Type systems for distributed programs: session communication

Distributed systems are everywhere around us and guaranteeing their correctness is of paramount importance. It is natural to expect that these systems interact and communicate among them to achieve a common task. In this work, we develop techniques based on types and type systems for the verification of correctness, consistency and safety properties related to communication in complex distributed systems. We study advanced safety properties related to communication, like deadlock or lock freedom and progress. We study session types in the pi-calculus describing distributed systems and communication-centric computation. Most importantly, we de- fine an encoding of the session pi-calculus into the standard typed pi-calculus in order to understand the expressive power of these concurrent calculi. We show how to derive in the session pi-calculus basic properties, like type safety or complex ones, like progress, by exploiting this encoding

Progress as Compositional Lock-Freedom

International audienceA session-based process satisfies the progress property if its sessions never get stuck when it is executed in an adequate context. Previous work studied how to define progress by introducing the notion of catalysers, execution contexts generated from the type of a process. In this paper, we refine such definition to capture a more intuitive notion of context adequacy for checking progress. Interestingly, our new catalysers lead to a novel characterisation of progress in terms of the standard notion of lock-freedom. Guided by this discovery, we also develop a conservative extension of catalysers that does not depend on types, generalising the notion of progress to untyped session-based processes. We combine our results with existing techniques for lock-freedom, obtaining a new methodology for proving progress. Our methodology captures new processes wrt previous progress analysis based on session types

Simulation of Real-Time Scheduling with Various Execution Time Models

Presented during the Work-in-Progress session (WiP session)International audienceIn this paper, we present SimSo, a simulator that aims at facilitating the design of experimental evaluations for real-time scheduling algorithms. Currently, more than twenty-five algorithms were implemented. Special attention is paid to the execution time model of tasks. We show that the worst-case execution time for experimental simulation can introduce a bias in evaluation and we discuss as a work in progress how cache effects could be taken into consideration in the simulation

Affine Sessions

Session types describe the structure of communications implemented by channels. In particular, they prescribe the sequence of communications, whether they are input or output actions, and the type of value exchanged. Crucial to any language with session types is the notion of linearity, which is essential to ensure that channels exhibit the behaviour prescribed by their type without interference in the presence of concurrency. In this work we relax the condition of linearity to that of affinity, by which channels exhibit at most the behaviour prescribed by their types. This more liberal setting allows us to incorporate an elegant error handling mechanism which simplifies and improves related works on exceptions. Moreover, our treatment does not affect the progress properties of the language: sessions never get stuck

Paper Session III-C - The Horizon Mission Methodology- Work in Progress

Far-term, impossible space missions can, be directly relevant to today\u27s R&D decisions, relating to future space capabilities. That is the surprising premise of the Horizon Mission Methodology (HMM), Progenitors of revolutionary space capabilities of the future exist today as highly innovative or breakthrough space technology concepts or perspectives or not yet space-oriented new technology frontiers, collectively called breakthrough technology options (BTOs). The HMM was developed initially as a method of systematic analysis and evaluation of space-related BTOs. However, enthusiastic response from early \u27users of the HMM: \u27has indicated much broader applicability - to technology innovation and R&D decision-making for space,, aeronautics or indeed .any field in which technology innovation is crucial. The HM.M forces users into a shift of viewpoint - a change of paradigm; it forces them to stand in a different place conceptually to think about, and evaluate choices for the future. Currently, the HMM is being applied to several, different mission/technology .areas. The HMM is described in this paper as arc the objectives, scope, Horizon Missions and status of five study/workshops

Explicit connection actions in multiparty session types

This work extends asynchronous multiparty session types (MPST) with explicit connection actions to support protocols with op- tional and dynamic participants. The actions by which endpoints are connected and disconnected are a key element of real-world protocols that is not treated in existing MPST works. In addition, the use cases motivating explicit connections often require a more relaxed form of mul- tiparty choice: these extensions do not satisfy the conservative restric- tions used to ensure safety in standard syntactic MPST. Instead, we de- velop a modelling-based approach to validate MPST safety and progress for these enriched protocols. We present a toolchain implementation, for distributed programming based on our extended MPST in Java, and a core formalism, demonstrating the soundness of our approach. We discuss key implementation issues related to the proposed extensions: a practi- cal treatment of choice subtyping for MPST progress, and multiparty correlation of dynamic binary connections

The Third United Nations Conference on the Law of the Sea: the 1975 Geneva Session

The second substantive session of the Third United Nations Conference on the Law of the Sea was held at Geneva from March 26 to May 10, 1975. It was decided at the outset that this would be a negotiating session. There was no general debate. Few formal meetings were held. Even informal working groups of the whole tended to rely on smaller groups the work of which was necessarily removed from public view. Progress, in many respects substantial progress, was made toward producing generally acceptable texts in this way. However, the Conference did not complete the negotiation of a new Law of the Sea Convention or approved texts.</jats:p