using System;

using System.Threading.Tasks;

namespace SingletonDemo

{

    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

        {

            get

            { 

                lock(InstanceLock)

                {

                if (instance == null)

                    instance = new Singleton();

                return instance;

                }

            }

        }  

        private Singleton()

        {

            counter++;

            Console.WriteLine("Counter Value " + counter.ToString());

        }    

        public void PrintDetails(string message)

        {

            Console.WriteLine(message);

        }

    }

 public class Program

    {

     public  static void Main(string[] args)

        {

            Parallel.Invoke(

                () => PrintTeacherDetails(),

                () => PrintStudentdetails()

                );

           Console.ReadLine();

        }

        private static void PrintTeacherDetails()

        {

            Singleton fromTeacher = Singleton.GetInstance;

            fromTeacher.PrintDetails("From Teacher");

        }

        private static void PrintStudentdetails()

        {

            Singleton fromStudent = Singleton.GetInstance;

            fromStudent.PrintDetails("From Student");

        }

 }

​

}