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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: Tasking performance between Ada83 and Ada95
Date: 1997/06/09
Message-ID: <dewar.865870961@merv>#1/1
X-Deja-AN: 247273127
References: <1997Jun6.115223.7384@relay.nswc.navy.mil> <dewar.865693453@merv>
 <7h6UFCAdNsmzEwg3@walsh.demon.co.uk>
Organization: New York University
Newsgroups: comp.lang.ada
Date: 1997-06-09T00:00:00+00:00
List-Id: <comp.lang.ada>


Edmond Walsh said

<<We had a similar problem when moving some Ada 83 code running on a
Harris NightHawk to Ada 95 (Gnat) on an SG.  It took a lot of effort to
get the code running reasonably on the SG.  The underlying problem was
the mapping of the Ada Tasks to Unix threads.  The Harris (now
Concurrent) system was very good, reflecting the Real Time background of
Harris. (I was not involved in the porting, I was just an interested
observer.)>>

Of course, the mapping of Ada tasks to Unix threads is certainly a *good
thing* if you need to take advantage of the flexibility of this mapping.
For example, if you are using one of SGI's high end MP's, then you 
definitely want this mapping. But there certainly is an efficiency
penalty to be paid. 

Actualy from your post it is not quite clear what exactly you are referring
to in "lot of effort" and "underlying problem" here. Were there problems
other than efficiency? Sometimes, especially in Ada 83 programs, where the
dispatching semantics were not defined, programs make assumptions about the
dispatching that are non-portable. This is avoided in Ada 95 if you are using
a compiler that implements full Annex D semantics (true of the SGI compiler
for example), but that does not necessarily help the porting of legacy code.

Robert dewar
Ada Core Technologies