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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.26 by jsr166, Sun Jul 26 13:34:25 2009 UTC vs.
Revision 1.91 by dl, Tue Feb 22 00:39:31 2011 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.util.ArrayList;
10		import java.util.Arrays;
11		import java.util.Collection;
12		import java.util.Collections;
13		import java.util.List;
14	<	import java.util.concurrent.locks.Condition;
14	>	import java.util.Random;
15	>	import java.util.concurrent.AbstractExecutorService;
16	>	import java.util.concurrent.Callable;
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	<	import java.util.concurrent.atomic.AtomicInteger;
20	<	import java.util.concurrent.atomic.AtomicLong;
26	>	import java.util.concurrent.locks.Condition;
27
28		/**
29	<	* An {@link ExecutorService} for running {@link ForkJoinTask}s.  A
30	<	* ForkJoinPool provides the entry point for submissions from
31	<	* non-ForkJoinTasks, as well as management and monitoring operations.
32	<	* Normally a single ForkJoinPool is used for a large number of
27	<	* submitted tasks. Otherwise, use would not usually outweigh the
28	<	* construction and bookkeeping overhead of creating a large set of
29	<	* threads.
29	>	* An {@link ExecutorService} for running {@link ForkJoinTask}s.
30	>	* A {@code ForkJoinPool} provides the entry point for submissions
31	>	* from non-{@code ForkJoinTask} clients, as well as management and
32	>	* monitoring operations.
33		*
34	<	* <p>ForkJoinPools differ from other kinds of Executors mainly in
35	<	* that they provide <em>work-stealing</em>: all threads in the pool
36	<	* attempt to find and execute subtasks created by other active tasks
37	<	* (eventually blocking if none exist). This makes them efficient when
38	<	* most tasks spawn other subtasks (as do most ForkJoinTasks), as well
39	<	* as the mixed execution of some plain Runnable- or Callable- based
40	<	* activities along with ForkJoinTasks. When setting
41	<	* {@code setAsyncMode}, a ForkJoinPools may also be appropriate for
42	<	* use with fine-grained tasks that are never joined. Otherwise, other
40	<	* ExecutorService implementations are typically more appropriate
41	<	* choices.
34	>	* <p>A {@code ForkJoinPool} differs from other kinds of {@link
35	>	* ExecutorService} mainly by virtue of employing
36	>	* <em>work-stealing</em>: all threads in the pool attempt to find and
37	>	* execute subtasks created by other active tasks (eventually blocking
38	>	* waiting for work if none exist). This enables efficient processing
39	>	* when most tasks spawn other subtasks (as do most {@code
40	>	* ForkJoinTask}s). When setting <em>asyncMode</em> to true in
41	>	* constructors, {@code ForkJoinPool}s may also be appropriate for use
42	>	* with event-style tasks that are never joined.
43		*
44	<	* <p>A ForkJoinPool may be constructed with a given parallelism level
45	<	* (target pool size), which it attempts to maintain by dynamically
46	<	* adding, suspending, or resuming threads, even if some tasks are
47	<	* waiting to join others. However, no such adjustments are performed
48	<	* in the face of blocked IO or other unmanaged synchronization. The
49	<	* nested {@code ManagedBlocker} interface enables extension of
50	<	* the kinds of synchronization accommodated.  The target parallelism
51	<	* level may also be changed dynamically ({@code setParallelism})
52	<	* and thread construction can be limited using methods
52	<	* {@code setMaximumPoolSize} and/or
53	<	* {@code setMaintainsParallelism}.
44	>	* <p>A {@code ForkJoinPool} is constructed with a given target
45	>	* parallelism level; by default, equal to the number of available
46	>	* processors. The pool attempts to maintain enough active (or
47	>	* available) threads by dynamically adding, suspending, or resuming
48	>	* internal worker threads, even if some tasks are stalled waiting to
49	>	* join others. However, no such adjustments are guaranteed in the
50	>	* face of blocked IO or other unmanaged synchronization. The nested
51	>	* {@link ManagedBlocker} interface enables extension of the kinds of
52	>	* synchronization accommodated.
53		*
54		* <p>In addition to execution and lifecycle control methods, this
55		* class provides status check methods (for example
56	<	* {@code getStealCount}) that are intended to aid in developing,
56	>	* {@link #getStealCount}) that are intended to aid in developing,
57		* tuning, and monitoring fork/join applications. Also, method
58	<	* {@code toString} returns indications of pool state in a
58	>	* {@link #toString} returns indications of pool state in a
59		* convenient form for informal monitoring.
60		*
61	+	* <p> As is the case with other ExecutorServices, there are three
62	+	* main task execution methods summarized in the following
63	+	* table. These are designed to be used by clients not already engaged
64	+	* in fork/join computations in the current pool.  The main forms of
65	+	* these methods accept instances of {@code ForkJoinTask}, but
66	+	* overloaded forms also allow mixed execution of plain {@code
67	+	* Runnable}- or {@code Callable}- based activities as well.  However,
68	+	* tasks that are already executing in a pool should normally
69	+	* <em>NOT</em> use these pool execution methods, but instead use the
70	+	* within-computation forms listed in the table.
71	+	*
72	+	* <table BORDER CELLPADDING=3 CELLSPACING=1>
73	+	*  <tr>
74	+	*    <td></td>
75	+	*    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
76	+	*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
77	+	*  </tr>
78	+	*  <tr>
79	+	*    <td> <b>Arrange async execution</td>
80	+	*    <td> {@link #execute(ForkJoinTask)}</td>
81	+	*    <td> {@link ForkJoinTask#fork}</td>
82	+	*  </tr>
83	+	*  <tr>
84	+	*    <td> <b>Await and obtain result</td>
85	+	*    <td> {@link #invoke(ForkJoinTask)}</td>
86	+	*    <td> {@link ForkJoinTask#invoke}</td>
87	+	*  </tr>
88	+	*  <tr>
89	+	*    <td> <b>Arrange exec and obtain Future</td>
90	+	*    <td> {@link #submit(ForkJoinTask)}</td>
91	+	*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
92	+	*  </tr>
93	+	* </table>
94	+	*
95	+	* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
96	+	* used for all parallel task execution in a program or subsystem.
97	+	* Otherwise, use would not usually outweigh the construction and
98	+	* bookkeeping overhead of creating a large set of threads. For
99	+	* example, a common pool could be used for the {@code SortTasks}
100	+	* illustrated in {@link RecursiveAction}. Because {@code
101	+	* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
102	+	* daemon} mode, there is typically no need to explicitly {@link
103	+	* #shutdown} such a pool upon program exit.
104	+	*
105	+	* <pre>
106	+	* static final ForkJoinPool mainPool = new ForkJoinPool();
107	+	* ...
108	+	* public void sort(long[] array) {
109	+	*   mainPool.invoke(new SortTask(array, 0, array.length));
110	+	* }
111	+	* </pre>
112	+	*
113		* <p><b>Implementation notes</b>: This implementation restricts the
114		* maximum number of running threads to 32767. Attempts to create
115	<	* pools with greater than the maximum result in
116	<	* IllegalArgumentExceptions.
115	>	* pools with greater than the maximum number result in
116	>	* {@code IllegalArgumentException}.
117	>	*
118	>	* <p>This implementation rejects submitted tasks (that is, by throwing
119	>	* {@link RejectedExecutionException}) only when the pool is shut down
120	>	* or internal resources have been exhausted.
121		*
122		* @since 1.7
123		* @author Doug Lea
#	Line 70 | Line 125 | import java.util.concurrent.atomic.Atomi
125		public class ForkJoinPool extends AbstractExecutorService {
126
127		/*
128	<	* See the extended comments interspersed below for design,
129	<	* rationale, and walkthroughs.
130	<	*/
131	<
132	<	/** Mask for packing and unpacking shorts */
133	<	private static final int  shortMask = 0xffff;
134	<
135	<	/** Max pool size -- must be a power of two minus 1 */
136	<	private static final int MAX_THREADS =  0x7FFF;
137	<
138	<	/**
139	<	* Factory for creating new ForkJoinWorkerThreads.  A
140	<	* ForkJoinWorkerThreadFactory must be defined and used for
141	<	* ForkJoinWorkerThread subclasses that extend base functionality
142	<	* or initialize threads with different contexts.
128	>	* Implementation Overview
129	>	*
130	>	* This class provides the central bookkeeping and control for a
131	>	* set of worker threads: Submissions from non-FJ threads enter
132	>	* into a submission queue. Workers take these tasks and typically
133	>	* split them into subtasks that may be stolen by other workers.
134	>	* Preference rules give first priority to processing tasks from
135	>	* their own queues (LIFO or FIFO, depending on mode), then to
136	>	* randomized FIFO steals of tasks in other worker queues, and
137	>	* lastly to new submissions.
138	>	*
139	>	* The main throughput advantages of work-stealing stem from
140	>	* decentralized control -- workers mostly take tasks from
141	>	* themselves or each other. We cannot negate this in the
142	>	* implementation of other management responsibilities. The main
143	>	* tactic for avoiding bottlenecks is packing nearly all
144	>	* essentially atomic control state into a single 64bit volatile
145	>	* variable ("ctl"). This variable is read on the order of 10-100
146	>	* times as often as it is modified (always via CAS). (There is
147	>	* some additional control state, for example variable "shutdown"
148	>	* for which we can cope with uncoordinated updates.)  This
149	>	* streamlines synchronization and control at the expense of messy
150	>	* constructions needed to repack status bits upon updates.
151	>	* Updates tend not to contend with each other except during
152	>	* bursts while submitted tasks begin or end.  In some cases when
153	>	* they do contend, threads can instead do something else
154	>	* (usually, scan for tesks) until contention subsides.
155	>	*
156	>	* To enable packing, we restrict maximum parallelism to (1<<15)-1
157	>	* (which is far in excess of normal operating range) to allow
158	>	* ids, counts, and their negations (used for thresholding) to fit
159	>	* into 16bit fields.
160	>	*
161	>	* Recording Workers.  Workers are recorded in the "workers" array
162	>	* that is created upon pool construction and expanded if (rarely)
163	>	* necessary.  This is an array as opposed to some other data
164	>	* structure to support index-based random steals by workers.
165	>	* Updates to the array recording new workers and unrecording
166	>	* terminated ones are protected from each other by a seqLock
167	>	* (scanGuard) but the array is otherwise concurrently readable,
168	>	* and accessed directly by workers. To simplify index-based
169	>	* operations, the array size is always a power of two, and all
170	>	* readers must tolerate null slots. To avoid flailing during
171	>	* start-up, the array is presized to hold twice #parallelism
172	>	* workers (which is unlikely to need further resizing during
173	>	* execution). But to avoid dealing with so many null slots,
174	>	* variable scanGuard includes a mask for the nearest power of two
175	>	* that contains all current workers.  All worker thread creation
176	>	* is on-demand, triggered by task submissions, replacement of
177	>	* terminated workers, and/or compensation for blocked
178	>	* workers. However, all other support code is set up to work with
179	>	* other policies.  To ensure that we do not hold on to worker
180	>	* references that would prevent GC, ALL accesses to workers are
181	>	* via indices into the workers array (which is one source of some
182	>	* of the messy code constructions here). In essence, the workers
183	>	* array serves as a weak reference mechanism. Thus for example
184	>	* the wait queue field of ctl stores worker indices, not worker
185	>	* references.  Access to the workers in associated methods (for
186	>	* example signalWork) must both index-check and null-check the
187	>	* IDs. All such accesses ignore bad IDs by returning out early
188	>	* from what they are doing, since this can only be associated
189	>	* with termination, in which case it is OK to give up.
190	>	*
191	>	* All uses of the workers array, as well as queue arrays, check
192	>	* that the array is non-null (even if previously non-null). This
193	>	* allows nulling during termination, which is currently not
194	>	* necessary, but remains an option for resource-revocation-based
195	>	* shutdown schemes.
196	>	*
197	>	* Wait Queuing. Unlike HPC work-stealing frameworks, we cannot
198	>	* let workers spin indefinitely scanning for tasks when none are
199	>	* can be immediately found, and we cannot start/resume workers
200	>	* unless there appear to be tasks available.  On the other hand,
201	>	* we must quickly prod them into action when new tasks are
202	>	* submitted or generated.  We park/unpark workers after placing
203	>	* in an event wait queue when they cannot find work. This "queue"
204	>	* is actually a simple Treiber stack, headed by the "id" field of
205	>	* ctl, plus a 15bit counter value to both wake up waiters (by
206	>	* advancing their count) and avoid ABA effects. Successors are
207	>	* held in worker field "nextWait".  Queuing deals with several
208	>	* intrinsic races, mainly that a task-producing thread can miss
209	>	* seeing (and signalling) another thread that gave up looking for
210	>	* work but has not yet entered the wait queue. We solve this by
211	>	* requiring a full sweep of all workers both before (in scan())
212	>	* and after (in awaitWork()) a newly waiting worker is added to
213	>	* the wait queue. During a rescan, the worker might release some
214	>	* other queued worker rather than itself, which has the same net
215	>	* effect.
216	>	*
217	>	* Signalling.  We create or wake up workers only when there
218	>	* appears to be at least one task they might be able to find and
219	>	* execute.  When a submission is added or another worker adds a
220	>	* task to a queue that previously had two or fewer tasks, they
221	>	* signal waiting workers (or trigger creation of new ones if
222	>	* fewer than the given parallelism level -- see signalWork).
223	>	* These primary signals are buttressed by signals during rescans
224	>	* as well as those performed when a worker steals a task and
225	>	* notices that there are more tasks too; together these cover the
226	>	* signals needed in cases when more than two tasks are pushed
227	>	* but untaken.
228	>	*
229	>	* Trimming workers. To release resources after periods of lack of
230	>	* use, a worker starting to wait when the pool is quiescent will
231	>	* time out and terminate if the pool has remained quiescent for
232	>	* SHRINK_RATE nanosecs.
233	>	*
234	>	* Submissions. External submissions are maintained in an
235	>	* array-based queue that is structured identically to
236	>	* ForkJoinWorkerThread queues (which see) except for the use of
237	>	* submissionLock in method addSubmission. Unlike worker queues,
238	>	* multiple external threads can add new submissions.
239	>	*
240	>	* Compensation. Beyond work-stealing support and lifecycle
241	>	* control, the main responsibility of this framework is to take
242	>	* actions when one worker is waiting to join a task stolen (or
243	>	* always held by) another.  Because we are multiplexing many
244	>	* tasks on to a pool of workers, we can't just let them block (as
245	>	* in Thread.join).  We also cannot just reassign the joiner's
246	>	* run-time stack with another and replace it later, which would
247	>	* be a form of "continuation", that even if possible is not
248	>	* necessarily a good idea since we sometimes need both an
249	>	* unblocked task and its continuation to progress. Instead we
250	>	* combine two tactics:
251	>	*
252	>	*   Helping: Arranging for the joiner to execute some task that it
253	>	*      would be running if the steal had not occurred.  Method
254	>	*      ForkJoinWorkerThread.joinTask tracks joining->stealing
255	>	*      links to try to find such a task.
256	>	*
257	>	*   Compensating: Unless there are already enough live threads,
258	>	*      method tryPreBlock() may create or re-activate a spare
259	>	*      thread to compensate for blocked joiners until they
260	>	*      unblock.
261	>	*
262	>	* The ManagedBlocker extension API can't use helping so relies
263	>	* only on compensation in method awaitBlocker.
264	>	*
265	>	* It is impossible to keep exactly the target parallelism number
266	>	* of threads running at any given time.  Determining the
267	>	* existence of conservatively safe helping targets, the
268	>	* availability of already-created spares, and the apparent need
269	>	* to create new spares are all racy and require heuristic
270	>	* guidance, so we rely on multiple retries of each.  Currently,
271	>	* in keeping with on-demand signalling policy, we compensate only
272	>	* if blocking would leave less than one active (non-waiting,
273	>	* non-blocked) worker. Additionally, to avoid some false alarms
274	>	* due to GC, lagging counters, system activity, etc, compensated
275	>	* blocking for joins is only attempted after a number of rechecks
276	>	* proportional to the current apparent deficit (where retries are
277	>	* interspersed with Thread.yield, for good citizenship).  The
278	>	* variable blockedCount, incremented before blocking and
279	>	* decremented after, is sometimes needed to distinguish cases of
280	>	* waiting for work vs blocking on joins or other managed sync,
281	>	* but both the cases are equivalent for most pool control, so we
282	>	* can update non-atomically. (Additionally, contention on
283	>	* blockedCount alleviates some contention on ctl).
284	>	*
285	>	* Shutdown and Termination. A call to shutdownNow atomically sets
286	>	* the ctl stop bit and then (non-atomically) sets each workers
287	>	* "terminate" status, cancels all unprocessed tasks, and wakes up
288	>	* all waiting workers.  Detecting whether termination should
289	>	* commence after a non-abrupt shutdown() call requires more work
290	>	* and bookkeeping. We need consensus about quiesence (i.e., that
291	>	* there is no more work) which is reflected in active counts so
292	>	* long as there are no current blockers, as well as possible
293	>	* re-evaluations during independent changes in blocking or
294	>	* quiescing workers.
295	>	*
296	>	* Style notes: There is a lot of representation-level coupling
297	>	* among classes ForkJoinPool, ForkJoinWorkerThread, and
298	>	* ForkJoinTask.  Most fields of ForkJoinWorkerThread maintain
299	>	* data structures managed by ForkJoinPool, so are directly
300	>	* accessed.  Conversely we allow access to "workers" array by
301	>	* workers, and direct access to ForkJoinTask.status by both
302	>	* ForkJoinPool and ForkJoinWorkerThread.  There is little point
303	>	* trying to reduce this, since any associated future changes in
304	>	* representations will need to be accompanied by algorithmic
305	>	* changes anyway. All together, these low-level implementation
306	>	* choices produce as much as a factor of 4 performance
307	>	* improvement compared to naive implementations, and enable the
308	>	* processing of billions of tasks per second, at the expense of
309	>	* some ugliness.
310	>	*
311	>	* Methods signalWork() and scan() are the main bottlenecks so are
312	>	* especially heavily micro-optimized/mangled.  There are lots of
313	>	* inline assignments (of form "while ((local = field) != 0)")
314	>	* which are usually the simplest way to ensure the required read
315	>	* orderings (which are sometimes critical). This leads to a
316	>	* "C"-like style of listing declarations of these locals at the
317	>	* heads of methods or blocks.  There are several occurrences of
318	>	* the unusual "do {} while (!cas...)"  which is the simplest way
319	>	* to force an update of a CAS'ed variable. There are also other
320	>	* coding oddities that help some methods perform reasonably even
321	>	* when interpreted (not compiled).
322	>	*
323	>	* The order of declarations in this file is: (1) declarations of
324	>	* statics (2) fields (along with constants used when unpacking
325	>	* some of them), listed in an order that tends to reduce
326	>	* contention among them a bit under most JVMs.  (3) internal
327	>	* control methods (4) callbacks and other support for
328	>	* ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
329	>	* methods (plus a few little helpers). (6) static block
330	>	* initializing all statics in a minimally dependent order.
331	>	*/
332	>
333	>	/**
334	>	* Factory for creating new {@link ForkJoinWorkerThread}s.
335	>	* A {@code ForkJoinWorkerThreadFactory} must be defined and used
336	>	* for {@code ForkJoinWorkerThread} subclasses that extend base
337	>	* functionality or initialize threads with different contexts.
338		*/
339		public static interface ForkJoinWorkerThreadFactory {
340		/**
341		* Returns a new worker thread operating in the given pool.
342		*
343		* @param pool the pool this thread works in
344	<	* @throws NullPointerException if pool is null
344	>	* @throws NullPointerException if the pool is null
345		*/
346		public ForkJoinWorkerThread newThread(ForkJoinPool pool);
347		}
#	Line 100 | Line 350 | public class ForkJoinPool extends Abstra
350		* Default ForkJoinWorkerThreadFactory implementation; creates a
351		* new ForkJoinWorkerThread.
352		*/
353	<	static class  DefaultForkJoinWorkerThreadFactory
353	>	static class DefaultForkJoinWorkerThreadFactory
354		implements ForkJoinWorkerThreadFactory {
355		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
356	<	try {
107	<	return new ForkJoinWorkerThread(pool);
108	<	} catch (OutOfMemoryError oom)  {
109	<	return null;
110	<	}
356	>	return new ForkJoinWorkerThread(pool);
357		}
358		}
359
#	Line 116 | Line 362 | public class ForkJoinPool extends Abstra
362		* overridden in ForkJoinPool constructors.
363		*/
364		public static final ForkJoinWorkerThreadFactory
365	<	defaultForkJoinWorkerThreadFactory =
120	<	new DefaultForkJoinWorkerThreadFactory();
365	>	defaultForkJoinWorkerThreadFactory;
366
367		/**
368		* Permission required for callers of methods that may start or
369		* kill threads.
370		*/
371	<	private static final RuntimePermission modifyThreadPermission =
127	<	new RuntimePermission("modifyThread");
371	>	private static final RuntimePermission modifyThreadPermission;
372
373		/**
374		* If there is a security manager, makes sure caller has
#	Line 139 | Line 383 | public class ForkJoinPool extends Abstra
383		/**
384		* Generator for assigning sequence numbers as pool names.
385		*/
386	<	private static final AtomicInteger poolNumberGenerator =
143	<	new AtomicInteger();
386	>	private static final AtomicInteger poolNumberGenerator;
387
388		/**
389	<	* Array holding all worker threads in the pool. Initialized upon
390	<	* first use. Array size must be a power of two.  Updates and
391	<	* replacements are protected by workerLock, but it is always kept
392	<	* in a consistent enough state to be randomly accessed without
393	<	* locking by workers performing work-stealing.
389	>	* Generator for initial random seeds for worker victim
390	>	* selection. This is used only to create initial seeds. Random
391	>	* steals use a cheaper xorshift generator per steal attempt. We
392	>	* don't expect much contention on seedGenerator, so just use a
393	>	* plain Random.
394		*/
395	<	volatile ForkJoinWorkerThread[] workers;
395	>	static final Random workerSeedGenerator;
396
397		/**
398	<	* Lock protecting access to workers.
398	>	* Array holding all worker threads in the pool.  Initialized upon
399	>	* construction. Array size must be a power of two.  Updates and
400	>	* replacements are protected by scanGuard, but the array is
401	>	* always kept in a consistent enough state to be randomly
402	>	* accessed without locking by workers performing work-stealing,
403	>	* as well as other traversal-based methods in this class, so long
404	>	* as reads memory-acquire by first reading ctl. All readers must
405	>	* tolerate that some array slots may be null.
406		*/
407	<	private final ReentrantLock workerLock;
407	>	ForkJoinWorkerThread[] workers;
408
409		/**
410	<	* Condition for awaitTermination.
410	>	* Initial size for submission queue array. Must be a power of
411	>	* two.  In many applications, these always stay small so we use a
412	>	* small initial cap.
413		*/
414	<	private final Condition termination;
414	>	private static final int INITIAL_QUEUE_CAPACITY = 8;
415	>
416	>	/**
417	>	* Maximum size for submission queue array. Must be a power of two
418	>	* less than or equal to 1 << (31 - width of array entry) to
419	>	* ensure lack of index wraparound, but is capped at a lower
420	>	* value to help users trap runaway computations.
421	>	*/
422	>	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 24; // 16M
423
424		/**
425	<	* The uncaught exception handler used when any worker
166	<	* abruptly terminates
425	>	* Array serving as submission queue. Initialized upon construction.
426		*/
427	<	private Thread.UncaughtExceptionHandler ueh;
427	>	private ForkJoinTask<?>[] submissionQueue;
428	>
429	>	/**
430	>	* Lock protecting submissions array for addSubmission
431	>	*/
432	>	private final ReentrantLock submissionLock;
433	>
434	>	/**
435	>	* Condition for awaitTermination, using submissionLock for
436	>	* convenience.
437	>	*/
438	>	private final Condition termination;
439
440		/**
441		* Creation factory for worker threads.
#	Line 173 | Line 443 | public class ForkJoinPool extends Abstra
443		private final ForkJoinWorkerThreadFactory factory;
444
445		/**
446	<	* Head of stack of threads that were created to maintain
447	<	* parallelism when other threads blocked, but have since
178	<	* suspended when the parallelism level rose.
446	>	* The uncaught exception handler used when any worker abruptly
447	>	* terminates.
448		*/
449	<	private volatile WaitQueueNode spareStack;
449	>	final Thread.UncaughtExceptionHandler ueh;
450
451		/**
452	<	* Sum of per-thread steal counts, updated only when threads are
184	<	* idle or terminating.
452	>	* Prefix for assigning names to worker threads
453		*/
454	<	private final AtomicLong stealCount;
454	>	private final String workerNamePrefix;
455
456		/**
457	<	* Queue for external submissions.
457	>	* Sum of per-thread steal counts, updated only when threads are
458	>	* idle or terminating.
459		*/
460	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
460	>	private volatile long stealCount;
461
462		/**
463	<	* Head of Treiber stack for barrier sync. See below for explanation.
463	>	* Main pool control -- a long packed with:
464	>	* AC: Number of active running workers minus target parallelism (16 bits)
465	>	* TC: Number of total workers minus target parallelism (16bits)
466	>	* ST: true if pool is terminating (1 bit)
467	>	* EC: the wait count of top waiting thread (15 bits)
468	>	* ID: ~poolIndex of top of Treiber stack of waiting threads (16 bits)
469	>	*
470	>	* When convenient, we can extract the upper 32 bits of counts and
471	>	* the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e =
472	>	* (int)ctl.  The ec field is never accessed alone, but always
473	>	* together with id and st. The offsets of counts by the target
474	>	* parallelism and the positionings of fields makes it possible to
475	>	* perform the most common checks via sign tests of fields: When
476	>	* ac is negative, there are not enough active workers, when tc is
477	>	* negative, there are not enough total workers, when id is
478	>	* negative, there is at least one waiting worker, and when e is
479	>	* negative, the pool is terminating.  To deal with these possibly
480	>	* negative fields, we use casts in and out of "short" and/or
481	>	* signed shifts to maintain signedness.  Note: AC_SHIFT is
482	>	* redundantly declared in ForkJoinWorkerThread in order to
483	>	* integrate a surplus-threads check.
484		*/
485	<	private volatile WaitQueueNode syncStack;
485	>	volatile long ctl;
486	>
487	>	// bit positions/shifts for fields
488	>	private static final int  AC_SHIFT   = 48;
489	>	private static final int  TC_SHIFT   = 32;
490	>	private static final int  ST_SHIFT   = 31;
491	>	private static final int  EC_SHIFT   = 16;
492	>
493	>	// bounds
494	>	private static final int  MAX_ID     = 0x7fff;  // max poolIndex
495	>	private static final int  SMASK      = 0xffff;  // mask short bits
496	>	private static final int  SHORT_SIGN = 1 << 15;
497	>	private static final int  INT_SIGN   = 1 << 31;
498	>
499	>	// masks
500	>	private static final long STOP_BIT   = 0x0001L << ST_SHIFT;
501	>	private static final long AC_MASK    = ((long)SMASK) << AC_SHIFT;
502	>	private static final long TC_MASK    = ((long)SMASK) << TC_SHIFT;
503	>
504	>	// units for incrementing and decrementing
505	>	private static final long TC_UNIT    = 1L << TC_SHIFT;
506	>	private static final long AC_UNIT    = 1L << AC_SHIFT;
507	>
508	>	// masks and units for dealing with u = (int)(ctl >>> 32)
509	>	private static final int  UAC_SHIFT  = AC_SHIFT - 32;
510	>	private static final int  UTC_SHIFT  = TC_SHIFT - 32;
511	>	private static final int  UAC_MASK   = SMASK << UAC_SHIFT;
512	>	private static final int  UTC_MASK   = SMASK << UTC_SHIFT;
513	>	private static final int  UAC_UNIT   = 1 << UAC_SHIFT;
514	>	private static final int  UTC_UNIT   = 1 << UTC_SHIFT;
515	>
516	>	// masks and units for dealing with e = (int)ctl
517	>	private static final int  E_MASK     = 0x7fffffff; // no STOP_BIT
518	>	private static final int  EC_UNIT    = 1 << EC_SHIFT;
519
520		/**
521	<	* The count for event barrier
521	>	* The target parallelism level.
522		*/
523	<	private volatile long eventCount;
523	>	final int parallelism;
524
525		/**
526	<	* Pool number, just for assigning useful names to worker threads
526	>	* Index (mod submission queue length) of next element to take
527	>	* from submission queue.
528		*/
529	<	private final int poolNumber;
529	>	volatile int queueBase;
530
531		/**
532	<	* The maximum allowed pool size
532	>	* Index (mod submission queue length) of next element to add
533	>	* in submission queue.
534		*/
535	<	private volatile int maxPoolSize;
535	>	int queueTop;
536
537		/**
538	<	* The desired parallelism level, updated only under workerLock.
538	>	* True when shutdown() has been called.
539		*/
540	<	private volatile int parallelism;
540	>	volatile boolean shutdown;
541
542		/**
543		* True if use local fifo, not default lifo, for local polling
544	+	* Read by, and replicated by ForkJoinWorkerThreads
545		*/
546	<	private volatile boolean locallyFifo;
546	>	final boolean locallyFifo;
547
548		/**
549	<	* Holds number of total (i.e., created and not yet terminated)
550	<	* and running (i.e., not blocked on joins or other managed sync)
551	<	* threads, packed into one int to ensure consistent snapshot when
227	<	* making decisions about creating and suspending spare
228	<	* threads. Updated only by CAS.  Note: CASes in
229	<	* updateRunningCount and preJoin assume that running active count
230	<	* is in low word, so need to be modified if this changes.
549	>	* The number of threads in ForkJoinWorkerThreads.helpQuiescePool.
550	>	* When non-zero, suppresses automatic shutdown when active
551	>	* counts become zero.
552		*/
553	<	private volatile int workerCounts;
553	>	volatile int quiescerCount;
554
555	<	private static int totalCountOf(int s)           { return s >>> 16;  }
556	<	private static int runningCountOf(int s)         { return s & shortMask; }
557	<	private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
555	>	/**
556	>	* The number of threads blocked in join.
557	>	*/
558	>	volatile int blockedCount;
559
560		/**
561	<	* Adds delta (which may be negative) to running count.  This must
240	<	* be called before (with negative arg) and after (with positive)
241	<	* any managed synchronization (i.e., mainly, joins).
242	<	*
243	<	* @param delta the number to add
561	>	* Counter for worker Thread names (unrelated to their poolIndex)
562		*/
563	<	final void updateRunningCount(int delta) {
246	<	int s;
247	<	do {} while (!casWorkerCounts(s = workerCounts, s + delta));
248	<	}
563	>	private volatile int nextWorkerNumber;
564
565		/**
566	<	* Adds delta (which may be negative) to both total and running
252	<	* count.  This must be called upon creation and termination of
253	<	* worker threads.
254	<	*
255	<	* @param delta the number to add
566	>	* The index for the next created worker. Accessed under scanGuard.
567		*/
568	<	private void updateWorkerCount(int delta) {
258	<	int d = delta + (delta << 16); // add to both lo and hi parts
259	<	int s;
260	<	do {} while (!casWorkerCounts(s = workerCounts, s + d));
261	<	}
568	>	private int nextWorkerIndex;
569
570		/**
571	<	* Lifecycle control. High word contains runState, low word
572	<	* contains the number of workers that are (probably) executing
573	<	* tasks. This value is atomically incremented before a worker
574	<	* gets a task to run, and decremented when worker has no tasks
575	<	* and cannot find any. These two fields are bundled together to
576	<	* support correct termination triggering.  Note: activeCount
577	<	* CAS'es cheat by assuming active count is in low word, so need
578	<	* to be modified if this changes
571	>	* SeqLock and index masking for for updates to workers array.
572	>	* Locked when SG_UNIT is set. Unlocking clears bit by adding
573	>	* SG_UNIT. Staleness of read-only operations can be checked by
574	>	* comparing scanGuard to value before the reads. The low 16 bits
575	>	* (i.e, anding with SMASK) hold (the smallest power of two
576	>	* covering all worker indices, minus one, and is used to avoid
577	>	* dealing with large numbers of null slots when the workers array
578	>	* is overallocated.
579		*/
580	<	private volatile int runControl;
580	>	volatile int scanGuard;
581
582	<	// RunState values. Order among values matters
276	<	private static final int RUNNING     = 0;
277	<	private static final int SHUTDOWN    = 1;
278	<	private static final int TERMINATING = 2;
279	<	private static final int TERMINATED  = 3;
582	>	private static final int SG_UNIT = 1 << 16;
583
584	<	private static int runStateOf(int c)             { return c >>> 16; }
585	<	private static int activeCountOf(int c)          { return c & shortMask; }
586	<	private static int runControlFor(int r, int a)   { return (r << 16) + a; }
584	>	/**
585	>	* The wakeup interval (in nanoseconds) for a worker waiting for a
586	>	* task when the pool is quiescent to instead try to shrink the
587	>	* number of workers.  The exact value does not matter too
588	>	* much. It must be short enough to release resources during
589	>	* sustained periods of idleness, but not so short that threads
590	>	* are continually re-created.
591	>	*/
592	>	private static final long SHRINK_RATE =
593	>	4L * 1000L * 1000L * 1000L; // 4 seconds
594
595		/**
596	<	* Tries incrementing active count; fails on contention.
597	<	* Called by workers before/during executing tasks.
596	>	* Top-level loop for worker threads: On each step: if the
597	>	* previous step swept through all queues and found no tasks, or
598	>	* there are excess threads, then possibly blocks. Otherwise,
599	>	* scans for and, if found, executes a task. Returns when pool
600	>	* and/or worker terminate.
601		*
602	<	* @return true on success
602	>	* @param w the worker
603	>	*/
604	>	final void work(ForkJoinWorkerThread w) {
605	>	boolean swept = false;                // true on empty scans
606	>	long c;
607	>	while (!w.terminate && (int)(c = ctl) >= 0) {
608	>	int a;                            // active count
609	>	if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0)
610	>	swept = scan(w, a);
611	>	else if (tryAwaitWork(w, c))
612	>	swept = false;
613	>	}
614	>	}
615	>
616	>	// Signalling
617	>
618	>	/**
619	>	* Wakes up or creates a worker.
620		*/
621	<	final boolean tryIncrementActiveCount() {
622	<	int c = runControl;
623	<	return casRunControl(c, c+1);
621	>	final void signalWork() {
622	>	/*
623	>	* The while condition is true if: (there is are too few total
624	>	* workers OR there is at least one waiter) AND (there are too
625	>	* few active workers OR the pool is terminating).  The value
626	>	* of e distinguishes the remaining cases: zero (no waiters)
627	>	* for create, negative if terminating (in which case do
628	>	* nothing), else release a waiter. The secondary checks for
629	>	* release (non-null array etc) can fail if the pool begins
630	>	* terminating after the test, and don't impose any added cost
631	>	* because JVMs must perform null and bounds checks anyway.
632	>	*/
633	>	long c; int e, u;
634	>	while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) &
635	>	(INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN) && e >= 0) {
636	>	if (e > 0) {                         // release a waiting worker
637	>	int i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
638	>	if ((ws = workers) == null ||
639	>	(i = ~e & SMASK) >= ws.length ||
640	>	(w = ws[i]) == null)
641	>	break;
642	>	long nc = (((long)(w.nextWait & E_MASK)) |
643	>	((long)(u + UAC_UNIT) << 32));
644	>	if (w.eventCount == e &&
645	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
646	>	w.eventCount = (e + EC_UNIT) & E_MASK;
647	>	if (w.parked)
648	>	UNSAFE.unpark(w);
649	>	break;
650	>	}
651	>	}
652	>	else if (UNSAFE.compareAndSwapLong
653	>	(this, ctlOffset, c,
654	>	(long)(((u + UTC_UNIT) & UTC_MASK) |
655	>	((u + UAC_UNIT) & UAC_MASK)) << 32)) {
656	>	addWorker();
657	>	break;
658	>	}
659	>	}
660		}
661
662		/**
663	<	* Tries decrementing active count; fails on contention.
664	<	* Possibly triggers termination on success.
299	<	* Called by workers when they can't find tasks.
663	>	* Variant of signalWork to help release waiters on rescans.
664	>	* Tries once to release a waiter if active count < 0.
665		*
666	<	* @return true on success
666	>	* @return false if failed due to contention, else true
667		*/
668	<	final boolean tryDecrementActiveCount() {
669	<	int c = runControl;
670	<	int nextc = c - 1;
671	<	if (!casRunControl(c, nextc))
672	<	return false;
673	<	if (canTerminateOnShutdown(nextc))
674	<	terminateOnShutdown();
668	>	private boolean tryReleaseWaiter() {
669	>	long c; int e, i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws;
670	>	if ((e = (int)(c = ctl)) > 0 &&
671	>	(int)(c >> AC_SHIFT) < 0 &&
672	>	(ws = workers) != null &&
673	>	(i = ~e & SMASK) < ws.length &&
674	>	(w = ws[i]) != null) {
675	>	long nc = ((long)(w.nextWait & E_MASK) |
676	>	((c + AC_UNIT) & (AC_MASK|TC_MASK)));
677	>	if (w.eventCount != e ||
678	>	!UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
679	>	return false;
680	>	w.eventCount = (e + EC_UNIT) & E_MASK;
681	>	if (w.parked)
682	>	UNSAFE.unpark(w);
683	>	}
684		return true;
685		}
686
687	+	// Scanning for tasks
688	+
689		/**
690	<	* Returns true if argument represents zero active count and
691	<	* nonzero runstate, which is the triggering condition for
692	<	* terminating on shutdown.
690	>	* Scans for and, if found, executes one task. Scans start at a
691	>	* random index of workers array, and randomly select the first
692	>	* (2*#workers)-1 probes, and then, if all empty, resort to 2
693	>	* circular sweeps, which is necessary to check quiescence. and
694	>	* taking a submission only if no stealable tasks were found.  The
695	>	* steal code inside the loop is a specialized form of
696	>	* ForkJoinWorkerThread.deqTask, followed bookkeeping to support
697	>	* helpJoinTask and signal propagation. The code for submission
698	>	* queues is almost identical. On each steal, the worker completes
699	>	* not only the task, but also all local tasks that this task may
700	>	* have generated. On detecting staleness or contention when
701	>	* trying to take a task, this method returns without finishing
702	>	* sweep, which allows global state rechecks before retry.
703	>	*
704	>	* @param w the worker
705	>	* @param a the number of active workers
706	>	* @return true if swept all queues without finding a task
707		*/
708	<	private static boolean canTerminateOnShutdown(int c) {
709	<	// i.e. least bit is nonzero runState bit
710	<	return ((c & -c) >>> 16) != 0;
708	>	private boolean scan(ForkJoinWorkerThread w, int a) {
709	>	int g = scanGuard; // mask 0 avoids useless scans if only one active
710	>	int m = parallelism == 1 - a? 0 : g & SMASK;
711	>	ForkJoinWorkerThread[] ws = workers;
712	>	if (ws == null || ws.length <= m)         // staleness check
713	>	return false;
714	>	for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) {
715	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
716	>	ForkJoinWorkerThread v = ws[k & m];
717	>	if (v != null && (b = v.queueBase) != v.queueTop &&
718	>	(q = v.queue) != null && (i = (q.length - 1) & b) >= 0) {
719	>	long u = (i << ASHIFT) + ABASE;
720	>	if ((t = q[i]) != null && v.queueBase == b &&
721	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
722	>	int d = (v.queueBase = b + 1) - v.queueTop;
723	>	v.stealHint = w.poolIndex;
724	>	if (d != 0)
725	>	signalWork();             // propagate if nonempty
726	>	w.execTask(t);
727	>	}
728	>	r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5);
729	>	return false;                     // store next seed
730	>	}
731	>	else if (j < 0) {                     // xorshift
732	>	r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
733	>	}
734	>	else
735	>	++k;
736	>	}
737	>	if (scanGuard != g)                       // staleness check
738	>	return false;
739	>	else {                                    // try to take submission
740	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
741	>	if ((b = queueBase) != queueTop &&
742	>	(q = submissionQueue) != null &&
743	>	(i = (q.length - 1) & b) >= 0) {
744	>	long u = (i << ASHIFT) + ABASE;
745	>	if ((t = q[i]) != null && queueBase == b &&
746	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
747	>	queueBase = b + 1;
748	>	w.execTask(t);
749	>	}
750	>	return false;
751	>	}
752	>	return true;                         // all queues empty
753	>	}
754		}
755
756		/**
757	<	* Transition run state to at least the given state. Return true
758	<	* if not already at least given state.
757	>	* Tries to enqueue worker in wait queue and await change in
758	>	* worker's eventCount.  Before blocking, rescans queues to avoid
759	>	* missed signals.  If the pool is quiescent, possibly terminates
760	>	* worker upon exit.
761	>	*
762	>	* @param w the calling worker
763	>	* @param c the ctl value on entry
764	>	* @return true if waited or another thread was released upon enq
765		*/
766	<	private boolean transitionRunStateTo(int state) {
767	<	for (;;) {
768	<	int c = runControl;
769	<	if (runStateOf(c) >= state)
770	<	return false;
771	<	if (casRunControl(c, runControlFor(state, activeCountOf(c))))
766	>	private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) {
767	>	int v = w.eventCount;
768	>	w.nextWait = (int)c;                       // w's successor record
769	>	long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
770	>	if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
771	>	long d = ctl; // return true if lost to a deq, to force rescan
772	>	return (int)d != (int)c && ((d - c) & AC_MASK) >= 0L;
773	>	}
774	>	boolean rescanned = false;
775	>	for (int sc;;) {
776	>	if (w.eventCount != v)
777		return true;
778	+	if ((sc = w.stealCount) != 0) {
779	+	long s = stealCount;               // accumulate stealCount
780	+	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s+sc))
781	+	w.stealCount = 0;
782	+	}
783	+	else if (!rescanned) {
784	+	int g = scanGuard, m = g & SMASK;
785	+	ForkJoinWorkerThread[] ws = workers;
786	+	if (ws != null && m < ws.length) {
787	+	rescanned = true;
788	+	for (int i = 0; i <= m; ++i) {
789	+	ForkJoinWorkerThread u = ws[i];
790	+	if (u != null) {
791	+	if (u.queueBase != u.queueTop &&
792	+	!tryReleaseWaiter())
793	+	rescanned = false; // contended
794	+	if (w.eventCount != v)
795	+	return true;
796	+	}
797	+	}
798	+	}
799	+	if (scanGuard != g ||              // stale
800	+	(queueBase != queueTop && !tryReleaseWaiter()))
801	+	rescanned = false;
802	+	if (!rescanned)
803	+	Thread.yield();                // reduce contention
804	+	else
805	+	Thread.interrupted();          // clear before park
806	+	}
807	+	else if (parallelism + (int)(ctl >> AC_SHIFT) == 0 &&
808	+	blockedCount == 0 && quiescerCount == 0)
809	+	idleAwaitWork(w, v);               // quiescent -- maybe shrink
810	+	else {
811	+	w.parked = true;                   // must recheck
812	+	if (w.eventCount != v) {
813	+	w.parked = false;
814	+	return true;
815	+	}
816	+	LockSupport.park(this);
817	+	rescanned = w.parked = false;
818	+	}
819		}
820		}
821
822		/**
823	<	* Controls whether to add spares to maintain parallelism
824	<	*/
825	<	private volatile boolean maintainsParallelism;
823	>	* If pool is quiescent, checks for termination, and waits for
824	>	* event signal for up to SHRINK_RATE nanosecs. On timeout, if ctl
825	>	* has not changed, terminates the worker. Upon its termination
826	>	* (see deregisterWorker), it may wake up another worker to
827	>	* possibly repeat this process.
828	>	*
829	>	* @param w the calling worker
830	>	* @param v the eventCount w must wait until changed
831	>	*/
832	>	private void idleAwaitWork(ForkJoinWorkerThread w, int v) {
833	>	ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs
834	>	if (shutdown)
835	>	tryTerminate(false);
836	>	long c = ctl;
837	>	long nc = (((c & (AC_MASK|TC_MASK)) + AC_UNIT) |
838	>	(long)(w.nextWait & E_MASK)); // ctl value to release w
839	>	if (w.eventCount == v &&
840	>	parallelism + (int)(c >> AC_SHIFT) == 0 &&
841	>	blockedCount == 0 && quiescerCount == 0) {
842	>	long startTime = System.nanoTime();
843	>	Thread.interrupted();
844	>	if (w.eventCount == v) {
845	>	w.parked = true;
846	>	if (w.eventCount == v)
847	>	LockSupport.parkNanos(this, SHRINK_RATE);
848	>	w.parked = false;
849	>	if (w.eventCount == v && ctl == c &&
850	>	System.nanoTime() - startTime >= SHRINK_RATE &&
851	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
852	>	w.terminate = true;
853	>	w.eventCount = ((int)c + EC_UNIT) & E_MASK;
854	>	}
855	>	}
856	>	}
857	>	}
858
859	<	// Constructors
859	>	// Submissions
860
861		/**
862	<	* Creates a ForkJoinPool with a pool size equal to the number of
863	<	* processors available on the system, using the default
347	<	* ForkJoinWorkerThreadFactory.
862	>	* Enqueues the given task in the submissionQueue.  Same idea as
863	>	* ForkJoinWorkerThread.pushTask except for use of submissionLock.
864		*
865	<	* @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")}
865	>	* @param t the task
866		*/
867	<	public ForkJoinPool() {
868	<	this(Runtime.getRuntime().availableProcessors(),
869	<	defaultForkJoinWorkerThreadFactory);
867	>	private void addSubmission(ForkJoinTask<?> t) {
868	>	final ReentrantLock lock = this.submissionLock;
869	>	lock.lock();
870	>	try {
871	>	ForkJoinTask<?>[] q; int s, m;
872	>	if ((q = submissionQueue) != null) {    // ignore if queue removed
873	>	long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE;
874	>	UNSAFE.putOrderedObject(q, u, t);
875	>	queueTop = s + 1;
876	>	if (s - queueBase == m)
877	>	growSubmissionQueue();
878	>	}
879	>	} finally {
880	>	lock.unlock();
881	>	}
882	>	signalWork();
883		}
884
885	+	//  (pollSubmission is defined below with exported methods)
886	+
887		/**
888	<	* Creates a ForkJoinPool with the indicated parallelism level
889	<	* threads and using the default ForkJoinWorkerThreadFactory.
362	<	*
363	<	* @param parallelism the number of worker threads
364	<	* @throws IllegalArgumentException if parallelism less than or
365	<	* equal to zero
366	<	* @throws SecurityException if a security manager exists and
367	<	*         the caller is not permitted to modify threads
368	<	*         because it does not hold {@link
369	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
888	>	* Creates or doubles submissionQueue array.
889	>	* Basically identical to ForkJoinWorkerThread version
890		*/
891	<	public ForkJoinPool(int parallelism) {
892	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
891	>	private void growSubmissionQueue() {
892	>	ForkJoinTask<?>[] oldQ = submissionQueue;
893	>	int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY;
894	>	if (size > MAXIMUM_QUEUE_CAPACITY)
895	>	throw new RejectedExecutionException("Queue capacity exceeded");
896	>	if (size < INITIAL_QUEUE_CAPACITY)
897	>	size = INITIAL_QUEUE_CAPACITY;
898	>	ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size];
899	>	int mask = size - 1;
900	>	int top = queueTop;
901	>	int oldMask;
902	>	if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) {
903	>	for (int b = queueBase; b != top; ++b) {
904	>	long u = ((b & oldMask) << ASHIFT) + ABASE;
905	>	Object x = UNSAFE.getObjectVolatile(oldQ, u);
906	>	if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null))
907	>	UNSAFE.putObjectVolatile
908	>	(q, ((b & mask) << ASHIFT) + ABASE, x);
909	>	}
910	>	}
911	>	}
912	>
913	>	// Blocking support
914	>
915	>	/**
916	>	* Tries to increment blockedCount, decrement active count
917	>	* (sometimes implicitly) and possibly release or create a
918	>	* compensating worker in preparation for blocking. Fails
919	>	* on contention or termination.
920	>	*
921	>	* @return true if the caller can block, else should recheck and retry
922	>	*/
923	>	private boolean tryPreBlock() {
924	>	int b = blockedCount;
925	>	if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) {
926	>	int pc = parallelism;
927	>	do {
928	>	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
929	>	int e, ac, tc, rc, i;
930	>	long c = ctl;
931	>	int u = (int)(c >>> 32);
932	>	if ((e = (int)c) < 0) {
933	>	// skip -- terminating
934	>	}
935	>	else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 &&
936	>	(ws = workers) != null &&
937	>	(i = ~e & SMASK) < ws.length &&
938	>	(w = ws[i]) != null) {
939	>	long nc = ((long)(w.nextWait & E_MASK) |
940	>	(c & (AC_MASK|TC_MASK)));
941	>	if (w.eventCount == e &&
942	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
943	>	w.eventCount = (e + EC_UNIT) & E_MASK;
944	>	if (w.parked)
945	>	UNSAFE.unpark(w);
946	>	return true;             // release an idle worker
947	>	}
948	>	}
949	>	else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
950	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
951	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
952	>	return true;             // no compensation needed
953	>	}
954	>	else if (tc + pc < MAX_ID) {
955	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
956	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
957	>	addWorker();
958	>	return true;            // create a replacement
959	>	}
960	>	}
961	>	// try to back out on any failure and let caller retry
962	>	} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
963	>	b = blockedCount, b - 1));
964	>	}
965	>	return false;
966		}
967
968		/**
969	<	* Creates a ForkJoinPool with parallelism equal to the number of
377	<	* processors available on the system and using the given
378	<	* ForkJoinWorkerThreadFactory.
379	<	*
380	<	* @param factory the factory for creating new threads
381	<	* @throws NullPointerException if factory is null
382	<	* @throws SecurityException if a security manager exists and
383	<	*         the caller is not permitted to modify threads
384	<	*         because it does not hold {@link
385	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
969	>	* Decrements blockedCount and increments active count
970		*/
971	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
972	<	this(Runtime.getRuntime().availableProcessors(), factory);
971	>	private void postBlock() {
972	>	long c;
973	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset,  // no mask
974	>	c = ctl, c + AC_UNIT));
975	>	int b;
976	>	do {} while(!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
977	>	b = blockedCount, b - 1));
978		}
979
980		/**
981	<	* Creates a ForkJoinPool with the given parallelism and factory.
981	>	* Possibly blocks waiting for the given task to complete, or
982	>	* cancels the task if terminating.  Fails to wait if contended.
983		*
984	<	* @param parallelism the targeted number of worker threads
395	<	* @param factory the factory for creating new threads
396	<	* @throws IllegalArgumentException if parallelism less than or
397	<	* equal to zero, or greater than implementation limit
398	<	* @throws NullPointerException if factory is null
399	<	* @throws SecurityException if a security manager exists and
400	<	*         the caller is not permitted to modify threads
401	<	*         because it does not hold {@link
402	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
984	>	* @param joinMe the task
985		*/
986	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
987	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
988	<	throw new IllegalArgumentException();
989	<	if (factory == null)
990	<	throw new NullPointerException();
991	<	checkPermission();
992	<	this.factory = factory;
993	<	this.parallelism = parallelism;
994	<	this.maxPoolSize = MAX_THREADS;
995	<	this.maintainsParallelism = true;
996	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
415	<	this.workerLock = new ReentrantLock();
416	<	this.termination = workerLock.newCondition();
417	<	this.stealCount = new AtomicLong();
418	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
419	<	// worker array and workers are lazily constructed
986	>	final void tryAwaitJoin(ForkJoinTask<?> joinMe) {
987	>	int s;
988	>	Thread.interrupted(); // clear interrupts before checking termination
989	>	if (joinMe.status >= 0) {
990	>	if (tryPreBlock()) {
991	>	joinMe.tryAwaitDone(0L);
992	>	postBlock();
993	>	}
994	>	if ((ctl & STOP_BIT) != 0L)
995	>	joinMe.cancelIgnoringExceptions();
996	>	}
997		}
998
999		/**
1000	<	* Creates a new worker thread using factory.
1000	>	* Possibly blocks the given worker waiting for joinMe to
1001	>	* complete or timeout
1002		*
1003	<	* @param index the index to assign worker
1004	<	* @return new worker, or null of factory failed
1003	>	* @param joinMe the task
1004	>	* @param millis the wait time for underlying Object.wait
1005		*/
1006	<	private ForkJoinWorkerThread createWorker(int index) {
1007	<	Thread.UncaughtExceptionHandler h = ueh;
1008	<	ForkJoinWorkerThread w = factory.newThread(this);
1009	<	if (w != null) {
1010	<	w.poolIndex = index;
1011	<	w.setDaemon(true);
1012	<	w.setAsyncMode(locallyFifo);
1013	<	w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
1014	<	if (h != null)
1015	<	w.setUncaughtExceptionHandler(h);
1006	>	final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) {
1007	>	while (joinMe.status >= 0) {
1008	>	Thread.interrupted();
1009	>	if ((ctl & STOP_BIT) != 0L) {
1010	>	joinMe.cancelIgnoringExceptions();
1011	>	break;
1012	>	}
1013	>	if (tryPreBlock()) {
1014	>	long last = System.nanoTime();
1015	>	while (joinMe.status >= 0) {
1016	>	long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
1017	>	if (millis <= 0)
1018	>	break;
1019	>	joinMe.tryAwaitDone(millis);
1020	>	if (joinMe.status < 0)
1021	>	break;
1022	>	if ((ctl & STOP_BIT) != 0L) {
1023	>	joinMe.cancelIgnoringExceptions();
1024	>	break;
1025	>	}
1026	>	long now = System.nanoTime();
1027	>	nanos -= now - last;
1028	>	last = now;
1029	>	}
1030	>	postBlock();
1031	>	break;
1032	>	}
1033		}
439	–	return w;
1034		}
1035
1036		/**
1037	<	* Returns a good size for worker array given pool size.
444	<	* Currently requires size to be a power of two.
1037	>	* If necessary, compensates for blocker, and blocks
1038		*/
1039	<	private static int arraySizeFor(int poolSize) {
1040	<	return (poolSize <= 1) ? 1 :
1041	<	(1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
1039	>	private void awaitBlocker(ManagedBlocker blocker)
1040	>	throws InterruptedException {
1041	>	while (!blocker.isReleasable()) {
1042	>	if (tryPreBlock()) {
1043	>	try {
1044	>	do {} while (!blocker.isReleasable() && !blocker.block());
1045	>	} finally {
1046	>	postBlock();
1047	>	}
1048	>	break;
1049	>	}
1050	>	}
1051		}
1052
1053	+	// Creating, registering and deregistring workers
1054	+
1055		/**
1056	<	* Creates or resizes array if necessary to hold newLength.
1057	<	* Call only under exclusion.
454	<	*
455	<	* @return the array
1056	>	* Tries to create and start a worker; minimally rolls back counts
1057	>	* on failure.
1058		*/
1059	<	private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
1060	<	ForkJoinWorkerThread[] ws = workers;
1061	<	if (ws == null)
1062	<	return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
1063	<	else if (newLength > ws.length)
1064	<	return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
1059	>	private void addWorker() {
1060	>	Throwable ex = null;
1061	>	ForkJoinWorkerThread t = null;
1062	>	try {
1063	>	t = factory.newThread(this);
1064	>	} catch (Throwable e) {
1065	>	ex = e;
1066	>	}
1067	>	if (t == null) {  // null or exceptional factory return
1068	>	long c;       // adjust counts
1069	>	do {} while (!UNSAFE.compareAndSwapLong
1070	>	(this, ctlOffset, c = ctl,
1071	>	(((c - AC_UNIT) & AC_MASK) |
1072	>	((c - TC_UNIT) & TC_MASK) |
1073	>	(c & ~(AC_MASK|TC_MASK)))));
1074	>	// Propagate exception if originating from an external caller
1075	>	if (!tryTerminate(false) && ex != null &&
1076	>	!(Thread.currentThread() instanceof ForkJoinWorkerThread))
1077	>	UNSAFE.throwException(ex);
1078	>	}
1079		else
1080	<	return ws;
1080	>	t.start();
1081		}
1082
1083		/**
1084	<	* Tries to shrink workers into smaller array after one or more terminate.
1084	>	* Callback from ForkJoinWorkerThread constructor to assign a
1085	>	* public name
1086		*/
1087	<	private void tryShrinkWorkerArray() {
1088	<	ForkJoinWorkerThread[] ws = workers;
1089	<	if (ws != null) {
1090	<	int len = ws.length;
1091	<	int last = len - 1;
475	<	while (last >= 0 && ws[last] == null)
476	<	--last;
477	<	int newLength = arraySizeFor(last+1);
478	<	if (newLength < len)
479	<	workers = Arrays.copyOf(ws, newLength);
1087	>	final String nextWorkerName() {
1088	>	for (int n;;) {
1089	>	if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset,
1090	>	n = nextWorkerNumber, ++n))
1091	>	return workerNamePrefix + n;
1092		}
1093		}
1094
1095		/**
1096	<	* Initializes workers if necessary.
1096	>	* Callback from ForkJoinWorkerThread constructor to
1097	>	* determine its poolIndex and record in workers array.
1098	>	*
1099	>	* @param w the worker
1100	>	* @return the worker's pool index
1101		*/
1102	<	final void ensureWorkerInitialization() {
1103	<	ForkJoinWorkerThread[] ws = workers;
1104	<	if (ws == null) {
1105	<	final ReentrantLock lock = this.workerLock;
1106	<	lock.lock();
1107	<	try {
1108	<	ws = workers;
1109	<	if (ws == null) {
1110	<	int ps = parallelism;
1111	<	ws = ensureWorkerArrayCapacity(ps);
1112	<	for (int i = 0; i < ps; ++i) {
1113	<	ForkJoinWorkerThread w = createWorker(i);
1114	<	if (w != null) {
1115	<	ws[i] = w;
1116	<	w.start();
1117	<	updateWorkerCount(1);
1102	>	final int registerWorker(ForkJoinWorkerThread w) {
1103	>	/*
1104	>	* In the typical case, a new worker acquires the lock, uses
1105	>	* next available index and returns quickly.  Since we should
1106	>	* not block callers (ultimately from signalWork or
1107	>	* tryPreBlock) waiting for the lock needed to do this, we
1108	>	* instead help release other workers while waiting for the
1109	>	* lock.
1110	>	*/
1111	>	for (int g;;) {
1112	>	ForkJoinWorkerThread[] ws;
1113	>	if (((g = scanGuard) & SG_UNIT) == 0 &&
1114	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1115	>	g, g | SG_UNIT)) {
1116	>	int k = nextWorkerIndex;
1117	>	try {
1118	>	if ((ws = workers) != null) { // ignore on shutdown
1119	>	int n = ws.length;
1120	>	if (k < 0 || k >= n || ws[k] != null) {
1121	>	for (k = 0; k < n && ws[k] != null; ++k)
1122	>	;
1123	>	if (k == n)
1124	>	ws = workers = Arrays.copyOf(ws, n << 1);
1125		}
1126	+	ws[k] = w;
1127	+	nextWorkerIndex = k + 1;
1128	+	int m = g & SMASK;
1129	+	g = k >= m? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1);
1130	+	}
1131	+	} finally {
1132	+	scanGuard = g;
1133	+	}
1134	+	return k;
1135	+	}
1136	+	else if ((ws = workers) != null) { // help release others
1137	+	for (ForkJoinWorkerThread u : ws) {
1138	+	if (u != null && u.queueBase != u.queueTop) {
1139	+	if (tryReleaseWaiter())
1140	+	break;
1141		}
1142		}
505	–	} finally {
506	–	lock.unlock();
1143		}
1144		}
1145		}
1146
1147		/**
1148	<	* Worker creation and startup for threads added via setParallelism.
1148	>	* Final callback from terminating worker.  Removes record of
1149	>	* worker from array, and adjusts counts. If pool is shutting
1150	>	* down, tries to complete termination.
1151	>	*
1152	>	* @param w the worker
1153		*/
1154	<	private void createAndStartAddedWorkers() {
1155	<	resumeAllSpares();  // Allow spares to convert to nonspare
1156	<	int ps = parallelism;
1157	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
1158	<	int len = ws.length;
1159	<	// Sweep through slots, to keep lowest indices most populated
1160	<	int k = 0;
1161	<	while (k < len) {
1162	<	if (ws[k] != null) {
1163	<	++k;
1164	<	continue;
1154	>	final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) {
1155	>	int idx = w.poolIndex;
1156	>	int sc = w.stealCount;
1157	>	int steps = 0;
1158	>	// Remove from array, adjust worker counts and collect steal count.
1159	>	// We can intermix failed removes or adjusts with steal updates
1160	>	do {
1161	>	long s, c;
1162	>	int g;
1163	>	if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 &&
1164	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1165	>	g, g |= SG_UNIT)) {
1166	>	ForkJoinWorkerThread[] ws = workers;
1167	>	if (ws != null && idx >= 0 &&
1168	>	idx < ws.length && ws[idx] == w)
1169	>	ws[idx] = null;    // verify
1170	>	nextWorkerIndex = idx;
1171	>	scanGuard = g + SG_UNIT;
1172	>	steps = 1;
1173	>	}
1174	>	if (steps == 1 &&
1175	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1176	>	(((c - AC_UNIT) & AC_MASK) |
1177	>	((c - TC_UNIT) & TC_MASK) |
1178	>	(c & ~(AC_MASK|TC_MASK)))))
1179	>	steps = 2;
1180	>	if (sc != 0 &&
1181	>	UNSAFE.compareAndSwapLong(this, stealCountOffset,
1182	>	s = stealCount, s + sc))
1183	>	sc = 0;
1184	>	} while (steps != 2 || sc != 0);
1185	>	if (!tryTerminate(false)) {
1186	>	if (ex != null)   // possibly replace if died abnormally
1187	>	signalWork();
1188	>	else
1189	>	tryReleaseWaiter();
1190	>	}
1191	>	}
1192	>
1193	>	// Shutdown and termination
1194	>
1195	>	/**
1196	>	* Possibly initiates and/or completes termination.
1197	>	*
1198	>	* @param now if true, unconditionally terminate, else only
1199	>	* if shutdown and empty queue and no active workers
1200	>	* @return true if now terminating or terminated
1201	>	*/
1202	>	private boolean tryTerminate(boolean now) {
1203	>	long c;
1204	>	while (((c = ctl) & STOP_BIT) == 0) {
1205	>	if (!now) {
1206	>	if ((int)(c >> AC_SHIFT) != -parallelism)
1207	>	return false;
1208	>	if (!shutdown || blockedCount != 0 || quiescerCount != 0 ||
1209	>	queueTop - queueBase > 0) {
1210	>	if (ctl == c) // staleness check
1211	>	return false;
1212	>	continue;
1213	>	}
1214		}
1215	<	int s = workerCounts;
1216	<	int tc = totalCountOf(s);
1217	<	int rc = runningCountOf(s);
1218	<	if (rc >= ps || tc >= ps)
1219	<	break;
1220	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
1221	<	ForkJoinWorkerThread w = createWorker(k);
1222	<	if (w != null) {
1223	<	ws[k++] = w;
1224	<	w.start();
1215	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT))
1216	>	startTerminating();
1217	>	}
1218	>	if ((short)(c >>> TC_SHIFT) == -parallelism) {
1219	>	submissionLock.lock();
1220	>	termination.signalAll();
1221	>	submissionLock.unlock();
1222	>	}
1223	>	return true;
1224	>	}
1225	>
1226	>	/**
1227	>	* Runs up to three passes through workers: (0) Setting
1228	>	* termination status for each worker, followed by wakeups up
1229	>	* queued workers (1) helping cancel tasks (2) interrupting
1230	>	* lagging threads (likely in external tasks, but possibly also
1231	>	* blocked in joins).  Each pass repeats previous steps because of
1232	>	* potential lagging thread creation.
1233	>	*/
1234	>	private void startTerminating() {
1235	>	cancelSubmissions();
1236	>	for (int pass = 0; pass < 3; ++pass) {
1237	>	ForkJoinWorkerThread[] ws = workers;
1238	>	if (ws != null) {
1239	>	for (ForkJoinWorkerThread w : ws) {
1240	>	if (w != null) {
1241	>	w.terminate = true;
1242	>	if (pass > 0) {
1243	>	w.cancelTasks();
1244	>	if (pass > 1 && !w.isInterrupted()) {
1245	>	try {
1246	>	w.interrupt();
1247	>	} catch (SecurityException ignore) {
1248	>	}
1249	>	}
1250	>	}
1251	>	}
1252		}
1253	<	else {
1254	<	updateWorkerCount(-1); // back out on failed creation
1255	<	break;
1253	>	terminateWaiters();
1254	>	}
1255	>	}
1256	>	}
1257	>
1258	>	/**
1259	>	* Polls and cancels all submissions. Called only during termination.
1260	>	*/
1261	>	private void cancelSubmissions() {
1262	>	while (queueBase != queueTop) {
1263	>	ForkJoinTask<?> task = pollSubmission();
1264	>	if (task != null) {
1265	>	try {
1266	>	task.cancel(false);
1267	>	} catch (Throwable ignore) {
1268		}
1269		}
1270		}
1271		}
1272
1273	<	// Execution methods
1273	>	/**
1274	>	* Tries to set the termination status of waiting workers, and
1275	>	* then wake them up (after which they will terminate).
1276	>	*/
1277	>	private void terminateWaiters() {
1278	>	ForkJoinWorkerThread[] ws = workers;
1279	>	if (ws != null) {
1280	>	ForkJoinWorkerThread w; long c; int i, e;
1281	>	int n = ws.length;
1282	>	while ((i = ~(e = (int)(c = ctl)) & SMASK) < n &&
1283	>	(w = ws[i]) != null && w.eventCount == (e & E_MASK)) {
1284	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c,
1285	>	(long)(w.nextWait & E_MASK) |
1286	>	((c + AC_UNIT) & AC_MASK) |
1287	>	(c & (TC_MASK|STOP_BIT)))) {
1288	>	w.terminate = true;
1289	>	w.eventCount = e + EC_UNIT;
1290	>	if (w.parked)
1291	>	UNSAFE.unpark(w);
1292	>	}
1293	>	}
1294	>	}
1295	>	}
1296	>
1297	>	// misc ForkJoinWorkerThread support
1298
1299		/**
1300	<	* Common code for execute, invoke and submit
1300	>	* Increment or decrement quiescerCount. Needed only to prevent
1301	>	* triggering shutdown if a worker is transiently inactive while
1302	>	* checking quiescence.
1303	>	*
1304	>	* @param delta 1 for increment, -1 for decrement
1305		*/
1306	<	private <T> void doSubmit(ForkJoinTask<T> task) {
1307	<	if (task == null)
1306	>	final void addQuiescerCount(int delta) {
1307	>	int c;
1308	>	do {} while(!UNSAFE.compareAndSwapInt(this, quiescerCountOffset,
1309	>	c = quiescerCount, c + delta));
1310	>	}
1311	>
1312	>	/**
1313	>	* Directly increment or decrement active count without
1314	>	* queuing. This method is used to transiently assert inactivation
1315	>	* while checking quiescence.
1316	>	*
1317	>	* @param delta 1 for increment, -1 for decrement
1318	>	*/
1319	>	final void addActiveCount(int delta) {
1320	>	long d = delta < 0 ? -AC_UNIT : AC_UNIT;
1321	>	long c;
1322	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1323	>	((c + d) & AC_MASK) |
1324	>	(c & ~AC_MASK)));
1325	>	}
1326	>
1327	>	/**
1328	>	* Returns the approximate (non-atomic) number of idle threads per
1329	>	* active thread.
1330	>	*/
1331	>	final int idlePerActive() {
1332	>	// Approximate at powers of two for small values, saturate past 4
1333	>	int p = parallelism;
1334	>	int a = p + (int)(ctl >> AC_SHIFT);
1335	>	return (a > (p >>>= 1) ? 0 :
1336	>	a > (p >>>= 1) ? 1 :
1337	>	a > (p >>>= 1) ? 2 :
1338	>	a > (p >>>= 1) ? 4 :
1339	>	8);
1340	>	}
1341	>
1342	>	// Exported methods
1343	>
1344	>	// Constructors
1345	>
1346	>	/**
1347	>	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1348	>	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1349	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1350	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1351	>	*
1352	>	* @throws SecurityException if a security manager exists and
1353	>	*         the caller is not permitted to modify threads
1354	>	*         because it does not hold {@link
1355	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1356	>	*/
1357	>	public ForkJoinPool() {
1358	>	this(Runtime.getRuntime().availableProcessors(),
1359	>	defaultForkJoinWorkerThreadFactory, null, false);
1360	>	}
1361	>
1362	>	/**
1363	>	* Creates a {@code ForkJoinPool} with the indicated parallelism
1364	>	* level, the {@linkplain
1365	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1366	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1367	>	*
1368	>	* @param parallelism the parallelism level
1369	>	* @throws IllegalArgumentException if parallelism less than or
1370	>	*         equal to zero, or greater than implementation limit
1371	>	* @throws SecurityException if a security manager exists and
1372	>	*         the caller is not permitted to modify threads
1373	>	*         because it does not hold {@link
1374	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1375	>	*/
1376	>	public ForkJoinPool(int parallelism) {
1377	>	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1378	>	}
1379	>
1380	>	/**
1381	>	* Creates a {@code ForkJoinPool} with the given parameters.
1382	>	*
1383	>	* @param parallelism the parallelism level. For default value,
1384	>	* use {@link java.lang.Runtime#availableProcessors}.
1385	>	* @param factory the factory for creating new threads. For default value,
1386	>	* use {@link #defaultForkJoinWorkerThreadFactory}.
1387	>	* @param handler the handler for internal worker threads that
1388	>	* terminate due to unrecoverable errors encountered while executing
1389	>	* tasks. For default value, use {@code null}.
1390	>	* @param asyncMode if true,
1391	>	* establishes local first-in-first-out scheduling mode for forked
1392	>	* tasks that are never joined. This mode may be more appropriate
1393	>	* than default locally stack-based mode in applications in which
1394	>	* worker threads only process event-style asynchronous tasks.
1395	>	* For default value, use {@code false}.
1396	>	* @throws IllegalArgumentException if parallelism less than or
1397	>	*         equal to zero, or greater than implementation limit
1398	>	* @throws NullPointerException if the factory is null
1399	>	* @throws SecurityException if a security manager exists and
1400	>	*         the caller is not permitted to modify threads
1401	>	*         because it does not hold {@link
1402	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1403	>	*/
1404	>	public ForkJoinPool(int parallelism,
1405	>	ForkJoinWorkerThreadFactory factory,
1406	>	Thread.UncaughtExceptionHandler handler,
1407	>	boolean asyncMode) {
1408	>	checkPermission();
1409	>	if (factory == null)
1410		throw new NullPointerException();
1411	<	if (isShutdown())
1412	<	throw new RejectedExecutionException();
1413	<	if (workers == null)
1414	<	ensureWorkerInitialization();
1415	<	submissionQueue.offer(task);
1416	<	signalIdleWorkers();
1411	>	if (parallelism <= 0 || parallelism > MAX_ID)
1412	>	throw new IllegalArgumentException();
1413	>	this.parallelism = parallelism;
1414	>	this.factory = factory;
1415	>	this.ueh = handler;
1416	>	this.locallyFifo = asyncMode;
1417	>	long np = (long)(-parallelism); // offset ctl counts
1418	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
1419	>	this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
1420	>	// initialize workers array with room for 2*parallelism if possible
1421	>	int n = parallelism << 1;
1422	>	if (n >= MAX_ID)
1423	>	n = MAX_ID;
1424	>	else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
1425	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
1426	>	}
1427	>	workers = new ForkJoinWorkerThread[n + 1];
1428	>	this.submissionLock = new ReentrantLock();
1429	>	this.termination = submissionLock.newCondition();
1430	>	StringBuilder sb = new StringBuilder("ForkJoinPool-");
1431	>	sb.append(poolNumberGenerator.incrementAndGet());
1432	>	sb.append("-worker-");
1433	>	this.workerNamePrefix = sb.toString();
1434		}
1435
1436	+	// Execution methods
1437	+
1438		/**
1439		* Performs the given task, returning its result upon completion.
1440	+	* If the computation encounters an unchecked Exception or Error,
1441	+	* it is rethrown as the outcome of this invocation.  Rethrown
1442	+	* exceptions behave in the same way as regular exceptions, but,
1443	+	* when possible, contain stack traces (as displayed for example
1444	+	* using {@code ex.printStackTrace()}) of both the current thread
1445	+	* as well as the thread actually encountering the exception;
1446	+	* minimally only the latter.
1447		*
1448		* @param task the task
1449		* @return the task's result
1450	<	* @throws NullPointerException if task is null
1451	<	* @throws RejectedExecutionException if pool is shut down
1450	>	* @throws NullPointerException if the task is null
1451	>	* @throws RejectedExecutionException if the task cannot be
1452	>	*         scheduled for execution
1453		*/
1454		public <T> T invoke(ForkJoinTask<T> task) {
1455	<	doSubmit(task);
1456	<	return task.join();
1455	>	Thread t = Thread.currentThread();
1456	>	if (task == null)
1457	>	throw new NullPointerException();
1458	>	if (shutdown)
1459	>	throw new RejectedExecutionException();
1460	>	if ((t instanceof ForkJoinWorkerThread) &&
1461	>	((ForkJoinWorkerThread)t).pool == this)
1462	>	return task.invoke();  // bypass submit if in same pool
1463	>	else {
1464	>	addSubmission(task);
1465	>	return task.join();
1466	>	}
1467	>	}
1468	>
1469	>	/**
1470	>	* Unless terminating, forks task if within an ongoing FJ
1471	>	* computation in the current pool, else submits as external task.
1472	>	*/
1473	>	private <T> void forkOrSubmit(ForkJoinTask<T> task) {
1474	>	ForkJoinWorkerThread w;
1475	>	Thread t = Thread.currentThread();
1476	>	if (shutdown)
1477	>	throw new RejectedExecutionException();
1478	>	if ((t instanceof ForkJoinWorkerThread) &&
1479	>	(w = (ForkJoinWorkerThread)t).pool == this)
1480	>	w.pushTask(task);
1481	>	else
1482	>	addSubmission(task);
1483		}
1484
1485		/**
1486		* Arranges for (asynchronous) execution of the given task.
1487		*
1488		* @param task the task
1489	<	* @throws NullPointerException if task is null
1490	<	* @throws RejectedExecutionException if pool is shut down
1489	>	* @throws NullPointerException if the task is null
1490	>	* @throws RejectedExecutionException if the task cannot be
1491	>	*         scheduled for execution
1492		*/
1493	<	public <T> void execute(ForkJoinTask<T> task) {
1494	<	doSubmit(task);
1493	>	public void execute(ForkJoinTask<?> task) {
1494	>	if (task == null)
1495	>	throw new NullPointerException();
1496	>	forkOrSubmit(task);
1497		}
1498
1499		// AbstractExecutorService methods
1500
1501	+	/**
1502	+	* @throws NullPointerException if the task is null
1503	+	* @throws RejectedExecutionException if the task cannot be
1504	+	*         scheduled for execution
1505	+	*/
1506		public void execute(Runnable task) {
1507	+	if (task == null)
1508	+	throw new NullPointerException();
1509		ForkJoinTask<?> job;
1510		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1511		job = (ForkJoinTask<?>) task;
1512		else
1513	<	job = new AdaptedRunnable<Void>(task, null);
1514	<	doSubmit(job);
594	<	}
595	<
596	<	public <T> ForkJoinTask<T> submit(Callable<T> task) {
597	<	ForkJoinTask<T> job = new AdaptedCallable<T>(task);
598	<	doSubmit(job);
599	<	return job;
600	<	}
601	<
602	<	public <T> ForkJoinTask<T> submit(Runnable task, T result) {
603	<	ForkJoinTask<T> job = new AdaptedRunnable<T>(task, result);
604	<	doSubmit(job);
605	<	return job;
606	<	}
607	<
608	<	public ForkJoinTask<?> submit(Runnable task) {
609	<	ForkJoinTask<?> job;
610	<	if (task instanceof ForkJoinTask<?>) // avoid re-wrap
611	<	job = (ForkJoinTask<?>) task;
612	<	else
613	<	job = new AdaptedRunnable<Void>(task, null);
614	<	doSubmit(job);
615	<	return job;
1513	>	job = ForkJoinTask.adapt(task, null);
1514	>	forkOrSubmit(job);
1515		}
1516
1517		/**
#	Line 620 | Line 1519 | public class ForkJoinPool extends Abstra
1519		*
1520		* @param task the task to submit
1521		* @return the task
1522	+	* @throws NullPointerException if the task is null
1523		* @throws RejectedExecutionException if the task cannot be
1524		*         scheduled for execution
625	–	* @throws NullPointerException if the task is null
1525		*/
1526		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1527	<	doSubmit(task);
1527	>	if (task == null)
1528	>	throw new NullPointerException();
1529	>	forkOrSubmit(task);
1530		return task;
1531		}
1532
1533		/**
1534	<	* Adaptor for Runnables. This implements RunnableFuture
1535	<	* to be compliant with AbstractExecutorService constraints.
1534	>	* @throws NullPointerException if the task is null
1535	>	* @throws RejectedExecutionException if the task cannot be
1536	>	*         scheduled for execution
1537		*/
1538	<	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1539	<	implements RunnableFuture<T> {
1540	<	final Runnable runnable;
1541	<	final T resultOnCompletion;
1542	<	T result;
1543	<	AdaptedRunnable(Runnable runnable, T result) {
642	<	if (runnable == null) throw new NullPointerException();
643	<	this.runnable = runnable;
644	<	this.resultOnCompletion = result;
645	<	}
646	<	public T getRawResult() { return result; }
647	<	public void setRawResult(T v) { result = v; }
648	<	public boolean exec() {
649	<	runnable.run();
650	<	result = resultOnCompletion;
651	<	return true;
652	<	}
653	<	public void run() { invoke(); }
654	<	private static final long serialVersionUID = 5232453952276885070L;
1538	>	public <T> ForkJoinTask<T> submit(Callable<T> task) {
1539	>	if (task == null)
1540	>	throw new NullPointerException();
1541	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1542	>	forkOrSubmit(job);
1543	>	return job;
1544		}
1545
1546		/**
1547	<	* Adaptor for Callables
1548	<	*/
1549	<	static final class AdaptedCallable<T> extends ForkJoinTask<T>
1550	<	implements RunnableFuture<T> {
1551	<	final Callable<T> callable;
1552	<	T result;
1553	<	AdaptedCallable(Callable<T> callable) {
1554	<	if (callable == null) throw new NullPointerException();
1555	<	this.callable = callable;
1556	<	}
668	<	public T getRawResult() { return result; }
669	<	public void setRawResult(T v) { result = v; }
670	<	public boolean exec() {
671	<	try {
672	<	result = callable.call();
673	<	return true;
674	<	} catch (Error err) {
675	<	throw err;
676	<	} catch (RuntimeException rex) {
677	<	throw rex;
678	<	} catch (Exception ex) {
679	<	throw new RuntimeException(ex);
680	<	}
681	<	}
682	<	public void run() { invoke(); }
683	<	private static final long serialVersionUID = 2838392045355241008L;
1547	>	* @throws NullPointerException if the task is null
1548	>	* @throws RejectedExecutionException if the task cannot be
1549	>	*         scheduled for execution
1550	>	*/
1551	>	public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1552	>	if (task == null)
1553	>	throw new NullPointerException();
1554	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1555	>	forkOrSubmit(job);
1556	>	return job;
1557		}
1558
1559	+	/**
1560	+	* @throws NullPointerException if the task is null
1561	+	* @throws RejectedExecutionException if the task cannot be
1562	+	*         scheduled for execution
1563	+	*/
1564	+	public ForkJoinTask<?> submit(Runnable task) {
1565	+	if (task == null)
1566	+	throw new NullPointerException();
1567	+	ForkJoinTask<?> job;
1568	+	if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1569	+	job = (ForkJoinTask<?>) task;
1570	+	else
1571	+	job = ForkJoinTask.adapt(task, null);
1572	+	forkOrSubmit(job);
1573	+	return job;
1574	+	}
1575	+
1576	+	/**
1577	+	* @throws NullPointerException       {@inheritDoc}
1578	+	* @throws RejectedExecutionException {@inheritDoc}
1579	+	*/
1580		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
1581		ArrayList<ForkJoinTask<T>> forkJoinTasks =
1582		new ArrayList<ForkJoinTask<T>>(tasks.size());
1583		for (Callable<T> task : tasks)
1584	<	forkJoinTasks.add(new AdaptedCallable<T>(task));
1584	>	forkJoinTasks.add(ForkJoinTask.adapt(task));
1585		invoke(new InvokeAll<T>(forkJoinTasks));
1586
1587		@SuppressWarnings({"unchecked", "rawtypes"})
1588	<	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1588	>	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1589		return futures;
1590		}
1591
#	Line 705 | Line 1599 | public class ForkJoinPool extends Abstra
1599		private static final long serialVersionUID = -7914297376763021607L;
1600		}
1601
708	–	// Configuration and status settings and queries
709	–
1602		/**
1603		* Returns the factory used for constructing new workers.
1604		*
#	Line 720 | Line 1612 | public class ForkJoinPool extends Abstra
1612		* Returns the handler for internal worker threads that terminate
1613		* due to unrecoverable errors encountered while executing tasks.
1614		*
1615	<	* @return the handler, or null if none
1615	>	* @return the handler, or {@code null} if none
1616		*/
1617		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1618	<	Thread.UncaughtExceptionHandler h;
727	<	final ReentrantLock lock = this.workerLock;
728	<	lock.lock();
729	<	try {
730	<	h = ueh;
731	<	} finally {
732	<	lock.unlock();
733	<	}
734	<	return h;
1618	>	return ueh;
1619		}
1620
1621		/**
1622	<	* Sets the handler for internal worker threads that terminate due
739	<	* to unrecoverable errors encountered while executing tasks.
740	<	* Unless set, the current default or ThreadGroup handler is used
741	<	* as handler.
1622	>	* Returns the targeted parallelism level of this pool.
1623		*
1624	<	* @param h the new handler
744	<	* @return the old handler, or null if none
745	<	* @throws SecurityException if a security manager exists and
746	<	*         the caller is not permitted to modify threads
747	<	*         because it does not hold {@link
748	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
749	<	*/
750	<	public Thread.UncaughtExceptionHandler
751	<	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
752	<	checkPermission();
753	<	Thread.UncaughtExceptionHandler old = null;
754	<	final ReentrantLock lock = this.workerLock;
755	<	lock.lock();
756	<	try {
757	<	old = ueh;
758	<	ueh = h;
759	<	ForkJoinWorkerThread[] ws = workers;
760	<	if (ws != null) {
761	<	for (int i = 0; i < ws.length; ++i) {
762	<	ForkJoinWorkerThread w = ws[i];
763	<	if (w != null)
764	<	w.setUncaughtExceptionHandler(h);
765	<	}
766	<	}
767	<	} finally {
768	<	lock.unlock();
769	<	}
770	<	return old;
771	<	}
772	<
773	<
774	<	/**
775	<	* Sets the target parallelism level of this pool.
776	<	*
777	<	* @param parallelism the target parallelism
778	<	* @throws IllegalArgumentException if parallelism less than or
779	<	* equal to zero or greater than maximum size bounds
780	<	* @throws SecurityException if a security manager exists and
781	<	*         the caller is not permitted to modify threads
782	<	*         because it does not hold {@link
783	<	*         java.lang.RuntimePermission}{@code ("modifyThread")}
784	<	*/
785	<	public void setParallelism(int parallelism) {
786	<	checkPermission();
787	<	if (parallelism <= 0 || parallelism > maxPoolSize)
788	<	throw new IllegalArgumentException();
789	<	final ReentrantLock lock = this.workerLock;
790	<	lock.lock();
791	<	try {
792	<	if (!isTerminating()) {
793	<	int p = this.parallelism;
794	<	this.parallelism = parallelism;
795	<	if (parallelism > p)
796	<	createAndStartAddedWorkers();
797	<	else
798	<	trimSpares();
799	<	}
800	<	} finally {
801	<	lock.unlock();
802	<	}
803	<	signalIdleWorkers();
804	<	}
805	<
806	<	/**
807	<	* Returns the targeted number of worker threads in this pool.
808	<	*
809	<	* @return the targeted number of worker threads in this pool
1624	>	* @return the targeted parallelism level of this pool
1625		*/
1626		public int getParallelism() {
1627		return parallelism;
#	Line 814 | Line 1629 | public class ForkJoinPool extends Abstra
1629
1630		/**
1631		* Returns the number of worker threads that have started but not
1632	<	* yet terminated.  This result returned by this method may differ
1633	<	* from {@code getParallelism} when threads are created to
1632	>	* yet terminated.  The result returned by this method may differ
1633	>	* from {@link #getParallelism} when threads are created to
1634		* maintain parallelism when others are cooperatively blocked.
1635		*
1636		* @return the number of worker threads
1637		*/
1638		public int getPoolSize() {
1639	<	return totalCountOf(workerCounts);
825	<	}
826	<
827	<	/**
828	<	* Returns the maximum number of threads allowed to exist in the
829	<	* pool, even if there are insufficient unblocked running threads.
830	<	*
831	<	* @return the maximum
832	<	*/
833	<	public int getMaximumPoolSize() {
834	<	return maxPoolSize;
835	<	}
836	<
837	<	/**
838	<	* Sets the maximum number of threads allowed to exist in the
839	<	* pool, even if there are insufficient unblocked running threads.
840	<	* Setting this value has no effect on current pool size. It
841	<	* controls construction of new threads.
842	<	*
843	<	* @throws IllegalArgumentException if negative or greater then
844	<	* internal implementation limit
845	<	*/
846	<	public void setMaximumPoolSize(int newMax) {
847	<	if (newMax < 0 || newMax > MAX_THREADS)
848	<	throw new IllegalArgumentException();
849	<	maxPoolSize = newMax;
850	<	}
851	<
852	<
853	<	/**
854	<	* Returns true if this pool dynamically maintains its target
855	<	* parallelism level. If false, new threads are added only to
856	<	* avoid possible starvation.
857	<	* This setting is by default true.
858	<	*
859	<	* @return true if maintains parallelism
860	<	*/
861	<	public boolean getMaintainsParallelism() {
862	<	return maintainsParallelism;
1639	>	return parallelism + (short)(ctl >>> TC_SHIFT);
1640		}
1641
1642		/**
1643	<	* Sets whether this pool dynamically maintains its target
867	<	* parallelism level. If false, new threads are added only to
868	<	* avoid possible starvation.
869	<	*
870	<	* @param enable true to maintains parallelism
871	<	*/
872	<	public void setMaintainsParallelism(boolean enable) {
873	<	maintainsParallelism = enable;
874	<	}
875	<
876	<	/**
877	<	* Establishes local first-in-first-out scheduling mode for forked
878	<	* tasks that are never joined. This mode may be more appropriate
879	<	* than default locally stack-based mode in applications in which
880	<	* worker threads only process asynchronous tasks.  This method is
881	<	* designed to be invoked only when pool is quiescent, and
882	<	* typically only before any tasks are submitted. The effects of
883	<	* invocations at other times may be unpredictable.
884	<	*
885	<	* @param async if true, use locally FIFO scheduling
886	<	* @return the previous mode
887	<	*/
888	<	public boolean setAsyncMode(boolean async) {
889	<	boolean oldMode = locallyFifo;
890	<	locallyFifo = async;
891	<	ForkJoinWorkerThread[] ws = workers;
892	<	if (ws != null) {
893	<	for (int i = 0; i < ws.length; ++i) {
894	<	ForkJoinWorkerThread t = ws[i];
895	<	if (t != null)
896	<	t.setAsyncMode(async);
897	<	}
898	<	}
899	<	return oldMode;
900	<	}
901	<
902	<	/**
903	<	* Returns true if this pool uses local first-in-first-out
1643	>	* Returns {@code true} if this pool uses local first-in-first-out
1644		* scheduling mode for forked tasks that are never joined.
1645		*
1646	<	* @return true if this pool uses async mode
1646	>	* @return {@code true} if this pool uses async mode
1647		*/
1648		public boolean getAsyncMode() {
1649		return locallyFifo;
#	Line 912 | Line 1652 | public class ForkJoinPool extends Abstra
1652		/**
1653		* Returns an estimate of the number of worker threads that are
1654		* not blocked waiting to join tasks or for other managed
1655	<	* synchronization.
1655	>	* synchronization. This method may overestimate the
1656	>	* number of running threads.
1657		*
1658		* @return the number of worker threads
1659		*/
1660		public int getRunningThreadCount() {
1661	<	return runningCountOf(workerCounts);
1661	>	int r = parallelism + (int)(ctl >> AC_SHIFT);
1662	>	return r <= 0? 0 : r; // suppress momentarily negative values
1663		}
1664
1665		/**
#	Line 928 | Line 1670 | public class ForkJoinPool extends Abstra
1670		* @return the number of active threads
1671		*/
1672		public int getActiveThreadCount() {
1673	<	return activeCountOf(runControl);
1673	>	int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount;
1674	>	return r <= 0? 0 : r; // suppress momentarily negative values
1675		}
1676
1677		/**
1678	<	* Returns an estimate of the number of threads that are currently
1679	<	* idle waiting for tasks. This method may underestimate the
1680	<	* number of idle threads.
1678	>	* Returns {@code true} if all worker threads are currently idle.
1679	>	* An idle worker is one that cannot obtain a task to execute
1680	>	* because none are available to steal from other threads, and
1681	>	* there are no pending submissions to the pool. This method is
1682	>	* conservative; it might not return {@code true} immediately upon
1683	>	* idleness of all threads, but will eventually become true if
1684	>	* threads remain inactive.
1685		*
1686	<	* @return the number of idle threads
940	<	*/
941	<	final int getIdleThreadCount() {
942	<	int c = runningCountOf(workerCounts) - activeCountOf(runControl);
943	<	return (c <= 0) ? 0 : c;
944	<	}
945	<
946	<	/**
947	<	* Returns true if all worker threads are currently idle. An idle
948	<	* worker is one that cannot obtain a task to execute because none
949	<	* are available to steal from other threads, and there are no
950	<	* pending submissions to the pool. This method is conservative;
951	<	* it might not return true immediately upon idleness of all
952	<	* threads, but will eventually become true if threads remain
953	<	* inactive.
954	<	*
955	<	* @return true if all threads are currently idle
1686	>	* @return {@code true} if all threads are currently idle
1687		*/
1688		public boolean isQuiescent() {
1689	<	return activeCountOf(runControl) == 0;
1689	>	return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0;
1690		}
1691
1692		/**
#	Line 970 | Line 1701 | public class ForkJoinPool extends Abstra
1701		* @return the number of steals
1702		*/
1703		public long getStealCount() {
1704	<	return stealCount.get();
974	<	}
975	<
976	<	/**
977	<	* Accumulates steal count from a worker.
978	<	* Call only when worker known to be idle.
979	<	*/
980	<	private void updateStealCount(ForkJoinWorkerThread w) {
981	<	int sc = w.getAndClearStealCount();
982	<	if (sc != 0)
983	<	stealCount.addAndGet(sc);
1704	>	return stealCount;
1705		}
1706
1707		/**
#	Line 995 | Line 1716 | public class ForkJoinPool extends Abstra
1716		*/
1717		public long getQueuedTaskCount() {
1718		long count = 0;
1719	<	ForkJoinWorkerThread[] ws = workers;
1720	<	if (ws != null) {
1721	<	for (int i = 0; i < ws.length; ++i) {
1722	<	ForkJoinWorkerThread t = ws[i];
1723	<	if (t != null)
1724	<	count += t.getQueueSize();
1004	<	}
1719	>	ForkJoinWorkerThread[] ws;
1720	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1721	>	(ws = workers) != null) {
1722	>	for (ForkJoinWorkerThread w : ws)
1723	>	if (w != null)
1724	>	count -= w.queueBase - w.queueTop; // must read base first
1725		}
1726		return count;
1727		}
1728
1729		/**
1730	<	* Returns an estimate of the number tasks submitted to this pool
1731	<	* that have not yet begun executing. This method takes time
1732	<	* proportional to the number of submissions.
1730	>	* Returns an estimate of the number of tasks submitted to this
1731	>	* pool that have not yet begun executing.  This meThod may take
1732	>	* time proportional to the number of submissions.
1733		*
1734		* @return the number of queued submissions
1735		*/
1736		public int getQueuedSubmissionCount() {
1737	<	return submissionQueue.size();
1737	>	return -queueBase + queueTop;
1738		}
1739
1740		/**
1741	<	* Returns true if there are any tasks submitted to this pool
1742	<	* that have not yet begun executing.
1741	>	* Returns {@code true} if there are any tasks submitted to this
1742	>	* pool that have not yet begun executing.
1743		*
1744		* @return {@code true} if there are any queued submissions
1745		*/
1746		public boolean hasQueuedSubmissions() {
1747	<	return !submissionQueue.isEmpty();
1747	>	return queueBase != queueTop;
1748		}
1749
1750		/**
#	Line 1032 | Line 1752 | public class ForkJoinPool extends Abstra
1752		* available.  This method may be useful in extensions to this
1753		* class that re-assign work in systems with multiple pools.
1754		*
1755	<	* @return the next submission, or null if none
1755	>	* @return the next submission, or {@code null} if none
1756		*/
1757		protected ForkJoinTask<?> pollSubmission() {
1758	<	return submissionQueue.poll();
1758	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
1759	>	while ((b = queueBase) != queueTop &&
1760	>	(q = submissionQueue) != null &&
1761	>	(i = (q.length - 1) & b) >= 0) {
1762	>	long u = (i << ASHIFT) + ABASE;
1763	>	if ((t = q[i]) != null &&
1764	>	queueBase == b &&
1765	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1766	>	queueBase = b + 1;
1767	>	return t;
1768	>	}
1769	>	}
1770	>	return null;
1771		}
1772
1773		/**
1774		* Removes all available unexecuted submitted and forked tasks
1775		* from scheduling queues and adds them to the given collection,
1776		* without altering their execution status. These may include
1777	<	* artificially generated or wrapped tasks. This method is designed
1778	<	* to be invoked only when the pool is known to be
1777	>	* artificially generated or wrapped tasks. This method is
1778	>	* designed to be invoked only when the pool is known to be
1779		* quiescent. Invocations at other times may not remove all
1780		* tasks. A failure encountered while attempting to add elements
1781		* to collection {@code c} may result in elements being in
#	Line 1055 | Line 1787 | public class ForkJoinPool extends Abstra
1787		* @param c the collection to transfer elements into
1788		* @return the number of elements transferred
1789		*/
1790	<	protected int drainTasksTo(Collection<ForkJoinTask<?>> c) {
1791	<	int n = submissionQueue.drainTo(c);
1792	<	ForkJoinWorkerThread[] ws = workers;
1793	<	if (ws != null) {
1794	<	for (int i = 0; i < ws.length; ++i) {
1795	<	ForkJoinWorkerThread w = ws[i];
1796	<	if (w != null)
1065	<	n += w.drainTasksTo(c);
1790	>	protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1791	>	int count = 0;
1792	>	while (queueBase != queueTop) {
1793	>	ForkJoinTask<?> t = pollSubmission();
1794	>	if (t != null) {
1795	>	c.add(t);
1796	>	++count;
1797		}
1798		}
1799	<	return n;
1799	>	ForkJoinWorkerThread[] ws;
1800	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1801	>	(ws = workers) != null) {
1802	>	for (ForkJoinWorkerThread w : ws)
1803	>	if (w != null)
1804	>	count += w.drainTasksTo(c);
1805	>	}
1806	>	return count;
1807		}
1808
1809		/**
#	Line 1076 | Line 1814 | public class ForkJoinPool extends Abstra
1814		* @return a string identifying this pool, as well as its state
1815		*/
1816		public String toString() {
1079	–	int ps = parallelism;
1080	–	int wc = workerCounts;
1081	–	int rc = runControl;
1817		long st = getStealCount();
1818		long qt = getQueuedTaskCount();
1819		long qs = getQueuedSubmissionCount();
1820	+	int pc = parallelism;
1821	+	long c = ctl;
1822	+	int tc = pc + (short)(c >>> TC_SHIFT);
1823	+	int rc = pc + (int)(c >> AC_SHIFT);
1824	+	if (rc < 0) // ignore transient negative
1825	+	rc = 0;
1826	+	int ac = rc + blockedCount;
1827	+	String level;
1828	+	if ((c & STOP_BIT) != 0)
1829	+	level = (tc == 0)? "Terminated" : "Terminating";
1830	+	else
1831	+	level = shutdown? "Shutting down" : "Running";
1832		return super.toString() +
1833	<	"[" + runStateToString(runStateOf(rc)) +
1834	<	", parallelism = " + ps +
1835	<	", size = " + totalCountOf(wc) +
1836	<	", active = " + activeCountOf(rc) +
1837	<	", running = " + runningCountOf(wc) +
1833	>	"[" + level +
1834	>	", parallelism = " + pc +
1835	>	", size = " + tc +
1836	>	", active = " + ac +
1837	>	", running = " + rc +
1838		", steals = " + st +
1839		", tasks = " + qt +
1840		", submissions = " + qs +
1841		"]";
1842		}
1843
1097	–	private static String runStateToString(int rs) {
1098	–	switch(rs) {
1099	–	case RUNNING: return "Running";
1100	–	case SHUTDOWN: return "Shutting down";
1101	–	case TERMINATING: return "Terminating";
1102	–	case TERMINATED: return "Terminated";
1103	–	default: throw new Error("Unknown run state");
1104	–	}
1105	–	}
1106	–
1107	–	// lifecycle control
1108	–
1844		/**
1845		* Initiates an orderly shutdown in which previously submitted
1846		* tasks are executed, but no new tasks will be accepted.
#	Line 1120 | Line 1855 | public class ForkJoinPool extends Abstra
1855		*/
1856		public void shutdown() {
1857		checkPermission();
1858	<	transitionRunStateTo(SHUTDOWN);
1859	<	if (canTerminateOnShutdown(runControl))
1125	<	terminateOnShutdown();
1858	>	shutdown = true;
1859	>	tryTerminate(false);
1860		}
1861
1862		/**
1863	<	* Attempts to stop all actively executing tasks, and cancels all
1864	<	* waiting tasks.  Tasks that are in the process of being
1865	<	* submitted or executed concurrently during the course of this
1866	<	* method may or may not be rejected. Unlike some other executors,
1867	<	* this method cancels rather than collects non-executed tasks
1868	<	* upon termination, so always returns an empty list. However, you
1869	<	* can use method {@code drainTasksTo} before invoking this
1870	<	* method to transfer unexecuted tasks to another collection.
1863	>	* Attempts to cancel and/or stop all tasks, and reject all
1864	>	* subsequently submitted tasks.  Tasks that are in the process of
1865	>	* being submitted or executed concurrently during the course of
1866	>	* this method may or may not be rejected. This method cancels
1867	>	* both existing and unexecuted tasks, in order to permit
1868	>	* termination in the presence of task dependencies. So the method
1869	>	* always returns an empty list (unlike the case for some other
1870	>	* Executors).
1871		*
1872		* @return an empty list
1873		* @throws SecurityException if a security manager exists and
#	Line 1143 | Line 1877 | public class ForkJoinPool extends Abstra
1877		*/
1878		public List<Runnable> shutdownNow() {
1879		checkPermission();
1880	<	terminate();
1880	>	shutdown = true;
1881	>	tryTerminate(true);
1882		return Collections.emptyList();
1883		}
1884
#	Line 1153 | Line 1888 | public class ForkJoinPool extends Abstra
1888		* @return {@code true} if all tasks have completed following shut down
1889		*/
1890		public boolean isTerminated() {
1891	<	return runStateOf(runControl) == TERMINATED;
1891	>	long c = ctl;
1892	>	return ((c & STOP_BIT) != 0L &&
1893	>	(short)(c >>> TC_SHIFT) == -parallelism);
1894		}
1895
1896		/**
1897		* Returns {@code true} if the process of termination has
1898	<	* commenced but possibly not yet completed.
1898	>	* commenced but not yet completed.  This method may be useful for
1899	>	* debugging. A return of {@code true} reported a sufficient
1900	>	* period after shutdown may indicate that submitted tasks have
1901	>	* ignored or suppressed interruption, or are waiting for IO,
1902	>	* causing this executor not to properly terminate. (See the
1903	>	* advisory notes for class {@link ForkJoinTask} stating that
1904	>	* tasks should not normally entail blocking operations.  But if
1905	>	* they do, they must abort them on interrupt.)
1906		*
1907	<	* @return {@code true} if terminating
1907	>	* @return {@code true} if terminating but not yet terminated
1908		*/
1909		public boolean isTerminating() {
1910	<	return runStateOf(runControl) >= TERMINATING;
1910	>	long c = ctl;
1911	>	return ((c & STOP_BIT) != 0L &&
1912	>	(short)(c >>> TC_SHIFT) != -parallelism);
1913	>	}
1914	>
1915	>	/**
1916	>	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1917	>	*/
1918	>	final boolean isAtLeastTerminating() {
1919	>	return (ctl & STOP_BIT) != 0L;
1920		}
1921
1922		/**
#	Line 1172 | Line 1925 | public class ForkJoinPool extends Abstra
1925		* @return {@code true} if this pool has been shut down
1926		*/
1927		public boolean isShutdown() {
1928	<	return runStateOf(runControl) >= SHUTDOWN;
1928	>	return shutdown;
1929		}
1930
1931		/**
#	Line 1189 | Line 1942 | public class ForkJoinPool extends Abstra
1942		public boolean awaitTermination(long timeout, TimeUnit unit)
1943		throws InterruptedException {
1944		long nanos = unit.toNanos(timeout);
1945	<	final ReentrantLock lock = this.workerLock;
1945	>	final ReentrantLock lock = this.submissionLock;
1946		lock.lock();
1947		try {
1948		for (;;) {
#	Line 1204 | Line 1957 | public class ForkJoinPool extends Abstra
1957		}
1958		}
1959
1207	–	// Shutdown and termination support
1208	–
1209	–	/**
1210	–	* Callback from terminating worker. Nulls out the corresponding
1211	–	* workers slot, and if terminating, tries to terminate; else
1212	–	* tries to shrink workers array.
1213	–	*
1214	–	* @param w the worker
1215	–	*/
1216	–	final void workerTerminated(ForkJoinWorkerThread w) {
1217	–	updateStealCount(w);
1218	–	updateWorkerCount(-1);
1219	–	final ReentrantLock lock = this.workerLock;
1220	–	lock.lock();
1221	–	try {
1222	–	ForkJoinWorkerThread[] ws = workers;
1223	–	if (ws != null) {
1224	–	int idx = w.poolIndex;
1225	–	if (idx >= 0 && idx < ws.length && ws[idx] == w)
1226	–	ws[idx] = null;
1227	–	if (totalCountOf(workerCounts) == 0) {
1228	–	terminate(); // no-op if already terminating
1229	–	transitionRunStateTo(TERMINATED);
1230	–	termination.signalAll();
1231	–	}
1232	–	else if (!isTerminating()) {
1233	–	tryShrinkWorkerArray();
1234	–	tryResumeSpare(true); // allow replacement
1235	–	}
1236	–	}
1237	–	} finally {
1238	–	lock.unlock();
1239	–	}
1240	–	signalIdleWorkers();
1241	–	}
1242	–
1243	–	/**
1244	–	* Initiates termination.
1245	–	*/
1246	–	private void terminate() {
1247	–	if (transitionRunStateTo(TERMINATING)) {
1248	–	stopAllWorkers();
1249	–	resumeAllSpares();
1250	–	signalIdleWorkers();
1251	–	cancelQueuedSubmissions();
1252	–	cancelQueuedWorkerTasks();
1253	–	interruptUnterminatedWorkers();
1254	–	signalIdleWorkers(); // resignal after interrupt
1255	–	}
1256	–	}
1257	–
1258	–	/**
1259	–	* Possibly terminates when on shutdown state.
1260	–	*/
1261	–	private void terminateOnShutdown() {
1262	–	if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
1263	–	terminate();
1264	–	}
1265	–
1266	–	/**
1267	–	* Clears out and cancels submissions.
1268	–	*/
1269	–	private void cancelQueuedSubmissions() {
1270	–	ForkJoinTask<?> task;
1271	–	while ((task = pollSubmission()) != null)
1272	–	task.cancel(false);
1273	–	}
1274	–
1275	–	/**
1276	–	* Cleans out worker queues.
1277	–	*/
1278	–	private void cancelQueuedWorkerTasks() {
1279	–	final ReentrantLock lock = this.workerLock;
1280	–	lock.lock();
1281	–	try {
1282	–	ForkJoinWorkerThread[] ws = workers;
1283	–	if (ws != null) {
1284	–	for (int i = 0; i < ws.length; ++i) {
1285	–	ForkJoinWorkerThread t = ws[i];
1286	–	if (t != null)
1287	–	t.cancelTasks();
1288	–	}
1289	–	}
1290	–	} finally {
1291	–	lock.unlock();
1292	–	}
1293	–	}
1294	–
1295	–	/**
1296	–	* Sets each worker's status to terminating. Requires lock to avoid
1297	–	* conflicts with add/remove.
1298	–	*/
1299	–	private void stopAllWorkers() {
1300	–	final ReentrantLock lock = this.workerLock;
1301	–	lock.lock();
1302	–	try {
1303	–	ForkJoinWorkerThread[] ws = workers;
1304	–	if (ws != null) {
1305	–	for (int i = 0; i < ws.length; ++i) {
1306	–	ForkJoinWorkerThread t = ws[i];
1307	–	if (t != null)
1308	–	t.shutdownNow();
1309	–	}
1310	–	}
1311	–	} finally {
1312	–	lock.unlock();
1313	–	}
1314	–	}
1315	–
1316	–	/**
1317	–	* Interrupts all unterminated workers.  This is not required for
1318	–	* sake of internal control, but may help unstick user code during
1319	–	* shutdown.
1320	–	*/
1321	–	private void interruptUnterminatedWorkers() {
1322	–	final ReentrantLock lock = this.workerLock;
1323	–	lock.lock();
1324	–	try {
1325	–	ForkJoinWorkerThread[] ws = workers;
1326	–	if (ws != null) {
1327	–	for (int i = 0; i < ws.length; ++i) {
1328	–	ForkJoinWorkerThread t = ws[i];
1329	–	if (t != null && !t.isTerminated()) {
1330	–	try {
1331	–	t.interrupt();
1332	–	} catch (SecurityException ignore) {
1333	–	}
1334	–	}
1335	–	}
1336	–	}
1337	–	} finally {
1338	–	lock.unlock();
1339	–	}
1340	–	}
1341	–
1342	–
1343	–	/*
1344	–	* Nodes for event barrier to manage idle threads.  Queue nodes
1345	–	* are basic Treiber stack nodes, also used for spare stack.
1346	–	*
1347	–	* The event barrier has an event count and a wait queue (actually
1348	–	* a Treiber stack).  Workers are enabled to look for work when
1349	–	* the eventCount is incremented. If they fail to find work, they
1350	–	* may wait for next count. Upon release, threads help others wake
1351	–	* up.
1352	–	*
1353	–	* Synchronization events occur only in enough contexts to
1354	–	* maintain overall liveness:
1355	–	*
1356	–	*   - Submission of a new task to the pool
1357	–	*   - Resizes or other changes to the workers array
1358	–	*   - pool termination
1359	–	*   - A worker pushing a task on an empty queue
1360	–	*
1361	–	* The case of pushing a task occurs often enough, and is heavy
1362	–	* enough compared to simple stack pushes, to require special
1363	–	* handling: Method signalWork returns without advancing count if
1364	–	* the queue appears to be empty.  This would ordinarily result in
1365	–	* races causing some queued waiters not to be woken up. To avoid
1366	–	* this, the first worker enqueued in method sync (see
1367	–	* syncIsReleasable) rescans for tasks after being enqueued, and
1368	–	* helps signal if any are found. This works well because the
1369	–	* worker has nothing better to do, and so might as well help
1370	–	* alleviate the overhead and contention on the threads actually
1371	–	* doing work.  Also, since event counts increments on task
1372	–	* availability exist to maintain liveness (rather than to force
1373	–	* refreshes etc), it is OK for callers to exit early if
1374	–	* contending with another signaller.
1375	–	*/
1376	–	static final class WaitQueueNode {
1377	–	WaitQueueNode next; // only written before enqueued
1378	–	volatile ForkJoinWorkerThread thread; // nulled to cancel wait
1379	–	final long count; // unused for spare stack
1380	–
1381	–	WaitQueueNode(long c, ForkJoinWorkerThread w) {
1382	–	count = c;
1383	–	thread = w;
1384	–	}
1385	–
1386	–	/**
1387	–	* Wakes up waiter, returning false if known to already
1388	–	*/
1389	–	boolean signal() {
1390	–	ForkJoinWorkerThread t = thread;
1391	–	if (t == null)
1392	–	return false;
1393	–	thread = null;
1394	–	LockSupport.unpark(t);
1395	–	return true;
1396	–	}
1397	–
1398	–	/**
1399	–	* Awaits release on sync.
1400	–	*/
1401	–	void awaitSyncRelease(ForkJoinPool p) {
1402	–	while (thread != null && !p.syncIsReleasable(this))
1403	–	LockSupport.park(this);
1404	–	}
1405	–
1406	–	/**
1407	–	* Awaits resumption as spare.
1408	–	*/
1409	–	void awaitSpareRelease() {
1410	–	while (thread != null) {
1411	–	if (!Thread.interrupted())
1412	–	LockSupport.park(this);
1413	–	}
1414	–	}
1415	–	}
1416	–
1417	–	/**
1418	–	* Ensures that no thread is waiting for count to advance from the
1419	–	* current value of eventCount read on entry to this method, by
1420	–	* releasing waiting threads if necessary.
1421	–	*
1422	–	* @return the count
1423	–	*/
1424	–	final long ensureSync() {
1425	–	long c = eventCount;
1426	–	WaitQueueNode q;
1427	–	while ((q = syncStack) != null && q.count < c) {
1428	–	if (casBarrierStack(q, null)) {
1429	–	do {
1430	–	q.signal();
1431	–	} while ((q = q.next) != null);
1432	–	break;
1433	–	}
1434	–	}
1435	–	return c;
1436	–	}
1437	–
1438	–	/**
1439	–	* Increments event count and releases waiting threads.
1440	–	*/
1441	–	private void signalIdleWorkers() {
1442	–	long c;
1443	–	do {} while (!casEventCount(c = eventCount, c+1));
1444	–	ensureSync();
1445	–	}
1446	–
1447	–	/**
1448	–	* Signals threads waiting to poll a task. Because method sync
1449	–	* rechecks availability, it is OK to only proceed if queue
1450	–	* appears to be non-empty, and OK to skip under contention to
1451	–	* increment count (since some other thread succeeded).
1452	–	*/
1453	–	final void signalWork() {
1454	–	long c;
1455	–	WaitQueueNode q;
1456	–	if (syncStack != null &&
1457	–	casEventCount(c = eventCount, c+1) &&
1458	–	(((q = syncStack) != null && q.count <= c) &&
1459	–	(!casBarrierStack(q, q.next) || !q.signal())))
1460	–	ensureSync();
1461	–	}
1462	–
1463	–	/**
1464	–	* Waits until event count advances from last value held by
1465	–	* caller, or if excess threads, caller is resumed as spare, or
1466	–	* caller or pool is terminating. Updates caller's event on exit.
1467	–	*
1468	–	* @param w the calling worker thread
1469	–	*/
1470	–	final void sync(ForkJoinWorkerThread w) {
1471	–	updateStealCount(w); // Transfer w's count while it is idle
1472	–
1473	–	while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
1474	–	long prev = w.lastEventCount;
1475	–	WaitQueueNode node = null;
1476	–	WaitQueueNode h;
1477	–	while (eventCount == prev &&
1478	–	((h = syncStack) == null || h.count == prev)) {
1479	–	if (node == null)
1480	–	node = new WaitQueueNode(prev, w);
1481	–	if (casBarrierStack(node.next = h, node)) {
1482	–	node.awaitSyncRelease(this);
1483	–	break;
1484	–	}
1485	–	}
1486	–	long ec = ensureSync();
1487	–	if (ec != prev) {
1488	–	w.lastEventCount = ec;
1489	–	break;
1490	–	}
1491	–	}
1492	–	}
1493	–
1494	–	/**
1495	–	* Returns true if worker waiting on sync can proceed:
1496	–	*  - on signal (thread == null)
1497	–	*  - on event count advance (winning race to notify vs signaller)
1498	–	*  - on interrupt
1499	–	*  - if the first queued node, we find work available
1500	–	* If node was not signalled and event count not advanced on exit,
1501	–	* then we also help advance event count.
1502	–	*
1503	–	* @return true if node can be released
1504	–	*/
1505	–	final boolean syncIsReleasable(WaitQueueNode node) {
1506	–	long prev = node.count;
1507	–	if (!Thread.interrupted() && node.thread != null &&
1508	–	(node.next != null ||
1509	–	!ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
1510	–	eventCount == prev)
1511	–	return false;
1512	–	if (node.thread != null) {
1513	–	node.thread = null;
1514	–	long ec = eventCount;
1515	–	if (prev <= ec) // help signal
1516	–	casEventCount(ec, ec+1);
1517	–	}
1518	–	return true;
1519	–	}
1520	–
1521	–	/**
1522	–	* Returns true if a new sync event occurred since last call to
1523	–	* sync or this method, if so, updating caller's count.
1524	–	*/
1525	–	final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1526	–	long lc = w.lastEventCount;
1527	–	long ec = ensureSync();
1528	–	if (ec == lc)
1529	–	return false;
1530	–	w.lastEventCount = ec;
1531	–	return true;
1532	–	}
1533	–
1534	–	//  Parallelism maintenance
1535	–
1536	–	/**
1537	–	* Decrements running count; if too low, adds spare.
1538	–	*
1539	–	* Conceptually, all we need to do here is add or resume a
1540	–	* spare thread when one is about to block (and remove or
1541	–	* suspend it later when unblocked -- see suspendIfSpare).
1542	–	* However, implementing this idea requires coping with
1543	–	* several problems: we have imperfect information about the
1544	–	* states of threads. Some count updates can and usually do
1545	–	* lag run state changes, despite arrangements to keep them
1546	–	* accurate (for example, when possible, updating counts
1547	–	* before signalling or resuming), especially when running on
1548	–	* dynamic JVMs that don't optimize the infrequent paths that
1549	–	* update counts. Generating too many threads can make these
1550	–	* problems become worse, because excess threads are more
1551	–	* likely to be context-switched with others, slowing them all
1552	–	* down, especially if there is no work available, so all are
1553	–	* busy scanning or idling.  Also, excess spare threads can
1554	–	* only be suspended or removed when they are idle, not
1555	–	* immediately when they aren't needed. So adding threads will
1556	–	* raise parallelism level for longer than necessary.  Also,
1557	–	* FJ applications often encounter highly transient peaks when
1558	–	* many threads are blocked joining, but for less time than it
1559	–	* takes to create or resume spares.
1560	–	*
1561	–	* @param joinMe if non-null, return early if done
1562	–	* @param maintainParallelism if true, try to stay within
1563	–	* target counts, else create only to avoid starvation
1564	–	* @return true if joinMe known to be done
1565	–	*/
1566	–	final boolean preJoin(ForkJoinTask<?> joinMe,
1567	–	boolean maintainParallelism) {
1568	–	maintainParallelism &= maintainsParallelism; // overrride
1569	–	boolean dec = false;  // true when running count decremented
1570	–	while (spareStack == null || !tryResumeSpare(dec)) {
1571	–	int counts = workerCounts;
1572	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1573	–	// CAS cheat
1574	–	if (!needSpare(counts, maintainParallelism))
1575	–	break;
1576	–	if (joinMe.status < 0)
1577	–	return true;
1578	–	if (tryAddSpare(counts))
1579	–	break;
1580	–	}
1581	–	}
1582	–	return false;
1583	–	}
1584	–
1585	–	/**
1586	–	* Same idea as preJoin
1587	–	*/
1588	–	final boolean preBlock(ManagedBlocker blocker,
1589	–	boolean maintainParallelism) {
1590	–	maintainParallelism &= maintainsParallelism;
1591	–	boolean dec = false;
1592	–	while (spareStack == null || !tryResumeSpare(dec)) {
1593	–	int counts = workerCounts;
1594	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1595	–	if (!needSpare(counts, maintainParallelism))
1596	–	break;
1597	–	if (blocker.isReleasable())
1598	–	return true;
1599	–	if (tryAddSpare(counts))
1600	–	break;
1601	–	}
1602	–	}
1603	–	return false;
1604	–	}
1605	–
1606	–	/**
1607	–	* Returns true if a spare thread appears to be needed.  If
1608	–	* maintaining parallelism, returns true when the deficit in
1609	–	* running threads is more than the surplus of total threads, and
1610	–	* there is apparently some work to do.  This self-limiting rule
1611	–	* means that the more threads that have already been added, the
1612	–	* less parallelism we will tolerate before adding another.
1613	–	*
1614	–	* @param counts current worker counts
1615	–	* @param maintainParallelism try to maintain parallelism
1616	–	*/
1617	–	private boolean needSpare(int counts, boolean maintainParallelism) {
1618	–	int ps = parallelism;
1619	–	int rc = runningCountOf(counts);
1620	–	int tc = totalCountOf(counts);
1621	–	int runningDeficit = ps - rc;
1622	–	int totalSurplus = tc - ps;
1623	–	return (tc < maxPoolSize &&
1624	–	(rc == 0 || totalSurplus < 0 ||
1625	–	(maintainParallelism &&
1626	–	runningDeficit > totalSurplus &&
1627	–	ForkJoinWorkerThread.hasQueuedTasks(workers))));
1628	–	}
1629	–
1630	–	/**
1631	–	* Adds a spare worker if lock available and no more than the
1632	–	* expected numbers of threads exist.
1633	–	*
1634	–	* @return true if successful
1635	–	*/
1636	–	private boolean tryAddSpare(int expectedCounts) {
1637	–	final ReentrantLock lock = this.workerLock;
1638	–	int expectedRunning = runningCountOf(expectedCounts);
1639	–	int expectedTotal = totalCountOf(expectedCounts);
1640	–	boolean success = false;
1641	–	boolean locked = false;
1642	–	// confirm counts while locking; CAS after obtaining lock
1643	–	try {
1644	–	for (;;) {
1645	–	int s = workerCounts;
1646	–	int tc = totalCountOf(s);
1647	–	int rc = runningCountOf(s);
1648	–	if (rc > expectedRunning || tc > expectedTotal)
1649	–	break;
1650	–	if (!locked && !(locked = lock.tryLock()))
1651	–	break;
1652	–	if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
1653	–	createAndStartSpare(tc);
1654	–	success = true;
1655	–	break;
1656	–	}
1657	–	}
1658	–	} finally {
1659	–	if (locked)
1660	–	lock.unlock();
1661	–	}
1662	–	return success;
1663	–	}
1664	–
1665	–	/**
1666	–	* Adds the kth spare worker. On entry, pool counts are already
1667	–	* adjusted to reflect addition.
1668	–	*/
1669	–	private void createAndStartSpare(int k) {
1670	–	ForkJoinWorkerThread w = null;
1671	–	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
1672	–	int len = ws.length;
1673	–	// Probably, we can place at slot k. If not, find empty slot
1674	–	if (k < len && ws[k] != null) {
1675	–	for (k = 0; k < len && ws[k] != null; ++k)
1676	–	;
1677	–	}
1678	–	if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
1679	–	ws[k] = w;
1680	–	w.start();
1681	–	}
1682	–	else
1683	–	updateWorkerCount(-1); // adjust on failure
1684	–	signalIdleWorkers();
1685	–	}
1686	–
1687	–	/**
1688	–	* Suspends calling thread w if there are excess threads.  Called
1689	–	* only from sync.  Spares are enqueued in a Treiber stack using
1690	–	* the same WaitQueueNodes as barriers.  They are resumed mainly
1691	–	* in preJoin, but are also woken on pool events that require all
1692	–	* threads to check run state.
1693	–	*
1694	–	* @param w the caller
1695	–	*/
1696	–	private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1697	–	WaitQueueNode node = null;
1698	–	int s;
1699	–	while (parallelism < runningCountOf(s = workerCounts)) {
1700	–	if (node == null)
1701	–	node = new WaitQueueNode(0, w);
1702	–	if (casWorkerCounts(s, s-1)) { // representation-dependent
1703	–	// push onto stack
1704	–	do {} while (!casSpareStack(node.next = spareStack, node));
1705	–	// block until released by resumeSpare
1706	–	node.awaitSpareRelease();
1707	–	return true;
1708	–	}
1709	–	}
1710	–	return false;
1711	–	}
1712	–
1713	–	/**
1714	–	* Tries to pop and resume a spare thread.
1715	–	*
1716	–	* @param updateCount if true, increment running count on success
1717	–	* @return true if successful
1718	–	*/
1719	–	private boolean tryResumeSpare(boolean updateCount) {
1720	–	WaitQueueNode q;
1721	–	while ((q = spareStack) != null) {
1722	–	if (casSpareStack(q, q.next)) {
1723	–	if (updateCount)
1724	–	updateRunningCount(1);
1725	–	q.signal();
1726	–	return true;
1727	–	}
1728	–	}
1729	–	return false;
1730	–	}
1731	–
1732	–	/**
1733	–	* Pops and resumes all spare threads. Same idea as ensureSync.
1734	–	*
1735	–	* @return true if any spares released
1736	–	*/
1737	–	private boolean resumeAllSpares() {
1738	–	WaitQueueNode q;
1739	–	while ( (q = spareStack) != null) {
1740	–	if (casSpareStack(q, null)) {
1741	–	do {
1742	–	updateRunningCount(1);
1743	–	q.signal();
1744	–	} while ((q = q.next) != null);
1745	–	return true;
1746	–	}
1747	–	}
1748	–	return false;
1749	–	}
1750	–
1751	–	/**
1752	–	* Pops and shuts down excessive spare threads. Call only while
1753	–	* holding lock. This is not guaranteed to eliminate all excess
1754	–	* threads, only those suspended as spares, which are the ones
1755	–	* unlikely to be needed in the future.
1756	–	*/
1757	–	private void trimSpares() {
1758	–	int surplus = totalCountOf(workerCounts) - parallelism;
1759	–	WaitQueueNode q;
1760	–	while (surplus > 0 && (q = spareStack) != null) {
1761	–	if (casSpareStack(q, null)) {
1762	–	do {
1763	–	updateRunningCount(1);
1764	–	ForkJoinWorkerThread w = q.thread;
1765	–	if (w != null && surplus > 0 &&
1766	–	runningCountOf(workerCounts) > 0 && w.shutdown())
1767	–	--surplus;
1768	–	q.signal();
1769	–	} while ((q = q.next) != null);
1770	–	}
1771	–	}
1772	–	}
1773	–
1960		/**
1961		* Interface for extending managed parallelism for tasks running
1962	<	* in ForkJoinPools. A ManagedBlocker provides two methods.
1963	<	* Method {@code isReleasable} must return true if blocking is not
1964	<	* necessary. Method {@code block} blocks the current thread if
1965	<	* necessary (perhaps internally invoking {@code isReleasable}
1966	<	* before actually blocking.).
1962	>	* in {@link ForkJoinPool}s.
1963	>	*
1964	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1965	>	* {@code isReleasable} must return {@code true} if blocking is
1966	>	* not necessary. Method {@code block} blocks the current thread
1967	>	* if necessary (perhaps internally invoking {@code isReleasable}
1968	>	* before actually blocking). The unusual methods in this API
1969	>	* accommodate synchronizers that may, but don't usually, block
1970	>	* for long periods. Similarly, they allow more efficient internal
1971	>	* handling of cases in which additional workers may be, but
1972	>	* usually are not, needed to ensure sufficient parallelism.
1973	>	* Toward this end, implementations of method {@code isReleasable}
1974	>	* must be amenable to repeated invocation.
1975		*
1976		* <p>For example, here is a ManagedBlocker based on a
1977		* ReentrantLock:
#	Line 1795 | Line 1989 | public class ForkJoinPool extends Abstra
1989		*     return hasLock || (hasLock = lock.tryLock());
1990		*   }
1991		* }}</pre>
1992	+	*
1993	+	* <p>Here is a class that possibly blocks waiting for an
1994	+	* item on a given queue:
1995	+	*  <pre> {@code
1996	+	* class QueueTaker<E> implements ManagedBlocker {
1997	+	*   final BlockingQueue<E> queue;
1998	+	*   volatile E item = null;
1999	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
2000	+	*   public boolean block() throws InterruptedException {
2001	+	*     if (item == null)
2002	+	*       item = queue.take();
2003	+	*     return true;
2004	+	*   }
2005	+	*   public boolean isReleasable() {
2006	+	*     return item != null || (item = queue.poll()) != null;
2007	+	*   }
2008	+	*   public E getItem() { // call after pool.managedBlock completes
2009	+	*     return item;
2010	+	*   }
2011	+	* }}</pre>
2012		*/
2013		public static interface ManagedBlocker {
2014		/**
2015		* Possibly blocks the current thread, for example waiting for
2016		* a lock or condition.
2017		*
2018	<	* @return true if no additional blocking is necessary (i.e.,
2019	<	* if isReleasable would return true)
2018	>	* @return {@code true} if no additional blocking is necessary
2019	>	* (i.e., if isReleasable would return true)
2020		* @throws InterruptedException if interrupted while waiting
2021		* (the method is not required to do so, but is allowed to)
2022		*/
2023		boolean block() throws InterruptedException;
2024
2025		/**
2026	<	* Returns true if blocking is unnecessary.
2026	>	* Returns {@code true} if blocking is unnecessary.
2027		*/
2028		boolean isReleasable();
2029		}
2030
2031		/**
2032		* Blocks in accord with the given blocker.  If the current thread
2033	<	* is a ForkJoinWorkerThread, this method possibly arranges for a
2034	<	* spare thread to be activated if necessary to ensure parallelism
2035	<	* while the current thread is blocked.  If
1822	<	* {@code maintainParallelism} is true and the pool supports
1823	<	* it ({@link #getMaintainsParallelism}), this method attempts to
1824	<	* maintain the pool's nominal parallelism. Otherwise it activates
1825	<	* a thread only if necessary to avoid complete starvation. This
1826	<	* option may be preferable when blockages use timeouts, or are
1827	<	* almost always brief.
2033	>	* is a {@link ForkJoinWorkerThread}, this method possibly
2034	>	* arranges for a spare thread to be activated if necessary to
2035	>	* ensure sufficient parallelism while the current thread is blocked.
2036		*
2037	<	* <p> If the caller is not a ForkJoinTask, this method is behaviorally
2038	<	* equivalent to
2037	>	* <p>If the caller is not a {@link ForkJoinTask}, this method is
2038	>	* behaviorally equivalent to
2039		*  <pre> {@code
2040		* while (!blocker.isReleasable())
2041		*   if (blocker.block())
2042		*     return;
2043		* }</pre>
2044	<	* If the caller is a ForkJoinTask, then the pool may first
2045	<	* be expanded to ensure parallelism, and later adjusted.
2044	>	*
2045	>	* If the caller is a {@code ForkJoinTask}, then the pool may
2046	>	* first be expanded to ensure parallelism, and later adjusted.
2047		*
2048		* @param blocker the blocker
1840	–	* @param maintainParallelism if true and supported by this pool,
1841	–	* attempt to maintain the pool's nominal parallelism; otherwise
1842	–	* activate a thread only if necessary to avoid complete
1843	–	* starvation.
2049		* @throws InterruptedException if blocker.block did so
2050		*/
2051	<	public static void managedBlock(ManagedBlocker blocker,
1847	<	boolean maintainParallelism)
2051	>	public static void managedBlock(ManagedBlocker blocker)
2052		throws InterruptedException {
2053		Thread t = Thread.currentThread();
2054	<	ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
2055	<	((ForkJoinWorkerThread) t).pool : null);
2056	<	if (!blocker.isReleasable()) {
2057	<	try {
2058	<	if (pool == null ||
2059	<	!pool.preBlock(blocker, maintainParallelism))
1856	<	awaitBlocker(blocker);
1857	<	} finally {
1858	<	if (pool != null)
1859	<	pool.updateRunningCount(1);
1860	<	}
2054	>	if (t instanceof ForkJoinWorkerThread) {
2055	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
2056	>	w.pool.awaitBlocker(blocker);
2057	>	}
2058	>	else {
2059	>	do {} while (!blocker.isReleasable() && !blocker.block());
2060		}
2061		}
2062
2063	<	private static void awaitBlocker(ManagedBlocker blocker)
2064	<	throws InterruptedException {
2065	<	do {} while (!blocker.isReleasable() && !blocker.block());
1867	<	}
1868	<
1869	<	// AbstractExecutorService overrides
2063	>	// AbstractExecutorService overrides.  These rely on undocumented
2064	>	// fact that ForkJoinTask.adapt returns ForkJoinTasks that also
2065	>	// implement RunnableFuture.
2066
2067		protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
2068	<	return new AdaptedRunnable<T>(runnable, value);
2068	>	return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
2069		}
2070
2071		protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
2072	<	return new AdaptedCallable<T>(callable);
2072	>	return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
2073		}
2074
2075	+	// Unsafe mechanics
2076	+	private static final sun.misc.Unsafe UNSAFE;
2077	+	private static final long ctlOffset;
2078	+	private static final long stealCountOffset;
2079	+	private static final long blockedCountOffset;
2080	+	private static final long quiescerCountOffset;
2081	+	private static final long scanGuardOffset;
2082	+	private static final long nextWorkerNumberOffset;
2083	+	private static final long ABASE;
2084	+	private static final int ASHIFT;
2085	+
2086	+	static {
2087	+	poolNumberGenerator = new AtomicInteger();
2088	+	workerSeedGenerator = new Random();
2089	+	modifyThreadPermission = new RuntimePermission("modifyThread");
2090	+	defaultForkJoinWorkerThreadFactory =
2091	+	new DefaultForkJoinWorkerThreadFactory();
2092	+	int s;
2093	+	try {
2094	+	UNSAFE = getUnsafe();
2095	+	Class k = ForkJoinPool.class;
2096	+	ctlOffset = UNSAFE.objectFieldOffset
2097	+	(k.getDeclaredField("ctl"));
2098	+	stealCountOffset = UNSAFE.objectFieldOffset
2099	+	(k.getDeclaredField("stealCount"));
2100	+	blockedCountOffset = UNSAFE.objectFieldOffset
2101	+	(k.getDeclaredField("blockedCount"));
2102	+	quiescerCountOffset = UNSAFE.objectFieldOffset
2103	+	(k.getDeclaredField("quiescerCount"));
2104	+	scanGuardOffset = UNSAFE.objectFieldOffset
2105	+	(k.getDeclaredField("scanGuard"));
2106	+	nextWorkerNumberOffset = UNSAFE.objectFieldOffset
2107	+	(k.getDeclaredField("nextWorkerNumber"));
2108	+	Class a = ForkJoinTask[].class;
2109	+	ABASE = UNSAFE.arrayBaseOffset(a);
2110	+	s = UNSAFE.arrayIndexScale(a);
2111	+	} catch (Exception e) {
2112	+	throw new Error(e);
2113	+	}
2114	+	if ((s & (s-1)) != 0)
2115	+	throw new Error("data type scale not a power of two");
2116	+	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
2117	+	}
2118
2119	<	// Unsafe mechanics for jsr166y 3rd party package.
2119	>	/**
2120	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
2121	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
2122	>	* into a jdk.
2123	>	*
2124	>	* @return a sun.misc.Unsafe
2125	>	*/
2126		private static sun.misc.Unsafe getUnsafe() {
2127		try {
2128		return sun.misc.Unsafe.getUnsafe();
2129		} catch (SecurityException se) {
2130		try {
2131		return java.security.AccessController.doPrivileged
2132	<	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
2132	>	(new java.security
2133	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
2134		public sun.misc.Unsafe run() throws Exception {
2135	<	return getUnsafeByReflection();
2135	>	java.lang.reflect.Field f = sun.misc
2136	>	.Unsafe.class.getDeclaredField("theUnsafe");
2137	>	f.setAccessible(true);
2138	>	return (sun.misc.Unsafe) f.get(null);
2139		}});
2140		} catch (java.security.PrivilegedActionException e) {
2141		throw new RuntimeException("Could not initialize intrinsics",
#	Line 1894 | Line 2143 | public class ForkJoinPool extends Abstra
2143		}
2144		}
2145		}
1897	–
1898	–	private static sun.misc.Unsafe getUnsafeByReflection()
1899	–	throws NoSuchFieldException, IllegalAccessException {
1900	–	java.lang.reflect.Field f =
1901	–	sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
1902	–	f.setAccessible(true);
1903	–	return (sun.misc.Unsafe) f.get(null);
1904	–	}
1905	–
1906	–	private static long fieldOffset(String fieldName, Class<?> klazz) {
1907	–	try {
1908	–	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName));
1909	–	} catch (NoSuchFieldException e) {
1910	–	// Convert Exception to Error
1911	–	NoSuchFieldError error = new NoSuchFieldError(fieldName);
1912	–	error.initCause(e);
1913	–	throw error;
1914	–	}
1915	–	}
1916	–
1917	–	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1918	–	private static final long eventCountOffset =
1919	–	fieldOffset("eventCount", ForkJoinPool.class);
1920	–	private static final long workerCountsOffset =
1921	–	fieldOffset("workerCounts", ForkJoinPool.class);
1922	–	private static final long runControlOffset =
1923	–	fieldOffset("runControl", ForkJoinPool.class);
1924	–	private static final long syncStackOffset =
1925	–	fieldOffset("syncStack",ForkJoinPool.class);
1926	–	private static final long spareStackOffset =
1927	–	fieldOffset("spareStack", ForkJoinPool.class);
1928	–
1929	–	private boolean casEventCount(long cmp, long val) {
1930	–	return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
1931	–	}
1932	–	private boolean casWorkerCounts(int cmp, int val) {
1933	–	return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
1934	–	}
1935	–	private boolean casRunControl(int cmp, int val) {
1936	–	return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
1937	–	}
1938	–	private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
1939	–	return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
1940	–	}
1941	–	private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
1942	–	return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
1943	–	}
2146		}

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