MPI_Comm_dup is collective call

It is used in ```MPI_Send``` and ```MPI_Recv``` to create a new comm and differentiate from ```MPI_COMM_WORLD``` if ```rep_error_handler``` is invoked. But ```MPI_Comm_dup``` is collective hence if only some processes are calling ```MPI_Send``` and ```MPI_Recv``` program will stuck.

Find some other alternate to differentiate comms. 