Safe sessions of channel actions in Clojure: A tour of the Discourje Project

To simplify shared-memory concurrent programming, in addition to low-level synchronisation primitives, several modern programming languages have started to offer core support for higher-level communication primitives as well, in the guise of message passing through channels. Yet, a growing body of evidence suggests that channel-based programming abstractions for shared memory also have their issues. The Discourje project aims to help programmers cope with message-passing concurrency bugs in Clojure programs, based on run-time verification and dynamic monitoring. The idea is that programmers write not only implementations, but also specifications (of sessions of channel actions). Discourje then offers a library to ensure that implementations run safely relative to specifications (= “bad” channel actions never happen). This paper gives a tour of the current state of Discourje, by example; it is intended to serve both as a general overview for readers who are unfamiliar with previous work on Discourje, and as an introduction to new features for readers who are familiar

Multiparty motion coordination: from choreographies to robotics programs

We present a programming model and typing discipline for complex multi-robot coordination programming. Our model encompasses both synchronisation through message passing and continuous-time dynamic motion primitives in physical space. We specify continuous-time motion primitives in an assume-guarantee logic that ensures compatibility of motion primitives as well as collision freedom. We specify global behaviour of programs in a choreographic type system that extends multiparty session types with jointly executed motion primitives, predicated refinements, as well as a separating conjunction that allows reasoning about subsets of interacting robots. We describe a notion of well-formedness for global types that ensures motion and communication can be correctly synchronised and provide algorithms for checking well-formedness, projecting a type, and local type checking. A well-typed program is communication safe, motion compatible, and collision free. Our type system provides a compositional approach to ensuring these properties. We have implemented our model on top of the ROS framework. This allows us to program multi-robot coordination scenarios on top of commercial and custom robotics hardware platforms. We show through case studies that we can model and statically verify quite complex manoeuvres involving multiple manipulators and mobile robots---such examples are beyond the scope of previous approaches

A Decentralized Analysis of Multiparty Protocols

Protocols provide the unifying glue in concurrent and distributed software today; verifying that message-passing programs conform to such governing protocols is important but difficult. Static approaches based on multiparty session types (MPST) use protocols as types to avoid protocol violations and deadlocks in programs. An elusive problem for MPST is to ensure both protocol conformance and deadlock freedom for implementations with interleaved and delegated protocols. We propose a decentralized analysis of multiparty protocols, specified as global types and implemented as interacting processes in an asynchronous $\pi$-calculus. Our solution rests upon two novel notions: router processes and relative types. While router processes use the global type to enable the composition of participant implementations in arbitrary process networks, relative types extract from the global type the intended interactions and dependencies between pairs of participants. In our analysis, processes are typed using APCP, a type system that ensures protocol conformance and deadlock freedom with respect to binary protocols, developed in prior work. Our decentralized, router-based analysis enables the sound and complete transference of protocol conformance and deadlock freedom from APCP to multiparty protocols.Comment: revision following anonymous review

A decentralized analysis of multiparty protocols

Protocols provide the unifying glue in concurrent and distributed software today; verifying that message-passing programs conform to such governing protocols is important but difficult. Static approaches based on multiparty session types (MPST) use protocols as types to avoid protocol violations and deadlocks in programs. An elusive problem for MPST is to ensure both protocol conformance and deadlock-freedom for implementations with interleaved and delegated protocols. We propose a decentralized analysis of multiparty protocols, specified as global types and implemented as interacting processes in an asynchronous π-calculus. Our solution rests upon two novel notions: router processes and relative types. While router processes use the global type to enable the composition of participant implementations in arbitrary process networks, relative types extract from the global type the intended interactions and dependencies between pairs of participants. In our analysis, processes are typed using APCP, a type system that ensures protocol conformance and deadlock-freedom with respect to binary protocols, developed in prior work. Our decentralized, router-based analysis enables the sound and complete transference of protocol conformance and deadlock-freedom from APCP to multiparty protocols