Inference of Global Progress Properties for Dynamically Interleaved Multiparty Sessions

Abstract

A multiparty session forms a unit of structured interactions among several processes which follow a specified protocol described as a global type. Well-known communication-oriented type systems guarantee communication safety and progress within single sessions, but do not take into account the dependencies arising from the interleaving of simultaneously active sessions and from session delegations. As a consequence, a system of well typed processes may fail to have progress, even assuming that helper processes can join the system after its execution has started. In this paper we develop a static analysis technique, specified as a set of syntax-directed inference rules, that is capable of verifying whether a system of processes engaged in simultaneously active multiparty sessions has the progress property.

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

“…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. Inference of progress properties akin to lock freedom for session-based calculi has been studied in [17,3], although only finite types are considered in these works.…”

Choreographies in the wild

“…(a) Intuitively, for a set of participants to share knowledge, they may interact either via a single (multiparty) session or via several binary sessions. However, guaranteeing safety and liveness properties across several, possibly interleaved, sessions is a notoriously difficult problem (see [19] for instance) and it is even harder to check for semantic properties such as knowledge sharing. Instead, intrasessions properties are much easier to attain [3]; and in our case a broker is able to take a well-informed decision before starting a session by analysing its choreography.…”

“…However, session type based systems do not cater for a notion of "culpability", and are generally unable to guarantee progress for processes interacting on multiple interleaved sessions without strong assumptions on their execution context. The problem of guaranteeing progress in a composition of processes interacting through several interleaved sessions is tackled in [19,32] via a complex typing system. Their results include that a well-typed compositions of processes can interact on multiple interleaved sessions without deadlocking -and thus, in our setting, without remaining persistently culpable.…”

“…In the present paper, a similar progress result is provided for systems of honest participants (Corollary 6.3): a main difference wrt. [19,32] is that the honesty of each participant is checked "in isolation", without assumptions on the runtime context. Another related approach in the context of multiparty session types is that of run-time monitoring [38,39].…”

Honesty by Typing

“…Honesty is a sort of progress property, and our type system allows participants to interleave many sessions as done in [15]. A crucial difference with respect to [15] is that the typing discipline there requires the consistency of the local types of any two participants interacting in a session. Namely, if in a session s, A and B are typed as T A and T B respectively and they interact then the projection of T A with respect to B must be dual of the projection of T B with respect to A.…”