Closer to Reliable Software: Verifying Functional Behaviour of Concurrent Programs

Static formal verification techniques are an e↵ective method for verification of software. They exploit the advantages of formal methods to statically prove that the implementation of a program satisfies its formally written specification. This makes formal verification especially powerful: any execution of the program is guaranteed to behave correctly. Therefore, these techniques are especially attractive for safety-critical systems, where correctness of the code is a crucial requirement. Applying formal techniques for verification of concurrent software is appealing. First, concurrent software today is omnipresent, but it is especially prone to errors. Second, finding errors in concurrent software using standard dynamic testing techniques is di cult, because of the non-deterministic behaviour of this software. Unfortunately, formal verification of concurrent software is hard and faces many challenges. This thesis contributes with novel formal techniques for verification of multithreaded programs. We focus mainly on verification of functional properties, i.e., properties that describe the behaviour of the program. Concretely, we work with axiomatic reasoning and use permission-based separation logic as our basic program logic. First, we propose a new modular technique for verification of class invariants in concurrent programs. This technique allows breaking of class invariants at certain safe places in the program. The technique is flexible and permissive, and thus, can be applied in a broad range of practical examples. This approach is formalised on a concurrent object-oriented language. Second, we propose a new way of specifying and verifying functional behaviour of methods in the program. Our technique uses separation logic-based reasoning to build an abstraction of the program represented as a process algebra term; by reasoning about the abstract model, we prove properties about the original program. This approach allows very expressive and intuitive specifications.