Re: [boost] [interprocess] Atomic ops supports for Alpha processors.

From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2007-10-18 12:26:22

Markus Schöpflin escribió:
> Hello,
> 
> attached patch introduces support for the atomic ops needed by 
> interprocess on Tru64/CXX/Alpha. It currently misses support for atomic 
> add and sub, but those are not used right now.

Applied in SVN. If I've introduced any error (I've applied the patch by 
hand), please feel free to commit a fix.

> There are a few issues I would like to raise regarding the atomic 
> operations:
> 
> 1) Currently it is not specified whether an atomic operation implies a 
> memory barrier or not. This should be explicitly stated.

They should imply a barrier. Since this was an internal header, I 
haven't documented anything. Now that people is contributing, at least, 
I should add a comment to the header.

> 2) atomic_sub32 does not return the old value, but atomic_add32 does. 
> This seems inconsistent to me.

I agree. Nevertheless, I think atomic_add32 is enough since atomic_sub32 
can be implemented as with atomic_add32(boost::uint32(-val)). I'm 
planning on removing some unused operations, to maybe is time to remove 
atomic_add32/atomic_sub32.

> 3) Has the use of the low level atomic ops API as proposed in WG21/N2047 
> (see http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2047.html) 
> been considered. If yes, why has it been rejected? If no, would it makes 
> sense to use this API?

If you are talking about using N2047 in Interprocess, I always thought 
that boost/interprocess/detail/atomic.hpp was a temporary solution until 
an atomic operations library was developed. I just needed some basic 
operations and a full barriers were good enough for me. Developing an 
atomic operations library is rocket science for me.

> 4) Is there a need for an atomic ops boost library? I seem to remember 
> that other libraries need atomic ops as well.

Definitely yes. I'm still surprised that there are no atomic operations 
on Boost apart from shared_ptr internals. I think we have people with 
deep knowledge on atomic operations, so let's put some pressure on the 
mailing list...

> Regards,
> Markus

Regards,

Ion