How to handle wrong target framework System.Reactive in the GAC?

[reyqn]

We have an application targeting 4.8, which uses ReactiveUI.WPF 18.4.1 net48 referencing ReactiveUI 18.4.1 net472, in turn referencing System.Reactive 5.0.0. The dll comes from the nuget net472 lib. This works well.

However, some of our clients are using a third party program which puts System.Reactive targeting netstandard2.0 in their GAC.
When loading the dll in their environment, the dll from the GAC is prioritized over our dll, which causes a crash since DispatcherScheduler.Current doesn't exist in the netstandard2.0 dll of System.Reactive (https://github.com/reactiveui/ReactiveUI/blob/main/src/ReactiveUI.Wpf/Registrations.cs#L40)

Unhandled Exception: System.TypeInitializationException: The type initializer for 'ReactiveUI.RxApp' threw an exception. ---> System.TypeLoadException: Could not load type 'System.Reactive.Concurrency.DispatcherScheduler' from assembly 'System.Reactive, Version=5.0.0.0, Culture=neutral, PublicKeyToken=94bc3704cddfc263'.
   at ReactiveUI.Wpf.Registrations.<>c.<Register>b__0_10()
   at ReactiveUI.WaitForDispatcherScheduler.AttemptToCreateScheduler() in /_/src/ReactiveUI/Scheduler/WaitForDispatcherScheduler.cs:line 61
   at ReactiveUI.WaitForDispatcherScheduler..ctor(Func`1 schedulerFactory) in /_/src/ReactiveUI/Scheduler/WaitForDispatcherScheduler.cs:line 34
   at ReactiveUI.Wpf.Registrations.Register(Action`2 registerFunction) in /_/src/ReactiveUI.Wpf/Registrations.cs:line 40
   at ReactiveUI.DependencyResolverMixins.ProcessRegistrationForNamespace(String namespaceName, AssemblyName assemblyName, IMutableDependencyResolver resolver) in /_/src/ReactiveUI/Mixins/DependencyResolverMixins.cs:line 153
   at ReactiveUI.DependencyResolverMixins.InitializeReactiveUI(IMutableDependencyResolver resolver, RegistrationNamespace[] registrationNamespaces) in /_/src/ReactiveUI/Mixins/DependencyResolverMixins.cs:line 74
   at ReactiveUI.RxApp.<>c.<.cctor>b__9_0() in /_/src/ReactiveUI/RxApp.cs:line 92
   at Splat.InternalLocator.RegisterResolverCallbackChanged(Action callback) in /_/src/Splat/ServiceLocation/InternalLocator.cs:line 117
   at Splat.Locator.RegisterResolverCallbackChanged(Action callback) in /_/src/Splat/ServiceLocation/Locator.cs:line 81
   at ReactiveUI.RxApp..cctor() in /_/src/ReactiveUI/RxApp.cs:line 85
   --- End of inner exception stack trace ---
   at ReactiveUI.RxApp.get_MainThreadScheduler()
   at WpfApplication1.ExceptionService.Initialize() in C:\Users\reyan\RiderProjects\WpfApplication1\WpfApplication1\App.xaml.cs:line 24
   at WpfApplication1.App.OnStartup(StartupEventArgs e) in C:\Users\reyan\RiderProjects\WpfApplication1\WpfApplication1\App.xaml.cs:line 15
   at System.Windows.Application.<.ctor>b__1_0(Object unused)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.DispatcherOperation.InvokeImpl()
   at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
   at MS.Internal.CulturePreservingExecutionContext.CallbackWrapper(Object obj)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at MS.Internal.CulturePreservingExecutionContext.Run(CulturePreservingExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Windows.Threading.DispatcherOperation.Invoke()
   at System.Windows.Threading.Dispatcher.ProcessQueue()
   at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.WrappedInvoke(Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
   at System.Windows.Threading.Dispatcher.Invoke(DispatcherPriority priority, Delegate method, Object arg)
   at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
   at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
   at System.Windows.Threading.Dispatcher.TranslateAndDispatchMessage(MSG& msg)
   at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
   at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
   at System.Windows.Threading.Dispatcher.Run()
   at System.Windows.Application.RunDispatcher(Object ignore)
   at System.Windows.Application.RunInternal(Window window)
   at System.Windows.Application.Run(Window window)
   at System.Windows.Application.Run()
   at WpfApplication1.App.Main()

Here is a light reproduction solution (you have to add the included System.Reactive to your GAC).
WpfApplication1.zip

We know this isn't a bug in reactiveUI, which is why we aren't opening an issue, but we've searched far and wide and we're really stumped with this issue, so any help is very welcome even if it's just telling us to ask somewhere else (where else?).

What should we do here? Right now we've upgraded to a newer version of ReactiveUI referencing System.Reactive 6.0.0, but what can we do if someone adds it to the GAC again?

Thanks.

[thomaswelter]

Hello I just want to chime in to say that there might be more users impacted by this problem (without them knowing). A program I was using had this exact issue. Removing the "System.Reactive.dll" from the GAC solved it.

[dpvreony]

few options you can try

1. remove the strong naming from the System.Reactive dll as part of your build process (and potentially other dll's)
2. force a binding redirect in your app.config
3. use ilmerge to merge system.reactive into your app
4. resign all the dll's during the build
5. move to NET8 etc as this doesn't use the gac (this might be your easiest route, depending on what is keeping you on netfx)

references:

• https://stackoverflow.com/questions/38716653/remove-the-strong-name-from-3rd-party-assemblies
• https://stackoverflow.com/questions/991293/forcing-the-asp-net-application-to-load-the-assembly-from-bin-not-from-gac
• https://stackoverflow.com/questions/1606867/how-to-prevent-a-net-application-from-loading-referencing-an-assembly-from-the
• https://www.nuget.org/packages/Brutal.Dev.StrongNameSigner/

[reyqn]

I'd rather not play with strong naming to fix this, so 1 and 4 are out. 3 is also very invasive. I'm not sure how to do 2, but it would be nice if it worked.
Obviously 5 is the better solution, and we are working on a transition out of netfx, but this takes time.

I'll try 2 when I have time and report back, but I'm not convinced this can work because of this: dotnet/runtime#84618

Actually removing the auto-generated bindingredirect seems to work better, whenever there is a bindingredirect the gac will be considered from what I saw.