arXiv subjects

Julien Lange

Publications and source records attributed to Julien Lange.

At least 19 recordsLinked to original sources

arXiv2026

Welterweight Go: Boxing, Structural Subtyping, and Generics (Extended Version)

Go's unique combination of structural subtyping between generics and types with non-uniform runtime representations presents significant challenges for formalising the language. We introduce WG (Welterweight Go), a core model of Go that captures key features excluded by prior work, including underlying types, type unions and type sets, and proposed new features, such as generic methods. We also develop LWG, a lower-level language that models Go's runtime mechanisms, notably the distinction between raw struct values and interface values that carry runtime type information (RTTI). We give a type-directed compilation from WG to LWG that demonstrates how the proposed features can be implemented while observing important design and implementation goals for Go: compatibility with separate compilation, and no runtime code generation. Unlike existing approaches based on static monomorphisation, our compilation strategy uses runtime type conversions and adaptor methods to handle the complex interactions between structural subtyping, generics, and Go's runtime infrastructure.

cs.PL↗

arXiv2025

RustMC: Extending the GenMC stateless model checker to Rust

RustMC is a stateless model checker that enables verification of concurrent Rust programs. As both Rust and C/C++ compile to LLVM IR, RustMC builds on GenMC which provides a verification framework for LLVM IR. This enables the automatic verification of Rust code and any C/C++ dependencies. This tool paper presents the key challenges we addressed to extend GenMC. These challenges arise from Rust's unique compilation strategy and include intercepting threading operations, handling memory intrinsics and uninitialized accesses. Through case studies adapted from real-world programs, we demonstrate RustMC's effectiveness at finding concurrency bugs stemming from unsafe Rust code, FFI calls to C/C++, and incorrect use of atomic operations.

cs.PL↗

arXiv2022

A model of actors and grey failures

Existing models for the analysis of concurrent processes tend to focus on fail-stop failures, where processes are either working or permanently stopped, and their state (working/stopped) is known. In fact, systems are often affected by grey failures: failures that are latent, possibly transient, and may affect the system in subtle ways that later lead to major issues (such as crashes, limited availability, overload). We introduce a model of actor-based systems with grey failures, based on two interlinked layers: an actor model, given as an asynchronous process calculus with discrete time, and a failure model that represents failure patterns to inject in the system. Our failure model captures not only fail-stop node and link failures, but also grey failures (e.g., partial, transient). We give a behavioural equivalence relation based on weak barbed bisimulation to compare systems on the basis of their ability to recover from failures, and on this basis we define some desirable properties of reliable systems. By doing so, we reduce the problem of checking reliability properties of systems to the problem of checking bisimulation.

cs.FL↗

arXiv2022

Provable GPU Data-Races in Static Race Detection

We extend the theory behind the Faial tool-chain, which can soundly prove that CUDA programs (aka, kernels) are data-race free using specialized behavioral types called memory access protocols (MAPs). In this paper we extend the theory of MAPs to characterize kernels for which alarms can be identified as true alarms. We introduce a core calculus for CUDA, which we named BabyCUDA, and a behavioral type system for it. We show that if a BabyCUDA program can be assigned a MAP, then any alarm raised by Faial for this program is a true alarm.

cs.PL↗

arXiv2021

kmclib: Automated Inference and Verification of Session Types

Theories and tools based on multiparty session types offer correctness guarantees for concurrent programs that communicate using message-passing. These guarantees usually come at the cost of an intrinsically top-down approach, which requires the communication behaviour of the entire program to be specified as a global type. This paper introduces kmclib: an OCaml library that supports the development of correct message-passing programs without having to write any types. The library utilises the meta-programming facilities of OCaml to automatically infer the session types of concurrent programs and verify their compatibility (k-MC). Well-typed programs, written with kmclib, do not lead to communication errors and cannot get stuck.

cs.PL↗

arXiv2021

Proceedings 14th Interaction and Concurrency Experience

This volume contains the proceedings of ICE'21, the 14th Interaction and Concurrency Experience, which was held online on the 18th of June 2021, as a satellite event of DisCoTec'21. The ICE workshop series features a distinguishing review and selection procedure, allowing PC members to interact anonymously with authors. As in the past 13 editions, this interaction considerably improved the accuracy of the feedback from the reviewers and the quality of accepted papers, and offered the basis for lively discussion during the workshop. The 2021 edition of ICE included double blind reviewing of original research papers, in order to increase fairness and avoid bias in reviewing. Each paper was reviewed by three or four PC members, and altogether 5 papers were accepted for publication - plus 4 oral presentations which are not part of this volume. We were proud to host 2 invited talks, by Laura Bocchi and Helene Coullon. The abstracts of these talks are included in this volume together with the regular papers. The final versions of the contributions, taking into account the discussion at the workshop, are included.

cs.PL↗

arXiv2021

A Session Subtyping Tool (Extended Version)

Session types are becoming popular and have been integrated in several mainstream programming languages. Nevertheless, while many programming languages consider asynchronous fifo channel communication, the notion of subtyping used in session type implementations is the one defined by Gay and Hole for synchronous communication. This might be because there are several notions of asynchronous session subtyping, these notions are usually undecidable, and only recently sound (but not complete) algorithmic characterizations for these subtypings have been proposed. But the fact that the definition of asynchronous session subtyping and the theory behind related algorithms are not easily accessible to non-experts may also prevent further integration. The aim of this paper, and of the tool presented therein, is to make the growing body of knowledge about asynchronous session subtyping more accessible, thus promoting its integration in practical applications of session types.

cs.PL↗

arXiv2021

A Sound Algorithm for Asynchronous Session Subtyping and its Implementation

Session types, types for structuring communication between endpoints in distributed systems, are recently being integrated into mainstream programming languages. In practice, a very important notion for dealing with such types is that of subtyping, since it allows for typing larger classes of system, where a program has not precisely the expected behaviour but a similar one. Unfortunately, recent work has shown that subtyping for session types in an asynchronous setting is undecidable. To cope with this negative result, the only approaches we are aware of either restrict the syntax of session types or limit communication (by considering forms of bounded asynchrony). Both approaches are too restrictive in practice, hence we proceed differently by presenting an algorithm for checking subtyping which is sound, but not complete (in some cases it terminates without returning a decisive verdict). The algorithm is based on a tree representation of the coinductive definition of asynchronous subtyping; this tree could be infinite, and the algorithm checks for the presence of finite witnesses of infinite successful subtrees. Furthermore, we provide a tool that implements our algorithm. We use this tool to test our algorithm on many examples that cannot be managed with the previous approaches, and to provide an empirical evaluation of the time and space cost of the algorithm.

cs.PL↗

arXiv2021

Fair Asynchronous Session Subtyping

Session types are widely used as abstractions of asynchronous message passing systems. Refinement for such abstractions is crucial as it allows improvements of a given component without compromising its compatibility with the rest of the system. In the context of session types, the most general notion of refinement is asynchronous session subtyping, which allows message emissions to be anticipated w.r.t. a bounded amount of message consumptions. In this paper we investigate the possibility to anticipate emissions w.r.t. an unbounded amount of consumptions: to this aim we propose to consider fair compliance over asynchronous session types and fair refinement as the relation that preserves it. This allows us to propose a novel variant of session subtyping that leverages the notion of controllability from service contract theory and that is a sound characterisation of fair refinement. In addition, we show that both fair refinement and our novel subtyping are undecidable. We also present a sound algorithm which deals with examples that feature potentially unbounded buffering. Finally, we present an implementation of our algorithm and an empirical evaluation of it on synthetic benchmarks.

cs.PL↗

arXiv2020

Featherweight Go

We describe a design for generics in Go inspired by previous work on Featherweight Java by Igarashi, Pierce, and Wadler. Whereas subtyping in Java is nominal, in Go it is structural, and whereas generics in Java are defined via erasure, in Go we use monomorphisation. Although monomorphisation is widely used, we are one of the first to formalise it. Our design also supports a solution to The Expression Problem.

cs.PL↗

arXiv2020

Proceedings 13th Interaction and Concurrency Experience

This volume contains the proceedings of ICE'20, the 13th Interaction and Concurrency Experience, which was held online on the 19th of June 2020, as a satellite event of DisCoTec'20. The ICE workshop series features a distinguishing review and selection procedure, allowing PC members to interact anonymously with authors. As in the past 12 editions, this interaction considerably improved the accuracy of the feedback from the reviewers and the quality of accepted papers, and offered the basis for lively discussion during the workshop. The 2020 edition of ICE included double blind reviewing of original research papers, in order to increase fairness and avoid bias in reviewing. Each paper was reviewed by three PC members, and altogether 5 papers were accepted for publication - plus 5 oral presentations which are not part of this volume. We were proud to host 2 invited talks, by Cinzia Di Giusto and Karoliina Lehtinen. The abstracts of these talks are included in this volume together with the regular papers. The final versions of the contributions, taking into account the discussion at the workshop, are included.

cs.PL↗

arXiv2020

Bounded verification of message-passing concurrency in Go using Promela and Spin

This paper describes a static verification framework for the message-passing fragment of the Go programming language. Our framework extracts models that over-approximate the message-passing behaviour of a program. These models, or behavioural types, are encoded in Promela, hence can be efficiently verified with Spin. We improve on previous works by verifying programs that include communication-related parameters that are unknown at compile-time, i.e., programs that spawn a parameterised number of threads or that create channels with a parameterised capacity. These programs are checked via a bounded verification approach with bounds provided by the user.

cs.PL↗

arXiv2019

Verifying Asynchronous Interactions via Communicating Session Automata

This paper proposes a sound procedure to verify properties of communicating session automata (CSA), i.e., communicating automata that include multiparty session types. We introduce a new asynchronous compatibility property for CSA, called k-multiparty compatibility (k-MC), which is a strict superset of the synchronous multiparty compatibility used in theories and tools based on session types. It is decomposed into two bounded properties: (i) a condition called k-safety which guarantees that, within the bound, all sent messages can be received and each automaton can make a move; and (ii) a condition called k-exhaustivity which guarantees that all k-reachable send actions can be fired within the bound. We show that k-exhaustivity implies existential boundedness, and soundly and completely characterises systems where each automaton behaves equivalently under bounds greater than or equal to k. We show that checking k-MC is PSPACE-complete, and demonstrate its performance empirically over large systems using partial order reduction.

cs.PL↗

arXiv2017

Fencing off Go: Liveness and Safety for Channel-based Programming (extended version)

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 mismatches 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 procedures to check for liveness and safety in types which in turn approximates liveness and safety in Go programs. We have implemented a type inference and liveness and safety checks in a tool-chain and tested it against publicly available Go programs. Note: This is a revised extended version of a paper that appeared in POPL 2017, see page 13 for details.

cs.PL↗

arXiv2016

Multiparty Compatibility for Concurrent Objects

Objects and actors are communicating state machines, offering and consuming different services at different points in their lifecycle. Two complementary challenges arise when programming such systems. When objects interact, their state machines must be "compatible", so that services are requested only when they are available. Dually, when objects refine other objects, their state machines must be "compliant", so that services are honoured whenever they are promised. In this paper we show how the idea of multiparty compatibility from the session types literature can be applied to both of these problems. We present an untyped language in which concurrent objects are checked automatically for compatibility and compliance. For simple objects, checking can be exhaustive and has the feel of a type system. More complex objects can be partially validated via test cases, leading to a methodology closer to continuous testing. Our proof-of-concept implementation is limited in some important respects, but demonstrates the potential value of the approach and the relationship to existing software development practices.

cs.PL↗

arXiv2015

Characteristic Formulae for Session Types (extended version)

Subtyping is a crucial ingredient of session type theory and its applications, notably to programming language implementations. In this paper, we study effective ways to check whether a session type is a subtype of another by applying a characteristic formulae approach to the problem. Our core contribution is an algorithm to generate a modal mu-calculus formula that characterises all the supertypes (or subtypes) of a given type. Subtyping checks can then be off-loaded to model checkers, thus incidentally yielding an efficient algorithm to check safety of session types, soundly and completely. We have implemented our theory and compared its cost with other classical subtyping algorithms.

cs.LO↗

arXiv2013

Choreography Synthesis as Contract Agreement

We propose a formal model for distributed systems, where each participant advertises its requirements and obligations as behavioural contracts, and where multiparty sessions are started when a set of contracts allows to synthesise a choreography. Our framework is based on the CO2 calculus for contract-oriented computing, and borrows concepts and results from the session type literature. It supports sessions where the number of participants is not determined beforehand, and keeps CO2's ability to rule out participants that are culpable if contracts are not fulfilled at runtime. We show that we have progress and session fidelity in CO2, as a result of the honesty of participants - i.e., their ability to always adhere to their contracts.

cs.LO↗

arXiv2012

Synthesising Choreographies from Local Session Types (extended version)

Designing and analysing multiparty distributed interactions can be achieved either by means of a global view (e.g. in choreography-based approaches) or by composing available computational entities (e.g. in service orchestration). This paper proposes a typing systems which allows, under some conditions, to synthesise a choreography (i.e. a multiparty global type) from a set of local session types which describe end-point behaviours (i.e. local types).

cs.PL↗