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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 1.58 by dl, Wed Nov 24 15:48:01 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 {@code Phaser} has an associated phase number. The
38	>	* phase number starts at zero, and advances when all parties arrive
39	>	* at the barrier, 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 barrier 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 at a
49	>	*       barrier. These methods do not block, but return an associated
50	>	*       <em>arrival phase number</em>; that is, the phase number of
51	>	*       the barrier to which the arrival applied. When the final
52	>	*       party for a given phase arrives, an optional barrier action
53	>	*       is performed and the phase advances.  Barrier actions,
54	>	*       performed by the party triggering a phase advance, are
55	>	*       arranged by overriding method {@link #onAdvance(int, int)},
56	>	*       which also controls termination. Overriding this method is
57	>	*       similar to, but more flexible than, providing a barrier
58	>	*       action to a {@code CyclicBarrier}.
59	>	*
60	>	*   <li> <b>Waiting.</b> Method {@link #awaitAdvance} requires an
61	>	*       argument indicating an arrival phase number, and returns when
62	>	*       the barrier 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 barrier. 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 {@code Phaser} may enter a
78	+	* <em>termination</em> state in which all synchronization methods
79	+	* immediately return without updating phaser state or waiting for
80	+	* advance, and indicating (via a negative phase value) that execution
81	+	* is complete.  Termination is triggered when an invocation of {@code
82	+	* onAdvance} returns {@code true}.  As illustrated below, when
83	+	* phasers control actions with a fixed number of iterations, it is
84	+	* often convenient to override this method to cause termination when
85	+	* the current phase number reaches a threshold. Method {@link
86	+	* #forceTermination} is also available to abruptly release waiting
87	+	* threads and allow them to terminate.
88		*
89	<	* <li> Barrier actions, performed by the task triggering a phase
90	<	* advance while others may be waiting, are arranged by overriding
91	<	* method <tt>onAdvance</tt>, that also controls termination.
92	<	*
93	<	* <li> Phasers may enter a <em>termination</em> state in which all
94	<	* await actions immediately return, indicating (via a negative phase
95	<	* 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.
89	>	* <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e.,
90	>	* constructed in tree structures) to reduce contention. Phasers with
91	>	* large numbers of parties that would otherwise experience heavy
92	>	* synchronization contention costs may instead be set up so that
93	>	* groups of sub-phasers share a common parent.  This may greatly
94	>	* increase throughput even though it incurs greater per-operation
95	>	* overhead.
96		*
97	<	* </ul>
97	>	* <p><b>Monitoring.</b> While synchronization methods may be invoked
98	>	* only by registered parties, the current state of a phaser may be
99	>	* monitored by any caller.  At any given moment there are {@link
100	>	* #getRegisteredParties} parties in total, of which {@link
101	>	* #getArrivedParties} have arrived at the current phase ({@link
102	>	* #getPhase}).  When the remaining ({@link #getUnarrivedParties})
103	>	* parties arrive, the phase advances.  The values returned by these
104	>	* methods may reflect transient states and so are not in general
105	>	* useful for synchronization control.  Method {@link #toString}
106	>	* returns snapshots of these state queries in a form convenient for
107	>	* informal monitoring.
108	>	*
109	>	* <p><b>Sample usages:</b>
110	>	*
111	>	* <p>A {@code Phaser} may be used instead of a {@code CountDownLatch}
112	>	* to control a one-shot action serving a variable number of parties.
113	>	* The typical idiom is for the method setting this up to first
114	>	* register, then start the actions, then deregister, as in:
115	>	*
116	>	*  <pre> {@code
117	>	* void runTasks(List<Runnable> tasks) {
118	>	*   final Phaser phaser = new Phaser(1); // "1" to register self
119	>	*   // create and start threads
120	>	*   for (Runnable task : tasks) {
121	>	*     phaser.register();
122	>	*     new Thread() {
123	>	*       public void run() {
124	>	*         phaser.arriveAndAwaitAdvance(); // await all creation
125	>	*         task.run();
126	>	*       }
127	>	*     }.start();
128	>	*   }
129	>	*
130	>	*   // allow threads to start and deregister self
131	>	*   phaser.arriveAndDeregister();
132	>	* }}</pre>
133	>	*
134	>	* <p>One way to cause a set of threads to repeatedly perform actions
135	>	* for a given number of iterations is to override {@code onAdvance}:
136	>	*
137	>	*  <pre> {@code
138	>	* void startTasks(List<Runnable> tasks, final int iterations) {
139	>	*   final Phaser phaser = new Phaser() {
140	>	*     protected boolean onAdvance(int phase, int registeredParties) {
141	>	*       return phase >= iterations || registeredParties == 0;
142	>	*     }
143	>	*   };
144	>	*   phaser.register();
145	>	*   for (final Runnable task : tasks) {
146	>	*     phaser.register();
147	>	*     new Thread() {
148	>	*       public void run() {
149	>	*         do {
150	>	*           task.run();
151	>	*           phaser.arriveAndAwaitAdvance();
152	>	*         } while (!phaser.isTerminated());
153	>	*       }
154	>	*     }.start();
155	>	*   }
156	>	*   phaser.arriveAndDeregister(); // deregister self, don't wait
157	>	* }}</pre>
158		*
159	<	* <p><b>Sample usage:</b>
159	>	* If the main task must later await termination, it
160	>	* may re-register and then execute a similar loop:
161	>	*  <pre> {@code
162	>	*   // ...
163	>	*   phaser.register();
164	>	*   while (!phaser.isTerminated())
165	>	*     phaser.arriveAndAwaitAdvance();}</pre>
166		*
167	<	* <p>[todo: non-FJ example]
167	>	* <p>Related constructions may be used to await particular phase numbers
168	>	* in contexts where you are sure that the phase will never wrap around
169	>	* {@code Integer.MAX_VALUE}. For example:
170		*
171	<	* <p> A Phaser may be used to support a style of programming in
172	<	* which a task waits for others to complete, without otherwise
173	<	* needing to keep track of which tasks it is waiting for. This is
174	<	* similar to the "sync" construct in Cilk and "clocks" in X10.
175	<	* Special constructions based on such barriers are available using
176	<	* the <tt>LinkedAsyncAction</tt> and <tt>CyclicAction</tt> classes,
177	<	* but they can be useful in other contexts as well.  For a simple
178	<	* (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();
171	>	*  <pre> {@code
172	>	* void awaitPhase(Phaser phaser, int phase) {
173	>	*   int p = phaser.register(); // assumes caller not already registered
174	>	*   while (p < phase) {
175	>	*     if (phaser.isTerminated())
176	>	*       // ... deal with unexpected termination
177	>	*     else
178	>	*       p = phaser.arriveAndAwaitAdvance();
179		*   }
180	<	*   protected void compute() {
181	<	*     int n = argument;
182	<	*     if (n &lt;= 1)
183	<	*        result = n;
184	<	*     else {
185	<	*        Phaser childBarrier = new Phaser(1);
186	<	*        BarrierFibonacci f1 = new BarrierFibonacci(n - 1, childBarrier);
187	<	*        BarrierFibonacci f2 = new BarrierFibonacci(n - 2, childBarrier);
188	<	*        f1.fork();
189	<	*        f2.fork();
190	<	*        childBarrier.arriveAndAwait();
191	<	*        result = f1.result + f2.result;
180	>	*   phaser.arriveAndDeregister();
181	>	* }}</pre>
182	>	*
183	>	*
184	>	* <p>To create a set of tasks using a tree of phasers,
185	>	* you could use code of the following form, assuming a
186	>	* Task class with a constructor accepting a phaser that
187	>	* it registers with upon construction:
188	>	*
189	>	*  <pre> {@code
190	>	* void build(Task[] actions, int lo, int hi, Phaser ph) {
191	>	*   if (hi - lo > TASKS_PER_PHASER) {
192	>	*     for (int i = lo; i < hi; i += TASKS_PER_PHASER) {
193	>	*       int j = Math.min(i + TASKS_PER_PHASER, hi);
194	>	*       build(actions, i, j, new Phaser(ph));
195		*     }
196	<	*     parentBarrier.arriveAndDeregister();
196	>	*   } else {
197	>	*     for (int i = lo; i < hi; ++i)
198	>	*       actions[i] = new Task(ph);
199	>	*       // assumes new Task(ph) performs ph.register()
200		*   }
201		* }
202	<	* </pre>
202	>	* // .. initially called, for n tasks via
203	>	* build(new Task[n], 0, n, new Phaser());}</pre>
204	>	*
205	>	* The best value of {@code TASKS_PER_PHASER} depends mainly on
206	>	* expected barrier synchronization rates. A value as low as four may
207	>	* be appropriate for extremely small per-barrier task bodies (thus
208	>	* high rates), or up to hundreds for extremely large ones.
209		*
210		* <p><b>Implementation notes</b>: This implementation restricts the
211	<	* maximum number of parties to 65535. Attempts to register
212	<	* additional parties result in IllegalStateExceptions.
211	>	* maximum number of parties to 65535. Attempts to register additional
212	>	* parties result in {@code IllegalStateException}. However, you can and
213	>	* should create tiered phasers to accommodate arbitrarily large sets
214	>	* of participants.
215	>	*
216	>	* @since 1.7
217	>	* @author Doug Lea
218		*/
219		public class Phaser {
220		/*
221		* This class implements an extension of X10 "clocks".  Thanks to
222	<	* Vijay Saraswat for the idea of applying it to ForkJoinTasks,
223	<	* and to Vivek Sarkar for enhancements to extend functionality.
222	>	* Vijay Saraswat for the idea, and to Vivek Sarkar for
223	>	* enhancements to extend functionality.
224		*/
225
226		/**
227		* Barrier state representation. Conceptually, a barrier contains
228		* four values:
229		*
230	<	* * parties -- the number of parties to wait (16 bits)
231	<	* * unarrived -- the number of parties yet to hit barrier (16 bits)
232	<	* * phase -- the generation of the barrier (31 bits)
233	<	* * terminated -- set if barrier is terminated (1 bit)
230	>	* * unarrived -- the number of parties yet to hit barrier (bits  0-15)
231	>	* * parties -- the number of parties to wait              (bits 16-31)
232	>	* * phase -- the generation of the barrier                (bits 32-62)
233	>	* * terminated -- set if barrier is terminated            (bit  63 / sign)
234		*
235		* However, to efficiently maintain atomicity, these values are
236	<	* packed into a single AtomicLong. Termination uses the sign bit
237	<	* of 32 bit representation of phase, so phase is set to -1 on
238	<	* termination.
239	<	*/
240	<	private final AtomicLong state;
241	<
242	<	/**
243	<	* Head of Treiber stack for waiting nonFJ threads.
244	<	*/
245	<	private final AtomicReference<QNode> head = new AtomicReference<QNode>();
236	>	* packed into a single (atomic) long. Termination uses the sign
237	>	* bit of 32 bit representation of phase, so phase is set to -1 on
238	>	* termination. Good performance relies on keeping state decoding
239	>	* and encoding simple, and keeping race windows short.
240	>	*/
241	>	private volatile long state;
242	>
243	>	private static final int  MAX_PARTIES    = 0xffff;
244	>	private static final int  MAX_PHASE      = 0x7fffffff;
245	>	private static final int  PARTIES_SHIFT  = 16;
246	>	private static final int  PHASE_SHIFT    = 32;
247	>	private static final int  UNARRIVED_MASK = 0xffff;
248	>	private static final long PARTIES_MASK   = 0xffff0000L; // for masking long
249	>	private static final long ONE_ARRIVAL    = 1L;
250	>	private static final long ONE_PARTY      = 1L << PARTIES_SHIFT;
251	>	private static final long TERMINATION_PHASE  = -1L << PHASE_SHIFT;
252
253	<	private static final int ushortBits = 16;
148	<	private static final int ushortMask =  (1 << ushortBits) - 1;
149	<	private static final int phaseMask = 0x7fffffff;
253	>	// The following unpacking methods are usually manually inlined
254
255		private static int unarrivedOf(long s) {
256	<	return (int)(s & ushortMask);
256	>	return (int)s & UNARRIVED_MASK;
257		}
258
259		private static int partiesOf(long s) {
260	<	return (int)(s & (ushortMask << 16)) >>> 16;
260	>	return (int)s >>> PARTIES_SHIFT;
261		}
262
263		private static int phaseOf(long s) {
264	<	return (int)(s >>> 32);
264	>	return (int) (s >>> PHASE_SHIFT);
265		}
266
267		private static int arrivedOf(long s) {
268		return partiesOf(s) - unarrivedOf(s);
269		}
270
271	<	private static long stateFor(int phase, int parties, int unarrived) {
272	<	return (((long)phase) << 32) | ((parties << 16) | unarrived);
271	>	/**
272	>	* The parent of this phaser, or null if none
273	>	*/
274	>	private final Phaser parent;
275	>
276	>	/**
277	>	* The root of phaser tree. Equals this if not in a tree.  Used to
278	>	* support faster state push-down.
279	>	*/
280	>	private final Phaser root;
281	>
282	>	/**
283	>	* Heads of Treiber stacks for waiting threads. To eliminate
284	>	* contention when releasing some threads while adding others, we
285	>	* use two of them, alternating across even and odd phases.
286	>	* Subphasers share queues with root to speed up releases.
287	>	*/
288	>	private final AtomicReference<QNode> evenQ;
289	>	private final AtomicReference<QNode> oddQ;
290	>
291	>	private AtomicReference<QNode> queueFor(int phase) {
292	>	return ((phase & 1) == 0) ? evenQ : oddQ;
293	>	}
294	>
295	>	/**
296	>	* Main implementation for methods arrive and arriveAndDeregister.
297	>	* Manually tuned to speed up and minimize race windows for the
298	>	* common case of just decrementing unarrived field.
299	>	*
300	>	* @param adj - adjustment to apply to state -- either
301	>	* ONE_ARRIVAL (for arrive) or
302	>	* ONE_ARRIVAL|ONE_PARTY (for arriveAndDeregister)
303	>	*/
304	>	private int doArrive(long adj) {
305	>	for (;;) {
306	>	long s = state;
307	>	int phase = (int)(s >>> PHASE_SHIFT);
308	>	if (phase < 0)
309	>	return phase;
310	>	int unarrived = (int)s & UNARRIVED_MASK;
311	>	if (unarrived == 0)
312	>	checkBadArrive(s);
313	>	else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) {
314	>	if (unarrived == 1) {
315	>	long p = s & PARTIES_MASK; // unshifted parties field
316	>	long lu = p >>> PARTIES_SHIFT;
317	>	int u = (int)lu;
318	>	int nextPhase = (phase + 1) & MAX_PHASE;
319	>	long next = ((long)nextPhase << PHASE_SHIFT) | p | lu;
320	>	final Phaser parent = this.parent;
321	>	if (parent == null) {
322	>	if (onAdvance(phase, u))
323	>	next |= TERMINATION_PHASE; // obliterate phase
324	>	UNSAFE.compareAndSwapLong(this, stateOffset, s, next);
325	>	releaseWaiters(phase);
326	>	}
327	>	else {
328	>	parent.doArrive((u == 0) ?
329	>	ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL);
330	>	if ((int)(parent.state >>> PHASE_SHIFT) != nextPhase ||
331	>	((int)(state >>> PHASE_SHIFT) != nextPhase &&
332	>	!UNSAFE.compareAndSwapLong(this, stateOffset,
333	>	s, next)))
334	>	reconcileState();
335	>	}
336	>	}
337	>	return phase;
338	>	}
339	>	}
340	>	}
341	>
342	>	/**
343	>	* Rechecks state and throws bounds exceptions on arrival -- called
344	>	* only if unarrived is apparently zero.
345	>	*/
346	>	private void checkBadArrive(long s) {
347	>	if (reconcileState() == s)
348	>	throw new IllegalStateException
349	>	("Attempted arrival of unregistered party for " +
350	>	stateToString(s));
351	>	}
352	>
353	>	/**
354	>	* Implementation of register, bulkRegister
355	>	*
356	>	* @param registrations number to add to both parties and
357	>	* unarrived fields. Must be greater than zero.
358	>	*/
359	>	private int doRegister(int registrations) {
360	>	// adjustment to state
361	>	long adj = ((long)registrations << PARTIES_SHIFT) | registrations;
362	>	final Phaser parent = this.parent;
363	>	for (;;) {
364	>	long s = (parent == null) ? state : reconcileState();
365	>	int parties = (int)s >>> PARTIES_SHIFT;
366	>	int phase = (int)(s >>> PHASE_SHIFT);
367	>	if (phase < 0)
368	>	return phase;
369	>	else if (parties != 0 && ((int)s & UNARRIVED_MASK) == 0)
370	>	internalAwaitAdvance(phase, null); // wait for onAdvance
371	>	else if (registrations > MAX_PARTIES - parties)
372	>	throw new IllegalStateException(badRegister(s));
373	>	else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s + adj))
374	>	return phase;
375	>	}
376	>	}
377	>
378	>	/**
379	>	* Returns message string for out of bounds exceptions on registration.
380	>	*/
381	>	private String badRegister(long s) {
382	>	return "Attempt to register more than " +
383	>	MAX_PARTIES + " parties for " + stateToString(s);
384		}
385
386	<	private static IllegalStateException badBounds(int parties, int unarrived) {
387	<	return new IllegalStateException("Attempt to set " + unarrived +
388	<	" unarrived of " + parties + " parties");
386	>	/**
387	>	* Recursively resolves lagged phase propagation from root if necessary.
388	>	*/
389	>	private long reconcileState() {
390	>	Phaser par = parent;
391	>	long s = state;
392	>	if (par != null) {
393	>	Phaser rt = root;
394	>	int phase, rPhase;
395	>	while ((phase = (int)(s >>> PHASE_SHIFT)) >= 0 &&
396	>	(rPhase = (int)(rt.state >>> PHASE_SHIFT)) != phase) {
397	>	if ((int)(par.state >>> PHASE_SHIFT) != rPhase)
398	>	par.reconcileState();
399	>	else if (rPhase < 0 || ((int)s & UNARRIVED_MASK) == 0) {
400	>	long u = s & PARTIES_MASK; // reset unarrived to parties
401	>	long next = ((((long) rPhase) << PHASE_SHIFT) | u |
402	>	(u >>> PARTIES_SHIFT));
403	>	if (state == s &&
404	>	UNSAFE.compareAndSwapLong(this, stateOffset,
405	>	s, s = next))
406	>	break;
407	>	}
408	>	s = state;
409	>	}
410	>	}
411	>	return s;
412		}
413
414		/**
415	<	* Creates a new Phaser without any initially registered parties,
416	<	* and initial phase number 0.
415	>	* Creates a new phaser without any initially registered parties,
416	>	* initial phase number 0, and no parent. Any thread using this
417	>	* phaser will need to first register for it.
418		*/
419		public Phaser() {
420	<	state = new AtomicLong(stateFor(0, 0, 0));
420	>	this(null, 0);
421		}
422
423		/**
424	<	* Creates a new Phaser with the given numbers of registered
425	<	* unarrived parties and initial phase number 0.
426	<	* @param parties the number of parties required to trip barrier.
424	>	* Creates a new phaser with the given number of registered
425	>	* unarrived parties, initial phase number 0, and no parent.
426	>	*
427	>	* @param parties the number of parties required to trip barrier
428		* @throws IllegalArgumentException if parties less than zero
429	<	* or greater than the maximum number of parties supported.
429	>	* or greater than the maximum number of parties supported
430		*/
431		public Phaser(int parties) {
432	<	if (parties < 0 || parties > ushortMask)
432	>	this(null, parties);
433	>	}
434	>
435	>	/**
436	>	* Equivalent to {@link #Phaser(Phaser, int) Phaser(parent, 0)}.
437	>	*
438	>	* @param parent the parent phaser
439	>	*/
440	>	public Phaser(Phaser parent) {
441	>	this(parent, 0);
442	>	}
443	>
444	>	/**
445	>	* Creates a new phaser with the given parent and number of
446	>	* registered unarrived parties. If parent is non-null, this
447	>	* phaser is registered with the parent and its initial phase
448	>	* number is the same as that of parent phaser.  If the number of
449	>	* parties is zero, the parent phaser will not proceed until this
450	>	* child phaser registers parties and advances, or this child
451	>	* phaser deregisters with its parent, or the parent is otherwise
452	>	* terminated.  This child Phaser will be deregistered from its
453	>	* parent automatically upon any invocation of the child's {@link
454	>	* #arriveAndDeregister} method that results in the child's number
455	>	* of registered parties becoming zero. (Although rarely
456	>	* appropriate, this child may also explicity deregister from its
457	>	* parent using {@code getParent().arriveAndDeregister()}.)  After
458	>	* deregistration, the child cannot re-register. (Instead, you can
459	>	* create a new child Phaser.)
460	>	*
461	>	* @param parent the parent phaser
462	>	* @param parties the number of parties required to trip barrier
463	>	* @throws IllegalArgumentException if parties less than zero
464	>	* or greater than the maximum number of parties supported
465	>	*/
466	>	public Phaser(Phaser parent, int parties) {
467	>	if (parties >>> PARTIES_SHIFT != 0)
468		throw new IllegalArgumentException("Illegal number of parties");
469	<	state = new AtomicLong(stateFor(0, parties, parties));
469	>	int phase;
470	>	this.parent = parent;
471	>	if (parent != null) {
472	>	Phaser r = parent.root;
473	>	this.root = r;
474	>	this.evenQ = r.evenQ;
475	>	this.oddQ = r.oddQ;
476	>	phase = parent.doRegister(1);
477	>	}
478	>	else {
479	>	this.root = this;
480	>	this.evenQ = new AtomicReference<QNode>();
481	>	this.oddQ = new AtomicReference<QNode>();
482	>	phase = 0;
483	>	}
484	>	long p = (long)parties;
485	>	this.state = (((long)phase) << PHASE_SHIFT) | p | (p << PARTIES_SHIFT);
486		}
487
488		/**
489		* Adds a new unarrived party to this phaser.
490	<	* @return the current barrier phase number upon registration
490	>	* If an ongoing invocation of {@link #onAdvance} is in progress,
491	>	* this method may wait until its completion before registering.
492	>	*
493	>	* @return the arrival phase number to which this registration applied
494		* @throws IllegalStateException if attempting to register more
495	<	* than the maximum supported number of parties.
495	>	* than the maximum supported number of parties
496		*/
497	<	public int register() { // increment both parties and unarrived
498	<	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	<	}
497	>	public int register() {
498	>	return doRegister(1);
499		}
500
501		/**
502	<	* Arrives at the barrier, but does not wait for others.  (You can
503	<	* in turn wait for others via {@link #awaitAdvance}).
502	>	* Adds the given number of new unarrived parties to this phaser.
503	>	* If an ongoing invocation of {@link #onAdvance} is in progress,
504	>	* this method may wait until its completion before registering.
505		*
506	<	* @return the current barrier phase number upon entry to
507	<	* this method, or a negative value if terminated;
508	<	* @throws IllegalStateException if the number of unarrived
509	<	* parties would become negative.
506	>	* @param parties the number of additional parties required to trip barrier
507	>	* @return the arrival phase number to which this registration applied
508	>	* @throws IllegalStateException if attempting to register more
509	>	* than the maximum supported number of parties
510	>	* @throws IllegalArgumentException if {@code parties < 0}
511		*/
512	<	public int arrive() { // decrement unarrived. If zero, trip
513	<	final AtomicLong state = this.state;
514	<	for (;;) {
515	<	long s = state.get();
516	<	int phase = phaseOf(s);
517	<	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	<	}
512	>	public int bulkRegister(int parties) {
513	>	if (parties < 0)
514	>	throw new IllegalArgumentException();
515	>	if (parties == 0)
516	>	return getPhase();
517	>	return doRegister(parties);
518		}
519
520		/**
521	<	* Arrives at the barrier, and deregisters from it, without
522	<	* waiting for others.
521	>	* Arrives at the barrier, but does not wait for others.  (You can
522	>	* in turn wait for others via {@link #awaitAdvance}).  It is an
523	>	* unenforced usage error for an unregistered party to invoke this
524	>	* method.
525		*
526	<	* @return the current barrier phase number upon entry to
527	<	* this method, or a negative value if terminated;
528	<	* @throws IllegalStateException if the number of registered or
529	<	* unarrived parties would become negative.
530	<	*/
531	<	public int arriveAndDeregister() { // Same as arrive, plus decrement parties
254	<	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	<	}
526	>	* @return the arrival phase number, or a negative value if terminated
527	>	* @throws IllegalStateException if not terminated and the number
528	>	* of unarrived parties would become negative
529	>	*/
530	>	public int arrive() {
531	>	return doArrive(ONE_ARRIVAL);
532		}
533
534		/**
535	<	* Arrives at the barrier and awaits others. Unlike other arrival
536	<	* methods, this method returns the arrival index of the
537	<	* caller. The caller tripping the barrier returns zero, the
538	<	* previous caller 1, and so on.
539	<	* @return the arrival index
540	<	* @throws IllegalStateException if the number of unarrived
541	<	* parties would become negative.
535	>	* Arrives at the barrier and deregisters from it without waiting
536	>	* for others. Deregistration reduces the number of parties
537	>	* required to trip the barrier in future phases.  If this phaser
538	>	* has a parent, and deregistration causes this phaser to have
539	>	* zero parties, this phaser also arrives at and is deregistered
540	>	* from its parent.  It is an unenforced usage error for an
541	>	* unregistered party to invoke this method.
542	>	*
543	>	* @return the arrival phase number, or a negative value if terminated
544	>	* @throws IllegalStateException if not terminated and the number
545	>	* of registered or unarrived parties would become negative
546	>	*/
547	>	public int arriveAndDeregister() {
548	>	return doArrive(ONE_ARRIVAL|ONE_PARTY);
549	>	}
550	>
551	>	/**
552	>	* Arrives at the barrier and awaits others. Equivalent in effect
553	>	* to {@code awaitAdvance(arrive())}.  If you need to await with
554	>	* interruption or timeout, you can arrange this with an analogous
555	>	* construction using one of the other forms of the {@code
556	>	* awaitAdvance} method.  If instead you need to deregister upon
557	>	* arrival, use {@link #arriveAndDeregister}. It is an unenforced
558	>	* usage error for an unregistered party to invoke this method.
559	>	*
560	>	* @return the arrival phase number, or a negative number if terminated
561	>	* @throws IllegalStateException if not terminated and the number
562	>	* of unarrived parties would become negative
563		*/
564		public int arriveAndAwaitAdvance() {
565	<	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	<	}
565	>	return awaitAdvance(arrive());
566		}
567
568		/**
569	<	* Awaits the phase of the barrier to advance from the given
570	<	* value, or returns immediately if this barrier is terminated.
571	<	* @param phase the phase on entry to this method
572	<	* @return the phase on exit from this method
569	>	* Awaits the phase of the barrier to advance from the given phase
570	>	* value, returning immediately if the current phase of the
571	>	* barrier is not equal to the given phase value or this barrier
572	>	* is terminated.
573	>	*
574	>	* @param phase an arrival phase number, or negative value if
575	>	* terminated; this argument is normally the value returned by a
576	>	* previous call to {@code arrive} or its variants
577	>	* @return the next arrival phase number, or a negative value
578	>	* if terminated or argument is negative
579		*/
580		public int awaitAdvance(int phase) {
581		if (phase < 0)
582		return phase;
583	<	Thread current = Thread.currentThread();
584	<	if (current instanceof ForkJoinWorkerThread)
585	<	return helpingWait(phase);
312	<	if (untimedWait(current, phase, false))
313	<	current.interrupt();
314	<	return phaseOf(state.get());
583	>	long s = (parent == null) ? state : reconcileState();
584	>	int p = (int)(s >>> PHASE_SHIFT);
585	>	return (p != phase) ? p : internalAwaitAdvance(phase, null);
586		}
587
588		/**
589	<	* Awaits the phase of the barrier to advance from the given
590	<	* value, or returns immediately if this barrier is terminated, or
591	<	* throws InterruptedException if interrupted while waiting.
592	<	* @param phase the phase on entry to this method
593	<	* @return the phase on exit from this method
589	>	* Awaits the phase of the barrier to advance from the given phase
590	>	* value, throwing {@code InterruptedException} if interrupted
591	>	* while waiting, or returning immediately if the current phase of
592	>	* the barrier is not equal to the given phase value or this
593	>	* barrier is terminated.
594	>	*
595	>	* @param phase an arrival phase number, or negative value if
596	>	* terminated; this argument is normally the value returned by a
597	>	* previous call to {@code arrive} or its variants
598	>	* @return the next arrival phase number, or a negative value
599	>	* if terminated or argument is negative
600		* @throws InterruptedException if thread interrupted while waiting
601		*/
602	<	public int awaitAdvanceInterruptibly(int phase) throws InterruptedException {
602	>	public int awaitAdvanceInterruptibly(int phase)
603	>	throws InterruptedException {
604		if (phase < 0)
605		return phase;
606	<	Thread current = Thread.currentThread();
607	<	if (current instanceof ForkJoinWorkerThread)
608	<	return helpingWait(phase);
609	<	else if (Thread.interrupted() || untimedWait(current, phase, true))
610	<	throw new InterruptedException();
611	<	else
612	<	return phaseOf(state.get());
606	>	long s = (parent == null) ? state : reconcileState();
607	>	int p = (int)(s >>> PHASE_SHIFT);
608	>	if (p == phase) {
609	>	QNode node = new QNode(this, phase, true, false, 0L);
610	>	p = internalAwaitAdvance(phase, node);
611	>	if (node.wasInterrupted)
612	>	throw new InterruptedException();
613	>	}
614	>	return p;
615		}
616
617		/**
618	<	* Awaits the phase of the barrier to advance from the given value
619	<	* or the given timeout elapses, or returns immediately if this
620	<	* barrier is terminated.
621	<	* @param phase the phase on entry to this method
622	<	* @return the phase on exit from this method
618	>	* Awaits the phase of the barrier to advance from the given phase
619	>	* value or the given timeout to elapse, throwing {@code
620	>	* InterruptedException} if interrupted while waiting, or
621	>	* returning immediately if the current phase of the barrier is
622	>	* not equal to the given phase value or this barrier is
623	>	* terminated.
624	>	*
625	>	* @param phase an arrival phase number, or negative value if
626	>	* terminated; this argument is normally the value returned by a
627	>	* previous call to {@code arrive} or its variants
628	>	* @param timeout how long to wait before giving up, in units of
629	>	*        {@code unit}
630	>	* @param unit a {@code TimeUnit} determining how to interpret the
631	>	*        {@code timeout} parameter
632	>	* @return the next arrival phase number, or a negative value
633	>	* if terminated or argument is negative
634		* @throws InterruptedException if thread interrupted while waiting
635		* @throws TimeoutException if timed out while waiting
636		*/
637	<	public int awaitAdvanceInterruptibly(int phase, long timeout, TimeUnit unit)
637	>	public int awaitAdvanceInterruptibly(int phase,
638	>	long timeout, TimeUnit unit)
639		throws InterruptedException, TimeoutException {
640		if (phase < 0)
641		return phase;
642	<	long nanos = unit.toNanos(timeout);
643	<	Thread current = Thread.currentThread();
644	<	if (current instanceof ForkJoinWorkerThread)
645	<	return timedHelpingWait(phase, nanos);
646	<	timedWait(current, phase, nanos);
647	<	return phaseOf(state.get());
642	>	long s = (parent == null) ? state : reconcileState();
643	>	int p = (int)(s >>> PHASE_SHIFT);
644	>	if (p == phase) {
645	>	long nanos = unit.toNanos(timeout);
646	>	QNode node = new QNode(this, phase, true, true, nanos);
647	>	p = internalAwaitAdvance(phase, node);
648	>	if (node.wasInterrupted)
649	>	throw new InterruptedException();
650	>	else if (p == phase)
651	>	throw new TimeoutException();
652	>	}
653	>	return p;
654		}
655
656		/**
657	<	* Forces this barrier to enter termination state. Counts of
658	<	* arrived and registered parties are unaffected. This method may
659	<	* be useful for coordinating recovery after one or more tasks
657	>	* Forces this barrier to enter termination state.  Counts of
658	>	* arrived and registered parties are unaffected.  If this phaser
659	>	* is a member of a tiered set of phasers, then all of the phasers
660	>	* in the set are terminated.  If this phaser is already
661	>	* terminated, this method has no effect.  This method may be
662	>	* useful for coordinating recovery after one or more tasks
663		* encounter unexpected exceptions.
664		*/
665		public void forceTermination() {
666	<	final AtomicLong state = this.state;
667	<	for (;;) {
668	<	long s = state.get();
669	<	int phase = phaseOf(s);
670	<	int parties = partiesOf(s);
671	<	int unarrived = unarrivedOf(s);
672	<	if (phase < 0 ||
673	<	state.compareAndSet(s, stateFor(-1, parties, unarrived))) {
373	<	if (head.get() != null)
374	<	releaseWaiters(-1);
666	>	// Only need to change root state
667	>	final Phaser root = this.root;
668	>	long s;
669	>	while ((s = root.state) >= 0) {
670	>	if (UNSAFE.compareAndSwapLong(root, stateOffset,
671	>	s, s | TERMINATION_PHASE)) {
672	>	releaseWaiters(0); // signal all threads
673	>	releaseWaiters(1);
674		return;
675		}
676		}
677		}
678
679		/**
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	–	/**
680		* Returns the current phase number. The maximum phase number is
681	<	* <tt>Integer.MAX_VALUE</tt>, after which it restarts at
681	>	* {@code Integer.MAX_VALUE}, after which it restarts at
682		* zero. Upon termination, the phase number is negative.
683	+	*
684		* @return the phase number, or a negative value if terminated
685		*/
686	<	public int getPhase() {
687	<	return phaseOf(state.get());
686	>	public final int getPhase() {
687	>	return (int)(root.state >>> PHASE_SHIFT);
688		}
689
690		/**
691		* Returns the number of parties registered at this barrier.
692	+	*
693		* @return the number of parties
694		*/
695		public int getRegisteredParties() {
696	<	return partiesOf(state.get());
696	>	return partiesOf(state);
697		}
698
699		/**
700	<	* Returns the number of parties that have arrived at the current
701	<	* phase of this barrier.
700	>	* Returns the number of registered parties that have arrived at
701	>	* the current phase of this barrier.
702	>	*
703		* @return the number of arrived parties
704		*/
705		public int getArrivedParties() {
706	<	return arrivedOf(state.get());
706	>	return arrivedOf(parent==null? state : reconcileState());
707		}
708
709		/**
710		* Returns the number of registered parties that have not yet
711		* arrived at the current phase of this barrier.
712	+	*
713		* @return the number of unarrived parties
714		*/
715		public int getUnarrivedParties() {
716	<	return unarrivedOf(state.get());
716	>	return unarrivedOf(parent==null? state : reconcileState());
717	>	}
718	>
719	>	/**
720	>	* Returns the parent of this phaser, or {@code null} if none.
721	>	*
722	>	* @return the parent of this phaser, or {@code null} if none
723	>	*/
724	>	public Phaser getParent() {
725	>	return parent;
726		}
727
728		/**
729	<	* Returns true if this barrier has been terminated.
730	<	* @return true if this barrier has been terminated
729	>	* Returns the root ancestor of this phaser, which is the same as
730	>	* this phaser if it has no parent.
731	>	*
732	>	* @return the root ancestor of this phaser
733	>	*/
734	>	public Phaser getRoot() {
735	>	return root;
736	>	}
737	>
738	>	/**
739	>	* Returns {@code true} if this barrier has been terminated.
740	>	*
741	>	* @return {@code true} if this barrier has been terminated
742		*/
743		public boolean isTerminated() {
744	<	return phaseOf(state.get()) < 0;
744	>	return root.state < 0L;
745		}
746
747		/**
748	<	* Overridable method to perform an action upon phase advance, and
749	<	* to control termination. This method is invoked whenever the
750	<	* barrier is tripped (and thus all other waiting parties are
751	<	* dormant). If it returns true, then, rather than advance the
752	<	* phase number, this barrier will be set to a final termination
753	<	* state, and subsequent calls to <tt>isTerminated</tt> will
754	<	* return true.
748	>	* Overridable method to perform an action upon impending phase
749	>	* advance, and to control termination. This method is invoked
750	>	* upon arrival of the party tripping the barrier (when all other
751	>	* waiting parties are dormant).  If this method returns {@code
752	>	* true}, then, rather than advance the phase number, this barrier
753	>	* will be set to a final termination state, and subsequent calls
754	>	* to {@link #isTerminated} will return true. Any (unchecked)
755	>	* Exception or Error thrown by an invocation of this method is
756	>	* propagated to the party attempting to trip the barrier, in
757	>	* which case no advance occurs.
758		*
759	<	* <p> The default version returns true when the number of
759	>	* <p>The arguments to this method provide the state of the phaser
760	>	* prevailing for the current transition.  The effects of invoking
761	>	* arrival, registration, and waiting methods on this Phaser from
762	>	* within {@code onAdvance} are unspecified and should not be
763	>	* relied on.
764	>	*
765	>	* <p>If this Phaser is a member of a tiered set of Phasers, then
766	>	* {@code onAdvance} is invoked only for its root Phaser on each
767	>	* advance.
768	>	*
769	>	* <p>The default version returns {@code true} when the number of
770		* registered parties is zero. Normally, overrides that arrange
771		* termination for other reasons should also preserve this
772		* property.
773		*
774		* @param phase the phase number on entering the barrier
775	<	* @param registeredParties the current number of registered
776	<	* parties.
458	<	* @return true if this barrier should terminate
775	>	* @param registeredParties the current number of registered parties
776	>	* @return {@code true} if this barrier should terminate
777		*/
778		protected boolean onAdvance(int phase, int registeredParties) {
779		return registeredParties <= 0;
780		}
781
782		/**
783	<	* Returns a string identifying this barrier, as well as its
783	>	* Returns a string identifying this phaser, as well as its
784		* state.  The state, in brackets, includes the String {@code
785	<	* "phase ="} followed by the phase number, {@code "parties ="}
785	>	* "phase = "} followed by the phase number, {@code "parties = "}
786		* followed by the number of registered parties, and {@code
787	<	* "arrived ="} followed by the number of arrived parties
787	>	* "arrived = "} followed by the number of arrived parties.
788		*
789		* @return a string identifying this barrier, as well as its state
790		*/
791		public String toString() {
792	<	long s = state.get();
475	<	return super.toString() + "[phase = " + phaseOf(s) + " parties = " + partiesOf(s) + " arrived = " + arrivedOf(s) + "]";
792	>	return stateToString(reconcileState());
793		}
794
478	–	// methods for tripping and waiting
479	–
795		/**
796	<	* Advance the current phase (or terminate)
796	>	* Implementation of toString and string-based error messages
797		*/
798	<	private void trip(int phase, int parties) {
799	<	int next = onAdvance(phase, parties)? -1 : ((phase + 1) & phaseMask);
800	<	state.set(stateFor(next, parties, parties));
801	<	if (head.get() != null)
802	<	releaseWaiters(next);
798	>	private String stateToString(long s) {
799	>	return super.toString() +
800	>	"[phase = " + phaseOf(s) +
801	>	" parties = " + partiesOf(s) +
802	>	" arrived = " + arrivedOf(s) + "]";
803		}
804
805	<	private int helpingWait(int phase) {
806	<	final AtomicLong state = this.state;
805	>	// Waiting mechanics
806	>
807	>	/**
808	>	* Removes and signals threads from queue for phase.
809	>	*/
810	>	private void releaseWaiters(int phase) {
811	>	AtomicReference<QNode> head = queueFor(phase);
812	>	QNode q;
813		int p;
814	<	while ((p = phaseOf(state.get())) == phase) {
815	<	ForkJoinTask<?> t = ForkJoinWorkerThread.pollTask();
816	<	if (t != null) {
817	<	if ((p = phaseOf(state.get())) == phase)
818	<	t.exec();
498	<	else {   // push task and exit if barrier advanced
499	<	t.fork();
500	<	break;
501	<	}
502	<	}
814	>	while ((q = head.get()) != null &&
815	>	((p = q.phase) == phase ||
816	>	(int)(root.state >>> PHASE_SHIFT) != p)) {
817	>	if (head.compareAndSet(q, q.next))
818	>	q.signal();
819		}
504	–	return p;
820		}
821
822	<	private int timedHelpingWait(int phase, long nanos) throws TimeoutException {
823	<	final AtomicLong state = this.state;
824	<	long lastTime = System.nanoTime();
822	>	/** The number of CPUs, for spin control */
823	>	private static final int NCPU = Runtime.getRuntime().availableProcessors();
824	>
825	>	/**
826	>	* The number of times to spin before blocking while waiting for
827	>	* advance, per arrival while waiting. On multiprocessors, fully
828	>	* blocking and waking up a large number of threads all at once is
829	>	* usually a very slow process, so we use rechargeable spins to
830	>	* avoid it when threads regularly arrive: When a thread in
831	>	* internalAwaitAdvance notices another arrival before blocking,
832	>	* and there appear to be enough CPUs available, it spins
833	>	* SPINS_PER_ARRIVAL more times before blocking. Plus, even on
834	>	* uniprocessors, there is at least one intervening Thread.yield
835	>	* before blocking. The value trades off good-citizenship vs big
836	>	* unnecessary slowdowns.
837	>	*/
838	>	static final int SPINS_PER_ARRIVAL = (NCPU < 2) ? 1 : 1 << 8;
839	>
840	>	/**
841	>	* Possibly blocks and waits for phase to advance unless aborted.
842	>	*
843	>	* @param phase current phase
844	>	* @param node if non-null, the wait node to track interrupt and timeout;
845	>	* if null, denotes noninterruptible wait
846	>	* @return current phase
847	>	*/
848	>	private int internalAwaitAdvance(int phase, QNode node) {
849	>	Phaser current = this;       // to eventually wait at root if tiered
850	>	boolean queued = false;      // true when node is enqueued
851	>	int lastUnarrived = -1;      // to increase spins upon change
852	>	int spins = SPINS_PER_ARRIVAL;
853	>	long s;
854		int p;
855	<	while ((p = phaseOf(state.get())) == phase) {
856	<	long now = System.nanoTime();
857	<	nanos -= now - lastTime;
858	<	lastTime = now;
859	<	if (nanos <= 0) {
860	<	if ((p = phaseOf(state.get())) == phase)
861	<	throw new TimeoutException();
862	<	else
519	<	break;
855	>	while ((p = (int)((s = current.state) >>> PHASE_SHIFT)) == phase) {
856	>	Phaser par;
857	>	int unarrived = (int)s & UNARRIVED_MASK;
858	>	if (unarrived != lastUnarrived) {
859	>	if (lastUnarrived == -1) // ensure old queue clean
860	>	releaseWaiters(phase-1);
861	>	if ((lastUnarrived = unarrived) < NCPU)
862	>	spins += SPINS_PER_ARRIVAL;
863		}
864	<	ForkJoinTask<?> t = ForkJoinWorkerThread.pollTask();
865	<	if (t != null) {
866	<	if ((p = phaseOf(state.get())) == phase)
867	<	t.exec();
868	<	else {   // push task and exit if barrier advanced
869	<	t.fork();
864	>	else if (unarrived == 0 && (par = current.parent) != null) {
865	>	current = par;       // if all arrived, use parent
866	>	par = par.parent;
867	>	lastUnarrived = -1;
868	>	}
869	>	else if (spins > 0) {
870	>	if (--spins == (SPINS_PER_ARRIVAL >>> 1))
871	>	Thread.yield();  // yield midway through spin
872	>	}
873	>	else if (node == null)   // must be noninterruptible
874	>	node = new QNode(this, phase, false, false, 0L);
875	>	else if (node.isReleasable()) {
876	>	if ((p = (int)(root.state >>> PHASE_SHIFT)) != phase)
877		break;
878	+	else
879	+	return phase;    // aborted
880	+	}
881	+	else if (!queued) {      // push onto queue
882	+	AtomicReference<QNode> head = queueFor(phase);
883	+	QNode q = head.get();
884	+	if (q == null || q.phase == phase) {
885	+	node.next = q;
886	+	if ((p = (int)(root.state >>> PHASE_SHIFT)) != phase)
887	+	break;       // recheck to avoid stale enqueue
888	+	else
889	+	queued = head.compareAndSet(q, node);
890	+	}
891	+	}
892	+	else {
893	+	try {
894	+	ForkJoinPool.managedBlock(node);
895	+	} catch (InterruptedException ie) {
896	+	node.wasInterrupted = true;
897		}
898		}
899		}
900	+	releaseWaiters(phase);
901	+	if (node != null)
902	+	node.onRelease();
903		return p;
904		}
905
906		/**
907	<	* 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.
907	>	* Wait nodes for Treiber stack representing wait queue
908		*/
909	<	static final class QNode {
910	<	QNode next;
541	<	volatile Thread thread; // nulled to cancel wait
909	>	static final class QNode implements ForkJoinPool.ManagedBlocker {
910	>	final Phaser phaser;
911		final int phase;
912	<	QNode(Thread t, int c) {
913	<	thread = t;
914	<	phase = c;
912	>	final boolean interruptible;
913	>	final boolean timed;
914	>	boolean wasInterrupted;
915	>	long nanos;
916	>	long lastTime;
917	>	volatile Thread thread; // nulled to cancel wait
918	>	QNode next;
919	>
920	>	QNode(Phaser phaser, int phase, boolean interruptible,
921	>	boolean timed, long nanos) {
922	>	this.phaser = phaser;
923	>	this.phase = phase;
924	>	this.interruptible = interruptible;
925	>	this.nanos = nanos;
926	>	this.timed = timed;
927	>	this.lastTime = timed? System.nanoTime() : 0L;
928	>	thread = Thread.currentThread();
929		}
547	–	}
930
931	<	private void releaseWaiters(int currentPhase) {
932	<	final AtomicReference<QNode> head = this.head;
933	<	QNode p;
934	<	while ((p = head.get()) != null && p.phase != currentPhase) {
935	<	if (head.compareAndSet(p, null)) {
936	<	do {
937	<	Thread t = p.thread;
938	<	if (t != null) {
939	<	p.thread = null;
940	<	LockSupport.unpark(t);
931	>	public boolean isReleasable() {
932	>	Thread t = thread;
933	>	if (t != null) {
934	>	if (phaser.getPhase() != phase)
935	>	t = null;
936	>	else {
937	>	if (Thread.interrupted())
938	>	wasInterrupted = true;
939	>	if (interruptible && wasInterrupted)
940	>	t = null;
941	>	else if (timed) {
942	>	if (nanos > 0) {
943	>	long now = System.nanoTime();
944	>	nanos -= now - lastTime;
945	>	lastTime = now;
946	>	}
947	>	if (nanos <= 0)
948	>	t = null;
949		}
950	<	} while ((p = p.next) != null);
950	>	}
951	>	if (t != null)
952	>	return false;
953	>	thread = null;
954		}
955	+	return true;
956		}
563	–	}
957
958	<	/** The number of CPUs, for spin control */
959	<	static final int NCPUS = Runtime.getRuntime().availableProcessors();
958	>	public boolean block() {
959	>	if (isReleasable())
960	>	return true;
961	>	else if (!timed)
962	>	LockSupport.park(this);
963	>	else if (nanos > 0)
964	>	LockSupport.parkNanos(this, nanos);
965	>	return isReleasable();
966	>	}
967
968	<	/**
969	<	* The number of times to spin before blocking in timed waits.
970	<	* The value is empirically derived.
971	<	*/
972	<	static final int maxTimedSpins = (NCPUS < 2)? 0 : 32;
968	>	void signal() {
969	>	Thread t = thread;
970	>	if (t != null) {
971	>	thread = null;
972	>	LockSupport.unpark(t);
973	>	}
974	>	}
975
976	<	/**
977	<	* The number of times to spin before blocking in untimed waits.
978	<	* This is greater than timed value because untimed waits spin
979	<	* faster since they don't need to check times on each spin.
980	<	*/
981	<	static final int maxUntimedSpins = maxTimedSpins * 32;
976	>	void onRelease() { // actions upon return from internalAwaitAdvance
977	>	if (!interruptible && wasInterrupted)
978	>	Thread.currentThread().interrupt();
979	>	if (thread != null)
980	>	thread = null;
981	>	}
982
983	<	/**
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;
983	>	}
984
985	<	/**
986	<	* Enqueues node and waits unless aborted or signalled.
987	<	*/
988	<	private boolean untimedWait(Thread thread, int currentPhase,
989	<	boolean abortOnInterrupt) {
990	<	final AtomicReference<QNode> head = this.head;
991	<	final AtomicLong state = this.state;
992	<	boolean wasInterrupted = false;
993	<	QNode node = null;
994	<	boolean queued = false;
995	<	int spins = maxUntimedSpins;
996	<	while (phaseOf(state.get()) == currentPhase) {
997	<	QNode h;
998	<	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;
985	>	// Unsafe mechanics
986	>
987	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
988	>	private static final long stateOffset =
989	>	objectFieldOffset("state", Phaser.class);
990	>
991	>	private static long objectFieldOffset(String field, Class<?> klazz) {
992	>	try {
993	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
994	>	} catch (NoSuchFieldException e) {
995	>	// Convert Exception to corresponding Error
996	>	NoSuchFieldError error = new NoSuchFieldError(field);
997	>	error.initCause(e);
998	>	throw error;
999		}
630	–	if (node != null)
631	–	node.thread = null;
632	–	return wasInterrupted;
1000		}
1001
1002		/**
1003	<	* Messier timeout version
1003	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1004	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
1005	>	* into a jdk.
1006	>	*
1007	>	* @return a sun.misc.Unsafe
1008		*/
1009	<	private void timedWait(Thread thread, int currentPhase, long nanos)
1010	<	throws InterruptedException, TimeoutException {
1011	<	final AtomicReference<QNode> head = this.head;
1012	<	final AtomicLong state = this.state;
1013	<	long lastTime = System.nanoTime();
1014	<	QNode node = null;
1015	<	boolean queued = false;
1016	<	int spins = maxTimedSpins;
1017	<	while (phaseOf(state.get()) == currentPhase) {
1018	<	QNode h;
1019	<	long now = System.nanoTime();
1020	<	nanos -= now - lastTime;
1021	<	lastTime = now;
1022	<	if (nanos <= 0) {
1023	<	if (node != null)
1024	<	node.thread = null;
1025	<	if (phaseOf(state.get()) == currentPhase)
655	<	throw new TimeoutException();
656	<	else
657	<	break;
1009	>	private static sun.misc.Unsafe getUnsafe() {
1010	>	try {
1011	>	return sun.misc.Unsafe.getUnsafe();
1012	>	} catch (SecurityException se) {
1013	>	try {
1014	>	return java.security.AccessController.doPrivileged
1015	>	(new java.security
1016	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1017	>	public sun.misc.Unsafe run() throws Exception {
1018	>	java.lang.reflect.Field f = sun.misc
1019	>	.Unsafe.class.getDeclaredField("theUnsafe");
1020	>	f.setAccessible(true);
1021	>	return (sun.misc.Unsafe) f.get(null);
1022	>	}});
1023	>	} catch (java.security.PrivilegedActionException e) {
1024	>	throw new RuntimeException("Could not initialize intrinsics",
1025	>	e.getCause());
1026		}
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;
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;
1027		}
690	–	if (node != null)
691	–	node.thread = null;
1028		}
693	–
1029		}

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