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Begining UDP Gaming Server: Best practises?


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#1 Mayouuu   Members   -  Reputation: 116

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Posted 06 June 2012 - 08:30 AM

Hi,

I am new to gaming server development, i am currently starting a new server, my first one and a huge one :D
I have allways programmed in C/C++, i come from embedded systems programming in pure C in the las year :D, now i have been told that developing that gaming server/framework will be much easier in C#, so I am in the way :)

The gaming server goal is to be able to manage 50k clients using some normal hardware, core i7 4-8 cores, 12Gb of RAM ....etc... some good machine but not a NASA one :D

I have made one layer that will accept and Log in gamers into the server using TCP, TCP will be used for login and some kind of ping with every user. This part seems to be working at the moment.

I have a thread that is getting datagrams from udpInputSocket of the server, it will only take that datagrams from every user and delegate them to other stage that will process them in many stages/threads.

Now what I am trying to do is just taking every datagram from every user (currently simulating 1k users) and then re-stream this packet to every user, the problem is that it is taking too long.... it is so so slow compared to the UDPReceiveThread.....

The thing here is that the receive thread enqueues every message received and the "broadcaster" thread is taking every queued message and sending it to each of the 1k users, this seems a huge task as it is running so slowly, i just loop over every messange and the over ever client calling socket.SendTo(.........).

The main question here is, am I doing it as it should be done? is it a matter of more "broadcaster threads" needed? or am I missing something like socket multicasting or broadcasting. I think I can´t broadcast or multicast becouse we are not aiming at LAN gaming rather than online internet gaming and i don´t know if in that scenario we can use that broadcast/multicast techniques.

Any help or suggestions in my new challange??

Thank you very much to every body! :D


PD: This would be the "broadcaster thread":


private void UDPBroadCastThread()
	    {
		    List<String> broadcastQueue = new List<string>();
		    ASCIIEncoding encoder = new ASCIIEncoding();
		    byte[] buffer;
		    _udpSendSocket.SendTimeout = 1; //Miliseconds timeout
		    while (true)
		    {
			    if (broadcastQueue.Count > 0)
			    {
				    for (int i = 0; i < broadcastQueue.Count; i++) // Loop through List of messages to broadcast
				    {
					    // Wait until it is safe to enter.
					    _clientsListMutex.WaitOne();
					    for (int client = 0; client < _myClientsList.Count; client++) // Loop through every user
					    {
						    buffer = encoder.GetBytes(broadcastQueue[i]);
						    int bytesSent = 0;
						    bytesSent = _udpSendSocket.SendTo(buffer, broadcastQueue[i].Count(), 0, (EndPoint)_myClientsList[client]._clientUDPEndPoint);
						    if (bytesSent != broadcastQueue[i].Count())
						    {
							    Console.WriteLine("Error sending data: {0}", broadcastQueue[i]);
						    }
					    }
					    // Release the Mutex.
					    _clientsListMutex.ReleaseMutex();
				    }
				    broadcastQueue.Clear();
			    }
			    else
			    {
				    Thread.Sleep(10);
				    // Wait until it is safe to enter.
				    this._broadCastMutex.WaitOne();
				    broadcastQueue = (List<String>)this._newBroadcastQueue;
				    this._newBroadcastQueue = new List<String>();
				    // Release the Mutex.
				    _broadCastMutex.ReleaseMutex();
			    }
			   
		    }
	    }

Edited by Mayouuu, 06 June 2012 - 08:31 AM.


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#2 hplus0603   Moderators   -  Reputation: 5363

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Posted 06 June 2012 - 10:10 AM

Have you profiled the loop? Does it actually saturate one CPU core?

I would expect that the network buffer would fill up, and the UDP send function might block, stalling execution. If that happens, you know that you're trying to send more data than your network link can handle. The only way around that problem is to send less! (design for less bandwidth)

Another option is that the byte encoding takes too long, or returns too big an array. Because the bytes are the same each time you send them, you can encode once, outside the loop, and re-use the array each time you call send.

But this is just guessing -- knowing for sure what the problem is requires profiling and perhaps some network analysis. I know for a fact that a single thread with a good network card and good network link and sufficient buffering can easily do 250,000 UDP packets per second, and likely much more.
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#3 Mayouuu   Members   -  Reputation: 116

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Posted 07 June 2012 - 08:14 AM

Thank you very much for your reply, it is an N*N problem, it is not scalable so i think we have to modify the server structure, it will not re-stream to every client, it will create a message and send it to every user, this way the numer of sendTo calls(and bandwidth) will sacale more linearly and not exponentially, i think this will make the server much more responsive for 50k users :D, i am working on that idea now...

#4 larspensjo   Members   -  Reputation: 1541

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Posted 09 June 2012 - 04:22 PM

The scaling you had was quadratic, not exponential. But that is still bad enough.

A common way to handle that is to use octree to partition a 3D world into dynamic sub sections. This will add a linear cost, but it will no longer be quadratic. I think it will be something like O(n*log(n)).
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#5 larspensjo   Members   -  Reputation: 1541

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Posted 09 June 2012 - 04:29 PM

Are you sure you should go for UDP instead of TCP? Yes, UPD is more efficient, in theory. But that means you have to implement all the control structures yourself. This can be quite difficult to get right, and efficient at the same time. While the TCP implementation is very optimized and optimal. And easier to use.
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#6 Rasterman   Members   -  Reputation: 206

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Posted 11 June 2012 - 11:12 AM

Without profiling there is no point, you are just guessing. At the very minimum though you should move the encoding out of the client loop. Also shouldn't you have a mutex around the broadcast queue?

#7 dburner   Members   -  Reputation: 151

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Posted 20 July 2012 - 12:06 PM

I think there is another simple option for your problem. You could use ThreadPool class to send the data.
ThreadPool.QueueUserWorkItem( s=> (_udpSendSocket.SendTo(buffer, broadcastQueue[i].Count(), 0, (EndPoint)_myClientsList[client]._clientUDPEndPoint));
EDIT: And set the number of worker threads at about 20(mabye even 30).

Edited by dburner, 20 July 2012 - 03:57 PM.





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