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 |
271 |
|
private static final int PHASE_SHIFT = 32; |
272 |
|
private static final int UNARRIVED_MASK = 0xffff; // to mask ints |
273 |
|
private static final long PARTIES_MASK = 0xffff0000L; // to mask longs |
274 |
+ |
private static final long COUNTS_MASK = 0xffffffffL; |
275 |
|
private static final long TERMINATION_BIT = 1L << 63; |
276 |
|
|
277 |
|
// some special values |
278 |
|
private static final int ONE_ARRIVAL = 1; |
279 |
|
private static final int ONE_PARTY = 1 << PARTIES_SHIFT; |
280 |
+ |
private static final int ONE_DEREGISTER = ONE_ARRIVAL|ONE_PARTY; |
281 |
|
private static final int EMPTY = 1; |
282 |
|
|
283 |
|
// The following unpacking methods are usually manually inlined |
284 |
|
|
285 |
|
private static int unarrivedOf(long s) { |
286 |
|
int counts = (int)s; |
287 |
< |
return (counts == EMPTY) ? 0 : counts & UNARRIVED_MASK; |
287 |
> |
return (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK); |
288 |
|
} |
289 |
|
|
290 |
|
private static int partiesOf(long s) { |
345 |
|
* Manually tuned to speed up and minimize race windows for the |
346 |
|
* common case of just decrementing unarrived field. |
347 |
|
* |
348 |
< |
* @param deregister false for arrive, true for arriveAndDeregister |
348 |
> |
* @param adjust value to subtract from state; |
349 |
> |
* ONE_ARRIVAL for arrive, |
350 |
> |
* ONE_DEREGISTER for arriveAndDeregister |
351 |
|
*/ |
352 |
< |
private int doArrive(boolean deregister) { |
349 |
< |
int adj = deregister ? ONE_ARRIVAL|ONE_PARTY : ONE_ARRIVAL; |
352 |
> |
private int doArrive(int adjust) { |
353 |
|
final Phaser root = this.root; |
354 |
|
for (;;) { |
355 |
|
long s = (root == this) ? state : reconcileState(); |
356 |
|
int phase = (int)(s >>> PHASE_SHIFT); |
354 |
– |
int counts = (int)s; |
355 |
– |
int unarrived = (counts & UNARRIVED_MASK) - 1; |
357 |
|
if (phase < 0) |
358 |
|
return phase; |
359 |
< |
else if (counts == EMPTY || unarrived < 0) { |
360 |
< |
if (root == this || reconcileState() == s) |
361 |
< |
throw new IllegalStateException(badArrive(s)); |
362 |
< |
} |
363 |
< |
else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adj)) { |
364 |
< |
if (unarrived == 0) { |
359 |
> |
int counts = (int)s; |
360 |
> |
int unarrived = (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK); |
361 |
> |
if (unarrived <= 0) |
362 |
> |
throw new IllegalStateException(badArrive(s)); |
363 |
> |
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, s-=adjust)) { |
364 |
> |
if (unarrived == 1) { |
365 |
|
long n = s & PARTIES_MASK; // base of next state |
366 |
|
int nextUnarrived = (int)n >>> PARTIES_SHIFT; |
367 |
< |
if (root != this) |
368 |
< |
return parent.doArrive(nextUnarrived == 0); |
369 |
< |
if (onAdvance(phase, nextUnarrived)) |
370 |
< |
n |= TERMINATION_BIT; |
371 |
< |
else if (nextUnarrived == 0) |
372 |
< |
n |= EMPTY; |
367 |
> |
if (root == this) { |
368 |
> |
if (onAdvance(phase, nextUnarrived)) |
369 |
> |
n |= TERMINATION_BIT; |
370 |
> |
else if (nextUnarrived == 0) |
371 |
> |
n |= EMPTY; |
372 |
> |
else |
373 |
> |
n |= nextUnarrived; |
374 |
> |
int nextPhase = (phase + 1) & MAX_PHASE; |
375 |
> |
n |= (long)nextPhase << PHASE_SHIFT; |
376 |
> |
UNSAFE.compareAndSwapLong(this, stateOffset, s, n); |
377 |
> |
releaseWaiters(phase); |
378 |
> |
} |
379 |
> |
else if (nextUnarrived == 0) { // propagate deregistration |
380 |
> |
phase = parent.doArrive(ONE_DEREGISTER); |
381 |
> |
UNSAFE.compareAndSwapLong(this, stateOffset, |
382 |
> |
s, s | EMPTY); |
383 |
> |
} |
384 |
|
else |
385 |
< |
n |= nextUnarrived; |
374 |
< |
n |= (long)((phase + 1) & MAX_PHASE) << PHASE_SHIFT; |
375 |
< |
UNSAFE.compareAndSwapLong(this, stateOffset, s, n); |
376 |
< |
releaseWaiters(phase); |
385 |
> |
phase = parent.doArrive(ONE_ARRIVAL); |
386 |
|
} |
387 |
|
return phase; |
388 |
|
} |
397 |
|
*/ |
398 |
|
private int doRegister(int registrations) { |
399 |
|
// adjustment to state |
400 |
< |
long adj = ((long)registrations << PARTIES_SHIFT) | registrations; |
400 |
> |
long adjust = ((long)registrations << PARTIES_SHIFT) | registrations; |
401 |
|
final Phaser parent = this.parent; |
402 |
|
int phase; |
403 |
|
for (;;) { |
404 |
< |
long s = state; |
404 |
> |
long s = (parent == null) ? state : reconcileState(); |
405 |
|
int counts = (int)s; |
406 |
|
int parties = counts >>> PARTIES_SHIFT; |
407 |
|
int unarrived = counts & UNARRIVED_MASK; |
408 |
|
if (registrations > MAX_PARTIES - parties) |
409 |
|
throw new IllegalStateException(badRegister(s)); |
410 |
< |
else if ((phase = (int)(s >>> PHASE_SHIFT)) < 0) |
410 |
> |
phase = (int)(s >>> PHASE_SHIFT); |
411 |
> |
if (phase < 0) |
412 |
|
break; |
413 |
< |
else if (counts != EMPTY) { // not 1st registration |
413 |
> |
if (counts != EMPTY) { // not 1st registration |
414 |
|
if (parent == null || reconcileState() == s) { |
415 |
|
if (unarrived == 0) // wait out advance |
416 |
|
root.internalAwaitAdvance(phase, null); |
417 |
|
else if (UNSAFE.compareAndSwapLong(this, stateOffset, |
418 |
< |
s, s + adj)) |
418 |
> |
s, s + adjust)) |
419 |
|
break; |
420 |
|
} |
421 |
|
} |
422 |
|
else if (parent == null) { // 1st root registration |
423 |
< |
long next = ((long)phase << PHASE_SHIFT) | adj; |
423 |
> |
long next = ((long)phase << PHASE_SHIFT) | adjust; |
424 |
|
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, next)) |
425 |
|
break; |
426 |
|
} |
427 |
|
else { |
428 |
|
synchronized (this) { // 1st sub registration |
429 |
|
if (state == s) { // recheck under lock |
430 |
< |
parent.doRegister(1); |
431 |
< |
do { // force current phase |
430 |
> |
phase = parent.doRegister(1); |
431 |
> |
if (phase < 0) |
432 |
> |
break; |
433 |
> |
// finish registration whenever parent registration |
434 |
> |
// succeeded, even when racing with termination, |
435 |
> |
// since these are part of the same "transaction". |
436 |
> |
while (!UNSAFE.compareAndSwapLong |
437 |
> |
(this, stateOffset, s, |
438 |
> |
((long)phase << PHASE_SHIFT) | adjust)) { |
439 |
> |
s = state; |
440 |
|
phase = (int)(root.state >>> PHASE_SHIFT); |
441 |
< |
// assert phase < 0 || (int)state == EMPTY; |
442 |
< |
} while (!UNSAFE.compareAndSwapLong |
425 |
< |
(this, stateOffset, state, |
426 |
< |
((long)phase << PHASE_SHIFT) | adj)); |
441 |
> |
// assert (int)s == EMPTY; |
442 |
> |
} |
443 |
|
break; |
444 |
|
} |
445 |
|
} |
454 |
|
* subphasers have not yet done so, in which case they must finish |
455 |
|
* their own advance by setting unarrived to parties (or if |
456 |
|
* parties is zero, resetting to unregistered EMPTY state). |
441 |
– |
* However, this method may also be called when "floating" |
442 |
– |
* subphasers with possibly some unarrived parties are merely |
443 |
– |
* catching up to current phase, in which case counts are |
444 |
– |
* unaffected. |
457 |
|
* |
458 |
|
* @return reconciled state |
459 |
|
*/ |
461 |
|
final Phaser root = this.root; |
462 |
|
long s = state; |
463 |
|
if (root != this) { |
464 |
< |
int phase, u, p; |
465 |
< |
// CAS root phase with current parties; possibly trip unarrived |
464 |
> |
int phase, p; |
465 |
> |
// CAS to root phase with current parties, tripping unarrived |
466 |
|
while ((phase = (int)(root.state >>> PHASE_SHIFT)) != |
467 |
|
(int)(s >>> PHASE_SHIFT) && |
468 |
|
!UNSAFE.compareAndSwapLong |
469 |
|
(this, stateOffset, s, |
470 |
|
s = (((long)phase << PHASE_SHIFT) | |
471 |
< |
(s & PARTIES_MASK) | |
472 |
< |
((p = (int)s >>> PARTIES_SHIFT) == 0 ? EMPTY : |
473 |
< |
(u = (int)s & UNARRIVED_MASK) == 0 ? p : u)))) |
471 |
> |
((phase < 0) ? (s & COUNTS_MASK) : |
472 |
> |
(((p = (int)s >>> PARTIES_SHIFT) == 0) ? EMPTY : |
473 |
> |
((s & PARTIES_MASK) | p)))))) |
474 |
|
s = state; |
475 |
|
} |
476 |
|
return s; |
602 |
|
* of unarrived parties would become negative |
603 |
|
*/ |
604 |
|
public int arrive() { |
605 |
< |
return doArrive(false); |
605 |
> |
return doArrive(ONE_ARRIVAL); |
606 |
|
} |
607 |
|
|
608 |
|
/** |
622 |
|
* of registered or unarrived parties would become negative |
623 |
|
*/ |
624 |
|
public int arriveAndDeregister() { |
625 |
< |
return doArrive(true); |
625 |
> |
return doArrive(ONE_DEREGISTER); |
626 |
|
} |
627 |
|
|
628 |
|
/** |
649 |
|
for (;;) { |
650 |
|
long s = (root == this) ? state : reconcileState(); |
651 |
|
int phase = (int)(s >>> PHASE_SHIFT); |
640 |
– |
int counts = (int)s; |
641 |
– |
int unarrived = (counts & UNARRIVED_MASK) - 1; |
652 |
|
if (phase < 0) |
653 |
|
return phase; |
654 |
< |
else if (counts == EMPTY || unarrived < 0) { |
655 |
< |
if (reconcileState() == s) |
656 |
< |
throw new IllegalStateException(badArrive(s)); |
657 |
< |
} |
658 |
< |
else if (UNSAFE.compareAndSwapLong(this, stateOffset, s, |
659 |
< |
s -= ONE_ARRIVAL)) { |
660 |
< |
if (unarrived != 0) |
654 |
> |
int counts = (int)s; |
655 |
> |
int unarrived = (counts == EMPTY) ? 0 : (counts & UNARRIVED_MASK); |
656 |
> |
if (unarrived <= 0) |
657 |
> |
throw new IllegalStateException(badArrive(s)); |
658 |
> |
if (UNSAFE.compareAndSwapLong(this, stateOffset, s, |
659 |
> |
s -= ONE_ARRIVAL)) { |
660 |
> |
if (unarrived > 1) |
661 |
|
return root.internalAwaitAdvance(phase, null); |
662 |
|
if (root != this) |
663 |
|
return parent.arriveAndAwaitAdvance(); |
790 |
|
if (UNSAFE.compareAndSwapLong(root, stateOffset, |
791 |
|
s, s | TERMINATION_BIT)) { |
792 |
|
// signal all threads |
793 |
< |
releaseWaiters(0); |
794 |
< |
releaseWaiters(1); |
793 |
> |
releaseWaiters(0); // Waiters on evenQ |
794 |
> |
releaseWaiters(1); // Waiters on oddQ |
795 |
|
return; |
796 |
|
} |
797 |
|
} |
997 |
|
|
998 |
|
/** |
999 |
|
* Possibly blocks and waits for phase to advance unless aborted. |
1000 |
< |
* Call only from root node. |
1000 |
> |
* Call only on root phaser. |
1001 |
|
* |
1002 |
|
* @param phase current phase |
1003 |
|
* @param node if non-null, the wait node to track interrupt and timeout; |
1005 |
|
* @return current phase |
1006 |
|
*/ |
1007 |
|
private int internalAwaitAdvance(int phase, QNode node) { |
1008 |
+ |
// assert root == this; |
1009 |
|
releaseWaiters(phase-1); // ensure old queue clean |
1010 |
|
boolean queued = false; // true when node is enqueued |
1011 |
|
int lastUnarrived = 0; // to increase spins upon change |
1142 |
|
private static sun.misc.Unsafe getUnsafe() { |
1143 |
|
try { |
1144 |
|
return sun.misc.Unsafe.getUnsafe(); |
1145 |
< |
} catch (SecurityException se) { |
1146 |
< |
try { |
1147 |
< |
return java.security.AccessController.doPrivileged |
1148 |
< |
(new java.security |
1149 |
< |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1150 |
< |
public sun.misc.Unsafe run() throws Exception { |
1151 |
< |
java.lang.reflect.Field f = sun.misc |
1152 |
< |
.Unsafe.class.getDeclaredField("theUnsafe"); |
1153 |
< |
f.setAccessible(true); |
1154 |
< |
return (sun.misc.Unsafe) f.get(null); |
1155 |
< |
}}); |
1156 |
< |
} catch (java.security.PrivilegedActionException e) { |
1157 |
< |
throw new RuntimeException("Could not initialize intrinsics", |
1158 |
< |
e.getCause()); |
1159 |
< |
} |
1145 |
> |
} catch (SecurityException tryReflectionInstead) {} |
1146 |
> |
try { |
1147 |
> |
return java.security.AccessController.doPrivileged |
1148 |
> |
(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1149 |
> |
public sun.misc.Unsafe run() throws Exception { |
1150 |
> |
Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class; |
1151 |
> |
for (java.lang.reflect.Field f : k.getDeclaredFields()) { |
1152 |
> |
f.setAccessible(true); |
1153 |
> |
Object x = f.get(null); |
1154 |
> |
if (k.isInstance(x)) |
1155 |
> |
return k.cast(x); |
1156 |
> |
} |
1157 |
> |
throw new NoSuchFieldError("the Unsafe"); |
1158 |
> |
}}); |
1159 |
> |
} catch (java.security.PrivilegedActionException e) { |
1160 |
> |
throw new RuntimeException("Could not initialize intrinsics", |
1161 |
> |
e.getCause()); |
1162 |
|
} |
1163 |
|
} |
1164 |
|
} |