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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.10 by jsr166, Mon Jul 20 23:07:43 2009 UTC vs.
Revision 1.78 by dl, Tue Sep 7 14:52:24 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.CountDownLatch;
17	>	import java.util.concurrent.ExecutorService;
18	>	import java.util.concurrent.Future;
19	>	import java.util.concurrent.RejectedExecutionException;
20	>	import java.util.concurrent.RunnableFuture;
21	>	import java.util.concurrent.TimeUnit;
22	>	import java.util.concurrent.TimeoutException;
23	>	import java.util.concurrent.atomic.AtomicInteger;
24	>	import java.util.concurrent.locks.LockSupport;
25	>	import java.util.concurrent.locks.ReentrantLock;
26
27		/**
28	<	* An {@link ExecutorService} for running {@link ForkJoinTask}s.  A
29	<	* ForkJoinPool provides the entry point for submissions from
30	<	* non-ForkJoinTasks, as well as management and monitoring operations.
31	<	* 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.
28	>	* An {@link ExecutorService} for running {@link ForkJoinTask}s.
29	>	* A {@code ForkJoinPool} provides the entry point for submissions
30	>	* from non-{@code ForkJoinTask} clients, as well as management and
31	>	* monitoring operations.
32		*
33	<	* <p>ForkJoinPools differ from other kinds of Executors mainly in
34	<	* that they provide <em>work-stealing</em>: all threads in the pool
35	<	* attempt to find and execute subtasks created by other active tasks
36	<	* (eventually blocking if none exist). This makes them efficient when
37	<	* most tasks spawn other subtasks (as do most ForkJoinTasks), as well
38	<	* as the mixed execution of some plain Runnable- or Callable- based
39	<	* activities along with ForkJoinTasks. When setting
40	<	* {@code setAsyncMode}, a ForkJoinPools may also be appropriate for
41	<	* use with fine-grained tasks that are never joined. Otherwise, other
33	<	* ExecutorService implementations are typically more appropriate
34	<	* choices.
33	>	* <p>A {@code ForkJoinPool} differs from other kinds of {@link
34	>	* ExecutorService} mainly by virtue of employing
35	>	* <em>work-stealing</em>: all threads in the pool attempt to find and
36	>	* execute subtasks created by other active tasks (eventually blocking
37	>	* waiting for work if none exist). This enables efficient processing
38	>	* when most tasks spawn other subtasks (as do most {@code
39	>	* ForkJoinTask}s). When setting <em>asyncMode</em> to true in
40	>	* constructors, {@code ForkJoinPool}s may also be appropriate for use
41	>	* with event-style tasks that are never joined.
42		*
43	<	* <p>A ForkJoinPool may be constructed with a given parallelism level
44	<	* (target pool size), which it attempts to maintain by dynamically
45	<	* adding, suspending, or resuming threads, even if some tasks are
46	<	* waiting to join others. However, no such adjustments are performed
47	<	* in the face of blocked IO or other unmanaged synchronization. The
48	<	* nested {@code ManagedBlocker} interface enables extension of
49	<	* the kinds of synchronization accommodated.  The target parallelism
50	<	* level may also be changed dynamically ({@code setParallelism})
51	<	* and thread construction can be limited using methods
45	<	* {@code setMaximumPoolSize} and/or
46	<	* {@code setMaintainsParallelism}.
43	>	* <p>A {@code ForkJoinPool} is constructed with a given target
44	>	* parallelism level; by default, equal to the number of available
45	>	* processors. The pool attempts to maintain enough active (or
46	>	* available) threads by dynamically adding, suspending, or resuming
47	>	* internal worker threads, even if some tasks are stalled waiting to
48	>	* join others. However, no such adjustments are guaranteed in the
49	>	* face of blocked IO or other unmanaged synchronization. The nested
50	>	* {@link ManagedBlocker} interface enables extension of the kinds of
51	>	* synchronization accommodated.
52		*
53		* <p>In addition to execution and lifecycle control methods, this
54		* class provides status check methods (for example
55	<	* {@code getStealCount}) that are intended to aid in developing,
55	>	* {@link #getStealCount}) that are intended to aid in developing,
56		* tuning, and monitoring fork/join applications. Also, method
57	<	* {@code toString} returns indications of pool state in a
57	>	* {@link #toString} returns indications of pool state in a
58		* convenient form for informal monitoring.
59		*
60	+	* <p> As is the case with other ExecutorServices, there are three
61	+	* main task execution methods summarized in the following
62	+	* table. These are designed to be used by clients not already engaged
63	+	* in fork/join computations in the current pool.  The main forms of
64	+	* these methods accept instances of {@code ForkJoinTask}, but
65	+	* overloaded forms also allow mixed execution of plain {@code
66	+	* Runnable}- or {@code Callable}- based activities as well.  However,
67	+	* tasks that are already executing in a pool should normally
68	+	* <em>NOT</em> use these pool execution methods, but instead use the
69	+	* within-computation forms listed in the table.
70	+	*
71	+	* <table BORDER CELLPADDING=3 CELLSPACING=1>
72	+	*  <tr>
73	+	*    <td></td>
74	+	*    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
75	+	*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
76	+	*  </tr>
77	+	*  <tr>
78	+	*    <td> <b>Arrange async execution</td>
79	+	*    <td> {@link #execute(ForkJoinTask)}</td>
80	+	*    <td> {@link ForkJoinTask#fork}</td>
81	+	*  </tr>
82	+	*  <tr>
83	+	*    <td> <b>Await and obtain result</td>
84	+	*    <td> {@link #invoke(ForkJoinTask)}</td>
85	+	*    <td> {@link ForkJoinTask#invoke}</td>
86	+	*  </tr>
87	+	*  <tr>
88	+	*    <td> <b>Arrange exec and obtain Future</td>
89	+	*    <td> {@link #submit(ForkJoinTask)}</td>
90	+	*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
91	+	*  </tr>
92	+	* </table>
93	+	*
94	+	* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
95	+	* used for all parallel task execution in a program or subsystem.
96	+	* Otherwise, use would not usually outweigh the construction and
97	+	* bookkeeping overhead of creating a large set of threads. For
98	+	* example, a common pool could be used for the {@code SortTasks}
99	+	* illustrated in {@link RecursiveAction}. Because {@code
100	+	* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
101	+	* daemon} mode, there is typically no need to explicitly {@link
102	+	* #shutdown} such a pool upon program exit.
103	+	*
104	+	* <pre>
105	+	* static final ForkJoinPool mainPool = new ForkJoinPool();
106	+	* ...
107	+	* public void sort(long[] array) {
108	+	*   mainPool.invoke(new SortTask(array, 0, array.length));
109	+	* }
110	+	* </pre>
111	+	*
112		* <p><b>Implementation notes</b>: This implementation restricts the
113		* maximum number of running threads to 32767. Attempts to create
114	<	* pools with greater than the maximum result in
115	<	* IllegalArgumentExceptions.
114	>	* pools with greater than the maximum number result in
115	>	* {@code IllegalArgumentException}.
116	>	*
117	>	* <p>This implementation rejects submitted tasks (that is, by throwing
118	>	* {@link RejectedExecutionException}) only when the pool is shut down
119	>	* or internal resources have been exhausted.
120	>	*
121	>	* @since 1.7
122	>	* @author Doug Lea
123		*/
124		public class ForkJoinPool extends AbstractExecutorService {
125
126		/*
127	<	* See the extended comments interspersed below for design,
128	<	* rationale, and walkthroughs.
129	<	*/
130	<
131	<	/** Mask for packing and unpacking shorts */
132	<	private static final int  shortMask = 0xffff;
133	<
134	<	/** Max pool size -- must be a power of two minus 1 */
135	<	private static final int MAX_THREADS =  0x7FFF;
136	<
137	<	/**
138	<	* Factory for creating new ForkJoinWorkerThreads.  A
139	<	* ForkJoinWorkerThreadFactory must be defined and used for
140	<	* ForkJoinWorkerThread subclasses that extend base functionality
141	<	* or initialize threads with different contexts.
127	>	* Implementation Overview
128	>	*
129	>	* This class provides the central bookkeeping and control for a
130	>	* set of worker threads: Submissions from non-FJ threads enter
131	>	* into a submission queue. Workers take these tasks and typically
132	>	* split them into subtasks that may be stolen by other workers.
133	>	* The main work-stealing mechanics implemented in class
134	>	* ForkJoinWorkerThread give first priority to processing tasks
135	>	* from their own queues (LIFO or FIFO, depending on mode), then
136	>	* to randomized FIFO steals of tasks in other worker queues, and
137	>	* lastly to new submissions. These mechanics do not consider
138	>	* affinities, loads, cache localities, etc, so rarely provide the
139	>	* best possible performance on a given machine, but portably
140	>	* provide good throughput by averaging over these factors.
141	>	* (Further, even if we did try to use such information, we do not
142	>	* usually have a basis for exploiting it. For example, some sets
143	>	* of tasks profit from cache affinities, but others are harmed by
144	>	* cache pollution effects.)
145	>	*
146	>	* Beyond work-stealing support and essential bookkeeping, the
147	>	* main responsibility of this framework is to take actions when
148	>	* one worker is waiting to join a task stolen (or always held by)
149	>	* another.  Because we are multiplexing many tasks on to a pool
150	>	* of workers, we can't just let them block (as in Thread.join).
151	>	* We also cannot just reassign the joiner's run-time stack with
152	>	* another and replace it later, which would be a form of
153	>	* "continuation", that even if possible is not necessarily a good
154	>	* idea. Given that the creation costs of most threads on most
155	>	* systems mainly surrounds setting up runtime stacks, thread
156	>	* creation and switching is usually not much more expensive than
157	>	* stack creation and switching, and is more flexible). Instead we
158	>	* combine two tactics:
159	>	*
160	>	*   Helping: Arranging for the joiner to execute some task that it
161	>	*      would be running if the steal had not occurred.  Method
162	>	*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
163	>	*      links to try to find such a task.
164	>	*
165	>	*   Compensating: Unless there are already enough live threads,
166	>	*      method helpMaintainParallelism() may create or
167	>	*      re-activate a spare thread to compensate for blocked
168	>	*      joiners until they unblock.
169	>	*
170	>	* It is impossible to keep exactly the target (parallelism)
171	>	* number of threads running at any given time.  Determining
172	>	* existence of conservatively safe helping targets, the
173	>	* availability of already-created spares, and the apparent need
174	>	* to create new spares are all racy and require heuristic
175	>	* guidance, so we rely on multiple retries of each.  Compensation
176	>	* occurs in slow-motion. It is triggered only upon timeouts of
177	>	* Object.wait used for joins. This reduces poor decisions that
178	>	* would otherwise be made when threads are waiting for others
179	>	* that are stalled because of unrelated activities such as
180	>	* garbage collection.
181	>	*
182	>	* The ManagedBlocker extension API can't use helping so relies
183	>	* only on compensation in method awaitBlocker.
184	>	*
185	>	* The main throughput advantages of work-stealing stem from
186	>	* decentralized control -- workers mostly steal tasks from each
187	>	* other. We do not want to negate this by creating bottlenecks
188	>	* implementing other management responsibilities. So we use a
189	>	* collection of techniques that avoid, reduce, or cope well with
190	>	* contention. These entail several instances of bit-packing into
191	>	* CASable fields to maintain only the minimally required
192	>	* atomicity. To enable such packing, we restrict maximum
193	>	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
194	>	* unbalanced increments and decrements) to fit into a 16 bit
195	>	* field, which is far in excess of normal operating range.  Even
196	>	* though updates to some of these bookkeeping fields do sometimes
197	>	* contend with each other, they don't normally cache-contend with
198	>	* updates to others enough to warrant memory padding or
199	>	* isolation. So they are all held as fields of ForkJoinPool
200	>	* objects.  The main capabilities are as follows:
201	>	*
202	>	* 1. Creating and removing workers. Workers are recorded in the
203	>	* "workers" array. This is an array as opposed to some other data
204	>	* structure to support index-based random steals by workers.
205	>	* Updates to the array recording new workers and unrecording
206	>	* terminated ones are protected from each other by a lock
207	>	* (workerLock) but the array is otherwise concurrently readable,
208	>	* and accessed directly by workers. To simplify index-based
209	>	* operations, the array size is always a power of two, and all
210	>	* readers must tolerate null slots. Currently, all worker thread
211	>	* creation is on-demand, triggered by task submissions,
212	>	* replacement of terminated workers, and/or compensation for
213	>	* blocked workers. However, all other support code is set up to
214	>	* work with other policies.
215	>	*
216	>	* To ensure that we do not hold on to worker references that
217	>	* would prevent GC, ALL accesses to workers are via indices into
218	>	* the workers array (which is one source of some of the unusual
219	>	* code constructions here). In essence, the workers array serves
220	>	* as a WeakReference mechanism. Thus for example the event queue
221	>	* stores worker indices, not worker references. Access to the
222	>	* workers in associated methods (for example releaseEventWaiters)
223	>	* must both index-check and null-check the IDs. All such accesses
224	>	* ignore bad IDs by returning out early from what they are doing,
225	>	* since this can only be associated with shutdown, in which case
226	>	* it is OK to give up. On termination, we just clobber these
227	>	* data structures without trying to use them.
228	>	*
229	>	* 2. Bookkeeping for dynamically adding and removing workers. We
230	>	* aim to approximately maintain the given level of parallelism.
231	>	* When some workers are known to be blocked (on joins or via
232	>	* ManagedBlocker), we may create or resume others to take their
233	>	* place until they unblock (see below). Implementing this
234	>	* requires counts of the number of "running" threads (i.e., those
235	>	* that are neither blocked nor artificially suspended) as well as
236	>	* the total number.  These two values are packed into one field,
237	>	* "workerCounts" because we need accurate snapshots when deciding
238	>	* to create, resume or suspend.  Note however that the
239	>	* correspondence of these counts to reality is not guaranteed. In
240	>	* particular updates for unblocked threads may lag until they
241	>	* actually wake up.
242	>	*
243	>	* 3. Maintaining global run state. The run state of the pool
244	>	* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
245	>	* those in other Executor implementations, as well as a count of
246	>	* "active" workers -- those that are, or soon will be, or
247	>	* recently were executing tasks. The runLevel and active count
248	>	* are packed together in order to correctly trigger shutdown and
249	>	* termination. Without care, active counts can be subject to very
250	>	* high contention.  We substantially reduce this contention by
251	>	* relaxing update rules.  A worker must claim active status
252	>	* prospectively, by activating if it sees that a submitted or
253	>	* stealable task exists (it may find after activating that the
254	>	* task no longer exists). It stays active while processing this
255	>	* task (if it exists) and any other local subtasks it produces,
256	>	* until it cannot find any other tasks. It then tries
257	>	* inactivating (see method preStep), but upon update contention
258	>	* instead scans for more tasks, later retrying inactivation if it
259	>	* doesn't find any.
260	>	*
261	>	* 4. Managing idle workers waiting for tasks. We cannot let
262	>	* workers spin indefinitely scanning for tasks when none are
263	>	* available. On the other hand, we must quickly prod them into
264	>	* action when new tasks are submitted or generated.  We
265	>	* park/unpark these idle workers using an event-count scheme.
266	>	* Field eventCount is incremented upon events that may enable
267	>	* workers that previously could not find a task to now find one:
268	>	* Submission of a new task to the pool, or another worker pushing
269	>	* a task onto a previously empty queue.  (We also use this
270	>	* mechanism for configuration and termination actions that
271	>	* require wakeups of idle workers).  Each worker maintains its
272	>	* last known event count, and blocks when a scan for work did not
273	>	* find a task AND its lastEventCount matches the current
274	>	* eventCount. Waiting idle workers are recorded in a variant of
275	>	* Treiber stack headed by field eventWaiters which, when nonzero,
276	>	* encodes the thread index and count awaited for by the worker
277	>	* thread most recently calling eventSync. This thread in turn has
278	>	* a record (field nextEventWaiter) for the next waiting worker.
279	>	* In addition to allowing simpler decisions about need for
280	>	* wakeup, the event count bits in eventWaiters serve the role of
281	>	* tags to avoid ABA errors in Treiber stacks. Upon any wakeup,
282	>	* released threads also try to release at most two others.  The
283	>	* net effect is a tree-like diffusion of signals, where released
284	>	* threads (and possibly others) help with unparks.  To further
285	>	* reduce contention effects a bit, failed CASes to increment
286	>	* field eventCount are tolerated without retries in signalWork.
287	>	* Conceptually they are merged into the same event, which is OK
288	>	* when their only purpose is to enable workers to scan for work.
289	>	*
290	>	* 5. Managing suspension of extra workers. When a worker notices
291	>	* (usually upon timeout of a wait()) that there are too few
292	>	* running threads, we may create a new thread to maintain
293	>	* parallelism level, or at least avoid starvation. Usually, extra
294	>	* threads are needed for only very short periods, yet join
295	>	* dependencies are such that we sometimes need them in
296	>	* bursts. Rather than create new threads each time this happens,
297	>	* we suspend no-longer-needed extra ones as "spares". For most
298	>	* purposes, we don't distinguish "extra" spare threads from
299	>	* normal "core" threads: On each call to preStep (the only point
300	>	* at which we can do this) a worker checks to see if there are
301	>	* now too many running workers, and if so, suspends itself.
302	>	* Method helpMaintainParallelism looks for suspended threads to
303	>	* resume before considering creating a new replacement. The
304	>	* spares themselves are encoded on another variant of a Treiber
305	>	* Stack, headed at field "spareWaiters".  Note that the use of
306	>	* spares is intrinsically racy.  One thread may become a spare at
307	>	* about the same time as another is needlessly being created. We
308	>	* counteract this and related slop in part by requiring resumed
309	>	* spares to immediately recheck (in preStep) to see whether they
310	>	* should re-suspend.
311	>	*
312	>	* 6. Killing off unneeded workers. A timeout mechanism is used to
313	>	* shed unused workers: The oldest (first) event queue waiter uses
314	>	* a timed rather than hard wait. When this wait times out without
315	>	* a normal wakeup, it tries to shutdown any one (for convenience
316	>	* the newest) other spare or event waiter via
317	>	* tryShutdownUnusedWorker. This eventually reduces the number of
318	>	* worker threads to a minimum of one after a long enough period
319	>	* without use.
320	>	*
321	>	* 7. Deciding when to create new workers. The main dynamic
322	>	* control in this class is deciding when to create extra threads
323	>	* in method helpMaintainParallelism. We would like to keep
324	>	* exactly #parallelism threads running, which is an impossible
325	>	* task. We always need to create one when the number of running
326	>	* threads would become zero and all workers are busy. Beyond
327	>	* this, we must rely on heuristics that work well in the
328	>	* presence of transient phenomena such as GC stalls, dynamic
329	>	* compilation, and wake-up lags. These transients are extremely
330	>	* common -- we are normally trying to fully saturate the CPUs on
331	>	* a machine, so almost any activity other than running tasks
332	>	* impedes accuracy. Our main defense is to allow parallelism to
333	>	* lapse for a while during joins, and use a timeout to see if,
334	>	* after the resulting settling, there is still a need for
335	>	* additional workers.  This also better copes with the fact that
336	>	* some of the methods in this class tend to never become compiled
337	>	* (but are interpreted), so some components of the entire set of
338	>	* controls might execute 100 times faster than others. And
339	>	* similarly for cases where the apparent lack of work is just due
340	>	* to GC stalls and other transient system activity.
341	>	*
342	>	* Beware that there is a lot of representation-level coupling
343	>	* among classes ForkJoinPool, ForkJoinWorkerThread, and
344	>	* ForkJoinTask.  For example, direct access to "workers" array by
345	>	* workers, and direct access to ForkJoinTask.status by both
346	>	* ForkJoinPool and ForkJoinWorkerThread.  There is little point
347	>	* trying to reduce this, since any associated future changes in
348	>	* representations will need to be accompanied by algorithmic
349	>	* changes anyway.
350	>	*
351	>	* Style notes: There are lots of inline assignments (of form
352	>	* "while ((local = field) != 0)") which are usually the simplest
353	>	* way to ensure the required read orderings (which are sometimes
354	>	* critical). Also several occurrences of the unusual "do {}
355	>	* while (!cas...)" which is the simplest way to force an update of
356	>	* a CAS'ed variable. There are also other coding oddities that
357	>	* help some methods perform reasonably even when interpreted (not
358	>	* compiled), at the expense of some messy constructions that
359	>	* reduce byte code counts.
360	>	*
361	>	* The order of declarations in this file is: (1) statics (2)
362	>	* fields (along with constants used when unpacking some of them)
363	>	* (3) internal control methods (4) callbacks and other support
364	>	* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
365	>	* methods (plus a few little helpers).
366	>	*/
367	>
368	>	/**
369	>	* Factory for creating new {@link ForkJoinWorkerThread}s.
370	>	* A {@code ForkJoinWorkerThreadFactory} must be defined and used
371	>	* for {@code ForkJoinWorkerThread} subclasses that extend base
372	>	* functionality or initialize threads with different contexts.
373		*/
374		public static interface ForkJoinWorkerThreadFactory {
375		/**
376		* Returns a new worker thread operating in the given pool.
377		*
378		* @param pool the pool this thread works in
379	<	* @throws NullPointerException if pool is null;
379	>	* @throws NullPointerException if the pool is null
380		*/
381		public ForkJoinWorkerThread newThread(ForkJoinPool pool);
382		}
383
384		/**
385	<	* Default ForkJoinWorkerThreadFactory implementation, creates a
385	>	* Default ForkJoinWorkerThreadFactory implementation; creates a
386		* new ForkJoinWorkerThread.
387		*/
388	<	static class  DefaultForkJoinWorkerThreadFactory
388	>	static class DefaultForkJoinWorkerThreadFactory
389		implements ForkJoinWorkerThreadFactory {
390		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
391	<	try {
97	<	return new ForkJoinWorkerThread(pool);
98	<	} catch (OutOfMemoryError oom)  {
99	<	return null;
100	<	}
391	>	return new ForkJoinWorkerThread(pool);
392		}
393		}
394
#	Line 133 | Line 424 | public class ForkJoinPool extends Abstra
424		new AtomicInteger();
425
426		/**
427	<	* Array holding all worker threads in the pool. Initialized upon
428	<	* first use. Array size must be a power of two.  Updates and
429	<	* replacements are protected by workerLock, but it is always kept
430	<	* in a consistent enough state to be randomly accessed without
431	<	* locking by workers performing work-stealing.
427	>	* The time to block in a join (see awaitJoin) before checking if
428	>	* a new worker should be (re)started to maintain parallelism
429	>	* level. The value should be short enough to maintain global
430	>	* responsiveness and progress but long enough to avoid
431	>	* counterproductive firings during GC stalls or unrelated system
432	>	* activity, and to not bog down systems with continual re-firings
433	>	* on GCs or legitimately long waits.
434	>	*/
435	>	private static final long JOIN_TIMEOUT_MILLIS = 250L; // 4 per second
436	>
437	>	/**
438	>	* The wakeup interval (in nanoseconds) for the oldest worker
439	>	* waiting for an event to invoke tryShutdownUnusedWorker to
440	>	* shrink the number of workers.  The exact value does not matter
441	>	* too much. It must be short enough to release resources during
442	>	* sustained periods of idleness, but not so short that threads
443	>	* are continually re-created.
444	>	*/
445	>	private static final long SHRINK_RATE_NANOS =
446	>	30L * 1000L * 1000L * 1000L; // 2 per minute
447	>
448	>	/**
449	>	* Absolute bound for parallelism level. Twice this number plus
450	>	* one (i.e., 0xfff) must fit into a 16bit field to enable
451	>	* word-packing for some counts and indices.
452	>	*/
453	>	private static final int MAX_WORKERS   = 0x7fff;
454	>
455	>	/**
456	>	* Array holding all worker threads in the pool.  Array size must
457	>	* be a power of two.  Updates and replacements are protected by
458	>	* workerLock, but the array is always kept in a consistent enough
459	>	* state to be randomly accessed without locking by workers
460	>	* performing work-stealing, as well as other traversal-based
461	>	* methods in this class. All readers must tolerate that some
462	>	* array slots may be null.
463		*/
464		volatile ForkJoinWorkerThread[] workers;
465
466		/**
467	<	* Lock protecting access to workers.
467	>	* Queue for external submissions.
468		*/
469	<	private final ReentrantLock workerLock;
469	>	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
470
471		/**
472	<	* Condition for awaitTermination.
472	>	* Lock protecting updates to workers array.
473		*/
474	<	private final Condition termination;
474	>	private final ReentrantLock workerLock;
475
476		/**
477	<	* The uncaught exception handler used when any worker
156	<	* abruptly terminates
477	>	* Latch released upon termination.
478		*/
479	<	private Thread.UncaughtExceptionHandler ueh;
479	>	private final Phaser termination;
480
481		/**
482		* Creation factory for worker threads.
#	Line 163 | Line 484 | public class ForkJoinPool extends Abstra
484		private final ForkJoinWorkerThreadFactory factory;
485
486		/**
166	–	* Head of stack of threads that were created to maintain
167	–	* parallelism when other threads blocked, but have since
168	–	* suspended when the parallelism level rose.
169	–	*/
170	–	private volatile WaitQueueNode spareStack;
171	–
172	–	/**
487		* Sum of per-thread steal counts, updated only when threads are
488		* idle or terminating.
489		*/
490	<	private final AtomicLong stealCount;
490	>	private volatile long stealCount;
491
492		/**
493	<	* Queue for external submissions.
493	>	* Encoded record of top of Treiber stack of threads waiting for
494	>	* events. The top 32 bits contain the count being waited for. The
495	>	* bottom 16 bits contains one plus the pool index of waiting
496	>	* worker thread. (Bits 16-31 are unused.)
497		*/
498	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
498	>	private volatile long eventWaiters;
499
500	<	/**
501	<	* Head of Treiber stack for barrier sync. See below for explanation
185	<	*/
186	<	private volatile WaitQueueNode syncStack;
500	>	private static final int  EVENT_COUNT_SHIFT = 32;
501	>	private static final long WAITER_ID_MASK    = (1L << 16) - 1L;
502
503		/**
504	<	* The count for event barrier
504	>	* A counter for events that may wake up worker threads:
505	>	*   - Submission of a new task to the pool
506	>	*   - A worker pushing a task on an empty queue
507	>	*   - termination
508		*/
509	<	private volatile long eventCount;
509	>	private volatile int eventCount;
510
511		/**
512	<	* Pool number, just for assigning useful names to worker threads
512	>	* Encoded record of top of Treiber stack of spare threads waiting
513	>	* for resumption. The top 16 bits contain an arbitrary count to
514	>	* avoid ABA effects. The bottom 16bits contains one plus the pool
515	>	* index of waiting worker thread.
516		*/
517	<	private final int poolNumber;
517	>	private volatile int spareWaiters;
518
519	<	/**
520	<	* The maximum allowed pool size
200	<	*/
201	<	private volatile int maxPoolSize;
519	>	private static final int SPARE_COUNT_SHIFT = 16;
520	>	private static final int SPARE_ID_MASK     = (1 << 16) - 1;
521
522		/**
523	<	* The desired parallelism level, updated only under workerLock.
523	>	* Lifecycle control. The low word contains the number of workers
524	>	* that are (probably) executing tasks. This value is atomically
525	>	* incremented before a worker gets a task to run, and decremented
526	>	* when worker has no tasks and cannot find any.  Bits 16-18
527	>	* contain runLevel value. When all are zero, the pool is
528	>	* running. Level transitions are monotonic (running -> shutdown
529	>	* -> terminating -> terminated) so each transition adds a bit.
530	>	* These are bundled together to ensure consistent read for
531	>	* termination checks (i.e., that runLevel is at least SHUTDOWN
532	>	* and active threads is zero).
533	>	*
534	>	* Notes: Most direct CASes are dependent on these bitfield
535	>	* positions.  Also, this field is non-private to enable direct
536	>	* performance-sensitive CASes in ForkJoinWorkerThread.
537		*/
538	<	private volatile int parallelism;
538	>	volatile int runState;
539
540	<	/**
541	<	* True if use local fifo, not default lifo, for local polling
542	<	*/
543	<	private volatile boolean locallyFifo;
540	>	// Note: The order among run level values matters.
541	>	private static final int RUNLEVEL_SHIFT     = 16;
542	>	private static final int SHUTDOWN           = 1 << RUNLEVEL_SHIFT;
543	>	private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
544	>	private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
545	>	private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
546
547		/**
548		* Holds number of total (i.e., created and not yet terminated)
549		* and running (i.e., not blocked on joins or other managed sync)
550	<	* threads, packed into one int to ensure consistent snapshot when
550	>	* threads, packed together to ensure consistent snapshot when
551		* making decisions about creating and suspending spare
552	<	* threads. Updated only by CAS.  Note: CASes in
553	<	* updateRunningCount and preJoin running active count is in low
554	<	* word, so need to be modified if this changes
552	>	* threads. Updated only by CAS. Note that adding a new worker
553	>	* requires incrementing both counts, since workers start off in
554	>	* running state.
555		*/
556		private volatile int workerCounts;
557
558	<	private static int totalCountOf(int s)           { return s >>> 16;  }
559	<	private static int runningCountOf(int s)         { return s & shortMask; }
560	<	private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
558	>	private static final int TOTAL_COUNT_SHIFT  = 16;
559	>	private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1;
560	>	private static final int ONE_RUNNING        = 1;
561	>	private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
562
563		/**
564	<	* Adds delta (which may be negative) to running count.  This must
565	<	* be called before (with negative arg) and after (with positive)
231	<	* any managed synchronization (i.e., mainly, joins).
232	<	* @param delta the number to add
564	>	* The target parallelism level.
565	>	* Accessed directly by ForkJoinWorkerThreads.
566		*/
567	<	final void updateRunningCount(int delta) {
235	<	int s;
236	<	do;while (!casWorkerCounts(s = workerCounts, s + delta));
237	<	}
567	>	final int parallelism;
568
569		/**
570	<	* Adds delta (which may be negative) to both total and running
571	<	* count.  This must be called upon creation and termination of
242	<	* worker threads.
243	<	* @param delta the number to add
570	>	* True if use local fifo, not default lifo, for local polling
571	>	* Read by, and replicated by ForkJoinWorkerThreads
572		*/
573	<	private void updateWorkerCount(int delta) {
246	<	int d = delta + (delta << 16); // add to both lo and hi parts
247	<	int s;
248	<	do;while (!casWorkerCounts(s = workerCounts, s + d));
249	<	}
573	>	final boolean locallyFifo;
574
575		/**
576	<	* Lifecycle control. High word contains runState, low word
577	<	* contains the number of workers that are (probably) executing
254	<	* tasks. This value is atomically incremented before a worker
255	<	* gets a task to run, and decremented when worker has no tasks
256	<	* and cannot find any. These two fields are bundled together to
257	<	* support correct termination triggering.  Note: activeCount
258	<	* CAS'es cheat by assuming active count is in low word, so need
259	<	* to be modified if this changes
576	>	* The uncaught exception handler used when any worker abruptly
577	>	* terminates.
578		*/
579	<	private volatile int runControl;
579	>	private final Thread.UncaughtExceptionHandler ueh;
580
581	<	// RunState values. Order among values matters
582	<	private static final int RUNNING     = 0;
583	<	private static final int SHUTDOWN    = 1;
584	<	private static final int TERMINATING = 2;
267	<	private static final int TERMINATED  = 3;
581	>	/**
582	>	* Pool number, just for assigning useful names to worker threads
583	>	*/
584	>	private final int poolNumber;
585
586	<	private static int runStateOf(int c)             { return c >>> 16; }
587	<	private static int activeCountOf(int c)          { return c & shortMask; }
271	<	private static int runControlFor(int r, int a)   { return (r << 16) + a; }
586	>	// Utilities for CASing fields. Note that most of these
587	>	// are usually manually inlined by callers
588
589		/**
590	<	* Try incrementing active count; fail on contention. Called by
275	<	* workers before/during executing tasks.
276	<	* @return true on success;
590	>	* Increments running count part of workerCounts
591		*/
592	<	final boolean tryIncrementActiveCount() {
593	<	int c = runControl;
594	<	return casRunControl(c, c+1);
592	>	final void incrementRunningCount() {
593	>	int c;
594	>	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
595	>	c = workerCounts,
596	>	c + ONE_RUNNING));
597		}
598
599		/**
600	<	* Tries decrementing active count; fails on contention.
285	<	* Possibly triggers termination on success.
286	<	* Called by workers when they can't find tasks.
287	<	* @return true on success
600	>	* Tries to decrement running count unless already zero
601		*/
602	<	final boolean tryDecrementActiveCount() {
603	<	int c = runControl;
604	<	int nextc = c - 1;
292	<	if (!casRunControl(c, nextc))
602	>	final boolean tryDecrementRunningCount() {
603	>	int wc = workerCounts;
604	>	if ((wc & RUNNING_COUNT_MASK) == 0)
605		return false;
606	<	if (canTerminateOnShutdown(nextc))
607	<	terminateOnShutdown();
608	<	return true;
606	>	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
607	>	wc, wc - ONE_RUNNING);
608	>	}
609	>
610	>	/**
611	>	* Forces decrement of encoded workerCounts, awaiting nonzero if
612	>	* (rarely) necessary when other count updates lag.
613	>	*
614	>	* @param dr -- either zero or ONE_RUNNING
615	>	* @param dt -- either zero or ONE_TOTAL
616	>	*/
617	>	private void decrementWorkerCounts(int dr, int dt) {
618	>	for (;;) {
619	>	int wc = workerCounts;
620	>	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
621	>	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) {
622	>	if ((runState & TERMINATED) != 0)
623	>	return; // lagging termination on a backout
624	>	Thread.yield();
625	>	}
626	>	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
627	>	wc, wc - (dr + dt)))
628	>	return;
629	>	}
630		}
631
632		/**
633	<	* Returns true if argument represents zero active count and
634	<	* nonzero runstate, which is the triggering condition for
302	<	* terminating on shutdown.
633	>	* Tries decrementing active count; fails on contention.
634	>	* Called when workers cannot find tasks to run.
635		*/
636	<	private static boolean canTerminateOnShutdown(int c) {
637	<	return ((c & -c) >>> 16) != 0; // i.e. least bit is nonzero runState bit
636	>	final boolean tryDecrementActiveCount() {
637	>	int c;
638	>	return UNSAFE.compareAndSwapInt(this, runStateOffset,
639	>	c = runState, c - 1);
640		}
641
642		/**
643	<	* Transition run state to at least the given state. Return true
644	<	* if not already at least given state.
643	>	* Advances to at least the given level. Returns true if not
644	>	* already in at least the given level.
645		*/
646	<	private boolean transitionRunStateTo(int state) {
646	>	private boolean advanceRunLevel(int level) {
647		for (;;) {
648	<	int c = runControl;
649	<	if (runStateOf(c) >= state)
648	>	int s = runState;
649	>	if ((s & level) != 0)
650		return false;
651	<	if (casRunControl(c, runControlFor(state, activeCountOf(c))))
651	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level))
652		return true;
653		}
654		}
655
656	+	// workers array maintenance
657	+
658		/**
659	<	* Controls whether to add spares to maintain parallelism
659	>	* Records and returns a workers array index for new worker.
660		*/
661	<	private volatile boolean maintainsParallelism;
661	>	private int recordWorker(ForkJoinWorkerThread w) {
662	>	// Try using slot totalCount-1. If not available, scan and/or resize
663	>	int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1;
664	>	final ReentrantLock lock = this.workerLock;
665	>	lock.lock();
666	>	try {
667	>	ForkJoinWorkerThread[] ws = workers;
668	>	int n = ws.length;
669	>	if (k < 0 || k >= n || ws[k] != null) {
670	>	for (k = 0; k < n && ws[k] != null; ++k)
671	>	;
672	>	if (k == n)
673	>	ws = Arrays.copyOf(ws, n << 1);
674	>	}
675	>	ws[k] = w;
676	>	workers = ws; // volatile array write ensures slot visibility
677	>	} finally {
678	>	lock.unlock();
679	>	}
680	>	return k;
681	>	}
682
683	<	// Constructors
683	>	/**
684	>	* Nulls out record of worker in workers array.
685	>	*/
686	>	private void forgetWorker(ForkJoinWorkerThread w) {
687	>	int idx = w.poolIndex;
688	>	// Locking helps method recordWorker avoid unnecessary expansion
689	>	final ReentrantLock lock = this.workerLock;
690	>	lock.lock();
691	>	try {
692	>	ForkJoinWorkerThread[] ws = workers;
693	>	if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify
694	>	ws[idx] = null;
695	>	} finally {
696	>	lock.unlock();
697	>	}
698	>	}
699
700		/**
701	<	* Creates a ForkJoinPool with a pool size equal to the number of
702	<	* processors available on the system and using the default
703	<	* ForkJoinWorkerThreadFactory,
704	<	* @throws SecurityException if a security manager exists and
705	<	*         the caller is not permitted to modify threads
335	<	*         because it does not hold {@link
336	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
701	>	* Final callback from terminating worker.  Removes record of
702	>	* worker from array, and adjusts counts. If pool is shutting
703	>	* down, tries to complete termination.
704	>	*
705	>	* @param w the worker
706		*/
707	<	public ForkJoinPool() {
708	<	this(Runtime.getRuntime().availableProcessors(),
709	<	defaultForkJoinWorkerThreadFactory);
707	>	final void workerTerminated(ForkJoinWorkerThread w) {
708	>	forgetWorker(w);
709	>	decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL);
710	>	while (w.stealCount != 0) // collect final count
711	>	tryAccumulateStealCount(w);
712	>	tryTerminate(false);
713		}
714
715	+	// Waiting for and signalling events
716	+
717		/**
718	<	* Creates a ForkJoinPool with the indicated parallelism level
719	<	* threads, and using the default ForkJoinWorkerThreadFactory,
720	<	* @param parallelism the number of worker threads
721	<	* @throws IllegalArgumentException if parallelism less than or
348	<	* equal to zero
349	<	* @throws SecurityException if a security manager exists and
350	<	*         the caller is not permitted to modify threads
351	<	*         because it does not hold {@link
352	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
718	>	* Releases workers blocked on a count not equal to current count.
719	>	* Normally called after precheck that eventWaiters isn't zero to
720	>	* avoid wasted array checks. Gives up upon a change in count or
721	>	* upon releasing two workers, letting others take over.
722		*/
723	<	public ForkJoinPool(int parallelism) {
724	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
723	>	private void releaseEventWaiters() {
724	>	ForkJoinWorkerThread[] ws = workers;
725	>	int n = ws.length;
726	>	long h = eventWaiters;
727	>	int ec = eventCount;
728	>	boolean releasedOne = false;
729	>	ForkJoinWorkerThread w; int id;
730	>	while ((id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 &&
731	>	(int)(h >>> EVENT_COUNT_SHIFT) != ec &&
732	>	id < n && (w = ws[id]) != null) {
733	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
734	>	h,  w.nextWaiter)) {
735	>	LockSupport.unpark(w);
736	>	if (releasedOne) // exit on second release
737	>	break;
738	>	releasedOne = true;
739	>	}
740	>	if (eventCount != ec)
741	>	break;
742	>	h = eventWaiters;
743	>	}
744		}
745
746		/**
747	<	* Creates a ForkJoinPool with parallelism equal to the number of
748	<	* processors available on the system and using the given
361	<	* ForkJoinWorkerThreadFactory,
362	<	* @param factory the factory for creating new threads
363	<	* @throws NullPointerException if factory is null
364	<	* @throws SecurityException if a security manager exists and
365	<	*         the caller is not permitted to modify threads
366	<	*         because it does not hold {@link
367	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
747	>	* Tries to advance eventCount and releases waiters. Called only
748	>	* from workers.
749		*/
750	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
751	<	this(Runtime.getRuntime().availableProcessors(), factory);
750	>	final void signalWork() {
751	>	int c; // try to increment event count -- CAS failure OK
752	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
753	>	if (eventWaiters != 0L)
754	>	releaseEventWaiters();
755		}
756
757		/**
758	<	* Creates a ForkJoinPool with the given parallelism and factory.
758	>	* Adds the given worker to event queue and blocks until
759	>	* terminating or event count advances from the given value
760		*
761	<	* @param parallelism the targeted number of worker threads
762	<	* @param factory the factory for creating new threads
378	<	* @throws IllegalArgumentException if parallelism less than or
379	<	* equal to zero, or greater than implementation limit.
380	<	* @throws NullPointerException if factory is null
381	<	* @throws SecurityException if a security manager exists and
382	<	*         the caller is not permitted to modify threads
383	<	*         because it does not hold {@link
384	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
761	>	* @param w the calling worker thread
762	>	* @param ec the count
763		*/
764	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
765	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
766	<	throw new IllegalArgumentException();
767	<	if (factory == null)
768	<	throw new NullPointerException();
769	<	checkPermission();
770	<	this.factory = factory;
771	<	this.parallelism = parallelism;
772	<	this.maxPoolSize = MAX_THREADS;
773	<	this.maintainsParallelism = true;
774	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
775	<	this.workerLock = new ReentrantLock();
776	<	this.termination = workerLock.newCondition();
399	<	this.stealCount = new AtomicLong();
400	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
401	<	// worker array and workers are lazily constructed
764	>	private void eventSync(ForkJoinWorkerThread w, int ec) {
765	>	long nh = (((long)ec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
766	>	long h;
767	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
768	>	(((int)((h = eventWaiters) & WAITER_ID_MASK)) == 0 ||
769	>	(int)(h >>> EVENT_COUNT_SHIFT) == ec) &&
770	>	eventCount == ec) {
771	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
772	>	w.nextWaiter = h, nh)) {
773	>	awaitEvent(w, ec);
774	>	break;
775	>	}
776	>	}
777		}
778
779		/**
780	<	* Create new worker using factory.
781	<	* @param index the index to assign worker
782	<	* @return new worker, or null of factory failed
780	>	* Blocks the given worker (that has already been entered as an
781	>	* event waiter) until terminating or event count advances from
782	>	* the given value. The oldest (first) waiter uses a timed wait to
783	>	* occasionally one-by-one shrink the number of workers (to a
784	>	* minimum of one) if the pool has not been used for extended
785	>	* periods.
786	>	*
787	>	* @param w the calling worker thread
788	>	* @param ec the count
789		*/
790	<	private ForkJoinWorkerThread createWorker(int index) {
791	<	Thread.UncaughtExceptionHandler h = ueh;
792	<	ForkJoinWorkerThread w = factory.newThread(this);
793	<	if (w != null) {
794	<	w.poolIndex = index;
795	<	w.setDaemon(true);
796	<	w.setAsyncMode(locallyFifo);
797	<	w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
798	<	if (h != null)
799	<	w.setUncaughtExceptionHandler(h);
790	>	private void awaitEvent(ForkJoinWorkerThread w, int ec) {
791	>	while (eventCount == ec) {
792	>	if (tryAccumulateStealCount(w)) { // transfer while idle
793	>	boolean untimed = (w.nextWaiter != 0L ||
794	>	(workerCounts & RUNNING_COUNT_MASK) <= 1);
795	>	long startTime = untimed? 0 : System.nanoTime();
796	>	Thread.interrupted();         // clear/ignore interrupt
797	>	if (eventCount != ec || w.runState != 0 ||
798	>	runState >= TERMINATING)  // recheck after clear
799	>	break;
800	>	if (untimed)
801	>	LockSupport.park(w);
802	>	else {
803	>	LockSupport.parkNanos(w, SHRINK_RATE_NANOS);
804	>	if (eventCount != ec || w.runState != 0 ||
805	>	runState >= TERMINATING)
806	>	break;
807	>	if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS)
808	>	tryShutdownUnusedWorker(ec);
809	>	}
810	>	}
811		}
420	–	return w;
812		}
813
814	+	// Maintaining parallelism
815	+
816		/**
817	<	* Returns a good size for worker array given pool size.
425	<	* Currently requires size to be a power of two.
817	>	* Pushes worker onto the spare stack.
818		*/
819	<	private static int arraySizeFor(int ps) {
820	<	return ps <= 1? 1 : (1 << (32 - Integer.numberOfLeadingZeros(ps-1)));
819	>	final void pushSpare(ForkJoinWorkerThread w) {
820	>	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1);
821	>	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
822	>	w.nextSpare = spareWaiters,ns));
823		}
824
825		/**
826	<	* Creates or resizes array if necessary to hold newLength.
827	<	* Call only under exclusion or lock.
434	<	* @return the array
826	>	* Tries (once) to resume a spare if the number of running
827	>	* threads is less than target.
828		*/
829	<	private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
829	>	private void tryResumeSpare() {
830	>	int sw, id;
831		ForkJoinWorkerThread[] ws = workers;
832	<	if (ws == null)
833	<	return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
834	<	else if (newLength > ws.length)
835	<	return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
836	<	else
837	<	return ws;
832	>	int n = ws.length;
833	>	ForkJoinWorkerThread w;
834	>	if ((sw = spareWaiters) != 0 &&
835	>	(id = (sw & SPARE_ID_MASK) - 1) >= 0 &&
836	>	id < n && (w = ws[id]) != null &&
837	>	(workerCounts & RUNNING_COUNT_MASK) < parallelism &&
838	>	spareWaiters == sw &&
839	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
840	>	sw, w.nextSpare)) {
841	>	int c; // increment running count before resume
842	>	do {} while (!UNSAFE.compareAndSwapInt
843	>	(this, workerCountsOffset,
844	>	c = workerCounts, c + ONE_RUNNING));
845	>	if (w.tryUnsuspend())
846	>	LockSupport.unpark(w);
847	>	else   // back out if w was shutdown
848	>	decrementWorkerCounts(ONE_RUNNING, 0);
849	>	}
850		}
851
852		/**
853	<	* Try to shrink workers into smaller array after one or more terminate
854	<	*/
855	<	private void tryShrinkWorkerArray() {
856	<	ForkJoinWorkerThread[] ws = workers;
857	<	if (ws != null) {
858	<	int len = ws.length;
859	<	int last = len - 1;
860	<	while (last >= 0 && ws[last] == null)
861	<	--last;
862	<	int newLength = arraySizeFor(last+1);
863	<	if (newLength < len)
864	<	workers = Arrays.copyOf(ws, newLength);
853	>	* Tries to increase the number of running workers if below target
854	>	* parallelism: If a spare exists tries to resume it via
855	>	* tryResumeSpare.  Otherwise, if not enough total workers or all
856	>	* existing workers are busy, adds a new worker. In all cases also
857	>	* helps wake up releasable workers waiting for work.
858	>	*/
859	>	private void helpMaintainParallelism() {
860	>	int pc = parallelism;
861	>	int wc, rs, tc;
862	>	while (((wc = workerCounts) & RUNNING_COUNT_MASK) < pc &&
863	>	(rs = runState) < TERMINATING) {
864	>	if (spareWaiters != 0)
865	>	tryResumeSpare();
866	>	else if ((tc = wc >>> TOTAL_COUNT_SHIFT) >= MAX_WORKERS ||
867	>	(tc >= pc && (rs & ACTIVE_COUNT_MASK) != tc))
868	>	break;   // enough total
869	>	else if (runState == rs && workerCounts == wc &&
870	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
871	>	wc + (ONE_RUNNING|ONE_TOTAL))) {
872	>	ForkJoinWorkerThread w = null;
873	>	try {
874	>	w = factory.newThread(this);
875	>	} finally { // adjust on null or exceptional factory return
876	>	if (w == null) {
877	>	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
878	>	tryTerminate(false); // handle failure during shutdown
879	>	}
880	>	}
881	>	if (w == null)
882	>	break;
883	>	w.start(recordWorker(w), ueh);
884	>	if ((workerCounts >>> TOTAL_COUNT_SHIFT) >= pc) {
885	>	int c; // advance event count
886	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
887	>	c = eventCount, c+1);
888	>	break; // add at most one unless total below target
889	>	}
890	>	}
891		}
892	+	if (eventWaiters != 0L)
893	+	releaseEventWaiters();
894		}
895
896		/**
897	<	* Initialize workers if necessary
897	>	* Callback from the oldest waiter in awaitEvent waking up after a
898	>	* period of non-use. If all workers are idle, tries (once) to
899	>	* shutdown an event waiter or a spare, if one exists. Note that
900	>	* we don't need CAS or locks here because the method is called
901	>	* only from one thread occasionally waking (and even misfires are
902	>	* OK). Note that until the shutdown worker fully terminates,
903	>	* workerCounts will overestimate total count, which is tolerable.
904	>	*
905	>	* @param ec the event count waited on by caller (to abort
906	>	* attempt if count has since changed).
907		*/
908	<	final void ensureWorkerInitialization() {
909	<	ForkJoinWorkerThread[] ws = workers;
910	<	if (ws == null) {
911	<	final ReentrantLock lock = this.workerLock;
912	<	lock.lock();
913	<	try {
914	<	ws = workers;
915	<	if (ws == null) {
916	<	int ps = parallelism;
917	<	ws = ensureWorkerArrayCapacity(ps);
918	<	for (int i = 0; i < ps; ++i) {
919	<	ForkJoinWorkerThread w = createWorker(i);
920	<	if (w != null) {
921	<	ws[i] = w;
922	<	w.start();
923	<	updateWorkerCount(1);
924	<	}
925	<	}
908	>	private void tryShutdownUnusedWorker(int ec) {
909	>	if (runState == 0 && eventCount == ec) { // only trigger if all idle
910	>	ForkJoinWorkerThread[] ws = workers;
911	>	int n = ws.length;
912	>	ForkJoinWorkerThread w = null;
913	>	boolean shutdown = false;
914	>	int sw;
915	>	long h;
916	>	if ((sw = spareWaiters) != 0) { // prefer killing spares
917	>	int id = (sw & SPARE_ID_MASK) - 1;
918	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
919	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
920	>	sw, w.nextSpare))
921	>	shutdown = true;
922	>	}
923	>	else if ((h = eventWaiters) != 0L) {
924	>	long nh;
925	>	int id = ((int)(h & WAITER_ID_MASK)) - 1;
926	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
927	>	(nh = w.nextWaiter) != 0L && // keep at least one worker
928	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh))
929	>	shutdown = true;
930	>	}
931	>	if (w != null && shutdown) {
932	>	w.shutdown();
933	>	LockSupport.unpark(w);
934	>	}
935	>	}
936	>	releaseEventWaiters(); // in case of interference
937	>	}
938	>
939	>	/**
940	>	* Callback from workers invoked upon each top-level action (i.e.,
941	>	* stealing a task or taking a submission and running it).
942	>	* Performs one or more of the following:
943	>	*
944	>	* 1. If the worker is active and either did not run a task
945	>	*    or there are too many workers, try to set its active status
946	>	*    to inactive and update activeCount. On contention, we may
947	>	*    try again in this or a subsequent call.
948	>	*
949	>	* 2. If not enough total workers, help create some.
950	>	*
951	>	* 3. If there are too many running workers, suspend this worker
952	>	*    (first forcing inactive if necessary).  If it is not needed,
953	>	*    it may be shutdown while suspended (via
954	>	*    tryShutdownUnusedWorker).  Otherwise, upon resume it
955	>	*    rechecks running thread count and need for event sync.
956	>	*
957	>	* 4. If worker did not run a task, await the next task event via
958	>	*    eventSync if necessary (first forcing inactivation), upon
959	>	*    which the worker may be shutdown via
960	>	*    tryShutdownUnusedWorker.  Otherwise, help release any
961	>	*    existing event waiters that are now releasable,
962	>	*
963	>	* @param w the worker
964	>	* @param ran true if worker ran a task since last call to this method
965	>	*/
966	>	final void preStep(ForkJoinWorkerThread w, boolean ran) {
967	>	int wec = w.lastEventCount;
968	>	boolean active = w.active;
969	>	boolean inactivate = false;
970	>	int pc = parallelism;
971	>	int rs;
972	>	while (w.runState == 0 && (rs = runState) < TERMINATING) {
973	>	if ((inactivate || (active && (rs & ACTIVE_COUNT_MASK) >= pc)) &&
974	>	UNSAFE.compareAndSwapInt(this, runStateOffset, rs, rs - 1))
975	>	inactivate = active = w.active = false;
976	>	int wc = workerCounts;
977	>	if ((wc & RUNNING_COUNT_MASK) > pc) {
978	>	if (!(inactivate |= active) && // must inactivate to suspend
979	>	workerCounts == wc &&      // try to suspend as spare
980	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
981	>	wc, wc - ONE_RUNNING))
982	>	w.suspendAsSpare();
983	>	}
984	>	else if ((wc >>> TOTAL_COUNT_SHIFT) < pc)
985	>	helpMaintainParallelism();     // not enough workers
986	>	else if (!ran) {
987	>	long h = eventWaiters;
988	>	int ec = eventCount;
989	>	if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != ec)
990	>	releaseEventWaiters();     // release others before waiting
991	>	else if (ec != wec) {
992	>	w.lastEventCount = ec;     // no need to wait
993	>	break;
994		}
995	<	} finally {
996	<	lock.unlock();
995	>	else if (!(inactivate |= active))
996	>	eventSync(w, wec);         // must inactivate before sync
997		}
998	+	else
999	+	break;
1000		}
1001		}
1002
1003		/**
1004	<	* Worker creation and startup for threads added via setParallelism.
1004	>	* Helps and/or blocks awaiting join of the given task.
1005	>	* See above for explanation.
1006	>	*
1007	>	* @param joinMe the task to join
1008	>	* @param worker the current worker thread
1009		*/
1010	<	private void createAndStartAddedWorkers() {
1011	<	resumeAllSpares();  // Allow spares to convert to nonspare
1012	<	int ps = parallelism;
1013	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
1014	<	int len = ws.length;
1015	<	// Sweep through slots, to keep lowest indices most populated
1016	<	int k = 0;
1017	<	while (k < len) {
1018	<	if (ws[k] != null) {
1019	<	++k;
1020	<	continue;
1010	>	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) {
1011	>	int retries = 2 + (parallelism >> 2); // #helpJoins before blocking
1012	>	while (joinMe.status >= 0) {
1013	>	int wc;
1014	>	worker.helpJoinTask(joinMe);
1015	>	if (joinMe.status < 0)
1016	>	break;
1017	>	else if (retries > 0)
1018	>	--retries;
1019	>	else if (((wc = workerCounts) & RUNNING_COUNT_MASK) != 0 &&
1020	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1021	>	wc, wc - ONE_RUNNING)) {
1022	>	int stat, c; long h;
1023	>	while ((stat = joinMe.status) >= 0 &&
1024	>	(h = eventWaiters) != 0L && // help release others
1025	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1026	>	releaseEventWaiters();
1027	>	if (stat >= 0 &&
1028	>	((workerCounts & RUNNING_COUNT_MASK) == 0 ||
1029	>	(stat =
1030	>	joinMe.internalAwaitDone(JOIN_TIMEOUT_MILLIS)) >= 0))
1031	>	helpMaintainParallelism(); // timeout or no running workers
1032	>	do {} while (!UNSAFE.compareAndSwapInt
1033	>	(this, workerCountsOffset,
1034	>	c = workerCounts, c + ONE_RUNNING));
1035	>	if (stat < 0)
1036	>	break;   // else restart
1037		}
1038	<	int s = workerCounts;
1039	<	int tc = totalCountOf(s);
1040	<	int rc = runningCountOf(s);
1041	<	if (rc >= ps || tc >= ps)
1038	>	}
1039	>	}
1040	>
1041	>	/**
1042	>	* Same idea as awaitJoin, but no helping, retries, or timeouts.
1043	>	*/
1044	>	final void awaitBlocker(ManagedBlocker blocker)
1045	>	throws InterruptedException {
1046	>	while (!blocker.isReleasable()) {
1047	>	int wc = workerCounts;
1048	>	if ((wc & RUNNING_COUNT_MASK) != 0 &&
1049	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1050	>	wc, wc - ONE_RUNNING)) {
1051	>	try {
1052	>	while (!blocker.isReleasable()) {
1053	>	long h = eventWaiters;
1054	>	if (h != 0L &&
1055	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1056	>	releaseEventWaiters();
1057	>	else if ((workerCounts & RUNNING_COUNT_MASK) == 0 &&
1058	>	runState < TERMINATING)
1059	>	helpMaintainParallelism();
1060	>	else if (blocker.block())
1061	>	break;
1062	>	}
1063	>	} finally {
1064	>	int c;
1065	>	do {} while (!UNSAFE.compareAndSwapInt
1066	>	(this, workerCountsOffset,
1067	>	c = workerCounts, c + ONE_RUNNING));
1068	>	}
1069		break;
1070	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
1071	<	ForkJoinWorkerThread w = createWorker(k);
1070	>	}
1071	>	}
1072	>	}
1073	>
1074	>	/**
1075	>	* Possibly initiates and/or completes termination.
1076	>	*
1077	>	* @param now if true, unconditionally terminate, else only
1078	>	* if shutdown and empty queue and no active workers
1079	>	* @return true if now terminating or terminated
1080	>	*/
1081	>	private boolean tryTerminate(boolean now) {
1082	>	if (now)
1083	>	advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
1084	>	else if (runState < SHUTDOWN ||
1085	>	!submissionQueue.isEmpty() ||
1086	>	(runState & ACTIVE_COUNT_MASK) != 0)
1087	>	return false;
1088	>
1089	>	if (advanceRunLevel(TERMINATING))
1090	>	startTerminating();
1091	>
1092	>	// Finish now if all threads terminated; else in some subsequent call
1093	>	if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1094	>	advanceRunLevel(TERMINATED);
1095	>	termination.arrive();
1096	>	}
1097	>	return true;
1098	>	}
1099	>
1100	>	/**
1101	>	* Actions on transition to TERMINATING
1102	>	*
1103	>	* Runs up to four passes through workers: (0) shutting down each
1104	>	* (without waking up if parked) to quickly spread notifications
1105	>	* without unnecessary bouncing around event queues etc (1) wake
1106	>	* up and help cancel tasks (2) interrupt (3) mop up races with
1107	>	* interrupted workers
1108	>	*/
1109	>	private void startTerminating() {
1110	>	cancelSubmissions();
1111	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1112	>	int c; // advance event count
1113	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
1114	>	c = eventCount, c+1);
1115	>	eventWaiters = 0L; // clobber lists
1116	>	spareWaiters = 0;
1117	>	for (ForkJoinWorkerThread w : workers) {
1118		if (w != null) {
1119	<	ws[k++] = w;
1120	<	w.start();
1121	<	}
1122	<	else {
1123	<	updateWorkerCount(-1); // back out on failed creation
1124	<	break;
1119	>	w.shutdown();
1120	>	if (passes > 0 && !w.isTerminated()) {
1121	>	w.cancelTasks();
1122	>	LockSupport.unpark(w);
1123	>	if (passes > 1) {
1124	>	try {
1125	>	w.interrupt();
1126	>	} catch (SecurityException ignore) {
1127	>	}
1128	>	}
1129	>	}
1130		}
1131		}
1132		}
1133		}
1134
1135	+	/**
1136	+	* Clears out and cancels submissions, ignoring exceptions.
1137	+	*/
1138	+	private void cancelSubmissions() {
1139	+	ForkJoinTask<?> task;
1140	+	while ((task = submissionQueue.poll()) != null) {
1141	+	try {
1142	+	task.cancel(false);
1143	+	} catch (Throwable ignore) {
1144	+	}
1145	+	}
1146	+	}
1147	+
1148	+	// misc support for ForkJoinWorkerThread
1149	+
1150	+	/**
1151	+	* Returns pool number.
1152	+	*/
1153	+	final int getPoolNumber() {
1154	+	return poolNumber;
1155	+	}
1156	+
1157	+	/**
1158	+	* Tries to accumulate steal count from a worker, clearing
1159	+	* the worker's value if successful.
1160	+	*
1161	+	* @return true if worker steal count now zero
1162	+	*/
1163	+	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1164	+	int sc = w.stealCount;
1165	+	long c = stealCount;
1166	+	// CAS even if zero, for fence effects
1167	+	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1168	+	if (sc != 0)
1169	+	w.stealCount = 0;
1170	+	return true;
1171	+	}
1172	+	return sc == 0;
1173	+	}
1174	+
1175	+	/**
1176	+	* Returns the approximate (non-atomic) number of idle threads per
1177	+	* active thread.
1178	+	*/
1179	+	final int idlePerActive() {
1180	+	int pc = parallelism; // use parallelism, not rc
1181	+	int ac = runState;    // no mask -- artificially boosts during shutdown
1182	+	// Use exact results for small values, saturate past 4
1183	+	return ((pc <= ac) ? 0 :
1184	+	(pc >>> 1 <= ac) ? 1 :
1185	+	(pc >>> 2 <= ac) ? 3 :
1186	+	pc >>> 3);
1187	+	}
1188	+
1189	+	// Public and protected methods
1190	+
1191	+	// Constructors
1192	+
1193	+	/**
1194	+	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1195	+	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1196	+	* #defaultForkJoinWorkerThreadFactory default thread factory},
1197	+	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1198	+	*
1199	+	* @throws SecurityException if a security manager exists and
1200	+	*         the caller is not permitted to modify threads
1201	+	*         because it does not hold {@link
1202	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1203	+	*/
1204	+	public ForkJoinPool() {
1205	+	this(Runtime.getRuntime().availableProcessors(),
1206	+	defaultForkJoinWorkerThreadFactory, null, false);
1207	+	}
1208	+
1209	+	/**
1210	+	* Creates a {@code ForkJoinPool} with the indicated parallelism
1211	+	* level, the {@linkplain
1212	+	* #defaultForkJoinWorkerThreadFactory default thread factory},
1213	+	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1214	+	*
1215	+	* @param parallelism the parallelism level
1216	+	* @throws IllegalArgumentException if parallelism less than or
1217	+	*         equal to zero, or greater than implementation limit
1218	+	* @throws SecurityException if a security manager exists and
1219	+	*         the caller is not permitted to modify threads
1220	+	*         because it does not hold {@link
1221	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1222	+	*/
1223	+	public ForkJoinPool(int parallelism) {
1224	+	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1225	+	}
1226	+
1227	+	/**
1228	+	* Creates a {@code ForkJoinPool} with the given parameters.
1229	+	*
1230	+	* @param parallelism the parallelism level. For default value,
1231	+	* use {@link java.lang.Runtime#availableProcessors}.
1232	+	* @param factory the factory for creating new threads. For default value,
1233	+	* use {@link #defaultForkJoinWorkerThreadFactory}.
1234	+	* @param handler the handler for internal worker threads that
1235	+	* terminate due to unrecoverable errors encountered while executing
1236	+	* tasks. For default value, use {@code null}.
1237	+	* @param asyncMode if true,
1238	+	* establishes local first-in-first-out scheduling mode for forked
1239	+	* tasks that are never joined. This mode may be more appropriate
1240	+	* than default locally stack-based mode in applications in which
1241	+	* worker threads only process event-style asynchronous tasks.
1242	+	* For default value, use {@code false}.
1243	+	* @throws IllegalArgumentException if parallelism less than or
1244	+	*         equal to zero, or greater than implementation limit
1245	+	* @throws NullPointerException if the factory is null
1246	+	* @throws SecurityException if a security manager exists and
1247	+	*         the caller is not permitted to modify threads
1248	+	*         because it does not hold {@link
1249	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1250	+	*/
1251	+	public ForkJoinPool(int parallelism,
1252	+	ForkJoinWorkerThreadFactory factory,
1253	+	Thread.UncaughtExceptionHandler handler,
1254	+	boolean asyncMode) {
1255	+	checkPermission();
1256	+	if (factory == null)
1257	+	throw new NullPointerException();
1258	+	if (parallelism <= 0 || parallelism > MAX_WORKERS)
1259	+	throw new IllegalArgumentException();
1260	+	this.parallelism = parallelism;
1261	+	this.factory = factory;
1262	+	this.ueh = handler;
1263	+	this.locallyFifo = asyncMode;
1264	+	int arraySize = initialArraySizeFor(parallelism);
1265	+	this.workers = new ForkJoinWorkerThread[arraySize];
1266	+	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1267	+	this.workerLock = new ReentrantLock();
1268	+	this.termination = new Phaser(1);
1269	+	this.poolNumber = poolNumberGenerator.incrementAndGet();
1270	+	}
1271	+
1272	+	/**
1273	+	* Returns initial power of two size for workers array.
1274	+	* @param pc the initial parallelism level
1275	+	*/
1276	+	private static int initialArraySizeFor(int pc) {
1277	+	// If possible, initially allocate enough space for one spare
1278	+	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1279	+	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1280	+	size |= size >>> 1;
1281	+	size |= size >>> 2;
1282	+	size |= size >>> 4;
1283	+	size |= size >>> 8;
1284	+	return size + 1;
1285	+	}
1286	+
1287		// Execution methods
1288
1289		/**
1290		* Common code for execute, invoke and submit
1291		*/
1292		private <T> void doSubmit(ForkJoinTask<T> task) {
1293	<	if (isShutdown())
1293	>	if (task == null)
1294	>	throw new NullPointerException();
1295	>	if (runState >= SHUTDOWN)
1296		throw new RejectedExecutionException();
532	–	if (workers == null)
533	–	ensureWorkerInitialization();
1297		submissionQueue.offer(task);
1298	<	signalIdleWorkers();
1298	>	int c; // try to increment event count -- CAS failure OK
1299	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
1300	>	helpMaintainParallelism(); // create, start, or resume some workers
1301		}
1302
1303		/**
1304	<	* Performs the given task; returning its result upon completion
1304	>	* Performs the given task, returning its result upon completion.
1305	>	*
1306		* @param task the task
1307		* @return the task's result
1308	<	* @throws NullPointerException if task is null
1309	<	* @throws RejectedExecutionException if pool is shut down
1308	>	* @throws NullPointerException if the task is null
1309	>	* @throws RejectedExecutionException if the task cannot be
1310	>	*         scheduled for execution
1311		*/
1312		public <T> T invoke(ForkJoinTask<T> task) {
1313		doSubmit(task);
#	Line 549 | Line 1316 | public class ForkJoinPool extends Abstra
1316
1317		/**
1318		* Arranges for (asynchronous) execution of the given task.
1319	+	*
1320		* @param task the task
1321	<	* @throws NullPointerException if task is null
1322	<	* @throws RejectedExecutionException if pool is shut down
1321	>	* @throws NullPointerException if the task is null
1322	>	* @throws RejectedExecutionException if the task cannot be
1323	>	*         scheduled for execution
1324		*/
1325	<	public <T> void execute(ForkJoinTask<T> task) {
1325	>	public void execute(ForkJoinTask<?> task) {
1326		doSubmit(task);
1327		}
1328
1329		// AbstractExecutorService methods
1330
1331	+	/**
1332	+	* @throws NullPointerException if the task is null
1333	+	* @throws RejectedExecutionException if the task cannot be
1334	+	*         scheduled for execution
1335	+	*/
1336		public void execute(Runnable task) {
1337	<	doSubmit(new AdaptedRunnable<Void>(task, null));
1337	>	ForkJoinTask<?> job;
1338	>	if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1339	>	job = (ForkJoinTask<?>) task;
1340	>	else
1341	>	job = ForkJoinTask.adapt(task, null);
1342	>	doSubmit(job);
1343	>	}
1344	>
1345	>	/**
1346	>	* Submits a ForkJoinTask for execution.
1347	>	*
1348	>	* @param task the task to submit
1349	>	* @return the task
1350	>	* @throws NullPointerException if the task is null
1351	>	* @throws RejectedExecutionException if the task cannot be
1352	>	*         scheduled for execution
1353	>	*/
1354	>	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1355	>	doSubmit(task);
1356	>	return task;
1357		}
1358
1359	+	/**
1360	+	* @throws NullPointerException if the task is null
1361	+	* @throws RejectedExecutionException if the task cannot be
1362	+	*         scheduled for execution
1363	+	*/
1364		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1365	<	ForkJoinTask<T> job = new AdaptedCallable<T>(task);
1365	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1366		doSubmit(job);
1367		return job;
1368		}
1369
1370	+	/**
1371	+	* @throws NullPointerException if the task is null
1372	+	* @throws RejectedExecutionException if the task cannot be
1373	+	*         scheduled for execution
1374	+	*/
1375		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1376	<	ForkJoinTask<T> job = new AdaptedRunnable<T>(task, result);
1376	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1377		doSubmit(job);
1378		return job;
1379		}
1380
1381	+	/**
1382	+	* @throws NullPointerException if the task is null
1383	+	* @throws RejectedExecutionException if the task cannot be
1384	+	*         scheduled for execution
1385	+	*/
1386		public ForkJoinTask<?> submit(Runnable task) {
1387	<	ForkJoinTask<Void> job = new AdaptedRunnable<Void>(task, null);
1387	>	ForkJoinTask<?> job;
1388	>	if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1389	>	job = (ForkJoinTask<?>) task;
1390	>	else
1391	>	job = ForkJoinTask.adapt(task, null);
1392		doSubmit(job);
1393		return job;
1394		}
1395
1396		/**
1397	<	* Adaptor for Runnables. This implements RunnableFuture
1398	<	* to be compliant with AbstractExecutorService constraints
1397	>	* @throws NullPointerException       {@inheritDoc}
1398	>	* @throws RejectedExecutionException {@inheritDoc}
1399		*/
588	–	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
589	–	implements RunnableFuture<T> {
590	–	final Runnable runnable;
591	–	final T resultOnCompletion;
592	–	T result;
593	–	AdaptedRunnable(Runnable runnable, T result) {
594	–	if (runnable == null) throw new NullPointerException();
595	–	this.runnable = runnable;
596	–	this.resultOnCompletion = result;
597	–	}
598	–	public T getRawResult() { return result; }
599	–	public void setRawResult(T v) { result = v; }
600	–	public boolean exec() {
601	–	runnable.run();
602	–	result = resultOnCompletion;
603	–	return true;
604	–	}
605	–	public void run() { invoke(); }
606	–	}
607	–
608	–	/**
609	–	* Adaptor for Callables
610	–	*/
611	–	static final class AdaptedCallable<T> extends ForkJoinTask<T>
612	–	implements RunnableFuture<T> {
613	–	final Callable<T> callable;
614	–	T result;
615	–	AdaptedCallable(Callable<T> callable) {
616	–	if (callable == null) throw new NullPointerException();
617	–	this.callable = callable;
618	–	}
619	–	public T getRawResult() { return result; }
620	–	public void setRawResult(T v) { result = v; }
621	–	public boolean exec() {
622	–	try {
623	–	result = callable.call();
624	–	return true;
625	–	} catch (Error err) {
626	–	throw err;
627	–	} catch (RuntimeException rex) {
628	–	throw rex;
629	–	} catch (Exception ex) {
630	–	throw new RuntimeException(ex);
631	–	}
632	–	}
633	–	public void run() { invoke(); }
634	–	}
635	–
1400		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
1401	<	ArrayList<ForkJoinTask<T>> ts =
1401	>	ArrayList<ForkJoinTask<T>> forkJoinTasks =
1402		new ArrayList<ForkJoinTask<T>>(tasks.size());
1403	<	for (Callable<T> c : tasks)
1404	<	ts.add(new AdaptedCallable<T>(c));
1405	<	invoke(new InvokeAll<T>(ts));
1406	<	return (List<Future<T>>)(List)ts;
1403	>	for (Callable<T> task : tasks)
1404	>	forkJoinTasks.add(ForkJoinTask.adapt(task));
1405	>	invoke(new InvokeAll<T>(forkJoinTasks));
1406	>
1407	>	@SuppressWarnings({"unchecked", "rawtypes"})
1408	>	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1409	>	return futures;
1410		}
1411
1412		static final class InvokeAll<T> extends RecursiveAction {
1413		final ArrayList<ForkJoinTask<T>> tasks;
1414		InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; }
1415		public void compute() {
1416	<	try { invokeAll(tasks); } catch(Exception ignore) {}
1416	>	try { invokeAll(tasks); }
1417	>	catch (Exception ignore) {}
1418		}
1419	+	private static final long serialVersionUID = -7914297376763021607L;
1420		}
1421
653	–	// Configuration and status settings and queries
654	–
1422		/**
1423	<	* Returns the factory used for constructing new workers
1423	>	* Returns the factory used for constructing new workers.
1424		*
1425		* @return the factory used for constructing new workers
1426		*/
#	Line 664 | Line 1431 | public class ForkJoinPool extends Abstra
1431		/**
1432		* Returns the handler for internal worker threads that terminate
1433		* due to unrecoverable errors encountered while executing tasks.
667	–	* @return the handler, or null if none
668	–	*/
669	–	public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
670	–	Thread.UncaughtExceptionHandler h;
671	–	final ReentrantLock lock = this.workerLock;
672	–	lock.lock();
673	–	try {
674	–	h = ueh;
675	–	} finally {
676	–	lock.unlock();
677	–	}
678	–	return h;
679	–	}
680	–
681	–	/**
682	–	* Sets the handler for internal worker threads that terminate due
683	–	* to unrecoverable errors encountered while executing tasks.
684	–	* Unless set, the current default or ThreadGroup handler is used
685	–	* as handler.
1434		*
1435	<	* @param h the new handler
688	<	* @return the old handler, or null if none
689	<	* @throws SecurityException if a security manager exists and
690	<	*         the caller is not permitted to modify threads
691	<	*         because it does not hold {@link
692	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
693	<	*/
694	<	public Thread.UncaughtExceptionHandler
695	<	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
696	<	checkPermission();
697	<	Thread.UncaughtExceptionHandler old = null;
698	<	final ReentrantLock lock = this.workerLock;
699	<	lock.lock();
700	<	try {
701	<	old = ueh;
702	<	ueh = h;
703	<	ForkJoinWorkerThread[] ws = workers;
704	<	if (ws != null) {
705	<	for (int i = 0; i < ws.length; ++i) {
706	<	ForkJoinWorkerThread w = ws[i];
707	<	if (w != null)
708	<	w.setUncaughtExceptionHandler(h);
709	<	}
710	<	}
711	<	} finally {
712	<	lock.unlock();
713	<	}
714	<	return old;
715	<	}
716	<
717	<
718	<	/**
719	<	* Sets the target parallelism level of this pool.
720	<	* @param parallelism the target parallelism
721	<	* @throws IllegalArgumentException if parallelism less than or
722	<	* equal to zero or greater than maximum size bounds.
723	<	* @throws SecurityException if a security manager exists and
724	<	*         the caller is not permitted to modify threads
725	<	*         because it does not hold {@link
726	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
1435	>	* @return the handler, or {@code null} if none
1436		*/
1437	<	public void setParallelism(int parallelism) {
1438	<	checkPermission();
730	<	if (parallelism <= 0 || parallelism > maxPoolSize)
731	<	throw new IllegalArgumentException();
732	<	final ReentrantLock lock = this.workerLock;
733	<	lock.lock();
734	<	try {
735	<	if (!isTerminating()) {
736	<	int p = this.parallelism;
737	<	this.parallelism = parallelism;
738	<	if (parallelism > p)
739	<	createAndStartAddedWorkers();
740	<	else
741	<	trimSpares();
742	<	}
743	<	} finally {
744	<	lock.unlock();
745	<	}
746	<	signalIdleWorkers();
1437	>	public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1438	>	return ueh;
1439		}
1440
1441		/**
1442	<	* Returns the targeted number of worker threads in this pool.
1442	>	* Returns the targeted parallelism level of this pool.
1443		*
1444	<	* @return the targeted number of worker threads in this pool
1444	>	* @return the targeted parallelism level of this pool
1445		*/
1446		public int getParallelism() {
1447		return parallelism;
#	Line 757 | Line 1449 | public class ForkJoinPool extends Abstra
1449
1450		/**
1451		* Returns the number of worker threads that have started but not
1452	<	* yet terminated.  This result returned by this method may differ
1453	<	* from {@code getParallelism} when threads are created to
1452	>	* yet terminated.  The result returned by this method may differ
1453	>	* from {@link #getParallelism} when threads are created to
1454		* maintain parallelism when others are cooperatively blocked.
1455		*
1456		* @return the number of worker threads
1457		*/
1458		public int getPoolSize() {
1459	<	return totalCountOf(workerCounts);
768	<	}
769	<
770	<	/**
771	<	* Returns the maximum number of threads allowed to exist in the
772	<	* pool, even if there are insufficient unblocked running threads.
773	<	* @return the maximum
774	<	*/
775	<	public int getMaximumPoolSize() {
776	<	return maxPoolSize;
777	<	}
778	<
779	<	/**
780	<	* Sets the maximum number of threads allowed to exist in the
781	<	* pool, even if there are insufficient unblocked running threads.
782	<	* Setting this value has no effect on current pool size. It
783	<	* controls construction of new threads.
784	<	* @throws IllegalArgumentException if negative or greater then
785	<	* internal implementation limit.
786	<	*/
787	<	public void setMaximumPoolSize(int newMax) {
788	<	if (newMax < 0 || newMax > MAX_THREADS)
789	<	throw new IllegalArgumentException();
790	<	maxPoolSize = newMax;
791	<	}
792	<
793	<
794	<	/**
795	<	* Returns true if this pool dynamically maintains its target
796	<	* parallelism level. If false, new threads are added only to
797	<	* avoid possible starvation.
798	<	* This setting is by default true;
799	<	* @return true if maintains parallelism
800	<	*/
801	<	public boolean getMaintainsParallelism() {
802	<	return maintainsParallelism;
803	<	}
804	<
805	<	/**
806	<	* Sets whether this pool dynamically maintains its target
807	<	* parallelism level. If false, new threads are added only to
808	<	* avoid possible starvation.
809	<	* @param enable true to maintains parallelism
810	<	*/
811	<	public void setMaintainsParallelism(boolean enable) {
812	<	maintainsParallelism = enable;
813	<	}
814	<
815	<	/**
816	<	* Establishes local first-in-first-out scheduling mode for forked
817	<	* tasks that are never joined. This mode may be more appropriate
818	<	* than default locally stack-based mode in applications in which
819	<	* worker threads only process asynchronous tasks.  This method is
820	<	* designed to be invoked only when pool is quiescent, and
821	<	* typically only before any tasks are submitted. The effects of
822	<	* invocations at other times may be unpredictable.
823	<	*
824	<	* @param async if true, use locally FIFO scheduling
825	<	* @return the previous mode.
826	<	*/
827	<	public boolean setAsyncMode(boolean async) {
828	<	boolean oldMode = locallyFifo;
829	<	locallyFifo = async;
830	<	ForkJoinWorkerThread[] ws = workers;
831	<	if (ws != null) {
832	<	for (int i = 0; i < ws.length; ++i) {
833	<	ForkJoinWorkerThread t = ws[i];
834	<	if (t != null)
835	<	t.setAsyncMode(async);
836	<	}
837	<	}
838	<	return oldMode;
1459	>	return workerCounts >>> TOTAL_COUNT_SHIFT;
1460		}
1461
1462		/**
1463	<	* Returns true if this pool uses local first-in-first-out
1463	>	* Returns {@code true} if this pool uses local first-in-first-out
1464		* scheduling mode for forked tasks that are never joined.
1465		*
1466	<	* @return true if this pool uses async mode.
1466	>	* @return {@code true} if this pool uses async mode
1467		*/
1468		public boolean getAsyncMode() {
1469		return locallyFifo;
#	Line 851 | Line 1472 | public class ForkJoinPool extends Abstra
1472		/**
1473		* Returns an estimate of the number of worker threads that are
1474		* not blocked waiting to join tasks or for other managed
1475	<	* synchronization.
1475	>	* synchronization. This method may overestimate the
1476	>	* number of running threads.
1477		*
1478		* @return the number of worker threads
1479		*/
1480		public int getRunningThreadCount() {
1481	<	return runningCountOf(workerCounts);
1481	>	return workerCounts & RUNNING_COUNT_MASK;
1482		}
1483
1484		/**
1485		* Returns an estimate of the number of threads that are currently
1486		* stealing or executing tasks. This method may overestimate the
1487		* number of active threads.
1488	<	* @return the number of active threads.
1488	>	*
1489	>	* @return the number of active threads
1490		*/
1491		public int getActiveThreadCount() {
1492	<	return activeCountOf(runControl);
870	<	}
871	<
872	<	/**
873	<	* Returns an estimate of the number of threads that are currently
874	<	* idle waiting for tasks. This method may underestimate the
875	<	* number of idle threads.
876	<	* @return the number of idle threads.
877	<	*/
878	<	final int getIdleThreadCount() {
879	<	int c = runningCountOf(workerCounts) - activeCountOf(runControl);
880	<	return (c <= 0)? 0 : c;
1492	>	return runState & ACTIVE_COUNT_MASK;
1493		}
1494
1495		/**
1496	<	* Returns true if all worker threads are currently idle. An idle
1497	<	* worker is one that cannot obtain a task to execute because none
1498	<	* are available to steal from other threads, and there are no
1499	<	* pending submissions to the pool. This method is conservative:
1500	<	* It might not return true immediately upon idleness of all
1501	<	* threads, but will eventually become true if threads remain
1502	<	* inactive.
1503	<	* @return true if all threads are currently idle
1496	>	* Returns {@code true} if all worker threads are currently idle.
1497	>	* An idle worker is one that cannot obtain a task to execute
1498	>	* because none are available to steal from other threads, and
1499	>	* there are no pending submissions to the pool. This method is
1500	>	* conservative; it might not return {@code true} immediately upon
1501	>	* idleness of all threads, but will eventually become true if
1502	>	* threads remain inactive.
1503	>	*
1504	>	* @return {@code true} if all threads are currently idle
1505		*/
1506		public boolean isQuiescent() {
1507	<	return activeCountOf(runControl) == 0;
1507	>	return (runState & ACTIVE_COUNT_MASK) == 0;
1508		}
1509
1510		/**
#	Line 899 | Line 1512 | public class ForkJoinPool extends Abstra
1512		* one thread's work queue by another. The reported value
1513		* underestimates the actual total number of steals when the pool
1514		* is not quiescent. This value may be useful for monitoring and
1515	<	* tuning fork/join programs: In general, steal counts should be
1515	>	* tuning fork/join programs: in general, steal counts should be
1516		* high enough to keep threads busy, but low enough to avoid
1517		* overhead and contention across threads.
1518	<	* @return the number of steals.
1518	>	*
1519	>	* @return the number of steals
1520		*/
1521		public long getStealCount() {
1522	<	return stealCount.get();
909	<	}
910	<
911	<	/**
912	<	* Accumulate steal count from a worker. Call only
913	<	* when worker known to be idle.
914	<	*/
915	<	private void updateStealCount(ForkJoinWorkerThread w) {
916	<	int sc = w.getAndClearStealCount();
917	<	if (sc != 0)
918	<	stealCount.addAndGet(sc);
1522	>	return stealCount;
1523		}
1524
1525		/**
#	Line 925 | Line 1529 | public class ForkJoinPool extends Abstra
1529		* an approximation, obtained by iterating across all threads in
1530		* the pool. This method may be useful for tuning task
1531		* granularities.
1532	<	* @return the number of queued tasks.
1532	>	*
1533	>	* @return the number of queued tasks
1534		*/
1535		public long getQueuedTaskCount() {
1536		long count = 0;
1537	<	ForkJoinWorkerThread[] ws = workers;
1538	<	if (ws != null) {
1539	<	for (int i = 0; i < ws.length; ++i) {
935	<	ForkJoinWorkerThread t = ws[i];
936	<	if (t != null)
937	<	count += t.getQueueSize();
938	<	}
939	<	}
1537	>	for (ForkJoinWorkerThread w : workers)
1538	>	if (w != null)
1539	>	count += w.getQueueSize();
1540		return count;
1541		}
1542
1543		/**
1544	<	* Returns an estimate of the number tasks submitted to this pool
1545	<	* that have not yet begun executing. This method takes time
1544	>	* Returns an estimate of the number of tasks submitted to this
1545	>	* pool that have not yet begun executing.  This method takes time
1546		* proportional to the number of submissions.
1547	<	* @return the number of queued submissions.
1547	>	*
1548	>	* @return the number of queued submissions
1549		*/
1550		public int getQueuedSubmissionCount() {
1551		return submissionQueue.size();
1552		}
1553
1554		/**
1555	<	* Returns true if there are any tasks submitted to this pool
1556	<	* that have not yet begun executing.
1557	<	* @return {@code true} if there are any queued submissions.
1555	>	* Returns {@code true} if there are any tasks submitted to this
1556	>	* pool that have not yet begun executing.
1557	>	*
1558	>	* @return {@code true} if there are any queued submissions
1559		*/
1560		public boolean hasQueuedSubmissions() {
1561		return !submissionQueue.isEmpty();
#	Line 963 | Line 1565 | public class ForkJoinPool extends Abstra
1565		* Removes and returns the next unexecuted submission if one is
1566		* available.  This method may be useful in extensions to this
1567		* class that re-assign work in systems with multiple pools.
1568	<	* @return the next submission, or null if none
1568	>	*
1569	>	* @return the next submission, or {@code null} if none
1570		*/
1571		protected ForkJoinTask<?> pollSubmission() {
1572		return submissionQueue.poll();
#	Line 973 | Line 1576 | public class ForkJoinPool extends Abstra
1576		* Removes all available unexecuted submitted and forked tasks
1577		* from scheduling queues and adds them to the given collection,
1578		* without altering their execution status. These may include
1579	<	* artificially generated or wrapped tasks. This method is designed
1580	<	* to be invoked only when the pool is known to be
1579	>	* artificially generated or wrapped tasks. This method is
1580	>	* designed to be invoked only when the pool is known to be
1581		* quiescent. Invocations at other times may not remove all
1582		* tasks. A failure encountered while attempting to add elements
1583		* to collection {@code c} may result in elements being in
#	Line 982 | Line 1585 | public class ForkJoinPool extends Abstra
1585		* exception is thrown.  The behavior of this operation is
1586		* undefined if the specified collection is modified while the
1587		* operation is in progress.
1588	+	*
1589		* @param c the collection to transfer elements into
1590		* @return the number of elements transferred
1591		*/
1592	<	protected int drainTasksTo(Collection<ForkJoinTask<?>> c) {
1593	<	int n = submissionQueue.drainTo(c);
1594	<	ForkJoinWorkerThread[] ws = workers;
1595	<	if (ws != null) {
1596	<	for (int i = 0; i < ws.length; ++i) {
1597	<	ForkJoinWorkerThread w = ws[i];
994	<	if (w != null)
995	<	n += w.drainTasksTo(c);
996	<	}
997	<	}
998	<	return n;
1592	>	protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1593	>	int count = submissionQueue.drainTo(c);
1594	>	for (ForkJoinWorkerThread w : workers)
1595	>	if (w != null)
1596	>	count += w.drainTasksTo(c);
1597	>	return count;
1598		}
1599
1600		/**
#	Line 1006 | Line 1605 | public class ForkJoinPool extends Abstra
1605		* @return a string identifying this pool, as well as its state
1606		*/
1607		public String toString() {
1009	–	int ps = parallelism;
1010	–	int wc = workerCounts;
1011	–	int rc = runControl;
1608		long st = getStealCount();
1609		long qt = getQueuedTaskCount();
1610		long qs = getQueuedSubmissionCount();
1611	+	int wc = workerCounts;
1612	+	int tc = wc >>> TOTAL_COUNT_SHIFT;
1613	+	int rc = wc & RUNNING_COUNT_MASK;
1614	+	int pc = parallelism;
1615	+	int rs = runState;
1616	+	int ac = rs & ACTIVE_COUNT_MASK;
1617		return super.toString() +
1618	<	"[" + runStateToString(runStateOf(rc)) +
1619	<	", parallelism = " + ps +
1620	<	", size = " + totalCountOf(wc) +
1621	<	", active = " + activeCountOf(rc) +
1622	<	", running = " + runningCountOf(wc) +
1618	>	"[" + runLevelToString(rs) +
1619	>	", parallelism = " + pc +
1620	>	", size = " + tc +
1621	>	", active = " + ac +
1622	>	", running = " + rc +
1623		", steals = " + st +
1624		", tasks = " + qt +
1625		", submissions = " + qs +
1626		"]";
1627		}
1628
1629	<	private static String runStateToString(int rs) {
1630	<	switch(rs) {
1631	<	case RUNNING: return "Running";
1632	<	case SHUTDOWN: return "Shutting down";
1633	<	case TERMINATING: return "Terminating";
1032	<	case TERMINATED: return "Terminated";
1033	<	default: throw new Error("Unknown run state");
1034	<	}
1629	>	private static String runLevelToString(int s) {
1630	>	return ((s & TERMINATED) != 0 ? "Terminated" :
1631	>	((s & TERMINATING) != 0 ? "Terminating" :
1632	>	((s & SHUTDOWN) != 0 ? "Shutting down" :
1633	>	"Running")));
1634		}
1635
1037	–	// lifecycle control
1038	–
1636		/**
1637		* Initiates an orderly shutdown in which previously submitted
1638		* tasks are executed, but no new tasks will be accepted.
1639		* Invocation has no additional effect if already shut down.
1640		* Tasks that are in the process of being submitted concurrently
1641		* during the course of this method may or may not be rejected.
1642	+	*
1643		* @throws SecurityException if a security manager exists and
1644		*         the caller is not permitted to modify threads
1645		*         because it does not hold {@link
1646	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
1646	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1647		*/
1648		public void shutdown() {
1649		checkPermission();
1650	<	transitionRunStateTo(SHUTDOWN);
1651	<	if (canTerminateOnShutdown(runControl))
1054	<	terminateOnShutdown();
1650	>	advanceRunLevel(SHUTDOWN);
1651	>	tryTerminate(false);
1652		}
1653
1654		/**
1655	<	* Attempts to stop all actively executing tasks, and cancels all
1656	<	* waiting tasks.  Tasks that are in the process of being
1657	<	* submitted or executed concurrently during the course of this
1658	<	* method may or may not be rejected. Unlike some other executors,
1659	<	* this method cancels rather than collects non-executed tasks
1660	<	* upon termination, so always returns an empty list. However, you
1661	<	* can use method {@code drainTasksTo} before invoking this
1662	<	* method to transfer unexecuted tasks to another collection.
1655	>	* Attempts to cancel and/or stop all tasks, and reject all
1656	>	* subsequently submitted tasks.  Tasks that are in the process of
1657	>	* being submitted or executed concurrently during the course of
1658	>	* this method may or may not be rejected. This method cancels
1659	>	* both existing and unexecuted tasks, in order to permit
1660	>	* termination in the presence of task dependencies. So the method
1661	>	* always returns an empty list (unlike the case for some other
1662	>	* Executors).
1663	>	*
1664		* @return an empty list
1665		* @throws SecurityException if a security manager exists and
1666		*         the caller is not permitted to modify threads
1667		*         because it does not hold {@link
1668	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
1668	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1669		*/
1670		public List<Runnable> shutdownNow() {
1671		checkPermission();
1672	<	terminate();
1672	>	tryTerminate(true);
1673		return Collections.emptyList();
1674		}
1675
#	Line 1081 | Line 1679 | public class ForkJoinPool extends Abstra
1679		* @return {@code true} if all tasks have completed following shut down
1680		*/
1681		public boolean isTerminated() {
1682	<	return runStateOf(runControl) == TERMINATED;
1682	>	return runState >= TERMINATED;
1683		}
1684
1685		/**
1686		* Returns {@code true} if the process of termination has
1687	<	* commenced but possibly not yet completed.
1687	>	* commenced but not yet completed.  This method may be useful for
1688	>	* debugging. A return of {@code true} reported a sufficient
1689	>	* period after shutdown may indicate that submitted tasks have
1690	>	* ignored or suppressed interruption, causing this executor not
1691	>	* to properly terminate.
1692		*
1693	<	* @return {@code true} if terminating
1693	>	* @return {@code true} if terminating but not yet terminated
1694		*/
1695		public boolean isTerminating() {
1696	<	return runStateOf(runControl) >= TERMINATING;
1696	>	return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
1697		}
1698
1699		/**
#	Line 1100 | Line 1702 | public class ForkJoinPool extends Abstra
1702		* @return {@code true} if this pool has been shut down
1703		*/
1704		public boolean isShutdown() {
1705	<	return runStateOf(runControl) >= SHUTDOWN;
1705	>	return runState >= SHUTDOWN;
1706		}
1707
1708		/**
#	Line 1116 | Line 1718 | public class ForkJoinPool extends Abstra
1718		*/
1719		public boolean awaitTermination(long timeout, TimeUnit unit)
1720		throws InterruptedException {
1119	–	long nanos = unit.toNanos(timeout);
1120	–	final ReentrantLock lock = this.workerLock;
1121	–	lock.lock();
1122	–	try {
1123	–	for (;;) {
1124	–	if (isTerminated())
1125	–	return true;
1126	–	if (nanos <= 0)
1127	–	return false;
1128	–	nanos = termination.awaitNanos(nanos);
1129	–	}
1130	–	} finally {
1131	–	lock.unlock();
1132	–	}
1133	–	}
1134	–
1135	–	// Shutdown and termination support
1136	–
1137	–	/**
1138	–	* Callback from terminating worker. Null out the corresponding
1139	–	* workers slot, and if terminating, try to terminate, else try to
1140	–	* shrink workers array.
1141	–	* @param w the worker
1142	–	*/
1143	–	final void workerTerminated(ForkJoinWorkerThread w) {
1144	–	updateStealCount(w);
1145	–	updateWorkerCount(-1);
1146	–	final ReentrantLock lock = this.workerLock;
1147	–	lock.lock();
1148	–	try {
1149	–	ForkJoinWorkerThread[] ws = workers;
1150	–	if (ws != null) {
1151	–	int idx = w.poolIndex;
1152	–	if (idx >= 0 && idx < ws.length && ws[idx] == w)
1153	–	ws[idx] = null;
1154	–	if (totalCountOf(workerCounts) == 0) {
1155	–	terminate(); // no-op if already terminating
1156	–	transitionRunStateTo(TERMINATED);
1157	–	termination.signalAll();
1158	–	}
1159	–	else if (!isTerminating()) {
1160	–	tryShrinkWorkerArray();
1161	–	tryResumeSpare(true); // allow replacement
1162	–	}
1163	–	}
1164	–	} finally {
1165	–	lock.unlock();
1166	–	}
1167	–	signalIdleWorkers();
1168	–	}
1169	–
1170	–	/**
1171	–	* Initiate termination.
1172	–	*/
1173	–	private void terminate() {
1174	–	if (transitionRunStateTo(TERMINATING)) {
1175	–	stopAllWorkers();
1176	–	resumeAllSpares();
1177	–	signalIdleWorkers();
1178	–	cancelQueuedSubmissions();
1179	–	cancelQueuedWorkerTasks();
1180	–	interruptUnterminatedWorkers();
1181	–	signalIdleWorkers(); // resignal after interrupt
1182	–	}
1183	–	}
1184	–
1185	–	/**
1186	–	* Possibly terminates when on shutdown state.
1187	–	*/
1188	–	private void terminateOnShutdown() {
1189	–	if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
1190	–	terminate();
1191	–	}
1192	–
1193	–	/**
1194	–	* Clears out and cancels submissions.
1195	–	*/
1196	–	private void cancelQueuedSubmissions() {
1197	–	ForkJoinTask<?> task;
1198	–	while ((task = pollSubmission()) != null)
1199	–	task.cancel(false);
1200	–	}
1201	–
1202	–	/**
1203	–	* Cleans out worker queues.
1204	–	*/
1205	–	private void cancelQueuedWorkerTasks() {
1206	–	final ReentrantLock lock = this.workerLock;
1207	–	lock.lock();
1208	–	try {
1209	–	ForkJoinWorkerThread[] ws = workers;
1210	–	if (ws != null) {
1211	–	for (int i = 0; i < ws.length; ++i) {
1212	–	ForkJoinWorkerThread t = ws[i];
1213	–	if (t != null)
1214	–	t.cancelTasks();
1215	–	}
1216	–	}
1217	–	} finally {
1218	–	lock.unlock();
1219	–	}
1220	–	}
1221	–
1222	–	/**
1223	–	* Sets each worker's status to terminating. Requires lock to avoid
1224	–	* conflicts with add/remove.
1225	–	*/
1226	–	private void stopAllWorkers() {
1227	–	final ReentrantLock lock = this.workerLock;
1228	–	lock.lock();
1721		try {
1722	<	ForkJoinWorkerThread[] ws = workers;
1723	<	if (ws != null) {
1232	<	for (int i = 0; i < ws.length; ++i) {
1233	<	ForkJoinWorkerThread t = ws[i];
1234	<	if (t != null)
1235	<	t.shutdownNow();
1236	<	}
1237	<	}
1238	<	} finally {
1239	<	lock.unlock();
1240	<	}
1241	<	}
1242	<
1243	<	/**
1244	<	* Interrupts all unterminated workers.  This is not required for
1245	<	* sake of internal control, but may help unstick user code during
1246	<	* shutdown.
1247	<	*/
1248	<	private void interruptUnterminatedWorkers() {
1249	<	final ReentrantLock lock = this.workerLock;
1250	<	lock.lock();
1251	<	try {
1252	<	ForkJoinWorkerThread[] ws = workers;
1253	<	if (ws != null) {
1254	<	for (int i = 0; i < ws.length; ++i) {
1255	<	ForkJoinWorkerThread t = ws[i];
1256	<	if (t != null && !t.isTerminated()) {
1257	<	try {
1258	<	t.interrupt();
1259	<	} catch (SecurityException ignore) {
1260	<	}
1261	<	}
1262	<	}
1263	<	}
1264	<	} finally {
1265	<	lock.unlock();
1266	<	}
1267	<	}
1268	<
1269	<
1270	<	/*
1271	<	* Nodes for event barrier to manage idle threads.  Queue nodes
1272	<	* are basic Treiber stack nodes, also used for spare stack.
1273	<	*
1274	<	* The event barrier has an event count and a wait queue (actually
1275	<	* a Treiber stack).  Workers are enabled to look for work when
1276	<	* the eventCount is incremented. If they fail to find work, they
1277	<	* may wait for next count. Upon release, threads help others wake
1278	<	* up.
1279	<	*
1280	<	* Synchronization events occur only in enough contexts to
1281	<	* maintain overall liveness:
1282	<	*
1283	<	*   - Submission of a new task to the pool
1284	<	*   - Resizes or other changes to the workers array
1285	<	*   - pool termination
1286	<	*   - A worker pushing a task on an empty queue
1287	<	*
1288	<	* The case of pushing a task occurs often enough, and is heavy
1289	<	* enough compared to simple stack pushes, to require special
1290	<	* handling: Method signalWork returns without advancing count if
1291	<	* the queue appears to be empty.  This would ordinarily result in
1292	<	* races causing some queued waiters not to be woken up. To avoid
1293	<	* this, the first worker enqueued in method sync (see
1294	<	* syncIsReleasable) rescans for tasks after being enqueued, and
1295	<	* helps signal if any are found. This works well because the
1296	<	* worker has nothing better to do, and so might as well help
1297	<	* alleviate the overhead and contention on the threads actually
1298	<	* doing work.  Also, since event counts increments on task
1299	<	* availability exist to maintain liveness (rather than to force
1300	<	* refreshes etc), it is OK for callers to exit early if
1301	<	* contending with another signaller.
1302	<	*/
1303	<	static final class WaitQueueNode {
1304	<	WaitQueueNode next; // only written before enqueued
1305	<	volatile ForkJoinWorkerThread thread; // nulled to cancel wait
1306	<	final long count; // unused for spare stack
1307	<
1308	<	WaitQueueNode(long c, ForkJoinWorkerThread w) {
1309	<	count = c;
1310	<	thread = w;
1311	<	}
1312	<
1313	<	/**
1314	<	* Wakes up waiter, returning false if known to already
1315	<	*/
1316	<	boolean signal() {
1317	<	ForkJoinWorkerThread t = thread;
1318	<	if (t == null)
1319	<	return false;
1320	<	thread = null;
1321	<	LockSupport.unpark(t);
1322	<	return true;
1323	<	}
1324	<
1325	<	/**
1326	<	* Awaits release on sync.
1327	<	*/
1328	<	void awaitSyncRelease(ForkJoinPool p) {
1329	<	while (thread != null && !p.syncIsReleasable(this))
1330	<	LockSupport.park(this);
1331	<	}
1332	<
1333	<	/**
1334	<	* Awaits resumption as spare.
1335	<	*/
1336	<	void awaitSpareRelease() {
1337	<	while (thread != null) {
1338	<	if (!Thread.interrupted())
1339	<	LockSupport.park(this);
1340	<	}
1341	<	}
1342	<	}
1343	<
1344	<	/**
1345	<	* Ensures that no thread is waiting for count to advance from the
1346	<	* current value of eventCount read on entry to this method, by
1347	<	* releasing waiting threads if necessary.
1348	<	* @return the count
1349	<	*/
1350	<	final long ensureSync() {
1351	<	long c = eventCount;
1352	<	WaitQueueNode q;
1353	<	while ((q = syncStack) != null && q.count < c) {
1354	<	if (casBarrierStack(q, null)) {
1355	<	do {
1356	<	q.signal();
1357	<	} while ((q = q.next) != null);
1358	<	break;
1359	<	}
1360	<	}
1361	<	return c;
1362	<	}
1363	<
1364	<	/**
1365	<	* Increments event count and releases waiting threads.
1366	<	*/
1367	<	private void signalIdleWorkers() {
1368	<	long c;
1369	<	do;while (!casEventCount(c = eventCount, c+1));
1370	<	ensureSync();
1371	<	}
1372	<
1373	<	/**
1374	<	* Signals threads waiting to poll a task. Because method sync
1375	<	* rechecks availability, it is OK to only proceed if queue
1376	<	* appears to be non-empty, and OK to skip under contention to
1377	<	* increment count (since some other thread succeeded).
1378	<	*/
1379	<	final void signalWork() {
1380	<	long c;
1381	<	WaitQueueNode q;
1382	<	if (syncStack != null &&
1383	<	casEventCount(c = eventCount, c+1) &&
1384	<	(((q = syncStack) != null && q.count <= c) &&
1385	<	(!casBarrierStack(q, q.next) || !q.signal())))
1386	<	ensureSync();
1387	<	}
1388	<
1389	<	/**
1390	<	* Waits until event count advances from last value held by
1391	<	* caller, or if excess threads, caller is resumed as spare, or
1392	<	* caller or pool is terminating. Updates caller's event on exit.
1393	<	* @param w the calling worker thread
1394	<	*/
1395	<	final void sync(ForkJoinWorkerThread w) {
1396	<	updateStealCount(w); // Transfer w's count while it is idle
1397	<
1398	<	while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
1399	<	long prev = w.lastEventCount;
1400	<	WaitQueueNode node = null;
1401	<	WaitQueueNode h;
1402	<	while (eventCount == prev &&
1403	<	((h = syncStack) == null || h.count == prev)) {
1404	<	if (node == null)
1405	<	node = new WaitQueueNode(prev, w);
1406	<	if (casBarrierStack(node.next = h, node)) {
1407	<	node.awaitSyncRelease(this);
1408	<	break;
1409	<	}
1410	<	}
1411	<	long ec = ensureSync();
1412	<	if (ec != prev) {
1413	<	w.lastEventCount = ec;
1414	<	break;
1415	<	}
1416	<	}
1417	<	}
1418	<
1419	<	/**
1420	<	* Returns true if worker waiting on sync can proceed:
1421	<	*  - on signal (thread == null)
1422	<	*  - on event count advance (winning race to notify vs signaller)
1423	<	*  - on Interrupt
1424	<	*  - if the first queued node, we find work available
1425	<	* If node was not signalled and event count not advanced on exit,
1426	<	* then we also help advance event count.
1427	<	* @return true if node can be released
1428	<	*/
1429	<	final boolean syncIsReleasable(WaitQueueNode node) {
1430	<	long prev = node.count;
1431	<	if (!Thread.interrupted() && node.thread != null &&
1432	<	(node.next != null ||
1433	<	!ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
1434	<	eventCount == prev)
1722	>	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1723	>	} catch (TimeoutException ex) {
1724		return false;
1436	–	if (node.thread != null) {
1437	–	node.thread = null;
1438	–	long ec = eventCount;
1439	–	if (prev <= ec) // help signal
1440	–	casEventCount(ec, ec+1);
1441	–	}
1442	–	return true;
1443	–	}
1444	–
1445	–	/**
1446	–	* Returns true if a new sync event occurred since last call to
1447	–	* sync or this method, if so, updating caller's count.
1448	–	*/
1449	–	final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1450	–	long lc = w.lastEventCount;
1451	–	long ec = ensureSync();
1452	–	if (ec == lc)
1453	–	return false;
1454	–	w.lastEventCount = ec;
1455	–	return true;
1456	–	}
1457	–
1458	–	//  Parallelism maintenance
1459	–
1460	–	/**
1461	–	* Decrements running count; if too low, adds spare.
1462	–	*
1463	–	* Conceptually, all we need to do here is add or resume a
1464	–	* spare thread when one is about to block (and remove or
1465	–	* suspend it later when unblocked -- see suspendIfSpare).
1466	–	* However, implementing this idea requires coping with
1467	–	* several problems: We have imperfect information about the
1468	–	* states of threads. Some count updates can and usually do
1469	–	* lag run state changes, despite arrangements to keep them
1470	–	* accurate (for example, when possible, updating counts
1471	–	* before signalling or resuming), especially when running on
1472	–	* dynamic JVMs that don't optimize the infrequent paths that
1473	–	* update counts. Generating too many threads can make these
1474	–	* problems become worse, because excess threads are more
1475	–	* likely to be context-switched with others, slowing them all
1476	–	* down, especially if there is no work available, so all are
1477	–	* busy scanning or idling.  Also, excess spare threads can
1478	–	* only be suspended or removed when they are idle, not
1479	–	* immediately when they aren't needed. So adding threads will
1480	–	* raise parallelism level for longer than necessary.  Also,
1481	–	* FJ applications often encounter highly transient peaks when
1482	–	* many threads are blocked joining, but for less time than it
1483	–	* takes to create or resume spares.
1484	–	*
1485	–	* @param joinMe if non-null, return early if done
1486	–	* @param maintainParallelism if true, try to stay within
1487	–	* target counts, else create only to avoid starvation
1488	–	* @return true if joinMe known to be done
1489	–	*/
1490	–	final boolean preJoin(ForkJoinTask<?> joinMe, boolean maintainParallelism) {
1491	–	maintainParallelism &= maintainsParallelism; // overrride
1492	–	boolean dec = false;  // true when running count decremented
1493	–	while (spareStack == null || !tryResumeSpare(dec)) {
1494	–	int counts = workerCounts;
1495	–	if (dec || (dec = casWorkerCounts(counts, --counts))) { // CAS cheat
1496	–	if (!needSpare(counts, maintainParallelism))
1497	–	break;
1498	–	if (joinMe.status < 0)
1499	–	return true;
1500	–	if (tryAddSpare(counts))
1501	–	break;
1502	–	}
1503	–	}
1504	–	return false;
1505	–	}
1506	–
1507	–	/**
1508	–	* Same idea as preJoin
1509	–	*/
1510	–	final boolean preBlock(ManagedBlocker blocker, boolean maintainParallelism){
1511	–	maintainParallelism &= maintainsParallelism;
1512	–	boolean dec = false;
1513	–	while (spareStack == null || !tryResumeSpare(dec)) {
1514	–	int counts = workerCounts;
1515	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1516	–	if (!needSpare(counts, maintainParallelism))
1517	–	break;
1518	–	if (blocker.isReleasable())
1519	–	return true;
1520	–	if (tryAddSpare(counts))
1521	–	break;
1522	–	}
1523	–	}
1524	–	return false;
1525	–	}
1526	–
1527	–	/**
1528	–	* Returns true if a spare thread appears to be needed.  If
1529	–	* maintaining parallelism, returns true when the deficit in
1530	–	* running threads is more than the surplus of total threads, and
1531	–	* there is apparently some work to do.  This self-limiting rule
1532	–	* means that the more threads that have already been added, the
1533	–	* less parallelism we will tolerate before adding another.
1534	–	* @param counts current worker counts
1535	–	* @param maintainParallelism try to maintain parallelism
1536	–	*/
1537	–	private boolean needSpare(int counts, boolean maintainParallelism) {
1538	–	int ps = parallelism;
1539	–	int rc = runningCountOf(counts);
1540	–	int tc = totalCountOf(counts);
1541	–	int runningDeficit = ps - rc;
1542	–	int totalSurplus = tc - ps;
1543	–	return (tc < maxPoolSize &&
1544	–	(rc == 0 || totalSurplus < 0 ||
1545	–	(maintainParallelism &&
1546	–	runningDeficit > totalSurplus &&
1547	–	ForkJoinWorkerThread.hasQueuedTasks(workers))));
1548	–	}
1549	–
1550	–	/**
1551	–	* Adds a spare worker if lock available and no more than the
1552	–	* expected numbers of threads exist.
1553	–	* @return true if successful
1554	–	*/
1555	–	private boolean tryAddSpare(int expectedCounts) {
1556	–	final ReentrantLock lock = this.workerLock;
1557	–	int expectedRunning = runningCountOf(expectedCounts);
1558	–	int expectedTotal = totalCountOf(expectedCounts);
1559	–	boolean success = false;
1560	–	boolean locked = false;
1561	–	// confirm counts while locking; CAS after obtaining lock
1562	–	try {
1563	–	for (;;) {
1564	–	int s = workerCounts;
1565	–	int tc = totalCountOf(s);
1566	–	int rc = runningCountOf(s);
1567	–	if (rc > expectedRunning || tc > expectedTotal)
1568	–	break;
1569	–	if (!locked && !(locked = lock.tryLock()))
1570	–	break;
1571	–	if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
1572	–	createAndStartSpare(tc);
1573	–	success = true;
1574	–	break;
1575	–	}
1576	–	}
1577	–	} finally {
1578	–	if (locked)
1579	–	lock.unlock();
1580	–	}
1581	–	return success;
1582	–	}
1583	–
1584	–	/**
1585	–	* Adds the kth spare worker. On entry, pool counts are already
1586	–	* adjusted to reflect addition.
1587	–	*/
1588	–	private void createAndStartSpare(int k) {
1589	–	ForkJoinWorkerThread w = null;
1590	–	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
1591	–	int len = ws.length;
1592	–	// Probably, we can place at slot k. If not, find empty slot
1593	–	if (k < len && ws[k] != null) {
1594	–	for (k = 0; k < len && ws[k] != null; ++k)
1595	–	;
1596	–	}
1597	–	if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
1598	–	ws[k] = w;
1599	–	w.start();
1600	–	}
1601	–	else
1602	–	updateWorkerCount(-1); // adjust on failure
1603	–	signalIdleWorkers();
1604	–	}
1605	–
1606	–	/**
1607	–	* Suspends calling thread w if there are excess threads.  Called
1608	–	* only from sync.  Spares are enqueued in a Treiber stack using
1609	–	* the same WaitQueueNodes as barriers.  They are resumed mainly
1610	–	* in preJoin, but are also woken on pool events that require all
1611	–	* threads to check run state.
1612	–	* @param w the caller
1613	–	*/
1614	–	private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1615	–	WaitQueueNode node = null;
1616	–	int s;
1617	–	while (parallelism < runningCountOf(s = workerCounts)) {
1618	–	if (node == null)
1619	–	node = new WaitQueueNode(0, w);
1620	–	if (casWorkerCounts(s, s-1)) { // representation-dependent
1621	–	// push onto stack
1622	–	do;while (!casSpareStack(node.next = spareStack, node));
1623	–	// block until released by resumeSpare
1624	–	node.awaitSpareRelease();
1625	–	return true;
1626	–	}
1627	–	}
1628	–	return false;
1629	–	}
1630	–
1631	–	/**
1632	–	* Tries to pop and resume a spare thread.
1633	–	* @param updateCount if true, increment running count on success
1634	–	* @return true if successful
1635	–	*/
1636	–	private boolean tryResumeSpare(boolean updateCount) {
1637	–	WaitQueueNode q;
1638	–	while ((q = spareStack) != null) {
1639	–	if (casSpareStack(q, q.next)) {
1640	–	if (updateCount)
1641	–	updateRunningCount(1);
1642	–	q.signal();
1643	–	return true;
1644	–	}
1645	–	}
1646	–	return false;
1647	–	}
1648	–
1649	–	/**
1650	–	* Pops and resumes all spare threads. Same idea as ensureSync.
1651	–	* @return true if any spares released
1652	–	*/
1653	–	private boolean resumeAllSpares() {
1654	–	WaitQueueNode q;
1655	–	while ( (q = spareStack) != null) {
1656	–	if (casSpareStack(q, null)) {
1657	–	do {
1658	–	updateRunningCount(1);
1659	–	q.signal();
1660	–	} while ((q = q.next) != null);
1661	–	return true;
1662	–	}
1663	–	}
1664	–	return false;
1665	–	}
1666	–
1667	–	/**
1668	–	* Pops and shuts down excessive spare threads. Call only while
1669	–	* holding lock. This is not guaranteed to eliminate all excess
1670	–	* threads, only those suspended as spares, which are the ones
1671	–	* unlikely to be needed in the future.
1672	–	*/
1673	–	private void trimSpares() {
1674	–	int surplus = totalCountOf(workerCounts) - parallelism;
1675	–	WaitQueueNode q;
1676	–	while (surplus > 0 && (q = spareStack) != null) {
1677	–	if (casSpareStack(q, null)) {
1678	–	do {
1679	–	updateRunningCount(1);
1680	–	ForkJoinWorkerThread w = q.thread;
1681	–	if (w != null && surplus > 0 &&
1682	–	runningCountOf(workerCounts) > 0 && w.shutdown())
1683	–	--surplus;
1684	–	q.signal();
1685	–	} while ((q = q.next) != null);
1686	–	}
1725		}
1726		}
1727
1728		/**
1729		* Interface for extending managed parallelism for tasks running
1730	<	* in ForkJoinPools. A ManagedBlocker provides two methods.
1731	<	* Method {@code isReleasable} must return true if blocking is not
1732	<	* necessary. Method {@code block} blocks the current thread
1733	<	* if necessary (perhaps internally invoking isReleasable before
1734	<	* actually blocking.).
1730	>	* in {@link ForkJoinPool}s.
1731	>	*
1732	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1733	>	* {@code isReleasable} must return {@code true} if blocking is
1734	>	* not necessary. Method {@code block} blocks the current thread
1735	>	* if necessary (perhaps internally invoking {@code isReleasable}
1736	>	* before actually blocking). The unusual methods in this API
1737	>	* accommodate synchronizers that may, but don't usually, block
1738	>	* for long periods. Similarly, they allow more efficient internal
1739	>	* handling of cases in which additional workers may be, but
1740	>	* usually are not, needed to ensure sufficient parallelism.
1741	>	* Toward this end, implementations of method {@code isReleasable}
1742	>	* must be amenable to repeated invocation.
1743	>	*
1744		* <p>For example, here is a ManagedBlocker based on a
1745		* ReentrantLock:
1746	<	* <pre>
1747	<	*   class ManagedLocker implements ManagedBlocker {
1748	<	*     final ReentrantLock lock;
1749	<	*     boolean hasLock = false;
1750	<	*     ManagedLocker(ReentrantLock lock) { this.lock = lock; }
1751	<	*     public boolean block() {
1752	<	*        if (!hasLock)
1753	<	*           lock.lock();
1754	<	*        return true;
1755	<	*     }
1756	<	*     public boolean isReleasable() {
1757	<	*        return hasLock || (hasLock = lock.tryLock());
1758	<	*     }
1746	>	*  <pre> {@code
1747	>	* class ManagedLocker implements ManagedBlocker {
1748	>	*   final ReentrantLock lock;
1749	>	*   boolean hasLock = false;
1750	>	*   ManagedLocker(ReentrantLock lock) { this.lock = lock; }
1751	>	*   public boolean block() {
1752	>	*     if (!hasLock)
1753	>	*       lock.lock();
1754	>	*     return true;
1755	>	*   }
1756	>	*   public boolean isReleasable() {
1757	>	*     return hasLock || (hasLock = lock.tryLock());
1758	>	*   }
1759	>	* }}</pre>
1760	>	*
1761	>	* <p>Here is a class that possibly blocks waiting for an
1762	>	* item on a given queue:
1763	>	*  <pre> {@code
1764	>	* class QueueTaker<E> implements ManagedBlocker {
1765	>	*   final BlockingQueue<E> queue;
1766	>	*   volatile E item = null;
1767	>	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1768	>	*   public boolean block() throws InterruptedException {
1769	>	*     if (item == null)
1770	>	*       item = queue.take();
1771	>	*     return true;
1772	>	*   }
1773	>	*   public boolean isReleasable() {
1774	>	*     return item != null || (item = queue.poll()) != null;
1775		*   }
1776	<	* </pre>
1776	>	*   public E getItem() { // call after pool.managedBlock completes
1777	>	*     return item;
1778	>	*   }
1779	>	* }}</pre>
1780		*/
1781		public static interface ManagedBlocker {
1782		/**
1783		* Possibly blocks the current thread, for example waiting for
1784		* a lock or condition.
1785	<	* @return true if no additional blocking is necessary (i.e.,
1786	<	* if isReleasable would return true).
1785	>	*
1786	>	* @return {@code true} if no additional blocking is necessary
1787	>	* (i.e., if isReleasable would return true)
1788		* @throws InterruptedException if interrupted while waiting
1789	<	* (the method is not required to do so, but is allowed to).
1789	>	* (the method is not required to do so, but is allowed to)
1790		*/
1791		boolean block() throws InterruptedException;
1792
1793		/**
1794	<	* Returns true if blocking is unnecessary.
1794	>	* Returns {@code true} if blocking is unnecessary.
1795		*/
1796		boolean isReleasable();
1797		}
1798
1799		/**
1800		* Blocks in accord with the given blocker.  If the current thread
1801	<	* is a ForkJoinWorkerThread, this method possibly arranges for a
1802	<	* spare thread to be activated if necessary to ensure parallelism
1803	<	* while the current thread is blocked.  If
1804	<	* {@code maintainParallelism} is true and the pool supports
1805	<	* it ({@link #getMaintainsParallelism}), this method attempts to
1806	<	* maintain the pool's nominal parallelism. Otherwise if activates
1807	<	* a thread only if necessary to avoid complete starvation. This
1808	<	* option may be preferable when blockages use timeouts, or are
1809	<	* almost always brief.
1810	<	*
1811	<	* <p> If the caller is not a ForkJoinTask, this method is behaviorally
1812	<	* equivalent to
1813	<	* <pre>
1814	<	*   while (!blocker.isReleasable())
1748	<	*      if (blocker.block())
1749	<	*         return;
1750	<	* </pre>
1751	<	* If the caller is a ForkJoinTask, then the pool may first
1752	<	* be expanded to ensure parallelism, and later adjusted.
1801	>	* is a {@link ForkJoinWorkerThread}, this method possibly
1802	>	* arranges for a spare thread to be activated if necessary to
1803	>	* ensure sufficient parallelism while the current thread is blocked.
1804	>	*
1805	>	* <p>If the caller is not a {@link ForkJoinTask}, this method is
1806	>	* behaviorally equivalent to
1807	>	*  <pre> {@code
1808	>	* while (!blocker.isReleasable())
1809	>	*   if (blocker.block())
1810	>	*     return;
1811	>	* }</pre>
1812	>	*
1813	>	* If the caller is a {@code ForkJoinTask}, then the pool may
1814	>	* first be expanded to ensure parallelism, and later adjusted.
1815		*
1816		* @param blocker the blocker
1817	<	* @param maintainParallelism if true and supported by this pool,
1756	<	* attempt to maintain the pool's nominal parallelism; otherwise
1757	<	* activate a thread only if necessary to avoid complete
1758	<	* starvation.
1759	<	* @throws InterruptedException if blocker.block did so.
1817	>	* @throws InterruptedException if blocker.block did so
1818		*/
1819	<	public static void managedBlock(ManagedBlocker blocker,
1762	<	boolean maintainParallelism)
1819	>	public static void managedBlock(ManagedBlocker blocker)
1820		throws InterruptedException {
1821		Thread t = Thread.currentThread();
1822	<	ForkJoinPool pool = (t instanceof ForkJoinWorkerThread?
1823	<	((ForkJoinWorkerThread)t).pool : null);
1824	<	if (!blocker.isReleasable()) {
1825	<	try {
1826	<	if (pool == null ||
1827	<	!pool.preBlock(blocker, maintainParallelism))
1771	<	awaitBlocker(blocker);
1772	<	} finally {
1773	<	if (pool != null)
1774	<	pool.updateRunningCount(1);
1775	<	}
1822	>	if (t instanceof ForkJoinWorkerThread) {
1823	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1824	>	w.pool.awaitBlocker(blocker);
1825	>	}
1826	>	else {
1827	>	do {} while (!blocker.isReleasable() && !blocker.block());
1828		}
1829		}
1830
1831	<	private static void awaitBlocker(ManagedBlocker blocker)
1832	<	throws InterruptedException {
1833	<	do;while (!blocker.isReleasable() && !blocker.block());
1782	<	}
1783	<
1784	<	// AbstractExecutorService overrides
1831	>	// AbstractExecutorService overrides.  These rely on undocumented
1832	>	// fact that ForkJoinTask.adapt returns ForkJoinTasks that also
1833	>	// implement RunnableFuture.
1834
1835		protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
1836	<	return new AdaptedRunnable(runnable, value);
1836	>	return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
1837		}
1838
1839		protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
1840	<	return new AdaptedCallable(callable);
1840	>	return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
1841		}
1842
1843	+	// Unsafe mechanics
1844
1845	<	// Temporary Unsafe mechanics for preliminary release
1846	<	private static Unsafe getUnsafe() throws Throwable {
1845	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1846	>	private static final long workerCountsOffset =
1847	>	objectFieldOffset("workerCounts", ForkJoinPool.class);
1848	>	private static final long runStateOffset =
1849	>	objectFieldOffset("runState", ForkJoinPool.class);
1850	>	private static final long eventCountOffset =
1851	>	objectFieldOffset("eventCount", ForkJoinPool.class);
1852	>	private static final long eventWaitersOffset =
1853	>	objectFieldOffset("eventWaiters", ForkJoinPool.class);
1854	>	private static final long stealCountOffset =
1855	>	objectFieldOffset("stealCount", ForkJoinPool.class);
1856	>	private static final long spareWaitersOffset =
1857	>	objectFieldOffset("spareWaiters", ForkJoinPool.class);
1858	>
1859	>	private static long objectFieldOffset(String field, Class<?> klazz) {
1860	>	try {
1861	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1862	>	} catch (NoSuchFieldException e) {
1863	>	// Convert Exception to corresponding Error
1864	>	NoSuchFieldError error = new NoSuchFieldError(field);
1865	>	error.initCause(e);
1866	>	throw error;
1867	>	}
1868	>	}
1869	>
1870	>	/**
1871	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1872	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
1873	>	* into a jdk.
1874	>	*
1875	>	* @return a sun.misc.Unsafe
1876	>	*/
1877	>	private static sun.misc.Unsafe getUnsafe() {
1878		try {
1879	<	return Unsafe.getUnsafe();
1879	>	return sun.misc.Unsafe.getUnsafe();
1880		} catch (SecurityException se) {
1881		try {
1882		return java.security.AccessController.doPrivileged
1883	<	(new java.security.PrivilegedExceptionAction<Unsafe>() {
1884	<	public Unsafe run() throws Exception {
1885	<	return getUnsafePrivileged();
1883	>	(new java.security
1884	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1885	>	public sun.misc.Unsafe run() throws Exception {
1886	>	java.lang.reflect.Field f = sun.misc
1887	>	.Unsafe.class.getDeclaredField("theUnsafe");
1888	>	f.setAccessible(true);
1889	>	return (sun.misc.Unsafe) f.get(null);
1890		}});
1891		} catch (java.security.PrivilegedActionException e) {
1892	<	throw e.getCause();
1892	>	throw new RuntimeException("Could not initialize intrinsics",
1893	>	e.getCause());
1894		}
1895		}
1896		}
1811	–
1812	–	private static Unsafe getUnsafePrivileged()
1813	–	throws NoSuchFieldException, IllegalAccessException {
1814	–	Field f = Unsafe.class.getDeclaredField("theUnsafe");
1815	–	f.setAccessible(true);
1816	–	return (Unsafe) f.get(null);
1817	–	}
1818	–
1819	–	private static long fieldOffset(String fieldName)
1820	–	throws NoSuchFieldException {
1821	–	return _unsafe.objectFieldOffset
1822	–	(ForkJoinPool.class.getDeclaredField(fieldName));
1823	–	}
1824	–
1825	–	static final Unsafe _unsafe;
1826	–	static final long eventCountOffset;
1827	–	static final long workerCountsOffset;
1828	–	static final long runControlOffset;
1829	–	static final long syncStackOffset;
1830	–	static final long spareStackOffset;
1831	–
1832	–	static {
1833	–	try {
1834	–	_unsafe = getUnsafe();
1835	–	eventCountOffset = fieldOffset("eventCount");
1836	–	workerCountsOffset = fieldOffset("workerCounts");
1837	–	runControlOffset = fieldOffset("runControl");
1838	–	syncStackOffset = fieldOffset("syncStack");
1839	–	spareStackOffset = fieldOffset("spareStack");
1840	–	} catch (Throwable e) {
1841	–	throw new RuntimeException("Could not initialize intrinsics", e);
1842	–	}
1843	–	}
1844	–
1845	–	private boolean casEventCount(long cmp, long val) {
1846	–	return _unsafe.compareAndSwapLong(this, eventCountOffset, cmp, val);
1847	–	}
1848	–	private boolean casWorkerCounts(int cmp, int val) {
1849	–	return _unsafe.compareAndSwapInt(this, workerCountsOffset, cmp, val);
1850	–	}
1851	–	private boolean casRunControl(int cmp, int val) {
1852	–	return _unsafe.compareAndSwapInt(this, runControlOffset, cmp, val);
1853	–	}
1854	–	private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
1855	–	return _unsafe.compareAndSwapObject(this, spareStackOffset, cmp, val);
1856	–	}
1857	–	private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
1858	–	return _unsafe.compareAndSwapObject(this, syncStackOffset, cmp, val);
1859	–	}
1897		}

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