manual_broadcast.c

/******************************************************************/
/*                                                                */
/* Question 2: Broadcast simple en utilisant MPI_Send et MPI_Recv */
/*                                                                */
/******************************************************************/
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <mpi.h>
#include <sys/time.h>

#define BUFLEN 65536

long ms_time(void) 
{
  struct timeval tv;

  gettimeofday(&tv, NULL);
  return(tv.tv_sec*1000 + tv.tv_usec/1000);
}

void long_computation(void) 
{
   long now=ms_time();
   while(ms_time()<now+4000) 
     {
     }
}

void my_broadcast(void *buffer, int count, MPI_Datatype datatype, int root) {
  int my_id, nb_proc;
  MPI_Status status;
  int i;

  MPI_Comm_rank(MPI_COMM_WORLD,&my_id);
  MPI_Comm_size(MPI_COMM_WORLD,&nb_proc);
  
  if (my_id == root) {
    for (i=0; i<nb_proc; i++) {
      if (i != root) {
	MPI_Send(buffer, count, datatype,i,0,MPI_COMM_WORLD);
      }
    }
  } else {
    MPI_Recv(buffer,count,datatype, root, 0, MPI_COMM_WORLD, &status);
  }
}


int main(int argc, char **argv) 
{
  int nb_proc;
  int my_id;
  int buffer[BUFLEN];
  long int start_time, end_time;

  MPI_Init(&argc,&argv);
  MPI_Comm_size(MPI_COMM_WORLD,&nb_proc);
  MPI_Comm_rank(MPI_COMM_WORLD,&my_id);
 

  start_time = ms_time();

  my_broadcast(buffer,BUFLEN,MPI_INT,0);
  long_computation();
  end_time = ms_time();
  printf("[proc P%d] Done within %ld milliseconds.\n", my_id, end_time - start_time);


  MPI_Finalize();

  return (0);
}