How to debug .NET Windows Service OnStart method?

Question

I have code written in .net that only fails when installed as a windows service. The failure doesn't allow the service to even start. I can't figure out how I can step into the OnStart method.

http://msdn.microsoft.com/en-us/library/7a50syb3%28VS.80%29.aspx gives a tantalizing clue:

Attaching to the service's process allows you to debug most but not all of the service's code; for example, because the service has already been started, you cannot debug the code in the service's OnStart method this way, or the code in the Main method that is used to load the service. One way to work around this is to create a temporary second service in your service application that exists only to aid in debugging. You can install both services, and then start this "dummy" service to load the service process. Once the temporary service has started the process, you can then use the Debug menu in Visual Studio to attach to the service process.

However, I'm not clear how it is exactly that you are supposed to create the dummy service to load the service process.

Answer 1

One thing you could do as a temporary workaround is to launch the debugger as the first line of code in the OnStart

System.Diagnostics.Debugger.Launch()

This will prompt you for the debugger you'd like to use. Simply have the solution already open in Visual Studio and choose that instance from the list.

Answer 2

You can add a line of code like this:

System.Diagnostics.Debugger.Break()

which will bring up a window prompting you to choose which debugger to use to debug, e.g. allowing you to attach with Visual Studio and step into the code.

see:

http://msdn.microsoft.com/en-us/library/system.diagnostics.debugger.break.aspx

Answer 3

Try adding Debugger.Break inside the problematic method. When the service will start an exception will be thrown and widows should offer to debug it using visual studio.

Answer 4

I tend to add a method like this:

    [Conditional("DEBUG")]
    private void AttachDebugger()
    {
        Debugger.Break();
    }

it will only get called on Debug builds of you project and it will pause execution and allow you to attach the debugger.

Answer 5

I usually have a console app that pretends to be the SCM e.g. calls Start, Stop which I can then just F5 into for my main coding/debugging purposes, and use the Debugger.Break for debugging when the service has been installed and started via the SCM.

It means a bit more work to start with, I have a class lib that contains all the service code, with a class that exposes Start and Stop that the Windows Service class and the console app can both call.

Matt