Jeff Squyres wrote:

Let's also acknowledge that a significant "artificial constraint" is backwards compatibility for existing applications. We can't just change all the C bindings to make the millions of lines of MPI code out there no longer be compilable.

I agree that backward compatibility is a good thing. However, are not the C bindings insulated from this? If the new interface specifies intptr_t for the count argument, and the existing program supplies an int (conforming to the old standard) the argument will be automatically promoted in the caller. I guess I don't see a problem there.

Let's be fair -- *parallel programming* is hard.

Yes, certainly true.

MPI fits some kinds of parallel program models very well; MPI is a bad match for other kinds of parallel program models. The same can be said for all parallel programming systems. I think the last 20+ years have shown that there is no one-size-fits-all for parallel programming.

After many years of attrition, the still standing parallel models seem to be shared memory (OpenMP, which works for small numbers of processors) and SPMD (overwhelmingly MPI, which scales to large systems). The hardest part of an SPMD program is designing the data layout and synchronizing the processors. For a Fortran programmer like me, MPI is still an awkward way to express the resulting design. But that's the best option most people have at this point. Cheers, Bill -- Bill Long [email protected] Fortran Technical Support & voice: 651-605-9024 Bioinformatics Software Development fax: 651-605-9142 Cray Inc., 1340 Mendota Heights Rd., Mendota Heights, MN, 55120