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

Comparing jsr166/src/jsr166y/Phaser.java (file contents):
Revision 1.21 by jsr166, Sun Jul 26 05:55:34 2009 UTC vs.
Revision 1.36 by dl, Sun Aug 23 20:12:24 2009 UTC

#	Line 19 | Line 19 | import java.util.concurrent.locks.LockSu
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
22	>	* <li> The number of parties <em>registered</em> to synchronize on a
23	>	* phaser may vary over time.  Tasks may be registered at any time
24	>	* (using methods {@link #register}, {@link #bulkRegister}, or forms
25	>	* of constructors establishing initial numbers of parties), and may
26	>	* optionally be deregistered upon any arrival (using {@link
27	>	* #arriveAndDeregister}).  As is the case with most basic
28	>	* synchronization constructs, registration and deregistration affect
29	>	* only internal counts; they do not establish any further internal
30	>	* bookkeeping, so tasks cannot query whether they are
31		* registered. (However, you can introduce such bookkeeping by
32		* subclassing this class.)
33		*
34	<	* <li> Each generation has an associated phase value, starting at
35	<	* zero, and advancing when all parties reach the barrier (wrapping
36	<	* around to zero after reaching {@code Integer.MAX_VALUE}).
37	<	*
38	<	* <li> Like a CyclicBarrier, a Phaser may be repeatedly awaited.
39	<	* Method {@code arriveAndAwaitAdvance} has effect analogous to
40	<	* {@code CyclicBarrier.await}.  However, Phasers separate two
41	<	* aspects of coordination, that may also be invoked independently:
34	>	* <li> Each generation has an associated phase number. The phase
35	>	* number starts at zero, amd advances when all parties arrive at the
36	>	* barrier, wrapping around to zero after reaching {@code
37	>	* Integer.MAX_VALUE}.
38	>	*
39	>	* <li> Like a {@code CyclicBarrier}, a phaser may be repeatedly
40	>	* awaited.  Method {@link #arriveAndAwaitAdvance} has effect
41	>	* analogous to {@link java.util.concurrent.CyclicBarrier#await
42	>	* CyclicBarrier.await}.  However, phasers separate two aspects of
43	>	* coordination, which may also be invoked independently:
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.
47	>	*   <li> Arriving at a barrier. Methods {@link #arrive} and
48	>	*       {@link #arriveAndDeregister} do not block, but return
49	>	*       an associated <em>arrival phase number</em>;
50	>	*       that is, the phase number of the barrier to which the
51	>	*       arrival applied.
52	>	*
53	>	*   <li> Awaiting others. Method {@link #awaitAdvance} requires an
54	>	*       argument indicating an arrival phase number, and returns
55	>	*       when the barrier advances to a new phase.
56		* </ul>
57		*
51	–	*
58		* <li> Barrier actions, performed by the task triggering a phase
59	<	* advance while others may be waiting, are arranged by overriding
60	<	* method {@code onAdvance}, that also controls termination.
61	<	* Overriding this method may be used to similar but more flexible
62	<	* effect as providing a barrier action to a CyclicBarrier.
59	>	* advance, are arranged by overriding method {@link #onAdvance(int,
60	>	* int)}, which also controls termination. Overriding this method is
61	>	* similar to, but more flexible than, providing a barrier action to a
62	>	* {@code CyclicBarrier}.
63		*
64		* <li> Phasers may enter a <em>termination</em> state in which all
65		* actions immediately return without updating phaser state or waiting
66		* for advance, and indicating (via a negative phase value) that
67	<	* execution is complete.  Termination is triggered by executing the
68	<	* overridable {@code onAdvance} method that is invoked each time the
69	<	* barrier is about to be tripped. When a Phaser is controlling an
70	<	* action with a fixed number of iterations, it is often convenient to
71	<	* override this method to cause termination when the current phase
72	<	* number reaches a threshold. Method {@code forceTermination} is also
73	<	* available to abruptly release waiting threads and allow them to
68	<	* terminate.
67	>	* execution is complete.  Termination is triggered when an invocation
68	>	* of {@code onAdvance} returns {@code true}.  When a phaser is
69	>	* controlling an action with a fixed number of iterations, it is
70	>	* often convenient to override this method to cause termination when
71	>	* the current phase number reaches a threshold. Method {@link
72	>	* #forceTermination} is also available to abruptly release waiting
73	>	* threads and allow them to terminate.
74		*
75		* <li> Phasers may be tiered to reduce contention. Phasers with large
76		* numbers of parties that would otherwise experience heavy
#	Line 75 | Line 80 | import java.util.concurrent.locks.LockSu
80		*
81		* <li> By default, {@code awaitAdvance} continues to wait even if
82		* the waiting thread is interrupted. And unlike the case in
83	<	* CyclicBarriers, exceptions encountered while tasks wait
83	>	* {@code CyclicBarrier}, exceptions encountered while tasks wait
84		* interruptibly or with timeout do not change the state of the
85		* barrier. If necessary, you can perform any associated recovery
86		* within handlers of those exceptions, often after invoking
87		* {@code forceTermination}.
88		*
89	<	* <li>Phasers ensure lack of starvation when used by ForkJoinTasks.
89	>	* <li>Phasers may be used to coordinate tasks executing in a {@link
90	>	* ForkJoinPool}, which will ensure sufficient parallelism to execute
91	>	* tasks when others are blocked waiting for a phase to advance.
92	>	*
93	>	* <li>The current state of a phaser may be monitored.  At any given
94	>	* moment there are {@link #getRegisteredParties}, where {@link
95	>	* #getArrivedParties} have arrived at the current phase ({@link
96	>	* #getPhase}). When the remaining {@link #getUnarrivedParties})
97	>	* arrive, the phase advances. Method {@link #toString} returns
98	>	* snapshots of these state queries in a form convenient for
99	>	* informal monitoring.
100		*
101		* </ul>
102		*
103		* <p><b>Sample usages:</b>
104		*
105	<	* <p>A Phaser may be used instead of a {@code CountDownLatch} to control
106	<	* a one-shot action serving a variable number of parties. The typical
107	<	* idiom is for the method setting this up to first register, then
108	<	* start the actions, then deregister, as in:
105	>	* <p>A {@code Phaser} may be used instead of a {@code CountDownLatch}
106	>	* to control a one-shot action serving a variable number of
107	>	* parties. The typical idiom is for the method setting this up to
108	>	* first register, then start the actions, then deregister, as in:
109		*
110		*  <pre> {@code
111	<	* void runTasks(List<Runnable> list) {
111	>	* void runTasks(List<Runnable> tasks) {
112		*   final Phaser phaser = new Phaser(1); // "1" to register self
113	<	*   for (Runnable r : list) {
113	>	*   // create and start threads
114	>	*   for (Runnable task : tasks) {
115		*     phaser.register();
116		*     new Thread() {
117		*       public void run() {
118		*         phaser.arriveAndAwaitAdvance(); // await all creation
119	<	*         r.run();
104	<	*         phaser.arriveAndDeregister();   // signal completion
119	>	*         task.run();
120		*       }
121		*     }.start();
122		*   }
123		*
124	<	*   doSomethingOnBehalfOfWorkers();
125	<	*   phaser.arrive(); // allow threads to start
111	<	*   int p = phaser.arriveAndDeregister(); // deregister self  ...
112	<	*   p = phaser.awaitAdvance(p); // ... and await arrival
113	<	*   otherActions(); // do other things while tasks execute
114	<	*   phaser.awaitAdvance(p); // await final completion
124	>	*   // allow threads to start and deregister self
125	>	*   phaser.arriveAndDeregister();
126		* }}</pre>
127		*
128		* <p>One way to cause a set of threads to repeatedly perform actions
129		* for a given number of iterations is to override {@code onAdvance}:
130		*
131		*  <pre> {@code
132	<	* void startTasks(List<Runnable> list, final int iterations) {
132	>	* void startTasks(List<Runnable> tasks, final int iterations) {
133		*   final Phaser phaser = new Phaser() {
134		*     public boolean onAdvance(int phase, int registeredParties) {
135		*       return phase >= iterations || registeredParties == 0;
136		*     }
137		*   };
138		*   phaser.register();
139	<	*   for (Runnable r : list) {
139	>	*   for (Runnable task : tasks) {
140		*     phaser.register();
141		*     new Thread() {
142		*       public void run() {
143		*         do {
144	<	*           r.run();
144	>	*           task.run();
145		*           phaser.arriveAndAwaitAdvance();
146		*         } while(!phaser.isTerminated();
147		*       }
#	Line 139 | Line 150 | import java.util.concurrent.locks.LockSu
150		*   phaser.arriveAndDeregister(); // deregister self, don't wait
151		* }}</pre>
152		*
153	<	* <p> To create a set of tasks using a tree of Phasers,
153	>	* <p>To create a set of tasks using a tree of phasers,
154		* you could use code of the following form, assuming a
155	<	* Task class with a constructor accepting a Phaser that
155	>	* Task class with a constructor accepting a phaser that
156		* it registers for upon construction:
157		*  <pre> {@code
158		* void build(Task[] actions, int lo, int hi, Phaser b) {
#	Line 171 | Line 182 | import java.util.concurrent.locks.LockSu
182		*
183		* <p><b>Implementation notes</b>: This implementation restricts the
184		* maximum number of parties to 65535. Attempts to register additional
185	<	* parties result in IllegalStateExceptions. However, you can and
185	>	* parties result in {@code IllegalStateException}. However, you can and
186		* should create tiered phasers to accommodate arbitrarily large sets
187		* of participants.
188		*
#	Line 249 | Line 260 | public class Phaser {
260		private final Phaser parent;
261
262		/**
263	<	* The root of Phaser tree. Equals this if not in a tree.  Used to
263	>	* The root of phaser tree. Equals this if not in a tree.  Used to
264		* support faster state push-down.
265		*/
266		private final Phaser root;
#	Line 300 | Line 311 | public class Phaser {
311		}
312
313		/**
314	<	* Creates a new Phaser without any initially registered parties,
314	>	* Creates a new phaser without any initially registered parties,
315		* initial phase number 0, and no parent. Any thread using this
316	<	* Phaser will need to first register for it.
316	>	* phaser will need to first register for it.
317		*/
318		public Phaser() {
319		this(null);
320		}
321
322		/**
323	<	* Creates a new Phaser with the given numbers of registered
323	>	* Creates a new phaser with the given numbers of registered
324		* unarrived parties, initial phase number 0, and no parent.
325		*
326		* @param parties the number of parties required to trip barrier
#	Line 321 | Line 332 | public class Phaser {
332		}
333
334		/**
335	<	* Creates a new Phaser with the given parent, without any
335	>	* Creates a new phaser with the given parent, without any
336		* initially registered parties. If parent is non-null this phaser
337		* is registered with the parent and its initial phase number is
338		* the same as that of parent phaser.
#	Line 341 | Line 352 | public class Phaser {
352		}
353
354		/**
355	<	* Creates a new Phaser with the given parent and numbers of
355	>	* Creates a new phaser with the given parent and numbers of
356		* registered unarrived parties. If parent is non-null, this phaser
357		* is registered with the parent and its initial phase number is
358		* the same as that of parent phaser.
#	Line 368 | Line 379 | public class Phaser {
379		/**
380		* Adds a new unarrived party to this phaser.
381		*
382	<	* @return the current barrier phase number upon registration
382	>	* @return the arrival phase number to which this registration applied
383		* @throws IllegalStateException if attempting to register more
384		* than the maximum supported number of parties
385		*/
#	Line 380 | Line 391 | public class Phaser {
391		* Adds the given number of new unarrived parties to this phaser.
392		*
393		* @param parties the number of parties required to trip barrier
394	<	* @return the current barrier phase number upon registration
394	>	* @return the arrival phase number to which this registration applied
395		* @throws IllegalStateException if attempting to register more
396		* than the maximum supported number of parties
397		*/
#	Line 417 | Line 428 | public class Phaser {
428		* Arrives at the barrier, but does not wait for others.  (You can
429		* in turn wait for others via {@link #awaitAdvance}).
430		*
431	<	* @return the barrier phase number upon entry to this method, or a
421	<	* negative value if terminated
431	>	* @return the arrival phase number, or a negative value if terminated
432		* @throws IllegalStateException if not terminated and the number
433		* of unarrived parties would become negative
434		*/
#	Line 463 | Line 473 | public class Phaser {
473		}
474
475		/**
476	<	* Arrives at the barrier, and deregisters from it, without
477	<	* waiting for others. Deregistration reduces number of parties
476	>	* Arrives at the barrier and deregisters from it without waiting
477	>	* for others. Deregistration reduces the number of parties
478		* required to trip the barrier in future phases.  If this phaser
479		* has a parent, and deregistration causes this phaser to have
480	<	* zero parties, this phaser is also deregistered from its parent.
480	>	* zero parties, this phaser also arrives at and is deregistered
481	>	* from its parent.
482		*
483	<	* @return the current barrier phase number upon entry to
473	<	* this method, or a negative value if terminated
483	>	* @return the arrival phase number, or a negative value if terminated
484		* @throws IllegalStateException if not terminated and the number
485		* of registered or unarrived parties would become negative
486		*/
#	Line 520 | Line 530 | public class Phaser {
530
531		/**
532		* Arrives at the barrier and awaits others. Equivalent in effect
533	<	* to {@code awaitAdvance(arrive())}.  If you instead need to
534	<	* await with interruption of timeout, and/or deregister upon
535	<	* arrival, you can arrange them using analogous constructions.
533	>	* to {@code awaitAdvance(arrive())}.  If you need to await with
534	>	* interruption or timeout, you can arrange this with an analogous
535	>	* construction using one of the other forms of the awaitAdvance
536	>	* method.  If instead you need to deregister upon arrival use
537	>	* {@code arriveAndDeregister}.
538		*
539	<	* @return the phase on entry to this method
539	>	* @return the arrival phase number, or a negative number if terminated
540		* @throws IllegalStateException if not terminated and the number
541		* of unarrived parties would become negative
542		*/
#	Line 533 | Line 545 | public class Phaser {
545		}
546
547		/**
548	<	* Awaits the phase of the barrier to advance from the given
549	<	* value, or returns immediately if argument is negative or this
550	<	* barrier is terminated.
551	<	*
552	<	* @param phase the phase on entry to this method
553	<	* @return the phase on exit from this method
548	>	* Awaits the phase of the barrier to advance from the given phase
549	>	* value, returning immediately if the current phase of the
550	>	* barrier is not equal to the given phase value or this barrier
551	>	* is terminated.
552	>	*
553	>	* @param phase an arrival phase number, or negative value if
554	>	* terminated; this argument is normally the value returned by a
555	>	* previous call to {@code arrive} or its variants
556	>	* @return the next arrival phase number, or a negative value
557	>	* if terminated or argument is negative
558		*/
559		public int awaitAdvance(int phase) {
560		if (phase < 0)
#	Line 554 | Line 570 | public class Phaser {
570		}
571
572		/**
573	<	* Awaits the phase of the barrier to advance from the given
574	<	* value, or returns immediately if argument is negative or this
575	<	* barrier is terminated, or throws InterruptedException if
576	<	* interrupted while waiting.
577	<	*
578	<	* @param phase the phase on entry to this method
579	<	* @return the phase on exit from this method
573	>	* Awaits the phase of the barrier to advance from the given phase
574	>	* value, throwing {@code InterruptedException} if interrupted while
575	>	* waiting, or returning immediately if the current phase of the
576	>	* barrier is not equal to the given phase value or this barrier
577	>	* is terminated.
578	>	*
579	>	* @param phase an arrival phase number, or negative value if
580	>	* terminated; this argument is normally the value returned by a
581	>	* previous call to {@code arrive} or its variants
582	>	* @return the next arrival phase number, or a negative value
583	>	* if terminated or argument is negative
584		* @throws InterruptedException if thread interrupted while waiting
585		*/
586		public int awaitAdvanceInterruptibly(int phase)
#	Line 577 | Line 597 | public class Phaser {
597		}
598
599		/**
600	<	* Awaits the phase of the barrier to advance from the given value
601	<	* or the given timeout elapses, or returns immediately if
602	<	* argument is negative or this barrier is terminated.
603	<	*
604	<	* @param phase the phase on entry to this method
605	<	* @return the phase on exit from this method
600	>	* Awaits the phase of the barrier to advance from the given phase
601	>	* value or the given timeout to elapse, throwing
602	>	* {@code InterruptedException} if interrupted while waiting, or
603	>	* returning immediately if the current phase of the barrier is not
604	>	* equal to the given phase value or this barrier is terminated.
605	>	*
606	>	* @param phase an arrival phase number, or negative value if
607	>	* terminated; this argument is normally the value returned by a
608	>	* previous call to {@code arrive} or its variants
609	>	* @param timeout how long to wait before giving up, in units of
610	>	*        {@code unit}
611	>	* @param unit a {@code TimeUnit} determining how to interpret the
612	>	*        {@code timeout} parameter
613	>	* @return the next arrival phase number, or a negative value
614	>	* if terminated or argument is negative
615		* @throws InterruptedException if thread interrupted while waiting
616		* @throws TimeoutException if timed out while waiting
617		*/
#	Line 636 | Line 665 | public class Phaser {
665		}
666
667		/**
639	–	* Returns {@code true} if the current phase number equals the given phase.
640	–	*
641	–	* @param phase the phase
642	–	* @return {@code true} if the current phase number equals the given phase
643	–	*/
644	–	public final boolean hasPhase(int phase) {
645	–	return phaseOf(getReconciledState()) == phase;
646	–	}
647	–
648	–	/**
668		* Returns the number of parties registered at this barrier.
669		*
670		* @return the number of parties
#	Line 655 | Line 674 | public class Phaser {
674		}
675
676		/**
677	<	* Returns the number of parties that have arrived at the current
678	<	* phase of this barrier.
677	>	* Returns the number of registered parties that have arrived at
678	>	* the current phase of this barrier.
679		*
680		* @return the number of arrived parties
681		*/
#	Line 675 | Line 694 | public class Phaser {
694		}
695
696		/**
697	<	* Returns the parent of this phaser, or null if none.
697	>	* Returns the parent of this phaser, or {@code null} if none.
698		*
699	<	* @return the parent of this phaser, or null if none
699	>	* @return the parent of this phaser, or {@code null} if none
700		*/
701		public Phaser getParent() {
702		return parent;
#	Line 706 | Line 725 | public class Phaser {
725		* Overridable method to perform an action upon phase advance, and
726		* to control termination. This method is invoked whenever the
727		* barrier is tripped (and thus all other waiting parties are
728	<	* dormant). If it returns true, then, rather than advance the
729	<	* phase number, this barrier will be set to a final termination
730	<	* state, and subsequent calls to {@code isTerminated} will
731	<	* return true.
728	>	* dormant). If it returns {@code true}, then, rather than advance
729	>	* the phase number, this barrier will be set to a final
730	>	* termination state, and subsequent calls to {@link #isTerminated}
731	>	* will return true.
732		*
733	<	* <p> The default version returns true when the number of
733	>	* <p>The default version returns {@code true} when the number of
734		* registered parties is zero. Normally, overrides that arrange
735		* termination for other reasons should also preserve this
736		* property.
737		*
738	<	* <p> You may override this method to perform an action with side
738	>	* <p>You may override this method to perform an action with side
739		* effects visible to participating tasks, but it is in general
740		* only sensible to do so in designs where all parties register
741	<	* before any arrive, and all {@code awaitAdvance} at each phase.
742	<	* Otherwise, you cannot ensure lack of interference. In
743	<	* particular, this method may be invoked more than once per
725	<	* transition if other parties successfully register while the
726	<	* invocation of this method is in progress, thus postponing the
727	<	* transition until those parties also arrive, re-triggering this
728	<	* method.
741	>	* before any arrive, and all {@link #awaitAdvance} at each phase.
742	>	* Otherwise, you cannot ensure lack of interference from other
743	>	* parties during the invocation of this method.
744		*
745		* @param phase the phase number on entering the barrier
746		* @param registeredParties the current number of registered parties
#	Line 930 | Line 945 | public class Phaser {
945		return p;
946		}
947
948	<	// Unsafe mechanics for jsr166y 3rd party package.
948	>	// Unsafe mechanics
949	>
950	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
951	>	private static final long stateOffset =
952	>	objectFieldOffset("state", Phaser.class);
953	>
954	>	private final boolean casState(long cmp, long val) {
955	>	return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
956	>	}
957	>
958	>	private static long objectFieldOffset(String field, Class<?> klazz) {
959	>	try {
960	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
961	>	} catch (NoSuchFieldException e) {
962	>	// Convert Exception to corresponding Error
963	>	NoSuchFieldError error = new NoSuchFieldError(field);
964	>	error.initCause(e);
965	>	throw error;
966	>	}
967	>	}
968	>
969	>	/**
970	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
971	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
972	>	* into a jdk.
973	>	*
974	>	* @return a sun.misc.Unsafe
975	>	*/
976		private static sun.misc.Unsafe getUnsafe() {
977		try {
978		return sun.misc.Unsafe.getUnsafe();
979		} catch (SecurityException se) {
980		try {
981		return java.security.AccessController.doPrivileged
982	<	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
982	>	(new java.security
983	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
984		public sun.misc.Unsafe run() throws Exception {
985	<	return getUnsafeByReflection();
985	>	java.lang.reflect.Field f = sun.misc
986	>	.Unsafe.class.getDeclaredField("theUnsafe");
987	>	f.setAccessible(true);
988	>	return (sun.misc.Unsafe) f.get(null);
989		}});
990		} catch (java.security.PrivilegedActionException e) {
991		throw new RuntimeException("Could not initialize intrinsics",
#	Line 947 | Line 993 | public class Phaser {
993		}
994		}
995		}
950	–
951	–	private static sun.misc.Unsafe getUnsafeByReflection()
952	–	throws NoSuchFieldException, IllegalAccessException {
953	–	java.lang.reflect.Field f =
954	–	sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
955	–	f.setAccessible(true);
956	–	return (sun.misc.Unsafe) f.get(null);
957	–	}
958	–
959	–	private static long fieldOffset(String fieldName, Class<?> klazz) {
960	–	try {
961	–	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName));
962	–	} catch (NoSuchFieldException e) {
963	–	// Convert Exception to Error
964	–	NoSuchFieldError error = new NoSuchFieldError(fieldName);
965	–	error.initCause(e);
966	–	throw error;
967	–	}
968	–	}
969	–
970	–	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
971	–	private static final long stateOffset =
972	–	fieldOffset("state", Phaser.class);
973	–
974	–	private final boolean casState(long cmp, long val) {
975	–	return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
976	–	}
996		}

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