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

Comparing jsr166/src/jsr166y/Phaser.java (file contents):
Revision 1.64 by jsr166, Mon Nov 29 20:58:06 2010 UTC vs.
Revision 1.65 by dl, Wed Dec 1 17:20:41 2010 UTC

#	Line 183 | 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,
187	<	* you could use code of the following form, assuming a
188	<	* Task class with a constructor accepting a {@code Phaser} that
189	<	* it registers with upon construction:
186	>	* <p>To create a set of {@code n} tasks using a tree of phasers, you
187	>	* could use code of the following form, assuming a Task class with a
188	>	* constructor accepting a {@code Phaser} that it registers with upon
189	>	* construction. After invocation of {@code build(new Task[n], 0, n,
190	>	* new Phaser())}, these tasks could then be started, for example by
191	>	* submitting to a pool:
192		*
193		*  <pre> {@code
194	<	* void build(Task[] actions, int lo, int hi, Phaser ph) {
194	>	* void build(Task[] tasks, int lo, int hi, Phaser ph) {
195		*   if (hi - lo > TASKS_PER_PHASER) {
196		*     for (int i = lo; i < hi; i += TASKS_PER_PHASER) {
197		*       int j = Math.min(i + TASKS_PER_PHASER, hi);
198	<	*       build(actions, i, j, new Phaser(ph));
198	>	*       build(tasks, i, j, new Phaser(ph));
199		*     }
200		*   } else {
201		*     for (int i = lo; i < hi; ++i)
202	<	*       actions[i] = new Task(ph);
202	>	*       tasks[i] = new Task(ph);
203		*       // assumes new Task(ph) performs ph.register()
204		*   }
205	<	* }
204	<	* // .. initially called, for n tasks via
205	<	* build(new Task[n], 0, n, new Phaser());}</pre>
205	>	* }}</pre>
206		*
207		* The best value of {@code TASKS_PER_PHASER} depends mainly on
208		* expected synchronization rates. A value as low as four may
#	Line 233 | Line 233 | public class Phaser {
233		* * phase -- the generation of the barrier                (bits 32-62)
234		* * terminated -- set if barrier is terminated            (bit  63 / sign)
235		*
236	<	* However, to efficiently maintain atomicity, these values are
237	<	* packed into a single (atomic) long. Termination uses the sign
238	<	* bit of 32 bit representation of phase, so phase is set to -1 on
239	<	* termination. Good performance relies on keeping state decoding
240	<	* and encoding simple, and keeping race windows short.
236	>	* Except that a phaser with no registered parties is
237	>	* distinguished with the otherwise illegal state of having zero
238	>	* parties and one unarrived parties (encoded as EMPTY below).
239	>	*
240	>	* To efficiently maintain atomicity, these values are packed into
241	>	* a single (atomic) long. Good performance relies on keeping
242	>	* state decoding and encoding simple, and keeping race windows
243	>	* short.
244	>	*
245	>	* All state updates are performed via CAS except initial
246	>	* registration of a sub-phaser (i.e., one with a non-null
247	>	* parent).  In this (relatively rare) case, we use built-in
248	>	* synchronization to lock while first registering with its
249	>	* parent.
250	>	*
251	>	* The phase of a subphaser is allowed to lag that of its
252	>	* ancestors until it is actually accessed.  Method reconcileState
253	>	* is usually attempted only only when the number of unarrived
254	>	* parties appears to be zero, which indicates a potential lag in
255	>	* updating phase after the root advanced.
256		*/
257		private volatile long state;
258
#	Line 247 | Line 262 | public class Phaser {
262		private static final int  PHASE_SHIFT     = 32;
263		private static final int  UNARRIVED_MASK  = 0xffff;      // to mask ints
264		private static final long PARTIES_MASK    = 0xffff0000L; // to mask longs
250	–	private static final long ONE_ARRIVAL     = 1L;
251	–	private static final long ONE_PARTY       = 1L << PARTIES_SHIFT;
265		private static final long TERMINATION_BIT = 1L << 63;
266
267	+	// some special values
268	+	private static final int  ONE_ARRIVAL     = 1;
269	+	private static final int  ONE_PARTY       = 1 << PARTIES_SHIFT;
270	+	private static final int  EMPTY           = 1;
271	+
272		// The following unpacking methods are usually manually inlined
273
274		private static int unarrivedOf(long s) {
275	<	return (int)s & UNARRIVED_MASK;
275	>	int counts = (int)s;
276	>	return (counts == EMPTY)? 0 : counts & UNARRIVED_MASK;
277		}
278
279		private static int partiesOf(long s) {
280	<	return (int)s >>> PARTIES_SHIFT;
280	>	int counts = (int)s;
281	>	return (counts == EMPTY)? 0 : counts >>> PARTIES_SHIFT;
282		}
283
284		private static int phaseOf(long s) {
#	Line 266 | Line 286 | public class Phaser {
286		}
287
288		private static int arrivedOf(long s) {
289	<	return partiesOf(s) - unarrivedOf(s);
289	>	int counts = (int)s;
290	>	return (counts == EMPTY)? 0 :
291	>	(counts >>> PARTIES_SHIFT) - (counts & UNARRIVED_MASK);
292		}
293
294		/**
#	Line 275 | Line 297 | public class Phaser {
297		private final Phaser parent;
298
299		/**
300	<	* The root of phaser tree. Equals this if not in a tree.  Used to
279	<	* support faster state push-down.
300	>	* The root of phaser tree. Equals this if not in a tree.
301		*/
302		private final Phaser root;
303
#	Line 314 | Line 335 | public class Phaser {
335		* Manually tuned to speed up and minimize race windows for the
336		* common case of just decrementing unarrived field.
337		*
338	<	* @param adj - adjustment to apply to state -- either
318	<	* ONE_ARRIVAL (for arrive) or
319	<	* ONE_ARRIVAL|ONE_PARTY (for arriveAndDeregister)
338	>	* @param deregister false for arrive, true for arriveAndDeregister
339		*/
340	<	private int doArrive(long adj) {
341	<	for (;;) {
342	<	long s = state;
343	<	int unarrived = (int)s & UNARRIVED_MASK;
344	<	int phase = (int)(s >>> PHASE_SHIFT);
345	<	if (phase < 0)
346	<	return phase;
347	<	else if (unarrived == 0) {
348	<	if (reconcileState() == s)     // recheck
340	>	private int doArrive(boolean deregister) {
341	>	int adj = deregister ? ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL;
342	>	long s;
343	>	int phase;
344	>	while ((phase = (int)((s = state) >>> PHASE_SHIFT)) >= 0) {
345	>	int counts = (int)s;
346	>	int unarrived = counts & UNARRIVED_MASK;
347	>	if (counts == EMPTY || unarrived == 0) {
348	>	if (reconcileState() == s)
349		throw new IllegalStateException(badArrive(s));
350		}
351		else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) {
352		if (unarrived == 1) {
353	<	long p = s & PARTIES_MASK; // unshifted parties field
354	<	long lu = p >>> PARTIES_SHIFT;
355	<	int u = (int)lu;
356	<	int nextPhase = (phase + 1) & MAX_PHASE;
357	<	long next = ((long)nextPhase << PHASE_SHIFT) | p | lu;
358	<	final Phaser parent = this.parent;
340	<	if (parent == null) {
341	<	if (onAdvance(phase, u))
342	<	next |= TERMINATION_BIT;
343	<	UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
344	<	releaseWaiters(phase);
353	>	long n = s & PARTIES_MASK;       // unshifted parties field
354	>	int u = ((int)n) >>> PARTIES_SHIFT;
355	>	Phaser par = parent;
356	>	if (par != null) {
357	>	par.doArrive(u == 0);
358	>	reconcileState();
359		}
360		else {
361	<	parent.doArrive((u == 0) ?
362	<	ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL);
363	<	if ((int)(parent.state >>> PHASE_SHIFT) != nextPhase)
364	<	reconcileState();
365	<	else if (state == s)
366	<	UNSAFE.compareAndSwapLong(this, stateOffset, s,
367	<	next);
361	>	n |= (((long)((phase+1) & MAX_PHASE)) << PHASE_SHIFT);
362	>	if (onAdvance(phase, u))
363	>	n |= TERMINATION_BIT;
364	>	else if (u == 0)
365	>	n |= EMPTY;             // reset to unregistered
366	>	else
367	>	n |= (long)u;           // reset unarr to parties
368	>	// assert state == s || isTerminated();
369	>	UNSAFE.compareAndSwapLong(this, stateOffset, s, n);
370	>	releaseWaiters(phase);
371		}
372		}
373	<	return phase;
373	>	break;
374		}
375		}
376	+	return phase;
377		}
378
379		/**
#	Line 367 | Line 385 | public class Phaser {
385		private int doRegister(int registrations) {
386		// adjustment to state
387		long adj = ((long)registrations << PARTIES_SHIFT) | registrations;
388	<	final Phaser parent = this.parent;
388	>	Phaser par = parent;
389	>	int phase;
390		for (;;) {
391	<	long s = (parent == null) ? state : reconcileState();
392	<	int parties = (int)s >>> PARTIES_SHIFT;
393	<	int phase = (int)(s >>> PHASE_SHIFT);
394	<	if (phase < 0)
395	<	return phase;
377	<	else if (registrations > MAX_PARTIES - parties)
391	>	long s = state;
392	>	int counts = (int)s;
393	>	int parties = counts >>> PARTIES_SHIFT;
394	>	int unarrived = counts & UNARRIVED_MASK;
395	>	if (registrations > MAX_PARTIES - parties)
396		throw new IllegalStateException(badRegister(s));
397	<	else if ((parties == 0 && parent == null) || // first reg of root
398	<	((int)s & UNARRIVED_MASK) != 0) {   // not advancing
399	<	if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj))
400	<	return phase;
401	<	}
402	<	else if (parties != 0)               // wait for onAdvance
403	<	root.internalAwaitAdvance(phase, null);
404	<	else {                               // 1st registration of child
405	<	synchronized (this) {            // register parent first
406	<	if (reconcileState() == s) { // recheck under lock
407	<	parent.doRegister(1);    // OK if throws IllegalState
408	<	for (;;) {               // simpler form of outer loop
409	<	s = reconcileState();
410	<	phase = (int)(s >>> PHASE_SHIFT);
411	<	if (phase < 0 ||
412	<	UNSAFE.compareAndSwapLong(this, stateOffset,
413	<	s, s + adj))
414	<	return phase;
415	<	}
397	>	else if ((phase = (int)(s >>> PHASE_SHIFT)) < 0)
398	>	break;
399	>	else if (counts != EMPTY) {             // not 1st registration
400	>	if (par == null || reconcileState() == s) {
401	>	if (unarrived == 0)             // wait out advance
402	>	root.internalAwaitAdvance(phase, null);
403	>	else if (UNSAFE.compareAndSwapLong(this, stateOffset,
404	>	s, s + adj))
405	>	break;
406	>	}
407	>	}
408	>	else if (par == null) {                 // 1st root registration
409	>	long next = (((long) phase) << PHASE_SHIFT) | adj;
410	>	if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next))
411	>	break;
412	>	}
413	>	else {
414	>	synchronized(this) {                // 1st sub registration
415	>	if (state == s) {               // recheck under lock
416	>	par.doRegister(1);
417	>	do {                        // force current phase
418	>	phase = (int)(root.state >>> PHASE_SHIFT);
419	>	// assert phase < 0 || (int)state == EMPTY;
420	>	} while (!UNSAFE.compareAndSwapLong
421	>	(this, stateOffset, state,
422	>	(((long) phase) << PHASE_SHIFT) | adj));
423	>	break;
424		}
425		}
426		}
427		}
428	+	return phase;
429		}
430
431		/**
432	<	* Recursively resolves lagged phase propagation from root if necessary.
432	>	* Resolves lagged phase propagation from root if necessary.
433		*/
434		private long reconcileState() {
435	<	Phaser par = parent;
435	>	Phaser rt = root;
436		long s = state;
437	<	if (par != null) {
438	<	Phaser rt = root;
439	<	int phase, rPhase;
440	<	while ((phase = (int)(s >>> PHASE_SHIFT)) >= 0 &&
441	<	(rPhase = (int)(rt.state >>> PHASE_SHIFT)) != phase) {
442	<	if (par != rt && (int)(par.state >>> PHASE_SHIFT) != rPhase)
443	<	par.reconcileState();
444	<	else if (rPhase < 0 || ((int)s & UNARRIVED_MASK) == 0) {
445	<	long u = s & PARTIES_MASK; // reset unarrived to parties
446	<	long next = ((((long) rPhase) << PHASE_SHIFT) | u |
447	<	(u >>> PARTIES_SHIFT));
448	<	UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
437	>	if (rt != this) {
438	>	int phase;
439	>	while ((phase = (int)(rt.state >>> PHASE_SHIFT)) !=
440	>	(int)(s >>> PHASE_SHIFT)) {
441	>	// assert phase < 0 || unarrivedOf(s) == 0
442	>	long t;                             // to reread s
443	>	long p = s & PARTIES_MASK;          // unshifted parties field
444	>	long n = (((long) phase) << PHASE_SHIFT) | p;
445	>	if (phase >= 0) {
446	>	if (p == 0L)
447	>	n |= EMPTY;                 // reset to empty
448	>	else
449	>	n |= p >>> PARTIES_SHIFT;   // set unarr to parties
450		}
451	<	s = state;
451	>	if ((t = state) == s &&
452	>	UNSAFE.compareAndSwapLong(this, stateOffset, s, s = n))
453	>	break;
454	>	s = t;
455		}
456		}
457		return s;
#	Line 478 | Line 509 | public class Phaser {
509		public Phaser(Phaser parent, int parties) {
510		if (parties >>> PARTIES_SHIFT != 0)
511		throw new IllegalArgumentException("Illegal number of parties");
512	<	long s = ((long) parties) | (((long) parties) << PARTIES_SHIFT);
512	>	int phase = 0;
513		this.parent = parent;
514		if (parent != null) {
515		Phaser r = parent.root;
#	Line 486 | Line 517 | public class Phaser {
517		this.evenQ = r.evenQ;
518		this.oddQ = r.oddQ;
519		if (parties != 0)
520	<	s |= ((long)(parent.doRegister(1))) << PHASE_SHIFT;
520	>	phase = parent.doRegister(1);
521		}
522		else {
523		this.root = this;
524		this.evenQ = new AtomicReference<QNode>();
525		this.oddQ = new AtomicReference<QNode>();
526		}
527	<	this.state = s;
527	>	this.state = (parties == 0)? ((long) EMPTY) :
528	>	((((long) phase) << PHASE_SHIFT) |
529	>	(((long) parties) << PARTIES_SHIFT) |
530	>	((long) parties));
531		}
532
533		/**
#	Line 547 | Line 581 | public class Phaser {
581		* of unarrived parties would become negative
582		*/
583		public int arrive() {
584	<	return doArrive(ONE_ARRIVAL);
584	>	return doArrive(false);
585		}
586
587		/**
#	Line 567 | Line 601 | public class Phaser {
601		* of registered or unarrived parties would become negative
602		*/
603		public int arriveAndDeregister() {
604	<	return doArrive(ONE_ARRIVAL|ONE_PARTY);
604	>	return doArrive(true);
605		}
606
607		/**
#	Line 588 | Line 622 | public class Phaser {
622		* of unarrived parties would become negative
623		*/
624		public int arriveAndAwaitAdvance() {
625	<	return awaitAdvance(doArrive(ONE_ARRIVAL));
625	>	return awaitAdvance(doArrive(false));
626		}
627
628		/**
#	Line 607 | Line 641 | public class Phaser {
641		int p = (int)(state >>> PHASE_SHIFT);
642		if (phase < 0)
643		return phase;
644	<	if (p == phase &&
645	<	(p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase)
646	<	return rt.internalAwaitAdvance(phase, null);
644	>	if (p == phase) {
645	>	if ((p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase)
646	>	return rt.internalAwaitAdvance(phase, null);
647	>	reconcileState();
648	>	}
649		return p;
650		}
651
#	Line 633 | Line 669 | public class Phaser {
669		int p = (int)(state >>> PHASE_SHIFT);
670		if (phase < 0)
671		return phase;
672	<	if (p == phase &&
673	<	(p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
674	<	QNode node = new QNode(this, phase, true, false, 0L);
675	<	p = rt.internalAwaitAdvance(phase, node);
676	<	if (node.wasInterrupted)
677	<	throw new InterruptedException();
672	>	if (p == phase) {
673	>	if ((p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
674	>	QNode node = new QNode(this, phase, true, false, 0L);
675	>	p = rt.internalAwaitAdvance(phase, node);
676	>	if (node.wasInterrupted)
677	>	throw new InterruptedException();
678	>	}
679	>	else
680	>	reconcileState();
681		}
682		return p;
683		}
#	Line 670 | Line 709 | public class Phaser {
709		int p = (int)(state >>> PHASE_SHIFT);
710		if (phase < 0)
711		return phase;
712	<	if (p == phase &&
713	<	(p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
714	<	QNode node = new QNode(this, phase, true, true, nanos);
715	<	p = rt.internalAwaitAdvance(phase, node);
716	<	if (node.wasInterrupted)
717	<	throw new InterruptedException();
718	<	else if (p == phase)
719	<	throw new TimeoutException();
712	>	if (p == phase) {
713	>	if ((p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
714	>	QNode node = new QNode(this, phase, true, true, nanos);
715	>	p = rt.internalAwaitAdvance(phase, node);
716	>	if (node.wasInterrupted)
717	>	throw new InterruptedException();
718	>	else if (p == phase)
719	>	throw new TimeoutException();
720	>	}
721	>	else
722	>	reconcileState();
723		}
724		return p;
725		}
726
727		/**
728		* Forces this phaser to enter termination state.  Counts of
729	<	* arrived and registered parties are unaffected.  If this phaser
730	<	* is a member of a tiered set of phasers, then all of the phasers
731	<	* in the set are terminated.  If this phaser is already
732	<	* terminated, this method has no effect.  This method may be
733	<	* useful for coordinating recovery after one or more tasks
734	<	* encounter unexpected exceptions.
729	>	* registered parties are unaffected.  If this phaser is a member
730	>	* of a tiered set of phasers, then all of the phasers in the set
731	>	* are terminated.  If this phaser is already terminated, this
732	>	* method has no effect.  This method may be useful for
733	>	* coordinating recovery after one or more tasks encounter
734	>	* unexpected exceptions.
735		*/
736		public void forceTermination() {
737		// Only need to change root state
738		final Phaser root = this.root;
739		long s;
740		while ((s = root.state) >= 0) {
741	<	if (UNSAFE.compareAndSwapLong(root, stateOffset,
742	<	s, s | TERMINATION_BIT)) {
741	>	long next = (s & ~(long)(MAX_PARTIES)) | TERMINATION_BIT;
742	>	if (UNSAFE.compareAndSwapLong(root, stateOffset, s, next)) {
743		releaseWaiters(0); // signal all threads
744		releaseWaiters(1);
745		return;
#	Line 734 | Line 776 | public class Phaser {
776		* @return the number of arrived parties
777		*/
778		public int getArrivedParties() {
779	<	long s = state;
738	<	int u = unarrivedOf(s); // only reconcile if possibly needed
739	<	return (u != 0 || parent == null) ?
740	<	partiesOf(s) - u :
741	<	arrivedOf(reconcileState());
779	>	return arrivedOf(reconcileState());
780		}
781
782		/**
#	Line 748 | Line 786 | public class Phaser {
786		* @return the number of unarrived parties
787		*/
788		public int getUnarrivedParties() {
789	<	int u = unarrivedOf(state);
752	<	return (u != 0 || parent == null) ? u : unarrivedOf(reconcileState());
789	>	return unarrivedOf(reconcileState());
790		}
791
792		/**
#	Line 785 | Line 822 | public class Phaser {
822		* advance, and to control termination. This method is invoked
823		* upon arrival of the party advancing this phaser (when all other
824		* waiting parties are dormant).  If this method returns {@code
825	<	* true}, then, rather than advance the phase number, this phaser
826	<	* will be set to a final termination state, and subsequent calls
827	<	* to {@link #isTerminated} will return true. Any (unchecked)
828	<	* Exception or Error thrown by an invocation of this method is
829	<	* propagated to the party attempting to advance this phaser, in
830	<	* which case no advance occurs.
825	>	* true}, this phaser will be set to a final termination state
826	>	* upon advance, and subsequent calls to {@link #isTerminated}
827	>	* will return true. Any (unchecked) Exception or Error thrown by
828	>	* an invocation of this method is propagated to the party
829	>	* attempting to advance this phaser, in which case no advance
830	>	* occurs.
831		*
832		* <p>The arguments to this method provide the state of the phaser
833		* prevailing for the current transition.  The effects of invoking
#	Line 856 | Line 893 | public class Phaser {
893		QNode q;   // first element of queue
894		int p;     // its phase
895		Thread t;  // its thread
896	+	//        assert phase != phaseOf(root.state);
897		AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ;
898		while ((q = head.get()) != null &&
899	<	((p = q.phase) == phase ||
862	<	(int)(root.state >>> PHASE_SHIFT) != p)) {
899	>	q.phase != (int)(root.state >>> PHASE_SHIFT)) {
900		if (head.compareAndSet(q, q.next) &&
901		(t = q.thread) != null) {
902		q.thread = null;
#	Line 935 | Line 972 | public class Phaser {
972		node.thread = null;       // avoid need for unpark()
973		if (node.wasInterrupted && !node.interruptible)
974		Thread.currentThread().interrupt();
975	<	if ((p = (int)(state >>> PHASE_SHIFT)) == phase)
975	>	if (p == phase && (p = (int)(state >>> PHASE_SHIFT)) == phase)
976		return p;                 // recheck abort
977		}
978		releaseWaiters(phase);

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