Open Multiparty Sessions

Abstract

Multiparty sessions are systems of concurrent processes, which allow several participants to communicate by sending and receiving messages. Their overall behaviour can be described by means of global types. Typable multiparty session enjoy lock-freedom. We look at multiparty sessions as open systems by a suitable definition of connection transforming compatible processes into gateways (forwarders). A relation resembling the standard subtyping relation for session types is used to formalise compatibility. We show that the session obtained by connection can be typed by manipulating the global types of the starting sessions. This allows us to prove that lock-freedom is preserved by connection. * Partially supported by the project "Piano Triennale Ricerca" DMI-Università di Catania. † Partially supported by Ateneo/Compagnia di San Paolo 2016/2018 project "MnemoComputing -Components for Processing In Memory". Definition 2.3 (LTS for Multiparty Sessions) The labelled transition system (LTS) for multiparty sessions is the closure under structural congruence of the reduction specified by the unique rule: [COMM] makes the communication possible: participant p sends message ℓ to participant q. This rule is non-deterministic in the choice of messages. The condition msg(Λ) ⊆ msg(Λ ′ ) assures that the sender can freely choose the message, since the receiver must offer all sender messages and possibly more. This allows us to distinguish in the operational semantics between internal and external choices.We use M λ − → M ′ as shorthand for M pℓq − − → M ′ . We sometimes omit the label writing −→. As usual, −→ * denotes the reflexive and transitive closure of −→.Example 2.4 Let us consider a system (inspired by a similar one in [1]) with participants p, q, and h interacting according the following protocol. Participant p keeps on sending text messages to q, which

Choreography Automata

“…A run of an FSA A = S, L, →, s 0 is a (possibly empty or infinite) sequence of consecutive transitions starting at s 0 . The 4 obtained by concatenating the labels of the run, namely w = λ 0 • λ 1 • • • λ n ; if the run is empty then w = ǫ. The language of A, written L(A), is the set of traces of A.…”

“…Composition The composition of c-automata is defined in Section 5 as a refinement of the product of c-automata through the blending operation. This operation is inspired by one of the composition approaches in [4,5]. The composition of arbitrary c-automata may not preserve well-formedness (and hence the behaviour at the local level).…”

A type language for message passing component-based systems

“…We discuss some closely related work, starting by Open Multiparty Sessions [3] which to some extent shares the same goals and the same background (cf. [9]).…”

“…[9]). The approach in [3] targets the composition of protocols by considering that one of the participants can actually be instantiated by an external environment. Two protocols can then be connected if there is a participant in each that can serve as the interface to the other interaction.…”

Composition and decomposition of multiparty sessions

“…The present paper is a revised and extended version of [3]. The definition of the composition operation, first presented in [3], is considerably improved here, enabling us to simplify and make more readable also the proofs of most of the related results. This paper includes also a number of new contributions.…”