TcpListener Pending method returns wrong values

Question

I have the following code in my server side:

// Bind to a specific local port number (SERVER_PORT) and any local IP address.
m_tlServer = new TcpListener(IPAddress.Any, SERVER_PORT);

// Start listening for connection attempts.
m_tlServer.Start();

// Start accepting new clients.
// Sleep until a new client(s) will try to connect to the server.
while (!m_bStopThread)
{
    if (!m_tlServer.Pending())
    {
        // Sleep and try again.
        Thread.Sleep(LISTENING_SLEEP_TIME);
        continue;
    }
    else
    {
        // Accept a new client in a new thread. 
        Thread newthread = new Thread(new ThreadStart(HandleNewConnection)); 
        newthread.Start();
    }
}

My problem is that when a client tries to connect to the server, the method Pending returns true several times (usually 4 times) and several thread are created. I tried to replace that while loop by a loop that uses the AcceptTcpClient method (without knowing if there are any connection attempts) and it's works fine. So, I think the problem is caused by Pending method. Can anyone help me? Thanks, Ofer.

Answer 1

Use AcceptTcpClient not Pending and it will work.

Why what you're doing is producing theses steps :

1. Listener thread see Pending == true
2. Start accept thread
3. Listener thread see Pending == true
4. Start accept thread
5. Listener thread see Pending == true
6. Start accept thread
7. First accept thread begin to run
8. Listener thread see Pending == false

In a nutshell that's not because you start a thread that some random instruction inside is executed immediately. The point of the thread is exactly that : It will execute later.

If you want to have a way to stop the listening process use WaitHandles :

// In your class somewhere stopEvent is a ManualResetEvent

while(true)
{

    var asyncResult = listener.BeginAcceptTcpClient(null, null);

    var waitHandles = new [] { stopEvent, asyncResult.AsyncWaitHandle };

    var waitResult = WaitHandle.WaitAny(waitHandles);

    if (waitResult == 0) return;

    var client = EndAcceptTcpClient(asyncResult);
    // Create thread to speak with this client

}

Your method that want to stop the thread will just need to stopEvent.Set()