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

Comparing jsr166/src/jsr166y/ForkJoinWorkerThread.java (file contents):
Revision 1.37 by dl, Fri Jul 23 14:09:17 2010 UTC vs.
Revision 1.51 by jsr166, Mon Sep 20 20:42:37 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 182 | Line 172 | public class ForkJoinWorkerThread extend
172
173		/**
174		* Maximum work-stealing queue array size.  Must be less than or
175	<	* equal to 1 << 28 to ensure lack of index wraparound. (This
176	<	* is less than usual bounds, because we need leftshift by 3
177	<	* to be in int range).
175	>	* equal to 1 << (31 - width of array entry) to ensure lack of
176	>	* index wraparound. The value is set in the static block
177	>	* at the end of this file after obtaining width.
178		*/
179	<	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 28;
179	>	private static final int MAXIMUM_QUEUE_CAPACITY;
180
181		/**
182		* The pool this thread works in. Accessed directly by ForkJoinTask.
#	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		/**
233	<	* Number of LockSupport.park calls to block this thread for
234	<	* 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	<	/**
248	<	* Number of steals, transferred and reset in pool callbacks pool
249	<	* when idle Accessed directly by pool.
233	>	* Number of steals. Directly accessed (and reset) by
234	>	* pool.tryAccumulateStealCount when idle.
235		*/
236		int stealCount;
237
#	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
#	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.
289	>	* to help other stealers in helpJoinTask. Written only by this
290	>	* thread, but read by others.
291		*/
292		private volatile ForkJoinTask<?> currentJoin;
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 this 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		}
314
315		/**
316	<	* Performs additional initialization and starts this thread
316	>	* Performs additional initialization and starts this thread.
317		*/
318		final void start(int poolIndex, UncaughtExceptionHandler ueh) {
319		this.poolIndex = poolIndex;
320		if (ueh != null)
321		setUncaughtExceptionHandler(ueh);
326	–	setDaemon(true);
322		start();
323		}
324
#	Line 354 | Line 349 | public class ForkJoinWorkerThread extend
349		/**
350		* Initializes internal state after construction but before
351		* processing any tasks. If you override this method, you must
352	<	* invoke super.onStart() at the beginning of the method.
352	>	* invoke @code{super.onStart()} at the beginning of the method.
353		* Initialization requires care: Most fields must have legal
354		* default values, to ensure that attempted accesses from other
355		* threads work correctly even before this thread starts
#	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 414 | Line 416 | public class ForkJoinWorkerThread extend
416		// helpers for run()
417
418		/**
419	<	* Find and execute tasks and check status while running
419	>	* Finds and executes tasks, and checks 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	>	* Tries 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	+	// This loop is needed in case attempt to activate fails, in
457	+	// which case we only retry if there still appears to be a
458	+	// submission.
459		while (p.hasQueuedSubmissions()) {
460	<	if (active || (active = p.tryIncrementActiveCount())) {
461	<	ForkJoinTask<?> t = p.pollSubmission();
462	<	if (t != null) {
463	<	currentSteal = t;
464	<	return t;
460	>	ForkJoinTask<?> t; int a;
461	>	if (active || // inline p.tryIncrementActiveCount
462	>	(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
463	>	a = p.runState, a + 1))) {
464	>	if ((t = p.pollSubmission()) != null) {
465	>	UNSAFE.putOrderedObject(this, currentStealOffset, t);
466	>	t.quietlyExec();
467	>	UNSAFE.putOrderedObject(this, currentStealOffset, null);
468	>	if (sp != base)
469	>	execLocalTasks();
470	>	return true;
471		}
467	–	return scan(); // if missed, rescan
472		}
473		}
474	<	return null;
474	>	return false;
475	>	}
476	>
477	>	/**
478	>	* Runs local tasks until queue is empty or shut down.  Call only
479	>	* while active.
480	>	*/
481	>	private void execLocalTasks() {
482	>	while (runState == 0) {
483	>	ForkJoinTask<?> t = locallyFifo ? locallyDeqTask() : popTask();
484	>	if (t != null)
485	>	t.quietlyExec();
486	>	else if (sp == base)
487	>	break;
488	>	}
489		}
490
491		/*
492		* Intrinsics-based atomic writes for queue slots. These are
493	<	* basically the same as methods in AtomicObjectArray, but
493	>	* basically the same as methods in AtomicReferenceArray, but
494		* specialized for (1) ForkJoinTask elements (2) requirement that
495		* nullness and bounds checks have already been performed by
496		* callers and (3) effective offsets are known not to overflow
497		* from int to long (because of MAXIMUM_QUEUE_CAPACITY). We don't
498		* need corresponding version for reads: plain array reads are OK
499	<	* because they protected by other volatile reads and are
499	>	* because they are protected by other volatile reads and are
500		* confirmed by CASes.
501		*
502		* Most uses don't actually call these methods, but instead contain
#	Line 502 | Line 520 | public class ForkJoinWorkerThread extend
520		* range. This method is used only during resets and backouts.
521		*/
522		private static final void writeSlot(ForkJoinTask<?>[] q, int i,
523	<	ForkJoinTask<?> t) {
523	>	ForkJoinTask<?> t) {
524		UNSAFE.putObjectVolatile(q, (i << qShift) + qBase, t);
525		}
526
#	Line 535 | Line 553 | public class ForkJoinWorkerThread extend
553		ForkJoinTask<?> t;
554		ForkJoinTask<?>[] q;
555		int b, i;
556	<	if ((b = base) != sp &&
556	>	if (sp != (b = base) &&
557		(q = queue) != null && // must read q after b
558		(t = q[i = (q.length - 1) & b]) != null && base == b &&
559		UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
#	Line 547 | Line 565 | public class ForkJoinWorkerThread extend
565
566		/**
567		* Tries to take a task from the base of own queue. Assumes active
568	<	* status.  Called only by current thread.
568	>	* status.  Called only by this thread.
569		*
570		* @return a task, or null if none
571		*/
#	Line 570 | Line 588 | public class ForkJoinWorkerThread extend
588
589		/**
590		* Returns a popped task, or null if empty. Assumes active status.
591	<	* Called only by current thread.
591	>	* Called only by this thread.
592		*/
593	<	final ForkJoinTask<?> popTask() {
594	<	int s;
595	<	ForkJoinTask<?>[] q;
596	<	if (base != (s = sp) && (q = queue) != null) {
597	<	int i = (q.length - 1) & --s;
598	<	ForkJoinTask<?> t = q[i];
599	<	if (t != null && UNSAFE.compareAndSwapObject
600	<	(q, (i << qShift) + qBase, t, null)) {
601	<	sp = s;
602	<	return t;
593	>	private ForkJoinTask<?> popTask() {
594	>	ForkJoinTask<?>[] q = queue;
595	>	if (q != null) {
596	>	int s;
597	>	while ((s = sp) != base) {
598	>	int i = (q.length - 1) & --s;
599	>	long u = (i << qShift) + qBase; // raw offset
600	>	ForkJoinTask<?> t = q[i];
601	>	if (t == null)   // lost to stealer
602	>	break;
603	>	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
604	>	sp = s; // putOrderedInt may encourage more timely write
605	>	// UNSAFE.putOrderedInt(this, spOffset, s);
606	>	return t;
607	>	}
608		}
609		}
610		return null;
#	Line 589 | Line 612 | public class ForkJoinWorkerThread extend
612
613		/**
614		* Specialized version of popTask to pop only if topmost element
615	<	* is the given task. Called only by current thread while
593	<	* active.
615	>	* is the given task. Called only by this thread while active.
616		*
617		* @param t the task. Caller must ensure non-null.
618		*/
619		final boolean unpushTask(ForkJoinTask<?> t) {
620		int s;
621	<	ForkJoinTask<?>[] q;
622	<	if (base != (s = sp) && (q = queue) != null &&
621	>	ForkJoinTask<?>[] q = queue;
622	>	if ((s = sp) != base && q != null &&
623		UNSAFE.compareAndSwapObject
624		(q, (((q.length - 1) & --s) << qShift) + qBase, t, null)) {
625	<	sp = s;
625	>	sp = s; // putOrderedInt may encourage more timely write
626	>	// UNSAFE.putOrderedInt(this, spOffset, s);
627		return true;
628		}
629		return false;
630		}
631
632		/**
633	<	* Returns next task or null if empty or contended
633	>	* Returns next task, or null if empty or contended.
634		*/
635		final ForkJoinTask<?> peekTask() {
636		ForkJoinTask<?>[] q = queue;
#	Line 649 | Line 672 | public class ForkJoinWorkerThread extend
672		* Computes next value for random victim probe in scan().  Scans
673		* don't require a very high quality generator, but also not a
674		* crummy one.  Marsaglia xor-shift is cheap and works well enough.
675	<	* Note: This is manually inlined in scan()
675	>	* Note: This is manually inlined in scan().
676		*/
677		private static final int xorShift(int r) {
678		r ^= r << 13;
#	Line 688 | Line 711 | public class ForkJoinWorkerThread extend
711		for (;;) {
712		ForkJoinWorkerThread v = ws[k & mask];
713		r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // inline xorshift
714	<	if (v != null && v.base != v.sp) {
715	<	if (canSteal ||       // ensure active status
716	<	(canSteal = active = p.tryIncrementActiveCount())) {
717	<	int b = v.base;   // inline specialized deqTask
718	<	ForkJoinTask<?>[] q;
719	<	if (b != v.sp && (q = v.queue) != null) {
720	<	ForkJoinTask<?> t;
721	<	int i = (q.length - 1) & b;
722	<	long u = (i << qShift) + qBase; // raw offset
723	<	if ((t = q[i]) != null && v.base == b &&
724	<	UNSAFE.compareAndSwapObject(q, u, t, null)) {
725	<	currentSteal = t;
726	<	v.stealHint = poolIndex;
727	<	v.base = b + 1;
728	<	seed = r;
729	<	++stealCount;
730	<	return t;
731	<	}
714	>	ForkJoinTask<?>[] q; ForkJoinTask<?> t; int b, a;
715	>	if (v != null && (b = v.base) != v.sp &&
716	>	(q = v.queue) != null) {
717	>	int i = (q.length - 1) & b;
718	>	long u = (i << qShift) + qBase; // raw offset
719	>	int pid = poolIndex;
720	>	if ((t = q[i]) != null) {
721	>	if (!canSteal &&  // inline p.tryIncrementActiveCount
722	>	UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
723	>	a = p.runState, a + 1))
724	>	canSteal = active = true;
725	>	if (canSteal && v.base == b++ &&
726	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
727	>	v.base = b;
728	>	v.stealHint = pid;
729	>	UNSAFE.putOrderedObject(this,
730	>	currentStealOffset, t);
731	>	seed = r;
732	>	++stealCount;
733	>	return t;
734		}
735		}
736		j = -n;
#	Line 725 | Line 750 | public class ForkJoinWorkerThread extend
750		// Run State management
751
752		// status check methods used mainly by ForkJoinPool
753	<	final boolean isTerminating() { return (runState & TERMINATING) != 0; }
753	>	final boolean isRunning()     { return runState == 0; }
754		final boolean isTerminated()  { return (runState & TERMINATED) != 0; }
755		final boolean isSuspended()   { return (runState & SUSPENDED) != 0; }
756		final boolean isTrimmed()     { return (runState & TRIMMED) != 0; }
757
758	+	final boolean isTerminating() {
759	+	if ((runState & TERMINATING) != 0)
760	+	return true;
761	+	if (pool.isAtLeastTerminating()) { // propagate pool state
762	+	shutdown();
763	+	return true;
764	+	}
765	+	return false;
766	+	}
767	+
768		/**
769	<	* Sets state to TERMINATING, also resuming if suspended.
769	>	* Sets state to TERMINATING. Does NOT unpark or interrupt
770	>	* to wake up if currently blocked. Callers must do so if desired.
771		*/
772		final void shutdown() {
773		for (;;) {
774		int s = runState;
775	+	if ((s & (TERMINATING|TERMINATED)) != 0)
776	+	break;
777		if ((s & SUSPENDED) != 0) { // kill and wakeup if suspended
778		if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
779		(s & ~SUSPENDED) |
780	<	(TRIMMED|TERMINATING))) {
743	<	LockSupport.unpark(this);
780	>	(TRIMMED|TERMINATING)))
781		break;
745	–	}
782		}
783		else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
784		s | TERMINATING))
#	Line 751 | Line 787 | public class ForkJoinWorkerThread extend
787		}
788
789		/**
790	<	* Sets state to TERMINATED. Called only by this thread.
790	>	* Sets state to TERMINATED. Called only by onTermination().
791		*/
792		private void setTerminated() {
793		int s;
#	Line 761 | Line 797 | public class ForkJoinWorkerThread extend
797		}
798
799		/**
800	<	* Instrumented version of park used by ForkJoinPool.awaitEvent
801	<	*/
766	<	final void doPark() {
767	<	++parkCount;
768	<	LockSupport.park(this);
769	<	}
770	<
771	<	/**
772	<	* If suspended, tries to set status to unsuspended and unparks.
800	>	* If suspended, tries to set status to unsuspended.
801	>	* Does NOT wake up if blocked.
802		*
803		* @return true if successful
804		*/
805	<	final boolean tryResumeSpare() {
806	<	int s = runState;
807	<	if ((s & SUSPENDED) != 0 &&
808	<	UNSAFE.compareAndSwapInt(this, runStateOffset, s,
809	<	s & ~SUSPENDED)) {
810	<	LockSupport.unpark(this);
782	<	return true;
805	>	final boolean tryUnsuspend() {
806	>	int s;
807	>	while (((s = runState) & SUSPENDED) != 0) {
808	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
809	>	s & ~SUSPENDED))
810	>	return true;
811		}
812		return false;
813		}
814
815		/**
816	<	* Sets suspended status and blocks as spare until resumed,
817	<	* shutdown, or timed out.
790	<	*
791	<	* @return false if trimmed
816	>	* Sets suspended status and blocks as spare until resumed
817	>	* or shutdown.
818		*/
819	<	final boolean suspendAsSpare() {
820	<	for (;;) {               // set suspended unless terminating
819	>	final void suspendAsSpare() {
820	>	for (;;) {                  // set suspended unless terminating
821		int s = runState;
822		if ((s & TERMINATING) != 0) { // must kill
823		if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
824		s | (TRIMMED | TERMINATING)))
825	<	return false;
825	>	return;
826		}
827		else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
828		s | SUSPENDED))
829		break;
830		}
831	<	boolean timed;
832	<	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
831	>	ForkJoinPool p = pool;
832	>	p.pushSpare(this);
833		while ((runState & SUSPENDED) != 0) {
834	<	++parkCount;
835	<	if (!timed)
834	>	if (p.tryAccumulateStealCount(this)) {
835	>	interrupted();          // clear/ignore interrupts
836	>	if ((runState & SUSPENDED) == 0)
837	>	break;
838		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;
839		}
840		}
835	–	return true;
841		}
842
843		// Misc support methods for ForkJoinPool
#	Line 842 | Line 847 | public class ForkJoinWorkerThread extend
847		* used by ForkJoinTask.
848		*/
849		final int getQueueSize() {
850	<	return -base + sp;
850	>	int n; // external calls must read base first
851	>	return (n = -base + sp) <= 0 ? 0 : n;
852		}
853
854		/**
#	Line 850 | Line 856 | public class ForkJoinWorkerThread extend
856		* thread.
857		*/
858		final void cancelTasks() {
859	<	ForkJoinTask<?> cj = currentJoin; // try to kill live tasks
859	>	ForkJoinTask<?> cj = currentJoin; // try to cancel ongoing tasks
860		if (cj != null) {
861		currentJoin = null;
862		cj.cancelIgnoringExceptions();
863	+	try {
864	+	this.interrupt(); // awaken wait
865	+	} catch (SecurityException ignore) {
866	+	}
867		}
868		ForkJoinTask<?> cs = currentSteal;
869		if (cs != null) {
#	Line 892 | Line 902 | public class ForkJoinWorkerThread extend
902		* @return a task, if available
903		*/
904		final ForkJoinTask<?> pollLocalTask() {
905	+	ForkJoinPool p = pool;
906		while (sp != base) {
907	<	if (active || (active = pool.tryIncrementActiveCount()))
908	<	return locallyFifo? locallyDeqTask() : popTask();
907	>	int a; // inline p.tryIncrementActiveCount
908	>	if (active ||
909	>	(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
910	>	a = p.runState, a + 1)))
911	>	return locallyFifo ? locallyDeqTask() : popTask();
912		}
913		return null;
914		}
#	Line 905 | Line 919 | public class ForkJoinWorkerThread extend
919		* @return a task, if available
920		*/
921		final ForkJoinTask<?> pollTask() {
922	<	ForkJoinTask<?> t;
923	<	return (t = pollLocalTask()) != null ? t : scan();
922	>	ForkJoinTask<?> t = pollLocalTask();
923	>	if (t == null) {
924	>	t = scan();
925	>	// cannot retain/track/help steal
926	>	UNSAFE.putOrderedObject(this, currentStealOffset, null);
927	>	}
928	>	return t;
929		}
930
931		/**
932		* 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.
933		*
934		* @param joinMe the task to join
921	–	* @return task status on exit
935		*/
936	<	final int joinTask(ForkJoinTask<?> joinMe) {
937	<	int stat;
936	>	final void joinTask(ForkJoinTask<?> joinMe) {
937	>	// currentJoin only written by this thread; only need ordered store
938		ForkJoinTask<?> prevJoin = currentJoin;
939	<	currentJoin = joinMe;
940	<	if ((stat = joinMe.status) >= 0 &&
941	<	(sp == base || (stat = localHelpJoinTask(joinMe)) >= 0)) {
942	<	ForkJoinPool p = pool;
943	<	int helpRetries = 2;     // initial patience values
944	<	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;
939	>	UNSAFE.putOrderedObject(this, currentJoinOffset, joinMe);
940	>	if (sp != base)
941	>	localHelpJoinTask(joinMe);
942	>	if (joinMe.status >= 0)
943	>	pool.awaitJoin(joinMe, this);
944	>	UNSAFE.putOrderedObject(this, currentJoinOffset, prevJoin);
945		}
946
947		/**
948		* Run tasks in local queue until given task is done.
949		*
950		* @param joinMe the task to join
956	–	* @return task status on exit
951		*/
952	<	private int localHelpJoinTask(ForkJoinTask<?> joinMe) {
953	<	int stat, s;
952	>	private void localHelpJoinTask(ForkJoinTask<?> joinMe) {
953	>	int s;
954		ForkJoinTask<?>[] q;
955	<	while ((stat = joinMe.status) >= 0 &&
962	<	base != (s = sp) && (q = queue) != null) {
963	<	ForkJoinTask<?> t;
955	>	while (joinMe.status >= 0 && (s = sp) != base && (q = queue) != null) {
956		int i = (q.length - 1) & --s;
957		long u = (i << qShift) + qBase; // raw offset
958	<	if ((t = q[i]) != null &&
959	<	UNSAFE.compareAndSwapObject(q, u, t, null)) {
958	>	ForkJoinTask<?> t = q[i];
959	>	if (t == null)  // lost to a stealer
960	>	break;
961	>	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
962		/*
963		* This recheck (and similarly in helpJoinTask)
964		* handles cases where joinMe is independently
#	Line 972 | Line 966 | public class ForkJoinWorkerThread extend
966		* available. Back out of the pop by putting t back
967		* into slot before we commit by writing sp.
968		*/
969	<	if ((stat = joinMe.status) < 0) {
969	>	if (joinMe.status < 0) {
970		UNSAFE.putObjectVolatile(q, u, t);
971		break;
972		}
973		sp = s;
974	<	t.tryExec();
974	>	// UNSAFE.putOrderedInt(this, spOffset, s);
975	>	t.quietlyExec();
976		}
977		}
983	–	return stat;
978		}
979
980		/**
981	<	* Tries to locate and help perform tasks for a stealer of the
982	<	* given task, or in turn one of its stealers.  Traces
983	<	* currentSteal->currentJoin links looking for a thread working on
984	<	* a descendant of the given task and with a non-empty queue to
985	<	* steal back and execute tasks from. Restarts search upon
986	<	* encountering chains that are stale, unknown, or of length
987	<	* greater than MAX_HELP_DEPTH links, to avoid unbounded cycles.
988	<	*
989	<	* The implementation is very branchy to cope with the restart
990	<	* cases.  Returns void, not task status (which must be reread by
991	<	* caller anyway) to slightly simplify control paths.
981	>	* Unless terminating, tries to locate and help perform tasks for
982	>	* a stealer of the given task, or in turn one of its stealers.
983	>	* Traces currentSteal->currentJoin links looking for a thread
984	>	* working on a descendant of the given task and with a non-empty
985	>	* queue to steal back and execute tasks from.
986	>	*
987	>	* The implementation is very branchy to cope with potential
988	>	* inconsistencies or loops encountering chains that are stale,
989	>	* unknown, or of length greater than MAX_HELP_DEPTH links.  All
990	>	* of these cases are dealt with by just returning back to the
991	>	* caller, who is expected to retry if other join mechanisms also
992	>	* don't work out.
993		*
994		* @param joinMe the task to join
995		*/
996	<	final void helpJoinTask(ForkJoinTask<?> joinMe, int retries) {
997	<	ForkJoinWorkerThread[] ws = pool.workers;
996	>	final void helpJoinTask(ForkJoinTask<?> joinMe) {
997	>	ForkJoinWorkerThread[] ws;
998		int n;
999	<	if (ws == null || (n = ws.length) <= 1)
1000	<	return;                   // need at least 2 workers
1001	<
1002	<	restart:while (joinMe.status >= 0 && --retries >= 0) {
1003	<	ForkJoinTask<?> task = joinMe;        // base of chain
1004	<	ForkJoinWorkerThread thread = this;   // thread with stolen task
1005	<	for (int depth = 0; depth < MAX_HELP_DEPTH; ++depth) {
1006	<	// Try to find v, the stealer of task, by first using hint
1007	<	ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)];
1008	<	if (v == null || v.currentSteal != task) {
1009	<	for (int j = 0; ; ++j) {      // search array
1010	<	if (task.status < 0 || j == n)
1011	<	continue restart;     // stale or no stealer
1012	<	if ((v = ws[j]) != null && v.currentSteal == task) {
1013	<	thread.stealHint = j; // save for next time
1014	<	break;
1015	<	}
1016	<	}
1017	<	}
1018	<	// Try to help v, using specialized form of deqTask
1019	<	int b;
1020	<	ForkJoinTask<?>[] q;
1021	<	while ((b = v.base) != v.sp && (q = v.queue) != null) {
1022	<	int i = (q.length - 1) & b;
1023	<	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
999	>	if (joinMe.status < 0)                // already done
1000	>	return;
1001	>	if ((runState & TERMINATING) != 0) {  // cancel if shutting down
1002	>	joinMe.cancelIgnoringExceptions();
1003	>	return;
1004	>	}
1005	>	if ((ws = pool.workers) == null || (n = ws.length) <= 1)
1006	>	return;                           // need at least 2 workers
1007	>
1008	>	ForkJoinTask<?> task = joinMe;        // base of chain
1009	>	ForkJoinWorkerThread thread = this;   // thread with stolen task
1010	>	for (int d = 0; d < MAX_HELP_DEPTH; ++d) { // chain length
1011	>	// Try to find v, the stealer of task, by first using hint
1012	>	ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)];
1013	>	if (v == null || v.currentSteal != task) {
1014	>	for (int j = 0; ; ++j) {      // search array
1015	>	if (j < n) {
1016	>	ForkJoinTask<?> vs;
1017	>	if ((v = ws[j]) != null &&
1018	>	(vs = v.currentSteal) != null) {
1019	>	if (joinMe.status < 0 || task.status < 0)
1020	>	return;       // stale or done
1021	>	if (vs == task) {
1022	>	thread.stealHint = j;
1023	>	break;        // save hint for next time
1024		}
1040	–	ForkJoinTask<?> prevSteal = currentSteal;
1041	–	currentSteal = t;
1042	–	v.stealHint = poolIndex;
1043	–	v.base = b + 1;
1044	–	t.tryExec();
1045	–	currentSteal = prevSteal;
1025		}
1026		}
1027	<	if (joinMe.status < 0)
1028	<	return;
1027	>	else
1028	>	return;               // no stealer
1029		}
1030	<	// Try to descend to find v's stealer
1031	<	ForkJoinTask<?> next = v.currentJoin;
1053	<	if (next == null || task.status < 0)
1054	<	continue restart;             // no descendent or stale
1030	>	}
1031	>	for (;;) { // Try to help v, using specialized form of deqTask
1032		if (joinMe.status < 0)
1033		return;
1034	<	task = next;
1035	<	thread = v;
1034	>	int b = v.base;
1035	>	ForkJoinTask<?>[] q = v.queue;
1036	>	if (b == v.sp || q == null)
1037	>	break;
1038	>	int i = (q.length - 1) & b;
1039	>	long u = (i << qShift) + qBase;
1040	>	ForkJoinTask<?> t = q[i];
1041	>	int pid = poolIndex;
1042	>	ForkJoinTask<?> ps = currentSteal;
1043	>	if (task.status < 0)
1044	>	return;                   // stale or done
1045	>	if (t != null && v.base == b++ &&
1046	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1047	>	if (joinMe.status < 0) {
1048	>	UNSAFE.putObjectVolatile(q, u, t);
1049	>	return;               // back out on cancel
1050	>	}
1051	>	v.base = b;
1052	>	v.stealHint = pid;
1053	>	UNSAFE.putOrderedObject(this, currentStealOffset, t);
1054	>	t.quietlyExec();
1055	>	UNSAFE.putOrderedObject(this, currentStealOffset, ps);
1056	>	}
1057		}
1058	+	// Try to descend to find v's stealer
1059	+	ForkJoinTask<?> next = v.currentJoin;
1060	+	if (task.status < 0 || next == null || next == task ||
1061	+	joinMe.status < 0)
1062	+	return;
1063	+	task = next;
1064	+	thread = v;
1065		}
1066		}
1067
1068		/**
1069	+	* Implements ForkJoinTask.getSurplusQueuedTaskCount().
1070		* Returns an estimate of the number of tasks, offset by a
1071		* function of number of idle workers.
1072		*
#	Line 1115 | Line 1121 | public class ForkJoinWorkerThread extend
1121		* Runs tasks until {@code pool.isQuiescent()}.
1122		*/
1123		final void helpQuiescePool() {
1124	+	ForkJoinTask<?> ps = currentSteal; // to restore below
1125		for (;;) {
1126		ForkJoinTask<?> t = pollLocalTask();
1127	<	if (t != null || (t = scan()) != null) {
1128	<	t.tryExec();
1122	<	currentSteal = null;
1123	<	}
1127	>	if (t != null || (t = scan()) != null)
1128	>	t.quietlyExec();
1129		else {
1130		ForkJoinPool p = pool;
1131	+	int a; // to inline CASes
1132		if (active) {
1133	+	if (!UNSAFE.compareAndSwapInt
1134	+	(p, poolRunStateOffset, a = p.runState, a - 1))
1135	+	continue;   // retry later
1136		active = false; // inactivate
1137	<	do {} while (!p.tryDecrementActiveCount());
1137	>	UNSAFE.putOrderedObject(this, currentStealOffset, ps);
1138		}
1139		if (p.isQuiescent()) {
1140		active = true; // re-activate
1141	<	do {} while (!p.tryIncrementActiveCount());
1141	>	do {} while (!UNSAFE.compareAndSwapInt
1142	>	(p, poolRunStateOffset, a = p.runState, a+1));
1143		return;
1144		}
1145		}
#	Line 1139 | Line 1149 | public class ForkJoinWorkerThread extend
1149		// Unsafe mechanics
1150
1151		private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1152	+	private static final long spOffset =
1153	+	objectFieldOffset("sp", ForkJoinWorkerThread.class);
1154		private static final long runStateOffset =
1155		objectFieldOffset("runState", ForkJoinWorkerThread.class);
1156	+	private static final long currentJoinOffset =
1157	+	objectFieldOffset("currentJoin", ForkJoinWorkerThread.class);
1158	+	private static final long currentStealOffset =
1159	+	objectFieldOffset("currentSteal", ForkJoinWorkerThread.class);
1160		private static final long qBase =
1161		UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
1162	<	private static final long threadStatusOffset =
1163	<	objectFieldOffset("threadStatus", Thread.class);
1162	>	private static final long poolRunStateOffset = // to inline CAS
1163	>	objectFieldOffset("runState", ForkJoinPool.class);
1164	>
1165		private static final int qShift;
1166
1167		static {
#	Line 1152 | Line 1169 | public class ForkJoinWorkerThread extend
1169		if ((s & (s-1)) != 0)
1170		throw new Error("data type scale not a power of two");
1171		qShift = 31 - Integer.numberOfLeadingZeros(s);
1172	+	MAXIMUM_QUEUE_CAPACITY = 1 << (31 - qShift);
1173		}
1174
1175		private static long objectFieldOffset(String field, Class<?> klazz) {

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