Subj : Re: double-checked locking in C
To   : comp.programming.threads
From : David Schwartz
Date : Thu Jul 07 2005 02:33 pm


"Laurent Deniau" <Laurent.Deniau@cern.ch> wrote in message 
news:daiqas$5k4$1@sunnews.cern.ch...

> Then if I stick to standards, the C norm is enough (6.7.3-6 which says all 
> and nothing) and I just have to use volatile. At the sequence points, the 
> value is correct even if modified by side effects. But as you know, it 
> doesn't solve anything because of the presence of caches on processors, 
> something absent from the norm and very uncommon at the time volatile was 
> invented.

    If 'volatile' was ever enough but it's not enough now, it must be for 
one of three reasons:

    1) Today's compilers don't properly implement 'volatile' and are all 
broken. We should file complaints and blame them.

    2) Today's hardware is not capable of supporting the C standard.

    3) The code was never portable to begin with because it *assumed* that 
the problems it dealt with are the only possible problems that there could 
be, in the absence of *guarantees* that the code would work.

    Which do you think it is?

    DS

.