23种设计模式--单例模式-Singleton

一、单例模式的介绍

     单例模式简单说就是掌握系统的至高点，在程序中只实例化一次，这样就是单例模式，在系统比如说你是该系统的登录的第多少人，还有数据库的连接池等地方会使用，单例模式是最简单，最常用的模式之一，面试经常会问答，所以我们在程序考虑什么地方会用到单例模式，单例模式写法有很多种，这里我下面列举2种写法很普遍的写法，然后做个多线程计数的例子大家来理解一下单例模式的用法。

二、单例模式Demo

     /// <summary>
    /// 利用C#的特性单例模式
    /// </summary>

     public sealed  class SampleSingleton1
    {
        private int m_Counter = 0;
        private SampleSingleton1()
        {
            Console.WriteLine("初始化SampleSingle1");
        }

        public static readonly SampleSingleton1 singleton = new SampleSingleton1();
        /// <summary>
        /// 调用次数计数器
        /// </summary>
        public void Counter()
        {
            m_Counter++;
        }
    }

    /// <summary>
    /// 线程安全的单例模式
    /// </summary>
    public  class SampleSingleton2
    {
        private static volatile SampleSingleton2 m_Instance = null;
        private int m_Counter = 0;
        private SampleSingleton2()
        {
            Console.WriteLine("初始化SampleSingleton2.");
        }
        public static SampleSingleton2 Singleton
        {
            get
            {
                if (m_Instance == null)
                {
                    lock (typeof(SampleSingleton2))
                    {
                        if (m_Instance == null)
                        {
                            m_Instance = new SampleSingleton2();
                        }
                    }
                }
                return m_Instance;
            }
        }
        /// <summary>
        /// 调用计数器
        /// </summary>
        public void Couter()
        {
            m_Counter++;
        }
    }

     /// <summary>
    /// 测试2种模式的效率和调用的方式
    /// </summary>

            DateTime milestone;
            int maxCallTimes= 100000000;

            // 第一次调用SampleSingleton1的Counter方法
            Console.WriteLine("第一次调用SampleSingleton1的Counter方法");
            SampleSingleton1.singleton.Counter();

            // 计算10000次调用的耗费时间
            milestone = DateTime.Now;
            for (int i = 0; i < maxCallTimes; i++)
            {
                SampleSingleton1.singleton.Counter();
            }
            Console.WriteLine(maxCallTimes.ToString() + "次调用执行时间为：" + ((TimeSpan)(DateTime.Now - milestone)).TotalMilliseconds.ToString());
            Console.WriteLine("");


            // 第一次调用SampleSingleton2的Counter方法
            Console.WriteLine("第一次调用SampleSingleton2的Counter方法");
            SampleSingleton2.Singleton.Couter();

            // 计算10000次调用的耗费时间
            milestone = DateTime.Now;
            for (int i = 0; i < maxCallTimes; i++)
            {
                SampleSingleton2.Singleton.Couter();
            }
            Console.WriteLine(maxCallTimes.ToString() + "次调用执行时间为：" + ((TimeSpan)(DateTime.Now - milestone)).TotalMilliseconds.ToString());

            string str = Console.ReadLine();
        }

 三、GitHub的地址

       https://github.com/wangtongzhou520/Designpattern