Three examples of writing singleton patterns in C

The first one is the simplest, but it doesn't take thread safety into account. It may cause problems when multithreaded, but I have never seen any mistakes and scorn me...

public class Singleton

{

    private static Singleton _instance = null;

    private Singleton(){}

    public static Singleton CreateInstance()

    {

        if(_instance == null)

        {

            _instance = new Singleton();

        }

        return _instance;

    }

}

The second considers thread security, but it's a little tedious, but it's absolutely formal, classic fork

public class Singleton

{

    private volatile static Singleton _instance = null;

    private static readonly object lockHelper = new object();

    private Singleton(){}

    public static Singleton CreateInstance()

    {

        if(_instance == null)

        {

            lock(lockHelper)

            {

                if(_instance == null)

                     _instance = new Singleton();

            }

        }

        return _instance;

    }

}

The third may be unique to a high-level language like C#, which is surprisingly lazy

public class Singleton

{

    private Singleton(){}

    public static readonly Singleton instance = new Singleton();

} 

Oh, shit!