NullReferenceException, no stack trace... where to start?

Question

I have a WPF audio application.

Occasionally (and even in the debugger) I'm seeing a NullReferenceException which carries no stack trace information with it.

How can one start debugging such an issue?

Some background:

I'm P/Invoking functions in WinMM.dll which involves registering a callback when calling waveOutOpen

    [DllImport("winmm.dll")]
    public static extern MmResult waveOutOpen(out IntPtr phwo, IntPtr uDeviceID, WaveFmt pwfx, WaveCallbk dwCallback, IntPtr dwInstance, int fdwOpen);

This has proved difficult to get stable, especially at the point where I call waveOutClose, and immediately call waveOutOpen again (usually to change the output format).

I suspect that the problem may be related to the calls I've been describing above (although on so little knowlege, I could be completely off-target).

Reproducing the problem is currently proving elusive, although I can supply a build to a user who is fairly consistently seeing this problem. I might try to speed up the operations that are causing the problem to the point where reproducing the problem in the debugger is more of a certainty.

With regards to the debugger, I haven't tinkered with any of the settings (including Enable unmanaged code debugging) or any of the Debug -> Exceptions... settings. To be honest, I'm fairly clueless about what's on offer here, so any hints are welcome.

How might an exception not have a stack trace? Have you seen this before? Help!

Dolan

Yes, this sort of thing happens all to often when working with unmanaged code. And it it a total PITA. Personally I would love to have a checklist of things to go through. – Menken

A checklist would be awesomely handy. Anyone? – Dolan

Answer 1

The most helpful thing you can do in the debugger is instruct it to break on a first-chance exception (Debug -> Exceptions):

This will cause a break into the debugger at the exact point a NullReferenceException is thrown, which is pretty much the best you can ever hope for while debugging.

Regalado

Good. Just got to make it happen in the debugger... ger... grrrr. – Dolan

Many thanks! This has moved in VS 2015 in case you are wondering.. Debug->Windows->Exception Setting. There it has a search, so probably easiest to use search box for NullReference. – Crick