On Wed, Sep 12, 2018 at 2:55 PM Balaji, Pavan via mpiwg-rma <[email protected]> wrote:

Yes, correct. Although, Nathan had a ticket at some point where he wanted to allow MPI to overwrite the padding bytes in such cases.

This issue of padding bytes in atomic updates to a struct came up in the past few C++ meetings: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0528r3.html For more explanation, see http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0528r0.html . The goal is that compare-and-exchange shouldn't always return false if the padding bits don't participate in the value representation of a struct. mfh