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root/jsr166/jsr166/src/jsr166y/Phaser.java

Comparing jsr166/src/jsr166y/Phaser.java (file contents):
Revision 1.19 by jsr166, Fri Jul 24 23:47:01 2009 UTC vs.
Revision 1.43 by dl, Mon Aug 24 23:08:18 2009 UTC

#	Line 7 | Line 7
7		package jsr166y;
8
9		import java.util.concurrent.*;
10	<	import java.util.concurrent.atomic.*;
10	>
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
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>
21	<	*
22	<	* <li> The number of parties synchronizing on a phaser may vary over
23	<	* time.  A task may register to be a party at any time, and may
24	<	* deregister upon arriving at the barrier.  As is the case with most
25	<	* basic synchronization constructs, registration and deregistration
26	<	* affect only internal counts; they do not establish any further
27	<	* internal bookkeeping, so tasks cannot query whether they are
28	<	* registered. (However, you can introduce such bookkeeping by
29	<	* subclassing this class.)
30	<	*
31	<	* <li> Each generation has an associated phase value, starting at
32	<	* zero, and advancing when all parties reach the barrier (wrapping
33	<	* around to zero after reaching {@code Integer.MAX_VALUE}).
34	<	*
35	<	* <li> Like a CyclicBarrier, a Phaser may be repeatedly awaited.
36	<	* Method {@code arriveAndAwaitAdvance} has effect analogous to
37	<	* {@code CyclicBarrier.await}.  However, Phasers separate two
38	<	* aspects of coordination, that may also be invoked independently:
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	>	* <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 {@code arrive} and
48	<	*       {@code arriveAndDeregister} do not block, but return
49	<	*       the phase value current upon entry to the method.
50	<	*
51	<	*   <li> Awaiting others. Method {@code awaitAdvance} requires an
52	<	*       argument indicating the entry phase, and returns when the
53	<	*       barrier advances to a new phase.
54	<	* </ul>
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	<	* <li> Barrier actions, performed by the task triggering a phase
78	<	* advance while others may be waiting, are arranged by overriding
79	<	* method {@code onAdvance}, that also controls termination.
80	<	* Overriding this method may be used to similar but more flexible
81	<	* effect as providing a barrier action to a CyclicBarrier.
82	<	*
83	<	* <li> Phasers may enter a <em>termination</em> state in which all
84	<	* actions immediately return without updating phaser state or waiting
85	<	* for advance, and indicating (via a negative phase value) that
86	<	* execution is complete.  Termination is triggered by executing the
87	<	* overridable {@code onAdvance} method that is invoked each time the
62	<	* barrier is about to be tripped. When a Phaser is controlling an
63	<	* action with a fixed number of iterations, it is often convenient to
64	<	* override this method to cause termination when the current phase
65	<	* number reaches a threshold. Method {@code forceTermination} is also
66	<	* available to abruptly release waiting threads and allow them to
67	<	* terminate.
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> Phasers may be tiered to reduce contention. Phasers with large
89	>	* <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e., arranged
90	>	* in tree structures) to reduce contention. Phasers with large
91		* numbers of parties that would otherwise experience heavy
92	<	* synchronization contention costs may instead be arranged in trees.
93	<	* This will typically greatly increase throughput even though it
94	<	* incurs somewhat greater per-operation overhead.
95	<	*
96	<	* <li> By default, {@code awaitAdvance} continues to wait even if
97	<	* the waiting thread is interrupted. And unlike the case in
98	<	* CyclicBarriers, exceptions encountered while tasks wait
99	<	* interruptibly or with timeout do not change the state of the
100	<	* barrier. If necessary, you can perform any associated recovery
101	<	* within handlers of those exceptions, often after invoking
102	<	* {@code forceTermination}.
103	<	*
104	<	* <li>Phasers ensure lack of starvation when used by ForkJoinTasks.
105	<	*
106	<	* </ul>
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	>	* <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 Phaser may be used instead of a {@code CountDownLatch} to control
112	<	* a one-shot action serving a variable number of parties. The typical
113	<	* idiom is for the method setting this up to first register, then
114	<	* start the actions, then deregister, as in:
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
113	>	* parties. The typical idiom is for the method setting this up to
114	>	* first register, then start the actions, then deregister, as in:
115		*
116		*  <pre> {@code
117	<	* void runTasks(List<Runnable> list) {
117	>	* void runTasks(List<Runnable> tasks) {
118		*   final Phaser phaser = new Phaser(1); // "1" to register self
119	<	*   for (Runnable r : list) {
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	<	*         r.run();
103	<	*         phaser.arriveAndDeregister();   // signal completion
125	>	*         task.run();
126		*       }
127		*     }.start();
128		*   }
129		*
130	<	*   doSomethingOnBehalfOfWorkers();
131	<	*   phaser.arrive(); // allow threads to start
110	<	*   int p = phaser.arriveAndDeregister(); // deregister self  ...
111	<	*   p = phaser.awaitAdvance(p); // ... and await arrival
112	<	*   otherActions(); // do other things while tasks execute
113	<	*   phaser.awaitAdvance(p); // await final completion
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> list, final int iterations) {
138	>	* void startTasks(List<Runnable> tasks, final int iterations) {
139		*   final Phaser phaser = new Phaser() {
140	<	*     public boolean onAdvance(int phase, int registeredParties) {
140	>	*     protected boolean onAdvance(int phase, int registeredParties) {
141		*       return phase >= iterations || registeredParties == 0;
142		*     }
143		*   };
144		*   phaser.register();
145	<	*   for (Runnable r : list) {
145	>	*   for (Runnable task : tasks) {
146		*     phaser.register();
147		*     new Thread() {
148		*       public void run() {
149		*         do {
150	<	*           r.run();
150	>	*           task.run();
151		*           phaser.arriveAndAwaitAdvance();
152		*         } while(!phaser.isTerminated();
153		*       }
#	Line 138 | Line 156 | import java.util.concurrent.locks.LockSu
156		*   phaser.arriveAndDeregister(); // deregister self, don't wait
157		* }}</pre>
158		*
159	<	* <p> To create a set of tasks using a tree of Phasers,
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();
166	>	* }</pre>
167	>	*
168	>	* Related constructions may be used to await particular phase numbers
169	>	* in contexts where you are sure that the phase will never wrap around
170	>	* {@code Integer.MAX_VALUE}. For example:
171	>	*
172	>	* <pre> {@code
173	>	*   void awaitPhase(Phaser phaser, int phase) {
174	>	*     int p = phaser.register(); // assumes caller not already registered
175	>	*     while (p < phase) {
176	>	*       if (phaser.isTerminated())
177	>	*         // ... deal with unexpected termination
178	>	*       else
179	>	*         p = phaser.arriveAndAwaitAdvance();
180	>	*     }
181	>	*     phaser.arriveAndDeregister();
182	>	*   }
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 Phaser that
188	>	* Task class with a constructor accepting a phaser that
189		* it registers for upon construction:
190		*  <pre> {@code
191		* void build(Task[] actions, int lo, int hi, Phaser b) {
#	Line 170 | Line 215 | import java.util.concurrent.locks.LockSu
215		*
216		* <p><b>Implementation notes</b>: This implementation restricts the
217		* maximum number of parties to 65535. Attempts to register additional
218	<	* parties result in IllegalStateExceptions. However, you can and
218	>	* parties result in {@code IllegalStateException}. However, you can and
219		* should create tiered phasers to accommodate arbitrarily large sets
220		* of participants.
221		*
#	Line 204 | Line 249 | public class Phaser {
249		*/
250		private volatile long state;
251
207	–	private static final int ushortBits = 16;
252		private static final int ushortMask = 0xffff;
253		private static final int phaseMask  = 0x7fffffff;
254
#	Line 248 | Line 292 | public class Phaser {
292		private final Phaser parent;
293
294		/**
295	<	* The root of Phaser tree. Equals this if not in a tree.  Used to
295	>	* The root of phaser tree. Equals this if not in a tree.  Used to
296		* support faster state push-down.
297		*/
298		private final Phaser root;
#	Line 299 | Line 343 | public class Phaser {
343		}
344
345		/**
346	<	* Creates a new Phaser without any initially registered parties,
346	>	* Creates a new phaser without any initially registered parties,
347		* initial phase number 0, and no parent. Any thread using this
348	<	* Phaser will need to first register for it.
348	>	* phaser will need to first register for it.
349		*/
350		public Phaser() {
351		this(null);
352		}
353
354		/**
355	<	* Creates a new Phaser with the given numbers of registered
355	>	* Creates a new phaser with the given numbers of registered
356		* unarrived parties, initial phase number 0, and no parent.
357		*
358		* @param parties the number of parties required to trip barrier
#	Line 320 | Line 364 | public class Phaser {
364		}
365
366		/**
367	<	* Creates a new Phaser with the given parent, without any
367	>	* Creates a new phaser with the given parent, without any
368		* initially registered parties. If parent is non-null this phaser
369		* is registered with the parent and its initial phase number is
370		* the same as that of parent phaser.
#	Line 340 | Line 384 | public class Phaser {
384		}
385
386		/**
387	<	* Creates a new Phaser with the given parent and numbers of
387	>	* Creates a new phaser with the given parent and numbers of
388		* registered unarrived parties. If parent is non-null, this phaser
389		* is registered with the parent and its initial phase number is
390		* the same as that of parent phaser.
#	Line 367 | Line 411 | public class Phaser {
411		/**
412		* Adds a new unarrived party to this phaser.
413		*
414	<	* @return the current barrier phase number upon registration
414	>	* @return the arrival phase number to which this registration applied
415		* @throws IllegalStateException if attempting to register more
416		* than the maximum supported number of parties
417		*/
#	Line 379 | Line 423 | public class Phaser {
423		* Adds the given number of new unarrived parties to this phaser.
424		*
425		* @param parties the number of parties required to trip barrier
426	<	* @return the current barrier phase number upon registration
426	>	* @return the arrival phase number to which this registration applied
427		* @throws IllegalStateException if attempting to register more
428		* than the maximum supported number of parties
429		*/
#	Line 414 | Line 458 | public class Phaser {
458
459		/**
460		* Arrives at the barrier, but does not wait for others.  (You can
461	<	* in turn wait for others via {@link #awaitAdvance}).
461	>	* in turn wait for others via {@link #awaitAdvance}).  It is an
462	>	* unenforced usage error for an unregistered party to invoke this
463	>	* method.
464		*
465	<	* @return the barrier phase number upon entry to this method, or a
420	<	* negative value if terminated
465	>	* @return the arrival phase number, or a negative value if terminated
466		* @throws IllegalStateException if not terminated and the number
467		* of unarrived parties would become negative
468		*/
#	Line 462 | Line 507 | public class Phaser {
507		}
508
509		/**
510	<	* Arrives at the barrier, and deregisters from it, without
511	<	* waiting for others. Deregistration reduces number of parties
510	>	* Arrives at the barrier and deregisters from it without waiting
511	>	* for others. Deregistration reduces the number of parties
512		* required to trip the barrier in future phases.  If this phaser
513		* has a parent, and deregistration causes this phaser to have
514	<	* zero parties, this phaser is also deregistered from its parent.
514	>	* zero parties, this phaser also arrives at and is deregistered
515	>	* from its parent.  It is an unenforced usage error for an
516	>	* unregistered party to invoke this method.
517		*
518	<	* @return the current barrier phase number upon entry to
472	<	* this method, or a negative value if terminated
518	>	* @return the arrival phase number, or a negative value if terminated
519		* @throws IllegalStateException if not terminated and the number
520		* of registered or unarrived parties would become negative
521		*/
#	Line 519 | Line 565 | public class Phaser {
565
566		/**
567		* Arrives at the barrier and awaits others. Equivalent in effect
568	<	* to {@code awaitAdvance(arrive())}.  If you instead need to
569	<	* await with interruption of timeout, and/or deregister upon
570	<	* arrival, you can arrange them using analogous constructions.
568	>	* to {@code awaitAdvance(arrive())}.  If you need to await with
569	>	* interruption or timeout, you can arrange this with an analogous
570	>	* construction using one of the other forms of the awaitAdvance
571	>	* method.  If instead you need to deregister upon arrival use
572	>	* {@code arriveAndDeregister}. It is an unenforced usage error
573	>	* for an unregistered party to invoke this method.
574		*
575	<	* @return the phase on entry to this method
575	>	* @return the arrival phase number, or a negative number if terminated
576		* @throws IllegalStateException if not terminated and the number
577		* of unarrived parties would become negative
578		*/
#	Line 532 | Line 581 | public class Phaser {
581		}
582
583		/**
584	<	* Awaits the phase of the barrier to advance from the given
585	<	* value, or returns immediately if argument is negative or this
586	<	* barrier is terminated.
587	<	*
588	<	* @param phase the phase on entry to this method
589	<	* @return the phase on exit from this method
584	>	* Awaits the phase of the barrier to advance from the given phase
585	>	* value, returning immediately if the current phase of the
586	>	* barrier is not equal to the given phase value or this barrier
587	>	* is terminated.  It is an unenforced usage error for an
588	>	* unregistered party to invoke this method.
589	>	*
590	>	* @param phase an arrival phase number, or negative value if
591	>	* terminated; this argument is normally the value returned by a
592	>	* previous call to {@code arrive} or its variants
593	>	* @return the next arrival phase number, or a negative value
594	>	* if terminated or argument is negative
595		*/
596		public int awaitAdvance(int phase) {
597		if (phase < 0)
#	Line 553 | Line 607 | public class Phaser {
607		}
608
609		/**
610	<	* Awaits the phase of the barrier to advance from the given
611	<	* value, or returns immediately if argument is negative or this
612	<	* barrier is terminated, or throws InterruptedException if
613	<	* interrupted while waiting.
614	<	*
615	<	* @param phase the phase on entry to this method
616	<	* @return the phase on exit from this method
610	>	* Awaits the phase of the barrier to advance from the given phase
611	>	* value, throwing {@code InterruptedException} if interrupted
612	>	* while waiting, or returning immediately if the current phase of
613	>	* the barrier is not equal to the given phase value or this
614	>	* barrier is terminated. It is an unenforced usage error for an
615	>	* unregistered party to invoke this method.
616	>	*
617	>	* @param phase an arrival phase number, or negative value if
618	>	* terminated; this argument is normally the value returned by a
619	>	* previous call to {@code arrive} or its variants
620	>	* @return the next arrival phase number, or a negative value
621	>	* if terminated or argument is negative
622		* @throws InterruptedException if thread interrupted while waiting
623		*/
624		public int awaitAdvanceInterruptibly(int phase)
#	Line 576 | Line 635 | public class Phaser {
635		}
636
637		/**
638	<	* Awaits the phase of the barrier to advance from the given value
639	<	* or the given timeout elapses, or returns immediately if
640	<	* argument is negative or this barrier is terminated.
641	<	*
642	<	* @param phase the phase on entry to this method
643	<	* @return the phase on exit from this method
638	>	* Awaits the phase of the barrier to advance from the given phase
639	>	* value or the given timeout to elapse, throwing {@code
640	>	* InterruptedException} if interrupted while waiting, or
641	>	* returning immediately if the current phase of the barrier is
642	>	* not equal to the given phase value or this barrier is
643	>	* terminated.  It is an unenforced usage error for an
644	>	* unregistered party to invoke this method.
645	>	*
646	>	* @param phase an arrival phase number, or negative value if
647	>	* terminated; this argument is normally the value returned by a
648	>	* previous call to {@code arrive} or its variants
649	>	* @param timeout how long to wait before giving up, in units of
650	>	*        {@code unit}
651	>	* @param unit a {@code TimeUnit} determining how to interpret the
652	>	*        {@code timeout} parameter
653	>	* @return the next arrival phase number, or a negative value
654	>	* if terminated or argument is negative
655		* @throws InterruptedException if thread interrupted while waiting
656		* @throws TimeoutException if timed out while waiting
657		*/
#	Line 635 | Line 705 | public class Phaser {
705		}
706
707		/**
638	–	* Returns {@code true} if the current phase number equals the given phase.
639	–	*
640	–	* @param phase the phase
641	–	* @return {@code true} if the current phase number equals the given phase
642	–	*/
643	–	public final boolean hasPhase(int phase) {
644	–	return phaseOf(getReconciledState()) == phase;
645	–	}
646	–
647	–	/**
708		* Returns the number of parties registered at this barrier.
709		*
710		* @return the number of parties
#	Line 654 | Line 714 | public class Phaser {
714		}
715
716		/**
717	<	* Returns the number of parties that have arrived at the current
718	<	* phase of this barrier.
717	>	* Returns the number of registered parties that have arrived at
718	>	* the current phase of this barrier.
719		*
720		* @return the number of arrived parties
721		*/
#	Line 674 | Line 734 | public class Phaser {
734		}
735
736		/**
737	<	* Returns the parent of this phaser, or null if none.
737	>	* Returns the parent of this phaser, or {@code null} if none.
738		*
739	<	* @return the parent of this phaser, or null if none
739	>	* @return the parent of this phaser, or {@code null} if none
740		*/
741		public Phaser getParent() {
742		return parent;
#	Line 702 | Line 762 | public class Phaser {
762		}
763
764		/**
765	<	* Overridable method to perform an action upon phase advance, and
766	<	* to control termination. This method is invoked whenever the
767	<	* barrier is tripped (and thus all other waiting parties are
768	<	* dormant). If it returns true, then, rather than advance the
769	<	* phase number, this barrier will be set to a final termination
770	<	* state, and subsequent calls to {@code isTerminated} will
771	<	* return true.
765	>	* Overridable method to perform an action upon impending phase
766	>	* advance, and to control termination. This method is invoked
767	>	* upon arrival of the party tripping the barrier (when all other
768	>	* waiting parties are dormant).  If this method returns {@code
769	>	* true}, then, rather than advance the phase number, this barrier
770	>	* will be set to a final termination state, and subsequent calls
771	>	* to {@link #isTerminated} will return true. Any (unchecked)
772	>	* Exception or Error thrown by an invocation of this method is
773	>	* propagated to the party attempting to trip the barrier, in
774	>	* which case no advance occurs.
775	>	*
776	>	* <p>The arguments to this method provide the state of the phaser
777	>	* prevailing for the current transition. (When called from within
778	>	* an implementation of {@code onAdvance} the values returned by
779	>	* methods such as {@code getPhase} may or may not reliably
780	>	* indicate the state to which this transition applies.)
781		*
782	<	* <p> The default version returns true when the number of
782	>	* <p>The default version returns {@code true} when the number of
783		* registered parties is zero. Normally, overrides that arrange
784		* termination for other reasons should also preserve this
785		* property.
786		*
787	<	* <p> You may override this method to perform an action with side
788	<	* effects visible to participating tasks, but it is in general
789	<	* only sensible to do so in designs where all parties register
790	<	* before any arrive, and all {@code awaitAdvance} at each phase.
791	<	* Otherwise, you cannot ensure lack of interference. In
792	<	* particular, this method may be invoked more than once per
793	<	* transition if other parties successfully register while the
725	<	* invocation of this method is in progress, thus postponing the
726	<	* transition until those parties also arrive, re-triggering this
727	<	* method.
787	>	* <p>You may override this method to perform an action with side
788	>	* effects visible to participating tasks, but doing so requires
789	>	* care: Method {@code onAdvance} may be invoked more than once
790	>	* per transition.  Further, unless all parties register before
791	>	* any arrive, and all {@link #awaitAdvance} at each phase, then
792	>	* you cannot ensure lack of interference from other parties
793	>	* during the invocation of this method.
794		*
795		* @param phase the phase number on entering the barrier
796		* @param registeredParties the current number of registered parties
#	Line 929 | Line 995 | public class Phaser {
995		return p;
996		}
997
998	<	// Unsafe mechanics for jsr166y 3rd party package.
998	>	// Unsafe mechanics
999	>
1000	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1001	>	private static final long stateOffset =
1002	>	objectFieldOffset("state", Phaser.class);
1003	>
1004	>	private final boolean casState(long cmp, long val) {
1005	>	return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
1006	>	}
1007	>
1008	>	private static long objectFieldOffset(String field, Class<?> klazz) {
1009	>	try {
1010	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1011	>	} catch (NoSuchFieldException e) {
1012	>	// Convert Exception to corresponding Error
1013	>	NoSuchFieldError error = new NoSuchFieldError(field);
1014	>	error.initCause(e);
1015	>	throw error;
1016	>	}
1017	>	}
1018	>
1019	>	/**
1020	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1021	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
1022	>	* into a jdk.
1023	>	*
1024	>	* @return a sun.misc.Unsafe
1025	>	*/
1026		private static sun.misc.Unsafe getUnsafe() {
1027		try {
1028		return sun.misc.Unsafe.getUnsafe();
1029		} catch (SecurityException se) {
1030		try {
1031		return java.security.AccessController.doPrivileged
1032	<	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1032	>	(new java.security
1033	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1034		public sun.misc.Unsafe run() throws Exception {
1035	<	return getUnsafeByReflection();
1035	>	java.lang.reflect.Field f = sun.misc
1036	>	.Unsafe.class.getDeclaredField("theUnsafe");
1037	>	f.setAccessible(true);
1038	>	return (sun.misc.Unsafe) f.get(null);
1039		}});
1040		} catch (java.security.PrivilegedActionException e) {
1041		throw new RuntimeException("Could not initialize intrinsics",
#	Line 946 | Line 1043 | public class Phaser {
1043		}
1044		}
1045		}
949	–
950	–	private static sun.misc.Unsafe getUnsafeByReflection()
951	–	throws NoSuchFieldException, IllegalAccessException {
952	–	java.lang.reflect.Field f =
953	–	sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
954	–	f.setAccessible(true);
955	–	return (sun.misc.Unsafe) f.get(null);
956	–	}
957	–
958	–	private static long fieldOffset(String fieldName, Class<?> klazz) {
959	–	try {
960	–	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName));
961	–	} catch (NoSuchFieldException e) {
962	–	// Convert Exception to Error
963	–	NoSuchFieldError error = new NoSuchFieldError(fieldName);
964	–	error.initCause(e);
965	–	throw error;
966	–	}
967	–	}
968	–
969	–	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
970	–	static final long stateOffset =
971	–	fieldOffset("state", Phaser.class);
972	–
973	–	final boolean casState(long cmp, long val) {
974	–	return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
975	–	}
1046		}

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