Multiparty Session C: Safe Parallel Programming with Message Optimisation

Abstract. This paper presents a new efficient programming toolchain for message-passing parallel algorithms which can fully ensure, for any typable programs and for any execution path, deadlock-freedom, com-munication safety and global progress through a static checking. The methodology is embodied as a multiparty session-based programming environment for C and its runtime libraries, which we call Session C. Programming starts from specifying a global protocol for a target par-allel algorithm, using a protocol description language. From this global protocol, the projection algorithm generates endpoint protocols, based on which each endpoint C program is designed and implemented with a small number of concise session primitives. The endpoint protocol can further be refined to a more optimised protocol through subtyping for asynchronous communication, preserving original safety guarantees. The underlying theory can ensure that the complexity of the toolchain stays in polynomial time against the size of programs. We apply this frame-work to representative parallel algorithms with complex communication topologies. The benchmark results show that Session C performs com-petitively against MPI.

Multiparty Session Types Meet Communicating Automata

Abstract. Communicating finite state machines (CFSMs) represent processes which communicate by asynchronous exchanges of messages via FIFO channels. Their major impact has been in characterising essential properties of communications such as freedom from deadlock and communication error, and buffer boundedness. CFSMs are known to be computationally hard: most of these properties are undecidable even in restricted cases. At the same time, multiparty session types are a recent typed framework whose main feature is its ability to efficiently enforce these properties for mobile processes and programming languages. This paper ties the links between the two frameworks to achieve a two-fold goal. On one hand, we present a generalised variant of multiparty session types that have a direct semantical correspondence to CFSMs. Our calculus can treat expressive forking, merging and joining protocols that are absent from existing session frameworks, and our typing system can ensure properties such as safety, boundedness and liveness on distributed processes by a polynomial time type checking. On the other hand, multiparty session types allow us to identify a new class of CF-SMs that automatically enjoy the aforementioned properties, generalising Gouda et al’s work [13] (for two machines) to an arbitrary number of machines.