How do you debug a Windows Service?

Question

I read the MSDN article on the topic. To quote:

Because a service must be run from within the context of the Services Control Manager rather than

Answer 1

I stole this from C. Lawrence Wenham, so I can't really take credit, but you can programmatically attach a debugger to a service, WITHOUT breaking execution at that point, with the following code:

System.Diagnostics.Debugger.Launch();

Put this in your service's OnStart() method, as the first line, and it will prompt you to choose an instance of VS to attach its debugger. From there, the system will stop at breakpoints you set, and on exceptions thrown out. I would put an #if DEBUG clause around the code so a Release build won't include it; or you can just strip it out after you find the problem.

Answer 2

One thing I do (which may be kind of a hack) is put a Thread.Sleep(10000) right at the beginning of my OnStart() method. This gives me a 10-second window to attach my debugger to the service before it does anything else.

Of course I remove the Thread.Sleep() statement when I'm done debugging.

One other thing you may do is the following:

public override void OnStart()
{
    try
    {
        // all your OnStart() logic here
    }
    catch(Exception ex)
    {
        // Log ex.Message
        if (!EventLog.SourceExists("MyApplication"))
            EventLog.CreateEventSource("MyApplication", "Application");

        EventLog.WriteEntry("MyApplication", "Failed to start: " + ex.Message);
        throw;
    }
}

When you log ex.Message, you may get a more detailed error message. Furthermore, you could just log ex.ToString() to get the whole stack trace, and if your .pdb files are in the same directory as your executable, it will even tell you what line the Exception occurred on.

Answer 3

Debugging services is a pain, particularly since startup seems to be when many of the problems manifest (at least for us).

What we typically do is extract as much of the logic as possible to a single class that has start and stop methods. Those class methods are all that the service calls directly. We then create a WinForm application that has two buttons: one to invoke start, another to invoke stop. We can then run this WinForm applicaiton directly from the debugger and see what is happening.

Not the most elegant solution, but it works for us.

Answer 4

You could use a parameter to let your application decide whether to start as service or regular app (i.e. in this case show a Form or start the service):

static void Main(string[] args)
{
    if ((1 == args.Length) && ("-runAsApp" == args[0]))
    {
        Application.Run(new application_form());
    }
    else
    {
        System.ServiceProcess.ServiceBase[] ServicesToRun;
        ServicesToRun = new ServiceBase[] { new MyService() };
        System.ServiceProcess.ServiceBase.Run(ServicesToRun);
    }
}

Now if you pass the parameter "-runAsApp" you can debug the application normally - the SCM won't pass this parameter, so you can also use it as service w/o any code change (provided you derive from ServiceBase)

Edit:

The other difference with windows services is identity (this might be especially important with InterOp) - you want to make sure you are testing under the same identity in "app" mode as well as service mode.

To do so you can use impersonation (I can post a C# wrapper if it helps, but this can be easily googled) in app mode to use the same identity your windows service will be running under i.e. usually LocalService or NetworkService.

If another identity is required you can add settings to the app.config that allow you to decide whether to use credentials, and if so which user to impersonate - these settings would be active when running as app, but turned off for the windows service (since the service is already running under the desired identity):

  <appSettings>
    <add key="useCredentials" value="false"/>
    <add key="user" value="Foo"/>
    <add key="password" value="Bar"/>
  </appSettings>

Answer 5

Use following Code in Service OnStart Method:

System.Diagnostics.Debugger.Launch();

Choose Visual Studio option from Pop Up message

Answer 6

Check out this question, which discusses how to catch unhandled exceptions in a window service.