using System;

using System.Threading.Tasks;

public sealed class Singleton

{

    private static int counter =0;

    private static Singleton instance = null;

    private static readonly object instanceLock = new object();

    public static Singleton GetInstance()

    {

        if(instance == null)

        {

            lock(instanceLock)

            {

                if(instance==null)

                {

                    instance = new Singleton();

                }

            }

        }

        return instance;

    }

    private Singleton()

    {

        counter++;

        Console.WriteLine("Counter incremented to "+counter);

    }

    public void PrintMessage(string message)

    {

        Console.WriteLine(message);

    }

}

​

public class Program

{

    public static void Main()

    {

        Parallel.Invoke(

        ()=>PrintTeacherDetails(),

        ()=>PrintStudentDetails()

        );

    }

    public static void PrintTeacherDetails()

    {

        Singleton fromTeacher = Singleton.GetInstance();

        fromTeacher.PrintMessage("Teacher Object");

    }

    public static void PrintStudentDetails()

    {

        Singleton fromStudents = Singleton.GetInstance();

        fromStudents.PrintMessage("Students Object");

    }

}