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root/jsr166/jsr166/src/jsr166y/ForkJoinWorkerThread.java

Comparing jsr166/src/jsr166y/ForkJoinWorkerThread.java (file contents):
Revision 1.36 by dl, Fri Jul 23 13:07:43 2010 UTC vs.
Revision 1.43 by jsr166, Wed Sep 1 20:12:39 2010 UTC

#	Line 97 | Line 97 | public class ForkJoinWorkerThread extend
97		* technique for implementing efficient futures" SIGPLAN Notices,
98		* 1993 (http://portal.acm.org/citation.cfm?id=155354). It differs
99		* in that: (1) We only maintain dependency links across workers
100	<	* upon steals, rather than maintain per-task bookkeeping.  This
101	<	* may require a linear scan of workers array to locate stealers,
102	<	* but usually doesn't because stealers leave hints (that may
103	<	* become stale/wrong) of where to locate the kathem. This
104	<	* isolates cost to when it is needed, rather than adding to
105	<	* per-task overhead.  (2) It is "shallow", ignoring nesting and
106	<	* potentially cyclic mutual steals.  (3) It is intentionally
107	<	* racy: field currentJoin is updated only while actively joining,
108	<	* which means that we could miss links in the chain during
109	<	* long-lived tasks, GC stalls etc.  (4) We bound the number of
110	<	* attempts to find work (see MAX_HELP_DEPTH) and fall back to
111	<	* suspending the worker and if necessary replacing it with a
112	<	* spare (see ForkJoinPool.tryAwaitJoin).
100	>	* upon steals, rather than use per-task bookkeeping.  This may
101	>	* require a linear scan of workers array to locate stealers, but
102	>	* usually doesn't because stealers leave hints (that may become
103	>	* stale/wrong) of where to locate them. This isolates cost to
104	>	* when it is needed, rather than adding to per-task overhead.
105	>	* (2) It is "shallow", ignoring nesting and potentially cyclic
106	>	* mutual steals.  (3) It is intentionally racy: field currentJoin
107	>	* is updated only while actively joining, which means that we
108	>	* miss links in the chain during long-lived tasks, GC stalls etc
109	>	* (which is OK since blocking in such cases is usually a good
110	>	* idea).  (4) We bound the number of attempts to find work (see
111	>	* MAX_HELP_DEPTH) and fall back to suspending the worker and if
112	>	* necessary replacing it with a spare (see
113	>	* ForkJoinPool.awaitJoin).
114		*
115		* Efficient implementation of these algorithms currently relies
116		* on an uncomfortable amount of "Unsafe" mechanics. To maintain
#	Line 154 | Line 155 | public class ForkJoinWorkerThread extend
155		private static final Random seedGenerator = new Random();
156
157		/**
157	–	* The timeout value for suspending spares. Spare workers that
158	–	* remain unsignalled for more than this time may be trimmed
159	–	* (killed and removed from pool).  Since our goal is to avoid
160	–	* long-term thread buildup, the exact value of timeout does not
161	–	* matter too much so long as it avoids most false-alarm timeouts
162	–	* under GC stalls or momentarily high system load.
163	–	*/
164	–	private static final long SPARE_KEEPALIVE_NANOS =
165	–	5L * 1000L * 1000L * 1000L; // 5 secs
166	–
167	–	/**
158		* The maximum stolen->joining link depth allowed in helpJoinTask.
159		* Depths for legitimate chains are unbounded, but we use a fixed
160		* constant to avoid (otherwise unchecked) cycles and bound
#	Line 198 | Line 188 | public class ForkJoinWorkerThread extend
188		* Initialized in onStart, to improve memory locality.
189		*/
190		private ForkJoinTask<?>[] queue;
191	<
191	>
192		/**
193		* Index (mod queue.length) of least valid queue slot, which is
194		* always the next position to steal from if nonempty.
#	Line 227 | Line 217 | public class ForkJoinWorkerThread extend
217		* Run state of this worker. In addition to the usual run levels,
218		* tracks if this worker is suspended as a spare, and if it was
219		* killed (trimmed) while suspended. However, "active" status is
220	<	* maintained separately.
220	>	* maintained separately and modified only in conjunction with
221	>	* CASes of the pool's runState (which are currently sadly
222	>	* manually inlined for performance.)  Accessed directly by pool
223	>	* to simplify checks for normal (zero) status.
224		*/
225	<	private volatile int runState;
225	>	volatile int runState;
226
227		private static final int TERMINATING = 0x01;
228		private static final int TERMINATED  = 0x02;
#	Line 237 | Line 230 | public class ForkJoinWorkerThread extend
230		private static final int TRIMMED     = 0x08; // killed while suspended
231
232		/**
240	–	* Number of LockSupport.park calls to block this thread for
241	–	* suspension or event waits. Used for internal instrumention;
242	–	* currently not exported but included because volatile write upon
243	–	* park also provides a workaround for a JVM bug.
244	–	*/
245	–	volatile int parkCount;
246	–
247	–	/**
233		* Number of steals, transferred and reset in pool callbacks pool
234		* when idle Accessed directly by pool.
235		*/
#	Line 256 | Line 241 | public class ForkJoinWorkerThread extend
241		*/
242		private int seed;
243
259	–
244		/**
245		* Activity status. When true, this worker is considered active.
246		* Accessed directly by pool.  Must be false upon construction.
#	Line 265 | Line 249 | public class ForkJoinWorkerThread extend
249
250		/**
251		* True if use local fifo, not default lifo, for local polling.
252	<	* Shadows value from ForkJoinPool, which resets it if changed
269	<	* pool-wide.
252	>	* Shadows value from ForkJoinPool.
253		*/
254		private final boolean locallyFifo;
255	<
255	>
256		/**
257		* Index of this worker in pool array. Set once by pool before
258		* running, and accessed directly by pool to locate this worker in
#	Line 284 | Line 267 | public class ForkJoinWorkerThread extend
267		int lastEventCount;
268
269		/**
270	<	* Encoded index and event count of next event waiter. Used only
271	<	* by ForkJoinPool for managing event waiters.
270	>	* Encoded index and event count of next event waiter. Accessed
271	>	* only by ForkJoinPool for managing event waiters.
272		*/
273		volatile long nextWaiter;
274
275		/**
276	+	* Number of times this thread suspended as spare. Accessed only
277	+	* by pool.
278	+	*/
279	+	int spareCount;
280	+
281	+	/**
282	+	* Encoded index and count of next spare waiter. Accessed only
283	+	* by ForkJoinPool for managing spares.
284	+	*/
285	+	volatile int nextSpare;
286	+
287	+	/**
288		* The task currently being joined, set only when actively trying
289		* to helpStealer. Written only by current thread, but read by
290		* others.
291		*/
292		private volatile ForkJoinTask<?> currentJoin;
293	<
293	>
294		/**
295		* The task most recently stolen from another worker (or
296	<	* submission queue).  Not volatile because always read/written in
297	<	* presence of related volatiles in those cases where it matters.
296	>	* submission queue).  Written only by current thread, but read by
297	>	* others.
298		*/
299	<	private ForkJoinTask<?> currentSteal;
299	>	private volatile ForkJoinTask<?> currentSteal;
300
301		/**
302		* Creates a ForkJoinWorkerThread operating in the given pool.
#	Line 312 | Line 307 | public class ForkJoinWorkerThread extend
307		protected ForkJoinWorkerThread(ForkJoinPool pool) {
308		this.pool = pool;
309		this.locallyFifo = pool.locallyFifo;
310	+	setDaemon(true);
311		// To avoid exposing construction details to subclasses,
312		// remaining initialization is in start() and onStart()
313		}
#	Line 323 | Line 319 | public class ForkJoinWorkerThread extend
319		this.poolIndex = poolIndex;
320		if (ueh != null)
321		setUncaughtExceptionHandler(ueh);
326	–	setDaemon(true);
322		start();
323		}
324
#	Line 382 | Line 377 | public class ForkJoinWorkerThread extend
377		*/
378		protected void onTermination(Throwable exception) {
379		try {
380	+	ForkJoinPool p = pool;
381	+	if (active) {
382	+	int a; // inline p.tryDecrementActiveCount
383	+	active = false;
384	+	do {} while (!UNSAFE.compareAndSwapInt
385	+	(p, poolRunStateOffset, a = p.runState, a - 1));
386	+	}
387		cancelTasks();
388		setTerminated();
389	<	pool.workerTerminated(this);
389	>	p.workerTerminated(this);
390		} catch (Throwable ex) {        // Shouldn't ever happen
391		if (exception == null)      // but if so, at least rethrown
392		exception = ex;
#	Line 417 | Line 419 | public class ForkJoinWorkerThread extend
419		* Find and execute tasks and check status while running
420		*/
421		private void mainLoop() {
422	<	int emptyScans = 0; // consecutive times failed to find work
422	>	boolean ran = false; // true if ran a task on last step
423		ForkJoinPool p = pool;
424		for (;;) {
425	<	p.preStep(this, emptyScans);
425	>	p.preStep(this, ran);
426		if (runState != 0)
427	<	return;
428	<	ForkJoinTask<?> t; // try to get and run stolen or submitted task
427	<	if ((t = scan()) != null || (t = pollSubmission()) != null) {
428	<	t.tryExec();
429	<	if (base != sp)
430	<	runLocalTasks();
431	<	currentSteal = null;
432	<	emptyScans = 0;
433	<	}
434	<	else
435	<	++emptyScans;
427	>	break;
428	>	ran = tryExecSteal() || tryExecSubmission();
429		}
430		}
431
432		/**
433	<	* Runs local tasks until queue is empty or shut down.  Call only
434	<	* while active.
433	>	* Try to steal a task and execute it
434	>	*
435	>	* @return true if ran a task
436		*/
437	<	private void runLocalTasks() {
438	<	while (runState == 0) {
439	<	ForkJoinTask<?> t = locallyFifo? locallyDeqTask() : popTask();
440	<	if (t != null)
441	<	t.tryExec();
442	<	else if (base == sp)
443	<	break;
437	>	private boolean tryExecSteal() {
438	>	ForkJoinTask<?> t;
439	>	if ((t = scan()) != null) {
440	>	t.quietlyExec();
441	>	UNSAFE.putOrderedObject(this, currentStealOffset, null);
442	>	if (sp != base)
443	>	execLocalTasks();
444	>	return true;
445		}
446	+	return false;
447		}
448
449		/**
450	<	* If a submission exists, try to activate and take it
450	>	* If a submission exists, try to activate and run it;
451		*
452	<	* @return a task, if available
452	>	* @return true if ran a task
453		*/
454	<	private ForkJoinTask<?> pollSubmission() {
454	>	private boolean tryExecSubmission() {
455		ForkJoinPool p = pool;
456		while (p.hasQueuedSubmissions()) {
457	<	if (active || (active = p.tryIncrementActiveCount())) {
458	<	ForkJoinTask<?> t = p.pollSubmission();
459	<	if (t != null) {
460	<	currentSteal = t;
461	<	return t;
457	>	ForkJoinTask<?> t; int a;
458	>	if (active || // inline p.tryIncrementActiveCount
459	>	(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
460	>	a = p.runState, a + 1))) {
461	>	if ((t = p.pollSubmission()) != null) {
462	>	UNSAFE.putOrderedObject(this, currentStealOffset, t);
463	>	t.quietlyExec();
464	>	UNSAFE.putOrderedObject(this, currentStealOffset, null);
465	>	if (sp != base)
466	>	execLocalTasks();
467	>	return true;
468		}
467	–	return scan(); // if missed, rescan
469		}
470		}
471	<	return null;
471	>	return false;
472	>	}
473	>
474	>	/**
475	>	* Runs local tasks until queue is empty or shut down.  Call only
476	>	* while active.
477	>	*/
478	>	private void execLocalTasks() {
479	>	while (runState == 0) {
480	>	ForkJoinTask<?> t = locallyFifo? locallyDeqTask() : popTask();
481	>	if (t != null)
482	>	t.quietlyExec();
483	>	else if (sp == base)
484	>	break;
485	>	}
486		}
487
488		/*
#	Line 535 | Line 550 | public class ForkJoinWorkerThread extend
550		ForkJoinTask<?> t;
551		ForkJoinTask<?>[] q;
552		int b, i;
553	<	if ((b = base) != sp &&
553	>	if (sp != (b = base) &&
554		(q = queue) != null && // must read q after b
555		(t = q[i = (q.length - 1) & b]) != null && base == b &&
556		UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
#	Line 570 | Line 585 | public class ForkJoinWorkerThread extend
585
586		/**
587		* Returns a popped task, or null if empty. Assumes active status.
588	<	* Called only by current thread.
588	>	* Called only by current thread.
589		*/
590	<	final ForkJoinTask<?> popTask() {
591	<	int s;
592	<	ForkJoinTask<?>[] q;
593	<	if (base != (s = sp) && (q = queue) != null) {
594	<	int i = (q.length - 1) & --s;
595	<	ForkJoinTask<?> t = q[i];
596	<	if (t != null && UNSAFE.compareAndSwapObject
597	<	(q, (i << qShift) + qBase, t, null)) {
598	<	sp = s;
599	<	return t;
590	>	private ForkJoinTask<?> popTask() {
591	>	ForkJoinTask<?>[] q = queue;
592	>	if (q != null) {
593	>	int s;
594	>	while ((s = sp) != base) {
595	>	int i = (q.length - 1) & --s;
596	>	long u = (i << qShift) + qBase; // raw offset
597	>	ForkJoinTask<?> t = q[i];
598	>	if (t == null)   // lost to stealer
599	>	break;
600	>	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
601	>	sp = s; // putOrderedInt may encourage more timely write
602	>	// UNSAFE.putOrderedInt(this, spOffset, s);
603	>	return t;
604	>	}
605		}
606		}
607		return null;
#	Line 596 | Line 616 | public class ForkJoinWorkerThread extend
616		*/
617		final boolean unpushTask(ForkJoinTask<?> t) {
618		int s;
619	<	ForkJoinTask<?>[] q;
620	<	if (base != (s = sp) && (q = queue) != null &&
619	>	ForkJoinTask<?>[] q = queue;
620	>	if ((s = sp) != base && q != null &&
621		UNSAFE.compareAndSwapObject
622		(q, (((q.length - 1) & --s) << qShift) + qBase, t, null)) {
623	<	sp = s;
623	>	sp = s; // putOrderedInt may encourage more timely write
624	>	// UNSAFE.putOrderedInt(this, spOffset, s);
625		return true;
626		}
627		return false;
#	Line 688 | Line 709 | public class ForkJoinWorkerThread extend
709		for (;;) {
710		ForkJoinWorkerThread v = ws[k & mask];
711		r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // inline xorshift
712	<	if (v != null && v.base != v.sp) {
713	<	if (canSteal ||       // ensure active status
714	<	(canSteal = active = p.tryIncrementActiveCount())) {
715	<	int b = v.base;   // inline specialized deqTask
716	<	ForkJoinTask<?>[] q;
717	<	if (b != v.sp && (q = v.queue) != null) {
718	<	ForkJoinTask<?> t;
719	<	int i = (q.length - 1) & b;
720	<	long u = (i << qShift) + qBase; // raw offset
721	<	if ((t = q[i]) != null && v.base == b &&
722	<	UNSAFE.compareAndSwapObject(q, u, t, null)) {
723	<	currentSteal = t;
724	<	v.stealHint = poolIndex;
725	<	v.base = b + 1;
726	<	seed = r;
727	<	++stealCount;
728	<	return t;
729	<	}
712	>	ForkJoinTask<?>[] q; ForkJoinTask<?> t; int b, a;
713	>	if (v != null && (b = v.base) != v.sp &&
714	>	(q = v.queue) != null) {
715	>	int i = (q.length - 1) & b;
716	>	long u = (i << qShift) + qBase; // raw offset
717	>	int pid = poolIndex;
718	>	if ((t = q[i]) != null) {
719	>	if (!canSteal &&  // inline p.tryIncrementActiveCount
720	>	UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
721	>	a = p.runState, a + 1))
722	>	canSteal = active = true;
723	>	if (canSteal && v.base == b++ &&
724	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
725	>	v.base = b;
726	>	v.stealHint = pid;
727	>	UNSAFE.putOrderedObject(this,
728	>	currentStealOffset, t);
729	>	seed = r;
730	>	++stealCount;
731	>	return t;
732		}
733		}
734		j = -n;
#	Line 725 | Line 748 | public class ForkJoinWorkerThread extend
748		// Run State management
749
750		// status check methods used mainly by ForkJoinPool
751	+	final boolean isRunning()     { return runState == 0; }
752		final boolean isTerminating() { return (runState & TERMINATING) != 0; }
753		final boolean isTerminated()  { return (runState & TERMINATED) != 0; }
754		final boolean isSuspended()   { return (runState & SUSPENDED) != 0; }
755		final boolean isTrimmed()     { return (runState & TRIMMED) != 0; }
756
757		/**
758	<	* Sets state to TERMINATING, also resuming if suspended.
758	>	* Sets state to TERMINATING. Does NOT unpark or interrupt
759	>	* to wake up if currently blocked. Callers must do so if desired.
760		*/
761		final void shutdown() {
762		for (;;) {
763		int s = runState;
764	+	if ((s & (TERMINATING|TERMINATED)) != 0)
765	+	break;
766		if ((s & SUSPENDED) != 0) { // kill and wakeup if suspended
767		if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
768		(s & ~SUSPENDED) |
769	<	(TRIMMED|TERMINATING))) {
743	<	LockSupport.unpark(this);
769	>	(TRIMMED|TERMINATING)))
770		break;
745	–	}
771		}
772		else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
773		s | TERMINATING))
#	Line 751 | Line 776 | public class ForkJoinWorkerThread extend
776		}
777
778		/**
779	<	* Sets state to TERMINATED. Called only by this thread.
779	>	* Sets state to TERMINATED. Called only by onTermination()
780		*/
781		private void setTerminated() {
782		int s;
#	Line 761 | Line 786 | public class ForkJoinWorkerThread extend
786		}
787
788		/**
789	<	* Instrumented version of park used by ForkJoinPool.awaitEvent
790	<	*/
766	<	final void doPark() {
767	<	++parkCount;
768	<	LockSupport.park(this);
769	<	}
770	<
771	<	/**
772	<	* If suspended, tries to set status to unsuspended and unparks.
789	>	* If suspended, tries to set status to unsuspended.
790	>	* Does NOT wake up if blocked.
791		*
792		* @return true if successful
793		*/
794	<	final boolean tryResumeSpare() {
795	<	int s = runState;
796	<	if ((s & SUSPENDED) != 0 &&
797	<	UNSAFE.compareAndSwapInt(this, runStateOffset, s,
798	<	s & ~SUSPENDED)) {
799	<	LockSupport.unpark(this);
782	<	return true;
794	>	final boolean tryUnsuspend() {
795	>	int s;
796	>	while (((s = runState) & SUSPENDED) != 0) {
797	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
798	>	s & ~SUSPENDED))
799	>	return true;
800		}
801		return false;
802		}
803
804		/**
805	<	* Sets suspended status and blocks as spare until resumed,
806	<	* shutdown, or timed out.
790	<	*
791	<	* @return false if trimmed
805	>	* Sets suspended status and blocks as spare until resumed
806	>	* or shutdown.
807		*/
808	<	final boolean suspendAsSpare() {
809	<	for (;;) {               // set suspended unless terminating
808	>	final void suspendAsSpare() {
809	>	for (;;) {                  // set suspended unless terminating
810		int s = runState;
811		if ((s & TERMINATING) != 0) { // must kill
812		if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
813		s | (TRIMMED | TERMINATING)))
814	<	return false;
814	>	return;
815		}
816		else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
817		s | SUSPENDED))
818		break;
819		}
820	<	boolean timed;
821	<	long nanos;
807	<	long startTime;
808	<	if (poolIndex < pool.parallelism) {
809	<	timed = false;
810	<	nanos = 0L;
811	<	startTime = 0L;
812	<	}
813	<	else {
814	<	timed = true;
815	<	nanos = SPARE_KEEPALIVE_NANOS;
816	<	startTime = System.nanoTime();
817	<	}
818	<	pool.accumulateStealCount(this);
819	<	lastEventCount = 0;      // reset upon resume
820	<	interrupted();           // clear/ignore interrupts
820	>	ForkJoinPool p = pool;
821	>	p.pushSpare(this);
822		while ((runState & SUSPENDED) != 0) {
823	<	++parkCount;
824	<	if (!timed)
823	>	if (p.tryAccumulateStealCount(this)) {
824	>	interrupted();          // clear/ignore interrupts
825	>	if ((runState & SUSPENDED) == 0)
826	>	break;
827		LockSupport.park(this);
825	–	else if ((nanos -= (System.nanoTime() - startTime)) > 0)
826	–	LockSupport.parkNanos(this, nanos);
827	–	else { // try to trim on timeout
828	–	int s = runState;
829	–	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
830	–	(s & ~SUSPENDED) |
831	–	(TRIMMED|TERMINATING)))
832	–	return false;
828		}
829		}
835	–	return true;
830		}
831
832		// Misc support methods for ForkJoinPool
#	Line 842 | Line 836 | public class ForkJoinWorkerThread extend
836		* used by ForkJoinTask.
837		*/
838		final int getQueueSize() {
839	<	return -base + sp;
839	>	int n; // external calls must read base first
840	>	return (n = -base + sp) <= 0 ? 0 : n;
841		}
842
843		/**
#	Line 850 | Line 845 | public class ForkJoinWorkerThread extend
845		* thread.
846		*/
847		final void cancelTasks() {
848	<	ForkJoinTask<?> cj = currentJoin; // try to kill live tasks
848	>	ForkJoinTask<?> cj = currentJoin; // try to cancel ongoing tasks
849		if (cj != null) {
850		currentJoin = null;
851		cj.cancelIgnoringExceptions();
852	+	try {
853	+	this.interrupt(); // awaken wait
854	+	} catch (SecurityException ignore) {
855	+	}
856		}
857		ForkJoinTask<?> cs = currentSteal;
858		if (cs != null) {
#	Line 892 | Line 891 | public class ForkJoinWorkerThread extend
891		* @return a task, if available
892		*/
893		final ForkJoinTask<?> pollLocalTask() {
894	+	ForkJoinPool p = pool;
895		while (sp != base) {
896	<	if (active || (active = pool.tryIncrementActiveCount()))
896	>	int a; // inline p.tryIncrementActiveCount
897	>	if (active ||
898	>	(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
899	>	a = p.runState, a + 1)))
900		return locallyFifo? locallyDeqTask() : popTask();
901		}
902		return null;
#	Line 905 | Line 908 | public class ForkJoinWorkerThread extend
908		* @return a task, if available
909		*/
910		final ForkJoinTask<?> pollTask() {
911	<	ForkJoinTask<?> t;
912	<	return (t = pollLocalTask()) != null ? t : scan();
911	>	ForkJoinTask<?> t = pollLocalTask();
912	>	if (t == null) {
913	>	t = scan();
914	>	// cannot retain/track/help steal
915	>	UNSAFE.putOrderedObject(this, currentStealOffset, null);
916	>	}
917	>	return t;
918		}
919
920		/**
921		* Possibly runs some tasks and/or blocks, until task is done.
914	–	* The main body is basically a big spinloop, alternating between
915	–	* calls to helpJoinTask and pool.tryAwaitJoin with increased
916	–	* patience parameters until either the task is done without
917	–	* waiting, or we have, if necessary, created or resumed a
918	–	* replacement for this thread while it blocks.
922		*
923		* @param joinMe the task to join
921	–	* @return task status on exit
924		*/
925	<	final int joinTask(ForkJoinTask<?> joinMe) {
926	<	int stat;
925	>	final void joinTask(ForkJoinTask<?> joinMe) {
926	>	// currentJoin only written by this thread; only need ordered store
927		ForkJoinTask<?> prevJoin = currentJoin;
928	<	currentJoin = joinMe;
929	<	if ((stat = joinMe.status) >= 0 &&
930	<	(sp == base || (stat = localHelpJoinTask(joinMe)) >= 0)) {
931	<	ForkJoinPool p = pool;
932	<	int helpRetries = 2;     // initial patience values
933	<	int awaitRetries = -1;   // -1 is sentinel for replace-check only
932	<	do {
933	<	helpJoinTask(joinMe, helpRetries);
934	<	if ((stat = joinMe.status) < 0)
935	<	break;
936	<	boolean busy = p.tryAwaitJoin(joinMe, awaitRetries);
937	<	if ((stat = joinMe.status) < 0)
938	<	break;
939	<	if (awaitRetries == -1)
940	<	awaitRetries = 0;
941	<	else if (busy)
942	<	++awaitRetries;
943	<	if (helpRetries < p.parallelism)
944	<	helpRetries <<= 1;
945	<	Thread.yield(); // tame unbounded loop
946	<	} while (joinMe.status >= 0);
947	<	}
948	<	currentJoin = prevJoin;
949	<	return stat;
928	>	UNSAFE.putOrderedObject(this, currentJoinOffset, joinMe);
929	>	if (sp != base)
930	>	localHelpJoinTask(joinMe);
931	>	if (joinMe.status >= 0)
932	>	pool.awaitJoin(joinMe, this);
933	>	UNSAFE.putOrderedObject(this, currentJoinOffset, prevJoin);
934		}
935
936		/**
937		* Run tasks in local queue until given task is done.
938		*
939		* @param joinMe the task to join
956	–	* @return task status on exit
940		*/
941	<	private int localHelpJoinTask(ForkJoinTask<?> joinMe) {
942	<	int stat, s;
941	>	private void localHelpJoinTask(ForkJoinTask<?> joinMe) {
942	>	int s;
943		ForkJoinTask<?>[] q;
944	<	while ((stat = joinMe.status) >= 0 &&
962	<	base != (s = sp) && (q = queue) != null) {
963	<	ForkJoinTask<?> t;
944	>	while (joinMe.status >= 0 && (s = sp) != base && (q = queue) != null) {
945		int i = (q.length - 1) & --s;
946		long u = (i << qShift) + qBase; // raw offset
947	<	if ((t = q[i]) != null &&
948	<	UNSAFE.compareAndSwapObject(q, u, t, null)) {
947	>	ForkJoinTask<?> t = q[i];
948	>	if (t == null)  // lost to a stealer
949	>	break;
950	>	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
951		/*
952		* This recheck (and similarly in helpJoinTask)
953		* handles cases where joinMe is independently
#	Line 972 | Line 955 | public class ForkJoinWorkerThread extend
955		* available. Back out of the pop by putting t back
956		* into slot before we commit by writing sp.
957		*/
958	<	if ((stat = joinMe.status) < 0) {
958	>	if (joinMe.status < 0) {
959		UNSAFE.putObjectVolatile(q, u, t);
960		break;
961		}
962		sp = s;
963	<	t.tryExec();
963	>	// UNSAFE.putOrderedInt(this, spOffset, s);
964	>	t.quietlyExec();
965		}
966		}
983	–	return stat;
967		}
968
969		/**
970	<	* Tries to locate and help perform tasks for a stealer of the
971	<	* given task, or in turn one of its stealers.  Traces
972	<	* currentSteal->currentJoin links looking for a thread working on
973	<	* a descendant of the given task and with a non-empty queue to
974	<	* steal back and execute tasks from. Restarts search upon
975	<	* encountering chains that are stale, unknown, or of length
976	<	* greater than MAX_HELP_DEPTH links, to avoid unbounded cycles.
977	<	*
978	<	* The implementation is very branchy to cope with the restart
979	<	* cases.  Returns void, not task status (which must be reread by
980	<	* caller anyway) to slightly simplify control paths.
970	>	* Unless terminating, tries to locate and help perform tasks for
971	>	* a stealer of the given task, or in turn one of its stealers.
972	>	* Traces currentSteal->currentJoin links looking for a thread
973	>	* working on a descendant of the given task and with a non-empty
974	>	* queue to steal back and execute tasks from.
975	>	*
976	>	* The implementation is very branchy to cope with potential
977	>	* inconsistencies or loops encountering chains that are stale,
978	>	* unknown, or of length greater than MAX_HELP_DEPTH links.  All
979	>	* of these cases are dealt with by just returning back to the
980	>	* caller, who is expected to retry if other join mechanisms also
981	>	* don't work out.
982		*
983		* @param joinMe the task to join
984		*/
985	<	final void helpJoinTask(ForkJoinTask<?> joinMe, int retries) {
986	<	ForkJoinWorkerThread[] ws = pool.workers;
985	>	final void helpJoinTask(ForkJoinTask<?> joinMe) {
986	>	ForkJoinWorkerThread[] ws;
987		int n;
988	<	if (ws == null || (n = ws.length) <= 1)
989	<	return;                   // need at least 2 workers
990	<
991	<	restart:while (joinMe.status >= 0 && --retries >= 0) {
992	<	ForkJoinTask<?> task = joinMe;        // base of chain
993	<	ForkJoinWorkerThread thread = this;   // thread with stolen task
994	<	for (int depth = 0; depth < MAX_HELP_DEPTH; ++depth) {
995	<	// Try to find v, the stealer of task, by first using hint
996	<	ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)];
997	<	if (v == null || v.currentSteal != task) {
998	<	for (int j = 0; ; ++j) {      // search array
999	<	if (task.status < 0 || j == n)
1000	<	continue restart;     // stale or no stealer
1001	<	if ((v = ws[j]) != null && v.currentSteal == task) {
1002	<	thread.stealHint = j; // save for next time
1003	<	break;
1004	<	}
1005	<	}
1006	<	}
1007	<	// Try to help v, using specialized form of deqTask
1008	<	int b;
1009	<	ForkJoinTask<?>[] q;
1010	<	while ((b = v.base) != v.sp && (q = v.queue) != null) {
1011	<	int i = (q.length - 1) & b;
1012	<	long u = (i << qShift) + qBase;
1029	<	ForkJoinTask<?> t = q[i];
1030	<	if (task.status < 0)          // stale
1031	<	continue restart;
1032	<	if (v.base == b) {            // recheck after reading t
1033	<	if (t == null)            // producer stalled
1034	<	continue restart;     // retry via restart
1035	<	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
1036	<	if (joinMe.status < 0) {
1037	<	UNSAFE.putObjectVolatile(q, u, t);
1038	<	return;           // back out on cancel
988	>	if (joinMe.status < 0)                // already done
989	>	return;
990	>	if ((runState & TERMINATING) != 0) {  // cancel if shutting down
991	>	joinMe.cancelIgnoringExceptions();
992	>	return;
993	>	}
994	>	if ((ws = pool.workers) == null || (n = ws.length) <= 1)
995	>	return;                           // need at least 2 workers
996	>
997	>	ForkJoinTask<?> task = joinMe;        // base of chain
998	>	ForkJoinWorkerThread thread = this;   // thread with stolen task
999	>	for (int d = 0; d < MAX_HELP_DEPTH; ++d) { // chain length
1000	>	// Try to find v, the stealer of task, by first using hint
1001	>	ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)];
1002	>	if (v == null || v.currentSteal != task) {
1003	>	for (int j = 0; ; ++j) {      // search array
1004	>	if (j < n) {
1005	>	ForkJoinTask<?> vs;
1006	>	if ((v = ws[j]) != null &&
1007	>	(vs = v.currentSteal) != null) {
1008	>	if (joinMe.status < 0 || task.status < 0)
1009	>	return;       // stale or done
1010	>	if (vs == task) {
1011	>	thread.stealHint = j;
1012	>	break;        // save hint for next time
1013		}
1040	–	ForkJoinTask<?> prevSteal = currentSteal;
1041	–	currentSteal = t;
1042	–	v.stealHint = poolIndex;
1043	–	v.base = b + 1;
1044	–	t.tryExec();
1045	–	currentSteal = prevSteal;
1014		}
1015		}
1016	<	if (joinMe.status < 0)
1017	<	return;
1016	>	else
1017	>	return;               // no stealer
1018		}
1019	<	// Try to descend to find v's stealer
1020	<	ForkJoinTask<?> next = v.currentJoin;
1053	<	if (next == null || task.status < 0)
1054	<	continue restart;             // no descendent or stale
1019	>	}
1020	>	for (;;) { // Try to help v, using specialized form of deqTask
1021		if (joinMe.status < 0)
1022		return;
1023	<	task = next;
1024	<	thread = v;
1023	>	int b = v.base;
1024	>	ForkJoinTask<?>[] q = v.queue;
1025	>	if (b == v.sp || q == null)
1026	>	break;
1027	>	int i = (q.length - 1) & b;
1028	>	long u = (i << qShift) + qBase;
1029	>	ForkJoinTask<?> t = q[i];
1030	>	int pid = poolIndex;
1031	>	ForkJoinTask<?> ps = currentSteal;
1032	>	if (task.status < 0)
1033	>	return;                   // stale or done
1034	>	if (t != null && v.base == b++ &&
1035	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1036	>	if (joinMe.status < 0) {
1037	>	UNSAFE.putObjectVolatile(q, u, t);
1038	>	return;               // back out on cancel
1039	>	}
1040	>	v.base = b;
1041	>	v.stealHint = pid;
1042	>	UNSAFE.putOrderedObject(this, currentStealOffset, t);
1043	>	t.quietlyExec();
1044	>	UNSAFE.putOrderedObject(this, currentStealOffset, ps);
1045	>	}
1046		}
1047	+	// Try to descend to find v's stealer
1048	+	ForkJoinTask<?> next = v.currentJoin;
1049	+	if (task.status < 0 || next == null || next == task ||
1050	+	joinMe.status < 0)
1051	+	return;
1052	+	task = next;
1053	+	thread = v;
1054		}
1055		}
1056
#	Line 1115 | Line 1109 | public class ForkJoinWorkerThread extend
1109		* Runs tasks until {@code pool.isQuiescent()}.
1110		*/
1111		final void helpQuiescePool() {
1112	+	ForkJoinTask<?> ps = currentSteal; // to restore below
1113		for (;;) {
1114		ForkJoinTask<?> t = pollLocalTask();
1115	<	if (t != null || (t = scan()) != null) {
1116	<	t.tryExec();
1122	<	currentSteal = null;
1123	<	}
1115	>	if (t != null || (t = scan()) != null)
1116	>	t.quietlyExec();
1117		else {
1118		ForkJoinPool p = pool;
1119	+	int a; // to inline CASes
1120		if (active) {
1121	+	if (!UNSAFE.compareAndSwapInt
1122	+	(p, poolRunStateOffset, a = p.runState, a - 1))
1123	+	continue;   // retry later
1124		active = false; // inactivate
1125	<	do {} while (!p.tryDecrementActiveCount());
1125	>	UNSAFE.putOrderedObject(this, currentStealOffset, ps);
1126		}
1127		if (p.isQuiescent()) {
1128		active = true; // re-activate
1129	<	do {} while (!p.tryIncrementActiveCount());
1129	>	do {} while (!UNSAFE.compareAndSwapInt
1130	>	(p, poolRunStateOffset, a = p.runState, a+1));
1131		return;
1132		}
1133		}
#	Line 1139 | Line 1137 | public class ForkJoinWorkerThread extend
1137		// Unsafe mechanics
1138
1139		private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1140	+	private static final long spOffset =
1141	+	objectFieldOffset("sp", ForkJoinWorkerThread.class);
1142		private static final long runStateOffset =
1143		objectFieldOffset("runState", ForkJoinWorkerThread.class);
1144	+	private static final long currentJoinOffset =
1145	+	objectFieldOffset("currentJoin", ForkJoinWorkerThread.class);
1146	+	private static final long currentStealOffset =
1147	+	objectFieldOffset("currentSteal", ForkJoinWorkerThread.class);
1148		private static final long qBase =
1149		UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
1150	<	private static final long threadStatusOffset =
1151	<	objectFieldOffset("threadStatus", Thread.class);
1150	>	private static final long poolRunStateOffset = // to inline CAS
1151	>	objectFieldOffset("runState", ForkJoinPool.class);
1152	>
1153		private static final int qShift;
1154
1155		static {

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