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PTHREAD_ONCE(3) Library Functions Manual PTHREAD_ONCE(3)

pthread_oncedynamic package initialization

#include <pthread.h>

pthread_once_t once_control = PTHREAD_ONCE_INIT;

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

The first call to () by any thread in a process, with a given once_control, will call the () 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 () is not a cancellation point. However, if () 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 in the header file <pthread.h>.

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

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


pthread_once() conforms to ISO/IEC 9945-1:1996 (“POSIX.1”).

September 14, 2015 OpenBSD-6.3