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From: kaz@vision.crest.nt.com (Kaz Kylheku)
Subject: Re: Waiver question
Date: 1997/05/01
Message-ID: <5kb8ol$18o@bcrkh13.bnr.ca>#1/1
X-Deja-AN: 238766385
References: <dewar.861594356@merv> <1997Apr28.151327.1@eisner>
 <5k52k2$7v0$1@news.nyu.edu> <E9G869.CqB@world.std.com>
Organization: Prism Systems Inc.
Newsgroups: comp.lang.ada
Date: 1997-05-01T00:00:00+00:00
List-Id: <comp.lang.ada>



In article <E9G869.CqB@world.std.com>,
Robert A Duff <bobduff@world.std.com> wrote:
>In article <5k52k2$7v0$1@news.nyu.edu>,
>Richard Kenner <kenner@lab.ultra.nyu.edu> wrote:
>>The problem with these sequences is that they are not atomic.  That
>>is that problem that will be remedied on Alpha processors starting
>>with EV56.
>
>Why is that a problem?

Because you may wish to code an interrupt service routine for an embedded
system without dropping down to the assembly language level. In that case
it becomes important to know that you can modify some variable atomically;
you suddenly care how the access is compiled into machine code. It's not
practical or desirable to write interrupt service routines in assembly
language.

If access to that object is not atomic, the process that was interrupted could
have been in the middle of trying to read that variable.