Saturday, February 2, 2008

Samples of Design Patterns

Singleton Pattern
-----------------

CacheManager?

ProfileProvider/RoleProvider/MembershipProvider

LoadBalancer



using System;
using System.Collections;

namespace DoFactory.GangOfFour.Singleton.NETOptimized
{

// MainApp test application

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");
}

// All are the same instance -- use b1 arbitrarily
// Load balance 15 requests for a server
for (int i = 0; i < 15; i++)
{
Console.WriteLine(b1.Server);
}

// Wait for user
Console.Read();
}
}

// Singleton

sealed class LoadBalancer
{
// Static members are lazily initialized.
// .NET guarantees thread safety for static initialization
private static readonly LoadBalancer instance =
new LoadBalancer();

private ArrayList servers = new ArrayList();
private Random random = new Random();

// Note: constructor is private.
private LoadBalancer()
{
// List of available servers
servers.Add("ServerI");
servers.Add("ServerII");
servers.Add("ServerIII");
servers.Add("ServerIV");
servers.Add("ServerV");
}

public static LoadBalancer GetLoadBalancer()
{
return instance;
}

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


Output

Same instance

ServerIV
ServerIV
ServerIII
ServerV
ServerII
ServerV
ServerII
ServerII
ServerI
ServerIV
ServerIV
ServerII
ServerI
ServerV
ServerIV

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