Memory leak when subscribing to observables from XAML in a data template

Bug description

Subscribing to an observable from XAML (using a caret ^ syntax, e.g. IsVisible="{Binding Foo^}") in a data template causes a memory leak: the binding recipient remains in the memory after it’s long gone from the visual tree.

Likely related to #3527

Reproduction

Bind to a long-lived observable in a data template.

Minimal example, based on the default template: repo link (most relevant stuff is in the MainWindow). Dummy controls are used to track a leak.

To confirm a leak, I’ve used the managed memory profiler in VS 2019.

Expected behavior

All bindings made in XAML should be auto-disposed when control is detached. That seems to be true when using normal bindings (e.g. IsVisible="{Binding $parent[UserControl].Foo}" — included in the example).

Desktop

• Windows 10 Pro (v2004)
• Avalonia 0.10.3

Commentary

In my 100%-reactive app this issue causes colossal memory leaks: just switching a page bumps the memory gauge by 50-70 Mb. It stacks nicely with (up to) 350 Mb from the graphics bug (the one that causes memory issues when resizing a window).

I do not know if the issues is caused by a data template or a binding, but having the bug down the tree causes a huge chunk of the tree to leak, likely through a parent reference.

[grokys]

Yeah this is a difficult one. I’ve been unable to write a unit test so far that reproduces the problem, even. Seems to be related to the fact that an observable is producing a collection via the stream operator which creates data templates which themselves have observables subscribed via the stream operator.

I need to move onto something else now, but will hopefully have time to take another look soon.

[unofficialdev]

I’m having a similar problem. i try to rewrite 1 wpf app with avalonia, wpf app only use ~50mb memory, but avalonia app go up to ~400mb