once_flag
extern void call_once(once_flag *, void (*)(void));
call_once(once_flag *flag, void (*func)(void))
if (once->once_flag == PTHREAD_ONCE_NOTDONE) {
if (once->once_flag == PTHREAD_ONCE_NOTDONE) {
once->once_flag = PTHREAD_ONCE_DONE;
static once_flag co_once = ONCE_FLAG_INIT;