Singleton

Check out the discussion of singleton here:
http://www.yoda.arachsys.com/csharp/singleton.html
Sample code extracted from the above URL :

public sealed class Singleton
{
  static Singleton instance=null;
  static readonly object lock_obj = new object();

  Singleton()
  {
  }

  public static Singleton Instance
  {
      get
      {
          if (instance==null)
          {
              lock (lock_obj)
              {
                  if (instance==null)
                  {
                      instance = new Singleton();
                  }
              }
          }

          return instance;
      }
  }
}