1 |
/* |
2 |
* Written by Doug Lea with assistance from members of JCP JSR-166 |
3 |
* Expert Group and released to the public domain, as explained at |
4 |
* http://creativecommons.org/licenses/publicdomain |
5 |
*/ |
6 |
|
7 |
package jsr166y; |
8 |
|
9 |
import java.util.concurrent.*; |
10 |
import java.util.concurrent.atomic.*; |
11 |
import java.util.concurrent.locks.LockSupport; |
12 |
import sun.misc.Unsafe; |
13 |
import java.lang.reflect.*; |
14 |
|
15 |
/** |
16 |
* A reusable synchronization barrier, similar in functionality to a |
17 |
* {@link java.util.concurrent.CyclicBarrier CyclicBarrier} and |
18 |
* {@link java.util.concurrent.CountDownLatch CountDownLatch} |
19 |
* but supporting more flexible usage. |
20 |
* |
21 |
* <ul> |
22 |
* |
23 |
* <li> The number of parties synchronizing on a phaser may vary over |
24 |
* time. A task may register to be a party at any time, and may |
25 |
* deregister upon arriving at the barrier. As is the case with most |
26 |
* basic synchronization constructs, registration and deregistration |
27 |
* affect only internal counts; they do not establish any further |
28 |
* internal bookkeeping, so tasks cannot query whether they are |
29 |
* registered. (However, you can introduce such bookkeeping by |
30 |
* subclassing this class.) |
31 |
* |
32 |
* <li> Each generation has an associated phase value, starting at |
33 |
* zero, and advancing when all parties reach the barrier (wrapping |
34 |
* around to zero after reaching {@code Integer.MAX_VALUE}). |
35 |
* |
36 |
* <li> Like a CyclicBarrier, a Phaser may be repeatedly awaited. |
37 |
* Method {@code arriveAndAwaitAdvance} has effect analogous to |
38 |
* {@code CyclicBarrier.await}. However, Phasers separate two |
39 |
* aspects of coordination, that 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 |
45 |
* the phase value current upon entry to the method. |
46 |
* |
47 |
* <li> Awaiting others. Method {@code 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. |
58 |
* |
59 |
* <li> Phasers may enter a <em>termination</em> state in which all |
60 |
* await actions immediately return, indicating (via a negative phase |
61 |
* value) that execution is complete. Termination is triggered by |
62 |
* executing the overridable {@code onAdvance} method that is invoked |
63 |
* each time the barrier is about to be tripped. 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 |
67 |
* {@code forceTermination} is also available to abruptly release |
68 |
* waiting 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 |
72 |
* synchronization contention costs may instead be arranged in trees. |
73 |
* This will typically greatly increase throughput even though it |
74 |
* incurs somewhat greater per-operation overhead. |
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 |
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 |
* </ul> |
85 |
* |
86 |
* <p><b>Sample usages:</b> |
87 |
* |
88 |
* <p>A Phaser may be used instead of a {@code CountDownLatch} to control |
89 |
* a one-shot action serving a variable number of parties. The typical |
90 |
* idiom is for the method setting this up to first register, then |
91 |
* start the actions, then deregister, as in: |
92 |
* |
93 |
* <pre> |
94 |
* void runTasks(List<Runnable> list) { |
95 |
* final Phaser phaser = new Phaser(1); // "1" to register self |
96 |
* for (Runnable r : list) { |
97 |
* phaser.register(); |
98 |
* new Thread() { |
99 |
* public void run() { |
100 |
* phaser.arriveAndAwaitAdvance(); // await all creation |
101 |
* r.run(); |
102 |
* phaser.arriveAndDeregister(); // signal completion |
103 |
* } |
104 |
* }.start(); |
105 |
* } |
106 |
* |
107 |
* doSomethingOnBehalfOfWorkers(); |
108 |
* phaser.arrive(); // allow threads to start |
109 |
* int p = phaser.arriveAndDeregister(); // deregister self ... |
110 |
* p = phaser.awaitAdvance(p); // ... and await arrival |
111 |
* otherActions(); // do other things while tasks execute |
112 |
* phaser.awaitAdvance(p); // await final completion |
113 |
* } |
114 |
* </pre> |
115 |
* |
116 |
* <p>One way to cause a set of threads to repeatedly perform actions |
117 |
* for a given number of iterations is to override {@code onAdvance}: |
118 |
* |
119 |
* <pre> |
120 |
* void startTasks(List<Runnable> list, final int iterations) { |
121 |
* final Phaser phaser = new Phaser() { |
122 |
* public boolean onAdvance(int phase, int registeredParties) { |
123 |
* return phase >= iterations || registeredParties == 0; |
124 |
* } |
125 |
* }; |
126 |
* phaser.register(); |
127 |
* for (Runnable r : list) { |
128 |
* phaser.register(); |
129 |
* new Thread() { |
130 |
* public void run() { |
131 |
* do { |
132 |
* r.run(); |
133 |
* phaser.arriveAndAwaitAdvance(); |
134 |
* } while(!phaser.isTerminated(); |
135 |
* } |
136 |
* }.start(); |
137 |
* } |
138 |
* phaser.arriveAndDeregister(); // deregister self, don't wait |
139 |
* } |
140 |
* </pre> |
141 |
* |
142 |
* <p> To create a set of tasks using a tree of Phasers, |
143 |
* you could use code of the following form, assuming a |
144 |
* Task class with a constructor accepting a Phaser that |
145 |
* it registers for upon construction: |
146 |
* <pre> |
147 |
* void build(Task[] actions, int lo, int hi, Phaser b) { |
148 |
* int step = (hi - lo) / TASKS_PER_PHASER; |
149 |
* if (step > 1) { |
150 |
* int i = lo; |
151 |
* while (i < hi) { |
152 |
* int r = Math.min(i + step, hi); |
153 |
* build(actions, i, r, new Phaser(b)); |
154 |
* i = r; |
155 |
* } |
156 |
* } |
157 |
* else { |
158 |
* for (int i = lo; i < hi; ++i) |
159 |
* actions[i] = new Task(b); |
160 |
* // assumes new Task(b) performs b.register() |
161 |
* } |
162 |
* } |
163 |
* // .. initially called, for n tasks via |
164 |
* build(new Task[n], 0, n, new Phaser()); |
165 |
* </pre> |
166 |
* |
167 |
* The best value of {@code TASKS_PER_PHASER} depends mainly on |
168 |
* expected barrier synchronization rates. A value as low as four may |
169 |
* be appropriate for extremely small per-barrier task bodies (thus |
170 |
* high rates), or up to hundreds for extremely large ones. |
171 |
* |
172 |
* </pre> |
173 |
* |
174 |
* <p><b>Implementation notes</b>: This implementation restricts the |
175 |
* maximum number of parties to 65535. Attempts to register additional |
176 |
* parties result in IllegalStateExceptions. However, you can and |
177 |
* should create tiered phasers to accommodate arbitrarily large sets |
178 |
* of participants. |
179 |
*/ |
180 |
public class Phaser { |
181 |
/* |
182 |
* This class implements an extension of X10 "clocks". Thanks to |
183 |
* Vijay Saraswat for the idea, and to Vivek Sarkar for |
184 |
* enhancements to extend functionality. |
185 |
*/ |
186 |
|
187 |
/** |
188 |
* Barrier state representation. Conceptually, a barrier contains |
189 |
* four values: |
190 |
* |
191 |
* * parties -- the number of parties to wait (16 bits) |
192 |
* * unarrived -- the number of parties yet to hit barrier (16 bits) |
193 |
* * phase -- the generation of the barrier (31 bits) |
194 |
* * terminated -- set if barrier is terminated (1 bit) |
195 |
* |
196 |
* However, to efficiently maintain atomicity, these values are |
197 |
* packed into a single (atomic) long. Termination uses the sign |
198 |
* bit of 32 bit representation of phase, so phase is set to -1 on |
199 |
* termination. Good performance relies on keeping state decoding |
200 |
* and encoding simple, and keeping race windows short. |
201 |
* |
202 |
* Note: there are some cheats in arrive() that rely on unarrived |
203 |
* being lowest 16 bits. |
204 |
*/ |
205 |
private volatile long state; |
206 |
|
207 |
private static final int ushortBits = 16; |
208 |
private static final int ushortMask = (1 << ushortBits) - 1; |
209 |
private static final int phaseMask = 0x7fffffff; |
210 |
|
211 |
private static int unarrivedOf(long s) { |
212 |
return (int)(s & ushortMask); |
213 |
} |
214 |
|
215 |
private static int partiesOf(long s) { |
216 |
return (int)(s & (ushortMask << 16)) >>> 16; |
217 |
} |
218 |
|
219 |
private static int phaseOf(long s) { |
220 |
return (int)(s >>> 32); |
221 |
} |
222 |
|
223 |
private static int arrivedOf(long s) { |
224 |
return partiesOf(s) - unarrivedOf(s); |
225 |
} |
226 |
|
227 |
private static long stateFor(int phase, int parties, int unarrived) { |
228 |
return (((long)phase) << 32) | ((parties << 16) | unarrived); |
229 |
} |
230 |
|
231 |
private static long trippedStateFor(int phase, int parties) { |
232 |
return (((long)phase) << 32) | ((parties << 16) | parties); |
233 |
} |
234 |
|
235 |
private static IllegalStateException badBounds(int parties, int unarrived) { |
236 |
return new IllegalStateException |
237 |
("Attempt to set " + unarrived + |
238 |
" unarrived of " + parties + " parties"); |
239 |
} |
240 |
|
241 |
/** |
242 |
* The parent of this phaser, or null if none |
243 |
*/ |
244 |
private final Phaser parent; |
245 |
|
246 |
/** |
247 |
* The root of Phaser tree. Equals this if not in a tree. Used to |
248 |
* support faster state push-down. |
249 |
*/ |
250 |
private final Phaser root; |
251 |
|
252 |
// Wait queues |
253 |
|
254 |
/** |
255 |
* Heads of Treiber stacks waiting for nonFJ threads. To eliminate |
256 |
* contention while releasing some threads while adding others, we |
257 |
* use two of them, alternating across even and odd phases. |
258 |
*/ |
259 |
private final AtomicReference<QNode> evenQ = new AtomicReference<QNode>(); |
260 |
private final AtomicReference<QNode> oddQ = new AtomicReference<QNode>(); |
261 |
|
262 |
private AtomicReference<QNode> queueFor(int phase) { |
263 |
return (phase & 1) == 0? evenQ : oddQ; |
264 |
} |
265 |
|
266 |
/** |
267 |
* Returns current state, first resolving lagged propagation from |
268 |
* root if necessary. |
269 |
*/ |
270 |
private long getReconciledState() { |
271 |
return parent == null? state : reconcileState(); |
272 |
} |
273 |
|
274 |
/** |
275 |
* Recursively resolves state. |
276 |
*/ |
277 |
private long reconcileState() { |
278 |
Phaser p = parent; |
279 |
long s = state; |
280 |
if (p != null) { |
281 |
while (unarrivedOf(s) == 0 && phaseOf(s) != phaseOf(root.state)) { |
282 |
long parentState = p.getReconciledState(); |
283 |
int parentPhase = phaseOf(parentState); |
284 |
int phase = phaseOf(s = state); |
285 |
if (phase != parentPhase) { |
286 |
long next = trippedStateFor(parentPhase, partiesOf(s)); |
287 |
if (casState(s, next)) { |
288 |
releaseWaiters(phase); |
289 |
s = next; |
290 |
} |
291 |
} |
292 |
} |
293 |
} |
294 |
return s; |
295 |
} |
296 |
|
297 |
/** |
298 |
* Creates a new Phaser without any initially registered parties, |
299 |
* initial phase number 0, and no parent. |
300 |
*/ |
301 |
public Phaser() { |
302 |
this(null); |
303 |
} |
304 |
|
305 |
/** |
306 |
* Creates a new Phaser with the given numbers of registered |
307 |
* unarrived parties, initial phase number 0, and no parent. |
308 |
* @param parties the number of parties required to trip barrier. |
309 |
* @throws IllegalArgumentException if parties less than zero |
310 |
* or greater than the maximum number of parties supported. |
311 |
*/ |
312 |
public Phaser(int parties) { |
313 |
this(null, parties); |
314 |
} |
315 |
|
316 |
/** |
317 |
* Creates a new Phaser with the given parent, without any |
318 |
* initially registered parties. If parent is non-null this phaser |
319 |
* is registered with the parent and its initial phase number is |
320 |
* the same as that of parent phaser. |
321 |
* @param parent the parent phaser. |
322 |
*/ |
323 |
public Phaser(Phaser parent) { |
324 |
int phase = 0; |
325 |
this.parent = parent; |
326 |
if (parent != null) { |
327 |
this.root = parent.root; |
328 |
phase = parent.register(); |
329 |
} |
330 |
else |
331 |
this.root = this; |
332 |
this.state = trippedStateFor(phase, 0); |
333 |
} |
334 |
|
335 |
/** |
336 |
* Creates a new Phaser with the given parent and numbers of |
337 |
* registered unarrived parties. If parent is non-null this phaser |
338 |
* is registered with the parent and its initial phase number is |
339 |
* the same as that of parent phaser. |
340 |
* @param parent the parent phaser. |
341 |
* @param parties the number of parties required to trip barrier. |
342 |
* @throws IllegalArgumentException if parties less than zero |
343 |
* or greater than the maximum number of parties supported. |
344 |
*/ |
345 |
public Phaser(Phaser parent, int parties) { |
346 |
if (parties < 0 || parties > ushortMask) |
347 |
throw new IllegalArgumentException("Illegal number of parties"); |
348 |
int phase = 0; |
349 |
this.parent = parent; |
350 |
if (parent != null) { |
351 |
this.root = parent.root; |
352 |
phase = parent.register(); |
353 |
} |
354 |
else |
355 |
this.root = this; |
356 |
this.state = trippedStateFor(phase, parties); |
357 |
} |
358 |
|
359 |
/** |
360 |
* Adds a new unarrived party to this phaser. |
361 |
* @return the current barrier phase number upon registration |
362 |
* @throws IllegalStateException if attempting to register more |
363 |
* than the maximum supported number of parties. |
364 |
*/ |
365 |
public int register() { |
366 |
return doRegister(1); |
367 |
} |
368 |
|
369 |
/** |
370 |
* Adds the given number of new unarrived parties to this phaser. |
371 |
* @param parties the number of parties required to trip barrier. |
372 |
* @return the current barrier phase number upon registration |
373 |
* @throws IllegalStateException if attempting to register more |
374 |
* than the maximum supported number of parties. |
375 |
*/ |
376 |
public int bulkRegister(int parties) { |
377 |
if (parties < 0) |
378 |
throw new IllegalArgumentException(); |
379 |
if (parties == 0) |
380 |
return getPhase(); |
381 |
return doRegister(parties); |
382 |
} |
383 |
|
384 |
/** |
385 |
* Shared code for register, bulkRegister |
386 |
*/ |
387 |
private int doRegister(int registrations) { |
388 |
int phase; |
389 |
for (;;) { |
390 |
long s = getReconciledState(); |
391 |
phase = phaseOf(s); |
392 |
int unarrived = unarrivedOf(s) + registrations; |
393 |
int parties = partiesOf(s) + registrations; |
394 |
if (phase < 0) |
395 |
break; |
396 |
if (parties > ushortMask || unarrived > ushortMask) |
397 |
throw badBounds(parties, unarrived); |
398 |
if (phase == phaseOf(root.state) && |
399 |
casState(s, stateFor(phase, parties, unarrived))) |
400 |
break; |
401 |
} |
402 |
return phase; |
403 |
} |
404 |
|
405 |
/** |
406 |
* Arrives at the barrier, but does not wait for others. (You can |
407 |
* in turn wait for others via {@link #awaitAdvance}). |
408 |
* |
409 |
* @return the barrier phase number upon entry to this method, or a |
410 |
* negative value if terminated; |
411 |
* @throws IllegalStateException if not terminated and the number |
412 |
* of unarrived parties would become negative. |
413 |
*/ |
414 |
public int arrive() { |
415 |
int phase; |
416 |
for (;;) { |
417 |
long s = state; |
418 |
phase = phaseOf(s); |
419 |
int parties = partiesOf(s); |
420 |
int unarrived = unarrivedOf(s) - 1; |
421 |
if (unarrived > 0) { // Not the last arrival |
422 |
if (casState(s, s - 1)) // s-1 adds one arrival |
423 |
break; |
424 |
} |
425 |
else if (unarrived == 0) { // the last arrival |
426 |
Phaser par = parent; |
427 |
if (par == null) { // directly trip |
428 |
if (casState |
429 |
(s, |
430 |
trippedStateFor(onAdvance(phase, parties)? -1 : |
431 |
((phase + 1) & phaseMask), parties))) { |
432 |
releaseWaiters(phase); |
433 |
break; |
434 |
} |
435 |
} |
436 |
else { // cascade to parent |
437 |
if (casState(s, s - 1)) { // zeroes unarrived |
438 |
par.arrive(); |
439 |
reconcileState(); |
440 |
break; |
441 |
} |
442 |
} |
443 |
} |
444 |
else if (phase < 0) // Don't throw exception if terminated |
445 |
break; |
446 |
else if (phase != phaseOf(root.state)) // or if unreconciled |
447 |
reconcileState(); |
448 |
else |
449 |
throw badBounds(parties, unarrived); |
450 |
} |
451 |
return phase; |
452 |
} |
453 |
|
454 |
/** |
455 |
* Arrives at the barrier, and deregisters from it, without |
456 |
* waiting for others. Deregistration reduces number of parties |
457 |
* required to trip the barrier in future phases. If this phaser |
458 |
* has a parent, and deregistration causes this phaser to have |
459 |
* zero parties, this phaser is also deregistered from its parent. |
460 |
* |
461 |
* @return the current barrier phase number upon entry to |
462 |
* this method, or a negative value if terminated; |
463 |
* @throws IllegalStateException if not terminated and the number |
464 |
* of registered or unarrived parties would become negative. |
465 |
*/ |
466 |
public int arriveAndDeregister() { |
467 |
// similar code to arrive, but too different to merge |
468 |
Phaser par = parent; |
469 |
int phase; |
470 |
for (;;) { |
471 |
long s = state; |
472 |
phase = phaseOf(s); |
473 |
int parties = partiesOf(s) - 1; |
474 |
int unarrived = unarrivedOf(s) - 1; |
475 |
if (parties >= 0) { |
476 |
if (unarrived > 0 || (unarrived == 0 && par != null)) { |
477 |
if (casState |
478 |
(s, |
479 |
stateFor(phase, parties, unarrived))) { |
480 |
if (unarrived == 0) { |
481 |
par.arriveAndDeregister(); |
482 |
reconcileState(); |
483 |
} |
484 |
break; |
485 |
} |
486 |
continue; |
487 |
} |
488 |
if (unarrived == 0) { |
489 |
if (casState |
490 |
(s, |
491 |
trippedStateFor(onAdvance(phase, parties)? -1 : |
492 |
((phase + 1) & phaseMask), parties))) { |
493 |
releaseWaiters(phase); |
494 |
break; |
495 |
} |
496 |
continue; |
497 |
} |
498 |
if (phase < 0) |
499 |
break; |
500 |
if (par != null && phase != phaseOf(root.state)) { |
501 |
reconcileState(); |
502 |
continue; |
503 |
} |
504 |
} |
505 |
throw badBounds(parties, unarrived); |
506 |
} |
507 |
return phase; |
508 |
} |
509 |
|
510 |
/** |
511 |
* Arrives at the barrier and awaits others. Equivalent in effect |
512 |
* to {@code awaitAdvance(arrive())}. If you instead need to |
513 |
* await with interruption of timeout, and/or deregister upon |
514 |
* arrival, you can arrange them using analogous constructions. |
515 |
* @return the phase on entry to this method |
516 |
* @throws IllegalStateException if not terminated and the number |
517 |
* of unarrived parties would become negative. |
518 |
*/ |
519 |
public int arriveAndAwaitAdvance() { |
520 |
return awaitAdvance(arrive()); |
521 |
} |
522 |
|
523 |
/** |
524 |
* Awaits the phase of the barrier to advance from the given |
525 |
* value, or returns immediately if argument is negative or this |
526 |
* barrier is terminated. |
527 |
* @param phase the phase on entry to this method |
528 |
* @return the phase on exit from this method |
529 |
*/ |
530 |
public int awaitAdvance(int phase) { |
531 |
if (phase < 0) |
532 |
return phase; |
533 |
long s = getReconciledState(); |
534 |
int p = phaseOf(s); |
535 |
if (p != phase) |
536 |
return p; |
537 |
if (unarrivedOf(s) == 0) |
538 |
parent.awaitAdvance(phase); |
539 |
// Fall here even if parent waited, to reconcile and help release |
540 |
return untimedWait(phase); |
541 |
} |
542 |
|
543 |
/** |
544 |
* Awaits the phase of the barrier to advance from the given |
545 |
* value, or returns immediately if argument is negative or this |
546 |
* barrier is terminated, or throws InterruptedException if |
547 |
* interrupted while waiting. |
548 |
* @param phase the phase on entry to this method |
549 |
* @return the phase on exit from this method |
550 |
* @throws InterruptedException if thread interrupted while waiting |
551 |
*/ |
552 |
public int awaitAdvanceInterruptibly(int phase) throws InterruptedException { |
553 |
if (phase < 0) |
554 |
return phase; |
555 |
long s = getReconciledState(); |
556 |
int p = phaseOf(s); |
557 |
if (p != phase) |
558 |
return p; |
559 |
if (unarrivedOf(s) != 0) |
560 |
parent.awaitAdvanceInterruptibly(phase); |
561 |
return interruptibleWait(phase); |
562 |
} |
563 |
|
564 |
/** |
565 |
* Awaits the phase of the barrier to advance from the given value |
566 |
* or the given timeout elapses, or returns immediately if |
567 |
* argument is negative or this barrier is terminated. |
568 |
* @param phase the phase on entry to this method |
569 |
* @return the phase on exit from this method |
570 |
* @throws InterruptedException if thread interrupted while waiting |
571 |
* @throws TimeoutException if timed out while waiting |
572 |
*/ |
573 |
public int awaitAdvanceInterruptibly(int phase, long timeout, TimeUnit unit) |
574 |
throws InterruptedException, TimeoutException { |
575 |
if (phase < 0) |
576 |
return phase; |
577 |
long s = getReconciledState(); |
578 |
int p = phaseOf(s); |
579 |
if (p != phase) |
580 |
return p; |
581 |
if (unarrivedOf(s) == 0) |
582 |
parent.awaitAdvanceInterruptibly(phase, timeout, unit); |
583 |
return timedWait(phase, unit.toNanos(timeout)); |
584 |
} |
585 |
|
586 |
/** |
587 |
* Forces this barrier to enter termination state. Counts of |
588 |
* arrived and registered parties are unaffected. If this phaser |
589 |
* has a parent, it too is terminated. This method may be useful |
590 |
* for coordinating recovery after one or more tasks encounter |
591 |
* unexpected exceptions. |
592 |
*/ |
593 |
public void forceTermination() { |
594 |
for (;;) { |
595 |
long s = getReconciledState(); |
596 |
int phase = phaseOf(s); |
597 |
int parties = partiesOf(s); |
598 |
int unarrived = unarrivedOf(s); |
599 |
if (phase < 0 || |
600 |
casState(s, stateFor(-1, parties, unarrived))) { |
601 |
releaseWaiters(0); |
602 |
releaseWaiters(1); |
603 |
if (parent != null) |
604 |
parent.forceTermination(); |
605 |
return; |
606 |
} |
607 |
} |
608 |
} |
609 |
|
610 |
/** |
611 |
* Returns the current phase number. The maximum phase number is |
612 |
* {@code Integer.MAX_VALUE}, after which it restarts at |
613 |
* zero. Upon termination, the phase number is negative. |
614 |
* @return the phase number, or a negative value if terminated |
615 |
*/ |
616 |
public final int getPhase() { |
617 |
return phaseOf(getReconciledState()); |
618 |
} |
619 |
|
620 |
/** |
621 |
* Returns {@code true} if the current phase number equals the given phase. |
622 |
* @param phase the phase |
623 |
* @return {@code true} if the current phase number equals the given phase |
624 |
*/ |
625 |
public final boolean hasPhase(int phase) { |
626 |
return phaseOf(getReconciledState()) == phase; |
627 |
} |
628 |
|
629 |
/** |
630 |
* Returns the number of parties registered at this barrier. |
631 |
* @return the number of parties |
632 |
*/ |
633 |
public int getRegisteredParties() { |
634 |
return partiesOf(state); |
635 |
} |
636 |
|
637 |
/** |
638 |
* Returns the number of parties that have arrived at the current |
639 |
* phase of this barrier. |
640 |
* @return the number of arrived parties |
641 |
*/ |
642 |
public int getArrivedParties() { |
643 |
return arrivedOf(state); |
644 |
} |
645 |
|
646 |
/** |
647 |
* Returns the number of registered parties that have not yet |
648 |
* arrived at the current phase of this barrier. |
649 |
* @return the number of unarrived parties |
650 |
*/ |
651 |
public int getUnarrivedParties() { |
652 |
return unarrivedOf(state); |
653 |
} |
654 |
|
655 |
/** |
656 |
* Returns the parent of this phaser, or null if none. |
657 |
* @return the parent of this phaser, or null if none |
658 |
*/ |
659 |
public Phaser getParent() { |
660 |
return parent; |
661 |
} |
662 |
|
663 |
/** |
664 |
* Returns the root ancestor of this phaser, which is the same as |
665 |
* this phaser if it has no parent. |
666 |
* @return the root ancestor of this phaser |
667 |
*/ |
668 |
public Phaser getRoot() { |
669 |
return root; |
670 |
} |
671 |
|
672 |
/** |
673 |
* Returns {@code true} if this barrier has been terminated. |
674 |
* @return {@code true} if this barrier has been terminated |
675 |
*/ |
676 |
public boolean isTerminated() { |
677 |
return getPhase() < 0; |
678 |
} |
679 |
|
680 |
/** |
681 |
* Overridable method to perform an action upon phase advance, and |
682 |
* to control termination. This method is invoked whenever the |
683 |
* barrier is tripped (and thus all other waiting parties are |
684 |
* dormant). If it returns true, then, rather than advance the |
685 |
* phase number, this barrier will be set to a final termination |
686 |
* state, and subsequent calls to {@code isTerminated} will |
687 |
* return true. |
688 |
* |
689 |
* <p> The default version returns true when the number of |
690 |
* registered parties is zero. Normally, overrides that arrange |
691 |
* termination for other reasons should also preserve this |
692 |
* property. |
693 |
* |
694 |
* <p> You may override this method to perform an action with side |
695 |
* effects visible to participating tasks, but it is in general |
696 |
* only sensible to do so in designs where all parties register |
697 |
* before any arrive, and all {@code awaitAdvance} at each phase. |
698 |
* Otherwise, you cannot ensure lack of interference. In |
699 |
* particular, this method may be invoked more than once per |
700 |
* transition if other parties successfully register while the |
701 |
* invocation of this method is in progress, thus postponing the |
702 |
* transition until those parties also arrive, re-triggering this |
703 |
* method. |
704 |
* |
705 |
* @param phase the phase number on entering the barrier |
706 |
* @param registeredParties the current number of registered parties |
707 |
* @return {@code true} if this barrier should terminate |
708 |
*/ |
709 |
protected boolean onAdvance(int phase, int registeredParties) { |
710 |
return registeredParties <= 0; |
711 |
} |
712 |
|
713 |
/** |
714 |
* Returns a string identifying this phaser, as well as its |
715 |
* state. The state, in brackets, includes the String {@code |
716 |
* "phase = "} followed by the phase number, {@code "parties = "} |
717 |
* followed by the number of registered parties, and {@code |
718 |
* "arrived = "} followed by the number of arrived parties. |
719 |
* |
720 |
* @return a string identifying this barrier, as well as its state |
721 |
*/ |
722 |
public String toString() { |
723 |
long s = getReconciledState(); |
724 |
return super.toString() + |
725 |
"[phase = " + phaseOf(s) + |
726 |
" parties = " + partiesOf(s) + |
727 |
" arrived = " + arrivedOf(s) + "]"; |
728 |
} |
729 |
|
730 |
// methods for waiting |
731 |
|
732 |
/** The number of CPUs, for spin control */ |
733 |
static final int NCPUS = Runtime.getRuntime().availableProcessors(); |
734 |
|
735 |
/** |
736 |
* The number of times to spin before blocking in timed waits. |
737 |
* The value is empirically derived. |
738 |
*/ |
739 |
static final int maxTimedSpins = (NCPUS < 2)? 0 : 32; |
740 |
|
741 |
/** |
742 |
* The number of times to spin before blocking in untimed waits. |
743 |
* This is greater than timed value because untimed waits spin |
744 |
* faster since they don't need to check times on each spin. |
745 |
*/ |
746 |
static final int maxUntimedSpins = maxTimedSpins * 32; |
747 |
|
748 |
/** |
749 |
* The number of nanoseconds for which it is faster to spin |
750 |
* rather than to use timed park. A rough estimate suffices. |
751 |
*/ |
752 |
static final long spinForTimeoutThreshold = 1000L; |
753 |
|
754 |
/** |
755 |
* Wait nodes for Treiber stack representing wait queue for non-FJ |
756 |
* tasks. |
757 |
*/ |
758 |
static final class QNode { |
759 |
QNode next; |
760 |
volatile Thread thread; // nulled to cancel wait |
761 |
QNode() { |
762 |
thread = Thread.currentThread(); |
763 |
} |
764 |
void signal() { |
765 |
Thread t = thread; |
766 |
if (t != null) { |
767 |
thread = null; |
768 |
LockSupport.unpark(t); |
769 |
} |
770 |
} |
771 |
} |
772 |
|
773 |
/** |
774 |
* Removes and signals waiting threads from wait queue |
775 |
*/ |
776 |
private void releaseWaiters(int phase) { |
777 |
AtomicReference<QNode> head = queueFor(phase); |
778 |
QNode q; |
779 |
while ((q = head.get()) != null) { |
780 |
if (head.compareAndSet(q, q.next)) |
781 |
q.signal(); |
782 |
} |
783 |
} |
784 |
|
785 |
/** |
786 |
* Enqueues node and waits unless aborted or signalled. |
787 |
*/ |
788 |
private int untimedWait(int phase) { |
789 |
int spins = maxUntimedSpins; |
790 |
QNode node = null; |
791 |
boolean interrupted = false; |
792 |
boolean queued = false; |
793 |
int p; |
794 |
while ((p = getPhase()) == phase) { |
795 |
interrupted = Thread.interrupted(); |
796 |
if (node != null) { |
797 |
if (!queued) { |
798 |
AtomicReference<QNode> head = queueFor(phase); |
799 |
queued = head.compareAndSet(node.next = head.get(), node); |
800 |
} |
801 |
else if (node.thread != null) |
802 |
LockSupport.park(this); |
803 |
} |
804 |
else if (spins <= 0) |
805 |
node = new QNode(); |
806 |
else |
807 |
--spins; |
808 |
} |
809 |
if (node != null) |
810 |
node.thread = null; |
811 |
if (interrupted) |
812 |
Thread.currentThread().interrupt(); |
813 |
releaseWaiters(phase); |
814 |
return p; |
815 |
} |
816 |
|
817 |
/** |
818 |
* Messier interruptible version |
819 |
*/ |
820 |
private int interruptibleWait(int phase) throws InterruptedException { |
821 |
int spins = maxUntimedSpins; |
822 |
QNode node = null; |
823 |
boolean queued = false; |
824 |
boolean interrupted = false; |
825 |
int p; |
826 |
while ((p = getPhase()) == phase) { |
827 |
if (interrupted = Thread.interrupted()) |
828 |
break; |
829 |
if (node != null) { |
830 |
if (!queued) { |
831 |
AtomicReference<QNode> head = queueFor(phase); |
832 |
queued = head.compareAndSet(node.next = head.get(), node); |
833 |
} |
834 |
else if (node.thread != null) |
835 |
LockSupport.park(this); |
836 |
} |
837 |
else if (spins <= 0) |
838 |
node = new QNode(); |
839 |
else |
840 |
--spins; |
841 |
} |
842 |
if (node != null) |
843 |
node.thread = null; |
844 |
if (interrupted) |
845 |
throw new InterruptedException(); |
846 |
releaseWaiters(phase); |
847 |
return p; |
848 |
} |
849 |
|
850 |
/** |
851 |
* Even messier timeout version. |
852 |
*/ |
853 |
private int timedWait(int phase, long nanos) |
854 |
throws InterruptedException, TimeoutException { |
855 |
int p; |
856 |
if ((p = getPhase()) == phase) { |
857 |
long lastTime = System.nanoTime(); |
858 |
int spins = maxTimedSpins; |
859 |
QNode node = null; |
860 |
boolean queued = false; |
861 |
boolean interrupted = false; |
862 |
while ((p = getPhase()) == phase) { |
863 |
if (interrupted = Thread.interrupted()) |
864 |
break; |
865 |
long now = System.nanoTime(); |
866 |
if ((nanos -= now - lastTime) <= 0) |
867 |
break; |
868 |
lastTime = now; |
869 |
if (node != null) { |
870 |
if (!queued) { |
871 |
AtomicReference<QNode> head = queueFor(phase); |
872 |
queued = head.compareAndSet(node.next = head.get(), node); |
873 |
} |
874 |
else if (node.thread != null && |
875 |
nanos > spinForTimeoutThreshold) { |
876 |
LockSupport.parkNanos(this, nanos); |
877 |
} |
878 |
} |
879 |
else if (spins <= 0) |
880 |
node = new QNode(); |
881 |
else |
882 |
--spins; |
883 |
} |
884 |
if (node != null) |
885 |
node.thread = null; |
886 |
if (interrupted) |
887 |
throw new InterruptedException(); |
888 |
if (p == phase && (p = getPhase()) == phase) |
889 |
throw new TimeoutException(); |
890 |
} |
891 |
releaseWaiters(phase); |
892 |
return p; |
893 |
} |
894 |
|
895 |
// Temporary Unsafe mechanics for preliminary release |
896 |
|
897 |
static final Unsafe _unsafe; |
898 |
static final long stateOffset; |
899 |
|
900 |
static { |
901 |
try { |
902 |
if (Phaser.class.getClassLoader() != null) { |
903 |
Field f = Unsafe.class.getDeclaredField("theUnsafe"); |
904 |
f.setAccessible(true); |
905 |
_unsafe = (Unsafe)f.get(null); |
906 |
} |
907 |
else |
908 |
_unsafe = Unsafe.getUnsafe(); |
909 |
stateOffset = _unsafe.objectFieldOffset |
910 |
(Phaser.class.getDeclaredField("state")); |
911 |
} catch (Exception e) { |
912 |
throw new RuntimeException("Could not initialize intrinsics", e); |
913 |
} |
914 |
} |
915 |
|
916 |
final boolean casState(long cmp, long val) { |
917 |
return _unsafe.compareAndSwapLong(this, stateOffset, cmp, val); |
918 |
} |
919 |
} |