[BUG] Splat.Microsoft.Extensions.DependencyInjection causes System.InvalidOperationException: Call from invalid thread

[Leon99]

Just trying to put together Avalonia's routing sample and Splat.Microsoft.Extensions.DependencyInjection. Pressing Go next button throws the exception below when Splat.Microsoft.Extensions.DependencyInjection is used. Works fine if services.UseMicrosoftDependencyResolver(); is commented out.

Repro: AvaRxUI.zip

System.InvalidOperationException: Call from invalid thread
   at Avalonia.Threading.Dispatcher.<VerifyAccess>g__ThrowVerifyAccess|16_0() in /_/src/Avalonia.Base/Threading/Dispatcher.cs:line 77
   at Avalonia.Threading.Dispatcher.VerifyAccess() in /_/src/Avalonia.Base/Threading/Dispatcher.cs:line 78
   at Avalonia.AvaloniaObject.VerifyAccess() in /_/src/Avalonia.Base/AvaloniaObject.cs:line 111
   at Avalonia.AvaloniaObject.GetValue[T](StyledProperty`1 property) in /_/src/Avalonia.Base/AvaloniaObject.cs:line 226
   at Avalonia.Controls.Button.get_Command() in /_/src/Avalonia.Controls/Button.cs:line 138
   at Avalonia.Controls.Button.CanExecuteChanged(Object sender, EventArgs e) in /_/src/Avalonia.Controls/Button.cs:line 560
   at ReactiveUI.ReactiveCommandBase`2.OnCanExecuteChanged(Boolean newValue) in /_/src/ReactiveUI/ReactiveCommand/ReactiveCommandBase.cs:line 219
   at System.Reactive.AnonymousSafeObserver`1.OnNext(T value) in /_/Rx.NET/Source/src/System.Reactive/AnonymousSafeObserver.cs:line 43
   at System.Reactive.Sink`1.ForwardOnNext(TTarget value) in /_/Rx.NET/Source/src/System.Reactive/Internal/Sink.cs:line 49
   at System.Reactive.IdentitySink`1.OnNext(T value) in /_/Rx.NET/Source/src/System.Reactive/Internal/IdentitySink.cs:line 15
   at System.Reactive.Subjects.FastImmediateObserver`1.EnsureActive(Int32 count) in /_/Rx.NET/Source/src/System.Reactive/Subjects/ReplaySubject.cs:line 863
   at System.Reactive.Subjects.FastImmediateObserver`1.EnsureActive() in /_/Rx.NET/Source/src/System.Reactive/Subjects/ReplaySubject.cs:line 765
   at System.Reactive.Subjects.ReplaySubject`1.ReplayBase.OnNext(T value) in /_/Rx.NET/Source/src/System.Reactive/Subjects/ReplaySubject.cs:line 270
   at System.Reactive.Subjects.ReplaySubject`1.OnNext(T value) in /_/Rx.NET/Source/src/System.Reactive/Subjects/ReplaySubject.cs:line 161
   at System.Reactive.Sink`1.ForwardOnNext(TTarget value) in /_/Rx.NET/Source/src/System.Reactive/Internal/Sink.cs:line 49
   at System.Reactive.IdentitySink`1.OnNext(T value) in /_/Rx.NET/Source/src/System.Reactive/Internal/IdentitySink.cs:line 15
   at System.Reactive.Sink`1.ForwardOnNext(TTarget value) in /_/Rx.NET/Source/src/System.Reactive/Internal/Sink.cs:line 49
   at System.Reactive.Linq.ObservableImpl.DistinctUntilChanged`2._.OnNext(TSource value) in /_/Rx.NET/Source/src/System.Reactive/Linq/Observable/DistinctUntilChanged.cs:line 72
   at System.Reactive.Sink`1.ForwardOnNext(TTarget value) in /_/Rx.NET/Source/src/System.Reactive/Internal/Sink.cs:line 49
   at System.Reactive.Linq.ObservableImpl.CombineLatest`3._.SecondObserver.OnNext(TSecond value) in /_/Rx.NET/Source/src/System.Reactive/Linq/Observable/CombineLatest.cs:line 177
   at System.Reactive.Sink`1.ForwardOnNext(TTarget value) in /_/Rx.NET/Source/src/System.Reactive/Internal/Sink.cs:line 49
   at System.Reactive.IdentitySink`1.OnNext(T value) in /_/Rx.NET/Source/src/System.Reactive/Internal/IdentitySink.cs:line 15
   at System.Reactive.Subjects.FastImmediateObserver`1.EnsureActive(Int32 count) in /_/Rx.NET/Source/src/System.Reactive/Subjects/ReplaySubject.cs:line 863
   at System.Reactive.Subjects.FastImmediateObserver`1.EnsureActive() in /_/Rx.NET/Source/src/System.Reactive/Subjects/ReplaySubject.cs:line 765
   at System.Reactive.Subjects.ReplaySubject`1.ReplayBase.OnNext(T value) in /_/Rx.NET/Source/src/System.Reactive/Subjects/ReplaySubject.cs:line 270
   at System.Reactive.Subjects.ReplaySubject`1.OnNext(T value) in /_/Rx.NET/Source/src/System.Reactive/Subjects/ReplaySubject.cs:line 161
   at System.Reactive.Sink`1.ForwardOnNext(TTarget value) in /_/Rx.NET/Source/src/System.Reactive/Internal/Sink.cs:line 49
   at System.Reactive.IdentitySink`1.OnNext(T value) in /_/Rx.NET/Source/src/System.Reactive/Internal/IdentitySink.cs:line 15
   at System.Reactive.Sink`1.ForwardOnNext(TTarget value) in /_/Rx.NET/Source/src/System.Reactive/Internal/Sink.cs:line 49
   at System.Reactive.Linq.ObservableImpl.DistinctUntilChanged`2._.OnNext(TSource value) in /_/Rx.NET/Source/src/System.Reactive/Linq/Observable/DistinctUntilChanged.cs:line 72
   at System.Reactive.Sink`1.ForwardOnNext(TTarget value) in /_/Rx.NET/Source/src/System.Reactive/Internal/Sink.cs:line 49
   at System.Reactive.IdentitySink`1.OnNext(T value) in /_/Rx.NET/Source/src/System.Reactive/Internal/IdentitySink.cs:line 15
   at System.Reactive.Sink`1.ForwardOnNext(TTarget value) in /_/Rx.NET/Source/src/System.Reactive/Internal/Sink.cs:line 49
   at System.Reactive.Linq.ObservableImpl.Select`2.Selector._.OnNext(TSource value) in /_/Rx.NET/Source/src/System.Reactive/Linq/Observable/Select.cs:line 47
   at System.Reactive.Sink`1.ForwardOnNext(TTarget value) in /_/Rx.NET/Source/src/System.Reactive/Internal/Sink.cs:line 49
   at System.Reactive.Linq.ObservableImpl.Scan`2._.OnNext(TSource value) in /_/Rx.NET/Source/src/System.Reactive/Linq/Observable/Scan.cs:line 48
   at System.Reactive.SafeObserver`1.WrappingSafeObserver.OnNext(TSource value) in /_/Rx.NET/Source/src/System.Reactive/Internal/SafeObserver.cs:line 30
   at System.Reactive.Sink`1.ForwardOnNext(TTarget value) in /_/Rx.NET/Source/src/System.Reactive/Internal/Sink.cs:line 49
   at System.Reactive.ObserveOnObserverLongRunning`1.Drain() in /_/Rx.NET/Source/src/System.Reactive/Internal/ScheduledObserver.cs:line 732
   at System.Reactive.ObserveOnObserverLongRunning`1.<>c.<.cctor>b__17_0(ObserveOnObserverLongRunning`1 self, ICancelable cancelable) in /_/Rx.NET/Source/src/System.Reactive/Internal/ScheduledObserver.cs:line 680
   at System.Reactive.Concurrency.DefaultScheduler.LongRunning.LongScheduledWorkItem`1.<>c.<.ctor>b__3_0(Object thisObject) in /_/Rx.NET/Source/src/System.Reactive/Concurrency/DefaultScheduler.cs:line 181
   at System.Reactive.Concurrency.ConcurrencyAbstractionLayerImpl.<>c.<StartThread>b__8_0(Object itemObject) in /_/Rx.NET/Source/src/System.Reactive/Concurrency/ConcurrencyAbstractionLayerImpl.cs:line 75

[glennawatson]

I'm guessing what's happening is Avalonia is sensitive that the logic in Avalonia.Controls.Button.CanExecuteChanged be run on the main UI thread.

Part of the CanExecute observable called into ReactiveCommand is being evaluated on another thread which is causing issues with Avalonia.

The Avalonia team maintain their own RxUI plugin but I'd imagine they might have a extension to convert an observable to run on the main ui thread.

[Leon99]

Thanks for the quick response @glennawatson!

Why do you reckon it doesn't happen when using Splat's built-in resolver?

[Leon99]

Same issue with Splat.DryIoc.

[glennawatson]

Splat tends to be a dictionary based system that creates on whatever thread is calling it. So it'll call a Func method, so could be to do with that.

I can have a look later today.

[Leon99]

I used a Func for MS DI (you can see it in the repro code) but not with DryIoc. This is the code:

        var container = new Container();
        container.Register<MainWindowViewModel>();
        container.Register<FirstViewModel>();
        container.Register<IViewFor<FirstViewModel>, FirstView>();
        container.RegisterMapping<IScreen, MainWindowViewModel>();
        container.UseDryIocDependencyResolver();

Happy to do some debugging if you point me in the right direction.

[glennawatson]

Let me have a look properly tomorrow for you. We are in the same Timezone. @ChrisPulman may have time in our evenings if life permits.

[ChrisPulman]

I can try to take a look this evening, having the repo is really helpful, thank you.

[ChrisPulman]

AvaRxUI_V2.zip
Please try this version, hopefully this will make things easier for you.

[ChrisPulman]

AvaloniaUI/Avalonia#12261
I have created a PR, hopefully the Avalonia Team will accept it.
Meanwhile <PackageReference Include="CP.Avalonia.ReactiveUI.Splat.DryIoc" Version="1.0.0" /> OR <PackageReference Include="CP.Avalonia.ReactiveUI.Splat.MicrosoftDependencyResolver" Version="1.0.0" /> could be used.

[ChrisPulman]

Avalonia have decided that they don't want to add the suggested packages to their codebase.
We will see if there's a better home for this otherwise I will continue to provide the necessary support from my repository.

[glennawatson]

I guess we could take the hit somewhere in the rxui repo so it's more official.

[glennawatson]

Discussed with @ChrisPulman offline, we'll make official Splat packages supporting the Avalonia use case for the different DI containers. It'll be minimal invasive to our stuff.

[Leon99]

Thanks @ChrisPulman & @glennawatson, much appreciated!

Just a couple of things after looking at the code:

• Is RxApp.MainThreadScheduler = AvaloniaScheduler.Instance; going to affect something else other then the DI container? If so, it's a bit questionable to set it inside UseSplatWith... as it might cause unexpected side-effects. On the other hand, I'm not an expert but looking at the XML documentation for both RxApp.MainThreadScheduler and AvaloniaScheduler.Instance gives me an impression that they are supposed to be equal regardless. If so, isn't that a responsibility of Avalonia.ReactiveUI to set?
• Given that it's just a few lines of code, could it be better to package the .cs as content, and avoid overhead of having another dll?

[ChrisPulman]

The end Splat packages will be a single alternative package for Avalonia and not an additional one, and be an extension of the existing code with a single dll.

RxApp.MainThreadScheduler should be set to AvaloniaScheduler.Instance and is done in the UseReactiveUI section of Avalonia.ReactiveUI, however when initialisation of Splat with the new DI occurs the RxApp.MainThreadScheduler is reset causing the issue you experienced.
We will need to document the order in which the AppBuilder extensions are added in order to ensure that things are initialised in the correct order. I will most likely wrap the UseReactiveUI inside the extension to be certain it's done in the right order. Something like UseReactiveUiWithDryIoc(container => {})

[ChrisPulman]

The following packages have been released:
ReactiveUI.Avalonia
ReactiveUI.Avalonia.DryIoc
ReactiveUI.Avalonia.Autofac
ReactiveUI.Avalonia.Ninject
ReactiveUI.Avalonia.Microsoft.Extensions.DependencyInjection

Each is a single dll that replaces the need to include either Avalonia.ReactiveUI or the relevant Splat container package.
Only one call to UseReactiveUI OR UseReactiveUIWithxxxxxx OR UseReactiveUIWithDIContainer (where xxxxxx is the DI container) should be used with the AppBuilder.

[github-actions]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.