A natural form for a server that is to perform one of several tasks is to receive the message from any source and with any tag, and then use the tag to determine the task to perform.


    while (not done) {
	MPI_Recv( buf, 256, MPI_CHAR, MPI_ANY_SOURCE, MPI_ANY_TAG, 
		  master_comm, &status );
	switch (status.MPI_TAG) {
	case MSG_EXIT: 
	    code for exit message; 
	    break;
	case MSG_PRINT_UNORDERED:
	    code for unordered message;
	    break;
	case MSG_PRINT_ORDERED:
	    code for ordered message;
	    break;
	}
    }

An alternate approach explored in a related assignment is to use MPI_Probe instead.