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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 1.64 by jsr166, Mon Nov 29 20:58:06 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 tasks using a tree of phasers,
187	>	* you could use code of the following form, assuming a
188	>	* Task class with a constructor accepting a {@code Phaser} that
189	>	* it registers with upon construction:
190	>	*
191	>	*  <pre> {@code
192	>	* void build(Task[] actions, int lo, int hi, Phaser ph) {
193	>	*   if (hi - lo > TASKS_PER_PHASER) {
194	>	*     for (int i = lo; i < hi; i += TASKS_PER_PHASER) {
195	>	*       int j = Math.min(i + TASKS_PER_PHASER, hi);
196	>	*       build(actions, i, j, new Phaser(ph));
197		*     }
198	<	*     parentBarrier.arriveAndDeregister();
198	>	*   } else {
199	>	*     for (int i = lo; i < hi; ++i)
200	>	*       actions[i] = new Task(ph);
201	>	*       // assumes new Task(ph) performs ph.register()
202		*   }
203		* }
204	<	* </pre>
204	>	* // .. initially called, for n tasks via
205	>	* build(new Task[n], 0, n, new Phaser());}</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;
237	>	* packed into a single (atomic) long. Termination uses the sign
238	>	* bit of 32 bit representation of phase, so phase is set to -1 on
239	>	* termination. Good performance relies on keeping state decoding
240	>	* and encoding simple, and keeping race windows short.
241	>	*/
242	>	private volatile long state;
243	>
244	>	private static final int  MAX_PARTIES     = 0xffff;
245	>	private static final int  MAX_PHASE       = 0x7fffffff;
246	>	private static final int  PARTIES_SHIFT   = 16;
247	>	private static final int  PHASE_SHIFT     = 32;
248	>	private static final int  UNARRIVED_MASK  = 0xffff;      // to mask ints
249	>	private static final long PARTIES_MASK    = 0xffff0000L; // to mask longs
250	>	private static final long ONE_ARRIVAL     = 1L;
251	>	private static final long ONE_PARTY       = 1L << PARTIES_SHIFT;
252	>	private static final long TERMINATION_BIT = 1L << 63;
253
254	<	/**
143	<	* Head of Treiber stack for waiting nonFJ threads.
144	<	*/
145	<	private final AtomicReference<QNode> head = new AtomicReference<QNode>();
146	<
147	<	private static final int ushortBits = 16;
148	<	private static final int ushortMask =  (1 << ushortBits) - 1;
149	<	private static final int phaseMask = 0x7fffffff;
254	>	// The following unpacking methods are usually manually inlined
255
256		private static int unarrivedOf(long s) {
257	<	return (int)(s & ushortMask);
257	>	return (int)s & UNARRIVED_MASK;
258		}
259
260		private static int partiesOf(long s) {
261	<	return (int)(s & (ushortMask << 16)) >>> 16;
261	>	return (int)s >>> PARTIES_SHIFT;
262		}
263
264		private static int phaseOf(long s) {
265	<	return (int)(s >>> 32);
265	>	return (int) (s >>> PHASE_SHIFT);
266		}
267
268		private static int arrivedOf(long s) {
269		return partiesOf(s) - unarrivedOf(s);
270		}
271
272	<	private static long stateFor(int phase, int parties, int unarrived) {
273	<	return (((long)phase) << 32) | ((parties << 16) | unarrived);
274	<	}
272	>	/**
273	>	* The parent of this phaser, or null if none
274	>	*/
275	>	private final Phaser parent;
276
277	<	private static IllegalStateException badBounds(int parties, int unarrived) {
278	<	return new IllegalStateException("Attempt to set " + unarrived +
279	<	" unarrived of " + parties + " parties");
280	<	}
277	>	/**
278	>	* The root of phaser tree. Equals this if not in a tree.  Used to
279	>	* support faster state push-down.
280	>	*/
281	>	private final Phaser root;
282
283		/**
284	<	* Creates a new Phaser without any initially registered parties,
285	<	* and initial phase number 0.
284	>	* Heads of Treiber stacks for waiting threads. To eliminate
285	>	* contention when releasing some threads while adding others, we
286	>	* use two of them, alternating across even and odd phases.
287	>	* Subphasers share queues with root to speed up releases.
288		*/
289	<	public Phaser() {
290	<	state = new AtomicLong(stateFor(0, 0, 0));
289	>	private final AtomicReference<QNode> evenQ;
290	>	private final AtomicReference<QNode> oddQ;
291	>
292	>	private AtomicReference<QNode> queueFor(int phase) {
293	>	return ((phase & 1) == 0) ? evenQ : oddQ;
294		}
295
296		/**
297	<	* Creates a new Phaser with the given numbers of registered
186	<	* unarrived parties and initial phase number 0.
187	<	* @param parties the number of parties required to trip barrier.
188	<	* @throws IllegalArgumentException if parties less than zero
189	<	* or greater than the maximum number of parties supported.
297	>	* Returns message string for bounds exceptions on arrival.
298		*/
299	<	public Phaser(int parties) {
300	<	if (parties < 0 || parties > ushortMask)
301	<	throw new IllegalArgumentException("Illegal number of parties");
194	<	state = new AtomicLong(stateFor(0, parties, parties));
299	>	private String badArrive(long s) {
300	>	return "Attempted arrival of unregistered party for " +
301	>	stateToString(s);
302		}
303
304		/**
305	<	* Adds a new unarrived party to this phaser.
199	<	* @return the current barrier phase number upon registration
200	<	* @throws IllegalStateException if attempting to register more
201	<	* than the maximum supported number of parties.
305	>	* Returns message string for bounds exceptions on registration.
306		*/
307	<	public int register() { // increment both parties and unarrived
308	<	final AtomicLong state = this.state;
309	<	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	<	}
307	>	private String badRegister(long s) {
308	>	return "Attempt to register more than " +
309	>	MAX_PARTIES + " parties for " + stateToString(s);
310		}
311
312		/**
313	<	* Arrives at the barrier, but does not wait for others.  (You can
314	<	* in turn wait for others via {@link #awaitAdvance}).
313	>	* Main implementation for methods arrive and arriveAndDeregister.
314	>	* Manually tuned to speed up and minimize race windows for the
315	>	* common case of just decrementing unarrived field.
316		*
317	<	* @return the current barrier phase number upon entry to
318	<	* this method, or a negative value if terminated;
319	<	* @throws IllegalStateException if the number of unarrived
224	<	* parties would become negative.
317	>	* @param adj - adjustment to apply to state -- either
318	>	* ONE_ARRIVAL (for arrive) or
319	>	* ONE_ARRIVAL|ONE_PARTY (for arriveAndDeregister)
320		*/
321	<	public int arrive() { // decrement unarrived. If zero, trip
227	<	final AtomicLong state = this.state;
321	>	private int doArrive(long adj) {
322		for (;;) {
323	<	long s = state.get();
324	<	int phase = phaseOf(s);
325	<	int parties = partiesOf(s);
326	<	int unarrived = unarrivedOf(s) - 1;
233	<	if (unarrived < 0)
234	<	throw badBounds(parties, unarrived);
235	<	if (unarrived == 0 && phase >= 0) {
236	<	trip(phase, parties);
323	>	long s = state;
324	>	int unarrived = (int)s & UNARRIVED_MASK;
325	>	int phase = (int)(s >>> PHASE_SHIFT);
326	>	if (phase < 0)
327		return phase;
328	+	else if (unarrived == 0) {
329	+	if (reconcileState() == s)     // recheck
330	+	throw new IllegalStateException(badArrive(s));
331		}
332	<	if (state.compareAndSet(s, stateFor(phase, parties, unarrived)))
332	>	else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) {
333	>	if (unarrived == 1) {
334	>	long p = s & PARTIES_MASK; // unshifted parties field
335	>	long lu = p >>> PARTIES_SHIFT;
336	>	int u = (int)lu;
337	>	int nextPhase = (phase + 1) & MAX_PHASE;
338	>	long next = ((long)nextPhase << PHASE_SHIFT) | p | lu;
339	>	final Phaser parent = this.parent;
340	>	if (parent == null) {
341	>	if (onAdvance(phase, u))
342	>	next |= TERMINATION_BIT;
343	>	UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
344	>	releaseWaiters(phase);
345	>	}
346	>	else {
347	>	parent.doArrive((u == 0) ?
348	>	ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL);
349	>	if ((int)(parent.state >>> PHASE_SHIFT) != nextPhase)
350	>	reconcileState();
351	>	else if (state == s)
352	>	UNSAFE.compareAndSwapLong(this, stateOffset, s,
353	>	next);
354	>	}
355	>	}
356		return phase;
357	+	}
358		}
359		}
360
361		/**
362	<	* Arrives at the barrier, and deregisters from it, without
246	<	* waiting for others.
362	>	* Implementation of register, bulkRegister
363		*
364	<	* @return the current barrier phase number upon entry to
365	<	* this method, or a negative value if terminated;
250	<	* @throws IllegalStateException if the number of registered or
251	<	* unarrived parties would become negative.
364	>	* @param registrations number to add to both parties and
365	>	* unarrived fields. Must be greater than zero.
366		*/
367	<	public int arriveAndDeregister() { // Same as arrive, plus decrement parties
368	<	final AtomicLong state = this.state;
367	>	private int doRegister(int registrations) {
368	>	// adjustment to state
369	>	long adj = ((long)registrations << PARTIES_SHIFT) | registrations;
370	>	final Phaser parent = this.parent;
371		for (;;) {
372	<	long s = state.get();
373	<	int phase = phaseOf(s);
374	<	int parties = partiesOf(s) - 1;
375	<	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);
372	>	long s = (parent == null) ? state : reconcileState();
373	>	int parties = (int)s >>> PARTIES_SHIFT;
374	>	int phase = (int)(s >>> PHASE_SHIFT);
375	>	if (phase < 0)
376		return phase;
377	+	else if (registrations > MAX_PARTIES - parties)
378	+	throw new IllegalStateException(badRegister(s));
379	+	else if ((parties == 0 && parent == null) || // first reg of root
380	+	((int)s & UNARRIVED_MASK) != 0) {   // not advancing
381	+	if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj))
382	+	return phase;
383	+	}
384	+	else if (parties != 0)               // wait for onAdvance
385	+	root.internalAwaitAdvance(phase, null);
386	+	else {                               // 1st registration of child
387	+	synchronized (this) {            // register parent first
388	+	if (reconcileState() == s) { // recheck under lock
389	+	parent.doRegister(1);    // OK if throws IllegalState
390	+	for (;;) {               // simpler form of outer loop
391	+	s = reconcileState();
392	+	phase = (int)(s >>> PHASE_SHIFT);
393	+	if (phase < 0 ||
394	+	UNSAFE.compareAndSwapLong(this, stateOffset,
395	+	s, s + adj))
396	+	return phase;
397	+	}
398	+	}
399	+	}
400		}
266	–	if (state.compareAndSet(s, stateFor(phase, parties, unarrived)))
267	–	return phase;
401		}
402		}
403
404		/**
405	<	* Arrives at the barrier and awaits others. Unlike other arrival
273	<	* methods, this method returns the arrival index of the
274	<	* caller. The caller tripping the barrier returns zero, the
275	<	* previous caller 1, and so on.
276	<	* @return the arrival index
277	<	* @throws IllegalStateException if the number of unarrived
278	<	* parties would become negative.
405	>	* Recursively resolves lagged phase propagation from root if necessary.
406		*/
407	<	public int arriveAndAwaitAdvance() {
408	<	final AtomicLong state = this.state;
409	<	for (;;) {
410	<	long s = state.get();
411	<	int phase = phaseOf(s);
412	<	int parties = partiesOf(s);
413	<	int unarrived = unarrivedOf(s) - 1;
414	<	if (unarrived < 0)
415	<	throw badBounds(parties, unarrived);
416	<	if (unarrived == 0 && phase >= 0) {
417	<	trip(phase, parties);
418	<	return 0;
419	<	}
420	<	if (state.compareAndSet(s, stateFor(phase, parties, unarrived))) {
421	<	awaitAdvance(phase);
422	<	return unarrived;
407	>	private long reconcileState() {
408	>	Phaser par = parent;
409	>	long s = state;
410	>	if (par != null) {
411	>	Phaser rt = root;
412	>	int phase, rPhase;
413	>	while ((phase = (int)(s >>> PHASE_SHIFT)) >= 0 &&
414	>	(rPhase = (int)(rt.state >>> PHASE_SHIFT)) != phase) {
415	>	if (par != rt && (int)(par.state >>> PHASE_SHIFT) != rPhase)
416	>	par.reconcileState();
417	>	else if (rPhase < 0 || ((int)s & UNARRIVED_MASK) == 0) {
418	>	long u = s & PARTIES_MASK; // reset unarrived to parties
419	>	long next = ((((long) rPhase) << PHASE_SHIFT) | u |
420	>	(u >>> PARTIES_SHIFT));
421	>	UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
422	>	}
423	>	s = state;
424		}
425		}
426	+	return s;
427		}
428
429		/**
430	<	* Awaits the phase of the barrier to advance from the given
431	<	* value, or returns immediately if this barrier is terminated.
432	<	* @param phase the phase on entry to this method
433	<	* @return the phase on exit from this method
430	>	* Creates a new phaser with no initially registered parties, no
431	>	* parent, and initial phase number 0. Any thread using this
432	>	* phaser will need to first register for it.
433	>	*/
434	>	public Phaser() {
435	>	this(null, 0);
436	>	}
437	>
438	>	/**
439	>	* Creates a new phaser with the given number of registered
440	>	* unarrived parties, no parent, and initial phase number 0.
441	>	*
442	>	* @param parties the number of parties required to advance to the
443	>	* next phase
444	>	* @throws IllegalArgumentException if parties less than zero
445	>	* or greater than the maximum number of parties supported
446	>	*/
447	>	public Phaser(int parties) {
448	>	this(null, parties);
449	>	}
450	>
451	>	/**
452	>	* Equivalent to {@link #Phaser(Phaser, int) Phaser(parent, 0)}.
453	>	*
454	>	* @param parent the parent phaser
455	>	*/
456	>	public Phaser(Phaser parent) {
457	>	this(parent, 0);
458	>	}
459	>
460	>	/**
461	>	* Creates a new phaser with the given parent and number of
462	>	* registered unarrived parties. Registration and deregistration
463	>	* of this child phaser with its parent are managed automatically.
464	>	* If the given parent is non-null, whenever this child phaser has
465	>	* any registered parties (as established in this constructor,
466	>	* {@link #register}, or {@link #bulkRegister}), this child phaser
467	>	* is registered with its parent. Whenever the number of
468	>	* registered parties becomes zero as the result of an invocation
469	>	* of {@link #arriveAndDeregister}, this child phaser is
470	>	* deregistered from its parent.
471	>	*
472	>	* @param parent the parent phaser
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
477	>	*/
478	>	public Phaser(Phaser parent, int parties) {
479	>	if (parties >>> PARTIES_SHIFT != 0)
480	>	throw new IllegalArgumentException("Illegal number of parties");
481	>	long s = ((long) parties) | (((long) parties) << PARTIES_SHIFT);
482	>	this.parent = parent;
483	>	if (parent != null) {
484	>	Phaser r = parent.root;
485	>	this.root = r;
486	>	this.evenQ = r.evenQ;
487	>	this.oddQ = r.oddQ;
488	>	if (parties != 0)
489	>	s |= ((long)(parent.doRegister(1))) << PHASE_SHIFT;
490	>	}
491	>	else {
492	>	this.root = this;
493	>	this.evenQ = new AtomicReference<QNode>();
494	>	this.oddQ = new AtomicReference<QNode>();
495	>	}
496	>	this.state = s;
497	>	}
498	>
499	>	/**
500	>	* Adds a new unarrived party to this phaser.  If an ongoing
501	>	* invocation of {@link #onAdvance} is in progress, this method
502	>	* may await its completion before returning.  If this phaser has
503	>	* a parent, and this phaser previously had no registered parties,
504	>	* this phaser is also registered with its parent.
505	>	*
506	>	* @return the arrival phase number to which this registration applied
507	>	* @throws IllegalStateException if attempting to register more
508	>	* than the maximum supported number of parties
509	>	*/
510	>	public int register() {
511	>	return doRegister(1);
512	>	}
513	>
514	>	/**
515	>	* Adds the given number of new unarrived parties to this phaser.
516	>	* If an ongoing invocation of {@link #onAdvance} is in progress,
517	>	* this method may await its completion before returning.  If this
518	>	* phaser has a parent, and the given number of parities is
519	>	* greater than zero, and this phaser previously had no registered
520	>	* parties, this phaser is also registered with its parent.
521	>	*
522	>	* @param parties the number of additional parties required to
523	>	* advance to the next phase
524	>	* @return the arrival phase number to which this registration applied
525	>	* @throws IllegalStateException if attempting to register more
526	>	* than the maximum supported number of parties
527	>	* @throws IllegalArgumentException if {@code parties < 0}
528	>	*/
529	>	public int bulkRegister(int parties) {
530	>	if (parties < 0)
531	>	throw new IllegalArgumentException();
532	>	if (parties == 0)
533	>	return getPhase();
534	>	return doRegister(parties);
535	>	}
536	>
537	>	/**
538	>	* Arrives at this phaser, without waiting for others to arrive.
539	>	*
540	>	* <p>It is a usage error for an unregistered party to invoke this
541	>	* method.  However, this error may result in an {@code
542	>	* IllegalStateException} only upon some subsequent operation on
543	>	* this phaser, if ever.
544	>	*
545	>	* @return the arrival phase number, or a negative value if terminated
546	>	* @throws IllegalStateException if not terminated and the number
547	>	* of unarrived parties would become negative
548	>	*/
549	>	public int arrive() {
550	>	return doArrive(ONE_ARRIVAL);
551	>	}
552	>
553	>	/**
554	>	* Arrives at this phaser and deregisters from it without waiting
555	>	* for others to arrive. Deregistration reduces the number of
556	>	* parties required to advance in future phases.  If this phaser
557	>	* has a parent, and deregistration causes this phaser to have
558	>	* zero parties, this phaser is also deregistered from its parent.
559	>	*
560	>	* <p>It is a usage error for an unregistered party to invoke this
561	>	* method.  However, this error may result in an {@code
562	>	* IllegalStateException} only upon some subsequent operation on
563	>	* this phaser, if ever.
564	>	*
565	>	* @return the arrival phase number, or a negative value if terminated
566	>	* @throws IllegalStateException if not terminated and the number
567	>	* of registered or unarrived parties would become negative
568	>	*/
569	>	public int arriveAndDeregister() {
570	>	return doArrive(ONE_ARRIVAL|ONE_PARTY);
571	>	}
572	>
573	>	/**
574	>	* Arrives at this phaser and awaits others. Equivalent in effect
575	>	* to {@code awaitAdvance(arrive())}.  If you need to await with
576	>	* interruption or timeout, you can arrange this with an analogous
577	>	* construction using one of the other forms of the {@code
578	>	* awaitAdvance} method.  If instead you need to deregister upon
579	>	* arrival, use {@code awaitAdvance(arriveAndDeregister())}.
580	>	*
581	>	* <p>It is a usage error for an unregistered party to invoke this
582	>	* method.  However, this error may result in an {@code
583	>	* IllegalStateException} only upon some subsequent operation on
584	>	* this phaser, if ever.
585	>	*
586	>	* @return the arrival phase number, or a negative number if terminated
587	>	* @throws IllegalStateException if not terminated and the number
588	>	* of unarrived parties would become negative
589	>	*/
590	>	public int arriveAndAwaitAdvance() {
591	>	return awaitAdvance(doArrive(ONE_ARRIVAL));
592	>	}
593	>
594	>	/**
595	>	* Awaits the phase of this phaser to advance from the given phase
596	>	* value, returning immediately if the current phase is not equal
597	>	* to the given phase value or this phaser is terminated.
598	>	*
599	>	* @param phase an arrival phase number, or negative value if
600	>	* terminated; this argument is normally the value returned by a
601	>	* previous call to {@code arrive} or {@code arriveAndDeregister}.
602	>	* @return the next arrival phase number, or a negative value
603	>	* if terminated or argument is negative
604		*/
605		public int awaitAdvance(int phase) {
606	+	Phaser rt;
607	+	int p = (int)(state >>> PHASE_SHIFT);
608		if (phase < 0)
609		return phase;
610	<	Thread current = Thread.currentThread();
611	<	if (current instanceof ForkJoinWorkerThread)
612	<	return helpingWait(phase);
613	<	if (untimedWait(current, phase, false))
313	<	current.interrupt();
314	<	return phaseOf(state.get());
610	>	if (p == phase &&
611	>	(p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase)
612	>	return rt.internalAwaitAdvance(phase, null);
613	>	return p;
614		}
615
616		/**
617	<	* Awaits the phase of the barrier to advance from the given
618	<	* value, or returns immediately if this barrier is terminated, or
619	<	* throws InterruptedException if interrupted while waiting.
620	<	* @param phase the phase on entry to this method
621	<	* @return the phase on exit from this method
617	>	* Awaits the phase of this phaser to advance from the given phase
618	>	* value, throwing {@code InterruptedException} if interrupted
619	>	* while waiting, or returning immediately if the current phase is
620	>	* not equal to the given phase value or this phaser is
621	>	* terminated.
622	>	*
623	>	* @param phase an arrival phase number, or negative value if
624	>	* terminated; this argument is normally the value returned by a
625	>	* previous call to {@code arrive} or {@code arriveAndDeregister}.
626	>	* @return the next arrival phase number, or a negative value
627	>	* if terminated or argument is negative
628		* @throws InterruptedException if thread interrupted while waiting
629		*/
630	<	public int awaitAdvanceInterruptibly(int phase) throws InterruptedException {
630	>	public int awaitAdvanceInterruptibly(int phase)
631	>	throws InterruptedException {
632	>	Phaser rt;
633	>	int p = (int)(state >>> PHASE_SHIFT);
634		if (phase < 0)
635		return phase;
636	<	Thread current = Thread.currentThread();
637	<	if (current instanceof ForkJoinWorkerThread)
638	<	return helpingWait(phase);
639	<	else if (Thread.interrupted() || untimedWait(current, phase, true))
640	<	throw new InterruptedException();
641	<	else
642	<	return phaseOf(state.get());
636	>	if (p == phase &&
637	>	(p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
638	>	QNode node = new QNode(this, phase, true, false, 0L);
639	>	p = rt.internalAwaitAdvance(phase, node);
640	>	if (node.wasInterrupted)
641	>	throw new InterruptedException();
642	>	}
643	>	return p;
644		}
645
646		/**
647	<	* Awaits the phase of the barrier to advance from the given value
648	<	* or the given timeout elapses, or returns immediately if this
649	<	* barrier is terminated.
650	<	* @param phase the phase on entry to this method
651	<	* @return the phase on exit from this method
647	>	* Awaits the phase of this phaser to advance from the given phase
648	>	* value or the given timeout to elapse, throwing {@code
649	>	* InterruptedException} if interrupted while waiting, or
650	>	* returning immediately if the current phase is not equal to the
651	>	* given phase value or this phaser is terminated.
652	>	*
653	>	* @param phase an arrival phase number, or negative value if
654	>	* terminated; this argument is normally the value returned by a
655	>	* previous call to {@code arrive} or {@code arriveAndDeregister}.
656	>	* @param timeout how long to wait before giving up, in units of
657	>	*        {@code unit}
658	>	* @param unit a {@code TimeUnit} determining how to interpret the
659	>	*        {@code timeout} parameter
660	>	* @return the next arrival phase number, or a negative value
661	>	* if terminated or argument is negative
662		* @throws InterruptedException if thread interrupted while waiting
663		* @throws TimeoutException if timed out while waiting
664		*/
665	<	public int awaitAdvanceInterruptibly(int phase, long timeout, TimeUnit unit)
665	>	public int awaitAdvanceInterruptibly(int phase,
666	>	long timeout, TimeUnit unit)
667		throws InterruptedException, TimeoutException {
668	+	long nanos = unit.toNanos(timeout);
669	+	Phaser rt;
670	+	int p = (int)(state >>> PHASE_SHIFT);
671		if (phase < 0)
672		return phase;
673	<	long nanos = unit.toNanos(timeout);
674	<	Thread current = Thread.currentThread();
675	<	if (current instanceof ForkJoinWorkerThread)
676	<	return timedHelpingWait(phase, nanos);
677	<	timedWait(current, phase, nanos);
678	<	return phaseOf(state.get());
673	>	if (p == phase &&
674	>	(p = (int)((rt = root).state >>> PHASE_SHIFT)) == phase) {
675	>	QNode node = new QNode(this, phase, true, true, nanos);
676	>	p = rt.internalAwaitAdvance(phase, node);
677	>	if (node.wasInterrupted)
678	>	throw new InterruptedException();
679	>	else if (p == phase)
680	>	throw new TimeoutException();
681	>	}
682	>	return p;
683		}
684
685		/**
686	<	* Forces this barrier to enter termination state. Counts of
687	<	* arrived and registered parties are unaffected. This method may
688	<	* be useful for coordinating recovery after one or more tasks
686	>	* Forces this phaser to enter termination state.  Counts of
687	>	* arrived and registered parties are unaffected.  If this phaser
688	>	* is a member of a tiered set of phasers, then all of the phasers
689	>	* in the set are terminated.  If this phaser is already
690	>	* terminated, this method has no effect.  This method may be
691	>	* useful for coordinating recovery after one or more tasks
692		* encounter unexpected exceptions.
693		*/
694		public void forceTermination() {
695	<	final AtomicLong state = this.state;
696	<	for (;;) {
697	<	long s = state.get();
698	<	int phase = phaseOf(s);
699	<	int parties = partiesOf(s);
700	<	int unarrived = unarrivedOf(s);
701	<	if (phase < 0 ||
702	<	state.compareAndSet(s, stateFor(-1, parties, unarrived))) {
373	<	if (head.get() != null)
374	<	releaseWaiters(-1);
695	>	// Only need to change root state
696	>	final Phaser root = this.root;
697	>	long s;
698	>	while ((s = root.state) >= 0) {
699	>	if (UNSAFE.compareAndSwapLong(root, stateOffset,
700	>	s, s | TERMINATION_BIT)) {
701	>	releaseWaiters(0); // signal all threads
702	>	releaseWaiters(1);
703		return;
704		}
705		}
706		}
707
708		/**
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	–	/**
709		* Returns the current phase number. The maximum phase number is
710	<	* <tt>Integer.MAX_VALUE</tt>, after which it restarts at
711	<	* zero. Upon termination, the phase number is negative.
710	>	* {@code Integer.MAX_VALUE}, after which it restarts at
711	>	* zero. Upon termination, the phase number is negative,
712	>	* in which case the prevailing phase prior to termination
713	>	* may be obtained via {@code getPhase() + Integer.MIN_VALUE}.
714	>	*
715		* @return the phase number, or a negative value if terminated
716		*/
717	<	public int getPhase() {
718	<	return phaseOf(state.get());
717	>	public final int getPhase() {
718	>	return (int)(root.state >>> PHASE_SHIFT);
719		}
720
721		/**
722	<	* Returns the number of parties registered at this barrier.
722	>	* Returns the number of parties registered at this phaser.
723	>	*
724		* @return the number of parties
725		*/
726		public int getRegisteredParties() {
727	<	return partiesOf(state.get());
727	>	return partiesOf(state);
728		}
729
730		/**
731	<	* Returns the number of parties that have arrived at the current
732	<	* phase of this barrier.
731	>	* Returns the number of registered parties that have arrived at
732	>	* the current phase of this phaser.
733	>	*
734		* @return the number of arrived parties
735		*/
736		public int getArrivedParties() {
737	<	return arrivedOf(state.get());
737	>	long s = state;
738	>	int u = unarrivedOf(s); // only reconcile if possibly needed
739	>	return (u != 0 || parent == null) ?
740	>	partiesOf(s) - u :
741	>	arrivedOf(reconcileState());
742		}
743
744		/**
745		* Returns the number of registered parties that have not yet
746	<	* arrived at the current phase of this barrier.
746	>	* arrived at the current phase of this phaser.
747	>	*
748		* @return the number of unarrived parties
749		*/
750		public int getUnarrivedParties() {
751	<	return unarrivedOf(state.get());
751	>	int u = unarrivedOf(state);
752	>	return (u != 0 || parent == null) ? u : unarrivedOf(reconcileState());
753		}
754
755		/**
756	<	* Returns true if this barrier has been terminated.
757	<	* @return true if this barrier has been terminated
756	>	* Returns the parent of this phaser, or {@code null} if none.
757	>	*
758	>	* @return the parent of this phaser, or {@code null} if none
759	>	*/
760	>	public Phaser getParent() {
761	>	return parent;
762	>	}
763	>
764	>	/**
765	>	* Returns the root ancestor of this phaser, which is the same as
766	>	* this phaser if it has no parent.
767	>	*
768	>	* @return the root ancestor of this phaser
769	>	*/
770	>	public Phaser getRoot() {
771	>	return root;
772	>	}
773	>
774	>	/**
775	>	* Returns {@code true} if this phaser has been terminated.
776	>	*
777	>	* @return {@code true} if this phaser has been terminated
778		*/
779		public boolean isTerminated() {
780	<	return phaseOf(state.get()) < 0;
780	>	return root.state < 0L;
781		}
782
783		/**
784	<	* Overridable method to perform an action upon phase advance, and
785	<	* to control termination. This method is invoked whenever the
786	<	* barrier is tripped (and thus all other waiting parties are
787	<	* dormant). If it returns true, then, rather than advance the
788	<	* phase number, this barrier will be set to a final termination
789	<	* state, and subsequent calls to <tt>isTerminated</tt> will
790	<	* return true.
791	<	*
792	<	* <p> The default version returns true when the number of
793	<	* registered parties is zero. Normally, overrides that arrange
794	<	* termination for other reasons should also preserve this
795	<	* property.
796	<	*
797	<	* @param phase the phase number on entering the barrier
798	<	* @param registeredParties the current number of registered
799	<	* parties.
800	<	* @return true if this barrier should terminate
784	>	* Overridable method to perform an action upon impending phase
785	>	* advance, and to control termination. This method is invoked
786	>	* upon arrival of the party advancing this phaser (when all other
787	>	* waiting parties are dormant).  If this method returns {@code
788	>	* true}, then, rather than advance the phase number, this phaser
789	>	* will be set to a final termination state, and subsequent calls
790	>	* to {@link #isTerminated} will return true. Any (unchecked)
791	>	* Exception or Error thrown by an invocation of this method is
792	>	* propagated to the party attempting to advance this phaser, in
793	>	* which case no advance occurs.
794	>	*
795	>	* <p>The arguments to this method provide the state of the phaser
796	>	* prevailing for the current transition.  The effects of invoking
797	>	* arrival, registration, and waiting methods on this phaser from
798	>	* within {@code onAdvance} are unspecified and should not be
799	>	* relied on.
800	>	*
801	>	* <p>If this phaser is a member of a tiered set of phasers, then
802	>	* {@code onAdvance} is invoked only for its root phaser on each
803	>	* advance.
804	>	*
805	>	* <p>To support the most common use cases, the default
806	>	* implementation of this method returns {@code true} when the
807	>	* number of registered parties has become zero as the result of a
808	>	* party invoking {@code arriveAndDeregister}.  You can disable
809	>	* this behavior, thus enabling continuation upon future
810	>	* registrations, by overriding this method to always return
811	>	* {@code false}:
812	>	*
813	>	* <pre> {@code
814	>	* Phaser phaser = new Phaser() {
815	>	*   protected boolean onAdvance(int phase, int parties) { return false; }
816	>	* }}</pre>
817	>	*
818	>	* @param phase the current phase number on entry to this method,
819	>	* before this phaser is advanced
820	>	* @param registeredParties the current number of registered parties
821	>	* @return {@code true} if this phaser should terminate
822		*/
823		protected boolean onAdvance(int phase, int registeredParties) {
824	<	return registeredParties <= 0;
824	>	return registeredParties == 0;
825		}
826
827		/**
828	<	* Returns a string identifying this barrier, as well as its
828	>	* Returns a string identifying this phaser, as well as its
829		* state.  The state, in brackets, includes the String {@code
830	<	* "phase ="} followed by the phase number, {@code "parties ="}
830	>	* "phase = "} followed by the phase number, {@code "parties = "}
831		* followed by the number of registered parties, and {@code
832	<	* "arrived ="} followed by the number of arrived parties
832	>	* "arrived = "} followed by the number of arrived parties.
833		*
834	<	* @return a string identifying this barrier, as well as its state
834	>	* @return a string identifying this phaser, as well as its state
835		*/
836		public String toString() {
837	<	long s = state.get();
475	<	return super.toString() + "[phase = " + phaseOf(s) + " parties = " + partiesOf(s) + " arrived = " + arrivedOf(s) + "]";
837	>	return stateToString(reconcileState());
838		}
839
478	–	// methods for tripping and waiting
479	–
840		/**
841	<	* Advance the current phase (or terminate)
841	>	* Implementation of toString and string-based error messages
842		*/
843	<	private void trip(int phase, int parties) {
844	<	int next = onAdvance(phase, parties)? -1 : ((phase + 1) & phaseMask);
845	<	state.set(stateFor(next, parties, parties));
846	<	if (head.get() != null)
847	<	releaseWaiters(next);
843	>	private String stateToString(long s) {
844	>	return super.toString() +
845	>	"[phase = " + phaseOf(s) +
846	>	" parties = " + partiesOf(s) +
847	>	" arrived = " + arrivedOf(s) + "]";
848		}
849
850	<	private int helpingWait(int phase) {
851	<	final AtomicLong state = this.state;
852	<	int p;
853	<	while ((p = phaseOf(state.get())) == phase) {
854	<	ForkJoinTask<?> t = ForkJoinWorkerThread.pollTask();
855	<	if (t != null) {
856	<	if ((p = phaseOf(state.get())) == phase)
857	<	t.exec();
858	<	else {   // push task and exit if barrier advanced
859	<	t.fork();
860	<	break;
861	<	}
850	>	// Waiting mechanics
851	>
852	>	/**
853	>	* Removes and signals threads from queue for phase.
854	>	*/
855	>	private void releaseWaiters(int phase) {
856	>	QNode q;   // first element of queue
857	>	int p;     // its phase
858	>	Thread t;  // its thread
859	>	AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ;
860	>	while ((q = head.get()) != null &&
861	>	((p = q.phase) == phase ||
862	>	(int)(root.state >>> PHASE_SHIFT) != p)) {
863	>	if (head.compareAndSet(q, q.next) &&
864	>	(t = q.thread) != null) {
865	>	q.thread = null;
866	>	LockSupport.unpark(t);
867		}
868		}
504	–	return p;
869		}
870
871	<	private int timedHelpingWait(int phase, long nanos) throws TimeoutException {
872	<	final AtomicLong state = this.state;
873	<	long lastTime = System.nanoTime();
871	>	/** The number of CPUs, for spin control */
872	>	private static final int NCPU = Runtime.getRuntime().availableProcessors();
873	>
874	>	/**
875	>	* The number of times to spin before blocking while waiting for
876	>	* advance, per arrival while waiting. On multiprocessors, fully
877	>	* blocking and waking up a large number of threads all at once is
878	>	* usually a very slow process, so we use rechargeable spins to
879	>	* avoid it when threads regularly arrive: When a thread in
880	>	* internalAwaitAdvance notices another arrival before blocking,
881	>	* and there appear to be enough CPUs available, it spins
882	>	* SPINS_PER_ARRIVAL more times before blocking. The value trades
883	>	* off good-citizenship vs big unnecessary slowdowns.
884	>	*/
885	>	static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8;
886	>
887	>	/**
888	>	* Possibly blocks and waits for phase to advance unless aborted.
889	>	* Call only from root node.
890	>	*
891	>	* @param phase current phase
892	>	* @param node if non-null, the wait node to track interrupt and timeout;
893	>	* if null, denotes noninterruptible wait
894	>	* @return current phase
895	>	*/
896	>	private int internalAwaitAdvance(int phase, QNode node) {
897	>	releaseWaiters(phase-1);          // ensure old queue clean
898	>	boolean queued = false;           // true when node is enqueued
899	>	int lastUnarrived = 0;            // to increase spins upon change
900	>	int spins = SPINS_PER_ARRIVAL;
901	>	long s;
902		int p;
903	<	while ((p = phaseOf(state.get())) == phase) {
904	<	long now = System.nanoTime();
905	<	nanos -= now - lastTime;
906	<	lastTime = now;
907	<	if (nanos <= 0) {
908	<	if ((p = phaseOf(state.get())) == phase)
909	<	throw new TimeoutException();
910	<	else
911	<	break;
912	<	}
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;
903	>	while ((p = (int)((s = state) >>> PHASE_SHIFT)) == phase) {
904	>	if (node == null) {           // spinning in noninterruptible mode
905	>	int unarrived = (int)s & UNARRIVED_MASK;
906	>	if (unarrived != lastUnarrived &&
907	>	(lastUnarrived = unarrived) < NCPU)
908	>	spins += SPINS_PER_ARRIVAL;
909	>	boolean interrupted = Thread.interrupted();
910	>	if (interrupted || --spins < 0) { // need node to record intr
911	>	node = new QNode(this, phase, false, false, 0L);
912	>	node.wasInterrupted = interrupted;
913		}
914		}
915	+	else if (node.isReleasable()) // done or aborted
916	+	break;
917	+	else if (!queued) {           // push onto queue
918	+	AtomicReference<QNode> head = (phase & 1) == 0 ? evenQ : oddQ;
919	+	QNode q = node.next = head.get();
920	+	if ((q == null || q.phase == phase) &&
921	+	(int)(state >>> PHASE_SHIFT) == phase) // avoid stale enq
922	+	queued = head.compareAndSet(q, node);
923	+	}
924	+	else {
925	+	try {
926	+	ForkJoinPool.managedBlock(node);
927	+	} catch (InterruptedException ie) {
928	+	node.wasInterrupted = true;
929	+	}
930	+	}
931	+	}
932	+
933	+	if (node != null) {
934	+	if (node.thread != null)
935	+	node.thread = null;       // avoid need for unpark()
936	+	if (node.wasInterrupted && !node.interruptible)
937	+	Thread.currentThread().interrupt();
938	+	if ((p = (int)(state >>> PHASE_SHIFT)) == phase)
939	+	return p;                 // recheck abort
940		}
941	+	releaseWaiters(phase);
942		return p;
943		}
944
945		/**
946	<	* 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.
946	>	* Wait nodes for Treiber stack representing wait queue
947		*/
948	<	static final class QNode {
949	<	QNode next;
541	<	volatile Thread thread; // nulled to cancel wait
948	>	static final class QNode implements ForkJoinPool.ManagedBlocker {
949	>	final Phaser phaser;
950		final int phase;
951	<	QNode(Thread t, int c) {
952	<	thread = t;
953	<	phase = c;
951	>	final boolean interruptible;
952	>	final boolean timed;
953	>	boolean wasInterrupted;
954	>	long nanos;
955	>	long lastTime;
956	>	volatile Thread thread; // nulled to cancel wait
957	>	QNode next;
958	>
959	>	QNode(Phaser phaser, int phase, boolean interruptible,
960	>	boolean timed, long nanos) {
961	>	this.phaser = phaser;
962	>	this.phase = phase;
963	>	this.interruptible = interruptible;
964	>	this.nanos = nanos;
965	>	this.timed = timed;
966	>	this.lastTime = timed ? System.nanoTime() : 0L;
967	>	thread = Thread.currentThread();
968		}
547	–	}
969
970	<	private void releaseWaiters(int currentPhase) {
971	<	final AtomicReference<QNode> head = this.head;
972	<	QNode p;
973	<	while ((p = head.get()) != null && p.phase != currentPhase) {
974	<	if (head.compareAndSet(p, null)) {
975	<	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);
970	>	public boolean isReleasable() {
971	>	if (thread == null)
972	>	return true;
973	>	if (phaser.getPhase() != phase) {
974	>	thread = null;
975	>	return true;
976		}
977	+	if (Thread.interrupted())
978	+	wasInterrupted = true;
979	+	if (wasInterrupted && interruptible) {
980	+	thread = null;
981	+	return true;
982	+	}
983	+	if (timed) {
984	+	if (nanos > 0L) {
985	+	long now = System.nanoTime();
986	+	nanos -= now - lastTime;
987	+	lastTime = now;
988	+	}
989	+	if (nanos <= 0L) {
990	+	thread = null;
991	+	return true;
992	+	}
993	+	}
994	+	return false;
995		}
563	–	}
564	–
565	–	/** The number of CPUs, for spin control */
566	–	static final int NCPUS = Runtime.getRuntime().availableProcessors();
996
997	<	/**
998	<	* The number of times to spin before blocking in timed waits.
999	<	* The value is empirically derived.
1000	<	*/
1001	<	static final int maxTimedSpins = (NCPUS < 2)? 0 : 32;
1002	<
1003	<	/**
1004	<	* The number of times to spin before blocking in untimed waits.
1005	<	* This is greater than timed value because untimed waits spin
1006	<	* faster since they don't need to check times on each spin.
578	<	*/
579	<	static final int maxUntimedSpins = maxTimedSpins * 32;
997	>	public boolean block() {
998	>	if (isReleasable())
999	>	return true;
1000	>	else if (!timed)
1001	>	LockSupport.park(this);
1002	>	else if (nanos > 0)
1003	>	LockSupport.parkNanos(this, nanos);
1004	>	return isReleasable();
1005	>	}
1006	>	}
1007
1008	<	/**
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;
1008	>	// Unsafe mechanics
1009
1010	<	/**
1011	<	* Enqueues node and waits unless aborted or signalled.
1012	<	*/
1013	<	private boolean untimedWait(Thread thread, int currentPhase,
1014	<	boolean abortOnInterrupt) {
1015	<	final AtomicReference<QNode> head = this.head;
1016	<	final AtomicLong state = this.state;
1017	<	boolean wasInterrupted = false;
1018	<	QNode node = null;
1019	<	boolean queued = false;
1020	<	int spins = maxUntimedSpins;
1021	<	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;
1010	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1011	>	private static final long stateOffset =
1012	>	objectFieldOffset("state", Phaser.class);
1013	>
1014	>	private static long objectFieldOffset(String field, Class<?> klazz) {
1015	>	try {
1016	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1017	>	} catch (NoSuchFieldException e) {
1018	>	// Convert Exception to corresponding Error
1019	>	NoSuchFieldError error = new NoSuchFieldError(field);
1020	>	error.initCause(e);
1021	>	throw error;
1022		}
630	–	if (node != null)
631	–	node.thread = null;
632	–	return wasInterrupted;
1023		}
1024
1025		/**
1026	<	* Messier timeout version
1026	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1027	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
1028	>	* into a jdk.
1029	>	*
1030	>	* @return a sun.misc.Unsafe
1031		*/
1032	<	private void timedWait(Thread thread, int currentPhase, long nanos)
1033	<	throws InterruptedException, TimeoutException {
1034	<	final AtomicReference<QNode> head = this.head;
1035	<	final AtomicLong state = this.state;
1036	<	long lastTime = System.nanoTime();
1037	<	QNode node = null;
1038	<	boolean queued = false;
1039	<	int spins = maxTimedSpins;
1040	<	while (phaseOf(state.get()) == currentPhase) {
1041	<	QNode h;
1042	<	long now = System.nanoTime();
1043	<	nanos -= now - lastTime;
1044	<	lastTime = now;
1045	<	if (nanos <= 0) {
1046	<	if (node != null)
1047	<	node.thread = null;
1048	<	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	<	}
669	<	}
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;
1032	>	private static sun.misc.Unsafe getUnsafe() {
1033	>	try {
1034	>	return sun.misc.Unsafe.getUnsafe();
1035	>	} catch (SecurityException se) {
1036	>	try {
1037	>	return java.security.AccessController.doPrivileged
1038	>	(new java.security
1039	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1040	>	public sun.misc.Unsafe run() throws Exception {
1041	>	java.lang.reflect.Field f = sun.misc
1042	>	.Unsafe.class.getDeclaredField("theUnsafe");
1043	>	f.setAccessible(true);
1044	>	return (sun.misc.Unsafe) f.get(null);
1045	>	}});
1046	>	} catch (java.security.PrivilegedActionException e) {
1047	>	throw new RuntimeException("Could not initialize intrinsics",
1048	>	e.getCause());
1049		}
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;
1050		}
690	–	if (node != null)
691	–	node.thread = null;
1051		}
693	–
1052		}

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