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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.59 by dl, Fri Jul 23 14:09:17 2010 UTC vs.
Revision 1.82 by dl, Sun Oct 10 11:56:11 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 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 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 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_THREADS = 0x7fff;
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;
500	>	private static final long WAITER_ID_MASK    = (1L << 16) - 1L;
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;
#	Line 555 | Line 607 | public class ForkJoinPool extends Abstra
607		}
608
609		/**
610	<	* Tries to increment running count
611	<	*/
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.
610	>	* Forces decrement of encoded workerCounts, awaiting nonzero if
611	>	* (rarely) necessary when other count updates lag.
612		*
613	<	* @return true on success
613	>	* @param dr -- either zero or ONE_RUNNING
614	>	* @param dt -- either zero or ONE_TOTAL
615		*/
616	<	final boolean tryIncrementActiveCount() {
617	<	int c;
618	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
619	<	c = runState, c + ONE_ACTIVE);
616	>	private void decrementWorkerCounts(int dr, int dt) {
617	>	for (;;) {
618	>	int wc = workerCounts;
619	>	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
620	>	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) {
621	>	if ((runState & TERMINATED) != 0)
622	>	return; // lagging termination on a backout
623	>	Thread.yield();
624	>	}
625	>	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
626	>	wc, wc - (dr + dt)))
627	>	return;
628	>	}
629		}
630
631		/**
#	Line 582 | Line 635 | public class ForkJoinPool extends Abstra
635		final boolean tryDecrementActiveCount() {
636		int c;
637		return UNSAFE.compareAndSwapInt(this, runStateOffset,
638	<	c = runState, c - ONE_ACTIVE);
638	>	c = runState, c - 1);
639		}
640
641		/**
#	Line 611 | Line 664 | public class ForkJoinPool extends Abstra
664		lock.lock();
665		try {
666		ForkJoinWorkerThread[] ws = workers;
667	<	int nws = ws.length;
668	<	if (k < 0 || k >= nws || ws[k] != null) {
669	<	for (k = 0; k < nws && ws[k] != null; ++k)
667	>	int n = ws.length;
668	>	if (k < 0 || k >= n || ws[k] != null) {
669	>	for (k = 0; k < n && ws[k] != null; ++k)
670		;
671	<	if (k == nws)
672	<	ws = Arrays.copyOf(ws, nws << 1);
671	>	if (k == n)
672	>	ws = Arrays.copyOf(ws, n << 1);
673		}
674		ws[k] = w;
675		workers = ws; // volatile array write ensures slot visibility
#	Line 627 | Line 680 | public class ForkJoinPool extends Abstra
680		}
681
682		/**
683	<	* Nulls out record of worker in workers array
683	>	* Nulls out record of worker in workers array.
684		*/
685		private void forgetWorker(ForkJoinWorkerThread w) {
686		int idx = w.poolIndex;
687	<	// Locking helps method recordWorker avoid unecessary expansion
687	>	// Locking helps method recordWorker avoid unnecessary expansion
688		final ReentrantLock lock = this.workerLock;
689		lock.lock();
690		try {
#	Line 643 | Line 696 | public class ForkJoinPool extends Abstra
696		}
697		}
698
646	–	// adding and removing workers
647	–
699		/**
700	<	* Tries to create and add new worker. Assumes that worker counts
701	<	* are already updated to accommodate the worker, so adjusts on
702	<	* failure.
700	>	* Final callback from terminating worker.  Removes record of
701	>	* worker from array, and adjusts counts. If pool is shutting
702	>	* down, tries to complete termination.
703		*
704	<	* @return new worker or null if creation failed
704	>	* @param w the worker
705		*/
706	<	private ForkJoinWorkerThread addWorker() {
707	<	ForkJoinWorkerThread w = null;
708	<	try {
709	<	w = factory.newThread(this);
710	<	} finally { // Adjust on either null or exceptional factory return
711	<	if (w == null) {
661	<	onWorkerCreationFailure();
662	<	return null;
663	<	}
664	<	}
665	<	w.start(recordWorker(w), ueh);
666	<	return w;
706	>	final void workerTerminated(ForkJoinWorkerThread w) {
707	>	forgetWorker(w);
708	>	decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL);
709	>	while (w.stealCount != 0) // collect final count
710	>	tryAccumulateStealCount(w);
711	>	tryTerminate(false);
712		}
713
714	+	// Waiting for and signalling events
715	+
716		/**
717	<	* Adjusts counts upon failure to create worker
717	>	* Releases workers blocked on a count not equal to current count.
718	>	* Normally called after precheck that eventWaiters isn't zero to
719	>	* avoid wasted array checks. Gives up upon a change in count or
720	>	* upon releasing two workers, letting others take over.
721		*/
722	<	private void onWorkerCreationFailure() {
723	<	for (;;) {
724	<	int wc = workerCounts;
725	<	if ((wc >>> TOTAL_COUNT_SHIFT) == 0)
726	<	Thread.yield(); // wait for other counts to settle
727	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
728	<	wc - (ONE_RUNNING|ONE_TOTAL)))
722	>	private void releaseEventWaiters() {
723	>	ForkJoinWorkerThread[] ws = workers;
724	>	int n = ws.length;
725	>	long h = eventWaiters;
726	>	int ec = eventCount;
727	>	boolean releasedOne = false;
728	>	ForkJoinWorkerThread w; int id;
729	>	while ((id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 &&
730	>	(int)(h >>> EVENT_COUNT_SHIFT) != ec &&
731	>	id < n && (w = ws[id]) != null) {
732	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
733	>	h,  w.nextWaiter)) {
734	>	LockSupport.unpark(w);
735	>	if (releasedOne) // exit on second release
736	>	break;
737	>	releasedOne = true;
738	>	}
739	>	if (eventCount != ec)
740		break;
741	+	h = eventWaiters;
742		}
681	–	tryTerminate(false); // in case of failure during shutdown
743		}
744
745		/**
746	<	* Creates and/or resumes enough workers to establish target
747	<	* parallelism, giving up if terminating or addWorker fails
687	<	*
688	<	* TODO: recast this to support lazier creation and automated
689	<	* parallelism maintenance
746	>	* Tries to advance eventCount and releases waiters. Called only
747	>	* from workers.
748		*/
749	<	private void ensureEnoughWorkers() {
750	<	while ((runState & TERMINATING) == 0) {
751	<	int pc = parallelism;
752	<	int wc = workerCounts;
753	<	int rc = wc & RUNNING_COUNT_MASK;
696	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
697	<	if (tc < pc) {
698	<	if (UNSAFE.compareAndSwapInt
699	<	(this, workerCountsOffset,
700	<	wc, wc + (ONE_RUNNING|ONE_TOTAL)) &&
701	<	addWorker() == null)
702	<	break;
703	<	}
704	<	else if (tc > pc && rc < pc &&
705	<	tc > (runState & ACTIVE_COUNT_MASK)) {
706	<	ForkJoinWorkerThread spare = null;
707	<	ForkJoinWorkerThread[] ws = workers;
708	<	int nws = ws.length;
709	<	for (int i = 0; i < nws; ++i) {
710	<	ForkJoinWorkerThread w = ws[i];
711	<	if (w != null && w.isSuspended()) {
712	<	if ((workerCounts & RUNNING_COUNT_MASK) > pc)
713	<	return;
714	<	if (w.tryResumeSpare())
715	<	incrementRunningCount();
716	<	break;
717	<	}
718	<	}
719	<	}
720	<	else
721	<	break;
722	<	}
749	>	final void signalWork() {
750	>	int c; // try to increment event count -- CAS failure OK
751	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
752	>	if (eventWaiters != 0L)
753	>	releaseEventWaiters();
754		}
755
756		/**
757	<	* Final callback from terminating worker.  Removes record of
758	<	* worker from array, and adjusts counts. If pool is shutting
728	<	* down, tries to complete terminatation, else possibly replaces
729	<	* the worker.
757	>	* Adds the given worker to event queue and blocks until
758	>	* terminating or event count advances from the given value
759		*
760	<	* @param w the worker
760	>	* @param w the calling worker thread
761	>	* @param ec the count
762		*/
763	<	final void workerTerminated(ForkJoinWorkerThread w) {
764	<	if (w.active) { // force inactive
765	<	w.active = false;
766	<	do {} while (!tryDecrementActiveCount());
767	<	}
768	<	forgetWorker(w);
769	<
770	<	// Decrement total count, and if was running, running count
771	<	// Spin (waiting for other updates) if either would be negative
772	<	int nr = w.isTrimmed() ? 0 : ONE_RUNNING;
743	<	int unit = ONE_TOTAL + nr;
744	<	for (;;) {
745	<	int wc = workerCounts;
746	<	int rc = wc & RUNNING_COUNT_MASK;
747	<	if (rc - nr < 0 || (wc >>> TOTAL_COUNT_SHIFT) == 0)
748	<	Thread.yield(); // back off if waiting for other updates
749	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
750	<	wc, wc - unit))
763	>	private void eventSync(ForkJoinWorkerThread w, int ec) {
764	>	long nh = (((long)ec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
765	>	long h;
766	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
767	>	(((int)((h = eventWaiters) & WAITER_ID_MASK)) == 0 ||
768	>	(int)(h >>> EVENT_COUNT_SHIFT) == ec) &&
769	>	eventCount == ec) {
770	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
771	>	w.nextWaiter = h, nh)) {
772	>	awaitEvent(w, ec);
773		break;
774	+	}
775		}
753	–
754	–	accumulateStealCount(w); // collect final count
755	–	if (!tryTerminate(false))
756	–	ensureEnoughWorkers();
776		}
777
759	–	// Waiting for and signalling events
760	–
778		/**
779	<	* Releases workers blocked on a count not equal to current count.
780	<	* @return true if any released
779	>	* Blocks the given worker (that has already been entered as an
780	>	* event waiter) until terminating or event count advances from
781	>	* the given value. The oldest (first) waiter uses a timed wait to
782	>	* occasionally one-by-one shrink the number of workers (to a
783	>	* minimum of one) if the pool has not been used for extended
784	>	* periods.
785	>	*
786	>	* @param w the calling worker thread
787	>	* @param ec the count
788		*/
789	<	private void releaseWaiters() {
790	<	long top;
791	<	while ((top = eventWaiters) != 0L) {
792	<	ForkJoinWorkerThread[] ws = workers;
793	<	int n = ws.length;
794	<	for (;;) {
795	<	int i = ((int)(top & WAITER_ID_MASK)) - 1;
796	<	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == eventCount)
797	<	return;
798	<	ForkJoinWorkerThread w;
799	<	if (i < n && (w = ws[i]) != null &&
800	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
801	<	top, w.nextWaiter)) {
802	<	LockSupport.unpark(w);
803	<	top = eventWaiters;
789	>	private void awaitEvent(ForkJoinWorkerThread w, int ec) {
790	>	while (eventCount == ec) {
791	>	if (tryAccumulateStealCount(w)) { // transfer while idle
792	>	boolean untimed = (w.nextWaiter != 0L ||
793	>	(workerCounts & RUNNING_COUNT_MASK) <= 1);
794	>	long startTime = untimed? 0 : System.nanoTime();
795	>	Thread.interrupted();         // clear/ignore interrupt
796	>	if (eventCount != ec || w.isTerminating())
797	>	break;                    // recheck after clear
798	>	if (untimed)
799	>	LockSupport.park(w);
800	>	else {
801	>	LockSupport.parkNanos(w, SHRINK_RATE_NANOS);
802	>	if (eventCount != ec || w.isTerminating())
803	>	break;
804	>	if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS)
805	>	tryShutdownUnusedWorker(ec);
806		}
781	–	else
782	–	break;      // possibly stale; reread
807		}
808		}
809		}
810
811	+	// Maintaining parallelism
812	+
813		/**
814	<	* Ensures eventCount on exit is different (mod 2^32) than on
789	<	* entry and wakes up all waiters
814	>	* Pushes worker onto the spare stack.
815		*/
816	<	private void signalEvent() {
817	<	int c;
818	<	do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset,
819	<	c = eventCount, c+1));
795	<	releaseWaiters();
816	>	final void pushSpare(ForkJoinWorkerThread w) {
817	>	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1);
818	>	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
819	>	w.nextSpare = spareWaiters,ns));
820		}
821
822		/**
823	<	* Advances eventCount and releases waiters until interference by
824	<	* other releasing threads is detected.
823	>	* Tries (once) to resume a spare if the number of running
824	>	* threads is less than target.
825		*/
826	<	final void signalWork() {
827	<	int c;
828	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, c=eventCount, c+1);
829	<	long top;
830	<	while ((top = eventWaiters) != 0L) {
831	<	int ec = eventCount;
832	<	ForkJoinWorkerThread[] ws = workers;
833	<	int n = ws.length;
834	<	for (;;) {
835	<	int i = ((int)(top & WAITER_ID_MASK)) - 1;
836	<	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
837	<	return;
838	<	ForkJoinWorkerThread w;
839	<	if (i < n && (w = ws[i]) != null &&
840	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
841	<	top, top = w.nextWaiter)) {
842	<	LockSupport.unpark(w);
843	<	if (top != eventWaiters) // let someone else take over
844	<	return;
845	<	}
822	<	else
823	<	break;      // possibly stale; reread
824	<	}
826	>	private void tryResumeSpare() {
827	>	int sw, id;
828	>	ForkJoinWorkerThread[] ws = workers;
829	>	int n = ws.length;
830	>	ForkJoinWorkerThread w;
831	>	if ((sw = spareWaiters) != 0 &&
832	>	(id = (sw & SPARE_ID_MASK) - 1) >= 0 &&
833	>	id < n && (w = ws[id]) != null &&
834	>	(workerCounts & RUNNING_COUNT_MASK) < parallelism &&
835	>	spareWaiters == sw &&
836	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
837	>	sw, w.nextSpare)) {
838	>	int c; // increment running count before resume
839	>	do {} while (!UNSAFE.compareAndSwapInt
840	>	(this, workerCountsOffset,
841	>	c = workerCounts, c + ONE_RUNNING));
842	>	if (w.tryUnsuspend())
843	>	LockSupport.unpark(w);
844	>	else   // back out if w was shutdown
845	>	decrementWorkerCounts(ONE_RUNNING, 0);
846		}
847		}
848
849		/**
850	<	* If worker is inactive, blocks until terminating or event count
851	<	* advances from last value held by worker; in any case helps
852	<	* release others.
853	<	*
854	<	* @param w the calling worker thread
834	<	* @param retries the number of scans by caller failing to find work
835	<	* @return false if now too many threads running
850	>	* Tries to increase the number of running workers if below target
851	>	* parallelism: If a spare exists tries to resume it via
852	>	* tryResumeSpare.  Otherwise, if not enough total workers or all
853	>	* existing workers are busy, adds a new worker. In all cases also
854	>	* helps wake up releasable workers waiting for work.
855		*/
856	<	private boolean eventSync(ForkJoinWorkerThread w, int retries) {
857	<	int wec = w.lastEventCount;
858	<	if (retries > 1) { // can only block after 2nd miss
859	<	long nextTop = (((long)wec << EVENT_COUNT_SHIFT) |
860	<	((long)(w.poolIndex + 1)));
861	<	long top;
862	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
863	<	(((int)(top = eventWaiters) & WAITER_ID_MASK) == 0 ||
864	<	(int)(top >>> EVENT_COUNT_SHIFT) == wec) &&
865	<	eventCount == wec) {
866	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
867	<	w.nextWaiter = top, nextTop)) {
868	<	accumulateStealCount(w); // transfer steals while idle
869	<	Thread.interrupted();    // clear/ignore interrupt
870	<	while (eventCount == wec)
871	<	w.doPark();
856	>	private void helpMaintainParallelism() {
857	>	int pc = parallelism;
858	>	int wc, rs, tc;
859	>	while (((wc = workerCounts) & RUNNING_COUNT_MASK) < pc &&
860	>	(rs = runState) < TERMINATING) {
861	>	if (spareWaiters != 0)
862	>	tryResumeSpare();
863	>	else if ((tc = wc >>> TOTAL_COUNT_SHIFT) >= MAX_WORKERS ||
864	>	(tc >= pc && (rs & ACTIVE_COUNT_MASK) != tc))
865	>	break;   // enough total
866	>	else if (runState == rs && workerCounts == wc &&
867	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
868	>	wc + (ONE_RUNNING|ONE_TOTAL))) {
869	>	ForkJoinWorkerThread w = null;
870	>	Throwable fail = null;
871	>	try {
872	>	w = factory.newThread(this);
873	>	} catch (Throwable ex) {
874	>	fail = ex;
875	>	}
876	>	if (w == null) { // null or exceptional factory return
877	>	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
878	>	tryTerminate(false); // handle failure during shutdown
879	>	// If originating from an external caller,
880	>	// propagate exception, else ignore
881	>	if (fail != null && runState < TERMINATING &&
882	>	!(Thread.currentThread() instanceof
883	>	ForkJoinWorkerThread))
884	>	UNSAFE.throwException(fail);
885		break;
886		}
887	+	w.start(recordWorker(w), ueh);
888	+	if ((workerCounts >>> TOTAL_COUNT_SHIFT) >= pc) {
889	+	int c; // advance event count
890	+	UNSAFE.compareAndSwapInt(this, eventCountOffset,
891	+	c = eventCount, c+1);
892	+	break; // add at most one unless total below target
893	+	}
894		}
856	–	wec = eventCount;
895		}
896	<	releaseWaiters();
897	<	int wc = workerCounts;
898	<	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
899	<	w.lastEventCount = wec;
900	<	return true;
896	>	if (eventWaiters != 0L)
897	>	releaseEventWaiters();
898	>	}
899	>
900	>	/**
901	>	* Callback from the oldest waiter in awaitEvent waking up after a
902	>	* period of non-use. If all workers are idle, tries (once) to
903	>	* shutdown an event waiter or a spare, if one exists. Note that
904	>	* we don't need CAS or locks here because the method is called
905	>	* only from one thread occasionally waking (and even misfires are
906	>	* OK). Note that until the shutdown worker fully terminates,
907	>	* workerCounts will overestimate total count, which is tolerable.
908	>	*
909	>	* @param ec the event count waited on by caller (to abort
910	>	* attempt if count has since changed).
911	>	*/
912	>	private void tryShutdownUnusedWorker(int ec) {
913	>	if (runState == 0 && eventCount == ec) { // only trigger if all idle
914	>	ForkJoinWorkerThread[] ws = workers;
915	>	int n = ws.length;
916	>	ForkJoinWorkerThread w = null;
917	>	boolean shutdown = false;
918	>	int sw;
919	>	long h;
920	>	if ((sw = spareWaiters) != 0) { // prefer killing spares
921	>	int id = (sw & SPARE_ID_MASK) - 1;
922	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
923	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
924	>	sw, w.nextSpare))
925	>	shutdown = true;
926	>	}
927	>	else if ((h = eventWaiters) != 0L) {
928	>	long nh;
929	>	int id = ((int)(h & WAITER_ID_MASK)) - 1;
930	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
931	>	(nh = w.nextWaiter) != 0L && // keep at least one worker
932	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh))
933	>	shutdown = true;
934	>	}
935	>	if (w != null && shutdown) {
936	>	w.shutdown();
937	>	LockSupport.unpark(w);
938	>	}
939		}
940	<	if (wec != w.lastEventCount) // back up if may re-wait
865	<	w.lastEventCount = wec - (wc >>> TOTAL_COUNT_SHIFT);
866	<	return false;
940	>	releaseEventWaiters(); // in case of interference
941		}
942
943		/**
944		* Callback from workers invoked upon each top-level action (i.e.,
945	<	* stealing a task or taking a submission and running
946	<	* it). Performs one or both of the following:
945	>	* stealing a task or taking a submission and running it).
946	>	* Performs one or more of the following:
947		*
948	<	* * If the worker cannot find work, updates its active status to
949	<	* inactive and updates activeCount unless there is contention, in
950	<	* which case it may try again (either in this or a subsequent
951	<	* call).  Additionally, awaits the next task event and/or helps
952	<	* wake up other releasable waiters.
953	<	*
954	<	* * If there are too many running threads, suspends this worker
955	<	* (first forcing inactivation if necessary).  If it is not
956	<	* resumed before a keepAlive elapses, the worker may be "trimmed"
957	<	* -- killed while suspended within suspendAsSpare. Otherwise,
958	<	* upon resume it rechecks to make sure that it is still needed.
948	>	* 1. If the worker is active and either did not run a task
949	>	*    or there are too many workers, try to set its active status
950	>	*    to inactive and update activeCount. On contention, we may
951	>	*    try again in this or a subsequent call.
952	>	*
953	>	* 2. If not enough total workers, help create some.
954	>	*
955	>	* 3. If there are too many running workers, suspend this worker
956	>	*    (first forcing inactive if necessary).  If it is not needed,
957	>	*    it may be shutdown while suspended (via
958	>	*    tryShutdownUnusedWorker).  Otherwise, upon resume it
959	>	*    rechecks running thread count and need for event sync.
960	>	*
961	>	* 4. If worker did not run a task, await the next task event via
962	>	*    eventSync if necessary (first forcing inactivation), upon
963	>	*    which the worker may be shutdown via
964	>	*    tryShutdownUnusedWorker.  Otherwise, help release any
965	>	*    existing event waiters that are now releasable,
966		*
967		* @param w the worker
968	<	* @param retries the number of scans by caller failing to find work
888	<	* find any (in which case it may block waiting for work).
968	>	* @param ran true if worker ran a task since last call to this method
969		*/
970	<	final void preStep(ForkJoinWorkerThread w, int retries) {
970	>	final void preStep(ForkJoinWorkerThread w, boolean ran) {
971	>	int wec = w.lastEventCount;
972		boolean active = w.active;
973	<	boolean inactivate = active && retries != 0;
974	<	for (;;) {
975	<	int rs, wc;
976	<	if (inactivate &&
977	<	UNSAFE.compareAndSwapInt(this, runStateOffset,
978	<	rs = runState, rs - ONE_ACTIVE))
973	>	boolean inactivate = false;
974	>	int pc = parallelism;
975	>	while (w.runState == 0) {
976	>	int rs = runState;
977	>	if (rs >= TERMINATING) { // propagate shutdown
978	>	w.shutdown();
979	>	break;
980	>	}
981	>	if ((inactivate || (active && (rs & ACTIVE_COUNT_MASK) >= pc)) &&
982	>	UNSAFE.compareAndSwapInt(this, runStateOffset, rs, rs - 1))
983		inactivate = active = w.active = false;
984	<	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= parallelism) {
985	<	if (active || eventSync(w, retries))
984	>	int wc = workerCounts;
985	>	if ((wc & RUNNING_COUNT_MASK) > pc) {
986	>	if (!(inactivate |= active) && // must inactivate to suspend
987	>	workerCounts == wc &&      // try to suspend as spare
988	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
989	>	wc, wc - ONE_RUNNING))
990	>	w.suspendAsSpare();
991	>	}
992	>	else if ((wc >>> TOTAL_COUNT_SHIFT) < pc)
993	>	helpMaintainParallelism();     // not enough workers
994	>	else if (!ran) {
995	>	long h = eventWaiters;
996	>	int ec = eventCount;
997	>	if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != ec)
998	>	releaseEventWaiters();     // release others before waiting
999	>	else if (ec != wec) {
1000	>	w.lastEventCount = ec;     // no need to wait
1001		break;
1002	+	}
1003	+	else if (!(inactivate |= active))
1004	+	eventSync(w, wec);         // must inactivate before sync
1005		}
1006	<	else if (!(inactivate |= active) &&  // must inactivate to suspend
904	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
905	<	wc, wc - ONE_RUNNING) &&
906	<	!w.suspendAsSpare())             // false if trimmed
1006	>	else
1007		break;
1008		}
1009		}
1010
1011		/**
1012	<	* Awaits join of the given task if enough threads, or can resume
1013	<	* or create a spare. Fails (in which case the given task might
914	<	* not be done) upon contention or lack of decision about
915	<	* blocking. Returns void because caller must check
916	<	* task status on return anyway.
917	<	*
918	<	* We allow blocking if:
919	<	*
920	<	* 1. There would still be at least as many running threads as
921	<	*    parallelism level if this thread blocks.
922	<	*
923	<	* 2. A spare is resumed to replace this worker. We tolerate
924	<	*    slop in the decision to replace if a spare is found without
925	<	*    first decrementing run count.  This may release too many,
926	<	*    but if so, the superfluous ones will re-suspend via
927	<	*    preStep().
928	<	*
929	<	* 3. After #spares repeated checks, there are no fewer than #spare
930	<	*    threads not running. We allow this slack to avoid hysteresis
931	<	*    and as a hedge against lag/uncertainty of running count
932	<	*    estimates when signalling or unblocking stalls.
933	<	*
934	<	* 4. All existing workers are busy (as rechecked via repeated
935	<	*    retries by caller) and a new spare is created.
936	<	*
937	<	* If none of the above hold, we try to escape out by
938	<	* re-incrementing count and returning to caller, which can retry
939	<	* later.
1012	>	* Helps and/or blocks awaiting join of the given task.
1013	>	* See above for explanation.
1014		*
1015		* @param joinMe the task to join
1016	<	* @param retries if negative, then serve only as a precheck
943	<	*   that the thread can be replaced by a spare. Otherwise,
944	<	*   the number of repeated calls to this method returning busy
945	<	* @return true if the call must be retried because there
946	<	*   none of the blocking checks hold
1016	>	* @param worker the current worker thread
1017		*/
1018	<	final boolean tryAwaitJoin(ForkJoinTask<?> joinMe, int retries) {
1019	<	if (joinMe.status < 0) // precheck for cancellation
1020	<	return false;
1021	<	if ((runState & TERMINATING) != 0) { // shutting down
1022	<	joinMe.cancelIgnoringExceptions();
1023	<	return false;
1024	<	}
955	<
956	<	int pc = parallelism;
957	<	boolean running = true; // false when running count decremented
958	<	outer:for (;;) {
959	<	int wc = workerCounts;
960	<	int rc = wc & RUNNING_COUNT_MASK;
961	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
962	<	if (running) { // replace with spare or decrement count
963	<	if (rc <= pc && tc > pc &&
964	<	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
965	<	ForkJoinWorkerThread[] ws = workers;
966	<	int nws = ws.length;
967	<	for (int i = 0; i < nws; ++i) { // search for spare
968	<	ForkJoinWorkerThread w = ws[i];
969	<	if (w != null) {
970	<	if (joinMe.status < 0)
971	<	return false;
972	<	if (w.isSuspended()) {
973	<	if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
974	<	w.tryResumeSpare()) {
975	<	running = false;
976	<	break outer;
977	<	}
978	<	continue outer; // rescan
979	<	}
980	<	}
981	<	}
982	<	}
983	<	if (retries < 0 || // < 0 means replacement check only
984	<	rc == 0 || joinMe.status < 0 || workerCounts != wc ||
985	<	!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
986	<	wc, wc - ONE_RUNNING))
987	<	return false; // done or inconsistent or contended
988	<	running = false;
989	<	if (rc > pc)
990	<	break;
1018	>	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) {
1019	>	int retries = 2 + (parallelism >> 2); // #helpJoins before blocking
1020	>	while (joinMe.status >= 0) {
1021	>	int wc;
1022	>	if (runState >= TERMINATING) {
1023	>	joinMe.cancelIgnoringExceptions();
1024	>	break;
1025		}
1026	<	else { // allow blocking if enough threads
1027	<	if (rc >= pc || joinMe.status < 0)
1028	<	break;
1029	<	int sc = tc - pc + 1; // = spare threads, plus the one to add
1030	<	if (retries > sc) {
1031	<	if (rc > 0 && rc >= pc - sc) // allow slack
1032	<	break;
1033	<	if (tc < MAX_THREADS &&
1034	<	tc == (runState & ACTIVE_COUNT_MASK) &&
1035	<	workerCounts == wc &&
1036	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1037	<	wc+(ONE_RUNNING|ONE_TOTAL))) {
1038	<	addWorker();
1039	<	break;
1040	<	}
1041	<	}
1042	<	if (workerCounts == wc &&        // back out to allow rescan
1043	<	UNSAFE.compareAndSwapInt (this, workerCountsOffset,
1044	<	wc, wc + ONE_RUNNING)) {
1045	<	releaseWaiters();            // help others progress
1046	<	return true;                 // let caller retry
1047	<	}
1026	>	worker.helpJoinTask(joinMe);
1027	>	if (joinMe.status < 0)
1028	>	break;
1029	>	else if (retries > 0)
1030	>	--retries;
1031	>	else if (((wc = workerCounts) & RUNNING_COUNT_MASK) != 0 &&
1032	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1033	>	wc, wc - ONE_RUNNING)) {
1034	>	int stat, c; long h;
1035	>	while ((stat = joinMe.status) >= 0 &&
1036	>	(h = eventWaiters) != 0L && // help release others
1037	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1038	>	releaseEventWaiters();
1039	>	if (stat >= 0 &&
1040	>	((workerCounts & RUNNING_COUNT_MASK) == 0 ||
1041	>	(stat =
1042	>	joinMe.internalAwaitDone(JOIN_TIMEOUT_MILLIS)) >= 0))
1043	>	helpMaintainParallelism(); // timeout or no running workers
1044	>	do {} while (!UNSAFE.compareAndSwapInt
1045	>	(this, workerCountsOffset,
1046	>	c = workerCounts, c + ONE_RUNNING));
1047	>	if (stat < 0)
1048	>	break;   // else restart
1049		}
1050		}
1016	–	// arrive here if can block
1017	–	joinMe.internalAwaitDone();
1018	–	int c;                      // to inline incrementRunningCount
1019	–	do {} while (!UNSAFE.compareAndSwapInt
1020	–	(this, workerCountsOffset,
1021	–	c = workerCounts, c + ONE_RUNNING));
1022	–	return false;
1051		}
1052
1053		/**
1054	<	* Same idea as (and shares many code snippets with) tryAwaitJoin,
1027	<	* but self-contained because there are no caller retries.
1028	<	* TODO: Rework to use simpler API.
1054	>	* Same idea as awaitJoin, but no helping, retries, or timeouts.
1055		*/
1056		final void awaitBlocker(ManagedBlocker blocker)
1057		throws InterruptedException {
1058	<	boolean done;
1033	<	if (done = blocker.isReleasable())
1034	<	return;
1035	<	int pc = parallelism;
1036	<	int retries = 0;
1037	<	boolean running = true; // false when running count decremented
1038	<	outer:for (;;) {
1058	>	while (!blocker.isReleasable()) {
1059		int wc = workerCounts;
1060	<	int rc = wc & RUNNING_COUNT_MASK;
1061	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1062	<	if (running) {
1063	<	if (rc <= pc && tc > pc &&
1064	<	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
1065	<	ForkJoinWorkerThread[] ws = workers;
1066	<	int nws = ws.length;
1067	<	for (int i = 0; i < nws; ++i) {
1068	<	ForkJoinWorkerThread w = ws[i];
1069	<	if (w != null) {
1070	<	if (done = blocker.isReleasable())
1071	<	return;
1072	<	if (w.isSuspended()) {
1073	<	if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
1054	<	w.tryResumeSpare()) {
1055	<	running = false;
1056	<	break outer;
1057	<	}
1058	<	continue outer; // rescan
1059	<	}
1060	<	}
1061	<	}
1062	<	}
1063	<	if (done = blocker.isReleasable())
1064	<	return;
1065	<	if (rc == 0 || workerCounts != wc ||
1066	<	!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1067	<	wc, wc - ONE_RUNNING))
1068	<	continue;
1069	<	running = false;
1070	<	if (rc > pc)
1071	<	break;
1072	<	}
1073	<	else {
1074	<	if (rc >= pc || (done = blocker.isReleasable()))
1075	<	break;
1076	<	int sc = tc - pc + 1;
1077	<	if (retries++ > sc) {
1078	<	if (rc > 0 && rc >= pc - sc)
1079	<	break;
1080	<	if (tc < MAX_THREADS &&
1081	<	tc == (runState & ACTIVE_COUNT_MASK) &&
1082	<	workerCounts == wc &&
1083	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1084	<	wc+(ONE_RUNNING|ONE_TOTAL))) {
1085	<	addWorker();
1086	<	break;
1060	>	if ((wc & RUNNING_COUNT_MASK) != 0 &&
1061	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1062	>	wc, wc - ONE_RUNNING)) {
1063	>	try {
1064	>	while (!blocker.isReleasable()) {
1065	>	long h = eventWaiters;
1066	>	if (h != 0L &&
1067	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1068	>	releaseEventWaiters();
1069	>	else if ((workerCounts & RUNNING_COUNT_MASK) == 0 &&
1070	>	runState < TERMINATING)
1071	>	helpMaintainParallelism();
1072	>	else if (blocker.block())
1073	>	break;
1074		}
1075	+	} finally {
1076	+	int c;
1077	+	do {} while (!UNSAFE.compareAndSwapInt
1078	+	(this, workerCountsOffset,
1079	+	c = workerCounts, c + ONE_RUNNING));
1080		}
1081	<	Thread.yield();
1090	<	}
1091	<	}
1092	<
1093	<	try {
1094	<	if (!done)
1095	<	do {} while (!blocker.isReleasable() && !blocker.block());
1096	<	} finally {
1097	<	if (!running) {
1098	<	int c;
1099	<	do {} while (!UNSAFE.compareAndSwapInt
1100	<	(this, workerCountsOffset,
1101	<	c = workerCounts, c + ONE_RUNNING));
1081	>	break;
1082		}
1083		}
1084		}
#	Line 1129 | Line 1109 | public class ForkJoinPool extends Abstra
1109		return true;
1110		}
1111
1112	+
1113		/**
1114		* Actions on transition to TERMINATING
1115	+	*
1116	+	* Runs up to four passes through workers: (0) shutting down each
1117	+	* (without waking up if parked) to quickly spread notifications
1118	+	* without unnecessary bouncing around event queues etc (1) wake
1119	+	* up and help cancel tasks (2) interrupt (3) mop up races with
1120	+	* interrupted workers
1121		*/
1122		private void startTerminating() {
1123	<	for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers
1124	<	cancelSubmissions();
1125	<	shutdownWorkers();
1126	<	cancelWorkerTasks();
1127	<	signalEvent();
1128	<	interruptWorkers();
1123	>	cancelSubmissions();
1124	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1125	>	int c; // advance event count
1126	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
1127	>	c = eventCount, c+1);
1128	>	eventWaiters = 0L; // clobber lists
1129	>	spareWaiters = 0;
1130	>	for (ForkJoinWorkerThread w : workers) {
1131	>	if (w != null) {
1132	>	w.shutdown();
1133	>	if (passes > 0 && !w.isTerminated()) {
1134	>	w.cancelTasks();
1135	>	LockSupport.unpark(w);
1136	>	if (passes > 1 && !w.isInterrupted()) {
1137	>	try {
1138	>	w.interrupt();
1139	>	} catch (SecurityException ignore) {
1140	>	}
1141	>	}
1142	>	}
1143	>	}
1144	>	}
1145		}
1146		}
1147
1148		/**
1149	<	* Clear out and cancel submissions, ignoring exceptions
1149	>	* Clears out and cancels submissions, ignoring exceptions.
1150		*/
1151		private void cancelSubmissions() {
1152		ForkJoinTask<?> task;
#	Line 1155 | Line 1158 | public class ForkJoinPool extends Abstra
1158		}
1159		}
1160
1158	–	/**
1159	–	* Sets all worker run states to at least shutdown,
1160	–	* also resuming suspended workers
1161	–	*/
1162	–	private void shutdownWorkers() {
1163	–	ForkJoinWorkerThread[] ws = workers;
1164	–	int nws = ws.length;
1165	–	for (int i = 0; i < nws; ++i) {
1166	–	ForkJoinWorkerThread w = ws[i];
1167	–	if (w != null)
1168	–	w.shutdown();
1169	–	}
1170	–	}
1171	–
1172	–	/**
1173	–	* Clears out and cancels all locally queued tasks
1174	–	*/
1175	–	private void cancelWorkerTasks() {
1176	–	ForkJoinWorkerThread[] ws = workers;
1177	–	int nws = ws.length;
1178	–	for (int i = 0; i < nws; ++i) {
1179	–	ForkJoinWorkerThread w = ws[i];
1180	–	if (w != null)
1181	–	w.cancelTasks();
1182	–	}
1183	–	}
1184	–
1185	–	/**
1186	–	* Unsticks all workers blocked on joins etc
1187	–	*/
1188	–	private void interruptWorkers() {
1189	–	ForkJoinWorkerThread[] ws = workers;
1190	–	int nws = ws.length;
1191	–	for (int i = 0; i < nws; ++i) {
1192	–	ForkJoinWorkerThread w = ws[i];
1193	–	if (w != null && !w.isTerminated()) {
1194	–	try {
1195	–	w.interrupt();
1196	–	} catch (SecurityException ignore) {
1197	–	}
1198	–	}
1199	–	}
1200	–	}
1201	–
1161		// misc support for ForkJoinWorkerThread
1162
1163		/**
1164	<	* Returns pool number
1164	>	* Returns pool number.
1165		*/
1166		final int getPoolNumber() {
1167		return poolNumber;
1168		}
1169
1170		/**
1171	<	* Accumulates steal count from a worker, clearing
1172	<	* the worker's value
1171	>	* Tries to accumulate steal count from a worker, clearing
1172	>	* the worker's value if successful.
1173	>	*
1174	>	* @return true if worker steal count now zero
1175		*/
1176	<	final void accumulateStealCount(ForkJoinWorkerThread w) {
1176	>	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1177		int sc = w.stealCount;
1178	<	if (sc != 0) {
1179	<	long c;
1180	<	w.stealCount = 0;
1181	<	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1182	<	c = stealCount, c + sc));
1178	>	long c = stealCount;
1179	>	// CAS even if zero, for fence effects
1180	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1181	>	if (sc != 0)
1182	>	w.stealCount = 0;
1183	>	return true;
1184		}
1185	+	return sc == 0;
1186		}
1187
1188		/**
#	Line 1228 | Line 1191 | public class ForkJoinPool extends Abstra
1191		*/
1192		final int idlePerActive() {
1193		int pc = parallelism; // use parallelism, not rc
1194	<	int ac = runState;    // no mask -- artifically boosts during shutdown
1194	>	int ac = runState;    // no mask -- artificially boosts during shutdown
1195		// Use exact results for small values, saturate past 4
1196	<	return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1196	>	return ((pc <= ac) ? 0 :
1197	>	(pc >>> 1 <= ac) ? 1 :
1198	>	(pc >>> 2 <= ac) ? 3 :
1199	>	pc >>> 3);
1200		}
1201
1202		// Public and protected methods
#	Line 1280 | Line 1246 | public class ForkJoinPool extends Abstra
1246		* use {@link #defaultForkJoinWorkerThreadFactory}.
1247		* @param handler the handler for internal worker threads that
1248		* terminate due to unrecoverable errors encountered while executing
1249	<	* tasks. For default value, use <code>null</code>.
1249	>	* tasks. For default value, use {@code null}.
1250		* @param asyncMode if true,
1251		* establishes local first-in-first-out scheduling mode for forked
1252		* tasks that are never joined. This mode may be more appropriate
1253		* than default locally stack-based mode in applications in which
1254		* worker threads only process event-style asynchronous tasks.
1255	<	* For default value, use <code>false</code>.
1255	>	* For default value, use {@code false}.
1256		* @throws IllegalArgumentException if parallelism less than or
1257		*         equal to zero, or greater than implementation limit
1258		* @throws NullPointerException if the factory is null
#	Line 1302 | Line 1268 | public class ForkJoinPool extends Abstra
1268		checkPermission();
1269		if (factory == null)
1270		throw new NullPointerException();
1271	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1271	>	if (parallelism <= 0 || parallelism > MAX_WORKERS)
1272		throw new IllegalArgumentException();
1273		this.parallelism = parallelism;
1274		this.factory = factory;
#	Line 1321 | Line 1287 | public class ForkJoinPool extends Abstra
1287		* @param pc the initial parallelism level
1288		*/
1289		private static int initialArraySizeFor(int pc) {
1290	<	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1291	<	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1290	>	// If possible, initially allocate enough space for one spare
1291	>	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1292	>	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1293		size |= size >>> 1;
1294		size |= size >>> 2;
1295		size |= size >>> 4;
#	Line 1333 | Line 1300 | public class ForkJoinPool extends Abstra
1300		// Execution methods
1301
1302		/**
1303	<	* Common code for execute, invoke and submit
1303	>	* Submits task and creates, starts, or resumes some workers if necessary
1304		*/
1305		private <T> void doSubmit(ForkJoinTask<T> task) {
1339	–	if (task == null)
1340	–	throw new NullPointerException();
1341	–	if (runState >= SHUTDOWN)
1342	–	throw new RejectedExecutionException();
1306		submissionQueue.offer(task);
1307	<	signalEvent();
1308	<	ensureEnoughWorkers();
1307	>	int c; // try to increment event count -- CAS failure OK
1308	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
1309	>	helpMaintainParallelism();
1310		}
1311
1312		/**
1313		* Performs the given task, returning its result upon completion.
1350	–	* If the caller is already engaged in a fork/join computation in
1351	–	* the current pool, this method is equivalent in effect to
1352	–	* {@link ForkJoinTask#invoke}.
1314		*
1315		* @param task the task
1316		* @return the task's result
#	Line 1358 | Line 1319 | public class ForkJoinPool extends Abstra
1319		*         scheduled for execution
1320		*/
1321		public <T> T invoke(ForkJoinTask<T> task) {
1322	<	doSubmit(task);
1323	<	return task.join();
1322	>	if (task == null)
1323	>	throw new NullPointerException();
1324	>	if (runState >= SHUTDOWN)
1325	>	throw new RejectedExecutionException();
1326	>	Thread t = Thread.currentThread();
1327	>	if ((t instanceof ForkJoinWorkerThread) &&
1328	>	((ForkJoinWorkerThread)t).pool == this)
1329	>	return task.invoke();  // bypass submit if in same pool
1330	>	else {
1331	>	doSubmit(task);
1332	>	return task.join();
1333	>	}
1334	>	}
1335	>
1336	>	/**
1337	>	* Unless terminating, forks task if within an ongoing FJ
1338	>	* computation in the current pool, else submits as external task.
1339	>	*/
1340	>	private <T> void forkOrSubmit(ForkJoinTask<T> task) {
1341	>	if (runState >= SHUTDOWN)
1342	>	throw new RejectedExecutionException();
1343	>	Thread t = Thread.currentThread();
1344	>	if ((t instanceof ForkJoinWorkerThread) &&
1345	>	((ForkJoinWorkerThread)t).pool == this)
1346	>	task.fork();
1347	>	else
1348	>	doSubmit(task);
1349		}
1350
1351		/**
1352		* Arranges for (asynchronous) execution of the given task.
1367	–	* If the caller is already engaged in a fork/join computation in
1368	–	* the current pool, this method is equivalent in effect to
1369	–	* {@link ForkJoinTask#fork}.
1353		*
1354		* @param task the task
1355		* @throws NullPointerException if the task is null
#	Line 1374 | Line 1357 | public class ForkJoinPool extends Abstra
1357		*         scheduled for execution
1358		*/
1359		public void execute(ForkJoinTask<?> task) {
1360	<	doSubmit(task);
1360	>	if (task == null)
1361	>	throw new NullPointerException();
1362	>	forkOrSubmit(task);
1363		}
1364
1365		// AbstractExecutorService methods
#	Line 1385 | Line 1370 | public class ForkJoinPool extends Abstra
1370		*         scheduled for execution
1371		*/
1372		public void execute(Runnable task) {
1373	+	if (task == null)
1374	+	throw new NullPointerException();
1375		ForkJoinTask<?> job;
1376		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1377		job = (ForkJoinTask<?>) task;
1378		else
1379		job = ForkJoinTask.adapt(task, null);
1380	<	doSubmit(job);
1380	>	forkOrSubmit(job);
1381		}
1382
1383		/**
1384		* Submits a ForkJoinTask for execution.
1398	–	* If the caller is already engaged in a fork/join computation in
1399	–	* the current pool, this method is equivalent in effect to
1400	–	* {@link ForkJoinTask#fork}.
1385		*
1386		* @param task the task to submit
1387		* @return the task
#	Line 1406 | Line 1390 | public class ForkJoinPool extends Abstra
1390		*         scheduled for execution
1391		*/
1392		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1393	<	doSubmit(task);
1393	>	if (task == null)
1394	>	throw new NullPointerException();
1395	>	forkOrSubmit(task);
1396		return task;
1397		}
1398
#	Line 1416 | Line 1402 | public class ForkJoinPool extends Abstra
1402		*         scheduled for execution
1403		*/
1404		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1405	+	if (task == null)
1406	+	throw new NullPointerException();
1407		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1408	<	doSubmit(job);
1408	>	forkOrSubmit(job);
1409		return job;
1410		}
1411
#	Line 1427 | Line 1415 | public class ForkJoinPool extends Abstra
1415		*         scheduled for execution
1416		*/
1417		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1418	+	if (task == null)
1419	+	throw new NullPointerException();
1420		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1421	<	doSubmit(job);
1421	>	forkOrSubmit(job);
1422		return job;
1423		}
1424
#	Line 1438 | Line 1428 | public class ForkJoinPool extends Abstra
1428		*         scheduled for execution
1429		*/
1430		public ForkJoinTask<?> submit(Runnable task) {
1431	+	if (task == null)
1432	+	throw new NullPointerException();
1433		ForkJoinTask<?> job;
1434		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1435		job = (ForkJoinTask<?>) task;
1436		else
1437		job = ForkJoinTask.adapt(task, null);
1438	<	doSubmit(job);
1438	>	forkOrSubmit(job);
1439		return job;
1440		}
1441
#	Line 1503 | Line 1495 | public class ForkJoinPool extends Abstra
1495
1496		/**
1497		* Returns the number of worker threads that have started but not
1498	<	* yet terminated.  This result returned by this method may differ
1498	>	* yet terminated.  The result returned by this method may differ
1499		* from {@link #getParallelism} when threads are created to
1500		* maintain parallelism when others are cooperatively blocked.
1501		*
#	Line 1588 | Line 1580 | public class ForkJoinPool extends Abstra
1580		*/
1581		public long getQueuedTaskCount() {
1582		long count = 0;
1583	<	ForkJoinWorkerThread[] ws = workers;
1592	<	int nws = ws.length;
1593	<	for (int i = 0; i < nws; ++i) {
1594	<	ForkJoinWorkerThread w = ws[i];
1583	>	for (ForkJoinWorkerThread w : workers)
1584		if (w != null)
1585		count += w.getQueueSize();
1597	–	}
1586		return count;
1587		}
1588
#	Line 1648 | Line 1636 | public class ForkJoinPool extends Abstra
1636		* @return the number of elements transferred
1637		*/
1638		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1639	<	int n = submissionQueue.drainTo(c);
1640	<	ForkJoinWorkerThread[] ws = workers;
1653	<	int nws = ws.length;
1654	<	for (int i = 0; i < nws; ++i) {
1655	<	ForkJoinWorkerThread w = ws[i];
1639	>	int count = submissionQueue.drainTo(c);
1640	>	for (ForkJoinWorkerThread w : workers)
1641		if (w != null)
1642	<	n += w.drainTasksTo(c);
1658	<	}
1659	<	return n;
1660	<	}
1661	<
1662	<	/**
1663	<	* Returns count of total parks by existing workers.
1664	<	* Used during development only since not meaningful to users.
1665	<	*/
1666	<	private int collectParkCount() {
1667	<	int count = 0;
1668	<	ForkJoinWorkerThread[] ws = workers;
1669	<	int nws = ws.length;
1670	<	for (int i = 0; i < nws; ++i) {
1671	<	ForkJoinWorkerThread w = ws[i];
1672	<	if (w != null)
1673	<	count += w.parkCount;
1674	<	}
1642	>	count += w.drainTasksTo(c);
1643		return count;
1644		}
1645
#	Line 1692 | Line 1660 | public class ForkJoinPool extends Abstra
1660		int pc = parallelism;
1661		int rs = runState;
1662		int ac = rs & ACTIVE_COUNT_MASK;
1695	–	//        int pk = collectParkCount();
1663		return super.toString() +
1664		"[" + runLevelToString(rs) +
1665		", parallelism = " + pc +
#	Line 1702 | Line 1669 | public class ForkJoinPool extends Abstra
1669		", steals = " + st +
1670		", tasks = " + qt +
1671		", submissions = " + qs +
1705	–	//            ", parks = " + pk +
1672		"]";
1673		}
1674
#	Line 1777 | Line 1743 | public class ForkJoinPool extends Abstra
1743		}
1744
1745		/**
1746	+	* Returns true if terminating or terminated. Used by ForkJoinWorkerThread.
1747	+	*/
1748	+	final boolean isAtLeastTerminating() {
1749	+	return runState >= TERMINATING;
1750	+	}
1751	+
1752	+	/**
1753		* Returns {@code true} if this pool has been shut down.
1754		*
1755		* @return {@code true} if this pool has been shut down
#	Line 1800 | Line 1773 | public class ForkJoinPool extends Abstra
1773		throws InterruptedException {
1774		try {
1775		return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1776	<	} catch(TimeoutException ex) {
1776	>	} catch (TimeoutException ex) {
1777		return false;
1778		}
1779		}
#	Line 1809 | Line 1782 | public class ForkJoinPool extends Abstra
1782		* Interface for extending managed parallelism for tasks running
1783		* in {@link ForkJoinPool}s.
1784		*
1785	<	* <p>A {@code ManagedBlocker} provides two methods.
1786	<	* Method {@code isReleasable} must return {@code true} if
1787	<	* blocking is not necessary. Method {@code block} blocks the
1788	<	* current thread if necessary (perhaps internally invoking
1789	<	* {@code isReleasable} before actually blocking).
1785	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1786	>	* {@code isReleasable} must return {@code true} if blocking is
1787	>	* not necessary. Method {@code block} blocks the current thread
1788	>	* if necessary (perhaps internally invoking {@code isReleasable}
1789	>	* before actually blocking). The unusual methods in this API
1790	>	* accommodate synchronizers that may, but don't usually, block
1791	>	* for long periods. Similarly, they allow more efficient internal
1792	>	* handling of cases in which additional workers may be, but
1793	>	* usually are not, needed to ensure sufficient parallelism.
1794	>	* Toward this end, implementations of method {@code isReleasable}
1795	>	* must be amenable to repeated invocation.
1796		*
1797		* <p>For example, here is a ManagedBlocker based on a
1798		* ReentrantLock:
#	Line 1831 | Line 1810 | public class ForkJoinPool extends Abstra
1810		*     return hasLock || (hasLock = lock.tryLock());
1811		*   }
1812		* }}</pre>
1813	+	*
1814	+	* <p>Here is a class that possibly blocks waiting for an
1815	+	* item on a given queue:
1816	+	*  <pre> {@code
1817	+	* class QueueTaker<E> implements ManagedBlocker {
1818	+	*   final BlockingQueue<E> queue;
1819	+	*   volatile E item = null;
1820	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1821	+	*   public boolean block() throws InterruptedException {
1822	+	*     if (item == null)
1823	+	*       item = queue.take();
1824	+	*     return true;
1825	+	*   }
1826	+	*   public boolean isReleasable() {
1827	+	*     return item != null || (item = queue.poll()) != null;
1828	+	*   }
1829	+	*   public E getItem() { // call after pool.managedBlock completes
1830	+	*     return item;
1831	+	*   }
1832	+	* }}</pre>
1833		*/
1834		public static interface ManagedBlocker {
1835		/**
#	Line 1873 | Line 1872 | public class ForkJoinPool extends Abstra
1872		public static void managedBlock(ManagedBlocker blocker)
1873		throws InterruptedException {
1874		Thread t = Thread.currentThread();
1875	<	if (t instanceof ForkJoinWorkerThread)
1876	<	((ForkJoinWorkerThread) t).pool.awaitBlocker(blocker);
1875	>	if (t instanceof ForkJoinWorkerThread) {
1876	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1877	>	w.pool.awaitBlocker(blocker);
1878	>	}
1879		else {
1880		do {} while (!blocker.isReleasable() && !blocker.block());
1881		}
#	Line 1902 | Line 1903 | public class ForkJoinPool extends Abstra
1903		private static final long eventCountOffset =
1904		objectFieldOffset("eventCount", ForkJoinPool.class);
1905		private static final long eventWaitersOffset =
1906	<	objectFieldOffset("eventWaiters",ForkJoinPool.class);
1906	>	objectFieldOffset("eventWaiters", ForkJoinPool.class);
1907		private static final long stealCountOffset =
1908	<	objectFieldOffset("stealCount",ForkJoinPool.class);
1908	>	objectFieldOffset("stealCount", ForkJoinPool.class);
1909	>	private static final long spareWaitersOffset =
1910	>	objectFieldOffset("spareWaiters", ForkJoinPool.class);
1911
1912		private static long objectFieldOffset(String field, Class<?> klazz) {
1913		try {

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