Singleton模式(一) 简单多线程计数器

1. 经典的设计模式中的代码

public class Singleton
    {
        private static Singleton instance;   // 唯一实例
        protected Singleton() { }   // 封闭客户程序的直接实例化

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

  在多线程环境下存在缺陷, 最终将会保存最后创建的那个实例

2. 改进后的多线程Singleton

class Singleton
    {
        private Singleton() { }
        [ThreadStatic]
        public static readonly Singleton Instance = new Singleton();
    }

3. 线程计数器

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

        private int value;
        public int Next { get { return ++value; } }
        public void Reset() { value = 0; }
    }

4. 调用代码

  ThreadCounter.Instance.Next