{"id":100,"date":"2008-03-04T15:53:05","date_gmt":"2008-03-04T15:53:05","guid":{"rendered":""},"modified":"2008-03-04T15:53:05","modified_gmt":"2008-03-04T15:53:05","slug":"100","status":"publish","type":"post","link":"https:\/\/www.poloo.org\/?p=100","title":{"rendered":"\u5355\u4f8b\u6a21\u5f0f(Singleton Pattern)"},"content":{"rendered":"

\u4e00\u3001 \u5355\u4f8b\uff08Singleton\uff09\u6a21\u5f0f
\u5355\u4f8b\u6a21\u5f0f\u7684\u7279\u70b9\uff1a<\/p>\n

\u5355\u4f8b\u7c7b\u53ea\u80fd\u6709\u4e00\u4e2a\u5b9e\u4f8b\u3002
\u5355\u4f8b\u7c7b\u5fc5\u987b\u81ea\u5df1\u521b\u5efa\u81ea\u5df1\u7684\u552f\u4e00\u5b9e\u4f8b\u3002
\u5355\u4f8b\u7c7b\u5fc5\u987b\u7ed9\u6240\u6709\u5176\u5b83\u5bf9\u8c61\u63d0\u4f9b\u8fd9\u4e00\u5b9e\u4f8b\u3002
\u5355\u4f8b\u6a21\u5f0f\u5e94\u7528\uff1a<\/p>\n

\u6bcf\u53f0\u8ba1\u7b97\u673a\u53ef\u4ee5\u6709\u82e5\u5e72\u4e2a\u6253\u5370\u673a\uff0c\u4f46\u53ea\u80fd\u6709\u4e00\u4e2aPrinter Spooler\uff0c\u907f\u514d\u4e24\u4e2a\u6253\u5370\u4f5c\u4e1a\u540c\u65f6\u8f93\u51fa\u5230\u6253\u5370\u673a\u3002
\u4e00\u4e2a\u5177\u6709\u81ea\u52a8\u7f16\u53f7\u4e3b\u952e\u7684\u8868\u53ef\u4ee5\u6709\u591a\u4e2a\u7528\u6237\u540c\u65f6\u4f7f\u7528\uff0c\u4f46\u6570\u636e\u5e93\u4e2d\u53ea\u80fd\u6709\u4e00\u4e2a\u5730\u65b9\u5206\u914d\u4e0b\u4e00\u4e2a\u4e3b\u952e\u7f16\u53f7\u3002\u5426\u5219\u4f1a\u51fa\u73b0\u4e3b\u952e\u91cd\u590d\u3002 <\/p>\n

\u4e8c\u3001 Singleton\u6a21\u5f0f\u7684\u7ed3\u6784\uff1a

Singleton\u6a21\u5f0f\u5305\u542b\u7684\u89d2\u8272\u53ea\u6709\u4e00\u4e2a\uff0c\u5c31\u662fSingleton\u3002Singleton\u62e5\u6709\u4e00\u4e2a\u79c1\u6709\u6784\u9020\u51fd\u6570\uff0c\u786e\u4fdd\u7528\u6237\u65e0\u6cd5\u901a\u8fc7new\u76f4\u63a5\u5b9e\u4f8b\u5b83\u3002\u9664\u6b64\u4e4b\u5916\uff0c\u8be5\u6a21\u5f0f\u4e2d\u5305\u542b\u4e00\u4e2a\u9759\u6001\u79c1\u6709\u6210\u5458\u53d8\u91cfinstance\u4e0e\u9759\u6001\u516c\u6709\u65b9\u6cd5Instance()\u3002Instance\u65b9\u6cd5\u8d1f\u8d23\u68c0\u9a8c\u5e76\u5b9e\u4f8b\u5316\u81ea\u5df1\uff0c\u7136\u540e\u5b58\u50a8\u5728\u9759\u6001\u6210\u5458\u53d8\u91cf\u4e2d\uff0c\u4ee5\u786e\u4fdd\u53ea\u6709\u4e00\u4e2a\u5b9e\u4f8b\u88ab\u521b\u5efa\u3002\uff08\u5173\u4e8e\u7ebf\u7a0b\u95ee\u9898\u4ee5\u53caC#\u6240\u7279\u6709\u7684Singleton\u5c06\u5728\u540e\u9762\u8be6\u7ec6\u8bba\u8ff0\uff09\u3002<\/p>\n

\u4e09\u3001 \u7a0b\u5e8f\u4e3e\u4f8b\uff1a
\u8be5\u7a0b\u5e8f\u6f14\u793a\u4e86Singleton\u7684\u7ed3\u6784\uff0c\u672c\u8eab\u4e0d\u5177\u6709\u4efb\u4f55\u5b9e\u9645\u4ef7\u503c\u3002
\/\/ Singleton pattern -- Structural example  
using System;<\/p>\n

\/\/ \"Singleton\"
class Singleton
{
  \/\/ Fields
  private static Singleton instance;<\/p>\n

  \/\/ Constructor
  protected Singleton() {}<\/p>\n

  \/\/ Methods
  public static Singleton Instance()
  {
    \/\/ Uses \"Lazy initialization\"
    if( instance == null )
      instance = new Singleton();<\/p>\n

    return instance;
  }
}<\/p>\n

\/**\/\/\/\/ <summary>
\/\/\/ Client test
\/\/\/ <\/summary>
public class Client
{
  public static void Main()
  {
    \/\/ Constructor is protected -- cannot use new
    Singleton s1 = Singleton.Instance();
    Singleton s2 = Singleton.Instance();<\/p>\n

    if( s1 == s2 )
      Console.WriteLine( \"The same instance\" );
  }
}
<\/code><\/p>\n

\u56db\u3001 \u5728\u4ec0\u4e48\u60c5\u5f62\u4e0b\u4f7f\u7528\u5355\u4f8b\u6a21\u5f0f\uff1a
\u4f7f\u7528Singleton\u6a21\u5f0f\u6709\u4e00\u4e2a\u5fc5\u8981\u6761\u4ef6\uff1a\u5728\u4e00\u4e2a\u7cfb\u7edf\u8981\u6c42\u4e00\u4e2a\u7c7b\u53ea\u6709\u4e00\u4e2a\u5b9e\u4f8b\u65f6\u624d\u5e94\u5f53\u4f7f\u7528\u5355\u4f8b\u6a21\u5f0f\u3002\u53cd\u8fc7\u6765\uff0c\u5982\u679c\u4e00\u4e2a\u7c7b\u53ef\u4ee5\u6709\u51e0\u4e2a\u5b9e\u4f8b\u5171\u5b58\uff0c\u5c31\u4e0d\u8981\u4f7f\u7528\u5355\u4f8b\u6a21\u5f0f\u3002<\/p>\n

\u6ce8\u610f\uff1a<\/p>\n

\u4e0d\u8981\u4f7f\u7528\u5355\u4f8b\u6a21\u5f0f\u5b58\u53d6\u5168\u5c40\u53d8\u91cf\u3002\u8fd9\u8fdd\u80cc\u4e86\u5355\u4f8b\u6a21\u5f0f\u7684\u7528\u610f\uff0c\u6700\u597d\u653e\u5230\u5bf9\u5e94\u7c7b\u7684\u9759\u6001\u6210\u5458\u4e2d\u3002<\/p>\n

\u4e0d\u8981\u5c06\u6570\u636e\u5e93\u8fde\u63a5\u505a\u6210\u5355\u4f8b\uff0c\u56e0\u4e3a\u4e00\u4e2a\u7cfb\u7edf\u53ef\u80fd\u4f1a\u4e0e\u6570\u636e\u5e93\u6709\u591a\u4e2a\u8fde\u63a5\uff0c\u5e76\u4e14\u5728\u6709\u8fde\u63a5\u6c60\u7684\u60c5\u51b5\u4e0b\uff0c\u5e94\u5f53\u5c3d\u53ef\u80fd\u53ca\u65f6\u91ca\u653e\u8fde\u63a5\u3002Singleton\u6a21\u5f0f\u7531\u4e8e\u4f7f\u7528\u9759\u6001\u6210\u5458\u5b58\u50a8\u7c7b\u5b9e\u4f8b\uff0c\u6240\u4ee5\u53ef\u80fd\u4f1a\u9020\u6210\u8d44\u6e90\u65e0\u6cd5\u53ca\u65f6\u91ca\u653e\uff0c\u5e26\u6765\u95ee\u9898\u3002<\/p>\n

\u4e94\u3001 Singleton\u6a21\u5f0f\u5728\u5b9e\u9645\u7cfb\u7edf\u4e2d\u7684\u5b9e\u73b0
\u4e0b\u9762\u8fd9\u6bb5Singleton\u4ee3\u7801\u6f14\u793a\u4e86\u8d1f\u8f7d\u5747\u8861\u5bf9\u8c61\u3002\u5728\u8d1f\u8f7d\u5747\u8861\u6a21\u578b\u4e2d\uff0c\u6709\u591a\u53f0\u670d\u52a1\u5668\u53ef\u63d0\u4f9b\u670d\u52a1\uff0c\u4efb\u52a1\u5206\u914d\u5668\u968f\u673a\u6311\u9009\u4e00\u53f0\u670d\u52a1\u5668\u63d0\u4f9b\u670d\u52a1\uff0c\u4ee5\u786e\u4fdd\u4efb\u52a1\u5747\u8861\uff08\u5b9e\u9645\u60c5\u51b5\u6bd4\u8fd9\u4e2a\u590d\u6742\u7684\u591a\uff09\u3002\u8fd9\u91cc\uff0c\u4efb\u52a1\u5206\u914d\u5b9e\u4f8b\u53ea\u80fd\u6709\u4e00\u4e2a\uff0c\u8d1f\u8d23\u6311\u9009\u670d\u52a1\u5668\u5e76\u5206\u914d\u4efb\u52a1\u3002
\/\/ Singleton pattern -- Real World example  <\/p>\n

using System;
using System.Collections;
using System.Threading;<\/p>\n

\/\/ \"Singleton\"
class LoadBalancer
{
  \/\/ Fields
  private static LoadBalancer balancer;
  private ArrayList servers = new ArrayList();
  private Random random = new Random();<\/p>\n

  \/\/ Constructors (protected)
  protected LoadBalancer()
  {
    \/\/ List of available servers
    servers.Add( \"ServerI\" );
    servers.Add( \"ServerII\" );
    servers.Add( \"ServerIII\" );
    servers.Add( \"ServerIV\" );
    servers.Add( \"ServerV\" );
  }<\/p>\n

  \/\/ Methods
  public static LoadBalancer GetLoadBalancer()
  {
    \/\/ Support multithreaded applications through
    \/\/ \"Double checked locking\" pattern which avoids
    \/\/ locking every time the method is invoked
    if( balancer == null )
    {
      \/\/ Only one thread can obtain a mutex
      Mutex mutex = new Mutex();
      mutex.WaitOne();<\/p>\n

      if( balancer == null )
        balancer = new LoadBalancer();<\/p>\n

      mutex.Close();
    }
    return balancer;
  }<\/p>\n

  \/\/ Properties
  public string Server
  {
    get
    {
      \/\/ Simple, but effective random load balancer
      int r = random.Next( servers.Count );
      return servers[ r ].ToString();
    }
  }
}<\/p>\n

\/**\/\/\/\/ <summary>
\/\/\/ SingletonApp test
\/\/\/ <\/summary>
\/\/\/
public class SingletonApp
{
  public static void Main( string[] args )
  {
    LoadBalancer b1 = LoadBalancer.GetLoadBalancer();
    LoadBalancer b2 = LoadBalancer.GetLoadBalancer();
    LoadBalancer b3 = LoadBalancer.GetLoadBalancer();
    LoadBalancer b4 = LoadBalancer.GetLoadBalancer();<\/p>\n

    \/\/ Same instance?
    if( (b1 == b2) && (b2 == b3) && (b3 == b4) )
      Console.WriteLine( \"Same instance\" );<\/p>\n

    \/\/ Do the load balancing
    Console.WriteLine( b1.Server );
    Console.WriteLine( b2.Server );
    Console.WriteLine( b3.Server );
    Console.WriteLine( b4.Server );
  }
}
[\/cdoe]<\/p>\n

\u516d\u3001 C#\u4e2d\u7684Singleton\u6a21\u5f0f
C#\u7684\u72ec\u7279\u8bed\u8a00\u7279\u6027\u51b3\u5b9a\u4e86C#\u62e5\u6709\u5b9e\u73b0Singleton\u6a21\u5f0f\u7684\u72ec\u7279\u65b9\u6cd5\u3002\u8fd9\u91cc\u4e0d\u518d\u8d58\u8ff0\u539f\u56e0\uff0c\u7ed9\u51fa\u51e0\u4e2a\u7ed3\u679c\uff1a<\/p>\n

\u65b9\u6cd5\u4e00\uff1a<\/p>\n

\u4e0b\u9762\u662f\u5229\u7528.NET Framework\u5e73\u53f0\u4f18\u52bf\u5b9e\u73b0Singleton\u6a21\u5f0f\u7684\u4ee3\u7801\uff1a
[code]sealed class Singleton
{
   private Singleton();
   public static readonly Singleton Instance=new Singleton();
}
<\/code><\/p>\n

\u8fd9\u4f7f\u5f97\u4ee3\u7801\u51cf\u5c11\u4e86\u8bb8\u591a\uff0c\u540c\u65f6\u4e5f\u89e3\u51b3\u4e86\u7ebf\u7a0b\u95ee\u9898\u5e26\u6765\u7684\u6027\u80fd\u4e0a\u635f\u5931\u3002\u90a3\u4e48\u5b83\u53c8\u662f\u600e\u6837\u5de5\u4f5c\u7684\u5462\uff1f<\/p>\n

\u6ce8\u610f\u5230\uff0cSingleton\u7c7b\u88ab\u58f0\u660e\u4e3asealed\uff0c\u4ee5\u6b64\u4fdd\u8bc1\u5b83\u81ea\u5df1\u4e0d\u4f1a\u88ab\u7ee7\u627f\uff0c\u5176\u6b21\u6ca1\u6709\u4e86Instance\u7684\u65b9\u6cd5\uff0c\u5c06\u539f\u6765_instance\u6210\u5458\u53d8\u91cf\u53d8\u6210public readonly\uff0c\u5e76\u5728\u58f0\u660e\u65f6\u88ab\u521d\u59cb\u5316\u3002\u901a\u8fc7\u8fd9\u4e9b\u6539\u53d8\uff0c\u6211\u4eec\u786e\u5b9e\u5f97\u5230\u4e86Singleton\u7684\u6a21\u5f0f\uff0c\u539f\u56e0\u662f\u5728JIT\u7684\u5904\u7406\u8fc7\u7a0b\u4e2d\uff0c\u5982\u679c\u7c7b\u4e2d\u7684static\u5c5e\u6027\u88ab\u4efb\u4f55\u65b9\u6cd5\u4f7f\u7528\u65f6\uff0c.NET Framework\u5c06\u5bf9\u8fd9\u4e2a\u5c5e\u6027\u8fdb\u884c\u521d\u59cb\u5316\uff0c\u4e8e\u662f\u5728\u521d\u59cb\u5316Instance\u5c5e\u6027\u7684\u540c\u65f6Singleton\u7c7b\u5b9e\u4f8b\u5f97\u4ee5\u521b\u5efa\u548c\u88c5\u8f7d\u3002\u800c\u79c1\u6709\u7684\u6784\u9020\u51fd\u6570\u548creadonly(\u53ea\u8bfb)\u4fdd\u8bc1\u4e86Singleton\u4e0d\u4f1a\u88ab\u518d\u6b21\u5b9e\u4f8b\u5316\uff0c\u8fd9\u6b63\u662fSingleton\u8bbe\u8ba1\u6a21\u5f0f\u7684\u610f\u56fe\u3002<\/p>\n

\u4e0d\u8fc7\u8fd9\u4e5f\u5e26\u6765\u4e86\u4e00\u4e9b\u95ee\u9898\uff0c\u6bd4\u5982\u65e0\u6cd5\u7ee7\u627f\uff0c\u5b9e\u4f8b\u5728\u7a0b\u5e8f\u4e00\u8fd0\u884c\u5c31\u88ab\u521d\u59cb\u5316\uff0c\u65e0\u6cd5\u5b9e\u73b0\u5ef6\u8fdf\u521d\u59cb\u5316\u7b49\u3002<\/p>\n

\u8be6\u7ec6\u60c5\u51b5\u53ef\u4ee5\u53c2\u8003\u5fae\u8f6fMSDN\u6587\u7ae0\uff1a\u300aExploring the Singleton Design Pattern\u300b<\/p>\n

\u65b9\u6cd5\u4e8c\uff1a<\/p>\n

\u65e2\u7136\u65b9\u6cd5\u4e00\u5b58\u5728\u95ee\u9898\uff0c\u6211\u4eec\u8fd8\u6709\u5176\u5b83\u529e\u6cd5\u3002

public sealed class Singleton
{
  Singleton()
  {
  }<\/p>\n

  public static Singleton GetInstance()
  {
    return Nested.instance;
  }
    
  class Nested
  {
    \/\/ Explicit static constructor to tell C# compiler
    \/\/ not to mark type as beforefieldinit
    static Nested()
    {
    }<\/p>\n

    internal static readonly Singleton instance = new Singleton();
  }
}
<\/code><\/p>\n

\u8fd9\u5b9e\u73b0\u4e86\u5ef6\u8fdf\u521d\u59cb\u5316\uff0c\u5e76\u5177\u6709\u5f88\u591a\u4f18\u52bf\uff0c\u5f53\u7136\u4e5f\u5b58\u5728\u4e00\u4e9b\u7f3a\u70b9\u3002\u8be6\u7ec6\u5185\u5bb9\u8bf7\u8bbf\u95ee\uff1a\u300aImplementing the Singleton Pattern in C#\u300b<\/a>\u3002\u6587\u7ae0\u5305\u542b\u4e94\u79cdSingleton\u5b9e\u73b0\uff0c\u5c31\u6a21\u5f0f\u3001\u7ebf\u7a0b\u3001\u6548\u7387\u3001\u5ef6\u8fdf\u521d\u59cb\u5316\u7b49\u5f88\u591a\u65b9\u9762\u8fdb\u884c\u4e86\u8be6\u7ec6\u8bba\u8ff0\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"

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