C# 3.0 Cookbook, 3rd Edition

18.6. Granting Multiple Access to Resources with a Semaphore

Problem

You have a resource you want only a certain number of clients to access at a given time.

Solution

Use a semaphore to enable resource-counted access to the resource. For example, if you have an Xbox 360 and a copy of Halo3 (the resource) and a development staff eager to blow off some steam (the clients), you have to synchronize access to the Xbox 360. Since the Xbox 360 has four controllers, up to four clients can be playing at any given time. The rules of the house are that when you die, you give up your controller.

To accomplish this, create a class called Halo3Session with a Semaphore called _Xbox360 like this:

	public class Halo3Session
	{
	    // A semaphore that simulates a limited resource pool.
	    private static Semaphore _Xbox360;

In order to get things rolling, you need to call the Play method, as shown in Example 18-5, on the Halo3Session class.

Example 18-5. Play method

public static void Play( ) { // An Xbox360 has 4 controller ports so 4 people can play at a time // We use 4 as the max and zero to start with, as we want Players // to queue up at first until the Xbox360 boots and loads the game // using (_Xbox360 = new Semaphore(0, 4, "Xbox360")) { using (ManualResetEvent GameOver = new ManualResetEvent(false)) { // // 9 Players log in to play // List<Xbox360Player.PlayerInfo> players = new List<Xbox360Player.PlayerInfo>( ) { new Xbox360Player.PlayerInfo { Name="Igor", Dead=GameOver}, new Xbox360Player.PlayerInfo { ...