pthread_once − once‐only initialization


 = PTHREAD_ONCE_INIT;pthread_once_t once_control

, void (*int pthread_once(pthread_once_t *once_control

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

pthread_once always returns 0.


Xavier Leroy <>