Session Types Meet Separation Logic

Abstract

Session types and separation logic are two leading methodologies for software verification. Session types allow users to write protocols that concurrent programs must adhere to; a session type specifies the order in which messages have to be exchanged, and the types of the data those messages carry. By checking that programs follow compatible session types, we can reason about the ways processes interact, ultimately guaranteeing the absence of deadlocks and race conditions in sessions. Separation logic is an extension of Hoare logic that is typically used to prove full functional correctness of sequential stateful programs; using separation logic, we can write pre- and post-conditions for program statements that use mutable stores such as a heap and modularly verify that they satisfy these specifications. Separation logic is more expressive than session types when it comes to data: with it we can state properties such as "x is a number greater than five", whereas session types can only express that "x is a number". On the other hand, session types offer a powerful means of checking that the communications among concurrent programs do not interfere with each other or deadlock.