Towards Modern C plus plus Language Support for MPI

The C++ programming language has made significant strides in improving performance and productivity across a broad spectrum of applications and hardware. The C++ language bindings to MPI had been deleted since MPI 3.0 (circa 2009) because it reportedly added only minimal functionality over the existing C bindings relative to modern C++ practice while incurring significant amount of maintenance to the MPI standard specification. Two years after the MPI C++ interface was eliminated, the ISO C++11 standard was published, which paved the way for modern C++ through numerous improvements to the core language. Since then, there has been continuous enthusiasm among application developers and the MPI Forum for modern C++ bindings to MPI. In this paper, we discuss ongoing efforts of the recently formed MPI working group on language bindings in the context of providing modern C++ (C++11 and beyond) support to MPI. Because of the lack of standardized bindings, C++-based MPI applications will often layer their own custom subsets of C++ MPI functionality on top of lower-level C; application- and/or domain-specific abstractions are subsequently layered on this custom subset. From such efforts, it is apparently a challenge to devise a compact set of C++ bindings over MPI with the "right" level of abstractions to support a variety of application uses cases under the expected performance/memory constraints. However, we are convinced that it is possible to identify and eventually standardize a normative set of C++ bindings to MPI that can provide the basic functionality required by distributed-memory applications. To engage with the broader MPI and C++ communities, we discuss a prototypical interface derived from mpl, an open-source C++17 message passing library based on MPI.