| #include "pthread_impl.h" |
| |
| static void undo(void *control) |
| { |
| /* Wake all waiters, since the waiter status is lost when |
| * resetting control to the initial state. */ |
| if (a_swap(control, 0) == 3) |
| __wake(control, -1, 1); |
| } |
| |
| int __pthread_once_full(pthread_once_t *control, void (*init)(void)) |
| { |
| /* Try to enter initializing state. Four 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 |
| * 3 - another thread is running init, waiters present; wait */ |
| |
| for (;;) switch (a_cas(control, 0, 1)) { |
| case 0: |
| pthread_cleanup_push(undo, control); |
| init(); |
| pthread_cleanup_pop(0); |
| |
| if (a_swap(control, 2) == 3) |
| __wake(control, -1, 1); |
| return 0; |
| case 1: |
| /* If this fails, so will __wait. */ |
| a_cas(control, 1, 3); |
| case 3: |
| __wait(control, 0, 3, 1); |
| continue; |
| case 2: |
| return 0; |
| } |
| } |
| |
| 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 (*(volatile int *)control == 2) { |
| a_barrier(); |
| return 0; |
| } |
| return __pthread_once_full(control, init); |
| } |
| |
| weak_alias(__pthread_once, pthread_once); |