Re: [boost] volatile and thread-safety

From: Stefan Seefeld (seefeld_at_[hidden])
Date: 2003-10-01 16:07:49

David Abrahams wrote:
> I had heard Andrei did something like this a while ago, but I missed
> the details until just now, when I stumbled across the article at
> http://www.cuj.com/documents/s=7998/cujcexp1902alexandr/.  I was a
> little disappointed at first because I always imagined something much
> more sophisticated, but the simplicity of Andrei's technique is also
> its beauty.  I wonder if it makes sense for us to implement:
> 
>   a. A coding guideline in which threadsafe member functions are
>      volatile
> 
>   b. Some infrastructure similar to his LockingPtr

I remember the article, and I also remember long and heated discussions
in comp.lang.c++[.moderated] and comp.programming.threads. Many 
arguments were brought forward concerning the relation between
the volatile keyword and all the different memory types a computer
(more precisely: a CPU) may or may not possess.

Andrei is only talking about registers, but not about CPU caches (L1,
L2), or about memory barriers. IIRC, people in the end agreed that
using volatile is by no means a guarantee for thread-safe access to
memory, at least not in multi-processor architectures.

Regards,
                Stefan