singleton&doublecheck

通常的Singleton写法，C#为例：

class Singleton
    {
        private static Singleton instance;
        private Singleton() { }

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

 

通常的doublecheck写法：

    class DoubleCheck
    {
        private static volatile DoubleCheck instance = null;

        private static object lockHelper = new object();
        
        private DoubleCheck() { }

        public static DoubleCheck Instance
        {
            get 
            {
                if (instance == null)
                {
                    lock (lockHelper)
                    {
                        if (instance == null)
                        {
                            instance = new DoubleCheck();
                        }
                    }
                }
                return instance;
            }
        }
    }

 

改进写法，同时适用单线程与多线程：

    class SingletonAndDoubleCheck
    {
        public static readonly SingletonAndDoubleCheck Instance = new SingletonAndDoubleCheck();
        private SingletonAndDoubleCheck() { }
    }

 

新写法的不足之处就是不能使用参数化构造函数，需要另写初始化函数。