[boost] Re: [shared_ptr] Interlocked* - possible bug?

From: Alexander Terekhov (terekhov_at_[hidden])
Date: 2004-09-30 11:24:10

Peter Dimov wrote:
[...]
> An implementation can do that if it wants to, but I don't want to impose it
> as a requirement. It's better to allow use_count() to lag behind in MT code
> for performance reasons, because idiomatic weak_ptr use does not rely on the
> latest value anyway.

Agreed.

> 
> >>> It's PDQ in practice (unless you have a
> >>> compiler smart enough to ignore volatile hack and use a cached
> >>> copy in spite of it because you're not supposed to noticed the
> >>> difference according to the MT memory model rules).
> >>
> >> You need to insert lots of "in theory" here.
> >>
> >> * "volatile" is specifically intended to prevent "smartness".
> >
> > Your use of a volatile variable is indistinguishable (no change
> > in behavior whatsoever) from a non-volatile variable if/when run
> > single-thread.
> 
> No, it's not; C++ behavior _is defined in terms of_ volatile (and I/O
> calls), not the other way around.

As if rule. And C++ says nothing about mutiple threads.

http://groups.google.com/groups?selm=4152B42E.2B271094%40web.de

regards,
alexander.