I'm building a (LAN) network application, so there is always the possibility that a connection will be disconnected, for various possible reasons. I am trying to think of a good design for handling this issue, such that it doesn't affect the rest of the application. I wrote a quick thing to try to do it, but I think it can be enhanced a lot. I appreciate your help and experience about the best way to handle this issue.
This is my first trial:
class ConnectionWrapper {
NetworkStream stream;
StreamReader reader;
Endpoint endPoint;
bool endOfStream;
int maxRetries = 5;
public void connect() {
// ... code to initialize a (TCP) socket to endPoint
this.stream = new NetworkStream(socket, true);
this.reader = new StreamReader(stream);
}
string readNextMsg() {
try {
string msg = reader.ReadLine();
if (msg == "EOF") endOfStream = true;
return msg;
}
catch (IOException e) {
Exception ex = e;
while (maxRetries-- > 0) {
try { connect(); ex = null; }
catch (Exception e2) { ex = e2; }
}
if (x != null) throw ex;
}
}
}
Not very elegant, and probably not the best that can be done. Could you please share your experience, and may be even suggest an existing library?
Thank you.
I honestly don't think you should let the connection wrapper contain logic to handle its own connection policy. I think this should be done from outside of this class, and especially not in the catch statement. Have some kind of ConnectionController object to deal with whether the connection should be retried once it fails.
I was going to edit my post, but this should be completely separate from my last one.
Your logic is all wrong in my opinion, you should have a thread within the ConnectionWrapper which spins on the StreamReader pulling off messages and placing them on a queue. This queue then notifies listeners of a change. The listeners then go and retrieve the data themselves and decide what needs to be done with them.
class ConnectionWrapper {
NetworkStream stream;
StreamReader reader;
Endpoint endPoint;
bool endOfStream;
int maxRetries = 5;
ArrayList arr;
public void connect() {
// ... code to initialize a (TCP) socket to endPoint
this.stream = new NetworkStream(socket, true);
this.reader = new StreamReader(stream);
}
private void initReceiverThread() {
String line;
while(stream.isConnected() && (line = reader.readLine()) != null) {
// notify observers of a change
arr.add(line);
}
}
}
This is pseudo-code I warn you, I've never done this in C#. A typical reader actually waits on a readLine statement, so the while loop won't go crazy. It's also best to put initReceiverThread code in a Thread, that way it won't block the rest of the application. By notifying the observers of a change they can then go and get the ArrayList by doing something like myConnectionWrapper.getMessages(); which will return an ArrayList, but also clearing out the ArrayList at the same time, like so:
public ArrayList getMessages() {
ArrayList temp = arr;
arr.clear();
return temp;
}
That way you get ALL of the messages and clear them off the queue.
I've written network clients before, and this is the general design of one. You'll have two threads constantly spinning, one to receiver messages, and one to send them.
The logic should be dealt with some kind of manager code to determine whether to continue, or reconnect or whatever you want to do.
Related
I have a small game server I'm making that will have dozens of connections sending player data constantly. While I've finally accomplished some basics and now have data sending/receiving, I now face a problem of flooding the server and the client with too much data. I've tried to throttle it back but even then I am hitting 90-100% cpu simply because of receiving and processing the data received running up the CPU.
The method below is a bare version of receiving data from the server. The server sends a List of data to be received by the player, then it goes through that list. I've thought perhaps instead just using a dictionary with a key based on type rather than for looping but I don't think that will significantly improve it, the problem is that it is processing data non-stop because player positions are constantly being updated, sent to the server, then send to other players.
The code below shows receive for the client, the server receive looks very similar. How might I begin to overcome this issue? Please be nice, I am still new to network programming.
private void Receive(System.Object client)
{
MemoryStream memStream = null;
TcpClient thisClient = (TcpClient)client;
List<System.Object> objects = new List<System.Object>();
while (thisClient.Connected && playerConnected == true)
{
try
{
do
{
//when receiving data, first comes length then comes the data
byte[] buffer = GetStreamByteBuffer(netStream, 4); //blocks while waiting for data
int msgLenth = BitConverter.ToInt32(buffer, 0);
if (msgLenth <= 0)
{
playerConnected = false;
thisClient.Close();
break;
}
if (msgLenth > 0)
{
buffer = GetStreamByteBuffer(netStream, msgLenth);
memStream = new MemoryStream(buffer);
}
} while (netStream.DataAvailable);
if (memStream != null)
{
BinaryFormatter formatter = new BinaryFormatter();
memStream.Position = 0;
objects = new List<System.Object>((List<System.Object>)formatter.Deserialize(memStream));
}
}
catch (Exception ex)
{
Console.WriteLine("Exception: " + ex.ToString());
if (thisClient.Connected == false)
{
playerConnected = false;
netStream.Close();
thisClient.Close();
break;
}
}
try
{
if (objects != null)
{
for (int i = 0; i < objects.Count; i++)
{
if(objects[i] != null)
{
if (objects[i].GetType() == typeof(GameObject))
{
GameObject p = (GameObject)objects[i];
GameObject item;
if (mapGameObjects.TryGetValue(p.objectID, out item))
{
mapGameObjects[p.objectID] = p;;
}
else
{
mapGameObjects.Add(p.objectID, p);
}
}
}
}
}
}
catch (Exception ex)
{
Console.WriteLine("Exception " + ex.ToString());
if (thisClient.Connected == false)
{
playerConnected = false;
netStream.Close();
break;
}
}
}
Console.WriteLine("Receive thread closed for client.");
}
public static byte[] GetStreamByteBuffer(NetworkStream stream, int n)
{
byte[] buffer = new byte[n];
int bytesRead = 0;
int chunk = 0;
while (bytesRead < n)
{
chunk = stream.Read(buffer, (int)bytesRead, buffer.Length - (int)bytesRead);
if (chunk == 0)
{
break;
}
bytesRead += chunk;
}
return buffer;
}
Based on the code shown, I can't say why the CPU utilization is high. The loop will wait for data, and the wait should not consume CPU. That said, it still polls the connection in checking the DataAvailable property, which is inefficient and can cause you to ignore received data (in the implementation shown...that's not an inherent problem with DataAvailable).
I'll go one further than the other answer and state that you should simply rewrite the code. Polling the socket is just no way to handle network I/O. This would be true in any scenario, but it is especially problematic if you are trying to write a game server, because you're going to use up a lot of your CPU bandwidth needlessly, taking it away from game logic.
The two biggest changes you should make here are:
Don't use the DataAvailable property. Ever. Instead, use one of the asynchronous APIs for dealing with network I/O. My favorite approach with the latest .NET is to wrap the Socket in a NetworkStream (or get the NetworkStream from a TcpClient as you do in your code) and then use the Stream.ReadAsync() along with async and await. But the older asynchronous APIs for Sockets work well also.
Separate your network I/O code from the game logic code. The Receive() method you show here has both the I/O and the actual processing of the data relative to the game state in the same method. This two pieces of functionality really belong in two separate classes. Keep both classes, and especially the interface between them, very simple and the code will be a lot easier to write and to maintain.
If you decide to ignore all of the above, you should at least be aware that your GetStreamByteBuffer() method has a bug in it: if you reach the end of the stream before reading as many bytes were requested, you still return a buffer as large as was requested, with no way for the caller to know the buffer is incomplete.
And finally, IMHO you should be more careful about how you shutdown and close the connection. Read about "graceful closure" for the TCP protocol. It's important that each end signal that they are done sending, and that each end receive the other end's signal, before either end actually closes the connection. This will allow the underlying networking protocol to release resources as efficiently and as quickly as possible. Note that TcpClient exposes the socket as the Client property, which you can use to call Shutdown().
Polling is rarely a good approach to communication, unless you're programming 16-bit microcontrollers (and even then, probably not the best solution).
What you need to do is to switch to a producer-consumer pattern, where your input port (a serial port, an input file, or a TCP socket) will act as a producer filling a FIFO buffer (a queue of bytes), and some other part of your program will be able to asynchronously consume the enqueued data.
In C#, there are several ways to do it: you can simply write a couple of methods using a ConcurrentQueue<byte>, or a BlockingCollection, or you can try a library like the TPL Dataflow Library which IMO doesn't add too much value over existing structures in .NET 4. Prior to .NET 4, you would simply use a Queue<byte>, a lock, and a AutoResetEvent to do the same job.
So the general idea is:
When your input port fires a "data received" event, enqueue all received data into the FIFO buffer and set a synchronization event to notify the consumer,
In your consumer thread, wait for the synchonization event. When the signal is received, check if there is enough data in the queue. If yes, process it, if not, continue waiting for the next signal.
For robustness, use an additional watchdog timer (or simply "time since last received data") to be able to fail on timeout.
You want to use the Task-based Asynchronous Pattern. Probably making liberal use of the async function modifier and the await keyword.
You'd be best replacing GetStreamByteBuffer with a direct call to ReadAsync.
For instance you could asynchronously read from a stream like this.
private static async Task<T> ReadAsync<T>(
Stream source,
CancellationToken token)
{
int requestLength;
{
var initialBuffer = new byte[sizeof(int)];
var readCount = await source.ReadAsync(
initialBuffer,
0,
sizeof(int),
token);
if (readCount != sizeof(int))
{
throw new InvalidOperationException(
"Not enough bytes in stream to read request length.");
}
requestLength = BitConvertor.ToInt32(initialBuffer, 0);
}
var requestBuffer = new byte[requestLength];
var bytesRead = await source.ReadAsync(
requestBuffer,
0,
requestLength,
token);
if (bytesRead != requestLength)
{
throw new InvalidDataException(
string.Format(
"Not enough bytes in stream to match request length." +
" Expected:{0}, Actual:{1}",
requestLength,
bytesRead));
}
var serializer = new BinaryFormatter();
using (var requestData = new MemoryStream(requestBuffer))
{
return (T)serializer.Deserialize(requestData);
}
}
Like your code this reads an int from the stream to get the length, then reads that number of bytes and uses the BinaryFormatter to deserialize the data to the specified generic type.
Using this generic function you can simplify your logic,
private Task Receive(
TcpClient thisClient,
CancellationToken token)
{
IList<object> objects;
while (thisClient.Connected && playerConnected == true)
{
try
{
objects = ReadAsync<List<object>>(netStream, token);
}
catch (Exception ex)
{
Console.WriteLine("Exception: " + ex.ToString());
if (thisClient.Connected == false)
{
playerConnected = false;
netStream.Close();
thisClient.Close();
break;
}
}
try
{
foreach (var p in objects.OfType<GameObject>())
{
if (p != null)
{
mapGameObjects[p.objectID] = p;
}
}
}
catch (Exception ex)
{
Console.WriteLine("Exception " + ex.ToString());
if (thisClient.Connected == false)
{
playerConnected = false;
netStream.Close();
break;
}
}
}
Console.WriteLine("Receive thread closed for client.");
}
You need to put a Thread.Sleep(10) in your while loop. This is also a very fragile way to receive tcp data because it assumes the other side has sent all data before you call this receive. If the other side has only sent half of the data this method fails. This can be countered by either sending fixed sized packages or sending the length of a package first.
Your player position update is similar to the framebuffer update in the VNC protocol where the client request a screen frame & server responds to it with the updated screen data. But there is one exception, VNC server doesn't blindly send the new screen it only sends the changes if there is one. So you need to change the logic from sending all the requested list of objects to only to the objects which are changed after the last sent. Also in addition to it, you should send entire object only once after that send only the changed properties, this will greatly reduce the size of data sent & processed both at clients & server.
I need to connect a server (with ip and port) and create a read-loop that will get messages from the server as XML. sometimes there are no messages from the server.
I tried to create a connection (works fine) and read messages, I get the first message from the server and when I'm trying to read another one - it get stuck. I think that maybe there are no messages right now but I need that the loop will continue until there will be messages... it doesn't even go to "catch" or "finally", just do nothing..
public class Connection
{
public Connection()
{
Socket server = null;
try
{
string p = string.Empty;
using (var client = new TcpClient(myIPAddress, myPort))
using (var stream = client.GetStream())
using (var reader = new StreamReader(stream))
{
while (p != null)
{
try
{
p = reader.ReadLine();
}
catch (Exception e)
{
//
}
}
}
}
catch (Exception e)
{
//
}
finally {
server.Close();
}
}
}
The loop is continuing, waiting for data. The issue here seems to be simply that ReadLine() is a blocking call. You mention that there might not be a message yet; well, ReadLine() is going to block until one of two conditions is met:
it can successfully read some data, terminated by a newline (or EOF, i.e. a message without a newline followed by socket closure) - in which case it returns the line of data
no more data is received and the stream is closed, in which case it returns null
So basically, ReadLine() is going to wait until either a message comes in, or the socket is closed. That is simply the behaviour of ReadLine(). If that is problematic, you could work closer to the socket, and check NetworkStream.DataAvailable but: note that only tells you if some data is currently available; it doesn't mean "this is an entire message", nor can it be used to tell if more messages will arrive. The main use of DataAvailable is to decide between sync and async access. Plus if you work close to the socket you'll have to do all your own buffering and encoding/decoding.
It looks to me like ReadLine() is working successfully. The only thing I would do here is re-phrase it a bit:
string line;
while((line = reader.ReadLine()) != null) {
// line is meaningful; do something
}
One last thought: xml is not always trivially split into messages simply on a "per-line" basis. You might want to consider some other form of framing, but that may well mean working closer to the socket, rather than a StreamReader.
You have to wait till data arrives at the stream, you could try using follwing,
if(reader.EndOfStream)
continue;
I have a simple class that handles the connection being made between a client and server.
To let more than one user communicate with the server at one time each new Client connection is made on a separate thread.
In this class I create two streams that act as the inbound and outbound streams for the client. I create the fields first and then initialise the object in a separate method, simply because the object is used in several other places.
I've come to the point where I want to refactor the code to make it more robust, my first port of call was memory management. I've come to love the using() statement but noticed that I can't really see a way to do implement it due to the way the code is structured.
This means I have a fairly annoying method that is just used for closing the underlying connections and nothing more.
Furthermore, I came to implement exception handling and was curious whether the notion of wrapping the entire code in a method with a try{} statement and then having sequential catch() blocks with the applicable exception types was the best idea.
I hope I explained myself correctly, I'll post a snippet for you to look at.
Thanks!
//Fields
TcpClient tcpClient;
//The thread that will send information to the client
private Thread thrSender;
private StreamReader srReceiver;
private StreamWriter swSender;
private string currentUser;
private string strResponse;
//The constructor of the class takes in a TCP connection
public Connection(TcpClient tcpCon)
{
tcpClient = tcpCon;
//The thread that accepts the client and waits messages
thrSender = new Thread(AcceptClient);
//The thread calls the AcceptClient method
thrSender.Start();
}
private void CloseConnection()
{
//Close the currently open objects
tcpClient.Close();
srReceiver.Close();
swSender.Close();
}
//Occurs when a new client is accepted
private void AcceptClient()
{
srReceiver = new StreamReader(tcpClient.GetStream());
swSender = new StreamWriter(tcpClient.GetStream());
//Read account information from the client
currentUser = srReceiver.ReadLine();
//Examine response from client
if (currentUser != "")
{
//Store the user name in the hash table
if (ChatServer.htUsers.Contains(currentUser) == true)
{
//0 means not connected - Writes error to Client and Server log
swSender.WriteLine("0|This username already exists.");
swSender.Flush();
CloseConnection();
return;
}
//More if/else if/else statements
//...
}
}
You can dispose of the two streams fairly easily within the AcceptClient method by making them local variables since they aren't referenced elsewhere something like this:
private void AcceptClient()
{
using (StreamReader srReceiver = new StreamReader(tcpClient.GetStream()))
{
using (StreamWriter swSender = new StreamWriter(tcpClient.GetStream()))
{
// ...
}
}
}
The tcpClient is more tricky because it is being created on one thread and cleaned up on another. Unless you can change that then perhaps the best option is going to be to implement the cleanup within a try/finally.
private void AcceptClient()
{
try
{
using (StreamReader srReceiver = new StreamReader(tcpClient.GetStream()))
{
using (StreamWriter swSender = new StreamWriter(tcpClient.GetStream()))
{
// ...
}
}
}
finally
{
tcpClient.Dispose();
}
}
The finally clause will get called whether or not the try clause throws an exception.
I have around 5000 modem (thin clients), and I want to communicate with them, one of a my method is like this : string GetModemData(modemID), now I have an open port in server that listens to modem and I'm using socket programming to send data to modems (calling related function), but when i want send data to multiple modem in a same time and get response from them, I don't know what should i do? I can send data to one modem and waiting for its response and then send another data to other modems (sequential), but the problem is client should be wait long time to get answer(may be some different client want to get some information from modems so they all will be wait into the Q or something like this), I think one way to solving this problem is to use multiple port and listen for each modem to related port, but it takes too many ports and also may be memory usage going up and exceed my available memory space, so some lost may be occurred (is this true?). what should to do ? I'd thinking about Parallelism, but i think its not related i should to wait for one port, because i don't know should to pass current received data to which client. I'm using asp.net.
currently I'm doing like this:
private void StartListener()
{
ModemTcpListener = new TcpListener(ModemPort);
//ClientTcpListener = new TcpListener(ClientPort);
ModemTcpListener.Start();
ModemTcpListener.BeginAcceptTcpClient(new AsyncCallback(DoAcceptModemCallback), ModemTcpListener);
}
and in return
private void DoReadModemCallback(IAsyncResult ar)
{
try
{
bool bRet = ar.AsyncWaitHandle.WaitOne(420000);
Modem modem = ar.AsyncState as Modem;
if (!bRet || modem == null)
{
return;
}
}
catch{}
// now send data to which client?????? if i'm going to use async????
}
and :
private void DoAcceptModemCallback(IAsyncResult ar)
{
try
{
ModemTcpListener.BeginAcceptTcpClient(new AsyncCallback(DoAcceptModemCallback), ModemTcpListener);
TcpClient tcpClient = ModemTcpListener.EndAcceptTcpClient(ar);
Modem modem= new Modem(tcpClient, "");
tcpClient.GetStream().BeginRead(modem.Buffer, 0, tcpClient.ReceiveBufferSize, new AsyncCallback(DoReadModemCallback), modem);
ModemTcpListener.BeginAcceptTcpClient(new AsyncCallback(DoAcceptModemCallback), ModemTcpListener);
Log.Write("a Modem connect ...");
}
catch (Exception ex)
{
}
}
Heres an example keeping track of all your clients. I've compacted it for readability. You should really split it up into multiple classes.
I'm using Pool (which I just created and commited) and SimpleServer. Both classes are part of a library that I'm currently building (but far from done).
Don't be afraid of having 5000 sockets open, they do not consume much resources when you are using asynchronous operations.
public class SuperServer
{
private List<ClientContext> _clients = new List<ClientContext>();
private SimpleServer _server;
private Pool<byte[]> _bufferPool;
public SuperServer()
{
// Create a buffer pool to be able to reuse buffers
// since your clients will most likely connect and disconnect
// often.
//
// The pool takes a anonymous function which should return a new buffer.
_bufferPool = new Pool<byte[]>(() => new byte[65535]);
}
public void Start(IPEndPoint listenAddress)
{
_server = new SimpleServer(listenAddress, OnAcceptedSocket);
// Allow five connections to be queued (to be accepted)
_server.Start(5);
}
// you should handle exceptions for the BeginSend
// and remove the client accordingly.
public void SendToAll(byte[] info)
{
lock (_clients)
{
foreach (var client in _clients)
client.Socket.BeginSend(info, 0, info.Length, SocketFlags.None, null, null);
}
}
// Server have accepted a new client.
private void OnAcceptedSocket(Socket socket)
{
var context = new ClientContext();
context.Inbuffer = _bufferPool.Dequeue();
context.Socket = socket;
lock (_clients)
_clients.Add(context);
// this method will eat very few resources and
// there should be no problem having 5000 waiting sockets.
context.Socket.BeginReceive(context.Inbuffer, 0, context.Inbuffer.Length, SocketFlags.None, OnRead,
context);
}
//Woho! You have received data from one of the clients.
private void OnRead(IAsyncResult ar)
{
var context = (ClientContext) ar.AsyncState;
try
{
var bytesRead = context.Socket.EndReceive(ar);
if (bytesRead == 0)
{
HandleClientDisconnection(context);
return;
}
// process context.Inbuffer here.
}
catch (Exception err)
{
//log exception here.
HandleClientDisconnection(context);
return;
}
// use a new try/catch to make sure that we start
// read again event if processing of last bytes failed.
try
{
context.Socket.BeginReceive(context.Inbuffer, 0, context.Inbuffer.Length, SocketFlags.None, OnRead,
context);
}
catch (Exception err)
{
//log exception here.
HandleClientDisconnection(context);
}
}
// A client have disconnected.
private void HandleClientDisconnection(ClientContext context)
{
_bufferPool.Enqueue(context.Inbuffer);
try
{
context.Socket.Close();
lock (_clients)
_clients.Remove(context);
}
catch(Exception err)
{
//log exception
}
}
// One of your modems
// add your own state info.
private class ClientContext
{
public byte[] Inbuffer;
public Socket Socket;
}
}
Used classes:
Pool: http://fadd.codeplex.com/SourceControl/changeset/view/58858#1054902
SimpleServer: http://fadd.codeplex.com/SourceControl/changeset/view/58859#1054893
You need to use the asynchronous tcp/ip methods. This article shows how:
http://www.codeproject.com/KB/IP/asyncsockets.aspx
The critical piece is the BeginReceive() and related callback functions. Any more q's, please leave comments to this answer ;) BEST OF LUCK!
You need multi threading, whenever a client establishes a connection to the server start a new thread for it and start communication send/receive.
Here are some articles explaining multithreading in c#,
c-sharpcorner
codeproject
And here's a sample server application with multithreading,
http://www.dotnetspider.com/resources/2829-A-multi-readed-server-C-which-finds-prime-num.aspx
I've written a very complex multi-server IRC bot recently, and have encountered an issue..
I have stripped down the code as much as I could which can be viewed here.
My issue is that when I call the Disconnect() the connection is voided instead of disconnecting and closing the given server. It also just freezes the calling class instead of stopping the correct instance of the Class.
Any help or experience with a similar issue would be greatly appreciated.
Please include code if you can.
First off, you need to add a break so that this:
foreach (Connection connect in connections)
{
if (searching == true)
{
if (connect.SERVERID == ServerID)
{
connect.Stop();
isFound = true;
searching = false;
connections.Remove(connect);
}
}
}
Becomes:
foreach (Connection connect in connections)
{
if (connect.SERVERID == ServerID)
{
connect.Stop();
isFound = true;
connections.Remove(connect);
break;
}
}
Because you are modifying the collection, rather than using the searching == true clause. Much more efficient.
Next, I would change your thread run to look like this:
public void Run()
{
bool WhileOn = true;
NetworkStream stream;
string inputLine;
StreamReader reader;
try
{
using(TcpClient irc = new TcpClient(SERVER, PORT))
{
...
}
}
catch (ThreadAbortException)
{
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
Thread.Sleep(5000);
}
}
So that your connection gets properly disposed. You should do similarly for your stream.
And finally, I would add an Abort() call on your thread in the Stop function after a set timeout. If a TCP socket is blocked by the OS, however, I'm not sure if an abort call will interrupt it...