double check locking in singleton pattern

Question

it may be basic question

to have a singleton in multi-threaded environment we can use a lock. Please refer the code snippet. But why do we need double-checked locki

Answer 1

Multithreaded Singleton : The best approach to use double check locking

public sealed class Singleton
{
   private static volatile Singleton _instance;
   private static readonly object InstanceLoker= new Object();

   private Singleton() {}

   public static Singleton Instance
   {
      get 
      {
         if (_instance == null) 
         {
            lock (InstanceLoker) 
            {
               if (_instance == null) 
                  _instance = new Singleton();
            }
         }

         return _instance;
      }
   }
}