Reference can't be toggled

[badcel]

Here is an example https://github.com/tarachom/TreeExpanderTest

Everything works fine as long as the collection is small.

As soon as the collection grows, the program crashes. I need to know how to block the repeated execution of the Gio.ListModel? CreateFunc(GObject.Object item) function until the previous CreateFunc call is completed. That is, the user has opened a branch and cannot close or open another one while CreateFunc is running

screen-recording-2026-01-16-204845_80fi8Zq0.mp4

Originally posted by @tarachom in #1447 (comment)

• Any new instance (ref count = 1) inside a callback with transferownership full which is returned must get an additional ref.
• Check if out parameters are supported. They might need this, too
• write Unit Test

[badcel]

@tarachom I forked your code and will trim it down even more. I can reproduce the issue pretty good with it. Thanks for your report ❤️

It's not that easy to fix as it's probably related to multithreading (already tried it for some time). But I will try my best. Perhaps even with support from @jwharm 🚀

[badcel]

@tarachom: I finished trimming it down. For me it still breaks. Can you confirm?

It's round about half the code from before. Next time please try to minimize as far as possible. As it took me some time to get to this state. See: https://github.com/badcel/TreeExpanderTest

[tarachom]

I understand you. Yes, this code that you shortened works.
Thank you for taking the time to understand my code.

[badcel]

Adding this fixed it

//TreeListModelCreateModelFuncNotifiedHandler.cs

NativeCallback = (IntPtr item, IntPtr userData) => {
    var itemNative = (GObject.Object) GObject.Internal.InstanceWrapper.WrapHandle<GObject.Object>(item, false);

    Gio.ListModel? managedCallbackResult = default;
managedCallbackResult = managedCallback(itemNative);

    if(managedCallbackResult is not null) //NEW
        GObject.Internal.Object.Ref(managedCallbackResult.Handle.DangerousGetHandle()); //NEW
   
    return managedCallbackResult?.Handle.DangerousGetHandle() ?? IntPtr.Zero;
};

This means it is not related to some race but a double free bug.

[tarachom]

Thank you for your promptness and for what you found and fixed