I assume that MPI_Status is not opaque because somebody asserted that function call overhead was too much for some use cases. Was there more to it than this? Why does the standard say there is an opaque part for elements and cancelled, but not make those visible? The lack of consistency here doesn't make a lot of sense to me. MPI_Status not being opaque was a horrible mistake but I would like to be less mad about it by learning what possible reasons for it existed in 1995. Thanks, Jeff -- Jeff Hammond [email protected] http://jeffhammond.github.io/