Detection of Violations to the MPI Standard in Hybrid OpenMP/MPI Applications

The MPI standard allows the usage of multiple threads per process. The main idea was that an MPI call executed at one thread should not block other threads. In the MPI-2 standard this was refined by introducing the so called

level of thread support

which describes how threads may interact with MPI. The multi-threaded usage is restricted by several rules stated in the MPI standard. In this paper we describe the work on an MPI checker called MARMOT[1] to enhance its capabilities towards a verification that ensures that these rules are not violated. A first implementation is capable of detecting violations if they actually occur in a run made with MARMOT. As most of these violations occur due to missing thread synchronization it is likely that they don’t appear in every run of the application. To detect whether there is a run that violates one of the MPI restrictions it is necessary to analyze the OpenMP usage. Thus we introduced artificial data races that only occur if the application violates one of the MPI rules. By this design all tools capable of detecting data races can also detect violations to some of the MPI rules. To confirm this idea we used the Intel® Thread Checker.