smpi_mpi_send(header_buf, HEADER_SIZE, MPI_INT, to, tag, comm);
smpi_mpi_recv(tmp_buf, count, datatype, from, tag, comm, &status);
smpi_mpi_send(header_buf, HEADER_SIZE, MPI_INT, to, tag, comm);
smpi_mpi_recv(tmp_buf, count, datatype, from, tag, comm, &status);