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Thread Singleton

There are a couple of classes in most projects that end up being singletons. The two most adept for this paradigm are Configuration and Database Handle Pooling. Both get used by many objects, both should only be instantiated once for efficiency and data integrity and we don't want to have to pass either of them around all the time. Voila, perfect candidate for singleton's.

When i started working with ASP.NET, however I ran into a problem with this, since ASP.NET persists over many requests and is multithreaded. For configuration that's user specific, that could be a problem. For transactional Database handles it's definitely a problem. Simplest way is to put it into the HttpContext.Current.Items collection. But now your code is tied to ASP.NET. You could write wrappers that test the environment and wrap the objects in singleton or HttpContext as appropriate, but that still leaves the singleton being shared across threads, should you write other multi-threaded apps.

I finally found a solution (sorry, i can't give credit because it's been a while and I can't find the original article) to this in the form of a Thread Singleton. This pattern uses the System.Runtime.Remoting.Messaging.CallContext to store our singleton. I've used it so many times now, that i figured i'd better write it down here so i don't have to dig through old code every time i want to re-use it:

using System;
using System.Runtime.Remoting.Messaging;

namespace Claassen.Util
    public class ThreadSingleton
        /// <summary>
        /// Some unique string that identifies this class.. I just use the
        /// Namespace qualified name
        /// </summary>
        const string SINGLETON_ID = "Claassen.Util.ThreadSingleton";

        /// <summary>
        /// Accessor/Factory for the ThreadSingleton
        /// </summary>
        private static ThreadSingleton Current
                // pull the object from the CallContext
                ThreadSingleton threadSingleton = (ThreadSingleton)CallContext.GetData(SINGLETON_ID);
                if( threadSingleton == null )
                    // if there was nothing in the CallContext, create and add it
                    threadSingleton = new ThreadSingleton();
                return threadSingleton;

        // Class code would follow

Mouse Clicks and LFS

Wrote a little program that launches LFS, clicks the appropriate buttons and sends strings to connect to a server defined by IP (it's called local in LFS for some reason), puts the player in the game and starts the game.

All works nicely, but man, is it ever an ugly hack. Hard-coding screen coordinates, putting in Thread.Sleep(n) so the UI can catch up, etc. But at least there is a way to automate the client.

Back to coding: Click this

Having run into a number of things I cannot accomplish with InSim in LFS, I've decided to venture down the ugly route of simulating the mouse. Not that horrible. InSim was never really designed for client automation.

I haven't tested this on LFS yet, just Calc.exe, but I finally found a way to do mouse clicks in another application from .NET.

The first route i went down was the SendMessage from user32.dll. Tried many different ways of getting the windowhandle and all that stuff, but no click ever materialized. Also found this method weird. Why do i have to tell it what window i'm clicking when i give it the cursor position. It's likely i just never figured out the proper syntax, but the docs i found certainly didn't aid me much.

Then i found mouse_event also from user32.dll. This one just sent a click event for the current location of the mouse. Just the way i would have expected. And it works!

Here's the sample code:

const int WM_LBUTTONDOWN = 0x0201;
const int WM_LBUTTONUP = 0x0202;
const int SC_MAXIMIZE = 0xF030;
const UInt32 MouseEventLeftDown = 0x0002;
const UInt32 MouseEventLeftUp = 0x0004;

[DllImport("user32.dll", EntryPoint="SendMessage", CharSet=CharSet.Auto)]
public static extern void SendMessage(IntPtr hWnd, int msg, int wParam, int lParam);

static extern void mouse_event(uint dwFlags, uint dx, uint dy, uint dwData, UIntPtr dwExtraInfo);

public static void Test()
    Process myProc = new Process();
    myProc.StartInfo.FileName = @"calc.exe";

    // maximizing so we know where the button is (cheap ass hack for testing)

    Point p = new Point(150,150); // the 6 button
    Cursor.Position = p;

    if (myProc.WaitForInputIdle(3000))
        // This one works !!!
        mouse_event(MouseEventLeftDown,0,0,0,new System.UIntPtr());
        mouse_event(MouseEventLeftUp,0,0,0,new System.UIntPtr());

        // This one doesn't do anything :(
        SendMessage(myProc.MainWindowHandle,WM_LBUTTONDOWN, Cursor.Position.X, Cursor.Position.Y);
        SendMessage(myProc.MainWindowHandle,WM_LBUTTONDOWN, Cursor.Position.X, Cursor.Position.Y);

Track your Head

Ok, more geek, than programming.

Been spending a lot of time with LFS S2 lately. The new Alpha is out and with my tweaked setup for the GTT is finally drivable. I can even drift it a fair amount. Fantastic game!

Well, i took advantage of the discount that LFS offered on the TrackIR Pro. It looks like a camera, and it is one, but for the infrared spectrum. It tracks your heads movements and adjusts your POV in-game. It uses a progressive exageration of your head movement, so only a couple of degrees left of right and you are looking behind yourself.

Tried it out with LFS and the extra immersion is intense. It comes completely natural to you. You just move your head and you are looking in that direction and the exageration doesn't seem out of place. Makes driving a little funky, since you are no longer driving in the direction you are looking, necessarily. Physics feedback be nice, right about now :) Still, i think i'll adjust. Went for a lap with some AI opponents and being able to look left and right and see your opponents going into a turn was a tremendous help. This device kicks ass!

Live For Speed InSim API 0.01a

I've been playing Racing Simulations for a while. I have an Act Labs Force RS, a wheel I truly enjoy, even though Act Labs has decided to get out of that market. My true love was Need For Speed: Porsche Unleashed. I think it was the best NFS game of the series. A good balance between Arcade and Simulator. However it is also the one that did the worst commercially and now NFS is pretty much a Console arcade racing franchise. Oh well.

I've spent some time with TOCA: Race Driver 2, a beautiful engine, but i never liked the feel of the cars. Grand Prix Legends, is of course the reigning champion among Simulation junkies, so much so that the 10 year(?) old game has been lovingly kept up to date by a devoted fanbase. But talk about hard to drive, and I am really more of a GT racing kind of guy.

While I've known about Live For Speed for a while and played the demo, it wasn't until a couple of weeks ago that I finally broke down and bought the full game. And man, it's shaping up to be my favorite simulator. S1 is already incredible, and graphically good enough. The driving is fun and challenging and extend to which you can tweak your car setup is incredible. And what's been posted of S2 pretty much puts at the top of the genre, if you ask me.

And then there is InSim, a UDP protocol for communicating with either the individual game or a game server to control many aspects, or syphon racing statistics from it. Being a geek, I was drawn to this protocol almost as much as to the racing itself and so I've been busy building an Object/Event model to encapsulate the protocol in C#. Finally all the playing with binary serialization has paid off. The first version of the lib with a VS.NET winforms tester solution can be found here, the full NDoc generate docs are here. Right now this is a binary release of the Lib itself, but once i lock down the Model, i'll release the full source, most likely under the General Public License.

This initial release understands all InSim packets, but I have not built objects around them, so really the only capabilities exposed are:

  • Connect to an LFS instance, and if so configured, automatically respond to keep alive packets
  • Access the LFS version information
  • Send and receive messages
  • Request and subscribe to Status packets.

It'll probably take me a month to flesh out the rest, at my current pace.

C style strings into C

I've been spending some time building an Object Model around an binary wire protocol. It uses traditional C style strings which are null terminated. C# strings have no problem '\0', so i was getting some funny text messages, as well no way to see an empty string. I was hoping that there was something in BitConverter or Encoding that would truncate the byte array magically, but i wasn't able to find it. So, pending a a better solution, i convert the whole thing to a string, then use IndexOf() to find the first '\0' and then copy the substring up to the null into another string. Ugly, IMHO, but it works.

System.Windows.Forms.ListBox bug with BeginUpdate()/EndUpdate()

Came across an annoying bug with ListBox. If you use BeginUpdate() and EndUpdate() and only add a single item to a cleared Item collection, then that Item does not show up on Refresh. However if you leave the BeginUpdate()/EndUpdate() out, it works fine, resulting in a need for code like this:

if( itemList.Count > 1 )
    //only use the Begin/End cycle if we have more than one item
foreach( object item in itemList )
if( group.Strings.Count > 1 )
    //only use the Begin/End cycle if we have more than one item

Image Clipping and Alignment with CSS

The clip attribute in CSS is not what I would call the simplest to understand. Never mind that the rect() function uses a space separated list instead of a comma separated one, but that some browsers still understand comma separated. But the ordering of the clip rect of top right bottom left is just bizarre. Finally to understand what clipping does, it's important to realize that the clip rect defines a rectangle of what will be shown, defined from the origin, but it does not affect positioning of the image, which still starts at the origin, clipped areas not withstanding.

log4net filepaths and how to get at Appenders at runtime

Just a note of something simple and silly enough that I shouldn't forget it again: Filepaths in log4net configurations still have to escape the DOS separator backslash. I know it should be obvious, you use \ in a text file, you escape it.

Well, i was too used to the @"c:\foo\bar.txt" syntax from C# that when i took the path out of the code and into the log4net XML config, i left it in the c:\foo\bar.txt format. I wasn't able to wrap a debugger around the deployed code and couldn't figure out why my logger wasn't writing. I figured out how to get to the currently available appenders at runtime and wrote that to the web page trace and seeing that there was no filename for the RollingFile appender, smacked me in the head with the "escape the backslash, stupid".

The silly part out of the way, this did give me some useful insight into log4net internals. So to get at the configured appenders you can do this:

// Just grabbing the first logger, since we want to use it to grab it's parent,
// the root logger
log4net.Repository.Hierarchy.Logger logger
    = (log4net.Repository.Hierarchy.Logger)log.Logger.Repository.GetCurrentLoggers()[0];
Console.WriteLine("Logger: {0}",logger.Name);
foreach( log4net.Appender.IAppender appender in logger.Parent.Appenders )
    Console.WriteLine("  Appender: {0}",appender.Name);
    // just checking for RollingFile here, but could just as well check for all other appenders
    if(appender.GetType() == typeof(log4net.Appender.RollingFileAppender))
        log4net.Appender.RollingFileAppender rolling
            = (log4net.Appender.RollingFileAppender)appender;
        Console.WriteLine("    Rolling File: {0}",rolling.File);

Mind you this is just a place to get started from. It does make a number of assumptions you shouldn't make in production code. It is good enough though to help you debug log4net behavior.