Question

I have a receive callback from an async client method that is supposed to call socket.BeginReceive internally to check if data is done being sent. The code is as follows:

    private void ReceiveCallback(IAsyncResult ar)
    {
        try
        {
            StateObject state = (StateObject)ar.AsyncState;
            Socket client = state.workSocket;
            int bytesRead = client.EndReceive(ar);

            if (bytesRead > 0)
            {
                state.sb.Append(Encoding.ASCII.GetString(state.buffer, 0, bytesRead));
                client.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0, 
                    new AsyncCallback(ReceiveCallback), state);
            }
            else
            {
                if (state.sb.Length > 1)
                {
                    response = state.sb.ToString();
                }
                File.AppendAllText(DataDisplay.Properties.Settings.Default.rawDataLog, response + "\r\n");
                receiveDone.Set();
            }
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }

The problem with this is that when the code reaches the client.BeginReceive call, nothing happens. I know that sounds vague, so let me try to explain. I have set breakpoints throughout the code to see where it could possibly be going, and I can’t figure it out. I have tried the else case, the beginning of the ReceiveCallback, where the receivedone.Set() returns to in the main code, the catch statement, etc. to no avail.

The part that is most confusing is that when I run it with a test server I wrote, it works as I would expect. This code is essentially from the MSDN example on async sockets, in case it looks familiar. Only when I try it with the third party device, I get stymied.

Any ideas what could be going on here?

Answer 1

Is it possible that while you are debugging, nothing is actually being received so its essentially permanently waiting on the receive thread? Note that BeginReceive will use a ThreadPool thread, and will callback to the method you post. If its not calling back, then my first impression is that its not received anything.