单例模式的核心思想就是保证内存中存在一个实例
适用场景：多次及重复的调用类的实例，做重复的内容；全局管理及调用；提高效率的时候；
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace ConsoleApplication5 { /// <summary> /// 饿汉模式，类装载中完成实例化， /// 1.避免出现多线程多次构造 /// 2.不调用会造成资源浪费 /// /// </summary> class Singleton { public long Result { get; private set; } public Singleton() { for(int i = 0; i < 10000000; i++) { Result += i; } Console.WriteLine("构造函数 执行"); } ~Singleton() { Console.WriteLine("析构函数"); } private static Singleton _Instance = new Singleton(); public static Singleton Instance { get { return _Instance; } } public void Dispose() { if (_Instance != null) { _Instance = null; Console.WriteLine("销毁"); } } } /// <summary> /// 饿汉模式，静态构造里完成实例化 /// 1.避免出现多线程多次构造 /// 2.不调用会造成资源浪费 /// /// </summary> class Singleton2 { public long Result { get; private set; } public Singleton2() { for (int i = 0; i < 10000000; i++) { Result += i; } Console.WriteLine("构造函数 执行"); } ~Singleton2() { Console.WriteLine("析构函数"); } private static Singleton2 _Instance = null; static Singleton2() { _Instance = new Singleton2(); } public static Singleton2 Instance { get { return _Instance; } } public void Dispose() { if (_Instance != null) { _Instance = null; Console.WriteLine("销毁"); } } } /// <summary> /// 懒汉模式，调用的时候实例化 /// 1.适用与单线程，不适合多线程，出现多次构造实力 /// 180，254 /// </summary> class Singleton3 { public long Result { get; private set; } public Singleton3() { for (int i = 0; i < 10000000; i++) { Result += i; } Console.WriteLine("构造函数 执行"); } ~Singleton3() { Console.WriteLine("析构函数"); } private static Singleton3 _Instance = null; public static Singleton3 Instance { get { if(_Instance == null) { _Instance = new Singleton3(); } return _Instance; } } public void Dispose() { if(_Instance != null) { _Instance = null; Console.WriteLine("销毁"); } } } /// <summary> /// 懒汉模式，双重检测，经典方法 /// </summary> class Singleton4 { public long Result { get; private set; } public Singleton4() { for (int i = 0; i < 10000000; i++) { Result += i; } Console.WriteLine("构造函数 执行"); } ~Singleton4() { Console.WriteLine("析构函数"); } private static Singleton4 _Instance = null; private static object _testLock = new object(); public static Singleton4 Instance { get { if (_Instance == null)//所有的并发线程进入这里检测 { lock (_testLock)//锁住一个线程，其他线程等待 { if (_Instance == null)//第一个进入的线程开始创建实例，其他线程进入后需要检测是否已经创建过 { _Instance = new Singleton4(); } } } return _Instance; } } public void Dispose() { if (_Instance != null) { _Instance = null; Console.WriteLine("销毁"); } } } } 客户端测试 Console.WriteLine("-------------------------------------------------单线程分割线------------------------------------------------------"); Stopwatch watch = new Stopwatch(); watch.Start(); for (int i = 0; i < 100; i++) { Console.WriteLine("ID{0} Result {1},Thread {2}", i, Singleton4.Instance.Result, Thread.CurrentThread.ManagedThreadId); } watch.Stop(); Console.WriteLine("单线程中的单例耗时：{0}",watch.ElapsedMilliseconds); Singleton3.Instance.Dispose(); GC.Collect(); Console.WriteLine("-------------------------------------------------多线程分割线------------------------------------------------------"); Stopwatch watch2 = new Stopwatch(); watch2.Start(); List<Task> taskList = new List<Task>(); TaskFactory taskFactory = new TaskFactory(); for (int i = 0; i < 100; i++) { taskList.Add(taskFactory.StartNew(() => { Console.WriteLine("ID{0} Result {1},Thread {2}", i, Singleton4.Instance.Result, Thread.CurrentThread.ManagedThreadId); })); } Task.WaitAll(taskList.ToArray()); watch2.Stop(); Console.WriteLine("多线程中的单例耗时：{0}", watch2.ElapsedMilliseconds);
