Re: One or many instances?

[Jerome Vuarand <jerome.vuarand@...>]

2010/1/8 Christopher Eykamp <chris@eykamp.com>:
> I'm the lead developer for Bitfighter (http://bitfighter.org), written in
> C++ and Lunar, and have been working on creating Lua scripted robot players
> for a while.  There is one script per robot, and several robots could be
> running the same script, or each could be running a different one.
>  Typically, I would expect no more than 10 robots would exist at any time.
>
> Currently, management is quite easy: we create a single Lua instance for
> each robot, each with a function that gets called one per game-cycle.
> Because they are running in their own instance, there is no possibility of
> one robot mucking up the environment of another, and it seems a very clean
> solution.  When a robot is removed from the game, we simply delete the
> instance, and everything associated with that robot is gone.
>
> Lately, however, I've been thinking about adding event listeners to the
> robots, in the form of a series of functions with a name like
> "onPlayerAdded(player)", "onShipKilled(ship, killer)", etc. that would be
> called from C++ as needed.  This complicates things a bit because instead of
> calling each script once per game cycle, we might be calling different
> functions within the same script a dozen times each cycle. Multiplied over
> the number of robots, this becomes a lot of calls, and I'm afraid of the
> increasing overhead this might incur.
>
> So I've been rethinking my original design, and am wondering if it might
> make sense to have the robots all running in a single process, which would
> get called once per event, with some sort of Lua management script calling
> the event handlers in each robot.  Furthermore, management of timers and
> keeping track of which robots implement which listeners might be easier, as
> there could be one timer management script for all robots, rather than the
> current practice of one-per-robot.  And it seems that keeping track of which
> robots implement which listener would be easier in Lua than in C++, which
> would also argue against the one-instance-per-bot design.
>
> So the question is what is the best architecture for this sort of problem?
>  My two key goals are maintaining adequate performance, and making the bot
> scripting as simple as possible, which would seem to imply that each robot
> should feel like it has it's own global namespace.  How have others
> addressed this issue?

Whether you dispatch the event to the multiple listeners (the robots)
in C or in some Lua script, the same amount of functions will be
called. I can't tell which language would be the fastest to do it, but
I suspect the difference is pretty small. So in the end it might not
be worth giving up your clean robot separation for that little (if
any) speed improvement.