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

 once_control

    Address of a record (control block) that defines the one-time
    initialization code. Any one-time initialization routine in
    static storage specified by once_control must have its own unique
    pthread_once_t record.

 init_routine

    Address of a procedure that performs the initialization. This
    routine is called only once, regardless of the number of times it
    and its associated once_control are passed to tis_once().