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From: thp@westhawk.UUCP ("Timothy H Panton.")
Newsgroups: comp.windows.x
Subject: Re: programming strategy for interactive simulator
Message-ID: <9103241127.AA03992@westhawk.uucp>
Date: 24 Mar 91 11:27:04 GMT
Sender: westhawk!thp@relay.eu.net
Organization: The Internet
Lines: 39


pefv700@perv.pe.utexas.edu wrote:

> My question is: should I have 2 processes, one that controls the simulator?
> If so, what is the best way to get data from the FORTRAN program? sockets?
> Or should I have just one process that just checks for keyboard and button
> events periodically?

I've been contracting on a chemical plant simulator and we chose the first 
route with no real regrets. The origional frontend ran on a PC with GEM , 
so we  already had a suitable command-line type interface on the UNIX backend.
We added a couple of new "commands" to it to allow it to support our new 
X frontend and off we went.

Up until a month ago I'd have said that there was only one problem 
	- designing the comms protocol.
 
However I recently improved the backend so that it could respond much
faster to external events, and found to my horror that the machine (a Sparc)
was spending about 25% of the time context switching. I spent last week
de-tuning the response of the frontend-backend link so that requests are
serviced within 1 sec, rather than within 10 millisec. The 10 millisec stuff
was implemented to support some inter-machine I/O and I'd just assumed it
would be nice to use it on the intra-machine link. Not so.

On the communication front we arrange for both processes to expect to see
the other on stdio, and we have a third process that creates the links,
dups a bit forks them both and then waits around, this allows easy debugging
and we also do a "recover" when the parent process sees that one of its
children terminated abnormally and starts a replacement.

Hope that helps a bit.
Tim.
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|Tim Panton, Westhawk Ltd.    "Do not meddle in the affairs of Wizards, for  |
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