typedef struct _mpi_data_t {
    uint64_t *array1;
    uint64_t *array2;
    size_t array1_size;
    size_t array2_size;
} mpi_data_t;

MPI_Get_address(&mpi_data_send, &address[0]);
MPI_Get_address(&mpi_data_send.array1[0], &address[1]);
MPI_Get_address(&mpi_data_send.array2[0], &address[2]);
MPI_Get_address(&mpi_data_send.array1_size, &address[3]);
displacements[0] = address[1] - address[0];
displacements[1] = address[2] - address[0];
displacements[2] = address[3] - address[0];

int block_count[3] = {mpi_data_send.array1_size, mpi_data_send.array2_size, 2};