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

    This routine acquires a read-write lock for write access. This
    routine waits for any other active locks (for either read or
    write access) to be unlocked before this acquisition request is
    granted.

    This routine returns when the specified read-write lock is
    acquired for write access.