单例模式

单例模式：保证一个类仅有一个实例，并提供一个访问它的全局访问点。

结构图：

 //单线程

    class Singleton
    {
        private static Singleton instance;

        private Singleton()
        { }

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

 

//多线程

    class Singleton2
    {
        private static Singleton2 instance;
        private static readonly object synvRoot = new object();

        private Singleton2()
        { }

        public static Singleton2 GetInstance()
        {
            if (instance == null)
            {
                lock (synvRoot)
                {
                    if (instance == null)
                    {
                        instance = new Singleton2();
                    }
                }
            }
            return instance;
        }

        //线程【串行化】的方式睡眠了 20 毫秒
        public static void ddd()
        {
            lock (synvRoot)
                System.Threading.Thread.Sleep(20);
        }
    }

 

 主函数：

    class Program
    {
        static void Main(string[] args)
        {
            Singleton s1 = Singleton.GetInstance();
            Singleton s2 = Singleton.GetInstance();
            if (s1 == s2)
            {
                Console.WriteLine("s1和s2是相同实例");
            }

            //多线程
            Singleton2 s3 = Singleton2.GetInstance();
            Singleton2 s4 = Singleton2.GetInstance();
            if (s3 == s4)
            {
                Console.WriteLine("s1和s2是相同实例");
            }

            Console.ReadKey();
        }
    }

Lock是确保当一个线程位于代码的临界区时，另一个线程不进入临界区，如果其他线程试图进入锁定的代码，侧他将一直等待，直到被该对象释放。