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;
    }
}
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第二种考虑了线程安全，不过有点烦，但绝对是正规写法，经典的一叉
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;
    }
}
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第三种可能是C#这样的高级语言特有的，实在懒得出奇
public class Singleton
{
    private Singleton(){}
    public static readonly Singleton instance = new Singleton();
}
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哦，shit！