PTHREAD_ONCE(3)

NAME
pthread_once - dynamic package initialization

SYNOPSIS
#include <pthread.h>

pthread_once once_control = PTHREAD_ONCE_INIT;
int
pthread_once(pthread_once_t *once_control, void *(*init_routine)(void));

DESCRIPTION
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 is defined by header <pthread.h>.

The behavior of pthread_once() is undefined if once_control has automatic storage duration or is not initialized by PTHREAD_ONCE_INIT.

RETURN VALUES
If successful, the pthread_once() function will return zero. Otherwise an error number will be returned to indicate the error.

ERRORS
None.

STANDARDS
pthread_once() is expected to conform to IEEE (“POSIX”) Std 1003.1c when it is published.