To: J3 J3/22-171 From: Jeff Hammond Subject: MPI Liason Report Date: 2022-July-18 MPI 4.0 added "large count" support to address the challenge of supporting buffers with more than 2 billion elements. The relevant MPI functions have a new symbol with "_c" appended for explicitly call the large count funcion. The MPI F08 module uses interfaces to make the explicit large count call unnecessary. For example, a Fortran user can call MPI_Bcast_c with a INTEGER(KIND=MPI_COUNT_KIND) count, or they can just call MPI_Bcast and the module will invoke the appropriate specific procedure. The key challenge for MPI and Fortran now is the lack of adoption of the MPI F08 module, which depends on compiler features that are not yet univerally available. The MPI Forum has a working group related to language support targeting MPI-5. This working group is considering the needs of languages other than C, such as Rust, C++ and Python. The Fortran community is encouraged to engage that effort if there are ideas to improve the way MPI supports Fortran.