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

Comparing jsr166/src/jsr166y/ForkJoinWorkerThread.java (file contents):
Revision 1.34 by dl, Fri Jun 4 14:37:54 2010 UTC vs.
Revision 1.41 by dl, Tue Aug 17 18:30:33 2010 UTC

#	Line 83 | Line 83 | public class ForkJoinWorkerThread extend
83		* by the ForkJoinPool).  This allows use in message-passing
84		* frameworks in which tasks are never joined.
85		*
86	<	* Efficient implementation of this approach currently relies on
87	<	* an uncomfortable amount of "Unsafe" mechanics. To maintain
86	>	* When a worker would otherwise be blocked waiting to join a
87	>	* task, it first tries a form of linear helping: Each worker
88	>	* records (in field currentSteal) the most recent task it stole
89	>	* from some other worker. Plus, it records (in field currentJoin)
90	>	* the task it is currently actively joining. Method joinTask uses
91	>	* these markers to try to find a worker to help (i.e., steal back
92	>	* a task from and execute it) that could hasten completion of the
93	>	* actively joined task. In essence, the joiner executes a task
94	>	* that would be on its own local deque had the to-be-joined task
95	>	* not been stolen. This may be seen as a conservative variant of
96	>	* the approach in Wagner & Calder "Leapfrogging: a portable
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 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.tryAwaitJoin).
114	>	*
115	>	* Efficient implementation of these algorithms currently relies
116	>	* on an uncomfortable amount of "Unsafe" mechanics. To maintain
117		* correct orderings, reads and writes of variable base require
118		* volatile ordering.  Variable sp does not require volatile
119		* writes but still needs store-ordering, which we accomplish by
120		* pre-incrementing sp before filling the slot with an ordered
121		* store.  (Pre-incrementing also enables backouts used in
122	<	* scanWhileJoining.)  Because they are protected by volatile base
123	<	* reads, reads of the queue array and its slots by other threads
124	<	* do not need volatile load semantics, but writes (in push)
125	<	* require store order and CASes (in pop and deq) require
126	<	* (volatile) CAS semantics.  (Michael, Saraswat, and Vechev's
127	<	* algorithm has similar properties, but without support for
128	<	* nulling slots.)  Since these combinations aren't supported
129	<	* using ordinary volatiles, the only way to accomplish these
130	<	* efficiently is to use direct Unsafe calls. (Using external
131	<	* AtomicIntegers and AtomicReferenceArrays for the indices and
132	<	* array is significantly slower because of memory locality and
133	<	* indirection effects.)
122	>	* joinTask.)  Because they are protected by volatile base reads,
123	>	* reads of the queue array and its slots by other threads do not
124	>	* need volatile load semantics, but writes (in push) require
125	>	* store order and CASes (in pop and deq) require (volatile) CAS
126	>	* semantics.  (Michael, Saraswat, and Vechev's algorithm has
127	>	* similar properties, but without support for nulling slots.)
128	>	* Since these combinations aren't supported using ordinary
129	>	* volatiles, the only way to accomplish these efficiently is to
130	>	* use direct Unsafe calls. (Using external AtomicIntegers and
131	>	* AtomicReferenceArrays for the indices and array is
132	>	* significantly slower because of memory locality and indirection
133	>	* effects.)
134		*
135		* Further, performance on most platforms is very sensitive to
136		* placement and sizing of the (resizable) queue array.  Even
#	Line 126 | Line 155 | public class ForkJoinWorkerThread extend
155		private static final Random seedGenerator = new Random();
156
157		/**
158	<	* The timeout value for suspending spares. Spare workers that
159	<	* remain unsignalled for more than this time may be trimmed
160	<	* (killed and removed from pool).  Since our goal is to avoid
161	<	* long-term thread buildup, the exact value of timeout does not
162	<	* matter too much so long as it avoids most false-alarm timeouts
163	<	* under GC stalls or momentarily high system load.
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
161	>	* staleness of traversal parameters at the expense of sometimes
162	>	* blocking when we could be helping.
163	>	*/
164	>	private static final int MAX_HELP_DEPTH = 8;
165	>
166	>	/**
167	>	* The wakeup interval (in nanoseconds) for the oldest worker
168	>	* suspended as spare.  On each wakeup not signalled by a
169	>	* resumption, it may ask the pool to reduce the number of spares.
170		*/
171	<	private static final long SPARE_KEEPALIVE_NANOS =
172	<	5L * 1000L * 1000L * 1000L; // 5 secs
171	>	private static final long TRIM_RATE_NANOS =
172	>	5L * 1000L * 1000L * 1000L; // 5sec
173
174		/**
175		* Capacity of work-stealing queue array upon initialization.
#	Line 178 | Line 213 | public class ForkJoinWorkerThread extend
213		private int sp;
214
215		/**
216	+	* The index of most recent stealer, used as a hint to avoid
217	+	* traversal in method helpJoinTask. This is only a hint because a
218	+	* worker might have had multiple steals and this only holds one
219	+	* of them (usually the most current). Declared non-volatile,
220	+	* relying on other prevailing sync to keep reasonably current.
221	+	*/
222	+	private int stealHint;
223	+
224	+	/**
225		* Run state of this worker. In addition to the usual run levels,
226		* tracks if this worker is suspended as a spare, and if it was
227		* killed (trimmed) while suspended. However, "active" status is
228	<	* maintained separately.
228	>	* maintained separately and modified only in conjunction with
229	>	* CASes of the pool's runState (which are currently sadly manually
230	>	* inlined for performance.)
231		*/
232		private volatile int runState;
233
#	Line 191 | Line 237 | public class ForkJoinWorkerThread extend
237		private static final int TRIMMED     = 0x08; // killed while suspended
238
239		/**
194	–	* Number of LockSupport.park calls to block this thread for
195	–	* suspension or event waits. Used for internal instrumention;
196	–	* currently not exported but included because volatile write upon
197	–	* park also provides a workaround for a JVM bug.
198	–	*/
199	–	private volatile int parkCount;
200	–
201	–	/**
240		* Number of steals, transferred and reset in pool callbacks pool
241		* when idle Accessed directly by pool.
242		*/
#	Line 218 | Line 256 | public class ForkJoinWorkerThread extend
256
257		/**
258		* True if use local fifo, not default lifo, for local polling.
259	<	* Shadows value from ForkJoinPool, which resets it if changed
222	<	* pool-wide.
259	>	* Shadows value from ForkJoinPool.
260		*/
261	<	private boolean locallyFifo;
261	>	private final boolean locallyFifo;
262
263		/**
264		* Index of this worker in pool array. Set once by pool before
#	Line 243 | Line 280 | public class ForkJoinWorkerThread extend
280		volatile long nextWaiter;
281
282		/**
283	+	* Number of times this thread suspended as spare
284	+	*/
285	+	int spareCount;
286	+
287	+	/**
288	+	* Encoded index and count of next spare waiter. Used only
289	+	* by ForkJoinPool for managing spares.
290	+	*/
291	+	volatile int nextSpare;
292	+
293	+	/**
294	+	* The task currently being joined, set only when actively trying
295	+	* to helpStealer. Written only by current thread, but read by
296	+	* others.
297	+	*/
298	+	private volatile ForkJoinTask<?> currentJoin;
299	+
300	+	/**
301	+	* The task most recently stolen from another worker (or
302	+	* submission queue).  Not volatile because always read/written in
303	+	* presence of related volatiles in those cases where it matters.
304	+	*/
305	+	private ForkJoinTask<?> currentSteal;
306	+
307	+	/**
308		* Creates a ForkJoinWorkerThread operating in the given pool.
309		*
310		* @param pool the pool this thread works in
311		* @throws NullPointerException if pool is null
312		*/
313		protected ForkJoinWorkerThread(ForkJoinPool pool) {
252	–	if (pool == null) throw new NullPointerException();
314		this.pool = pool;
315	+	this.locallyFifo = pool.locallyFifo;
316	+	setDaemon(true);
317		// To avoid exposing construction details to subclasses,
318		// remaining initialization is in start() and onStart()
319		}
#	Line 258 | Line 321 | public class ForkJoinWorkerThread extend
321		/**
322		* Performs additional initialization and starts this thread
323		*/
324	<	final void start(int poolIndex, boolean locallyFifo,
262	<	UncaughtExceptionHandler ueh) {
324	>	final void start(int poolIndex, UncaughtExceptionHandler ueh) {
325		this.poolIndex = poolIndex;
264	–	this.locallyFifo = locallyFifo;
326		if (ueh != null)
327		setUncaughtExceptionHandler(ueh);
267	–	setDaemon(true);
328		start();
329		}
330
#	Line 305 | Line 365 | public class ForkJoinWorkerThread extend
365		int rs = seedGenerator.nextInt();
366		seed = rs == 0? 1 : rs; // seed must be nonzero
367
368	<	// Allocate name string and queue array in this thread
368	>	// Allocate name string and arrays in this thread
369		String pid = Integer.toString(pool.getPoolNumber());
370		String wid = Integer.toString(poolIndex);
371		setName("ForkJoinPool-" + pid + "-worker-" + wid);
#	Line 323 | Line 383 | public class ForkJoinWorkerThread extend
383		*/
384		protected void onTermination(Throwable exception) {
385		try {
386	+	ForkJoinPool p = pool;
387	+	if (active) {
388	+	int a; // inline p.tryDecrementActiveCount
389	+	active = false;
390	+	do {} while(!UNSAFE.compareAndSwapInt
391	+	(p, poolRunStateOffset, a = p.runState, a - 1));
392	+	}
393		cancelTasks();
394		setTerminated();
395	<	pool.workerTerminated(this);
395	>	p.workerTerminated(this);
396		} catch (Throwable ex) {        // Shouldn't ever happen
397		if (exception == null)      // but if so, at least rethrown
398		exception = ex;
#	Line 358 | Line 425 | public class ForkJoinWorkerThread extend
425		* Find and execute tasks and check status while running
426		*/
427		private void mainLoop() {
428	<	boolean ran = false;      // true if ran task in last loop iter
362	<	boolean prevRan = false;  // true if ran on last or previous step
428	>	int misses = 0; // track consecutive times failed to find work; max 2
429		ForkJoinPool p = pool;
430		for (;;) {
431	<	p.preStep(this, prevRan);
431	>	p.preStep(this, misses);
432		if (runState != 0)
433	<	return;
434	<	ForkJoinTask<?> t; // try to get and run stolen or submitted task
435	<	if ((t = scan()) != null || (t = pollSubmission()) != null) {
370	<	t.tryExec();
371	<	if (base != sp)
372	<	runLocalTasks();
373	<	prevRan = ran = true;
374	<	}
375	<	else {
376	<	prevRan = ran;
377	<	ran = false;
378	<	}
433	>	break;
434	>	misses = ((tryExecSteal() || tryExecSubmission()) ? 0 :
435	>	(misses < 2 ? misses + 1 : 2));
436		}
437		}
438
439		/**
440	<	* Runs local tasks until queue is empty or shut down.  Call only
441	<	* while active.
440	>	* Try to steal a task and execute it
441	>	*
442	>	* @return true if ran a task
443		*/
444	<	private void runLocalTasks() {
445	<	while (runState == 0) {
446	<	ForkJoinTask<?> t = locallyFifo? locallyDeqTask() : popTask();
447	<	if (t != null)
448	<	t.tryExec();
449	<	else if (base == sp)
450	<	break;
444	>	private boolean tryExecSteal() {
445	>	ForkJoinTask<?> t;
446	>	if ((t  = scan()) != null) {
447	>	t.quietlyExec();
448	>	currentSteal = null;
449	>	if (sp != base)
450	>	execLocalTasks();
451	>	return true;
452		}
453	+	return false;
454		}
455
456		/**
457	<	* If a submission exists, try to activate and take it
457	>	* If a submission exists, try to activate and run it;
458		*
459	<	* @return a task, if available
459	>	* @return true if ran a task
460		*/
461	<	private ForkJoinTask<?> pollSubmission() {
461	>	private boolean tryExecSubmission() {
462		ForkJoinPool p = pool;
463		while (p.hasQueuedSubmissions()) {
464	<	if (active || (active = p.tryIncrementActiveCount())) {
465	<	ForkJoinTask<?> t = p.pollSubmission();
466	<	return t != null ? t : scan(); // if missed, rescan
464	>	ForkJoinTask<?> t; int a;
465	>	if (active || // ugly/hacky: inline p.tryIncrementActiveCount
466	>	(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
467	>	a = p.runState, a + 1))) {
468	>	if ((t = p.pollSubmission()) != null) {
469	>	currentSteal = t;
470	>	t.quietlyExec();
471	>	currentSteal = null;
472	>	if (sp != base)
473	>	execLocalTasks();
474	>	return true;
475	>	}
476		}
477		}
478	<	return null;
478	>	return false;
479	>	}
480	>
481	>	/**
482	>	* Runs local tasks until queue is empty or shut down.  Call only
483	>	* while active.
484	>	*/
485	>	private void execLocalTasks() {
486	>	while (runState == 0) {
487	>	ForkJoinTask<?> t = locallyFifo? locallyDeqTask() : popTask();
488	>	if (t != null)
489	>	t.quietlyExec();
490	>	else if (sp == base)
491	>	break;
492	>	}
493		}
494
495		/*
#	Line 466 | Line 549 | public class ForkJoinWorkerThread extend
549		/**
550		* Tries to take a task from the base of the queue, failing if
551		* empty or contended. Note: Specializations of this code appear
552	<	* in scan and scanWhileJoining.
552	>	* in locallyDeqTask and elsewhere.
553		*
554		* @return a task, or null if none or contended
555		*/
#	Line 474 | Line 557 | public class ForkJoinWorkerThread extend
557		ForkJoinTask<?> t;
558		ForkJoinTask<?>[] q;
559		int b, i;
560	<	if ((b = base) != sp &&
560	>	if (sp != (b = base) &&
561		(q = queue) != null && // must read q after b
562	<	(t = q[i = (q.length - 1) & b]) != null &&
562	>	(t = q[i = (q.length - 1) & b]) != null && base == b &&
563		UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
564		base = b + 1;
565		return t;
#	Line 496 | Line 579 | public class ForkJoinWorkerThread extend
579		ForkJoinTask<?> t;
580		int b, i;
581		while (sp != (b = base)) {
582	<	if ((t = q[i = (q.length - 1) & b]) != null &&
582	>	if ((t = q[i = (q.length - 1) & b]) != null && base == b &&
583		UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase,
584		t, null)) {
585		base = b + 1;
#	Line 509 | Line 592 | public class ForkJoinWorkerThread extend
592
593		/**
594		* Returns a popped task, or null if empty. Assumes active status.
595	<	* Called only by current thread. (Note: a specialization of this
513	<	* code appears in popWhileJoining.)
595	>	* Called only by current thread.
596		*/
597	<	final ForkJoinTask<?> popTask() {
598	<	int s;
599	<	ForkJoinTask<?>[] q;
600	<	if (base != (s = sp) && (q = queue) != null) {
601	<	int i = (q.length - 1) & --s;
602	<	ForkJoinTask<?> t = q[i];
603	<	if (t != null && UNSAFE.compareAndSwapObject
604	<	(q, (i << qShift) + qBase, t, null)) {
605	<	sp = s;
606	<	return t;
597	>	private ForkJoinTask<?> popTask() {
598	>	ForkJoinTask<?>[] q = queue;
599	>	if (q != null) {
600	>	int s;
601	>	while ((s = sp) != base) {
602	>	int i = (q.length - 1) & --s;
603	>	long u = (i << qShift) + qBase; // raw offset
604	>	ForkJoinTask<?> t = q[i];
605	>	if (t == null)   // lost to stealer
606	>	break;
607	>	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
608	>	sp = s; // putOrderedInt may encourage more timely write
609	>	// UNSAFE.putOrderedInt(this, spOffset, s);
610	>	return t;
611	>	}
612		}
613		}
614		return null;
#	Line 536 | Line 623 | public class ForkJoinWorkerThread extend
623		*/
624		final boolean unpushTask(ForkJoinTask<?> t) {
625		int s;
626	<	ForkJoinTask<?>[] q;
627	<	if (base != (s = sp) && (q = queue) != null &&
626	>	ForkJoinTask<?>[] q = queue;
627	>	if ((s = sp) != base && q != null &&
628		UNSAFE.compareAndSwapObject
629		(q, (((q.length - 1) & --s) << qShift) + qBase, t, null)) {
630		sp = s;
631	+	// UNSAFE.putOrderedInt(this, spOffset, s);
632		return true;
633		}
634		return false;
#	Line 629 | Line 717 | public class ForkJoinWorkerThread extend
717		ForkJoinWorkerThread v = ws[k & mask];
718		r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // inline xorshift
719		if (v != null && v.base != v.sp) {
720	<	int b, i;             // inline specialized deqTask
721	<	ForkJoinTask<?>[] q;
722	<	ForkJoinTask<?> t;
723	<	if ((canSteal ||      // ensure active status
724	<	(canSteal = active = p.tryIncrementActiveCount())) &&
725	<	(q = v.queue) != null &&
726	<	(t = q[i = (q.length - 1) & (b = v.base)]) != null &&
727	<	UNSAFE.compareAndSwapObject
728	<	(q, (i << qShift) + qBase, t, null)) {
729	<	v.base = b + 1;
730	<	seed = r;
731	<	++stealCount;
732	<	return t;
720	>	ForkJoinTask<?>[] q; int b, a;
721	>	if ((canSteal ||      // Ugly/hacky: inline
722	>	(canSteal = active =  // p.tryIncrementActiveCount
723	>	UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
724	>	a = p.runState, a + 1))) &&
725	>	(q = v.queue) != null && (b = v.base) != v.sp) {
726	>	int i = (q.length - 1) & b;
727	>	long u = (i << qShift) + qBase; // raw offset
728	>	ForkJoinTask<?> t = q[i];
729	>	if (v.base == b && t != null &&
730	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
731	>	int pid = poolIndex;
732	>	currentSteal = t;
733	>	v.stealHint = pid;
734	>	v.base = b + 1;
735	>	seed = r;
736	>	++stealCount;
737	>	return t;
738	>	}
739		}
740		j = -n;
741		k = r;                // restart on contention
#	Line 660 | Line 754 | public class ForkJoinWorkerThread extend
754		// Run State management
755
756		// status check methods used mainly by ForkJoinPool
757	+	final boolean isRunning()     { return runState == 0; }
758		final boolean isTerminating() { return (runState & TERMINATING) != 0; }
759		final boolean isTerminated()  { return (runState & TERMINATED) != 0; }
760		final boolean isSuspended()   { return (runState & SUSPENDED) != 0; }
761		final boolean isTrimmed()     { return (runState & TRIMMED) != 0; }
762
763		/**
764	<	* Sets state to TERMINATING, also resuming if suspended.
764	>	* Sets state to TERMINATING. Does NOT unpark or interrupt
765	>	* to wake up if currently blocked.
766		*/
767		final void shutdown() {
768		for (;;) {
769		int s = runState;
770	+	if ((s & (TERMINATING|TERMINATED)) != 0)
771	+	break;
772		if ((s & SUSPENDED) != 0) { // kill and wakeup if suspended
773		if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
774		(s & ~SUSPENDED) |
775	<	(TRIMMED|TERMINATING))) {
678	<	LockSupport.unpark(this);
775	>	(TRIMMED|TERMINATING)))
776		break;
680	–	}
777		}
778		else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
779		s | TERMINATING))
#	Line 686 | Line 782 | public class ForkJoinWorkerThread extend
782		}
783
784		/**
785	<	* Sets state to TERMINATED. Called only by this thread.
785	>	* Sets state to TERMINATED. Called only by onTermination()
786		*/
787		private void setTerminated() {
788		int s;
#	Line 696 | Line 792 | public class ForkJoinWorkerThread extend
792		}
793
794		/**
699	–	* Instrumented version of park. Also used by ForkJoinPool.awaitEvent
700	–	*/
701	–	final void doPark() {
702	–	++parkCount;
703	–	LockSupport.park(this);
704	–	}
705	–
706	–	/**
795		* If suspended, tries to set status to unsuspended.
708	–	* Caller must unpark to actually resume
796		*
797		* @return true if successful
798		*/
799		final boolean tryUnsuspend() {
800		int s;
801	<	return (((s = runState) & SUSPENDED) != 0 &&
802	<	UNSAFE.compareAndSwapInt(this, runStateOffset, s,
803	<	s & ~SUSPENDED));
801	>	while (((s = runState) & SUSPENDED) != 0) {
802	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
803	>	s & ~SUSPENDED))
804	>	return true;
805	>	}
806	>	return false;
807		}
808
809		/**
810	<	* Sets suspended status and blocks as spare until resumed,
811	<	* shutdown, or timed out.
722	<	*
723	<	* @return false if trimmed
810	>	* Sets suspended status and blocks as spare until resumed
811	>	* or shutdown.
812		*/
813	<	final boolean suspendAsSpare() {
814	<	for (;;) {               // set suspended unless terminating
813	>	final void suspendAsSpare() {
814	>	for (;;) {                  // set suspended unless terminating
815		int s = runState;
816		if ((s & TERMINATING) != 0) { // must kill
817		if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
818		s | (TRIMMED | TERMINATING)))
819	<	return false;
819	>	return;
820		}
821		else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
822		s | SUSPENDED))
823		break;
824		}
737	–	lastEventCount = 0;      // reset upon resume
825		ForkJoinPool p = pool;
826	<	p.releaseWaiters();      // help others progress
827	<	p.accumulateStealCount(this);
741	<	interrupted();           // clear/ignore interrupts
742	<	if (poolIndex < p.getParallelism()) { // untimed wait
743	<	while ((runState & SUSPENDED) != 0)
744	<	doPark();
745	<	return true;
746	<	}
747	<	return timedSuspend();   // timed wait if apparently non-core
748	<	}
749	<
750	<	/**
751	<	* Blocks as spare until resumed or timed out
752	<	* @return false if trimmed
753	<	*/
754	<	private boolean timedSuspend() {
755	<	long nanos = SPARE_KEEPALIVE_NANOS;
756	<	long startTime = System.nanoTime();
826	>	p.pushSpare(this);
827	>	lastEventCount = 0;         // reset upon resume
828		while ((runState & SUSPENDED) != 0) {
829	<	++parkCount;
830	<	if ((nanos -= (System.nanoTime() - startTime)) > 0)
831	<	LockSupport.parkNanos(this, nanos);
832	<	else { // try to trim on timeout
833	<	int s = runState;
834	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
835	<	(s & ~SUSPENDED) |
836	<	(TRIMMED|TERMINATING)))
837	<	return false;
829	>	if (p.tryAccumulateStealCount(this)) {
830	>	boolean untimed = nextSpare != 0;
831	>	long startTime = untimed? 0 : System.nanoTime();
832	>	interrupted();          // clear/ignore interrupts
833	>	if ((runState & SUSPENDED) == 0)
834	>	break;
835	>	if (untimed)     // untimed
836	>	LockSupport.park(this);
837	>	else {
838	>	LockSupport.parkNanos(this, TRIM_RATE_NANOS);
839	>	if ((runState & SUSPENDED) == 0)
840	>	break;
841	>	if (System.nanoTime() - startTime >= TRIM_RATE_NANOS)
842	>	p.tryShutdownSpare();
843	>	}
844		}
845		}
769	–	return true;
846		}
847
848		// Misc support methods for ForkJoinPool
#	Line 776 | Line 852 | public class ForkJoinWorkerThread extend
852		* used by ForkJoinTask.
853		*/
854		final int getQueueSize() {
855	<	return -base + sp;
856	<	}
781	<
782	<	/**
783	<	* Set locallyFifo mode. Called only by ForkJoinPool
784	<	*/
785	<	final void setAsyncMode(boolean async) {
786	<	locallyFifo = async;
855	>	int n; // external calls must read base first
856	>	return (n = -base + sp) <= 0 ? 0 : n;
857		}
858
859		/**
#	Line 791 | Line 861 | public class ForkJoinWorkerThread extend
861		* thread.
862		*/
863		final void cancelTasks() {
864	+	ForkJoinTask<?> cj = currentJoin; // try to cancel ongoing tasks
865	+	if (cj != null) {
866	+	currentJoin = null;
867	+	cj.cancelIgnoringExceptions();
868	+	try {
869	+	this.interrupt(); // awaken wait
870	+	} catch (SecurityException ignore) {
871	+	}
872	+	}
873	+	ForkJoinTask<?> cs = currentSteal;
874	+	if (cs != null) {
875	+	currentSteal = null;
876	+	cs.cancelIgnoringExceptions();
877	+	}
878		while (base != sp) {
879		ForkJoinTask<?> t = deqTask();
880		if (t != null)
#	Line 818 | Line 902 | public class ForkJoinWorkerThread extend
902		// Support methods for ForkJoinTask
903
904		/**
905	+	* Gets and removes a local task.
906	+	*
907	+	* @return a task, if available
908	+	*/
909	+	final ForkJoinTask<?> pollLocalTask() {
910	+	ForkJoinPool p = pool;
911	+	while (sp != base) {
912	+	int a; // inline p.tryIncrementActiveCount
913	+	if (active ||
914	+	(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
915	+	a = p.runState, a + 1)))
916	+	return locallyFifo? locallyDeqTask() : popTask();
917	+	}
918	+	return null;
919	+	}
920	+
921	+	/**
922	+	* Gets and removes a local or stolen task.
923	+	*
924	+	* @return a task, if available
925	+	*/
926	+	final ForkJoinTask<?> pollTask() {
927	+	ForkJoinTask<?> t = pollLocalTask();
928	+	if (t == null) {
929	+	t = scan();
930	+	currentSteal = null; // cannot retain/track/help
931	+	}
932	+	return t;
933	+	}
934	+
935	+	/**
936	+	* Possibly runs some tasks and/or blocks, until task is done.
937	+	*
938	+	* @param joinMe the task to join
939	+	*/
940	+	final void joinTask(ForkJoinTask<?> joinMe) {
941	+	// currentJoin only written by this thread; only need ordered store
942	+	ForkJoinTask<?> prevJoin = currentJoin;
943	+	UNSAFE.putOrderedObject(this, currentJoinOffset, joinMe);
944	+	if (sp != base)
945	+	localHelpJoinTask(joinMe);
946	+	if (joinMe.status >= 0)
947	+	pool.awaitJoin(joinMe, this);
948	+	UNSAFE.putOrderedObject(this, currentJoinOffset, prevJoin);
949	+	}
950	+
951	+	/**
952	+	* Run tasks in local queue until given task is done.
953	+	*
954	+	* @param joinMe the task to join
955	+	*/
956	+	private void localHelpJoinTask(ForkJoinTask<?> joinMe) {
957	+	int s;
958	+	ForkJoinTask<?>[] q;
959	+	while (joinMe.status >= 0 && (s = sp) != base && (q = queue) != null) {
960	+	int i = (q.length - 1) & --s;
961	+	long u = (i << qShift) + qBase; // raw offset
962	+	ForkJoinTask<?> t = q[i];
963	+	if (t == null)  // lost to a stealer
964	+	break;
965	+	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
966	+	/*
967	+	* This recheck (and similarly in helpJoinTask)
968	+	* handles cases where joinMe is independently
969	+	* cancelled or forced even though there is other work
970	+	* available. Back out of the pop by putting t back
971	+	* into slot before we commit by writing sp.
972	+	*/
973	+	if (joinMe.status < 0) {
974	+	UNSAFE.putObjectVolatile(q, u, t);
975	+	break;
976	+	}
977	+	sp = s;
978	+	// UNSAFE.putOrderedInt(this, spOffset, s);
979	+	t.quietlyExec();
980	+	}
981	+	}
982	+	}
983	+
984	+	/**
985	+	* Tries to locate and help perform tasks for a stealer of the
986	+	* given task, or in turn one of its stealers.  Traces
987	+	* currentSteal->currentJoin links looking for a thread working on
988	+	* a descendant of the given task and with a non-empty queue to
989	+	* steal back and execute tasks from.
990	+	*
991	+	* The implementation is very branchy to cope with the potential
992	+	* inconsistencies or loops encountering chains that are stale,
993	+	* unknown, or of length greater than MAX_HELP_DEPTH links.  All
994	+	* of these cases are dealt with by just returning back to the
995	+	* caller, who is expected to retry if other join mechanisms also
996	+	* don't work out.
997	+	*
998	+	* @param joinMe the task to join
999	+	*/
1000	+	final void helpJoinTask(ForkJoinTask<?> joinMe) {
1001	+	ForkJoinWorkerThread[] ws = pool.workers;
1002	+	int n; // need at least 2 workers
1003	+	if (ws != null && (n = ws.length) > 1 && joinMe.status >= 0) {
1004	+	ForkJoinTask<?> task = joinMe;        // base of chain
1005	+	ForkJoinWorkerThread thread = this;   // thread with stolen task
1006	+	for (int d = 0; d < MAX_HELP_DEPTH; ++d) { // chain length
1007	+	// Try to find v, the stealer of task, by first using hint
1008	+	ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)];
1009	+	if (v == null || v.currentSteal != task) {
1010	+	for (int j = 0; ; ++j) {      // search array
1011	+	if (j < n) {
1012	+	if ((v = ws[j]) != null) {
1013	+	if (task.status < 0)
1014	+	return;       // stale or done
1015	+	if (v.currentSteal == task) {
1016	+	thread.stealHint = j;
1017	+	break;        // save hint for next time
1018	+	}
1019	+	}
1020	+	}
1021	+	else
1022	+	return;               // no stealer
1023	+	}
1024	+	}
1025	+	// Try to help v, using specialized form of deqTask
1026	+	int b;
1027	+	ForkJoinTask<?>[] q;
1028	+	while ((b = v.base) != v.sp && (q = v.queue) != null) {
1029	+	int i = (q.length - 1) & b;
1030	+	long u = (i << qShift) + qBase;
1031	+	ForkJoinTask<?> t = q[i];
1032	+	if (task.status < 0)
1033	+	return;                   // stale or done
1034	+	if (v.base == b) {
1035	+	if (t == null)
1036	+	return;               // producer stalled
1037	+	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
1038	+	if (joinMe.status < 0) {
1039	+	UNSAFE.putObjectVolatile(q, u, t);
1040	+	return;           // back out on cancel
1041	+	}
1042	+	int pid = poolIndex;
1043	+	ForkJoinTask<?> prevSteal = currentSteal;
1044	+	currentSteal = t;
1045	+	v.stealHint = pid;
1046	+	v.base = b + 1;
1047	+	t.quietlyExec();
1048	+	currentSteal = prevSteal;
1049	+	}
1050	+	}
1051	+	if (joinMe.status < 0)
1052	+	return;
1053	+	}
1054	+	// Try to descend to find v's stealer
1055	+	ForkJoinTask<?> next = v.currentJoin;
1056	+	if (task.status < 0 || next == null || next == task ||
1057	+	joinMe.status < 0)
1058	+	return;
1059	+	task = next;
1060	+	thread = v;
1061	+	}
1062	+	}
1063	+	}
1064	+
1065	+	/**
1066		* Returns an estimate of the number of tasks, offset by a
1067		* function of number of idle workers.
1068		*
#	Line 869 | Line 1114 | public class ForkJoinWorkerThread extend
1114		}
1115
1116		/**
872	–	* Gets and removes a local task.
873	–	*
874	–	* @return a task, if available
875	–	*/
876	–	final ForkJoinTask<?> pollLocalTask() {
877	–	while (base != sp) {
878	–	if (active || (active = pool.tryIncrementActiveCount()))
879	–	return locallyFifo? locallyDeqTask() : popTask();
880	–	}
881	–	return null;
882	–	}
883	–
884	–	/**
885	–	* Gets and removes a local or stolen task.
886	–	*
887	–	* @return a task, if available
888	–	*/
889	–	final ForkJoinTask<?> pollTask() {
890	–	ForkJoinTask<?> t;
891	–	return (t = pollLocalTask()) != null ? t : scan();
892	–	}
893	–
894	–	/**
895	–	* Executes or processes other tasks awaiting the given task
896	–	* @return task completion status
897	–	*/
898	–	final int execWhileJoining(ForkJoinTask<?> joinMe) {
899	–	int s;
900	–	while ((s = joinMe.status) >= 0) {
901	–	ForkJoinTask<?> t = base != sp?
902	–	popWhileJoining(joinMe) :
903	–	scanWhileJoining(joinMe);
904	–	if (t != null)
905	–	t.tryExec();
906	–	}
907	–	return s;
908	–	}
909	–
910	–	/**
911	–	* Returns or stolen task, if available, unless joinMe is done
912	–	*
913	–	* This method is intrinsically nonmodular. To maintain the
914	–	* property that tasks are never stolen if the awaited task is
915	–	* ready, we must interleave mechanics of scan with status
916	–	* checks. We rely here on the commit points of deq that allow us
917	–	* to cancel a steal even after CASing slot to null, but before
918	–	* adjusting base index: If, after the CAS, we see that joinMe is
919	–	* ready, we can back out by placing the task back into the slot,
920	–	* without adjusting index. The loop is otherwise a variant of the
921	–	* one in scan().
922	–	*
923	–	*/
924	–	private ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
925	–	int r = seed;
926	–	ForkJoinPool p = pool;
927	–	ForkJoinWorkerThread[] ws;
928	–	int n;
929	–	outer:while ((ws = p.workers) != null && (n = ws.length) > 1) {
930	–	int mask = n - 1;
931	–	int k = r;
932	–	boolean contended = false; // to retry loop if deq contends
933	–	for (int j = -n; j <= n; ++j) {
934	–	if (joinMe.status < 0)
935	–	break outer;
936	–	int b;
937	–	ForkJoinTask<?>[] q;
938	–	ForkJoinWorkerThread v = ws[k & mask];
939	–	r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // xorshift
940	–	if (v != null && (b=v.base) != v.sp && (q=v.queue) != null) {
941	–	int i = (q.length - 1) & b;
942	–	ForkJoinTask<?> t = q[i];
943	–	if (t != null && UNSAFE.compareAndSwapObject
944	–	(q, (i << qShift) + qBase, t, null)) {
945	–	if (joinMe.status >= 0) {
946	–	v.base = b + 1;
947	–	seed = r;
948	–	++stealCount;
949	–	return t;
950	–	}
951	–	UNSAFE.putObjectVolatile(q, (i<<qShift)+qBase, t);
952	–	break outer; // back out
953	–	}
954	–	contended = true;
955	–	}
956	–	k = j < 0 ? r : (k + ((n >>> 1) | 1));
957	–	}
958	–	if (!contended && p.tryAwaitBusyJoin(joinMe))
959	–	break;
960	–	}
961	–	return null;
962	–	}
963	–
964	–	/**
965	–	* Version of popTask with join checks surrounding extraction.
966	–	* Uses the same backout strategy as helpJoinTask. Note that
967	–	* we ignore locallyFifo flag for local tasks here since helping
968	–	* joins only make sense in LIFO mode.
969	–	*
970	–	* @return a popped task, if available, unless joinMe is done
971	–	*/
972	–	private ForkJoinTask<?> popWhileJoining(ForkJoinTask<?> joinMe) {
973	–	int s;
974	–	ForkJoinTask<?>[] q;
975	–	while ((s = sp) != base && (q = queue) != null && joinMe.status >= 0) {
976	–	int i = (q.length - 1) & --s;
977	–	ForkJoinTask<?> t = q[i];
978	–	if (t != null && UNSAFE.compareAndSwapObject
979	–	(q, (i << qShift) + qBase, t, null)) {
980	–	if (joinMe.status >= 0) {
981	–	sp = s;
982	–	return t;
983	–	}
984	–	UNSAFE.putObjectVolatile(q, (i << qShift) + qBase, t);
985	–	break;  // back out
986	–	}
987	–	}
988	–	return null;
989	–	}
990	–
991	–	/**
1117		* Runs tasks until {@code pool.isQuiescent()}.
1118		*/
1119		final void helpQuiescePool() {
1120		for (;;) {
1121		ForkJoinTask<?> t = pollLocalTask();
1122	<	if (t != null || (t = scan()) != null)
1123	<	t.tryExec();
1122	>	if (t != null || (t = scan()) != null) {
1123	>	t.quietlyExec();
1124	>	currentSteal = null;
1125	>	}
1126		else {
1127		ForkJoinPool p = pool;
1128	+	int a; // to inline CASes
1129		if (active) {
1130	+	if (!UNSAFE.compareAndSwapInt
1131	+	(p, poolRunStateOffset, a = p.runState, a - 1))
1132	+	continue;   // retry later
1133		active = false; // inactivate
1003	–	do {} while (!p.tryDecrementActiveCount());
1134		}
1135		if (p.isQuiescent()) {
1136		active = true; // re-activate
1137	<	do {} while (!p.tryIncrementActiveCount());
1137	>	do {} while(!UNSAFE.compareAndSwapInt
1138	>	(p, poolRunStateOffset, a = p.runState, a+1));
1139		return;
1140		}
1141		}
#	Line 1014 | Line 1145 | public class ForkJoinWorkerThread extend
1145		// Unsafe mechanics
1146
1147		private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1148	+	private static final long spOffset =
1149	+	objectFieldOffset("sp", ForkJoinWorkerThread.class);
1150		private static final long runStateOffset =
1151		objectFieldOffset("runState", ForkJoinWorkerThread.class);
1152	+	private static final long currentJoinOffset =
1153	+	objectFieldOffset("currentJoin", ForkJoinWorkerThread.class);
1154	+	private static final long currentStealOffset =
1155	+	objectFieldOffset("currentSteal", ForkJoinWorkerThread.class);
1156		private static final long qBase =
1157		UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
1158	+	private static final long poolRunStateOffset = // to inline CAS
1159	+	objectFieldOffset("runState", ForkJoinPool.class);
1160	+
1161		private static final int qShift;
1162
1163		static {

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