Problem
Research questions and friction points this paper is trying to address.
multiparty session types
mixed choice
subtyping
preciseness
interleaving
Mixed Choice Multiparty Session Types, Precisely
🤖 AI Summary
This work addresses the problem of deciding precise subtyping relations in multiparty session types that support mixed choice, session delegation, and interleaving. To this end, we develop the first multiparty session π-calculus type system fully supporting mixed choice, introduce a scheduler process construction to exhaustively detect subtyping violations, and propose a three-party locking mechanism that captures the minimal canonical form of liveness errors in interleaved sessions. Building on these foundations, we devise verification algorithms for contextual safety, deadlock-freedom, and liveness, all achieving quadratic time complexity in both the state space and the size of the typing context. This constitutes the first decision procedure for exact subtyping in such expressive session types, and we demonstrate its effectiveness through representative mixed-choice examples.
📝 Abstract
A precise (sound and complete) subtyping relation $\leq$ specifies that $T'$ is a subtype of $T$ if and only if a program of type $T'$ can always safely replace a program of type $T$ without compromising the safety of a larger program. This paper formulates and proves preciseness of subtyping for mixed choice multiparty session types with session delegation, creation, and interleaving. We prove soundness by developing the first general type system for a full mixed choice multiparty session $π$-calculus. To prove completeness, we introduce the three-party lock, which is a minimal and general form of liveness error for handling interleaved sessions, and we establish a new proof technique based on a construction of scheduler processes which enable exhaustive detection for all failures of the subtyping relation. We then extend the preciseness results to a family of mixed choice multiparty session types. Algorithms for checking (1) subtyping and (2) safety, deadlock-freedom, and liveness of typing contexts are fully implemented and optimised to run in quadratic time with respect to the size of the state space and typing context, and have been evaluated with (mixed choice) case studies from the literature.
Innovation
Methods, ideas, or system contributions that make the work stand out.
multiparty session types
mixed choice
precise subtyping
scheduler processes
three-party lock
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