Launching A Server

To launch a single job spanning multiple MPI implementations (with a common
MPI_COMM_WORLD), a two-step process will be needed in general. The first step is to launch a `server' process to be used as the rendezvous point for the different implementations:

        impirun -server <count> -port <port_number>

Here, <count> is the number of client connections that the server expects to see. When impirun is started with the `-server' option, it creates a TCP/IP socket for listening and then prints both the IP address of the local host (in standard dot notation) and the port number of the socket (to stdout, if on a UNIX machine). If the `-port' option is specified, the server will attempt to start on the given <port_number>. If the `-port' option is not given, the server is free to choose any port number.

Rationale.Printing the complete address instead of only the port number allows for an easy cut-and-paste of the output. And using the IP address instead of the hostname eliminates potential name-lookup problems.(End of rationale.)

Discussion.The term ``server'' as it is used here is slightly inaccurate, since that usually implies some sort of persistence.(End of discussion.)