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Comparing jsr166/src/jsr166y/Phaser.java (file contents):
Revision 1.2 by jsr166, Fri Jul 25 18:10:41 2008 UTC vs.
Revision 1.9 by jsr166, Mon Jan 5 09:11:26 2009 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	<	import jsr166y.forkjoin.*;
8	>
9		import java.util.concurrent.*;
10		import java.util.concurrent.atomic.*;
11		import java.util.concurrent.locks.LockSupport;
12	+	import sun.misc.Unsafe;
13	+	import java.lang.reflect.*;
14
15		/**
16		* A reusable synchronization barrier, similar in functionality to a
17	<	* {@link java.util.concurrent.CyclicBarrier}, but supporting more
18	<	* flexible usage.
17	>	* {@link java.util.concurrent.CyclicBarrier CyclicBarrier} and
18	>	* {@link java.util.concurrent.CountDownLatch CountDownLatch}
19	>	* but supporting more flexible usage.
20		*
21		* <ul>
22		*
23	<	* <li> The number of parties synchronizing on the barrier may vary
24	<	* over time.  A task may register to be a party in a barrier at any
25	<	* time, and may deregister upon arriving at the barrier.  As is the
26	<	* case with most basic synchronization constructs, registration
27	<	* and deregistration affect only internal counts; they do not
28	<	* establish any further internal bookkeeping, so tasks cannot query
29	<	* whether they are registered.
23	>	* <li> The number of parties synchronizing on a phaser may vary over
24	>	* time.  A task may register to be a party at any time, and may
25	>	* deregister upon arriving at the barrier.  As is the case with most
26	>	* basic synchronization constructs, registration and deregistration
27	>	* affect only internal counts; they do not establish any further
28	>	* internal bookkeeping, so tasks cannot query whether they are
29	>	* registered. (However, you can introduce such bookkeeping by
30	>	* subclassing this class.)
31		*
32		* <li> Each generation has an associated phase value, starting at
33		* zero, and advancing when all parties reach the barrier (wrapping
34	<	* around to zero after reaching <tt>Integer.MAX_VALUE</tt>).
35	<	*
34	>	* around to zero after reaching {@code Integer.MAX_VALUE}).
35	>	*
36		* <li> Like a CyclicBarrier, a Phaser may be repeatedly awaited.
37	<	* Method <tt>arriveAndAwaitAdvance</tt> has effect analogous to
38	<	* <tt>CyclicBarrier.await</tt>.  However, Phasers separate two
39	<	* aspects of coordination, that may be invoked independently:
37	>	* Method {@code arriveAndAwaitAdvance} has effect analogous to
38	>	* {@code CyclicBarrier.await}.  However, Phasers separate two
39	>	* aspects of coordination, that may also be invoked independently:
40		*
41		* <ul>
42		*
43	<	*   <li> Arriving at a barrier. Methods <tt>arrive</tt> and
44	<	*       <tt>arriveAndDeregister</tt> do not block, but return
45	<	*       the phase value on entry to the method.
43	>	*   <li> Arriving at a barrier. Methods {@code arrive} and
44	>	*       {@code arriveAndDeregister} do not block, but return
45	>	*       the phase value current upon entry to the method.
46		*
47	<	*   <li> Awaiting others. Method <tt>awaitAdvance</tt> requires an
47	>	*   <li> Awaiting others. Method {@code awaitAdvance} requires an
48		*       argument indicating the entry phase, and returns when the
49		*       barrier advances to a new phase.
50		* </ul>
#	Line 48 | Line 52 | import java.util.concurrent.locks.LockSu
52		*
53		* <li> Barrier actions, performed by the task triggering a phase
54		* advance while others may be waiting, are arranged by overriding
55	<	* method <tt>onAdvance</tt>, that also controls termination.
55	>	* method {@code onAdvance}, that also controls termination.
56	>	* Overriding this method may be used to similar but more flexible
57	>	* effect as providing a barrier action to a CyclicBarrier.
58		*
59		* <li> Phasers may enter a <em>termination</em> state in which all
60		* await actions immediately return, indicating (via a negative phase
61		* value) that execution is complete.  Termination is triggered by
62	<	* executing the overridable <tt>onAdvance</tt> method that is invoked
63	<	* each time the barrier is tripped. When a Phaser is controlling an
64	<	* action with a fixed number of iterations, it is often convenient to
65	<	* override this method to cause termination when the current phase
66	<	* number reaches a threshold.  Method <tt>forceTermination</tt> is
67	<	* also available to assist recovery actions upon failure.
68	<	*
69	<	* <li> Unlike most synchronizers, a Phaser may also be used with
70	<	* ForkJoinTasks (as well as plain threads).
71	<	*
72	<	* <li> By default, <tt>awaitAdvance</tt> continues to wait even if
73	<	* the current thread is interrupted. And unlike the case in
62	>	* executing the overridable {@code onAdvance} method that is invoked
63	>	* each time the barrier is about to be tripped. When a Phaser is
64	>	* controlling an action with a fixed number of iterations, it is
65	>	* often convenient to override this method to cause termination when
66	>	* the current phase number reaches a threshold. Method
67	>	* {@code forceTermination} is also available to abruptly release
68	>	* waiting threads and allow them to terminate.
69	>	*
70	>	* <li> Phasers may be tiered to reduce contention. Phasers with large
71	>	* numbers of parties that would otherwise experience heavy
72	>	* synchronization contention costs may instead be arranged in trees.
73	>	* This will typically greatly increase throughput even though it
74	>	* incurs somewhat greater per-operation overhead.
75	>	*
76	>	* <li> By default, {@code awaitAdvance} continues to wait even if
77	>	* the waiting thread is interrupted. And unlike the case in
78		* CyclicBarriers, exceptions encountered while tasks wait
79		* interruptibly or with timeout do not change the state of the
80		* barrier. If necessary, you can perform any associated recovery
81	<	* within handlers of those exceptions.
81	>	* within handlers of those exceptions, often after invoking
82	>	* {@code forceTermination}.
83		*
84		* </ul>
85		*
86	<	* <p><b>Sample usage:</b>
76	<	*
77	<	* <p>[todo: non-FJ example]
86	>	* <p><b>Sample usages:</b>
87		*
88	<	* <p> A Phaser may be used to support a style of programming in
89	<	* which a task waits for others to complete, without otherwise
90	<	* needing to keep track of which tasks it is waiting for. This is
91	<	* similar to the "sync" construct in Cilk and "clocks" in X10.
83	<	* Special constructions based on such barriers are available using
84	<	* the <tt>LinkedAsyncAction</tt> and <tt>CyclicAction</tt> classes,
85	<	* but they can be useful in other contexts as well.  For a simple
86	<	* (but not very useful) example, here is a variant of Fibonacci:
88	>	* <p>A Phaser may be used instead of a {@code CountDownLatch} to control
89	>	* a one-shot action serving a variable number of parties. The typical
90	>	* idiom is for the method setting this up to first register, then
91	>	* start the actions, then deregister, as in:
92		*
93		* <pre>
94	<	* class BarrierFibonacci extends RecursiveAction {
95	<	*   int argument, result;
96	<	*   final Phaser parentBarrier;
97	<	*   BarrierFibonacci(int n, Phaser parentBarrier) {
98	<	*     this.argument = n;
99	<	*     this.parentBarrier = parentBarrier;
100	<	*     parentBarrier.register();
94	>	*  void runTasks(List&lt;Runnable&gt; list) {
95	>	*    final Phaser phaser = new Phaser(1); // "1" to register self
96	>	*    for (Runnable r : list) {
97	>	*      phaser.register();
98	>	*      new Thread() {
99	>	*        public void run() {
100	>	*          phaser.arriveAndAwaitAdvance(); // await all creation
101	>	*          r.run();
102	>	*          phaser.arriveAndDeregister();   // signal completion
103	>	*        }
104	>	*      }.start();
105		*   }
106	<	*   protected void compute() {
107	<	*     int n = argument;
108	<	*     if (n &lt;= 1)
109	<	*        result = n;
110	<	*     else {
111	<	*        Phaser childBarrier = new Phaser(1);
112	<	*        BarrierFibonacci f1 = new BarrierFibonacci(n - 1, childBarrier);
113	<	*        BarrierFibonacci f2 = new BarrierFibonacci(n - 2, childBarrier);
114	<	*        f1.fork();
115	<	*        f2.fork();
116	<	*        childBarrier.arriveAndAwait();
117	<	*        result = f1.result + f2.result;
118	<	*     }
119	<	*     parentBarrier.arriveAndDeregister();
106	>	*
107	>	*   doSomethingOnBehalfOfWorkers();
108	>	*   phaser.arrive(); // allow threads to start
109	>	*   int p = phaser.arriveAndDeregister(); // deregister self  ...
110	>	*   p = phaser.awaitAdvance(p); // ... and await arrival
111	>	*   otherActions(); // do other things while tasks execute
112	>	*   phaser.awaitAdvance(p); // await final completion
113	>	* }
114	>	* </pre>
115	>	*
116	>	* <p>One way to cause a set of threads to repeatedly perform actions
117	>	* for a given number of iterations is to override {@code onAdvance}:
118	>	*
119	>	* <pre>
120	>	*  void startTasks(List&lt;Runnable&gt; list, final int iterations) {
121	>	*    final Phaser phaser = new Phaser() {
122	>	*       public boolean onAdvance(int phase, int registeredParties) {
123	>	*         return phase &gt;= iterations || registeredParties == 0;
124	>	*       }
125	>	*    };
126	>	*    phaser.register();
127	>	*    for (Runnable r : list) {
128	>	*      phaser.register();
129	>	*      new Thread() {
130	>	*        public void run() {
131	>	*           do {
132	>	*             r.run();
133	>	*             phaser.arriveAndAwaitAdvance();
134	>	*           } while(!phaser.isTerminated();
135	>	*        }
136	>	*      }.start();
137		*   }
138	+	*   phaser.arriveAndDeregister(); // deregister self, don't wait
139		* }
140		* </pre>
141		*
142	+	* <p> To create a set of tasks using a tree of Phasers,
143	+	* you could use code of the following form, assuming a
144	+	* Task class with a constructor accepting a Phaser that
145	+	* it registers for upon construction:
146	+	* <pre>
147	+	*  void build(Task[] actions, int lo, int hi, Phaser b) {
148	+	*    int step = (hi - lo) / TASKS_PER_PHASER;
149	+	*    if (step &gt; 1) {
150	+	*       int i = lo;
151	+	*       while (i &lt; hi) {
152	+	*         int r = Math.min(i + step, hi);
153	+	*         build(actions, i, r, new Phaser(b));
154	+	*         i = r;
155	+	*       }
156	+	*    }
157	+	*    else {
158	+	*      for (int i = lo; i &lt; hi; ++i)
159	+	*        actions[i] = new Task(b);
160	+	*        // assumes new Task(b) performs b.register()
161	+	*    }
162	+	*  }
163	+	*  // .. initially called, for n tasks via
164	+	*  build(new Task[n], 0, n, new Phaser());
165	+	* </pre>
166	+	*
167	+	* The best value of {@code TASKS_PER_PHASER} depends mainly on
168	+	* expected barrier synchronization rates. A value as low as four may
169	+	* be appropriate for extremely small per-barrier task bodies (thus
170	+	* high rates), or up to hundreds for extremely large ones.
171	+	*
172	+	* </pre>
173	+	*
174		* <p><b>Implementation notes</b>: This implementation restricts the
175	<	* maximum number of parties to 65535. Attempts to register
176	<	* additional parties result in IllegalStateExceptions.
175	>	* maximum number of parties to 65535. Attempts to register additional
176	>	* parties result in IllegalStateExceptions. However, you can and
177	>	* should create tiered phasers to accommodate arbitrarily large sets
178	>	* of participants.
179		*/
180		public class Phaser {
181		/*
182		* This class implements an extension of X10 "clocks".  Thanks to
183	<	* Vijay Saraswat for the idea of applying it to ForkJoinTasks,
184	<	* and to Vivek Sarkar for enhancements to extend functionality.
183	>	* Vijay Saraswat for the idea, and to Vivek Sarkar for
184	>	* enhancements to extend functionality.
185		*/
186
187		/**
188		* Barrier state representation. Conceptually, a barrier contains
189		* four values:
190	<	*
190	>	*
191		* * parties -- the number of parties to wait (16 bits)
192		* * unarrived -- the number of parties yet to hit barrier (16 bits)
193		* * phase -- the generation of the barrier (31 bits)
194		* * terminated -- set if barrier is terminated (1 bit)
195		*
196		* However, to efficiently maintain atomicity, these values are
197	<	* packed into a single AtomicLong. Termination uses the sign bit
198	<	* of 32 bit representation of phase, so phase is set to -1 on
199	<	* termination.
200	<	*/
201	<	private final AtomicLong state;
202	<
203	<	/**
143	<	* Head of Treiber stack for waiting nonFJ threads.
197	>	* packed into a single (atomic) long. Termination uses the sign
198	>	* bit of 32 bit representation of phase, so phase is set to -1 on
199	>	* termination. Good performance relies on keeping state decoding
200	>	* and encoding simple, and keeping race windows short.
201	>	*
202	>	* Note: there are some cheats in arrive() that rely on unarrived
203	>	* being lowest 16 bits.
204		*/
205	<	private final AtomicReference<QNode> head = new AtomicReference<QNode>();
205	>	private volatile long state;
206
207		private static final int ushortBits = 16;
208		private static final int ushortMask =  (1 << ushortBits) - 1;
#	Line 168 | Line 228 | public class Phaser {
228		return (((long)phase) << 32) | ((parties << 16) | unarrived);
229		}
230
231	+	private static long trippedStateFor(int phase, int parties) {
232	+	return (((long)phase) << 32) | ((parties << 16) | parties);
233	+	}
234	+
235		private static IllegalStateException badBounds(int parties, int unarrived) {
236	<	return new IllegalStateException("Attempt to set " + unarrived +
237	<	" unarrived of " + parties + " parties");
236	>	return new IllegalStateException
237	>	("Attempt to set " + unarrived +
238	>	" unarrived of " + parties + " parties");
239	>	}
240	>
241	>	/**
242	>	* The parent of this phaser, or null if none
243	>	*/
244	>	private final Phaser parent;
245	>
246	>	/**
247	>	* The root of Phaser tree. Equals this if not in a tree.  Used to
248	>	* support faster state push-down.
249	>	*/
250	>	private final Phaser root;
251	>
252	>	// Wait queues
253	>
254	>	/**
255	>	* Heads of Treiber stacks waiting for nonFJ threads. To eliminate
256	>	* contention while releasing some threads while adding others, we
257	>	* use two of them, alternating across even and odd phases.
258	>	*/
259	>	private final AtomicReference<QNode> evenQ = new AtomicReference<QNode>();
260	>	private final AtomicReference<QNode> oddQ  = new AtomicReference<QNode>();
261	>
262	>	private AtomicReference<QNode> queueFor(int phase) {
263	>	return (phase & 1) == 0? evenQ : oddQ;
264	>	}
265	>
266	>	/**
267	>	* Returns current state, first resolving lagged propagation from
268	>	* root if necessary.
269	>	*/
270	>	private long getReconciledState() {
271	>	return parent == null? state : reconcileState();
272	>	}
273	>
274	>	/**
275	>	* Recursively resolves state.
276	>	*/
277	>	private long reconcileState() {
278	>	Phaser p = parent;
279	>	long s = state;
280	>	if (p != null) {
281	>	while (unarrivedOf(s) == 0 && phaseOf(s) != phaseOf(root.state)) {
282	>	long parentState = p.getReconciledState();
283	>	int parentPhase = phaseOf(parentState);
284	>	int phase = phaseOf(s = state);
285	>	if (phase != parentPhase) {
286	>	long next = trippedStateFor(parentPhase, partiesOf(s));
287	>	if (casState(s, next)) {
288	>	releaseWaiters(phase);
289	>	s = next;
290	>	}
291	>	}
292	>	}
293	>	}
294	>	return s;
295		}
296
297		/**
298		* Creates a new Phaser without any initially registered parties,
299	<	* and initial phase number 0.
299	>	* initial phase number 0, and no parent.
300		*/
301		public Phaser() {
302	<	state = new AtomicLong(stateFor(0, 0, 0));
302	>	this(null);
303		}
304
305		/**
306		* Creates a new Phaser with the given numbers of registered
307	<	* unarrived parties and initial phase number 0.
307	>	* unarrived parties, initial phase number 0, and no parent.
308		* @param parties the number of parties required to trip barrier.
309		* @throws IllegalArgumentException if parties less than zero
310		* or greater than the maximum number of parties supported.
311		*/
312		public Phaser(int parties) {
313	+	this(null, parties);
314	+	}
315	+
316	+	/**
317	+	* Creates a new Phaser with the given parent, without any
318	+	* initially registered parties. If parent is non-null this phaser
319	+	* is registered with the parent and its initial phase number is
320	+	* the same as that of parent phaser.
321	+	* @param parent the parent phaser.
322	+	*/
323	+	public Phaser(Phaser parent) {
324	+	int phase = 0;
325	+	this.parent = parent;
326	+	if (parent != null) {
327	+	this.root = parent.root;
328	+	phase = parent.register();
329	+	}
330	+	else
331	+	this.root = this;
332	+	this.state = trippedStateFor(phase, 0);
333	+	}
334	+
335	+	/**
336	+	* Creates a new Phaser with the given parent and numbers of
337	+	* registered unarrived parties. If parent is non-null this phaser
338	+	* is registered with the parent and its initial phase number is
339	+	* the same as that of parent phaser.
340	+	* @param parent the parent phaser.
341	+	* @param parties the number of parties required to trip barrier.
342	+	* @throws IllegalArgumentException if parties less than zero
343	+	* or greater than the maximum number of parties supported.
344	+	*/
345	+	public Phaser(Phaser parent, int parties) {
346		if (parties < 0 || parties > ushortMask)
347		throw new IllegalArgumentException("Illegal number of parties");
348	<	state = new AtomicLong(stateFor(0, parties, parties));
348	>	int phase = 0;
349	>	this.parent = parent;
350	>	if (parent != null) {
351	>	this.root = parent.root;
352	>	phase = parent.register();
353	>	}
354	>	else
355	>	this.root = this;
356	>	this.state = trippedStateFor(phase, parties);
357		}
358
359		/**
#	Line 200 | Line 362 | public class Phaser {
362		* @throws IllegalStateException if attempting to register more
363		* than the maximum supported number of parties.
364		*/
365	<	public int register() { // increment both parties and unarrived
366	<	final AtomicLong state = this.state;
365	>	public int register() {
366	>	return doRegister(1);
367	>	}
368	>
369	>	/**
370	>	* Adds the given number of new unarrived parties to this phaser.
371	>	* @param parties the number of parties required to trip barrier.
372	>	* @return the current barrier phase number upon registration
373	>	* @throws IllegalStateException if attempting to register more
374	>	* than the maximum supported number of parties.
375	>	*/
376	>	public int bulkRegister(int parties) {
377	>	if (parties < 0)
378	>	throw new IllegalArgumentException();
379	>	if (parties == 0)
380	>	return getPhase();
381	>	return doRegister(parties);
382	>	}
383	>
384	>	/**
385	>	* Shared code for register, bulkRegister
386	>	*/
387	>	private int doRegister(int registrations) {
388	>	int phase;
389		for (;;) {
390	<	long s = state.get();
391	<	int phase = phaseOf(s);
392	<	int parties = partiesOf(s) + 1;
393	<	int unarrived = unarrivedOf(s) + 1;
390	>	long s = getReconciledState();
391	>	phase = phaseOf(s);
392	>	int unarrived = unarrivedOf(s) + registrations;
393	>	int parties = partiesOf(s) + registrations;
394	>	if (phase < 0)
395	>	break;
396		if (parties > ushortMask || unarrived > ushortMask)
397		throw badBounds(parties, unarrived);
398	<	if (state.compareAndSet(s, stateFor(phase, parties, unarrived)))
399	<	return phase;
398	>	if (phase == phaseOf(root.state) &&
399	>	casState(s, stateFor(phase, parties, unarrived)))
400	>	break;
401		}
402	+	return phase;
403		}
404
405		/**
406		* Arrives at the barrier, but does not wait for others.  (You can
407		* in turn wait for others via {@link #awaitAdvance}).
408		*
409	<	* @return the current barrier phase number upon entry to
410	<	* this method, or a negative value if terminated;
411	<	* @throws IllegalStateException if the number of unarrived
412	<	* parties would become negative.
409	>	* @return the barrier phase number upon entry to this method, or a
410	>	* negative value if terminated;
411	>	* @throws IllegalStateException if not terminated and the number
412	>	* of unarrived parties would become negative.
413		*/
414	<	public int arrive() { // decrement unarrived. If zero, trip
415	<	final AtomicLong state = this.state;
414	>	public int arrive() {
415	>	int phase;
416		for (;;) {
417	<	long s = state.get();
418	<	int phase = phaseOf(s);
417	>	long s = state;
418	>	phase = phaseOf(s);
419		int parties = partiesOf(s);
420		int unarrived = unarrivedOf(s) - 1;
421	<	if (unarrived < 0)
422	<	throw badBounds(parties, unarrived);
423	<	if (unarrived == 0 && phase >= 0) {
424	<	trip(phase, parties);
425	<	return phase;
421	>	if (unarrived > 0) {        // Not the last arrival
422	>	if (casState(s, s - 1)) // s-1 adds one arrival
423	>	break;
424	>	}
425	>	else if (unarrived == 0) {  // the last arrival
426	>	Phaser par = parent;
427	>	if (par == null) {      // directly trip
428	>	if (casState
429	>	(s,
430	>	trippedStateFor(onAdvance(phase, parties)? -1 :
431	>	((phase + 1) & phaseMask), parties))) {
432	>	releaseWaiters(phase);
433	>	break;
434	>	}
435	>	}
436	>	else {                  // cascade to parent
437	>	if (casState(s, s - 1)) { // zeroes unarrived
438	>	par.arrive();
439	>	reconcileState();
440	>	break;
441	>	}
442	>	}
443		}
444	<	if (state.compareAndSet(s, stateFor(phase, parties, unarrived)))
445	<	return phase;
444	>	else if (phase < 0) // Don't throw exception if terminated
445	>	break;
446	>	else if (phase != phaseOf(root.state)) // or if unreconciled
447	>	reconcileState();
448	>	else
449	>	throw badBounds(parties, unarrived);
450		}
451	+	return phase;
452		}
453
454		/**
455		* Arrives at the barrier, and deregisters from it, without
456	<	* waiting for others.
456	>	* waiting for others. Deregistration reduces number of parties
457	>	* required to trip the barrier in future phases.  If this phaser
458	>	* has a parent, and deregistration causes this phaser to have
459	>	* zero parties, this phaser is also deregistered from its parent.
460		*
461		* @return the current barrier phase number upon entry to
462		* this method, or a negative value if terminated;
463	<	* @throws IllegalStateException if the number of registered or
464	<	* unarrived parties would become negative.
463	>	* @throws IllegalStateException if not terminated and the number
464	>	* of registered or unarrived parties would become negative.
465		*/
466	<	public int arriveAndDeregister() { // Same as arrive, plus decrement parties
467	<	final AtomicLong state = this.state;
466	>	public int arriveAndDeregister() {
467	>	// similar code to arrive, but too different to merge
468	>	Phaser par = parent;
469	>	int phase;
470		for (;;) {
471	<	long s = state.get();
472	<	int phase = phaseOf(s);
471	>	long s = state;
472	>	phase = phaseOf(s);
473		int parties = partiesOf(s) - 1;
474		int unarrived = unarrivedOf(s) - 1;
475	<	if (parties < 0 || unarrived < 0)
476	<	throw badBounds(parties, unarrived);
477	<	if (unarrived == 0 && phase >= 0) {
478	<	trip(phase, parties);
479	<	return phase;
475	>	if (parties >= 0) {
476	>	if (unarrived > 0 || (unarrived == 0 && par != null)) {
477	>	if (casState
478	>	(s,
479	>	stateFor(phase, parties, unarrived))) {
480	>	if (unarrived == 0) {
481	>	par.arriveAndDeregister();
482	>	reconcileState();
483	>	}
484	>	break;
485	>	}
486	>	continue;
487	>	}
488	>	if (unarrived == 0) {
489	>	if (casState
490	>	(s,
491	>	trippedStateFor(onAdvance(phase, parties)? -1 :
492	>	((phase + 1) & phaseMask), parties))) {
493	>	releaseWaiters(phase);
494	>	break;
495	>	}
496	>	continue;
497	>	}
498	>	if (phase < 0)
499	>	break;
500	>	if (par != null && phase != phaseOf(root.state)) {
501	>	reconcileState();
502	>	continue;
503	>	}
504		}
505	<	if (state.compareAndSet(s, stateFor(phase, parties, unarrived)))
267	<	return phase;
505	>	throw badBounds(parties, unarrived);
506		}
507	+	return phase;
508		}
509
510		/**
511	<	* Arrives at the barrier and awaits others. Unlike other arrival
512	<	* methods, this method returns the arrival index of the
513	<	* caller. The caller tripping the barrier returns zero, the
514	<	* previous caller 1, and so on.
515	<	* @return the arrival index
516	<	* @throws IllegalStateException if the number of unarrived
517	<	* parties would become negative.
511	>	* Arrives at the barrier and awaits others. Equivalent in effect
512	>	* to {@code awaitAdvance(arrive())}.  If you instead need to
513	>	* await with interruption of timeout, and/or deregister upon
514	>	* arrival, you can arrange them using analogous constructions.
515	>	* @return the phase on entry to this method
516	>	* @throws IllegalStateException if not terminated and the number
517	>	* of unarrived parties would become negative.
518		*/
519		public int arriveAndAwaitAdvance() {
520	<	final AtomicLong state = this.state;
282	<	for (;;) {
283	<	long s = state.get();
284	<	int phase = phaseOf(s);
285	<	int parties = partiesOf(s);
286	<	int unarrived = unarrivedOf(s) - 1;
287	<	if (unarrived < 0)
288	<	throw badBounds(parties, unarrived);
289	<	if (unarrived == 0 && phase >= 0) {
290	<	trip(phase, parties);
291	<	return 0;
292	<	}
293	<	if (state.compareAndSet(s, stateFor(phase, parties, unarrived))) {
294	<	awaitAdvance(phase);
295	<	return unarrived;
296	<	}
297	<	}
520	>	return awaitAdvance(arrive());
521		}
522
523		/**
524		* Awaits the phase of the barrier to advance from the given
525	<	* value, or returns immediately if this barrier is terminated.
525	>	* value, or returns immediately if argument is negative or this
526	>	* barrier is terminated.
527		* @param phase the phase on entry to this method
528		* @return the phase on exit from this method
529		*/
530		public int awaitAdvance(int phase) {
531		if (phase < 0)
532		return phase;
533	<	Thread current = Thread.currentThread();
534	<	if (current instanceof ForkJoinWorkerThread)
535	<	return helpingWait(phase);
536	<	if (untimedWait(current, phase, false))
537	<	current.interrupt();
538	<	return phaseOf(state.get());
533	>	long s = getReconciledState();
534	>	int p = phaseOf(s);
535	>	if (p != phase)
536	>	return p;
537	>	if (unarrivedOf(s) == 0)
538	>	parent.awaitAdvance(phase);
539	>	// Fall here even if parent waited, to reconcile and help release
540	>	return untimedWait(phase);
541		}
542
543		/**
544		* Awaits the phase of the barrier to advance from the given
545	<	* value, or returns immediately if this barrier is terminated, or
546	<	* throws InterruptedException if interrupted while waiting.
545	>	* value, or returns immediately if argument is negative or this
546	>	* barrier is terminated, or throws InterruptedException if
547	>	* interrupted while waiting.
548		* @param phase the phase on entry to this method
549		* @return the phase on exit from this method
550		* @throws InterruptedException if thread interrupted while waiting
#	Line 325 | Line 552 | public class Phaser {
552		public int awaitAdvanceInterruptibly(int phase) throws InterruptedException {
553		if (phase < 0)
554		return phase;
555	<	Thread current = Thread.currentThread();
556	<	if (current instanceof ForkJoinWorkerThread)
557	<	return helpingWait(phase);
558	<	else if (Thread.interrupted() || untimedWait(current, phase, true))
559	<	throw new InterruptedException();
560	<	else
561	<	return phaseOf(state.get());
555	>	long s = getReconciledState();
556	>	int p = phaseOf(s);
557	>	if (p != phase)
558	>	return p;
559	>	if (unarrivedOf(s) != 0)
560	>	parent.awaitAdvanceInterruptibly(phase);
561	>	return interruptibleWait(phase);
562		}
563
564		/**
565		* Awaits the phase of the barrier to advance from the given value
566	<	* or the given timeout elapses, or returns immediately if this
567	<	* barrier is terminated.
566	>	* or the given timeout elapses, or returns immediately if
567	>	* argument is negative or this barrier is terminated.
568		* @param phase the phase on entry to this method
569		* @return the phase on exit from this method
570		* @throws InterruptedException if thread interrupted while waiting
571		* @throws TimeoutException if timed out while waiting
572		*/
573	<	public int awaitAdvanceInterruptibly(int phase, long timeout, TimeUnit unit)
573	>	public int awaitAdvanceInterruptibly(int phase, long timeout, TimeUnit unit)
574		throws InterruptedException, TimeoutException {
575		if (phase < 0)
576		return phase;
577	<	long nanos = unit.toNanos(timeout);
578	<	Thread current = Thread.currentThread();
579	<	if (current instanceof ForkJoinWorkerThread)
580	<	return timedHelpingWait(phase, nanos);
581	<	timedWait(current, phase, nanos);
582	<	return phaseOf(state.get());
577	>	long s = getReconciledState();
578	>	int p = phaseOf(s);
579	>	if (p != phase)
580	>	return p;
581	>	if (unarrivedOf(s) == 0)
582	>	parent.awaitAdvanceInterruptibly(phase, timeout, unit);
583	>	return timedWait(phase, unit.toNanos(timeout));
584		}
585
586		/**
587		* Forces this barrier to enter termination state. Counts of
588	<	* arrived and registered parties are unaffected. This method may
589	<	* be useful for coordinating recovery after one or more tasks
590	<	* encounter unexpected exceptions.
588	>	* arrived and registered parties are unaffected. If this phaser
589	>	* has a parent, it too is terminated. This method may be useful
590	>	* for coordinating recovery after one or more tasks encounter
591	>	* unexpected exceptions.
592		*/
593		public void forceTermination() {
365	–	final AtomicLong state = this.state;
594		for (;;) {
595	<	long s = state.get();
595	>	long s = getReconciledState();
596		int phase = phaseOf(s);
597		int parties = partiesOf(s);
598		int unarrived = unarrivedOf(s);
599		if (phase < 0 ||
600	<	state.compareAndSet(s, stateFor(-1, parties, unarrived))) {
601	<	if (head.get() != null)
602	<	releaseWaiters(-1);
600	>	casState(s, stateFor(-1, parties, unarrived))) {
601	>	releaseWaiters(0);
602	>	releaseWaiters(1);
603	>	if (parent != null)
604	>	parent.forceTermination();
605		return;
606		}
607		}
608		}
609
610		/**
611	<	* Resets the barrier with the given numbers of registered unarrived
612	<	* parties and phase number 0. This method allows repeated reuse
613	<	* of this barrier, but only if it is somehow known not to be in
614	<	* use for other purposes.
385	<	* @param parties the number of parties required to trip barrier.
386	<	* @throws IllegalArgumentException if parties less than zero
387	<	* or greater than the maximum number of parties supported.
611	>	* Returns the current phase number. The maximum phase number is
612	>	* {@code Integer.MAX_VALUE}, after which it restarts at
613	>	* zero. Upon termination, the phase number is negative.
614	>	* @return the phase number, or a negative value if terminated
615		*/
616	<	public void reset(int parties) {
617	<	if (parties < 0 || parties > ushortMask)
391	<	throw new IllegalArgumentException("Illegal number of parties");
392	<	state.set(stateFor(0, parties, parties));
393	<	if (head.get() != null)
394	<	releaseWaiters(0);
616	>	public final int getPhase() {
617	>	return phaseOf(getReconciledState());
618		}
619
620		/**
621	<	* Returns the current phase number. The maximum phase number is
622	<	* <tt>Integer.MAX_VALUE</tt>, after which it restarts at
623	<	* zero. Upon termination, the phase number is negative.
401	<	* @return the phase number, or a negative value if terminated
621	>	* Returns {@code true} if the current phase number equals the given phase.
622	>	* @param phase the phase
623	>	* @return {@code true} if the current phase number equals the given phase
624		*/
625	<	public int getPhase() {
626	<	return phaseOf(state.get());
625	>	public final boolean hasPhase(int phase) {
626	>	return phaseOf(getReconciledState()) == phase;
627		}
628
629		/**
#	Line 409 | Line 631 | public class Phaser {
631		* @return the number of parties
632		*/
633		public int getRegisteredParties() {
634	<	return partiesOf(state.get());
634	>	return partiesOf(state);
635		}
636
637		/**
#	Line 418 | Line 640 | public class Phaser {
640		* @return the number of arrived parties
641		*/
642		public int getArrivedParties() {
643	<	return arrivedOf(state.get());
643	>	return arrivedOf(state);
644		}
645
646		/**
#	Line 427 | Line 649 | public class Phaser {
649		* @return the number of unarrived parties
650		*/
651		public int getUnarrivedParties() {
652	<	return unarrivedOf(state.get());
652	>	return unarrivedOf(state);
653	>	}
654	>
655	>	/**
656	>	* Returns the parent of this phaser, or null if none.
657	>	* @return the parent of this phaser, or null if none
658	>	*/
659	>	public Phaser getParent() {
660	>	return parent;
661		}
662
663		/**
664	<	* Returns true if this barrier has been terminated.
665	<	* @return true if this barrier has been terminated
664	>	* Returns the root ancestor of this phaser, which is the same as
665	>	* this phaser if it has no parent.
666	>	* @return the root ancestor of this phaser
667	>	*/
668	>	public Phaser getRoot() {
669	>	return root;
670	>	}
671	>
672	>	/**
673	>	* Returns {@code true} if this barrier has been terminated.
674	>	* @return {@code true} if this barrier has been terminated
675		*/
676		public boolean isTerminated() {
677	<	return phaseOf(state.get()) < 0;
677	>	return getPhase() < 0;
678		}
679
680		/**
#	Line 444 | Line 683 | public class Phaser {
683		* barrier is tripped (and thus all other waiting parties are
684		* dormant). If it returns true, then, rather than advance the
685		* phase number, this barrier will be set to a final termination
686	<	* state, and subsequent calls to <tt>isTerminated</tt> will
686	>	* state, and subsequent calls to {@code isTerminated} will
687		* return true.
688	<	*
688	>	*
689		* <p> The default version returns true when the number of
690		* registered parties is zero. Normally, overrides that arrange
691		* termination for other reasons should also preserve this
692		* property.
693		*
694	+	* <p> You may override this method to perform an action with side
695	+	* effects visible to participating tasks, but it is in general
696	+	* only sensible to do so in designs where all parties register
697	+	* before any arrive, and all {@code awaitAdvance} at each phase.
698	+	* Otherwise, you cannot ensure lack of interference. In
699	+	* particular, this method may be invoked more than once per
700	+	* transition if other parties successfully register while the
701	+	* invocation of this method is in progress, thus postponing the
702	+	* transition until those parties also arrive, re-triggering this
703	+	* method.
704	+	*
705		* @param phase the phase number on entering the barrier
706	<	* @param registeredParties the current number of registered
707	<	* parties.
458	<	* @return true if this barrier should terminate
706	>	* @param registeredParties the current number of registered parties
707	>	* @return {@code true} if this barrier should terminate
708		*/
709		protected boolean onAdvance(int phase, int registeredParties) {
710		return registeredParties <= 0;
711		}
712
713		/**
714	<	* Returns a string identifying this barrier, as well as its
714	>	* Returns a string identifying this phaser, as well as its
715		* state.  The state, in brackets, includes the String {@code
716	<	* "phase ="} followed by the phase number, {@code "parties ="}
716	>	* "phase = "} followed by the phase number, {@code "parties = "}
717		* followed by the number of registered parties, and {@code
718	<	* "arrived ="} followed by the number of arrived parties
718	>	* "arrived = "} followed by the number of arrived parties.
719		*
720		* @return a string identifying this barrier, as well as its state
721		*/
722		public String toString() {
723	<	long s = state.get();
724	<	return super.toString() + "[phase = " + phaseOf(s) + " parties = " + partiesOf(s) + " arrived = " + arrivedOf(s) + "]";
725	<	}
726	<
727	<	// methods for tripping and waiting
479	<
480	<	/**
481	<	* Advance the current phase (or terminate)
482	<	*/
483	<	private void trip(int phase, int parties) {
484	<	int next = onAdvance(phase, parties)? -1 : ((phase + 1) & phaseMask);
485	<	state.set(stateFor(next, parties, parties));
486	<	if (head.get() != null)
487	<	releaseWaiters(next);
488	<	}
489	<
490	<	private int helpingWait(int phase) {
491	<	final AtomicLong state = this.state;
492	<	int p;
493	<	while ((p = phaseOf(state.get())) == phase) {
494	<	ForkJoinTask<?> t = ForkJoinWorkerThread.pollTask();
495	<	if (t != null) {
496	<	if ((p = phaseOf(state.get())) == phase)
497	<	t.exec();
498	<	else {   // push task and exit if barrier advanced
499	<	t.fork();
500	<	break;
501	<	}
502	<	}
503	<	}
504	<	return p;
505	<	}
506	<
507	<	private int timedHelpingWait(int phase, long nanos) throws TimeoutException {
508	<	final AtomicLong state = this.state;
509	<	long lastTime = System.nanoTime();
510	<	int p;
511	<	while ((p = phaseOf(state.get())) == phase) {
512	<	long now = System.nanoTime();
513	<	nanos -= now - lastTime;
514	<	lastTime = now;
515	<	if (nanos <= 0) {
516	<	if ((p = phaseOf(state.get())) == phase)
517	<	throw new TimeoutException();
518	<	else
519	<	break;
520	<	}
521	<	ForkJoinTask<?> t = ForkJoinWorkerThread.pollTask();
522	<	if (t != null) {
523	<	if ((p = phaseOf(state.get())) == phase)
524	<	t.exec();
525	<	else {   // push task and exit if barrier advanced
526	<	t.fork();
527	<	break;
528	<	}
529	<	}
530	<	}
531	<	return p;
723	>	long s = getReconciledState();
724	>	return super.toString() +
725	>	"[phase = " + phaseOf(s) +
726	>	" parties = " + partiesOf(s) +
727	>	" arrived = " + arrivedOf(s) + "]";
728		}
729
730	<	/**
535	<	* Wait nodes for Treiber stack representing wait queue for non-FJ
536	<	* tasks. The waiting scheme is an adaptation of the one used in
537	<	* forkjoin.PoolBarrier.
538	<	*/
539	<	static final class QNode {
540	<	QNode next;
541	<	volatile Thread thread; // nulled to cancel wait
542	<	final int phase;
543	<	QNode(Thread t, int c) {
544	<	thread = t;
545	<	phase = c;
546	<	}
547	<	}
548	<
549	<	private void releaseWaiters(int currentPhase) {
550	<	final AtomicReference<QNode> head = this.head;
551	<	QNode p;
552	<	while ((p = head.get()) != null && p.phase != currentPhase) {
553	<	if (head.compareAndSet(p, null)) {
554	<	do {
555	<	Thread t = p.thread;
556	<	if (t != null) {
557	<	p.thread = null;
558	<	LockSupport.unpark(t);
559	<	}
560	<	} while ((p = p.next) != null);
561	<	}
562	<	}
563	<	}
730	>	// methods for waiting
731
732		/** The number of CPUs, for spin control */
733		static final int NCPUS = Runtime.getRuntime().availableProcessors();
#	Line 569 | Line 736 | public class Phaser {
736		* The number of times to spin before blocking in timed waits.
737		* The value is empirically derived.
738		*/
739	<	static final int maxTimedSpins = (NCPUS < 2)? 0 : 32;
739	>	static final int maxTimedSpins = (NCPUS < 2)? 0 : 32;
740
741		/**
742		* The number of times to spin before blocking in untimed waits.
#	Line 585 | Line 752 | public class Phaser {
752		static final long spinForTimeoutThreshold = 1000L;
753
754		/**
755	+	* Wait nodes for Treiber stack representing wait queue for non-FJ
756	+	* tasks.
757	+	*/
758	+	static final class QNode {
759	+	QNode next;
760	+	volatile Thread thread; // nulled to cancel wait
761	+	QNode() {
762	+	thread = Thread.currentThread();
763	+	}
764	+	void signal() {
765	+	Thread t = thread;
766	+	if (t != null) {
767	+	thread = null;
768	+	LockSupport.unpark(t);
769	+	}
770	+	}
771	+	}
772	+
773	+	/**
774	+	* Removes and signals waiting threads from wait queue
775	+	*/
776	+	private void releaseWaiters(int phase) {
777	+	AtomicReference<QNode> head = queueFor(phase);
778	+	QNode q;
779	+	while ((q = head.get()) != null) {
780	+	if (head.compareAndSet(q, q.next))
781	+	q.signal();
782	+	}
783	+	}
784	+
785	+	/**
786		* Enqueues node and waits unless aborted or signalled.
787		*/
788	<	private boolean untimedWait(Thread thread, int currentPhase,
789	<	boolean abortOnInterrupt) {
592	<	final AtomicReference<QNode> head = this.head;
593	<	final AtomicLong state = this.state;
594	<	boolean wasInterrupted = false;
788	>	private int untimedWait(int phase) {
789	>	int spins = maxUntimedSpins;
790		QNode node = null;
791	+	boolean interrupted = false;
792		boolean queued = false;
793	<	int spins = maxUntimedSpins;
794	<	while (phaseOf(state.get()) == currentPhase) {
795	<	QNode h;
796	<	if (node != null && queued) {
797	<	if (node.thread != null) {
798	<	LockSupport.park();
799	<	if (Thread.interrupted()) {
604	<	wasInterrupted = true;
605	<	if (abortOnInterrupt)
606	<	break;
607	<	}
793	>	int p;
794	>	while ((p = getPhase()) == phase) {
795	>	interrupted = Thread.interrupted();
796	>	if (node != null) {
797	>	if (!queued) {
798	>	AtomicReference<QNode> head = queueFor(phase);
799	>	queued = head.compareAndSet(node.next = head.get(), node);
800		}
801	+	else if (node.thread != null)
802	+	LockSupport.park(this);
803		}
804	<	else if ((h = head.get()) != null && h.phase != currentPhase) {
805	<	if (phaseOf(state.get()) == currentPhase) { // must recheck
806	<	if (head.compareAndSet(h, h.next)) {
807	<	Thread t = h.thread; // help clear out old waiters
808	<	if (t != null) {
809	<	h.thread = null;
810	<	LockSupport.unpark(t);
811	<	}
812	<	}
804	>	else if (spins <= 0)
805	>	node = new QNode();
806	>	else
807	>	--spins;
808	>	}
809	>	if (node != null)
810	>	node.thread = null;
811	>	if (interrupted)
812	>	Thread.currentThread().interrupt();
813	>	releaseWaiters(phase);
814	>	return p;
815	>	}
816	>
817	>	/**
818	>	* Messier interruptible version
819	>	*/
820	>	private int interruptibleWait(int phase) throws InterruptedException {
821	>	int spins = maxUntimedSpins;
822	>	QNode node = null;
823	>	boolean queued = false;
824	>	boolean interrupted = false;
825	>	int p;
826	>	while ((p = getPhase()) == phase) {
827	>	if (interrupted = Thread.interrupted())
828	>	break;
829	>	if (node != null) {
830	>	if (!queued) {
831	>	AtomicReference<QNode> head = queueFor(phase);
832	>	queued = head.compareAndSet(node.next = head.get(), node);
833		}
834	<	else
835	<	break;
834	>	else if (node.thread != null)
835	>	LockSupport.park(this);
836		}
623	–	else if (node != null)
624	–	queued = head.compareAndSet(node.next = h, node);
837		else if (spins <= 0)
838	<	node = new QNode(thread, currentPhase);
838	>	node = new QNode();
839		else
840		--spins;
841		}
842		if (node != null)
843		node.thread = null;
844	<	return wasInterrupted;
844	>	if (interrupted)
845	>	throw new InterruptedException();
846	>	releaseWaiters(phase);
847	>	return p;
848		}
849
850		/**
851	<	* Messier timeout version
851	>	* Even messier timeout version.
852		*/
853	<	private void timedWait(Thread thread, int currentPhase, long nanos)
853	>	private int timedWait(int phase, long nanos)
854		throws InterruptedException, TimeoutException {
855	<	final AtomicReference<QNode> head = this.head;
856	<	final AtomicLong state = this.state;
857	<	long lastTime = System.nanoTime();
858	<	QNode node = null;
859	<	boolean queued = false;
860	<	int spins = maxTimedSpins;
861	<	while (phaseOf(state.get()) == currentPhase) {
862	<	QNode h;
863	<	long now = System.nanoTime();
649	<	nanos -= now - lastTime;
650	<	lastTime = now;
651	<	if (nanos <= 0) {
652	<	if (node != null)
653	<	node.thread = null;
654	<	if (phaseOf(state.get()) == currentPhase)
655	<	throw new TimeoutException();
656	<	else
855	>	int p;
856	>	if ((p = getPhase()) == phase) {
857	>	long lastTime = System.nanoTime();
858	>	int spins = maxTimedSpins;
859	>	QNode node = null;
860	>	boolean queued = false;
861	>	boolean interrupted = false;
862	>	while ((p = getPhase()) == phase) {
863	>	if (interrupted = Thread.interrupted())
864		break;
865	<	}
866	<	else if (node != null && queued) {
867	<	if (node.thread != null &&
868	<	nanos > spinForTimeoutThreshold) {
869	<	//                LockSupport.parkNanos(this, nanos);
870	<	LockSupport.parkNanos(nanos);
871	<	if (Thread.interrupted()) {
872	<	node.thread = null;
666	<	throw new InterruptedException();
865	>	long now = System.nanoTime();
866	>	if ((nanos -= now - lastTime) <= 0)
867	>	break;
868	>	lastTime = now;
869	>	if (node != null) {
870	>	if (!queued) {
871	>	AtomicReference<QNode> head = queueFor(phase);
872	>	queued = head.compareAndSet(node.next = head.get(), node);
873		}
874	<	}
875	<	}
876	<	else if ((h = head.get()) != null && h.phase != currentPhase) {
671	<	if (phaseOf(state.get()) == currentPhase) { // must recheck
672	<	if (head.compareAndSet(h, h.next)) {
673	<	Thread t = h.thread; // help clear out old waiters
674	<	if (t != null) {
675	<	h.thread = null;
676	<	LockSupport.unpark(t);
677	<	}
874	>	else if (node.thread != null &&
875	>	nanos > spinForTimeoutThreshold) {
876	>	LockSupport.parkNanos(this, nanos);
877		}
878		}
879	+	else if (spins <= 0)
880	+	node = new QNode();
881		else
882	<	break;
882	>	--spins;
883	>	}
884	>	if (node != null)
885	>	node.thread = null;
886	>	if (interrupted)
887	>	throw new InterruptedException();
888	>	if (p == phase && (p = getPhase()) == phase)
889	>	throw new TimeoutException();
890	>	}
891	>	releaseWaiters(phase);
892	>	return p;
893	>	}
894	>
895	>	// Temporary Unsafe mechanics for preliminary release
896	>
897	>	static final Unsafe _unsafe;
898	>	static final long stateOffset;
899	>
900	>	static {
901	>	try {
902	>	if (Phaser.class.getClassLoader() != null) {
903	>	Field f = Unsafe.class.getDeclaredField("theUnsafe");
904	>	f.setAccessible(true);
905	>	_unsafe = (Unsafe)f.get(null);
906		}
683	–	else if (node != null)
684	–	queued = head.compareAndSet(node.next = h, node);
685	–	else if (spins <= 0)
686	–	node = new QNode(thread, currentPhase);
907		else
908	<	--spins;
908	>	_unsafe = Unsafe.getUnsafe();
909	>	stateOffset = _unsafe.objectFieldOffset
910	>	(Phaser.class.getDeclaredField("state"));
911	>	} catch (Exception e) {
912	>	throw new RuntimeException("Could not initialize intrinsics", e);
913		}
690	–	if (node != null)
691	–	node.thread = null;
914		}
915
916	+	final boolean casState(long cmp, long val) {
917	+	return _unsafe.compareAndSwapLong(this, stateOffset, cmp, val);
918	+	}
919		}
695	–

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