Multiparty Session Types Meet Communicating Automata

Abstract

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 CFSMs that automatically enjoy the aforementioned properties, generalising Gouda et al's work [13] (for two machines) to an arbitrary number of machines.

Type Reconstruction Algorithms for Deadlock-Free and Lock-Free Linear π-Calculi

“…There is a substantial methodological difference between our approach and those addressing sessions, particularly multiparty sessions [8,6]. Session-based approaches are top down and type driven: types/protocols come first, and are used as a guidance for developing programs that follow them.…”

“…Also, some protocols are hard to describe a priori. For example, describing the essence of full-duplex communications (Example 2.1) is far from trivial [6]. In general, processes making use of channel mobility (delegation) and session interleaving, or dynamic network topologies with variable number of processes, are supported by our approach (within the limits imposed by the type systems), but are challenging to handle in top-down approaches.…”

Choreographies in the wild

“…We express contracts using the syntax of local session types, in the style of [12,13]. Let P and P be disjoint sets of, respectively, participant names (ranged over by A, B, .…”

“…Like in the contract-oriented approach [10], we assume that applications are built bottom-up, by composing services whose advertised contracts admit agreements. However, unlike in previous contract-oriented calculi, service contracts are local session types, in a form similar to those used in [12,13]. A set of contracts admits an agreement whenever it is possible to synthesise from them a choreography -i.e.…”

Explicit Connection Actions in Multiparty Session Types

“…The minimal examples above illustrate some of the issues at hand. P1 features a choice involving only A and B in one case, and A and C in the other (which is not permitted in [22,12,17,18]), that is repeated continuously by the recursion (not permitted in [18]). However, P1 does satisfy the intuitive notion of MPST safety (e.g., no reception errors or deadlocks); and under an assumption of output choice fairness, i.e., provided A does not starve B or C of messages, P1 also satisfies MPST progress (otherwise, if, e.g., A talks only to B, then C remains in the session but never progresses).…”