bsend

#include <mpi.h>
#include <stdio.h>
#include <string>

int main(int argc, char** argv) {
    // Initialize the MPI environment
    MPI_Init(&argc, &argv);

    // Get the number of processes
    int world_size;
    MPI_Comm_size(MPI_COMM_WORLD, &world_size);

    // Get the rank of the process
    int world_rank;
    MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);

    const int ITERATION_NUMBER = 1000;

    switch (world_rank) {
    case 0: {
        double time = MPI_Wtime();

        // Send
        for (int i = 0; i < ITERATION_NUMBER; i++)
            MPI_Send(&i, 1, MPI_INT, 1, 0, MPI_COMM_WORLD);
        time = MPI_Wtime() - time;
        printf("Send: %.10f\n", time / ITERATION_NUMBER * 1E6);

        // Bsend
        int buffer_attached_size = ITERATION_NUMBER * (MPI_BSEND_OVERHEAD + sizeof(int));
        char* buffer_attached = (char*)malloc(buffer_attached_size);
        MPI_Buffer_attach(buffer_attached, buffer_attached_size);
        time = MPI_Wtime();
        for (int i = 0; i < ITERATION_NUMBER; i++)
            MPI_Bsend(&i, 1, MPI_INT, 1, 0, MPI_COMM_WORLD);
        time = MPI_Wtime() - time;
        printf("Bsend: %.10f\n", time / ITERATION_NUMBER * 1E6);
        MPI_Buffer_detach(buffer_attached, &buffer_attached_size);
        free(buffer_attached);


        // Isend
        MPI_Request requests[ITERATION_NUMBER];
        MPI_Status statuses[ITERATION_NUMBER];
        time = MPI_Wtime();
        for (int i = 0; i < ITERATION_NUMBER; i++)
            MPI_Isend(&i, 1, MPI_INT, 1, 0, MPI_COMM_WORLD, &requests[i]);
        MPI_Waitall(ITERATION_NUMBER, requests, statuses);
        time = MPI_Wtime() - time;
        printf("Isend: %.10f\n", time / ITERATION_NUMBER * 1E6);

        break;
    }
    case 1: {
        MPI_Status status;
        MPI_Request requests[ITERATION_NUMBER];
        MPI_Status statuses[ITERATION_NUMBER];
        int rec[ITERATION_NUMBER];
        for (int i = 0; i < ITERATION_NUMBER; i++) {
            MPI_Recv(&rec[i], 1, MPI_INT, 0, 0, MPI_COMM_WORLD, &status);
        }
        for (int i = 0; i < ITERATION_NUMBER; i++) {
            MPI_Recv(&rec[i], 1, MPI_INT, 0, 0, MPI_COMM_WORLD, &status);
        }

        for (int i = 0; i < ITERATION_NUMBER; i++) {
            MPI_Irecv(&rec[i], 1, MPI_INT, 0, 0, MPI_COMM_WORLD, &requests[i]);

        }
        MPI_Waitall(ITERATION_NUMBER, requests, statuses);
        break;
    }
    default: {
        break;
    }
    }

    // Finalize the MPI environment.
    MPI_Finalize();
}