pthread_once - once-only initialization

#include <pthread.h>

pthread_once_t once_control = PTHREAD_ONCE_INIT;

int pthread_once(pthread_once_t *once_control, typeof(void (void)) *init_routine;

The purpose of pthread_once() is to ensure that a piece of initialization code is executed at most once. The once_control argument points to a static or extern variable statically initialized to PTHREAD_ONCE_INIT.

The first time pthread_once() is called with a given once_control argument, it calls init_routine with no argument and changes the value of the once_control variable to record that initialization has been performed. Subsequent calls to pthread_once() with the same once_control argument do nothing.

pthread_once() always returns 0.