Using ZeroMQ with C# with inproc transport

Question

I'm experimenting with ZeroMQ and trying to get something working. My first thought was to set up a REP/REQ using the inproc transport to see if I could send messages between two threads. Most of the below code is taken from the clzmq examples, but it doesn't seem to work.

Both the server and the client are bound to the transport, but when the client tries to do a Send it blocks and just sits there. I have no ZeroMQ experience so I'm not sure where to look first, any help would be greatly appreciated. Here's the offending (offensive) code:

using System;
using System.Diagnostics;
using System.Threading;
using NUnit.Framework;
using ZMQ;

namespace PostBox
{
    [TestFixture]
    public class Class1
    {

        private const string Address = "inproc://test";
        private const uint MessageSize = 10;
        private const int RoundtripCount = 100;

        [Test]
        public void Should()
        {
            var clientThread = new Thread(StartClient);
            clientThread.Start();

            var serverThread = new Thread(StartServer);
            serverThread.Start();

            clientThread.Join();
            serverThread.Join();

            Console.WriteLine("Done with life");
        }

        private void StartServer()
        {


            //  Initialise 0MQ infrastructure
            using (var ctx = new Context(1))
            {
                using (var skt = ctx.Socket(SocketType.REP))
                {
                    skt.Bind(Address);

                    Console.WriteLine("Server has bound");

                    //  Bounce the messages.
                    for (var i = 0; i < RoundtripCount; i++)
                    {
                        var msg = skt.Recv();
                        Debug.Assert(msg.Length == MessageSize);
                        skt.Send(msg);
                    }
                    Thread.Sleep(1000);
                }
            }

            Console.WriteLine("Done with server");
        }

        private void StartClient()
        {
            Thread.Sleep(2000);

            //  Initialise 0MQ infrastructure
            using (var ctx = new Context(1))
            {
                using (var skt = ctx.Socket(SocketType.REQ))
                {
                    skt.Bind(Address);

                    Console.WriteLine("Client has bound");

                    //  Create a message to send.
                    var msg = new byte[MessageSize];

                    //  Start measuring the time.
                    var watch = new Stopwatch();
                    watch.Start();

                    //  Start sending messages.
                    for (var i = 0; i < RoundtripCount; i++)
                    {
                        skt.Send(msg);
                        msg = skt.Recv();
                        Debug.Assert(msg.Length == MessageSize);

                        Console.Write(".");
                    }

                    //  Stop measuring the time.
                    watch.Stop();
                    var elapsedTime = watch.ElapsedTicks;

                    //  Print out the test parameters.
                    Console.WriteLine("message size: " + MessageSize + " [B]");
                    Console.WriteLine("roundtrip count: " + RoundtripCount);

                    //  Compute and print out the latency.
                    var latency = (double)(elapsedTime) / RoundtripCount / 2 *
                        1000000 / Stopwatch.Frequency;
                    Console.WriteLine("Your average latency is {0} [us]",
                        latency.ToString("f2"));
                }
            }

            Console.WriteLine("Done with client");
        }

    }
}

Edit:

I got this working with the help of the below answer, but it also required me to change a Bind to a Connect, which makes sense when you think about it as we have a server binding to a local transport and a client connecting to a remote transport. Here's the updated code:

using System;
using System.Diagnostics;
using System.Threading;
using NUnit.Framework;
using ZMQ;

namespace PostBox
{
    [TestFixture]
    public class Class1
    {

        private const string Address = "inproc://test";
        private const uint MessageSize = 10;
        private const int RoundtripCount = 100;

        private static Context ctx;

        [Test]
        public void Should()
        {
            using (ctx = new Context(1))
            {
                var clientThread = new Thread(StartClient);
                clientThread.Start();

                var serverThread = new Thread(StartServer);
                serverThread.Start();

                clientThread.Join();
                serverThread.Join();

                Console.WriteLine("Done with life");
            }
        }

        private void StartServer()
        {
            try
            {
                using (var skt = ctx.Socket(SocketType.REP))
                {
                    skt.Bind(Address);

                    Console.WriteLine("Server has bound");

                    //  Bounce the messages.
                    for (var i = 0; i < RoundtripCount; i++)
                    {
                        var msg = skt.Recv();
                        Debug.Assert(msg.Length == MessageSize);
                        skt.Send(msg);
                    }
                    Thread.Sleep(1000);
                }

                Console.WriteLine("Done with server");
            }
            catch (System.Exception e)
            {
                Console.WriteLine(e.Message);
            }
        }

        private void StartClient()
        {
            Thread.Sleep(2000);

            try
            {
                //  Initialise 0MQ infrastructure
                using (var skt = ctx.Socket(SocketType.REQ))
                {
                    skt.Connect(Address);

                    Console.WriteLine("Client has bound");

                    //  Create a message to send.
                    var msg = new byte[MessageSize];

                    //  Start measuring the time.
                    var watch = new Stopwatch();
                    watch.Start();

                    //  Start sending messages.
                    for (var i = 0; i < RoundtripCount; i++)
                    {
                        skt.Send(msg);
                        msg = skt.Recv();
                        Debug.Assert(msg.Length == MessageSize);

                        Console.Write(".");
                    }

                    //  Stop measuring the time.
                    watch.Stop();
                    var elapsedTime = watch.ElapsedTicks;

                    //  Print out the test parameters.
                    Console.WriteLine("message size: " + MessageSize + " [B]");
                    Console.WriteLine("roundtrip count: " + RoundtripCount);

                    //  Compute and print out the latency.
                    var latency = (double)(elapsedTime) / RoundtripCount / 2 *
                                  1000000 / Stopwatch.Frequency;
                    Console.WriteLine("Your average latency is {0} [us]",
                                      latency.ToString("f2"));
                }

                Console.WriteLine("Done with client");
            }
            catch (System.Exception e)
            {
                Console.WriteLine(e.Message);
            }
        }

    }
}

Answer 1

I believe, both threads need to use the same Context. Zeromq guide does recommend not to use more than one context in a process. Create a context, share that context between both the threads. This should work.

From http://zguide.zeromq.org/chapter:all

You MUST create a 'context' object for your process, and pass that to all threads. The context collects ØMQ's state. To create a connection across the inproc: transport, both server and client thread must share the same context object.

Answer 2

Only one end can Bind the other must Connect, you can have multiple connections.