If any thread in a process with a once_control parameter makes a call to pthread_once(), the first call will summon the init_routine(), but subsequent calls will not. The once_control parameter determines whether the associated initialization routine has been called. The init_routine() is complete upon return of pthread_once().

pthread_once() is not a cancellation point; however, if the function init_routine() is a cancellation point and is canceled, the effect on once_control is the same as if pthread_once() had never been called.

The constant PTHREAD_ONCE_INIT is defined in the <pthread.h> header.

If once_control has automatic storage duration or is not initialized by PTHREAD_ONCE_INIT, the behavior of pthread_once() is undefined.

Upon successful completion, pthread_once() returns 0. Otherwise, an error number is returned to indicate the error.

EINVAL

once_control or init_routine is NULL.

See attributes(5) for descriptions of the following attributes:

attributes(5)

Solaris threads do not offer this functionality.