lab 5.1

#include <iostream>
#include <mpi.h>

using namespace std;

typedef struct three_args_struct {
    int first;
    int second;
    double third;
} triplet;

void buildDerivedType(MPI_Datatype* mpi_triplet_type) {
    int nitems = 3;
    int block_lengths[3] = { 1, 1, 1 };
    MPI_Aint offsets[3];
    MPI_Datatype typelist[3] = { MPI_INT, MPI_INT, MPI_DOUBLE };

    offsets[0] = offsetof(triplet, first);
    offsets[1] = offsetof(triplet, second);
    offsets[2] = offsetof(triplet, third);

    MPI_Type_create_struct(nitems, block_lengths, offsets, typelist, mpi_triplet_type);
    MPI_Type_commit(mpi_triplet_type);
}

void initializeArray(triplet* arr, int size) {
    for (int i = 0; i < size; i++) {
        arr[i].first = i;
        arr[i].second = i * i;
        arr[i].third = i / 10.0;
    }
}

int main(int argc, char* argv[]) {
    MPI_Init(&argc, &argv);
    cout << "prj5.1" << endl;
    double startTime = MPI_Wtime();

    int rank;
    int threads_count;
    MPI_Status status;

    MPI_Comm_size(MPI_COMM_WORLD, &threads_count);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    int side_threads_count = threads_count - 1;

    if (threads_count < 2) {
        fprintf(stderr, "Requires at least two processes.\n");
        exit(-1);
    }

    triplet* buf = new triplet[threads_count];
    if (rank == 0) {
        initializeArray(buf, threads_count);
        for (int i = 0; i < threads_count; i++) {
            cout << i << ". first = " << buf[i].first << ", second = " << buf[i].second << ", third = " << buf[i].third << endl;
        }
    }

    MPI_Datatype* mpi_triplet_type = new MPI_Datatype;
    buildDerivedType(mpi_triplet_type);
    triplet* receivedInf = new triplet;

    MPI_Scatter(buf, 1, *mpi_triplet_type, receivedInf, 1, *mpi_triplet_type, 0, MPI_COMM_WORLD);
    int flag = 0;
    if (rank == 0) {
        flag = -1;
        MPI_Send(&flag, 1, MPI_INT, 1, 0, MPI_COMM_WORLD);
    }
    else {
        MPI_Recv(&flag, 1, MPI_INT, rank - 1, 0, MPI_COMM_WORLD, &status);
        cout << rank << ". Printing structure: first = " << receivedInf->first << ", second = " << receivedInf->second << ", third = " << receivedInf->third << endl;
        if (rank != threads_count - 1) {
            MPI_Send(&flag, 1, MPI_INT, rank + 1, 0, MPI_COMM_WORLD);
        }
    }

    double endTime = MPI_Wtime();
    double elapsed = endTime - startTime;
    cout << "Program runtime: " << elapsed << endl;
    MPI_Finalize();
}