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Date: 13 Oct 92 20:51:50 GMT
From: sdd.hp.com!caen!nic.umass.edu!hudson@hplabs.hpl.hp.com  (Rick Hudson)
Subject: Re: Ada and real-time
Message-ID: <HUDSON.92Oct13155150@yough.cs.umass.edu>
List-Id: <comp.lang.ada>

>>>>> On 13 Oct 92 15:32:17 GMT, russ@alliant.com (Russell McFatter) said:

Russ> (3)  No self-imposed nondeterminism:

Russ>      Can a language be nondeterministic?  Sure it can.  Take LISP, for
Russ>      example...

Russ> 	"Whoa!  That missile flew right over our heads and this thing
Russ> 	 didn't even try to intercept it!"

Russ> 	"Bummer of a time to do a garbage collection.  Sorry 'bout your
Russ> 	 city, man."


Actually, there have been techniques for doing real time GC around since the
seventies. Most Lisp systems do not utilize these techniques due to the total
overhead required (a bounded number of extra instruction on each memory read).
The fact that all Ada systems fail to offer GC is an implementation decision.
There is nothing in the Ada language definition that would prevent implementati
on
of a full blown generational copy collector and I suspect this was not by
accident. There is nothing in the Lisp language definition that prevents
real time garbage collection either.

Other than this we have considerable common ground when it comes to describing
what real time means.
--

                Richard L. Hudson, Research Associate
                University Computing Services
                Lederle Graduate Research Center
                University of Massachusetts
                Amherst, MA  01003
                (413) 545-1220; Hudson@cs.umass.edu