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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 */ if (*control == 2) 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; } } |