NetMQ gets stuck when I try to dispose the Poller (Request-Reply pattern)

Question

This is my first project using the NetMQ (ZMQ) framework, so, maybe I didn't understand how to use it exactly.

I create a Windows Forms project with two applications, one send a "ping" to the other and receives a "pong" as an answer. The protocol is not so complex and uses the Request-Reply pattern, all the commands have a first part that identifies the objective, like "query" or "inform", and a second part that contains the command or the message itself. In this case one app send a "query-ping" and the other answer with "inform-pong".

I create a class to encapsulate all the dirty job, so the main form can use the protocol in a very simple way. Everything is working fine, but when I try to close the app, it gets stuck in the poller and the app never closes. In Visual Studio I can see the pause and stop button but I don't get any exception or errors:

and when I click in pause button I get this message (The application is in break mode):

If I click in 'Continue execution' the app back to same state and never closes.

If I remove the poller the app closes normally, but of course, the poller doesn't work and the app doesn't answer anymore.

This is the code from the Form1:

using CommomLib;
using System;
using System.Windows.Forms;

namespace Test1
{
    public partial class Form1 : Form
    {

        ZmqCommunication zmqComm = new ZmqCommunication();
        int portNumber;
        string status;

        public Form1()
        {
            InitializeComponent();
            
            InitializeZmqComm();
        }

        public void InitializeZmqComm()
        {
            // Calls the ZMQ initialization.
            portNumber = zmqComm.InitializeComm();
            if (portNumber == 0)
                status = "Ini error";
            else
                status = "Ini ok";
        }

        // Executes a ping command.
        private void button1_Click(object sender, EventArgs e)
        {
            richTextBox1.Clear();
            richTextBox1.AppendText(zmqComm.RequestPing(55001) + "\n");
        }


    }

}

And this is the code from my NetMQ class. It is in a separated library project. In my Dispose method I tried all combinations of Remove, Dispose and StopAsync and nothing works:

using NetMQ;
using NetMQ.Sockets;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Threading;

namespace CommomLib
{
    public class ZmqCommunication
    {
        ResponseSocket serverComm = new ResponseSocket();
        NetMQPoller serverPoller;

        int _portNumber;

        public ZmqCommunication()
        {
            _portNumber = 55000;
        }

        // Problem here! The serverPoller gets stuck. 
        public void Dispose()
        {
            //serverPoller.RemoveAndDispose(serverComm);
            //serverComm.Dispose();

            if (serverPoller.IsDisposed)
                Debug.WriteLine("A");

            //serverPoller.RemoveAndDispose(serverComm);
            serverPoller.Remove(serverComm);
            //serverPoller.StopAsync();
            serverPoller.Dispose();

            serverComm.Dispose();

            if (serverPoller.IsDisposed)
                Debug.WriteLine("B");

            Thread.Sleep(500);

            if (serverPoller.IsDisposed)
                Debug.WriteLine("C");

            Thread.Sleep(500);

            if (serverPoller.IsDisposed)
                Debug.WriteLine("D");

        }

        // ZMQ initialization.
        public int InitializeComm()
        {
            bool ok = true;
            bool tryAgain = true;

            // Looks for a port.
            while (tryAgain && ok)
            {
                try
                {
                    serverComm.Bind("tcp://127.0.0.1:" + _portNumber);
                    tryAgain = false;
                }
                catch (NetMQ.AddressAlreadyInUseException)
                {
                    _portNumber++;
                    tryAgain = true;
                }
                catch
                {
                    ok = false;
                }
            }

            if (!ok)
                return 0;   // Error.


            // Set up the pooler.
            serverPoller = new NetMQPoller { serverComm };
            serverComm.ReceiveReady += (s, a) =>
                {
                    RequestInterpreter();
                };

            // start polling (on this thread)
            serverPoller.RunAsync();

            return _portNumber;
        }

        // Message interpreter.
        private void RequestInterpreter()
        {

            List<string> message = new List<string>();

            if (serverComm.TryReceiveMultipartStrings(ref message, 2))
            {
                if (message[0].Contains("query"))
                {
                    // Received the command "ping" and answers with a "pong".
                    if (message[1].Contains("ping"))
                    {
                        serverComm.SendMoreFrame("inform").SendFrame("pong");
                    }

                }
            }

        }

        // Send the command "ping".
        public string RequestPing(int port)
        {

            using (var requester = new RequestSocket())
            {
                Debug.WriteLine("Running request port {0}", port);

                requester.Connect("tcp://127.0.0.1:" + port);

                List<string> msgResp = new List<string>();

                requester.SendMoreFrame("query").SendFrame("ping");

                if (requester.TryReceiveMultipartStrings(new TimeSpan(0, 0, 10), ref msgResp, 2))
                {
                    if (msgResp[0].Contains("inform"))
                    {
                        return msgResp[1];
                    }
                }

            }

            return "error";

        }


    }
}

Answer 1

Place a breakpoint and see if you even get to ZmqCommunication.Dispose - that might be the issue - the form class not disposing the ZmqCommunication class.

Answer 2

Can you try to call NetMQConfig.Cleanup(); in window close event?

Answer 3

Thanks guys for the answers, they were not the solution but pointed me in the right direction.

After a lot of debugging, I figured out it was a silly problem. I have two programs almost identical (I had both opened at the same time), one of them had the method Dispose() and the other no. During the debugging, in the breaking point, I thought I was in one program but I was in the other one. Really silly.