Hi all, I have a question on the "Semantics of Point-to-Point Communication" in a multithreaded context. For me the situation for the code below is not clear, especially with respect to the paragraph in MPI-3.1 p.41, l.10-17 : void test(int rank) { int msg = 0; if (rank == 0) { #pragma omp parallel num_threads(2) #pragma omp critical { MPI_Send(&msg, 1, MPI_INT, 1, 42, MPI_COMM_WORLD); msg++; } } else if (rank == 1) { MPI_Recv(&msg, 1, MPI_INT, 0, 42, MPI_COMM_WORLD, MPI_STATUS_IGNORE); printf("Received %i\n", msg); MPI_Recv(&msg, 1, MPI_INT, 0, 42, MPI_COMM_WORLD, MPI_STATUS_IGNORE); printf("Received %i\n", msg); } } Two threads on the first process send a message, the first thread sends 0, the second thread send 1. From OpenMP semantics, the first send happens before the second send. Is there a guarantee, that the other process receives the 0 first? Thanks, Joachim -- Dipl.-Inf. Joachim Protze IT Center Group: High Performance Computing Division: Computational Science and Engineering RWTH Aachen University Seffenter Weg 23 D 52074 Aachen (Germany) Tel: +49 241 80- 24765 Fax: +49 241 80-624765 [email protected] www.itc.rwth-aachen.de