C#中单例模式的三种写法示例

第一种最简单，但没有考虑线程安全，在多线程时可能会出问题，不过俺从没看过出错的现象，表鄙视我……

public class Singleton

{

    private static Singleton _instance = null;

    private Singleton(){}

    public static Singleton CreateInstance()

    {

        if(_instance == null)

        {

            _instance = new Singleton();

        }

        return _instance;

    }

}

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;

    }

}

public class Singleton

{

    private Singleton(){}

    public static readonly Singleton instance = new Singleton();

}