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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.2 by dl, Wed Jan 7 16:07:37 2009 UTC vs.
Revision 1.88 by dl, Tue Nov 23 01:06:00 2010 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	<	import java.util.*;
9	<	import java.util.concurrent.*;
10	<	import java.util.concurrent.locks.*;
11	<	import java.util.concurrent.atomic.*;
12	<	import sun.misc.Unsafe;
13	<	import java.lang.reflect.*;
8	>
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.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;
25
26		/**
27	<	* An {@link ExecutorService} for running {@link ForkJoinTask}s.  A
28	<	* 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
20	<	* submitted tasks. Otherwise, use would not usually outweigh the
21	<	* construction and bookkeeping overhead of creating a large set of
22	<	* threads.
27	>	* An {@link ExecutorService} for running {@link ForkJoinTask}s.
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. Otherwise, other
39	<	* ExecutorService implementations are typically more appropriate
40	<	* 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 <code>ManagedBlocker</code> interface enables extension of
48	<	* the kinds of synchronization accommodated.  The target parallelism
49	<	* level may also be changed dynamically (<code>setParallelism</code>)
50	<	* and dynamically thread construction can be limited using methods
43	<	* <code>setMaximumPoolSize</code> and/or
44	<	* <code>setMaintainsParallelism</code>.
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
54	<	* <code>getStealCount</code>) that are intended to aid in developing,
54	>	* {@link #getStealCount}) that are intended to aid in developing,
55		* tuning, and monitoring fork/join applications. Also, method
56	<	* <code>toString</code> returns indications of pool state in a
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
122		*/
123		public class ForkJoinPool extends AbstractExecutorService {
124
125		/*
126	<	* See the extended comments interspersed below for design,
127	<	* rationale, and walkthroughs.
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
65	–	/** Mask for packing and unpacking shorts */
66	–	private static final int  shortMask = 0xffff;
67	–
68	–	/** Max pool size -- must be a power of two minus 1 */
69	–	private static final int MAX_THREADS =  0x7FFF;
70	–
367		/**
368	<	* Factory for creating new ForkJoinWorkerThreads.  A
369	<	* ForkJoinWorkerThreadFactory must be defined and used for
370	<	* ForkJoinWorkerThread subclasses that extend base functionality
371	<	* or initialize threads with different contexts.
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		}
382
383		/**
384	<	* Default ForkJoinWorkerThreadFactory implementation, creates a
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 {
95	<	return new ForkJoinWorkerThread(pool);
96	<	} catch (OutOfMemoryError oom)  {
97	<	return null;
98	<	}
390	>	return new ForkJoinWorkerThread(pool);
391		}
392		}
393
#	Line 131 | Line 423 | public class ForkJoinPool extends Abstra
423		new AtomicInteger();
424
425		/**
426	<	* Array holding all worker threads in the pool. Array size must
427	<	* be a power of two.  Updates and replacements are protected by
428	<	* workerLock, but it is always kept in a consistent enough state
429	<	* to be randomly accessed without locking by workers performing
430	<	* 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	<	volatile ForkJoinWorkerThread[] workers;
434	>	private static final long JOIN_TIMEOUT_MILLIS = 250L; // 4 per second
435
436		/**
437	<	* Lock protecting access to workers.
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 final ReentrantLock workerLock;
444	>	private static final long SHRINK_RATE_NANOS =
445	>	30L * 1000L * 1000L * 1000L; // 2 per minute
446
447		/**
448	<	* Condition for awaitTermination.
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 final Condition termination;
452	>	private static final int MAX_WORKERS   = 0x7fff;
453
454		/**
455	<	* The uncaught exception handler used when any worker
456	<	* abrupty terminates
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	<	private Thread.UncaughtExceptionHandler ueh;
463	>	volatile ForkJoinWorkerThread[] workers;
464
465		/**
466	<	* Creation factory for worker threads.
466	>	* Queue for external submissions.
467		*/
468	<	private final ForkJoinWorkerThreadFactory factory;
468	>	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
469
470		/**
471	<	* Head of stack of threads that were created to maintain
165	<	* parallelism when other threads blocked, but have since
166	<	* suspended when the parallelism level rose.
471	>	* Lock protecting updates to workers array.
472		*/
473	<	private volatile WaitQueueNode spareStack;
473	>	private final ReentrantLock workerLock;
474
475		/**
476	<	* Sum of per-thread steal counts, updated only when threads are
172	<	* idle or terminating.
476	>	* Latch released upon termination.
477		*/
478	<	private final AtomicLong stealCount;
478	>	private final Phaser termination;
479
480		/**
481	<	* Queue for external submissions.
481	>	* Creation factory for worker threads.
482		*/
483	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
483	>	private final ForkJoinWorkerThreadFactory factory;
484
485		/**
486	<	* Head of Treiber stack for barrier sync. See below for explanation
486	>	* Sum of per-thread steal counts, updated only when threads are
487	>	* idle or terminating.
488		*/
489	<	private volatile WaitQueueNode barrierStack;
489	>	private volatile long stealCount;
490
491		/**
492	<	* The count for event barrier
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 volatile long eventCount;
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	<	* Pool number, just for assigning useful names to worker threads
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 final int poolNumber;
508	>	private volatile int eventCount;
509
510		/**
511	<	* The maximum allowed pool size
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 int maxPoolSize;
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	<	* The desired parallelism level, updated only under workerLock.
523	<	*/
524	<	private volatile int parallelism;
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	>	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		* 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 into one int to ensure consistent snapshot when
549	>	* threads, packed together to ensure consistent snapshot when
550		* making decisions about creating and suspending spare
551	<	* threads. Updated only by CAS.  Note: CASes in
552	<	* updateRunningCount and preJoin running active count is in low
553	<	* word, so need to be modified if this changes
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 workerCounts;
556
557	<	private static int totalCountOf(int s)           { return s >>> 16;  }
558	<	private static int runningCountOf(int s)         { return s & shortMask; }
559	<	private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
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	<	* Add delta (which may be negative) to running count.  This must
564	<	* be called before (with negative arg) and after (with positive)
224	<	* any managed synchronization (i.e., mainly, joins)
225	<	* @param delta the number to add
563	>	* The target parallelism level.
564	>	* Accessed directly by ForkJoinWorkerThreads.
565		*/
566	<	final void updateRunningCount(int delta) {
228	<	int s;
229	<	do;while (!casWorkerCounts(s = workerCounts, s + delta));
230	<	}
566	>	final int parallelism;
567
568		/**
569	<	* Add delta (which may be negative) to both total and running
570	<	* count.  This must be called upon creation and termination of
235	<	* worker threads.
236	<	* @param delta the number to add
569	>	* True if use local fifo, not default lifo, for local polling
570	>	* Read by, and replicated by ForkJoinWorkerThreads
571		*/
572	<	private void updateWorkerCount(int delta) {
239	<	int d = delta + (delta << 16); // add to both lo and hi parts
240	<	int s;
241	<	do;while (!casWorkerCounts(s = workerCounts, s + d));
242	<	}
572	>	final boolean locallyFifo;
573
574		/**
575	<	* Lifecycle control. High word contains runState, low word
576	<	* contains the number of workers that are (probably) executing
577	<	* tasks. This value is atomically incremented before a worker
578	<	* gets a task to run, and decremented when worker has no tasks
579	<	* and cannot find any. These two fields are bundled together to
580	<	* support correct termination triggering.  Note: activeCount
581	<	* CAS'es cheat by assuming active count is in low word, so need
252	<	* to be modified if this changes
575	>	* The uncaught exception handler used when any worker abruptly
576	>	* terminates.
577	>	*/
578	>	private final Thread.UncaughtExceptionHandler ueh;
579	>
580	>	/**
581	>	* Pool number, just for assigning useful names to worker threads
582		*/
583	<	private volatile int runControl;
583	>	private final int poolNumber;
584
585	<	// RunState values. Order among values matters
586	<	private static final int RUNNING     = 0;
258	<	private static final int SHUTDOWN    = 1;
259	<	private static final int TERMINATING = 2;
260	<	private static final int TERMINATED  = 3;
585	>	// Utilities for CASing fields. Note that most of these
586	>	// are usually manually inlined by callers
587
588	<	private static int runStateOf(int c)             { return c >>> 16; }
589	<	private static int activeCountOf(int c)          { return c & shortMask; }
590	<	private static int runControlFor(int r, int a)   { return (r << 16) + a; }
588	>	/**
589	>	* Increments running count part of workerCounts.
590	>	*/
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	<	* Increment active count. Called by workers before/during
268	<	* executing tasks.
599	>	* Tries to increment running count part of workerCounts.
600		*/
601	<	final void incrementActiveCount() {
601	>	final boolean tryIncrementRunningCount() {
602		int c;
603	<	do;while (!casRunControl(c = runControl, c+1));
603	>	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
604	>	c = workerCounts,
605	>	c + ONE_RUNNING);
606	>	}
607	>
608	>	/**
609	>	* Tries to decrement running count unless already zero.
610	>	*/
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	<	* Decrement active count; possibly trigger termination.
621	<	* 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	>	* @param dr -- either zero or ONE_RUNNING
624	>	* @param dt -- either zero or ONE_TOTAL
625		*/
626	<	final void decrementActiveCount() {
627	<	int c, nextc;
628	<	do;while (!casRunControl(c = runControl, nextc = c-1));
629	<	if (canTerminateOnShutdown(nextc))
630	<	terminateOnShutdown();
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	<	* Return true if argument represents zero active count and
643	<	* nonzero runstate, which is the triggering condition for
289	<	* 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	<	return ((c & -c) >>> 16) != 0; // i.e. least bit is nonzero runState bit
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 and using the default
713	<	* ForkJoinWorkerThreadFactory,
714	<	* @throws SecurityException if a security manager exists and
715	<	*         the caller is not permitted to modify threads
322	<	*         because it does not hold {@link
323	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
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	>	* @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 parellelism level
729	<	* threads, and using the default ForkJoinWorkerThreadFactory,
730	<	* @param parallelism the number of worker threads
731	<	* @throws IllegalArgumentException if parallelism less than or
335	<	* equal to zero
336	<	* @throws SecurityException if a security manager exists and
337	<	*         the caller is not permitted to modify threads
338	<	*         because it does not hold {@link
339	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
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
348	<	* ForkJoinWorkerThreadFactory,
349	<	* @param factory the factory for creating new threads
350	<	* @throws NullPointerException if factory is null
351	<	* @throws SecurityException if a security manager exists and
352	<	*         the caller is not permitted to modify threads
353	<	*         because it does not hold {@link
354	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
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
365	<	* @throws IllegalArgumentException if parallelism less than or
366	<	* equal to zero, or greater than implementation limit.
367	<	* @throws NullPointerException if factory is null
368	<	* @throws SecurityException if a security manager exists and
369	<	*         the caller is not permitted to modify threads
370	<	*         because it does not hold {@link
371	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
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();
386	<	this.stealCount = new AtomicLong();
387	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
388	<	createAndStartInitialWorkers(parallelism);
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	<	* Create new worker using factory.
791	<	* @param index the index to assign worker
792	<	* @return new worker, or null of factory failed
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 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.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
807	<	if (h != null)
808	<	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		}
406	–	return w;
820		}
821
822	+	// Maintaining parallelism
823	+
824		/**
825	<	* Return a good size for worker array given pool size.
411	<	* Currently requires size to be a power of two.
825	>	* Pushes worker onto the spare stack.
826		*/
827	<	private static int arraySizeFor(int ps) {
828	<	return ps <= 1? 1 : (1 << (32 - Integer.numberOfLeadingZeros(ps-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	<	* Create or resize array if necessary to hold newLength
835	<	* @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	<	* Try 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	<	int len = ws.length;
923	<	int last = len - 1;
924	<	while (last >= 0 && ws[last] == null)
925	<	--last;
926	<	int newLength = arraySizeFor(last+1);
927	<	if (newLength < len)
928	<	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	<	* Initial worker array and worker creation and startup. (This
953	<	* must be done under lock to avoid interference by some of the
954	<	* newly started threads while creating others.)
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	<	private void createAndStartInitialWorkers(int ps) {
979	<	final ReentrantLock lock = this.workerLock;
980	<	lock.lock();
981	<	try {
982	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
983	<	for (int i = 0; i < ps; ++i) {
984	<	ForkJoinWorkerThread w = createWorker(i);
985	<	if (w != null) {
986	<	ws[i] = w;
987	<	w.start();
988	<	updateWorkerCount(1);
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	<	} finally {
998	<	lock.unlock();
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	<	* Worker creation and startup for threads added via setParallelism.
1026	<	*/
1027	<	private void createAndStartAddedWorkers() {
1028	<	resumeAllSpares();  // Allow spares to convert to nonspare
1029	<	int ps = parallelism;
1030	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
1031	<	int len = ws.length;
1032	<	// Sweep through slots, to keep lowest indices most populated
1033	<	int k = 0;
1034	<	while (k < len) {
1035	<	if (ws[k] != null) {
1036	<	++k;
1037	<	continue;
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 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	<	int s = workerCounts;
1044	<	int tc = totalCountOf(s);
485	<	int rc = runningCountOf(s);
486	<	if (rc >= ps || tc >= ps)
1043	>	running = worker.helpJoinTask(joinMe, running);
1044	>	if (joinMe.status < 0)
1045		break;
1046	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
1047	<	ForkJoinWorkerThread w = createWorker(k);
1048	<	if (w != null) {
1049	<	ws[k++] = w;
1050	<	w.start();
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	<	else {
1059	<	updateWorkerCount(-1); // back out on failed creation
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	>	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	+	* Same idea as awaitJoin, but no helping, retries, or timeouts.
1096	+	*/
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		}
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	+	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) {
508	–	if (isShutdown())
509	–	throw new RejectedExecutionException();
1347		submissionQueue.offer(task);
1348	<	signalIdleWorkers(true);
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		/**
1354	<	* Performs the given task; returning its result upon completion
1354	>	* Performs the given task, returning its result upon completion.
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	<	doSubmit(new AdaptedRunnable<Void>(task, null));
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 = ForkJoinTask.adapt(task, null);
1421	>	forkOrSubmit(job);
1422		}
1423
1424	<	public <T> ForkJoinTask<T> submit(Callable<T> task) {
1425	<	ForkJoinTask<T> job = new AdaptedCallable<T>(task);
1426	<	doSubmit(job);
1427	<	return job;
1424	>	/**
1425	>	* Submits a ForkJoinTask for execution.
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
1432	>	*/
1433	>	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1434	>	if (task == null)
1435	>	throw new NullPointerException();
1436	>	forkOrSubmit(task);
1437	>	return task;
1438		}
1439
1440	<	public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1441	<	ForkJoinTask<T> job = new AdaptedRunnable<T>(task, result);
1442	<	doSubmit(job);
1440	>	/**
1441	>	* @throws NullPointerException if the task is null
1442	>	* @throws RejectedExecutionException if the task cannot be
1443	>	*         scheduled for execution
1444	>	*/
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	<	public ForkJoinTask<?> submit(Runnable task) {
1454	<	ForkJoinTask<Void> job = new AdaptedRunnable<Void>(task, null);
1455	<	doSubmit(job);
1453	>	/**
1454	>	* @throws NullPointerException if the task is null
1455	>	* @throws RejectedExecutionException if the task cannot be
1456	>	*         scheduled for execution
1457	>	*/
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	<	* Adaptor for Runnables. This implements RunnableFuture
1468	<	* to be compliant with AbstractExecutorService constraints
1467	>	* @throws NullPointerException if the task is null
1468	>	* @throws RejectedExecutionException if the task cannot be
1469	>	*         scheduled for execution
1470		*/
1471	<	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1472	<	implements RunnableFuture<T> {
1473	<	final Runnable runnable;
1474	<	final T resultOnCompletion;
1475	<	T result;
1476	<	AdaptedRunnable(Runnable runnable, T result) {
1477	<	if (runnable == null) throw new NullPointerException();
1478	<	this.runnable = runnable;
1479	<	this.resultOnCompletion = result;
1480	<	}
574	<	public T getRawResult() { return result; }
575	<	public void setRawResult(T v) { result = v; }
576	<	public boolean exec() {
577	<	runnable.run();
578	<	result = resultOnCompletion;
579	<	return true;
580	<	}
581	<	public void run() { invoke(); }
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	<	* Adaptor for Callables
1484	>	* @throws NullPointerException       {@inheritDoc}
1485	>	* @throws RejectedExecutionException {@inheritDoc}
1486		*/
587	–	static final class AdaptedCallable<T> extends ForkJoinTask<T>
588	–	implements RunnableFuture<T> {
589	–	final Callable<T> callable;
590	–	T result;
591	–	AdaptedCallable(Callable<T> callable) {
592	–	if (callable == null) throw new NullPointerException();
593	–	this.callable = callable;
594	–	}
595	–	public T getRawResult() { return result; }
596	–	public void setRawResult(T v) { result = v; }
597	–	public boolean exec() {
598	–	try {
599	–	result = callable.call();
600	–	return true;
601	–	} catch (Error err) {
602	–	throw err;
603	–	} catch (RuntimeException rex) {
604	–	throw rex;
605	–	} catch (Exception ex) {
606	–	throw new RuntimeException(ex);
607	–	}
608	–	}
609	–	public void run() { invoke(); }
610	–	}
611	–
1487		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
1488	<	ArrayList<ForkJoinTask<T>> ts =
1488	>	ArrayList<ForkJoinTask<T>> forkJoinTasks =
1489		new ArrayList<ForkJoinTask<T>>(tasks.size());
1490	<	for (Callable<T> c : tasks)
1491	<	ts.add(new AdaptedCallable<T>(c));
1492	<	invoke(new InvokeAll<T>(ts));
1493	<	return (List<Future<T>>)(List)ts;
1490	>	for (Callable<T> task : tasks)
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;
1496	>	return futures;
1497		}
1498
1499		static final class InvokeAll<T> extends RecursiveAction {
1500		final ArrayList<ForkJoinTask<T>> tasks;
1501		InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; }
1502		public void compute() {
1503	<	try { invokeAll(tasks); } catch(Exception ignore) {}
1503	>	try { invokeAll(tasks); }
1504	>	catch (Exception ignore) {}
1505		}
1506	+	private static final long serialVersionUID = -7914297376763021607L;
1507		}
1508
629	–	// Configuration and status settings and queries
630	–
1509		/**
1510	<	* Returns the factory used for constructing new workers
1510	>	* Returns the factory used for constructing new workers.
1511		*
1512		* @return the factory used for constructing new workers
1513		*/
#	Line 640 | Line 1518 | public class ForkJoinPool extends Abstra
1518		/**
1519		* Returns the handler for internal worker threads that terminate
1520		* due to unrecoverable errors encountered while executing tasks.
643	–	* @return the handler, or null if none
644	–	*/
645	–	public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
646	–	Thread.UncaughtExceptionHandler h;
647	–	final ReentrantLock lock = this.workerLock;
648	–	lock.lock();
649	–	try {
650	–	h = ueh;
651	–	} finally {
652	–	lock.unlock();
653	–	}
654	–	return h;
655	–	}
656	–
657	–	/**
658	–	* Sets the handler for internal worker threads that terminate due
659	–	* to unrecoverable errors encountered while executing tasks.
660	–	* Unless set, the current default or ThreadGroup handler is used
661	–	* as handler.
1521		*
1522	<	* @param h the new handler
664	<	* @return the old handler, or null if none
665	<	* @throws SecurityException if a security manager exists and
666	<	*         the caller is not permitted to modify threads
667	<	*         because it does not hold {@link
668	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
1522	>	* @return the handler, or {@code null} if none
1523		*/
1524	<	public Thread.UncaughtExceptionHandler
1525	<	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
672	<	checkPermission();
673	<	Thread.UncaughtExceptionHandler old = null;
674	<	final ReentrantLock lock = this.workerLock;
675	<	lock.lock();
676	<	try {
677	<	old = ueh;
678	<	ueh = h;
679	<	ForkJoinWorkerThread[] ws = workers;
680	<	for (int i = 0; i < ws.length; ++i) {
681	<	ForkJoinWorkerThread w = ws[i];
682	<	if (w != null)
683	<	w.setUncaughtExceptionHandler(h);
684	<	}
685	<	} finally {
686	<	lock.unlock();
687	<	}
688	<	return old;
689	<	}
690	<
691	<
692	<	/**
693	<	* Sets the target paralleism level of this pool.
694	<	* @param parallelism the target parallelism
695	<	* @throws IllegalArgumentException if parallelism less than or
696	<	* equal to zero or greater than maximum size bounds.
697	<	* @throws SecurityException if a security manager exists and
698	<	*         the caller is not permitted to modify threads
699	<	*         because it does not hold {@link
700	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
701	<	*/
702	<	public void setParallelism(int parallelism) {
703	<	checkPermission();
704	<	if (parallelism <= 0 || parallelism > maxPoolSize)
705	<	throw new IllegalArgumentException();
706	<	final ReentrantLock lock = this.workerLock;
707	<	lock.lock();
708	<	try {
709	<	if (!isTerminating()) {
710	<	int p = this.parallelism;
711	<	this.parallelism = parallelism;
712	<	if (parallelism > p)
713	<	createAndStartAddedWorkers();
714	<	else
715	<	trimSpares();
716	<	}
717	<	} finally {
718	<	lock.unlock();
719	<	}
720	<	signalIdleWorkers(false);
1524	>	public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1525	>	return ueh;
1526		}
1527
1528		/**
1529	<	* Returns the targeted number of worker threads in this pool.
1529	>	* Returns the targeted parallelism level of this pool.
1530		*
1531	<	* @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 731 | 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
1540	<	* from <code>getParallelism</code> when threads are created to
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);
742	<	}
743	<
744	<	/**
745	<	* Returns the maximum number of threads allowed to exist in the
746	<	* pool, even if there are insufficient unblocked running threads.
747	<	* @return the maximum
748	<	*/
749	<	public int getMaximumPoolSize() {
750	<	return maxPoolSize;
751	<	}
752	<
753	<	/**
754	<	* Sets the maximum number of threads allowed to exist in the
755	<	* pool, even if there are insufficient unblocked running threads.
756	<	* Setting this value has no effect on current pool size. It
757	<	* controls construction of new threads.
758	<	* @throws IllegalArgumentException if negative or greater then
759	<	* internal implementation limit.
760	<	*/
761	<	public void setMaximumPoolSize(int newMax) {
762	<	if (newMax < 0 || newMax > MAX_THREADS)
763	<	throw new IllegalArgumentException();
764	<	maxPoolSize = newMax;
765	<	}
766	<
767	<
768	<	/**
769	<	* Returns true if this pool dynamically maintains its target
770	<	* parallelism level. If false, new threads are added only to
771	<	* avoid possible starvation.
772	<	* This setting is by default true;
773	<	* @return true if maintains parallelism
774	<	*/
775	<	public boolean getMaintainsParallelism() {
776	<	return maintainsParallelism;
1546	>	return workerCounts >>> TOTAL_COUNT_SHIFT;
1547		}
1548
1549		/**
1550	<	* Sets whether this pool dynamically maintains its target
1551	<	* parallelism level. If false, new threads are added only to
1552	<	* avoid possible starvation.
1553	<	* @param enable true to maintains parallelism
1550	>	* Returns {@code true} if this pool uses local first-in-first-out
1551	>	* scheduling mode for forked tasks that are never joined.
1552	>	*
1553	>	* @return {@code true} if this pool uses async mode
1554		*/
1555	<	public void setMaintainsParallelism(boolean enable) {
1556	<	maintainsParallelism = enable;
1555	>	public boolean getAsyncMode() {
1556	>	return locallyFifo;
1557		}
1558
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		/**
1572		* Returns an estimate of the number of threads that are currently
1573		* stealing or executing tasks. This method may overestimate the
1574		* number of active threads.
1575	<	* @return the number of active threads.
1575	>	*
1576	>	* @return the number of active threads
1577		*/
1578		public int getActiveThreadCount() {
1579	<	return activeCountOf(runControl);
808	<	}
809	<
810	<	/**
811	<	* Returns an estimate of the number of threads that are currently
812	<	* idle waiting for tasks. This method may underestimate the
813	<	* number of idle threads.
814	<	* @return the number of idle threads.
815	<	*/
816	<	final int getIdleThreadCount() {
817	<	int c = runningCountOf(workerCounts) - activeCountOf(runControl);
818	<	return (c <= 0)? 0 : c;
1579	>	return runState & ACTIVE_COUNT_MASK;
1580		}
1581
1582		/**
1583	<	* Returns true if all worker threads are currently idle. An idle
1584	<	* worker is one that cannot obtain a task to execute because none
1585	<	* are available to steal from other threads, and there are no
1586	<	* pending submissions to the pool. This method is conservative:
1587	<	* It might not return true immediately upon idleness of all
1588	<	* threads, but will eventually become true if threads remain
1589	<	* inactive.
1590	<	* @return true if all threads are currently idle
1583	>	* Returns {@code true} if all worker threads are currently idle.
1584	>	* An idle worker is one that cannot obtain a task to execute
1585	>	* because none are available to steal from other threads, and
1586	>	* there are no pending submissions to the pool. This method is
1587	>	* conservative; it might not return {@code true} immediately upon
1588	>	* idleness of all threads, but will eventually become true if
1589	>	* threads remain inactive.
1590	>	*
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 837 | Line 1599 | public class ForkJoinPool extends Abstra
1599		* one thread's work queue by another. The reported value
1600		* underestimates the actual total number of steals when the pool
1601		* is not quiescent. This value may be useful for monitoring and
1602	<	* tuning fork/join programs: In general, steal counts should be
1602	>	* tuning fork/join programs: in general, steal counts should be
1603		* high enough to keep threads busy, but low enough to avoid
1604		* overhead and contention across threads.
1605	<	* @return the number of steals.
1605	>	*
1606	>	* @return the number of steals
1607		*/
1608		public long getStealCount() {
1609	<	return stealCount.get();
847	<	}
848	<
849	<	/**
850	<	* Accumulate steal count from a worker. Call only
851	<	* when worker known to be idle.
852	<	*/
853	<	private void updateStealCount(ForkJoinWorkerThread w) {
854	<	int sc = w.getAndClearStealCount();
855	<	if (sc != 0)
856	<	stealCount.addAndGet(sc);
1609	>	return stealCount;
1610		}
1611
1612		/**
#	Line 863 | Line 1616 | public class ForkJoinPool extends Abstra
1616		* an approximation, obtained by iterating across all threads in
1617		* the pool. This method may be useful for tuning task
1618		* granularities.
1619	<	* @return the number of queued tasks.
1619	>	*
1620	>	* @return the number of queued tasks
1621		*/
1622		public long getQueuedTaskCount() {
1623		long count = 0;
1624	<	ForkJoinWorkerThread[] ws = workers;
1625	<	for (int i = 0; i < ws.length; ++i) {
1626	<	ForkJoinWorkerThread t = ws[i];
873	<	if (t != null)
874	<	count += t.getQueueSize();
875	<	}
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	<	* @return the number of queued submissions.
1634	>	*
1635	>	* @return the number of queued submissions
1636		*/
1637		public int getQueuedSubmissionCount() {
1638		return submissionQueue.size();
1639		}
1640
1641		/**
1642	<	* Returns true if there are any tasks submitted to this pool
1643	<	* that have not yet begun executing.
1644	<	* @return <code>true</code> if there are any queued submissions.
1642	>	* Returns {@code true} if there are any tasks submitted to this
1643	>	* pool that have not yet begun executing.
1644	>	*
1645	>	* @return {@code true} if there are any queued submissions
1646		*/
1647		public boolean hasQueuedSubmissions() {
1648		return !submissionQueue.isEmpty();
#	Line 899 | Line 1652 | public class ForkJoinPool extends Abstra
1652		* Removes and returns the next unexecuted submission if one is
1653		* available.  This method may be useful in extensions to this
1654		* class that re-assign work in systems with multiple pools.
1655	<	* @return the next submission, or null if none
1655	>	*
1656	>	* @return the next submission, or {@code null} if none
1657		*/
1658		protected ForkJoinTask<?> pollSubmission() {
1659		return submissionQueue.poll();
1660		}
1661
1662		/**
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
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
1671	+	* neither, either or both collections when the associated
1672	+	* exception is thrown.  The behavior of this operation is
1673	+	* undefined if the specified collection is modified while the
1674	+	* operation is in progress.
1675	+	*
1676	+	* @param c the collection to transfer elements into
1677	+	* @return the number of elements transferred
1678	+	*/
1679	+	protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
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	+	/**
1688		* Returns a string identifying this pool, as well as its state,
1689		* including indications of run state, parallelism level, and
1690		* worker and task counts.
#	Line 913 | Line 1692 | public class ForkJoinPool extends Abstra
1692		* @return a string identifying this pool, as well as its state
1693		*/
1694		public String toString() {
916	–	int ps = parallelism;
917	–	int wc = workerCounts;
918	–	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";
939	<	case TERMINATED: return "Terminated";
940	<	default: throw new Error("Unknown run state");
941	<	}
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
944	–	// lifecycle control
945	–
1723		/**
1724		* Initiates an orderly shutdown in which previously submitted
1725		* tasks are executed, but no new tasks will be accepted.
1726		* Invocation has no additional effect if already shut down.
1727		* Tasks that are in the process of being submitted concurrently
1728		* during the course of this method may or may not be rejected.
1729	+	*
1730		* @throws SecurityException if a security manager exists and
1731		*         the caller is not permitted to modify threads
1732		*         because it does not hold {@link
1733	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
1733	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1734		*/
1735		public void shutdown() {
1736		checkPermission();
1737	<	transitionRunStateTo(SHUTDOWN);
1738	<	if (canTerminateOnShutdown(runControl))
961	<	terminateOnShutdown();
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	<	* so always returns an empty list.
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
1753		*         the caller is not permitted to modify threads
1754		*         because it does not hold {@link
1755	<	*         java.lang.RuntimePermission}<code>("modifyThread")</code>,
1755	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1756		*/
1757		public List<Runnable> shutdownNow() {
1758		checkPermission();
1759	<	terminate();
1759	>	tryTerminate(true);
1760		return Collections.emptyList();
1761		}
1762
1763		/**
1764	<	* Returns <code>true</code> if all tasks have completed following shut down.
1764	>	* Returns {@code true} if all tasks have completed following shut down.
1765		*
1766	<	* @return <code>true</code> if all tasks have completed following shut down
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</code> if the process of termination has
1774	<	* commenced but possibly not yet completed.
1773	>	* Returns {@code true} if the process of termination has
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</code> 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 <code>true</code> if this pool has been shut down.
1790	>	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1791	>	*/
1792	>	final boolean isAtLeastTerminating() {
1793	>	return runState >= TERMINATING;
1794	>	}
1795	>
1796	>	/**
1797	>	* Returns {@code true} if this pool has been shut down.
1798		*
1799	<	* @return <code>true</code> if this pool has been shut down
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 1015 | Line 1809 | public class ForkJoinPool extends Abstra
1809		*
1810		* @param timeout the maximum time to wait
1811		* @param unit the time unit of the timeout argument
1812	<	* @return <code>true</code> if this executor terminated and
1813	<	*         <code>false</code> if the timeout elapsed before termination
1812	>	* @return {@code true} if this executor terminated and
1813	>	*         {@code false} if the timeout elapsed before termination
1814		* @throws InterruptedException if interrupted while waiting
1815		*/
1816		public boolean awaitTermination(long timeout, TimeUnit unit)
1817		throws InterruptedException {
1024	–	long nanos = unit.toNanos(timeout);
1025	–	final ReentrantLock lock = this.workerLock;
1026	–	lock.lock();
1027	–	try {
1028	–	for (;;) {
1029	–	if (isTerminated())
1030	–	return true;
1031	–	if (nanos <= 0)
1032	–	return false;
1033	–	nanos = termination.awaitNanos(nanos);
1034	–	}
1035	–	} finally {
1036	–	lock.unlock();
1037	–	}
1038	–	}
1039	–
1040	–	// Shutdown and termination support
1041	–
1042	–	/**
1043	–	* Callback from terminating worker. Null out the corresponding
1044	–	* workers slot, and if terminating, try to terminate, else try to
1045	–	* shrink workers array.
1046	–	* @param w the worker
1047	–	*/
1048	–	final void workerTerminated(ForkJoinWorkerThread w) {
1049	–	updateStealCount(w);
1050	–	updateWorkerCount(-1);
1051	–	final ReentrantLock lock = this.workerLock;
1052	–	lock.lock();
1818		try {
1819	<	ForkJoinWorkerThread[] ws = workers;
1820	<	int idx = w.poolIndex;
1056	<	if (idx >= 0 && idx < ws.length && ws[idx] == w)
1057	<	ws[idx] = null;
1058	<	if (totalCountOf(workerCounts) == 0) {
1059	<	terminate(); // no-op if already terminating
1060	<	transitionRunStateTo(TERMINATED);
1061	<	termination.signalAll();
1062	<	}
1063	<	else if (!isTerminating()) {
1064	<	tryShrinkWorkerArray();
1065	<	tryResumeSpare(true); // allow replacement
1066	<	}
1067	<	} finally {
1068	<	lock.unlock();
1069	<	}
1070	<	signalIdleWorkers(false);
1071	<	}
1072	<
1073	<	/**
1074	<	* Initiate termination.
1075	<	*/
1076	<	private void terminate() {
1077	<	if (transitionRunStateTo(TERMINATING)) {
1078	<	stopAllWorkers();
1079	<	resumeAllSpares();
1080	<	signalIdleWorkers(true);
1081	<	cancelQueuedSubmissions();
1082	<	cancelQueuedWorkerTasks();
1083	<	interruptUnterminatedWorkers();
1084	<	signalIdleWorkers(true); // resignal after interrupt
1085	<	}
1086	<	}
1087	<
1088	<	/**
1089	<	* Possibly terminate when on shutdown state
1090	<	*/
1091	<	private void terminateOnShutdown() {
1092	<	if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
1093	<	terminate();
1094	<	}
1095	<
1096	<	/**
1097	<	* Clear out and cancel submissions
1098	<	*/
1099	<	private void cancelQueuedSubmissions() {
1100	<	ForkJoinTask<?> task;
1101	<	while ((task = pollSubmission()) != null)
1102	<	task.cancel(false);
1103	<	}
1104	<
1105	<	/**
1106	<	* Clean out worker queues.
1107	<	*/
1108	<	private void cancelQueuedWorkerTasks() {
1109	<	final ReentrantLock lock = this.workerLock;
1110	<	lock.lock();
1111	<	try {
1112	<	ForkJoinWorkerThread[] ws = workers;
1113	<	for (int i = 0; i < ws.length; ++i) {
1114	<	ForkJoinWorkerThread t = ws[i];
1115	<	if (t != null)
1116	<	t.cancelTasks();
1117	<	}
1118	<	} finally {
1119	<	lock.unlock();
1120	<	}
1121	<	}
1122	<
1123	<	/**
1124	<	* Set each worker's status to terminating. Requires lock to avoid
1125	<	* conflicts with add/remove
1126	<	*/
1127	<	private void stopAllWorkers() {
1128	<	final ReentrantLock lock = this.workerLock;
1129	<	lock.lock();
1130	<	try {
1131	<	ForkJoinWorkerThread[] ws = workers;
1132	<	for (int i = 0; i < ws.length; ++i) {
1133	<	ForkJoinWorkerThread t = ws[i];
1134	<	if (t != null)
1135	<	t.shutdownNow();
1136	<	}
1137	<	} finally {
1138	<	lock.unlock();
1139	<	}
1140	<	}
1141	<
1142	<	/**
1143	<	* Interrupt all unterminated workers.  This is not required for
1144	<	* sake of internal control, but may help unstick user code during
1145	<	* shutdown.
1146	<	*/
1147	<	private void interruptUnterminatedWorkers() {
1148	<	final ReentrantLock lock = this.workerLock;
1149	<	lock.lock();
1150	<	try {
1151	<	ForkJoinWorkerThread[] ws = workers;
1152	<	for (int i = 0; i < ws.length; ++i) {
1153	<	ForkJoinWorkerThread t = ws[i];
1154	<	if (t != null && !t.isTerminated()) {
1155	<	try {
1156	<	t.interrupt();
1157	<	} catch (SecurityException ignore) {
1158	<	}
1159	<	}
1160	<	}
1161	<	} finally {
1162	<	lock.unlock();
1163	<	}
1164	<	}
1165	<
1166	<
1167	<	/*
1168	<	* Nodes for event barrier to manage idle threads.
1169	<	*
1170	<	* The event barrier has an event count and a wait queue (actually
1171	<	* a Treiber stack).  Workers are enabled to look for work when
1172	<	* the eventCount is incremented. If they fail to find some,
1173	<	* they may wait for next count. Synchronization events occur only
1174	<	* in enough contexts to maintain overall liveness:
1175	<	*
1176	<	*   - Submission of a new task to the pool
1177	<	*   - Creation or termination of a worker
1178	<	*   - pool termination
1179	<	*   - A worker pushing a task on an empty queue
1180	<	*
1181	<	* The last case (pushing a task) occurs often enough, and is
1182	<	* heavy enough compared to simple stack pushes to require some
1183	<	* special handling: Method signalNonEmptyWorkerQueue returns
1184	<	* without advancing count if the queue appears to be empty.  This
1185	<	* would ordinarily result in races causing some queued waiters
1186	<	* not to be woken up. To avoid this, a worker in sync
1187	<	* rescans for tasks after being enqueued if it was the first to
1188	<	* enqueue, and aborts the wait if finding one, also helping to
1189	<	* signal others. This works well because the worker has nothing
1190	<	* better to do anyway, and so might as well help alleviate the
1191	<	* overhead and contention on the threads actually doing work.
1192	<	*
1193	<	* Queue nodes are basic Treiber stack nodes, also used for spare
1194	<	* stack.
1195	<	*/
1196	<	static final class WaitQueueNode {
1197	<	WaitQueueNode next; // only written before enqueued
1198	<	volatile ForkJoinWorkerThread thread; // nulled to cancel wait
1199	<	final long count; // unused for spare stack
1200	<	WaitQueueNode(ForkJoinWorkerThread w, long c) {
1201	<	count = c;
1202	<	thread = w;
1203	<	}
1204	<	final boolean signal() {
1205	<	ForkJoinWorkerThread t = thread;
1206	<	thread = null;
1207	<	if (t != null) {
1208	<	LockSupport.unpark(t);
1209	<	return true;
1210	<	}
1819	>	termination.awaitAdvanceInterruptibly(0, timeout, unit);
1820	>	} catch (TimeoutException ex) {
1821		return false;
1822		}
1823	<	}
1214	<
1215	<	/**
1216	<	* Release at least one thread waiting for event count to advance,
1217	<	* if one exists. If initial attempt fails, release all threads.
1218	<	* @param all if false, at first try to only release one thread
1219	<	* @return current event
1220	<	*/
1221	<	private long releaseIdleWorkers(boolean all) {
1222	<	long c;
1223	<	for (;;) {
1224	<	WaitQueueNode q = barrierStack;
1225	<	c = eventCount;
1226	<	long qc;
1227	<	if (q == null || (qc = q.count) >= c)
1228	<	break;
1229	<	if (!all) {
1230	<	if (casBarrierStack(q, q.next) && q.signal())
1231	<	break;
1232	<	all = true;
1233	<	}
1234	<	else if (casBarrierStack(q, null)) {
1235	<	do {
1236	<	q.signal();
1237	<	} while ((q = q.next) != null);
1238	<	break;
1239	<	}
1240	<	}
1241	<	return c;
1242	<	}
1243	<
1244	<	/**
1245	<	* Returns current barrier event count
1246	<	* @return current barrier event count
1247	<	*/
1248	<	final long getEventCount() {
1249	<	long ec = eventCount;
1250	<	releaseIdleWorkers(true); // release to ensure accurate result
1251	<	return ec;
1252	<	}
1253	<
1254	<	/**
1255	<	* Increment event count and release at least one waiting thread,
1256	<	* if one exists (released threads will in turn wake up others).
1257	<	* @param all if true, try to wake up all
1258	<	*/
1259	<	final void signalIdleWorkers(boolean all) {
1260	<	long c;
1261	<	do;while (!casEventCount(c = eventCount, c+1));
1262	<	releaseIdleWorkers(all);
1263	<	}
1264	<
1265	<	/**
1266	<	* Wake up threads waiting to steal a task. Because method
1267	<	* sync rechecks availability, it is OK to only proceed if
1268	<	* queue appears to be non-empty.
1269	<	*/
1270	<	final void signalNonEmptyWorkerQueue() {
1271	<	// If CAS fails another signaller must have succeeded
1272	<	long c;
1273	<	if (barrierStack != null && casEventCount(c = eventCount, c+1))
1274	<	releaseIdleWorkers(false);
1275	<	}
1276	<
1277	<	/**
1278	<	* Waits until event count advances from count, or some thread is
1279	<	* waiting on a previous count, or there is stealable work
1280	<	* available. Help wake up others on release.
1281	<	* @param w the calling worker thread
1282	<	* @param prev previous value returned by sync (or 0)
1283	<	* @return current event count
1284	<	*/
1285	<	final long sync(ForkJoinWorkerThread w, long prev) {
1286	<	updateStealCount(w);
1287	<
1288	<	while (!w.isShutdown() && !isTerminating() &&
1289	<	(parallelism >= runningCountOf(workerCounts) ||
1290	<	!suspendIfSpare(w))) { // prefer suspend to waiting here
1291	<	WaitQueueNode node = null;
1292	<	boolean queued = false;
1293	<	for (;;) {
1294	<	if (!queued) {
1295	<	if (eventCount != prev)
1296	<	break;
1297	<	WaitQueueNode h = barrierStack;
1298	<	if (h != null && h.count != prev)
1299	<	break; // release below and maybe retry
1300	<	if (node == null)
1301	<	node = new WaitQueueNode(w, prev);
1302	<	queued = casBarrierStack(node.next = h, node);
1303	<	}
1304	<	else if (Thread.interrupted() ||
1305	<	node.thread == null ||
1306	<	(node.next == null && w.prescan()) ||
1307	<	eventCount != prev) {
1308	<	node.thread = null;
1309	<	if (eventCount == prev) // help trigger
1310	<	casEventCount(prev, prev+1);
1311	<	break;
1312	<	}
1313	<	else
1314	<	LockSupport.park(this);
1315	<	}
1316	<	long ec = eventCount;
1317	<	if (releaseIdleWorkers(false) != prev)
1318	<	return ec;
1319	<	}
1320	<	return prev; // return old count if aborted
1321	<	}
1322	<
1323	<	//  Parallelism maintenance
1324	<
1325	<	/**
1326	<	* Decrement running count; if too low, add spare.
1327	<	*
1328	<	* Conceptually, all we need to do here is add or resume a
1329	<	* spare thread when one is about to block (and remove or
1330	<	* suspend it later when unblocked -- see suspendIfSpare).
1331	<	* However, implementing this idea requires coping with
1332	<	* several problems: We have imperfect information about the
1333	<	* states of threads. Some count updates can and usually do
1334	<	* lag run state changes, despite arrangements to keep them
1335	<	* accurate (for example, when possible, updating counts
1336	<	* before signalling or resuming), especially when running on
1337	<	* dynamic JVMs that don't optimize the infrequent paths that
1338	<	* update counts. Generating too many threads can make these
1339	<	* problems become worse, because excess threads are more
1340	<	* likely to be context-switched with others, slowing them all
1341	<	* down, especially if there is no work available, so all are
1342	<	* busy scanning or idling.  Also, excess spare threads can
1343	<	* only be suspended or removed when they are idle, not
1344	<	* immediately when they aren't needed. So adding threads will
1345	<	* raise parallelism level for longer than necessary.  Also,
1346	<	* FJ applications often enounter highly transient peaks when
1347	<	* many threads are blocked joining, but for less time than it
1348	<	* takes to create or resume spares.
1349	<	*
1350	<	* @param joinMe if non-null, return early if done
1351	<	* @param maintainParallelism if true, try to stay within
1352	<	* target counts, else create only to avoid starvation
1353	<	* @return true if joinMe known to be done
1354	<	*/
1355	<	final boolean preJoin(ForkJoinTask<?> joinMe, boolean maintainParallelism) {
1356	<	maintainParallelism &= maintainsParallelism; // overrride
1357	<	boolean dec = false;  // true when running count decremented
1358	<	while (spareStack == null || !tryResumeSpare(dec)) {
1359	<	int counts = workerCounts;
1360	<	if (dec || (dec = casWorkerCounts(counts, --counts))) { // CAS cheat
1361	<	if (!needSpare(counts, maintainParallelism))
1362	<	break;
1363	<	if (joinMe.status < 0)
1364	<	return true;
1365	<	if (tryAddSpare(counts))
1366	<	break;
1367	<	}
1368	<	}
1369	<	return false;
1370	<	}
1371	<
1372	<	/**
1373	<	* Same idea as preJoin
1374	<	*/
1375	<	final boolean preBlock(ManagedBlocker blocker, boolean maintainParallelism){
1376	<	maintainParallelism &= maintainsParallelism;
1377	<	boolean dec = false;
1378	<	while (spareStack == null || !tryResumeSpare(dec)) {
1379	<	int counts = workerCounts;
1380	<	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1381	<	if (!needSpare(counts, maintainParallelism))
1382	<	break;
1383	<	if (blocker.isReleasable())
1384	<	return true;
1385	<	if (tryAddSpare(counts))
1386	<	break;
1387	<	}
1388	<	}
1389	<	return false;
1390	<	}
1391	<
1392	<	/**
1393	<	* Returns true if a spare thread appears to be needed.  If
1394	<	* maintaining parallelism, returns true when the deficit in
1395	<	* running threads is more than the surplus of total threads, and
1396	<	* there is apparently some work to do.  This self-limiting rule
1397	<	* means that the more threads that have already been added, the
1398	<	* less parallelism we will tolerate before adding another.
1399	<	* @param counts current worker counts
1400	<	* @param maintainParallelism try to maintain parallelism
1401	<	*/
1402	<	private boolean needSpare(int counts, boolean maintainParallelism) {
1403	<	int ps = parallelism;
1404	<	int rc = runningCountOf(counts);
1405	<	int tc = totalCountOf(counts);
1406	<	int runningDeficit = ps - rc;
1407	<	int totalSurplus = tc - ps;
1408	<	return (tc < maxPoolSize &&
1409	<	(rc == 0 || totalSurplus < 0 ||
1410	<	(maintainParallelism &&
1411	<	runningDeficit > totalSurplus && mayHaveQueuedWork())));
1412	<	}
1413	<
1414	<	/**
1415	<	* Returns true if at least one worker queue appears to be
1416	<	* nonempty. This is expensive but not often called. It is not
1417	<	* critical that this be accurate, but if not, more or fewer
1418	<	* running threads than desired might be maintained.
1419	<	*/
1420	<	private boolean mayHaveQueuedWork() {
1421	<	ForkJoinWorkerThread[] ws = workers;
1422	<	int len = ws.length;
1423	<	ForkJoinWorkerThread v;
1424	<	for (int i = 0; i < len; ++i) {
1425	<	if ((v = ws[i]) != null && v.getRawQueueSize() > 0) {
1426	<	releaseIdleWorkers(false); // help wake up stragglers
1427	<	return true;
1428	<	}
1429	<	}
1430	<	return false;
1431	<	}
1432	<
1433	<	/**
1434	<	* Add a spare worker if lock available and no more than the
1435	<	* expected numbers of threads exist
1436	<	* @return true if successful
1437	<	*/
1438	<	private boolean tryAddSpare(int expectedCounts) {
1439	<	final ReentrantLock lock = this.workerLock;
1440	<	int expectedRunning = runningCountOf(expectedCounts);
1441	<	int expectedTotal = totalCountOf(expectedCounts);
1442	<	boolean success = false;
1443	<	boolean locked = false;
1444	<	// confirm counts while locking; CAS after obtaining lock
1445	<	try {
1446	<	for (;;) {
1447	<	int s = workerCounts;
1448	<	int tc = totalCountOf(s);
1449	<	int rc = runningCountOf(s);
1450	<	if (rc > expectedRunning || tc > expectedTotal)
1451	<	break;
1452	<	if (!locked && !(locked = lock.tryLock()))
1453	<	break;
1454	<	if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
1455	<	createAndStartSpare(tc);
1456	<	success = true;
1457	<	break;
1458	<	}
1459	<	}
1460	<	} finally {
1461	<	if (locked)
1462	<	lock.unlock();
1463	<	}
1464	<	return success;
1465	<	}
1466	<
1467	<	/**
1468	<	* Add the kth spare worker. On entry, pool coounts are already
1469	<	* adjusted to reflect addition.
1470	<	*/
1471	<	private void createAndStartSpare(int k) {
1472	<	ForkJoinWorkerThread w = null;
1473	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
1474	<	int len = ws.length;
1475	<	// Probably, we can place at slot k. If not, find empty slot
1476	<	if (k < len && ws[k] != null) {
1477	<	for (k = 0; k < len && ws[k] != null; ++k)
1478	<	;
1479	<	}
1480	<	if (k < len && (w = createWorker(k)) != null) {
1481	<	ws[k] = w;
1482	<	w.start();
1483	<	}
1484	<	else
1485	<	updateWorkerCount(-1); // adjust on failure
1486	<	signalIdleWorkers(false);
1487	<	}
1488	<
1489	<	/**
1490	<	* Suspend calling thread w if there are excess threads.  Called
1491	<	* only from sync.  Spares are enqueued in a Treiber stack
1492	<	* using the same WaitQueueNodes as barriers.  They are resumed
1493	<	* mainly in preJoin, but are also woken on pool events that
1494	<	* require all threads to check run state.
1495	<	* @param w the caller
1496	<	*/
1497	<	private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1498	<	WaitQueueNode node = null;
1499	<	int s;
1500	<	while (parallelism < runningCountOf(s = workerCounts)) {
1501	<	if (node == null)
1502	<	node = new WaitQueueNode(w, 0);
1503	<	if (casWorkerCounts(s, s-1)) { // representation-dependent
1504	<	// push onto stack
1505	<	do;while (!casSpareStack(node.next = spareStack, node));
1506	<
1507	<	// block until released by resumeSpare
1508	<	while (node.thread != null) {
1509	<	if (!Thread.interrupted())
1510	<	LockSupport.park(this);
1511	<	}
1512	<	w.activate(); // help warm up
1513	<	return true;
1514	<	}
1515	<	}
1516	<	return false;
1517	<	}
1518	<
1519	<	/**
1520	<	* Try to pop and resume a spare thread.
1521	<	* @param updateCount if true, increment running count on success
1522	<	* @return true if successful
1523	<	*/
1524	<	private boolean tryResumeSpare(boolean updateCount) {
1525	<	WaitQueueNode q;
1526	<	while ((q = spareStack) != null) {
1527	<	if (casSpareStack(q, q.next)) {
1528	<	if (updateCount)
1529	<	updateRunningCount(1);
1530	<	q.signal();
1531	<	return true;
1532	<	}
1533	<	}
1534	<	return false;
1535	<	}
1536	<
1537	<	/**
1538	<	* Pop and resume all spare threads. Same idea as
1539	<	* releaseIdleWorkers.
1540	<	* @return true if any spares released
1541	<	*/
1542	<	private boolean resumeAllSpares() {
1543	<	WaitQueueNode q;
1544	<	while ( (q = spareStack) != null) {
1545	<	if (casSpareStack(q, null)) {
1546	<	do {
1547	<	updateRunningCount(1);
1548	<	q.signal();
1549	<	} while ((q = q.next) != null);
1550	<	return true;
1551	<	}
1552	<	}
1553	<	return false;
1554	<	}
1555	<
1556	<	/**
1557	<	* Pop and shutdown excessive spare threads. Call only while
1558	<	* holding lock. This is not guaranteed to eliminate all excess
1559	<	* threads, only those suspended as spares, which are the ones
1560	<	* unlikely to be needed in the future.
1561	<	*/
1562	<	private void trimSpares() {
1563	<	int surplus = totalCountOf(workerCounts) - parallelism;
1564	<	WaitQueueNode q;
1565	<	while (surplus > 0 && (q = spareStack) != null) {
1566	<	if (casSpareStack(q, null)) {
1567	<	do {
1568	<	updateRunningCount(1);
1569	<	ForkJoinWorkerThread w = q.thread;
1570	<	if (w != null && surplus > 0 &&
1571	<	runningCountOf(workerCounts) > 0 && w.shutdown())
1572	<	--surplus;
1573	<	q.signal();
1574	<	} while ((q = q.next) != null);
1575	<	}
1576	<	}
1577	<	}
1578	<
1579	<	/**
1580	<	* Returns approximate number of spares, just for diagnostics.
1581	<	*/
1582	<	private int countSpares() {
1583	<	int sum = 0;
1584	<	for (WaitQueueNode q = spareStack; q != null; q = q.next)
1585	<	++sum;
1586	<	return sum;
1823	>	return true;
1824		}
1825
1826		/**
1827		* Interface for extending managed parallelism for tasks running
1828	<	* in ForkJoinPools. A ManagedBlocker provides two methods.
1829	<	* Method <code>isReleasable</code> must return true if blocking is not
1830	<	* necessary. Method <code>block</code> blocks the current thread
1831	<	* if necessary (perhaps internally invoking isReleasable before
1832	<	* 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:
1844	<	* <pre>
1845	<	*   class ManagedLocker implements ManagedBlocker {
1846	<	*     final ReentrantLock lock;
1847	<	*     boolean hasLock = false;
1848	<	*     ManagedLocker(ReentrantLock lock) { this.lock = lock; }
1849	<	*     public boolean block() {
1850	<	*        if (!hasLock)
1851	<	*           lock.lock();
1852	<	*        return true;
1853	<	*     }
1854	<	*     public boolean isReleasable() {
1855	<	*        return hasLock || (hasLock = lock.tryLock());
1610	<	*     }
1844	>	*  <pre> {@code
1845	>	* class ManagedLocker implements ManagedBlocker {
1846	>	*   final ReentrantLock lock;
1847	>	*   boolean hasLock = false;
1848	>	*   ManagedLocker(ReentrantLock lock) { this.lock = lock; }
1849	>	*   public boolean block() {
1850	>	*     if (!hasLock)
1851	>	*       lock.lock();
1852	>	*     return true;
1853	>	*   }
1854	>	*   public boolean isReleasable() {
1855	>	*     return hasLock || (hasLock = lock.tryLock());
1856		*   }
1857	<	* </pre>
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		/**
1881		* Possibly blocks the current thread, for example waiting for
1882		* a lock or condition.
1883	<	* @return true if no additional blocking is necessary (i.e.,
1884	<	* if isReleasable would return true).
1883	>	*
1884	>	* @return {@code true} if no additional blocking is necessary
1885	>	* (i.e., if isReleasable would return true)
1886		* @throws InterruptedException if interrupted while waiting
1887	<	* (the method is not required to do so, but is allowe to).
1887	>	* (the method is not required to do so, but is allowed to)
1888		*/
1889		boolean block() throws InterruptedException;
1890
1891		/**
1892	<	* Returns true if blocking is unnecessary.
1892	>	* Returns {@code true} if blocking is unnecessary.
1893		*/
1894		boolean isReleasable();
1895		}
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
1902	<	* <code>maintainParallelism</code> is true and the pool supports
1903	<	* it ({@link #getMaintainsParallelism}), this method attempts to
1904	<	* maintain the pool's nominal parallelism. Otherwise if activates
1905	<	* a thread only if necessary to avoid complete starvation. This
1906	<	* option may be preferable when blockages use timeouts, or are
1907	<	* almost always brief.
1908	<	*
1909	<	* <p> If the caller is not a ForkJoinTask, this method is behaviorally
1910	<	* equivalent to
1911	<	* <pre>
1912	<	*   while (!blocker.isReleasable())
1647	<	*      if (blocker.block())
1648	<	*         return;
1649	<	* </pre>
1650	<	* If the caller is a ForkJoinTask, then the pool may first
1651	<	* be expanded to ensure parallelism, and later adjusted.
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 {@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	>	*
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
1915	<	* @param maintainParallelism if true and supported by this pool,
1655	<	* attempt to maintain the pool's nominal parallelism; otherwise
1656	<	* activate a thread only if necessary to avoid complete
1657	<	* starvation.
1658	<	* @throws InterruptedException if blocker.block did so.
1915	>	* @throws InterruptedException if blocker.block did so
1916		*/
1917	<	public static void managedBlock(ManagedBlocker blocker,
1661	<	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))
1670	<	awaitBlocker(blocker);
1671	<	} finally {
1672	<	if (pool != null)
1673	<	pool.updateRunningCount(1);
1674	<	}
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());
1681	<	}
1682	<
1683	<	// 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(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(callable);
1938	>	return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
1939		}
1940
1941	+	// Unsafe mechanics
1942
1943	<	// Temporary Unsafe mechanics for preliminary release
1943	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1944	>	private static final long workerCountsOffset =
1945	>	objectFieldOffset("workerCounts", ForkJoinPool.class);
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	<	static final Unsafe _unsafe;
1697	<	static final long eventCountOffset;
1698	<	static final long workerCountsOffset;
1699	<	static final long runControlOffset;
1700	<	static final long barrierStackOffset;
1701	<	static final long spareStackOffset;
1702	<
1703	<	static {
1957	>	private static long objectFieldOffset(String field, Class<?> klazz) {
1958		try {
1959	<	if (ForkJoinPool.class.getClassLoader() != null) {
1960	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
1961	<	f.setAccessible(true);
1962	<	_unsafe = (Unsafe)f.get(null);
1963	<	}
1964	<	else
1711	<	_unsafe = Unsafe.getUnsafe();
1712	<	eventCountOffset = _unsafe.objectFieldOffset
1713	<	(ForkJoinPool.class.getDeclaredField("eventCount"));
1714	<	workerCountsOffset = _unsafe.objectFieldOffset
1715	<	(ForkJoinPool.class.getDeclaredField("workerCounts"));
1716	<	runControlOffset = _unsafe.objectFieldOffset
1717	<	(ForkJoinPool.class.getDeclaredField("runControl"));
1718	<	barrierStackOffset = _unsafe.objectFieldOffset
1719	<	(ForkJoinPool.class.getDeclaredField("barrierStack"));
1720	<	spareStackOffset = _unsafe.objectFieldOffset
1721	<	(ForkJoinPool.class.getDeclaredField("spareStack"));
1722	<	} catch (Exception e) {
1723	<	throw new RuntimeException("Could not initialize intrinsics", e);
1959	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1960	>	} catch (NoSuchFieldException e) {
1961	>	// Convert Exception to corresponding Error
1962	>	NoSuchFieldError error = new NoSuchFieldError(field);
1963	>	error.initCause(e);
1964	>	throw error;
1965		}
1966		}
1967
1968	<	private boolean casEventCount(long cmp, long val) {
1969	<	return _unsafe.compareAndSwapLong(this, eventCountOffset, cmp, val);
1970	<	}
1971	<	private boolean casWorkerCounts(int cmp, int val) {
1972	<	return _unsafe.compareAndSwapInt(this, workerCountsOffset, cmp, val);
1973	<	}
1974	<	private boolean casRunControl(int cmp, int val) {
1975	<	return _unsafe.compareAndSwapInt(this, runControlOffset, cmp, val);
1976	<	}
1977	<	private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
1978	<	return _unsafe.compareAndSwapObject(this, spareStackOffset, cmp, val);
1979	<	}
1980	<	private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
1981	<	return _unsafe.compareAndSwapObject(this, barrierStackOffset, cmp, val);
1968	>	/**
1969	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1970	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
1971	>	* into a jdk.
1972	>	*
1973	>	* @return a sun.misc.Unsafe
1974	>	*/
1975	>	private static sun.misc.Unsafe getUnsafe() {
1976	>	try {
1977	>	return sun.misc.Unsafe.getUnsafe();
1978	>	} catch (SecurityException se) {
1979	>	try {
1980	>	return java.security.AccessController.doPrivileged
1981	>	(new java.security
1982	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1983	>	public sun.misc.Unsafe run() throws Exception {
1984	>	java.lang.reflect.Field f = sun.misc
1985	>	.Unsafe.class.getDeclaredField("theUnsafe");
1986	>	f.setAccessible(true);
1987	>	return (sun.misc.Unsafe) f.get(null);
1988	>	}});
1989	>	} catch (java.security.PrivilegedActionException e) {
1990	>	throw new RuntimeException("Could not initialize intrinsics",
1991	>	e.getCause());
1992	>	}
1993	>	}
1994		}
1995		}

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