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

    This routine locks the global mutex. The global mutex is
    recursive. For example, if you called tis_lock_global() three
    times, tis_unlock_global() unlocks the global mutex when you call
    it the third time.

    For more information about actions taken when threads are
    present, refer to the pthread_lock_global_np() description.