Inductive Sequentialization of Asynchronous Programs

Published in ACM SIGPLAN Conference on Programming Language Design and Implementation (PLDI), 2020

Recommended citation: Bernhard Kragl, Constantin Enea, Thomas Henzinger, Suha Mutluergil and Shaz Qadeer. "Inductive Sequentialization of Asynchronous Programs." In Proceedings of the 41st ACM SIGPLAN Conference on Programming Language Design and Implementation, 2020.

This paper introduces a new proof rule that can be combined with the standard abstraction and reduction techniques that can be useful for proving correctness of concurrent inductive programs.


Abstract. Asynchronous programs are notoriously difficult to reason about because they spawn computation tasks which take effect asynchronously in a nondeterministic way. Devising inductive invariants for such programs requires understanding and stating complex relationships between an unbounded number of computation tasks in arbitrarily long executions. In this paper, we introduce inductive sequentialization, a new proof rule that sidesteps this complexity via a sequential reduction, a sequential program that captures every behavior of the original program up to reordering of coarse-grained commutative actions. A sequential reduction of a concurrent program is easy to reason about since it corresponds to a simple execution of the program in an idealized synchronous environment, where processes act in a fixed order and at the same speed. We have implemented and integrated our proof rule in the CIVL verifier, allowing us to provably derive fine-grained implementations of asynchronous programs. We have successfully applied our proof rule to a diverse set of message-passing protocols, including leader election protocols, two-phase commit, and Paxos.