Comunicazione bidirezionale

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/times.h>
#include <unistd.h>
#include "mpi.h"

struct timeval tv;
struct timezone tz;

double wallclocktime(){
  static int startflag=1;
  static double tsecs0, tsecs1, dt;
  (void) gettimeofday(&tv,&tz);
  tsecs1 = tv.tv_sec + tv.tv_usec*1.0e-6;
  return tsecs1;
}


int main(int argc, char **argv){
  char name[BUFSIZ];
  int length,procnum,numprocs,size,i=0,n;
  MPI_Status *recv_status;
  void *buf;
  int mark=123;
  double start,stop,timetot;
  double bandwith;
  double nbytetot;

  MPI_Init(&argc, &argv);
  /* Find out this host name */
  MPI_Get_processor_name(name, &length);
  /* Find out this processor number */
  MPI_Comm_rank(MPI_COMM_WORLD, &procnum);
  /* Find out the number of processors */
  MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
  size=atoi(argv[1]);
  n=atoi(argv[2]);
  buf=malloc(size);
  
  if(buf==NULL) printf("Malloc error!!\n");

  if((procnum % 2)==0){
    MPI_Barrier (MPI_COMM_WORLD);
    for(i=0;i<n;i++){
       MPI_Recv(buf,size, MPI_BYTE,(procnum+1),mark, 
                MPI_COMM_WORLD,recv_status);
       MPI_Send(buf,size,MPI_BYTE,(procnum+1),mark,
                MPI_COMM_WORLD);
    }
  }else{
    MPI_Barrier (MPI_COMM_WORLD);
    start=wallclocktime();
    for(i=0;i<n;i++){
      MPI_Send(buf,size,MPI_BYTE,(procnum-1),mark,
               MPI_COMM_WORLD);
      MPI_Recv(buf,size, MPI_BYTE,(procnum-1),mark, 
               MPI_COMM_WORLD,recv_status);
    }
    stop=wallclocktime();
    timetot=(stop-start);
    nbytetot=( ( (double)size/1024.0 )*n );
    bandwith=(nbytetot/timetot);
    fprintf(stderr,"%d packsize: %d byte, timetot: %.3f sec, 
                    nbytetot: %.3f Kbyte, 
                    bw: %.3f Kbyte/sec,ping: %d\n",
                    procnum,size,timetot,nbytetot,bandwith,n );
  }
  MPI_Finalize();
}