On Sep 21 2012, Jeff Hammond wrote: I said that I wouldn't follow up, but I can't let this pass.

I only use MPI from C but I have never seen or heard any evidence to justify this concern. Can you state exactly which MPI functions and semantics are "seriously incompatible with C89 and/or C99"? Exactly which C compilers do not work with MPI?

Passive one-sided communication, for a start. I no longer have access to the sort of systems on which that would fail, and I have never seen it used. When I did have such access, I did write code that caused its underlying assumptions to break, while investigating problems on the systems I managed.

At least in C89 and C99, C doesn't have a memory model but instead inherits this from the hardware. I think this ambiguity is a far bigger issue than anything MPI nonblocking is doing and somehow C manages to be used in many places.

That is total nonsense. I was involved in both standardisation efforts, including as a UK expert on that very area. The model was defined in terms of sequence points, though C99 also added effective types. What you say was true for K&R C, but has not been since. Regards, Nick Maclaren.