Certifying Data in Multiparty Session Types

© Springer International Publishing Switzerland 2016.Multiparty session types (MPST) are a typing discipline for ensuring the coordination and orchestration of multi-agent communication in concurrent and distributed programs. However, by mostly focusing on the communication aspects of concurrency, MPST are often unable to capture important data invariants in programs. In this work we propose to increase the expressiveness of MPST by considering a notion of value dependencies in order to certify invariants of exchanged data in concurrent and distributed settings

Fencing off go: liveness and safety for channel-based programming

Go is a production-level statically typed programming language whose design features explicit message-passing primitives and lightweight threads, enabling (and encouraging) programmers to develop concurrent systems where components interact through communication more so than by lock-based shared memory concurrency. Go can only detect global deadlocks at runtime, but provides no compile-time protection against all too common communication mis-matches or partial deadlocks. This work develops a static verification framework for liveness and safety in Go programs, able to detect communication errors and partial deadlocks in a general class of realistic concurrent programs, including those with dynamic channel creation, unbounded thread creation and recursion. Our approach infers from a Go program a faithful representation of its communication patterns as a behavioural type. By checking a syntactic restriction on channel usage, dubbed fencing, we ensure that programs are made up of finitely many different communication patterns that may be repeated infinitely many times. This restriction allows us to implement a decision procedure for liveness and safety in types which in turn statically ensures liveness and safety in Go programs. We have implemented a type inference and decision procedures in a tool-chain and tested it against publicly available Go programs

On polymorphic sessions and functions: A talk of two (fully abstract) encodings

This work exploits the logical foundation of session types to determine what kind of type discipline for the π -calculus can exactly capture, and is captured by, λ -calculus behaviours. Leveraging the proof theoretic content of the soundness and completeness of sequent calculus and natural deduction presentations of linear logic, we develop the first mutually inverse and fully abstract processes-as-functions and functions-as-processes encodings between a polymorphic session π -calculus and a linear formulation of System F. We are then able to derive results of the session calculus from the theory of the λ -calculus: (1) we obtain a characterisation of inductive and coinductive session types via their algebraic representations in System F; and (2) we extend our results to account for value and process passing, entailing strong normalisation

Depending on session typed process

This work proposes a dependent type theory that combines functions and session-typed processes (with value dependencies) through a contextual monad, internalising typed processes in a dependently-typed λ -calculus. The proposed framework, by allowing session processes to depend on functions and vice-versa, enables us to specify and statically verify protocols where the choice of the next communication action can depend on specific values of received data. Moreover, the type theoretic nature of the framework endows us with the ability to internally describe and prove predicates on process behaviours. Our main results are type soundness of the framework, and a faithful embedding of the functional layer of the calculus within the session-typed layer, showcasing the expressiveness of dependent session types