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root/jsr166/jsr166/src/jsr166y/Phaser.java

Comparing jsr166/src/jsr166y/Phaser.java (file contents):
Revision 1.50 by dl, Sat Nov 6 16:12:10 2010 UTC vs.
Revision 1.58 by dl, Wed Nov 24 15:48:01 2010 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	<	import java.util.concurrent.*;
9	>	import java.util.concurrent.TimeUnit;
10	>	import java.util.concurrent.TimeoutException;
11		import java.util.concurrent.atomic.AtomicReference;
12		import java.util.concurrent.locks.LockSupport;
13
#	Line 85 | Line 86 | import java.util.concurrent.locks.LockSu
86		* #forceTermination} is also available to abruptly release waiting
87		* threads and allow them to terminate.
88		*
89	<	* <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e., arranged
90	<	* in tree structures) to reduce contention. Phasers with large
91	<	* numbers of parties that would otherwise experience heavy
89	>	* <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e.,
90	>	* constructed in tree structures) to reduce contention. Phasers with
91	>	* large numbers of parties that would otherwise experience heavy
92		* synchronization contention costs may instead be set up so that
93		* groups of sub-phasers share a common parent.  This may greatly
94		* increase throughput even though it incurs greater per-operation
#	Line 226 | Line 227 | public class Phaser {
227		* Barrier state representation. Conceptually, a barrier contains
228		* four values:
229		*
230	<	* * parties -- the number of parties to wait (16 bits)
231	<	* * unarrived -- the number of parties yet to hit barrier (16 bits)
232	<	* * phase -- the generation of the barrier (31 bits)
233	<	* * terminated -- set if barrier is terminated (1 bit)
230	>	* * unarrived -- the number of parties yet to hit barrier (bits  0-15)
231	>	* * parties -- the number of parties to wait              (bits 16-31)
232	>	* * phase -- the generation of the barrier                (bits 32-62)
233	>	* * terminated -- set if barrier is terminated            (bit  63 / sign)
234		*
235		* However, to efficiently maintain atomicity, these values are
236		* packed into a single (atomic) long. Termination uses the sign
237		* bit of 32 bit representation of phase, so phase is set to -1 on
238		* termination. Good performance relies on keeping state decoding
239		* and encoding simple, and keeping race windows short.
239	–	*
240	–	* Note: there are some cheats in arrive() that rely on unarrived
241	–	* count being lowest 16 bits.
240		*/
241		private volatile long state;
242
243	<	private static final int ushortMask = 0xffff;
244	<	private static final int phaseMask  = 0x7fffffff;
243	>	private static final int  MAX_PARTIES    = 0xffff;
244	>	private static final int  MAX_PHASE      = 0x7fffffff;
245	>	private static final int  PARTIES_SHIFT  = 16;
246	>	private static final int  PHASE_SHIFT    = 32;
247	>	private static final int  UNARRIVED_MASK = 0xffff;
248	>	private static final long PARTIES_MASK   = 0xffff0000L; // for masking long
249	>	private static final long ONE_ARRIVAL    = 1L;
250	>	private static final long ONE_PARTY      = 1L << PARTIES_SHIFT;
251	>	private static final long TERMINATION_PHASE  = -1L << PHASE_SHIFT;
252	>
253	>	// The following unpacking methods are usually manually inlined
254
255		private static int unarrivedOf(long s) {
256	<	return (int) (s & ushortMask);
256	>	return (int)s & UNARRIVED_MASK;
257		}
258
259		private static int partiesOf(long s) {
260	<	return ((int) s) >>> 16;
260	>	return (int)s >>> PARTIES_SHIFT;
261		}
262
263		private static int phaseOf(long s) {
264	<	return (int) (s >>> 32);
264	>	return (int) (s >>> PHASE_SHIFT);
265		}
266
267		private static int arrivedOf(long s) {
268		return partiesOf(s) - unarrivedOf(s);
269		}
270
264	–	private static long stateFor(int phase, int parties, int unarrived) {
265	–	return ((((long) phase) << 32) | (((long) parties) << 16) |
266	–	(long) unarrived);
267	–	}
268	–
269	–	private static long trippedStateFor(int phase, int parties) {
270	–	long lp = (long) parties;
271	–	return (((long) phase) << 32) | (lp << 16) | lp;
272	–	}
273	–
274	–	/**
275	–	* Returns message string for bad bounds exceptions.
276	–	*/
277	–	private static String badBounds(int parties, int unarrived) {
278	–	return ("Attempt to set " + unarrived +
279	–	" unarrived of " + parties + " parties");
280	–	}
281	–
271		/**
272		* The parent of this phaser, or null if none
273		*/
#	Line 290 | Line 279 | public class Phaser {
279		*/
280		private final Phaser root;
281
293	–	// Wait queues
294	–
282		/**
283		* Heads of Treiber stacks for waiting threads. To eliminate
284		* contention when releasing some threads while adding others, we
#	Line 306 | Line 293 | public class Phaser {
293		}
294
295		/**
296	<	* Returns current state, first resolving lagged propagation from
297	<	* root if necessary.
296	>	* Main implementation for methods arrive and arriveAndDeregister.
297	>	* Manually tuned to speed up and minimize race windows for the
298	>	* common case of just decrementing unarrived field.
299	>	*
300	>	* @param adj - adjustment to apply to state -- either
301	>	* ONE_ARRIVAL (for arrive) or
302	>	* ONE_ARRIVAL|ONE_PARTY (for arriveAndDeregister)
303	>	*/
304	>	private int doArrive(long adj) {
305	>	for (;;) {
306	>	long s = state;
307	>	int phase = (int)(s >>> PHASE_SHIFT);
308	>	if (phase < 0)
309	>	return phase;
310	>	int unarrived = (int)s & UNARRIVED_MASK;
311	>	if (unarrived == 0)
312	>	checkBadArrive(s);
313	>	else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) {
314	>	if (unarrived == 1) {
315	>	long p = s & PARTIES_MASK; // unshifted parties field
316	>	long lu = p >>> PARTIES_SHIFT;
317	>	int u = (int)lu;
318	>	int nextPhase = (phase + 1) & MAX_PHASE;
319	>	long next = ((long)nextPhase << PHASE_SHIFT) | p | lu;
320	>	final Phaser parent = this.parent;
321	>	if (parent == null) {
322	>	if (onAdvance(phase, u))
323	>	next |= TERMINATION_PHASE; // obliterate phase
324	>	UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
325	>	releaseWaiters(phase);
326	>	}
327	>	else {
328	>	parent.doArrive((u == 0) ?
329	>	ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL);
330	>	if ((int)(parent.state >>> PHASE_SHIFT) != nextPhase ||
331	>	((int)(state >>> PHASE_SHIFT) != nextPhase &&
332	>	!UNSAFE.compareAndSwapLong(this, stateOffset,
333	>	s, next)))
334	>	reconcileState();
335	>	}
336	>	}
337	>	return phase;
338	>	}
339	>	}
340	>	}
341	>
342	>	/**
343	>	* Rechecks state and throws bounds exceptions on arrival -- called
344	>	* only if unarrived is apparently zero.
345		*/
346	<	private long getReconciledState() {
347	<	return (parent == null) ? state : reconcileState();
346	>	private void checkBadArrive(long s) {
347	>	if (reconcileState() == s)
348	>	throw new IllegalStateException
349	>	("Attempted arrival of unregistered party for " +
350	>	stateToString(s));
351		}
352
353		/**
354	<	* Recursively resolves state.
354	>	* Implementation of register, bulkRegister
355	>	*
356	>	* @param registrations number to add to both parties and
357	>	* unarrived fields. Must be greater than zero.
358	>	*/
359	>	private int doRegister(int registrations) {
360	>	// adjustment to state
361	>	long adj = ((long)registrations << PARTIES_SHIFT) | registrations;
362	>	final Phaser parent = this.parent;
363	>	for (;;) {
364	>	long s = (parent == null) ? state : reconcileState();
365	>	int parties = (int)s >>> PARTIES_SHIFT;
366	>	int phase = (int)(s >>> PHASE_SHIFT);
367	>	if (phase < 0)
368	>	return phase;
369	>	else if (parties != 0 && ((int)s & UNARRIVED_MASK) == 0)
370	>	internalAwaitAdvance(phase, null); // wait for onAdvance
371	>	else if (registrations > MAX_PARTIES - parties)
372	>	throw new IllegalStateException(badRegister(s));
373	>	else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj))
374	>	return phase;
375	>	}
376	>	}
377	>
378	>	/**
379	>	* Returns message string for out of bounds exceptions on registration.
380	>	*/
381	>	private String badRegister(long s) {
382	>	return "Attempt to register more than " +
383	>	MAX_PARTIES + " parties for " + stateToString(s);
384	>	}
385	>
386	>	/**
387	>	* Recursively resolves lagged phase propagation from root if necessary.
388		*/
389		private long reconcileState() {
390		Phaser par = parent;
391		long s = state;
392		if (par != null) {
393	<	int phase, rootPhase;
394	<	while ((phase = phaseOf(s)) >= 0 &&
395	<	(rootPhase = phaseOf(root.state)) != phase &&
396	<	(rootPhase < 0 || unarrivedOf(s) == 0)) {
397	<	int parentPhase = phaseOf(par.getReconciledState());
398	<	if (parentPhase != phase) {
399	<	long next = trippedStateFor(parentPhase, partiesOf(s));
400	<	if (state == s)
401	<	UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
393	>	Phaser rt = root;
394	>	int phase, rPhase;
395	>	while ((phase = (int)(s >>> PHASE_SHIFT)) >= 0 &&
396	>	(rPhase = (int)(rt.state >>> PHASE_SHIFT)) != phase) {
397	>	if ((int)(par.state >>> PHASE_SHIFT) != rPhase)
398	>	par.reconcileState();
399	>	else if (rPhase < 0 || ((int)s & UNARRIVED_MASK) == 0) {
400	>	long u = s & PARTIES_MASK; // reset unarrived to parties
401	>	long next = ((((long) rPhase) << PHASE_SHIFT) | u |
402	>	(u >>> PARTIES_SHIFT));
403	>	if (state == s &&
404	>	UNSAFE.compareAndSwapLong(this, stateOffset,
405	>	s, s = next))
406	>	break;
407		}
408		s = state;
409		}
#	Line 358 | Line 433 | public class Phaser {
433		}
434
435		/**
436	<	* Creates a new phaser with the given parent, without any
362	<	* initially registered parties. If parent is non-null this phaser
363	<	* is registered with the parent and its initial phase number is
364	<	* the same as that of parent phaser.
436	>	* Equivalent to {@link #Phaser(Phaser, int) Phaser(parent, 0)}.
437		*
438		* @param parent the parent phaser
439		*/
#	Line 371 | Line 443 | public class Phaser {
443
444		/**
445		* Creates a new phaser with the given parent and number of
446	<	* registered unarrived parties. If parent is non-null, this phaser
447	<	* is registered with the parent and its initial phase number is
448	<	* the same as that of parent phaser.
446	>	* registered unarrived parties. If parent is non-null, this
447	>	* phaser is registered with the parent and its initial phase
448	>	* number is the same as that of parent phaser.  If the number of
449	>	* parties is zero, the parent phaser will not proceed until this
450	>	* child phaser registers parties and advances, or this child
451	>	* phaser deregisters with its parent, or the parent is otherwise
452	>	* terminated.  This child Phaser will be deregistered from its
453	>	* parent automatically upon any invocation of the child's {@link
454	>	* #arriveAndDeregister} method that results in the child's number
455	>	* of registered parties becoming zero. (Although rarely
456	>	* appropriate, this child may also explicity deregister from its
457	>	* parent using {@code getParent().arriveAndDeregister()}.)  After
458	>	* deregistration, the child cannot re-register. (Instead, you can
459	>	* create a new child Phaser.)
460		*
461		* @param parent the parent phaser
462		* @param parties the number of parties required to trip barrier
#	Line 381 | Line 464 | public class Phaser {
464		* or greater than the maximum number of parties supported
465		*/
466		public Phaser(Phaser parent, int parties) {
467	<	if (parties < 0 || parties > ushortMask)
467	>	if (parties >>> PARTIES_SHIFT != 0)
468		throw new IllegalArgumentException("Illegal number of parties");
469		int phase;
470		this.parent = parent;
#	Line 390 | Line 473 | public class Phaser {
473		this.root = r;
474		this.evenQ = r.evenQ;
475		this.oddQ = r.oddQ;
476	<	phase = parent.register();
476	>	phase = parent.doRegister(1);
477		}
478		else {
479		this.root = this;
#	Line 398 | Line 481 | public class Phaser {
481		this.oddQ = new AtomicReference<QNode>();
482		phase = 0;
483		}
484	<	this.state = trippedStateFor(phase, parties);
484	>	long p = (long)parties;
485	>	this.state = (((long)phase) << PHASE_SHIFT) | p | (p << PARTIES_SHIFT);
486		}
487
488		/**
#	Line 434 | Line 518 | public class Phaser {
518		}
519
520		/**
437	–	* Shared code for register, bulkRegister
438	–	*/
439	–	private int doRegister(int registrations) {
440	–	Phaser par = parent;
441	–	long s;
442	–	int phase;
443	–	while ((phase = phaseOf(s = par==null? state:reconcileState())) >= 0) {
444	–	int p = partiesOf(s);
445	–	int u = unarrivedOf(s);
446	–	int unarrived = u + registrations;
447	–	int parties = p + registrations;
448	–	if (u == 0 && p != 0)  // if tripped, wait for advance
449	–	untimedWait(phase);
450	–	else if (parties > ushortMask)
451	–	throw new IllegalStateException(badBounds(parties, unarrived));
452	–	else if (par == null || phaseOf(root.state) == phase) {
453	–	long next = stateFor(phase, parties, unarrived);
454	–	if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next))
455	–	break;
456	–	}
457	–	}
458	–	return phase;
459	–	}
460	–
461	–	/**
521		* Arrives at the barrier, but does not wait for others.  (You can
522		* in turn wait for others via {@link #awaitAdvance}).  It is an
523		* unenforced usage error for an unregistered party to invoke this
#	Line 469 | Line 528 | public class Phaser {
528		* of unarrived parties would become negative
529		*/
530		public int arrive() {
531	<	Phaser par = parent;
473	<	long s;
474	<	int phase;
475	<	while ((phase = phaseOf(s = par==null? state:reconcileState())) >= 0) {
476	<	int parties = partiesOf(s);
477	<	int unarrived = unarrivedOf(s) - 1;
478	<	if (unarrived > 0) {                // Not the last arrival
479	<	if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s - 1))
480	<	break;                      // s-1 adds one arrival
481	<	}
482	<	else if (unarrived < 0)
483	<	throw new IllegalStateException(badBounds(parties, unarrived));
484	<	else if (par == null) {             // directly trip
485	<	long next = trippedStateFor(onAdvance(phase, parties) ? -1 :
486	<	((phase + 1) & phaseMask),
487	<	parties);
488	<	if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) {
489	<	releaseWaiters(phase);
490	<	break;
491	<	}
492	<	}
493	<	else if (phaseOf(root.state) == phase &&
494	<	UNSAFE.compareAndSwapLong(this, stateOffset, s, s - 1)) {
495	<	par.arrive();                   // cascade to parent
496	<	reconcileState();
497	<	break;
498	<	}
499	<	}
500	<	return phase;
531	>	return doArrive(ONE_ARRIVAL);
532		}
533
534		/**
#	Line 514 | Line 545 | public class Phaser {
545		* of registered or unarrived parties would become negative
546		*/
547		public int arriveAndDeregister() {
548	<	// similar to arrive, but too different to merge
518	<	Phaser par = parent;
519	<	long s;
520	<	int phase;
521	<	while ((phase = phaseOf(s = par==null? state:reconcileState())) >= 0) {
522	<	int parties = partiesOf(s) - 1;
523	<	int unarrived = unarrivedOf(s) - 1;
524	<	if (unarrived > 0) {
525	<	long next = stateFor(phase, parties, unarrived);
526	<	if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next))
527	<	break;
528	<	}
529	<	else if (unarrived < 0)
530	<	throw new IllegalStateException(badBounds(parties, unarrived));
531	<	else if (par == null) {
532	<	long next = trippedStateFor(onAdvance(phase, parties)? -1:
533	<	(phase + 1) & phaseMask,
534	<	parties);
535	<	if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) {
536	<	releaseWaiters(phase);
537	<	break;
538	<	}
539	<	}
540	<	else if (phaseOf(root.state) == phase) {
541	<	long next = stateFor(phase, parties, 0);
542	<	if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) {
543	<	if (parties == 0)
544	<	par.arriveAndDeregister();
545	<	else
546	<	par.arrive();
547	<	reconcileState();
548	<	break;
549	<	}
550	<	}
551	<	}
552	<	return phase;
548	>	return doArrive(ONE_ARRIVAL|ONE_PARTY);
549		}
550
551		/**
#	Line 584 | Line 580 | public class Phaser {
580		public int awaitAdvance(int phase) {
581		if (phase < 0)
582		return phase;
583	<	int p = getPhase();
584	<	if (p != phase)
585	<	return p;
590	<	return untimedWait(phase);
583	>	long s = (parent == null) ? state : reconcileState();
584	>	int p = (int)(s >>> PHASE_SHIFT);
585	>	return (p != phase) ? p : internalAwaitAdvance(phase, null);
586		}
587
588		/**
#	Line 608 | Line 603 | public class Phaser {
603		throws InterruptedException {
604		if (phase < 0)
605		return phase;
606	<	int p = getPhase();
607	<	if (p != phase)
608	<	return p;
609	<	return interruptibleWait(phase);
606	>	long s = (parent == null) ? state : reconcileState();
607	>	int p = (int)(s >>> PHASE_SHIFT);
608	>	if (p == phase) {
609	>	QNode node = new QNode(this, phase, true, false, 0L);
610	>	p = internalAwaitAdvance(phase, node);
611	>	if (node.wasInterrupted)
612	>	throw new InterruptedException();
613	>	}
614	>	return p;
615		}
616
617		/**
#	Line 637 | Line 637 | public class Phaser {
637		public int awaitAdvanceInterruptibly(int phase,
638		long timeout, TimeUnit unit)
639		throws InterruptedException, TimeoutException {
640	–	long nanos = unit.toNanos(timeout);
640		if (phase < 0)
641		return phase;
642	<	int p = getPhase();
643	<	if (p != phase)
644	<	return p;
645	<	return timedWait(phase, nanos);
642	>	long s = (parent == null) ? state : reconcileState();
643	>	int p = (int)(s >>> PHASE_SHIFT);
644	>	if (p == phase) {
645	>	long nanos = unit.toNanos(timeout);
646	>	QNode node = new QNode(this, phase, true, true, nanos);
647	>	p = internalAwaitAdvance(phase, node);
648	>	if (node.wasInterrupted)
649	>	throw new InterruptedException();
650	>	else if (p == phase)
651	>	throw new TimeoutException();
652	>	}
653	>	return p;
654		}
655
656		/**
657	<	* Forces this barrier to enter termination state. Counts of
658	<	* arrived and registered parties are unaffected. If this phaser
659	<	* has a parent, it too is terminated. This method may be useful
660	<	* for coordinating recovery after one or more tasks encounter
661	<	* unexpected exceptions.
657	>	* Forces this barrier to enter termination state.  Counts of
658	>	* arrived and registered parties are unaffected.  If this phaser
659	>	* is a member of a tiered set of phasers, then all of the phasers
660	>	* in the set are terminated.  If this phaser is already
661	>	* terminated, this method has no effect.  This method may be
662	>	* useful for coordinating recovery after one or more tasks
663	>	* encounter unexpected exceptions.
664		*/
665		public void forceTermination() {
666	<	Phaser r = root;    // force at root then reconcile
666	>	// Only need to change root state
667	>	final Phaser root = this.root;
668		long s;
669	<	while (phaseOf(s = r.state) >= 0)
670	<	UNSAFE.compareAndSwapLong(r, stateOffset, s,
671	<	stateFor(-1, partiesOf(s),
672	<	unarrivedOf(s)));
673	<	reconcileState();
674	<	releaseWaiters(0);  // ensure wakeups on both queues
675	<	releaseWaiters(1);
669	>	while ((s = root.state) >= 0) {
670	>	if (UNSAFE.compareAndSwapLong(root, stateOffset,
671	>	s, s | TERMINATION_PHASE)) {
672	>	releaseWaiters(0); // signal all threads
673	>	releaseWaiters(1);
674	>	return;
675	>	}
676	>	}
677		}
678
679		/**
#	Line 673 | Line 684 | public class Phaser {
684		* @return the phase number, or a negative value if terminated
685		*/
686		public final int getPhase() {
687	<	return phaseOf(getReconciledState());
687	>	return (int)(root.state >>> PHASE_SHIFT);
688		}
689
690		/**
#	Line 682 | Line 693 | public class Phaser {
693		* @return the number of parties
694		*/
695		public int getRegisteredParties() {
696	<	return partiesOf(getReconciledState());
696	>	return partiesOf(state);
697		}
698
699		/**
#	Line 692 | Line 703 | public class Phaser {
703		* @return the number of arrived parties
704		*/
705		public int getArrivedParties() {
706	<	return arrivedOf(getReconciledState());
706	>	return arrivedOf(parent==null? state : reconcileState());
707		}
708
709		/**
#	Line 702 | Line 713 | public class Phaser {
713		* @return the number of unarrived parties
714		*/
715		public int getUnarrivedParties() {
716	<	return unarrivedOf(getReconciledState());
716	>	return unarrivedOf(parent==null? state : reconcileState());
717		}
718
719		/**
#	Line 730 | Line 741 | public class Phaser {
741		* @return {@code true} if this barrier has been terminated
742		*/
743		public boolean isTerminated() {
744	<	return getPhase() < 0;
744	>	return root.state < 0L;
745		}
746
747		/**
#	Line 746 | Line 757 | public class Phaser {
757		* which case no advance occurs.
758		*
759		* <p>The arguments to this method provide the state of the phaser
760	<	* prevailing for the current transition.  The results and effects
761	<	* of invoking phase-related methods (including {@code getPhase}
751	<	* as well as arrival, registration, and waiting methods) from
760	>	* prevailing for the current transition.  The effects of invoking
761	>	* arrival, registration, and waiting methods on this Phaser from
762		* within {@code onAdvance} are unspecified and should not be
763	<	* relied on. Similarly, while it is possible to override this
764	<	* method to produce side-effects visible to participating tasks,
765	<	* it is in general safe to do so only in designs in which all
766	<	* parties register before any arrive, and all {@link
767	<	* #awaitAdvance} at each phase.
763	>	* relied on.
764	>	*
765	>	* <p>If this Phaser is a member of a tiered set of Phasers, then
766	>	* {@code onAdvance} is invoked only for its root Phaser on each
767	>	* advance.
768		*
769		* <p>The default version returns {@code true} when the number of
770		* registered parties is zero. Normally, overrides that arrange
#	Line 779 | Line 789 | public class Phaser {
789		* @return a string identifying this barrier, as well as its state
790		*/
791		public String toString() {
792	<	long s = getReconciledState();
792	>	return stateToString(reconcileState());
793	>	}
794	>
795	>	/**
796	>	* Implementation of toString and string-based error messages
797	>	*/
798	>	private String stateToString(long s) {
799		return super.toString() +
800		"[phase = " + phaseOf(s) +
801		" parties = " + partiesOf(s) +
802		" arrived = " + arrivedOf(s) + "]";
803		}
804
805	<	// methods for waiting
805	>	// Waiting mechanics
806	>
807	>	/**
808	>	* Removes and signals threads from queue for phase.
809	>	*/
810	>	private void releaseWaiters(int phase) {
811	>	AtomicReference<QNode> head = queueFor(phase);
812	>	QNode q;
813	>	int p;
814	>	while ((q = head.get()) != null &&
815	>	((p = q.phase) == phase ||
816	>	(int)(root.state >>> PHASE_SHIFT) != p)) {
817	>	if (head.compareAndSet(q, q.next))
818	>	q.signal();
819	>	}
820	>	}
821	>
822	>	/** The number of CPUs, for spin control */
823	>	private static final int NCPU = Runtime.getRuntime().availableProcessors();
824	>
825	>	/**
826	>	* The number of times to spin before blocking while waiting for
827	>	* advance, per arrival while waiting. On multiprocessors, fully
828	>	* blocking and waking up a large number of threads all at once is
829	>	* usually a very slow process, so we use rechargeable spins to
830	>	* avoid it when threads regularly arrive: When a thread in
831	>	* internalAwaitAdvance notices another arrival before blocking,
832	>	* and there appear to be enough CPUs available, it spins
833	>	* SPINS_PER_ARRIVAL more times before blocking. Plus, even on
834	>	* uniprocessors, there is at least one intervening Thread.yield
835	>	* before blocking. The value trades off good-citizenship vs big
836	>	* unnecessary slowdowns.
837	>	*/
838	>	static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8;
839	>
840	>	/**
841	>	* Possibly blocks and waits for phase to advance unless aborted.
842	>	*
843	>	* @param phase current phase
844	>	* @param node if non-null, the wait node to track interrupt and timeout;
845	>	* if null, denotes noninterruptible wait
846	>	* @return current phase
847	>	*/
848	>	private int internalAwaitAdvance(int phase, QNode node) {
849	>	Phaser current = this;       // to eventually wait at root if tiered
850	>	boolean queued = false;      // true when node is enqueued
851	>	int lastUnarrived = -1;      // to increase spins upon change
852	>	int spins = SPINS_PER_ARRIVAL;
853	>	long s;
854	>	int p;
855	>	while ((p = (int)((s = current.state) >>> PHASE_SHIFT)) == phase) {
856	>	Phaser par;
857	>	int unarrived = (int)s & UNARRIVED_MASK;
858	>	if (unarrived != lastUnarrived) {
859	>	if (lastUnarrived == -1) // ensure old queue clean
860	>	releaseWaiters(phase-1);
861	>	if ((lastUnarrived = unarrived) < NCPU)
862	>	spins += SPINS_PER_ARRIVAL;
863	>	}
864	>	else if (unarrived == 0 && (par = current.parent) != null) {
865	>	current = par;       // if all arrived, use parent
866	>	par = par.parent;
867	>	lastUnarrived = -1;
868	>	}
869	>	else if (spins > 0) {
870	>	if (--spins == (SPINS_PER_ARRIVAL >>> 1))
871	>	Thread.yield();  // yield midway through spin
872	>	}
873	>	else if (node == null)   // must be noninterruptible
874	>	node = new QNode(this, phase, false, false, 0L);
875	>	else if (node.isReleasable()) {
876	>	if ((p = (int)(root.state >>> PHASE_SHIFT)) != phase)
877	>	break;
878	>	else
879	>	return phase;    // aborted
880	>	}
881	>	else if (!queued) {      // push onto queue
882	>	AtomicReference<QNode> head = queueFor(phase);
883	>	QNode q = head.get();
884	>	if (q == null || q.phase == phase) {
885	>	node.next = q;
886	>	if ((p = (int)(root.state >>> PHASE_SHIFT)) != phase)
887	>	break;       // recheck to avoid stale enqueue
888	>	else
889	>	queued = head.compareAndSet(q, node);
890	>	}
891	>	}
892	>	else {
893	>	try {
894	>	ForkJoinPool.managedBlock(node);
895	>	} catch (InterruptedException ie) {
896	>	node.wasInterrupted = true;
897	>	}
898	>	}
899	>	}
900	>	releaseWaiters(phase);
901	>	if (node != null)
902	>	node.onRelease();
903	>	return p;
904	>	}
905
906		/**
907		* Wait nodes for Treiber stack representing wait queue
#	Line 794 | Line 909 | public class Phaser {
909		static final class QNode implements ForkJoinPool.ManagedBlocker {
910		final Phaser phaser;
911		final int phase;
797	–	final long startTime;
798	–	final long nanos;
799	–	final boolean timed;
912		final boolean interruptible;
913	<	volatile boolean wasInterrupted = false;
913	>	final boolean timed;
914	>	boolean wasInterrupted;
915	>	long nanos;
916	>	long lastTime;
917		volatile Thread thread; // nulled to cancel wait
918		QNode next;
919
920		QNode(Phaser phaser, int phase, boolean interruptible,
921	<	boolean timed, long startTime, long nanos) {
921	>	boolean timed, long nanos) {
922		this.phaser = phaser;
923		this.phase = phase;
809	–	this.timed = timed;
924		this.interruptible = interruptible;
811	–	this.startTime = startTime;
925		this.nanos = nanos;
926	+	this.timed = timed;
927	+	this.lastTime = timed? System.nanoTime() : 0L;
928		thread = Thread.currentThread();
929		}
930
931		public boolean isReleasable() {
932	<	return (thread == null ||
933	<	phaser.getPhase() != phase ||
934	<	(interruptible && wasInterrupted) ||
935	<	(timed && (nanos - (System.nanoTime() - startTime)) <= 0));
932	>	Thread t = thread;
933	>	if (t != null) {
934	>	if (phaser.getPhase() != phase)
935	>	t = null;
936	>	else {
937	>	if (Thread.interrupted())
938	>	wasInterrupted = true;
939	>	if (interruptible && wasInterrupted)
940	>	t = null;
941	>	else if (timed) {
942	>	if (nanos > 0) {
943	>	long now = System.nanoTime();
944	>	nanos -= now - lastTime;
945	>	lastTime = now;
946	>	}
947	>	if (nanos <= 0)
948	>	t = null;
949	>	}
950	>	}
951	>	if (t != null)
952	>	return false;
953	>	thread = null;
954	>	}
955	>	return true;
956		}
957
958		public boolean block() {
959	<	if (Thread.interrupted()) {
960	<	wasInterrupted = true;
961	<	if (interruptible)
827	<	return true;
828	<	}
829	<	if (!timed)
959	>	if (isReleasable())
960	>	return true;
961	>	else if (!timed)
962		LockSupport.park(this);
963	<	else {
964	<	long waitTime = nanos - (System.nanoTime() - startTime);
833	<	if (waitTime <= 0)
834	<	return true;
835	<	LockSupport.parkNanos(this, waitTime);
836	<	}
963	>	else if (nanos > 0)
964	>	LockSupport.parkNanos(this, nanos);
965		return isReleasable();
966		}
967
#	Line 845 | Line 973 | public class Phaser {
973		}
974		}
975
976	<	boolean doWait() {
977	<	if (thread != null) {
978	<	try {
979	<	ForkJoinPool.managedBlock(this);
980	<	} catch (InterruptedException ie) {
853	<	wasInterrupted = true; // can't currently happen
854	<	}
855	<	}
856	<	return wasInterrupted;
857	<	}
858	<	}
859	<
860	<	/**
861	<	* Removes and signals waiting threads from wait queue.
862	<	*/
863	<	private void releaseWaiters(int phase) {
864	<	AtomicReference<QNode> head = queueFor(phase);
865	<	QNode q;
866	<	while ((q = head.get()) != null) {
867	<	if (head.compareAndSet(q, q.next))
868	<	q.signal();
869	<	}
870	<	}
871	<
872	<	/**
873	<	* Tries to enqueue given node in the appropriate wait queue.
874	<	*
875	<	* @return true if successful
876	<	*/
877	<	private boolean tryEnqueue(QNode node) {
878	<	AtomicReference<QNode> head = queueFor(node.phase);
879	<	return head.compareAndSet(node.next = head.get(), node);
880	<	}
881	<
882	<	/**
883	<	* The number of times to spin before blocking waiting for advance.
884	<	*/
885	<	static final int MAX_SPINS =
886	<	Runtime.getRuntime().availableProcessors() == 1 ? 0 : 1 << 8;
887	<
888	<	/**
889	<	* Enqueues node and waits unless aborted or signalled.
890	<	*
891	<	* @return current phase
892	<	*/
893	<	private int untimedWait(int phase) {
894	<	QNode node = null;
895	<	boolean queued = false;
896	<	boolean interrupted = false;
897	<	int spins = MAX_SPINS;
898	<	int p;
899	<	while ((p = getPhase()) == phase) {
900	<	if (Thread.interrupted())
901	<	interrupted = true;
902	<	else if (spins > 0) {
903	<	if (--spins == 0)
904	<	Thread.yield();
905	<	}
906	<	else if (node == null)
907	<	node = new QNode(this, phase, false, false, 0, 0);
908	<	else if (!queued)
909	<	queued = tryEnqueue(node);
910	<	else if (node.doWait())
911	<	interrupted = true;
912	<	}
913	<	if (node != null)
914	<	node.thread = null;
915	<	releaseWaiters(phase);
916	<	if (interrupted)
917	<	Thread.currentThread().interrupt();
918	<	return p;
919	<	}
920	<
921	<	/**
922	<	* Interruptible version
923	<	* @return current phase
924	<	*/
925	<	private int interruptibleWait(int phase) throws InterruptedException {
926	<	QNode node = null;
927	<	boolean queued = false;
928	<	boolean interrupted = false;
929	<	int spins = MAX_SPINS;
930	<	int p;
931	<	while ((p = getPhase()) == phase && !interrupted) {
932	<	if (Thread.interrupted())
933	<	interrupted = true;
934	<	else if (spins > 0) {
935	<	if (--spins == 0)
936	<	Thread.yield();
937	<	}
938	<	else if (node == null)
939	<	node = new QNode(this, phase, true, false, 0, 0);
940	<	else if (!queued)
941	<	queued = tryEnqueue(node);
942	<	else if (node.doWait())
943	<	interrupted = true;
976	>	void onRelease() { // actions upon return from internalAwaitAdvance
977	>	if (!interruptible && wasInterrupted)
978	>	Thread.currentThread().interrupt();
979	>	if (thread != null)
980	>	thread = null;
981		}
945	–	if (node != null)
946	–	node.thread = null;
947	–	if (p != phase || (p = getPhase()) != phase)
948	–	releaseWaiters(phase);
949	–	if (interrupted)
950	–	throw new InterruptedException();
951	–	return p;
952	–	}
982
954	–	/**
955	–	* Timeout version.
956	–	* @return current phase
957	–	*/
958	–	private int timedWait(int phase, long nanos)
959	–	throws InterruptedException, TimeoutException {
960	–	long startTime = System.nanoTime();
961	–	QNode node = null;
962	–	boolean queued = false;
963	–	boolean interrupted = false;
964	–	int spins = MAX_SPINS;
965	–	int p;
966	–	while ((p = getPhase()) == phase && !interrupted) {
967	–	if (Thread.interrupted())
968	–	interrupted = true;
969	–	else if (nanos - (System.nanoTime() - startTime) <= 0)
970	–	break;
971	–	else if (spins > 0) {
972	–	if (--spins == 0)
973	–	Thread.yield();
974	–	}
975	–	else if (node == null)
976	–	node = new QNode(this, phase, true, true, startTime, nanos);
977	–	else if (!queued)
978	–	queued = tryEnqueue(node);
979	–	else if (node.doWait())
980	–	interrupted = true;
981	–	}
982	–	if (node != null)
983	–	node.thread = null;
984	–	if (p != phase || (p = getPhase()) != phase)
985	–	releaseWaiters(phase);
986	–	if (interrupted)
987	–	throw new InterruptedException();
988	–	if (p == phase)
989	–	throw new TimeoutException();
990	–	return p;
983		}
984
985		// Unsafe mechanics

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