// An MPI implementation of the Sieve of Eratosthenes
//
// This program comes in two parts. You will also need the file sieve.c
//
// To compile do
//
//    [mymachine]: mpicc -o generate generate.c
//    [mymachine]: mpicc -o sieve sieve.c
//
// and to run the program do
//
//    [mymachine]: mpirun --oversubscribe ./generate 25
//
// where the number (here 25) gives the upper bound on the region
// within which to search for primes.

#include <stdio.h>
#include <mpi.h>
#include <unistd.h>
#include <stdlib.h>

int main(int argc, char *argv[]) {
  MPI_Comm nextComm;                    // this will house the first sieve
  int candidate = 2, N = atoi(argv[1]);  

  MPI_Init(&argc, &argv);         
  // Create the first sieve
  MPI_Comm_spawn("./sieve", argv, 1, MPI_INFO_NULL, 0, 
                 MPI_COMM_WORLD, &nextComm, MPI_ERRCODES_IGNORE);

  // Generate the sequence of candidates
  while (candidate<N) {
    MPI_Send(&candidate, 1, MPI_INT, 0, 0, nextComm);
    candidate++;
  }

  // Send the "no more candidates" signal
  candidate = -1;
  MPI_Send(&candidate, 1, MPI_INT, 0, 0, nextComm);
  MPI_Finalize();
}