Null Reference Exception

Question

Frustrated have been looking at this all day... I am creating a windows service...this code works fine on a regular console application and does not work on the windows service. I am getting a null reference exception:

Null reference in OnStart(): Object reference not set to an instance of an object. 
 at VNurseService.Server.RequestServer..ctor(Server s)
 at VNurseService.VNurseServer.OnStart(String[] args)

Code looks like:

protected override void OnStart(string[] args)
    {

        eventLog1.WriteEntry("In OnStart");
       Start:
        try
        {
            server = new Server();

            Server.RequestServer reference = new Server.RequestServer(server);
            new Thread(reference.run).Start();
            //r1 = new Thread(reference.run); r1.Start();

            Server.ResponseServer reference2 = new Server.ResponseServer(server);
            new Thread(reference2.run).Start();
            //r2 = new Thread(reference.run); r2.Start();

            Server.reference3 = new Server.ConfirmationServer(server);

            server.guiServer = new Guicom();
            server.restartServer = new Restart();

            eventLog1.WriteEntry("Restart in server is " + server.RESTART.ToString());

            new Thread(server.guiServer.accept).Start();
            new Thread(server.restartServer.accept).Start();
            goto check;

        check:
            while (true)
            {
                eventLog1.WriteEntry("CheckRestart is " + server.checkRestart().ToString());
                if (server.checkRestart())
                {
                    reference.cleanup();
                    //r1.Abort();
                    reference2.cleanup();
                    //r2.Abort();
                    //server = null;
                    goto Start;
                }
            }
        }
        catch (NullReferenceException ex)
        {
            eventLog1.WriteEntry("Null reference in OnStart(): " + ex.Message+ " " + ex.InnerException + @"\n " + ex.StackTrace);
        }
    }

And something is giving me a null reference exception and I don't know where it is.

Thanks for the help in advance.

If you're not getting a line number, make sure to put the .pdb file alongside the service exe. — Blorgbeard, Mar 10 '11 at 23:06
So, did you do any debugging, or "have been looking at this all day" was meant literally? @Nix: two! one that is actually a loop and one that is a semicolon. — R. Martinho Fernandes, Mar 10 '11 at 23:06
Looks like it's in VNurseService.Server.RequestServer..ctor(Server s) so probably when it's trying to create the RequestServer object... — timothyclifford, Mar 10 '11 at 23:07
the code for the `RequestServer` constructor would help, the problem seems to be there. — BrokenGlass, Mar 10 '11 at 23:08
This really is impossible without seeing what is calling OnStart and a valid stack trace. — Nix, Mar 10 '11 at 23:14

Simen S · Answer 1 · 2011-03-10T23:14:01.367

5

You can add a forced breakpoint in code at service startup ...

protected override void OnStart(string[] args)     
{   
    System.Diagnostics.Debugger.Break();       

    eventLog1.WriteEntry("In OnStart"); 
    ...
}

.. and attach a debugger to the process

edited Mar 10 '11 at 23:14

answered Mar 10 '11 at 23:06

Simen S

3,210
18
24

1

Additional reading recommendations [How to: Debug Windows Service Applications](http://msdn.microsoft.com/en-us/library/7a50syb3.aspx) and [What is a NullReferenceException in .NET?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-in-net) – R. Martinho Fernandes Mar 10 '11 at 23:14

Hans Passant · Answer 2 · 2011-03-14T13:05:19.850

1

 eventLog1.WriteEntry("Null reference in OnStart(): " + ...);

I think your are a victim of your own message. The exception didn't actually occur in OnStart, even though your message says it did. It bombed in the RequestServer class, code you didn't post. Note how the call stack does give you the right info. The .ctor() listed there is the constructor for the class, that's the one that bombed.

Have a look at it. And fix the WriteEntry() argument, I'd recommend something like "Startup failure".

edited Mar 14 '11 at 13:05

answered Mar 11 '11 at 00:15

Hans Passant

922,412
146
1,693
2,536

doesn't a *class* constructor get called `cctor` ? – AakashM Mar 14 '11 at 12:59
@Aak - yes, temporary brain freeze. Thanks :) – Hans Passant Mar 14 '11 at 13:05

score 0 · Answer 3 · answered Mar 11 '11 at 01:51

Better still, launch a debugger:

protected override void OnStart( string [] args )
{
    if ( args.Contains( "debug" ) ) System.Diagnostics.Debugger.Launch();
}

In services.msc, you can add parameters to be passed on startup by right clicking on the (stopped) service, "Properties/General/Start Parameters"

Null Reference Exception

3 Answers3

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