title: Asynchronous socket calls freezing UI Thread
body: <p>I have been working on a client to server chat messenger and I have run into some issues regarding asynchronous calls. I have been trying, with no success, to fix them for a while.</p>
  
  <p>The issue is with the client, there is no problem connecting to the server but once the first 'BeginSend' method is called the whole client stops responding.(It doesn't stop 100% it occasionally responds but after a ridiculous response time of 30 seconds+). The rest of the calls operate fine but the UI wont respond. The server responds fine as well.</p>
  
  <p>Here is the code, I have commented HERE where the client first freezes. </p>
  
  <pre><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.Windows.Forms.VisualStyles;
  using System.Net.Sockets;
  using System.Net;
  
  namespace Client_GUI_Design_Test
  {
      public partial class Login : Form
      {
          public Socket clientSocket;
          public string strName;
          public byte[] byteData = new byte[1024];
          public List&lt;String&gt; contacts = new List&lt;String&gt;();
          public Boolean needUpdate = true;
         // public Panel globalPanel;
          public Login()
          {
              InitializeComponent();
          }
  
          public struct Contact
          {
              public string strName;
          }
  
  
          public int num1 = 0;
          public void addContact(String contactName, String message, int status, int imageNum)
          {
              //MessageBox.Show(this.Size.Width.ToString());
              panel1.HorizontalScroll.Enabled = false;
              panel1.HorizontalScroll.Visible = false;
              if (num1 &gt;= panel1.Size.Height - 47)
              {
                  panel1.Size = new Size(257, 514);
                  this.Size = new Size(277, this.Size.Height);
                  panel1.AutoScroll = true;
                  panel1.HorizontalScroll.Enabled = false;
                  panel1.HorizontalScroll.Visible = false;
                  panel1.VerticalScroll.Visible = true;
              }
              panel1.VerticalScroll.Value = 0;
              //Contact Panel
              Panel contactPanel = new Panel();
              contactPanel.Size = new Size(249, 47);
              contactPanel.Margin = new System.Windows.Forms.Padding(0, 0, 0, 0);
  
              //Name Label
              Label name = new Label();
              //Font
              float size = 12.00f;
              name.Font = new Font("Microsoft Sans Serif", size, FontStyle.Bold);
              //Location
              name.Location = new Point(29, 3);
              //Size
              name.Size = new Size(112, 20);
              name.Text = contactName;
              //Events
              #region
              name.MouseEnter += delegate
              {
                  contactPanel.BackColor = Color.Gainsboro;
              };
              name.MouseLeave += delegate
              {
                  contactPanel.BackColor = System.Drawing.SystemColors.Control;
              };
              #endregion
              contactPanel.Controls.Add(name);
  
              //Image Box
              PictureBox image = new PictureBox();
              //Image
              image.Image = imageList1.Images[imageNum];
              //Size
              image.Size = new Size(56, 42);
              //Location
              image.Location = new Point(187, 4);
              //Events
              #region
              image.MouseEnter += delegate
              {
                  contactPanel.BackColor = Color.Gainsboro;
              };
              image.MouseLeave += delegate
              {
                  contactPanel.BackColor = System.Drawing.SystemColors.Control;
              };
              #endregion
              contactPanel.Controls.Add(image);
  
              //Status
              PictureBox statusPic = new PictureBox();
              //Image
              statusPic.Image = imageList2.Images[status];
              //Size
              statusPic.Size = new Size(20, 20);
              //Location
              statusPic.Location = new Point(3, 3);
              //Events
              #region
              statusPic.MouseEnter += delegate
              {
                  contactPanel.BackColor = Color.Gainsboro;
              };
              statusPic.MouseLeave += delegate
              {
                  contactPanel.BackColor = System.Drawing.SystemColors.Control;
              };
              #endregion
              contactPanel.Controls.Add(statusPic);
  
              //Message Label
              Label messageL = new Label();
              //Font
              float sizem = 11.25f;
              messageL.Font = new Font("Microsoft Sans Serif", sizem, FontStyle.Bold);
              messageL.ForeColor = Color.Gray;
              //Location
              messageL.Location = new Point(29, 23);
              //Size
              messageL.Size = new Size(153, 18);
              //Text
              messageL.Text = message;
              //Events
              #region
              messageL.MouseEnter += delegate
              {
                  contactPanel.BackColor = Color.Gainsboro;
              };
              messageL.MouseLeave += delegate
              {
                  contactPanel.BackColor = System.Drawing.SystemColors.Control;
              };
              messageL.MouseHover += delegate
              {
                  ToolTip tip = new ToolTip();
                  tip.Tag = messageL.Text;
                  tip.Show(messageL.Text, messageL, 1, 1, 750);
              };
              #endregion
  
              contactPanel.Controls.Add(messageL);
  
              contactPanel.Paint += new PaintEventHandler(contactPanel_Paint);
              {
  
  
              };
              contactPanel.MouseEnter += delegate
              {
                  contactPanel.BackColor = Color.Gainsboro;
              };
              contactPanel.MouseLeave += delegate
              {
                  contactPanel.BackColor = System.Drawing.SystemColors.Control;
              };
              contactPanel.Location = new Point(0, num1);
              //globalPanel = contactPanel;
              //panel1.Controls.Add(contactPanel);
              addPanel(contactPanel);
              num1 += 47;
  
  
          }
  
          public delegate void UpdatePanelCallBack(Panel panel);
          private void addPanel(Panel panel)
          {
              if (InvokeRequired)
              {
                  object[] pList = { panel };
                  panel1.BeginInvoke(new
                     UpdatePanelCallBack(OnUpdatePanel), pList);
              }
  
              else
              {
                  OnUpdatePanel(panel);
              }
          }
  
          private void OnUpdatePanel(Panel panel)
          {
              panel1.Controls.Add(panel);
          }
  
          VisualStyleRenderer renderer = new VisualStyleRenderer(VisualStyleElement.Button.PushButton.Normal);
          void contactPanel_Paint(object sender, PaintEventArgs e)
          {
              renderer.DrawEdge(e.Graphics, panel1.ClientRectangle,
                  Edges.Top,
                  EdgeStyle.Bump, EdgeEffects.Flat);
          }
  
          private void button3_Click(object sender, EventArgs e)
          {
              try
              {
                  clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
  
                  //IPAddress ipAddress = IPAddress.Parse(txtServerIP.Text);
                  //Server is listening on port 43594
                  IPEndPoint ipEndPoint = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 43594);
  
                  //Connect to the server
                  clientSocket.BeginConnect(ipEndPoint, new AsyncCallback(OnConnect), null);
              }
              catch (Exception ex)
              {
                  MessageBox.Show(ex.Message, "SGSclient", MessageBoxButtons.OK, MessageBoxIcon.Error);
              }
  
  
          }
  
          private void OnSend(IAsyncResult ar)
          {
              try
              {
                  Socket client = (Socket)ar.AsyncState;
                  client.EndSend(ar);
                  //clientSocket.EndSend(ar);
                 //strName = textBox2.Text;
                 // DialogResult = DialogResult.OK;
              }
              catch (Exception ex)
              {
                  MessageBox.Show(ex.Message, "SGSclient", MessageBoxButtons.OK, MessageBoxIcon.Error);
              }
          }
  
          private void OnConnect(IAsyncResult ar)
          {
              try
              {
                  clientSocket.EndConnect(ar);
  
                  //We are connected so we login into the server
                  Data msgToSend = new Data();
                  msgToSend.cmdCommand = Command.Login;
                  msgToSend.strName = textBox2.Text;
                  msgToSend.strMessage = null;
  
                  byte[] b = msgToSend.ToByte();
  
                  //Send the message to the server
                  //HERE - Starts freezing the UI thread, continues to do background operations
                  clientSocket.BeginSend(b, 0, b.Length, SocketFlags.None, new AsyncCallback(OnSend), clientSocket);
  
                  clientSocket.BeginReceive(byteData,
                                         0,
                                         byteData.Length,
                                         SocketFlags.None,
                                         new AsyncCallback(OnReceive),
                                         clientSocket);
              }
              catch (Exception ex)
              {
                  MessageBox.Show(ex.Message, "SGSclient", MessageBoxButtons.OK, MessageBoxIcon.Error);
              }
  
              panel4.Visible = false;
              panel1.Visible = true;
          }
  
          public void OnReceive(IAsyncResult ar)
          {
              try
              {
                  clientSocket.EndReceive(ar);
  
                  Data msgReceived = new Data(byteData);
                  //Accordingly process the message received
                  switch (msgReceived.cmdCommand)
                  {
                      case Command.Login:
                          //lstChatters.Items.Add(msgReceived.strName);
                          break;
  
                      case Command.Logout:
                          //lstChatters.Items.Remove(msgReceived.strName);
                          break;
  
                      case Command.Message:
                          break;
  
                      case Command.List:
                          MessageBox.Show(msgReceived.strName);
                          //contacts.Add(msgReceived.strName);
                          needUpdate = true;
                          //lstChatters.Items.AddRange(msgReceived.strMessage.Split('*'));
                          //lstChatters.Items.RemoveAt(lstChatters.Items.Count - 1);
                          //txtChatBox.Text += "&lt;&lt;&lt;" + strName + " has joined the room&gt;&gt;&gt;\r\n";
  
                          break;
                  }
  
                  byteData = new byte[1024];
  
                  clientSocket.BeginReceive(byteData,
                                            0,
                                            byteData.Length,
                                            SocketFlags.None,
                                            new AsyncCallback(OnReceive),
                                            clientSocket);
  
              }
              catch (ObjectDisposedException)
              { }
              catch (Exception ex)
              {
                  MessageBox.Show(ex.Message, "SGSclientTCP: " + strName, MessageBoxButtons.OK, MessageBoxIcon.Error);
              }
  
          }
  
          private void Login_Load(object sender, EventArgs e)
          {
              CheckForIllegalCrossThreadCalls = false;
              //backgroundWorker1.RunWorkerAsync();
  
          }
  
          private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
          {
              while (true)
              {
                  if(needUpdate){
  
                  }
              }
          }
  
  
          private void Login_DoubleClick(object sender, EventArgs e)
          {
              MessageBox.Show("");
              foreach (string s in contacts)
              {
                  addContact(s, "Random Message", 0, 1);
                  needUpdate = false;
              }
          }
      }
  }
  </code></pre>
  
  <p>Fixed the problem in the other classes, however still having issues in OnReceive (Might help to faster identify the issue)</p>
  
  <pre><code>public void OnReceive(IAsyncResult ar)
          {
              try
              {
                  Socket client = (Socket)ar.AsyncState;
                  client.EndReceive(ar);
  
                  Data msgReceived = new Data(byteData);
                  //Accordingly process the message received
                  switch (msgReceived.cmdCommand)
                  {
                      case Command.Login:
                          //lstChatters.Items.Add(msgReceived.strName);
                          break;
  
                      case Command.Logout:
                          //lstChatters.Items.Remove(msgReceived.strName);
                          break;
  
                      case Command.Message:
                          break;
  
                      case Command.List:
                          MessageBox.Show(msgReceived.strName);
                          //contacts.Add(msgReceived.strName);
                          needUpdate = true;
                          //lstChatters.Items.AddRange(msgReceived.strMessage.Split('*'));
                          //lstChatters.Items.RemoveAt(lstChatters.Items.Count - 1);
                          //txtChatBox.Text += "&lt;&lt;&lt;" + strName + " has joined the room&gt;&gt;&gt;\r\n";
  
                          break;
                  }
  
                  byteData = new byte[1024];
  
                 /* client.BeginReceive(byteData,
                                            0,
                                            byteData.Length,
                                            SocketFlags.None,
                                            new AsyncCallback(OnReceive),
                                            client);*/
  
              }
              catch (ObjectDisposedException)
              { }
              catch (Exception ex)
              {
                  MessageBox.Show(ex.Message, "SGSclientTCP: " + strName, MessageBoxButtons.OK, MessageBoxIcon.Error);
              }
  
          }
  </code></pre>
  
  <p>I know it is a lot of code, I am sorry but this is my last option I am completely stuck. Any help would be greatly appreciated :)</p>