MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &req);
MPI_Recv (buf1, buf_size, MPI_INT, 1, 0, MPI_COMM_WORLD, &status);
MPI_Send (buf1, buf_size, MPI_INT, 1, 0, MPI_COMM_WORLD);
MPI_ANY_SOURCE, 0, MPI_COMM_WORLD, &req);
MPI_Recv (buf1, buf_size, MPI_INT, 1, 0, MPI_COMM_WORLD, &status);
MPI_Send (buf1, buf_size, MPI_INT, 1, 0, MPI_COMM_WORLD);