using System;

using System.Threading;

using System.Threading.Tasks;

​

public class Program

{

    public static void Main()

    {

        int messagesPerTask = 20000;

        int unitsOfWork = 4;

        var logger = new Logger();

        var state = new StateObject();

        Parallel.For(0, unitsOfWork, (tasknumber) => 

                     {

                         lock (state)

                         {

                             for (int i = 0; i < messagesPerTask; i++)

                             {

                                 logger.Log("Message {0}" + i.ToString());

                             }

                         }

                     });

        Console.WriteLine("{0} Expected", messagesPerTask * unitsOfWork);

        Console.WriteLine("{0} Actual", Logger.TotalMessages);

        Console.ReadLine();

    }

}

​

public class Logger

{

    public static int TotalMessages = 0;

    public void Log(string message)

    {

        TotalMessages++;

    }

}

​

public class StateObject

{

}