保證一個(gè)類僅有一個(gè)實(shí)例，并提供一個(gè)訪問(wèn)它的全局訪問(wèn)點(diǎn)。
在計(jì)算機(jī)系統(tǒng)中，線程池、緩存、日志對(duì)象、對(duì)話框、打印機(jī)、顯卡的驅(qū)動(dòng)程序?qū)ο蟪１辉O(shè)計(jì)成單例。

public class SingletonTest{public static void Test(){var tasks = new List<Task>();for (int i = 0; i < 20; i++){tasks.Add(new Task(() =>{Singleton singleton = Singleton.Instance();singleton.GetData();}));}//并發(fā)執(zhí)行20個(gè)任務(wù)tasks.AsParallel().ForAll(p => p.Start());}private class Singleton{/// <summary>/// 靜態(tài)實(shí)例，利用靜態(tài)字段把實(shí)例緩存起來(lái)/// </summary>private static Singleton singleton;/// <summary>/// 返回對(duì)象的唯一實(shí)例/// </summary>/// <returns></returns>public static Singleton Instance(){if (singleton == null){Console.WriteLine("實(shí)例化對(duì)象");singleton = new Singleton();}return singleton;}public void GetData(){Console.WriteLine("調(diào)用了getdata()");}} }

看下執(zhí)行結(jié)果

實(shí)例化對(duì)象動(dòng)作執(zhí)行了4次，說(shuō)明并發(fā)情況下有問(wèn)題；

改下實(shí)現(xiàn)方式,增加鎖

public static Singleton Instance(){if (singleton == null){lock (lockObj){Console.WriteLine("實(shí)例化對(duì)象");singleton = new Singleton();}}return singleton;}

看下執(zhí)行結(jié)果

依然不能保證

加鎖并雙重驗(yàn)證

public static Singleton Instance(){if (singleton == null){lock (lockObj){if (singleton == null){Console.WriteLine("實(shí)例化對(duì)象");singleton = new Singleton();}}}return singleton;}

看下執(zhí)行結(jié)果

這下就不會(huì)有并發(fā)的問(wèn)題了

轉(zhuǎn)載于:https://www.cnblogs.com/sands/p/11460249.html

總結(jié)

以上是生活随笔為你收集整理的Singleton单例模式的全部?jī)?nèi)容，希望文章能夠幫你解決所遇到的問(wèn)題。

如果覺(jué)得生活随笔網(wǎng)站內(nèi)容還不錯(cuò)，歡迎將生活随笔推薦給好友。