[Boost-users] Using Boost.MPI with gather , data becomes overwritten after gather operation

Subject: [Boost-users] Using Boost.MPI with gather , data becomes overwritten after gather operation
From: hgc-01134_at_[hidden]
Date: 2010-08-31 12:26:54

Hi,
I am trying to use Boost.MPI to do a very simple program that
1. Processes from different ranks do a gather operation
2. The gather operation will gather the CoProcessInfo ( which is just
a data structure of rank# and hostname) into a vector
3. After the gather operation, Rank 0 will print the CoProcessInfo
one by one in the vector.

------------------------------------------------------------------------------------------------------------------------------------------------------
My testing environment consists of TWO virtual machine ( each of the
machine has two cores ):
Centos 5.5
mpich2
Boost.mpich2
Boost 1.41
mpiexec
------------------------------------------------------------------------------------------------------------------------------------------------------

The expected output of the program should be something like  ( just an
example order of ranks ):

Host VM1, Rank 0
Host VM1, Rank 1
Host VM2, Rank 2
Host VM2, Rank 3

----------------------------------------------------------------------------------------------------------------------------------------------------------
However, I got something like: ( just an example order of ranks ), the
hostname is incorrect after gather operation ( three VM2 appears!)

Host VM1, Rank 0
Host VM2, Rank 1
Host VM2, Rank 2
Host VM2, Rank 3

I found that each process CAN correctly found out the hostname and
rank#, however, the data will become a bit like overwritten, after the
gather operation. Thank you very much.

-------------------------------------------  Source Code
-------------------------------------------------------------------
#include <boost/asio/ip/host_name.hpp>
#include <iostream>
#include <vector>
#include <string>
#include <boost/mpi/environment.hpp>
#include <boost/mpi/communicator.hpp>
#include <boost/mpi.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <sstream>
#include <fstream>

using namespace std;
namespace mpi = boost::mpi;

class CoProcessInfo
{
        private:

        string hostname;
        int rank;

    friend class boost::serialization::access;
    template<class Archive>
    void serialize(Archive & ar, const unsigned int /* version */)
    {
        ar & hostname & rank;
    }

        public:
        CoProcessInfo()
        {
                hostname = boost::asio::ip::host_name();	    	
                rank = 0;
        }

        void setRank(int _rank)
        {
                rank = _rank;
        }

        string getHostname() const
        {
               return hostname;
        }

        int getRank() const
        {
                return rank;
        }
};

int main(int argc, char* argv[])
{
    int myrank;

  mpi::environment env(argc, argv);
  mpi::communicator world;
  myrank = world.rank();
        
    CoProcessInfo localInfo;
    localInfo.setRank( myrank );

       std::vector<CoProcessInfo> coProcInfo;
       mpi::gather(world, localInfo, coProcInfo, 0);
        
        if( myrank == 0 ){	
                 for (std::vector<CoProcessInfo>::const_iterator it = coProcInfo.begin();
                                                 it !=coProcInfo.end(); ++it) {
                         cout << endl << " Host :  " << it->getHostname() << " ,  Rank : "
<< it->getRank() << endl;
                 }
        }
    return 0;
}
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Regards,
Joseph