Markus Schöpflin:
Ion Gaztañaga wrote:
Markus Schöpflin escribió:
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.
You need to know what kind of memory synchronization is implied. Acquire for atomic load, release for atomic store and acquire+release is a reasonably safe bet in situations such as this one where the author isn't quite sure. :-) Last I looked at the various implementations, most of the routines did not provide these guarantees, though. Your use of volatile is also a bit suspect. Volatile operations may be atomic without implying an acquire (release) constraint, both for the hardware and for the compiler. On Alpha, you'll probably need to add a memory barrier after the loads, a memory barrier before the stores, and one before and one after the read/modify/write operations. This would require that the compiler is smart enough to recognize the barrier and not move code across.