Stuck on an issue?

Lightrun Answers was designed to reduce the constant googling that comes with debugging 3rd party libraries. It collects links to all the places you might be looking at while hunting down a tough bug.

And, if you’re still stuck at the end, we’re happy to hop on a call to see how we can help out.

Threading mode toggle does not work with realm

See original GitHub issue

While looking into #13580 on master, on most attempts to switch the threading mode, I get:

2021-06-19 15:33:42 [error]: System.Exception: Realm accessed from incorrect thread.
2021-06-19 15:33:42 [error]: at Realms.NativeException.ThrowIfNecessary(Func`2 overrider)
2021-06-19 15:33:42 [error]: at Realms.SharedRealmHandle.Refresh()
2021-06-19 15:33:42 [error]: at Realms.Realm.Refresh()
2021-06-19 15:33:42 [error]: at osu.Game.Database.RealmContextFactory.Update() in /home/dachb/Dokumenty/opensource/osu/osu.Game/Database/RealmContextFactory.cs:line 84

The context was created on the update thread, but is being accessed on the main thread after the threading mode change. I thought this was going to be pretty easy to get past by just purging realm contexts on threading mode switch, so I applied the following change. But then after some more debugging of the aforementioned issue I was hit by this:

2021-06-19 15:29:20 [error]: Realms.Exceptions.RealmClosedException: This object belongs to a closed realm.
2021-06-19 15:29:20 [error]: at Realms.NativeException.ThrowIfNecessary(Func`2 overrider)
2021-06-19 15:29:20 [error]: at Realms.ObjectHandle.GetValue(String propertyName, Metadata metadata, Realm realm)
2021-06-19 15:29:20 [error]: at Realms.RealmObjectBase.GetValue(String propertyName)
2021-06-19 15:29:20 [error]: at osu.Game.Input.Bindings.RealmKeyBinding.get_KeyCombinationString()
2021-06-19 15:29:20 [error]: at osu.Game.Input.Bindings.RealmKeyBinding.get_KeyCombination() in /home/dachb/Dokumenty/opensource/osu/osu.Game/Input/Bindings/RealmKeyBinding.cs:line 23
2021-06-19 15:29:20 [error]: at osu.Game.Overlays.Toolbar.ToolbarButton.updateKeyBindingTooltip() in /home/dachb/Dokumenty/opensource/osu/osu.Game/Overlays/Toolbar/ToolbarButton.cs:line 227

Which is worse to get past, and is why I’m opening this issue for discussion. It looks like any live objects are no longer safe to hold onto after a threading mode change and they need to all be invalidated. I think Live<T> will have to return in some capacity to resolve this; I don’t immediately see any other way out.