Conference bulova::decw_jan-89_to_nov-90

3598.0. "Distributed Decwindows programming dilemma..." by SUBWAY::SAPIENZA (Knowledge applied is wisdom gained.) Wed Nov 07 1990 11:37

    
       I have some questions regarding a Decwindows programming dilemma I
    am faced with. The problem arises in two possible situations:
    
    1)                                 VAX A                   VAX B
       +----------------+      +------------------+      +-------------+
       |                | LAT  |                  | Dnet |             |
       |  User (VT1x00) | <--> | Proc 1:          | <--> | Proc 3:     |
       |                |      |  DECW$DWT_DECNET |      |  A user     |
       +----------------+      |                  |      |  written    |
                               | Proc 2:          |      |  Decwindows |
                               |  A user applic., |      |  applic.    |
                               |  not necessarily |      |             |
                               |  Decwindows      |      +-------------+
                               |                  |
                               +------------------+
    
       A user sitting at a VT1x00 begins a LAT X session to VAX A. A job
    is spawned to run DECW$DWT_DECNET and a server number of 'N' is
    assigned to the user.
    
       Question: How can the application that is process #2 on VAX A
    determine the server number assigned by DECW$DWT_DECNET so that this
    server number can be communicated to the decwindows application that is
    running on VAX B?
    
    
    2)                                 VAX A                   VAX B
       +----------------+      +------------------+      +-------------+
       |                | Dnet |                  | Dnet |             |
       | User (PC under | <--> | Proc 1:          | <--> | Proc 2:     |
       | PCDecwindows)  |      |  A user applic., |      |  A user     |
       +----------------+      |  not necessarily |      |  written    |
                               |  Decwindows      |      |  Decwindows |
                               |                  |      |  applic.    |
                               +------------------+      |             |
                                                         +-------------+
    
       A user sitting at a PC of some flavor starts up a PCDecwindows
    session to VAX A.
    
       Question: How can the application that is process #1 on VAX A
    determine the node name and server number that is being used by the PC
    so that this can be communicated to the process on VAX B?
    
    
    Notes:
    a) In situation #1, we know that the SHOW DISPLAY information is
    useless since X$OPEN_DISPLAY can't deal with LAT transport connections.
    And even if it could, there's no guarantee that VAX B could see the
    VT1x00 over LAT anyway.
       So, DECW$DWT_DECNET has to be used to provide a passthru server
    running on VAX A. Unfortunately, the workings of DWT_DECNET are a
    mystery to anyone but the folks that wrote it. Come to think of it,
    anything having to do with decwindows servers is a mystery. (I haven't
    found a shred of documentation that describes how they operate. You
    know, in the off chance that you'd actually like to write your own.)
    
    b) In situation #2, a SHOW DISPLAY indicates the correct node and
    server information that is needed by the remote application on VAX B.
    Unfortunately, a call to X$DISPLAY_NAME doesn't provide this
    information and SHOW DISPLAY/SYMBOL can't be used in this particular
    application (take my word for it).
    
    
       *ANY* help, information, examples, pointer, requests for
    clarification, etcetera... would be most greatly appreciated. Reply
    here or send VAXMAIL to SUBWAY::SAPIENZA, ALL-IN-1 Mail to "Frank
    Sapienza@LIO".
    
    Frank
    

    >    Question: How can the application that is process #2 on VAX A
    > determine the server number assigned by DECW$DWT_DECNET so that this
    > server number can be communicated to the decwindows application that is
    > running on VAX B?

    If you define the logical DECW$DWT_DECNET_SERVER to a number bigger
    than 10, the server will be started using this server number.  This
    allows you to use a known server number rather than a random one.

    >    Question: How can the application that is process #1 on VAX A
    > determine the node name and server number that is being used by the PC
    > so that this can be communicated to the process on VAX B?

    I have written some code that extracts the node, transport, server and
    screen from a passed WSAn: device name.  Let me know if you want to
    see the code.  The code is derived from the VMS SETSHODIS sources
    so you can't give the source to the customer but you may be able to
    give them an .OBJ file to link with.

    						MJC