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Comparing jsr166/src/jsr166y/Phaser.java (file contents):
Revision 1.49 by dl, Fri Nov 5 23:01:47 2010 UTC vs.
Revision 1.60 by dl, Sun Nov 28 15:49:49 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 17 | 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 75 | 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 180 | 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 209 | 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 226 | Line 229 | public class Phaser {
229		* Barrier state representation. Conceptually, a barrier contains
230		* four values:
231		*
232	<	* * parties -- the number of parties to wait (16 bits)
233	<	* * unarrived -- the number of parties yet to hit barrier (16 bits)
234	<	* * phase -- the generation of the barrier (31 bits)
235	<	* * terminated -- set if barrier is terminated (1 bit)
232	>	* * unarrived -- the number of parties yet to hit barrier (bits  0-15)
233	>	* * parties -- the number of parties to wait              (bits 16-31)
234	>	* * phase -- the generation of the barrier                (bits 32-62)
235	>	* * terminated -- set if barrier is terminated            (bit  63 / sign)
236		*
237		* However, to efficiently maintain atomicity, these values are
238		* packed into a single (atomic) long. Termination uses the sign
239		* bit of 32 bit representation of phase, so phase is set to -1 on
240		* termination. Good performance relies on keeping state decoding
241		* 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.
242		*/
243		private volatile long state;
244
245	<	private static final int ushortMask = 0xffff;
246	<	private static final int phaseMask  = 0x7fffffff;
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
257		private static int unarrivedOf(long s) {
258	<	return (int) (s & ushortMask);
258	>	return (int)s & UNARRIVED_MASK;
259		}
260
261		private static int partiesOf(long s) {
262	<	return ((int) s) >>> 16;
262	>	return (int)s >>> PARTIES_SHIFT;
263		}
264
265		private static int phaseOf(long s) {
266	<	return (int) (s >>> 32);
266	>	return (int) (s >>> PHASE_SHIFT);
267		}
268
269		private static int arrivedOf(long s) {
270		return partiesOf(s) - unarrivedOf(s);
271		}
272
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	–
273		/**
274		* The parent of this phaser, or null if none
275		*/
#	Line 290 | Line 281 | public class Phaser {
281		*/
282		private final Phaser root;
283
293	–	// Wait queues
294	–
284		/**
285		* Heads of Treiber stacks for waiting threads. To eliminate
286		* contention when releasing some threads while adding others, we
287		* use two of them, alternating across even and odd phases.
288		* Subphasers share queues with root to speed up releases.
289		*/
290	<	private final AtomicReference<QNode> evenQ = new AtomicReference<QNode>();
291	<	private final AtomicReference<QNode> oddQ  = new AtomicReference<QNode>();
290	>	private final AtomicReference<QNode> evenQ;
291	>	private final AtomicReference<QNode> oddQ;
292
293		private AtomicReference<QNode> queueFor(int phase) {
294	<	Phaser r = root;
306	<	return ((phase & 1) == 0) ? r.evenQ : r.oddQ;
294	>	return ((phase & 1) == 0) ? evenQ : oddQ;
295		}
296
297		/**
298	<	* Returns current state, first resolving lagged propagation from
311	<	* root if necessary.
298	>	* Returns message string for bounds exceptions on arrival.
299		*/
300	<	private long getReconciledState() {
301	<	return (parent == null) ? state : reconcileState();
300	>	private String badArrive(long s) {
301	>	return "Attempted arrival of unregistered party for " +
302	>	stateToString(s);
303		}
304
305		/**
306	<	* Recursively resolves state.
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.
317	>	*
318	>	* @param adj - adjustment to apply to state -- either
319	>	* ONE_ARRIVAL (for arrive) or
320	>	* ONE_ARRIVAL|ONE_PARTY (for arriveAndDeregister)
321	>	*/
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	>	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
336	>	long lu = p >>> PARTIES_SHIFT;
337	>	int u = (int)lu;
338	>	int nextPhase = (phase + 1) & MAX_PHASE;
339	>	long next = ((long)nextPhase << PHASE_SHIFT) | p | lu;
340	>	final Phaser parent = this.parent;
341	>	if (parent == null) {
342	>	if (onAdvance(phase, u))
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 ||
351	>	((int)(state >>> PHASE_SHIFT) != nextPhase &&
352	>	!UNSAFE.compareAndSwapLong(this, stateOffset,
353	>	s, next)))
354	>	reconcileState();
355	>	}
356	>	}
357	>	return phase;
358	>	}
359	>	}
360	>	}
361	>
362	>	/**
363	>	* Implementation of register, bulkRegister
364	>	*
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) {
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;
378	>	else if (registrations > MAX_PARTIES - parties)
379	>	throw new IllegalStateException(badRegister(s));
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	>	/**
406	>	* Recursively resolves lagged phase propagation from root if necessary.
407		*/
408		private long reconcileState() {
409		Phaser par = parent;
410		long s = state;
411		if (par != null) {
412	<	int phase, rootPhase;
413	<	while ((phase = phaseOf(s)) >= 0 &&
414	<	(rootPhase = phaseOf(root.state)) != phase &&
415	<	(rootPhase < 0 || unarrivedOf(s) == 0)) {
416	<	long parentState = par.getReconciledState();
417	<	int parentPhase = phaseOf(parentState);
418	<	int parties = partiesOf(s);
419	<	long next = trippedStateFor(parentPhase, parties);
420	<	if (phaseOf(root.state) == rootPhase &&
421	<	parentPhase != phase &&
422	<	state == s && casState(s, next)) {
335	<	releaseWaiters(phase);
336	<	if (parties == 0) // exit if the final deregistration
337	<	break;
412	>	Phaser rt = root;
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)
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	>	UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
423		}
424		s = state;
425		}
#	Line 343 | 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);
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 364 | Line 449 | public class Phaser {
449		}
450
451		/**
452	<	* Creates a new phaser with the given parent, without any
368	<	* initially registered parties. If parent is non-null this phaser
369	<	* is registered with the parent and its initial phase number is
370	<	* 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	<	int phase = 0;
376	<	this.parent = parent;
377	<	if (parent != null) {
378	<	this.root = parent.root;
379	<	phase = parent.register();
380	<	}
381	<	else
382	<	this.root = this;
383	<	this.state = trippedStateFor(phase, 0);
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
476		*/
477		public Phaser(Phaser parent, int parties) {
478	<	if (parties < 0 || parties > ushortMask)
478	>	if (parties >>> PARTIES_SHIFT != 0)
479		throw new IllegalArgumentException("Illegal number of parties");
480	<	int phase = 0;
480	>	long s = ((long) parties) | (((long) parties) << PARTIES_SHIFT);
481		this.parent = parent;
482		if (parent != null) {
483	<	this.root = parent.root;
484	<	phase = parent.register();
483	>	Phaser r = parent.root;
484	>	this.root = r;
485	>	this.evenQ = r.evenQ;
486	>	this.oddQ = r.oddQ;
487	>	if (parties != 0)
488	>	s |= ((long)(parent.doRegister(1))) << PHASE_SHIFT;
489		}
490	<	else
490	>	else {
491		this.root = this;
492	<	this.state = trippedStateFor(phase, parties);
492	>	this.evenQ = new AtomicReference<QNode>();
493	>	this.oddQ = new AtomicReference<QNode>();
494	>	}
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 waits 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 422 | 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 waits 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 441 | Line 533 | public class Phaser {
533		}
534
535		/**
536	<	* Shared code for register, bulkRegister
537	<	*/
538	<	private int doRegister(int registrations) {
539	<	Phaser par = parent;
540	<	long s;
541	<	int phase;
450	<	while ((phase = phaseOf(s = par==null? state:reconcileState())) >= 0) {
451	<	int p = partiesOf(s);
452	<	int u = unarrivedOf(s);
453	<	int unarrived = u + registrations;
454	<	int parties = p + registrations;
455	<	if (par == null || phase == phaseOf(root.state)) {
456	<	if (parties > ushortMask || unarrived > ushortMask)
457	<	throw new IllegalStateException(badBounds(parties,
458	<	unarrived));
459	<	else if (p != 0 && u == 0)       // back off if advancing
460	<	Thread.yield();              // not worth actually blocking
461	<	else if (casState(s, stateFor(phase, parties, unarrived)))
462	<	break;
463	<	}
464	<	}
465	<	return phase;
466	<	}
467	<
468	<	/**
469	<	* Arrives at the barrier, but does not wait for others.  (You can
470	<	* in turn wait for others via {@link #awaitAdvance}).  It is an
471	<	* unenforced usage error for an unregistered party to invoke this
472	<	* 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
545		* of unarrived parties would become negative
546		*/
547		public int arrive() {
548	<	Phaser par = parent;
480	<	long s;
481	<	int phase;
482	<	while ((phase = phaseOf(s = par==null? state:reconcileState())) >= 0) {
483	<	int parties = partiesOf(s);
484	<	int unarrived = unarrivedOf(s) - 1;
485	<	if (parties == 0 || unarrived < 0)
486	<	throw new IllegalStateException(badBounds(parties,
487	<	unarrived));
488	<	else if (unarrived > 0) {           // Not the last arrival
489	<	if (casState(s, s - 1))         // s-1 adds one arrival
490	<	break;
491	<	}
492	<	else if (par == null) {             // directly trip
493	<	if (casState(s, trippedStateFor(onAdvance(phase, parties) ? -1 :
494	<	((phase + 1) & phaseMask),
495	<	parties))) {
496	<	releaseWaiters(phase);
497	<	break;
498	<	}
499	<	}
500	<	else if (phaseOf(root.state) == phase && casState(s, s - 1)) {
501	<	par.arrive();                   // cascade to parent
502	<	reconcileState();
503	<	break;
504	<	}
505	<	}
506	<	return phase;
548	>	return doArrive(ONE_ARRIVAL);
549		}
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
566		* of registered or unarrived parties would become negative
567		*/
568		public int arriveAndDeregister() {
569	<	// similar to arrive, but too different to merge
524	<	Phaser par = parent;
525	<	long s;
526	<	int phase;
527	<	while ((phase = phaseOf(s = par==null? state:reconcileState())) >= 0) {
528	<	int parties = partiesOf(s) - 1;
529	<	int unarrived = unarrivedOf(s) - 1;
530	<	if (parties < 0 || unarrived < 0)
531	<	throw new IllegalStateException(badBounds(parties,
532	<	unarrived));
533	<	else if (unarrived > 0) {
534	<	if (casState(s, stateFor(phase, parties, unarrived)))
535	<	break;
536	<	}
537	<	else if (par == null) {
538	<	if (casState(s, trippedStateFor(onAdvance(phase, parties)? -1:
539	<	(phase + 1) & phaseMask,
540	<	parties))) {
541	<	releaseWaiters(phase);
542	<	break;
543	<	}
544	<	}
545	<	else if (phaseOf(root.state) == phase &&
546	<	casState(s, stateFor(phase, parties, 0))) {
547	<	if (parties == 0)
548	<	par.arriveAndDeregister();
549	<	else
550	<	par.arrive();
551	<	reconcileState();
552	<	break;
553	<	}
554	<	}
555	<	return phase;
569	>	return doArrive(ONE_ARRIVAL|ONE_PARTY);
570		}
571
572		/**
#	Line 561 | 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
#	Line 576 | Line 594 | public class Phaser {
594		* Awaits the phase of the barrier to advance from the given phase
595		* value, returning immediately if the current phase of the
596		* barrier is not equal to the given phase value or this barrier
597	<	* is terminated.  It is an unenforced usage error for an
580	<	* unregistered party to invoke this method.
597	>	* is terminated.
598		*
599		* @param phase an arrival phase number, or negative value if
600		* terminated; this argument is normally the value returned by a
#	Line 586 | Line 603 | public class Phaser {
603		* if terminated or argument is negative
604		*/
605		public int awaitAdvance(int phase) {
606	+	Phaser r;
607	+	int p = (int)(state >>> PHASE_SHIFT);
608		if (phase < 0)
609		return phase;
610	<	int p = getPhase();
611	<	if (p != phase)
612	<	return p;
613	<	return untimedWait(phase);
610	>	if (p == phase &&
611	>	(p = (int)((r = root).state >>> PHASE_SHIFT)) == phase)
612	>	return r.internalAwaitAdvance(phase, null);
613	>	return p;
614		}
615
616		/**
#	Line 599 | Line 618 | public class Phaser {
618		* value, throwing {@code InterruptedException} if interrupted
619		* while waiting, or returning immediately if the current phase of
620		* the barrier is not equal to the given phase value or this
621	<	* barrier is terminated. It is an unenforced usage error for an
603	<	* unregistered party to invoke this method.
621	>	* barrier is terminated.
622		*
623		* @param phase an arrival phase number, or negative value if
624		* terminated; this argument is normally the value returned by a
#	Line 611 | Line 629 | public class Phaser {
629		*/
630		public int awaitAdvanceInterruptibly(int phase)
631		throws InterruptedException {
632	+	Phaser r;
633	+	int p = (int)(state >>> PHASE_SHIFT);
634		if (phase < 0)
635		return phase;
636	<	int p = getPhase();
637	<	if (p != phase)
638	<	return p;
639	<	return interruptibleWait(phase);
636	>	if (p == phase &&
637	>	(p = (int)((r = root).state >>> PHASE_SHIFT)) == phase) {
638	>	QNode node = new QNode(this, phase, true, false, 0L);
639	>	p = r.internalAwaitAdvance(phase, node);
640	>	if (node.wasInterrupted)
641	>	throw new InterruptedException();
642	>	}
643	>	return p;
644		}
645
646		/**
#	Line 625 | Line 649 | public class Phaser {
649		* InterruptedException} if interrupted while waiting, or
650		* returning immediately if the current phase of the barrier is
651		* not equal to the given phase value or this barrier is
652	<	* terminated.  It is an unenforced usage error for an
629	<	* unregistered party to invoke this method.
652	>	* terminated.
653		*
654		* @param phase an arrival phase number, or negative value if
655		* terminated; this argument is normally the value returned by a
#	Line 644 | Line 667 | public class Phaser {
667		long timeout, TimeUnit unit)
668		throws InterruptedException, TimeoutException {
669		long nanos = unit.toNanos(timeout);
670	+	Phaser r;
671	+	int p = (int)(state >>> PHASE_SHIFT);
672		if (phase < 0)
673		return phase;
674	<	int p = getPhase();
675	<	if (p != phase)
676	<	return p;
677	<	return timedWait(phase, nanos);
674	>	if (p == phase &&
675	>	(p = (int)((r = root).state >>> PHASE_SHIFT)) == phase) {
676	>	QNode node = new QNode(this, phase, true, true, nanos);
677	>	p = r.internalAwaitAdvance(phase, node);
678	>	if (node.wasInterrupted)
679	>	throw new InterruptedException();
680	>	else if (p == phase)
681	>	throw new TimeoutException();
682	>	}
683	>	return p;
684		}
685
686		/**
687	<	* Forces this barrier to enter termination state. Counts of
688	<	* arrived and registered parties are unaffected. If this phaser
689	<	* has a parent, it too is terminated. This method may be useful
690	<	* for coordinating recovery after one or more tasks encounter
691	<	* unexpected exceptions.
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
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.
694		*/
695		public void forceTermination() {
696	<	Phaser r = root;    // force at root then reconcile
696	>	// Only need to change root state
697	>	final Phaser root = this.root;
698		long s;
699	<	while (phaseOf(s = r.state) >= 0)
700	<	r.casState(s, stateFor(-1, partiesOf(s), unarrivedOf(s)));
701	<	reconcileState();
702	<	releaseWaiters(0);  // ensure wakeups on both queues
703	<	releaseWaiters(1);
699	>	while ((s = root.state) >= 0) {
700	>	if (UNSAFE.compareAndSwapLong(root, stateOffset,
701	>	s, s | TERMINATION_BIT)) {
702	>	releaseWaiters(0); // signal all threads
703	>	releaseWaiters(1);
704	>	return;
705	>	}
706	>	}
707		}
708
709		/**
#	Line 677 | Line 714 | public class Phaser {
714		* @return the phase number, or a negative value if terminated
715		*/
716		public final int getPhase() {
717	<	return phaseOf(getReconciledState());
717	>	return (int)(root.state >>> PHASE_SHIFT);
718		}
719
720		/**
#	Line 686 | Line 723 | public class Phaser {
723		* @return the number of parties
724		*/
725		public int getRegisteredParties() {
726	<	return partiesOf(getReconciledState());
726	>	return partiesOf(state);
727		}
728
729		/**
#	Line 696 | Line 733 | public class Phaser {
733		* @return the number of arrived parties
734		*/
735		public int getArrivedParties() {
736	<	return arrivedOf(getReconciledState());
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 706 | Line 747 | public class Phaser {
747		* @return the number of unarrived parties
748		*/
749		public int getUnarrivedParties() {
750	<	return unarrivedOf(getReconciledState());
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 734 | Line 776 | public class Phaser {
776		* @return {@code true} if this barrier has been terminated
777		*/
778		public boolean isTerminated() {
779	<	return getPhase() < 0;
779	>	return root.state < 0L;
780		}
781
782		/**
#	Line 749 | 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
795	<	* prevailing for the current transition. (When called from within
796	<	* an implementation of {@code onAdvance} the values returned by
797	<	* methods such as {@code getPhase} may or may not reliably
798	<	* indicate the state to which this transition applies.)
799	<	*
800	<	* <p>The default version returns {@code true} when the number of
801	<	* registered parties is zero. Normally, overrides that arrange
802	<	* termination for other reasons should also preserve this
803	<	* property.
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
798	>	* relied on.
799	>	*
800	>	* <p>If this Phaser is a member of a tiered set of Phasers, then
801	>	* {@code onAdvance} is invoked only for its root Phaser on each
802	>	* advance.
803	>	*
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
#	Line 769 | Line 823 | public class Phaser {
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 778 | Line 832 | public class Phaser {
832		* @return a string identifying this barrier, as well as its state
833		*/
834		public String toString() {
835	<	long s = getReconciledState();
835	>	return stateToString(reconcileState());
836	>	}
837	>
838	>	/**
839	>	* Implementation of toString and string-based error messages
840	>	*/
841	>	private String stateToString(long s) {
842		return super.toString() +
843		"[phase = " + phaseOf(s) +
844		" parties = " + partiesOf(s) +
845		" arrived = " + arrivedOf(s) + "]";
846		}
847
848	<	// methods for waiting
848	>	// Waiting mechanics
849	>
850	>	/**
851	>	* Removes and signals threads from queue for phase.
852	>	*/
853	>	private void releaseWaiters(int phase) {
854	>	AtomicReference<QNode> head = queueFor(phase);
855	>	QNode q;
856	>	int p;
857	>	while ((q = head.get()) != null &&
858	>	((p = q.phase) == phase ||
859	>	(int)(root.state >>> PHASE_SHIFT) != p)) {
860	>	if (head.compareAndSet(q, q.next))
861	>	q.signal();
862	>	}
863	>	}
864	>
865	>	/** The number of CPUs, for spin control */
866	>	private static final int NCPU = Runtime.getRuntime().availableProcessors();
867	>
868	>	/**
869	>	* The number of times to spin before blocking while waiting for
870	>	* advance, per arrival while waiting. On multiprocessors, fully
871	>	* blocking and waking up a large number of threads all at once is
872	>	* usually a very slow process, so we use rechargeable spins to
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
878	>	* before blocking. The value trades off good-citizenship vs big
879	>	* unnecessary slowdowns.
880	>	*/
881	>	static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8;
882	>
883	>	/**
884	>	* Possibly blocks and waits for phase to advance unless aborted.
885	>	* Call only from root node.
886	>	*
887	>	* @param phase current phase
888	>	* @param node if non-null, the wait node to track interrupt and timeout;
889	>	* if null, denotes noninterruptible wait
890	>	* @return current phase
891	>	*/
892	>	private int internalAwaitAdvance(int phase, QNode node) {
893	>	boolean queued = false;      // true when node is enqueued
894	>	int lastUnarrived = -1;      // to increase spins upon change
895	>	int spins = SPINS_PER_ARRIVAL;
896	>	long s;
897	>	int p;
898	>	while ((p = (int)((s = state) >>> PHASE_SHIFT)) == phase) {
899	>	int unarrived = (int)s & UNARRIVED_MASK;
900	>	if (unarrived != lastUnarrived) {
901	>	if (lastUnarrived == -1) // ensure old queue clean
902	>	releaseWaiters(phase-1);
903	>	if ((lastUnarrived = unarrived) < NCPU)
904	>	spins += SPINS_PER_ARRIVAL;
905	>	}
906	>	else if (spins > 0) {
907	>	if (--spins == (SPINS_PER_ARRIVAL >>> 1))
908	>	Thread.yield();  // yield midway through spin
909	>	}
910	>	else if (node == null)   // must be noninterruptible
911	>	node = new QNode(this, phase, false, false, 0L);
912	>	else if (node.isReleasable()) {
913	>	p = (int)(state >>> PHASE_SHIFT);
914	>	break;               // aborted
915	>	}
916	>	else if (!queued) {      // push onto queue
917	>	AtomicReference<QNode> head = queueFor(phase);
918	>	QNode q = head.get();
919	>	if (q == null || q.phase == phase) {
920	>	node.next = q;
921	>	if ((p = (int)(state >>> PHASE_SHIFT)) != phase)
922	>	break;       // recheck to avoid stale enqueue
923	>	else
924	>	queued = head.compareAndSet(q, node);
925	>	}
926	>	}
927	>	else {
928	>	try {
929	>	ForkJoinPool.managedBlock(node);
930	>	} catch (InterruptedException ie) {
931	>	node.wasInterrupted = true;
932	>	}
933	>	}
934	>	}
935	>
936	>	if (node != null) {
937	>	if (node.thread != null)
938	>	node.thread = null; // disable unpark() in node.signal
939	>	if (!node.interruptible && node.wasInterrupted)
940	>	Thread.currentThread().interrupt();
941	>	}
942	>	if (p != phase)
943	>	releaseWaiters(phase);
944	>	return p;
945	>	}
946
947		/**
948		* Wait nodes for Treiber stack representing wait queue
#	Line 793 | Line 950 | public class Phaser {
950		static final class QNode implements ForkJoinPool.ManagedBlocker {
951		final Phaser phaser;
952		final int phase;
796	–	final long startTime;
797	–	final long nanos;
798	–	final boolean timed;
953		final boolean interruptible;
954	<	volatile boolean wasInterrupted = false;
954	>	final boolean timed;
955	>	boolean wasInterrupted;
956	>	long nanos;
957	>	long lastTime;
958		volatile Thread thread; // nulled to cancel wait
959		QNode next;
960
961		QNode(Phaser phaser, int phase, boolean interruptible,
962	<	boolean timed, long startTime, long nanos) {
962	>	boolean timed, long nanos) {
963		this.phaser = phaser;
964		this.phase = phase;
808	–	this.timed = timed;
965		this.interruptible = interruptible;
810	–	this.startTime = startTime;
966		this.nanos = nanos;
967	+	this.timed = timed;
968	+	this.lastTime = timed? System.nanoTime() : 0L;
969		thread = Thread.currentThread();
970		}
971
972		public boolean isReleasable() {
973	<	return (thread == null ||
974	<	phaser.getPhase() != phase ||
975	<	(interruptible && wasInterrupted) ||
976	<	(timed && (nanos - (System.nanoTime() - startTime)) <= 0));
973	>	Thread t = thread;
974	>	if (t != null) {
975	>	if (phaser.getPhase() != phase)
976	>	t = null;
977	>	else {
978	>	if (Thread.interrupted())
979	>	wasInterrupted = true;
980	>	if (interruptible && wasInterrupted)
981	>	t = null;
982	>	else if (timed) {
983	>	if (nanos > 0) {
984	>	long now = System.nanoTime();
985	>	nanos -= now - lastTime;
986	>	lastTime = now;
987	>	}
988	>	if (nanos <= 0)
989	>	t = null;
990	>	}
991	>	}
992	>	if (t != null)
993	>	return false;
994	>	thread = null;
995	>	}
996	>	return true;
997		}
998
999		public boolean block() {
1000	<	if (Thread.interrupted()) {
1001	<	wasInterrupted = true;
1002	<	if (interruptible)
826	<	return true;
827	<	}
828	<	if (!timed)
1000	>	if (isReleasable())
1001	>	return true;
1002	>	else if (!timed)
1003		LockSupport.park(this);
1004	<	else {
1005	<	long waitTime = nanos - (System.nanoTime() - startTime);
832	<	if (waitTime <= 0)
833	<	return true;
834	<	LockSupport.parkNanos(this, waitTime);
835	<	}
1004	>	else if (nanos > 0)
1005	>	LockSupport.parkNanos(this, nanos);
1006		return isReleasable();
1007		}
1008
#	Line 843 | Line 1013 | public class Phaser {
1013		LockSupport.unpark(t);
1014		}
1015		}
846	–
847	–	boolean doWait() {
848	–	if (thread != null) {
849	–	try {
850	–	ForkJoinPool.managedBlock(this);
851	–	} catch (InterruptedException ie) {
852	–	wasInterrupted = true; // can't currently happen
853	–	}
854	–	}
855	–	return wasInterrupted;
856	–	}
857	–	}
858	–
859	–	/**
860	–	* Removes and signals waiting threads from wait queue.
861	–	*/
862	–	private void releaseWaiters(int phase) {
863	–	AtomicReference<QNode> head = queueFor(phase);
864	–	QNode q;
865	–	while ((q = head.get()) != null) {
866	–	if (head.compareAndSet(q, q.next))
867	–	q.signal();
868	–	}
869	–	}
870	–
871	–	/**
872	–	* Tries to enqueue given node in the appropriate wait queue.
873	–	*
874	–	* @return true if successful
875	–	*/
876	–	private boolean tryEnqueue(QNode node) {
877	–	AtomicReference<QNode> head = queueFor(node.phase);
878	–	return head.compareAndSet(node.next = head.get(), node);
879	–	}
880	–
881	–	/**
882	–	* Enqueues node and waits unless aborted or signalled.
883	–	*
884	–	* @return current phase
885	–	*/
886	–	private int untimedWait(int phase) {
887	–	QNode node = null;
888	–	boolean queued = false;
889	–	boolean interrupted = false;
890	–	int p;
891	–	while ((p = getPhase()) == phase) {
892	–	if (Thread.interrupted())
893	–	interrupted = true;
894	–	else if (node == null)
895	–	node = new QNode(this, phase, false, false, 0, 0);
896	–	else if (!queued)
897	–	queued = tryEnqueue(node);
898	–	else if (node.doWait())
899	–	interrupted = true;
900	–	}
901	–	if (node != null)
902	–	node.thread = null;
903	–	releaseWaiters(phase);
904	–	if (interrupted)
905	–	Thread.currentThread().interrupt();
906	–	return p;
907	–	}
908	–
909	–	/**
910	–	* Interruptible version
911	–	* @return current phase
912	–	*/
913	–	private int interruptibleWait(int phase) throws InterruptedException {
914	–	QNode node = null;
915	–	boolean queued = false;
916	–	boolean interrupted = false;
917	–	int p;
918	–	while ((p = getPhase()) == phase && !interrupted) {
919	–	if (Thread.interrupted())
920	–	interrupted = true;
921	–	else if (node == null)
922	–	node = new QNode(this, phase, true, false, 0, 0);
923	–	else if (!queued)
924	–	queued = tryEnqueue(node);
925	–	else if (node.doWait())
926	–	interrupted = true;
927	–	}
928	–	if (node != null)
929	–	node.thread = null;
930	–	if (p != phase || (p = getPhase()) != phase)
931	–	releaseWaiters(phase);
932	–	if (interrupted)
933	–	throw new InterruptedException();
934	–	return p;
935	–	}
936	–
937	–	/**
938	–	* Timeout version.
939	–	* @return current phase
940	–	*/
941	–	private int timedWait(int phase, long nanos)
942	–	throws InterruptedException, TimeoutException {
943	–	long startTime = System.nanoTime();
944	–	QNode node = null;
945	–	boolean queued = false;
946	–	boolean interrupted = false;
947	–	int p;
948	–	while ((p = getPhase()) == phase && !interrupted) {
949	–	if (Thread.interrupted())
950	–	interrupted = true;
951	–	else if (nanos - (System.nanoTime() - startTime) <= 0)
952	–	break;
953	–	else if (node == null)
954	–	node = new QNode(this, phase, true, true, startTime, nanos);
955	–	else if (!queued)
956	–	queued = tryEnqueue(node);
957	–	else if (node.doWait())
958	–	interrupted = true;
959	–	}
960	–	if (node != null)
961	–	node.thread = null;
962	–	if (p != phase || (p = getPhase()) != phase)
963	–	releaseWaiters(phase);
964	–	if (interrupted)
965	–	throw new InterruptedException();
966	–	if (p == phase)
967	–	throw new TimeoutException();
968	–	return p;
1016		}
1017
1018		// Unsafe mechanics
#	Line 974 | Line 1021 | public class Phaser {
1021		private static final long stateOffset =
1022		objectFieldOffset("state", Phaser.class);
1023
977	–	private final boolean casState(long cmp, long val) {
978	–	return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
979	–	}
980	–
1024		private static long objectFieldOffset(String field, Class<?> klazz) {
1025		try {
1026		return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));

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