A Sound Algorithm for Asynchronous Session Subtyping

Mario Bravetti (1, 2) , Marco Carbone (3) , Julien Lange (4) , Nobuko Yoshida (5) , Gianluigi Zavattaro (1, 2)

1 DISI - Department of Computer Science and Engineering [Bologna]
2 FOCUS - Foundations of Component-based Ubiquitous Systems
3 ITU - IT University of Copenhagen
4 University of Kent [Canterbury]
5 Imperial College London

Session types, types for structuring communication between endpoints in distributed systems, are recently being integrated into mainstream programming languages. In practice, a very important notion for dealing with such types is that of subtyping, since it allows for typing larger classes of system, where a program has not precisely the expected behavior but a similar one. Unfortunately, recent work has shown that subtyping for session types in an asynchronous setting is undecidable. To cope with this negative result, the only approaches we are aware of either restrict the syntax of session types or limit communication (by considering forms of bounded asynchrony). Both approaches are too restrictive in practice, hence we proceed differently by presenting an algorithm for checking subtyping which is sound, but not complete (in some cases it terminates without returning a decisive verdict). The algorithm is based on a tree representation of the coinductive definition of asynchronous subtyping; this tree could be infinite, and the algorithm checks for the presence of finite witnesses of infinite successful subtrees. Furthermore, we provide a tool that implements our algorithm and we apply it to many examples that cannot be managed with the previous approaches.

Mots clés: Session types; Concurrency; Subtyping; Algorithm

Domaines: Informatique et langage [cs.CL]

Mario Bravetti, Marco Carbone, Julien Lange, Nobuko Yoshida, Gianluigi Zavattaro. A Sound Algorithm for Asynchronous Session Subtyping. CONCUR 2019 - 30th International Conference on Concurrency Theory, Aug 2019, Amsterdam, Netherlands. ⟨10.4230/LIPIcs.CONCUR.2019.38⟩. ⟨hal-02387473⟩