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class Singleton{ private static Singleton instance = new Singleton(); /// <summary> /// 构造函数声明为私有 /// </summary> private Singleton() { Console.WriteLine("执行构造函数"); } public static Singleton Get() { return instance; }}

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class Singleton{ private static Singleton instance = null; private static readonly object lockobj = new object(); /// <summary> /// 构造函数声明为私有 /// </summary> private Singleton() { Console.WriteLine("执行构造函数"); } /// <summary> /// 双检锁 /// </summary> /// <param name="owner"></param> /// <returns></returns> public static Singleton Get() { if (instance == null) { lock (lockobj) { if (instance == null) { instance = new Singleton(); } } } return instance; }}

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using System;using System.Threading;namespace Singleton{ // This Singleton implementation is called "double check lock". It is safe // in multithreaded environment and provides lazy initialization for the // Singleton object. class Singleton { private Singleton() { } private static Singleton _instance; // We now have a lock object that will be used to synchronize threads // during first access to the Singleton. private static readonly object _lock = new object(); public static Singleton GetInstance(string value) { // This conditional is needed to prevent threads stumbling over the // lock once the instance is ready. if (_instance == null) { // Now, imagine that the program has just been launched. Since // there's no Singleton instance yet, multiple threads can // simultaneously pass the previous conditional and reach this // point almost at the same time. The first of them will acquire // lock and will proceed further, while the rest will wait here. lock (_lock) { // The first thread to acquire the lock, reaches this // conditional, goes inside and creates the Singleton // instance. Once it leaves the lock block, a thread that // might have been waiting for the lock release may then // enter this section. But since the Singleton field is // already initialized, the thread won't create a new // object. if (_instance == null) { _instance = new Singleton(); _instance.Value = value; } } } return _instance; } // We'll use this property to prove that our Singleton really works. public string Value { get; set; } } class Program { static void Main(string[] args) { // The client code. Console.WriteLine( "{0}\n{1}\n\n{2}\n", "If you see the same value, then singleton was reused (yay!)", "If you see different values, then 2 singletons were created (booo!!)", "RESULT:" ); Thread process1 = new Thread(() => { TestSingleton("FOO"); }); Thread process2 = new Thread(() => { TestSingleton("BAR"); }); process1.Start(); process2.Start(); process1.Join(); process2.Join(); } public static void TestSingleton(string value) { Singleton singleton = Singleton.GetInstance(value); Console.WriteLine(singleton.Value); } }}

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FOOFOO