17 |
|
* {@link java.util.concurrent.CountDownLatch CountDownLatch} |
18 |
|
* but supporting more flexible usage. |
19 |
|
* |
20 |
< |
* <p> <b>Registration.</b> Unlike the case for other barriers, the |
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 |
30 |
|
* (However, you can introduce such bookkeeping by subclassing this |
31 |
|
* class.) |
32 |
|
* |
33 |
< |
* <p> <b>Synchronization.</b> Like a {@code CyclicBarrier}, a {@code |
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 |
44 |
|
* |
45 |
|
* <ul> |
46 |
|
* |
47 |
< |
* <li> <b>Arrival.</b> Methods {@link #arrive} and |
47 |
> |
* <li><b>Arrival.</b> Methods {@link #arrive} and |
48 |
|
* {@link #arriveAndDeregister} record arrival. These methods |
49 |
|
* do not block, but return an associated <em>arrival phase |
50 |
|
* number</em>; that is, the phase number of the phaser to which |
57 |
|
* flexible than, providing a barrier action to a {@code |
58 |
|
* CyclicBarrier}. |
59 |
|
* |
60 |
< |
* <li> <b>Waiting.</b> Method {@link #awaitAdvance} requires an |
60 |
> |
* <li><b>Waiting.</b> Method {@link #awaitAdvance} requires an |
61 |
|
* argument indicating an arrival phase number, and returns when |
62 |
|
* the phaser advances to (or is already at) a different phase. |
63 |
|
* Unlike similar constructions using {@code CyclicBarrier}, |
74 |
|
* |
75 |
|
* </ul> |
76 |
|
* |
77 |
< |
* <p> <b>Termination.</b> A phaser may enter a <em>termination</em> |
77 |
> |
* <p><b>Termination.</b> A phaser may enter a <em>termination</em> |
78 |
|
* state, that may be checked using method {@link #isTerminated}. Upon |
79 |
|
* termination, all synchronization methods immediately return without |
80 |
|
* waiting for advance, as indicated by a negative return value. |
89 |
|
* also available to abruptly release waiting threads and allow them |
90 |
|
* to terminate. |
91 |
|
* |
92 |
< |
* <p> <b>Tiering.</b> Phasers may be <em>tiered</em> (i.e., |
92 |
> |
* <p><b>Tiering.</b> Phasers may be <em>tiered</em> (i.e., |
93 |
|
* constructed in tree structures) to reduce contention. Phasers with |
94 |
|
* large numbers of parties that would otherwise experience heavy |
95 |
|
* synchronization contention costs may instead be set up so that |
193 |
|
* phaser.arriveAndDeregister(); |
194 |
|
* }}</pre> |
195 |
|
* |
196 |
– |
* |
196 |
|
* <p>To create a set of {@code n} tasks using a tree of phasers, you |
197 |
|
* could use code of the following form, assuming a Task class with a |
198 |
|
* constructor accepting a {@code Phaser} that it registers with upon |
270 |
|
private static final int PHASE_SHIFT = 32; |
271 |
|
private static final int UNARRIVED_MASK = 0xffff; // to mask ints |
272 |
|
private static final long PARTIES_MASK = 0xffff0000L; // to mask longs |
273 |
+ |
private static final long COUNTS_MASK = 0xffffffffL; |
274 |
|
private static final long TERMINATION_BIT = 1L << 63; |
275 |
|
|
276 |
|
// some special values |
453 |
|
* subphasers have not yet done so, in which case they must finish |
454 |
|
* their own advance by setting unarrived to parties (or if |
455 |
|
* parties is zero, resetting to unregistered EMPTY state). |
456 |
– |
* However, this method may also be called when "floating" |
457 |
– |
* subphasers with possibly some unarrived parties are merely |
458 |
– |
* catching up to current phase, in which case counts are |
459 |
– |
* unaffected. |
456 |
|
* |
457 |
|
* @return reconciled state |
458 |
|
*/ |
460 |
|
final Phaser root = this.root; |
461 |
|
long s = state; |
462 |
|
if (root != this) { |
463 |
< |
int phase, u, p; |
464 |
< |
// CAS root phase with current parties; possibly trip unarrived |
463 |
> |
int phase, p; |
464 |
> |
// CAS to root phase with current parties, tripping unarrived |
465 |
|
while ((phase = (int)(root.state >>> PHASE_SHIFT)) != |
466 |
|
(int)(s >>> PHASE_SHIFT) && |
467 |
|
!UNSAFE.compareAndSwapLong |
468 |
|
(this, stateOffset, s, |
469 |
|
s = (((long)phase << PHASE_SHIFT) | |
470 |
< |
(s & PARTIES_MASK) | |
471 |
< |
((p = (int)s >>> PARTIES_SHIFT) == 0 ? EMPTY : |
472 |
< |
((u = (int)s & UNARRIVED_MASK) == 0 && phase >= 0) ? |
477 |
< |
p : u)))) |
470 |
> |
((phase < 0) ? (s & COUNTS_MASK) : |
471 |
> |
(((p = (int)s >>> PARTIES_SHIFT) == 0) ? EMPTY : |
472 |
> |
((s & PARTIES_MASK) | p)))))) |
473 |
|
s = state; |
474 |
|
} |
475 |
|
return s; |
1141 |
|
private static sun.misc.Unsafe getUnsafe() { |
1142 |
|
try { |
1143 |
|
return sun.misc.Unsafe.getUnsafe(); |
1144 |
< |
} catch (SecurityException se) { |
1145 |
< |
try { |
1146 |
< |
return java.security.AccessController.doPrivileged |
1147 |
< |
(new java.security |
1148 |
< |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1149 |
< |
public sun.misc.Unsafe run() throws Exception { |
1150 |
< |
java.lang.reflect.Field f = sun.misc |
1151 |
< |
.Unsafe.class.getDeclaredField("theUnsafe"); |
1152 |
< |
f.setAccessible(true); |
1153 |
< |
return (sun.misc.Unsafe) f.get(null); |
1154 |
< |
}}); |
1155 |
< |
} catch (java.security.PrivilegedActionException e) { |
1156 |
< |
throw new RuntimeException("Could not initialize intrinsics", |
1157 |
< |
e.getCause()); |
1158 |
< |
} |
1144 |
> |
} catch (SecurityException tryReflectionInstead) {} |
1145 |
> |
try { |
1146 |
> |
return java.security.AccessController.doPrivileged |
1147 |
> |
(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1148 |
> |
public sun.misc.Unsafe run() throws Exception { |
1149 |
> |
Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class; |
1150 |
> |
for (java.lang.reflect.Field f : k.getDeclaredFields()) { |
1151 |
> |
f.setAccessible(true); |
1152 |
> |
Object x = f.get(null); |
1153 |
> |
if (k.isInstance(x)) |
1154 |
> |
return k.cast(x); |
1155 |
> |
} |
1156 |
> |
throw new NoSuchFieldError("the Unsafe"); |
1157 |
> |
}}); |
1158 |
> |
} catch (java.security.PrivilegedActionException e) { |
1159 |
> |
throw new RuntimeException("Could not initialize intrinsics", |
1160 |
> |
e.getCause()); |
1161 |
|
} |
1162 |
|
} |
1163 |
|
} |