單例模式(singleton)，模式(singleton)

單例模式(singleton)，模式(singleton)

1. 使用場景　　　　

　　來著stackorverflow　　

• controls concurrent access to a shared resource.
• access to the resource will be requested from multiple, disparate parts of the system.
• there can be only one object.
• from (http://stackoverflow.com/questions/228164/on-design-patterns-when-to-use-the-singleton)

2. 簡單模式

public class BaseSingle
{
　　public void Method()
　　{
　　　　Console.WriteLine("{1}.Method:{0}", this.GetHashCode(),this.GetType().ToString());
　　}
}

public class UnsafeSingle : BaseSingle
{

private static UnsafeSingle _single;

public static UnsafeSingle UnsafeSingleInstatce()
{
　　if (null == _single)
　　　　_single = new UnsafeSingle();

　　return _single;
}

private UnsafeSingle()
{
　　Console.WriteLine(DateTime.Now.ToString() + ": 構造函數！");
}

}

缺點：對象未創建時，多線程同時訪問返回的對象並非一個；

測試代碼如下：

internal delegate void InstanceFun();

public void GetInstatnce()
{
　　UnsafeSingle.UnsafeSingleInstatce().Method();
}

public void MutilThreadTest(InstanceFun instanceFun)
{
　　var started = DateTime.Now;
　　Thread[] threads = new Thread[100];

for (var index = 0; index < 100; index++)
{
　　Thread thread = new Thread(new ThreadStart(instanceFun));
　　threads[index] = thread;
}

　　foreach (var thread in threads)
　　{
　　　　thread.Start();
　　}
　　Console.WriteLine("運行時長：{0};僅臨時測試", (DateTime.Now - started).Milliseconds);
}

　　測試結果：　　

DesignPattern.UnsafeSingle.Method:45338574
DesignPattern.UnsafeSingle.Method:30944461
DesignPattern.UnsafeSingle.Method:62452338
DesignPattern.UnsafeSingle.Method:43921088
DesignPattern.UnsafeSingle.Method:18573725
DesignPattern.UnsafeSingle.Method:8935080
DesignPattern.UnsafeSingle.Method:48823647
DesignPattern.UnsafeSingle.Method:28613802
DesignPattern.UnsafeSingle.Method:40642054
DesignPattern.UnsafeSingle.Method:52962918
DesignPattern.UnsafeSingle.Method:29095347
DesignPattern.UnsafeSingle.Method:62694277
DesignPattern.UnsafeSingle.Method:54643837
DesignPattern.UnsafeSingle.Method:36302867
DesignPattern.UnsafeSingle.Method:49913678
DesignPattern.UnsafeSingle.Method:52482287
DesignPattern.UnsafeSingle.Method:41829035
DesignPattern.UnsafeSingle.Method:57978397
DesignPattern.UnsafeSingle.Method:13456355
DesignPattern.UnsafeSingle.Method:23736788
DesignPattern.UnsafeSingle.Method:42195492
DesignPattern.UnsafeSingle.Method:28113429
DesignPattern.UnsafeSingle.Method:2875151
DesignPattern.UnsafeSingle.Method:56858914
DesignPattern.UnsafeSingle.Method:2735313
DesignPattern.UnsafeSingle.Method:50717245
DesignPattern.UnsafeSingle.Method:30697644
DesignPattern.UnsafeSingle.Method:47515266
DesignPattern.UnsafeSingle.Method:30183720
DesignPattern.UnsafeSingle.Method:65195544
DesignPattern.UnsafeSingle.Method:22695823
DesignPattern.UnsafeSingle.Method:8561069
DesignPattern.UnsafeSingle.Method:33135541
DesignPattern.UnsafeSingle.Method:17719913
DesignPattern.UnsafeSingle.Method:32493892
DesignPattern.UnsafeSingle.Method:57339132
DesignPattern.UnsafeSingle.Method:38516275
DesignPattern.UnsafeSingle.Method:33858004
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
DesignPattern.UnsafeSingle.Method:58042889
運行時長：115
DesignPattern.UnsafeSingle.Method:58042889

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