Contact: (λ x y . “email@example.com”) “glen” “mevel”.
PhD student (2018–2022), team Cambium at Inria Paris & Laboratoire Méthodes Formelles at ENS Paris-Saclay (successor to team VALS at LRI), France.
With my advisors François Pottier (Inria) and Jacques‐Henri Jourdan (LMF), we aim at establishing a program logic for proving correctness of Multicore OCaml programs. For that, we are using the Coq proof assistant and the Iris separation logic.
Research interests: functional programming, proof of programs, separation logic, concurrent programming…
May 2022: I gave a talk about time debits at the second Iris workshop. [slides]
We use Cosmo, a modern concurrent separation logic, to formally specify and verify an implementation of a multiple-producer multiple-consumer concurrent queue in the setting of the Multicore OCaml weak memory model. We view this result as a demonstration and experimental verification of the manner in which Cosmo allows modular and formal reasoning about advanced concurrent data structures. In particular, we show how the joint use of logically atomic triples and of Cosmo's views makes it possible to describe precisely in the specification the interaction between the queue library and the weak memory model.
Multicore OCaml extends OCaml with support for shared-memory concurrency. It is equipped with a weak memory model, for which an operational semantics has been published. This begs the question: what reasoning rules can one rely upon while writing or verifying Multicore OCaml code? To answer it, we instantiate Iris, a modern descendant of Concurrent Separation Logic, for Multicore OCaml. This yields a low-level program logic whose reasoning rules expose the details of the memory model. On top of it, we build a higher-level logic, Cosmo, which trades off some expressive power in return for a simple set of reasoning rules that allow accessing nonatomic locations in a data-race-free manner, exploiting the sequentially-consistent behavior of atomic locations, and exploiting the release/acquire behavior of atomic locations. Cosmo allows both low-level reasoning, where the details of the Multicore OCaml memory model are apparent, and high-level reasoning, which is independent of this memory model. We illustrate this claim via a number of case studies: we verify several implementations of locks with respect to a classic, memory-model-independent specification. Thus, a coarse-grained application that uses locks as the sole means of synchronization can be verified in the Concurrent-Separation-Logic fragment of Cosmo, without any knowledge of the weak memory model.
We present a machine-checked extension of the program logic Iris with time credits and time receipts, two dual means of reasoning about time. Whereas time credits are used to establish an upper bound on a program's execution time, time receipts can be used to establish a lower bound. More strikingly, time receipts can be used to prove that certain undesirable events — such as integer overflows — cannot occur until a very long time has elapsed. We present several machine-checked applications of time credits and time receipts, including an application where both concepts are exploited.