今天继续百无聊赖。
许多公司在招人的时候都会要求写一个singleton，我觉得这个本身就蛮可笑的。这个有啥写的，不会的人看5分钟都背出来了。
一般这么写会让你通过。
public sealed class Singleton
{
static Singleton instance=null;
Singleton()
{
}
public static Singleton Instance
{
get
{
if (instance==null)
{
instance = new Singleton();
}
return instance;
}
}
}
但是多线程的时候这个会有多个实例出来的。
所以比较好的还是用下面这个，我把test page和class包括了，还有点注释。我喜欢用page而不是console做test，呵呵。
参考了：
http://www.aspcool.com/lanmu/browse1.asp?ID=1138&bbsuser=csharp
这个作者还有另外一种实现，但是我觉得lazy instantiation还要客户端去单独写代码保证线程同步是有问题的。最好还是在singlton类内部做。
using System;
using System.Threading;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
public partial class Design_Pattern_Singleton : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
Thread thread0 = Thread.CurrentThread;
thread0.Name = "Thread 0";
Thread thread1 = new Thread(new ThreadStart(this.DoSomeWork));
thread1.Name = "Thread 1";
Thread thread2 = new Thread(new ThreadStart(this.DoSomeWork));
thread2.Name = "Thread 2";
Thread thread3 = new Thread(new ThreadStart(this.DoSomeWork));
thread3.Name = "Thread 3";
thread1.Start();
thread2.Start();
thread3.Start();
DoSomeWork(); // thread0 do the same work
}
public void DoSomeWork()
{
MySingleton mySingleton = MySingleton.GetInstance();
for (int i = 1; i < 5; i++)
{
mySingleton.Add();
Response.Write("Thread" + Thread.CurrentThread.Name.ToString() + "report: the current counter number is " + mySingleton.GetNumber().ToString() + "<br>");
}
}
}
public class MySingleton
{
private MySingleton() { }//it is must for a singleton
private int totalNum = 0;//for test in test page.
private static MySingleton mySingleton = new MySingleton();//that means early instantiation, it's safe for multi-thread
//client get the instance by this method
public static MySingleton GetInstance()
{
return mySingleton;
}
// add the value by 1
public void Add()
{
totalNum++;
}
//get the count number, for test in test page.
public int GetNumber()
{
return totalNum;
}
}
