Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!rutgers!cs.utexas.edu!usc!ucsd!telesoft!rlk
From: rlk@telesoft.com (Bob Kitzberger @sation)
Newsgroups: comp.lang.misc
Subject: Re: CSP
Summary: more similar than different
Message-ID: <636@telesoft.com>
Date: 21 Dec 89 05:25:04 GMT
References: <8912161925.AA04979@terra.oscs.montana.edu>
Organization: TeleSoft, San Diego, CA.
Lines: 51

In article umpty-ump, iphwk@TERRA.OSCS.MONTANA.EDU (Bill Kinnersley) writes:

> I doubt that Hoare would enjoy seeing Ada proposed as a substitute for
> CSP!  

I didn't propose it as a substitute, merely stated that "Ada's tasking model is
largely based on CSP".

> He has been one of the most vocal critics of Ada.  

I assume you are referring to his 1980 Turing Award Lecture?  I don't have a
copy present, but as I recall Hoare's complaints about Ada stemmed from a
perceived complexity and Exceptions, not the tasking model used.  But I'd 
be very interested in any any other comments Hoare has made about Ada's
tasking - please let me know.

> While both CSP and Ada deal with communication between sequential processes, 
> they are at opposite extremes in terms of complexity.

I've just been perusing "Rationale for the Design of the Ada Progamming
Language".  The designers of Ada spend about five pages comparing and
contrasting CSP and Ada tasking.  The similarities are many, the differences
are few.

	o CSP communication is symmetric, i.e. both caller and server
	  need to know each other's name.  As Hoare himself points out,
	  this symmetry prevents development of library routines to provide
	  service to arbitrary users.

	  Ada communication is asymmetric, i.e. only the caller need know the
	  server's name.  Library routine creation is possible.

	o Ada adds the concept of the extended rendezvous (P. Brinch Hansen,
	  "Distributed Processes : a concurrent programming concept"), which 
	  allows arbitrary computations to occur within the rendezvous.  

	o CSP notation is terse; Ada notation is verbose.
	  
Yours for a kindler, gentler NERDnet,

	.Bob.


-- 
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