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manually "shrink wrap" fast path in pthread_once

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this change is a workaround for the inability of current compilers to
perform "shrink wrapping" optimizations. in casual testing, it roughly
doubled the performance of pthread_once when called on an
already-finished once control object.
This commit is contained in:
Rich Felker
2014-10-20 00:22:51 -04:00
parent 60a4783ed4
commit dc95322e18
1 changed files with 12 additions and 8 deletions
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20
src/thread/pthread_once.c
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@ -8,15 +8,8 @@ static void undo(void *control)
__wake(control, -1, 1); __wake(control, -1, 1);
} }
int __pthread_once(pthread_once_t *control, void (*init)(void)) int __pthread_once_full(pthread_once_t *control, void (*init)(void))
{ {
/* Return immediately if init finished before, but ensure that
* effects of the init routine are visible to the caller. */
if (*control == 2) {
a_barrier();
return 0;
}
/* Try to enter initializing state. Four possibilities: /* Try to enter initializing state. Four possibilities:
* 0 - we're the first or the other cancelled; run init * 0 - we're the first or the other cancelled; run init
* 1 - another thread is running init; wait * 1 - another thread is running init; wait
@ -43,4 +36,15 @@ int __pthread_once(pthread_once_t *control, void (*init)(void))
} }
} }
int __pthread_once(pthread_once_t *control, void (*init)(void))
{
/* Return immediately if init finished before, but ensure that
* effects of the init routine are visible to the caller. */
if (*control == 2) {
a_barrier();
return 0;
}
return __pthread_once_full(control, init);
}
weak_alias(__pthread_once, pthread_once); weak_alias(__pthread_once, pthread_once);