You can call this routine only after you call LBR$INI_CONTROL and
    before you call any other LBR routine except LBR$OUTPUT_HELP.

    When the library is successfully opened, the LBR routine reads
    the library header into memory and sets the default index to 1.

    If the library cannot be opened because it is already open for a
    write operation, LBR$OPEN retries the open operation every second
    for a maximum of 30 seconds before returning the RMS error, RMS$_
    FLK, to the caller.