pi_mpi_non_blocking.c

#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <math.h>
#include <time.h>

#define SEED     921
#define NUM_ITER 1000000000

int main(int argc, char *argv[]){
    int rank, size, provided;
    double tstart, tstop, pi;
    int root = 0;

    //initialize mpi
    MPI_Init_thread(&argc, &argv, MPI_THREAD_SINGLE, &provided);

    tstart = MPI_Wtime();

    //get total processes
    MPI_Comm_size(MPI_COMM_WORLD, &size);

    //get process rank
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    
    srand(rank * SEED);

    int count= 0; int total_count = 0;

    
    double x, y, z;


    int proc_iter = ceil((NUM_ITER/size));


    if(rank != root){
        //send count to process 0
        // Calculate PI following a Monte Carlo method
        for (int iter =  0; iter < proc_iter; iter++)
        {
            // Generate random (X,Y) points
            x = (double)random() / (double)RAND_MAX;
            y = (double)random() / (double)RAND_MAX;
            z = sqrt((x*x) + (y*y));
            
            // Check if point is in unit circle
            if (z <= 1.0)
            {
                count++;
            }
        }

        MPI_Request request;
        MPI_Isend(&count, 1, MPI_INT, 0, 0, MPI_COMM_WORLD, &request);
    }
    else{
        int counts[size - 1];
        MPI_Request requests[size - 1];
        

        for(int i = 1; i < size; i++){
            MPI_Irecv(&counts[i - 1], 1, MPI_INT, i, 0, MPI_COMM_WORLD, &requests[i - 1]);
        }

        // Calculate PI following a Monte Carlo method
        for (int iter =  0; iter < proc_iter; iter++)
        {
            // Generate random (X,Y) points
            x = (double)random() / (double)RAND_MAX;
            y = (double)random() / (double)RAND_MAX;
            z = sqrt((x*x) + (y*y));
            
            // Check if point is in unit circle
            if (z <= 1.0)
            {
                count++;
            }
        }

        MPI_Waitall(size-1, requests, MPI_STATUS_IGNORE);

        total_count = count;
        for(int i = 0; i < size -1; i++){
            total_count += counts[i];
        }

        pi = ((double)total_count / (double)(proc_iter * size)) * 4.0;
    }

 
    tstop = MPI_Wtime();
    
    if(rank == root){
        printf("The result of pi is %f\n", pi);
        printf("Total elapsed time is %f\n", (tstop -tstart));
    }

    MPI_Finalize();

    return 0;
}