1. 單例模式（單線程和多線程）
2. 單例模式的三種寫法
3. 單例模式的優(yōu)缺點和應(yīng)用場景

單例保證了整個進(jìn)程中該對象只被實例化一次
常駐內(nèi)存

普通類型是需要的時候被初始化，用完被GC回收

namespace singletonpattern {/// <summary>/// 1. 私有化構(gòu)造函數(shù)，外部不能用new創(chuàng)建對象/// 2. 一個私有的靜態(tài)變量/// 3. 一個靜態(tài)的對象創(chuàng)建方法/// </summary>class Singleton{private Singleton () {Thread.Sleep(1000);//耗時string bigSize = "占用10M內(nèi)存";//耗計算資源string resource = "占用多個線程和數(shù)據(jù)庫連接資源";//耗有限資源Console.WriteLine("{0}被構(gòu)造，線程id={1}", this.GetType().Name, Thread.CurrentThread.ManagedThreadId);}private static Singleton _Singleton = null;//單進(jìn)程時候的單例//public static Singleton CreateInstance()//{// if (_Singleton == null)// {// _Singleton = new Singleton();// }// return _Singleton;//}//多進(jìn)程下的單例，雙重if+lockprivate static object Singleto_Lock = new object();public static Singleton CreateInstance(){if (_Singleton == null)//保證對象初始化之后的所有線程，不需要等待鎖 {Console.WriteLine("準(zhǔn)備進(jìn)入lock");lock (Singleto_Lock) //保證只有一個線程進(jìn)去判斷 {Thread.Sleep(1000);if (_Singleton == null) //保證對象為空才真的創(chuàng)建 {_Singleton = new Singleton();}}}return _Singleton;}public void Show(){Console.WriteLine("這里調(diào)用了{(lán)0}.Show", this.GetType().Name);}} }

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namespace singletonpattern {class SingletonSecond{private SingletonSecond() {Thread.Sleep(1000);//耗時string bigSize = "占用10M內(nèi)存";//耗計算資源string resource = "占用多個線程和數(shù)據(jù)庫連接資源";//耗有限資源Console.WriteLine("{0}被構(gòu)造，線程id={1}", this.GetType().Name, Thread.CurrentThread.ManagedThreadId);}private static SingletonSecond _Singleton = null;/// <summary>/// 靜態(tài)構(gòu)造函數(shù)：由CLR保證，在第一次使用這個類之前，調(diào)用并且只調(diào)用一次/// </summary>static SingletonSecond (){_Singleton = new SingletonSecond();}public static SingletonSecond CreateInstance(){return _Singleton;}public void Show(){Console.WriteLine("這里調(diào)用了{(lán)0}.Show", this.GetType().Name);}} } namespace singletonpattern {class SingletonThird{private SingletonThird() {Thread.Sleep(1000);//耗時string bigSize = "占用10M內(nèi)存";//耗計算資源string resource = "占用多個線程和數(shù)據(jù)庫連接資源";//耗有限資源Console.WriteLine("{0}被構(gòu)造，線程id={1}", this.GetType().Name, Thread.CurrentThread.ManagedThreadId);}/// <summary>/// 靜態(tài)變量：會在類型第一次使用的時候初始化，并且只初始化一次/// </summary>private static SingletonThird _Singleton = new SingletonThird();public static SingletonThird CreateInstance(){return _Singleton;}public void Show(){Console.WriteLine("這里調(diào)用了{(lán)0}.Show", this.GetType().Name);}} }

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轉(zhuǎn)載于:https://www.cnblogs.com/xiao9426926/p/6126224.html

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