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

Comparing jsr166/src/jsr166y/Phaser.java (file contents):
Revision 1.13 by jsr166, Mon Jul 20 22:40:09 2009 UTC vs.
Revision 1.27 by dl, Sat Aug 8 19:36:52 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;
12	–	import sun.misc.Unsafe;
13	–	import java.lang.reflect.*;
13
14		/**
15		* A reusable synchronization barrier, similar in functionality to a
#	Line 33 | Line 32 | import java.lang.reflect.*;
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
69	<	* 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 76 | Line 75 | import java.lang.reflect.*;
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();
105	–	*         phaser.arriveAndDeregister();   // signal completion
107		*       }
108		*     }.start();
109		*   }
110		*
111	<	*   doSomethingOnBehalfOfWorkers();
112	<	*   phaser.arrive(); // allow threads to start
112	<	*   int p = phaser.arriveAndDeregister(); // deregister self  ...
113	<	*   p = phaser.awaitAdvance(p); // ... and await arrival
114	<	*   otherActions(); // do other things while tasks execute
115	<	*   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 140 | Line 137 | import java.lang.reflect.*;
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 175 | Line 172 | import java.lang.reflect.*;
172		* parties result in IllegalStateExceptions. However, you can and
173		* should create tiered phasers to accommodate arbitrarily large sets
174		* of participants.
175	+	*
176	+	* @since 1.7
177	+	* @author Doug Lea
178		*/
179		public class Phaser {
180		/*
#	Line 208 | Line 208 | public class Phaser {
208		private static final int phaseMask  = 0x7fffffff;
209
210		private static int unarrivedOf(long s) {
211	<	return (int)(s & ushortMask);
211	>	return (int) (s & ushortMask);
212		}
213
214		private static int partiesOf(long s) {
215	<	return ((int)s) >>> 16;
215	>	return ((int) s) >>> 16;
216		}
217
218		private static int phaseOf(long s) {
219	<	return (int)(s >>> 32);
219	>	return (int) (s >>> 32);
220		}
221
222		private static int arrivedOf(long s) {
#	Line 224 | Line 224 | public class Phaser {
224		}
225
226		private static long stateFor(int phase, int parties, int unarrived) {
227	<	return ((((long)phase) << 32) | (((long)parties) << 16) |
228	<	(long)unarrived);
227	>	return ((((long) phase) << 32) | (((long) parties) << 16) |
228	>	(long) unarrived);
229		}
230
231		private static long trippedStateFor(int phase, int parties) {
232	<	long lp = (long)parties;
233	<	return (((long)phase) << 32) | (lp << 16) | lp;
232	>	long lp = (long) parties;
233	>	return (((long) phase) << 32) | (lp << 16) | lp;
234		}
235
236		/**
237	<	* Returns message string for bad bounds exceptions
237	>	* Returns message string for bad bounds exceptions.
238		*/
239		private static String badBounds(int parties, int unarrived) {
240		return ("Attempt to set " + unarrived +
#	Line 247 | 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 263 | Line 263 | public class Phaser {
263		private final AtomicReference<QNode> oddQ  = new AtomicReference<QNode>();
264
265		private AtomicReference<QNode> queueFor(int phase) {
266	<	return (phase & 1) == 0? evenQ : oddQ;
266	>	return ((phase & 1) == 0) ? evenQ : oddQ;
267		}
268
269		/**
#	Line 271 | Line 271 | public class Phaser {
271		* root if necessary.
272		*/
273		private long getReconciledState() {
274	<	return parent == null? state : reconcileState();
274	>	return (parent == null) ? state : reconcileState();
275		}
276
277		/**
#	Line 298 | 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	<	* @param parties the number of parties required to trip barrier.
312	>	*
313	>	* @param parties the number of parties required to trip barrier
314		* @throws IllegalArgumentException if parties less than zero
315	<	* or greater than the maximum number of parties supported.
315	>	* or greater than the maximum number of parties supported
316		*/
317		public Phaser(int parties) {
318		this(null, parties);
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.
326	<	* @param parent the parent phaser.
326	>	*
327	>	* @param parent the parent phaser
328		*/
329		public Phaser(Phaser parent) {
330		int phase = 0;
#	Line 337 | Line 339 | public class Phaser {
339		}
340
341		/**
342	<	* Creates a new Phaser with the given parent and numbers of
343	<	* registered unarrived parties. If parent is non-null this phaser
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.
346	<	* @param parent the parent phaser.
347	<	* @param parties the number of parties required to trip barrier.
346	>	*
347	>	* @param parent the parent phaser
348	>	* @param parties the number of parties required to trip barrier
349		* @throws IllegalArgumentException if parties less than zero
350	<	* or greater than the maximum number of parties supported.
350	>	* or greater than the maximum number of parties supported
351		*/
352		public Phaser(Phaser parent, int parties) {
353		if (parties < 0 || parties > ushortMask)
#	Line 362 | Line 365 | public class Phaser {
365
366		/**
367		* Adds a new unarrived party to this phaser.
368	+	*
369		* @return the current barrier phase number upon registration
370		* @throws IllegalStateException if attempting to register more
371	<	* than the maximum supported number of parties.
371	>	* than the maximum supported number of parties
372		*/
373		public int register() {
374		return doRegister(1);
#	Line 372 | Line 376 | public class Phaser {
376
377		/**
378		* Adds the given number of new unarrived parties to this phaser.
379	<	* @param parties the number of parties required to trip barrier.
379	>	*
380	>	* @param parties the number of parties required to trip barrier
381		* @return the current barrier phase number upon registration
382		* @throws IllegalStateException if attempting to register more
383	<	* than the maximum supported number of parties.
383	>	* than the maximum supported number of parties
384		*/
385		public int bulkRegister(int parties) {
386		if (parties < 0)
#	Line 411 | Line 416 | public class Phaser {
416		* in turn wait for others via {@link #awaitAdvance}).
417		*
418		* @return the barrier phase number upon entry to this method, or a
419	<	* negative value if terminated;
419	>	* negative value if terminated
420		* @throws IllegalStateException if not terminated and the number
421	<	* of unarrived parties would become negative.
421	>	* of unarrived parties would become negative
422		*/
423		public int arrive() {
424		int phase;
#	Line 433 | Line 438 | public class Phaser {
438		if (par == null) {      // directly trip
439		if (casState
440		(s,
441	<	trippedStateFor(onAdvance(phase, parties)? -1 :
441	>	trippedStateFor(onAdvance(phase, parties) ? -1 :
442		((phase + 1) & phaseMask), parties))) {
443		releaseWaiters(phase);
444		break;
#	Line 456 | 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;
472	>	* this method, or a negative value if terminated
473		* @throws IllegalStateException if not terminated and the number
474	<	* of registered or unarrived parties would become negative.
474	>	* of registered or unarrived parties would become negative
475		*/
476		public int arriveAndDeregister() {
477		// similar code to arrive, but too different to merge
#	Line 494 | Line 500 | public class Phaser {
500		if (unarrived == 0) {
501		if (casState
502		(s,
503	<	trippedStateFor(onAdvance(phase, parties)? -1 :
503	>	trippedStateFor(onAdvance(phase, parties) ? -1 :
504		((phase + 1) & phaseMask), parties))) {
505		releaseWaiters(phase);
506		break;
#	Line 513 | 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
530	<	* of unarrived parties would become negative.
530	>	* of unarrived parties would become negative
531		*/
532		public int arriveAndAwaitAdvance() {
533		return awaitAdvance(arrive());
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 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
544		*/
#	Line 549 | Line 560 | public class Phaser {
560		* value, or returns immediately if argument is negative or this
561		* barrier is terminated, or throws InterruptedException if
562		* interrupted while waiting.
563	+	*
564		* @param phase the phase on entry to this method
565		* @return the phase on exit from this method
566		* @throws InterruptedException if thread interrupted while waiting
#	Line 570 | Line 582 | public class Phaser {
582		* Awaits the phase of the barrier to advance from the given value
583		* or the given timeout elapses, or returns immediately if
584		* argument is negative or this barrier is terminated.
585	+	*
586		* @param phase the phase on entry to this method
587		* @return the phase on exit from this method
588		* @throws InterruptedException if thread interrupted while waiting
589		* @throws TimeoutException if timed out while waiting
590		*/
591	<	public int awaitAdvanceInterruptibly(int phase, long timeout, TimeUnit unit)
591	>	public int awaitAdvanceInterruptibly(int phase,
592	>	long timeout, TimeUnit unit)
593		throws InterruptedException, TimeoutException {
594		if (phase < 0)
595		return phase;
#	Line 616 | Line 630 | public class Phaser {
630		* Returns the current phase number. The maximum phase number is
631		* {@code Integer.MAX_VALUE}, after which it restarts at
632		* zero. Upon termination, the phase number is negative.
633	+	*
634		* @return the phase number, or a negative value if terminated
635		*/
636		public final int getPhase() {
#	Line 623 | Line 638 | public class Phaser {
638		}
639
640		/**
626	–	* Returns {@code true} if the current phase number equals the given phase.
627	–	* @param phase the phase
628	–	* @return {@code true} if the current phase number equals the given phase
629	–	*/
630	–	public final boolean hasPhase(int phase) {
631	–	return phaseOf(getReconciledState()) == phase;
632	–	}
633	–
634	–	/**
641		* Returns the number of parties registered at this barrier.
642	+	*
643		* @return the number of parties
644		*/
645		public int getRegisteredParties() {
#	Line 642 | Line 649 | public class Phaser {
649		/**
650		* Returns the number of parties that have arrived at the current
651		* phase of this barrier.
652	+	*
653		* @return the number of arrived parties
654		*/
655		public int getArrivedParties() {
#	Line 651 | Line 659 | public class Phaser {
659		/**
660		* Returns the number of registered parties that have not yet
661		* arrived at the current phase of this barrier.
662	+	*
663		* @return the number of unarrived parties
664		*/
665		public int getUnarrivedParties() {
#	Line 658 | Line 667 | public class Phaser {
667		}
668
669		/**
670	<	* Returns the parent of this phaser, or null if none.
671	<	* @return 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 {@code null} if none
673		*/
674		public Phaser getParent() {
675		return parent;
#	Line 668 | Line 678 | public class Phaser {
678		/**
679		* Returns the root ancestor of this phaser, which is the same as
680		* this phaser if it has no parent.
681	+	*
682		* @return the root ancestor of this phaser
683		*/
684		public Phaser getRoot() {
#	Line 676 | Line 687 | public class Phaser {
687
688		/**
689		* Returns {@code true} if this barrier has been terminated.
690	+	*
691		* @return {@code true} if this barrier has been terminated
692		*/
693		public boolean isTerminated() {
#	Line 686 | 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
705	<	* transition if other parties successfully register while the
706	<	* invocation of this method is in progress, thus postponing the
707	<	* transition until those parties also arrive, re-triggering this
708	<	* 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 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 799 | Line 807 | public class Phaser {
807		}
808
809		/**
810	<	* Removes and signals waiting threads from wait queue
810	>	* Removes and signals waiting threads from wait queue.
811		*/
812		private void releaseWaiters(int phase) {
813		AtomicReference<QNode> head = queueFor(phase);
#	Line 811 | Line 819 | public class Phaser {
819		}
820
821		/**
822	<	* Tries to enqueue given node in the appropriate wait queue
822	>	* Tries to enqueue given node in the appropriate wait queue.
823	>	*
824		* @return true if successful
825		*/
826		private boolean tryEnqueue(QNode node) {
#	Line 821 | Line 830 | public class Phaser {
830
831		/**
832		* Enqueues node and waits unless aborted or signalled.
833	+	*
834		* @return current phase
835		*/
836		private int untimedWait(int phase) {
#	Line 908 | Line 918 | public class Phaser {
918		return p;
919		}
920
921	<	// Temporary Unsafe mechanics for preliminary release
912	<	private static Unsafe getUnsafe() throws Throwable {
913	<	try {
914	<	return Unsafe.getUnsafe();
915	<	} catch (SecurityException se) {
916	<	try {
917	<	return java.security.AccessController.doPrivileged
918	<	(new java.security.PrivilegedExceptionAction<Unsafe>() {
919	<	public Unsafe run() throws Exception {
920	<	return getUnsafePrivileged();
921	<	}});
922	<	} catch (java.security.PrivilegedActionException e) {
923	<	throw e.getCause();
924	<	}
925	<	}
926	<	}
921	>	// Unsafe mechanics
922
923	<	private static Unsafe getUnsafePrivileged()
924	<	throws NoSuchFieldException, IllegalAccessException {
925	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
931	<	f.setAccessible(true);
932	<	return (Unsafe) f.get(null);
933	<	}
923	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
924	>	private static final long stateOffset =
925	>	objectFieldOffset("state", Phaser.class);
926
927	<	private static long fieldOffset(String fieldName)
928	<	throws NoSuchFieldException {
937	<	return _unsafe.objectFieldOffset
938	<	(Phaser.class.getDeclaredField(fieldName));
927	>	private final boolean casState(long cmp, long val) {
928	>	return UNSAFE.compareAndSwapLong(this, stateOffset, cmp, val);
929		}
930
931	<	static final Unsafe _unsafe;
942	<	static final long stateOffset;
943	<
944	<	static {
931	>	private static long objectFieldOffset(String field, Class<?> klazz) {
932		try {
933	<	_unsafe = getUnsafe();
934	<	stateOffset = fieldOffset("state");
935	<	} catch (Throwable e) {
936	<	throw new RuntimeException("Could not initialize intrinsics", e);
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	<	final boolean casState(long cmp, long val) {
943	<	return _unsafe.compareAndSwapLong(this, stateOffset, cmp, val);
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
956	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
957	>	public sun.misc.Unsafe run() throws Exception {
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",
965	>	e.getCause());
966	>	}
967	>	}
968		}
969		}

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