RUN_ONCE() provides a functionality similar to
pthread_once(3). It ensures that, for a given
control,
init_func() is executed (successfully) exactly once. It is considered as a successful execution if and only if
init_func() returned 0. As long as there was no successful execution,
RUN_ONCE() will try again each time it is called.
RUN_ONCE() can sleep if it's called concurrently.