	* submitted tasks. Otherwise, use would not usually outweigh the
28	<	* construction and bookkeeping overhead of creating a large set of
29	<	* threads.
23	>	* A {@code ForkJoinPool} provides the entry point for submissions
24	>	* from non-{@code ForkJoinTask}s, as well as management and
25	>	* monitoring operations.
26		*
27	<	* <p>ForkJoinPools differ from other kinds of Executors mainly in
28	<	* that they provide <em>work-stealing</em>: all threads in the pool
29	<	* attempt to find and execute subtasks created by other active tasks
30	<	* (eventually blocking if none exist). This makes them efficient when
31	<	* most tasks spawn other subtasks (as do most ForkJoinTasks), as well
32	<	* as the mixed execution of some plain Runnable- or Callable- based
33	<	* activities along with ForkJoinTasks. When setting {@linkplain
34	<	* #setAsyncMode async mode}, a ForkJoinPool may also be appropriate
35	<	* for use with fine-grained tasks that are never joined. Otherwise,
36	<	* other ExecutorService implementations are typically more
37	<	* 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). A {@code ForkJoinPool} may also be used for mixed
34	>	* execution of some plain {@code Runnable}- or {@code Callable}-
35	>	* based activities along with {@code ForkJoinTask}s. When setting
36	>	* {@linkplain #setAsyncMode async mode}, a {@code ForkJoinPool} may
37	>	* also be appropriate for use with fine-grained tasks of any form
38	>	* that are never joined. Otherwise, other {@code ExecutorService}
39	>	* implementations are typically more appropriate choices.
40		*
41	<	* <p>A ForkJoinPool may be constructed with a given parallelism level
42	<	* (target pool size), which it attempts to maintain by dynamically
43	<	* adding, suspending, or resuming threads, even if some tasks are
44	<	* waiting to join others. However, no such adjustments are performed
45	<	* in the face of blocked IO or other unmanaged synchronization. The
46	<	* nested {@link ManagedBlocker} interface enables extension of
47	<	* the kinds of synchronization accommodated.  The target parallelism
48	<	* level may also be changed dynamically ({@link #setParallelism})
49	<	* and thread construction can be limited using methods
50	<	* {@link #setMaximumPoolSize} and/or
51	<	* {@link #setMaintainsParallelism}.
41	>	* <p>A {@code ForkJoinPool} is constructed with a given target
42	>	* parallelism level; by default, equal to the number of available
43	>	* processors. Unless configured otherwise via {@link
44	>	* #setMaintainsParallelism}, the pool attempts to maintain this
45	>	* number of active (or available) threads by dynamically adding,
46	>	* suspending, or resuming internal worker threads, even if some tasks
47	>	* are stalled waiting to join others. However, no such adjustments
48	>	* are performed in the face of blocked IO or other unmanaged
49	>	* synchronization. The nested {@link ManagedBlocker} interface
50	>	* enables extension of the kinds of synchronization accommodated.
51	>	* The target parallelism level may also be changed dynamically
52	>	* ({@link #setParallelism}). The total number of threads may be
53	>	* limited using method {@link #setMaximumPoolSize}, in which case it
54	>	* may become possible for the activities of a pool to stall due to
55	>	* the lack of available threads to process new tasks. When the pool
56	>	* is executing tasks, these and other configuration setting methods
57	>	* may only gradually affect actual pool sizes. It is normally best
58	>	* practice to invoke these methods only when the pool is known to be
59	>	* quiescent.
60		*
61		* <p>In addition to execution and lifecycle control methods, this
62		* class provides status check methods (for example
#	Line 59 | Line 65 | import java.util.concurrent.atomic.Atomi
65		* {@link #toString} returns indications of pool state in a
66		* convenient form for informal monitoring.
67		*
68	+	* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
69	+	* used for all parallel task execution in a program or subsystem.
70	+	* Otherwise, use would not usually outweigh the construction and
71	+	* bookkeeping overhead of creating a large set of threads. For
72	+	* example, a common pool could be used for the {@code SortTasks}
73	+	* illustrated in {@link RecursiveAction}. Because {@code
74	+	* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
75	+	* daemon} mode, there is typically no need to explicitly {@link
76	+	* #shutdown} such a pool upon program exit.
77	+	*
78	+	* <pre>
79	+	* static final ForkJoinPool mainPool = new ForkJoinPool();
80	+	* ...
81	+	* public void sort(long[] array) {
82	+	*   mainPool.invoke(new SortTask(array, 0, array.length));
83	+	* }
84	+	* </pre>
85	+	*
86		* <p><b>Implementation notes</b>: This implementation restricts the
87		* maximum number of running threads to 32767. Attempts to create
88	<	* pools with greater than the maximum result in
89	<	* IllegalArgumentExceptions.
88	>	* pools with greater than the maximum number result in
89	>	* {@code IllegalArgumentException}.
90	>	*
91	>	* <p>This implementation rejects submitted tasks (that is, by throwing
92	>	* {@link RejectedExecutionException}) only when the pool is shut down.
93		*
94		* @since 1.7
95		* @author Doug Lea
#	Line 70 | Line 97 | import java.util.concurrent.atomic.Atomi
97		public class ForkJoinPool extends AbstractExecutorService {
98
99		/*
100	<	* See the extended comments interspersed below for design,
101	<	* rationale, and walkthroughs.
102	<	*/
103	<
104	<	/** Mask for packing and unpacking shorts */
105	<	private static final int  shortMask = 0xffff;
106	<
107	<	/** Max pool size -- must be a power of two minus 1 */
108	<	private static final int MAX_THREADS =  0x7FFF;
109	<
110	<	/**
111	<	* Factory for creating new ForkJoinWorkerThreads.  A
112	<	* ForkJoinWorkerThreadFactory must be defined and used for
113	<	* ForkJoinWorkerThread subclasses that extend base functionality
114	<	* or initialize threads with different contexts.
100	>	* Implementation Overview
101	>	*
102	>	* This class provides the central bookkeeping and control for a
103	>	* set of worker threads: Submissions from non-FJ threads enter
104	>	* into a submission queue. Workers take these tasks and typically
105	>	* split them into subtasks that may be stolen by other workers.
106	>	* The main work-stealing mechanics implemented in class
107	>	* ForkJoinWorkerThread give first priority to processing tasks
108	>	* from their own queues (LIFO or FIFO, depending on mode), then
109	>	* to randomized FIFO steals of tasks in other worker queues, and
110	>	* lastly to new submissions. These mechanics do not consider
111	>	* affinities, loads, cache localities, etc, so rarely provide the
112	>	* best possible performance on a given machine, but portably
113	>	* provide good throughput by averaging over these factors.
114	>	* (Further, even if we did try to use such information, we do not
115	>	* usually have a basis for exploiting it. For example, some sets
116	>	* of tasks profit from cache affinities, but others are harmed by
117	>	* cache pollution effects.)
118	>	*
119	>	* The main throughput advantages of work-stealing stem from
120	>	* decentralized control -- workers mostly steal tasks from each
121	>	* other. We do not want to negate this by creating bottlenecks
122	>	* implementing the management responsibilities of this class. So
123	>	* we use a collection of techniques that avoid, reduce, or cope
124	>	* well with contention. These entail several instances of
125	>	* bit-packing into CASable fields to maintain only the minimally
126	>	* required atomicity. To enable such packing, we restrict maximum
127	>	* parallelism to (1<<15)-1 (enabling twice this to fit into a 16
128	>	* bit field), which is far in excess of normal operating range.
129	>	* Even though updates to some of these bookkeeping fields do
130	>	* sometimes contend with each other, they don't normally
131	>	* cache-contend with updates to others enough to warrant memory
132	>	* padding or isolation. So they are all held as fields of
133	>	* ForkJoinPool objects.  The main capabilities are as follows:
134	>	*
135	>	* 1. Creating and removing workers. Workers are recorded in the
136	>	* "workers" array. This is an array as opposed to some other data
137	>	* structure to support index-based random steals by workers.
138	>	* Updates to the array recording new workers and unrecording
139	>	* terminated ones are protected from each other by a lock
140	>	* (workerLock) but the array is otherwise concurrently readable,
141	>	* and accessed directly by workers. To simplify index-based
142	>	* operations, the array size is always a power of two, and all
143	>	* readers must tolerate null slots. Currently, all but the first
144	>	* worker thread creation is on-demand, triggered by task
145	>	* submissions, replacement of terminated workers, and/or
146	>	* compensation for blocked workers. However, all other support
147	>	* code is set up to work with other policies.
148	>	*
149	>	* 2. Bookkeeping for dynamically adding and removing workers. We
150	>	* maintain a given level of parallelism (or, if
151	>	* maintainsParallelism is false, at least avoid starvation). When
152	>	* some workers are known to be blocked (on joins or via
153	>	* ManagedBlocker), we may create or resume others to take their
154	>	* place until they unblock (see below). Implementing this
155	>	* requires counts of the number of "running" threads (i.e., those
156	>	* that are neither blocked nor artifically suspended) as well as
157	>	* the total number.  These two values are packed into one field,
158	>	* "workerCounts" because we need accurate snapshots when deciding
159	>	* to create, resume or suspend.  To support these decisions,
160	>	* updates must be prospective (not retrospective).  For example,
161	>	* the running count is decremented before blocking by a thread
162	>	* about to block, but incremented by the thread about to unblock
163	>	* it. (In a few cases, these prospective updates may need to be
164	>	* rolled back, for example when deciding to create a new worker
165	>	* but the thread factory fails or returns null. In these cases,
166	>	* we are no worse off wrt other decisions than we would be
167	>	* otherwise.)  Updates to the workerCounts field sometimes
168	>	* transiently encounter a fair amount of contention when join
169	>	* dependencies are such that many threads block or unblock at
170	>	* about the same time. We alleviate this by sometimes bundling
171	>	* updates (for example blocking one thread on join and resuming a
172	>	* spare cancel each other out), and in most other cases
173	>	* performing an alternative action (like releasing waiters and
174	>	* finding spares; see below) as a more productive form of
175	>	* backoff.
176	>	*
177	>	* 3. Maintaining global run state. The run state of the pool
178	>	* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
179	>	* those in other Executor implementations, as well as a count of
180	>	* "active" workers -- those that are, or soon will be, or
181	>	* recently were executing tasks. The runLevel and active count
182	>	* are packed together in order to correctly trigger shutdown and
183	>	* termination. Without care, active counts can be subject to very
184	>	* high contention.  We substantially reduce this contention by
185	>	* relaxing update rules.  A worker must claim active status
186	>	* prospectively, by activating if it sees that a submitted or
187	>	* stealable task exists (it may find after activating that the
188	>	* task no longer exists). It stays active while processing this
189	>	* task (if it exists) and any other local subtasks it produces,
190	>	* until it cannot find any other tasks. It then tries
191	>	* inactivating (see method preStep), but upon update contention
192	>	* instead scans for more tasks, later retrying inactivation if it
193	>	* doesn't find any.
194	>	*
195	>	* 4. Managing idle workers waiting for tasks. We cannot let
196	>	* workers spin indefinitely scanning for tasks when none are
197	>	* available. On the other hand, we must quickly prod them into
198	>	* action when new tasks are submitted or generated.  We
199	>	* park/unpark these idle workers using an event-count scheme.
200	>	* Field eventCount is incremented upon events that may enable
201	>	* workers that previously could not find a task to now find one:
202	>	* Submission of a new task to the pool, or another worker pushing
203	>	* a task onto a previously empty queue.  (We also use this
204	>	* mechanism for termination and reconfiguration actions that
205	>	* require wakeups of idle workers).  Each worker maintains its
206	>	* last known event count, and blocks when a scan for work did not
207	>	* find a task AND its lastEventCount matches the current
208	>	* eventCount. Waiting idle workers are recorded in a variant of
209	>	* Treiber stack headed by field eventWaiters which, when nonzero,
210	>	* encodes the thread index and count awaited for by the worker
211	>	* thread most recently calling eventSync. This thread in turn has
212	>	* a record (field nextEventWaiter) for the next waiting worker.
213	>	* In addition to allowing simpler decisions about need for
214	>	* wakeup, the event count bits in eventWaiters serve the role of
215	>	* tags to avoid ABA errors in Treiber stacks.  To reduce delays
216	>	* in task diffusion, workers not otherwise occupied may invoke
217	>	* method releaseWaiters, that removes and signals (unparks)
218	>	* workers not waiting on current count. To minimize task
219	>	* production stalls associate with signalling, any worker pushing
220	>	* a task on an empty queue invokes the weaker method signalWork,
221	>	* that only releases idle workers until it detects interference
222	>	* by other threads trying to release, and lets them take
223	>	* over. The net effect is a tree-like diffusion of signals, where
224	>	* released threads and possibly others) help with unparks.  To
225	>	* further reduce contention effects a bit, failed CASes to
226	>	* increment field eventCount are tolerated without retries.
227	>	* Conceptually they are merged into the same event, which is OK
228	>	* when their only purpose is to enable workers to scan for work.
229	>	*
230	>	* 5. Managing suspension of extra workers. When a worker is about
231	>	* to block waiting for a join (or via ManagedBlockers), we may
232	>	* create a new thread to maintain parallelism level, or at least
233	>	* avoid starvation (see below). Usually, extra threads are needed
234	>	* for only very short periods, yet join dependencies are such
235	>	* that we sometimes need them in bursts. Rather than create new
236	>	* threads each time this happens, we suspend no-longer-needed
237	>	* extra ones as "spares". For most purposes, we don't distinguish
238	>	* "extra" spare threads from normal "core" threads: On each call
239	>	* to preStep (the only point at which we can do this) a worker
240	>	* checks to see if there are now too many running workers, and if
241	>	* so, suspends itself.  Methods preJoin and doBlock look for
242	>	* suspended threads to resume before considering creating a new
243	>	* replacement. We don't need a special data structure to maintain
244	>	* spares; simply scanning the workers array looking for
245	>	* worker.isSuspended() is fine because the calling thread is
246	>	* otherwise not doing anything useful anyway; we are at least as
247	>	* happy if after locating a spare, the caller doesn't actually
248	>	* block because the join is ready before we try to adjust and
249	>	* compensate.  Note that this is intrinsically racy.  One thread
250	>	* may become a spare at about the same time as another is
251	>	* needlessly being created. We counteract this and related slop
252	>	* in part by requiring resumed spares to immediately recheck (in
253	>	* preStep) to see whether they they should re-suspend. The only
254	>	* effective difference between "extra" and "core" threads is that
255	>	* we allow the "extra" ones to time out and die if they are not
256	>	* resumed within a keep-alive interval of a few seconds. This is
257	>	* implemented mainly within ForkJoinWorkerThread, but requires
258	>	* some coordination (isTrimmed() -- meaning killed while
259	>	* suspended) to correctly maintain pool counts.
260	>	*
261	>	* 6. Deciding when to create new workers. The main dynamic
262	>	* control in this class is deciding when to create extra threads,
263	>	* in methods preJoin and doBlock. We always need to create one
264	>	* when the number of running threads becomes zero. But because
265	>	* blocked joins are typically dependent, we don't necessarily
266	>	* need or want one-to-one replacement. Using a one-to-one
267	>	* compensation rule often leads to enough useless overhead
268	>	* creating, suspending, resuming, and/or killing threads to
269	>	* signficantly degrade throughput.  We use a rule reflecting the
270	>	* idea that, the more spare threads you already have, the more
271	>	* evidence you need to create another one; where "evidence" is
272	>	* expressed as the current deficit -- target minus running
273	>	* threads. To reduce flickering and drift around target values,
274	>	* the relation is quadratic: adding a spare if (dc*dc)>=(sc*pc)
275	>	* (where dc is deficit, sc is number of spare threads and pc is
276	>	* target parallelism.)  This effectively reduces churn at the
277	>	* price of systematically undershooting target parallelism when
278	>	* many threads are blocked.  However, biasing toward undeshooting
279	>	* partially compensates for the above mechanics to suspend extra
280	>	* threads, that normally lead to overshoot because we can only
281	>	* suspend workers in-between top-level actions. It also better
282	>	* copes with the fact that some of the methods in this class tend
283	>	* to never become compiled (but are interpreted), so some
284	>	* components of the entire set of controls might execute many
285	>	* times faster than others. And similarly for cases where the
286	>	* apparent lack of work is just due to GC stalls and other
287	>	* transient system activity.
288	>	*
289	>	* 7. Maintaining other configuration parameters and monitoring
290	>	* statistics. Updates to fields controlling parallelism level,
291	>	* max size, etc can only meaningfully take effect for individual
292	>	* threads upon their next top-level actions; i.e., between
293	>	* stealing/running tasks/submission, which are separated by calls
294	>	* to preStep.  Memory ordering for these (assumed infrequent)
295	>	* reconfiguration calls is ensured by using reads and writes to
296	>	* volatile field workerCounts (that must be read in preStep anyway)
297	>	* as "fences" -- user-level reads are preceded by reads of
298	>	* workCounts, and writes are followed by no-op CAS to
299	>	* workerCounts. The values reported by other management and
300	>	* monitoring methods are either computed on demand, or are kept
301	>	* in fields that are only updated when threads are otherwise
302	>	* idle.
303	>	*
304	>	* Beware that there is a lot of representation-level coupling
305	>	* among classes ForkJoinPool, ForkJoinWorkerThread, and
306	>	* ForkJoinTask.  For example, direct access to "workers" array by
307	>	* workers, and direct access to ForkJoinTask.status by both
308	>	* ForkJoinPool and ForkJoinWorkerThread.  There is little point
309	>	* trying to reduce this, since any associated future changes in
310	>	* representations will need to be accompanied by algorithmic
311	>	* changes anyway.
312	>	*
313	>	* Style notes: There are lots of inline assignments (of form
314	>	* "while ((local = field) != 0)") which are usually the simplest
315	>	* way to ensure read orderings. Also several occurrences of the
316	>	* unusual "do {} while(!cas...)" which is the simplest way to
317	>	* force an update of a CAS'ed variable. There are also a few
318	>	* other coding oddities that help some methods perform reasonably
319	>	* even when interpreted (not compiled).
320	>	*
321	>	* The order of declarations in this file is: (1) statics (2)
322	>	* fields (along with constants used when unpacking some of them)
323	>	* (3) internal control methods (4) callbacks and other support
324	>	* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
325	>	* methods (plus a few little helpers).
326	>	*/
327	>
328	>	/**
329	>	* Factory for creating new {@link ForkJoinWorkerThread}s.
330	>	* A {@code ForkJoinWorkerThreadFactory} must be defined and used
331	>	* for {@code ForkJoinWorkerThread} subclasses that extend base
332	>	* functionality or initialize threads with different contexts.
333		*/
334		public static interface ForkJoinWorkerThreadFactory {
335		/**
336		* Returns a new worker thread operating in the given pool.
337		*
338		* @param pool the pool this thread works in
339	<	* @throws NullPointerException if pool is null
339	>	* @throws NullPointerException if the pool is null
340		*/
341		public ForkJoinWorkerThread newThread(ForkJoinPool pool);
342		}
#	Line 103 | Line 348 | public class ForkJoinPool extends Abstra
348		static class  DefaultForkJoinWorkerThreadFactory
349		implements ForkJoinWorkerThreadFactory {
350		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
351	<	try {
107	<	return new ForkJoinWorkerThread(pool);
108	<	} catch (OutOfMemoryError oom)  {
109	<	return null;
110	<	}
351	>	return new ForkJoinWorkerThread(pool);
352		}
353		}
354
#	Line 143 | Line 384 | public class ForkJoinPool extends Abstra
384		new AtomicInteger();
385
386		/**
387	<	* Array holding all worker threads in the pool. Initialized upon
388	<	* first use. Array size must be a power of two.  Updates and
389	<	* replacements are protected by workerLock, but it is always kept
390	<	* in a consistent enough state to be randomly accessed without
391	<	* locking by workers performing work-stealing.
387	>	* Absolute bound for parallelism level. Twice this number must
388	>	* fit into a 16bit field to enable word-packing for some counts.
389	>	*/
390	>	private static final int MAX_THREADS = 0x7fff;
391	>
392	>	/**
393	>	* Array holding all worker threads in the pool.  Array size must
394	>	* be a power of two.  Updates and replacements are protected by
395	>	* workerLock, but the array is always kept in a consistent enough
396	>	* state to be randomly accessed without locking by workers
397	>	* performing work-stealing, as well as other traversal-based
398	>	* methods in this class. All readers must tolerate that some
399	>	* array slots may be null.
400		*/
401		volatile ForkJoinWorkerThread[] workers;
402
403		/**
404	<	* Lock protecting access to workers.
404	>	* Queue for external submissions.
405		*/
406	<	private final ReentrantLock workerLock;
406	>	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
407
408		/**
409	<	* Condition for awaitTermination.
409	>	* Lock protecting updates to workers array.
410		*/
411	<	private final Condition termination;
411	>	private final ReentrantLock workerLock;
412
413		/**
414	<	* The uncaught exception handler used when any worker
166	<	* abruptly terminates
414	>	* Latch released upon termination.
415		*/
416	<	private Thread.UncaughtExceptionHandler ueh;
416	>	private final CountDownLatch terminationLatch;
417
418		/**
419		* Creation factory for worker threads.
#	Line 173 | Line 421 | public class ForkJoinPool extends Abstra
421		private final ForkJoinWorkerThreadFactory factory;
422
423		/**
424	<	* Head of stack of threads that were created to maintain
425	<	* parallelism when other threads blocked, but have since
178	<	* suspended when the parallelism level rose.
424	>	* Sum of per-thread steal counts, updated only when threads are
425	>	* idle or terminating.
426		*/
427	<	private volatile WaitQueueNode spareStack;
427	>	private volatile long stealCount;
428
429		/**
430	<	* Sum of per-thread steal counts, updated only when threads are
431	<	* idle or terminating.
430	>	* Encoded record of top of treiber stack of threads waiting for
431	>	* events. The top 32 bits contain the count being waited for. The
432	>	* bottom word contains one plus the pool index of waiting worker
433	>	* thread.
434		*/
435	<	private final AtomicLong stealCount;
435	>	private volatile long eventWaiters;
436	>
437	>	private static final int  EVENT_COUNT_SHIFT = 32;
438	>	private static final long WAITER_INDEX_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
439
440		/**
441	<	* Queue for external submissions.
441	>	* A counter for events that may wake up worker threads:
442	>	*   - Submission of a new task to the pool
443	>	*   - A worker pushing a task on an empty queue
444	>	*   - termination and reconfiguration
445		*/
446	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
446	>	private volatile int eventCount;
447
448		/**
449	<	* Head of Treiber stack for barrier sync. See below for explanation.
449	>	* Lifecycle control. The low word contains the number of workers
450	>	* that are (probably) executing tasks. This value is atomically
451	>	* incremented before a worker gets a task to run, and decremented
452	>	* when worker has no tasks and cannot find any.  Bits 16-18
453	>	* contain runLevel value. When all are zero, the pool is
454	>	* running. Level transitions are monotonic (running -> shutdown
455	>	* -> terminating -> terminated) so each transition adds a bit.
456	>	* These are bundled together to ensure consistent read for
457	>	* termination checks (i.e., that runLevel is at least SHUTDOWN
458	>	* and active threads is zero).
459	>	*/
460	>	private volatile int runState;
461	>
462	>	// Note: The order among run level values matters.
463	>	private static final int RUNLEVEL_SHIFT     = 16;
464	>	private static final int SHUTDOWN           = 1 << RUNLEVEL_SHIFT;
465	>	private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
466	>	private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
467	>	private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
468	>	private static final int ONE_ACTIVE         = 1; // active update delta
469	>
470	>	/**
471	>	* Holds number of total (i.e., created and not yet terminated)
472	>	* and running (i.e., not blocked on joins or other managed sync)
473	>	* threads, packed together to ensure consistent snapshot when
474	>	* making decisions about creating and suspending spare
475	>	* threads. Updated only by CAS. Note that adding a new worker
476	>	* requires incrementing both counts, since workers start off in
477	>	* running state.  This field is also used for memory-fencing
478	>	* configuration parameters.
479	>	*/
480	>	private volatile int workerCounts;
481	>
482	>	private static final int TOTAL_COUNT_SHIFT  = 16;
483	>	private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1;
484	>	private static final int ONE_RUNNING        = 1;
485	>	private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
486	>
487	>	/*
488	>	* Fields parallelism. maxPoolSize, locallyFifo,
489	>	* maintainsParallelism, and ueh are non-volatile, but external
490	>	* reads/writes use workerCount fences to ensure visability.
491		*/
196	–	private volatile WaitQueueNode syncStack;
492
493		/**
494	<	* The count for event barrier
494	>	* The target parallelism level.
495		*/
496	<	private volatile long eventCount;
496	>	private int parallelism;
497
498		/**
499	<	* Pool number, just for assigning useful names to worker threads
499	>	* The maximum allowed pool size.
500		*/
501	<	private final int poolNumber;
501	>	private int maxPoolSize;
502
503		/**
504	<	* The maximum allowed pool size
504	>	* True if use local fifo, not default lifo, for local polling
505	>	* Replicated by ForkJoinWorkerThreads
506		*/
507	<	private volatile int maxPoolSize;
507	>	private boolean locallyFifo;
508
509		/**
510	<	* The desired parallelism level, updated only under workerLock.
510	>	* Controls whether to add spares to maintain parallelism
511		*/
512	<	private volatile int parallelism;
512	>	private boolean maintainsParallelism;
513
514		/**
515	<	* True if use local fifo, not default lifo, for local polling
515	>	* The uncaught exception handler used when any worker
516	>	* abruptly terminates
517		*/
518	<	private volatile boolean locallyFifo;
518	>	private Thread.UncaughtExceptionHandler ueh;
519
520		/**
521	<	* Holds number of total (i.e., created and not yet terminated)
225	<	* and running (i.e., not blocked on joins or other managed sync)
226	<	* threads, packed into one int to ensure consistent snapshot when
227	<	* making decisions about creating and suspending spare
228	<	* threads. Updated only by CAS.  Note: CASes in
229	<	* updateRunningCount and preJoin assume that running active count
230	<	* is in low word, so need to be modified if this changes.
521	>	* Pool number, just for assigning useful names to worker threads
522		*/
523	<	private volatile int workerCounts;
523	>	private final int poolNumber;
524
525	<	private static int totalCountOf(int s)           { return s >>> 16;  }
235	<	private static int runningCountOf(int s)         { return s & shortMask; }
236	<	private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
525	>	// utilities for updating fields
526
527		/**
528	<	* Adds delta (which may be negative) to running count.  This must
240	<	* be called before (with negative arg) and after (with positive)
241	<	* any managed synchronization (i.e., mainly, joins).
528	>	* Adds delta to running count.  Used mainly by ForkJoinTask.
529		*
530		* @param delta the number to add
531		*/
532		final void updateRunningCount(int delta) {
533	<	int s;
534	<	do {} while (!casWorkerCounts(s = workerCounts, s + delta));
533	>	int wc;
534	>	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
535	>	wc = workerCounts,
536	>	wc + delta));
537		}
538
539		/**
540	<	* Adds delta (which may be negative) to both total and running
541	<	* count.  This must be called upon creation and termination of
253	<	* worker threads.
254	<	*
255	<	* @param delta the number to add
540	>	* Write fence for user modifications of pool parameters
541	>	* (parallelism. etc).  Note that it doesn't matter if CAS fails.
542		*/
543	<	private void updateWorkerCount(int delta) {
544	<	int d = delta + (delta << 16); // add to both lo and hi parts
545	<	int s;
546	<	do {} while (!casWorkerCounts(s = workerCounts, s + d));
543	>	private void workerCountWriteFence() {
544	>	int wc;
545	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
546	>	wc = workerCounts, wc);
547		}
548
549		/**
550	<	* Lifecycle control. High word contains runState, low word
551	<	* contains the number of workers that are (probably) executing
552	<	* tasks. This value is atomically incremented before a worker
553	<	* gets a task to run, and decremented when worker has no tasks
554	<	* and cannot find any. These two fields are bundled together to
555	<	* support correct termination triggering.  Note: activeCount
270	<	* CAS'es cheat by assuming active count is in low word, so need
271	<	* to be modified if this changes
272	<	*/
273	<	private volatile int runControl;
274	<
275	<	// RunState values. Order among values matters
276	<	private static final int RUNNING     = 0;
277	<	private static final int SHUTDOWN    = 1;
278	<	private static final int TERMINATING = 2;
279	<	private static final int TERMINATED  = 3;
280	<
281	<	private static int runStateOf(int c)             { return c >>> 16; }
282	<	private static int activeCountOf(int c)          { return c & shortMask; }
283	<	private static int runControlFor(int r, int a)   { return (r << 16) + a; }
550	>	* Read fence for external reads of pool parameters
551	>	* (parallelism. maxPoolSize, etc).
552	>	*/
553	>	private void workerCountReadFence() {
554	>	int ignore = workerCounts;
555	>	}
556
557		/**
558		* Tries incrementing active count; fails on contention.
559	<	* Called by workers before/during executing tasks.
559	>	* Called by workers before executing tasks.
560		*
561		* @return true on success
562		*/
563		final boolean tryIncrementActiveCount() {
564	<	int c = runControl;
565	<	return casRunControl(c, c+1);
564	>	int c;
565	>	return UNSAFE.compareAndSwapInt(this, runStateOffset,
566	>	c = runState, c + ONE_ACTIVE);
567		}
568
569		/**
570		* Tries decrementing active count; fails on contention.
571	<	* Possibly triggers termination on success.
299	<	* Called by workers when they can't find tasks.
300	<	*
301	<	* @return true on success
571	>	* Called when workers cannot find tasks to run.
572		*/
573		final boolean tryDecrementActiveCount() {
574	<	int c = runControl;
575	<	int nextc = c - 1;
576	<	if (!casRunControl(c, nextc))
574	>	int c;
575	>	return UNSAFE.compareAndSwapInt(this, runStateOffset,
576	>	c = runState, c - ONE_ACTIVE);
577	>	}
578	>
579	>	/**
580	>	* Advances to at least the given level. Returns true if not
581	>	* already in at least the given level.
582	>	*/
583	>	private boolean advanceRunLevel(int level) {
584	>	for (;;) {
585	>	int s = runState;
586	>	if ((s & level) != 0)
587	>	return false;
588	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level))
589	>	return true;
590	>	}
591	>	}
592	>
593	>	// workers array maintenance
594	>
595	>	/**
596	>	* Records and returns a workers array index for new worker.
597	>	*/
598	>	private int recordWorker(ForkJoinWorkerThread w) {
599	>	// Try using slot totalCount-1. If not available, scan and/or resize
600	>	int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1;
601	>	final ReentrantLock lock = this.workerLock;
602	>	lock.lock();
603	>	try {
604	>	ForkJoinWorkerThread[] ws = workers;
605	>	int len = ws.length;
606	>	if (k < 0 || k >= len || ws[k] != null) {
607	>	for (k = 0; k < len && ws[k] != null; ++k)
608	>	;
609	>	if (k == len)
610	>	ws = Arrays.copyOf(ws, len << 1);
611	>	}
612	>	ws[k] = w;
613	>	workers = ws; // volatile array write ensures slot visibility
614	>	} finally {
615	>	lock.unlock();
616	>	}
617	>	return k;
618	>	}
619	>
620	>	/**
621	>	* Nulls out record of worker in workers array
622	>	*/
623	>	private void forgetWorker(ForkJoinWorkerThread w) {
624	>	int idx = w.poolIndex;
625	>	// Locking helps method recordWorker avoid unecessary expansion
626	>	final ReentrantLock lock = this.workerLock;
627	>	lock.lock();
628	>	try {
629	>	ForkJoinWorkerThread[] ws = workers;
630	>	if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify
631	>	ws[idx] = null;
632	>	} finally {
633	>	lock.unlock();
634	>	}
635	>	}
636	>
637	>	// adding and removing workers
638	>
639	>	/**
640	>	* Tries to create and add new worker. Assumes that worker counts
641	>	* are already updated to accommodate the worker, so adjusts on
642	>	* failure.
643	>	*
644	>	* @return new worker or null if creation failed
645	>	*/
646	>	private ForkJoinWorkerThread addWorker() {
647	>	ForkJoinWorkerThread w = null;
648	>	try {
649	>	w = factory.newThread(this);
650	>	} finally { // Adjust on either null or exceptional factory return
651	>	if (w == null) {
652	>	onWorkerCreationFailure();
653	>	return null;
654	>	}
655	>	}
656	>	w.start(recordWorker(w), locallyFifo, ueh);
657	>	return w;
658	>	}
659	>
660	>	/**
661	>	* Adjusts counts upon failure to create worker
662	>	*/
663	>	private void onWorkerCreationFailure() {
664	>	int c;
665	>	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
666	>	c = workerCounts,
667	>	c - (ONE_RUNNING|ONE_TOTAL)));
668	>	tryTerminate(false); // in case of failure during shutdown
669	>	}
670	>
671	>	/**
672	>	* Create enough total workers to establish target parallelism,
673	>	* giving up if terminating or addWorker fails
674	>	*/
675	>	private void ensureEnoughTotalWorkers() {
676	>	int wc;
677	>	while (runState < TERMINATING &&
678	>	((wc = workerCounts) >>> TOTAL_COUNT_SHIFT) < parallelism) {
679	>	if ((UNSAFE.compareAndSwapInt(this, workerCountsOffset,
680	>	wc, wc + (ONE_RUNNING|ONE_TOTAL)) &&
681	>	addWorker() == null))
682	>	break;
683	>	}
684	>	}
685	>
686	>	/**
687	>	* Final callback from terminating worker.  Removes record of
688	>	* worker from array, and adjusts counts. If pool is shutting
689	>	* down, tries to complete terminatation, else possibly replaces
690	>	* the worker.
691	>	*
692	>	* @param w the worker
693	>	*/
694	>	final void workerTerminated(ForkJoinWorkerThread w) {
695	>	if (w.active) { // force inactive
696	>	w.active = false;
697	>	do {} while (!tryDecrementActiveCount());
698	>	}
699	>	forgetWorker(w);
700	>
701	>	// decrement total count, and if was running, running count
702	>	int unit = w.isTrimmed()? ONE_TOTAL : (ONE_RUNNING|ONE_TOTAL);
703	>	int wc;
704	>	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
705	>	wc = workerCounts, wc - unit));
706	>
707	>	accumulateStealCount(w); // collect final count
708	>	if (!tryTerminate(false))
709	>	ensureEnoughTotalWorkers();
710	>	}
711	>
712	>	// Waiting for and signalling events
713	>
714	>	/**
715	>	* Ensures eventCount on exit is different (mod 2^32) than on
716	>	* entry.  CAS failures are OK -- any change in count suffices.
717	>	*/
718	>	private void advanceEventCount() {
719	>	int c;
720	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
721	>	}
722	>
723	>	/**
724	>	* Releases workers blocked on a count not equal to current count.
725	>	*/
726	>	final void releaseWaiters() {
727	>	long top;
728	>	int id;
729	>	while ((id = (int)((top = eventWaiters) & WAITER_INDEX_MASK)) > 0 &&
730	>	(int)(top >>> EVENT_COUNT_SHIFT) != eventCount) {
731	>	ForkJoinWorkerThread[] ws = workers;
732	>	ForkJoinWorkerThread w;
733	>	if (ws.length >= id && (w = ws[id - 1]) != null &&
734	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
735	>	top, w.nextWaiter))
736	>	LockSupport.unpark(w);
737	>	}
738	>	}
739	>
740	>	/**
741	>	* Advances eventCount and releases waiters until interference by
742	>	* other releasing threads is detected.
743	>	*/
744	>	final void signalWork() {
745	>	int ec;
746	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, ec=eventCount, ec+1);
747	>	outer:for (;;) {
748	>	long top = eventWaiters;
749	>	ec = eventCount;
750	>	for (;;) {
751	>	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
752	>	int id = (int)(top & WAITER_INDEX_MASK);
753	>	if (id <= 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
754	>	return;
755	>	if ((ws = workers).length < id || (w = ws[id - 1]) == null ||
756	>	!UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
757	>	top, top = w.nextWaiter))
758	>	continue outer;      // possibly stale; reread
759	>	LockSupport.unpark(w);
760	>	if (top != eventWaiters) // let someone else take over
761	>	return;
762	>	}
763	>	}
764	>	}
765	>
766	>	/**
767	>	* If worker is inactive, blocks until terminating or event count
768	>	* advances from last value held by worker; in any case helps
769	>	* release others.
770	>	*
771	>	* @param w the calling worker thread
772	>	*/
773	>	private void eventSync(ForkJoinWorkerThread w) {
774	>	if (!w.active) {
775	>	int prev = w.lastEventCount;
776	>	long nextTop = (((long)prev << EVENT_COUNT_SHIFT) |
777	>	((long)(w.poolIndex + 1)));
778	>	long top;
779	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
780	>	(((int)(top = eventWaiters) & WAITER_INDEX_MASK) == 0 ||
781	>	(int)(top >>> EVENT_COUNT_SHIFT) == prev) &&
782	>	eventCount == prev) {
783	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
784	>	w.nextWaiter = top, nextTop)) {
785	>	accumulateStealCount(w); // transfer steals while idle
786	>	Thread.interrupted();    // clear/ignore interrupt
787	>	while (eventCount == prev)
788	>	w.doPark();
789	>	break;
790	>	}
791	>	}
792	>	w.lastEventCount = eventCount;
793	>	}
794	>	releaseWaiters();
795	>	}
796	>
797	>	/**
798	>	* Callback from workers invoked upon each top-level action (i.e.,
799	>	* stealing a task or taking a submission and running
800	>	* it). Performs one or both of the following:
801	>	*
802	>	* * If the worker cannot find work, updates its active status to
803	>	* inactive and updates activeCount unless there is contention, in
804	>	* which case it may try again (either in this or a subsequent
805	>	* call).  Additionally, awaits the next task event and/or helps
806	>	* wake up other releasable waiters.
807	>	*
808	>	* * If there are too many running threads, suspends this worker
809	>	* (first forcing inactivation if necessary).  If it is not
810	>	* resumed before a keepAlive elapses, the worker may be "trimmed"
811	>	* -- killed while suspended within suspendAsSpare. Otherwise,
812	>	* upon resume it rechecks to make sure that it is still needed.
813	>	*
814	>	* @param w the worker
815	>	* @param worked false if the worker scanned for work but didn't
816	>	* find any (in which case it may block waiting for work).
817	>	*/
818	>	final void preStep(ForkJoinWorkerThread w, boolean worked) {
819	>	boolean active = w.active;
820	>	boolean inactivate = !worked & active;
821	>	for (;;) {
822	>	if (inactivate) {
823	>	int c = runState;
824	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset,
825	>	c, c - ONE_ACTIVE))
826	>	inactivate = active = w.active = false;
827	>	}
828	>	int wc = workerCounts;
829	>	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
830	>	if (!worked)
831	>	eventSync(w);
832	>	return;
833	>	}
834	>	if (!(inactivate |= active) &&  // must inactivate to suspend
835	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
836	>	wc, wc - ONE_RUNNING) &&
837	>	!w.suspendAsSpare())        // false if trimmed
838	>	return;
839	>	}
840	>	}
841	>
842	>	/**
843	>	* Adjusts counts and creates or resumes compensating threads for
844	>	* a worker about to block on task joinMe, returning early if
845	>	* joinMe becomes ready. First tries resuming an existing spare
846	>	* (which usually also avoids any count adjustment), but must then
847	>	* decrement running count to determine whether a new thread is
848	>	* needed. See above for fuller explanation.
849	>	*/
850	>	final void preJoin(ForkJoinTask<?> joinMe) {
851	>	boolean dec = false;       // true when running count decremented
852	>	for (;;) {
853	>	releaseWaiters();      // help other threads progress
854	>
855	>	if (joinMe.status < 0) // surround spare search with done checks
856	>	return;
857	>	ForkJoinWorkerThread spare = null;
858	>	for (ForkJoinWorkerThread w : workers) {
859	>	if (w != null && w.isSuspended()) {
860	>	spare = w;
861	>	break;
862	>	}
863	>	}
864	>	if (joinMe.status < 0)
865	>	return;
866	>
867	>	if (spare != null && spare.tryUnsuspend()) {
868	>	if (dec || joinMe.requestSignal() < 0) {
869	>	int c;
870	>	do {} while (!UNSAFE.compareAndSwapInt(this,
871	>	workerCountsOffset,
872	>	c = workerCounts,
873	>	c + ONE_RUNNING));
874	>	} // else no net count change
875	>	LockSupport.unpark(spare);
876	>	return;
877	>	}
878	>
879	>	int wc = workerCounts; // decrement running count
880	>	if (!dec && (wc & RUNNING_COUNT_MASK) != 0 &&
881	>	(dec = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
882	>	wc, wc -= ONE_RUNNING)) &&
883	>	joinMe.requestSignal() < 0) { // cannot block
884	>	int c;                        // back out
885	>	do {} while (!UNSAFE.compareAndSwapInt(this,
886	>	workerCountsOffset,
887	>	c = workerCounts,
888	>	c + ONE_RUNNING));
889	>	return;
890	>	}
891	>
892	>	if (dec) {
893	>	int tc = wc >>> TOTAL_COUNT_SHIFT;
894	>	int pc = parallelism;
895	>	int dc = pc - (wc & RUNNING_COUNT_MASK); // deficit count
896	>	if ((dc < pc && (dc <= 0 || (dc * dc < (tc - pc) * pc) ||
897	>	!maintainsParallelism)) ||
898	>	tc >= maxPoolSize) // cannot add
899	>	return;
900	>	if (spare == null &&
901	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
902	>	wc + (ONE_RUNNING|ONE_TOTAL))) {
903	>	addWorker();
904	>	return;
905	>	}
906	>	}
907	>	}
908	>	}
909	>
910	>	/**
911	>	* Same idea as preJoin but with too many differing details to
912	>	* integrate: There are no task-based signal counts, and only one
913	>	* way to do the actual blocking. So for simplicity it is directly
914	>	* incorporated into this method.
915	>	*/
916	>	final void doBlock(ManagedBlocker blocker, boolean maintainPar)
917	>	throws InterruptedException {
918	>	maintainPar &= maintainsParallelism; // override
919	>	boolean dec = false;
920	>	boolean done = false;
921	>	for (;;) {
922	>	releaseWaiters();
923	>	if (done = blocker.isReleasable())
924	>	break;
925	>	ForkJoinWorkerThread spare = null;
926	>	for (ForkJoinWorkerThread w : workers) {
927	>	if (w != null && w.isSuspended()) {
928	>	spare = w;
929	>	break;
930	>	}
931	>	}
932	>	if (done = blocker.isReleasable())
933	>	break;
934	>	if (spare != null && spare.tryUnsuspend()) {
935	>	if (dec) {
936	>	int c;
937	>	do {} while (!UNSAFE.compareAndSwapInt(this,
938	>	workerCountsOffset,
939	>	c = workerCounts,
940	>	c + ONE_RUNNING));
941	>	}
942	>	LockSupport.unpark(spare);
943	>	break;
944	>	}
945	>	int wc = workerCounts;
946	>	if (!dec && (wc & RUNNING_COUNT_MASK) != 0)
947	>	dec = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
948	>	wc, wc -= ONE_RUNNING);
949	>	if (dec) {
950	>	int tc = wc >>> TOTAL_COUNT_SHIFT;
951	>	int pc = parallelism;
952	>	int dc = pc - (wc & RUNNING_COUNT_MASK);
953	>	if ((dc < pc && (dc <= 0 || (dc * dc < (tc - pc) * pc) ||
954	>	!maintainPar)) ||
955	>	tc >= maxPoolSize)
956	>	break;
957	>	if (spare == null &&
958	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
959	>	wc + (ONE_RUNNING|ONE_TOTAL))){
960	>	addWorker();
961	>	break;
962	>	}
963	>	}
964	>	}
965	>
966	>	try {
967	>	if (!done)
968	>	do {} while (!blocker.isReleasable() && !blocker.block());
969	>	} finally {
970	>	if (dec) {
971	>	int c;
972	>	do {} while (!UNSAFE.compareAndSwapInt(this,
973	>	workerCountsOffset,
974	>	c = workerCounts,
975	>	c + ONE_RUNNING));
976	>	}
977	>	}
978	>	}
979	>
980	>	/**
981	>	* Possibly initiates and/or completes termination.
982	>	*
983	>	* @param now if true, unconditionally terminate, else only
984	>	* if shutdown and empty queue and no active workers
985	>	* @return true if now terminating or terminated
986	>	*/
987	>	private boolean tryTerminate(boolean now) {
988	>	if (now)
989	>	advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
990	>	else if (runState < SHUTDOWN ||
991	>	!submissionQueue.isEmpty() ||
992	>	(runState & ACTIVE_COUNT_MASK) != 0)
993		return false;
994	<	if (canTerminateOnShutdown(nextc))
995	<	terminateOnShutdown();
994	>
995	>	if (advanceRunLevel(TERMINATING))
996	>	startTerminating();
997	>
998	>	// Finish now if all threads terminated; else in some subsequent call
999	>	if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1000	>	advanceRunLevel(TERMINATED);
1001	>	terminationLatch.countDown();
1002	>	}
1003		return true;
1004		}
1005
1006		/**
1007	<	* Returns {@code true} if argument represents zero active count
1008	<	* and nonzero runstate, which is the triggering condition for
1009	<	* terminating on shutdown.
1007	>	* Actions on transition to TERMINATING
1008	>	*/
1009	>	private void startTerminating() {
1010	>	// Clear out and cancel submissions, ignoring exceptions
1011	>	ForkJoinTask<?> task;
1012	>	while ((task = submissionQueue.poll()) != null) {
1013	>	try {
1014	>	task.cancel(false);
1015	>	} catch (Throwable ignore) {
1016	>	}
1017	>	}
1018	>	// Propagate run level
1019	>	for (ForkJoinWorkerThread w : workers) {
1020	>	if (w != null)
1021	>	w.shutdown();    // also resumes suspended workers
1022	>	}
1023	>	// Ensure no straggling local tasks
1024	>	for (ForkJoinWorkerThread w : workers) {
1025	>	if (w != null)
1026	>	w.cancelTasks();
1027	>	}
1028	>	// Wake up idle workers
1029	>	advanceEventCount();
1030	>	releaseWaiters();
1031	>	// Unstick pending joins
1032	>	for (ForkJoinWorkerThread w : workers) {
1033	>	if (w != null && !w.isTerminated()) {
1034	>	try {
1035	>	w.interrupt();
1036	>	} catch (SecurityException ignore) {
1037	>	}
1038	>	}
1039	>	}
1040	>	}
1041	>
1042	>	// misc support for ForkJoinWorkerThread
1043	>
1044	>	/**
1045	>	* Returns pool number
1046		*/
1047	<	private static boolean canTerminateOnShutdown(int c) {
1048	<	// i.e. least bit is nonzero runState bit
320	<	return ((c & -c) >>> 16) != 0;
1047	>	final int getPoolNumber() {
1048	>	return poolNumber;
1049		}
1050
1051		/**
1052	<	* Transition run state to at least the given state. Return true
1053	<	* if not already at least given state.
1052	>	* Accumulates steal count from a worker, clearing
1053	>	* the worker's value
1054		*/
1055	<	private boolean transitionRunStateTo(int state) {
1056	<	for (;;) {
1057	<	int c = runControl;
1058	<	if (runStateOf(c) >= state)
1059	<	return false;
1060	<	if (casRunControl(c, runControlFor(state, activeCountOf(c))))
1061	<	return true;
1055	>	final void accumulateStealCount(ForkJoinWorkerThread w) {
1056	>	int sc = w.stealCount;
1057	>	if (sc != 0) {
1058	>	long c;
1059	>	w.stealCount = 0;
1060	>	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1061	>	c = stealCount, c + sc));
1062		}
1063		}
1064
1065		/**
1066	<	* Controls whether to add spares to maintain parallelism
1066	>	* Returns the approximate (non-atomic) number of idle threads per
1067	>	* active thread.
1068	>	*/
1069	>	final int idlePerActive() {
1070	>	int ac = runState;    // no mask -- artifically boosts during shutdown
1071	>	int pc = parallelism; // use targeted parallelism, not rc
1072	>	// Use exact results for small values, saturate past 4
1073	>	return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1074	>	}
1075	>
1076	>	/**
1077	>	* Returns the approximate (non-atomic) difference between running
1078	>	* and active counts.
1079		*/
1080	<	private volatile boolean maintainsParallelism;
1080	>	final int inactiveCount() {
1081	>	return (workerCounts & RUNNING_COUNT_MASK) -
1082	>	(runState & ACTIVE_COUNT_MASK);
1083	>	}
1084	>
1085	>	// Public and protected methods
1086
1087		// Constructors
1088
1089		/**
1090	<	* Creates a ForkJoinPool with a pool size equal to the number of
1091	<	* processors available on the system, using the default
1092	<	* ForkJoinWorkerThreadFactory.
1090	>	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1091	>	* java.lang.Runtime#availableProcessors}, and using the {@linkplain
1092	>	* #defaultForkJoinWorkerThreadFactory default thread factory}.
1093		*
1094		* @throws SecurityException if a security manager exists and
1095		*         the caller is not permitted to modify threads
#	Line 357 | Line 1102 | public class ForkJoinPool extends Abstra
1102		}
1103
1104		/**
1105	<	* Creates a ForkJoinPool with the indicated parallelism level
1106	<	* threads and using the default ForkJoinWorkerThreadFactory.
1105	>	* Creates a {@code ForkJoinPool} with the indicated parallelism
1106	>	* level and using the {@linkplain
1107	>	* #defaultForkJoinWorkerThreadFactory default thread factory}.
1108		*
1109	<	* @param parallelism the number of worker threads
1109	>	* @param parallelism the parallelism level
1110		* @throws IllegalArgumentException if parallelism less than or
1111	<	* equal to zero
1111	>	*         equal to zero, or greater than implementation limit
1112		* @throws SecurityException if a security manager exists and
1113		*         the caller is not permitted to modify threads
1114		*         because it does not hold {@link
#	Line 373 | Line 1119 | public class ForkJoinPool extends Abstra
1119		}
1120
1121		/**
1122	<	* Creates a ForkJoinPool with parallelism equal to the number of
1123	<	* processors available on the system and using the given
1124	<	* ForkJoinWorkerThreadFactory.
1122	>	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1123	>	* java.lang.Runtime#availableProcessors}, and using the given
1124	>	* thread factory.
1125		*
1126		* @param factory the factory for creating new threads
1127	<	* @throws NullPointerException if factory is null
1127	>	* @throws NullPointerException if the factory is null
1128		* @throws SecurityException if a security manager exists and
1129		*         the caller is not permitted to modify threads
1130		*         because it does not hold {@link
#	Line 389 | Line 1135 | public class ForkJoinPool extends Abstra
1135		}
1136
1137		/**
1138	<	* Creates a ForkJoinPool with the given parallelism and factory.
1138	>	* Creates a {@code ForkJoinPool} with the given parallelism and
1139	>	* thread factory.
1140		*
1141	<	* @param parallelism the targeted number of worker threads
1141	>	* @param parallelism the parallelism level
1142		* @param factory the factory for creating new threads
1143		* @throws IllegalArgumentException if parallelism less than or
1144	<	* equal to zero, or greater than implementation limit
1145	<	* @throws NullPointerException if factory is null
1144	>	*         equal to zero, or greater than implementation limit
1145	>	* @throws NullPointerException if the factory is null
1146		* @throws SecurityException if a security manager exists and
1147		*         the caller is not permitted to modify threads
1148		*         because it does not hold {@link
1149		*         java.lang.RuntimePermission}{@code ("modifyThread")}
1150		*/
1151		public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
1152	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
406	<	throw new IllegalArgumentException();
1152	>	checkPermission();
1153		if (factory == null)
1154		throw new NullPointerException();
1155	<	checkPermission();
1156	<	this.factory = factory;
1155	>	if (parallelism <= 0 || parallelism > MAX_THREADS)
1156	>	throw new IllegalArgumentException();
1157	>	this.poolNumber = poolNumberGenerator.incrementAndGet();
1158	>	int arraySize = initialArraySizeFor(parallelism);
1159		this.parallelism = parallelism;
1160	+	this.factory = factory;
1161		this.maxPoolSize = MAX_THREADS;
1162		this.maintainsParallelism = true;
1163	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
415	<	this.workerLock = new ReentrantLock();
416	<	this.termination = workerLock.newCondition();
417	<	this.stealCount = new AtomicLong();
1163	>	this.workers = new ForkJoinWorkerThread[arraySize];
1164		this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1165	<	// worker array and workers are lazily constructed
1166	<	}
1167	<
1168	<	/**
1169	<	* Creates a new worker thread using factory.
424	<	*
425	<	* @param index the index to assign worker
426	<	* @return new worker, or null of factory failed
427	<	*/
428	<	private ForkJoinWorkerThread createWorker(int index) {
429	<	Thread.UncaughtExceptionHandler h = ueh;
430	<	ForkJoinWorkerThread w = factory.newThread(this);
431	<	if (w != null) {
432	<	w.poolIndex = index;
433	<	w.setDaemon(true);
434	<	w.setAsyncMode(locallyFifo);
435	<	w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
436	<	if (h != null)
437	<	w.setUncaughtExceptionHandler(h);
438	<	}
439	<	return w;
440	<	}
441	<
442	<	/**
443	<	* Returns a good size for worker array given pool size.
444	<	* Currently requires size to be a power of two.
445	<	*/
446	<	private static int arraySizeFor(int poolSize) {
447	<	return (poolSize <= 1) ? 1 :
448	<	(1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
449	<	}
450	<
451	<	/**
452	<	* Creates or resizes array if necessary to hold newLength.
453	<	* Call only under exclusion.
454	<	*
455	<	* @return the array
456	<	*/
457	<	private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
458	<	ForkJoinWorkerThread[] ws = workers;
459	<	if (ws == null)
460	<	return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
461	<	else if (newLength > ws.length)
462	<	return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
463	<	else
464	<	return ws;
465	<	}
466	<
467	<	/**
468	<	* Tries to shrink workers into smaller array after one or more terminate.
469	<	*/
470	<	private void tryShrinkWorkerArray() {
471	<	ForkJoinWorkerThread[] ws = workers;
472	<	if (ws != null) {
473	<	int len = ws.length;
474	<	int last = len - 1;
475	<	while (last >= 0 && ws[last] == null)
476	<	--last;
477	<	int newLength = arraySizeFor(last+1);
478	<	if (newLength < len)
479	<	workers = Arrays.copyOf(ws, newLength);
480	<	}
1165	>	this.workerLock = new ReentrantLock();
1166	>	this.terminationLatch = new CountDownLatch(1);
1167	>	// Start first worker; remaining workers added upon first submission
1168	>	workerCounts = ONE_RUNNING | ONE_TOTAL;
1169	>	addWorker();
1170		}
1171
1172		/**
1173	<	* Initializes workers if necessary.
1174	<	*/
1175	<	final void ensureWorkerInitialization() {
1176	<	ForkJoinWorkerThread[] ws = workers;
1177	<	if (ws == null) {
1178	<	final ReentrantLock lock = this.workerLock;
1179	<	lock.lock();
1180	<	try {
1181	<	ws = workers;
1182	<	if (ws == null) {
1183	<	int ps = parallelism;
495	<	ws = ensureWorkerArrayCapacity(ps);
496	<	for (int i = 0; i < ps; ++i) {
497	<	ForkJoinWorkerThread w = createWorker(i);
498	<	if (w != null) {
499	<	ws[i] = w;
500	<	w.start();
501	<	updateWorkerCount(1);
502	<	}
503	<	}
504	<	}
505	<	} finally {
506	<	lock.unlock();
507	<	}
508	<	}
509	<	}
510	<
511	<	/**
512	<	* Worker creation and startup for threads added via setParallelism.
513	<	*/
514	<	private void createAndStartAddedWorkers() {
515	<	resumeAllSpares();  // Allow spares to convert to nonspare
516	<	int ps = parallelism;
517	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
518	<	int len = ws.length;
519	<	// Sweep through slots, to keep lowest indices most populated
520	<	int k = 0;
521	<	while (k < len) {
522	<	if (ws[k] != null) {
523	<	++k;
524	<	continue;
525	<	}
526	<	int s = workerCounts;
527	<	int tc = totalCountOf(s);
528	<	int rc = runningCountOf(s);
529	<	if (rc >= ps || tc >= ps)
530	<	break;
531	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
532	<	ForkJoinWorkerThread w = createWorker(k);
533	<	if (w != null) {
534	<	ws[k++] = w;
535	<	w.start();
536	<	}
537	<	else {
538	<	updateWorkerCount(-1); // back out on failed creation
539	<	break;
540	<	}
541	<	}
542	<	}
1173	>	* Returns initial power of two size for workers array.
1174	>	* @param pc the initial parallelism level
1175	>	*/
1176	>	private static int initialArraySizeFor(int pc) {
1177	>	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1178	>	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1179	>	size |= size >>> 1;
1180	>	size |= size >>> 2;
1181	>	size |= size >>> 4;
1182	>	size |= size >>> 8;
1183	>	return size + 1;
1184		}
1185
1186		// Execution methods
#	Line 550 | Line 1191 | public class ForkJoinPool extends Abstra
1191		private <T> void doSubmit(ForkJoinTask<T> task) {
1192		if (task == null)
1193		throw new NullPointerException();
1194	<	if (isShutdown())
1194	>	if (runState >= SHUTDOWN)
1195		throw new RejectedExecutionException();
555	–	if (workers == null)
556	–	ensureWorkerInitialization();
1196		submissionQueue.offer(task);
1197	<	signalIdleWorkers();
1197	>	advanceEventCount();
1198	>	releaseWaiters();
1199	>	if ((workerCounts >>> TOTAL_COUNT_SHIFT) < parallelism)
1200	>	ensureEnoughTotalWorkers();
1201		}
1202
1203		/**
#	Line 563 | Line 1205 | public class ForkJoinPool extends Abstra
1205		*
1206		* @param task the task
1207		* @return the task's result
1208	<	* @throws NullPointerException if task is null
1209	<	* @throws RejectedExecutionException if pool is shut down
1208	>	* @throws NullPointerException if the task is null
1209	>	* @throws RejectedExecutionException if the task cannot be
1210	>	*         scheduled for execution
1211		*/
1212		public <T> T invoke(ForkJoinTask<T> task) {
1213		doSubmit(task);
#	Line 575 | Line 1218 | public class ForkJoinPool extends Abstra
1218		* Arranges for (asynchronous) execution of the given task.
1219		*
1220		* @param task the task
1221	<	* @throws NullPointerException if task is null
1222	<	* @throws RejectedExecutionException if pool is shut down
1221	>	* @throws NullPointerException if the task is null
1222	>	* @throws RejectedExecutionException if the task cannot be
1223	>	*         scheduled for execution
1224		*/
1225	<	public <T> void execute(ForkJoinTask<T> task) {
1225	>	public void execute(ForkJoinTask<?> task) {
1226		doSubmit(task);
1227		}
1228
1229		// AbstractExecutorService methods
1230
1231	+	/**
1232	+	* @throws NullPointerException if the task is null
1233	+	* @throws RejectedExecutionException if the task cannot be
1234	+	*         scheduled for execution
1235	+	*/
1236		public void execute(Runnable task) {
1237		ForkJoinTask<?> job;
1238		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1239		job = (ForkJoinTask<?>) task;
1240		else
1241	<	job = new AdaptedRunnable<Void>(task, null);
1241	>	job = ForkJoinTask.adapt(task, null);
1242		doSubmit(job);
1243		}
1244
1245	+	/**
1246	+	* @throws NullPointerException if the task is null
1247	+	* @throws RejectedExecutionException if the task cannot be
1248	+	*         scheduled for execution
1249	+	*/
1250		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1251	<	ForkJoinTask<T> job = new AdaptedCallable<T>(task);
1251	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1252		doSubmit(job);
1253		return job;
1254		}
1255
1256	+	/**
1257	+	* @throws NullPointerException if the task is null
1258	+	* @throws RejectedExecutionException if the task cannot be
1259	+	*         scheduled for execution
1260	+	*/
1261		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1262	<	ForkJoinTask<T> job = new AdaptedRunnable<T>(task, result);
1262	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1263		doSubmit(job);
1264		return job;
1265		}
1266
1267	+	/**
1268	+	* @throws NullPointerException if the task is null
1269	+	* @throws RejectedExecutionException if the task cannot be
1270	+	*         scheduled for execution
1271	+	*/
1272		public ForkJoinTask<?> submit(Runnable task) {
1273		ForkJoinTask<?> job;
1274		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1275		job = (ForkJoinTask<?>) task;
1276		else
1277	<	job = new AdaptedRunnable<Void>(task, null);
1277	>	job = ForkJoinTask.adapt(task, null);
1278		doSubmit(job);
1279		return job;
1280		}
#	Line 620 | Line 1284 | public class ForkJoinPool extends Abstra
1284		*
1285		* @param task the task to submit
1286		* @return the task
1287	+	* @throws NullPointerException if the task is null
1288		* @throws RejectedExecutionException if the task cannot be
1289		*         scheduled for execution
625	–	* @throws NullPointerException if the task is null
1290		*/
1291		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1292		doSubmit(task);
#	Line 630 | Line 1294 | public class ForkJoinPool extends Abstra
1294		}
1295
1296		/**
1297	<	* Adaptor for Runnables. This implements RunnableFuture
1298	<	* to be compliant with AbstractExecutorService constraints.
1297	>	* @throws NullPointerException       {@inheritDoc}
1298	>	* @throws RejectedExecutionException {@inheritDoc}
1299		*/
636	–	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
637	–	implements RunnableFuture<T> {
638	–	final Runnable runnable;
639	–	final T resultOnCompletion;
640	–	T result;
641	–	AdaptedRunnable(Runnable runnable, T result) {
642	–	if (runnable == null) throw new NullPointerException();
643	–	this.runnable = runnable;
644	–	this.resultOnCompletion = result;
645	–	}
646	–	public T getRawResult() { return result; }
647	–	public void setRawResult(T v) { result = v; }
648	–	public boolean exec() {
649	–	runnable.run();
650	–	result = resultOnCompletion;
651	–	return true;
652	–	}
653	–	public void run() { invoke(); }
654	–	private static final long serialVersionUID = 5232453952276885070L;
655	–	}
656	–
657	–	/**
658	–	* Adaptor for Callables
659	–	*/
660	–	static final class AdaptedCallable<T> extends ForkJoinTask<T>
661	–	implements RunnableFuture<T> {
662	–	final Callable<T> callable;
663	–	T result;
664	–	AdaptedCallable(Callable<T> callable) {
665	–	if (callable == null) throw new NullPointerException();
666	–	this.callable = callable;
667	–	}
668	–	public T getRawResult() { return result; }
669	–	public void setRawResult(T v) { result = v; }
670	–	public boolean exec() {
671	–	try {
672	–	result = callable.call();
673	–	return true;
674	–	} catch (Error err) {
675	–	throw err;
676	–	} catch (RuntimeException rex) {
677	–	throw rex;
678	–	} catch (Exception ex) {
679	–	throw new RuntimeException(ex);
680	–	}
681	–	}
682	–	public void run() { invoke(); }
683	–	private static final long serialVersionUID = 2838392045355241008L;
684	–	}
685	–
1300		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
1301		ArrayList<ForkJoinTask<T>> forkJoinTasks =
1302		new ArrayList<ForkJoinTask<T>>(tasks.size());
1303		for (Callable<T> task : tasks)
1304	<	forkJoinTasks.add(new AdaptedCallable<T>(task));
1304	>	forkJoinTasks.add(ForkJoinTask.adapt(task));
1305		invoke(new InvokeAll<T>(forkJoinTasks));
1306
1307		@SuppressWarnings({"unchecked", "rawtypes"})
#	Line 705 | Line 1319 | public class ForkJoinPool extends Abstra
1319		private static final long serialVersionUID = -7914297376763021607L;
1320		}
1321
708	–	// Configuration and status settings and queries
709	–
1322		/**
1323		* Returns the factory used for constructing new workers.
1324		*
#	Line 723 | Line 1335 | public class ForkJoinPool extends Abstra
1335		* @return the handler, or {@code null} if none
1336		*/
1337		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1338	<	Thread.UncaughtExceptionHandler h;
1339	<	final ReentrantLock lock = this.workerLock;
728	<	lock.lock();
729	<	try {
730	<	h = ueh;
731	<	} finally {
732	<	lock.unlock();
733	<	}
734	<	return h;
1338	>	workerCountReadFence();
1339	>	return ueh;
1340		}
1341
1342		/**
#	Line 750 | Line 1355 | public class ForkJoinPool extends Abstra
1355		public Thread.UncaughtExceptionHandler
1356		setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
1357		checkPermission();
1358	<	Thread.UncaughtExceptionHandler old = null;
1359	<	final ReentrantLock lock = this.workerLock;
1360	<	lock.lock();
756	<	try {
757	<	old = ueh;
1358	>	workerCountReadFence();
1359	>	Thread.UncaughtExceptionHandler old = ueh;
1360	>	if (h != old) {
1361		ueh = h;
1362	<	ForkJoinWorkerThread[] ws = workers;
1363	<	if (ws != null) {
1364	<	for (int i = 0; i < ws.length; ++i) {
1365	<	ForkJoinWorkerThread w = ws[i];
763	<	if (w != null)
764	<	w.setUncaughtExceptionHandler(h);
765	<	}
1362	>	workerCountWriteFence();
1363	>	for (ForkJoinWorkerThread w : workers) {
1364	>	if (w != null)
1365	>	w.setUncaughtExceptionHandler(h);
1366		}
767	–	} finally {
768	–	lock.unlock();
1367		}
1368		return old;
1369		}
1370
773	–
1371		/**
1372		* Sets the target parallelism level of this pool.
1373		*
#	Line 786 | Line 1383 | public class ForkJoinPool extends Abstra
1383		checkPermission();
1384		if (parallelism <= 0 || parallelism > maxPoolSize)
1385		throw new IllegalArgumentException();
1386	<	final ReentrantLock lock = this.workerLock;
1387	<	lock.lock();
1388	<	try {
1389	<	if (!isTerminating()) {
1390	<	int p = this.parallelism;
1391	<	this.parallelism = parallelism;
1392	<	if (parallelism > p)
1393	<	createAndStartAddedWorkers();
1394	<	else
1395	<	trimSpares();
1386	>	workerCountReadFence();
1387	>	int pc = this.parallelism;
1388	>	if (pc != parallelism) {
1389	>	this.parallelism = parallelism;
1390	>	workerCountWriteFence();
1391	>	// Release spares. If too many, some will die after re-suspend
1392	>	for (ForkJoinWorkerThread w : workers) {
1393	>	if (w != null && w.tryUnsuspend()) {
1394	>	updateRunningCount(1);
1395	>	LockSupport.unpark(w);
1396	>	}
1397		}
1398	<	} finally {
1399	<	lock.unlock();
1398	>	ensureEnoughTotalWorkers();
1399	>	advanceEventCount();
1400	>	releaseWaiters(); // force config recheck by existing workers
1401		}
803	–	signalIdleWorkers();
1402		}
1403
1404		/**
1405	<	* Returns the targeted number of worker threads in this pool.
1405	>	* Returns the targeted parallelism level of this pool.
1406		*
1407	<	* @return the targeted number of worker threads in this pool
1407	>	* @return the targeted parallelism level of this pool
1408		*/
1409		public int getParallelism() {
1410	+	//        workerCountReadFence(); // inlined below
1411	+	int ignore = workerCounts;
1412		return parallelism;
1413		}
1414
#	Line 821 | Line 1421 | public class ForkJoinPool extends Abstra
1421		* @return the number of worker threads
1422		*/
1423		public int getPoolSize() {
1424	<	return totalCountOf(workerCounts);
1424	>	return workerCounts >>> TOTAL_COUNT_SHIFT;
1425		}
1426
1427		/**
1428		* Returns the maximum number of threads allowed to exist in the
1429	<	* pool, even if there are insufficient unblocked running threads.
1429	>	* pool. Unless set using {@link #setMaximumPoolSize}, the
1430	>	* maximum is an implementation-defined value designed only to
1431	>	* prevent runaway growth.
1432		*
1433		* @return the maximum
1434		*/
1435		public int getMaximumPoolSize() {
1436	+	workerCountReadFence();
1437		return maxPoolSize;
1438		}
1439
1440		/**
1441		* Sets the maximum number of threads allowed to exist in the
1442	<	* pool, even if there are insufficient unblocked running threads.
1443	<	* Setting this value has no effect on current pool size. It
1444	<	* controls construction of new threads.
1442	>	* pool. The given value should normally be greater than or equal
1443	>	* to the {@link #getParallelism parallelism} level. Setting this
1444	>	* value has no effect on current pool size. It controls
1445	>	* construction of new threads.
1446		*
1447	<	* @throws IllegalArgumentException if negative or greater then
1447	>	* @throws IllegalArgumentException if negative or greater than
1448		* internal implementation limit
1449		*/
1450		public void setMaximumPoolSize(int newMax) {
1451		if (newMax < 0 || newMax > MAX_THREADS)
1452		throw new IllegalArgumentException();
1453		maxPoolSize = newMax;
1454	+	workerCountWriteFence();
1455		}
1456
852	–
1457		/**
1458		* Returns {@code true} if this pool dynamically maintains its
1459		* target parallelism level. If false, new threads are added only
#	Line 858 | Line 1462 | public class ForkJoinPool extends Abstra
1462		* @return {@code true} if maintains parallelism
1463		*/
1464		public boolean getMaintainsParallelism() {
1465	+	workerCountReadFence();
1466		return maintainsParallelism;
1467		}
1468
#	Line 870 | Line 1475 | public class ForkJoinPool extends Abstra
1475		*/
1476		public void setMaintainsParallelism(boolean enable) {
1477		maintainsParallelism = enable;
1478	+	workerCountWriteFence();
1479		}
1480
1481		/**
#	Line 886 | Line 1492 | public class ForkJoinPool extends Abstra
1492		* @see #getAsyncMode
1493		*/
1494		public boolean setAsyncMode(boolean async) {
1495	+	workerCountReadFence();
1496		boolean oldMode = locallyFifo;
1497	<	locallyFifo = async;
1498	<	ForkJoinWorkerThread[] ws = workers;
1499	<	if (ws != null) {
1500	<	for (int i = 0; i < ws.length; ++i) {
1501	<	ForkJoinWorkerThread t = ws[i];
1502	<	if (t != null)
896	<	t.setAsyncMode(async);
1497	>	if (oldMode != async) {
1498	>	locallyFifo = async;
1499	>	workerCountWriteFence();
1500	>	for (ForkJoinWorkerThread w : workers) {
1501	>	if (w != null)
1502	>	w.setAsyncMode(async);
1503		}
1504		}
1505		return oldMode;
#	Line 907 | Line 1513 | public class ForkJoinPool extends Abstra
1513		* @see #setAsyncMode
1514		*/
1515		public boolean getAsyncMode() {
1516	+	workerCountReadFence();
1517		return locallyFifo;
1518		}
1519
1520		/**
1521		* Returns an estimate of the number of worker threads that are
1522		* not blocked waiting to join tasks or for other managed
1523	<	* synchronization.
1523	>	* synchronization. This method may overestimate the
1524	>	* number of running threads.
1525		*
1526		* @return the number of worker threads
1527		*/
1528		public int getRunningThreadCount() {
1529	<	return runningCountOf(workerCounts);
1529	>	return workerCounts & RUNNING_COUNT_MASK;
1530		}
1531
1532		/**
#	Line 929 | Line 1537 | public class ForkJoinPool extends Abstra
1537		* @return the number of active threads
1538		*/
1539		public int getActiveThreadCount() {
1540	<	return activeCountOf(runControl);
933	<	}
934	<
935	<	/**
936	<	* Returns an estimate of the number of threads that are currently
937	<	* idle waiting for tasks. This method may underestimate the
938	<	* number of idle threads.
939	<	*
940	<	* @return the number of idle threads
941	<	*/
942	<	final int getIdleThreadCount() {
943	<	int c = runningCountOf(workerCounts) - activeCountOf(runControl);
944	<	return (c <= 0) ? 0 : c;
1540	>	return runState & ACTIVE_COUNT_MASK;
1541		}
1542
1543		/**
#	Line 956 | Line 1552 | public class ForkJoinPool extends Abstra
1552		* @return {@code true} if all threads are currently idle
1553		*/
1554		public boolean isQuiescent() {
1555	<	return activeCountOf(runControl) == 0;
1555	>	return (runState & ACTIVE_COUNT_MASK) == 0;
1556		}
1557
1558		/**
#	Line 971 | Line 1567 | public class ForkJoinPool extends Abstra
1567		* @return the number of steals
1568		*/
1569		public long getStealCount() {
1570	<	return stealCount.get();
975	<	}
976	<
977	<	/**
978	<	* Accumulates steal count from a worker.
979	<	* Call only when worker known to be idle.
980	<	*/
981	<	private void updateStealCount(ForkJoinWorkerThread w) {
982	<	int sc = w.getAndClearStealCount();
983	<	if (sc != 0)
984	<	stealCount.addAndGet(sc);
1570	>	return stealCount;
1571		}
1572
1573		/**
#	Line 996 | Line 1582 | public class ForkJoinPool extends Abstra
1582		*/
1583		public long getQueuedTaskCount() {
1584		long count = 0;
1585	<	ForkJoinWorkerThread[] ws = workers;
1586	<	if (ws != null) {
1587	<	for (int i = 0; i < ws.length; ++i) {
1002	<	ForkJoinWorkerThread t = ws[i];
1003	<	if (t != null)
1004	<	count += t.getQueueSize();
1005	<	}
1585	>	for (ForkJoinWorkerThread w : workers) {
1586	>	if (w != null)
1587	>	count += w.getQueueSize();
1588		}
1589		return count;
1590		}
1591
1592		/**
1593	<	* Returns an estimate of the number tasks submitted to this pool
1594	<	* that have not yet begun executing. This method takes time
1593	>	* Returns an estimate of the number of tasks submitted to this
1594	>	* pool that have not yet begun executing.  This method takes time
1595		* proportional to the number of submissions.
1596		*
1597		* @return the number of queued submissions
#	Line 1043 | Line 1625 | public class ForkJoinPool extends Abstra
1625		* Removes all available unexecuted submitted and forked tasks
1626		* from scheduling queues and adds them to the given collection,
1627		* without altering their execution status. These may include
1628	<	* artificially generated or wrapped tasks. This method is designed
1629	<	* to be invoked only when the pool is known to be
1628	>	* artificially generated or wrapped tasks. This method is
1629	>	* designed to be invoked only when the pool is known to be
1630		* quiescent. Invocations at other times may not remove all
1631		* tasks. A failure encountered while attempting to add elements
1632		* to collection {@code c} may result in elements being in
#	Line 1056 | Line 1638 | public class ForkJoinPool extends Abstra
1638		* @param c the collection to transfer elements into
1639		* @return the number of elements transferred
1640		*/
1641	<	protected int drainTasksTo(Collection<ForkJoinTask<?>> c) {
1641	>	protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1642		int n = submissionQueue.drainTo(c);
1643	<	ForkJoinWorkerThread[] ws = workers;
1644	<	if (ws != null) {
1645	<	for (int i = 0; i < ws.length; ++i) {
1064	<	ForkJoinWorkerThread w = ws[i];
1065	<	if (w != null)
1066	<	n += w.drainTasksTo(c);
1067	<	}
1643	>	for (ForkJoinWorkerThread w : workers) {
1644	>	if (w != null)
1645	>	n += w.drainTasksTo(c);
1646		}
1647		return n;
1648		}
#	Line 1077 | Line 1655 | public class ForkJoinPool extends Abstra
1655		* @return a string identifying this pool, as well as its state
1656		*/
1657		public String toString() {
1080	–	int ps = parallelism;
1081	–	int wc = workerCounts;
1082	–	int rc = runControl;
1658		long st = getStealCount();
1659		long qt = getQueuedTaskCount();
1660		long qs = getQueuedSubmissionCount();
1661	+	int wc = workerCounts;
1662	+	int tc = wc >>> TOTAL_COUNT_SHIFT;
1663	+	int rc = wc & RUNNING_COUNT_MASK;
1664	+	int pc = parallelism;
1665	+	int rs = runState;
1666	+	int ac = rs & ACTIVE_COUNT_MASK;
1667		return super.toString() +
1668	<	"[" + runStateToString(runStateOf(rc)) +
1669	<	", parallelism = " + ps +
1670	<	", size = " + totalCountOf(wc) +
1671	<	", active = " + activeCountOf(rc) +
1672	<	", running = " + runningCountOf(wc) +
1668	>	"[" + runLevelToString(rs) +
1669	>	", parallelism = " + pc +
1670	>	", size = " + tc +
1671	>	", active = " + ac +
1672	>	", running = " + rc +
1673		", steals = " + st +
1674		", tasks = " + qt +
1675		", submissions = " + qs +
1676		"]";
1677		}
1678
1679	<	private static String runStateToString(int rs) {
1680	<	switch(rs) {
1681	<	case RUNNING: return "Running";
1682	<	case SHUTDOWN: return "Shutting down";
1683	<	case TERMINATING: return "Terminating";
1103	<	case TERMINATED: return "Terminated";
1104	<	default: throw new Error("Unknown run state");
1105	<	}
1679	>	private static String runLevelToString(int s) {
1680	>	return ((s & TERMINATED) != 0 ? "Terminated" :
1681	>	((s & TERMINATING) != 0 ? "Terminating" :
1682	>	((s & SHUTDOWN) != 0 ? "Shutting down" :
1683	>	"Running")));
1684		}
1685
1108	–	// lifecycle control
1109	–
1686		/**
1687		* Initiates an orderly shutdown in which previously submitted
1688		* tasks are executed, but no new tasks will be accepted.
#	Line 1121 | Line 1697 | public class ForkJoinPool extends Abstra
1697		*/
1698		public void shutdown() {
1699		checkPermission();
1700	<	transitionRunStateTo(SHUTDOWN);
1701	<	if (canTerminateOnShutdown(runControl))
1126	<	terminateOnShutdown();
1700	>	advanceRunLevel(SHUTDOWN);
1701	>	tryTerminate(false);
1702		}
1703
1704		/**
1705	<	* Attempts to stop all actively executing tasks, and cancels all
1706	<	* waiting tasks.  Tasks that are in the process of being
1707	<	* submitted or executed concurrently during the course of this
1708	<	* method may or may not be rejected. Unlike some other executors,
1709	<	* this method cancels rather than collects non-executed tasks
1710	<	* upon termination, so always returns an empty list. However, you
1711	<	* can use method {@link #drainTasksTo} before invoking this
1712	<	* method to transfer unexecuted tasks to another collection.
1705	>	* Attempts to cancel and/or stop all tasks, and reject all
1706	>	* subsequently submitted tasks.  Tasks that are in the process of
1707	>	* being submitted or executed concurrently during the course of
1708	>	* this method may or may not be rejected. This method cancels
1709	>	* both existing and unexecuted tasks, in order to permit
1710	>	* termination in the presence of task dependencies. So the method
1711	>	* always returns an empty list (unlike the case for some other
1712	>	* Executors).
1713		*
1714		* @return an empty list
1715		* @throws SecurityException if a security manager exists and
#	Line 1144 | Line 1719 | public class ForkJoinPool extends Abstra
1719		*/
1720		public List<Runnable> shutdownNow() {
1721		checkPermission();
1722	<	terminate();
1722	>	tryTerminate(true);
1723		return Collections.emptyList();
1724		}
1725
#	Line 1154 | Line 1729 | public class ForkJoinPool extends Abstra
1729		* @return {@code true} if all tasks have completed following shut down
1730		*/
1731		public boolean isTerminated() {
1732	<	return runStateOf(runControl) == TERMINATED;
1732	>	return runState >= TERMINATED;
1733		}
1734
1735		/**
1736		* Returns {@code true} if the process of termination has
1737	<	* commenced but possibly not yet completed.
1737	>	* commenced but not yet completed.  This method may be useful for
1738	>	* debugging. A return of {@code true} reported a sufficient
1739	>	* period after shutdown may indicate that submitted tasks have
1740	>	* ignored or suppressed interruption, causing this executor not
1741	>	* to properly terminate.
1742		*
1743	<	* @return {@code true} if terminating
1743	>	* @return {@code true} if terminating but not yet terminated
1744		*/
1745		public boolean isTerminating() {
1746	<	return runStateOf(runControl) >= TERMINATING;
1746	>	return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
1747		}
1748
1749		/**
#	Line 1173 | Line 1752 | public class ForkJoinPool extends Abstra
1752		* @return {@code true} if this pool has been shut down
1753		*/
1754		public boolean isShutdown() {
1755	<	return runStateOf(runControl) >= SHUTDOWN;
1755	>	return runState >= SHUTDOWN;
1756		}
1757
1758		/**
#	Line 1189 | Line 1768 | public class ForkJoinPool extends Abstra
1768		*/
1769		public boolean awaitTermination(long timeout, TimeUnit unit)
1770		throws InterruptedException {
1771	<	long nanos = unit.toNanos(timeout);
1193	<	final ReentrantLock lock = this.workerLock;
1194	<	lock.lock();
1195	<	try {
1196	<	for (;;) {
1197	<	if (isTerminated())
1198	<	return true;
1199	<	if (nanos <= 0)
1200	<	return false;
1201	<	nanos = termination.awaitNanos(nanos);
1202	<	}
1203	<	} finally {
1204	<	lock.unlock();
1205	<	}
1206	<	}
1207	<
1208	<	// Shutdown and termination support
1209	<
1210	<	/**
1211	<	* Callback from terminating worker. Nulls out the corresponding
1212	<	* workers slot, and if terminating, tries to terminate; else
1213	<	* tries to shrink workers array.
1214	<	*
1215	<	* @param w the worker
1216	<	*/
1217	<	final void workerTerminated(ForkJoinWorkerThread w) {
1218	<	updateStealCount(w);
1219	<	updateWorkerCount(-1);
1220	<	final ReentrantLock lock = this.workerLock;
1221	<	lock.lock();
1222	<	try {
1223	<	ForkJoinWorkerThread[] ws = workers;
1224	<	if (ws != null) {
1225	<	int idx = w.poolIndex;
1226	<	if (idx >= 0 && idx < ws.length && ws[idx] == w)
1227	<	ws[idx] = null;
1228	<	if (totalCountOf(workerCounts) == 0) {
1229	<	terminate(); // no-op if already terminating
1230	<	transitionRunStateTo(TERMINATED);
1231	<	termination.signalAll();
1232	<	}
1233	<	else if (!isTerminating()) {
1234	<	tryShrinkWorkerArray();
1235	<	tryResumeSpare(true); // allow replacement
1236	<	}
1237	<	}
1238	<	} finally {
1239	<	lock.unlock();
1240	<	}
1241	<	signalIdleWorkers();
1242	<	}
1243	<
1244	<	/**
1245	<	* Initiates termination.
1246	<	*/
1247	<	private void terminate() {
1248	<	if (transitionRunStateTo(TERMINATING)) {
1249	<	stopAllWorkers();
1250	<	resumeAllSpares();
1251	<	signalIdleWorkers();
1252	<	cancelQueuedSubmissions();
1253	<	cancelQueuedWorkerTasks();
1254	<	interruptUnterminatedWorkers();
1255	<	signalIdleWorkers(); // resignal after interrupt
1256	<	}
1257	<	}
1258	<
1259	<	/**
1260	<	* Possibly terminates when on shutdown state.
1261	<	*/
1262	<	private void terminateOnShutdown() {
1263	<	if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
1264	<	terminate();
1265	<	}
1266	<
1267	<	/**
1268	<	* Clears out and cancels submissions.
1269	<	*/
1270	<	private void cancelQueuedSubmissions() {
1271	<	ForkJoinTask<?> task;
1272	<	while ((task = pollSubmission()) != null)
1273	<	task.cancel(false);
1274	<	}
1275	<
1276	<	/**
1277	<	* Cleans out worker queues.
1278	<	*/
1279	<	private void cancelQueuedWorkerTasks() {
1280	<	final ReentrantLock lock = this.workerLock;
1281	<	lock.lock();
1282	<	try {
1283	<	ForkJoinWorkerThread[] ws = workers;
1284	<	if (ws != null) {
1285	<	for (int i = 0; i < ws.length; ++i) {
1286	<	ForkJoinWorkerThread t = ws[i];
1287	<	if (t != null)
1288	<	t.cancelTasks();
1289	<	}
1290	<	}
1291	<	} finally {
1292	<	lock.unlock();
1293	<	}
1294	<	}
1295	<
1296	<	/**
1297	<	* Sets each worker's status to terminating. Requires lock to avoid
1298	<	* conflicts with add/remove.
1299	<	*/
1300	<	private void stopAllWorkers() {
1301	<	final ReentrantLock lock = this.workerLock;
1302	<	lock.lock();
1303	<	try {
1304	<	ForkJoinWorkerThread[] ws = workers;
1305	<	if (ws != null) {
1306	<	for (int i = 0; i < ws.length; ++i) {
1307	<	ForkJoinWorkerThread t = ws[i];
1308	<	if (t != null)
1309	<	t.shutdownNow();
1310	<	}
1311	<	}
1312	<	} finally {
1313	<	lock.unlock();
1314	<	}
1315	<	}
1316	<
1317	<	/**
1318	<	* Interrupts all unterminated workers.  This is not required for
1319	<	* sake of internal control, but may help unstick user code during
1320	<	* shutdown.
1321	<	*/
1322	<	private void interruptUnterminatedWorkers() {
1323	<	final ReentrantLock lock = this.workerLock;
1324	<	lock.lock();
1325	<	try {
1326	<	ForkJoinWorkerThread[] ws = workers;
1327	<	if (ws != null) {
1328	<	for (int i = 0; i < ws.length; ++i) {
1329	<	ForkJoinWorkerThread t = ws[i];
1330	<	if (t != null && !t.isTerminated()) {
1331	<	try {
1332	<	t.interrupt();
1333	<	} catch (SecurityException ignore) {
1334	<	}
1335	<	}
1336	<	}
1337	<	}
1338	<	} finally {
1339	<	lock.unlock();
1340	<	}
1341	<	}
1342	<
1343	<
1344	<	/*
1345	<	* Nodes for event barrier to manage idle threads.  Queue nodes
1346	<	* are basic Treiber stack nodes, also used for spare stack.
1347	<	*
1348	<	* The event barrier has an event count and a wait queue (actually
1349	<	* a Treiber stack).  Workers are enabled to look for work when
1350	<	* the eventCount is incremented. If they fail to find work, they
1351	<	* may wait for next count. Upon release, threads help others wake
1352	<	* up.
1353	<	*
1354	<	* Synchronization events occur only in enough contexts to
1355	<	* maintain overall liveness:
1356	<	*
1357	<	*   - Submission of a new task to the pool
1358	<	*   - Resizes or other changes to the workers array
1359	<	*   - pool termination
1360	<	*   - A worker pushing a task on an empty queue
1361	<	*
1362	<	* The case of pushing a task occurs often enough, and is heavy
1363	<	* enough compared to simple stack pushes, to require special
1364	<	* handling: Method signalWork returns without advancing count if
1365	<	* the queue appears to be empty.  This would ordinarily result in
1366	<	* races causing some queued waiters not to be woken up. To avoid
1367	<	* this, the first worker enqueued in method sync (see
1368	<	* syncIsReleasable) rescans for tasks after being enqueued, and
1369	<	* helps signal if any are found. This works well because the
1370	<	* worker has nothing better to do, and so might as well help
1371	<	* alleviate the overhead and contention on the threads actually
1372	<	* doing work.  Also, since event counts increments on task
1373	<	* availability exist to maintain liveness (rather than to force
1374	<	* refreshes etc), it is OK for callers to exit early if
1375	<	* contending with another signaller.
1376	<	*/
1377	<	static final class WaitQueueNode {
1378	<	WaitQueueNode next; // only written before enqueued
1379	<	volatile ForkJoinWorkerThread thread; // nulled to cancel wait
1380	<	final long count; // unused for spare stack
1381	<
1382	<	WaitQueueNode(long c, ForkJoinWorkerThread w) {
1383	<	count = c;
1384	<	thread = w;
1385	<	}
1386	<
1387	<	/**
1388	<	* Wakes up waiter, returning false if known to already
1389	<	*/
1390	<	boolean signal() {
1391	<	ForkJoinWorkerThread t = thread;
1392	<	if (t == null)
1393	<	return false;
1394	<	thread = null;
1395	<	LockSupport.unpark(t);
1396	<	return true;
1397	<	}
1398	<
1399	<	/**
1400	<	* Awaits release on sync.
1401	<	*/
1402	<	void awaitSyncRelease(ForkJoinPool p) {
1403	<	while (thread != null && !p.syncIsReleasable(this))
1404	<	LockSupport.park(this);
1405	<	}
1406	<
1407	<	/**
1408	<	* Awaits resumption as spare.
1409	<	*/
1410	<	void awaitSpareRelease() {
1411	<	while (thread != null) {
1412	<	if (!Thread.interrupted())
1413	<	LockSupport.park(this);
1414	<	}
1415	<	}
1416	<	}
1417	<
1418	<	/**
1419	<	* Ensures that no thread is waiting for count to advance from the
1420	<	* current value of eventCount read on entry to this method, by
1421	<	* releasing waiting threads if necessary.
1422	<	*
1423	<	* @return the count
1424	<	*/
1425	<	final long ensureSync() {
1426	<	long c = eventCount;
1427	<	WaitQueueNode q;
1428	<	while ((q = syncStack) != null && q.count < c) {
1429	<	if (casBarrierStack(q, null)) {
1430	<	do {
1431	<	q.signal();
1432	<	} while ((q = q.next) != null);
1433	<	break;
1434	<	}
1435	<	}
1436	<	return c;
1437	<	}
1438	<
1439	<	/**
1440	<	* Increments event count and releases waiting threads.
1441	<	*/
1442	<	private void signalIdleWorkers() {
1443	<	long c;
1444	<	do {} while (!casEventCount(c = eventCount, c+1));
1445	<	ensureSync();
1446	<	}
1447	<
1448	<	/**
1449	<	* Signals threads waiting to poll a task. Because method sync
1450	<	* rechecks availability, it is OK to only proceed if queue
1451	<	* appears to be non-empty, and OK to skip under contention to
1452	<	* increment count (since some other thread succeeded).
1453	<	*/
1454	<	final void signalWork() {
1455	<	long c;
1456	<	WaitQueueNode q;
1457	<	if (syncStack != null &&
1458	<	casEventCount(c = eventCount, c+1) &&
1459	<	(((q = syncStack) != null && q.count <= c) &&
1460	<	(!casBarrierStack(q, q.next) || !q.signal())))
1461	<	ensureSync();
1462	<	}
1463	<
1464	<	/**
1465	<	* Waits until event count advances from last value held by
1466	<	* caller, or if excess threads, caller is resumed as spare, or
1467	<	* caller or pool is terminating. Updates caller's event on exit.
1468	<	*
1469	<	* @param w the calling worker thread
1470	<	*/
1471	<	final void sync(ForkJoinWorkerThread w) {
1472	<	updateStealCount(w); // Transfer w's count while it is idle
1473	<
1474	<	while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
1475	<	long prev = w.lastEventCount;
1476	<	WaitQueueNode node = null;
1477	<	WaitQueueNode h;
1478	<	while (eventCount == prev &&
1479	<	((h = syncStack) == null || h.count == prev)) {
1480	<	if (node == null)
1481	<	node = new WaitQueueNode(prev, w);
1482	<	if (casBarrierStack(node.next = h, node)) {
1483	<	node.awaitSyncRelease(this);
1484	<	break;
1485	<	}
1486	<	}
1487	<	long ec = ensureSync();
1488	<	if (ec != prev) {
1489	<	w.lastEventCount = ec;
1490	<	break;
1491	<	}
1492	<	}
1493	<	}
1494	<
1495	<	/**
1496	<	* Returns {@code true} if worker waiting on sync can proceed:
1497	<	*  - on signal (thread == null)
1498	<	*  - on event count advance (winning race to notify vs signaller)
1499	<	*  - on interrupt
1500	<	*  - if the first queued node, we find work available
1501	<	* If node was not signalled and event count not advanced on exit,
1502	<	* then we also help advance event count.
1503	<	*
1504	<	* @return {@code true} if node can be released
1505	<	*/
1506	<	final boolean syncIsReleasable(WaitQueueNode node) {
1507	<	long prev = node.count;
1508	<	if (!Thread.interrupted() && node.thread != null &&
1509	<	(node.next != null ||
1510	<	!ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
1511	<	eventCount == prev)
1512	<	return false;
1513	<	if (node.thread != null) {
1514	<	node.thread = null;
1515	<	long ec = eventCount;
1516	<	if (prev <= ec) // help signal
1517	<	casEventCount(ec, ec+1);
1518	<	}
1519	<	return true;
1520	<	}
1521	<
1522	<	/**
1523	<	* Returns {@code true} if a new sync event occurred since last
1524	<	* call to sync or this method, if so, updating caller's count.
1525	<	*/
1526	<	final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1527	<	long lc = w.lastEventCount;
1528	<	long ec = ensureSync();
1529	<	if (ec == lc)
1530	<	return false;
1531	<	w.lastEventCount = ec;
1532	<	return true;
1533	<	}
1534	<
1535	<	//  Parallelism maintenance
1536	<
1537	<	/**
1538	<	* Decrements running count; if too low, adds spare.
1539	<	*
1540	<	* Conceptually, all we need to do here is add or resume a
1541	<	* spare thread when one is about to block (and remove or
1542	<	* suspend it later when unblocked -- see suspendIfSpare).
1543	<	* However, implementing this idea requires coping with
1544	<	* several problems: we have imperfect information about the
1545	<	* states of threads. Some count updates can and usually do
1546	<	* lag run state changes, despite arrangements to keep them
1547	<	* accurate (for example, when possible, updating counts
1548	<	* before signalling or resuming), especially when running on
1549	<	* dynamic JVMs that don't optimize the infrequent paths that
1550	<	* update counts. Generating too many threads can make these
1551	<	* problems become worse, because excess threads are more
1552	<	* likely to be context-switched with others, slowing them all
1553	<	* down, especially if there is no work available, so all are
1554	<	* busy scanning or idling.  Also, excess spare threads can
1555	<	* only be suspended or removed when they are idle, not
1556	<	* immediately when they aren't needed. So adding threads will
1557	<	* raise parallelism level for longer than necessary.  Also,
1558	<	* FJ applications often encounter highly transient peaks when
1559	<	* many threads are blocked joining, but for less time than it
1560	<	* takes to create or resume spares.
1561	<	*
1562	<	* @param joinMe if non-null, return early if done
1563	<	* @param maintainParallelism if true, try to stay within
1564	<	* target counts, else create only to avoid starvation
1565	<	* @return true if joinMe known to be done
1566	<	*/
1567	<	final boolean preJoin(ForkJoinTask<?> joinMe,
1568	<	boolean maintainParallelism) {
1569	<	maintainParallelism &= maintainsParallelism; // overrride
1570	<	boolean dec = false;  // true when running count decremented
1571	<	while (spareStack == null || !tryResumeSpare(dec)) {
1572	<	int counts = workerCounts;
1573	<	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1574	<	// CAS cheat
1575	<	if (!needSpare(counts, maintainParallelism))
1576	<	break;
1577	<	if (joinMe.status < 0)
1578	<	return true;
1579	<	if (tryAddSpare(counts))
1580	<	break;
1581	<	}
1582	<	}
1583	<	return false;
1584	<	}
1585	<
1586	<	/**
1587	<	* Same idea as preJoin
1588	<	*/
1589	<	final boolean preBlock(ManagedBlocker blocker,
1590	<	boolean maintainParallelism) {
1591	<	maintainParallelism &= maintainsParallelism;
1592	<	boolean dec = false;
1593	<	while (spareStack == null || !tryResumeSpare(dec)) {
1594	<	int counts = workerCounts;
1595	<	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1596	<	if (!needSpare(counts, maintainParallelism))
1597	<	break;
1598	<	if (blocker.isReleasable())
1599	<	return true;
1600	<	if (tryAddSpare(counts))
1601	<	break;
1602	<	}
1603	<	}
1604	<	return false;
1605	<	}
1606	<
1607	<	/**
1608	<	* Returns {@code true} if a spare thread appears to be needed.
1609	<	* If maintaining parallelism, returns true when the deficit in
1610	<	* running threads is more than the surplus of total threads, and
1611	<	* there is apparently some work to do.  This self-limiting rule
1612	<	* means that the more threads that have already been added, the
1613	<	* less parallelism we will tolerate before adding another.
1614	<	*
1615	<	* @param counts current worker counts
1616	<	* @param maintainParallelism try to maintain parallelism
1617	<	*/
1618	<	private boolean needSpare(int counts, boolean maintainParallelism) {
1619	<	int ps = parallelism;
1620	<	int rc = runningCountOf(counts);
1621	<	int tc = totalCountOf(counts);
1622	<	int runningDeficit = ps - rc;
1623	<	int totalSurplus = tc - ps;
1624	<	return (tc < maxPoolSize &&
1625	<	(rc == 0 || totalSurplus < 0 ||
1626	<	(maintainParallelism &&
1627	<	runningDeficit > totalSurplus &&
1628	<	ForkJoinWorkerThread.hasQueuedTasks(workers))));
1629	<	}
1630	<
1631	<	/**
1632	<	* Adds a spare worker if lock available and no more than the
1633	<	* expected numbers of threads exist.
1634	<	*
1635	<	* @return true if successful
1636	<	*/
1637	<	private boolean tryAddSpare(int expectedCounts) {
1638	<	final ReentrantLock lock = this.workerLock;
1639	<	int expectedRunning = runningCountOf(expectedCounts);
1640	<	int expectedTotal = totalCountOf(expectedCounts);
1641	<	boolean success = false;
1642	<	boolean locked = false;
1643	<	// confirm counts while locking; CAS after obtaining lock
1644	<	try {
1645	<	for (;;) {
1646	<	int s = workerCounts;
1647	<	int tc = totalCountOf(s);
1648	<	int rc = runningCountOf(s);
1649	<	if (rc > expectedRunning || tc > expectedTotal)
1650	<	break;
1651	<	if (!locked && !(locked = lock.tryLock()))
1652	<	break;
1653	<	if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
1654	<	createAndStartSpare(tc);
1655	<	success = true;
1656	<	break;
1657	<	}
1658	<	}
1659	<	} finally {
1660	<	if (locked)
1661	<	lock.unlock();
1662	<	}
1663	<	return success;
1664	<	}
1665	<
1666	<	/**
1667	<	* Adds the kth spare worker. On entry, pool counts are already
1668	<	* adjusted to reflect addition.
1669	<	*/
1670	<	private void createAndStartSpare(int k) {
1671	<	ForkJoinWorkerThread w = null;
1672	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
1673	<	int len = ws.length;
1674	<	// Probably, we can place at slot k. If not, find empty slot
1675	<	if (k < len && ws[k] != null) {
1676	<	for (k = 0; k < len && ws[k] != null; ++k)
1677	<	;
1678	<	}
1679	<	if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
1680	<	ws[k] = w;
1681	<	w.start();
1682	<	}
1683	<	else
1684	<	updateWorkerCount(-1); // adjust on failure
1685	<	signalIdleWorkers();
1686	<	}
1687	<
1688	<	/**
1689	<	* Suspends calling thread w if there are excess threads.  Called
1690	<	* only from sync.  Spares are enqueued in a Treiber stack using
1691	<	* the same WaitQueueNodes as barriers.  They are resumed mainly
1692	<	* in preJoin, but are also woken on pool events that require all
1693	<	* threads to check run state.
1694	<	*
1695	<	* @param w the caller
1696	<	*/
1697	<	private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1698	<	WaitQueueNode node = null;
1699	<	int s;
1700	<	while (parallelism < runningCountOf(s = workerCounts)) {
1701	<	if (node == null)
1702	<	node = new WaitQueueNode(0, w);
1703	<	if (casWorkerCounts(s, s-1)) { // representation-dependent
1704	<	// push onto stack
1705	<	do {} while (!casSpareStack(node.next = spareStack, node));
1706	<	// block until released by resumeSpare
1707	<	node.awaitSpareRelease();
1708	<	return true;
1709	<	}
1710	<	}
1711	<	return false;
1712	<	}
1713	<
1714	<	/**
1715	<	* Tries to pop and resume a spare thread.
1716	<	*
1717	<	* @param updateCount if true, increment running count on success
1718	<	* @return true if successful
1719	<	*/
1720	<	private boolean tryResumeSpare(boolean updateCount) {
1721	<	WaitQueueNode q;
1722	<	while ((q = spareStack) != null) {
1723	<	if (casSpareStack(q, q.next)) {
1724	<	if (updateCount)
1725	<	updateRunningCount(1);
1726	<	q.signal();
1727	<	return true;
1728	<	}
1729	<	}
1730	<	return false;
1731	<	}
1732	<
1733	<	/**
1734	<	* Pops and resumes all spare threads. Same idea as ensureSync.
1735	<	*
1736	<	* @return true if any spares released
1737	<	*/
1738	<	private boolean resumeAllSpares() {
1739	<	WaitQueueNode q;
1740	<	while ( (q = spareStack) != null) {
1741	<	if (casSpareStack(q, null)) {
1742	<	do {
1743	<	updateRunningCount(1);
1744	<	q.signal();
1745	<	} while ((q = q.next) != null);
1746	<	return true;
1747	<	}
1748	<	}
1749	<	return false;
1750	<	}
1751	<
1752	<	/**
1753	<	* Pops and shuts down excessive spare threads. Call only while
1754	<	* holding lock. This is not guaranteed to eliminate all excess
1755	<	* threads, only those suspended as spares, which are the ones
1756	<	* unlikely to be needed in the future.
1757	<	*/
1758	<	private void trimSpares() {
1759	<	int surplus = totalCountOf(workerCounts) - parallelism;
1760	<	WaitQueueNode q;
1761	<	while (surplus > 0 && (q = spareStack) != null) {
1762	<	if (casSpareStack(q, null)) {
1763	<	do {
1764	<	updateRunningCount(1);
1765	<	ForkJoinWorkerThread w = q.thread;
1766	<	if (w != null && surplus > 0 &&
1767	<	runningCountOf(workerCounts) > 0 && w.shutdown())
1768	<	--surplus;
1769	<	q.signal();
1770	<	} while ((q = q.next) != null);
1771	<	}
1772	<	}
1771	>	return terminationLatch.await(timeout, unit);
1772		}
1773
1774		/**
1775		* Interface for extending managed parallelism for tasks running
1776	<	* in ForkJoinPools. A ManagedBlocker provides two methods.
1776	>	* in {@link ForkJoinPool}s.
1777	>	*
1778	>	* <p>A {@code ManagedBlocker} provides two methods.
1779		* Method {@code isReleasable} must return {@code true} if
1780		* blocking is not necessary. Method {@code block} blocks the
1781		* current thread if necessary (perhaps internally invoking
1782	<	* {@code isReleasable} before actually blocking.).
1782	>	* {@code isReleasable} before actually blocking).
1783		*
1784		* <p>For example, here is a ManagedBlocker based on a
1785		* ReentrantLock:
#	Line 1817 | Line 1818 | public class ForkJoinPool extends Abstra
1818
1819		/**
1820		* Blocks in accord with the given blocker.  If the current thread
1821	<	* is a ForkJoinWorkerThread, this method possibly arranges for a
1822	<	* spare thread to be activated if necessary to ensure parallelism
1823	<	* while the current thread is blocked.  If
1824	<	* {@code maintainParallelism} is {@code true} and the pool supports
1825	<	* it ({@link #getMaintainsParallelism}), this method attempts to
1826	<	* maintain the pool's nominal parallelism. Otherwise it activates
1827	<	* a thread only if necessary to avoid complete starvation. This
1828	<	* option may be preferable when blockages use timeouts, or are
1829	<	* almost always brief.
1821	>	* is a {@link ForkJoinWorkerThread}, this method possibly
1822	>	* arranges for a spare thread to be activated if necessary to
1823	>	* ensure parallelism while the current thread is blocked.
1824	>	*
1825	>	* <p>If {@code maintainParallelism} is {@code true} and the pool
1826	>	* supports it ({@link #getMaintainsParallelism}), this method
1827	>	* attempts to maintain the pool's nominal parallelism. Otherwise
1828	>	* it activates a thread only if necessary to avoid complete
1829	>	* starvation. This option may be preferable when blockages use
1830	>	* timeouts, or are almost always brief.
1831		*
1832	<	* <p> If the caller is not a ForkJoinTask, this method is behaviorally
1833	<	* equivalent to
1832	>	* <p>If the caller is not a {@link ForkJoinTask}, this method is
1833	>	* behaviorally equivalent to
1834		*  <pre> {@code
1835		* while (!blocker.isReleasable())
1836		*   if (blocker.block())
1837		*     return;
1838		* }</pre>
1839	<	* If the caller is a ForkJoinTask, then the pool may first
1840	<	* be expanded to ensure parallelism, and later adjusted.
1839	>	*
1840	>	* If the caller is a {@code ForkJoinTask}, then the pool may
1841	>	* first be expanded to ensure parallelism, and later adjusted.
1842		*
1843		* @param blocker the blocker
1844		* @param maintainParallelism if {@code true} and supported by
#	Line 1848 | Line 1851 | public class ForkJoinPool extends Abstra
1851		boolean maintainParallelism)
1852		throws InterruptedException {
1853		Thread t = Thread.currentThread();
1854	<	ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
1855	<	((ForkJoinWorkerThread) t).pool : null);
1856	<	if (!blocker.isReleasable()) {
1857	<	try {
1858	<	if (pool == null ||
1856	<	!pool.preBlock(blocker, maintainParallelism))
1857	<	awaitBlocker(blocker);
1858	<	} finally {
1859	<	if (pool != null)
1860	<	pool.updateRunningCount(1);
1861	<	}
1862	<	}
1854	>	if (t instanceof ForkJoinWorkerThread)
1855	>	((ForkJoinWorkerThread) t).pool.
1856	>	doBlock(blocker, maintainParallelism);
1857	>	else
1858	>	awaitBlocker(blocker);
1859		}
1860
1861	+	/**
1862	+	* Performs Non-FJ blocking
1863	+	*/
1864		private static void awaitBlocker(ManagedBlocker blocker)
1865		throws InterruptedException {
1866		do {} while (!blocker.isReleasable() && !blocker.block());
1867		}
1868
1869	<	// AbstractExecutorService overrides
1869	>	// AbstractExecutorService overrides.  These rely on undocumented
1870	>	// fact that ForkJoinTask.adapt returns ForkJoinTasks that also
1871	>	// implement RunnableFuture.
1872
1873		protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
1874	<	return new AdaptedRunnable<T>(runnable, value);
1874	>	return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
1875		}
1876
1877		protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
1878	<	return new AdaptedCallable<T>(callable);
1878	>	return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
1879		}
1880
1881		// Unsafe mechanics
1882
1883		private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1883	–	private static final long eventCountOffset =
1884	–	objectFieldOffset("eventCount", ForkJoinPool.class);
1884		private static final long workerCountsOffset =
1885		objectFieldOffset("workerCounts", ForkJoinPool.class);
1886	<	private static final long runControlOffset =
1887	<	objectFieldOffset("runControl", ForkJoinPool.class);
1888	<	private static final long syncStackOffset =
1889	<	objectFieldOffset("syncStack",ForkJoinPool.class);
1890	<	private static final long spareStackOffset =
1891	<	objectFieldOffset("spareStack", ForkJoinPool.class);
1892	<
1893	<	private boolean casEventCount(long cmp, long val) {
1894	<	return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
1896	<	}
1897	<	private boolean casWorkerCounts(int cmp, int val) {
1898	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
1899	<	}
1900	<	private boolean casRunControl(int cmp, int val) {
1901	<	return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
1902	<	}
1903	<	private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
1904	<	return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
1905	<	}
1906	<	private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
1907	<	return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
1908	<	}
1886	>	private static final long runStateOffset =
1887	>	objectFieldOffset("runState", ForkJoinPool.class);
1888	>	private static final long eventCountOffset =
1889	>	objectFieldOffset("eventCount", ForkJoinPool.class);
1890	>	private static final long eventWaitersOffset =
1891	>	objectFieldOffset("eventWaiters",ForkJoinPool.class);
1892	>	private static final long stealCountOffset =
1893	>	objectFieldOffset("stealCount",ForkJoinPool.class);
1894	>
1895
1896		private static long objectFieldOffset(String field, Class<?> klazz) {
1897		try {

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