Three ways to style C # Singleton

The first is the simplest, but does not consider thread safety, in multi-threading may be problematic, but I have never seen the phenomenon of error, the table despise me ...

PublicClassSingleton
{
PrivateStaticSingleton _instance=Null;
PrivateSingleton (){}
    public  static  Singleton createinstance ()
    {
        if (_instance ==  null< Span style= "LINE-HEIGHT:19PX; Color: #000000; " >)

{
_instance= new singleton ();
        }
        return _instance;
    }
"

The second consideration is thread safety, but a bit annoying, but definitely formal, classic

PublicClassSingleton
{
PrivateVolatileStaticSingleton _instance=Null;
PrivateStaticReadOnlyObjectLockhelper=NewObject();
PrivateSingleton (){}
PublicStaticSingleton CreateInstance ()
{
If(_instance==Null)
{
Lock(Lockhelper)
{
If(_instance==Null)
_instance=NewSingleton ();
             }
         }
        return _instance;
    }
}

The third may be a high-level language specific to C #, and it's really lazy.

Public class Singleton
{

private  singleton () {}
    public static   Readonly singleton instance = new< Span style= "LINE-HEIGHT:19PX; Color: #000000; " > singleton ();
}  

Three ways to type C # Singleton mode