Question

thanks to this answer I was able to determine if Server is listening on a given port or not:

How to configure socket connect timeout

now I’m trying to create an endless loop, which will be loaded on form_load event and will be constantly checking if server is listening.

here is my code:

            Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            IAsyncResult result = socket.BeginConnect("192.168.0.131", 1095, null, null);

            bool success = result.AsyncWaitHandle.WaitOne(500, true);

            if (!socket.Connected)
            {label3.Text = "can't use"; socket.Close();}
            else
            {label3.Text = "start action";}

If I put following code into “on_button_click” event – everything works fine (except for – I have to click the button every single time I want to refresh status)

and when I create endless loop – I’m not getting any results at all:

while (true)
        {
            Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            IAsyncResult result = socket.BeginConnect("192.168.0.131", 1095, null, null);

            bool success = result.AsyncWaitHandle.WaitOne(500, true);

            if (!socket.Connected)
            {
                label3.Text = "can't use";
                socket.Close();
            }
            else
            {
                //success = true;
                label3.Text = "start action";
                socket.Close();
            }
        }

I guess it has something to do with threading but I just can’t figure it out. What might be the problem?

Edit:

timer tick solution:

private void Form1_Load_1(object sender, EventArgs e)
        {
            System.Windows.Forms.Timer MyTimer = new System.Windows.Forms.Timer();
            MyTimer.Interval = (200);
            MyTimer.Tick += new EventHandler(MyTimer_Tick);
            MyTimer.Start();
        }

        public void MyTimer_Tick(object sender, EventArgs e)
        {

                Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                IAsyncResult result = socket.BeginConnect("192.168.0.131", 1095, null, null);

                bool success = result.AsyncWaitHandle.WaitOne(500, true);

                if (!socket.Connected)
                {

                    label3.Text = "can't use";
                    socket.Close();
                    //throw new ApplicationException();
                }
                else
                {
                    //success = true;
                    label3.Text = "start action";
                    socket.Close();
                }   

        }

Answer 1

You can add a Timer object to your form. Start the timer on the form load, and in the timer Tick event, run your code that you have in the infinite loop.

Note: DO NOT include the while(true) loop, just the code inside the loop. You really don’t want an infinite loop in your GUI thread 🙂

EDIT
I still think you may need to consider a redesign of the app behavior, but this should be better than the Timer I suggested earlier

A somewhat better approach to the Timer (which should take care of the UI lag issue) would be for you to add a BackgroundWorker to your UI. Add a DoWork method similar to this:

void DoWork(object sender, DoWorkEventArgs e)
{
    while(!_bw.CancellationPending)
    {
        // Do your socket connection stuff

        // you can either update some member variables and call
        // the progresschanged method or you can use a BeginIvoke call
        // to update the labels, you CANNOT update the labels in this method
        if (!_bw.CancellationPending)
        {
            // Checking the cancel pending before sleeping so that we don't sleep
            // while a cancel is pending. There are better ways to do this with
            // event handles, but this should get you off and running.
            Thread.Sleep(1000);
        }
    }
    e.Cancel = true;
}

Note: If you were using .Net 4.0, you may want to consider using the task factory and a cancellation token rather than the BackgroundWorker, but either one should get you up and running.