Re: Boost.Threads draft library submission

From: williamkempf_at_[hidden]
Date: 2001-03-15 19:27:52

--- In boost_at_y..., Beman Dawes <bdawes_at_a...> wrote:
> At 04:28 PM 3/15/2001, williamkempf_at_h... wrote:
> 
>  >> Am I missing something?
>  >
>  >Just a small detail.  A classic example is the "Double-Checked
>  >Locking Optimization" pattern.  On MP (multiple processor) 
machines
>  >the machines architecture does some optimizations that can result 
in
>  >this pattern not working.  In addition to language constructs 
such as
>  >volatile you need to use a platform specific "memory barrier" to
>  >insure the CPU(s) don't optimize the code in such a way as to 
cause
>  >incorrect behavior in this pattern.  The atomic_t type built on 
using
>  >a mutex may be subject to this same error (this goes beyond my
>  >expertise on the subject).  There was a recent thread on this 
subject
>  >on the Usenet.
> 
> So if I understand you correctly, on some platforms the hoops you 
have to 
> jump through are multi-step sequences of platform specific 
features.  Very 
> tricky, but doesn't the logic still hold?  You can make it work as 
long as 
> you follow the platform's rules.

Yes.

>  >The point is, however, these issues can all be addressed in a
>  >platform specific manner with out the need for a change to the
>  >interface of atomic_t.
> 
> Yes, understood.
> 
> Just out of curiosity, what platforms are we talking about?  Are 
they 
> exotic ones where users expect to have to do a lot of hand 
tailoring?

They didn't sound exotic, but I don't recall which platforms were 
mentioned explicitly.  Search the Usenet for double-checked locking 
and memory barriers and you'll probably find the thread I recall 
which will do much better at illustrating this stuff than I can do.

Bill Kempf