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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.1 by dl, Tue Jan 6 14:30:31 2009 UTC vs.
Revision 1.92 by dl, Tue Feb 22 10:50:51 2011 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	<	import java.util.*;
9	<	import java.util.concurrent.*;
10	<	import java.util.concurrent.locks.*;
11	<	import java.util.concurrent.atomic.*;
12	<	import sun.misc.Unsafe;
13	<	import java.lang.reflect.*;
8	>
9	>	import java.util.ArrayList;
10	>	import java.util.Arrays;
11	>	import java.util.Collection;
12	>	import java.util.Collections;
13	>	import java.util.List;
14	>	import java.util.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.locks.Condition;
27
28		/**
29	<	* Host for a group of ForkJoinWorkerThreads.  A ForkJoinPool provides
30	<	* the entry point for tasks submitted from non-ForkJoinTasks, as well
31	<	* as management and monitoring operations.  Normally a single
32	<	* ForkJoinPool is used for a large number of submitted
20	<	* tasks. Otherwise, use would not usually outweigh the construction
21	<	* and bookkeeping overhead of creating a large set of threads.
22	<	*
23	<	* <p>ForkJoinPools differ from other kinds of Executor mainly in that
24	<	* they provide <em>work-stealing</em>: all threads in the pool
25	<	* attempt to find and execute subtasks created by other active tasks
26	<	* (eventually blocking if none exist). This makes them efficient when
27	<	* most tasks spawn other subtasks (as do most ForkJoinTasks) but
28	<	* possibly less so otherwise. It is however fine to combine execution
29	<	* of some plain Runnable- or Callable- based activities with that of
30	<	* ForkJoinTasks.
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>A ForkJoinPool may be constructed with a given parallelism level
35	<	* (target pool size), which it attempts to maintain by dynamically
36	<	* adding, suspending, or resuming threads, even if some tasks have
37	<	* blocked waiting to join others. However, no such adjustments are
38	<	* performed in the face of blocked IO or other unmanaged
39	<	* synchronization. The nested ManagedBlocker interface enables
40	<	* extension of the kinds of synchronization accommodated.
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>The target parallelism level may also be set dynamically. You
45	<	* can limit the number of threads dynamically constructed using
46	<	* method <tt>setMaximumPoolSize</tt> and/or
47	<	* <tt>setMaintainParallelism</tt>.
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	<	* <tt>getStealCount</tt>) 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	<	* <tt>toString</tt> returns indications of pool state in a convenient
59	<	* form for informal monitoring.
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 parallelism to 32767. Attempts to create pools with greater
115	<	* than the maximum result in IllegalArgumentExceptions.
114	>	* maximum number of running threads to 32767. Attempts to create
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
124		*/
125	<	public class ForkJoinPool extends AbstractExecutorService
57	<	implements ExecutorService {
125	>	public class ForkJoinPool extends AbstractExecutorService {
126
127		/*
128	<	* See the extended comments interspersed below for design,
129	<	* rationale, and walkthroughs.
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
64	–	/** Mask for packing and unpacking shorts */
65	–	private static final int  shortMask = 0xffff;
66	–
67	–	/** Max pool size -- must be a power of two minus 1 */
68	–	private static final int MAX_THREADS =  0x7FFF;
69	–
333		/**
334	<	* Factory for creating new ForkJoinWorkerThreads.  A
335	<	* ForkJoinWorkerThreadFactory must be defined and used for
336	<	* ForkJoinWorkerThread subclasses that extend base functionality
337	<	* or initialize threads with different contexts.
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		}
348
349		/**
350	<	* Default ForkJoinWorkerThreadFactory implementation, creates a
350	>	* Default ForkJoinWorkerThreadFactory implementation; creates a
351		* new ForkJoinWorkerThread.
352		*/
353	<	public static class  DefaultForkJoinWorkerThreadFactory
353	>	static class DefaultForkJoinWorkerThreadFactory
354		implements ForkJoinWorkerThreadFactory {
355		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
356	<	try {
94	<	return new ForkJoinWorkerThread(pool);
95	<	} catch (OutOfMemoryError oom)  {
96	<	return null;
97	<	}
356	>	return new ForkJoinWorkerThread(pool);
357		}
358		}
359
360		/**
361	<	* The default ForkJoinWorkerThreadFactory, used unless overridden
362	<	* in ForkJoinPool constructors.
361	>	* Creates a new ForkJoinWorkerThread. This factory is used unless
362	>	* overridden in ForkJoinPool constructors.
363		*/
364	<	private static final DefaultForkJoinWorkerThreadFactory
365	<	defaultForkJoinWorkerThreadFactory =
107	<	new DefaultForkJoinWorkerThreadFactory();
108	<
364	>	public static final ForkJoinWorkerThreadFactory
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 =
115	<	new RuntimePermission("modifyThread");
371	>	private static final RuntimePermission modifyThreadPermission;
372
373		/**
374		* If there is a security manager, makes sure caller has
#	Line 127 | Line 383 | public class ForkJoinPool extends Abstra
383		/**
384		* Generator for assigning sequence numbers as pool names.
385		*/
386	<	private static final AtomicInteger poolNumberGenerator =
131	<	new AtomicInteger();
386	>	private static final AtomicInteger poolNumberGenerator;
387
388		/**
389	<	* Array holding all worker threads in the pool. Array size must
390	<	* be a power of two.  Updates and replacements are protected by
391	<	* workerLock, but it is always kept in a consistent enough state
392	<	* to be randomly accessed without locking by workers performing
393	<	* 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	>	* Array serving as submission queue. Initialized upon construction.
426	>	*/
427	>	private ForkJoinTask<?>[] submissionQueue;
428	>
429	>	/**
430	>	* Lock protecting submissions array for addSubmission
431	>	*/
432	>	private final ReentrantLock submissionLock;
433
434		/**
435	<	* The uncaught exception handler used when any worker
436	<	* abrupty terminates
435	>	* Condition for awaitTermination, using submissionLock for
436	>	* convenience.
437		*/
438	<	private Thread.UncaughtExceptionHandler ueh;
438	>	private final Condition termination;
439
440		/**
441		* Creation factory for worker threads.
#	Line 161 | 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
448	<	* suspended when the parallelism level rose.
446	>	* The uncaught exception handler used when any worker abruptly
447	>	* terminates.
448	>	*/
449	>	final Thread.UncaughtExceptionHandler ueh;
450	>
451	>	/**
452	>	* Prefix for assigning names to worker threads
453		*/
454	<	private volatile WaitQueueNode spareStack;
454	>	private final String workerNamePrefix;
455
456		/**
457		* Sum of per-thread steal counts, updated only when threads are
458		* idle or terminating.
459		*/
460	<	private final AtomicLong stealCount;
460	>	private volatile long stealCount;
461
462		/**
463	<	* Queue for external submissions.
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 final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
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	<	* Head of Treiber stack for barrier sync. See below for explanation
521	>	* The target parallelism level.
522		*/
523	<	private volatile WaitQueueNode barrierStack;
523	>	final int parallelism;
524
525		/**
526	<	* The count for event barrier
526	>	* Index (mod submission queue length) of next element to take
527	>	* from submission queue.
528		*/
529	<	private volatile long eventCount;
529	>	volatile int queueBase;
530
531		/**
532	<	* Pool number, just for assigning useful names to worker threads
532	>	* Index (mod submission queue length) of next element to add
533	>	* in submission queue.
534		*/
535	<	private final int poolNumber;
535	>	int queueTop;
536
537		/**
538	<	* The maximum allowed pool size
538	>	* True when shutdown() has been called.
539		*/
540	<	private volatile int maxPoolSize;
540	>	volatile boolean shutdown;
541
542		/**
543	<	* The desired parallelism level, updated only under workerLock.
543	>	* True if use local fifo, not default lifo, for local polling
544	>	* Read by, and replicated by ForkJoinWorkerThreads
545		*/
546	<	private volatile int parallelism;
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
210	<	* making decisions about creating and suspending spare
211	<	* threads. Updated only by CAS.  Note: CASes in
212	<	* updateRunningCount and preJoin running active count is in low
213	<	* 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	<	* Add delta (which may be negative) to running count.  This must
223	<	* be called before (with negative arg) and after (with positive)
224	<	* any managed synchronization (i.e., mainly, joins)
225	<	* @param delta the number to add
561	>	* Counter for worker Thread names (unrelated to their poolIndex)
562		*/
563	<	final void updateRunningCount(int delta) {
228	<	int s;
229	<	do;while (!casWorkerCounts(s = workerCounts, s + delta));
230	<	}
563	>	private volatile int nextWorkerNumber;
564
565		/**
566	<	* Add delta (which may be negative) to both total and running
234	<	* count.  This must be called upon creation and termination of
235	<	* worker threads.
236	<	* @param delta the number to add
566	>	* The index for the next created worker. Accessed under scanGuard.
567		*/
568	<	private void updateWorkerCount(int delta) {
239	<	int d = delta + (delta << 16); // add to both lo and hi parts
240	<	int s;
241	<	do;while (!casWorkerCounts(s = workerCounts, s + d));
242	<	}
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
257	<	private static final int RUNNING     = 0;
258	<	private static final int SHUTDOWN    = 1;
259	<	private static final int TERMINATING = 2;
260	<	private static final int TERMINATED  = 3;
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	<	* Increment active count. Called by workers before/during
597	<	* 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	>	* @param w the worker
603		*/
604	<	final void incrementActiveCount() {
605	<	int c;
606	<	do;while (!casRunControl(c = runControl, c+1));
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 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	<	* Decrement active count; possibly trigger termination.
664	<	* 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 false if failed due to contention, else true
667		*/
668	<	final void decrementActiveCount() {
669	<	int c, nextc;
670	<	do;while (!casRunControl(c = runControl, nextc = c-1));
671	<	if (canTerminateOnShutdown(nextc))
672	<	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	>	* 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 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	<	* Return true if argument represents zero active count and
758	<	* nonzero runstate, which is the triggering condition for
759	<	* terminating on shutdown.
760	<	*/
761	<	private static boolean canTerminateOnShutdown(int c) {
762	<	return ((c & -c) >>> 16) != 0; // i.e. least bit is nonzero runState bit
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 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	>	if (parallelism + (int)(c >> AC_SHIFT) == 1 &&
775	>	blockedCount == 0 && quiescerCount == 0)
776	>	idleAwaitWork(w, v);               // quiescent -- maybe shrink
777	>
778	>	boolean rescanned = false;
779	>	for (int sc;;) {
780	>	if (w.eventCount != v)
781	>	return true;
782	>	if ((sc = w.stealCount) != 0) {
783	>	long s = stealCount;               // accumulate stealCount
784	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s+sc))
785	>	w.stealCount = 0;
786	>	}
787	>	else if (!rescanned) {
788	>	int g = scanGuard, m = g & SMASK;
789	>	ForkJoinWorkerThread[] ws = workers;
790	>	if (ws != null && m < ws.length) {
791	>	rescanned = true;
792	>	for (int i = 0; i <= m; ++i) {
793	>	ForkJoinWorkerThread u = ws[i];
794	>	if (u != null) {
795	>	if (u.queueBase != u.queueTop &&
796	>	!tryReleaseWaiter())
797	>	rescanned = false; // contended
798	>	if (w.eventCount != v)
799	>	return true;
800	>	}
801	>	}
802	>	}
803	>	if (scanGuard != g ||              // stale
804	>	(queueBase != queueTop && !tryReleaseWaiter()))
805	>	rescanned = false;
806	>	if (!rescanned)
807	>	Thread.yield();                // reduce contention
808	>	else
809	>	Thread.interrupted();          // clear before park
810	>	}
811	>	else {
812	>	w.parked = true;                   // must recheck
813	>	if (w.eventCount != v) {
814	>	w.parked = false;
815	>	return true;
816	>	}
817	>	LockSupport.park(this);
818	>	rescanned = w.parked = false;
819	>	}
820	>	}
821		}
822
823		/**
824	<	* Transition run state to at least the given state. Return true
825	<	* if not already at least given state.
824	>	* If pool is quiescent, checks for termination, and waits for
825	>	* event signal for up to SHRINK_RATE nanosecs. On timeout, if ctl
826	>	* has not changed, terminates the worker. Upon its termination
827	>	* (see deregisterWorker), it may wake up another worker to
828	>	* possibly repeat this process.
829	>	*
830	>	* @param w the calling worker
831	>	* @param v the eventCount w must wait until changed
832		*/
833	<	private boolean transitionRunStateTo(int state) {
834	<	for (;;) {
835	<	int c = runControl;
836	<	if (runStateOf(c) >= state)
837	<	return false;
838	<	if (casRunControl(c, runControlFor(state, activeCountOf(c))))
839	<	return true;
833	>	private void idleAwaitWork(ForkJoinWorkerThread w, int v) {
834	>	ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs
835	>	if (shutdown)
836	>	tryTerminate(false);
837	>	long c = ctl;
838	>	long nc = (((c & (AC_MASK|TC_MASK)) + AC_UNIT) |
839	>	(long)(w.nextWait & E_MASK)); // ctl value to release w
840	>	if (w.eventCount == v &&
841	>	parallelism + (int)(c >> AC_SHIFT) == 0 &&
842	>	blockedCount == 0 && quiescerCount == 0) {
843	>	long startTime = System.nanoTime();
844	>	Thread.interrupted();
845	>	if (w.eventCount == v) {
846	>	w.parked = true;
847	>	if (w.eventCount == v)
848	>	LockSupport.parkNanos(this, SHRINK_RATE);
849	>	w.parked = false;
850	>	if (w.eventCount == v && ctl == c &&
851	>	System.nanoTime() - startTime >= SHRINK_RATE &&
852	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
853	>	w.terminate = true;
854	>	w.eventCount = ((int)c + EC_UNIT) & E_MASK;
855	>	}
856	>	}
857		}
858		}
859
860	+	// Submissions
861	+
862		/**
863	<	* Controls whether to add spares to maintain parallelism
863	>	* Enqueues the given task in the submissionQueue.  Same idea as
864	>	* ForkJoinWorkerThread.pushTask except for use of submissionLock.
865	>	*
866	>	* @param t the task
867		*/
868	<	private volatile boolean maintainsParallelism;
868	>	private void addSubmission(ForkJoinTask<?> t) {
869	>	final ReentrantLock lock = this.submissionLock;
870	>	lock.lock();
871	>	try {
872	>	ForkJoinTask<?>[] q; int s, m;
873	>	if ((q = submissionQueue) != null) {    // ignore if queue removed
874	>	long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE;
875	>	UNSAFE.putOrderedObject(q, u, t);
876	>	queueTop = s + 1;
877	>	if (s - queueBase == m)
878	>	growSubmissionQueue();
879	>	}
880	>	} finally {
881	>	lock.unlock();
882	>	}
883	>	signalWork();
884	>	}
885
886	<	// Constructors
886	>	//  (pollSubmission is defined below with exported methods)
887
888		/**
889	<	* Creates a ForkJoinPool with a pool size equal to the number of
890	<	* processors available on the system and using the default
319	<	* ForkJoinWorkerThreadFactory,
320	<	* @throws SecurityException if a security manager exists and
321	<	*         the caller is not permitted to modify threads
322	<	*         because it does not hold {@link
323	<	*         java.lang.RuntimePermission}<tt>("modifyThread")</tt>,
889	>	* Creates or doubles submissionQueue array.
890	>	* Basically identical to ForkJoinWorkerThread version
891		*/
892	<	public ForkJoinPool() {
893	<	this(Runtime.getRuntime().availableProcessors(),
894	<	defaultForkJoinWorkerThreadFactory);
892	>	private void growSubmissionQueue() {
893	>	ForkJoinTask<?>[] oldQ = submissionQueue;
894	>	int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY;
895	>	if (size > MAXIMUM_QUEUE_CAPACITY)
896	>	throw new RejectedExecutionException("Queue capacity exceeded");
897	>	if (size < INITIAL_QUEUE_CAPACITY)
898	>	size = INITIAL_QUEUE_CAPACITY;
899	>	ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size];
900	>	int mask = size - 1;
901	>	int top = queueTop;
902	>	int oldMask;
903	>	if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) {
904	>	for (int b = queueBase; b != top; ++b) {
905	>	long u = ((b & oldMask) << ASHIFT) + ABASE;
906	>	Object x = UNSAFE.getObjectVolatile(oldQ, u);
907	>	if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null))
908	>	UNSAFE.putObjectVolatile
909	>	(q, ((b & mask) << ASHIFT) + ABASE, x);
910	>	}
911	>	}
912		}
913
914	+	// Blocking support
915	+
916		/**
917	<	* Creates a ForkJoinPool with the indicated parellelism level
918	<	* threads, and using the default ForkJoinWorkerThreadFactory,
919	<	* @param parallelism the number of worker threads
920	<	* @throws IllegalArgumentException if parallelism less than or
921	<	* equal to zero
922	<	* @throws SecurityException if a security manager exists and
337	<	*         the caller is not permitted to modify threads
338	<	*         because it does not hold {@link
339	<	*         java.lang.RuntimePermission}<tt>("modifyThread")</tt>,
917	>	* Tries to increment blockedCount, decrement active count
918	>	* (sometimes implicitly) and possibly release or create a
919	>	* compensating worker in preparation for blocking. Fails
920	>	* on contention or termination.
921	>	*
922	>	* @return true if the caller can block, else should recheck and retry
923		*/
924	<	public ForkJoinPool(int parallelism) {
925	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
924	>	private boolean tryPreBlock() {
925	>	int b = blockedCount;
926	>	if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) {
927	>	int pc = parallelism;
928	>	do {
929	>	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
930	>	int e, ac, tc, rc, i;
931	>	long c = ctl;
932	>	int u = (int)(c >>> 32);
933	>	if ((e = (int)c) < 0) {
934	>	// skip -- terminating
935	>	}
936	>	else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 &&
937	>	(ws = workers) != null &&
938	>	(i = ~e & SMASK) < ws.length &&
939	>	(w = ws[i]) != null) {
940	>	long nc = ((long)(w.nextWait & E_MASK) |
941	>	(c & (AC_MASK|TC_MASK)));
942	>	if (w.eventCount == e &&
943	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
944	>	w.eventCount = (e + EC_UNIT) & E_MASK;
945	>	if (w.parked)
946	>	UNSAFE.unpark(w);
947	>	return true;             // release an idle worker
948	>	}
949	>	}
950	>	else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
951	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
952	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc))
953	>	return true;             // no compensation needed
954	>	}
955	>	else if (tc + pc < MAX_ID) {
956	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
957	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) {
958	>	addWorker();
959	>	return true;            // create a replacement
960	>	}
961	>	}
962	>	// try to back out on any failure and let caller retry
963	>	} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
964	>	b = blockedCount, b - 1));
965	>	}
966	>	return false;
967		}
968
969		/**
970	<	* Creates a ForkJoinPool with a pool size equal to the number of
347	<	* processors available on the system and using the given
348	<	* ForkJoinWorkerThreadFactory,
349	<	* @param factory the factory for creating new threads
350	<	* @throws NullPointerException if factory is null
351	<	* @throws SecurityException if a security manager exists and
352	<	*         the caller is not permitted to modify threads
353	<	*         because it does not hold {@link
354	<	*         java.lang.RuntimePermission}<tt>("modifyThread")</tt>,
970	>	* Decrements blockedCount and increments active count
971		*/
972	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
973	<	this(Runtime.getRuntime().availableProcessors(), factory);
972	>	private void postBlock() {
973	>	long c;
974	>	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset,  // no mask
975	>	c = ctl, c + AC_UNIT));
976	>	int b;
977	>	do {} while(!UNSAFE.compareAndSwapInt(this, blockedCountOffset,
978	>	b = blockedCount, b - 1));
979		}
980
981		/**
982	<	* Creates a ForkJoinPool with the indicated target number of
983	<	* worker threads and the given factory.
982	>	* Possibly blocks waiting for the given task to complete, or
983	>	* cancels the task if terminating.  Fails to wait if contended.
984		*
985	<	* @param parallelism the targeted number of worker threads
365	<	* @param factory the factory for creating new threads
366	<	* @throws IllegalArgumentException if parallelism less than or
367	<	* equal to zero, or greater than implementation limit.
368	<	* @throws NullPointerException if factory is null
369	<	* @throws SecurityException if a security manager exists and
370	<	*         the caller is not permitted to modify threads
371	<	*         because it does not hold {@link
372	<	*         java.lang.RuntimePermission}<tt>("modifyThread")</tt>,
985	>	* @param joinMe the task
986		*/
987	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
988	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
989	<	throw new IllegalArgumentException();
990	<	if (factory == null)
991	<	throw new NullPointerException();
992	<	checkPermission();
993	<	this.factory = factory;
994	<	this.parallelism = parallelism;
995	<	this.maxPoolSize = MAX_THREADS;
996	<	this.maintainsParallelism = true;
997	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
385	<	this.workerLock = new ReentrantLock();
386	<	this.termination = workerLock.newCondition();
387	<	this.stealCount = new AtomicLong();
388	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
389	<	createAndStartInitialWorkers(parallelism);
987	>	final void tryAwaitJoin(ForkJoinTask<?> joinMe) {
988	>	int s;
989	>	Thread.interrupted(); // clear interrupts before checking termination
990	>	if (joinMe.status >= 0) {
991	>	if (tryPreBlock()) {
992	>	joinMe.tryAwaitDone(0L);
993	>	postBlock();
994	>	}
995	>	if ((ctl & STOP_BIT) != 0L)
996	>	joinMe.cancelIgnoringExceptions();
997	>	}
998		}
999
1000		/**
1001	<	* Create new worker using factory.
1002	<	* @param index the index to assign worker
1003	<	* @return new worker, or null of factory failed
1001	>	* Possibly blocks the given worker waiting for joinMe to
1002	>	* complete or timeout
1003	>	*
1004	>	* @param joinMe the task
1005	>	* @param millis the wait time for underlying Object.wait
1006		*/
1007	<	private ForkJoinWorkerThread createWorker(int index) {
1008	<	Thread.UncaughtExceptionHandler h = ueh;
1009	<	ForkJoinWorkerThread w = factory.newThread(this);
1010	<	if (w != null) {
1011	<	w.poolIndex = index;
1012	<	w.setDaemon(true);
1013	<	w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
1014	<	if (h != null)
1015	<	w.setUncaughtExceptionHandler(h);
1007	>	final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) {
1008	>	while (joinMe.status >= 0) {
1009	>	Thread.interrupted();
1010	>	if ((ctl & STOP_BIT) != 0L) {
1011	>	joinMe.cancelIgnoringExceptions();
1012	>	break;
1013	>	}
1014	>	if (tryPreBlock()) {
1015	>	long last = System.nanoTime();
1016	>	while (joinMe.status >= 0) {
1017	>	long millis = TimeUnit.NANOSECONDS.toMillis(nanos);
1018	>	if (millis <= 0)
1019	>	break;
1020	>	joinMe.tryAwaitDone(millis);
1021	>	if (joinMe.status < 0)
1022	>	break;
1023	>	if ((ctl & STOP_BIT) != 0L) {
1024	>	joinMe.cancelIgnoringExceptions();
1025	>	break;
1026	>	}
1027	>	long now = System.nanoTime();
1028	>	nanos -= now - last;
1029	>	last = now;
1030	>	}
1031	>	postBlock();
1032	>	break;
1033	>	}
1034		}
407	–	return w;
1035		}
1036
1037		/**
1038	<	* Return a good size for worker array given pool size.
412	<	* Currently requires size to be a power of two.
1038	>	* If necessary, compensates for blocker, and blocks
1039		*/
1040	<	private static int arraySizeFor(int ps) {
1041	<	return ps <= 1? 1 : (1 << (32 - Integer.numberOfLeadingZeros(ps-1)));
1040	>	private void awaitBlocker(ManagedBlocker blocker)
1041	>	throws InterruptedException {
1042	>	while (!blocker.isReleasable()) {
1043	>	if (tryPreBlock()) {
1044	>	try {
1045	>	do {} while (!blocker.isReleasable() && !blocker.block());
1046	>	} finally {
1047	>	postBlock();
1048	>	}
1049	>	break;
1050	>	}
1051	>	}
1052		}
1053
1054	+	// Creating, registering and deregistring workers
1055	+
1056		/**
1057	<	* Create or resize array if necessary to hold newLength
1058	<	* @return the array
1057	>	* Tries to create and start a worker; minimally rolls back counts
1058	>	* on failure.
1059		*/
1060	<	private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
1061	<	ForkJoinWorkerThread[] ws = workers;
1062	<	if (ws == null)
1063	<	return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
1064	<	else if (newLength > ws.length)
1065	<	return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
1060	>	private void addWorker() {
1061	>	Throwable ex = null;
1062	>	ForkJoinWorkerThread t = null;
1063	>	try {
1064	>	t = factory.newThread(this);
1065	>	} catch (Throwable e) {
1066	>	ex = e;
1067	>	}
1068	>	if (t == null) {  // null or exceptional factory return
1069	>	long c;       // adjust counts
1070	>	do {} while (!UNSAFE.compareAndSwapLong
1071	>	(this, ctlOffset, c = ctl,
1072	>	(((c - AC_UNIT) & AC_MASK) |
1073	>	((c - TC_UNIT) & TC_MASK) |
1074	>	(c & ~(AC_MASK|TC_MASK)))));
1075	>	// Propagate exception if originating from an external caller
1076	>	if (!tryTerminate(false) && ex != null &&
1077	>	!(Thread.currentThread() instanceof ForkJoinWorkerThread))
1078	>	UNSAFE.throwException(ex);
1079	>	}
1080		else
1081	<	return ws;
1081	>	t.start();
1082		}
1083
1084		/**
1085	<	* Try to shrink workers into smaller array after one or more terminate
1085	>	* Callback from ForkJoinWorkerThread constructor to assign a
1086	>	* public name
1087		*/
1088	<	private void tryShrinkWorkerArray() {
1089	<	ForkJoinWorkerThread[] ws = workers;
1090	<	int len = ws.length;
1091	<	int last = len - 1;
1092	<	while (last >= 0 && ws[last] == null)
1093	<	--last;
441	<	int newLength = arraySizeFor(last+1);
442	<	if (newLength < len)
443	<	workers = Arrays.copyOf(ws, newLength);
1088	>	final String nextWorkerName() {
1089	>	for (int n;;) {
1090	>	if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset,
1091	>	n = nextWorkerNumber, ++n))
1092	>	return workerNamePrefix + n;
1093	>	}
1094		}
1095
1096		/**
1097	<	* Initial worker array and worker creation and startup. (This
1098	<	* must be done under lock to avoid interference by some of the
1099	<	* newly started threads while creating others.)
1097	>	* Callback from ForkJoinWorkerThread constructor to
1098	>	* determine its poolIndex and record in workers array.
1099	>	*
1100	>	* @param w the worker
1101	>	* @return the worker's pool index
1102		*/
1103	<	private void createAndStartInitialWorkers(int ps) {
1104	<	final ReentrantLock lock = this.workerLock;
1105	<	lock.lock();
1106	<	try {
1107	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
1108	<	for (int i = 0; i < ps; ++i) {
1109	<	ForkJoinWorkerThread w = createWorker(i);
1110	<	if (w != null) {
1111	<	ws[i] = w;
1112	<	w.start();
1113	<	updateWorkerCount(1);
1103	>	final int registerWorker(ForkJoinWorkerThread w) {
1104	>	/*
1105	>	* In the typical case, a new worker acquires the lock, uses
1106	>	* next available index and returns quickly.  Since we should
1107	>	* not block callers (ultimately from signalWork or
1108	>	* tryPreBlock) waiting for the lock needed to do this, we
1109	>	* instead help release other workers while waiting for the
1110	>	* lock.
1111	>	*/
1112	>	for (int g;;) {
1113	>	ForkJoinWorkerThread[] ws;
1114	>	if (((g = scanGuard) & SG_UNIT) == 0 &&
1115	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1116	>	g, g | SG_UNIT)) {
1117	>	int k = nextWorkerIndex;
1118	>	try {
1119	>	if ((ws = workers) != null) { // ignore on shutdown
1120	>	int n = ws.length;
1121	>	if (k < 0 || k >= n || ws[k] != null) {
1122	>	for (k = 0; k < n && ws[k] != null; ++k)
1123	>	;
1124	>	if (k == n)
1125	>	ws = workers = Arrays.copyOf(ws, n << 1);
1126	>	}
1127	>	ws[k] = w;
1128	>	nextWorkerIndex = k + 1;
1129	>	int m = g & SMASK;
1130	>	g = k >= m? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1);
1131	>	}
1132	>	} finally {
1133	>	scanGuard = g;
1134	>	}
1135	>	return k;
1136	>	}
1137	>	else if ((ws = workers) != null) { // help release others
1138	>	for (ForkJoinWorkerThread u : ws) {
1139	>	if (u != null && u.queueBase != u.queueTop) {
1140	>	if (tryReleaseWaiter())
1141	>	break;
1142	>	}
1143		}
1144		}
464	–	} finally {
465	–	lock.unlock();
1145		}
1146		}
1147
1148		/**
1149	<	* Worker creation and startup for threads added via setParallelism.
1149	>	* Final callback from terminating worker.  Removes record of
1150	>	* worker from array, and adjusts counts. If pool is shutting
1151	>	* down, tries to complete termination.
1152	>	*
1153	>	* @param w the worker
1154		*/
1155	<	private void createAndStartAddedWorkers() {
1156	<	resumeAllSpares();  // Allow spares to convert to nonspare
1157	<	int ps = parallelism;
1158	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
1159	<	int len = ws.length;
1160	<	// Sweep through slots, to keep lowest indices most populated
1161	<	int k = 0;
1162	<	while (k < len) {
1163	<	if (ws[k] != null) {
1164	<	++k;
1165	<	continue;
1155	>	final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) {
1156	>	int idx = w.poolIndex;
1157	>	int sc = w.stealCount;
1158	>	int steps = 0;
1159	>	// Remove from array, adjust worker counts and collect steal count.
1160	>	// We can intermix failed removes or adjusts with steal updates
1161	>	do {
1162	>	long s, c;
1163	>	int g;
1164	>	if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 &&
1165	>	UNSAFE.compareAndSwapInt(this, scanGuardOffset,
1166	>	g, g |= SG_UNIT)) {
1167	>	ForkJoinWorkerThread[] ws = workers;
1168	>	if (ws != null && idx >= 0 &&
1169	>	idx < ws.length && ws[idx] == w)
1170	>	ws[idx] = null;    // verify
1171	>	nextWorkerIndex = idx;
1172	>	scanGuard = g + SG_UNIT;
1173	>	steps = 1;
1174	>	}
1175	>	if (steps == 1 &&
1176	>	UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1177	>	(((c - AC_UNIT) & AC_MASK) |
1178	>	((c - TC_UNIT) & TC_MASK) |
1179	>	(c & ~(AC_MASK|TC_MASK)))))
1180	>	steps = 2;
1181	>	if (sc != 0 &&
1182	>	UNSAFE.compareAndSwapLong(this, stealCountOffset,
1183	>	s = stealCount, s + sc))
1184	>	sc = 0;
1185	>	} while (steps != 2 || sc != 0);
1186	>	if (!tryTerminate(false)) {
1187	>	if (ex != null)   // possibly replace if died abnormally
1188	>	signalWork();
1189	>	else
1190	>	tryReleaseWaiter();
1191	>	}
1192	>	}
1193	>
1194	>	// Shutdown and termination
1195	>
1196	>	/**
1197	>	* Possibly initiates and/or completes termination.
1198	>	*
1199	>	* @param now if true, unconditionally terminate, else only
1200	>	* if shutdown and empty queue and no active workers
1201	>	* @return true if now terminating or terminated
1202	>	*/
1203	>	private boolean tryTerminate(boolean now) {
1204	>	long c;
1205	>	while (((c = ctl) & STOP_BIT) == 0) {
1206	>	if (!now) {
1207	>	if ((int)(c >> AC_SHIFT) != -parallelism)
1208	>	return false;
1209	>	if (!shutdown || blockedCount != 0 || quiescerCount != 0 ||
1210	>	queueTop - queueBase > 0) {
1211	>	if (ctl == c) // staleness check
1212	>	return false;
1213	>	continue;
1214	>	}
1215		}
1216	<	int s = workerCounts;
1217	<	int tc = totalCountOf(s);
1218	<	int rc = runningCountOf(s);
1219	<	if (rc >= ps || tc >= ps)
1220	<	break;
1221	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
1222	<	ForkJoinWorkerThread w = createWorker(k);
1223	<	if (w != null) {
1224	<	ws[k++] = w;
1225	<	w.start();
1216	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT))
1217	>	startTerminating();
1218	>	}
1219	>	if ((short)(c >>> TC_SHIFT) == -parallelism) {
1220	>	submissionLock.lock();
1221	>	termination.signalAll();
1222	>	submissionLock.unlock();
1223	>	}
1224	>	return true;
1225	>	}
1226	>
1227	>	/**
1228	>	* Runs up to three passes through workers: (0) Setting
1229	>	* termination status for each worker, followed by wakeups up
1230	>	* queued workers (1) helping cancel tasks (2) interrupting
1231	>	* lagging threads (likely in external tasks, but possibly also
1232	>	* blocked in joins).  Each pass repeats previous steps because of
1233	>	* potential lagging thread creation.
1234	>	*/
1235	>	private void startTerminating() {
1236	>	cancelSubmissions();
1237	>	for (int pass = 0; pass < 3; ++pass) {
1238	>	ForkJoinWorkerThread[] ws = workers;
1239	>	if (ws != null) {
1240	>	for (ForkJoinWorkerThread w : ws) {
1241	>	if (w != null) {
1242	>	w.terminate = true;
1243	>	if (pass > 0) {
1244	>	w.cancelTasks();
1245	>	if (pass > 1 && !w.isInterrupted()) {
1246	>	try {
1247	>	w.interrupt();
1248	>	} catch (SecurityException ignore) {
1249	>	}
1250	>	}
1251	>	}
1252	>	}
1253		}
1254	<	else {
1255	<	updateWorkerCount(-1); // back out on failed creation
1256	<	break;
1254	>	terminateWaiters();
1255	>	}
1256	>	}
1257	>	}
1258	>
1259	>	/**
1260	>	* Polls and cancels all submissions. Called only during termination.
1261	>	*/
1262	>	private void cancelSubmissions() {
1263	>	while (queueBase != queueTop) {
1264	>	ForkJoinTask<?> task = pollSubmission();
1265	>	if (task != null) {
1266	>	try {
1267	>	task.cancel(false);
1268	>	} catch (Throwable ignore) {
1269	>	}
1270	>	}
1271	>	}
1272	>	}
1273	>
1274	>	/**
1275	>	* Tries to set the termination status of waiting workers, and
1276	>	* then wake them up (after which they will terminate).
1277	>	*/
1278	>	private void terminateWaiters() {
1279	>	ForkJoinWorkerThread[] ws = workers;
1280	>	if (ws != null) {
1281	>	ForkJoinWorkerThread w; long c; int i, e;
1282	>	int n = ws.length;
1283	>	while ((i = ~(e = (int)(c = ctl)) & SMASK) < n &&
1284	>	(w = ws[i]) != null && w.eventCount == (e & E_MASK)) {
1285	>	if (UNSAFE.compareAndSwapLong(this, ctlOffset, c,
1286	>	(long)(w.nextWait & E_MASK) |
1287	>	((c + AC_UNIT) & AC_MASK) |
1288	>	(c & (TC_MASK|STOP_BIT)))) {
1289	>	w.terminate = true;
1290	>	w.eventCount = e + EC_UNIT;
1291	>	if (w.parked)
1292	>	UNSAFE.unpark(w);
1293		}
1294		}
1295		}
1296		}
1297
1298	+	// misc ForkJoinWorkerThread support
1299	+
1300	+	/**
1301	+	* Increment or decrement quiescerCount. Needed only to prevent
1302	+	* triggering shutdown if a worker is transiently inactive while
1303	+	* checking quiescence.
1304	+	*
1305	+	* @param delta 1 for increment, -1 for decrement
1306	+	*/
1307	+	final void addQuiescerCount(int delta) {
1308	+	int c;
1309	+	do {} while(!UNSAFE.compareAndSwapInt(this, quiescerCountOffset,
1310	+	c = quiescerCount, c + delta));
1311	+	}
1312	+
1313	+	/**
1314	+	* Directly increment or decrement active count without
1315	+	* queuing. This method is used to transiently assert inactivation
1316	+	* while checking quiescence.
1317	+	*
1318	+	* @param delta 1 for increment, -1 for decrement
1319	+	*/
1320	+	final void addActiveCount(int delta) {
1321	+	long d = delta < 0 ? -AC_UNIT : AC_UNIT;
1322	+	long c;
1323	+	do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl,
1324	+	((c + d) & AC_MASK) |
1325	+	(c & ~AC_MASK)));
1326	+	}
1327	+
1328	+	/**
1329	+	* Returns the approximate (non-atomic) number of idle threads per
1330	+	* active thread.
1331	+	*/
1332	+	final int idlePerActive() {
1333	+	// Approximate at powers of two for small values, saturate past 4
1334	+	int p = parallelism;
1335	+	int a = p + (int)(ctl >> AC_SHIFT);
1336	+	return (a > (p >>>= 1) ? 0 :
1337	+	a > (p >>>= 1) ? 1 :
1338	+	a > (p >>>= 1) ? 2 :
1339	+	a > (p >>>= 1) ? 4 :
1340	+	8);
1341	+	}
1342	+
1343	+	// Exported methods
1344	+
1345	+	// Constructors
1346	+
1347		/**
1348	<	* Sets the handler for internal worker threads that terminate due
1349	<	* to unrecoverable errors encountered while executing tasks.
1350	<	* Unless set, the current default or ThreadGroup handler is used
1351	<	* as handler.
1348	>	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1349	>	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1350	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1351	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1352		*
509	–	* @param h the new handler
510	–	* @return the old handler, or null if none
1353		* @throws SecurityException if a security manager exists and
1354		*         the caller is not permitted to modify threads
1355		*         because it does not hold {@link
1356	<	*         java.lang.RuntimePermission}<tt>("modifyThread")</tt>,
1356	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1357		*/
1358	<	public Thread.UncaughtExceptionHandler
1359	<	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
1360	<	checkPermission();
519	<	Thread.UncaughtExceptionHandler old = null;
520	<	final ReentrantLock lock = this.workerLock;
521	<	lock.lock();
522	<	try {
523	<	old = ueh;
524	<	ueh = h;
525	<	ForkJoinWorkerThread[] ws = workers;
526	<	for (int i = 0; i < ws.length; ++i) {
527	<	ForkJoinWorkerThread w = ws[i];
528	<	if (w != null)
529	<	w.setUncaughtExceptionHandler(h);
530	<	}
531	<	} finally {
532	<	lock.unlock();
533	<	}
534	<	return old;
1358	>	public ForkJoinPool() {
1359	>	this(Runtime.getRuntime().availableProcessors(),
1360	>	defaultForkJoinWorkerThreadFactory, null, false);
1361		}
1362
1363		/**
1364	<	* Returns the handler for internal worker threads that terminate
1365	<	* due to unrecoverable errors encountered while executing tasks.
1366	<	* @return the handler, or null if none
1364	>	* Creates a {@code ForkJoinPool} with the indicated parallelism
1365	>	* level, the {@linkplain
1366	>	* #defaultForkJoinWorkerThreadFactory default thread factory},
1367	>	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1368	>	*
1369	>	* @param parallelism the parallelism level
1370	>	* @throws IllegalArgumentException if parallelism less than or
1371	>	*         equal to zero, or greater than implementation limit
1372	>	* @throws SecurityException if a security manager exists and
1373	>	*         the caller is not permitted to modify threads
1374	>	*         because it does not hold {@link
1375	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1376		*/
1377	<	public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1378	<	Thread.UncaughtExceptionHandler h;
544	<	final ReentrantLock lock = this.workerLock;
545	<	lock.lock();
546	<	try {
547	<	h = ueh;
548	<	} finally {
549	<	lock.unlock();
550	<	}
551	<	return h;
1377	>	public ForkJoinPool(int parallelism) {
1378	>	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1379		}
1380
554	–	// Execution methods
555	–
1381		/**
1382	<	* Common code for execute, invoke and submit
1382	>	* Creates a {@code ForkJoinPool} with the given parameters.
1383	>	*
1384	>	* @param parallelism the parallelism level. For default value,
1385	>	* use {@link java.lang.Runtime#availableProcessors}.
1386	>	* @param factory the factory for creating new threads. For default value,
1387	>	* use {@link #defaultForkJoinWorkerThreadFactory}.
1388	>	* @param handler the handler for internal worker threads that
1389	>	* terminate due to unrecoverable errors encountered while executing
1390	>	* tasks. For default value, use {@code null}.
1391	>	* @param asyncMode if true,
1392	>	* establishes local first-in-first-out scheduling mode for forked
1393	>	* tasks that are never joined. This mode may be more appropriate
1394	>	* than default locally stack-based mode in applications in which
1395	>	* worker threads only process event-style asynchronous tasks.
1396	>	* For default value, use {@code false}.
1397	>	* @throws IllegalArgumentException if parallelism less than or
1398	>	*         equal to zero, or greater than implementation limit
1399	>	* @throws NullPointerException if the factory is null
1400	>	* @throws SecurityException if a security manager exists and
1401	>	*         the caller is not permitted to modify threads
1402	>	*         because it does not hold {@link
1403	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1404		*/
1405	<	private <T> void doSubmit(ForkJoinTask<T> task) {
1406	<	if (isShutdown())
1407	<	throw new RejectedExecutionException();
1408	<	submissionQueue.offer(task);
1409	<	signalIdleWorkers(true);
1405	>	public ForkJoinPool(int parallelism,
1406	>	ForkJoinWorkerThreadFactory factory,
1407	>	Thread.UncaughtExceptionHandler handler,
1408	>	boolean asyncMode) {
1409	>	checkPermission();
1410	>	if (factory == null)
1411	>	throw new NullPointerException();
1412	>	if (parallelism <= 0 || parallelism > MAX_ID)
1413	>	throw new IllegalArgumentException();
1414	>	this.parallelism = parallelism;
1415	>	this.factory = factory;
1416	>	this.ueh = handler;
1417	>	this.locallyFifo = asyncMode;
1418	>	long np = (long)(-parallelism); // offset ctl counts
1419	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
1420	>	this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
1421	>	// initialize workers array with room for 2*parallelism if possible
1422	>	int n = parallelism << 1;
1423	>	if (n >= MAX_ID)
1424	>	n = MAX_ID;
1425	>	else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
1426	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
1427	>	}
1428	>	workers = new ForkJoinWorkerThread[n + 1];
1429	>	this.submissionLock = new ReentrantLock();
1430	>	this.termination = submissionLock.newCondition();
1431	>	StringBuilder sb = new StringBuilder("ForkJoinPool-");
1432	>	sb.append(poolNumberGenerator.incrementAndGet());
1433	>	sb.append("-worker-");
1434	>	this.workerNamePrefix = sb.toString();
1435		}
1436
1437	+	// Execution methods
1438	+
1439		/**
1440	<	* Performs the given task; returning its result upon completion
1440	>	* Performs the given task, returning its result upon completion.
1441	>	* If the computation encounters an unchecked Exception or Error,
1442	>	* it is rethrown as the outcome of this invocation.  Rethrown
1443	>	* exceptions behave in the same way as regular exceptions, but,
1444	>	* when possible, contain stack traces (as displayed for example
1445	>	* using {@code ex.printStackTrace()}) of both the current thread
1446	>	* as well as the thread actually encountering the exception;
1447	>	* minimally only the latter.
1448	>	*
1449		* @param task the task
1450		* @return the task's result
1451	<	* @throws NullPointerException if task is null
1452	<	* @throws RejectedExecutionException if pool is shut down
1451	>	* @throws NullPointerException if the task is null
1452	>	* @throws RejectedExecutionException if the task cannot be
1453	>	*         scheduled for execution
1454		*/
1455		public <T> T invoke(ForkJoinTask<T> task) {
1456	<	doSubmit(task);
1457	<	return task.join();
1456	>	Thread t = Thread.currentThread();
1457	>	if (task == null)
1458	>	throw new NullPointerException();
1459	>	if (shutdown)
1460	>	throw new RejectedExecutionException();
1461	>	if ((t instanceof ForkJoinWorkerThread) &&
1462	>	((ForkJoinWorkerThread)t).pool == this)
1463	>	return task.invoke();  // bypass submit if in same pool
1464	>	else {
1465	>	addSubmission(task);
1466	>	return task.join();
1467	>	}
1468	>	}
1469	>
1470	>	/**
1471	>	* Unless terminating, forks task if within an ongoing FJ
1472	>	* computation in the current pool, else submits as external task.
1473	>	*/
1474	>	private <T> void forkOrSubmit(ForkJoinTask<T> task) {
1475	>	ForkJoinWorkerThread w;
1476	>	Thread t = Thread.currentThread();
1477	>	if (shutdown)
1478	>	throw new RejectedExecutionException();
1479	>	if ((t instanceof ForkJoinWorkerThread) &&
1480	>	(w = (ForkJoinWorkerThread)t).pool == this)
1481	>	w.pushTask(task);
1482	>	else
1483	>	addSubmission(task);
1484		}
1485
1486		/**
1487		* Arranges for (asynchronous) execution of the given task.
1488	+	*
1489		* @param task the task
1490	<	* @throws NullPointerException if task is null
1491	<	* @throws RejectedExecutionException if pool is shut down
1490	>	* @throws NullPointerException if the task is null
1491	>	* @throws RejectedExecutionException if the task cannot be
1492	>	*         scheduled for execution
1493		*/
1494	<	public <T> void execute(ForkJoinTask<T> task) {
1495	<	doSubmit(task);
1494	>	public void execute(ForkJoinTask<?> task) {
1495	>	if (task == null)
1496	>	throw new NullPointerException();
1497	>	forkOrSubmit(task);
1498		}
1499
1500		// AbstractExecutorService methods
1501
1502	+	/**
1503	+	* @throws NullPointerException if the task is null
1504	+	* @throws RejectedExecutionException if the task cannot be
1505	+	*         scheduled for execution
1506	+	*/
1507		public void execute(Runnable task) {
1508	<	doSubmit(new AdaptedRunnable<Void>(task, null));
1508	>	if (task == null)
1509	>	throw new NullPointerException();
1510	>	ForkJoinTask<?> job;
1511	>	if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1512	>	job = (ForkJoinTask<?>) task;
1513	>	else
1514	>	job = ForkJoinTask.adapt(task, null);
1515	>	forkOrSubmit(job);
1516		}
1517
1518	<	public <T> ForkJoinTask<T> submit(Callable<T> task) {
1519	<	ForkJoinTask<T> job = new AdaptedCallable<T>(task);
1520	<	doSubmit(job);
1521	<	return job;
1518	>	/**
1519	>	* Submits a ForkJoinTask for execution.
1520	>	*
1521	>	* @param task the task to submit
1522	>	* @return the task
1523	>	* @throws NullPointerException if the task is null
1524	>	* @throws RejectedExecutionException if the task cannot be
1525	>	*         scheduled for execution
1526	>	*/
1527	>	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1528	>	if (task == null)
1529	>	throw new NullPointerException();
1530	>	forkOrSubmit(task);
1531	>	return task;
1532		}
1533
1534	<	public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1535	<	ForkJoinTask<T> job = new AdaptedRunnable<T>(task, result);
1536	<	doSubmit(job);
1534	>	/**
1535	>	* @throws NullPointerException if the task is null
1536	>	* @throws RejectedExecutionException if the task cannot be
1537	>	*         scheduled for execution
1538	>	*/
1539	>	public <T> ForkJoinTask<T> submit(Callable<T> task) {
1540	>	if (task == null)
1541	>	throw new NullPointerException();
1542	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1543	>	forkOrSubmit(job);
1544		return job;
1545		}
1546
1547	<	public ForkJoinTask<?> submit(Runnable task) {
1548	<	ForkJoinTask<Void> job = new AdaptedRunnable<Void>(task, null);
1549	<	doSubmit(job);
1547	>	/**
1548	>	* @throws NullPointerException if the task is null
1549	>	* @throws RejectedExecutionException if the task cannot be
1550	>	*         scheduled for execution
1551	>	*/
1552	>	public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1553	>	if (task == null)
1554	>	throw new NullPointerException();
1555	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1556	>	forkOrSubmit(job);
1557		return job;
1558		}
1559
612	–	protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
613	–	return new AdaptedRunnable(runnable, value);
614	–	}
615	–
616	–	protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
617	–	return new AdaptedCallable(callable);
618	–	}
619	–
1560		/**
1561	<	* Adaptor for Runnables. This implements RunnableFuture
1562	<	* to be compliant with AbstractExecutorService constraints
1561	>	* @throws NullPointerException if the task is null
1562	>	* @throws RejectedExecutionException if the task cannot be
1563	>	*         scheduled for execution
1564		*/
1565	<	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1566	<	implements RunnableFuture<T> {
1567	<	final Runnable runnable;
1568	<	final T resultOnCompletion;
1569	<	T result;
1570	<	AdaptedRunnable(Runnable runnable, T result) {
1571	<	if (runnable == null) throw new NullPointerException();
1572	<	this.runnable = runnable;
1573	<	this.resultOnCompletion = result;
1574	<	}
634	<	public T getRawResult() { return result; }
635	<	public void setRawResult(T v) { result = v; }
636	<	public boolean exec() {
637	<	runnable.run();
638	<	result = resultOnCompletion;
639	<	return true;
640	<	}
641	<	public void run() { invoke(); }
1565	>	public ForkJoinTask<?> submit(Runnable task) {
1566	>	if (task == null)
1567	>	throw new NullPointerException();
1568	>	ForkJoinTask<?> job;
1569	>	if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1570	>	job = (ForkJoinTask<?>) task;
1571	>	else
1572	>	job = ForkJoinTask.adapt(task, null);
1573	>	forkOrSubmit(job);
1574	>	return job;
1575		}
1576
1577		/**
1578	<	* Adaptor for Callables
1578	>	* @throws NullPointerException       {@inheritDoc}
1579	>	* @throws RejectedExecutionException {@inheritDoc}
1580		*/
647	–	static final class AdaptedCallable<T> extends ForkJoinTask<T>
648	–	implements RunnableFuture<T> {
649	–	final Callable<T> callable;
650	–	T result;
651	–	AdaptedCallable(Callable<T> callable) {
652	–	if (callable == null) throw new NullPointerException();
653	–	this.callable = callable;
654	–	}
655	–	public T getRawResult() { return result; }
656	–	public void setRawResult(T v) { result = v; }
657	–	public boolean exec() {
658	–	try {
659	–	result = callable.call();
660	–	return true;
661	–	} catch (Error err) {
662	–	throw err;
663	–	} catch (RuntimeException rex) {
664	–	throw rex;
665	–	} catch (Exception ex) {
666	–	throw new RuntimeException(ex);
667	–	}
668	–	}
669	–	public void run() { invoke(); }
670	–	}
671	–
1581		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
1582	<	ArrayList<ForkJoinTask<T>> ts =
1582	>	ArrayList<ForkJoinTask<T>> forkJoinTasks =
1583		new ArrayList<ForkJoinTask<T>>(tasks.size());
1584	<	for (Callable<T> c : tasks)
1585	<	ts.add(new AdaptedCallable<T>(c));
1586	<	invoke(new InvokeAll<T>(ts));
1587	<	return (List<Future<T>>)(List)ts;
1584	>	for (Callable<T> task : tasks)
1585	>	forkJoinTasks.add(ForkJoinTask.adapt(task));
1586	>	invoke(new InvokeAll<T>(forkJoinTasks));
1587	>
1588	>	@SuppressWarnings({"unchecked", "rawtypes"})
1589	>	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1590	>	return futures;
1591		}
1592
1593		static final class InvokeAll<T> extends RecursiveAction {
1594		final ArrayList<ForkJoinTask<T>> tasks;
1595		InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; }
1596		public void compute() {
1597	<	try { invokeAll(tasks); } catch(Exception ignore) {}
1597	>	try { invokeAll(tasks); }
1598	>	catch (Exception ignore) {}
1599		}
1600	+	private static final long serialVersionUID = -7914297376763021607L;
1601		}
1602
689	–	// Configuration and status settings and queries
690	–
1603		/**
1604	<	* Returns the factory used for constructing new workers
1604	>	* Returns the factory used for constructing new workers.
1605		*
1606		* @return the factory used for constructing new workers
1607		*/
#	Line 698 | Line 1610 | public class ForkJoinPool extends Abstra
1610		}
1611
1612		/**
1613	<	* Sets the target paralleism level of this pool.
1614	<	* @param parallelism the target parallelism
1615	<	* @throws IllegalArgumentException if parallelism less than or
1616	<	* equal to zero or greater than maximum size bounds.
705	<	* @throws SecurityException if a security manager exists and
706	<	*         the caller is not permitted to modify threads
707	<	*         because it does not hold {@link
708	<	*         java.lang.RuntimePermission}<tt>("modifyThread")</tt>,
1613	>	* Returns the handler for internal worker threads that terminate
1614	>	* due to unrecoverable errors encountered while executing tasks.
1615	>	*
1616	>	* @return the handler, or {@code null} if none
1617		*/
1618	<	public void setParallelism(int parallelism) {
1619	<	checkPermission();
712	<	if (parallelism <= 0 || parallelism > maxPoolSize)
713	<	throw new IllegalArgumentException();
714	<	final ReentrantLock lock = this.workerLock;
715	<	lock.lock();
716	<	try {
717	<	if (!isTerminating()) {
718	<	int p = this.parallelism;
719	<	this.parallelism = parallelism;
720	<	if (parallelism > p)
721	<	createAndStartAddedWorkers();
722	<	else
723	<	trimSpares();
724	<	}
725	<	} finally {
726	<	lock.unlock();
727	<	}
728	<	signalIdleWorkers(false);
1618	>	public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1619	>	return ueh;
1620		}
1621
1622		/**
1623	<	* Returns the targeted number of worker threads in this pool.
733	<	* This value does not necessarily reflect transient changes as
734	<	* threads are added, removed, or abruptly terminate.
1623	>	* Returns the targeted parallelism level of this pool.
1624		*
1625	<	* @return the targeted number of worker threads in this pool
1625	>	* @return the targeted parallelism level of this pool
1626		*/
1627		public int getParallelism() {
1628		return parallelism;
#	Line 741 | Line 1630 | public class ForkJoinPool extends Abstra
1630
1631		/**
1632		* Returns the number of worker threads that have started but not
1633	<	* yet terminated.  This result returned by this method may differ
1634	<	* from <tt>getParallelism</tt> when threads are created to
1633	>	* yet terminated.  The result returned by this method may differ
1634	>	* from {@link #getParallelism} when threads are created to
1635		* maintain parallelism when others are cooperatively blocked.
1636		*
1637		* @return the number of worker threads
1638		*/
1639		public int getPoolSize() {
1640	<	return totalCountOf(workerCounts);
752	<	}
753	<
754	<	/**
755	<	* Returns the maximum number of threads allowed to exist in the
756	<	* pool, even if there are insufficient unblocked running threads.
757	<	* @return the maximum
758	<	*/
759	<	public int getMaximumPoolSize() {
760	<	return maxPoolSize;
761	<	}
762	<
763	<	/**
764	<	* Sets the maximum number of threads allowed to exist in the
765	<	* pool, even if there are insufficient unblocked running threads.
766	<	* Setting this value has no effect on current pool size. It
767	<	* controls construction of new threads.
768	<	* @throws IllegalArgumentException if negative or greater then
769	<	* internal implementation limit.
770	<	*/
771	<	public void setMaximumPoolSize(int newMax) {
772	<	if (newMax < 0 || newMax > MAX_THREADS)
773	<	throw new IllegalArgumentException();
774	<	maxPoolSize = newMax;
775	<	}
776	<
777	<
778	<	/**
779	<	* Returns true if this pool dynamically maintains its target
780	<	* parallelism level. If false, new threads are added only to
781	<	* avoid possible starvation.
782	<	* This setting is by default true;
783	<	* @return true if maintains parallelism
784	<	*/
785	<	public boolean getMaintainsParallelism() {
786	<	return maintainsParallelism;
1640	>	return parallelism + (short)(ctl >>> TC_SHIFT);
1641		}
1642
1643		/**
1644	<	* Sets whether this pool dynamically maintains its target
1645	<	* parallelism level. If false, new threads are added only to
1646	<	* avoid possible starvation.
1647	<	* @param enable true to maintains parallelism
1644	>	* Returns {@code true} if this pool uses local first-in-first-out
1645	>	* scheduling mode for forked tasks that are never joined.
1646	>	*
1647	>	* @return {@code true} if this pool uses async mode
1648		*/
1649	<	public void setMaintainsParallelism(boolean enable) {
1650	<	maintainsParallelism = enable;
1649	>	public boolean getAsyncMode() {
1650	>	return locallyFifo;
1651		}
1652
1653		/**
1654	<	* Returns the approximate number of worker threads that are not
1655	<	* blocked waiting to join tasks or for other managed
1656	<	* synchronization.
1654	>	* Returns an estimate of the number of worker threads that are
1655	>	* not blocked waiting to join tasks or for other managed
1656	>	* synchronization. This method may overestimate the
1657	>	* number of running threads.
1658		*
1659		* @return the number of worker threads
1660		*/
1661		public int getRunningThreadCount() {
1662	<	return runningCountOf(workerCounts);
1662	>	int r = parallelism + (int)(ctl >> AC_SHIFT);
1663	>	return r <= 0? 0 : r; // suppress momentarily negative values
1664		}
1665
1666		/**
1667	<	* Returns the approximate number of threads that are currently
1667	>	* Returns an estimate of the number of threads that are currently
1668		* stealing or executing tasks. This method may overestimate the
1669		* number of active threads.
1670	<	* @return the number of active threads.
1670	>	*
1671	>	* @return the number of active threads
1672		*/
1673		public int getActiveThreadCount() {
1674	<	return activeCountOf(runControl);
1674	>	int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount;
1675	>	return r <= 0? 0 : r; // suppress momentarily negative values
1676		}
1677
1678		/**
1679	<	* Returns the approximate number of threads that are currently
1680	<	* idle waiting for tasks. This method may underestimate the
1681	<	* number of idle threads.
1682	<	* @return the number of idle threads.
1683	<	*/
1684	<	final int getIdleThreadCount() {
1685	<	int c = runningCountOf(workerCounts) - activeCountOf(runControl);
1686	<	return (c <= 0)? 0 : c;
1687	<	}
830	<
831	<	/**
832	<	* Returns true if all worker threads are currently idle. An idle
833	<	* worker is one that cannot obtain a task to execute because none
834	<	* are available to steal from other threads, and there are no
835	<	* pending submissions to the pool. This method is conservative:
836	<	* It might not return true immediately upon idleness of all
837	<	* threads, but will eventually become true if threads remain
838	<	* inactive.
839	<	* @return true if all threads are currently idle
1679	>	* Returns {@code true} if all worker threads are currently idle.
1680	>	* An idle worker is one that cannot obtain a task to execute
1681	>	* because none are available to steal from other threads, and
1682	>	* there are no pending submissions to the pool. This method is
1683	>	* conservative; it might not return {@code true} immediately upon
1684	>	* idleness of all threads, but will eventually become true if
1685	>	* threads remain inactive.
1686	>	*
1687	>	* @return {@code true} if all threads are currently idle
1688		*/
1689		public boolean isQuiescent() {
1690	<	return activeCountOf(runControl) == 0;
1690	>	return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0;
1691		}
1692
1693		/**
#	Line 847 | Line 1695 | public class ForkJoinPool extends Abstra
1695		* one thread's work queue by another. The reported value
1696		* underestimates the actual total number of steals when the pool
1697		* is not quiescent. This value may be useful for monitoring and
1698	<	* tuning fork/join programs: In general, steal counts should be
1698	>	* tuning fork/join programs: in general, steal counts should be
1699		* high enough to keep threads busy, but low enough to avoid
1700		* overhead and contention across threads.
1701	<	* @return the number of steals.
1701	>	*
1702	>	* @return the number of steals
1703		*/
1704		public long getStealCount() {
1705	<	return stealCount.get();
857	<	}
858	<
859	<	/**
860	<	* Accumulate steal count from a worker. Call only
861	<	* when worker known to be idle.
862	<	*/
863	<	private void updateStealCount(ForkJoinWorkerThread w) {
864	<	int sc = w.getAndClearStealCount();
865	<	if (sc != 0)
866	<	stealCount.addAndGet(sc);
1705	>	return stealCount;
1706		}
1707
1708		/**
1709	<	* Returns the total number of tasks currently held in queues by
1710	<	* worker threads (but not including tasks submitted to the pool
1711	<	* that have not begun executing). This value is only an
1712	<	* approximation, obtained by iterating across all threads in the
1713	<	* pool. This method may be useful for tuning task granularities.
1714	<	* @return the number of queued tasks.
1709	>	* Returns an estimate of the total number of tasks currently held
1710	>	* in queues by worker threads (but not including tasks submitted
1711	>	* to the pool that have not begun executing). This value is only
1712	>	* an approximation, obtained by iterating across all threads in
1713	>	* the pool. This method may be useful for tuning task
1714	>	* granularities.
1715	>	*
1716	>	* @return the number of queued tasks
1717		*/
1718		public long getQueuedTaskCount() {
1719		long count = 0;
1720	<	ForkJoinWorkerThread[] ws = workers;
1721	<	for (int i = 0; i < ws.length; ++i) {
1722	<	ForkJoinWorkerThread t = ws[i];
1723	<	if (t != null)
1724	<	count += t.getQueueSize();
1720	>	ForkJoinWorkerThread[] ws;
1721	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1722	>	(ws = workers) != null) {
1723	>	for (ForkJoinWorkerThread w : ws)
1724	>	if (w != null)
1725	>	count -= w.queueBase - w.queueTop; // must read base first
1726		}
1727		return count;
1728		}
1729
1730		/**
1731	<	* Returns the approximate number tasks submitted to this pool
1732	<	* that have not yet begun executing. This method takes time
1733	<	* proportional to the number of submissions.
1734	<	* @return the number of queued submissions.
1731	>	* Returns an estimate of the number of tasks submitted to this
1732	>	* pool that have not yet begun executing.  This meThod may take
1733	>	* time proportional to the number of submissions.
1734	>	*
1735	>	* @return the number of queued submissions
1736		*/
1737		public int getQueuedSubmissionCount() {
1738	<	return submissionQueue.size();
1738	>	return -queueBase + queueTop;
1739		}
1740
1741		/**
1742	<	* Returns true if there are any tasks submitted to this pool
1743	<	* that have not yet begun executing.
1744	<	* @return <tt>true</tt> if there are any queued submissions.
1742	>	* Returns {@code true} if there are any tasks submitted to this
1743	>	* pool that have not yet begun executing.
1744	>	*
1745	>	* @return {@code true} if there are any queued submissions
1746		*/
1747		public boolean hasQueuedSubmissions() {
1748	<	return !submissionQueue.isEmpty();
1748	>	return queueBase != queueTop;
1749		}
1750
1751		/**
1752		* Removes and returns the next unexecuted submission if one is
1753		* available.  This method may be useful in extensions to this
1754		* class that re-assign work in systems with multiple pools.
1755	<	* @return the next submission, or null if none
1755	>	*
1756	>	* @return the next submission, or {@code null} if none
1757		*/
1758		protected ForkJoinTask<?> pollSubmission() {
1759	<	return submissionQueue.poll();
1759	>	ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i;
1760	>	while ((b = queueBase) != queueTop &&
1761	>	(q = submissionQueue) != null &&
1762	>	(i = (q.length - 1) & b) >= 0) {
1763	>	long u = (i << ASHIFT) + ABASE;
1764	>	if ((t = q[i]) != null &&
1765	>	queueBase == b &&
1766	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1767	>	queueBase = b + 1;
1768	>	return t;
1769	>	}
1770	>	}
1771	>	return null;
1772	>	}
1773	>
1774	>	/**
1775	>	* Removes all available unexecuted submitted and forked tasks
1776	>	* from scheduling queues and adds them to the given collection,
1777	>	* without altering their execution status. These may include
1778	>	* artificially generated or wrapped tasks. This method is
1779	>	* designed to be invoked only when the pool is known to be
1780	>	* quiescent. Invocations at other times may not remove all
1781	>	* tasks. A failure encountered while attempting to add elements
1782	>	* to collection {@code c} may result in elements being in
1783	>	* neither, either or both collections when the associated
1784	>	* exception is thrown.  The behavior of this operation is
1785	>	* undefined if the specified collection is modified while the
1786	>	* operation is in progress.
1787	>	*
1788	>	* @param c the collection to transfer elements into
1789	>	* @return the number of elements transferred
1790	>	*/
1791	>	protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1792	>	int count = 0;
1793	>	while (queueBase != queueTop) {
1794	>	ForkJoinTask<?> t = pollSubmission();
1795	>	if (t != null) {
1796	>	c.add(t);
1797	>	++count;
1798	>	}
1799	>	}
1800	>	ForkJoinWorkerThread[] ws;
1801	>	if ((short)(ctl >>> TC_SHIFT) > -parallelism &&
1802	>	(ws = workers) != null) {
1803	>	for (ForkJoinWorkerThread w : ws)
1804	>	if (w != null)
1805	>	count += w.drainTasksTo(c);
1806	>	}
1807	>	return count;
1808		}
1809
1810		/**
#	Line 922 | Line 1815 | public class ForkJoinPool extends Abstra
1815		* @return a string identifying this pool, as well as its state
1816		*/
1817		public String toString() {
925	–	int ps = parallelism;
926	–	int wc = workerCounts;
927	–	int rc = runControl;
1818		long st = getStealCount();
1819		long qt = getQueuedTaskCount();
1820		long qs = getQueuedSubmissionCount();
1821	+	int pc = parallelism;
1822	+	long c = ctl;
1823	+	int tc = pc + (short)(c >>> TC_SHIFT);
1824	+	int rc = pc + (int)(c >> AC_SHIFT);
1825	+	if (rc < 0) // ignore transient negative
1826	+	rc = 0;
1827	+	int ac = rc + blockedCount;
1828	+	String level;
1829	+	if ((c & STOP_BIT) != 0)
1830	+	level = (tc == 0)? "Terminated" : "Terminating";
1831	+	else
1832	+	level = shutdown? "Shutting down" : "Running";
1833		return super.toString() +
1834	<	"[" + runStateToString(runStateOf(rc)) +
1835	<	", parallelism = " + ps +
1836	<	", size = " + totalCountOf(wc) +
1837	<	", active = " + activeCountOf(rc) +
1838	<	", running = " + runningCountOf(wc) +
1834	>	"[" + level +
1835	>	", parallelism = " + pc +
1836	>	", size = " + tc +
1837	>	", active = " + ac +
1838	>	", running = " + rc +
1839		", steals = " + st +
1840		", tasks = " + qt +
1841		", submissions = " + qs +
1842		"]";
1843		}
1844
943	–	private static String runStateToString(int rs) {
944	–	switch(rs) {
945	–	case RUNNING: return "Running";
946	–	case SHUTDOWN: return "Shutting down";
947	–	case TERMINATING: return "Terminating";
948	–	case TERMINATED: return "Terminated";
949	–	default: throw new Error("Unknown run state");
950	–	}
951	–	}
952	–
953	–	// lifecycle control
954	–
1845		/**
1846		* Initiates an orderly shutdown in which previously submitted
1847		* tasks are executed, but no new tasks will be accepted.
1848		* Invocation has no additional effect if already shut down.
1849		* Tasks that are in the process of being submitted concurrently
1850		* during the course of this method may or may not be rejected.
1851	+	*
1852		* @throws SecurityException if a security manager exists and
1853		*         the caller is not permitted to modify threads
1854		*         because it does not hold {@link
1855	<	*         java.lang.RuntimePermission}<tt>("modifyThread")</tt>,
1855	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1856		*/
1857		public void shutdown() {
1858		checkPermission();
1859	<	transitionRunStateTo(SHUTDOWN);
1860	<	if (canTerminateOnShutdown(runControl))
970	<	terminateOnShutdown();
1859	>	shutdown = true;
1860	>	tryTerminate(false);
1861		}
1862
1863		/**
1864	<	* Attempts to stop all actively executing tasks, and cancels all
1865	<	* waiting tasks.  Tasks that are in the process of being
1866	<	* submitted or executed concurrently during the course of this
1867	<	* method may or may not be rejected. Unlike some other executors,
1868	<	* this method cancels rather than collects non-executed tasks,
1869	<	* so always returns an empty list.
1864	>	* Attempts to cancel and/or stop all tasks, and reject all
1865	>	* subsequently submitted tasks.  Tasks that are in the process of
1866	>	* being submitted or executed concurrently during the course of
1867	>	* this method may or may not be rejected. This method cancels
1868	>	* both existing and unexecuted tasks, in order to permit
1869	>	* termination in the presence of task dependencies. So the method
1870	>	* always returns an empty list (unlike the case for some other
1871	>	* Executors).
1872	>	*
1873		* @return an empty list
1874		* @throws SecurityException if a security manager exists and
1875		*         the caller is not permitted to modify threads
1876		*         because it does not hold {@link
1877	<	*         java.lang.RuntimePermission}<tt>("modifyThread")</tt>,
1877	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1878		*/
1879		public List<Runnable> shutdownNow() {
1880		checkPermission();
1881	<	terminate();
1881	>	shutdown = true;
1882	>	tryTerminate(true);
1883		return Collections.emptyList();
1884		}
1885
1886		/**
1887	<	* Returns <tt>true</tt> if all tasks have completed following shut down.
1887	>	* Returns {@code true} if all tasks have completed following shut down.
1888		*
1889	<	* @return <tt>true</tt> if all tasks have completed following shut down
1889	>	* @return {@code true} if all tasks have completed following shut down
1890		*/
1891		public boolean isTerminated() {
1892	<	return runStateOf(runControl) == TERMINATED;
1892	>	long c = ctl;
1893	>	return ((c & STOP_BIT) != 0L &&
1894	>	(short)(c >>> TC_SHIFT) == -parallelism);
1895		}
1896
1897		/**
1898	<	* Returns <tt>true</tt> if the process of termination has
1899	<	* commenced but possibly not yet completed.
1898	>	* Returns {@code true} if the process of termination has
1899	>	* commenced but not yet completed.  This method may be useful for
1900	>	* debugging. A return of {@code true} reported a sufficient
1901	>	* period after shutdown may indicate that submitted tasks have
1902	>	* ignored or suppressed interruption, or are waiting for IO,
1903	>	* causing this executor not to properly terminate. (See the
1904	>	* advisory notes for class {@link ForkJoinTask} stating that
1905	>	* tasks should not normally entail blocking operations.  But if
1906	>	* they do, they must abort them on interrupt.)
1907		*
1908	<	* @return <tt>true</tt> if terminating
1908	>	* @return {@code true} if terminating but not yet terminated
1909		*/
1910		public boolean isTerminating() {
1911	<	return runStateOf(runControl) >= TERMINATING;
1911	>	long c = ctl;
1912	>	return ((c & STOP_BIT) != 0L &&
1913	>	(short)(c >>> TC_SHIFT) != -parallelism);
1914	>	}
1915	>
1916	>	/**
1917	>	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1918	>	*/
1919	>	final boolean isAtLeastTerminating() {
1920	>	return (ctl & STOP_BIT) != 0L;
1921		}
1922
1923		/**
1924	<	* Returns <tt>true</tt> if this pool has been shut down.
1924	>	* Returns {@code true} if this pool has been shut down.
1925		*
1926	<	* @return <tt>true</tt> if this pool has been shut down
1926	>	* @return {@code true} if this pool has been shut down
1927		*/
1928		public boolean isShutdown() {
1929	<	return runStateOf(runControl) >= SHUTDOWN;
1929	>	return shutdown;
1930		}
1931
1932		/**
#	Line 1024 | Line 1936 | public class ForkJoinPool extends Abstra
1936		*
1937		* @param timeout the maximum time to wait
1938		* @param unit the time unit of the timeout argument
1939	<	* @return <tt>true</tt> if this executor terminated and
1940	<	*         <tt>false</tt> if the timeout elapsed before termination
1939	>	* @return {@code true} if this executor terminated and
1940	>	*         {@code false} if the timeout elapsed before termination
1941		* @throws InterruptedException if interrupted while waiting
1942		*/
1943		public boolean awaitTermination(long timeout, TimeUnit unit)
1944		throws InterruptedException {
1945		long nanos = unit.toNanos(timeout);
1946	<	final ReentrantLock lock = this.workerLock;
1946	>	final ReentrantLock lock = this.submissionLock;
1947		lock.lock();
1948		try {
1949		for (;;) {
#	Line 1046 | Line 1958 | public class ForkJoinPool extends Abstra
1958		}
1959		}
1960
1049	–	// Shutdown and termination support
1050	–
1051	–	/**
1052	–	* Callback from terminating worker. Null out the corresponding
1053	–	* workers slot, and if terminating, try to terminate, else try to
1054	–	* shrink workers array.
1055	–	* @param w the worker
1056	–	*/
1057	–	final void workerTerminated(ForkJoinWorkerThread w) {
1058	–	updateStealCount(w);
1059	–	updateWorkerCount(-1);
1060	–	final ReentrantLock lock = this.workerLock;
1061	–	lock.lock();
1062	–	try {
1063	–	ForkJoinWorkerThread[] ws = workers;
1064	–	int idx = w.poolIndex;
1065	–	if (idx >= 0 && idx < ws.length && ws[idx] == w)
1066	–	ws[idx] = null;
1067	–	if (totalCountOf(workerCounts) == 0) {
1068	–	terminate(); // no-op if already terminating
1069	–	transitionRunStateTo(TERMINATED);
1070	–	termination.signalAll();
1071	–	}
1072	–	else if (!isTerminating()) {
1073	–	tryShrinkWorkerArray();
1074	–	tryResumeSpare(true); // allow replacement
1075	–	}
1076	–	} finally {
1077	–	lock.unlock();
1078	–	}
1079	–	signalIdleWorkers(false);
1080	–	}
1081	–
1082	–	/**
1083	–	* Initiate termination.
1084	–	*/
1085	–	private void terminate() {
1086	–	if (transitionRunStateTo(TERMINATING)) {
1087	–	stopAllWorkers();
1088	–	resumeAllSpares();
1089	–	signalIdleWorkers(true);
1090	–	cancelQueuedSubmissions();
1091	–	cancelQueuedWorkerTasks();
1092	–	interruptUnterminatedWorkers();
1093	–	signalIdleWorkers(true); // resignal after interrupt
1094	–	}
1095	–	}
1096	–
1097	–	/**
1098	–	* Possibly terminate when on shutdown state
1099	–	*/
1100	–	private void terminateOnShutdown() {
1101	–	if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
1102	–	terminate();
1103	–	}
1104	–
1105	–	/**
1106	–	* Clear out and cancel submissions
1107	–	*/
1108	–	private void cancelQueuedSubmissions() {
1109	–	ForkJoinTask<?> task;
1110	–	while ((task = pollSubmission()) != null)
1111	–	task.cancel(false);
1112	–	}
1113	–
1114	–	/**
1115	–	* Clean out worker queues.
1116	–	*/
1117	–	private void cancelQueuedWorkerTasks() {
1118	–	final ReentrantLock lock = this.workerLock;
1119	–	lock.lock();
1120	–	try {
1121	–	ForkJoinWorkerThread[] ws = workers;
1122	–	for (int i = 0; i < ws.length; ++i) {
1123	–	ForkJoinWorkerThread t = ws[i];
1124	–	if (t != null)
1125	–	t.cancelTasks();
1126	–	}
1127	–	} finally {
1128	–	lock.unlock();
1129	–	}
1130	–	}
1131	–
1132	–	/**
1133	–	* Set each worker's status to terminating. Requires lock to avoid
1134	–	* conflicts with add/remove
1135	–	*/
1136	–	private void stopAllWorkers() {
1137	–	final ReentrantLock lock = this.workerLock;
1138	–	lock.lock();
1139	–	try {
1140	–	ForkJoinWorkerThread[] ws = workers;
1141	–	for (int i = 0; i < ws.length; ++i) {
1142	–	ForkJoinWorkerThread t = ws[i];
1143	–	if (t != null)
1144	–	t.shutdownNow();
1145	–	}
1146	–	} finally {
1147	–	lock.unlock();
1148	–	}
1149	–	}
1150	–
1151	–	/**
1152	–	* Interrupt all unterminated workers.  This is not required for
1153	–	* sake of internal control, but may help unstick user code during
1154	–	* shutdown.
1155	–	*/
1156	–	private void interruptUnterminatedWorkers() {
1157	–	final ReentrantLock lock = this.workerLock;
1158	–	lock.lock();
1159	–	try {
1160	–	ForkJoinWorkerThread[] ws = workers;
1161	–	for (int i = 0; i < ws.length; ++i) {
1162	–	ForkJoinWorkerThread t = ws[i];
1163	–	if (t != null && !t.isTerminated()) {
1164	–	try {
1165	–	t.interrupt();
1166	–	} catch (SecurityException ignore) {
1167	–	}
1168	–	}
1169	–	}
1170	–	} finally {
1171	–	lock.unlock();
1172	–	}
1173	–	}
1174	–
1175	–
1176	–	/*
1177	–	* Nodes for event barrier to manage idle threads.
1178	–	*
1179	–	* The event barrier has an event count and a wait queue (actually
1180	–	* a Treiber stack).  Workers are enabled to look for work when
1181	–	* the eventCount is incremented. If they fail to find some,
1182	–	* they may wait for next count. Synchronization events occur only
1183	–	* in enough contexts to maintain overall liveness:
1184	–	*
1185	–	*   - Submission of a new task to the pool
1186	–	*   - Creation or termination of a worker
1187	–	*   - pool termination
1188	–	*   - A worker pushing a task on an empty queue
1189	–	*
1190	–	* The last case (pushing a task) occurs often enough, and is
1191	–	* heavy enough compared to simple stack pushes to require some
1192	–	* special handling: Method signalNonEmptyWorkerQueue returns
1193	–	* without advancing count if the queue appears to be empty.  This
1194	–	* would ordinarily result in races causing some queued waiters
1195	–	* not to be woken up. To avoid this, a worker in sync
1196	–	* rescans for tasks after being enqueued if it was the first to
1197	–	* enqueue, and aborts the wait if finding one, also helping to
1198	–	* signal others. This works well because the worker has nothing
1199	–	* better to do anyway, and so might as well help alleviate the
1200	–	* overhead and contention on the threads actually doing work.
1201	–	*
1202	–	* Queue nodes are basic Treiber stack nodes, also used for spare
1203	–	* stack.
1204	–	*/
1205	–	static final class WaitQueueNode {
1206	–	WaitQueueNode next; // only written before enqueued
1207	–	volatile ForkJoinWorkerThread thread; // nulled to cancel wait
1208	–	final long count; // unused for spare stack
1209	–	WaitQueueNode(ForkJoinWorkerThread w, long c) {
1210	–	count = c;
1211	–	thread = w;
1212	–	}
1213	–	final boolean signal() {
1214	–	ForkJoinWorkerThread t = thread;
1215	–	thread = null;
1216	–	if (t != null) {
1217	–	LockSupport.unpark(t);
1218	–	return true;
1219	–	}
1220	–	return false;
1221	–	}
1222	–	}
1223	–
1224	–	/**
1225	–	* Release at least one thread waiting for event count to advance,
1226	–	* if one exists. If initial attempt fails, release all threads.
1227	–	* @param all if false, at first try to only release one thread
1228	–	* @return current event
1229	–	*/
1230	–	private long releaseIdleWorkers(boolean all) {
1231	–	long c;
1232	–	for (;;) {
1233	–	WaitQueueNode q = barrierStack;
1234	–	c = eventCount;
1235	–	long qc;
1236	–	if (q == null || (qc = q.count) >= c)
1237	–	break;
1238	–	if (!all) {
1239	–	if (casBarrierStack(q, q.next) && q.signal())
1240	–	break;
1241	–	all = true;
1242	–	}
1243	–	else if (casBarrierStack(q, null)) {
1244	–	do {
1245	–	q.signal();
1246	–	} while ((q = q.next) != null);
1247	–	break;
1248	–	}
1249	–	}
1250	–	return c;
1251	–	}
1252	–
1253	–	/**
1254	–	* Returns current barrier event count
1255	–	* @return current barrier event count
1256	–	*/
1257	–	final long getEventCount() {
1258	–	long ec = eventCount;
1259	–	releaseIdleWorkers(true); // release to ensure accurate result
1260	–	return ec;
1261	–	}
1262	–
1263	–	/**
1264	–	* Increment event count and release at least one waiting thread,
1265	–	* if one exists (released threads will in turn wake up others).
1266	–	* @param all if true, try to wake up all
1267	–	*/
1268	–	final void signalIdleWorkers(boolean all) {
1269	–	long c;
1270	–	do;while (!casEventCount(c = eventCount, c+1));
1271	–	releaseIdleWorkers(all);
1272	–	}
1273	–
1274	–	/**
1275	–	* Wake up threads waiting to steal a task. Because method
1276	–	* sync rechecks availability, it is OK to only proceed if
1277	–	* queue appears to be non-empty.
1278	–	*/
1279	–	final void signalNonEmptyWorkerQueue() {
1280	–	// If CAS fails another signaller must have succeeded
1281	–	long c;
1282	–	if (barrierStack != null && casEventCount(c = eventCount, c+1))
1283	–	releaseIdleWorkers(false);
1284	–	}
1285	–
1286	–	/**
1287	–	* Waits until event count advances from count, or some thread is
1288	–	* waiting on a previous count, or there is stealable work
1289	–	* available. Help wake up others on release.
1290	–	* @param w the calling worker thread
1291	–	* @param prev previous value returned by sync (or 0)
1292	–	* @return current event count
1293	–	*/
1294	–	final long sync(ForkJoinWorkerThread w, long prev) {
1295	–	updateStealCount(w);
1296	–
1297	–	while (!w.isShutdown() && !isTerminating() &&
1298	–	(parallelism >= runningCountOf(workerCounts) ||
1299	–	!suspendIfSpare(w))) { // prefer suspend to waiting here
1300	–	WaitQueueNode node = null;
1301	–	boolean queued = false;
1302	–	for (;;) {
1303	–	if (!queued) {
1304	–	if (eventCount != prev)
1305	–	break;
1306	–	WaitQueueNode h = barrierStack;
1307	–	if (h != null && h.count != prev)
1308	–	break; // release below and maybe retry
1309	–	if (node == null)
1310	–	node = new WaitQueueNode(w, prev);
1311	–	queued = casBarrierStack(node.next = h, node);
1312	–	}
1313	–	else if (Thread.interrupted() ||
1314	–	node.thread == null ||
1315	–	(node.next == null && w.prescan()) ||
1316	–	eventCount != prev) {
1317	–	node.thread = null;
1318	–	if (eventCount == prev) // help trigger
1319	–	casEventCount(prev, prev+1);
1320	–	break;
1321	–	}
1322	–	else
1323	–	LockSupport.park(this);
1324	–	}
1325	–	long ec = eventCount;
1326	–	if (releaseIdleWorkers(false) != prev)
1327	–	return ec;
1328	–	}
1329	–	return prev; // return old count if aborted
1330	–	}
1331	–
1332	–	//  Parallelism maintenance
1333	–
1334	–	/**
1335	–	* Decrement running count; if too low, add spare.
1336	–	*
1337	–	* Conceptually, all we need to do here is add or resume a
1338	–	* spare thread when one is about to block (and remove or
1339	–	* suspend it later when unblocked -- see suspendIfSpare).
1340	–	* However, implementing this idea requires coping with
1341	–	* several problems: We have imperfect information about the
1342	–	* states of threads. Some count updates can and usually do
1343	–	* lag run state changes, despite arrangements to keep them
1344	–	* accurate (for example, when possible, updating counts
1345	–	* before signalling or resuming), especially when running on
1346	–	* dynamic JVMs that don't optimize the infrequent paths that
1347	–	* update counts. Generating too many threads can make these
1348	–	* problems become worse, because excess threads are more
1349	–	* likely to be context-switched with others, slowing them all
1350	–	* down, especially if there is no work available, so all are
1351	–	* busy scanning or idling.  Also, excess spare threads can
1352	–	* only be suspended or removed when they are idle, not
1353	–	* immediately when they aren't needed. So adding threads will
1354	–	* raise parallelism level for longer than necessary.  Also,
1355	–	* FJ applications often enounter highly transient peaks when
1356	–	* many threads are blocked joining, but for less time than it
1357	–	* takes to create or resume spares.
1358	–	*
1359	–	* @param joinMe if non-null, return early if done
1360	–	* @param maintainParallelism if true, try to stay within
1361	–	* target counts, else create only to avoid starvation
1362	–	* @return true if joinMe known to be done
1363	–	*/
1364	–	final boolean preJoin(ForkJoinTask<?> joinMe, boolean maintainParallelism) {
1365	–	maintainParallelism &= maintainsParallelism; // overrride
1366	–	boolean dec = false;  // true when running count decremented
1367	–	while (spareStack == null || !tryResumeSpare(dec)) {
1368	–	int counts = workerCounts;
1369	–	if (dec || (dec = casWorkerCounts(counts, --counts))) { // CAS cheat
1370	–	if (!needSpare(counts, maintainParallelism))
1371	–	break;
1372	–	if (joinMe.status < 0)
1373	–	return true;
1374	–	if (tryAddSpare(counts))
1375	–	break;
1376	–	}
1377	–	}
1378	–	return false;
1379	–	}
1380	–
1381	–	/**
1382	–	* Same idea as preJoin
1383	–	*/
1384	–	final boolean preBlock(ManagedBlocker blocker, boolean maintainParallelism){
1385	–	maintainParallelism &= maintainsParallelism;
1386	–	boolean dec = false;
1387	–	while (spareStack == null || !tryResumeSpare(dec)) {
1388	–	int counts = workerCounts;
1389	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1390	–	if (!needSpare(counts, maintainParallelism))
1391	–	break;
1392	–	if (blocker.isReleasable())
1393	–	return true;
1394	–	if (tryAddSpare(counts))
1395	–	break;
1396	–	}
1397	–	}
1398	–	return false;
1399	–	}
1400	–
1401	–	/**
1402	–	* Returns true if a spare thread appears to be needed.  If
1403	–	* maintaining parallelism, returns true when the deficit in
1404	–	* running threads is more than the surplus of total threads, and
1405	–	* there is apparently some work to do.  This self-limiting rule
1406	–	* means that the more threads that have already been added, the
1407	–	* less parallelism we will tolerate before adding another.
1408	–	* @param counts current worker counts
1409	–	* @param maintainParallelism try to maintain parallelism
1410	–	*/
1411	–	private boolean needSpare(int counts, boolean maintainParallelism) {
1412	–	int ps = parallelism;
1413	–	int rc = runningCountOf(counts);
1414	–	int tc = totalCountOf(counts);
1415	–	int runningDeficit = ps - rc;
1416	–	int totalSurplus = tc - ps;
1417	–	return (tc < maxPoolSize &&
1418	–	(rc == 0 || totalSurplus < 0 ||
1419	–	(maintainParallelism &&
1420	–	runningDeficit > totalSurplus && mayHaveQueuedWork())));
1421	–	}
1422	–
1423	–	/**
1424	–	* Returns true if at least one worker queue appears to be
1425	–	* nonempty. This is expensive but not often called. It is not
1426	–	* critical that this be accurate, but if not, more or fewer
1427	–	* running threads than desired might be maintained.
1428	–	*/
1429	–	private boolean mayHaveQueuedWork() {
1430	–	ForkJoinWorkerThread[] ws = workers;
1431	–	int len = ws.length;
1432	–	ForkJoinWorkerThread v;
1433	–	for (int i = 0; i < len; ++i) {
1434	–	if ((v = ws[i]) != null && v.getRawQueueSize() > 0) {
1435	–	releaseIdleWorkers(false); // help wake up stragglers
1436	–	return true;
1437	–	}
1438	–	}
1439	–	return false;
1440	–	}
1441	–
1442	–	/**
1443	–	* Add a spare worker if lock available and no more than the
1444	–	* expected numbers of threads exist
1445	–	* @return true if successful
1446	–	*/
1447	–	private boolean tryAddSpare(int expectedCounts) {
1448	–	final ReentrantLock lock = this.workerLock;
1449	–	int expectedRunning = runningCountOf(expectedCounts);
1450	–	int expectedTotal = totalCountOf(expectedCounts);
1451	–	boolean success = false;
1452	–	boolean locked = false;
1453	–	// confirm counts while locking; CAS after obtaining lock
1454	–	try {
1455	–	for (;;) {
1456	–	int s = workerCounts;
1457	–	int tc = totalCountOf(s);
1458	–	int rc = runningCountOf(s);
1459	–	if (rc > expectedRunning || tc > expectedTotal)
1460	–	break;
1461	–	if (!locked && !(locked = lock.tryLock()))
1462	–	break;
1463	–	if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
1464	–	createAndStartSpare(tc);
1465	–	success = true;
1466	–	break;
1467	–	}
1468	–	}
1469	–	} finally {
1470	–	if (locked)
1471	–	lock.unlock();
1472	–	}
1473	–	return success;
1474	–	}
1475	–
1476	–	/**
1477	–	* Add the kth spare worker. On entry, pool coounts are already
1478	–	* adjusted to reflect addition.
1479	–	*/
1480	–	private void createAndStartSpare(int k) {
1481	–	ForkJoinWorkerThread w = null;
1482	–	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
1483	–	int len = ws.length;
1484	–	// Probably, we can place at slot k. If not, find empty slot
1485	–	if (k < len && ws[k] != null) {
1486	–	for (k = 0; k < len && ws[k] != null; ++k)
1487	–	;
1488	–	}
1489	–	if (k < len && (w = createWorker(k)) != null) {
1490	–	ws[k] = w;
1491	–	w.start();
1492	–	}
1493	–	else
1494	–	updateWorkerCount(-1); // adjust on failure
1495	–	signalIdleWorkers(false);
1496	–	}
1497	–
1498	–	/**
1499	–	* Suspend calling thread w if there are excess threads.  Called
1500	–	* only from sync.  Spares are enqueued in a Treiber stack
1501	–	* using the same WaitQueueNodes as barriers.  They are resumed
1502	–	* mainly in preJoin, but are also woken on pool events that
1503	–	* require all threads to check run state.
1504	–	* @param w the caller
1505	–	*/
1506	–	private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1507	–	WaitQueueNode node = null;
1508	–	int s;
1509	–	while (parallelism < runningCountOf(s = workerCounts)) {
1510	–	if (node == null)
1511	–	node = new WaitQueueNode(w, 0);
1512	–	if (casWorkerCounts(s, s-1)) { // representation-dependent
1513	–	// push onto stack
1514	–	do;while (!casSpareStack(node.next = spareStack, node));
1515	–
1516	–	// block until released by resumeSpare
1517	–	while (node.thread != null) {
1518	–	if (!Thread.interrupted())
1519	–	LockSupport.park(this);
1520	–	}
1521	–	w.activate(); // help warm up
1522	–	return true;
1523	–	}
1524	–	}
1525	–	return false;
1526	–	}
1527	–
1528	–	/**
1529	–	* Try to pop and resume a spare thread.
1530	–	* @param updateCount if true, increment running count on success
1531	–	* @return true if successful
1532	–	*/
1533	–	private boolean tryResumeSpare(boolean updateCount) {
1534	–	WaitQueueNode q;
1535	–	while ((q = spareStack) != null) {
1536	–	if (casSpareStack(q, q.next)) {
1537	–	if (updateCount)
1538	–	updateRunningCount(1);
1539	–	q.signal();
1540	–	return true;
1541	–	}
1542	–	}
1543	–	return false;
1544	–	}
1545	–
1546	–	/**
1547	–	* Pop and resume all spare threads. Same idea as
1548	–	* releaseIdleWorkers.
1549	–	* @return true if any spares released
1550	–	*/
1551	–	private boolean resumeAllSpares() {
1552	–	WaitQueueNode q;
1553	–	while ( (q = spareStack) != null) {
1554	–	if (casSpareStack(q, null)) {
1555	–	do {
1556	–	updateRunningCount(1);
1557	–	q.signal();
1558	–	} while ((q = q.next) != null);
1559	–	return true;
1560	–	}
1561	–	}
1562	–	return false;
1563	–	}
1564	–
1565	–	/**
1566	–	* Pop and shutdown excessive spare threads. Call only while
1567	–	* holding lock. This is not guaranteed to eliminate all excess
1568	–	* threads, only those suspended as spares, which are the ones
1569	–	* unlikely to be needed in the future.
1570	–	*/
1571	–	private void trimSpares() {
1572	–	int surplus = totalCountOf(workerCounts) - parallelism;
1573	–	WaitQueueNode q;
1574	–	while (surplus > 0 && (q = spareStack) != null) {
1575	–	if (casSpareStack(q, null)) {
1576	–	do {
1577	–	updateRunningCount(1);
1578	–	ForkJoinWorkerThread w = q.thread;
1579	–	if (w != null && surplus > 0 &&
1580	–	runningCountOf(workerCounts) > 0 && w.shutdown())
1581	–	--surplus;
1582	–	q.signal();
1583	–	} while ((q = q.next) != null);
1584	–	}
1585	–	}
1586	–	}
1587	–
1588	–	/**
1589	–	* Returns approximate number of spares, just for diagnostics.
1590	–	*/
1591	–	private int countSpares() {
1592	–	int sum = 0;
1593	–	for (WaitQueueNode q = spareStack; q != null; q = q.next)
1594	–	++sum;
1595	–	return sum;
1596	–	}
1597	–
1961		/**
1962		* Interface for extending managed parallelism for tasks running
1963	<	* in ForkJoinPools. A ManagedBlocker provides two methods.
1964	<	* Method <tt>isReleasable</tt> must return true if blocking is not
1965	<	* necessary. Method <tt>block</tt> blocks the current thread
1966	<	* if necessary (perhaps internally invoking isReleasable before
1967	<	* actually blocking.).
1963	>	* in {@link ForkJoinPool}s.
1964	>	*
1965	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1966	>	* {@code isReleasable} must return {@code true} if blocking is
1967	>	* not necessary. Method {@code block} blocks the current thread
1968	>	* if necessary (perhaps internally invoking {@code isReleasable}
1969	>	* before actually blocking). The unusual methods in this API
1970	>	* accommodate synchronizers that may, but don't usually, block
1971	>	* for long periods. Similarly, they allow more efficient internal
1972	>	* handling of cases in which additional workers may be, but
1973	>	* usually are not, needed to ensure sufficient parallelism.
1974	>	* Toward this end, implementations of method {@code isReleasable}
1975	>	* must be amenable to repeated invocation.
1976	>	*
1977		* <p>For example, here is a ManagedBlocker based on a
1978		* ReentrantLock:
1979	<	* <pre>
1980	<	*   class ManagedLocker implements ManagedBlocker {
1981	<	*     final ReentrantLock lock;
1982	<	*     boolean hasLock = false;
1983	<	*     ManagedLocker(ReentrantLock lock) { this.lock = lock; }
1984	<	*     public boolean block() {
1985	<	*        if (!hasLock)
1986	<	*           lock.lock();
1987	<	*        return true;
1988	<	*     }
1989	<	*     public boolean isReleasable() {
1990	<	*        return hasLock || (hasLock = lock.tryLock());
1991	<	*     }
1979	>	*  <pre> {@code
1980	>	* class ManagedLocker implements ManagedBlocker {
1981	>	*   final ReentrantLock lock;
1982	>	*   boolean hasLock = false;
1983	>	*   ManagedLocker(ReentrantLock lock) { this.lock = lock; }
1984	>	*   public boolean block() {
1985	>	*     if (!hasLock)
1986	>	*       lock.lock();
1987	>	*     return true;
1988	>	*   }
1989	>	*   public boolean isReleasable() {
1990	>	*     return hasLock || (hasLock = lock.tryLock());
1991	>	*   }
1992	>	* }}</pre>
1993	>	*
1994	>	* <p>Here is a class that possibly blocks waiting for an
1995	>	* item on a given queue:
1996	>	*  <pre> {@code
1997	>	* class QueueTaker<E> implements ManagedBlocker {
1998	>	*   final BlockingQueue<E> queue;
1999	>	*   volatile E item = null;
2000	>	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
2001	>	*   public boolean block() throws InterruptedException {
2002	>	*     if (item == null)
2003	>	*       item = queue.take();
2004	>	*     return true;
2005		*   }
2006	<	* </pre>
2006	>	*   public boolean isReleasable() {
2007	>	*     return item != null || (item = queue.poll()) != null;
2008	>	*   }
2009	>	*   public E getItem() { // call after pool.managedBlock completes
2010	>	*     return item;
2011	>	*   }
2012	>	* }}</pre>
2013		*/
2014		public static interface ManagedBlocker {
2015		/**
2016		* Possibly blocks the current thread, for example waiting for
2017		* a lock or condition.
2018	<	* @return true if no additional blocking is necessary (i.e.,
2019	<	* if isReleasable would return true).
2018	>	*
2019	>	* @return {@code true} if no additional blocking is necessary
2020	>	* (i.e., if isReleasable would return true)
2021		* @throws InterruptedException if interrupted while waiting
2022	<	* (the method is not required to do so, but is allowe to).
2022	>	* (the method is not required to do so, but is allowed to)
2023		*/
2024		boolean block() throws InterruptedException;
2025
2026		/**
2027	<	* Returns true if blocking is unnecessary.
2027	>	* Returns {@code true} if blocking is unnecessary.
2028		*/
2029		boolean isReleasable();
2030		}
2031
2032		/**
2033		* Blocks in accord with the given blocker.  If the current thread
2034	<	* is a ForkJoinWorkerThread, this method possibly arranges for a
2035	<	* spare thread to be activated if necessary to ensure parallelism
2036	<	* while the current thread is blocked.  If
2037	<	* <tt>maintainParallelism</tt> is true and the pool supports it
2038	<	* (see <tt>getMaintainsParallelism</tt>), this method attempts to
2039	<	* maintain the pool's nominal parallelism. Otherwise if activates
2040	<	* a thread only if necessary to avoid complete starvation. This
2041	<	* option may be preferable when blockages use timeouts, or are
2042	<	* almost always brief.
2043	<	*
2044	<	* <p> If the caller is not a ForkJoinTask, this method is behaviorally
2045	<	* equivalent to
2046	<	* <pre>
2047	<	*   while (!blocker.isReleasable())
1656	<	*      if (blocker.block())
1657	<	*         return;
1658	<	* </pre>
1659	<	* If the caller is a ForkJoinTask, then the pool may first
1660	<	* be expanded to ensure parallelism, and later adjusted.
2034	>	* is a {@link ForkJoinWorkerThread}, this method possibly
2035	>	* arranges for a spare thread to be activated if necessary to
2036	>	* ensure sufficient parallelism while the current thread is blocked.
2037	>	*
2038	>	* <p>If the caller is not a {@link ForkJoinTask}, this method is
2039	>	* behaviorally equivalent to
2040	>	*  <pre> {@code
2041	>	* while (!blocker.isReleasable())
2042	>	*   if (blocker.block())
2043	>	*     return;
2044	>	* }</pre>
2045	>	*
2046	>	* If the caller is a {@code ForkJoinTask}, then the pool may
2047	>	* first be expanded to ensure parallelism, and later adjusted.
2048		*
2049		* @param blocker the blocker
2050	<	* @param maintainParallelism if true and supported by this pool,
1664	<	* attempt to maintain the pool's nominal parallelism; otherwise
1665	<	* activate a thread only if necessary to avoid complete
1666	<	* starvation.
1667	<	* @throws InterruptedException if blocker.block did so.
2050	>	* @throws InterruptedException if blocker.block did so
2051		*/
2052	<	public static void managedBlock(ManagedBlocker blocker,
1670	<	boolean maintainParallelism)
2052	>	public static void managedBlock(ManagedBlocker blocker)
2053		throws InterruptedException {
2054		Thread t = Thread.currentThread();
2055	<	ForkJoinPool pool = (t instanceof ForkJoinWorkerThread?
2056	<	((ForkJoinWorkerThread)t).pool : null);
2057	<	if (!blocker.isReleasable()) {
2058	<	try {
2059	<	if (pool == null ||
2060	<	!pool.preBlock(blocker, maintainParallelism))
1679	<	awaitBlocker(blocker);
1680	<	} finally {
1681	<	if (pool != null)
1682	<	pool.updateRunningCount(1);
1683	<	}
2055	>	if (t instanceof ForkJoinWorkerThread) {
2056	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
2057	>	w.pool.awaitBlocker(blocker);
2058	>	}
2059	>	else {
2060	>	do {} while (!blocker.isReleasable() && !blocker.block());
2061		}
2062		}
2063
2064	<	private static void awaitBlocker(ManagedBlocker blocker)
2065	<	throws InterruptedException {
2066	<	do;while (!blocker.isReleasable() && !blocker.block());
1690	<	}
2064	>	// AbstractExecutorService overrides.  These rely on undocumented
2065	>	// fact that ForkJoinTask.adapt returns ForkJoinTasks that also
2066	>	// implement RunnableFuture.
2067
2068	+	protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
2069	+	return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
2070	+	}
2071
2072	<	// Temporary Unsafe mechanics for preliminary release
2072	>	protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
2073	>	return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
2074	>	}
2075
2076	<	static final Unsafe _unsafe;
2077	<	static final long eventCountOffset;
2078	<	static final long workerCountsOffset;
2079	<	static final long runControlOffset;
2080	<	static final long barrierStackOffset;
2081	<	static final long spareStackOffset;
2076	>	// Unsafe mechanics
2077	>	private static final sun.misc.Unsafe UNSAFE;
2078	>	private static final long ctlOffset;
2079	>	private static final long stealCountOffset;
2080	>	private static final long blockedCountOffset;
2081	>	private static final long quiescerCountOffset;
2082	>	private static final long scanGuardOffset;
2083	>	private static final long nextWorkerNumberOffset;
2084	>	private static final long ABASE;
2085	>	private static final int ASHIFT;
2086
2087		static {
2088	+	poolNumberGenerator = new AtomicInteger();
2089	+	workerSeedGenerator = new Random();
2090	+	modifyThreadPermission = new RuntimePermission("modifyThread");
2091	+	defaultForkJoinWorkerThreadFactory =
2092	+	new DefaultForkJoinWorkerThreadFactory();
2093	+	int s;
2094		try {
2095	<	if (ForkJoinPool.class.getClassLoader() != null) {
2096	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
2097	<	f.setAccessible(true);
2098	<	_unsafe = (Unsafe)f.get(null);
2099	<	}
2100	<	else
2101	<	_unsafe = Unsafe.getUnsafe();
2102	<	eventCountOffset = _unsafe.objectFieldOffset
2103	<	(ForkJoinPool.class.getDeclaredField("eventCount"));
2104	<	workerCountsOffset = _unsafe.objectFieldOffset
2105	<	(ForkJoinPool.class.getDeclaredField("workerCounts"));
2106	<	runControlOffset = _unsafe.objectFieldOffset
2107	<	(ForkJoinPool.class.getDeclaredField("runControl"));
2108	<	barrierStackOffset = _unsafe.objectFieldOffset
2109	<	(ForkJoinPool.class.getDeclaredField("barrierStack"));
2110	<	spareStackOffset = _unsafe.objectFieldOffset
2111	<	(ForkJoinPool.class.getDeclaredField("spareStack"));
2095	>	UNSAFE = getUnsafe();
2096	>	Class k = ForkJoinPool.class;
2097	>	ctlOffset = UNSAFE.objectFieldOffset
2098	>	(k.getDeclaredField("ctl"));
2099	>	stealCountOffset = UNSAFE.objectFieldOffset
2100	>	(k.getDeclaredField("stealCount"));
2101	>	blockedCountOffset = UNSAFE.objectFieldOffset
2102	>	(k.getDeclaredField("blockedCount"));
2103	>	quiescerCountOffset = UNSAFE.objectFieldOffset
2104	>	(k.getDeclaredField("quiescerCount"));
2105	>	scanGuardOffset = UNSAFE.objectFieldOffset
2106	>	(k.getDeclaredField("scanGuard"));
2107	>	nextWorkerNumberOffset = UNSAFE.objectFieldOffset
2108	>	(k.getDeclaredField("nextWorkerNumber"));
2109	>	Class a = ForkJoinTask[].class;
2110	>	ABASE = UNSAFE.arrayBaseOffset(a);
2111	>	s = UNSAFE.arrayIndexScale(a);
2112		} catch (Exception e) {
2113	<	throw new RuntimeException("Could not initialize intrinsics", e);
2113	>	throw new Error(e);
2114		}
2115	+	if ((s & (s-1)) != 0)
2116	+	throw new Error("data type scale not a power of two");
2117	+	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
2118		}
2119
2120	<	private boolean casEventCount(long cmp, long val) {
2121	<	return _unsafe.compareAndSwapLong(this, eventCountOffset, cmp, val);
2122	<	}
2123	<	private boolean casWorkerCounts(int cmp, int val) {
2124	<	return _unsafe.compareAndSwapInt(this, workerCountsOffset, cmp, val);
2125	<	}
2126	<	private boolean casRunControl(int cmp, int val) {
2127	<	return _unsafe.compareAndSwapInt(this, runControlOffset, cmp, val);
2128	<	}
2129	<	private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
2130	<	return _unsafe.compareAndSwapObject(this, spareStackOffset, cmp, val);
2131	<	}
2132	<	private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
2133	<	return _unsafe.compareAndSwapObject(this, barrierStackOffset, cmp, val);
2120	>	/**
2121	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
2122	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
2123	>	* into a jdk.
2124	>	*
2125	>	* @return a sun.misc.Unsafe
2126	>	*/
2127	>	private static sun.misc.Unsafe getUnsafe() {
2128	>	try {
2129	>	return sun.misc.Unsafe.getUnsafe();
2130	>	} catch (SecurityException se) {
2131	>	try {
2132	>	return java.security.AccessController.doPrivileged
2133	>	(new java.security
2134	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
2135	>	public sun.misc.Unsafe run() throws Exception {
2136	>	java.lang.reflect.Field f = sun.misc
2137	>	.Unsafe.class.getDeclaredField("theUnsafe");
2138	>	f.setAccessible(true);
2139	>	return (sun.misc.Unsafe) f.get(null);
2140	>	}});
2141	>	} catch (java.security.PrivilegedActionException e) {
2142	>	throw new RuntimeException("Could not initialize intrinsics",
2143	>	e.getCause());
2144	>	}
2145	>	}
2146		}
2147		}

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