Extending JML for Modular Specification and Verification of Multi-threaded Programs

The Java Modeling Language (JML) is a formal specification language for Java that allows developers to specify rich software contracts for interfaces and classes, using pre- and postconditions and invariants. Although JML has been widely studied and has robust tool support based on a variety of automated verification technologies, it shares a problem with many similar object-oriented specification languages—it currently only deals with sequential programs. In this paper, we extend JML to allow for effective specification of multi-threaded Java programs. The new constructs rely on the non-interference notion of

method atomicity

, and allow developers to specify locking and other non-interference properties of methods. Atomicity enables effective specification of method pre- and postconditions and supports Hoare-style modular reasoning about methods. Thus the new constructs mesh well with JML’s existing features. We validate the specification language design by specifying the behavior of a number of complex Java classes designed for use in multi-threaded programs. We also demonstrate that it is amenable to automated verification using model checking technology.