[gameprogrammer] Re: Multiplayer networking advice

[Brian <brian.ripoff@gmail.com>]

Threading can be too complicated for this kind of scenario. On a
webserver each request is independant, so there is little reason not
to use threads. In a game you would have to implement locking etc to
prevent memory corruption or other concurrent programming issues,
which will take more time and probably be slower than the alternative.

The alternative is to use a function like select() on a group of
sockets. This way you can tell which sockets you can recv() from
without stalling your application. Another alternative is to set the
sockets into non-blocking mode, in which case calling recv() on them
will return immediatly if there is no data ready.

Both of these scale better than threads for such an application, would
be my guess. It depends on how many clients you want to serve
simultaneously.

Using UDP you only need a single socket, making the above slightly
easier should you choose to go that route.

Do consider using a high-level UDP protocol, not just "raw" UDP. There
are a few libraries available which implement optional reliability and
ordering. For example, chat could be reliable and ordered, movement
could be reliable (and you manually discard out of order movement
commands) etc. UDP usually delivers less latentcy, so is a good option
to consider. On the other side, if you end up making every message
reliable and ordered you probably should opt for TCP, since it does
that anyway but also handles congestion in a more network friendly
way.

As for your image - why host it via a URL? Instead the client could
(optionally) upload it as part of the login procedure. If you choose
to use a database, the client could have their image stored on the
server along with username/password.

Be very careful writing code that accepts variable length data from
the client - for example strings or raw binary data (like the image
above) not to write buffer overflows. When I last wrote a server in
C++ I found using the varous dynamic data structure in the Standard
C++ Library to be invaluable (compared to using raw char arrays as
demonstrated in your doc :).

On 1/28/08, Alan Wolfe <alan.wolfe@gmail.com> wrote:
> Multithreaded server
>
> If you haven't ever done anything with threads you may want to for the
> server.  A model that web servers etc use that I've also used for
> games with pretty decent success is this...
>
>  Have 1 main thread that is in a loop like this:
>
> while(GameRunning)
> {
>    while(NewConnections())
>        AcceptNewConnectionAndSpawnNewThreadsForIt();
>
>    sleep(500);
> }

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