Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!bu-cs!encore!cloud9!tomc
From: tomc@cloud9.Stratus.COM (Tom Clark)
Newsgroups: comp.arch
Subject: Re: Multi-Processor Serializability
Summary: volatile doesnt do it
Keywords: data ordering, coherence, shared memory multiprocessing
Message-ID: <3507@cloud9.Stratus.COM>
Date: 2 Feb 89 07:09:56 GMT
References: <3492@cloud9.Stratus.COM> <19635@lll-winken.LLNL.GOV>
Organization: Stratus Computer, Inc., Marlboro, MA
Lines: 18

In article <19635@lll-winken.LLNL.GOV>, brooks@vette.llnl.gov (Eugene Brooks) writes:
> In article <3492@cloud9.Stratus.COM> tomc@cloud9.Stratus.COM (Tom Clark) writes:
> >In  any computer system, the programmer expects operations in the source
> >code to be carried out in the order specified.  This is especially  true
> >in  a  multi-processor  system  where multiple processes may share data.
> 
> In ANSI C the tool to use to enforce reference order for reads and writes
> is the keyword volatile, although I suppose that the purveyors of this keyword
> did not have shared memory multiprocessors in mind when they inserted it into
> the ANSI C definition.

Unfortunately volatile does not do it.  Volatile does indeed force a write
to memory instead of holding an intermediate result in a register, but it
says nothing about ordering of instructions.  Such a construct does not
exist in most languages, except for the disabling of optimization.  Sigh.


        Tom Clark, Stratus Computer