Rehan Khan Rehan Khan - 22 days ago 7
ASP.NET (C#) Question

AsyncCallback not firing

Trying to implement Asynchronous Client/Server app in WinForms. Clientside code is as following:

using System;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace AsyncClient
{
public partial class AsyncClient : Form
{
public AsyncClient()
{
InitializeComponent();
}

//ManualResetEvent for notifying asyncronous threads that an event has occured
private static ManualResetEvent connectDone = new ManualResetEvent(false);
private static ManualResetEvent sendDone = new ManualResetEvent(false);
private static ManualResetEvent receiveDone = new ManualResetEvent(false);

//Response from the remote device (server)
private static String response = String.Empty;

//start client
private void button1_Click(object sender, EventArgs e)
{
TcpClient clientSocket = new TcpClient();
try
{
var message = System.Text.Encoding.UTF8.GetBytes(txtFromClient.Text); //convert message to bytes for sending over the wire
using (clientSocket)/*(var clientSocket = new TcpClient("127.0.0.1", 1234)) *///make connection with the host
{
clientSocket.BeginConnect(IPAddress.Loopback, 1234, new AsyncCallback(connectCallBack), clientSocket);
sendDone.WaitOne();
lblConnectionStatus.Text = "Connect is successfully established with the remote device.";
//send data to remote device
NetworkStream stream = clientSocket.GetStream(); //obtain network stream
stream.Write(message, 0, message.Length); //send data to the remote device
//sendDone.WaitOne();
}
}
finally
{
clientSocket.Close();
}
}

private static void connectCallBack(IAsyncResult ar)
{
try
{
var clientSocket = (TcpClient)ar.AsyncState; //retrieve socket from state object (IAsyncResult)
clientSocket.EndConnect(ar); //complete the connection
connectDone.Set();
}
finally
{

}
}

private void txtFromClient_Click(object sender, EventArgs e)
{
txtFromClient.Text = "";
}
}
}


When I
button1
to send text, UI is freezing. During dubug mode I found that
AsyncCallback(connectCallBack)
in line

clientSocket.BeginConnect(IPAddress.Loopback, 1234, new AsyncCallback(connectCallBack), clientSocket);


is not firing and hence
connectCallBack
is not being executed. Program is rather halt on line

sendDone.WaitOne();


Any ideas why? Can someone please help?

Answer

You are waiting for sendDone.WaitOne(); and in your call back you use

connectDone.Set();

You should replace sendDone.WaitOne(); with connectDone.WaitOne();