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

Comparing jsr166/src/jsr166y/Phaser.java (file contents):
Revision 1.57 by dl, Fri Nov 19 16:03:24 2010 UTC vs.
Revision 1.62 by dl, Mon Nov 29 00:52:28 2010 UTC

#	Line 18 | Line 18 | import java.util.concurrent.locks.LockSu
18		* but supporting more flexible usage.
19		*
20		* <p> <b>Registration.</b> Unlike the case for other barriers, the
21	<	* number of parties <em>registered</em> to synchronize on a phaser
21	>	* number of parties <em>registered</em> to synchronize on a Phaser
22		* may vary over time.  Tasks may be registered at any time (using
23		* methods {@link #register}, {@link #bulkRegister}, or forms of
24		* constructors establishing initial numbers of parties), and
#	Line 76 | Line 76 | import java.util.concurrent.locks.LockSu
76		*
77		* <p> <b>Termination.</b> A {@code Phaser} may enter a
78		* <em>termination</em> state in which all synchronization methods
79	<	* immediately return without updating phaser state or waiting for
79	>	* immediately return without updating Phaser state or waiting for
80		* advance, and indicating (via a negative phase value) that execution
81		* is complete.  Termination is triggered when an invocation of {@code
82	<	* onAdvance} returns {@code true}.  As illustrated below, when
83	<	* phasers control actions with a fixed number of iterations, it is
82	>	* onAdvance} returns {@code true}. The default implementation returns
83	>	* {@code true} if a deregistration has caused the number of
84	>	* registered parties to become zero.  As illustrated below, when
85	>	* Phasers control actions with a fixed number of iterations, it is
86		* often convenient to override this method to cause termination when
87		* the current phase number reaches a threshold. Method {@link
88		* #forceTermination} is also available to abruptly release waiting
89		* threads and allow them to terminate.
90		*
91	<	* <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e., arranged
92	<	* in tree structures) to reduce contention. Phasers with large
93	<	* numbers of parties that would otherwise experience heavy
91	>	* <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e.,
92	>	* constructed in tree structures) to reduce contention. Phasers with
93	>	* large numbers of parties that would otherwise experience heavy
94		* synchronization contention costs may instead be set up so that
95		* groups of sub-phasers share a common parent.  This may greatly
96		* increase throughput even though it incurs greater per-operation
97		* overhead.
98		*
99		* <p><b>Monitoring.</b> While synchronization methods may be invoked
100	<	* only by registered parties, the current state of a phaser may be
100	>	* only by registered parties, the current state of a Phaser may be
101		* monitored by any caller.  At any given moment there are {@link
102		* #getRegisteredParties} parties in total, of which {@link
103		* #getArrivedParties} have arrived at the current phase ({@link
#	Line 181 | Line 183 | import java.util.concurrent.locks.LockSu
183		* }}</pre>
184		*
185		*
186	<	* <p>To create a set of tasks using a tree of phasers,
186	>	* <p>To create a set of tasks using a tree of Phasers,
187		* you could use code of the following form, assuming a
188	<	* Task class with a constructor accepting a phaser that
188	>	* Task class with a constructor accepting a Phaser that
189		* it registers with upon construction:
190		*
191		*  <pre> {@code
#	Line 210 | Line 212 | import java.util.concurrent.locks.LockSu
212		* <p><b>Implementation notes</b>: This implementation restricts the
213		* maximum number of parties to 65535. Attempts to register additional
214		* parties result in {@code IllegalStateException}. However, you can and
215	<	* should create tiered phasers to accommodate arbitrarily large sets
215	>	* should create tiered Phasers to accommodate arbitrarily large sets
216		* of participants.
217		*
218		* @since 1.7
#	Line 240 | Line 242 | public class Phaser {
242		*/
243		private volatile long state;
244
245	<	private static final int  MAX_PARTIES    = 0xffff;
246	<	private static final int  MAX_PHASE      = 0x7fffffff;
247	<	private static final int  PARTIES_SHIFT  = 16;
248	<	private static final int  PHASE_SHIFT    = 32;
249	<	private static final int  UNARRIVED_MASK = 0xffff;
250	<	private static final long PARTIES_MASK   = 0xffff0000L; // for masking long
251	<	private static final long ONE_ARRIVAL    = 1L;
252	<	private static final long ONE_PARTY      = 1L << PARTIES_SHIFT;
253	<	private static final long TERMINATION_PHASE  = -1L << PHASE_SHIFT;
245	>	private static final int  MAX_PARTIES     = 0xffff;
246	>	private static final int  MAX_PHASE       = 0x7fffffff;
247	>	private static final int  PARTIES_SHIFT   = 16;
248	>	private static final int  PHASE_SHIFT     = 32;
249	>	private static final int  UNARRIVED_MASK  = 0xffff;      // to mask ints
250	>	private static final long PARTIES_MASK    = 0xffff0000L; // to mask longs
251	>	private static final long ONE_ARRIVAL     = 1L;
252	>	private static final long ONE_PARTY       = 1L << PARTIES_SHIFT;
253	>	private static final long TERMINATION_BIT = 1L << 63;
254
255		// The following unpacking methods are usually manually inlined
256
#	Line 293 | Line 295 | public class Phaser {
295		}
296
297		/**
298	+	* Returns message string for bounds exceptions on arrival.
299	+	*/
300	+	private String badArrive(long s) {
301	+	return "Attempted arrival of unregistered party for " +
302	+	stateToString(s);
303	+	}
304	+
305	+	/**
306	+	* Returns message string for bounds exceptions on registration.
307	+	*/
308	+	private String badRegister(long s) {
309	+	return "Attempt to register more than " +
310	+	MAX_PARTIES + " parties for " + stateToString(s);
311	+	}
312	+
313	+	/**
314		* Main implementation for methods arrive and arriveAndDeregister.
315		* Manually tuned to speed up and minimize race windows for the
316		* common case of just decrementing unarrived field.
#	Line 304 | Line 322 | public class Phaser {
322		private int doArrive(long adj) {
323		for (;;) {
324		long s = state;
325	+	int unarrived = (int)s & UNARRIVED_MASK;
326		int phase = (int)(s >>> PHASE_SHIFT);
327		if (phase < 0)
328		return phase;
329	<	int unarrived = (int)s & UNARRIVED_MASK;
330	<	if (unarrived == 0)
331	<	checkBadArrive(s);
329	>	else if (unarrived == 0) {
330	>	if (reconcileState() == s)     // recheck
331	>	throw new IllegalStateException(badArrive(s));
332	>	}
333		else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) {
334		if (unarrived == 1) {
335		long p = s & PARTIES_MASK; // unshifted parties field
#	Line 320 | Line 340 | public class Phaser {
340		final Phaser parent = this.parent;
341		if (parent == null) {
342		if (onAdvance(phase, u))
343	<	next |= TERMINATION_PHASE; // obliterate phase
343	>	next |= TERMINATION_BIT;
344		UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
345		releaseWaiters(phase);
346		}
347		else {
348		parent.doArrive((u == 0) ?
349		ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL);
350	<	if ((int)(parent.state >>> PHASE_SHIFT) != nextPhase ||
331	<	((int)(state >>> PHASE_SHIFT) != nextPhase &&
332	<	!UNSAFE.compareAndSwapLong(this, stateOffset,
333	<	s, next)))
350	>	if ((int)(parent.state >>> PHASE_SHIFT) != nextPhase)
351		reconcileState();
352	+	else if (state == s)
353	+	UNSAFE.compareAndSwapLong(this, stateOffset, s,
354	+	next);
355		}
356		}
357		return phase;
#	Line 340 | Line 360 | public class Phaser {
360		}
361
362		/**
343	–	* Rechecks state and throws bounds exceptions on arrival -- called
344	–	* only if unarrived is apparently zero.
345	–	*/
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	–	/**
363		* Implementation of register, bulkRegister
364		*
365	<	* @param registrations number to add to both parties and unarrived fields
365	>	* @param registrations number to add to both parties and
366	>	* unarrived fields. Must be greater than zero.
367		*/
368		private int doRegister(int registrations) {
359	–	// assert registrations > 0;
369		// adjustment to state
370		long adj = ((long)registrations << PARTIES_SHIFT) | registrations;
371		final Phaser parent = this.parent;
372		for (;;) {
373		long s = (parent == null) ? state : reconcileState();
374	+	int parties = (int)s >>> PARTIES_SHIFT;
375		int phase = (int)(s >>> PHASE_SHIFT);
376		if (phase < 0)
377		return phase;
368	–	int parties = (int)s >>> PARTIES_SHIFT;
369	–	if (parties != 0 && ((int)s & UNARRIVED_MASK) == 0)
370	–	internalAwaitAdvance(phase, null); // wait for onAdvance
378		else if (registrations > MAX_PARTIES - parties)
379		throw new IllegalStateException(badRegister(s));
380	<	else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj))
381	<	return phase;
380	>	else if ((parties == 0 && parent == null) || // first reg of root
381	>	((int)s & UNARRIVED_MASK) != 0) {   // not advancing
382	>	if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj))
383	>	return phase;
384	>	}
385	>	else if (parties != 0)               // wait for onAdvance
386	>	root.internalAwaitAdvance(phase, null);
387	>	else {                               // 1st registration of child
388	>	synchronized (this) {            // register parent first
389	>	if (reconcileState() == s) { // recheck under lock
390	>	parent.doRegister(1);    // OK if throws IllegalState
391	>	for (;;) {               // simpler form of outer loop
392	>	s = reconcileState();
393	>	phase = (int)(s >>> PHASE_SHIFT);
394	>	if (phase < 0 ||
395	>	UNSAFE.compareAndSwapLong(this, stateOffset,
396	>	s, s + adj))
397	>	return phase;
398	>	}
399	>	}
400	>	}
401	>	}
402		}
403		}
404
405		/**
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	–	/**
406		* Recursively resolves lagged phase propagation from root if necessary.
407		*/
408		private long reconcileState() {
#	Line 394 | Line 413 | public class Phaser {
413		int phase, rPhase;
414		while ((phase = (int)(s >>> PHASE_SHIFT)) >= 0 &&
415		(rPhase = (int)(rt.state >>> PHASE_SHIFT)) != phase) {
416	<	if ((int)(par.state >>> PHASE_SHIFT) != rPhase)
416	>	if (par != rt && (int)(par.state >>> PHASE_SHIFT) != rPhase)
417		par.reconcileState();
418		else if (rPhase < 0 || ((int)s & UNARRIVED_MASK) == 0) {
419		long u = s & PARTIES_MASK; // reset unarrived to parties
420		long next = ((((long) rPhase) << PHASE_SHIFT) | u |
421		(u >>> PARTIES_SHIFT));
422	<	if (state == s &&
404	<	UNSAFE.compareAndSwapLong(this, stateOffset,
405	<	s, s = next))
406	<	break;
422	>	UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
423		}
424		s = state;
425		}
#	Line 412 | Line 428 | public class Phaser {
428		}
429
430		/**
431	<	* Creates a new phaser without any initially registered parties,
431	>	* Creates a new Phaser without any initially registered parties,
432		* initial phase number 0, and no parent. Any thread using this
433	<	* phaser will need to first register for it.
433	>	* Phaser will need to first register for it.
434		*/
435		public Phaser() {
436		this(null, 0);
437		}
438
439		/**
440	<	* Creates a new phaser with the given number of registered
440	>	* Creates a new Phaser with the given number of registered
441		* unarrived parties, initial phase number 0, and no parent.
442		*
443		* @param parties the number of parties required to trip barrier
#	Line 433 | Line 449 | public class Phaser {
449		}
450
451		/**
452	<	* Creates a new phaser with the given parent, without any
437	<	* initially registered parties. If parent is non-null this phaser
438	<	* is registered with the parent and its initial phase number is
439	<	* the same as that of parent phaser.
452	>	* Equivalent to {@link #Phaser(Phaser, int) Phaser(parent, 0)}.
453		*
454	<	* @param parent the parent phaser
454	>	* @param parent the parent Phaser
455		*/
456		public Phaser(Phaser parent) {
457		this(parent, 0);
458		}
459
460		/**
461	<	* Creates a new phaser with the given parent and number of
462	<	* registered unarrived parties. If parent is non-null, this phaser
463	<	* is registered with the parent and its initial phase number is
464	<	* the same as that of parent phaser.
461	>	* Creates a new Phaser with the given parent and number of
462	>	* registered unarrived parties. Registration and deregistration
463	>	* of this child Phaser with its parent are managed automatically.
464	>	* If the given parent is non-null, whenever this child Phaser has
465	>	* any registered parties (as established in this constructor,
466	>	* {@link #register}, or {@link #bulkRegister}), this child Phaser
467	>	* is registered with its parent. Whenever the number of
468	>	* registered parties becomes zero as the result of an invocation
469	>	* of {@link #arriveAndDeregister}, this child Phaser is
470	>	* deregistered from its parent.
471		*
472	<	* @param parent the parent phaser
472	>	* @param parent the parent Phaser
473		* @param parties the number of parties required to trip barrier
474		* @throws IllegalArgumentException if parties less than zero
475		* or greater than the maximum number of parties supported
#	Line 458 | Line 477 | public class Phaser {
477		public Phaser(Phaser parent, int parties) {
478		if (parties >>> PARTIES_SHIFT != 0)
479		throw new IllegalArgumentException("Illegal number of parties");
480	<	int phase;
480	>	long s = ((long) parties) | (((long) parties) << PARTIES_SHIFT);
481		this.parent = parent;
482		if (parent != null) {
483		Phaser r = parent.root;
484		this.root = r;
485		this.evenQ = r.evenQ;
486		this.oddQ = r.oddQ;
487	<	phase = parent.register();
487	>	if (parties != 0)
488	>	s |= ((long)(parent.doRegister(1))) << PHASE_SHIFT;
489		}
490		else {
491		this.root = this;
492		this.evenQ = new AtomicReference<QNode>();
493		this.oddQ = new AtomicReference<QNode>();
474	–	phase = 0;
494		}
495	<	long p = (long)parties;
477	<	this.state = (((long)phase) << PHASE_SHIFT) | p | (p << PARTIES_SHIFT);
495	>	this.state = s;
496		}
497
498		/**
499	<	* Adds a new unarrived party to this phaser.
500	<	* If an ongoing invocation of {@link #onAdvance} is in progress,
501	<	* this method may wait until its completion before registering.
499	>	* Adds a new unarrived party to this Phaser.  If an ongoing
500	>	* invocation of {@link #onAdvance} is in progress, this method
501	>	* may await its completion before returning.  If this Phaser has
502	>	* a parent, and this Phaser previously had no registered parties,
503	>	* this Phaser is also registered with its parent.
504		*
505		* @return the arrival phase number to which this registration applied
506		* @throws IllegalStateException if attempting to register more
#	Line 491 | Line 511 | public class Phaser {
511		}
512
513		/**
514	<	* Adds the given number of new unarrived parties to this phaser.
514	>	* Adds the given number of new unarrived parties to this Phaser.
515		* If an ongoing invocation of {@link #onAdvance} is in progress,
516	<	* this method may wait until its completion before registering.
516	>	* this method may await its completion before returning.  If this
517	>	* Phaser has a parent, and the given number of parities is
518	>	* greater than zero, and this Phaser previously had no registered
519	>	* parties, this Phaser is also registered with its parent.
520		*
521		* @param parties the number of additional parties required to trip barrier
522		* @return the arrival phase number to which this registration applied
#	Line 510 | Line 533 | public class Phaser {
533		}
534
535		/**
536	<	* Arrives at the barrier, but does not wait for others.  (You can
537	<	* in turn wait for others via {@link #awaitAdvance}).  It is an
538	<	* unenforced usage error for an unregistered party to invoke this
539	<	* method.
536	>	* Arrives at the barrier, without waiting for others to arrive.
537	>	*
538	>	* <p>It is a usage error for an unregistered party to invoke this
539	>	* method.  However, this error may result in an {@code
540	>	* IllegalStateException} only upon some subsequent operation on
541	>	* this Phaser, if ever.
542		*
543		* @return the arrival phase number, or a negative value if terminated
544		* @throws IllegalStateException if not terminated and the number
#	Line 525 | Line 550 | public class Phaser {
550
551		/**
552		* Arrives at the barrier and deregisters from it without waiting
553	<	* for others. Deregistration reduces the number of parties
554	<	* required to trip the barrier in future phases.  If this phaser
555	<	* has a parent, and deregistration causes this phaser to have
556	<	* zero parties, this phaser also arrives at and is deregistered
557	<	* from its parent.  It is an unenforced usage error for an
558	<	* unregistered party to invoke this method.
553	>	* for others to arrive. Deregistration reduces the number of
554	>	* parties required to trip the barrier in future phases.  If this
555	>	* Phaser has a parent, and deregistration causes this Phaser to
556	>	* have zero parties, this Phaser is also deregistered from its
557	>	* parent.
558	>	*
559	>	* <p>It is a usage error for an unregistered party to invoke this
560	>	* method.  However, this error may result in an {@code
561	>	* IllegalStateException} only upon some subsequent operation on
562	>	* this Phaser, if ever.
563		*
564		* @return the arrival phase number, or a negative value if terminated
565		* @throws IllegalStateException if not terminated and the number
#	Line 546 | Line 575 | public class Phaser {
575		* interruption or timeout, you can arrange this with an analogous
576		* construction using one of the other forms of the {@code
577		* awaitAdvance} method.  If instead you need to deregister upon
578	<	* arrival, use {@link #arriveAndDeregister}. It is an unenforced
579	<	* usage error for an unregistered party to invoke this method.
578	>	* arrival, use {@code awaitAdvance(arriveAndDeregister())}.
579	>	*
580	>	* <p>It is a usage error for an unregistered party to invoke this
581	>	* method.  However, this error may result in an {@code
582	>	* IllegalStateException} only upon some subsequent operation on
583	>	* this Phaser, if ever.
584		*
585		* @return the arrival phase number, or a negative number if terminated
586		* @throws IllegalStateException if not terminated and the number
587		* of unarrived parties would become negative
588		*/
589		public int arriveAndAwaitAdvance() {
590	<	return awaitAdvance(arrive());
590	>	return awaitAdvance(doArrive(ONE_ARRIVAL));
591		}
592
593		/**
#	Line 570 | Line 603 | public class Phaser {
603		* if terminated or argument is negative
604		*/
605		public int awaitAdvance(int phase) {
606	+	Phaser rt;
607	+	int p = (int)(state >>> PHASE_SHIFT);
608		if (phase < 0)
609		return phase;
610	<	long s = (parent == null) ? state : reconcileState();
611	<	int p = (int)(s >>> PHASE_SHIFT);
612	<	return (p != phase) ? p : internalAwaitAdvance(phase, null);
610	>	if (p == phase &&
611	>	(p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase)
612	>	return rt.internalAwaitAdvance(phase, null);
613	>	return p;
614		}
615
616		/**
#	Line 593 | Line 629 | public class Phaser {
629		*/
630		public int awaitAdvanceInterruptibly(int phase)
631		throws InterruptedException {
632	+	Phaser rt;
633	+	int p = (int)(state >>> PHASE_SHIFT);
634		if (phase < 0)
635		return phase;
636	<	long s = (parent == null) ? state : reconcileState();
637	<	int p = (int)(s >>> PHASE_SHIFT);
600	<	if (p == phase) {
636	>	if (p == phase &&
637	>	(p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
638		QNode node = new QNode(this, phase, true, false, 0L);
639	<	p = internalAwaitAdvance(phase, node);
639	>	p = rt.internalAwaitAdvance(phase, node);
640		if (node.wasInterrupted)
641		throw new InterruptedException();
642		}
#	Line 629 | Line 666 | public class Phaser {
666		public int awaitAdvanceInterruptibly(int phase,
667		long timeout, TimeUnit unit)
668		throws InterruptedException, TimeoutException {
669	+	long nanos = unit.toNanos(timeout);
670	+	Phaser rt;
671	+	int p = (int)(state >>> PHASE_SHIFT);
672		if (phase < 0)
673		return phase;
674	<	long s = (parent == null) ? state : reconcileState();
675	<	int p = (int)(s >>> PHASE_SHIFT);
636	<	if (p == phase) {
637	<	long nanos = unit.toNanos(timeout);
674	>	if (p == phase &&
675	>	(p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
676		QNode node = new QNode(this, phase, true, true, nanos);
677	<	p = internalAwaitAdvance(phase, node);
677	>	p = rt.internalAwaitAdvance(phase, node);
678		if (node.wasInterrupted)
679		throw new InterruptedException();
680		else if (p == phase)
#	Line 647 | Line 685 | public class Phaser {
685
686		/**
687		* Forces this barrier to enter termination state.  Counts of
688	<	* arrived and registered parties are unaffected.  If this phaser
689	<	* is a member of a tiered set of phasers, then all of the phasers
690	<	* in the set are terminated.  If this phaser is already
688	>	* arrived and registered parties are unaffected.  If this Phaser
689	>	* is a member of a tiered set of Phasers, then all of the Phasers
690	>	* in the set are terminated.  If this Phaser is already
691		* terminated, this method has no effect.  This method may be
692		* useful for coordinating recovery after one or more tasks
693		* encounter unexpected exceptions.
#	Line 660 | Line 698 | public class Phaser {
698		long s;
699		while ((s = root.state) >= 0) {
700		if (UNSAFE.compareAndSwapLong(root, stateOffset,
701	<	s, s | TERMINATION_PHASE)) {
701	>	s, s | TERMINATION_BIT)) {
702		releaseWaiters(0); // signal all threads
703		releaseWaiters(1);
704		return;
#	Line 695 | Line 733 | public class Phaser {
733		* @return the number of arrived parties
734		*/
735		public int getArrivedParties() {
736	<	return arrivedOf(parent==null? state : reconcileState());
736	>	long s = state;
737	>	int u = unarrivedOf(s); // only reconcile if possibly needed
738	>	return (u != 0 || parent == null) ?
739	>	partiesOf(s) - u :
740	>	arrivedOf(reconcileState());
741		}
742
743		/**
#	Line 705 | Line 747 | public class Phaser {
747		* @return the number of unarrived parties
748		*/
749		public int getUnarrivedParties() {
750	<	return unarrivedOf(parent==null? state : reconcileState());
750	>	int u = unarrivedOf(state);
751	>	return (u != 0 || parent == null) ? u : unarrivedOf(reconcileState());
752		}
753
754		/**
755	<	* Returns the parent of this phaser, or {@code null} if none.
755	>	* Returns the parent of this Phaser, or {@code null} if none.
756		*
757	<	* @return the parent of this phaser, or {@code null} if none
757	>	* @return the parent of this Phaser, or {@code null} if none
758		*/
759		public Phaser getParent() {
760		return parent;
761		}
762
763		/**
764	<	* Returns the root ancestor of this phaser, which is the same as
765	<	* this phaser if it has no parent.
764	>	* Returns the root ancestor of this Phaser, which is the same as
765	>	* this Phaser if it has no parent.
766		*
767	<	* @return the root ancestor of this phaser
767	>	* @return the root ancestor of this Phaser
768		*/
769		public Phaser getRoot() {
770		return root;
#	Line 748 | Line 791 | public class Phaser {
791		* propagated to the party attempting to trip the barrier, in
792		* which case no advance occurs.
793		*
794	<	* <p>The arguments to this method provide the state of the phaser
794	>	* <p>The arguments to this method provide the state of the Phaser
795		* prevailing for the current transition.  The effects of invoking
796		* arrival, registration, and waiting methods on this Phaser from
797		* within {@code onAdvance} are unspecified and should not be
#	Line 758 | Line 801 | public class Phaser {
801		* {@code onAdvance} is invoked only for its root Phaser on each
802		* advance.
803		*
804	<	* <p>The default version returns {@code true} when the number of
805	<	* registered parties is zero. Normally, overrides that arrange
806	<	* termination for other reasons should also preserve this
807	<	* property.
804	>	* <p>To support the most common use cases, the default
805	>	* implementation of this method returns {@code true} when the
806	>	* number of registered parties has become zero as the result of a
807	>	* party invoking {@code arriveAndDeregister}.  You can disable
808	>	* this behavior, thus enabling continuation upon future
809	>	* registrations, by overriding this method to always return
810	>	* {@code false}:
811	>	*
812	>	* <pre> {@code
813	>	* Phaser phaser = new Phaser() {
814	>	*   protected boolean onAdvance(int phase, int parties) { return false; }
815	>	* }}</pre>
816		*
817		* @param phase the phase number on entering the barrier
818		* @param registeredParties the current number of registered parties
819		* @return {@code true} if this barrier should terminate
820		*/
821		protected boolean onAdvance(int phase, int registeredParties) {
822	<	return registeredParties <= 0;
822	>	return registeredParties == 0;
823		}
824
825		/**
826	<	* Returns a string identifying this phaser, as well as its
826	>	* Returns a string identifying this Phaser, as well as its
827		* state.  The state, in brackets, includes the String {@code
828		* "phase = "} followed by the phase number, {@code "parties = "}
829		* followed by the number of registered parties, and {@code
#	Line 800 | Line 851 | public class Phaser {
851		* Removes and signals threads from queue for phase.
852		*/
853		private void releaseWaiters(int phase) {
854	<	AtomicReference<QNode> head = queueFor(phase);
854	>	AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ;
855		QNode q;
856		int p;
857		while ((q = head.get()) != null &&
#	Line 822 | Line 873 | public class Phaser {
873		* avoid it when threads regularly arrive: When a thread in
874		* internalAwaitAdvance notices another arrival before blocking,
875		* and there appear to be enough CPUs available, it spins
876	<	* SPINS_PER_ARRIVAL more times before blocking. Plus, even on
877	<	* uniprocessors, there is at least one intervening Thread.yield
827	<	* before blocking. The value trades off good-citizenship vs big
828	<	* unnecessary slowdowns.
876	>	* SPINS_PER_ARRIVAL more times before blocking. The value trades
877	>	* off good-citizenship vs big unnecessary slowdowns.
878		*/
879		static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8;
880
881		/**
882		* Possibly blocks and waits for phase to advance unless aborted.
883	+	* Call only from root node.
884		*
885		* @param phase current phase
886		* @param node if non-null, the wait node to track interrupt and timeout;
#	Line 838 | Line 888 | public class Phaser {
888		* @return current phase
889		*/
890		private int internalAwaitAdvance(int phase, QNode node) {
841	–	Phaser current = this;       // to eventually wait at root if tiered
891		boolean queued = false;      // true when node is enqueued
892		int lastUnarrived = -1;      // to increase spins upon change
893		int spins = SPINS_PER_ARRIVAL;
894		long s;
895		int p;
896	<	while ((p = (int)((s = current.state) >>> PHASE_SHIFT)) == phase) {
848	<	Phaser par;
896	>	while ((p = (int)((s = state) >>> PHASE_SHIFT)) == phase) {
897		int unarrived = (int)s & UNARRIVED_MASK;
898	<	if (unarrived != lastUnarrived) {
898	>	if (node != null && node.isReleasable()) {
899	>	p = (int)(state >>> PHASE_SHIFT);
900	>	break;               // done or aborted
901	>	}
902	>	else if (node == null && Thread.interrupted()) {
903	>	node = new QNode(this, phase, false, false, 0L);
904	>	node.wasInterrupted = true;
905	>	}
906	>	else if (unarrived != lastUnarrived) {
907		if (lastUnarrived == -1) // ensure old queue clean
908		releaseWaiters(phase-1);
909		if ((lastUnarrived = unarrived) < NCPU)
910		spins += SPINS_PER_ARRIVAL;
911		}
912	<	else if (unarrived == 0 && (par = current.parent) != null) {
913	<	current = par;       // if all arrived, use parent
914	<	par = par.parent;
859	<	lastUnarrived = -1;
860	<	}
861	<	else if (spins > 0) {
862	<	if (--spins == (SPINS_PER_ARRIVAL >>> 1))
863	<	Thread.yield();  // yield midway through spin
864	<	}
865	<	else if (node == null)   // must be noninterruptible
912	>	else if (spins > 0)
913	>	--spins;
914	>	else if (node == null)   // null if noninterruptible mode
915		node = new QNode(this, phase, false, false, 0L);
867	–	else if (node.isReleasable()) {
868	–	if ((p = (int)(root.state >>> PHASE_SHIFT)) != phase)
869	–	break;
870	–	else
871	–	return phase;    // aborted
872	–	}
916		else if (!queued) {      // push onto queue
917	<	AtomicReference<QNode> head = queueFor(phase);
917	>	AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ;
918		QNode q = head.get();
919		if (q == null || q.phase == phase) {
920		node.next = q;
921	<	if ((p = (int)(root.state >>> PHASE_SHIFT)) != phase)
921	>	if ((p = (int)(state >>> PHASE_SHIFT)) != phase)
922		break;       // recheck to avoid stale enqueue
923	<	else
881	<	queued = head.compareAndSet(q, node);
923	>	queued = head.compareAndSet(q, node);
924		}
925		}
926		else {
#	Line 889 | Line 931 | public class Phaser {
931		}
932		}
933		}
934	<	releaseWaiters(phase);
935	<	if (node != null)
936	<	node.onRelease();
934	>
935	>	if (node != null) {
936	>	if (node.thread != null)
937	>	node.thread = null; // disable unpark() in node.signal
938	>	if (node.wasInterrupted && !node.interruptible)
939	>	Thread.currentThread().interrupt();
940	>	}
941	>	if (p != phase)
942	>	releaseWaiters(phase);
943		return p;
944		}
945
#	Line 928 | Line 976 | public class Phaser {
976		else {
977		if (Thread.interrupted())
978		wasInterrupted = true;
979	<	if (interruptible && wasInterrupted)
979	>	if (wasInterrupted && interruptible)
980		t = null;
981		else if (timed) {
982		if (nanos > 0) {
#	Line 964 | Line 1012 | public class Phaser {
1012		LockSupport.unpark(t);
1013		}
1014		}
967	–
968	–	void onRelease() { // actions upon return from internalAwaitAdvance
969	–	if (!interruptible && wasInterrupted)
970	–	Thread.currentThread().interrupt();
971	–	if (thread != null)
972	–	thread = null;
973	–	}
974	–
1015		}
1016
1017		// Unsafe mechanics

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