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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 1.62 by dl, Wed Aug 11 20:28:22 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 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.  Becauae 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.
159	>	*   Compensating: Unless there are already enough live threads,
160	>	*      method helpMaintainParallelism() may create or or
161	>	*      re-activate a spare thread to compensate for blocked
162	>	*      joiners until they unblock.
163		*
164		* Because the determining existence of conservatively safe
165		* helping targets, the availability of already-created spares,
166		* and the apparent need to create new spares are all racy and
167	<	* require heuristic guidance, joins (in
168	<	* ForkJoinWorkerThread.joinTask) interleave these options until
169	<	* successful.  Creating a new spare always succeeds, but also
170	<	* increases application footprint, so we try to avoid it, within
171	<	* reason.
167	>	* require heuristic guidance, we rely on multiple retries of
168	>	* each. Further, because it is impossible to keep exactly the
169	>	* target (parallelism) number of threads running at any given
170	>	* time, we allow compensation during joins to fail, and enlist
171	>	* all other threads to help out whenever they are not otherwise
172	>	* occupied (i.e., mainly in method preStep).
173		*
174	<	* The ManagedBlocker extension API can't use option (1) so uses a
175	<	* special version of (2) in method awaitBlocker.
174	>	* The ManagedBlocker extension API can't use helping so relies
175	>	* only on compensation in method awaitBlocker.
176		*
177		* The main throughput advantages of work-stealing stem from
178		* decentralized control -- workers mostly steal tasks from each
#	Line 207 | Line 205 | public class ForkJoinPool extends Abstra
205		* blocked workers. However, all other support code is set up to
206		* work with other policies.
207		*
208	+	* To ensure that we do not hold on to worker references that
209	+	* would prevent GC, ALL accesses to workers are via indices into
210	+	* the workers array (which is one source of some of the unusual
211	+	* code constructions here). In essence, the workers array serves
212	+	* as a WeakReference mechanism. Thus for example the event queue
213	+	* stores worker indices, not worker references. Access to the
214	+	* workers in associated methods (for example releaseEventWaiters)
215	+	* must both index-check and null-check the IDs. All such accesses
216	+	* ignore bad IDs by returning out early from what they are doing,
217	+	* since this can only be associated with shutdown, in which case
218	+	* it is OK to give up. On termination, we just clobber these
219	+	* data structures without trying to use them.
220	+	*
221		* 2. Bookkeeping for dynamically adding and removing workers. We
222		* aim to approximately maintain the given level of parallelism.
223		* When some workers are known to be blocked (on joins or via
#	Line 248 | Line 259 | public class ForkJoinPool extends Abstra
259		* workers that previously could not find a task to now find one:
260		* Submission of a new task to the pool, or another worker pushing
261		* a task onto a previously empty queue.  (We also use this
262	<	* mechanism for termination and reconfiguration actions that
263	<	* require wakeups of idle workers).  Each worker maintains its
264	<	* last known event count, and blocks when a scan for work did not
265	<	* find a task AND its lastEventCount matches the current
266	<	* eventCount. Waiting idle workers are recorded in a variant of
267	<	* Treiber stack headed by field eventWaiters which, when nonzero,
268	<	* encodes the thread index and count awaited for by the worker
269	<	* thread most recently calling eventSync. This thread in turn has
270	<	* a record (field nextEventWaiter) for the next waiting worker.
271	<	* In addition to allowing simpler decisions about need for
272	<	* wakeup, the event count bits in eventWaiters serve the role of
273	<	* tags to avoid ABA errors in Treiber stacks.  To reduce delays
274	<	* in task diffusion, workers not otherwise occupied may invoke
275	<	* method releaseWaiters, that removes and signals (unparks)
276	<	* workers not waiting on current count. To minimize task
277	<	* production stalls associate with signalling, any worker pushing
278	<	* a task on an empty queue invokes the weaker method signalWork,
279	<	* that only releases idle workers until it detects interference
280	<	* by other threads trying to release, and lets them take
281	<	* over. The net effect is a tree-like diffusion of signals, where
282	<	* released threads (and possibly others) help with unparks.  To
283	<	* further reduce contention effects a bit, failed CASes to
262	>	* mechanism for termination actions that require wakeups of idle
263	>	* workers).  Each worker maintains its last known event count,
264	>	* and blocks when a scan for work did not find a task AND its
265	>	* lastEventCount matches the current eventCount. Waiting idle
266	>	* workers are recorded in a variant of Treiber stack headed by
267	>	* field eventWaiters which, when nonzero, encodes the thread
268	>	* index and count awaited for by the worker thread most recently
269	>	* calling eventSync. This thread in turn has a record (field
270	>	* nextEventWaiter) for the next waiting worker.  In addition to
271	>	* allowing simpler decisions about need for wakeup, the event
272	>	* count bits in eventWaiters serve the role of tags to avoid ABA
273	>	* errors in Treiber stacks.  To reduce delays in task diffusion,
274	>	* workers not otherwise occupied may invoke method
275	>	* releaseEventWaiters, that removes and signals (unparks) workers
276	>	* not waiting on current count. To reduce stalls, To minimize
277	>	* task production stalls associate with signalling, any worker
278	>	* pushing a task on an empty queue invokes the weaker method
279	>	* signalWork, that only releases idle workers until it detects
280	>	* interference by other threads trying to release, and lets them
281	>	* take over.  The net effect is a tree-like diffusion of signals,
282	>	* where released threads (and possibly others) help with unparks.
283	>	* To further reduce contention effects a bit, failed CASes to
284		* increment field eventCount are tolerated without retries.
285		* Conceptually they are merged into the same event, which is OK
286		* when their only purpose is to enable workers to scan for work.
#	Line 285 | Line 296 | public class ForkJoinPool extends Abstra
296		* spare threads from normal "core" threads: On each call to
297		* preStep (the only point at which we can do this) a worker
298		* checks to see if there are now too many running workers, and if
299	<	* so, suspends itself.  Methods tryAwaitJoin and awaitBlocker
300	<	* look for suspended threads to resume before considering
301	<	* creating a new replacement. We don't need a special data
302	<	* structure to maintain spares; simply scanning the workers array
303	<	* looking for worker.isSuspended() is fine because the calling
304	<	* thread is otherwise not doing anything useful anyway; we are at
305	<	* least as happy if after locating a spare, the caller doesn't
306	<	* actually block because the join is ready before we try to
307	<	* adjust and compensate.  Note that this is intrinsically racy.
308	<	* One thread may become a spare at about the same time as another
309	<	* is needlessly being created. We counteract this and related
310	<	* slop in part by requiring resumed spares to immediately recheck
311	<	* (in preStep) to see whether they they should re-suspend. The
312	<	* only effective difference between "extra" and "core" threads is
313	<	* that we allow the "extra" ones to time out and die if they are
303	<	* not resumed within a keep-alive interval of a few seconds. This
304	<	* is implemented mainly within ForkJoinWorkerThread, but requires
305	<	* some coordination (isTrimmed() -- meaning killed while
306	<	* suspended) to correctly maintain pool counts.
299	>	* so, suspends itself.  Method helpMaintainParallelism looks for
300	>	* suspended threads to resume before considering creating a new
301	>	* replacement. The spares themselves are encoded on another
302	>	* variant of a Treiber Stack, headed at field "spareWaiters".
303	>	* Note that the use of spares is intrinsically racy.  One thread
304	>	* may become a spare at about the same time as another is
305	>	* needlessly being created. We counteract this and related slop
306	>	* in part by requiring resumed spares to immediately recheck (in
307	>	* preStep) to see whether they they should re-suspend.  To avoid
308	>	* long-term build-up of spares, the oldest spare (see
309	>	* ForkJoinWorkerThread.suspendAsSpare) occasionally wakes up if
310	>	* not signalled and calls tryTrimSpare, which uses two different
311	>	* thresholds: Always killing if the number of spares is greater
312	>	* that 25% of total, and killing others only at a slower rate
313	>	* (UNUSED_SPARE_TRIM_RATE_NANOS).
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.
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 impossble
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 the
322	>	* presence of transients 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 some slack in
327	>	* creation thresholds, using rules that reflect the fact that the
328	>	* more threads we have running, the more likely that we are
329	>	* underestimating the number running threads. The rules also
330	>	* better cope with the fact that some of the methods in this
331	>	* class tend to never become compiled (but are interpreted), so
332	>	* some components of the entire set of controls might execute 100
333	>	* times faster than others. And similarly for cases where the
334	>	* apparent lack of work is just due to GC stalls and other
335	>	* transient system activity.
336		*
337		* Beware that there is a lot of representation-level coupling
338		* among classes ForkJoinPool, ForkJoinWorkerThread, and
#	Line 335 | Line 345 | public class ForkJoinPool extends Abstra
345		*
346		* Style notes: There are lots of inline assignments (of form
347		* "while ((local = field) != 0)") which are usually the simplest
348	<	* way to ensure read orderings. Also several occurrences of the
349	<	* unusual "do {} while(!cas...)" which is the simplest way to
350	<	* force an update of a CAS'ed variable. There are also other
351	<	* coding oddities that help some methods perform reasonably even
352	<	* when interpreted (not compiled), at the expense of messiness.
348	>	* way to ensure the required read orderings (which are sometimes
349	>	* critical). Also several occurrences of the unusual "do {}
350	>	* while(!cas...)" which is the simplest way to force an update of
351	>	* a CAS'ed variable. There are also other coding oddities that
352	>	* help some methods perform reasonably even when interpreted (not
353	>	* compiled), at the expense of some messy constructions that
354	>	* reduce byte code counts.
355		*
356		* The order of declarations in this file is: (1) statics (2)
357		* fields (along with constants used when unpacking some of them)
#	Line 407 | Line 419 | public class ForkJoinPool extends Abstra
419		new AtomicInteger();
420
421		/**
422	<	* Absolute bound for parallelism level. Twice this number must
423	<	* fit into a 16bit field to enable word-packing for some counts.
422	>	* Absolute bound for parallelism level. Twice this number plus
423	>	* one (i.e., 0xfff) must fit into a 16bit field to enable
424	>	* word-packing for some counts and indices.
425		*/
426	<	private static final int MAX_THREADS = 0x7fff;
426	>	private static final int MAX_WORKERS   = 0x7fff;
427
428		/**
429		* Array holding all worker threads in the pool.  Array size must
#	Line 450 | Line 463 | public class ForkJoinPool extends Abstra
463		private volatile long stealCount;
464
465		/**
466	+	* The last nanoTime that a spare thread was trimmed
467	+	*/
468	+	private volatile long trimTime;
469	+
470	+	/**
471	+	* The rate at which to trim unused spares
472	+	*/
473	+	static final long UNUSED_SPARE_TRIM_RATE_NANOS =
474	+	1000L * 1000L * 1000L; // 1 sec
475	+
476	+	/**
477		* Encoded record of top of treiber stack of threads waiting for
478		* events. The top 32 bits contain the count being waited for. The
479	<	* bottom word contains one plus the pool index of waiting worker
480	<	* thread.
479	>	* bottom 16 bits contains one plus the pool index of waiting
480	>	* worker thread. (Bits 16-31 are unused.)
481		*/
482		private volatile long eventWaiters;
483
484		private static final int  EVENT_COUNT_SHIFT = 32;
485	<	private static final long WAITER_ID_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
485	>	private static final long WAITER_ID_MASK    = (1L << 16) - 1L;
486
487		/**
488		* A counter for events that may wake up worker threads:
489		*   - Submission of a new task to the pool
490		*   - A worker pushing a task on an empty queue
491	<	*   - termination and reconfiguration
491	>	*   - termination
492		*/
493		private volatile int eventCount;
494
495		/**
496	+	* Encoded record of top of treiber stack of spare threads waiting
497	+	* for resumption. The top 16 bits contain an arbitrary count to
498	+	* avoid ABA effects. The bottom 16bits contains one plus the pool
499	+	* index of waiting worker thread.
500	+	*/
501	+	private volatile int spareWaiters;
502	+
503	+	private static final int SPARE_COUNT_SHIFT = 16;
504	+	private static final int SPARE_ID_MASK     = (1 << 16) - 1;
505	+
506	+	/**
507		* Lifecycle control. The low word contains the number of workers
508		* that are (probably) executing tasks. This value is atomically
509		* incremented before a worker gets a task to run, and decremented
#	Line 497 | Line 532 | public class ForkJoinPool extends Abstra
532		* making decisions about creating and suspending spare
533		* threads. Updated only by CAS. Note that adding a new worker
534		* requires incrementing both counts, since workers start off in
535	<	* running state.  This field is also used for memory-fencing
501	<	* configuration parameters.
535	>	* running state.
536		*/
537		private volatile int workerCounts;
538
#	Line 530 | Line 564 | public class ForkJoinPool extends Abstra
564		*/
565		private final int poolNumber;
566
567	+
568		// Utilities for CASing fields. Note that several of these
569		// are manually inlined by callers
570
571		/**
572	<	* Increments running count.  Also used by ForkJoinTask.
572	>	* Increments running count part of workerCounts
573		*/
574		final void incrementRunningCount() {
575		int c;
#	Line 555 | Line 590 | public class ForkJoinPool extends Abstra
590		}
591
592		/**
593	<	* Tries to increment running count
593	>	* Forces decrement of encoded workerCounts, awaiting nonzero if
594	>	* (rarely) necessary when other count updates lag.
595	>	*
596	>	* @param dr -- either zero or ONE_RUNNING
597	>	* @param dt == either zero or ONE_TOTAL
598		*/
599	<	final boolean tryIncrementRunningCount() {
600	<	int wc;
601	<	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
602	<	wc = workerCounts, wc + ONE_RUNNING);
599	>	private void decrementWorkerCounts(int dr, int dt) {
600	>	for (;;) {
601	>	int wc = workerCounts;
602	>	if (wc == 0 && (runState & TERMINATED) != 0)
603	>	return; // lagging termination on a backout
604	>	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
605	>	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0)
606	>	Thread.yield();
607	>	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
608	>	wc, wc - (dr + dt)))
609	>	return;
610	>	}
611	>	}
612	>
613	>	/**
614	>	* Increments event count
615	>	*/
616	>	private void advanceEventCount() {
617	>	int c;
618	>	do {} while(!UNSAFE.compareAndSwapInt(this, eventCountOffset,
619	>	c = eventCount, c+1));
620		}
621
622		/**
#	Line 611 | Line 667 | public class ForkJoinPool extends Abstra
667		lock.lock();
668		try {
669		ForkJoinWorkerThread[] ws = workers;
670	<	int nws = ws.length;
671	<	if (k < 0 || k >= nws || ws[k] != null) {
672	<	for (k = 0; k < nws && ws[k] != null; ++k)
670	>	int n = ws.length;
671	>	if (k < 0 || k >= n || ws[k] != null) {
672	>	for (k = 0; k < n && ws[k] != null; ++k)
673		;
674	<	if (k == nws)
675	<	ws = Arrays.copyOf(ws, nws << 1);
674	>	if (k == n)
675	>	ws = Arrays.copyOf(ws, n << 1);
676		}
677		ws[k] = w;
678		workers = ws; // volatile array write ensures slot visibility
#	Line 649 | Line 705 | public class ForkJoinPool extends Abstra
705		* Tries to create and add new worker. Assumes that worker counts
706		* are already updated to accommodate the worker, so adjusts on
707		* failure.
652	–	*
653	–	* @return new worker or null if creation failed
708		*/
709	<	private ForkJoinWorkerThread addWorker() {
709	>	private void addWorker() {
710		ForkJoinWorkerThread w = null;
711		try {
712		w = factory.newThread(this);
713		} finally { // Adjust on either null or exceptional factory return
714		if (w == null) {
715	<	onWorkerCreationFailure();
716	<	return null;
715	>	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
716	>	tryTerminate(false); // in case of failure during shutdown
717		}
718		}
719	<	w.start(recordWorker(w), ueh);
720	<	return w;
667	<	}
668	<
669	<	/**
670	<	* Adjusts counts upon failure to create worker
671	<	*/
672	<	private void onWorkerCreationFailure() {
673	<	for (;;) {
674	<	int wc = workerCounts;
675	<	if ((wc >>> TOTAL_COUNT_SHIFT) == 0)
676	<	Thread.yield(); // wait for other counts to settle
677	<	else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
678	<	wc - (ONE_RUNNING|ONE_TOTAL)))
679	<	break;
680	<	}
681	<	tryTerminate(false); // in case of failure during shutdown
682	<	}
683	<
684	<	/**
685	<	* Creates and/or resumes enough workers to establish target
686	<	* parallelism, giving up if terminating or addWorker fails
687	<	*
688	<	* TODO: recast this to support lazier creation and automated
689	<	* parallelism maintenance
690	<	*/
691	<	private void ensureEnoughWorkers() {
692	<	while ((runState & TERMINATING) == 0) {
693	<	int pc = parallelism;
694	<	int wc = workerCounts;
695	<	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	<	}
719	>	if (w != null)
720	>	w.start(recordWorker(w), ueh);
721		}
722
723		/**
724		* Final callback from terminating worker.  Removes record of
725		* worker from array, and adjusts counts. If pool is shutting
726	<	* down, tries to complete terminatation, else possibly replaces
729	<	* the worker.
726	>	* down, tries to complete terminatation.
727		*
728		* @param w the worker
729		*/
730		final void workerTerminated(ForkJoinWorkerThread w) {
734	–	if (w.active) { // force inactive
735	–	w.active = false;
736	–	do {} while (!tryDecrementActiveCount());
737	–	}
731		forgetWorker(w);
732	<
733	<	// Decrement total count, and if was running, running count
734	<	// Spin (waiting for other updates) if either would be negative
735	<	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))
751	<	break;
752	<	}
753	<
754	<	accumulateStealCount(w); // collect final count
755	<	if (!tryTerminate(false))
756	<	ensureEnoughWorkers();
732	>	decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL);
733	>	while (w.stealCount != 0) // collect final count
734	>	tryAccumulateStealCount(w);
735	>	tryTerminate(false);
736		}
737
738		// Waiting for and signalling events
739
740		/**
741		* Releases workers blocked on a count not equal to current count.
742	<	* @return true if any released
742	>	* Normally called after precheck that eventWaiters isn't zero to
743	>	* avoid wasted array checks.
744	>	*
745	>	* @param signalling true if caller is a signalling worker so can
746	>	* exit upon (conservatively) detected contention by other threads
747	>	* who will continue to release
748		*/
749	<	private void releaseWaiters() {
750	<	long top;
751	<	while ((top = eventWaiters) != 0L) {
752	<	ForkJoinWorkerThread[] ws = workers;
753	<	int n = ws.length;
754	<	for (;;) {
755	<	int i = ((int)(top & WAITER_ID_MASK)) - 1;
756	<	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == eventCount)
757	<	return;
758	<	ForkJoinWorkerThread w;
759	<	if (i < n && (w = ws[i]) != null &&
760	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
761	<	top, w.nextWaiter)) {
778	<	LockSupport.unpark(w);
779	<	top = eventWaiters;
780	<	}
781	<	else
782	<	break;      // possibly stale; reread
783	<	}
749	>	private void releaseEventWaiters(boolean signalling) {
750	>	ForkJoinWorkerThread[] ws = workers;
751	>	int n = ws.length;
752	>	long h; // head of stack
753	>	ForkJoinWorkerThread w; int id, ec;
754	>	while ((id = ((int)((h = eventWaiters) & WAITER_ID_MASK)) - 1) >= 0 &&
755	>	(int)(h >>> EVENT_COUNT_SHIFT) != (ec = eventCount) &&
756	>	id < n && (w = ws[id]) != null) {
757	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
758	>	h, h = w.nextWaiter))
759	>	LockSupport.unpark(w);
760	>	if (signalling && (eventCount != ec || eventWaiters != h))
761	>	break;
762		}
763		}
764
765		/**
766	<	* Ensures eventCount on exit is different (mod 2^32) than on
767	<	* entry and wakes up all waiters
766	>	* Tries to advance eventCount and releases waiters. Called only
767	>	* from workers.
768		*/
769	<	private void signalEvent() {
770	<	int c;
771	<	do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset,
772	<	c = eventCount, c+1));
773	<	releaseWaiters();
769	>	final void signalWork() {
770	>	int c; // try to increment event count -- CAS failure OK
771	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
772	>	if (eventWaiters != 0L)
773	>	releaseEventWaiters(true);
774		}
775
776		/**
777	<	* Advances eventCount and releases waiters until interference by
778	<	* other releasing threads is detected.
777	>	* Blocks worker until terminating or event count
778	>	* advances from last value held by worker
779	>	*
780	>	* @param w the calling worker thread
781		*/
782	<	final void signalWork() {
783	<	int c;
784	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, c=eventCount, c+1);
785	<	long top;
786	<	while ((top = eventWaiters) != 0L) {
787	<	int ec = eventCount;
788	<	ForkJoinWorkerThread[] ws = workers;
789	<	int n = ws.length;
790	<	for (;;) {
791	<	int i = ((int)(top & WAITER_ID_MASK)) - 1;
792	<	if (i < 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
793	<	return;
794	<	ForkJoinWorkerThread w;
795	<	if (i < n && (w = ws[i]) != null &&
796	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
797	<	top, top = w.nextWaiter)) {
798	<	LockSupport.unpark(w);
819	<	if (top != eventWaiters) // let someone else take over
820	<	return;
782	>	private void eventSync(ForkJoinWorkerThread w) {
783	>	int wec = w.lastEventCount;
784	>	long nh = (((long)wec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
785	>	long h;
786	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
787	>	((h = eventWaiters) == 0L ||
788	>	(int)(h >>> EVENT_COUNT_SHIFT) == wec) &&
789	>	eventCount == wec) {
790	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
791	>	w.nextWaiter = h, nh)) {
792	>	while (runState < TERMINATING && eventCount == wec) {
793	>	if (!tryAccumulateStealCount(w))  // transfer while idle
794	>	continue;
795	>	Thread.interrupted();             // clear/ignore interrupt
796	>	if (eventCount != wec)
797	>	break;
798	>	LockSupport.park(w);
799		}
800	<	else
823	<	break;      // possibly stale; reread
800	>	break;
801		}
802		}
803	+	w.lastEventCount = eventCount;
804		}
805
806	+	// Maintaining spares
807	+
808		/**
809	<	* If worker is inactive, blocks until terminating or event count
830	<	* advances from last value held by worker; in any case helps
831	<	* release others.
832	<	*
833	<	* @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
809	>	* Pushes worker onto the spare stack
810		*/
811	<	private boolean eventSync(ForkJoinWorkerThread w, int retries) {
812	<	int wec = w.lastEventCount;
813	<	if (retries > 1) { // can only block after 2nd miss
814	<	long nextTop = (((long)wec << EVENT_COUNT_SHIFT) |
815	<	((long)(w.poolIndex + 1)));
816	<	long top;
817	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
818	<	(((int)(top = eventWaiters) & WAITER_ID_MASK) == 0 ||
819	<	(int)(top >>> EVENT_COUNT_SHIFT) == wec) &&
820	<	eventCount == wec) {
821	<	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
822	<	w.nextWaiter = top, nextTop)) {
823	<	accumulateStealCount(w); // transfer steals while idle
824	<	Thread.interrupted();    // clear/ignore interrupt
825	<	while (eventCount == wec)
826	<	w.doPark();
827	<	break;
828	<	}
811	>	final void pushSpare(ForkJoinWorkerThread w) {
812	>	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex+1);
813	>	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
814	>	w.nextSpare = spareWaiters,ns));
815	>	}
816	>
817	>	/**
818	>	* Tries (once) to resume a spare if running count is less than
819	>	* target parallelism. Fails on contention or stale workers.
820	>	*/
821	>	private void tryResumeSpare() {
822	>	int sw, id;
823	>	ForkJoinWorkerThread w;
824	>	ForkJoinWorkerThread[] ws;
825	>	if ((id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 &&
826	>	id < (ws = workers).length && (w = ws[id]) != null &&
827	>	(workerCounts & RUNNING_COUNT_MASK) < parallelism &&
828	>	eventWaiters == 0L &&
829	>	spareWaiters == sw &&
830	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
831	>	sw, w.nextSpare) &&
832	>	w.tryUnsuspend()) {
833	>	int c; // try increment; if contended, finish after unpark
834	>	boolean inc = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
835	>	c = workerCounts,
836	>	c + ONE_RUNNING);
837	>	LockSupport.unpark(w);
838	>	if (!inc) {
839	>	do {} while(!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
840	>	c = workerCounts,
841	>	c + ONE_RUNNING));
842		}
856	–	wec = eventCount;
843		}
844	<	releaseWaiters();
844	>	}
845	>
846	>	/**
847	>	* Callback from oldest spare occasionally waking up.  Tries
848	>	* (once) to shutdown a spare if more than 25% spare overage, or
849	>	* if UNUSED_SPARE_TRIM_RATE_NANOS have elapsed and there are at
850	>	* least #parallelism running threads. Note that we don't need CAS
851	>	* or locks here because the method is called only from the oldest
852	>	* suspended spare occasionally waking (and even misfires are OK).
853	>	*
854	>	* @param now the wake up nanoTime of caller
855	>	*/
856	>	final void tryTrimSpare(long now) {
857	>	long lastTrim = trimTime;
858	>	trimTime = now;
859	>	helpMaintainParallelism(); // first, help wake up any needed spares
860	>	int sw, id;
861	>	ForkJoinWorkerThread w;
862	>	ForkJoinWorkerThread[] ws;
863	>	int pc = parallelism;
864		int wc = workerCounts;
865	<	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
866	<	w.lastEventCount = wec;
867	<	return true;
865	>	if ((wc & RUNNING_COUNT_MASK) >= pc &&
866	>	(((wc >>> TOTAL_COUNT_SHIFT) - pc) > (pc >>> 2) + 1 ||// approx 25%
867	>	now - lastTrim >= UNUSED_SPARE_TRIM_RATE_NANOS) &&
868	>	(id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 &&
869	>	id < (ws = workers).length && (w = ws[id]) != null &&
870	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
871	>	sw, w.nextSpare))
872	>	w.shutdown(false);
873	>	}
874	>
875	>	/**
876	>	* Does at most one of:
877	>	*
878	>	* 1. Help wake up existing workers waiting for work via
879	>	*    releaseEventWaiters. (If any exist, then it probably doesn't
880	>	*    matter right now if under target parallelism level.)
881	>	*
882	>	* 2. If below parallelism level and a spare exists, try (once)
883	>	*    to resume it via tryResumeSpare.
884	>	*
885	>	* 3. If neither of the above, tries (once) to add a new
886	>	*    worker if either there are not enough total, or if all
887	>	*    existing workers are busy, there are either no running
888	>	*    workers or the deficit is at least twice the surplus.
889	>	*/
890	>	private void helpMaintainParallelism() {
891	>	// uglified to work better when not compiled
892	>	int pc, wc, rc, tc, rs; long h;
893	>	if ((h = eventWaiters) != 0L) {
894	>	if ((int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
895	>	releaseEventWaiters(false); // avoid useless call
896	>	}
897	>	else if ((pc = parallelism) >
898	>	(rc = ((wc = workerCounts) & RUNNING_COUNT_MASK))) {
899	>	if (spareWaiters != 0)
900	>	tryResumeSpare();
901	>	else if ((rs = runState) < TERMINATING &&
902	>	((tc = wc >>> TOTAL_COUNT_SHIFT) < pc ||
903	>	(tc == (rs & ACTIVE_COUNT_MASK) && // all busy
904	>	(rc == 0 ||                       // must add
905	>	rc < pc - ((tc - pc) << 1)) &&   // within slack
906	>	tc < MAX_WORKERS && runState == rs)) && // recheck busy
907	>	workerCounts == wc &&
908	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
909	>	wc + (ONE_RUNNING|ONE_TOTAL)))
910	>	addWorker();
911		}
864	–	if (wec != w.lastEventCount) // back up if may re-wait
865	–	w.lastEventCount = wec - (wc >>> TOTAL_COUNT_SHIFT);
866	–	return false;
912		}
913
914		/**
915		* Callback from workers invoked upon each top-level action (i.e.,
916		* stealing a task or taking a submission and running
917	<	* it). Performs one or both of the following:
917	>	* it). Performs one or more of the following:
918	>	*
919	>	* 1. If the worker cannot find work (misses > 0), updates its
920	>	*    active status to inactive and updates activeCount unless
921	>	*    this is the first miss and there is contention, in which
922	>	*    case it may try again (either in this or a subsequent
923	>	*    call).
924	>	*
925	>	* 2. If there are at least 2 misses, awaits the next task event
926	>	*    via eventSync
927	>	*
928	>	* 3. If there are too many running threads, suspends this worker
929	>	*    (first forcing inactivation if necessary).  If it is not
930	>	*    needed, it may be killed while suspended via
931	>	*    tryTrimSpare. Otherwise, upon resume it rechecks to make
932	>	*    sure that it is still needed.
933		*
934	<	* * If the worker cannot find work, updates its active status to
935	<	* inactive and updates activeCount unless there is contention, in
876	<	* which case it may try again (either in this or a subsequent
877	<	* call).  Additionally, awaits the next task event and/or helps
878	<	* wake up other releasable waiters.
879	<	*
880	<	* * If there are too many running threads, suspends this worker
881	<	* (first forcing inactivation if necessary).  If it is not
882	<	* resumed before a keepAlive elapses, the worker may be "trimmed"
883	<	* -- killed while suspended within suspendAsSpare. Otherwise,
884	<	* upon resume it rechecks to make sure that it is still needed.
934	>	* 4. Helps release and/or reactivate other workers via
935	>	*    helpMaintainParallelism
936		*
937		* @param w the worker
938	<	* @param retries the number of scans by caller failing to find work
939	<	* find any (in which case it may block waiting for work).
938	>	* @param misses the number of scans by caller failing to find work
939	>	* (saturating at 2 just to avoid wraparound)
940		*/
941	<	final void preStep(ForkJoinWorkerThread w, int retries) {
941	>	final void preStep(ForkJoinWorkerThread w, int misses) {
942		boolean active = w.active;
943	<	boolean inactivate = active && retries != 0;
943	>	int pc = parallelism;
944		for (;;) {
945	<	int rs, wc;
946	<	if (inactivate &&
947	<	UNSAFE.compareAndSwapInt(this, runStateOffset,
948	<	rs = runState, rs - ONE_ACTIVE))
949	<	inactivate = active = w.active = false;
950	<	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= parallelism) {
951	<	if (active || eventSync(w, retries))
945	>	int wc = workerCounts;
946	>	int rc = wc & RUNNING_COUNT_MASK;
947	>	if (active && (misses > 0 || rc > pc)) {
948	>	int rs;                      // try inactivate
949	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset,
950	>	rs = runState, rs - ONE_ACTIVE))
951	>	active = w.active = false;
952	>	else if (misses > 1 || rc > pc ||
953	>	(rs & ACTIVE_COUNT_MASK) >= pc)
954	>	continue;                // force inactivate
955	>	}
956	>	if (misses > 1) {
957	>	misses = 0;                  // don't re-sync
958	>	eventSync(w);                // continue loop to recheck rc
959	>	}
960	>	else if (rc > pc) {
961	>	if (workerCounts == wc &&   // try to suspend as spare
962	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
963	>	wc, wc - ONE_RUNNING) &&
964	>	!w.suspendAsSpare())    // false if killed
965		break;
966		}
967	<	else if (!(inactivate |= active) &&  // must inactivate to suspend
968	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
969	<	wc, wc - ONE_RUNNING) &&
906	<	!w.suspendAsSpare())             // false if trimmed
967	>	else {
968	>	if (rc < pc || eventWaiters != 0L)
969	>	helpMaintainParallelism();
970		break;
971	+	}
972		}
973		}
974
975		/**
976	<	* Awaits join of the given task if enough threads, or can resume
977	<	* or create a spare. Fails (in which case the given task might
978	<	* not be done) upon contention or lack of decision about
979	<	* blocking. Returns void because caller must check
980	<	* 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.
976	>	* Helps and/or blocks awaiting join of the given task.
977	>	* Alternates between helpJoinTask() and helpMaintainParallelism()
978	>	* as many times as there is a deficit in running count (or longer
979	>	* if running count would become zero), then blocks if task still
980	>	* not done.
981		*
982		* @param joinMe the task to join
942	–	* @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
983		*/
984	<	final boolean tryAwaitJoin(ForkJoinTask<?> joinMe, int retries) {
985	<	if (joinMe.status < 0) // precheck for cancellation
986	<	return false;
987	<	if ((runState & TERMINATING) != 0) { // shutting down
988	<	joinMe.cancelIgnoringExceptions();
989	<	return false;
990	<	}
991	<
992	<	int pc = parallelism;
993	<	boolean running = true; // false when running count decremented
994	<	outer:for (;;) {
995	<	int wc = workerCounts;
996	<	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;
984	>	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) {
985	>	int threshold = parallelism;         // descend blocking thresholds
986	>	while (joinMe.status >= 0) {
987	>	boolean block; int wc;
988	>	worker.helpJoinTask(joinMe);
989	>	if (joinMe.status < 0)
990	>	break;
991	>	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) {
992	>	if (threshold > 0)
993	>	--threshold;
994	>	else
995	>	advanceEventCount(); // force release
996	>	block = false;
997		}
998	<	else { // allow blocking if enough threads
999	<	if (rc >= pc || joinMe.status < 0)
1000	<	break;
1001	<	int sc = tc - pc + 1; // = spare threads, plus the one to add
1002	<	if (retries > sc) {
1003	<	if (rc > 0 && rc >= pc - sc) // allow slack
1004	<	break;
1005	<	if (tc < MAX_THREADS &&
1006	<	tc == (runState & ACTIVE_COUNT_MASK) &&
1007	<	workerCounts == wc &&
1008	<	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	<	}
998	>	else
999	>	block = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1000	>	wc, wc - ONE_RUNNING);
1001	>	helpMaintainParallelism();
1002	>	if (block) {
1003	>	int c;
1004	>	joinMe.internalAwaitDone();
1005	>	do {} while (!UNSAFE.compareAndSwapInt
1006	>	(this, workerCountsOffset,
1007	>	c = workerCounts, c + ONE_RUNNING));
1008	>	break;
1009		}
1010		}
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;
1011		}
1012
1013		/**
1014	<	* 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.
1014	>	* Same idea as awaitJoin, but no helping
1015		*/
1016		final void awaitBlocker(ManagedBlocker blocker)
1017		throws InterruptedException {
1018	<	boolean done;
1019	<	if (done = blocker.isReleasable())
1020	<	return;
1021	<	int pc = parallelism;
1022	<	int retries = 0;
1023	<	boolean running = true; // false when running count decremented
1024	<	outer:for (;;) {
1025	<	int wc = workerCounts;
1026	<	int rc = wc & RUNNING_COUNT_MASK;
1041	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
1042	<	if (running) {
1043	<	if (rc <= pc && tc > pc &&
1044	<	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
1045	<	ForkJoinWorkerThread[] ws = workers;
1046	<	int nws = ws.length;
1047	<	for (int i = 0; i < nws; ++i) {
1048	<	ForkJoinWorkerThread w = ws[i];
1049	<	if (w != null) {
1050	<	if (done = blocker.isReleasable())
1051	<	return;
1052	<	if (w.isSuspended()) {
1053	<	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;
1018	>	int threshold = parallelism;
1019	>	while (!blocker.isReleasable()) {
1020	>	boolean block; int wc;
1021	>	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) {
1022	>	if (threshold > 0)
1023	>	--threshold;
1024	>	else
1025	>	advanceEventCount();
1026	>	block = false;
1027		}
1028	<	else {
1029	<	if (rc >= pc || (done = blocker.isReleasable()))
1030	<	break;
1031	<	int sc = tc - pc + 1;
1032	<	if (retries++ > sc) {
1033	<	if (rc > 0 && rc >= pc - sc)
1034	<	break;
1035	<	if (tc < MAX_THREADS &&
1036	<	tc == (runState & ACTIVE_COUNT_MASK) &&
1037	<	workerCounts == wc &&
1038	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1039	<	wc+(ONE_RUNNING|ONE_TOTAL))) {
1085	<	addWorker();
1086	<	break;
1087	<	}
1028	>	else
1029	>	block = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1030	>	wc, wc - ONE_RUNNING);
1031	>	helpMaintainParallelism();
1032	>	if (block) {
1033	>	try {
1034	>	do {} while (!blocker.isReleasable() && !blocker.block());
1035	>	} finally {
1036	>	int c;
1037	>	do {} while (!UNSAFE.compareAndSwapInt
1038	>	(this, workerCountsOffset,
1039	>	c = workerCounts, c + ONE_RUNNING));
1040		}
1041	<	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));
1041	>	break;
1042		}
1043		}
1044		}
#	Line 1131 | Line 1071 | public class ForkJoinPool extends Abstra
1071
1072		/**
1073		* Actions on transition to TERMINATING
1074	+	*
1075	+	* Runs up to four passes through workers: (0) shutting down each
1076	+	* quietly (without waking up if parked) to quickly spread
1077	+	* notifications without unnecessary bouncing around event queues
1078	+	* etc (1) wake up and help cancel tasks (2) interrupt (3) mop up
1079	+	* races with interrupted workers
1080		*/
1081		private void startTerminating() {
1082	<	for (int i = 0; i < 2; ++i) { // twice to mop up newly created workers
1083	<	cancelSubmissions();
1084	<	shutdownWorkers();
1085	<	cancelWorkerTasks();
1086	<	signalEvent();
1087	<	interruptWorkers();
1082	>	cancelSubmissions();
1083	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1084	>	advanceEventCount();
1085	>	eventWaiters = 0L; // clobber lists
1086	>	spareWaiters = 0;
1087	>	ForkJoinWorkerThread[] ws = workers;
1088	>	int n = ws.length;
1089	>	for (int i = 0; i < n; ++i) {
1090	>	ForkJoinWorkerThread w = ws[i];
1091	>	if (w != null) {
1092	>	w.shutdown(true);
1093	>	if (passes > 0 && !w.isTerminated()) {
1094	>	w.cancelTasks();
1095	>	LockSupport.unpark(w);
1096	>	if (passes > 1) {
1097	>	try {
1098	>	w.interrupt();
1099	>	} catch (SecurityException ignore) {
1100	>	}
1101	>	}
1102	>	}
1103	>	}
1104	>	}
1105		}
1106		}
1107
#	Line 1155 | Line 1118 | public class ForkJoinPool extends Abstra
1118		}
1119		}
1120
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	–
1121		// misc support for ForkJoinWorkerThread
1122
1123		/**
#	Line 1209 | Line 1128 | public class ForkJoinPool extends Abstra
1128		}
1129
1130		/**
1131	<	* Accumulates steal count from a worker, clearing
1132	<	* the worker's value
1131	>	* Tries to accumulates steal count from a worker, clearing
1132	>	* the worker's value.
1133	>	*
1134	>	* @return true if worker steal count now zero
1135		*/
1136	<	final void accumulateStealCount(ForkJoinWorkerThread w) {
1136	>	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1137		int sc = w.stealCount;
1138	<	if (sc != 0) {
1139	<	long c;
1140	<	w.stealCount = 0;
1141	<	do {} while (!UNSAFE.compareAndSwapLong(this, stealCountOffset,
1142	<	c = stealCount, c + sc));
1138	>	long c = stealCount;
1139	>	// CAS even if zero, for fence effects
1140	>	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1141	>	if (sc != 0)
1142	>	w.stealCount = 0;
1143	>	return true;
1144		}
1145	+	return sc == 0;
1146		}
1147
1148		/**
#	Line 1302 | Line 1225 | public class ForkJoinPool extends Abstra
1225		checkPermission();
1226		if (factory == null)
1227		throw new NullPointerException();
1228	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
1228	>	if (parallelism <= 0 || parallelism > MAX_WORKERS)
1229		throw new IllegalArgumentException();
1230		this.parallelism = parallelism;
1231		this.factory = factory;
#	Line 1314 | Line 1237 | public class ForkJoinPool extends Abstra
1237		this.workerLock = new ReentrantLock();
1238		this.termination = new Phaser(1);
1239		this.poolNumber = poolNumberGenerator.incrementAndGet();
1240	+	this.trimTime = System.nanoTime();
1241		}
1242
1243		/**
#	Line 1321 | Line 1245 | public class ForkJoinPool extends Abstra
1245		* @param pc the initial parallelism level
1246		*/
1247		private static int initialArraySizeFor(int pc) {
1248	<	// See Hackers Delight, sec 3.2. We know MAX_THREADS < (1 >>> 16)
1249	<	int size = pc < MAX_THREADS ? pc + 1 : MAX_THREADS;
1248	>	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1249	>	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1250		size |= size >>> 1;
1251		size |= size >>> 2;
1252		size |= size >>> 4;
#	Line 1341 | Line 1265 | public class ForkJoinPool extends Abstra
1265		if (runState >= SHUTDOWN)
1266		throw new RejectedExecutionException();
1267		submissionQueue.offer(task);
1268	<	signalEvent();
1269	<	ensureEnoughWorkers();
1268	>	advanceEventCount();
1269	>	helpMaintainParallelism();         // start or wake up workers
1270		}
1271
1272		/**
#	Line 1589 | Line 1513 | public class ForkJoinPool extends Abstra
1513		public long getQueuedTaskCount() {
1514		long count = 0;
1515		ForkJoinWorkerThread[] ws = workers;
1516	<	int nws = ws.length;
1517	<	for (int i = 0; i < nws; ++i) {
1516	>	int n = ws.length;
1517	>	for (int i = 0; i < n; ++i) {
1518		ForkJoinWorkerThread w = ws[i];
1519		if (w != null)
1520		count += w.getQueueSize();
#	Line 1648 | Line 1572 | public class ForkJoinPool extends Abstra
1572		* @return the number of elements transferred
1573		*/
1574		protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1575	<	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;
1575	>	int count = submissionQueue.drainTo(c);
1576		ForkJoinWorkerThread[] ws = workers;
1577	<	int nws = ws.length;
1578	<	for (int i = 0; i < nws; ++i) {
1577	>	int n = ws.length;
1578	>	for (int i = 0; i < n; ++i) {
1579		ForkJoinWorkerThread w = ws[i];
1580		if (w != null)
1581	<	count += w.parkCount;
1581	>	count += w.drainTasksTo(c);
1582		}
1583		return count;
1584		}
#	Line 1692 | Line 1600 | public class ForkJoinPool extends Abstra
1600		int pc = parallelism;
1601		int rs = runState;
1602		int ac = rs & ACTIVE_COUNT_MASK;
1695	–	//        int pk = collectParkCount();
1603		return super.toString() +
1604		"[" + runLevelToString(rs) +
1605		", parallelism = " + pc +
#	Line 1702 | Line 1609 | public class ForkJoinPool extends Abstra
1609		", steals = " + st +
1610		", tasks = " + qt +
1611		", submissions = " + qs +
1705	–	//            ", parks = " + pk +
1612		"]";
1613		}
1614
#	Line 1809 | Line 1715 | public class ForkJoinPool extends Abstra
1715		* Interface for extending managed parallelism for tasks running
1716		* in {@link ForkJoinPool}s.
1717		*
1718	<	* <p>A {@code ManagedBlocker} provides two methods.
1719	<	* Method {@code isReleasable} must return {@code true} if
1720	<	* blocking is not necessary. Method {@code block} blocks the
1721	<	* current thread if necessary (perhaps internally invoking
1722	<	* {@code isReleasable} before actually blocking).
1718	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1719	>	* {@code isReleasable} must return {@code true} if blocking is
1720	>	* not necessary. Method {@code block} blocks the current thread
1721	>	* if necessary (perhaps internally invoking {@code isReleasable}
1722	>	* before actually blocking). The unusual methods in this API
1723	>	* accommodate synchronizers that may, but don't usually, block
1724	>	* for long periods. Similarly, they allow more efficient internal
1725	>	* handling of cases in which additional workers may be, but
1726	>	* usually are not, needed to ensure sufficient parallelism.
1727	>	* Toward this end, implementations of method {@code isReleasable}
1728	>	* must be amenable to repeated invocation.
1729		*
1730		* <p>For example, here is a ManagedBlocker based on a
1731		* ReentrantLock:
#	Line 1831 | Line 1743 | public class ForkJoinPool extends Abstra
1743		*     return hasLock || (hasLock = lock.tryLock());
1744		*   }
1745		* }}</pre>
1746	+	*
1747	+	* <p>Here is a class that possibly blocks waiting for an
1748	+	* item on a given queue:
1749	+	*  <pre> {@code
1750	+	* class QueueTaker<E> implements ManagedBlocker {
1751	+	*   final BlockingQueue<E> queue;
1752	+	*   volatile E item = null;
1753	+	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1754	+	*   public boolean block() throws InterruptedException {
1755	+	*     if (item == null)
1756	+	*       item = queue.take
1757	+	*     return true;
1758	+	*   }
1759	+	*   public boolean isReleasable() {
1760	+	*     return item != null || (item = queue.poll) != null;
1761	+	*   }
1762	+	*   public E getItem() { // call after pool.managedBlock completes
1763	+	*     return item;
1764	+	*   }
1765	+	* }}</pre>
1766		*/
1767		public static interface ManagedBlocker {
1768		/**
#	Line 1873 | Line 1805 | public class ForkJoinPool extends Abstra
1805		public static void managedBlock(ManagedBlocker blocker)
1806		throws InterruptedException {
1807		Thread t = Thread.currentThread();
1808	<	if (t instanceof ForkJoinWorkerThread)
1809	<	((ForkJoinWorkerThread) t).pool.awaitBlocker(blocker);
1808	>	if (t instanceof ForkJoinWorkerThread) {
1809	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1810	>	w.pool.awaitBlocker(blocker);
1811	>	}
1812		else {
1813		do {} while (!blocker.isReleasable() && !blocker.block());
1814		}
#	Line 1905 | Line 1839 | public class ForkJoinPool extends Abstra
1839		objectFieldOffset("eventWaiters",ForkJoinPool.class);
1840		private static final long stealCountOffset =
1841		objectFieldOffset("stealCount",ForkJoinPool.class);
1842	+	private static final long spareWaitersOffset =
1843	+	objectFieldOffset("spareWaiters",ForkJoinPool.class);
1844
1845		private static long objectFieldOffset(String field, Class<?> klazz) {
1846		try {

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