openpa: replacement of openpa

[minsii]

Git repository of openpa might be deleted at some point as it is not used in MPICH now. We might want to find replacement for it.

[jeffhammond]

Can we assume C11 now or not?

[minsii]

I'd just assume C11 for most platforms. But not sure K and Fugaku. Fujitsu compiler seems a bit old.

[jeffhammond]

C11 is also old at this point :-)

On A64fx, I use Cray, NV/PGI, GCC, and ARM Clang, all of which support C11 atomics AFAIK so I don't think Fugaku is an issue.

Is the K machine even on anymore? If FX100 cannot support C11, I consider that a FJ problem.

[minsii]

Fair point. Then we can use c11 atomics to replace openpa.