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Add Singleton implementation.
1 parent 7465f32 commit 5b52425

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+304
-16
lines changed

‎Singleton/Participants.txt

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‎Singleton/Program.OptimizedCode.cs

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using System;
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using System.Collections.Generic;
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/// <summary>
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/// The.NET optimized code demonstrates the same code as above but uses more modern, built-in .NET features.
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/// Here an elegant .NET specific solution is offered.The Singleton pattern simply uses a private constructor
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/// and a static readonly instance variable that is lazily initialized.Thread safety is guaranteed by the compiler.
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/// </summary>
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namespace DoFactory.GangOfFour.Singleton.NETOptimized
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{
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/// <summary>
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/// MainApp startup class for .NET optimized
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/// Singleton Design Pattern.
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/// </summary>
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class MainApp
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{
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/// <summary>
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/// Entry point into console application.
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/// </summary>
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static void Main()
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{
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LoadBalancer b1 = LoadBalancer.GetLoadBalancer();
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LoadBalancer b2 = LoadBalancer.GetLoadBalancer();
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LoadBalancer b3 = LoadBalancer.GetLoadBalancer();
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LoadBalancer b4 = LoadBalancer.GetLoadBalancer();
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// Confirm these are the same instance
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if (b1 == b2 && b2 == b3 && b3 == b4)
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{
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Console.WriteLine("Same instance\n");
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}
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// Next, load balance 15 requests for a server
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LoadBalancer balancer = LoadBalancer.GetLoadBalancer();
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for (int i = 0; i < 15; i++)
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{
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string serverName = balancer.NextServer.Name;
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Console.WriteLine("Dispatch request to: " + serverName);
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}
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// Wait for user
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Console.ReadKey();
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}
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}
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/// <summary>
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/// The 'Singleton' class
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/// </summary>
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sealed class LoadBalancer
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{
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// Static members are 'eagerly initialized', that is,
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// immediately when class is loaded for the first time.
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// .NET guarantees thread safety for static initialization
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private static readonly LoadBalancer _instance =
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new LoadBalancer();
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// Type-safe generic list of servers
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private List<Server> _servers;
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private Random _random = new Random();
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// Note: constructor is 'private'
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private LoadBalancer()
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{
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// Load list of available servers
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_servers = new List<Server>
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{
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new Server{ Name = "ServerI", IP = "120.14.220.18" },
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new Server{ Name = "ServerII", IP = "120.14.220.19" },
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new Server{ Name = "ServerIII", IP = "120.14.220.20" },
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new Server{ Name = "ServerIV", IP = "120.14.220.21" },
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new Server{ Name = "ServerV", IP = "120.14.220.22" },
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};
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}
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public static LoadBalancer GetLoadBalancer()
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{
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return _instance;
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}
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// Simple, but effective load balancer
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public Server NextServer
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{
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get
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{
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int r = _random.Next(_servers.Count);
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return _servers[r];
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}
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}
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}
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/// <summary>
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/// Represents a server machine
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/// </summary>
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class Server
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{
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// Gets or sets server name
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public string Name { get; set; }
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// Gets or sets server IP address
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public string IP { get; set; }
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}
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}
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//Output
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//Same instance
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//ServerIV
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//ServerIV
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//ServerIII
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//ServerV
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//ServerII
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//ServerV
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//ServerII
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//ServerII
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//ServerI
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//ServerIV
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//ServerIV
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//ServerII
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//ServerI
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//ServerV
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//ServerIV

‎Singleton/Program.RealWorldCode.cs

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using System;
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using System.Collections.Generic;
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using System.Threading;
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namespace DoFactory.GangOfFour.Singleton.RealWorld
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{
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/// <summary>
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/// MainApp startup class for Real-World
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/// Singleton Design Pattern.
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/// </summary>
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class MainApp
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{
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/// <summary>
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/// Entry point into console application.
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/// </summary>
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static void Main()
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{
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LoadBalancer b1 = LoadBalancer.GetLoadBalancer();
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LoadBalancer b2 = LoadBalancer.GetLoadBalancer();
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LoadBalancer b3 = LoadBalancer.GetLoadBalancer();
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LoadBalancer b4 = LoadBalancer.GetLoadBalancer();
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// Same instance?
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if (b1 == b2 && b2 == b3 && b3 == b4)
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{
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Console.WriteLine("Same instance\n");
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}
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// Load balance 15 server requests
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LoadBalancer balancer = LoadBalancer.GetLoadBalancer();
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for (int i = 0; i < 15; i++)
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{
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string server = balancer.Server;
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Console.WriteLine("Dispatch Request to: " + server);
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}
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// Wait for user
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Console.ReadKey();
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}
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}
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/// <summary>
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/// The 'Singleton' class
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/// </summary>
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class LoadBalancer
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{
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private static LoadBalancer _instance;
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private List<string> _servers = new List<string>();
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private Random _random = new Random();
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// Lock synchronization object
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private static object syncLock = new object();
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// Constructor (protected)
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protected LoadBalancer()
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{
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// List of available servers
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_servers.Add("ServerI");
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_servers.Add("ServerII");
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_servers.Add("ServerIII");
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_servers.Add("ServerIV");
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_servers.Add("ServerV");
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}
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public static LoadBalancer GetLoadBalancer()
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{
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// Support multithreaded applications through
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// 'Double checked locking' pattern which (once
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// the instance exists) avoids locking each
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// time the method is invoked
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if (_instance == null)
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{
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lock (syncLock)
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{
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if (_instance == null)
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{
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_instance = new LoadBalancer();
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}
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}
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}
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return _instance;
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}
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// Simple, but effective random load balancer
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public string Server
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{
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get
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{
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int r = _random.Next(_servers.Count);
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return _servers[r].ToString();
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}
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}
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}
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}
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//Output
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//Same instance
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//ServerIII
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//ServerII
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//ServerI
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//ServerII
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//ServerI
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//ServerIII
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//ServerI
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//ServerIII
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//ServerIV
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//ServerII
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//ServerII
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//ServerIII
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//ServerIV
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//ServerII
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//ServerIV

‎Singleton/Program.Structural.cs

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using System;
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namespace DoFactory.GangOfFour.Singleton.Structural
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{
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/// <summary>
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/// MainApp startup class for Structural
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/// Singleton Design Pattern.
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/// </summary>
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class MainApp
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{
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/// <summary>
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/// Entry point into console application.
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/// </summary>
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static void Main()
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{
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// Constructor is protected -- cannot use new
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Singleton s1 = Singleton.Instance();
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Singleton s2 = Singleton.Instance();
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// Test for same instance
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if (s1 == s2)
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{
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Console.WriteLine("Objects are the same instance");
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}
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// Wait for user
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Console.ReadKey();
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}
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}
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/// <summary>
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/// The 'Singleton' class
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/// </summary>
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class Singleton
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{
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private static Singleton _instance;
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// Constructor is 'protected'
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protected Singleton()
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{
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}
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public static Singleton Instance()
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{
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// Uses lazy initialization.
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// Note: this is not thread safe.
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if (_instance == null)
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{
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_instance = new Singleton();
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}
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return _instance;
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}
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}
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}
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//Output
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//Objects are the same instance

‎Singleton/Program.cs

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This file was deleted.

‎Singleton/Singleton.csproj

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<Reference Include="System.Xml" />
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</ItemGroup>
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<ItemGroup>
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<Compile Include="Program.cs" />
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<Compile Include="Program.OptimizedCode.cs" />
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<Compile Include="Program.RealWorldCode.cs" />
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<Compile Include="Program.Structural.cs" />
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<Compile Include="Properties\AssemblyInfo.cs" />
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</ItemGroup>
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<ItemGroup>
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<None Include="App.config" />
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</ItemGroup>
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<ItemGroup>
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<Content Include="Participants.txt" />
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<Content Include="singleton.gif" />
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</ItemGroup>
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<Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
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<!-- To modify your build process, add your task inside one of the targets below and uncomment it.
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Other similar extension points exist, see Microsoft.Common.targets.

‎Singleton/singleton.gif

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