C# - Singleton Basisklasse (thread-safe, generic, Lazy Creation)

/// <summary>
/// This class provide a generic and thread-safe interface for Singleton classes.
/// </summary>
/// <typeparam name="T">The specialized singleton which is derived
/// from SingletonBase&lt;T&gt;</typeparam>
public abstract class SingletonBase<T>
  where T : SingletonBase<T>
{
  /* the lock object */
  private static object _lock = new object();

  /* the static instance */
  private static T _instance = null;
  /// <summary>
  /// Get the unique instance of <typeparamref name="T"/>.
  /// This property is thread-safe!
  /// </summary>
  public static T Instance
  {
    get
    {
      if (_instance == null)
      {
        lock (_lock)
        {
          if (_instance == null)
          {
            /* Create a object without to use new (where you need a public ctor) */
            object obj = FormatterServices.GetUninitializedObject(typeof(T));
            if (obj != null)  // just 4 safety, but i think obj == null shouldn't be possible
            {
              /* an extra test of the correct type is redundant,
               * because we have an uninitialised object of type == typeof(T) */
              _instance = obj as T;
              _instance.Init(); // now the singleton will be initialized
            }
          }
        }
      }
      else
      {
        _instance.Refresh();  // has only effect if overridden in sub class
      }
      return _instance;
    }
  }

  /// <summary>
  /// Called while instantiation of singleton sub-class.
  /// This could be used to set some default stuff in the singleton.
  /// </summary>
  protected virtual void Init()
  { }

  /// <summary>
  /// If overridden this will called on every request of the Instance but
  /// the instance was already created. Refresh will not called during
  /// the first instantiation, for this will call Init.
  /// </summary>
  protected virtual void Refresh()
  { }
}

// usage:
class SingletonTest
  : SingletonBase<SingletonTest>
{
  ~SingletonTest()
  { Console.WriteLine("~SingletonTest called ..."); }

  public void DoSomething()
  { Console.WriteLine("SingletonTest::DoSomething called ..."); }

  public void DoAnother()
  { Console.WriteLine("SingletonTest::DoAnother called ..."); }

  protected override void Init()
  { Console.WriteLine("SingletonTest::Init called ..."); }

  protected override void Refresh()
  { Console.WriteLine("SingletonTest::Refresh called ..."); }
}

public class Program
{
  public static void Main(string[] args)
  {
    SingletonTest.Instance.DoSomething();
    SingletonTest.Instance.DoAnother();

    Console.WriteLine("press any key ...");
    Console.ReadKey(true);
  }
}