PTHREAD_ONCE(3) Library Functions Manual PTHREAD_ONCE(3)
pthread_once -- dynamic package initialization
POSIX Threads Library (libpthread, -lpthread)
pthread_once(pthread_once_t *once_control, void (*init_routine)(void));
pthread_once_t once_control = PTHREAD_ONCE_INIT;
The first call to pthread_once() by any thread in a process, with a given
once_control, will call the init_routine() with no arguments. Subsequent
calls to pthread_once() with the same once_control will not call the
init_routine(). On return from pthread_once(), it is guaranteed that
init_routine() has completed. The once_control parameter is used to
determine whether the associated initialization routine has been called.
The function pthread_once() is not a cancellation point. However, if
init_routine() is a cancellation point and is cancelled, the effect on
once_control is as if pthread_once() was never called.
The constant PTHREAD_ONCE_INIT initializes the static once
synchronization control structure once_control to be used with
pthread_once(). The behavior of pthread_once() is undefined if
once_control has automatic storage duration or is not initialized by
If successful, the pthread_once() function will return zero. Otherwise
an error number will be returned to indicate the error.
The function conforms to IEEE Std 1003.1-2001 (``POSIX.1'').
NetBSD 6.1.5 July 9, 2010 NetBSD 6.1.5