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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.58 by dl, Fri Jul 23 13:07:43 2010 UTC vs.
Revision 1.86 by dl, Sun Nov 21 20:42:18 2010 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.util.ArrayList;
10		import java.util.Arrays;
11		import java.util.Collection;
12		import java.util.Collections;
13		import java.util.List;
14	+	import java.util.concurrent.AbstractExecutorService;
15	+	import java.util.concurrent.Callable;
16	+	import java.util.concurrent.ExecutorService;
17	+	import java.util.concurrent.Future;
18	+	import java.util.concurrent.RejectedExecutionException;
19	+	import java.util.concurrent.RunnableFuture;
20	+	import java.util.concurrent.TimeUnit;
21	+	import java.util.concurrent.TimeoutException;
22	+	import java.util.concurrent.atomic.AtomicInteger;
23		import java.util.concurrent.locks.LockSupport;
24		import java.util.concurrent.locks.ReentrantLock;
18	–	import java.util.concurrent.atomic.AtomicInteger;
19	–	import java.util.concurrent.CountDownLatch;
25
26		/**
27		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
#	Line 52 | Line 57 | import java.util.concurrent.CountDownLat
57		* convenient form for informal monitoring.
58		*
59		* <p> As is the case with other ExecutorServices, there are three
60	<	* main task execution methods summarized in the follwoing
60	>	* main task execution methods summarized in the following
61		* table. These are designed to be used by clients not already engaged
62		* in fork/join computations in the current pool.  The main forms of
63		* these methods accept instances of {@code ForkJoinTask}, but
#	Line 60 | Line 65 | import java.util.concurrent.CountDownLat
65		* Runnable}- or {@code Callable}- based activities as well.  However,
66		* tasks that are already executing in a pool should normally
67		* <em>NOT</em> use these pool execution methods, but instead use the
68	<	* within-computation forms listed in the table.
68	>	* within-computation forms listed in the table.
69		*
70		* <table BORDER CELLPADDING=3 CELLSPACING=1>
71		*  <tr>
#	Line 69 | Line 74 | import java.util.concurrent.CountDownLat
74		*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
75		*  </tr>
76		*  <tr>
77	<	*    <td> <b>Arange async execution</td>
77	>	*    <td> <b>Arrange async execution</td>
78		*    <td> {@link #execute(ForkJoinTask)}</td>
79		*    <td> {@link ForkJoinTask#fork}</td>
80		*  </tr>
#	Line 84 | Line 89 | import java.util.concurrent.CountDownLat
89		*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
90		*  </tr>
91		* </table>
92	<	*
92	>	*
93		* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
94		* used for all parallel task execution in a program or subsystem.
95		* Otherwise, use would not usually outweigh the construction and
#	Line 110 | Line 115 | import java.util.concurrent.CountDownLat
115		*
116		* <p>This implementation rejects submitted tasks (that is, by throwing
117		* {@link RejectedExecutionException}) only when the pool is shut down
118	<	* or internal resources have been exhuasted.
118	>	* or internal resources have been exhausted.
119		*
120		* @since 1.7
121		* @author Doug Lea
#	Line 138 | Line 143 | public class ForkJoinPool extends Abstra
143		* cache pollution effects.)
144		*
145		* Beyond work-stealing support and essential bookkeeping, the
146	<	* main responsibility of this framework is to arrange tactics for
147	<	* when one worker is waiting to join a task stolen (or always
148	<	* held by) another.  Becauae we are multiplexing many tasks on to
149	<	* a pool of workers, we can't just let them block (as in
150	<	* Thread.join).  We also cannot just reassign the joiner's
151	<	* run-time stack with another and replace it later, which would
152	<	* be a form of "continuation", that even if possible is not
153	<	* necessarily a good idea. Given that the creation costs of most
154	<	* threads on most systems mainly surrounds setting up runtime
155	<	* stacks, thread creation and switching is usually not much more
156	<	* expensive than stack creation and switching, and is more
157	<	* flexible). Instead we combine two tactics:
146	>	* main responsibility of this framework is to take actions when
147	>	* one worker is waiting to join a task stolen (or always held by)
148	>	* another.  Because we are multiplexing many tasks on to a pool
149	>	* of workers, we can't just let them block (as in Thread.join).
150	>	* We also cannot just reassign the joiner's run-time stack with
151	>	* another and replace it later, which would be a form of
152	>	* "continuation", that even if possible is not necessarily a good
153	>	* idea. Given that the creation costs of most threads on most
154	>	* systems mainly surrounds setting up runtime stacks, thread
155	>	* creation and switching is usually not much more expensive than
156	>	* stack creation and switching, and is more flexible). Instead we
157	>	* combine two tactics:
158		*
159	<	*   1. Arranging for the joiner to execute some task that it
159	>	*   Helping: Arranging for the joiner to execute some task that it
160		*      would be running if the steal had not occurred.  Method
161		*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
162		*      links to try to find such a task.
163		*
164	<	*   2. Unless there are already enough live threads, creating or
165	<	*      or re-activating a spare thread to compensate for the
166	<	*      (blocked) joiner until it unblocks.  Spares then suspend
167	<	*      at their next opportunity or eventually die if unused for
168	<	*      too long.  See below and the internal documentation
169	<	*      for tryAwaitJoin for more details about compensation
170	<	*      rules.
171	<	*
172	<	* Because the determining existence of conservatively safe
173	<	* helping targets, the availability of already-created spares,
174	<	* and the apparent need to create new spares are all racy and
175	<	* require heuristic guidance, joins (in
176	<	* ForkJoinWorkerThread.joinTask) interleave these options until
177	<	* successful.  Creating a new spare always succeeds, but also
178	<	* increases application footprint, so we try to avoid it, within
179	<	* reason.
164	>	*   Compensating: Unless there are already enough live threads,
165	>	*      method helpMaintainParallelism() may create or
166	>	*      re-activate a spare thread to compensate for blocked
167	>	*      joiners until they unblock.
168	>	*
169	>	* It is impossible to keep exactly the target (parallelism)
170	>	* number of threads running at any given time.  Determining
171	>	* existence of conservatively safe helping targets, the
172	>	* availability of already-created spares, and the apparent need
173	>	* to create new spares are all racy and require heuristic
174	>	* guidance, so we rely on multiple retries of each.  Compensation
175	>	* occurs in slow-motion. It is triggered only upon timeouts of
176	>	* Object.wait used for joins. This reduces poor decisions that
177	>	* would otherwise be made when threads are waiting for others
178	>	* that are stalled because of unrelated activities such as
179	>	* garbage collection.
180		*
181	<	* The ManagedBlocker extension API can't use option (1) so uses a
182	<	* special version of (2) in method awaitBlocker.
181	>	* The ManagedBlocker extension API can't use helping so relies
182	>	* only on compensation in method awaitBlocker.
183		*
184		* The main throughput advantages of work-stealing stem from
185		* decentralized control -- workers mostly steal tasks from each
#	Line 207 | Line 212 | public class ForkJoinPool extends Abstra
212		* blocked workers. However, all other support code is set up to
213		* work with other policies.
214		*
215	+	* To ensure that we do not hold on to worker references that
216	+	* would prevent GC, ALL accesses to workers are via indices into
217	+	* the workers array (which is one source of some of the unusual
218	+	* code constructions here). In essence, the workers array serves
219	+	* as a WeakReference mechanism. Thus for example the event queue
220	+	* stores worker indices, not worker references. Access to the
221	+	* workers in associated methods (for example releaseEventWaiters)
222	+	* must both index-check and null-check the IDs. All such accesses
223	+	* ignore bad IDs by returning out early from what they are doing,
224	+	* since this can only be associated with shutdown, in which case
225	+	* it is OK to give up. On termination, we just clobber these
226	+	* data structures without trying to use them.
227	+	*
228		* 2. Bookkeeping for dynamically adding and removing workers. We
229		* aim to approximately maintain the given level of parallelism.
230		* When some workers are known to be blocked (on joins or via
231		* ManagedBlocker), we may create or resume others to take their
232		* place until they unblock (see below). Implementing this
233		* requires counts of the number of "running" threads (i.e., those
234	<	* that are neither blocked nor artifically suspended) as well as
234	>	* that are neither blocked nor artificially suspended) as well as
235		* the total number.  These two values are packed into one field,
236		* "workerCounts" because we need accurate snapshots when deciding
237		* to create, resume or suspend.  Note however that the
238	<	* correspondance of these counts to reality is not guaranteed. In
238	>	* correspondence of these counts to reality is not guaranteed. In
239		* particular updates for unblocked threads may lag until they
240		* actually wake up.
241		*
#	Line 248 | Line 266 | public class ForkJoinPool extends Abstra
266		* workers that previously could not find a task to now find one:
267		* Submission of a new task to the pool, or another worker pushing
268		* a task onto a previously empty queue.  (We also use this
269	<	* mechanism for termination and reconfiguration actions that
269	>	* mechanism for configuration and termination actions that
270		* require wakeups of idle workers).  Each worker maintains its
271		* last known event count, and blocks when a scan for work did not
272		* find a task AND its lastEventCount matches the current
#	Line 259 | Line 277 | public class ForkJoinPool extends Abstra
277		* a record (field nextEventWaiter) for the next waiting worker.
278		* In addition to allowing simpler decisions about need for
279		* wakeup, the event count bits in eventWaiters serve the role of
280	<	* tags to avoid ABA errors in Treiber stacks.  To reduce delays
281	<	* in task diffusion, workers not otherwise occupied may invoke
282	<	* method releaseWaiters, that removes and signals (unparks)
283	<	* workers not waiting on current count. To minimize task
284	<	* production stalls associate with signalling, any worker pushing
285	<	* a task on an empty queue invokes the weaker method signalWork,
268	<	* that only releases idle workers until it detects interference
269	<	* by other threads trying to release, and lets them take
270	<	* over. The net effect is a tree-like diffusion of signals, where
271	<	* released threads (and possibly others) help with unparks.  To
272	<	* further reduce contention effects a bit, failed CASes to
273	<	* increment field eventCount are tolerated without retries.
280	>	* tags to avoid ABA errors in Treiber stacks. Upon any wakeup,
281	>	* released threads also try to release at most two others.  The
282	>	* net effect is a tree-like diffusion of signals, where released
283	>	* threads (and possibly others) help with unparks.  To further
284	>	* reduce contention effects a bit, failed CASes to increment
285	>	* field eventCount are tolerated without retries in signalWork.
286		* Conceptually they are merged into the same event, which is OK
287		* when their only purpose is to enable workers to scan for work.
288		*
289	<	* 5. Managing suspension of extra workers. When a worker is about
290	<	* to block waiting for a join (or via ManagedBlockers), we may
291	<	* create a new thread to maintain parallelism level, or at least
292	<	* avoid starvation. Usually, extra threads are needed for only
293	<	* very short periods, yet join dependencies are such that we
294	<	* sometimes need them in bursts. Rather than create new threads
295	<	* each time this happens, we suspend no-longer-needed extra ones
296	<	* as "spares". For most purposes, we don't distinguish "extra"
297	<	* spare threads from normal "core" threads: On each call to
298	<	* preStep (the only point at which we can do this) a worker
299	<	* checks to see if there are now too many running workers, and if
300	<	* so, suspends itself.  Methods tryAwaitJoin and awaitBlocker
301	<	* look for suspended threads to resume before considering
302	<	* creating a new replacement. We don't need a special data
303	<	* structure to maintain spares; simply scanning the workers array
304	<	* looking for worker.isSuspended() is fine because the calling
305	<	* thread is otherwise not doing anything useful anyway; we are at
306	<	* least as happy if after locating a spare, the caller doesn't
307	<	* actually block because the join is ready before we try to
308	<	* adjust and compensate.  Note that this is intrinsically racy.
309	<	* One thread may become a spare at about the same time as another
310	<	* is needlessly being created. We counteract this and related
311	<	* slop in part by requiring resumed spares to immediately recheck
312	<	* (in preStep) to see whether they they should re-suspend. The
313	<	* only effective difference between "extra" and "core" threads is
314	<	* that we allow the "extra" ones to time out and die if they are
315	<	* not resumed within a keep-alive interval of a few seconds. This
316	<	* is implemented mainly within ForkJoinWorkerThread, but requires
317	<	* some coordination (isTrimmed() -- meaning killed while
318	<	* suspended) to correctly maintain pool counts.
319	<	*
320	<	* 6. Deciding when to create new workers. The main dynamic
321	<	* control in this class is deciding when to create extra threads,
322	<	* in methods awaitJoin and awaitBlocker. We always need to create
323	<	* one when the number of running threads would become zero and
324	<	* all workers are busy. However, this is not easy to detect
325	<	* reliably in the presence of transients so we use retries and
326	<	* allow slack (in tryAwaitJoin) to reduce false alarms.  These
327	<	* effectively reduce churn at the price of systematically
328	<	* undershooting target parallelism when many threads are blocked.
329	<	* However, biasing toward undeshooting partially compensates for
330	<	* the above mechanics to suspend extra threads, that normally
331	<	* lead to overshoot because we can only suspend workers
332	<	* in-between top-level actions. It also better copes with the
333	<	* fact that some of the methods in this class tend to never
334	<	* become compiled (but are interpreted), so some components of
335	<	* the entire set of controls might execute many times faster than
336	<	* others. And similarly for cases where the apparent lack of work
337	<	* is just due to GC stalls and other transient system activity.
289	>	* 5. Managing suspension of extra workers. When a worker notices
290	>	* (usually upon timeout of a wait()) that there are too few
291	>	* running threads, we may create a new thread to maintain
292	>	* parallelism level, or at least avoid starvation. Usually, extra
293	>	* threads are needed for only very short periods, yet join
294	>	* dependencies are such that we sometimes need them in
295	>	* bursts. Rather than create new threads each time this happens,
296	>	* we suspend no-longer-needed extra ones as "spares". For most
297	>	* purposes, we don't distinguish "extra" spare threads from
298	>	* normal "core" threads: On each call to preStep (the only point
299	>	* at which we can do this) a worker checks to see if there are
300	>	* now too many running workers, and if so, suspends itself.
301	>	* Method helpMaintainParallelism looks for suspended threads to
302	>	* resume before considering creating a new replacement. The
303	>	* spares themselves are encoded on another variant of a Treiber
304	>	* Stack, headed at field "spareWaiters".  Note that the use of
305	>	* spares is intrinsically racy.  One thread may become a spare at
306	>	* about the same time as another is needlessly being created. We
307	>	* counteract this and related slop in part by requiring resumed
308	>	* spares to immediately recheck (in preStep) to see whether they
309	>	* should re-suspend.
310	>	*
311	>	* 6. Killing off unneeded workers. A timeout mechanism is used to
312	>	* shed unused workers: The oldest (first) event queue waiter uses
313	>	* a timed rather than hard wait. When this wait times out without
314	>	* a normal wakeup, it tries to shutdown any one (for convenience
315	>	* the newest) other spare or event waiter via
316	>	* tryShutdownUnusedWorker. This eventually reduces the number of
317	>	* worker threads to a minimum of one after a long enough period
318	>	* without use.
319	>	*
320	>	* 7. Deciding when to create new workers. The main dynamic
321	>	* control in this class is deciding when to create extra threads
322	>	* in method helpMaintainParallelism. We would like to keep
323	>	* exactly #parallelism threads running, which is an impossible
324	>	* task. We always need to create one when the number of running
325	>	* threads would become zero and all workers are busy. Beyond
326	>	* this, we must rely on heuristics that work well in the
327	>	* presence of transient phenomena such as GC stalls, dynamic
328	>	* compilation, and wake-up lags. These transients are extremely
329	>	* common -- we are normally trying to fully saturate the CPUs on
330	>	* a machine, so almost any activity other than running tasks
331	>	* impedes accuracy. Our main defense is to allow parallelism to
332	>	* lapse for a while during joins, and use a timeout to see if,
333	>	* after the resulting settling, there is still a need for
334	>	* additional workers.  This also better copes with the fact that
335	>	* some of the methods in this class tend to never become compiled
336	>	* (but are interpreted), so some components of the entire set of
337	>	* controls might execute 100 times faster than others. And
338	>	* similarly for cases where the apparent lack of work is just due
339	>	* to GC stalls and other transient system activity.
340		*
341		* Beware that there is a lot of representation-level coupling
342		* among classes ForkJoinPool, ForkJoinWorkerThread, and
#	Line 335 | Line 349 | public class ForkJoinPool extends Abstra
349		*
350		* Style notes: There are lots of inline assignments (of form
351		* "while ((local = field) != 0)") which are usually the simplest
352	<	* way to ensure read orderings. Also several occurrences of the
353	<	* unusual "do {} while(!cas...)" which is the simplest way to
354	<	* force an update of a CAS'ed variable. There are also other
355	<	* coding oddities that help some methods perform reasonably even
356	<	* when interpreted (not compiled), at the expense of messiness.
352	>	* way to ensure the required read orderings (which are sometimes
353	>	* critical). Also several occurrences of the unusual "do {}
354	>	* while (!cas...)" which is the simplest way to force an update of
355	>	* a CAS'ed variable. There are also other coding oddities that
356	>	* help some methods perform reasonably even when interpreted (not
357	>	* compiled), at the expense of some messy constructions that
358	>	* reduce byte code counts.
359		*
360		* The order of declarations in this file is: (1) statics (2)
361		* fields (along with constants used when unpacking some of them)
#	Line 407 | Line 423 | public class ForkJoinPool extends Abstra
423		new AtomicInteger();
424
425		/**
426	<	* Absolute bound for parallelism level. Twice this number must
427	<	* fit into a 16bit field to enable word-packing for some counts.
426	>	* The time to block in a join (see awaitJoin) before checking if
427	>	* a new worker should be (re)started to maintain parallelism
428	>	* level. The value should be short enough to maintain global
429	>	* responsiveness and progress but long enough to avoid
430	>	* counterproductive firings during GC stalls or unrelated system
431	>	* activity, and to not bog down systems with continual re-firings
432	>	* on GCs or legitimately long waits.
433	>	*/
434	>	private static final long JOIN_TIMEOUT_MILLIS = 250L; // 4 per second
435	>
436	>	/**
437	>	* The wakeup interval (in nanoseconds) for the oldest worker
438	>	* waiting for an event to invoke tryShutdownUnusedWorker to
439	>	* shrink the number of workers.  The exact value does not matter
440	>	* too much. It must be short enough to release resources during
441	>	* sustained periods of idleness, but not so short that threads
442	>	* are continually re-created.
443		*/
444	<	private static final int MAX_THREADS = 0x7fff;
444	>	private static final long SHRINK_RATE_NANOS =
445	>	30L * 1000L * 1000L * 1000L; // 2 per minute
446	>
447	>	/**
448	>	* Absolute bound for parallelism level. Twice this number plus
449	>	* one (i.e., 0xfff) must fit into a 16bit field to enable
450	>	* word-packing for some counts and indices.
451	>	*/
452	>	private static final int MAX_WORKERS   = 0x7fff;
453
454		/**
455		* Array holding all worker threads in the pool.  Array size must
#	Line 450 | Line 489 | public class ForkJoinPool extends Abstra
489		private volatile long stealCount;
490
491		/**
492	<	* Encoded record of top of treiber stack of threads waiting for
492	>	* Encoded record of top of Treiber stack of threads waiting for
493		* events. The top 32 bits contain the count being waited for. The
494	<	* bottom word contains one plus the pool index of waiting worker
495	<	* thread.
494	>	* bottom 16 bits contains one plus the pool index of waiting
495	>	* worker thread. (Bits 16-31 are unused.)
496		*/
497		private volatile long eventWaiters;
498
499	<	private static final int  EVENT_COUNT_SHIFT = 32;
500	<	private static final long WAITER_ID_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
499	>	private static final int EVENT_COUNT_SHIFT = 32;
500	>	private static final int WAITER_ID_MASK    = (1 << 16) - 1;
501
502		/**
503		* A counter for events that may wake up worker threads:
504		*   - Submission of a new task to the pool
505		*   - A worker pushing a task on an empty queue
506	<	*   - termination and reconfiguration
506	>	*   - termination
507		*/
508		private volatile int eventCount;
509
510		/**
511	+	* Encoded record of top of Treiber stack of spare threads waiting
512	+	* for resumption. The top 16 bits contain an arbitrary count to
513	+	* avoid ABA effects. The bottom 16bits contains one plus the pool
514	+	* index of waiting worker thread.
515	+	*/
516	+	private volatile int spareWaiters;
517	+
518	+	private static final int SPARE_COUNT_SHIFT = 16;
519	+	private static final int SPARE_ID_MASK     = (1 << 16) - 1;
520	+
521	+	/**
522		* Lifecycle control. The low word contains the number of workers
523		* that are (probably) executing tasks. This value is atomically
524		* incremented before a worker gets a task to run, and decremented
525	<	* when worker has no tasks and cannot find any.  Bits 16-18
525	>	* when a worker has no tasks and cannot find any.  Bits 16-18
526		* contain runLevel value. When all are zero, the pool is
527		* running. Level transitions are monotonic (running -> shutdown
528		* -> terminating -> terminated) so each transition adds a bit.
529		* These are bundled together to ensure consistent read for
530		* termination checks (i.e., that runLevel is at least SHUTDOWN
531		* and active threads is zero).
532	+	*
533	+	* Notes: Most direct CASes are dependent on these bitfield
534	+	* positions.  Also, this field is non-private to enable direct
535	+	* performance-sensitive CASes in ForkJoinWorkerThread.
536		*/
537	<	private volatile int runState;
537	>	volatile int runState;
538
539		// Note: The order among run level values matters.
540		private static final int RUNLEVEL_SHIFT     = 16;
#	Line 488 | Line 542 | public class ForkJoinPool extends Abstra
542		private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
543		private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
544		private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
491	–	private static final int ONE_ACTIVE         = 1; // active update delta
545
546		/**
547		* Holds number of total (i.e., created and not yet terminated)
#	Line 497 | Line 550 | public class ForkJoinPool extends Abstra
550		* making decisions about creating and suspending spare
551		* threads. Updated only by CAS. Note that adding a new worker
552		* requires incrementing both counts, since workers start off in
553	<	* running state.  This field is also used for memory-fencing
501	<	* configuration parameters.
553	>	* running state.
554		*/
555		private volatile int workerCounts;
556
#	Line 530 | Line 582 | public class ForkJoinPool extends Abstra
582		*/
583		private final int poolNumber;
584
585	<	// Utilities for CASing fields. Note that several of these
586	<	// are manually inlined by callers
585	>	// Utilities for CASing fields. Note that most of these
586	>	// are usually manually inlined by callers
587
588		/**
589	<	* Increments running count.  Also used by ForkJoinTask.
589	>	* Increments running count part of workerCounts
590		*/
591		final void incrementRunningCount() {
592		int c;
593		do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
594	<	c = workerCounts,
594	>	c = workerCounts,
595		c + ONE_RUNNING));
596		}
597
598		/**
599	+	* Tries to increment running count part of workerCounts
600	+	*/
601	+	final boolean tryIncrementRunningCount() {
602	+	int c;
603	+	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
604	+	c = workerCounts,
605	+	c + ONE_RUNNING);
606	+	}
607	+
608	+	/**
609		* Tries to decrement running count unless already zero
610		*/
611		final boolean tryDecrementRunningCount() {
#	Line 555 | Line 617 | public class ForkJoinPool extends Abstra
617		}
618
619		/**
620	<	* Tries to increment running count
621	<	*/
560	<	final boolean tryIncrementRunningCount() {
561	<	int wc;
562	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
563	<	wc = workerCounts, wc + ONE_RUNNING);
564	<	}
565	<
566	<	/**
567	<	* Tries incrementing active count; fails on contention.
568	<	* Called by workers before executing tasks.
620	>	* Forces decrement of encoded workerCounts, awaiting nonzero if
621	>	* (rarely) necessary when other count updates lag.
622		*
623	<	* @return true on success
623	>	* @param dr -- either zero or ONE_RUNNING
624	>	* @param dt -- either zero or ONE_TOTAL
625		*/
626	<	final boolean tryIncrementActiveCount() {
627	<	int c;
628	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
629	<	c = runState, c + ONE_ACTIVE);
626	>	private void decrementWorkerCounts(int dr, int dt) {
627	>	for (;;) {
628	>	int wc = workerCounts;
629	>	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
630	>	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) {
631	>	if ((runState & TERMINATED) != 0)
632	>	return; // lagging termination on a backout
633	>	Thread.yield();
634	>	}
635	>	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
636	>	wc, wc - (dr + dt)))
637	>	return;
638	>	}
639		}
640
641		/**
#	Line 582 | Line 645 | public class ForkJoinPool extends Abstra
645		final boolean tryDecrementActiveCount() {
646		int c;
647		return UNSAFE.compareAndSwapInt(this, runStateOffset,
648	<	c = runState, c - ONE_ACTIVE);
648	>	c = runState, c - 1);
649		}
650
651		/**
#	Line 611 | Line 674 | public class ForkJoinPool extends Abstra
674		lock.lock();
675		try {
676		ForkJoinWorkerThread[] ws = workers;
677	<	int nws = ws.length;
678	<	if (k < 0 || k >= nws || ws[k] != null) {
679	<	for (k = 0; k < nws && ws[k] != null; ++k)
677	>	int n = ws.length;
678	>	if (k < 0 || k >= n || ws[k] != null) {
679	>	for (k = 0; k < n && ws[k] != null; ++k)
680		;
681	<	if (k == nws)
682	<	ws = Arrays.copyOf(ws, nws << 1);
681	>	if (k == n)
682	>	ws = workers = Arrays.copyOf(ws, n << 1);
683		}
684		ws[k] = w;
685	<	workers = ws; // volatile array write ensures slot visibility
685	>	int c = eventCount; // advance event count to ensure visibility
686	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c, c+1);
687		} finally {
688		lock.unlock();
689		}
#	Line 627 | Line 691 | public class ForkJoinPool extends Abstra
691		}
692
693		/**
694	<	* Nulls out record of worker in workers array
694	>	* Nulls out record of worker in workers array.
695		*/
696		private void forgetWorker(ForkJoinWorkerThread w) {
697		int idx = w.poolIndex;
698	<	// Locking helps method recordWorker avoid unecessary expansion
698	>	// Locking helps method recordWorker avoid unnecessary expansion
699		final ReentrantLock lock = this.workerLock;
700		lock.lock();
701		try {
#	Line 643 | Line 707 | public class ForkJoinPool extends Abstra
707		}
708		}
709
646	–	// adding and removing workers
647	–
710		/**
711	<	* Tries to create and add new worker. Assumes that worker counts
712	<	* are already updated to accommodate the worker, so adjusts on
713	<	* failure.
711	>	* Final callback from terminating worker.  Removes record of
712	>	* worker from array, and adjusts counts. If pool is shutting
713	>	* down, tries to complete termination.
714		*
715	<	* @return new worker or null if creation failed
715	>	* @param w the worker
716		*/
717	<	private ForkJoinWorkerThread addWorker() {
718	<	ForkJoinWorkerThread w = null;
719	<	try {
720	<	w = factory.newThread(this);
721	<	} finally { // Adjust on either null or exceptional factory return
722	<	if (w == null) {
661	<	onWorkerCreationFailure();
662	<	return null;
663	<	}
664	<	}
665	<	w.start(recordWorker(w), ueh);
666	<	return w;
717	>	final void workerTerminated(ForkJoinWorkerThread w) {
718	>	forgetWorker(w);
719	>	decrementWorkerCounts(w.isTrimmed() ? 0 : ONE_RUNNING, ONE_TOTAL);
720	>	while (w.stealCount != 0) // collect final count
721	>	tryAccumulateStealCount(w);
722	>	tryTerminate(false);
723		}
724
725	+	// Waiting for and signalling events
726	+
727		/**
728	<	* Adjusts counts upon failure to create worker
728	>	* Releases workers blocked on a count not equal to current count.
729	>	* Normally called after precheck that eventWaiters isn't zero to
730	>	* avoid wasted array checks. Gives up upon a change in count or
731	>	* upon releasing two workers, letting others take over.
732		*/
733	<	private void onWorkerCreationFailure() {
734	<	for (;;) {
735	<	int wc = workerCounts;
736	<	if ((wc >>> TOTAL_COUNT_SHIFT) == 0)
737	<	Thread.yield(); // wait for other counts to settle
738	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
739	<	wc - (ONE_RUNNING|ONE_TOTAL)))
733	>	private void releaseEventWaiters() {
734	>	ForkJoinWorkerThread[] ws = workers;
735	>	int n = ws.length;
736	>	long h = eventWaiters;
737	>	int ec = eventCount;
738	>	boolean releasedOne = false;
739	>	ForkJoinWorkerThread w; int id;
740	>	while ((id = (((int)h) & WAITER_ID_MASK) - 1) >= 0 &&
741	>	(int)(h >>> EVENT_COUNT_SHIFT) != ec &&
742	>	id < n && (w = ws[id]) != null) {
743	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
744	>	h,  w.nextWaiter)) {
745	>	LockSupport.unpark(w);
746	>	if (releasedOne) // exit on second release
747	>	break;
748	>	releasedOne = true;
749	>	}
750	>	if (eventCount != ec)
751		break;
752	+	h = eventWaiters;
753		}
681	–	tryTerminate(false); // in case of failure during shutdown
754		}
755
756		/**
757	<	* Creates and/or resumes enough workers to establish target
758	<	* parallelism, giving up if terminating or addWorker fails
687	<	*
688	<	* TODO: recast this to support lazier creation and automated
689	<	* parallelism maintenance
757	>	* Tries to advance eventCount and releases waiters. Called only
758	>	* from workers.
759		*/
760	<	private void ensureEnoughWorkers() {
761	<	for (;;) {
762	<	int pc = parallelism;
763	<	int wc = workerCounts;
764	<	int rc = wc & RUNNING_COUNT_MASK;
696	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
697	<	if (tc < pc) {
698	<	if (runState == TERMINATING ||
699	<	(UNSAFE.compareAndSwapInt
700	<	(this, workerCountsOffset,
701	<	wc, wc + (ONE_RUNNING|ONE_TOTAL)) &&
702	<	addWorker() == null))
703	<	break;
704	<	}
705	<	else if (tc > pc && rc < pc &&
706	<	tc > (runState & ACTIVE_COUNT_MASK)) {
707	<	ForkJoinWorkerThread spare = null;
708	<	ForkJoinWorkerThread[] ws = workers;
709	<	int nws = ws.length;
710	<	for (int i = 0; i < nws; ++i) {
711	<	ForkJoinWorkerThread w = ws[i];
712	<	if (w != null && w.isSuspended()) {
713	<	if ((workerCounts & RUNNING_COUNT_MASK) > pc ||
714	<	runState == TERMINATING)
715	<	return;
716	<	if (w.tryResumeSpare())
717	<	incrementRunningCount();
718	<	break;
719	<	}
720	<	}
721	<	}
722	<	else
723	<	break;
724	<	}
760	>	final void signalWork() {
761	>	int c; // try to increment event count -- CAS failure OK
762	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
763	>	if (eventWaiters != 0L)
764	>	releaseEventWaiters();
765		}
766
767		/**
768	<	* Final callback from terminating worker.  Removes record of
769	<	* worker from array, and adjusts counts. If pool is shutting
730	<	* down, tries to complete terminatation, else possibly replaces
731	<	* the worker.
768	>	* Adds the given worker to event queue and blocks until
769	>	* terminating or event count advances from the given value
770		*
771	<	* @param w the worker
771	>	* @param w the calling worker thread
772	>	* @param ec the count
773		*/
774	<	final void workerTerminated(ForkJoinWorkerThread w) {
775	<	if (w.active) { // force inactive
776	<	w.active = false;
777	<	do {} while (!tryDecrementActiveCount());
778	<	}
779	<	forgetWorker(w);
780	<
781	<	// Decrement total count, and if was running, running count
782	<	// Spin (waiting for other updates) if either would be negative
783	<	int nr = w.isTrimmed() ? 0 : ONE_RUNNING;
745	<	int unit = ONE_TOTAL + nr;
746	<	for (;;) {
747	<	int wc = workerCounts;
748	<	int rc = wc & RUNNING_COUNT_MASK;
749	<	if (rc - nr < 0 || (wc >>> TOTAL_COUNT_SHIFT) == 0)
750	<	Thread.yield(); // back off if waiting for other updates
751	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
752	<	wc, wc - unit))
774	>	private void eventSync(ForkJoinWorkerThread w, int ec) {
775	>	long nh = (((long)ec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
776	>	long h;
777	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
778	>	(((int)(h = eventWaiters) & WAITER_ID_MASK) == 0 ||
779	>	(int)(h >>> EVENT_COUNT_SHIFT) == ec) &&
780	>	eventCount == ec) {
781	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
782	>	w.nextWaiter = h, nh)) {
783	>	awaitEvent(w, ec);
784		break;
785	+	}
786		}
755	–
756	–	accumulateStealCount(w); // collect final count
757	–	if (!tryTerminate(false))
758	–	ensureEnoughWorkers();
787		}
788
761	–	// Waiting for and signalling events
762	–
789		/**
790	<	* Releases workers blocked on a count not equal to current count.
791	<	* @return true if any released
790	>	* Blocks the given worker (that has already been entered as an
791	>	* event waiter) until terminating or event count advances from
792	>	* the given value. The oldest (first) waiter uses a timed wait to
793	>	* occasionally one-by-one shrink the number of workers (to a
794	>	* minimum of one) if the pool has not been used for extended
795	>	* periods.
796	>	*
797	>	* @param w the calling worker thread
798	>	* @param ec the count
799		*/
800	<	private void releaseWaiters() {
801	<	long top;
802	<	while ((top = eventWaiters) != 0L) {
803	<	ForkJoinWorkerThread[] ws = workers;
804	<	int n = ws.length;
805	<	for (;;) {
806	<	int i = ((int)(top & WAITER_ID_MASK)) - 1;
807	<	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == eventCount)
808	<	return;
809	<	ForkJoinWorkerThread w;
810	<	if (i < n && (w = ws[i]) != null &&
811	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
812	<	top, w.nextWaiter)) {
813	<	LockSupport.unpark(w);
814	<	top = eventWaiters;
800	>	private void awaitEvent(ForkJoinWorkerThread w, int ec) {
801	>	while (eventCount == ec) {
802	>	if (tryAccumulateStealCount(w)) { // transfer while idle
803	>	boolean untimed = (w.nextWaiter != 0L ||
804	>	(workerCounts & RUNNING_COUNT_MASK) <= 1);
805	>	long startTime = untimed ? 0 : System.nanoTime();
806	>	Thread.interrupted();         // clear/ignore interrupt
807	>	if (w.isTerminating() || eventCount != ec)
808	>	break;                    // recheck after clear
809	>	if (untimed)
810	>	LockSupport.park(w);
811	>	else {
812	>	LockSupport.parkNanos(w, SHRINK_RATE_NANOS);
813	>	if (eventCount != ec || w.isTerminating())
814	>	break;
815	>	if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS)
816	>	tryShutdownUnusedWorker(ec);
817		}
783	–	else
784	–	break;      // possibly stale; reread
818		}
819		}
820		}
821
822	+	// Maintaining parallelism
823	+
824		/**
825	<	* Ensures eventCount on exit is different (mod 2^32) than on
791	<	* entry and wakes up all waiters
825	>	* Pushes worker onto the spare stack.
826		*/
827	<	private void signalEvent() {
828	<	int c;
829	<	do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset,
830	<	c = eventCount, c+1));
797	<	releaseWaiters();
827	>	final void pushSpare(ForkJoinWorkerThread w) {
828	>	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1);
829	>	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
830	>	w.nextSpare = spareWaiters,ns));
831		}
832
833		/**
834	<	* Advances eventCount and releases waiters until interference by
835	<	* other releasing threads is detected.
834	>	* Tries (once) to resume a spare if the number of running
835	>	* threads is less than target.
836		*/
837	<	final void signalWork() {
838	<	int c;
839	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, c=eventCount, c+1);
840	<	long top;
841	<	while ((top = eventWaiters) != 0L) {
842	<	int ec = eventCount;
843	<	ForkJoinWorkerThread[] ws = workers;
844	<	int n = ws.length;
845	<	for (;;) {
846	<	int i = ((int)(top & WAITER_ID_MASK)) - 1;
847	<	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
848	<	return;
849	<	ForkJoinWorkerThread w;
850	<	if (i < n && (w = ws[i]) != null &&
851	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
852	<	top, top = w.nextWaiter)) {
853	<	LockSupport.unpark(w);
854	<	if (top != eventWaiters) // let someone else take over
855	<	return;
856	<	}
857	<	else
825	<	break;      // possibly stale; reread
826	<	}
837	>	private void tryResumeSpare() {
838	>	int sw, id;
839	>	ForkJoinWorkerThread[] ws = workers;
840	>	int n = ws.length;
841	>	ForkJoinWorkerThread w;
842	>	if ((sw = spareWaiters) != 0 &&
843	>	(id = (sw & SPARE_ID_MASK) - 1) >= 0 &&
844	>	id < n && (w = ws[id]) != null &&
845	>	(runState >= TERMINATING ||
846	>	(workerCounts & RUNNING_COUNT_MASK) < parallelism) &&
847	>	spareWaiters == sw &&
848	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
849	>	sw, w.nextSpare)) {
850	>	int c; // increment running count before resume
851	>	do {} while (!UNSAFE.compareAndSwapInt
852	>	(this, workerCountsOffset,
853	>	c = workerCounts, c + ONE_RUNNING));
854	>	if (w.tryUnsuspend())
855	>	LockSupport.unpark(w);
856	>	else   // back out if w was shutdown
857	>	decrementWorkerCounts(ONE_RUNNING, 0);
858		}
859		}
860
861		/**
862	<	* If worker is inactive, blocks until terminating or event count
863	<	* advances from last value held by worker; in any case helps
864	<	* release others.
865	<	*
866	<	* @param w the calling worker thread
836	<	* @param retries the number of scans by caller failing to find work
837	<	* @return false if now too many threads running
862	>	* Tries to increase the number of running workers if below target
863	>	* parallelism: If a spare exists tries to resume it via
864	>	* tryResumeSpare.  Otherwise, if not enough total workers or all
865	>	* existing workers are busy, adds a new worker. In all cases also
866	>	* helps wake up releasable workers waiting for work.
867		*/
868	<	private boolean eventSync(ForkJoinWorkerThread w, int retries) {
869	<	int wec = w.lastEventCount;
870	<	if (retries > 1) { // can only block after 2nd miss
871	<	long nextTop = (((long)wec << EVENT_COUNT_SHIFT) |
872	<	((long)(w.poolIndex + 1)));
873	<	long top;
874	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
875	<	(((int)(top = eventWaiters) & WAITER_ID_MASK) == 0 ||
876	<	(int)(top >>> EVENT_COUNT_SHIFT) == wec) &&
877	<	eventCount == wec) {
878	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
879	<	w.nextWaiter = top, nextTop)) {
880	<	accumulateStealCount(w); // transfer steals while idle
881	<	Thread.interrupted();    // clear/ignore interrupt
882	<	while (eventCount == wec)
883	<	w.doPark();
868	>	private void helpMaintainParallelism() {
869	>	int pc = parallelism;
870	>	int wc, rs, tc;
871	>	while (((wc = workerCounts) & RUNNING_COUNT_MASK) < pc &&
872	>	(rs = runState) < TERMINATING) {
873	>	if (spareWaiters != 0)
874	>	tryResumeSpare();
875	>	else if ((tc = wc >>> TOTAL_COUNT_SHIFT) >= MAX_WORKERS ||
876	>	(tc >= pc && (rs & ACTIVE_COUNT_MASK) != tc))
877	>	break;   // enough total
878	>	else if (runState == rs && workerCounts == wc &&
879	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
880	>	wc + (ONE_RUNNING|ONE_TOTAL))) {
881	>	ForkJoinWorkerThread w = null;
882	>	Throwable fail = null;
883	>	try {
884	>	w = factory.newThread(this);
885	>	} catch (Throwable ex) {
886	>	fail = ex;
887	>	}
888	>	if (w == null) { // null or exceptional factory return
889	>	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
890	>	tryTerminate(false); // handle failure during shutdown
891	>	// If originating from an external caller,
892	>	// propagate exception, else ignore
893	>	if (fail != null && runState < TERMINATING &&
894	>	!(Thread.currentThread() instanceof
895	>	ForkJoinWorkerThread))
896	>	UNSAFE.throwException(fail);
897		break;
898		}
899	+	w.start(recordWorker(w), ueh);
900	+	if ((workerCounts >>> TOTAL_COUNT_SHIFT) >= pc)
901	+	break; // add at most one unless total below target
902		}
858	–	wec = eventCount;
903		}
904	<	releaseWaiters();
905	<	int wc = workerCounts;
906	<	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
907	<	w.lastEventCount = wec;
908	<	return true;
904	>	if (eventWaiters != 0L)
905	>	releaseEventWaiters();
906	>	}
907	>
908	>	/**
909	>	* Callback from the oldest waiter in awaitEvent waking up after a
910	>	* period of non-use. If all workers are idle, tries (once) to
911	>	* shutdown an event waiter or a spare, if one exists. Note that
912	>	* we don't need CAS or locks here because the method is called
913	>	* only from one thread occasionally waking (and even misfires are
914	>	* OK). Note that until the shutdown worker fully terminates,
915	>	* workerCounts will overestimate total count, which is tolerable.
916	>	*
917	>	* @param ec the event count waited on by caller (to abort
918	>	* attempt if count has since changed).
919	>	*/
920	>	private void tryShutdownUnusedWorker(int ec) {
921	>	if (runState == 0 && eventCount == ec) { // only trigger if all idle
922	>	ForkJoinWorkerThread[] ws = workers;
923	>	int n = ws.length;
924	>	ForkJoinWorkerThread w = null;
925	>	boolean shutdown = false;
926	>	int sw;
927	>	long h;
928	>	if ((sw = spareWaiters) != 0) { // prefer killing spares
929	>	int id = (sw & SPARE_ID_MASK) - 1;
930	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
931	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
932	>	sw, w.nextSpare))
933	>	shutdown = true;
934	>	}
935	>	else if ((h = eventWaiters) != 0L) {
936	>	long nh;
937	>	int id = (((int)h) & WAITER_ID_MASK) - 1;
938	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
939	>	(nh = w.nextWaiter) != 0L && // keep at least one worker
940	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh))
941	>	shutdown = true;
942	>	}
943	>	if (w != null && shutdown) {
944	>	w.shutdown();
945	>	LockSupport.unpark(w);
946	>	}
947		}
948	<	if (wec != w.lastEventCount) // back up if may re-wait
867	<	w.lastEventCount = wec - (wc >>> TOTAL_COUNT_SHIFT);
868	<	return false;
948	>	releaseEventWaiters(); // in case of interference
949		}
950
951		/**
952		* Callback from workers invoked upon each top-level action (i.e.,
953	<	* stealing a task or taking a submission and running
954	<	* it). Performs one or both of the following:
953	>	* stealing a task or taking a submission and running it).
954	>	* Performs one or more of the following:
955		*
956	<	* * If the worker cannot find work, updates its active status to
957	<	* inactive and updates activeCount unless there is contention, in
958	<	* which case it may try again (either in this or a subsequent
959	<	* call).  Additionally, awaits the next task event and/or helps
960	<	* wake up other releasable waiters.
961	<	*
962	<	* * If there are too many running threads, suspends this worker
963	<	* (first forcing inactivation if necessary).  If it is not
964	<	* resumed before a keepAlive elapses, the worker may be "trimmed"
965	<	* -- killed while suspended within suspendAsSpare. Otherwise,
966	<	* upon resume it rechecks to make sure that it is still needed.
956	>	* 1. If the worker is active and either did not run a task
957	>	*    or there are too many workers, try to set its active status
958	>	*    to inactive and update activeCount. On contention, we may
959	>	*    try again in this or a subsequent call.
960	>	*
961	>	* 2. If not enough total workers, help create some.
962	>	*
963	>	* 3. If there are too many running workers, suspend this worker
964	>	*    (first forcing inactive if necessary).  If it is not needed,
965	>	*    it may be shutdown while suspended (via
966	>	*    tryShutdownUnusedWorker).  Otherwise, upon resume it
967	>	*    rechecks running thread count and need for event sync.
968	>	*
969	>	* 4. If worker did not run a task, await the next task event via
970	>	*    eventSync if necessary (first forcing inactivation), upon
971	>	*    which the worker may be shutdown via
972	>	*    tryShutdownUnusedWorker.  Otherwise, help release any
973	>	*    existing event waiters that are now releasable,
974		*
975		* @param w the worker
976	<	* @param retries the number of scans by caller failing to find work
890	<	* find any (in which case it may block waiting for work).
976	>	* @param ran true if worker ran a task since last call to this method
977		*/
978	<	final void preStep(ForkJoinWorkerThread w, int retries) {
978	>	final void preStep(ForkJoinWorkerThread w, boolean ran) {
979	>	int wec = w.lastEventCount;
980		boolean active = w.active;
981	<	boolean inactivate = active && retries != 0;
982	<	for (;;) {
983	<	int rs, wc;
984	<	if (inactivate &&
985	<	UNSAFE.compareAndSwapInt(this, runStateOffset,
986	<	rs = runState, rs - ONE_ACTIVE))
981	>	boolean inactivate = false;
982	>	int pc = parallelism;
983	>	while (w.runState == 0) {
984	>	int rs = runState;
985	>	if (rs >= TERMINATING) {           // propagate shutdown
986	>	w.shutdown();
987	>	break;
988	>	}
989	>	if ((inactivate || (active && (rs & ACTIVE_COUNT_MASK) >= pc)) &&
990	>	UNSAFE.compareAndSwapInt(this, runStateOffset, rs, --rs)) {
991		inactivate = active = w.active = false;
992	<	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= parallelism) {
993	<	if (active || eventSync(w, retries))
994	<	break;
992	>	if (rs == SHUTDOWN) {          // all inactive and shut down
993	>	tryTerminate(false);
994	>	continue;
995	>	}
996	>	}
997	>	int wc = workerCounts;             // try to suspend as spare
998	>	if ((wc & RUNNING_COUNT_MASK) > pc) {
999	>	if (!(inactivate |= active) && // must inactivate to suspend
1000	>	workerCounts == wc &&
1001	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1002	>	wc, wc - ONE_RUNNING))
1003	>	w.suspendAsSpare();
1004		}
1005	<	else if (!(inactivate |= active) &&  // must inactivate to suspend
1006	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1007	<	wc, wc - ONE_RUNNING) &&
908	<	!w.suspendAsSpare())             // false if trimmed
1005	>	else if ((wc >>> TOTAL_COUNT_SHIFT) < pc)
1006	>	helpMaintainParallelism();     // not enough workers
1007	>	else if (ran)
1008		break;
1009	+	else {
1010	+	long h = eventWaiters;
1011	+	int ec = eventCount;
1012	+	if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != ec)
1013	+	releaseEventWaiters();     // release others before waiting
1014	+	else if (ec != wec) {
1015	+	w.lastEventCount = ec;     // no need to wait
1016	+	break;
1017	+	}
1018	+	else if (!(inactivate |= active))
1019	+	eventSync(w, wec);         // must inactivate before sync
1020	+	}
1021		}
1022		}
1023
1024		/**
1025	<	* Awaits join of the given task if enough threads, or can resume
1026	<	* or create a spare. Fails (in which case the given task might
916	<	* not be done) upon contention or lack of decision about
917	<	* blocking. Returns void because caller must check
918	<	* task status on return anyway.
919	<	*
920	<	* We allow blocking if:
921	<	*
922	<	* 1. There would still be at least as many running threads as
923	<	*    parallelism level if this thread blocks.
924	<	*
925	<	* 2. A spare is resumed to replace this worker. We tolerate
926	<	*    slop in the decision to replace if a spare is found without
927	<	*    first decrementing run count.  This may release too many,
928	<	*    but if so, the superfluous ones will re-suspend via
929	<	*    preStep().
930	<	*
931	<	* 3. After #spares repeated checks, there are no fewer than #spare
932	<	*    threads not running. We allow this slack to avoid hysteresis
933	<	*    and as a hedge against lag/uncertainty of running count
934	<	*    estimates when signalling or unblocking stalls.
935	<	*
936	<	* 4. All existing workers are busy (as rechecked via repeated
937	<	*    retries by caller) and a new spare is created.
938	<	*
939	<	* If none of the above hold, we try to escape out by
940	<	* re-incrementing count and returning to caller, which can retry
941	<	* later.
1025	>	* Helps and/or blocks awaiting join of the given task.
1026	>	* See above for explanation.
1027		*
1028		* @param joinMe the task to join
1029	<	* @param retries if negative, then serve only as a precheck
1030	<	*   that the thread can be replaced by a spare. Otherwise,
1031	<	*   the number of repeated calls to this method returning busy
1032	<	* @return true if the call must be retried because there
1033	<	*   none of the blocking checks hold
1034	<	*/
1035	<	final boolean tryAwaitJoin(ForkJoinTask<?> joinMe, int retries) {
1036	<	if (joinMe.status < 0) // precheck to prime loop
1037	<	return false;
1038	<	int pc = parallelism;
1039	<	boolean running = true; // false when running count decremented
1040	<	outer:for (;;) {
1029	>	* @param worker the current worker thread
1030	>	* @param timed true if wait should time out
1031	>	* @param nanos timeout value if timed
1032	>	*/
1033	>	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker,
1034	>	boolean timed, long nanos) {
1035	>	long startTime = timed? System.nanoTime() : 0L;
1036	>	int retries = 2 + (parallelism >> 2); // #helpJoins before blocking
1037	>	boolean running = true;               // false when count decremented
1038	>	while (joinMe.status >= 0) {
1039	>	if (runState >= TERMINATING) {
1040	>	joinMe.cancelIgnoringExceptions();
1041	>	break;
1042	>	}
1043	>	running = worker.helpJoinTask(joinMe, running);
1044	>	if (joinMe.status < 0)
1045	>	break;
1046	>	if (retries > 0) {
1047	>	--retries;
1048	>	continue;
1049	>	}
1050		int wc = workerCounts;
1051	<	int rc = wc & RUNNING_COUNT_MASK;
1052	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1053	<	if (running) { // replace with spare or decrement count
1054	<	if (rc <= pc && tc > pc &&
1055	<	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
1056	<	ForkJoinWorkerThread[] ws = workers;
963	<	int nws = ws.length;
964	<	for (int i = 0; i < nws; ++i) { // search for spare
965	<	ForkJoinWorkerThread w = ws[i];
966	<	if (w != null) {
967	<	if (joinMe.status < 0)
968	<	return false;
969	<	if (w.isSuspended()) {
970	<	if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
971	<	w.tryResumeSpare()) {
972	<	running = false;
973	<	break outer;
974	<	}
975	<	continue outer; // rescan
976	<	}
977	<	}
978	<	}
1051	>	if ((wc & RUNNING_COUNT_MASK) != 0) {
1052	>	if (running) {
1053	>	if (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1054	>	wc, wc - ONE_RUNNING))
1055	>	continue;
1056	>	running = false;
1057		}
1058	<	if (retries < 0 || // < 0 means replacement check only
1059	<	rc == 0 || joinMe.status < 0 || workerCounts != wc ||
1060	<	!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1061	<	wc, wc - ONE_RUNNING))
984	<	return false; // done or inconsistent or contended
985	<	running = false;
986	<	if (rc > pc)
987	<	break;
988	<	}
989	<	else { // allow blocking if enough threads
990	<	if (rc >= pc || joinMe.status < 0)
1058	>	long h = eventWaiters;
1059	>	if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1060	>	releaseEventWaiters();
1061	>	if (joinMe.status < 0)
1062		break;
1063	<	int sc = tc - pc + 1; // = spare threads, plus the one to add
1064	<	if (retries > sc) {
1065	<	if (rc > 0 && rc >= pc - sc) // allow slack
1066	<	break;
1067	<	if (tc < MAX_THREADS &&
997	<	tc == (runState & ACTIVE_COUNT_MASK) &&
998	<	workerCounts == wc &&
999	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1000	<	wc+(ONE_RUNNING|ONE_TOTAL))) {
1001	<	addWorker();
1002	<	break;
1063	>	if ((workerCounts & RUNNING_COUNT_MASK) != 0) {
1064	>	long ms; int ns;
1065	>	if (!timed) {
1066	>	ms = JOIN_TIMEOUT_MILLIS;
1067	>	ns = 0;
1068		}
1069	<	}
1070	<	if (workerCounts == wc &&        // back out to allow rescan
1071	<	UNSAFE.compareAndSwapInt (this, workerCountsOffset,
1072	<	wc, wc + ONE_RUNNING)) {
1073	<	releaseWaiters();            // help others progress
1074	<	return true;                 // let caller retry
1069	>	else { // at most JOIN_TIMEOUT_MILLIS per wait
1070	>	long nt = nanos - (System.nanoTime() - startTime);
1071	>	if (nt <= 0L)
1072	>	break;
1073	>	ms = nt / 1000000;
1074	>	if (ms > JOIN_TIMEOUT_MILLIS) {
1075	>	ms = JOIN_TIMEOUT_MILLIS;
1076	>	ns = 0;
1077	>	}
1078	>	else
1079	>	ns = (int) (nt % 1000000);
1080	>	}
1081	>	if (joinMe.internalAwaitDone(ms, ns) < 0)
1082	>	break;
1083		}
1084		}
1085	+	helpMaintainParallelism();
1086	+	}
1087	+	if (!running) {
1088	+	int c;
1089	+	do {} while (!UNSAFE.compareAndSwapInt
1090	+	(this, workerCountsOffset,
1091	+	c = workerCounts, c + ONE_RUNNING));
1092		}
1013	–	// arrive here if can block
1014	–	joinMe.internalAwaitDone();
1015	–	int c;                      // to inline incrementRunningCount
1016	–	do {} while (!UNSAFE.compareAndSwapInt
1017	–	(this, workerCountsOffset,
1018	–	c = workerCounts, c + ONE_RUNNING));
1019	–	return false;
1093		}
1094
1095		/**
1096	<	* Same idea as (and shares many code snippets with) tryAwaitJoin,
1024	<	* but self-contained because there are no caller retries.
1025	<	* TODO: Rework to use simpler API.
1096	>	* Same idea as awaitJoin, but no helping, retries, or timeouts.
1097		*/
1098		final void awaitBlocker(ManagedBlocker blocker)
1099		throws InterruptedException {
1100	<	boolean done;
1030	<	if (done = blocker.isReleasable())
1031	<	return;
1032	<	int pc = parallelism;
1033	<	int retries = 0;
1034	<	boolean running = true; // false when running count decremented
1035	<	outer:for (;;) {
1100	>	while (!blocker.isReleasable()) {
1101		int wc = workerCounts;
1102	<	int rc = wc & RUNNING_COUNT_MASK;
1103	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1104	<	if (running) {
1105	<	if (rc <= pc && tc > pc &&
1106	<	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
1107	<	ForkJoinWorkerThread[] ws = workers;
1108	<	int nws = ws.length;
1109	<	for (int i = 0; i < nws; ++i) {
1110	<	ForkJoinWorkerThread w = ws[i];
1111	<	if (w != null) {
1112	<	if (done = blocker.isReleasable())
1113	<	return;
1114	<	if (w.isSuspended()) {
1115	<	if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
1116	<	w.tryResumeSpare()) {
1052	<	running = false;
1053	<	break outer;
1054	<	}
1055	<	continue outer; // rescan
1056	<	}
1057	<	}
1058	<	}
1059	<	}
1060	<	if (done = blocker.isReleasable())
1061	<	return;
1062	<	if (rc == 0 || workerCounts != wc ||
1063	<	!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1064	<	wc, wc - ONE_RUNNING))
1065	<	continue;
1066	<	running = false;
1067	<	if (rc > pc)
1068	<	break;
1069	<	}
1070	<	else {
1071	<	if (rc >= pc || (done = blocker.isReleasable()))
1072	<	break;
1073	<	int sc = tc - pc + 1;
1074	<	if (retries++ > sc) {
1075	<	if (rc > 0 && rc >= pc - sc)
1076	<	break;
1077	<	if (tc < MAX_THREADS &&
1078	<	tc == (runState & ACTIVE_COUNT_MASK) &&
1079	<	workerCounts == wc &&
1080	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1081	<	wc+(ONE_RUNNING|ONE_TOTAL))) {
1082	<	addWorker();
1083	<	break;
1102	>	if ((wc & RUNNING_COUNT_MASK) == 0)
1103	>	helpMaintainParallelism();
1104	>	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1105	>	wc, wc - ONE_RUNNING)) {
1106	>	try {
1107	>	while (!blocker.isReleasable()) {
1108	>	long h = eventWaiters;
1109	>	if (h != 0L &&
1110	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1111	>	releaseEventWaiters();
1112	>	else if ((workerCounts & RUNNING_COUNT_MASK) == 0 &&
1113	>	runState < TERMINATING)
1114	>	helpMaintainParallelism();
1115	>	else if (blocker.block())
1116	>	break;
1117		}
1118	+	} finally {
1119	+	int c;
1120	+	do {} while (!UNSAFE.compareAndSwapInt
1121	+	(this, workerCountsOffset,
1122	+	c = workerCounts, c + ONE_RUNNING));
1123		}
1124	<	Thread.yield();
1087	<	}
1088	<	}
1089	<
1090	<	try {
1091	<	if (!done)
1092	<	do {} while (!blocker.isReleasable() && !blocker.block());
1093	<	} finally {
1094	<	if (!running) {
1095	<	int c;
1096	<	do {} while (!UNSAFE.compareAndSwapInt
1097	<	(this, workerCountsOffset,
1098	<	c = workerCounts, c + ONE_RUNNING));
1124	>	break;
1125		}
1126		}
1127	<	}
1127	>	}
1128
1129		/**
1130		* Possibly initiates and/or completes termination.
#	Line 1121 | Line 1147 | public class ForkJoinPool extends Abstra
1147		// Finish now if all threads terminated; else in some subsequent call
1148		if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1149		advanceRunLevel(TERMINATED);
1150	<	termination.arrive();
1150	>	termination.forceTermination();
1151		}
1152		return true;
1153		}
1154
1155		/**
1156		* Actions on transition to TERMINATING
1157	+	*
1158	+	* Runs up to four passes through workers: (0) shutting down each
1159	+	* (without waking up if parked) to quickly spread notifications
1160	+	* without unnecessary bouncing around event queues etc (1) wake
1161	+	* up and help cancel tasks (2) interrupt (3) mop up races with
1162	+	* interrupted workers
1163		*/
1164		private void startTerminating() {
1165	<	for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers
1166	<	cancelSubmissions();
1167	<	shutdownWorkers();
1168	<	cancelWorkerTasks();
1169	<	signalEvent();
1170	<	interruptWorkers();
1165	>	cancelSubmissions();
1166	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1167	>	int c; // advance event count
1168	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
1169	>	c = eventCount, c+1);
1170	>	eventWaiters = 0L; // clobber lists
1171	>	spareWaiters = 0;
1172	>	for (ForkJoinWorkerThread w : workers) {
1173	>	if (w != null) {
1174	>	w.shutdown();
1175	>	if (passes > 0 && !w.isTerminated()) {
1176	>	w.cancelTasks();
1177	>	LockSupport.unpark(w);
1178	>	if (passes > 1 && !w.isInterrupted()) {
1179	>	try {
1180	>	w.interrupt();
1181	>	} catch (SecurityException ignore) {
1182	>	}
1183	>	}
1184	>	}
1185	>	}
1186	>	}
1187		}
1188		}
1189
1190		/**
1191	<	* Clear out and cancel submissions, ignoring exceptions
1191	>	* Clears out and cancels submissions, ignoring exceptions.
1192		*/
1193		private void cancelSubmissions() {
1194		ForkJoinTask<?> task;
#	Line 1152 | Line 1200 | public class ForkJoinPool extends Abstra
1200		}
1201		}
1202
1155	–	/**
1156	–	* Sets all worker run states to at least shutdown,
1157	–	* also resuming suspended workers
1158	–	*/
1159	–	private void shutdownWorkers() {
1160	–	ForkJoinWorkerThread[] ws = workers;
1161	–	int nws = ws.length;
1162	–	for (int i = 0; i < nws; ++i) {
1163	–	ForkJoinWorkerThread w = ws[i];
1164	–	if (w != null)
1165	–	w.shutdown();
1166	–	}
1167	–	}
1168	–
1169	–	/**
1170	–	* Clears out and cancels all locally queued tasks
1171	–	*/
1172	–	private void cancelWorkerTasks() {
1173	–	ForkJoinWorkerThread[] ws = workers;
1174	–	int nws = ws.length;
1175	–	for (int i = 0; i < nws; ++i) {
1176	–	ForkJoinWorkerThread w = ws[i];
1177	–	if (w != null)
1178	–	w.cancelTasks();
1179	–	}
1180	–	}
1181	–
1182	–	/**
1183	–	* Unsticks all workers blocked on joins etc
1184	–	*/
1185	–	private void interruptWorkers() {
1186	–	ForkJoinWorkerThread[] ws = workers;
1187	–	int nws = ws.length;
1188	–	for (int i = 0; i < nws; ++i) {
1189	–	ForkJoinWorkerThread w = ws[i];
1190	–	if (w != null && !w.isTerminated()) {
1191	–	try {
1192	–	w.interrupt();
1193	–	} catch (SecurityException ignore) {
1194	–	}
1195	–	}
1196	–	}
1197	–	}
1198	–
1203		// misc support for ForkJoinWorkerThread
1204
1205		/**
1206	<	* Returns pool number
1206	>	* Returns pool number.
1207		*/
1208		final int getPoolNumber() {
1209		return poolNumber;
1210		}
1211
1212		/**
1213	<	* Accumulates steal count from a worker, clearing
1214	<	* the worker's value
1213	>	* Tries to accumulate steal count from a worker, clearing
1214	>	* the worker's value if successful.
1215	>	*
1216	>	* @return true if worker steal count now zero
1217		*/
1218	<	final void accumulateStealCount(ForkJoinWorkerThread w) {
1218	>	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1219		int sc = w.stealCount;
1220	<	if (sc != 0) {
1221	<	long c;
1222	<	w.stealCount = 0;
1223	<	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1224	<	c = stealCount, c + sc));
1220	>	long c = stealCount;
1221	>	// CAS even if zero, for fence effects
1222	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1223	>	if (sc != 0)
1224	>	w.stealCount = 0;
1225	>	return true;
1226		}
1227	+	return sc == 0;
1228		}
1229
1230		/**
#	Line 1225 | Line 1233 | public class ForkJoinPool extends Abstra
1233		*/
1234		final int idlePerActive() {
1235		int pc = parallelism; // use parallelism, not rc
1236	<	int ac = runState;    // no mask -- artifically boosts during shutdown
1236	>	int ac = runState;    // no mask -- artificially boosts during shutdown
1237		// Use exact results for small values, saturate past 4
1238	<	return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1238	>	return ((pc <= ac) ? 0 :
1239	>	(pc >>> 1 <= ac) ? 1 :
1240	>	(pc >>> 2 <= ac) ? 3 :
1241	>	pc >>> 3);
1242		}
1243
1244		// Public and protected methods
#	Line 1275 | Line 1286 | public class ForkJoinPool extends Abstra
1286		* use {@link java.lang.Runtime#availableProcessors}.
1287		* @param factory the factory for creating new threads. For default value,
1288		* use {@link #defaultForkJoinWorkerThreadFactory}.
1289	<	* @param handler the handler for internal worker threads that
1290	<	* terminate due to unrecoverable errors encountered while executing
1291	<	* tasks. For default value, use <code>null</code>.
1292	<	* @param asyncMode if true,
1289	>	* @param handler the handler for internal worker threads that
1290	>	* terminate due to unrecoverable errors encountered while executing
1291	>	* tasks. For default value, use {@code null}.
1292	>	* @param asyncMode if true,
1293		* establishes local first-in-first-out scheduling mode for forked
1294		* tasks that are never joined. This mode may be more appropriate
1295		* than default locally stack-based mode in applications in which
1296		* worker threads only process event-style asynchronous tasks.
1297	<	* For default value, use <code>false</code>.
1297	>	* For default value, use {@code false}.
1298		* @throws IllegalArgumentException if parallelism less than or
1299		*         equal to zero, or greater than implementation limit
1300		* @throws NullPointerException if the factory is null
#	Line 1292 | Line 1303 | public class ForkJoinPool extends Abstra
1303		*         because it does not hold {@link
1304		*         java.lang.RuntimePermission}{@code ("modifyThread")}
1305		*/
1306	<	public ForkJoinPool(int parallelism,
1306	>	public ForkJoinPool(int parallelism,
1307		ForkJoinWorkerThreadFactory factory,
1308		Thread.UncaughtExceptionHandler handler,
1309		boolean asyncMode) {
1310		checkPermission();
1311		if (factory == null)
1312		throw new NullPointerException();
1313	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1313	>	if (parallelism <= 0 || parallelism > MAX_WORKERS)
1314		throw new IllegalArgumentException();
1315		this.parallelism = parallelism;
1316		this.factory = factory;
#	Line 1318 | Line 1329 | public class ForkJoinPool extends Abstra
1329		* @param pc the initial parallelism level
1330		*/
1331		private static int initialArraySizeFor(int pc) {
1332	<	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1333	<	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1332	>	// If possible, initially allocate enough space for one spare
1333	>	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1334	>	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1335		size |= size >>> 1;
1336		size |= size >>> 2;
1337		size |= size >>> 4;
#	Line 1330 | Line 1342 | public class ForkJoinPool extends Abstra
1342		// Execution methods
1343
1344		/**
1345	<	* Common code for execute, invoke and submit
1345	>	* Submits task and creates, starts, or resumes some workers if necessary
1346		*/
1347		private <T> void doSubmit(ForkJoinTask<T> task) {
1336	–	if (task == null)
1337	–	throw new NullPointerException();
1338	–	if (runState >= SHUTDOWN)
1339	–	throw new RejectedExecutionException();
1348		submissionQueue.offer(task);
1349	<	signalEvent();
1350	<	ensureEnoughWorkers();
1349	>	int c; // try to increment event count -- CAS failure OK
1350	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
1351	>	helpMaintainParallelism();
1352		}
1353
1354		/**
1355		* Performs the given task, returning its result upon completion.
1347	–	* If the caller is already engaged in a fork/join computation in
1348	–	* the current pool, this method is equivalent in effect to
1349	–	* {@link ForkJoinTask#invoke}.
1356		*
1357		* @param task the task
1358		* @return the task's result
#	Line 1355 | Line 1361 | public class ForkJoinPool extends Abstra
1361		*         scheduled for execution
1362		*/
1363		public <T> T invoke(ForkJoinTask<T> task) {
1364	<	doSubmit(task);
1365	<	return task.join();
1364	>	if (task == null)
1365	>	throw new NullPointerException();
1366	>	if (runState >= SHUTDOWN)
1367	>	throw new RejectedExecutionException();
1368	>	Thread t = Thread.currentThread();
1369	>	if ((t instanceof ForkJoinWorkerThread) &&
1370	>	((ForkJoinWorkerThread)t).pool == this)
1371	>	return task.invoke();  // bypass submit if in same pool
1372	>	else {
1373	>	doSubmit(task);
1374	>	return task.join();
1375	>	}
1376	>	}
1377	>
1378	>	/**
1379	>	* Unless terminating, forks task if within an ongoing FJ
1380	>	* computation in the current pool, else submits as external task.
1381	>	*/
1382	>	private <T> void forkOrSubmit(ForkJoinTask<T> task) {
1383	>	if (runState >= SHUTDOWN)
1384	>	throw new RejectedExecutionException();
1385	>	Thread t = Thread.currentThread();
1386	>	if ((t instanceof ForkJoinWorkerThread) &&
1387	>	((ForkJoinWorkerThread)t).pool == this)
1388	>	task.fork();
1389	>	else
1390	>	doSubmit(task);
1391		}
1392
1393		/**
1394		* Arranges for (asynchronous) execution of the given task.
1364	–	* If the caller is already engaged in a fork/join computation in
1365	–	* the current pool, this method is equivalent in effect to
1366	–	* {@link ForkJoinTask#fork}.
1395		*
1396		* @param task the task
1397		* @throws NullPointerException if the task is null
#	Line 1371 | Line 1399 | public class ForkJoinPool extends Abstra
1399		*         scheduled for execution
1400		*/
1401		public void execute(ForkJoinTask<?> task) {
1402	<	doSubmit(task);
1402	>	if (task == null)
1403	>	throw new NullPointerException();
1404	>	forkOrSubmit(task);
1405		}
1406
1407		// AbstractExecutorService methods
#	Line 1382 | Line 1412 | public class ForkJoinPool extends Abstra
1412		*         scheduled for execution
1413		*/
1414		public void execute(Runnable task) {
1415	+	if (task == null)
1416	+	throw new NullPointerException();
1417		ForkJoinTask<?> job;
1418		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1419		job = (ForkJoinTask<?>) task;
1420		else
1421		job = ForkJoinTask.adapt(task, null);
1422	<	doSubmit(job);
1422	>	forkOrSubmit(job);
1423		}
1424
1425		/**
1426		* Submits a ForkJoinTask for execution.
1395	–	* If the caller is already engaged in a fork/join computation in
1396	–	* the current pool, this method is equivalent in effect to
1397	–	* {@link ForkJoinTask#fork}.
1427		*
1428		* @param task the task to submit
1429		* @return the task
#	Line 1403 | Line 1432 | public class ForkJoinPool extends Abstra
1432		*         scheduled for execution
1433		*/
1434		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1435	<	doSubmit(task);
1435	>	if (task == null)
1436	>	throw new NullPointerException();
1437	>	forkOrSubmit(task);
1438		return task;
1439		}
1440
#	Line 1413 | Line 1444 | public class ForkJoinPool extends Abstra
1444		*         scheduled for execution
1445		*/
1446		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1447	+	if (task == null)
1448	+	throw new NullPointerException();
1449		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1450	<	doSubmit(job);
1450	>	forkOrSubmit(job);
1451		return job;
1452		}
1453
#	Line 1424 | Line 1457 | public class ForkJoinPool extends Abstra
1457		*         scheduled for execution
1458		*/
1459		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1460	+	if (task == null)
1461	+	throw new NullPointerException();
1462		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1463	<	doSubmit(job);
1463	>	forkOrSubmit(job);
1464		return job;
1465		}
1466
#	Line 1435 | Line 1470 | public class ForkJoinPool extends Abstra
1470		*         scheduled for execution
1471		*/
1472		public ForkJoinTask<?> submit(Runnable task) {
1473	+	if (task == null)
1474	+	throw new NullPointerException();
1475		ForkJoinTask<?> job;
1476		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1477		job = (ForkJoinTask<?>) task;
1478		else
1479		job = ForkJoinTask.adapt(task, null);
1480	<	doSubmit(job);
1480	>	forkOrSubmit(job);
1481		return job;
1482		}
1483
#	Line 1500 | Line 1537 | public class ForkJoinPool extends Abstra
1537
1538		/**
1539		* Returns the number of worker threads that have started but not
1540	<	* yet terminated.  This result returned by this method may differ
1540	>	* yet terminated.  The result returned by this method may differ
1541		* from {@link #getParallelism} when threads are created to
1542		* maintain parallelism when others are cooperatively blocked.
1543		*
#	Line 1585 | Line 1622 | public class ForkJoinPool extends Abstra
1622		*/
1623		public long getQueuedTaskCount() {
1624		long count = 0;
1625	<	ForkJoinWorkerThread[] ws = workers;
1589	<	int nws = ws.length;
1590	<	for (int i = 0; i < nws; ++i) {
1591	<	ForkJoinWorkerThread w = ws[i];
1625	>	for (ForkJoinWorkerThread w : workers)
1626		if (w != null)
1627		count += w.getQueueSize();
1594	–	}
1628		return count;
1629		}
1630
#	Line 1645 | Line 1678 | public class ForkJoinPool extends Abstra
1678		* @return the number of elements transferred
1679		*/
1680		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1681	<	int n = submissionQueue.drainTo(c);
1682	<	ForkJoinWorkerThread[] ws = workers;
1650	<	int nws = ws.length;
1651	<	for (int i = 0; i < nws; ++i) {
1652	<	ForkJoinWorkerThread w = ws[i];
1653	<	if (w != null)
1654	<	n += w.drainTasksTo(c);
1655	<	}
1656	<	return n;
1657	<	}
1658	<
1659	<	/**
1660	<	* Returns count of total parks by existing workers.
1661	<	* Used during development only since not meaningful to users.
1662	<	*/
1663	<	private int collectParkCount() {
1664	<	int count = 0;
1665	<	ForkJoinWorkerThread[] ws = workers;
1666	<	int nws = ws.length;
1667	<	for (int i = 0; i < nws; ++i) {
1668	<	ForkJoinWorkerThread w = ws[i];
1681	>	int count = submissionQueue.drainTo(c);
1682	>	for (ForkJoinWorkerThread w : workers)
1683		if (w != null)
1684	<	count += w.parkCount;
1671	<	}
1684	>	count += w.drainTasksTo(c);
1685		return count;
1686		}
1687
#	Line 1689 | Line 1702 | public class ForkJoinPool extends Abstra
1702		int pc = parallelism;
1703		int rs = runState;
1704		int ac = rs & ACTIVE_COUNT_MASK;
1692	–	//        int pk = collectParkCount();
1705		return super.toString() +
1706		"[" + runLevelToString(rs) +
1707		", parallelism = " + pc +
#	Line 1699 | Line 1711 | public class ForkJoinPool extends Abstra
1711		", steals = " + st +
1712		", tasks = " + qt +
1713		", submissions = " + qs +
1702	–	//            ", parks = " + pk +
1714		"]";
1715		}
1716
#	Line 1774 | Line 1785 | public class ForkJoinPool extends Abstra
1785		}
1786
1787		/**
1788	+	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1789	+	*/
1790	+	final boolean isAtLeastTerminating() {
1791	+	return runState >= TERMINATING;
1792	+	}
1793	+
1794	+	/**
1795		* Returns {@code true} if this pool has been shut down.
1796		*
1797		* @return {@code true} if this pool has been shut down
#	Line 1796 | Line 1814 | public class ForkJoinPool extends Abstra
1814		public boolean awaitTermination(long timeout, TimeUnit unit)
1815		throws InterruptedException {
1816		try {
1817	<	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1818	<	} catch(TimeoutException ex) {
1817	>	termination.awaitAdvanceInterruptibly(0, timeout, unit);
1818	>	} catch (TimeoutException ex) {
1819		return false;
1820		}
1821	+	return true;
1822		}
1823
1824		/**
1825		* Interface for extending managed parallelism for tasks running
1826		* in {@link ForkJoinPool}s.
1827		*
1828	<	* <p>A {@code ManagedBlocker} provides two methods.
1829	<	* Method {@code isReleasable} must return {@code true} if
1830	<	* blocking is not necessary. Method {@code block} blocks the
1831	<	* current thread if necessary (perhaps internally invoking
1832	<	* {@code isReleasable} before actually blocking).
1828	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1829	>	* {@code isReleasable} must return {@code true} if blocking is
1830	>	* not necessary. Method {@code block} blocks the current thread
1831	>	* if necessary (perhaps internally invoking {@code isReleasable}
1832	>	* before actually blocking). The unusual methods in this API
1833	>	* accommodate synchronizers that may, but don't usually, block
1834	>	* for long periods. Similarly, they allow more efficient internal
1835	>	* handling of cases in which additional workers may be, but
1836	>	* usually are not, needed to ensure sufficient parallelism.
1837	>	* Toward this end, implementations of method {@code isReleasable}
1838	>	* must be amenable to repeated invocation.
1839		*
1840		* <p>For example, here is a ManagedBlocker based on a
1841		* ReentrantLock:
#	Line 1828 | Line 1853 | public class ForkJoinPool extends Abstra
1853		*     return hasLock || (hasLock = lock.tryLock());
1854		*   }
1855		* }}</pre>
1856	+	*
1857	+	* <p>Here is a class that possibly blocks waiting for an
1858	+	* item on a given queue:
1859	+	*  <pre> {@code
1860	+	* class QueueTaker<E> implements ManagedBlocker {
1861	+	*   final BlockingQueue<E> queue;
1862	+	*   volatile E item = null;
1863	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1864	+	*   public boolean block() throws InterruptedException {
1865	+	*     if (item == null)
1866	+	*       item = queue.take();
1867	+	*     return true;
1868	+	*   }
1869	+	*   public boolean isReleasable() {
1870	+	*     return item != null || (item = queue.poll()) != null;
1871	+	*   }
1872	+	*   public E getItem() { // call after pool.managedBlock completes
1873	+	*     return item;
1874	+	*   }
1875	+	* }}</pre>
1876		*/
1877		public static interface ManagedBlocker {
1878		/**
#	Line 1870 | Line 1915 | public class ForkJoinPool extends Abstra
1915		public static void managedBlock(ManagedBlocker blocker)
1916		throws InterruptedException {
1917		Thread t = Thread.currentThread();
1918	<	if (t instanceof ForkJoinWorkerThread)
1919	<	((ForkJoinWorkerThread) t).pool.awaitBlocker(blocker);
1918	>	if (t instanceof ForkJoinWorkerThread) {
1919	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1920	>	w.pool.awaitBlocker(blocker);
1921	>	}
1922		else {
1923		do {} while (!blocker.isReleasable() && !blocker.block());
1924		}
#	Line 1899 | Line 1946 | public class ForkJoinPool extends Abstra
1946		private static final long eventCountOffset =
1947		objectFieldOffset("eventCount", ForkJoinPool.class);
1948		private static final long eventWaitersOffset =
1949	<	objectFieldOffset("eventWaiters",ForkJoinPool.class);
1949	>	objectFieldOffset("eventWaiters", ForkJoinPool.class);
1950		private static final long stealCountOffset =
1951	<	objectFieldOffset("stealCount",ForkJoinPool.class);
1951	>	objectFieldOffset("stealCount", ForkJoinPool.class);
1952	>	private static final long spareWaitersOffset =
1953	>	objectFieldOffset("spareWaiters", ForkJoinPool.class);
1954
1955		private static long objectFieldOffset(String field, Class<?> klazz) {
1956		try {

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