Abstract

Abstract. This paper investigates an approach for statically preventing race conditions in an object-oriented language. The setting of this work is a variant of Gordon and Hankin's concurrent object calculus. We enrich that calculus with a form of dependent object types that enables us to verify that threads invoke and update methods only after acquiring appropriate locks. We establish that well-typed programs do not have race conditions. 1 Introduction Concurrent object-oriented programs suffer from many of the errors common inconcurrent programs of other sorts. In particular, the use of objects does not diminish the importance of careful synchronization. With objects or withoutthem, improper synchronization may lead to race conditions (that is, two processes accessing a shared resource simultaneously) and ultimately to incorrectbehavior. A standard approach for eliminating race conditions consists in protectingeach shared resource with a lock, requiring that a process acquires the corresponding lock before using the resource [5]. Object-oriented programs oftenrely on this approach, but with some peculiar patterns. It is common to group related resources into an object, and to attach the lock that protects the re-sources to this object. Processes may acquire the lock before invoking the methods of the object; alternatively, the methods may acquire this lock at the start oftheir execution. With constructs such as Java's

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