Singleton Example, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    //Singleton class that returns only one object.
    public class SingleInstanceClass
    {
        //create a mutex object to lock shared statement in GetInstance
        //method
        private static readonly object mutex = new object();        
        private static SingleInstanceClass instance = null;
        
        private SingleInstanceClass()
        {
        }
 
        public static SingleInstanceClass GetInstance()
        {
            if (instance == null)
            {
                lock (mutex)
                {
                    if (instance == null)
                    {
                        instance = new SingleInstanceClass();
                    }
                }
            }
 
            return instance;
        }       
 
        public void Display(){
            Console.WriteLine("Singleton class");
        } 
    }
 
    //CLIENT CLODE
 
    class Program
    {
        public static void Main(string[] args)
        {
            //Create 2 objects of the singleton class
            SingleInstanceClass obj1 = SingleInstanceClass.GetInstance();
            obj1.Display();
            SingleInstanceClass obj2 = SingleInstanceClass.GetInstance();
            obj2.Display();
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,14 sec, absolute running time: 0,08 sec, cpu time: 0,08 sec, average memory usage: 12 Mb, average nr of threads: 3