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

Comparing jsr166/src/jsr166y/ForkJoinWorkerThread.java (file contents):
Revision 1.39 by dl, Sat Jul 24 20:28:18 2010 UTC vs.
Revision 1.48 by jsr166, Tue Sep 7 14:37:28 2010 UTC

#	Line 110 | Line 110 | public class ForkJoinWorkerThread extend
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).
113	>	* ForkJoinPool.awaitJoin).
114		*
115		* Efficient implementation of these algorithms currently relies
116		* on an uncomfortable amount of "Unsafe" mechanics. To maintain
#	Line 155 | 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.
164	–	*/
165	–	private static final long SPARE_KEEPALIVE_NANOS =
166	–	5L * 1000L * 1000L * 1000L; // 5 secs
167	–
168	–	/**
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 183 | 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 228 | 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 238 | 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;
243	<	* currently not exported but included because volatile write upon
244	<	* park also provides a workaround for a JVM bug.
245	<	*/
246	<	volatile int parkCount;
247	<
248	<	/**
249	<	* Number of steals, transferred and reset in pool callbacks pool
250	<	* 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 283 | 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 311 | 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;
323	–	setDaemon(true);
320		if (ueh != null)
321		setUncaughtExceptionHandler(ueh);
322		start();
#	Line 353 | 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 381 | 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 413 | 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
426	<	if ((t = scan()) != null || (t = pollSubmission()) != null) {
427	<	t.tryExec();
428	<	if (base != sp)
429	<	runLocalTasks();
430	<	currentSteal = null;
431	<	emptyScans = 0;
432	<	}
433	<	else
434	<	++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		}
466	–	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 501 | 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 534 | 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 546 | 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 569 | 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 588 | 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
592	<	* 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 648 | 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 687 | 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 724 | Line 750 | public class ForkJoinWorkerThread extend
750		// Run State management
751
752		// status check methods used mainly by ForkJoinPool
753	+	final boolean isRunning()     { return runState == 0; }
754		final boolean isTerminating() { return (runState & TERMINATING) != 0; }
755		final boolean isTerminated()  { return (runState & TERMINATED) != 0; }
756		final boolean isSuspended()   { return (runState & SUSPENDED) != 0; }
757		final boolean isTrimmed()     { return (runState & TRIMMED) != 0; }
758
759		/**
760	<	* Sets state to TERMINATING, also resuming if suspended.
760	>	* Sets state to TERMINATING. Does NOT unpark or interrupt
761	>	* to wake up if currently blocked. Callers must do so if desired.
762		*/
763		final void shutdown() {
764		for (;;) {
765		int s = runState;
766	+	if ((s & (TERMINATING|TERMINATED)) != 0)
767	+	break;
768		if ((s & SUSPENDED) != 0) { // kill and wakeup if suspended
769		if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
770		(s & ~SUSPENDED) |
771	<	(TRIMMED|TERMINATING))) {
742	<	LockSupport.unpark(this);
771	>	(TRIMMED|TERMINATING)))
772		break;
744	–	}
773		}
774		else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
775		s | TERMINATING))
#	Line 750 | Line 778 | public class ForkJoinWorkerThread extend
778		}
779
780		/**
781	<	* Sets state to TERMINATED. Called only by this thread.
781	>	* Sets state to TERMINATED. Called only by onTermination().
782		*/
783		private void setTerminated() {
784		int s;
#	Line 760 | Line 788 | public class ForkJoinWorkerThread extend
788		}
789
790		/**
791	<	* Instrumented version of park used by ForkJoinPool.eventSync
792	<	*/
765	<	final void doPark() {
766	<	++parkCount;
767	<	LockSupport.park(this);
768	<	}
769	<
770	<	/**
771	<	* If suspended, tries to set status to unsuspended and unparks.
791	>	* If suspended, tries to set status to unsuspended.
792	>	* Does NOT wake up if blocked.
793		*
794		* @return true if successful
795		*/
796	<	final boolean tryResumeSpare() {
797	<	int s = runState;
798	<	if ((s & SUSPENDED) != 0 &&
799	<	UNSAFE.compareAndSwapInt(this, runStateOffset, s,
800	<	s & ~SUSPENDED)) {
801	<	LockSupport.unpark(this);
781	<	return true;
796	>	final boolean tryUnsuspend() {
797	>	int s;
798	>	while (((s = runState) & SUSPENDED) != 0) {
799	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
800	>	s & ~SUSPENDED))
801	>	return true;
802		}
803		return false;
804		}
805
806		/**
807	<	* Sets suspended status and blocks as spare until resumed,
808	<	* shutdown, or timed out.
789	<	*
790	<	* @return false if trimmed
807	>	* Sets suspended status and blocks as spare until resumed
808	>	* or shutdown.
809		*/
810	<	final boolean suspendAsSpare() {
811	<	for (;;) {               // set suspended unless terminating
810	>	final void suspendAsSpare() {
811	>	for (;;) {                  // set suspended unless terminating
812		int s = runState;
813		if ((s & TERMINATING) != 0) { // must kill
814		if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
815		s | (TRIMMED | TERMINATING)))
816	<	return false;
816	>	return;
817		}
818		else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
819		s | SUSPENDED))
820		break;
821		}
822	<	int pc = pool.parallelism;
823	<	pool.accumulateStealCount(this);
806	<	boolean timed;
807	<	long nanos;
808	<	long startTime;
809	<	if (poolIndex < pc) { // untimed wait for core threads
810	<	timed = false;
811	<	nanos = 0L;
812	<	startTime = 0L;
813	<	}
814	<	else {                // timed wait for added threads
815	<	timed = true;
816	<	nanos = SPARE_KEEPALIVE_NANOS;
817	<	startTime = System.nanoTime();
818	<	}
819	<	lastEventCount = 0;      // reset upon resume
820	<	interrupted();           // clear/ignore interrupts
822	>	ForkJoinPool p = pool;
823	>	p.pushSpare(this);
824		while ((runState & SUSPENDED) != 0) {
825	<	++parkCount;
826	<	if (!timed)
825	>	if (p.tryAccumulateStealCount(this)) {
826	>	interrupted();          // clear/ignore interrupts
827	>	if ((runState & SUSPENDED) == 0)
828	>	break;
829		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;
830		}
831		}
835	–	return true;
832		}
833
834		// Misc support methods for ForkJoinPool
#	Line 842 | Line 838 | public class ForkJoinWorkerThread extend
838		* used by ForkJoinTask.
839		*/
840		final int getQueueSize() {
841	<	return -base + sp;
841	>	int n; // external calls must read base first
842	>	return (n = -base + sp) <= 0 ? 0 : n;
843		}
844
845		/**
#	Line 850 | Line 847 | public class ForkJoinWorkerThread extend
847		* thread.
848		*/
849		final void cancelTasks() {
850	<	ForkJoinTask<?> cj = currentJoin; // try to kill live tasks
850	>	ForkJoinTask<?> cj = currentJoin; // try to cancel ongoing tasks
851		if (cj != null) {
852		currentJoin = null;
853		cj.cancelIgnoringExceptions();
854	+	try {
855	+	this.interrupt(); // awaken wait
856	+	} catch (SecurityException ignore) {
857	+	}
858		}
859		ForkJoinTask<?> cs = currentSteal;
860		if (cs != null) {
#	Line 892 | Line 893 | public class ForkJoinWorkerThread extend
893		* @return a task, if available
894		*/
895		final ForkJoinTask<?> pollLocalTask() {
896	+	ForkJoinPool p = pool;
897		while (sp != base) {
898	<	if (active || (active = pool.tryIncrementActiveCount()))
899	<	return locallyFifo? locallyDeqTask() : popTask();
898	>	int a; // inline p.tryIncrementActiveCount
899	>	if (active ||
900	>	(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
901	>	a = p.runState, a + 1)))
902	>	return locallyFifo ? locallyDeqTask() : popTask();
903		}
904		return null;
905		}
#	Line 908 | Line 913 | public class ForkJoinWorkerThread extend
913		ForkJoinTask<?> t = pollLocalTask();
914		if (t == null) {
915		t = scan();
916	<	currentSteal = null; // cannot retain/track
916	>	// cannot retain/track/help steal
917	>	UNSAFE.putOrderedObject(this, currentStealOffset, null);
918		}
919		return t;
920		}
921
922		/**
923		* Possibly runs some tasks and/or blocks, until task is done.
918	–	* The main body is basically a big spinloop, alternating between
919	–	* calls to helpJoinTask and pool.tryAwaitJoin with increased
920	–	* patience parameters until either the task is done without
921	–	* waiting, or we have, if necessary, created or resumed a
922	–	* replacement for this thread while it blocks.
924		*
925		* @param joinMe the task to join
925	–	* @return task status on exit
926		*/
927	<	final int joinTask(ForkJoinTask<?> joinMe) {
928	<	int stat;
927	>	final void joinTask(ForkJoinTask<?> joinMe) {
928	>	// currentJoin only written by this thread; only need ordered store
929		ForkJoinTask<?> prevJoin = currentJoin;
930	–	// Only written by this thread; only need ordered store
930		UNSAFE.putOrderedObject(this, currentJoinOffset, joinMe);
931	<	if ((stat = joinMe.status) >= 0 &&
932	<	(sp == base || (stat = localHelpJoinTask(joinMe)) >= 0)) {
933	<	for (int retries = 0; ; ++retries) {
934	<	helpJoinTask(joinMe, retries);
936	<	if ((stat = joinMe.status) < 0)
937	<	break;
938	<	pool.tryAwaitJoin(joinMe, retries);
939	<	if ((stat = joinMe.status) < 0)
940	<	break;
941	<	Thread.yield(); // tame unbounded loop
942	<	}
943	<	}
931	>	if (sp != base)
932	>	localHelpJoinTask(joinMe);
933	>	if (joinMe.status >= 0)
934	>	pool.awaitJoin(joinMe, this);
935		UNSAFE.putOrderedObject(this, currentJoinOffset, prevJoin);
945	–	return stat;
936		}
937
938		/**
939		* Run tasks in local queue until given task is done.
940		*
941		* @param joinMe the task to join
952	–	* @return task status on exit
942		*/
943	<	private int localHelpJoinTask(ForkJoinTask<?> joinMe) {
944	<	int stat, s;
943	>	private void localHelpJoinTask(ForkJoinTask<?> joinMe) {
944	>	int s;
945		ForkJoinTask<?>[] q;
946	<	while ((stat = joinMe.status) >= 0 &&
958	<	base != (s = sp) && (q = queue) != null) {
959	<	ForkJoinTask<?> t;
946	>	while (joinMe.status >= 0 && (s = sp) != base && (q = queue) != null) {
947		int i = (q.length - 1) & --s;
948		long u = (i << qShift) + qBase; // raw offset
949	<	if ((t = q[i]) != null &&
950	<	UNSAFE.compareAndSwapObject(q, u, t, null)) {
949	>	ForkJoinTask<?> t = q[i];
950	>	if (t == null)  // lost to a stealer
951	>	break;
952	>	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
953		/*
954		* This recheck (and similarly in helpJoinTask)
955		* handles cases where joinMe is independently
#	Line 968 | Line 957 | public class ForkJoinWorkerThread extend
957		* available. Back out of the pop by putting t back
958		* into slot before we commit by writing sp.
959		*/
960	<	if ((stat = joinMe.status) < 0) {
960	>	if (joinMe.status < 0) {
961		UNSAFE.putObjectVolatile(q, u, t);
962		break;
963		}
964		sp = s;
965	<	t.tryExec();
965	>	// UNSAFE.putOrderedInt(this, spOffset, s);
966	>	t.quietlyExec();
967		}
968		}
979	–	return stat;
969		}
970
971		/**
972	<	* Tries to locate and help perform tasks for a stealer of the
973	<	* given task, or in turn one of its stealers.  Traces
974	<	* currentSteal->currentJoin links looking for a thread working on
975	<	* a descendant of the given task and with a non-empty queue to
976	<	* steal back and execute tasks from. Restarts search upon
977	<	* encountering chains that are stale, unknown, or of length
978	<	* greater than MAX_HELP_DEPTH links, to avoid unbounded cycles.
979	<	*
980	<	* The implementation is very branchy to cope with the restart
981	<	* cases.  Returns void, not task status (which must be reread by
982	<	* caller anyway) to slightly simplify control paths.
972	>	* Unless terminating, tries to locate and help perform tasks for
973	>	* a stealer of the given task, or in turn one of its stealers.
974	>	* Traces currentSteal->currentJoin links looking for a thread
975	>	* working on a descendant of the given task and with a non-empty
976	>	* queue to steal back and execute tasks from.
977	>	*
978	>	* The implementation is very branchy to cope with potential
979	>	* inconsistencies or loops encountering chains that are stale,
980	>	* unknown, or of length greater than MAX_HELP_DEPTH links.  All
981	>	* of these cases are dealt with by just returning back to the
982	>	* caller, who is expected to retry if other join mechanisms also
983	>	* don't work out.
984		*
985		* @param joinMe the task to join
996	–	* @param rescans the number of times to recheck for work
986		*/
987	<	private void helpJoinTask(ForkJoinTask<?> joinMe, int rescans) {
988	<	ForkJoinWorkerThread[] ws = pool.workers;
987	>	final void helpJoinTask(ForkJoinTask<?> joinMe) {
988	>	ForkJoinWorkerThread[] ws;
989		int n;
990	<	if (ws == null || (n = ws.length) <= 1)
991	<	return;                   // need at least 2 workers
992	<	restart:while (rescans-- >= 0 && joinMe.status >= 0) {
993	<	ForkJoinTask<?> task = joinMe;        // base of chain
994	<	ForkJoinWorkerThread thread = this;   // thread with stolen task
995	<	for (int depth = 0; depth < MAX_HELP_DEPTH; ++depth) {
996	<	// Try to find v, the stealer of task, by first using hint
997	<	ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)];
998	<	if (v == null || v.currentSteal != task) {
999	<	for (int j = 0; ; ++j) {      // search array
1000	<	if (task.status < 0 || j == n)
1001	<	continue restart;     // stale or no stealer
1002	<	if ((v = ws[j]) != null && v.currentSteal == task) {
1003	<	thread.stealHint = j; // save for next time
1004	<	break;
1005	<	}
1006	<	}
1007	<	}
1008	<	// Try to help v, using specialized form of deqTask
1009	<	int b;
1010	<	ForkJoinTask<?>[] q;
1011	<	while ((b = v.base) != v.sp && (q = v.queue) != null) {
1012	<	int i = (q.length - 1) & b;
1013	<	long u = (i << qShift) + qBase;
1014	<	ForkJoinTask<?> t = q[i];
1026	<	if (task.status < 0)          // stale
1027	<	continue restart;
1028	<	if (t != null) {
1029	<	if (v.base == b &&
1030	<	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1031	<	if (joinMe.status < 0) {
1032	<	UNSAFE.putObjectVolatile(q, u, t);
1033	<	return;           // back out on cancel
990	>	if (joinMe.status < 0)                // already done
991	>	return;
992	>	if ((runState & TERMINATING) != 0) {  // cancel if shutting down
993	>	joinMe.cancelIgnoringExceptions();
994	>	return;
995	>	}
996	>	if ((ws = pool.workers) == null || (n = ws.length) <= 1)
997	>	return;                           // need at least 2 workers
998	>
999	>	ForkJoinTask<?> task = joinMe;        // base of chain
1000	>	ForkJoinWorkerThread thread = this;   // thread with stolen task
1001	>	for (int d = 0; d < MAX_HELP_DEPTH; ++d) { // chain length
1002	>	// Try to find v, the stealer of task, by first using hint
1003	>	ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)];
1004	>	if (v == null || v.currentSteal != task) {
1005	>	for (int j = 0; ; ++j) {      // search array
1006	>	if (j < n) {
1007	>	ForkJoinTask<?> vs;
1008	>	if ((v = ws[j]) != null &&
1009	>	(vs = v.currentSteal) != null) {
1010	>	if (joinMe.status < 0 || task.status < 0)
1011	>	return;       // stale or done
1012	>	if (vs == task) {
1013	>	thread.stealHint = j;
1014	>	break;        // save hint for next time
1015		}
1035	–	ForkJoinTask<?> prevSteal = currentSteal;
1036	–	currentSteal = t;
1037	–	v.stealHint = poolIndex;
1038	–	v.base = b + 1;
1039	–	t.tryExec();
1040	–	currentSteal = prevSteal;
1016		}
1017		}
1018	<	else if (v.base == b)          // producer stalled
1019	<	continue restart;          // retry via restart
1045	<	if (joinMe.status < 0)
1046	<	return;
1018	>	else
1019	>	return;               // no stealer
1020		}
1021	<	// Try to descend to find v's stealer
1022	<	ForkJoinTask<?> next = v.currentJoin;
1050	<	if (next == null || next == task || task.status < 0)
1051	<	continue restart;             // no descendent or stale
1021	>	}
1022	>	for (;;) { // Try to help v, using specialized form of deqTask
1023		if (joinMe.status < 0)
1024		return;
1025	<	task = next;
1026	<	thread = v;
1025	>	int b = v.base;
1026	>	ForkJoinTask<?>[] q = v.queue;
1027	>	if (b == v.sp || q == null)
1028	>	break;
1029	>	int i = (q.length - 1) & b;
1030	>	long u = (i << qShift) + qBase;
1031	>	ForkJoinTask<?> t = q[i];
1032	>	int pid = poolIndex;
1033	>	ForkJoinTask<?> ps = currentSteal;
1034	>	if (task.status < 0)
1035	>	return;                   // stale or done
1036	>	if (t != null && v.base == b++ &&
1037	>	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	>	v.base = b;
1043	>	v.stealHint = pid;
1044	>	UNSAFE.putOrderedObject(this, currentStealOffset, t);
1045	>	t.quietlyExec();
1046	>	UNSAFE.putOrderedObject(this, currentStealOffset, ps);
1047	>	}
1048		}
1049	+	// Try to descend to find v's stealer
1050	+	ForkJoinTask<?> next = v.currentJoin;
1051	+	if (task.status < 0 || next == null || next == task ||
1052	+	joinMe.status < 0)
1053	+	return;
1054	+	task = next;
1055	+	thread = v;
1056		}
1057		}
1058
1059		/**
1060	+	* Implements ForJoinTask.getSurplusQueuedTaskCount().
1061		* Returns an estimate of the number of tasks, offset by a
1062		* function of number of idle workers.
1063		*
#	Line 1112 | Line 1112 | public class ForkJoinWorkerThread extend
1112		* Runs tasks until {@code pool.isQuiescent()}.
1113		*/
1114		final void helpQuiescePool() {
1115	+	ForkJoinTask<?> ps = currentSteal; // to restore below
1116		for (;;) {
1117		ForkJoinTask<?> t = pollLocalTask();
1118	<	if (t != null || (t = scan()) != null) {
1119	<	t.tryExec();
1119	<	currentSteal = null;
1120	<	}
1118	>	if (t != null || (t = scan()) != null)
1119	>	t.quietlyExec();
1120		else {
1121		ForkJoinPool p = pool;
1122	+	int a; // to inline CASes
1123		if (active) {
1124	+	if (!UNSAFE.compareAndSwapInt
1125	+	(p, poolRunStateOffset, a = p.runState, a - 1))
1126	+	continue;   // retry later
1127		active = false; // inactivate
1128	<	do {} while (!p.tryDecrementActiveCount());
1128	>	UNSAFE.putOrderedObject(this, currentStealOffset, ps);
1129		}
1130		if (p.isQuiescent()) {
1131		active = true; // re-activate
1132	<	do {} while (!p.tryIncrementActiveCount());
1132	>	do {} while (!UNSAFE.compareAndSwapInt
1133	>	(p, poolRunStateOffset, a = p.runState, a+1));
1134		return;
1135		}
1136		}
#	Line 1136 | Line 1140 | public class ForkJoinWorkerThread extend
1140		// Unsafe mechanics
1141
1142		private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1143	+	private static final long spOffset =
1144	+	objectFieldOffset("sp", ForkJoinWorkerThread.class);
1145		private static final long runStateOffset =
1146		objectFieldOffset("runState", ForkJoinWorkerThread.class);
1147		private static final long currentJoinOffset =
1148		objectFieldOffset("currentJoin", ForkJoinWorkerThread.class);
1149	+	private static final long currentStealOffset =
1150	+	objectFieldOffset("currentSteal", ForkJoinWorkerThread.class);
1151		private static final long qBase =
1152		UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
1153	+	private static final long poolRunStateOffset = // to inline CAS
1154	+	objectFieldOffset("runState", ForkJoinPool.class);
1155	+
1156		private static final int qShift;
1157
1158		static {
#	Line 1149 | Line 1160 | public class ForkJoinWorkerThread extend
1160		if ((s & (s-1)) != 0)
1161		throw new Error("data type scale not a power of two");
1162		qShift = 31 - Integer.numberOfLeadingZeros(s);
1163	+	MAXIMUM_QUEUE_CAPACITY = 1 << (31 - qShift);
1164		}
1165
1166		private static long objectFieldOffset(String field, Class<?> klazz) {

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