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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.31 by dl, Wed Jul 29 22:48:54 2009 UTC vs.
Revision 1.88 by dl, Tue Nov 23 01:06:00 2010 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.util.ArrayList;
10		import java.util.Arrays;
11		import java.util.Collection;
12		import java.util.Collections;
13		import java.util.List;
14	<	import java.util.concurrent.locks.Condition;
14	>	import java.util.concurrent.AbstractExecutorService;
15	>	import java.util.concurrent.Callable;
16	>	import java.util.concurrent.ExecutorService;
17	>	import java.util.concurrent.Future;
18	>	import java.util.concurrent.RejectedExecutionException;
19	>	import java.util.concurrent.RunnableFuture;
20	>	import java.util.concurrent.TimeUnit;
21	>	import java.util.concurrent.TimeoutException;
22	>	import java.util.concurrent.atomic.AtomicInteger;
23		import java.util.concurrent.locks.LockSupport;
24		import java.util.concurrent.locks.ReentrantLock;
19	–	import java.util.concurrent.atomic.AtomicInteger;
20	–	import java.util.concurrent.atomic.AtomicLong;
25
26		/**
27		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
28	<	* A ForkJoinPool provides the entry point for submissions from
29	<	* non-ForkJoinTasks, as well as management and monitoring operations.
30	<	* 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.
28	>	* A {@code ForkJoinPool} provides the entry point for submissions
29	>	* from non-{@code ForkJoinTask} clients, as well as management and
30	>	* monitoring operations.
31		*
32	<	* <p>ForkJoinPools differ from other kinds of Executors mainly in
33	<	* that they provide <em>work-stealing</em>: all threads in the pool
34	<	* attempt to find and execute subtasks created by other active tasks
35	<	* (eventually blocking if none exist). This makes them efficient when
36	<	* most tasks spawn other subtasks (as do most ForkJoinTasks), as well
37	<	* as the mixed execution of some plain Runnable- or Callable- based
38	<	* activities along with ForkJoinTasks. When setting {@linkplain
39	<	* #setAsyncMode async mode}, a ForkJoinPool may also be appropriate
40	<	* for use with fine-grained tasks that are never joined. Otherwise,
40	<	* other ExecutorService implementations are typically more
41	<	* appropriate choices.
32	>	* <p>A {@code ForkJoinPool} differs from other kinds of {@link
33	>	* ExecutorService} mainly by virtue of employing
34	>	* <em>work-stealing</em>: all threads in the pool attempt to find and
35	>	* execute subtasks created by other active tasks (eventually blocking
36	>	* waiting for work if none exist). This enables efficient processing
37	>	* when most tasks spawn other subtasks (as do most {@code
38	>	* ForkJoinTask}s). When setting <em>asyncMode</em> to true in
39	>	* constructors, {@code ForkJoinPool}s may also be appropriate for use
40	>	* with event-style tasks that are never joined.
41		*
42	<	* <p>A ForkJoinPool may be constructed with a given parallelism level
43	<	* (target pool size), which it attempts to maintain by dynamically
44	<	* adding, suspending, or resuming threads, even if some tasks are
45	<	* waiting to join others. However, no such adjustments are performed
46	<	* in the face of blocked IO or other unmanaged synchronization. The
47	<	* nested {@link ManagedBlocker} interface enables extension of
48	<	* the kinds of synchronization accommodated.  The target parallelism
49	<	* level may also be changed dynamically ({@link #setParallelism})
50	<	* and thread construction can be limited using methods
52	<	* {@link #setMaximumPoolSize} and/or
53	<	* {@link #setMaintainsParallelism}.
42	>	* <p>A {@code ForkJoinPool} is constructed with a given target
43	>	* parallelism level; by default, equal to the number of available
44	>	* processors. The pool attempts to maintain enough active (or
45	>	* available) threads by dynamically adding, suspending, or resuming
46	>	* internal worker threads, even if some tasks are stalled waiting to
47	>	* join others. However, no such adjustments are guaranteed in the
48	>	* face of blocked IO or other unmanaged synchronization. The nested
49	>	* {@link ManagedBlocker} interface enables extension of the kinds of
50	>	* synchronization accommodated.
51		*
52		* <p>In addition to execution and lifecycle control methods, this
53		* class provides status check methods (for example
#	Line 59 | Line 56 | import java.util.concurrent.atomic.Atomi
56		* {@link #toString} returns indications of pool state in a
57		* convenient form for informal monitoring.
58		*
59	+	* <p> As is the case with other ExecutorServices, there are three
60	+	* main task execution methods summarized in the following
61	+	* table. These are designed to be used by clients not already engaged
62	+	* in fork/join computations in the current pool.  The main forms of
63	+	* these methods accept instances of {@code ForkJoinTask}, but
64	+	* overloaded forms also allow mixed execution of plain {@code
65	+	* Runnable}- or {@code Callable}- based activities as well.  However,
66	+	* tasks that are already executing in a pool should normally
67	+	* <em>NOT</em> use these pool execution methods, but instead use the
68	+	* within-computation forms listed in the table.
69	+	*
70	+	* <table BORDER CELLPADDING=3 CELLSPACING=1>
71	+	*  <tr>
72	+	*    <td></td>
73	+	*    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
74	+	*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
75	+	*  </tr>
76	+	*  <tr>
77	+	*    <td> <b>Arrange async execution</td>
78	+	*    <td> {@link #execute(ForkJoinTask)}</td>
79	+	*    <td> {@link ForkJoinTask#fork}</td>
80	+	*  </tr>
81	+	*  <tr>
82	+	*    <td> <b>Await and obtain result</td>
83	+	*    <td> {@link #invoke(ForkJoinTask)}</td>
84	+	*    <td> {@link ForkJoinTask#invoke}</td>
85	+	*  </tr>
86	+	*  <tr>
87	+	*    <td> <b>Arrange exec and obtain Future</td>
88	+	*    <td> {@link #submit(ForkJoinTask)}</td>
89	+	*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
90	+	*  </tr>
91	+	* </table>
92	+	*
93	+	* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
94	+	* used for all parallel task execution in a program or subsystem.
95	+	* Otherwise, use would not usually outweigh the construction and
96	+	* bookkeeping overhead of creating a large set of threads. For
97	+	* example, a common pool could be used for the {@code SortTasks}
98	+	* illustrated in {@link RecursiveAction}. Because {@code
99	+	* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
100	+	* daemon} mode, there is typically no need to explicitly {@link
101	+	* #shutdown} such a pool upon program exit.
102	+	*
103	+	* <pre>
104	+	* static final ForkJoinPool mainPool = new ForkJoinPool();
105	+	* ...
106	+	* public void sort(long[] array) {
107	+	*   mainPool.invoke(new SortTask(array, 0, array.length));
108	+	* }
109	+	* </pre>
110	+	*
111		* <p><b>Implementation notes</b>: This implementation restricts the
112		* maximum number of running threads to 32767. Attempts to create
113	<	* pools with greater than the maximum result in
114	<	* IllegalArgumentExceptions.
113	>	* pools with greater than the maximum number result in
114	>	* {@code IllegalArgumentException}.
115	>	*
116	>	* <p>This implementation rejects submitted tasks (that is, by throwing
117	>	* {@link RejectedExecutionException}) only when the pool is shut down
118	>	* or internal resources have been exhausted.
119		*
120		* @since 1.7
121		* @author Doug Lea
#	Line 70 | Line 123 | import java.util.concurrent.atomic.Atomi
123		public class ForkJoinPool extends AbstractExecutorService {
124
125		/*
126	<	* See the extended comments interspersed below for design,
127	<	* rationale, and walkthroughs.
128	<	*/
129	<
130	<	/** Mask for packing and unpacking shorts */
131	<	private static final int  shortMask = 0xffff;
132	<
133	<	/** Max pool size -- must be a power of two minus 1 */
134	<	private static final int MAX_THREADS =  0x7FFF;
135	<
136	<	/**
137	<	* Factory for creating new ForkJoinWorkerThreads.  A
138	<	* ForkJoinWorkerThreadFactory must be defined and used for
139	<	* ForkJoinWorkerThread subclasses that extend base functionality
140	<	* or initialize threads with different contexts.
126	>	* Implementation Overview
127	>	*
128	>	* This class provides the central bookkeeping and control for a
129	>	* set of worker threads: Submissions from non-FJ threads enter
130	>	* into a submission queue. Workers take these tasks and typically
131	>	* split them into subtasks that may be stolen by other workers.
132	>	* The main work-stealing mechanics implemented in class
133	>	* ForkJoinWorkerThread give first priority to processing tasks
134	>	* from their own queues (LIFO or FIFO, depending on mode), then
135	>	* to randomized FIFO steals of tasks in other worker queues, and
136	>	* lastly to new submissions. These mechanics do not consider
137	>	* affinities, loads, cache localities, etc, so rarely provide the
138	>	* best possible performance on a given machine, but portably
139	>	* provide good throughput by averaging over these factors.
140	>	* (Further, even if we did try to use such information, we do not
141	>	* usually have a basis for exploiting it. For example, some sets
142	>	* of tasks profit from cache affinities, but others are harmed by
143	>	* cache pollution effects.)
144	>	*
145	>	* Beyond work-stealing support and essential bookkeeping, the
146	>	* main responsibility of this framework is to take actions when
147	>	* one worker is waiting to join a task stolen (or always held by)
148	>	* another.  Because we are multiplexing many tasks on to a pool
149	>	* of workers, we can't just let them block (as in Thread.join).
150	>	* We also cannot just reassign the joiner's run-time stack with
151	>	* another and replace it later, which would be a form of
152	>	* "continuation", that even if possible is not necessarily a good
153	>	* idea. Given that the creation costs of most threads on most
154	>	* systems mainly surrounds setting up runtime stacks, thread
155	>	* creation and switching is usually not much more expensive than
156	>	* stack creation and switching, and is more flexible). Instead we
157	>	* combine two tactics:
158	>	*
159	>	*   Helping: Arranging for the joiner to execute some task that it
160	>	*      would be running if the steal had not occurred.  Method
161	>	*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
162	>	*      links to try to find such a task.
163	>	*
164	>	*   Compensating: Unless there are already enough live threads,
165	>	*      method helpMaintainParallelism() may create or
166	>	*      re-activate a spare thread to compensate for blocked
167	>	*      joiners until they unblock.
168	>	*
169	>	* It is impossible to keep exactly the target (parallelism)
170	>	* number of threads running at any given time.  Determining
171	>	* existence of conservatively safe helping targets, the
172	>	* availability of already-created spares, and the apparent need
173	>	* to create new spares are all racy and require heuristic
174	>	* guidance, so we rely on multiple retries of each.  Compensation
175	>	* occurs in slow-motion. It is triggered only upon timeouts of
176	>	* Object.wait used for joins. This reduces poor decisions that
177	>	* would otherwise be made when threads are waiting for others
178	>	* that are stalled because of unrelated activities such as
179	>	* garbage collection.
180	>	*
181	>	* The ManagedBlocker extension API can't use helping so relies
182	>	* only on compensation in method awaitBlocker.
183	>	*
184	>	* The main throughput advantages of work-stealing stem from
185	>	* decentralized control -- workers mostly steal tasks from each
186	>	* other. We do not want to negate this by creating bottlenecks
187	>	* implementing other management responsibilities. So we use a
188	>	* collection of techniques that avoid, reduce, or cope well with
189	>	* contention. These entail several instances of bit-packing into
190	>	* CASable fields to maintain only the minimally required
191	>	* atomicity. To enable such packing, we restrict maximum
192	>	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
193	>	* unbalanced increments and decrements) to fit into a 16 bit
194	>	* field, which is far in excess of normal operating range.  Even
195	>	* though updates to some of these bookkeeping fields do sometimes
196	>	* contend with each other, they don't normally cache-contend with
197	>	* updates to others enough to warrant memory padding or
198	>	* isolation. So they are all held as fields of ForkJoinPool
199	>	* objects.  The main capabilities are as follows:
200	>	*
201	>	* 1. Creating and removing workers. Workers are recorded in the
202	>	* "workers" array. This is an array as opposed to some other data
203	>	* structure to support index-based random steals by workers.
204	>	* Updates to the array recording new workers and unrecording
205	>	* terminated ones are protected from each other by a lock
206	>	* (workerLock) but the array is otherwise concurrently readable,
207	>	* and accessed directly by workers. To simplify index-based
208	>	* operations, the array size is always a power of two, and all
209	>	* readers must tolerate null slots. Currently, all worker thread
210	>	* creation is on-demand, triggered by task submissions,
211	>	* replacement of terminated workers, and/or compensation for
212	>	* blocked workers. However, all other support code is set up to
213	>	* work with other policies.
214	>	*
215	>	* To ensure that we do not hold on to worker references that
216	>	* would prevent GC, ALL accesses to workers are via indices into
217	>	* the workers array (which is one source of some of the unusual
218	>	* code constructions here). In essence, the workers array serves
219	>	* as a WeakReference mechanism. Thus for example the event queue
220	>	* stores worker indices, not worker references. Access to the
221	>	* workers in associated methods (for example releaseEventWaiters)
222	>	* must both index-check and null-check the IDs. All such accesses
223	>	* ignore bad IDs by returning out early from what they are doing,
224	>	* since this can only be associated with shutdown, in which case
225	>	* it is OK to give up. On termination, we just clobber these
226	>	* data structures without trying to use them.
227	>	*
228	>	* 2. Bookkeeping for dynamically adding and removing workers. We
229	>	* aim to approximately maintain the given level of parallelism.
230	>	* When some workers are known to be blocked (on joins or via
231	>	* ManagedBlocker), we may create or resume others to take their
232	>	* place until they unblock (see below). Implementing this
233	>	* requires counts of the number of "running" threads (i.e., those
234	>	* that are neither blocked nor artificially suspended) as well as
235	>	* the total number.  These two values are packed into one field,
236	>	* "workerCounts" because we need accurate snapshots when deciding
237	>	* to create, resume or suspend.  Note however that the
238	>	* correspondence of these counts to reality is not guaranteed. In
239	>	* particular updates for unblocked threads may lag until they
240	>	* actually wake up.
241	>	*
242	>	* 3. Maintaining global run state. The run state of the pool
243	>	* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
244	>	* those in other Executor implementations, as well as a count of
245	>	* "active" workers -- those that are, or soon will be, or
246	>	* recently were executing tasks. The runLevel and active count
247	>	* are packed together in order to correctly trigger shutdown and
248	>	* termination. Without care, active counts can be subject to very
249	>	* high contention.  We substantially reduce this contention by
250	>	* relaxing update rules.  A worker must claim active status
251	>	* prospectively, by activating if it sees that a submitted or
252	>	* stealable task exists (it may find after activating that the
253	>	* task no longer exists). It stays active while processing this
254	>	* task (if it exists) and any other local subtasks it produces,
255	>	* until it cannot find any other tasks. It then tries
256	>	* inactivating (see method preStep), but upon update contention
257	>	* instead scans for more tasks, later retrying inactivation if it
258	>	* doesn't find any.
259	>	*
260	>	* 4. Managing idle workers waiting for tasks. We cannot let
261	>	* workers spin indefinitely scanning for tasks when none are
262	>	* available. On the other hand, we must quickly prod them into
263	>	* action when new tasks are submitted or generated.  We
264	>	* park/unpark these idle workers using an event-count scheme.
265	>	* Field eventCount is incremented upon events that may enable
266	>	* workers that previously could not find a task to now find one:
267	>	* Submission of a new task to the pool, or another worker pushing
268	>	* a task onto a previously empty queue.  (We also use this
269	>	* mechanism for configuration and termination actions that
270	>	* require wakeups of idle workers).  Each worker maintains its
271	>	* last known event count, and blocks when a scan for work did not
272	>	* find a task AND its lastEventCount matches the current
273	>	* eventCount. Waiting idle workers are recorded in a variant of
274	>	* Treiber stack headed by field eventWaiters which, when nonzero,
275	>	* encodes the thread index and count awaited for by the worker
276	>	* thread most recently calling eventSync. This thread in turn has
277	>	* a record (field nextEventWaiter) for the next waiting worker.
278	>	* In addition to allowing simpler decisions about need for
279	>	* wakeup, the event count bits in eventWaiters serve the role of
280	>	* tags to avoid ABA errors in Treiber stacks. Upon any wakeup,
281	>	* released threads also try to release at most two others.  The
282	>	* net effect is a tree-like diffusion of signals, where released
283	>	* threads (and possibly others) help with unparks.  To further
284	>	* reduce contention effects a bit, failed CASes to increment
285	>	* field eventCount are tolerated without retries in signalWork.
286	>	* Conceptually they are merged into the same event, which is OK
287	>	* when their only purpose is to enable workers to scan for work.
288	>	*
289	>	* 5. Managing suspension of extra workers. When a worker notices
290	>	* (usually upon timeout of a wait()) that there are too few
291	>	* running threads, we may create a new thread to maintain
292	>	* parallelism level, or at least avoid starvation. Usually, extra
293	>	* threads are needed for only very short periods, yet join
294	>	* dependencies are such that we sometimes need them in
295	>	* bursts. Rather than create new threads each time this happens,
296	>	* we suspend no-longer-needed extra ones as "spares". For most
297	>	* purposes, we don't distinguish "extra" spare threads from
298	>	* normal "core" threads: On each call to preStep (the only point
299	>	* at which we can do this) a worker checks to see if there are
300	>	* now too many running workers, and if so, suspends itself.
301	>	* Method helpMaintainParallelism looks for suspended threads to
302	>	* resume before considering creating a new replacement. The
303	>	* spares themselves are encoded on another variant of a Treiber
304	>	* Stack, headed at field "spareWaiters".  Note that the use of
305	>	* spares is intrinsically racy.  One thread may become a spare at
306	>	* about the same time as another is needlessly being created. We
307	>	* counteract this and related slop in part by requiring resumed
308	>	* spares to immediately recheck (in preStep) to see whether they
309	>	* should re-suspend.
310	>	*
311	>	* 6. Killing off unneeded workers. A timeout mechanism is used to
312	>	* shed unused workers: The oldest (first) event queue waiter uses
313	>	* a timed rather than hard wait. When this wait times out without
314	>	* a normal wakeup, it tries to shutdown any one (for convenience
315	>	* the newest) other spare or event waiter via
316	>	* tryShutdownUnusedWorker. This eventually reduces the number of
317	>	* worker threads to a minimum of one after a long enough period
318	>	* without use.
319	>	*
320	>	* 7. Deciding when to create new workers. The main dynamic
321	>	* control in this class is deciding when to create extra threads
322	>	* in method helpMaintainParallelism. We would like to keep
323	>	* exactly #parallelism threads running, which is an impossible
324	>	* task. We always need to create one when the number of running
325	>	* threads would become zero and all workers are busy. Beyond
326	>	* this, we must rely on heuristics that work well in the
327	>	* presence of transient phenomena such as GC stalls, dynamic
328	>	* compilation, and wake-up lags. These transients are extremely
329	>	* common -- we are normally trying to fully saturate the CPUs on
330	>	* a machine, so almost any activity other than running tasks
331	>	* impedes accuracy. Our main defense is to allow parallelism to
332	>	* lapse for a while during joins, and use a timeout to see if,
333	>	* after the resulting settling, there is still a need for
334	>	* additional workers.  This also better copes with the fact that
335	>	* some of the methods in this class tend to never become compiled
336	>	* (but are interpreted), so some components of the entire set of
337	>	* controls might execute 100 times faster than others. And
338	>	* similarly for cases where the apparent lack of work is just due
339	>	* to GC stalls and other transient system activity.
340	>	*
341	>	* Beware that there is a lot of representation-level coupling
342	>	* among classes ForkJoinPool, ForkJoinWorkerThread, and
343	>	* ForkJoinTask.  For example, direct access to "workers" array by
344	>	* workers, and direct access to ForkJoinTask.status by both
345	>	* ForkJoinPool and ForkJoinWorkerThread.  There is little point
346	>	* trying to reduce this, since any associated future changes in
347	>	* representations will need to be accompanied by algorithmic
348	>	* changes anyway.
349	>	*
350	>	* Style notes: There are lots of inline assignments (of form
351	>	* "while ((local = field) != 0)") which are usually the simplest
352	>	* way to ensure the required read orderings (which are sometimes
353	>	* critical). Also several occurrences of the unusual "do {}
354	>	* while (!cas...)" which is the simplest way to force an update of
355	>	* a CAS'ed variable. There are also other coding oddities that
356	>	* help some methods perform reasonably even when interpreted (not
357	>	* compiled), at the expense of some messy constructions that
358	>	* reduce byte code counts.
359	>	*
360	>	* The order of declarations in this file is: (1) statics (2)
361	>	* fields (along with constants used when unpacking some of them)
362	>	* (3) internal control methods (4) callbacks and other support
363	>	* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
364	>	* methods (plus a few little helpers).
365	>	*/
366	>
367	>	/**
368	>	* Factory for creating new {@link ForkJoinWorkerThread}s.
369	>	* A {@code ForkJoinWorkerThreadFactory} must be defined and used
370	>	* for {@code ForkJoinWorkerThread} subclasses that extend base
371	>	* functionality or initialize threads with different contexts.
372		*/
373		public static interface ForkJoinWorkerThreadFactory {
374		/**
375		* Returns a new worker thread operating in the given pool.
376		*
377		* @param pool the pool this thread works in
378	<	* @throws NullPointerException if pool is null
378	>	* @throws NullPointerException if the pool is null
379		*/
380		public ForkJoinWorkerThread newThread(ForkJoinPool pool);
381		}
#	Line 100 | Line 384 | public class ForkJoinPool extends Abstra
384		* Default ForkJoinWorkerThreadFactory implementation; creates a
385		* new ForkJoinWorkerThread.
386		*/
387	<	static class  DefaultForkJoinWorkerThreadFactory
387	>	static class DefaultForkJoinWorkerThreadFactory
388		implements ForkJoinWorkerThreadFactory {
389		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
390	<	try {
107	<	return new ForkJoinWorkerThread(pool);
108	<	} catch (OutOfMemoryError oom)  {
109	<	return null;
110	<	}
390	>	return new ForkJoinWorkerThread(pool);
391		}
392		}
393
#	Line 143 | Line 423 | public class ForkJoinPool extends Abstra
423		new AtomicInteger();
424
425		/**
426	<	* Array holding all worker threads in the pool. Initialized upon
427	<	* first use. Array size must be a power of two.  Updates and
428	<	* replacements are protected by workerLock, but it is always kept
429	<	* in a consistent enough state to be randomly accessed without
430	<	* locking by workers performing work-stealing.
426	>	* The time to block in a join (see awaitJoin) before checking if
427	>	* a new worker should be (re)started to maintain parallelism
428	>	* level. The value should be short enough to maintain global
429	>	* responsiveness and progress but long enough to avoid
430	>	* counterproductive firings during GC stalls or unrelated system
431	>	* activity, and to not bog down systems with continual re-firings
432	>	* on GCs or legitimately long waits.
433	>	*/
434	>	private static final long JOIN_TIMEOUT_MILLIS = 250L; // 4 per second
435	>
436	>	/**
437	>	* The wakeup interval (in nanoseconds) for the oldest worker
438	>	* waiting for an event to invoke tryShutdownUnusedWorker to
439	>	* shrink the number of workers.  The exact value does not matter
440	>	* too much. It must be short enough to release resources during
441	>	* sustained periods of idleness, but not so short that threads
442	>	* are continually re-created.
443	>	*/
444	>	private static final long SHRINK_RATE_NANOS =
445	>	30L * 1000L * 1000L * 1000L; // 2 per minute
446	>
447	>	/**
448	>	* Absolute bound for parallelism level. Twice this number plus
449	>	* one (i.e., 0xfff) must fit into a 16bit field to enable
450	>	* word-packing for some counts and indices.
451	>	*/
452	>	private static final int MAX_WORKERS   = 0x7fff;
453	>
454	>	/**
455	>	* Array holding all worker threads in the pool.  Array size must
456	>	* be a power of two.  Updates and replacements are protected by
457	>	* workerLock, but the array is always kept in a consistent enough
458	>	* state to be randomly accessed without locking by workers
459	>	* performing work-stealing, as well as other traversal-based
460	>	* methods in this class. All readers must tolerate that some
461	>	* array slots may be null.
462		*/
463		volatile ForkJoinWorkerThread[] workers;
464
465		/**
466	<	* Lock protecting access to workers.
466	>	* Queue for external submissions.
467		*/
468	<	private final ReentrantLock workerLock;
468	>	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
469
470		/**
471	<	* Condition for awaitTermination.
471	>	* Lock protecting updates to workers array.
472		*/
473	<	private final Condition termination;
473	>	private final ReentrantLock workerLock;
474
475		/**
476	<	* The uncaught exception handler used when any worker
166	<	* abruptly terminates
476	>	* Latch released upon termination.
477		*/
478	<	private Thread.UncaughtExceptionHandler ueh;
478	>	private final Phaser termination;
479
480		/**
481		* Creation factory for worker threads.
#	Line 173 | Line 483 | public class ForkJoinPool extends Abstra
483		private final ForkJoinWorkerThreadFactory factory;
484
485		/**
176	–	* Head of stack of threads that were created to maintain
177	–	* parallelism when other threads blocked, but have since
178	–	* suspended when the parallelism level rose.
179	–	*/
180	–	private volatile WaitQueueNode spareStack;
181	–
182	–	/**
486		* Sum of per-thread steal counts, updated only when threads are
487		* idle or terminating.
488		*/
489	<	private final AtomicLong stealCount;
489	>	private volatile long stealCount;
490
491		/**
492	<	* Queue for external submissions.
492	>	* Encoded record of top of Treiber stack of threads waiting for
493	>	* events. The top 32 bits contain the count being waited for. The
494	>	* bottom 16 bits contains one plus the pool index of waiting
495	>	* worker thread. (Bits 16-31 are unused.)
496		*/
497	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
497	>	private volatile long eventWaiters;
498	>
499	>	private static final int EVENT_COUNT_SHIFT = 32;
500	>	private static final int WAITER_ID_MASK    = (1 << 16) - 1;
501
502		/**
503	<	* Head of Treiber stack for barrier sync. See below for explanation.
503	>	* A counter for events that may wake up worker threads:
504	>	*   - Submission of a new task to the pool
505	>	*   - A worker pushing a task on an empty queue
506	>	*   - termination
507		*/
508	<	private volatile WaitQueueNode syncStack;
508	>	private volatile int eventCount;
509
510		/**
511	<	* The count for event barrier
511	>	* Encoded record of top of Treiber stack of spare threads waiting
512	>	* for resumption. The top 16 bits contain an arbitrary count to
513	>	* avoid ABA effects. The bottom 16bits contains one plus the pool
514	>	* index of waiting worker thread.
515		*/
516	<	private volatile long eventCount;
516	>	private volatile int spareWaiters;
517	>
518	>	private static final int SPARE_COUNT_SHIFT = 16;
519	>	private static final int SPARE_ID_MASK     = (1 << 16) - 1;
520
521		/**
522	<	* Pool number, just for assigning useful names to worker threads
522	>	* Lifecycle control. The low word contains the number of workers
523	>	* that are (probably) executing tasks. This value is atomically
524	>	* incremented before a worker gets a task to run, and decremented
525	>	* when a worker has no tasks and cannot find any.  Bits 16-18
526	>	* contain runLevel value. When all are zero, the pool is
527	>	* running. Level transitions are monotonic (running -> shutdown
528	>	* -> terminating -> terminated) so each transition adds a bit.
529	>	* These are bundled together to ensure consistent read for
530	>	* termination checks (i.e., that runLevel is at least SHUTDOWN
531	>	* and active threads is zero).
532	>	*
533	>	* Notes: Most direct CASes are dependent on these bitfield
534	>	* positions.  Also, this field is non-private to enable direct
535	>	* performance-sensitive CASes in ForkJoinWorkerThread.
536		*/
537	<	private final int poolNumber;
537	>	volatile int runState;
538	>
539	>	// Note: The order among run level values matters.
540	>	private static final int RUNLEVEL_SHIFT     = 16;
541	>	private static final int SHUTDOWN           = 1 << RUNLEVEL_SHIFT;
542	>	private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
543	>	private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
544	>	private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
545
546		/**
547	<	* The maximum allowed pool size
547	>	* Holds number of total (i.e., created and not yet terminated)
548	>	* and running (i.e., not blocked on joins or other managed sync)
549	>	* threads, packed together to ensure consistent snapshot when
550	>	* making decisions about creating and suspending spare
551	>	* threads. Updated only by CAS. Note that adding a new worker
552	>	* requires incrementing both counts, since workers start off in
553	>	* running state.
554		*/
555	<	private volatile int maxPoolSize;
555	>	private volatile int workerCounts;
556	>
557	>	private static final int TOTAL_COUNT_SHIFT  = 16;
558	>	private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1;
559	>	private static final int ONE_RUNNING        = 1;
560	>	private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
561
562		/**
563	<	* The desired parallelism level, updated only under workerLock.
563	>	* The target parallelism level.
564	>	* Accessed directly by ForkJoinWorkerThreads.
565		*/
566	<	private volatile int parallelism;
566	>	final int parallelism;
567
568		/**
569		* True if use local fifo, not default lifo, for local polling
570	+	* Read by, and replicated by ForkJoinWorkerThreads
571		*/
572	<	private volatile boolean locallyFifo;
572	>	final boolean locallyFifo;
573
574		/**
575	<	* Holds number of total (i.e., created and not yet terminated)
576	<	* 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.
575	>	* The uncaught exception handler used when any worker abruptly
576	>	* terminates.
577		*/
578	<	private volatile int workerCounts;
233	<
234	<	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; }
578	>	private final Thread.UncaughtExceptionHandler ueh;
579
580		/**
581	<	* 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).
242	<	*
243	<	* @param delta the number to add
581	>	* Pool number, just for assigning useful names to worker threads
582		*/
583	<	final void updateRunningCount(int delta) {
584	<	int s;
585	<	do {} while (!casWorkerCounts(s = workerCounts, s + delta));
586	<	}
583	>	private final int poolNumber;
584	>
585	>	// Utilities for CASing fields. Note that most of these
586	>	// are usually manually inlined by callers
587
588		/**
589	<	* Adds delta (which may be negative) to both total and running
252	<	* count.  This must be called upon creation and termination of
253	<	* worker threads.
254	<	*
255	<	* @param delta the number to add
589	>	* Increments running count part of workerCounts.
590		*/
591	<	private void updateWorkerCount(int delta) {
592	<	int d = delta + (delta << 16); // add to both lo and hi parts
593	<	int s;
594	<	do {} while (!casWorkerCounts(s = workerCounts, s + d));
591	>	final void incrementRunningCount() {
592	>	int c;
593	>	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
594	>	c = workerCounts,
595	>	c + ONE_RUNNING));
596		}
597
598		/**
599	<	* Lifecycle control. High word contains runState, low word
265	<	* contains the number of workers that are (probably) executing
266	<	* tasks. This value is atomically incremented before a worker
267	<	* gets a task to run, and decremented when worker has no tasks
268	<	* and cannot find any. These two fields are bundled together to
269	<	* 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
599	>	* Tries to increment running count part of workerCounts.
600		*/
601	<	private volatile int runControl;
602	<
603	<	// RunState values. Order among values matters
604	<	private static final int RUNNING     = 0;
605	<	private static final int SHUTDOWN    = 1;
606	<	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; }
601	>	final boolean tryIncrementRunningCount() {
602	>	int c;
603	>	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
604	>	c = workerCounts,
605	>	c + ONE_RUNNING);
606	>	}
607
608		/**
609	<	* Tries incrementing active count; fails on contention.
287	<	* Called by workers before/during executing tasks.
288	<	*
289	<	* @return true on success
609	>	* Tries to decrement running count unless already zero.
610		*/
611	<	final boolean tryIncrementActiveCount() {
612	<	int c = runControl;
613	<	return casRunControl(c, c+1);
611	>	final boolean tryDecrementRunningCount() {
612	>	int wc = workerCounts;
613	>	if ((wc & RUNNING_COUNT_MASK) == 0)
614	>	return false;
615	>	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
616	>	wc, wc - ONE_RUNNING);
617		}
618
619		/**
620	<	* Tries decrementing active count; fails on contention.
621	<	* Possibly triggers termination on success.
299	<	* Called by workers when they can't find tasks.
620	>	* Forces decrement of encoded workerCounts, awaiting nonzero if
621	>	* (rarely) necessary when other count updates lag.
622		*
623	<	* @return true on success
623	>	* @param dr -- either zero or ONE_RUNNING
624	>	* @param dt -- either zero or ONE_TOTAL
625		*/
626	<	final boolean tryDecrementActiveCount() {
627	<	int c = runControl;
628	<	int nextc = c - 1;
629	<	if (!casRunControl(c, nextc))
630	<	return false;
631	<	if (canTerminateOnShutdown(nextc))
632	<	terminateOnShutdown();
633	<	return true;
626	>	private void decrementWorkerCounts(int dr, int dt) {
627	>	for (;;) {
628	>	int wc = workerCounts;
629	>	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
630	>	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) {
631	>	if ((runState & TERMINATED) != 0)
632	>	return; // lagging termination on a backout
633	>	Thread.yield();
634	>	}
635	>	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
636	>	wc, wc - (dr + dt)))
637	>	return;
638	>	}
639		}
640
641		/**
642	<	* Returns {@code true} if argument represents zero active count
643	<	* and nonzero runstate, which is the triggering condition for
316	<	* terminating on shutdown.
642	>	* Tries decrementing active count; fails on contention.
643	>	* Called when workers cannot find tasks to run.
644		*/
645	<	private static boolean canTerminateOnShutdown(int c) {
646	<	// i.e. least bit is nonzero runState bit
647	<	return ((c & -c) >>> 16) != 0;
645	>	final boolean tryDecrementActiveCount() {
646	>	int c;
647	>	return UNSAFE.compareAndSwapInt(this, runStateOffset,
648	>	c = runState, c - 1);
649		}
650
651		/**
652	<	* Transition run state to at least the given state. Return true
653	<	* if not already at least given state.
652	>	* Advances to at least the given level. Returns true if not
653	>	* already in at least the given level.
654		*/
655	<	private boolean transitionRunStateTo(int state) {
655	>	private boolean advanceRunLevel(int level) {
656		for (;;) {
657	<	int c = runControl;
658	<	if (runStateOf(c) >= state)
657	>	int s = runState;
658	>	if ((s & level) != 0)
659		return false;
660	<	if (casRunControl(c, runControlFor(state, activeCountOf(c))))
660	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level))
661		return true;
662		}
663		}
664
665	+	// workers array maintenance
666	+
667		/**
668	<	* Controls whether to add spares to maintain parallelism
668	>	* Records and returns a workers array index for new worker.
669		*/
670	<	private volatile boolean maintainsParallelism;
670	>	private int recordWorker(ForkJoinWorkerThread w) {
671	>	// Try using slot totalCount-1. If not available, scan and/or resize
672	>	int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1;
673	>	final ReentrantLock lock = this.workerLock;
674	>	lock.lock();
675	>	try {
676	>	ForkJoinWorkerThread[] ws = workers;
677	>	int n = ws.length;
678	>	if (k < 0 || k >= n || ws[k] != null) {
679	>	for (k = 0; k < n && ws[k] != null; ++k)
680	>	;
681	>	if (k == n)
682	>	ws = workers = Arrays.copyOf(ws, n << 1);
683	>	}
684	>	ws[k] = w;
685	>	int c = eventCount; // advance event count to ensure visibility
686	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c, c+1);
687	>	} finally {
688	>	lock.unlock();
689	>	}
690	>	return k;
691	>	}
692
693	<	// Constructors
693	>	/**
694	>	* Nulls out record of worker in workers array.
695	>	*/
696	>	private void forgetWorker(ForkJoinWorkerThread w) {
697	>	int idx = w.poolIndex;
698	>	// Locking helps method recordWorker avoid unnecessary expansion
699	>	final ReentrantLock lock = this.workerLock;
700	>	lock.lock();
701	>	try {
702	>	ForkJoinWorkerThread[] ws = workers;
703	>	if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify
704	>	ws[idx] = null;
705	>	} finally {
706	>	lock.unlock();
707	>	}
708	>	}
709
710		/**
711	<	* Creates a ForkJoinPool with a pool size equal to the number of
712	<	* processors available on the system, using the default
713	<	* ForkJoinWorkerThreadFactory.
711	>	* Final callback from terminating worker.  Removes record of
712	>	* worker from array, and adjusts counts. If pool is shutting
713	>	* down, tries to complete termination.
714		*
715	<	* @throws SecurityException if a security manager exists and
350	<	*         the caller is not permitted to modify threads
351	<	*         because it does not hold {@link
352	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
715	>	* @param w the worker
716		*/
717	<	public ForkJoinPool() {
718	<	this(Runtime.getRuntime().availableProcessors(),
719	<	defaultForkJoinWorkerThreadFactory);
717	>	final void workerTerminated(ForkJoinWorkerThread w) {
718	>	forgetWorker(w);
719	>	decrementWorkerCounts(w.isTrimmed() ? 0 : ONE_RUNNING, ONE_TOTAL);
720	>	while (w.stealCount != 0) // collect final count
721	>	tryAccumulateStealCount(w);
722	>	tryTerminate(false);
723		}
724
725	+	// Waiting for and signalling events
726	+
727		/**
728	<	* Creates a ForkJoinPool with the indicated parallelism level
729	<	* threads and using the default ForkJoinWorkerThreadFactory.
730	<	*
731	<	* @param parallelism the number of worker threads
364	<	* @throws IllegalArgumentException if parallelism less than or
365	<	* equal to zero
366	<	* @throws SecurityException if a security manager exists and
367	<	*         the caller is not permitted to modify threads
368	<	*         because it does not hold {@link
369	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
728	>	* Releases workers blocked on a count not equal to current count.
729	>	* Normally called after precheck that eventWaiters isn't zero to
730	>	* avoid wasted array checks. Gives up upon a change in count or
731	>	* upon releasing two workers, letting others take over.
732		*/
733	<	public ForkJoinPool(int parallelism) {
734	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
733	>	private void releaseEventWaiters() {
734	>	ForkJoinWorkerThread[] ws = workers;
735	>	int n = ws.length;
736	>	long h = eventWaiters;
737	>	int ec = eventCount;
738	>	boolean releasedOne = false;
739	>	ForkJoinWorkerThread w; int id;
740	>	while ((id = (((int)h) & WAITER_ID_MASK) - 1) >= 0 &&
741	>	(int)(h >>> EVENT_COUNT_SHIFT) != ec &&
742	>	id < n && (w = ws[id]) != null) {
743	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
744	>	h,  w.nextWaiter)) {
745	>	LockSupport.unpark(w);
746	>	if (releasedOne) // exit on second release
747	>	break;
748	>	releasedOne = true;
749	>	}
750	>	if (eventCount != ec)
751	>	break;
752	>	h = eventWaiters;
753	>	}
754		}
755
756		/**
757	<	* Creates a ForkJoinPool with parallelism equal to the number of
758	<	* processors available on the system and using the given
378	<	* ForkJoinWorkerThreadFactory.
379	<	*
380	<	* @param factory the factory for creating new threads
381	<	* @throws NullPointerException if factory is null
382	<	* @throws SecurityException if a security manager exists and
383	<	*         the caller is not permitted to modify threads
384	<	*         because it does not hold {@link
385	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
757	>	* Tries to advance eventCount and releases waiters. Called only
758	>	* from workers.
759		*/
760	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
761	<	this(Runtime.getRuntime().availableProcessors(), factory);
760	>	final void signalWork() {
761	>	int c; // try to increment event count -- CAS failure OK
762	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
763	>	if (eventWaiters != 0L)
764	>	releaseEventWaiters();
765		}
766
767		/**
768	<	* Creates a ForkJoinPool with the given parallelism and factory.
768	>	* Adds the given worker to event queue and blocks until
769	>	* terminating or event count advances from the given value
770		*
771	<	* @param parallelism the targeted number of worker threads
772	<	* @param factory the factory for creating new threads
396	<	* @throws IllegalArgumentException if parallelism less than or
397	<	* equal to zero, or greater than implementation limit
398	<	* @throws NullPointerException if factory is null
399	<	* @throws SecurityException if a security manager exists and
400	<	*         the caller is not permitted to modify threads
401	<	*         because it does not hold {@link
402	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
771	>	* @param w the calling worker thread
772	>	* @param ec the count
773		*/
774	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
775	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
776	<	throw new IllegalArgumentException();
777	<	if (factory == null)
778	<	throw new NullPointerException();
779	<	checkPermission();
780	<	this.factory = factory;
781	<	this.parallelism = parallelism;
782	<	this.maxPoolSize = MAX_THREADS;
783	<	this.maintainsParallelism = true;
784	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
785	<	this.workerLock = new ReentrantLock();
786	<	this.termination = workerLock.newCondition();
417	<	this.stealCount = new AtomicLong();
418	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
419	<	// worker array and workers are lazily constructed
774	>	private void eventSync(ForkJoinWorkerThread w, int ec) {
775	>	long nh = (((long)ec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
776	>	long h;
777	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
778	>	(((int)(h = eventWaiters) & WAITER_ID_MASK) == 0 ||
779	>	(int)(h >>> EVENT_COUNT_SHIFT) == ec) &&
780	>	eventCount == ec) {
781	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
782	>	w.nextWaiter = h, nh)) {
783	>	awaitEvent(w, ec);
784	>	break;
785	>	}
786	>	}
787		}
788
789		/**
790	<	* Creates a new worker thread using factory.
790	>	* Blocks the given worker (that has already been entered as an
791	>	* event waiter) until terminating or event count advances from
792	>	* the given value. The oldest (first) waiter uses a timed wait to
793	>	* occasionally one-by-one shrink the number of workers (to a
794	>	* minimum of one) if the pool has not been used for extended
795	>	* periods.
796		*
797	<	* @param index the index to assign worker
798	<	* @return new worker, or null of factory failed
797	>	* @param w the calling worker thread
798	>	* @param ec the count
799		*/
800	<	private ForkJoinWorkerThread createWorker(int index) {
801	<	Thread.UncaughtExceptionHandler h = ueh;
802	<	ForkJoinWorkerThread w = factory.newThread(this);
803	<	if (w != null) {
804	<	w.poolIndex = index;
805	<	w.setDaemon(true);
806	<	w.setAsyncMode(locallyFifo);
807	<	w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
808	<	if (h != null)
809	<	w.setUncaughtExceptionHandler(h);
800	>	private void awaitEvent(ForkJoinWorkerThread w, int ec) {
801	>	while (eventCount == ec) {
802	>	if (tryAccumulateStealCount(w)) { // transfer while idle
803	>	boolean untimed = (w.nextWaiter != 0L ||
804	>	(workerCounts & RUNNING_COUNT_MASK) <= 1);
805	>	long startTime = untimed ? 0 : System.nanoTime();
806	>	Thread.interrupted();         // clear/ignore interrupt
807	>	if (w.isTerminating() || eventCount != ec)
808	>	break;                    // recheck after clear
809	>	if (untimed)
810	>	LockSupport.park(w);
811	>	else {
812	>	LockSupport.parkNanos(w, SHRINK_RATE_NANOS);
813	>	if (eventCount != ec || w.isTerminating())
814	>	break;
815	>	if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS)
816	>	tryShutdownUnusedWorker(ec);
817	>	}
818	>	}
819		}
439	–	return w;
820		}
821
822	+	// Maintaining parallelism
823	+
824		/**
825	<	* Returns a good size for worker array given pool size.
444	<	* Currently requires size to be a power of two.
825	>	* Pushes worker onto the spare stack.
826		*/
827	<	private static int arraySizeFor(int poolSize) {
828	<	return (poolSize <= 1) ? 1 :
829	<	(1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
827	>	final void pushSpare(ForkJoinWorkerThread w) {
828	>	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1);
829	>	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
830	>	w.nextSpare = spareWaiters,ns));
831		}
832
833		/**
834	<	* Creates or resizes array if necessary to hold newLength.
835	<	* Call only under exclusion.
454	<	*
455	<	* @return the array
834	>	* Tries (once) to resume a spare if the number of running
835	>	* threads is less than target.
836		*/
837	<	private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
837	>	private void tryResumeSpare() {
838	>	int sw, id;
839		ForkJoinWorkerThread[] ws = workers;
840	<	if (ws == null)
841	<	return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
842	<	else if (newLength > ws.length)
843	<	return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
844	<	else
845	<	return ws;
840	>	int n = ws.length;
841	>	ForkJoinWorkerThread w;
842	>	if ((sw = spareWaiters) != 0 &&
843	>	(id = (sw & SPARE_ID_MASK) - 1) >= 0 &&
844	>	id < n && (w = ws[id]) != null &&
845	>	(runState >= TERMINATING ||
846	>	(workerCounts & RUNNING_COUNT_MASK) < parallelism) &&
847	>	spareWaiters == sw &&
848	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
849	>	sw, w.nextSpare)) {
850	>	int c; // increment running count before resume
851	>	do {} while (!UNSAFE.compareAndSwapInt
852	>	(this, workerCountsOffset,
853	>	c = workerCounts, c + ONE_RUNNING));
854	>	if (w.tryUnsuspend())
855	>	LockSupport.unpark(w);
856	>	else   // back out if w was shutdown
857	>	decrementWorkerCounts(ONE_RUNNING, 0);
858	>	}
859	>	}
860	>
861	>	/**
862	>	* Tries to increase the number of running workers if below target
863	>	* parallelism: If a spare exists tries to resume it via
864	>	* tryResumeSpare.  Otherwise, if not enough total workers or all
865	>	* existing workers are busy, adds a new worker. In all cases also
866	>	* helps wake up releasable workers waiting for work.
867	>	*/
868	>	private void helpMaintainParallelism() {
869	>	int pc = parallelism;
870	>	int wc, rs, tc;
871	>	while (((wc = workerCounts) & RUNNING_COUNT_MASK) < pc &&
872	>	(rs = runState) < TERMINATING) {
873	>	if (spareWaiters != 0)
874	>	tryResumeSpare();
875	>	else if ((tc = wc >>> TOTAL_COUNT_SHIFT) >= MAX_WORKERS ||
876	>	(tc >= pc && (rs & ACTIVE_COUNT_MASK) != tc))
877	>	break;   // enough total
878	>	else if (runState == rs && workerCounts == wc &&
879	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
880	>	wc + (ONE_RUNNING|ONE_TOTAL))) {
881	>	ForkJoinWorkerThread w = null;
882	>	Throwable fail = null;
883	>	try {
884	>	w = factory.newThread(this);
885	>	} catch (Throwable ex) {
886	>	fail = ex;
887	>	}
888	>	if (w == null) { // null or exceptional factory return
889	>	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
890	>	tryTerminate(false); // handle failure during shutdown
891	>	// If originating from an external caller,
892	>	// propagate exception, else ignore
893	>	if (fail != null && runState < TERMINATING &&
894	>	!(Thread.currentThread() instanceof
895	>	ForkJoinWorkerThread))
896	>	UNSAFE.throwException(fail);
897	>	break;
898	>	}
899	>	w.start(recordWorker(w), ueh);
900	>	if ((workerCounts >>> TOTAL_COUNT_SHIFT) >= pc)
901	>	break; // add at most one unless total below target
902	>	}
903	>	}
904	>	if (eventWaiters != 0L)
905	>	releaseEventWaiters();
906		}
907
908		/**
909	<	* Tries to shrink workers into smaller array after one or more terminate.
909	>	* Callback from the oldest waiter in awaitEvent waking up after a
910	>	* period of non-use. If all workers are idle, tries (once) to
911	>	* shutdown an event waiter or a spare, if one exists. Note that
912	>	* we don't need CAS or locks here because the method is called
913	>	* only from one thread occasionally waking (and even misfires are
914	>	* OK). Note that until the shutdown worker fully terminates,
915	>	* workerCounts will overestimate total count, which is tolerable.
916	>	*
917	>	* @param ec the event count waited on by caller (to abort
918	>	* attempt if count has since changed).
919		*/
920	<	private void tryShrinkWorkerArray() {
921	<	ForkJoinWorkerThread[] ws = workers;
922	<	if (ws != null) {
923	<	int len = ws.length;
924	<	int last = len - 1;
925	<	while (last >= 0 && ws[last] == null)
926	<	--last;
927	<	int newLength = arraySizeFor(last+1);
928	<	if (newLength < len)
929	<	workers = Arrays.copyOf(ws, newLength);
920	>	private void tryShutdownUnusedWorker(int ec) {
921	>	if (runState == 0 && eventCount == ec) { // only trigger if all idle
922	>	ForkJoinWorkerThread[] ws = workers;
923	>	int n = ws.length;
924	>	ForkJoinWorkerThread w = null;
925	>	boolean shutdown = false;
926	>	int sw;
927	>	long h;
928	>	if ((sw = spareWaiters) != 0) { // prefer killing spares
929	>	int id = (sw & SPARE_ID_MASK) - 1;
930	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
931	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
932	>	sw, w.nextSpare))
933	>	shutdown = true;
934	>	}
935	>	else if ((h = eventWaiters) != 0L) {
936	>	long nh;
937	>	int id = (((int)h) & WAITER_ID_MASK) - 1;
938	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
939	>	(nh = w.nextWaiter) != 0L && // keep at least one worker
940	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh))
941	>	shutdown = true;
942	>	}
943	>	if (w != null && shutdown) {
944	>	w.shutdown();
945	>	LockSupport.unpark(w);
946	>	}
947	>	}
948	>	releaseEventWaiters(); // in case of interference
949	>	}
950	>
951	>	/**
952	>	* Callback from workers invoked upon each top-level action (i.e.,
953	>	* stealing a task or taking a submission and running it).
954	>	* Performs one or more of the following:
955	>	*
956	>	* 1. If the worker is active and either did not run a task
957	>	*    or there are too many workers, try to set its active status
958	>	*    to inactive and update activeCount. On contention, we may
959	>	*    try again in this or a subsequent call.
960	>	*
961	>	* 2. If not enough total workers, help create some.
962	>	*
963	>	* 3. If there are too many running workers, suspend this worker
964	>	*    (first forcing inactive if necessary).  If it is not needed,
965	>	*    it may be shutdown while suspended (via
966	>	*    tryShutdownUnusedWorker).  Otherwise, upon resume it
967	>	*    rechecks running thread count and need for event sync.
968	>	*
969	>	* 4. If worker did not run a task, await the next task event via
970	>	*    eventSync if necessary (first forcing inactivation), upon
971	>	*    which the worker may be shutdown via
972	>	*    tryShutdownUnusedWorker.  Otherwise, help release any
973	>	*    existing event waiters that are now releasable,
974	>	*
975	>	* @param w the worker
976	>	* @param ran true if worker ran a task since last call to this method
977	>	*/
978	>	final void preStep(ForkJoinWorkerThread w, boolean ran) {
979	>	int wec = w.lastEventCount;
980	>	boolean active = w.active;
981	>	boolean inactivate = false;
982	>	int pc = parallelism;
983	>	while (w.runState == 0) {
984	>	int rs = runState;
985	>	if (rs >= TERMINATING) {           // propagate shutdown
986	>	w.shutdown();
987	>	break;
988	>	}
989	>	if ((inactivate || (active && (rs & ACTIVE_COUNT_MASK) >= pc)) &&
990	>	UNSAFE.compareAndSwapInt(this, runStateOffset, rs, --rs)) {
991	>	inactivate = active = w.active = false;
992	>	if (rs == SHUTDOWN) {          // all inactive and shut down
993	>	tryTerminate(false);
994	>	continue;
995	>	}
996	>	}
997	>	int wc = workerCounts;             // try to suspend as spare
998	>	if ((wc & RUNNING_COUNT_MASK) > pc) {
999	>	if (!(inactivate |= active) && // must inactivate to suspend
1000	>	workerCounts == wc &&
1001	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1002	>	wc, wc - ONE_RUNNING))
1003	>	w.suspendAsSpare();
1004	>	}
1005	>	else if ((wc >>> TOTAL_COUNT_SHIFT) < pc)
1006	>	helpMaintainParallelism();     // not enough workers
1007	>	else if (ran)
1008	>	break;
1009	>	else {
1010	>	long h = eventWaiters;
1011	>	int ec = eventCount;
1012	>	if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != ec)
1013	>	releaseEventWaiters();     // release others before waiting
1014	>	else if (ec != wec) {
1015	>	w.lastEventCount = ec;     // no need to wait
1016	>	break;
1017	>	}
1018	>	else if (!(inactivate |= active))
1019	>	eventSync(w, wec);         // must inactivate before sync
1020	>	}
1021		}
1022		}
1023
1024		/**
1025	<	* Initializes workers if necessary.
1025	>	* Helps and/or blocks awaiting join of the given task.
1026	>	* See above for explanation.
1027	>	*
1028	>	* @param joinMe the task to join
1029	>	* @param worker the current worker thread
1030	>	* @param timed true if wait should time out
1031	>	* @param nanos timeout value if timed
1032		*/
1033	<	final void ensureWorkerInitialization() {
1034	<	ForkJoinWorkerThread[] ws = workers;
1035	<	if (ws == null) {
1036	<	final ReentrantLock lock = this.workerLock;
1037	<	lock.lock();
1038	<	try {
1039	<	ws = workers;
1040	<	if (ws == null) {
1041	<	int ps = parallelism;
1042	<	ws = ensureWorkerArrayCapacity(ps);
1043	<	for (int i = 0; i < ps; ++i) {
1044	<	ForkJoinWorkerThread w = createWorker(i);
1045	<	if (w != null) {
1046	<	ws[i] = w;
1047	<	w.start();
1048	<	updateWorkerCount(1);
1033	>	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker,
1034	>	boolean timed, long nanos) {
1035	>	long startTime = timed? System.nanoTime() : 0L;
1036	>	int retries = 2 + (parallelism >> 2); // #helpJoins before blocking
1037	>	boolean running = true;               // false when count decremented
1038	>	while (joinMe.status >= 0) {
1039	>	if (runState >= TERMINATING) {
1040	>	joinMe.cancelIgnoringExceptions();
1041	>	break;
1042	>	}
1043	>	running = worker.helpJoinTask(joinMe, running);
1044	>	if (joinMe.status < 0)
1045	>	break;
1046	>	if (retries > 0) {
1047	>	--retries;
1048	>	continue;
1049	>	}
1050	>	int wc = workerCounts;
1051	>	if ((wc & RUNNING_COUNT_MASK) != 0) {
1052	>	if (running) {
1053	>	if (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1054	>	wc, wc - ONE_RUNNING))
1055	>	continue;
1056	>	running = false;
1057	>	}
1058	>	long h = eventWaiters;
1059	>	if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1060	>	releaseEventWaiters();
1061	>	if ((workerCounts & RUNNING_COUNT_MASK) != 0) {
1062	>	long ms; int ns;
1063	>	if (!timed) {
1064	>	ms = JOIN_TIMEOUT_MILLIS;
1065	>	ns = 0;
1066	>	}
1067	>	else { // at most JOIN_TIMEOUT_MILLIS per wait
1068	>	long nt = nanos - (System.nanoTime() - startTime);
1069	>	if (nt <= 0L)
1070	>	break;
1071	>	ms = nt / 1000000;
1072	>	if (ms > JOIN_TIMEOUT_MILLIS) {
1073	>	ms = JOIN_TIMEOUT_MILLIS;
1074	>	ns = 0;
1075		}
1076	+	else
1077	+	ns = (int) (nt % 1000000);
1078		}
1079	+	joinMe.internalAwaitDone(ms, ns);
1080		}
1081	<	} finally {
1082	<	lock.unlock();
1081	>	if (joinMe.status < 0)
1082	>	break;
1083		}
1084	+	helpMaintainParallelism();
1085	+	}
1086	+	if (!running) {
1087	+	int c;
1088	+	do {} while (!UNSAFE.compareAndSwapInt
1089	+	(this, workerCountsOffset,
1090	+	c = workerCounts, c + ONE_RUNNING));
1091		}
1092		}
1093
1094		/**
1095	<	* Worker creation and startup for threads added via setParallelism.
1095	>	* Same idea as awaitJoin, but no helping, retries, or timeouts.
1096		*/
1097	<	private void createAndStartAddedWorkers() {
1098	<	resumeAllSpares();  // Allow spares to convert to nonspare
1099	<	int ps = parallelism;
1100	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
1101	<	int len = ws.length;
1102	<	// Sweep through slots, to keep lowest indices most populated
1103	<	int k = 0;
1104	<	while (k < len) {
1105	<	if (ws[k] != null) {
1106	<	++k;
1107	<	continue;
1108	<	}
1109	<	int s = workerCounts;
1110	<	int tc = totalCountOf(s);
1111	<	int rc = runningCountOf(s);
1112	<	if (rc >= ps || tc >= ps)
1097	>	final void awaitBlocker(ManagedBlocker blocker)
1098	>	throws InterruptedException {
1099	>	while (!blocker.isReleasable()) {
1100	>	int wc = workerCounts;
1101	>	if ((wc & RUNNING_COUNT_MASK) == 0)
1102	>	helpMaintainParallelism();
1103	>	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1104	>	wc, wc - ONE_RUNNING)) {
1105	>	try {
1106	>	while (!blocker.isReleasable()) {
1107	>	long h = eventWaiters;
1108	>	if (h != 0L &&
1109	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1110	>	releaseEventWaiters();
1111	>	else if ((workerCounts & RUNNING_COUNT_MASK) == 0 &&
1112	>	runState < TERMINATING)
1113	>	helpMaintainParallelism();
1114	>	else if (blocker.block())
1115	>	break;
1116	>	}
1117	>	} finally {
1118	>	int c;
1119	>	do {} while (!UNSAFE.compareAndSwapInt
1120	>	(this, workerCountsOffset,
1121	>	c = workerCounts, c + ONE_RUNNING));
1122	>	}
1123		break;
1124	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
1125	<	ForkJoinWorkerThread w = createWorker(k);
1124	>	}
1125	>	}
1126	>	}
1127	>
1128	>	/**
1129	>	* Possibly initiates and/or completes termination.
1130	>	*
1131	>	* @param now if true, unconditionally terminate, else only
1132	>	* if shutdown and empty queue and no active workers
1133	>	* @return true if now terminating or terminated
1134	>	*/
1135	>	private boolean tryTerminate(boolean now) {
1136	>	if (now)
1137	>	advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
1138	>	else if (runState < SHUTDOWN ||
1139	>	!submissionQueue.isEmpty() ||
1140	>	(runState & ACTIVE_COUNT_MASK) != 0)
1141	>	return false;
1142	>
1143	>	if (advanceRunLevel(TERMINATING))
1144	>	startTerminating();
1145	>
1146	>	// Finish now if all threads terminated; else in some subsequent call
1147	>	if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1148	>	advanceRunLevel(TERMINATED);
1149	>	termination.forceTermination();
1150	>	}
1151	>	return true;
1152	>	}
1153	>
1154	>	/**
1155	>	* Actions on transition to TERMINATING
1156	>	*
1157	>	* Runs up to four passes through workers: (0) shutting down each
1158	>	* (without waking up if parked) to quickly spread notifications
1159	>	* without unnecessary bouncing around event queues etc (1) wake
1160	>	* up and help cancel tasks (2) interrupt (3) mop up races with
1161	>	* interrupted workers
1162	>	*/
1163	>	private void startTerminating() {
1164	>	cancelSubmissions();
1165	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1166	>	int c; // advance event count
1167	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
1168	>	c = eventCount, c+1);
1169	>	eventWaiters = 0L; // clobber lists
1170	>	spareWaiters = 0;
1171	>	for (ForkJoinWorkerThread w : workers) {
1172		if (w != null) {
1173	<	ws[k++] = w;
1174	<	w.start();
1175	<	}
1176	<	else {
1177	<	updateWorkerCount(-1); // back out on failed creation
1178	<	break;
1173	>	w.shutdown();
1174	>	if (passes > 0 && !w.isTerminated()) {
1175	>	w.cancelTasks();
1176	>	LockSupport.unpark(w);
1177	>	if (passes > 1 && !w.isInterrupted()) {
1178	>	try {
1179	>	w.interrupt();
1180	>	} catch (SecurityException ignore) {
1181	>	}
1182	>	}
1183	>	}
1184		}
1185		}
1186		}
1187		}
1188
1189	+	/**
1190	+	* Clears out and cancels submissions, ignoring exceptions.
1191	+	*/
1192	+	private void cancelSubmissions() {
1193	+	ForkJoinTask<?> task;
1194	+	while ((task = submissionQueue.poll()) != null) {
1195	+	try {
1196	+	task.cancel(false);
1197	+	} catch (Throwable ignore) {
1198	+	}
1199	+	}
1200	+	}
1201	+
1202	+	// misc support for ForkJoinWorkerThread
1203	+
1204	+	/**
1205	+	* Returns pool number.
1206	+	*/
1207	+	final int getPoolNumber() {
1208	+	return poolNumber;
1209	+	}
1210	+
1211	+	/**
1212	+	* Tries to accumulate steal count from a worker, clearing
1213	+	* the worker's value if successful.
1214	+	*
1215	+	* @return true if worker steal count now zero
1216	+	*/
1217	+	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1218	+	int sc = w.stealCount;
1219	+	long c = stealCount;
1220	+	// CAS even if zero, for fence effects
1221	+	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1222	+	if (sc != 0)
1223	+	w.stealCount = 0;
1224	+	return true;
1225	+	}
1226	+	return sc == 0;
1227	+	}
1228	+
1229	+	/**
1230	+	* Returns the approximate (non-atomic) number of idle threads per
1231	+	* active thread.
1232	+	*/
1233	+	final int idlePerActive() {
1234	+	int pc = parallelism; // use parallelism, not rc
1235	+	int ac = runState;    // no mask -- artificially boosts during shutdown
1236	+	// Use exact results for small values, saturate past 4
1237	+	return ((pc <= ac) ? 0 :
1238	+	(pc >>> 1 <= ac) ? 1 :
1239	+	(pc >>> 2 <= ac) ? 3 :
1240	+	pc >>> 3);
1241	+	}
1242	+
1243	+	// Public and protected methods
1244	+
1245	+	// Constructors
1246	+
1247	+	/**
1248	+	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1249	+	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1250	+	* #defaultForkJoinWorkerThreadFactory default thread factory},
1251	+	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1252	+	*
1253	+	* @throws SecurityException if a security manager exists and
1254	+	*         the caller is not permitted to modify threads
1255	+	*         because it does not hold {@link
1256	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1257	+	*/
1258	+	public ForkJoinPool() {
1259	+	this(Runtime.getRuntime().availableProcessors(),
1260	+	defaultForkJoinWorkerThreadFactory, null, false);
1261	+	}
1262	+
1263	+	/**
1264	+	* Creates a {@code ForkJoinPool} with the indicated parallelism
1265	+	* level, the {@linkplain
1266	+	* #defaultForkJoinWorkerThreadFactory default thread factory},
1267	+	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1268	+	*
1269	+	* @param parallelism the parallelism level
1270	+	* @throws IllegalArgumentException if parallelism less than or
1271	+	*         equal to zero, or greater than implementation limit
1272	+	* @throws SecurityException if a security manager exists and
1273	+	*         the caller is not permitted to modify threads
1274	+	*         because it does not hold {@link
1275	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1276	+	*/
1277	+	public ForkJoinPool(int parallelism) {
1278	+	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1279	+	}
1280	+
1281	+	/**
1282	+	* Creates a {@code ForkJoinPool} with the given parameters.
1283	+	*
1284	+	* @param parallelism the parallelism level. For default value,
1285	+	* use {@link java.lang.Runtime#availableProcessors}.
1286	+	* @param factory the factory for creating new threads. For default value,
1287	+	* use {@link #defaultForkJoinWorkerThreadFactory}.
1288	+	* @param handler the handler for internal worker threads that
1289	+	* terminate due to unrecoverable errors encountered while executing
1290	+	* tasks. For default value, use {@code null}.
1291	+	* @param asyncMode if true,
1292	+	* establishes local first-in-first-out scheduling mode for forked
1293	+	* tasks that are never joined. This mode may be more appropriate
1294	+	* than default locally stack-based mode in applications in which
1295	+	* worker threads only process event-style asynchronous tasks.
1296	+	* For default value, use {@code false}.
1297	+	* @throws IllegalArgumentException if parallelism less than or
1298	+	*         equal to zero, or greater than implementation limit
1299	+	* @throws NullPointerException if the factory is null
1300	+	* @throws SecurityException if a security manager exists and
1301	+	*         the caller is not permitted to modify threads
1302	+	*         because it does not hold {@link
1303	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1304	+	*/
1305	+	public ForkJoinPool(int parallelism,
1306	+	ForkJoinWorkerThreadFactory factory,
1307	+	Thread.UncaughtExceptionHandler handler,
1308	+	boolean asyncMode) {
1309	+	checkPermission();
1310	+	if (factory == null)
1311	+	throw new NullPointerException();
1312	+	if (parallelism <= 0 || parallelism > MAX_WORKERS)
1313	+	throw new IllegalArgumentException();
1314	+	this.parallelism = parallelism;
1315	+	this.factory = factory;
1316	+	this.ueh = handler;
1317	+	this.locallyFifo = asyncMode;
1318	+	int arraySize = initialArraySizeFor(parallelism);
1319	+	this.workers = new ForkJoinWorkerThread[arraySize];
1320	+	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1321	+	this.workerLock = new ReentrantLock();
1322	+	this.termination = new Phaser(1);
1323	+	this.poolNumber = poolNumberGenerator.incrementAndGet();
1324	+	}
1325	+
1326	+	/**
1327	+	* Returns initial power of two size for workers array.
1328	+	* @param pc the initial parallelism level
1329	+	*/
1330	+	private static int initialArraySizeFor(int pc) {
1331	+	// If possible, initially allocate enough space for one spare
1332	+	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1333	+	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1334	+	size |= size >>> 1;
1335	+	size |= size >>> 2;
1336	+	size |= size >>> 4;
1337	+	size |= size >>> 8;
1338	+	return size + 1;
1339	+	}
1340	+
1341		// Execution methods
1342
1343		/**
1344	<	* Common code for execute, invoke and submit
1344	>	* Submits task and creates, starts, or resumes some workers if necessary
1345		*/
1346		private <T> void doSubmit(ForkJoinTask<T> task) {
551	–	if (task == null)
552	–	throw new NullPointerException();
553	–	if (isShutdown())
554	–	throw new RejectedExecutionException();
555	–	if (workers == null)
556	–	ensureWorkerInitialization();
1347		submissionQueue.offer(task);
1348	<	signalIdleWorkers();
1348	>	int c; // try to increment event count -- CAS failure OK
1349	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
1350	>	helpMaintainParallelism();
1351		}
1352
1353		/**
#	Line 563 | Line 1355 | public class ForkJoinPool extends Abstra
1355		*
1356		* @param task the task
1357		* @return the task's result
1358	<	* @throws NullPointerException if task is null
1359	<	* @throws RejectedExecutionException if pool is shut down
1358	>	* @throws NullPointerException if the task is null
1359	>	* @throws RejectedExecutionException if the task cannot be
1360	>	*         scheduled for execution
1361		*/
1362		public <T> T invoke(ForkJoinTask<T> task) {
1363	<	doSubmit(task);
1364	<	return task.join();
1363	>	if (task == null)
1364	>	throw new NullPointerException();
1365	>	if (runState >= SHUTDOWN)
1366	>	throw new RejectedExecutionException();
1367	>	Thread t = Thread.currentThread();
1368	>	if ((t instanceof ForkJoinWorkerThread) &&
1369	>	((ForkJoinWorkerThread)t).pool == this)
1370	>	return task.invoke();  // bypass submit if in same pool
1371	>	else {
1372	>	doSubmit(task);
1373	>	return task.join();
1374	>	}
1375	>	}
1376	>
1377	>	/**
1378	>	* Unless terminating, forks task if within an ongoing FJ
1379	>	* computation in the current pool, else submits as external task.
1380	>	*/
1381	>	private <T> void forkOrSubmit(ForkJoinTask<T> task) {
1382	>	if (runState >= SHUTDOWN)
1383	>	throw new RejectedExecutionException();
1384	>	Thread t = Thread.currentThread();
1385	>	if ((t instanceof ForkJoinWorkerThread) &&
1386	>	((ForkJoinWorkerThread)t).pool == this)
1387	>	task.fork();
1388	>	else
1389	>	doSubmit(task);
1390		}
1391
1392		/**
1393		* Arranges for (asynchronous) execution of the given task.
1394		*
1395		* @param task the task
1396	<	* @throws NullPointerException if task is null
1397	<	* @throws RejectedExecutionException if pool is shut down
1396	>	* @throws NullPointerException if the task is null
1397	>	* @throws RejectedExecutionException if the task cannot be
1398	>	*         scheduled for execution
1399		*/
1400	<	public <T> void execute(ForkJoinTask<T> task) {
1401	<	doSubmit(task);
1400	>	public void execute(ForkJoinTask<?> task) {
1401	>	if (task == null)
1402	>	throw new NullPointerException();
1403	>	forkOrSubmit(task);
1404		}
1405
1406		// AbstractExecutorService methods
1407
1408	+	/**
1409	+	* @throws NullPointerException if the task is null
1410	+	* @throws RejectedExecutionException if the task cannot be
1411	+	*         scheduled for execution
1412	+	*/
1413		public void execute(Runnable task) {
1414	+	if (task == null)
1415	+	throw new NullPointerException();
1416		ForkJoinTask<?> job;
1417		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1418		job = (ForkJoinTask<?>) task;
1419		else
1420	<	job = new AdaptedRunnable<Void>(task, null);
1421	<	doSubmit(job);
594	<	}
595	<
596	<	public <T> ForkJoinTask<T> submit(Callable<T> task) {
597	<	ForkJoinTask<T> job = new AdaptedCallable<T>(task);
598	<	doSubmit(job);
599	<	return job;
600	<	}
601	<
602	<	public <T> ForkJoinTask<T> submit(Runnable task, T result) {
603	<	ForkJoinTask<T> job = new AdaptedRunnable<T>(task, result);
604	<	doSubmit(job);
605	<	return job;
606	<	}
607	<
608	<	public ForkJoinTask<?> submit(Runnable task) {
609	<	ForkJoinTask<?> job;
610	<	if (task instanceof ForkJoinTask<?>) // avoid re-wrap
611	<	job = (ForkJoinTask<?>) task;
612	<	else
613	<	job = new AdaptedRunnable<Void>(task, null);
614	<	doSubmit(job);
615	<	return job;
1420	>	job = ForkJoinTask.adapt(task, null);
1421	>	forkOrSubmit(job);
1422		}
1423
1424		/**
#	Line 620 | Line 1426 | public class ForkJoinPool extends Abstra
1426		*
1427		* @param task the task to submit
1428		* @return the task
1429	+	* @throws NullPointerException if the task is null
1430		* @throws RejectedExecutionException if the task cannot be
1431		*         scheduled for execution
625	–	* @throws NullPointerException if the task is null
1432		*/
1433		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1434	<	doSubmit(task);
1434	>	if (task == null)
1435	>	throw new NullPointerException();
1436	>	forkOrSubmit(task);
1437		return task;
1438		}
1439
1440		/**
1441	<	* Adaptor for Runnables. This implements RunnableFuture
1442	<	* to be compliant with AbstractExecutorService constraints.
1441	>	* @throws NullPointerException if the task is null
1442	>	* @throws RejectedExecutionException if the task cannot be
1443	>	*         scheduled for execution
1444		*/
1445	<	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1446	<	implements RunnableFuture<T> {
1447	<	final Runnable runnable;
1448	<	final T resultOnCompletion;
1449	<	T result;
1450	<	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;
1445	>	public <T> ForkJoinTask<T> submit(Callable<T> task) {
1446	>	if (task == null)
1447	>	throw new NullPointerException();
1448	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1449	>	forkOrSubmit(job);
1450	>	return job;
1451		}
1452
1453		/**
1454	<	* Adaptor for Callables
1454	>	* @throws NullPointerException if the task is null
1455	>	* @throws RejectedExecutionException if the task cannot be
1456	>	*         scheduled for execution
1457		*/
1458	<	static final class AdaptedCallable<T> extends ForkJoinTask<T>
1459	<	implements RunnableFuture<T> {
1460	<	final Callable<T> callable;
1461	<	T result;
1462	<	AdaptedCallable(Callable<T> callable) {
1463	<	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;
1458	>	public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1459	>	if (task == null)
1460	>	throw new NullPointerException();
1461	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1462	>	forkOrSubmit(job);
1463	>	return job;
1464		}
1465
1466	+	/**
1467	+	* @throws NullPointerException if the task is null
1468	+	* @throws RejectedExecutionException if the task cannot be
1469	+	*         scheduled for execution
1470	+	*/
1471	+	public ForkJoinTask<?> submit(Runnable task) {
1472	+	if (task == null)
1473	+	throw new NullPointerException();
1474	+	ForkJoinTask<?> job;
1475	+	if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1476	+	job = (ForkJoinTask<?>) task;
1477	+	else
1478	+	job = ForkJoinTask.adapt(task, null);
1479	+	forkOrSubmit(job);
1480	+	return job;
1481	+	}
1482	+
1483	+	/**
1484	+	* @throws NullPointerException       {@inheritDoc}
1485	+	* @throws RejectedExecutionException {@inheritDoc}
1486	+	*/
1487		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
1488		ArrayList<ForkJoinTask<T>> forkJoinTasks =
1489		new ArrayList<ForkJoinTask<T>>(tasks.size());
1490		for (Callable<T> task : tasks)
1491	<	forkJoinTasks.add(new AdaptedCallable<T>(task));
1491	>	forkJoinTasks.add(ForkJoinTask.adapt(task));
1492		invoke(new InvokeAll<T>(forkJoinTasks));
1493
1494		@SuppressWarnings({"unchecked", "rawtypes"})
1495	<	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1495	>	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1496		return futures;
1497		}
1498
#	Line 705 | Line 1506 | public class ForkJoinPool extends Abstra
1506		private static final long serialVersionUID = -7914297376763021607L;
1507		}
1508
708	–	// Configuration and status settings and queries
709	–
1509		/**
1510		* Returns the factory used for constructing new workers.
1511		*
#	Line 723 | Line 1522 | public class ForkJoinPool extends Abstra
1522		* @return the handler, or {@code null} if none
1523		*/
1524		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1525	<	Thread.UncaughtExceptionHandler h;
727	<	final ReentrantLock lock = this.workerLock;
728	<	lock.lock();
729	<	try {
730	<	h = ueh;
731	<	} finally {
732	<	lock.unlock();
733	<	}
734	<	return h;
1525	>	return ueh;
1526		}
1527
1528		/**
1529	<	* Sets the handler for internal worker threads that terminate due
739	<	* to unrecoverable errors encountered while executing tasks.
740	<	* Unless set, the current default or ThreadGroup handler is used
741	<	* as handler.
1529	>	* Returns the targeted parallelism level of this pool.
1530		*
1531	<	* @param h the new handler
744	<	* @return the old handler, or {@code null} if none
745	<	* @throws SecurityException if a security manager exists and
746	<	*         the caller is not permitted to modify threads
747	<	*         because it does not hold {@link
748	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
749	<	*/
750	<	public Thread.UncaughtExceptionHandler
751	<	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
752	<	checkPermission();
753	<	Thread.UncaughtExceptionHandler old = null;
754	<	final ReentrantLock lock = this.workerLock;
755	<	lock.lock();
756	<	try {
757	<	old = ueh;
758	<	ueh = h;
759	<	ForkJoinWorkerThread[] ws = workers;
760	<	if (ws != null) {
761	<	for (int i = 0; i < ws.length; ++i) {
762	<	ForkJoinWorkerThread w = ws[i];
763	<	if (w != null)
764	<	w.setUncaughtExceptionHandler(h);
765	<	}
766	<	}
767	<	} finally {
768	<	lock.unlock();
769	<	}
770	<	return old;
771	<	}
772	<
773	<
774	<	/**
775	<	* Sets the target parallelism level of this pool.
776	<	*
777	<	* @param parallelism the target parallelism
778	<	* @throws IllegalArgumentException if parallelism less than or
779	<	* equal to zero or greater than maximum size bounds
780	<	* @throws SecurityException if a security manager exists and
781	<	*         the caller is not permitted to modify threads
782	<	*         because it does not hold {@link
783	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
784	<	*/
785	<	public void setParallelism(int parallelism) {
786	<	checkPermission();
787	<	if (parallelism <= 0 || parallelism > maxPoolSize)
788	<	throw new IllegalArgumentException();
789	<	final ReentrantLock lock = this.workerLock;
790	<	lock.lock();
791	<	try {
792	<	if (!isTerminating()) {
793	<	int p = this.parallelism;
794	<	this.parallelism = parallelism;
795	<	if (parallelism > p)
796	<	createAndStartAddedWorkers();
797	<	else
798	<	trimSpares();
799	<	}
800	<	} finally {
801	<	lock.unlock();
802	<	}
803	<	signalIdleWorkers();
804	<	}
805	<
806	<	/**
807	<	* Returns the targeted number of worker threads in this pool.
808	<	*
809	<	* @return the targeted number of worker threads in this pool
1531	>	* @return the targeted parallelism level of this pool
1532		*/
1533		public int getParallelism() {
1534		return parallelism;
#	Line 814 | Line 1536 | public class ForkJoinPool extends Abstra
1536
1537		/**
1538		* Returns the number of worker threads that have started but not
1539	<	* yet terminated.  This result returned by this method may differ
1539	>	* yet terminated.  The result returned by this method may differ
1540		* from {@link #getParallelism} when threads are created to
1541		* maintain parallelism when others are cooperatively blocked.
1542		*
1543		* @return the number of worker threads
1544		*/
1545		public int getPoolSize() {
1546	<	return totalCountOf(workerCounts);
825	<	}
826	<
827	<	/**
828	<	* Returns the maximum number of threads allowed to exist in the
829	<	* pool, even if there are insufficient unblocked running threads.
830	<	*
831	<	* @return the maximum
832	<	*/
833	<	public int getMaximumPoolSize() {
834	<	return maxPoolSize;
835	<	}
836	<
837	<	/**
838	<	* Sets the maximum number of threads allowed to exist in the
839	<	* pool, even if there are insufficient unblocked running threads.
840	<	* Setting this value has no effect on current pool size. It
841	<	* controls construction of new threads.
842	<	*
843	<	* @throws IllegalArgumentException if negative or greater then
844	<	* internal implementation limit
845	<	*/
846	<	public void setMaximumPoolSize(int newMax) {
847	<	if (newMax < 0 || newMax > MAX_THREADS)
848	<	throw new IllegalArgumentException();
849	<	maxPoolSize = newMax;
850	<	}
851	<
852	<
853	<	/**
854	<	* Returns {@code true} if this pool dynamically maintains its
855	<	* target parallelism level. If false, new threads are added only
856	<	* to avoid possible starvation.  This setting is by default true.
857	<	*
858	<	* @return {@code true} if maintains parallelism
859	<	*/
860	<	public boolean getMaintainsParallelism() {
861	<	return maintainsParallelism;
862	<	}
863	<
864	<	/**
865	<	* Sets whether this pool dynamically maintains its target
866	<	* parallelism level. If false, new threads are added only to
867	<	* avoid possible starvation.
868	<	*
869	<	* @param enable {@code true} to maintain parallelism
870	<	*/
871	<	public void setMaintainsParallelism(boolean enable) {
872	<	maintainsParallelism = enable;
873	<	}
874	<
875	<	/**
876	<	* Establishes local first-in-first-out scheduling mode for forked
877	<	* tasks that are never joined. This mode may be more appropriate
878	<	* than default locally stack-based mode in applications in which
879	<	* worker threads only process asynchronous tasks.  This method is
880	<	* designed to be invoked only when the pool is quiescent, and
881	<	* typically only before any tasks are submitted. The effects of
882	<	* invocations at other times may be unpredictable.
883	<	*
884	<	* @param async if {@code true}, use locally FIFO scheduling
885	<	* @return the previous mode
886	<	* @see #getAsyncMode
887	<	*/
888	<	public boolean setAsyncMode(boolean async) {
889	<	boolean oldMode = locallyFifo;
890	<	locallyFifo = async;
891	<	ForkJoinWorkerThread[] ws = workers;
892	<	if (ws != null) {
893	<	for (int i = 0; i < ws.length; ++i) {
894	<	ForkJoinWorkerThread t = ws[i];
895	<	if (t != null)
896	<	t.setAsyncMode(async);
897	<	}
898	<	}
899	<	return oldMode;
1546	>	return workerCounts >>> TOTAL_COUNT_SHIFT;
1547		}
1548
1549		/**
#	Line 904 | Line 1551 | public class ForkJoinPool extends Abstra
1551		* scheduling mode for forked tasks that are never joined.
1552		*
1553		* @return {@code true} if this pool uses async mode
907	–	* @see #setAsyncMode
1554		*/
1555		public boolean getAsyncMode() {
1556		return locallyFifo;
#	Line 913 | Line 1559 | public class ForkJoinPool extends Abstra
1559		/**
1560		* Returns an estimate of the number of worker threads that are
1561		* not blocked waiting to join tasks or for other managed
1562	<	* synchronization.
1562	>	* synchronization. This method may overestimate the
1563	>	* number of running threads.
1564		*
1565		* @return the number of worker threads
1566		*/
1567		public int getRunningThreadCount() {
1568	<	return runningCountOf(workerCounts);
1568	>	return workerCounts & RUNNING_COUNT_MASK;
1569		}
1570
1571		/**
#	Line 929 | Line 1576 | public class ForkJoinPool extends Abstra
1576		* @return the number of active threads
1577		*/
1578		public int getActiveThreadCount() {
1579	<	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;
1579	>	return runState & ACTIVE_COUNT_MASK;
1580		}
1581
1582		/**
#	Line 956 | Line 1591 | public class ForkJoinPool extends Abstra
1591		* @return {@code true} if all threads are currently idle
1592		*/
1593		public boolean isQuiescent() {
1594	<	return activeCountOf(runControl) == 0;
1594	>	return (runState & ACTIVE_COUNT_MASK) == 0;
1595		}
1596
1597		/**
#	Line 971 | Line 1606 | public class ForkJoinPool extends Abstra
1606		* @return the number of steals
1607		*/
1608		public long getStealCount() {
1609	<	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);
1609	>	return stealCount;
1610		}
1611
1612		/**
#	Line 996 | Line 1621 | public class ForkJoinPool extends Abstra
1621		*/
1622		public long getQueuedTaskCount() {
1623		long count = 0;
1624	<	ForkJoinWorkerThread[] ws = workers;
1625	<	if (ws != null) {
1626	<	for (int i = 0; i < ws.length; ++i) {
1002	<	ForkJoinWorkerThread t = ws[i];
1003	<	if (t != null)
1004	<	count += t.getQueueSize();
1005	<	}
1006	<	}
1624	>	for (ForkJoinWorkerThread w : workers)
1625	>	if (w != null)
1626	>	count += w.getQueueSize();
1627		return count;
1628		}
1629
1630		/**
1631	<	* Returns an estimate of the number tasks submitted to this pool
1632	<	* that have not yet begun executing. This method takes time
1631	>	* Returns an estimate of the number of tasks submitted to this
1632	>	* pool that have not yet begun executing.  This method takes time
1633		* proportional to the number of submissions.
1634		*
1635		* @return the number of queued submissions
#	Line 1043 | Line 1663 | public class ForkJoinPool extends Abstra
1663		* Removes all available unexecuted submitted and forked tasks
1664		* from scheduling queues and adds them to the given collection,
1665		* without altering their execution status. These may include
1666	<	* artificially generated or wrapped tasks. This method is designed
1667	<	* to be invoked only when the pool is known to be
1666	>	* artificially generated or wrapped tasks. This method is
1667	>	* designed to be invoked only when the pool is known to be
1668		* quiescent. Invocations at other times may not remove all
1669		* tasks. A failure encountered while attempting to add elements
1670		* to collection {@code c} may result in elements being in
#	Line 1057 | Line 1677 | public class ForkJoinPool extends Abstra
1677		* @return the number of elements transferred
1678		*/
1679		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1680	<	int n = submissionQueue.drainTo(c);
1681	<	ForkJoinWorkerThread[] ws = workers;
1682	<	if (ws != null) {
1683	<	for (int i = 0; i < ws.length; ++i) {
1684	<	ForkJoinWorkerThread w = ws[i];
1065	<	if (w != null)
1066	<	n += w.drainTasksTo(c);
1067	<	}
1068	<	}
1069	<	return n;
1680	>	int count = submissionQueue.drainTo(c);
1681	>	for (ForkJoinWorkerThread w : workers)
1682	>	if (w != null)
1683	>	count += w.drainTasksTo(c);
1684	>	return count;
1685		}
1686
1687		/**
#	Line 1077 | Line 1692 | public class ForkJoinPool extends Abstra
1692		* @return a string identifying this pool, as well as its state
1693		*/
1694		public String toString() {
1080	–	int ps = parallelism;
1081	–	int wc = workerCounts;
1082	–	int rc = runControl;
1695		long st = getStealCount();
1696		long qt = getQueuedTaskCount();
1697		long qs = getQueuedSubmissionCount();
1698	+	int wc = workerCounts;
1699	+	int tc = wc >>> TOTAL_COUNT_SHIFT;
1700	+	int rc = wc & RUNNING_COUNT_MASK;
1701	+	int pc = parallelism;
1702	+	int rs = runState;
1703	+	int ac = rs & ACTIVE_COUNT_MASK;
1704		return super.toString() +
1705	<	"[" + runStateToString(runStateOf(rc)) +
1706	<	", parallelism = " + ps +
1707	<	", size = " + totalCountOf(wc) +
1708	<	", active = " + activeCountOf(rc) +
1709	<	", running = " + runningCountOf(wc) +
1705	>	"[" + runLevelToString(rs) +
1706	>	", parallelism = " + pc +
1707	>	", size = " + tc +
1708	>	", active = " + ac +
1709	>	", running = " + rc +
1710		", steals = " + st +
1711		", tasks = " + qt +
1712		", submissions = " + qs +
1713		"]";
1714		}
1715
1716	<	private static String runStateToString(int rs) {
1717	<	switch(rs) {
1718	<	case RUNNING: return "Running";
1719	<	case SHUTDOWN: return "Shutting down";
1720	<	case TERMINATING: return "Terminating";
1103	<	case TERMINATED: return "Terminated";
1104	<	default: throw new Error("Unknown run state");
1105	<	}
1716	>	private static String runLevelToString(int s) {
1717	>	return ((s & TERMINATED) != 0 ? "Terminated" :
1718	>	((s & TERMINATING) != 0 ? "Terminating" :
1719	>	((s & SHUTDOWN) != 0 ? "Shutting down" :
1720	>	"Running")));
1721		}
1722
1108	–	// lifecycle control
1109	–
1723		/**
1724		* Initiates an orderly shutdown in which previously submitted
1725		* tasks are executed, but no new tasks will be accepted.
#	Line 1121 | Line 1734 | public class ForkJoinPool extends Abstra
1734		*/
1735		public void shutdown() {
1736		checkPermission();
1737	<	transitionRunStateTo(SHUTDOWN);
1738	<	if (canTerminateOnShutdown(runControl)) {
1126	<	if (workers == null) { // shutting down before workers created
1127	<	final ReentrantLock lock = this.workerLock;
1128	<	lock.lock();
1129	<	try {
1130	<	if (workers == null) {
1131	<	terminate();
1132	<	transitionRunStateTo(TERMINATED);
1133	<	termination.signalAll();
1134	<	}
1135	<
1136	<	} finally {
1137	<	lock.unlock();
1138	<	}
1139	<	}
1140	<	terminateOnShutdown();
1141	<	}
1737	>	advanceRunLevel(SHUTDOWN);
1738	>	tryTerminate(false);
1739		}
1740
1741		/**
1742	<	* Attempts to stop all actively executing tasks, and cancels all
1743	<	* waiting tasks.  Tasks that are in the process of being
1744	<	* submitted or executed concurrently during the course of this
1745	<	* method may or may not be rejected. Unlike some other executors,
1746	<	* this method cancels rather than collects non-executed tasks
1747	<	* upon termination, so always returns an empty list. However, you
1748	<	* can use method {@link #drainTasksTo} before invoking this
1749	<	* method to transfer unexecuted tasks to another collection.
1742	>	* Attempts to cancel and/or stop all tasks, and reject all
1743	>	* subsequently submitted tasks.  Tasks that are in the process of
1744	>	* being submitted or executed concurrently during the course of
1745	>	* this method may or may not be rejected. This method cancels
1746	>	* both existing and unexecuted tasks, in order to permit
1747	>	* termination in the presence of task dependencies. So the method
1748	>	* always returns an empty list (unlike the case for some other
1749	>	* Executors).
1750		*
1751		* @return an empty list
1752		* @throws SecurityException if a security manager exists and
#	Line 1159 | Line 1756 | public class ForkJoinPool extends Abstra
1756		*/
1757		public List<Runnable> shutdownNow() {
1758		checkPermission();
1759	<	terminate();
1759	>	tryTerminate(true);
1760		return Collections.emptyList();
1761		}
1762
#	Line 1169 | Line 1766 | public class ForkJoinPool extends Abstra
1766		* @return {@code true} if all tasks have completed following shut down
1767		*/
1768		public boolean isTerminated() {
1769	<	return runStateOf(runControl) == TERMINATED;
1769	>	return runState >= TERMINATED;
1770		}
1771
1772		/**
1773		* Returns {@code true} if the process of termination has
1774	<	* commenced but possibly not yet completed.
1774	>	* commenced but not yet completed.  This method may be useful for
1775	>	* debugging. A return of {@code true} reported a sufficient
1776	>	* period after shutdown may indicate that submitted tasks have
1777	>	* ignored or suppressed interruption, or are waiting for IO,
1778	>	* causing this executor not to properly terminate. (See the
1779	>	* advisory notes for class {@link ForkJoinTask} stating that
1780	>	* tasks should not normally entail blocking operations.  But if
1781	>	* they do, they must abort them on interrupt.)
1782		*
1783	<	* @return {@code true} if terminating
1783	>	* @return {@code true} if terminating but not yet terminated
1784		*/
1785		public boolean isTerminating() {
1786	<	return runStateOf(runControl) >= TERMINATING;
1786	>	return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
1787	>	}
1788	>
1789	>	/**
1790	>	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1791	>	*/
1792	>	final boolean isAtLeastTerminating() {
1793	>	return runState >= TERMINATING;
1794		}
1795
1796		/**
#	Line 1188 | Line 1799 | public class ForkJoinPool extends Abstra
1799		* @return {@code true} if this pool has been shut down
1800		*/
1801		public boolean isShutdown() {
1802	<	return runStateOf(runControl) >= SHUTDOWN;
1802	>	return runState >= SHUTDOWN;
1803		}
1804
1805		/**
#	Line 1204 | Line 1815 | public class ForkJoinPool extends Abstra
1815		*/
1816		public boolean awaitTermination(long timeout, TimeUnit unit)
1817		throws InterruptedException {
1207	–	long nanos = unit.toNanos(timeout);
1208	–	final ReentrantLock lock = this.workerLock;
1209	–	lock.lock();
1210	–	try {
1211	–	for (;;) {
1212	–	if (isTerminated())
1213	–	return true;
1214	–	if (nanos <= 0)
1215	–	return false;
1216	–	nanos = termination.awaitNanos(nanos);
1217	–	}
1218	–	} finally {
1219	–	lock.unlock();
1220	–	}
1221	–	}
1222	–
1223	–	// Shutdown and termination support
1224	–
1225	–	/**
1226	–	* Callback from terminating worker. Nulls out the corresponding
1227	–	* workers slot, and if terminating, tries to terminate; else
1228	–	* tries to shrink workers array.
1229	–	*
1230	–	* @param w the worker
1231	–	*/
1232	–	final void workerTerminated(ForkJoinWorkerThread w) {
1233	–	updateStealCount(w);
1234	–	updateWorkerCount(-1);
1235	–	final ReentrantLock lock = this.workerLock;
1236	–	lock.lock();
1818		try {
1819	<	ForkJoinWorkerThread[] ws = workers;
1820	<	if (ws != null) {
1240	<	int idx = w.poolIndex;
1241	<	if (idx >= 0 && idx < ws.length && ws[idx] == w)
1242	<	ws[idx] = null;
1243	<	if (totalCountOf(workerCounts) == 0) {
1244	<	terminate(); // no-op if already terminating
1245	<	transitionRunStateTo(TERMINATED);
1246	<	termination.signalAll();
1247	<	}
1248	<	else if (!isTerminating()) {
1249	<	tryShrinkWorkerArray();
1250	<	tryResumeSpare(true); // allow replacement
1251	<	}
1252	<	}
1253	<	} finally {
1254	<	lock.unlock();
1255	<	}
1256	<	signalIdleWorkers();
1257	<	}
1258	<
1259	<	/**
1260	<	* Initiates termination.
1261	<	*/
1262	<	private void terminate() {
1263	<	if (transitionRunStateTo(TERMINATING)) {
1264	<	stopAllWorkers();
1265	<	resumeAllSpares();
1266	<	signalIdleWorkers();
1267	<	cancelQueuedSubmissions();
1268	<	cancelQueuedWorkerTasks();
1269	<	interruptUnterminatedWorkers();
1270	<	signalIdleWorkers(); // resignal after interrupt
1271	<	}
1272	<	}
1273	<
1274	<	/**
1275	<	* Possibly terminates when on shutdown state.
1276	<	*/
1277	<	private void terminateOnShutdown() {
1278	<	if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
1279	<	terminate();
1280	<	}
1281	<
1282	<	/**
1283	<	* Clears out and cancels submissions.
1284	<	*/
1285	<	private void cancelQueuedSubmissions() {
1286	<	ForkJoinTask<?> task;
1287	<	while ((task = pollSubmission()) != null)
1288	<	task.cancel(false);
1289	<	}
1290	<
1291	<	/**
1292	<	* Cleans out worker queues.
1293	<	*/
1294	<	private void cancelQueuedWorkerTasks() {
1295	<	final ReentrantLock lock = this.workerLock;
1296	<	lock.lock();
1297	<	try {
1298	<	ForkJoinWorkerThread[] ws = workers;
1299	<	if (ws != null) {
1300	<	for (int i = 0; i < ws.length; ++i) {
1301	<	ForkJoinWorkerThread t = ws[i];
1302	<	if (t != null)
1303	<	t.cancelTasks();
1304	<	}
1305	<	}
1306	<	} finally {
1307	<	lock.unlock();
1308	<	}
1309	<	}
1310	<
1311	<	/**
1312	<	* Sets each worker's status to terminating. Requires lock to avoid
1313	<	* conflicts with add/remove.
1314	<	*/
1315	<	private void stopAllWorkers() {
1316	<	final ReentrantLock lock = this.workerLock;
1317	<	lock.lock();
1318	<	try {
1319	<	ForkJoinWorkerThread[] ws = workers;
1320	<	if (ws != null) {
1321	<	for (int i = 0; i < ws.length; ++i) {
1322	<	ForkJoinWorkerThread t = ws[i];
1323	<	if (t != null)
1324	<	t.shutdownNow();
1325	<	}
1326	<	}
1327	<	} finally {
1328	<	lock.unlock();
1329	<	}
1330	<	}
1331	<
1332	<	/**
1333	<	* Interrupts all unterminated workers.  This is not required for
1334	<	* sake of internal control, but may help unstick user code during
1335	<	* shutdown.
1336	<	*/
1337	<	private void interruptUnterminatedWorkers() {
1338	<	final ReentrantLock lock = this.workerLock;
1339	<	lock.lock();
1340	<	try {
1341	<	ForkJoinWorkerThread[] ws = workers;
1342	<	if (ws != null) {
1343	<	for (int i = 0; i < ws.length; ++i) {
1344	<	ForkJoinWorkerThread t = ws[i];
1345	<	if (t != null && !t.isTerminated()) {
1346	<	try {
1347	<	t.interrupt();
1348	<	} catch (SecurityException ignore) {
1349	<	}
1350	<	}
1351	<	}
1352	<	}
1353	<	} finally {
1354	<	lock.unlock();
1355	<	}
1356	<	}
1357	<
1358	<
1359	<	/*
1360	<	* Nodes for event barrier to manage idle threads.  Queue nodes
1361	<	* are basic Treiber stack nodes, also used for spare stack.
1362	<	*
1363	<	* The event barrier has an event count and a wait queue (actually
1364	<	* a Treiber stack).  Workers are enabled to look for work when
1365	<	* the eventCount is incremented. If they fail to find work, they
1366	<	* may wait for next count. Upon release, threads help others wake
1367	<	* up.
1368	<	*
1369	<	* Synchronization events occur only in enough contexts to
1370	<	* maintain overall liveness:
1371	<	*
1372	<	*   - Submission of a new task to the pool
1373	<	*   - Resizes or other changes to the workers array
1374	<	*   - pool termination
1375	<	*   - A worker pushing a task on an empty queue
1376	<	*
1377	<	* The case of pushing a task occurs often enough, and is heavy
1378	<	* enough compared to simple stack pushes, to require special
1379	<	* handling: Method signalWork returns without advancing count if
1380	<	* the queue appears to be empty.  This would ordinarily result in
1381	<	* races causing some queued waiters not to be woken up. To avoid
1382	<	* this, the first worker enqueued in method sync (see
1383	<	* syncIsReleasable) rescans for tasks after being enqueued, and
1384	<	* helps signal if any are found. This works well because the
1385	<	* worker has nothing better to do, and so might as well help
1386	<	* alleviate the overhead and contention on the threads actually
1387	<	* doing work.  Also, since event counts increments on task
1388	<	* availability exist to maintain liveness (rather than to force
1389	<	* refreshes etc), it is OK for callers to exit early if
1390	<	* contending with another signaller.
1391	<	*/
1392	<	static final class WaitQueueNode {
1393	<	WaitQueueNode next; // only written before enqueued
1394	<	volatile ForkJoinWorkerThread thread; // nulled to cancel wait
1395	<	final long count; // unused for spare stack
1396	<
1397	<	WaitQueueNode(long c, ForkJoinWorkerThread w) {
1398	<	count = c;
1399	<	thread = w;
1400	<	}
1401	<
1402	<	/**
1403	<	* Wakes up waiter, returning false if known to already
1404	<	*/
1405	<	boolean signal() {
1406	<	ForkJoinWorkerThread t = thread;
1407	<	if (t == null)
1408	<	return false;
1409	<	thread = null;
1410	<	LockSupport.unpark(t);
1411	<	return true;
1412	<	}
1413	<
1414	<	/**
1415	<	* Awaits release on sync.
1416	<	*/
1417	<	void awaitSyncRelease(ForkJoinPool p) {
1418	<	while (thread != null && !p.syncIsReleasable(this))
1419	<	LockSupport.park(this);
1420	<	}
1421	<
1422	<	/**
1423	<	* Awaits resumption as spare.
1424	<	*/
1425	<	void awaitSpareRelease() {
1426	<	while (thread != null) {
1427	<	if (!Thread.interrupted())
1428	<	LockSupport.park(this);
1429	<	}
1430	<	}
1431	<	}
1432	<
1433	<	/**
1434	<	* Ensures that no thread is waiting for count to advance from the
1435	<	* current value of eventCount read on entry to this method, by
1436	<	* releasing waiting threads if necessary.
1437	<	*
1438	<	* @return the count
1439	<	*/
1440	<	final long ensureSync() {
1441	<	long c = eventCount;
1442	<	WaitQueueNode q;
1443	<	while ((q = syncStack) != null && q.count < c) {
1444	<	if (casBarrierStack(q, null)) {
1445	<	do {
1446	<	q.signal();
1447	<	} while ((q = q.next) != null);
1448	<	break;
1449	<	}
1450	<	}
1451	<	return c;
1452	<	}
1453	<
1454	<	/**
1455	<	* Increments event count and releases waiting threads.
1456	<	*/
1457	<	private void signalIdleWorkers() {
1458	<	long c;
1459	<	do {} while (!casEventCount(c = eventCount, c+1));
1460	<	ensureSync();
1461	<	}
1462	<
1463	<	/**
1464	<	* Signals threads waiting to poll a task. Because method sync
1465	<	* rechecks availability, it is OK to only proceed if queue
1466	<	* appears to be non-empty, and OK to skip under contention to
1467	<	* increment count (since some other thread succeeded).
1468	<	*/
1469	<	final void signalWork() {
1470	<	long c;
1471	<	WaitQueueNode q;
1472	<	if (syncStack != null &&
1473	<	casEventCount(c = eventCount, c+1) &&
1474	<	(((q = syncStack) != null && q.count <= c) &&
1475	<	(!casBarrierStack(q, q.next) || !q.signal())))
1476	<	ensureSync();
1477	<	}
1478	<
1479	<	/**
1480	<	* Waits until event count advances from last value held by
1481	<	* caller, or if excess threads, caller is resumed as spare, or
1482	<	* caller or pool is terminating. Updates caller's event on exit.
1483	<	*
1484	<	* @param w the calling worker thread
1485	<	*/
1486	<	final void sync(ForkJoinWorkerThread w) {
1487	<	updateStealCount(w); // Transfer w's count while it is idle
1488	<
1489	<	while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
1490	<	long prev = w.lastEventCount;
1491	<	WaitQueueNode node = null;
1492	<	WaitQueueNode h;
1493	<	while (eventCount == prev &&
1494	<	((h = syncStack) == null || h.count == prev)) {
1495	<	if (node == null)
1496	<	node = new WaitQueueNode(prev, w);
1497	<	if (casBarrierStack(node.next = h, node)) {
1498	<	node.awaitSyncRelease(this);
1499	<	break;
1500	<	}
1501	<	}
1502	<	long ec = ensureSync();
1503	<	if (ec != prev) {
1504	<	w.lastEventCount = ec;
1505	<	break;
1506	<	}
1507	<	}
1508	<	}
1509	<
1510	<	/**
1511	<	* Returns {@code true} if worker waiting on sync can proceed:
1512	<	*  - on signal (thread == null)
1513	<	*  - on event count advance (winning race to notify vs signaller)
1514	<	*  - on interrupt
1515	<	*  - if the first queued node, we find work available
1516	<	* If node was not signalled and event count not advanced on exit,
1517	<	* then we also help advance event count.
1518	<	*
1519	<	* @return {@code true} if node can be released
1520	<	*/
1521	<	final boolean syncIsReleasable(WaitQueueNode node) {
1522	<	long prev = node.count;
1523	<	if (!Thread.interrupted() && node.thread != null &&
1524	<	(node.next != null ||
1525	<	!ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
1526	<	eventCount == prev)
1819	>	termination.awaitAdvanceInterruptibly(0, timeout, unit);
1820	>	} catch (TimeoutException ex) {
1821		return false;
1528	–	if (node.thread != null) {
1529	–	node.thread = null;
1530	–	long ec = eventCount;
1531	–	if (prev <= ec) // help signal
1532	–	casEventCount(ec, ec+1);
1822		}
1823		return true;
1824		}
1825
1826		/**
1538	–	* Returns {@code true} if a new sync event occurred since last
1539	–	* call to sync or this method, if so, updating caller's count.
1540	–	*/
1541	–	final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1542	–	long lc = w.lastEventCount;
1543	–	long ec = ensureSync();
1544	–	if (ec == lc)
1545	–	return false;
1546	–	w.lastEventCount = ec;
1547	–	return true;
1548	–	}
1549	–
1550	–	//  Parallelism maintenance
1551	–
1552	–	/**
1553	–	* Decrements running count; if too low, adds spare.
1554	–	*
1555	–	* Conceptually, all we need to do here is add or resume a
1556	–	* spare thread when one is about to block (and remove or
1557	–	* suspend it later when unblocked -- see suspendIfSpare).
1558	–	* However, implementing this idea requires coping with
1559	–	* several problems: we have imperfect information about the
1560	–	* states of threads. Some count updates can and usually do
1561	–	* lag run state changes, despite arrangements to keep them
1562	–	* accurate (for example, when possible, updating counts
1563	–	* before signalling or resuming), especially when running on
1564	–	* dynamic JVMs that don't optimize the infrequent paths that
1565	–	* update counts. Generating too many threads can make these
1566	–	* problems become worse, because excess threads are more
1567	–	* likely to be context-switched with others, slowing them all
1568	–	* down, especially if there is no work available, so all are
1569	–	* busy scanning or idling.  Also, excess spare threads can
1570	–	* only be suspended or removed when they are idle, not
1571	–	* immediately when they aren't needed. So adding threads will
1572	–	* raise parallelism level for longer than necessary.  Also,
1573	–	* FJ applications often encounter highly transient peaks when
1574	–	* many threads are blocked joining, but for less time than it
1575	–	* takes to create or resume spares.
1576	–	*
1577	–	* @param joinMe if non-null, return early if done
1578	–	* @param maintainParallelism if true, try to stay within
1579	–	* target counts, else create only to avoid starvation
1580	–	* @return true if joinMe known to be done
1581	–	*/
1582	–	final boolean preJoin(ForkJoinTask<?> joinMe,
1583	–	boolean maintainParallelism) {
1584	–	maintainParallelism &= maintainsParallelism; // overrride
1585	–	boolean dec = false;  // true when running count decremented
1586	–	while (spareStack == null || !tryResumeSpare(dec)) {
1587	–	int counts = workerCounts;
1588	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1589	–	// CAS cheat
1590	–	if (!needSpare(counts, maintainParallelism))
1591	–	break;
1592	–	if (joinMe.status < 0)
1593	–	return true;
1594	–	if (tryAddSpare(counts))
1595	–	break;
1596	–	}
1597	–	}
1598	–	return false;
1599	–	}
1600	–
1601	–	/**
1602	–	* Same idea as preJoin
1603	–	*/
1604	–	final boolean preBlock(ManagedBlocker blocker,
1605	–	boolean maintainParallelism) {
1606	–	maintainParallelism &= maintainsParallelism;
1607	–	boolean dec = false;
1608	–	while (spareStack == null || !tryResumeSpare(dec)) {
1609	–	int counts = workerCounts;
1610	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1611	–	if (!needSpare(counts, maintainParallelism))
1612	–	break;
1613	–	if (blocker.isReleasable())
1614	–	return true;
1615	–	if (tryAddSpare(counts))
1616	–	break;
1617	–	}
1618	–	}
1619	–	return false;
1620	–	}
1621	–
1622	–	/**
1623	–	* Returns {@code true} if a spare thread appears to be needed.
1624	–	* If maintaining parallelism, returns true when the deficit in
1625	–	* running threads is more than the surplus of total threads, and
1626	–	* there is apparently some work to do.  This self-limiting rule
1627	–	* means that the more threads that have already been added, the
1628	–	* less parallelism we will tolerate before adding another.
1629	–	*
1630	–	* @param counts current worker counts
1631	–	* @param maintainParallelism try to maintain parallelism
1632	–	*/
1633	–	private boolean needSpare(int counts, boolean maintainParallelism) {
1634	–	int ps = parallelism;
1635	–	int rc = runningCountOf(counts);
1636	–	int tc = totalCountOf(counts);
1637	–	int runningDeficit = ps - rc;
1638	–	int totalSurplus = tc - ps;
1639	–	return (tc < maxPoolSize &&
1640	–	(rc == 0 || totalSurplus < 0 ||
1641	–	(maintainParallelism &&
1642	–	runningDeficit > totalSurplus &&
1643	–	ForkJoinWorkerThread.hasQueuedTasks(workers))));
1644	–	}
1645	–
1646	–	/**
1647	–	* Adds a spare worker if lock available and no more than the
1648	–	* expected numbers of threads exist.
1649	–	*
1650	–	* @return true if successful
1651	–	*/
1652	–	private boolean tryAddSpare(int expectedCounts) {
1653	–	final ReentrantLock lock = this.workerLock;
1654	–	int expectedRunning = runningCountOf(expectedCounts);
1655	–	int expectedTotal = totalCountOf(expectedCounts);
1656	–	boolean success = false;
1657	–	boolean locked = false;
1658	–	// confirm counts while locking; CAS after obtaining lock
1659	–	try {
1660	–	for (;;) {
1661	–	int s = workerCounts;
1662	–	int tc = totalCountOf(s);
1663	–	int rc = runningCountOf(s);
1664	–	if (rc > expectedRunning || tc > expectedTotal)
1665	–	break;
1666	–	if (!locked && !(locked = lock.tryLock()))
1667	–	break;
1668	–	if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
1669	–	createAndStartSpare(tc);
1670	–	success = true;
1671	–	break;
1672	–	}
1673	–	}
1674	–	} finally {
1675	–	if (locked)
1676	–	lock.unlock();
1677	–	}
1678	–	return success;
1679	–	}
1680	–
1681	–	/**
1682	–	* Adds the kth spare worker. On entry, pool counts are already
1683	–	* adjusted to reflect addition.
1684	–	*/
1685	–	private void createAndStartSpare(int k) {
1686	–	ForkJoinWorkerThread w = null;
1687	–	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
1688	–	int len = ws.length;
1689	–	// Probably, we can place at slot k. If not, find empty slot
1690	–	if (k < len && ws[k] != null) {
1691	–	for (k = 0; k < len && ws[k] != null; ++k)
1692	–	;
1693	–	}
1694	–	if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
1695	–	ws[k] = w;
1696	–	w.start();
1697	–	}
1698	–	else
1699	–	updateWorkerCount(-1); // adjust on failure
1700	–	signalIdleWorkers();
1701	–	}
1702	–
1703	–	/**
1704	–	* Suspends calling thread w if there are excess threads.  Called
1705	–	* only from sync.  Spares are enqueued in a Treiber stack using
1706	–	* the same WaitQueueNodes as barriers.  They are resumed mainly
1707	–	* in preJoin, but are also woken on pool events that require all
1708	–	* threads to check run state.
1709	–	*
1710	–	* @param w the caller
1711	–	*/
1712	–	private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1713	–	WaitQueueNode node = null;
1714	–	int s;
1715	–	while (parallelism < runningCountOf(s = workerCounts)) {
1716	–	if (node == null)
1717	–	node = new WaitQueueNode(0, w);
1718	–	if (casWorkerCounts(s, s-1)) { // representation-dependent
1719	–	// push onto stack
1720	–	do {} while (!casSpareStack(node.next = spareStack, node));
1721	–	// block until released by resumeSpare
1722	–	node.awaitSpareRelease();
1723	–	return true;
1724	–	}
1725	–	}
1726	–	return false;
1727	–	}
1728	–
1729	–	/**
1730	–	* Tries to pop and resume a spare thread.
1731	–	*
1732	–	* @param updateCount if true, increment running count on success
1733	–	* @return true if successful
1734	–	*/
1735	–	private boolean tryResumeSpare(boolean updateCount) {
1736	–	WaitQueueNode q;
1737	–	while ((q = spareStack) != null) {
1738	–	if (casSpareStack(q, q.next)) {
1739	–	if (updateCount)
1740	–	updateRunningCount(1);
1741	–	q.signal();
1742	–	return true;
1743	–	}
1744	–	}
1745	–	return false;
1746	–	}
1747	–
1748	–	/**
1749	–	* Pops and resumes all spare threads. Same idea as ensureSync.
1750	–	*
1751	–	* @return true if any spares released
1752	–	*/
1753	–	private boolean resumeAllSpares() {
1754	–	WaitQueueNode q;
1755	–	while ( (q = spareStack) != null) {
1756	–	if (casSpareStack(q, null)) {
1757	–	do {
1758	–	updateRunningCount(1);
1759	–	q.signal();
1760	–	} while ((q = q.next) != null);
1761	–	return true;
1762	–	}
1763	–	}
1764	–	return false;
1765	–	}
1766	–
1767	–	/**
1768	–	* Pops and shuts down excessive spare threads. Call only while
1769	–	* holding lock. This is not guaranteed to eliminate all excess
1770	–	* threads, only those suspended as spares, which are the ones
1771	–	* unlikely to be needed in the future.
1772	–	*/
1773	–	private void trimSpares() {
1774	–	int surplus = totalCountOf(workerCounts) - parallelism;
1775	–	WaitQueueNode q;
1776	–	while (surplus > 0 && (q = spareStack) != null) {
1777	–	if (casSpareStack(q, null)) {
1778	–	do {
1779	–	updateRunningCount(1);
1780	–	ForkJoinWorkerThread w = q.thread;
1781	–	if (w != null && surplus > 0 &&
1782	–	runningCountOf(workerCounts) > 0 && w.shutdown())
1783	–	--surplus;
1784	–	q.signal();
1785	–	} while ((q = q.next) != null);
1786	–	}
1787	–	}
1788	–	}
1789	–
1790	–	/**
1827		* Interface for extending managed parallelism for tasks running
1828	<	* in ForkJoinPools. A ManagedBlocker provides two methods.
1829	<	* Method {@code isReleasable} must return {@code true} if
1830	<	* blocking is not necessary. Method {@code block} blocks the
1831	<	* current thread if necessary (perhaps internally invoking
1832	<	* {@code isReleasable} before actually blocking.).
1828	>	* in {@link ForkJoinPool}s.
1829	>	*
1830	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1831	>	* {@code isReleasable} must return {@code true} if blocking is
1832	>	* not necessary. Method {@code block} blocks the current thread
1833	>	* if necessary (perhaps internally invoking {@code isReleasable}
1834	>	* before actually blocking). The unusual methods in this API
1835	>	* accommodate synchronizers that may, but don't usually, block
1836	>	* for long periods. Similarly, they allow more efficient internal
1837	>	* handling of cases in which additional workers may be, but
1838	>	* usually are not, needed to ensure sufficient parallelism.
1839	>	* Toward this end, implementations of method {@code isReleasable}
1840	>	* must be amenable to repeated invocation.
1841		*
1842		* <p>For example, here is a ManagedBlocker based on a
1843		* ReentrantLock:
#	Line 1811 | Line 1855 | public class ForkJoinPool extends Abstra
1855		*     return hasLock || (hasLock = lock.tryLock());
1856		*   }
1857		* }}</pre>
1858	+	*
1859	+	* <p>Here is a class that possibly blocks waiting for an
1860	+	* item on a given queue:
1861	+	*  <pre> {@code
1862	+	* class QueueTaker<E> implements ManagedBlocker {
1863	+	*   final BlockingQueue<E> queue;
1864	+	*   volatile E item = null;
1865	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1866	+	*   public boolean block() throws InterruptedException {
1867	+	*     if (item == null)
1868	+	*       item = queue.take();
1869	+	*     return true;
1870	+	*   }
1871	+	*   public boolean isReleasable() {
1872	+	*     return item != null || (item = queue.poll()) != null;
1873	+	*   }
1874	+	*   public E getItem() { // call after pool.managedBlock completes
1875	+	*     return item;
1876	+	*   }
1877	+	* }}</pre>
1878		*/
1879		public static interface ManagedBlocker {
1880		/**
#	Line 1832 | Line 1896 | public class ForkJoinPool extends Abstra
1896
1897		/**
1898		* Blocks in accord with the given blocker.  If the current thread
1899	<	* is a ForkJoinWorkerThread, this method possibly arranges for a
1900	<	* spare thread to be activated if necessary to ensure parallelism
1901	<	* while the current thread is blocked.  If
1838	<	* {@code maintainParallelism} is {@code true} and the pool supports
1839	<	* it ({@link #getMaintainsParallelism}), this method attempts to
1840	<	* maintain the pool's nominal parallelism. Otherwise it activates
1841	<	* a thread only if necessary to avoid complete starvation. This
1842	<	* option may be preferable when blockages use timeouts, or are
1843	<	* almost always brief.
1899	>	* is a {@link ForkJoinWorkerThread}, this method possibly
1900	>	* arranges for a spare thread to be activated if necessary to
1901	>	* ensure sufficient parallelism while the current thread is blocked.
1902		*
1903	<	* <p> If the caller is not a ForkJoinTask, this method is behaviorally
1904	<	* equivalent to
1903	>	* <p>If the caller is not a {@link ForkJoinTask}, this method is
1904	>	* behaviorally equivalent to
1905		*  <pre> {@code
1906		* while (!blocker.isReleasable())
1907		*   if (blocker.block())
1908		*     return;
1909		* }</pre>
1910	<	* If the caller is a ForkJoinTask, then the pool may first
1911	<	* be expanded to ensure parallelism, and later adjusted.
1910	>	*
1911	>	* If the caller is a {@code ForkJoinTask}, then the pool may
1912	>	* first be expanded to ensure parallelism, and later adjusted.
1913		*
1914		* @param blocker the blocker
1856	–	* @param maintainParallelism if {@code true} and supported by
1857	–	* this pool, attempt to maintain the pool's nominal parallelism;
1858	–	* otherwise activate a thread only if necessary to avoid
1859	–	* complete starvation.
1915		* @throws InterruptedException if blocker.block did so
1916		*/
1917	<	public static void managedBlock(ManagedBlocker blocker,
1863	<	boolean maintainParallelism)
1917	>	public static void managedBlock(ManagedBlocker blocker)
1918		throws InterruptedException {
1919		Thread t = Thread.currentThread();
1920	<	ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
1921	<	((ForkJoinWorkerThread) t).pool : null);
1922	<	if (!blocker.isReleasable()) {
1923	<	try {
1924	<	if (pool == null ||
1925	<	!pool.preBlock(blocker, maintainParallelism))
1872	<	awaitBlocker(blocker);
1873	<	} finally {
1874	<	if (pool != null)
1875	<	pool.updateRunningCount(1);
1876	<	}
1920	>	if (t instanceof ForkJoinWorkerThread) {
1921	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1922	>	w.pool.awaitBlocker(blocker);
1923	>	}
1924	>	else {
1925	>	do {} while (!blocker.isReleasable() && !blocker.block());
1926		}
1927		}
1928
1929	<	private static void awaitBlocker(ManagedBlocker blocker)
1930	<	throws InterruptedException {
1931	<	do {} while (!blocker.isReleasable() && !blocker.block());
1883	<	}
1884	<
1885	<	// AbstractExecutorService overrides
1929	>	// AbstractExecutorService overrides.  These rely on undocumented
1930	>	// fact that ForkJoinTask.adapt returns ForkJoinTasks that also
1931	>	// implement RunnableFuture.
1932
1933		protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
1934	<	return new AdaptedRunnable<T>(runnable, value);
1934	>	return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
1935		}
1936
1937		protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
1938	<	return new AdaptedCallable<T>(callable);
1938	>	return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
1939		}
1940
1941		// Unsafe mechanics
1942
1943		private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1898	–	private static final long eventCountOffset =
1899	–	objectFieldOffset("eventCount", ForkJoinPool.class);
1944		private static final long workerCountsOffset =
1945		objectFieldOffset("workerCounts", ForkJoinPool.class);
1946	<	private static final long runControlOffset =
1947	<	objectFieldOffset("runControl", ForkJoinPool.class);
1948	<	private static final long syncStackOffset =
1949	<	objectFieldOffset("syncStack",ForkJoinPool.class);
1950	<	private static final long spareStackOffset =
1951	<	objectFieldOffset("spareStack", ForkJoinPool.class);
1952	<
1953	<	private boolean casEventCount(long cmp, long val) {
1954	<	return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
1955	<	}
1912	<	private boolean casWorkerCounts(int cmp, int val) {
1913	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
1914	<	}
1915	<	private boolean casRunControl(int cmp, int val) {
1916	<	return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
1917	<	}
1918	<	private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
1919	<	return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
1920	<	}
1921	<	private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
1922	<	return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
1923	<	}
1946	>	private static final long runStateOffset =
1947	>	objectFieldOffset("runState", ForkJoinPool.class);
1948	>	private static final long eventCountOffset =
1949	>	objectFieldOffset("eventCount", ForkJoinPool.class);
1950	>	private static final long eventWaitersOffset =
1951	>	objectFieldOffset("eventWaiters", ForkJoinPool.class);
1952	>	private static final long stealCountOffset =
1953	>	objectFieldOffset("stealCount", ForkJoinPool.class);
1954	>	private static final long spareWaitersOffset =
1955	>	objectFieldOffset("spareWaiters", ForkJoinPool.class);
1956
1957		private static long objectFieldOffset(String field, Class<?> klazz) {
1958		try {

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