VMS Help POSIX Threads, PTHREAD routines, pthread_once, Arguments  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 once_control

    Address of a record that controls the one-time execution code.
    Each one-time execution routine must have its own unique pthread_
    once_t record.

 routine

    Address of a procedure to be executed once. This routine is
    called only once, regardless of the number of times it and its
    associated once_control block are passed to pthread_once().