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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 1.69 by jsr166, Wed Sep 1 20:12:39 2010 UTC

#	Line 52 | Line 52 | import java.util.concurrent.CountDownLat
52		* convenient form for informal monitoring.
53		*
54		* <p> As is the case with other ExecutorServices, there are three
55	<	* main task execution methods summarized in the follwoing
55	>	* main task execution methods summarized in the following
56		* table. These are designed to be used by clients not already engaged
57		* in fork/join computations in the current pool.  The main forms of
58		* these methods accept instances of {@code ForkJoinTask}, but
#	Line 69 | Line 69 | import java.util.concurrent.CountDownLat
69		*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
70		*  </tr>
71		*  <tr>
72	<	*    <td> <b>Arange async execution</td>
72	>	*    <td> <b>Arrange async execution</td>
73		*    <td> {@link #execute(ForkJoinTask)}</td>
74		*    <td> {@link ForkJoinTask#fork}</td>
75		*  </tr>
#	Line 110 | Line 110 | import java.util.concurrent.CountDownLat
110		*
111		* <p>This implementation rejects submitted tasks (that is, by throwing
112		* {@link RejectedExecutionException}) only when the pool is shut down
113	<	* or internal resources have been exhuasted.
113	>	* or internal resources have been exhausted.
114		*
115		* @since 1.7
116		* @author Doug Lea
#	Line 138 | Line 138 | public class ForkJoinPool extends Abstra
138		* cache pollution effects.)
139		*
140		* Beyond work-stealing support and essential bookkeeping, the
141	<	* main responsibility of this framework is to arrange tactics for
142	<	* when one worker is waiting to join a task stolen (or always
143	<	* held by) another.  Becauae we are multiplexing many tasks on to
144	<	* a pool of workers, we can't just let them block (as in
145	<	* Thread.join).  We also cannot just reassign the joiner's
146	<	* run-time stack with another and replace it later, which would
147	<	* be a form of "continuation", that even if possible is not
148	<	* necessarily a good idea. Given that the creation costs of most
149	<	* threads on most systems mainly surrounds setting up runtime
150	<	* stacks, thread creation and switching is usually not much more
151	<	* expensive than stack creation and switching, and is more
152	<	* flexible). Instead we combine two tactics:
141	>	* main responsibility of this framework is to take actions when
142	>	* one worker is waiting to join a task stolen (or always held by)
143	>	* another.  Because we are multiplexing many tasks on to a pool
144	>	* of workers, we can't just let them block (as in Thread.join).
145	>	* We also cannot just reassign the joiner's run-time stack with
146	>	* another and replace it later, which would be a form of
147	>	* "continuation", that even if possible is not necessarily a good
148	>	* idea. Given that the creation costs of most threads on most
149	>	* systems mainly surrounds setting up runtime stacks, thread
150	>	* creation and switching is usually not much more expensive than
151	>	* stack creation and switching, and is more flexible). Instead we
152	>	* combine two tactics:
153		*
154	<	*   1. Arranging for the joiner to execute some task that it
154	>	*   Helping: Arranging for the joiner to execute some task that it
155		*      would be running if the steal had not occurred.  Method
156		*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
157		*      links to try to find such a task.
158		*
159	<	*   2. Unless there are already enough live threads, creating or
160	<	*      or re-activating a spare thread to compensate for the
161	<	*      (blocked) joiner until it unblocks.  Spares then suspend
162	<	*      at their next opportunity or eventually die if unused for
163	<	*      too long.  See below and the internal documentation
164	<	*      for tryAwaitJoin for more details about compensation
165	<	*      rules.
166	<	*
167	<	* Because the determining existence of conservatively safe
168	<	* helping targets, the availability of already-created spares,
169	<	* and the apparent need to create new spares are all racy and
170	<	* require heuristic guidance, joins (in
171	<	* ForkJoinWorkerThread.joinTask) interleave these options until
172	<	* successful.  Creating a new spare always succeeds, but also
173	<	* increases application footprint, so we try to avoid it, within
174	<	* reason.
159	>	*   Compensating: Unless there are already enough live threads,
160	>	*      method helpMaintainParallelism() may create or
161	>	*      re-activate a spare thread to compensate for blocked
162	>	*      joiners until they unblock.
163	>	*
164	>	* It is impossible to keep exactly the target (parallelism)
165	>	* number of threads running at any given time.  Determining
166	>	* existence of conservatively safe helping targets, the
167	>	* availability of already-created spares, and the apparent need
168	>	* to create new spares are all racy and require heuristic
169	>	* guidance, so we rely on multiple retries of each.  Compensation
170	>	* occurs in slow-motion. It is triggered only upon timeouts of
171	>	* Object.wait used for joins. This reduces poor decisions that
172	>	* would otherwise be made when threads are waiting for others
173	>	* that are stalled because of unrelated activities such as
174	>	* garbage collection.
175		*
176	<	* The ManagedBlocker extension API can't use option (1) so uses a
177	<	* special version of (2) in method awaitBlocker.
176	>	* The ManagedBlocker extension API can't use helping so relies
177	>	* only on compensation in method awaitBlocker.
178		*
179		* The main throughput advantages of work-stealing stem from
180		* decentralized control -- workers mostly steal tasks from each
#	Line 207 | Line 207 | public class ForkJoinPool extends Abstra
207		* blocked workers. However, all other support code is set up to
208		* work with other policies.
209		*
210	+	* To ensure that we do not hold on to worker references that
211	+	* would prevent GC, ALL accesses to workers are via indices into
212	+	* the workers array (which is one source of some of the unusual
213	+	* code constructions here). In essence, the workers array serves
214	+	* as a WeakReference mechanism. Thus for example the event queue
215	+	* stores worker indices, not worker references. Access to the
216	+	* workers in associated methods (for example releaseEventWaiters)
217	+	* must both index-check and null-check the IDs. All such accesses
218	+	* ignore bad IDs by returning out early from what they are doing,
219	+	* since this can only be associated with shutdown, in which case
220	+	* it is OK to give up. On termination, we just clobber these
221	+	* data structures without trying to use them.
222	+	*
223		* 2. Bookkeeping for dynamically adding and removing workers. We
224		* aim to approximately maintain the given level of parallelism.
225		* When some workers are known to be blocked (on joins or via
226		* ManagedBlocker), we may create or resume others to take their
227		* place until they unblock (see below). Implementing this
228		* requires counts of the number of "running" threads (i.e., those
229	<	* that are neither blocked nor artifically suspended) as well as
229	>	* that are neither blocked nor artificially suspended) as well as
230		* the total number.  These two values are packed into one field,
231		* "workerCounts" because we need accurate snapshots when deciding
232		* to create, resume or suspend.  Note however that the
233	<	* correspondance of these counts to reality is not guaranteed. In
233	>	* correspondence of these counts to reality is not guaranteed. In
234		* particular updates for unblocked threads may lag until they
235		* actually wake up.
236		*
#	Line 248 | Line 261 | public class ForkJoinPool extends Abstra
261		* workers that previously could not find a task to now find one:
262		* Submission of a new task to the pool, or another worker pushing
263		* a task onto a previously empty queue.  (We also use this
264	<	* mechanism for termination and reconfiguration actions that
264	>	* mechanism for configuration and termination actions that
265		* require wakeups of idle workers).  Each worker maintains its
266		* last known event count, and blocks when a scan for work did not
267		* find a task AND its lastEventCount matches the current
#	Line 259 | Line 272 | public class ForkJoinPool extends Abstra
272		* a record (field nextEventWaiter) for the next waiting worker.
273		* In addition to allowing simpler decisions about need for
274		* wakeup, the event count bits in eventWaiters serve the role of
275	<	* tags to avoid ABA errors in Treiber stacks.  To reduce delays
276	<	* in task diffusion, workers not otherwise occupied may invoke
277	<	* method releaseWaiters, that removes and signals (unparks)
278	<	* workers not waiting on current count. To minimize task
279	<	* production stalls associate with signalling, any worker pushing
280	<	* 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.
275	>	* tags to avoid ABA errors in Treiber stacks. Upon any wakeup,
276	>	* released threads also try to release at most two others.  The
277	>	* net effect is a tree-like diffusion of signals, where released
278	>	* threads (and possibly others) help with unparks.  To further
279	>	* reduce contention effects a bit, failed CASes to increment
280	>	* field eventCount are tolerated without retries in signalWork.
281		* Conceptually they are merged into the same event, which is OK
282		* when their only purpose is to enable workers to scan for work.
283		*
284	<	* 5. Managing suspension of extra workers. When a worker is about
285	<	* to block waiting for a join (or via ManagedBlockers), we may
286	<	* create a new thread to maintain parallelism level, or at least
287	<	* avoid starvation. Usually, extra threads are needed for only
288	<	* very short periods, yet join dependencies are such that we
289	<	* sometimes need them in bursts. Rather than create new threads
290	<	* each time this happens, we suspend no-longer-needed extra ones
291	<	* as "spares". For most purposes, we don't distinguish "extra"
292	<	* spare threads from normal "core" threads: On each call to
293	<	* preStep (the only point at which we can do this) a worker
294	<	* checks to see if there are now too many running workers, and if
295	<	* so, suspends itself.  Methods tryAwaitJoin and awaitBlocker
296	<	* look for suspended threads to resume before considering
297	<	* creating a new replacement. We don't need a special data
298	<	* structure to maintain spares; simply scanning the workers array
299	<	* looking for worker.isSuspended() is fine because the calling
300	<	* thread is otherwise not doing anything useful anyway; we are at
301	<	* least as happy if after locating a spare, the caller doesn't
302	<	* actually block because the join is ready before we try to
303	<	* adjust and compensate.  Note that this is intrinsically racy.
304	<	* One thread may become a spare at about the same time as another
305	<	* is needlessly being created. We counteract this and related
306	<	* slop in part by requiring resumed spares to immediately recheck
307	<	* (in preStep) to see whether they they should re-suspend. The
308	<	* only effective difference between "extra" and "core" threads is
309	<	* that we allow the "extra" ones to time out and die if they are
310	<	* not resumed within a keep-alive interval of a few seconds. This
311	<	* is implemented mainly within ForkJoinWorkerThread, but requires
312	<	* some coordination (isTrimmed() -- meaning killed while
313	<	* suspended) to correctly maintain pool counts.
314	<	*
315	<	* 6. Deciding when to create new workers. The main dynamic
316	<	* control in this class is deciding when to create extra threads,
317	<	* in methods awaitJoin and awaitBlocker. We always need to create
318	<	* one when the number of running threads would become zero and
319	<	* all workers are busy. However, this is not easy to detect
320	<	* reliably in the presence of transients so we use retries and
321	<	* allow slack (in tryAwaitJoin) to reduce false alarms.  These
322	<	* effectively reduce churn at the price of systematically
323	<	* undershooting target parallelism when many threads are blocked.
324	<	* However, biasing toward undeshooting partially compensates for
325	<	* the above mechanics to suspend extra threads, that normally
326	<	* lead to overshoot because we can only suspend workers
327	<	* in-between top-level actions. It also better copes with the
328	<	* fact that some of the methods in this class tend to never
329	<	* become compiled (but are interpreted), so some components of
330	<	* the entire set of controls might execute many times faster than
331	<	* others. And similarly for cases where the apparent lack of work
332	<	* is just due to GC stalls and other transient system activity.
284	>	* 5. Managing suspension of extra workers. When a worker notices
285	>	* (usually upon timeout of a wait()) that there are too few
286	>	* running threads, we may create a new thread to maintain
287	>	* parallelism level, or at least avoid starvation. Usually, extra
288	>	* threads are needed for only very short periods, yet join
289	>	* dependencies are such that we sometimes need them in
290	>	* bursts. Rather than create new threads each time this happens,
291	>	* we suspend no-longer-needed extra ones as "spares". For most
292	>	* purposes, we don't distinguish "extra" spare threads from
293	>	* normal "core" threads: On each call to preStep (the only point
294	>	* at which we can do this) a worker checks to see if there are
295	>	* now too many running workers, and if so, suspends itself.
296	>	* Method helpMaintainParallelism looks for suspended threads to
297	>	* resume before considering creating a new replacement. The
298	>	* spares themselves are encoded on another variant of a Treiber
299	>	* Stack, headed at field "spareWaiters".  Note that the use of
300	>	* spares is intrinsically racy.  One thread may become a spare at
301	>	* about the same time as another is needlessly being created. We
302	>	* counteract this and related slop in part by requiring resumed
303	>	* spares to immediately recheck (in preStep) to see whether they
304	>	* they should re-suspend.
305	>	*
306	>	* 6. Killing off unneeded workers. A timeout mechanism is used to
307	>	* shed unused workers: The oldest (first) event queue waiter uses
308	>	* a timed rather than hard wait. When this wait times out without
309	>	* a normal wakeup, it tries to shutdown any one (for convenience
310	>	* the newest) other spare or event waiter via
311	>	* tryShutdownUnusedWorker. This eventually reduces the number of
312	>	* worker threads to a minimum of one after a long enough period
313	>	* without use.
314	>	*
315	>	* 7. Deciding when to create new workers. The main dynamic
316	>	* control in this class is deciding when to create extra threads
317	>	* in method helpMaintainParallelism. We would like to keep
318	>	* exactly #parallelism threads running, which is an impossible
319	>	* task. We always need to create one when the number of running
320	>	* threads would become zero and all workers are busy. Beyond
321	>	* this, we must rely on heuristics that work well in the
322	>	* presence of transient phenomena such as GC stalls, dynamic
323	>	* compilation, and wake-up lags. These transients are extremely
324	>	* common -- we are normally trying to fully saturate the CPUs on
325	>	* a machine, so almost any activity other than running tasks
326	>	* impedes accuracy. Our main defense is to allow parallelism to
327	>	* lapse for a while during joins, and use a timeout to see if,
328	>	* after the resulting settling, there is still a need for
329	>	* additional workers.  This also better copes with the fact that
330	>	* some of the methods in this class tend to never become compiled
331	>	* (but are interpreted), so some components of the entire set of
332	>	* controls might execute 100 times faster than others. And
333	>	* similarly for cases where the apparent lack of work is just due
334	>	* to GC stalls and other transient system activity.
335		*
336		* Beware that there is a lot of representation-level coupling
337		* among classes ForkJoinPool, ForkJoinWorkerThread, and
#	Line 335 | Line 344 | public class ForkJoinPool extends Abstra
344		*
345		* Style notes: There are lots of inline assignments (of form
346		* "while ((local = field) != 0)") which are usually the simplest
347	<	* way to ensure read orderings. Also several occurrences of the
348	<	* unusual "do {} while(!cas...)" which is the simplest way to
349	<	* force an update of a CAS'ed variable. There are also other
350	<	* coding oddities that help some methods perform reasonably even
351	<	* when interpreted (not compiled), at the expense of messiness.
347	>	* way to ensure the required read orderings (which are sometimes
348	>	* critical). Also several occurrences of the unusual "do {}
349	>	* while (!cas...)" which is the simplest way to force an update of
350	>	* a CAS'ed variable. There are also other coding oddities that
351	>	* help some methods perform reasonably even when interpreted (not
352	>	* compiled), at the expense of some messy constructions that
353	>	* reduce byte code counts.
354		*
355		* The order of declarations in this file is: (1) statics (2)
356		* fields (along with constants used when unpacking some of them)
#	Line 407 | Line 418 | public class ForkJoinPool extends Abstra
418		new AtomicInteger();
419
420		/**
421	<	* Absolute bound for parallelism level. Twice this number must
422	<	* fit into a 16bit field to enable word-packing for some counts.
421	>	* The time to block in a join (see awaitJoin) before checking if
422	>	* a new worker should be (re)started to maintain parallelism
423	>	* level. The value should be short enough to maintain global
424	>	* responsiveness and progress but long enough to avoid
425	>	* counterproductive firings during GC stalls or unrelated system
426	>	* activity, and to not bog down systems with continual re-firings
427	>	* on GCs or legitimately long waits.
428	>	*/
429	>	private static final long JOIN_TIMEOUT_MILLIS = 250L; // 4 per second
430	>
431	>	/**
432	>	* The wakeup interval (in nanoseconds) for the oldest worker
433	>	* worker waiting for an event invokes tryShutdownUnusedWorker to shrink
434	>	* the number of workers.  The exact value does not matter too
435	>	* much, but should be long enough to slowly release resources
436	>	* during long periods without use without disrupting normal use.
437	>	*/
438	>	private static final long SHRINK_RATE_NANOS =
439	>	30L * 1000L * 1000L * 1000L; // 2 per minute
440	>
441	>	/**
442	>	* Absolute bound for parallelism level. Twice this number plus
443	>	* one (i.e., 0xfff) must fit into a 16bit field to enable
444	>	* word-packing for some counts and indices.
445		*/
446	<	private static final int MAX_THREADS = 0x7fff;
446	>	private static final int MAX_WORKERS   = 0x7fff;
447
448		/**
449		* Array holding all worker threads in the pool.  Array size must
#	Line 450 | Line 483 | public class ForkJoinPool extends Abstra
483		private volatile long stealCount;
484
485		/**
486	<	* Encoded record of top of treiber stack of threads waiting for
486	>	* Encoded record of top of Treiber stack of threads waiting for
487		* events. The top 32 bits contain the count being waited for. The
488	<	* bottom word contains one plus the pool index of waiting worker
489	<	* thread.
488	>	* bottom 16 bits contains one plus the pool index of waiting
489	>	* worker thread. (Bits 16-31 are unused.)
490		*/
491		private volatile long eventWaiters;
492
493		private static final int  EVENT_COUNT_SHIFT = 32;
494	<	private static final long WAITER_ID_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
494	>	private static final long WAITER_ID_MASK    = (1L << 16) - 1L;
495
496		/**
497		* A counter for events that may wake up worker threads:
498		*   - Submission of a new task to the pool
499		*   - A worker pushing a task on an empty queue
500	<	*   - termination and reconfiguration
500	>	*   - termination
501		*/
502		private volatile int eventCount;
503
504		/**
505	+	* Encoded record of top of Treiber stack of spare threads waiting
506	+	* for resumption. The top 16 bits contain an arbitrary count to
507	+	* avoid ABA effects. The bottom 16bits contains one plus the pool
508	+	* index of waiting worker thread.
509	+	*/
510	+	private volatile int spareWaiters;
511	+
512	+	private static final int SPARE_COUNT_SHIFT = 16;
513	+	private static final int SPARE_ID_MASK     = (1 << 16) - 1;
514	+
515	+	/**
516		* Lifecycle control. The low word contains the number of workers
517		* that are (probably) executing tasks. This value is atomically
518		* incremented before a worker gets a task to run, and decremented
#	Line 479 | Line 523 | public class ForkJoinPool extends Abstra
523		* These are bundled together to ensure consistent read for
524		* termination checks (i.e., that runLevel is at least SHUTDOWN
525		* and active threads is zero).
526	+	*
527	+	* Notes: Most direct CASes are dependent on these bitfield
528	+	* positions.  Also, this field is non-private to enable direct
529	+	* performance-sensitive CASes in ForkJoinWorkerThread.
530		*/
531	<	private volatile int runState;
531	>	volatile int runState;
532
533		// Note: The order among run level values matters.
534		private static final int RUNLEVEL_SHIFT     = 16;
#	Line 488 | Line 536 | public class ForkJoinPool extends Abstra
536		private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
537		private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
538		private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
491	–	private static final int ONE_ACTIVE         = 1; // active update delta
539
540		/**
541		* Holds number of total (i.e., created and not yet terminated)
#	Line 497 | Line 544 | public class ForkJoinPool extends Abstra
544		* making decisions about creating and suspending spare
545		* threads. Updated only by CAS. Note that adding a new worker
546		* requires incrementing both counts, since workers start off in
547	<	* running state.  This field is also used for memory-fencing
501	<	* configuration parameters.
547	>	* running state.
548		*/
549		private volatile int workerCounts;
550
#	Line 530 | Line 576 | public class ForkJoinPool extends Abstra
576		*/
577		private final int poolNumber;
578
579	<	// Utilities for CASing fields. Note that several of these
580	<	// are manually inlined by callers
579	>	// Utilities for CASing fields. Note that most of these
580	>	// are usually manually inlined by callers
581
582		/**
583	<	* Increments running count.  Also used by ForkJoinTask.
583	>	* Increments running count part of workerCounts
584		*/
585		final void incrementRunningCount() {
586		int c;
#	Line 555 | Line 601 | public class ForkJoinPool extends Abstra
601		}
602
603		/**
604	<	* Tries to increment running count
605	<	*/
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.
604	>	* Forces decrement of encoded workerCounts, awaiting nonzero if
605	>	* (rarely) necessary when other count updates lag.
606		*
607	<	* @return true on success
607	>	* @param dr -- either zero or ONE_RUNNING
608	>	* @param dt == either zero or ONE_TOTAL
609		*/
610	<	final boolean tryIncrementActiveCount() {
611	<	int c;
612	<	return UNSAFE.compareAndSwapInt(this, runStateOffset,
613	<	c = runState, c + ONE_ACTIVE);
610	>	private void decrementWorkerCounts(int dr, int dt) {
611	>	for (;;) {
612	>	int wc = workerCounts;
613	>	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
614	>	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) {
615	>	if ((runState & TERMINATED) != 0)
616	>	return; // lagging termination on a backout
617	>	Thread.yield();
618	>	}
619	>	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
620	>	wc, wc - (dr + dt)))
621	>	return;
622	>	}
623		}
624
625		/**
#	Line 582 | Line 629 | public class ForkJoinPool extends Abstra
629		final boolean tryDecrementActiveCount() {
630		int c;
631		return UNSAFE.compareAndSwapInt(this, runStateOffset,
632	<	c = runState, c - ONE_ACTIVE);
632	>	c = runState, c - 1);
633		}
634
635		/**
#	Line 611 | Line 658 | public class ForkJoinPool extends Abstra
658		lock.lock();
659		try {
660		ForkJoinWorkerThread[] ws = workers;
661	<	int nws = ws.length;
662	<	if (k < 0 || k >= nws || ws[k] != null) {
663	<	for (k = 0; k < nws && ws[k] != null; ++k)
661	>	int n = ws.length;
662	>	if (k < 0 || k >= n || ws[k] != null) {
663	>	for (k = 0; k < n && ws[k] != null; ++k)
664		;
665	<	if (k == nws)
666	<	ws = Arrays.copyOf(ws, nws << 1);
665	>	if (k == n)
666	>	ws = Arrays.copyOf(ws, n << 1);
667		}
668		ws[k] = w;
669		workers = ws; // volatile array write ensures slot visibility
#	Line 631 | Line 678 | public class ForkJoinPool extends Abstra
678		*/
679		private void forgetWorker(ForkJoinWorkerThread w) {
680		int idx = w.poolIndex;
681	<	// Locking helps method recordWorker avoid unecessary expansion
681	>	// Locking helps method recordWorker avoid unnecessary expansion
682		final ReentrantLock lock = this.workerLock;
683		lock.lock();
684		try {
#	Line 643 | Line 690 | public class ForkJoinPool extends Abstra
690		}
691		}
692
646	–	// adding and removing workers
647	–
693		/**
694	<	* Tries to create and add new worker. Assumes that worker counts
695	<	* are already updated to accommodate the worker, so adjusts on
696	<	* failure.
694	>	* Final callback from terminating worker.  Removes record of
695	>	* worker from array, and adjusts counts. If pool is shutting
696	>	* down, tries to complete termination.
697		*
698	<	* @return new worker or null if creation failed
698	>	* @param w the worker
699		*/
700	<	private ForkJoinWorkerThread addWorker() {
701	<	ForkJoinWorkerThread w = null;
702	<	try {
703	<	w = factory.newThread(this);
704	<	} finally { // Adjust on either null or exceptional factory return
705	<	if (w == null) {
661	<	onWorkerCreationFailure();
662	<	return null;
663	<	}
664	<	}
665	<	w.start(recordWorker(w), ueh);
666	<	return w;
700	>	final void workerTerminated(ForkJoinWorkerThread w) {
701	>	forgetWorker(w);
702	>	decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL);
703	>	while (w.stealCount != 0) // collect final count
704	>	tryAccumulateStealCount(w);
705	>	tryTerminate(false);
706		}
707
708	+	// Waiting for and signalling events
709	+
710		/**
711	<	* Adjusts counts upon failure to create worker
711	>	* Releases workers blocked on a count not equal to current count.
712	>	* Normally called after precheck that eventWaiters isn't zero to
713	>	* avoid wasted array checks. Gives up upon a change in count or
714	>	* upon releasing two workers, letting others take over.
715		*/
716	<	private void onWorkerCreationFailure() {
717	<	for (;;) {
718	<	int wc = workerCounts;
719	<	if ((wc >>> TOTAL_COUNT_SHIFT) == 0)
720	<	Thread.yield(); // wait for other counts to settle
721	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
722	<	wc - (ONE_RUNNING|ONE_TOTAL)))
716	>	private void releaseEventWaiters() {
717	>	ForkJoinWorkerThread[] ws = workers;
718	>	int n = ws.length;
719	>	long h = eventWaiters;
720	>	int ec = eventCount;
721	>	boolean releasedOne = false;
722	>	ForkJoinWorkerThread w; int id;
723	>	while ((id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 &&
724	>	(int)(h >>> EVENT_COUNT_SHIFT) != ec &&
725	>	id < n && (w = ws[id]) != null) {
726	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
727	>	h,  w.nextWaiter)) {
728	>	LockSupport.unpark(w);
729	>	if (releasedOne) // exit on second release
730	>	break;
731	>	releasedOne = true;
732	>	}
733	>	if (eventCount != ec)
734		break;
735	+	h = eventWaiters;
736		}
681	–	tryTerminate(false); // in case of failure during shutdown
737		}
738
739		/**
740	<	* Creates and/or resumes enough workers to establish target
741	<	* parallelism, giving up if terminating or addWorker fails
687	<	*
688	<	* TODO: recast this to support lazier creation and automated
689	<	* parallelism maintenance
740	>	* Tries to advance eventCount and releases waiters. Called only
741	>	* from workers.
742		*/
743	<	private void ensureEnoughWorkers() {
744	<	while ((runState & TERMINATING) == 0) {
745	<	int pc = parallelism;
746	<	int wc = workerCounts;
747	<	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	<	}
743	>	final void signalWork() {
744	>	int c; // try to increment event count -- CAS failure OK
745	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
746	>	if (eventWaiters != 0L)
747	>	releaseEventWaiters();
748		}
749
750		/**
751	<	* Final callback from terminating worker.  Removes record of
752	<	* worker from array, and adjusts counts. If pool is shutting
728	<	* down, tries to complete terminatation, else possibly replaces
729	<	* the worker.
751	>	* Adds the given worker to event queue and blocks until
752	>	* terminating or event count advances from the given value
753		*
754	<	* @param w the worker
754	>	* @param w the calling worker thread
755	>	* @param ec the count
756		*/
757	<	final void workerTerminated(ForkJoinWorkerThread w) {
758	<	if (w.active) { // force inactive
759	<	w.active = false;
760	<	do {} while (!tryDecrementActiveCount());
761	<	}
762	<	forgetWorker(w);
763	<
764	<	// Decrement total count, and if was running, running count
765	<	// Spin (waiting for other updates) if either would be negative
766	<	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))
757	>	private void eventSync(ForkJoinWorkerThread w, int ec) {
758	>	long nh = (((long)ec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
759	>	long h;
760	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
761	>	(((int)((h = eventWaiters) & WAITER_ID_MASK)) == 0 ||
762	>	(int)(h >>> EVENT_COUNT_SHIFT) == ec) &&
763	>	eventCount == ec) {
764	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
765	>	w.nextWaiter = h, nh)) {
766	>	awaitEvent(w, ec);
767		break;
768	+	}
769		}
753	–
754	–	accumulateStealCount(w); // collect final count
755	–	if (!tryTerminate(false))
756	–	ensureEnoughWorkers();
770		}
771
759	–	// Waiting for and signalling events
760	–
772		/**
773	<	* Releases workers blocked on a count not equal to current count.
774	<	* @return true if any released
773	>	* Blocks the given worker (that has already been entered as an
774	>	* event waiter) until terminating or event count advances from
775	>	* the given value. The oldest (first) waiter uses a timed wait to
776	>	* occasionally one-by-one shrink the number of workers (to a
777	>	* minimum of one) if the pool has not been used for extended
778	>	* periods.
779	>	*
780	>	* @param w the calling worker thread
781	>	* @param ec the count
782		*/
783	<	private void releaseWaiters() {
784	<	long top;
785	<	while ((top = eventWaiters) != 0L) {
786	<	ForkJoinWorkerThread[] ws = workers;
787	<	int n = ws.length;
788	<	for (;;) {
789	<	int i = ((int)(top & WAITER_ID_MASK)) - 1;
790	<	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == eventCount)
791	<	return;
792	<	ForkJoinWorkerThread w;
793	<	if (i < n && (w = ws[i]) != null &&
794	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
795	<	top, w.nextWaiter)) {
796	<	LockSupport.unpark(w);
797	<	top = eventWaiters;
783	>	private void awaitEvent(ForkJoinWorkerThread w, int ec) {
784	>	while (eventCount == ec) {
785	>	if (tryAccumulateStealCount(w)) { // transfer while idle
786	>	boolean untimed = (w.nextWaiter != 0L ||
787	>	(workerCounts & RUNNING_COUNT_MASK) <= 1);
788	>	long startTime = untimed? 0 : System.nanoTime();
789	>	Thread.interrupted();         // clear/ignore interrupt
790	>	if (eventCount != ec || w.runState != 0 ||
791	>	runState >= TERMINATING)  // recheck after clear
792	>	break;
793	>	if (untimed)
794	>	LockSupport.park(w);
795	>	else {
796	>	LockSupport.parkNanos(w, SHRINK_RATE_NANOS);
797	>	if (eventCount != ec || w.runState != 0 ||
798	>	runState >= TERMINATING)
799	>	break;
800	>	if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS)
801	>	tryShutdownUnusedWorker(ec);
802		}
781	–	else
782	–	break;      // possibly stale; reread
803		}
804		}
805		}
806
807	+	// Maintaining parallelism
808	+
809		/**
810	<	* Ensures eventCount on exit is different (mod 2^32) than on
789	<	* entry and wakes up all waiters
810	>	* Pushes worker onto the spare stack
811		*/
812	<	private void signalEvent() {
813	<	int c;
814	<	do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset,
815	<	c = eventCount, c+1));
795	<	releaseWaiters();
812	>	final void pushSpare(ForkJoinWorkerThread w) {
813	>	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1);
814	>	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
815	>	w.nextSpare = spareWaiters,ns));
816		}
817
818		/**
819	<	* Advances eventCount and releases waiters until interference by
820	<	* other releasing threads is detected.
819	>	* Tries (once) to resume a spare if the number of running
820	>	* threads is less than target.
821		*/
822	<	final void signalWork() {
823	<	int c;
824	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, c=eventCount, c+1);
825	<	long top;
826	<	while ((top = eventWaiters) != 0L) {
827	<	int ec = eventCount;
828	<	ForkJoinWorkerThread[] ws = workers;
829	<	int n = ws.length;
830	<	for (;;) {
831	<	int i = ((int)(top & WAITER_ID_MASK)) - 1;
832	<	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
833	<	return;
834	<	ForkJoinWorkerThread w;
835	<	if (i < n && (w = ws[i]) != null &&
836	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
837	<	top, top = w.nextWaiter)) {
838	<	LockSupport.unpark(w);
839	<	if (top != eventWaiters) // let someone else take over
840	<	return;
841	<	}
822	<	else
823	<	break;      // possibly stale; reread
824	<	}
822	>	private void tryResumeSpare() {
823	>	int sw, id;
824	>	ForkJoinWorkerThread[] ws = workers;
825	>	int n = ws.length;
826	>	ForkJoinWorkerThread w;
827	>	if ((sw = spareWaiters) != 0 &&
828	>	(id = (sw & SPARE_ID_MASK) - 1) >= 0 &&
829	>	id < n && (w = ws[id]) != null &&
830	>	(workerCounts & RUNNING_COUNT_MASK) < parallelism &&
831	>	spareWaiters == sw &&
832	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
833	>	sw, w.nextSpare)) {
834	>	int c; // increment running count before resume
835	>	do {} while (!UNSAFE.compareAndSwapInt
836	>	(this, workerCountsOffset,
837	>	c = workerCounts, c + ONE_RUNNING));
838	>	if (w.tryUnsuspend())
839	>	LockSupport.unpark(w);
840	>	else   // back out if w was shutdown
841	>	decrementWorkerCounts(ONE_RUNNING, 0);
842		}
843		}
844
845		/**
846	<	* If worker is inactive, blocks until terminating or event count
847	<	* advances from last value held by worker; in any case helps
848	<	* release others.
849	<	*
850	<	* @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
846	>	* Tries to increase the number of running workers if below target
847	>	* parallelism: If a spare exists tries to resume it via
848	>	* tryResumeSpare.  Otherwise, if not enough total workers or all
849	>	* existing workers are busy, adds a new worker. In all cases also
850	>	* helps wake up releasable workers waiting for work.
851		*/
852	<	private boolean eventSync(ForkJoinWorkerThread w, int retries) {
853	<	int wec = w.lastEventCount;
854	<	if (retries > 1) { // can only block after 2nd miss
855	<	long nextTop = (((long)wec << EVENT_COUNT_SHIFT) |
856	<	((long)(w.poolIndex + 1)));
857	<	long top;
858	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
859	<	(((int)(top = eventWaiters) & WAITER_ID_MASK) == 0 ||
860	<	(int)(top >>> EVENT_COUNT_SHIFT) == wec) &&
861	<	eventCount == wec) {
862	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
863	<	w.nextWaiter = top, nextTop)) {
864	<	accumulateStealCount(w); // transfer steals while idle
865	<	Thread.interrupted();    // clear/ignore interrupt
866	<	while (eventCount == wec)
867	<	w.doPark();
852	>	private void helpMaintainParallelism() {
853	>	int pc = parallelism;
854	>	int wc, rs, tc;
855	>	while (((wc = workerCounts) & RUNNING_COUNT_MASK) < pc &&
856	>	(rs = runState) < TERMINATING) {
857	>	if (spareWaiters != 0)
858	>	tryResumeSpare();
859	>	else if ((tc = wc >>> TOTAL_COUNT_SHIFT) >= MAX_WORKERS ||
860	>	(tc >= pc && (rs & ACTIVE_COUNT_MASK) != tc))
861	>	break;   // enough total
862	>	else if (runState == rs && workerCounts == wc &&
863	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
864	>	wc + (ONE_RUNNING|ONE_TOTAL))) {
865	>	ForkJoinWorkerThread w = null;
866	>	try {
867	>	w = factory.newThread(this);
868	>	} finally { // adjust on null or exceptional factory return
869	>	if (w == null) {
870	>	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
871	>	tryTerminate(false); // handle failure during shutdown
872	>	}
873	>	}
874	>	if (w == null)
875		break;
876	+	w.start(recordWorker(w), ueh);
877	+	if ((workerCounts >>> TOTAL_COUNT_SHIFT) >= pc) {
878	+	int c; // advance event count
879	+	UNSAFE.compareAndSwapInt(this, eventCountOffset,
880	+	c = eventCount, c+1);
881	+	break; // add at most one unless total below target
882		}
883		}
856	–	wec = eventCount;
884		}
885	<	releaseWaiters();
886	<	int wc = workerCounts;
887	<	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
888	<	w.lastEventCount = wec;
889	<	return true;
885	>	if (eventWaiters != 0L)
886	>	releaseEventWaiters();
887	>	}
888	>
889	>	/**
890	>	* Callback from the oldest waiter in awaitEvent waking up after a
891	>	* period of non-use. If all workers are idle, tries (once) to
892	>	* shutdown an event waiter or a spare, if one exists. Note that
893	>	* we don't need CAS or locks here because the method is called
894	>	* only from one thread occasionally waking (and even misfires are
895	>	* OK). Note that until the shutdown worker fully terminates,
896	>	* workerCounts will overestimate total count, which is tolerable.
897	>	*
898	>	* @param ec the event count waited on by caller (to abort
899	>	* attempt if count has since changed).
900	>	*/
901	>	private void tryShutdownUnusedWorker(int ec) {
902	>	if (runState == 0 && eventCount == ec) { // only trigger if all idle
903	>	ForkJoinWorkerThread[] ws = workers;
904	>	int n = ws.length;
905	>	ForkJoinWorkerThread w = null;
906	>	boolean shutdown = false;
907	>	int sw;
908	>	long h;
909	>	if ((sw = spareWaiters) != 0) { // prefer killing spares
910	>	int id = (sw & SPARE_ID_MASK) - 1;
911	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
912	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
913	>	sw, w.nextSpare))
914	>	shutdown = true;
915	>	}
916	>	else if ((h = eventWaiters) != 0L) {
917	>	long nh;
918	>	int id = ((int)(h & WAITER_ID_MASK)) - 1;
919	>	if (id >= 0 && id < n && (w = ws[id]) != null &&
920	>	(nh = w.nextWaiter) != 0L && // keep at least one worker
921	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh))
922	>	shutdown = true;
923	>	}
924	>	if (w != null && shutdown) {
925	>	w.shutdown();
926	>	LockSupport.unpark(w);
927	>	}
928		}
929	<	if (wec != w.lastEventCount) // back up if may re-wait
865	<	w.lastEventCount = wec - (wc >>> TOTAL_COUNT_SHIFT);
866	<	return false;
929	>	releaseEventWaiters(); // in case of interference
930		}
931
932		/**
933		* Callback from workers invoked upon each top-level action (i.e.,
934	<	* stealing a task or taking a submission and running
935	<	* it). Performs one or both of the following:
934	>	* stealing a task or taking a submission and running it).
935	>	* Performs one or more of the following:
936		*
937	<	* * If the worker cannot find work, updates its active status to
938	<	* inactive and updates activeCount unless there is contention, in
939	<	* which case it may try again (either in this or a subsequent
940	<	* call).  Additionally, awaits the next task event and/or helps
941	<	* wake up other releasable waiters.
942	<	*
943	<	* * If there are too many running threads, suspends this worker
944	<	* (first forcing inactivation if necessary).  If it is not
945	<	* resumed before a keepAlive elapses, the worker may be "trimmed"
946	<	* -- killed while suspended within suspendAsSpare. Otherwise,
947	<	* upon resume it rechecks to make sure that it is still needed.
937	>	* 1. If the worker is active and either did not run a task
938	>	*    or there are too many workers, try to set its active status
939	>	*    to inactive and update activeCount. On contention, we may
940	>	*    try again in this or a subsequent call.
941	>	*
942	>	* 2. If not enough total workers, help create some.
943	>	*
944	>	* 3. If there are too many running workers, suspend this worker
945	>	*    (first forcing inactive if necessary).  If it is not needed,
946	>	*    it may be shutdown while suspended (via
947	>	*    tryShutdownUnusedWorker).  Otherwise, upon resume it
948	>	*    rechecks running thread count and need for event sync.
949	>	*
950	>	* 4. If worker did not run a task, await the next task event via
951	>	*    eventSync if necessary (first forcing inactivation), upon
952	>	*    which the worker may be shutdown via
953	>	*    tryShutdownUnusedWorker.  Otherwise, help release any
954	>	*    existing event waiters that are now releasable,
955		*
956		* @param w the worker
957	<	* @param retries the number of scans by caller failing to find work
888	<	* find any (in which case it may block waiting for work).
957	>	* @param ran true if worker ran a task since last call to this method
958		*/
959	<	final void preStep(ForkJoinWorkerThread w, int retries) {
959	>	final void preStep(ForkJoinWorkerThread w, boolean ran) {
960	>	int wec = w.lastEventCount;
961		boolean active = w.active;
962	<	boolean inactivate = active && retries != 0;
963	<	for (;;) {
964	<	int rs, wc;
965	<	if (inactivate &&
966	<	UNSAFE.compareAndSwapInt(this, runStateOffset,
967	<	rs = runState, rs - ONE_ACTIVE))
962	>	boolean inactivate = false;
963	>	int pc = parallelism;
964	>	int rs;
965	>	while (w.runState == 0 && (rs = runState) < TERMINATING) {
966	>	if ((inactivate || (active && (rs & ACTIVE_COUNT_MASK) >= pc)) &&
967	>	UNSAFE.compareAndSwapInt(this, runStateOffset, rs, rs - 1))
968		inactivate = active = w.active = false;
969	<	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= parallelism) {
970	<	if (active || eventSync(w, retries))
969	>	int wc = workerCounts;
970	>	if ((wc & RUNNING_COUNT_MASK) > pc) {
971	>	if (!(inactivate |= active) && // must inactivate to suspend
972	>	workerCounts == wc &&      // try to suspend as spare
973	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
974	>	wc, wc - ONE_RUNNING))
975	>	w.suspendAsSpare();
976	>	}
977	>	else if ((wc >>> TOTAL_COUNT_SHIFT) < pc)
978	>	helpMaintainParallelism();     // not enough workers
979	>	else if (!ran) {
980	>	long h = eventWaiters;
981	>	int ec = eventCount;
982	>	if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != ec)
983	>	releaseEventWaiters();     // release others before waiting
984	>	else if (ec != wec) {
985	>	w.lastEventCount = ec;     // no need to wait
986		break;
987	+	}
988	+	else if (!(inactivate |= active))
989	+	eventSync(w, wec);         // must inactivate before sync
990		}
991	<	else if (!(inactivate |= active) &&  // must inactivate to suspend
904	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
905	<	wc, wc - ONE_RUNNING) &&
906	<	!w.suspendAsSpare())             // false if trimmed
991	>	else
992		break;
993		}
994		}
995
996		/**
997	<	* Awaits join of the given task if enough threads, or can resume
998	<	* 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.
997	>	* Helps and/or blocks awaiting join of the given task.
998	>	* See above for explanation.
999		*
1000		* @param joinMe the task to join
1001	<	* @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
1001	>	* @param worker the current worker thread
1002		*/
1003	<	final boolean tryAwaitJoin(ForkJoinTask<?> joinMe, int retries) {
1004	<	if (joinMe.status < 0) // precheck for cancellation
1005	<	return false;
1006	<	if ((runState & TERMINATING) != 0) { // shutting down
1007	<	joinMe.cancelIgnoringExceptions();
1008	<	return false;
1009	<	}
1010	<
1011	<	int pc = parallelism;
1012	<	boolean running = true; // false when running count decremented
1013	<	outer:for (;;) {
1014	<	int wc = workerCounts;
1015	<	int rc = wc & RUNNING_COUNT_MASK;
1016	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1017	<	if (running) { // replace with spare or decrement count
1018	<	if (rc <= pc && tc > pc &&
1019	<	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
1020	<	ForkJoinWorkerThread[] ws = workers;
1021	<	int nws = ws.length;
1022	<	for (int i = 0; i < nws; ++i) { // search for spare
1023	<	ForkJoinWorkerThread w = ws[i];
1024	<	if (w != null) {
1025	<	if (joinMe.status < 0)
1026	<	return false;
1027	<	if (w.isSuspended()) {
1028	<	if ((workerCounts & RUNNING_COUNT_MASK)>=pc &&
1029	<	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;
991	<	}
992	<	else { // allow blocking if enough threads
993	<	if (rc >= pc || joinMe.status < 0)
994	<	break;
995	<	int sc = tc - pc + 1; // = spare threads, plus the one to add
996	<	if (retries > sc) {
997	<	if (rc > 0 && rc >= pc - sc) // allow slack
998	<	break;
999	<	if (tc < MAX_THREADS &&
1000	<	tc == (runState & ACTIVE_COUNT_MASK) &&
1001	<	workerCounts == wc &&
1002	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1003	<	wc+(ONE_RUNNING|ONE_TOTAL))) {
1004	<	addWorker();
1005	<	break;
1006	<	}
1007	<	}
1008	<	if (workerCounts == wc &&        // back out to allow rescan
1009	<	UNSAFE.compareAndSwapInt (this, workerCountsOffset,
1010	<	wc, wc + ONE_RUNNING)) {
1011	<	releaseWaiters();            // help others progress
1012	<	return true;                 // let caller retry
1013	<	}
1003	>	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) {
1004	>	int retries = 2 + (parallelism >> 2); // #helpJoins before blocking
1005	>	while (joinMe.status >= 0) {
1006	>	int wc;
1007	>	worker.helpJoinTask(joinMe);
1008	>	if (joinMe.status < 0)
1009	>	break;
1010	>	else if (retries > 0)
1011	>	--retries;
1012	>	else if (((wc = workerCounts) & RUNNING_COUNT_MASK) != 0 &&
1013	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1014	>	wc, wc - ONE_RUNNING)) {
1015	>	int stat, c; long h;
1016	>	while ((stat = joinMe.status) >= 0 &&
1017	>	(h = eventWaiters) != 0L && // help release others
1018	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1019	>	releaseEventWaiters();
1020	>	if (stat >= 0 &&
1021	>	((workerCounts & RUNNING_COUNT_MASK) == 0 ||
1022	>	(stat =
1023	>	joinMe.internalAwaitDone(JOIN_TIMEOUT_MILLIS)) >= 0))
1024	>	helpMaintainParallelism(); // timeout or no running workers
1025	>	do {} while (!UNSAFE.compareAndSwapInt
1026	>	(this, workerCountsOffset,
1027	>	c = workerCounts, c + ONE_RUNNING));
1028	>	if (stat < 0)
1029	>	break;   // else restart
1030		}
1031		}
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;
1032		}
1033
1034		/**
1035	<	* 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.
1035	>	* Same idea as awaitJoin, but no helping, retries, or timeouts.
1036		*/
1037		final void awaitBlocker(ManagedBlocker blocker)
1038		throws InterruptedException {
1039	<	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 (;;) {
1039	>	while (!blocker.isReleasable()) {
1040		int wc = workerCounts;
1041	<	int rc = wc & RUNNING_COUNT_MASK;
1042	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1043	<	if (running) {
1044	<	if (rc <= pc && tc > pc &&
1045	<	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
1046	<	ForkJoinWorkerThread[] ws = workers;
1047	<	int nws = ws.length;
1048	<	for (int i = 0; i < nws; ++i) {
1049	<	ForkJoinWorkerThread w = ws[i];
1050	<	if (w != null) {
1051	<	if (done = blocker.isReleasable())
1052	<	return;
1053	<	if (w.isSuspended()) {
1054	<	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;
1041	>	if ((wc & RUNNING_COUNT_MASK) != 0 &&
1042	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1043	>	wc, wc - ONE_RUNNING)) {
1044	>	try {
1045	>	while (!blocker.isReleasable()) {
1046	>	long h = eventWaiters;
1047	>	if (h != 0L &&
1048	>	(int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
1049	>	releaseEventWaiters();
1050	>	else if ((workerCounts & RUNNING_COUNT_MASK) == 0 &&
1051	>	runState < TERMINATING)
1052	>	helpMaintainParallelism();
1053	>	else if (blocker.block())
1054	>	break;
1055		}
1056	+	} finally {
1057	+	int c;
1058	+	do {} while (!UNSAFE.compareAndSwapInt
1059	+	(this, workerCountsOffset,
1060	+	c = workerCounts, c + ONE_RUNNING));
1061		}
1062	<	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));
1062	>	break;
1063		}
1064		}
1065		}
#	Line 1131 | Line 1092 | public class ForkJoinPool extends Abstra
1092
1093		/**
1094		* Actions on transition to TERMINATING
1095	+	*
1096	+	* Runs up to four passes through workers: (0) shutting down each
1097	+	* (without waking up if parked) to quickly spread notifications
1098	+	* without unnecessary bouncing around event queues etc (1) wake
1099	+	* up and help cancel tasks (2) interrupt (3) mop up races with
1100	+	* interrupted workers
1101		*/
1102		private void startTerminating() {
1103	<	for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers
1104	<	cancelSubmissions();
1105	<	shutdownWorkers();
1106	<	cancelWorkerTasks();
1107	<	signalEvent();
1108	<	interruptWorkers();
1103	>	cancelSubmissions();
1104	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1105	>	int c; // advance event count
1106	>	UNSAFE.compareAndSwapInt(this, eventCountOffset,
1107	>	c = eventCount, c+1);
1108	>	eventWaiters = 0L; // clobber lists
1109	>	spareWaiters = 0;
1110	>	ForkJoinWorkerThread[] ws = workers;
1111	>	int n = ws.length;
1112	>	for (int i = 0; i < n; ++i) {
1113	>	ForkJoinWorkerThread w = ws[i];
1114	>	if (w != null) {
1115	>	w.shutdown();
1116	>	if (passes > 0 && !w.isTerminated()) {
1117	>	w.cancelTasks();
1118	>	LockSupport.unpark(w);
1119	>	if (passes > 1) {
1120	>	try {
1121	>	w.interrupt();
1122	>	} catch (SecurityException ignore) {
1123	>	}
1124	>	}
1125	>	}
1126	>	}
1127	>	}
1128		}
1129		}
1130
#	Line 1155 | Line 1141 | public class ForkJoinPool extends Abstra
1141		}
1142		}
1143
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	–
1144		// misc support for ForkJoinWorkerThread
1145
1146		/**
#	Line 1209 | Line 1151 | public class ForkJoinPool extends Abstra
1151		}
1152
1153		/**
1154	<	* Accumulates steal count from a worker, clearing
1155	<	* the worker's value
1154	>	* Tries to accumulates steal count from a worker, clearing
1155	>	* the worker's value.
1156	>	*
1157	>	* @return true if worker steal count now zero
1158		*/
1159	<	final void accumulateStealCount(ForkJoinWorkerThread w) {
1159	>	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1160		int sc = w.stealCount;
1161	<	if (sc != 0) {
1162	<	long c;
1163	<	w.stealCount = 0;
1164	<	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1165	<	c = stealCount, c + sc));
1161	>	long c = stealCount;
1162	>	// CAS even if zero, for fence effects
1163	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1164	>	if (sc != 0)
1165	>	w.stealCount = 0;
1166	>	return true;
1167		}
1168	+	return sc == 0;
1169		}
1170
1171		/**
#	Line 1228 | Line 1174 | public class ForkJoinPool extends Abstra
1174		*/
1175		final int idlePerActive() {
1176		int pc = parallelism; // use parallelism, not rc
1177	<	int ac = runState;    // no mask -- artifically boosts during shutdown
1177	>	int ac = runState;    // no mask -- artificially boosts during shutdown
1178		// Use exact results for small values, saturate past 4
1179		return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1180		}
#	Line 1302 | Line 1248 | public class ForkJoinPool extends Abstra
1248		checkPermission();
1249		if (factory == null)
1250		throw new NullPointerException();
1251	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1251	>	if (parallelism <= 0 || parallelism > MAX_WORKERS)
1252		throw new IllegalArgumentException();
1253		this.parallelism = parallelism;
1254		this.factory = factory;
#	Line 1321 | Line 1267 | public class ForkJoinPool extends Abstra
1267		* @param pc the initial parallelism level
1268		*/
1269		private static int initialArraySizeFor(int pc) {
1270	<	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1271	<	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1270	>	// If possible, initially allocate enough space for one spare
1271	>	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1272	>	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1273		size |= size >>> 1;
1274		size |= size >>> 2;
1275		size |= size >>> 4;
#	Line 1341 | Line 1288 | public class ForkJoinPool extends Abstra
1288		if (runState >= SHUTDOWN)
1289		throw new RejectedExecutionException();
1290		submissionQueue.offer(task);
1291	<	signalEvent();
1292	<	ensureEnoughWorkers();
1291	>	int c; // try to increment event count -- CAS failure OK
1292	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
1293	>	helpMaintainParallelism(); // create, start, or resume some workers
1294		}
1295
1296		/**
1297		* 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}.
1298		*
1299		* @param task the task
1300		* @return the task's result
#	Line 1364 | Line 1309 | public class ForkJoinPool extends Abstra
1309
1310		/**
1311		* 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}.
1312		*
1313		* @param task the task
1314		* @throws NullPointerException if the task is null
#	Line 1395 | Line 1337 | public class ForkJoinPool extends Abstra
1337
1338		/**
1339		* 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}.
1340		*
1341		* @param task the task to submit
1342		* @return the task
#	Line 1589 | Line 1528 | public class ForkJoinPool extends Abstra
1528		public long getQueuedTaskCount() {
1529		long count = 0;
1530		ForkJoinWorkerThread[] ws = workers;
1531	<	int nws = ws.length;
1532	<	for (int i = 0; i < nws; ++i) {
1531	>	int n = ws.length;
1532	>	for (int i = 0; i < n; ++i) {
1533		ForkJoinWorkerThread w = ws[i];
1534		if (w != null)
1535		count += w.getQueueSize();
#	Line 1648 | Line 1587 | public class ForkJoinPool extends Abstra
1587		* @return the number of elements transferred
1588		*/
1589		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1590	<	int n = submissionQueue.drainTo(c);
1652	<	ForkJoinWorkerThread[] ws = workers;
1653	<	int nws = ws.length;
1654	<	for (int i = 0; i < nws; ++i) {
1655	<	ForkJoinWorkerThread w = ws[i];
1656	<	if (w != null)
1657	<	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;
1590	>	int count = submissionQueue.drainTo(c);
1591		ForkJoinWorkerThread[] ws = workers;
1592	<	int nws = ws.length;
1593	<	for (int i = 0; i < nws; ++i) {
1592	>	int n = ws.length;
1593	>	for (int i = 0; i < n; ++i) {
1594		ForkJoinWorkerThread w = ws[i];
1595		if (w != null)
1596	<	count += w.parkCount;
1596	>	count += w.drainTasksTo(c);
1597		}
1598		return count;
1599		}
#	Line 1692 | Line 1615 | public class ForkJoinPool extends Abstra
1615		int pc = parallelism;
1616		int rs = runState;
1617		int ac = rs & ACTIVE_COUNT_MASK;
1695	–	//        int pk = collectParkCount();
1618		return super.toString() +
1619		"[" + runLevelToString(rs) +
1620		", parallelism = " + pc +
#	Line 1702 | Line 1624 | public class ForkJoinPool extends Abstra
1624		", steals = " + st +
1625		", tasks = " + qt +
1626		", submissions = " + qs +
1705	–	//            ", parks = " + pk +
1627		"]";
1628		}
1629
#	Line 1800 | Line 1721 | public class ForkJoinPool extends Abstra
1721		throws InterruptedException {
1722		try {
1723		return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1724	<	} catch(TimeoutException ex) {
1724	>	} catch (TimeoutException ex) {
1725		return false;
1726		}
1727		}
#	Line 1809 | Line 1730 | public class ForkJoinPool extends Abstra
1730		* Interface for extending managed parallelism for tasks running
1731		* in {@link ForkJoinPool}s.
1732		*
1733	<	* <p>A {@code ManagedBlocker} provides two methods.
1734	<	* Method {@code isReleasable} must return {@code true} if
1735	<	* blocking is not necessary. Method {@code block} blocks the
1736	<	* current thread if necessary (perhaps internally invoking
1737	<	* {@code isReleasable} before actually blocking).
1733	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1734	>	* {@code isReleasable} must return {@code true} if blocking is
1735	>	* not necessary. Method {@code block} blocks the current thread
1736	>	* if necessary (perhaps internally invoking {@code isReleasable}
1737	>	* before actually blocking). The unusual methods in this API
1738	>	* accommodate synchronizers that may, but don't usually, block
1739	>	* for long periods. Similarly, they allow more efficient internal
1740	>	* handling of cases in which additional workers may be, but
1741	>	* usually are not, needed to ensure sufficient parallelism.
1742	>	* Toward this end, implementations of method {@code isReleasable}
1743	>	* must be amenable to repeated invocation.
1744		*
1745		* <p>For example, here is a ManagedBlocker based on a
1746		* ReentrantLock:
#	Line 1831 | Line 1758 | public class ForkJoinPool extends Abstra
1758		*     return hasLock || (hasLock = lock.tryLock());
1759		*   }
1760		* }}</pre>
1761	+	*
1762	+	* <p>Here is a class that possibly blocks waiting for an
1763	+	* item on a given queue:
1764	+	*  <pre> {@code
1765	+	* class QueueTaker<E> implements ManagedBlocker {
1766	+	*   final BlockingQueue<E> queue;
1767	+	*   volatile E item = null;
1768	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1769	+	*   public boolean block() throws InterruptedException {
1770	+	*     if (item == null)
1771	+	*       item = queue.take();
1772	+	*     return true;
1773	+	*   }
1774	+	*   public boolean isReleasable() {
1775	+	*     return item != null || (item = queue.poll()) != null;
1776	+	*   }
1777	+	*   public E getItem() { // call after pool.managedBlock completes
1778	+	*     return item;
1779	+	*   }
1780	+	* }}</pre>
1781		*/
1782		public static interface ManagedBlocker {
1783		/**
#	Line 1873 | Line 1820 | public class ForkJoinPool extends Abstra
1820		public static void managedBlock(ManagedBlocker blocker)
1821		throws InterruptedException {
1822		Thread t = Thread.currentThread();
1823	<	if (t instanceof ForkJoinWorkerThread)
1824	<	((ForkJoinWorkerThread) t).pool.awaitBlocker(blocker);
1823	>	if (t instanceof ForkJoinWorkerThread) {
1824	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1825	>	w.pool.awaitBlocker(blocker);
1826	>	}
1827		else {
1828		do {} while (!blocker.isReleasable() && !blocker.block());
1829		}
#	Line 1905 | Line 1854 | public class ForkJoinPool extends Abstra
1854		objectFieldOffset("eventWaiters",ForkJoinPool.class);
1855		private static final long stealCountOffset =
1856		objectFieldOffset("stealCount",ForkJoinPool.class);
1857	+	private static final long spareWaitersOffset =
1858	+	objectFieldOffset("spareWaiters",ForkJoinPool.class);
1859
1860		private static long objectFieldOffset(String field, Class<?> klazz) {
1861		try {

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