using System;
using System.Collections.Generic;
namespace Patterns
{
class MainApp
{
static void Main()
{
LoadBalancer b1 = LoadBalancer.GetLoadBalancer();
LoadBalancer b2 = LoadBalancer.GetLoadBalancer();
LoadBalancer b3 = LoadBalancer.GetLoadBalancer();
LoadBalancer b4 = LoadBalancer.GetLoadBalancer();
// Confirm these are the same instance
if (b1 == b2 && b2 == b3 && b3 == b4)
{
Console.WriteLine("Same instance\n");
}
// Next, load balance 15 requests for a server
LoadBalancer balancer = LoadBalancer.GetLoadBalancer();
for (int i = 0; i < 15; i++)
{
string serverName = balancer.NextServer.Name;
Console.WriteLine("Dispatch request to: " + serverName);
}
// Wait for user
Console.ReadKey();
}
}
/// <summary>
/// The 'Singleton' class
/// </summary>
sealed class LoadBalancer
{
// Static members are 'eagerly initialized', that is,
// immediately when class is loaded for the first time.
// .NET guarantees thread safety for static initialization
private static readonly LoadBalancer _instance =
new LoadBalancer();
// Type-safe generic list of servers
private List<Server> _servers;
private Random _random = new Random();
// Note: constructor is 'private'
private LoadBalancer()
{
// Load list of available servers
_servers = new List<Server>
{
new Server{ Name = "ServerI", IP = "120.14.220.18" },
new Server{ Name = "ServerII", IP = "120.14.220.19" },
new Server{ Name = "ServerIII", IP = "120.14.220.20" },
new Server{ Name = "ServerIV", IP = "120.14.220.21" },
new Server{ Name = "ServerV", IP = "120.14.220.22" },
};
}
public static LoadBalancer GetLoadBalancer()
{
return _instance;
}
// Simple, but effective load balancer
public Server NextServer
{
get
{
int r = _random.Next(_servers.Count);
return _servers[r];
}
}
}
/// <summary>
/// Represents a server machine
/// </summary>
class Server
{
// Gets or sets server name
public string Name { get; set; }
// Gets or sets server IP address
public string IP { get; set; }
}
}