Socket Program Freezing

Question

I've made a short program where the user enters an IP address of a computer, and the program proceeds to check if the computer is online by trying to connect to it with port 80 (the assumption is that if a computer is turned on, it's connected to the internet).

Now, the problem is, everytime I click the Start button it does nothing for a few seconds and then it crashes.

Here's the code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Net;
using System.Net.Sockets;
using System.Threading;

namespace Online_Checker
{
    public partial class Form1 : Form
    {
        int success;
        Socket client = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            IPEndPoint ep = new IPEndPoint(IPAddress.Parse(ipAddress.Text), 80);
            while (true)
            {
                success = 1;
                try { client.Connect(ep); }
                catch { status.BackColor = Color.Red; status.Text = "OFFLINE"; success = 0; }
                if (success == 1)
                {
                    status.BackColor = Color.Red;
                    status.Text = "ONLINE";
                    client.Close();
                }
                Thread.Sleep(5000);
            }
        }
    }
}

As you can see I've even made a delay of 5 seconds between each check to make sure it doesn't crash.

So where's the problem? And how can I solve it?

No error. I just click the start button, the start button freezes, and the whole form freezes. Even if it sometimes doesn't crash after a few seconds, it goes into "Not Responding" mode and I can't do anything inside it. Vipar, I caught the socket connection exception (to check if the computer is turned on/off), as you can see. — BlueRay101, Dec 18 '13 at 16:36
On just a quick glance I noticed that you're trying to connect via UDP; only TCP implements connection handshakes. — OnoSendai, Dec 18 '13 at 16:36
Even with TCP, 'trying to connect to it with port 80 (the assumption is that if a computer is turned on, it's connected to the internet).' Sure - as a CLIENT. Most boxes will not be running a server on port 80. — Martin James, Dec 18 '13 at 16:46

score 1 · Accepted Answer · answered Dec 18 '13 at 16:37

1

You can't do an infinite while/sleep loop on the UI thread: the UI thread is required to service the windows event queue - and if that is ignored it can't paint and is logged as "not responding".

Consider either a timer or a background worker instead.

answered Dec 18 '13 at 16:37

Marc Gravell

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score 1 · Answer 2 · edited May 23 '17 at 11:44

You're implementing an UDP socket. According to MSDN,

Since the UDP protocol is connectionless, the Connect method does not block.

There'll be no error to be Catched; thus, you enter an infinite loop on your main thread.

Socket Program Freezing

2 Answers2