Safe parallel programming with session Java

The session-typed programming language Session Java (SJ) has proved to be an effective tool for distributed programming, promoting productivity and compile-time safety. This paper investigates the use of SJ for session-typed parallel programming, and introduces new language primitives for chained iteration and multi-channel communication. These primitives allow the efficient coordination of parallel computation across multiple processes, thus enabling SJ to express the complex communication topologies often used by parallel algorithms with static safety guarantees. We demonstrate that the new primitives yield clearer and safer code for pipeline, ring and mesh topologies, and through implementations of a parallel Jacobi method and an n-Body simulation. We then present a semantics and session typing system including the new primitives, and prove type soundness and deadlockfreedom for our parallel algorithm implementations. Finally, we benchmark several implementations of the n-Body simulation on a hybrid computing cluster, demonstrating the performance gains due to the new primitives. The SJ implementation is also substantially faster than an MPJ Express1 implementation used as reference