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#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); } hidden 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); |