Recommendations on multiple types of games server

Question

Hi, I've already developed some online games (like chess, checkers, risk clone) using server side programming (PHP and C++) and Flash (for the GUI). Now, I'd like to develop some kind of game portal (like www.mytopia.com). In order to do so, I must decide what is a good way to structure my server logic.

At first I thought in programming separated game servers for each game. In this way, each game will be an isolated program that opens a specific port to the client. I thought also in creating different servers to each game room (each game room allow 100 clients connected on the same time). Of course I'd use database to link everything (like highscores, etc).

Then, I guess it is not the best way to structure a game portal server. I'm reading about thread programming and I think that is the best way to do it. So, I thought in doing something like a connection thread that will listen only to new connection clients (that way every type of game client will connect in only one port), validate this client (login) and then tranfer this client to the specific game thread (like chess thread, checkers thread, etc). I'll be using select (or variants) to handle the asynchronous clients (I guess the "one thread per client" is not suited this time). This structure seems to be the best but how do I make the communication between threads? I've read about race conditions and global scope variables, so one solution is to have a global clients array (vector or map) that need to be locked by connection thread or game thread everytime it is changed (new connection, logout, change states, etc). Is it right?

Has anyone worked in anything like this? Any recommendations?

Thanks very much

Answer 1

If you use threads you might have an easier time sharing data but you'll have to be more careful about security for exactly the same reason. That of course doesn't address MT issues in general.

Answer 2

TBH I've been doing a voip system where the server can send out many streams and the client can listen to many streams. The best architecture I've come up with so far is just to bind to a single port and use sendto and recvfrom to handle communications. If i receive a valid connect packet from a client on a new address then I add the client to an internal list and begin sending audio data to them. The packet receive and response management (RRM) all happens in one thread. The audio, as it becomes ready, then gets sent to all the clients from the audio thread. The clients respond saying they received the audio and that gets handle on the RRM thread. If the client fails to respond for longer than 30 seconds then I send a disconnect and remove the client from my internal list. I don't need to be particularly fault tolerant.

As for how to do this in a games situation my main thought was to send a set of impulse vectors (the current one and 'n' previous ones). This way if the client moves out of sync it can check how out of sync it is by checking the last few impulses it should have received for a given object. If it doesn't correspond to what its got then it can either correct or if it is too far out of sync it can ask for a game state reset. The idea being to try and avoid doig a full game state reset as it is going to be quite an expensive thing to do.

Obviously each packet would be hashed so the client can check the validity of incoming packets but it also allows for the client to ignore an invalid packet and still get the info it needs in the next update and thus helping prevent the state reset.

On top of that its worth doing things like keeping an eye on where the client is. There is no point in sending updates to a client when the client is looking in the other direction or there is something in the way (ie the client can't see the object its being told about). This also limits the effectiveness of a wallhack packet sniffing the incoming packets. Obviously you have to start sending things a tad before the object becomes visible, however, or you will get things popping into existence at inconvenient moments.

Anyway ... thats just some random thoughts. I have to add that I've never actually written a multiplayer engine for a game so I hope my musings help ya a bit :)

Answer 3

A portal needs to be robust, scalable and extensible so that you can cope with larger audiences, more games/servers being added, etc. A good place to start is to look into the way MMOs and distributed systems are designed. This might help too: http://onlinegametechniques.blogspot.com/

Personally, I'd centralise the users by having an authentication server, then a separate game server for each game that validates users against the authentication server.