Collective Contracts for Message-Passing Parallel Programs

Abstract Procedure contracts are a well-known approach for specifying programs in a modular way. We investigate a new contract theory for collective procedures in parallel message-passing programs. As in the sequential setting, one can verify that a procedure f conforms to its contract using only the contracts, and not the implementations, of the collective procedures called by f. We apply this approach to C programs that use the Message Passing Interface (MPI), introducing a new contract language that extends the ANSI/ISO C Specification Language. We present contracts for the standard MPI collective functions, as well as many user-defined collective functions. A prototype verification system has been implemented using the CIVL model checker for checking contract satisfaction within small bounds on the number of processes.