[regression] PropertyGrid GDI leak

[kirsan31]

• .NET Core Version: 5.0.3 - 5.0.6 tested.

• Have you experienced this same bug with .NET Framework?: NO. Also this bug is not present in .net core 3.1

Problem description:
For several months I am was investigating huge (up to critical 10000) GDI leak in our app (beginning after switching from .net core 3.1 to .Net 5). And finally found it out (I am happy 🙄). Facts:

• Leaking are DC and Bitmap in approximately the same proportions.
• This is not managed leaks - managed heap have not any increasing elements. So GC not helping here and if PropertyGrid inside childe window, closing it will not help too.
• Leaks are not reproduce on local machine. Only when you connect to rdp session. So if your rdp session is open - all is fine, to leak you need close rdp window and connect again. Tested on Win10 1909/20H2 hosts.
• I think amount of leaks are some how related to displaying property's, because some window leak more than others.

GDI.mp4

Our scenario was: we have an mdi app with many child windows that's have PropertyGrid, for one rdp connect we losing about 100 GDI objects. So, after ~80 connects, our app was crushing. For now we monitor GDI objects count and restarting app when needed.

Expected behavior:
No GDI leak.

Minimal repro:
GDI_test.zip

[JeremyKuhne]

Interesting. First guess here is that connecting probably fires WM_SETTINGCHANGE and that may be causing the color pickers to drop handles.

[kirsan31]

@JeremyKuhne

Interesting. First guess here is that connecting probably fires WM_SETTINGCHANGE and that may be causing the color pickers to drop handles.

I am afraid that the problem not in the property's (color pickers etc), but in the PropertyGrid itself, because it's leak with this simple class as SelectedObject:

public class TestClass
{
    public int A { get; set; }
}

GDI2.mp4

------ UPD ------

Yes, it's leaking even while empty (SelectedObject == null). About 10 GDI handles per reconnect.

[JeremyKuhne]

Thanks @kirsan31

[weltkante]

WM_SETTINGCHANGE causes the PropertyGrid to reload its ImageList without disposing the old one, leaking the handles owned by it. When running a debug build you hit the assert. See also #4928 and #3567

There may be more things leaking, but disposing the ImageList before reassigning it helps fixing at least some of the leaks.

[RussKie]

Am I hearing it right that you're sending a PR? 😉

[weltkante]

Am I hearing it right that you're sending a PR? 😉

Sure, was holding off since @JeremyKuhne was already investigating and I don't know how far he got, its better to coordinate than two people trying to do a PR for the same bug ;)

Also I think thats not the only leak here, but I couldn't see anything immediately obvious, probably needs further investigation. If you want a partial fix for just the ImageList disposal thats easily done.

[JeremyKuhne]

its better to coordinate than two people trying to do a PR for the same bug ;)

@weltkante Thanks for investigating! By all means, please create a PR. :) I've been held up by other things and haven't been able to dig into it fully yet.