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Comparing jsr166/src/jsr166y/Phaser.java (file contents):
Revision 1.3 by jsr166, Fri Jul 25 18:11:53 2008 UTC vs.
Revision 1.67 by jsr166, Fri Dec 3 21:29:34 2010 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	<	import jsr166y.forkjoin.*;
9	<	import java.util.concurrent.*;
10	<	import java.util.concurrent.atomic.*;
8	>
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
14		/**
15	<	* A reusable synchronization barrier, similar in functionality to a
16	<	* {@link java.util.concurrent.CyclicBarrier}, but supporting more
17	<	* flexible usage.
15	>	* A reusable synchronization barrier, similar in functionality to
16	>	* {@link java.util.concurrent.CyclicBarrier CyclicBarrier} and
17	>	* {@link java.util.concurrent.CountDownLatch CountDownLatch}
18	>	* but supporting more flexible usage.
19		*
20	<	* <ul>
20	>	* <p> <b>Registration.</b> Unlike the case for other barriers, the
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
25	>	* optionally deregistered upon any arrival (using {@link
26	>	* #arriveAndDeregister}).  As is the case with most basic
27	>	* synchronization constructs, registration and deregistration affect
28	>	* only internal counts; they do not establish any further internal
29	>	* bookkeeping, so tasks cannot query whether they are registered.
30	>	* (However, you can introduce such bookkeeping by subclassing this
31	>	* class.)
32		*
33	<	* <li> The number of parties synchronizing on the barrier may vary
34	<	* over time.  A task may register to be a party in a barrier at any
35	<	* time, and may deregister upon arriving at the barrier.  As is the
36	<	* case with most basic synchronization constructs, registration
37	<	* and deregistration affect only internal counts; they do not
38	<	* establish any further internal bookkeeping, so tasks cannot query
39	<	* whether they are registered.
40	<	*
41	<	* <li> Each generation has an associated phase value, starting at
42	<	* zero, and advancing when all parties reach the barrier (wrapping
43	<	* around to zero after reaching <tt>Integer.MAX_VALUE</tt>).
31	<	*
32	<	* <li> Like a CyclicBarrier, a Phaser may be repeatedly awaited.
33	<	* Method <tt>arriveAndAwaitAdvance</tt> has effect analogous to
34	<	* <tt>CyclicBarrier.await</tt>.  However, Phasers separate two
35	<	* aspects of coordination, that may be invoked independently:
33	>	* <p> <b>Synchronization.</b> Like a {@code CyclicBarrier}, a {@code
34	>	* Phaser} may be repeatedly awaited.  Method {@link
35	>	* #arriveAndAwaitAdvance} has effect analogous to {@link
36	>	* java.util.concurrent.CyclicBarrier#await CyclicBarrier.await}. Each
37	>	* generation of a phaser has an associated phase number. The phase
38	>	* number starts at zero, and advances when all parties arrive at the
39	>	* phaser, wrapping around to zero after reaching {@code
40	>	* Integer.MAX_VALUE}. The use of phase numbers enables independent
41	>	* control of actions upon arrival at a phaser and upon awaiting
42	>	* others, via two kinds of methods that may be invoked by any
43	>	* registered party:
44		*
45		* <ul>
46		*
47	<	*   <li> Arriving at a barrier. Methods <tt>arrive</tt> and
48	<	*       <tt>arriveAndDeregister</tt> do not block, but return
49	<	*       the phase value on entry to the method.
50	<	*
51	<	*   <li> Awaiting others. Method <tt>awaitAdvance</tt> requires an
52	<	*       argument indicating the entry phase, and returns when the
53	<	*       barrier advances to a new phase.
47	>	*   <li> <b>Arrival.</b> Methods {@link #arrive} and
48	>	*       {@link #arriveAndDeregister} record arrival.  These methods
49	>	*       do not block, but return an associated <em>arrival phase
50	>	*       number</em>; that is, the phase number of the phaser to which
51	>	*       the arrival applied. When the final party for a given phase
52	>	*       arrives, an optional action is performed and the phase
53	>	*       advances.  These actions are performed by the party
54	>	*       triggering a phase advance, and are arranged by overriding
55	>	*       method {@link #onAdvance(int, int)}, which also controls
56	>	*       termination. Overriding this method is similar to, but more
57	>	*       flexible than, providing a barrier action to a {@code
58	>	*       CyclicBarrier}.
59	>	*
60	>	*   <li> <b>Waiting.</b> Method {@link #awaitAdvance} requires an
61	>	*       argument indicating an arrival phase number, and returns when
62	>	*       the phaser advances to (or is already at) a different phase.
63	>	*       Unlike similar constructions using {@code CyclicBarrier},
64	>	*       method {@code awaitAdvance} continues to wait even if the
65	>	*       waiting thread is interrupted. Interruptible and timeout
66	>	*       versions are also available, but exceptions encountered while
67	>	*       tasks wait interruptibly or with timeout do not change the
68	>	*       state of the phaser. If necessary, you can perform any
69	>	*       associated recovery within handlers of those exceptions,
70	>	*       often after invoking {@code forceTermination}.  Phasers may
71	>	*       also be used by tasks executing in a {@link ForkJoinPool},
72	>	*       which will ensure sufficient parallelism to execute tasks
73	>	*       when others are blocked waiting for a phase to advance.
74	>	*
75		* </ul>
76		*
77	+	* <p> <b>Termination.</b> A phaser may enter a <em>termination</em>
78	+	* state in which all synchronization methods immediately return
79	+	* without updating phaser state or waiting for advance, and
80	+	* indicating (via a negative phase value) that execution is complete.
81	+	* Termination is triggered when an invocation of {@code onAdvance}
82	+	* returns {@code true}. The default implementation returns {@code
83	+	* true} if a deregistration has caused the number of registered
84	+	* parties to become zero.  As illustrated below, when phasers control
85	+	* actions with a fixed number of iterations, it is often convenient
86	+	* to override this method to cause termination when the current phase
87	+	* number reaches a threshold. Method {@link #forceTermination} is
88	+	* also available to abruptly release waiting threads and allow them
89	+	* to terminate.
90		*
91	<	* <li> Barrier actions, performed by the task triggering a phase
92	<	* advance while others may be waiting, are arranged by overriding
93	<	* method <tt>onAdvance</tt>, that also controls termination.
94	<	*
95	<	* <li> Phasers may enter a <em>termination</em> state in which all
96	<	* await actions immediately return, indicating (via a negative phase
97	<	* value) that execution is complete.  Termination is triggered by
56	<	* executing the overridable <tt>onAdvance</tt> method that is invoked
57	<	* each time the barrier is tripped. When a Phaser is controlling an
58	<	* action with a fixed number of iterations, it is often convenient to
59	<	* override this method to cause termination when the current phase
60	<	* number reaches a threshold.  Method <tt>forceTermination</tt> is
61	<	* also available to assist recovery actions upon failure.
62	<	*
63	<	* <li> Unlike most synchronizers, a Phaser may also be used with
64	<	* ForkJoinTasks (as well as plain threads).
65	<	*
66	<	* <li> By default, <tt>awaitAdvance</tt> continues to wait even if
67	<	* the current thread is interrupted. And unlike the case in
68	<	* CyclicBarriers, exceptions encountered while tasks wait
69	<	* interruptibly or with timeout do not change the state of the
70	<	* barrier. If necessary, you can perform any associated recovery
71	<	* within handlers of those exceptions.
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	<	* </ul>
99	>	* <p><b>Monitoring.</b> While synchronization methods may be invoked
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
104	>	* #getPhase}).  When the remaining ({@link #getUnarrivedParties})
105	>	* parties arrive, the phase advances.  The values returned by these
106	>	* methods may reflect transient states and so are not in general
107	>	* useful for synchronization control.  Method {@link #toString}
108	>	* returns snapshots of these state queries in a form convenient for
109	>	* informal monitoring.
110	>	*
111	>	* <p><b>Sample usages:</b>
112	>	*
113	>	* <p>A {@code Phaser} may be used instead of a {@code CountDownLatch}
114	>	* to control a one-shot action serving a variable number of parties.
115	>	* The typical idiom is for the method setting this up to first
116	>	* register, then start the actions, then deregister, as in:
117	>	*
118	>	*  <pre> {@code
119	>	* void runTasks(List<Runnable> tasks) {
120	>	*   final Phaser phaser = new Phaser(1); // "1" to register self
121	>	*   // create and start threads
122	>	*   for (Runnable task : tasks) {
123	>	*     phaser.register();
124	>	*     new Thread() {
125	>	*       public void run() {
126	>	*         phaser.arriveAndAwaitAdvance(); // await all creation
127	>	*         task.run();
128	>	*       }
129	>	*     }.start();
130	>	*   }
131	>	*
132	>	*   // allow threads to start and deregister self
133	>	*   phaser.arriveAndDeregister();
134	>	* }}</pre>
135	>	*
136	>	* <p>One way to cause a set of threads to repeatedly perform actions
137	>	* for a given number of iterations is to override {@code onAdvance}:
138	>	*
139	>	*  <pre> {@code
140	>	* void startTasks(List<Runnable> tasks, final int iterations) {
141	>	*   final Phaser phaser = new Phaser() {
142	>	*     protected boolean onAdvance(int phase, int registeredParties) {
143	>	*       return phase >= iterations || registeredParties == 0;
144	>	*     }
145	>	*   };
146	>	*   phaser.register();
147	>	*   for (final Runnable task : tasks) {
148	>	*     phaser.register();
149	>	*     new Thread() {
150	>	*       public void run() {
151	>	*         do {
152	>	*           task.run();
153	>	*           phaser.arriveAndAwaitAdvance();
154	>	*         } while (!phaser.isTerminated());
155	>	*       }
156	>	*     }.start();
157	>	*   }
158	>	*   phaser.arriveAndDeregister(); // deregister self, don't wait
159	>	* }}</pre>
160		*
161	<	* <p><b>Sample usage:</b>
161	>	* If the main task must later await termination, it
162	>	* may re-register and then execute a similar loop:
163	>	*  <pre> {@code
164	>	*   // ...
165	>	*   phaser.register();
166	>	*   while (!phaser.isTerminated())
167	>	*     phaser.arriveAndAwaitAdvance();}</pre>
168		*
169	<	* <p>[todo: non-FJ example]
169	>	* <p>Related constructions may be used to await particular phase numbers
170	>	* in contexts where you are sure that the phase will never wrap around
171	>	* {@code Integer.MAX_VALUE}. For example:
172		*
173	<	* <p> A Phaser may be used to support a style of programming in
174	<	* which a task waits for others to complete, without otherwise
175	<	* needing to keep track of which tasks it is waiting for. This is
176	<	* similar to the "sync" construct in Cilk and "clocks" in X10.
177	<	* Special constructions based on such barriers are available using
178	<	* the <tt>LinkedAsyncAction</tt> and <tt>CyclicAction</tt> classes,
179	<	* but they can be useful in other contexts as well.  For a simple
180	<	* (but not very useful) example, here is a variant of Fibonacci:
87	<	*
88	<	* <pre>
89	<	* class BarrierFibonacci extends RecursiveAction {
90	<	*   int argument, result;
91	<	*   final Phaser parentBarrier;
92	<	*   BarrierFibonacci(int n, Phaser parentBarrier) {
93	<	*     this.argument = n;
94	<	*     this.parentBarrier = parentBarrier;
95	<	*     parentBarrier.register();
173	>	*  <pre> {@code
174	>	* void awaitPhase(Phaser phaser, int phase) {
175	>	*   int p = phaser.register(); // assumes caller not already registered
176	>	*   while (p < phase) {
177	>	*     if (phaser.isTerminated())
178	>	*       // ... deal with unexpected termination
179	>	*     else
180	>	*       p = phaser.arriveAndAwaitAdvance();
181		*   }
182	<	*   protected void compute() {
183	<	*     int n = argument;
184	<	*     if (n &lt;= 1)
185	<	*        result = n;
186	<	*     else {
187	<	*        Phaser childBarrier = new Phaser(1);
188	<	*        BarrierFibonacci f1 = new BarrierFibonacci(n - 1, childBarrier);
189	<	*        BarrierFibonacci f2 = new BarrierFibonacci(n - 2, childBarrier);
190	<	*        f1.fork();
191	<	*        f2.fork();
192	<	*        childBarrier.arriveAndAwait();
193	<	*        result = f1.result + f2.result;
182	>	*   phaser.arriveAndDeregister();
183	>	* }}</pre>
184	>	*
185	>	*
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[] 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(tasks, i, j, new Phaser(ph));
199		*     }
200	<	*     parentBarrier.arriveAndDeregister();
200	>	*   } else {
201	>	*     for (int i = lo; i < hi; ++i)
202	>	*       tasks[i] = new Task(ph);
203	>	*       // assumes new Task(ph) performs ph.register()
204		*   }
205	<	* }
206	<	* </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
209	>	* be appropriate for extremely small per-phase task bodies (thus
210	>	* high rates), or up to hundreds for extremely large ones.
211		*
212		* <p><b>Implementation notes</b>: This implementation restricts the
213	<	* maximum number of parties to 65535. Attempts to register
214	<	* additional parties result in IllegalStateExceptions.
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
216	>	* of participants.
217	>	*
218	>	* @since 1.7
219	>	* @author Doug Lea
220		*/
221		public class Phaser {
222		/*
223		* This class implements an extension of X10 "clocks".  Thanks to
224	<	* Vijay Saraswat for the idea of applying it to ForkJoinTasks,
225	<	* and to Vivek Sarkar for enhancements to extend functionality.
224	>	* Vijay Saraswat for the idea, and to Vivek Sarkar for
225	>	* enhancements to extend functionality.
226		*/
227
228		/**
229	<	* Barrier state representation. Conceptually, a barrier contains
128	<	* four values:
229	>	* Primary state representation, holding four fields:
230		*
231	<	* * parties -- the number of parties to wait (16 bits)
232	<	* * unarrived -- the number of parties yet to hit barrier (16 bits)
233	<	* * phase -- the generation of the barrier (31 bits)
234	<	* * terminated -- set if barrier is terminated (1 bit)
231	>	* * unarrived -- the number of parties yet to hit barrier (bits  0-15)
232	>	* * parties -- the number of parties to wait              (bits 16-31)
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 AtomicLong. Termination uses the sign bit
238	<	* of 32 bit representation of phase, so phase is set to -1 on
239	<	* termination.
240	<	*/
241	<	private final AtomicLong state;
242	<
243	<	/**
244	<	* Head of Treiber stack for waiting nonFJ threads.
245	<	*/
246	<	private final AtomicReference<QNode> head = new AtomicReference<QNode>();
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	>
259	>	private static final int  MAX_PARTIES     = 0xffff;
260	>	private static final int  MAX_PHASE       = 0x7fffffff;
261	>	private static final int  PARTIES_SHIFT   = 16;
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
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	<	private static final int ushortBits = 16;
148	<	private static final int ushortMask =  (1 << ushortBits) - 1;
149	<	private static final int phaseMask = 0x7fffffff;
272	>	// The following unpacking methods are usually manually inlined
273
274		private static int unarrivedOf(long s) {
275	<	return (int)(s & ushortMask);
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 & (ushortMask << 16)) >>> 16;
280	>	int counts = (int)s;
281	>	return (counts == EMPTY) ? 0 : counts >>> PARTIES_SHIFT;
282		}
283
284		private static int phaseOf(long s) {
285	<	return (int)(s >>> 32);
285	>	return (int) (s >>> PHASE_SHIFT);
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	>	/**
295	>	* The parent of this phaser, or null if none
296	>	*/
297	>	private final Phaser parent;
298	>
299	>	/**
300	>	* The root of phaser tree. Equals this if not in a tree.
301	>	*/
302	>	private final Phaser root;
303	>
304	>	/**
305	>	* Heads of Treiber stacks for waiting threads. To eliminate
306	>	* contention when releasing some threads while adding others, we
307	>	* use two of them, alternating across even and odd phases.
308	>	* Subphasers share queues with root to speed up releases.
309	>	*/
310	>	private final AtomicReference<QNode> evenQ;
311	>	private final AtomicReference<QNode> oddQ;
312	>
313	>	private AtomicReference<QNode> queueFor(int phase) {
314	>	return ((phase & 1) == 0) ? evenQ : oddQ;
315		}
316
317	<	private static long stateFor(int phase, int parties, int unarrived) {
318	<	return (((long)phase) << 32) | ((parties << 16) | unarrived);
317	>	/**
318	>	* Returns message string for bounds exceptions on arrival.
319	>	*/
320	>	private String badArrive(long s) {
321	>	return "Attempted arrival of unregistered party for " +
322	>	stateToString(s);
323	>	}
324	>
325	>	/**
326	>	* Returns message string for bounds exceptions on registration.
327	>	*/
328	>	private String badRegister(long s) {
329	>	return "Attempt to register more than " +
330	>	MAX_PARTIES + " parties for " + stateToString(s);
331		}
332
333	<	private static IllegalStateException badBounds(int parties, int unarrived) {
334	<	return new IllegalStateException("Attempt to set " + unarrived +
335	<	" unarrived of " + parties + " parties");
333	>	/**
334	>	* Main implementation for methods arrive and arriveAndDeregister.
335	>	* Manually tuned to speed up and minimize race windows for the
336	>	* common case of just decrementing unarrived field.
337	>	*
338	>	* @param deregister false for arrive, true for arriveAndDeregister
339	>	*/
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 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	>	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	>	break;
374	>	}
375	>	}
376	>	return phase;
377		}
378
379		/**
380	<	* Creates a new Phaser without any initially registered parties,
381	<	* and initial phase number 0.
380	>	* Implementation of register, bulkRegister
381	>	*
382	>	* @param registrations number to add to both parties and
383	>	* unarrived fields. Must be greater than zero.
384	>	*/
385	>	private int doRegister(int registrations) {
386	>	// adjustment to state
387	>	long adj = ((long)registrations << PARTIES_SHIFT) | registrations;
388	>	Phaser par = parent;
389	>	int phase;
390	>	for (;;) {
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 ((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	>	* Resolves lagged phase propagation from root if necessary.
433	>	*/
434	>	private long reconcileState() {
435	>	Phaser rt = root;
436	>	long s = state;
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	>	if ((t = state) == s &&
452	>	UNSAFE.compareAndSwapLong(this, stateOffset, s, s = n))
453	>	break;
454	>	s = t;
455	>	}
456	>	}
457	>	return s;
458	>	}
459	>
460	>	/**
461	>	* Creates a new phaser with no initially registered parties, no
462	>	* parent, and initial phase number 0. Any thread using this
463	>	* phaser will need to first register for it.
464		*/
465		public Phaser() {
466	<	state = new AtomicLong(stateFor(0, 0, 0));
466	>	this(null, 0);
467		}
468
469		/**
470	<	* Creates a new Phaser with the given numbers of registered
471	<	* unarrived parties and initial phase number 0.
472	<	* @param parties the number of parties required to trip barrier.
470	>	* Creates a new phaser with the given number of registered
471	>	* unarrived parties, no parent, and initial phase number 0.
472	>	*
473	>	* @param parties the number of parties required to advance to the
474	>	* next phase
475		* @throws IllegalArgumentException if parties less than zero
476	<	* or greater than the maximum number of parties supported.
476	>	* or greater than the maximum number of parties supported
477		*/
478		public Phaser(int parties) {
479	<	if (parties < 0 || parties > ushortMask)
479	>	this(null, parties);
480	>	}
481	>
482	>	/**
483	>	* Equivalent to {@link #Phaser(Phaser, int) Phaser(parent, 0)}.
484	>	*
485	>	* @param parent the parent phaser
486	>	*/
487	>	public Phaser(Phaser parent) {
488	>	this(parent, 0);
489	>	}
490	>
491	>	/**
492	>	* Creates a new phaser with the given parent and number of
493	>	* registered unarrived parties. Registration and deregistration
494	>	* of this child phaser with its parent are managed automatically.
495	>	* If the given parent is non-null, whenever this child phaser has
496	>	* any registered parties (as established in this constructor,
497	>	* {@link #register}, or {@link #bulkRegister}), this child phaser
498	>	* is registered with its parent. Whenever the number of
499	>	* registered parties becomes zero as the result of an invocation
500	>	* of {@link #arriveAndDeregister}, this child phaser is
501	>	* deregistered from its parent.
502	>	*
503	>	* @param parent the parent phaser
504	>	* @param parties the number of parties required to advance to the
505	>	* next phase
506	>	* @throws IllegalArgumentException if parties less than zero
507	>	* or greater than the maximum number of parties supported
508	>	*/
509	>	public Phaser(Phaser parent, int parties) {
510	>	if (parties >>> PARTIES_SHIFT != 0)
511		throw new IllegalArgumentException("Illegal number of parties");
512	<	state = new AtomicLong(stateFor(0, parties, parties));
512	>	int phase = 0;
513	>	this.parent = parent;
514	>	if (parent != null) {
515	>	Phaser r = parent.root;
516	>	this.root = r;
517	>	this.evenQ = r.evenQ;
518	>	this.oddQ = r.oddQ;
519	>	if (parties != 0)
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 = (parties == 0) ? ((long) EMPTY) :
528	>	((((long) phase) << PHASE_SHIFT) |
529	>	(((long) parties) << PARTIES_SHIFT) |
530	>	((long) parties));
531		}
532
533		/**
534	<	* Adds a new unarrived party to this phaser.
535	<	* @return the current barrier phase number upon registration
534	>	* Adds a new unarrived party to this phaser.  If an ongoing
535	>	* invocation of {@link #onAdvance} is in progress, this method
536	>	* may await its completion before returning.  If this phaser has
537	>	* a parent, and this phaser previously had no registered parties,
538	>	* this phaser is also registered with its parent.
539	>	*
540	>	* @return the arrival phase number to which this registration applied
541		* @throws IllegalStateException if attempting to register more
542	<	* than the maximum supported number of parties.
542	>	* than the maximum supported number of parties
543		*/
544	<	public int register() { // increment both parties and unarrived
545	<	final AtomicLong state = this.state;
205	<	for (;;) {
206	<	long s = state.get();
207	<	int phase = phaseOf(s);
208	<	int parties = partiesOf(s) + 1;
209	<	int unarrived = unarrivedOf(s) + 1;
210	<	if (parties > ushortMask || unarrived > ushortMask)
211	<	throw badBounds(parties, unarrived);
212	<	if (state.compareAndSet(s, stateFor(phase, parties, unarrived)))
213	<	return phase;
214	<	}
544	>	public int register() {
545	>	return doRegister(1);
546		}
547
548		/**
549	<	* Arrives at the barrier, but does not wait for others.  (You can
550	<	* in turn wait for others via {@link #awaitAdvance}).
549	>	* Adds the given number of new unarrived parties to this phaser.
550	>	* If an ongoing invocation of {@link #onAdvance} is in progress,
551	>	* this method may await its completion before returning.  If this
552	>	* phaser has a parent, and the given number of parties is
553	>	* greater than zero, and this phaser previously had no registered
554	>	* parties, this phaser is also registered with its parent.
555		*
556	<	* @return the current barrier phase number upon entry to
557	<	* this method, or a negative value if terminated;
558	<	* @throws IllegalStateException if the number of unarrived
559	<	* parties would become negative.
556	>	* @param parties the number of additional parties required to
557	>	* advance to the next phase
558	>	* @return the arrival phase number to which this registration applied
559	>	* @throws IllegalStateException if attempting to register more
560	>	* than the maximum supported number of parties
561	>	* @throws IllegalArgumentException if {@code parties < 0}
562		*/
563	<	public int arrive() { // decrement unarrived. If zero, trip
564	<	final AtomicLong state = this.state;
565	<	for (;;) {
566	<	long s = state.get();
567	<	int phase = phaseOf(s);
568	<	int parties = partiesOf(s);
232	<	int unarrived = unarrivedOf(s) - 1;
233	<	if (unarrived < 0)
234	<	throw badBounds(parties, unarrived);
235	<	if (unarrived == 0 && phase >= 0) {
236	<	trip(phase, parties);
237	<	return phase;
238	<	}
239	<	if (state.compareAndSet(s, stateFor(phase, parties, unarrived)))
240	<	return phase;
241	<	}
563	>	public int bulkRegister(int parties) {
564	>	if (parties < 0)
565	>	throw new IllegalArgumentException();
566	>	if (parties == 0)
567	>	return getPhase();
568	>	return doRegister(parties);
569		}
570
571		/**
572	<	* Arrives at the barrier, and deregisters from it, without
246	<	* waiting for others.
572	>	* Arrives at this phaser, without waiting for others to arrive.
573		*
574	<	* @return the current barrier phase number upon entry to
575	<	* this method, or a negative value if terminated;
576	<	* @throws IllegalStateException if the number of registered or
577	<	* unarrived parties would become negative.
574	>	* <p>It is a usage error for an unregistered party to invoke this
575	>	* method.  However, this error may result in an {@code
576	>	* IllegalStateException} only upon some subsequent operation on
577	>	* this phaser, if ever.
578	>	*
579	>	* @return the arrival phase number, or a negative value if terminated
580	>	* @throws IllegalStateException if not terminated and the number
581	>	* of unarrived parties would become negative
582		*/
583	<	public int arriveAndDeregister() { // Same as arrive, plus decrement parties
584	<	final AtomicLong state = this.state;
255	<	for (;;) {
256	<	long s = state.get();
257	<	int phase = phaseOf(s);
258	<	int parties = partiesOf(s) - 1;
259	<	int unarrived = unarrivedOf(s) - 1;
260	<	if (parties < 0 || unarrived < 0)
261	<	throw badBounds(parties, unarrived);
262	<	if (unarrived == 0 && phase >= 0) {
263	<	trip(phase, parties);
264	<	return phase;
265	<	}
266	<	if (state.compareAndSet(s, stateFor(phase, parties, unarrived)))
267	<	return phase;
268	<	}
583	>	public int arrive() {
584	>	return doArrive(false);
585		}
586
587		/**
588	<	* Arrives at the barrier and awaits others. Unlike other arrival
589	<	* methods, this method returns the arrival index of the
590	<	* caller. The caller tripping the barrier returns zero, the
591	<	* previous caller 1, and so on.
592	<	* @return the arrival index
593	<	* @throws IllegalStateException if the number of unarrived
594	<	* parties would become negative.
588	>	* Arrives at this phaser and deregisters from it without waiting
589	>	* for others to arrive. Deregistration reduces the number of
590	>	* parties required to advance in future phases.  If this phaser
591	>	* has a parent, and deregistration causes this phaser to have
592	>	* zero parties, this phaser is also deregistered from its parent.
593	>	*
594	>	* <p>It is a usage error for an unregistered party to invoke this
595	>	* method.  However, this error may result in an {@code
596	>	* IllegalStateException} only upon some subsequent operation on
597	>	* this phaser, if ever.
598	>	*
599	>	* @return the arrival phase number, or a negative value if terminated
600	>	* @throws IllegalStateException if not terminated and the number
601	>	* of registered or unarrived parties would become negative
602	>	*/
603	>	public int arriveAndDeregister() {
604	>	return doArrive(true);
605	>	}
606	>
607	>	/**
608	>	* Arrives at this phaser and awaits others. Equivalent in effect
609	>	* to {@code awaitAdvance(arrive())}.  If you need to await with
610	>	* interruption or timeout, you can arrange this with an analogous
611	>	* construction using one of the other forms of the {@code
612	>	* awaitAdvance} method.  If instead you need to deregister upon
613	>	* arrival, use {@code awaitAdvance(arriveAndDeregister())}.
614	>	*
615	>	* <p>It is a usage error for an unregistered party to invoke this
616	>	* method.  However, this error may result in an {@code
617	>	* IllegalStateException} only upon some subsequent operation on
618	>	* this phaser, if ever.
619	>	*
620	>	* @return the arrival phase number, or a negative number if terminated
621	>	* @throws IllegalStateException if not terminated and the number
622	>	* of unarrived parties would become negative
623		*/
624		public int arriveAndAwaitAdvance() {
625	<	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	<	}
625	>	return awaitAdvance(doArrive(false));
626		}
627
628		/**
629	<	* Awaits the phase of the barrier to advance from the given
630	<	* value, or returns immediately if this barrier is terminated.
631	<	* @param phase the phase on entry to this method
632	<	* @return the phase on exit from this method
629	>	* Awaits the phase of this phaser to advance from the given phase
630	>	* value, returning immediately if the current phase is not equal
631	>	* to the given phase value or this phaser is terminated.
632	>	*
633	>	* @param phase an arrival phase number, or negative value if
634	>	* terminated; this argument is normally the value returned by a
635	>	* previous call to {@code arrive} or {@code arriveAndDeregister}.
636	>	* @return the next arrival phase number, or a negative value
637	>	* if terminated or argument is negative
638		*/
639		public int awaitAdvance(int phase) {
640	+	Phaser rt;
641	+	int p = (int)(state >>> PHASE_SHIFT);
642		if (phase < 0)
643		return phase;
644	<	Thread current = Thread.currentThread();
645	<	if (current instanceof ForkJoinWorkerThread)
646	<	return helpingWait(phase);
647	<	if (untimedWait(current, phase, false))
648	<	current.interrupt();
649	<	return phaseOf(state.get());
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
652		/**
653	<	* Awaits the phase of the barrier to advance from the given
654	<	* value, or returns immediately if this barrier is terminated, or
655	<	* throws InterruptedException if interrupted while waiting.
656	<	* @param phase the phase on entry to this method
657	<	* @return the phase on exit from this method
653	>	* Awaits the phase of this phaser to advance from the given phase
654	>	* value, throwing {@code InterruptedException} if interrupted
655	>	* while waiting, or returning immediately if the current phase is
656	>	* not equal to the given phase value or this phaser is
657	>	* terminated.
658	>	*
659	>	* @param phase an arrival phase number, or negative value if
660	>	* terminated; this argument is normally the value returned by a
661	>	* previous call to {@code arrive} or {@code arriveAndDeregister}.
662	>	* @return the next arrival phase number, or a negative value
663	>	* if terminated or argument is negative
664		* @throws InterruptedException if thread interrupted while waiting
665		*/
666	<	public int awaitAdvanceInterruptibly(int phase) throws InterruptedException {
666	>	public int awaitAdvanceInterruptibly(int phase)
667	>	throws InterruptedException {
668	>	Phaser rt;
669	>	int p = (int)(state >>> PHASE_SHIFT);
670		if (phase < 0)
671		return phase;
672	<	Thread current = Thread.currentThread();
673	<	if (current instanceof ForkJoinWorkerThread)
674	<	return helpingWait(phase);
675	<	else if (Thread.interrupted() || untimedWait(current, phase, true))
676	<	throw new InterruptedException();
677	<	else
678	<	return phaseOf(state.get());
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		}
684
685		/**
686	<	* Awaits the phase of the barrier to advance from the given value
687	<	* or the given timeout elapses, or returns immediately if this
688	<	* barrier is terminated.
689	<	* @param phase the phase on entry to this method
690	<	* @return the phase on exit from this method
686	>	* Awaits the phase of this phaser to advance from the given phase
687	>	* value or the given timeout to elapse, throwing {@code
688	>	* InterruptedException} if interrupted while waiting, or
689	>	* returning immediately if the current phase is not equal to the
690	>	* given phase value or this phaser is terminated.
691	>	*
692	>	* @param phase an arrival phase number, or negative value if
693	>	* terminated; this argument is normally the value returned by a
694	>	* previous call to {@code arrive} or {@code arriveAndDeregister}.
695	>	* @param timeout how long to wait before giving up, in units of
696	>	*        {@code unit}
697	>	* @param unit a {@code TimeUnit} determining how to interpret the
698	>	*        {@code timeout} parameter
699	>	* @return the next arrival phase number, or a negative value
700	>	* if terminated or argument is negative
701		* @throws InterruptedException if thread interrupted while waiting
702		* @throws TimeoutException if timed out while waiting
703		*/
704	<	public int awaitAdvanceInterruptibly(int phase, long timeout, TimeUnit unit)
704	>	public int awaitAdvanceInterruptibly(int phase,
705	>	long timeout, TimeUnit unit)
706		throws InterruptedException, TimeoutException {
707	+	long nanos = unit.toNanos(timeout);
708	+	Phaser rt;
709	+	int p = (int)(state >>> PHASE_SHIFT);
710		if (phase < 0)
711		return phase;
712	<	long nanos = unit.toNanos(timeout);
713	<	Thread current = Thread.currentThread();
714	<	if (current instanceof ForkJoinWorkerThread)
715	<	return timedHelpingWait(phase, nanos);
716	<	timedWait(current, phase, nanos);
717	<	return phaseOf(state.get());
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 barrier to enter termination state. Counts of
729	<	* arrived and registered parties are unaffected. This method may
730	<	* be useful for coordinating recovery after one or more tasks
731	<	* encounter unexpected exceptions.
728	>	* Forces this phaser to enter termination state.  Counts of
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	<	final AtomicLong state = this.state;
738	<	for (;;) {
739	<	long s = state.get();
740	<	int phase = phaseOf(s);
741	<	int parties = partiesOf(s);
742	<	int unarrived = unarrivedOf(s);
743	<	if (phase < 0 ||
744	<	state.compareAndSet(s, stateFor(-1, parties, unarrived))) {
373	<	if (head.get() != null)
374	<	releaseWaiters(-1);
737	>	// Only need to change root state
738	>	final Phaser root = this.root;
739	>	long s;
740	>	while ((s = root.state) >= 0) {
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;
746		}
747		}
748		}
749
750		/**
381	–	* Resets the barrier with the given numbers of registered unarrived
382	–	* parties and phase number 0. This method allows repeated reuse
383	–	* of this barrier, but only if it is somehow known not to be in
384	–	* 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.
388	–	*/
389	–	public void reset(int parties) {
390	–	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);
395	–	}
396	–
397	–	/**
751		* Returns the current phase number. The maximum phase number is
752	<	* <tt>Integer.MAX_VALUE</tt>, after which it restarts at
753	<	* zero. Upon termination, the phase number is negative.
752	>	* {@code Integer.MAX_VALUE}, after which it restarts at
753	>	* zero. Upon termination, the phase number is negative,
754	>	* in which case the prevailing phase prior to termination
755	>	* may be obtained via {@code getPhase() + Integer.MIN_VALUE}.
756	>	*
757		* @return the phase number, or a negative value if terminated
758		*/
759	<	public int getPhase() {
760	<	return phaseOf(state.get());
759	>	public final int getPhase() {
760	>	return (int)(root.state >>> PHASE_SHIFT);
761		}
762
763		/**
764	<	* Returns the number of parties registered at this barrier.
764	>	* Returns the number of parties registered at this phaser.
765	>	*
766		* @return the number of parties
767		*/
768		public int getRegisteredParties() {
769	<	return partiesOf(state.get());
769	>	return partiesOf(state);
770		}
771
772		/**
773	<	* Returns the number of parties that have arrived at the current
774	<	* phase of this barrier.
773	>	* Returns the number of registered parties that have arrived at
774	>	* the current phase of this phaser.
775	>	*
776		* @return the number of arrived parties
777		*/
778		public int getArrivedParties() {
779	<	return arrivedOf(state.get());
779	>	return arrivedOf(reconcileState());
780		}
781
782		/**
783		* Returns the number of registered parties that have not yet
784	<	* arrived at the current phase of this barrier.
784	>	* arrived at the current phase of this phaser.
785	>	*
786		* @return the number of unarrived parties
787		*/
788		public int getUnarrivedParties() {
789	<	return unarrivedOf(state.get());
789	>	return unarrivedOf(reconcileState());
790		}
791
792		/**
793	<	* Returns true if this barrier has been terminated.
794	<	* @return true if this barrier has been terminated
793	>	* Returns the parent of this phaser, or {@code null} if none.
794	>	*
795	>	* @return the parent of this phaser, or {@code null} if none
796	>	*/
797	>	public Phaser getParent() {
798	>	return parent;
799	>	}
800	>
801	>	/**
802	>	* Returns the root ancestor of this phaser, which is the same as
803	>	* this phaser if it has no parent.
804	>	*
805	>	* @return the root ancestor of this phaser
806	>	*/
807	>	public Phaser getRoot() {
808	>	return root;
809	>	}
810	>
811	>	/**
812	>	* Returns {@code true} if this phaser has been terminated.
813	>	*
814	>	* @return {@code true} if this phaser has been terminated
815		*/
816		public boolean isTerminated() {
817	<	return phaseOf(state.get()) < 0;
817	>	return root.state < 0L;
818		}
819
820		/**
821	<	* Overridable method to perform an action upon phase advance, and
822	<	* to control termination. This method is invoked whenever the
823	<	* barrier is tripped (and thus all other waiting parties are
824	<	* dormant). If it returns true, then, rather than advance the
825	<	* phase number, this barrier will be set to a final termination
826	<	* state, and subsequent calls to <tt>isTerminated</tt> will
827	<	* return true.
828	<	*
829	<	* <p> The default version returns true when the number of
830	<	* registered parties is zero. Normally, overrides that arrange
831	<	* termination for other reasons should also preserve this
832	<	* property.
833	<	*
834	<	* @param phase the phase number on entering the barrier
835	<	* @param registeredParties the current number of registered
836	<	* parties.
837	<	* @return true if this barrier should terminate
821	>	* Overridable method to perform an action upon impending phase
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}, 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
834	>	* arrival, registration, and waiting methods on this phaser from
835	>	* within {@code onAdvance} are unspecified and should not be
836	>	* relied on.
837	>	*
838	>	* <p>If this phaser is a member of a tiered set of phasers, then
839	>	* {@code onAdvance} is invoked only for its root phaser on each
840	>	* advance.
841	>	*
842	>	* <p>To support the most common use cases, the default
843	>	* implementation of this method returns {@code true} when the
844	>	* number of registered parties has become zero as the result of a
845	>	* party invoking {@code arriveAndDeregister}.  You can disable
846	>	* this behavior, thus enabling continuation upon future
847	>	* registrations, by overriding this method to always return
848	>	* {@code false}:
849	>	*
850	>	* <pre> {@code
851	>	* Phaser phaser = new Phaser() {
852	>	*   protected boolean onAdvance(int phase, int parties) { return false; }
853	>	* }}</pre>
854	>	*
855	>	* @param phase the current phase number on entry to this method,
856	>	* before this phaser is advanced
857	>	* @param registeredParties the current number of registered parties
858	>	* @return {@code true} if this phaser should terminate
859		*/
860		protected boolean onAdvance(int phase, int registeredParties) {
861	<	return registeredParties <= 0;
861	>	return registeredParties == 0;
862		}
863
864		/**
865	<	* Returns a string identifying this barrier, as well as its
865	>	* Returns a string identifying this phaser, as well as its
866		* state.  The state, in brackets, includes the String {@code
867	<	* "phase ="} followed by the phase number, {@code "parties ="}
867	>	* "phase = "} followed by the phase number, {@code "parties = "}
868		* followed by the number of registered parties, and {@code
869	<	* "arrived ="} followed by the number of arrived parties
869	>	* "arrived = "} followed by the number of arrived parties.
870		*
871	<	* @return a string identifying this barrier, as well as its state
871	>	* @return a string identifying this phaser, as well as its state
872		*/
873		public String toString() {
874	<	long s = state.get();
475	<	return super.toString() + "[phase = " + phaseOf(s) + " parties = " + partiesOf(s) + " arrived = " + arrivedOf(s) + "]";
874	>	return stateToString(reconcileState());
875		}
876
478	–	// methods for tripping and waiting
479	–
877		/**
878	<	* Advance the current phase (or terminate)
878	>	* Implementation of toString and string-based error messages
879		*/
880	<	private void trip(int phase, int parties) {
881	<	int next = onAdvance(phase, parties)? -1 : ((phase + 1) & phaseMask);
882	<	state.set(stateFor(next, parties, parties));
883	<	if (head.get() != null)
884	<	releaseWaiters(next);
880	>	private String stateToString(long s) {
881	>	return super.toString() +
882	>	"[phase = " + phaseOf(s) +
883	>	" parties = " + partiesOf(s) +
884	>	" arrived = " + arrivedOf(s) + "]";
885		}
886
887	<	private int helpingWait(int phase) {
888	<	final AtomicLong state = this.state;
889	<	int p;
890	<	while ((p = phaseOf(state.get())) == phase) {
891	<	ForkJoinTask<?> t = ForkJoinWorkerThread.pollTask();
892	<	if (t != null) {
893	<	if ((p = phaseOf(state.get())) == phase)
894	<	t.exec();
895	<	else {   // push task and exit if barrier advanced
896	<	t.fork();
897	<	break;
898	<	}
887	>	// Waiting mechanics
888	>
889	>	/**
890	>	* Removes and signals threads from queue for phase.
891	>	*/
892	>	private void releaseWaiters(int phase) {
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	>	q.phase != (int)(root.state >>> PHASE_SHIFT)) {
900	>	if (head.compareAndSet(q, q.next) &&
901	>	(t = q.thread) != null) {
902	>	q.thread = null;
903	>	LockSupport.unpark(t);
904		}
905		}
504	–	return p;
906		}
907
908	<	private int timedHelpingWait(int phase, long nanos) throws TimeoutException {
909	<	final AtomicLong state = this.state;
910	<	long lastTime = System.nanoTime();
908	>	/** The number of CPUs, for spin control */
909	>	private static final int NCPU = Runtime.getRuntime().availableProcessors();
910	>
911	>	/**
912	>	* The number of times to spin before blocking while waiting for
913	>	* advance, per arrival while waiting. On multiprocessors, fully
914	>	* blocking and waking up a large number of threads all at once is
915	>	* usually a very slow process, so we use rechargeable spins to
916	>	* avoid it when threads regularly arrive: When a thread in
917	>	* internalAwaitAdvance notices another arrival before blocking,
918	>	* and there appear to be enough CPUs available, it spins
919	>	* SPINS_PER_ARRIVAL more times before blocking. The value trades
920	>	* off good-citizenship vs big unnecessary slowdowns.
921	>	*/
922	>	static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8;
923	>
924	>	/**
925	>	* Possibly blocks and waits for phase to advance unless aborted.
926	>	* Call only from root node.
927	>	*
928	>	* @param phase current phase
929	>	* @param node if non-null, the wait node to track interrupt and timeout;
930	>	* if null, denotes noninterruptible wait
931	>	* @return current phase
932	>	*/
933	>	private int internalAwaitAdvance(int phase, QNode node) {
934	>	releaseWaiters(phase-1);          // ensure old queue clean
935	>	boolean queued = false;           // true when node is enqueued
936	>	int lastUnarrived = 0;            // to increase spins upon change
937	>	int spins = SPINS_PER_ARRIVAL;
938	>	long s;
939		int p;
940	<	while ((p = phaseOf(state.get())) == phase) {
941	<	long now = System.nanoTime();
942	<	nanos -= now - lastTime;
943	<	lastTime = now;
944	<	if (nanos <= 0) {
945	<	if ((p = phaseOf(state.get())) == phase)
946	<	throw new TimeoutException();
947	<	else
948	<	break;
940	>	while ((p = (int)((s = state) >>> PHASE_SHIFT)) == phase) {
941	>	if (node == null) {           // spinning in noninterruptible mode
942	>	int unarrived = (int)s & UNARRIVED_MASK;
943	>	if (unarrived != lastUnarrived &&
944	>	(lastUnarrived = unarrived) < NCPU)
945	>	spins += SPINS_PER_ARRIVAL;
946	>	boolean interrupted = Thread.interrupted();
947	>	if (interrupted || --spins < 0) { // need node to record intr
948	>	node = new QNode(this, phase, false, false, 0L);
949	>	node.wasInterrupted = interrupted;
950	>	}
951		}
952	<	ForkJoinTask<?> t = ForkJoinWorkerThread.pollTask();
953	<	if (t != null) {
954	<	if ((p = phaseOf(state.get())) == phase)
955	<	t.exec();
956	<	else {   // push task and exit if barrier advanced
957	<	t.fork();
958	<	break;
952	>	else if (node.isReleasable()) // done or aborted
953	>	break;
954	>	else if (!queued) {           // push onto queue
955	>	AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ;
956	>	QNode q = node.next = head.get();
957	>	if ((q == null || q.phase == phase) &&
958	>	(int)(state >>> PHASE_SHIFT) == phase) // avoid stale enq
959	>	queued = head.compareAndSet(q, node);
960	>	}
961	>	else {
962	>	try {
963	>	ForkJoinPool.managedBlock(node);
964	>	} catch (InterruptedException ie) {
965	>	node.wasInterrupted = true;
966		}
967		}
968		}
969	+
970	+	if (node != null) {
971	+	if (node.thread != null)
972	+	node.thread = null;       // avoid need for unpark()
973	+	if (node.wasInterrupted && !node.interruptible)
974	+	Thread.currentThread().interrupt();
975	+	if (p == phase && (p = (int)(state >>> PHASE_SHIFT)) == phase)
976	+	return p;                 // recheck abort
977	+	}
978	+	releaseWaiters(phase);
979		return p;
980		}
981
982		/**
983	<	* 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.
983	>	* Wait nodes for Treiber stack representing wait queue
984		*/
985	<	static final class QNode {
986	<	QNode next;
541	<	volatile Thread thread; // nulled to cancel wait
985	>	static final class QNode implements ForkJoinPool.ManagedBlocker {
986	>	final Phaser phaser;
987		final int phase;
988	<	QNode(Thread t, int c) {
989	<	thread = t;
990	<	phase = c;
988	>	final boolean interruptible;
989	>	final boolean timed;
990	>	boolean wasInterrupted;
991	>	long nanos;
992	>	long lastTime;
993	>	volatile Thread thread; // nulled to cancel wait
994	>	QNode next;
995	>
996	>	QNode(Phaser phaser, int phase, boolean interruptible,
997	>	boolean timed, long nanos) {
998	>	this.phaser = phaser;
999	>	this.phase = phase;
1000	>	this.interruptible = interruptible;
1001	>	this.nanos = nanos;
1002	>	this.timed = timed;
1003	>	this.lastTime = timed ? System.nanoTime() : 0L;
1004	>	thread = Thread.currentThread();
1005		}
547	–	}
1006
1007	<	private void releaseWaiters(int currentPhase) {
1008	<	final AtomicReference<QNode> head = this.head;
1009	<	QNode p;
1010	<	while ((p = head.get()) != null && p.phase != currentPhase) {
1011	<	if (head.compareAndSet(p, null)) {
1012	<	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);
1007	>	public boolean isReleasable() {
1008	>	if (thread == null)
1009	>	return true;
1010	>	if (phaser.getPhase() != phase) {
1011	>	thread = null;
1012	>	return true;
1013		}
1014	+	if (Thread.interrupted())
1015	+	wasInterrupted = true;
1016	+	if (wasInterrupted && interruptible) {
1017	+	thread = null;
1018	+	return true;
1019	+	}
1020	+	if (timed) {
1021	+	if (nanos > 0L) {
1022	+	long now = System.nanoTime();
1023	+	nanos -= now - lastTime;
1024	+	lastTime = now;
1025	+	}
1026	+	if (nanos <= 0L) {
1027	+	thread = null;
1028	+	return true;
1029	+	}
1030	+	}
1031	+	return false;
1032		}
563	–	}
1033
1034	<	/** The number of CPUs, for spin control */
1035	<	static final int NCPUS = Runtime.getRuntime().availableProcessors();
1036	<
1037	<	/**
1038	<	* The number of times to spin before blocking in timed waits.
1039	<	* The value is empirically derived.
1040	<	*/
1041	<	static final int maxTimedSpins = (NCPUS < 2)? 0 : 32;
1042	<
1043	<	/**
575	<	* The number of times to spin before blocking in untimed waits.
576	<	* This is greater than timed value because untimed waits spin
577	<	* faster since they don't need to check times on each spin.
578	<	*/
579	<	static final int maxUntimedSpins = maxTimedSpins * 32;
1034	>	public boolean block() {
1035	>	if (isReleasable())
1036	>	return true;
1037	>	else if (!timed)
1038	>	LockSupport.park(this);
1039	>	else if (nanos > 0)
1040	>	LockSupport.parkNanos(this, nanos);
1041	>	return isReleasable();
1042	>	}
1043	>	}
1044
1045	<	/**
582	<	* The number of nanoseconds for which it is faster to spin
583	<	* rather than to use timed park. A rough estimate suffices.
584	<	*/
585	<	static final long spinForTimeoutThreshold = 1000L;
1045	>	// Unsafe mechanics
1046
1047	<	/**
1048	<	* Enqueues node and waits unless aborted or signalled.
1049	<	*/
1050	<	private boolean untimedWait(Thread thread, int currentPhase,
1051	<	boolean abortOnInterrupt) {
1052	<	final AtomicReference<QNode> head = this.head;
1053	<	final AtomicLong state = this.state;
1054	<	boolean wasInterrupted = false;
1055	<	QNode node = null;
1056	<	boolean queued = false;
1057	<	int spins = maxUntimedSpins;
1058	<	while (phaseOf(state.get()) == currentPhase) {
599	<	QNode h;
600	<	if (node != null && queued) {
601	<	if (node.thread != null) {
602	<	LockSupport.park();
603	<	if (Thread.interrupted()) {
604	<	wasInterrupted = true;
605	<	if (abortOnInterrupt)
606	<	break;
607	<	}
608	<	}
609	<	}
610	<	else if ((h = head.get()) != null && h.phase != currentPhase) {
611	<	if (phaseOf(state.get()) == currentPhase) { // must recheck
612	<	if (head.compareAndSet(h, h.next)) {
613	<	Thread t = h.thread; // help clear out old waiters
614	<	if (t != null) {
615	<	h.thread = null;
616	<	LockSupport.unpark(t);
617	<	}
618	<	}
619	<	}
620	<	else
621	<	break;
622	<	}
623	<	else if (node != null)
624	<	queued = head.compareAndSet(node.next = h, node);
625	<	else if (spins <= 0)
626	<	node = new QNode(thread, currentPhase);
627	<	else
628	<	--spins;
1047	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1048	>	private static final long stateOffset =
1049	>	objectFieldOffset("state", Phaser.class);
1050	>
1051	>	private static long objectFieldOffset(String field, Class<?> klazz) {
1052	>	try {
1053	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1054	>	} catch (NoSuchFieldException e) {
1055	>	// Convert Exception to corresponding Error
1056	>	NoSuchFieldError error = new NoSuchFieldError(field);
1057	>	error.initCause(e);
1058	>	throw error;
1059		}
630	–	if (node != null)
631	–	node.thread = null;
632	–	return wasInterrupted;
1060		}
1061
1062		/**
1063	<	* Messier timeout version
1063	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1064	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
1065	>	* into a jdk.
1066	>	*
1067	>	* @return a sun.misc.Unsafe
1068		*/
1069	<	private void timedWait(Thread thread, int currentPhase, long nanos)
1070	<	throws InterruptedException, TimeoutException {
1071	<	final AtomicReference<QNode> head = this.head;
1072	<	final AtomicLong state = this.state;
1073	<	long lastTime = System.nanoTime();
1074	<	QNode node = null;
1075	<	boolean queued = false;
1076	<	int spins = maxTimedSpins;
1077	<	while (phaseOf(state.get()) == currentPhase) {
1078	<	QNode h;
1079	<	long now = System.nanoTime();
1080	<	nanos -= now - lastTime;
1081	<	lastTime = now;
1082	<	if (nanos <= 0) {
1083	<	if (node != null)
1084	<	node.thread = null;
1085	<	if (phaseOf(state.get()) == currentPhase)
655	<	throw new TimeoutException();
656	<	else
657	<	break;
658	<	}
659	<	else if (node != null && queued) {
660	<	if (node.thread != null &&
661	<	nanos > spinForTimeoutThreshold) {
662	<	//                LockSupport.parkNanos(this, nanos);
663	<	LockSupport.parkNanos(nanos);
664	<	if (Thread.interrupted()) {
665	<	node.thread = null;
666	<	throw new InterruptedException();
667	<	}
668	<	}
1069	>	private static sun.misc.Unsafe getUnsafe() {
1070	>	try {
1071	>	return sun.misc.Unsafe.getUnsafe();
1072	>	} catch (SecurityException se) {
1073	>	try {
1074	>	return java.security.AccessController.doPrivileged
1075	>	(new java.security
1076	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1077	>	public sun.misc.Unsafe run() throws Exception {
1078	>	java.lang.reflect.Field f = sun.misc
1079	>	.Unsafe.class.getDeclaredField("theUnsafe");
1080	>	f.setAccessible(true);
1081	>	return (sun.misc.Unsafe) f.get(null);
1082	>	}});
1083	>	} catch (java.security.PrivilegedActionException e) {
1084	>	throw new RuntimeException("Could not initialize intrinsics",
1085	>	e.getCause());
1086		}
670	–	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	–	}
678	–	}
679	–	}
680	–	else
681	–	break;
682	–	}
683	–	else if (node != null)
684	–	queued = head.compareAndSet(node.next = h, node);
685	–	else if (spins <= 0)
686	–	node = new QNode(thread, currentPhase);
687	–	else
688	–	--spins;
1087		}
690	–	if (node != null)
691	–	node.thread = null;
1088		}
693	–
1089		}

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