GC.KeepAlive()似乎没有效果

我在打开GC.KeepAlive()并注释掉的情况下运行下面的代码示例，但它是相同的。如何编码，这样我可以看到的差异。

// A simple class that exposes two static Win32 functions.
// One is a delegate type and the other is an enumerated type.
public class MyWin32 
{
    // Declare the SetConsoleCtrlHandler function 
    // as external and receiving a delegate.   
    [DllImport("Kernel32")] 
    public static extern Boolean SetConsoleCtrlHandler(HandlerRoutine Handler, 
        Boolean Add);
    // A delegate type to be used as the handler routine 
    // for SetConsoleCtrlHandler.
    public delegate Boolean HandlerRoutine(CtrlTypes CtrlType);
    // An enumerated type for the control messages 
    // sent to the handler routine.
    public enum CtrlTypes 
    {
        CTRL_C_EVENT = 0,
        CTRL_BREAK_EVENT,
        CTRL_CLOSE_EVENT,   
        CTRL_LOGOFF_EVENT = 5,
        CTRL_SHUTDOWN_EVENT
    }
}
public class MyApp 
{
    // A private static handler function in the MyApp class.
    static Boolean Handler(MyWin32.CtrlTypes CtrlType)
    {
        String message = "This message should never be seen!";
        // A switch to handle the event type.
        switch(CtrlType)
        {
            case MyWin32.CtrlTypes.CTRL_C_EVENT:
                message = "A CTRL_C_EVENT was raised by the user.";
                break;
            case MyWin32.CtrlTypes.CTRL_BREAK_EVENT:
                message = "A CTRL_BREAK_EVENT was raised by the user.";
                break;
            case MyWin32.CtrlTypes.CTRL_CLOSE_EVENT:   
                message = "A CTRL_CLOSE_EVENT was raised by the user.";
                break;
            case MyWin32.CtrlTypes.CTRL_LOGOFF_EVENT:
                message = "A CTRL_LOGOFF_EVENT was raised by the user.";
                break;
            case MyWin32.CtrlTypes.CTRL_SHUTDOWN_EVENT:
                message = "A CTRL_SHUTDOWN_EVENT was raised by the user.";
                break;
        }
        // Use interop to display a message for the type of event.
        Console.WriteLine(message);
        return true;
    }
    public static void Main()
    {         
        // Use interop to set a console control handler.
        MyWin32.HandlerRoutine hr = new MyWin32.HandlerRoutine(Handler);
        MyWin32.SetConsoleCtrlHandler(hr, true);
        // Give the user some time to raise a few events.
        Console.WriteLine("Waiting 30 seconds for console ctrl events...");
        // The object hr is not referred to again.
        // The garbage collector can detect that the object has no
        // more managed references and might clean it up here while
        // the unmanaged SetConsoleCtrlHandler method is still using it.      
        // Force a garbage collection to demonstrate how the hr
        // object will be handled.
        GC.Collect();
        GC.WaitForPendingFinalizers();
        GC.Collect();
        Thread.Sleep(30000);
        // Display a message to the console when the unmanaged method
        // has finished its work.
        Console.WriteLine("Finished!");
        // Call GC.KeepAlive(hr) at this point to maintain a reference to hr. 
        // This will prevent the garbage collector from collecting the 
        // object during the execution of the SetConsoleCtrlHandler method.
        GC.KeepAlive(hr);   
        Console.Read();
    }
}

http://msdn.microsoft.com/en-us/library/system.gc.keepalive.aspx

谢谢。

GC.KeepAlive(hr);