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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 1.29 by jsr166, Wed Aug 12 04:02:45 2009 UTC

#	Line 32 | Line 32 | import java.util.concurrent.locks.LockSu
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:
35	>	* <li> Like a {@code CyclicBarrier}, a phaser may be repeatedly
36	>	* awaited.  Method {@link #arriveAndAwaitAdvance} has effect
37	>	* analogous to {@link java.util.concurrent.CyclicBarrier#await
38	>	* CyclicBarrier.await}.  However, phasers separate two aspects of
39	>	* coordination, which may also be invoked independently:
40		*
41		* <ul>
42		*
43	<	*   <li> Arriving at a barrier. Methods {@code arrive} and
44	<	*       {@code arriveAndDeregister} do not block, but return
43	>	*   <li> Arriving at a barrier. Methods {@link #arrive} and
44	>	*       {@link #arriveAndDeregister} do not block, but return
45		*       the phase value current upon entry to the method.
46		*
47	<	*   <li> Awaiting others. Method {@code awaitAdvance} requires an
47	>	*   <li> Awaiting others. Method {@link #awaitAdvance} requires an
48		*       argument indicating the entry phase, and returns when the
49		*       barrier advances to a new phase.
50		* </ul>
51		*
52		*
53		* <li> Barrier actions, performed by the task triggering a phase
54	<	* advance while others may be waiting, are arranged by overriding
55	<	* method {@code onAdvance}, that also controls termination.
56	<	* Overriding this method may be used to similar but more flexible
57	<	* effect as providing a barrier action to a CyclicBarrier.
54	>	* advance, are arranged by overriding method {@link #onAdvance(int,
55	>	* int)}, which also controls termination. Overriding this method is
56	>	* similar to, but more flexible than, providing a barrier action to a
57	>	* {@code CyclicBarrier}.
58		*
59		* <li> Phasers may enter a <em>termination</em> state in which all
60		* actions immediately return without updating phaser state or waiting
61		* for advance, and indicating (via a negative phase value) that
62	<	* execution is complete.  Termination is triggered by executing the
63	<	* overridable {@code onAdvance} method that is invoked each time the
64	<	* barrier is about to be tripped. When a Phaser is controlling an
65	<	* action with a fixed number of iterations, it is often convenient to
66	<	* override this method to cause termination when the current phase
67	<	* number reaches a threshold. Method {@code forceTermination} is also
68	<	* available to abruptly release waiting threads and allow them to
68	<	* terminate.
62	>	* execution is complete.  Termination is triggered when an invocation
63	>	* of {@code onAdvance} returns {@code true}.  When a phaser is
64	>	* controlling an action with a fixed number of iterations, it is
65	>	* often convenient to override this method to cause termination when
66	>	* the current phase number reaches a threshold. Method {@link
67	>	* #forceTermination} is also available to abruptly release waiting
68	>	* threads and allow them to terminate.
69		*
70		* <li> Phasers may be tiered to reduce contention. Phasers with large
71		* numbers of parties that would otherwise experience heavy
#	Line 75 | Line 75 | import java.util.concurrent.locks.LockSu
75		*
76		* <li> By default, {@code awaitAdvance} continues to wait even if
77		* the waiting thread is interrupted. And unlike the case in
78	<	* CyclicBarriers, exceptions encountered while tasks wait
78	>	* {@code CyclicBarrier}, exceptions encountered while tasks wait
79		* interruptibly or with timeout do not change the state of the
80		* barrier. If necessary, you can perform any associated recovery
81		* within handlers of those exceptions, often after invoking
82		* {@code forceTermination}.
83		*
84	<	* <li>Phasers ensure lack of starvation when used by ForkJoinTasks.
84	>	* <li>Phasers may be used to coordinate tasks executing in a {@link
85	>	* ForkJoinPool}, which will ensure sufficient parallelism to execute
86	>	* tasks when others are blocked waiting for a phase to advance.
87		*
88		* </ul>
89		*
90		* <p><b>Sample usages:</b>
91		*
92	<	* <p>A Phaser may be used instead of a {@code CountDownLatch} to control
93	<	* a one-shot action serving a variable number of parties. The typical
94	<	* idiom is for the method setting this up to first register, then
95	<	* start the actions, then deregister, as in:
92	>	* <p>A {@code Phaser} may be used instead of a {@code CountDownLatch}
93	>	* to control a one-shot action serving a variable number of
94	>	* parties. The typical idiom is for the method setting this up to
95	>	* first register, then start the actions, then deregister, as in:
96		*
97		*  <pre> {@code
98		* void runTasks(List<Runnable> list) {
99		*   final Phaser phaser = new Phaser(1); // "1" to register self
100	+	*   // create and start threads
101		*   for (Runnable r : list) {
102		*     phaser.register();
103		*     new Thread() {
104		*       public void run() {
105		*         phaser.arriveAndAwaitAdvance(); // await all creation
106		*         r.run();
104	–	*         phaser.arriveAndDeregister();   // signal completion
107		*       }
108		*     }.start();
109		*   }
110		*
111	<	*   doSomethingOnBehalfOfWorkers();
112	<	*   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
111	>	*   // allow threads to start and deregister self
112	>	*   phaser.arriveAndDeregister();
113		* }}</pre>
114		*
115		* <p>One way to cause a set of threads to repeatedly perform actions
#	Line 139 | Line 137 | import java.util.concurrent.locks.LockSu
137		*   phaser.arriveAndDeregister(); // deregister self, don't wait
138		* }}</pre>
139		*
140	<	* <p> To create a set of tasks using a tree of Phasers,
140	>	* <p>To create a set of tasks using a tree of phasers,
141		* you could use code of the following form, assuming a
142	<	* Task class with a constructor accepting a Phaser that
142	>	* Task class with a constructor accepting a phaser that
143		* it registers for upon construction:
144		*  <pre> {@code
145		* void build(Task[] actions, int lo, int hi, Phaser b) {
#	Line 249 | Line 247 | public class Phaser {
247		private final Phaser parent;
248
249		/**
250	<	* The root of Phaser tree. Equals this if not in a tree.  Used to
250	>	* The root of phaser tree. Equals this if not in a tree.  Used to
251		* support faster state push-down.
252		*/
253		private final Phaser root;
#	Line 300 | Line 298 | public class Phaser {
298		}
299
300		/**
301	<	* Creates a new Phaser without any initially registered parties,
301	>	* Creates a new phaser without any initially registered parties,
302		* initial phase number 0, and no parent. Any thread using this
303	<	* Phaser will need to first register for it.
303	>	* phaser will need to first register for it.
304		*/
305		public Phaser() {
306		this(null);
307		}
308
309		/**
310	<	* Creates a new Phaser with the given numbers of registered
310	>	* Creates a new phaser with the given numbers of registered
311		* unarrived parties, initial phase number 0, and no parent.
312		*
313		* @param parties the number of parties required to trip barrier
#	Line 321 | Line 319 | public class Phaser {
319		}
320
321		/**
322	<	* Creates a new Phaser with the given parent, without any
322	>	* Creates a new phaser with the given parent, without any
323		* initially registered parties. If parent is non-null this phaser
324		* is registered with the parent and its initial phase number is
325		* the same as that of parent phaser.
#	Line 341 | Line 339 | public class Phaser {
339		}
340
341		/**
342	<	* Creates a new Phaser with the given parent and numbers of
342	>	* Creates a new phaser with the given parent and numbers of
343		* registered unarrived parties. If parent is non-null, this phaser
344		* is registered with the parent and its initial phase number is
345		* the same as that of parent phaser.
#	Line 463 | Line 461 | public class Phaser {
461		}
462
463		/**
464	<	* Arrives at the barrier, and deregisters from it, without
465	<	* waiting for others. Deregistration reduces number of parties
464	>	* Arrives at the barrier and deregisters from it without waiting
465	>	* for others. Deregistration reduces the number of parties
466		* required to trip the barrier in future phases.  If this phaser
467		* has a parent, and deregistration causes this phaser to have
468	<	* zero parties, this phaser is also deregistered from its parent.
468	>	* zero parties, this phaser also arrives at and is deregistered
469	>	* from its parent.
470		*
471		* @return the current barrier phase number upon entry to
472		* this method, or a negative value if terminated
#	Line 520 | Line 519 | public class Phaser {
519
520		/**
521		* Arrives at the barrier and awaits others. Equivalent in effect
522	<	* to {@code awaitAdvance(arrive())}.  If you instead need to
523	<	* await with interruption of timeout, and/or deregister upon
524	<	* arrival, you can arrange them using analogous constructions.
522	>	* to {@code awaitAdvance(arrive())}.  If you need to await with
523	>	* interruption or timeout, you can arrange this with an analogous
524	>	* construction using one of the other forms of the awaitAdvance
525	>	* method.  If instead you need to deregister upon arrival use
526	>	* {@code arriveAndDeregister}.
527		*
528		* @return the phase on entry to this method
529		* @throws IllegalStateException if not terminated and the number
#	Line 533 | Line 534 | public class Phaser {
534		}
535
536		/**
537	<	* Awaits the phase of the barrier to advance from the given
538	<	* value, or returns immediately if argument is negative or this
539	<	* barrier is terminated.
537	>	* Awaits the phase of the barrier to advance from the given phase
538	>	* value, or returns immediately if the current phase of the barrier
539	>	* is not equal to the given phase value or this barrier is
540	>	* terminated.
541		*
542		* @param phase the phase on entry to this method
543		* @return the phase on exit from this method
#	Line 636 | Line 638 | public class Phaser {
638		}
639
640		/**
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	–	/**
641		* Returns the number of parties registered at this barrier.
642		*
643		* @return the number of parties
#	Line 675 | Line 667 | public class Phaser {
667		}
668
669		/**
670	<	* Returns the parent of this phaser, or null if none.
670	>	* Returns the parent of this phaser, or {@code null} if none.
671		*
672	<	* @return the parent of this phaser, or null if none
672	>	* @return the parent of this phaser, or {@code null} if none
673		*/
674		public Phaser getParent() {
675		return parent;
#	Line 706 | Line 698 | public class Phaser {
698		* Overridable method to perform an action upon phase advance, and
699		* to control termination. This method is invoked whenever the
700		* barrier is tripped (and thus all other waiting parties are
701	<	* dormant). If it returns true, then, rather than advance the
702	<	* phase number, this barrier will be set to a final termination
703	<	* state, and subsequent calls to {@code isTerminated} will
704	<	* return true.
701	>	* dormant). If it returns {@code true}, then, rather than advance
702	>	* the phase number, this barrier will be set to a final
703	>	* termination state, and subsequent calls to {@link #isTerminated}
704	>	* will return true.
705		*
706	<	* <p> The default version returns true when the number of
706	>	* <p>The default version returns {@code true} when the number of
707		* registered parties is zero. Normally, overrides that arrange
708		* termination for other reasons should also preserve this
709		* property.
710		*
711	<	* <p> You may override this method to perform an action with side
711	>	* <p>You may override this method to perform an action with side
712		* effects visible to participating tasks, but it is in general
713		* only sensible to do so in designs where all parties register
714	<	* before any arrive, and all {@code awaitAdvance} at each phase.
715	<	* Otherwise, you cannot ensure lack of interference. In
716	<	* 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.
714	>	* before any arrive, and all {@link #awaitAdvance} at each phase.
715	>	* Otherwise, you cannot ensure lack of interference from other
716	>	* parties during the invocation of this method.
717		*
718		* @param phase the phase number on entering the barrier
719		* @param registeredParties the current number of registered parties
#	Line 930 | Line 918 | public class Phaser {
918		return p;
919		}
920
921	<	// Unsafe mechanics for jsr166y 3rd party package.
921	>	// Unsafe mechanics
922	>
923	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
924	>	private static final long stateOffset =
925	>	objectFieldOffset("state", Phaser.class);
926	>
927	>	private final boolean casState(long cmp, long val) {
928	>	return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
929	>	}
930	>
931	>	private static long objectFieldOffset(String field, Class<?> klazz) {
932	>	try {
933	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
934	>	} catch (NoSuchFieldException e) {
935	>	// Convert Exception to corresponding Error
936	>	NoSuchFieldError error = new NoSuchFieldError(field);
937	>	error.initCause(e);
938	>	throw error;
939	>	}
940	>	}
941	>
942	>	/**
943	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
944	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
945	>	* into a jdk.
946	>	*
947	>	* @return a sun.misc.Unsafe
948	>	*/
949		private static sun.misc.Unsafe getUnsafe() {
950		try {
951		return sun.misc.Unsafe.getUnsafe();
952		} catch (SecurityException se) {
953		try {
954		return java.security.AccessController.doPrivileged
955	<	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
955	>	(new java.security
956	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
957		public sun.misc.Unsafe run() throws Exception {
958	<	return getUnsafeByReflection();
958	>	java.lang.reflect.Field f = sun.misc
959	>	.Unsafe.class.getDeclaredField("theUnsafe");
960	>	f.setAccessible(true);
961	>	return (sun.misc.Unsafe) f.get(null);
962		}});
963		} catch (java.security.PrivilegedActionException e) {
964		throw new RuntimeException("Could not initialize intrinsics",
#	Line 947 | Line 966 | public class Phaser {
966		}
967		}
968		}
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	–	}
969		}

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