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Subject: [OMPI users] Problem with getting started
From: Manuel Freiberger (manuel.freiberger_at_[hidden])
Date: 2008-06-11 12:52:52


Hello everybody!

First of all I wanted to point out that I'm beginner regarding openMPI and all
I try to achieve is to get a simple program working on two PCs.
So far I've installed openMPI 1.2.6 on two PCs (one running OpenSUSE 10.2, the
other one Gentoo).
I set up two identical users on both systems and made sure that I can make an
SSH connection between them using private/public key authentication.

Next I ran the command
  mpirun -np 2 --hostfile myhosts uptime
which gave the result
  6:41pm up 1 day 5:16, 4 users, load average: 0.00, 0.07, 0.17
 18:43:45 up 7:36, 6 users, load average: 0.00, 0.02, 0.05
so I concluded that MPI should work in principle.

Next I tried the following code which I copied from Boost.MPI:
---- snip
#include <mpi.h>
#include <iostream>

int main(int argc, char* argv[])
{
  MPI_Init(&argc, &argv);
  int rank;
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  if (rank == 0)
  {
    std::cout << "Rank 0 is going to send" << std::endl;
    int value = 17;
    int result = MPI_Send(&value, 1, MPI_INT, 1, 0, MPI_COMM_WORLD);
    if (result == MPI_SUCCESS)
      std::cout << "Rank 0 OK!" << std::endl;
  }
  else if (rank == 1)
  {
    std::cout << "Rank 1 is waiting for answer" << std::endl;
    int value;
    MPI_Status status;
    int result = MPI_Recv(&value, 1, MPI_INT, 0, 0, MPI_COMM_WORLD,
                          &status);
    if (result == MPI_SUCCESS && value == 17)
      std::cout << "Rank 1 OK!" << std::endl;
  }
  MPI_Finalize();
  return 0;
}
---- snap

Starting a parallel job using
  mpirun -np 2 --hostfile myhosts mpi-test
I get the answer
  Rank 0 is going to send
  Rank 1 is waiting for answer
  Rank 0 OK!
and than the program locks. So the strange thing is that obviously the
recv()-command is blocking, which is what I do not understand.

Could anybody provide some hints, where I should start looking for the
mistake? Any help is welcome!

Best regards,
Manuel

-- 
Manuel Freiberger
Institute of Medical Engineering
Graz University of Technology
manuel.freiberger_at_[hidden]