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

    This routine destroys the specified read-write lock object. Prior
    to calling this routine, ensure that there are no locks granted
    to the specified read-write lock and that there are no threads
    waiting for pending lock acquisitions on the specified read-write
    lock.

    This routine should be called only after all reader threads (and
    perhaps one writer thread) have finished using the specified
    read-write lock.