Message pump in .NET Windows service

Thanks all for your suggestions. Richard & overslacked, the link you provided in the comments was very helpful. Also, I did not have to allow the service to interact with the desktop in order to manually start a message pump with Application.Run. Apparently, you only need to allow the service to interact with the desktop if you want Windows to start a message pump automatically for you.

For everyone’s edification, here is what I ended up doing to manually start a message pump for this 3rd party API:

internal class MessageHandler : NativeWindow
{
    public event EventHandler<MessageData> MessageReceived;

    public MessageHandler ()
    {
        CreateHandle(new CreateParams());
    }

    protected override void WndProc(ref Message msg)
    {
        // filter messages here for your purposes

        EventHandler<MessageData> handler = MessageReceived;
        if (handler != null) handler(ref msg);

        base.WndProc(ref msg);
    }
}

public class MessagePumpManager
{
    private readonly Thread messagePump;
    private AutoResetEvent messagePumpRunning = new AutoResetEvent(false);

    public StartMessagePump()
    {
        // start message pump in its own thread
        messagePump = new Thread(RunMessagePump) {Name = "ManualMessagePump"};
        messagePump.Start();
        messagePumpRunning.WaitOne();
    }

    // Message Pump Thread
    private void RunMessagePump()
    {
        // Create control to handle windows messages
        MessageHandler messageHandler = new MessageHandler();

        // Initialize 3rd party dll 
        DLL.Init(messageHandler.Handle);

        Console.WriteLine("Message Pump Thread Started");
        messagePumpRunning.Set();
        Application.Run();
    }
}

I had to overcome a few hurdles to get this to work. One is that you need to make certain to create the Form on the same thread that you execute Application.Run. You also can only access the Handle property from that same thread, so I found it easiest to simply initialized the DLL on that thread as well. For all I know, it is expecting to be initialized from a GUI thread anyway.

Also, in my implementation, the MessagePumpManager class is a Singleton instance, so that only one message pump runs for all instances of my device class. Make sure that you truly lazy-initialize your singleton instance if you start the thread in your constructor. If you start the thread from a static context (such as private static MessagePumpManager instance = new MessagePumpManager();) the runtime will never context switch into the newly created thread, and you will deadlock while waiting for the message pump to start.