Tuesday, March 20, 2012

Debugging .NET Windows Service apps more easily

Here at work, I keep seeing a couple of my fellow developers struggle to debug their Windows Service apps that they're writing.  What they have to do is remove the service, install the new version of the service, start the service, then attach the debugger.

If there's an error when the service first starts up, the workaround is to introduce a Thread.Sleep before it actually does anything, giving you enough time to attach the debugger.

By default, you can't directly run the service from within Visual Studio. If you try, you get the following message:



If you look at the code that actually starts the service, you'll see that it's not that different from a console app.

By default, it looks something like this:

    internal static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        private static void Main()
        {
            ServiceBase[] ServicesToRun;
            ServicesToRun = new ServiceBase[] { new Service1() };
            ServiceBase.Run(ServicesToRun);
        }
    }
And the Service1 class looks like this:

    public partial class Service1 : ServiceBase
    {
        public Service1()
        {
            this.InitializeComponent();
        }
 
        protected override void OnStart(string[] args)
        {
            Console.WriteLine("Hello, world!");
        }
 
        protected override void OnStop()
        {
        }
    }
The code that runs when the service Starts happens in OnStart() .  There are other events that you can override, such as OnPowerEvent, OnSessionChange, OnShutdown, but for the most part, you'd primarily be concerned about OnStart.

So how can we get a Windows Service to run like a console app?  Pretty simply actually. I'm just going to post the solution here and walk you through it:

    internal static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        private static void Main(string[] args)
        {
            var service = new Service1();
            if (Environment.UserInteractive)
            {
                service.Start(args);
                Thread.Sleep(Timeout.Infinite);
            }
            else
            {
                var servicesToRun = new ServiceBase[] { service };
                ServiceBase.Run(servicesToRun);
            }
        }
    }


First, you should change the signature of Main() to include an array of arguments.
  private static void Main(string[] args)
Next, we'll want to create a new instance of Service1 and keep that in a variable.
var service = new Service1();
Now comes the magic part.  We want to be able to check whether the app is being ran as an application, or as a service.  How can we determine that?  Simple:
if (Environment.UserInteractive)
The above code checks if the application is being ran by the user, or as a service.  If it's being ran by the user, then we want to treat it like a console application, otherwise, run it as a service.  This gives us the flexibility of being able to run it in two different modes.

Next, you'll see me calling a method on Service1 called "Start" instead of "OnStart".  The problem is that OnStart is protected, which means we can only access that method from derived classes, and since Program is not deriving Service1, we can't access that method.  The simplest way to be able to call the "OnStart" method would be to just add a public method to Service1 that will do it for us:

        public void Start(string[] args)
        {
            this.OnStart(args);
        }

And now you can run and debug your service from Visual Studio without having to go through the trouble of installing it.  Once you feel that you have it working, you can then install it by creating a Installer Project, or manually installing it using the "installutil".