[Playerstage-developers] P/S name service

[brian g. <bg...@us...>]

hi,

I've just added two new things to Player, that are useful with Stage (on HEAD;
will merge to patch branch later):

  * The ability to auto-assign ports.  With the right command-line flags, you
    can give Player a single base port, and let it find as many other free
    ports as you need.  It is an error if the base port is not available.
    Free ports are found by counting up from the base port.

  * The ability to lookup the port that is associated with a given robot's
    name.  There is a now an ioctl to Player that does this.  It's implemented
    in the C++ client as PlayerClient::LookupPort() and there's a C++ example
    called lookupport.cc.

Put together, these features allow you to run simulations with lots of robots
but not worry about which ports are being used, which can be a very good thing,
especially in multi-user environments.  Just let Player auto-assign the ports
and then use the name service mechansim to find your robots at runtime (you
would connect to the base port, where you know that Player will be listening).

A couple of Stage .world-file notes:

  * To try out this feature, use the "base_port" keyword anywhere in your
    .world, outside of any block, e.g.:
        base_port 40000
    Then you can find Player on port 40000 and ask it where to connect to talk
    to other robots.

  * To actually use this feature, you must give your robots names.  Stage
    already supports the "name" keyword; check everything.world for examples.

This solution allows you to find out which robots a given instance of Player is
serving (for use with Stage), but it doesn't allow you to find multiple
instances of Player on a network (for use with real robots).  The latter is
more in the realm of the broadcast-based discovery mechanism that Reed has
proposed.  In the end, it would be nice to have the functionality of both, but
I haven't thought of a nice way to integrate them, and I think that the Stage
issue is more pressing.  I'm open to suggestion on this front.

        brian.