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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.57 by dl, Wed Jul 7 19:52:31 2010 UTC vs.
Revision 1.60 by dl, Sat Jul 24 20:28:18 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 60 | Line 60 | import java.util.concurrent.CountDownLat
60		* Runnable}- or {@code Callable}- based activities as well.  However,
61		* tasks that are already executing in a pool should normally
62		* <em>NOT</em> use these pool execution methods, but instead use the
63	<	* within-computation forms listed in the table. To avoid inadvertant
64	<	* cyclic task dependencies and to improve performance, task
65	<	* submissions to the current pool by an ongoing fork/join
66	<	* computations may be implicitly translated to the corresponding
67	<	* ForkJoinTask forms.
63	>	* within-computation forms listed in the table.
64		*
65		* <table BORDER CELLPADDING=3 CELLSPACING=1>
66		*  <tr>
#	Line 88 | Line 84 | import java.util.concurrent.CountDownLat
84		*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
85		*  </tr>
86		* </table>
87	<	*
87	>	*
88		* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
89		* used for all parallel task execution in a program or subsystem.
90		* Otherwise, use would not usually outweigh the construction and
#	Line 113 | Line 109 | import java.util.concurrent.CountDownLat
109		* {@code IllegalArgumentException}.
110		*
111		* <p>This implementation rejects submitted tasks (that is, by throwing
112	<	* {@link RejectedExecutionException}) only when the pool is shut down.
112	>	* {@link RejectedExecutionException}) only when the pool is shut down
113	>	* or internal resources have been exhuasted.
114		*
115		* @since 1.7
116		* @author Doug Lea
#	Line 140 | Line 137 | public class ForkJoinPool extends Abstra
137		* of tasks profit from cache affinities, but others are harmed by
138		* cache pollution effects.)
139		*
140	+	* Beyond work-stealing support and essential bookkeeping, the
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	+	*   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	+	*   Compensating: Unless there are already enough live threads,
160	+	*      creating or or re-activating a spare thread to compensate
161	+	*      for the (blocked) joiner until it unblocks.  Spares then
162	+	*      suspend at their next opportunity or eventually die if
163	+	*      unused for too long.  See below and the internal
164	+	*      documentation for tryAwaitJoin for more details about
165	+	*      compensation 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.
175	+	*
176	+	* The ManagedBlocker extension API can't use helping so uses a
177	+	* special version of compensation in method awaitBlocker.
178	+	*
179		* The main throughput advantages of work-stealing stem from
180		* decentralized control -- workers mostly steal tasks from each
181		* other. We do not want to negate this by creating bottlenecks
182	<	* implementing the management responsibilities of this class. So
183	<	* we use a collection of techniques that avoid, reduce, or cope
184	<	* well with contention. These entail several instances of
185	<	* bit-packing into CASable fields to maintain only the minimally
186	<	* required atomicity. To enable such packing, we restrict maximum
187	<	* parallelism to (1<<15)-1 (enabling twice this to fit into a 16
188	<	* bit field), which is far in excess of normal operating range.
189	<	* Even though updates to some of these bookkeeping fields do
190	<	* sometimes contend with each other, they don't normally
191	<	* cache-contend with updates to others enough to warrant memory
192	<	* padding or isolation. So they are all held as fields of
193	<	* ForkJoinPool objects.  The main capabilities are as follows:
182	>	* implementing other management responsibilities. So we use a
183	>	* collection of techniques that avoid, reduce, or cope well with
184	>	* contention. These entail several instances of bit-packing into
185	>	* CASable fields to maintain only the minimally required
186	>	* atomicity. To enable such packing, we restrict maximum
187	>	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
188	>	* unbalanced increments and decrements) to fit into a 16 bit
189	>	* field, which is far in excess of normal operating range.  Even
190	>	* though updates to some of these bookkeeping fields do sometimes
191	>	* contend with each other, they don't normally cache-contend with
192	>	* updates to others enough to warrant memory padding or
193	>	* isolation. So they are all held as fields of ForkJoinPool
194	>	* objects.  The main capabilities are as follows:
195		*
196		* 1. Creating and removing workers. Workers are recorded in the
197		* "workers" array. This is an array as opposed to some other data
#	Line 179 | Line 216 | public class ForkJoinPool extends Abstra
216		* that are neither blocked nor artifically suspended) as well as
217		* the total number.  These two values are packed into one field,
218		* "workerCounts" because we need accurate snapshots when deciding
219	<	* to create, resume or suspend.  To support these decisions,
220	<	* updates to spare counts must be prospective (not
221	<	* retrospective).  For example, the running count is decremented
222	<	* before blocking by a thread about to block as a spare, but
186	<	* incremented by the thread about to unblock it. Updates upon
187	<	* resumption ofr threads blocking in awaitJoin or awaitBlocker
188	<	* cannot usually be prospective, so the running count is in
189	<	* general an upper bound of the number of productively running
190	<	* threads Updates to the workerCounts field sometimes transiently
191	<	* encounter a fair amount of contention when join dependencies
192	<	* are such that many threads block or unblock at about the same
193	<	* time. We alleviate this by sometimes performing an alternative
194	<	* action on contention like releasing waiters or locating spares.
219	>	* to create, resume or suspend.  Note however that the
220	>	* correspondance of these counts to reality is not guaranteed. In
221	>	* particular updates for unblocked threads may lag until they
222	>	* actually wake up.
223		*
224		* 3. Maintaining global run state. The run state of the pool
225		* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
#	Line 249 | Line 277 | public class ForkJoinPool extends Abstra
277		* 5. Managing suspension of extra workers. When a worker is about
278		* to block waiting for a join (or via ManagedBlockers), we may
279		* create a new thread to maintain parallelism level, or at least
280	<	* avoid starvation (see below). Usually, extra threads are needed
281	<	* for only very short periods, yet join dependencies are such
282	<	* that we sometimes need them in bursts. Rather than create new
283	<	* threads each time this happens, we suspend no-longer-needed
284	<	* extra ones as "spares". For most purposes, we don't distinguish
285	<	* "extra" spare threads from normal "core" threads: On each call
286	<	* to preStep (the only point at which we can do this) a worker
280	>	* avoid starvation. Usually, extra threads are needed for only
281	>	* very short periods, yet join dependencies are such that we
282	>	* sometimes need them in bursts. Rather than create new threads
283	>	* each time this happens, we suspend no-longer-needed extra ones
284	>	* as "spares". For most purposes, we don't distinguish "extra"
285	>	* spare threads from normal "core" threads: On each call to
286	>	* preStep (the only point at which we can do this) a worker
287		* checks to see if there are now too many running workers, and if
288	<	* so, suspends itself.  Methods awaitJoin and awaitBlocker look
289	<	* for suspended threads to resume before considering creating a
290	<	* new replacement. We don't need a special data structure to
291	<	* maintain spares; simply scanning the workers array looking for
292	<	* worker.isSuspended() is fine because the calling thread is
293	<	* otherwise not doing anything useful anyway; we are at least as
294	<	* happy if after locating a spare, the caller doesn't actually
295	<	* block because the join is ready before we try to adjust and
296	<	* compensate.  Note that this is intrinsically racy.  One thread
297	<	* may become a spare at about the same time as another is
298	<	* needlessly being created. We counteract this and related slop
299	<	* in part by requiring resumed spares to immediately recheck (in
300	<	* preStep) to see whether they they should re-suspend. The only
301	<	* effective difference between "extra" and "core" threads is that
302	<	* we allow the "extra" ones to time out and die if they are not
303	<	* resumed within a keep-alive interval of a few seconds. This is
304	<	* implemented mainly within ForkJoinWorkerThread, but requires
288	>	* so, suspends itself.  Methods tryAwaitJoin and awaitBlocker
289	>	* look for suspended threads to resume before considering
290	>	* creating a new replacement. We don't need a special data
291	>	* structure to maintain spares; simply scanning the workers array
292	>	* looking for worker.isSuspended() is fine because the calling
293	>	* thread is otherwise not doing anything useful anyway; we are at
294	>	* least as happy if after locating a spare, the caller doesn't
295	>	* actually block because the join is ready before we try to
296	>	* adjust and compensate.  Note that this is intrinsically racy.
297	>	* One thread may become a spare at about the same time as another
298	>	* is needlessly being created. We counteract this and related
299	>	* slop in part by requiring resumed spares to immediately recheck
300	>	* (in preStep) to see whether they they should re-suspend. The
301	>	* only effective difference between "extra" and "core" threads is
302	>	* 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.
307		*
308		* 6. Deciding when to create new workers. The main dynamic
309		* control in this class is deciding when to create extra threads,
310		* in methods awaitJoin and awaitBlocker. We always need to create
311	<	* one when the number of running threads becomes zero. But
312	<	* because blocked joins are typically dependent, we don't
313	<	* necessarily need or want one-to-one replacement. Instead, we
314	<	* use a combination of heuristics that adds threads only when the
315	<	* pool appears to be approaching starvation.  These effectively
316	<	* reduce churn at the price of systematically undershooting
317	<	* target parallelism when many threads are blocked.  However,
318	<	* biasing toward undeshooting partially compensates for the above
319	<	* mechanics to suspend extra threads, that normally lead to
320	<	* overshoot because we can only suspend workers in-between
321	<	* top-level actions. It also better copes with the fact that some
322	<	* of the methods in this class tend to never become compiled (but
323	<	* are interpreted), so some components of the entire set of
324	<	* controls might execute many times faster than others. And
325	<	* similarly for cases where the apparent lack of work is just due
298	<	* to GC stalls and other transient system activity.
311	>	* one when the number of running threads would become zero and
312	>	* all workers are busy. However, this is not easy to detect
313	>	* reliably in the presence of transients so we use retries and
314	>	* allow slack (in tryAwaitJoin) to reduce false alarms.  These
315	>	* effectively reduce churn at the price of systematically
316	>	* undershooting target parallelism when many threads are blocked.
317	>	* However, biasing toward undeshooting partially compensates for
318	>	* the above mechanics to suspend extra threads, that normally
319	>	* lead to overshoot because we can only suspend workers
320	>	* in-between top-level actions. It also better copes with the
321	>	* fact that some of the methods in this class tend to never
322	>	* become compiled (but are interpreted), so some components of
323	>	* the entire set of controls might execute many times faster than
324	>	* others. And similarly for cases where the apparent lack of work
325	>	* is just due to GC stalls and other transient system activity.
326		*
327		* Beware that there is a lot of representation-level coupling
328		* among classes ForkJoinPool, ForkJoinWorkerThread, and
#	Line 310 | Line 337 | public class ForkJoinPool extends Abstra
337		* "while ((local = field) != 0)") which are usually the simplest
338		* way to ensure read orderings. Also several occurrences of the
339		* unusual "do {} while(!cas...)" which is the simplest way to
340	<	* force an update of a CAS'ed variable. There are also a few
341	<	* other coding oddities that help some methods perform reasonably
342	<	* even when interpreted (not compiled).
340	>	* force an update of a CAS'ed variable. There are also other
341	>	* coding oddities that help some methods perform reasonably even
342	>	* when interpreted (not compiled), at the expense of messiness.
343		*
344		* The order of declarations in this file is: (1) statics (2)
345		* fields (along with constants used when unpacking some of them)
#	Line 431 | Line 458 | public class ForkJoinPool extends Abstra
458		private volatile long eventWaiters;
459
460		private static final int  EVENT_COUNT_SHIFT = 32;
461	<	private static final long WAITER_INDEX_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
461	>	private static final long WAITER_ID_MASK = (1L << EVENT_COUNT_SHIFT)-1L;
462
463		/**
464		* A counter for events that may wake up worker threads:
#	Line 470 | Line 497 | public class ForkJoinPool extends Abstra
497		* making decisions about creating and suspending spare
498		* threads. Updated only by CAS. Note that adding a new worker
499		* requires incrementing both counts, since workers start off in
500	<	* running state.  This field is also used for memory-fencing
474	<	* configuration parameters.
500	>	* running state.
501		*/
502		private volatile int workerCounts;
503
#	Line 503 | Line 529 | public class ForkJoinPool extends Abstra
529		*/
530		private final int poolNumber;
531
532	<	// utilities for updating fields
532	>	// Utilities for CASing fields. Note that several of these
533	>	// are manually inlined by callers
534
535		/**
536		* Increments running count.  Also used by ForkJoinTask.
#	Line 511 | Line 538 | public class ForkJoinPool extends Abstra
538		final void incrementRunningCount() {
539		int c;
540		do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
541	<	c = workerCounts,
541	>	c = workerCounts,
542		c + ONE_RUNNING));
543		}
544	<
544	>
545		/**
546		* Tries to decrement running count unless already zero
547		*/
#	Line 527 | Line 554 | public class ForkJoinPool extends Abstra
554		}
555
556		/**
557	+	* Tries to increment running count
558	+	*/
559	+	final boolean tryIncrementRunningCount() {
560	+	int wc;
561	+	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
562	+	wc = workerCounts, wc + ONE_RUNNING);
563	+	}
564	+
565	+	/**
566		* Tries incrementing active count; fails on contention.
567		* Called by workers before executing tasks.
568		*
#	Line 620 | Line 656 | public class ForkJoinPool extends Abstra
656		try {
657		w = factory.newThread(this);
658		} finally { // Adjust on either null or exceptional factory return
659	<	if (w == null) {
659	>	if (w == null)
660		onWorkerCreationFailure();
625	–	return null;
626	–	}
661		}
662	<	w.start(recordWorker(w), ueh);
662	>	if (w != null)
663	>	w.start(recordWorker(w), ueh);
664		return w;
665		}
666
#	Line 635 | Line 670 | public class ForkJoinPool extends Abstra
670		private void onWorkerCreationFailure() {
671		for (;;) {
672		int wc = workerCounts;
673	<	if ((wc >>> TOTAL_COUNT_SHIFT) > 0 &&
674	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
675	<	wc, wc - (ONE_RUNNING|ONE_TOTAL)))
673	>	int rc = wc & RUNNING_COUNT_MASK;
674	>	int tc = wc >>> TOTAL_COUNT_SHIFT;
675	>	if (rc == 0 || wc == 0)
676	>	Thread.yield(); // must 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	<	* Create enough total workers to establish target parallelism,
685	>	* Creates enough total workers to establish target parallelism,
686		* giving up if terminating or addWorker fails
687		*/
688		private void ensureEnoughTotalWorkers() {
#	Line 680 | Line 718 | public class ForkJoinPool extends Abstra
718		for (;;) {
719		int wc = workerCounts;
720		int rc = wc & RUNNING_COUNT_MASK;
721	<	if (rc - nr < 0 || (wc >>> TOTAL_COUNT_SHIFT) == 0)
721	>	int tc = wc >>> TOTAL_COUNT_SHIFT;
722	>	if (rc - nr < 0 || tc == 0)
723		Thread.yield(); // back off if waiting for other updates
724		else if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
725		wc, wc - unit))
#	Line 696 | Line 735 | public class ForkJoinPool extends Abstra
735
736		/**
737		* Releases workers blocked on a count not equal to current count.
738	+	* @return true if any released
739		*/
740		private void releaseWaiters() {
741		long top;
742	<	int id;
703	<	while ((id = (int)((top = eventWaiters) & WAITER_INDEX_MASK)) > 0 &&
704	<	(int)(top >>> EVENT_COUNT_SHIFT) != eventCount) {
742	>	while ((top = eventWaiters) != 0L) {
743		ForkJoinWorkerThread[] ws = workers;
744	<	ForkJoinWorkerThread w;
745	<	if (ws.length >= id && (w = ws[id - 1]) != null &&
746	<	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
747	<	top, w.nextWaiter))
748	<	LockSupport.unpark(w);
744	>	int n = ws.length;
745	>	for (;;) {
746	>	int i = ((int)(top & WAITER_ID_MASK)) - 1;
747	>	int e = (int)(top >>> EVENT_COUNT_SHIFT);
748	>	if (i < 0 || e == eventCount)
749	>	return;
750	>	ForkJoinWorkerThread w;
751	>	if (i < n && (w = ws[i]) != null &&
752	>	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
753	>	top, w.nextWaiter)) {
754	>	LockSupport.unpark(w);
755	>	top = eventWaiters;
756	>	}
757	>	else
758	>	break;      // possibly stale; reread
759	>	}
760		}
761		}
762
#	Line 717 | Line 766 | public class ForkJoinPool extends Abstra
766		*/
767		private void signalEvent() {
768		int c;
769	<	do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset,
769	>	do {} while (!UNSAFE.compareAndSwapInt(this, eventCountOffset,
770		c = eventCount, c+1));
771		releaseWaiters();
772		}
#	Line 727 | Line 776 | public class ForkJoinPool extends Abstra
776		* other releasing threads is detected.
777		*/
778		final void signalWork() {
779	<	// EventCount CAS failures are OK -- any change in count suffices.
780	<	int ec;
781	<	UNSAFE.compareAndSwapInt(this, eventCountOffset, ec=eventCount, ec+1);
782	<	outer:for (;;) {
783	<	long top = eventWaiters;
784	<	ec = eventCount;
779	>	int c;
780	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c=eventCount, c+1);
781	>	long top;
782	>	while ((top = eventWaiters) != 0L) {
783	>	int ec = eventCount;
784	>	ForkJoinWorkerThread[] ws = workers;
785	>	int n = ws.length;
786		for (;;) {
787	<	ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w;
788	<	int id = (int)(top & WAITER_INDEX_MASK);
789	<	if (id <= 0 || (int)(top >>> EVENT_COUNT_SHIFT) == ec)
740	<	return;
741	<	if ((ws = workers).length < id || (w = ws[id - 1]) == null ||
742	<	!UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
743	<	top, top = w.nextWaiter))
744	<	continue outer;      // possibly stale; reread
745	<	LockSupport.unpark(w);
746	<	if (top != eventWaiters) // let someone else take over
787	>	int i = ((int)(top & WAITER_ID_MASK)) - 1;
788	>	int e = (int)(top >>> EVENT_COUNT_SHIFT);
789	>	if (i < 0 || e == ec)
790		return;
791	+	ForkJoinWorkerThread w;
792	+	if (i < n && (w = ws[i]) != null &&
793	+	UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
794	+	top, top = w.nextWaiter)) {
795	+	LockSupport.unpark(w);
796	+	if (top != eventWaiters) // let someone else take over
797	+	return;
798	+	}
799	+	else
800	+	break;      // possibly stale; reread
801		}
802		}
803		}
804
805		/**
806	<	* If worker is inactive, blocks until terminating or event count
807	<	* advances from last value held by worker; in any case helps
755	<	* release others.
806	>	* Blockss worker until terminating or event count
807	>	* advances from last value held by worker
808		*
809		* @param w the calling worker thread
810		*/
811		private void eventSync(ForkJoinWorkerThread w) {
812	<	if (!w.active) {
813	<	int prev = w.lastEventCount;
814	<	long nextTop = (((long)prev << EVENT_COUNT_SHIFT) |
815	<	((long)(w.poolIndex + 1)));
816	<	long top;
817	<	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
818	<	(((int)(top = eventWaiters) & WAITER_INDEX_MASK) == 0 ||
819	<	(int)(top >>> EVENT_COUNT_SHIFT) == prev) &&
820	<	eventCount == prev) {
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 == prev)
826	<	w.doPark();
775	<	break;
776	<	}
812	>	int wec = w.lastEventCount;
813	>	long nextTop = (((long)wec << EVENT_COUNT_SHIFT) |
814	>	((long)(w.poolIndex + 1)));
815	>	long top;
816	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
817	>	(((int)(top = eventWaiters) & WAITER_ID_MASK) == 0 ||
818	>	(int)(top >>> EVENT_COUNT_SHIFT) == wec) &&
819	>	eventCount == wec) {
820	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
821	>	w.nextWaiter = top, nextTop)) {
822	>	accumulateStealCount(w); // transfer steals while idle
823	>	Thread.interrupted();    // clear/ignore interrupt
824	>	while (eventCount == wec)
825	>	w.doPark();
826	>	break;
827		}
778	–	w.lastEventCount = eventCount;
828		}
829	<	releaseWaiters();
829	>	w.lastEventCount = eventCount;
830		}
831
832		/**
#	Line 798 | Line 847 | public class ForkJoinPool extends Abstra
847		* upon resume it rechecks to make sure that it is still needed.
848		*
849		* @param w the worker
850	<	* @param worked false if the worker scanned for work but didn't
850	>	* @param retries the number of scans by caller failing to find work
851		* find any (in which case it may block waiting for work).
852		*/
853	<	final void preStep(ForkJoinWorkerThread w, boolean worked) {
853	>	final void preStep(ForkJoinWorkerThread w, int retries) {
854		boolean active = w.active;
855	<	boolean inactivate = !worked & active;
855	>	boolean inactivate = active && retries > 0;
856		for (;;) {
857	<	if (inactivate) {
858	<	int rs = runState;
859	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset,
860	<	rs, rs - ONE_ACTIVE))
861	<	inactivate = active = w.active = false;
862	<	}
863	<	int wc = workerCounts;
864	<	if ((wc & RUNNING_COUNT_MASK) <= parallelism) {
865	<	if (!worked)
866	<	eventSync(w);
867	<	return;
857	>	int rs, wc;
858	>	if (inactivate &&
859	>	UNSAFE.compareAndSwapInt(this, runStateOffset,
860	>	rs = runState, rs - ONE_ACTIVE))
861	>	inactivate = active = w.active = false;
862	>	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= parallelism) {
863	>	if (retries > 0) {
864	>	if (retries > 1 && !active)
865	>	eventSync(w);
866	>	releaseWaiters();
867	>	}
868	>	break;
869		}
870		if (!(inactivate |= active) &&  // must inactivate to suspend
871		UNSAFE.compareAndSwapInt(this, workerCountsOffset,
872		wc, wc - ONE_RUNNING) &&
873	<	!w.suspendAsSpare())        // false if trimmed
874	<	return;
873	>	!w.suspendAsSpare())             // false if trimmed
874	>	break;
875		}
876		}
877
878		/**
879	<	* Tries to decrement running count, and if so, possibly creates
880	<	* or resumes compensating threads before blocking on task joinMe.
881	<	* This code is sprawled out with manual inlining to evade some
882	<	* JIT oddities.
879	>	* Awaits join of the given task if enough threads, or can resume
880	>	* or create a spare. Fails (in which case the given task might
881	>	* not be done) upon contention or lack of decision about
882	>	* blocking.
883	>	*
884	>	* We allow blocking if:
885	>	*
886	>	* 1. There would still be at least as many running threads as
887	>	*    parallelism level if this thread blocks.
888	>	*
889	>	* 2. A spare is resumed to replace this worker. We tolerate
890	>	*    races in the decision to replace when a spare is found.
891	>	*    This may release too many, but if so, the superfluous ones
892	>	*    will re-suspend via preStep().
893	>	*
894	>	* 3. After #spares repeated retries, there are fewer than #spare
895	>	*    threads not running. We allow this slack to avoid hysteresis
896	>	*    and as a hedge against lag/uncertainty of running count
897	>	*    estimates when signalling or unblocking stalls.
898	>	*
899	>	* 4. All existing workers are busy (as rechecked via #spares
900	>	*    repeated retries by caller) and a new spare is created.
901	>	*
902	>	* If none of the above hold, we escape out by re-incrementing
903	>	* count and returning to caller, which can retry later.
904		*
905		* @param joinMe the task to join
906	<	* @return task status on exit
906	>	* @param retries the number of calls to this method for this join
907		*/
908	<	final int tryAwaitJoin(ForkJoinTask<?> joinMe) {
909	<	int cw = workerCounts; // read now to spoil CAS if counts change as ...
910	<	releaseWaiters();      // ... a byproduct of releaseWaiters
911	<	int stat = joinMe.status;
912	<	if (stat >= 0 && // inline variant of tryDecrementRunningCount
913	<	(cw & RUNNING_COUNT_MASK) > 0 &&
914	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
915	<	cw, cw - ONE_RUNNING)) {
916	<	int pc = parallelism;
917	<	int scans = 0;  // to require confirming passes to add threads
918	<	outer: while ((workerCounts & RUNNING_COUNT_MASK) < pc) {
919	<	if ((stat = joinMe.status) < 0)
920	<	break;
921	<	ForkJoinWorkerThread spare = null;
922	<	ForkJoinWorkerThread[] ws = workers;
923	<	int nws = ws.length;
924	<	for (int i = 0; i < nws; ++i) {
925	<	ForkJoinWorkerThread w = ws[i];
926	<	if (w != null && w.isSuspended()) {
927	<	spare = w;
928	<	break;
908	>	final void tryAwaitJoin(ForkJoinTask<?> joinMe, int retries) {
909	>	int pc = parallelism;
910	>	boolean running = true; // false when running count decremented
911	>	outer:while (joinMe.status >= 0) {
912	>	int wc = workerCounts;
913	>	int rc = wc & RUNNING_COUNT_MASK;
914	>	int tc = wc >>> TOTAL_COUNT_SHIFT;
915	>	if (running) { // replace with spare or decrement count
916	>	if (rc <= pc && tc > pc &&
917	>	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
918	>	ForkJoinWorkerThread[] ws = workers; // search for spare
919	>	int nws = ws.length;
920	>	for (int i = 0; i < nws; ++i) {
921	>	ForkJoinWorkerThread w = ws[i];
922	>	if (w != null && w.isSuspended()) {
923	>	if ((workerCounts & RUNNING_COUNT_MASK) > pc)
924	>	continue outer;
925	>	if (joinMe.status < 0)
926	>	break outer;
927	>	if (w.tryResumeSpare()) {
928	>	running = false;
929	>	break outer;
930	>	}
931	>	continue outer; // rescan on failure to resume
932	>	}
933		}
934		}
935	<	if ((stat = joinMe.status) < 0) // recheck to narrow race
936	<	break;
862	<	int wc = workerCounts;
863	<	int rc = wc & RUNNING_COUNT_MASK;
864	<	if (rc >= pc)
935	>	if ((rc <= pc && (rc == 0 || --retries < 0)) || // no retry
936	>	joinMe.status < 0)
937		break;
938	<	if (spare != null) {
939	<	if (spare.tryUnsuspend()) {
940	<	int c; // inline incrementRunningCount
941	<	do {} while (!UNSAFE.compareAndSwapInt
942	<	(this, workerCountsOffset,
943	<	c = workerCounts, c + ONE_RUNNING));
944	<	LockSupport.unpark(spare);
945	<	break;
946	<	}
947	<	continue;
948	<	}
949	<	int tc = wc >>> TOTAL_COUNT_SHIFT;
878	<	int sc = tc - pc;
879	<	if (rc > 0) {
880	<	int p = pc;
881	<	int s = sc;
882	<	while (s-- >= 0) { // try keeping 3/4 live
883	<	if (rc > (p -= (p >>> 2) + 1))
884	<	break outer;
885	<	}
886	<	}
887	<	if (scans++ > sc && tc < MAX_THREADS &&
938	>	if (workerCounts == wc &&
939	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
940	>	wc, wc - ONE_RUNNING))
941	>	running = false;
942	>	}
943	>	else { // allow blocking if enough threads
944	>	int sc = tc - pc + 1;          // = spares, plus the one to add
945	>	if (sc > 0 && rc > 0 && rc >= pc - sc && rc > pc - retries)
946	>	break;
947	>	if (--retries > sc && tc < MAX_THREADS &&
948	>	tc == (runState & ACTIVE_COUNT_MASK) &&
949	>	workerCounts == wc &&
950		UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
951		wc + (ONE_RUNNING|ONE_TOTAL))) {
952	<	addWorker();
952	>	addWorker();
953	>	break;
954	>	}
955	>	if (workerCounts == wc &&
956	>	UNSAFE.compareAndSwapInt (this, workerCountsOffset,
957	>	wc, wc + ONE_RUNNING)) {
958	>	running = true;            // back out; allow retry
959		break;
960		}
961		}
962	<	if (stat >= 0)
963	<	stat = joinMe.internalAwaitDone();
964	<	int c; // inline incrementRunningCount
962	>	}
963	>	if (!running) { // can block
964	>	int c;                      // to inline incrementRunningCount
965	>	joinMe.internalAwaitDone();
966		do {} while (!UNSAFE.compareAndSwapInt
967		(this, workerCountsOffset,
968		c = workerCounts, c + ONE_RUNNING));
969		}
901	–	return stat;
970		}
971
972		/**
973	<	* Same idea as (and mostly pasted from) tryAwaitJoin, but
974	<	* self-contained
973	>	* Same idea as (and shares many code snippets with) tryAwaitJoin,
974	>	* but self-contained because there are no caller retries.
975	>	* TODO: Rework to use simpler API.
976		*/
977		final void awaitBlocker(ManagedBlocker blocker)
978		throws InterruptedException {
910	–	for (;;) {
911	–	if (blocker.isReleasable())
912	–	return;
913	–	int cw = workerCounts;
914	–	releaseWaiters();
915	–	if ((cw & RUNNING_COUNT_MASK) > 0 &&
916	–	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
917	–	cw, cw - ONE_RUNNING))
918	–	break;
919	–	}
920	–	boolean done = false;
979		int pc = parallelism;
980	<	int scans = 0;
981	<	outer: while ((workerCounts & RUNNING_COUNT_MASK) < pc) {
982	<	if (done = blocker.isReleasable())
983	<	break;
926	<	ForkJoinWorkerThread spare = null;
927	<	ForkJoinWorkerThread[] ws = workers;
928	<	int nws = ws.length;
929	<	for (int i = 0; i < nws; ++i) {
930	<	ForkJoinWorkerThread w = ws[i];
931	<	if (w != null && w.isSuspended()) {
932	<	spare = w;
933	<	break;
934	<	}
935	<	}
936	<	if (done = blocker.isReleasable())
937	<	break;
980	>	boolean running = true;
981	>	int retries = 0;
982	>	boolean done;
983	>	outer:while (!(done = blocker.isReleasable())) {
984		int wc = workerCounts;
985		int rc = wc & RUNNING_COUNT_MASK;
940	–	if (rc >= pc)
941	–	break;
942	–	if (spare != null) {
943	–	if (spare.tryUnsuspend()) {
944	–	int c;
945	–	do {} while (!UNSAFE.compareAndSwapInt
946	–	(this, workerCountsOffset,
947	–	c = workerCounts, c + ONE_RUNNING));
948	–	LockSupport.unpark(spare);
949	–	break;
950	–	}
951	–	continue;
952	–	}
986		int tc = wc >>> TOTAL_COUNT_SHIFT;
987	<	int sc = tc - pc;
988	<	if (rc > 0) {
989	<	int p = pc;
990	<	int s = sc;
991	<	while (s-- >= 0) {
992	<	if (rc > (p -= (p >>> 2) + 1))
993	<	break outer;
987	>	if (running) {
988	>	if (rc <= pc && tc > pc &&
989	>	(retries > 0 || tc > (runState & ACTIVE_COUNT_MASK))) {
990	>	ForkJoinWorkerThread[] ws = workers;
991	>	int nws = ws.length;
992	>	for (int i = 0; i < nws; ++i) {
993	>	ForkJoinWorkerThread w = ws[i];
994	>	if (w != null && w.isSuspended()) {
995	>	if ((workerCounts & RUNNING_COUNT_MASK) > pc)
996	>	continue outer;
997	>	if (done = blocker.isReleasable())
998	>	break outer;
999	>	if (w.tryResumeSpare()) {
1000	>	running = false;
1001	>	break outer;
1002	>	}
1003	>	continue outer;
1004	>	}
1005	>	}
1006	>	if (done = blocker.isReleasable())
1007	>	break;
1008	>	}
1009	>	if (rc > 0 && workerCounts == wc &&
1010	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1011	>	wc, wc - ONE_RUNNING)) {
1012	>	running = false;
1013	>	if (rc > pc)
1014	>	break;
1015		}
1016		}
1017	<	if (scans++ > sc && tc < MAX_THREADS &&
1018	<	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1019	<	wc + (ONE_RUNNING|ONE_TOTAL))) {
1020	<	addWorker();
1017	>	else if (rc >= pc)
1018	>	break;
1019	>	else if (tc < MAX_THREADS &&
1020	>	tc == (runState & ACTIVE_COUNT_MASK) &&
1021	>	workerCounts == wc &&
1022	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
1023	>	wc + (ONE_RUNNING|ONE_TOTAL))) {
1024	>	addWorker();
1025		break;
1026		}
1027	+	else if (workerCounts == wc &&
1028	+	UNSAFE.compareAndSwapInt (this, workerCountsOffset,
1029	+	wc, wc + ONE_RUNNING)) {
1030	+	Thread.yield();
1031	+	++retries;
1032	+	running = true;            // allow rescan
1033	+	}
1034		}
1035	+
1036		try {
1037		if (!done)
1038	<	do {} while (!blocker.isReleasable() &&
973	<	!blocker.block());
1038	>	do {} while (!blocker.isReleasable() && !blocker.block());
1039		} finally {
1040	<	int c;
1041	<	do {} while (!UNSAFE.compareAndSwapInt
1042	<	(this, workerCountsOffset,
1043	<	c = workerCounts, c + ONE_RUNNING));
1040	>	if (!running) {
1041	>	int c;
1042	>	do {} while (!UNSAFE.compareAndSwapInt
1043	>	(this, workerCountsOffset,
1044	>	c = workerCounts, c + ONE_RUNNING));
1045	>	}
1046		}
1047	<	}
1047	>	}
1048
1049		/**
1050		* Possibly initiates and/or completes termination.
#	Line 1103 | Line 1170 | public class ForkJoinPool extends Abstra
1170		* active thread.
1171		*/
1172		final int idlePerActive() {
1173	<	int pc = parallelism; // use targeted parallelism, not rc
1173	>	int pc = parallelism; // use parallelism, not rc
1174		int ac = runState;    // no mask -- artifically boosts during shutdown
1175		// Use exact results for small values, saturate past 4
1176		return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
#	Line 1154 | Line 1221 | public class ForkJoinPool extends Abstra
1221		* use {@link java.lang.Runtime#availableProcessors}.
1222		* @param factory the factory for creating new threads. For default value,
1223		* use {@link #defaultForkJoinWorkerThreadFactory}.
1224	<	* @param handler the handler for internal worker threads that
1225	<	* terminate due to unrecoverable errors encountered while executing
1224	>	* @param handler the handler for internal worker threads that
1225	>	* terminate due to unrecoverable errors encountered while executing
1226		* tasks. For default value, use <code>null</code>.
1227	<	* @param asyncMode if true,
1227	>	* @param asyncMode if true,
1228		* establishes local first-in-first-out scheduling mode for forked
1229		* tasks that are never joined. This mode may be more appropriate
1230		* than default locally stack-based mode in applications in which
#	Line 1171 | Line 1238 | public class ForkJoinPool extends Abstra
1238		*         because it does not hold {@link
1239		*         java.lang.RuntimePermission}{@code ("modifyThread")}
1240		*/
1241	<	public ForkJoinPool(int parallelism,
1241	>	public ForkJoinPool(int parallelism,
1242		ForkJoinWorkerThreadFactory factory,
1243		Thread.UncaughtExceptionHandler handler,
1244		boolean asyncMode) {
#	Line 1216 | Line 1283 | public class ForkJoinPool extends Abstra
1283		throw new NullPointerException();
1284		if (runState >= SHUTDOWN)
1285		throw new RejectedExecutionException();
1286	<	// Convert submissions to current pool into forks
1287	<	Thread t = Thread.currentThread();
1288	<	ForkJoinWorkerThread w;
1222	<	if ((t instanceof ForkJoinWorkerThread) &&
1223	<	(w = (ForkJoinWorkerThread) t).pool == this)
1224	<	w.pushTask(task);
1225	<	else {
1226	<	submissionQueue.offer(task);
1227	<	signalEvent();
1228	<	ensureEnoughTotalWorkers();
1229	<	}
1286	>	submissionQueue.offer(task);
1287	>	signalEvent();
1288	>	ensureEnoughTotalWorkers();
1289		}
1290
1291		/**
1292		* Performs the given task, returning its result upon completion.
1293		* If the caller is already engaged in a fork/join computation in
1294	<	* the current pool, this method is equivalent in effect to
1294	>	* the current pool, this method is equivalent in effect to
1295		* {@link ForkJoinTask#invoke}.
1296		*
1297		* @param task the task
#	Line 1249 | Line 1308 | public class ForkJoinPool extends Abstra
1308		/**
1309		* Arranges for (asynchronous) execution of the given task.
1310		* If the caller is already engaged in a fork/join computation in
1311	<	* the current pool, this method is equivalent in effect to
1311	>	* the current pool, this method is equivalent in effect to
1312		* {@link ForkJoinTask#fork}.
1313		*
1314		* @param task the task
#	Line 1280 | Line 1339 | public class ForkJoinPool extends Abstra
1339		/**
1340		* Submits a ForkJoinTask for execution.
1341		* If the caller is already engaged in a fork/join computation in
1342	<	* the current pool, this method is equivalent in effect to
1342	>	* the current pool, this method is equivalent in effect to
1343		* {@link ForkJoinTask#fork}.
1344		*
1345		* @param task the task to submit

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