Performance impact of using netmq poller

Question

In the following code, I send and receive 100000 messages using netmq push/pull sockets. I first tried to do a simple blocking call using ReceiveFrameString (ReceiveSimple method) on my pull socket, then I tried to use a poller to do the same (ReceiveWithPoller method).

Using the poller has a significant impact on the time it takes to send / receive the messages. I tried to figure out why by myself using dotTrace and I found that lot of time is spent waiting for Socket.Select to execute.

Can somebody confirm or explain this difference ?

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using NetMQ;
using NetMQ.Sockets;

namespace PushPull
{
    class Program
    {
        static int messageReceived = 0;

        const int sampleCount = 100 * 1000;

        static void Main(string[] args)
        {
            // Create psu socket
            PushSocket pushSocket = new PushSocket();
            pushSocket.Bind("tcp://localhost:5555");

            // Create pull socket
            PullSocket pullSocket = new PullSocket();
            pullSocket.Connect("tcp://localhost:5555");

            Console.WriteLine("Ready...press any key to start");
            Console.ReadKey();
            Console.WriteLine();

            // Start sending
            Task.Run(() =>
            {
                for (int i = 0; i < sampleCount; i++)
                {
                    pushSocket.SendFrame(Encoding.UTF8.GetBytes("ping"));
                }
            });

            Stopwatch sw = Stopwatch.StartNew();

            //ReceiveSimple(pullSocket);

            ReceiveWithPoller(pullSocket);

            // Display result.
            sw.Stop();
            Console.WriteLine();
            Console.WriteLine("{0} message exchanged in {1} msecs", sampleCount, sw.Elapsed.TotalMilliseconds);
        }

        private static void ReceiveSimple(PullSocket pullSocket)
        {
            messageReceived = 0;
            do
            {
                pullSocket.ReceiveFrameString();
            } while (!HandleMessage());
        }

        private static void ReceiveWithPoller(PullSocket pullSocket)
        {
            NetMQPoller poller = new NetMQPoller();
            poller.Add(pullSocket);
            pullSocket.ReceiveReady += (sender, eventArgs) =>
            {
                if (HandleMessage())
                {
                    poller.Stop();
                }
            };
            poller.Run();
        }

        private static bool HandleMessage()
        {
            messageReceived++;

            if (messageReceived % 10000 == 0)
            {
                Console.WriteLine("10k");
            }

            return messageReceived == sampleCount;
        }
    }
}

Answer 1

Poller is expensive when you handle a lot of messages, but there is a very simple solution for this.

Fetch all messages in the queue when you receive the ready event, you can do so with Try* methods, in your example like so:

 pullSocket.ReceiveReady += (sender, eventArgs) =>
 {
    string message;
    while (pullSocket.TryReceiveFrameString(out message) 
    {
        if (HandleMessage())
        {
            poller.Stop();
        }
    }
 };