[Grid] Crash trying to reference garbage collected variable

[pedropaulosuzuki]

Description
I was just messing around with the Grid and saw Pinta crashing due to a garbage collected variable trying to be accessed.

To Reproduce
Not sure the optimal steps to reproduce, but I was able to do it twice by doing the following:

1. Open Pinta
2. Enable the Grid
3. Enable the Axonometric Grid
4. Disable the Grid
5. Disable the Axonometric Grid
6. Pick any tool (example: Clone Tool or Brush Tool) and try to draw on the canvas

Additional Info

Unhandled exception. System.Exception: Could not toggle reference to strong. It got garbage collected.
   at GObject.Internal.ToggleRef.ToggleReference(Boolean isLastRef)
   at GObject.Internal.InstanceCache.ToggleNotify(IntPtr data, IntPtr object, Int32 isLastRef)

Version
Latest git

[cameronwhite]

I haven't been able to reproduce it yet, but wasn't sure about the right clicking mentioned in the instructions (the clone stamp tool just supports left clicking or ctrl+clicking)

Does the --debug command line flag make it easier for you to track down what triggers it? (that mode runs the GC much more frequently)

[fedaj]

The same thing just happened to me three times, same trace:

Unhandled exception. System.Exception: Could not toggle reference to strong. It got garbage collected.
   at GObject.Internal.ToggleRef.ToggleReference(Boolean isLastRef)
   at GObject.Internal.InstanceCache.ToggleNotify(IntPtr data, IntPtr object, Int32 isLastRef)
Aborted (core dumped)

I was trying to compose a silly image, so I was doing the following:

• Create an image and paste something found on the internet.
• Create another image and paste a headshot of a teammate.
• Erase part of the headshot to just leave the head and resize it.
• Paste the head on a new layer on the first image.
• Move the head so it overlaps another head in the original image.
• Right click on the layer to try to merge it down.

The first time I got the crash on the right click, the next two when trying to move the head. I understand most of what I wrote is probably irrelevant, but I'd rather be as specific as possible as I don't know what could be helpful in reproducing and debugging this.

P.S.: I am assuming the three crashes are the same, as for the first two I didn't see it because I started Pinta from Ubuntu's desktop GUI and only for the last one did I start from the terminal in order to be able to see the exception message. Pinta is installed as a Ubuntu Snap (3.1.1), the OS version being 24.04.4 LTS (noble).

[badcel]

The latest GireCore release adds a debug statement to give some more information: https://github.com/gircore/gir.core/blob/a1ff833506e137e3faf11f3b8e98a03ec5ecde47/src/Libs/GObject-2.0/Internal/InstanceCache.cs#L81

But you would need to build Pinta yourself including GirCore.

There are even more debug statements in GirCore which allow you to trace what is happening to instances. Without those it will probably be hard to determine what's going on.

Version 0.7.0 has probably some good logging, too. Just adding the new line to the code is probably good enough until pinta switches to the new GirCore version.

[cameronwhite]

After #2050 I'll try building Pinta against a debug gir.core and see if I can reproduce it 👍

[badcel]

Note: GirCore 0.8.0 has changes in its memory management compared to 0.7.0. So it could behave differently (but it should not).

[pedropaulosuzuki]

Here's a video of this happening. I'm able to reproduce it with some consistency in latest git.

1. View > Canvas Grid... > Show Grid
2. View > Canvas Grid... > Show Axonometric Grid
3. Do the same to remove the grids.
4. Select pretty much any tool
5. Click on the canvas
6. See the following error message in the terminal:

Unhandled exception. System.Exception: Could not toggle reference to strong. It got garbage collected.
   at GObject.Internal.ToggleRef.ToggleReference(Boolean isLastRef)
   at GObject.Internal.InstanceCache.ToggleNotify(IntPtr data, IntPtr object, Int32 isLastRef)

Screencast.from.17-03-2026.14.47.17.webm

[fedaj]

I've tried to build Pinta with a local copy of gir.core, but I'm stuck at the following error:

Restore complete (1.5s)
  Pinta.AddinUtils net8.0 succeeded (0.1s) → installer/addins/bin/Debug/net8.0/Pinta.AddinUtils.dll
  GLib-2.0 net8.0 failed with 1 error(s) (0.1s)
    CSC : error CS2001: Source file '/home/fede/Dev/gir.core/src/Libs/GLib-2.0/../GObject-2.0/Internal/ImportResolver.Generated.cs' could not be found.

Build failed with 1 error(s) in 2.0s

If some kind soul can pity me and provide some simple and detailed instructions on how to build this, I'd like to at least try to provide some more information that can help track down the issue.

(Web developer here so I'm not completely useless, but almost :P. Should be able to follow simple commands if you use short enough words :) ).

[cameronwhite]

From that error message, perhaps gir.core wasn't built correctly?
It has some build steps that you need to manually run to generate the GTK bindings, before you would run dotnet build for Pinta:
https://github.com/gircore/gir.core?tab=readme-ov-file#build

[cameronwhite]

BTW, building against PR #2069 should work with the latest version of gir.core (there are many warnings still to fix, but it runs)

[fedaj]

Thank you, using that branch and the latest commit on gir.core's main branch I was able to build - with a bunch of warnings, as advertised :) . I have not been able to reproduce the issue so far. I did have Pinta just disappear when running it using dotnet run --project Pinta, but after following the instructions for installation and running from there it seems to be happy staying alive, so to speak. The terminal didn't show any messages, error or otherwise, after the "disappearance" (I hesitate to call it crash as it just... wasn't there anymore when I came back from the browser after checking my own steps).

I followed the same steps as in my original report (different images though, I no longer have the ones that failed originally) and Pinta finished the operations without crashing. Right now it's still sitting there, silly face pasted over silly image after merging the layers down. It is showing some "critical" error messages though, but I have no idea how relevant they are or if they are an already known issue:

$ ./pinta 

(process:25864): Gtk-WARNING **: 23:07:53.043: Locale not supported by C library.
	Using the fallback 'C' locale.

(dotnet:25864): GLib-GObject-CRITICAL **: 23:08:16.374: g_object_unref: assertion 'G_IS_OBJECT (object)' failed

(dotnet:25864): GLib-GObject-CRITICAL **: 23:08:27.885: g_object_unref: assertion 'G_IS_OBJECT (object)' failed

I will keep trying to break it whenever I have the chance and report back if I'm able to reproduce the original issue. Perhaps, with luck, whatever it was is fixed, either in Pinta or gir.core.