Concepts for designing modern C++ interfaces for MPI

2025-06-17

AI Summary

This paper identifies a fundamental semantic tension between MPI and modern C++—manifesting in type safety, RAII-based object lifetime management, and communication buffer semantics (value semantics vs. raw pointers)—and exposes multiple ambiguities and inconsistencies in the MPI standard. Method: We propose a concept-driven design paradigm grounded in C++20 Concepts, constraints, `std::span`, and move semantics, moving beyond syntactic wrapper libraries to formally model and verify semantic consistency across abstractions. Contribution/Results: Our analysis clarifies three core design conflicts, pinpoints several standard ambiguities, and establishes foundational design principles and a theoretical framework for high-performance, portable, and idiomatic C++ MPI bindings. The work provides both a rigorous conceptual foundation and a practical pathway toward community-standardized, semantically sound C++ MPI interfaces.

Technology Category

• Multiagent Systems: Agent Communication
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Cognitive Modeling & Cognitive Systems: Conceptual Inference and Reasoning

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Data management and stream processing for Web, mobile and wireless applications
• Security and Privacy: Data transparency and provenance
• User Modeling, Personalization and Recommendation: User modeling and simulation for interactive and conversational systems

Abstract

Since the C++ bindings were deleted in 2008, the Message Passing Interface (MPI) community has revived efforts in building high-level modern C++ interfaces. Such interfaces are either built to serve specific scientific application needs (with limited coverage to the underlying MPI functionalities), or as an exercise in general-purpose programming model building, with the hope that bespoke interfaces can be broadly adopted to construct a variety of distributed-memory scientific applications. However, with the advent of modern C++-based heterogeneous programming models, GPUs and widespread Machine Learning (ML) usage in contemporary scientific computing, the role of prospective community-standardized high-level C++ interfaces to MPI is evolving. The success of such an interface clearly will depend on providing robust abstractions and features adhering to the generic programming principles that underpin the C++ programming language, without compromising on either performance and portability, the core principles upon which MPI was founded. However, there is a tension between idiomatic C++ handling of types and lifetimes, and, MPI's loose interpretation of object lifetimes/ownership and insistence on maintaining global states. Instead of proposing"yet another"high-level C++ interface to MPI, overlooking or providing partial solutions to work around the key issues concerning the dissonance between MPI semantics and idiomatic C++, this paper focuses on the three fundamental aspects of a high-level interface: type system, object lifetimes and communication buffers, also identifying inconsistencies in the MPI specification. Presumptive solutions can be unrefined, and we hope the broader MPI and C++ communities will engage with us in productive exchange of ideas and concerns.

Problem

• Designing modern C++ interfaces for MPI with robust abstractions
• Resolving tension between C++ types/lifetimes and MPI semantics
• Addressing type system, object lifetimes, and communication buffers

Innovation

• Modern C++ interfaces for MPI
• Type system and object lifetimes
• Communication buffers optimization