| 108 |
|
* idea). (4) We bound the number of attempts to find work (see |
| 109 |
|
* MAX_HELP_DEPTH) and fall back to suspending the worker and if |
| 110 |
|
* necessary replacing it with a spare (see |
| 111 |
< |
* ForkJoinPool.tryAwaitJoin). |
| 111 |
> |
* ForkJoinPool.awaitJoin). |
| 112 |
|
* |
| 113 |
|
* Efficient implementation of these algorithms currently relies |
| 114 |
|
* on an uncomfortable amount of "Unsafe" mechanics. To maintain |
| 162 |
|
private static final int MAX_HELP_DEPTH = 8; |
| 163 |
|
|
| 164 |
|
/** |
| 165 |
– |
* The wakeup interval (in nanoseconds) for the oldest worker |
| 166 |
– |
* suspended as spare. On each wakeup not signalled by a |
| 167 |
– |
* resumption, it may ask the pool to reduce the number of spares. |
| 168 |
– |
*/ |
| 169 |
– |
private static final long TRIM_RATE_NANOS = |
| 170 |
– |
5L * 1000L * 1000L * 1000L; // 5sec |
| 171 |
– |
|
| 172 |
– |
/** |
| 165 |
|
* Capacity of work-stealing queue array upon initialization. |
| 166 |
|
* Must be a power of two. Initial size must be at least 4, but is |
| 167 |
|
* padded to minimize cache effects. |
| 216 |
|
* tracks if this worker is suspended as a spare, and if it was |
| 217 |
|
* killed (trimmed) while suspended. However, "active" status is |
| 218 |
|
* maintained separately and modified only in conjunction with |
| 219 |
< |
* CASes of the pool's runState (which are currently sadly manually |
| 220 |
< |
* inlined for performance.) |
| 219 |
> |
* CASes of the pool's runState (which are currently sadly |
| 220 |
> |
* manually inlined for performance.) Accessed directly by pool |
| 221 |
> |
* to simplify checks for normal (zero) status. |
| 222 |
|
*/ |
| 223 |
< |
private volatile int runState; |
| 223 |
> |
volatile int runState; |
| 224 |
|
|
| 225 |
|
private static final int TERMINATING = 0x01; |
| 226 |
|
private static final int TERMINATED = 0x02; |
| 265 |
|
int lastEventCount; |
| 266 |
|
|
| 267 |
|
/** |
| 268 |
< |
* Encoded index and event count of next event waiter. Used only |
| 269 |
< |
* by ForkJoinPool for managing event waiters. |
| 268 |
> |
* Encoded index and event count of next event waiter. Accessed |
| 269 |
> |
* only by ForkJoinPool for managing event waiters. |
| 270 |
|
*/ |
| 271 |
|
volatile long nextWaiter; |
| 272 |
|
|
| 273 |
|
/** |
| 274 |
< |
* Number of times this thread suspended as spare |
| 274 |
> |
* Number of times this thread suspended as spare. Accessed only |
| 275 |
> |
* by pool. |
| 276 |
|
*/ |
| 277 |
|
int spareCount; |
| 278 |
|
|
| 279 |
|
/** |
| 280 |
< |
* Encoded index and count of next spare waiter. Used only |
| 280 |
> |
* Encoded index and count of next spare waiter. Accessed only |
| 281 |
|
* by ForkJoinPool for managing spares. |
| 282 |
|
*/ |
| 283 |
|
volatile int nextSpare; |
| 291 |
|
|
| 292 |
|
/** |
| 293 |
|
* The task most recently stolen from another worker (or |
| 294 |
< |
* submission queue). Not volatile because always read/written in |
| 295 |
< |
* presence of related volatiles in those cases where it matters. |
| 294 |
> |
* submission queue). Written only by current thread, but read by |
| 295 |
> |
* others. |
| 296 |
|
*/ |
| 297 |
< |
private ForkJoinTask<?> currentSteal; |
| 297 |
> |
private volatile ForkJoinTask<?> currentSteal; |
| 298 |
|
|
| 299 |
|
/** |
| 300 |
|
* Creates a ForkJoinWorkerThread operating in the given pool. |
| 417 |
|
* Find and execute tasks and check status while running |
| 418 |
|
*/ |
| 419 |
|
private void mainLoop() { |
| 420 |
< |
int misses = 0; // track consecutive times failed to find work; max 2 |
| 420 |
> |
boolean ran = false; // true if ran a task on last step |
| 421 |
|
ForkJoinPool p = pool; |
| 422 |
|
for (;;) { |
| 423 |
< |
p.preStep(this, misses); |
| 423 |
> |
p.preStep(this, ran); |
| 424 |
|
if (runState != 0) |
| 425 |
|
break; |
| 426 |
< |
misses = ((tryExecSteal() || tryExecSubmission()) ? 0 : |
| 433 |
< |
(misses < 2 ? misses + 1 : 2)); |
| 426 |
> |
ran = tryExecSteal() || tryExecSubmission(); |
| 427 |
|
} |
| 428 |
|
} |
| 429 |
|
|
| 434 |
|
*/ |
| 435 |
|
private boolean tryExecSteal() { |
| 436 |
|
ForkJoinTask<?> t; |
| 437 |
< |
if ((t = scan()) != null) { |
| 437 |
> |
if ((t = scan()) != null) { |
| 438 |
|
t.quietlyExec(); |
| 439 |
< |
currentSteal = null; |
| 439 |
> |
UNSAFE.putOrderedObject(this, currentStealOffset, null); |
| 440 |
|
if (sp != base) |
| 441 |
|
execLocalTasks(); |
| 442 |
|
return true; |
| 453 |
|
ForkJoinPool p = pool; |
| 454 |
|
while (p.hasQueuedSubmissions()) { |
| 455 |
|
ForkJoinTask<?> t; int a; |
| 456 |
< |
if (active || // ugly/hacky: inline p.tryIncrementActiveCount |
| 456 |
> |
if (active || // inline p.tryIncrementActiveCount |
| 457 |
|
(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset, |
| 458 |
|
a = p.runState, a + 1))) { |
| 459 |
|
if ((t = p.pollSubmission()) != null) { |
| 460 |
< |
currentSteal = t; |
| 460 |
> |
UNSAFE.putOrderedObject(this, currentStealOffset, t); |
| 461 |
|
t.quietlyExec(); |
| 462 |
< |
currentSteal = null; |
| 462 |
> |
UNSAFE.putOrderedObject(this, currentStealOffset, null); |
| 463 |
|
if (sp != base) |
| 464 |
|
execLocalTasks(); |
| 465 |
|
return true; |
| 618 |
|
if ((s = sp) != base && q != null && |
| 619 |
|
UNSAFE.compareAndSwapObject |
| 620 |
|
(q, (((q.length - 1) & --s) << qShift) + qBase, t, null)) { |
| 621 |
< |
sp = s; |
| 621 |
> |
sp = s; // putOrderedInt may encourage more timely write |
| 622 |
|
// UNSAFE.putOrderedInt(this, spOffset, s); |
| 623 |
|
return true; |
| 624 |
|
} |
| 707 |
|
for (;;) { |
| 708 |
|
ForkJoinWorkerThread v = ws[k & mask]; |
| 709 |
|
r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // inline xorshift |
| 710 |
< |
if (v != null && v.base != v.sp) { |
| 711 |
< |
ForkJoinTask<?>[] q; int b, a; |
| 712 |
< |
if ((canSteal || // Ugly/hacky: inline |
| 713 |
< |
(canSteal = active = // p.tryIncrementActiveCount |
| 714 |
< |
UNSAFE.compareAndSwapInt(p, poolRunStateOffset, |
| 715 |
< |
a = p.runState, a + 1))) && |
| 716 |
< |
(q = v.queue) != null && (b = v.base) != v.sp) { |
| 717 |
< |
int i = (q.length - 1) & b; |
| 718 |
< |
long u = (i << qShift) + qBase; // raw offset |
| 719 |
< |
ForkJoinTask<?> t = q[i]; |
| 720 |
< |
if (v.base == b && t != null && |
| 710 |
> |
ForkJoinTask<?>[] q; ForkJoinTask<?> t; int b, a; |
| 711 |
> |
if (v != null && (b = v.base) != v.sp && |
| 712 |
> |
(q = v.queue) != null) { |
| 713 |
> |
int i = (q.length - 1) & b; |
| 714 |
> |
long u = (i << qShift) + qBase; // raw offset |
| 715 |
> |
int pid = poolIndex; |
| 716 |
> |
if ((t = q[i]) != null) { |
| 717 |
> |
if (!canSteal && // inline p.tryIncrementActiveCount |
| 718 |
> |
UNSAFE.compareAndSwapInt(p, poolRunStateOffset, |
| 719 |
> |
a = p.runState, a + 1)) |
| 720 |
> |
canSteal = active = true; |
| 721 |
> |
if (canSteal && v.base == b++ && |
| 722 |
|
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
| 723 |
< |
int pid = poolIndex; |
| 730 |
< |
currentSteal = t; |
| 723 |
> |
v.base = b; |
| 724 |
|
v.stealHint = pid; |
| 725 |
< |
v.base = b + 1; |
| 725 |
> |
UNSAFE.putOrderedObject(this, |
| 726 |
> |
currentStealOffset, t); |
| 727 |
|
seed = r; |
| 728 |
|
++stealCount; |
| 729 |
|
return t; |
| 754 |
|
|
| 755 |
|
/** |
| 756 |
|
* Sets state to TERMINATING. Does NOT unpark or interrupt |
| 757 |
< |
* to wake up if currently blocked. |
| 757 |
> |
* to wake up if currently blocked. Callers must do so if desired. |
| 758 |
|
*/ |
| 759 |
|
final void shutdown() { |
| 760 |
|
for (;;) { |
| 785 |
|
|
| 786 |
|
/** |
| 787 |
|
* If suspended, tries to set status to unsuspended. |
| 788 |
+ |
* Does NOT wake up if blocked. |
| 789 |
|
* |
| 790 |
|
* @return true if successful |
| 791 |
|
*/ |
| 817 |
|
} |
| 818 |
|
ForkJoinPool p = pool; |
| 819 |
|
p.pushSpare(this); |
| 825 |
– |
lastEventCount = 0; // reset upon resume |
| 820 |
|
while ((runState & SUSPENDED) != 0) { |
| 821 |
|
if (p.tryAccumulateStealCount(this)) { |
| 828 |
– |
boolean untimed = nextSpare != 0; |
| 829 |
– |
long startTime = untimed? 0 : System.nanoTime(); |
| 822 |
|
interrupted(); // clear/ignore interrupts |
| 823 |
|
if ((runState & SUSPENDED) == 0) |
| 824 |
|
break; |
| 825 |
< |
if (untimed) // untimed |
| 834 |
< |
LockSupport.park(this); |
| 835 |
< |
else { |
| 836 |
< |
LockSupport.parkNanos(this, TRIM_RATE_NANOS); |
| 837 |
< |
if ((runState & SUSPENDED) == 0) |
| 838 |
< |
break; |
| 839 |
< |
if (System.nanoTime() - startTime >= TRIM_RATE_NANOS) |
| 840 |
< |
p.tryShutdownSpare(); |
| 841 |
< |
} |
| 825 |
> |
LockSupport.park(this); |
| 826 |
|
} |
| 827 |
|
} |
| 828 |
|
} |
| 909 |
|
ForkJoinTask<?> t = pollLocalTask(); |
| 910 |
|
if (t == null) { |
| 911 |
|
t = scan(); |
| 912 |
< |
currentSteal = null; // cannot retain/track/help |
| 912 |
> |
// cannot retain/track/help steal |
| 913 |
> |
UNSAFE.putOrderedObject(this, currentStealOffset, null); |
| 914 |
|
} |
| 915 |
|
return t; |
| 916 |
|
} |
| 965 |
|
} |
| 966 |
|
|
| 967 |
|
/** |
| 968 |
< |
* Tries to locate and help perform tasks for a stealer of the |
| 969 |
< |
* given task, or in turn one of its stealers. Traces |
| 970 |
< |
* currentSteal->currentJoin links looking for a thread working on |
| 971 |
< |
* a descendant of the given task and with a non-empty queue to |
| 972 |
< |
* steal back and execute tasks from. |
| 968 |
> |
* Unless terminating, tries to locate and help perform tasks for |
| 969 |
> |
* a stealer of the given task, or in turn one of its stealers. |
| 970 |
> |
* Traces currentSteal->currentJoin links looking for a thread |
| 971 |
> |
* working on a descendant of the given task and with a non-empty |
| 972 |
> |
* queue to steal back and execute tasks from. |
| 973 |
|
* |
| 974 |
< |
* The implementation is very branchy to cope with the potential |
| 974 |
> |
* The implementation is very branchy to cope with potential |
| 975 |
|
* inconsistencies or loops encountering chains that are stale, |
| 976 |
|
* unknown, or of length greater than MAX_HELP_DEPTH links. All |
| 977 |
|
* of these cases are dealt with by just returning back to the |
| 981 |
|
* @param joinMe the task to join |
| 982 |
|
*/ |
| 983 |
|
final void helpJoinTask(ForkJoinTask<?> joinMe) { |
| 984 |
< |
ForkJoinWorkerThread[] ws = pool.workers; |
| 985 |
< |
int n; // need at least 2 workers |
| 986 |
< |
if (ws != null && (n = ws.length) > 1 && joinMe.status >= 0) { |
| 987 |
< |
ForkJoinTask<?> task = joinMe; // base of chain |
| 988 |
< |
ForkJoinWorkerThread thread = this; // thread with stolen task |
| 989 |
< |
for (int d = 0; d < MAX_HELP_DEPTH; ++d) { // chain length |
| 990 |
< |
// Try to find v, the stealer of task, by first using hint |
| 991 |
< |
ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)]; |
| 992 |
< |
if (v == null || v.currentSteal != task) { |
| 993 |
< |
for (int j = 0; ; ++j) { // search array |
| 994 |
< |
if (j < n) { |
| 995 |
< |
if ((v = ws[j]) != null) { |
| 996 |
< |
if (task.status < 0) |
| 997 |
< |
return; // stale or done |
| 998 |
< |
if (v.currentSteal == task) { |
| 999 |
< |
thread.stealHint = j; |
| 1000 |
< |
break; // save hint for next time |
| 1001 |
< |
} |
| 984 |
> |
ForkJoinWorkerThread[] ws; |
| 985 |
> |
int n; |
| 986 |
> |
if (joinMe.status < 0) // already done |
| 987 |
> |
return; |
| 988 |
> |
if ((runState & TERMINATING) != 0) { // cancel if shutting down |
| 989 |
> |
joinMe.cancelIgnoringExceptions(); |
| 990 |
> |
return; |
| 991 |
> |
} |
| 992 |
> |
if ((ws = pool.workers) == null || (n = ws.length) <= 1) |
| 993 |
> |
return; // need at least 2 workers |
| 994 |
> |
|
| 995 |
> |
ForkJoinTask<?> task = joinMe; // base of chain |
| 996 |
> |
ForkJoinWorkerThread thread = this; // thread with stolen task |
| 997 |
> |
for (int d = 0; d < MAX_HELP_DEPTH; ++d) { // chain length |
| 998 |
> |
// Try to find v, the stealer of task, by first using hint |
| 999 |
> |
ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)]; |
| 1000 |
> |
if (v == null || v.currentSteal != task) { |
| 1001 |
> |
for (int j = 0; ; ++j) { // search array |
| 1002 |
> |
if (j < n) { |
| 1003 |
> |
ForkJoinTask<?> vs; |
| 1004 |
> |
if ((v = ws[j]) != null && |
| 1005 |
> |
(vs = v.currentSteal) != null) { |
| 1006 |
> |
if (joinMe.status < 0 || task.status < 0) |
| 1007 |
> |
return; // stale or done |
| 1008 |
> |
if (vs == task) { |
| 1009 |
> |
thread.stealHint = j; |
| 1010 |
> |
break; // save hint for next time |
| 1011 |
|
} |
| 1012 |
|
} |
| 1019 |
– |
else |
| 1020 |
– |
return; // no stealer |
| 1013 |
|
} |
| 1014 |
+ |
else |
| 1015 |
+ |
return; // no stealer |
| 1016 |
|
} |
| 1017 |
< |
// Try to help v, using specialized form of deqTask |
| 1018 |
< |
int b; |
| 1019 |
< |
ForkJoinTask<?>[] q; |
| 1020 |
< |
while ((b = v.base) != v.sp && (q = v.queue) != null) { |
| 1021 |
< |
int i = (q.length - 1) & b; |
| 1022 |
< |
long u = (i << qShift) + qBase; |
| 1023 |
< |
ForkJoinTask<?> t = q[i]; |
| 1024 |
< |
if (task.status < 0) |
| 1025 |
< |
return; // stale or done |
| 1026 |
< |
if (v.base == b) { |
| 1027 |
< |
if (t == null) |
| 1028 |
< |
return; // producer stalled |
| 1029 |
< |
if (UNSAFE.compareAndSwapObject(q, u, t, null)) { |
| 1030 |
< |
if (joinMe.status < 0) { |
| 1031 |
< |
UNSAFE.putObjectVolatile(q, u, t); |
| 1032 |
< |
return; // back out on cancel |
| 1033 |
< |
} |
| 1034 |
< |
int pid = poolIndex; |
| 1035 |
< |
ForkJoinTask<?> prevSteal = currentSteal; |
| 1036 |
< |
currentSteal = t; |
| 1043 |
< |
v.stealHint = pid; |
| 1044 |
< |
v.base = b + 1; |
| 1045 |
< |
t.quietlyExec(); |
| 1046 |
< |
currentSteal = prevSteal; |
| 1047 |
< |
} |
| 1017 |
> |
} |
| 1018 |
> |
for (;;) { // Try to help v, using specialized form of deqTask |
| 1019 |
> |
if (joinMe.status < 0) |
| 1020 |
> |
return; |
| 1021 |
> |
int b = v.base; |
| 1022 |
> |
ForkJoinTask<?>[] q = v.queue; |
| 1023 |
> |
if (b == v.sp || q == null) |
| 1024 |
> |
break; |
| 1025 |
> |
int i = (q.length - 1) & b; |
| 1026 |
> |
long u = (i << qShift) + qBase; |
| 1027 |
> |
ForkJoinTask<?> t = q[i]; |
| 1028 |
> |
int pid = poolIndex; |
| 1029 |
> |
ForkJoinTask<?> ps = currentSteal; |
| 1030 |
> |
if (task.status < 0) |
| 1031 |
> |
return; // stale or done |
| 1032 |
> |
if (t != null && v.base == b++ && |
| 1033 |
> |
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
| 1034 |
> |
if (joinMe.status < 0) { |
| 1035 |
> |
UNSAFE.putObjectVolatile(q, u, t); |
| 1036 |
> |
return; // back out on cancel |
| 1037 |
|
} |
| 1038 |
< |
if (joinMe.status < 0) |
| 1039 |
< |
return; |
| 1038 |
> |
v.base = b; |
| 1039 |
> |
v.stealHint = pid; |
| 1040 |
> |
UNSAFE.putOrderedObject(this, currentStealOffset, t); |
| 1041 |
> |
t.quietlyExec(); |
| 1042 |
> |
UNSAFE.putOrderedObject(this, currentStealOffset, ps); |
| 1043 |
|
} |
| 1052 |
– |
// Try to descend to find v's stealer |
| 1053 |
– |
ForkJoinTask<?> next = v.currentJoin; |
| 1054 |
– |
if (task.status < 0 || next == null || next == task || |
| 1055 |
– |
joinMe.status < 0) |
| 1056 |
– |
return; |
| 1057 |
– |
task = next; |
| 1058 |
– |
thread = v; |
| 1044 |
|
} |
| 1045 |
+ |
// Try to descend to find v's stealer |
| 1046 |
+ |
ForkJoinTask<?> next = v.currentJoin; |
| 1047 |
+ |
if (task.status < 0 || next == null || next == task || |
| 1048 |
+ |
joinMe.status < 0) |
| 1049 |
+ |
return; |
| 1050 |
+ |
task = next; |
| 1051 |
+ |
thread = v; |
| 1052 |
|
} |
| 1053 |
|
} |
| 1054 |
|
|
| 1107 |
|
* Runs tasks until {@code pool.isQuiescent()}. |
| 1108 |
|
*/ |
| 1109 |
|
final void helpQuiescePool() { |
| 1110 |
+ |
ForkJoinTask<?> ps = currentSteal; // to restore below |
| 1111 |
|
for (;;) { |
| 1112 |
|
ForkJoinTask<?> t = pollLocalTask(); |
| 1113 |
< |
if (t != null || (t = scan()) != null) { |
| 1113 |
> |
if (t != null || (t = scan()) != null) |
| 1114 |
|
t.quietlyExec(); |
| 1122 |
– |
currentSteal = null; |
| 1123 |
– |
} |
| 1115 |
|
else { |
| 1116 |
|
ForkJoinPool p = pool; |
| 1117 |
|
int a; // to inline CASes |
| 1120 |
|
(p, poolRunStateOffset, a = p.runState, a - 1)) |
| 1121 |
|
continue; // retry later |
| 1122 |
|
active = false; // inactivate |
| 1123 |
+ |
UNSAFE.putOrderedObject(this, currentStealOffset, ps); |
| 1124 |
|
} |
| 1125 |
|
if (p.isQuiescent()) { |
| 1126 |
|
active = true; // re-activate |
