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#include "pthread_impl.h"
static void undo(void *control)
{
a_store(control, 0);
__wake(control, 1, 0);
}
int pthread_once(pthread_once_t *control, void (*init)(void))
{
static int waiters;
/* Return immediately if init finished before, but ensure that
* effects of the init routine are visible to the caller. */
if (*control == 2) {
/* Otherwise-useless cas just to get a barrier. */
a_cas(&(int){0},0,0);
return 0;
}
/* Try to enter initializing state. Three possibilities:
* 0 - we're the first or the other cancelled; run init
* 1 - another thread is running init; wait
* 2 - another thread finished running init; just return */
for (;;) switch (a_cas(control, 0, 1)) {
case 0:
pthread_cleanup_push(undo, control);
init();
pthread_cleanup_pop(0);
a_store(control, 2);
if (waiters) __wake(control, -1, 0);
return 0;
case 1:
__wait(control, &waiters, 1, 0);
continue;
case 2:
return 0;
}
}
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