c# - A simple implementation of a Singleton

Question

Isn't this a simpler as well as safe (and hence better) way to implement a singleton instead of doing double-checked locking mambo-jambo? Any drawbacks of this approach?

public class Singleton
{
    private static Singleton _instance;
    private Singleton() { Console.WriteLine("Instance created"); }

    public static Singleton Instance
    {
        get
        {
            if (_instance == null)
            {
                Interlocked.CompareExchange(ref _instance, new Singleton(), null);
            }
            return _instance;
        }
    }
    public void DoStuff() { }
}

EDIT: the test for thread-safety failed, can anyone explain why? How come Interlocked.CompareExchange isn't truly atomic?

public class Program
{
   static void Main(string[] args)
   {
      Parallel.For(0, 1000000, delegate(int i) { Singleton.Instance.DoStuff(); });
   }
} 

Result (4 cores, 4 logical processors)
Instance created
Instance created
Instance created
Instance created
Instance created

Answer 1

If your singleton is ever in danger of initializing itself multiple times, you have a lot worse problems. Why not just use:

public class Singleton
{
  private static Singleton instance=new Singleton();
  private Singleton() {}

  public static Singleton Instance{get{return instance;}}
}

Absolutely thread-safe in regards to initialization.

Edit: in case I wasn't clear, your code is horribly wrong. Both the if check and the new are not thread-safe! You need to use a proper singleton class.