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From: Buehring@Intellection.COM (Walt Buehring)
Newsgroups: comp.windows.x
Subject: Robust multi-display clients
Message-ID: <WALT.91May4173316@arrisun3.utarl.edu>
Date: 4 May 91 22:33:16 GMT
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Organization: Intellection, Inc.  Dallas, Texas
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Question (in a nutshell):

How do *you* go about writing an X application that displays windows on
many X servers, is insensitive to remote server crashes, provides
reasonable interactive response time to all users, and does not
consume oceans of virtual memory?


Possible answers:

1.  Within a single process open a separate connection to each display
and use XtAppPending, XtAppProcessEvent and friends to dispatch events
from each display.  

Advantage: 
        - Single process space consumes least memory.
        - UI in same process as application eases access to functions and data.
        - No context switching.

Disadvantage:
        - If a single display crashes Xlib is hosed (right???).
        - Any event that triggers a lengthy computation causes all displays
          to wait (perhaps a LONG time).


2. Split UI and application into separate processes and fork a UI
process for each display.  Communicate with application code thru IPC
channel via some home-grown command protocol.

Advantage:
        - Application is insensitive to remote server crashes.
        - UI and application may run on separate machines if needed.
        - During lengthy calculations by the application code, user
          can still refresh windows, pulldown menus, etc.

Disadvantage:
        - You may end up context switching your guts out.
        - Given the size of Xt and Motif libraries, each UI process
          may become *huge* and impose severe paging penalties.
        - Access to application code and data is made cumbersome.


This question probably comes up often but I've not been tuned in to this
group.  I'd appreciate any advice, past articles of interests, pointers to
examples, etc.  I'm going nuts looking for the "right" answer to this
problem -- it'd sure be nice to have some company! :-)

A few other details about our application in case it matters.  It must
support 10-40 users (displays), may embark on calculations that require
10-15 minutes to complete, and must run on Unix and VMS (using
DECwindows/Motif).


Thanks,
\/\/

Walt Buehring
Intellection, Inc.

Internet:  Buehring@Intellection.COM
UUCP:      uupsi!intell!buehring