Simple MPI Program

Question

I am trying to do some MPI, and here is a simple program using MPI_Send, MPI_Recv (yes, blocking). Rank 0 sends messages to all other processes and the others receive it. However, my MPI_Send never returns. Am I missing something here? Thanks!

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

int main(int argc, char **argv)
{

int rank, size, i;
MPI_Status status;
char message[20];
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &size);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
strcpy(message, "Hello, world");
if (rank==0){
   for(i=1;i<size;i++){

         printf("I am sending %s\n", message);
         MPI_Send(message, 23, MPI_BYTE, 0, 7, MPI_COMM_WORLD);
         printf("Sending node=%d, message=%s\n", rank, message);
 }
}
else{
                     MPI_Recv(message, 23, MPI_BYTE, MPI_ANY_SOURCE, 7, MPI_COMM_WORLD,&status);
                     printf("Receiving node=%d, message=%s\n", rank, message);
 }
MPI_Finalize();
return 0;
}

cnicutar cnicutar · Accepted Answer · 2011-05-10T04:56:54

You are sending the message to yourself:

MPI_Send(message, 23, MPI_BYTE, 0, 7, MPI_COMM_WORLD);

I believe this should be

MPI_Send(message, 23, MPI_BYTE, i, 7, MPI_COMM_WORLD);

Simple MPI Program

2 Answers