Path: utzoo!attcan!uunet!wuarchive!emory!stiatl!srchtec!johnb
From: johnb@srchtec.UUCP (John T. Baldwin)
Newsgroups: comp.realtime
Subject: Re: Software primitives for real-time programming languages
Message-ID: <224@srchtec.UUCP>
Date: 24 Sep 90 15:19:26 GMT
References: <12682@cs.utexas.edu> <1844@tuvie>
Organization: search technology, inc.
Lines: 57

In article <1844@tuvie> alex@vmars.tuwien.ac.at (Alexander Vrchoticky) writes:
av>
av> To stimulate discussions I suggest that the 
av> following should *not* be used for hard real-time systems: 
av>
av>	o  Explicit scheduling statements (of the `at 16:30 start foo' type).

Does this also preclude the following:

   1. Event "reenter-retro-burn" tied to task "calc-execute-reenter".
   2. Hard-schedule: reenter-retro-burn at 16:30:00.5 GMT.

If so, why?


av>	o  Unbounded loops and recursions.

While I can certainly fathom the reason this would be desirable, how can
it be (practically) enforced so as not to grossly interfere with the
primary goal: getting the system to run in the first place?

av>	o  Dynamic task creation and termination.

Once again, having this constraint would surely make it easier to
assert that a given real-time system meets its timing constraints.
Yet doesn't this (in general) automatically preclude application of
real-time in the AI domain?  This is critically important to me,
personally and professionally, since I am involved with the real-time
aspects of an AI system.

To broaden the horizon of this particular discussion thread: stochastic
behavior of some tasks in the system can really be a pain, and cause
all sorts of heartache (and heartburn! :-)) for the real-time practitioner,
but it is also a fact of life.  Some algorithms simply don't have a *known*
alternative having deterministic execution time.  We *sure* don't want to
pad out the nondeterministic ones out to their worst case!  :) :) :)


av>I'd like to encourage discussions on this topic and hope that
av>we can get something more controversial and stimulating going on 
                                               ^^^^^^^^^^^
av>than discussions of the `anyone have a bar-compiler for the foo-board?' type.

Absolutely!
(cf. my earlier plea, and BTW, thanks to everyone for a great list of
     pointers to good r-t reading material!)

av>Alexander Vrchoticky  Technical University Vienna, Dept for Real-Time Systems
av>Voice:  +43/222/58801-8168   Fax: +43/222/569149
av>e-mail: alex@vmars.tuwien.ac.at or vmars!alex@relay.eu.net  (Don't use 'r'!)


-- 
John T. Baldwin                      |  johnb%srchtec.uucp@mathcs.emory.edu
Search Technology, Inc.              | 
                                     | "... I had an infinite loop,
My opinions; not my employers'.      |  but it was only for a little while..."