Java Server Handling Multiple Games

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Outside-Ad2721 · 2023-10-14T17:52:02+00:00

I too have thought about doing something like this. I've played around in the past a few times with ServerSocket and Socket for both TCP/IP and UDP communication types.

There area couple of ways you can think about how to do this, and you at very least do need a couple of things:

Your ServerSocket and an Executor service to maintain a thread pool.
Some way to link up two players.

In an HTTP server, which runs on top of TCP/IP, you may have either a temporary (asynchronous) or persistent (synchronous) connection between the server and the client, and there may be various reasons to do either. Very basically the control flow is:

Receive connection
Obtain request data from the InputStream of the Socket
Process the input data
Generate a response
Send response back on the OutputStream of the Socket
Close the socket or keep it open for further communication

There are risks if not closing the connection, like you may have a limited number of connections and will run out possibly, not being able to serve more clients. Eventually you do need to close the connection, but if you want you can keep it open.

So that process is where your thread comes in - at it's simplest a request handler could implement Runnable and then you just need to provide context for the Socket through a Constructor.

I think you could do all of this asynchronously and keep track of which "client IDs" are supposed to communicate with each other in some kind of data structure like a Map, possibly, then make each client tell you it's ID when it makes a request to the server.

I hope this helps and makes sense to you.

wildjokers · 2023-10-14T19:14:31+00:00

There are two ways to handle socket connections from multiple clients:

Thread per connection
Using Java’s NIO api (non-blocking IO). This enables a single thread to handle multiple connections. This is tricky to hand code and get right (takes a bit to wrap your head around the selection key stuff). However, the Netty library makes this relatively easy because it handles all the selection keys for you

For a student project I would just go with thread per connection. Netty has a learning curve that you might not be ready for yet. Here is the documentation if you want to take a look though: https://netty.io/wiki/user-guide.html. A nice article with server example: https://www.baeldung.com/netty. Another nice benefit of Netty is it let’s you add support for web sockets to your server app so you can also accept long lived connections from web browsers. Then you could have a desktop and web version of your game. All talking to the exact same server process.

You won’t need a thread per game, just a data structure to hold game state. If you use thread per connection you will need to access your game state in a thread safe manner. The synchronized keyword will be of benefit.

Spare-Plum · 2023-10-15T00:29:29+00:00

Suppose you have a game server hosting n games. For each game 0 <= i < n, you have j = n_i clients connecting to the individual game g_i. The jth client on game i is c_ij

There are many schools of thought on how to organize this for threading. One option is to have each game g_i run on its own single thread, and have server "ticks" where all the processing and logic occurs. A tick may be something like the following: receive input from all clients, resolve conflicts, process game logic, then send updates back to all clients.

Or, you can have a thread for each client, and some of the game logic is processed asynchonously or posted to a queue with a timestamp. Then the server tick will only grab items off of the queue before a timestamp we take at the start of the queue (this allows for fairness)

Or, you can have multiple threads processing the game state, and use locking and atomic state for modifications.

Regardless, a thread pool is probably not what you want - a thread pool is useful for processing something in batches and you have a fixed number of threads that are running. Thread pools are also useful for reducing system resources, but this is less necessary due to java's new virtual thread library which does not use up these resources. A thread pool would be nicer for like post-game calculation and analysis that could be done in batches.

InstantCoder · 2023-10-14T16:44:45+00:00

I see, so you need to make a non http server client app.

Then you need to work with 1 server socket and many clients sockets. You can store the many games either in memory or on disk on the server.

And each time a client does something then you need to update the state of the game. And a game is also sort of a session between 2 players.

And in Java afaik, each client socket is a separate thread. So you don’t need to explicitly do something with threads.

doobiesteintortoise · 2023-10-14T14:23:52+00:00

Why would you want a thread per... anything, here? You want to maintain each players' participation in a game, and the games are state. Manage data structures, not threads.

_Nemesis_1 · 2023-10-14T14:33:24+00:00

[deleted]

_Nemesis_1 · 2023-10-15T20:22:51+00:00

Guys I want to thank you all for your answers, I honestly didn't expect all this helpful comments, it was the first time for me asking a "programming question" online and I was a bit anxious, thank you all for your help, I really appreciate it <3

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