[mpich-discuss] MPI_Comm_Spawn question

[Eric Hui]

I started my MPI program with one process only and tried to use MPI_Comm_Spawn to launch three more copies like this:

//main
         MPI_Comm ParentComm;
         MPI_Comm InterComm;

         MPI_Comm_get_parent (&ParentComm);

         if (ParentComm == MPI_COMM_NULL)
         {
            MPI_Comm_spawn("myapp.exe", argv, NumMPIHelpers, MPI_INFO_NULL, 0, MPI_COMM_SELF, &InterComm, MPI_ERRCODES_IGNORE);

            ShowRank (InterComm);  //*<-- this shows size = 1, rank = 0
         }
         else
         {
            ShowRank (ParentComm);  //* this shows size = 3, rank = 0, 1 or 2 for the childs
         }

//showrank function
void ShowRank (MPI_Comm Com)
{
   MPI_Comm_rank (Com, &MPIRank);      /* get current process id */
   MPI_Comm_size (Com, &MPISize);         /* get number of processes */

   DWORD Pid = GetCurrentProcessId();

   CString Msg;

   Msg.Format ("MPI_Comm = %ld, Process ID = %ld, Size = %ld, Rank = %ld", Com, Pid, MPISize, MPIRank);

   AddMsg (Msg);
}

I am trying to join the parents and the children together into one group.

Do I need to call MPI_Intercomm_merge?  I thought the "InterComm" is already supposed to have size = 4 with rank = 0, 1, 2 and 3.

Thanks,
Eric
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