Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!inria!irisa!news
From: leguerni@irisa.irisa.fr (Paul Le Guernic)
Newsgroups: comp.realtime
Subject: Re: Why concurrency in real-time systems design?
Message-ID: <1990Mar2.122113.2196@irisa.fr>
Date: 2 Mar 90 12:21:13 GMT
References: <1990Mar1.152922.1005@axion.bt.co.uk>
Sender: news@irisa.fr
Organization: IRISA, Rennes (FR)
Lines: 21

From article <1990Mar1.152922.1005@axion.bt.co.uk>, by rdoyle@axion.bt.co.uk (Number Six):
> 
>  Can anyone give me any ideas/references on why you need
> to use concurrent tasks in the design of real-time systems?

I see two different questions in the above one.
1. Why to use concurrent tasks to design real-time application ? The answer
was given by David B. Stewart : just because a real time system interacts with
concurrent external tasks.
2. Is it necessary to implement it with concurrent tasks (activation,
interruptions, priorities,...) ? 
-If online changes to the system may occurs, it is necessary to be able
to suppress and create tasks.
-If you want to build a single task (automaton), you have to build it by some
product of simpler automata; this work is analogous to removing procedure
calls. First of all, because of its complexity, you need a compiler to do it;
but even if such a compiler is available, this product of automata may result
in an exponential (even if finite) expansion of memory; then you need system
functions to handle more than one automaton (tasks). Nevertheless, most of
real time system could be built with a very small subset of task handling
structures.