Call-ordering constraints

Several kinds of call-ordering problems have been identified, all of which present subtle difficulties in ensuring the correctness of a sequential program. They include object protocols, synchronisation patterns and re-entrance restrictions. This paper presents call-ordering constraints as a unifying solution to these problems. These constraints are new classes of contracts in addition to traditional preconditions, postconditions and invariants. They extend the traditional notion of behavioural subtyping. The paper shows how constraint inheritance can almost ensure behavioural subtyping conformance. The paper also shows how these constraints may be monitored at run time. Call-ordering constraints are included in the BECON contract system, which has been implemented on the Common Language Infrastructure (CLI).