Ion Gaztañaga wrote:
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.
OK, I need to add memory barriers to the code then.
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.
The interface for add32 takes unsigned integers, so you can't just call add_32(-val). But as both operations are unused, it's probably best to remove them.
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.
Understood.
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...
Probably not the best time right now, being close to the next release, but otherwise I agree with you. Regards, Markus